Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32177 Publications
The new installation at the FZD: The Hochfeld-Magnetlabor Dresden
Wosnitza, J.;
Abstrakt hat nicht vorgelegen!
  • Invited lecture (Conferences)
    EuroMagNET council meeting, 26.01.2007, Toulouse, France

Publ.-Id: 10207 - Permalink


Investigation of the radial ionization distribution of heavy ions with an optical particle track chamber and Monte-Carlo simulation
Laczkó, G.;
In the present work we applied the Optically read out PArticle track Chamber, OPAC, for the measurement of radial dose distributions, d(r), around tracks of heavy ions passing through the gas-filled sensitive volume of the chamber. The measured data were compared with d(r) functions derived from data calculated with the Monte Carlo particle transport code, TRAX – which is used for the heavy ion therapy planning at GSI.
To measure this quantity we have used here an optically read out time projection chamber (OPAC) with a parallel-drift field and one or several electron and light amplification stages. The two dimensional projection of the three dimensional ionization pattern caused by the ionizing particle passing through the chamber is captured by an image intensified CCD camera.
The work is motivated by the role the radial dose distribution plays in the estimation of the relative biological effectiveness (RBE) of heavy ions, e.g. in radiation therapy and in radiation protection. The most successful model for high-dose irradiation with ions (applicable e.g. for heavy ion therapy) is found to be the local effect model (LEM). The present work intends to deliver measured data for one of the basic physical parameters which serve as input for the application of the local effect model: the radial dose distribution, d(r).
The first goal of our measurement program was the measurement of d(r) distributions around carbon ions of different energies from 400 MeV/u down to the Bragg peak regions. We found an excellent agreement between the measured and simulated distributions at all carbon energies for the r–range in which the measurements deliver useful results. The lower limit of this range is about 100 nm and the upper limit is 6000 nm at a resolution of down to 33 nm ­ if scaled to water density.
Despite the simplifications in the TRAX code (e.g. binary encounter theory for the emission ionization electrons), the discrepancies between the simulated and measured d(r) distributions are found to be lower than the measurement uncertainties at most measured carbon ion energies in almost the whole observed r-range. Hence, within the limitations of our measurements we can conclude that the precision of TRAX is sufficient to simulate the d(r) distributions around carbon ions to serve as input parameter for therapy planning. However, this conclusion is only valid for larger radial distances (r >100 nm). For smaller radial distances the measured data are dominated by the diffusion.
Apart from carbon ion tracks, tracks of very heavy ions (40Ar, 84Kr and 238U) were also measured with OPAC. The simulated d(r) values were typically slightly or significantly higher than the measured data in the 100 nm < r < 5000 nm region.
The energy values of the very heavy ions were selected with the aim of comparing the track structures - and namely the d(r) distributions - of ions with largely different atomic mass but similar LET values. From the Z­dependency of the stopping power we know that for heavier ions a higher specific ion energy (expressed in MeV/u) is required to provide the same LET. For example the common LET of 315 keV/μm was achieved at largely different specific energy levels of 4,4 MeV/u for 12C, 65 MeV/u for 40Ar and 650 MeV/u for 84Kr ions. The difference in the track structures was expected mainly due to the different ion velocities and thus e.g. different ranges of δ-electrons. This expectation could be confirmed by the measurements. The reason why ­in line with the simulations ­ no strong differences could be observed in the d(r) distributions of the argon and krypton ions is the relatively small difference in the velocities of the both ion types in conjunction with the limited range in r, where the data can be compared. In contrary, the d(r) function of the carbon ion shows a qualitatively different behavior than the heavier ions inside the observable radius-range ­ in agreement with the simulations.
Keywords: Time projection chamber, radiation therapy, carbon ions, Monte Carlo simulation, ionization density distribution, GSI, particle track, RBE, LET, gas chamber
  • Book (Editorship)
    Bremenhaven: Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, 2007
    0164 Seiten
    ISBN: 978-3-86509-634-0
  • Invited lecture (Conferences)
    Institutskolloquium bei der Physikalisch-Technischen Bundesanstalt, 24.05.2007, Braunschweig, Germany

Publ.-Id: 10204 - Permalink


Electronic properties of quasi-two-dimensional organic metals and superconductors
Wosnitza, J.;
es hat kein Abstrakt vorgelegen!
  • Invited lecture (Conferences)
    WE-Heraeus-Seminar "Physics of Highly Ordered Organic Interfaces and Layers", 22.-24.01.2007, Bad Honnef, Deutschland

Publ.-Id: 10203 - Permalink


Das Hochfeld-Magnetlabor Dresden: Forschung in hohen Magnetfeldern
Wosnitza, J.;
es hat kein Abstrakt vorgelegen!
  • Invited lecture (Conferences)
    Physikalisches Kolloquium der TU Chemnitz, 03.01.2007, Chemnitz, Germany

Publ.-Id: 10202 - Permalink


Widerstand zwecklos - Aktuelles zur Supraleitung
Wosnitza, J.;
kein Abstrakt vorgelegen
  • Lecture (others)
    Vorlesung in der Reihe "Physik am Samstag" der Fachrichtung Physik der TU Dresden, 02.12.2006, Dresden, Deutschland

Publ.-Id: 10201 - Permalink


SPICE simulations of self-actuated piezoresistive cantilever arrays
Frank, A.; Zöllner, J.-P.; Sarov, Y.; Ivanov, T.; Rangelow, I. W.; Swiatkowski, M.; Gotszalk, T.; Nikolov, N.; Zier, M.; Schmidt, B.;
A 2-dimensional massively parallel self-actuated piezoresistive cantilever arrays are a possible candidate for use in high speed AFM based surface imaging systems. By the utilization of cantilever arrays consisting of several hundred of cantilevers the AFM inspection speed of the next generations IC can be significantly increased. In the frame of the European Project PRONANO we are developing such arrays based on self-actuated piezoresistive cantilever. For design optimization and error detection in MEMS structures, which include a lot of CMOS processing, a device and process simulations are useful and essential. Besides the description of the electro-mechanic behaviour of the MEMS-part a parasitic effects (electrical crosstalk, noise, and temperature influence) of the CMOS have to be included. SPICE is well suitable tool for these investigations.
The investigated cantilever system consists of a p-doped piezoresistive sensor and a p-doped heater is represented qualitatively in Figure 2. The meander structure is the ion implanted heater to control the thermal bending of the silicon beam. An AC power supply is applied to the heater to bring the beam in resonant oscillation and to steer the position of the free end of the beam. The beam bending is determined with the piezoresistor. Experimentally a current crosstalk was detected. At the configuration a voltage peak occurs during the positive half wave of the sensor signal. The magnitude of this voltage peak depends on the dc-voltage of the heater signal. To simulate this effect a suitable equivalent network model was developed. The heater and the piezoresistor were modeled by resistor chains, which are interconnected to the n-doped silicon body (resistor network) by diodes including the junction capacitance. Additionally pnp-transistors were inserted in the equivalent circuit, where heater and piezoresistor are located near each other.
With this circuit model the experimentally determined behavior could be simulated and the effect could be explained as a current crosstalk across the parasitic transistors. We will show that this effect can be significantly suppressed by applying a certain substrate bias and corresponding design optimisation.
Keywords: Self-actuated piezoresistive cantilever, cantilever arrays, SPICE, crosstalk
  • Poster
    33rd International Conference on Micro- and Nano-Engineering (MNE07), 23.-26.09.2007, Copenhagen, Denmark

Publ.-Id: 10200 - Permalink


Transverse momentum spectra and elliptic flow: Hydrodynamics with QCD-based equations of state
Bluhm, M.; Kämpfer, B.; Heinz, U.;
We present a family of equations of state described within a quasiparticle model adjusted to first-principles lattice QCD calculations and study the impact on azimuthal flow anisotropies and transverse momentum spectra within hydrodynamic simulations for heavy-ion collisions at energies relevant for LHC.
  • Journal of Physics G 35(2008), 054001

Publ.-Id: 10199 - Permalink


Novel experimental measuring techniques required to provide data for CFD validation
Prasser, H. M.;
CFD code validation requires experimental data that characterize distributions of parameters within large flow domains. On the other hand, the development of geometry-independent closure relations for CFD codes have to rely on instrumentation and experimental techniques appropriate for the phenomena that are to be modelled, which usually requires high spatial and time resolution. The presentation reports about the use of wire-mesh sensors to study turbulent mixing processes in the single-phase flow as well as to characterize the dynamics of the gas-liquid interface in a vertical pipe flow. Experiments at a pipe of a nominal diameter of 200 mm are taken as the basis for the development and test of closure relations describing bubble coalescence and break-up, interfacial momentum transfer and turbulence modulation for a multi-bubble-class model. This is done by measuring the evolution of the flow structure along the pipe. The transferability of the extended CFD code to more complicated 3D flow situations is assessed against measured data from tests involving two-phase flow around an asymmetric obstacle placed in a vertical pipe. The obstacle, a half-moonshaped diaphragm, is movable in the direction of the pipe axis; this allows the 3D gas fraction field to be recorded without changing the sensor position. In the outlook, the pressure chamber of TOPFLOW is presented, which will be used as the containment for a test facility, in which experiments can be conducted in pressure equilibrium with the inner atmosphere of the tank. In this way, flow structures can be observed by optical means through large-scale windows even at pressures of up to 5 MPa. The so-called “Diving Chamber” technology will be used for Pressurized Thermal Shock (PTS) tests. Finally, some important trends in instrumentation for multi-phase flows will be given. This includes the state-of-art of X-ray and gamma tomography, new multi-component wire-mesh sensors, and a discussion of the potential of other non-intrusive techniques, such as neutron radiography and Magnetic Resonance Imaging (MRI).
Keywords: CFD, wire-mesh sensors, bubble coalescence and break-up, interfacial momentum transfer, turbulence modulation, multi-bubble-class model, 3D flow situation, vertical pipe
  • Invited lecture (Conferences)
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS), 05.-09.09.2006, Garching, Germany
  • Contribution to proceedings
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS), 05.-09.09.2006, Garching, Germany
  • Nuclear Engineering and Design 238(2008), 744-770
    DOI: 10.1016/j.nucengdes.2007.02.050

Publ.-Id: 10198 - Permalink


Thermomechanische Modellierung eines Reaktordruckbehälters in der Spätphase eines Kernschmelzunfalls
Willschütz, H.-G.;
Für das unwahrscheinliche Szenario eines Kernschmelzunfalls in einem Leichtwasserreaktor mit Bildung eines Schmelzesees in der Bodenkalotte des Reaktordruckbehälters (RDB) ist es notwendig, mögliche Versagensformen des RDB sowie Versagenszeiträume zu ermitteln, um die daraus resultierende mögliche Belastung des Sicherheitsbehälters bestimmen zu können. In dieser Arbeit wird ein integrales Modell entwickelt, das die Vorgänge im unteren Plenum beschreibt. Dabei sind zwei prinzipielle Modellbereiche zu unterscheiden: Das Temperaturfeld in der Schmelze und im RDB wird mit einem thermodynamischen Modell berechnet, während für die Strukturanalyse des RDB ein mechanisches Modell verwendet wird.
Das thermodynamische und das mechanische Modell können rekursiv gekoppelt werden, wodurch die wechselseitige Beeinflussung berücksichtigt werden kann. Insbesondere werden damit neben der Temperaturabhängigkeit der Materialparameter und den thermisch induzierten Spannungen im mechanischen Modell auch die Rückwirkungen der Behälterverformung auf das Temperaturfeld selber erfasst.
Für die Kriech- und Schädigungssimulation werden in dieser Arbeit neue Verfahren angewendet. Durch die Entwicklung und den Einsatz einer Kriechdatenbasis konnte die bei sehr unterschiedlichen Temperaturen, Spannungen und Dehnungen ungeeignete Verwendung einzelner Kriechgesetze umgangen werden. Aufbauend auf experimentellen Untersuchungen wurde eine Kriechdatenbasis für einen RDB-Stahl entwickelt und an Hand von Kriechversuchen verschiedener Geometrie und Dimension validiert.
Die wesentlichen Ergebnisse dieser Arbeit lassen sich wie folgt zusammenfassen: Aufgrund des thermodynamischen Verhaltens eines großen Schmelzesees mit inneren Wärmequellen erfolgt die höchste thermomechanische Belastung des RDB im oberen Drittel der Bodenkalotte. Dieser Bereich wird als heißer Fokus bezeichnet. Der untere Bereich der Kalotte weist hingegen eine höhere Festigkeit auf und verlagert sich deswegen bei entsprechender Belastung des RDB im wesentlichen senkrecht nach unten. Bei einer externen Flutung besteht auch bei hohen Innendrücken für einen Reaktor großer Leistung die Möglichkeit, die Schmelze im RDB zurückzuhalten. Ohne interne oder externe Flutung besteht für das betrachtete Szenario keine Aussicht für eine Schmelzerückhaltung im RDB.
Aus den gewonnenen Erkenntnissen wurden zwei Patente abgeleitet. Dabei handelt es sich um passiv wirkende Einrichtungen zur Schadensbegrenzung: Die erste reduziert durch Abstützen des unteren Kalottenzentrums die Maximalspannungen im hochbeanspruchten Bereich des heißen Fokus und kann damit ein Versagen verhindern oder zumindest verzögern. Die zweite Einrichtung ermöglicht die passive Auslösung einer Flutung, indem die Abwärtsbewegung der Kalotte zur Steuerung genutzt wird. Hierdurch kann beispielsweise ein Ventil geöffnet werden, um Wasser aus im Gebäude höher angeordneten Reservoirs in die Reaktorgrube zu leiten.
Abweichend von bisherigen Annahmen kann festgehalten werden, dass eine Kernschmelzerückhaltung im Reaktordruckbehälter auch für Reaktoren größerer Leistung möglich ist.
Keywords: Light Water Reactor, Severe Accident, Core Melt Down, In-Vessel-Retention, thermal and mechanical Simulation
  • atw - International Journal for Nuclear Power 52(2007)12, 799-806

Publ.-Id: 10197 - Permalink


Annual Report 2006 - Institute of Radiation Physics
Fahmy, K.; Grosse, E.; Kämpfer, B.; Schneidereit, C.; Wagner, A.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-461 2007

Downloads:

Publ.-Id: 10196 - Permalink


Annual Report 2006 - Institute of Safety Research
Weiß, F.-P.; Rindelhardt, U.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-465 2007

Downloads:

Publ.-Id: 10195 - Permalink


Experimental studies of photodisintegration in the p-process
Beyer, R.; Erhard, M.; Grosse, E.; Junghans, A. R.; Klug, J.; Kosev, K.; Nair, C.; Rusev, G.; Schilling, K. D.; Schwengner, R.; Wagner, A.;
In explosive nucleosynthesis temperatures are high enough for photodissociation reactions to occur, e.g. leading to the production of p-process nuclei. In order to understand the reaction rates of element production and element disruption we started an experimental program at the new bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ-Rossendorf, Dresden. The bremsstrahlung facility and the detector setup are designed such that the scattering of photons from nuclei and the photodissociation of nuclei around the particle separation energies can be studied under optimized background conditions. In activation measurements with bremsstrahlung at end-point energy from 10.0 to 16.5 MeV (gamma,p), (gamma,n) and (gamma,alpha) reactions of 92,100 Mo. have been studied. Our activation yields can be described within a factor 2-3 or better with calculations using the cross sections from recent Hauser-Feshbach models.
  • Invited lecture (Conferences)
    XXXVIII. Arbeitstreffen Kernphysik, 22.02.-01.03.2007, Schleching, Deutschland

Publ.-Id: 10194 - Permalink


Dipole-strength distributions up to the Giant Dipole Resonance deduced from photon scattering
Schwengner, R.;
  • Invited lecture (Conferences)
    9th International Spring Seminar on Nuclear Physics - Changing Facets of Nuclear Structure, 20.-24.5.2007, Vico Equense, Italy

Publ.-Id: 10193 - Permalink


Experimental results on the flow structure in liquid metal two-phase
Zhang, C.; Eckert, S.; Gerbeth, G.;
In our experiments we investigated the consequence of an application of a DC magnetic field on both the bubble and the liquid velocity. The motion of single argon bubbles rising in GaInSn were analyzed in terms of the terminal velocity, the drag coefficient, the oscillation frequency of the bubble velocity and the Strouhal number. Because the gas bubble is electrically non-conducting, it does not experience the effect of the electromagnetic force directly. However, the bubble behaviour is influenced by the magnetically induced modifications in the liquid flow structure around the bubble. The measurements reveal a distinct effect of the magnetic field on the bubble velocity as well as the bubble wake. The magnetic field application leads to a mitigation of the horizontal components of the bubble velocity resulting in a more rectilinear bubble path. A restructuring of the entire flow field can be observed if a bubble plume is exposed to a DC magnetic field. As a result of the interaction between magnetic field and liquid flow electric currents were induced inside the liquid causing a damping of the flow by Joule dissipation. However, a characteristic feature of the electromagnetic dissipation is the anisotropy. Thus, the application of a transverse field leads not only to a general damping of the flow, but also favours the occurrence of vortices aligned parallel to the magnetic field direction.
Keywords: Liquid metal, bubble plume, DC magnetic field, Ultrasound Doppler Velocimetry
  • Lecture (Conference)
    International Symposium on Multi-Phase Flows: Simulation, Experiment and Application, 25.-27.04.2007, Dresden, Deutschland

Publ.-Id: 10192 - Permalink


Development of a superconducting radio frequency photoelectron injector
Arnold, A.; Büttig, H.; Janssen, D.; Kamps, T.; Klemz, G.; Lehmann, W. D.; Lehnert, U.; Lipka, D.; Marhauser, F.; Michel, P.; Möller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Stephan, J.; Teichert, J.; Volkov, V.; Will, I.; Xiang, R.;
A superconducting radio frequency (RF) photoelectron injector (SRF gun) is under development at the Research Center Dresden–Rossendorf. This project aims mainly at replacing the present thermionic gun of the superconducting electron linac ELBE. Thereby the beam quality is greatly improved. Especially, the normalized transverse emittance can be reduced by up to one order of magnitude depending on the operating conditions. The length of the electron bunches will be shortened by about two orders of magnitude making the present bunchers in the injection beam line dispensable. The maximum obtainable bunch charge of the present thermionic gun amounts to 80 pC. The SRF gun is designed to deliver also higher bunch charge values up to 2.5 nC. Therefore, this gun can be used also for advanced facilities such as energy recovery linacs (ERLs) and soft X-ray FELs. The SRF gun is designed as a Click to view the MathML source cell cavity structure with three cells basically TESLA cells supplemented by a newly developed gun cell and a choke filter. The exit energy is projected to be 9.5 MeV. In this paper, we present a description of the design of the SRF gun with special emphasis on the physical and technical problems arising from the necessity of integrating a photocathode into the superconducting cavity structure. Preparation, transfer, cooling and alignment of the photocathode are discussed. In designing the SRF gun cryostat for most components wherever possible the technical solutions were adapted from the ELBE cryostat in some cases with major modifications. As concerns the status of the project the design is finished, most parts are manufactured and the gun is being assembled. Some of the key components are tested in special test arrangements such as cavity warm tuning, cathode cooling, the mechanical behavior of the tuners and the effectiveness of the magnetic screening of the cavity.
Keywords: Superconductivity; Radio frequency; Photoelectron injector; Cavity; Laser

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Publ.-Id: 10191 - Permalink


Binding properties of a phosphonate clip towards nucleic acid building blocks
Raditzky, B.; Eilzer, M.;
Water-soluble clips are possible molecules to study the weak, non-covalent interactions, responsible for many biological processes. The complexation behaviour of naphthalene clips, substituted with phosphonate or phosphate groups, has been studied by time-resolved laser-induced fluorescence spectroscopy with ultrafast pulses (fs-TRLFS). As guest molecules we used nucleic bases, nucleosides and nucleotides. The determined association constants for the 1:1 complexes range from log Ka = 3.9 – 4.2 and are around one order of magnitude higher than published in literature. The measured spectra assumes the appearance of excited state species or dimerization of the clip.
Keywords: moleculare clips, nuclic bases, nucleosides, nucleotides, fs-TRLFS, association
  • Lecture (Conference)
    4th SUPRAPHONE/3rd WG Meeting COST D31, 31.05.-03.06.2007, Lipari, Italy

Publ.-Id: 10190 - Permalink


X-ray study of ion-beam induced amorphous-crystalline ripples in silicon
Biermanns, A.; Grigorian, S.; Pietsch, U.; Hanisch, A.; Facsko, S.; Grenzer, J.;
Ripple formation with a spatial periodicity in the sub-micrometer range on obliquely ion-bombarded solid surfaces has become a topic of intense research in the context of fabrication of nanoscale textured materials [1]. Ion-beam induced ripples are produced by the interplay between a roughening process caused by ion beam erosion (sputtering) of the surface and smoothening processes caused by thermally or ion-induced surface diffusion. Recently we have shown that Ar- ion irradiation of Si (001) surfaces under an angle of about 60° with respect to surface normal and using ion energies of about 60keV results in periodic crystalline ripple formation where the crystalline ripples are covered by a partially amorphous surface layer [2, 3]. In this contribution we report on investigations of patterned Si (001) surfaces after irradiation with Xe-ions using ion-energies between 5 and 40keV. Besides AFM measurements, the structure of the amorphous layer and the amorphous-crystalline interface were studied by means of grazing-incidence small-angle scattering (GISAXS) and grazing-incidence diffraction (GID) using synchrotron-radiation. The data reveal that both surface and crystalline ripples appear for all ion energies used. These ripples show asymmetric side-facets where the degree of asymmetry decreases for increasing ion-energy. They show short-range ordering; the ripple wavelength and thickness of the amorphous layer increase as a function of the ion-energy.

Acknowledgement: One of the authors (A.B.) would like to thank the ESRF for financial support and the ID01 beamline-staff for providing beamtime and valuable help.

[1] M.A. Makeev, R Cuerno and A.-L. Barabasi, Nuc. Inst. and Meth. in Phys. Res. B 197, 185 (2002).
[2] S.Hazra, T.K. Chini, M.S. Sanyal, J. Grenzer U. Pietsch , Phys. Rev. B 70, 121307(R) (2004).
[3] S. Grigorian, J. Grenzer, D. P. Datta, S. Hazra, T.K. Chini, M. K. Sanyal and U. Pietsch, Appl. Phys. Lett 89, 231915 (2006).
Keywords: Ion beam patterning, x-ray diffraction
  • Lecture (Conference)
    Nanopatterning via Ions, Photon beam and Epitaxy, 23.-27.09.2007, Sestri Levante, Italy

Publ.-Id: 10189 - Permalink


Velocity measurements in liquid metal flows driven by intermittently or alternately applied rotating magnetic fields using the ultrasonic Doppler method
Räbiger, D.; Eckert, S.; Nikrityuk, P. A.; Eckert, K.;
Model experiments with low melting point liquid metals become an important tool to investigate the flow structure and related transport processes in melt flows being relevant for metallurgical applications. This approach is encouraged by recent developments of appropriate flow measuring techniques in the temperature range until about 300°C. The ultrasound Doppler velocimetry (UDV) which delivers instantaneous profiles of the local velocity along the ultrasonic beam is a very attractive technique to attain experimental data from flows of opaque liquids.
AC magnetic fields are used in industrial practice for melt stirring. The requirements are manifold for miscellaneous metallurgical operations or casting technologies, mainly the magnetic field application should provide an efficient mixing of the melt in order to achieve homogeneous distributions of solute and/or temperature. Here the standard case of electromagnetic stirring by means of a rotating magnetic field (RMF) is considered. Especially, we study the melt flow excited by an application of an intermittently or alternately applied RMF.
Keywords: lqiud metal, velocity measurements, Ultrasound Doppler Velocimetry, rotating magnetic field
  • Poster
    2nd International Workshop on Measuring Techniques for Liquid Metal Flows (MTLM2007), 23.-25.04.2007, Dresden, Deutschland

Publ.-Id: 10187 - Permalink


Determination of the flow field in the vicinity of a solidification front by X ray radioscopy
Boden, S.; Eckert, S.; Willers, B.; Gerbeth, G.;
Melt convection significantly affects the solidification of metallic alloys. Therefore, the knowledge of the flow field in the melt is an important issue. Velocity measurements in liquid metals are complicated by the specific material properties. Recently, X-ray radioscopic methods became an important diagnostic tool for real-time and in-situ observation of the solidification front with a spatial resolution of a few microns.
Solidification experiments using Ga-30wt%In alloy (melting point 38°C) have been conducted. The metal alloy was poured in a flat solidification cell (150 µm gap thickness) made from two fused quartz glasses, and was heated above its melting point and was subsequently solidified by cooling of the solidification cell’s bottom. A microfocus X-ray radioscopy setup was used for qualitative real-time visualisation of concentration fluctuations and structure formation within the solidifying melt at a spatial resolution of 10 µm. Image integration times of 440 ms were found to be sufficient to ensure sufficient temporal sampling rate.
The optical flow method has been adopted to determine the velocity of the liquid and the dendritic growth rate from translocations of concentration contour lines appearing during a temporal image sequence. Therefore, Gaussian spatio-temporal low-pass filtering was applied to smooth spurious image brightness fluctuations caused by noise. Then any local image brightness variation was related to a certain amount of change in the local alloy composition. Image pattern deformations due to diffusion processes in the melt are considered to be negligible. Thus, the continuity equation was used as a first constraint to compute local translocation velocities in image regions providing sufficient brightness gradients. The physically justified assumption of a locally smooth velocity field was used as a second constraint.
Keywords: X-ray radioscopy, solidification, Ga-In alloys, thermo-solutal convection
  • Lecture (Conference)
    2nd International Workshop on Measuring Techniques for Liquid Metal Flows (MTLM2007), 23.-25.04.2007, Dresden, Deutschland

Publ.-Id: 10186 - Permalink


Ultrasound Velocimeter with frequency modulated signals for 2d2c measurements of non-stationary flows with high temporal resolution
Lenz, M.; Czarske, J.; Eckert, S.; Gerbeth, G.;
In conjunction with flow measurements in nontransparent fluids like liquid metals, there is an increasing demand for the measurement of non-stationary flows. Ultrasound Doppler Velocimeters (UDV) belong to the standard equipment of research. UDV emit short ultrasound pulses into the fluid which have a typical duration equivalent to 2-8 wavelengths. The ultrasound is partly reflected by small tracer particles inside the fluid and scattered back to the transducer. The tracer particles are assumed to move without slip. The echo signals are recorded and can be used to estimate the fluid velocity. The measurement principle of Ultrasound Doppler Velocimetry, however, suffers from inherent constraints: One problem is the limitation in time resolution. For non-stationary flows a high temporal resolution is essential, because the relevant flow information is partly contained in the high frequency part of the velocity signal. In practice, the problem of time resolution occurs because an average over several send pulses is required to get accurate velocity estimates. Another problem is the maximum velocity that can be detected unambiguously with Doppler systems and related narrowband methods.
The actual problem with time resolution is the fact that a sending pulse only contains little signal energy, which leads to a low signal to noise ratio (SNR). The method under examination uses sending signals with a length of ~20µs instead of typically 0.5µs to 2µs in UDV systems. Long sending signals contain more signal energy and result in a better signal quality in terms of SNR. With higher SNR, however, less averaging is needed, and thus time resolution can be increased.
We propose the use of a short (~20µs) sending signal with linear chirp. The coding is similar to that of Frequency Modulated Continuous Wave Radar (FMCW Radar). The chirp is needed to obtain spatial resolution. Similar to the crosscorrelation approach in Pulse Doppler Ultrasound, it finally leads to a time-of-flight evaluation. The main difference, however, is that more ultrasound energy can be sent into the fluid. Also, the maximum velocity limit of Doppler systems does not apply for this method, so that velocities above this limit can be detected unambiguously.
Keywords: Ultrasound Doppler Velocimetry, Flow mapping, Frequency modulated signals
  • Lecture (Conference)
    2nd International Workshop on Measurement Techniques for Liquid Metal Flows (MTLM2007), 23.-25.04.2007, Dresden, Deutschland

Publ.-Id: 10185 - Permalink


Application of the Ultrasonic Doppler Method in liquid metal flows: examples and perspectives
Eckert, S.; Zhang, C.; Gundrum, T.; Gerbeth, G.;
The Ultrasound Doppler Velocimetry (UDV) is a non-intrusive technique to measure velocities of liquid flows. Because of the ability to work in opaque fluids and to deliver complete velocity profiles in real time it becomes very attractive for liquid metal applications. But, in case of hot metallic melts the user is confronted with a number of specific problems: First of all the application of the ultrasonic transducers is usually restricted to maximum temperatures of about 150°C. The transmission of a sufficient amount of ultrasonic energy from the transducer to the fluid has to be guaranteed. Here, the acoustic coupling and the wetting conditions have to be considered as important issues. Moreover, the flow has to be seeded with reflecting particles to obtain Doppler signals from the fluid.
The feasibility of velocity profile measurements by UDV has already been demonstrated for low temperature liquid metals as mercury and gallium. Complications arise for UDV applications in liquid metal flows at high temperatures. Recently, an integrated ultrasonic sensor with acoustic wave guide has been developed. The feasibility of this sensor concept has been demonstrated in diverse experiments using miscellaneous metallic melts until temperatures of about 700°C.
In this presentation we show various applications of UDV in liquid metal flows to demonstrate the capabilities and current restrictions of this technique. For instance, we consider single- and multi-transducer arrangements for flow mapping or present velocity measurements obtained during the solidification of a metallic melt. Besides the determination of velocity profiles in the liquid phase the UDV data allow for an assessment of the current position of the solidification front too. Specific problems arising in the context of UDV measurements in liquid metal experiments will be discussed.
Keywords: liquid metal, Velocity measurements, Ultrasound Doppler Velocimetry, Acoustic waveguide, High temperature applications
  • Lecture (Conference)
    2nd International Workshop on Measuring Techniques for Liquid Metal Flows (MTLM2007), 23.-25.04.2007, Dresden, Deutschland

Publ.-Id: 10184 - Permalink


Velocity measurements in liquid metal two-phase flows by means of the ultrasonic Doppler method
Zhang, C.; Eckert, S.; Gerbeth, G.;
Bubble driven flows have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenize the physical and chemical properties of the melt or to refine the melt. For such gas-liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way.
Compared to the numerous experimental studies on the movement of bubbles in transparent liquids , especially in water, the number of publications dealing with gas bubbles rising in liquid metals is comparatively small. The shortage of suitable measuring techniques can be considered as one reason for the slow progress in the investigations of gas-liquid metal flows. Powerful optical methods are obviously not available for measurements in liquid metals. The majority of measurements in liquid metal two-phase flows published until now was obtained using local conductivity probes, hot wire anemometer or optical fiber probes to determine quantities such as void fraction, bubble and liquid velocity or the bubble size. However, measurements with any local probe disturb the flow in a significant way, especially if the structures to be investigated reach dimensions comparable to the probes. In the case of opaque liquids the application of acoustic or ultrasonic sensors offers a possibility to get information about the flow structure and bubble quantities. We applied the Ultrasound Doppler Velocimetry (UDV) for measurements of the velocity structure in liquid metal bubbly flows. Because of the ability to work non-invasively in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications.
Keywords: liquid metal, bubble plume, Ultrasound Doppler Velocimetry, DC magnetic field
  • Lecture (Conference)
    2nd International Workshop on Measuring Techniques for Liquid Metal Flows (MTLM2007), 23.-25.04.2007, Dresden, Deutschland

Publ.-Id: 10183 - Permalink


The Role of Magnetic Forces in Electrochemical Reactions - Numerics and Experiments
Mutschke, G.; Gerbeth, G.; Bund, A.;
It is well known, that Lorentz forces can be used to enhance the convection in electrochemical cells. Usually this enhancement leads to an increased limiting current [1], i.e. an increased deposition rate in the case of metal deposition. Currently, the influence of magnetic fields on the morphology of the deposited layers and the action of concentration gradient forces on deposition are intensively discussed. [2,3]
In our presentation, we will discuss the effect of magnetic forces during the electrodeposition of copper for different orientations of the external magnetic field. Besides new analytical findings, by numerical methods, we will present results on the velocity and the concentration field inside the cell from which interesting conclusions can be drawn. Three-dimensional effects are found to play an important role. Finally, a comparison with recent experimental results [4] will be performed.

[1] T.Z. Fahidy, J. Appl. Electrochem. 13 (1983) 553.
[2] A. Bund, H.H. Kuehnlein, J. Phys. Chem. B 109 (2005) 19845.
[3] J. M. D. Coey, F. M. F. Rhen, P. Dunne, S. McMurry, J. Solid State Electrochem. DOI: 10.1007/s10008-006-0254-4.
[4] A. Bund, S. Koehler, H.H. Kühnlein, W. Plieth, Electrochimica Acta 49 (2003) 147.
  • Lecture (Conference)
    58th Annual Meeting of the International Society of Electrochemistry, 09.-14.09.2007, Banff, Canada

Publ.-Id: 10182 - Permalink


Journal of Low Temperature Physics Special Issue Dedicated to Frank Pobell Volume 146, Numbers 5/6, March 2007
Herrmannsdörfer, T.; Krotscheck, E.; (Editors)
Preface:

For more than a decade, Prof. Frank Pobell has worked as an editor for the Journal of Low Temperature Physics. He has, along with Horst Meyer (Duke University, USA) and recently Neil Sullivan (University of Florida, USA), advanced the Journal of Low Temperature Physics to a highly regarded magazine and the worldwide leading publication medium in low temperature and high magnetic field physics. Due to his imminent retirement, Frank Pobell has recently handed on the baton to Mikko Paalanen (Helsinki University of Technology, Finland) who has taken over as an editor as of September 2005.
During the 24th International Conference on Low Temperature Physics (LT24) in Orlando, the undersigned and Horst Meyer have discussed the idea to thank Frank Pobell for his dedication to the JLTP with a special issue. Publishing special issues has emerged as an effective concept for JLTP to honour outstanding members of the community. It has been applied at various occasions. We have therefore invited colleagues and companions of his scientific locations at Munich, Cornell, Jülich, Bayreuth and Dresden to contribute articles to the "Special Issue to honour Frank Pobell for his dedication for the Journal of Low Temperature Physics as an editor".
Frank Pobell dedicated his scientific live to the physics of matter under extreme conditions. Most of us got to know him because of his quest for ultra-low temperatures. With his groups in Jülich and Bayreuth, he achieved several records of the lowest equilibrium temperature. The last record, T = 1.5 µK, which has been reached through the adiabatic demagnetization of Platinum is valid since a decade. He built up several nuclear demagnetization refrigerators which enabled outstanding investigations of solids and quantum fluids down to lowest temperatures. He attended to nuclear-spin ordering phenomena, superconductors, magnetic superconductors, magnets, spin glasses, liquid and solid 3He and 4He. Frank Pobell shared his cooling machines and experimental techniques with the international community. His institute in Bayreuth had the status of an EU user facility during the 3rd and 4th research framework programme of the European Community.
Frank Pobell was acting as an editor for JLTP even in the recent years, when he was the director of Forschungszentrum Rossendorf, a large research centre in Dresden, as well as the president of the Leibniz Society, one of the four large science communities of Germany. During that time, Frank Pobell also emphasized the importance of physics in high magnetic fields, in particular in a field range, B > 50 T, not available to the wide science community, so far. In consequence, he accompanied by four other research institutes in Dresden, successfully applied for the German high magnetic field project, the Hochfeld-Magnetlabor Dresden (HLD), a user facility for experiments in very high pulsed magnetic fields up to 100 T which will go into operation in mid 2007. Until 2005, Frank Pobell also headed the build-up team of the HLD.
One of us (TH) had the opportunity both to be a member of his µK laboratory in Bayreuth and to participate in the construction of pulsed field installations at HLD. "As one of his former students, I am very grateful to Frank Pobell who has taught us much more than only low-temperature physics." Acting as guest editors for this issue, we got an impression on the amount of work which is necessary to keep that journal a vivid publication medium for the international low-temperature science community.
Thomas Herrmannsdoerfer, Hochfeld-Magnetlabor Dresden (HLD), Germany
Eckhard Krotscheck, Johannes Kepler Univ. Linz, Austria
Keywords: physics and techniques at low temperatures and in high magnetic fields, superconductivity, superfluidity, magnetism
  • Book (Editorship)
    New York: Springer, 2007
    297 Seiten

Publ.-Id: 10181 - Permalink


Selenite reduction by mackinawite, magnetite and siderite: XAS characterization of redox products
Scheinost, A. C.; Charlet, L.;
Suboxic soils and sediments contain the reactive Fe-bearing mineral phases mackinawite (FeS), siderite (FeCO3) and the Fe(II/III) oxide magnetite (Fe3O4), which should be able to reduce Se to oxidation states 0, -I and –II, forming elemental Se and iron selenides of low solubility. While the reduction of selenate or selenite to Se(0) by green rust, pyrite and by Fe2+ sorbed to montmorillonite in a slow (weeks), kinetically limited redox reaction has been demonstrated earlier, we show here that selenite is rapidly (within one day) reduced by nanoparticulate mackinawite and magnetite, while only 1/3 of selenite is reduced by the larger siderite crystals within one day. Depending on Fe(II)-bearing phase and pH, we observed four different reaction products, α-monoclinic and trigonal (hexagonal) elemental Se, and two iron selenides with structures similar to Fe7Se8 and FeSe. The thermodynamically most stable iron selenide, ferroselite (FeSe2) was not observed. The local structure suggests formation of nanoscale clusters, which may be much more soluble than the corresponding macrocrystalline solids, and mobile in case the physicochemical parameters of groundwater favor formation of stable colloidal suspensions (e.g. low IS and pH close to PZC).
  • Environmental Science & Technology 42(2008), 1984-1989

Publ.-Id: 10180 - Permalink


A finite-time thermodynamics of unsteady flows - from the onset of vortex shedding to developed homogeneous turbulence
Noack, B. R.; Schlegel, M.; Ahlborn, B.; Mutschke, G.; Morzynski, M.; Comte, P.;
Turbulent fluid has often been conceptualized as transient thermodynamic phase. Here, a finite-time thermodynamics (FTT) formalism [1] is proposed to compute mean flow and fluctuation levels of unsteady incompressible flows. That formalism builds upon a traditional Galerkin model which simplifies a continuum 3D fluid motion into a finite-dimensional phase-space dynamics and subsequently, into a thermodynamics energy problem. This model consists of a velocity field expansion in terms of flow configuration dependent eigenmodes and of a dynamical system describing the temporal evolution of the mode coefficients. Each mode may be considered as a wave, parameterized by a wave number and frequency. In our FTT framework, the mode is treated as one thermodynamic degree of freedom, characterized by an energy level. The dynamical system approaches local thermal equilibrium where each mode has the same energy if it is governed only by internal (triadic) mode interactions. However, the full system approaches only partial thermal equilibrium by strongly mode-dependent external interactions. In these interactions, large-scale modes typically gain energy from the mean flow while small-scale modes loose energy to the heat bath. The energy flow cascade from large to small scales is thus a finite-time transition phenomenon. The FTT model has been successfully applied to predict the cascade for flows with simple to complex dynamics. Examples include laminar vortex shedding which is dominated by 2 eigenmodes and homogeneous shear turbulence which has been modeled with 1459 modes. In addition, the onset of vortex shedding is described in the Galerkin and vortex picture as a finite time scale phenomenon.

[1] B. Andresen, P. Salamon & R.S. Berry, J. Chem. Phys. 66 (1977) 1571-1577.
Keywords: finite-time thermodynamics, vortex shedding, turbulence
  • Lecture (Conference)
    Joint European Thermodynamics Conference IX, 12.-15.06.2007, Saint Entienne, France
  • Contribution to proceedings
    Joint European Thermodynamics Conference IX, 12.-15.06.2007, Saint Entienne, France
    Proceedings, 129-132

Publ.-Id: 10179 - Permalink


Planar channeling radiation in the presence of a hypersonic superlattice
Grigoryan, L. S.; Mkrtchyan, A. H.; Wagner, W.; Atanesyan, A. K.; Khachatryan, H. F.; Azadegan, B.;
The radiation emitted by a relativistic electron/positron planar channeled in a single crystal and simultaneously swinging transversely due to longitudinal hypersonic (HS) vibrations excited in the crystal has been investigated. In the present case, the continuum potential of crystallographic planes has been obtained by averaging the corresponding atomic potentials over an area, the size of which was chosen to be much smaller than the wavelength of the quasi-stationary HS field. The spatially periodic HS superlattice involves a zone structure of the channeling states. Probabilities of radiant transitions as well as spectral-angular distributions of the intensity of the corresponding channeling radiation have been calculated assuming parametric resonance. Numerical results are given for several crystallographic planes of -quartz.
Keywords: channeling radiation, piezoelectric crystals, quartz, ultrasound
  • Poster
    VII Symposium RREPS-07, Radiation from relativistic electrons in periodic structures, 24.-28.09.2007, Prague, Czech Republic

Publ.-Id: 10178 - Permalink


Interactions of uranium with Brassica
Viehweger, K.; Geipel, G.;
Uranium is a widespread radioactive toxic heavy metal, released into the biosphere mostly by military purposes and nuclear industry. It is taken up by plant root systems and its chemical toxicity is much more dangerous than the radiological. Thus cell suspensions of rape (Brassica napus) revealed similar defence mechanisms after uranium exposure as described for other heavy metals (Clemens 2001). Some of them will be presented in detail, e.g. the pH-shift of the outer medium, the uptake and cellular sequestration revealed by ICP-MS and confocal microscopy. The speciation of uranium in aqueous solutions depends strongly on the pH-value, ionic composition and strength and thus plays an important role in bioavailability and cytotoxicity respectively. To investigate the speciation of uranium time-resolved laser-induced fluorescence spectroscopy (TRLFS) was performed. Further investigations are under way to clarify the molecular interactions between possible cellular ligands and uranium.

Clemens, S. (2001). "Molecular mechanisms of plant metal tolerance and homeostasis." Planta V212 (4): 475-486.
Keywords: uranium, heavy metal, plant cell suspension, defence mechanisms, confocal microscopy, TRLFS
  • Poster
    Botanikertagung Hamburg 2007, 03.-07.09.2007, Hamburg, Germany

Publ.-Id: 10177 - Permalink


Concepts for a sub-millimetre resolving gamma ray CT for nondestructive testing applications
Zippe, C.; Hoppe, D.; Bieberle, A.; Hampel, U.;
Recently we have developed a high resolution gamma ray CT system for process diagnostics. Typical application areas are nuclear fuel element bundles, chemical reactors, and hydrodynamic machines. In order to use gamma ray CT for non-destructive testing application, such as crack detection in metal parts, an increase in spatial resolution is required. Therefore, we tested two different approaches to increase resolution. The first technique is spatial collimation, where scanning is performed with an additional tungsten collimator in front of the detector arc. The collimator comprises slits of 0.33 mm width to narrow the sampling radiation beams. Thereby, the collimator also provides additional protection against false detection of scattered gamma photons. For a full sampling of the projection space the collimated detector needs to be laterally moved in six steps in addition to the rotary scanning motion of the tomography system. This increases measurement time proportionally and further requires an additional precise translation stage. As an alternative we tested a so called wobbling scheme that has frequently been used with earlier emission and transmission type CT scanners to increase resolution. With the wobbling scheme the detector has to be displaced laterally as with the collimation technique but the collimator is no longer needed. Since the collimator is a heavy and expensive part this approach is attractive. However, to produce the same sharp projection information as with the collimated detector it is necessary to deconvolve the measurement data with the detector’s response function. In our article and presentation we will discuss the methods in details and compare results that have been obtained from practical measurements on phantoms and industrial objects.
Keywords: gamma ray tomography, high resolution
  • Contribution to proceedings
    5th World Congress on Industrial Process Tomography, 03.-06.09.2007, Bergen, Norway
    Proceedings of the 5th World Congress on Industrial Process Tomography, Paper No TSD01, 38-44
  • Lecture (Conference)
    5th World Congress on Industrial Process Tomography, 03.-06.09.2007, Bergen, Norway

Publ.-Id: 10176 - Permalink


Fracture mechanical evaluation of an in-vessel melt retention scenario
Abendroth, M.; Willschütz, H. G.; Altstadt, E.;
This paper presents methods to compute j-integral values for cracks in two- and three-dimensional thermo-mechanical loaded structures using the finite element code ANSYS. The developed methods are used to evaluate the behavior of a crack on the outside of an emergency cooled reactor pressure vessel (RPV) during a severe core melt down accident. It will be shown, that water cooling of the outer surface of a RPV during a core melt down accident can prevent vessel failure due to creep and ductile rupture. Further on, we present j-integral values for an assumed crack at the outside of the lower plenum of the RPV, at its most stressed location for an emergency cooling (thermal shock) scenario.
Keywords: in-vessel retention, thermal shock, j-integral

Publ.-Id: 10175 - Permalink


Strahleninduzierte Zellschädigung
Beyreuther, E.;
no abstract available
  • Lecture (others)
    Seminar Klinik- und Poliklinik für Nuklearmedizin Universitätsklinikum Carl Gustav Carus, TU Dresden, 11.06.2007, Dresden, Deutschland

Publ.-Id: 10174 - Permalink


Design of an Electron Beam Energy Control Loop Using Transverse Dispersion
Justus, M.; Lehnert, U.; Michel, P.; Evtushenko, P.;
Stability in mean electron beam energy is of highest interest for a number of experiments performed at the ELBE accelerator. Energy drifts affect parameters of the generated Bremsstrahlung spectra, X-rays or infrared light, as well as the beam trajectory at the production targets or through the FEL waveguide, respectively.
In practise, we observe a slow drifting of the effective accelerating field during the first hours after a machine power-up or after switching to different nominal beam energies. Initially, this effect was compensated manually. A first order automation solution has been developed that corrects the resulting energy drift continuously, using a non-intrusive beam position monitor placed in a transversely dispersive part of the beam guide.
This paper describes the beam line setup and the simplified dynamic model of the control loop derived from it. Calculation of controller parameters using standard a standard method is shown. The user interface of the control system and working conditions for the loop are explained. Operational performance and conclusions towards improvements close this contribution.
Keywords: accelerator control, feedback, electron beam, beam energy
  • Contribution to proceedings
    DIPAC 2007 - 8th European Workshop on Beam Diagnostics and Instrumentation for Particle Accelerators, 20.-23.05.2007, Venezia, Italy
  • Poster
    DIPAC 2007 - 8th European Workshop on Beam Diagnostics and Instrumentation for Particle Accelerators, 20.-23.05.2007, Venezia, Italy

Publ.-Id: 10173 - Permalink


Superconductivity and Magnetism at low temperatures, in high magnetic fields, and in reduced dimensions
Herrmannsdörfer, T.;
Survey on recent investigations on the superconducting and magnetic properties of micro- and nanogranular materials at very low temperatures and high magnetic fields
Keywords: superconductivity, magnetism, nanoclusters, very low temperatures, high magnetic fields
  • Invited lecture (Conferences)
    233. PTB Seminar "Physik und Metrologie bei tiefen Temperaturen", 05.-06.06.2007, Berlin, Deutschland

Publ.-Id: 10172 - Permalink


Röntgen- und Gamma-Tomographie in der Technik
Hampel, U.;
Der Vortrag gibt einen Überblick über den Einsatz von Röntgen- und Gamma-Tomographieverfahren in der Technik.
Keywords: X-ray tomography, gamma ray tomography
  • Lecture (others)
    Lehrerfortbildung 2007, 16.2.2007, Dresden, Germany

Publ.-Id: 10171 - Permalink


Measurement techniques and experimental investigations for multiphase flows
Hampel, U.;
The presentation is a short-course lecture that introduced the current state of the art in multiphase flow measurement techniques. Sensors and measurement techniques, which are intoduced are: electrical and optical needle probes, wire-mesh sensors and tomography techniques. Beside the physical measuring and sensor construction principles the presentation addresses the topic of data processing for multiphase flow measurements.
Keywords: multiphase flow measurment, multiphase flow sensors
  • Contribution to proceedings
    Multi-Phase Flows: Simulation, Experiment and Application, 25.-27.04.2007, Dresden, Germany
    Proceedings of Multi-Phase Flows: Simulation, Experiment and Application
  • Invited lecture (Conferences)
    Multi-Phase Flows: Simulation, Experiment and Application, 25.-27.04.2007, Dresden, Germany
  • Invited lecture (Conferences)
    Multiphase Flows - Simulation, Experiment and Application, 24.-26.06.2008, Dresden, Germany
  • Invited lecture (Conferences)
    Multiphase Flows - Simulation, Experiment and Application, 26.-28.05.2009, Dresden, Germany
  • Invited lecture (Conferences)
    SIAMUF – Multiphase Flows Meeting, 21.-22.10.2009, Gothenburg, Sweden
  • Invited lecture (Conferences)
    Multiphase Flows - Simulation, Experiment and Application, 22.-24.06.2010, Dresden, Germany
  • Invited lecture (Conferences)
    Multiphase Flows - Simulation, Experiment and Application, 08.-10.06.2011, Dresden, Germany

Publ.-Id: 10170 - Permalink


Orrientation dependant nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding
Martinavičius, A.; Abrasonis, G.; Möller, W.; Templier, C.; Declemy, A.;
Nitrogen diffusion in single crystalline stainless steel during ion beam nitrding is investigated. Single crystalline [orientations (001), (110) and (111)] AISI 316L austenitic stainless steel was ion beam nitrided at 400 °C using a Kaufman-type ion source with ion energy and flux of 1.2 keV and 0.5 mA cm−2, respectively. Phase structure was determined by X-ray diffraction (XRD) while nitrogen distribution profiles were obtained by nuclear reaction analysis (NRA). XRD analysis shows the presence of the phase usually called “expanded” austenite or γN phase. The NRA nitrogen depth distribution can be depicted by an initial quasilinear decrease followed by a sharp leading edge. It is observed that nitrogen penetration depth depends on the orientation: the fastest diffusion is observed in single crystalline samples with orientation (001) than in (011) or (111), while the orientations (110) and (111) showed similar penetration depth. The NRA profiles were compared with theoretical calculated employing ‘trapping-detrapping’ model. This comparison shows that the full experimental profile shape can be theoretically reproduced. In addition, this allows extracting diffusion coefficient values for different orientations.
Keywords: Nitriding; Anisotropic diffusion; Stainless steel
  • Poster
    VEIT 2007 - Fifteenth International Summer School on Vacuum, Electron and Ion Technologies, 17.-21.09.2007, Sozopol, Bulgaria

Publ.-Id: 10169 - Permalink


Results of the PROMISE experiment on helical magnetorotational instability
Stefani, F.; Gerbeth, G.; Gundrum, T.; Rüdiger, G.; Szklarski, J.; Hollerbach, R.;
The PROMISE experiment relies on the fact that the critical Reynolds number for the appearance
of the magnetorotational instability (MRI) in liquid metal flows drastically decreases when the the purely axial magnetic field is replaced by a helical one. We report the results of two series of experiments which differ slightly in the radial electric boundary conditions. It is shown that the helical MRI emerges as a travelling wave with a frequency that is in good correspondence with numerical predictions. Special focus is laid on the role of the radial jet region where the two Ekman vortices from the top and the bottom meet each other.
  • Lecture (Conference)
    MHD Laboratory Experiments for Geophysics and Astrophysics, 01.-03.10.2007, Catania, Italy

Publ.-Id: 10168 - Permalink


Noise induced relaxation oscillations and Earth's magnetic field reversals
Stefani, F.; Gerbeth, G.; Günther, U.; Xu, M.; Sorriso-Valvo, L.;
The magnetic field of the Earth is known to undergo polarity reversals with a mean reversal rate that varies between zero during the superchrons and around 5 per Myr in the present. Typically, these reversals have an asymmetric, saw-toothed shape with a slow decay and a fast recreation of the dipole. This asymmetry points to a possible connection with relaxation oscillations as they are well known from the van der Pol oscillator. A simple mean-field dynamo model with a spherically symmetric helical turbulence parameter which is quenched by the magnetic energy and disturbed by additional noise is analysed with view on this similarity. The basic features of geomagnetic polarity reversals are shown to be generic consequences of the dynamo action in the vicinity of branching points of the spectrum of the dynamo operator where two real eigenvalues coalesce and continue as a complex conjugated pair of eigenvalues. A comparison of the time series and the phase space trajectories with those of paleomagnetic measurements is carried out. For the case of highly supercritical dynamos a very good agreement with the paleomagnetic data is achieved. We explain also why such highly supercritical dynamos have a general tendency to self-tune into reversal prone states. The similar clustering properties of numerical and paleomagnetic reversal sequences are discussed. Spectral theory of the non-selfadjoint dynamo operator is also invoked to speculate that the growth of the inner core might be responsible for the long term changes of the reversal rate and for the occurrence of superchrons.
  • Lecture (Conference)
    XXIV IUGG General Assembly, 02.-13.07.2007, Perugia, Italy
  • Contribution to proceedings
    XXIV IUGG General Assembly, 02.-13.07.2007, Perugia, Italy
    Earth: our changing planet, Proceedings of IUGG XXIV General Assembly, Perugia: Umbria Scientific Meeting Association, 978-88-95852-25-4, 2483

Publ.-Id: 10167 - Permalink


Hybrid soft-magnetic lateral exchange spring films prepared by ion irradiation
McCord, J.; Schultz, L.; Fassbender, J.ORC
Magnetic stripe patterns in a magnetically patterned lateral exchange spring film are created by ion implantation. Periodic domain patterns with predefined positions are created by local alloying. The laterally confined modulation of magnetic properties opens new opportunities to the tuning of functionalities of soft-magnetic thin films.
Keywords: magnetism, ion irradiation, magnetic patterning, modification, Kerr microscopy
  • Advanced Materials 20(2008), 2090
    DOI: DOI: 10.1002/adma.200700623
  • Poster
    6th International Symposium on Metallic Multilayers, 15.-19.10.2007, Perth, Australia

Publ.-Id: 10166 - Permalink


Comparison of isoscalar vector meson production cross sections in proton-proton collisions
Abdel-Bary, A.; Abdel-Samad, S.; Brinkmann, K.-T.; Clement, H.; Dietrich, J.; Doroshkevich, E.; Dshemuchadse, S.; Ehrhardt, K.; Erhardt, A.; Eyrich, W.; Filippi, A.; Freiesleben, H.; Fritsch, A.; Gillitzer, A.; Hesselbarth, D.; Jaekel, R.; Karsch, L.; Kilian, K.; Kuhlmann, E.; Marcello, S.; Michel, P.; Moeller, K.; Morsch, H. P.; Pizzolotto, C.; Plettner, C.; Ritman, J.; Roderburg, E.; Schoenmeier, P.; Schroeder, W.; Schulte-Wissermann, M.; Steinke, M.; Sun, G. J.; Ullrich, W.; Wenzel, R.; Wintz, P.; Wagner, M.; Wilms, A.; Wirth, S.; Zupranski, P.;
The reaction pp→ppω was investigated with the TOF spectrometer, which is an external experiment at the accelerator COSY (Forschungszentrum Jülich, Germany). Total as well as differential cross sections were determined at an excess energy of 93 MeV (pbeam=2950 MeV/c). Using the total cross section of (9.0±0.7±1.1) μb for the reaction pp→ppω determined here and existing data for the reaction pp→ppphi, the ratio Click to view the MathML source turns out to be significantly larger than expected by the Okubo–Zweig–Iizuka (OZI) rule. The uncertainty of this ratio is considerably smaller than in previous determinations. The differential distributions show that the ω production is still dominated by S-wave production at this excess energy, however higher partial waves clearly contribute. A comparison of the measured angular distributions for ω production to published distributions for phi production at 83 MeV shows that the data are consistent with an identical production mechanism for both vector mesons.
Keywords: Vector meson production; pp→ppω; Cross sections; Angular distributions; OZI-violation; Strangeness of the nucleon

Publ.-Id: 10165 - Permalink


Impact of interface formation on intersubband transtitions in MBE GaInAs:Si/AlAsSb multiple coupled DQWs
Biermann, K.; Kuenzel, H.; Tribuzy, C. V.-B.; Ohser, S.; Schneider, H.; Helm, M.;
The impact of indium segregation and diffusion of antimony on intersubband transition (IST) wavelengths in AlAsSb/GaInAs multiple quantum well (MQW) and double quantum well (DQW) structures has been evaluated. By means of 8-band k·p calculations the effect of non-abrupt interfaces on IST wavelengths in such structures is elucidated. Comparison of measured and calculated absorption spectra reveals the sacrificial character of AlAs interfacial layers for diffused or segregated atoms and allows for estimating the limits of the intersubband approach as regards short wavelength relaxation transitions.
Keywords: intersubband transition, quantum well, AlAsSb/GaInAs, diffusion, segregation
  • Lecture (Conference)
    19th International Conference on Indium Phosphide and Related Materials (IPRM'07), 14.-18.05.2007, Matsue, Japan
  • Contribution to proceedings
    19th International Conference on Indium Phosphide and Related Materials (IPRM'07), 14.-18.05.2007, Matsue, Japan

Publ.-Id: 10164 - Permalink


Modelling of plasma-target interaction during reactive magnetron sputtering of TiN
Möller, W.; Güttler, D.;
The nitrogen incorporation at the target during reactive magnetron sputtering of TiN is described by a simple stationary global model of the magnetron plasma, in combination with an analytical two-layer stationary surface model or dynamic collisional computer simulation (TRIDYN) of the surface processes. Results are shown for different nitrogen gas additions in Ar/N2 and Xe/N2 gas mixtures at a total pressure of 0.3 Pa and a magnetron current of 0.3 A. The nitrogen incorporation predicted by the analytical model significantly less than obtained from computer simulation. The computer simulation yields nitrogen depth profiles which extend to about 2.5 nm, exhibiting a quasi-rectangular shape in case of stoichiometric saturation with an integrated nitrogen areal density of ~1.25•1016 N/cm2. The stationary-state nitrogen incorporation results from the balance of surface adsorption in connection with recoil implantation, direct ion implantation, and re-sputtering. The most relevant species are nitrogen gas molecules for adsorption, molecular nitrogen ions for implantation, and inert gas ions for recoil implantation and sputtering. The model results are in good agreement with experiment provided that unity sticking of nitrogen gas molecules is assumed on the unsaturated surface. The analytical surface model is preferable, which favours the picture of a continuous transition to bulk and surface saturation rather than discrete local saturation which is inherent in TRIDYN. Also the relative nitrogen incorporation for Xe/N2 versus Ar/N2 gas mixtures is well described.
Keywords: Magnetron sputtering, Modelling, Plasma surface interaction, Target poisoning
  • Journal of Applied Physics 102(2007), 094501

Publ.-Id: 10163 - Permalink


Multicellular Tumor Spheroids as a Model System for the Evaluation of PET Radiotracer Uptake
Oswald, J.; Marschner, K.; Kunz-Schughart, L. A.; Schwenzer, B.; Pietzsch, J.;
Aim:
Three-dimensional multicellular tumor spheroids (MCTS) of tumor cell lines are a promising model system which reflects the in vivo situation of tumor microregions with increasing accuracy compared with conventional monolayer culture. In this study we quantified the uptake of radiotracers [18F]FDG and [18F]FMISO in various types of MCTS at different diameters and after defined times in culture.

Material and Methods:
Human tumor cell lines FaDu, HT-29, MCF-7 and EJ-28 and the murine line B16-F10 were cultured in 96 well plates. Culturing was performed in the presence of 0.24% methylcellulose for 3 to 7 days and with seeding densities of 1,000, 5,000, 10,000 and 30,000 cells per well. Diameters of individual spheroids were assessed and cellular uptake of [18F]FDG and [18F]FMISO was recorded after an incubation interval of 2 to 4 hours. MCTS were then harvested, washed onto filters and the individual uptake per spheroid was measured with a gamma counter.

Results:
Between day 3 and day 7, spheroids of a starting concentration of 10,000 cells showed an increase in diameter of 1.4-fold for HT-29, 1.2-fold for FaDu, 1.3-fold for MCF-7 and 1.1-fold for both EJ-28 and B16-F10 cells. In all cell lines, we observed a good correlation between uptake of [18F]FDG and spheroid diameter and protein content, respectively. With an experimental setting of 10.000 initiated cells and 3 days of culturing, the highest [18F]FDG uptake was achieved in B16-F10 cell spheroids with a value of 1.46±0.41 percent injected dose per MCTS (%ID/MCTS). In comparison, FaDu uptake was 0.63±0.15%ID/MCTS and 0.38±0.05%ID/MCTS in HT-29. EJ-28 and MCF-7 exhibited less than 0.2%ID/MCTS. In parallel, a different uptake pattern was observed for [18F]FMISO. Highest uptake was documented in B16-F10 with 0.23±0.11%ID/MCTS, whereas all other cell lines showed an uptake of 0.03%ID/MCTS or less. These data indicate larger areas of hypoxia in the cores of B16-F10 spheroids compared to other cell lines.

Conclusion:
Our data show a spheroid-type specific increase in the uptake of both [18F]FDG and the hypoxia marker [18F]FMISO as a function of the spheroid diameters which is indicative for an increasing amount of metabolically active cells and an increment of hypoxic areas in growing spheroids. We conclude (i) that radiotracer uptake is a promising approach to monitor the pathophysiological situation in MCTS and (ii) that MCTS are a valuable tool to study the uptake of new radiotracers in a pathophysiological tumor milieu.
  • Lecture (Conference)
    EANM 2007 - Annual Congress of the European Association of Nuclear Medicine, 13.-17.10.2007, Copenhagen, Denmark
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 34(2007)Suppl. 2, S138

Publ.-Id: 10162 - Permalink


Actinides in Biosystems - Complexation studies with relevant bioligands
Glorius, M.;
Biosystems such as microorganisms, plants, algae’s etc. are influencing for instance the migration of actinides in the environment. It is important to include these processes in the risk assessment of potential high level nuclear waste disposal sites and other affected areas. In general, the overall interaction process of actinides with microbes can be divided into a) direct interaction path ways such as biosorption, bioaccumulation and biotransformation/bioreduction and b) indirect interaction paths such as complexation with released bioligands. The potential of microbes to mobilize actinides by means of the formed bioligands is less investigated.

Our approach is focused on the investigation of selected bioligands having relevant functionalities for a better understanding of the complex actinide interaction processes in biological systems on a molecular level. To achieve this goal a variety of spectroscopic techniques such as time-resolved laser fluorescence spectroscopy (TRLFS) and/or absorption spectroscopy in the ultraviolet-visible-near infrared (UV-vis-NIR) wavelength range will be applied depending on the nature of the actinide element and the bioligand.
The presentation gives an overview about our ongoing research in this area especially the studies about the complexation of uranium with hydroxamic acids.

This work was funded by the BMWA under contract number 02E9985.
Keywords: uranium, complexation, hydroxamic acids, spectroscopy
  • Lecture (others)
    Institutsseminar, 28.-29.06.2007, Köln, Germany

Publ.-Id: 10161 - Permalink


Comparing Long Term Operation Experience Of Large PV-Systems
Becker, G.; Rehm, W.; Kumerle, G.; Bächler, M.; Rindelhardt, U.;
The aim of this work is to compare the operation experiences of large grid connected PV systems in the Megawatt class. Two systems with a total power of more than 2000 kWP are located on the roofs of the new Munich Trade Fair Centre, the two others are situated in West Saxonia near Leipzig (5000 kWp ) and Meerane (1000 kWp). In November 1997 the 1016 kWP solar roof on the new Munich Trade Fair was connected to the grid. Since then, until the end of December 2006, more than 8.900 MWh of solar electricity on the AC-side have been fed into the local 20-kV-medium-voltage-grid. The photovoltaic generator consists of 7812 modules, each one showing a nominal power of 130 WP. System voltages up to 600 V DC are applied. The cables on the DC-side show cross-sections up to 600 mm². One central inverter - three 330-kVA-units in master-slave-operation - transforms the DC energy into AC. The neighbour system, which was installed 5 years after the first PV system, shows a nominal power of 1056 kWP. Although equipped with key components such as modules and inverters from the same manufacturers as the first system, it shows some differences coming from the lessons learned from the first system. After some initial problems (over temperature in the inverter rooms, grid fluctuations causing inverter shut downs and damages, faulty isolation measurements, poor designed string fuses) the systems now operates highly reliable and at superior performance. The Saxon systems were put into operation in 2004. In both plants central inverters are used in master-slave operation. The generators of both systems are mounted on ground of former waste sites. It is the purpose of this work to compare the operation of these PV plants. First, a detailed comparison of the yields will be done. Where do the differences come from? Which are the influences of irradiation, modules and their tilt angle, inverters and their operation mode, maintenance etc? In the next step the operation experiences will be compared. Have there been any severe damages? Are there any lessons learned from initial operation? What about the long term behavior of modules, cables, boxes, inverters? As a conclusion recommendations will be given to improve the long term behavior of large PV systems.
Keywords: PV plants, performance
  • Contribution to proceedings
    22. European Photovoltaic Solar Energy Conference, 03.-07.09.2007, Milano, Italy, 3-936338-22-1, 2956-2959
  • Lecture (Conference)
    22. European Photovoltaic Solar Energy Conference, 03.-07.09.2007, Milano, Italy

Publ.-Id: 10160 - Permalink


Speciation analysis using lasers
Geipel, G.;
Lasers in speciation analysis are used mainly as excitation source for spectroscopic methods.
Laser-induced methods as Laser-induced photoacoustic spectroscopy (LIPAS), Laser-induced thermal lensing spectroscopy (TLS) and laser-induced fluorescence (luminescence) spectroscopy (LIF) as well as the laser-induced time-resolved fluorescence spectroscopy (TRLIF) are common methods for elemental speciation analysis.
The main advantages of these methods are:
Non-invasive methods
Non-destructive
Low detection limits
Especially the last advantage has great importance in actinide chemistry, due to the radioactivity of these elements.
TLS has no great importance in speciation analysis due to the use of an additional probe laser, which has to be aligned with the pump laser beam.
Due to the destruction of species laser ablation combined with spectroscopic methods will not considered in this chapter
The chapter will review the application of both methods (LIPAS and TRLFS) to determine the elemental speciation mainly of lanthanides and actinides in solution. Examples for speciation analysis in solids will be given, here namely focussed to the assignment of some uranium minerals. In the chapter excitation wavelength (spectra) as well as the emission properties will be reviewed.
Additionally shortly the application of TRLFS to determine organic species will be taken into consideration. However, due to the numerous organic species only a short introduction with few examples can be given.
Keywords: Laser, speciation, elements
  • Book chapter
    in: Lasers in Chemistry,Volume One: Probing, Weinheim: VCH Wiley, 2008, 978-3-527-31997-8, 423-439

Publ.-Id: 10159 - Permalink


Complex Formation of Uranium(VI) with L-Phenylalanine and 3-Phenylpropionic Acid Studied by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy
Barkleit, A.; Foerstendorf, H.; Heim, K.; Sachs, S.; Bernhard, G.;
Uranyl complexes with phenylalanine and the analogous ligand phenylpropionate were investigated in aqueous solution by attenuated total reflection (ATR) Fourier transform infrared (FT-IR) spectroscopy. The assignment of the observed bands to vibrational modes was accomplished using spectra of the pure ligands recorded at different pH values and spectra of the 15N labeled analogous compounds of the amino acid. The results presented in this work provide a detailed description of the binding states of the uranyl complexes in solution. A bidentate binding of the carboxylate group to the actinide ion was observed by the characteristic shifts of the carboxylate modes. From the spectra the presence of the protonated amino group in the actinide complex can be derived. Due to these findings, contributions of the amino group to the binding to the uranyl ion in the amino acid complex can be ruled out.
Keywords: Uranyl; Complexation; Amino acid; Infrared spectroscopy; IR spectroscopy; Attenuated total reflection; ATR; Fourier transform infrared spectroscopy; FT-IR spectroscopy; Phenylalanine; Phenylpropionate.

Publ.-Id: 10158 - Permalink


Extracellular signal-regulated kinase mediates steroidogenesis induced by native and oxidized low-density lipoprotein
Kopprasch, S.; Ansurudeen, I.; Pietzsch, J.; Graessler, J.; Bornstein, S. R.;
Objectives:
Oxidative stress with resulting oxidation of low-density lipoproteins (LDL) plays a critical role in the atherogenesis. Since hypertension and dyslipidemia are associated with hormonal dysregulation we examined the effect of oxidatively modified LDL on adrenocortical aldosterone and cortisol synthesis.

Methods:
LDL obtained from healthy volunteers by very fast ultracentrifugation was oxidized in vitro by sodium hypochlorite resulting in molar oxidant to LDL ratios of 272:1 (oxLDL-272, minimally oxidized LDL), 543:1 (oxLDL-543, mildly oxidized LDL), and 2716:1 (oxLDL-2716, heavily oxidized LDL). Human NCI-H295R adrenocortical cells were cultured in DMEM/F12. Cell proteins were separated by SDS-PAGE (10%) and immunoblotted with a polyclonal antibody against pERK 1/2 (1:1000). Aldosterone was measured by RIA and cortisol release was determined by competitive luminometric assay.

Results:
Incubation of adrenocortical cells with 10 to 100µg/mL native LDL (natLDL) or oxidized LDL (oxLDL) for 24h stimulated aldosterone release dose-dependently up to 3-fold. Subsequent stimulation of NCI-H295R cells with angiotensin II induced an additional aldosterone secretion up to 2.9-fold in LDL-pretreated samples. Similar effects were observed for cortisol release. Compared to natLDL, oxLDL induced a smaller hormone release. The ability of oxLDL to induce hormone release decreased with increasing degree of LDL oxidation. NatLDL and oxLDL induced ERK phosphorylation with a maximum at 5min poststimulation. Blocking ERK activation with U0126, the inhibitor of ERK upstream kinase MEK, markedly reduced aldosterone release.

Conclusion:
Oxidative modification of LDL decreases adrenocortical aldosterone and cortisol release. The ERK signalling cascade is critically involved in LDL-induced hormone release.
  • Poster
    51st Annual Meeting of the German Society of Endocrinology (DGE) and 12th Annual Meeting of the Austrian Society of Endocrinology and Metabolism, 07.-10.03.2007, Salzburg, Österreich
  • Abstract in refereed journal
    Experimental and Clinical Endocrinology & Diabetes 115(2007)Suppl 1, S75

Publ.-Id: 10157 - Permalink


Hydromagnetische Dynamos in und auf der Erde
Stefani, F.;
Im Vortrag werden sowohl die sehr frühen Vorstellungen zur Entstehung des Erdmagnetfeldes als auch die moderne Theorie des Geodynamos vorgestellt. Es folgt eine kritische Diskussion der Dynamoexperimente in Riga, Karlsruhe und Cadarache sowie des PROMISE-Experiments zum Nachweis der Magnetorotationsinstabilität.
  • Invited lecture (Conferences)
    Geophysikalisches Kolloquium, 12.06.2007, Münster, Deutschland

Publ.-Id: 10156 - Permalink


Das alpha und das Omega experimenteller Dynamos
Stefani, F.;
Im Vortrag werden sowohl die frühen Vorstellungen zur Entstehung des Erdmagnetfeldes vorgestellt als auch die moderne Dynamotheorie, die ganz massgeblich von Professor Fritz Krause in den 60er Jahren des 20. Jahrhunderts entwickelt worden war. Es folgt eine Diskussion der Experimente zum Nachweis des alpha-Effektes sowie der Dynamoexperimente in Riga, Karlsruhe und Cadarache.
  • Invited lecture (Conferences)
    Ehrenkolloquium zum 80. Geburtstag von Professor Fritz Krause, 05.06.2007, Potsdam, Deutschland

Publ.-Id: 10155 - Permalink


Wie entsteht das Magnetfeld der Erde?
Stefani, F.;
Der Vortrag spannt einen Bogen von den sehr frühen Vorstellungen zur Entstehung des Erdmagnetfeldes
bis hin zur modernen Theorie des Geodynamos. Die Dynamoexperimente in Riga, Karlsruhe und Cadarache sowie das PROMISE-Experiment zum Nachweis der Magnetorotationsinstabilität werden vorgestellt.
  • Invited lecture (Conferences)
    Abschlusskolloquium der Forschergruppe "Magnetofluiddynamik", 31.05.-01.06.2007, Ilmenau, Deutschland

Publ.-Id: 10154 - Permalink


Characterization of ZnO nanorods by AFM
Hou, Y.; Andreev, A.; Teichert, C.; Brauer, G.; Djurisic, A.;
  • Poster
    E-MRS 2007 Spring Meeting, SYMPOSIUM M, 28.05.-01.06.2007, Strasbourg, France
  • Lecture (Conference)
    Materials Today Asia, 03.-05.09.2007, Beijing, China

Publ.-Id: 10153 - Permalink


THz sources: from the large to the small
Helm, M.;
I will describe a large source dedicated to research, the Dresden IR & THz free-electron laser, and a compact, scalable emitter, which is a photoconductive antenna with an interdigitated electrode structure.
Keywords: free electron laser, THz sources, THZ antenna
  • Invited lecture (Conferences)
    4th meeting of GDR-E THz: Semiconductor sources and detectors for THz radiation, 01.-02,06.2007, Bombannes, France

Publ.-Id: 10152 - Permalink


Quality of performance assessment of PV plants based on irradiance maps
Drews, A.; Beyer, H.-G.; Rindelhardt, U.;
For the estimation of the expected annual energy yield and the month-by-month check of a PV system’s performance, methods based on irradiance maps published by weather services, both general or dedicated to solar energy application, are in use. Examples for this type of information for Germany are the annual and monthly radiation maps as published by the German Weather Service DWD, the data bank of hourly irradiance data with continuous spatial coverage prepared by the University of Oldenburg, and the radiation data products of the Climate Monitoring Satellite Application Facility CMSAF assembled by a consortium of European Weather Services.
To assess the validity of these data sets for the aforementioned tasks, a case study for a region covering the German federal state of Saxony is performed using data for the year 2005. For this region a set of ground-measured irradiance data from meteorological stations operated by the German Weather Service DWD is available. The comparison of hourly information on radiation sums is on one hand performed by the monthly analysis of the bias and the RMS-error for the Oldenburg data bank of hourly values versus the ground station data. For an additional inter-comparison of the different data sources, the annual maps presenting the estimates of the irradiance sums for 2005 are analyzed, giving information of data accuracy with respect to the spatial structure of the irradiance field.
The assessment of the end use accuracy of the irradiance data is made by investigating a set of monthly energy yield data of grid-connected PV systems. This is done via the estimation of the energy yield using a PV system simulation applying the irradiance data generated at the University of Oldenburg.
Keywords: PV system, solar radiation, monitoring

Publ.-Id: 10151 - Permalink


Stromgewinnung aus regenerativer Wasserkraft - Potenzialanalyse
Wagner, E.; Rindelhardt, U.;
Ausgehend vom derzeitigen Nutzungsstand wird das vorhandene Wasserkraftpotenzial in Duetschland bewertet. Eine zusätzliche und maximal mögliche jährliche Stromgewinnung durch Neubau, Erweiterung und Erneuerung von Anlagen, wird von den Ländern derzeit mit etwa 2,4 TWh angenommen. Damit würde sich eine Stromgewinnung von insgesamt gut 22 TWh ergeben.
Die Verfasser halten Zuwächse von etwa 1 TWh pro Jahrzehnt für möglich. Im Jahr 2015 könnte demnach etwa 21 TWh Wasserkraftstrom zur Verfügung stehen. Das setzt auskömmliche wirtschaftliche Rahmenbedingungen für die Anlagenbetreiber voraus. Allerdings steht das Umweltrecht/Wasserhaushaltsgesetz dem Bau von Anlagen an bisher nicht genutzten Standorten schwerwiegend entgegen.
Das gesamte technisch nutzbare Potenzial regenerativer Wasserkräfte beziffern die Verfasser auf etwa 25,5 TWh. Die derzeitige Nutzung dieses Potenzials erfolgt demnach zu etwa 78%.
Keywords: Wasserkraft, regenerative Energie, Potenzial
  • EW : Das Magazin für die Energiewirtschaft (2008)1-2, 78-81

Publ.-Id: 10150 - Permalink


Stromgewinnung aus regenerativer Wasserkraft in Deutschland – Überblick
Wagner, E.; Rindelhardt, U.;
Die Stromgewinnung aus regenerativer Wasserkraft erfolgt in Deutschland wesentlich aus Laufwasser- und Speicherkraftwerken. Derzeit beträgt deren Leistung etwa 3.960 MW, davon Speicherkraftwerke 350 MW. Die Stromgewinnung aus diesen Anlagen einschließlich der aus natürlichen Zuflüssen in "Pumpspeicher-Kraftwerken mit natürlichem Zufluss" (etwa 0,6 TWh/a) beträgt - Stand 2005 - als Wert des Regelarbeitsvermögens, gleichbedeutend dem Wert der Erzeugung im Regeljahr, etwa 20 TWh. Die Leistung aller Pumpspeicher-Kraftwerke wird bei der Beurteilung der Möglichkeiten der Nutzung regenerativer Wasserkräfte nicht berücksichtigt.
In den zurückliegenden drei Jahrzehnten ist ein durchschnittlicher Anstieg der Stromerzeugung aus regenerativer Wasserkraft von etwa 1 TWh pro Jahrzehnt erkenntlich.
Keywords: Wasserkraft, Stromgewinnung
  • EW : Das Magazin für die Energiewirtschaft 106(2007)25-26, 52-57

Publ.-Id: 10149 - Permalink


Greifswald VVER-440 RPV investigations: Neutron dosimetry and material tests
Konheiser, J.; Viehrig, H.-W.; Rindelhardt, U.; Noack, K.; Gleisberg, B.;
The Greifswald NPP was operated between 1973 and 1990. The units are of Russian WWER-440-230 type. Now trepans from the RPV were gained to investigate the post mortem properties of the material.
The paper describes the results of weld metal originating from the critical weld of the RPV of unit 1. The RPV of this unit was annealed after 14 years of operation, followed by two additional years of operation.
The neutron dosimetry was based on fluence calculations as well as retrospective Nb dosimetry. Both approaches are shortly described. A decrease of 60% through the thickness of the RPV was found by both methods.
The ongoing material test results comprise Charpy-V, tensile and fracture toughness parameters. The main interest is focussed on the comparison of assessment codes applied in Russia and other European countries where WWER-440 reactors are operated. An additional aspect is the comparison of results determined on sub-size Charpy specimens after the annealing procedure. The RPV of Greifswald Unit 1 is uncladded. After the annealing templates of weld metal were taken from the inner RPV wall. The toughness of the weld metal was measured with sub size Charpy specimens.
Keywords: Reactor pressure vessel, neutron embrittlement
  • Contribution to proceedings
    5th International Conference: Safety Assurance of NPP with WWER, 29.05.-01.06.2007, Podolsk, Russia
    Conference Proceedings, paper 137
  • Lecture (Conference)
    5th International Conference: Safety Assurance of NPP with WWER, 29.05.-01.06.2007, Podolsk, Russia

Publ.-Id: 10148 - Permalink


Best Practice Guidelines for the Use of CFD in Nuclear Reactor Safety Applications
Mahaffy, J.; Chung, B.; Dubois, F.; Ducros, F.; Graffard, E.; Heitsch, M.; Henriksson, M.; Komen, E.; Moretti, F.; Mori, T.; Mühlbauer, P.; Rohde, U.; Scheuerer, M.; Smith, B. L.; Song, C.; Watanabe, T.; Zigh, G.;
The document provides an internally compltete set of guidelines for a range of single phase applications of CFD to NRS problems. However, it is not meant to be comprehensive. The document should provide direct guidance on the key considerarions in known single phase applications, as nodalization, model selection and validation, and general directions for resolving renmaining details. It is intended to serve as a template for further applicationb specific BPG documents.
Keywords: computational fluid dynamics, nuclear reactor saftey, best practice guidelines
  • Other report
    Issy-les-Moulineaux: OECD Nuclear Energy Agency, 2007
    166 Seiten

Publ.-Id: 10147 - Permalink


Ab Initio atomic simulations of antisite pair recovery in cubic silicon carbide
Gao, F.; Du, J.; Bylaska, E. J.; Posselt, M.; Weber, W. J.;
The thermal stability of an antisite pair in cubic silicon carbide (3C-SiC) is studied using ab initio
molecular dynamics within the framework of density functional theory. The lifetime of the antisite
pair configuration is calculated for temperatures between 1800 and 2250 K, and the effective
activation energy for antisite pair recombination is determined to be 2.52 eV. The recombination
energy path and static energy barrier are also calculated using the nudged elastic band method along
with the dimer method to accurately locate the transition states. The consistency of the results
suggests that the antisite pair cannot be correlated with the DI photoluminescence center, as
proposed previously by theoretical interpretations. An extended exchange mechanism is found for
the antisite pair recombination.
Keywords: SiC, defects, ab-initio simulation

Publ.-Id: 10145 - Permalink


Phenomenology of brane-world cosmological models
Günther, U.; Zhuk, A.;
We present a brief review of brane-world models — models in which our observable Universe with its standard matter fields is assumed as localized on a domain wall (three-brane) in a higher dimensional surrounding (bulk) spacetime. Models of this type arise naturally in M-theory and have been intensively studied during the last years. We pay particular attention to the covariant projection approach, the Cardassian scenario, to induced gravity models, self-tuning models and the Ekpyrotic scenario. A brief discussion is given of their basic properties and their connection with conventional FRW cosmology.
Keywords: M-theory, string theory, cosmology, brane-worlds, Cardassian scenario, Ekpyrotic scenario, Friedman-Robertson-Walker cosmology
  • Contribution to proceedings
    Astrophysics And Cosmology After Gamow - Theory And Observations: Gamow Memorial International Conference Dedicated To The 100th Anniversary of George Gamow, 08.-14.08.2004, Odessa, Ukraine
    Astrophysics and Cosmology after Gamow: Theory and Observations, Cambridge, UK: Cambridge Scientific Publishers Ltd, UK, 978-1-904868-38-5, 79-98

Publ.-Id: 10144 - Permalink


Magnetic properties of ion implanted diamond
Höhne, R.; Esquinazi, P.; Heera, V.; Weishart, H.;
Single crystalline diamond samples of type IIa were implanted with boron and CVD diamond samples with fluorine or iron ions. Defect rich surface layers extending to a depth of about 300 nm for boron and 1 μm for fluorine and iron were produced by multiple energy implantation. The ion concentrations at the implanted regions were between 30 and 600 ppm for iron and fluorine and 0.5 to 1.5 at.% for boron. In all samples the magnetic properties were dominated by the diamagnetism of pure diamond. The main influence of iron and fluorine implantation on the magnetic properties of diamond is the creation of paramagnetic centres induced by disorder. Whereas diamond implanted with boron at a temperature of 900 °C does not show detectable paramagnetism. After subtraction of the linear background all implanted samples show small ferromagnetic-like loops. Although these signals are clearly above the detection limit and appear to be caused by ferromagnetism, we show that the measured loops are mainly caused by a SQUID artefact. We did not find any evidence for the existence of superconductivity in boron-doped diamond samples prepared under the used conditions.
Keywords: Diamond; Ion implantation; Magnetic properties; Irradiation effects

Publ.-Id: 10143 - Permalink


Confinement of paramagnetic ions under magnetic field influence: Lorentz- versus concentration gradient force based explanations
Weier, T.; Eckert, K.; Mühlenhoff, S.; Cierpka, C.; Bund, A.; Uhlemann, M.;
Concentration variations observed at circular electrodes with their axis parallel to a magnetic and normal to the gravitational field have previously been attributed elsewhere to the concentration gradient force only. The present paper aims to show that Lorentz force driven convection is a more likely explanation.
Keywords: magnetoelectrochemistry, Lorentz force, concentration gradient force, particle image velocimetry, synthetic schlieren, interferometry

Publ.-Id: 10142 - Permalink


Liquid Metal Magnetohydrodynamics – astrophysical relevance and engineering applications
Gerbeth, G.; Grants, I.; Gundrum, T.; Stefani, F.;
Magnetic fields influence the motion of liquid metals, but the melt motion modifies magnetic field distributions as well. Eventually, melt motions are able to create a magnetic field, known as the dynamo effect.
We present various laboratory experiments demonstrating this interaction between the flow and magnetic fields.
  • Lecture (Conference)
    Fifth International Conference on Fluid Mechanics, 15.-19.08.2007, Shanghai, China
  • Contribution to external collection
    F.G. Zhuang, J.C. Li: New Trends in Fluid Mechanics Research, Peking: Tsinghua-Springer, 2007, 690-693

Publ.-Id: 10141 - Permalink


Projective Hilbert space structures at exceptional points and their extension to line bundles over spectral Riemann surfaces
Günther, U.; Rotter, I.; Samsonov, B.;
A non-Hermitian complex symmetric 2×2 matrix toy model is used to study projective Hilbert space structures in the vicinity of exceptional points (EPs). The bi-orthogonal eigenvectors of a diagonalizable matrix are Puiseux-expanded in terms of the root vectors at the EP. It is shown that the apparent contradiction between the two incompatible normalization conditions with finite and singular behavior in the EP-limit can be resolved by projectively extending the original Hilbert space. The complementary normalization conditions correspond then to two different affine charts of this enlarged projective Hilbert space. Geometric phase and phase jump behavior are analyzed and the usefulness of the phase rigidity as measure for the distance to EP configurations is demonstrated. The EP-related quantum brachistochrone problem of PT-symmetrically extended Quantum Mechanics is discussed. Finally, aspects of a smooth globally defined line bundle structure over spectral Riemann surfaces are sketched.

The talk is partially based on arXiv:0704.1291v2 [math-ph] and includes newer findings going beyond this e-print.
Keywords: exceptional points, branch points, projective Hilbert space, geometric phase, singularities, PT-symmetric Quantum Mechanics, quantum brachistochrone problem, spectral Riemann surface, line bundle
  • Invited lecture (Conferences)
    Analytic and algebraic methods III, 19.06.2007, Prague, Czech Republic

Publ.-Id: 10140 - Permalink


On the interaction of molecular hydrogen with diamonds: An experimental study using nuclear probes and thermal desorption
Shiryaev, A. A.; Grambole, D.; Rivera, A.; Herrmann, F.;
Hydrogen behavior in monocrystalline diamonds with different concentrations and types of nitrogen defects was studied using Nuclear Reaction and micro-Elastic Recoil Detection Analyses and Thermal Desorption Spectroscopy. Diamonds were studied in as-received state, after HPHT treatment and after hydrogenation in molecular hydrogen. A considerable amount of hydrogen was found to be bonded to diamond surfaces. Kinetics of surface hydrogen desorption is similar to what was reported for plasma-hydrogenated diamonds. The solubility of hydrogen in type IIa diamonds is very low. The efficiency of hydrogen traps in diamond bulk varies with the dominant type of nitrogen-related defects. The cross-section of traps decreases in row Ib > IaA > IaB diamonds, though binding energy in type IaB crystals may be higher, than in type IaA. Dislocations may promote hydrogen diffusion. A marked dependency of the hydrogen content and diffusivity between diamond growth sectors were observed for some samples. The total hydrogen content is higher in octahedral sectors.
Keywords: Diamond crystal; Diffusion; Defect characterization; Hydrogen
  • Diamond and Related Materials 16(2007), 1479-1485

Publ.-Id: 10139 - Permalink


Effects of radiation damage in minerals on their electron back-scatter coefficient
Nasdala, L.; Kronz, A.; Tichomirowa, M.; Grambole, D.; Trullenque, G.;
The structural state (i.e., order-disorder) of minerals and other solids analyzed in an electron microprobe or scanning electron microscope may notably affect the back-scattering of incident beam electrons. Structural heterogeneity, as it is commonly observed in radiation-damaged minerals, may thus contribute to signal intensity variations in back-scattered electron (BSE) images. Such structural BSE effects are easily overlooked because they may be insignificant in cases of minerals with high internal Z contrast. Correspondingly, it has generally been assumed that BSE images of single-crystals of minerals are mainly controlled by the sample’s chemical heterogeneity. However, structural heterogeneity cannot be neglected in the discussion of BSE images; this is especially the case if crystals only show minor Z variations.
We show with two examples that radiation damage (i.e., gradual to complete destruction of the crystal lattice) results in a significant increase of the back-scatter coefficient. The phenomenon is assigned to lowered penetration depths of electrons and thus related to electron channelling contrast. The BSE of natural zircon crystals is in most cases predominantly controlled by radiation damage. Annealing studies revealed that after structural reconstitution, the BSE intensity is notably decreased and much more uniform, in spite of the same chemical heterogeneity (especially concentrations of Hf and U) as before the treatment. As an even more unambiguous example we present observations on irradiation-damaged silicon. Damage up to complete amorphization was produced upon implantation of Si ions. Consequently there are no chemical variations and no Z contrast in this case. Examples show that the degree of structural damage needs to be considered in the discussion and interpretation of BSE images of radiation-damaged minerals.
  • Lecture (Conference)
    Frontiers in Mineral Sciences, 26.-28.06.2007, Cambridge, UK
  • Contribution to proceedings
    Frontiers in Mineral Sciences, 26.-28.06.2007, Cambridge, UK
    Programme and Abstracts, 85-86

Publ.-Id: 10138 - Permalink


Raman study of irradiation damage in silicon
Nasdala, L.; Grambole, D.;
We have studied irradiation damage in a single-crystal silicon wafer prepared parallel to (100) by micro-Raman spectroscopy. Surficial structural damage in areas ~150 µm in size was produced by irradiation with a microbeam loaded with 600 keV Si+ ions at a 3MV Tandetron accelerator, Rossendorf (GRAMBOLE et al., 2007). Several implantations were done with a uniform fluence of 5 × 1014 cm-2, however, at different temperatures to produce areas with different degrees of damage. Full amorphisation was reached at implantation temperatures below 140 °C (NASDALA et al., 2007). Monte Carlo simulations using the SRIM code (ZIEGLER et al., 1985) predict that trajectory lengths of implanted ions are below 1 µm. This still exceeds the low penetration depth of light in silicon and, with that, the depth probed by Raman spectroscopy. Spectra obtained from partially amorphised areas virtually consist of an overlap of the two Raman spectra of amorphous and crystalline silicon, i.e., the LO=TO band of crystalline silicon at ~ 521 cm-1 shows only minor band broadening and shift when compared to the spectrum of the unirradiated host wafer. This indicates that the majority of the structural damage is located in amorphous clusters whereas the remnant crystalline silicon fraction shows only low levels of point defects as caused by atomic displacements.

References
GRAMBOLE, D., HERRMANN, F., HEERA, V. & MEIJER, J. (2007): Nucl. Instr. Meth. Phys. Res. B (in press).
NASDALA, L., GRAMBOLE, D., KRONZ, A. & TRULLENQUE, G. (2007): Am. Mineral. (accepted).
ZIEGLER, J. F., BIERSACK, J. P. & LITTMARK. U. (1985): The Stopping and Range of Ions in Solids.
Pergamon, New York.
  • Lecture (Conference)
    MinPet 2007 - Tagung der Österreichischen Mineralogischen Gesellschaft gemeinsam mit dem Geologischen Dienst der Autonomen Provinz Bozen, 16.-21.09.2007, Meran, Italy
  • Open Access LogoAbstract in refereed journal
    Mitteilungen der Österreichischen Mineralogischen Gesellschaft 153(2007), 85

Publ.-Id: 10137 - Permalink


Formung von Ge Nanopartikeln mit MeV Ionen
Schmidt, B.;
The deformation of Ge-nancrystals embedded in SiO2 during high energy ion irradiation has been investigated. For this purpose 200 nm thermally grown SiO2 was covered with a 5 nm Ge layer and a 100 nm SiO2 top layer by sputter deposition. Subsequent thermal annealing at 950 °C for 300s transformed the embedded continuous Ge layer through spinodal dewetting into Ge nanocrystals with a mean diameter of 20 nm. Afterwards, the Ge nanocrystals buried in SiO2 were irradiated at room temperature with 38 MeV I7+ ions in the dose range (1-4)x1015 cm-2. The ion current density was 40 nA/cm2. Cross-section TEM investigation of the irradiated samples showed that under given irradiation conditions the spherical Ge nanocrystal were shaped mainly into oblate-like Ge particles, which are in the amorphous state. As a result of the investigations we conclude that Ge nanoparticles embedded in SiO2 show the same form transformation behaviour under ion irradiation as irradiated amorphous silica colloides, namely, an expansion perpendicular to the ion beam direction and a contraction parallel to the ion beam direction. Mechanisms of the observed ion beam induced anisotropic deformation of Ge nanoparticles are discussed.
Keywords: heavy ion irradiation, ion beam shaping, nanoparticles
  • Lecture (Conference)
    Workshop Ionenstrahlphysik und Nanotechnologie, 10.-11.05.2007, Bochum, Germany

Publ.-Id: 10136 - Permalink


Fabrication of nanostructures by FIB: cobalt disilicide nanowires in silicon
Schmidt, B.;
In the introduction of the talk the Rossendorf FIB tool and the application possibilities in nanofabrication will be described.
The main part of the contribution is focused on cobalt FIB ion beam synthesis of CoSi2 nanowires with feature dimensions of about 20-50 nm in diameter and wire lengths of some µm. Using the Rossendorf FIB equipped with a CANION 31Mplus FIB column (Orsay Physics) a focusing of the Co++ ion beam down to a spot diameter of 30-50 nm was achieved. The ion energy was chosen to be 60 keV corresponding to a mean ion penetration depth of Rp = 53 nm. For the study of the conventional ion beam synthesis of CoSi2 nanowires (phase separation through precipitation and wire ripening during thermal treatment) and their decay into chains of nanoparticles due to nanowire instabilities the samples were implanted with high doses (1x1016-2x1017 cm-2) and at 420 °C sample temperature. Additionally, the scan direction of the FIB relative to the crystal directions was varied (normal FIB scan-direction was parallel to the [110]-direction on the Si surface). Small misalignment of the FIB trace relative to the [110] orientations leads to the decay of the CoSi2 nanowires into chains of more or less prolonged CoSi2 nanoparticles. Samples implanted at lower ion doses (1014-1016 cm-2) and at room temperature were used to investigate the influence of locally FIB induced irradiation defects on the CoSi2 nanowire growth. In this case, nanowires were again formed during thermal treatment by reacting of cobalt from a thin evaporated layer on the sample back side with defects induced by Co+ ion implantation with the FIB. The nanowires here are self-aligned along the in-plane [110] silicon crystal directions in (001)- and (111)-Si. In contrast to conventional ion beam synthesis of CoSi2 nanowires by high dose FIB implantation along a narrow trace defect-induced and self-aligned nanowire growth seems to be more stable.
Finally, in the outlook some examples of FIB based fabrication of nanostructures for different applications (e.g. 3D-nanostructures) will be discussed.
Keywords: Focused ion beam, ion beam synthesis, nanowires
  • Invited lecture (Conferences)
    Ion Beam Nanofabrication, NANO 2007 AAMU/Huntsville Nanotechnology Meeting, 21.-22.05.2007, Huntsville, Alabama, USA

Publ.-Id: 10135 - Permalink


Mikro-PET-Untersuchungen zu Bioverteilung und Metabolismus von F-18-fluorbenzoylierten Aminosäuren und Dipeptiden in den Nieren
Hultsch, C.; Wüst, F.; Pawelke, B.; Bergmann, R.;
kein Abstract verfügbar
  • Lecture (Conference)
    42. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 21.-24.04.2004, Rostock, Germany

Publ.-Id: 10134 - Permalink


Technetium-Fettsäuren (TcFS): Synthesen und biologische Evaluierung von 99mTc-markierten Fettsäuren für die Anwendung in Herzstoffwechsel-Untersuchungen
Walther, M.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Ruhr-Universität Bochum, 27.-28.03.2006, Bochum, Germany

Publ.-Id: 10133 - Permalink


Characterization of Pyoverdins Secreted by a Subsurface Strain of Pseudomonas fluorescens and Their Interactions with Uranium(VI)
Moll, H.; Glorius, M.; Bernhard, G.; Johnsson, A.; Pedersen, K.; Schäfer, M.; Budzikiewicz, H.;
Fluorescent Pseudomonas species secrete pyoverdin-type siderophores with a high potential to dissolve, bind, and thus transport uranium in the environment. The formation of complexes of UO22+ with pyoverdins released by the groundwater bacterium Pseudomonas fluorescens (CCUG 32456) isolated at a depth of 70 m depth in the Äspö Hard Rock Laboratory, Sweden, was studied. Mass spectrometry indicated that the cells produce a pyoverdinmixture with four main components: pyoverdin with a succinamide side chain, pyoverdin with a succinic acid side chain, ferribactin with a succinamide side chain, and ferribactin with a glutamic acid side chain. Three pK values could be determined from the pH-dependent changes in the absorption spectra of the pyoverdin mixture: log ß012 = 22.67 ± 0.15 (pK1 = 4.40), log ß013 = 29.15 ± 0.05 (pK2 = 6.48), and log ß014 = 33.55 ± 0.05 (pK3 = 10.47). The fluorescence properties of the pyoverdin mixture were pH dependent. The emission maximum changed from 448 nm at pH = 2.1 to 466 nm in the pH3.88.9 range. At pH > 4 a mono-exponential fluorescence decay dominates with a decay time of 5865 ± 640 ps. A drastic change in the intrinsic fluorescence properties, e.g., static fluorescence quenching, occurred due to the complex formation with UO22+. Species containing UO22+ of the type MpLqHr were identified from the dependencies observed in the ultraviolet visible and time-resolved laser-induced fluorescence spectroscopy spectra at pyoverdin concentrations below 0.1 mM. The following average formation constants were determined: log β112 = 30.00 ± 0.64 and log β111 = 26.00 ± 0.85 at ionic strength I = 0.1 M (NaClO4). The determined stability constants can be used directly in safety calculations of the mobilizing effect of released pyoverdins on uranium, in uranium-contaminated environments such as mine waste disposal sites.
Keywords: Uranyl, Pyoverdins, UV-vis spectra, fs-TRLFS spectra, Complexation

Publ.-Id: 10131 - Permalink


Positronen-Emissions-Tomographie (PET): Wie radioaktive Substanzen den Körper biochemisch transparent machen.
Wüst, F.;
kein Abstract verfügbar
  • Lecture (others)
    Lange Nacht der Wissenschaften, 30.06.2006, Dresden, Germany

Publ.-Id: 10130 - Permalink


Radiopharmaka-Herstellung/Manufacturing of radiophatrmaceuticals
Füchtner, F.; Zessin, J.; Preusche, S.; Steinbach, J.;
kein Abstract verfügbar
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-469 April 2007, 48-51

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Publ.-Id: 10129 - Permalink


[18F]Fluoracetat: Vom Gift zum PET-Tracer [18F]Fluoroacetate: From toxin to PET-tracer
Bergmann, R.; Richter, S.; Pietzsch, J.; Wüst, F.;
kein Abstract verfügbar
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-469 April 2007, 36-38

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Publ.-Id: 10128 - Permalink


Radioaktive Metalle für die Tumortherapie
Pietzsch, H.-J.; Stephan, H.; Steinbach, J.;
kein Abstract verfügbar
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-451 März 2006, 19-22

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Publ.-Id: 10127 - Permalink


PET-Bilder – scharf gemacht
Bühler, P.; Just, U.; Möckel, D.; Langner, J.; van den Hoff, J.;
kein Abstract verfügbar
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-421 März 2005, 20-21

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Publ.-Id: 10126 - Permalink


Strain profile of (001) silicon implanted with nitrogen by plasma immersion
Diaz, B.; Abramof, E.; Castro, R. M.; Ueda, M.; Reuther, H.;
In this work, we investigate the strain and defect state of silicon implanted with nitrogen by plasma immersion ion implantation, with doses between 4.5 1016 and 8.7 1016 cm 2. For this purpose, we have used Auger electron spectroscopy, x-ray reflectivity, and high-resolution x-ray diffraction. Auger spectra showed that nitrogen concentration profiles broaden and shift deeper into the substrate as the dose increases. High oxygen concentration in the first 20 nm suggested the presence of an amorphous oxide layer at the sample surface, which was confirmed by x-ray reflectivity measurements. Reciprocal space maps revealed a tensile strain perpendicular to the surface, while no in-plane strain was detected. Since no significant diffuse scattering was found, randomly distributed point defects must be predominant in the strained region compared to large displacement field defects such as clusters and dislocations. 2 scans around (004) Bragg reflection were fitted using dynamical theory of x-ray diffraction. The strain profiles obtained from the best fits correlated well with nitrogen concentration depth profiles, signaling interstitial nitrogen as the main source of strain.
  • Journal of Applied Physics 101(2007), 103523

Publ.-Id: 10125 - Permalink


Vom Radioiod zum molekularen Imaging: Potential und Grenzen der Radiopharmazie
Steinbach, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Fachforum der Hanns-Seidel-Stiftung, 27.-29.10.2006, Kolster Banz, Germany

Publ.-Id: 10124 - Permalink


Radiopharmaceutical research at Saxony - an overview
Steinbach, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    General Electric Meeting, 30.09.2006, Dresden, Germany

Publ.-Id: 10123 - Permalink


A short overview to radiopharmaceutical research at Saxony (Germany)
Steinbach, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Fa. Esteve (Laboratorios del Dr. Esteve, S.A.), 09.06.2006, Barcelona, Spain

Publ.-Id: 10122 - Permalink


Potential, limitations and application of organic PET- radiochemistry
Steinbach, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Fa. Esteve (Laboratorios del Dr. Esteve, S.A.), 09.06.2006, Barcelona, Spain

Publ.-Id: 10121 - Permalink


Wissenschaftliche und organisatorische Perspektiven des Instituts für Bioanorganische und Radiopharmazeutische Chemie beim Übergang zum Institut für Radiopharmazie
Steinbach, J.;
kein Abstract verfügbar
  • Lecture (others)
    Alumni-Treff des Instituts für Bioanorganische und Radiopharmazeutische Chemie, 02.-03.12.2005, Gohrisch, Germand

Publ.-Id: 10120 - Permalink


Entwicklung hochtemperaturstabiler Kontakte auf SiC
Weishart, H.; Heera, V.;
  • Lecture (others)
    3. NanoHoch-Projekttreffen in Dresden, 25.05.2007, Dresden, Germany

Publ.-Id: 10119 - Permalink


Magnetic patterning by means of ion irradiation and implantation
Fassbender, J.ORC; McCord, J.
A pure magnetic patterning by means of ion irradiation which relies on a local modification of the magnetic anisotropy of a magnetic multilayer structure has been first demonstrated in 1998. Since then also other magnetic properties like the interlayer exchange coupling, the exchange bias effect, the magnetic damping behavior and the saturation magnetization to name a few have also been demonstrated to be affected by ion irradiation or ion implantation. Consequently, all these effects can be used if combined with a masking technique or employing direct focused ion beam writing for a magnetic patterning and thus an imprinting of an artificial magnetic domain structure, which subsequently modifies the integral magnetization reversal behavior or the magnetization dynamics of the film investigated. The present review will summarize how ion irradiation and implantation can affect the magnetic properties by means of structural modifications. The main part will cover the present status with respect to the pure magnetic patterning of micro- and nanostructures.
Keywords: magnetism, patterning, ion irradiation, ion implantation

Publ.-Id: 10118 - Permalink


Properties of unflattened photon beams shaped by a multi leaf collimator
Pönisch, F.;
  • Poster
    AAPM Konferenz, 01.06.2006, Orlando, USA

Publ.-Id: 10116 - Permalink


Entwicklung eines Verfahrens zur Korrektur der Atembewegung in der Positronen-Emissions-Tomographie (PET)
Möckel, D.;
  • Lecture (others)
    Seminarvortrag Martin-Luther-Universität, 01.10.2004, Halle-Wittenberg, Dtl.

Publ.-Id: 10115 - Permalink


Design Criteria for an In-beam PET
Enghardt, W.;
  • Invited lecture (Conferences)
    Scientific Workshop for In-beam PET, 09.-10.05.2006, Dresden, Deutschland

Publ.-Id: 10114 - Permalink


Mikro-spill extraction
Crespo, P.;
  • Invited lecture (Conferences)
    Scientific Workshop for In-beam PET, 09.-10.05.2006, Dresden, Dtl.

Publ.-Id: 10113 - Permalink


Study of graded Ni-Ti Shape Memory Alloy film growth on Si(100) substrate
Martins, R. M. S.; Mücklich, A.; Reuther, H.; Beckers, M.; Schell, N.; Silva, R. J. C.; Pereira, L.; Braz Fernandes, F. M.;
In-situ x-ray diffraction (XRD) was employed to study the effect of the deliberate change of the ratio Ti/Ni during the deposition of Ni-Ti films. Thus, graded films were deposited exhibiting distinctive composition and crystalline structure along the growth direction. The as-sputtered films were ex-situ characterized by Auger Electron Spectroscopy (AES), Cross-sectional Transmission Electron Microscopy (XTEM), and Electrical Resistivity (ER) measurements (during thermal cycling). In this paper results are presented concerning a film with a Ti-rich composition in the central part and near-equiatomic composition in the extremities, following 4 distinct deposition periods (different Ti target powers). During the initial deposition step (near-equiatomic composition) the Ni-Ti B2 phase starts by stacking onto (h00) planes on the naturally oxidized Si(100) substrate due to the presence of the native Si oxide (2-3 nm). The increase of the power of the Ti target in the second and third steps induced the precipitation of Ti2Ni. When stopping the Ti co-sputtering, Ti2Ni “dissolves” and, thus, plays the role of a reservoir for the formation of B2 phase now preferentially stacking onto (110) with the system approaching again the equiatomic composition. The ex-situ study of the interface’s morphology has shown the presence of NiSi2 silicides (A-NiSi2 and B-NiSi2), Ti4Ni4Si7, Ti2Ni and a non-identified phase constituted by Ni, Ti and Si, most likely amorphous. During thermal cycling, electrical resistivity measurements revealed phase transitions associated with the B2, R-phase and B19’ phases. This type of studies allow the identification of intermediate states during deposition and annealing, and the correlation with the final structure of the film, being useful for the optimisation of the deposition parameters in order to fabricate films with a two-way reversible actuation.
Keywords: Ni-Ti thin films; Co-sputtering deposition; In-situ x-ray diffraction; Texture development; Interfacial diffusion
  • Applied Physics A 91(2008)2, 291-299

Publ.-Id: 10112 - Permalink


COVERS WP4 Benchmark 1 Fracture mechanical analysis of a thermal shock scenario for a VVER-440 RPV
Abendroth, M.; Altstadt, E.;
This paper describes the analytical work done by modelling and evaluating a thermal shock in a WWER-440 reactor pressure vessel due to an emergency case. An axial oriented semielliptical underclad/surface crack is assumed to be located in the core weld line. Threedimensional finite element models are used to compute the global transient temperature and stress-strain fields. By using a three-dimensional submodel, which includes the crack, the local crack stress-strain field is obtained. With a subsequent postprocessing using the j-integral technique the stress intensity factors KI along the crack front are obtained. The results for the underclad and surface crack are provided and compared, together with a critical discussion of the VERLIFE code.
Keywords: thermal shock, crack intensity factor, j-integral, fracture toughness, VVER-440
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-474 2007

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Publ.-Id: 10111 - Permalink


Jahresbericht 2006 / Annual Report 2006
Forschungszentrum Dresden - Rossendorf, Vorstand;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-469 2007

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Publ.-Id: 10110 - Permalink


Annual Report 2006 - Institute of Ion Beam Physics and Materials Research
von Borany, J.; Heera, V.; Helm, M.; Möller, W.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-466 2007

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Publ.-Id: 10108 - Permalink


4-[18F]Fluorobenzaldehyde-O-(2-{2-[2-(pyrol-2,5-dion-1-yl)ethoxy] ethoxy}ethyl)oxim ([18F]FBOM): A novel prosthetic group for mild labelling of SH-group bearing biomacromolecules
Vogler, L.; Berndt, M.; Pietzsch, J.; Hultsch, C.; Wüst, F.;
The synthesis and application of 4-[18F]fluorobenzaldehyde-O-(2-{2-[2-(pyrol-2,5-dion-1-yl)ethoxy]ethoxy}ethyl)oxim ([18F]FBOM) as a novel prosthetic group for 18F labelling of SH-group bearing biomacromolecules is described.
The aminooxy-functionalised labelling precursor for the radiosynthesis of [18F]FBOM was synthesised in a four-step synthesis sequence with a total yield of 14%. [18F]FBOM could be obtained in a condensation reaction between the labelling precursor and [18F]fluorobenzaldehyde through formation of an oxim. The radiochemical yield ranged between 14 and 19% (decay-corrected). In a typical experiment, starting from 6.5 GBq of [18F]fluoride 730MBq of [18F]FBOM could be obtained within 80 minutes (including HPLC purification). The specific activity was determined to be 51 GBq/µmol. The lipophilicity of [18F]FBOM was determined to be logP = 0.84. The use of [18F]FBOM as SH-reactive group prosthetic group was demonstrated by the reaction with glutathion, low densitiy lipoproteins (LDL) and modified neurotensin derivatives. [18F]FBOM can easily be synthesised, and [18F]FBOM represents an interesting novel prosthetic group for the labelling of SH-group containing biomacromolecules with 18F under mild conditions.
  • Lecture (others)
    14. Arbeitsgruppentagung Radiochemie/Radiopharmazie, 04.-05.10.2006, Marburg, Germany

Publ.-Id: 10107 - Permalink


Formation and morphology control of nanostructures produced by PIII
Shevchenko, N.; Weber, J.; Reuther, H.; Kolitsch, A.;
Development of novel materials and structures for drug delivery systems is currently a very active field of research. Recently the drug-eluting stents were designed to deliver a drug locally from a surface layer to reduce restenosis. Noble gas ion implantation into metals can be used to form nanoscale cavities or sponge like structures. These nanostructures have unique characteristics which offer potential for medical applications such as metal-based drug-eluting stents.
Investigations of the influence of implantation parameters on the surface morphology and cavity characteristics (e.g. size, distribution, and degree of interconnection) have to date been rather limited.
In the present work we have studied the formation of nanostructures on stainless steel surfaces by plasma immersion ion implantation (PIII) using different gases (helium or argon), ion energies (between 5 – 35 keV) and ion fluences (> 1e18 at/cm2). The surface topography and structure of the modified materials have been analyzed by scanning electron microscopy and atomic force microscopy. The phase and element compositions have been examined by grazing incidence X-ray diffraction analysis (GIXRD), X-ray photoelectron spectroscopy, and elastic recoil detection analysis.
Varying the ion energy, fluences, and substrate temperature has been found to produce either void or sponge like structures on the nano- (~10 nm) to micro-scale (~1 µm). Apart from the austenite iron peaks, the GIXRD patterns of the implanted samples display weak peaks of ferrite (bcc iron) as well as oxide phases.
Keywords: Spongy structures, nanostructures, ion implantation, noble gas, stainless steel, drug-eluting stents
  • Poster
    PBII&D 07 - 9th International Workshop on Plasma Based Ion Implantation and Deposition, 02.-6.09.2007, Leipzig, Germany

Publ.-Id: 10106 - Permalink


Structural properties of thin HfSiO films
Teichert, S.; Muehle, U.; Fachmann, J.; Steinhoff, J.; Kudelka, S.; Wilde, L.; von Borany, J.; Eichhorn, F.;
Kein Abstract vorhanden.
  • Lecture (Conference)
    11th International Conference on the Formation of Semiconductor Interfaces (ICFSI), 19.-24.08.2007, Manaus-Amazonas, Brazil

Publ.-Id: 10105 - Permalink


Polymorphism in ferroic functional elements - Bridging length and time scales
Gemming, S.; Luschtinetz, R.; Chaplygin, I.; Seifert, G.; Loppacher, C.; Eng, L. M.; Kunze, T.; Olbrich, C.;
The present study describes an approach for the scale-bridging modeling of ferroic materials as functional elements in micro- and nanoelectronic devices. Ferroic materials are characterized by temperature-dependent complex ordering phenomena of the internal magnetic, electronic, and structural degrees of freedom with several involved length and time scales. Hence, the modelling of such compounds is not straightforward, but relies on a combination of electronic-structure-based methods like ab-initio and density-functional schemes with classical particle-based approaches given by Monte-Carlo simulations with Ising, lattice-gas, or Heisenberg Hamiltonians, which incorporate material-specific parameters both from theory and experiment. The interplay of those methods is demonstrated for device concepts based on electroceramic materials like ferroelectrics and multiferroics, whose functionality is closely related with their propensity towards structural and magnetic polymorphism.

In the present case, such scale-bridging techniques are employed to aid the development of an organic field effect transistor on a ferroelectric substrate generated by the self-assembly of field-sensitive molecules on the surfaces of ferroic oxides. Electronic-structure-based methods yield the microscopic properties of the oxide, the surface, the molecules, and the respective interactions. They are combined with classical particle-based methods on a scale-hopping basis. This combination allows to study the morphology evolution during the self-assembly of larger adsorbate arrays on the (defective) oxide surface and to investigate the interplay of low-temperature magnetic ordering phenomena with the ferroelectric functionality at higher temperatures in multiferroic oxides like the hexagonal manganites. The combination of density-functional data with classical continuum modelling also yielded a model Hamiltonian for the quick determination of the properties of a gate structure based on bio-functionalized carbon nanotubes.
Keywords: multiferroic, density-functional, tight-binding, Ising, Monte-Carlo, simulation, OFET

Publ.-Id: 10104 - Permalink


Neue Möglichkeiten der Modellierung und Beeinflussung der Strömungsverhältnisse in Gießprozessen
Eckert, S.; Boden, S.; Galindo, V.; Gerbeth, G.; Stefani, F.; Willers, B.;
Metallschmelzen in industriellen Prozessen unterliegen in der Regel verschiedenen Arten von Strömungen. Diese Strömungen haben einen entscheidenden Einfluss auf den Wärme- und Stofftransport, und damit zumeist auch auf die Effizienz des Prozesses oder die Qualität des Endproduktes. Zukünftige Anstrengungen im Hinblick auf eine Optimierung derartiger Anlagen oder Technologien müssen aus diesem Grund eine wirksame Strömungskontrolle berücksichtigen.
Elektromagnetische Felder eröffnen aufgrund des kontaktlosen Zugangs und der einfachen Regelbarkeit eine attraktive Möglichkeit zur Strömungskontrolle. Eine gezielte Einflussnahme setzt aber ein umfangreiches Wissen über das Strömungsfeld und die Wechselwirkung mit den elektromagnetischen Kraftfeldern voraus. Neben numerischen Simulationen sind Modellexperimente mit sogenannten „kalten“ Schmelzen, d.h. mit Flüssigmetallen mit einem Schmelzpunkt < 300°C, ein unverzichtbares Mittel, um die Strömungsvorgänge besser zu verstehen und geeignete Maßnahmen zur Strömungskontrolle zu ergreifen.
Im Vortrag werden an ausgewählten Beispielen mit Bezügen zu industriellen Anwendungen die Möglichkeiten einer elektromagnetischen Strömungskontrolle erläutert. In diesem Zusammenhang wird auf die wechselseitige Abhängigkeit von numerischen Berechnungen und Modellexperimenten mit „kalten“ Modellschmelzen hingewiesen. Es werden neue Entwicklungen auf dem Gebiet Messtechnik für Flüssigmetalle vorgestellt, die einen wirkungsvollen Einsatz der Modellexperimente erst ermöglichen.
Keywords: liquid metal flow, electromagnetic flow control, cold models, measuring techniques, casting, solidification
  • Invited lecture (Conferences)
    VDG-Seminar "Technologie des Feingießens - Innovation durch fundiertes Wissen", 23.-24.05.2007, Bad Dürkheim, Deutschland

Publ.-Id: 10103 - Permalink


Nanostructured metal surfaces by plasma immersion ion implantation
Shevchenko, N.; Weber, J.; Kolitsch, A.;
For bare metal stents the in-stent restenosis was a serious problem for about 25 - 35% of the patients and this spurred the medical device companies to come up with a solution. Drug-eluting stents are designed to deliver a drug locally from a polymeric coating to reduce tissue in growth and reduce restenosis to less then 8% of the treated patients. Development of novel materials and structures for drug delivery systems is still very actual topic.
In the present work plasma immersion ion implantation (PIII) using helium or argon plasmas has been employed for the nanostructures formation on metal surfaces with a view to their applications for metal-based drug-eluting stents. A multi-layer pore system on stent surfaces in the range from nanoscale to microscale sizes is desired for drug loading and controlling the rate of elution of therapeutic agents.
Recently we have investigate the formation of nanostructures on stainless steel surfaces by PIII at different gases (He, Ar), ion energies (between 5 – 35 keV) and ion fluences (> 1e18 at/cm2). The surface topography and structure of the implanted materials were analysed by scanning electron microscopy and atomic force microscopy. The phase and element compositions were examined by grazing incidence X-ray diffraction analysis, auger electron spectroscopy, and elastic recoil detection analysis.
Variety of nanostructures as well as their characteristics (e.g. size, distribution, degree of interconnection) can be controlled by varying the implantation parameters. The results of these studies have demonstrated that PIII is a promising technique for the surface topography modification of stainless steel for cardiovascular application.
Keywords: nanostructures, metal surfaces, ion implantation, PIII, stents, drug delivery systems
  • Poster
    EuroNanoForum 2007, 19.-21.06.2007, Düsseldorf, Germany

Publ.-Id: 10102 - Permalink


Tetrahydroquinoline and tetrahydroisoquinoline mixed ligand rhenium complexes with the SNS/S donor atom set
Zablotskaya, A.; Segal, I.; Lukevics, E.; Belyakov, S.; Spies, H.;
New oxorhenium complexes with 3-methylazapentane-1,5-dithiolate (SNMeS) and thiol functionalized monodentate tetrahydroquinolyl and tetrahydroisoquinolyl derivatives have been synthesized by simultaneous reaction of [PPh3]2[Re(O)Cl3] with tridentate HSNMeSH and the corresponding N-heterocycle containing thiol. The characterization of complexes involved elemental analysis, IR, 1H and 13C NMR spectroscopy and X-ray crystallographic analysis. The nature of the heterocycle in monodentate ligand, even situated at the distance of two methylene group length, has been found to have a significant influence on the molecular conformation. Metal complexes were found to be active in psychotropic in vivo and cytotoxicity in vitro screening.
Keywords: rhenium • mixed-ligand oxorhenium complexes • tetrahydroquinoline • tetrahydroisoquinoline • molecular structure • psychotropic activity • cytotoxicity • metal-based drugs

Publ.-Id: 10101 - Permalink


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