Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32179 Publications
Operational Experiences with Megawatt PV Plants in Central Germany
Rindelhardt, U.; Bodach, M.;
Stimulated by the German Feed-in-Law, a number of grid-connected Megawatt PV plants have been put into operation during the last 5 years. Because of the higher irradiance these plants were originally concentrated in the southern part of Germany (Bavaria and Baden-Wuerttemberg). Starting in 2004 some plants have been also installed in Central Germany. The paper describes design and operation results of seven plants operating in the region of Saxony and Thuringia.

Locations and design
The most plants are concentrated in a region earlier defined by the DWD as "solar island" around Leipzig and Chemnitz. One plant is located in north-west Thuringia.
All plants were built on heavily used or loaded areas (former industrial sites or waste sites). Different types of fundaments and rack support constructions (desks) were used for the module mounting. The connection with the grid was done in the 10 to 20 kV voltage level, the distance between the plants and the grid was several thousands meters in some cases. All plants started their operation before 2006. The operation of the plants is monitored by the owners or by professional service providers.

Results and conclusions
The operation results of the year 2006 are exemplarily presented. The solar irradiance in 2006 was higher than the long year average, similar to the years before. The final yield of the plants ranges between 950 and 1050 kWh/kW. These surprisingly high values are near the values which were only found in Germany south of 50° latitude so far. The final yield of the tracked plant in Borna surpasses the yield of the other plants by 25%.
The performance ratios were determined to be between 0.77 and 0.84. The sources of energy losses are analysed and discussed. Beside component failures in the plants also grid disconnections reduced the feed-in energy in some cases.
Finally a long term estimation of the yield for the different plants will be given. Based on the data of the year 2006 a mean yield between 900 and 1000 kWh/kW can be expected.
Keywords: photovoltaics, PV plants, performance
  • Contribution to proceedings
    22. European Photovoltaic Solar Energy Conference, 03.-07.09.2007, Milano, Italy
    Operational Experiences with Megawatt PV Plants in Central Germany, 3-936338-22-1, 2952-2955
  • Lecture (Conference)
    22. European Photovoltaic Solar Energy Conference, 03.-07.09.2007, Milano, Italy

Publ.-Id: 9581 - Permalink

Kernenergie im 21. Jahrhundert - Herausforderungen und Möglichkeiten
Rindelhardt, U.;
Im Beitrag werden die Optionen und die Herausforderung für die Nutzung der Kernenergie im 21. Jahrhundert aufgezeigt. Ausgangspunkt sind die vorhandenen Vorräte an Kernbrennstoff und die Darstellung seiner derzeitigen Nutzung. Die Entwicklung der Kernkraftwerkstechnik seit 1960 wird beispielhaft dargestellt. Die Optionen und Entwicklungsziele der Kernreaktoren der 4. Generation (EInsatz etwa ab 2040) werden exemplarisch vorgestellt. Dabei wird besonders auf die zentrale Rolle der schnellen Brutreaktoren eingegangen.Ein besonderer Abschnitt ist der Wiederaufarbeitung und Endlagerung von Kernbrennstoff gewidmet.
Keywords: Kernenergie, Kernkraftwerke, Kernbrennstoff
  • Lecture (others)
    Informationsveranstaltung, 18.04.2007, Chemnitz, Deutschland

Publ.-Id: 9580 - Permalink

Laserinduzierte Breakdown-Detektion (LIBD)
Zänker, H.; Weiß, S.;
Die LIBD ist eine Methode, die Kolloidpartikel in sehr niedrigen Konzentrationen zu vermessen vermag. Sie wurde bisher vorwiegend zur Untersuchung von Kolloidproblemen in der Umweltforschung eingesetzt. Wegen ihrer hohen Empfindlichkeit könnte die LIBD potentiell aber auch für die Überwachung von Reinst- und Prozesswässern in der Halbleiterindustrie interessant sein. Hier ist die etablierte Methode zur Überwachung der Partikelfreiheit von Wässern das Single Particle Counting (SPC), vor allem mit den kommerziellen Geräten von PMS und Horiba. Es wird gezeigt, dass (i) für Kolloidpartikel > 50 nm das SPC der LIBD bezüglich der Konzentrationsempfindlichkeit deutlich überlegen ist, (ii) für Kolloidpartikel < 50 nm die Konzentrationsempfindlichkeit der LIBD heute unbefriedigend ist (sie liegt über den zu vermutenden typischen Konzentrationen der Partikel < 50 nm in den Reinstwässern der Halbleiterindustrie), (iii) die LIBD die einzige Methode ist, die überhaupt eine Information über Partikel < 50 nm liefern kann und (iv) durch technische Weiterentwicklung die LIBD wahrscheinlich in den erforderlichen Bereich der Partikelkonzentrationsempfindlichkeit gebracht werden könnte. Die Methode würde (nach Weiterentwicklung) für die Halbleiterindustrie interessant, wenn Partikel der Größe < 50 nm als Verunreinigungen interessant werden.

Keywords: Particle-free waters, semiconductor industries, colloids, laser-induced breakdown detection (LIBD), single particle counting (SPC)
  • Invited lecture (Conferences)
    Seminar über Partikelmessung an Reinstwässern der Halbeiterindustrie, 20.03.2007, Dresden, Deutschland

Publ.-Id: 9579 - Permalink

K0 and Λ production in Ni+Ni collisions near threshold
Merschmeyer, M.; Lopez, X.; Bastid, N.; Crochet, P.; Herrmann, N.; Andronic, A.; Barret, V.; Basrak, Z.; Benabderrahmane, M. L.; Caplar, R.; Cordier, E.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasparic, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kis, M.; Matulewicz, T.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Mangiarotti, A.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; Ryu, M. S.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Stoicea, G.; Tyminski, Z.; Wisniewski, K.; Xiao, Z.; Xu, H. S.; Yushmanov, I.; Zhang, X. Y.; Zhilin, A.;
New results concerning the production of neutral strange particles, K0 and Λ in Ni+Ni collisions at 1.93 AGeV, measured with the FOPI detector at GSI Darmstadt, are presented. Rapidity density distributions and Boltzmann slope parameter distributions are measured in nearly the full phase space of the reaction. The observables are compared to existing K+ and proton data. While the K0 data agree with previously reported K+ measurements, the Λ distributions show a different behavior relative to that of protons. The strangeness balance and the production yield per participating nucleon as a function of the centrality of the reaction are discussed, for the first time at SIS energies.

Publ.-Id: 9578 - Permalink

Confinement of strongly anisotropic hot-ion plasma in a compact mirror
Anikeev, A. V.; Bagryansky, P. A.; Ivanov, A. A.; Lizunov, A. A.; Murakhtin, S. V.; Prikhodko, V. V.; Solomakhin, A. L.; Noack, K.;
The paper presents the results of recent study of anisotropic plasma with thermonuclear ions confined in the axially symmetric Gas Dynamic Trap (GDT) mirror. Anisotropic ions are produced by the perpendicular injection of two focused 18 keV neutral beams in the small mirror section attached to the GDT central cell. We observed build-up of density of anisotropic ions up to approximately 10^13cm^−3 with the localized spatial profile and the mean energy of 7 keV. The average fast ion density three times exceeded the background plasma density. Fast ion accumulation is accompanied by the decrease of the plasma flux from the central cell recorded outside the mirror, that was qualified as a potential barrier development causing confinement improvement. Analysis of measurement results compared with estimates of plasma parameters in the compact mirror allows to scale to the experiments with next generation neutral beams with increased power and pulse duration.
Keywords: Compact mirror, Anisotropic ions

Publ.-Id: 9577 - Permalink

Practical experiences with the synthesis of [11C]CH3 trough gas phase iodination reaction using a TRACERlabFXC synthesis module
Knieß, T.; Rode, K.; Wüst, F.;
The results of [11C]CH3I synthesis through hydrogen gas reduction of [11C]CO2 on different nickel catalysts (HARSHAW-nickel, SHIMALITE-nickel, nickel on silica/alumina, nickel nanosize 99.99%) followed by gas phase iodination using a TRACERlab FXC synthesis unit are reported. Further reaction parameters such as furnace temperatures, flow rate of hydrogen gas and reduction time were optimized. It was found that reduction of [11C]CO2 proceeded in 28-83% yield depending on the nickel catalyst and temperature. The gas phase iodination (methane conversion) gave 31-62% of [11C]CH3I depending on temperature and amount of iodine in the iodine furnace. [11C]CH3I was used for heteroatom methylation reactions exemplified by a piperazine and a phenol (1 and 3). The specific activity of the 11C-labelled products 2 and 4 was determined after HPLC purification and solid-phase extraction. Compounds 2 and 4 were obtained in 8-14% radiochemical yield (decay-corrected, based upon trapped [11C]CH4) within 30 minutes. The specific activity was determined to be in the range of 20-30 GBq/µmol at the end-of-synthesis. Nickel catalyst nanosize was found to be superior compared with other Ni catalysts tested. The relatively low specific activity may be mainly due to carbon contaminations originating from the long copper tubing (500m) between the cyclotron and the radiochemistry facility.
Keywords: [11C]CH4, [11C]CH3I, gas phase iodination, TRACERlabFXC

Publ.-Id: 9576 - Permalink

Dielectron production in C+C and p+p collisions with HADES
Pietraszko, J.; Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Durán, I.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P. J. R.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; González-Díaz, D.; Grosse, E.; Guber, F.; Hadjivasiliou, C.; Heilmann, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Krücken, R.; Kugler, A.; Kühn, W.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, S.; Lopez, L.; Mangiarotti, A.; Marín, J.; Markert, J.; Metag, V.; Michalska, B.; Mishra, D.; Moriniere, E.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Pechenov, V.; Pérez, T.; Pleskac, R.; Pospísil, V.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Senger, P.; Shileev, K.; Simon, R.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Wen, H.; Wiśniowski, M.; Wójcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.;
The High Acceptance Di-Electron Spectrometer HADES has been constructed at the SIS accelerator (GSI Darmstadt) to investigate electron-positron pairs produced in proton, pion and heavy ion induced reactions. The main goal of these studies is to explore properties of hadrons in nuclear matter. The apparatus and the experimental results from C+C at 2.0 AGeV and 1.0 AGeV and p+p at 2.2 GeV compared with Monte-Carlo events from a generator based on known cross-sections and branching ratios are presented.
  • International Journal of Modern Physics A 22(2007), 388-396

Publ.-Id: 9575 - Permalink

Experimental investigation of a flow driven by a combination of a rotating and a traveling magnetic field
Cramer, A.; Pal, J.; Gerbeth, G.;
Velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating (RMF) and a traveling magnetic field (TMF). In a cylindrical container, an RMF as well as a TMF alone cause axisymmetric volume forces, which drive according axisymmetric base flows. The combination of both fields gives rise to an inherent three-dimensional part of the electromagnetic force distribution. In case of equal frequencies, this drives a three-dimensional flow consisting of a single large-scale helical motion, which implicates an intense mixing of the melt. The necessary admixture of a TMF to accomplish a qualitative change of the flow structure in a given RMF is shown to be two orders of magnitude smaller in case of equal field frequencies compared to the case of differing frequencies.
  • Physics of Fluids 19(2007)11, 118109

Publ.-Id: 9574 - Permalink

The spherically symmetric α2-dynamo and some of its spectral peculiarities
Günther, U.; Kirillov, O.; Samsonov, B.; Stefani, F.;
A brief overview is given over recent results on the spectral properties of spherically symmetric MHD α2-dynamos. In particular, the spectra of sphere-confined fluid or plasma configurations with physically realistic boundary conditions (BCs) (surrounding vacuum) and with idealized BCs (super-conducting surrounding) are discussed. The subjects comprise third-order branch points of the spectrum, self-adjointness of the dynamo operator in a Krein space as well as the resonant unfolding of diabolical points. It is sketched how certain classes of dynamos with a strongly localized α-profile embedded in a conducting surrounding can be mode decoupled by a diagonalization of the dynamo operator matrix. A mapping of the dynamo eigenvalue problem to that of a quantum mechanical Hamiltonian with energy dependent potential is used to obtain qualitative information about the spectral behavior. Links to supersymmetric Quantum Mechanics and to the Dirac equation are indicated.
Keywords: MHD dynamo, operator theory, spectrum, Krein space, boundary conditions, third-order branch points, Jordan structures, diabolical points, resonance, Korteveg-de Vries equation, supersymmetry, Quantum Mechanics, Dirac equation
  • Open Access LogoActa Polytechnica 47(2007)2-3, 75-81

Publ.-Id: 9573 - Permalink

High Performance Thermal Imaging Using Quantum Well Infrared Photodetector Arrays
Schneider, H.;
Quantum well infrared photodetector (QWIP) technology has opened up new opportunities to realize focal plane arrays (FPA) for high-performance thermal imaging [1]. High thermal and spatial resolution, low 1/f noise, low fixed-pattern noise, and high pixel operability makes QWIP FPAs appropriate for many applications. Due to their narrow absorption bands with relative spectral widths of the order of 10%, QWIPs are particularly suitable for thermal imaging applications involving several atmospheric transmission bands or several colors within the same band. For dual-band/dual-color FPAs, QWIP technology has the unique property that the active region for the long-wavelength band is transparent for the short-wavelength band. In this talk, I will report on typical QWIP structures optimized for thermal imaging applications and on the performance of some state-of-the-art QWIP cameras which were jointly realized by the Fraunhofer-Institute for Applied Solid State Physics (Freiburg, Germany) and AIM Infrarot-Module GmbH (Heilbronn, Germany). Besides imagers for the 8 – 12 µm long-wavelength infrared (LWIR) and 3 – 5 µm mid-wavelength infrared (MWIR) regimes these include a LWIR/MWIR dual-band QWIP FPA with 384x288 pixels which, at 6.8 ms integration time, exhibits a noise-equivalent temperature difference as low as 20.6 mK in the LWIR and 26.7 mK in the MWIR spectral bands. A specially designed diffraction grating is used for optical coupling of both spectral regimes. The array, which is based on a photoconductive QWIP for the MWIR and a photovoltaic "low-noise" QWIP for the LWIR, allows for synchronous and pixel-registered image acquisition in both bands. This functionality yields several advantages, including better distinction between target and background clutter, operation in a much wider range of ambient conditions, and the ability of remote absolute temperature measurement.
[1] H. Schneider and H. C. Liu, Quantum Well Infrared Photodetectors: Physics and Applications, ISBN 3540363238, Springer Series in Optical Sciences Vol. 126, 2006.
Keywords: quantum well infrared photodetector, QWIP, focal plane array, thermal imaging, noise-equivalent temperature difference, GaAs/AlGaAs
  • Invited lecture (Conferences)
    March Meeting of the American Physical Society, 05.-09.03.2007, Denver, CO, USA

Publ.-Id: 9572 - Permalink

Four-Quark Condensates in Nucleon QCD Sum Rules
Thomas, R.; Hilger, T.; Kämpfer, B.;
The in-medium behaviour of the nucleon spectral density including self-energies is revisited within the framework of QCD sum rules. Special emphasis is given to the density dependence of four-quark condensates. A complete catalog of four-quark condensates is presented and relations among them are derived. Generic differences of such four-quark condensates occuring in QCD sum rules for light baryons and light vector mesons are discussed.

Publ.-Id: 9571 - Permalink

An analytical solution for a simple time dependent neutron transport problem with external source
Merk, B.;
An analytical solution for the startup of an external source in a homogeneous subcritical reactor problem is developed. The problem is described through an approximation of the Boltzmann Transport equation, the Telegrapher's or time dependent P1 equation. The analytical solution to the problem is expressed in terms of a Green's function.
Keywords: Telegrapher's equation, Neutron Transport, Space-Time Dependent Transport
  • Contribution to proceedings
    20th International Conference on Transport Theory, 22.-28.07.07, Obninsk, Russia
    Book of Abstracts
  • Lecture (Conference)
    20th International Conference on Transport Theory, 22.-28.07.07, Obninsk, Russia

Publ.-Id: 9570 - Permalink

High resolution gamma ray tomography scanner for flow measurement and non-destructive testing applications
Hampel, U.; Bieberle, A.; Hoppe, D.; Kronenberg, J.; Schleicher, E.; Sühnel, T.; Zimmermann, F.; Zippe, C.;
We report on the development of a high resolution gamma ray tomography scanner that is operated with a Cs-137 isotopic source at 662 keV gamma photon energy and achieves a spatial image resolution of 0.2 lp/mm at 10% MTF for non-collimated detectors. It is primarily intended for the scientific study of flow regimes and phase fraction distributions in fuel element assemblies, chemical reactors, pipelines and hydrodynamic machines. Furthermore, it is applicable to non-destructive testing of larger radiologically dense objects. The radiation detector is based on advanced avalanche photo diode technology in conjunction with LYSO scintillation crystals. The detector arc comprises 320 single detector elements which are operated in pulse counting mode. For measurements at fixed vessels or plant components we built a CT scanner gantry that comprises rotational and translational stages, power supply via slip rings and data communication to the measurement PC via wireless LAN.
Keywords: Gamma ray tomography, gamma ray detector

Publ.-Id: 9567 - Permalink

The suppression of temperature fluctuations by a rotating magnetic field in a high aspect ratio Czochralski configuration
Grants, I.; Gerbeth, G.;
We demonstrate experimentally in a low temperature model that a rotating magnetic field (RMF) has the potential to stabilize the inverse temperature gradient in a medium scale Czochralski facility with a high initial melt level. This stabilization occurs as a result of a flow transition from large scale buoyancy driven to small scale magnetically driven turbulence. The dependency of the required field strength is found vs.\ the imposed temperature drop for an at least 10 times higher Grashof number than in earlier experiments. The observed scaling agrees well with previous results. It is observed that the flow transition becomes even more pronounced, i.e. occurs in a more narrow range of the magnetic forcing, as the Grashof number is increased. The influence of the RMF frequency is investigated. It is found that an increasing frequency of the RMF gradually eliminates the stabilizing effect. The optimum dimensionless frequency is found minimizing the required strength of the RMF. The characteristic azimuthal velocity of the flow is measured by the temperature correlation technique.
  • Journal of Crystal Growth 308(2007)2, 290-296

Publ.-Id: 9566 - Permalink

Thermophysical properties of Nd-, Er-, YNi- alloys
Plevachuk, Y.; Sklyarchuk, V.; Hermann, R.; Gerbeth, G.;
Nd-Fe-B alloys are widely used in many technical applications due to their excellent permanent magnetic properties. YNi2B2C intermetallic compounds own much attention because of the coexistence of superconductivity and magnetic ordering phenomena. Er2PdSi3 alloys with hexagonal AlB2-type crystallographic structure are of special interest because of their complex magnetic ordering, Kondo and heavy fermion behaviour. The thermophysical properties (electrical conductivity, thermoelectric power, thermal conductivity and viscosity) of these liquid multicomponent intermetallic alloys have been measured in order to supply necessary information for crystal growth and casting processes. Good reproducibility of the results has been obtained.
  • International Journal of Materials Research 99(2008), 261-264

Publ.-Id: 9565 - Permalink

Thermal expansion of single-crystalline HoNi2B2C
Schneider, M.; Gladun, A.; Kreyssig, A.; Wosnitza, J.; Souptel, D.; Behr, G.;
The thermal expansion a has been measured for single-crystalline HoNi2B2C in the range between 2 and 200 K. At low temperatures, a is dominated by magnetic contributions leading to a strongly anisotropic behaviour with different signs for the expansion coefficients near the antiferromagnetic phase transition. Analysing the magnetic and lattice contributions of a well above this temperature, a nearly isotropic behaviour of the latter one can be deduced. Using the Ehrenfest relation, a relatively weak pressure dependence of the superconducting transition temperature of dTc=dp ¼ 0:1K=GPa was determined for pressure applied along the c direction which points to a rather small pressure-induced lattice stiffening. The ratio between expansion coefficient and specific-heat features large values at the onset of magnetic order.
  • Journal of Magnetism and Magnetic Materials 311(2007), 489-493

Publ.-Id: 9564 - Permalink

Structure and dielectric function of two- and single-domain ZnO epitaxial films
Vinnichenko, M.; Shevchenko, N.; Rogozin, A.; Grötzschel, R.; Mücklich, A.; Kolitsch, A.; Möller, W.;
The differences between two- and single-domain ZnO epitaxial films, grown by reactive pulsed magnetron sputtering, have been studied with respect to their texture development and x-ray coherence length behavior at various substrate temperatures and oxygen partial pressures. The film in-plane ordering depends on the surface pretreatment of the sapphire substrate. After pretreatment in an oxygen radio-frequency plasma, single-domain films form even at a substrate temperature of 100 degrees C in a wide range of oxygen pressures, and at a growth rate up to 1.2 nm/s. The single-domain films show a linear dependence of the x-ray coherence length on the substrate temperature, while a steplike dependence is characteristic of the two-domain films. The ZnO complex dielectric function was obtained using a parametrized semiconductor oscillator model for spectroscopic ellipsometry data analysis. For the films grown at 550 degrees C, the band gap of 3.29 +/- 0.01 eV is independent of the type of in-plane ordering and variation of the texture. The oscillator broadening correlates with the width of (0002) diffraction peak rocking curve. Both parameters increase at high oxygen pressure and low substrate temperature, which is attributed to a higher defect (dislocation) density.
Keywords: ZnO, reactive pulsed magnetron sputtering, epitaxial growth, in-plane ordering, texture, spectroscopic ellipsometry, dielectric function

Publ.-Id: 9563 - Permalink

Novel supported Pd hydrogenation bionanocatalyst for hybrid homogeneous/heterogeneous catalysis
Creamer, N.; Mikheenko, I.; Yong, P.; Deplanche, K.; Sanyahumbi, D.; Wood, J.; Pollmann, K.; Merroun, M.; Selenska-Pobell, S.; Macaskie, L.;
Homogeneous and heterogeneous catalysis approaches to hydrogenation have different advantages and disadvantages and hybrid approaches are sought to maximise the advantages of both. Bacterial cells, of length 1-2 microns, present an economical alternative to conventional micro-scale supports such as graphite and alumina. Certain strains of bacteria can reduce soluble Pd(II), from stock solutions or acid extracts of spent catalysts, forming nanocrystals of Pd which are supported within the bacterial cell surface layers. The biologically-supported nano-Pd contains particles of size ~ 5nm and below, as determined using magnetic measurements (SQUID) and EXAFS. Bio-nano-Pd supported on exemplar Gram negative and Gram positive bacterial types catalysed the hydrogenation of itaconic acid (initial rates 1.1 and 1.2 × 10-4 mol gPd-1 s-1 ) comparing well with commercial 5% Pd-graphite (1.3 × 10-4 mol gPd-1 s-1).
Keywords: Bacillus sphaericus Desulfovibrio desulfuricans, heterogeneous catalyst, hydrogenation, itaconic acid, palladium

Publ.-Id: 9562 - Permalink

A new FEFF-based wavelet for EXAFS data analysis
Funke, H.; Chukalina, M.; Scheinost, A.;
A new mother wavelet function for extended X-ray absorption fine-structure (EXAFS) data analysis has been designed, combining a model EXAFS function derived from the ab initio EXAFS code FEFF8.20 and the complex Morlet wavelet. This new FEFF–Morlet mother wavelet routine allows the generation of wavelets well adapted to specific EXAFS problems. A substantial gain in resolution of the wavelet ridges in k and r space is achieved. The method is applied to a structural problem of Zn–Al double-layer hydroxides, demonstrating unequivocally the homogeneity of the metal cation distribution in the hydroxide layers.
Keywords: EXAFS; wavelet transform; data evaluation; layered double hydroxides

Publ.-Id: 9561 - Permalink

Interactions of U(VI) with members of a microbial consortium recovered from a uranium mining waste pile
Reitz, T.; Geissler, A.; Merroun, M.; Selenska-Pobell, S.;
Treatments of a soil sample from a uranium mining waste pile with uranyl nitrate led to a shifting in the crenarchaeal populations from subgroup 1.1a to 1.1b. Efforts to culture members of these Crenarchaeota resulted in an enrichment of a mixed microbial consortium consisting of representatives of 1.1b Crenarchaeota and Firmicutes.
In this study interactions of U(VI) with a pure culture of Paenibacillus sp. JG35+U4-B1 isolated from the mentioned consortium were studied by using a combination of wet chemistry and microscopic methods. Preliminary analyses on U sorption showed that the Paenibacillus strain studied accumulated up to 85 mg U/g dry biomass from a solution with an initial uranium concentration of 120 mg U/l. Live/Dead cell staining indicated that less than 10% of the U-treated cells were viable. Transmission electron microscope (TEM) analyses showed that the cells of the isolated strain accumulated uranium intracellularly as needle-like fibrils (Fig. 1A), and also at the cell surface (Fig. 2A). Energy dispersive X-ray (EDX) analysis of these U accumulates demonstrated the presence of U and P peaks (Figs. 1B and 2B) indicating that in both cases the phosphate groups are, probably, the main functional binding sites for U(VI).
  • Lecture (Conference)
    Journées des Actinides 2007, 24.-27.03.2007, Sesimbra, Portugal
  • Contribution to proceedings
    37ièmes Journées des Actinides, 24.-27.03.2007, Sesimbra, Portugal
    Programme and Abstracts, 56

Publ.-Id: 9560 - Permalink

Deviations from Vegard's rule in Al1-xInxN (0001) alloy thin films grown by magnetron sputter epitaxy
Seppänen, T.; Hultman, L.; Birch, J.; Beckers, M.; Kreißig, U.;
Al1−xInxN (0001) thin films of the pseudobinary AlN–InN system were grown epitaxially onto (111)-oriented MgO wafers with seed layers of Ti1−yZryN by dual direct current magnetron
sputtering under ultrahigh vacuum conditions. The relaxed film c-axis lattice parameters determined
by x-ray diffraction were studied as a function of composition in the range of 0.07 < x < 0.82 measured by Rutherford backscattering spectrometry. We find a relative deviation by as much as
37% from the linear dependency described by Vegard’s rule for the lattice parameter versus film
composition. The highest relative deviations were found at low InN mole fractions, while the largest
absolute deviation was found at x=0.63. This shows that Vegard’s rule is not directly applicable to
determine the compositions in the wurtzite Al1−xInxN system. © 2007 American Institute of Physics.
[DOI: 10.1063/1.2450675 ]
  • Journal of Applied Physics 101(2007), 043519

Publ.-Id: 9559 - Permalink

Use of metal plasma immersion ion implantation and deposition for preparation of hemocompatible titanium-based coatings
in Russian
Tsyganov, I. A.; Mashina, A. I.; Richter, E.; Maitz, M. F.; Rustichelli, F.;
Metal plasma immersion ion implantation and deposition (MePIIID) provides a useful technique to control composition and structure of metal-based thin films. By this method Ti-based coatings such as Ti nitrides, oxides or oxynitrides are formed on the objects with an irregular shape from a plasma produced by cathodic arc evaporation of Ti under addition of nitrogen and/or oxygen to the ambient near the substrate. Coating with Ti oxide or Ti-nitride-oxide (TiNOX) is a promising method to improve the blood compatibility of materials for use as medical implants.
Keywords: Metal plasma immersion ion implantation and deposition (MePIIID) , Titanium oxynitride, Phase composition, Hemocompatibility
  • Contribution to proceedings
    International Conference on Advanced Technologies and Equipment in Mechanical Engineering and Metallurgy, 11.-12.05.2006, Lipetsk, Russia

Publ.-Id: 9558 - Permalink

Correlation between physical surface properties and blood compatibility of titanium-based coatings prepared by metal plasma immersion ion implantation and deposition
Tsyganov, I. A.; Maitz, M. F.; Richter, E.; Reuther, H.; Mashina, A. I.;
In this work layers of the ternary system Ti-N-O were produced in a wide range of composition by MePIIID and their structure, physicochemical properties and blood compatibility were investigated. In the dependence on the relation of the reactive gases partial pressure Ti nitride and oxide have been produced as crystalline phases. For pure N2 flow and for the relationship p(O2)/p(N2) = 1/3 XRD patterns are typical for the fcc structure of TiN. For p(N2) = p(O2) a two-phase system of fcc TiN and fcc TiO has been found. Further enhancing O2 flow leads to the beginning formation of rutile and anatase modifications of TiO2. For p(O2)/p(N2) = 1/3 up to p(N2) = p(O2) in addition to the phases detected by the XRD the amorphous TiO2 phase with nitrogen substitution has been found.
The polar component of the surface energy and the hydrophobicity of the surface show a dependence on the composition of the coating. The crystalline TiO2 surface was the most hydrophobic, but also the crystalline TiN phase showed a slightly higher hydrophobicity than the mainly amorphous mixed phases.
The clotting time of blood plasma, the thrombocyte adhesion and activation as well as the fibrinogen adsorption on the surface were investigated to study the correlation between structure of the coating and blood compatibility. The blood compatibility of Ti oxide can be improved by the addition of N into the layer. TiN and oxynitrides show the longest clotting time in comparison with TiO2 (rutile). The lowest platelet activation was found on TiN and oxynitrides in comparison with rutile. The thrombocyte adhesion and fibrinogen adsorption were lower for TiNxOy than for TiO2. This behavior is correlated with the decreasing of contact angle and is inversely correlated with the increasing of surface energy (especially with its polar component).
In this study the blood platelet adhesion on the surfaces in general was very low, usually below 3% of the whole amount of blood platelets present in the plasma sample. It renders this class of surfaces a promising candidate for good blood compatibility and low clotting activation.
Keywords: Titanium oxynitride, Metal plasma immersion ion implantation and deposition (MePIIID), Filtered arc, Phase formation, Hemocompatibility
  • Lecture (Conference)
    15th International Conference on Ion Beam Modification of Materials, 18.-22.09.2006, Taormina, Italy

Publ.-Id: 9557 - Permalink

Photon scattering experiments on the quasistable, odd-odd mass nucleus 176Lu
Walter, S.; Stedile, F.; Carroll, J. J.; Fransen, C.; Friessner, G.; Hollmann, N.; von Garrel, H.; Jolie, J.; Karg, O.; Käppeler, F.; Kneissl, U.; Kohstall, C.; von Neumann-Cosel, P.; Linnemann, A.; Mücher, D.; Pietralla, N.; Pitz, H. H.; Rusev, G.; Scheck, M.; Scholl, C.; Schwengner, R.; Werner, V.; Wisshak, K.;
The quasistable odd-odd-mass nucleus 176 Lu is of special interest in nuclear structure physics and, above all, in nuclear astrophysics. Systematic photon scattering experiments have been performed at the bremsstrahlung facility of the 4.3-MV Stuttgart Dynamitron accelerator with bremsstrahlung end-point energies of 2.3 and 3.1 MeV to determine the low-energy dipole strength distribution in the s-only isotope 176 Lu. The main goal was to pin down possible intermediate states (IS) for the photoactivation of the short-lived 123-keV isomer, which is the key process determining the effective lifetime of 176 Lu in a stellar photon bath and hence for the use of this isotope as a stellar chronometer. Using an enriched sample, 29 transitions ascribed to 176 Lu were detected below 2.9-MeV excitation energy. The corresponding excitation strengths were determined. For the previously proposed lowest IS at 839 keV, an upper limit for the excitation strength corresponding to a lifetime of 1.5 ps can be given. Astrophysical consequences, also in view of new Stuttgart photoactivation experiments, are discussed. The fragmentation of the dipole strength is compared to those in neighboring even-even and odd-even nuclei.
Keywords: Nuclear Structure, Nuclear Astrophysics, Photon scattering, Photoactivation.

Publ.-Id: 9556 - Permalink

DYN3D/ATHLET and ANSYS CFX calculations of the OECD VVER-1000 coolant transient benchmark
Kliem, S.; Höhne, T.; Rohde, U.; Kozmenkov, Y.;
Plant-measured data provided within the specification of the OECD/NEA VVER-1000 coolant transient benchmark (V1000CT) were used to validate the DYN3D/ATHLET coupled code system. Phase 1 of the benchmark (V1000CT-1) refers to the main coolant pump (MCP) switching-on experiment conducted in the frame of the plant-commissioning activities at the NPP Kozloduy-6 in Bulgaria.
The transient is characterized by a rapid increase in the primary coolant flow through the core and, as a consequence, a decrease of the space-dependent core inlet temperature. A DYN3D/ATHLET model of the primary and secondary circuit of the plant including MCP characteristics, boundary conditions and benchmark-specified nuclear data library was created. For an adequate modeling of the redistribution of the coolant flow in the reactor pressure vessel (RPV) during the transient a simplified mixing model for the DYN3D/ATHLET code was developed and validated against a computational fluid dynamics (CFD) calculation with the code ANSYS CFX. The results of the coupled code calculation are in good agreement with the available experimental data. The discrepancies between experimental data and the results of the calculation do not exceed the accuracy of the measurement data. This concerns the initial steady state data as well as the time histories during the transient.
The above mentioned CFD model was used also in the second phase of the benchmark (V1000CT-2). In this part of the benchmark, post-test calculations of coolant mixing experiments at the same NPP are carried out. The comparison is made with assembly-wise mixing coefficients being the results of the experiments. The numerical grid model contains 4.7*106 tetrahedral elements. Different advanced turbulence models were used in the numerical simulations. The best agreement with the experimental data at the core inlet shows the Detached-Eddy-Simulation. Strong fluctuations occur in the downcomer of the RPV. The results show a clear sector formation of the affected loop in the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.3%.
  • Contribution to proceedings
    5th International conference on safety assurance of NPP with WWER, 29.05.-01.06.2007, Podolsk, Russia
    Proceedings of the 5th International conference on safety assurance of NPP with WWER
  • Lecture (Conference)
    5th International conference on safety assurance of NPP with WWER, 29.05.-01.06.2007, Podolsk, Russia

Publ.-Id: 9555 - Permalink

A Comparative Study of U(VI) and U(V) Carbonato Complexes in Aqueous Solution
Ikeda, A.; Hennig, C.; Tsushima, S.; Takao, K.; Ikeda, Y.; Scheinost, A.; Bernhard, G.;
Electrochemical, complexation, and electronic properties of uranyl(VI)- and uranyl(V) carbonato complexes in aqueous Na2CO3 solution have been investigated to define the appropriate conditions for preparing pure uranyl(V) samples and to understand the difference in coordination character between UO22+ and UO2+. Cyclic voltammetry (CV) using three different working electrodes of Pt, Au, and glassy carbon has suggested that the electrochemical reaction of uranyl(VI) carbonate species proceeds quasireversibly. Electrolysis of UO22+ has been performed in the Na2CO3 solutions more than 0.8 M with the limited pH range of 11.7 < pH < 12.0 using a Pt mesh electrode. It produces high purity of uranyl(V) carbonate solution that has been confirmed to be stable at least for two weeks in a sealed glass cuvette. EXAFS measurements revealed the structural arrangement of uranyl(VI)- and uranyl(V) tricarbonato complexes, [UO2(CO3)3]n- (n = 4 for uranyl(VI), 5 for uranyl(V)). The bond distances of U-Oax, U-Oeq, U-C, and U-Odist are determined to be 1.81, 2.44, 2.92, and 4.17 Å for the uranyl(VI) complex, and 1.91, 2.50, 2.93, and 4.23 Å for the uranyl(V) complex, respectively. The validity of the structural parameters obtained from EXAFS has been supported by quantum chemical calculations for the uranyl(VI) complex. The uranium LI- and LIII-edge XANES spectra have been interpreted in terms of electron transitions and multiple scattering features.
Keywords: uranium, uranyl, carbonate, solution, U(VI), U(V), electrochemistry, cyclic voltammetry, UV-visible absorption, XAFS, EXAFS, XANES, complex, coordination


Publ.-Id: 9553 - Permalink

Selbstorganisierende bakterielle Hüllproteine als Grundlage für die Entwicklung neuartiger Nanomaterialien
Pollmann, K.; Raff, J.; Merroun, M.; Selenska-Pobell, S.; Herrmannsdörfer, T.;
Die Kombination von Bio- und Nanotechnologie eröffnet ein großes Potential für die Entwicklung neuer Materialien. Da sich Nanopartikel in ihren chemischen und physikalischen Eigenschaften oft grundlegend von ihren Ausgangsmaterialien unterscheiden, sind sie von großem Interesse für die Entwicklung neuer Materialien und Werkstoffe wie Katalysatoren oder Biosensoren, in der Nanoelektronik, in der optischen Industrie, Halbleiterindustrie, aber auch für biomedizinische Anwendungen.
Eine aussichtsreiche, unkomplizierte Alternative zu konventionellen Methoden bei der Herstellung regelmäßig angeordneter Nanopartikel ist die Verwendung von selbstorganisierenden biologischen Trägermaterialien als Matrix. Besonders aussichtsreiche Biomoleküle sind hierbei die selbstorganisierenden Hüllproteine (S-Layer) von Bakterien.

In einem interdisziplinären Ansatz werden neuartige Materialien auf der Basis von Nanopartikeln aus metallischen, magnetischen und halbleitenden Materialien entwickelt. Für ihre Synthese werden verschiedene bakterielle Hüllproteine (S-Layer) als biologische Trägermaterialien (sogen. Template) verwendet. Diese bestehen meist aus Proteinmonomeren, welche nach ihrer Sekretion an der Zelloberfläche regelmäßige Gitterstrukturen unterschiedlicher Symmetrie ausbilden. Für ihre technische Nutzung ist es bemerkenswert, dass die isolierten Monomere ihre Eigenschaft der Selbstorganisation beibehalten und an Grenzflächen parakristalline Monolagen bilden. Die regelmäßig angeordneten Poren dieser Proteine bieten ideale Strukturen für die Bindung von Metallkomplexen und die Synthese von hochgeordneten Nanopartikeln definierter Größe. Die Synthese erfolgt dabei zweistufig: Nach der Anbindung der Metallkomplexe aus einer wässerigen Metallsalzlösung und anschließender Dialyse erfolgt eine Reduktion der Komplexe durch die Zugabe eines Reduktionsmittels. Auf diese Weise konnten bislang erfolgreich Pd-, Pt-, Au- und Pb-Nanopartikel einer einheitlichen Größe hergestellt werden, deren chemische und magnetische Eigenschaften sich z.T. erheblich von denen der jeweiligen makroskopischen Materialien unterscheiden. Durch die Beschichtung verschiedener technisch relevanter Materialien wie Keramiken, Zeolithe, Aluminiumoxid, Siliziumdioxid und Kohlenstoff mit den Proteinen sollen neuartige Materialien entwickelt werden, die in der Industrie Verwendung finden können.
  • Poster
    6. Präsentation BMBF BioFuture, 29.-30.01.2007, Berlin, Deutschland

Publ.-Id: 9551 - Permalink

DNA-wrapped Carbon Nanotubes
Enyashin, A. N.; Gemming, S.; Seifert, G.;
The stability and electronic properties of the associates of the single-walled carbon nanotubes wrapped by homopolymeric single-stranded DNA molecules (CNT@DNA) are considered using a quantum mechanical density-functional tight-binding method (DFTB). A phenomenological model of the CNT@DNA formation energy depending on the nanotube radii is developed, which shows that the decoration of a CNT by a few DNA chains leads to a high water solubility of CNT@DNA. Pyrimidine-based DNAs are found to be more effective to wrap the CNTs than other DNAs. The densities-of-states of the CNT@DNA complexes are close to the superposition of those of the “free” components with some additional states below Fermi level. The band gap in a hybrid CNT@DNA system is determined by the competition between the Fermi levels of the “free” DNA and CNT. In a few specific cases a considerable charge transfer from the DNA to the CNT was observed, combined with an additional gain in the CNT@DNA formation energy.
Keywords: Nanotube, CNT, DNA, DFT, tight-binding

Publ.-Id: 9550 - Permalink

Self-assembly of Mo6S8 Clusters on the Au(111) Surface
Popov, I.; Kunze, T.; Gemming, S.; Seifert, G.;
The preferred adsorption sites and the propensity for a self-organised growth of the molybdenum sulfide cluster Mo6S8 on the Au(111) surface are investigated by density-functional band-structure calculations with pseudopotentials and a plane wave basis set. The quasi-cubic cluster preferentially adsorbs via a face and remains structurally intact. It experiences a strong, mostly non-ionic attraction to the surface at several quasi-isoenergetic adsorption positions. A scan of the potential energy surface exhibits only small barriers between adjacent strong adsorption sites. Hence, the cluster may move in a potential well with degenerate local energy minima at room temperature. The analysis of the electronic structure reveals a negligible electron transfer and S-Au hybridised states, which indicate that the luster-surface interaction is dominated by S-Au bonds, with minor contributions from the Mo atom in the surface vicinity. All results indicate that Mo6S8 clusters on the Au(111) surface can undergo a template-mediated self-assembly to an ordered inorganic monolayer, which is still redox active and may be employed as surface-active agent in the integration of noble metal and ionic or biological components within nano-devices. Therefore, a classical potential model was developed on the basis of the DFT data, which allows to study larger cluster assemblies on the Au(111).
Keywords: adsorption, self-assembly, metal surface, chalcogenide cluster

Publ.-Id: 9549 - Permalink

High Temperature Plasma Immersion Ion Implantation
Ueda, M.; Silva, M. M.; Lepienski, C. M.; Soares, P. C. J.; Gonçalves, J. A. N.; Reuther, H.;
We have performed high temperature nitrogen plasma immersion ion implantation (PIII) of Ti6Al4V by heating the samples for up to 800 °C, using tungsten filaments inside the sample holder. Ion implantation was done with the high voltage pulser at 5 kV, 40 μs duration and 400 Hz frequency, and a nitrogen glow discharge as the plasma source. Nanoindentation analysis of the treated surface indicated an improvement of 5 times in hardness for PIII treatment of 120 min. X-ray diffraction indicated the formation of Ti2N. Auger Electron Spectroscopy (AES) showed that the peak concentration is greater than 30% in the implanted nitrogen with the maximum penetration of 150 nm for the sample treated during 120 min.
  • Surface & Coatings Technology 201(2007), 4953-4956

Publ.-Id: 9548 - Permalink

Plasma Immersion Ion Implantation in Arc and Glow Discharge Plasmas Submitted to Low Magnetic Fields
Tan, I. H.; Ueda, M.; Oliveira, R. M.; Dallaqua, R. S.; Reuther, H.;
The influence of low magnetic fields (B≤130 G) on the plasma parameters of a DC nitrogen glow discharge is investigated with a double Langmuir probe. The discharge was optimized for maximum plasma density for different values of a magnetic field, and a condition was found in which density was enhanced by an order of magnitude. In this condition partial suppression of secondary electron emission was obtained during ion implantation experiments. Silicon samples implanted in this optimum density condition showed larger retained dose and penetration depth compared with samples treated in non-magnetized plasmas as shown by Auger electron spectroscopy depth profile analysis. These results were compared with previous similar experiments in much denser magnetized vacuum arc plasmas, in which total suppression of secondary electrons (SE) was obtained, corroborating the theory that the maintenance of a virtual cathode for SE suppression is favored by higher plasma density. Silicon samples implanted in magnetized magnesium plasmas exhibited much larger doses (as expected) and penetration depths (not so obvious) than the ones treated in non-magnetized plasmas. The deeper ion penetration obtained in magnetized gaseous and vacuum arc plasmas indicates that an enhanced diffusion may be taking place induced by the large ion bombardment in dense plasmas.
  • Surface & Coatings Technology 201(2007), 4826-4831

Publ.-Id: 9547 - Permalink

Structure and Speciation of U(VI) sulfate in aqueous solution
Hennig, C.; Schmeide, K.; Brendler, V.; Moll, H.; Tsushima, S.; Ikeda, A.; Scheinost, A. C.; Skanthakumar, S.; Wilson, R.; Soderholm, L.; Servaes, K.; van Deun, R.; Görller-Walrand, C.;
The local structure of U(VI) sulfato complexes in aqueous solution has been investigated by U L3-edge EXAFS, high energy x-ray scattering (HEXS), x-ray diffraction (XRD) and UV-Vis spectroscopy using samples of 50 mM U(VI) and total sulfate concentrations, 0.05 ≤ [SO42-] ≤ 3 M at pH 1 and 2. At low [SO42-]/[UO22+] ratio (~1), where the UO2SO4(aq) species prevails, the sulfate coordinates in a monodentate fashion. At high [SO42-]/[UO22+] ratio, where UO2(SO4)22- species prevails, bidentate sulfate coordination becomes dominant. In all cases, the equatorial coordination number NOeq, remains 5. According to the bond-valence rule this is in line with the average bond distance between U(VI) and oxygen of ~2.42 Å observed by EXAFS and HEXS. The bidentate sulfate reaches a maximal coordination number NSbid of 2 for a [SO42-]/[UO22+] ratio of 60, hence, related with the structure of [UO2(SO4)2bidH2O]2-. The upper limit of NSbid allows to rule out the existence of a species with three monodentate coordinated sulfate groups, [UO2(SO4)3bid]4-. This observation has been confirmed by MCD measurements. Therefore, the species UO2(SO4)34- might be related with the structure [UO2(SO4)2bid(SO4)mon]4-. The existence of two bidentate coordinated sulfate groups has up to now never been observed in crystal structures. The evaporation of the above mentioned solutions with several [SO42-]/[UO22+] ratios resulted always in crystal structures where the sulfate group acts monodentate-bridging. The coordination of U(VI) by two bidentate coordinated sulfate groups might be restricted to solution species. This observation indicates a structural re-arrangement of SO42- during the crystallization. The potential structures in solution were modeled by DFT calculation and compared with the experimental data from EXAFS and HEXS.
Keywords: Uranyl sulfate, U(VI), solution, speciation, structure, EXAFS, XRD, HEXS, MCD, UV-vis
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 36
  • Lecture (Conference)
    Migration 2007, 26.-31.08.2007, München, Germany

Publ.-Id: 9546 - Permalink

Hydrolysis of U(VI). An infrared spectroscopic verification of uranyl species
Müller, K.; Foerstendorf, H.;
Detailed information about aqueous species of uranium(VI) is an indispensable prerequisite for a reliable assessment of its migration in the environment. Up to now the identification of distinct U(VI) species in aqueous solution was mostly accomplished by thermodynamical calculations based on non-structural experiments such as potentiometric titration [1] and by spectroscopic investigations of UO22+ solutions in the upper millimolar range at low pH values [2,3].
Attenuated total reflectance (ATR)-FT-IR spectroscopy has shown to be a useful tool for investigations of molecule complexes formed during sorption processes in aqueous solutions [4]. In this study we focus on the hydrolysis reactions of U(VI) under atmospheric conditions throughout a wide pH range (pH 2 – 9).
First, we investigated diluted uranyl(VI) solutions. Due to the low concentration ([UO22+] = 20 µM) the acquisition of infrared spectra of UO22+ solutions have become feasible even at high pH values avoiding the precipitation of solid uranyl phases. Our results clearly demonstrate that already at pH values < 4 not yet identified hydroxo uranyl complexes considerably contribute to the infrared spectra which is in contrast to recent thermodynamical calculations. It is also quite conceivable that we identified new U(VI) species in aqueous solutions. At higher pH values (> 7) the spectra indicate the formation of another uranyl species possibly with contributions of atmospheric carbonate anions which can be derived from model spectra of the pure UO2(CO3)34− complex.
In a second series of experiments we studied the hydroxo species of uranium(VI) at different concentrations (5 mM – 5 µM UO22+) at a constant pH value (pH 4). Upon lowering the concentration below 500 µM the fraction of the uncomplexed uranyl species is significantly reduced and can not be detected at a concentration of 50 µM any longer. Simultaneously two other hydroxo complexes are obviously formed at these lower concentrations.
A critical evaluation of literature data and the obtained spectral data constitute a reference to a modified speciation of U(VI) in particular at lower pH values and at concentrations in the micromolar range.

[1] R. Guillaumont et al. (OECD-NEA TDB), Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium, Elsevier, 2003.
[2] H. Moll et al., Radiochim. Acta 88, 411 (2000).
[3] F. Quilès and A. Burneau, Vib. Spec. 23, 231 (2000).
[4] G. Lefèvre, Adv. Colloid Interface Sci. 107, 109 (2004).
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 187-188
  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany

Publ.-Id: 9545 - Permalink

A bis(2-pyridylmethyl) derivative of 1,4,7-triazacyclononane as highly hydrophilic chelation agent for copper
Gasser, G.; Tijoe, L.; Belousoff, M. J.; Spiccia, L.; Graham, B.; Juran, S.; Walther, M.; Künstler, J.-U.; Bergmann, R.; Stephan, H.;
Highly thermodynamically stable Cu(II) complexes are required for the development of new copper(II) target-specific radiopharmaceuticals. In this perspective, azamacrocycle derivatives [1], and in particular a 1,4,7-triazacyclononane derivative containing two pyridine pendant arms [2] is a potentially promising ligand candidate. The further addition of a carboxylic group to this chelating agent could provide an attractive lead for the labelling of biomolecules with copper radionuclides.

A new ligand, 2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]acetic acid (1), has been synthesised, and the X-ray structure of a corresponding copper(II)-complex determined. A bioconjugate (2) was obtained by coupling a modified bombesin derivative [3] to 1 (HBTU, DIPEA, DMF, r.t.). 2 was purified by semi-preparative HPLC. The free ligand 1 and the bioconjugate 2 were labelled with 64Cu. To 100 µl of ligand solution (0.0001 M ligand dissolved in 0.05 M NH4OAc), 200 kBq of 64CuCl2 was added. Labelling yields were studied by TLC.

Results and Discussion:
The structure of [1-Cu-complex]2+ was solved by X-ray single-crystal diffraction and indicates that the ligand is able to bind Cu2+ in a hexacoordinate manner. A high complex stability (logK1 > 20) was determined. The bioconjugation of 1 to a bombesin derivative was successfully achieved via amide coupling to give 2. The free ligand 1 and the bioconjugate 2 were labelled with 64Cu and the resulting complexes were found to be stable in the presence of a large excess of competing ligands such as cyclam and glutathione as well as in rat plasma. These 64Cu complexes are highly hydrophilic (logDo/w < -2.3).

A bis(2-pyridylmethyl) derivative of 1,4,7-triazacyclononane 1 and its bombesin bioconjugate 2 can readily form 64Cu complexes with high stability. The bifunctional chelating agent 1 may be an attractive candidate for developing new copper radiopharmaceuticals. Preliminary biodistribution studies of 64Cu complexes of 2 are currently underway.

[1] K. P. Guerra et al., Dalton Trans., 2006, 4124-4133.
[2] G. A. McLachlan et al., Inorg. Chem. 1994, 33, 4663-4668.
[3] E. Garcia Garayoa et al., Quart. J. Nucl. Med. Molec. Imaging, 2006, 50, 15-16.
  • Poster
    17th International Symposium on Radiopharmaceutical Sciences, 30.04.-04.05.2007, Aachen, Deutschland
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 50(2007)Suppl. 1, S230

Publ.-Id: 9544 - Permalink

Binding properties of a phosphonate substituted clip towards nucleosides
Raditzky, B.; Stephan, H.; Weiß, S.; Geipel, G.; Polkowska, J.; Klärner, F.-G.;
Molecular recognition and self-assembly, based on weak non-covalent interactions, are significant processes in chemical and biological systems [1], e.g. in enzyme-substrate binding or formation of protein complexes. So, the development of efficient synthetic receptors with the ability to bind substrates selectively is important. The water-soluble naphthalene clip with substituted phosphonate groups (Fig. 1) offers electron-rich side walls, which are suitable to bind electron-poor guests [2]. The complexation behavior of this clip toward nucleosides has been studied by time resolved laser fluorescence spectroscopy with ultrafast pulses (fs-TRLFS).

[1] Vögtle, F. (1997) Supramolekulare Chemie, Teubner Verlag, Stuttgart.
[2] Jasper, C. et al. (2002) Angew. Chem. 114, 1411-1415.
  • Poster
    COST D31 3nd Workshop, 28.-31.03.2007, Athens, Greece

Publ.-Id: 9543 - Permalink

Toward Bio-Inspired Photoadressable Supramolecular Systems. Synthesis, Light-Emission, Dynamics, Biomedical Application
Stephan, H.;
Noncovalent intermolecular forces play a fundamental, ubiquitous role in living systems particularly in view of molecular recognition and self-organization / self-assembly. In an increasing extent the principles found in organized biological systems are utilized for the development of artificial structures which are able to mimic certain properties of the naturally occurring systems. In this context, some novel supramolecular receptors such as dendritic hosts, molecular tweezers, helical systems, and synthetic flavylium salts gain more and more importance. Fine-tuning of photochemical, photophysical and electrochemical properties of host-guest systems provide the possibility of tailoring the supramolecular reactivity opening fascinating and important development in biomedical application such as the design of novel diagnostic and therapeutic agents. This field is in its infancy, and in particular a deep understanding about binding and transport behaviour in both aqueous and mixed organic-aqueous systems must be achieved. The study of molecular recognition and self-assembly processes in the most competitive environment - the aqueous media - is still a challenge and a stimulus for the creation of novel supramolecular ensembles which possess more simple structures but similar functions as the complex biological systems.
  • Lecture (Conference)
    COST D31 3nd Workshop, 28.-31.03.2007, Athens, Greece

Publ.-Id: 9542 - Permalink

Development of a neutron time-of-flight source at the ELBE accelerator
Klug, J.; Altstadt, E.; Beckert, C.; Beyer, R.; Freiesleben, H.; Galindo, V.; Grosse, E.; Junghans, A. R.; Legrady, D.; Naumann, B.; Noack, K.; Rusev, G.; Schilling, K. D.; Schlenk, R.; Schneider, S.; Wagner, A.; Weiß, F.-P.;
The radiation source ELBE at Forschungszentrum Dresden-Rossendorf (FZD) has a superconducting linear accelerator with electron energies up to 40 MeV as a central instrument, and it will be used to produce intense neutron beams. The neutron radiator consists of a liquid lead circuit where bremsstrahlung photons generated from the electron beam produce neutrons in (gamma,n) reactions. Monte Carlo simulations with MCNP4C3/MCNP5 were performed to characterise neutron and photon intensities as well as time and energy distributions, and to optimise the neutron transport.

The short beam pulses (5 ps at FWHM) provide the basis for an excellent time resolution for neutron time-of-flight experiments, allowing an energy resolution of about 1 % with a flight path of 4 m when using a fast detector stop signal (e. g., 1 ns for 5 MeV neutrons). The neutron beam is shaped by a 2.4 m long collimator made from borated polyethylene and lead, reducing the background of scattered neutrons and of photons at the sample position. About 96 % of the neutrons at the experiment site retain their correct energy to time-of-flight correlation. The neutron flux at the sample position is calculated to be 10^7 cm^−2 s^−1. As ELBE will be able to deliver a full intensity beam with a repetition rate of 0.5 MHz, the usable neutron energy range goes from 50 keV up to 10 MeV. In this energy interval, there is a need for neutron cross section measurements relevant for the transmutation of minor actinides in nuclear waste, as well as for applications to fission and fusion reactors.

A BaF2 scintillation detector array of 42 crystals is being constructed for neutron-capture gamma-rays. The setup covers up to 96 % of the total solid angle. Simulations of gamma-ray cascades from 56Fe(n,gamma)57Fe reactions have been combined with detector simulations to characterise the response of the detector setup.
Keywords: superconducting electron accelerator; liquid-lead radiator; neutron beam; neutron time-of-flight; nToF; neutron scattering; neutron detector

Publ.-Id: 9541 - Permalink

Polarization of Human Hematopoietic Progenitors During Contact with Multipotent Mesenchymal Stromal Cells: Effects on Proliferation and Clonogenicity
Freund, D.; Bauer, N.; Boxberger, S.; Feldmann, S.; Streller, U.; Ehninger, G.; Werner, C.; Bornhäuser, M.; Oswald, J.; Corbeil, D.;
Establishment of a defined cell culture system that facilitates ex vivo expansion of isolated hematopoietic stem and progenitor cells (HSPCs) is a crucial issue in hematology and stem cell transplantation. Here we have evaluated the capacity of primary human multipotent mesenchymal stromal cells (MSCs) to support the ex vivo expansion of peripheral CD34+-enriched HSPCs. We observed that HSPCs co-cultured on MSCs showed a substantially higher total expansion rate compared to those growing without. Moreover, in addition to the expansion of
CD34+CD3133+ and CD34+CD133-cells, a third population of CD133+CD34- stem cells became detectable after expansion. Direct contact between HSPCs and the feeder layer appears beneficial for the expansion of HSPCs harboring
CD133+phenotype, i.e., CD34+CD133+ and CD3133SUP>+CD34- contrast to CD34+CD133- cells.
Interestingly, electron microscopy and immunofluorescence analyses revealed that adherent HSPCs display various morphologies; they are either round with, in some cases, the appearance of a microvillar pole or exhibit several distinct types of plasma membrane protrusions such as lamellipodium and magnupodium. CD133 is selectively concentrated therein, whereas CD34 is randomly distributed over the entire surface of HSPCs. Together, this co-culture offers a unique experimental system to further characterize the biology and role of markers of rare stem cell populations.
  • Stem Cells and Development 15(2006), 815-829

Publ.-Id: 9540 - Permalink

Development of novel nanomaterials based on self-organising bacterial S-layer proteins
Pollmann, K.; Raff, J.; Merroun, M.; Selenska-Pobell, S.; Herrmannsdörfer, T.;
Nanoparticles attract great attention for the development of new materials since their properties usually differ significantly from those of the bulk material. They play a key role in future technologies and are used for the manufacturing of novel nanocatalysts, biosensors, for biomedical applications and nanoelectronic devices. The development of cluster-assembled materials with discrete, size-selected nanoparticles is of great interest to enable the fine-tuning of the properties of the nanoparticles. The use of self-assembling biological templates which allow the synthesis of a wide range of inorganic nanocrystals is a promising approach to produce arrays of nanoparticles in a simple way.
We present a unique interdisciplinary approach to produce arrays of nanoparticles of a defined size which posses magnetic, semiconducting, or catalytic properties. In this approach the proteinaceous self-assembling bacterial surface layers (S-layers) are used as biological templates. Most of the S-layers are composed of protein monomers with the ability to self-assemble into two-dimensional arrays. The regular distributed pores of these paracrystalline arrays work as binding sites for various metals such as Pt, Pd, Au, Fe, and offer ideal structures for the formation of regular distributed nanoclusters of a defined size [1]. Such arrays of inorganic nanoparticles as hybrids with self-assembling biological molecules, which possess a high stability [2], are very attractive for technical applications such as the development of novel catalysts, biomedical applications, the programmed assembly of nanometer scale electronic devices, and optical industry.

[1] Pollmann, K., J. Raff, M. Merroun, K. Fahmy, S. Selenska-Pobell. 2006. Metal binding by bacteria from uranium mining waste piles and its technological applications. Biotechnol. Adv. 24: 58-68.
[2] Fahmy, K., M. Merroun, K. Pollmann, J. Raff, O. Savchuk, C. Hennig, S. Selenska-Pobell. 2006. Secondary structure and Pd(II) coordination in S-layer proteins from Bacillus sphaericus studied by infrared and X-ray absorption spectroscopy. Biophys. J. 91: 996-1007.
  • Lecture (Conference)
    NanoBio-Europe 2007, 13.-15.06.2007, Münster, Germany

Publ.-Id: 9539 - Permalink

Speciation of Np(V) in aqueous solution investigated by FT-IR spectroscopy.
Müller, K.; Foerstendorf, H.; Bernhard, G.;
The distribution of aqueous species of neptunium, one of the most relevant radionuclides for long-term emplacement of nuclear waste, primarily defines its geochemical reactions and migration behavior. Current knowledge about Np(V) species is mainly based on thermodynamical calculations relying on data obtained by non-structural experiments such as potentiometric titration [1]. A spectroscopic verification of these Np(V) speciations is still lacking. Furthermore, there is still considerable uncertainty about the predominating neptunyl species, whether they arise from hydrolysis or carbonate complexation.
Vibrational spectroscopy is a useful tool for the identification of different molecular species. Due to the difficulty to obtain IR spectra from aqueous solutions mainly Raman studies of high concentrated Np(V) solutions were carried out [2-4]. Attenuated Total Reflectance Fourier-transform Infrared (ATR-FTIR) spectroscopy allows the direct measurement of liquid samples and provides additional important spectral information even at low neptunyl concentrations.
In this study we investigate Np(V) hydrolysis and neptunyl carbonate complexation using ATR-FTIR spectroscopy. We focus on micromolar neptunyl concentrations and present infrared spectra recorded over a wide pH range (pH 2-10). The speciation of Np(V), i.e. its hydrolysis at lower pH (< 6) and its complexation with atmospheric carbonate at higher pH values is compared to previous thermodynamic data.

[1] R. Guillaumont et al. (OECD-NEA TDB), Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium, Elsevier, 2003.
[2] Gregoire-Kappenstein, A. C. et al., Radiochim. Acta 91, 665 (2003).
[3] Jones, L. H. et al., J. Chem. Phys. 21, 542 (1953).
[4] Madic, C. et al., Inorg. Chem. 22, 1494 (1983).
  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 180

Publ.-Id: 9538 - Permalink

Carbonate effects on surface speciation of uranyl at the ferrihydrite-water interface: New insights from advanced EXAFS data analysis
Rossberg, A.; Tsushima, S.; Ulrich, K.-U.; Scheinost, A. C.;
The assessment of uranium migration requires the proper use of geochemical specition and reactive transport models due to the complexity of reactions and phase interactions. In the past decades the main focus has shifted from improving the modelling algorithms to a proper formulation of reaction mechanisms and the validation of thermodynamic data [1]. Thermodynamic constants should only be used if the corresponding reaction mechanism is supported by structural data (spectroscopic data, or theoretical calculations) [1]. This recommendation assumes that the spectroscopic studies provide reliable structural models. However, a comparison of recent literature on U(VI)-iron(hydr)oxide sorption complexes showed that XAS data enable a variety of interpretations and structural assemblies. Most data analysis routines do not address the multivariate character of such systems. The EXAFS spectra of the aqueous system U(VI)/ferrihydrite(Fh)/carbonate show a strong dependence on pH and CO2 partial pressure (pCO2). We used advanced multi-factorial analysis such as ITFA (Iterative Target Transformation Factor Analysis) [2] for the extraction of end-member spectra from the EXAFS spectral mixtures; and MCTFA (Monte Carlo Target Transformation Factor Analysis) [3] for the 3-dimensional structure analysis of the sorption complexes. We found that the whole set of EXAFS spectra derived from the experimental system U(VI)/Fh/pH/pCO2 supports only two structurally different sorption complexes. The two isolated species are: (i) a binary inner-sphere U(VI)-Fh sorption complex in which U(VI) shares the edge of an FeO6 octahedron, and (ii) an outer-sphere U(VI)-carbonato complex. The structure of the outer-sphere complex matches the structure of the aqueous UO2(CO3)34- complex. For the 3-dimensional analysis of the UO2(CO3)34- complex we included multiple scattering calculations in the MCTFA algorithm. By this combination the radial pair distribution functions and the spatial disorder of the backscattering atoms were determined at the first time for an isolated aqueous metal complex. We compare the structure of the UO2(CO3)34- complex and the spatial atomic disorder with quantum chemical calculations. The EXAFS spectra of the binary inner-sphere complex are more difficult to interprete. A Fourier Transform (FT) peak at 2.4 Å seems to be present in many U(VI) systems and may disturb the analysis of the EXAFS data. Up to now, this feature was either neglected, or attributed to C-atoms at a radial distance of 2.9 Å. Based on this latter interpretation, ternary U(VI)-iron(hydr)oxide carbonato complexes have been proposed even at pH as low as 4.6, where carbonato complexes are highly unlikely according to thermodynamic considerations [4]. Implications for the modelling of sorption data are manyfold. For example, Lenhart et al. (1999) [5] modelled the sorption of U(VI) onto hematite under atmospheric conditions and found that their sorption edges can be explained without the inclusion of inner-sphere ternary carbonato complexes as proposed by Bargar et al. (2000) [4]. However, Lenhart et al. (1999) [5] followed the general recommendation that the reaction mechanism should be supported by structural data [1], hence included a ternary U(VI)-iron(hydr)oxide carbonato complex into their sorption model. We present a tentative structural model for the binary inner-sphere complex and discuss the origin of the FT peak at 2.4 Å.

[1] J. van der Lee, C. Lomenech, Radiochimica Acta 92, 811 (2004).
[2] A. Rossberg, T. Reich, G. Bernhard, Anal. and Bioanal. Chem. 376, 631 (2003).
[3] A. Rossberg, A. C. Scheinost, Anal. and Bioanal. Chem. 383(1), 56 (2005).
[4] J. R. Bargar, R. Reitmeyer, J. J. Lenhart, J. A. Davis, Geochim. Et Cosmochim. Acta 64, 2749
[5] J. J., Lenhart, B. D. Honeyman, Geochim. Et Cosmochim. Acta 63, 2891 (1999).
Keywords: Monte Carlo Simulation EXAFS factor analyis
  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 85

Publ.-Id: 9537 - Permalink

Microbacterium isolates fromthe vicinityofa radioactivewaste depositoryand their interactionswith uranium
Nedelkova, M.; Merroun, M.; Rossberg, A.; Hennig, C.; Selenska-Pobell, S.;
Three oligotrophic bacterial strains were cultured from the ground water of the deep-well monitoring site S15 of the Siberian radioactive waste depository Tomsk-7, Russia. They were affiliated with Actinobacteria from the genus Microbacterium. The almost fully sequenced 16S rRNA genes of two of the isolates, S15-M2 and S15-M5, were identical to those of cultured representatives of the species Microbacterium oxydans. The third isolate, S15-M4, shared 99.8% of 16S rRNA gene identity with them. The latter isolate possessed a distinct cell morphology as well as carbon source utilization pattern from the M. oxydans strains S15-M2 and S15-M5. The three isolates tolerated equal amounts of uranium, lead, copper, silver and chromium but they differed in their tolerance of cadmium and nickel. The cells of all three strains accumulated high amounts of uranium, i.e. up to 240 mgU (g dry biomass)1 in the case of M. oxydans S15-M2. X-ray absorption spectroscopy (XAS) analysis showed that this strain precipitated U(VI) at pH 4.5 as a meta-autunite-like phase. At pH 2, the uranium formed complexes with organically bound phosphate groups on the cell surface. The results of the XAS studies were consistent with those obtained by transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX).

Publ.-Id: 9536 - Permalink

Atomistic simulations of epitaxial recrystallization in 4H-SiC along the [0001] direction
Gao, F.; Zhang, Y.; Devanathan, R.; Posselt, M.; Weber, W. J.;
Molecular dynamics methods have been employed to study epitaxial recrystallization and the amorphous-to-crystalline (a–c) transition in 4H-SiC along the [0001] direction, with simulation times of up to a few hundred nanoseconds and at temperatures of 1500 and 2000 K. The results are compared with those simulated previously along the [-12-10] and [-1010] directions to investigate the anisotropies of recrystallization processes. The recovery of bond defects at the interfaces is an important process driving the initial epitaxial recrystallization of the amorphous layers. The amorphous layers with the a–c interface normal along the [0001] direction can be completely recrystallized at 2000 K, but the recrystallized region contains dislocation loops. The temperature required for complete recrystallization is in good agreement with those observed experimentally.
Keywords: Defects, Epitaxial recrystallization, Computer simulations, Silicon carbide
  • Nuclear Instruments and Methods in Physics Research B 255(2007), 136-140

Publ.-Id: 9535 - Permalink

Imaging and functional characterization of metabolic pathways of modified lipoproteins and proteins in vivo using small animal positron emission tomography (PET)
Pietzsch, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Gastvortrag am Department of Pediatrics, Division of Clinical Chemistry & Biochemistry, University of Zurich, 21.02.2007, Zürich, Schweiz

Publ.-Id: 9534 - Permalink

Rhenium cluster complexes as promising metal drugs for cancer therapeutics and diagnostics
Fedorov, V. E.; Mironov, Y.; Brylev, K.; Shestopalov, M.; Efremova, O.; Kim, S.; Spies, H.; Pietzsch, H.-J.; Stephan, H.; Röhrich, A.;
During the last years the mononuclear rhenium complexes have been studied intensively in radiopharmaceutical chemistry because of the favorable properties of 186Re and 188Re radioactive isotopes for cancer therapeutics and diagnostics. Considering that the acting element of such preparations is metal atoms, the rhenium cluster complexes may be promising metal drugs. On the other hand, many rhenium cluster complexes possessing bright red luminescence have considerable potential to be used in photodynamic therapy. Having used these two remarkable properties for medical treatment, it seems, the rhenium cluster complexes can provide synergetic therapeutic efficacy. Thus, the development of cluster rhenium chemistry and design of hybrid cluster complexes by introducing appropriate organic molecules (e.g. sugars, PEG, small peptides) into the cluster moiety to make them water-soluble and acceptable for living cells is very interesting and important task.
Here we report our recent results on synthesis of novel hybrid chalcogenide (Q=S, Se, Te) rhenium tetranuclear Re4Q4L12, hexanuclear Re6Q8L6 and dodecanuclear Re12CS17L6 cluster complexes with inorganic and organic ligands L, study of their crystal and electronic structures, physico-chemical properties and biomedical behavior.
  • Lecture (Conference)
    ICBIC XIII, 13th International Conference on Biological Inorganic Chemistry, 15.-20.07.2007, Wien, Austria
  • Abstract in refereed journal
    Journal of Biological Inorganic Chemistry 12(2007)Suppl. 1, S18

Publ.-Id: 9533 - Permalink

Competences and perception of the management in slovak companies
KožÍková, O.; Joehnk, P.;
Vortrag auf CO-MAT-TECH 2006
  • Invited lecture (Conferences)
    CO-MAT-TECH 2006,14. International Scientific Conference, 19.-20.10.2006, Trnava, Slovakia

Publ.-Id: 9532 - Permalink

Aqueous uranium(IV) fluoride complexes: determination of fluorescence properties by means of TRLFS
Lehmann, S.; Geipel, G.; Bernhard, G.;
Fluorescence properties of uranium(IV) complexes have only been little investigated up to now. Our research contributes first data on uranium(IV) fluoride complexes in an aqueous environment. Investigations were carried out using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The excitation wavelength for all samples applied was 245 nm. Samples investigated comprised a constant uranium(IV) concentration. Fluoride was added with varying concentrations (stoichiometrical deficiency up to an excess with respect to uranium).
The fluorescence spectrum of a pure uranium(IV) solution without the addition of fluoride is in accordance with the ones described by [1] and [2]. Positions of 5 main peaks were determined: 291, 320, 335, 394 and 409 nm. Addition of a stoichiometrically deficient proportion of fluoride of one tenth the uranium concentration does not a result in a change of the fluorescence spectrum. There is no shift of peaks or increase or decrease of fluorescence intensity observable. However, raising the fluoride concentration up to one third the concentration of uranium(IV) affects the spectra in a way that all the peaks commence to diminish, best observable via the main peaks at 319 and 409 nm.
At the same time, a new peak in the region around 400 nm occurs. This peak broadens with increasing fluoride concentration. In addition, a peak around 320 nm starts to build up and superimpose the original uranium(IV) peak at 320 nm. Enhancing the fluoride concentration further on up to half the uranium(IV) concentration results in an increase of the fluorescence spectrum of the complex formed. A further increase of the fluoride concentration does not affect the spectrum. The position of the new formed peaks as well as the fluorescence intensity remain stable. Hence, the formation of the uranium(IV)-fluoride complex has been complete.
Future investigations aim at the determination of the complex formation constants of the uranium(IV) fluoride complexes.
Keywords: uranium(IV) fluoride, TRLFS, formation constant
  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 180-181

Publ.-Id: 9531 - Permalink

Exact propagators for SUSY partners
Pupasov, A.; Samsonov, B.; Günther, U.;
Pairs of SUSY partner Hamiltonians are studied which are interrelated by usual (linear) or polynomial supersymmetry. Assuming the model of one of the Hamiltonians as exactly solvable with known propagator, expressions for propagators of partner models are derived. The corresponding general results are applied to "a particle in a box", the Harmonic oscillator and a free particle (i.e. to transparent potentials).
Keywords: linear supersymmetry, polynomial supersymmetry, quantum mechanics, propagator, Green function, harmonic oscillator, transparent potential

Publ.-Id: 9530 - Permalink

Investigations into the formation of real colloids and pseudocolloids of uranium(IV)
Zänker, H.; Opel, K.; Weiß, S.; Hübener, S.; Bernhard, G.;
The formation of real colloids and pseudocolloids of uranium(IV) was investigated. Coulometric titrations of strongly acidic U(IV) solutions in HClO4/NaClO4 medium were carried out in order to find the pH of first colloid formation. Laser-induced breakdown detection (LIBD) was applied for the detection of traces of uranium colloids as the pH was increased. The pH values at the onset of colloid formation were used for thermodynamic calculations aimed at determining the solubility products of crystalline and amorphous uranium dioxide. For uranium(IV) this novel approach was applied for the first time. Published solubility products for UO2 obtained by classic techniques vary by several orders of magnitude. Our experiments provided solubility products of log Ksp0 = 59.6 ± 1.0 for UO2(cr) and log Ksp0 = -54.1 ± 1.0 for UO2·xH2O(am) for the given reaction UO2·xH2O + 4 H+ ↔ U4+ + (2+x) H2O. Furthermore, the UO2·xH2O(am) colloids were investigated for their colloidal stability. Zeta potentials of ≥ 30 mV were found for pH values of less than 4. The point of zero charge was at pH ~ 6.9. Colloidal suspensions of 1 mMol/L UO2·xH2O(am) at a pH value of 2.5 proved to be stable over > 1.5 years. The interaction of the forming UO2·xH2O(am) colloids with other colloid-forming species was tested. Therefore, coulometric titrations of U(IV) solutions in the presence of (a) dissolved Al(III) and (b) dissolved silicate were carried out. The presence of Al(III) does not significantly influence the formation of the UO2·xH2O(am) colloids, and the presence of U(IV) does not significantly influence the behaviour of Al(III). There is more interaction of the U(IV) with silicate. Silicate, on the one hand, does not significantly influence the pH value of first UO2·xH2O(am) colloid formation, i.e. it does not significantly influence UO2·xH2O(am) solubility. However, the presence of U(IV) significantly influences the precipitation behaviour of the silicate (formation of U(IV) pseudocolloids due to coprecipitation). The nature of the interaction between the silicate and the U(IV) is not yet known. Adsorption of the silicate onto the UO2·xH2O(am) colloids and/or formation of a coffinite precursor come into question. EXAFS experiments to elucidate the local structure around the U(IV) atoms in the pseudocolloids are underway.
Keywords: colloids, uranium dioxide, laser-induced breakdown detection, coprecipitation
  • Lecture (Conference)
    Migration 2007, 26.-31.8.2007, München, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 161-162

Publ.-Id: 9529 - Permalink

Vibrational excitations and tilted rotation in Lu-163
Almehed, D.; Nazmitdinov, R. G.; Doenau, F.;
Using a microscopic self-consistent model, we analyse the excitation built upon the rotational band in Lu-163, which has been identified as a wobbling excitation on top of the rotation of a triaxial, trongly deformed shape. We find that the presence of pairing correlations substantially affects the energy of the excitation. Our calculations predict the onset of tilted rotation at a critical rotational requency where the energy of the excitation approaches zero.
  • Physica Scripta T 125(2006), 139-141

Publ.-Id: 9528 - Permalink

Orbits, shapes and currents
Frauendorf, S.;
Shapes and current distributions of nuclei and alkali clusters are discussed in terms of the single particle motion of fermions in the average potential. For small particle number, an interpretation in terms of the lowest spherical harmonics is presented. For large particle number, an interpretation in terms of classical periodic orbits is presented.
  • Physica Scripta T125(2006)
  • Lecture (Conference)
    Int. Conf. on Finite Fermionic Systems, Nilsson Model 50 Years, 14.06.2005, Lund, Sweden

Publ.-Id: 9527 - Permalink

Scanning capacitance microscopy and the role of localized charges in dielectric films: Infering or challenging?
Beyer, R.; Schmidt, B.;
Scanning capacitance microscopy (SCM) is considered a suitable technique to examine dopant profiles and to provide images of the charge carrier distribution in real device structures. A drawback of the application is the sensitivity of the method to different kinds of charges in the surface passivation layer. For a systematic study silicon structures with stripe patterns of different doping concentrations, covered either by a native oxide or by a thermally grown silicondioxide layer, were examined. The dependence of the dC/dV characteristic
on the sweep rate of the tip bias and on the bias sweep direction was analyzed. Local charge trapping in the passivation layer was estimated from shifts of the peak position of the dC/dV versus V curves. It is demonstrated as to how features related to the charge trapping in the passivation layer and induced by a certain dc bias at the tip superimpose the dopant related features in the SCM image.
Keywords: Scanning capacitance microscopy; Dopant profiling; Oxide layer; Charge trapping

Publ.-Id: 9526 - Permalink

Comparison between wire-mesh sensors and conductive needle-probes for measurements of two-phase flow parameters
Manera, A.; Ozar, B.; Paranjape, S.; Ishii, M.; Prasser, H.-M.;
Measurements of two-phase flow parameters such as void-fraction, bubble velocities, and interfacial area densities have been performed in an upwards air-water flow at atmospheric pressure by means of a four-tip needle-probe and a wire-mesh sensor. For the first time, a direct comparison between the two measuring techniques has been carried out. Both techniques are based on the measurement of the fluid conductivity. For void fraction and velocity measurements, similarity exists between the two methodologies for signal analysis. A significantly different approach is followed, instead, for the estimation of the interfacial area concentration: while the evaluation based on the needle-probe signal is carried out by using projections of the gas-liquid interface velocity, the evaluation based on the wire-mesh signals consist in a full reconstruction of the bubbles interfaces. The comparison between the two techniques shows a good agreement.
Keywords: two-phase flow, interfacial area, needle-probe, wire-mesh sensor
  • Contribution to proceedings
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.2007, Nagoya, Japan
    paper ICONE15-10312
  • Lecture (Conference)
    15th International Conference on Nuclear Engineering (ICONE15), 22.-26.04.2007, Nagoya, Japan
  • Nuclear Engineering and Design 239(2009)9, 1718-1724
    DOI: doi:10.1016/j.nucengdes.2008.06.015

Publ.-Id: 9525 - Permalink

Observation of two-magnon bound states in the Spin-1 Anisotropic Heisenberg Antiferromagnetic Chain System NiCl2-4SC(NH2)2
Zvyagin, S.;
NiCl2-4SC(NH2)2 (DTN) is a quantum S = 1 chain system with strong easy-pane anisotropy and a new candidate for the field-induced Bose-Einstein condensation of the spin degrees of freedom. ESR studies of magnetic excitations in DTN in fields up to 25 T are presented. Based on analysis of the single-magnon excitation mode in the high- field spin-polarized phase and previous experimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set of spin-Hamiltonian parameters is obtained. Our results yield D = 8:9 K, Jc = 2:2 K, and Ja;b = 0:18 K for the anisotropy, intrachain, and interchain exchange interactions, respectively. These values are used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Excellent quantitative agreement between the theory and experimental data is obtained.
  • Lecture (others)
    The International Conference on Strongly Correlated Electron Systems (SCES07), 13.-18.05.2007, Houston, United States

Publ.-Id: 9524 - Permalink

Spin Dynamics in the Spin-1 Large-D Antiferromagnetic Chain System NiCl2-4SC(NH2)2 in high magnetic fields
Zvyagin, S.;
NiCl2-4SC(NH2)2 (DTN) is a quantum S = 1 chain system with strong easy-pane anisotropy and a new candidate for the field-induced Bose-Einstein condensation of the spin degrees of freedom. ESR studies of magnetic excitations in DTN in fields up to 25 T are presented. Based on analysis of the single-magnon excitation mode in the high- field spin-polarized phase and previous experimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set of spin-Hamiltonian parameters is obtained. Our results yield D = 8:9 K, Jc = 2:2 K, and Ja;b = 0:18 K for the anisotropy, intrachain, and interchain exchange interactions, respectively. These values are used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Excellent quantitative agreement between the theory and experimental data is obtained.
  • Invited lecture (Conferences)
    Kolloquium an der Clemson University, Greenville, 02.03.2007, Greenville, USA

Publ.-Id: 9523 - Permalink

Hydrogen 3D-distribution and the kinetics in a Ti/H system studied by micro-ERDA, NRA and XRD
Wang, T. S.; Grambole, D.; Herrmann, F.; Peng, H. B.; Wang, S. W.;
The micro kinetics of titanium hydrogenation is studied by measuring the three-dimensional hydrogen distribution in titanium subsurfaces by elastic recoil detection analysis with a heavy ion micro-beam, H-1(N-15, alpha gamma) C-12 resonant nuclear reaction analysis and X-ray diffraction. The hydrogen rich layers in the titanium subsurface region are formed by mechanical polishing and hydrogen ion implantation. An inhomogeneous hydrogen distribution is found in the subsurface region. The inhomogeneity varies with hydrogen concentration and depth. The hydrogen loaded by surface polishing distributes roughly homogeneously in the near surface with a high concentration up by 60 at.%, whereas the implanted hydrogen distributes inhomogeneously inside the sample with a lower concentration. Nevertheless, the inhomogeneity changes with the implantation fluence; the higher the fluence, the better the homogeneity. This phenomenon is considered to be affected by complications such as the hydrogen ingression process, hydrogen states, titanium grain size and orientation, etc.
Keywords: hydrogen ingression process, hydrogen states, titanium grain size and orientation
  • Surface and Interface Analysis 39(2007), 52-57

Publ.-Id: 9522 - Permalink

The Relative Biological Effectiveness of X-rays
Beyreuther, E.;
The Relative biological effectiveness of X-rays
  • Lecture (others)
    Seminar der AG Mikrobiologie, 05.10.2006, Freiberg, Deutschland

Publ.-Id: 9521 - Permalink

Adhesion Issues in PBO/Epoxy Composites
Liu, J.; Gao, S. L.; Mäder, E.; Bianchi, A. D.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S. A.; Wosnitza, J.;
The high performance of poly p-phenylene-2,6-benzobisoxazole (PBO) fibre in mechanical properties and environmental resistance provides great potential applications as reinforcement fibres for composites. However, poor adhesion between PBO fibre and matrix is found because of the chemically inactive and/or relatively smooth surface of the reinforcement fibre. Here, we report the surface modification of PBO fibres by O2 and NH3 plasma treatments. The surface energy and roughness are increased for both sized and extracted fibres after plasma treatments. The sized fibre shows marginal improvement in interfacial adhesion and no change in fibre tensile strength because of the barrier effect of the sizing layer. For the extracted fibre, the plasma treatments cause reduction in both interfacial adhesion and the tensile strength, which is sensitive to plasma treatment conditions as revealed by a bimodal Weibull statistical distribution analysis. The fibre surface roughness is increased and more surface flaws are induced, which could result in coarse interface structures when the treated fibre surface has no adequate wetting and functional groups.
  • Key Engineering Materials 334-335(2007), 233-236

Publ.-Id: 9519 - Permalink

Bilateral nasal remission spectroscopy allows the side separated continuous measurement of changes in swelling of the nasal mucosa
Wuestenberg, E.; Hampel, U.; Schleicher, E.; Huettenbrink, K.; Zahnert, T.;
In earlier studies optical transmission spectroscopy showed that continuous monitoring of changes in the swelling of the nasal mucosa is possible. However, independent measurement in both sides of the nose cannot be achieved by this method. With the aim of achieving real-time monitoring of endonasal swelling separately for both nostrils we developed the new method of bilateral nasal remission spectroscopy for this pilot study.
In nasal remission spectroscopy, light at a wavelength of 790 nm (close to the isobestic point of hemoglobin) is beamed into each side of the nose, and the light that is backscattered by the internal nasal tissue is measured continuously on the same nasal side. To evaluate the principle of this new method a pilot study was conducted in five healthy probands subjected to a one-sided (unilateral) nasal histamine provocation test (0.14 ml, 2 mg/ml).
In each proband single-sided nasal histamine provocation led to an increase in light extinction on the provoked side by an average of 0.18 optical densities (OD). In four of the five probands a slight increase (0.04 OD) in light extinction was observed on the other side of the nose.
Nasal remission spectroscopy seems to allow single-side, continuous monitoring on both sides of the nose. Therefore, the method could also be suitable for use in studies of the nasal cycle, as well as for objectivisation of nasal allergen provocation tests.
Keywords: optical rhinometry, nasal provocation test
  • HNO 55(2007)4, 254-257

Publ.-Id: 9518 - Permalink

Round-Robin Exercise on Instrumented Impact Testing of Precracked Charpy Specimens (IAEA Coordinated Research Program Phase 8)
Lucon, E.; Viehrig, H.-W.;
Within topic area 2 (Loading Rate Effects) of the IAEA Coordinated Research Project Phase 8 (CRP-8), a round-robin exercise (RRE) was performed, aimed at the measurement of impact fracture toughness in the ductile-to-brittle transition region using precracked Charpy pecimens of the JRQ steel tested on instrumented pendulum machines. The objective of the round-robin was twofold: 1) assessing the applicability of the Master Curve approach (ASTM E1921-05) to data obtained at impact loading rates of the order of 105 MPa√m/s; 2)
validating a draft test procedure developed by sub-committee TC5 of the European Structural Integrity Society (ESIS), in the absence of an official testing standard (ISO or ASTM). A comprehensive analysis of the RRE results received to date will be presented in this paper, including an assessment of the overall data scatter and the lab-to-lab variability. In this context, an outlier data set has been identified and investigated in great detail. Based on the results presented, it is noted that the test procedure appears reliable and easy to follow for the various participants.
Keywords: instrumented impact testing, dynamic fracture toughness, Master Curve, reactor pressure vessel steel
  • Contribution to proceedings
    2007 ASME Pressure Vessels and Piping Division Conference, 22.-26.07.2007, San Antonio, Texas, USA
    Proceedings of PVP2007: ASME Publications

Publ.-Id: 9517 - Permalink

IAEA Coordinated Research Project on Master Curve Approach to Monitor Fracture Toughness of Reactor Pressure Vessel Steels: Effect of Loading Rate
Viehrig, H.-W.; Lucon, E.;
In the final evaluation for the application of the Master Curve in the IAEA Coordinated Research Project Phase 5 (CRP-5), one of the areas which was identified as needing further work concerning the effects of loading rate on the reference temperature To up to impact loading conditions. This subject represents one of the three topic areas within the current CRP-8.
The effect of loading rate can be broken down into two distinct aspects: 1) the effect of loading rate on the determined Master Curve To values for loading rates within the loading rate range specified in ASTM E1921-05 for quasi-static loading, and; 2) the effect of loading rate on determined Master Curve To values for higher loading rates including impact conditions using instrumented precracked Charpy (PCC) specimens. The new CRP includes both aspects, but primarily focuses on the second element of loading rate effects, i.e. loading rate ranges beyond the upper limit of the E1921-05 standard (2 MPam/s). These issues are investigated within the topic area#2 Loading Rate Effects – Impact Loading.
The mandatory portion of this topic area required participation in a round-robin exercise to validate the application of the Master Curve approach to PCC specimens tested in the ductile-to-brittle transition region using an instrumented pendulum (10 tests per participant on the JRQ material). The current status of the round-robin is presented in the paper PVP2007-26087.
The non-mandatory portion of the topic area consists in providing Master Curve data obtained at different loading rates on various RPV steels, in order to assess the loading rate dependence of To and compare it with an empirical model proposed by Wallin. Moreover, additional topics will be addressed, such as:
- comparison of results from unloading compliance and monotonic loading in the quasi-static range;
- estimation of fracture toughness from Charpy V-notch data;
- assessment of crack arrest properties from instrumented Charpy results;
- effect of irradiation on the relationship between static and dynamic fracture toughness.
Keywords: fracture toughness, Master Curve, dynamic loading, reactor pressure vessel steels
  • Contribution to proceedings
    2007 ASME Pressure Vessels and Piping Division Conference, 22.-26.07.2007, San Antonio, Texas, USA
    Proceedings of PVP2007: ASME Publication

Publ.-Id: 9516 - Permalink

Magnetic Excitations in the Spin-1 Anisotropic Heisenberg Antiferromagnetic Chain System NiCl2-4SC(NH2)2
Zvyagin, S.;
Electron spin resonance studies of magnetic excitations in NiCl2-4SC(NH2)2 (DTN, a quantum S = 1 chain system with strong easy-pane anisotropy and a new candidate for the Bose-Einstein condensation of the spin degrees of freedom) in fields up to 25 T are presented. Based on analysis of the frequency-field dependence of single-magnon mode in the high- field spin-polarized phase and previous experimental results [Phys. Rev. Lett. 96, 07724 (2006)], a revised set of spin- Hamiltonian parameters is obtained. Our results yield D = 8.9 K, Jc = 2.2 K, and Ja,b = 0.18 K for the anisotropy, intra- and inter-chain exchange interactions, respectively. These values are used to calculate the AFMphase boundary, low- temperature magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Excellent quantitative agreement with experimental data is obtained.
  • Lecture (Conference)
    MAR07 Meeting of The American Physical Society, 05.-09.03.2007, Denver, USA

Publ.-Id: 9515 - Permalink

Design of Non-destructive Pulsed Magnets at the HLD
Zherlitsyn, S.; Herrmannsdörfer, T.; Skourski, Y.; Sytcheva, A.; Wosnitza, J.;
In this paper, we consider several aspects of the design and construction of non-destructive pulsed magnets on the basis of work which is under way at the Dresden High Magnetic Field Laboratory (HLD). A number of pulsed magnets including 60 T/1.5MJ and 70 T/8.5 MJ mono-coils have been successfully tested and are ready for operation. Some perspectives of the pulsed-magnet development are discussed. A way to achieve 100T in nondestructive pulsed magnets and the role of various factors and challenges are addressed. Results of the finite element analysis (FEA) of the designed coils are presented.

Publ.-Id: 9514 - Permalink

Quasi-Two-Dimensional Organic Superconductors
Wosnitza, J.;
A review on selected normal-state and superconducting properties of the quasi-two-dimensional organic superconductors is given. Thereby, the focus is laid on the charge-transfer salts based on bisethylenedithio-tetrathiafulvalene, or ET for short, the building block of most of the to-date known organic superconductors. Some basic features of the crystallographic structure, the highly anisotropic electronic band structure for some materials, as well as unusual electronic-transport properties are highlighted. The principal phasediagram of the κ-phase salts and the fundamental difficulties of a purely electronic explanation of the observed features are discussed. A brief overview on the anisotropic superconducting properties as well as the still very controversial notion on the nature of the superconducting state is presented.

Publ.-Id: 9513 - Permalink

Stand der Entwicklung für LWR Brennelemente und Auslegungsmethoden
Weiß, F.-P.; (Editor)
Die Fachgruppen „Brennelemente und Kernbauteile" und „Reaktor-physik und Berechnungsmethoden" der Kerntechnischen Gesell-schaft e.V. veranstalten vom 2.– 3. März 2006 im Forschungszentrum Rossendorf eine gemeinsame zweitägige Fachtagung mit dem Thema „Stand der Entwicklung für LWR Brennelemente und Auslegungsme-thoden“. Den Teilnehmern wird in der Fachtagung dieser Themenbereich anhand von ausgewählten Vorträgen von Fachleuten dargestellt werden. Schwerpunkte bilden neue Aspekte der Brennstabauslegung, fortschrittliche Verfahren zur Kernauslegung, MOX Einsatz sowie betriebliche Erfahrungen.
Keywords: nuclear reactors, fuel assemblies, reactor calculations, core loading fuel cycle
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2006
    350 Seiten

Publ.-Id: 9512 - Permalink

Enhanced superconductivity of Pb nanograins on a biological substrate
Herrmannsdörfer, T.; Ignatchik, O.; Papageorgiou, T. P.; Pobell, F.; Walter, C.; Wosnitza, J.; Hennig, C.; Merroun, M.; Pollmann, K.; Raff, J.; Selenska-Pobell, S.; von Borany, J.;
Nanogranular materials attract more and more attention due to their exciting physical properties as well as their key role in future technologies. Compared to their bulk counterparts, nanogranular materials can reveal strongly altered properties. As an example, we have demonstrated that the Stoner enhancement factor of the d conductionelectron susceptibility of Pd and Pt nanoclusters is clearly reduced compared to the one of the bulk transition metals. Now we have focused on superconducting properties of lead particles of a well defined single grain size of 19 nm. As for Pd and Pt, these metal nanoclusters have been deposited on a biological template, a purified self-assembling paracrystalline surface layer (S-layer) of Bacillus sphaericus JG-A12 which is composed of identical protein monomers. After a determination of their grain size using x-ray powder diffraction, we have investigated their superconducting B-T phase diagram by means of SQUID magnetometry. The Pb clusters reveal a superconducting critical field of the size of several Tesla which is strongly enhanced compared to the corresponding critical magnetic field of 0.09 T for bulk Pb.
  • Poster
    71. Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 26.-30.03.2007, Regensburg, Germany
  • Lecture (Conference)
    International School "Magnetic Fields for Science", 27.08.-08.09.2007, Cargèse, France

Publ.-Id: 9511 - Permalink

Ru moment in the magnetically ordered superconductor RuSr2GdCu2O8
Papageorgiou, T. P.; Casini, E.; Skourski, Y.; Herrmannsdörfer, T.; Freudenberger, J.; Braun, H. F.; Wosnitza, J.;
Magnetization measurements of the superconducting (Tc ≈ 47 K) and magnetically ordered (TRuM ≈ 130 K)RuSr2GdCu2O8 (Ru1212) have been performed in pulsed magnetic fields up to 47 T. The average Ru-moment, determined by using NbSr2GdCu2O8 as reference, is 1.8 μB suggesting that the investigated sample is in a mixed valence state containing 87% Ru5+ (2 μB) and 13% Ru4+ (0.9 μB). This ratio is consistent with an underdoped nature of the superconducting state with a hole concentration in the CuO2 plane of p ≈ 0.065. It is suggested that the magnetic structure of Ru1212 consists of a main antiferromagnetic phase formed by Ru5+ions interrupted by ferromagnetic stripes, where double exchange between Ru5+ and Ru4+ ions takes place. Different Ru5+/Ru4+ ratios, due to different preparation conditions, could explain some of the diverse superconducting and magnetic properties reported in the literature for Ru1212.
  • Poster
    Frühjahrstagung der DPG, 26.-30.03.2007, Regensburg, Deutschland

Publ.-Id: 9510 - Permalink

Quantum Thermal Conductance of Electrons in a One-Dimensional Wire
Chiatti, O.; Nicholls, J. T.; Proskuryakov, Y. Y.; Lumpkin, N.; Farrer, I.; Ritchie, D. A.;
An electron thermometer was used to measure the temperature rise of approximately 2 × 105 electrons in a two-dimensional box, due to heat flow into the box through a ballistic one-dimensional (1D) constriction. Using a simple model we deduce the thermal conductance κ(Vg) of the 1D constriction and compare it to the electrical conductance characteristics. For the first four 1D subbands the heat carried by the electrons passing through the wire is proportional to its electrical conductance G(Vg). In the vicinity of the 0.7 structure this proportionality breaks down, and a plateau at the thermal-conductance quantum, π2k2B T/3h, is observed. [Phys. Rev. Lett. 97, 056601 (2006)]
  • Poster
    Frühjahrstagung der DPG, 26.-30.03.2007, Regensburg, Deutschland
  • Lecture (others)
    Institutsseminar, Institut für Festkörperphysik, 13.11.2007, Dresden, Deutschland

Publ.-Id: 9509 - Permalink

Listmode-basierte Ganzkörperuntersuchungen mit dem PET-Scanner ECAT Exact HR+
Mölle, H.; Langner, J.; Pötzsch, C.; Will, E.; van den Hoff, J.;
Ganzkörperuntersuchungen mit PET-Scannern werden im sog. Frame- oder Histogramm-Modus (HM) durchgeführt. Dies spart Speicherplatz und Rechenzeit, jedoch geht die Information über die Einzelereignisse verloren, weshalb z.B. event-basierte Algorithmen zur Korrektur der Atembewegung nicht angewendet werden können. Zur Erhaltung der Information erlauben PET-Scanner, darunter der ECAT Exact HR+, die Akquirierung der Einzelereignisse, Listmode (LM) genannt. Bisher konnte dieser Modus in der klinischen Routine nur bei dynamischen Hirnuntersuchungen eingesetzt werden. Bei Ganzkörperuntersuchungen lässt sich das existierende Protokoll des ECAT Exact HR+ nur im HM betreiben. Um die Vorteile einer LM-Messung auch für Ganzkörperuntersuchungen zu nutzen, wurde eine spezielle Software entwickelt. Diese ermöglicht nicht nur routinemäßige Ganzkörperuntersuchungen im LM sondern auch die kompletteWeiterverarbeitung bis zum
rekonstruierten PET-Volumen.

Ganzkörperuntersuchungen setzen sich aus mehreren, durch Bettvorschübe unterbrochene Emissions und
Transmissionsmessungen zusammen. Nach der Messung erfolgen die Rekonstruktionen der einzelnen Bettpositionen und deren Zusammenfügen zu einem Bildvolumen. Für die Befehlsabfolge der Ganzkörperuntersuchung am ECAT Exact HR+ existiert keinerlei Dokumentation. Daher wurde die Abfolge im HM analysiert und analog in den LM überführt. Aus gerätetechnischen Gründen erfolgt die Transmissionsmessung weiterhin im HM. Aus diesem Grund muss ein Transmissionseintrag in die Patientendatenbank eingefügt werden, weshalb die zur Datenbank gehörenden Bibliotheken analysiert wurden. Außerdem musste die Integrität der Datenbank gewährleistet werden. Der Untersuchung aller notwendigen Befehle folgte deren Umsetzung in Software. Zur Konzeption der Software wurde die UML und zur Implementierung die objektorientierte Entwicklungsbibliothek Qt genutzt.

Die Implementierung der neuen Software ermöglicht erstmals LM-basierte Emissionsmessungen bei
Ganzkörperuntersuchungen in der klinischen Routine. Methoden zum automatischen ändern von Einträgen in der Patientendatenbank und die Sicherung der Datenbankintegrität vereinfachen die Datenverwaltung des PET-Scanners. Die Nutzung von UML und der objektorientierten Entwicklungsbibliothek Qt machen Veränderungen und Erweiterungen der Software problemlos möglich.

Mit der Umsetzung LM-basierter Ganzkörperuntersuchungen beim ECAT Exact HR+ Scanner ist die
Voraussetzung geschaffen, Methoden zur listmode-basierten Korrektur der Patientenatmung/-bewegung zu entwickeln und in die klinische Routine einzuführen. Des Weiteren erlauben die Methoden zum Ändern der Patientendatenbank eine Verbesserung der Handhabung der Archivierungssoftware des PET-Scanners.
  • Lecture (Conference)
    45. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2007, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 46(2007), A11

Publ.-Id: 9508 - Permalink

Quantitative Auswertemethoden für die Beurteilung von Patientenbewegungen in der klinischen PET
Langner, J.; Oehme, L.; Beuthien-Baumann, B.; van den Hoff, J.;
Aufgrund der kontinuierlich gestiegenen Auflösung der Geräte stellen Patientenbewegungen während einer PET-Aufnahme vor allem bei der Analyse kleiner Strukturen ein wachsendes Problem dar. Dies macht immer häufiger den Einsatz von Bewegungskorrekturmethoden notwendig. Um den Zeitbedarf für die Berechnungen in einem vertretbaren Rahmen zu halten, müssen geeignete Schwellwerte aus den Bewegungsdaten ermittelt werden, unterhalb derer eine Bewegungskorrektur vermieden werden kann. Die sechs die Bewegung beschreibenden Transformationsparameter sind hierzu nur bedingt geeignet, da der kombinierte Einfluss aller Parameter auf die Bewegung nicht einfach abschätzbar ist. Unsere Studie greift dies auf und zeigt am Beispiel von Hirnuntersuchungen wie aus den Daten eines externen Bewegungsmesssystems aussagefähige Schwellwerte abgeleitet werden können. Wir zeigen ferner wie eine routinemäßige Nutzung der Bewegungsanalyse für die Qualitätskontrolle genutzt werden kann.

Die bei einer PET-Aufnahme von einem Bewegungstracker aufgezeichneten Daten werden automatisch mittels des statistischen Analysewerkzeuges ‚R’ verarbeitet. Es werden statistische Kenngrößen bzgl. der Stabilität der Bewegungsmessung berechnet, sowie die Daten der sechs Translations-/Rotations-Freiheitsgrade graphisch dargestellt und hieraus Transformationsmatrizen berechnet. Zur Analyse des Bewegungseinflusses innerhalb des relevanten Bildvolumens werden die (zeitabhängigen) Transformationsmatrizen auf die Oberfläche einer Kugel von ; 20 cm angewandt. Hierbei wird jeder Punkt eines Gitternetzes transformiert und die euklidische Längen der
Differenzvektoren zwischen ursprünglichem und transformiertem Gitternetz berechnet. Anhand eines Schwellwertes für diese Verschiebung werden die Transformationsmatrizen ausgewählt, die für eine Bewegungskorrektur relevant sind. Zusätzlich ist es möglich, Zielkoordinaten wie z.B. die des Striatums einzugeben, um die berechneten Bewegungsmatrizen auf eine beliebige ROI anzuwenden und somit unmittelbar Bewegungsinformationen für dieses Areal zu erhalten.

Die entwickelten Methoden generieren nach einer Bewegungsmessung automatisch Auswertungen in Form einer PDF-Datei. Diese beinhaltet neben verschiedenen graphischen Statistiken eine Zusammenfassung über die als relevant eingestuften Bewegungen des Patienten und lokalisiert Areale, welche kritisch von Bewegungen betroffen sind.

Durch die Integration der vorgestellten Auswertemethoden in die klinische PET lässt sich die Qualität einer Untersuchung in Hinblick auf den Einfluss der Patientenbewegung objektiver beurteilen. Es ist hiermit möglich, routinemäßige Bewegungsanalysen für PET-Untersuchungen durchzuführen und diese für eine akkurate, in Hinblick auf den Rechenaufwand optimierte Bewegungskorrektur zu nutzen.
  • Lecture (Conference)
    45. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2007, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 46(2007), A34

Publ.-Id: 9507 - Permalink

Hydraulic jump in a closed horizontal two-phase flow channel
Vallee, C.;
The hydraulic jump in a co-current two-phase flow was investigated in the Horizontal Air/Water Channel (HAWAC) of Forschungszentrum Dresden-Rossendorf. The hydraulic jump is the discontinuous transition between super- and subcritical flow and is characterised by a steep rising of the water surface with high turbulence production.
High-speed video observations were performed in the channel and an algorithm was developed to recognise the interface in the camera frames. This allows a water level measurement in any cross-section. Since the interface is very dynamic due to the high turbulence in the jump, a statistical approach is proposed in order to reflect the structure of the interface over the time. The probability distribution of the water levels was calculated in each vertical cross-section and is shown in pictures of the test-section.
Furthermore, experiments were performed to point out the influence of the air flow rate on the hydraulic jump in a closed channel. Due to the momentum exchange between the phases, the position of the hydraulic jump from the inlet increases sensibly with the air flow rate. Moreover, an increasing smearing of the probability distributions was observed with higher air flow rate. This indicates that the oscillations of the interface are increasing with the air flow rate, which can be attributed to the flow regime downstream of the hydraulic jump, in particular to the transition to slug flow.
Keywords: hydraulic jump, stratified two-phase flow, horizontal channel
  • Contribution to proceedings
    International Conference on Multiphase Flow 2007, 09.-13.07.2007, Leipzig, Germany
    Paper N° S5_Fri_A_63
  • Lecture (Conference)
    International Conference on Multiphase Flow 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9506 - Permalink

Experimental investigation of time-dependent flow driven by a travelling magnetic field
Cramer, A.; Pal, J.; Zhang, C.; Eckert, S.; Gerbeth, G.;
Recently, the flow generated by a travelling magnetic field (TMF) has received increasing attention. This comprises industrial applications in crystal growth as well as basic research on stability and on time-dependent flow for higher values of the forcing parameter, the latter aiming at metallurgical processes. Whereas the flow driven by rotating magnetic fields (RMF) might be said to be fairly understood, this does not hold for the TMF. Moreover, there exist experimental investigations on RMFs but studies on TMF almost restrict to numerical simulations. Also in the case of an RMF, most experiments dealt only with the mean flow. The present work is devoted to both mean flow and turbulence in an electrically conducting melt subjected to a TMF.
  • Contribution to proceedings
    11th EUROMECH European Turbulence Conference, 25.-28.06.2007, Porto, Portugal
    Springer Proceedings in Physics 117: Advances in Turbulence XI, Berlin: Springer, 978-3-540-72603-6, p.750
  • Poster
    11th EUROMECH European Turbulence Conference, 25.-28.06.2007, Porto, Portugal

Publ.-Id: 9505 - Permalink

Extraktionsuntersuchungen mit radiomarkierten Verbindungen zur Charakterisierung neuer Wirt/Gast-Systeme
Stephan, H.;
Die thermodynamische Behandlung von Extraktionsgleichgewichten in flüssigen Zweiphasensystemen gestattet Aussagen zur stöchiometrischen Zusammensetzung extrahierter Komplexe sowie die Ableitung thermodynamischer Daten wie Extraktions-, Komplexstabilitäts-, Verteilungs- und Assoziationskonstanten. Bei Einsatz von radioaktiv markierten Verbindungen zur Konzentrationsbestimmung ergeben sich Vorteile hinsichtlich Substanzbedarf, Reproduzierbarkeit, Genauigkeit und Schnelligkeit gegenüber einer Reihe von anderen Methoden wie NMR-, ICP- und UV/VIS-Spektroskopie, die häufig zur Charakterisierung der Bindungseigenschaften von neuen organischen Liganden herangezogen werden.[1]
Untersuchungen zur Flüssig-Flüssig-Extraktion radioaktiver Kupferkomplexe mit lipophilen Oxobathophenanthrolin-Liganden I werden vorgestellt, die Aussagen zur Komplex-bildungskinetik und Stöchiometrie der gebildeten Komplexe gestatten.[2] Am Beispiel trifunktionalisierter Triphenylketalrezeptoren II wird die Bestimmung von Assoziations-konstanten für Koffein, Theophyllin und Trimethylharnsäure mithilfe der Extraktions-methode diskutiert.[3] Verteilungsuntersuchungen im Zweiphasensystem 1-Octanol/Wasser werden häufig zur Abschätzung der Lipophilie pharmazeutisch relevanter Verbindungen herangezogen, um Vorhersagen zur Bioverteilung treffen zu können. In diesem Zusammenhang werden Ergebnisse zur Charakterisierung von neuen radioaktiv markierten Kupferkomplexen vorgestellt, die für einen Einsatz in der Nuklearmedizin von Interesse sind.

[1] H. Stephan, S. Juran, B. Antonioli, K. Gloe, K. Gloe, Extraction Methods in Analytical Methods in Supramolecular Chemistry, C. Schalley (ed.), Wiley-VCH, Weinheim, 2007, 79-103.
[2] H. Stephan, G. Geipel, G. Bernhard, P. Comba, G. Rajaraman, U. Hahn, F. Vögtle, Eur. J. Inorg. Chem. 2005, 4501-4508
[3] M. Bomkamp, C. Siering, K. Landrock, H. Stephan, R. Fröhlich, S. Waldvogel, Chem. Eur. J. 2007, im Druck (DOI: 10.1002/chem.200601231)
  • Lecture (Conference)
    Wissenschaftsforum Chemie 2007, 16.-19.09.2007, Ulm, Germany

Publ.-Id: 9504 - Permalink

Entwicklung von radioaktiven Kupferkomplexen auf der Basis hexadentater Bispidinliganden
Juran, S.; Walther, M.; Stephan, H.; Bergmann, R.; Steinbach, J.; Comba, P.;
Die Entwicklung von Chelatbildnern für Kupferradionuklide im Hinblick auf einen Einsatz in der Nuklearmedizin (64Cu: PET, 67Cu: Endoradionuklidtherapie) ist ein intensiv bearbeitetes Forschungsgebiet. [1, 2] In diesem Zusammenhang stellen Liganden auf der Basis des Bispidins – Derivate des 3,7-Diazabicyclo[3.3.1]nonans – eine neue interessante Stoffklasse dar, weil sie sehr stabile Kupfer(II)-Komplexe bilden. [3] Darüber hinaus weisen Bispidinliganden weitere günstige Eigenschaften wie eine schnelle Komplexbildungskinetik sowie vielfältige Modifizierungsmöglichkeiten auf, und sind damit für die Entwicklung zielsuchender Radioliganden prädestiniert. [4] Es wird über die Synthese verschiedener hexadentater Bispidine berichtet und über Möglichkeiten zur Einführung kopplungsfähiger Ankergruppen, die eine Verknüpfung mit biologisch relevanten Molekülen gestatten, diskutiert (Bild 1). An ausgewählte Bispidinliganden wurden Biomoleküle wie Neurotensin NT(8-13) und Bombesin BBN(7-13) gekoppelt. Untersuchungen zur Radiochemie und auch zur Radiopharmakologie entsprechender 64Cu-markierter Biokonjugate werden vorgestellt. Dafür werden in vitro- (Challengeversuche in Anwesenheit von Konkurrenzliganden, Plasmastabilität) und in vivo-Studien an Wistar-Ratten (Bioverteilung, Kleintier-PET) herangezogen.

[1] S. V. Smith, J. Inorg. Biochem. 2004, 98, 1874-1901.
[2] S. J. DeNardo, Semin. Nucl. Med. 2005, 35, 143-151
[3] P. Comba, M. Kerscher, W. Schiek, Prog. Inorg. Chem. 2007, in press
[4] H. Stephan, S. Juran, M. Walther, J. Steinbach, K. Born, P. Comba, in „Technetium, Rhenium, and other
Metals in Chemistry and Nuclear Medicine“, U. Mazzi (Ed.), SGE Editoriali, Padova, Italy, 2006, 7, 219-222.
  • Lecture (Conference)
    Wissenschaftsforum Chemie 2007, 16.-19.09.2007, Ulm, Germany

Publ.-Id: 9503 - Permalink

Das Auflösungsvermögen optischer Mikroskope - wo liegt die Grenze?
Winnerl, S.;
Das Abbe´sche Prinzip und das Rayleigh-Kriterium werden eingeführt. Weiterhin werden wichtige Mikroskoptypen wie Konfokalmikroskop und Fluoreszenzmikroskop vorgestellt. Modene Varianten mit hoher Auflösung wie das Zwei-Photon-Fluoreszenzmikroskop und das Stimulated-Emission-Depletion Mikroskop werden besprochen. Im letzten Teil werden verschiedene Bauformen von Nahfeldmikroskopen und ihre Funktionsweise erläutert, schließlich wird ein Experiment mit einem IR-Nahfeldmikroskop diskutiert, bei dem der Rossendorfer FEL als durchstimmbare Lichtquelle eingesetzt wird.
  • Lecture (others)
    Lehrerfortbildung "Bildgebende Verfahren", 16.02.2007, Dresden, Deutschland

Publ.-Id: 9502 - Permalink

Bonding Network in Filtered-Arc-Deposited Carbon Films: Simulation and Characterization
Gago, R.; Jiménez, I.; Vinnichenko, M.; Jäger, H. U.; Belov, A. Y.;
This work address the bonding structure of amorphous carbon films (a-C) with varying sp2 content deposited by filtered-cathodic-vacuum arc (FCVA) at different substrate temperatures (up to 700 K). Experimentally, the arrangement of carbon atoms within the atomic network is assesed by the combination of x-ray absorption near edge spectroscopy (XANES) and spectroscopic ellipsometry (SE) studies. The experimental evolution of sp2 hybrids with temperature is contrasted with theoretical predictions from molecular-dynamics (MD) deposition simulations.
Keywords: amorphous carbon , filtered-cathodic-vacuum arc (FCVA), substrate temperature, sp2 content , x-ray absorption near edge spectroscopy (XANES), spectroscopic ellipsometry (SE), molecular-dynamics (MD)
  • Invited lecture (Conferences)
    International Conference on Metallurgical Coatings and Thin Films (ICMCTF 2007), 23.-27.04.2007, San Diego, California, USA

Publ.-Id: 9501 - Permalink

An octahedral rhenium cluster compound K4[Re6S8(CN)6]: synthesis, structural characterization and biodistribution
Fedorov, V.; Mironov, Y.; Kim, S.-J.; Gaidash, A.; Trunova, V.; Röhrich, A.; Stephan, H.; Pietzsch, H.-J.;
Polynuclear metal compounds may have considerable potential as metallic drugs. Some types of polyoxometalates, derived from Mo, W, Re and others, are able to be transported into cells and mitochondria. Certain representatives show antiviral and anti-tumour properties.[1-3] Deposited in target cells, metal clusters have promising properties to be used in photon activation therapy (PAT) or photodynamic therapy. In this nexus, octahedral cluster rhenium compounds possess bright red luminescence to make them interesting for medical treatment of cancer.[4] Furthermore, the combination of anti-tumour activity and photodynamic therapy can provide synergetic medical efficacy.
We want to present the synthesis, structural characterization and preliminary pharmacological properties of an octahedral rhenium cluster compound. In the latter concern, it is important to know its biodistribution, metabolism and toxicity. So, the goal of the work presented was the determination of biodistribution of K4[Re6S8(CN)6] and lethal dose LD100 in rats. Experiments were carried out on male rats. As formulation the cluster compound K4[Re6S8(CN)6], dissolved in water (different concentrations in the range from 0.01 to 0.5%), was intra-peritoneally administered. The animals were distributed into 5 groups, each group had 5 rats; one rat was control. The formulation has been injected (one mL of solution every one hour during the day). It was determined that 0.5 mg of K4[Re6S8(CN)6] per one gram of live weight of the rats provokes 100% fatal outcome of experimental animals during first day. This value was accepted as the lethal dose LD100 at intraperitoneal administration of the compound.
Biodistribution experiments were carried out in the format of acute toxicity with single injecting preparation of 1/5LD50 dose. The data of biodistribution are shown that the cluster compound is mainly accumulated in the liver the kidney and spleen. No correlation between the concentrations of rhenium and iron in the internal was found. This can be evidenced of the fact that cyanide groups of compound K4[Re6S8(CN)6] are indifferent to molecular forms of iron in which it is presented in organism. Accumulation in spleen may be interpreted as a location of cluster compound in immune structures. This allows to consider cluster rhenium complexes as promising compounds for treatment of lymphoma proliferation sicknesses and first of all the lymphomas.

[1] J. T. Rhule, C. L. Hill, D. A. Judd, R. F. Schinazi, Chem. Rev. 1998, 98, 327-357.
[2] B. Hasenknopf, Front. Biosci. 2005, 10, 275-287.
[3] C. E. Müller, J. Iqbal, Y. Baqi, H. Zimmermann, A. Röllich, H. Stephan, Bioorg. Med. Chem. Lett. 2006, 16, 5943-5947.
[4] Y. V. Mironov, M. A. Shestopalov, K. A. Brylev, A. S. Yarovoi, G. V. Romanenko, V. E. Fedorov, H. Spies, H.-J. Pietzsch, H. Stephan, G. Geipel, G. Bernhard, W. Kraus, Eur. J. Inorg. Chem. 2005, 657-661.
  • Poster
    International Symposium on Polymer Therapeutics, 19.-21.02.2007, Berlin, Deutschland

Publ.-Id: 9500 - Permalink

Carbohydration of branches ligands with a cyclam-core
Röhrich, A.; Noll, S.; Stephan, H.; Steinbach, J.; Kirchner, R.; Seidel, J.;
Radiopharmaceuticals based on the metallic radionuclides 64/67Cu, 99mTc, 186/188Re and 90Y are often used for diagnostic and therapeutic purposes. Cyclam and its derivatives are one of the most important ligands for the radionuclides mentioned above.[1] A 99mTc-labelled cyclam derivative with attached nitro-triazole units has the potential to be utilized as a marker for tumor hypoxia.[2] Promising tumor accumulation properties have been found for a 99mTc complex of a water-soluble cyclam-containing porphyrin.[3] Recently, we could show that a star-like cyclam ligand appended with four PEG-arms rapidly forms stable copper(II) complexes.[4] Currently, we are focusing our attention on the development of dendritic ligands having both enhanced complex stability and improved bio-availability. In this nexus, we built up two glycodendrimers possessing a cyclam core modified with thiourea-linked sugar residues at the periphery of the molecule (see scheme). Dendrons possessing such sugar moieties show both unique cell uptake behaviour and specific carbohydrate-protein interaction.[5, 6]

We want to report the 99mTc-labelling of the dendritic ligands synthesized. Furthermore, the interaction of these ligands with concanavalin A has been studied using isothermal titration microcalorimetry. In this nexus, a cluster glycoside effect could be clearly shown.[7]

[1] X. Liang, P. Sadler, Chem. Soc. Rev. 2004, 33, 246-266.
[2] S. Murugesan, S. J. Shetty, O. P. D. Noronha, A. M. Samuel, T. S. Srivastava, C. K. K. Nair, L. Kothari, Appl. Radiat. Isot. 2001, 54, 81-88.
[3] S. Murugesan, S. J. Shetty, T. S. Srivastava, O. P. D. Noronha, A. M. Samuel, Appl. Radiat. Isot. 2001, 55, 641-646.
[4] H. Stephan, G. Geipel, D. Appelhans, G. Bernhard, D. Tabuani, H. Komber, B. Voit, Tetrahedron Lett. 2005, 46, 3209-3212.
[5] L. Vannucci, A. Fiserova, K. Sadalapure, T. K. Lindhorst, M. Kuldova,, P. Rossmann, O. Horvath, V. Kren, P. Krist, K. Bezouska, M. Luptovcova, F. Mosca, M. Pospisil, Int. J. Oncology 2003, 23, 285-296.
[6] P. Krist, L. Vannucci, M. Kuzma, P. Man, K. Sadalapure, A. Patel, K. Bezouska, M. Pospisil, L. Petrus, T. K. Lindhorst, V. Kren, CHEMBIOCHEM 2004, 5, 445-452.
  • Poster
    International Symposium on Polymer Therapeutics, 19.-21.02.2007, Berlin, Deutschland

Publ.-Id: 9499 - Permalink

„TRLFS fingerprinting for uranyl(VI) surface species on clay model substances“
Brendler, V.; Trepte, P.; Krepelova, A.; Baumann, N.;
The U(VI) binding to complex systems such as clays, which play an important role in nuclear waste disposal design, is still to be clarified. An efficient tool to study the relevant speciation in-situ is required, thus TRLFS (time-resolved laser-induced fluorescence spectroscopy) was applied. Silica gel (providing higher binding site concentrations as quartz) and gibbsite were used as model substances for the investigation of silianol and aluminol binding sites, respectively, in clays. Kaolinite, offering both types of surface groups, served as a further model system.

All measurements were using 10 mg silica gel in 40 ml 0.1 M NaClO4 and a uranium concentration of 5•10-6 mol/l. The pH was varied between 4.5 and 9. For the TRLFS measurements the solid phase was centrifuged and resuspended with a NaClO4 solution with pH and ionic strength identical to the original but without uranium. A Nd:YAG diode laser with an excitation wavelength of 266 nm was used to study the sorbed species. Spectra were recorded by a diode array in the wavelength range between 460 and 620 nm. The delay times covered 30 ns up to 200 µs. For further details of the experimental set-up see [1]. All measurements were performed under oxygen atmosphere and at room temperature.

For silica gel, at least three U(VI) surface complexes with fluorescence decay constants  of 47 µs, 185 µs and 299 µs were observable. Peak maxima were red-shifted by 10-16 nm compared to the free uranyl cation. Concerning gibbsite, two species with fluorescence lifetimes of 2.4 and 13.2 µs were present throughout the whole pH range, with a third surface species occurring at pH > 7 ( = 51 µs). Finally, the investigation with kaolinite yielded two surface species with lifetimes of 5.9 and 42.5 µs. For pH values below 7 this is closer to the gibbsite results, indicating that aluminol sites dominate uranyl sorption onto alumosilicates.

[1] Sachs, S. et al. (2007) Radiochim. Acta 95, 103-110.
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 72-73
  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany

Publ.-Id: 9498 - Permalink

Terahertz spectroscopy of electron-doped superconductors in magnetic field
Pronin, A.; Pimenov, A.; Loidl, A.; Tsukada, A.; Naito, M.;
In the terahertz and infrared regions we measured the optical conductivity and penetration depth of the electron-doped cuprate superconductor La2-xCexCuO4. In the frequencytemperature behavior of conductivity we observe remarkable differences between the samples with different Ce content, suggesting the gap anisotropy to be a function of the doping level. At terahertz frequencies, we performed measurements in high magnetic fields to suppress superconductivity below Tc. From the conductivity spectra we extract the quasiparticle scattering rate as a function of temperature, and compare its behavior in the superconducting and normal states below Tc. We find a small but measurable optical magnetoresistance at all doping levels, and no signatures for the pseudogap. We also discuss the applicability of ‘universal scaling laws’ to our data on conductivity and penetration depth.
  • Lecture (Conference)
    71. Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 26.-30.03.2007, Regensburg, Germany

Publ.-Id: 9497 - Permalink

Magnetic-field-induced Change of the Fermi Surface in CeBiPt
Bartkowiak, M.; Bergk, B.; Skourski, Y.; Wosnitza, J.; Opahle, I.; Elgazzar, S.; Richter, M.; Löhneysen, H. V.; Yoshino, T.; Takabatake, T.;
Comparative experiments between the two semimetals CeBiPt and LaBiPt reveal changes of the Fermi surface in CeBiPt with respect to temperature, applied magnetic, field and chemical composition. It must be concluded that the strong temperature dependence of the Shubnikov-de Haas (SdH) frequency as well as the change of carrier concentration above a sample dependent critical field are associated with the 4f electrons introduced by the Ce atoms. We present Hall and magnetoresistance measurements up to 70T obtained at our new pulsed high magnetic field laboratory in Dresden. We observe the disappearance of the SdH signal and a change of the Hall coefficient above a sample-dependent threshold field. Rather than at 25 T, as reported previously, we measured a threshold field of ~40 T demonstrating the strong dependence of the Fermi surface on stoichiometry.
  • Poster
    Frühjahrstagung DPG, 26.-30.03.2007, Regensburg, Deutschland

Publ.-Id: 9496 - Permalink

Determination of the band structure of LuNi2B2C
Bergk, B.; Bartkowiak, M.; Ignatchik, O.; Jäckel, M.; Wosnitza, J.; Rosner, H.; Petzold, V.; Canfield, P.;
We present de Haas-van Alphen (dHvA) investigations on the nonmagnetic borocarbide superconductor LuNi2B2C which have been performed by use of the torque method in high magnetic fields up to 32 T and at low temperatures down to 50 mK. The complex band structure is extracted from the quantum oscillations in the normal state. In comparison with full-potential-local-orbital calculations of the band structure we are able to assign the observed dHvA frequencies to the different bands. Temperature dependent dHvA investigations allowed the extraction of the effective band masses for the several Fermi-surface sheets. We observe an enhancement of the effective masses compared to the theoretical calculations which is due to electron-phonon interaction. Finally, we are able to examine the angular dependence of the electron-phonon coupling for the different Fermi-surface sheets.
  • Poster
    Frühjahrstagung der DPG, 26.-30.03.2007, Regensburg, Deutschland

Publ.-Id: 9495 - Permalink

The spherically symmetric α2-dynamo, resonant unfolding of diabolical points and third-order exceptional points in Krein space related setups
Günther, U.; Kirillov, O.; Stefani, F.;
In the first part of the talk we consider the spectral behavior of the spherically symmetric α2-dynamo with idealized boundary conditions. The corresponding operator is self-adjoint in a Krein space and therefore it shares many features with Hamiltonians of PT-symmetric Quantum Mechanics. The spectrum of a dynamo with constant α-profile contains a countably infinite number of diabolical points which under inhomogeneous perturbations unfold in a very specific and resonant way. We describe this mechanism in detail and discuss its physical implications.

In the second part of the talk we discuss coalescing second-order exceptional points in Krein space related models and the emergence of third-order Jordan structures. We demonstrate the basic mechanism on a most simple PT-symmetric 4x4 matrix model and use the obtained results to identify similar structures in the spectral decomposition of α2-dynamo operators.
Keywords: Krein space, MHD dynamo, diabolical point, exceptional point, triple point, Jordan structure, resonance
  • Invited lecture (Conferences)
    Analytic and algebraic methods in physics., 20.02.2007, Prague, Czech Republic

Publ.-Id: 9494 - Permalink

U(VI)-Kaolinite Surface Complexation in Absence and Presence of Humic Acid Studied by TRLFS
Krepelova, A.; Brendler, V.; Sachs, S.; Baumann, N.; Bernhard, G.;
Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied to study the U(VI) surface complexes on kaolinite in presence and absence of humic acid (HA). Two uranyl surface species with fluorescence lifetimes of 5900  700 and 42500  1700 ns and 4400  600 and 30900  3600 ns were identified in the binary (U(VI)-kaolinite) and ternary system (U(VI)-HA-kaolinite), respectively. The fluorescence spectra of adsorbed uranyl surface species were described with six and five fluorescence emission bands in the binary and ternary system, respectively. Positions of peak maxima are shifted significantly to higher wavelengths compared to the free uranyl ion in perchlorate medium. HA has no influence on positions of the fluorescence emission bands. In the binary system, both surface species can be attributed to adsorbed bidentate mononuclear surface complexes, which differ in the number of water molecules in their coordination environment. In the ternary system, U(VI) prefers direct binding on kaolinite rather than via HA, but it is sorbed as a uranyl-humate complex. Thus, the hydration shell of the U(VI) surface complexes is partly displaced with complexed HA, which is simultaneously partly distributed between kaolinite particles. Aluminol binding sites are assumed to control the sorption of U(VI) onto kaolinite.
Keywords: U(VI), Kaolinite, Surface, Complexation, Humic Acid, TRLFS, Sorption
  • Environmental Science & Technology 41(2007)17, 6142-6147

Publ.-Id: 9493 - Permalink

Influence of Humic Acid on the Am(III) Sorption onto Kaolinite
Krepelova, A.; Sachs, S.; Geipel, G.; Bernhard, G.;
The influence of humic acid (HA) on the sorption of Am(III) onto kaolinite KGa-1b (Clay Minerals Society Source Repository) as a model mineral was studied by batch experiments. The sorption experiments were performed under ambient atmosphere (pCO2 = 10-3.5 atm) in a glove box, for a Am(III) concentration of 110-6 M and a HA concentration of 10 mg/L in 0.01 M NaClO4 solution. The solid/solution ratio was 4 g/L and the pH values were varied between pH 3 and 10.
In the absence of HA, Am(III) exhibits a very strong sorption onto kaolinite, which is almost independent on the pH value. The percentage of sorbed Am(III) amounts to 98% at pH 3 and to almost 100% at higher pH values. Presumably the high solid/solution ratio used in the sorption experiments represents the reason for no observation of a sorption edge at lower pH values. In the presence of HA, there are small changes in the Am(III) sorption in comparison to the system without HA. At pH < 5, HA enhances very slightly the sorption of Am(III). At pH ≥ 5.5, the sorption of Am(III) decreases in comparison to the HA-free system due to the formation of dissolved Am(III)-humate complexes. The formation of such binary and ternary Am(III)-humate complexes was reported by Kim et al. [1] and Morgenstern et al. [2]. However, the drop of the Am(III) sorption onto kaolinite observed in this study is very small. Generally, the trend in the sorption behavior of Am(III) in the presence of HA is consistent with the results reported in literature for trivalent actinides. At low pH values the sorption is enhanced by the presence of HA, while at high pH the presence of HA lowers the sorption. At pH > 8.5, HA has no influence on the Am(III) sorption onto kaolinite. Further batch experiments with varying experimental conditions will be performed.
First laser-induced fluorescence spectroscopic measurements were carried out in the systems Am(III)-kaolinite and Am(III)-HA-kaolinite to study the surface complexes of Am(III) on kaolinite. HA decreases the fluorescence intensity of the samples. The shape of the measured fluorescence spectra in both systems, binary and ternary, differs from the spectrum observed in the solution.

[1] J.I. Kim et al., Radiochim. Acta 48, 135 (1989).
[2] M. Morgenstern et al., Radiochim. Acta 88, 7 (2000).

Keywords: Sorption, Kaolinite, Humic Acid, Am(III), Fluorescence Spectroscopy
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 65
  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany

Publ.-Id: 9492 - Permalink

Mixed complexes of alkaline earth uranyl cabonates: A laser-induced time-resolved fluorescence spectroscopic study
Geipel, G.; Amayri, S.; Bernhard, G.;
The interaction of the alkaline earth ions Mg2+, Sr2+ and Ba2+ with the uranyl tricarbonate complex has been studied by time resolved laser-induced fluorescence spectroscopy. In contrast to the non-luminescent uranyl tricarbonate complex the formed products show slight luminescence properties. These have been used to determine the stoichiometry and complex stabilities of the formed compounds. As the alkaline earth elements are located in an outer shell of the complex the influence of the type of the alkaline earth element on the stability constant is not very drastic. Therefore all obtained data were averaged in order to derive an common stability constant for the described complexes. These stability constants result in log β°113 = 26.24 ± 0.08 for the first reaction step and in log β°213 = 30.42 ± 0.23 for the overall complex formation with two alkaline earth ions.
Keywords: Alkaline earth elements, uranium, carbonate, luminescence, complex formation

Publ.-Id: 9491 - Permalink

Probing the phase separation in transition metal implanted semiconductors using synchrotron radiation x-ray diffraction
Zhou, S.; Potzger, K.; von Borany, J.; Skorupa, W.; Helm, M.; Fassbender, J.ORC
Traditional electronics can be greatly stimulated by a combination of magnetic and semiconducting properties where spins provide an additional freedom degree. Recently theoretical works predict that some semiconductors (e.g. ZnO, GaN, TiO2, and Si) doped with transition metal (TM) are diluted magnetic semiconductors (DMS) [1]. In DMS materials, TM ions are substituted onto cation sites of the host semiconductor and are coupled with free carriers via indirect interaction resulting in ferromagnetism. However most experimental works have only concentrated on reporting high Tc and interpreted the observed ferromagnetism in terms of DMS without detail structural characterization. In this work, we have prepared magnetic ZnO, TiO2 and Si samples doped with TM by implantation, and correlated their magnetic and structural properties [2-5]. By synchrotron radiation x-ray diffraction, phase separations (Fe, Ni, Co and Mn-silicide nanocrystals) are observed in our samples, and are responsible for the magnetism. Depending on their crystalline structure, those nanocrystals are crystallographically oriented with respect to the host matrix. The structural information is well agreeable with the magnetic properties measured by SQUID. Additionally due to their orientation nature (crystallographically oriented or randomly oriented with respect to the host crystal), these nanocrystals in some cases are very difficult to detect by a simple Bragg-Brentano scan. This nature results in the pitfall of using XRD to exclude secondary phase in DMS materials.
[1] T. Dietl, et al, Science 287, 1019 (2000).
[2] K. Potzger, Shengqiang Zhou , et al, Appl. Phys. Lett. 88, 052508 (2006).
[3] Shengqiang Zhou, et al., J. Appl. Phys. 100, 114304 (2006).
[4] Shengqiang Zhou, et al., to be published at Phys. Rev. B75, 085203 (2007).
[5] Shengqiang Zhou, et al., to be published at J. Phys. D: Appl. Phys. 40, 964 (2007).
  • Lecture (Conference)
    Work shop on "Ion beam processing and magnetic properties of semiconductors", 13.02.2007, Leuven, Belgium

Publ.-Id: 9490 - Permalink

Schwingungsspektroskopische Analyse von Actinylkomplexen in wässrigen Lösungen und an festen Oberflächen
Foerstendorf, H.;
Die Molekülstrukturen von Actinidenkomplexen können mittels der FT-IR-Spektroskopie identifiziert werden. Die ATR-Technik erlaubt Untersuchungen von wässrigen Lösungen gelöster Komplexe. Damit sind in situ Experimente unter naturnahen Bedingungen mit definierten Parametern (pH, Konzentration, Ionenstärke) möglich. Es werden aktuelle Ergebnisse zur Hydrolysespeziation von U(VI) und zur Komplexbildung mit organischen Liganden und an mineralischen Phasen präsentiert. Die Anwendung des Freie Elektronen Lasers am Beschleuniger ELBE erlaubt die Anwendung oberflächenspezifischer IR-Techniken. Erste Resultate zeigen potentielle Anwendungsmöglichkeiten für Sorptionsproben von Actiniden an definierten Mineraloberflächen.
Keywords: FT-IR spectroscopy; ATR; uranyl(VI); neptunyl(V); FEL; photothermal techniques
  • Lecture (others)
    Institutskolloquium des Instituts für Interdisziplinäre Isotopenforschung Leipzig, 26.02.2007, Leipzig, Germany

Publ.-Id: 9489 - Permalink

Reaction of uranium(VI) with lipopolysaccharide - a laser spectroscopic study
Barkleit, A.; Moll, H.; Bernhard, G.;
Bacteria in the environment have a significant influence on the transport of heavy metals in nature. To estimate the mobility of actinides in natural systems, studies on the molecular level are essential to understand the accumulation and metabolism processes. The bacterial cell surfaces consists of various components which represent a wide range of reactive groups like phosphonate, carboxylate and hydroxyl groups, which are able to bind heavy metals, such as lipopolysaccharides [1].
We investigated the complex behaviour of the lipopolysaccharide (LPS) of pseudomonas aeruginosa serotype 10 with uranium(VI) in the aqueous system at pH 2 to 9 by time-resolved laser-induced fluorescence spectroscopy (TRLFS). The complexation of uranium(VI) by LPS effects a strong red shift of the fluorescence emission bands, connected with an increase of the fluorescence intensity, compared to the free uranyl ion, even at low pH ranges.
The shift of the emission bands shows clearly two different types of complexes. One complex appears only at very low pH (2 to 3) with a red shift of 8-9 nm compared to UO22+(aq). At higher pH the emission bands are even shifted 11-12 nm. This kind of red shift is clearly caused by phosphate groups [2,3]. The complex with the lower red shift at very low pH range can be assigned to a hydrogen phosphonate species, and the complex with the stronger red shift can be dedicated to a dehydrogenated phosphonate species.
The evaluation of the time-resolved measurement shows at least three different lifetimes, indicating more than two uranyl-LPS complex types, which are not to distinguish by the shift of the emission bands, but only by lifetime. Two lifetimes of about 8 and 15 µs can be associated with the two uranyl phosphonate complex types.
The complexation of the uranyl ion was completed even at a lesser molar extent of phosphonate groups over a wide pH range (2 to 7). This indicates a participation of carboxyl or hydroxyl groups, which can describe a further form of uranyl-LPS complex type, associated with a lifetime of about 100 µs.

[1] T.J. Beveridge, R.J. Doyle, Metal Ion and Bacteria, John Wiley & Sons Inc., New York, NY, 1989.
[2] A. Koban, G. Bernhard, J. Inorg. Biochem., in press, DOI: 10.1016/j.jinorgbio.2007.01.001 (2007).
[3] S. Scapolan, E. Ansoborlo, C. Moulin, C. Madic, J. Alloys Comp. 271-273, 106-111 (1998).
Keywords: Uranyl, TRLFS, Lipopolysaccharides, Complexation
  • Lecture (Conference)
    Migration 2007, 26.-31.08.2007, München, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 288-289

Publ.-Id: 9488 - Permalink

Electromagnetic Excitations in Nuclei: From Photon Scattering to Photo-dissociation
Junghans, A.;
In explosive nucleosynthesis temperatures are high enough for photo dissociation reaction to occur, e.g. leading to the production of p- process nuclei. In order to understand the details 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 photo dissociation of nuclei around the particle separation energies can be studied under optimized background conditions. The results of photon scattering experiments from the Z=42 nuclei 92,98,100-Mo and the N=50 nuclei 88-Sr, 89-Y,Land 90 Zr will be shown and compared to calculations based on a random-phase approximation method for deformed nuclei. In activation measurements with bremsstrahlung at end point energy from 10.5 to 16 MeV (gamma, p), (gamma, n) and (gamma,alpha) reactions of 92,100-Mo. have been studied. The results are compared to recent astrophysical network calculations to investigate if the underproduction of Mo, Ru isotopes in the p- process is due to incorrect nuclear reaction rates.
  • Lecture (others)
    Seminar bei Konan Universität, Kobe, Japan, 14.03.2006, Kobe, Japan

Publ.-Id: 9487 - Permalink

Photodissociation studies of p-process nuclei with bremsstrahlung at ELBE
Junghans, A.;
Photodissociation studies of p-process nuclei with bremsstrahlung at ELBE
  • Invited lecture (Conferences)
    International Workshop XXXIV on Gross Properties of Nuclei and Nuclear Excitations, 15.-21.01.2006, Hirschegg, Kleinwalsertal, Austria

Publ.-Id: 9486 - Permalink

Effect of visible and UV illumination on the water contact angle of TiO2 thin films with incorperated nitrogen
Borras, A.; Lopez, C.; Rico, V.; Gonzalez-Elipe, A. R.; Richter, E.; Battiston, G.; Gerbasi, R.; Mcsporran, N.; Sauthier, G.; György, E.;
kein Abstract vorhanden
  • Journal of Physical Chemistry C 111(2007)4, 1801-1808

Publ.-Id: 9485 - Permalink

Possible magnetic-field-induced Lifshitz transition in Ce1−xLaxBiPt
Wosnitza, J.; Bartkowiak, M.; Bergk, B.; Bianchi, A. D.; Goll, G.; von Löhneysen, H.; Yoshino, T.; Takabatake, T.;
Usually the electronic band structure is a rather robust property of the metallic state, especially when applying magnetic fields. For the half-Heusler compounds Ce1−xLaxBiPt, however, we observe magnetic-field-induced band-structure changes in strong magnetic fields. This is evidenced by Shubnikov-de Haas (SdH) and Hall-effect measurements performed in pulsed magnetic fields up to 70 Tesla. Above sample-dependent threshold fields, both in CeBiPt as well as in Ce0.95La0.05BiPt single crystals, the SdH signals vanish and the Hall coefficients change drastically. Such kind of effects are absent in the non-4f compound LaBiPt. Electronic-band-structure calculations can well explain the observed behavior by a 4f-polarization-induced Fermi-surface modification, i.e., a fieldinduced
Lifshitz transition.1,2

1 N. Kozlova et al., Phys. Rev. Lett. 95, 086403 (2005).
2 J. Wosnitza et al., New J. Phys. 8, 174 (2006).
  • Lecture (Conference)
    The International Conference on Strongly Correlated Electron Systems, 13.-18.05.2007, Houston, USA

Publ.-Id: 9484 - Permalink

Binary-collision modeling of ion-induced stress relaxation in cubic BN and amorphous C thin films
Abendroth, B.; Jäger, H. U.; Möller, W.; Bilek, M.;
It is demonstrated that ion-bombardment-induced stress release during physical vapor deposition of cubic boron nitride cBN and amorphous carbon aC films is related to collisional relocation of atoms. A model based on TRIM and molecular dynamics computer simulations is presented.
Experimental results obtained using pulsed substrate bias are in good agreement with the model predictions at adequately chosen threshold energies of atomic relocation. The collisional relaxation model describes the experimental data significantly better than the widely applied thermal spike model.
Keywords: stress relief, ion implantation, cubic boron nitride, amorphous carbon, binary collision approximation, thermal spike
  • Applied Physics Letters 90(2007), 181910

Publ.-Id: 9483 - Permalink

An elementary model of Earth's magnetic field reversals
Stefani, F.; Gerbeth, G.; Günther, U.; Xu, M.; Sorriso-Valvo, L.;
The Earth's magnetic field undergoes polarity reversals with a mean reversal rate that varies from zero during superchrons to 4 per Myr in the present. Typically, these reversals have a strongly asymmetric shape with a decay time of around 50 kyr and a recreation time of around 5 kyr. Despite the recent successes of three-dimensional fully coupled dynamo models, there is no agreement yet on the basic principle of reversal. We investigate a simple mean-field dynamo model and compare the resulting time series and the phase space trajectories with those of paleomagnetic measurements. In the case of highly supercritical dynamos a very good agreement with recent paleomagnetic data is achieved. We show that the typical reversal dynamics traces back to the spectral properties of non-selfadjoint dynamo operators which exhibit so-called exceptional points where two real eigenvalues coalesce and continue as a complex conjugated pair of eigenvalues. Within this picture we can also explain the observed general tendency of highly supercritical dynamos to self-tune into reversal prone states. We conclude with a speculation on the possible role of the inner core growth for the long term changes
of the reversal rate and for the occurrence of superchrons.
  • Invited lecture (Conferences)
    LGIT Research Seminar, 22.03.2007, Grenoble, France

Publ.-Id: 9482 - Permalink

Non-destructive characterization of vertical ZnO nanowire arrays by slow positron implantation spectroscopy, atomic force microscopy, and nuclear reaction analysis
Brauer, G.; Anwand, W.; Grambole, D.; Skorupa, W.; Hou, Y.; Andreev, A.; Teichert, C.; Tam, K. H.; Djurisic, A. B.;
ZnO nanorods, grown by a hydrothermal method, have been characterized by slow positron implantation spectroscopy (SPIS) and atomic force microscopy (AFM). It has been demonstrated that such non-destructive characterization techniques can provide a comprehensive picture of the nanorod structure (including its length, shape, orientation, and seed layer thickness), as well as provide additional information about defects present in the structure. Nanorods were also characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and it was found that the combination SPIS/AFM is more sensitive to the nanorod orientation and the thickness of the seed layer. To obtain still more information about defects in the nanorods, as well as to confirm the findings on the sample structure, nuclear reaction analysis (NRA) was performed and a large concentration of bound hydrogen was found. The results obtained by different characterization techniques are discussed.
Keywords: zinc oxide, nanorods, slow positron implantation spectroscopy, atomic force microscopy, scanning electron microscopy, X-ray diffraction, nuclear reaction analysis
  • Nanotechnology 18(2007), 195301

Publ.-Id: 9481 - Permalink

Some physical data of the near eutectic liquid lead-bismuth
Plevachuk, Y.; Sklyarchuk, V.; Eckert, S.; Gerbeth, G.;
Lead-bismuth alloys are under intense consideration as target material of spallation sources. The thermohydraulic design of such a target or related coolant systems requires a reliable data basis regarding the temperature dependent physical properties of such alloys. We present measurements of the electrical conductivity and thermoelectric power up to about one hundred degree above the melting point for various alloy compositions. For the eutectic alloy the measurements were performed up to much higher temperatures including, in addition, viscosity and thermal conductivity. A comparison with data and scaling relations available in literature is given.
  • Journal of Nuclear Materials 373(2008), 335-342

Publ.-Id: 9480 - Permalink

Experimental results on magnetorotational instability
Gerbeth, G.; Gundrum, T.; Stefani, F.; Hollerbach, R.; Rüdiger, G.;
The magnetorotational instability (MRI) plays a key role in the formation of stars and black holes, by enabling outward angular momentum transport in accretion disks. A recent paper [R. Hollerbach and G. Rüdiger, Phys. Rev. Lett., Vol. 95, 124501 (2005)] has shown that the threshold for the onset of the MRI in a liquid metal Taylor-Couette flow is dramatically reduced if both axial and azimuthal magnetic fields are imposed. In agreement with this prediction, a variety of experimental results of a Taylor-Couette experiment with the liquid metal alloy GaInSn is presented, showing evidence for the existence of the MRI at Reynolds numbers of order 1000 and Hartmann numbers of order 10.
  • Invited lecture (Conferences)
    Julius Hartmann Meeting, 15.-16.02.2007, Coventry, UK

Publ.-Id: 9479 - Permalink

XAFS Study of Uranyl Carbonate Complexes in Aqueous Solution
Ikeda, A.; Hennig, C.; Tsushima, S.; Rossberg, A.; Scheinost, A.; Bernhard, G.;
The carbonate complex of uranium is one of the most fundamental chemical species for the migration study on the geological disposal of radioactive wastes or the remediation study of closed uranium mining. In this study, the carbonate complexes of uranyl(VI)- and uranyl(V) ions were investigated in aqueous solution by using electrochemical (cyclic voltammetry and electrolysis) and spectroscopic (UV-visible and XAFS) techniques.
From the electrochemical study, it was found that the UVO2+-carbonate complex was stable only in the limited concentration range of 0.8 M < [Na2CO3] < 1.4 M. Therefore, the UVO2+ samples for XAFS measurements were prepared in 1.4 M-Na2CO3 solution by using a Pt-mesh working electrode. The results of XAFS measurement indicated that both uranyl(V) and uranyl(VI) ions form the tricarbonate complex, [UO2(CO3)3]n- (n = 5 for uranyl(V) and 4 for uranyl(VI)). The coordination occurs in a bidentate manner and, in general, all bond lengths for the uranyl(V) complex were longer than those for the uranyl(VI) complex. These results are in good agreement with the DFT calculations at least for the uranyl(VI) complex. Additionally, a chemical shift was also observed in the U LI- and LIII-XANES spectra, which can be interpreted as the combination of electronic transitions and multiple scattering features.
  • Poster
    ESRF Users Meeting 2007, 07.02.2007, Grenoble, France

Publ.-Id: 9478 - Permalink

Photoresponse in the visible range from Cr doped TiO2 nanotubes
Ghicov, A.; Schmidt, B.; Kunze, J.; Schmuki, P.;
Layers of TiO2 nanotubes have been fabricated by electrochemical anodization of Ti. After annealing the tubes to an anatase structure Cr doping was carried out by ion implantation at an energy of 60 keV and at two nominal fluences, 5x1015 cm-2 and 5x1016 cm-2. XRD measurements reveal that the anatase structure shows a certain degree of amorphization after ion implantation. However, this effect can be reversed by subsequent thermal annealing. Photoelectrochemical measurements show a visible photoresponse for the Cr+ implanted tubes. Reannealing the tubes, leads to an increase in the photoresponce magnitude in the visible range of the solar spectrum.
Keywords: Nanotubes, ion implantation, photoelectrochemical measurement
  • Chemical Physics Letters 433(2007), 323-326

Publ.-Id: 9477 - Permalink

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