Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41347 Publications

Field-focusing imaging sensor for visualization of multiphase flows

Da Silva, M. J.; Thiele, S.; Schleicher, E.; Hampel, U.

We introduce a novel sensor modality for imaging of multiphase flows based on capacitance measurements. The basic idea of the new approach is to place a multitude of electrodes at two opposing walls of a vessel whereby the walls are parallel and each plane of electrodes are positioned perpendicular to each other. This arrangement combined with a special excitation-sensing scheme realizes a focusing of the electrical field in a given region of the interrogating volume allowing images to be generated.

Keywords: multiphase flow; flow visualization; capacitance measurement

  • Contribution to proceedings
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Germany
    Proceedings of EUROSENSORS XXII, Duesseldorf: VDI, 978-3-00-025217-4, 736-739
  • Lecture (Conference)
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Germany

Publ.-Id: 11387

Creation of Nanohillocks on CaF2 Surfaces by Single Slow Highly Charged Ions

El-Said, A. S.; Heller, R.; Meissl, W.; Ritter, R.; Facsko, S.; Lemell, C.; Solleder, B.; Gebeshuber, I. C.; Betz, G.; Toulemonde, M.; Möller, W.; Burgdörfer, J.; Aumayr, F.

Upon impact on a solid surface, the potential energy stored in slow highly charged ions is primarily deposited into the electronic system of the target. By decelerating the projectile ions to kinetic energies as low as 150 q eV, we find first unambiguous experimental evidence that potential energy alone is sufficient to cause permanent nanosized hillocks on the (111) surface of a CaF2 single crystal. Our investigations reveal a surprisingly sharp and well-defined threshold of potential energy for hillock
formation which can be linked to a solid-liquid phase transition.

Keywords: Highly Charged Ions

  • Physical Review Letters 100(2008)23, 237601

Publ.-Id: 11386

Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika - Verbundprojekt "Actinidenmigration im natürlichen Tongestein"

Bernhard, G.

  • wird nachgereicht
  • Lecture (others)
    8. Projektstatusgespräch zur Forschungsförderung zur Entsorgung gefährlicher Abfälle in tiefen geologischen Formationen, 06.-07.05.2008, Karlsruhe, Deutschland

Publ.-Id: 11385

Bacterial surface layers (S-layers) as building blocks for photocatalytic nanocomposites

Pollmann, K.; Raff, J.; Marquard, A.; Scholz, A.

Nanoscaled materials comprised of organic and inorganic components are becoming more and more important in nanotechnology due to the diversity of applications. Self-assembling organic systems as part of such a hybrid material can be used as template for the fabrication of arrays of inorganic nanoparticles. Especially the proteinaceous bacterial surface layers (S-layers) that envelop bacterial cells are attractive for fabricating and patterning of nanostructures. These proteins are composed of protein monomers with the ability to self-assemble into two-dimensional arrays. The regular distributed pores of these paracrystalline arrays work as binding sites for various metals and offer ideal structures for the formation of regular distributed metallic nanoclusters of a defined size [1]. Such arrays are very attractive for technical applications ranging from the development of novel catalysts to biomedical applications, the programmed assembly of nanometre scale electronic devices, and optical industry [2]. Another approach is the embedding of S-layer proteins into ceramics thus producing metal binding functionalized nanocomposites [3].
Here we present the synthesis and characterization of S-layer templated ZnO-nanoclusters of a size of 16 nm. The photocatalytic properties of ZnO-particles are interesting for the application as nanoscaled catalytic material. We used these nanoparticles for photocatalytic degradation of the parmaceutical Diclofenac at a wavelength of 365 nm. The widespread occurrence of pharmaceutical residues such as Diclofenac in the environment has been reported in numerous investigations [4], thus establishing these compounds as a new class of pollutants. Therefore, the need of novel technologies for removal of these compounds has become evident. Our future work will concentrate on the development of photocatalytic active nanocomposites by the use of S-Layer produced ZnO-particles.

  • Poster
    NanoBioEurope2008, 09.-13.06.2008, Barcelona, Spain
  • Contribution to proceedings
    NanoBioEurope2008, 09.-13.06.2008, Barcelona, Spain

Publ.-Id: 11384

The Impact of Microorganisms on the Behaviour of Actinides in Natural Environments

Selenska-Pobell, S.

The behaviour of uranium and other actinides in the environment is strongly influenced by a broad range of biogeochemical factors and also by their own, often very complex chemistry. The major biotic factors in the radioactively polluted environments are the unicellular prokaryotic microorganisms (bacteria and archaea) which, in contrast to the other forms of life on Earth, possess fascinating robustness to these extremely harsh and life-unfriendly surroundings. Microorganisms have developed very effective protection mechanisms against radionuclides and other heavy metals which are based on their ability for oxidative or reductive biotransformations, bioaccumulation, and/or biomineralization of these toxic elements (1 - 3).

  • Invited lecture (Conferences)
    Actinide XAS 2008, 15.-17.07.2008, Soleil, France

Publ.-Id: 11382

Coordination of U(IV) and U(VI) sulfate hydrate in aqueous solution

Hennig, C.; Tsushima, S.; Brendler, V.; Ikeda, A.; Scheinost, A. C.; Bernhard, G.

Sulfuric acid has been used to perform in situ leaching of uranium ore at several sites in the world, among them in Königstein/Germany. The remaining leaching solvents cause questions concerning their environmental problems. The actual thermodynamic data, describing the species distribution in aqueous solution, are not sufficient because typical leaching solutions easily exceed the limit of ionic strengths where conventional models provide trustful results. The application of spectroscopic techniques may help to provide the required data. Therefore, the coordination of U(IV) and U(VI) sulfate in aqueous solutions with high ionic strengths has been recently investigated by several spectroscopic techniques (mainly EXAFS) combined with XRD studies and DFT calculations. The observed results expand the actual knowledge of the aquatic chemistry which is based mainly on thermodynamic data. The recent results are summarized in this contribution.

  • Lecture (Conference)
    5th International Conference Uranium Mining and Hydrogeology, 14.-18.09.2008, Freiberg, Germany
  • Contribution to external collection
    Broder J. Merkel, Andrea Hasche-Berger: Uranium, Mining and Hydrogeology, Berlin: Springer Verlag, 2008, 978-3-540-87745-5, 603-613

Publ.-Id: 11381

A new database on upwards air-water flow in a large pipe

Lucas, D.; Beyer, M.; Kussin, J.; Schütz, P.

A new database for stationary upward air-water flows in a vertical pipe with an inner diameter of 195.3 mm using the wire-mesh sensor technology is presented. During the experiments the sensor was always mounted on the top of the test section while the distance between gas injection and measuring plane was varied to up to 18 different L/D by using gas injection chambers at different vertical positions. The gas was injected via holes in the pipe wall. The pressure was kept at 0.25 MPa (absolute) at the location of the active gas injection while the temperature was constant at 30°C +-1K. This procedure exactly represents the evolution of the flow along the pipe, as it would be observed for an injection at a constant height position and a shifting of the measurement plane. The experiments were done for 48 combinations of air and water superficial velocities varying from 0.04 m/s to 1.6 m/s for water and 0.0025 m/s to 3.2 m/s for air. From the raw data time averaged data as: radial gas volume fraction profiles, bubble size distributions, radial volume fraction profiles decomposed according to the bubble size and the radial profiles of the gas velocity were calculated. All data were checked regarding their plausibility. They are characterized by a high resolution in space what makes them suitable for the development and validation of closure models for CFD-codes (e.g. for models on bubble forces or on coalescence and break-up) as well as for the test and validation of approaches for poly-dispersed flow.

Keywords: multiphase flow; bubbly flow; churn turbulent flow; annular flow; bubble size; pipe flow

  • Lecture (Conference)
    46th European Two-Phase Flow Group Meeting, 28.-30.05.2008, Pisa, Italy

Publ.-Id: 11380

Magnetization dynamics of Landau structures: tuning the response of mesoscopic magnetic objects using defects

Kuepper, K.; Wintz, S.; Raabe, J.; Buess, M.; Akhmadaliev, C.; Bischoff, L.; Quitmann, C.; Fassbender, J.

Magnetic vortex cores are interacting with and can be annihilated by artificial defects, such as holes. We report the imaging of the magnetic excitation spectrum in presence of holes, fabricated by focussed ion beam milling, in the magnetic domains, domain walls, and the center of Landau structures by means of x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM). Due to the very high lateral and temporal resolution the magnetization dynamics, which is characteristic for the vortex-hole interaction, is investigated in detail. We find that the vortex as well as domain walls can be trapped by small holes. As a consequence the frequency vortex gyrotropic motion is enhanced with a significant lower amplitude in case of non centric holes in domain walls. Non centric holes in domains lead to no frequency shift, but a higher amplitude of the vortex gyration due to attractive vortex-hole interaction. The experimental results are compared to micromagnetic simulations.

Keywords: magnetism; magnetization dynamics; vortex; defects; magnetic domain; XMCD; simulations

Publ.-Id: 11379

Controlled generation of ferromagnetic martensite from paramagnetic austenite in AISI 316L austenitic stainless steel

Menendez, E.; Sort, J.; Liedke, M. O.; Fassbender, J.; Surinach, S.; Baro, M. D.; Nogues, J.

The strain-induced austenite (gamma) to martensite (alpha') transformation in AISI 316L austenitic stainless steel, either in powders or bulk specimens, has been investigated. The phase transformation is accomplished by means of either ball milling processes (in powders) –dynamic approach– or by uniaxial compression tests (in bulk specimens) –quasi-static approach–. Remarkably, an increase of the strain rate causes opposite effects in each case: (i) it increases the amount of transformed alpha' in ball milling procedures, but (ii) it decreases the amount of alpha' in pressed samples. Both the microstructural changes (e.g., crystallite size refinement, microstrains or type of stacking faults) in the parent gamma phase and the role of the concomitant temperature rise during deformation seem to be responsible for these opposite trends. Furthermore, the results show the correlation between the gamma to alpha' phase transformation and the development of magnetism and enhanced hardness.

Keywords: phase transformation; steel; strain; ball milling; compression

Publ.-Id: 11378

Surface energy and magnetocapacitance of superconductors under electric field bias

Morawetz, K.; Lipavsky, P.; Kolacek, J.; Brandt, E. H.

A superconducting layer exposed to a perpendicular electric field and a parallel magnetic field is considered within the Ginzburg-Landau (GL) approach. The GL equation is solved near the surface and the surface energy is calculated. The nucleation critical field of superconducting state at the surface depends on the magnetic and electric fields. Special consideration is paid to the induced magnetic-field effect cause d by diamagnetic surface currents. The latter effect is strongly dependent on the thickness of the sample . The effective inverse capacitance determines the effective penetration depth. It is found that the capacitance exhibits a jump at the surface critical field. An experiment is suggested for determining the change in the effective capacitance of the layer.

Keywords: Superconducting surfaces; magneto-capacitance

Publ.-Id: 11377

Atomistic simulation of amorphous germanium

Gabriel, A.; Posselt, M.

Electrical doping of Ge is usually performed by ion implantation and subsequent annealing. In many cases ion bombardment leads to formation of an amorphous layer. During annealing the layer recrystallizes by solid-phase epitaxial regrowth. In order to investigate this process by classical molecular dynamics simulations, first of all amorphous Ge with realistic properties must be prepared. This is the subject of the present work. The atomistic simulations use the Stillinger-Weber interatomic potential with a parameter set that yields correct or reasonable structural, thermodynamic and defect properties of diamond-structure Ge. In the first simulation step liquid Ge is prepared. Then, the system is cooled down slowly to 300 K using the method of Luedtke and Landman which was applied to simulate amorphous silicon. Finally, an equilibration at 300 K and zero pressure is performed. The characterization of amorphous Ge obtained in this manner includes density and cohesive energy, radial distribution function and static structure factor, coordination number, bond-angle distribution, distribution of interatomic distances as well as melting temperature and heat of fusion. The simulation results show very good agreement with experimental data and are consistent with previous theoretical investigations.

Keywords: amorphous Germanium; atomistic simulation

  • Poster
    E-MRS 2008 Spring Meeting, Symposium J: Beyond Silicon Technology: Materials and Devices for Post-Si CMOS, 26.-30.05.2008, Strasbourg, France
  • Poster
    9th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2008), 12.-17.10.2008, Beijing, China

Publ.-Id: 11376

Molecular dynamics simulation of solid phase epitaxial regrowth of amorphous Ge layers

Gabriel, A.; Posselt, M.

In Ge the regrowth of an amorphous layer formed by ion implantation occurs in a similar manner as in Si, namely by solid phase epitaxy. In most cases this process takes place in the very first stage of annealing before dopant diffusion and activation. In the present work the solid phase epitaxial regrowth (SPER) is investigated by classical molecular dynamics simulations. The Stillinger-Weber interatomic potential is used with an adapted parameter set that yields correct or reasonable structural, thermodynamic and defect properties of diamond-structure Ge. First of all a realistic atomic system with an amorphous-crystalline interface which is nearly parallel to a {100} plane is prepared and characterized. The properties of the simulated amorphous Ge are compared with experimental and theoretical data and a very good agreement is found. Then, the system is heated to a given temperature and the regrowth of the amorphous layer is monitored by different methods including visualization and statistical analysis. Regrowth velocities are calculated for a wide temperature range and the effective migration barrier is determined. The results are compared to experimental data from literature. During SPER the evolution of the roughness and the morphology of the amorphous-crystalline interface are investigated. In order to improve the physical understanding of SPER the rearrangement of atoms at the amorphous-crystalline interface is studied in detail.

Keywords: Germanium; atomistic simulation; solid phase epitaxy

  • Lecture (Conference)
    E-MRS 2008 Spring Meeting, Symposium J: Beyond Silicon Technology: Materials and Devices for Post-Si CMOS, 26.-30.05.2008, Strasbourg, France
  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM 2008), 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11375

n+ doping of Ge by P or As implantation and flash-lamp annealing

Wündisch, C.; Posselt, M.; Anwand, W.; Schmidt, B.; Grötzschel, R.; Mücklich, A.; Skorupa, W.; Simoen, E.; Clarysse, T.; Satta, A.; Hortenbach, H.; Möller, A.; Pelzing, P.

The increasing interest in Ge as a high mobility substrate has led to numerous investigations on shallow junction formation by ion beam processing. It has been shown that p+ doping yields junctions with the required properties whereas the formation of n+ junctions is complicated by the high diffusivity and the low solubility of the dopants.
The present work is focused on the application of flash-lamp annealing to the formation of shallow n+ layers since this method has the potential of good dopant activation while dopant diffusion is suppressed. Shallow layers with high concentrations of P or As are formed by ion implantation. Then the samples are pre-heated at relatively low temperatures (e.g. 400 °C, for 240 s) in order to achieve the regrowth of the amorphous layer formed during implantation. Subsequently, flash-lamp annealing is performed at 800 and 900 °C, for 0.84, 3 and 20 ms. RBS/C is applied to monitor the regrowth of the amorphous layer. Selected samples are studied by XTEM in order to search for precipitates and end-of-range defects. The depth distributions of P and As are measured by SIMS. The sheet resistance of the shallow n+ layer is obtained by the variable probe spacing method. Spreading resistance profiling is applied to determine the carrier depth profile. Results on phosphorus show that dopant diffusion only occurs at 900 °C for 20 ms whereas the maximum activation is in the order of 4-6x1019 cm-3.

Keywords: Germanium; n-doping; ion implantation; annealing

  • Lecture (Conference)
    E-MRS 2008 Spring Meeting, Symposium J: Beyond Silicon Technology: Materials and Devices for Post-Si CMOS, 26.-30.05.2008, Strasbourg, France
  • Lecture (Conference)
    16th International Conference on Ion Beam Modification of Materials (IBMM 2008), 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11374

Atomistic simulation of solid phase epitaxial regrowth in Si: A critical review

Posselt, M.

During ultra-shallow junction formation, pre-amorphization or dopant implantation may lead to the formation of an amorphous (a-)layer. In the first stage of annealing the solid phase epitaxial regrowth (SPER) of the a-layer takes place. During SPER, redistribution of the dopants occurs, and they are incorporated into crystalline Si (c-Si), either substitutionally or within clusters containing dopant atoms, self-interstitials (Is) and/or vacancies. The SPER process leaves beyond the original a/c interface the end-of-range (EOR) damage which contains an excess of Is. During further annealing, free Is are emitted from the EOR damage and diffuse towards the surface. In this period the diffusion of dopants is considerably enhanced. It is highly desirable to obtain the initial conditions for calculations of dopant diffusion and activation, i.e. the fractions of dopants on substitutional sites and in clusters as well as the cluster morphology, from atomistic simulations of SPER. This work gives a critical review of previous simulations that are based on classical molecular dynamics. It is shown that even for pure Si the experimental regrowth rates cannot be reproduced reasonably well. The main cause for the disagreement is the inaccuracy of the interatomic potentials used. Proposals for physically-based improvements are discussed. They are based on a better description of the amorphous phase using a modified potential, without changing the well-established potential for c-Si.

Keywords: silicon; atomistic simulation; solid phase epitaxy

  • Lecture (Conference)
    E-MRS 2008 Spring Meeting, Symposium I: Front-end junction and contact formation in future Silicon/Germanium based devices, 26.-30.05.2008, Strasbourg, France

Publ.-Id: 11373

Neutron dosimetry study in the region of the support structure of a VVER-1000 type reactor

Borodkin, G.; Khrennikov, N.; Konheiser, J.; Noack, K.

The support structure of a reactor pressure vessel experiences a high mechanical stress during reactor operations. In addition, supposed accident conditions and ferritic steel properties result in a low limiting value for the ductile-to-brittle transition temperature and, therefore, a low maximal irradiation load is permitted for this region compared with others. In case of a VVER-1000 reactor, the same applies to weld #5, which is closely above the support structure. The Russian Reactor Operation Rules lay down that profound analyses of the components integrity have to be regularly done if the neutron fluence above the neutron energy of 0.5 MeV must be expected to accumulate a value greater than 1·1018 n/cm2 during the projected operation time of forty years. Therefore, it was necessary to reliably clarify whether this area of the pressure vessel falls into the category of permanent inspection or not. To this end, highly precise fluence calculations were carried out. Applied codes and nuclear data sets were verified by special neutron activiation measurements, which were done just in the near neighborhood of the support structure and of weld #5. The calculation results show that in certain subareas of both construction elements the neutron fluence will exceed the limiting value if the reactor is nominally operated during the projected life-time.

Keywords: reactor; dosimetry; neutron; fluence; support; VVER-1000; TRAMO; DORT; synthesis method

  • Lecture (Conference)
    13th International Symposium on reactor Dosimetry, 25.-31.05.2008, Alkmaar, Netherlands
  • Contribution to proceedings
    13th International Symposium on Reactor Dosimetry, 25.-31.05.2008, Alkmaar, Netherlands
    Reactor Dosimetry State of the Art 2008, New Jersey London Singapore: World Scientific Publishing Co. Pte. Ltd., 13 978-981-4271-10-3, 688-699

Publ.-Id: 11372

Neutron dosimetry on the full-core first generation VVER-440 aimed at reactor support structure load evaluation

Borodkin, P.; Borodkin, G.; Khrennikov, N.; Konheiser, J.; Noack, K.

Reactor support structures (RSS), especially ferritic steel wall of water tank, of VVER-440 of first generation are non-restorable reactor equipment and their lifetime may restrict plant-life at whole. All operated Russian first generation VVER-440 have a reduced core with dummy assemblies except reactor of Unit 4 of Novovoronezh NPP. In comparison with other reactors, the full-core loading scheme of this reactor provides the highest neutron fluence on the reactor pressure vessel (RPV) and RSS accumulated over design service-life and its prolongation. The radiation load parameters on the RPV and RSS resulted from this core loading scheme should be evaluated by means of precise calculations and validated by ex-vessel neutron dosimetry to provide the reliable assessment of embrittlement parameters of these reactor components. The results of different types of calculations and their comparison with measured data have been analyzed in this paper. The calculational analysis of RSS fluence rate variation in dependence on core loading scheme, including standard and low leakage core as well as dummy assemblies, has been presented in paper.

Keywords: reactor; dosimetry; neutron; fluence; support; VVER-440; TRAMO; DORT; synthesis method

  • Lecture (Conference)
    13th International Symposium on Reactor Dosimetry, 25.-31.05.2008, Alkmaar, Netherlands
  • Contribution to proceedings
    13th International Symposium on Reactor Dosimetry, 25.-31.05.2008, Alkmaar, Netherlands
    Reactor Dosimetry State of the Art 2008, New Jersey London Singapore: World Scientific Publishing Co. Pte. Ltd., 13 978-981-4271-10-3, 300-309

Publ.-Id: 11371

Investigation of the beltline welding seam of the Greifswald WWER-440 unit 1 reactor pressure vessel

Viehrig, H.-W.; Schuhknecht, J.; Rindelhardt, U.; Weiss, F.-P.

The investigation of reactor pressure vessel (RPV) materials from decommissioned NPPs offers the unique opportunity to scrutinize the irradiation behaviour under real conditions. Material samples taken from the RPV wall enable a comprehensive material characterisation. The paper describes the investigation of trepans taken from the decommissioned WWER-440 1st generation RPVs of the Greifswald NPP. The Greifswald RPVs represent different material conditions such as irradiated (I), irradiated and recovery annealed (IA) and irradiated, recovery annealed and re-irradiated (IAI). The working program is focussed on the characterisation of the RPV steels (base and weld metal) through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the ASTM Test Standard E1921-05 to determine the fracture toughness of the RPV steel in different thickness locations.
In a first step the trepan taken from the RPV Greifswald Unit 1 containing the X-butt multilayer submerged welding seam located in the beltline region was investigated. This welding seam represents the IAI condition. It is shown that the Master Curve approach as adopted in ASTM E1921 is applicable to the investigated original WWER-440 weld metal. The evaluated T0 varies through the thickness of the welding seam. After an initial increase of T0 from 10°C at the inner surface to 49°C at 22 mm distance from it, T0 again decreases to 41°C at a distance of 70 mm, finally increasing again to maximum 20°C towards the outer RPV wall. The lowest T0 value was measured in the root region of the welding seam representing a uniform fine grain ferritic structure. Beyond the welding root T0 shows a wavelike behaviour with a span of about 50 K. The highest T0 of the weld seam was not measured at the inner wall surface. This is important for the assessment of ductile-to-brittle temperatures measured on sub size Charpy specimens made of weld metal compact samples removed from the inner RPV wall. Our findings imply that these samples do not represent the most conservative condition. Nevertheless, the Charpy transition temperature TT41J estimated with results of sub size specimens after the recovery annealing was confirmed by the testing of standard Charpy V-notch specimens.

Keywords: Russian WWER-type reactor; reactor pressure vessel steel; weld metal; trepans; fracture toughness; Master Curve

  • Journal of ASTM International 6(2009)5
  • Lecture (Conference)
    24th Symposium on Effects of Radiation on Nuclear Materials and the Nuclear Fuel Cycle, 24.-26.06.2008, Denver, United States

Publ.-Id: 11370

Homotopic Arnold tongues deformation of the MHD α2-dynamo

Günther, U.; Kirillov, O.

We consider a mean-field α2-dynamo with helical turbulence parameter α(r)=α0+γΔα(r) and a boundary homotopy with parameter β ∈[0,1] interpolating between Dirichlet (idealized, β=0) and Robin (physically realistic, β=1) boundary conditions. It is shown that the zones of oscillatory solutions at β=1 end up at the diabolical points for β=0 under the homotopic deformation. The underlying network of the diabolical points for β=0 substantially determines the choreography of eigenvalues and thus the character of the dynamo instability for β=1. Using perturbation theory we derive the first-order approximations to the resonance (Arnold's) tongues in the (α0,β,γ)-space, which turn out to be cones in the vicinity of the diabolical points, selected by the Fourier coefficients of Δα(r). The space orientation of the 3D tongues is determined by the Krein signature of the modes involved in the diabolical crossings at the apexes of the cones. The Krein space induced geometry of the resonance zones explains the subtleties in finding α-profiles leading to oscillatory dynamos, and it explicitly predicts the locations of the spectral exceptional points, which are important ingredients in the recent theories of polarity reversals of the geomagnetic field.

Keywords: MHD dynamo; operator theory; Krein space; exceptional point; diabolical point; perturbation theory; spectral mesh; homotopy; Arnold tongue; field reversal

  • Open Access Logo Proceedings in Applied Mathematics and Mechanics 8(2008), 10719-10720
    DOI: 10.1002/pamm.200810719
    ISSN: 1617-7061

Publ.-Id: 11369

Quantum Chemical Calculations of the Redox Potential of the Pu(VII)/Pu(VIII) Couple

Tsushima, S.

The redox potential of the Pu(VII)/Pu(VIII) couple was studied by density functional theory calculations. The spin-orbit effect was corrected at the CASSCF level. The redox potential (relative to the standard hydrogen potential) of the Pu(VII)/Pu(VIII) couple in alkaline solution was found to vary from 4.36 to 1.06 V depending on the number of Pu-O oxo bonds, coordination numbers, and coordination modes. The redox potential drops substantially as the number of Pu-O oxo bonds increases. Pu(VIII) may be synthesized in strong alkaline solution assuming that both Pu(VII) and Pu(VIII) exist in penta-oxo form, PuVIIO5OH4- and PuVIIIO5OH3-, respectively. The Mulliken population of Pu in Pu(VII) and Pu(VIII) complexes are very similar, suggesting that the spin-orbit effect is rather small in Pu(VII) complexes and that when Pu(VII) is oxidized to Pu(VIII) the electron is stripped mainly from the ligand. Consequently, Pu(VIII) is in an unstable oxidation state and easily reduced back to Pu(VII) by the solvent water molecules. In acidic medium, the Pu(VII)/Pu(VIII) redox potential is too high to get the Pu(VIII) valence state.

Publ.-Id: 11368

A hybrid finite volume -- boundary element method (FV-BEM) for the numerical solution of the kinematic induction equation.

Giesecke, A.; Stefani, F.; Gerbeth, G.

The experimental realization of dynamo excitation as well as theoretical and numerical examinations of the induction equation have shown the relevance of boundary conditions and material properties for a self-sustaining dynamo.

Laboratory (insulating) boundary conditions in non-spherical geometry, in general, are treated by elaborated schemes (e.g. solving of the Laplace equation in an extended domain) or by simplifying approximations (pseudo vacuum, vanishing tangential field).

Rather precise results for the numerical solution of the kinematic induction equation are provided by the integral equation approach which also considers insulating boundary conditions exactly.

However, the application possibilities are limited because of enormous computational resources that are required by this method.
In particular in the context of inverse problems -- e.g. estimation of the velocity structure from measurements of induced electric and/or magnetic fields -- solving the forward model turned out to be the most time consuming part.

Therefore, a more flexible approach utilizing a local discretization like the constraint transport (CT) method as a well known realization of a finite volume scheme (FV) is adopted for solving the induction equation. The CT-scheme ensures a fast, robust and accurate solution of the kinematic dynamo problem and intrinsically maintains the solenoidal character of the magnetic field.
Within the framework of the finite volume scheme insulator boundary conditions are treated by a modified integral equation procedure,
commonly known as the boundary element method (BEM).

On the boundaries the magnetic flux density B can be expressed as the gradient of a scalar potential B=-\nabla \Phi, where Phi is
described by a Laplace equation: $\Delta Phi = 0$. Integrating the Laplace equation only on the boundaries requires less computational
power than the full integral equation approach.

Combining both methods in a hybrid FV-BEM scheme offers the flexibility of a local discretization with a stringent treatment of insulating magnetic boundary conditions in almost arbitrary geometries.

The fast and easy to handle algorithm exhibits further advantages when considering spatial varying material properties like electrical conductivity of container walls or localized high-permeability material. Discontinuities of material coefficients are treated within the framework of the FV-BEM scheme under utilization of appropriate averaging procedures for the permeability/conductivity on the contact interfaces which ensures that the corresponding jump conditions for the magnetic flux density B and/or the electric field E are fulfilled.

Several test computations with prescribed alpha-effect or velocity distribution reproduce well known key results and demonstrate the applicability and reliability of the approach. Future examinations are intended to understand the behavior of the VKS-dynamo experiment where the field producing flow is driven by ferrous propellers and the dynamo mechanism probably is strongly influenced by this high permeability material. Indeed, preliminary results including ferromagnetic material inside the computational domain show a certain reduction in the critical magnetic Reynolds number Rm=LV/eta but, up till now, they cannot explain the dominating axisymmetric field mode that is observed in the experiment. Other applications of the hybrid scheme may also be important for the
evaluation of forthcoming dynamo experiments for which a precise knowledge of the critical magnetic Reynolds number is essential. Finally, the method is of interest for the treatment of inverse problems in industrial applications like estimation of the liquid metal flow in continuous casting from measurements of induced magnetic fields via contactless inductive flow tomography.

Keywords: induction equation; boundary conditions; permeability discontinuity; computing methods

  • Lecture (Conference)
    8th. World Congress on Computational Mechanics (WCCM8) / 5th. European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2008), 29.06.-04.07.2008, Venedig, Italy

Publ.-Id: 11367

Aqueous Suspensions of Carbon Nanotubes: Surface Oxidation, Colloidal Stability and Uranium Sorption

Schierz, A.; Zänker, H.

Our study is aimed at gaining information on the behaviour of carbon nanotubes (CNTs) as potential carriers of pollutants in the case of accidental CNT release to the environment and on the properties of CNTs as a potential adsorbent material in water purification. The effects of acid treatment of CNTs on (i) the surface properties, (ii) the colloidal stability and (iii) heavy metal sorption are investigated, the latter being exemplified by uranium(VI) sorption. There is a pronounced influence of surface treatment on the behaviour of the CNTs in aqueous suspension. Results showed that the acid treatment increases the amount of acidic surface groups on the CNTs. Acid treatment has a great impact on the colloidal stability of the CNTs and on their adsorption capacity for U(VI). Furthermore, pristine CNT colloids can be stabilised by the addition of humic acid.

Keywords: carbon nanotube; surface oxidation; uranium; sorption; colloidal stability

Publ.-Id: 11366

Fraktografische Untersuchungen an unbestrahlten und bestrahlten Reaktordruckbehälterstählen

Müller, G.

Der Druckbehälter eines Kernkraftwerkes ist von herausragender sicherheitstechnischer Bedeutung. Während des Betriebes eines Kernkraftwerkes kommt es zur Verschlechterung der mechanischen Eigenschaften des Reaktordruckbehälterstahls infolge der Strahlenbelastung - das Material altert.
Das Institut für Sicherheitsforschung im Forschungszentrum Dresden – Rossendorf besitzt die Kompetenz, mikrostrukturelle und bruchmechanische Untersuchungen an bestrahlten Werkstoffen durchzuführen sowie die thermomechanische Beanspruchung von Bauteilen zu bestimmen mit dem Ziel, die Integrität von Reaktorkomponenten zu beurteilen.
Bei der bruchmechanischen Charakterisierung des Zähigkeitsverhaltens der Reak-tordruckbehälterstähle werden dynamische und quasistatische Kennwerte ermittelt und unter Anwendung statistischer Methoden nach dem Master-Curve-Konzept ausgewertet. Die fraktografischen Untersuchungen der Bruchflächen der geprüften Pro-ben mit dem Rasterelektronenmikroskop dienen zusätzlich der Interpretation und Absicherung der ermittelten Bruchzähigkeitswerte. Insbesondere die Charakterisierung der Bruchtypen, der Rissfrontverlauf, die Ausbildung einer Stretchzone, Rissinitiierungspunkte sowie Besonderheiten auf der Bruchfläche stehen im Mittelpunkt der des Interesses. Da bestrahlte oder radioaktiv kontaminierte Proben nicht unmittelbar im REM untersucht werden können, kommt hierfür eine speziell entwickelte Abdrucktechnik zur Anwendung. Die Abdrücke sind kontaminationsfrei und detailgenau, die Methode muss in einer Heißen Zelle praktikabel sein.
Für die REM- und EDX- Untersuchungen wird ein Zeiss EVO 50 mit einem Bruker Leichtelement-X-Flash-Detektor 4010 verwendet.

  • Invited lecture (Conferences)
    Multi Purpose SEM User Meeting 2008, 02.-03.06.2008, Jena, Deutschland

Publ.-Id: 11365

The tunable-frequency ESR as a tool to study magnetic excitations in highly-correlated spin systems

Zvyagin, S. A.

es hat kein Abstrakt vorgelegen.

  • Invited lecture (Conferences)
    Annual Meeting at the Grenoble High Magnetic Field Laboratory, 13.-17.05.2008, Grenoble, Frankreich

Publ.-Id: 11364

Neuartige Impedanzsensoren für die Visualisierung von Mehrphasenströmungen

Da Silva, M. J.; Hampel, U.

In diesem Beitrag werden zwei neuartige, bildgebende Messverfahren zur Untersuchung von Mehrphasenströmungen vorgestellt. Beide Messverfahren basieren auf der mehrkanaligen Messung der elektrischen Impedanz eines strömenden Fluides. Sie sind in der Lage, zeitlich und räumlich hoch aufgelöste Bilder der Phasenverteilung einer Mehrphasenströmung zu erzeugen. Weiterhin werden im Beitrag die neuen Sensoren messtechnisch bewertet (Messgenauigkeit, Zeitverhalten, etc.) und es werden ausgewählte Beispiele aus der Strömungsdiagnostik präsentiert.

Keywords: multiphase flow; electrical impedance; flow visualization

  • Contribution to proceedings
    XXII. Messtechnisches Symposium, 11.-13.09.2008, Dresden, Germany
    Tagungsband XXII. Messtechnisches Symposium, Aachen: Shaker, 978-3-8322-7506-8, 25-34
  • Lecture (Conference)
    XXII. Messtechnisches Symposium, 11.-13.09.2008, Dresden, Germany

Publ.-Id: 11363

Synthesis and spectroscopic analysis of uranyl sugar complexes

Steudtner, R.

The bonding of uranium with glucose and alpha cyclodextrin were investigated by time resolved laser fluorescence spectroscopy (TRLFS), attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) and confocal laser scanning microscopy (CLSM). Two different uranyl-sugar complexes could be synthesized. Both complexes show a strong fluorescence signal by excitation with 266 nm. The emission maxima were detected at 497 nm for the uranyl-glucose complex and 494 nm for the uranyl-alpha-cyclodextrin complex respectively. The time resolved investigations show a fluorescence lifetime of 36 µs for the uranyl-glucose complex and 37 µs for the uranyl-alpha-cyclodextrin complex.

Keywords: Uranyl; Sugar; TRLFS; ATR-FTIR; CLSM

  • Lecture (Conference)
    5th SUPRAPHONE/4th WG Meeting COST D31, 29.-31.05.2008, Prague, Czech Republic

Publ.-Id: 11362

Thermophysical properties of Al-Cu and Al-Si liquid alloys

Plevachuk, Y.; Sklyarchuk, V.; Yakymovych, A.; Gerbeth, G.; Eckert, S.; Willers, B.; Eigenfeld, K.

New workable aluminium-based light alloys are a key issue in current materials science. Al-Cu alloys, for instance AlCu4TiMg (A356), are the most utilized casting alloys in the aluminium industry. The distinctive characteristics of these alloys are low density, high melting temperature, good thermal conductivity and excellent oxidation resistance. Al-Cu alloys are ubiquitous in technical applications: they are the main components for screw machine products, truck frames, aircraft structures, jet engine impellers and aircraft engine cylinder heads. Moreover, binary Al-Cu alloys are in the focus of numerous, academic studies which are especially concerned with solidification processes and consider for instance, the columnar-to equiaxed transition, the formation of macrosegregation zones, the visualization of the dendritic growth, the impact of melt convection or the application of electromagnetic stirring. The solidification process of a liquid alloy has a profound impact on the structure and properties of the solid material. Therefore, the knowledge of the physical properties of the molten alloys prior to solidification becomes very important for the development of materials with predetermined characteristics.
Aluminium alloy castings have achieved wide usage in automobile, aerospace and other applications because of their high strength to weight ratio. Al–Si–Mg alloys, a group of heat treatable cast Al–Si alloys, exhibit good castability and corrosion resistance in addition to high strength to weight ratio. However, the pursuit of high quality castings with consistent mechanical properties depends upon the proper processing of the alloy, including grain refinement, modification and precipitation heat treatment, etc.
Among all physical properties, the structure-sensitive characteristics of the liquid phase play a prominent role. The density is directly related to the atomic structure and potential short range order of the liquid; on the other hand, it is a fundamental quantity for all technological applications, since it determines fundamental non-dimensional parameters characterising the fluid flow, such as the Reynolds or the Rayleigh number. Reliable information about the structural heterogeneity of the melt can be also obtained from studies considering the temperature dependence of the electrical conductivity and the viscosity. The knowledge of the viscosity is of particular importance considering the relationship between melt convection and solidification.
In that paper we present data of the thermophysical properties of Al-Cu liquid alloys (Al96Cu4, Al80Cu20, Al70Cu30, and AlCu4TiMg in wt.%) and Al-Si liquid alloys (AlSi7, AlSi7Mg, AlSi8Cu3), namely density, viscosity and electrical conductivity. The measurements cover a wide temperature range above the liquidus. The anomalies with respect to the concentration dependence of the electrical conductivity in some Al-Cu alloys are explained in terms of the s–d hybridization model. A comparison with data and scaling relations available in literature is given.

  • Lecture (Conference)
    18th European Conference on Thermophysical Properties, 01.-04.09.2008, Pau, France

Publ.-Id: 11361

Capacitance planar array sensor for fast multiphase flow imaging

Thiele, S.; Da Silva, M. J.; Hampel, U.

In this paper, we introduce a novel planar array sensor based on electrical capacitance (permittivity) measurements to visualize flows of multiphase mixtures along the surface of objects. The prototype sensor is formed by 32 × 32 interdigital sensing structures. It can be mounted onto the wall of pipes or vessels and thus has minimal influence on the flow. An associated electronics measures the capacitance of the fluid at each sensing structure in a multiplexed manner at high sampling rate. This way, images of the fluid distribution are produced. The electronics is able to generate up to 15,000 images per second. Results of system evaluation and results of two exemplary flow experiments are presented and discussed.

Keywords: interdigital electrodes; permittivity measurement; flow visualization; multiphase flow

Publ.-Id: 11360

The origin of the Energy-Dose window in SIMOX processing and defect engeneering

Ou, X.; Kögler, R.; Skorupa, W.; Möller, W.; Wang, X.; Rauschenbach, B.

The excess of implantation-induced point defects controls the oxygen redistribution in silicon during a high-temperature treatment such as in SIMOX (Separation-by-IMplanted-Oxygen). The Energy-Dose window for the formation of a perfect homogeneous and planar buried oxide layer is caused by excess point defects. Quantitative relations are given between the distribution of the initially generated excess defects and the finally formed oxide layer. Different methods of defect engineering by vacancy introduction via He implantation are discussed.

Keywords: Implantation defects; SIMOX; Cavities; Silicon; Oxygen

  • Lecture (Conference)
    European Materials Research Society Conference, 25.-30.05.2008, Strasbourg, France

Publ.-Id: 11359

The role of implantation-induced point defects for the redistribution of oxygen in silicon at high-temperature processing

Kögler, R.; Ou, X.; Skorupa, W.; Möller, W.

The excess of implantation-induced point defects controls the oxygen redistribution in silicon during a high-temperature treatment such as in SIMOX (Separation-by-IMplanted-Oxygen). The Energy-Dose window for the formation of a perfect homogeneous and planar buried oxide layer is caused by excess point defects. Quantitative relations are given between the distribution of the initially generated excess defects and the finally formed oxide layer. Moreover, implantation-induced defects can explain the depth positions of different oxide precipitate layers and of silicon islands inside the oxide layer. Other defects, e.g. dislocations, which form during thermal treatment, can relocate the Energy-Dose window towards lower oxygen dose.

Keywords: Implantation defects; SIMOX; Silicon; Oxygen

Publ.-Id: 11358

Binding properties between ferroic oxides and metals

Pankoke, V.; Gemming, S.

The structural parameters and the electronic structure of palladium films with different thickness on the piezo-electric ceramic PbMg{1/3}Nb{2/3}O3 (PMN) were studied. The calculations were performed using density functional theory in the local density approximation. Binding properties were examined via total energies differences and densities of states for the different metal/ceramic interfaces.
The Pd films are located on top of the O atoms of the NbO_2 terminated (100) PMN surface and have an fcc structure as the bulk Pd.
Local bonding at the interface can be characterized in terms of overlapping electron densities of the contributing atoms. Furthermore the rearrangement of the electron density at the interface is discussed.

Keywords: PMN; Pd; interfaces; thin films

  • European Physical Journal B 67(2009)1, 57-62

Publ.-Id: 11357

Radioaktiv markierte Kern-Hüll-Nanopartikel auf der Basis von Stärke-umhülltem Magnetit

Matterna, M.

kein Abstract verfügbar

  • Lecture (others)
    Seminar, Universität Jena, Institut für Diagnostische und Interventionelle Radiologie, 14.04.2008, Jena, Deutschland

Publ.-Id: 11356

Diagnostik und Therapie mit radioaktiven Substanzen

Stephan, H.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Hochschule Zittau/Görlitz (FH), 22.05.2008, Zittau, Deutschland

Publ.-Id: 11355

18F-radiolabeled S100 proteins as potential probes for molecular imaging of inflammatory processes in vivo

Hoppmann, S.; Richter, S.; Pietzsch, J.

Interaction of certain extracellular S100 proteins with the receptor for advanced glycation endproducts (RAGE) is considered to play a crucial role in various inflammatory diseases. However, data concerning the interaction of circulating S100 proteins with RAGE in inflammatory processes in vivo are scarce. One reason is the shortage of suitable radiotracer methods. To address this question, we report a novel methodology using recombinant human S100A1, S100B, and S100A12 for radiolabeling with the positron emitter fluorine-18 (18F) and the use of 18F-S100 proteins in cell association assays in vitro and in dynamic small animal positron emission tomography (PET) studies in Wistar rats in vivo. Human S100 proteins were cloned in the bacterial expression vector pGEX-6P-1, expressed in E. coli BL21, and purified. Purified S100 proteins were radiolabeled with N-succinimidyl-4-[18F]fluorobenzoate. Cellular association studies in human THP-1 macrophages and human aortic endothelial cells (HAEC) showed specific binding of all 18F-S100 proteins to the non-internalizing RAGE as confirmed by inhibitory effects exerted either by other RAGE ligands, e.g., glycated LDL, or by soluble RAGE. Of interest, uptake of 18F-S100 proteins in THP-1 and HAEC mediated by various scavenger receptors was observed. The in vitro data are consistent with in vivo PET data showing a pronounced temporary association of 18F-S100 proteins with tissues expressing RAGE, e.g., lung and vessels. Moreover, a significant accumulation of 18F-S100 proteins in tissues that are rich in cells expressing scavenger receptors (tissue macrophages) such as liver and spleen was observed. In conclusion, 18F-labeling of S100 proteins and the use of small animal PET provide a valuable tool to discriminate the kinetics and the metabolic fate of S100 proteins in vivo. Furthermore, the approach provides novel probes for imaging of RAGE-ligand interaction in inflammatory processes, e.g., in rodent models of disease.

  • Poster
    5th International EDHF Symposium - Endothelium, Vasoactive Factors and Inflammation, 24.-27.06.2008, Tampere, Finland
  • Abstract in refereed journal
    Basic & Clinical Pharmacology & Toxicology 102(2008)S1, 49
    ISSN: 1742-7835

Publ.-Id: 11354

Labelling methods in (PET-)Radiopharmacy: Do we need alternatives?

Steinbach, J.

Labelling of molecules was introduced by Georg von Hevesy already decades ago utilizing radiophosphorus. With the availability of C-14 and H-3 a long period of isotopic labelling started in the fifties of the last century following Rudolf Schönheimer´s idea to label biomolecules with deuterium. This was the scientific base of the modern biochemistry enabling detailed study of metabolism and of modern pharmacokinetics. With the use of radioiodine fur human investigations and therapy the era of Nuclear Medicine began during that time.
All these applications require different labelling techniques for the radiotracer synthesis. Most of them have been derived from organic microchemistry and have been further developed for the special radiochemical conditions such as radiation protection and the limited amount of substance matter.
The introduction of radiometals to Nuclear Medicine, first of all Tc-99m, opened a new challenge. This was the need to mimic organic molecules by coordination compounds – utilizing knowledge from inorganic, organic and radiochemistry.
At the end of the seventies the Positron Emission Tomography came into the focus of science and later on of medicine. Completely new methods had to be developed due to the application of the no carrier added positron emitting radionuclides in connection with their short half lifes first of all for F-18 and C-11.

Nowadays thousands of compounds have been labelled – organic and inorganic. Hundreds of methods have been developed to introduce e.g. carbon isotopes, radiohalogens and radiometals into the desired positions of molecules comprising a wide variety of substance classes.
Have we reached a saturation of demand for labelling methods?
Of course – for small molecules the requirements for real new developments may be limited. But new demands are at the horizon: This are biomacromolecules such as proteins, peptides, oligonucleotides which are sensitive to the “classic” conditions of chemical reactions. Other problems are connected with the need for regioselective, site specific labelling.
There is and will be done a lot of work – also in the future for applied purposes.

  • Invited lecture (Conferences)
    15th Workshop "The Synthesis and Applications of Isotopes and Isotopically Labelled Compounds", 12.-13.06.2008, Bad Soden, Deutschland
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)7, 257
    ISSN: 0362-4803

Publ.-Id: 11352

Retrospective dosimetry study at the RPV of NPP Greifswald unit 1

Konheiser, J.; Mittag, S.; Noack, K.; Rindelhardt, U.; Borodkin, G.; Borodkin, P.; Gleisberg, B.

For the first time, trepans from a decommissioned VVER-440 (Greifswald-1) reactor pressure vessel (RPV) have been examined. Activities of a trepan, taken at the RPV weld with the highest fast-neutron load, were measured and estimated on the basis of fluence calculations by the codes TRAMO and DORT. A maximum fluence of 4.05*1019 n/cm2 (E>0.5 MeV) was calculated. The average deviation between the two codes is 2.6 %. Activities resulting from the reaction 93Nb(n,n’)93mNb were measured, niobium being a trace element in the RPV steel. Unfortunately, 93mNb is also produced by neutron capture in the alloy component 92Mo, the built-up 93Mo decaying by electron capture. The ratios of calculated to measured (C/E) 93mNb gamma activities for several trepan samples are between 0.42 and 0.97. The fact that all C/E ratios are below unity suggests that the measured values may have been additionally heightened by activities from other nuclides.

Keywords: reactor; retrospective dosimetry; neutron; fluence; VVER-440; TRAMO; Greifswald

  • Lecture (Conference)
    13th International Symposium on reactor Dosimetry, 25.-31.05.2008, Alkmaar, Netherlands
  • Contribution to proceedings
    13th International Symposium on Reactor Dosimetry, 25.-31.05.2008, JRC Petten, Netherlands
    Reactor Dosimetry State of the Art 2008, New Jersey London Singapore: World Scientific Publishing Co. Pte. Ltd., 13 978-981-4271-10-3, 23-33

Publ.-Id: 11351

Mass occurrence of penetrative trace fossils in triassic lake deposits (Madygen mossil site, Kyrgyzstan, Central Asia)

Voigt, S.; Hoppe, D.

Bioturbation and the breakdown of organic detritus by burrowing macro-invertebrates are key factors for the energy flow in recent freshwater ecosystems due to the acceleration of nutrient cycling. According to the current state of knowledge, food webs similar to those ones of modern lakes were not operating until the Late Mesozoic, when a well-established freshwater infauna evolved. Here we describe laterally extended networks of irregularly branched burrows that constitute the most common ichnofossils in lacustrine deposits of the Middle to Late Triassic Madygen Formation, SW Kyrgyzstan. The shallow penetrative trace fossils assigned to Thalassinoides paradoxicus (Woodward, 1830) give evidence that underground exploitation of lake-bottom sediments by benthic invertebrates set up in the Early Mesozoic at the latest. Architecture and size of the fossil burrows indicate deposit-feeding, worm-like trace makers of similar morphology and behaviour to extant oligochaetes or aquatic insect larvae. Maximum intensity of bioturbation is recorded in mudstones of the transitional sublittoral to profundal lake zone which usually represents the thermocline/chemocline level in modern stratified lakes. Taking into account the low-oxygen tolerance of many recent oligochaetes and insect larvae we propose, that ecospace utilisation of deep-water lacustrine settings was originally impelled by two things: exploitation of additional food resources and avoidance of predation by carnivorous animals from well-aerated lake zones. Spatial restriction of the described fossil traces could offer a basic approach to subdivide the Mermia ichnofacies.

Keywords: Thalassinoides; bioturbation; Mermia ichnofacies; oligochaeta; insect larvae

Publ.-Id: 11350

Quality check of wire-mesh sensor measurements in a vertical air/water flow

Beyer, M.; Lucas, D.; Kussin, J.

Extensive measurements were executed for a vertical upward air/water flow to gen-erate a high-quality database for the development and validation of CFD-Codes for two-phase flows (e.g. for models on bubble forces or on coalescence and break-up). Thereto, in a pipe with a nominal diameter of 200 mm, the wire-mesh sensor technology was used. The present paper aims on the assessment of errors caused by the experimental procedure and especially global errors arising from the use of the wire-mesh sensor technology. Special attention was paid to the plausibility and accuracy of the data regarding the evolution of the vertical multiphase flow. In the result, a clear and consistent trend regarding their evolution with increasing distance from the position of the gas injection was found. Comparisons of the trend of time and cross-section averaged gas volume fraction along the pipe height with the theoretically expected values were carried out. From the measured radial profiles of the void fraction and the velocity of the gas phase, the superficial gas velocity at the wire-mesh sensor integrated over the cross-section is calculated and compared with the set value. Thus, a general error assessment of the sensor data is possible.

Keywords: multiphase flow; bubbly flow; bubble size distribution; wire-mesh sensor; accuracy check; drift velocity

Publ.-Id: 11349

Defect formation in Mn-implanted silicon probed by frequency and temperature dependent capacitance measurements on MOS capacitors

Zhou, S.; Bürger, D.; Beyer, V.; Schmidt, B.; Helm, M.; Schmidt, H.

In order to obtain magnetic Si the doping of it by Mn is one of the topics in this field. This opens the possibility to fabricate Si-based spintronic devices. Most of the research activities focused on material science, e.g. reporting higher Curie temperatures, and on characterizing their structural properties. However exploring the electrical properties after Mn doping is also important, so that the knowledge can be directly transferred to spintronic device fabrication. In these devices, an MIS (metal-insulator-semiconductor) structure is usually used and a high-quality oxide-semiconductor interface is therefore highly demanded. In this contribution, we investigate the defects in Si and in the interface between SiO2 and Si after the doping by Mn implantation into both p-type and n-type Si wafers. The implantation energy was 60 keV with a fluence of 2×10^15 cm^-2, resulting in a peak concentration of 5×10^20 cm^-3. A 15 nm thick SiO2 layer was grown during subsequent thermal oxidation at 900 °C. After this thermal treatment, the Mn atoms are solved in the Si wafer and partially in the SiO2 layer. Additionally, Mn in the region of the implanted profile with a nominal concentration above the solubility limit causes the formation of Mn-silicide nanoparticles [1]. The quality of SiO2/Si interface was checked by frequency dependent CV measurements. A large amount of defects was found at the SiO2/implanted-Si interface. Temperature dependent capacitance transient measurements reveal the formation of deep traps in the implanted Si, with energies of EV+0.54 eV, EV+0.41 eV in p-Si, and EC-0.57 eV, EC-0.23 eV, EC-0.11 eV in n-Si, respectively. All these electrical defects have to be considered when fabricating transition metal/SiO2/Mn-implanted Si structures for spin-dependent tunnelling devices.

[1] Shengqiang Zhou et al., Phys. Rev. B 75, 085203 (2007)

Keywords: Si; Mn; Ion implantation; DLTS

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.08, Dresden, Germany

Publ.-Id: 11348

Ferromagnetic transition metal implanted ZnO: a diluted magnetic semiconductor?

Zhou, S.; Potzger, K.; Xu, Q.; Lorenz, M.; Skorupa, W.; Helm, M.; Fassbender, J.; Grundmann, M.; Schmidt, H.

Traditional electronics can be greatly stimulated by a combination of magnetic and semiconducting properties where spins provide an additional degree of freedom. Recently theoretical works predict that some semiconductors (e.g. ZnO) doped with transition metal are diluted magnetic semiconductors (DMS) [1]. In binary DMS materials, transition metal ions substitute cation sites of the host semiconductor and are coupled by free carriers resulting in ferromagnetism. One of the main obstacles in creating DMS materials is the formation of secondary phases because of the solid-solubility limit. Ion implantation is a non-equilibrium method, and has been successfully used to create GaAs-based DMS [2]. In our study transition metal ions were implanted into ZnO single crystals with the peak concentrations of 0.5-10 at.%. We established a correlation between structural and magnetic properties. By synchrotron radiation X-ray diffraction secondary phases (Fe, Ni, Co and ferrite nanocrystals) were observed and have been identified as the source for ferromagnetism [3-6]. Due to their different crystallographic orientation with respect to the host crystal these nanocrystals in some cases are very difficult to be detected by a simple Bragg-Brentano scan. This results in the pitfall of using XRD to exclude secondary phase formation in DMS materials. For comparison, the solubility of Co diluted in ZnO films amounts to 10 at.% using pulsed laser deposition (PLD) [7]. Such diluted, Co-doped ZnO films show paramagnetic behaviour. However, only the magnetoresistance of Co-doped ZnO films reveals possible s-d exchange interaction as compared to Co-implanted ZnO single crystals.
[1] T. Dietl, et al., Science 2000; 287:1019.
[2] M. A. Scarpulla, et al, Appl. Phys. Lett. 2003; 82:1251.
[3] K. Potzger, et al., Appl. Phys. Lett. 2006; 88 :052508.
[4] Shengqiang Zhou, et al., J. Appl. Phys. 2008; 103:023902.
[5] Shengqiang Zhou, et al., Phys. Rev. B 2008 ; 77:035209.
[6] Qingyu Xu, et al., Phys. Rev. B 2006; 73:205342.

Keywords: ZnO; diluted magnetic semiconductor; Magnetic nanoparticles; Magnetoresistance

  • Invited lecture (Conferences)
    VII-th International Conference on Ion Implantation and other Applications of Ions and Electrons, 16.-19.06.08, Kazimierz Dolny, Poland
  • Vacuum 83(2009), S13

Publ.-Id: 11347

High-Transmission Planar X-ray Waveguides

Salditt, T.; Krüger, S. P.; Fuhse, C.; Bähtz, C.

We have studied the propagation of hard x rays in a planar x-ray waveguide with a sub-20 nm guiding layer. To optimize the transmission and to minimize absorption losses, a novel waveguide design based on a two-component cladding was implemented. Optimized transmission is achieved by placing an appropriate interlayer between the cladding and the guiding core. The experimental results along with simulations of field propagation show that high transmission values can be obtained in waveguide optics at parameters relevant for x-ray imaging. These are small beam diameters below 20 nm and the relatively long guiding length necessary for efficient blocking of multi-keV photon energy beams.

Keywords: X-ray optics; X-ray imaging; X-ray scattering

Publ.-Id: 11346

Model experiments on macroscopic thermoelectromagnetic convection

Zhang, X.; Cramer, A.; Lange, A.; Gerbeth, G.

The interaction between a thermoelectric current and an imposed magnetic field may produce thermoelectromagnetic convection (TEMC). In the present paper, an experimental study on TEMC in a generic configuration is reported. While the necessary temperature gradient grad T in a square box was accomplished by heating and cooling of two opposing side walls, respectively, utilising a massive nickel plate for the bottom of the electrically conducting container established a material discontinuity with respect to the liquid metal layer. In first place, such a jump in the related Seebeck coefficient non-parallel to grad T is a pre-requisite for the existence of a thermoelectric current. The second condition for TEMC, which is a non-vanishing curl of the Lorentz force, was fulfilled with a permanent magnet producing an inhomogeneous magnetic field. Ultrasonic Doppler velocimetry was used to quantify the TEMC flow field. The measurements demonstrate that even a moderate temperature difference can produce distinct convection. Locating the magnet, the direction of magnetization of which was parallel to grad T, close to either side wall produced a single vortex spreading throughout the entire box. Moving the magnet to the center led to a modified distribution of the magnetic field, which, in turn, altered the flow structure. A convective pattern consisting of four vortices developed and the velocity fluctuations were intensified. The numerical results for the distribution of the magnetic field in presence of the ferromagnetic bottom support the experimental findings.

  • Magnetohydrodynamics 45(2009), 25-42

Publ.-Id: 11345

Electromagnetic stirring with superimposed travelling and rotating magnetic fields.

Cramer, A.; Pal, J.; Gerbeth, G.

Velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating (RMF) and a travelling magnetic field (TMF). The combination of both fields gives rise to an inherent three-dimensional constituent of the electromagnetic force distribution, which implies an intense mixing of the melt.

  • Lecture (Conference)
    XVI International Congress on Electricity applications in modern world - UIE'08, 19.-21.05.2008, Krakow, Poland
  • Contribution to proceedings
    XVI International Congress on Electricity applications in modern world - UIE'08, 19.-21.05.2008, Krakow, Poland, 83-88415-80-8, 41-42

Publ.-Id: 11344

DNA double-strand break signalling: X-ray energy dependence of residual co- localised foci of -H2AX and 53BP1

Beyreuther, E.; Lessmann, E.; Pawelke, J.; Pieck, S.

The foci of gamma-H2AX alone or colocated with 53BP1 are currently used in a lot of different studies to detect DNA double-strand breaks (DSB) after ionizing radiation. The primary objective of our study was to compare the radiation energy, dose dependent induction and kinetics of DNA DSB, in particular with regard to differences between soft and higher energy X-rays with the colocated gamma-H2AX and 53BP1 foci. We chose the human mammary epithelial cell line 184A1 for these experiments due to the medical application of 25 kV X-rays, e.g. in mammography. X-ray energies applied were 25 kV and 10 kV, the latter one by reason of the proposed maximum biological effectiveness at this energy, and 200 kV X-rays as reference radiation source.
The time courses of foci appearance and loss showed a similarity in the kinetics for all energies applied with maxima at 2 h (2 Gy) and 0.5 h for (0.25 Gy) after irradiation. Despite these uniform kinetics, we investigated the dose dependence of the colocated foci, allowing to calculate the RBE of soft X-rays in the range of 1.3 to 2.2 (25 kV) and 2.9 to 6.4 (10 kV).

  • International Journal of Radiation Biology 85(2009)11, 1042-1050
    DOI: 10.3109/09553000903232884
    Cited 24 times in Scopus
  • Poster
    2nd Workshop on "Radiation and Multidrug Resistance Mediated via the Tumor Microenvironment", 09.-10.02.2009, Dresden, Germany

Publ.-Id: 11343

Characterisation of dissolved thioarsenite complexes and precipitated arsenic species in a low-pH sulphate-reducing bioreactor

Crouzet, C.; Delorme, F.; Battaglia-Brunet, F.; Burnol, A.; Scheinost, A.; Morin, D.; Touzelet, S.

Some mining effluents and mine drainage waters are acidic and highly polluted with arsenic. A bio-process performing the precipitation of arsenic sulphide would be very attractive, because the final solid waste would contain up to 60% arsenic in weight. In the framework of Biomine European Integrated project (contract NMP2-CT-2005-500329), a bacterial population able to reduce sulphate at pH 4.5 was selected and used to inoculate column bioreactors that were continuously fed with arsenic in acidic conditions. Arsenic precipitates with sulphide in acidic and low-sulphide solutions. With excess sulphide, soluble thioarsenite species are expected to form.The present work showed that sulphate-reducing bacteria can mediate the precipitation of arsenic sulphide in acidic conditions. The main part of the precipitate is composed of amorphous orpiment, however crisrtallised phases could be detected. The new method developed here to analyse of thioarsenite species in solution will facilitate the monitoring of anaerobic bioreactors treating arseniccontaining effluents and will allow the biogeochemical modelling of such systems.

Keywords: Arsenic; EXAFS; acid mine drainage

  • Poster
    2nd International Congress: As in the environment, 21.-23.05.2008, Valencia, Spain

Publ.-Id: 11342

Megawatt PV plants in Germany: A south-north performance comparison

Rindelhardt, U.; Dietrich, A.; Kedziora, K.; Hahn, A.

Stimulated by the German Feed-in-Law, a large number of grid-connected Megawatt PV plants have been put into operation during the last 5 years. Because of the higher irradiance these plants were originally concentrated in the southern part of Germany (Bavaria and Baden-Wuerttemberg). Starting in 2004 some plants have been also installed in other regions of Germany. The paper describes design and operation results of nine plants operating in different regions.

Locations and design
The plant locations are distributed between 47 and 52 degrees northern latitude (Fig.1), covering Germany from South to North. Some technical features of the investigated plants are given in the table below.

The most plants were built on heavily used or loaded areas (former industrial sites or waste sites). Different types of fundaments and rack support constructions (desks) were used for the module mounting (Fig.2.). The connection with the grid was done in the 10 to 20 kV voltage level, the distance between the plants and the grid was several thousands meters in some cases. The most plants started their operation before 2006. The operation of the plants is monitored by the owners or by professional service providers.

Results and conclusions
The operation results of the year 2007 are exemplarily presented. The solar irradiance in 2007 was higher than the long year average, similar to the years before. The final yield of the plants ranges between 940 and 1180 kWh/kW (Fig. 3). The final yield of the tracked plant in Borna surpasses the yield of the other plants by 25%.
The performance ratios were determined to be between 0.75 and 0.92 (Fig. 4). In the most cases the PR values surprisingly ranges between 0,82 and 0.86. The sources of energy losses are analysed and discussed. Finally a long term estimation of the yield for the different plants will be given.

Keywords: PV plants; performance; MW plants

  • Lecture (Conference)
    23rd European Photovoltaic Solar Energy Conference and Exhibition, 01.-05.09.2008, Valencia, Spain
  • Contribution to proceedings
    23rd European Photovoltaic Solar Energy Conference and Exhibition, 01.-05.09.2008, Valencia, Spain
    Proc. of the International Conference held in Valencia, Spain, 1-5 September 2008, München, 3-936338-24-8, 3236-3239

Publ.-Id: 11341

Kernenergie im 21. Jahrhundert

Rindelhardt, U.

Im Vortrag wird einleitend die Entwicklung der Kernenergie im 20. Jahrhundert dargestellt. Ausgehend vom bisher erreichten Stand werden die Perspektiven im 21. Jahrhundert entwickelt. Schwerpunkte dabei sind der Einsatz von Kraftwerken der 3. Generation, der Abfallbehandlung durch Transmutation und die Entwicklung von schnellen Brutreaktoren.

Keywords: Nuclear energy; neclear reactors; electricity

  • Lecture (others)
    Seniorenkolleg TU Chemnitz, 27.05.2008, Chemnitz, Deutschland

Publ.-Id: 11340

Electrochemical and Complexation Behavior of Neptunium in Aqueous Perchlorate and Nitrate Solutions

Ikeda, A.; Hennig, C.; Rossberg, A.; Funke, H.; Scheinost, A. C.; Bernhard, G.; Yaita, T.

Electrochemical and complexation properties of neptunium (Np) are investigated in aqueous perchlorate and nitrate solutions by means of cyclic voltammetry, bulk electrolysis, UV-visible absorption and Np LIII-edge X-ray absorption spectroscopies. The redox reactions of Np(III)/Np(IV) and Np(V)/Np(VI) couples are reversible or quasi-reversible, while the electrochemical reaction between Np(III/IV) and Np(V/VI) is irreversible because they undergo the structural rearrangement from spherical coordinating ions (Np3+ and Np4+) to transdioxo neptunyl ions (NpO2n+, n = 1 for Np(V) and 2 for Np(VI)). The redox reaction of the Np(V)/Np(VI) couple involves no structural rearrangement on their equatorial planes in acidic perchlorate and nitrate solutions. A detailed analysis on extended X-ray absorption fine structure (EXAFS) spectra suggests that Np(IV) forms a decaaquo complex of [Np(H2O)10]4+ in 1.0 M HClO4, while Np(V) and -(VI) exist dominantly as pentaaquo neptunyl complexes, [NpO2(H2O)5]n+ (n = 1 for Np(V) and 2 for Np(VI)). A systematic change is observed on the Fourier transforms (FTs) of the EXAF spectra for all the Np oxidation states as increasing the nitrate concentration in the sample, revealing that the hydrate water molecules are replaced by bidentate-coordinating nitrate ions on the primary coordination sphere of Np.

Keywords: Neptunium; Electrochemistry; Complexation; Cyclic Voltammetry; Electrolysis; UV-visible Absorption; X-ray Absorption Spectroscopy; Hydrate; Perchlorate; Nitrate; Aqueous Solution

  • Inorganic Chemistry 47(2008)18, 8294-8305

Publ.-Id: 11339

Magnetfeldkontrollierte Erstarrungsvorgänge in metallischen Legierungen

Eckert, S.; Boden, S.; Räbiger, D.; Willers, B.

Metallschmelzen in industriellen Prozessen unterliegen in der Regel verschiedenen Arten von Strömungen. Diese Strömungen haben einen entscheidenden Einfluss auf den Wärme- und Stofftransport, und damit zumeist auch auf die Effizienz des Prozesses oder die Qualität des Endproduktes. Zukünftige Anstrengungen im Hinblick auf eine Optimierung derartiger Anlagen oder Technologien müssen aus diesem Grund eine wirksame Strömungskontrolle berücksichtigen.
Elektromagnetische Felder eröffnen aufgrund des kontaktlosen Zugangs und der einfachen Regelbarkeit eine attraktive Möglichkeit zur Strömungskontrolle. Eine gezielte Einflussnahme setzt aber ein umfangreiches Wissen über das Strömungsfeld und die Wechselwirkung mit den elektromagnetischen Kraftfeldern voraus. Neben numerischen Simulationen sind Modellexperimente mit sogenannten „kalten“ Schmelzen, d.h. mit Flüssigmetallen mit einem Schmelzpunkt < 300°C, ein unverzichtbares Mittel, um die Strömungsvorgänge besser zu verstehen und geeignete Maßnahmen zur Strömungskontrolle zu ergreifen. Die Röntgenradioskopie hat sich dabei als ein wichtiges diagnostisches Mittel herausgestellt, um Erstarrungsvorgänge in-situ zu visualisieren. Auf Grundlage der Bewertung der Grauwertbilder mit Hilfe der "Optical Flow"-Methode ist es erstmalig gelungen, Strömungsstrukturen in unmittelbarer Umgebung zur Erstarrungsfront während der Erstarrung darzustellen.
Im Vortrag werden am Beispiel der Erstarrung Einsatzmöglichkeiten elektromagnetischer Felder in der Gießereiindustrie erläutert.

Keywords: solidification; metal alloys; electromagnetic fields; X-ray radioscopy; Optical Flow

  • Invited lecture (Conferences)
    Seminar "Struktur und Eigenschaften kondensierter Materie", 20.05.2008, Chemnitz, Deutschland

Publ.-Id: 11338

Complexation of Curium(III) and Europium(III) with Urea and in Human Urine

Heller, A.; Barkleit, A.; Bernhard, G.

The complexation of europium(III) and curium(III) in aqueous urea solution has been studied at pH 1 – 8, I = 0.1 (NaClO4), room temperature and trace metal concentrations using time-resolved laser-induced fluorescence spectroscopy. In case of curium(III) a red shift of the luminescence maximum occurs upon complexation, while for europium(III) emission wavelengths remain unaltered but the peak splitting is changed significantly. Both heavy metals form very weak complexes of the formulae ML3+ which are stable until pH 6. Stability constants were determined to be -0.12 ± 0.05 for europium(III) and -0.31 ± 0.13 for curium(III). In human urine samples the luminescence spectra of both heavy metals differ significantly from those in water and aqueous urea solution. Red shift of the luminescence maximum of curium(III) is more pronounced and peak splitting in case of europium(III) enhanced. Besides that, lifetimes of the species formed in human urine vary markedly from those of the ML3+ complexes with urea. Furthermore, the speciation of the heavy metals seems to depend on the pH of the urine sample.

Keywords: curium(III); europium(III); urea; complexation; urine; heavy metal speciation; TRLFS

  • Contribution to proceedings
    NRC7 - Seventh International Conference on Nuclear and Radiochemistry, 24.-29.08.2008, Budapest, Hungary

Publ.-Id: 11337

Ion irradiation induced local creation of ferromagnetism in Fe60Al40 alloys

Strache, T.; Liedke, M. O.; Fassbender, J.; Möller, W.; Menéndez, E.; Sort, J.; Suriñach, S.; Baró, M. D.; Gemming, T.; Weber, A.; Heyderman, L. J.; Rao, K. V.; Deevi, S. C.; Nogues, J.

Ion irradiation of Fe60Al40 alloys results in the phase transformation from the paramagnetic, chemically ordered B2-phase to the ferromagnetic, chemically disordered A2-phase. The magnetic phase transformation is related to the number of displacements per atom (dpa) during the irradiation. For heavy ions (Ar+, Kr+, Xe+) a universal curve is observed with a steep increase in the fraction of ferromagnetic phase reaching saturation, i. e., a complete phase transformation, at about 0.5 dpa. This proves the purely ballistic nature of the disordering process. If light ions are used (He+, Ne+) a pronounced deviation from the universal curve is observed. This is attributed to bulk vacancy diffusion from dilute collision cascades, which leads to a partial recovery of the thermodynamically favored B2-phase. Comparing different noble gas ion irradiation experiments allows to asses the corresponding counteracting contributions. In addition, the potential to create local ferromagnetic areas embedded in a paramagnetic matrix is demonstrated.

Keywords: magnetism; ion irradiation; binary alloys; intermetallic; FIB; patterning

  • Lecture (Conference)
    Ionenstrahlphysik und Nanotechnologie, GSI-Workshop, 11.-12.04.2008, Darmstadt, Germany

Publ.-Id: 11336

Magnetic lithography on paramagnetic FeAl alloys by selective ion irradiation

Sort, J.; Menendez, E.; Liedke, M. O.; Strache, T.; Fassbender, J.; Gemming, T.; Weber, A.; Heydermann, L. J.; Surinach, S.; Rao, K. V.; Deevi, S. C.; Baro, M. D.; Nogues, J.

The atomically-ordered Fe60Al40 (at. %) alloy is paramagnetic at room temperature but it becomes ferromagnetic when subject to structural disorder [1]. This effect has been recently used to generate arrays of sub-100 nm ferromagnetic dots embedded in a paramagnetic matrix. To selectively induce structural disorder, local irradiation procedures, either through lithographed masks or using focused ion beam, have been utilized. Due to the low ion doses used, the irradiation processes do not induce any surface corrugation, thus circumventing tribological problems. The fabricated entities exhibit a range of magnetic properties depending on the size and shape. Furthermore, when the patterned sheets are annealed at sufficiently high temperatures (i.e., around 900 K), the magnetic properties are erased due to the annealing-induced atomic reordering. This method may be extrapolated to a variety of other intermetallic systems such as Fe2AlMn, Ni3Sn2 or CoGa and also to austenitic steels. The obtained magnetic structures may have technological applications, such as magnetic sensors or patterned recording media.
Partial financial support from the Spanish 2005SGR-00401, MAT2007-66302-C02 and MAT2007-61629 research projects, the EU-RITA program “Center for the Application of Ion Beams in Materials Research” (under contract no. 025646) and the Swedish Agencies VINNOVA and SSF is acknowledged. E. M. acknowledges his FPI fellowship from the Spanish Ministerio de Educación y Ciencia, co-financed by the ESF.
[1] J. Nogués et al., Phys Rev. B Phys. Rev. B 74, 024407 (2006)

Keywords: magnetism; ion irradiation; focused ion beam; binary alloys; disordering

  • Invited lecture (Conferences)
    9th International Conference on Nanostructured Materials, 01.-06.06.2008, Rio de Janeiro, Brazil

Publ.-Id: 11334

Structures and Stoichiometry of Actinide Complexes: Challenges of Combining EXAFS and Quantum Chemistry

Tsushima, S.

EXAFS spectroscopy has been proved to be a very powerful tool for studying the structures of actinide complexes in aqueous and non-aqueous systems. The application of EXAFS spectroscopy has been extended to the systems with mixed species and / or species with very dilute concentration. Using EXAFS alone, however, has inherent limitations such as a lack of spatial information of the molecules and rather poor radial resolutions which make it difficult to differentiate two or more bonds with similar distances. Factor analysis by Rossberg et al., for example, was proven to be an effective method for separating individual species from the mixed ones [1]. Such method becomes even more powerful if corresponding 3D structural information can be provided by quantum chemical calculations.
Here, I show two examples in which density functional theory (DFT) calculations are proved to be very helpful for actinide speciation studies. In first case, Th(IV) hydroxo and sulfato complexes were studied by DFT calculations. A significant decrease in the coordination number (CN) was observed as a stepwise hydrolysis reaction of Th4+ ion proceeds. The fourth hydrolysis product, Th(OH)4 0, has a reduced CN of 6 and readily forms a dimeric complex via a Th-OH-Th bridging. The oligomerization makes Th(OH)4 0 to be an unstable aqueous species. In case of sulfate, the CN and the average Th-O distance of Th(SO4)2 0 remains essentially as same as Th4+ aquo ion. This result is in agreement with the EXAFS study by Hennig et al. [2].
In the second example, the reduction potential of Pu(VIII) / Pu(VII) couple was studied as the same way as in a recent study [3]. The geometries and the energies of the complexes were calculated at the B3LYP level. The spin-orbit effect for Pu(VII) species was corrected at the CASSCF level. The redox potential of the PuVIIIO4(OH)2 2-/ PuVIIO4(OH)2 3- couple was found to be as high as ~1.7V in alkaline solution which indicates that it is difficult to obtain Pu(VIII) in aqueous solution.
1. A. Roßberg, T. Reich, G. Bernhard, Anal. Bioanal. Chem. 376, 631-638, (2003).
2. C. Hennig, K. Schmeide, V. Brendler, H. Moll, S. Tsushima, A. C. Scheinost, Inorg. Chem. 46, 5882-5892 (2007).
3. S. Tsushima, U. Wahlgren, I. Grenthe, J. Phys. Chem. A 110, 9175-9182 (2006).

  • Invited lecture (Conferences)
    Actinide XAS 2008, 15.-17.07.2008, Soleil, France

Publ.-Id: 11333

Biogeochemical changes induced by uranyl nitrate in a uranium waste pile

Selenska-Pobell, S.; Geissler, A.; Flemming, K.; Merroun, M.; Geipel, G.; Reuther, H.

Treatments with uranyl nitrate induced strong changes in subsurface bacterial community of a uranium mining waste pile. Most of the bacterial populations, stimulated at the initial stages of the treatment, used the added nitrate for respiration. Mössbauer spectroscopic analyses showed that at the later incubation stages, when nitrate was reduced, reduction of Fe(III) to Fe(II) occurred. Time-resolved laser-induced fluorescence spectroscopic analysis revealed that most of the added U(VI) was bound in phosphate phases of biotic origin.

  • Contribution to external collection
    Broder J. Merkel, Andrea Hasche-Berger: Uranium, Mining and Hydrogeology, Berlin: Springer Verlag, 2008, 978-3-540-87745-5, 743-752

Publ.-Id: 11332

Study of the Influence of Humic Acid on the Am(III) Sorption onto Kaolinite

Krepelova, A.; Sachs, S.; Geipel, G.; Bernhard, G.

In order to determine the influence of humic acid (HA) on the sorption of Am(III) onto kaolinite batch experiments were performed ([Am(III)] = 1x10-6 M, [HA] = 0 or 10 mg/L, I = 0.01 M NaClO4, pH = 3-10, solid/solution ratio = 1 or 4 g/L, pCO2 = 10-3.5 atm). In addition to that, laser-induced fluorescence spectroscopy was applied to study Am(III) kaolinite surface complexes in absence and presence of HA. The obtained results show that the presence of humic acid can affect the Am(III) migration under environmentally relevant conditions.

Keywords: Americium; Am(III); Humic acid; Kaolinite; Clay; Sorption; Batch experiments; Laser-induced fluorescence spectroscopy

  • Lecture (others)
    4th RTDC-1 Meeting of FUNMIG, 20.-21.05.2008, Bürgenstock, Switzerland

Publ.-Id: 11331

Quasifree Lambda, Sigma0, and Sigma− electroproduction from 1,2H, 3,4He and carbon

Dohrmann, F.

A comprehensive study of kaon electroproduction on light nuclei has been conducted in Hall C of the Thomas Jefferson National Accelerator Facility by the E91-016 collaboration. Data were obtained using electron beams of 3.245 GeV impinging on special high density cryogenic targets of 1,2H, 3,4He, as well as on a solid carbon target. Specifically, the measurements on 3,4He are the first performed. Previously, the observation of hypernuclear bound states was discussed [1]. This presentation will give the final results of the data analysis, focussing on the quasifree production cross sections for the Lambda and Sigma hyperons for the various target nuclei [2]. We also derive effective proton numbers from our data and compare these numbers with model calculations. Deviations may indicate possible in-medium modifications of the kaon electroproduction mechanism.

[1] F. Dohrmann et al [E91016 collab.] Phys. Rev. Lett. 93 (2004) 242501
[2] F. Dohrmann et al [E91016 collab.] Phys. Rev. C 76 (2007) 054004

Keywords: electroproduction; quasifree; medium modifications; hyperons

  • Lecture (Conference)
    DPG Frühjahrstagung Darmstadt 2008, 10.-14.03.2008, Darmstadt, Deutschland

Publ.-Id: 11330

Time resolution of radiation hard Resistive Plate Chambers for the CBM experiment at FAIR

Bartos, D.; Caragheorgheopol, G.; Dohrmann, F.; Kämpfer, B.; Kotte, R.; Naumann, L.; Petris, M.; Petrovici, M.; Simion, V.; Stach, D.; Williams, C.; Wüstenfeld, J.

The Compressed Baryon Matter (CBM) experiment at FAIR/Darmstadt studies highly compressed nuclear matter at moderate temperatures in relativistic heavy-ion collisions. CBM uses rare probes for studying fundamental issues of QCD. Currently the technical design of CBM foresees a time-of-flight wall (TOF) equipped with resistive plate chambers (RPCs) 10 m downstream from the target. The inner part of the TOF covers 50-100 mrad around the beam axis with estimated flux densities of charged particles of ~2·10^4 per s and cm², thus radiation hard detector components are indispensable in the forward direction.

RPC tests were conducted at the superconducting electron linac ELBE at FZ Dresden-Rossendorf using MeV electron beams mimicking GeV minimum ionizing particles for detector studies. The pulse width of ~5 ps of the ELBE beam provides the possibility to use its radio frequency directly as a time reference. ELBE also provides high rates (up to 1 mA beam current).

Conventional timing RPCs with standard float glass electrodes are only efficient up to flux densities of < 1·10^3 per s and cm². Accelerating the charge transport requires electrodes with lower volume resistivity while maintaining the time resolution (< 100 ps).

Timing and rate parameters of various RPCs were tested at ELBE, including conventional RPCs with float glass electrodes, as well as RPC electrodes made of special glasses (silicated) with 3-4 orders of magnitude lower volume resistivity than float glass (10^13 Ohm·cm).

Results are reported with emphasis on alternative electrode materials, i.e. polypropylene material and Pestov glass. The NIPNE group developed a prototype RPC with Pestov glass electrodes (10^10 Ohm·cm) read-out via stripe lines or pads.

Also ceramics electrodes are suggested for high rate timing RPCs. New ceramics material have recently become available for laboratory and prototype tests.

These tests will provide data for a decision on the type of high rate RPCs for CBM at FAIR.

Keywords: Gaseous Detectors; Time-of-flight detectors; high rate detectors; new materials

  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany
    Conference Record, 978-1-4244-2715-4

Publ.-Id: 11329

Synthesis of inverted spinel ferrite nanocrystals inside ZnO by ion implantation and post-annealing

Zhou, S.; Potzger, K.; Kuepper, K.; Xu, Q.; Schmidt, H.; Helm, M.; Fassbender, J.

The hybrids of magnets and semiconductors show promising magneto-transport properties, and would enable the development of spin-dependent magneto-electronic and magneto-optic devices [1]. The most well studied system is MnAs/GaAs due to its chemically stable interface and the possibility of epitaxy [2]. Large magneto-resistance and Faraday rotation have been observed in GaAs with MnAs nanoclusters. However the Curie temperature of MnAs is 313 K, and limits its application at high temperatures. Spinel ferrites are a group of materials with similar crystal-structure and rich magnetic as well as electronic properties, e.g. NiFeO and CoFeO, are ferrimagnets with large Neel temperatures. Therefore the hybrids of spinel ferrites with semiconductors would allow versatile possibilities for spin-dependent devices. However the integration of ferrites with semiconductors remains challenging due to the fact that the growth of ferrites requires high temperatures and oxygen environment, which is detrimental to conventional semiconductors like Si and GaAs [3]. In this contribution, we show the possibility to incorporate inverted spinel ferrite nanocrystals with ZnO by ion implantation and post-annealing. Their magnetic and electronic properties were investigated by SQUID and x-ray absorption spectroscopy. These nanocrystals are crystallographically oriented inside ZnO, and show superparamagnetic characteristics. Large positive magneto-resistance has been observed, and we will discuss its origin with respect to ordinary magneto-resistance and to magnetic scattering by nano-ferrites. Our results suggest a new magnet-semiconductor heterostructure with potential application in magneto-electronics and microwave devices [3].

[1] G. Prinz, Science 250, 1092 (1990).
[2] L. Daweritz, Rep. Prog. Phys. 69, 2581 (2006).
[3] Z. Chen et al., Appl. Phys. Lett. 91, 182505 (2007).

Keywords: magnetism; diluted magnetic semiconductors; spinell structures; nanocrystals

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11328

Tuning coercivity in CoCrPt-SiO2 hard disk material

Strache, T.; Tibus, S.; Springer, F.; Rohrmann, H.; Albrecht, M.; Fassbender, J.

In order to continuously increase the storage capacity of modern computer disk drives and push the superparamagnetic limit to the smallest achievable bit sizes the material used has to fulfill a number of requirements: i) Maximum perpendicular magnetic anisotropy to guarantee thermal stability. Granular CoCrPt-SiO2 films are currently the material of choice. ii) Large remnant magnetization to achieve a good signal to noise ratio when reading the bit information. iii) Moderate coercive fields to allow for the writing of the bit information with the limited write head fields available. In order to increase the storage density, smaller grains with larger magnetic anisotropies are required for thermal stability which are accompanied by large coercive fields which obstruct the writing process. One route to overcome this problem is to independently reduce the coercive field without altering the magnetic anisotropy and the remnant magnetization by tailoring the intergranular exchange.
Ion irradiation and implantation has recently been demonstrated to be a viable tool to modify magnetic properties of thin magnetic films and multilayers [1, 2]. Here we demonstrate that by means of ion implantation of Co and Ne a continuous reduction of the coercive field can be achieved without significant modification of the remaining magnetic parameters. In addition to the magnetization reversal behavior of the entire film investigated by magneto-optic Kerr effect and SQUID magnetometry also the magnetic domain configuration in the demagnetized state is imaged by magnetic force microscopy. Moreover, these studies are supported by micromagnetic simulations which allow to further extract information about the intergranular exchange coupling which is the source of the modified coercive field.

[1] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D: Appl. Phys. 37, R179 (2004).
[2] J. Fassbender, J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).

Keywords: magnetism; ion irradiation; magnetic storage; hard disk; coercivity; anisotropy; magnetic domains

  • Lecture (Conference)
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland

Publ.-Id: 11327

Magnetic microstructures created by local interface mixing

Strache, T.; Fassbender, J.; Grenzer, J.; Möller, W.; Kaltofen, R.; Mönch, I.; McCord, J.

Magnetic micro- and nanostructures are of great interest due to the fundamental physics involved if the dimension is shrunk as well as due to the application potential in storage, sensing and logic devices. For the creation of such structures typically lithography is used in combination with either etching or lift-off processes. In both cases the magnetic element is defined by isolated topographic structures. An alternative approach relies on the local ion irradiation of a magnetic multilayer structure. As a result of the ion irradiation an interfacial mixing between ferromagnetic layers and non-magnetic interlayers is achieved which consequently reduce and finally fully suppress the ferromagnetism. In order to demonstrate this behaviour Ni80Fe20/Ta multilayers with a different number of repetitions are used. The structural and magnetic properties are investigated by x-ray reflectivity and magneto-optic Kerr effect magnetometry as a function of noble gas irradiation fluence and number of multilayer repetitions. The experimental results are accompanied by TRIDYN simulations. In addition magnetic microstructures are created by means of large area ion irradiation through lithographically defined masks. By choosing the irradiation fluence the exchange coupling between the microstrucutres can be switching on and off. The magnetic domain configuration in these elements is imaged by means of Kerr microscopy and magnetic force microscopy. Thus the modified magnetization reversal curves can be interpreted on the basis of the micromagnetic domain structure.

Keywords: magnetism; ion irradiation; magnetic patterning; intermixing; Kerr microscopy

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11326

Ion beam induced magnetic transformation in layered structures: nonmagnetic to ferromagnetic and vice versa

Dev, B. N.; Fassbender, J.; Grenzer, J.; Schell, N.; Bischoff, L.; Schmidt, B.; Grötzschel, R.; Allenstein, F.; Beddies, G.; McCord, J.

A nonmagnetic to ferromagnetic transformation is observed when a Pt/C multilayer stack (total thickness ~ 60 nm, thickness of individual layers ~ 2 nm) with a small amount of Fe impurity, grown on a glass substrate, is irradiated with 2 MeV Au ions [1]. Using a subnanometer depth resolution technique it was found that ion beam induced preferential migration of Fe from C to Pt layers and the subsequent formation of FePt nanoparticles were responsible for the magnetic transformation [2]. Fe concentration in the C layers decreases exponentially with increasing ion fluence with simultaneous increase of the coercive field in the magnetic hysteresis loop. An example of ion beam induced opposite transformation, namely, ferromagnetic to nonmagnetic, is shown using a Si(5nm)/Ni(10 nm)/Si trilayer system, where ion-beam-induced atomic displacements across the Si/Ni interfaces form a mixed Ni1-xSix layer leading to a ferromagnetic to nonmagnetic transformation. In this case, with increasing ion (30 keV Ga) fluence the coercive field in the hysteresis loop decreases with increasing ion fluence and eventually magnetization is destroyed at a critical fluence. Having identified the critical fluence, a focused ion beam (FIB, 30 keV Ga) was used to fabricate a lateral multistrip pattern in this thin (10 nm) magnetic layer with alternate magnetic/nonmagnetic strips of nanometer dimensions. Magnetooptical Kerr effect microscopy reveals the anisotropy of the magnetic domain structure along and perpendicular to the FIB-patterned strips. In the light of the observed phenomena, future developments in the area of nanotechnology, such as ultrahigh density magnetic storage devices, single-electron spin-valve transistors etc. will be discussed. Some nanoscale structures that can be fabricated using FIB will offer the possibility of exploring new scientific aspects, such as magnons in ordered ferromagnetic spot arrays, in these structures.

[1] B. N. Dev, S. Bera, B. Satpati, D. K. Goswami, K. Bhattacharjee, P. V. Satyam, K. Yamashita, O. M. Liedke, K. Potzger, J. Fassbender, F. Eichhorn and R. Groetzschel,
Microelectronic Engineering 83, 172 (2006).

[2] S. Bera, K. Bhattacharjee, G. Kuri and B. N. Dev
Phys. Rev. Lett. 98, 196103 (2007).

Keywords: magnetism; ion irradiation; magnetic transformation; XRD; Kerr microscopy

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland

Publ.-Id: 11325

Ga+ ion irradiation-induced changes of magnetic ordering in Pt/Co(3nm)/Pt films

Jaworowicz, J.; Kisielewski, M.; Maziewski, A.; Sveklo, I.; Jamet, J.-P.; Ferre, J.; Mougin, A.; Vernier, N.; Fassbender, J.; Henschke, A.; Bourhis, E.; Gierak, J.

In Pt/Co(d)/Pt ultrathin film structures a spin reorientation transition (SRT) from out-of-plane to in-plane magnetization states is known to occur at a critical Co thickness d=dSRT ~ 1.8nm. For thinner Co thicknesses this SRT can also be forced by ion irradiation. In the present work we demonstrate that also the reverse SRT, i. e. from in-plane to out-of-plane, can be achieved by ion irradiation in certain cases. Therefore, easy-plane magnetized Pt/Co(3nm)/Pt samples were irradiated by 30 keV Ga+ ions with doses D ranging from 1014 to 5x1016 ions/cm2. The ion irradiation induced effects were investigated by polar magnetooptical microscopy, magnetometry and atomic/magnetic force microscopy. At low dose the reverse SRT is observed with a large out-of-plane magnetization component giving rise to a square perpendicular hysteresis loop. Sub-micrometer perpendicular magnetic domain structures either field-induced or in the demagnetized state confirm this new behavior. At higher dose, the easy magnetization direction is turned in-plane again. Topologically, a film swelling effect is first evidenced at low dose, but surface etching dominates at higher dose. Similar effects are also observed under quasi-uniform irradiation performed by scanning a focused ion beam (FIB) on the Pt/Co(3nm)/Pt structure. The results will be also compared to those reported earlier for d < dSRT, where ion irradiation leads to a reduction of the Curie temperature, coercivity and magnetic anisotropy [1,2].
This work was partially supported by EU MC TOK project NanomagLab No MTKD-CT-2004-003177 and EU-RITA program “Centre for Application of Ion Beams in Materials Research” under contract no. 025646. J.J. has benefited of an EC Marie-Curie fellowship (contract MEST CT 2004-51437).

[1] J. Ferré, J.-P. Jamet, in Handbook of Magnetism and Advanced Magnetic Materials, H. Kronmüller, S. Parkin (eds), (2007) John Wiley & Sons, Ltd.
[2] J. Fassbender, J. McCord, J. Magn. Magn. Mat. 320 (2008) 579.

Keywords: magnetism; ion irradiation; FIB; magnetic anisotropy; Kerr microscopy

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
  • Poster
    Louis Neel Colloquim, 30.09.-03.10.2008, La Grande Motte, France

Publ.-Id: 11324

Irradiation induced magnetic patterning of soft-magnetic thin films

McCord, J.; Kaltofen, R.; Quandt, E.; Fassbender, J.

Numerous applications of ferromagnetic materials in magneto-electronics are based on multi-layer thin film technology. For most of the relevant applications the magnetic films are patterned by lithographic processes, which result in isolated magnetic elements. Here, we demonstrate the lateral alteration of magnetic properties of soft-magnetic thin films by ion irradiation. In contrast to traditionally patterned thin films, the interaction within the patterned structure occurs through direct magnetic exchange, resulting in novel effective magnetic properties and magnetization states fundamentally differing from conventionally magnetic thin films.
The method and a summary of ion-induced modifications of fundamental magnetic properties of different materials will be shown on single layer crystalline and amorphous thin films, and multi-layered systems. Examples include laterally modulated saturation polarization as well as locally varying magnetic anisotropy alignment, both resembling anisotropic as well as patterned soft-magnetic film behavior. The scaling behavior for the resulting structures will be discussed and the data will be compared to effects known so far only from multi-layered magnetic layers. Moreover it will be shown, that not only the regular static magnetic behavior, but also the magnetization dynamics of systems can be tuned and laterally modified by ion irradiation.
The local modulation of magnetic properties opens exciting new opportunities to the tuning of the integral properties of soft-magnetic thin films and establishes an additional path to thin film magnetic structures with novel functionality.

J. McCord, R. Schäfer, K. Theis-Bröhl et al., J. Appl. Phys. 97, 10K102 (2005).
J. McCord, J. Fassbender, E. Quandt et al., Appl. Phys. Lett. 89, 162502 (2005).
J. Fassbender, J. McCord, JMMM 320, 579–596 (2008).
J. McCord, L. Schultz, J. Fassbender, Adv. Mater., accepted for publication.

Keywords: magnetism; ion irradiation; ion implantation; Kerr microscopy; exchange spring; magnetic domains

  • Lecture (Conference)
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11323

Generation of micro/nano-scaled magnetic structures on AISI 304L austenitic stainless steel by ion beam nitriding

Menendez, E.; Martinavicius, A.; Liedke, M. O.; Abrasonis, G.; Fassbender, J.; Sommerlatte, J.; Nielsch, K.; Surinach, S.; Baro, M. D.; Nogues, J.; Sort, J.

Nitriding of austenitic stainless steel at moderate temperatures (~400ºC) leads to the formation of the supersaturated nitrogen solid solution often called in the literature “expanded austenite” or γN phase [1]. This causes an enhancement of the microhardness and the wear resistance without loss of the corrosion resistance. Moreover, this phase shows ferromagnetic behavior, whose origin is linked to the expansion of the austenite (γ) lattice due to the incorporation of nitrogen atoms into interstitial positions [2].

The influence of the processing temperature and time on the structural and magnetic properties of AISI 304L austenitic stainless steel, after ion beam nitriding, has been investigated by x-ray diffraction (XRD), nuclear reaction analysis (NRA), magneto-optical Kerr effect (MOKE) magnetometry and atomic/magnetic force microscopy (AFM/MFM). Furthermore, periodic arrays of ferromagnetic structures in the micrometer and sub-micrometer range have been prepared after nitriding through either 2000 mesh Cu transmission electron microscopy grids (mesh size of 7.5 x 7.5 µm2, 12.5 µm pitch, 20 µm thickness and 3.05 mm diameter) or self-assembled porous alumina membranes (5 µm thickness), both acting as shadow masks. The local character of the induced ferromagnetism is confirmed by magneto-optical Kerr effect measurements together with magnetic force microscopy imaging.

[1] G. Abrasonis, et al., J. Appl. Phys. 97, 083531 (2005)
[2] O. Öztürk and D.L. Williamson, J. Appl. Phys. 77, 3839 (1995)

Keywords: magnetism; ion beam processing; nitriding; stainless steel; magnetic patterning

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11322

Direct generation of nanoscale ferromagnetic dots by selective ion irradiation of paramagnetic FeAl alloys

Menendez, E.; Sort, J.; Liedke, M. O.; Strache, T.; Fassbender, J.; Möller, W.; Gemming, T.; Weber, A.; Heyderman, L. J.; Surinach, S.; Deevi, S. C.; Rao, K. V.; Sommerlatte, J.; Nielsch, K.; Baro, M. D.; Nogues, J.

Fe60Al40 (at. %) alloys show an interesting combination of magnetic and structural properties, where atomically ordered Fe60Al40 is paramagnetic at room temperature, whereas disordered Fe60Al40 becomes ferromagnetic [1]. The transformation from paramagnetic B2-phase to the ferromagnetic, A2-phase can be accomplished by means of homogeneous ion irradiation procedures. Furthermore, local ion irradiation procedures (i.e., focused ion beam or ion irradiation through masks) have been also used in order to fabricate periodic arrays of sub-50 nm ferromagnetic structures embedded in a paramagnetic matrix. Due to the low fluences used, this method does not induce any roughening of the surface, leading to topographically featureless dots. The fabricated entities exhibit a range of magnetic properties depending on the size and shape, which were investigated by means of magneto-optical Kerr effect magnetometry, while the local character of the induced ferromagnetism was examined by magnetic force microscopy. Interestingly, when the patterned sheets are annealed at sufficiently high temperatures, the ferromagnetic properties are removed due to the annealing-induced atomic reordering. Hence, these methods may lead to a novel type of patterned recording media free from tribological and exchange coupling effects. Moreover, these approaches can be easily extrapolated to a variety of other systems exhibiting disorder-induced magnetism.

[1] J. Nogués et al., Phys Rev. B Phys. Rev. B 74, 024407 (2006)

Keywords: magnetism; ion irradiation; FIB; magnetic patterning; binary alloys; disordering

  • Invited lecture (Conferences)
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11321

Influence of Cr-ions on the magnetic behaviour of FeCo film

Gupta, R.; Ansari, R.; Khandelwal, A.; Fassbender, J.; Gupta, A.

Implantation of Cr-ions in Fe70Co30 thin film have been performed to modify its structural and magnetic properties. From the XRD results, the lattice constant as well as the grain size of the film is increasing with the ion fluence. 1 X 1017 ions/cm2 Cr-ions reduces the coercivity of the film from 140(3) Oe to 44(3) Oe. Coercivity of the film follows the exponential decay as a function of Cr-ions fluence. 35 keV (projectile range 13.5 nm) and 100 keV Cr-ions (projectile range 34.3 nm) have been used to understand the effects of magnetic Cr-ions and the effects of ballistic collision cascade on the MOKE signal. Similar changes on the coercivity behaviour of the film implanted with these two energies have been observed. It appears that the implantation process creates a solid solution of Cr in FeCo without any other additional treatment in the film. After 5 X 1016 Cr-ions, film exhibit four fold magnetic anisotropy.

Keywords: magnetism; ion implantation; magneto-optic kerr effect; magnetic anisotropy

  • Nuclear Instruments and Methods in Physics Research B 266(2008), 1407-1410

Publ.-Id: 11320

Two-fold origin of the deformation-induced ferromagnetism in bulk Fe60Al40 (at-%) alloys

Menendez, E.; Sort, J.; Liedke, M. O.; Fassbender, J.; Surinach, S.; Baro, M. D.; Nogues, J.

The transition from the atomically ordered B2-phase to the chemically disordered A2-phase and the concomitant deformation-induced ferromagnetism have been investigated in bulk polycrystalline Fe60Al40 (at.%) alloys subjected to compression processes. A detailed correlation between structural, magnetic and mechanical properties reveals that the generated ferromagnetism depends on the stress level but is virtually independent of the loading rate. The mechanisms governing the induced ferromagnetism also vary as the stress level is increased. Namely, in the low-stress regime both lattice cell expansion and atomic intermixing play a role in the induced ferromagnetic behavior. Conversely, lattice expansion seems to become the main mechanism contributing to the generated ferromagnetism in the high-stress regime. Furthermore, a correlation is also observed between the order-disorder transition and the mechanical hardness. Hence, a combination of magnetic and mechanical measurements can be used, in synergetic manner, to investigate this deformation-induced phase transition.

Keywords: magnetism; binary alloys; ordering; disordering; ball milling; lattice expansion

  • Open Access Logo New Journal of Physics 10(2008), 103030

Publ.-Id: 11319

Patterning of magnetic structures on austenitic stainless steel by local ion beam nitriding

Menendez, E.; Martinavicius, A.; Liedke, M. O.; Abrasonis, G.; Fassbender, J.; Sommerlatte, J.; Nielsch, K.; Surinach, S.; Baro, M. D.; Nogues, J.; Sort, J.

Periodic arrays of ferromagnetic structures with micrometer and sub-micrometer lateral sizes have been prepared at the surface of a paramagnetic austenitic stainless steel by means of ion beam nitriding through different types of shadow masks (such as transmission electron microscopy grids or self-assembled porous alumina membranes). This method takes advantage of the formation of the ferromagnetic supersaturated nitrogen solid solution γN phase (i.e., expanded austenite) upon nitriding at moderate temperatures. The local character of the induced ferromagnetism is confirmed by magneto-optical Kerr effect measurements together with magnetic force microscopy imaging. Furthermore, the influence of the nitriding temperature and time on the induced ferromagnetic and structural properties has been analyzed.

Keywords: Magnetism, Ion-beam processing; X-ray diffraction; Austenitic steels; Interstitial diffusion; Magnetic patterning

Publ.-Id: 11318

Dynamic interaction between vortices, antivortices and holes in domain walls investigated by means of time resolved Photoemission Electron Microscopy (PEEM)

Kuepper, K.; Wintz, S.; Buess, M.; Raabe, J.; Quitmann, C.; Fassbender, J.

In this work we study the interaction of vortex cores with either holes in domain walls of Landau structures or other vortices and antivortices, which are also interconnected through the adjacent domain walls of a single cross-tie structure.
During the last few years the investigation of magnetic vortices and their dynamic properties has attracted great attention due to the fundamental interest in the physics of solitons and since they might be used as non volatile memory devices in future applications, e. g. [1,2]. One striking feature of magnetic vortices is that the cores are attracted and can be trapped by artificial defects. If more than one of such defects are created a switching between different vortex core trapped states, which might serve as discrete levels in a multivalent memory device, can be achieved. We report the imaging of the magnetic excitation spectrum in presence of holes, fabricated by focused ion beam milling, in the magnetic domains and domain walls of Landau structures by means of x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM). The vortex core in the center of the structure is not modified by ions, here we investigate the interaction of unmodified vortex cores with holes far away (> 1 Mikrometer) in the domain walls and the domains of Landau structures. Due to the very high lateral and temporal resolution the magnetization dynamics and the corresponding Eigen modes (Fig. 1), which are characteristic for the vortex-hole interaction, are investigated in detail [3]. Analyzing the vortex movement unravels an acceleration of the vortex gyrotropic mode if holes are present in the middle of domain walls. The presence of holes in the middle of domains has no significant influence on the vortex speed. The experimental results are compared to micromagnetic simulations.


[1] S. B. Choe et al., Science 304, 420 (2004), J. Raabe et al., Phys. Rev. Lett. 94, 217204 (2005).
[2] B. van Waeyenberge et al., Nature 444, 461 (2006)
[3] K. Kuepper et al., manuscript in preparation.
[4] K. Kuepper et al., Phys. Rev. Lett. 99, 167202 (2007)

Keywords: magnetism; magnetization dynamics; vortex; antivortex; defects; time-resolved; magnetic imaging

  • Invited lecture (Conferences)
    IEEE International Magnetics Conference - Intermag 2008, 04.-08.05.2008, Madrid, Spain
  • Invited lecture (Conferences)
    Workshop on high temporal and spatial resolution studies of magnetic nanostructures, 27.06.-02.07.2008, Augustow, Poland

Publ.-Id: 11317

Ga+ ion irradiation-induced out-of-plane magnetization in Pt/Co(3nm)/Pt films

Jaworowicz, J.; Kisielewski, M.; Maziewski, A.; Sveklo, I.; Jamet, J.-P.; Ferre, J.; Mougin, A.; Vernier, N.; Fassbender, J.

Ion beam irradiation under weak or moderate fluence allows to modify and even control the magnetic properties of thin film structures [1–2]. So, this method stands now as an elegant technique for magnetic nanopatterning [3].Spin reorientation transition form in-plane to out-of-plane state in Pt/Co/Pt film with cobalt thickness 3nm after irradiation by 30 keV Ga+ ions with doses of 0.5 x 1015 and 1015 ions/cm2 was observed. Experiments were made with magneto-optical base microscopy and magnetic force microscopy.

[1] C. Chappert, H. Bernas, J. Ferré, V. Kottler, J.-P. Jamet, Y. Chen, E. Cambril, T. Devolder, F. Rousseaux, V. Mathet, H. Launois, Science 280 (1998) 1919.
[2] J. Fassbender, J. McCord, J. Magn. Magn. Mat. 320 (2008) 579
[3] J. Ferré, J.-P. Jamet, in Handbook of Magnetism and Advanced Magnetic Materials, H. Kronmüller, S. Parkin (eds), (2007) John Wiley & Sons, Ltd, p 1710

Keywords: magnetism; ion irradiation; perpendicular anisotropy; Kerr microscopy; MFM

  • Poster
    IEEE International Magnetics Conference - INTERMAG 2008, 04.-08.05.2008, Madrid, Spain

Publ.-Id: 11316

Single Pi- production in np collisions for excess energies up to 90 MeV

Abdel-Bary, M.; Brinkmann, K.-T.; Clement, H.; Doroshkevich, E.; Dshemuchadse, S.; Erhardt, A.; Eyrich, W.; Freiesleben, H.; Gillitzer, A.; Jäkel, R.; Karsch, L.; Kilian, K.; Kuhlmann, E.; Möller, K.; Morsch, H. P.; Naumann, L.; Paul, N.; Pizzolotto, C.; Ritman, J.; Roderburg, E.; Schroeder, W.; Schulte-Wissermann, M.; Sefzick, T.; Teufel, A.; Ucar, A.; Ullrich, W.; Wintz, P.; Wüstner, P.; Zupranski, P.

The quasifree reaction np -> pppi- was studied in a kinematically complete experiment by bombarding a liquid-hydrogen target with a deuteron beam of momentum 1.85GeV/c and analyzing the data along the lines of the spectator model. In addition to the three charged ejectiles the spectator proton was also detected in the large-acceptance time-of-flight spectrometer COSY-TOF. It was identified by its momentum and flight direction thus yielding access to the Fermi motion of the bound neutron and to the effective neutron 4-momentum vector Pn which differed from event to event. A range of almost 90MeV excess energy above threshold was covered. Energy-dependent angular distributions, invariant-mass spectra as well as fully covered Dalitz plots were deduced. Sizeable pp FSI effects were found as were contributions of p and d partial waves. In comparison with existing literature data the results provide a sensitive test of the spectator model. The behavior of the elementary cross-section σ01 close to threshold is discussed in view of new cross-section data.

Keywords: 13.75.Cs - Nucleon-nucleon interactions (including antinucleons and deuterons etc.); 25.10.+s - Nuclear reactions involving few-nucleon systems

  • European Physical Journal A 36(2008), DOI: 10.1140/epja/i2007-10543-x

Publ.-Id: 11315

Radiation Source ELBE – Electromagnetic Radiation for Fundamental Research

Justus, M.

Since 2003, the Radiation Source ELBE at the Research Centre Dresden-Rossendorf (FZD) delivers infrared light, X-rays and Bremsstrahlung of high intensity for fundamental research. The experimental proposals are associated with the FZD programs “Advanced Materials Research”, “Cancer Research” as well as “Nuclear Safety Research and come from the institute itself, as well as from international guests.
The design and the technical implementation of the 40 MeV superconducting electron beam linear accelerator are explained with regard to the generation of the different types of secondary radiation. The article also highlights beam diagnostics and optimization of the beam quality and availability with respect to the different demands on its main properties (energy, bunch charge, emittance, time structure) and the ongoing installation of facility parts.

Keywords: ELBE

  • Lecture (Conference)
    DPG Frühjahrstagung Freiburg 08, 03.-07.03.2008, Freiburg, Deutschland


Publ.-Id: 11314

Die numerische Auswertung von Kleinwinkelstreukurven

Küchler, R.

Aus dem Streubild der Kleinwinkelstreuung kann im Allgemeinen, die die Streuvertei-lung erzeugende Struktur nicht eindeutig rekonstruiert werden. Die Ursache dafür wird erörtert und die damit verbundenen Einschränkungen bei der rechnerischen Auswertung der Streukurven an Beispielen veranschaulicht. Dies geschieht an Streukurven, die mit bekannten Größenverteilungen berechnet wurden. Weiterhin wird untersucht, welche Fit- Ansätze sich zur Auswertung der Kleinwinkelstreuexperimente am besten eignen. Als Fit- Ansätze wurden Reihenentwicklungen nach Trigonometrischen- und Polynomfunkti-onen und eine theoretisch motivierte Funktion verwendet. Neben dem entscheidenden Vergleich mit der Streukurve der Ausgangsfunktion werden die Ergebnisse auch den Rechnungen gegenübergestellt, die mit der weit verbreiteten Glatter- Methode erzielt werden.

Keywords: small-angle scattering; data evaluation; indirect fourier transformation; density distribution

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-496 2008
    ISSN: 1437-322X


Publ.-Id: 11313

First CoMFA Characterization of Vesamicol Analogs as Ligands for the Vesicular Acetylcholine Transporter

Szymoszek, A.; Wenzel, B.; Scheunemann, M.; Steinbach, J.; Schüürmann, G.

Vesamicol derivatives are promising candidates as ligands for the vesicular acetylcholine transporter (VAChT) to enable in vivo imaging of cholinergic deficiencies if applied as positron emission tomography radiotracers. So far, optimization of the binding affinity of vesamicol-type ligands was hampered by the lack of respective quantitative structure–activity relationships. We developed the first quantitative model to predict, from molecular structure, the binding affinity of vesamicol-type ligands toward VAChT employing comparative molecular field analysis (CoMFA) for a set of 37 ligands, covering three different structural types (4-phenylpiperidine, spiro, and tropan derivatives of vesamicol). The prediction capability was assessed by leave-one-out cross-validation (LOO) and through leaving out and predicting 50% of the compounds selected such that both the training and the prediction sets cover almost the whole range of experimental data. The statistics indicate a significant prediction power of the models (q2 (LOO) = 0.66, q2 (50% out) = 0.59–0.74). The discussion includes detailed analyses of CoMFA regions critical for ligand−VAChT binding, identifying structural implications for high binding affinity.

Publ.-Id: 11312

A population balance approach for polydispersed bubbly flows considering size dependent bubble forces

Krepper, E.; Frank, T.; Lucas, D.; Prasser, H.-M.; Zwart, P.

A generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into CFX-10. By simulating a poly-dispersed gas-liquid two-phase flow, the mass exchanged between bubble size classes by bubble coalescence and bubble fragmentation as well as the momentum exchange due to bubble size dependent bubble forces have to be considered. Particularly the lift force has been proven to play an important role for establishing a certain bubble size distribution dependent flow regime.
The derived model has been validated against experimental data from the TOPFLOW test facility at the Forschungszentrum Dresden-Rossendorf (FZD). The wire-mesh technology measuring local gas volume fractions, bubble size distributions and velocities of gas and liquid phases was applied. Numerous tests investigating air-water flow and steam-water flow at saturation conditions in vertical pipes having a length up to 8 m and a diameter up to 200 mm were performed and used for model validation. Furthermore in order to check the model framework for a more complex flow situation, further experiments on the flow field around a half moon shaped asymmetric obstacle were performed and the flow conditions were simulated by applying the inhomogeneous MUSIG model in direct comparison.
The paper describes the main concepts of the CFD model approach and presents model validation and application cases. The inhomogeneous MUSIG model approach was shown to be able to describe bubbly flows with higher gas content. Particularly the separation phenomenon of small and large bubbles, which was proven to be a key phenomenon for the establishment of the corresponding flow regime, is well described. Weaknesses in this approach can be attributed to the characterization of bubble coalescence and bubble fragmentation, which must be further investigated.

Keywords: bubbly flow; CFD; non-drag forces; bubble breakup; bubble coalescence; population balance; validation

  • Lecture (Conference)
    6th International Conference on COMPUTATIONAL FLUID DYNAMICS in the Oil & Gas, Metallurgical and Process Industries, 10.-12.06.2008, Trondheim, Norway
  • Contribution to proceedings
    6th International Conference on COMPUTATIONAL FLUID DYNAMICS in Oil & Gas, Metallurgical and Process Industries, 10.-12.06.2008, Trondheim, Norway

Publ.-Id: 11311

A study of uranium phosvitin complexation using ATR FT-IR and EXAFS spectroscopy

Li, B.; Raff, J.; Rossberg, A.; Foerstendorf, H.

Phosvitin is a highly water soluble 34 kDa protein containing 10 % (w/w) phosphate groups. It serves as an ideal model for the investigation of the interaction of U(VI) with phosphorylated proteins by attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy and EXAFS spectroscopy.
In our study, phosvitin and its complex with U(VI) were first studied in aqueous solution at various pH values by ATR FT-IR. In order to understand the inter-atomic coordination of the U(VI) to the functional groups of the protein, in particular to phosphate groups, the samples containing U(VI) phosvitin complex with different U(VI) concentrations were additionally investigated by EXAFS spectroscopy.
Different protonated states of phosphate groups on the protein have been first identified by infrared spectra of phosvitin in solution at different pH. Comparing the spectra with those of inorganic phosphate solutions, it is obvious that at pH 4 the phosphate groups appear as dihydrogen phosphate, and at pH 8 as hydrogen phosphate.
Upon the adsorption of uranium onto phosvitin the protein is irreversible denatured. Infrared spectra of the protein, which were denatured thermally in the absence of U(VI) or denatured by other bivalent metal ions, recorded at pH 4 demonstrate that deprotonation occurs during the protein denaturation. Among those spectra, the U(VI) phosvitin complexes with lower U(VI) concentrations (10−4 M, and 10−5 M) show a unique peak at or even lower than 918 cm−1, while this peak appears at 925 cm−1 for the complex with higher U(VI) concentration (10−3 M). As the characteristic νas(UO22+) mode representing a U(VI) complexation to carboxylic groups appears at 923 cm−1 on the IR spectra, the discovered unique peak indicates coordination of the U(VI) predominately to phosphate groups of the phosvitin.
The EXAFS spectra of the U(VI) phosvitin complex are in good agreement to the spectra of other organic U(VI) phosphate complexes confirming the results from IR spectroscopy. The formation of a U(VI) complex, which is similar to the so-called “Feldman complex” is discussed.

Keywords: Phosvitin; uranium; phosphorelated protein; ATR FT-IR; EXAFS

  • Contribution to proceedings
    BioMetals 2008, 14.-18.07.2008, Santiago de Compostela, Spain
  • Poster
    Biometals 2008, 14.-18.07.2008, Santiago de Compostela, Spain

Publ.-Id: 11310

MULTIMAG - A MULTIpurpose MAGnetic system for physical modelling in magnetohydrodynamics

Pal, J.; Cramer, A.; Gundrum, T.; Gerbeth, G.

At laboratory scales, liquid metal model experiments are an important tool to understand the details of the flow structure and the transport properties of flows occurring in real-scale facilities, as well as to validate the multitude of numerical codes for flow simulations. Our MULTIpurpose MAGnetic field system facility is based on a compact coil system to investigate the influence of different magnetic fields on electrically conducting fluids. Several features distinguish MULTIMAG from other systems: (i) With its large experimental volume of H = 400 mm and D = 365 mm industrially relevant parameter can be achieved. (II) Due to the absence of any ferromagnetic materials, the possibility of linear superposition of different magnetic field types (rotating, traveling, pulsating, DC-homogen and -cusp) exists. (III) Special developed current sources allow arbitrary waveforms for each of the field types in any phase relation. Besides the main aim to describe MULTIMAG, the present paper instances results of performed flow measurements.

Keywords: Magnetohydrodynamics; Stirring device; Tailored magnetic fields

  • Flow Measurement and Instrumentation 20(2009), 241-251

Publ.-Id: 11309

Non-covalent interactions between nucleosides and molecular clips – comparison of phosphate, phosphonate and sulphate containing clips

Raditzky, B.

Water-soluble clips are possible molecules to study the weak, non-covalent interactions, responsible for many biological processes. The association between nucleosides and sulphate containing clips, with naphthalene or anthracene sidewalls, has been studied by time-resolved laser-induced fluorescence spectroscopy with ultrafast pulses (fs-TRLFS). The determined association constants for the 1:1 complexes range from log Ka = 3.9 – 4.2. The measured spectra assumes the appearance of excited state species.

Keywords: moleculare clips; nucleosides; sulphate clips; fs-TRLFS; association

  • Lecture (Conference)
    5th SUPRAPHONE/4th WG Meeting COST D31, 29.-31.05.08, Prague, Czech Republic

Publ.-Id: 11308

Ion bombardment of shape memory alloy (SMA) Ni-Ti films

Martins, R. M. S.; Schell, N.; von Borany, J.; Mücklich, A.; Siva, R. J. C.; Mehesh, K. K.; Braz Fernandes, F. M.

Ni-Ti films were deposited by magnetron cosputtering using a chamber installed into the six-circle goniometer of the Rossendorf BeamLine at ESRF. The in-situ XRD studies enable us to identify different steps of the structural evolution during growth and annealing. The use of diverse type of substrates and the effect of the application of a bias voltage to the substrate during film deposition were major tools in this study. When a negative bias voltage is applied, it causes a higher energetic ion bombardment of the growing film, resulting in an enhanced surface-atom mobility, but at sufficiently high voltage, leads to defect formation. Cross-sectional TEM and SEM micrographs have shown a change in the morphology of the films linked with different levels of bias voltages (0, -45 and -90V in this study). The transformation behaviour of the sputtered Ni-Ti films (as shown by electrical resistivity measurements) is influenced by the energy of the bombarding ions. The microstructure details resulting from the deposition using different bias values are discussed.
Additionally, it has been commissioned an ion gun allowing post-deposition ion irradiation or ion bombardment during sputter deposition. In this first series of experiments, a Ni-Ti film was irradiated with He ions after deposition (without exposing the film to the atmosphere, i.e. reduced surface oxide formation) thus modifying deliberately the microstructure of the film locally. A layer of approximately 50% of the thickness of the film was selectively removed at the irradiated region (6 x 6 mm²).
This type of studies will be very useful for the easier design and miniaturization of Ni-Ti films based devices in the field of micro-electro-mechanical systems (MEMS).

Keywords: thin films; shape memory alloy; ion irradiation; X-ray studies; ROBL

  • Lecture (Conference)
    Microscience 2008, 23.-26.06.2008, London, United Kingdom

Publ.-Id: 11307

Synchronized force and PIV measurements on an electromagnetically forced separated flow

Cierpka, C.; Weier, T.; Gerbeth, G.

Periodic addition of momentum by wall--parallel electromagnetic forces has a strong influence on the separated region of a stalled airfoil. The controlled flow possesses typically a small number of relatively large vortices, which are believed to be related to the control mechanism.
In the present paper synchronized force and particle image velocimetry measurements of the excited flow at a NACA 0015 (\alpha = 20^{\circ}, Re = 1\cdot10^{5}) will be presented.

Keywords: flow separation control; PIV; NACA0015

  • Lecture (Conference)
    ICTAM2008 - International Congress of Theoretical and Applied Mechanics, 24.-30.08.2008, Adelaide, Australia
  • Contribution to proceedings
    ICTAM2008 - International Congress of Theoretical and Applied Mechanics, 25.08.-29.09.2008, Adelaide, Australia, 978-0-9805142-1-6

Publ.-Id: 11306

Was misst die „Perfusion-CT“?

van den Hoff, J.; Hietschold, V.; Abramyuk, A.; Abolmaali, N.; Kotzerke, J.


Dynamische CT-Untersuchungen nach Kontrastmittelgabe (KM) bilden die Grundlage der als „Perfusion-CT“ bezeichneten Quantifizierungsverfahren, welche zunehmend zur Bewertung der Gewebeperfusion genutzt werden. Diese Ansätze finden z.Zt. v.a. Beachtung bei onkologischen Untersuchungen an PET/CT-Geräten, um simultan Informationen zu Tumorstoffwechsel (PET)
und -perfusion (CT) zu erhalten. Ziel dieser Arbeit war eine Analyse der Aussagekraft der verwendeten Modelle unter Beachtung messtechnisch gegebener Randbedingungen.


Zwei Modelle wurden betrachtet: 1. das in der Perfusion-CT als Patlak-Modell bezeichnete, 2. die adiabatische Lösung des „tissue homogeneity“ Modells (vgl. z. B. [2]). Aus den Lösungen der Modellgleichungen wurden Gewebeantwortkurven berechnet und im Hinblick auf Parameteridentifizierbarkeit und korrekte Parameterinterpretation analysiert.


Der als „Patlak-Modell“ bezeichnete Ansatz ist identisch mit einem irreversiblen 1-Kompartment-Modell zzgl. eines Blutvolumenterms, welches auf die frühe Phase des KM-Transits angewandt wird. Eine Analyse verfügbarer Daten (z. B. [1)) zeigt, dass die allgemein als Perfusion interpretierte Steigung K des entsprechenden Patlak-Plots numerisch typischerweise um den Faktor 5-10 von realistischen Perfusionswerten abweicht. Wir interpretieren dies dahingehend, dass dieser Parameter, welcher dem unidirektionalen KM-Transport in den Extravasalraum entspricht, i.a. unkorreliert zur Gewebeperfusion ist, da die effektive Extraktion des KM sehr klein ist (typischerweise kleiner als etwa diejenige von FDG). Vielmehr entspricht dieser Parameter eher dem PS-Produkt des KM im Zielgewebe. Das „tissue homgeneity“ Modell enthält die Perfusion explizit als freien Parameter. Die Quantifizierung setzt jedoch voraus, dass die Boluspassage durch das Kapillarbett mit so hoher zeitlicher Auflösung erfasst wird, dass diese vom Zeitverhalten im arteriellen Blut unterscheidbar bleibt. Dies erscheint aufgrund der beschränkten statistischen Genauigkeit und verschiedener systematischer Fehlerquellen (wie Bewegungsartefakten) praktisch kaum möglich.


Der Begriff Perfusion-CT suggeriert die Fähigkeit, die Perfusion aus der Gewebediffusion von Kontrastmitteln analog zum Einsatz diffusibler Tracer in der PET bewerten zu können. Diese Fähigkeit ist aber im Allgemeinen nicht gegeben. Eine kritische Bewertung der Aussagekraft des Verfahrens, namentlich im Hinblick auf den Einsatz an PET/CT-Geräten bei onkologischen Fragestellungen erscheint dringend geboten.


(1) Ng, QS et al.: „Lung cancer perfusion at multi-detector row CT: reproducibility of whole tumor quantitative measurements.“, Radiology 239(2), pp. 547-53 (2006).
(2) Stewart et al.: „Correlation between hepatic tumor blood flow and glucose utilization in a rabbit liver tumor model.“, Radiology 239(3), pp. 740-50 (2006).

  • Lecture (Conference)
    46. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 23.-26.04.2008, Leipzig, Germany
  • Abstract in refereed journal
    Nuklearmedizin 47(2008)2, A60

Publ.-Id: 11305

Vergleich einer 2D- und 3D-basierten ROI-Auswertung beim F-18-DOPA-Hirn-PET in einem Normalkollektiv

Oehme, L.; Hofheinz, F.; Wolz, M.; Pötzsch, C.; van den Hoff, J.; Kotzerke, J.


Die in der Parkinsondiagnostik relevanten Strukturen, Nucleus caudatus und Putamen, sind komplexe dreidimensionale Strukturen. Ziel der Untersuchung war es, die Ergebnisse der bisherige 2D-basierte ROI-Auswertung (CAPP-Software, Siemens/CTI) mit einer ROI-Auswertung im 3D-Datensatz (Softwarepaket ROVER, ABX Radeberg) zu vergleichen.


Ausgewertet wurden neun F-18 -DOPA-Hirn-PET-Datensätze gesunder Kontrollpersonen (positives BfS-Gutachten und Ethikvotum). 60 min nach 150 mg Carbidopa per os sowie nach 10 min Transmissionsmessung erfolgte die dynamische Akquisition über 90 min mit Injektion von 185 MBq F-18-DOPA i.v. (ECAT EXACT HR+, Siemens/CTI). Die Auswertung erfolgte in einem Pseudo-2D-Verfahren (Summenbild 10-90min p.i., Ausrichtung Putamen horizontal, Addition von 4 Schichten auf Höhe von Nucl. Caudatus und Putamen, Positionierung von ROIs vordefinierter Größe und Anzahl über Nucl. Caudatus, Putamen, Referenzgewebe occipital) und in einem 3D-Datensatz (freie Positionierung o.g. ROIs vordefinierter Größe und Anzahl in allen 3 Raumebenen). Die Dopamin-Einstromraten wurden mittels Patlak-Analyse bestimmt. Beide Auswerteverfahren wurden verblindet von zwei Untersuchern ausgeführt. Verglichen wurden die Abweichungen innerhalb einer Auswertemethode zwischen den Untersuchern (U1, U2) sowie die Abweichungen zwischen den zwei Auswertemethoden (2D, 3D).


Die Auswertung mit der 3D-Methode war schneller und wurde als einfacher empfunden. Weder innerhalb einer Auswertemethode zwischen den 2 Untersuchern noch zwischen den 2 Auswertemethoden eines Untersuchers waren signifikante Unterschiede zu finden. Über das Kollektiv gemittelt betrugen die Einstromraten (1/min, m+/-sd) für U1-2D; U2-2D; U1-3D; U2-3D: Nucl. Caudatus rechts 0,0181+/-0,0010; 0,0174+/-0,0018; 0,0175+/-0,0022; 0,0174+/-0,0017; Nucl. Caudatus links 0,0185+/-0,0013; 0,0180+/-0,0019; 0,0179+/-0,0013; 0,0183+/-0,0020; Putamen rechts 0,0185+/-0,0006; 0,0180+/-0,0018; 0,0185+/-0,0013; 0,0185+/-0,0017; Putamen links 0,0185+/-0,0013; 0,0180+/-0,0018; 0,0182+/-0,0018; 0,0183+/-0,0015. Die relativen Abweichungen (Differenz/Summe) liegen für alle Paarvergleiche jeweils (gemittelt über alle ROIs) innerhalb +/-2 % (sd < 5 %), allerdings gibt es auch Ausreißer mit Unterschieden größer als +/- 10 %.


Die 2D- als auch die 3D-basierte Auswertung mittels Standard-ROIs definierter Anzahl und Größe lieferten in diesem Normalkollektiv vergleichbare Ergebnisse, wobei die 3D-Methode einen geringeren Zeitbedarf erfordert und als einfacher empfunden wird. In einem weiteren Schritt werden beide Auswertemethoden auf Datensätze von Patienten mit M. Parkinson mit unterschiedlicher Krankheitsintensität angewendet, um die Variabilität der Ergebnisse in Abhängigkeit von Auswertemethode und Untersucher abschätzen zu können.

  • Poster
    46. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 23.-26.04.2008, Leipzig, Germany
  • Abstract in refereed journal
    Nuklearmedizin 47(2008)2, A108

Publ.-Id: 11304

Determination of harmonic and pulsed eddy current distributions in a liquid metal

Forbriger, J.; Galindo, V.; Gerbeth, G.; Stefani, F.

The spatio-temporal distribution of harmonic and pulsed eddy currents in the liquid metal alloy GaInSn positioned above an excitation coil is determined by measuring the corresponding voltage drop in an electric potential probe. The resulting spatio-temporal eddy current field is compared with the corresponding analytical expressions for a conducting half-space. Deformations of the eddy current distribution due to a non-conducting ring immersed into the liquid metal are measured and compared with numerical results.

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Proceedings of the 7th International PAMIR Conference on Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 809-813
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Publ.-Id: 11303

Constraining the geodynamo by sequences of field reversals

Fischer, M.; Gerbeth, G.; Stefani, F.

Using a spherically symmetric mean field dynamo model with a quenched helical turbulence parameter alpha under the influence of noise and external periodic forcing we try to constrain its essential parameters by typical features of field reversal. Our results indicate that the geodynamo works in a highly supercritical state, that the relative strength of the periodic forcing due to the Milankovic cycle of the Earth’s orbit eccentricity is approximately 15 per cent of the general dynamo strength, and that the magnetic diffusion time is significantly reduced in comparison with the diffusion time resulting from the molecular conductivity.

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Proceedings of the 7th International PAMIR Conference on Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 225-229
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Publ.-Id: 11302

Liquid metal experiments on the helical magnetorotational instability

Stefani, F.; Gerbeth, G.; Gundrum, T.; Szklarski, J.; Rüdiger, G.; Hollerbach, R.

The magnetorotational instability (MRI) plays an essential role in the formation of stars and black holes. By destabilizing hydrodynamically stable Keplerian flows, the MRI triggers turbulence and enables outward transport of angular momentum in accretion discs. We present the results of a liquid metal Taylor-Couette experiment under the influence of helical magnetic fields that show typical features of MRI at Reynolds numbers of the order 1000 and Hartmann numbers of the order 10. Particular focus is laid on an improved experiment in which split end caps are used to minimize the Ekman pumping.

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Proceedings of the 7th International PAMIR Conference on Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 97-101
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
  • Magnetohydrodynamics 45(2009)2, 135-143
    ISSN: 0024-998X

Publ.-Id: 11301

Synthese und radiopharmakologische Charakterisierung von Kohlenstoff-11 markierten Chromenderivaten als neuartige nicht-steroidale Liganden für den Glucocorticoidrezeptor (GR)

Steiniger, B.; Bergmann, R.; Pietzsch, J.; Wüst, F.


Glucocorticoidrezeptoren (GR) nehmen innerhalb der Hypothalamus-Hypophysen-Nebennieren (HHN)-Achsenregulation eine wichtige Rolle ein. Störungen dieses wichtigen neuroendokrinen Regelsystems sind charakteristisch für verschiedene neuropsychiatrische Erkrankungen, wie z. B. Depression [1]. Ziel der vorliegenden Arbeit war die Entwicklung von Radiotracern für die Darstellung von GR im Gehirn mittels PET. Dabei sollten besonders verschiedene GR-bindende Chromenderivate als neueuartige nicht-steroidale GR-Liganden mit 11C markiert und radiopharmakologisch charakteri-siert werden.


Ausgehend von chromenbasierten Sulfonamiden wurden verschiedene nicht-steroidale Verbindungen als Liganden für den GR synthetisiert. Die Markierung der Desmethyl-Vorstufen erfolgte in einem automatisierten Synthesemodul über eine regioselektive O-Methylierung mit [11C]MeI. Die radio-pharmakologische Charakterisierung der hergestellten Verbindungen umfasste Bioverteilungs-untersuchungen, Autoradiographie und dynamische Kleintier-PET-Untersuchungen mit normalen Wistar-Ratten.


Die Radiomarkierung mit [11C]MeI konnte durch die Verwendung von NaH als Base und DMF als Lösungsmittel regioselektiv als O-Methylierung durchgeführt werden. Die als Konkurrenzreaktion stattfindende N-Methylierung konnte dadurch weitgehend unterdrückt werden. Die 11C-markierten Chromenderivate konnten in radiochemischen Ausbeuten von 33% und spezifischen Aktivitäten von 15 GBq/µmol erhalten werden. Bioverteilungsstudien zeigten Hirnanreicherungen von bis zu 1.6 %ID/g nach 5 min und 0.6 %ID/g nach 60 min. In den Kleintier-PET Aufnahmen waren GR-reiche Gehirnareale wie der Cortex gut sichtbar.


Das vorgestellte Chromengerüst eignet sich als vielversprechende Leitstruktur für die Entwicklung neuer GR-bindender Radiotracer mit moderater Lipophilie. Weitere radiopharmakologische Untersuchungen sind für eine abschließende Bewertung der vorgestellten Verbindungen als PET-Radiotracer für die Darstellung von GR im Gehirn notwendig.


[1] E. R. De Kloet et al. Endocr. Rev. 1998 19(3):269-301.

  • Lecture (Conference)
    46. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 23.-26.04.2008, Leipzig, Germany
  • Abstract in refereed journal
    Nuklearmedizin 47(2008)2, A31

Publ.-Id: 11300

A Novel Approach for Predicting the Positron Emitter Distributions Produced during Therapeutic Ion Irradiation

Priegnitz, M.; Fiedler, F.; Kunath, D.; Laube, K.; Parodi, K.; Sommerer, F.; Enghardt, W.

In-beam PET is a valuable method for a beam-delivery independent dose monitoring in radiation therapy with ion beams. The clinical feasibility of in-beam PET has been demonstrated for carbon and proton beams up to now. From radiobiological point of view it is highly desirable to perform tumor irradiation also with other ions. To extend the application of in-beam PET also to these ions, extensive knowledge about positron emitter production via nuclear fragmentation reactions during ion irradiation is necessary. To model the positron emitter production correctly, cross
sections for all possible nuclear reactions occurring in the tissue during irradiation and leading to positron emitters are required. Since for many ions of therapeutic interest these cross sections are not available in the required energy range, a novel approach for estimating the positron emitter production from experimental data is introduced. The prediction of positron emitter distributions is based on depth dependent thick target yields, which are deduced by linear superposition of measured yields in water, graphite and polyethylene as reference materials. First results on the prediction of positron emitter distributions in polymethyl methacrylate (PMMA) targets induced by Li and C irradiation are presented. By comparison with data deduced from experiments, it is shown that a rather accurate prediction of positron emitter distribution in PMMA is possible with this method.

  • Contribution to proceedings
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany
  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany

Publ.-Id: 11299

Synthesis and in vitro evaluation of new diphenyl ether derivatives as serotonin transporter ligands

Guo, Y.; Chen, X.; Jia, H.; Deuther-Conrad, W.; Brust, P.; Steinbach, J.; Vercouillie, J.; Liu, B.

For the development of new ligands as potential imaging agents for the serotonin transporter (SERT), a series of diphenyl ether derivatives have been synthesized, characterized, and evaluated for their in vitro binding affinities to the SERT. Among the above compounds, 2-(2-((dimethylamino)methyl)-4-fluorophenoxy)-5-bromobenzenamine (15) and 2-(2-((dimethylamino)methyl)-4-fluorophenoxy)-5-iodobenzene amine (16) show high binding affinities for the SERT with K i values of 0.28 and 0.20 nmol·L−1, respectively. They can be further labeled with carbon-11, fluorine-18, iodine-123 or bromine-76, and evaluated as useful imaging agents for the SERT. Moreover, the study of the structure-activity relationship (SAR) provides some useful information for the future design of new ligands.

Keywords: serotonin transporter; diphenyl ether; imaging agents; in vitro evaluation

Publ.-Id: 11298

Bacterial and archaeal communities' composition of uranium-contaminated soils in Bulgaria

Radeva, G.; Kenarova, A.; Buchvarova, V.; Flemming, K.; Selenska-Pobell, S.

The uranium mining waste piles, mill tailing, and disposal sites in several regions of Bulgaria are highly contaminated with toxic metals as a result of the U mining and milling performed in the past. In order to suggest appropriate bioremediation strategies for such environments, the phylogenetic composition and structure of the microbial communities in two uranium-contaminated sites were characterized by using molecular approaches. Three soil samples were studied: two of them were collected from different depths of a U mill tailings (Metallurg Buhovo, located in western Bulgaria), and the third - from a former U mining site (mine Sliven, South-Eastern Bulgaria). 16S rRNA gene libraries were generated from total community DNA, using universal bacterial and archaeal oligonucleotide primer sets. Four hundred fifty bacterial clones were analyzed and grouped in sixty eight operational taxonomic units (OTUs). Three hundred ninety two archaeal clones of the clone libraries from the two U mill tailings soil samples were organized in fourteen archaeal OTUs. Rarefaction analysis indicated a high diversity of bacterial sequences, while the archaeal sequences were less diverse. Most of the bacterial sequences were affiliated with Proteobacteria from Alpha- Beta-, and Gamma- subdivisions. 16S rRNA gene sequences representing Bacteroidetes, Acidobacteria, Verrucomicrobia, Actinobacteria, and Gemmatimonadete were found in various numbers as well. Our results showed that the composition of the microbial communities in the two different studied ecosystems was diverse and environment-specific. Acidobacteria and Bacteroidetes were predominant in the soil samples collected from the U mill tailings, whereas Gammaproteobacteria and Actinobacteria were characteristic for the soil from the U mining waste. All archaeal 16S rRNA gene sequences retrieved from the U mill tailings soil samples were affiliated with the group 1.1b of the mesophilic soil Crenarchaeota which still does not contain any cultured representatives. Closely related 16S rRNA gene sequences were repeatedly found earlier in soil samples from different U mining waste piles and mill tailings in the east part of Germany.
Taken into account the significance of Crenarchaeota in the global nitrogen cycle, the studied soil samples were assayed also for the presence of ammonia monooxygenase subunit A (amoA) gene. Using PCR primers targeting archaeal amoA genes, two clone libraries were constructed and analyzed.

Keywords: 16S rRNA; bacterial diversity; Archaea; uranium mining wastes

  • Contribution to proceedings
    XII International Congress of Bacteriology and Applied Microbiology, 05.-09.08.2008, Istanbul, Turkey

Publ.-Id: 11297

Accumulation of Heavy Metals by Microorganisms: Biomineralization and Nanocluster Formation

Selenska-Pobell, S.; Merroun, M.

Bacteria and archaea are the most ubiquitous organisms in terrestrial and aquatic environments. They play a major role in deposition and weathering of a large variety of minerals enriched with or consisting mainly of different metals, such as iron, manganese, copper, gold, and even radionuclides (e.g. uranium). The structure of biologically synthesized minerals is strongly influenced by the metabolic properties of the bacterial or archaeal strains involved in their production and also by the metal binding potentials of their cell wall components.
This chapter is focused on cell wall dependent accumulation and biomineralization of iron and uranium. By using transmission electron microscopic analysis in combination with x-ray absorption and time-resolved laser-induced fluorescence spectroscopic analyses it is demonstrated that the Gram-negative and most of the Gram-positive bacteria as well as some archaea immobilize U(VI) at their cell walls or extracellularly in a form of uranyl phosphate compounds. However, some Gram-positive bacteria which possess highly ordered proteinaceous surface layers (S-layers), are immobilizing U(VI) not only by phosphate groups mainly from their peptidoglycan but also by the carboxylic groups of the aspartate and glutamate stretches of their S-layers.
In addition, the cell wall supported formation of metallic palladium nanoclusters by some bacteria is presented as well. Despite the different mechanisms of the biological deposition of Pd by Gram-negative and Gram-positive bacteria, the nanoparticles formed by both organisms have almost identical size and catalytic activity.

  • Contribution to external collection
    König, H., Claus, H., Varma, A.: Prokaryotic Cell Wall Components – Structure and Biochemistry, Heidelberg: Springer Verlag, 2010, 483-500

Publ.-Id: 11295

Biodistribution and metabolism of hCT-derived cell-penetreting peptides

Bergmann, R.; Rennert, R.; Közle, I.; Franke, J.; Schlesinger, J.; Neundorf, I.


Cell-penetrating peptides (CPP) derived from the native peptide hormone human calcitonin (hCT) represent a high potential drug delivery system for in vivo intracellular targeting of diagnostic and therapeutic compounds. Cell penetration of hCT-derived substances was
verified in vitro, however, the knowledge about CPP in vivo distribution and metabolism is very limited. Therefore we studied the in vivo radiopharmacology of 68Ga radiolabeled DOTAmodified, hCT-derived CPP in rats using small animal PET.


Three hCT-derived peptides (hCT(9-32), LGTYTQDFNKFHTFPQTAIGVGAPNH2; [f12,16]-hCT(9-32), LGTfTQDfNKFHTFPQTAIGVGAP-NH2; random (rd)-hCT(9-32), FLTAGQNTIQTPVKTGGHFPFADY-NH2) were at the N-terminus modified with DOTA. The biodistribution and kinetics of the radiolabeled 68Ga-DOTA-hCT(9-32) or 68Ga-DOTA-[f12,16]-hCT(9-32) or 68Ga-DOTA-rd-hCT(9-32) were studied with small animal PET. The arterial blood at different time points, and urine were analyzed for radio-metabolites.


The radio-peptides were eliminated mainly by the renal system, more than 50% of the injected dose was found at 60 min after injection in the urine, only small amounts of the activity were detected in the intestine. The general activity retention in the body was low, except the kidneys. The blood clearance of the original peptides reached terminal half-lifes of 68Ga-DOTAhCT(9-32) 15.9 min, 68Ga-DOTA-[f12,16]-hCT(9-32) 20.9 min, 68Ga-DOTA-rd-hCT(9-32) 15.8 min; the relative AUC in comparison to 68Ga-DOTA-hCT(9-32) were 100%, 170%, and 51%, respectively. The patterns of metabolic cleavage in the arterial blood were different. The 68Ga-DOTA-[f12,16]-hCT(9-32) was metabolized to three radio-metabolites after 30 min, the other radiopeptides were degraded to more than five radioactive metabolites.


It was shown that D-amino acid modifications of the sequence hCT(9-32) resulted in an increased in vivo stability and lower retention in the kidney cortex. The blood clearance and the elimination of the 68Ga-DOTA-peptides were relatively high and should be decreased by
structural changes to enhance the tissue uptake of this drug carrier system.

  • Lecture (Conference)
    19th Meeting of the International Research group in Immuno-Scintigraphy and Therapy (IRIST), 25.-28.06.2008, Krakow, Poland

Publ.-Id: 11294

Bacteria Heavy Metal Interactions: Biomineralization and Nanoclusters Formation

Selenska-Pobell, S.

Bacteria exhibit fascinating resistant mechanisms to extreme temperatures, acidity, alkalinity, high metal, radionuclide, and salt concentrations. For this reason, they occupy not only the moderate habitats of humans, animals, plants, and insects but also extremely harsh environments such as hot springs, permafrost, acidic mine drainages, “dead” sees, etc.
Due to their ubiquitous distribution in terrestrial and aquatic environments bacteria play a major role in deposition and weathering in the earth’s crust of a large variety of minerals enriched with or consisting mainly of different metals, such as iron, manganese, copper, gold, and even radionuclides (e.g. uranium). The structure of biologically synthesized minerals is strongly influenced by the metabolic properties of the bacterial or archaeal strains involved in their production and also by the differences in their cell wall organization.

  • Invited lecture (Conferences)
    Invited talk at Ben Gurion University of the Negev, 02.04.2008, Negev, Israel

Publ.-Id: 11293

A comparative study of n.c.a. sodium [18F]fluoroacetate and sodium [11C]acetate in xenotransplanted tumor bearing mice

Bergmann, R.; Richter, S.; Pietzsch, J.; Beuthien-Baumann, B.; Wüst, F.

Objectives :

This study describes the radiosynthesis of [18F]fluoroacetate (18F-FAC), radiopharmacological characterization, and molecular imaging of oxidative metabolism in tumor bearing mice using 18F-FAC in comparison with 11C-ACE.

Methods :

The radiosynthesis of n.c.a. sodium 18F-FAC was performed in two step reaction sequence and subsequent SPE purification in a remotely controlled synthesis module.
Biodistribution, metabolism and small animal PET studies of 18F-FAC and 11C-ACE were carried out in rats and HT-29 tumor-bearing mice.

Results :

18F-FAC was obtained in radiochemical yields of 20-25% within 50 min. Biodistribution data showed higher initial radioactivity uptake in most organs and tissues for 18F-FAC; the initial brain uptake of 0.67 %ID/g at 5 min p.i. followed by a 22% clearance at 60 min p.i. Both radiotracers can clearly delineate the tumor. The tumor-to-muscle ration was 1.8 for 18F-FAC and 1.5 for 11C-ACE. Unlike 11C-ACE, 18F-FAC shows a slow transport of the free radiotracer from the blood pool into the tumor, and 10% of the free fraction of 18FFAC is trapped in tumor tissue.

Conclusions :

The highly reproducible remotely-controlled two step/one pot synthesis of 18FFAC represents an alternative to previously published synthesis routes. The successful PET imaging of xenotransplanted human colorectal adenocarcinoma tumor HT-29 by means of 18F-FAC shows that the radiotracer may not only be restricted for imaging of previously reported prostate cancer tumors. However, the exact mechanism of 18F-FAC tissue uptake remains unclear and should be subject of further studies.

Research Support : Supported in part by the EU FP6 ‘‘BioCare’’, proposal #505785.

  • Lecture (Conference)
    2008 SNM Annual Meeting, 14.-18.06.2008, New Orleans, USA

Publ.-Id: 11292

The impact of implantation defects in SIMOX processing

Kögler, R.; Ou, X.

The impact of implantation induced point defects in SIMOX (Separation by IMplantation of OXygen) processing is explained. The origin of the so-called energy-dose window is shown to be the point defects generated by the oxygen implantation.

Keywords: Oxygen implantation; SIMOX; point defects

  • Lecture (Conference)
    Arbeitstreffen "Punktdefekte", 03.-04.04.2008, Dresden, Deutschland

Publ.-Id: 11291

CFD simulation of convective flow boiling of refrigerant in a vertical annulus

Koncar, B.; Krepper, E.

In this paper a forced convective boiling of Refrigerant R-113 in a vertical annular channel has been simulated by a custom version of the CFX-5 code. The employed subcooled boiling model uses a special treatment of the wall boiling boundary, which assures the grid invariant solution. The simulation results have been validated against the published experimental data. In general a good agreement with the experimental data has been achieved, which shows that the current model may be applied for the Refrigerant R-113 without significantly changing the model parameters. The influence of non-drag forces, bubble diameter size and interfacial drag model on the numerical results has been investigated as well.

Keywords: forced convective boiling; refrigerant R-113; CFD simulations; validation

  • Nuclear Engineering and Design 238(2008), 693-706

Publ.-Id: 11290

Fluctuations due to nonlocal collisions

Morawetz, K.

It is shown that the collision integral describing the nonlocal character of collisions leads to the same mean-field fluctuations in the one-particle distribution as proposed by Boltzmann-Langevin pictures. It is argued that this appropriate collision integral contains the fluctuation-dissipation theorems in equilibrium itself and therefore there is no need to assume additionally stochasticity. This leads to tremendous simplifications in numerical simulation schemes.

  • Poster
    International Workshop on Chaos and Collectivity in Many-Body System, 05.-08.03.2008, Dresden, Germany

Publ.-Id: 11288

The concept of correlated density and its application

Morawetz, K.; Lipavsky, P.; Kolacek, J.; Brandt, E. H.; Schreiber, M.

The correlated density appears in many physical systems ranging from dense interacting gases up to Fermi liquids which develop a coherent state at low temperatures, the superconductivity. The underlying quantum statistical theory in nonequilibrium is the nonlocal kinetic theory developed earlier. One consequence of the correlated density is the Bernoulli potential in superconductors which compensates forces from dielectric currents which allows to access material parameters.

  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany

Publ.-Id: 11287

Contribution of the surface dipole to deformation of superconductors

Morawetz, K.; Lipavsky, P.; Kolacek, J.; Brandt, E. H.; Schreiber, M.

The interaction of the ionic lattice with the superconducting condensate is treated in terms of the electrostatic force in superconductors. It is shown that the surface dipole supplies the force responsible for the volume difference of the normal and superconducting states. Assuming this mechanism we argue
that the usual parametrization of the theory of deformable superconductors should be revisited.

  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany

Publ.-Id: 11286

Enhancement of pairing near reasonant atoms

Morawetz, K.

A correlated fermion system is considered surrounding a finite cavity with virtual levels. The pairing properties are calculated and the influence of the cavity is demonstrated. To this end the Gell-Mann and Goldberger formula is generalized to many-body systems. We find a possible enhancement of pairing temperature if the Fermi momentum times the cavity radius fulfills a certain resonance condition which suggests an experimental realization.

  • Poster
    International Workshop on Chaos and Collectivity in Many-Body Systems, 05.-08.03.2008, Dresden, Germany

Publ.-Id: 11285

Surface deformation and magnetocapacitance of superconductors

Morawetz, K.; Lipavsky, P.; Kolacek, J.; Brandt, E. H.

Electrostatic potentials have been measured at surfaces of superconductors in order to access directly the gap and material parameters. The reason why no thermodynamic corrections are measured as predicted by the theory, e.g. by Rickayzen, has remained a puzzle for almost 30 years. The solution is found in the Budd-Vannimenus theorem due to the surface dipoles. To access thermodynamic corrections one has to look deeper in the bulk like in an experiment by Kumagai et al measuring the quadrupole shift of the NMR in YBCO. The found large magnitude and unexpected sign is explained by the charge transfer between Cu chains and planes. To this end we develop the theory of electrostatic potentials above the Abrikosov vortex lattice within Bardeen's extension of the Ginzburg-Landau theory to low temperatures including the surface dipole.
As applications it is proposed:
(i) The deformation of the crystal due to the presence of vortices is calculated and the corresponding effective mass of vortices is suggested to be measured.
(ii) We found a jump of the magnetocapacitance at the surface critical magnetic field which should be experimentally accessible.

The experimentally confirmed Bernoulli potential is a consequence of the correla ted density which follows from the concept of nonlocal kinetic theory. Therefore we see this Bernoulli potential as a justification of our kinetic equation of nonlocal and non-instantaneous character which has unified the achievements of transport in dense gases with the quantum transport of dense Fermi systems.

  • Invited lecture (Conferences)
    1st Bilateral Estonian-German Workshop, 30.04.-02.05.2008, Tartu, Estland

Publ.-Id: 11284

Phase diagram for interacting Bose systems

Maennel, M.; Morawetz, K.; Schreiber, M.

no abstract available

  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany

Publ.-Id: 11283

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.] [329.] [330.] [331.] [332.] [333.] [334.] [335.] [336.] [337.] [338.] [339.] [340.] [341.] [342.] [343.] [344.] [345.] [346.] [347.] [348.] [349.]