Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39109 Publications

CFD modelling to predict the counter-current flow limitations of the air/water counter-current two-phase flow in 1/3rd flat channel model of a hot-leg pressurized water reactor

Deen, D.; Höhne, T.; Lucas, D.; Vallée, C.

The analytical simulation of the counter-current flow limitation phenomenon in a PWR is an essential element to understand safety-related issues in nuclear power plants. It is expected that the introduction of computational fluid dynamics (CFD) tools will enhance the accuracy of the simulation predictions compared to the established one-dimensional thermal hydraulic analyses. Nevertheless, the use of CFD for this complicated task is still a challenge today. Due to the need to understand the CCFL phenomenon in a PWR for reasons of safety and characterisation of normal operation, it is necessary to validate computer codes and to verify computational results using experimental data. Therefore it is also interest to prove the understanding of the general fluid dynamic mechanism leading CCFL and to identify the critical parameters affecting this phenomenon.

In order to improve the transient analysis of counter-current two-phase flows, experimental and numerical studies were conducted at Forschungszentrum Dresden-Rossendorf (FZD). A 1/3rd scale model of the hot leg PWR of a German Konvoy Pressurized Water Reactor with rectangular cross section was used. The experimental results on this topic were reported in previous reports [Deendarlianto et al. (2008) & Vallée et al. (2009)]. Selected an air-water CCFL experiment at 0.15 MPa and room temperature at FZD (experimental running number 30-09) was numerically modelled with three-dimensional two-fluid models of computer code CFX 12.0 (ANSYS CFX). The aim of this CFD simulation is to validate the prediction model of the CCFL with the existing multiphase flow models built in the commercial code ANSYS CFX. CFD simulation was performed using the multi-fluid Euler-Euler modeling approach or free surface model available in CFX. The calculation was carried out in fully transient manner using a gas/liquid inhomogeneous multiphase flow model coupled with a shear stress transport (SST) turbulence model. In the present numerical study, the drag coefficient was approach by using the Algebraic Interfacial Area Density (AIAD) model. The results indicated that quantitative agreement between calculation and experimental data was obtained for the occurrence of flooding point. Next, it was found also that a comparison with the high-speed video observations shows a good qualitative agreement.

Keywords: Computational fluid dynamic; Counter-current flow limitation; Algebraic Interfacial Area Density (AIAD) Model

  • Contribution to proceedings
    7th Multiphase Flows Workshop: Simulation, Experiment and Application, 22.-24.06.2010, Forschungszentrum Dresden, Germany
    CFD modelling to predict the counter-Current flow limitations of the air/water counter-current two-phase flow in 1/3rd flat channel model of a hot-leg pressurized water reactor
  • Lecture (Conference)
    7th Multiphase Flows Workshop: Simulation, Experiment and Application, 22.-24.06.2010, Forschungszentrum Dresden, Germany

Publ.-Id: 14243

CFD: Mixing process is it an art of science?

Höhne, T.

Basic Phenomenon
Boron 10 = strong thermal neutron absorber
Used as boric acid solved in the coolant of PWRs to compensate excess reactivity inadvertant or unavoidable decrease of boron concentration (boron dilution) might result in a reactivity transient
Power peak depends on coolant mixing in Cold leg, Downcomer Lower plenum Density differences can strongly influence the mixing

Keywords: CFD; mixing; boron dilution

  • Invited lecture (Conferences)
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia
  • Contribution to proceedings
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia

Publ.-Id: 14242

CFD: Validation of Multiphase flow

Höhne, T.

CFD codes for application in horizontal multiphase flows:

the investigation of the feasibility of numerical prediction of stratified two phase flow with existing multiphase flow models in ANSYS CFX to prove the understanding of the general fluid dynamic mechanism
to identify the critical parameters (like e.g. slug length, frequency and propagation velocity, pressure drop, CCFL) to improve the multiphase flow modeling (interfacial momentum transfer, turbulence at the free surface et.) experimental data required for the validation

Keywords: CFD; stratified two phase flow; turbulence; interfacial momentum transfer

  • Invited lecture (Conferences)
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia
  • Contribution to proceedings
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia

Publ.-Id: 14241

CFD: European experience of 15 years

Höhne, T.

CFD (Computational Fluid Dynamics) is the simulation of fluids engineering systems using modeling (mathematical physical problem formulation) and numerical methods (discretization methods, solvers, numerical parameters, and grid generations, etc.)
CFD made possible by the advent of digital computer and advancing with improvements of computer resources (500 Floating Point Operations per Second (flops), 1947 1 Petaflops, 2009)

Keywords: CFD

  • Invited lecture (Conferences)
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia
  • Contribution to proceedings
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia

Publ.-Id: 14240

CFD: In Nuclear Reactor Safety

Höhne, T.

Strong increase of usage of three-dimensional Computational Fluid Dynamics (CFD) in industrial applications because for instance
pressurized thermal shocks,
coolant mixing,
thermal striping
cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.

Keywords: CFD; Nuclear Safety

  • Invited lecture (Conferences)
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia
  • Contribution to proceedings
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia

Publ.-Id: 14239

Hot Electrons Transverse Refluxing in Ultraintense Laser-Solid Interactions

Buffechoux, S.; Psikal, J.; Nakatsutsumi, M.; Romagnani, L.; Andreev, A.; Zeil, K.; Amin, M.; Antici, P.; Burris-Mog, T.; Compant-La-Fontaine, A.; D’Humières, E.; Fourmaux, S.; Gaillard, S.; Gobet, F.; Hannachi, F.; Kraft, S.; Mancic, A.; Plaisir, C.; Sarri, G.; Tarisien, M.; Toncian, T.; Schramm, U.; Tampo, M.; Audebert, P.; Willi, O.; Cowan, T. E.; Pépin, H.; Tikhonchuk, V.; Borghesi, M.; Fuchs, J.

We have analyzed the coupling of ultraintense lasers (at ∼2×1019   W/cm2) with solid foils of limited transverse extent (∼10  s of μm) by monitoring the electrons and ions emitted from the target. We observe that reducing the target surface area allows electrons at the target surface to be reflected from the target edges during or shortly after the laser pulse. This transverse refluxing can maintain a hotter, denser and more homogeneous electron sheath around the target for a longer time. Consequently, when transverse refluxing takes places within the acceleration time of associated ions, we observe increased maximum proton energies (up to threefold), increased laser-to-ion conversion efficiency (up to a factor 30), and reduced divergence which bodes well for a number of applications.

Publ.-Id: 14238

Modeling poly-dispersed flows with the Inhomogeneous MUSIG model

Lucas, D.; Krepper, E.

The qualification of Computational Fluid Dynamics (CFD) codes for two-phase flows is an important topic in the frame of German CFD initiative initiated by the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS). This concerted action especially aims on phenomena in the primary system of light water reactors. Forschungszentrum Dresden-Rossendorf e.V. (FZD) is involved in both – the generation of CFD-grade databases and CFD model development and validation. The data obtained in our TOPFLOW experiments clearly show a separation of small and large bubbles over the pipe radius due to the action of the lateral lift force. This has a considerable influence on the local interfacial area density. Also the other bubble forces as drag and turbulent dispersion force clearly depend on the bubble size. For this reason it is important to introduce bubble size dependent velocities fields in a proper modeling of poly-dispersed flows.

Keywords: bubbly flow; interfacial area transport; dispersed flow; MUSIG; CFD

  • Contribution to proceedings
    ANS 2010 Winter Meeting, 07.-11.11.2010, Las Vegas, U.S.A.
    Transactions of the ANS 2010 Winter Meeting
  • Invited lecture (Conferences)
    ANS 2010 Winter Meeting, 07.-11.11.2010, Las Vegas, U.S.A.

Publ.-Id: 14237

CFD-grade databases on two-phase upwards vertical pipe flows

Lucas, D.; Beyer, M.; Szalinski, L.

The qualification of Computational Fluid Dynamics (CFD) codes for two-phase flows is an important topic in the frame of German CFD initiative initiated by the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS). This concerted action especially aims on phenomena in the primary system of light water reactors. The Transient twO Phase FLOW (TOPFLOW) test facility is one of the reference experimental facilities within this CFD network. One type of experiments aims on generation of CFD-grade data (i.e. data with high resolution in space and time) for poly-dispersed bubbly flows. Such data were obtained at the TOPFLOW facility for upwards vertical pipe flow using the wire-mesh sensor technique. Different experimental series were done for adiabatic air-water and steam-water flows as well as for condensing and evaporating flows. Beside bubbly flows the database also comprises measurements for slug, churn-turbulent and wispy-annular flows. The aim of this presentation is to give an overview on the available database.

Keywords: bubbly flow; interfacial area transport; pipe flow; bubble size distributions; CFD-grade data

  • Contribution to proceedings
    ANS 2010 Winter Meeting, 07.-11.11.2010, Las Vegas, U.S.A.
    Transactions of the ANS 2010 Winter Meeting
  • Invited lecture (Conferences)
    ANS 2010 Winter Meeting, 07.-11.11.2010, Las vegas, U.S.A.

Publ.-Id: 14236

Experimental observations related to the lateral lift force in poly-dispersed bubbly flows

Lucas, D.

The influence of the lateral lift force on trajectories of single bubbles under idealized conditions was investigated in the past by means of Direct Numerical Simulations (DNS) and by well defined experiments. However, contradictory discussions can be found in literature on the meaning of this force for poly-dispersed flows, i.e. flow with medium or high gas volume fraction. Usually such flows are turbulent and bubble-bubble interaction, i.e. bubble coalescence and breakup play an important role. For this reason it is not self-evident, that the correlation for the lift force coefficient obtained by Tomiyama can be applied for such flows.
The separation of small and large bubbles in poly-dispersed flows was clearly shown in experiments on vertical pipe flow basing on wire-mesh sensor measurements which allow the measurement of bubble size distributions. The critical diameter at which the lift force changes its sign predicted by the Tomiyama correlations (5.8 mm for air-water flow at ambient conditions) seems to fit in general well with the transition between wall and core peaks in the radial gas volume fraction profiles decomposed according to the bubble size. This was also confirmed for steam-water flows at a pressure of 6.5 MPa for which the critical diameter is at about 3.5 mm according to the correlation.
However in case of void fraction larger than about 5 % the effect of the lift force is superposed by dynamic effects as bubble coalescence and breakup and radial migration of the bubbles. For this reason it is not possible to conclude on the critical diameter directly from the shape of the radial gas volume fraction profiles. Also, it was argued, that the wall peak of small bubbles can be caused by large bubbles moving fast upwards in the pipe centre and pushing the small bubbles towards the wall. For this reason in the presented work the distribution of bubbles in dependence on radial position and on bubble sizes is investigated in detail for developing flows. New, high-quality data on air-water as well as on steam-water flows in a DN200 pipe are used for these investigations. The validity of the Tomiyama correlation can be confirmed for a wide range of flow rates. Finally the consequences of the lateral lift force on the flow bubble columns, on the stability of homogeneous bubbly flows and on bubble plumes produced by bubble entrainment from impinging jets are discussed.

Keywords: bubbly flow; lift force; dispersed flow

  • Lecture (Conference)
    48th European Two Phase Flow Group Meeting, 27.-30.06.2010, London, United Kingdom

Publ.-Id: 14235

Nitrogen interstitial induced texture depth gradient in stainless steel

Templier, C.; Stinville, J. C.; Renault, P. O.; Abrasonis, G.; Villechaise, P.; Riviere, J. P.; Drouet, M.

The microstructural changes induced by the incorporation of large quantities of nitrogen in austenitic stainless steel are analyzed. Phase and texture modification as well as grain rotation are investigated by X-ray and electron backscatter diffraction. A quantitative dependence of the rotation on the grain orientation is determined by means of depth profiling and diffraction techniques. Correlation between local nitrogen interstitial content, associated crystallographic rotation and degree of texturing is established.

Keywords: Texture; Lattice rotation; Nitriding; Stainless steel

Publ.-Id: 14234

Out-of-plane magnetic patterning on austenitic stainless steels using plasma nitriding

Menendez, E.; Stinville, J. C.; Tromas, C.; Templier, C.; Villechaise, P.; Rivière, J. P.; Drouet, M.; Martinavicius, A.; Abrasonis, G.; Fassbender, J.; Baro, M. D.; Sort, J.; Nogues, J.

A correlation between the grain orientation and the out-of-plane magnetic properties of nitrogen-enriched polycrystalline austenitic stainless steel surface is performed. Due to the competition between the magnetocrystalline anisotropy, the exchange and dipolar interactions, and the residual stresses induced by nitriding, the resulting effective magnetic easy-axis can lay along unusual directions. It is also demonstrated that, by choosing an appropriate stainless steel texturing, arrays of ferromagnetic structures with out-of-plane magnetization, embedded in a paramagnetic matrix, can be produced by local plasma nitriding through shadow masks.

Publ.-Id: 14233

On lattice plane rotation and crystallographic structure of the expanded austenite in plasma nitrided AISI 316L steel

Templier, C.; Stinville, J. C.; Villechaise, P.; Renault, P. O.; Abrasonis, G.; Riviere, J. P.; Martinavicius, A.; Drouet, M.

Crystallographic structure and lattice rotation of the ‘expanded’ austenite produced by means of low temperature plasma nitriding is investigated. The microstructure of the nitrogen enriched layer has been investigated by means of X-ray diffraction (XRD) while the lattice rotations in the nitrided zone were assessed by electron backscattered diffraction (EBSD). The nitrogen depth profiles have been determined by means of glow discharge optical emission spectroscopy and nuclear reaction analysis. XRD shows the presence of the ‘expanded’ austenite or γN phase in all the nitrided samples characterized by average larger lattice spacing in relation to non-nitrided steel matrix. EBSD investigation demonstrates that in addition to the lattice expansion nitrogen incorporation into the stainless steel matrix induces significant lattice rotations. The amount and direction of these crystallographic plane rotations are function of the initial orientation. An unusual evolution of the 220 γN line as a function of the nitriding duration is observed together with an anomalously high intensity ratio of the 111 and 200 γN and matrix lines. The XRD results are interpreted on the basis of the lattice rotations of diffracting planes, nitrogen concentration gradient, nitrogen diffusion anisotropy and residual stress. It shows that these rotations are a pertaining feature for the understanding of the γN microstructure.

Keywords: Plasma nitriding; Expanded austenite; XRD; EBSD; Lattice rotation; Austenitic stainless steel

Related publications

Publ.-Id: 14232

Nanoscale precipitation patterns in carbon-nickel nanocomposite thin films: period and tilt control via ion energy and deposition angle

Abrasonis, G.; Oates, T. W. H.; Kovacs, G.; Grenzer, J.; Persson, P. O. A.; H. Heinig, K.-H.; Martinavicius, A.; Jeutter, N.; Baehtz, C.; Tucker, M.; Bilek, M. M. M.; Moeller, W.

Periodic precipitation patterns in C:Ni nanocomposites grown by energetic ion co-deposition are investigated. Films were grown at room temperature by ionized physical vapor deposition using a pulsed filtered cathodic vacuum arc. We reveal the role of the film composition, ion energy and incidence angle on the film morphology using transmission electron microscopy and grazing incidence small angle x-ray scattering. Under these growth conditions, phase separation occurs in a thin surface layer which has a high atomic mobility due to energetic ion impacts. This layer is an advancing reaction front, which switches to an oscillatory mode, producing periodic precipitation patterns. Our results show that the ion induced atomic mobility is not random, as it would be in the case of thermal diffusion, but conserves to a large extent the initial direction of the incoming ions. This results in a tilted pattern under oblique ion incidence. A dependence of the nanopattern periodicity and tilt on the growth parameters is established and pattern morphology control via ion velocity is demonstrated.

Keywords: nanocomposites; phase separation; self-organization; thin films

Related publications

Publ.-Id: 14231

Estrogen detection in water by silicon based light emitters

Cherkouk, C.; Rebohle, L.; Skorupa, W.; Helm, M.

The immediate and accurate monitoring of chemical and biological substances is essential in environmental analysis for minimizing the health risk for citizens and their exposure to pollutants. Recently, considerable attention has been focused on endocrine-disrupting compounds (EDCs), such as estrogens, which constitute a wide group of environmental pollutants, especially in drinking water.
A new concept for measuring the concentration of such organic compounds by using Si-based, integrated light sources for fluorescence analysis is presented. In that concept the analyte, estrogen in this example, is labelled with a fluorescence marker and is immobilized at the passivated surface of the light emitter by receptor molecules.
The ion beam technology is one of the most essential steps of the light emitter fabrication. The integrated light emitters are based on a metal-oxide-semiconductor (MOS) structure. This oxide layer is implanted with Ge or rare earth ions (Gd and Tb) followed by annealing and SiON deposition. Depending on the implanted element there is a broad palette of MOS devices emitting light from the UV up to the red spectral region. The combination between Si-based integrated light emitter and this kind of biosensing opens a way to extremely small device dimensions and is of great interest for point-of-care measurements.

The current system was investigated Fourier-Transform infrared spectroscopy (FTIR), x-ray-photoelectron spectroscopy, photoluminescence (PL) and electroluminescence (EL) measurements.

  • Lecture (Conference)

Publ.-Id: 14230

Estrogen detection in waterish solutions by Silicon based light emitters

Cherkouk, C.; Rebohle, L.; Skorupa, W.; Helm, M.

Endocrine-disrupting compounds (EDC´s) constitute a wide group of environmental pollutants that causes severe effects on the people and wild life. Actually, considerable interests have been focused on quantification methods for analytical tracing of chemical substances in drinking water, as in food industry, and medical diagnostic.
A sensor concept for estrogen detection in waterish solutions by Silicon based light emitters (MOSLED) was developed. This concept is based on direct fluorescence analysis and consists of a certain arrangement of the bio- components and their fabrication methods as well as the measurement protocol.
The functionalization of the SiO2 surface of the MOSLED was realized by means of the new developed SSC (Spraying Spin Coating) method. The chemical precursors of this method are organofunctional silane groups with three different functional groups, namely the amino-, carboxyl-, and thiolgroups. These results have been compared with those of the literature. The optimization of the SSC-method was analyzed by means of standard surface science techniques like FTIR-, Raman-, and XPS-spectroscopy. The surface roughness was applied by using AFM-spectroscopy, which showed a smooth surface by the samples treated with the SSC-method.
In order to immobilize the hER(alpha) receptor at the surface, the receptor was bound to the molecular shell of the QDot655 dye and finally adsorbed to the silanized SiO2 surfaces. The fraction of the immobilized hER(alpha) receptors was controlled via Photoluminescence-measurements.
The whole concept of the sensor was tested at two water samples containing estrogen in different concentrations.

  • Lecture (Conference)
    From embedded sensors to sensorial materials, 07.-11.06.2010, Strasbourg, France

Publ.-Id: 14229

Quantitative observation of transport processes in soils with high-resolution PET

Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.; Zakhnini, A.; Enzmann, F.; Kersten, M.

Positron-Emission-Tomography (PET) enables direct and quantitative monitoring of the spatio-temporal distributions of dissolved inert and/or reactive PET-nuclides and PET-nuclide-labelled compounds during their passage through decimetre-scaled material samples. We apply PET exclusively to geological samples and reach the physical resolution limit of about 1 mm with our small-animal-PET scanner (ClearPET, Raytest). We suggest our GeoPET has unrivalled sensitivity and selectivity for tracer concentrations to some 107 tracer atoms/µl and thus is ideally suited for direct flow and transport process observations in soils. This lower limit of the tracer concentration in the order of about 1 kBq/µl outranges other process observation methods (e.g. NMR or resistivity tomography) by many orders of magnitude. Like in the common medical practice, a combination with µCT for structural imaging would be advantageous for improving the spatial significance.
In the past we demonstrated the feasibility of the method, applying in-house developed and medical PET-scanners. The installation of the PET scanner in our controlled area makes possible long-term experiments and the application of non-standard and long-living PET-nuclides (like 124I, decay time 4 days, and 58Co, decay time 71 days). The installation of a new cyclotron will also extend the availability of short-living PET-isotopes for fast process observations (e.g. 11C, decay time 20 min). Application of these nuclides extends the common radiopharmaceutical practice of labelling organic compounds with 18F (decay time 110 min).
The density of geomaterials may cause more than 50% of Compton-scattered events, which degrade the image quality. The quantification of the resulting artefacts is under way by Mont-Carlo model-based tools and will significantly empower the scatter-correction procedures.
Transport observation studies have been conducted on consolidated, partially fractured rocks and on soils, often showing more or less localized transport pathways. The effective volume and transport network, as well as the effective surface area for specific process conditions can be derived directly and quantitatively from the spatio-temporal tracer distribution in the sample, which can be visualized as 3D-movie, in contrast to indirect observations based on break-through curves at the endpoint of the sample. Comparisons with Lattice-Boltzmann simulations based on structural information obtained by µCT are indicating, that any actual transport field very much depends on elusive boundary conditions and therewith represents just one instance of a variety of possible spatio-temporal distributions with similar effective parameters.

Keywords: tracer; transport; PET; soil; process tomography

  • Lecture (Conference)
    Advanced Spectroscopy and Microscopic Characterisation Techniques - Tools to Enlighten Biogeochemical Interfaces in Soils, 04.-06.10.2010, Jena, Deutschalnd

Publ.-Id: 14228

Temperature Measurement in Rapid Thermal Processing with focus on the application to Flash Lamp Annealing

Reichel, D.; Skorupa, W.; Lerch, W.; Gelpey, J. C.

The present review intends to help its reader find a suitable method for temperature measurement in Millisecond Spike Annealing (MSA). For this purpose it is going to highlight current and former industrial and research approaches for both RTP (Rapid Thermal Processing) and MSA to measure the true wafer temperature.
The theoretical background of each measurement technique is considered along with its capability to be applied in MSA tools as well as its suitability for Industry in terms of time and temperature resolution.

Keywords: Rapid Thermal Annealing; Millisecond Annealing; Flash Lamp; Black Body Radiation; Temperature Measurement; Pyrometer

Publ.-Id: 14227

Leaving the structural ivory tower, assisted by interactive 3D PDF

Kumar, P.; Ziegler, A.; Grahn, A.; Hee, C. S.; Ziegler, A.

The ability to embed interactive three-dimensional (3D) models into electronic publications in portable document format (PDF) greatly enhances the accessibility of molecular structures. Here, we report advances in this procedure and discuss what is needed to develop this format into a truly useful tool for the structural biology community as well as for readers who are less well trained in molecular visualization.

Keywords: molecular visualization; structural biology; interactive graphics

Publ.-Id: 14226

Validation of the RELAP5 code for the modeling of flashing-induced instabilities under natural-circulation conditions using experimental data from the CIRCUS test facility

Kozmenkov, Y.; Rohde, U.; Manera, A.

This paper reports on the use of the RELAP5 code for the simulation of flashing-induced instabilities in natural circulation systems. The RELAP 5 code is intended to be used for the simulation of transient processes in the Russian RUTA reactor concept operating at atmospheric pressure with forced convection of coolant. However, during transient processes, natural circulation with flashing-induced instabilities might occur. The RELAP5 code is validated against measurement data from natural circulation experiments performed within the framework of a European project (NACUSP) on the CIRCUS facility. The facility, built at the Delft University of Technology in The Netherlands, is a water/steam 1:1 height-scaled loop of a typical natural-circulation-cooled BWR. It was shown that the RELAP5 code is able to model all relevant phenomena related to flashing induced instabilities. The magnitude and frequency of the oscillations were reproduced in a good agreement with the measurement data. The close correspondence to the experiments was reached by detailed modeling of all components of the CIRCUS facility including the heat exchanger, the buffer vessel and the steam dome at the top of the facility.

Keywords: Flashing; instabilities; experimental; numerical; low pressure

Publ.-Id: 14225

All optical laser cooling and diagnostics for relativistic ion beams

Bussmann, M.; Kroll, F.; Loeser, M.; Siebold, M.; Schramm, U.; Wen, W.; Winters, D. F.; Walther, T.; Beck, T.; Rein, B.; Birkl, G.; Kruse, J.; Nörtershaeuser, W.; Kühl, T.; Novotny, C.; Kozhuharov, C.; Geppert, C.; Steck, M.; Nolden, F.; Dimopoulou, C.; Ma, X.; Stöhlker, T.

Based on previous results on laser cooling of relativistic c3+ ion beams at the ESR storage ring we present new laser systems and optical diagnostics for laser cooling of relativistic ion beams.
In combination with a new Schottky detection and new beam profile measurement system currently tested at the ESR the new optical diagnostics will help to give new insight into the dynamics of laser cooled ion beams with unprecedented resolution.
With a scanning and a pulsed laser system newly introduced to the experiment we will be able to cool relativistic ion beams without the need of electron precooling. This will be of great importance for the laser cooling experiments at higher energies available at future storage rings.

Keywords: storage ring; laser cooling; ion beam; relativistic energies; scanning laser; pulsed laser; vuv detectors

  • Invited lecture (Conferences)
    SPARC in Lanzhou 7th SPARC Workshop and Collaboration Meeting, 24.-27.08.2010, Lanzhou, China

Publ.-Id: 14222


Knüpfer, A.; Bussmann, M.

Implementation of a modular Particle-in-Cell Algorithm for GPGPU Clusters

Keywords: gpu; gpgpu; graphic card; algorithm; simulation; particle-in-cell; pic; cuda; mpi; parallel; high-performance; computing

Related publications

  • Lecture (Conference)
    CiHPC Competence in High Performance Computing HPC Status Conference of Gauß-Allianz e.V., 22.-24.06.2010, Schwetzingen, Deutschland

Publ.-Id: 14221

Energy scaling of ultrashort pulse laser accelerated proton beams and first radiobiological applications

Schramm, U.

Talk on ion acceleration experiments at the FZD laser Draco and the first dose controlled irradiation of cell samples.

  • Invited lecture (Conferences)
    14th Advanced Accelerator Concepts Workshop, 13.-19.06.2010, Annapolis, MD, USA, USA

Publ.-Id: 14219

Status of the FZD lab combining 150 TW laser pulses with the sc electron linac ELBE

Schramm, U.

Talk on the status and prospects of the facility.

  • Lecture (Conference)
    14th Advanced Accelerator Concepts Workshop, 13.-19.06.2010, Annapolis, MD, USA, USA

Publ.-Id: 14218

What one learns from reactor pressure vessels of decommissioned nuclear power plants.

Viehrig, H.-W.; Houska, M.; Arora, K. S.; Rindelhardt, U.

Nuclear power plant operators must demonstrate that the structural integrity of a nuclear reactor pressure vessel (RPV) is assured during routine operations and under postulated accident conditions. The aging of the RPV steels is monitored via surveillance programs. Radiation loading, metallurgical and environmental histories, however, can differ between surveillance and RPV materials. Therefore, the investigation of RPV material from decommissioned NPPs offers the unique opportunity to evaluate the real toughness response. Such an opportunity is now available through the investigation of RPV material from the decommissioned Greifswald NPP (WWER-440/V-230).
The Greifswald RPVs of 4 units represent different material conditions as follows:
• Irradiated (Unit 4),
• irradiated and recovery annealed (Units 2 and 3), and
• irradiated, recovery annealed and re-irradiated (Unit1).
The recovery annealing of the RPV was performed at a temperature of 475° for about 152 hours and included a region covering ±0.70 m above and below the core beltline welding seam.
Material samples of a diameter of 119 mm called trepans were extracted from the RPV walls. The research program is focused on the characterisation of the RPV steels (base and weld metal) across the thickness of the RPV wall.
This paper presents test results measured on the trepans of the beltline welding seam and base metal of the above mentioned conditions. The key part of the testing is focussed on the determination of the reference temperature T0 following the ASTM standard E1921-09 to determine the facture toughness, and how it degrades under neutron irradiation and is recovered by thermal annealing. Other than that the mentioned test results include Charpy-V and tensile test results. Following results have been determined:
• The mitigation of the neutron embrittlement of the weld and base metal by recovery annealing could be confirmed.
• KJc values of the weld metals generally follow the course of the MC though with a large scatter.
• There is a large variation in the T0 values evaluated across the thickness of the multilayered welding seams.
• The T0 measured on TS oriented SE(B) specimens from different thickness locations of the welding seams strongly depends on the structure along the crack tip.
• It was demonstrated that T0 evaluated according to the SINTAP MC extension represents the brittle fraction of the data sets.
• A direct correlation between T0 and TT41J of the investigated weld metal is questionable due to the different thickness location of the crack tip and the notch root in pre-cracked SE(B) and the reconstituted Charpy-V specimens, respectively.
• A strong scatter of the fracture toughness KJc values of the recovery annealed base metal of Unit 1 is observed with clearly more than 2% of the values below the fracture toughness curve for 2% fracture probability. The application of the multimodal MC approach describes the temperature dependence of the KJc values in a satisfactory manner.

Keywords: nuclear power plant; reactor pressure vessel; neutron embrittlement; fracture toughness; Master Curce

  • Contribution to proceedings
    International Symposium FONTEVRAUD 7: Contribution of Materials Investigations to Improve the Safety and Performance of LWRs, 26.-30.09.2010, Avignon, France
    Proceedings of the International Symposium FONTEVRAUD 7: French Nuclear Energy Society
  • Lecture (Conference)
    International Symposium FONTEVRAUD 7: Contribution of Materials Investigations to Improve the Safety And Performance of LWRs, 26.-30.09.2010, Avignon, France

Publ.-Id: 14217

Glutathione – an important intracellular chelator of uranium

Viehweger, K.; Geipel, G.; Bernhard, G.

Plants are able to accumulate uranium (U) in roots and shoots /1/. Hence, we could detect an accumulation of this metal inside suspension cells of canola (Bassica napus) via fluorescence microscopy. Such uptake of highly toxic heavy metals requires skilled complex cellular defense mechanisms.
One example is the formation of metal complexes in the cytosol. A prominent candidate might be the tripeptide glutathione (GSH) bearing metal chelating functionalities like carboxylato- and thiol residues. Whereas at pH 5.7 the formed complex was stable over 6 hours, the initial complexes at pH > 6.0 degraded within 30 minutes. A reduction of U(VI) by GSH seems to be possible, because of strong spectral changes contributed by thiolate functionality. However, the spectra of the later formed chelates indicated an involvement of SH-groups in U complexation.
This is necessary for the formation of phytochelatins based on GSH. These metal binding peptides could be detected by HPLC in the cytosol 24 hours after U contact. U was bound to these peptides revealed by gelelectrophoresis of isolated cytoplasmic peptides and subsequent Laser-induced Fluorescence Spectroscopy. Despite these GSH consuming processes during U contact, the cytoplasmic GSH content decreased only slightly but not significantly compared to the control. Artificial depletion of GSH induced an up to twofold increased metabolic activity of cells challenging with U concentrations ≤ 10 µM whereas higher U contents dramatically reduced the metabolism. These data underlines the tight cellular regulation and the importance of GSH in maintaining defense reactions against U.

/1/ K. Viehweger, G. Geipel, Environmental and Experimental Botany 69 (2010) 39–46

  • Contribution to proceedings
    Biometals 2010, 25.-30.07.2010, Tucson, USA

Publ.-Id: 14216

Quercetin – a key substance in heavy metal uptake of plants?

Geipel, G.; Drewitz, S.; Viehweger, K.; Bernhard, G.; Henle, T.

Recently it could be reported, that uranium can occur in its tetravalent oxidation state on the Surface of roots of Arabidopsis halleri /1/. Nevertheless it is very unusual to find uranium in this oxidation state in soil compartments located close to the earth surface, where oxidizing conditions dominate. The oxidation state +6 should be the stable under these conditions.
Flavonoids are widely distributed in plants and have multifunctional properties. They are known for there antioxidant activity Within this class of compounds quercetin is very widespread. Considering that quercetin may be involved in the reduction process we carried out experiments to reduce uranium-(VI) by quercetin. The experiments were carried in under N2-atmosphere to avoid reoxidation of the formed uranium-(IV). Under these in vitro conditions quercetin was able to reduce up to 10% of the uranium. Uranium-(IV) was determined directly by Laser-Induced Photoacoustic Spectroscopy and UV-Vis spectroscopy.
However, this does not explain the existence of uranium-(VI) on the roots. The redox potential of quercetin was measured as function of pH. The shift of the redox potential supports the reduction of uranium with increasing pH /2/. Additionally quercetin can act as complex forming agent. We studied the complex formation of quercetin with uranium-(IV) and uranium-(VI). In both cases a 1:1 complex was found and the stability constants were determined to be log β11 = 20.36 /2/ and log β11 = 13.8 /3/, respectively. This shows a strong stabilization of the uranium-(IV) in its complex with quercetin.
/1/ K. Viehweger, G. Geipel, Environmental and Experimental Botany 69 (2010) 39–46
/2/ S. Drewitz, Diploma thesis, TU Dresden 2010
/3/ K. Viehweger, G. Geipel, In Wissenschaftlich-Technische Berichte FZD-511, Annual Report 2008, (2009) 41.

  • Contribution to proceedings
    Biometals 2010, 25.-30.07.2010, Tucson, USA

Publ.-Id: 14215

Annealing of Silicon Nanopatterns

Fritzsche, M.; Keller, A.; Facsko, S.; Lenz, K.; Fassbender, J.

The morphology of surfaces strongly influences optical, electrical, and magnetic properties of thin films. By changing the morphology it is possible to tailor the material properties. Oblique low energy ion beam sputtering produces periodic ripple structures with periodicities in the nanometer range. During sputtering the region near to the surface gets amorphous and some metal is deposited on the surface, i.e. Cu from the sample holder. These ripple patterns can be used as templates. By using amorphous ripples only polycrystalline films can be grown. These films have an morphology induced dipolar anisotropy. In order to grow the films epitaxially the ripples have to be crystalline. Hence, this could induce an additional anisotropy in a magnetic overlayer. One possible route to achieve crystalline ripples is annealing. Therefore, the annealing temperature dependence was studied using STM. With increasing temperature the ripples vanish. They are not removed by a reduction of the amplitude, but by the creation of circular voids. Inside these voids the surface exhibits few steps and is otherwise flat on an atomic scale. In the middle of the voids Cu clusters are found, which appear at steps. Inside the crystalline area of the voids the Si(111) "quasi 5×5" Cu surface is found. For larger temperatures the number and size of these voids increases until the ripples are removed from the whole surface.

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland
  • Poster
    Workshop Ion Beam Physics, 29.-31.03.2010, Dresden, Deutschland

Publ.-Id: 14213

Structural investigations of the grain growth induced by focused-ion-beam irradiation in thin magnetic films

Roshchupkina, O.; Grenzer, J.; Fritzsche, M.; Fassbender, J.

Focused ion beam (FIB) techniques are one way to modify locally the properties of magnetic thin films. In previous works it was demonstrated that focused-ion-beam irradiation causes a considerable grain growth in magnetic thin films under certain conditions and therefore a change of their magnetic properties [1]. Although the grain growth can be already qualified by simple REM images a crystallographic tool is needed for a qualitative analysis. We used the advantage of nondestructive X-ray diffraction to study the grain growth.
A magnetic thin film of 50nm thick permalloy film (Fe0.2Ni0.8) sputtered on Si was used for the investigations. We have analyzed two simple parameters such as the grain size and the microstrain depending on the ion dose and beam current. Due to the very small structures created by focused-ion-beam techniques (usually less then 0.4x0.4mm2 size) an optimized X-ray laboratory setup with a focused X-ray beam of 200µm was used.
[1] C.M. Park and J.A. Bain, J. Appl. Phys. 91, 6830(2002).

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 14212

PIXE-RBS survey of a Meissen Porcelain snuff box: First version or not?

Neelmeijer, C.; Roscher, R.

This 18th century object with delicate on-glaze decorations let arise doubts regarding its complete originality. Comparing both base body and cover, the shades of porcelain glazing differ visually. Moreover, the painting shows slight differences in color and flow. Simultaneous PIXE and RBS (Rutherford Backscattering Spectrometry) using the 4-MeV proton beam in air [1] proved ideal to get convincing answers. The maximum proton beam intensity was only 200 pA for 30 s acquisition time in order to ensure non-destructive analysis of the very sensitive material.
For the green colorant of leaves of trees, painted on both bottom and cover, the artist used copper green pigment [2]. For painting the bottom of the base body Cu was the starting material; brass was certainly applied for the cover as deduced from additional Zn lines displayed by PIXE. In the latter case the green pigment was obviously brightened by the addition of Co. Pink decoration of the cover could be identified as made from purple due to small Au-L lines. They were not visible analysing the pink skirt, painted on the bottom, because of superimposed intense Pb-L lines originating from the glazing. Comparatively, the X-ray spectrum obtained from pure glazing of the cover shows much lower Pb-L intensity. RBS was helpful for getting information on the depth distributions of Pb regarding the different types of glazing. This is illustrated in the graphs below. Whereas the bottom of the porcelain box comprises thick and lead containing glazing, the RBS spectrum taken from glazing of the cover makes clear that only little Pb exists, which is localized at the glazing surface. This can be attributed to a surface polishing process carried out in the past.

References: [1] C. Neelmeijer and M. Mäder, Nucl. Instr. Meth. B 189, 293 (2002).
[2] M. Mields, Keramische Zeitschrift 8, 453 (1963).

Keywords: Analysis; non-destructive; ion beam; PIXE; RBS; porcelain; on-glaze decoration

  • Lecture (Conference)
    12th International Conference on Particle Induced X-Ray Emission and its Analytical Applications, 27.06.-02.07.2010, Guildford, UK
  • X-Ray Spectrometry 41(2012)2, 93-97
    Online First (2012) DOI: 10.1002/xrs.2371
    Cited 1 times in Scopus

Publ.-Id: 14211

Sorption of uranium(VI) onto Opalinus Clay in the absence and presence of humic acid in Opalinus Clay pore water

Joseph, C.; Schmeide, K.; Sachs, S.; Brendler, V.; Geipel, G.; Bernhard, G.

The U(VI) sorption onto Opalinus Clay (OPA), a natural clay rock from Mont Terri, Switzerland, was investigated in the absence and presence of humic acid under aerobic conditions using synthetic OPA pore water (I = 0.34 M, pH 7.6) as background electrolyte. The results show that the U(VI) sorption onto OPA is low and not influenced by humic acid. This can be attributed to the dissolution of calcite, a mineral constituent of the clay. The resulting calcium ions (up to 25 mM) in the pore water influence both the U(VI) speciation and the speciation of humic acid. In OPA pore water the U(VI) speciation is dominated by the neutral complex Ca2UO2(CO3)3(aq) both in the absence and presence of humic acid. Its predominance was verified by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Speciation estimations for humic acid show that calcium ions saturate the humic acid binding sites almost completely. Thus, only few humic acid binding sites are available for U(VI) complexation at pH 7.6. For the sorption of U(VI) and humic acid onto OPA distribution coefficients, Kd, were determined and amount to (0.0222 ± 0.0004) m3/kg and (0.129 ± 0.006) m3/kg, respectively. In conclusion, calcium ions determine the interaction processes of U(VI) and humic acid in the OPA system.

Keywords: uranium(VI); humic acid; sorption; speciation; Opalinus Clay; calcium; Ca2UO2(CO3)3(aq); TRLFS

Publ.-Id: 14210

Identification of the uranium speciation in an underground acid mine drainage environment analysed by laser fluorescence spectroscopy

Arnold, T.; Baumann, N.; Krawczyk-Bärsch, E.; Brockmann, S.; Zimmermann, U.; Jenk, U.; Weiß, S.; Wobus, A.; Zirnstein, I.

The subsurface acid mine drainage (AMD) environment of an abandoned underground uranium mine in Königstein/Saxony/Germany, currently in the process of remediation, is characterized by low pH, high sulfate concentrations and elevated concentrations of heavy metals, in particular uranium. Acid streamers thrive in the mine drainage channels and are heavily coated with iron precipitates identified as schwertmannite and jarosite. These precipitates are biomineralisations and related to the presence of Fe-oxidizing microorganisms. Such precipitates were also observed in stalactite-like dripstone, called snottites, growing on the gallery ceilings. The bacterial diversity was identified on basis of analysed 16S rDNA sequences and revealed that the beta-proteobacterium Ferrovum myxofaciens dominates. Colloidal uranium, neither as U(IV)- or as U(VI) eigencolloids nor uranium adsorbed on colloids was detected as photon correlation spectroscopy analyses and centrifugation experiments of drainage water and snottite water at different centrifugal accelerations between 500 g and 46000 g showed.
The uranium speciation in the underground AMD waters flowing in mine galleries as well as dripping from the ceiling and forming stalactite-like dripstones were studied by time resolved laser-induced fluorescence spectroscopy (TRLFS). The fluorescence lifetime of both waters were best described with a mono-exponential decay, indicating the presence of one species only. The detected positions of the emission bands and by comparing it in a fingerprinting procedure with spectra obtained for acid sulfate reference solutions, in particular Fe - SO42- - UO22+ reference solutions, indicated that the uranium speciation in the AMD environment of Königstein is dominated in the pH range of 2.5 to 3.0 by the highly mobile aquatic uranium sulfate species UO2SO4(aq) and formation of uranium precipitates is rather unlikely as is retardation by sorption processes. The presence of iron in the AMD reduces the fluorescence lifetime of the UO2SO4(aq) species from 4.3 µs found in iron-free uranium sulfate reference solutions to 0.7 µs in both AMD waters of Königstein and in iron containing uranium sulfate reference solutions, respectively. Thermodynamic calculations indicated the presence of two additional uranium species, i.e. UO2(SO4)2- and UO22+ in AMD of Königstein, however TRLFS provided no spectroscopic evidence for their existence.
TRLFS was directly applied to complex solutions of acid mine drainage (AMD) environments intimately associated with microbiology and Fe-precipitates and shows that it is a suitable spectroscopic technique to identify the uranium speciation in natural solutions containing a multitude of different complexing agents.

Keywords: uranium speciation; time resolved laser-induced fluorescence spectroscopy; TRLFS; uranium mobility; acid mine drainage

  • Geochimica et Cosmochimica Acta 75(2011), 2200-2212

Publ.-Id: 14209

Atomistic study of copper-vacancy clusters in bcc-Fe

Posselt, M.; Al-Motasem, A.; Bergner, F.; Birkenheuer, U.

Copper-rich precipitates are assumed to be the main cause of hardening and embrittlement of Cu-bearing reactor pressure vessel steels since they act as obstacles to dislocation motion within the grains of polycrystalline bcc-Fe. Multiscale modeling contributes to a better understanding of point-defect-induced formation of these clusters during reactor operation. Rate theory is an efficient tool to simulate the cluster evolution on realistic time and length scales. However, many parameters used in rate theory, such as the diffusion coefficients of mobile species and the 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 the free binding energies are determined for small and medium-sized CunVm clusters in bcc-Fe. The most recent Fe-Cu interatomic potential by Pasianot and Malerba [1] is used. Enthalpy and entropy contributions are calculated using combinations of on-lattice Monte Carlo simulations and off-lattice molecular dynamics calculations.
[1] R. C. Pasianot and L. Malerba, J. Nucl. Mater. 360, 118 (2007).

Keywords: atomistic simulation; iron; copper; vacancies; clusters; precipitates

  • Lecture (Conference)
    5th Forum on New Materials, 14.-18.06.2010, Montecatini Terme, Italy

Publ.-Id: 14208

Structural phase transition in boron compounds at high pressure

Talati, M.; Jha, P. K.

The high-pressure induced structural phase transitions and pressure induced elastic and anharmonic behavior of boron compounds viz. BN, BP, and BAs have been investigated using an inter-ionic potential approach based on charge transfer effect. These compounds go to NaCl phase (B1) under pressure from zinc blende phase (B3). The variations of second-order elastic constants and their combinations follow a systematic trend with pressure, identical to that observed in other compounds of zinc blende structure family. Shear stiffness constants decrease with increasing pressure up to phase transition pressure. The bulk moduli of these compounds are in reasonably good agreement with other theoretical and experimental data. The values of phase transition pressure of these compounds obtained by using the present approach are also in good agreement with those predicted by using the pseudo potential approach. The present approach has also succeeded in predicting the Born and relative st!
ability criterion for stable zinc blende phase of these compounds. We also present a set of third-order elastic constants and pressure derivatives of second-order elastic constants for boron compounds.

Keywords: Phase transition; pressure; anharmonic properties


Publ.-Id: 14207

Interface polarization coupling in piezoelectric-semiconductor ferroelectric heterostructures

Voora, V.; Hofmann, T.; Brandt, M.; Lorenz, M.; Grundmann, M.; Ashkenov, N.; Schmidt, H.; Ianno, N.; Schubert, M.

Abstract: We present a dielectric continuum model approach for studying the electrical polarization properties of interface polarization coupled BaTiO3, BaTiO3-ZnO, and ZnO-BaTiO3-ZnO thin-film structures consisting of several hundred nanometer thick layers. Our model augments the effects of electric field driven switchable polarization and depletion layer formation with spontaneous interface polarization coupling. Wurtzite-structure (piezoelectric) n-type ZnO and perovskite-structure (ferroelectric) highly insulating BaTiO3 layers were prepared and investigated. The coupling between the nonswitchable spontaneous polarization of ZnO and the electrically switchable spontaneous polarization of BaTiO3 causes strong asymmetric polarization hysteresis behavior. The n-type ZnO reveals hysteresis-dependent capacitance variations upon formation of depletion layers at the ZnO/BTO interfaces. We obtain a very good agreement between our model generated data and our experiment. Our model approach allows for derivation of the amount and orientation of the spontaneous polarization of the piezoelectric constituents and can be generalized toward multiple-layer piezoelectric-semiconductor ferroelectric heterostructures. We identify interface polarization coupled triple-layer ZnO-BTO-ZnO heterostructures as two-terminal unipolar ferroelectric Bi-junction transistor for use in memory storage.


Publ.-Id: 14206

Mechanism of electrical properties degradation of ZnO:Al films during growth at elevated temperatures

Vinnichenko, M.; Gago, R.; Cornelius, S.; Rogozin, A.; Shevchenko, N.; Kolitsch, A.; Möller, W.

Resistivity of ZnO:Al (AZO) films is known to increase significantly during annealing or growth at temperatures higher than certain optimum value that is a problem during preparation of thin film solar cells. To understand this process, AZO films with different Al concentrations grown by reactive pulsed magnetron sputtering were studied. The electrical resistivity of the films shows a minimum at an optimum substrate temperature, which shifts from 400 °C to 200 °C with increasing Zn/O flux ratio. At higher temperatures, resistivity increases due to simultaneous decrease of the free electron density and mobility. It is accompanied by a significant deterioration of the film crystallinity, increase of Al concentration and drop of the growth rate. X-ray absorption near edge structures (XANES) excludes formation of aluminum oxides in this case. It shows formation of homologous phase (ZnO)3(Al2O3) whose formation is triggered by an increase of the Al/Zn ratio in the film. Therefore, at growth temperatures above the optimum value Al preferentially forms this phase instead of occupying Zn site in the lattice.

Keywords: Al-doped ZnO; transparent conductive oxides; homologous metastable phase; (ZnO)3(Al2O3)

  • Lecture (Conference)
    5th Forum on New Materials (in the framework of 12th International Conference on Modern Materials and Technologies - CIMTEC 2010), 13.-18.06.2010, Montecatini Terme, Italy

Publ.-Id: 14205

Biosensing for the Environment and Defence: Aqueous Uranyl Detection Using Bacterial Surface Layer Proteins

Conroy, D. J. R.; Millner, P. A.; Stewart, D. I.; Pollmann, K.

The fabrication of novel uranyl (UO2 2+) binding protein based sensors is reported. The new biosensor responds to picomolar levels of aqueous uranyl ions within minutes using Lysinibacillus sphaericus JG-A12 S-layer protein tethered to gold electrodes. In comparison to traditional self assembled monolayer based biosensors the porous bioconjugated layer gave greater stability, longer electrode life span and a denser protein layer. Biosensors responded specifically to UO2 2+ ions and showed minor interference from Ni2+, Cs+, Cd2+ and Co2+. Chemical modification of JG-A12 protein phosphate and carboxyl groups prevented UO2 2+ binding, showing that both moieties are involved in the recognition to UO2 2+.

Keywords: S-layer; surface layer; protein biosensor; uranium; uranyl; metal ion; sequestering; impedance spectroscopy

Publ.-Id: 14204

Effect of secondary phase formation on electrical and optical properties of Al-doped ZnO

Vinnichenko, M.; Cornelius, S.; Gago, R.; Krause, M.; Shevchenko, N.; Rogozin, A.; Munnik, F.; Kolitsch, A.; Möller, W.

It has been shown that increasing substrate temperature above its optimum value leads to an increase of Al concentration in the AZO films, which exceeds the solubility limit and triggers the formation of an insulating metastable homologous (ZnO)3Al2O3 phase. The formation of (ZnO)3Al2O3 is established for the AZO films grown in a given range of deposition conditions, while the films grown at substantially different conditions may show formation of other secondary phases (e.g. aluminium oxide or spinel). This (ZnO)3Al2O3 impedes crystal growth and causes a significant increase of free electron scattering. In turn, it leads to an increase of electrical resistivity of the films. This phase has been observed by XANES even in the films with the lowest Al concentration and the best crystallinity. Increase of this phase volume fraction with increasing Al concentration correlates with observed changes in the film Raman and optical constants spectra.

Keywords: Al-doped ZnO; homologous metastable phase; (ZnO)3Al2O3

  • Lecture (Conference)
    EFDS-Workshop „Transparente leitfähige Oxide - Festkörperphysikalische Grundlagen und Technologie“, 01.-02.06.2010, Dresden, Germany

Publ.-Id: 14203

Capabilities and limitations of spectroscopic ellipsometry for characterization of functional thin films

Vinnichenko, M.

An overview of different configurations of spectroscopic ellipsometers was given. The approaches for data acquisition and analysis in case of high refractive index materials and transparent conductive oxides were discussed.

  • Lecture (others)
    Invited lecture during visit to "Next Energy" EWE-Forschungszentrum für Energietechnologie e.V., 10.-11.02.2010, Oldenburg, Germany

Publ.-Id: 14202

Properties, structure and phase composition of transparent conductive oxide thin films grown by magnetron sputtering

Vinnichenko, M.; Cornelius, S.; Rogozin, A.; Shevchenko, N.; Gago, R.; Kolitsch, A.; Möller, W.

Understanding of the mechanisms of donor impurity incorporation, its electrical activation and charge carrier transport in transparent conducting oxides (TCO) is required for further improvement of functionality of this class of materials. The present work focuses on investigation of indium oxide (IO), Sn-doped indium oxide (ITO), ZnO, and ZnO:Al (AZO) films grown by reactive pulsed magnetron sputtering (RPMS) with a precise control of the oxygen partial pressure at substrate temperatures, Ts, ranging from RT to 550°C. In order to explore potential advantages of RPMS, the relationship between the deposition parameters and structure, phase composition and physical properties of these TCOs was investigated. The films were characterized by spectroscopic ellipsometry, Hall effect measurements, X-ray diffraction (XRD) and, in case of ZnO and AZO films, by X-ray absorption near edge structures (XANES). The Sn concentration in ITO was determined by Auger analysis, while the Al concentration in ZnO matrix was estimated by elastic recoil detection analysis and Rutherford back scattering.
The comparison of the real-time behavior of the IO and ITO film structure and electrical properties during annealing provides a direct evidence of Sn donor activation (with an estimated efficiency of 40%) in ITO due to amorphous-to-crystalline transition. The ITO film crystallinity always improves with increasing substrate temperature or during isothermal annealing, with the electrical resistivity decreasing. In contrast, the electrical resistivity of AZO films shows a clear minimum at an optimum substrate temperature (200-400 °C), which depends on metal/oxygen flux ratio and correlates with a maximum in crystallinity (grain size). In this case, the highest mobility value of 46 cm2 V-1 s-1 is comparable to the best values achieved in AZO films grown by less cost-efficient techniques. This value is achieved at the free electron density of 6x1020 cm-3 which corresponds to maximum ~30% electrical activation of Al impurity. At higher temperatures, the AZO electrical properties and crystalline quality deteriorate abruptly according to the following mechanism. Increasing Ts above its optimum value leads to a higher Al concentration in the AZO films, which exceeds the solubility limit and triggers the formation of an insulating metastable homologous (ZnO)3Al2O3 phase. This phase impedes crystal growth and causes a significant increase of free electron scattering both at grain boundaries and inclusions of this phase. In order to enable the growth of low-resistivity AZO films in a wider range of TS, lower metal/oxygen flux ratios should be used. The proposed approach to minimizing the influence of this undesirable phase may also be applied to other deposition methods of AZO involving high-energy particle bombardment.

Keywords: Al-doped ZnO; transparent conductive oxides; electrical properties; optical properties; phase composition

  • Lecture (others)
    Invited talk during visit to "Next Energy" EWE-Forschungszentrum für Energietechnologie e.V., 10.-11.02.2010, Oldenburg, Germany

Publ.-Id: 14201

RBS\channeling and TEM study of damage buildup in ion bombarded GaN

Pagowska, K.; Ratajczak, R.; Stonert, A.; Turos, A.; Nowicki, L.; Sathish, N.; Jozwik, P.; Muecklich, A.

A systematic study on structural defect buildup in 320 keV Ar-ion bombarded GaN epitaxial layers has been reported, by varying ion fluences ranged from 5x1012 to 1x1017 at/cm2. 1μm thick GaN epitaxial layers were grown on sapphire substrates using the MOVPE technique. RBS\channeling with 1.7 MeV 4He beam was applied for analysis. As a complementary method High Resolution Transmission Electron Microscopy (HRTEM) has been used. The later has revealed the presence of extended defects like dislocations, faulted loops and stacking faults. New version of the Monte Carlo simulation code McChasy has been developed that makes it possible to analyze such defects on the basis of the Bent Channel (BC) model. Damage accumulation curves for two distinct types of defects, i.e. Randomly Displaced Atoms (RDA) and extended defects (i.e BC) have been determined. They were evaluated in the frame of the MultiStep Damage Accumulation (MSDA) model, allowing numerical parameterization of defect transformations occurring upon ion bombardment. Displaced atoms buildup is a three step process for GaN and whereas extended defect buildup is always a two step process.

Keywords: GaN; ion bombardment; ion channeling; TEM; defect transformations

  • Lecture (Conference)
    VIII-th International Conference Ion Implantation and Other Applications of Ions and Electrons, 14.-17.06.2010, Kazimierz Dolny, Poland

Publ.-Id: 14200

Bildgebende Messverfahren und CFD-Simulation für die Energieverfahrenstechnik

Hampel, U.; Lucas, D.; Vallée, C.; Höhne, T.; Beyer, M.; Fischer, F.; Weiß, F.-P.

In diesem Beitrag werden ausgewählte tomographische Bildgebungsverfahren vorgestellt, die in den zurückliegenden Jahren am Forschungszentrum Dresden-Rossendorf für die Untersuchung von Mehrphasenströmungen entwickelt wurden. Neben einer Beschreibung der Messverfahren wird ihre Anwendung in der experimentellen Thermofluiddynamik und ihr Bezug zur Entwicklung und Validierung von CFD-Modellen für Zweiphasenströmungen diskutiert.

Keywords: multiphase flow; flow imaging techniques; CFD simulation

  • Contribution to external collection
    M. Beckmann, A. Hurtado: Kraftwerkstechnik - Sichere und nachhaltige Energieversorgung - Band 2,, Neuruppin: TK Verlag Karl Thomé-Kozmienski, 2010, 978-3-935317-57-3, 769-786
  • Lecture (Conference)
    42. Kraftwerkstechnisches Kolloquium, 12.-13.10.2010, Dresden, Germany

Publ.-Id: 14199

Synthesis of neurotensin(8-13)-phosphopeptide heterodimers via click chemistry

Richter, S.; Ramenda, T.; Bergmann, R.; Knieß, T.; Steinbach, J.; Pietzsch, J.; Wuest, F.

Two neurotensin(8-13)-containing peptide heterodimers were prepared via copper(I)-mediated click chemistry. The resulting peptide dimers could be obtained in 28-31% yield after HPLC purification. Neurotensin( 8-13)-containing peptide dimers were used in an in vitro binding assay to determine binding affinity towards the neurotensin receptor-1 (NTR1). The determined IC50 values of 8.3 µM and 0.7 µM indicate only very low binding affinity of the neurotensin(8-13)-containing peptide heterodimers towards the NTR1.

Keywords: Click chemistry; Neurotensin receptor; Phosphopeptide; Peptide heterodimer

Publ.-Id: 14198

Ferromagnetic resonance on metal nanocrystals in Fe and Ni implanted ZnO

Ankiewicz, A. O.; Martins, J. S.; Carmo, M. C.; Grundmann, M.; Zhou, S.; Schmidt, H.; Sobolev, N. A.

We studied the angular dependence of the ferromagnetic resonance (FMR) spectra of (0001)ZnO single crystals implanted with Ni and Fe ions and compared the results to the data obtained by other experimental techniques, especially, x-ray diffraction (XRD) and superconducting quantum interference device magnetometry. The FMR revealed the formation of metal nanocrystals (NCs) embedded in the ZnO lattice in an oriented way. Whereas in the case of Ni, the conclusions drawn from the FMR studies corroborated the XRD and magnetometry results with respect to the alignment of the NCs in the host lattice, in the case of the Fe NCs, the FMR clearly shows that the hard magnetization axis (which is < 111 > in bcc Fe) is oriented perpendicular to the sample surface (parallel to the [0001]ZnO axis), at variance with the former XRD observations.

Keywords: ferromagnetic resonance; II-VI semiconductors; ion implantation; iron; magnetisation; nanostructured materials; nickel; X-ray diffraction; zinc compounds

Publ.-Id: 14196

Encapsulation of Fluorescent Cluster Complexes into Dendritic Nanocontainer

Kuhlmann, M.

kein Abstract verfügbar

  • Lecture (Conference)
    7th Supraphone Meeting, 28.04.-01.05.2010, Maria Laach, D

Publ.-Id: 14195

Personen- und Produktschutz bei der Herstellung von PET Radiopharmaka

Füchtner, F.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    2. NZW Dresden - Onkologisch-Pharmazeutischer Fachkongress, 18.-19.06.2010, Dresden, D

Publ.-Id: 14194

Water repartitioning at the water lipid protein interface controls receptor activation in G-Protein coupled receptors

Eichler, S.; Fahmy, K.

G-Protein coupled receptors (GPCRs) play a fundamental role in many physiological processes. High ligand specifity of rhodopsin-like GPCRs in contrast to the highly conserved and class defining D(E)RY motif undergoing a protonation upon receptor activation suggests a general local activation mechanism acting as an autonomous functional module.
It has been shown that the D(E)RY motif positioned at the phase boundary acts as a pH-dependent switch which is governed by side chain partitioning between the aqueous and lipidic phase [1].
Here we have addressed the putative reverse effect, i.e. restructuring of the water lipid interface upon side chain protonation to elucidate the functional implication of water lipid protein interactions in the control of protein conformation. We have studied a TM3 derived transmembrane segment where a fluorescence reporter resides below the D(E)RY motif inside the helix. By fluorescence spectroscopy, FRET studies and FTIR-Fluorescence cross correlation experiments we show the pH dependent hydration site N-terminally of the D(E)RY motif. Thus the ionized D(E) side chain attracts water that dissolves the TM-sequence even beyond the two preceding hydrophobic residues.
These results argue for a key role of the rearrangement of the water lipid protein microstructure upon GPCR activation as it effects not only the phase boundary but even more hydrophobic environment inside the lipidic phase.
[1] S. Madathil, K.Fahmy, J Biol Chem 284, 28801-28809 (2009)

Keywords: membrane transport; protonation; FTIR spectroscopy; fluorescence spectroscopy; FRET; charge stabilization; bilayer; water reorganization

  • Lecture (Conference)
    Annual Meeting of the German Biophysical Society, 03.-06.10.2010, Bochum, Deutschland

Publ.-Id: 14193

Experiments and numerical simulations of horizontal two phase flow regimes using an interfacial area density model

Höhne, T.; Vallée, C.

Stratified two-phase flow regimes can occur in the main cooling lines of Pressurized Water Reactors, Chemical plants and Oil pipelines. A relevant problem occurring is the development of wavy stratified flows which can lead to slug generation. In the last decade, the stratified flows are increasingly modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated. The recent improvements of the multiphase flow modelling in the ANSYS CFX code make it now possible to simulate these mechanisms in detail. In order to validate existing and further developed multiphase flow models, high-resolution measurement data is needed in time and also in space. For the experimental investigation of co-current air/water flows, the HAWAC (Horizontal Air/Water Channel) was built. The channel allows in particular the study of air/water slug flow under atmospheric pressure. Parallel to the experiments, CFD calculations were carried out. The two-fluid model was applied with a special turbulence damping procedure at the free surface. An Algebraic Interfacial Area Density (AIAD) model on the basis of the implemented mixture model was introduced, which allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value. The behaviour of slug generation and propagation was qualitatively reproduced by the simulation, while local deviations require a continuation of the work. The creation of small instabilities due to pressure surge or an increase of interfacial momentum should be analysed in the future. Furthermore, experiments with pressure and velocity measurements are planned and will allow quantitative comparisons at other superficial velocities.

Keywords: CFD; AIAD; multiphase flow

  • The Journal of Computational Multiphase Flows 2(2010)3, 131-143

Publ.-Id: 14192

Blending magnetic properties - hybrid magnetic thin films

McCord, J.

The control of the effective magnetic anisotropy, saturation magnetization, as well as the dynamic magnetic properties in ferromagnetic thin films is of significant importance for most applications in spin electronics. Usually the magnetic anisotropy, e.g. uniaxial anisotropy or unidirectional anisotropy, in ferromagnetic single or multi-layers is initialized by applying a magnetic field during film deposition or by a magnetic field anneal, which results in an anisotropy aligned along the applied field direction. The saturation magnetization is mainly determined by the film's composition. Whereas anisotropy and saturation magnetization together determine the precessional frequency of the films, the magnetic damping parameter cannot easily be varied in a controlled way.
Here we give a summary on different ways to pattern magnetic films in terms of laterally varying magnetic properties and not by shape patterning [1]. Different samples of anisotropy [1,2], exchange bias [1,3], and saturation magnetization [4] modulated thin films are prepared by local oxidation, introducing local stress variation [5], and local ion irradiation or implantation. The magnetization reversal processes in the two-phase materials exhibit unique features, some of them so far only known from multilayer samples. The main emphasis of the investigations is on the role of magnetic domain formation and domain wall effects in stripe-like magnetic hybrid structures on the overall static and dynamic magnetic properties.
The presented paths of film preparation provide an additional degree of freedom for the tailoring of magnetic properties and functionality of soft-magnetic thin films.

  • Invited lecture (Conferences)
    Colloquium of the "Sonderforschungsbereich 855" - Magnetoelektrische Verbundwerkstoffe - biomagnetische Schnittstellen der Zukunft, 01.07.2010, Kiel, Deutschland

Publ.-Id: 14191

Effects of lateral fluid percussion injury on cholinergic markers in the newborn piglet brain

Donat, C. K.; Walter, B.; Kayser, T.; Deuther-Conrad, W.; Schliebs, R.; Nieber, K.; Bauer, R.; Haertig, W.; Brust, P.

Traumatic brain injury is a leading cause of death and disability in children. Studies using adult animal models showed alterations of the central cholinergic neurotransmission as a result of trauma. However, there is a lack of knowledge about consequences of brain trauma on cholinergic function in the immature brain. It is hypothesized that trauma affects the relative acetylcholine esterase activity and causes a loss of cholinergic neurons in the immature brain. Severe fluid percussion trauma (FP-TBI, 3.8 0.3 atm) was induced in 15 female newborn piglets, monitored for 6 h and compared with 12 control animals. The hemispheres ipsilateral to FP-TBI obtained from seven piglets were used for acetylcholine esterase istochemistry on frozen sagittal slices, while regional cerebral blood flow and oxygen availability was determined in the remaining eight FP-TBI animals. Post-fixed slices were immunohistochemically labelled for choline acetyltransferase as well as for lowaffinity neurotrophin receptor in order to characterize cholinergic neurons in the basal forebrain. Regional cerebral blood flow and brain oxygen availability were reduced during the first 2 h after FPTBI (P < 0.05). In addition, acetylcholine esterase activity was significantly increased in the neocortex, basal forebrain, hypothalamus and medulla after trauma (P < 0.05), whereas the number of choline acetyltransferase and low-affinity neurotrophin receptor positive cells in the basal forebrain were unaffected by the injury. Thus, traumatic brain injury evoked an increased relative activity of the acetylcholine esterase in the immature brain early after injury, without loss of cholinergic neurons in the basal forebrain. These changes may contribute to developmental impairments after immature traumatic brain injury.

Keywords: Traumatic brain injury; Immature brain; Cholinergic system; Acetylcholine esterase

Publ.-Id: 14190

Alterations of cholinergic receptors and the vesicular acetylcholine transporter after lateral fluid percussion injury in newborn piglets

Donat, C. K.; Walter, B.; Deuther-Conrad, W.; Nieber, K.; Brust, R.; Bauer, P.

Aims: Traumatic brain injury (TBI) is one of the leading causes of death and disability in children. Adult animal models of TBI showed cholinergic alterations. However, there is no comparable data on immature animals. Therefore, this study investigates cholinergic markers in a large animal model of juvenile TBI. Methods: Twenty-seven female newborn piglets were subjected to lateral fluid percussion (FP) injury and compared with 12 untreated animals. After 6 h, animals were sacrificed and the brains removed.The hemispheres ipsilateral to FP-TBI from seven piglets and corresponding hemispheres from six control animals were used for autoradiography. Receptor density was determined with [3H]epibatidine (nicotinic acetylcholine receptors) or [3H]QNB (muscarinic acetylcholine receptors). The density of the vesicular acetylcholine transporter (vAChT) was assessed with (-)-[3H]vesamicol. Cerebral blood flow was measured by coloured microsphere method. Results: Cerebral blood flow and brain oxygen delivery were transiently reduced early after FP-TBI (P < 0.05). TBI caused reductions of muscarinic acetylcholine receptor density (fmol/mg) in the basal forebrain (sham: 10797 1339, TBI: 8791 1031), while nicotinic acetylcholine receptor remained stable. Significant increases in vAChT density (fmol/mg) were observed in the basal forebrain (sham: 2347 171, TBI: 2884 544), putamen (sham: 2276 181, TBI: 2961 386), cortex (sham: 1928 262, TBI: 2377 294), thalamic areas (sham: 2133 272, TBI: 2659 413), hippocampus (sham: 2712 145, TBI: 3391 501) and hypothalamus (sham: 2659 139, TBI: 3084 304). Conclusions: Cholinergic markers are altered after mildto- moderate TBI in the immature brain.Whereas the ACh receptors are stable in almost any brain region after TBI, vAChT expression increases after trauma at the employed severity of this specific trauma model.

Keywords: muscarinic; newborn pig; nicotinic; receptor; traumatic brain injury; vesicular transporter

Publ.-Id: 14189

Neue fluoreszenzspektroskopische Untersuchungen zur Huminstoff-Komplexbildung konkurrierender Metalle und aktuelle Ergebnisse von Transportstudien mittels PET

Lippold, H.; Kulenkampff, J.; Gründig, M.; Eidner, S.; Kumke, M.

Für die Veranstaltung wurden keine Abstracts eingereicht.

Vorgestellt wurden TRLFS-Studien mittels Eu(III) an Systemen aus Huminstoff und Al(III) verschiedenen Alters. Innerhalb des untersuchten Zeitraums von ca. 2 Tagen wurde eine Zunahme im Konkurrenzeffekt von Al(III) bezüglich der Huminstoff-Komplexbildung anderer Metalle festgestellt. Ziel der spektroskopischen Messungen war ein Nachweis struktureller Veränderungen am Huminstoff, die den beobachteten Effekt erklären. Zwar konnte gezeigt werden, dass durch die Komplexbildung von Al(III) erhebliche Veränderungen in der Mikroumgebung des Sondenmetalls Eu(III) induziert werden. Diese entsprachen jedoch nicht dem zeitlichen Trend im Konkurrenzeffekt. Aus Spektrenanalysen ging hervor, dass ein solcher Trend bei der relativ hohen Konzentration des Sondenmetalls gar nicht auftritt.
Gezeigt wurden auch erste PET-Untersuchungen zum diffusiven Transport in einem Opalinuston-Bohrkern. Mit Hilfe verbesserter Korrekturverfahren und neuer Visualisierungstechniken konnte die Methodik erheblich voran gebracht werden. Bereits nach einer Versuchsdauer von 2 Wochen konnte ein Diffusionskoeffizient abgeschätzt werden, der in Übereinstimmung mit Literaturdaten stand. Die Erfassung räumlicher Inhomogenitäten im Ausbreitungsverhalten erfordert jedoch längere Messzeiten und einen modifizierten Versuchsaufbau, welcher ebenfalls vorgestellt wurde.

  • Lecture (others)
    8. Workshop zum Verbundvorhaben "Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 13.-14.04.2010, Dresden-Rossendorf, Deutschland

Publ.-Id: 14188

Novel Indole Derivatives as Potential Imaging Agents for Alzheimer’s Disease

Yu, L.; Scheunemann, M.; Deuther-Conrad, W.; Hiller, A.; Fischer, S.; Sorger, D.; Sabri, O.; Jia, H.; Steinbach, J.; Brust, P.; Liu, B.

kein Abstract verfügbar

Keywords: β-Amyloid; Indole; Positron emission tomography; Senile plaques

Publ.-Id: 14187

On the action of magnetic gradient forces in micro-structured copper deposition

Mutschke, G.; Tschulik, K.; Weier, T.; Uhlemann, M.; Bund, A.; Fröhlich, J.

In order to shed more light on the role of magnetic gradient forces and Lorentz forces on the deposition pattern found recently at copper electrodes, experiments and numerical simulations have been performed in a generic geometry that consists of a single small cylindrical permanent magnet which is placed behind the cathode. The cylinder axis coincides with the magnetization direction and points normal to the electrode surface. The electrode is oriented vertically which allows a separate discussion of the influence of both forces.

Experiments and numerical simulations are found to give very good agreement with respect to the deposition pattern. Our analysis clearly shows that the major influence is due to the action of the magnetic gradient force. Numerical simulations prove that the separate action of the Lorentz force does not reproduce the deposition structure. A detailed analytical discussion of the motion forced by the different magnetic forces in superposition with natural convection is given.

Keywords: Lorentz force; field gradient force; magnetoelectrochemistry

Publ.-Id: 14186

Tomographische Radiotraceruntersuchungen zu Transportprozessen im Salinar und seinem Deckgestein in Staßfurt Tomographic Investigations of Transport Processes with Radiotracers in Evaporitic Rock and its Hanging Wall in Staßfurt

Kulenkampff, J.; Wolf, M.; Gründig, M.; Mittmann, H.; Richter, M.

Positronen-Emissions-Tomographie (PET) wurde als Methode zur Untersuchung von Transportvorgängen in Bohrkernen aus dem Salinargestein und seinem Deckgebirge in Staßfurt eingesetzt. Die Ergebnisse dienen der Verbesserung des Verständnisses der hydraulischen und chemischen Prozesse im heterogenen, teils dichten Material. Es kann anhand von Beispielen gezeigt werden, dass diese Prozesse sich nicht allgemein durch einfache Modelle beschreiben lassen.

  • Exkursionsführer und Veröffentlichungen der Deutschen Gesellschaft für Geowissenschaften 242(2010), 95-97

Publ.-Id: 14185

Surface modeling and chemical solution deposition of SrO(SrTiO3)n Ruddlesden–Popper phases

Zschornak, M.; Gemming, S.; Gutmann, E.; Weißbach, T.; Stöcker, H.; Leisegang, T.; Riedl, T.; Tränkner, M.; Gemming, T.; Meyer, D. C.

Strontium titanate (STO) is a preferred substrate material for functional oxide growth, whose surface properties can be adjusted through the presence of Ruddlesden–Popper (RP) phases. Here, density functional theory (DFT) is used to model the (1 0 0) and (0 0 1) surfaces of SrO(SrTiO3)n RP phases. Relaxed surface structures, electronic properties and stability relations have been determined. In contrast to pure STO, the near-surface SrO–OSr stacking fault can be employed to control surface roughness by adjusting SrO and TiO2 surface rumpling, to stabilize SrO termination in an SrO-rich surrounding or to increase the band gap in the case of TiO2 termination. RP thin films have been epitaxially grown on (0 0 1) STO substrates by chemical solution deposition. In agreement with DFT results, the fraction of particular RP phases n = 1–3 changes with varying heating rate and molar ratio Sr:Ti. This is discussed in terms of bulk formation energy.

Keywords: functional oxide; oxide; DFT; Ruddlesden-Popper; TEM; X ray; surfaces

Publ.-Id: 14184

EXAFS, XANES, and DFT study of the mixed-valence compound YMn 2O 5: Site-selective substitution of Fe for Mn

Wunderlich, F.; Leisegang, T.; Weissbach, T.; Zschornak, M.; Dshemuchadse, J.; Lubk, A.; Führlich, T.; Welter, E.; Souptel, D.; Gemming, S.; Seifert, G.; Meyer, D. C.

In YMn2O5 the Mn atoms occupy two non-equivalent Wyckoff sites within the unit cell exhibiting different oxygen coordinations, i. e. the system can be characterized as a mixed-valence compound. For the formation of the orthorhombic crystal structure Jahn-Teller distortions are assumed to play an important role. In this study, we aimed at the investigation of the crystal structure on the substitution of Mn by the non-Jahn-Teller cation Fe+3. Therefore, we synthesized a series of YMn(2-x)FexO5 powder samples with x = 0; 0:5; 1 by a citrate technique. We utilized extended x-ray absorption fine structure (EXAFS), x-ray absorption near edge structure (XANES) analysis and Density Functional Theory to investigate the two non-equivalent Wyckoff sites within the orthorhombic crystal structure (confirmed for all compositions) occupied by transition-metal atoms. For quantitative determination of structural short-range order firstly all plausible options of substitution of Fe for Mn were discussed. On basis of these evaluations the EXAFS and XANES behavior was analyzed and appropriate crystallographic weights were assigned to the subset of structural models in accordance with the experimental data. From EXAFS analysis, using multiple scattering theory, we concluded only the 4h Wyckoff site to be occupied by Fe (occupancy refined was (100 +- 3)% in case of x = 1). Furthermore, taking the XANES spectra into account, we could verify the EXAFS results and additionally explain the differences in the Mn-K XANES spectra in dependence on x to be caused by changes of the dipole transitions to 4p final states. Since only one Wyckoff site is involved the experimentally observed limit to a maximum amount of x = 1 is explained. Additionally, a possible disorder, discussed in the literature, was not proven for our samples. With DFT calculations the experimental findings were verified on base of the total energy of the different possible electronic configurations. Crystal field effects were identified to be responsible for the site selective substitution of Fe for Mn.

Keywords: multiferroic; oxide; functional; DFT; XANES; XAFS; X-ray; ferrimagnet; antiferromagnet

Publ.-Id: 14183

Measurement of K*(892)0 and K0 mesons in Al+Al collisions at 1.9A GeV

Lopez, X.; Herrmann, N.; Piasecki, K.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Buehler, P.; Cargnelli, M.; Caplar, R.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fabbietti, L.; Fijal-Kirejczyk, I.; Fodor, Z.; Gasik, P.; Gasparic, I.; Grishkin, Y.; Hartmann, O.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kirejczyk, M.; Kim, Y. J.; Kis, M.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Manko, V.; Marton, J.; Matulewicz, T.; Merschmeyer, M.; Neubert, W.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Suzuki, K.; Tyminski, Z.; Wagner, P.; Widmann, E.; Wisniewski, K.; Xiao, Z. G.; Yushmanov, I.; Zhang, X. Y.; Zhilin, A.; Zmeskal, J.; Kienle, P.; Yamazaki, T.

A new measurement of subthreshold K∗(892)0 and K0 production is presented. The experimental data complete the measurement of strange particles produced in Al + Al collisions at 1.9AGeV measured with the FOPI detector at SIS at GSI (Darmstadt). The K∗(892)0/K0 yield ratio is found to be 0.0315 ± 0.006(stat.) ± 0.012(syst.) and is in good agreement with the transport model prediction. These measurements provide information on the in-medium cross section of K+-π− fusion, which is the dominant process in subthreshold K∗(892)0 production.

Publ.-Id: 14182

Experimental investigation of horizontal gas-liquid flow by means of wire-mesh sensor

Da Silva, M. J.; Hampel, U.; Arruda, L. V. R.; Amaral, C. E. F.; Morales, R. E. M.

The monitoring and visualization of two-phase flow is of great importance either from technical/practical point of view for process control and supervision or from scientific/theoretical point of view, for the understanding of physical phenomenon. A wire-mesh sensor was applied to experimentally investigate two-phase horizontal pipe flow. Furthermore, some physical flow parameters were extracted based on the raw measured data obtained by the sensor. In this article, first the work principle of wire-mesh sensors is revised and second the methodology of flow parameter extraction is described. A horizontal flow test section comprising of a pipe of 26 mm i.d. 9 m long was employed to generate slug flows under controlled conditions. A 8 × 8 wire-mesh sensor installed at the end of the test section delivers cross-sectional images of void fraction. Based on the raw data, mean void fraction, time series of void fraction and characteristic slug frequency are extracted and analyzed.

Keywords: oil-gas flow; horizontal two-phase flow; wire-mesh sensor

  • Open Access Logo Journal of the Brazilian Society of Mechanical Science and Engineering XXXIII(2011)3, 237-242

Publ.-Id: 14181

Validation Training with ANSYS CFX

Höhne, T.

Course in Mixing, Multiphase flow, and Turbulence modelling

Keywords: CFD; Mixing; Multiphase flow

  • Invited lecture (Conferences)
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia
  • Contribution to proceedings
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia
    CD-ROM, Hand-out

Publ.-Id: 14180

Numerische Strömungsberechnung/Computational Fluid Dynamics

Höhne, T.

Sektion 2 Thermo- und Fluiddynamik / Thermodynamics and Fluid Dynamics
Sitzung: Numerische Strömungsberechnung
Die Leitung der Sitzung hatte Herr Dr. Th. Höhne vom Forschungszentrum Dresden- Rossendorf e.V., Dresden inne.

Keywords: CFD; FZD

  • atw - International Journal for Nuclear Power (2010)10, 648-655
    ISSN: 1431-5254

Publ.-Id: 14178

In-situ X-ray diffraction studies during deposition of Ni-Ti films

Martins, R. M. S.; Schell, N.; Mahesh, K. K.; Silva, R. J. C.; Braz Fernandes, F. M.

The deposition of Ni-Ti films with definite stoichiometry and high purity remains still a challenge. Furthermore, important issues like the formation of film texture and its control are not yet resolved. Near equiatomic (~ 50.0 at.% Ti¨CNi) and Ti-rich (~ 50.8 at.% Ti¨CNi) Ni-Ti polycrystalline films (thickness values ¡Ü 800 nm) have been deposited by magnetron co-sputtering using a chamber installed into the six-circle diffractometer of the Rossendorf beamline at the European Synchrotron Radiation Facility. The in-situ X-ray diffraction studies enabled the identification of different steps of the structural evolution during films processing. Films exhibiting a (100) preferential orientation for the B2 phase have been successfully produced. A continuous increase of the B2(200) diffraction peak intensity has been observed for depositions on a 140 nm amorphous SiO2 buffer layer heated at 520¡ãC (without substrate bias voltage, Vb). A (100) texture has been observed for films as thick as 800 nm. Films deposited without and with Vb on a TiN coating with a topmost layer formed by <111> oriented grains have shown a preferential growth of <110> oriented grains of the B2 phase from the beginning of the deposition. Those trends have been observed for the growth of near equiatomic and Ti-rich films.

  • Lecture (Conference)
    E-MRS 2010 - Spring Meeting, 07.-10.06.2010, Strasbourg, France

Publ.-Id: 14177

Direct quantitative observation of transport processes with Positron-Emission-Tomography

Kulenkampff, J.; Gründig, M.; Wolf, M.; Lippmann-Pipke, J.; Richter, M.; Enzmann, F.

Positron-Emission-Tomography (PET) enables direct and quantitative monitoring of the spatio-temporal distributions of dissolved inert and/or reactive PET-nuclides and PET-nuclide-labeled colloids during their passage through decimeter-scaled material samples. We apply PET exclusively to geomaterial samples and reach the physical resolution limit of about 1 mm with our small-animal-PET scanner (ClearPET, Raytest). We suggest our GeoPET has unrivalled sensitivity and selectivity for our tracer concentrations to some 107 tracer atoms/µl and thus is ideally suited for direct flow and transport process observations in geomaterials. This lower limit of the tracer concentration in the order of about 1 kBq/µl outranges other process observation methods (e.g. NMR or resistivity tomography) by many orders of magnitude. Like in the common medical practice, a combination with µCT for structural imaging would be advantageous for improving the spatial significance.
In the past we demonstrated the feasibility of the method, applying in-house developed and medical PET-scanners (Richter et al., 2003, Gründig et al., 2007). The installation of ClearPET in our controlled area made possible long-term experiments, like diffusion of long-living PET-tracers (like 58Co, decay time 71 days) and flow observations over several days (with 124I-labelled compounds, decay time 4 days) (Kulenkampff et al. 2008, Wolf 2010). The installation of a new cyclotrone will extend the availability of short-living PET-isotopes for fast process observations (e.g. 11C, decay time 20 min).
The density of geomaterials may cause more than 50% of Compton-scattered events, which degrade image quality mainly by inhomogeneous reconstruction artifacts. These artifacts caused explicitly by geomaterials (and only insignificantly in medical applications) are currently being addressed by model-based scatter-correction procedures.
Application examples include the fluid flow visualization in saliniferous rock cores. Different types of flow regimes are identified: in rather dense and low porous rock samples we observe slowly propagating diffuse “clouds of tracer”, whereas in fractured halite and sandstone samples (Fig. 1) we identified networks of extremely localized pathways, each with locally varying propagation velocities (Fig. 2). Quantitative parameterization of pathway and velocity distributions is possible, but still pending. However, with GeoPET-process observations we are capable of evaluating the results of Lattice-Boltzmann simulations, based on structural information from voxel-wise segmented µCT of the same sample. With respect to localized pathways in the fracture system of the halite, the model yields comparable results.
Nevertheless, even the high resolution of µCT may be insufficient to visualize the pore-space characteristics in tighter material, and more complex compositions may impair segmentation results from µCT-images. Then, stochastic models which are generated from other information, like pore-size distributions (with missing network information) and integral transport parameters (with missing distribution information), can still be validated by comparing model results with GeoPET-observations.

Keywords: PET; transport; tracer; geomaterial; tomography

  • Lecture (Conference)
    Transport in porous materials, 19.-20.8.2010, Villigen, Schweiz

Publ.-Id: 14176

Ni-Ti surface modification for enhanced biocompatibility and corrosion performance in biomedical applications

Martins, R. M. S.; Barradas, N.; Alves, E.; Henke, D.; Reuther, H.; Carmezim, M. J.; Silva, T. M.; Fernandes, J. C. S.

The plasma-immersion ion implantation (PIII) technique was used to modify and improve the surface of a Ni-Ti alloy (» 50.2 at.% Ni) for biomedical applications. The main goal has been the formation of a Ni-depleted surface, which should serve as a barrier to out-diffusion of Ni ions from the bulk material. Ion implantation of oxygen was carried out. The depth profiles of the elemental distribution in the alloy surface region, obtained by Auger electron spectroscopy (AES), confirm the formation of a Ti-rich oxide layer. The working plan also comprised ion implantation of nitrogen. In this case, the formation of titanium oxynitride (TiNxOy) was observed. The AES depth profiles clearly show a Ni-depleted fraction for experiments performed with 40 keV.

Keywords: plasma-immersion ion implantation; Ni-Ti surface modification

  • Poster
    E-MRS 2010 - Spring Meeting (Symposium S: Shape Memory Materials for smart systems III);, 07.-10.06.2010, Strasbourg, France

Publ.-Id: 14175

The ternary system U(VI) / humic acid / Opalinus Clay

Joseph, C.; Schmeide, K.; Sachs, S.; Brendler, V.; Bernhard, G.

Beside salt dome and granite rock, also clay rock is discussed as a possible host rock for siting a nuclear waste repository in Germany. The focus of the present work is the investigation of the U(VI) interaction with Opalinus Clay from Mont Terri, Switzerland, used here as a generic test case for studying radionuclide-clay interaction. The influence of humic acid (HA), a representative of natural organic complexing agents, on the migration of U(VI) is studied in addition.
U(VI) sorption experiments with ground Opalinus Clay and U(VI) diffusion experiments with intact clay rock were performed in the absence and presence of HA using synthetic Opalinus Clay pore water (I = 0.36 M, pH 7.6; [1]) as the background electrolyte. It was found that the U(VI) sorption onto Opalinus Clay is low and it is not influenced by HA. Speciation calculations showed that, under pore water conditions, Ca2UO2(CO3)3(aq) [2] is the dominant U(VI) species in solution both in the absence and presence of HA. The U(VI) speciation is not influenced by HA, which is predominantly present as a Ca complex [3]. It can be concluded, that calcium ions released by the dissolution of calcite (13% of Opalinus Clay [4]) play an important role in the investigated system.

[1] F.J. Pearson, PSI Internal report TM-44-98-07, Paul Scherrer Institut, Villigen PSI, Switzerland, 1998.
[2] G. Bernhard, G. Geipel, T. Reich, V. Brendler, S. Amayri, H. Nitsche, Radiochim. Acta 89 (2001) 511.
[3] A. Paulenová, P. Rajec, M. Žemberyová, G. Sasköiová, V. Višacký, J. Radioanal. Nucl. Chem. 246 (2000) 623.
[4] Nagra, Nagra Technical Report NTB 02-03, Wettingen, Switzerland, 2002, p. 230.

Keywords: uranium(VI); humic acid; Opalinus Clay; pore water; sorption; diffusion; speciation; calcium

  • Lecture (others)
    Seminar at the Institute of Laboratory for Waste Management (LES) - Paul Scherrer Institut (PSI), 28.-30.06.2010, Villigen, Switzerland

Publ.-Id: 14174

Identifizierung von 11C-Radiotracern mittels 13C-NMR

Mamat, C.

kein Abstract verfügbar

  • Lecture (others)
    Dresdner NMR-Seminar, 30.03.2010, Dresden, D

Publ.-Id: 14173

Crystal structure of N-benzyl-4-fluorobenzamide, C14H12FNO, at 173 K

Mamat, C.; Flemming, A.; Köckerling, M.

C14H12FNO, monoclinic, P21/n (no. 14), a = 5.6653(2) Å,
b = 25.305(1) Å, c = 8.2832(3) Å, ß = 92.237(3)°,
V = 1186.6 Å3, Z = 4, Rgt(F) = 0.047, wRref(F2) = 0.123,
T = 173 K.

Publ.-Id: 14172

Recent Application of Click Chemistry for the Synthesis of Radiotracers for Molecular Imaging

Mamat, C.; Ramenda, T.; Wuest, F.

Click chemistry has received considerable attention as powerful modular synthesis approach, which has found numerous applications in many areas of modern organic chemistry, drug discovery and material science. Recently, click chemistry, and in particular the copper-mediated 1,3-dipolar [3+2] cycloaddition between azides and alkynes, has also entered the field of radiopharmaceutical sciences. This review addresses the recent developments of click chemistry for the synthesis of various radiotracers for molecular imaging purposes. Click chemistry-based radiotracers that will be covered include peptides and small organic molecules containing the short-lived positron emitters fluorine-18, and the gamma-emitters technetium-99m, indium-111, and iodine-125.

Keywords: Click chemistry; radiopharmaceutical science; radiotracer

  • Mini-Reviews in Organic Chemistry 6(2009), 21-34

Publ.-Id: 14171

Studying Obsidians from Milos by Complementary Techniques: An Application of Ion Beam and Instrumental Neutron Activation Analysis

Eder, F.; Neelmeijer, C.; Bichler, M.; Merchel, S.

The natural volcanic glass obsidian was an important raw material for tools and arms during prehistoric time and has been found by researchers at great distances from potential natural sources. Reliable provenancing can provide evidence of contacts over a certain dis-tance and information about exchange patterns and mobility of prehistoric people.
Instrumental Neutron Activation Analysis (INAA) is one of the major analytical techniques to solve the problem of obsidian provenancing by means of its highly specific chemical composition, the “chemical fingerprint” [1-4]. The advantages of bulk INAA are the absence of matrix effects, the large number of ele-ments simultaneoulsy detectable, its sensitivity and accuracy. However, INAA is limited as being destruc-tive and inclusions cannot be distinguished from the matrix applying routine analytical practice.
Additional application of non-destructive Ion Beam Analysis (IBA), consisting of Proton Induced X-ray Emission (PIXE), Proton Induced Gamma-ray Emission (PIGE) and Rutherford Backscattering Spectrometry (RBS), supplement INAA measurements by enabling systematic spatially resolved surface investigations and adding a complementary element spectrum [5-9]. Furthermore, a comparison of chemical compositions obtained by different analytical methods provide the actual degree of the reliability of the analytical results [10].
For this study, both INAA and IBA measurements have been applied to the same samples to gain a more complete set of elements and to check the self-consistency of the analytical results. The samples originate from the obsidian sources Demenegakion and Agia Nychia (Cape Bombarda) on the island of Melos (Greece) (Fig. 1). Our INAA studies have been performed at the TRIGA MkII 250 kW research reactor of the Atominstitut in Vienna, where 150 mg of ground aliquots have been irradiated for 1 min at a thermal neutron flux of 3.3x1012cm-2s-1. IBA measurements have been carried out using the 4 MeV proton beam in-air of the 5 MV tandem accelerator of the Ion Beam Centre of FZD [9,11].

Fig. 1: Geographical situation of obsidian sources on the island of Melos (after [12]).

Our investigations are part of a joint project to apply selected analytical methods, in particular INAA, IBA and Inductively Coupled Plasma-Mass Spec-trometry (ICP-MS), to reveal a maximum of compositional differences between easily available samples of the natural obsidian sources in Europe. This knowledge should enable to decide, which least invasive analytical method should be chosen for the analysis of a specific highly valuable archaeological artefact, on a case by case basis.

References: [1] Meloni S. et al. J. Radioanal. Nucl. Chem. 271 (2007) 533-539. [2] Arias A. et al. J. Radioanal. Nucl. Chem. 268 (2006) 371-386. [3] Kilikoglou V. et al. J. Archaeol. Sci. 23 (1996) 343–349. [4] Aspinall. A. et al. Nature 237 (1972) 333–334. [5] Bellot-Gurlet L. et al. C. R. Palevol 7 (2008) 419–427. [6] Calligaro T. X-Ray Spectrometry 37 (2008) 169–177. [7] Lugliè C. et al. C. R. Palevol 5 (2006) 995–1003. [8] Kim J.C. et al. IPPA Bull. 27 (2005) 122–128. [9] Bugoi R. and Neelmeijer C. NIMB 226 (2004) 136-146. [10] Hancock R.G.V. and Carter T. J. Archaeol. Sci. 37 (2010) 243–250. [11] Saminger S. et al. J. Radioanal. Nucl. Chem. 245 (2000) 375-383. [12] Higgins M. and Higgins R. (1996) A geological companion to Greece and the Aegean Cornell University Press.

Keywords: archaeometry; PIXE; PIGE; INAA

  • Lecture (Conference)
    6. Workshop RCA (Radiochemische Analytik bei Betrieb und Rückbau kerntechnischer Anlagen, der Deklaration von Abfällen und im Strahlenschutz) & 23. SAAGAS (Seminar Aktivierungsanalyse und Gammaspektroskopie), 06.-08.09.2010, Dresden, Deutschland

Publ.-Id: 14170

Cs2Te normal conducting photocathodes in the superconducting RF gun

Xiang, R.; Arnold, A.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schamlott, A.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Teichert, J.

The superconducting radio frequency photo-injector (SRF gun) is one of the latest applications of superconducting RF technology in the accelerator field. Since superconducting photocathodes with high quantum efficiency are still unavailable, normal conducting cathode material is the main choice for SRF photo-injectors. However, the compatibility between the photocathode and the cavity is one of the challenges for this concept. Recently, a SRF gun with Cs2Te cathode has been successfully operated in Forschungszentrum Dresden-Rossendorf (FZD). In this paper, we will present the physical properties of Cs2Te photocathodes in the SC cavity, such as the quantum efficiency, the life time, the rejuvenation, the charge saturation and the dark current.

Keywords: Cs2Te; photocathode; SRF gun; QE; life time; rejuvenation; dark current

Publ.-Id: 14169

Quantitative Tiefenprofilelementanalyse mit Subnanometer Tiefenauflösung

Kosmata, M.; Munnik, F.; Heller, R.; Neelmeijer, C.

Einleitung: Die quantitative Elementanalytik von Schichten und Schichtabfolgen im Dickenbereich we-niger Nanometer ist in den letzten Jahren in den Fokus aktueller Forschung gerückt. Im Mittelpunkt dieser materialwissenschaftlichen Fragestellungen steht die Bestimmung von Tiefenverteilungen von Elementen in dünnen Schichten, die durch spezielle Abscheidever-fahren oder nachfolgende Prozessschritte wie Temperung erzielt werden, aber auch der Nachweis unbeabsichtigter Kontamination in den Schichten. Daraus können Informationen im Hinblick auf gezielte Materialentwicklung gewonnen werden und die Qualität bestehender Prozessführungen lässt sich bewerten.
Ionenstrahlanalyse: Mittels Ionenstrahlanalyseverfahren kann die Zusammensetzung einer Probe angefangen von der Oberfläche bis in eine bestimmte Tiefe des Materials quantitativ untersucht werden. Hierzu werden auf die zu untersuchende Probe Ionen mit einer definierten Energie (2-40 MeV) geschossen und die Streuprozesse zur Analyse genutzt. Da die Wahrscheinlichkeit für einen bestimmten Prozess (Wirkungsquerschnitt) bekannt ist, ergibt sich aus deren absoluten Häufigkeit die Konzentration aller Elemente. Im Gegensatz zu den meisten konventionellen (nicht nuklearen) Analyseverfahren sind daher zur Quantifizierung der Ergebnisse keine Messungen gegen Referenzmaterialien gleicher Matrix notwendig.
Auf dem Weg durch die Probe verlieren die Ionen durch inelastische Stöße mit Elektronen und Kernen der Atome der Matrix kontinuierlich Energie. Diese weglängenabhängige Energieabgabe (Bremsvermögen) kann berechnet und damit die chemische Zusammensetzung der Probe tiefenabhängig bestimmt werden. Abhängig von der Anfangsenergie und Art der Ionen können Tiefen bis zu wenigen Mikrometern untersucht werden.
Subnanometer Tiefenauflösung: Mit konventionellen Ionenstrahlanalysemethoden sind Tiefenauflösungen im Bereich von Atommonolagen (< 1 nm) nicht zu erreichen. Hierzu ist eine Modifizierung des klassischen Messaufbaus notwendig. Am Forschungszentrum Dresden-Rossendorf (FZD) kommen hierbei Magnetspektrometer in Kombination mit den Ionenstrahlanalyseverfahren Rutherford-Rückstreu-Spektrometrie (RBS) und Elastische Rück-streuanalyse (ERD) zum Einsatz. Mittels dieser Erweiterung muss die tiefenbestimmende Energie nicht mit einem limitierenden Energiedetektor gemessen werden, sondern kann aufgrund der Lorentzkraft aus dem Flugradius im Magnetfeld der Magnetspektrometer ermittelt werden. Allein mittels dieser Erweiterung können oberflächennah Monolagen verschiedener Elemente bestimmt werden (s. Abb. 1).

Abb. 1: Sauerstoffkonzentration eines SiO2-Multischicht-systems bestimmt mittels konventioneller ERD und ERD im “high-resolution”-Mode (HR-ERD).

Wasserstoff: Eine Ausnahme bildet das leichteste Element: Wasserstoff. Dieses Element kann mittels Kernreaktionsanalyse (NRA) über die resonante Kernreaktion 1H(15N,αγ)12C ermittelt werden. Die Tiefenabhängigkeit ergibt sich hierbei ebenfalls aus inelastischen Stößen beim Durchqueren der Stickstoffionen durch die Probe bis zum Ort der Kernreaktion.
Performance: RBS, ERD und NRA können in der Regel zerstörungsarm durchgeführt werden. Bei einigen Matrices kann allerdings der Ionenbeschuss bei hohen Fluenzen durch Diffusionsverlust oder Sputtering zum Verlust des Analyten führen und limi-tiert so die Nachweisgrenze (s. Tab. 1). Bei der Durch-führung der RBS und ERD im „high-resolution“-Mode (HR-RBS / HR-ERD) muss zur exakten Quantifizierung das Auftreten wechselnder Ionenladungszustände berücksichtigt werden. Alle Ionenstrahlanalysemethoden können zudem mit lateraler Auflösung im Mikrometerbereich (Mikrosonde) durchgeführt werden.

Tab. 1: Performance der Ionenstrahlanalysemethoden mit und ohne „high-resolution“-Mode (HR) am FZD.
Analyt Tiefen-auflösung [nm] Nachweis-grenze [at%] max.
Analysen-tiefe [nm]
RBS > Si ≈ 15 0,01 1000
HR-RBS > Si < 1 1 20
ERD ≤ Si ≈ 20 0,01 500
HR-ERD ≤ Si < 1 1 20
NRA H (F) ≈ 1 0,02 2000

Keywords: High Resolution; ERD; ERDA; RBS; HR-ERD; HR-RBS; NRA; ubnanometer Tiefenauflösung; Magnetspektrometer; high-resolution; Mikrosonde

  • Lecture (Conference)
    6. Workshop RCA (Radiochemische Analytik bei Betrieb und Rückbau kerntechnischer Anlagen, der Deklaration von Abfällen und im Strahlenschutz) & 23. SAAGAS (Seminar Aktivierungsanalyse und Gammaspektroskopie), 06.-08.09.2010, FZD, Deutschland

Publ.-Id: 14168

All-optical Laser Cooling and Beam Diagnostics for Relativistic C3+ Ion Beams at ESR

Bussmann, M.; Kroll, F.; Loeser, M.; Siebold, M.; Schramm, U.; Wen, W.; Winters, D. F.; Walther, T.; Beck, T.; Rein, B.; Birkl, G.; Kruse, J.; Nörtershäuser, W.; Kühl, T.; Novotny, C.; Kozhuharov, C.; Geppert, C.; Steck, M.; Nolden, F.; Dimopoulou, C.; Ma, X.; Stöhlker, T.

We present the current status of the laser cooling experiment using relativistic C3+ ion beams at the Experimental Storage Ring (ESR) at GSI.
Based on the results of two previous beam times we show that with modern laser systems and new optical diagnostics all-optical cooling of an ion beam can be achieved and ion beam properties can be measured with high accuracy. Laser cooling can become an important tool for high-energy storage rings, because, unlike other beam cooling methods, laser cooling provides a cooling force that grows stronger for increasing beam energy.

Keywords: laser cooling; ion beam; relativistic; esr; optical; diagnostic

  • Invited lecture (Conferences)
    EMMI Workshop on Physics Prospects at the ESR and HiTrap, 27.-30.06.2010, Eisenach, Deutschland

Publ.-Id: 14167

Defect characterization of Er implanted, Ge-rich SiO2 layers using slow positron implantation spectroscopy

Anwand, W.; Kanjilal, A.; Wagner, A.; Butterling, M.; Brauer, G.; Cowan, T. E.; Rebohle, L.; Skorupa, W.

Electroluminescence in SiO2 layers can be created by Ge implantation and a subsequent heat treatment, which forms Ge nano-particles inside the SiO2. An additional implantation of Er, connected with a further annealing, led to an improvement of the luminescence properties. However, with exceeding an optimum concentration of the Er doping the intensity of the electro-luminescence was found to be drastically decreased.
Slow positron spectroscopy (single Doppler broadening (DB) and coincidence DB) was applied in order to probe ongoing processes at a microscopic level and, in particular an impact on the optical response depending on the concentration of rare earth Er. It could be shown that the increasing intensity of the electro-luminescence is connected with a crystalline structure of the SiO2 covering the nano-particles and the improved reverse energy transfer process between Er and Ge. Obtained positron annihilation results will be compared with Transmission Electron Microscopy investigations [1] and with conclusions in recently published papers [2, 3].

[1] A. Kanjilal, L. Rebohle, M. Voelskow, W. Skorupa, M. Helm
J. Appl. Phys. 106, 026104 (2009)
[2] C.L. Heng, E. Chelomentsev, Z.L. Peng, P. Mascher, P.J. Simpson
J Appl. Phys. 105, 014312 (2009)
[3] R.S. Yu, M. Maekawa, A. Kawasuso, T. Sekiguchi, B.Y. Wang, X.B. Qin, Q.Z. Wang
NIMB 267, 3097 (2009)

Keywords: Ge; Er doped SiO2; electro-luminescence; positron annihilation spectroscopy

  • Lecture (Conference)
    39th Polish Seminar on Positron Annihilation, 20.-25.06.2010, Kazimierz Dolny, Poland

Publ.-Id: 14166

Complex defect structure of oxides studied by positrons

Kuriplach, J.; Melikhova, O.; Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.

Transition metal oxides show a variety of interesting properties and attract wide attention because of a broad application potential. At the same time, oxides often exhibit a complex defect structure comprising vacancy-like defects and positron annihilation can be effectively used to investigate and, thereby, to understand such structures. In this contribution, we concentrate on two oxides, namely these are zinc oxide (ZnO) and yttria stabilized zirconia (YSZ), the latter being a solid solution of an appropriate amount of yttria (Y2O3) in zirconia (ZrO2). As hydrogen has been detected in both these oxides and its content is not negligible [1,2], we also deal with positron characteristics of H-related defects, in addition to ‘bare’ vacancies. The structure of studied defects is obtained using an ab initio computational technique. Since there is a large charge transfer between oxygen and transition metal atoms in oxides, self-consistent calculations including positron induced forces are necessary to determine reliably positron characteristics.
As for ZnO, we discuss briefly the structure of studied vacancy-like defects. Then, the results of positron lifetime calculations are shown and compared with experimental data. Next, we present calculated formation energies of the same defects. We conclude that all calculated data support idea that in hydrothermally grown ZnO positrons annihilate in Zn vacancy-hydrogen complexes. Concerning YSZ, due to yttria doping a significant amount of O vacancy-yttrium complexes is present. Despite of earlier assumptions our calculations indicate that such complexes do not constitute positron traps. We further concentrate on the Zr vacancy and its complexes with hydrogen. First results for positron calculations with positron induced forces are presented. Calculated positron lifetimes are compared with experimental data, which suggests that the Zr vacancy and its complexes with hydrogen could be responsible for positron trapping in YSZ. Finally, further prospects of positron studies of defects in oxides are outlined.

[1] G. Brauer et al., Phys. Rev. B 79, 115212 (2009)
[2] O. Melikhova et al., Mat. Res. Symp. Proc. 1216, W07-10 (2010)

Keywords: ZnO; yttria stabilized zirconia; H-related defects; ab initio computational technique; positron annihilation

  • Lecture (Conference)
    39th Polish Seminar on Positron Annihilation, 20.-25.06.2010, Kazimierz Dolny, Poland

Publ.-Id: 14165

Positron defect studies in oxides

Kuriplach, J.; Cizek, J.; Melikhova, O.; Prochazka, I.; Brauer, G.; Anwand, W.; Egger, W.; Sperr, P.

Transition metal oxides show a variety of interesting properties and attract wide attention because of a broad application potential. Oxides often exhibit a complex defect structure and understanding such defect structures is of primary importance for planned applications. Defects in oxides involve vacancy-like defects and positron annihilation can be effectively used to investigate them. In this lecture, we summarize results of our recent theoretical and experimental investigations carried out for zinc oxide (ZnO) and yttria stabilized zirconia (YSZ), the latter being a solid solution of an appropriate amount of yttria (Y2O3) in zirconia (ZrO2). Hydrogen-related defects in these two oxides are also considered as hydrogen is existing in a non-negligible amount in both these oxides [1,2]. The structure of defects expected to be present in the studied materials is obtained using an ab initio computational technique. Since there is a large charge transfer between oxygen and transition metal sublattices in oxides, self-consistent calculations including positron induced forces are necessary to determine reliably positron characteristics.

First, we report on positron lifetime measurements performed with a pulsed low energy positron beam system and a conventional setup on as-grown and hydrogen plasma treated single crystal ZnO samples produced under hydrothermal conditions. The results of lifetime measurements are compared with lifetimes calculated for various configurations of vacancy-like defects taking into account also defects’ formation energies. We conclude that all calculated data support the idea that in as-grown ZnO samples positrons far from the surface annihilate in Zn vacancy-hydrogen complexes. In hydrogen plasma treated samples the situation is similar, but a component originating from delocalized positrons appears, which is attributed to a reduced concentration of vacancy-like defects capable of positron trapping because of the hydrogen plasma treatment. Vacancy agglomerates are also found in the subsurface region of both types of samples.

As for YSZ, due to yttria doping a significant amount of O vacancy-yttrium complexes is present. Despite of earlier assumptions our calculations indicate that such complexes do not constitute positron traps. We further concentrate on the Zr vacancy and its complexes with hydrogen. First results for positron calculations with positron induced forces are presented. Calculated positron lifetimes are compared with experimental data obtained for YSZ single crystals, which suggests that the Zr vacancy and its complexes with hydrogen could be responsible for positron trapping in YSZ.

[1] G. Brauer et al., Phys. Rev. B 79, 115212 (2009)
[2] O. Melikhova et al., Mat. Res. Soc. Symp. Proc. 1216, W07-10 (2010)

Keywords: Transition metal oxides; defect structure; positron lifetime measurements and calculations

  • Invited lecture (Conferences)
    12th International Workshop on Slow Positron Beam Techniques for Solids and Surfaces (SLOPOS-12), 01.-06.08.2010, Magnetic Island/North Queensland, Australia

Publ.-Id: 14164

A Generic Approach for Developing Highly Scalable Particle-Mesh Codes for GPUs

Hönig, W.; Schmitt, F.; Widera, R.; Burau, H.; Juckeland, G.; Mueller, M. S.; Bussmann, M.

We present a general framework for GPU-based low-latency data transfer schemes that can be used for a variety of particlemesh algorithms [9]. This framework allows to hide the latency of the data transfer between GPU-accelerated computing nodes by interleaving it with the kernel execution on the GPU. We discuss as an example the fully relativistic particle-in-cell (PiC) code PIConGPU [6] currently used to simulate particle acceleration by extremely short high-energy laser pulses. The PiC algorithm is a versatile algorithm used frequently in plasma physics—especially for large-scale simulations of fusion plasmas [14]—, in astrophysics [10], or for the simulation of particle accelerators [12]. A special Cell processor version is used as a benchmark code for the Roadrunner system at Los Alamos National Lab [5]. The presented hybrid GPU-CPU data transfer and access framework can, furthermore, be used for general particle-mesh schemes. GPU memory access to particle data and mesh data are efficiently separated, while data that has to be exchanged between domains located on different GPUs is transferred during computing steps using GPU-CPU memory copy and MPI. A simulation of laser-wakefield acceleration of electrons in an underdense plasma serves as a real-world benchmark for the performance of the framework.

Keywords: gpu; gpgpu; performance; particle-mesh; particle-in-cell; pic; simulation; algorithm; communication; framework; laser; plasma

Publ.-Id: 14163

Divacancy-hydrogen complexes in zinc oxide

Kuriplach, J.; Brauer, G.; Melikhova, O.; Cizek, J.; Prochazka, I.; Anwand, W.

In the present work we study Zn+O divacancies filled up with varying amount of hydrogen atoms. Besides the structure and energy-related properties of such defects, we also investigate their capability to trap positrons taking into account positron induced forces. We show that the Zn+O divacancy may trap positrons when up to two hydrogen atoms are located inside the divacancy. The calculated properties are discussed in the context of other computational and experimental studies of ZnO.

Keywords: ZnO; Zn+O divacancies; hydrogen; computational and experimental studies

  • Contribution to proceedings
    Mater. Res. Soc. Symp., 30.11.-04.12.2009, Boston, MA, USA
    Zinc Oxide and Related Materials - 2009, edited by Steve Durbin, Martin Allen, and Holger von Wenckstern, Mater. Res. Soc. Symp. Proc. 1201, Warrendale, PA, 2010), 1201-H02-03 (6 pp)

Publ.-Id: 14162

Investigation of interaction of hydrogen with defects in zirconia

Melikhova, O.; Kuriplach, J.; Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.

In the present work we study theoretically hydrogen incorporated into several positions in the zirconia cubic and tetragonal lattices. These are positions in the interstitial space and in the zirconium vacancy (VZr). We examine the structure of such configurations and for VZr-related defects we also calculate selected positron characteristics in order to assess their capability of trapping positrons. It is shown that hydrogen atoms do not prefer to stay in the center of the largest interstitial space nor of VZr and they rather tend to create bonds with neighboring oxygen atoms. The positron lifetime of the VZr+1H complex is shorter than that for non-decorated VZr and positron trapping in VZr+1H complexes could, in principle, explain experimental lifetime data.

Keywords: zirconia; zirconium vacancy; theoretically incorporated hydrogen

  • Contribution to proceedings
    Mater. Res. Soc. Symp., 30.11.-04.12.2009, Boston, MA, USA
    Hydrogen Storage Materials, edited by E. Akiba, W. Tumas, P. Chen, M. Fichtner, and S. Zhang, (Mater. Res. Soc. Symp. Proc. 1216, Warrendale, PA, 2010), 1216-W07-10 (6 pp)

Publ.-Id: 14161

Quenched-in vacancies in Fe-Al alloys

Melikhova, O.; Cizek, J.; Prochazka, I.; Anwand, W.; Brauer, G.

Intermetallic Fe-Al alloys are perspective materials for industrial applications at elevated temperatures. A high concentration of vacancies is a specific feature of such alloys. The equilibrium concentration of thermal vacancies in these alloys is considerably higher than in pure metals and may be as high as several at.%. Moreover, a high concentration of thermal vacancies existing at elevated temperatures can be quenched-in down to room temperature. Hence, a detailed investigation of vacancies and other vacancy-like defects in Fe-Al based alloys is necessary for a deeper understanding of the physical properties of these materials.

Quenched-in vacancies in Fe-Al alloys were investigated in this work employing three complementary techniques of positron annihilation: Doppler broadening spectroscopy performed using a variable energy slow positron beam (SPIS = slow positron implantation spectroscopy), coincidence Doppler broadening (CDB) spectroscopy and positron lifetime (LT) measurements. It was found that quenched alloys exhibit a high concentration of vacancies. Although a free positron component cannot be resolved in our LT spectra, the concentration of quenched-in vacancies can still be determined from the shortening of the positron diffusion length measured by SPIS. Hence, SPIS is a very important technique for the investigation of defect-rich materials, like quenched Fe-Al alloys.

In the present work, the concentration of quenched-in vacancies was determined in Fe-Al based alloys at various Al content ranging from 24 up to 45 at.-%. The lowest concentration of quenched-in vacancies was found in the stoichiometric Fe3Al alloy, i.e. an alloy with an Al concentration of 25 at.-%. This concentration increases with an increasing degree of non-stoichiometry with respect to Fe3Al. Hence, the concentration of quenched-in vacancies increases both in alloys with under-stoichiometric as well as in those with over-stoichiometric Al content. However, the increase in concentration is more pronounced in the Al-rich alloys, i.e. alloys containing more than 25 at.% of Al. CDB revealed that quenched-in vacancies are surrounded predominantly by Al atoms which indicates that they occupy predominantly the Fe sub-lattice.

Keywords: Fe-Al alloys; quenched-in vacancies; slow positron implantation spectroscopy; positron lifetime measurements

  • Poster
    12th International Workshop on Slow Positron Beam Techniques for Solids and Surfaces (SLOPOS-12), 01.-06.08.2010, Magnetic Island/North Queensland, Australia

Publ.-Id: 14160

Characterization of point defects in yttria stabilized zirconia single crystals

Melikhova, O.; Cizek, J.; Kuriplach, J.; Prochazka, I.; Anwand, W.; Brauer, G.; Grambole, D.

Yttria stabilized zirconia (YSZ) has a big potential of use in a wide area of high-temperature applications. Although pure zirconia is monoclinic at room temperature and exhibits relatively poor mechanical properties, high temperature tetragonal or cubic zirconia phases with superior properties can be stabilized down to room temperature by the addition of an appropriate amount of yttria (Y2O3). The deviation from stoichiometry caused by the addition of trivalent yttrium ions leads to the formation of a high density of point defects in YSZ. These defects are believed to influence significantly not only phase stabilization itself but also material characteristics of YSZ’s important for their practical use. Hence, the detailed characterization of defects in YSZ is a very important task.
In this work we performed a thorough investigation of point defects in tetragonal and cubic YSZ single crystals. Experimental data were obtained by three complementary techniques of positron annihilation spectroscopy (PAS), namely slow positron implantation spectroscopy, positron lifetime measurements, and coincidence Doppler broadening. The interpretation of PAS data was performed with the help of state-of-the-art ab-inito theoretical calculations of positron parameters for various types of vacancy-like defects.
Present experimental data suggest that both tetragonal and cubic YSZ single crystals contain a high concentration of vacancy-like defects. Theoretical calculations showed that neither oxygen vacancies nor their neutral complexes with substitute yttrium atoms are capable of positron trapping. On the other hand, zirconium vacancies are deep positron traps and most probably responsible for positron trapping observed in YSZ single crystals. However, the calculated positron lifetime for a zirconium vacancy is apparently longer than the experimental value estimated for YSZ single crystals. We argue that this effect could be explained by hydrogen atoms trapped at zirconium vacancies. On the basis of structure relaxations, we found that zirconium vacancy – hydrogen complexes represent positron traps with the calculated lifetimes close to the experimental ones. In the vicinity of a zirconium vacancy the hydrogen atom forms an O-H bond with one of the nearest neighbour oxygen atoms. This result testifies that hydrogen is an important impurity in YSZ which strongly interacts with vacancies. Hence, the hydrogen content in YSZ materials should be considered as a very important parameter. In this work, therefore, we employed also nuclear reaction analysis for a determination of the hydrogen content in YSZ single crystals. It was found that the hydrogen content in our studied samples is in a range of 0.1-0.3 at.-%, which is sufficient for the formation of hydrogen complexes with zirconium vacancies capable of saturated positron trapping.

Keywords: Yttria stabilized zirconia; zirconium vacancy – hydrogen complexes; positron annihilation spectroscopy

  • Lecture (Conference)
    12th International Workshop on Slow Positron Beam Techniques for Solids and Surfaces (SLOPOS-12), 01.-06.08.2010, Magnetic Island/North Queensland, Australia
  • Open Access Logo Journal of Physics: Conference Series 262(2011), 012038
    DOI: 10.1088/1742-6596/262/1/012038
    Cited 3 times in Scopus

Publ.-Id: 14159

Hydrogen-induced surface modifications of ZnO single crystals

Prochazka, I.; Cizek, J.; Anwand, W.; Brauer, G.; Grambole, D.; Schmidt, H.

ZnO is a wide band gap semiconductor with a variety of applications including UV light emitting diodes and lasers, optoelectronic devices, and gas sensors. Due to a progress in crystal growth, high quality single crystals are nowadays available. However, properties which are essential for any of the applications mentioned are significantly influenced by the presence of lattice defects. A detailed characterization of lattice defects in ZnO crystals is, therefore, a key task in order to understand their physical properties. Defect studies of hydrothermally grown ZnO single crystals revealed that hydrogen is the most important impurity in ZnO crystals [1]. It was found that hydrogen is coupled with zinc vacancies in the form of vacancy-hydrogen complexes. Moreover, it has been demonstrated that a huge amount of hydrogen (30 at.-%) can be introduced into ZnO crystals by electrochemical loading [2].

Surface changes in ZnO crystals electrochemically doped with hydrogen were investigated in this work using slow positron implantation spectroscopy (SPIS) combined with atomic force microscopy (AFM) and optical microscopy (OM). It was found that hexagonally shaped pyramids were formed on the surface (Fig. 1). All these pyramids have the same crystallographic orientation as the ZnO matrix. The formation of pyramids can be explained by hydrogen-induced plastic deformation which is realized by slip in the [0001] direction. Such a picture is supported (i) by AFM where terraces of a height comparable with the c-lattice parameter were found at the base of the pyramids, and (ii) by SPIS which revealed a defected subsurface layer, being formed by the hydrogen-induced plastic deformation and exhibiting an enhanced concentration of open-volume defects.

Fig. 1 Optical microscopy image (taken using oblique light) of the surface of a ZnO crystal electrochemically loaded with hydrogen.

[1] G. Brauer, et al., Phys. Rev. B 79, 115212 (2009).
[2] J. Čížek, et al., J. Appl. Phys. 103, 053508 (2008).

Keywords: ZnO; vacancy-hydrogen complexes; hydrogen-induced plastic deformation; positron annihilation spectroscopy; atomic force microscopy

  • Lecture (Conference)
    12th International Workshop on Slow Positron Beam Techniques for Solids and Surfaces (SLOPOS-12), 01.-06.08.2010, Magnetic Island/North Queensland, Australia
  • Open Access Logo Journal of Physics: Conference Series 262(2011), 012050
    DOI: 10.1088/1742-6596/262/1/012050
    Cited 1 times in Scopus

Publ.-Id: 14158

Zur Bindungsform des Urans in Umweltkompartimenten

Bernhard, G.

  • wird nachgereicht
  • Invited lecture (Conferences)
    GDCh-Kolloquien im Sommersemester 2010, 03.06.2010, Dresden, Deutschland

Publ.-Id: 14157

Functional role of protonation and hydration at the lipid protein interface in membrane receptors

Eichler, S.; Madathil, S.; Fahmy, K.

The visual photoreceptor rhodopsin is a proto¬typical class-I (rhodopsin-like) G protein-coupled receptor (GPCR). Photoisomerization of the covalently bound ligand 11-cis-retinal leads to restructuring of the cytosolic face of rhodopsin. The ensuing protonation of Glu-134 in the class-conserved D(E)RY motif at the C-terminal end of trans¬membrane helix-3 promotes the formation of the G-protein-activating state. Using trans¬mem¬brane segments derived from helix-3 of bovine rhodopsin, we show that lipid protein interactions play a key role in this cytosolic "proton switch". Infra¬red- and fluo¬res¬cence-spectroscopic pKa deter¬minations reveal that the D(E)RY motif is an auto¬no¬mous functional module coupling side chain neu¬trali¬za¬tion to conformation and helix positio¬ning as evidenced by side chain to lipid headgroup Foerster-re¬so¬nance-energy-transfer. Using rapid scan FTIR spectroscopy, we show that the motif is also a local protonein hydration site. This dual function renders the proton acceptor group a key residue in conformational control by positioning helix-3 at the water lipid protein interface.

Keywords: membrane transport; protonation; FTIR spectroscopy; fluorescence spectroscopy; FRET; charge stabilization; bilayer

  • Contribution to proceedings
    Annual Meeting of the German Biophysical Society, 03.-06.10.2010, Ruhr-Universität-Bochum, Germany

Publ.-Id: 14156

The ELBE accelerator facility starts operation with the superconducting RF gun

Xiang, R.; Arnold, A.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Teichert, J.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.

As the first superconducting rf photo-injector (SRF gun) in practice, the FZD 3+1/2 cell SRF gun is successfully connected to the superconducting linac ELBE. This setting will improve the beam quality for ELBE users. It is the first example for an accelerator facility fully based on superconducting RF technology. For high average power FEL and ERL sources, the combination of SRF linac and SRF gun provides a new chance to produce beams of high average current and low emittance with relative low power consumption.
The main parameters achieved from the present SRF gun are the final electron energy of 3 MeV, 16 μA average current, and rms transverse normalized emittances of 3 mm mrad at 77 pC bunch charge. A modified 3+1/2 cell niobium cavity has been fabricated and tested, which will increase the rf gradient in the gun and thus better the beam parameters further. In this paper the status of the integration of the SRF gun with the ELBE linac will be presented, and the latest results of the beam experiments will be discussed.

Keywords: SRF gun; superconducting linac ELBE

  • Poster
    IPAC10, 23.-28.05.2010, Kyoto, Japan
  • Contribution to proceedings
    IPAC'10, 23.-28.05.2010, Kyoto, Japan
    Proceedings of IPAC'10, 1710-1712

Publ.-Id: 14155

Recent status of the GiPS facility at ELBE and first measurements

Butterling, M.; Anwand, W.; Brauer, G.; Cowan, T. E.; Hartmann, A.; Jungmann, M.; Kosev, K.; Krause-Rehberg, R.; Krille, A.; Schwengner, R.; Wagner, A.

At the superconducting LINAC ELBE [1] at Research Centre Dresden-Rossendorf the new facility for Gamma-induced Positron Spectroscopy (GiPS) is successfully running [2] and first measurements were done. Two AMOC (Age Momentum Correlation) spectrometers (each consisting of a barium fluoride timing detector and a high purity germanium detector for measuring the energy) and a detector setup for Coincidence Doppler Broadening Spectroscopy allow to measure standard positron techniques simultaneously.
Influences from the surroundings (e.g. randomly scattered photons) disturb the recorded energy and lifetime spectra (increase of background, several peaks in lifetime spectra). Therefore it is of great importance to avoid such disturbing influences and to get clear and corrected spectra.
Recent efforts to optimize the setup and to eliminate the negative influences of the surroundings are presented. Selected results of first measurements with GiPS show the great potential of this unique facility.

Keywords: Positron annihilation; Electron and positron beams; Positrons; Positron-induced reactions; Gamma-induced Positron Spectroscopy

  • Poster
    PSPA10 - 39th Polish Seminar on Positron Annihilation, 20.-25.06.2010, Kazimierz Dolny, Poland

Publ.-Id: 14154

Bispidine Derivatives for Dual-Modality Imaging

Fähnemann, S.

kein Abstract verfügbar

  • Lecture (Conference)
    7th Supraphone Meeting, 28.04.-01.05.2010, Maria Laach, Deutschland

Publ.-Id: 14153

Nuclear structure study of 19,20,21N nuclei by gamma spectroscopy

Elekes, Z.; Vajta, Z.; Dombradi, Z.; Aiba, T.; Aoi, N.; Baba, H.; Bemmerer, D.; Fulop, Z.; Iwasa, N.; Kiss, A.; Kobayashi, T.; Kondo, Y.; Motobayashi, T.; Nakabayashi, T.; Nannichi, T.; Sakurai, H.; Sohler, D.; Takeuchi, S.; Tanaka, K.; Togano, Y.; Yamada, K.; Yamaguchi, M.; Yoneda, K.

The structure of neutron rich nitrogen nuclei has been studied by use of neutron removal reaction and inelastic scattering. Mass and charge deformations have been deduced for the first excited state of 21N, which indicates the partial persitence of the N=14 subshell closure in nitrogen isotopes. The spectroscopic information obtained on the structure of 19,20,21N confirms the results from a previous experiment.

Keywords: nuclear structure; radioactive ion beam; nuclear astrophysics

Publ.-Id: 14152

From Molecular Chemistry to Solid State Physics – Chemical Concepts in Material Science

Gemming, S.

no abstract available

Keywords: density-functional; material science

  • Lecture (others)
    Institutskolloquium - Institut für Chemie und Biochemie / Physikalische und Theoretische Chemie der Freien Universität Berlin und Kolloquium des Graduiertenkollegs 788, 03.06.2010, Berlin, Deutschland

Publ.-Id: 14151

Irradiation damage and embrittlement in RPV steels under the aspect of long term operation – overview of the FP7 project LONGLIFE

Altstadt, E.; Bergner, F.; Hein, H.

The increasing age of the European NPPs and envisaged lifetime extensions up to 80 years require an improved understanding of RPV irradiation embrittlement effects connected with long term operation (LTO). Phenomena which might become important at high neutron fluences (such as late blooming effects and flux effects) must be considered adequately in the safety assessments. Therefore the project LONGLIFE was initiated within the 7th Framework Programme of the European Commission. The project aims at: i) improved knowledge on LTO phenomena relevant for European reactors; ii) assessment of prediction tools, codes, standards and surveillance guidelines. In the paper, we give an overview of the project structure and the related tasks. Furthermore we present two examples for the experimental evidence of LTO relevant phenomena: the first example is related to the flux dependence of defect cluster formation in a neutron irradiated weld material. We have found that the size of the irradiation induced defects exhibits a flux effect whereas the mechanical properties are almost independent of the flux. The second example refers to the acceleration of irradiation hardening after exceeding a threshold fluence. This effect was observed by means of both small angle neutron scattering (SANS) and tensile testing for low Cu RPV steels irradiated at a temperature of 255°C. These examples demonstrate that LTO irradiation effects have to be investigated in more detail to guarantee the applicability of the embrittlement surveillance guidelines beyond 40 years of operation.

Keywords: neutron irradiation embrittlement; reactor pressure vessel; long term operation; small angle neutron scattering; flux effect; late blooming effect

  • Contribution to proceedings
    18th International Conference on Nuclear Engineering ICONE18, 17.-21.05.2010, Xian, China
    Proceedings of the 18th International Conference on Nuclear Engineering ICONE18
  • Lecture (Conference)
    18th International Conference on Nuclear Engineering ICONE18, 17.-21.05.2010, Xian, China

Publ.-Id: 14150

Binary and Ternary Uranium(VI) Humate Complexes Studied by Attenuated Total Reflection Fourier-transform Infrared Spectroscopy

Steudtner, R.; Müller, K.; Schmeide, K.; Sachs, S.; Bernhard, G.

The complexation of U(VI) with humic acid (HA) in aqueous solution has been investigated at an ionic strength of 0.1 M (NaCl) in the pH range between pH 2 and 10 at different carbonate concentrations by attenuated total reflection Fourier-transform infrared (ATR FT IR) spectroscopy. For the first time, the formation of binary and ternary U(VI) humate complexes was directly verified by in-situ spectroscopic measurements. The complex formation constants for the binary U(VI) humate complex (UO2HA(II)) and the for ternary U(VI) mono hydroxo humate complex (UO2(OH)HA(I)) as well as the ternary U(VI) dicarbonato humate complex (UO2(CO3)2HA(II) 4−) determined from the spectroscopic data amount to log β0.1 M = 6.70 ± 0.25, log β0.1 M = 15.14 ± 0.25 and log β0.1 M = 24.47 ± 0.70, respectively and verify literature data.

Keywords: Actinides; Vibrational spectroscopy; Metal-organic frameworks; Radiochemistry

Publ.-Id: 14149

Iodine-124: A Promising Positron Emitter for Organic PET Chemistry

Koehler, L.; Gagnon, K.; Mcquarrie, S.; Wuest, F.

The use of radiopharmaceuticals for molecular imaging of biochemical and physiological processes in vivo has evolved into an important diagnostic tool in modern nuclear medicine and medical research. Positron emission tomography (PET) is currently the most sophisticated molecular imaging methodology, mainly due to the unrivalled high sensitivity which allows for the studying of biochemistry in vivo on the molecular level. The most frequently used radionuclides for PET have relatively short half-lives (e. g. C-11: 20.4 min; F-18: 109.8 min) which may limit both the synthesis procedures and the time frame of PET studies. Iodine-124 (I-124, t(1/2) = 4.2 d) is an alternative long-lived PET radionuclide attracting increasing interest for long term clinical and small animal PET studies. The present review gives a survey on the use of I-124 as promising PET radionuclide for molecular imaging. The first part describes the production of I-124. The second part covers basic radiochemistry with I-124 focused on the synthesis of I-124-labeled compounds for molecular imaging purposes. The review concludes with a summary and an outlook on the future prospective of using the long-lived positron emitter I-124 in the field of organic PET chemistry and molecular imaging.

Publ.-Id: 14148

Efficient preparation of 99mTc(III) ‘4+1’ mixed-ligand complexes for peptide labeling with high specific activity

Künstler, J.-U.; Seidel, G.; Pietzsch, H.-J.

An improved labeling procedure for peptides attached to organometallic 99mTc(III) ‘4+1’ mixed-ligand complexes in which the radiometal is coordinated by a tripodal tetradentate chelator 2,2',2''-nitrilotriethanethiol (NS3) and a monodentate isocyanide ligand is presented. The labeling procedure was evaluated by the synthesis of [99mTc(NS3)(L2-RGD)]. The containing radiopharmaceutically interesting RGD-peptide cyclo[Arg-Gly-Asp-D-Tyr-Lys] was modified with 4-isocyanobutanoic acid (L2) as linker conjugated to N6-Lys to get the monodentate ligand L2-RGD. The structural identity of the 99mTc-conjugate was confirmed by comparison to a Re reference compound. The Tc- and Re-conjugates had matching retention times under identical HPLC conditions. The 99mTc-labeling was performed in a novel one-step procedure using the eluate of a 99Mo/99mTc generator, NS3, the isocyanide modified peptide, SnCl2, Na2EDTA, mannitol and ascorbic acid in the reaction mixture. Using optimized reagents it is possible to label 50 nmol peptide with 99mTc within 60 min at room temperature with a radiochemical yield higher than 95% and a specific activity of ~20 GBq/mmol.

Keywords: Technetium-99m; ‘4+1’ mixed-ligand complexes; Peptide labeling; Specific activity

Publ.-Id: 14147

The impact of interstitials on diffusion in germanium under proton irradiation

Schneider, S.; Bracht, H.; Klug, J.; Lundsgaard Hansen, J.; Nylandsted Larsen, A.; Bougeard, D.; Haller, E.; Posselt, M.; Wündisch, C.

Experiments on the influence of 2.5 MeV proton irradiation on self- and dopant diffusion in germanium (Ge) were performed at 600 and 570°C, respectively. Ge isotope heterostructures consisting of 20 layers were used for the self-diffusion study. Ge with boron (B) doped multilayers and samples implanted with phosphorus (P) were utilized for the investigation of irradiation mediated dopant diffusion. Self-diffusion under irradiation reveals an unusual homogenous broadening of the isotope structure. This behaviour and the enhanced diffusion of B and retarded diffusion of P under irradiation demonstrates that an interstitial-mediated diffusion process dominates in Ge under irradiation. This discovery establishes new ways to suppress vacancy-mediated diffusion in Ge and to solve the donor deactivation problem that limits Ge-based nanoelectronics.

Keywords: germanium; diffusion; interstitials

  • Lecture (Conference)
    Gemeinsame DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), den Fachverbänden Kristallographe (KR), Strahlen und Medizinphysik (ST), Physik sozio-ökonomischer Systeme (SOE) und des Arbeitskreises Industrie und Wirtschaft (AIW), 21.-26.03.2010, Regensburg, Germany

Publ.-Id: 14146

Experimentelle und theoretische Untersuchungen zur elektrischen Aktivierung von Dotanden und zur Festphasenepitaxie in Ge

Posselt, M.

Review of recent results on electrical doping of Ge by ion implantation and ms flash lamp annealing, overview on atomistic simulation of solid phase epitaxial recrystallization of amorphous Ge

Keywords: germanium; electrical doping; ion implantation; flash lamp annealing; solid phase epitaxial recrystallization; computer simulation

  • Lecture (others)
    Seminar des Instituts für Materialphysik der Universität Münster, 01.06.2010, Münster, Deutschland

Publ.-Id: 14145

Interaction between molten corium UO2+x-ZrO2-FeOy and VVER vessel steel

Bechta, S. V.; Granovsky, V. S.; Khabensky, V. B.; Krushinov, E. V.; Vitol, S. A.; Sulatsky, A. A.; Gusarov, V. V.; Almiashev, V. I.; Lopukh, D. B.; Bottomley, D.; Fischer, M.; Piluso, P.; Miassoedov, A.; Tromm, W.; Altstadt, E.; Fichot, F.; Kymalainen, O.

In case of in-vessel corium retention during a severe accident in a light water reactor, weakening of the vessel wall and deterioration of the vessel steel properties can be caused both by the melting of the steel and by its physicochemical interaction with corium. The interaction behavior has been studied in medium-scale experiments with prototypic corium. The experiments yielded data for the steel corrosion rate during interaction with UO2+X - ZrO2 - FeOy melt in air and steam at different steel surface temperatures and heat fluxes from the corium to the steel. It has been observed that the corrosion rates in air and steam atmosphere are almost the same. Further, if the temperature at the interface increases beyond a certain level, corrosion intensifies. This is explained by the formation of liquid phases in the interaction zone. The available experimental data have been used to develop a correlation for the corrosion rate as a function of temperature and heat flux.

Keywords: severe accident; in-vessel; retention; vessel steel corrosion

  • Nuclear Technology 157(2010)4, 210-218

Publ.-Id: 14144

Evolution of Ion-Induced Ripple Patterns - Anisotropy, nonlinearity, and scaling

Keller, A.

This thesis addresses the evolution of nanoscale ripple patterns on solid surfaces during low-energy ion sputtering. Particular attention is paid to the long-time regime in which the surface evolution is dominated by nonlinear processes. This is explored in simulation and experiment.
In numerical simulations, the influence of anisotropy on the evolution of the surface patterns in the anisotropic stochastic Kuramoto-Sivashinsky (KS) equation with and without damping is studied. For a strong nonlinear anisotropy, a 90 rotation of the initial ripple pattern is observed and explained by anisotropic renormalization properties of the anisotropic KS equation. This explanation is supported by comparison with analytical predictions. In contrast to the isotropic stochastic KS equation, interrupted ripple coarsening is found in the presence of low damping. This coarsening seems to be a nonlinear anisotropy effect that occurs only in a narrow range of the nonlinear anisotropy parameter.
Ex-situ atomic force microscopy (AFM) investigations of Si(100) surfaces sputtered with sub-keV Ar ions under oblique ion incidence show the formation of a periodic ripple pattern. This pattern is oriented normal to the direction of the ion beam and has a periodicity well below 100 nm. With increasing ion fluence, the ripple pattern is superposed by larger corrugations that form another quasi-periodic pattern at high fluences.
This ripple-like pattern is oriented parallel to the direction of the ion beam and has a periodicity of around one micrometer. Interrupted wavelength coarsening is observed for both patterns. A dynamic scaling analysis of the AFM images shows the appearance of anisotropic scaling at large lateral scales and high fluences. Based on comparison with the predictions of different nonlinear continuum models, the recent hydrodynamic model of ion erosion, a generalization of the anisotropic KS equation, is considered as a potentially powerful continuum description of this experiment.
In further in-situ experiments, the dependence of the dynamic scaling behavior of the sputtered Si surface on small variations of the angle of incidence is investigated by grazing incidence small angle X-ray scattering (GISAXS). A transition from strongly anisotropic to isotropic scaling is observed. This indicates the presence of at least two fixed points in the system, an anisotropic and an isotropic one. The dynamic scaling exponents of the isotropic fixed point are in reasonable agreement with those of the Kardar-Parisi-Zhang (KPZ) equation. It remains to be seen whether the hydrodynamic model is able to show such a transition from anisotropic to isotropic KPZ-like scaling.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-519 2009
    ISSN: 1437-322X


Publ.-Id: 14143

Bi-Annual Report 2007/08 - Rossendorf Beamline at ESRF (ROBL-CRG)

Scheinost, A. C.; Baehtz, C.; (Editors)

The Rossendorf Beamline (ROBL) - located at BM20 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France - is in operation since 1998. This 6th report covers the period from January 2007 to December 2008. In these two years, 50 peerreviewed papers have been published based on experiments done at the beamline. The average citation index, which increased constantly over the years, has now reached 3.5 (RCH) and 3.0 (MRH), indicating that papers are predominately published in journals with high impact factors. Six exemplary highlight reports on the following pages should demonstrate the scientific strength and diversity of the experiments performed on the two end-stations of the beamline, dedicated to Radiochemistry (RCH) and Materials Research (MRH).
Demand for beamtime remains very high as in the previous years, with an average oversubscription rate of 1.8 for ESRF experiments. The attractiveness of our beamline is based upon the high specialization of its two end-stations. RCH is one of only two stations in Europe dedicated to x-ray absorption spectroscopy of actinides and other radionuclides. The INE beamline at ANKA provides superior experimental flexibility and extends to lower energies, including important elements like P and S. In contrast, ROBL-RCH provides a much higher photon flux, hence lower detection limits crucial for environmental samples, and a higher energy range extending to elements like Sb and I. Therefore, both beamlines are highly complementary, covering different aspects of radiochemistry research. Once the MARS beamline at SOLEIL is ready to run radionuclides (>2010), it will cover a third niche (Materials Science of actinides, including irradiated fuel) not accessible for the two other beamlines.
The Materials Research Hutch MRH has realized an increasing number of in-situ investigations in the last years. On the one hand thin film systems were characterized during magnetron sputtering. On the other hand diffraction experiments under controlled atmosphere were performed. A high variety of experimental parameters was covered by varying pressure, temperature and atmospheric compositions including highly reactive gases. Furthermore structural investigations were combined with electrical conductivity measurements. These kind of in-situ experiments are the key to monitor and understand reaction mechanism or the influence of process parameters, which are again the basis to tailor materials properties on demand. The core competences of MRH are these experimental possibilities, which make it unique among other diffraction beamlines. In fall 2007, ROBL was reviewed by an international panel on behalf of the ESRF. The very positive panel report recommended a renewal of the contract between ESRF and FZD for the next five years, and a major upgrade of critical optical components of the beamline to keep ROBL competitive for the next decade. The FZD will provide 2 Mio € from 2009 to 2011 for this upgrade, which will be performed in parallel to the major upgrade of the ESRF to minimize the downtime. According to the current plans of the ESRF, our users have to expect that ROBL will have only limited or no operation for several months from August 2011 on.
Since July 2004 the beamline is a member of the pooled facilities of ACTINET – European Network of Excellence. In the reported period, RCH has provided 27 % of its inhouse beamtime to perform 11 ACTINET experiments. The success of ACTINET within FP-6 has now led to a renewal of ACTINET within FP-7, running until end of 2011.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-517 2009
    ISSN: 1437-322X


Publ.-Id: 14142

Annual Report 2009 - Institute of Ion Beam Physics and Materials Research

von Borany, J.; Heera, V.; Faßbender, J.; Helm, M.; Möller, W.

The Institute of Ion Beam Physics and Materials Research (IIM) is one of the six institutes of the Forschungszentrum Dresden-Rossendorf (FZD), and contributes the largest part to its Research Program "Advanced Materials", mainly in the fields of semiconductor physics and materials research using ion beams. The institute operates a national and international Ion Beam Center, which, in addition to its own scientific activities, makes available fast ion technologies to universities, other research institutes, and industry. Parts of its activities are also dedicated to exploit the infrared/THz free-electron laser at the 40 MeV superconducting electron accelerator ELBE for condensed matter research. For both facilities the institute holds EU grants for funding access of external users.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-528 2010
    ISSN: 1437-322X


Publ.-Id: 14141

The formation of near surface SiGe layers with combined high-dose ion implantation and flash-lamp annealing

Voelskow, M.; Stoimenos, I.; Rebohle, L.; Skorupa, W.

The formation of near surface SiGe layers by means of combined high dose Ge ion implantation and flash lamp annealing will be addressed. Furthermore, we show that the formation of an undesirable facetted liquid/solid in-terface, which is well known for pulse melting in the mil-lisecond time regime, is less pronounced due to the de-creasing melting temperature of Si with increasing Ge concentration at the SiGe/Si interface. A dislocation net-work, which is observed by using transmission electron microscopy, is expected to play an important role to form these thin SiGe layers. We will demonstrate the depth profiles of Ge by Rutherford backscattering spectrometry and discuss the concerned mechanism.

Keywords: flash lamp annealing; ion implantation; SiGe; TEM; RBS

Related publications


Publ.-Id: 14140

Temperature dependence of lattice parameters of langasite single crystals

Krausslich, J.; Hofer, S.; Zastrau, U.; Jeutter, N.; Baehtz, C.

To determine the coefficient of thermal expansion of trigonal langasite (La3Ga5SiO14) the two independent lattice parameters a and c are measured over a temperature range of 800 degrees C using X-ray diffraction on single crystal samples. From the given nonlinear temperature dependence the linear and quadratic thermal coefficients of expansion alpha(11), beta(11) and alpha(33), beta(33) for the two lattice parameters a and c could be deduced.


Publ.-Id: 14139

Proton mu-PIXE mapping, AFM imaging and size statistics of mineral granules in a dental composite

Preoteasa, E.; Preoteasa, E.; Harangus, L.; Moldovan, A.; Dinescu, M.; Grambole, D.; Herrmann, F.

We applied proton microbeam particle-induced X-ray emission (mu-PIXE) for mapping Ca, Zr, Ba and Yb, and atomic force microscopy (AFM) for imaging the surface landscape of a dental composite which releases Ca2+ and F- for the protection of hard dental tissues. Three areas,similar to 250 x 250 mu m(2) located similar to 0.5-2 mm apart on a smooth surface specimen were mapped with 3.1 MeV protons focused to a similar to 3.0 mu m spot and at similar to 3.9 mu m pixel size sampling. The maps evidenced particles with diameters of 3.2-32 mu m (Ca), 20-60 mu m (Zr), <= 4 mu m (Ba) and 10-50 mu m (Yb). Cross-section area histograms of Ca-rich particles fitted with 2-6 Poisson functions revealed a polydisperse size distribution and substantial differences from an area to another, possibly implying large local variations of Ca2+ released in the hard tissue near a dental filling of a few millimeters in diameter. Such imbalances may lead to low local Ca2+ protection of the dental tissue!
, favoring the onset of secondary caries. Similarly, AFM images showed high zone-dependent differences in the distributions of grains with apparent diameters of 1-4 mu m, plausibly recognized as Ca- and Ba-containing particles. In a simple model based on demineralization data, lateral diffusion of Ca2+ between adjacent domains containing high- and low-area Ca-rich grains is described by exponential concentration gradients. These gradients may generate appreciable electromotive forces, which may enhance electrochemically the local tissue demineralization. Similar effects are to be expected in the protective action of F- ions released from microgranules of YbF3 and of Ba fluoroaluminosilicate glass.

  • X-Ray Spectrometry 39(2010)3, 208-215


Publ.-Id: 14138

Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.]