Posters

Konzeption eines integrierten Signalanalyse-Softwaresystems mit angeschlossener Metadatenverwaltung.
Peck P., A. Noll, P. Balazs und W.A. Deutsch
Institut für Schallforschung der Österreichischen Akademie der Wissenschaften, Liebiggasse 5, A-1010 Wien;
Die Anwendung digitaler Signalanalyseverfahren (FFT, Cepstrum, Spektrographie, AR, digitale Filter, psychoakustische Modelle) ist häufig verbunden mit der Aufnahme, Wiedergabe, Verwaltung und feinsegmentierten Beschreibung einer großen Anzahl von verschiedensten Tonaufnahmen. Es wird die Konzeption des Softwaresystems S_TOOLS präsentiert, das Signalakquisition, Speicherung, Signalanalyse, Metadatengenerierung und –verarbeitung mittels eines Objektorientierten Datenbanksystems in einer Applikation vereint. Für den Benutzer ergibt sich dadurch eine integrierte Oberfläche für die Analyse und Bearbeitung von digitalen Ton-Aufnahmen. Die Software wird auf handelsüblichen Multimedia-PCs lauffähig sein und keine Spezialhardware benötigen. Die Tauglichkeit dieser Konzeption wird anhand der Vorgängerversion von S_TOOLS, die bereits in mehreren Installationen im Einsatz ist, demonstriert. Anwendungen ergeben sich überall dort, wo im Zuge von Meßverfahren auf große Signaldatenmengen zugegriffen werden muß, in der Forschung und Lehre, ebenso jedoch in der Archivtechnik und im Multimediabereich.

Speech analysis application based on human auditory processing
Alefs B.G.,Deutsch W.A.
Acoustics Research Institute of the Austrian Academy of Sciences
Speech analysis applications seem to benefit from physiological and psychoacoustical modeling of the human auditory system. Studies on robustness of automatic speech recognition systems (ASR) show increased performance for auditory models based signal processing, above fast fourier transform based analysis (FFT) (Ghitz '92, Tchorz '98). However, speech analysis has more purposes than recognition only. This study develops an application for visualization and modeling of speech production cues, such as described by Fant (1956). The visual and auditory representation of these cues are compared for broadband and narrowband fourier analysis, a 1/3-octave filterbank and a gammatone auditory filterbank analysis. The latter shows slight advantage in visualizing low frequency modulations. Speech resynthesis show comparable intelligibility for linear prediction formant coding, as for low frequency temporal envelop coding of few filterbands. Furthermore, hidden Markov models are applied for phonetic segmentation purposes.

Measurement of local gas temperatures in SI engines using the emission of rotational lines of OH
A. Hirsch¹, E. Winklhofer², H. Jäger¹
Institut für Experimentalphysik, Technische Universität Graz
² AVL List GmbH
Engine development requires measurement methods to determine combustion gas properties without disturbing the combustion process and without excessive modifications to production engines. The approach chosen in this work is the application of plasma diagnostics techniques to the light emitted by the combustion flame in spark ignition engines. The intensities of several rotational lines of the OH radical were measured using high resolution spectroscopy. OH lines appear in the region of burned gas and are used for the determination of the peak temperature in the combustion chamber with a mean error of about 10 %.

Spectroscopic in-situ determination of the flue gas composition in a biomass-fired grate furnace
Thomas Fleckl¹, Helmut Jäger², Ingwald Obernberger^1,3
Institute of Chemical Engineering Fundamentals and Plant Engineering, Technical University Graz, Austria, ²Institute of Experimental Physics, Technical University Graz, Austria, ³BIOS - Bioenergy Systems, Graz, Austria
Utilisation of conventional suction probe gas analysis for hot gas measurements causes changes of the gas composition due to necessary cooling. This problem can be avoided by the performance of spectroscopic measurements directly in the hot furnace. For this reason a FT-IR spectrometer was adapted to perform in-situ absorption measurements. For quantitative analysis it is important to obtain absorption coefficients of the gaseous components to be measured at temperatures up to 1100°C. A calibration cell was designed to obtain calibration spectra for H₂O, CO, CO₂ and CH₄. Moreover, the HITRAN/HITEMP database was used to calculate synthetic high temperature spectra for H₂O, CO and CO₂, which showed good agreement with the spectra measured. First measurements performed at a pilot scale travelling grate furnace using wood chips and waste wood as fuels showed that quantitative detection of the gaseous components H₂O, CO, CO₂ and CH₄ was possible in reducing and oxidising zones of the furnace. The results achieved will be used as a basis for chemical kinetic simulations as well as to verify results from CFD simulations of the gas phase combustion process.

Discharge Phenomena in a Free-Burning Argon Arc
J. Reiche, G. Kuehn, F. Koenemann, W. Mende, E. Schulz-Gulde, M. Kock
Universität Hannover, Institut für Atom- und Molekülphysik, Abteilung Plasmaphysik
We present four different discharge modi observed in a free-burning argon arc depending on discharge parameters like argon pressure, arc current, cathode material and geometry. At currents less than 1A and preferrably at reduced discharge pressure a blue-column mode is formed and significant erosion of the cathode occurs. In the low-current regime a constricted plasma is formed on the cathode (spot mode) whereby the spot is moving in a random way on the cathode surface. Increasing the current the discharge changes into the so-called diffuse mode characterized by a plasma ball covering the cathode tip. At higher currents another specific new mode can be established showing a hot little plasma kernel in front of the cathode surface (blue kernel mode). With various diagnostic techniques like emission spectroscopy, Rayleigh- and Thomson-scattering and laser-induced fluorescence we are able to describe the different discharge phenomena.

3D-Atom-probe study of secondary hardening on Co bearing HS steels
H. Leitner¹, M. Leisch²
Institut für Metallkunde und Werkstoffprüfung, MU Leoben,
²Institut für Festkörperphysik, TU Graz, Austria
The three-dimensional atom-probe (3D-AP) is a new variant of the field ion microscope (FIM) combined with a time-of-flight mass spectrometer with single ion detection sensivity. From position sensitive measurement the elemental reconstruction of a small volume of about 15x15x10 nm of the specimen can be obtained with near atomic resolution. The technological important parameters in secondary hardening like morphology, composition, size and distribution of nanoprecipitates in the matrix can be obtained from a single experiment.Samples of commercial high speed steels with and without Co have been analyzed to study the local distribution of Co and the influence on the morphology of the nanoprecipitates after various thermal treatment. (work supported by the FWF, Project S 6206 unf P 12099)

A Method for Real Time Detection of PAN, PPN and MPAN in Ambient Air
A. Hansel and A. Wisthaler
Institut für Ionenphysik, Universität Innsbruck
A proton transfer reaction spectrometer (PTR-MS) and a selected ion flow drift tube (SIFDT) apparatus were used to study reactions of protonated water (H₃O⁺) and the proton bound water dimer (H₂O)₂H⁺ with PAN (peroxyacetic nitric anhydride, CH₃C(O)OONO₂ ), PPN (peroxypropionic nitric anhydride, CH₃CH₂(O)OONO₂ ) and MPAN (peroxymethacrylic nitric anhydride, CH₂C(CH₃)C(O)OONO₂ ). The protonated water hydrates react fast with PAN, PPN and MPAN. Product ion peaks using ambient air as reactant gas could unequivocally attributed to PAN, PPN and MPAN utilizing the thermal decomposition of these compounds on a hot surface. This method provides real time measurements of PAN, PPN and MPAN in ambient air with a detection limit < 70 pptv (S/N=2, 15 s integration time) to an overall accuracy of 15 %. This is a significant breakthrough for PAN measurements as GC techniques are limited in their sampling frequency by the retention time (several minutes for MPAN).
Part of the work is supported by the Austrian Fonds zur Förderung der wiss. Forschung.

Aircraft-based Comparison of two Measurement Techniques for Acetone and Acetonitrile
D. Sprung¹, C. Jost¹, T. Reiner¹, A. Wisthaler² and A. Hansel^2
1Max Planck Institut für Chemie, Mainz, Germany, ²Institut für Ionenphysik, Universität Innsbruck, Austria, armin.hansel@uibk.ac.at
We have performed aircraft-born comparison measurements between two instruments for the measurement of acetone and acetonitrile. The two techniques are: A Proton-Transfer-Reaction Mass-Spectrometer operated and developed by the University of Innsbruck, and an Atmospheric Pressure Chemical Ionization Mass Spectrometer (AP-CIMS) operated and developed by the Max Planck Institute for Chemistry. Both instruments were employed for atmospheric trace gas measurements over the Indian Ocean on board the NCAR C-130 research aircraft during the INDOEX intensive field phase in February and March 1999.
Both instruments use chemical reactions between primary ions and atmospheric trace gases followed by mass spectrometric detection of product ions. The comparison measurements were performed under a variety of different atmospheric conditions, including marine boundary layer air, free tropospheric air, polluted air, and pristine air from the southern hemisphere.

Organic Trace Gas Measurements During INDOEX: In Situ Data from the NCAR C-130 Aircraft
A. Hansel¹, A. Wisthaler¹, and P.J. Crutzen¹
Inst. f. Ionenphysik, Univers. Innsbruck, ²Max Planck Inst. f. Chemie, Mainz, BRD
During the Indian Ocean experiment (INDOEX) ambient air samples were analysed in-situ by the Innsbruck Proton Transfer Reaction Mass Spectrometer (PTR-MS) to gain gas phase information at the parts per trillion (pptv) level. Measurements were performed aboard the NCAR aircraft C-130. Volume mixing ratios (VMR) if various volatile organic compounds (VOCs), including acetonitrile, acetone, methanol etc. were monitored on-line during aircraft missions up to 6500 m altitude and in the marine boundary layer (MBL). Northern hemispheric (NH) air masses originating from the Indian subcontinent are generally more polluted than southern hemispheric (SH) air. Enhanced VMR of acetonitrile indicate a strong influence of combustion of biofuel. Strong concentration gradients of above mentioned VOCs are found when flying from the NH (6 N) to the SH (8 S) and crossing the intertropical convergence zone (ITCZ).

Simulation of Particle Acceleration in Front of a Lower-Hybrid Grill
D. Tskhakaya, S. Kuhn, and V. Petrzilka ^(*)
Plasma and Energy Physics Group, Department of Theoretical Physics, University of Innsbruck, Austria, (*) Institute of Plasma Physics, Academy of Sciences of the Czech Republic, CZ-18221 Prague, Czech Republic
The acceleration of plasma particles in a narrow ''resonant'' region in front of a Lower-Hybrid (LH) grill mouth is studied using Particle-in-Cell (PIC) simulation with the modified code XPDP2 from Berkley [1]. The LH wave - resonant electron interaction is modelled by a ponderomotive force that acts on the electrons in the resonant region [2]. By contrast with real LH wave - plasma coupling (PIC) simulations, where only a very short time scale (a few LH wave periods) is feasible [3], our simplified approach allows us to investigate long-time-scale processes, so that ion acceleration can be studed. Our 2d simulations confirm previous results of 1d simulations [2], according to which not only electrons but also ions are accelerated to high energies. The highly energetic ion beam has a larger radial width than the electron beam. The ion beam energy and the plasma density within the ''resonant'' region depend on the amplitude of the ponderomotive potential (i. e., on the LH power injected).
This work was performed within Project P1 of the Association Euratom-ÖAW. One of the authors (D. T.) acknowledges support from FWF Project P12477-TPH.
[1] V. Vahedi, G. DiPeso: J. Comput. Phys. 131, (1997) 149. [2] V. Petrzilka et al.: Czech. J. Phys. 49 (1999) 127. [3] K.M. Rantamäki, T.J.H. Pättikangas, S.J. Karttunen, X. Litaudon, and D. Moreau: Phys. Plasmas 5 (7) (1998) 2553.

Time-resolved mass spectrometry with a helium flushed probe system
J. Laimer, G. Misslinger, and H. Störi
Institut für Allgemeine Physik, Technische Universität Wien, Wiedner Hauptstraße 8-10, A-1040 Wien, Austria
At pressures higher than approximately 5 mbar it is nowadays common practice to use a two-stage pressure reduction set-up, consisting of a capillary tube as a first pressure reduction stage and an orifice as a second pressure reduction stage. We have improved the temporal resolution by using a helium flushed probe system and redesigning the vacuum system of the quadrupole mass spectrometer. An experimental investigation using a very fast chemical reaction revealed a temporal resolution of approximately 2 ms. It turned out that he temporal evolution of the mass spectrometer signal is predominantly affected by the broadening of the signal within the capillary tube due to diffusion and by the mean residence time of the extracted gas in the vacuum system of the mass spectrometer. The instrument response function of the set-up is basically a convolution of a slightly deformed Gauß function with an exponential function.

Plasma chemistry of diamond deposition utilizing chlorinated methanes
G. Misslinger, J. Laimer, and H. Störi
Institut für Allgemeine Physik, Technische Universität Wien, Wiedner Hauptstraße 8-10, A-1040 Wien, Austria
The plasma chemistry in process gases consisting of hydrogen with a small admixture of chlorinated methanes was investigated in a pulsed r.f. discharge. The temporal development of certain species in the plasma was explored by experiment and simulation. Experiment and simulation are in good agreement and show a very fast decomposition of the chlorinated methanes to the main stable species hydrogen chloride, methane, and acetylene. Chlorinated methyl radicals, which are possible diamond growth species, are created during the decomposition process. However, they decompose so quickly that they occur only within 1 ms after the first contact of the feed stock gas with the plasma. The simulation showed that atomic chlorine is besides atomic hydrogen and the methyl radical the third most important radical in the gas phase. Chlorine in the gas phase increases the methyl radical concentration at lower temperatures and generates active surface sites more efficiently than atomic hydrogen.

Non-uniform TiN deposition conditions in large pulsed d.c. plasma CVD systems – reasons and solutions
C. Kugler, J. Laimer, and H. Störi
Institut für Allgemeine Physik, Technische Universität Wien, Wiedner Hauptstraße 8-10, A-1040 Wien, Austria
Pulsed direct-current (d.c.) glow discharges are commonly used in systems for plasma-assisted chemical vapour deposition (plasma CVD) of hard coatings. Recent investigations of the dynamics of pulsed d.c. discharges relevant for the production of titanium nitride coatings in large reactors have shown, that when titanium tetrachloride is used as a feed stock gas, the spreading of the discharge is slow, reaching some parts of the reactor with substantial delay. The result is a non-uniform plasma power density in front of the substrates as well as a spatially varying exposure time of the surface to the plasma. These problems can be solved by measures, which increase the conductivity of the plasma at the beginning of the pulses. One way to achieve this goal is the use of synchronized additional short high voltage pulses. The present study investigates the dependence of the evolution of the discharge on parameters of the additional short high voltage pulses.

Simultaneous excitation of low-frequency instabilities in a magnetised plasma
D.G.Dimitriu², V.Ignatescu², C.Ionita^1,2, G.Popa², M.Sandoloviciu², R.Schrittwieser¹
1 Institute for Ion Physics, University of Innsbruck, A-6020 Innsbruck, Austria;
² Faculty of Physics, University "Al. I. Cuza", RO-Iasi, Romania
Electron currents through a magnetised plasma can excite nonlinear instabilities, as e.g. the potential relaxation instability (PRI) and/or the electrostatic ion-cyclotron instability (EICI). We report on the simultaneous excitation of PRI and EICI and the formation of sidebands around the EICI frequency with a frequency difference equal to the PRI frequency. In the Innsbruck Q-machine a K-plasma column with a density of about 10⁹ cm^-3 was produced by contact ionisation. The magnetic field is 0,1 - 0,25 T. Both instabilities are excited by a positively biased collector of 10 mm diam. at a distance d from the plasma source. When the collector current approaches the electron saturation regime, the frequency spectrum of the superimposed fluctuations shows a very complex behaviour with various peaks. These can be ascribed to the PRI and the EICI and to modulations of the EICI by the PRI. Strong formation of sidebands is also seen. For 0,13 T and a length of d = 27,5 cm, the PRI appears at f_pri = 11,35 kHz and the EICI frequency at f_eici = 62,20 kHz. In addition there are sidebands on both sides of the EICI frequency peak at f_eici ± f_pri and secondary sidebands at f_eici ± 2×f_pri.

Fusion Plasma Modelling
H. Bürbaumer, R. Schneider*,D. Coster*, F. Aumayr, HP. Winter
Institut für Allgemeine Physik, Association EURATOM-ÖAW, Wiedner Hauptstr. 8-10, A-1040 Wien. *Max-Planck-Institut f. Plasmaphysik, IPP-EURATOM Association, D-85748 Garching
The B2 code package has been developed in order to simulate the complete edge region of fusion plasmas. To enable an accurate simulation of diagnostic results, calculations on a high resolution grid are necessary. This can only be achieved in an tolerable amount of time using grid refinement. In the present work a method enabling such a grid refinement in the B2 code package is described and first tests of the new code are presented. The method followed in this paper creates two grid structures. A very fine curvilinear quasi-orthogonal 2D mesh produced directly from the magnetic flux surface structure of the experimental discharge acts as a basis grid on which a rough, flexible mesh can be modified depending on the physical situation. Grid refinement is realized by simply adding and removing cells of the basis grid into the rough cell and interpolating all physical values of the new rough cell. The five-point solver from the original B2 code can still be used in the new version, since the influence from each side of a rough cell is calculated by splitting and summing up all fluxes coming from direct neighbours in this direction.

Fusion plasma diagnostics with fast He beams
S. Menhart, M. Proschek, H.-D. Falter, F. Aumayr, and HP. Winter
Institut f. Allgemeine Physik, TU Wien, A-1040 Wien
Modelling calculations for a fast neutral He beam on its way through a tokamak plasma based on the collisional-radiative ADAS model have been performed. We are able to calculate radially-resolved population density- and line-intensity profiles for any initial composition of the diagnostic He beam and any plasma structure. The influence of a metastable triplet population in the incident beam on the line emission profiles is explored. A sensitivity study of the optical lines with respect to electron temperature and -density has been performed for the plasma edge- and core regions. To validate these model calculations, experiments using fast He beams and beam emission spectroscopy have been performed at ASDEX Upgrade (IPP Garching) and JET, by injecting He into the ion sources of respective H- or D heating beam systems. Work performed within Association EURATOM-ÖAW, and supported by Friedrich Schiedel-Stiftung für Energietechnik, Wien.

Interlayer diffusion of adatoms under surface strain
G. Leonardelli, M. Schmid, P. Varga
Technische Universität Wien, Institut für Allgemeine Physik, A-1040 Wien, Austria
It is well known that tensile surface strain increases the activation barrier of adatom self diffusion on the fcc(111) surface [1]. We now present calculations which investigate the influence of tensile and compressive strain on the step down diffusion of Pt and Ni adatoms on the Pt(111) surface at straight and kinked step edges. The usually tensile surface stress of metals causes an in-plane shift of the atoms in the upper terrace (step relaxation), which modifies the barriers of the diffusion processes at a step. Whereas the energy barrier for adatom self diffusion is increased by tensile strain we find that exchange processes (concerted motion) are facilitated.
[1] H. Brune, K. Bromann, H. Röder, K. Kern, J. Jacobsen, P. Stoltze, K. Jacobsen and J. Nørskov, Phys. Rev. B 52, 14380 (1995)

STM studies of singly- and multiply charged ion-induced surface damage on highly oriented pyrolytic graphite
G. Hayderer, S. Cernusca, M. Schmid, P. Varga, HP. Winter and F. Aumayr
Institut für Allgemeine Physik, TU Wien, Wiedner Hauptstr. 8- 10, A-1040 Vienna, Austria
Scanning tunneling microscopy (STM) with atomic scale resolution has been applied to study surface defects in highly oriented pyrolytic graphite (HOPG) which have been produced by impact of slow singly- and multiply charged Ar ions (charge state up to 9+, kinetic energy 150 eV). The only surface defects found in the STM images are protrusions (hillocks) with a lateral size of 0.8 - 1.25 nm and an average height of 0.22 nm. Their spatial density is in good agreement with the applied ion dose, implying that nearly every single ion impact causes such a protrusion. A surface reconstruction, as characteristic for interstitial defects in HOPG, is observed in the vicinity of almost all defects. As a remarkable result, however, we find that the measured mean diameter of the hillocks increases with projectile charge state while their height stays roughly the same. This finding indicates a possible "pre-equilibrium" effect of the stopping for slow multiply charged projectiles in HOPG.

Electron emission from LiF(001) for grazing incidence of hydrogen atoms
J. Stöckl, H. Eder, S. Lederer*, K. Maass*, A. Mertens*, H. Winter*, HP. Winter, and F. Aumayr
Institut für Allgemeine Physik, TU Wien, Wiedner Hauptstr. 8-10, A-1040 Wien, Austria *) Institut für Physik, Humboldt Universität zu Berlin, Invalidenstr. 110, D-10115 Berlin, Germany
Electron emission due to hydrogen atoms (0.3 - 5 keV) grazingly scattered off a LiF(001) single crystal surface has been studied for impact angles from 0.8° to 1.8°. We observe that the threshold energy for electron emission increases with smaller projectile impact angle, whereas at higher impact energies smaller angles become more efficient for producing electrons. In addition, the production of surface excitons has been investigated by energy loss measurements. Our data are analyzed in terms of position- and velocity-dependent electron - and exciton production rates, which indicate that an electron promotion mechanism is the precursor for electron emission and exciton production.

Reale mathematische Lösung maximierter Ladungsaggregation in „Giant-Thomson-Clusters“ (GTC). Neue Ergebnisse und Computermodelle für ionisierte Partikelsysteme
H.G.Loew, K.W.Kratky
Institut f. Experimentalphysik, Universität Wien
Wechselwirkungen geladener Partikel mit Materie sind energie abhängig und erfahren im „ultrakalten Zustand“ deutliche Veränderungen, die auf atomarer Ebene auch am Verhalten lasergekühlter Ionen in der „Paul-Falle “ zu sehen sind. Durch das Feld dieser magnetischen bzw. elektrostatischen „Falle“ wird eine Umgebungsbedingung geschaffen, die erst das künstliche Abkühlen eines Ionenclusters ermöglicht. Da es nicht bekannt ist, ob es Zustände hochgeladener Partikelsysteme gibt, die ohne das confinement eines Feldkäfigs stabil bestehen können wurde ein Computermodell realisiert, das die Untersuchung der Aufsättigung von konzentrisch-sphäroidalen Punktladungsensembles zum Gegenstand hat. Das Modell stellt u.a. eine Erweiterung der mathematischen Extremalprobleme von Tammes und Thomson dar. Durch alternierende Folgen von steigenden Sättigungsladungen konnte gezeigt werden, dass der eher wahrscheinliche „Repellor“-Zustand eines hochgeladenen Ensembles überwunden werden kann und kontraktile „Attraktor“-Ensembles (GTC) geschaffen werden können, deren potentielle Energie schwach negativ ist, die jedoch eine hohe Zahl von über 100 gleich polarisierte Elementarladungen binden können, ohne zu zerfallen.

Influence of fs-Lasercooling on the Isomerisation of trans-Stilbene
Ch. Warmuth¹, F. Milota¹, A. Tortschanoff¹, E. Pollak², and H. F. Kauffmann¹
Inst. f. Physikalische Chemie der Univ. Wien, Währingerstr. 42, A-1090 Wien ²Chemical Physics Department, Weizmann Inst. of Science, Rehovot, Israel
The ps-time-resolved fluorescence of thermal trans-stilbene in gas phase was measured at different excitation energies. Non exponential decays were found and analysed within a distributed model. The extracted decay times show a parabolic dependence on the detuning () from the S1S0 0-0 transition () with a maximum time in the region of . The same behaviour is still found in the presence of 1 atm of argon buffer gas and yields insight to the topology of the S1-Potential. We show that the transients are the result of lasercooling in the S1-state introduced by fs-excitation, which influences the photochemical trans-cis isomerisation [1]. The experiments [2] can be explained on the basis of a statistical-mechanical theory [3].
[1] G. Gershinsky, E. Pollak, J. Chem. Phys. 107, 812 (1997) [2] Ch. Warmuth et al., J. Chem. Phys. 112, 3938 (2000) [3] H. Wadi, E. Pollak, J. Chem. Phys. 110, 11890 (1999)

Development of a Kinetic Trajectory Simulation (KTS) model for magnetized plasma sheaths
R. Khanal and S. Kuhn
Plasma and Energy Physics Group, Department of Theoretical Physics, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
As reported previously¹ we propose a Kinetic Trajectory Simulation (KTS) model² of magnetized plasma sheaths, which is expected to yield more accurate results than similar other schemes. We follow exact ion trajectories to calculate the ion distribution function, whereas the electrons are assumed to have a density corresponding to a cut-off Maxwellian velocity distribution. Assuming a given injection ion distribution function, we start with an initial guess to the potential profile and iterate it towards the final self-consistent state. As a first step, we have started with a simple (1d,1v) test case, the results being in good agreement with earlier ones. We will next consider increasingly more complex and realistic cases involving an oblique magnetic field in front of the wall. From these studies we expect detailed insight into the physical phenomena taking place in the divertor sheath region of a tokamak.

This work was performed within project P1 of the Association Euratom-ÖAW.
R. K. acknowledges support from the Austrian Academic Exchange Service (ÖAD).
¹ R. Khanal and S. Kuhn, ÖPG-Jahrestagung 1999 (University of Innsbruck, 20-25 September 1999), Book of Abstracts, p. 84
² H. Pedit and S. Kuhn, Phys. Plasmas 1(1), 13 (1994).

The non-coincidence effect in methanol/CCl₄ mixtures
M. Musso, P. Ottaviani, H. Torii, A. Asenbaum, M.G. Giorgini
Institut für Physik und Biophysik, Universität Salzburg, Hellbrunnerstraße 34, A-5020 Salzburg, Austria
The concentration dependence of the Raman non-coincidence effect (NCE) of the CO and of the OH stretching band of methanol was investigated in methanol/CCl₄ chemical mixtures. The NCE of a Raman band describes the frequency difference between the positions of the anisotropic and the isotropic component of that band and its magnitude and sign is influenced by the microscopic liquid structure. In this work emphasis is mainly placed upon the comparison of MD simulation results with experimental results obtained taking into account the influence of dilution on the band shape (position, width and asymmetry), following the procedure used in our recent studies of acetone/CCl₄ mixtures and dimethylformamide (DMFA)/CCl₄ mixtures. The MD simulation results are in qualitative agreement with our experiment, and would indicate a more pronounced influence of hydrogen-bonded networks on the microscopic liquid structure.

Fullereninterferenz ist dekohärenzfrei
Olaf Nairz, Markus Arndt, Anton Zeilinger
Institut für Experimentalphysik, Universität Wien
Kürzlich konnte gezeigt werden, dass selbst so komplexe Moleküle wie die Buckminsterfullerene C60 und C70 Kohärenz zeigen können. Der mit einer thermischen Quelle erzeugte Fullerenstrahl wird bei diesen Experimenten auf ein nanostrukturiertes Beugungsgitter gelenkt. Im Vergleich zu den ersten publizierten Ergebnissen konnte der Kontrast des erhaltenen Beugungsbildes einerseits durch eine feinere Kollimation und andererseits durch eine grobe Geschwindigkeitsselektion wesentlich verbessert werden. Die gemessenen Daten sind innerhalb der Meßgenauigkeit mit der Annahme eines perfekten Kontrastes verträglich. Das Experiment gibt also keinerlei Hinweis auf irgendeinen Mechanismus einer Dekohärenz. Aufgrund dieser Resultate scheinen Interferenzexperimente mit noch größeren Objekten durchführbar.

Talbot-Lau Interferometrie, eine ideale Methode für Makromoleküle
J. Petschinka¹, W. Case^1,2, M. Arndt¹, A. Zeilinger¹
Universität Wien ²Grinnell College, Iowa, USA
Eine große experimentelle Herausforderung stellt die Realisierung von Interferometern für Makromoleküle dar. Bei Verwendung von Gitterbeugung für kohärente Strahlteilung werden daher die Beugungswinkel maximal von der Größenordnung von Winkelsekunden sein und damit wären notwendige Abmessungen für ein Interferometer im Fraunhoferbereich bei weiten zu groß.
Es bietet sich daher an, solche Interferometer im Nahfeldbereich zu betreiben unter Ausnutzung des Talbot-Effektes und des Lau Effektes. Hier kommt es zwar nicht zu einer vollständigen Trennung der interferierenden Strahlen, jedoch zu einer kohärenten Rekonstruktion der Amplitudenverteilung bei bestimmten Entfernungen.
Zur Vorbereitung auf die Molekülexperimente werden derzeit von uns die möglichen Geometrien experimentell in Talbot-Lau-Anordnungen mit Licht untersucht. Alles deutet darauf hin, dass ein solches Interferometer für Moleküle eine realistische Möglichkeit darstellt.

Laser-induced dynamic gratings in gases: Comparison of experimental results and a discrete kinetic theory
Kurt Iskra, Jürgen Flieser, und Theo Neger
Inst. f. Experimental Physics, Technical University Graz, Petersgasse 16, 8010 Graz
Four-wave mixing techniques such as coherent anti-Stokes Raman scattering (CARS), degenerate four-wave mixing (DFWM) and laser-induced thermal acoustics (LITA) have found a wide range of applications to the detection of both major and trace species in combustion processes and plasmas. For technically interesting pressure ranges moderate to high collisional and quenching rates give raise to various types of laser-induced dynamic gratings. Knowledge of the formation process and the temporal and spatial evolution of these gratings reveals valuable information on gas composition, temperature, adiabatic velocity of sound waves, and other gas-dynamic parameters. Commonly, linearized hydrodynamic theories have been applied to model such gratings, but recently developed discrete kinetic models suggest a number of interesting phenomena to take place. A number of experiments have been carried out to check the range of applicability of this new theory.

Spin Resonance in High Mobility Heterostuctures
R.Meisels¹, F. Ziouzia¹, F. Kuchar¹, R. Deutschmann²
Institute of Physics, University of Leoben, Austria, ² Walter Schottky Institute, TU Munich, Germany
In the two-dimensional electron system (2DES) of AlGaAs/GaAs heterostuctures the spin splitting is far smaller than the cyclotron energy. This has major consequences for the integer and fractional quantum Hall effects, e.g. the appearance of Skyrmions at filling factors =1, transitions between spin-polarized and unpolarized states at =2/3, or the huge longitudinal magnetoresistance (HLR). The experiments are performed on a high mobility (/Vs, n_s=1.5) sample. The electron spin resonance (ESR) is measured using a photoconductivity technique ( f = 35 to 55 GHz) in the temperature range from 0.3K to 6K. The ESR was observed in the sub-unity filling factor range. The ESR frequency was found to deviate from a linear (B) dependence. This is attributed to the conduction band non-parabolicity. The influence of nuclear spin polarization on the ESR will be discussed (Overhauser effect). This work was supported by the EU (TMR, FMRX- CT98-0180).

Testing the Scaling Theory of the Quantum Hall Effect at Millimeterwave Frequencies
R.Meisels¹, F. Dybko¹, F. Kuchar¹, G. Hein² and K. Pierz²
1 Inst. of Physics, University of Leoben, A-8700 Leoben, A, ² PTB, Brauschweig, D
The localization of the states in the Landau level tails of a two-dimensional electron system (2DES) is of crucial importance for the occurance of the quantum Hall plateaus. In the scaling theory the width of the localized states is determined by the relation between the localization length (E) = |E-E*|=2.34, E* Landau level center) and an effective sample size L_eff. Hall plateaus and minima of the longitudinal resistance R_xx appear when . For d.c. and low frequencies the effective sample size is temperature dependent (; p=2). This causes the widths of the R_xx peaks between the plateaus to behave as T= p). At high frequencies the effective sample size is frequency dependent and a corresponding relation exists between coherence time (, z=1) and the effective duration 1/f of a measurement at frequency f. Localization requires <1/f. This causes B to be frequency dependent: f =1/ z. We investigate the validity of this prediction of the frequency dependence of B for AlGaAs/GaAs heterostructures using a millimeterwave reflection bridge up to 55GHz. Agreement with the scaling theory is found for frequencies where f>kT/h, i.e. at T<<1.5K. Deviations occur due to the effect of attractive impurities in the vicinity of the 2DES. This work was supported by the EU (TMR, FMRX- CT98-0180).

Aufhebung der Entartung von Schwingungen in dimeren Fullerenen
W. Plank, T. Pichler, H. Kuzmany
Inst. f. Materialphysik, Univ. Wien, A & IFW Dresden, D
Es ist bekannt, dass RbC60 als Funktion der Temperatur verschiedene stabile Phasen einnimmt. Von besonderem Interesse sind Phasen die durch Aufheizen aus einer abgeschreckten, kubischen Tieftemperatur- phase hervorgehen. Mit steigender Temperatur wurde jeweils eine Dimer-, Monomer-, und Polymer-Phase in eben dieser Reihenfolge fest- gestellt und mittels Raman-Spektroskopie analysiert. Aufgrund der beobachteten, beispielhaften Aufspal- tung der fünffach entarteten Hg Moden liegt der Schwerpunkt der Analysen bei der Dimerphase. Zudem wurde im Dimerspektrum keinerlei Aufspaltung der Gg Moden beobachtet. Insgesamt ergibt sich so die Möglichkeit aussagekräftige Vergleiche mit C60 Spektren anzustellen.

Optische Eigenschaften von einwandigen Kohlenstoff-Nanoröhrchen
M.Mannsberger¹, T.Pichler^1,2, M.Hulman¹, H.Kuzmany¹
Inst. f. Materialphysik, Universität Wien, A, ²IFW Dresden, Dresden, D
Einzelne einwandige Kohlenstoff-Nanoröhrchen (SWNT) sind perfekte eindimensionale Systeme, die je nach Typ entweder metallisch oder halbleitend sind. Sie lassen sich als aufgerollte Graphene-Ebene beschreiben. Die van-Hove Singularitäten in der elektronischen Zustandsdichte führen zu scharfen Strukturen in der optischen Absorption, die charakteristisch für die verschiedenen Typen von SWNT sind.
In diesem Beitrag analysieren wir die Durchmesserverteilung in dünnen Schichten von SWNT mittels optischer Absorption - im Vergleich zu den mittels Ramanspektroskopie und aus "tight binding" Rechnungen erhaltenen Werten. Weiters wird der Effekt der Ausbildung von Bündeln von SWNT in diesen makroskopischen Schichten, und dessen Einfluß auf die optischen Eigenschaften untersucht.

Dispersion von Raman Moden in einwandigen Kohlenstoff Nanoröhrchen
A. Grüneis, M. Hulman, W. Plank, H. Kuzmany
Inst. f. Materialphysik, Universität Wien, Austria
Im Raman Spektrum von Kohlenstoff Nanoröhrchen ist die radiale Atmungsmode besonders ausgezeichnet, da sie eine starke photoselektive Resonanzstreuung zeigt. In einer kürzlich veröffentlichten Untersuchung wurde gezeigt, daß diese Resonanzstreuung oszillierenden Charakter hat. In dem vorliegenden Beitrag wird dieses Verhalten mit der Dispersion von anderen Raman Linien verglichen. Dieser Vergleich wird insbesondere für die D-Linie und für den Oberton der D-Linie durchgeführt.

Photo-Induced Increase of the Superconducting Coherence Lengths in Oxygen-Deficient YBaCuO Thin Films
C. Stockinger*, G. Heine*, W. Markowitsch*, W. Lang*, R. Adam**, Roman Sobolewski**, R. Rössler***, J. D. Pedarnig***, D. Bäuerle***
*Institut für Materialphysik der Universität Wien, Austria; **Department of Electrical and Computer Engineering and Laboratory for Laser Energetics, University of Rochester, USA; ***Angewandte Physik, Johannes-Kepler-Universität Linz, Austria
60-K YBaCuO thin films were photodoped with white light at various temperatures from 70 K to 290 K. Before and after the excitation, the magnetoconductivity was measured in a magnetic field B = 0.5 T, and the experimental results were fitted to the Aslamazov-Larkin theory of superconducting order-parameter fluctuations to determine the superconducting in-plane and out-of-plane coherence lenghts. We observed that the photodoping process enhanced both conherence lengths and that the amount increased with the photodoping temperature increase. On the other hand, the superconducting anisotropy (i.e. the quotient of the coherence lengths) decreased with increasing temperature. The photodoping effect enhances superconducting properties of partially oxygen- deficient YBCO samples and is considerably increased by high doping temperatures.

Phonon mean free path evaluation of REBa₂Cu₃O_7-d (RE = Y and Er) superconducting compounds
P.Predeep and Deepika Bhandari^*
Condensed Matter Physics Laboratory, Department of Physics, Sree Narayana College, Kollam, Kerala, India 691 001
^* Postgraduate Department of Physics, S.S Jain Subodh College, Jaipur, India 302004
High temperature superconducting composites of compositions Yba₂Cu₃O₇- and ErBa₂Cu₃O₇- are prepared by solid state sintering technique. Simultaneous measurement of thermal conductivity and thermal diffusivity of the composites have been made by using Transient Plane Source method. An attempt has been made to evaluate the phonon mean free path for these composites using the measured values of thermal conductivity, diffusivity and velocity of sound in these materials. The deduced value of phonon mean free path is found to be 5 and 4 micrometers for Yba₂Cu₃O₇- and ErBa₂Cu₃O₇ respectively. This indicates that the main phonon scattering mechanism in these composites must be associated with large structure defects as phase boundaries, grain boundaries, and porosity. The indication is also that the heat transfer in these materials is not affected by the presence of twin boundaries.

Heat capacities of some rare earth oxides
P.Predeep and Deepika Bhandari*
Condensed Matter Physics Laboratory, Department of Physics, Sree Narayana College, Kollam, Kerala, India 691 00, * Postgraduate Department of Physics, S.S Jain Subodh College, Jaipur, India 302004
Using Differential Scanning Calorimetry (DSC), the specific heat capacity, C_p of three rare earth oxides (Gadolinium, Samarium and Yttrium) are measured in the temperature range 28 ⁰C to 500 ⁰C. The variation of C_p with temperature has been discussed for all these three rare earth oxides. A second order phase transformation with associated excess heat capacity correspondingly spread over a temperature range was found to take place in the case of gadolinium and samarium oxide while no such transformation was observed for yttrium oxide in the temperature range studied.

Analyse von Ta I - Linien im Spektralbereich 420 - 440 nm
N.Jaritz, L. Windholz
Institut für Experimentalphysik, Technische Universität Graz
In Weiterführung unserer Arbeiten zur Feinstrukturanalyse des neutralen Tantal-Atoms wurden bislang unbekannte Spektrallinien, deren Wellenlänge aus Spektralaufnahmen hoher Dispersion ermittelt wurden, mit Laserlicht angeregt. Die im letzten Jahr gewonnenen Ergebnisse (neue Energieniveaus, Klassifizierung von Linien etc.) werden vorgestellt.

Application of secondary electron emission yield measurements to study Al and Mg oxidation
M.Steinbatz and O.Benka
Institut fuerExperimentalphysik, Universitaet Linz
The secondary electron emission yield is measured for impact of 3 keV electrons on polycrystalline Al and Mg as a function of O coverage for different O dosing pressures. The base pressure in the UHV chamber was about 1x10^-10 mbar, the O pressures varied in the range between 5x10^-9 and 1x10^-6 mbar. For Al it is found, that the yield for the same O exposure depends significantly on the O dosing pressure, whereas for Mg the yield at the first stage of oxidation is only a function of the O coverage. From a fit of the experimental results to a rate equation model the adsorption probabilities of O and oxidation rates could be evaluated.

Domain Structure of Irradiated HighTc Superconductors
H.N.Yeritsyan^a, A.A.Sahakyan^a, S.K.Nickogosyan^a, A.S.Hovhannesyan^a Ye.M. Keheyan^b
Yerevan Physics Institute,Yerevan 375036 Armenia
^b Institute of Nuclear Chemistry, CNR, 00016 Monterotondo Scalo Roma Italy
HighTc superconductors (HTSC) are very sensitive to the structure defects particularly to the defects formed by irradiation of HTSC materials. Basic to this problem is the local description of degrees of freedom of the atoms within the unit cell that must be related to the electronic states. We proposed to study the behaviour of magnetic domains as a structural change affecting the critical parameters of HTSC. The results of electron irradiation influence on the domain structure of YBaCuO are given to demonstrate the usefulness of considered approach. This is based on the conception of " magnetic charge" of domains that varies with irradiation dose. AC magnetic susceptibility measurements were performed to determine its real and imaginary parts allowing to investigate the critical parameters of HTSC.

NIS Junction Cooling Power and Back Tunneling
Bostjan Jug, Zvonko Trontelj
Faculty of Mathematics and Physics, University of Ljubljana, Slovenia
Properly voltage biased normal metal - insulator - superconductor (NIS) junctions are used in the milikelvin range as low cooling power on chip refrigerators. At bath temperatures well bellow the transition temperature anomalies in the temperature vs. biasing voltage characteristics of the refrigerators appear. They can be explained by considering several parasitic heat sources. Among these, the most important is the back tunneling of hot quasiparticles from the superconductive electrode to the normal metal one. The cooling power expression, taking into account the back tunneling phenomenon, is derived by analyzing the quasiparticle currents. It is shown that the cooling effect of the NIS junction can be overshadowed by the back tunneling at certain quasiparticle and electron temperatures in the superconductive and normal metal electrode, respectively. Knowing the nature of the back tunneling, some suggestions for the improved cooling efficiency are given.

Separation of inter- and intragrain critical current densities of YBCO ceramics measured in a Hall magnetometer
M.Reissner, H.Varahram, W.Steiner, H.Hauser¹
Institut für Angewandte und Technische Physik, TU Wien, Austria, ¹Institut für Elektronik und Materialwissenschaften
A Hall magnetometer was built up to determine both the inter- and the intragrain critical current densities in ceramic superconductors at high fields. Both currents were separated by comparison of the results obtained from measurements on ceramics (inter- and intragrain currents) and on powders (only intragrain currents). To calculate critical current densities from the measured local field at the position of the Hall sensor, a model was developed which takes into account the special geometry of the samples. Whereas the intergrain currents are flowing around the whole sample, for the powder sample the signal from each individual grain has to be considered. From the thus determined inter- and intragrain current densities the Hall signal for the ceramics could be calculated. A comparison with the measured signals gives deviations of less than 10%, thus confirming the validity of the chosen model.

Magnetic properties and neutron depolarization studies of nanocrystalline Pr₁₂Fe₈₂B₆
G. Badurek¹, R. ², M. Dahlgren²
Inst. f. Kernphysik and ²Inst.f. Experimentalphysik TU Wien
Nanocrystalline hardmagnetic material of Pr_11.76Fe_82.36B_5.88 was produced by rapidly quenching as well as by mechanical alloying leading to a single-phased material with 2/14/1 grains with a mean size of 30nm determined from x-ray line broadening. The temperature dependence of the magnetic properties was measured in a pulsed field system. At room temperature the ratio between remanence and saturation magnetization is about 0.7, and it decreases to about 0.6 at lower temperatures indicating a decoupling due to an increasing anisotropy. The anisotropy field HA increases dramatically with decreasing field. With neutron depolarization experiments the average domain size of the material can be determined conveniently: at 300K about 150 nm which means that a "magnetic domain" comprises about 4-5 nano-sized grains. For exchange-coupled magnetic materials domains in a classical sense do not exist. Instead, areas covering several grains with magnetic moments oriented in more or less the same direction form domain like structures, which are called exchange domains. At low temperatures two FOMPs were found caused by higher order anisotropy constants Evidently influencing the mean domain size below 150K.

Permanent Magnetic Field Prism Polarizer for Neutron Interferometric Applications
G. Badurek¹, R.J. Buchelt¹, G. Kroupa², M. Baron³ and M. Villa³
Inst. f. Kernphysik, TU Wien, ² ILL Grenoble, ³ Atominst. der Österr. Universitäten
Spin-dependent bi-refringence of thermal neutrons upon passage through the air gap of a prismatically shaped permanent magnet yoke is used to split the incident unpolarized beam in two polarized subbeams with slightly different propagation directions. Using a sequential arrangement of two such prisms with an apex angle of 116° and an effective field of about 0.9 T in a gap of 10 mm height, an angular separation of the two spin states of more than 25.7 microrad has been achieved at a neutron wavelength of 0.184 nm, which is more than twice the width of perfect crystal Bragg/Laue reflections. Since no material has to be traversed, this method is ideally suited to polarize the neutrons within perfect crystal neutron interferometers without any significant loss of intensity. In first test experiments a polarization degree of 97.2% of the forward beam (“O-beam”) emerging from the last crystal plate of the Mach-Zehnder-type interferometer could be achieved. An even higher polarization is likely to be reached without simply increasing the number of prisms by minimizing the mutual influence of the stray fields of the individual magnet yokes. This work was supported by the European Union TMR Network (Contract ERB-FMRX-CT96-0057).

A pulsed field magnetometer - a tool for characterising permanent magnets.
R. Grössinger¹, M. Küpferling¹, A. Wimmer¹, M. Taraba¹, W. Scholz¹, J. Dudding², P. Lethuillier³, B. Enzberg-Mahlke⁴, W. Fernengel⁵, G. Reyne⁶
Institut f. Experimentalphysik, TU Vienna, ²Hirst Magnetic Instruments Ltd., Cornwall, United Kingdom, ³CNRS, PO BOX 166X Grenoble, France, ⁴Magnetfabrik Schramberg, Germany, ⁵VAC, Hanau, Germany, ⁶Univ. Ensieg LEG, Saint-Martin D`Heres, France
A large bore pulsed field hysteresograph is described, it shall be used for a fast quality control of industrial permanent magnets consisting of a magnet which is driven by a 24 mF condenser battery (U = 2500 V) with a bore of 70 mm inner diameter and a maximum field of 10T. The pulse duration can be varied between 4 and 15.7 ms. A second system working with a smaller battery but also with two different pulse duration was constructed by Hirst. Applying two different pulse durations can be used to make eddy current corrections for the true shape of the loop. The magnetization scales linear with dH/dt - the slope is proportional to the resistivity. The experimental results are compared with analytical as well as finite element calculations.
This work is supported by the EC SMT4-CT98-2212

Hysteresis model for isotropic magnetization processes
Hans Hauser and Roland Grössinger
Inst.f. Experimentalphysik, TU Wien, Wiedner Hauptst. 8-10, A1040 Vienna, Austria
The energetic model of ferromagnetic hysteresis calculates the magnetic state of anisotropic materials by minimizing the total energy function for all statistical domains. It is now generalized for isotropic materials. Statistical domains are characterized by their volume fractions and the direction of their magnetization. The volume fractions of the real domain structure of the material at the demagnetized state represent the initial occupation probabilities. Magnetocrystalline anisotropy, shape anisotropy and strain energy give the easy directions for the domains in the crystal grains of isotropic materials which are considered by average values. All reversible contributions of the domain wall movements are described by a reversible energy. The domain walls move reversibly until an individual Barkhausen jump occurs. From this point the irreversible losses start to accumulate. The probability for an elastic movement distance is decreasing with increasing distance from pinning centres. At a point of field reversal the magnetic state of the material is classified by changing the probability in dependence of the so far covered irreversible jumps The approach shows a good agreement to the magnetization curves of both soft and hard magnetic materials. The such obtained parameters can be correlated with that of standard magnetization process models.

Magnetostriktionsmessungen im Austromag
R. Grössinger¹, P. Rzetecki¹, H. Sassik¹, N. Pillmayr²
Institut für Experimentalphysik, Techn. Univ. Wien,
²KELAG, Arnulfplatz 2, A-9020 Klagenfurt
An der T.U.Wien wird ein quasistatisches Hochfeldsystem (bis zu 40T und 1s) mit verschiedenen Meßsystemen aufgebaut. Die Stromsteuerung erfolgt mit einem Thyristorsystem mit einem digitalen PID Regler. Derzeit steht ein 25T Magnet mit einer Bohrung von 25 mm zur Verfügung. Ein für die Sensorik interessanter Meßparameter ist die Magnetostriktion. Sie kann mittels Dehnungsmesstreifen gemessen. Im Rahmen dieser Arbeit wurde ein Meßstab gebaut um damit Untersuchungen an hartmagnetischen Verbindungen als Funktion der Temperatur durchzuführen. Die Magnetostriktion ist von grundlegendem Interesse und für Anwendungen von großer Bedeutung. Interessant ist die Auswirkung des Magnetisierungsprozesses. An wohlbekannten Werkstoffen wie Bariumferrit als auch an modernen Permanentmagneten aus Seltene Erd-3d Verbindungen wurden Messungen durchgeführt.
Diese Arbeit wird vom FWF P13146-PHY und der KELAG gefördert.

Low temperature hardening of amorphous and nanocrystalline materials
R. Sato Turtelli, D.Holzer, R. Grössinger, H. Sassik
Inst.f. Experimentalphysik, TU Wien, Wiedner Hauptst. 8-10, A1040 Vienna
Amorphous ribbons of Fe_85-xCo_xB₁₅ exhibit interesting soft magnetic. Additionally are two systems known which show in the nanocrystalline state excellent soft magnetic properties which are explained by the exchange coupling between the grains: FINEMET and Fe-Zr-Cu-B. The temperature dependence of the hysteresis loop, the initial susceptibilty and the pinning field were measured between 4.2K and room temperature. The T-dependence of the coercivity of Fe_85-xCo_xB₁₅ show between approximately 50K and room temperature a part which decreases slowly with T. Since for the magnetostriction and the anisotropy scaling laws are used, it is worth to try a scaling law between the coercivity Hc and the saturation polarization Js too. Since the temperature dependence of the magnetization can be described by Bloch's law also the coercivity can be described by a similar equation down to about 50K very well. At lower temperatures an upturn of HC(T) and of the pinning field were found as in Finemet and in Fe-Zr-Cu-B in the amorphous state but also after a heat treatment, which can be explained with a small amount of crystallites as a pinning effect on these crystals. In the present case this behavior was also seen in pure amorphous systems, where local stress centers may act as pinning sites.

Simulation of plasma flows interacted with body surfaces and ambient magnetic fields
Maxim Ponomarjov
State Academy of Aviation Technology, Tutaev, Russian Federation
Time-dependent plasma flows are simulated taking into account the ambient magnetic field effect. The effects of interactions between solid surfaces and charged particle flows are simulated using the original image method. The flow disturbances are described by the model Boltzmann equation. In the case of the homogeneous magnetic field the equation is solved analytically taking into account collisions between plasma particles and the ambient neutral particles. The case of diffuse reflection of particles by surface is considered in detail. The disturbances of plasma concentration are calculated in 3D space. The isodensity contours of particle concentration are plotted using the computer simulation and modern software. These contours show developing stratifications and flute structures in plasma jets and wakes in correlation with the ambient magnetic field and drift velocity directions.

Order parameter correlation function and shear viscosity near the critical point in fluids
G.Flossmann, R.Folk and G.Moser*
Inst. f. Theoretical Physics, Univ. Linz
* Inst. f. Physics and Biophysics, Univ. Salzburg
We calculate the wave vector and frequeny dependent order parameter correlation function, which is important for light scattering, in the cross-over region from background to critical behavior near the gas - liquid transtion in fluids. It is possible to introduce a proper scaling function for the line width which is well defined in all limits of its arguments and in good agreement with experiments. The nonuniversal parameters needed for an explicite calculation are found from experiments at vanishing wave vector. Further we calculate the shear viscosity in the critical region within a renormalization group treatment including non asymptotic effects as well as the influence of gravity and frequency. Comparison with experiments in Xenon show that the shear viscosity at zero frequency is in satisfying agreement with the theoretical predictions, whereas at finite frequencies deviations appear which may be assigned to the one loop order approximation. Thus a complete two loop calculation is demanded and preliminary results will be presented.

This work is supported by the Fonds zur Förderung der wissenschaftlichen Forschung (Project 12422-TPH)

Kinetics of silver-hydrogen pair formation in silicon
H. Feichtinger
Institut für Experimentalphysik, Karl-Franzens-Universität Graz
Chemical etching of silicon with HNO₃-HF mixtures leads to injection of atomic hydrogen in the near-surface region. An amount of this hydrogen can be detected via DLTS since hydrogen forms pairs with background dopants or characteristic complexes with deep centers, preferentially acceptors. Contrary to p-type material, pair formation in n-type (phosphorus doped) silicon is far less pronounced and the thermal stability of P-H pairs is rather poor, at least at low doping levels. Therefore we have studied the formation of Ag-H complexes at higher phosphorus doping levels (>10¹⁵ /cm³) using the dissociation of P-H pairs as a hydrogen source. The annealing behavior at 100°C can be explained by a kinetic model according to which a local equilibrium within the P-H system is maintained from which atomic hydrogen gradually leaks out to form silver-hydrogen complexes of only the lowest order (Ag-H). The recovery kinetics of the phosphorus doping suggests the existence of hydrogen sources not covered by P-H pairing.

Point defects in polycrystalline silicon
B. Pivac¹, V. Borjanovic², and I. Kovacevic¹
Rudjer Boskovic Institute, P.O.B. 180, HR-10000 Zagreb, Croatia
There is a considerable current interest in polycrystalline silicon material grown in ribbon form because of the significant potential for reduced solar cells application. However, if this potential is to be realized, it is essential to understand much more about the impurities and other defects present in the source material. Of the particular importance are intrinsic point defects population in such samples due to their influence on the electronic properties of material. However, a study intrinsic point defects behavior is additionally complicated due to their interaction with the present impurities and different structural defects. Experiments were performed on EFG polycrystalline silicon material rich with carbon and different structural defects such as dislocations and various grain boundaries. Samples were irradiated with g-rays from ⁶⁰Co source and 2 MeV electrons to the doses of 1016 el/cm² to introduce simple point defects in to the bulk. The results obtained with DLTS spectroscopy showed a significant difference between single and poly-Si material. The results are discussed in the light of intrinsic-extrinsic point defects interaction.

Investigations on microstructure and microchemistry polycrystalline silicon materials for solar cells
M. Stöger*, P. Schattschneider*, W. Markowitsch**, V. Schlosser**, R. Schneider***, H. Kirmse***, W. Neumann***
*Institute of Applied and Technical Physics, Vienna University of Technology, Austria;**Institute for Material Physics, University of Vienna, Austria;***Humboldt University of Berlin, Institute of Physics, Chair of Crystallography, Germany
A p-i-n doped µc-silicon thin film grown by means of hot wire chemical vapour deposition (HW CVD) on a zinc oxide film was investigated by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The structure of both layers, the ZnO substrate layer as well as the silicon thin film, and the chemical composition at the interface were the subjects of our investigations. We observed that a layer of pure (nearly oxygen-free) silicon with a thickness of about 5 nm covered the substrate surface. A reliable model to derive information about the texture of the interface between ZnO and µc-Si, the origin and the thickness of the oxygen-poor Si-layer was developed.

Self-organized {105} nanofacets in SiGe/Si(001) heteroepitaxy
C. Hofer¹, C. Teichert¹, K. Lyutovich², M. Bauer², E. Kasper²
Department of Physics, University of Leoben, A-8700 Leoben, Austria; ²Institut für Halbleitertechnik, University of Stuttgart, D-70569 Stuttgart, Germany
SiGe alloys for hetero-bipolar transistors, as used in cellular phones, allow a significant improvement of the high-frequency behaviour. The virtual substrate concept [1] includes, that the strain relaxation within the buffer layer is promoted by point defects, which support the formation of misfit dislocations. Such point defects can be injected via low energy Si+ ions and through supersaturation resulting from low temperature (LT) growth. Using atomic-force microscopy we have found that the resulting morphologies of such layers are influenced by the interplay of {105}-faceted crystallites and the misfit dislocation network introduced after the LT stage. By controlling the density of misfit dislocations it is possible to obtain a checkerboard pattern of {105}-faceted pyramids and pits that extends the spectrum of strain induced nanoscale structures in SiGe/Si(001) [2]. [1] E. Kasper, et al., Thin Solid Films 336, 319 (1998). [2] C. Teichert, et al., Appl. Phys. A67, 675 (1998).

Capacitance-voltage profiling and deep level transient spectroscopy on epitaxially-grown Si, SiGe, SiC, SiGeC heterostructures
E. Thor¹, M. Mühlberger¹, L. Palmetshofer¹, F. Schäffler¹, M. Gitsch²
Institut für Halbleiter- und Festkörperphysik, Johannes Kepler Universität Linz, A-4040 Linz; ² Institut für Analytische Chemie, Getreidemarkt 9/151, A-1060 Wien
Si, SiGe, SiC and SiGeC heterostructures, grown by molecular beam epitaxy (MBE), have been characterized by capacitance-voltage (C-V) profiling and deep level transient spectroscopy (DLTS). C-V measurements were performed in the temperature range from 300 to 50 K and the results were fitted by a numerical solution of Poisson’s equation giving the depth profile of the donor concentration in the multilayer structures. This knowledge is essential to set the bias and filling pulse voltages during DLTS measurements correctly in order to monitor a certain depth region. Deep level defects have been studied in as-grown samples, either nominally undoped or Sb-doped, as well as after hydrogen bombardment. In particular carbon-related defects and dislocation-related defects have been found in the layers, which is of great importance for the optimization of the epitaxial growth.

Characterization of dielectric thin films by Conductive Atomic Force Microscopy
E. Pischler¹, S. Kremmer¹, C. Teichert¹, F. Kuchar¹ and M. Schatzmayer²
Department of Physics, University of Leoben, A-8700 Leoben, Austria;
² Austria Mikrosysteme International AG, Unterpremstätten, Austria
Dielectric breakdown mechanisms of silicon gate oxides have been investigated by conducting atomic force microscopy (C-AFM) under ultra high vacuum conditions. It was found that the accumulation of defects created by induced charges and a statistic path formation of these defects is one of the main mechanisms leading to dielectric breakdown. C-AFM was used to record I-V-curves for a characterization of the oxide breakdown and for determination of breakdown voltages for oxides of different thickness with lateral resolution of a few nm. To adapt the C-AFM as a method for the thickness determination of thin silicon gate oxides the Fowler Nordheim tunneling current was measured. From these data we obtained information on the dielectric quality and homogeneity of the oxide layers. In addition the time dependence of the Fowler Nordheim current and of the morphological damage of the oxide layer have been measured.

Constituent chemical bonds and dielectric properties of Cu-series ternary chalcopyrite semiconductors
D. Xue, K. Betzler, H. Hesse
Fachbereich Physik, Universität Osnabrück, D-49069 Osnabrück, Germany
From the chemical bond viewpoint of crystal materials (the extension of the dielectric theory of solids [1-3])[4], chemical bonding behaviors and related bond parameters of the Cu-series ternary chalcopyrite semiconductors have been quantitatively studied. In this work, we start from the crystal structure of these semiconductors, quantitatively analyze their dielectric properties (linear and second-order nonlinear optical responses at the long wavelengths) of all constituent chemical bonds, and their contributions to the total nonlinearity of the whole crystal. Furthermore, we can find some structural information concerning linear and nonlinear optical origins of these semiconductors, which is helpful for us to effectively modify their dielectric responses according to our needs.
[1] J. C. Phillips, Rev. Mod. Phys. 1970, 42, 317.
[2] J. A. Van Vechten, Phys. Rev. 1969, 182, 891.
[3] B. F. Levine, J. Chem. Phys. 1973, 59, 1463.
[4] D. Xue and S. Zhang, Physica B 1999, 262, 78.

TOF measurements on deuterium molecules scattered and desorbed from modified V(111) surfaces
C. Eibl and A. Winkler
Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria
The probability of dissociative adsorption of molecular deuterium on vanadium surfaces and the absorption into the bulk depends strongly on the chemical composition of the surface. The most prominent impurities, sulfur, carbon and oxygen, change the initially unactivated adsorption system into a strongly activated one. We have used time-of-flight spectroscopy to study the process of desorption from such modified V(111) surfaces. The samples have been previously exposed to atomic deuterium, which allows the storing of rather large amounts of deuterium in the bulk. Subsequently TOF experiments have been performed during isothermal desorption of deuterium from a sulfur covered V(111) surface at 950 K. The mean translational energy of the desorption flux corresponds roughly to a Maxwellian flux (E=2kT) with a temperature of at least 3000 K. In addition, we have measured the accommodation coefficient of deuterium molecules impinging on V(111) as function of different chemical species on the surface.

Internal state distribution of molecular hydrogen desorbing from a V(100)+S surface
D. Gleispach and A. Winkler
Institute of Solid State Physics,University of Technology, Petersgasse 16, 8010 Graz
We have applied REMPI spectroscopy to determine the population of the rotational and vibrational levels of H2 desorbing from a sulfur covered V(100) surface. The state selected ions were mildly accelerated into a time-of-flight spectrometer to obtain additional information on the translational energy of the desorbing molecules. In order to load the vanadium sample with sufficiently large amounts of hydrogen we have exposed the sample to atomic hydrogen. Usually several hundred monolayers of hydrogen were absorbed in the vanadium sample and subsequently REMPI spectra were taken during isothermal desorption at 950 K. The translational energy of the state selected H2 molecules desorbing from the sulfur covered V(100) surface is far in excess of the surface temperature, as the result of a high activation barrier. Boltzmann plots of the rotational state distribution of the vibrational ground state exhibit a strong overpopulation of low J-states (rotational cooling). This is in accord with the frequently observed steering of low J molecules during adsorption. The significant overpopulation of the first excited vibrational states (50-fold) in the desorption flux points to a strong translational-vibrational energy conversion during recombinative desorption (vibrational heating).

Interaction of atomic hydrogen with a sulfur covered Vanadium(100) surface
H. Schiechl and A. Winkler
Inst. of Solid State Physics, University of Technology, Petersgasse 16, A-8010 Graz
Vanadium is a frequently used material in hydrogen storage technology due to its ability to absorb hydrogen in the bulk. The limiting step of hydrogen uptake is the dissociation probability for molecular hydrogen on the surface, which is extremely sensitive to surface impurities, like oxygen, carbon and sulfur. We have recently shown that atomic hydrogen can be adsorbed and absorbed with much higher probability, even on surfaces contaminated with oxygen and carbon. In this work we present experimental data concerning the interaction of atomic hydrogen on a sulfur covered V(100) surface, by using thermal desorption spectroscopy. Heating of a sample, which has been exposed to atomic hydrogen at a surface temperature of 92 K, yields two desorption peaks. The low temperature peak (120-270 K) stems from surface hydrogen, whereas the high temperature peak (>800K) comes from bulk hydrogen. The initial adsorption (absorption) coefficient is 0.18, remaining nearly constant up to a total amount of about 40 monolayers. At higher surface temperature (532 K) the absorption coefficient increases to 0.26 and remains constant for the whole coverage range investigated (600 monolayers).

The role of the rotational energy in the adsorption of hydrogen on clean and on vanadium modified Pd(111)
M.Beutl, J.Lesnik, K.D.Rendulic
Institut für Festkoerperphysik, Technische Universitaet Graz
We have studied the adsorption dynamics of hydrogen on a clean and on vanadium modified Pd(111) planes using a supersonic molecular beam. The modified Pd(111) surfaces were prepared by deposition of small amounts of vanadium through evaporation at a crystal temperature of 300°C. At this temperature the adsorbed vanadium is transferred into the second layer forming a subsurface alloy. The subsurface vanadium leads to a strong decrease of the initial sticking coefficient of molecular hydrogen compared to the clean Pd(111). In addition, the strong rotational effects seen in the adsorption of hydrogen on Pd(111) disappear with increasing vanadium coverage. As a result no isotope effect between hydrogen and deuterium can be seen. The observed effects can be interpreted in terms of the modified electronic structure of the alloy surface.
This work was supported by the Austrian "Fonds zur Förderung der wissenschaftlichen Forschung", S8102.

Changes of the adsorption behavior of carbon monoxide on Pd(111) due to subsurface vanadium
J. Lesnik, M. Beutl and K.D. Rendulic
Institut für Festkörperphysik, Technische Universität Graz
Vanadium was deposited on the Pd(111) crystal through evaporation at a temperature of 300°C. At this temperature the vanadium diffuses into the second layer and forms a subsurface alloy. We have investigated the adsorption of carbon monoxide on such vanadium modified Pd(111) surfaces using a supersonic molecular beam and thermal spectroscopy. The subsurface vanadium leads to a strong decrease in the adsorption energy compared to the clean palladium surface. For 0.33 ML vanadium the desorption peak at low CO coverages shifts from 490 K to 410 K. The initial sticking coefficient for CO molecules originating from a room temperature nozzle is still unity, but it shows a stronger decrease with increasing energy compared to the clean palladium. With increasing V coverage the adsorption energy is further reduced resulting in a desorption peak around 285 K for 1.25 ML vanadium. This work was supported by the Austrian "Fonds zur Förderung der wissenschaftlichen Forschung", S8102.

Nanolithographie an Filmen von Silizium Clustern
P.Scheier*, B. Marsen und K. Sattler
Department of Physics and Astronomy, University of Hawaii at Manoa, 2505 Correa Rd., Honolulu HI-96822, USA, *Institut für Ionenphysik, Universität Innsbruck, Technikerstr.25, A-6020 Innsbruck, Austria
Mittels eines Magnetrons wurde reines Silizium zerstäubt. Der Siliziumdampf kondensierte an einer reinen Grafitoberfläche. Die dabei entstehenden Cluster bedecken gleichmäßig die ganze Oberfläche und haben erstaunlich einheitliche Größen. Diese Filme an Siliziumcluster wurden unter Verwendung eines Tunnelmikroskop untersucht. Tunnelspektroskopie an diesen Filmen weist auf eine sehr große Bandlücke (bis 10eV) hin. Erhöhung des Tunnelstroms führt zu einem partiellen Verdampfen der Siliziumcluster. Sehr hohe Tunnelspannungen dagegen läßt zwei Cluster verschmelzen und führt zu einer Kompaktifizierung der Clusterfilme. Diese werden einerseits mechanisch verfestigt, andererseits wird die elektrische Leitfähigkeit im Film erhöht. Beide Methoden zur Veränderung der Clusterfilme können zum Beschriften und Bemalen dieser Oberflächen benützt werden. Bisherige Untersuchungen zeigten keine zeitlichen Veränderungen der beschriebenen Oberflächen, was eine Menge an möglichen Anwendungen eröffnet.
Diese Arbeit wurde teilweise durch das APART Programm der ÖAW unterstützt.

Streuung von Elektronen an akustischen Phononen in Silizium
E. Vass
Inst. für Experimentalphysik, Universität Innsbruck. Technikerstr.25, A-6020 Innsbruck
Die in der Literatur existierenden theoretischen Berechnungen der Beweglichkeit sowie des mittleren Energieverlustes heißer Elektronen, welche mit akustischen Phononen wechselwirken, beruhen fast immer auf der Debye-, der Deformationspotential-, sowie der Äquipartitions-Näherung. Diese Näherungen implizieren, daß die Ladungsträger a priori nur mit langwelligen akustischen Phononen, für die die Kontinuumsnäherung zutrifft, wechselwirken. Um die Gültigkeitsschranken dieser Näherung zu bestimmen, wurden für Elektronen in Si die genannten Transportgrössen in Abhängigkeit der extern kontrollierbaren Parameter T, T_e und n_e störungstheoretisch berechnet. Hierfür wurden die exakte Verteilungsfunktion sowie die reale Dispersionsrelation akustischer Phononen verwendet und im Wechselwirkungsmatrixelement der Quadrupol- und Oktopolterm mitberücksichtigt.

Screening of the Photon Field in Surface Photoemission from Simple Metals
S.Natschläger¹, J.Alberich², N.Barberan², J.Bausells³, R.Ruppin⁴, C.Simo⁵
Inst.f.Theoret.Physik, Uni Linz, ²Dep.d'Estr. i Const.de la materia, Univ.deBarcelona, ³Centr.Nac.de Microelectronica Bellaterra, ⁴SOREQ NRC, Israel, ⁵Dept.de Matematica Apl. i Ana. Univ. de Barcelona
An improvement of a previous two step hydrodynamical model calculation of angle resolved photoemission has been performed modeling the surface with a soft analytic function. The same ground state potential is used to screen the photon field and to calculate the electronic wave functions. The implemented code is able to use arbitrary ground state densities. Mathematical and physical aspects related with the model are extensively discussed. The behaviour of the main peak of the spectrum with the variation of some parameters leads us to the conclusion that it cannot be interpreted as the excitation of multipole modes. This conclusion was suggested in the previous two step model calculation.

The sensitivity of electron-positron momentum densities to crystal potentials
H. Sormann¹ and M. Sob²
Institut für Theoretische Physik, TU Graz, Petersgasse 16, A-8010 Graz, Austria ²Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, CZ-616 62 Brno, Czech Republic
The main topic of this paper is the sensitivity of the electron-positron momentum densities in alkali and transition metals with respect to various electron and positron crystal potentials. Despite this sensitivity is a rather complicated quantity, the following general statements can be formulated: (i) The momentum density of electron-positron pairs (MDAP) is more sensitive to the crystal potential in transition metals than in alkali metals. (ii) In many cases investigated, especially for transition metals, the values of the sensitivities are significantly higher for valence electrons than for core electrons. (iii) The strong sensitivity of theoretically obtained MDAP in metals has the far-reaching consequence that it makes it very difficult or even impossible to use comparisons between theoretical and experimental MDAP results as a criterion for the quality of different electron-positron interaction theories.

Electron momentum densities in metals beyond the local density approximation
N. Bektas and H. Sormann
Institut für Technische Physik, Technische Universität Graz, Petersgasse 16, A-8010 Graz
In metal physics, the momentum density distribution of the electrons plays an important role because this quantity is experimentally accessible by, e. g., Compton scattering measurements. Theoretically, it is of special interest to investigate how this momentum density is influenced by electron-electron correlations, a task which has been successfully treated during the last decades for the homogeneous electron gas (jellium model). However, the description of such correlation effects is much more difficult in case of inhomogeneous electron gases as they appear in lattice-periodical crystal potentials. In these cases, the inclusion of electron-electron interactions into the theory is frequently performed by local density (LD) corrections to independent particle results. In this paper, we present a new theoretical approach where the propagators of the interacting electrons are treated as real Bloch states, in order to be able to describe dynamical scatterings between the electrons beyond the LD approximation. The influence of Bloch effects on the momentum density is demonstrated for several metals, namely, for Na, K, Al, Cs, and Cu.

Phases of He₃-He₄ mixtures in two dimensions
E. Krotscheck, J. Paaso, M. Saarela and K. Schoerkhuber
Institut für Theoretische Physik, Johannes Kepler Universität, A 4040 Linz, Austria Department of Physical Sciences, Theoretical Physics, University of Oulu, Finland
We examine the phase diagram of He₃-He₄ mixtures in two dimensions as a function of density and He₃ concentration. A number of features distinguish this system significantly from the three--dimensional counterpart. Specifically, we find that the He₃ phase consists, at low He₃ concentration and positive pressures, of loosely bound dimers. The dimerized liquid phase separates at a He₃ concentration of two to three percent. He₃-He₄ mixtures can be found only in a concentration regime above three percent, these are metastable. We discuss the physical causes for each of these features and verify, wherever possible, that our results are consistent with simulation data and exact estimates.

Scattering of He₄ and He₃ Atoms at He₄ Droplets and Detection of Ripplons and Rotons
R. Zillich and E. Krotscheck
Institut für Theoretische Physik, Kepler Univ. Linz
The inhomogeneous generalization of the microscopic Jastrov-Feenberg method is applied to the problem of a single particle scattering from a many-body system in its ground state. Specifically, we are interested in the cross sections of He₄ and He₃ atoms scattered at He₄ droplets, and in the properties of the droplet which can be retrieved from the cross sections. Excitations are treated in the framework of linear response theory. The method describes scattering into elastic channels and decay into a subset of all possible inelastic channels. We present results of the signature of the roton in the elastic He₄ scattering cross section and the He₃ absorption cross section; the discrete ripplon spectrum of the droplets observable in the inelastic cross section of He₃; and the momentum transfer from an incident particle to He₄ droplets.

Exchange Effects on Plasmons in Metallic Films
H.M. Böhm, E. Krotscheck and S. Natschläger
Institut für Theoretische Physik, Johannes Kepler Universität, A-4040 Linz, Austria
We determine the dispersion of collective excitations in various simple metal films and study the role of exchange effects in a way that goes beyond the common local density approximation. The non-local exchange contributions to the particle-hole interaction are localized in a manner suggested by parquet-diagram theory. The effects of correlations are treated by using an effective interaction derived from the Hypernetted-Chain (HNC) diagram summation technique together with infinite-order correlated basis functions theory. The correlations lead to a noticable change in the dispersion relations whereas they play no role when treated within the local density approximation.

A rapidly converging algorithm for solving the Kohn-Sham and related equations in electronic structure theory
Jakob Auer und Eckhard Krotscheck
Institut für Theoretische Physik, Universitaet Linz
We describe a rapidly converging algorithm for solving the Kohn-Sham equations and equations of similar structure that appear frequently in calculations of the structure of inhomogeneous electronic many-body systems. The algorithm has its roots in the Hohenberg-Kohn theorem and solves directly for the electron density; single-particle wave functions are only used as auxiliary quantities. The method has been implemented for symmetric "slabs" of jellium as well as for spherical jellium clusters, fullerenes and sodium clusters with azimuthal symmetry. Starting from very rough guesses for the initial electron density, convergence is reached within a few iterations.

Phase diagram of a symmetric binary fluid in a porous matrix
Elisabeth Paschinger, Dominique Levesque, Gerhard Kahl and Jean-Jacques Weis
Institut für Theoretische Physik and Center for Computational Materials Science, TU Wien, A-1040 Wien, Austria and Laboratoire de Physique Theorique, Universite de Paris-Sud, F-91405 Orsay Cedex, France
Our investigations of the phase diagram of a symmetric binary fluid in equilibrium with a porous matrix show that already moderate changes in the properties of the matrix or in the matrix-fluid interaction lead to drastic modifications of the phase diagram of the fluid. Thus our results confirm on a qualitative basis recent experimental data. The phase diagrams that we have obtained show a wide variation and can be classified in terms of archetypes of systems of two order parameters. These different types can be characterized in terms of the loci where the -line of the demixing transition intersects the first-order liquid-vapor coexistence curve. Results are based on the optimized random phase approximation and on grand canonical Monte Carlo simulations.

Interlayer diffusion of adatoms under surface strain
G. Leonardelli, M. Schmid, P. Varga
Technische Universität Wien, Institut für Allgemeine Physik, A-1040 Wien, Austria
It is well known that tensile surface strain increases the activation barrier of adatom self diffusion on the fcc(111) surface [1]. We now present calculations which investigate the influence of tensile and compressive strain on the step down diffusion of Pt and Ni adatoms on the Pt(111) surface at straight and kinked step edges. The usually tensile surface stress of metals causes an in-plane shift of the atoms in the upper terrace (step relaxation), which modifies the barriers of the diffusion processes at a step. Whereas the energy barrier for adatom self diffusion is increased by tensile strain we find that exchange processes (concerted motion) are facilitated.
[1] H. Brune, K. Bromann, H. Röder, K. Kern, J. Jacobsen, P. Stoltze, K. Jacobsen and J. Nørskov, Phys. Rev. B 52, 14380 (1995)

Growth of ultrathin Pd films on the clean and O-(1x5) reconstructed V(100) surface
Ch.Konvicka, A.Hammerschmid, E.Lundgren, M.Schmid and P.Varga
Institut für Allgemeine Physik, Technische Universität Wien, Wiedner Hauptstr.8-10, A-1040 Wien
Thin films of Pd were deposited on the V(100) surface at different substrate temperatures. By using STM, LEIS and AES, we find that at RT Pd atoms adsorb in the 4-fold hollow sites, forming small clusters and chains of atoms, distributed randomly over the surface. At substrate temperatures of around 300°C these clusters coalesce into larger Pd islands and attach to the step edges. Above 300°C the Pd forms an alloy with the V(100) surface, resulting in locally dense Pd clusters embedded in the substrate. The growth strongly depends on the amount of segragated or adsorbed oxygen on the surface. For coverages lower than 0.5 ML STM shows that Pd avoids to adsorb on the O-precovered areas, aligning itself in registry with the O-induced (1x5) reconstruction of the V(100) surface. Further, we observed an enhancement of the O-induced lines in between the Pd islands for higher temperatures, indicating a displacement of the oxygen from underneath the islands to the Pd-free parts of the surface.

Adsorbates induced reconstructions of low index vanadium single crystal surfaces
R.Koller, C.Konvicka, E.L.D.Hebenstreit, R.Hammerling, M.Schmid and P.Varga
Inst. f. Allgemeine Physik, TU Wien, Wiedner Hauptstr.8-10/134, A-1040 Wien
Vanadium surfaces are promising candidates for the design of so-called inverse SMSI (Strong Metal-Support Interaction) catalysts consisting of metal oxide islands (e.g. vanadium oxide) supported by a transition metal base (e.g. palladium, rhodium). As a first step of this the interaction of oxygen and carbon with vanadium (100), (110) and (111) surfaces has been investigated with scanning tunneling microscopy (STM) and quantitative low energy electron diffraction (LEED). Depending on the crystallographic orientation, different types of reconstructions appear: an oxygen induced (1x5) and a carbon induced c(2x2) reconstruction on V(100) and an oxygen induced c(6x2) reconstruction on V(110). In the case of V(111) a faceting into three-sided pyramids is observed. The structures of these unusual reconstructions will be presented.

Complete determination of the reflection coefficient in neutron specular reflection by absorptive non-magnetic media
H. Leeb¹, H. Groetz¹, J. Kasper¹, R. Lipperheide²
Institut f. Kernphysik, TU Wien, ²Festkörpertheorie, HMI Berlin
Neutron specular reflection experiments for a unique reconstruction of the scattering density profiles of absorptive non-magnetic media are proposed. The method makes use of magnetic reference layers and is a modification of a recently proposed technique for phase determination based on polarization measurements. In addition to previous proposals it allows the determination of the complex reflection coefficient for absorptive media for positive and negative values of the momenta. The feasibility of the reconstruction of the real and imaginary parts of scattering length density profiles is demonstrated by realistic examples with simulated data.

Deriving q-deformed thermodynamic properties in terms of extra q-deformed energies of the Harper-equation
C. Micu & E. Papp
Department of Physics, Str. Victoriei 76, North University of Baia Mare, RO-4800 Baia Mare, Romania
This paper deals with the extra q-deformation of quickly tractable 1/N - energy solutions to the Harper-equation established recently. One proceeds by inserting such q-deformed 1/N - energies into the "-classical" free-energy of the two-dimensional electron-gas threaded by a perpendicular and homogenous magnetic field. this opens the way to the derivation of parameter-dependent forms concerning both free-energies and thermodynamic properties, now by invoking the q-deformation parameter alluded to above.

XPS studies of graphite electrode materials for lithium ion batteries
R. I. R. Blyth^(a), H. Buqa^(b), F. P. Netzer^(a), M. G. Ramsey^(a), J. O. Besenhard^(b), P. Golob^(c) and M. Winter^(b)
Institut für Experimentalphysik, Universität Graz, 8010 Graz, Austria
^(b) Institut für Chemische Technologie Anorganischer Stoffe, Technische Universität Graz, 8010 Graz, Austria
^(c) FELMI, Technische Universität Graz, 8010 Graz, Austria
We compare graphite powders and carbon fibres as model materials for XPS studies of the effects of surface pre-treatment of graphitic electrode materials for lithium ion cells. For carbon fibres the surface carbon percentage was found to vary widely depending on the surface treatment, with corresponding changes in the relative proportion of graphitic compared to C-O bonds. In contrast, results from the graphite powders show very little change in surface chemical composition, being dominated by graphitic carbon. SEM data show the carbon fibre cross section to be composed of a radial array of layered graphite, leaving a surface consisting largely of prismatic planes, while the graphite powder consists of graphite platelets with the surface area predominantly of basal planes. We conclude that the chemical modification occurs at the prismatic planes, and that the powders are unsuitable as models for XPS studies of electrode surface modification, while the fibres are very well suited.

NEXAFS of an azimuthally oriented oligothiophene
G. Koller, R.I.R. Blyth, S. Eck, F.P. Netzer, M.G.Ramsey
Institut für Experimentalphysik, Karl Franzens-Universität Graz, Austria
Sulfur reconstructed Ni (110) and oxygen reconstructed Cu (110) single crystal surfaces have been used as templates for the adsorption of bithiophene films. Both templated substrates induce the molecules in the monolayer to adopt a preferred azimuthal orientation, as evidenced by a variety of techniques. In this contribution particular focus will be given to C_K and S_L2,3 NEXAFS and their ability to determine molecular geometry. High resolution NEXAFS of bithiophene multilayers are markedly different to thiophene - in particular the C_K spectra are clearly a superposition arising from the inequivalent carbon sites. On both surfaces the NEXAFS data unambigiously demonstrate that the molecules are considerably tilted with respect to the surface. The azimuthal ordering leads to significant differences in the angular variation of NEXAFS in the two principal surface azimuths. This must be taken into consideration when determining the molecular tilt. The molecular orientation thus determined will be discussed in the light of HREELS and ARUPS results. Research supported by the SFB Electroactive Materials of the Austrian Science Foundation.

Growth and surface structures of thin thallium overlayers on Ge(111)-c(2x8)
C. Castellarin Cudia, S. Surnev, M.G. Ramsey, F.P. Netzer
Institut für Expermentalphysik, Karl-Franzens-Universität Graz, A-8010 Graz, Austria
The deposition of Tl on Ge(111)-c(2x8) surface has been followed using scanning tunneling microscopy (STM), LEED and Auger spectroscopy; the surface phase diagram has been measured as a function of Tl coverage and temperature, between room temperature (RT) and 400° C. At RT and low coverages the Tl adsorbate forms both single adatoms and 2D aggregates. On the latter bright lines develop which are separated by distances of three substrate spacings. Locally the c(2x8) structure is destroyed, but its (2x2) and c(4x2) building elements remain intact. For Tl > 0.8 monolayer (ML) the surface is covered by a low-corrugation overlayer with a (1x1) periodicity. Concurrently the step edges of the substrate become ragged. At higher coverages (> 1 ML) epitaxial growth of rotationally oriented 3D islands is developed. Annealing the RT Tl overlayers to 330-360° C results in a (3x1) structure, which grows from the lower step edges into the terraces. The ragged step edges become straight again. At coverage < 1 ML the (3x1) structure and c(2x8) areas coexist. Possible models for the Ge(111)3x1-Tl structure, and a comparison with works on Tl on Si(111), and alkali adsorption on semiconducting surfaces, will be presented.

Adsorption and reaction of CO on vanadium oxide – Pd(111) “inverse“ model catalysts: An HREELS study
M. Sock, S. Surnev, M.G. Ramsey, and F.P. Netzer
Inst. für Experimentalphysik, Karl-Franzens-Universität Graz, A-8010 Graz, Austria
The room temperature adsorption and reaction of CO on Pd(111) surfaces decorated by submonolayer coverages of vanadium oxide was studied by high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The HREELS surface phonon spectra of the V oxide phases were measured and used to monitor the changes in the oxide as a result of the interaction with CO. The intramolecular C-O stretching frequency on the V-oxide/Pd(111) surfaces displays two vibrational loss components as a function of CO coverage. The relative intensities of the two vibrational features as a function of V oxide coverage suggest the preferential population of high coordination adsorption sites by CO in the vicinity of the oxide-metal interface. The analysis of the V oxide phonon spectra indicates that adsorbed CO partially reduces the V oxide at the boundaries of the oxide islands to the Pd metal. The reduction of V oxide by CO is dependent on the oxygen content of the V oxide phase, as confirmed by the behaviour of the XPS V 2p core level spectra. Research supported by the JRP “Gas-Surface-Interactions” of the Austrian Science Foundation.

Growth phenomena of phosphor on Ge(111)-c(2x8)
L.Vitali, M.G.Ramsey, F.P.Netzer
Institut für Experimentalphysik, Karl-Franzens-Universität, Graz
The adsorption of phosphor on Ge(111)-c(2x8) at room temperature and at elevated temperature has been investigated for the first time with STM, STS in conjunction with LEED and AES. Beside the characterisation of the phase diagram of this group-V element on Ge particular attention has been given to low coverages and to the first step of the adsorption process. Phosphor adsorbs on the Ge(111)-c(2x8) surface on the adatom T₄ positions and is seen as a trimer in negative bias and as a local minimum in positive sample bias. The germanium structure which is known as an incommensurate (2x2) is stabilised by the adsorbed phosphor also at room temperature. Here the phosphor is adsorbed mainly at the border between (2x2) and c(4x2) unit cells. A possible model for this preferred adsorption mode is presented. At higher coverages a trimer structure with (3)R30° is formed which transforms in a chain phase at higher temperature consisting of a sequence of dimers along the <1-10> directions with interesting bias effects. Models for the formation of the (3)R30° and for the chain phase are suggested.

High field Mössbauer and dc magnetic measurements on R₆Fe₁3X compounds
R.Ruzitschka, M.Reissner, W.Steiner, P.Rogl¹
Institut für Angewandte und Technische Physik, TU Wien, Austria, ¹Institut für Physikalische Chemie, Universität Wien, Austria
In R₆Fe₁3X the R atoms are placed on two and the Fe atoms on four crystallographically different sites. We report on magnetic measurements on compounds R₆Fe₁3X with R = Nd, Pr and X = Pd, Sn, Si in fields up to 14.5 T and temperatures between 2 and 290 K. ⁵⁷Fe Mössbauer spectra were recorded at 4.2 K in fields up to 13.5 T. At low temperatures and fields above 12 T a tendency for saturation with a moment of 37.5 /fu is observed for R₆Fe₁3Pd. For all other investigated compounds, independent of the R atom, no saturation and moments in the order of 14 to 19 /fu are obtained at comparable field and temperature values. Several step-like changes of the magnetization appear with increasing field, persisting up to high temperatures (e.g. 265 K for Nd₆Fe₁3Sn). The height of the steps excludes the simple picture that all moments of one of the four Fe sublattices flip from antiferromagnetic arrangement to complete alignment into the field direction.

Investigation of BaFe₂S₃ and BaFe₂Se₃ by ⁵⁷Fe Mössbauer spectroscopy
M.Reissner, W.Steiner, H.Boller¹
Institut für Angewandte und Technische Physik, TU Wien, Austria, ¹Institut für Allgemeine und Anorganische Chemie, Universität Linz, Austria
We report on ⁵⁷Fe Mössbauer investigations of polycrystalline BaFe₂S₃ and BaFe₂Se₃. Both compounds exhibit orthorhombic structure. Although according to the chemical composition a Fe²⁺ can be expected, the preceding susceptibility measurements does not show a Curie Weiss behaviour for X = S and exhibit a broad maximum around 250 K for X = Se. At room temperature only quadrupole split spectra are obtained for both compounds with comparable splitting and line width. In contradiction to the expected ionic state of Fe the quadrupole splitting is only slightly dependent on temperature. Below 100 K for both compounds magnetic hyperfine splitting appears. The value of the magnetic hyperfine field measured at 5 K is, however, strongly different. The results will be discussed in comparison with neutron diffraction measurements.

Determination of the autocorrelation function in spin glasses above the freezing temperature by both high field Mössbauer and µSR measurements
J.Bogner, M.Reissner, W.Steiner, R.Cywinsky¹, J.A.Dann¹, M.T.F.Telling²
Institut für Angewandte und Technische Physik, TU Wien, Austria, ¹School of Physics and Astronomy, University of St.Andrews, Scotland, ²ISIS, Rutherford Appleton Laboratory, England
mSR and Mössbauer measurements of the metallic spin glasses Y(Fe₀.65Al₀.35)₂ and Y(Fe₀.4Al₀.6)₂ above the freezing temperature (T_f) in terms of a model taking into account a dynamical process of stochastic formation and decay of magnetically correlated regions. By this model a comparison of the autocorrelation function determined by the two different measuring techniques is possible. For the temperature dependence of the autocorrelation time we find fair agreement between both experiments for T > 2T_f.

Characterization of radiation induced defects in ZnO probed by positron annihilation spectroscopy
S. Brunner*, W. Puff*, A.G. Balogh**, P. Mascher***
*Institut für Technische Physik, Technische Universität Graz, Austria, ** Department of Materials Science, Technische Hochschule Darmstadt, Germany, *** Department of Engineering Physics, McMaster University, Hamilton, Canada
In this study we discuss the microstructural changes after high-energy electron and proton irradiation and the thermal evolution of the radiation induced defects during isochronal annealing. Different ZnO single crystals were irradiated either with 3 MeV protons or with 1-3 MeV electrons. The investigations were performed with positron lifetime and Doppler-broadening measurements. The measurements were done at room temperature and in some cases down to 10 K to investigate the thermal dependence of the trapping characteristics of the positrons. The differently grown ZnO single crystals show positron bulk lifetimes in the range of 161 to 176 ps. After proton irradiation, divacancy-type open volume defects are observed, with a lifetime of about (260±7) ps. Isochronal annealing causes agglomeration to larger defect complexes with a positron lifetime of about (370±20) ps. There are three annealing stages, one at about 200 °C, a second at about 500 °C and a third at about ! 750 °C. After annealing at 1150 °C all radiation induced defects were annealed out. Electron irradiation of ZnO single crystals with 1 MeV leads to discoloration but does not change the positron annihilation characteristics. After irradiation with >2 MeV electrons monovacancy-type defects were introduced, which disappear during isochronal annealing up to 300-400 °C.

Low temperature properties of CeNi₉Ge₄
H. Michor¹, E.Bauer¹, M. Galli¹, G.Hilscher¹, P. Rogl²
Institut für Experimentalphysik, TU Wien, ²Inst. für Phys. Chemie, Universität Wien
The novel compound CeNi₉Ge₄ was characterized by X-ray Rietveld refinements revealing a fully ordered distribution of the Ce, Ni and Ge atoms in the space group I4/mcm. In the temperature range from 2 to 300 K CeNi₉Ge₄ is paramagnetic with an effective moment of 2.5 µB/f.u which is close to the free ion value of Ce³⁺ (2.54 µB). The specific heat measured from 2K - 100K reveals an almost logarithmic divergence of the magnetic low temperature contribution, C(T) -TlnT, which is indicative for a magnetic instability at T 0, i.e. a regime of strong magnetic fluctuations in the vicinity of a quantum phase transition. For studies of the transport properies we prepared a single crystal CeNi₉Ge₄ by the Czochralski method. Ac susceptibility measurements down to 20 mK indicate a magnetic phase transition at about 100-200 mK depending on the annealing conditions of the polycrystalline material.

Skutterudites: Novel thermoelectric materials
E. Bauer^*, St. Berger^*, M. Galli^*, H. Michor^*, C. Paul^*, G. Hilscher^*, A. Grytsiv⁺ and P. Rogl⁺
* Institut f. Experimentalphysik, Technische Universität Wien, A-1040 Wien
⁺Institut f. Physikalische Chemie, Universität Wien, A-1090 Wien
Filled skutterudites with the LaFe₄P₁₂-type structure attracted much attention because of their large thermoelectric potential as well as of the rich variety of observed ground state properties. Among them are superconductivity, magnetic ordering, metal to insulator transitions and heavy fermion behaviour. Beside their large thermopower values, these compounds are characterised by a reduced thermal conductivity of the lattice due to the fact that the rare earth metals exhibit exceptionally large thermal parameters, corresponding to a "rattling" (i.e., soft phonon mode) of these atoms in an oversized cage. In this work we present a survey of physical properties of YbFe₄Sb₁₂ and EuFe₄Sb₁₂. We show for both cases changes of the ground state properties due to a substituion of Fe by Co, Rh, Ir or Ni. In particular, such substitutions cause crossovers from a magnetically ordered ground state to a non-magnetic one or from a metallic behaviour to an insolating state where carrier transport is possible due to hopping conductivity. At low temperatures, variable range hopping is be observed. An outstanding feature of the Eu-based skutterudites is the huge positive magnetoresistance varying from about 130 % at T = 2 K and 12 T to about 30 % at room temperature. The thermoelectric properties of these series is accounted for in terms of the figure of merit and we discuss possibilities to improve the thermoelectric performance by appropriate substitutions.
Work supported by the Austrian FWF, project P 13778-PHY.

Magnetic Properties of Paramagnetic Complexes Containing M(AsF₆)₂ (M=Co,Mn)
Z. Jaglicic¹, J. Pirnat¹, J. Luznik¹, Z. Trontelj¹, K. Lutar², H. Borrmann³
Institute of Mathematics, Physics and Mechanics, Ljubljana, Slovenia, ²Jozef Stefan Institute, Ljubljana, Slovenia, ³MPI für Chem. Physik fester Stoffe, Dresden, Germany
New compounds of the type M(AsF₆)₂ (M=Co, Mn) are possible starting materials in fluorine chemistry for preparation of new binary fluorides of transition metals. SQUID magnetometer and superregenative NQR spectrometer have been used to study magnetic properties of five different M(AsF₆)₂ compounds. Measurements reveal paramagnetic behavior above 50 K in all the samples. The complex weak ferromagnetic behaviour below 50 K in all four Co compounds possibly indicates that each paramagnetic sample has a minor admixture of some other weakly ferromagnetic Co compound with a transition temperature around 40 K. The measured magnetization is then a superposition of paramagnetic and ferromagnetic behavior. Arsenic NQR spectrum is measurable in Co(AsF₆)₂.2AsF₃ above 180 K, well in the paramagnetic region. Three separate lines have been assigned to three chemically different As sites in the crystal structure.

Establishing the kinetics adsorption of the xantath organic thin films at the surface of Galena mineral using voltage-time computer interface
Daniela Todoran*, Radu Todoran*, Mihail Caraman**
*North University of Baia Mare, Str. Dr.V. Babes Nr. 62/A,Baia Mare, Romania; **Bacau University, Calea Marasesti, nr. 157, Romania
Knowing the kinetic evolution of the adsorption layers at the solid-liquid interface shows the limiting elements resulted from the experimental techniques which cannot use the methods based on the interaction between ion or electron beams and the interface.
The determinations of the light intensity modifications caused by the luminescence changes of the interface optical response are performed by using photo-sensitive transducers of InSb and ZnSe that turn the optical signal into an electrical one. To continuously establish the luminescence changes, and implicitly the state of the adsorbed layer, a logical interface voltage-time is used. The determinations performed by optical luminescence were compared to those obtained by optical reflectance resulted from a light signal reflected by the solid-liquid interface.

Polynuclear Copper(II) Azido Complexes. Structures and Magnetic Behaviour.
F.A. Mautner, M.A.S. Goher, M.A.M. Abu-Youssef, R. Vicente, A. Escuer
Institut für Physikalische und Theoretische Chemie, TU-Graz, Austria; Chemistry Department, Alexandria University, Egypt; Departament de Quimica Inorganica, Universitat de Barcelona, Spain
Polynuclear copper(II) complexes, with end-on (EO) azido bridging ligands and pyridine derivatives, have been syntesized and their crystal structures determined by X-ray diffraction methods. The dinuclear compounds [Cu₂(N₃)₂(4-ethylpyridine)₄(NO₃)₂] (1), [Cu₂(N₃)₂(3-aminopyridine)₄(NO₃)₂].EtOH (2), the trinuclear [Cu₃(N₃)₆(methylisonicotinate)₂(DMF)₂] (3) and [Cu₂(N₃)₄(4-ethylpyridine)₂]_n (4). Magnetic susceptibility data of (1)-(3), measured from 2 to 300 K, show strong ferromagnetic coupling for the dinuclear end-on compounds (1) and (2), and bulk moderate ferromagnetic coupling for the trinuclear compound (3). Partially supported by CICYT (grant PB96/0163) and OENB (grants 6630, 7967).

Can a homometallic chain be ferrimagnetic ?
A. Escuer, R. Vicente, M.A.M. Abu-Youssef, M.A.S. Goher, F.A. Mautner
Departament de Quimica Inorganica, Universitat de Barcelona, Spain; Chemistry Department, Alexandria University, Egypt; Institut für Physikalische und Theoretische Chemie, TU-Graz, Austria
In the one-dimensional systems trans-[Mn(N₃)₂(3-methylpyridine)₂]_n (1) and trans-[Mn(N₃)₂(methylnicotinate)₂]_n (2) each manganese atom is co-ordinated by two pyridinic ligands and four azido ligands in trans arrangement. Double azido bridges between neighbouring manganese atoms build the 1D system but compound (1) shows end-to-end (EE) and end-on (EO) double bridges in the sequence (-EE-EE-EO)n whereas compound (2) shows the sequence (-EE-EE-EE-EE-EO-)_n. From magnetic point of view, the expected interaction pattern should be (-AF-AF-F-)_n for (1) and (-F-F-F-F-AF-)_n for (2). (AF and F are antiferromagnetic and ferromagnetic coupling, respectively). Whereas (2) shows unprecedented magnetic behaviour, (1) shows the typical features of ferrimagnetic behaviour: Chi(m)T decreases from RT to minimum at 40K and then increases on cooling. Magnetization measurements indicate saturation values of S=5/6 and S=3/2 per Mn(II) atom, respectively.

Position resolved texture measurements in hot-deformed Nickel-base superalloys
Baohui Tian, Oskar Paris & Josef Keckes
Erich Schmid Institut für Materialwissenschaft, Österreichische Akademie der Wissenschaften & Institut für Metallphysik, Montanuniversität Leoben
During hot-deformation of complex multiphase alloys, the alloy microstructure is changed locally due to thermal and mechanical gradients. In order to better understand the complex interplay between the microstructural evolution and the deformation behavior, microstructural parameters such as texture or precipitate size and -volume fraction need to be determined locally as a function of position on the sample. As a result of dynamical re-crystallization a local texture develops during deformation, depending on the deformation state. We have characterized the local texture in an hot-deformed, partly re-crystallized Nimonic 80a alloy by means of position resolved X-ray diffraction. Utilizing an X-ray beam of 0.1 mm x 0.1 mm size, pole figures could be obtained from differently deformed regions and from re-crystallized and not re-crystallized parts in the sample. The results of this study will be presented and discussed. Work supported by the Materials Center Leoben (MCL), Project SP8.

TEM observation of stable screw dipoles in plastically deformed Ni₃Al
C. Rentenberger and H. P. Karnthaler
Institute of Materials Physics, University of Vienna, Boltzmanngasse 5, A-1090 Wien, Austria. http://www.univie.ac.at/Materialphysik/EM
Screw dipoles are not observed in plastically deformed fcc structures since the screw dislocations annihilate by cross slip. Contrary to this, ordered Ni₃Al deformed within the anomalous temperature regime of the yield stress shows a high density of screw dislocations forming dipoles. This marked difference is caused by a thermally activated cube cross-slip process of the screw dislocations occurring in the ordered structure at higher temperatures. A quantitative analysis of the screw dipoles using transmission electron microscopy (TEM) methods are carried out on a sample deformed at 400°C. The analysis reveals a certain angular distribution of the dipoles that has its maximum at a dipole angle of 40 degrees. This result is compared with calculations using anisotropic elasticity theory. The calculated stability region is in good agreement with the results of the TEM observations.

TEM investigation of dislocation reactions in an ordered Ni alloy
C. Bayreder, C. Rentenberger and H. P. Karnthaler
Institute of Materials Physics, University of Vienna, Boltzmanngasse 5, A-1090 Wien, Austria.
Ni based superalloys have a high strength at high temperatures, which makes them interesting for technical applications. Single crystalline samples of the g´-phase of the superalloy NIMONIC 105 show an anomalous increase of the yield stress with increasing temperature up to the peak temperature T_P. The deformation of samples compressed along [111] above T_P occurs by the glide of superlattice dislocations (a<110>) on {001} planes. Since several slip systems are activated simultaneously non-coplanar reactions are expected to occur. Transmission electron microscopy (TEM) investigations using bright field and weak-beam dark field images were carried out to study the three-dimensional structure of the dislocation reactions. The analysis applying the criterion of no contrast (gb=0) using <111> reflections leads to the conclusion that reactions according to a[-110]+a[1-10]=a[0-11] occur frequently. Based on glide processes a model explaining the details of the reaction is proposed.

Atomic structure of antiphase boundary faults in Ni₃Al
C. Rentenberger, C. Lang, T. Waitz and H. P. Karnthaler
Institute of Materials Physics, University of Vienna, Boltzmanngasse 5, A-1090 Wien, Austria. http://www.univie.ac.at/Materialphysik/EM
Antiphase boundary (APB) faults are a characteristic feature of long range ordered alloys, they are planar faults disturbing the order. Up till now they were considered as chemical faults containing no structural component. In Ni₃Al deformed at RT tubes bounded by APB faults are frequently observed, their displacement vector is R_C = a/2 <110>. The APB faults can be imaged and analysed by transmission electron microscopy (TEM) methods, no contrast of the APB faults should arise in fundamental reflections. The TEM analysis of the structure of APB tubes using different reflectionsshows unambiguously that in addition to their chemical fault R_C the APB faults contain a small structural displacement R_S; R_S lies in the plane of the fault and is perpendicular to R_C. The observation of R_S is consistent with the results of recently published ab-initio calculations. The occurrence of the R_S component explains the pronounced contrast of the APB faults that is observed in fundamental reflections.

TEM investigation of copper after severe plastic deformation
B. Mingler, H.P. Karnthaler and M. Zehetbauer
Institute of Materials Physics, University of Vienna, Boltzmanng. 5, A-1090 Vienna
Equal-channel angular (ECA) pressing is a procedure whereby samples are pressed through a special die several times to produce an ultrafine grain size in the submicrometer range. ECA pressing offers the possibility to enhance the mechanical properties as compared with the large grained material. Using transmission electron microscopy (TEM) methods the ECA deformed Cu samples are compared with samples that received a subsequent compression or combined torsion-compression after ECA pressing. ECA deformation leads to mean grain sizes of about 300 nm irrespective of the number of passes applied. An increase of the grain sizes by about 10% is observed when the sample is compressed after the ECA pressing. Combined torsion-compression after the ECA pressing yields a 50 % increase of the grain sizes. The subsequent deformations after ECA pressing result in a higher misorientation between the grains as compared to ECA deformation only. It is concluded that the mechanical stren! gth of the specimens is governed by the large misorientations rather than by their grain size. Financial support by the Austrian Science Foundation (FWF) is gratefully acknowledged.

Crystal defects in CoFe alloys induced by transformation strains
M. Putzer, T. Waitz and H. P. Karnthaler
Inst. of Materials Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna
Martensitic transformations are frequently connected with transformation strains. In CoFe alloys the transformation takes place between the fcc and the hcp phase. The transformation proceeds by the glide of transformation dislocations that form glissile interfaces. In addition, after the transformation a high density of sessile partial dislocations bounding stacking faults was observed in the hcp product phase by TEM methods. Light optical observations show the occurrence of striations at free crystal surfaces during the transformation in aggreement with a transformation induced shear deformation. It is proposed that the high shear strains are caused by transformation dislocations all having the same Burgers vector. In front of the interfaces the plastic deformation of the fcc matrix leads to the formation of total fcc glide dislocations. These dislocations can react with the transformation dislocations leading to the observed straight sessile partial dislocations. Stacking faults that terminate at the sessile partial dislocations are dragged out by the moving interface. Financial assistance of the Austrian FWF is acknowledged.

Analysis of nano scale interfacial dislocations arrays using HRTEM methods
T. Waitz and H. P. Karnthaler
Instit. of Materials Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna
The martensitic phase transformation between different close packed lattices were investigated in single crystals of Co-0.85 and 5.75at.%Fe. The transformations from hcp to dhcp and dhcp to fcc were observed directly in the transmission electron microscope during in-situ heating. The atomic structures at the glissile transformation fronts were analysed in detail using high-resolution transmission electron microscopy (HRTEM) methods. Structural models of the interfaces were obtained in terms of narrowly spaced interfacial dislocations. Dislocations that occur on adjacent lattice planes (0.2 nm apart) could be resolved and analysed separately. The dislocations form a regular array at a nano scale and cancel their long range strain fields to the most possible extent. The dislocations are in a dipolar or tripolar configuration in the case of the transformations hcp to dhcp and dhcp to fcc, respectively. Financial support from the Austrian FWF is acknowledged.

HRTEM contrast modulations caused by crystal tilt
T. Waitz and H. P. Karnthaler
Institute of Materials Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, http://www.univie.ac.at/Materialphysik/EM
In high-resolution transmission electron microscopy (HRTEM) images crystal tilt can cause a strong periodic intensity modulation of lattice planes. In addition, space group forbidden reflections may show up that are absent only at perfect crystal orientation. It was proposed in the literature that the contrast modulation is caused by the linear interactions of strongly excited forbidden reflections with the transmitted beam and by non-linear interactions of fundamental beams. In the present study the contrast formation was analysed in detail using the imaging theory based on linear interactions. In contrast to the results proposed in the literature it is shown that the modulation is mainly caused by linear interactions of fundamental diffracted beams. Financial assistance from the Austrian FWF is acknowledged.

Severe Plastic Deformation as a Tool to Produce Nanocrystalline Metals*)
1) M.Zehetbauer, E.Schafler, L.Stegelmann, H.P.Karnthaler, B.Mingler
2) H.P.Stüwe, P.Les, R.Pippan, T.Hebesberger
1) Institute of Materials Physics, Vienna University, Austria
2) Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben, Austria
Recent research has shown that nanocrystalline (NC) metals can be produced by severe plastic deformation (SPD) provided certain deformation modes will be applied. In comparison to all previous methods to produce NC metals, this technique will offer important advantages as concerns minimization in pore size and maximisation in sample size. First systematic investigations show that the hydrostatic pressure component rules the final grain size while the number of deformation axes seems to be responsible for their shape. As compared to conventional large strain deformation techniques, those of SPD yield about 1.2–3 times higher strength values which are reached at 4-30 times higher strains. Moreover, SPD yields markedly higher densities of deformation induced lattice defects which also appears to be a consequence of the enhanced hydrostatic pressure restricting atomic lattice diffusion.
*) Joint Project 12944-45 funded by the Austrian Science Foundation (FWF)

Silver precipitates in a Cu matrix studied by HRTEM methods
B. Mingler and H. P. Karnthaler
Institute of Materials Physics, University of Vienna, Boltzmanng. 5, A-1090 Vienna
A Cu-3.5 at.%Ag alloy combines high strength with high heat conductivity; the combination of these properties is of special interest for technical applications. In this alloy semi coherent Ag precipitates occur that govern the mechanical properties since Ag is hardly soluble in Cu even at high temperatures. High resolution transmission electron microscopy (HRTEM) images show that the interfaces between the Ag precipitates and the Cu matrix are parallel to (111) Cu planes. To compensate the difference in the lattice constants of Ag and Cu (0.409 and 0.362 nm, respectively) the presence of periodically arranged misfit dislocations is needed with a periodicity of about 9 atomic spacings on the Cu side. Some of these precipitates are in twin orientation with respect to the corresponding lattice planes in the Cu matrix. Both the twin plane and the interface are parallel to {111} planes. This orientation relationship is in contrast to results of previous investigations stat! ing that the interface is tilted by 15° to the twin plane. Financial support of the "Hochschuljubiläumsstiftung der Stadt Wien” is acknowledged.

Al-Mg-Si studied by HRTEM methods
B. Mingler and H.P. Karnthaler
Institute of Materials Physics, University of Vienna, Boltzmanng. 5, A-1090 Vienna
The mechanical properties of an Al-1wt.%Mg-1wt.%Si alloy are determined by the formation of precipitates. High resolution transmission electron microscopy (HRTEM) methods are the most appropriate technique to investigate structure and morphology of the precipitates since during the very early stages of precipitation their size is in the nanometer range. The HRTEM investigations must be performed with care to minimise the formation of radiation induced defects. We observed very fine disc or lath-shaped precipitates with a length of about 5 nm and a thickness of only 3-4 monolayers after the alloy was aged for 8 days at RT. These precipitates are completely coherent with the matrix. They lie parallel to {100} and show strong bright dot-like contrasts with a spacing of about 0.4 nm. It is suggested that this contrast is caused by an alternating arrangement of columns of Mg and Si. Adjacent monolayers are shifted by a half period (0.2 nm). It is concluded that precipitati! on starts at RT and that precipitates of disc or lath shape are formed consisting of a few layers of MgSi.

The measurement of dislocation densities by X-ray Bragg profile analysis and electrocal resistivity*
F. Sachslehner, E. Schafler and M. Zehetbauer
Institut für Materialphysik der Universität Wien, Strudelhofgasse 4, 1090 Wien
The dislocation density in rolled samples of high-purity aluminium and copper, and dilute copper gold alloys (0.075 at% and 0.3 at%) was investigated by X-ray Bragg profile analysis (XPA) and electrical resistivity measurements. The results of both methods are in good agreement for aluminium. In contrast, for copper and the dilute copper gold alloys there is a significant difference in the dislocation density obtained from the XPA-method and the electrical method: For true strains larger than 40 % the XPA-method yields only about 60 % of the dislocation density obtained from the electrical measurement. This discrepancy can be explained by the presensce of small dislocation loops (size smaller than 5 nm) originating from the agglomeration of deformation induced vacancies. The small loops are not seen by the XPA-method but they contribute to the dislocation resistivity.
* Work supported by the Austrian FWF under project 9930-PHY and 12945-PHY.

Thermophysical Properties of Liquid Copper
C.Cagran, A.Seifter, G.Pottlacher
Institut für Experimentalphysik, Technische Universität Graz
Using a subsecond ohmic pulse-heating technique it is possible to measure thermophysical properties of metals and alloys at temperature regions that are inaccesible to most other techniques. Pulse heating enables heating rates up to 108 K/s and thus is applied for short time (s) measurements of thermophysical properties of electrical conducting materials. Due to the short time of the experiments no chemical interactions between the sample and its environment occur. Using pulse-heating, measurements on wire-shaped Copper (Cu) specimens of 0.5 mm diameter and an average length of 50 mm were performed. The results - especially thermal conductivity and thermal diffusivity up to 500 K into the liquid phase - are discussed and compared to literature values.
This paper will also give first results on emissivity of liquid Copper measured by means of a high speed laser polarimeter system.
Research partially supported by FWF Grant P12775-PHY.

Normal spectral emissivity measurements on liquid metals, using a high speed polarimeter.
A. Seifter, F. Sachsenhofer, S. Krishnan, and G. Pottlacher
Institut für Experimentalphysik, Technische Universität Graz, Petersgasse 16, A - 8010 Graz, Austria
Temperature is the property of most interest when measuring thermophysical data. Due to the high temperatures achieved and the short duration of the experiments, the temperature measurements must be performed by optical methods. This requires the use of fast pyrometers and knowledge about the behavior of normal spectral emissivity as a function of temperature. Prior to now, all existing pulse heating systems capable of investigations on liquid samples could only measure the radiance temperature during the experiments. In order to determine true temperature it was necessary to assume that emissivity is constant over the entire temperature range with a value equal to that at the melting point. This assumption can cause large uncertainties in temperature measurements, especially at elevated temperatures. To avoid these uncertainties, a µs – Division of Amplitude Photopolarimeter (µ–DOAP) was added to our experiment. The µ–DOAP detects changes of the polarization state, and with elipsometric standard equations, the normal spectral emissivity can be calculated. First measurements at a wavelength of 684.5 nm on liquid Niobium, Tungsten and Nickel are presented.
This work is supported by FWF – Grant P12775-PHY.

The role of small angle scattering for the deviation from Matthiessen´s rule in dislocated copper and dilute copper alloys*
F. Sachslehner
Institut für Materialphysik der Universität Wien, Strudelhofgasse 4, 1090 Wien
Up to now investigations of the temperature dependence of the deviation from Matthiessen´s rule (DMR) consider only large angle scattering processes for the conduction electrons, and the influence of small angle electron-phonon scattering is neglected. The contribution of the latter to the ideal resistivity of copper and the related scattering anisotropy is estimated within a two-group model for the conduction electrons and the Deby model for the phonon spectrum. It is shown that the DMWs originating from phonons and impurities or dislocations are enlarged significantly by the strong scattering anisotropy of small angle electron-phonon scattering. As a result, the theoretical description of experimental DMR-curves is markedly improved.
* Supported by the Academic Research Collaboration between Austria and Britain.

Measurement of Screw and Edge Dislocation Density by means of X-Ray Bragg Peak Profile Analysis *)
¹E.Schafler, M.Zehetbauer, Ch.Sitkovich, Ch.Klüber, ²T.Ungar
1) Institute of Materials Physics, University Vienna, Austria
2) Institute for General Physics, Eötvös University Budapest, Hungary
In order to understand the dislocation mechanisms of work hardening in metals, there has been an urgent need for experimental quantification of the densities of specific dislocation types, i.e. of screws and edges. Recently, the abilities of X-ray Bragg Peak Profile Analysis (XPA) have been extended: by measuring a number of different Bragg reflections from a particular site of the plastically deformed sample, the so-called contrast factor of dislocations of this site is found experimentally. This contrast factor can be also written in terms of the orientations of diffraction-, Burgers-, and line vectors and of the number of specific types of dislocations considered so that the relative fraction f of screw and edge dislocations can be determined. Results of f will be presented and discussed as function of deformation degree, for single and polycrystals from different metals.
*) Project 12945 funded by the Austrian Science Foundation (FWF)

Position resolved texture measurements in hot-deformed Nickel-base superalloys
Baohui Tian, Oskar Paris & Josef Keckes
Erich Schmid Institut für Materialwissenschaft, Österreichische Akademie der Wissenschaften
During hot-deformation of complex multiphase alloys, the alloy microstructure is changed locally due to thermal and mechanical gradients. In order to better understand the complex interplay between the microstructural evolution and the deformation behavior, microstructural parameters such as texture or precipitate size and -volume fraction need to be determined locally as a function of position on the sample. As a result of dynamical re-crystallization a local texture develops during deformation, depending on the deformation state. We have characterized the local texture in an hot-deformed, partly re-crystallized Nickel-base superalloy (Nimonic 80a) by means of position resolved X-ray diffraction. Utilizing an X-ray beam of 0.1 mm x 0.1 mm size, pole figures could be obtained from differently deformed regions and from re-crystallized and not re-crystallized parts in the sample. The results of these measurements will be presented and discussed.

The mechanical properties of disordered tungsten-carbon thin
N. Radic¹, S. Seidler², T. Koch², M. Jakšic¹, A. Tonejc³, O. Milat⁴ B. Pivac¹, F. Meinardi⁵
Rudjer Boškovic Inst., P.O.B. 1016, HR-10000 Zagreb, Croatia, ²Inst. of Materials Science & Testing, Karlspl. 13, A-1040 Vienna, Austria, ³Dep. of Physics, Bijenièka 32, HR-10000 Zagreb, Croatia, ⁴Inst. of Physics, Bijenièka 46, HR-10000 Zagreb, Croatia, ⁵Universita degli Studi di Milano, Via Emanueli 15, I-20126 Milan, Italy
Tungsten-carbon thin films were prepared by reactive magnetron sputtering operated in argon + benzene gas mixture. The effects of benzene partial pressure (1,25-6,5%), substrate temperature (r.t.-400°C) and substrate bias voltage were investigated. Structure of the films is dominated by WC1-x nonstoichiometric carbide, imbedded with the unbound carbon. In the low-carbon-content films the WC1-x matrix structure changed from strongly disordered (111)-textured structure to small-grained microcrystalline (200)-textured structure with the temperature increase, while the structure in high-carbon-content films is a strongly disordered (111)-textured WC1-x in all cases (grain sizes being 7-16 nm). The amount of segregated carbon and the ratio between disordered and graphitic components of unbound carbon increased with substrate temperature and more strongly with the benzene partial pressure. The micromechanical properties of the films are governed mostly by the total amount of unbound carbon: the nanohardness decreases from 29-34 GPa for the films produced with the 1,25% and 2,5% benzene admixture to 13-30 GPa for the films prepared with 5% benzene.

2-Dimensional Ising Ferromagnetic Property in Nanoscopic Ni-MNC system
Yuko Ichiyanagi
Yokohama National University
Magnetic property of the precipitates from the mixing of the aqueous solutions of NiCl₂^.6H₂O and and Na₂SiO₃^.9H₂O was studied. It has been revealed by structural, chemical and magnetic analyses that the precipitates were 2-dimensional(2d) Ni(OH)₂ ferromagnetic clusters with average diameters of 2.5nm surrounded by amorphous SiO₂ networks.
The magnetization M of Ni(OH)₂ monolayer nanoclusters (Ni-MNC) in the magnetic field of 300kOe was measured by Pulsed Field Magnetometer at temperature of 4.2K. The magnetization at temperatures of 20K, 30K and 50K were measured by SQUID magnetometer applying magnetic fields between -50kOe and +50kOe.

High precision Doppler spectroscopy for the determination of defect sites in binary alloys
W.Egger¹, G.Bischof², V.Gröger³ and G.Krexner¹
Institute for Experimental Physics, University of Vienna, Austria
² FH Joanneum, Department of Automotive Engineering, Graz, Austria
³ Materials Physics Institute, University of Vienna, Austria
Measurements of high-momentum regions of Doppler annihilation spectra with largely reduced background are reported for binary alloys for situations where positrons are strongly trapped at defects. The background reduction is achieved by coincidence measurements with two germanium detectors accumulating energies as data pairs. The results are presented as two-dimensional annihilation spectra for the binary alloy AlAg and intermetallic compounds FeAl and Fe₃Si and for their pure constituents. The results are compared with calculations based on density functional theory using the local density approximation (LDA) and generalized gradient approximation (GGA). The agreement between theory and experiment is generally good for the elements investigated, the accuracy is sufficient to distinguish clearly between vacancies on different sublattices in intermetallic compounds and to estimate the proportions of elements present in precipitates in binary alloys if they trap positrons.

Local order in liquid Zintl alloys
Karin Seifert-Lorenz, Jürgen Hafner
Institut für Materialphysik der Universität Wien und Center of Computational Material Science
We will present ab-initio molecular dynamics of liquid Zintl alloys in the potassium-antimony and the potassium-tellurium system. It can be shown, that the structure of the solid counterparts is preserved to a certain degree on melting, but not to the extend experimental measurements of thermo- dynamic and electrical properties suggest. To solve this alleged disaccord we calculated the atomic positions as well as the electronic conf- figurations of the liquids K₃Sb, KSb and KTe over an time range of 12 ps.

Skutterudite: Novel thermoelectric materials
E. Bauer^*, St. Berger^*, M. Galli^*, H. Michor^*, C. Paul^*, G. Hilscher^*, A. Grytsiv⁺ and P. Rogl⁺
Institut f. Experimentalphysik, Technische Universität Wien, A-1040 Wien,
⁺Institut f. Physikalische Chemie, Universität Wien, A-1090 Wien
Filled skutterudites with the LaFe₄P₁₂-type structure attracted much attention because of their large thermoelectric potential as well as of the rich variety of observed ground state properties. Among them are superconductivity, magnetic ordering, metal to insulator transitions and heavy fermion behaviour.
Beside their large thermopower values, these compounds are characterised by a reduced thermal conductivity of the lattice due to the fact that the rare earth metals exhibit exceptionally large thermal parameters, corresponding to a "rattling" (i.e., soft phonon mode) of these atoms in an oversized cage.
In this work we present a survey of physical properties of YbFe₄Sb₁₂ and EuFe₄Sb₁₂. We show for both cases changes of the ground state properties due to a substituion of Fe by Co, Rh, Ir or Ni. In particular, such substitutions cause crossovers from a magnetically ordered ground state to a non-magnetic one or from a metallic behaviour to an insolating state where carrier transport is possible due to hopping conductivity. At low temperatures, variable range hopping is be observed.
An outstanding feature of the Eu-based skutterudites is the huge positive magnetoresistance varying from about 130 % at T = 2 K and 12 T to about 30 % at room temperature. The thermoelectric properties of these series is accounted for in terms of the figure of merit and we discuss possibilities to improve the thermoelectric performance by appropriate substitutions.
Work supported by the Austrian FWF, project P 13778-PHY.

Magnetic phase transition in rare-earth double molybdates – strongly anisotropic ising compounds
E.N. Khatsko
Institute for Low Temperature Physics
Double rare-earth molybdates compounds display a number of fascinating features associated with a low symmetry, a small value of exchange, a considerable contribution of the dipole-dipole interaction, and features of electron energy spectrum. Single crystals of MeR(MoO₄)₂, (Me = Cs, K; R = Dy, Er, Tm) belong to the rhombic or lower symmetry class. The rare-earth ions layers are separated with transition metal ions layers. This results in a low-dimensional magnetic structure. The magnetic susceptibility, the magnetisation and EPR investigations of these crystals are reported. The measurements were performed between 0.2 and 100K in magnetic fields up to 6T along principal magnetic axes. The magnetic properties are strongly anisotropic, that is dictated by the crystal structure and intricate character of the exchange interaction. The EPR investigations show almost one component of g-factor, so this compounds may be treated as Ising magnets. 3d magnetic ordering is found to occur in 1K region. The concrete magnetic structure depend on competition of single and different ions anisotropy and leads to sophisticated noncolinear magnetic structures.

Coagulation as the predominant coarsening mechanism
Richard Weinkamer and Peter Fratzl
Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, and Metal Physics Institute, University of Leoben, Jahnstrasse 12, A-8700 Leoben
At late stages of a precipitation reaction, the total amount of interface between matrix and precipitates is reduced by the growth of larger precipitates at the expense of smaller ones, a process commonly referred to as coarsening or Ostwald ripening. By means of diffusion, mediated in real alloys by migrating vacancies, the smaller precipitates are assumed to dissolve by the evaporation of monomers, which subsequently allow the growth of larger precipitates. In our three-dimensional Monte Carlo simulations using a vacancy mechanism, we show that a different process may occur and even dominates. Depending on the interaction of vacancies with the different atomic species, precipitates may diffuse as a whole and coalesce with other precipitates. Both coarsening mechanisms lead to a very similar microstructure.

Numerical simulation of the Quantum Hall Effect
Josef Oswald
Inst. of Physics, University of Leoben, Austria
Based on a new network model we present the simulation of a realistically shaped quantum Hall effect (QHE) sample. We calculate Rxx, Rxy and the internal potential distribution for the case of a combination of gate electrodes across the Hall bar and across the contact arms. While such kind of experiments have been done already 10 years ago[1], no theoretical model so far was able to achieve a quantitative modeling of these experiments. This is the first transport model, which is able to achieve a quantitative agreement with the experiments. Our calculation allows to visualize the development of edge strips during the sweeping magnetic field and their transformation from being transmitted through a gate to being reflected at a gate. This demonstrates at the same time, that the puzzling experimental observation of macroscopically wide edge strips is indeed possible without loosing the exact quantization of the QHE. [1] G. Mueller et al., Phys. Rev. B 42, 7633 (1990)

Anomalous Hall effect in high-temperature superconductors
W. Lang^a, W. Göb^a, W. Liebich^a, R. Sobolewski^b, R. Rössler^c, J.D. Pedarnig^c, D. Bäuerle^c
Institut für Materialphysik der Universität Wien, Austria, ^bDepartment of Electrical and Computer Engineering, University of Rochester, USA, ^cAngewandte Physik, Johannes-Kepler-Universität Linz, Austria
In type-II superconductors a phenomenon similar to the classical Hall effect can be observed that is associated with the dissipative vortex motion. In the cuprate high-temperature superconductors, however, the vortex Hall effect is in contrast to the traditional theoretical models - a fundamental problem of vortex dynamics in these materials. We report on the surprising observation that the Hall angle can reverse its sign below the critical temperature. In the experimental condition of strong pinning at twin boundaries and in very low magnetic fields we found even a double sign reversal of the Hall effect in YBCO thin films. In high transport current densities, or with the magnetic field tilted off the twin boundaries by a small angle, the second sign reversal vanishes. Our observations are interpreted as strong, disorder-type dependent vortex pinning and contradict previous claims that the Hall conductivity in high temperature superconductors is independent of pinning.

Anharmonic Phonon Coupling in Gallium Orthophosphate
F. Krispel^1,2, P. Knoll¹, W. Wallnöfer², P. W. Krempl²
Institut für Experimentalphysik, Karl Franzens-Universität Graz, Universitätsplatz 5, A-8010 Graz, ² AVL List GmbH, Hans List Platz 1, A-8020 Graz
Gallium orthophosphate (GaPO₄) is a new, synthesized crystal which has the same point group as quartz. But the phase transition at 573°C (a b modification) is frustrated so that most physical properties are stable against temperature up to 930°C. The factor group analysis shows a classification into 8 A1, 9 A2 and 17 E modes. The latter are degenerated twice. Raman investigations over a wide temperature range (12 K to 1200 K) are performed to assign the measured phonons to their modes and to investigate a possible softening of modes. The Raman line shapes can be fitted with a Lorentz function. Fit results show an anharmonic coupling of two phonons in A1 geometry. The experimental data are compared with a simple theoretical model.

Magnetic Brilluoin scattering in NiO
P. Knoll^1*, M. Musso², M. Pressl¹, A. Asenbaum²
Inst. f. Exp.Physik, Univ. Graz, Universitätsplatz 5, A-8010 Graz, Austria
²Inst. f. Physik, Univ. Salzburg, Austria
Magnetic Raman scattering has received strong interest in the last years because of the unconventional characteristics of the HTc-materials. NiO is one of the traditional classical 3-dimensional antiferromagnetic systems which is predestinated as a model substance in order to study anisotropies, high order magnetic interactions and details of vertex interactions with e.g. photons. With inelastic photon scattering we have investigated the low energetic excitations of the acoustical magnetic one-magnon branch as well as other low energetic quasi-particles as possible two-magnon states or surface magnons. Based on the data of the optical selection rules, the temperature dependence and the influence of the surface component of the wave vector we have developed a new mechanism of several interfering scattering channels which can explain most of the observed experimental features quantitatively.

Ab initio study of the oxygen ordering in YBa₂Cu₃O_7-x
C. Ambrosch-Draxl¹, P. Korzhavyi², and B. Johansson²
Institut f. Theoretische Physik, University Graz, Austria
²Condensed Matter Theory Group, Uppsala University, Sweden
The concentration and ordering of oxygen vacancies in the basal plane of the Y-1-2-3 high Tc compounds has a very important effect on the critical temperature. The question of thermodynamic stability of ordered superstructures within the Cu-O chains in YBa₂Cu₃O_7-x is studied theoretically on the basis of total energy calculations performed within the full-potential linearized augmented plane wave (LAPW) method. The calculated total energies of various ordered structures are used to obtain the effective energies of interatomic interaction in the system. The stability of experimentally reported long-period superstructures is analyzed.

Accelerator Mass Spectrometry at VERA across the nuclear chart
C. Vockenhuber, R. Golser, M. Kucera, W. Kutschera, A. Priller, S. Puchegger, W. Rom, P. Steier, A. Valenta, A. Wallner, E. Wild
Vienna Environmental Research Accelerator, Institut für Isotopenforschung und Kernphysik der Universität Wien, Währingerstrasse 17, A-1060 Wien, Austria
Accelerator Mass Spectrometry (AMS) has developed into a universal tool to measure longlived cosmogenic and anthropogenic radionuclides in almost every domain on Earth, and in extraterrestrial matter as well. By far the most used radionuclide is ¹⁴C, which is measured routinely at VERA. Besides ¹⁴C, the detection capability of other "routine" radionuclides such as ¹⁰Be, ²⁶Al, and ¹²⁹I has been developed. Beyond those, VERA is designed to analyze many more radionuclides across the whole nuclear chart, from the lightest (³H) to the heaviest (²⁴⁴Pu). however, this requires the development of sophisticated detection methods, particulary for the measurement of heavy radionuclides. We discuss the extension of AMS at VERA-both achieved and planned - to a variety of heavy and hitherto unused radionuclides such as ¹⁴⁶Sm, ¹⁸²Hf, ²¹⁰Pb,²³⁰U, ²⁴⁴Pu. Possible applications of these radionuclides will also be briefly mentioned.

Analyse zweifach negativ-geladener Cluster-Ionen mit Beschleuniger-Massenspektrometrie
Robin Golser, Georg Federmann, Walter Kutschera, Alfred Priller, Peter Steier, Christoph Vockenhuber
Vienna Environmental Research Accelerator, Institut für Isotopenforschung und Kernphysik, Universität Wien
Beschleuniger-Massenspektrometrie (AMS) ist eine extrem empfindliche Methode zum Nachweis von Radioisotopen, z.B. von ¹⁴C mit einer Nachweisgrenze für ¹⁴C/¹²C von 10^–15. Der dabei verwendete Tandem-Beschleuniger bewirkt zweierlei: Erstens werden negativ-geladene Molekül-Ionen im Stripper bei ca. 3MeV durch den Verlust von Bindungselektronen in atomare Ionen aufgebrochen. Diese bekommen dann, zweitens, als positive Ionen genügend Energie, um mit kernphysikalischen Methoden identifiziert zu werden. Diese Eigenschaften lassen sich auch für Untersuchungen an Cluster-Ionen aus stabilen Nukliden vorteilhaft nutzen, z.B wurden die zweifach negativ-geladenen Ionen (C₇)^2– und (BeC₄)^2– mit AMS erstmals eindeutig nachgewiesen. Wir möchten in diesem Beitrag zeigen, warum AMS hervorragend geeignet ist, diese sehr seltenen Ionen zu untersuchen. Erste Messungen mit der AMS Anlage VERA an Kohlenstoff-Clustern werden vorgestellt.

The finding place of the Iceman "Ötzi": Implications from new ¹⁴C dates
B. Jettmar¹, S. Bortenschlager², R. Golser¹, W. Kutschera¹, K. Oeggl², A. Priller¹, S. Puchegger¹, W. Rom¹, P. Steier¹, E.Wild¹
Vienna Environmental Research Accelerator, Institut für Isotopenforschung und Kernphysik, Univerität Wien, Währinger Strasse 17, A-1090 Wien, Austria ² Institut für Botanik, Universität Innsbruck, Sternwartestrasse 15, A-6020 Innsbruck, Austria
The Iceman "Ötzi" was found on 19 September 1991, emerging from a shallow ice-filled depression at a high mountain pass (3120 m) of the Ötztal Alps near the Italian-Austrian border. Ötzi is the remarkably well-preserved body of a man who lived in the Late Neolithis period. Radiocarbon dating of bone and tissue from the Iceman revealed that he must have lived somewhere within the time period from 3360 to 3100 B.C. In 1992 about 500 kg of sediments were collected from the rocky depression where Ötzi was found. These sediments where subsequently scrutinized at the Institute for Botany in Innsbruck for organic remains. We report on ¹⁴C AMS measurements from about 50 selected objects recovered from these sediments, including charcoal, wood, grass, leaves, moss, treeneedles, animal dung, hair, skin, and leather. The goal of this project is to find evidence for periodes of warmer climatic in this alpine region, since both fauna and flora are particularly sensitive to climatic changes at the borderline of their existence.

Study of the ²⁷Al(n,2n) ²⁶Al reaction and its potential for ion-temperature measurements in a D-T fusion plasma
A. Wallner¹, S.V. Chuvaev², A.A. Filatenkov², Y.Ikeda³, W.Kutschera¹, H. Vonach¹
Vienna Environmental Research Accelerator, Institut für Isotopenforschung und Kernphysik, Universität Wien, Währingerstrasse 17, A-1090 Wien, Austria
²V.G. Khlopin Radium Institute, 2nd Murinski Ave. 194021 St.Petersburg, Russia ³Fusion Neutronics Laboratory
A detailed measurment of the ²⁷Al(n,2n)²⁶Al reaction cross sections was performed in the near-threshold region (E_th=13.54 MeV), and its possible applicability for ion temperature measurements was investigated. The ²⁷Al(n,2n)²⁶ Al reaction is expected vo vary strongly with neutron energy above threshold. An accurate description of the excitation function is necessary to estimate the production of ²⁶Al (t_1/2=7.2 a) in a typical D-T fusion environment. Al samples were irradiated with 14-MeV neutrons at different laboratories. The resulting ²⁶Al content was measured via ²⁶Al/²⁷Al isotope ratios using the extremely sensitive method of accelerator mass spectrometry (AMS) at the Vienna Environmental Research Accelerator. Compared to previously available data, a greatly improved excitation function was obtained. With this knowledge the sensitivity for monitoring the ion temperature in a thermal D-T fusion plasma was estimated. It appears that temperature changes in the order of 5 to 15% should be detectable. An even higher sensitivity was found for non-thermal plasmas with neutral beam injection. Therefore, the ²⁷Al(n,2n)²⁶Al reaction may serve as a useful tool in plasma diagnostics, in particular in combination with the sensitive detection of ²⁶Al by AMS.

Nuclear Data Evaluation at the "Institut für Isotopenforschung und Kernphysik" (former I.R.K.), University of Vienna
Siegfried Tagesen and Herbert Vonach
Inst. f. Isotopenforschung und Kernphysik der Universität Wien Boltzmanngasse 3 A-1090 Wien
Abstract: From the users point of view it is very important that nuclear data are available with high quality. This implies completeness of related sets of data and reliable information on data uncertainties and correlations, i.e., a full covariance matrix. Our group participates since many years in an international effort hosted by the OECD Nuclear Energy Agency to improve nuclear reaction data quality by establishing and executing methods of data evaluation and quality assurance. The outcome are well tested data files to be included in international data libraries. The applied statistical principles and procedures as well as quality assurance methods are explained in the presentation.

New chronological frame for the Late Neolithic Baden Culture in Central Europe
E.M. Wild¹, S. Draxler¹, H. Friesinger¹, W. Kutschera¹, A. Priller¹, W. Rom¹, P. Stadler^2,3 and P. Steier¹
Vienna Environmental Research Accelerator, Institut für Isotopenforschung und Kernphysik, Universität Wien, Währinger Strasse 17, A-1090 Wien, Austria
² Inst. f. Ur- u. Frühgeschichte, Universität Wien, Franz Klein Gasse 1, A-1190 Wien
³ Prähistorische Abteilung, Naturhist. Museum, Burgring 7, A-1010 Wien, Austria
In Central Europe the Late Neolithic Baden Culture represents a period which is characterized by a typical decoration of the ceramics. In this period two main groups can be differentiated archaeologically, the Baden-Boleráz and the Baden-Classical group. In the course of a larger research project* 32 samples from the Baden Culture were dated with ¹⁴C AMS at VERA. Together with already existing results a total of 75 ¹⁴C dates are now available. Evaluation of the new Baden data showed that Baden-Boleráz begins about 200 years earlier than expected, at about 3640 BC lasting until 3370 BC. Baden-Classical extends from 3360 to 2930 BC. From this analysis it seems that – against former assumptions - the early Baden Culture (Boleráz) developed somewhere in Central Europe and spread from there to Eastern Europe. According to the ¹⁴C dates all eastern cultures showing similar characteristics as the Baden Culture seem to be coeval with the Baden-Classical period and are therefore younger than the Boleráz group. This new hypothesis that the Baden Culture spread from West to East should be verified by further dating of samples especially from the eastern groups. * Project P12253-PHY, supported by the Austrian Science Fund.

Age determination of fossil bones from the Vindija Neanderthal site in Croatia
E.M. Wild¹, M. Paunovic², G. Rabeder³, I. Steffan⁴ and P. Steier¹
Inst. f. Isotopenforschung u. Kernphysik, Univ. Wien, Währingerstr. 17, Wien
² Institute of Quaternary Paleontology and Geology, Croatian Academy of Sciences and Arts, A. Kovacica 5/II, 10000 Zagreb, Croatia
³ Institut für Paläontologie, Universität Wien, Althanstr. 14, A-1090 Wien, Austria
⁴ Inst. f. Analytische Chemie, Universität Wien, Währingerstr. 38, A-1090 Wien, A
The Vindija cave in Croatia is of great importance for archaeological, anthropological and paleontological sciences. Especially one layer (G) of the cave profile is of great interest, because this layer contains several bones originating from the Neanderthals. The site is also an ideal place for studying the evolution of cave bears. A large number of cave bear bones from different evolution levels were found in the profile. Cave bear bones were also found in layer G. We hoped that dating of the bear bones could give information not only about the evolution of the cave bears but also about the Neanderthal without destroying these valuable human remains. The presence of the Ursus deningeri indicates that the older bone material originates from a time period beyond the time range accessible with the ¹⁴C-method. Therefore we applied the U/Th dating method for the cave bear bones. Bone material from the younger profile layers was dated with the ¹⁴C-method as well. The results of our study are presented and discussed. The results of layer G are also compared with results of direct ¹⁴C dating of the Neanderthal performed at Oxford.

The DEAR Target and Detector System
W.H. Breunlich¹, M. Cargnelli¹, B. Gartner¹, A. Gruber¹, R. King¹, B. Lauss², J. Marton¹, M. Stifter¹, R. Ursin¹, J. Zmeskal¹, et al.³
IMEP, ÖAW, Vienna; ²IMEP, on leave at LNFrascati; ³Univ. Victoria, LNFrascati; Univ. Trieste; Tokyo Tech; Univ. Tokyo; RIKEN; KEK; Inst. Phys. and Nucl. Eng. Rom; Univ. Fribourg; Univ. Neuchatel; CalTech; Cal. State Univ.
The objective of DEAR is the determination of the isospin-dependent KN scattering lengths via the measurement of the strong interaction shifts and widths of the kaonic hydrogen and deuterium K-series x-ray lines. CCD detectors are best suited for this experiment (high efficiency, high energy resolution and excellent background rejection). A cryogenic target system and an optimised CCD detector system were designed and constructed at IMEP. These essential components of the DEAR experimental setup are described in detail. Systematic measurements of the background in the DEAR interaction region of DAFNE are presented.

The Antiproton Detector at the Antihydrogen Experiment ATRAP
W.H. Breunlich¹, M. Cargnelli¹, H. Fuhrmann¹, A. Gruber¹, R. King¹, R. Ursin¹, J. Zmeskal¹, et al.²
IMEP, ÖAW, Vienna; ²Univ. Bonn; Harvard Univ.; MPI Quantenoptik; IKP/KFA Julich.
The Antihydrogen-Collaboration ATRAP plans to do precise laser spectroscopy of antihydrogen. Comparing the 1s-2s transitions in antihydrogen and hydrogen atoms, will provide the most stringent test of CPT invariance involving baryons and leptons. The experimental setup at the Antiproton Decelerator (AD) at CERN is described in a short review. The antiproton-monitor is a position-sensitive ionization detector, used to steer the beam of antiprotons as they enter the experimental apparatus. The test and commissioning of this detector are the main subjects of this work.

Pionic Hydrogen: Precision Spectroscopy
W.H. Breunlich¹, M. Cargnelli¹, B. Gartner¹, M. Giersch¹, A. Gruber¹, R. King¹, B. Lauss², J. Marton¹, M. Stifter¹, R. Ursin¹, J. Zmeskal¹, et al.³
IMEP, ÖAW, Vienna; ²IMEP, on leave at LNFrascati; ³Aarhus Univ.; Inst. of Nucl. Research, Hung. Acad. of Sci.; Univ. Joannina; FA Jülich; Univ. Leicester; Univ. Neuchatel; EISI-St.Imier; Univ. P. et M. Curie; PSI; ETH Zurich; Univ. Zurich.
An experimental program to measure the width and shift of the K-alpha x-ray line of pionic hydrogen is being conducted at PSI. Due to the unprecedented precision of the measurement a new level of sensitivity will be reached for tests of chiral perturbation theory calculations of the pion nucleon scattering length. A cyclotron trap, a cryogenic target and a bent crystal spectrometer with CCD detector system will be used. Major components of the experimental setup are under development at IMEP/Vienna, in particular a new light weight gas target which is presented.

Simulation of Antiproton Transport in the ATRAP Beam Detector and Moderator
W.H. Breunlich¹, M. Cargnelli¹, H. Fuhrmann¹, A. Gruber¹, R. King¹, R. Ursin¹, J. Zmeskal¹, et al.²
IMEP, ÖAW, Vienna; ²Univ. Bonn; Harvard Univ.; MPI Quantenoptik; IKP/KFA Julich.
For the formation of antihydrogen atoms, antiprotons extracted from the AD/CERN are moderated to very low energies before being captured in a trap. In this energy range the Barkas effect contributes significantly. This effect is accounted for by introducing a Z to the third power term into the Bethe-Bloch formula for the stopping power. In our present work we introduce such a correction term in a simulation of antiproton transport. A precise simulation is essential to select moderator properties for optimal slow antiproton yield.

Hard photons: Production mechanisms and nuclear dynamics in intermediate energy heavy ion collision
C. Agodi
Istituto Nazionale di Fisica Nucleare, Roma, Italy
The occurrence in the photon spectra of a component between 30 and 50 MeV with inverse slope parameter smaller than the one expected in the first chance neutron - proton bremsstrahlung hypothesis is investigated in heavy ion collisions at intermediate energy.
The experiment has been performed at Laboratori Nazionali del Sud using the coupled MEDEA[1] and MULTICS[2] multidetectors arrays. The simultaneous detection of gamma-rays , light charged particles, IMF's and PLF's with high

efficiency and granularity allows a good characterization of the reaction events. ⁵⁸Ni+²⁷Al at 30A MeV and
⁵⁸Ni+¹⁹⁷Au at 30A and 45A MeV reactions have been studied. The experimental photon spectra can actually be described as the superposition of two exponential components with significantly different slopes. From the comparison
between the three reactions the mass and incident energy dependence of this phenomenon has been deduced.

Several observables have been studied to point out a possible different origin of high energy photons in selected energy bins. The interplay between photon production and particle emission has also been investigated.
[1] - E.Migneco et al. , Nucl.Instrum.Methods A314(1992)31.
[2] - I.Iori et al., Nucl.Instrum.Methods A325 (1993)458.

The CMS First-Level Trigger
M. Brugger, J. Eroe, M. Fierro, P. Porth, H. Rohringer, L. Rurua, H. Sakulin, A. Taurok, H. Woehri, C.-E. Wulz
Institut für Hochenergiephysik der Österreichischen Akademie der Wissenschaften, Nikolsdorfergasse 18, A-1050 Wien
The trigger is one of the crucial components of experiments at the CERN Large Hadron Collider. CMS will receive proton-proton collisions with a rate of 40 MHz. Only about 100 events per second will be written to mass storage. This reduction is achieved in several steps. The initial step is a custom designed electronics system, the First-Level Trigger, which has to decrease the rate to 100 kHz. The Higher Level Triggers are performed by a commercial processor farm. The complete First-Level Trigger system is presented. Austria's Institute for High Energy Physics is responsible for the construction of the Global Trigger Processor and the Muon Trigger Track Finder in the central region. Special emphasis will be given to these two items.

CMS and its Physics Potential
M. Brugger, J. Eroe, M. Fierro, P. Porth, H. Rohringer, H. Sakulin, A. Taurok, H. Woehri, C.-E. Wulz
Institut für Hochenergiephysik der Österreichischen Akademie der Wissenschaften, Nikolsdorfergasse 18, A-1050 Wien
CMS (Compact Muon Solenoid) is an experiment designed to study proton-proton and heavy-ion collisions at the Large Hadron Collider at CERN, Geneva. Detailed simulation studies are under way in order to be ready for the first collisions foreseen in 2005. Amongst the potential discovery targets are the Standard Model Higgs boson and supersymmetric particles. Their detection methods will be presented.

On the Origin of the Chiral Condensate in Compact QED
B.A. Berg¹, U.M. Heller¹, H. Markum², R. Pullirsch², W. Sakuler²
Department of Physics, The Florida State University, Tallahasse, ²Institut für Kernphysik, Technische Universitaet Wien
We analyze the spectrum of the staggered Dirac operator in compact QED. In the confinement phase we find quasi-zero modes which are responsible for the chiral condensate. In the Coulomb phase these quasi-zero modes do not exist and thus the value of the chiral condensate vanishes as expected. It is interesting to particularly understand the physical origin of the quasi-zero modes in U(1) gauge theory. In 4-dimensional SU(2) and SU(3) gauge theories the general interpretation is to link them and thus the non-vanishing value of the chiral condensate to the existence of instantons. It is desirable to study analogies between non-Abelian and U(1) gauge theories by investigating monopole-``instanton'' densities. In order to get actual zero modes instead of only quasi-zero modes one can analyze chiral actions.

Austrian activities at the nTOF facility at CERN
G.Badurek¹, H.Frais-Koelbl², E.Griesmayer², E.Jericha¹, H.Leeb¹, A.Pavlik³, H.Oberhummer¹, M.Tutz¹
Institut f. Kernphysik, TU Wien, ²FH-Studieng., Wr. Neustadt, ³Inst. f. Isotopenforschung und Kernphysik, Univ. Wien
The nTOF facility, a neutron spallation source at CERN, has started operation in spring 2000. It makes use of the 20-24 GeV proton beam of the proton synchrotron at CERN which is directed onto a lead target. The delivered high intensity neutron beam is used for neutron cross section measurements in the energy region between 1 eV and 250 MeV. Missing nuclear data relevant for waste transmutation, medical applications, nuclear astrophysics and fundamental nuclear physics will be determined. Within the nTOF Collaboration the activities of the Austrian participants are focussed on fast electronics of the data acquisition system, the measurement of (n,xn) cross sections and the nuclear data evaluation and theoretical modeling. A survey of the Austrian activities is given. *supported by EURATOM, nuclear fission and BMBWK

Jump conditions at fast shocks for an anisotropic magnetized plasma
D. F. Vogl, N. V. Erkaev, H. K. Biernat, S. Mühlbachler, and C. J. Farrugia
Space Research Inst., Austrian Academy of Sciences; Inst.of Computational Modelling, Krasnoyarsk; Inst.f. Geophysics, Astrophysics,and Meteorology,UoG; Inst. f. the Study of Earth,Oceans and Space,Univ. New Hampshire
Taking into account the pressure anisotropy in the solar wind, we study the magnetic field and plasma parameters downstream of a fast shock as functions of upstream parameters and the pressure anisotropy. We model two cases, the shock perpendicular and the shock inclined with respect to the magnetic field. The criterion of the mirror instability is used as a closure relation and gives limiting values for the plasma parameters and the magnetic field for pressure anisotropy >1. Analogous, the criterion of the fire hose instability gives limiting values for anisotropy <1. We found that the parallel pressure, the parallel temperature, and the tangential component of the velocity downstream of the shock are most sensitive to pressure anisotropy, whereas density, normal velocity, tangential component of the magnetic field, perpendicular pressure and perpendicular temperature downstream of the shock show less pronounced behaviour.

Petschek shocks of reconnection for anisotropic pressure
H. K. Biernat, S. Mühlbachler, V. S. Semenov, N. V. Erkaev, D. F. Vogl, and V. V. Ivanova
Space Research Institute, Austrian Academy of Sciences; Institute of Physics, St. Petersburg; Institute of Computational Modelling, Krasnoyarsk; Inst. for Geophysics, Astrophysics, and Meteorology, Univ. of Graz;
Magnetic reconnection is a very effective energy conversion process which allows topological different magnetic fields to interconnect. The Petschek-type kind of reconnection involves shocks which allow a very effective conversion of magnetic energy into plasma energy, e.g., kinetic energy. Because many observations show a difference between the pressure parallel and perpendicular to the magnetic field, it is reasonable to study the reconnection mechanism for the set of equations allowing for pressure anisotropy. We study the simplest case of a symmetric configuration where the initial plasma parameters are identical on both sides of the current sheet and the magnetic fields are antiparallel. It is found that the gas pressure has to be isotropic inside the outflow regions which are bounded by a slow shock of switch--off type. Both, steady-state and time-dependent regimes, are considered and possible applications are discussed.

Ein Modell für topologische Fermionen
Manfried Faber
Institut für Kernphysik, Technische Universität Wien, Wiedner Hauptstraße 8-10, A-1040 Wien
Geladene Teilchen werden als stabile topologische Anregungen beschrieben. Die Feldfreiheitsgrade leben auf einer Kugel in vier Dimensionen. Die elektrische Fluß durch eine Fläche entspricht einer Fläche auf dieser Kugel. Zwei Beiträge zur Hamiltonfunktion stabilisieren die Solitonen. Ein Krümmungsterm beschreibt die Energiedichte des elektromagnetischen Feldes und verhindert einen Kollaps der Solitonen, eine potentielle Energie stabilisiert die Solitonen. Bereits klassisch behandelte Solitonen zeigen wichtige Effekte, die üblicherweise durch die Quantenfeldtheorie erklärt werden müssen, wie Teilchen-Antiteilchen-Vernichtung und die Abhängigkeit der Ladung von der Stärke der Stöße. Die Masse dieser Solitonen ergibt sich als Feldenergie. Solitonen verhalten sich wie Teilchen mit relativistischen Eigenschaften. Das Modell enthält darüberhinaus freie elektromagnetische Felder und deren Wechselwirkung mit den Solitonen über Coulomb- und Lorentzkräfte.

A New Satellite Test of General Relativity
H. Lichtenegger, F. Gronwald, B. Mashhoon and K. Schwingenschuh
Institut für Weltraumforschung, Österreichische Akademie der Wissenschaften
In the weak field and low velocity limit of General Relativity, the gravitational field can be described in a similar way as the electromagnetic field in electrodynamics. In this approximation, the rotating Earth is expected to generate a dipolar gravitomagnetic field in much the same way as a rotating electrically charged sphere produces a magnetic dipole field. The interaction of an orbiting test particle with the gravitomagnetic field of the Earth leads to a small increase or decrease of the particle's velocity, depending on the direction of the motion and thus results in a difference in proper period for counterorbiting particles. To lowest order, this difference is independent of Newton's constant of gravity and the radius of the orbit. We briefly discuss the physics behind this effect and outline a possible satellite experiment aimed to detect gravitomagnetism by means of orbiting clocks.

Considerations about space and time
Gordano Cottini
The Joint Force Center for Studies and Military Applications (CISAM), Via della Bigattiera 10, 56010 S. Piero a Grado, Pisa, Italy
In the following work the author, starting from the consideration of some difficulties inherent to relativity theory, plus the fact that such theory doesn't explain why matter affects the metric of the spacetime and doesn't give full account of the physical meaning of force of gravity, hypothesizes elastic features of space and time, evidencing why, although they may be considered in the same way from an analitical point of view, have different carachters. From such considerations the author derives a possible physical expanding model of the average structure of space and time and, consequently, of the universe, using such model as starting hypothesis. From these hypotheses of an expanding, elastic model of the universe, the author, through a different approach than that used by Einstein, derives first a new theory of special relativity, in absence of matter, in which problems such as the twin's paradox disappear. Consequently the author explains why the matter affects the metric of the spacetime, deriving the equation of the relativistic invariant for the case of central point mass, without problems such as singularities in the vicinity of the center (as the one appearing in Shwartzshild's solution) and generalizing such equation to arrive to the theory of General Relativity. Subsequently the author demonstrates the physical meaning of the force of gravity.

The CMS Tracker Project
W. Adam, T. Bauer, M. Friedl, R. Frühwirth, J. Hrubec, M. Krammer, M. Pernicka, R. Wedenig
Institute of High Energy Physics of the Austrian Academy of Sciences, A-1050 Wien, Austria
The CMS experiment at the Large Hadron Collider LHC is especially optimized to identify muons, electrons and photons which are characteristic signatures for the decays of Higgs bosons and supersymmetric particles. The tracker is dedicated to measure precisely the tracks of charged particles emerging from the interaction region. Early this year the CMS collaboration decided to build the entire tracker with silicon as sensor material. The tracker will consist of up to 3 pixel layers close to the beam axis and 10 layers of strip detectors up to a radius of 1.23 m. Including the disks in the forward direction, 230 square meters of instrumented area will be covered by about 26000 silicon strip sensors of different geometries. An intensive program of research and development was carried out to define the specifications of these sensors and to evaluate the performance of the detector. The main activities of the institute in the tracker project are specified.

CMS Milestone Module Assembly in Vienna
W. Adam, T. Bauer, M. Friedl, J. Hrubec, M. Krammer, M. Pernicka, R. Wedenig
Institute of High Energy Physics of the Austrian Academy of Sciences, A-1050 Wien, Austria
The CMS experiment is designed for precise measurement and identification of muons, electrons and photons in order to tag the Higgs bosons and supersymmetric particles. The tracker consists of up to 3 pixel layers as close as possible to the interaction region and altogether 26000 Si-strip sensors in 10 cylinder layers and several forward disks. For the strip detectors special assembly and gluing procedures have been developed in order to achieve the assembly precision in the micrometer region needed for the new physics and taking into account the limited assembly time of 2 years. Thus, as a milestone, a prototype of the mechanical structure of one cylindrical layer has been equipped with modules with the highest strip density. At the institute one electrical working module and 13 mechanically equivalent dummy modules have been assembled. The statistics of the assembly precision and the final successful test of the working module in a test beam are presented.

A Simple Model of Charge Collection in Silicon Detectors
T.Bauer, M.Friedl, M.Krammer
Institute of High Energy Physics, Austrian Academy of Sciences, Vienna, Austria
The charge collection and the resulting currents of electrons and holes in silicon detectors are well described by a simple model derived from the basics of semiconductor theory. Depending on various parameters like resistivity, bias voltage and thickness, we calculate the currents resulting from charge movement across the detector. In heavily irradiated silicon detectors, the bulk converts from n- to p-type and the pn-junction moves from the readout side to the backplane side. Nevertheless, neglecting trapping due to radiation damage, it can be shown that the overall currents before and after this inversion are the same, although the single carrier contributions are quite different. Furthermore, the detector currents are applied to a model of the APV amplifier with CR-RC shaping and deconvolution. The amplifier output is studied for several parameter settings.

A ultra low level radionuclide laboratory to support the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO)
Schwaiger M, F. Steger, C. Schmitzer and T. Schröttner
Austrian Research Centers Seibersdorf, Division for Health Physics, A-2444 Seibersdorf, Austria
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) of 1996 bans nuclear explosions in all environments. Under CTBT a global system of 80 radionuclide monitoring stations and 16 Radionuclide Laboratorys (RL) is being established for verification of the treaty. The radionuclide laboratory at the Austrian Research Centers Seibersdorf (RL3) is going to be certified by the Technical Secreteriat to support the International Monitoring System (IMS). To achieve the demanded minimum detection limits, RL3 was constructed as an ultra low level laboratory. The background of a high-purity germanium gamma-spectrometer has been reduced by developing an active shielding, in addition to the conventional passive-shielding. This active-veto-shielding is used to suppress myon induced background. The system is encapsulated in an iron-chamber, placed into a concrete-shelter. By the installation of an air-conditioning system, the influence of radon was reduced too. The final background count rate, achieved over the energy interval from 40 keV to 2700 keV, amounts to 0.18 cps/kg germanium. The reduction factor, compared with the outdoor cout rate, is approximately 10³.

Search for Exclusive Decays of b-quark Baryons at LEP-1
Winfried A. Mitaroff
Institute of High Energy Physics, Austrian Academy of Sciences, Vienna
L_b baryons is performed in the decay channels J/ , with subsequent decays of to p K^- , p K^0s or (and c.c.). Our analysis uses 3.5 M hadronic Z⁰ decays acquired by the DELPHI detector in 1991-95. Two candidates are found in J/, and four more in . Estimates of kinematically fitted masses and exclusive decay branching fractions are presented.

The "HTR-Method" for the Measurement of the "Average" LET - A Critical Discussion
N. Vana^1,2, W. Schöner¹, T. Berger^1,2, M. Hajek^1,2
Atominstitute of the Austrian Universities, Stadionallee 2, 1020 Vienna, Austria; ² Austr. Society for Aerospace Medicine, Lustkandlgasse 52/3, 1090 Vienna, Austria
The HTR (High Temperature Ratio)-method, developed at the Atominstitute, utilizes the change of the peak height ratios in glowcurves of LiF-TLDs in dependence on the linear energy transfer (LET). Calibration was performed with high energetic ion beams, protons, alpha particles, neutrons and gamma radiation of various energies. The method was used with great success during many space missions, in aircraft and in therapeutic proton beams. The obtained results are in excellent agreement with data measured by TEPCs. The ICRP 26 quality factor / LET relation is very similar to the LET-dependence of the HTR in LiF and therefore the obtained results are independent of the LET-spectrum. For the spectrum of space radiation, the differences of the mean quality factor according to ICRP 60 and ICRP 26 are negligible. The analysis using Track Structure Theory shows that data from particles with a wide LET-spectrum fit into the LET-calibration curve. The HTR-method as a microdosimetric tool is discussed.

Measurement of Average LET and Absorbed Dose inside a Water-Filled Phantom onboard Space Station MIR
T. Berger^1,2, M. Hajek^1,2, W. Schöner¹, M. Fugger¹, N. Vana^1,2, M. Noll², R. Ebner¹, Y. Akatov³, V. Shurshakov³, V. Arkhangelsky³
Atominstitute of the Austrian Universities, Stadionallee 2, A-1020, Vienna, Austria; ²Austr. Society f. Aerospace Medicine, Lustkandlgasse 52/3, A-1090 Vienna, Austria; ³Institute for Biomedical Problems, Koroshovskoje sh. 75a, Moscow, Russia
The HTR-method for determination of absorbed dose and average LET in mixed radiation fields was developed at the Atominstitute of the Austrian Universities. This method was applied with great success during several space missions and on space station MIR in the past 10 years. It utilizes the changes of peak height ratios in LiF thermoluminescent glowcurves in dependence on the LET. Measurements inside tissue equivalent phantoms using the HTR method are possible due to the small size of these dosemeters. A water filled phantom with a diameter of 35 cm containing four channels where dosemeters can be exposed in different depths was developed by the Institute for Biomedical Problems. This opens the possibility to measure the depth distribution of the average LET and the dose equivalent simultaneously. The results of the following projects are presented: Phantom 1 [Commander cabin, 271 days (05.1997-02.1998)]; Phantom 2 [Board engineer cabin, 102 days (05.1998-08.1998)]; Phantom 3 [Modul KWANT 2, 199 days (08.1998-02.1999)].

Analysis of the Neutron Component atop High Altitude Mountains
M. Hajek^1,2, T. Berger^1,2, W. Schöner², N. Vana^1,2
Austr. Soc. f. Aerospace Medicine, Lustkandlgasse 52/3, A - 1090 Vienna, Austria; ²Atominstitute of the Austrian Universities, Stadionallee 2, A - 1020 Vienna, Austria
The European Council directive 96/29/Euratom requires dosimetric precautions of aircrew if the effective dose exceeds 1 mSv/a. Active (6LiI(Eu) scintillator) and passive (TLDs) Bonner sphere spectrometers were used to determine the neutron energy spectra atop Mt. Sonnblick and Mt. Kitzsteinhorn. Primary cosmic hadrons significantly contribute to the readings of active detectors. TLD-600 and TLD-700 in pair allow the determination of the thermal neutron flux. Unfolding of the detector data show two relative maxima around 1 MeV and 85 MeV, which have to be considered for the assessment of the biologically relevant dose equivalent. By convoluting the spectra with appropriate conversion functions the neutron dose equivalent rate was determined to be 150±15 nSv/h. The total dose equivalent rate determined by the HTR-method was 210±15 nSv/h. The neutron component contributes more than 50%. The results are in good agreement with LET-spectrometer and Sievert counter measurements carried out simultaneously.

The AUSTRON Accelerator Complex
Ph. Bryant¹, E. Griesmayer², M. Regler³, H. Schoenauer¹
CERN, Geneva, ²FH Wr. Neustadt, ³AUSTRON, Vienna
In view of the philosophy of building the AUSTRON accelerator with conventional technology and to fully profit from existing experience, in particular at ISIS, the scenario of a low-energy linear accelerator injecting in a rapid cycling synchrotron (RCS) was adopted, the latter with an energy of 1.6 GeV, a repetition cycle of 25 Hz, and an average beam power of 205 kW. Now a more ambitious development of the original concept is proposed, running at 0.5 MW at 1.6 GeV, pulsed at either 50 Hz or 10 Hz. The slow repetition rate is achieved by the addition of a storage ring holding four consecutive (single bunch) pulses from the 50 Hz RCS until a fifth pulse is accelerated and transferred to the target in a row with the four stored ones. In this way, an energy of per pulse of 50 kJ (one half of the pulse energy of the 5 MW ESS) is obtained, yielding about 3x10¹⁶ thermal neutrons per pulse. This peak flux matches well a number of innovative instruments.

AUSTRON - The Austrian neutron spallation source project
E. Jericha¹, G. Badurek¹ and H. Rauch²
1 Institut für Kernphysik, ² Atominstitut der Österreichischen Universitäten
The AUSTRON project aims at the realization of a pulsed neutron spallation source in Austria as an international centre for materials research, industrial development and fundamental physical questions. The facility consists of an advanced accelerator complex, a target station which houses a solid spallation target and a suite of instruments for a broad range of neutron physics experiments. The source, running at a repetition rate of 10 Hz, will produce the highest neutron peak flux available world-wide. The proposed instruments are particularly suited to be installed at a pulsed neutron source with their majority taking advantage of the low source repetition rate. Emphasis is thereby put on the use of cold neutrons. A well-balanced set of advanced standard type instruments is accompanied by novel instrumental concepts and techniques. Special attention is paid to new sample environment concepts like the installation of a separated instrument area under clean room conditions.

A New Neutron Tomography Facility at the Atominstitute
S. Körner^1,2, B. Schillinger³, H. Böck¹, H. Rauch¹
Atominstitut der Österreichischen Universitäten, Stadionallee 2; A - 1020 Wien; ²Paul Scherrer Institute, CH - 5232 Villigen PSI; ³TU - München, Fakultät für Physik E21, D - 85747 Garching;
For a 3D neutron tomographic reconstruction of the sample-interior, neutron transmission images of the object taken from different view angles are required. Therefore a rotary table has been installed at the sample position in front of the thermal column at the 250 kW TRIGA Mark II reactor, Vienna. An imaging device with the following detection principle has been developed: A neutron sensitive scintillator screen converts the neutrons to photons, which are reflected to a slow scan 16 bit CCD-camera by a mirror to allow placing the camera apart the direct neutron beam. All components are placed in a light tight enclosure. Camera and rotary table are controlled and coordinated by a computer. Exposure times can get as low as 20 s per image. This means that a complete tomography, which requires about 200 images of a sample from different view angles can easily be performed within one working day. The 3D reconstruction of the sample interior is made by filtered backprojection.

USANS - Recent activities at the Ultra Small Angle Neutron Scattering instrument S18, ILL, Grenoble
Hainbuchner, M., Baron, M., Jericha, E., Villa, M. and Rauch, H.
Atominstitut der Österreichischen Universitäten, Institut Laue-Langevin
In the recent years Ultra Small Angle Neutron Scattering (USANS) has developed into a powerful standard method of large scale structure investigations. The upgraded instrument S18 at the ILL´s high flux reactor is operating routinely with growing beam time demand. The q-range from 2x10^-5Å^-1 up to 5x10^-2Å^-1 can be covered with unprecedented neutron intensities. We present a summary of recent experiments which have been performed in cooperation with different groups from the international user community. This work comprises structure investigations on different types of solid specimens, such as sintered alumina, superconducting NbTi compounds, ceramic reinforced SiC/SiC structural material, petroliferous sedimentary rocks and photonic lattices. Time resolved studies on supra-molecular architectures of cellulose and supercritical fluids under various temperature conditions will also be presented.

Gravitationally induced quantum interference measurements with the very-cold-neutron interferometer
G. van der Zouw, A. Zeilinger, P. Høghøj, R. Gähler and P. Geltenbort
Inst. f. Exp. Physik, Universität Wien and Inst. Laue-Langevin
In the so-called COW experiments a neutron interferometer is tilted around its optical axis, resulting in a phase shift due to the difference in gravitational potential acting along the different beam paths. A whole series of experiments with silicon single crystal interferometers, starting with the original experiment by Colella, Overhauser and Werner, consistently show a discrepancy between experiment and theory after correction for dynamical diffraction effects and other known systematic errors.

This situation prompted us to investigate these effects with our interferometer for very cold neutrons at ILL. Using this different type of interferometer we recently obtained results that were in agreement with theory within the accuracy of 1%, excluding some, but not all, of the earlier results. We will present here the latest results of a new series of measurements with a higher accuracy, which allow us to exclude all earlier anomalous results and confirm theory at the same time.

Spin Dynamics in Polarized Neutron Interferometry
R.J. Buchelt, G. Badurek
Institute of Nuclear Physics, University of Technology, Vienna, 1020, Stadionallee 2
Perfect crystal interferometry with polarized neutrons has proved an illustrative experiment for the demonstration of quantum mechanical principles, as for instance the 720°-periodicity of spinor wave functions, the superposition of spin states or the dual nature of matter in the form of particles and waves. An important scenario with respect to applications in materials science is the presence of magnetic domains in one partial beam of the interferometer: it is then a remarkable effect, that not only the intensity emerging from the interferometer depends on the incident beam polarization, but that the emerging beam is polarized even upon a completely unpolarized incident beam. A newly developed theoretical formalism for an arbitrary sequence of domains as well as test measurements involving three-dimensional polarization analysis will be presented.
This new approach is also an important step towards the spin-tomographic visualization of ferromagnetic domain structures using neutron interferometry.
The work was supported by the Austrian Science Fund (P10969-PHY) and the European Union TMR Program (ERB-FMRX-CT96-0057).

Energy focusing of pulsed neutrons by means of magnetic fields
D.E. Schwab, J. Summhammer, H. Rauch
Atominstitut der österreichischen Universitäten, Stadionallee 2, 1020 Wien
Future spallation sources like Austron or the ESS need a more use of the produced neutrons. In contrast to laser and synchrotron sources, neutron sources produce a much lower phase space density. Thus we explore the possibility of an active neutron energy focusing system. Until now, material in form of turbine blades or moving crystals were involved in such devices causing relatively large losses of neutrons. Here we study the monochromatization of neutron pulses by interaction with magnetic fields. We show that the application of a magnetic field is the only appropriate chance for this purpose. Simulations show that a comoving magnetic field shaped like a harmonic oscillator or of a sinusoidal form causes as increase of the neutron intensity interest up to an order of magnitude in a variable but small velocity band. Another feasible set-up consists of spin-flip stages which change the velocity due to an energy exchange between the spin-flip resonator and the neutrons. Calculations and feasibility considerations for the required dimensions of the system are presented.

Conduction Electron Spin Resonance - a new tool to investigate the 2d electron gas
W. Jantsch¹, Z. Wilamowski², N. Sandersfeld¹ und F. Schaeffler¹
Inst. f. Halbleiterphysik, Johannes Kepler Universitaet, A-4040 Linz
²Inst. Physics, Polish Academy of Sciences, Warsaw
We make use of the conduction electron spin resonance in SiGe/Si quantum wells to determine the magnetic susceptibility, which is proportional to the density of states of the two-dimensional electron gas (2DEG) at the Fermi level and to the inverse screening length. The observed deviations from the expected step-like variation of an ideal density of states can be attributed to potential fluctuations which increase dramatically below a critical carrier density. We confirm thus experimentally that the metal to insulator transition (MIT) in the 2DEG is accompanied by a divergence of the screening length and vanishing compressibility. We attribute this divergence to the mutual dependence of screening length and fluctuation amplitude. This self-amplifying mechanism demonstrates the many-body character of the MIT.

Evaluation of a new frameless positioning system in radiotherapy
J. Reiterer¹, J. Bogner¹, K. Dieckmann¹, R. Pötter¹, and H. Aiginger²
Department of Radiotherapy and Radiobiology, University of Vienna, Austria, ²Nuclear Research Institute, Austrian Universities
The recently developed frameless positioning system ExacTrac (BrainLAB) provides a new approach for patient positioning in radiotherapy. ExacTrac is based on 4 - 20 infrared (IR) reflective CT markers which are attached to the patients surface. The positions of the markers are recorded during the CT scan. After treatment planning at Helax TMS the isocenter is transferred to the ExacTrac system via DICOM-RT. The recalculated positions are passed on to the IR navigation system in the treatment room and the patient is positioned according to the treatment plan. During treatment the isocenter deviation can be displayed on the ExacTrac console. In 95% of the 279 cases investigated the measured difference between the conventional positioning and ExacTrac was found within 2.8 mm in lateral, 2.1 mm in longitudinal and 2.5 mm in vertical direction, respectively. ExacTrac enables precise, highly reproducible and easy to handle positioning of patients. With the development of isocenter transfer tools by usage of DICOM-RT important progress, regarding accuracy and time efficiency, was made for the integration with the Helax TMS treatment planning system.

In-vivo dosimetry in radiotherapy using semiconductor detectors
C. Kuntner ¹, D. Georg ², H. Aiginger ¹, R. Pötter ²
Nuclear Research Institute, Austrian Universities
² Department of Radiotherapy and Radiobiology, University of Vienna, Austria
In-vivo dosimetry is an important tool for quality assurance in radiotherapy. With this method the applied dose can be directly measured and recorded during the irradiation treatment. Semiconductor detectors are more popular than TLDs due to the major advantage of “on-line” information during treatment delivery. If a discrepancy is observed between calculated and measured dose, it is possible to trace sources of errors by immediately verifying all treatment parameters. The disadvantage of the diodes is the signal dependence on several factors like doserate, temperature and accumulated dose. P-type diodes have been proved to be suitable in clinical application, because they show a smaller dependence on these factors than n-type diodes. In general, diodes are calibrated under reference conditions (FS 10x10cm², SSD 100cm). Commonly used treatment fields and distances in clinical routine differ from the reference geometry and therefore additional correction factors need to be applied.

Monte Carlo calculations for dosimetry in endovascular brachytherapy
C Kirisits, P Wexberg, H Aiginger, R Pötter
Nuclear Research Institute, Austrian Universities
Restenosis is severely limiting the clinical outcome of vascular interventions. Successful endovascular radiation therapy for prevention of restenosis is based on accurate dosimetric data at short distances near radioactive brachytherapy sources.
Precision dosimetric studies for different source geometries and nuclides have been performed using Monte Carlo calculations with EGS4 codes. and emitting sources were simulated in a plane-cylinder geometry model, using accurate emission energy spectra.
We calculated the relative dose at radial distances from 1 to 10 mm from the source center. Overlaying radial isodose-lines on to cross-sectional images of the arterial wall obtained with intravascular ultrasound illustrate the dose-distribution within specific anatomical layers for different endovascular brachytherapy devices.
The Monte Carlo method is a valuable tool to investigate device specific dosimetric parameters for adapting the therapy to the actual geometry of the treated vessel.

An Extended Range Bonner Sphere Spectrometer
A.Mitaroff^1,2, M.Silari¹, H.Aiginger²
CERN, CH-1211 Geneva 23, Switzerland; ²Atominstitut der österreichischen Universitäten, Schuettelstr. 115/141, A-1020 Vienna, Austria
Neutron dosimetry is an important task around hadron accelerators in physics, accelerators used in hadron therapy, waste transmutation and material science and also for aircraft personnel during flights at cruise altitudes. Neutrons of these radiation fields extend over an energy range from thermal up to several hundreds of MeV, thus making dosimetry difficult. A well known instrument for measuring neutron spectra from thermal energies up to about 10 MeV is the Bonner Sphere Spectrometer (BSS). In the last year a series of Monte Carlo calculations were carried out to design two new spheres with a good high-energy response to be added to the already existing BSS. In the past two months this new extended BSS was tested at CERN with an Am-Be source and at CERF (CERN-EU High Energy Reference Radiation Facility) in a well known mixed radiation field with a large component of high energy neutrons. A comparison of these results with the simulations will be presented and discussed.

Simulation der Protonen-Photonen Dosisverteilung zur Quantifizierung der Nebenwirkungen in der Strahlentherapie
K. Poljanc^1,2, T. Auberger², P. Lukas², H. Aiginger¹
Atominstitut der Österreichischen Universitäten, TU-Wien, ²Universitätsklinik für Strahlentherapie und Radioonkologie, Leopold-Franzens-Universität Innsbruck
In der modernen Strahlentherapie ist durch die Einführung der Hochpräzisionsbestrahlung mit Protonen und Ionen eine Möglichkeit geschaffen worden, bis dato nur unzureichend behandelbare Tumoren zu behandeln. Zur Bestimmung der Nebenwirkungen wurden Bestrahlungsplänen von insgesamt 13 Patienten mit optischen Gliomen und Chordomen erstellt. Der Vergleich wurde anhand eines Protonenplanes, eines stereotaktischen Photonenplanes und eines Photonenplanes (laterale Felder) mit Hilfe des Bestrahlungsplanungsprogramm TPNv3 durchgeführt. Die Berechnung der zu erwartenden Nebenwirkungen mit dem Endpunkt Abfall des Intelligenzquotienten wurde dem Endpunkt Nekrose bei allen Patienten gegenübergestellt. Zusätzlich wurde die Normalgewebekomplikationsrate auf den Endpunkt Blindheit des kontralateralen Sehnervs und des Chiasmas ausgewertet. Das Risiko der Erblindung innerhalb von 5 Jahren liegt bei den lateralen Gegenfeldern in der Größenordnung um 5-10%, bei der Behandlung mit Proton! en bzw. stereotaktisch geplanten Photonen in der Größenordnung von 1-2%.

Dosimetric quality assurance of a three dimensional treatment planning system (Helax - TMS): Actual investigation and proposal for a QM - Strategy
P. Urschütz, U. Wolff¹, H. Aiginger², R. Pötter¹
Department of Radiotherapy and Radiobiology, University of Vienna
²Nuclear Research Institut, Austrian Universities
The Helax-TMS was checked for relativ-dosimetric purposes. Calculated absolute dose values were compared to measured data. The obtained deviations were evaluated according to international guidelines. The results show that the TPS will calculate highly accurate the absorbed dose if there are easy irradiation situations like homogenous media or one field techniques. For more complex situations the deviations were sometimes higher than the guidelines. The TPS underestimates influences of a wedge during the irradiation up to 5.6%. Beam-hardening caused by the wedge was not taken into account for the database required to calculate dose values is not satisfying. Measurements behind inhomogenities (Teflon as substitute for the human bone) showed deviations up to 6%. Deviations could rise up to 7.3% for a summation of those influences. Research for the reasons of the deviations were done and a quality control procedure which includes the tasks and the minimum frequency period was suggested.

Experimenteller Beweis Ultraschall vermittelten Sauerstofftransportes an physiologisch verträglichen Perfluorcarbon-Mischfluiden als Bestandteile künstlichen Blutes
H.G.Loew¹, K.W.Kratky¹, R.Ebermann²
Inst. f. Experimentalphysik, Uni Wien, ²Inst. f. Ernährungswissenschaften, Uni Wien
Mikroemulsionen zur Imitierung des Sauerstofftransportes des Blutes erwecken zunehmendes Interesse auch in der Onkologie. Studien zeigen ,dass höhere perfluorierte chemische Verbindungen in dispergierter Form hohe Mengen Sauerstoffs aufnehmen und im Körper transportieren können. Bei gleichzeitiger Einwirkung von ionisierender Strahlung enstehen Radikalspezies, die eine Strahlungswirkung z.B im Tumor verstärken. Der Gastransport kann durch gepulste Ultraschalleinwirkung auf das wässrig-/perfluorierte Misch-Milieu gesteuert werden, wie das Experiment demonstriert. Nach einer Kette von 5 Pulsen zu 2 Minuten mit einem thermischen Energieeintrag von je 60 Joule kann eine Veränderung des Sauerstoffpartialdruckes um 200 mm Hg erreicht werden. Lokale Temperaturgradienten, die durch die Wechselwirkung der Schallwellen an den verschieden dichten Grenzflächen entstehen, beschleunigen diesen Vorgang. Im wässrigen Milieu steht der Sauerstoff für biologische Interaktionen z.B für Strahlentherapie oder Photochemotherapie in gelöster Form zur Verfügung. Molekulare Modelle zur Sauerstoffbindung in Perfluorcarbonen werden präsentiert.

Digitale Gradienten-Filmdosimetrie zur Auflösung steiler Dosisverläufe in der Brachytherapie und Teletherapie. Physikalische Charakterisierung eines neuen UMAX-Filmscanners zur dosimetrischen Analyse von GAF-Chromic Filmen.
H.G.Loew¹, S.Mayer², C.Fellner¹, H.Aiginger², R.Pötter¹
Univ.Klinik f. Strahlentherapie und - Strahlenbiologie, Universität Wien ²Atominstitut d. österreichischen Universitäten
Das zentrale Problem digitaler Filmdosimetrie ist die punktweise proportionale Abbildung von Filmschwärzung auf jeweils einen digitalen Zahlenwert, mit physikalischen Größen, wie Dosis, pixelweise korreliert wird. Die nach analogen optischen und elektronischen Signalumsetzungen erfolgende Diskretisierung der Abbildungsfunktion weist einen linearisierbaren und einen nicht linearisierbaren Anteil auf. Der erstere kann mittels Gammakorrektur ausgeglichen werden. Der nicht linearisierbare Anteil jedoch führt bei vielen Scannertypen in der Abbildung zu Bildartefakten, wie Glareeffekte oder optische Dichte-Anisotropien, die zu Fehlinterpretationen applizierter Dosis führen können. Für die Strahlentherapie wurde deshalb eine Scanner-Methode entwickelt um steile Dosisgradienten an GAF-Chromic Filmen mit hoher Präzision wiederzugeben. Hohe Dosis-Gradientenwerte wie z.B 25 Gy/mm, die bei brachytherapeutischen Ir-192 Afterlodingquellen auftreten, werden mit ca. 20 µm Ortsgenauigkeit und 5% Dosis-Präzision im Bild artefaktfrei dargestellt. Weitere Analysebeispiele, wie ophtalmologische Bestrahlungen am Gammaknife beweisen die hohe Güte des präsentierten Verfahrens.

High resolution MR-based polymer dosimetry for gamma knife application: sensitivity in the low dose regime (D < 4 Gy)
M. Pernkopf ¹, A. Berg ¹, A. Ertl², E. Moser¹
Inst. f. Medizinische Physik, ²Neurochirurgie, Univ. Wien
Introduction: In polymer gel dosimetry radiation induces polymerization of the monomers in an acrylamide gel matrix forming polymer chains. This reduces the spin-spin-relaxation time T2 of the hydrogen atoms in the irradiated area. MRI-methods based on parameter selective T2 imaging enable thus visualization of quasi 3D dose levels at high spatial resolution(VS:195x195x1000µm).The change in the relaxation rate R2=1/T2 is directly proportional to the applied dose up to high dose levels.
Subjects/Methods: A 3 T MRI System upgraded by a MR-microscopy unit enables high spatial resolution. We calibrated R2 vs dose levels between 0 and 70 Gy. Especially the low dose regime at fine dose accuracy was investigated for sensivity.
Results: Relative dose accuracy in high resolution gel dosimetry is mainly determined by T2-noise and amounts to about 0.6 Gy in the low dose regime which corresponds to a relative error of about 30% at 2 Gy. MR based dosimetry offers in principle high accuracy in quasi 3D dose imaging.

Erhöhung der Behandlungspräzision stereotaktischer Tumorbestrahlungen am menschlichen Auge. Neue Methode fiberoptischer Bulbus-stabilisation und interaktiv geführter Positionskontrolle. Darstellung und Entwicklung eines Computermodells zur fortlaufenden Bildanalyse nystagmischer Bewegungen unter Bestrahlungsbedingungen.
H.G.Loew, G.Kren, K.Diekmann, W. Binder, R.Pötter
Univ.Klinik f. Strahlentherapie und - Strahlenbiologie, Universität Wien
Tumorerkrankungen, deren Sitz sich am Augenbulbus befindet, lassen eine klassische stereotaktische Bestrahlungstechnik nicht zu. Einfache Augenbewegungen können den Tumor als Zielgebiet fast vollständig aus dem konvergenten ionisierenden stereotaktischen Strahlungsfeld eines Linearbeschleunigers verschieben, insbesondere wenn dieses geringe Größen aufweist (10-15 mm Durchmesser). Deshalb wurde eine Schädel-fixierungsvorrichtung mit glasfiberoptischem Kabel ausgestattet, das einen Pilotlichtpunkt unmittelbar vor dem Patientenauge erzeugt. Der Patient blickt auf ärztliche Anweisung auf den Lichtpunkt und stabilisiert damit die Augen. Gleichzeitig erzeugt eine Minikamera, die ebenfalls auf dem Schädelfixationsrahmen montiert ist, ein fortlaufendes Videosignal der Pupillenlage, die mit der Lage des Tumors korelliert. Kleine rasche Positionierungsabweichungen werden gegenüber langsamen größeren Abweichungen von der Sollposition durch gleitende Mittelwertbildung des Videosignalverlaufes gewichtet und als differentielles Signal grafisch dargestellt. Das Verfahren reduziert Abweichungen auf ca. 0,5 mm, die mittels Pixelintegral und interaktivem Signalhistogramm an einem Apple Mac Intosh Computer laufend verfolgt werden können.

The Austrian Radon Project
Harry Friedmann
Inst. f. Isotopenforschung u. Kernphysik der Universität Wien
An extrapolation from the lung cancer risk of underground miners, exposed to high levels of radon progenies, to the general population indicates a 10% contribution of radon to the overall lung cancer rate. This was the reason for the Ministry of Health and later the Federal Chancellery to initiate and to fund the Austrian Radon Project. The project started in 1991 with a search for already existing data which may indicate high indoor radon levels. In a second phase a pilot project for the subsequent nation- wide indoor radon survey was launched. After a fine-tuning of the methods used during the pilot phase the general survey started in 1995 and finished in 2000. During this survey approximately 30000 measurements in randomly selected homes were performed. The outcome of this project are maps indicating areas with either existing high indoor radon levels or areas with a high probability for enhanced indoor radon concentrations.

Austrian Project on Health Effects of Particulates
H. Hauck and O. Preining
Inst.Environmental Hygiene, University of Vienna and Clean Air Commission, Austrian Academy of Sciences
Based on epidemiological findings health effects caused by particulates at comparably low concentration levels became an important issue within the last years. In Austria a project on ambient aerosol properties and health effects of particulates (AUPHEP) as an interdisciplinary endeavor managed by the Clean Air Commission of the Austrian Academy of Sciences was initiated in 1998.
At four typical sites in Austria and over a one year period the ambient air quality and the exposure situation of the population is being investigated. In a two phase setup continuous monitoring of aerosol parameters and gaseous pollutants as well as chemical analyses of size dependent PM-samples are conducted at two sites simultaneously. In addition, information on the relation between various measuring methods for PM will be drawn from the data. At the same time also several epidemiologic studies particularly on children are performed to contribute to the scientific understanding of PM-related health effects. The ambient monitoring program started on June 1, 1999 at an urban station in Vienna and a rural station 30 km west of Vienna. Results of the first period will be presented.

Biomineralization and biomimetics - key technologies of the 21st century
Gebeshuber I.C.*^#, Rattay F.* and Stachelberger H.*
* TU-BioMed, Wiedner Hauptstr. 8-10/114, A-1040 Vienna, Austria, ^# Institut für Allgemeine Physik, TU Wien, Wiedner Hauptstr. 8-10, A-1040 Vienna, Austria
Biomimetics is a new interdisciplinary field seeking to understand relationships between structures and functions of biological composites in order to design and synthesize new materials, possibly without the toxic residues characteristic of non-biological modes of industrial mass production [Sarikaya, 1994; Mann, 1993]. Understanding the processes involved in biomineralisation may eventually allow to mimic these structures to produce optimised materials with minimal environmental impact. This research may lead to the synthesis of novel magnetic, electronic, magnetopharmaceutical or adhesive materials on a nanometer scale.
Mann, S., Molecular tectonics in biomineralization and biomimetic materials chemistry, Nature, 365, 499-505, 1993
Sarikaya, M., An introduction to biomimetics: A structural viewpoint, Microscopy Res. Techn., 27, 360-375, 1994

Ultraweak photon emission of human neutrophiles and its significance for low level laser therapy
H. Klima
Atomic Institute of the Austrian Universities, A-1020 Vienna, Stadionallee 2
Human neutrophiles are emitting native photons during phagocytosis. The sources of these photons are mainly singlet oxygen molecules emitting in the visible region at 480, 570, 633, 700, 760 nm and in the near infrared region at 1060 and 1270 nm. It is shown that low level laser light just of some of these wavelength have different influence on promotion or supression of cell division depending on the laser wavelength and on the applied irradiation of light.

Akkumulation radioaktiver Nuklide in Klärschlämmen
J. Huber¹, P. Schneider² und O. Ennemoser¹
Institut für Medizinische Physik , Karl-Franzens-Universität Innsbruck, Müllerstr. 44, A-6020 Innsbruck; ²Institut für Mineralogie , Karl-Franzens-Universität Innsbruck, Innrain 52, A-6020 Innsbruck
Erste Messungen an Klärschlämmen einer kommunalen Kläranlage in Tirol, unmittelbar nach dem Kernreaktorunfall von Tschernobyl, ergaben eine starke radioaktive Belastung der entwässerten Schlämme. Daher wurden in der Folge die Messungen intensiviert und auf mehrere Kläranlagen ausgeweitet. Es zeigte sich, dass radioaktive Nuklide während der Drift durch die Kläranlage aus dem zulaufenden Abwasser zum Teil entfernt und in den Klärschlämmen angereichert werden. Gammaspektroskopische Untersuchungen machten deutlich, dass verschie-dene Elemente unterschiedlich hoch angereichert werden. Der Vergleich der gemessenen Gammaaktivitäten in den Klärschlämmen unterschiedlicher Kläranlagen zeigte eine gute Übereinstimmung mit der durchschnittlichen Belastung von Bewuchsproben aus dem Einzugsgebiet der verschiedenen Anlagen. Die anhand von Düngeversuchen ermittelten Transferfaktoren aus Klärschlamm korrelieren sehr gut mit den in der Literatur beschriebenen Transferfaktoren aus Böden.

Aufnahme radioaktiver Nuklide durch E. coli und S. cerevisiae
P. Schneider¹, J. Huber² und O. Ennemoser²
Institut für Mineralogie, Karl-Franzens-Universität Innsbruck, Innrain 52, A-6020 Innsbruck, ²Institut für Medizinische Physik, Karl-Franzens-Universität Innsbruck, Müllerstr. 44, A-6020 Innsbruck;
Mittels Autoradiographie konnte an Mikroorganismen in Standardnähragar die Aufnahme von ⁸⁵Sr und ^134+137Cs in E. coli nachgewiesen werden. Experimente mit S. cerevisiae zeigten eine Aufnahmefähigkeit für ⁸⁵Sr und ^134+137Cs von S. cerevisiae ähnlich wie bei E.coli. Im Gegensatz zu E. coli wurde für S.cerevisiae auch die Aufnahme von ^103+106Ru mittels Autoradiographie nachgewiesen. Versuche in flüssigen Nährmedien ließen eine deutliche Anreicherung aller getesteten Nuklide (⁸⁵Sr, ^134+137Cs und ^103+106Ru) erkennen. Für E.coli und S. cerevisiae wurde in flüssigen Nährmedien eine ähnliche Aufnahmecharakteristik bezüglich aller getesteten Radionuklide gefunden. Für ¹³⁷Cs wurden an E.coli Transferfaktoren (aus einem flüssigen Standardnährmedium: Nutrient Broth) bestimmt. Als Resultat wurden Transferfaktoren von 0,12 bis 2,94 in Abhängikeit von der Höhe der im Nährmedium eingesetzten Aktivität ermittelt.

Intensity-Modulated Radiotherapy (IMRT) in routine - experiences from a feasibility study
¹W.F.O. Schmidt, ²L. Boeh, ¹W. Nespor, ¹P. Wirth, ¹F. Büchler, ¹R. Hawliczek
Inst f Radiooncology, Donauspital Vienna, A - 1220 Vienna, Langobardenstr. 122, Austria; ²NOMOS Corp. USA
1991 the Donauspital in Vienna was opened, 1996 a radiooncology institute was integrated. 1999 hard- and software were updated; a Multi-Leaf-Collimator (MLC) and different software tools were installed as well as the CORVUS system (NOMOS), planning IMRT-treatments by "inverse planning", mathematically driven by simulated annealing. So Intensity-Modulated Radiation Therapy (IMRT) became possible (patients are treated with field combinations, allowing different dose-intensities in the treatment field).
Verification of the planning results were more time consuming than basic data measurements. Dose-measurements with ionisation chamber were reproducible < 2%, TLD- and film-measurements agreed < ;5% and < ;10% resp.
Up to May 2000 13 patients were treated. Treatments proved to be possible in routine. Difficulties arose from missing tissue-sensitivity data. "Class solutions" are needed for comparisons. Inaccuracies result from patient positioning.
Especially in setting up the system and initial measurements role and responsibilities of the physicist in medical research and routine is essential and should be highlighted.

3D Finite Element Approach and Simulation of the Excitation of the Spinal Cord
K. Minassian^1,2, F. Rattay², H. Markum¹
Institut für Kernphysik, TU-Wien
²Institut für Analysis und Technische Mathematik, TU-Wien
The electric field generated by an implanted electrode in the region of the lower spinal cord is computed with the finite element method. The voltage profiles of spinal cord nerve fibers serve as input data for an electrical network model which is used to calculate the excitation thresholds of the fibers. The relationship between electrode position and excitation sequence of the different neural elements is studied. Direct results of the simulations inform about the excitabiliy of the different nerve structures and exhibit a definite relation between electrode position and the recruitment order of spinal cord nerves. The interpretation of clinical muscle twitch measurements using the predicted activation order of the lower limb muscles helps to identify the electrode position relative to spinal cord structures, which is not possible with X-ray or MRI techniques.

The cardiac depolarisation process represented as superficial electrical field - computer simulation and in-vitro experiment
Hofer E., Plank G. and Schafferhofer I.
Institut f. Medizinische Physik und Biophysik, Karl-Franzens-Universität Graz
Cardiac depolarisation forms a thin propagating wavefront (< 400 microns) of local currents inducing potential differences in the surrounding volume conductor. Due to this inhomogeneity of the electric near field its accurate measurement is technically very challenging. We measured the behaviour of the electric field by means of a micro-miniature four-pole-electrode probe. A computer-model was developed simulating the fields in the volume conductor to predict how the type of the activation sequence, how the chosen inter-electrode distances and how the probe orientation would change the measurements. We found the field describes a vector loop with diverse morphologies: planar wavefronts are represented as line-like closed loops, elliptic wavefronts as cudgel-like loops pointing opposite to the direction of propagation. These vector loops take on twisted and bent forms if inter-electrode distances larger than 100 microns are used.

Ultrahigh resolution, spectroscopic optical coherence tomography
W. Drexler¹, U. Morgner², F.X. Kärtner², R.K. Ghanta², E.P. Ippen², A.F. Fercher¹, J.G. Fujimoto²
Institute of Medical Physics, University of Vienna, Austria
²Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, USA
Optical coherence tomography (OCT) is a non-invasive optical biomedical imaging technology for high speed, non-invasive, high resolution in vivo imaging in a variety of medical fields. Its longitudinal resolution is typically limited to 10-15 µm, providing more detailed structural information than any other conventional technique. However many of the early changes associated with diseases are still below its detection limit, e.g. subcellular structures for early cancer diagnosis or detailed imaging of retinal layers for early ophthalmologic diagnosis. Using a state of the art femtosecond Ti:sapphire laser an ultrahigh resolution, spectroscopic OCT system has been developed, enabling in vivo OCT imaging with axial resolutions of 1 µm in biological tissues. The ability of OCT to perform in vivo optical biopsy with resolution close to that of conventional histopathology is demonstrated in the human retina and in different animal models. With an extension of this technique, extraction of spatially resolved spectroscopic information is enabled to improve image contrast and to obtain functional or biochemical properties of the investigated tissue.

3-dimensionale Kraftkalibration von optischen Pinzetten
W. Singer, S. Bernet, T. Haller, N. Hacker, P. Dietl, M. Ritsch-Marte
Institut für Medizinische Physik, Institut für Physiologie, Universität Innsbruck, Österreich; Sektion Physik, LMU München, Deutschland
Optische Pinzetten sind ein vielseitiges Werkzeug zur Untersuchung und Manipulation von mikroskopischen Teilchen. Bei vielen Anwendungen ist dabei die von der Pinzette ausgeübte Kraft von großem Interesse. Wir demonstrieren eine einfache Methode zur 3-dimensionalen Kraftkalibration optischer Pinzetten durch Auswertung der Einfangdynamik von Latex-Mikrokugeln. Als Anwendung wird eine medizinisch relevante Hypothese untersucht, nach der bestimmte Lungenzellen (Typ II) infolge mechanischer Dehnung zur Freisetzung von Surfactant Proteinen angeregt werden sollen. Durch Kombination der optischen Pinzette mit den Methoden der Fluoreszenzmikroskopie können lebende Lungenzellen sowohl gedehnt, als auch die Freisetzung der Surfactant Proteine beobachtet werden.

Optical Mapping of Shock-induced Membrane Potential Changes in Cardiac Tissue
H.Windisch, D.Dapra, Ch.Günter, M.Janschitz, Th.Münzer, H.Köhler, D.Platzer
Institut für Medizinische Physik und Biophysik, Universität Graz
Cardiac ventricular fibrillation is the most dangerous complication in heart disease, especially in cardiac infarction. The application of strong electrical shocks has become the most important treatment in stopping cardiac fibrillation. Field induced transmembrane potential changes, which depend on the extracellular electrical field, the location within the tissue and the structure of the electrical syncytium, play the key role in a defibrillation process and have become a focal point of cardiac investigation. High resolution optical potential mapping allowed us to study these potential changes in guinea pig papillary muscles within small regions (< 1 mm). Using the fluorescent potential sensitive dye di-4-ANEPPS and laser excitation, our measurements revealed the complex response of living cardiac tissue to electrical shocks (up to 13.5 V/cm, 5ms): local electrical activity and excitation waves during or after the pulse were induced and in regions of hyperpolarization the fast sodium inward current system could recover. All these phenomena can contribute to a successful defibrillation, but may, in the worst case, also induce refibrillation.

Monitoring field induced transmembrane potential changes in cardiac tissue using confocal fluorescence technique
D.Dapra, T.Muenzer, H.Ahammer, M.Lackner, H.Windisch
Med. Physik und Biophysik, Universität Graz
Abstract-We used a fast, fluorescent, potential sensitive indicator (di-4-ANEPPS) in combination with a specially designed setup consisting of a fluorescence microscope, a frequency doubled Nd-Yag laser and a 256 photodiode array system. The spot size projected onto a photodiode was 21µm x 21µm. In depth the light of about three cell-layers (40µm) was collected. The setup was reconstructed to a confocal laser microscope: an illumination pinhole array ( 300µm diameter each hole) and a detector pinhole array (256 holes, 1.1mm diameter) were inserted into the optical path. Fluorescence light of up to 6 spots of 12µm x 12µm was recorded simultaneously. The axial resolution of the confocal setup resulted in a FWHM (Full Width at Half Maximum) better then 15µm. The temporal resolution was up to 30KHz. Results revealed that field induced polarizations can change the polarity within a step in depth of only about 30 µm.

Dual Wavelength Excitation: a Calibration Aid in Bioelectrical Fluorescence Measurement
H.Köhler, D.Dapra, T.Muenzer, H.Ahammer, M.Lackner, H.Windisch
Med. Physik und Biophysik, Universität Graz
Besides traditional methods, optical fluorescence techniques are widely used to monitor membrane potential changes in cardiac cells and tissues. In experiments preparations are stained with a voltage sensitive, fluorescent dye (di-4-ANEPPS), which binds to cell membranes. When excited, fluorescence intensity changes proportional to membrane potential changes depending on the excitation-wavelength: Using lambda excitation of 532 nm resulted in a response of dF/F of approx. 10% per 100mV membrane potential change, and 457 nm in approx. 1% respectively. A dual wavelength-excitation protocol allowed us to correct the optical signal for bleaching induced deviations to an amount of about 1:10. The corrected signals could be calibrated in absolute values by estimating two typical membrane voltages as e.g. resting potential and action potential amplitude. In addition, when sampling the signal while periodically alternating excitation wavelengths, it was possible to reduce motion artefacts.

Cardiac Cells in Fieldstimulation Experiments: Observations and Simulations
D. Platzer, D. Dapra, C. Günter, H. Paier, H. Windisch
Institut für Medizinische Physik und Biophysik, Universität Graz
We combined optical fluorescense measurements using voltages-sensitive dyes with predictions from a simplified mathematical model of the field stimulation process to reveal and explain the particular complex behavior of cardiac cells exposed to different patterns of electric shock. Depending on strength and duration the applied field resulted in different responses from the cells. Short pulses near excitation threshold triggered regular action potentials, intermediate values of the field strength resulted in reduced upstroke velocities, and high strength electric shocks could even halt the excitation process at an intermediate state, causing delayed additional response after the field shock. Straight-forward modeling together with the optical recording technique helps to explain the underlying mechanism of this behavior. Closer investigation showed that optically monitored field stimulation experiments revealed behavior that can not be explained by common membrane kinetic descriptions and form the basis for a revised investigation of ionic conductance mechanisms in cardiac cell membrane.

The investigation was supported by the Austrian Science Fund, grant no. P12294-Med.

Spectroscopic investigations of selected yellow blooming flowers of ranunculaceae, brassicaceae and asteraceae
S. Galsterer¹, M. Musso², A. Asenbaum², D. Fürnkranz¹
Institut für Botanik, Universität Salzburg, Hellbrunnerstraße 34, A-5020 Salzburg, Austria, ²Institut für Physik und Biophysik, Universität Salzburg, Hellbrunnerstraße 34, A-5020 Salzburg, Austria
The aim of this work is to determine how the influence of gloss phenomena and anthesis-dependent UV pigment patterns has consequences on how insects notice these kinds of attractants. With a comparative study of spectral information, obtained by reflection spectroscopy and by Raman spectroscopy, it may be possible to deepen the knowledge of petal structure and pigment distribution of selected yellow blooming flowers.

LIPOMETER - a new optical device for body fat measurement. A comparison with other methods
Erwin Tafeit, Reinhard Möller, Karl Heinz Smolle, Thomas R. Pieber, Osman Ipsiroglu, Martina Düsse, Christian Huemer, Karl Sudi, Gilbert Reibnegger
Institute for Medical Chemistry
Interest in techniques for measuring body composition in general, and body fat in particular, has paralleled and, at the same time, promoted increased application of scientific methods in human biology, nutrition, medicine, and the sport sciences. Many methods exist which are based on a variety of underlying measurement priciples and assumptions. However, the standard methods have disadvantages, e.g., radiological burden (computed tomography), stress for the measured person (underwater weighing), lack of precision and reproducibility (caliper techniques), dependence on hydrational status (bioimpedance), time requirement (dilution methods), or high costs (nuclear magnetic resonance). A new computerized optical system ("LIPOMETER") was developed in order to permit a non-invasive, quick, precise and safe determination of the thickness of subcutaneous adipose tissue (SAT) at specified body sites. SAT of 20 healthy women and 18 healthy men was measured at 15 specified body sites. These measurements were used to calculate equations to estimate percentage total body fat (TBF%) of a subject. Total body electrical coductivity (TOBEC) was employed as reference method; caliper techniques and measurements of absorbances of infrared light in fat versus lean tissue were also compared. The LIPOMETER results show good agreement with TOBEC data (r=0.96).

Raman spectroscopic documentation of maturation processes in natural resins
W. Winkler¹, E.Ch. Kirchner¹, M. Musso², A. Asenbaum²
Institute of Mineralogy, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria, ² Institute of Physics and Biophysics, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria
The volatile and non-volatile fraction of natural resins is a mixture of mono-, sesqui-, di- and triterpenoids with the isoprene unit (C₅H₈) as their precursor. The non-volatile fraction can become fossilized under appropriate conditions of deposition. The information from the intensity ratio of the Raman bands at 1646 and at 1450 cm^-1 allows a differentiation between recent and fossil resins. Relatively low band intensities at 1646 cm^-1 point towards mature resins, caused by the reduction of n(C=C) stretching vibrations of the olefinic bonds with the maturation process of the resin. In this present study, the Raman spectroscopic investigation of resin maturation processes has been extended to a broader range of sample materials, including samples from modern trees, moreover also copals, and fossil resins from a wide age range.

Measurements of the zeta potential on intact and chemically modified assymetric porous polymer membranes
Robert Soster¹, Irena Kukovicic², Crtomir Stropnik², Milan Brumen^3,4, Volker Ribitsch⁵
University of Maribor, ¹Faculty of Mech. Engineering, ²Faculty of Chemistry and Chem. Engineering, ³Faculty of Education, Maribor and ⁴Jozef Stefan Inst., Ljubljana (Slovenia), ⁵ Karl Franzens-University, Inst. of Phys. Chemistry, Graz (Austria)
Asymmetric porous membranes were prepared from polysulfone by a wet-phase separation procedure. Different chemical modifications were applied to the upper membrane surface; i.e. the surface which was exposed to interaction with water in the coagulation bath during the membrane formation, in order to change a surface charge as well as to achieve a hydrophobic or a hydrophilic coating. The zeta potential was measured on both, unmodified and chemically modified membranes. It was found that specific chemical modifications of the membrane surface affect the zeta potential values. Reaction with 1-chlorodecane gave hydrophobic surface by nonpolar -(CH₂)₉-CH₃ groups and reaction with propylene oxide gave hydrophilic surface with polar group -CH(CH₃)-CH₂-OH which lower absolute values of zeta potential. A modification of the membrane surfaces with sulfuric (VI) acid brought ionizable (-SO₃H) functional groups at the surface that results in higher negative values of the zeta potential

Structure and mechanical properties of Wood
H. Lichtenegger¹, J. Färber¹, A. Reiterer², S. E. Tschegg², P. Fratzl¹
Erich Schmid Institut für Materialwissenschaft, Österreichische Akademie der Wissenschaften & Institut für Metallphysik, Montanuniversität Leoben
²Institut für Meteorologie und Physik, Universität für Bodenkultur, Wien
Wood exhibits excellent mechanical properties such as high strength and stiffness in spite of its low density. This is achieved by a cellular architecture and an intelligent optimization on mechanical requirements on all levels of hierarchy. On the nanometer scale the wood cell wall is a composite of stiff cellulose fibrils in a softer matrix. The tilt angle of the cellulose fibrils versus the longitudinal cell axis has been found to vary considerably within individual trees. Tensile tests showed that low tilt angles are correlated with a high stiffness of the wood cell wall, large tilt angles with a high extensibility. Indeed, large tilt angles are found in parts of a tree, such as young stems and branches, where a high flexibility is required. These findings suggest an optimization process: through variation of the cellulose tilt angle selected mechanical properties may be achieved.

Position resolved textures in bone
Daniel Jaschouz¹, Oskar Paris¹, Hae-Sook Hwang¹, Josef Keckes¹, Paul Roschger² & Peter Fratzl¹
Erich Schmid Institut für Materialwissenschaft, Österreichische Akademie der Wissenschaften & Institut für Metallphysik, Montanuniversität Leoben
²Ludwig Boltzmann Institut für Osteologie, Wien
Bone is a hierarchically organized material. Vertebral bone for example consists of a strongly porous, sponge-like structure. The walls between the pores (trabeculae) are some 100 micrometer thick and consist of a compound of organic fibers (collagen) and crystalline nano-particles (calcium phosphate). One special feature of biological materials like bone is based on the fact, that the structure is optimized for the respective mechanical function. At the lowest hierarchy level within the nanometer scale such an optimization is possible by fiber alignment. Techniques for obtaining position resolved textures are small-angle X-ray scattering (SAXS) and pole-figure analysis. We present a comparison of these two approaches, based on measurements on human vertebral bone of different age. The complementary information from both methods provides a picture for the local organization of the bone matrix and enables also the characterization of pathologically modified bone, e.g. after fluoride treatment.

Richtungsabhängiger Schutzabstand zwischen Stallungen und Wohnbebauung zur Vermeidung von Geruchsbelästigungen
G. Schauberger¹, M. Piringer², E. Petz²
Inst. für Medizinische Physik u. Biostatistik, Veterinärmedizinische Universität Wien
²Zentralanstalt für Meteorologie und Geodynamik, Wien
Der zeitliche Verlauf der Wahrnehmungsentfernung von Geruch, der aus Tierhaltungsbetrieben emittiert wird, wurde anhand des dynamischen Austrian Odour Dispersion Models (AODM) berechnet. Das Modell besteht aus drei Modulen: Das Emissionsmodul berechnet aufgrund der sensiblen Wärmebilanz des Stalles die Geruchsfreisetzung und den Volumenstrom. Das Ausbreitungsmodell basiert auf einem Gaußmodell. Das dritte Modul berechnet die Fluktuation der Immissionskonzentration. Dabei wird für die Andauer eines Atemzuges die zu erwartende Maximalkonzentration in Abhängigkeit von der Stabilität der Atmosphäre, der Windgeschwindigkeit und der Ausbreitungszeit berechnet. Die Modellrechnungen wurden mit einer zweijährigen Meßreihe (Wels, Oberösterreich) von Halbstundenwerten durchgeführt. Die durch das Ausbreitungsmodell berechneten Immissionskonzentartionen werden anhand von Überschreitungswahrscheinlichkeiten (zwischen 3 bis 10% des Jahres) und eines vorgegebenen Grenzwertes (zwischen 1 und 10 GE/m³) bewertet. Daraus ergeben sich richtungsabhängige Schutzabstände, die im Vergleich mit nationalen Richtlinien diskutiert werden.

Diurnal variation of the concentration of OH during the 27^th November 1999 at the Sonnblick Observatory (3106 m a.s.l.)
T. Karl¹, A. Jordan¹, R. Fall², P. J. Crutzen³, M. Mandl⁴, M. Staudinger⁴, and W. Lindinger¹
Institut für Ionenphysik, Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria, ²Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, ³Max-Planck-Institut für Chemie, Mainz, Germany
Using PTR-MS we measured the densities of several VOCs at the Sonnblick Observatory during the whole day of the 27^th November 1999. During daytime the concentrations showed a substantial decline, e.g. of about 50% in the case of pentenol, one of the most prominent VOCs present. The meteorological situation was characterized by strong inversion and very little wind activity. Thus any changes in VOC concentrations observed were solely due to reaction kinetics without significant influence of transport phenomena. Assuming that reaction with OH radicals is the main loss process for pentenol (k=6x10^-11cm³/s) we calculated the OH radical density as dependent on time. The concentration increased from zero at 8:00 local time to a maximum density of 1.0x10⁶ cm³ at 11:00 and declined thereafter reaching zero level at 15:00. This variation coincided well with the time dependence of solar radiation.

Eddy convariance measurements of VOC fluxes using the PTR-MS technique
T. Karl¹, A. Jordan¹, R. Fall², and W. Lindinger¹
Institut für Ionenphysik, Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria, ²Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309
NMHCs released from biogenic sources are known to be atmospheric precursors for aerosols, peroxynitrates and thus for ozone formation and destruction. Using Proton-Transfer-Reaction Mass Spectrometry (PTR-MS), which has proven to be a useful tool for the quantification of tropospheric VOCs, we gained data on emission rates of reactive aldehydes (hexenyl compounds) and other abundant VOCs such as methanol, acetaldehyde and acetone from drying grass. We obtained fluxes after cutting of grass using eddy covariance measurements and also by the micrometeorological gradient method (Obhukov-Similarity-Method). These investigations were done during 21^st and 22^nd of August 1999 above a field in Tyrol which was freshly mowed in the morning of August 21^st. We also performed various chamber experiments on the emissions of these VOCs. Comparison of the data obtained by the different methods shows satisfactory agreement. The highest fluxes for methanol during drying were 5 mg/m²h, for (Z)-3-hexenal 1.5 mg/m²h.

Release of pentenols from wounded and senescing leaves as a result of lipoxygenase-type reactions – observation of high mixing ratios on the Sonnblick
T. Karl¹, A. Jordan¹, R. Fall², and W. Lindinger¹
Institut für Ionenphysik, Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria, ²Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309
We used a PTR-MS-GC system to identify lipoxygenase peroxidation products during freezing induced wounding, senescing and general wounding in various plants. In all laboratory experiments we observed substantial production of 1-penten-3-ol, cis-2-penten-1-ol, hexenal and hexenol isomers, all reactive oxygenates that contribute to tropospheric chemistry. We want to draw special attention to the production of pentenols, compounds which have not been reported to be present in large amounts in the atmosphere. PTR-MS online measurements on the Sonnblick observatory in the Austrian Alps (3106m) show that even in the free troposphere substantial amounts of pentenols can be present as the result of ongoing freezing and senescing in deciduous plants. We also observed high mixing ratios of hexenals, acetaldehyde, methanol, 2-methylbutanal, 3-methylbutanal, EVK and acetone, all coming from local vegetation near the Sonnblick.

Events of strong anticorrelation between ozone and aromatic compoubds at the Sonnblick observatory (3106 m a. s. l.)
A. Jordan¹, T. Karl¹, R. Fall², P. J. Crutzen³, M. Mandl⁴, M. Staudinger⁴, C. Lindinger¹ , and W. Lindinger¹
Institut f. Ionenphysik, Universität Innsbruck, Austria, ²Dep. Chem. Biochemistry, and Cooperative Inst. for Research in Environmental Sciences, Univ. of Colorado, Boulder, CO 80309, ³Max-Planck-Institut f. Chemie, Mainz, Germany.
During the time span from 9^th till 11^th November 1999, an event of extremely high concentrations of aromatic compounds (1.4 ppbv toluene and 0.8 ppbv benzene) and acetaldehyde (20 ppbv) were observed at the Sonnblick Observatory which coincided with a decline of the ozone concentration from average levels of 50 ppbv before and after the event down to a minimum of 8 ppbv. Back trajectories infer that the air masses observed during this event had been travelling from north westerly directions and close to the surface prior to ascending the Sonnblick, and from the relative concentrations of benzene and toluene the age of the aromatic compounds is estimated to be less than a day. Thus the location of the origin of the air masses is most likely the area of Bavaria. This is also consistent with the high concentrations of acetaldehyde observed, originating from biogenic emissions, which are especially strong for acetaldehyde from dying vegetation in late autumn. The air masses at ground level contain little ozone - thus low concentrations were observed during the event, as there was not enough time for building up of higher ozone concentrations during the transport to the Sonnblick.

Die Messung der Fluenz bei polychromatischer UV-Strahlung mittels Mikroorganismen (Biodosimetrie).
A. Cabaj¹, R. Sommer² und W. Pribil²
Institut für Medizinische Physik und Biostatistik, Veterinärmedizinische Universität Wien, ²Klinisches Institut für Hygiene, Universität Wien
Die Messung der Reduktionsäquivalenten Fluenz (REF) ist bei UV-Trinkwasser-desinfektionsanlagen mit Hg-Niederdruckstrahlern (monochromatische Strahlung mit =254 nm) ein Routineverfahren. Anlagen mit diesem Strahlertyp sind derzeit die einzigen in Österreich zugelassenen (ÖNORM M 5873, Teil 1 Entwurf). Es bestehen jedoch starke Bestrebungen, Anlagen mit Hg-Mitteldruckstrahlern einzusetzen. Diese Strahler emittieren im gesamten Bereich von 240-400 nm Strahlung, es müssen also die biologischen Wirkungen polychromatischer UV-Strahlung in die Überlegungen eingeschlossen werden. Wir haben für das übliche Biodosimeter, nämlich Sporen von Bacillus subtilis ATCC 6633, die spektrale Empfindlichkeit bestimmt und den Einfluss der Form der monochromatischen und polychromatischen Überlebenskurven (Kalibrierkurven) auf das Resultat der Biodosimetrie, nämlich die REF, bestimmt.

Investigations in the field of Radiation and Air Pollution at IGAM
Dr. Erich Putz
Institute for Geophysics, Astrophysics, and Meteorology (IGAM)
Photochemistry of the atmosphere represents the central thematic of the RAP Research Group (Radiation and Air Pollution). Investigations in this field comprise the radiative transfer in the solar UV range and the nexus with clouds and aerosols, the photolysis frequencies of ozone and nitrogen dioxide, the erythemal UV-B, the influence of climate and solar radiation on trace gas concentrations as well as the contribution of halogenated chlorohydrocarbon photodecomposition to the photochemical cycle. In this work theoretical (radiative transfer and gas-phase photochemistry modeling) and experimental methods (ground-based and airborne measurements) are applied. Aside from various radiation sensors, three different DOAS systems (differential optical absorption spectroscopy) are operated: a bistatict and a monostatic instrument in order to assess the pollution load in the lower troposphere and a further instrument to measure the atmospheric ozone and nitrogen dioxide column content. These investigations are conducted in the framework of several international and national projects.

Simultane Bodenbeobachtungen der Jupiter-Dekameter-Radiostrahlung durch europäische Radiostationen
Rucker, H. O.¹, A. Lecacheux², A. Konovalenko³ und das Jupiter-Radio-Team Graz
Inst. f. Weltraumforschung, Österr. Akademie der Wissenschaften, Halbärthgasse 1, A-8010 Graz, helmut.rucker@oeaw.ac.at, ² Observatoire de Paris-Meudon, F-92195 Meudon Cedex, France, ³ Institute of Radio Astronomy, Kharkov, Ukraine
Im Rahmen des Frankreich-Österreich-Ukraine-Russland EU-INTAS Projektes "New Frontiers in Decametric Radio Astronomy" wurden Jupiter-Dekameter Beobachtungen simultan von den Radiostationen Nancay (Frankreich), Graz (Österreich) und Kharkov (Ukraine) durchgeführt. Ziel dieses Projektes ist die Erarbeitung von Grundlagen für die Planung eines "Ground-Based Giant Radio Telescope", welches im niederfrequenten Dekameter-Wellenlängenbereich Beobachtungen der Radioplaneten, der Sonne und galaktischer Radioquellen - insbesondere Pulsare - ermöglichen soll.
Im Rahmen von bislang zwei durchgeführten Radiobeobachtungskampagnen wurde die Jupiter-Radiostrahlung im Dekameterbereich untersucht und es konnten zum ersten Mal zeitlich und frequenzmäßig hochaufgelöste dynamische Spektren mit identen Radioempfängern (Digital-Spektropolarimeter, eine gemeinsame Entwicklung von Frankreich und Österreich) aufgenommen werden. Physikalische Parameter werden aus diesen Spektren herausgearbeitet, welche für die Theorie der Jupiter-Radiostrahlung von Relevanz sind. Ebenso können Aussagen über das von der Radiowelle durchlaufene Magnetoplasma getroffen werden.

Raumsonden zum Roten Planeten
Stumptner, W., und H. Lammer
Institut für Weltraumforschung der Österreichischen Akademie der Wissenschaften, Abteilung Physik des erdnahen Weltraums, Elisabethstrasse 20, A-8010 Graz, willibald.stumptner@oeaw.ac.at, Tel.: 0316-3210912, Fax: 0316-3210914
Mars - der Rote Planet - ist eines der primären Ziele für Weltraummissionen. Diese neue Generation von Raumsonden versucht das Rätsel des jungen Mars zu enträtseln, der einst der Erde recht ähnlich war - eine dichtere Atmosphäre, höhere Temperaturen, Wasser - vermutlich sogar Meere auf der Nordhalbkugel - sowie ein stärkeres Magnetfeld. Die amerikanische Mars Global Surveyor Mission - das Institut ist an der Auswertung der Daten des Magnetometers/Elektronen-Reflektometers beteiligt - entdeckte relativ starke Krusten-Magnetfelder. Diese sind Überreste eines starken frühen Magnetfeldes, welches den Planeten vor einem Teil der schädlichen Strahlung schützte und den Verlust an Atmosphärenbestandteilen in Grenzen hielt. In den nächsten Jahren wird uns auch die japanische Raumsonde PLANET-B ("Nozomi") erstmals Daten über die hohe Neutralgas-Atmosphäre liefern. Weitere Beteiligungen an zukünftigen europäischen und amerikanischen Raumsonden sind in Arbeit. Die gewonnenen Erkenntnisse über den Roten Planeten dienen insbesondere auch zum Verständnis der Evolution unseres eigenen "Blauen Planeten" Erde und der Entstehung des Lebens in der Frühzeit des Sonnensystems.

Numerical modelling of the lower ionospheres of Titan and Mars
G.J. Molina-Cuberos^1,2, K. Schwingenschuh¹, H.I. Lichtenegger¹, H.U. Eichelberger¹, J.J. Lopez-Moreno², and R. Rodrigo²
Institut für Weltraumforschuhng/OEAW, Inffeldgasse 12, A-8010, Graz, Austria. ²Instituto Astrofisica Andalucia/CSIC, PO Box 3004, 18080, Granada, Spain.
In November 2004 HUYGENS-CASSINI, a planetary probe of the European Space Agency (ESA) will investigate electrical properties of the atmosphere and surface of the Saturnian moon Titan. We have developed two numerical models of the lower ionosphere of Titan. First the ion-neutral chemistry of Titan has been modelled in order to calculate the concentration of electrons and ions. Using these results we have determined the electrical conductivity that will be measured by HUYGENS during its descent. We have also modelled the propagation of low frequency electromagnetic waves that could be generated by lightning phenomena at very low altitudes. A major emphasis of our work is on the investigation of the wave attenuation and on the influence of the surface electrical conductivity on the wave properties. The model has been adapted to investigate the ion-neutral chemistry of the lower atmosphere of Mars. First results will be presented too.

Die Untersuchung von "Space Weather" Vorgängen mit erdmagnetischen Pulsationen
Schwingenschuh K., W. Magnes, H. Schwarzl, T.L. Zhang, W. Riedler
Institut für Weltraumforschung/VAW, Inffeldgasse 12, A-8010 Graz
Beim "Space Weather" handelt es sich um Vorgänge auf der Sonne, im interplanetaren Raum oder in der Magnetosphäre/Ionosphäre der Erde, welche den Betrieb von Satelliten und die Funktion von Navigation- oder Kommunikationssystemen wesentlich stören können. Magnetische Stürme auf der Erdoberfläche sind in der Lage Hochspannungsnetze für eine gewisse Zeit lahm zu legen und sogar die Korrosion von Pipelines zu beschleunigen. Erdmagnetische Pulsationen mit Perioden im Bereich von 0.1 bis 600 Sekunden entstehen durch Eigenschwingungen der Magnetosphäre der Erde. Es wird ein einfaches physikalisches Modell zur Bestimmung der Plasmadichte in der unteren Magnetosphäre präsentiert. Dabei werden die Messdaten von Pulsationen auf der Erdoberfläche verwendet. Die Plasmadichte wird durch das "Space Weather" geändert und kann den Betrieb von Satelliten stören.

The Earth's magnetosheath: Modelling and data comparison
*Bruno P. Besser ^*, Johannes M. Fritzer ^*, Mikhail I. Pudovkin ^**, Svetlana A. Zaitseva ^**, Valentina V. Lebedeva ^**, and Claudia-Veronika Meister ^***
Space Research Institute, Austrian Academy of Sciences, Graz, Austria; ^** Institute of Physics, St. Petersburg State University, St. Petersburg, Russia; ^*** Astrophysical Institute, Potsdam, Germany
We study variations of the plasma parameters, like density, temperature, and magnetic field intensity, across the Earths magnetosheath using an anisotropic magnetohydrodynamic plasma model in the Chew-Goldberger-Low approximation. The temperature anisotropy significantly effects the plasma parameter profiles when the energy transfer between the direction parallel and perpendicular to the ambient magnetic field is not taken into account. For our calculations we assume intensive proton pitch- angle diffusionthe main energy transfer mechanism, which results in the relaxation of the proton temperature anisotropy, and compare the results with model calculations for isotropic magnetohydrodynamics. The results of our calculations are also compared with experimental data from magnetosheath crossings of different spacecraft.
^a This study has been financially supported by the project No. 7894 of the Austrian National Bank.

In-situ analysis of cometary dust particles by atomic force microscopy
K. Torkar¹, W. Riedler¹, J. Romstedt², A. Jaeckel², and the MIDAS Team
Space Research Institute, Austr. Academy of Sciences, Inffeldg. 12, 8010 Graz, A
²Space Science Department, ESA/ESTEC, 2201 Noordwijk, The Netherlands
The payload of the ROSETTA spacecraft to comet 46P/Wirtanen includes the Micro-Imaging Dust Analysis System (MIDAS), an instrument to collect and image dust particles from the cometary coma. At the heart of MIDAS is an atomic force microscope capable of producing three-dimensional images of the smallest dust grains at a resolution of a few nanometers. The topography of individual particles and the dust counting statistics will provide unique data on the composition of cometary material. The space environment puts high requirements on the instrument, and extraordinary technical solutions had to be found to cope with the launch environment and micro-vibrations, and to ensure sufficient lifetime and reliability for this long-duration mission. The spacecraft is to be launched in 2003 and to follow the comet to perihelion in 2013.

Reaction mechanism of the enzyme hydroxynitrile lyase
G. Gartler^1,2, K. Gruber¹, U.G. Wagner¹, C. Kratky^1,2
1 Inst. f. Chemie-Strukturbiologie, Karl-Franzens-Universität Graz, Heinrichstr. 28, 8010 Graz, ² SFB Biokatalyse, TU Graz, Stremayrgasse 16, 8010 Graz, Austria
The enzyme (S)-Hydroxynitrile lyase from Hevea brasiliensis (Hb-Hnl) catalyzes the reversible cleavage of cyanohydrins to prussic acid and the corresponding aldehydes or ketons. The enzyme belongs to the -hydrolase superfamily with an active site containing a catalytic triad formed by Ser80, His235 and Asp207. Based on crystal structures of complexes with substrates and inhibitors a reaction mechanism was suggested in 1999.
In an effort to further corroborate this suggested mechanism we modelled the structures of complexes of Hb-Hnl with the native substrat acetone cyanohydrin and with mandelonitrile and the cyanohydrin of isopropyl-methyl-ketone. Recently we tried to verify these results by experiments. The enzyme-substrate complexes were prepared by transferring crystals into reservoir solutions containing the substrates. Diffraction data were collected at cryotemperature at DESY (Hamburg). The modelled and experimental data are consistent with the proposed reaction mechanism.

Surface modification of PET fibres
Magda Sfiligoj Smole¹, Marjan Bele², Karin Stana-Kleinscheck¹, Volker Ribitsch³, Peter Zipper³
University of Maribor, Inst. of Textile Chemistry, Lab. for Characterisation & Processing of Polymers, Maribor, Slovenia, ²National Inst. of Chemistry, Ljubljana, Slovenia, ³Karl-Franzens-University Graz, Inst. of Chem., Rheology and Colloid Science, Graz, Austria
The commercial textile PET fibres are highly oriented semicrystalline systems consisting of a spectrum of regions ranging from highly crystalline to virtually noncrystalline. The closely packed fibre structure, high crystallinity, hydrophobic character, low swelling and the fact that unmodified PET fibres do not possess reactive groups are the reason for low affinity of dyes.
A technique for modifying polyester fibre surface to change the dyeability, water sorption properties and electrokinetic characteristics has been suggested and used. It includes the adsorption of gelatine on the fibre surface from an aqueous solution. A PET multifilament yarn with a linear density of 143 dtex with a highly developed fibrillar structure was used. In order to determine the changes of the fibre surface charge the zeta-potential was determined by streaming potential measurements as a function of pH. Both processes, the adsorption of polyelectrolytes on the fibre surface and the interaction of dye molecules with the modified fibres are mainly controlled by electrokinetic properties and their pH dependence.

Determination of the streaming potential by new oscillating test method
U. Zaismann¹ and V. Ribitsch²,
Joanneum Research, Graz, Austria
²University of Graz, Inst. of Chemistry, Rheology & Colloid Science, Graz Austria
The application for electrokinetic test methods in new fields requires new and extended demands on the measurement technology.
An essential criteria for the acceptance of a measuring method is a simple sample handling and data acquisition. The measurement of the streaming potential created by an oscillating (sinusoidal) electrolyte flow expands the application range of this technology considerably. Reasons are an improved accuracy due to the increases sampling rate, use of electrolyte systems with high conductivity, a simplification of the handling due to conception of new test cells.
Differently to the traditional procedures for the determination of the streaming potential of macroscopic materials no pressure ramp is applied with the new test method. An oscillating electrolyte flow accompanied by an oscillating pressure signal with the aid of a piston system is created. At frequencies below 100 Hz the resulting streaming potential does not exhibit any phase shift to the exciting flow. At higher frequencies one expects a additional information about the inhomogenities of the solids surface.
The main advantage is the immediate recording of the entire pressure and potential signal, moreover through approximation of the sine functions a compensation undesired side effects is possible. During one cycle several set of measurement date - pressure and the responding streaming potential - are obtained. Electrode polarization does not influence the results, it causes only a shift of the signals baseline. The variation of the frequency offers the possibility to adopt the procedure to a wide range of electrolyte concentrations and sample conditions.

Interaction of Block Copolymer Micelles
Alexander Bergmann, Gerhard Fritz and Otto Glatter
Institut für Chemie, Physikalische Chemie, Universität Graz
Block copolymers aggregate in selective solvents into micelles of different size and shape. The structure depends on the molecular architecture of the surfactant and on the interaction parameters. We have investigated the phase behaviour of aqueous Synperonic P94 (EO17-PO42-EO17) solutions by means of densiometry, viscosimetry, ultrasonic speed measurements and small angle scattering of X-rays and neutrons (SAXS, SANS). The polymer concentration has been varied from 0.05%(w/w) up to 40%(w/w) in a temperature range from 3°C to 75°C.

Fabrication of phase and relief gratings on polymer films
T. Kavc¹, G. Langer¹, W. Kern¹, G. Kranzelbinder², S. Voß³
Inst. f. Chem. Technol. organischer Stoffe, TU Graz, Stremayrgasse 16, A-8010 Graz
²Ecole Normale Superieure de Cachan, LPQM, 61 Avenue du Pres. Wilson, F-94230 Cachan
³Inst. f. Chem. Technol. anorganischer Stoffe, TU Graz, Stremayrgasse 16, 8010 Graz
Gratings in polymer films are important for optoelectronics and for the setup of organic lasers based upon distributed feedback ("DFB lasers"). We investigated photosensitive polymers bearing SCN groups, e.g. poly(4-vinylbenzyl thiocyanate) (PVBT). Upon UV irradiation (254 nm), the SCN groups undergo an photoisomerization to the corresponding isothiocyanates (NCS). The refractive index nD of PVBT increased from 1.629 to 1.660 after UV irradiation. A treatment of the irradiated PVBT films with gaseous amines resulted in the formation of thiourea groups. This gas phase modification was accompanied by a further change of the refractive index and an increase of the film thickness (+5 to +20 %). After patterned UV illumination (Cr / CaF₂ contact mask) and reaction with gaseous amines a surface relief was obtained. AFM images showed a grating period = 600 nm and a grating pitch d 20 nm. Thanks to F. Hofer and P. Pölt (FELMI Graz; EDX spectra and electron micrographs). Thanks to the "SFB Elektroaktive Stoffe" (TU Graz, project No. 921) for financial support.

Synthesis and Characterisation of new conjugated polymers
Franz Stelzer, Arnulf K. Mahler, Horst Schlick, Ruth Muellner, Farideh Meghdadi, Günther Leising
Institute for Chemistry and Technology of organic Materials, TU-Graz, Stremayrgasse 16, 8010 Graz
We synthesized various new substituted poly(m,p-phenylenevinylene)s containing alkoxy or alkyl substituents using the Wittig-Horner reaction. NMR, FT-IR and GPC measurements have been performed for the chemical characterization. The dependence of the UV/VIS absorption and PL spectra on the type of the substituents has been investigated. Devices were fabricated consisting of ITO/PEDOT/P/Ca/Al exhibiting high luminance and low onset voltages. Another method of synthesis was the ring opening metathesis polymerization which was used to synthesise poly(anthrylenevinylene). Poly(phenylenevinylene)s with liquid crystalline side groups should be used for polarised emission, actual results are given.

Synthesis, Characterization and Rheology of Model Side Chain Liquid Crystalline Polymers
A. Wewerka¹, K. Viertler¹, F. Stelzer¹, D. Vlassopoulos²
1 TU Graz, Inst. of Chemical Technology of Organic Substances, 8010 Graz, Austria
² FORTH, Institute of Electronic Structure and Laser, Heraklion, Crete 71110, Greece
We report the synthesis of polymeric liquid crystals with linearly attached side mesogenic groups prepared by Ring Opening Metathesis Polymerization (ROMP).Using DSC and optical microscopy we find a strong effect of the length of side chains; whereas C₅ forms nematic mesophase, C₉ forms smectic. The length of the main backbone affects the isotropic-nematic and isotropic-smectic transition temperatures, respectively. These results are confirmed by linear viscoelastic measurements, indicating a failure of the time-temperature superposition at the respective transition temperatures; moreover, whereas C₅ exhibits liquid-like behavior in the nematic region, C₉ is a clear smectic solid. All isotropic fluids exhibit Arrhenius behavior with activation energy of 15-20 KJ/mol, whereas the nematic C₅ exhbitis WLF and the smectic C₉ a double Arrhenius behavior.By applying large amplitude oscillatory shear the moduli drop by more than one decade; the relaxation time approaches 48 hours, suggesting a very slow structural reorganization. The implications in controlling mesophase dynamics and structural transition are discussed.

Phase diagram of a symmetric binary fluid in a porous matrix
Elisabeth Paschinger, Dominique Levesque, Gerhard Kahl and Jean-Jacques Weis
Institut für Theoretische Physik and Center for Computational Materials Science, TU Wien, A-1040 Wien, Austria and Laboratoire de Physique Theorique, Universite de Paris-Sud, F-91405 Orsay Cedex, France
Our investigations of the phase diagram of a symmetric binary fluid in equilibrium with a porous matrix show that already moderate changes in the properties of the matrix or in the matrix-fluid interaction lead to drastic modifications of the phase diagram of the fluid. Thus our results confirm on a qualitative basis recent experimental data. The phase diagrams that we have obtained show a wide variation and can be classified in terms of archetypes of systems of two order parameters. These different types can be characterized in terms of the loci where the -line of the demixing transition intersects the first-order liquid-vapor coexistence curve. Results are based on the optimized random phase approximation and on grand canonical Monte Carlo simulations.

Simultaneous determination of thickness and optical constants of organic nano-films from ellipsometric measurements
G. Jakopic, N. Koch, W. Papousek, G. Leising
Joanneum Research, Institute of Nanostructured Materials and Photonics, Franz-Pichler-Straße 30, A-8160 Weiz
Organic (ultra)thin films become more and more important in designing optical devices such as LEDs, waveguiding elements, etc... The accurate characterization of their optical properties plays an important role in the selecting process of suitable materials as well as in the understanding of the excitation processes occuring in the material. We have chosen the oligomer para-hexaphenyl (P6) deposited on different semiconductor surfaces wich leads to differences in the morphology of the films. Using ellipsometric measurements we show how to carry out the optical constants and the thickness of ultrathin films of P6 consisting only of several monolayers. Dealing with films with thicknesses of about 10 nm it is extremely important to avoid unknown optical and structural influences of the substrate. We demonstrate the sensitivity of ellipsometry to these influences and compare the obtained results with atomic-force-microscope measurements.

Unoriented phospholipid bilayers at full hydration by means of an inverse Fourier method
Georg Pabst, Michael Rappolt, Heinz Amenitsch, and Peter Laggner
Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Steyrerg. 17, A-8010 Graz
We present a novel method for analyzing Small Angle X-ray Scattering data on multilamellar phospholipid bilayer systems at full hydration. The method utilizes a modified Cailli theory [1] structure factor in combination with a model representation of the electron density profile such that it accounts also for the diffuse scattering between Bragg peaks [2]. Thus, the method is superior to the usual data analysis that fits diffraction peaks only, and meaningful structural information can be retrieved even if only a few diffraction orders are observed. As an example we present the structural changes of dimyristoylphosphatidylcholine (DMPC) 30% w/w in aqueous solution on the approach to the main transition temperature, which is close to a critical point [3].
[1] R. Zhang, R. M. Suter, and J. F. Nagle, Phys. Rev. E 50, 5047 (1994). [2] G. Pabst, M. Rappolt, H. Amenitsch, and P. Laggner, Phys. Rev. E, in press. [3] O. G. Mouritsen, Chem. Phys. Lipids 57, 178 (1991).

Vibrational Behaviour and Temperature Stability of Ladder Type Polyparaphenylen
D. Somitsch^1,3, F.P. Wenzl², G. Leising², P. Wilhelm³, U. Scherf⁴, K.O. Annan⁴, P. Knoll¹
Inst. f. Experimentalphysik, Universität Graz, Austria; ²Inst. f. Festkörperphysik TU Graz, Austria; ³Zentrum für Elektronenmikroskopie, Graz, Austria; ⁴Max-Plank-Institut f. Polymerforschung, Mainz, Germany
Recently, ladder type conjugated polymers are in the focus of intensive investigations because of their high potential for light emitting device applications. We investigated three ladder type poly(paraphenylene)s (LPPP) with different side-chains, in order to characterize the vibrational behavior as well as the thermal stability. Raman spectra were recorded between 104K up to 610K at laser excitation of 647nm. They show the high thermal stability (full regeneration of the polymers up to a high temperature range) as well as an unusual behavior of the aromatic streching mode in intensity with increasing temperature. The latter phenomenon we discuss in terms of instabilities of the side-chains. The Raman spectra were interpretated by comparing the three types of LPPP together with normal coordinate calculations on a simplified LPPP model.

Wide-angle X-ray studies on the structure of polypropylene foam mouldings made by gas-counterpressure process
S. Djoumaliisky¹, P. Zipper²
Institut of Metal Science, Bulgarian Academy of Sciences, Sofia, Bulgaria
²Institut für Chemie, Karl-Franzens-Universität Graz, Austria
Structural foam mouldings were produced from isotactic polypropylene Buplen 6631 (Neftochim) and 0.5 % (w/w) blowing agent azodicarbonamide Genitron AC-4 (Fisons Ltd.) on an on-line injection moulding machine KuASY 800/250 in a mould cavity pre-pressurized with nitrogen, by the classical low-pressure process and a low-pressure process combined with egression of foamed melt from the core. The specimens were composed of 3 co-axial cylinders differing in diameter (10, 20, 30 mm) and length; the injection direction and the sprue diamter (4, 7 mm) were varied. Sections were cut from the middle of each cylinder in different orientations (parallel and perpendicular to flow direction). The sections were investigated by different approaches of site-resolved WAXS, using a two-circle goniometer and a specially adapted Kratky camera. The results give information about the orientation of -PP crystallites, distribution of -PP crystallites and crystallite dimensions in dependence on the process papameters and the geometry of the specimens.
This work was supported by the Dr. Heinrich Jörg Stiftung, Karl-Franzens-University Graz.

Unoriented phospholipid bilayers at full hydration by means of an inverse Fourier method
Georg Pabst, Michael Rappolt, Heinz Amenitsch, and Peter Laggner
Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Steyrerg. 17, A-8010 Graz
We present a novel method for analyzing Small Angle X-ray Scattering data on multilamellar phospholipid bilayer systems at full hydration. The method utilizes a modified Cailli theory [1] structure factor in combination with a model representation of the electron density profile such that it accounts also for the diffuse scattering between Bragg peaks [2]. Thus, the method is superior to the usual data analysis that fits diffraction peaks only, and meaningful structural information can be retrieved even if only a few diffraction orders are observed. As an example we present the structural changes of dimyristoylphosphatidylcholine (DMPC) 30% w/w in aqueous solution on the approach to the main transition temperature, which is close to a critical point [3].
[1] R. Zhang, R. M. Suter, and J. F. Nagle, Phys. Rev. E 50, 5047 (1994). [2] G. Pabst, M. Rappolt, H. Amenitsch, and P. Laggner, Phys. Rev. E, in press. [3] O. G. Mouritsen, Chem. Phys. Lipids 57, 178 (1991).

Ergodic Properties of a Class of Model Systems
P. Kasperkovitz, H.C. Renezeder, C. Tutschka
Inst. f. Theoretische Physik, TU Wien, Wiedner Hauptstr. 8-10, A-1040 Wien, Austria
We consider the classical Herzfeld Goeppert-Mayer system [1] and its generalizations to D>1 (hard rods, squares, cubes etc. with attractive square-well pair interaction). As none of these systems is ergodic one has to find the generic ergodic components and the corresponding invariant measures in order to compute time averages as space averages. We propose such measures and show that the configurational integrals needed in this construction (as well as in the microcanonical and canonical partition functions) can be calculated exactly by means of a recursive scheme which makes use of combinatorics and the geometry of convex polyhedra. For some observables of physical interest (velocity distribution, pressure) the proposed space averages are compared to time averages obtained from molecular dynamics simulations of small systems.
[1] K.F. Herzfeld, M. Goeppert-Mayer, On States of Aggregation, J. Chem. Phys. 2, 38-45 (1934).

Bonding Agent-Free Cellulose Materials: Influence of Density and Effect of Water Immersion on Mechanical Properties
M. A. Svoboda¹, R. W. Lang^1,2
Institute of Polymer Technology, Joanneum Research, Leoben, A
² Institute of Materials Science and Testing of Plastics, Univ. of Leoben, Leoben, A
A patented technology to process various plants and wastes with high cellulose content allows the production of bonding agent-free cellulose materials called Zelfo. Due to the possible variations in raw materials and in the production process, values for density from 0.3 to 1.5 g/cm³ can be achieved. Investigations of various grades of dry Zelfo HG and Zelfo HZ with different densities, made from complete hemp plants and hemp cellulose, respectively, indicate a linear dependence of the tensile modulus on density. In contrast, tensile strength was found to increase disproportionally with density. Especially for material grades with high densities, significantly higher values for tensile strength were determined than a linear regression extrapolation based on data for lower density material grades would suggest. As all Zelfo materials reveal a significant tendency for moisture uptake due to the highly hydrophilic cellulose content, the effect of water immersion on moisture-uptake and on mechanical properties was also examined. For example, the flexural modulus of Zelfo HZ drops from more than 9000 MPa in the dry state to less than 500 MPa after immersion in water for 24 h. Some of the relevant mechanisms involved will be discussed in the presentation.

Analytic Example of a Free Energy Functional
G. Kahl, C. Tutschka
Inst. f. Theoretische Physik, TU Wien, Wiedner Hauptstr. 8-10, A-1040 Wien, Austria
We use ideas of Percus for the construction of classical density functionals for two model interactions: simple hard spheres and adhesive hard spheres (AHS). The required input, the properties of the uniform fluid, are taken from the analytic mean spherical solution for these two systems. For hard spheres we derive - by decomposing the direct correlation functions - a set of basis functions which is the same as the one presented by Rosenfeld in his fundamental measure theory framework. For AHS additional basis functions have to be considered to ensure the decomposition of the direct correlation functions; we present an expression for the free energy functional for the one-component case.

Lichttransport in metallischen Nanostrukturen: Fernfeld-Nahfeld Kopplung
B. Lamprecht, G. Schider, J. R. Krenn, N. Felidj, M. Salerno, A. Leitner, F. R. Aussenegg
Institut f. Experimentalphysik, Karl-Franzens-Universität Graz, Univ.pl. 5 8010 Graz
Die große technologische Bedeutung einer weiteren Miniaturisierung der Optik in den Subwellenlängen-Bereich (Nano-Optik) steht außer Frage. Zum Lichttransport auf nanoskopischer Gößenskala sind jedoch die Methoden der herkömmlichen Fernfeldoptik nicht einsetzbar. Als Alternative bieten sich metallische Nanostrukturen an. Zugrundeliegender physikalischer Mechanismus sind dabei resonante Kollektivoszillationen der Leitungselektronen, sogenannte Plasmawellen, in metallischen Bändern und nanoskopischen Partikelketten. Ein planares chipähnliches Dünnfilmsystem wird vorgestellt, in dem Licht einer makroskopischen Lichtquelle (Laser) in eine Lichtleitungsstruktur, bestehend aus metallischen Bändern und Partikelketten, eingekoppelt wird. Die Bänder übernehmen dabei den Lichttransport im Größenbereich von 2-50 Mikrometer, während die Partikelketten zum punktgenauen Transport in submikroskopischen Dimensionen eingesetzt werden.

Femtosekunden zeitaufgelöste Plasmonendynamik in metallischen Nanopartikeln
B. Lamprecht, G. Schider, J. R. Krenn, N. Felidj, M. Salerno, A. Leitner, F. R. Aussenegg
Institut f. Experimentalphysik, Karl-Franzens-Universität Graz, Univ.pl. 5, 8010 Graz
Nanoskopische Metallpartikel zeigen besondere optische Eigenschaften, da es bei der Anregung mit sichtbarem Licht zu einer resonanten Kollektivoszillation der Leitungselektronen in den Partikeln kommen kann (Partikel-Plasmon). Eine zeitaufgelöste Untersuchung der Elektronendynamik führt zu einem tieferen Verständnis der Dynamik und damit der grundlegenden Physik von Partikel-Plasmonen. Femtosekunden-Zeitauflösung wird durch Messen der Autokorrelationsfunktion des Zeitverlaufs der Elektronplasma-Oszillation erzielt. An der Partikeloberfläche erzeugte frequenzverdoppelte sowie frequenzverdreifachte Strahlung dient dabei als nichtinvasiver Sensor für das Partikel-Plasmon. Untersucht werden elektronenstrahllithographisch hergestellte 2D Gitter aus identischen Nanopartikeln. Dabei wird der Einfluß der Gitterkonstante auf die Plasmonenresonanz studiert.

Light absorption in onedimensional nanostructures
Dieter Gruber, Walter Papousek
Institut of Theoretical Physics, Technical University Graz
Electromagnetic reflection, transmission and absorption properties are basicly important for the optical characterization of multilayers used in optoelectronic and photovoltaic devices. They describe the interaction of the incident light with the layers of the system. Depending on the thicknesses and the optical constants of the individual layers the interaction of a polychromatic light source with a layered structure can be coherent, partial coherent or incoherent, respectively. Applying a new 2x2 matrix algebra the components of the electromagnetic field vectors in each layer can be calculated easily. Numerical simulations of multilayered structures on the nanometer scale show interesting spatial distributions of light absorption depending on the thicknesses and the optical constants of the individual layers.

Photocurrent action spectroscopy in organic photovoltaic cells
G. Meinhardt¹, D. Gruber^2,3, G. Jakopic²,W. Papousek^2,3,G.Leising^1,2
Institut für Festkörperphysik, Techn. Univ. Graz, Austria
²Institut für Nanostrukturierte Materialien & Photonik, Joanneum Research-GesmbH, Weiz, Austria
³Institut für Theoretische Physik, Techn. Univ. Graz, Austria
The organic materials Cu-phthalocyanine, the bisarylamidine-perylenes BBP-perylene resp. polyBBP-perylene and cyanoether polyparaphenylenevinylene possess the advantages of cheap processing, high stability, electron-donating resp. accepting-properties and absorption-spectra covering a wide range of the solar irradiance spectrum favoring their application in photovoltaic cells. We have used IV-characterization and photocurrent action spectroscopy to examine the predictions of a theoretical model describing the dependency of the power conversion efficiency on the thickness of the active layer. The photocurrent response is governed by the internal filter effect as well as the absorption density distribution in the device.

Effiziente Erzeugung von Licht bei 397 nm zur Laserkühlung von ⁴⁰Ca⁺ Ionen durch Frequenzverdopplung in periodisch gepoltem LiTaO₃
Madeleine Lederbauer, Paul Barton, Ferdinand Schmidt-Kaler,Raimer Blatt, Liv Hornekaer und Jan-Peter Meyn
Institut für Experimentalphysik, Universität Innsbruck
Für die Laserkühlung einzelner gespeicherter ⁴⁰Ca⁺ Ionen wird Licht bei 397 nm benötigt. Besonders hohe Effizienz erreicht man bei der Verdopplung eines Ti:Saphir Lasers bei 794 nm mittels eines periodisch gepolten LiTaO₃ Kristalls. Für Quasiphasenanpassung in erster Ordnung war die erzeugte UV-Leistung über 10mW bei 1W Pumpleistung im einfachen Durchgang und bei einer Temperatur der Kristalls von 200°C. Berücksichtigt man Reflektionsverluste und die Absorption von Licht bei 397 nm, entsprach unsere gemessene Konversionseffizienz dem zu erwartenden Wert [1,2] innerhalb der experimentellen Unsicherheiten. Zur Vermeidung von Reflektionsverlusten, wurde der Kristall im Brewster Winkel poliert. Damit sollte es möglich sein, den periodischen Kristall in einem Überhöhungsresonator einzusetzen. Bedingt durch die hohe Nichtlinearität sollte dann selbst mit einer Laserdiode effiziente Verdopplung möglich sein. Ein dazu optimierter Verdopplungsresonator wird vorgestellt. [1] J.-P. Meyn and M. M. Fejer, Optics Lett.22, 1214 (1997) [2] I. Shoji et al., J.Opt.Soc.Am.B 14,2268 (1997)

Possibility of creating supersensitive optical gyroscope for testing of fundamental physics
G.G.Karapetyan
Yerevan Physics Institute
It is proposed a novel method for creating supersensitive ring laser gyroscope (RLG). The method enables to improve Sagnac beat frequency in ring resonator (RR) of RLG by inserting into it a specially taylored phase shifter (PS) with negative value of phase first derivative. When appropriately installed that PS eliminates the linear part in functional dependence between the beat frequency and rotation rate. Then beat frequency becomes proportional to square root upon rotation rate and therefore hugely increases. For example: in that RLG with dimensions 1 m rotation rate 10^-9 grad/hour will produce beat frequency about 1 kHz, contrary to 10^-8 Hz in conventional RLG with the same dimensions. Thus proposed RLG enables the measurements of rotation rates below 10^-9grad/hour, for testing fundamental symmetries, dragg effect, detection of gravitational waves, etc.

Establishing the optical parameters of organic thin films
Radu Todoran, Daniela Todoran
North University of Baia Mare, Dr. Babes Str., No. 62/A, 4800 Baia Mare, Romania
The paper present the determinations of some kinetic parameters of the adsorption phenomenon of organic xanthate molecules on the surface of natural semiconductor mineral (galena, sphalerit) in order to understand the inward mechanism of this phenomenon. The methods chosen were optical ones relying on the change of the relative reflection of the liquid-mineral semiconductor interface, and permitting continuous inquires without disturbing the inward development of the processes. In the computation, we took into the consideration the roughness of the solid surface, the diffusion into liquid media and the energetic non-homegeneities of the surface. The (R_s/R_p)f() characteristic helps us to establish the thickness of the adsorbed layer, as well as to determine the optical parameters of the thin film. Using the Kramers-Kronig formalism and with the aid of optical reflection spectra UV-VIS, we could calculate the following optical functions for the absorption layers: the optical absorption coefficient ; the refraction index n; the adsorption index k; the effective valence number n_ef; the real part of the dielectric constant; the imaginary part 2 of the dielectric constant; the functions of the characteristic losses of the electrons -Im and -Im(1+; the effective dielectric constant ; the function . The experimental results allow us to get some information on the mineral-solution of xanthate, as well as to make estimations of the dynamic of the surface of a semiconductor solid body.

Excited state absorption measurement in Cr:YAG using relaxation oscillations study
S. Naumov, I. Sorokina, E. Sorokin
Institut für Photonik, Techniche Universität Wien
The Cr:YAG crystal with its broad absorption band centered at 1 m and luminescence band allowing laser wavelength tuning over the range of 1.34 – 1.6 m is of great interest for various laser applications. Recently, we demonstrated the first diode-pumped operation of this laser. One of the important factors limiting Cr:YAG laser efficiency and increasing the threshold is the excited state absorption at pump wavelength (ESA). Due to the principal difficulties of the ESA measurement, there is a significant spread in reported values of ESA in the literature. In this work we suggest and demonstrate an alternative method for measuring the ESA using the relaxation oscillations study. The resulting value of ESA cross-section was found to be as high as 1.7x10^-18 cm² (25% of the peak absorption cross section), reducing the maximum slope efficiency of Cr:YAG by 20%. This work has been supportd by the FWF projects T-64,12756-TPH and the ÖNB project 7913.

Conservation of the orbital angular momentum in parametric down-conversion
A.Vaziri, G.Weihs, A.Zeilinger
Institut für Experimentalphysik der Universität Wien
We have demonstrated that the orbital angular momentum of photons is conserved in spontaneous parametric down-conversion. Three different values of the angular momentum (-h-bar, 0, h-bar) of the pump beam were realized by astigmatic mode conversion from a Hermite-Gaussian mode. The angular momentum of the down converted photons were analyzed using computer-generated holograms. An interesting feature of the experiment is that photon states with (phase) singularities can be created from pump fields without singularities.

Entanglement purification without quantum controled-NOT gates
J.W. Pan, C. Simon, C. Brukner, A. Zeilinger
Institut für Experimentalphysik der Universität Wien
Entanglement purification is of paramount importance for future implementations of long-distance quantum networks. The classical protocols for entanglement purification rely on the quantum controled-NOT operation, which is hard to realize with current technology. We show that entanglement purification of general mixed states can be realized using only linear optical elements. Our schemes can be realized with parametric down-conversion using well established experimental techniques.

Invariant Information Content of Three Qubits
Walther E. Lawrence, Caslav Brukner, and Anton Zeilinger
Department of Physics, Dartmouth College,Hanover,NH 03755,USA; Institut für Experimentalphysik,Universität Wien,Boltzmanngasse 5,1090 Wien,Austria
The total information content of the system defined as the sum of the individual measures of information for mutually complementary observations is found to be invariant under the choice of the particular set of complementary observations and conserved in time if there is no information exchange with an environment. That invariant information content of a system results in N bits of information for a system consisting of N qubits. For explicit case of a composite system consisting of 3 qubits we investigate various possibilities for distribution of the total information over the 3 qubits.

Eindeutig bestimmbare Zustände von unvollständigen Beobachtungsebene
G. Adam
Institut für Theoretische Physik, Technische Universität Wien
Der Zustand eines Quantensystems kann durch die Messung der Mittelwerte eines vollständigen Satzes von Observablen eindeutig bestimmt werden. Sind hingegen nur die Mittelwerte eines unvollständigen Satzes von Observablen (ein solcher Satz wird auch Beobachtungsebene (BE) genannt) bekannt, ist im Allgemeinen der Systemzustand nicht eindeutig bestimmt. Viele unterschiedliche Systemzustände können im Allgemeinen die gemessenen Mittelwerte richtig wiedergeben. Jedoch gibt es die Ausnahme, dass für bestimmte Mittelwerte einer BE nur ein reiner Systemzustand existiert, der in dieser BE eindeutig bestimmt ist. Mit Hilfe des Entropiemaximum-Prinzips von Jaynes werden für verschiedene BE jene reinen Systemzustände angegeben, welche in der jeweiligen BE eindeutig bestimmbar sind.
Arbeit unterstützt vom Jubiläumsfonds der Österreichischen Nationalbank (Projekt Nr. 7720).

Saturation of a two-level atom in polychromatic fields
Z. Ficek, J. Seke, A. Soldatov, and G. Adam
Department of Physics and Centre for Laser Science, University of Queensland, Brisbane, Australia; Institut für Theoretische Physik, Technische Universitaet Wien; Department of Statistical Mechanics, Russian Academy of Science, Moscow
The response of a two-level atom in a strong polychromatic field composed of a large number of equidistant frequency components is investigated. We calculate numerically as well as analytically the stationary population inversion and show that the saturation of the atomic transition strongly depends on whether the driving field is composed of an even or odd number of frequency components. For a large odd number of the components the atom can remain in the ground state even for a strong Rabi frequency of the driving field. In addition, we find that the inversion is sensitive to the relative phase between the frequency components. When the atom is driven by an even number of fields, the atomic transition saturates quickly with the Rabi frequency independent of the relative phase.

Phase control of subharmonic resonances
Z. Ficek, J. Seke, A. Soldatov, and G. Adam
Department of Physics and Centre for Laser Science, University of Queensland, Brisbane, Australia; Institut für Theoretische Physik, Technische Universität Wien; Department of Statistical Mechanics, Russian Academy of Science, Moscow
We analyze the steady-state population inversion in a two-level atom driven by three laser fields of unequal frequencies. The dependence of the population inversion on the relative phase between the driving lasers and cancellation of subharmonic resonances are predicted and explained in terms of quantum interference between dressed states of the system.

Onicescu informational energy revisited
Ioan Sturzu, Spiridon Dumitru
Physics Department, Transilvania University Brasov, Romania
A mathematical-informational concept introduced by O. Onicescu 3 decades ago is revisited. Applications to quantum optics are found. The relation to informational entropy is discussed, and both are embadded in a more general mathematical concept.

Cold atoms in high-Q optical cavities
M. Gangl, P. Domokos, P. Horak and H. Ritsch
Institut für Theoretische Physik, Universität Innsbruck
We investigate the coupled dynamics of cold atoms in the field of a weakly pumped high-Q ring cavity. While the field mode amplitudes are coupled by the atoms depending on their positions, the motion of the atoms is influenced by the radiation pressure and dipole force induced by the total intracavity field. In the strong coupling regime, where the atom field coupling g dominates the atomic and cavity decay rates (, ) strong correlations between the atoms themselves and between the atoms and the light field build up. For suitable operating conditions an efficient motional cooling of the atoms occurs. We present applications of this scheme in laser cooling and quantum information.

Excited state absorption measurement in Cr:YAG using relaxation oscillations study.
S. Naumov, I. Sorokina, E. Sorokin
Institut für Photonik, Techniche Universität Wien
The Cr:YAG crystal with its broad absorption band centered at 1 m and luminescence band allowing laser wavelength tuning over the range of 1.34 – 1.6 m is of great interest for various laser applications. Recently, we demonstrated the first diode-pumped operation of this laser. One of the important factors limiting Cr:YAG laser efficiency and increasing the threshold is the excited state absorption at pump wavelength (ESA). Due to the principal difficulties of the ESA measurement, there is a significant spread in reported values of ESA in the literature. In this work we suggest and demonstrate an alternative method for measuring the ESA using the relaxation oscillations study. The resulting value of ESA cross-section was found to be as high as 1.7 10^-18 cm² (25% of the peak absorption cross section), reducing the maximum slope efficiency of Cr:YAG by 20%. This work has been supportd by the FWF projects T-64,12756- TPH and the ÖNB project 7913

Spectrally selective study of the photoluminescence decay of RuDPP between 300 K and 20 K
A. Schrammel, S. Draxler, M. E. Lippitsch, R. Czaputa
Institut für Experimentalphysik, Karl-Franzens-Universität Graz, Universitätsplatz 5, A-8010 Graz, Austria
Tris (4,7-diphenyl-1,10-phenanthroline)ruthenium(II) (abreviated RuDPP) incorporated in a polymer matrix is well suited as an oxygen sensor because of its reproducible dependence of the photoluminescence decay on the oxygen partial pressure. The emission spectrum that is rather unstructured at room temperature at low temperatures (down to 20 K) is resolved in several distinctive bands. The purpose of the present study is to find out how the stretched-exponential model that is well established at room temperature, has to be modified at deep temperatures.

Designing new fluorescence decaytime based indicators for sensing of ionic species
S. Draxler¹, A. Boila-Göckel^1,2, M. E. Lippitsch¹
Institute for Experimental Physics and ²Institute of Chemistry, Karl-Franzens-Universität Graz, A-8010 Graz, Austria
Fluorescence lifetime-based sensing has several well-appreciated advantages over other schemes: It is insensitive to fluctuations in the intensity of the exciting light source and the sensitivity of the detector, and it does not depend on the amount of indicator dye present in the sensor. Thus lifetime-based devices are not affected by inevitable variations in sensor composition, which leads to superior long-term operational stability and extended shelf-life. The purpose of this work was to explore possibilities to devise lifetime indicators for ionic species based on ruthenium (II) tris complexes, and to find molecular mechanisms modulating the energetic distance between the emitting and the competing states and/or the transition probability to these states upon binding or release of an ion. Complexes with substituted phenanthroline ligands were synthesised. The photophysical and photochemical properties of homo- and heteroleptic complexes were studied. Comparative investigations showed that the electron-donating or accepting ability of the substituent is of major influence on the lifetime. The next step on the route towards novel lifetime indicators for ionic species will be designing the proper ionophores to operate that switch in an efficient and selective manner.

Fuel cells and optical sensors
M. E. Lippitsch and S. Draxler
Institut für Experimentalphysik, Karl-Franzens-Universität Graz, Universitätsplatz 5, A-8010 Graz, Austria
In recent years fuel cells have gained much interest as efficient, non-polluting power sources. Although there are very few commercial manufacturers, laboratory development has reached a remarkably high level. Fuel cells may have significant advantages over combustion engines in the automotive sector. The efficiency of fuel cells is strongly dependent on temperature, pressure, current density, and gas composition. To achieve optimum performance all these parameters should be carefully controlled and hence need to be measured. To monitor gas composition, conventional chemical sensors (electrodes) are not usable because of the high operating temperatures (up to 1000 °C). Preliminary studies show that optical sensors based on luminescence lifetime as the transduction mechanism may be suitable alternatives.

Optical sensors for determination of blood Na⁺, K⁺ and Ca⁺⁺, based on a family of new fluoroionophores.
M.J.P. Leiner, H. He, M. Mortellaro, R. Fraatz, and J.K. Tusa
AVL BioSense, 235 Hembree Park Drive, Roswell, Georgia 30076
We present new Na⁺, K⁺ and Ca⁺⁺ selective fluoroionophores (FI) developed for optical sensors, implemented in a commercially available whole blood analyzer. At 37°C, pH 7.4 and ionic strength 145 mmol/l, reversible binding of Na, K⁺ and Ca⁺⁺ to an o-methoxyphenylaza-15-crown-5 (K_d = 77 mmol/l), a triaza-cryptand (K_d = 17 mmol/l), and a 2,5-diethoxyaniline-,N,N-diethoxyacetate (K_d = 1.09 mmol/l), respectively, trigger an increase in green fluorescence from an adjacent 4-aminonaphthalimide fluorophore, excitable with a blue LED. The three optical sensors share the same basic design. The sensing layer contains the immobilized FI and is attached on top of a transparent support, covered with a black overcoat. Both layers are hydrogels allowing the free and rapid diffusion of ions and restrict the passage of optically interfering blood constituents. The new FI’s satisfy the system requirements for selectivity, sensitivity and spectral accessibility. The design logic of the FI’s and the performance of the sensors will be described.

Prediction of the diffusion-controlled response behaviour of multilayer optical chemical gas sensors.
P. Hartmann ^a, G. Schappacher ^a, M.J.P. Leiner ^a, and E. Meisterhofer ^b
a AVL List GmbH, Biomedical Research and Development, A-8020 Graz, Austria.
^b Technisches Büro für Physik, A-8010 Graz, Austria.
Many challenges of optical chemical sensors are based on the diffusion properties of the analyte in the polymer host: The response times of such sensors to a step change of analyte concentration are of vital interest for many applications of fast responding sensors. Further, the diffusion properties govern their quenching behaviour and their sensitivity. The diffusion properties of simple sensor systems based on single layers may be modelled by solutions of the differential equations of diffusion, but in practice rather complicated multilayer systems are encountered, where general solutions cannot be obtained. Therefore, we have developed an add-on tool for MATLAB to calculate both the dynamic and steady-state diffusion properties of multilayer systems covering most sensor designs encountered in practice. This simulation software, which is based on numerical solutions of Fick’s laws of diffusion, allows definition of multilayer systems even with time-dependent boundaries, and is suitable for gas diffusion from both liquid and gaseous samples. We also discuss implications of diffusion on the luminescence calibration functions and quenching models.

Thermophysical Properties of Solid and Liquid 90Ti-6Al-4V in the Temperature Range 1500 to 2300 K
E. Kaschnitz¹, P. Reiter¹, J. L. McClure²
Österreichisches Gießerei-Institut, Parkstrasse 21, 8700 Leoben, ² Metallurgy Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
Heat capacity and electrical resistivity of 90Ti-6Al-4V in the temperature range 1500 to 2300 K were measured by two pulse-heating systems, operating in the millisecond and microsecond time regimes, respectively. The millisecond-resolution technique is based on self-heating of a tube-shaped specimen from room temperature to melting in less than 500 ms and measuring current through the specimen, voltage drop along a defined portion of the specimen, and temperature of the specimen every 0.5 millisecond. The microsecond-resolution technique is based on the same principle using a rod-shaped specimen, but the heating rate is faster by a factor of 10,000 and data is recorded every 0.5 microsecond.
Due to the rapid heating with the microsecond system, the specimen keeps its shape even in the liquid phase, and measurements were made up to approximately 300 K above the melting temperature. A comparison between the results obtained from the two systems with very different heating rates shows significant differences in the region of the phase transition from () to and changes in the melting behavior. The very high heating rate of the microsecond system shifts the solid-solid phase transition to a higher temperature and melting of the specimen occurs with a temperature plateau instead of a temperature interval.

Wasserstofftechnik für Kraftfahrzeuge
Helmut Buchner
Institut für Experimentalphysik / TU - Wien
Nach dem heutigen Stand der Technik können Fahrzeuge mit Verbrennungsmotoren völlig schadstofffrei betrieben werden, wenn als Kraftstoff statt Benzin Wasserstoff eingesetzt wird. Da jeder Benzinmotor entweder mit Wasserstoff oder mit Benzin angetrieben werden kann, bietet sich an, das Fahrzeug im Stadtgebiet mit Wasserstoff und außerhalb mit Benzin zu betreiben. Diese Variante erlaubt es, Speichergewicht und -kosten für Wasserstoff zu minimieren und gleichzeitig die von den Fahrzeugen verursachten Schadstoffemissionen im Stadtgebiet auf Null zu senken. Die Fahrten außerhalb der umweltsensiblen Regionen können dann durch Umschalten des Motors wie bisher mit Benzin (bivalenter Motorbetrieb) und den gewohnten Reichweiten erfolgen. Die Umrüstkosten des Verbrennungsmotors von Benzin- auf Wasserstoffbetrieb betragen <200 öS/kW - Werte,die für den Elektroantrieb mit Brennstoffzellen auch nicht annähernd erreichbar sind. Damit gibt es zum Verbrennungsmotor, selbst im Falle des schadstofffreien Antriebs, auch in Zukunft keine technisch und wirtschaftlich bessere Alternative. Wasserstoff kann an jeder Steckdose aus Wasser (Elektrolyse) und an jedem Erdgasanschluß mit Hilfe von Erdgasspaltanlagen hergestellt und damit in die existierende Energielandschaft von der Haustankstelle bis zur Großtankstelle (flächendeckend) integriert werden. Somit kann die existierende Infrastruktur für Strom und Wasser als Basis einer weitverzweigten Wasserstoffversorgung dienen,ohne diesen über ein neu zu installierendes Pipelinesystem verteilen zu müssen. Damit ließe sich das Problem der zunächst fehlenden Infrastruktur für gasförmigen Wasserstoff lösen. Die Speicherung des Wasserstoffs in Fahrzeugen erfolgt aus Gründen der Sicherheit, der kompakten Bauweise und der Anpassung an die verfügbare Wasserstoffversorgung mittels chemischer Bindung in Metallhydriden. Für 50-100 km Stadtfahrt werden 50-100 kg Hydridspeicher, mit Kosten von 20.000-35.000 öS benötigt. Die Umrüstkosten gegenüber dem Benzinmodell betragen einschließlich Speicher zwischen 30.000 -50.000 öS. Da die Lebensdauer der Speicher praktisch unbegrenzt ist, werden die Kosten für das schadstofffreie Fahren mit <10 öS je 100 km vertretbar niedrig.
Wasserstoff Haus/Auto Verbundsystem: Die im Hydridtank gespeicherte Motorabwärme kann bei der Betankung des Fahrzeugs mit Wasserstoff in der Garage gemeinsam mit der Elektrolyseabwärme für Heizzwecke (Warmwasser) im Haus genutzt,der gleichzeitig entstehende Sauerstoff zur Frisch- und Abwasseraufbereitung verwendet werden.

Dimensionsanalytische Herleitung physikalischer Gesetze
E. Vass
Inst. für Experimentalphysik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck
Unter der Dimension einer beliebigen physikalischer Größe versteht man die Gesamtheit aller Einheiten dieser Größe. In diesem Beitrag wird gezeigt, wie man mittels Dimensionsbetrachtungen (Dimensionsanalysen) fundamentale Relationen zwischen direkt und indirekt meßbaren physikalischen Größen auffinden kann, die bis auf einen numerischen Zahlenfaktor mit dem exakten Ergebnis übereinstimmen. Alle Dimensionsanalysen beruhen auf drei grundlegenden Annahmen: 1) Die Anzahl der physikalischen Grundgrössen und Naturkonstanten ist endlich. 2) Abgeleitete physikalische Größen lassen sich als Potenzprodukt von Basisgrößen darstellen. 3) Jede physikalische Größengleichung muß dimensionskorrekt sein. Davon ausgehend, werden im Rahmen dieses Beitrages sowohl populäre als auch weniger allgemein bekannte physikalische Gesetze und Effekte der aktuellen Forschung hergeleitet.

Physical Society in Lithuania
A.Bernotas, E.Makariuniene, Z.Rudzikas
Lithuanian Physical Society
Lithuanian Physical Society (LPS) was founded on March 23, 1963. It mainly unites the staff teaching physics at different Lithuanian universities, as well as physicists of the State research institutes, the PhD students, and the representatives of high technology industries, colleges and secondary schools. LPS is taking care of general problems of physics research and teaching in Lithuania, publishes textbooks in Lithuanian, edits the "Lithuanian Physics Journal". It is working on physical terminology and history of physics in Lithuania, encourages pupils to become more interested in studying physics, explaining to society, tax payers the exceptional role of physics, its influence on modern technology, other branches of science, etc. The Society participates in the organization of a special three years school by correspondence "Photon" for gifted pupils, National and International physics olympiads. Since 1992 LPS is the member of EPS. LPS has already organized 33 National physics conferences.