Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Rare earth implanted MOS light emitting devices
Rebohle, L.;
Rare earth implanted MOS light emitting devices are one of the most promising candidates for Si-based light emission and provide – depending on the implanted element – strong electroluminescence from the UV through the visible up to the IR. The talk will start with an introduction to rare earth’s and the special features of their electronic structure, and will focus than on the electroluminescence properties and the possibilities to enhance efficiency and operation life time of such devices. Finally the suitability for potential applications, especially in biosensing, will be discussed.
Keywords: Rare earth Si-based light emission electroluminescence
  • Lecture (others)
    Seminarvortrag, 8.5.2008, Hongkong, China

Publ.-Id: 13386 - Permalink


Selenium-79, a highly mobile radionuclide in the environment?
Scheinost, A. C.;
Current research results contradict the previously assumed high mobility of the radionuclide Se-79 from nuclear waste repositories
  • Lecture (others)
    Wissenschaft Presse Konferenz, 19.-20.01.2009, Grenoble, France

Publ.-Id: 13385 - Permalink


The Rossendorf Beamline at ESRF: Current status and prospects
Scheinost, A. C.;
overview on technical aspects as well as on research highlights in 2009
  • Lecture (Conference)
    10th Annual FWR/PSI-LES Meeting, 28.-29.10.2009, Villigen, Switzerland

Publ.-Id: 13384 - Permalink


A comparative study of actinide complexation in three ligand systems with increasing complexity
Jeanson, A.; Dahou, S.; Guillaumont, D.; Moisy, P.; Auwer, C. D.; Scheinost, A. C.; Hennig, C.; Vidaud, C.; Subra, G.; Solari, P. L.;
The complexation of thorium, neptunium and plutonium at oxidation state +IV with three ligands of increasing complexity has been investigated. These ligands are relevant for bio inorganic systems. The first ligand is the small nitrilotriacetic acid that often play the role of protecting ligands against hydrolysis. EXAFS results for the Th to Pu series have been correlated to quantum chemical calculations and show an homogeneous behavior of the actinide at oxidation state +IV. For larger ligands, steric effects may become significant and one can ask how the ligand may accommodate the large actinide cation coordination sphere. Model pentapeptides have been synthesized and tested as complexing agents. Comparison with NTA shows that the molecular arrangements are radically different. The third ligand system is transferrin, a diferric metalloptrotein that is well known to coordinate a large variety of cations from transition metals of f-elements. Metalloproteins bear primary, secondary and tertiary structures that all play a crucial role in bonding. At a given oxidation state (+IV), but for various atomic numbers (Th, Np, Pu) EXAFS data at the cation LIII edge exhibit significant coordination discrepancies that are related to a changes in protein geometry. In that sense, the metalloprotein may be viewed as a complex system.
Keywords: EXAFS actinoides complexation neptunium thorium plutonium
  • Lecture (Conference)
    XAFS14, 26.-31.07.2009, Camerino, Italy
  • Open Access LogoAbstract in refereed journal
    Journal of Physics: Conference Series 190(2009), 012185
    DOI: 10.1088/1742-6596/190/1/012185

Publ.-Id: 13383 - Permalink


The microbial ecology of land and water contaminated with radioactive waste; towards the development of bioremediation options for the nuclear industry
Geissler, A.; Selenska-Pobell, S.; Morris, K.; Livens, F. R.; Lloyd, J. R.;
The high financial and environmental costs associated with remediation of land contaminated through 60 years of global nuclear activity has underpinned the development of new passive in situ bioremediation processes for sites contaminated with nuclear waste. Many of these processes rely on successfully harnessing newly discovered natural biogeochemical cycles of key radionuclides and fission products. Of particular note are strategies that involve enzymatic and indirect redox transformations of actinides such as uranium, neptunium and plutonium and fission products such as technetium. This chapter will discuss the recent advances that have been made in understanding the microbial colonization of radioactive environments and the biological basis of microbial transformations of radioactive waste in these settings. In addition, the impact of co-contaminants such as nitrate on both the microbial ecology of sediments and radionuclide speciation will also be discussed.
  • Contribution to external collection
    L. Batty, K. Hallberg: Ecology of Industrial Pollution, Cambridge/United Kingdom: Cambridge University Press, 2010, 226-241

Publ.-Id: 13382 - Permalink


Monitoring of the biogeochemical changes induced by increased U(VI) concentrations in natural environments
Selenska-Pobell, S.;
Natural bacterial community structures in the wetlands of uranium mill-tailings with different geographic origin (Germany and USA) and possessing various levels of uranium contamination were studied. Comparative analyses of bacterial communities via direct molecular approaches based on 16S rRNA gene sequences revealed strong predominance of Gamma-, Beta-, or Deltaproteobacteria in dependence on the geographic origin and on the anthropologic history of the studied wastes. In all studied samples novel, yet to be cultured, Betaproteobacterial populations were identified. It was possible to culture representatives of Gamma-Pseudomonas as well as some Alphaproteobacteria (mainly representatives of Sphingomonas sp.) and also different groups of Firmicutes.
Treatments of the samples from one of the studied uranium wastes with uranyl nitrate resulted in a strong shifting in the natural bacterial community and proliferation of representatives of Gamma-, Betaproteobacteria, and/or Firmicutes, depending on the aeration conditions of the experiments. The increased size of the mentioned bacterial populations was confirmed by using a combination of direct monitoring methods based on 16S rRNA and narG genes.
The fate of the added U(VI) in a form of uranyl nitrate was monitored via Time Resolved Laser-induced Fluorescence Spectroscopic (TRLFS) analysis. The latter demonstrated that almost all added uranium was complexed in uranyl phosphate compounds.
Transmission Electron Microscopic (TEM) and X-ray Absorption Spectroscopic (XAS) analyses of the interactions of particular uranium waste bacterial isolates with U(VI) under conditions, corresponding to the natural ones, revealed that the added uranium is immobilized mainly on their cell walls via sorption by organic phosphate groups and/or via precipitation in inorganic uranyl phosphate mineral phases (biomineralization). The observed biomineralization process was connected to release of orthophosphate by the stressed by the treatments bacterial cells. No reduction of U(VI) to U(IV) was observed at the studied oligotrophic conditions which are relevant to the natural ones in the studied wastes.
  • Invited lecture (Conferences)
    Workshop on “Genetic monitoring in Wetlands -2009”, 12.-16.10.2009, Sofia, Bulgarien

Publ.-Id: 13381 - Permalink


Biomineralization of Uranium and Nanocluster Formation by Microorganisms
Selenska-Pobell, S.; Merroun, M.;
Bacteria and archaea are the most ubiquitous organisms in terrestrial and aquatic environments. They play a major role in deposition and weathering of a large variety of minerals enriched with or consisting mainly of different metals, such as iron, manganese, copper, gold, and even radionuclides (e.g. uranium). The structure of biologically synthesized minerals is strongly influenced by the metabolic properties of the bacterial or archaeal strains involved in their production and also by the different metal binding potential of their cell wall components.
The talk will focus on cell wall dependent accumulation and biomineralization of uranium by particular Gram-positive and Gram-negative bacteria recovered from uranium mining wastes. By using TEM, EXAFS and TRLF we were able to demonstrate that the Gram-negative and most of the Gram-positive bacteria inhabiting the oligotrophic uranium mining waste pile soils immobilize U(VI) at their cell walls or extracellularly in a form of uranyl phosphate compounds. Particular Gram-positive isolates, possessing highly ordered proteinaceous surface layers (S-layers), are immobilizing U(VI) by both phosphate groups from their peptidoglycan and also by the carboxylic groups of the aspartate and glutamate stretches of their S-layers.
In addition, the cell wall supported formation of metallic palladium and gold nano-clusters by some bacteria and archaea will be presented. Despite of the different mechanisms of the biological deposition of Pd by Gram-negative and Gram-positive bacteria, the nanoparticles formed by both had almost identical size and catalytic activity. The Au nanoclusters formed by bacteria and archaea had significantly different physical properties.
  • Lecture (Conference)
    13th IACIS International Conference on Surface and Colloid Science, Session: Biomineralization, 14.-19.06.2009, New York, USA

Publ.-Id: 13380 - Permalink


Bacterial isolates from extreme environments and their interactions wit uranium and other xenobiotics
Selenska-Pobell, S.;
Interactions of the natural isolate Pseudomonas rhodesiae R5 with U(VI) and different compounds were studied by using TEM, EXAFS and wet chemistry experiments. The ability of the strain to accumulate U(VI) via bio-sorption and bio-mineralization was demonstrated. TEM analyses revealed that the U(VI) accumulates were exclusively localized on the cell wall. EXAFS analyses demonstrated that the formed U(VI) accumulates represented meta-autunite-like phases.
The strain P. rhodesiae R5 demonstrated a high capability to utilize phenol compounds as well and was used for construction of biofilms on polyethylene oxide cryogels (PEO-biogels). The latter were effectively applied for decontamination of phenol polluted waters.
  • Lecture (others)
    Invited talk at the University of Sofia, Department of Ecology, 06.11.2009, Sofia, Bulgarien

Publ.-Id: 13379 - Permalink


Motion Compensation in Positron Emission Tomography: Performance of a Clinical Integration at the PET centre Dresden-Rossendorf
Langner, J.;
Positron emission tomography (PET) is a well-established functional imaging method used in nuclear medicine. It allows for retrieving information about biochemical and physiological processes in vivo. The currently achievable spatial resolution of PET is about 5mm for brain acquisitions and about 8mm for whole-body acquisitions. However, recent improvements in image reconstruction methods point to a resolution of 2mm in the near future. Typical acquisition times range from minutes to hours due to the low signal-to-noise ratio of the measuring principle of PET, as well as due to the monitoring of the metabolism of the patient over a certain time. Therefore, patient motion increasingly limits the possible spatial resolution of PET. In addition, patient immobilizations are only of limited benefit in this context. Thus, if kept uncorrected, patient motion leads to a relevant resolution degradation and incorrect quantification of metabolic parameters.
In this talk, the results of a novel motion compensation method for clinical brain PET acquisitions developed at the research centre Dresden-Rossendorf (Forschungszentrum Dresden-Rossendorf ) in cooperation with the nuclear medicine department of the university hospital of the Technical University Dresden are presented. By using an external motion tracking system, information about the head motion of a patient is continuously acquired during routine PET acquisitions. Based on the motion information, an event-based motion compensation algorithm performs spatial transformations of all registered coincidence events, thus utilizing the raw data of a PET system - the so-called list-mode data. For routine acquisition of this raw data, methods have been developed which allow for the first time to acquire list-mode data from an ECAT Exact HR+ PET scanner within an acceptable time frame. Furthermore, methods for acquiring the patient motion in clinical routine and methods for an automatic analysis of the registered motion have been developed. For the clinical integration of the aforementioned motion compensation approach, the development of additional methods (e.g. graphical user interfaces) was also part of this work.
After development, optimisation and integration of the event-based motion compensation in clinical use, analysis with example data sets have been performed. Noticeable changes could be demonstrated by analysis of the qualitative and quantitative effects after the motion compensation. From a qualitative point of view, image artefacts have been eliminated, while quantitatively, the results of a tracer kinetics analysis of a FDOPA acquisition showed relevant changes in the R0k3 rates of an irreversible reference tissue two-compartment model. Thus, it could be shown that an integration of an event-based motion compensation method which is based on the utilization of the raw data of a PET scanner, as well as the use of an external motion tracking system, is not only reasonable and possible for clinical use, but also shows relevant qualitative and quantitative improvements for PET imaging.
  • Invited lecture (Conferences)
    Columbia Kreitchman PET Center, 10.11.2009, New York, USA

Publ.-Id: 13377 - Permalink


Especiación química del uranio (VI) precipitado por la bacteria marina Idiomarina loihiensis MAH1: Caracterización espectroscópica por TRLFS
Morcillo De Amuedo, F.; Reitz, T.; Arias Peñalver, J. M.; Gonzalez Muñoz, M. T.; Merroun, M. L.;
Los océanos cubren aproximadamente un 70% de la superficie terrestre, de ahí que sean uno de los mayores sumideros de radionucleidos de origen antropogénicos (1). En el caso del mar mediterráneo, se ha estimado una deposición de 12 y 0.12 PBq de 137Cs and 239,240Pu, respectivamente, entre 1956 y 1996, debido principalmente a la realización de pruebas nucleares (2). El destino final de estos radionucleidos son los sedimentos marinos, aunque pueden permanecer en la columna de agua a concentraciones bajas, quedando biodisponibles para los organismos presentes. Algunos estudios han demostrado que estos ambientes marinos están habitados por una variedad de especies microbianas que podrían interaccionar con estos radionucleidos mediante diferentes mecanismos tales como bioadsorción, acumulación intracelular y precipitación, entre otros. Estos mecanismos ayudan tanto a la movilización como la inmovilización de estos elementos en el medio acuático, alterando, por tanto, su biodisponibilidad. El objetivo del trabajo actual era determinar la especiación química del uranio precipitado por la bacteria marina Idiomarina loihiensis MAH1 en agua de mar mediante espectroscopia de fluorescencia inducida por laser en tiempo resuelto (TRLFS) bajo condiciones medioambientales (a bajas concentraciones de U in agua de mar)

The oceans cover approximately 70% of the Earth’s surface. Hence, they are one of the biggest sinkhole for anthropogenic released radionuclides. In case of the Mediterranean sea, there has been estimated a deposition of 12 and 0.12 PBq of 137Cs and 239,240Pu, respectively, between 1956 and 1996 primarily due to the performance of nuclear tests. The marine sediments are the final destination of these radionuclides, although they can remain in the water column to low concentrations, remaining bioavailable for the present organisms. Some studies have demonstrated that these marine environments are inhabited by a variety of microbial species that might interact with these radionuclides by means of such different mechanisms like, for example, biosorption, intracellular accumulation and precipitation. These mechanisms support the mobilization or immobilization of these elements in the aquatic environment, altering, therefore, his bioavailability. The objective of the present work was to determine the chemical speciation of the uranium precipitated by the marine bacterium Idiomarina loihiensis MAH1 at environmental conditions (low concentrations of U) in sea water by using time-resolved laser-induced fluorescence spectroscopy (TRLFS).
  • Poster
    XXII Congreso Nacional de la Sociedad Española de Microbiología, 21.-24.09.2009, Almeria, Spanien

Publ.-Id: 13376 - Permalink


Investigation on primary side oriented accident management measures in a station blackout scenario for a VVER-1000 reactor
Tusheva, P.; Schaefer, F.; Reinke, N.; Altstadt, E.; Rohde, U.; Weiss, F.-P.; Hurtado, A.;
A consequence of a total loss of AC power supply (station blackout) leading to unavailability of major active safety systems is that the safety criteria ensuring a secure operation of the nuclear power plant would be violated and a consequent core heat-up with possible core degradation would occur. In such an accident a special accident management measure (primary side depressurization) can be applied to reduce the primary pressure and to activate the injection from the passive emergency core cooling systems (accumulators). The analyses presented in this paper are aiming at a detailed investigation of the accident sequence and the possibilities to prevent or to mitigate a damage of the reactor core. A main objective of the investigation is to evaluate the effectiveness of the applied accident management measure. The analyses are performed using the codes ASTEC and ATHLET developed by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and GRS (Gesellschaft für Anlagen- und Reaktorsicherheit mbH).
Keywords: severe accidents, accident management measures, station blackout, VVER-1000 reactors

Publ.-Id: 13375 - Permalink


Application of a grid based hybrid finite volume/boundary element method for simulations of the kinematic induction equation with insulating boundary conditions.
Giesecke, A.; Stefani, F.; Gerbeth, G.;
The experimental realization of dynamo excitation as well as theoretical and numerical examinations of the induction equation have shown the relevance of boundary conditions and material properties for a self-sustaining dynamo. Generally, in non-spherical geometry typical insulating boundary conditions are described by elaborated schemes (e.g. solving of the Laplace equation in an extended domain) or by simplifying approximations (pseudo vacuum). A different approach is provided by a modified integral equation procedure, commonly known as the boundary element method (BEM). Integrating the Laplace equation on the boundaries allows to overcome the difficulties of the non-local character of insulating boundary conditions and the direct computation of the magnetic field next to an insulator becomes possible. However, within the interior of a field producing domain geometric constraints or varying material properties (e.g. electrical conductivity of the container walls or localized high-permeability material) might also play a role.
Keywords: nunerical simulations dynamo insulator boundary conditions boundary element method
  • Lecture (others)
    SFB Meeting, 12.11.2009, Dresden, Deutschland

Publ.-Id: 13374 - Permalink


Quantitative Kelvin probe force microscopy
Baumgart, C.; Helm, M.; Schmidt, H.;
In this paper we report on the investigation of electrostatic forces between a conductive probe and semiconducting materials by means of Kelvin probe force microscopy measurements. Due to the formation of an asymmetric electric dipole at the semiconductor surface, the measured Kelvin bias is related with the difference between Fermi energy and respective band edge. Quantitative Kelvin probe force microscopy measurements on semiconductors, namely on a conventional dynamic random-access memory cell and on a cross-sectionally prepared Si epilayer structure, are presented.
  • Contribution to proceedings
    MRS Fall Meeting Boston, 30.11.-04.12.2009, Boston, MA, USA

Publ.-Id: 13373 - Permalink


Frequency dependent Kelvin probe force microscopy on locally doped Si
Baumgart, C.; Helm, M.; Schmidt, H.;
Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface potential. We present its applicability to buried doped regions in cross-sectionally prepared Si epilayer structures and to shallow doped regions in a conventional dynamic random access memory (DRAM) cell. Frequency dependent KPFM measurements were performed under ambient conditions by means of an Anfatec Level-AFM with a 2nd amplifier and p- and n-type conductive NSC15 probes from MikroMasch. Using an active mixer, the excitation amplitude of the NSC15 probes is almost independent of the operation frequency. The frequency dependence of the Kelvin bias above differently doped regions is discussed with respect to surface states and trapped charges in the thin oxide layer. As a result, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped Si are probed.
  • Poster
    MRS Fall Meeting Boston, 30.11.-04.12.2009, Boston, MA, USA

Publ.-Id: 13372 - Permalink


Solid state spectroscopy using an infrared free-electron laser
Helm, M.;
A free electron laser covering a wavelength range of nearly two spectral decades (3-300 µm or 1-100 THz) has been in operation at our research center for a few years. I will present a few examples of the research done with it, taking advantage if its high peak and average power and picosecond time structure.
I will present measurements of carrier relaxation in semiconductor quantum dots, where the relaxation time varies by three orders of magnitude (2 ps to 1.5 ns), if the energy level spacing is changed by only a factor of two (30 meV to 15 meV). This can be explained in the quantum dot polaron picture.
The high average power allows one to perform near-field microscopy experiments. We can image ferroelectric domains on BaTiO3 surfaces purely due to their optical contrast resulting from a slight anisotropy of the dielectric function. Sweeping the FEL wavelength across a phonon resonance results in a reversal of optical contrast, which demonstrates the resonant nature of the interaction. The spatial resolution is 150 nm, about 1/100 of the wavelength.
Finally I will discuss a nonlinear mixing experiment, where THz sidebands of 800 nm radiation are generated in a semiconductor quantum well system, and briefly describe first cyclotron resonance experiments using the FEL in the pulsed magnetic field.
Keywords: free electron laser, spectroscopy, infrared
  • Lecture (others)
    Kolloquium am Institute for Molecules and Materials, Radboud University, The Netherlands, 10.11.2009, Nijmegen, The Netherlands

Publ.-Id: 13371 - Permalink


Comparison of bismuth emitting liquid metal ion sources
Bischoff, L.; Pilz, W.; Mazarov, P.; Wieck, A. D.;
Four different liquid metal ion sources (LMIS), working with pure Bi as well as with Bi containing alloys (Au13Bi87, Ga38Bi62, Ga35Bi60Li5) were investigated with respect to the emission behaviour as a function of current and temperature, the mass spectra and the energy distribution of the individual ion species. Additionally, for the pure Bi LMIS the sputtering rates for Bi ions and clusters on a Si, SiO2 and Ge substrates were compared with that of Ga projectile ions using a mass separating focused ion beam system.
Keywords: Bismuth alloy LMIS; mass spectra; energy spread; FIB.

Publ.-Id: 13370 - Permalink


Quantitative Electrical Nanometrology - Kelvin Probe Force Microscopy Measurements on Semiconductors
Baumgart, C.; Streit, S.; Helm, M.; Schmidt, H.;
In this paper state of the art electrical nanometrology techniques are reviewed with the focus on semiconducting materials. The basics of scanning capacitance microscopy, scanning spreading resistance microscopy, scanning microwave microscopy, and Kelvin probe force microscopy, and their applicability on various material systems are discussed. Quantitative Kelvin probe force microscopy measurements on semiconductors, namely on a conventional dynamic random-access memory cell and on a cross-sectionally prepared Si epilayer structure, are presented.

Publ.-Id: 13369 - Permalink


Injected wake field acceleration with a 40 MeV electron linac
Kraft, S.; Jochmann, A.; Erler, C.; Debus, A.; Bussmann, M.; Sauerbrey, R.; Schramm, U.; Cowan, T.;
Over the last years multiple research groups achieved multi-MeV to GeV electron beams. Ultrashort bunches and a very low emittance combined with a high bunch charge offer a wide range of applications nevertheless the reproducibility of those beams is one of the main problems. External injection into a plasma wake is a promising concept to separate the influence of different input parameters from each other for more control of experimental results and to improve reproducibility. At the Research Center Dresden-Rossendorf the 150TW laser system DRACO was set up next to an superconducting electron accelerator. This will give the opportunity to study wake field acceleration in more detail. In this talk the present status of the experiment, ongoing upgrades and future plans will be described.
  • Lecture (Conference)
    51st Annual Meeting of the APS Division of Plasma Physics, 02.-06.11.2009, Atlanta, USA

Publ.-Id: 13368 - Permalink


Anwendung von Ultraschallverfahren zur Charakterisierung von Flüssigmetall-Zweiphasenströmungen
Eckert, S.; Zhang, C.; Gerbeth, G.;
Die Injektion von Gasblasen wird oft in metallurgischen Prozessen zur Veredlung oder Entgasung metallischer Schmelzen eingesetzt. Eine Optimierung der Prozessabläufe kann nur auf Grundlage eines umfassenden Verständnisses der Strömungs- und Transportvorgänge erfolgreich sein. Dies erfordert neben numerischen Simulationen eine realitätsnahe experimentelle Modellierung in Flüssigmetallen. Für diese Modellexperimente besteht ein großer Bedarf an geeigneter Messtechnik zur Bestimmung der Strömungsstruktur und der Blaseneigenschaften.
In den letzten Jahren hat die Ultraschallströmungsmesstechnik im Hinblick auf einen Einsatz in Flüssigmetallen eine spürbare Entwicklung erfahren und ihre Eignung für Messungen in Zweiphasenströmung unter Beweis gestellt. Im Vortrag werden das Ultraschall-Doppler und das Ultraschall-Laufzeitverfahren vorgestellt. Mit Hilfe des Ultraschall-Doppler Verfahrens können gleichzeitig Flüssigmetall- und Blasengeschwindigkeit bestimmt werden. Das Laufzeitverfahren liefert komplementäre Daten über die geometrische Struktur der Blasen und des Blasenschwarms. Dies betrifft insbesondere Blasendurchmesser, Blasenform und raumzeitliche Ausdehnung des Blasenschwarms. Spezifische Probleme der Verfahren, insbesondere bei höheren Gasgehalten, werden diskutiert und zukünftige Entwicklungsperspektiven aufgezeigt.
Keywords: Liquid metal two-phase flow, bubbly flow, Flow measurements, Ultrasound-Doppler method
  • Lecture (others)
    Festkolloquium anlässlich des 70. Geburtstags von Prof. Dr. E. Kaiser, 06.11.2009, Dresden, Deutschland

Publ.-Id: 13367 - Permalink


Prototype coupling of the CFD software ANSYS CFX with the 3D neutron kinetic core model DYN3D
Kliem, S.; Rohde, U.; Schütze, J.; Frank, T.;
The CFD code ANSYS CFX has been coupled with the neutron-kinetic core model DYN3D. ANSYS CFX calculates the fluid dynamics and related transport phenomena in the reactor’s coolant and provides the corresponding data to DYN3D. In the fluid flow simulation of the coolant, the core itself is modeled by the porous body approach. DYN3D calculates the neutron kinetics and the fuel behavior including the heat transfer to the coolant. The physical data interface between the codes is the volumetric heat release rate into the coolant. In the prototype that is currently available, the coupling is restricted to single-phase flow problems. In the time domain an explicit coupling of the codes has been implemented so far.
Steady-state and transient verification calculations for a small-size test problem confirm the correctness of the implementation of the prototype coupling. This test problem was a mini-core consisting of nine real-size fuel assemblies. Comparison was performed with the DYN3D stand-alone code. In the steady state, the effective multiplication factor obtained by the ANSYS CFX/DYN3D codes shows a deviation of 9.8 pcm from the DYN3D stand-alone solution. This difference can be attributed to the use of different water property packages in the two codes. The transient test case simulated the withdrawal of the control rod from the central fuel assembly at hot zero power. Power increase during the introduction of positive reactivity and power reduction due to fuel temperature increase are calculated in the same manner by the coupled and the stand-alone codes. The maximum values reached during the power rise differ by about 1 MW at a power level of 50 MW. Beside the different water property packages, these differences are caused by the use of different flow solvers.
Keywords: Computational Fluid Dynamics, 3D neutron kinetics, Code coupling
  • Contribution to proceedings
    PHYSOR 2010, 09.-14.05.2010, Pittsburgh, USA
    Proceedings of the PHYSOR 2010, La Grange Park, Illinois, USA: ANS, 9780894480799
  • Lecture (Conference)
    PHYSOR-2010, 09.-14.05.2010, Pittsburgh, USA

Publ.-Id: 13366 - Permalink


Integration der Positronen-Emissions-Tomographie in die Strahlentherapie mit hochenergetischen Photonen
Kunath, D.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-525 2009

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Publ.-Id: 13365 - Permalink


Messung des Wirkungsquerschnitts astrophysikalisch relevanter Kernreaktionen
Trompler, E.;
Die 14^N(p,gamma)^15O-Reaktion ist die langsamste im Bethe-Weizsäcker-Zyklus des Wasserstoffbrennens und bestimmt dessen Rate. Der Wirkungsquerschnitt dieser Reaktion wurde in der Vergangenheit über einen weiten Energiebereich gemessen. Erneute, genauere Messungen im niederenergetischen Bereich hatten gezeigt, dass der Wirkungsquerschnitt um einen Faktor zwei niedriger ist als erwartet. Im Rahmen dieser Arbeit soll überprüft werden, ob sich das auch für höhere Energien bestätigt.
Hierzu wurden Messungen am Protonenstrahl des 3 MV Tendetron-Beschleunigers, Forschungszentrum Dresden-Rossendorf, durchgeführt. Zunächst wird eine experimentelle Kalibrierung der gamma-Nachweiswahrscheinlichkeit dreier comptonunterdrückter Reinstgermanium-Detektoren im energiebereich von 0,7 bis 12 MeV durchgeführt. Das Ergebnis wird mit der bisher simulierten Effizienzkurve verglichen. Dann wird im Energiebereich von 0,5 bis 1,5 MeV der Wirkungsquerschnitt für 14^N(p,gamma)^15O*(6.7929), das heißt für den Einfang in den vierten angeregten von 15^O bei 6.792 keV, bestimmt. Der Einfang in diesen Zustand trägt mehr als die Hälfte zum extrapolierten Wirkungsquerschnitt bei Energien wie im Inneren der Sonne bei.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-523 2009

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Publ.-Id: 13364 - Permalink


Molecular Structure and Electrochemical Behavior of Uranyl(VI) Complex with Pentadentate Schiff Base Ligand: Prevention of Uranyl(V) Cation-Cation Interaction by Fully Chelating Equatorial Coordination Sites
Takao, K.; Kato, M.; Takao, S.; Nagasawa, A.; Bernhard, G.; Hennig, C.; Ikeda, Y.;
The UVI complex with a pentadentate Schiff base ligand (N,N’-disalicylidenediethylene-triaminate = saldien2–) was prepared as a starting material of a potentially stable UV complex without any possibility of UVO2+•••UVO2+ cation-cation interaction, and was found in three different crystal phases. Two of them had the same composition of UVIO2(saldien)•DMSO in orthorhombic and monoclinic systems (DMSO = dimethyl sulfoxide, 1a and 1c, respectively). The DMSO molecule in both 1a and 1c does not show any coordination to UVIO2(saldien), but it is just present as a solvent in the crystal structures. The other isolated crystals consisted only of UVIO2(saldien) without incorporation of solvent molecules (1b, orthorhombic). Different conformation of the coordinated saldien2– in 1c from those in 1a and 1b was observed. The conformers exchange each other in a solution through a flipping motion of the phenyl rings. The pentagonal equatorial coordination of UVIO2(saldien) remains unchanged even in strongly Lewis-basic solvents, DMSO and N,N-dimethylformamide. Cyclic voltammetry of UVIO2(saldien) in DMSO showed a quasireversible redox reaction without any successive reactions. The electron stoichiometry determined by the UV-vis-NIR spectroelectrochemical technique is close to 1, indicating that the reduction product of UVIO2(saldien) is [UVO2(saldien)]– which is stable in DMSO. The standard redox potential of [UVO2(saldien)]–/UVIO2(saldien) in DMSO is –1.584 V vs. Fc/Fc+. This UV complex shows the characteristic absorption bands due to f-f transitions in its 5f1 configuration and charge-transfer from the axial oxygen to U5+.
Keywords: Uranyl(V), Stabilization, Electrochemistry, f-f Transition
  • Inorganic Chemistry 49(2010)5, 2349-2359

Publ.-Id: 13363 - Permalink


First evaluation of a fast full 3D list-mode based image reconstruction for PET
Lougovski, A.; Mölle, H.; Langner, J.; Will, E.; van den Hoff, J.;
Ziel/Aim:
Despite the fact that all modern PET scanners support 3D data acquisition protocols, up to now only a few of them have supported full 3D image reconstruction. Normally the reconstruction task is performed in sinogram space and reduced to a 2D problem using Fourier rebinning. This implies certain approximations and can degrade image quality. 3D list-mode reconstruction potentially is able to overcome these limitations while allowing at the same time flexible integration of motion correction methods into the reconstruction. The very limited availability of corresponding open-sourced software motivated us to develop our own, platform independent, fully 3D list-mode reconstruction with the final goal of integration of our event-based motion correction into it.

Methodik/Methods:
As the basis for our reconstruction we have taken the Ordinary Poisson List-mode Ordered Subsets Expectation Maximization algorithm (OP-LMOSEM) with on-the-fly system matrix simulation using a ray-tracing technique. The source code (C++) supports multi-threading and allows distributed computing, both of which decreases reconstruction time considerably. It also includes all
necessary corrections (attenuation, normalization, randoms etc.). We use the Single Scatter Simulation algorithm to compensate for Compton scatter and have evaluated the new reconstruction by comparison with the standard OSEM-reconstruction available with our Siemens EXACT HR+ scanner. Phantom measurements were performed in list-mode using the software previously developed in our lab. The evaluation procedure has been divided into three parts: i) quantitative accuracy (ROI's mean value comparison); ii) spatial resolution (FWHM comparison); iii) Signal to Noise Ratio, SNR (ratio of standard deviation to mean value in homogeneous ROIs).

Ergebnisse/Results:
Relative to the standard reconstruction we obtain the following results: quantitatively, images show reasonable concordance with the reference, abstract-dialog | Abstract Management System
the differences are below 8%. The reconstructed spatial resolution is on average 10% better (up to 20% in smaller structures). The mean SNR shows 6% improvement (especially at the axial edges of the field of view). Currently, reconstruction time for a typical 5 minute FDG brain scan is 13 minutes using 64 cores running at 2.3 GHz.

Schlussfolgerungen/Conclusions:
3D list-mode reconstructions are approaching clinical usefulness and prospectively offer the optimal framework for incorporating event-based motion correction methods into the reconstruction. Our implementation has proven to provide results, which already are better then those of the standard reconstruction on our system, although there is still room for much improvement. In the next step we plan to incorporate motion correction into the algorithm.
  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A26
  • Lecture (Conference)
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D

Publ.-Id: 13362 - Permalink


Blood flow measurements using MRI and Arterial Spin Labeling: a comparison with radioactive microspheres
Bos, A.; Bergmann, R.; Strobel, K.; van den Hoff, J.;
Aim:
Arterial Spin Labeling (ASL) is a Magnetic Resonance Imaging (MRI) technique for quantitative blood flow measurements. While the principal validity of the technique has been shown, e.g. for human brain investigations, its practical applicability and accuracy depends very sensitively on the specific experimental setting. The purpose of this work was the evaluation of ASL for perfusion measurements in the rat brain by a comparison with microsphere derived regional perfusion information using dedicated small animal PET and SPECT systems.

Methods:
MRI measurements were performed first, immediately followed by the microsphere measurements. Before measurements, catheters were implanted through the right carotid artery into the left ventricle of the heart for administration of radio-labeled microspheres (20). The in-vivo distribution of radio-labeled microspheres was evaluated by PET (microPET P4, Siemens) using Cu-64 and Ga-68 microspheres. For SPECT (NanoSPECT, Bioscan) measurements Tc-99m microspheres were used. MRI perfusion measurements were performed in a 7T small animal system (BioSpec 70/30, BRUKER) with the vendor provided ASL protocol using a FAIR (flow-sensitive alternating inversion recovery) sequence with an adiabatic hyperbolic secant inversion pulse (length-bandwidth product: 80). The global and selective T1 images were used for calculation of perfusion values.

Results:
For normal rat brain (without catheter) we measured perfusion values using FAIR-ASL ranging from 1.2 to 1.4 ml/min/g in the caudate putamen. The implantation of the catheter created differences in the perfusion between the right and left hemisphere of the brain (due to the partial blocking of the right carotid artery), which are apparent from the left/right differences in the microsphere distribution. These differences are visible in the ASL-derived perfusion as well, ranging from 25 - 60%. ASL-derived perfusion exhibits substantial inter- and intra-individual variability, the cause of which is currently under investigation.

Conclusions:
Quantitative perfusion measurements in the rat brain using ASL seem possible but are very susceptible to minor deviations from the optimal setup (e.g. concerning shimming of the magnetic field and motion artifacts). Overall regional contrast is on average concordant with regional distribution of microspheres. In order to be useful for routine application in small animal imaging, ASL data acquisition and data evaluation needs to be further optimized. A final calibration via a quantitative comparison with radio-labeled microspheres seems mandatory.
  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A27
  • Lecture (Conference)
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D

Publ.-Id: 13361 - Permalink


Beam-Shape Effects in Nonlinear Compton and Thomson Scattering
Heinzl, T.; Seipt, D.; Kampfer, B.;
We discuss intensity effects in collisions between beams of optical photons from a high-power laser and relativistic electrons. Our main focus are the modifications of the emission spectra due to realistic finite-beam geometries. By carefully analyzing the classical limit we precisely quantify the distinction between strong-field QED Compton scattering and classical Thomson scattering. A purely classical, but fully covariant, calculation of the bremsstrahlung emitted by an electron in a plane wave laser field yields radiation into harmonics, as expected. This result is generalized to pulses of finite duration and explains the appearance of line broadening and harmonic substructure as an interference phenomenon. The ensuing numerical treatment confirms that strong focussing of the laser leads to a broad continuum while higher harmonics become visible only at moderate focussing, hence lower intensity. We present a scaling law for the backscattered photon spectral density which facilitates averaging over electron beam phase space. Finally, we propose a set of realistic parameters such that the observation of intensity induced spectral red-shift, higher harmonics, and their substructure, becomes feasible.
Keywords: high-intensity lasers, Compton scattering, Thomson scattering
  • Physical Review A 81(2010), 022125

Publ.-Id: 13360 - Permalink


Kann die Atembewegungskorrektur die Darstellung und Quantifizierung im Abdomenbereich verbessern?
Mölle, H.; Langner, J.; Beuthien-Baumann, B.; Oehme, L.; Hofheinz, F.; Kotzerke, J.; van den Hoff, J.;
Ziel/Aim:
Vor dem Hintergrund einer kontinuierlichen Verbesserung der apparativ erreichbaren räumlichen Auflösung in der PET stellen Patientenbewegungen einen maßgeblichen Faktor dar, der die praktisch realisierbare räumliche Auflösung beschränkt. Bei PET-Aufnahmen vom Thorax und Abdomen kommt es insbesondere durch die unvermeidbare Atembewegung des Patienten zur zyklischen Verschiebung der inneren Organe sowie anderer Zielstrukturen. Hieraus resultiert eine unter Umständen beträchtliche Bewegungsunschärfe in den tomographischen Bilddaten. Dies erschwert die visuelle Beurteilung und führt zu Fehlern bei der Bestimmung quantitativer Parameter wie der maximalen Traceranreicherung und dem Volumen der Strukturen. Besonders betroffen hiervon sind kleine Strukturen wie etwa die Nierenkelche. So war es Ziel dieser Arbeit, die Quantifizierung und die Erkennbarkeit von kleinen Strukturen im Abdomen zu verbessern.

Methodik/Methods:
Bei 40 Patienten wurde eine Ganzkörperuntersuchung mit F18-FDG am PET-Scanner ECAT Exact HR+ durchgeführt. Gleichzeitig erfassten Infrarot-Tracking-Kameras die Atembewegung der Patienten. Anschließend wurde eine Atemtriggerung anhand der Atembewegungsamplitude durchgeführt. Die Bewegung der Nieren wurde durch die Differenz der Nierenpositionen in der end-exspiratorischen und der end-inspiratorischen Atemphase bestimmt. Die Korrektur der Nierenbewegung erfolgte mit Hilfe einer rigiden Transformation, die alle Atemphasen auf eine gemeinsame Atemphase abbildet.

Ergebnisse/Results:
Von 40 F18-FDG Patienten konnte bei 26 die Bewegung der linken und bei 24 die Bewegung der rechten Niere ermittelt werden. Bei den übrigen Patienten war die F18-FDG-Anreicherung in den Nieren zu gering, um die Bewegung zu bestimmen. Die mittlere kraniokaudale Bewegung der linken Niere betrug 8,6 mm und die der rechten Niere 8,2 mm. Es wurde ein Vergleich des maximalen SUV und des Volumens einer lokalen Traceranreicherung in der Niere zwischen dem bewegungskorrigierten und dem unkorrigierten PET-Bild durchgeführt. Bei den Patienten zeigte sich eine maximale Reduktion des Volumens um 40% und eine maximale Zunahme des SUV um 20%.

Schlussfolgerungen/Conclusions:
Die Atembewegung beeinflusst maßgeblich die Darstellung und Quantifizierung im Abdomenbereich. Für eine verlässliche Quantifizierung ist eine Korrektur der Bewegung im Abdomen notwendig.
  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A28
  • Lecture (Conference)
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D

Publ.-Id: 13359 - Permalink


Einfluss der event-basierten Bewegungskorrektur auf die Bestimmung pharmakokinetischer Parameter bei PET-Hirnuntersuchungen
Langner, J.; Mölle, H.; Oehme, L.; Hofheinz, F.; Beuthien-Baumann, B.; van den Hoff, J.;
Ziel/Aim:
Patientenbewegungen sind in der PET unvermeidbar. So können hierdurch die Bilddaten z.B. verfälscht oder bei dynamischen Hirnuntersuchungen die Bestimmung von Zeit-Aktivitäts-Kurven (TAC) bzw. die Quantifizierung pharmakokinetischer Parameter beeinflusst werden. Die in diesem Zusammenhang in den letzten Jahren entwickelten Methoden zur Registrierung und Korrektur der Patientenbewegung stellen nützliche Werkzeuge zur Minimierung dieser Effekte zur Verfügung. In der vorliegenden Arbeit war es Ziel, den Einfluss einer bereits routinemäßig an unserer Einrichtung angewandten event-basierten Bewegungskorrektur, die auf der räumlichen Transformation jeder Line-of-Response (LOR) basiert, innerhalb eines größeren Patientenkollektivs zu untersuchen. Hierdurch sollten Aussagen darüber getroffen werden, in welchem Maße die Korrekturmethode in der Lage ist, den Einfluss der Bewegung auf die Auswertung von dynamischen Hirnuntersuchungen zu reduzieren.

Methodik/Methods:
Bei 645 [18F]DOPA-Untersuchungen mit Fragestellung Morbus Parkinson wurde eine Bewegungskorrektur durchgeführt. Hierbei wurde bei 20% eine maximale Bewegung größer 7 mm festgestellt. Für diese Untersuchungen wurden die Einstromraten (R0k3) mittels eines irreversiblen Zweikompartment-Modells mit Referenzgewebe (Patlak-Auswertung) sowohl vor als auch nach Bewegungskorrektur bestimmt. Hierfür wurden 8 ROIs innerhalb des Striatum sowie eine ROI im Referenzgewebe positioniert und für jede ROI im Striatum die Zeit-Aktivitäts-Kurve (TAC) sowie die Einstromrate berechnet. Des Weiteren wurden für jeden Datensatz parametrische Bilder erzeugt und mit den unkorrigierten Daten verglichen.

Ergebnisse/Results:
Die maximale Bewegung in den insgesamt 645 Untersuchungen verteilt sich wie folgt: (i) 31%: 0,5 – 3 mm, (ii) 31%: 3 – 5 mm, (iii) 18%: 5 – 7 mm, (iv) 20%: > 7 mm. Bei der quantitativen Auswertung zeigten sich Unterschiede im Verlauf der TAC von bis zu 30-40%. Die R0k3 Werte zeigten zum Teil Änderungen von mehreren hundert Prozent. Im Vergleich der parametrischen Bilder konnte dies verifiziert werden.

Schlussfolgerungen/Conclusions:
Die Quantifizierung tracerkinetischer Parameter wird von Patientenbewegungen, deren Ausmaß vergleichbar mit der Größe der Zielstrukturen ist, empfindlich beeinflusst und verliert u.U. ihre Gültigkeit. Eine event-basierte Bewegungskorrektur ist in der Lage, diese Fehlerquelle zu minimieren.
  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A36
  • Lecture (Conference)
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D

Publ.-Id: 13358 - Permalink


Fluorescence and Infrared Cross-Correlation Spectroscopy: A New Tool in Analysing Protein Conformational Coupling
Fahmy, K.;
The allosteric regulation of biomolecules such as enzymes or receptors is based on structural changes that are initiated at a ligand-binding site and become transmitted to a "distant" active site where enzymatic efficiency or interaction with effectors is altered. Understanding the molecular mechanisms of this long range coupling between distinct protein domains is crucial for many pharmacoligically relevant systems where the conformation of a target molecule has to be specifically affected by a designed ligand. We have developed a generalized multidimensional spectoscopic approach to investigate long range conformational coupling in proteins. It employs the integration of fluorescence emission and infrared absorption data recorded simultaneously from the same protein sample that undergoes conformational transitions in response to an external perturbation. Using attenuated total relfectance (ATR) Fourier-transform infrared (FTIR) difference spectroscopy, additional channels for excitation and detection of fluorescence where established by light guides positioned above the sample on the ATR crystal. Long range coupling in the signal transfer through rhodopsin has recently been identified by Fluorescence-IR-cross-correlation [1]. Using 2D-cross-correlation techniques, the kinetic asynchronicity of the emission from natural or artificial site-specific fluorophores relative to the secondary structure-sensitive IR-absorption bands can be determined. Thereby, IR absorptions can be identified in a model-free and unbiased way that can be assigned to secondary-strutural elements that become specifically stabilized by ligand interactions. Here, we demonstrate in a cytoskeletal protein the correlation of the loss of ligand-dependent static quenching of intrinsic tryptophan emission during thermal unfolding with the loss of structure monitored by FTIR spectroscopy. The high signal to noise ratio in 2D-correlation and the "synchronicity tagging" of the IR bands through their correlation with an independent monitor of ligand dissociation allows detecting ligand protein interactions with an accuracy that is not achieved by FTIR-spectroscopy alone. In addition, topological information can be obtained from the emission wavelength of the tryptophans that become gradually unquenched during temperature-induced ligand dissociation. Fluorescence-IR-cross-correlation spectroscopy thus extends the IR-based conformational analysis by the inclusion of site-specific information on local physical parameters (polarity, electrostatics, etc.) specifically affecting the emission of fluorophores. We show how this approach provides structural information on flavonoid binding to actin, a cytoskeletal and nuclear protein that has recently been shown to respond to the binding of these natural compounds by flavonoid-specific conformational changes [2].


Acknowledgement
We acknowledge financial support by the Deutsche Forschungsgemeinschaft to KF (grant 248/4)

References
[1] N. Lehmann, U. Alexiev, K. Fahmy, J. Mol. Biol. 336 (2007) 1129–1141.
[2] M. Boehl, S. Tietze, A. Sokoll, S. Madathil, F. Pfennig, J. Apostolakis, K. Fahmy, H.-O. Gutzeit,
Biophys. J. 93 (2007) 2767-2780.
  • Lecture (Conference)
    XIII European Conference on the Spectroscopy of Biological Molecules, 28.08.2009, Palermo, Italy

Publ.-Id: 13357 - Permalink


S-Layer protein from Lysinibacillus Sphaericus JG-A12 as matrix for AuIII sorption and Au-nanoparticle formation
Jankowski, U.; Merroun, M. L.; Selenska-Pobell, S.; Fahmy, K.;
The strain Lysinibacillus sphaericus JG-A12, isolated from the uranium mining site at Haberland, Saxony (Germany) selectively and reversibly accumulates radionuclides and toxic metals. Metal binding occurs to its surface layer (S-layer) surrounding the cells. Here, we have studied by Fourier-transform infrared (FTIR) spectroscopy the protein structure and stability as a function of AuIII binding and the subsequent reductively induced formation of Au-nanoclusters. Similar to previously studied complexes with PdII, Au-treated S-layers become resistant to acid denaturation evidenced by little response of their amide I absorption frequency. However, the strong effect of PdII exerted on the side chain carboxylate IR absorption intensity is not observed with gold. Particularly after reduction, the carboxyl absorption responds little to acidification and a fraction appears to be protonated already at neutral pH. We ascribe this to a hydrophobic environment of the carboxyl groups after formation of Au-nanoclusters. EXAFS spectra agree with the metallic Au-Au distance but the reduced coordination number indicates that the Au-nanoclusters do not exceed ~2 nm. Thus, the S-layer of L. sphaericus JG-A12 provides a biotemplate for efficient Au-nanocluster formation in an acid-resistant matrix and independently of cysteins.
Keywords: Au-nanocluster S-layer L. sphaericus JG-A12 Fourier Transform infrared spectroscopy EXAFS
  • Contribution to proceedings
    XIII European Conference on the Spectroscopy of Biological Molecules, 28.08.-02.09.2009, Palermo, Italy
    Spectroscopy 24(2010)1-2 Special Issue, Amsterdam: IOS-Press, 177-181

Publ.-Id: 13356 - Permalink


Characterization of a Halobacterium sp. isolate cultivated from samples collected from Arava Desert
Jankowski, U.; Flemming, K.; Selenska-Pobell, S.;
The Arava Desert is a hostile oligotrophic, extremely dry and hyper saline environment in Israel. Such environments are usually inhabited by microorganisms called extremophiles. In this study, an extreme halophilic Archaeon was cultivated from sand samples of the Arava Desert. The interactions of this archaeal isolate with radionuclides will be studied in the next future. Such studies are important because saline environments are perspective sites for deposition of radioactive wastes.
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-511 Februar 2009, 35-35

Publ.-Id: 13355 - Permalink


Wie beeinflussen mikrobielle Lebensgemeinschaften (Biofilme) Uran in der Umwelt?
Krawczyk-Bärsch, E.;
Biofilme sind Lebensgemeinschaften von verschieden Mikroorganismen, die allgegenwärtig sind. Über Poren und Kanäle in den Biofilmen werden Wasser, Nährstoffe, Signalstoffe, aber auch toxische Schwermetalle aus der umgebenden Lösung zu den einzelnen Mikroorganismen gebracht und Stoffwechselprodukte abgeführt. Am Beispiel von Uran als toxisches Schwermetall konnte eine Schutzfunktion und Überlebensstrategie der Biofilme nachgewiesen werden, durch die gelöstes Uran in wässrigen Lösungen zu unlöslichem Uran reduziert und in der Zwischenzellsubstanz der Biofilme „gespeichert“ wird.
  • Lecture (others)
    Tag des offenen Labors, 09.05.2009, Dresden, Deutschland

Publ.-Id: 13354 - Permalink


Spectroscopic characterization of Au complexation and nanoclusters formation on Bacillus sphaericus JG-A12 S-layer
Jankowski, U.; Fahmy, K.; Selenska-Pobell, S.; Merroun, M. M.;
Protein secondary structure and stability of S-layers from B. sphaericus JG-A12 in Au-complexes with Au(III) and in Au(0) nanoparticles, produced by reduction of Au(III), was studied by FTIR spectroscopy.
The data show a different role of side chain carboxylates in complex formation as compared to an analogous study on complexation of Pd(II) or Pt(II).
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-511 Februar 2009, 70-70

Publ.-Id: 13353 - Permalink


The European Physical Journal - Special Topics 177(2009)
'Advances in the Multi-Scale Computational Design of Condensed Matter Interfaces'

Emmerich, H.; Gemming, S.; (Editors)
Editorial - Materials have become an ever more important factor in most advanced technologies. It was no coincidence when the former State Secretary Christoph Matschie stated, at the opening of WING (Materials Innovations for Industry and Society initiated by the German Ministry for Education and Research), that nearly any new product is based on the improvement of an engineered material. This comes along with a constant quest for new materials, improved performance and decreased development costs. This quest is particularly strong for high-wage countries in the global market situation. Thus there is a steadily growing importance of systematic materials development supported by computer simulation methods in tailoring new materials for more and more specific demands for a wide range of applications from everyday household goods to opto-electronics and even further to medicine. In this context the tailoring of materials interfaces, respectively that of corresponding condensed matter systems, often used as model systems for the first ones, plays a particularly important role. The reason for this is that a material’s functional properties are to a large extent determined by its inner and outer interfaces. Prominent examples are corrosion-resistant surfaces of household goods, or likewise inert surfaces of prostheses engineered for medical applications. During materials processing the inner and outer interfaces of such functional materials evolve driven by the complex interplay of all the physical and chemical mechanisms contributing to interface energetics, interface kinetics and interface dynamics. Essentially, this opens a multiscale problem ranging from the quantum mechanical to the continuum scale.
Keywords: condensed matter, transport, multi-scale modeling, scale-bridging, concurrent, scale-hopping
  • Book (Editorship)
    Heidelberg: Springer, 2009
    205 Seiten

Publ.-Id: 13352 - Permalink


Numerical and experimental investigation of electromagnetic separation control using different wave forms
Albrecht, T.; Weier, T.; Gerbeth, G.; Metzkes, H.; Stiller, J.;
The separated flow around inclined airfoils can be controlled by unsteady actuation near the leading edge (LE), increasing the maximum lift coefficient without the need for heavy and complex high lift devices such as flaps. Zero net mass flow devices (ZNMF) are often used for this purpose. While certainly favorable for industrial application, actuation via ZNMF faces some problems. In particular, to independently control both amplitude and frequency of the excitation is considered a ``great challenge'' This is even more severe when the wave form of the actuation is non-sinusoidal, i.e., contains more than one frequency component. Lorentz forces do not suffer from such limitations; driven by an electric current, arbitrary wave forms can be generated easily. The main purpose here is to identify possibly different mechanisms triggered by different wave forms. In particular, we investigate electromagnetic excitation using a) a sinusoidal wave and b) rectangular waves at duty cycles of DC=1/4 and DC=1/8.
Keywords: flow control, Lorentz force
  • Lecture (Conference)
    5th AIAA Flow Control Conference, 28.06.-01.07.2010, Chicago, IL, USA

Publ.-Id: 13351 - Permalink


Structural determination of neptunium redox spezies in aqueous solution
Ikeda-Ohno, A.; Hennig, C.; Rossberg, A.; Funke, H.; Scheinost, A. C.; Bernhard, G.; Yaita, T.;
Neptunium (93Np) is one of the most important elements to be considered for the geological disposal of high-level radioactive wastes, because of a considerable content in the wastes, and the high radioactivity, half-lives and radiotoxicity of its nuclides. From a chemist’s point of view, it is also a very interesting element because of its diversity of oxidation states from III to VII [1]. Whether Np may be retained in the waste repository for millions of years, or whether it will migrate to the biosphere, depends heavily on its chemical forms (speciation). We assume that oxidation state will have a strong influence on the speciation. Therefore detailed knowledge about the interrelation between oxidation state and the structure of chemical species is critical for the development of safe nuclear waste repositories. This motivated us to perform X-ray absorption fine structure (XAFS) studies to determine the complex structure of Np species in aqueous solutions at different oxidation states. The experiments were performed at the Rossendorf Beamline (BM20), the only beamline at the ESRF, where such studies with aqueous Np samples can be performed.
Keywords: Neptunium, EXAFS
  • Contribution to external collection
    G. Admans: ESRF Highlights, Grenoble: European Synchrotron Radiation Facility, 2009, 99-100

Publ.-Id: 13350 - Permalink


Structure of early actinides(V) in acidic solutions
Di Giandomenico, M. V.; Le Naour, C.; Simoni, E.; Gulliaumont, D.; Moisy, P.; Hennig, C.; Conradson, C.; Den Auwer, C.;
Protactinium occupies a key position in the actinide series between thorium and uranium. In aqueous acidic solution, it is stable at oxidation state (V), occurring either as an oxocation or as a naked ion, depending on the media. Very few structural information on the hydration sphere of Pa(V) in acidic medium is available, in particular in hydrofluoric acid. Combined EXAFS and theoretical calculations have been used in this work to characterize the protactinium coordination sphere at various HF concentrations. The correlation of the XAFS data with quantum chemical calculations provides complementary structural and electronic models from ab initio techniques. At HF concentrations from 0.5 to 0.05 M, both theoretical calculations and EXAFS data suggest that the protactinium coordination sphere is mainly composed of fluoride ions. At the lowest HF concentration, the occurrence of a monooxo bond is observed with EXAFS, in agreement with the literature. A comparison of these data with related neptunium(V) and plutonium(V) diooxocations in perchloric acid is also presented.
Keywords: Actinide, Protactinium, EXAFS, Quantum chemistry

Publ.-Id: 13349 - Permalink


Complexation of U(VI) with highly phosphorylated protein, phosvitin. A vibrational spectroscopic approach
Li, B.; Barkleit, A.; Raff, J.; Bernhard, G.; Foerstendorf, H.;
The complexation of uranium(VI) to variant functional groups of the highly phosphorylated protein phosvitin in aqueous solution was investigated by Attenuated Total Reflection Fourier-transform Infrared (ATR FT-IR) spectroscopy. For the verification of the affinity of the actinyl ions to carboxyl and phosphate groups of the amino acid side chains, samples with different phosphate to uranium(VI) (P/U) ratios were investigated under denaturing conditions and as well as aqueous complexes. From a comparative study with other heavy metal ions, i.e. Ba2+ and Pb2+, a strong coordination of U(VI) to carboxyl and phosphoryl groups can be derived. Furthermore, the spectra indicate a preferential binding to phosphate groups at deficient U(VI) concentrations. These findings are confirmed by spectra of aqueous U(VI)-phosvitin complexes reflecting an explicit coordination of the uranyl ions to phosphate groups at a high P/U ratio. Our study provides a deeper insight into the molecular interactions between actinyl ions and basic biomolecules such as proteins, polysaccharides, nucleic acids.
Keywords: Phosvitin, U(VI), ATR FT-IR, complexation
  • Journal of Inorganic Biochemistry 104(2010)7, 718-725

Publ.-Id: 13348 - Permalink


Co-localisation of hypoxia and perfusion markers with parameters of glucose metabolism in human squamous cell carcinoma (hSCC) xenografts
Yaromina, A.; Quennet, V.; Zips, D.; Meyer, S.; Shakirin, G.; Mueller-Klieser, S.; Walenta, W.; Baumann, M.;
Purpose: To examine relationships between tumour hypoxia, perfusion and metabolic microenvironment at themicroregional level in three different human squamous cell carcinomas (hSCC). Materials and methods: Nude mice bearing FaDu, UT-SCC-15, and UT-SCC-5 hSCC were injected with pimonidazole hypoxia and Hoechst perfusion markers. Bioluminescence imaging was used to determine spatial distribution of glucose and lactate content in serial tumour sections. Metabolite levels were grouped in 10 concentration ranges. Images were co-registered and at each concentration range the proportion of area stained for pimonidazole and Hoechst was determinedin 11–13 tumours per tumour line.
Results: The spatial distribution of metabolites in pimonidazole hypoxic and Hoechst perfused areas is characterised by pronounced heterogeneity. In all three tumour lines glucose concentration decreased with increasing pimonidazole hypoxic fraction and increased with increasing perfused area at the microregional level. A weak albeit significant positive correlation between lactate concentration and pimonidazole hypoxic fraction was found only in UT-SCC-5. Lactate concentration consistently decreased with increasing perfused area in all three tumour lines. Conclusions: Both glucose consumption and supply may contribute to the microregional glucose levels. Microregional lactate accumulation in tumours may be governed by clearance potential. The extent of microregional hypoxia cannot be predicted from the lactate concentration indicating that both parameters need to be measured independently.
Keywords: biological imaging, glucose metabolism, pimonidazole hypoxia, perfusion, human tumour xenografts, tumour micromilieu
  • International Journal of Radiation Biology 85(2009)11, 972-980

Publ.-Id: 13347 - Permalink


Temperature dependence of nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding
Martinavicius, A.; Abrasonis, G.; Möller, W.;
Temperature dependence of the nitrogen diffusion coefficient in the expanded austenite γN of single crystalline austenitic stainless steel (ASS) during ion beam nitriding is investigated. Single crystalline [orientations (001), (110) and (111)] AISI 316L ASS samples have been ion beam nitrided in the temperature range of 370-430 °C for 60 min with an ion acceleration voltage of 1 keV and a current density of 0.5 mA cm−2. The N depth distribution profiles have been determined by means of nuclear reaction analysis (NRA), while the N diffusion coefficients D have been extracted by fitting the NRA profiles with the “trapping-detrapping” model. The results show that the nitrogen diffusivity strongly depends on the single crystal orientation in the sequence D001>D011>D111. These differences are not related to the activation energy which is similar for all three orientations, but to the diffusion coefficient exponential pre-factor D0 whose value varies by 3 orders of magnitude depending on the orientation. The results are discussed on the basis of ion irradiation effects such as defects and vibrational lattice excitations.
  • Poster
    VEIT 2009 - Fifteenth International Summer School on Vacuum, Electron and Ion Technologies, 28.09.-02.10.2009, Sunny Beach, Bulgaria

Publ.-Id: 13346 - Permalink


Atomic-level computer simulations of copper-vacancy clusters in alpha-Fe
Al-Asqalani, A. T.; Posselt, M.; Bergner, F.; Birkenheuer, U.;
Reactor pressure vessel (RPV) steels consist of polycrystalline alpha-Fe with different alloying elements, e.g. nickel, and different impurities, e.g. copper. During the operation of a nuclear fission reactor at a temperature of about 300 °C this material is continuously irradiated by neutrons and both vacancies and self-interstitials are formed. The presence of point defects enhances the diffusion of impurities and leads to precipitation if their solid solubility is small. The precipitates may not only contain the impurity species but also point defects since vacancies and/or self-interstitials take part in the process of clustering. Furthermore, pure vacancy and self-interstitial clusters may be formed. Copper-rich precipitates (CRP) are assumed to be the main cause of hardening and embrittlement of Cu-bearing RPV steels since these defects act as obstacles to dislocation motion within the grains of polycrystalline alpha-Fe. There is clear evidence that these nanoclusters remain small and have the bcc structure of the surrounding matrix. CRP and nanovoids have been observed by different experimental methods such as small angle neutron scattering, tomographic atom probe, positron annihilation spectroscopy, and high-resolution transmission electron microscopy. On the other hand, multiscale modeling contributes to a better understanding of the various physical processes that occur during the formation of clusters and precipitates. Rate theory is a useful and efficient tool to simulate defect evolution on realistic time and length scales. However, the values of many parameters used in rate theory, such as diffusion coefficients of mobile species and free binding energies of clusters, are not very well known from experimental investigations. Atomic-level computer simulations can provide these data.

In the present work a combination of Metropolis Monte Carlo simulations on a rigid bcc lattice and molecular dynamics simulations [1,2] is applied in order to determine the most stable configuration of numerous CunVm clusters. In all calculations the most recent Fe-Cu interatomic potential by Pasianot and Malerba [3] is used. Present investigations do not only yield formation energies of the most stable clusters but also the corresponding binding energies. The results are compared with literature data [1,2] obtained by the potentials of Ackland-Bacon [4] and Ludwig-Farkas [5]. The configuration of some clusters containing both copper and vacancies are visualized and their morphology is compared with the interpretation of recent experimental investigations.


References
[1] A. Takahashi, N. Soneda, S. Ishino, and G. Yagawa, Phys. Rev. B 67, 024104 (2003).
[2] D. Kulikov, L. Malerba, and M. Hou, Philos. Mag. 86, 141 (2006).
[3] R. C. Pasianot and L. Malerba, J. Nucl. Mater. 360, 118 (2007).
[4] G. J. Ackland, D. J. Bacon, A .F. Calder, and T. Harry, Philos. Mag. A 75, 713 (1997).
[5] M. Ludwig, D. Farkas, D. Pedraza, and S. Schmauder, Modelling Simul. Mater. Sci. Eng.
6, 19 (1998).
Keywords: Computer simulation iron defects
  • Poster
    First international school on materials for nuclear reactors (MATRE-1), 18.-23.10.2009, Rochehaut-sur-Semois, Belgium

Publ.-Id: 13345 - Permalink


Quenched-in vacancies in Fe-AL alloys
Melikhova, O.; Cizek, J.; Prochazka, I.; Kuriplach, J.; Lukac, F.; Cieslar, M.; Brauer, G.; Anwand, W.;
Quenched-in vacancies in Fe3Al-based intermetallics were studied in this work. A stoichiometric Fe3Al alloy was compared with non-stoichiometric specimens either with a deficiency or with an excess in Al content. Vacancies in specimens quenched from the disordered A2 phase were investigated by three independent techniques of positron annihilation spectroscopy: positron lifetime (LT) studies, slow positron implantation spectroscopy (SPIS) with a continuous slow positron beam, and coincidence Doppler broadening (CDB). It was found that the combination of LT and SPIS enables to determine reliably even very high concentrations of vacancies. Infor-mation about the local chemical environment of quenched-in vacancies was obtained from CDB measurements.

Publ.-Id: 13344 - Permalink


Polishing of titanium and enhancing the wear resistance of the titanium alloys with a low-energy high-current electron beam
Markov, A. B.; Reuther, H.; Shevchenko, N.;
Polishing of titanium and enhancing the wear resistance of the titanium alloys with a low-energy high-current electron beam
  • Lecture (Conference)
    14th International Conference on Radiation Physics and Chemistry of Inorganic Materials, 06.-10.10.2009, Astana, Kazakhstan
  • Izvestija vyssich ucebnych zavedenj 8(2009), 425-428

Publ.-Id: 13343 - Permalink


Transport of hot electron currents in solid targets irradiated by high intensity short laser pulses
Antici, P.; Borghesi, M.; Audebert, P.; Cowan, T.; Sentoku, Y.; Fuchs, J.;
We have analyzed the transport of hot electrons generated in the interaction between a short-pulse, ultra-high intensity laser beam (pulse duration \tau1018 W.cm-2.\my m2) and a solid or dense target through the use of proton emission imaging. We used targets of different material (Cu, Al, Au) with a regularly modulated rear target surface in order to compare the electron transport in different conditions. As result, we see that the electron transport depend on the target material and on the interaction conditions.

Publ.-Id: 13342 - Permalink


Investigation of high intensity laser proton acceleration with underdense targets
D'Humières, E.; Feugeas, J. L.; Nicolaï, P.; Gaillard, S.; Cowan, T.; Sentoku, Y.; Tikhonchuk, V.;
In the last few years, intense research has been conducted on laser-accelerated ion sources and their applications. Recently, experiments have shown that a gaseous target can produce proton beams with characteristics comparable to those obtained with solid targets. In underdense laser proton acceleration, volume effects dominate the acceleration, while in target normal sheath acceleration, the electric field value is directly related to the electron surface density. Using Particle-In-Cell simulations, we have studied in detail the effect of an underdense density gradient on proton acceleration with high intensity lasers. Underdense laser ion acceleration strongly depends on the length, the shape and the amplitude of the density gradient and on the laser pulse shape. The accelerated proton beam characteristics in the shock-like regime are very promising.

Publ.-Id: 13341 - Permalink


Proton acceleration from ultrahigh-intensity short-pulse laser-matter interactions with Cu micro-cone targets at an intrinsic ~10-8 contrast
Gaillard, S. A.; Flippo, K. A.; Lowenstern, M. E.; Mucino, J. E.; Rassuchine, J. M.; Gautier, D. C.; Workman, J.; Cowan, T. E.;
In this paper, we report on experiments performed on the 200 TW Trident laser (80 J, 600 fs, ~7 µm spot size, S-polarization and ~1.5x1020 W/cm2) at an intrinsic (to the system’s regenerative amplifier) ASE contrast of 10-8, using various geometries of conical Cu targets, as well as Cu flat foils for comparison. The work presented in this paper follows on some earlier work on proton acceleration on Trident (20 J, ~14 µm spot size, P-polarization, ~1019 W/cm2 and also at the intrinsic contrast of 10-8), using Flat Top Cone (FTC) targets [1] and which demonstrated an enhancement in both proton energies and conversion efficiencies. In the current experiment, an electron spectrometer was added, which shows linear correlation of electron temperatures and proton energies, as well as a Cu Kα imaging diagnostic, to determine the characteristics of laser absorption in the FTC, which demonstrates that the laser is absorbed in the preplasma filling the cone, preventing the previously observed enhancement in proton energies.

Publ.-Id: 13340 - Permalink


Status of the Leopard Laser Project in Nevada Terawatt Facility
Wiewior, P.; Astanovitskiy, A.; Aubry, G.; Batie, S.; Caron, J.; Chalyy, O.; Cowan, T.; Haefner, C.; Le Galloudec, B.; Le Galloudec, N.; Macaulay, D.; Nalajala, V.; Pettee, G.; Samek, S.; Stepanenko, Y.; Vesco, J.;
Nevada Terawatt Facility (NTF) currently operates a high-intensity laser system—Leopard. NTF already operates a powerful z-pinch device, called Zebra, for plasma and High Energy Density physics research. The unique research opportunities arise from the combination of NTF’s terawatt Zebra z-pinch with 50-terawatt-class Leopard laser. This combination also provides opportunities to address fundamental physics of inertial fusion and high energy density physics with intense laser beam. We report on the status, design and architecture of the Leopard laser project. A first experiments carried out with Leopard will be also briefly mentioned.

Publ.-Id: 13339 - Permalink


Importance of magnetic resistive fields in the heating of a micro-cone target irradiated by a high intensity laser
D’Humières, E.; Rassuchine, J.; Baton, S.; Fuchs, J.; Guillou, P.; Koenig, M.; Gremillet, L.; Rousseaux, C.; Kodama, R.; Nakatsutsumi, M.; Norimatsu, T.; Batani, D.; Morace, A.; Redaelli, R.; Dorchies, F.; Fourment, C.; Santos, J. J.; Adams, J.; Korgan, G.; Malekos, S.; Cowan, T. E.; Sentoku, Y.;
Obtaining keV ion temperatures at solid density, i.e. “warm dense matter”, in the laboratory would be of great interest to measure opacity and equations of state of matter under extremes conditions. Here we report a new means to effectively confine the energetic electrons and localize the energy deposition to a small, more uniformly heated, volume at the tip of nanofabricated micro-cone targets. This is achieved with very high contrast laser irradiation, which interacts with the cone wall to generate strong (~10 MG) localized resistive magnetic fields within the target bulk. Temperatures of up to ~200 eV are observed, with an input laser energy of 10 J. This new means has been investigated both experimentally and with Particle-In-Cell simulations.

Publ.-Id: 13338 - Permalink


THEREDA in an European context - comparison of thermodynamic databases
Brendler, V.;
- wird nachgereicht
  • Lecture (Conference)
    10. Koordinierungsgespräch FZD/IRC - PSI/LES, 28.-29.10.2009, Villigen, Schweiz

Publ.-Id: 13337 - Permalink


Neues zur Fluoreszenz von Actiniden
Geipel, G.;
- wird nachgereicht
  • Lecture (Conference)
    10. Koordinierungsgespräch FZD/IRC - PSI/LES, 28.-29.10.2009, Villigen, Schweiz

Publ.-Id: 13336 - Permalink


Reaction of Pu(IV) and Pu(III) with Fe minerals under anoxic conditions - XANES and EXAFS results
Kirsch, R.;
- wird nachgereicht
  • Lecture (Conference)
    10. Koordinierungsgespräch FZD/IRC - PSI/LES, 28.-29.10.2009, Villigen, Schweiz

Publ.-Id: 13335 - Permalink


Characterization of an uranium accumulating plant in its terrestrial ecosystem and under laboratory conditions
Viehweger, K.;
- wird nachgereicht
  • Lecture (Conference)
    10. Koordinierungsgespräch FZD/IRC - PSI/LES, 28.-29.10.2009, Villigen, Schweiz

Publ.-Id: 13334 - Permalink


Uranium(IV) colloids in near-neutral solutions - Preparation and stability
Dreissig, I.;
- wird nachgereicht
  • Lecture (Conference)
    10. Koordinierungsgespräch FZD/IRC - PSI/LES, 28.-29.10.2009, Villigen, Schweiz

Publ.-Id: 13333 - Permalink


Influence of calcite on the sorption of U(VI) and HA onto Opalinus clay
Joseph, C.;
- wird nachgereicht
  • Lecture (Conference)
    10. Koordinierungsgespräch FZD/IRC - PSI/LES, 28.-29.10.2009, Villigen, Schweiz

Publ.-Id: 13332 - Permalink


Transition metal sulfide clusters below the cluster-platelet transition theory and experiment
Gemming, S.; Seifert, G.; Götz, M.; Fischer, T.; Ganteför, G.;
The structural and electronic properties of neutral and anionic molybdenum sulfide clusters with the composi-tion Mo3Sn (n=0-12) were studied by density-functional calculations. The theoretical results are confirmed by a comparison with photoelectron spectra of the correspond-ing W3Sn- anions providing experimental values for the vertical detachment energies and the HOMO-LUMO gaps. For sulfur contents up to n=9 the clusters are com-posed of a central Mo3 unit, which is decorated by bridg-ing, terminal and three-fold coordinated S atoms. For n>9, a cleavage of the Mo3 center is observed. The formation of disulfide like ions is found for Mo3S9 and larger spe-cies. In accordance with investigations of MoSn, Mo2Sn and Mo4Sn clusters, the heat of formation and the vertical detachment energy reaches a maximum in the sulfur-rich region beyond the composition Mo : S = 1 : 2.
Keywords: molybdenum sulfide, clusters, density-functional, pulsed-arc, HOMO-LUMO gap, tungsten sulfide

Publ.-Id: 13331 - Permalink


Adsorption of nucleotides on the rutile (110) surface
Gemming, S.; Enyashin, A.; Frenzel, J.; Seifert, G.;
The present study aims at the computer-aided design of suitably functionalizedoxide surfaces for the integration of nanotubes into multi-purpose nano-electronic devices. The adsorption of cytidine monophosphate on the rutile(110) surface is investigated by density-functional-based tight-binding calculations. The most favorable amchoring of the nucleotide is bidentate via oxygen sites of the phosphate part. Adsorption occurs preferentially at two neighboring five-fold coordinated Ti atoms along the [001] direction, thus opening a pathway to an ordered adsorption of nanotubes along [001]. The electronic densities of states show that the aromatic part of the cytidine part remains unchanged upon adsoption on rutile. This implies that no significant changes occur in the nanotube binding capacity by pi-stacking of the aromatic part, hence, nucleotide-functionalized oxide surfaces are ideal substrates for the ordered, stable and electronically and chemically inert immobilization of nanotubes.
Keywords: CNT, DNA, nanotube, nucleotide, surface functionalization, rutile, adsorption, chemisorption

Publ.-Id: 13330 - Permalink


Electric field mediated switching of mechanical properties of strontium titanate at room temperature
Stöcker, H.; Zschornak, M.; Leisegang, T.; Shakhverdova, I.; Gemming, S.; Meyer, D. C.;
In situ application of an electric field to a SrTiO3 single crystal plate during nanoindentation led to a reversible change of the mechanical properties at room temperature. When a field of 8 kV/cm was applied, Meyer hardness and Young's modulus decreased by 0.6 GPa and 11 GPa, respectively. An explanation for this behaviour is given by the diffusion of oxygen vacancies resulting in a distortion of the perovskite-type of structure in the near-surface layer tested by nanoindentation. Simulations using density functional theory support the dependence of elasticity on the presence of vacancies. Thus, we can show the remarkable influence of electric fields on oxide materials which should be considered and used in designing future applications.
Keywords: strontium titanate, functional oxide, mechanical properties, density-functional, hardness, vacancy, point defect

Publ.-Id: 13329 - Permalink


Surface Nanostructures Induced by Low Energy Ion Sputtering
Facsko, S.; Keller, A.; Ranjan, M.; Möller, W.;
Under special conditions low energy ion sputtering of solid surfaces leads to the formation of regular nanopatterns. These surfaces represent an interesting example of spontaneous pattern formation in nonequilibrium systems exhibiting different features like wavelength coarsening or a transition to spatiotemporal chaos. Different pattern types are observed for different experimental conditions, i.e. wavelike ripple patterns and hexagonally ordered dot arrays under oblique and normal ion incidence, respectively [1]. These patterns have gained increasing interest in recent years as templates for thin film growth. According to the model of Bradley and Harper (BH) [2], the regular patterns result from the competition between curvature dependent roughening and smoothing of the surface. Since the local erosion rate is higher in the valleys than on crests, the eroded surface is unstable. In the presence of smoothing mechanisms, however, a wave vector selection occurs and a periodic pattern with one spatial frequency is observed. The pattern formation can be described by continuum equations based on the BH model. Several extensions have been proposed in the last years, with the stochastic Kuramoto-Sivashinsky (KS) equation being the most prominent one [3]. However, although most experimental investigations on ion-induced pattern formation were performed under oblique ion incidence, only few theoretical studies focused on the corresponding anisotropic KS (aKS) equation. We will also present studies of thin film growth on these patterns. Depending on the interface energy of the metal film with the substrate the films grow in a conformal way reproducing the surface topography or as nanoparticles on the substrate surface. Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles align parallel to the ripples, eventually coalescing and forming nanowires. Metal thin films grown in this way exhibit distinct optical properties due to their localized surface plasmon resonance. Because of the alignment these nanoparticles exhibit a strongly anisotropic plasmonic resonance [4]. In addition, the magnetic properties of ferromagnetic thin films grown on rippled surfaces are drastically change by the presence of the interface and surface periodic roughness [5].
[1] W. L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007)
[2] R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)
[3] R. Cuerno and A.-L. Barabási, Phys. Rev. Lett. 74 4746 (1995)
[4] T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).
[5] M. O. Liedke, B. Liedke, A. Keller, et al., Phys. Rev. B 75, 220407 (2007).
Keywords: ion beam sputtering, self-organized nanostructures
  • Invited lecture (Conferences)
    International Conference on Metallurgical Coatings and Thin Films, 26.-30.04.2010, San Diego, USA

Publ.-Id: 13328 - Permalink


Self-aligned metal nanoparticles and nanowires grown on ripple-templates
Facsko, S.; Ranjan, M.; Keller, A.; Oates, T. W. H.; Rosen, J.;
Nobel metal nanoparticles exhibit distinct optical properties due to their localized surface plasmon resonance. They are used nowadays in various applications, like solar cells, nonlinear optical devices or sensors. Especially for nanoscale optics aligned equidistant chains of metal nanoparticles are favored [1]. Ion beam sputtered surfaces featuring self-organized ripple patterns are excellent templates for the alignment of these metal nanoparticles. Depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanostructures align parallel to the ripples, eventually coalescing and forming nanowires [2]. Because of alignment the nanoparticles exhibit a strongly anisotropic plasmonic resonance [3]. We will present how Ag nanoparticles grow and align on ion beam rippled Si surfaces and how the optical properties depend on their shape, size, and alignment.

[1]S.A. Maier and H.A. Atwater, Jour. Appl. Phys. 98, 011101 (2005).
[2]T.W.H. Oates, A. Keller, S. Noda, et al., Appl. Phys. Lett. 93 (2008).
[3]T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).
Keywords: self-aligned clusters, ripple pattern, anostructures
  • Invited lecture (Conferences)
    MRS Fall Meeting, 29.11.-4.12.2009, Boston, USA

Publ.-Id: 13327 - Permalink


Selbstorganisierte Nanostrukturierung von Oberflächen mittels Ionenstrahlen
Facsko, S.; Keller, A.; Ranjan, M.;
Oberflächen und Grenzflächen spielen eine große Rolle in allen technologischen Bereichen. Kaum eine Anwendung kommt ohne Materialien aus, die aus Mehrfachschichten aufgebaut sind oder funktionale Oberflächen aufweisen. Die Herstellung und Erforschung dieser funktionalen Oberflächen bzw. Schichten mit Strukturen im Submikrometerbereich wurde deshalb in den letz-ten Jahren verstärkt vorangetrieben, da eine steigenden Nachfrage in der mikro- und optoe-lektronischen Industrie nach derartigen Strukturen zu erwarten ist. Zwei komplementäre Ansätze existieren zur Erzeugung von Nanostrukturen: Der Top-down- und der Bottom-up-Ansatz.
Der Top-down-Ansatz umfasst konventionelle Techniken wie optische oder Elektronen¬stahllithographie kombiniert mit Übertragung der geschriebenen Strukturen, während der Bot-tom-up-Ansatz Selbstorganisationsphänomene an Oberflächen oder beim Wachstum dünner Schichten ausnutzt. Die Ionenerosion von Festkörperoberflächen mit niederenergetischen Ionen ist eine vielversprechende Bottom-up-Methode zur Herstellung großflächiger Felder von Na-nostrukturen [1]. Diese Methode und Anwendungen, die darauf basieren, werden im Folgenden vorgestellt.
Keywords: surface nanostructures, ion beam sputtering
  • Contribution to proceedings
    Mikro- und Nanosrtukturen an Oberflächen - Herstellung und Anwendungen, 9.10.2009, Dresden, Deutschland
    Selbstorganisierte Nanosrtukturierung von Oberflächen mittels Ionenstrahlen

Publ.-Id: 13326 - Permalink


Analsyis of the spatial isotopic distributions during the burnup of UMOX- and ThMOX-fuels on unit cell basis
Merk, B.; Scholl, S.; Fridman, E.;
A detailed analysis of the plutonium burning in a representative PWR fuel pin is performed for comparison of the ThMOX and UMOX fuel performance. Special effort is made in the analysis of the changes in the spatial distribution of isotope concentrations during the burnup in a representative LWR fuel pin. This unique analysis of the changes in the spatial particle densities gives a new insight into the system behaviour. The different ways of plutonium breeding and reduction for the major isotopes of the two considered fuels are analyzed and discussed. Finally, the advantages and limitations of the use of Thorium based MOX fuel for the burning of plutonium are discussed. The calculations are performed with the licensing grade code module HELIOS 1.9.
Keywords: plutonium reduction, thorium fuels, actinide transmutation, PWRs
  • Contribution to proceedings
    PHYSOR 2010, 09.-14.05.2010, Pittsburgh, USA
  • Lecture (Conference)
    PHYSOR 2010, 09.-14.05.2010, Pittsburgh, USA

Publ.-Id: 13325 - Permalink


A solution for the telegrapher’s equation with external source: application to YALINA - SC3A and SC3B
Merk, B.; Glivici-Cotruta, V.; Weiß, F. P.;
This work represents the detailed comparison of the analytical solutions for the space and time Telegrapher’s equations with the experimental results, obtained for the YALINA-Booster subcritical facility in 2008. The derivation of analytical solution for the Telegrapher’s equation with a special temporal shape of the external source is described. The Green’s function method was applied. Qualitative results of the obtained solutions and the experimental results are analyzed. The special configuration of the YALINA-Booster facility is discussed.
Keywords: Yalina, experimental analysis, Green’s function, Telegrapher’s equation
  • Contribution to proceedings
    PHYSOR 2010, 09.-14.05.2010, Pittsburgh, USA
  • Lecture (Conference)
    PHYSOR 2010, 09.-14.05.2010, Pittsburgh, USA

Publ.-Id: 13324 - Permalink


Radiation enhanced diffusion in germanium
Schneider, H.; Bracht, H.; Klug, J. N.; Lundsgaard Hansen, J.; Bourgeard, D.; Liao, C. Y.; Haller, E. E.; Posselt, M.; Wündisch, C.;
Ge isotope heterostructures were irradiated with 2.5 MeV protons at temperatures between 550°C and 640°C. The applied proton flux was varied up to 3.8 μA per cm2. Secondary ion mass spectroscopy (SIMS) was utilized to record concentration profiles of the Ge-isotopes after the irradiation treatment. The SIMS profiles show a homogenous broadening of the multilayer structure. Continuum theoretical simulations were performed which are based on diffusion models that consider the formation of Frenkel-defects and their annihilation. Best fits to the experimental profiles are obtained when the boundary conditions for vacancies and self-interstitials are assumed differently. Ge self-interstitials are reflected at the surface, whereas the concentration of Ge vacancies approaches the thermal equilibrium value. To check these boundary conditions, experiments on the diffusion of n-type dopants under irradiation were performed.
Keywords: germanium diffusion irradiation
  • Lecture (Conference)
    25th International Conference on Defects in Semiconductors (ICDS-25), 20.-24.06.2009, St. Petersburg, Russia

Publ.-Id: 13323 - Permalink


Mikroskopische Aufnahmen neu gedeutet - Revolution in der Raster-Kelvin-Mikroskopie?
Baumgart, C.; Schmidt, H.;
In den letzten Jahren hat die Mikroskopie enorme Fortschritte gemacht. Moderne Mikroskope können Moleküle dreidimensional abbilden, kleinste Strukturen bis hin zu einzelnen Atomen erkennen und vor allem auch unterschiedliche Arten von Atomen sicher voneinander unterscheiden. Die "Raster-Kelvin-Mikroskopie" ist eine besondere Technik der Rasterkraft-Mikroskopie, wobei die ihr zugrunde liegende Methode auf Lord Kelvin zurück geht. Sie kam 1991 auf den Markt. Mit dem Raster-Kelvin-Mikroskop wurde eine wissenschaftliche Erklärung mitgeliefert, wie die Aufnahmen zu interpretieren seien. Daran rüttelt nun die Physikerin Christine Baumgart, die in der "Nanospintronik-Gruppe" am Forschungszentrum Dresden-Rossendorf (FZD) promoviert.
  • GIT Labor-Fachzeitschrift 53(2009), 680-681

Publ.-Id: 13322 - Permalink


Heavily Ga-doped Germanium Layers Produced by Ion Implantation and Flash Lamp Annealing - Structure and Electrical Activation
Heera, V.; Mücklich, A.; Posselt, M.; Voelskow, M.; Wündisch, C.; Schmidt, B.; Skrotzki, R.; Heinig, K. H.; Herrmannsdörfer, T.; Skorupa, W.;
Heavily p-type doped Ge layers were fabricated by 100 keV Ga implantation and subsequent flash lamp annealing for 3 ms in the temperature range between 700°C and 900°C. For comparison some samples were annealed in a rapid thermal processor for 60 s. Ga fluences of 2x1015cm-2, 6x1015cm-2 and 2x1016cm-2 were chosen in order to achieve Ga peak concentrations ranging from values slightly below the equilibrium solid solubility limit of 4.9x1020 cm-3 up to 3.5x1021 cm-3 which corresponds to a maximum Ga content of about 8 at-%. The structure of the doped layer and the Ga distribution were investigated by Rutherford backscattering spectrometry in combination with ion channelling, cross-sectional electron microscopy and secondary ion mass spectrometry. Temperature dependent Hall effect measurements were carried out in order to determine the electrical properties of the Ga doped layers. It is shown that by flash lamp annealing Ga diffusion into the bulk can be completely avoided and the Ga loss by outdiffusion from the surface is reduced. The lowest sheet resistances of 36 Ohm/sq. was achieved for the medium Ga concentration annealed at 900°C. The best Ga activation values are 73%, 60% and 24% for the three Ga fluences under investigation. The Ga activation is correlated with the layer regrowth. Incomplete epitaxial regrowth as observed in some samples leads to lower activation.
Keywords: Germanium, Ga implantation, electrical activation, flash lamp annealing, rapid thermal annealing, Hall effect measurements

Publ.-Id: 13321 - Permalink


Novel and compact accelerator concepts for radiation therapy
Schramm, U.; Cowan, T. E.; Bock, S.; Bussmann, M.; Debus, A.; Erler, C.; Illing, R.; Jochmann Metzges, J.; Kluge, T.; Kraft, S.; Kroll, F.; Richter, C.; Richter, T.; Seidl, W.; Siebold, M.; Wünsch, R.; Schwoerer, K.; Liesfeld, B.; Amthor, K.-U.; Ziegler, W.; Jäckel, O.; Pfotenhauer, S.; Podleska, S.; Bödefeld, R.; Hein, J.; Polz, J.; Ronneberger, F.; Schlenvoigt, H.-P.; Beleites, B.; Sauerbrey, R.;
scaling (optimizing) of conventional techniques
novel techniques: dielectric wall accelerators
new concepts: laser plasma acceleration and
local beam guiding systems
  • Invited lecture (Conferences)
    440th WE Heraeus Seminar,, 14.09.2009, Frauenwörth, Deutschland

Publ.-Id: 13320 - Permalink


Die Kraft des Lichts
Sauerbrey, R.;
Wenn die Intensität von Laserlicht, das mit Materie wechselwirkt, 1018 W/cm2 übersteigt, wird die Bewegung der Elektronen im Laserfeld relativistisch. Dies führt zu einer Vielzahl neuer optischer Effekte, die unter dem Namen „Relativistische Optik“ zusammengefasst werden. Der vielleicht wichtigste und zurzeit am meisten diskutierte neue Effekt, der in diesem Zusammenhang auftritt, ist die effiziente Laserbeschleunigung von Elektronen und Ionen. Mit Hochintensitätslasern kann man heute monochromatische Elektronenstrahlen mit Energien bis zu 1 GeV erzeugen. Kürzlich wurden auch monoenergetische Ionenstrahlen im MeV-Bereich durch Hochintensitätslaser erzeugt. In dem Vortrag werden die Mechanismen der Laser Teilchenbeschleunigung im Zusammenhang mit nun möglich erscheinenden Anwendungen dieser Teilchenstrahlen in der Medizin diskutiert.
  • Lecture (others)
    Kolloquium, 26.01.2009, Bochum, Deutschland

Publ.-Id: 13319 - Permalink


A solution for the Telegrapher’s equation with external source: development and first application
Merk, B.; Glivici-Cotruta, V.; Weiß, F. P.;
This work represents the detailed comparison of the analytical solutions for the space and time dependent diffusion and Telegrapher’s equations to the experimental results, obtained for the YALINA-Booster subcritical facility during the experimental campaign in 2008. The derivation of analytical solution for the Telegrapher’s equation with a special temporal shape of the external source (switch on followed by a switch off after a finite time period) is described. The Green’s function method was applied. Qualitative results of the obtained solutions and the experimental results are analyzed.
The special configuration of the YALINA-Booster facility is discussed.
Keywords: Yalina, subcritical system, Telegrapher's equation, Green's function, experimental analysis

Publ.-Id: 13318 - Permalink


Domain-wall pinning and depinning at soft spots in magnetic nanowires
Vogel, A.; Wintz, S.; Moser, J.; Bolte, M.; Strache, T.; Fritzsche, M.; Im, M.-Y.; Fischer, P.; Meier, G.; Fassbender, J.ORC
The local modification of magnetic properties by ion irradiation opens the possibility to create pinning sites for domain walls in magnetic nanowires without geometric constrictions. Implantation of chromium ions into Ni80Fe20 nanowires is used to cause a local reduction of the saturation magnetization Ms and thus a decrease of the exchange energy associated with the domain wall. Field-driven pinning and depinning of a domain wall at the here so-called magnetic soft spots is directly observed using magnetic transmission soft X-ray microscopy. The pinning rate and the depinning field considerably depend on the wire width and the chromium fluence.
Keywords: Domain walls and domain structure, Intrinsic properties of magnetically ordered materials, Magnetic properties of nanostructures, Magnetization reversal mechanisms.
  • Poster
    MML 2010 - IEEE 7th International Symposium on Magnetic Multilayers, 19.-24.09.2010, Berkeley, USA
  • IEEE Transactions on Magnetics 46(2010)6, 1708-1710

Publ.-Id: 13317 - Permalink


Untersuchung von Chlorophyllspezies in uranhaltigen Pflanzen
Woitha, D.;
In der vorliegenden Arbeit wurde die Auswirkung von Uran speziell auf Chlorophyll a und Chlorophyll b untersucht. Die Messungen erfolgten mittels HPLC-Analytik, mit photometrischen Messungen und Dünnschichtchromatographie. Es wurden die Absorptionsmaxima sowie die Retentionszeiten der Pigmente bestimmt. Den Untersuchungen lag die Frage zugrunde, ob ein Austausch des zentralen Magnesiums aus dem Chlorophyll-Molekül durch Uran möglich ist. Für die Messungen standen Proben von Löwenzahn und Arabidopsis zur Verfügung. Neben den hydroponisch herangezogenen Arabidopsis-Kulturen (mit und ohne Uranylnitrat in der Nährlösung) wurden auch Pflanzen einer unsanierten Uranerzhalde in Johanngeorgenstadt untersucht.
Die Messung von bioverfügbarem Uran in den Bodenproben aus Johanngeorgenstadt und die Akkumulation von 5 μg Uran pro g Frischgewicht in den Pflanzenblättern stellt die Voraussetzung eines Austausches von Magnesium gegen Uran im Chlorophyll-Molekül dar. Anhand der Chromatogramme und der Absorptionsspektren ließen sich jedoch keine Anzeichen für eine Modifikation des Chlorophylls identifizieren.
Keywords: Uran, Chlorophyll, Arabidopsis
  • Other report
    Masterarbeit (Studiengang Biotechnologie): HS Anhalt, 2009
    77 Seiten

Publ.-Id: 13316 - Permalink


Measuring the Saturation Magnetization in Samples with Unknown Magnetic Volume due to Intermixing by Ion Irradiation
Markó, D.; Lenz, K.; Strache, T.; Kaltofen, R.; Fassbender, J.ORC
We present a method to determine the saturation magnetization of samples for which the magnetic volume is unknown and thus cannot be calculated from the magnetic moment. This can happen, e.g., in multilayers, where the spacer material is likely to cause intermixing or whenever ion irradiation is used to modify the magnetic properties of samples on purpose. In both cases the active magnetic volume is altered from its nominal value in unknown manner. Therefore magnetometry like supraconducting quantum interference devices (SQUID) or vibrating sample magnetometry (VSM) fail, because they detect the magnetic moment but do not provide information on the respective magnetic volume. In this article we have used thin films of Permalloy (Py) and Py/Ta multilayers. Some of the Py/Ta samples were irradiated with Ne ions in order to modify the interfacial mixing. The saturation magnetization is determined by ferromagnetic resonance (FMR).
Keywords: Ferromagnetic Resonance, Saturation Magnetization, Ion Irradiation, Intermixing
  • Contribution to proceedings
    MMM/Intermag, 18.-22.01.2010, Washington DC, USA
    IEEE Transactions on Magnetics 46(2010)6, 1711-1714

Publ.-Id: 13315 - Permalink


Mode-locking via active gain modulation in quantum cascade lasers
Kuznetsova, L.; Wang, C. Y.; Gkortsas, V. M.; Diehl, L.; Kärtner, F.; Belkin, M. A.; Belyanin, A.; Li, X.; Ham, D.; Schneider, H.; Liu, H. C.; Capasso, F.;
A mode-locking mechanism by active gain modulation is studied numerically and experimentally. The parameter window for the emission of stable pulse trains was found. Pulses as short as 3ps (~0.5pJ) were characterized by second-order autocorrelation.
Keywords: Infrared and far-infrared lasers, mode-locked lasers, semiconductor lasers, quantum cascade lasers
  • Lecture (Conference)
    Conference on Lasers and Electro-Optics, 2009 and 2009 Conference on Quantum electronics and Laser Science Conference. CLEO/QELS 2009, 02.-04.06.2009, Baltimore, MD, USA
  • Contribution to proceedings
    Conference on Lasers and Electro-Optics, 2009 and 2009 Conference on Quantum electronics and Laser Science Conference, CLEO/QELS 2009, 02.-04.06.2009, Baltimore, MD, USA
    Proc. CLEO/QELS 2009 Persistent Link (OPAC): http://ieeexplore.ieee.org/servlet/opac?punumber=5197900

Publ.-Id: 13314 - Permalink


Recent results at LULI on fast electron transport with and without guiding cone in the context of fast ignitor
Baton, S. D.; Koenig, M.; Fuchs, J.; Gremillet, L.; Rousseaux, C.; Batani, D.; Morace, A.; Nakatsutsumi, M.; Kodama, R.; Norimatsu, T.; Nishida, A.; Dorchies, F.; Fourment, C.; Santos, J. J.; Rassuchine, J.; Cowan, T.;
We present experimental and numerical results obtained at LULI (Laboratoire pour l’Utilisation des Lasers intenses) on propagation and energy deposition of laser-generated fast electrons into conical targets. The experimental measurements were performed by means of several diagnostics in order to assess the predicted benefit of conical targets over standard planar ones. Various configurations have been tried, regarding the laser parameters with the aim of optimizing the laser-to-target coupling. Our best results have been obtained when the laser was frequency-doubled at 0.53 μm, corresponding to interaction conditions without laser pedestal due to the ASE (Amplified Spontaneous Emission). Our data pinpoint the detrimental influence of the pre-plasma generated by the laser pedestal at 1.057 μm, whose confinement is enhanced in conical geometry as evidenced by shadowgraphic measurements which is also confirmed by 2D Cu-Ka transverse images obtained from Cu cones. The consequence is the filling of the cone, preventing the laser beam from efficiently reaching the cone tip. These experimental results are compared to 2D PIC simulations modeling of the laser-cone interaction.

Publ.-Id: 13313 - Permalink


Betriebserfahrungen mit der 40-MW-Photovoltaik-Anlage Waldpolenz
Rindelhardt, U.; Fröhler, D.;
Deutschlands bis dahin größte Photovoltaikanlage (PVA) wurde von 2007 bis 2008 in der Nähe von Leipzig errichtet und schrittweise in Betrieb genommen. Sie befindet sich auf einer militärischen Konversionsfläche. Die PVA ist auf einer Fläche von ca. 120 Hektar mit insgesamt 589000 rahmenlosen CdTe-Modulen von First Solar (Leistung zwischen 65 und 75 W) ausgerüstet, die gesamte Modulfläche liegt bei etwa 40 Hektar. Jeweils 45 Module sind auf einen Tisch montiert und elektrisch zu 5 Strings verschaltet. Die 12440 Tische bestehen aus Aluminium-Profilen mit eingerammten Pfosten.
Betriebsergebnisse der PVA Waldpolenz wurden für die Jahre 2008 und 2009 ausgewertet. Der saisonale Verlauf der Erträge folgt den jeweiligen Einstrahlungen. Die Jahreserträge entsprechen den Erträgen von ertragstarken benachbarten PVA mit kristallinen Modulen. Auffallend sind die hohen PR-Werte der PVA (Jahr 2008: 90 %).
Keywords: photovoltaic, CdTe module, pv plant, performance
  • Contribution to proceedings
    25. Symposium Photovoltaische Solarenergie, 03.-05.03.2010, Staffelstein, Deutschland
    25. Symposium Photovoltaische Solarenergie, Regensburg: Otti, 978-3-941785-23-6, 152-157
  • Poster
    25. Symposium Photovoltaische Solarenergie, 03.02.-05.03.2010, Staffelstein, Deutschland

Publ.-Id: 13312 - Permalink


Laufwasserkraftwerke an der Saale
Rindelhardt, U.;
Die Arbeit beschreibt den Stand und die Perspektiven der Wasserkraftnutzung an der Saale in Thüringen und Sachsen-Anhalt. Das Arbeitsvermögen der derzeit bestehenden 33 Wasserkraftanlagen beträgt 120 GWh/a, dazu kommen 110 GWh/a regenerative Stromerzeugung aus den Pumpspeicherwerken Bleiloch und Hohenwarthe. Unter den derzeitigen Rahmenbedingungen ist ein Zubau um etwa 22 GWh/a möglich.
Keywords: Hydro power plants, Saale river
  • Wassertriebwerk 58(2009)12, 231-240

Publ.-Id: 13311 - Permalink


The molecular dynamics simulation of ion-induced ripple growth
Sule, P.; Heinig, K.-H.;
The wavelength-dependence of ion-sputtering induced growth of repetitive nanostructures, such as ripples has been studied by molecular dynamics (MD) simulations in Si. The early stage of the ion erosion driven development of ripples has been simulated on prepatterned Si stripes with a wavy surface. The time evolution of the height function and amplitude of the sinusoidal surface profile has been followed by simulated ion-sputtering. According to Bradley-Harper (BH) theory, we expect correlation between the wavelength of ripples and the stability of them. However, we find that in the small ripple wavelength regime BH theory fails to reproduce the results obtained by molecular dynamics. We find that at short wavelengths < 35 nm the adatom yield drops hence no surface diffusion takes place which is sufficient for ripple growth. The MD simulations predict that the growth of ripples with wavelengths > 35 nm are stabilized in accordance with the available experimental results. According to the simulations, few hundreds of ion impacts in wavelength-long and few nm wide Si ripples are sufficient for reaching saturation in surface growth for wavelengths > 35 nm ripples. In another words, ripples in the long wavelength limit seems to be stable against ion-sputtering. A qualitative comparison of our simulation results with recent experimental data on nanopatterning under irradiation is attempted.
Keywords: surface patterning, self-organisation, ion erosion, computer simulation, molecular dynamics
  • Journal of Chemical Physics 131(2009)20, 204704

Publ.-Id: 13310 - Permalink


Monte Carlo simulations of ion channeling in crystals containing extended defects
Turos, A.; Nowicki, L.; Stonert, A.; Pagowska, K.; Jagielski, J.; Muecklich, A.;
Monte Carlo simulations code of ion channeling in crystals containing extended defects has been developed. Bent channel model of lattice distortions produced by dislocations have been used for defect analysis in ion implanted GaN. To test the code energy dependence of dechanneling parameter has been calculated for crystals containing randomly displaced atoms and bent channels. It follows the 1/E and E1/2 dependence, respectively.
Keywords: Rutherford backscattering, ion channeling, Monte Carlo simulations, GaN epitaxial layers, ion bombardment, extended defects
  • Lecture (Conference)
    19th International Conference on Ion Beam Analysis, 07.-11.09.2009, Cambridge, United Kingdom
  • Nuclear Instruments and Methods in Physics Research B 268(2010)11-12, 1718-1722
    DOI: 10.1016/j.nimb.2010.02.046

Publ.-Id: 13309 - Permalink


Some lessons learned from the use of two-phase CFD for nuclear reactor thermalhydraulics
Bestion, D.; Lucas, D.; Boucker, M.; Anglart, H.; Tiselj, I.; Bartosiewicz, Y.;
Two-phase Computational Fluid Dynamics (2-phase CFD) is now increasingly applied to some Nuclear Reactor thermalhydraulic investigations. The main purpose of this paper is to give some guidance to two-phase CFD potential users, based on previous experience of these tools. This experience comes first from a Writing Group (WG3) of the OECD-CSNI-GAMA on the “extension of CFD to two-phase safety issues” which has identified a list of Nuclear Reactor Safety issues for which the use of 2-phase CFD can bring a real benefit and which proposed a general multi-step methodology. Then experience was gained with the NEPTUNE-CFD code which is being developed by EDF and CEA and sponsored by IRSN and AREVA-NP for nuclear application. Also the NURESIM Integrated Project of the European Commission 6th Framework Program has been using 2-phase CFD for Direct Contact Condensation, Pressurized Thermal Shock, boiling flow, DNB and Dry-Out investigations. Although some progress has been made on all these applications, several difficulties are encountered and are here identified. Based on this experience, this paper intends to update the state of the art, to review the main modeling difficulties and to make recommendations for future developments, validation and application of two-phase CFD. The choice of a basic model, of space and time resolution, the deterministic or statistical treatment of interfaces, the characterization of the interfacial structure, and the automatic recognition of the local flow structure are discussed. Transport of interfacial area, modeling of polydispersion and some closure problems for turbulent, wall, and interfacial transfers are also reviewed.
Keywords: Nuclear Reactor Thermalhydraulics, Two-phase CFD, Direct Contact Condensation, Pressurized Thermal Shock, boiling flow, DNB, Dry-Out
  • Contribution to proceedings
    The 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa, Japan
    Proceedings of the 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), Paper N13P1139

Publ.-Id: 13308 - Permalink


Spinodal decomposition and secondary phase formation in Fe-oversaturated GaN
Talut, G.; Reuther, H.; Grenzer, J.; Mücklich, A.; Shalimov, A.; Skorupa, W.; Stromberg, F.;
The flash-lamp annealing technique was applied to a GaN epilayer implanted with Fe in order to investigate the recovery of the crystal structure and the process of secondary phase formation. In the as-implanted state a spinodal decomposition occurs due to the oversaturation of Fe in GaN and a behavior similar to a spin-glass is observed. The precipitation occurs even after annealing for the shortest annealing time of 3 ms. Iron nitrides as well as bcc-Fe are formed upon annealing for 20 ms and are responsible for the ferromagnetic response. No indication of the formation of a diluted magnetic semiconductor is observed. The connection between the structure, magnetism and Fe-charge state was determined by x-ray diffraction, magnetometry and Mößbauer spectroscopy measurements.
Keywords: Fe, GaN, DMS, Mößbauer, flash-lamp annealing

Publ.-Id: 13307 - Permalink


Preparation of shallow n+-layers in Ge using flash lamp annealing
Wündisch, C.; Posselt, M.; Schmidt, B.; Mücklich, A.; Skorupa, W.; Clarysse, T.; Simoen, E.; Hortenbach, H.;
Although the first transistor was made on germanium, most integrated circuits are fabricated using silicon substrates. The main reasons for the change from Ge to Si are the excellent physical properties of the SiO2/Si interface. Today SiO2 is more and more replaced by high-k dielectrics. This fact and the advantage of the higher carrier mobility in Ge compared to Si have led to a renewed interest in Ge as material in future CMOS applications. Previous investigations on the formation of ultra shallow junctions by ion beam processing have shown that p+-doping using B implantation yields junctions that meet the requirements for the 22 nm technology node, whereas the formation of n+-junctions by P or As is complicated by the high diffusivity and the low solubility of the dopants.
The present work deals with the application of millisecond flash lamp annealing (FLA) to samples containing an implanted surface layer of about 100 nm thickness. The layers were formed using P ions with an energy of 30 keV and a fluence of 3x1015 cm-2. The investigations are focused on solid phase recrystallization, dopant redistribution and dopant activation. The dependence of these effects on the heat transfer to the sample during FLA as well as on pre-amorphization and pre-annealing treatment is discussed. The results are compared to typical data achievable by conventional rapid thermal annealing (RTA) with durations of some seconds. Different characterization methods are employed. Channeling Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy (XTEM) are used to monitor the recrystallization of the amorphous layers formed during implantation. The depth distributions of P are measured by secondary ion mass spectrometry. In order to determine the sheet resistance variable probe spacing and micro four point probe measurements are utilized. Selected samples are studied by XTEM to search for precipitates and end-of-range defects. While in RTA the concentration dependent dopant diffusion hinders the formation of shallow n+ layers, FLA does not cause any diffusion but leads to dopant activation up to about 5x1019 cm-3.
Keywords: germanium, shallow junction, flash lamp annealing, diffusion, activation
  • Lecture (Conference)
    Nordic semiconductor meeting, 14.-17.06.2009, Reykjavik, Island

Publ.-Id: 13306 - Permalink


Millisecond flash lamp annealing of shallow implanted layers in Ge
Wündisch, C.; Posselt, M.; Schmidt, B.; Heera, V.; Schumann, T.; Mücklich, A.; Grötzschel, R.; Skorupa, W.; Clarysse, T.; Simoen, E.; Hortenbach, H.;
Shallow n+ layers in Ge are formed by phosphorus implantation and subsequent millisecond flash lamp annealing. Present investigations are focused on the dependence of P redistribution, diffusion and electrical activation on heat input into the sample and flash duration. Furthermore, the influence of pre-amorphization implantation and pre-annealing is studied. In contrast to conventional annealing procedures an activation up to 6.5×1019 cm-3 is achieved without any dopant redistribution and noticeable diffusion. Present results suggest that independently of pre-treatment the maximum activation should be obtained at a flash energy that corresponds to the onset of P diffusion. The deactivation of P is explained qualitatively by mass action analysis which takes into account the formation of phosphorus-vacancy clusters.
Keywords: Germanium, millisecond annealing, electrical activation, shallow junctions
  • Applied Physics Letters 95(2009)25, 252107

Publ.-Id: 13305 - Permalink


Research at High Magnetic Fields
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    ILL-TAS Scientists Outing, 01.-02.10.2009, Lamastre, Frankreich

Publ.-Id: 13304 - Permalink


Electronic properties of quasi-two-dimensional organic superconductors
Wosnitza, J.;
Since the discovery of the first organic superconductor, about 30 years ago, these materials revealed many fascinating properties and allowed to study fundamental low-dimensional physics. Besides superconductivity, the organic metals show a wealth of different ground states such as antiferromagnetic, spin-Peierls, spin-density-wave, and charge-density-wave phases. These ground states are accessible by tuning the structure, counter anion, magnetic field, temperature, and pressure. The study of these fertile phase diagrams has led to new theoretical concepts; however, a solid understanding of some of these states still remains a challenge. Even the normal metallic phase of these electronically low-dimensional metals reveals unusual properties sometimes not in line with conventional Fermi-liquid theory. Here, a review on selected normal-state and superconducting properties of the layered quasi-two-dimensional organic superconductors will be given. Thereby, the focus will be laid on the charge-transfer salts based on bisethylenedithiotetrathiafulvalene, 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 will be highlighted. A brief overview on the superconducting properties including the recently reported evidence for the existence of a Fulde–Ferrell–Larkin–Ovchinnikov state will be presented.
  • Invited lecture (Conferences)
    I.F. Schegolev Memorial Conference "Low-Dimensional Metallic and Superconducting Systems", 10.-16.10.2009, Chernogolovska, Russia

Publ.-Id: 13303 - Permalink


Evolution of the Fermi Surface of the Electron-Doped High-Temperature Superconductor Nd2-xCexCuO4 Revealed by Shubnikov–de Haas Oscillations
Helm, T.; Kartsovnik, M. V.; Bartkowiak, M.; Bittner, N.; Lambacher, M.; Erb, A.; Wosnitza, J.; Gross, R.;
We report on the direct probing of the Fermi surface in the bulk of the electron-doped superconductor Nd2-xCexCuO4 at different doping levels by means of magnetoresistance quantum oscillations. Our data reveal a sharp qualitative change in the Fermi surface topology, due to translational symmetry breaking in the electronic system which occurs at a critical doping level significantly exceeding the optimal doping. This result implies that the (π/a, π/a) ordering, known to exist at low doping levels, survives up to the overdoped superconducting regime.
  • Physical Review Letters 103(2009), 157002

Publ.-Id: 13302 - Permalink


Complexation of curium(III) with pyoverdin-model compounds
Moll, H.; Bernhard, G.;
The aerobic groundwater bacterium Pseudomonas fluorescens (CCUG 32456) isolated from the aquifers at the Äspö Hard Rock Laboratory, Sweden secretes siderophores of the pyoverdin-type. Besides iron(III), these unique bioligands are also able to form strong complexes with actinides (e.g., U(VI), Np(V), and Cm(III)) [1-3]. For U(VI) and Np(V) we could show that mainly the catecholate and to less extend the hydroxamate functionalities of the pyoverdin molecule are involved in the actinide coordination [1, 2]. For Cm(III) it is still not clear which functional group of the pyoverdin molecule causes the great stability constants. In general, Cm(III) interactions with pyoverdin-model compounds and especially with chromophore-models are poorly understood. To address this lack, we thus present findings regarding the speciation of Cm(III) with 2,3­dihydroxynaphthalene in aqueous solution by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at trace Cm(III) concentrations (0.3 µM) over a wide pH range. TRLFS is a well established direct speciation technique for investigating the complexes formed by actinides in both geochemical and biochemical environments. Four Cm(III)- dihydroxynaphthalene species of the type MxLyHz could be identified from the spectroscopic measurements. The stability constants of these strong Cm(III)- bioligand complexes and their individual spectroscopic properties (excitation and emission spectra, lifetimes) are reported. TRLFS shows that Cm(III)- dihydroxynaphthalene species cause a strong red shift of the characteristic Cm(III) (aq) emission band at 593.8 to 614.4 nm. The findings of our Cm(III) speciation study in comparison with the literature indicate a stronger affinity of Cm(III) to the catechol functionality of the pyoverdin molecules as found for U(VI) and Np(V).

[1] H. Moll, M. Glorius, G. Bernhard, A. Johnsson, K. Pedersen, M. Schäfer, H. Budzikiewicz, Geomicrobiol. J. 25, 157-166 (2008).
[2] H. Moll, M. Glorius, A. Johnsson, M. Schäfer, H. Budzikiewicz, K. Pedersen, G. Bernhard, Radiochim. Acta, submitted (2009).
[3] H. Moll, A. Johnsson, M. Schäfer, K. Pedersen, H. Budzikiewicz, G. Bernhard, BioMetals 21, 219-228 (2008).
Keywords: Curium(III), TRLFS, Speciation, Pyoverdin, 2,3-Dihydroxynaphthalene, excitation spectra, Chromophore-models
  • Lecture (Conference)
    RadChem 2010 - 16th Radiochemical Conference, 18.-23.04.2010, Marianske Lazne, Czech Republic

Publ.-Id: 13301 - Permalink


Photodisintegration of the p-nuclei 92Mo and 144Sm in the astrophysically relevant energy window
Nair, C.; Erhard, M.; Junghans, A. R.; Bemmerer, D.; Beyer, R.; Grosse, E.; Klug, J.; Kosev, K.; Rusev, G.; Schilling, K. D.; Schwengner, R.; Wagner, A.;
The heavy neutron deficient p-nuclei are produced in explosive stellar environments via photodisintegration reactions like (g ,n), (g ,p) and (g ,alpha) on r- or s- seed nuclei. The reaction rates of p-nuclei are mostly based on theoretical parameterizations using statistical model calculations. We study experimentally the photodisintegration rates of heavy nuclei at the bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden-Rossendorf. Photoactivation measurements on the astrophysically relevant p-nuclei 92Mo and 144Sm have been performed with bremsstrahlung end-point energies from 10.0 to 16.5 MeV. The activation yields are compared with calculations using cross sections from recent Hauser-Feshbach models. The sensitivity of the statistical models to the input ingredients like photon strength function, optical potentials are tested against the experimental activation yield.
Keywords: photodisintegration, p-nuclei, photoactivation
  • Contribution to proceedings
    International conference Nuclei in Cosmos- X, 27.07.-01.08.2008, Mackinac Island, Michigan, United States
    Photodisintegration of the p-nuclei 92Mo and 144Sm in the astrophysically relevant energy window: Proceedings of Science

Publ.-Id: 13300 - Permalink


Application of Focused Ion and Electron Beams in Materials Research
Bischoff, L.;
At the beginning the lecture I will briefly give an overview about the organization of the Research Centre Dresden-Rossendorf with different Institutes and research topics. In the Institute of Ion Beam Physics and Materials Research the application of ion beams in advanced materials science is manifold: for example, they are used to generate new or improved functional surfaces, and they are ideally suited to produce micro- and nanostructures in semiconductors. For these purposes in the Institute a couple of modern ion beam instruments for the fabrication and analysis of nanostructures is available. Among them there are a mass separated focused ion beam (FIB) and a crossbeam system, consisting of a high resolution Ga-FIB and a scanning electron microscope (SEM), which will be discussed more in detail. During the last decades, focused ion beams became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and became an indispensable tool in nanotechnology. For special purposes like ion milling, ion beam writing for doping or patterning on μm- and nm-scale without any lithographic steps Ga+ and increasingly other ion species are of great interest. An introduction in design and operation of mass separated FIB systems (e.g. CANION31Mplus), equipped with metal alloy liquid ion sources as well as the development and characterization of them will be given. The combination of a focused electron beam with a high resolution FIB column in a crossbeam arrangement (NVision40) enables the in-situ inspection and analysis of FIB fabricated nanostructures with a resolution down to one nm without surface damaging. An included gas injection system allows the MO-CVD of nanostructures of different materials using either the focused ion or the electron beam. The fabrication possibilities of nanostructures, like nanowires, nanobridges and nanocantilevers by ion beam synthesis using different kinds of focused ion beams will be demonstrated and possible applications will be mentioned. Some examples, like ion beam synthesis of CoSi2 nano-structures, the generation of fluorescent colour centres, sputtering investigations and applications, the formation of ripples under FIB irradiation or the fabrication of NEMS structures on SOI substrates will be shown to demonstrate the manifold utilization of the microbeam technology. Furthermore, the possibility of varying the flux in the FIB by changing the pixel dwell-time in a wide range gives the opportunity to investigate radiation damage and dynamic annealing effects in Si, Ge, SiC and other materials at elevated implantation temperatures using different projectile ion species. Finally, the state-of art of FIB applications for TEM lamella preparation, FIB lithography of thin films and ion beam microscopy will be presented and shortly discussed.
Keywords: Focused Ion Beam; Liquid Metal Ion Source; Electron Microscopy; Nanotechnology
  • Invited lecture (Conferences)
    imdea nanociencia, 04.11.2009, Madrid, Spanien
  • Invited lecture (Conferences)
    Kolloquiumsvortrag, 10.12.2009, Leipzig, Deutschland

Publ.-Id: 13299 - Permalink


Pipe dream
Azzopardi, B.; Hampel, U.; Hunt, A.;
Gas-liquid flows are central to oil and gas production and because of the very flexible nature of the interface between the fluids, the flows can be very complex exhibiting a wide variety of three dimensional structures. In the field the steel pipes in which these two-phase mixture flow make it difficult to observe them. Even in the laboratory where pipes can be made of transparent plastic, we can still normally only see what is occurring near the pipe wall as bubbles clustering near the wall, or wavy films of liquid flowing along the walls, obscure what is occurring at the middle of the pipe. One way in which these visual limitations can be overcome is to employ electrical tomography methods. In research at the University of Nottingham we are working with Forschungzentrum Rossendorf-Dresden from Germany and Tomoflow Limited to use electrical tomography to 'see' into the pipe.
Keywords: multi-phase flow, wire mesh sensors, electrical capacitance tomography
  • TCE - The chemical engineer (2009)820, 39-41

Publ.-Id: 13298 - Permalink


Simulating Strongly Coupled Plasmas on High-Performance Computers
Bussmann, M.; Schramm, U.; Thirolf, P.; Habs, D.;
Simulating strongly coupled plasmas is a demanding computational task. When a plasma is strongly coupled, the mutual Coulomb energy between the plasma particles is much stronger than their kinetic energy. Such a system can undergo a phase transition into a state in which long-range ordering of the plasma constituents can be observed. In a realistic simulation of the plasma dynamics one has to compute the total mutual interaction of each particle with each other particle for particle numbers up to hundred thousand particles. To study the microscopic and macroscopic dynamics of the plasma on a long time scale one thus has to rely on the computational power which is only available at supercomputing centers such as the Leibniz Rechenzentrum.
Keywords: strong coupling, plasma, ocp, one-component plasma, simulation, molecular dynamics, checker-board algorithm, laser cooling, particle, highly-charged ion, hci, cooling, stopping
  • Contribution to proceedings
    HLRB, KONWIHR and Linux-Cluster Review and Results Workshop, 08.-09.12.2009, Garching, Germany

Publ.-Id: 13297 - Permalink


GPU-based Particle-in-Cell Simulation
Burau, H.; Bussmann, M.; Schramm, U.; Cowan, T.; Widera, R.; Hönig, W.; Juckeland, G.;
Accelerating Plasma Simulations using novel computing hardware is a promising way towards a cost-efficient decrease of the runtime of realistic plasma simulations. We present a new particle-in-cell algorithm for simulating laser plasma acceleration of particles which has been developed to run on a NVIDIA GPU system. Using a sliding-window technique we are able to run large-scale 2D simulations of laser wakefield acceleration. We present the algorithm in detail and show that it is easy to extend to 3D geometries. We will conclude by discussing both obstacles and promises encountered when porting the algorithm to a standard CPU-based Linux cluster in which each node is equipped with one or more GPUs.
Keywords: gpu, gpgpu, cuda, particle-in-cell, pic, simulation, algorithm, cluster, message passing interface, pic, vampir, laser, plasma, acceleration
  • Poster
    ICNSP 09 - 21st International Conference on Numerical Simulation of Plasmas 2009, 06.-09.10.2009, Lisboa, Portugal

Publ.-Id: 13296 - Permalink


The economy of Yb:lasers
Siebold, M.;
Introduction of high-energy class diode-pumped solid-state lasers (HEC-DPSSLs) worldwide, efficiency limitations and energy extraction issues of high-energy laser based on Yb-doped materials, room-temperature vs. cryogenically cooled lasers, simulation and experimental results obtained with multi-pass pumping - a technique for efficiency enhancement.
  • Lecture (others)
    workshop on High-Energy Class Diode-Pumped Solid-State Lasers (HEC-DPSSL), 10.-12.06.2009, Dresden, Deutschland

Publ.-Id: 13295 - Permalink


Neue Materialien für Hochintensitätslaser sowie deren Anwendungen
Siebold, M.;
Erzeugung hoher Lichtintensitäten mittels Ultrakurzpulslaser, Laser-Teilchenbeschleunigung, diodengepumpte Festkörperlaser, neue Ytterbium-dotierte Lasermaterialien für Kurzpulslaserverstärker
  • Invited lecture (Conferences)
    workshop: Festkörperlaser – Materialien und Anwendungen, 10.-11.09.2009, Berlin, Deutschland

Publ.-Id: 13294 - Permalink


Diode-pumped chirped pulse amplification to the TW level using Yb:CaF2
Siebold, M.; Hornung, M.; Hein, J.; Uecker, R.; Debus, A.; Kaluza, M. C.;
We present a terawatt diode-pumped chirped pulse amplifier using single-crystalline Yb:CaF2 as the gain medium. A maximum pulse energy of 420 mJ and a repetition rate of 1 Hz was obtained. After recompression, a pulse energy of 197 mJ and a pulse duration of 192 fs were achieved, corresponding to a peak power of 1TW.
Keywords: Diode-pumped lasers, Ytterbium-doped solid state lasers, optical pulse generation and pulse compression
  • Contribution to proceedings
    Ultra-Intense Laser Interaction Science (ULIS), 24.-29.05.2009, Frascati, Italia
    Diode-pumped chirped pulse amplification to the TW level using Yb:CaF2, vol. 2109: American Institute of Physics, 119-122
  • Poster
    Ultra-Intense Laser Interaction Science, 26.05.2009, Frascati, Italia

Publ.-Id: 13293 - Permalink


In-situ observation of secondary phase formation in Fe implanted GaN annealed in low pressure N-2 atmosphere
Talut, G.; Grenzer, J.; Reuther, H.; Shalimov, A.; Baehtz, C.; Novikov, D.; Walz, B.;
The formation of secondary phases in Fe implanted GaN upon annealing in low pressure N2-atmosphere was detected by means of in-situ x-ray diffraction and confirmed by magnetization measurements. A repeatable phase change from Fe2N at room temperature and Fe(3-x)N at 1023 K was observed in-situ. The phase transformation is explained by the change of lattice site and concentration of nitrogen within nitrides. The diffusion of Fe towards sample surface and oxidation with increasing annealing cycles limits the availability of secondary phase and hence the repeatability. At high temperature GaN dissolves and Ga as well as Fe oxidize due to presence of residual oxygen in the process gas. The ferromagnetism in the samples is related to nanometer sized interacting Fe(3-x)N crystallites.
Keywords: GaN, Fe-nitrides, DMS

Publ.-Id: 13292 - Permalink


Xe ion beam induced ripple structures on differently oriented single-crystalline Si surfaces
Hanisch, A.; Biermanns, A.; Pietsch, U.; Grenzer, J.; Facsko, S.;
We report on Xe+ induced ripple formation at medium-energy on single crystalline silicon surfaces of different orientation using substrates with an intentional miscut from the [001] direction and a [111] oriented wafer. The ion beam incidence angle in respect to the surface normal was kept fixed at 65° and the ion beam projection was parallel or perpendicular to the [110] direction. By a combination of atomic force microscopy, X-ray diffraction and high resolution transmission electron microscopy we found that the features of surface and the subsurface rippled structures such as ripple wavelength and amplitude and the degree of order do not depend on the surface orientation as assumed in recent models of pattern formation for semiconductor surfaces.
Keywords: ripples nanostructures Xe self-organisation silicon miscut ion implantation
  • Journal of Physics D: Applied Physics 43(2010)11, 112001

Publ.-Id: 13291 - Permalink


Bestimmung des Ausdampfverhaltens des Reaktorkerns bei Ausfall der Nachkühlung im Mitte-Loop-Betrieb bei geöffnetem Reaktordeckel auf Basis von Rechnungen mit dem Programm ATHLET
Kliem, S.;
Unter Verwendung des Rechenprogramms ATHLET wurde das Ausdampfverhalten des Reaktorkerns bei Ausfall der Nachkühlung untersucht. Dafür wurde der Primärkreislauf des Reaktors vom Austritt aus dem Pumpenbogen bis zum Eintritt in den Dampferzeuger modelliert. Bei einer fest vorgegebenen Nachzerfallsleistung von 22 MW wurde das axiale Profil variiert. Neben einem symmetrischen kosinusähnlichen Profil wurden jeweils ein Profil für den Beginn und das Ende eines Brennstoffzyklus eines typischen Druckwasserreaktorkerns verwendet.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2009
    FZD\FWS\2009\06
    26 Seiten

Publ.-Id: 13290 - Permalink


Characterization and tuning of ultrahigh gradient permanent magnet quadrupoles
Becker, S.; Bussmann, M.; Raith, S.; Fuchs, M.; Weingartner, R.; Kunz, P.; Lauth, W.; Schramm, U.; Ghazaly, M. E.; Grüner, F.; Backe, H.; Habs, D.;
The application of quadrupole devices with high field gradients and small apertures requires precise control over higher order multipole field components. We present a new scheme for performance control and tuning; which allows the illumination of most of the quadrupole device aperture because of the reduction of higher order field components. Consequently, the size of the aperture can be minimized to match the beam size achieving field gradients of up to 500 T m -1 at good imaging quality. The characterization method based on a Hall probe measurement and a Fourier analysis was confirmed using the high quality electron beam at the Mainz Microtron MAMI.
Keywords: compact, permanent, magnetic, quadrupole, lens, beam focusing, multipole, tuning, halbach, electron beam, x-fel

Publ.-Id: 13289 - Permalink


Measurement of Radiation Hardness of PET Components
Fiedler, F.; Braess, H.; Enghardt, W.;
In-beam PET has given valuable feedback on treatment quality over the 11 years of operation time between 1997 and 2008 of the heavy ion treatment facility at the Gesellschaft für Schwerionenforschung (GSI) Darmstadt. Based on this technical expertise a next generation of in-beam PET scanners will be developed. An experiment addressing the question whether the detectors and electronic components used in state-of-the-art PET-systems can be also utilized to configure a future in-beam PET scanner was performed at the medical beam line of GSI. The equipment for a new in-beam PET scanner should be tested whether it will resist the fluence of secondaries arising from the patient treatment of about 5 years. A ^12C beam of an energy of E=430.10AMeV was stopped in a PMMA phantom. The primary particle fluence of this irradiation was equivalent to about 5300 patient fractions (3 GyE per fraction). The detectors were placed at several angles to simulate a higher secondary particle fluence, i.e. a longer time of usage. They have been exposed to a secondary particle fluence equivalent up to 13 years of usage in an in-beam PET scanner. The equipment was provided by CPS and tested before and after the experiment. No damage was found applying the standard test procedure. analyzing the detectors after the experiment.
Keywords: radiation hardness, in-beam PET, ion therapy
  • Lecture (Conference)
    2009 IEEE Nuclear Science Symposium and Medical Imaging Conference, 25.-31.10.2009, Orlando, USA
  • Contribution to proceedings
    2009 IEEE Nuclear Science Symposium and Medical Imaging Conference, 23.10.-01.11.2009, Orlando, USA
    Conference Record

Publ.-Id: 13288 - Permalink


A FAIR equation of state
Schulze, R.; Kämpfer, B.;
kein Abstract verfügbar
Keywords: QCD, equation of state, FAIR, quasiparticles
  • Lecture (others)
    Institutsinternes WIP-Seminar, 16.10.2009, Dresden-Rossendorf, Deutschland

Publ.-Id: 13287 - Permalink


Discrimination of thioarsenites and thioarsenates by x-ray absorption spectroscopy
Suess, E.; Scheinost, A. C.; Bostick, B. C.; Merkel, B. J.; Wallschlaeger, D.; Planer-Friedrich, B.;
Soluble arsenic−sulfur compounds play important roles in the biogeochemistry of arsenic in sulfidic waters but conflicting analytical evidence identifies them as either thioarsenates (= AsV−sulfur species) or thioarsenites (= AsIII−sulfur species). Here, we present the first characterization of thioarsenates (mono-, di-, and tetrathioarsenate) by X-ray absorption spectroscopy and demonstrate that their spectra are distinctly different from those of AsIII−sulfur species, as well as from arsenite and arsenate. The absorption near edge energy decreases in the order arsenate > thioarsenates > arsenite > AsIII−sulfur species, and individual thioarsenates differ by 1 eV per sulfur atom. Fitted AsV−S and AsV−O bond distances in thioarsenates (2.13−2.18 Å and 1.70 Å, respectively) are significantly shorter than the corresponding AsIII−S and AsIII−O bond distances in AsIII−S species (2.24−2.34 Å and 1.78 Å, respectively). Finally, we demonstrate that thioarsenates can be identified by principal component analysis in mixtures containing AsIII−sulfur species. This capability is used to study the spontaneous reduction of tetrathioarsenate to AsIII−sulfur species (possibly trithioarsenite) upon acidification from pH 9.5 to 2.8.
Keywords: Arsenic speciation thioarsenite thioarsenate EXAFS XANES

Publ.-Id: 13286 - Permalink


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