Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33828 Publications

Vertical Gradient Freeze growth in a combined magnetic AC/DC field

Pätzold, O.; Lantzsch, R.; Grants, I.; Stelter, M.; Gerbeth, G.

The Vertical Gradient Freeze (VGF) method is an important technology for the melt growth of bulk compound semiconductors. The structural perfection of the crystals and the distribution of dopants in the material are closely connected to the conditions of heat and mass transport in the liquid phase. The application of external magnetic fields allows for tailoring the melt flow and, hence, gives the possibility to optimize the quality of the crystals and the yield of the growth process.
In this paper experimental and numerical results are presented, showing the influence of a combined traveling magnetic field (TMF) and steady axial magnetic field (DC) on the VGF growth of semiconducting GaAs and Ge single crystals. The quality of the crystals is characterized in terms of the interface deflection, axial/radial macrosegregation and microsegregation. The numerical simulations of the VGF growth are performed using the commercial code CrysMAS. The TMF melt flow and its influence on the interface deflection as well as the resulting local v. Mises stress are calculated on the basis of a global thermal model of the equipment.

Keywords: Vertical Gradient Freeze; crystal growth; traveling magnetic field

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 633-635
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Permalink: https://www.hzdr.de/publications/Publ-11711
Publ.-Id: 11711


An alternating magnetic field driven flow in a spinning cylindrical container and its three-dimensional linear stability analysis

Shatrov, V.; Gerbeth, G.; Hermann, R.

We present a numerical analysis of the free surface liquid metal flow and its three-dimensional linear stability. The flow is driven by an alternating magnetic field in a spinning cylindrical container. The electromagnetic and hydrodynamic fields are fully coupled via the shape of the liquid free surface.

Keywords: free surface liquid metal flow; three-dimensional linear stability

  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 525-529

Permalink: https://www.hzdr.de/publications/Publ-11710
Publ.-Id: 11710


Numerical modeling of the growth of small-diameter intermetallic compound crystals by a two-phase RF floating zone method

Krauze, A.; Priede, J.; Hermann, R.; Gerbeth, G.

We model numerically the growth of small–diameter single crystals of intermetallic compounds by the floating zone technique using two-phase radio-frequency (RF) electromagnetic heating. An axisymmetric quasi-stationary numerical model is implemented as several coupled computer programs for modeling electromagnetic fields, heat source and force density distributions, heat transfer, and turbulent melt flow. The results of model calculations are presented for the growth of Ni crystals of 2 mm in diameter. It is found that the stable molten zone exists in a very narrow range of inductor currents.

Keywords: crystal growth; electromagnetic heating; floating zone technique

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 851-855
  • Poster
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Permalink: https://www.hzdr.de/publications/Publ-11709
Publ.-Id: 11709


Interfacial heat and mass tansfer models

Krepper, E.; Scheuerer, G.

The lesson 4 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of mass and energy exchange between the phases based on the two fluid model approach. After the basic principles the lesson describes the simulation of subcooled boiling and the simulation of cavitation processes.

Keywords: CFD; Two fluid model; heat transfer; mass transfer; boiling; cavitation

  • Invited lecture (Conferences)
    6th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 24.-26.06.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-11708
Publ.-Id: 11708


Practical calculation of bubble column flow with CFX-11

Frank, T.; Lifante, C.; Krepper, E.

The lesson 6 of the "Short Course on Multiphase Flow Modelling" describes the practical simulation of the flow in a bubble column. The necessiy of the correct simulation of the momentum exchange between the phases is shown comparing different results with experiments.

Keywords: CFD; two fluid model; dispersed gaseous phase; drag bubble forces; non drag bubble forces; bubble column

  • Invited lecture (Conferences)
    6th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 24.-26.06.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-11707
Publ.-Id: 11707


Finite-time thermodynamics of shear flows - modelling attractors of simple to complex dynamics

Schlegel, M.; Noack, B.; Ahlborn, B.; Mutschke, G.; Morzynski, M.; Comte, P.; Tadmor, G.

A finite-time thermodynamics formalism is proposed to compute mean flow and fluctuation levels of unsteady incompressible flows. The formalism builds upon a Galerkin model framework (see Noack et al., J. Noneqilib. Thermodyn. 33 (2008) 103-148) and is applied to a periodic vortex shedding regime behind a circular cylinder, homogeneous shear turbulence and the Burgers equation.

Keywords: finite-time thermodynamics; Galerkin methods; turbulence

  • Poster
    Dynamics Days Europe 2008, 25.-29.08.2008, Delft, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-11706
Publ.-Id: 11706


Periodically modulated surfaces and interfaces: Introducing artificial length scales to tailor magnetic properties

Fassbender, J.; Liedke, M. O.; Strache, T.; Marko, D.; Lenz, K.; Keller, A.; Facsko, S.; Tibus, S.; Springer, F.; Albrecht, M.; Rohrmann, H.

In thin magnetic films different intrinsic length scales affect the magnetic properties, e.g., the exchange correlation length determined by the exchange constant and the anisotropy of the material or the grain size of polycrystalline materials determined mainly by the growth conditions and substrates used. In the latter case also the intergranular coupling influences the magnetic properties.

Introducing an artificial extrinsic length scale in the range 10 – 100 nm allows an additional degree of freedom to tailor the overall magnetic properties of the material of choice. This length scale is established by means of low energy ion erosion of semiconductor surfaces which lead to a periodically modulated surface (ripple structure). The periodicity and amplitude can easily be varied by means of the ion erosion parameters [1]. Hence upon thin film deposition modulated surfaces and interfaces of the magnetic films result.

Two different examples will be discussed. i) Induced magnetic anisotropies in soft magnetic films deposited on rippled substrates [2]. The microscopic origin can be extrinsic, due to dipolar stray fields, as well as intrinsic, due to spin-orbit coupling phenomena at monoatomic steps. The relative contribution of both microscopic effects to the macroscopically measurable material properties depend sensitively on the introduced ripple wavelength and amplitude. ii) Magnetic properties of hard magnetic CoCrPt-SiO2 perpendicular recording media [3]. Due to a combination of deposition on a modulated surface and post-deposition ion irradiation a predefined number of grains can be exchange coupled to act as one magnetic entity required for bit patterned media. The physical mechanisms will be discussed.

Support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged.

[1] S. Facsko, H. Kurz, T. Dekorsy, Energy dependence of quantum dot formation by ion sputtering, Phys. Rev. B 63, 165329 (2001).
[2] M. O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mücklich, S. Facsko, J. Fassbender, Induced anisotropies in exchange-coupled systems on rippled substrates, Phys. Rev. B 75, 220407(R) (2007).
[3] T. Strache, S. Tibus, F. Springer, H. Rohrmann, M. Albrecht, J. Fassbender, Tuning coercivity in CoCrPt-SiO2 hard disk material, OR15-4, International Conference on Ion Beam Modification of Materials, IBMM08, 31.08.-05.09.2008, Dresden, Germany

Keywords: magnetism; ion erosion; ion irradiation; modulated surfaces; MBE; intergranular coupling; induced anisotropies

  • Lecture (others)
    Seminar, National Institute of Standards and Technology, 03.11.2008, Boulder, USA
  • Invited lecture (Conferences)
    2nd International Conference on Physics at Surfaces and Interfaces, 23.-27.02.2009, Puri, Orissa, Indien
  • Lecture (others)
    Seminar, Institut für Physik, TU Ilmenau, 30.10.2008, Ilmenau, Deutschland
  • Invited lecture (Conferences)
    Symposium "Ion Beams and Nano-Engineering", MRS Spring Meeting, 13.-17.04.2009, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-11705
Publ.-Id: 11705


Application of GATE to detector optimisation in transmission gamma ray tomography

Hampel, U.; Kiessling, N.; Bieberle, A.

We present results of a simulation study on the role of different design parameters for the count rate accuracy of a high resolution gamma ray detector used for transmission tomography. The considered gamma ray tomography system is operated with a Cs-137 isotopic source and a special detector composing 320 single elements, made of LYSO scintillators coupled to APD. Typically, energy resolution of the detector elements (geometry 2mm x 2mm x 24mm) is limited to about 25% which leads to erroneous counting of photons which have been Compton scattered before detection in other parts of the detector and the object. This introduces a linearity error into the tomographic data which leads to artefacts and errors in the reconstructed images. We therefore performed a theoretical analysis with the GATE simulation software. Simulation of the count rate error for the existing configuration shows good agreement with measured detector cross-talk. In the following we assessed different virtual design changes regarding crystal geometry, separation, shielding and arrangement. Results show that further increase in accuracy is possible.

Keywords: Monte Carlo simulation; GATE; scattered radiation; radiation cross-talk; gamma ray tomography

  • Lecture (Conference)
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
    IEEE NSS/MIC/RTSD Conference Record

Permalink: https://www.hzdr.de/publications/Publ-11704
Publ.-Id: 11704


Ultra fast electron beam X-ray computed tomography for two-phase flow measurement

Fischer, F.; Hampel, U.

Electron beam X-ray CT is a new technique for a fast measurement of multiphase flows with frame rates of 1000 images per second and more. It gives, in principle, quantitatively accurate images of the flow at high spatial resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated by X-rays. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement studies we devised and built a fast scanned electron beam X-ray tomography scanner. The scanner consists of an electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current, with the required electron optics for beam adjustment, beam focussing and beam deflection unit and a fast circular CZT detector comprising 240 elements of 1.5 mm x 1.5 mm x 1.5 mm active pixel
area. X-ray radiation is produced on a circular water cooled tungsten target The CT system achieves up to 7000 frames per second with a spatial resolution of 1 millimetre. First two-phase flow experiments have been carried out on gas-water flows in bubble columns. On the basis of these data we developed image processing algorithms which enable to extract information on bubble shapes, bubble size distributions and interfacial area density distribution. Further, a vertical test section made of titanium alloy has been installed at the TOPFLOW facility and will be used in the future to study the evolution of two-phase gas-water pipe flow at high pressures and temperatures.

Keywords: Two-phase flow; electron beam tomography; CFD code validation

  • Contribution to proceedings
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
    Proceedings of XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety
  • Lecture (Conference)
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 12.09.2008, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-11703
Publ.-Id: 11703


Quadratic detection and autocorrelation measurements with two-photon quantum well infrared photodetectors

Schneider, H.; Winnerl, S.; Liu, H. C.; Drachenko, O.; Helm, M.; Walther, M.; Faist, J.

The two-photon quantum well infrared photodetector (QWIP) comprises three equidistant subbands, two of which are bound in the quantum well, and the third state in the continuum. This results in a resonantly enhanced optical nonlinearity, which is by six orders of magnitude stronger than in usual semiconductors. In addition, temporal resolution is only limited by the sub-ps intrinsic time constants of the quantum wells, namely the intersubband relaxation time and the dephasing time of the intersubband polarization. Both properties make this device very promising for quadratic autocorrelation measurements of pulsed mid-infrared sources, including modelocked quantum cascade lasers, radiation obtained by nonlinear optical frequency conversion, and free-electron lasers (FEL).
We have performed autocorrelation measurements of ps optical pulses from the free-electron laser (FEL) facility FELBE at the Forschungszentrum Rossendorf. Using a rapid-scan autocorrelation scheme at a scan frequency of 20 Hz, high-quality quadratic autocorrelation traces are obtained, yielding ratios close to the theoretically expected value of 8:1 between zero delay and large delay for interferometric autocorrelation, and 3:1 for intensity autocorrelation. Thus, two-photon QWIPs provide an excellent new approach to online pulse monitoring of the FEL. In addition, we have investigated the saturation mechanism of the photocurrent signal, which is due to internal space charges generated in the detector. We will also report on room temperature operation of two-photon QWIPs.

Keywords: quantum well infrared photodetector; two-photon absorption; intersubband transition; quadratic autocorrelation; GaAs/AlGaAs

  • Lecture (Conference)
    9th International Conference on Mid-Infrared Optoelectronics: Materials and Devices (MIOMD-IX), 07.-11.09.2008, Freiburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11702
Publ.-Id: 11702


Spannungs- und Ermüdungsanalyse für den Sicherheitsbehälter des KKW Krümmel

Altstadt, E.

Es handelt sich um einen vertraulichen Bericht, kein Abstract.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\07
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-11701
Publ.-Id: 11701


Spannungs- und Ermüdungsanalyse für die RDB-Einbauten des KKW Krümmel

Altstadt, E.; Werner, M.

Es handelt sich um einen vertraulichen Bericht, kein Abstract.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\06
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-11700
Publ.-Id: 11700


Spannungs- und Ermüdungsanalyse für den RDB-Boden des Kernkraftwerks Krümmel

Altstadt, E.

Es handelt sich um einen vertraulichen Bericht, kein Abstract.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\05
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-11699
Publ.-Id: 11699


In-beam Positron Emission Tomography for Ion Therapy Monitoring

Fiedler, F.; Laube, K.; Möckel, D.; Parodi, K.; Pawelke, J.; Priegnitz, M.; Shakirin, G.; Enghardt, W.

Due to the special characteristics of ion beams and delicate treatment situations, i.e. in close vicinity to organs at risk, a three-dimensional, in-vivo and in-situ monitoring of the dose delivery is highly desirable. At present, in-beam PET is the only method meeting these requirements. An in-beam PET system has been implemented for clinical application at the carbon ion therapy facility of the Gesellschaft für Schwerionenforschung (GSI) Darmstadt. So far, more than 400 patients have been monitored with this system. It could be demonstrated that this PET technique is capable of assessing relevant parameters for quality assurance of carbon ion therapy, measuring the particle range in tissue, the position of the irradiated volume with respect to anatomical landmarks, and estimating local deviations between the planned and applied dose. In-beam PET has become a tool providing valuable clinical feedback.
The implementation of the in-beam PET system at the medical beamline at GSI will be described. Clinical results will be shown with examples. Furthermore, the application of in-beam PET for protons, 3-He, 7-Li and 16-O shows promising results and will be presented.

Keywords: in-beam PET; ion therapy

  • Invited lecture (Conferences)
    IGRT Vienna 2008 - Visions and Perspectives in Image Guided Radiation Oncology, 24.-26.09.2008, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-11698
Publ.-Id: 11698


From multiply twinned to fcc nanoparticles via irradiation-induced transient amorphization

Järvi, T. T.; Pohl, D.; Albe, K.; Rellinghaus, B.; Schultz, L.; Fassbender, J.; Kuronen, A.; Nordlund, K.

We present experimental evidence for structural trransformation of multiply twinned CuAu nanoparticles to single crystalline morphology by 0.5 keV helium irradiation. This finding is unexpected as the stability of twin boundaries should not be affected by ion-beam induced Frenkel pairs. Molecular dynamics simulations reveal, however, a new transformation mechanism based on transient amorphization of the particle. By comparing with irradiation simulations of elemental nanoparticles, as well as alloyed bulk samples and surface cascades, we show that this transformation route is only present in alloyed particles. Moreover, the observed amorphization is more efficient for twinned than single-crystalline particles. This, together with the fast recrystallization kinetics in CuAu, explains the experimentally observed untwinning process.

Keywords: ion irradiation; nanoparticles; binary alloys; structural transformation; ordered phases

Permalink: https://www.hzdr.de/publications/Publ-11697
Publ.-Id: 11697


The effect of ion irradiation and annealing on exchange spring magnets

Fassbender, J.; Grenzer, J.; Roshchupkina, O.; Choi, Y.; Jiang, J. S.; Bader, S. D.

It is demonstrated that both the nucleation field and the irreversible switching field of Sm2Co7/Fe exchange spring bilayers is decreased by means of 10 keV He ion irradiation. The reduction is attributed to interfacial mixing and irradiation induced softening of the hard magnetic layer. By lowering the energy to 0.8 keV the ions do not penetrate the hard magnetic layer and consequently no softening is observed. However, although irradiation induced interfacial mixing is still present it is not large enough to create a graded interface layer and the nucleation field decreases. In contrast conventional annealing under appropriate conditions leads to an increase of the nucleation field. This distinct discrepancy can be explained by detailed investigation of the layer structure by x-ray reflectivity measurements.

Keywords: magnetism; ion irradiation; exchange spring; hard magnets

Permalink: https://www.hzdr.de/publications/Publ-11696
Publ.-Id: 11696


Simulation analysis of the spatial sensitivity of a wire-mesh sensor

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

The wire-mesh sensor is an imaging instrument which is able to generate cross-sectional phase distribution images with high spatial and temporal resolutions, thus being very well suitable for the investigation of multiphase flows. It has successfully been used in several research and industrial applications. In this article, we present the results of the precise simulation analysis of the spatial sensitivity of this device, which support further developments of the image data processing.

Keywords: wire-mesh sensor; spatial sensitivity; numerical field simulation

  • Contribution to proceedings
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Germany
    EUROSENSORS XXII, Duesseldorf: Verein Deutscher Ingenieure e.V. (VDI), 978-3-00-025217-4, 157-160
  • Poster
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-11695
Publ.-Id: 11695


Intraminiband relaxation in doped GaAs/AlGaAs superlattices studied by two-color infrared pump-probe experiments

Stehr, D.; Wagner, M.; Schneider, H.; Helm, M.; Andrews, A. M.; Roch, T.; Strasser, G.

no abstract available

Keywords: superlattice; free electron laser; infrared

  • Poster
    29th International Conference on the Physics of Semiconductors, 27.07.-01.08.2008, Rio de Janeiro, Brazil

Permalink: https://www.hzdr.de/publications/Publ-11694
Publ.-Id: 11694


Intersubband relaxation and dephasing in narrow InGaAs/AlAsSb quantum well structures

Villas-Boas Grimm, C.; Pfau, C.; Ohser, S.; Winnerl, S.; Schneider, H.; Helm, M.; Biermann, K.; Künzel, H.

no abstract available

Keywords: intersubband; quantum wells; infrared; dephasing

  • Poster
    29th International Conference on the Physics of Semiconductors, 27.07.-01.08.2008, Rio de Janeiro, Brazil

Permalink: https://www.hzdr.de/publications/Publ-11693
Publ.-Id: 11693


Structural identification of thioarsenates and their differentiation from thioarsenites by EXAFS

Suess, E.; Scheinost, A. C.; Bostick, B. C.; Merkel, B. J.; Wallschlaeger, D.; Planer-Friedrich, B.

Thioarsenic complexes play an important role in regulating arsenic solubility, mobility, and toxicity in sulfidic systems. Despite their importance, there is little consensus on their thermodynamic properties and structural identification. A major focus of current research is the unambiguous identification of the members of the two homologue series of monomeric thioarsenic species that are conceptually postulated to exist under sulfidic conditions, (oxy)thioarsenites and (oxy)thioarsenates. Here we report the unambiguous identification of synthetic mono-, di, and tetrathioarsenate using a combination of X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). As-O and As-S coordination numbers confirmed the structure as the expected mono-, di- and tetrathioarsenate compounds. The As-O bond distances of 1.69 to 1.70 $\AA$ are comparable with those stated for arsenates, and are easily distinguishable from those for arsenites at 1.78 $\AA$. The As-S distances in our standard materials with 2.17 $\AA$ are clearly shorter than those published for arsenite-sulfide minerals with 2.24 to 2.34 $\AA$. As expected, no As-O bonding was determined in tetrahedral tetrathioarsenate, which is fully coordinated to S. As the extent of thiol complexation increases, the position of the absorption-edge shifts systematically and linearly towards lower energies compared to that of arsenate. The structural data for the individual solid and liquid samples, measured at room temperature or at 15 K, did not show obvious differences, suggesting that the aqueous complexes have similar structures as the XRD-identified solids and are stable in natural waters. An interesting observation was made during the titration of the liquid tetrathioarsenate from pH 6 to 3. Below neutral pH, the absorption edge shifted to lower energies by $\sim$2 eV concomitant with an increase of the As-S bond length to 2.28 $\AA$ at pH 3, comparable with those of orpiment and indicative of either thioarsenites (which have been reported to exist in arsenite-sulfide-containing solutions) or colloidal orpiment. As for thioarsenates, the observed complexes also show a linear trend together with arsenite and orpiment, clearly distinguishable from the arsenate-based line. The present data demonstrate that it is possible to differentiate thioarsenates from thioarsenites by XAS. Combined with other recent studies, these data indicate that thioarsenates can be formed in sulfidic solutions under a broad range of conditions.

Keywords: arsenic; arsenite; arsenate; EXAFS

  • Poster
    2008 AGU Fall Meeting, 15.-19.12.2008, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-11692
Publ.-Id: 11692


High energy Xe+ ion beam induced rippled patterns on silicon

Hanisch, A.; Grenzer, J.; Facsko, S.; Biermanns, A.; Pietsch, U.; Metzger, T. H.; Carbone, G.

Under certain conditions ion beam bombardment on semiconductor surfaces leads to well-defined morphological structures in the nanoscale range caused by a self-organization process. Due to the ion impact as a start the surface-adjacent layer is amorphized before a periodical wave-like rippled structure on the surface as well as at the amorphous-crystalline interface is developed. So far we found that the ripple wavelength linearly scales with the ion energy in a range of 5 to 70 keV (50 to 300 nm). Furthermore, we try to evaluate the ripple patterns from the point of homogeneity and uniformity. Therefore, we defined a quality factor for the amplitude and a correlation length for the wavelength to characterize the structures over a larger scale. We used a routine to extract the ripple amplitude from the Atomic Force Microscopy (AFM) images. In order to determine the correlation length we prosecuted Grazing Incidence Small Angle X-Ray Scattering (GISAXS) measurements.
Also, we asked for the mechanisms behind the formation of ripples. The investigation of the amorphous-crystalline interface gives a first hint. The subsurface structure has been identified by both Transmission Electron Microscopy (TEM) and Rutherford backscattering (RBS). Applying two different ion types for the formation of rippled patterns we could identify clear differences in the structure of the amorphous layer.

Keywords: nanopatterns; ripples; self-organization

  • Poster
    IBMM 2008 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.08, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11691
Publ.-Id: 11691


Magnetic and transport properties of Cu1.05Cr0.89 Mg0.05O2 and Cu0.96Cr0.95 Mg0.05Mn0.04O2 films

Xu, Q.; Schmidt, H.; Zhou, S.; Potzger, K.; Helm, M.; Hochmuth, H.; Lorenz, M.; Meinecke, C.; Grundmann, M.

We prepared conductive, polycrystalline or amorphous Cu1.05Cr0.89 Mg0.05O2 films on a-plane sapphire substrates by pulsed laser deposition under different O2 partial pressure and substrate temperature. Hall measurements were performed to study the majority carrier type in these films. Polycrystalline Cu1.05Cr0.89 Mg0.05O2 is n-type conducting at 290 K, while in amorphous Cu1.05Cr0.89 Mg0.05O2 the type of majority charge carriers changes from electrons to holes at around 270 K. Interestingly, the structure has little influence on the magnetic properties of the films. A clear antiferromagnetic to paramagnetic transition was observed in both polycrystalline and amorphous Cu1.05Cr0.89 Mg0.05O2 films at 25 K. Similar electrical properties to Cu1.05Cr0.89 Mg0.05O2 film were observed for Cu0.96Cr0.95 Mg0.05Mn0.04O2 in dependence on the structure, while only paramagnetic without antiferromagnetic ordering was observed down to 5 K. Large negative magnetoresistance of 27% at 20 K was observed at 6 T in amorphous Cu1.05Cr0.89 Mg0.05O2 film.

Keywords: Oxide semiconductor; Hall effect; Magnetic properties; Magnetoresistance

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-11690
Publ.-Id: 11690


Simulation of a nano-scale magnetic switch

Pankoke, V.; Gemming, S.

We used ab-initio methods in the LDA with pseudo potentials and a plane wave basis to simulate the growth of thin palladium films on the piezo electric oxide PMN (Pb(Mg/Nb)O3). It is known that the palladium ground state is similar to the ground state of ferromagnetic nickel. A magnetic switch of nano-scale dimension might be possible if the palladium ground-state can be forced to get also ferromagnetic. The piezo electric property of PMN oxides can be used to achieve this by an expansion of the lattice constant. First calculations on bulk-Pd with all-electron and pseudo-potential methods lead to different results with respect to the magnetic ground state, but it seems, that the projector augmented wave method PAW describes the magnetism correctly. In PAW calculations pure fcc-palladium films remain non-magnetic during expansion, but a doping with cobalt can help to induce a magnetic state.

Keywords: Magnetism; magnetic transition; film growth

  • Lecture (Conference)
    Junior Euromat 2008, 14.-18.07.2008, Lausanne, Schwitzerland

Permalink: https://www.hzdr.de/publications/Publ-11689
Publ.-Id: 11689


Evolution of ripple morphologies on silicon during sub-keV ion sputtering

Keller, A.; Facsko, S.; Peverini, L.; Kozhevnikov, I. V.; Möller, W.

It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces may lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. The ripples produced in this way are oriented either parallel or normal to the projection of the ion beam and their wavelength scales with ion energy. These structures have been found on a large variety of materials, such as semiconductors, metals, and insulating surfaces. The formation and early evolution of the ripple patterns can be qualitatively reproduced by a linear continuum equation derived by Bradley and Harper. At longer times, however, nonlinear terms have to be taken into account leading to nonlinear models based on the Kuramoto-Sivashinsky equation.
The evolution of Si(100) surfaces during oblique sub-keV ion sputtering has been studied in-situ and ex-situ by means of surface sensitive X-ray techniques, namely X-ray Reflectivity and Grazing Incidence Small Angle X-ray Scattering (GISAXS), and atomic force microscopy, respectively. The observed morphologies are dominated by nanoscale ripples at short lateral scales but exhibit kinetic roughening at larger distances. The roughening of the surface is found to depend strongly on the angle of incidence and even small changes of only 2° lead to very different roughening dynamics. The obtained experimental results will be compared to predictions of different nonlinear continuum models of ion erosion.

  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-11688
Publ.-Id: 11688


Ferromagnetic structurally disordered ZnO implanted with Co ions

Potzger, K.; Zhou, S.; Xu, Q.; Shalimov, A.; Groetzschel, R.; Schmidt, H.; Muecklich, A.; Helm, M.; Fassbender, J.

We present superparamagnetic clusters of highly disordered Zn-Co-O created by high fluence Co ion implantation into ZnO (0001) single crystals at low temperatures. This secondary phase cannot be detected by x-ray diffraction but by high-resolution transmission electron microscopy. In contrast to many other secondary phases it shows anomalous Hall effect and thus is a candidate for magneto-electronics applications.

Keywords: ZnO; diluted magnetic semiconductors; ion implantation

  • Applied Physics Letters 93(2008)23, 232504

Permalink: https://www.hzdr.de/publications/Publ-11687
Publ.-Id: 11687


The Rossendorf Beamline at ESRF: the next 10 years of actinide XAFS

Scheinost, A. C.; Funke, H.; Hennig, C.; Rossberg, A.; Banerjee, D.; Hesse, M.

The Rossendorf Beamline as a dedicated X-ray absorption spectroscopy station for actinide research is in operation since 1998. It has served for hundreds of experiments in the past 10 years, ranging from Materials Science to Aquatic and Environmental Chemistry of actinides and other radionuclides. A short overview on research highlights will be given, including the current extensive work on redox processes.
The beamline’s strength is built on the high reliability and flux of the ESRF, which allows to run samples even at very low concentrations of a few ppm, and on the long experience with actinide EXAFS. After 10 years of operation, the beamline is ready to take the next step in order to further lower the concentration limits of XAFS and to extend the array of methods to -XRF, -XAFS and XRD. Essential optical components will be replaced parallel to the upgrade of the ESRF to increase the photon flux by about one order of magnitude to 1012 photons/sec on the sample, and to prepare the microfocus. Additional modifications like easily exchangeable monochromator crystals, additional mirror coatings and a routine quick-XAFS mode will widen the experimental possibilities without sacrificing the user friendly operation of the beamline.
These changes are planned for 2010, and will be installed and commissioned with little loss of beamtime. This is especially important, since the Rossendorf Beamline will continue to provide its facilities to the actinide community within the ACTINET network, in addition to the routine beamtime application paths via ESRF and FZD collaborations.
An overview on the current status of operation modes, technical details, access conditions and user support with advanced data analysis methods is presented, by updating earlier information and summarizing the features most important for prospective users.

Keywords: XAFS; actinides; synchrotron

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

Permalink: https://www.hzdr.de/publications/Publ-11686
Publ.-Id: 11686


SANS investigation of irradiation-induced phase separation in binary Fe-Cr-alloys

Ulbricht, A.; Bergner, F.; Heintze, C.; Eckerlebe, H.

Ferritic-martensitic chromium steels are candidate materials for future applications in both Gen-IV and fusion technology. Investigations of related binary Fe-Cr alloys will significantly contribute to the understanding of the behaviour of more complex alloys. The presented SANS results are focused on a Fe-9at.% Cr alloy neutron-irradiated up to a dose of 1.5 displacements per atom (dpa).
We have observed a pronounced increase of scattering intensities for two different irradiation conditions at scattering vectors Q > 0.2 nm-1 for both magnetic (figure (a)) and nuclear scattering. The reason for the increased intensities are irradiation-induced clusters with size distributions presented in figure (b). The A-ratio is about 2.8 for both irradiation conditions. This value is far from a value of 1.45 corresponding to nanovoids as scattering objects. This indicates that the irradiation-induced clusters are different from pure nanovoids and must contain Cr-atoms with the same or very similar average composition for both irradiation conditions. These clusters are interpreted as alpha’-phase. The volume fraction of clusters of this type increases slightly with neutron dose.

Keywords: SANS; irradiation-induced cluster; Fe-Cr alloy

  • Poster
    Deutsche Neutronenstreutagung 2008, 15.-17.09.2008, Garching, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11685
Publ.-Id: 11685


Influence of carbonate complexation on the sorption of U(VI) on montmorillonite

Marques Fernandes, M.; Dähn, R.; Baeyens, B.; Scheinost, A.; Bradbury, M. H.

Clay minerals play an important role in the retention/retardation of radio-contaminants in the near- and far-fields of a radioactive waste repository. Identifying and quantifying the radionuclide sorption processes occurring at clay/solution interface over a representative range of relevant conditions is indispensable for performance assessment.
Next to hydroxide ions, carbonate is the predominant inorganic ligand in most natural groundwaters and clay porewaters. Actinides are known to form very strong carbonate complexes in solution, which could potentially decrease the metal ion sorption and thus increase the migration rates of actinides. The aim of this study is:
To apply Extended X-Ray Absorbtion Spectroscopy to verify whether or not U(VI)-carbonato ternary complexes form at the montmorillonite surface

The macroscopic sorption data show a significant influence of dissolved carbonate on the sorption of U(VI)) on Na-montmorillonite.
Structural data obtained by EXAFS show unambiguously that U(VI) forms inner-sphere complexes at the montmorillonite surface (splitting of the Oeq shell, Si and Fe shell).
No difference is observed in the absence and the presence of carbonate (no C shell ~ 2.90 Å [1], no Odist shell), indicating that no U(VI)-carbonato ternary complexes
form at the montmorillonite surface.

Keywords: EXAFS; Uranium; Sorption; Montmorillonite; Carbonate

  • Poster
    Actinide-XAS 2008, 15.-17.07.2008, Saint Aubin, France

Permalink: https://www.hzdr.de/publications/Publ-11684
Publ.-Id: 11684


Bacterial cell walls - Promoters and inhibitors of mineral nucleation

Behrends, T.; Scheinost, A.; Shaw, S.; Benning, L.; van Cappellen, P.

Formation of minerals at the Earth’s surface can often be directly or indirectly assigned to the activity of microorganisms. Regarding a direct effect, several examples of microbially controlled, extracellular precipitation of minerals have been reported, which typically involve the enrichment of metal ions at the bacterial surface. However, sorption of metal ions to microbial cell walls might also inhibit mineral formation. Here, we present two examples in which interactions between metal ions and bacterial cell walls interfere with the formation of mineral although a promoting effect could be anticipated: the formation of UO2 as a consequence of microbial U reduction and the formation of Mn oxides in the presence of a Mn oxidizing organism. Microbial reduction of U(VI) to U(IV) is expected to result in the precipitation of solid UO2 at neutral pH.
However, EXAFS analyses of samples from incubation experiments with the organism Shewanella putrefaciens revealed that enzymatic reduction of U(VI) did not instantaneously lead to the formation of an UO2 precipitate but that U(IV) was monomerically associated with the bacterial cells. Indications were obtained that U(IV) in this form is very susceptible for reoxidation.
The kinetics of Mn(II) oxidation with and without the organism Pseudomonas putida were studied at pH 7.5 and 8.5.
The rates of Mn2+(aq) consumption in the presence of bacteria were similar at both pH values although the rates of abiotic Mn oxidation, determined in the absence of bacteria, were higher at pH 8.5. XANES analyses showed that the removal of Mn(II) from solution by the bacteria at pH 8.5 was, in contrast to pH 7.5, not caused by Mn oxidation. Consequently, not only enzymatic Mn(II) oxidation but also the abiotic oxidation were inhibited at pH 8.5 in the presence of bacteria. Possible mechanisms for the removal of dissolved Mn(II) by the bacteria and the inhibition of the abiotic oxidation at pH 8.5 will be discussed.

Keywords: Uranium; EXAFS; Redox; Shewanella; Mn oxides

  • Lecture (Conference)
    Goldschmidt 2008, 13.-18.07.2008, Vancouver, Canada
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 72(2008)12, A68

Permalink: https://www.hzdr.de/publications/Publ-11683
Publ.-Id: 11683


X-ray photoelectron and absorption spectroscopy investigation of Se-IV and Sb-V reduction by mackinawite

Banerjee, D.; Kirsch, R.; Scheinost, A. C.

Both Se and Sb exist in nature in a wide range of oxidation states and can be potential hazardous contaminants depending on their speciation and reactivity. While Se typically occurs as oxyanions (SeO3-2 and SeO4-2) in oxic conditions, it can be reduced by FeII containing minerals such as mackinawite (FeS) to Se0 and Se–II [1, 2]. Similarly, Sb occurs in several oxidations states (-III, 0, III, V) and is shown to strongly adsorb to Fe oxide minerals as Sb(OH)6 - and subsequently reduced to the more mobile form Sb(OH)3(aq) [3]. In this study we employed cryogenic-XPS and XAS techniques in order to understand the redox processes involving SeIV and SbV at the surface of mackinawite.
Fe 2p XPS spectrum of pure mackinawite surface revealed presence of both FeII-S and FeIII-S species and the proportion of the latter increased when reacted to SeIV suggesting oxidation of surface FeII. In addition, presence of elemental S at the surface of the reacted sample suggested oxidation of sulfur as well. Corresponding Se K-edge XANES spectra of the reacted sample confirmed reduction of Se with the formation of FeSe. These results suggest that Se reduction is coupled to both S-II/S0 and FeII/FeIII redox half reactions.
Sb 3d spectrum of the reacted sample revealed that SbV was completely reduced to SbIII at the surface of mackinawite.
However, the S 2p spectrum of the reacted sample remained largely unchanged except for a slight increase in surface monosulfide content. This suggests that in contrast to the SeIVmackinawite system, S did not take part in the redox reaction involving SbV. The Fe 2p spectrum, however, showed a distinct shoulder of FeIII-species indicating oxidation of surface FeII. Corresponding Sb K-edge EXAFS of the reacted sample confirmed that the SbIII was coordinated to three sulfur atoms at a distance of 2.5 Å as in Sb2S3, which most likely explains the slight increase in the surface monosulfide content in the S 2p spectrum.
These results demonstrate the importance of surface mediated redox reactions in controlling the fate of toxic
contaminats such as Se and Sb in soil and groundwater.
[1] Charlet et al. (2007) GCA 71, 5731-5749. [2] Scheinost & Charlet (2008) ES&T, online. [3] Scheinost et al. (2006) GCA 70, 3299-3312.

Keywords: XPS; XAFS; selenium; antimony; Se; Sb; redox

  • Lecture (Conference)
    Goldschmidt 2008, 13.-18.07.2008, Vancouver, Canada
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 72(2008)12, A51

Permalink: https://www.hzdr.de/publications/Publ-11682
Publ.-Id: 11682


EXAFS investigation of U(VI) speciation in cementitious materials

Macé, N.; Harfouche, M.; Dähn, R.; Tits, J.; Scheinost, A.; Wieland, E.

Cement in the Swiss radioactive waste management program is used as a waste matrix for the long-lived intermediate-level waste (ILW) disposal, where Uranium is an important radionuclide. Calcium Silicate Hydrates (C-S-H) are one of the major components of Hardened Cement Paste (HCP). In such a context, the understanding of Uranium uptake processes occurring in cementitious materials is necessary.

U(VI) uptake by C-S-H (CaO/SiO2 = 1.07) in Artificial Cement pore-Water (ACW) and HCP has been investigated using X-Ray Absorption Spectroscopy (XAS) technique in order to determine the chemical environment of sorbed and precipitated U(VI) species in cementitious matrices.

Phase X (CaUO4(H2O)x) and a uranophane ([Ca(H3O)2](UO2)2(SiO4)2(H2O)3) have been chosen as relevant reference compounds.

Similar coordination environment of U(VI) taken up by C-S-H and HCP
U(VI) sorbed species  a-uranophane-like structure
U(VI) precipitated species  phase-X-like structure
No split equatorial shell is observed
Complementary informations are expected using Time-Resolved Laser Fluorescence spectroscopy (TRLFS)

Keywords: Uranium; cement; EXAFS

  • Poster
    Actinide-XAS 2008, 15.-17.07.2008, Saint Aubin, France

Permalink: https://www.hzdr.de/publications/Publ-11681
Publ.-Id: 11681


Kinematic dynamos in cylindrical geometry

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

In order to understand the results of recent dynamo experiments, the behavior of kinematic dynamos in cylindrical geometries is analyzed. Simulations are performed applying a hybrid finite volume/boundary element method that allows a stringent treatment of insulating boundary conditions.

A suitable prescribed velocity field, either analytic or -- more realistic -- from measurement data from water experiments, leads to dynamo action, and a strong influence of boundary conditions and additional (stagnant) fluid layers around the active domain is observed.

An additional source term for dynamo action exists in case of a spatially varying conductivity distribution. A very simple set-up -- serving as a proof of concept -- is given by a steady axial flow in an infinite cylinder with inhomogenous container walls. Such a configuration is sufficient for dynamo action, however, the critical Reynolds number might be too large for the realisation in a simple laboratory-sized experiment.

Similiar effects appear in case of permeability inhomogenities, where increased gradients might also lead to a significant reduction of the critical Reynolds number.

Keywords: Dynamo; Boundary Conditions; Simulations

  • Lecture (Conference)
    EURO MHD 2008, 23.-26.09.2008, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-11680
Publ.-Id: 11680


Electromagnetic stirring with superimposed travelling and rotating magnetic fields

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

Flow visualization and velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating and a travelling magnetic field. The combination of both fields, which is not necessarily a linear superposition, may give rise to an inherent three-dimensional constituent of the electromagnetic force distribution. As the Lorentz force may also become time-dependent, a quite intense mixing of metallic melts is achievable.

Keywords: Electromagnetic processing of materials; liquid metal flow; combined magnetic fields; stirring

  • Electrical Review (2008)11, 144-148

Permalink: https://www.hzdr.de/publications/Publ-11679
Publ.-Id: 11679


Balance-based real-time monitoring – a tool to improve safety and efficiency of batch and semi-batch processes

Kryk, H.; Hessel, G.

In the fine chemical and pharmaceutical industry, batch and semi-batch processes are mostly used to produce special chemicals in small amounts. The behaviour of such strongly exothermic processes in stirred tank reactors is characterised by instationarity, non-linearity and a large number of influences which may affect the process safety and efficiency as well. Especially in multi purpose plants, such complex processes are usually controlled by conventional process variables, such as temperatures, pressures, dosing rates etc., but without any knowledge of the crucial parameters of a chemical reaction, the concentration profiles of reactants, products and intermediates. Thus, even experienced operators have difficulties to distinguish allowable from undesired process deviations and to identify the cause of process trends.
Therefore, it is of vital importance to establish industrially applicable methods for an objective detection of the actual process state and for alerting the operators in case of undesired process deviations. To avoid the use of expensive and fragile on-line analytics, a real-time monitoring approach based on adaptive energy and mass balances was developed, and related monitoring systems were tested at pilot scale and industrial applications as well.
Especially, if such a real-time monitoring approach is used as an integral part of a batch information management system (BIMS), the additional data could contribute to the enhancement of the process knowledge as a basis for continuative process optimisation. The additional process information provided by real-time monitoring systems enables application of advanced control strategies up to the point of a safety-oriented fully automated control of complex exothermic batch and semi-batch processes.

  • Invited lecture (Conferences)
    9th International Conference and Exhibition on The Scale-Up of Chemical Processes, 15.-17.09.2008, Rome, Italy
  • Contribution to proceedings
    9th International Conference and Exhibition on The Scale-Up of Chemical Processes, 15.-17.09.2008, Rome, Italy
    Conference Proceedings, Scale-up of Chemical Processes

Permalink: https://www.hzdr.de/publications/Publ-11678
Publ.-Id: 11678


X-ray spectroscopic and magnetic investigation of C : Ni nanocomposite films grown by ion beam cosputtering

Abrasonis, G.; Scheinost, A. C.; Zhou, S.; Torres, R.; Gago, R.; Jimenez, I.; Kuepper, K.; Potzger, K.; Krause, M.; Kolitsch, A.; Moller, W.; Bartkowski, S.; Neumann, M.; Gareev, R. R.

The nearest-neighbor coordination and electronic structure in C:Ni(∼30 at.%) nanocomposite films grown by ion beam cosputtering in the temperature range of room temperatue (RT) to 500 °C are investigated by the means of extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS). The obtained results are correlated with the composite nanostructure published elsewhere and magnetic properties determined by the means of X-ray magnetic circular dichroism (XMCD) and superconducting quantum interference device (SQUID) magnetometry. A combined use of EXAFS, XANES, and XPS shows that a carbidic Ni phase exhibiting only local atomic ordering is formed at low growth temperatures (e200 °C), while ordered carbidic Ni phase forms at ∼300 °C. Further increase in growth temperature results in the formation of face-centered cubic (fcc) Ni with a high degree of crystallinity. On the other hand, Ni incorporation strongly promotes the formation of carbon structures with the prominent peak in C K-edge XANES spectra positioned at 288.5 eV in the whole growth temperature range. The magnetic measurements show no magnetic response for the films grown at RT to 200 °C, superparamagnetic behavior for the film grown at 500 °C with >90% of the Ni atoms in metallic state, and a weak magnetic response for the film grown at 300 °C, indicating the presence of Ni-rich regions within carbon containing Ni nanoparticles with ∼3% of Ni atoms in metallic state.

  • Journal of Physical Chemistry C 112(2008), 12628-12637

Permalink: https://www.hzdr.de/publications/Publ-11677
Publ.-Id: 11677


Qualification of simulation tools for two-phase flows

Lucas, D.

According to the state of the art nuclear safety analyses related to thermohydraulics are mostly done using so-called system codes. Such one-dimensional codes base on empirical or semi-empirical correlations, which are generally geometry dependent and valid only within a limited range of scales. In principle the validation of such codes requires experimental data obtained for the same geometries, similar scales and flow conditions. In the past such codes were validated and successfully applied to many relevant flow situations. But the transferability to differing flow situations as well as the reliability for flows with pronounced 3D effects as they are observed e.g. in Reactor Pressure Vessel (RPV) is questionably. For this reason there is an interest to apply beside system codes also Computational Fluid Dynamics (CFD) codes for special analyses in future. Presently CFD codes are frequently used in practical applications for single phase flows, e.g. in automobile or aviation industries. Two-phase flow simulations using CFD codes are not yet mature due to the complex interactions between the phases. Closure models are needed to describe mass, momentum and energy transfer between the phases. Such models should consider only local flow parameters, i.e. correlations available for system codes cannot be transferred in general for the use in CFD codes. Such models have to be developed and validated basing on new experimental data with high resolution in space and time. Examples are poly-dispersed bubbly flows which require a multi bubble size modelling or models for separated flows in horizontal or near horizontal channels. TOPFLOW is a unique thermal hydraulic test facility for such two-phase flow studies. Experiments can be carried out for air-water or steam-water two phase flows at pressures up to 7 MPa. For steam production up to 4 MW heating power are available. The TOPFLOW facility is currently prepared for different types of flow experiments in vertical test sections and a large pressure chamber. Unique measurement devices, such as high-pressure wire-mesh sensors and an X-ray scanner are available. They provide CFD like data, which means data in high resolution in space and time. The lecture gives a general overview on the CFD model development and validation for two-phase flows, which is illustrated on the examples of poly-dispersed bubbly flows and Pressurized Thermal Shock (PTS). The experimental capabilities of the TOPFLOW facility and the applied measuring techniques are discussed.

Keywords: CFD; two-phase flow; modelling; experiment; polydispersed flow

  • Invited lecture (Conferences)
    Frédéric Joliot/Otto Hahn Summer School on Nuclear Reactors: "Physics, Fuels, and Systems", 20.-29.08.2008, Aix-en-Provence, France
  • Contribution to proceedings
    Frédéric Joliot/Otto Hahn Summer School on Nuclear Reactors: "Physics, Fuels, and Systems", 20.-29.08.2008, Aix-en-Provence, France
    Lecture notes of the 2008 Frédéric JOLIOT & Otto HAHN Summer School

Permalink: https://www.hzdr.de/publications/Publ-11676
Publ.-Id: 11676


Von PROMISE 1 zu PROMISE 2: Helikale MRI im Laborexperiment

Stefani, F.

Die Magneto-Rotationsinstabilität (MRI) ist verantwortlich für Turbulenz und Drehimpulstransport in kosmischen Akkretionsscheiben und ermöglicht damit das Wachstum von Sternen und Schwarzen Löchern. Im Vortrag wird das PROMISE-Experiment vorgestellt, mit dem die helikale Variante der MRI erstmalig nachgewiesen worden ist.

  • Invited lecture (Conferences)
    Kolloquium "10000 MHD-Tage in Potsdam", 01.09.2008, Potsdam, Germany

Permalink: https://www.hzdr.de/publications/Publ-11675
Publ.-Id: 11675


Site-specific substitution of Fe in YFexMn2-xO5: X-ray investigations and DFT

Weißbach, T.; Führlich, T.; Wunderlich, F.; Leisegang, T.; Dshemuchadse, J.; Rother, A.; Souptel, D.; Behr, G.; Chaplygin, I.; Seifert, G.; Gemming, S.; Meyer, D. C.

YMnFeO5 is a ferrimagnet below 165 K [1]. Its crystal structure is derived from that of the ferromagnetic and low-temperature ferroelectric YMn2O5 by occupation of the Mn position possessing pyramidal oxygen environment with Fe; the other Mn site is coordinated by oxygen in an octahedral manner. Powder samples for x = 0, 0.25, 0.5, 1 [2] were inspected by X-ray powder diffraction and EXAFS, single crystals (x = 0.07, 0.25) by single-crystal X-ray diffraction methods. The structure data show a significant displacement of Fe within the oxygen pyramid, while the Mn position remains nearly constant with respect to the surrounding oxygen atoms. All-electron density-functional calculations in the LSDA+U approximation for the x = 1 compound [3] are in good agreement with the collinear, commensurate ferrimagnetic ordering of the magnetic moments as proposed in [1]. [1] Munoz, A. et al., Chem. Mater. 16, 4087 (2004); [2] all materials prepared by D. Souptel at IFW Dresden; [3] FPLO: Koepernik, K. et al., Phys. Rev. B 59, 1743 (1999).

Keywords: ferrimagnet; magnet; multiferroic; manganite; density functional; DFT; X-ray; EXAFS

  • Poster
    16th International Conference on Solid Compounds of Transition Elements (SCTE2008), 26.-31.07.2008, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11674
Publ.-Id: 11674


Evolution of the crystal structure of YMn2-xFexO5 due to substitution of iron for manganese

Weißbach, T.; Wunderlich, F.; Führlich, T.; Dshemuchadse, J.; Souptel, D.; Behr, G.; Gemming, S.; Meyer, D. C.

YMnFeO5 is a ferrimagnet below 165 K [1]. Its crystal structure is derived from that of the ferromagnetic and low-temperature ferroelectric YMn2O5 by occupation of the Mn position possessing pyramidal oxygen environment with Fe; the other Mn site is coordinated by oxygen in an octahedral manner. Powder samples for x = 0, 0.25, 0.5, 1 [2] were inspected by X-ray powder diffraction and EXAFS, single crystals (x = 0.07, 0.25) by single-crystal X-ray diffraction methods. The structure data show a significant displacement of Fe within the oxygen pyramid, while the Mn position remains nearly constant with respect to the surrounding oxygen atoms. All-electron density-functional calculations in the LSDA+U approximation for the x = 1 compound [3] are in good agreement with the collinear, commensurate ferrimagnetic ordering of the magnetic moments as proposed in [1]. [1] Munoz, A. et al., Chem. Mater. 16, 4087 (2004); [2] all materials prepared by D. Souptel at IFW Dresden; [3] FPLO: Koepernik, K. et al., Phys. Rev. B 59, 1743 (1999).

Keywords: ferrimagnet; magnetic; multiferroic; DFT; density functional; X-ray; EXAFS; functional oxide

  • Poster
    16. Jahrestagung der Deutschen Gesellschaft für Kristallographie, 03.-06.03.2008, Erlangen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11673
Publ.-Id: 11673


Evolution of the crystal structure of YMn2-xFexO5 due to iron doping and DFT calculations for the x = 1 compound

Weißbach, T.; Souptel, D.; Behr, G.; Führlich, T.; Wunderlich, F.; Meyer, D. C.; Gemming, S.

YMnFeO5 is a ferrimagnet below 165 K [1]. Its crystal structure is derived from that of the ferromagnetic and low-temperature ferroelectric YMn2O5 by occupation of the Mn position possessing pyramidal oxygen environment with Fe; the other Mn site is coordinated by oxygen in an octahedral manner. Powder samples for x = 0, 0.25, 0.5, 1 [2] were inspected by X-ray powder diffraction and EXAFS, single crystals (x = 0.07, 0.25) by single-crystal X-ray diffraction methods. The structure data show a significant displacement of Fe within the oxygen pyramid, while the Mn position remains nearly constant with respect to the surrounding oxygen atoms. All-electron density-functional calculations in the LSDA+U approximation for the x = 1 compound [3] are in good agreement with the collinear, commensurate ferrimagnetic ordering of the magnetic moments as proposed in [1].
[1] Munoz, A. et al., Chem. Mater. 16, 4087 (2004);
[2] all materials prepared by D. Souptel at IFW Dresden;
[3] FPLO: Koepernik, K. et al., Phys. Rev. B 59, 1743 (1999)

Keywords: magnetism; multiferroic; ferrimagnet; calculation; DFT; density-functional; EXAFS; X-Ray

  • Poster
    72. Jahrestagung der Deutschen Physikalischen Gesellschaft (DPG) und DPG-Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11672
Publ.-Id: 11672


The helical magnetorotational instability in cylindrical Taylor--Couette flow

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

We present new results from the PROMISE experiment, consisting of a GaInSn alloy confined between differentially rotating cylinders, in the presence of a combined axial and azimuthal (helical) magnetic field. The apparatus has been upgraded to incorporate split-ring end-plates, thereby reducing end-effects. The resulting traveling-wave disturbances are in good agreement with theoretical predictions for the onset of the helical magnetorotational instability.

  • Lecture (Conference)
    XXII International Congress of Theoretical and Applied Mechanics, 24.-29.08.2008, Adelaide, Australia
  • Contribution to proceedings
    XXII International Congress of Theoretical and Applied Mechanics, 24.-29.08.2008, Adelaide, Australia
    Proceedings of the XXII International Congress of Theoretical and Applied Mechanics, Adelaide: IUTAM, 978-0-9805142-1-6, 11858

Permalink: https://www.hzdr.de/publications/Publ-11671
Publ.-Id: 11671


(Multi-)ferroic domain walls - a combined ab-initio and microscopical investigation

Rother, A.; Gemming, S.; Geiger, D.; Spaldin, N.

Interest in magnetoelectric multiferroic materials has increased exponentially over the last ten years, with considerable effort devoted both to combining magnetism and ferroelectricity in a single phase material and in obtaining magnetoelectric coupling between the two phenomena. Progress has been made on both front and a rich array of fundamental phenomena have been revealed in prototypical multiferroics such as bismuth ferrite, BiFeO3. Here we describe a new and previously unanticipated functionality: the observation – using conductive atomic force microscopy – of room temperature electronic conductivity at ferroelectric domain walls in BiFeO3. We explore the origin of the observed conductivity using high resolution transmission electron microscopy and first-principles density functional computations. Our results suggest the possibility of exploiting domain walls as a functional component in novel applications.

Keywords: multiferroic; ferroelectric; bismuth ferrate; domain; domain wall; functional material

  • Poster
    14th European Microscopy Conference (EMC 2008), 31.08.-05.09.2008, Aachen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11670
Publ.-Id: 11670


Spin Manipulation in Co-Doped ZnO

Xu, Q.; Hartmann, L.; Zhou, S.; Mcklich, A.; Helm, M.; Biehne, G.; Hochmuth, H.; Lorenz, M.; Grundmann, M.; Schmidt, H.

We report the clearly observed tunneling magnetoresistance at 5 K in magnetic tunnel junctions with Co-doped ZnO as a bottom ferromagnetic electrode and Co as a top ferromagnetic electrode prepared by pulsed laser deposition. Spin-polarized electrons were injected from Co-doped ZnO to the crystallized Al2O3 and tunnelled through the amorphous Al2O3 barrier. Our studies demonstrate the spin polarization in Co-doped ZnO and its possible application in future ZnO-based spintronics devices.

Keywords: ZnO; Diluted magnetic semiconductor; Tunneling magnetoresistance

Permalink: https://www.hzdr.de/publications/Publ-11669
Publ.-Id: 11669


57Fe and 119Sn CEMS Study of SnO2 Films Implanted with 57Fe

Nomura, K.; Rykov, A.; Iio, S.; Hirose, Y.; Hasegawa, I.; Reuther, H.

The origin of magnetic interactions in Diluted Magnetic Semiconductors (DMS) is attracting a great attention as a basic problem on magnetism[1-2]. This subject is still an issue of controversy. In all of these works, the observed ferromagnetism has been attributed to interactions between the magnetic impurities, but the main source has never been associated to magnetically ordered defects. We have reported the different types of magnetic source in case of Fe doped SnO2 powder [3], and the phonon density of states of rutile type structures [4]. Defects in DMS can also contribute to saturation magnetization. Here we have made the thin films of SnO2 implanted with 57Fe and characterized them by 57Fe and 119Sn conversion electron Mössbauer spectrometry (CEMS).

  • Poster
    International Symposium on the Industrial Applications of the Mössbauer Effect (ISIAME'08), 17.-22.08.2008, Budapest, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-11668
Publ.-Id: 11668


Mössbauer Spectroscopy as a Tool to Explore Diluted Magnetic Semiconductors

Reuther, H.

Worldwide, semiconductor spin transfer electronics (spintronics) is of strongly increasing interest. To realize such materials polarized carriers can be injected from a ferromagnetic metal into a diluted magnetic semiconductor (DMS). DMS are “conventional” semiconductors doped with transition metal or rare-earth ions which are diluted within the host matrix and ferromagnetically aligned via an indirect magnetic coupling.

Wide band gap semiconductors like GaN, ZnO, or TiO2 are promising candidates. Doping could be performed by Mn, V, Fe, Co or Ni with concentrations in the range of some %. In the case of 57Fe as doping ion, Mössbauer spectroscopy can be used to investigate how it is built in the host matrix. The 57Fe ion acts both as doping and probe.

In the present study, a survey about Mössbauer spectroscopy as a tool to explore such materials is given. It is very useful however it is insufficient for a full characterization. Other techniques like transmission electron microscopy, Zero-field-cooled/field-cooled SQUID measurements or X-ray diffraction are necessary as complementary methods.

  • Invited lecture (Conferences)
    International Symposium on the Industrial Applications of the Mössbauer Effect (ISIAME'08), 17.-22.08.2008, Budapest, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-11667
Publ.-Id: 11667


Swift-heavy-ion-induced shaping of spherical Ge nanoparticles into disks and rods

Schmidt, B.; Heinig, K.-H.; Mücklich, A.; Akhmadaliev, C.

The work reports on experimental features and theoretical studies of swift-heavy-ion-induced shaping of Ge nanospheres into disks. A stack of alternating Ge and SiO2 layers was sputtered on an oxidized Si wafer. The Ge layer thicknesses varied from 2.5 to 7.5 nm. Thermal treatment above the melting temperature of Ge transformed each Ge layer into a layer of Ge nanospheres. With growing Ge layer thickness the mean diameter increases from 8 to 37 nm. Irradiation with low fluences (~1014cm-2) of 38 MeV I7+ shaped medium-sized Ge nanospheres into disks, whereas smaller ones became rod-like and larger ones remained unchanged. At higher fluences, the larger Ge nanospheres shrink due to Ge loss and shape into disks too. A new model is presented and atomistic Monte-Carlo simulations are shown which describe the shaping evolution and the size thresholds for shaping quantitatively. The volume change of Ge upon melting has been identified as driving force.

Keywords: heavy ion irradiation; ion beam shaping; nanoparticles

  • Lecture (Conference)
    16th International Conference on Ion Beam Modification of Materials (IBMM 2008), 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1345-1348
    DOI: 10.1016/j.nimb.2009.01.062

Permalink: https://www.hzdr.de/publications/Publ-11666
Publ.-Id: 11666


Photodisintegration studies on 92Mo and 144Sm

Nair, C.; Junghans, A. R.; Erhard, M.; Bemmerer, D.; Beyer, R.; Grosse, E.; Klug, J.; Kosev, K.; Rusev, G.; Schilling, K. D.; Schwengner, R.; Wagner, A.

In burning stellar environments like supernova explosions, the temperatures are high enough for the production of heavy neutron deficient nuclei, the so-called p-nuclei. These are thought to be produced in such explosive scenarios either through chains of photodisintegration reactions on heavy seed nuclei. The modelling of the nucleosynthesis for the p-nuclei is mainly based on statistical model calculations. In this context, the knowledge of the experimental cross sections for the prediction of the p-nuclei abundances is of crucial importance and to forward in this direction we have started and experimental program at the bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden-Rossendorf . Photodisintegration measurements on the astrophysically relevant p-nuclei 92Mo and 144Sm have been performed via photoactivation technique with bremsstrahlung end-point energies from 10.0 to 16.5 MeV. In particular the (gamma,alpha) reactions of the mentioned nuclei were studied for the first time at different endpoint energies above and close to the threshold. The bremsstrahlung facility and the experimental area are deigned so as to facilitate the studies under optimized background conditions. To probe the fascinating investigations on short-lived nuclei a new pneumatic delivery system has been built recently. First experiments on the short-lived decays following the reaction 144Sm(gamma,n) is discussed. The activation yields from all measurements are compared with calculations using cross sections from recent Hauser-Feshbach models .

Keywords: photodisintegration; bremsstrahlung

  • Lecture (Conference)
    10th Symposium on the Nuclei in Cosmos, 27.07.-01.08.2008, Mackinac Island, Michigan, USA

Permalink: https://www.hzdr.de/publications/Publ-11665
Publ.-Id: 11665


Ion-irradiation-induced damage of steels characterized by means of nanoindentation

Heintze, C.; Recknagel, C.; Bergner, F.; Hernández-Mayoral, M.; Kolitsch, A.

Self-ion irradiation was used to simulate the damage caused by fast neutrons in the austenitic stainless steel SS 304 SA, the ferritic/martensitic steel Eurofer’97 and a Fe-9at%Cr model alloy. The irradiation-induced hardness change in the damage layer was evaluated by means of nanoindentation. Three-step irradiations were performed at room temperature and 300°C up to 1 and 10dpa. An irradiation-induced hardness change was shown for all materials. No influence of irradiation temperature could be resolved. Irradiation-induced hardening exhibits different fluence dependencies in Eurofer’97 and Fe-9at%Cr. While the data indicate a saturation-like behaviour for Fe-9at%Cr, a monotonous increase of hardness with fluence up to 10dpa was found for Eurofer’97.

Keywords: self-ion irradiation; nanoindentation; irradiation hardening; iron base alloys

  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1505-1508

Permalink: https://www.hzdr.de/publications/Publ-11664
Publ.-Id: 11664


Terahertz emission from a large-area GaInAsN emitter

Peter, F.; Winnerl, S.; Schneider, H.; Helm, M.; Köhler, K.

A large-area interdigitated terahertz (THz) emitter based on molecular-beam epitaxy grown GaInAsN with an additional AlGaAs heterostructure is investigated as THz source for excitation wavelengths between 1.1 and 1.5 µm. The optical and electrical properties of the emitter material exhibit absorption up to a wavelength of 1.5 µm and have a resistivity of 550 kΩ cm. Terahertz waves were detected by electro-optical sampling with a bandwidth exceeding 2 THz. Best performance is found for excitation wavelengths below 1.35 µm. Furthermore the emission properties for several excitation powers are investigated showing a linear increase of THz emission.

Keywords: TERAHERTZ; SPECTROSCOPY; ANTENNAS; BEAMS

Permalink: https://www.hzdr.de/publications/Publ-11663
Publ.-Id: 11663


RTA and FLA of ultra-shallow implanted layers in Ge

Wündisch, C.; Posselt, M.; Anwand, W.; Schmidt, B.; Mücklich, A.; Skorupa, W.; Clarysse, T.; Simoen, E.

The formation of ultra-shallow n+ layers by P or As implantation and subsequent rapid thermal annealing (RTA) or flash-lamp annealing (FLA) is investigated. The focus is on diffusion and activation of dopants. RTA leads to considerable broadening of the shallow as-implanted profiles by concentration-dependent diffusion. In contrast, FLA does not cause any diffusion and is therefore a promising method for producing ultra-shallow n+p junctions in Ge. Under present annealing conditions RTA yields maximum activation levels of about 1.1E19 and 6.5E18 for P and As, respectively. The maximum activation achieved by FLA is about 4.0E19 and 2.1E19 for P and As, respectively. Possible mechanisms for diffusion and deactivation of dopants are discussed.

Keywords: Germanium; ion implantation; annealing; electrical doping; diffusion; activation

  • Contribution to proceedings
    16th IEEE International Conference on Advanced Thermal Processing of Semiconductors (IEEE RTP 2008), 30.09.-03.10.2008, Las Vegas, NV, USA
    Proceedings of the 16th IEEE International Conference on Advanced Thermal Processing of Semiconductors, RTP 2008, September 30- October 3, 2008, Las Vegas, NV, USA, Piscataway, NJ: IEEE, 978-1-4244-1950-0, 245-249
  • Lecture (Conference)
    16th IEEE International Conference on Advanced Thermal Processing of Semiconductors (IEEE RTP 2008), 30.09.-03.10.2008, Las Vegas, NV, USA

Permalink: https://www.hzdr.de/publications/Publ-11662
Publ.-Id: 11662


Precision study of ground state capture in the 14N(p,gamma)15O reaction

Marta, M.; Formicola, A.; Gyurky, G.; Bemmerer, D.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Elekes, Z.; Fulop, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Imbriani, G.; Junker, M.; Kunz, R.; Lemut, A.; Limata, B.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Romano, M.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.; Vomiero, A.

The rate of the hydrogen-burning carbon-nitrogen-oxygen (CNO) cycle is controlled by the slowest process, 14N(p,gamma)15O, which proceeds by capture to the ground and several excited states in 15O. Previous extrapolations for the ground state contribution disagreed by a factor 2, corresponding to 15% uncertainty in the total astrophysical S-factor. At the Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator placed deep underground in the Gran Sasso facility in Italy, a new experiment on ground state capture has been carried out at 317.8, 334.4, and 353.3 keV center-of-mass energy. Systematic corrections have been reduced considerably with respect to previous studies by using a Clover detector and by adopting a relative analysis. The previous discrepancy has been resolved, and ground state capture no longer dominates the uncertainty of the total S-factor.

Keywords: Nuclear astrophysics; solar neutrinos; CNO cycle; radiative capture; in-beam gamma-spectrometry; underground; Gran Sasso; R-matrix; Clover detector

Permalink: https://www.hzdr.de/publications/Publ-11661
Publ.-Id: 11661


Nano-Biotechnologie für den Umweltschutz: Entwicklung neuer fotokatalytisch aktiver Verbundmaterialien

Pollmann, K.; Raff, J.

wird nachgereicht

  • Lecture (Conference)
    DECHEMA-Workshop zur Fördermaßnahme NanoNature des BMBF, 26.08.2008, Frankfurt, Deutschland
  • Poster
    DECHEMA-Workshop zur Fördermaßnahme NanoNature des BMBF, 26.08.2008, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11660
Publ.-Id: 11660


Metal removal and recovery by bacteria-based biocomposites

Raff, J.

Bacteria are simply organized, but apart from that and their small size they are an unbelievable complex and a highly efficient group of creatures. Some are able to thrive at the most forbidding, uninviting places on Earth, for example in hot springs, in the perpetual ice, in the deep sea or in deserts. For production of energy they can use different kinds of organic and inorganic matter or sun light. Furthermore, they successfully conquer also any other habitats, even so an environment is highly contaminated with toxic substances, like organic solvents, heavy metals and radionuclides. Adaptation and detoxification mechanisms allow them to resist high concentrations of toxic elements without getting sustainably affected. These mechanisms are very prospective for the development of innovative remediation strategies and for other biotechnical applications [1-6].
Within the radio-ecological research on the interaction of bacteria with actinides many reference strains and isolates were investigated for their interaction with heavy metals and radionuclides [7-11]. The studied bacteria possess different strategies to handle high metal concentrations in their environment. Namely, via an immobilization of the metals by biosorption, bioaccumulation inside the cell, biomineralization and biotransformation. In principle, all mentioned strategies are suitable for the development of new materials for bioremediation techniques and the removal of metals. In respect of the development of metal selective and reusable filter materials, several Bacillus and Lysinibacillus isolates from a uranium mining waste pile were preferentially investigated. The cells bind selectively and reversibly uranium on their surface. Furthermore the analyses results in the identification of new so called surface layer (S-layer) proteins, forming the outermost structure on many bacteria. This S-layers are able to bind and detain toxic heavy metals while essential ones may pass. To take advantage of this intelligence intact cells, spores and the S-layer proteins of the bacteria were immobilized in sol-gel ceramics [11, 12] and used for metal binding experiments. Ongoing experiments include also the production of biofilm based materials and the protein immobilization on conventional carriers. Especially the S-layer proteins not only bind heavy metals very selectively but also some precious metals. The superior aim is the development of metal selective filter materials for the removal of heavy metals and in future for the recovery of precious metals from aqueous solutions.

Ackowledgements
We gratefully acknowledge support by the DFG (Biocere, SE 671/1-2) and the BMWi/PTJ (BIOREM, 03EGSSN014).

References
[1] L. Hendrickx and M Mergeay (2007), Curr Opin Microbiol 10(3), 231-237
[2] R. Margesin and F. Schinner F. (2001), Appl Microbiol Biotechnol. 56(5-6) 650-663
[3] G. Antranikian (2005), Adv Biochem Eng Biotechnol, 96, 219-262
[4] M. Kalin et al. (2005), J Environ Radioact. 78(2),151-177
[5] B. Volesky and Z.R. Holan (1995), Biotechnol. Prog. 11, 235-250
[6] J. Raff and S. Selenska-Pobell (2006), Nuclear Engineering International 51(619) 34-36
[7] M. Merroun et al. (2005) Appl. Environ. Microbiol. 71(9): 5532-5543
[8] M. Merroun et al. (2006) Radiochimica Acta 94, 723-729
[9] H. Moll et al. (2008) BioMetals 21, 219-228
[10] H. Moll et al. (2006) Radiochimica Acta 94(2006), 815-824
[11] J. Raff et al. (2003), Chem. Mater. 15, 240-244
[12] K. Pollmann et al. (2006), Biotechn. Adv. 24 (1), 58-68

  • Lecture (Conference)
    Max Bergmann Symposium 08 on Molecular Designed Biological coatings, 04.-06.11.2008, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11659
Publ.-Id: 11659


Polyhedral Approximation and Practical Convex Hull Algorithm for Certain Classes of Voxel Sets

Schulz, H.

In this paper we introduce an algorithm for the creation of polyhedral approximations for certain kinds of digital objects in a three-dimensional space. The objects are sets of voxels represented as strongly connected subsets of an abstract cell complex. The proposed algorithm generates the convex hull of a given object and modifies the hull afterwards by recursive repetitions of generating convex hulls of subsets of the given voxel set or subsets of the background voxels. The result of this method is a polyhedron which separates object voxels from background voxels. The objects processed by this algorithm and also the background voxel components inside the convex hull of the objects are restricted to have genus 0. The second aim of this paper is to present some practical improvements to the discussed convex hull algorithm to reduce computation time.

Keywords: digital geometry; convex hull; abstract cell complex; abstract polyhedron; surface approximation

Permalink: https://www.hzdr.de/publications/Publ-11658
Publ.-Id: 11658


Bacterial surface layers proteins: self-organizing biomolecules as building blocks for nanostructured materials

Pollmann, K.; Raff, J.; Günther, T.; Fahmy, K.

Surface layer proteins (S-layers) form the outer sheet around the cells of many primitive microorganisms. They form two-dimensional paracrystalline arrays with repeating units on the scale of a few nanometers (10-9 m). We have established their utilization as a technology platform for innovative materials. The S-layer of Lysinibacillus sphaericus JG-A12 isolated from a uranium waste pile has been shown to exhibit highly ordered binding sites for various metals such as Pt, Pd, Au, suitable for the formation of regularly distributed nanoclusters of defined sizes. Such bioinorganic materials possess a great potential for the development of novel catalysts, new biomedical and bio¬analytical applications, the assembly of nanometer-scaled electronic devices, optical industry, and storage media. At the Institutes of Radiation Physics, Ion-beam Physics and Materials Research, and the Dresden High Magnetic Field Laboratory, the structure of such nanoparticles and their physical properties are currently analyzed in an interdisciplinary approach.

Keywords: S-layer; bioremidiation; spectroscopy; metal binding

  • Contribution to proceedings
    11th Vietnamese-German Seminar on Physics and Engineering, 31.03.-05.04.2008, Nha Trang, Vietnam
    Proceedings of the Eleventh Vietnamese-German Seminar on Physics and Engineering, Hanoi: Hanoi University

Permalink: https://www.hzdr.de/publications/Publ-11657
Publ.-Id: 11657


Measurement of the electrical conductivity of Pb-Bi alloys in the melting-solidification region

Plevachuk, Y.; Sklyarchuk, V.; Eckert, S.; Gerbeth, G.

The electrical conductivity of Pb-Bi alloys of eutectic and near eutectic compositions was investigated in the melting-solidification temperature region. The revealed discrepancies between the heating and cooling curves as well as a hysteresis observed in course of heating-cooling cycles suggest a metastable microheteregenous structure of the Pb-Bi melts.

Keywords: Pb-Bi alloys; electrical conductivity; eutectic transformation

  • Journal of Nuclear Materials 376(2008), 363-365

Permalink: https://www.hzdr.de/publications/Publ-11656
Publ.-Id: 11656


Gold nanoparticle tips for optical field confinement in infrared scattering near-field optical microscopy

Wenzel, M. T.; Härtling, T.; Olk, P.; Kehr, S. C.; Grafström, S.; Winnerl, S.; Helm, M.; Eng, L. M.

We report on the implementation of metal nanoparticles as probes for scattering and apertureless near-field optical investigations in the mid-infrared (mid-IR) spectral regime. At these wavelengths, an efficient electric-field confinement is necessary and achieved here through a gold metal nanoparticle of 80 nm in diameter (Au80-MNP) acting as the optical antenna. The Au80-MNP is attached to a standard AFM cantilever used as the spatial manipulator. When approached to a sample surface while being illuminated with an infrared beam, the Au80-MNP produces a considerably improved spatial confinement of the electric field compared to an ordinary scattering AFM tip. We demonstrate here the confinement normal to the sample surface by making use of a sample-induced phonon polariton resonance in a ferroelectric lithium niobate sample. Our experimental findings are in very good agreement with the quasistatic dipole model and show improved optical resolution via well-selected antenna particles.

  • Open Access Logo Optics Express 16(2008), 12302-12312

Permalink: https://www.hzdr.de/publications/Publ-11655
Publ.-Id: 11655


Correlated electron systems at high magnetic fields

Wosnitza, J.

High magnetic fields are one of the most powerful tools available to scientists for the study, modification, and control of the state of matter. The application of magnetic fields, therefore, has become a commonly used instrument for condensed-matter physics. For the observation of many phenomena very high magnetic fields are essential. Consequently, the demand for the highest possible magnetic-field strengths is increasing. At the Dresden High Magnetic Field Laboratory (HLD), that has just opened its doors for external users, pulsed magnetic fields up to 70 T are available and the ambitious goal of reaching 100 T has been set. Here, I will present the current status of the HLD and discuss some scientific results recently obtained at high magnetic fields. This covers e.g. the clear thermodynamic evidence for the existence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in a layered organic superconductor, the magnetic-field-induced change of the electronic band structure in the metal CeBiPt, and finally the determination of the band- and angle-resolved superconducting coupling strength in a borocarbide superconductor.

  • Invited lecture (Conferences)
    1st Bilateral Estonian-German Workshop Strong Nonlinear Vibronic and Electronic Interactions in Solids, 30.04.-02.05.2008, Tartu, Estonia

Permalink: https://www.hzdr.de/publications/Publ-11654
Publ.-Id: 11654


An insight into what superconducts in polycrystalline boron-doped diamonds based on investigations of microstructure

Dubrovinskaia, N.; Wirth, R.; Wosnitza, J.; Papageorgiou, T.; Braun, H. F.; Miyajima, N.; Dubrovinsky, L.

The discovery of superconductivity in polycrystalline boron-doped diamond (BDD) synthesized under high pressure and high temperatures [Ekimov, et al. (2004) Nature 428:542–545] has raised a number of questions on the origin of the superconducting state. It was suggested that the heavy boron doping of diamond eventually leads to superconductivity. To justify such statements more detailed information on the microstructure of the composite materials and on the exact boron content in the diamond grains is needed. For that we used high-resolution transmission electron microscopy and electron energy loss spectroscopy. For the studied superconducting BDD samples synthesized at high pressures and high temperatures the diamond grain sizes are ≈1–2 µm with a boron content between 0.2 (2) and 0.5 (1) at %. The grains are separated by 10- to 20-nm-thick layers and triangular-shaped pockets of predominantly (at least 95 at %) amorphous boron. These results render superconductivity caused by the heavy boron doping in diamond highly unlikely.

  • Proceedings of the National Academy of Sciences of the United States of America 105(2008)33, 11619-11622

Permalink: https://www.hzdr.de/publications/Publ-11653
Publ.-Id: 11653


Characterization of ZnO Nanostructures: A Challenge to Positron Annihilation Spectroscopy and other Methods

Brauer, G.; Anwand, W.; Grambole, D.; Egger, W.; Sperr, P.; Beynik, I.; Hofer, C.; Teichert, C.; Kuriplach, J.; Lang, J.; Zviagin, S.; Cizmar, E.; Ling, C. C.; Hsu, Y. F.; Xi, Y. Y.; Djurisic, A. B.; Skorupa, W.

ZnO is of considerable interest for optoelectronic device applications due to its wide band gap and high exciton binding energy. In spite of decades of study and recent progress in research on ZnO properties, there remained unresolved controversies which are mainly related to native defects formed during crystal growth. Positron annihilation spectroscopy (PAS) is among the methods to tackle this structural issue [1, 2].
ZnO nanostructures, like e.g. nanorods [3] and tetrapods [4], are of special interest for device applications [5, 6]. However, their characterization remains an ongoing challenge.
This talk intends to review our recent efforts and latest achievements in this direction. Results obtained will comprise PAS in the form of Slow Positron Implantation Spectroscopy (SPIS) and Pulsed Low Energy Positron Lifetime Spectroscopy (PLEPS), Nuclear Reaction Analysis (NRA), Atomic Force Microscopy (AFM), conductive AFM (C-AFM), Nuclear Magnetic Resonance (NMR), Electron Spin Resonance (ESR), Photoluminescence (PL) spectroscopy, and latest theoretical investigations of structure-related and positron properties of selected defects.
The fundamental importance of a relationship between fabrication conditions, native defect formation, and resulting optical and electronic properties is demonstrated by getting either inferior (nanorods) or significantly improved (tetrapods) optical properties compared to single crystal samples, depending on the nanostructure fabrication method.

  • Invited lecture (Conferences)
    XVth International Conference on Positron Annihilation (ICPA-15), 18.-23.01.2009, Kolkata, India

Permalink: https://www.hzdr.de/publications/Publ-11652
Publ.-Id: 11652


Activities towards p-Type Doping of ZnO

Brauer, G.; Kuriplach, J.; Djurisic, C. C.; Ling, A. B.

Zinc oxide (ZnO) is an interesting and promising semiconductor material for many potential applications, e.g. in opto-electronics and for sensor devices. However, its p-type doping represents a challenging problem, and the physical reasons of its mostly n-type conductivity are not perfectly clear at present.
Firstly, efforts to achieve p-type conductivity by ion implantation are reviewed, and the creation of a p-n junction by N+ ion implantation with post-implantation annealing is discussed.
Secondly, ways to achieve p-type ZnO nanorods by various growth conditions are presented. Their characterization by electrical, optical and positron annihilation spectroscopy methods will also be included.
Third, the preparation of Schottky contacts on ZnO with the surface pre-treatments of hydrogen peroxide is mentioned in some detail as this is a demand of the device formation process.
Finally, the possible incorporation of hydrogen and nitrogen into structural defects, which can act as trapping sites for positrons, is discussed. This will be discussed in the context of positron experimental and theoretical results and estimated H and N contents in a selected variety of ZnO materials.

  • Invited lecture (Conferences)
    8th International Conference on Position Sensitive Detectors (PSD 2008), 01.-05.09.2008, Prague, Czech Republic
  • Open Access Logo Journal of Physics: Conference Series 265(2011), 012002
    DOI: 10.1088/1742-6596/265/1/012002

Permalink: https://www.hzdr.de/publications/Publ-11651
Publ.-Id: 11651


Secondary Structure and Compliance of a Predicted Flexible Domain in Kinesin-1 Necessary for Co-operation of Motors

Crevenna, A. H.; Madathil, S.; Cohen, D. N.; Wagenbach, M.; Fahmy, K.; Howard, J.

While the mechanism by which a kinesin-1 molecule moves individually along a microtubule is quite well understood, the way that many kinesin-1 motor proteins bound to the same cargo move together along a microtubule is not. We have identified a 60-aa-long domain, termed Hinge 1, in kinesin-1 from Drosophila melanogaster that is located between the coiled coils of the neck and stalk domains. Its deletion reduces microtubule gliding speed in multiple–motor assays but not single-motor assays. Hinge 1 thus facilitates the co-operation of motors by preventing them from impeding each other. We have addressed the structural basis for this phenomenon. Video-microscopy of single microtubule-bound full-length motors reveals the sporadic occurrence of high compliance states alternating with longer-lived low compliance states. Deletion of Hinge 1 abolishes transitions to the high compliance state. Based on FTIR, CD, and fluorescence spectroscopy of Hinge 1 peptides, we propose that the low compliance states correspond to an unexpected structured organization of the central Hinge 1 region, whereas the high-compliance state corresponds to the loss of that structure. We hypothesize that strain accumulated during multiple-kinesin motility populates the high compliance state by unfolding helical secondary structure in the central Hinge 1 domain flanked by unordered regions, thereby preventing the motors from interfering with each other in multiple-motor situations.

Keywords: Gliding assay; single-molecule assay; torsional elasticity; protein flexibility; microtubule; spectroscopy

Permalink: https://www.hzdr.de/publications/Publ-11650
Publ.-Id: 11650


Interplay between Kondo-like behavior and short-range antiferromagnetism in EuCu2Si2 single crystals

Cao, C. D.; Klingeler, R.; Leps, N.; Vinzelberg, H.; Kataev, V.; Muranyi, F.; Tristan, N.; Teresiak, A.; Zhou, S.; Löser, W.; Behr, G.; Büchner, B.

The static and dynamic magnetic properties, electrical resistivity, specific heat, and magnetoresistance have been studied in EuCu2Si2 single crystals grown by a floating zone method. The magnetic susceptibility exhibits a considerable anisotropy and a steep rise below 10 K for external fields parallel to the c axis but with no evident magnetic ordering in the temperature range of 2–350 K. The data imply a gradual change in the Eu valence as a function of temperature. Electron spin resonance (ESR) measurements reveal a sizeable fraction of stable Eu2+ magnetic moments that interact with conduction electrons and develop quasistatic antiferromagnetic correlations on the ESR timescale. The electrical resistivity and specific heat demonstrate the presence of spin fluctuations and Kondo-like behavior, which apparently competes with the antiferromagnetic order. The analysis of experimental data enables to conclude that the remarkable diversity of the physical properties of EuCu2Si2 results from the variation of lattice parameters as well as of local crystal chemistry as a consequence of the particular preparation route employed for the growth of single crystals and polycrystals.

Permalink: https://www.hzdr.de/publications/Publ-11649
Publ.-Id: 11649


Arsenic doped zinc oxide

Volbers, N.; Lautenschläger, S.; Leichtweiss, T.; Laufer, A.; Graubner, S.; Meyer, B. K.; Potzger, K.; Zhou, S.

As-doping of zinc oxide has been approached by ion implantation and chemical vapor deposition. The effect of thermal annealing on the implanted samples has been investigated by using secondary ion mass spectrometry and Rutherford backscattering/channeling geometry. The crystal damage, the distribution of the arsenic, the diffusion of impurities, and the formation of secondary phases is discussed. For the thin films grown by vapor deposition, the composition has been determined with regard to the growth parameters. The bonding state of arsenic was investigated for both series of samples using x-ray photoelectron spectroscopy.

Keywords: ZnO; Doping

Permalink: https://www.hzdr.de/publications/Publ-11648
Publ.-Id: 11648


Electron beam CT – a potential tool for small animal imaging ?

Hampel, U.; Fischer, F.; Bergmann, R.

Electron beam CT has until today been exclusively used in cardiac imaging of human beings. As a high cost diagnostic tool with frame rates in the range of 20 Hz it has so far not been considered for small animal imaging. With recent progress in technology an application in this field becomes feasible. Especially perfusion imaging for heart and other organs using iodine based contrast agents may be a target of interest for electron beam CT. We present a small volume ultra fast electron beam CT scanner which was originally developed for process tomography applications and with it preliminary results of a small animal study showing visualization of heart motion and perfusion in a rat. We further discuss the potential of this new technology and novel technological principles which allow fast 3D electron beam imaging of small animals. Included in the discussion is an assessment of radiation effects.

Keywords: electron beam tomography; small animal imaging

  • Lecture (Conference)
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
    IEEE NSS/MIC/RTSD Conference Record

Permalink: https://www.hzdr.de/publications/Publ-11647
Publ.-Id: 11647


Application of CdTe and CZT detectors in ultra fast electron beam X-ray tomography

Hampel, U.; Fischer, F.

Ultra fast electron beam tomography has been developed as a novel tool for visualisation of fast processes. As in medical electron beam CT this technique is based on the generation of images from radiographs produced with a rapidly scanned electron beam. Thereby an electron beam of sufficiently high power (typically UB=150kV, power up to 10 kW) is scanned across a circular metal target producing X-rays in a small focal spot. With the rotation of the spot around an object radiographs from different viewing angles are produced and subsequently reconstructed to slice images. A fast electron beam scanner at FZD operates with beam sweeping of up to 7 kHz, producing up to 7000 images per second. The X-ray detector used in this device consists of 240 room temperature semiconductor elements operated in current mode. Photon flux at the detector is rather high, being >10^11 ph/s. The detector is sampled with 1 MHz frequency. It is known, that high flux current mode operation poses problems for semiconductor detectors made of CZT and CdTe due to polarization effects and decay time in the few hundred ns range. We have compared both types of detectors regarding their suitability in such an application. The presentation will give an overview on these results and furthermore give an introduction of this new fast imaging technique.

Keywords: electron beam tomography; CdTe detector; CZT detector

  • Invited lecture (Conferences)
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    IEEE - Workshop on X-Ray Micro Imaging of Materials, Devices, and Organisms, 22.-24.10.2008, Dresden, Germany
    IEEE NSS/MIC/RTSD Conference Record

Permalink: https://www.hzdr.de/publications/Publ-11646
Publ.-Id: 11646


Ultra fast electron beam X-ray tomography at FZD

Hampel, U.

The presentation gives an overview on recent developments in ultra fast electron beam X-ray tomography for process applications. Principles of this new tomographic imaging modality are discussed along with applications in flow measurement. A focus is given on potential extension of the technology towards high power electron beam CT using DC electron LINAC.

Keywords: electron beam tomography

  • Invited lecture (Conferences)
    Electron Beam Tomography Meeting at BUDKERS Institute Novosibirsk, 02.09.2008, Novosibirsk, Russia

Permalink: https://www.hzdr.de/publications/Publ-11644
Publ.-Id: 11644


Computed tomography methods in flow measurement

Hampel, U.

The lecture introduces computerized tomography as applied in process and flow diagnostics. In many indutrial fields multiphase flows play a key role in efficiency and safety aspects of indiustrial plants and processes. In the lecture principles of tomographic imaging modalities, such as electrical tomography, gamma and X-ray tomography, electron beam tomography, PET and PEPT are discussed along with exemplary applications in oil industry, chemical industry, nuclear engineering and other industrial and scientific fields.

Keywords: computed tomography; process tomography; multi-phase flow

  • Invited lecture (Conferences)
    FZD Lectures, 07.07.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-11643
Publ.-Id: 11643


Self-organized metallic nanoparticle and nanowire arrays from ion-sputtered silicon templates

Oates, T. W. H.; Keller, A.; Noda, S.; Facsko, S.

We demonstrate a production method for self-organized arrays of metal nanoparticles and aligned nanowires. Ion beam-sputtered Si/SiO2 substrates are used as templates for metallic vapor deposition, forming aligned arrays of 5–20 nm silver and cobalt nanoparticles with a period of 35 nm. The 20 nm diameter cobalt nanowires with lengths in excess of a micrometer are produced under appropriate conditions. All processing steps can be integrated into a single vacuum chamber and performed in a matter of minutes at mild temperatures. This inherently scalable technique can be extended to a range of substrate materials, array patterns, and nanoparticle materials.

Permalink: https://www.hzdr.de/publications/Publ-11642
Publ.-Id: 11642


Electromagnetic excitation of separated flows: Coherent structures and mean flow features

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

Flow separation and its control is a persistent topic of fluid dynamic research with large technological importance. Since the early 1990s, separation control by periodic addition of momentum, now commonly termed “active flow control”, has been a subject of intense research. Its main advantage compared to steady actuation is that a control goal, e.g. a specific lift increase, can typically be attained by orders of magnitude smaller momentum input . The significant actuation parameters are mainly the time averaged momentum input and the normalized excitation frequency.
The present lectures discusses the applicability of electromagnetic forces to control separated flows. Simultaneous time resolved force measurements and flow fields obtained by Particle Image Velocimetry on a NACA 0015 are presented. The effects of momentum coefficient, exciatation frequency and -wave-form on the coherent structures and the resulting mean flow are discussed.

Keywords: active flow control; Lorentz force; coherent structures

  • Lecture (Conference)
    European Drag Reduction and Flow Control Meeting (EDRFCM 2008), 08.-11.09.2008, Ostritz - St. Marienthal, Germany

Permalink: https://www.hzdr.de/publications/Publ-11641
Publ.-Id: 11641


Efficient oxygen gettering in Si by co-implantation of hydrogen and helium

Ou, X.; Koegler, R.; Mücklich, A.; Skorupa, W.; Möller, W.; Wang, X.; Gerlach, J. W.; Rauschenbach, B.

Hydrogen pre-implantation performed in addition to helium implantation efficiently shrinks the width of the gettering layer in Si and increases the empty volume fraction as well as the internal surface area per unit volume. The gettering efficiency for oxygen is significantly enhanced compared to the single helium implantation, and the helium implantation dose can be strongly reduced. The gas-filled bubble layer induced by the co-implantation of hydrogen and helium has the highest gettering efficiency for the oxygen accumulation. Direct evidence for oxygen gettering at the internal wall of the cavity is demonstrated by cross-sectional transmission electron microscopy (XTEM).

Keywords: ion implantation; gettering; oxygen; helium; hydrogen; silicon; SIMOX

Permalink: https://www.hzdr.de/publications/Publ-11640
Publ.-Id: 11640


Time-resolved semiconductor spectroscopy in the mid-infrared and Terahertz regimes

Schneider, H.

This talk will focus on several research topics exploiting our free-electron (FEL) and modelocked Ti:Sapphire lasers to investigate semiconductor nanostructures. Pump-probe spectroscopy and two-photon detection is used for time-resolved investigations of intersubband transitions in semiconductor quantum wells and for FEL pulse diagnostics, respectively. Terahertz emitters based on interdigitated metal stripe arrays will also be discussed.

  • Lecture (others)
    Seminar, Bhabha Atomic Research Centre, Mumbai, India, 07.08.2008, Mumbai, India

Permalink: https://www.hzdr.de/publications/Publ-11639
Publ.-Id: 11639


Tutorial on Intersubband Devices: Quantum Cascade Laser

Schneider, H.

There is no abstract.

  • Invited lecture (Conferences)
    Optoschool 2008, 27.07.-02.08.2008, Mumbai, India

Permalink: https://www.hzdr.de/publications/Publ-11638
Publ.-Id: 11638


Tutorial on Intersubband Devices: Quantum Well Infrared Photodetectors

Schneider, H.

There is no abstract.

  • Invited lecture (Conferences)
    Optoschool 2008, 27.07.-02.08.2008, Mumbai, India

Permalink: https://www.hzdr.de/publications/Publ-11637
Publ.-Id: 11637


Room-temperature mid-infrared two-photon photodetector

Schneider, H.; Liu, H. C.; Winnerl, S.; Drachenko, O.; Helm, M.; Faist, J.

We report on a two-photon detector based on resonantly enhanced nonlinear absorption between subbands in InGaAs/InAlAs quantum wells and demonstrate its use as a quadratic autocorrelator for mid-infrared pulses. Modified device design allows for device operation at room temperature, which is crucial for applications in practical systems.

Keywords: Quantum well intersubband photodetector; two-photon transition; quadratic autocorrelation; InGaAs/AlGaAs

Permalink: https://www.hzdr.de/publications/Publ-11636
Publ.-Id: 11636


Experimental observation of swirl accumulation in a magnetically driven flow

Grants, I.; Zhang, C.; Eckert, S.; Gerbeth, G.

Independent poloidal and azimuthal body forces are induced in a liquid metal cylinder by traveling and rotating magnetic fields of different frequencies, respectively. The bulk axial and azimuthal velocities are measured by the ultrasound Doppler method. Particle image velocimetry is used to observe the upper free surface velocity distribution. The transition from the poloidal to the azimuthal body force governed regime occurs at a fixed ratio of the respective force magnitude of around 100. This transition is marked by a formation of a concentrated vortex revealing several similarities to intense atmospheric vortices. The vortex structure is controlled by a relatively weak azimuthal force while the poloidal one holds the main control over the top speed of the top speed of the swirl is mainly governed by the poloidal one. Under a certain force ratio the average axial velocity changes its direction in the vortex core resembling the subsidence in an eye of a tropical cyclone or a large tornado. Multiple moving vortices encircle the vortex core in this regime.

  • Journal of Fluid Mechanics 616(2008), 135-152

Permalink: https://www.hzdr.de/publications/Publ-11635
Publ.-Id: 11635


Two phase flow 1D turbulence model for poly disperse upward flow in a vertical pipe

Al Issa, S.; Lucas, D.

A 1D test solver was developed in recent years for the modeling of two phase bubbly flow in pipe geometry. The solver considers number of bubble classes and calculates bubble-size resolved void fraction profiles in radial direction. A successful implementation was achieved regarding bubble forces models (non-drag forces). Discrepancies appeared when coalescence and breakup rates are significant. These rates depend upon local turbulent values, which are possible reason for shortcomings in calculating coalescence and breakup rates. Originally the test solver is equipped by Sato model (Sato et al. 1981) which accounts for turbulence via shear- and bubble-induced viscosities calculated out of empirical correlations. One-equation for the turbulent kinetic energy was considered. In order to improve the local values of turbulence parameters the existing turbulence model was replaced by two-equation turbulence model. The new model accounts for the bubble-induced turbulence via source term taken from literature. Comparisons between new and old turbulence modeling against experimental data showed better agreement of the new model. The experiments covered wide range of water and air superficial velocities for upward bubbly flow in two pipe’s diameters: 50 mm and 200 mm. Main feature of new calculations is providing values of turbulence parameters for application in coalescence and breakup models. A comparison with CFX 5.7 calculations in 50 mm pipe showed better calculation results when applying the source term. An implementation of the source term into CFX calculations is planned.

Keywords: Poly-disperse; bubbly Flow; bubble-induced turbulence; CFD

  • Nuclear Engineering and Design 239(2009)10, 1933-1943

Permalink: https://www.hzdr.de/publications/Publ-11634
Publ.-Id: 11634


Effect of melt convection on microstructure evolution of Nd-Fe-B and Ti-Al peritectic alloys

Hermann, R.; Gerbeth, G.; Biswas, K.; Filip, O.; Shatrov, V.; Priede, J.

The influence of melt convection on the microstructure during solidification of peritectic Nd-Fe-B and Ti-Al alloys has been investigated. Since the magnetic and mechanical properties of these technical relevant materials depend strongly on the microstructure and especially on the volume fraction of the properitectic phase, such investigation is of growing scientific interest. On the basis of numerical simulation of melt convection modes in an inductively heated metallic melt, novel techniques for the modification of the melt convection were developed. This is the forced rotation technique and a modified floating-zone facility equipped with a special designed double coil system enabling the application of additional magnetic fields. The forced rotation technique where the crucible rotates with well defined frequencies leads in accordance to numerical simulation to a strong reduction of the melt convection in dependence on the frequency. The volume fraction of the soft magnetic α-Fe phase could be drastically reduced in comparison to a common induction melting accompanied by a simultaneous reduction of the secondary dendritic arm spacing. The floating-zone facility with the patented double coil system allows the tailoring of the melt convection in a wide range from motion at rest to strong stirring. The microstructure of the investigated Ti-Al alloy changed from dendritic to globulitic morphology under strong stirring whereas the volume fraction of the properitectic phase increases with increasing stirring. The mechanical properties show a significant increased plastic deformation of the samples solidified under strong stirring. The possible reason of the change in morphology is explained as a result of spherical growth under forced convection. The study of the influence of melt convection on the microstructure formation of peritectic alloys showed the feasibility of tailoring the microstructure and the resulting alloy properties by customized melt convection using magnetic fields.

Keywords: Melt convection; Peritectic solidification; Nd-Fe-B alloys; Ti-Al alloys

  • Contribution to external collection
    D.Herlach: Phase transformations in multicomponent melts, Weinheim: Wiley-VCH, 2008, 245-261

Permalink: https://www.hzdr.de/publications/Publ-11633
Publ.-Id: 11633


Noble gas retention in the target during rotating cylindrical magnetron sputtering

Mahieu, S.; Leroy, W. P.; Depla, D.; Schreiber, S.; Moeller, W.

A rotating cylindrical magnetron with a Ti target was sputtered in pure Xe or in a mixture of Xe and N2. The atomic composition of the target surface during sputtering has been investigated by in situ Rutherford backscattering spectrometry. The noble gas atomic ratio at the target surface is around 3.4% or 9.8% for sputtering in pure Xe and with 10% N2 addition, respectively. Energy resolved mass spectrometry reveals that some of the implanted Xe atoms are sputtered from the target. A radiation enhanced diffusion/detrapping/sputtering mechanism is proposed to model the flux of noble gas leaving the target during sputtering

  • Applied Physics Letters 93(2008), 061501-1-061501-3

Permalink: https://www.hzdr.de/publications/Publ-11632
Publ.-Id: 11632


Boundary layer in the MRI experiment PROMISE

Szklarski, J.; Gerbeth, G.

One of the most convenient approaches to observe experimentally the magnetorotational instability (MRI) is to use a magnetized Taylor-Couette setup. The flow of liquid metal between two rotating, concentric cylinders can become unstable in the presence of an external magnetic field. One of the issues which should be addressed when designing such an experiment is the influence of plates enclosing the cylinders from the top and the bottom. In this paper we discuss properties of the boundary layer which arises near these plates. Our primary concern is the importance of this layer in the MRI experiment PROMISE.

  • Astronomische Nachrichten 329(2008)7, 667-674

Permalink: https://www.hzdr.de/publications/Publ-11631
Publ.-Id: 11631


Hexadentate bispidine radiocopper complexes: emerging opportunities for the application in nuclear medicine

Stephan, H.; Juran, S.; Walther, M.; Bergmann, R.; Steinbach, J.; Comba, P.

The advantageous properties of numerous 3,7-diazabicyclo[3.3.1]nonane (bispidine) derivatives have attracted much attention and caused intensive research efforts in different directions. An attractive goal represents the development of target-specific radiopharmaceuticals. For this purpose, bifunctional chelating agents are needed which have to show fast metal complexation kinetics, form complexes with high in vitro and in vivo stability and contain a group that can be linked to biomolecules. In this regard, hexadentate bispidines 1 – 3 containing pyridine units in C2, C4, N3, and N7 position have been shown to rapidly form stable radiocopper (such as 64Cu and 67Cu) complexes. Furthermore, the carboxylic groups of ligand 3 provide the possibility for coupling bio-molecules.

  • Lecture (Conference)
    2nd EuCheMS Chemistry Congress, 16.-20.09.2008, Torino, Italy

Permalink: https://www.hzdr.de/publications/Publ-11630
Publ.-Id: 11630


Radioaktive Substanzen helfen beim Suchen und Zerstören von Tumoren

Stephan, H.

Beim Aufspüren von Tumoren und deren Metastasen hat die Positronen-Emissions-Tomographie (PET) entscheidende Fortschritte gebracht. Mit speziellen radioaktiven Substanzen lassen sich Tumore viel früher finden als mit anderen bildgebenden Verfahren. Die PET-Bilder geben – oft in Kombination mit anderen Verfahren wie Computertomographie (CT) oder Magnetresonanztomographie (MRT) – die notwendigen Informationen für eine chirurgische oder externe strahlentherapeutische Behandlung von Tumorerkrankungen. Ihre Grenzen findet die externe Bestrahlung häufig bei der metastasierenden Erkrankung, wobei Tumorzellen über Blut oder Körperflüssigkeit abgeschwemmt werden und an neuen Orten weiter wachsen. In diesen Fällen muss die Behandlungsmethode systemisch sein, d.h. die Tumortherapeutika müssen über die Blutbahnen zu den (zum Teil nicht sichtbaren) Metastasen gelangen. Dies ist bisher der Chemotherapie vorbehalten. Mit Mitteln der internen Radionuklidtherapie sollen künftig die Heilungserfolge insbesondere bei der Bekämpfung solcher Metastasen verbessert werden.

  • Lecture (others)
    Lange Nacht der Wissenschaften, 04.07.2008, Dresden, Deutschland
  • Lecture (others)
    Jobbörse FH Zittau/Görlitz, 24.11.2010, Zittau, D

Permalink: https://www.hzdr.de/publications/Publ-11629
Publ.-Id: 11629


New versatile bifunctional chelating agents for developing copper radiopharmaceuticals

Stephan, H.

Radiopharmaceuticals based on metallic radionuclides, such as 64/67Cu, 99mTc, 186/188Re and 86/90Y, are often used for diagnostic and therapeutic purposes. These nuclides are usually enveloped in organic ligands, such as heteromacrocyclic systems. To be effective, the ligands have to show fast metal complexation kinetics, form complexes with high in vitro and in vivo stability and contain a group that can be linked to biomolecules. In this regard, we are developing new ligand scaffolds for copper radionuclides which satisfy these requirements. Ligands – based on hexadentate 3,7-diazabicyclo[3.3.1]nonane I (bispidine) and bis(2-pyridylmethyl) triazacyclononane (DMPTACN) II – are discussed. These derivatives allow the introduction of linker groups, such as carboxylic acids, maleinimide or isothiocyanate, thereby facilitating coupling of targeting molecules.

  • Lecture (others)
    COST BM0607 Action WG Meeting, 24.-25.06.2008, Krakow, Polen

Permalink: https://www.hzdr.de/publications/Publ-11628
Publ.-Id: 11628


Fracture mechanics characterisation of the WWER-440 reactor pressure vessel beltline welding seam of Greifswald Unit 8

Viehrig, H.-W.; Schuhknecht, J.

WWER-440 second generation (V-213) reactor pressure vessels (RPV) were produced by IZHORA in Russia and by SKODA in the former Czechoslovakia. The surveillance Charpy-V and fracture mechanics SE(B) specimens of both producers have different orientations. The main difference is the crack extension direction which is through the RPV thickness and circumferential for ISHORA and SKODA RPV, respectively. In particular for the investigation of weld metal from multilayer submerged welding seams the crack extension direction is of importance. Depending on the crack extension direction in the specimen there are different welding beads or a uniform structure along the crack front. The specimen orientation becomes more important when the fracture toughness of the weld metal is directly determined on surveillance specimens according to the Master Curve (MC) approach as standardised in the ASTM Standard Test Method E1921. This approach was applied on weld metal of the RPV beltline welding seam of Greifswald Unit 8 RPV. Charpy size SE(B) specimens from 13 locations equally spaced over the thickness of the welding seam were tested. The specimens are in TL and TS orientation.
The fracture toughness values measured on the SE(B) specimens with both orientations follow the course of the MC. Nearly all values lie within the fracture toughness curves for 5% and 95% fracture probability. There is a strong variation of the reference temperature T0 though the thickness of the welding seam, which can be explained with structural differences. The scatter is more pronounced for the TS SE(B) specimens. It can be shown that specimens with TS and TL orientation in the welding seam have a differentiating and integrating behaviour, respectively. The statistical assumptions behind the MC approach are valid for both specimen orientations even if the structure is not uniform along the crack front. By comparison crack extension, JR, curves measured on SE(B) specimens with TL and TS orientation show only minor differences within the mean variation.

Keywords: reactor pressure vessel steel; welding seam; surveillance programme; specimen orientation; fracture toughness; Master Curve concept

  • Lecture (Conference)
    34th MPA-Seminar and VGB-Symposium "Materials and Components Behaviour in Energy & Plant Technology", 09.-10.10.2008, Stuttgart, Deutschland
  • Contribution to proceedings
    34th MPA-Seminar and VGB-Symposium "Materials and Components Behaviour in Energy & Plant Technology", 09.-10.10.2008, Stuttgart, Deutschland
    Proceedings 34th MPA-Seminar and VGB-Symposium "Materials and Components Behaviour in Energy & Plant Technology", Stuttgart: MPA Stuttgart

Permalink: https://www.hzdr.de/publications/Publ-11627
Publ.-Id: 11627


Effects of Neutron Irradiation on Positron and Micro-Vickers Hardness of Fe-Cu Model Alloys and Reactor Pressure Vessel Steel

Hempel, A.; Hasegawa, M.; Brauer, G.; Plazaola, F.; Saneyasu, M.; Tang, Z.

  • Contribution to proceedings
    Ninth International Symposium on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, 01.-05.08.1999, Newport Beach, United States
    Proceedings of the Ninth International Symposium on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, 0-87339-475-5, 835-843

Permalink: https://www.hzdr.de/publications/Publ-11626
Publ.-Id: 11626


3-(4-(6-Fluoroalkoxy-3,4-dihydroisoquinolin-2(1H)-yl)cyclohexyl)-1H-indole-5-carbonitriles for SERT imaging: chemical synthesis, evaluation in vitro and radiofluorination

Funke, U.; Fischer, S.; Hiller, A.; Scheunemann, M.; Deuther-Conrad, W.; Brust, P.; Steinbach, J.

Aminocyclohexyl indoles bind with high affinity and specificity toward the serotonin transporter (SERT). Based on this structural lead, we designed fluoroalkoxydihydroisoquinoline-cyclohexyl indole carbonitriles for future application as 18F-labeled tracers for SERT imaging by PET. Six compounds, three pairs of cis- and trans-isomer derivatives, respectively, were synthesized and evaluated in vitro. The chemistry of the new compounds, their affinity and specificity data, the general route to the phenolic precursor for labeling, and the successful 18F-fluoroalkylation of one pair of compounds are described herein.

Keywords: Serotonin transporter; PET; Indole carbonitriles; Affinity; Radiolabeling; Fluorine-18

Permalink: https://www.hzdr.de/publications/Publ-11625
Publ.-Id: 11625


Synthesis and radioiodination of two Cdk4 inhibitors.

Köhler, L.; Graf, F.; Pietzsch, J.; Steinbach, J.; Wüst, F.

Aim:
Accurate cell proliferation is depending on the correct execution of the cell cycle. The cell cycle is controlled and coordinated by various enzymes and proteins like cyclins, cyclin-dependent kinases (Cdk) and cyclin-dependent kinase inhibitors (Cki). Many tumors show dysregulated Cdk activity and/or Cdk expression, and in 80 % of tumors the cell cycle relevant Cdk4-D1/INK4/pRb/E2F signal cascade is altered. Hence, appropriately radiolabeled Cdk4 inhibitors may be promising molecular probes for imaging cell proliferation processes and tumor visualization by PET. This work describes the design and synthesis of two 124I-labeled Cdk4 inhibitors 8-cyclopentyl-6-[124I]iodo-5-methyl-2-(4-piperazin-1-yl-phenylamino)-8H-pyrido[2,3-d]pyrimidin-7-one ([124I]CKIA) and 8-cyclopentyl-6-[124I]iodo-5-methyl-2-(5-(piperazin-1-yl)pyridin-2-ylamino)-8H-pyrido[2,3-d]pyrimidin-7-one ([124I]CKIB) (figure) as potential radiotracers for imaging Cdk4 expression in vivo.

Results:
Reference substances and labeling precursors were prepared with minor modifications according to the chemistry described by Barvian et al.1 and VanderWel et al.2. The trimethylstannane compounds CKIAP and CKIBP as labeling precursors for the radioiodination reaction with I-124 were prepared in a multi-step synthesis sequence. Radioiodination was achieved by regioselective destannylation reaction under mild conditions using [124I]NaI and Chloramine-T or Iodogen as oxidizing agents. Treatment of a solution (50 µl) containing CKIAP (5 mg/ml) with [124I]NaI (36 MBq) in Iodogen precoated tubes afforded 12 MBq (34 %, decay-corrected) of [124I]CKIA, including HPLC purification. The optimal reaction conditions for the [124I]CKIA synthesis were applied to the synthesis of [124I]CKIB. Starting from a 50 µl solution of CKIBP (5 mg/ml) and [124I]NaI (29 MBq), compound [124I]CKIB was obtained in a 34 % decay-corrected radiochemical yield, including HPLC purification. Both compounds were isolated in radiochemical purity exceeding 95 % and high chemical purity. The specific activities were determined to be 20 GBq/µmol and 4 GBq/µmol, respectively. The lipophilicity (logP) was experimentally measured. The logP value was 2.77 ± 0.13 for [124I]CKIA and 1.99 ± 0.03 for [124I]CKIB.

Conclusion:
The radiosynthesis of two 124I-labeled Cdk4 inhibitors has been developed. Both radiotracers were obtained in reproducible radiochemical yields and purity enabling further radiopharmacological characterization aimed at imaging Cdk4 expression by means of PET.

References:
1 : Barvian, M.; Boschelli, D. H.; Cossrow, J.; Dobrusin, E.; Fattaey, A.; Fritsch, A.; Fry, D.; Harvey, P.; Keller, P.; Garrett, M.; La, F.; Leopold, W.; McNamara, D.; Quin, M.; Trumpp-Kallmeyer, S.; Toogood, P.; Wu, Z. P.; Zhang, E. L. Journal of Medicinal Chemistry, 2000, 43, 4606-4616.
2 : VanderWel, S. N.; Harvey, P. J.; McNamara, D. J.; Repine, J. T.; Keller, P. R.; Quin, J.; Booth, R. J.; Elliott, W. L.; Dobrusin, E. M.; Fry, D. W.; Toogood, P. L. Journal of Medicinal Chemistry, 2005, 48, 2371-2387.

  • Lecture (others)
    16. Arbeitstagung der AG Radiochemie/Radiopharmazie, 25.-27.09.2008, Münster, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11624
Publ.-Id: 11624


Biological, biochemical and radiopharmacological properties of two Cdk4 inhibitors.

Graf, F.; Köhler, L.; Wüst, F.; Mosch, B.; Pietzsch, J.

Ziel/Aim:
The aim of our study was the biological, biochemical and radiopharmacological characterization of a known Cdk4 inhibitor CKIA, a derivative compound CKIB and their corresponding iodine-124 radiolabeled compounds in different tumor cell lines. Further we wanted to prove the hypothesis that potent Cdk4 inhibitors, which are interesting for cancer therapy are also suitable as radiotracers for imaging of cell proliferation processes in vivo and tumor visualization by positron emission tomography (PET).

Methodik/Methods:
Cell growth and cell cycle studies were performed in human tumor cell lines HT-29 (colon carcinoma), FaDu (head- and neck squamous cell carcinoma), and THP-1 (acute monocytic leukemia). Cdk4 specific pRb phosphorylation at Ser780 was analyzed in cell lysates by western blotting. mRNA expression of the pRb affected genes E2F-1 and PCNA was measured with quantitative real-time RT-PCR. Radiotracer uptake studies were performed using iodine-124 radiolabeled CKIA ([124I]CKIA) or CKIB ([124I]CKIB).

Ergebnisse/Results:
Tumor cell growth studies indicate a significantly reduced cell proliferation in all cell lines after 48 h of treatment with 0.1 (< 50%) and 1 µM (< 25%) CKIA. This effect is confirmed by cell cycle studies. Already 24 h after incubation with CKIA the percentage of tumor cells in G1 phase showed a concentration dependent increment up to 90%. pRb phosphorylation is decreased three- to tenfold after 24 h of treatment with 0.1 and 1 µM CKIA in all cell lines. Furthermore, a substantial downregulation of E2F-1 and PCNA mRNA expression could be demonstrated. In vitro radiotracer uptake studies in adherent tumor cells using [124I]CKIA (As = 20 GBq/µmol) showed a substantial uptake in HT-29 (1,649±117 %ID/mg protein) and FaDu cells (1,033±84 %ID/mg protein) after 2 h at 37°C. At 4°C an obvious lower uptake was detectable in both cell lines (258±30 %ID/mg protein in HT-29, 169±14 %ID/mg protein in FaDu).
Further, a new compound derived from CKIA was studied. CKIB shows similar effects on cell growth and cell cycle distribution. After 48 h of treatment with CKIB cell proliferation was reduced by 36% (0.1 µM) or 62% (1 µM) in HT-29 cells. Over 90% of HT-29 cells in G1 phase were obtained after 24 h of incubation with 1 µM CKIB. Results of pRb phosphorylation and both E2F-1 and PCNA mRNA expression analyses suggest a downregulation after 24 h of incubation with 1 µM CKIB in the tumor cells. In vitro studies with [124I]CKIB (As = 3.5 GBq/µmol) demonstrate a radiotracer uptake of 904±43 %ID/mg protein in HT-29 and 856±45 %ID/mg protein in FaDu cells after 2 h at 37°C. Radiotracer uptake at 4°C is substantially lower.

Schlussfolgerungen/Conclusions:
In conclusion, our data demonstrate a definite and specific inhibition of tumor cell proliferation after incubation with CKIA and CKIB due to an arrest of tumor cells in G1 phase as a result of Cdk4-cyclin D/ pRb/ E2F pathway inhibition. The radiotracer uptake of [124I]CKIA and [124I]CKIB observed in human tumor cells are a promising prerequisite for in vivo biodistribution and imaging studies by PET to further support our hypothesis that radiolabeled CKIA and corresponding compounds are suitable tracers for visualization of tumors using PET.


  • Lecture (others)
    16. Arbeitstagung der AG Radiochemie/Radiopharmazie, 25.-27.09.2008, Münster, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11623
Publ.-Id: 11623


Pyridinhaltige Liganden des 1,4,7-Triazacyclononans (TACN): Neue bifunktionelle Kupferchelatoren

Ruffani, A.; Stephan, H.; Fähnemann, S.; Steinbach, J.

Ziel/Aim:
Ziel der Arbeit ist die Entwicklung von bifunktionellen Markierungsbausteinen für eine milde und selektive radioaktive Markierung von Proteinen mit dem Positronenstrahler Kupfer-64. In diesem Zusammenhang sind pyridinhaltige Derivate des 1,4,7-Triazacyclononans 1 besonders geeignet, weil sie sehr stabile Kupfer(II)-Komplexe bilden sowie eine schnelle Komplexbildungskinetik aufweisen. Erste Untersuchungen zeigen, dass Komplexe von Kupfer-64 mit Verbindung 2 sowie einem entsprechenden Peptidkonjugat auf der Basis eines stabilisierten Bombesinfragments BBN(7-14) eine hohe in vitro und in vivo Stabilität besitzen.[1]

Methodik/Methods:
Das maleinimidhaltige Derivat 3 wurde durch Peptidkupplung mittels HBTU in Anwesenheit der Hünigbase DIPEA aus der Carbonsäure 2 und Aminoethylmaleinimid synthetisiert. Ein weiterer vielseitig einsetzbarer Synthesebaustein wurde durch Umsetzung von 1 mit einem Boc-geschützden Phenylendiamin-Derivat erhalten. Durch Abspaltung der Schutzgruppe wird das freie Amin 4 gebildet, das durch Behandlung mit Thiophosgen in das Isothiocyanat 5 überführt werden kann. Maleinimid-Derivate 6 mit unterschiedlicher aliphatischer Spacerlänge sind durch Amidkupplung von 4 mit Aktivester-Maleinimid-Derivaten zugänglich.

Ergebnisse/Results:
Markierungsstudien des Maleinimids 3 mit Kupfer-64 weisen auf eine sehr schnelle Komplexbildungskinetik unter physiologischen Bedingungen hin. Wie Untersuchungen mit dem Modellpeptid Glutathion zeigen, bindet dieser Markierungsbaustein sehr effektiv an Thiolgruppen.

Schlussfolgerungen/Conclusions:
Bifunktionelle Liganden auf der Basis von pyridinhaltigen TACN-Derivaten können unter milden Bedingungen effektiv mit Kupfer-64 markiert werden. Sie sind vielfältig modifizierbar. Damit eignen sie sich zur schonenden Konjugation an Biomoleküle mit unterschiedlichen funktionellen Gruppen.

Referenzen/Refrences:
[1] G. Gasser et al., Bioconjugate Chem. 2008, 19, 719-730.

  • Lecture (others)
    16. Arbeitstagung der AG Radiochemie/Radiopharmazie, 25.-27.09.2008, Münster, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11622
Publ.-Id: 11622


Entwicklung eines Pretargeting-Ansatzes unter Nutzung radioaktiv markierter L Oligonukleotide

Förster, C.; Schlesinger, J.; Közle, I.; Bergmann, R.; Walther, M.; Pietzsch, H.-J.; Steinbach, J.

Ziel:
Gegenstand der Forschungsarbeiten ist die systematische Entwicklung eines geeigneten Pretargeting-Modells für die Endoradionuklidtherapie unter Verwendung komplementärer L konfigurierter Oligonukleotide (L ON). Ziel dabei ist die Bewertung der in vivo Hybridisierungseigenschaften hinsichtlich ihrer Eignung zur radiodiagnostischen und -therapeutischen Verwendung bei Tumorerkrankungen.

Methodik:
Modifizierte 12- und 17-basige L-RNAs wurden mit DOTA-Derivaten funktionalisiert und im Anschluss mit den PET-Nukliden 68Ga und 86Y markiert. Die Hybridisierung wurde u. a. in Rattenvollblut in Abhängigkeit von der Konzentration untersucht. Weiterhin wurden die Bioverteilung sowie Metabolitenuntersuchungen in männlichen Wistar Ratten durchgeführt (1).
Als Modellsystem dienen DOTA-modifizierte Human Serum Albumin Mikrosphären (HSAM, Durchmesser 20 30 μm). Nach intravenöser Applikation dieser Partikel kommt es auf Grund ihrer Größe zum vollständigen Trapping der Mikrosphären in der Lunge (2, siehe Abb. 1). Analog zu diesen Untersuchungen ist geplant, diese Partikel mit L-ON zu modifizieren und somit eine in vivo Hybridisierung in der Lunge zu ermöglichen. Mit Hilfe dieses Ansatzes wäre man in der Lage, quantitative Beurteilungen des in vivo Hybridisierungsverhaltens komplementärer L-ON vorzunehmen. Zunächst erfolgen in vitro Tests, um das Hybridisierungspotenzial der auf der HSAM-Oberfläche präsentierten L ON zu verifizieren. Zudem wurde eine erste in vivo Untersuchung mittels Kleintier-PET und Urinanalyse durch aufeinander folgende intravenöse Verabreichung von L ON-HSAM-Konjugaten und der komplementären, radioaktiv markierten RNA Stränge vorgenommen.

Ergebnisse:
Die in Abbildung 2 dargestellten Ergebnisse unter Verwendung eines [86Y]Y-DOTA-17mers sind exemplarisch für die Bioverteilung der 86Y markierten L-ON. Bereits 5 min p. i. wurden 16 ± 5 % der injizierten Dosis renal ausgeschieden sowie 20 ± 2 % in der Niere akkumuliert (zum Vergleich zeigte ein 12mer eine renale Ausscheidung nach 5 min von nahezu 82 % ID). Nach 60 min sank die im Tier verbleibende Aktivitätsmenge auf 26 ± 2 %. Es lagen keine signifikanten Akkumulationen in anderen Organen vor (1). Die hohe in vivo Stabilität konnte anhand der Metabolitenanalyse nachgewiesen werden. 60 Minuten p. i. konnten im Urin 80 % und im Nierenhomogenat 81 % der vorliegenden markierten Substanz dem intakten 17mer zugeordnet werden. Konzentrationsabhängige Untersuchungen in Rattenvollblut ergaben eine maximale Hybridisierung bei einem Stoffmengenverhältnis von 1:1.
Aufgrund der vorteilhafteren Ergebnisse in Bezug auf biologische Verfügbarkeit und Hybridstabilität werden die nachfolgende Modellansätze mit 17-basigen L ON durchgeführt. Die kovalente Verknüpfung der RNA über eine Amid- oder Thioharnstoffbindung mit unbehandelten sowie DOTA-modifizierten HSAM ist auf Grund der Vielzahl an Amino- und Carboxylgruppen auf der Oberfläche der Partikel (elektrostatische Wechselwirkungen und starke Wasserstoffbrückenbindungen zwischen den Oligonukleotiden und HSAM) unter den bisher getesteten Bedingungen nur in geringen Ausbeuten möglich. Erste in vitro Hybridisierungstests ergaben positive Ergebnisse, wobei die entstandenen Hybride an der HSAM-Oberfläche lokalisiert sind. Bei einer in vivo Untersuchung wurde jedoch im Urin 45 % der vorhandenen Aktivitätsmenge den entstandenen Hybriden zugeordnet. Um das Problem der Adsorption von L ON auf der Partikeloberfläche zu lösen, werden die HSAM in weiteren Untersuchungen zuerst mit hydrophoben Reagenzien modifiziert, um eine kovalente Bindung zu gewährleisten. Als alternativer Ansatz werden zurzeit carboxylfunktionalisierte Polystyren-Mikrosphären analog modifiziert und untersucht. Zudem wird daran gearbeitet, die rasche renale Ausscheidung sowie die hohe Nierenakkumulation zu verringern. .....

  • Lecture (others)
    16. Arbeitstagung der AG Radiochemie/Radiopharmazie, 25.-27.09.2008, Münster, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11621
Publ.-Id: 11621


4-[18F]Fluoro-N-methyl-N-(prop-2-ynyl)benzenesulfonamide: A novel prosthetic group for click chemistry with peptides and proteins

Ramenda, T.; Knieß, T.; Steinbach, J.; Wüst, F.

Ziel/Aim:
The radiolabeling of peptides or proteins with the short-lived positron emitter 18F requires rapid and mild reaction conditions to maintain the structural and functional integrity of these bioactive compounds. Over the last two years several approaches have been published focused on the application of copper(I)-mediated 1,3-dipolar [3+2]cycloaddition of azides and alkynes for labeling peptides with 18F.1-4 The peptides were functionalized with an azide- or alkyne group to be reacted with an appropriately 18F-labeled azide or alkyne, respectively. In this work we report on the radiosynthesis and application of a novel 18F-labeled prosthetic group based upon a sulfonamide backbone suitable for click chemistry applications using azide-functionalized phosphopeptide and human serum albumin (HSA).

Methodik/Methods:
Two labeling precursors containing different leaving groups (nitro- and trimethylammoniumtriflate) and the reference substance were prepared by the reaction of N-methylpropargylamine with the corresponding sulfonic acid chlorides. Radiofluorination was performed in a single step. Different purification procedures have been developed including solid phase extraction and semi-preparative HPLC. The peptide and the protein were modified with an azide linker. Cycloaddition reactions were carried out in the presence of copper(I) salts in combination with different copper-chelating ligand systems.

Ergebnisse/Results:
The radiolabeled sulfonamide can be obtained in radiochemical yields of 23 % (decay corrected) in high radiochemical purity of >99 % after HPLC purification within 89 min. First promising results in labeling a phosphopeptide and a protein (HSA) could be achieved.

Schlussfolgerungen/Conclusions:
The novel prosthetic group for peptide and protein labeling with 18F via click chemistry can be prepared in reasonable radiochemical yields and high radiochemical purity. Moreover, for the first time click chemistry was successfully applied to the 18F labeling of a a phosphopeptide and a protein.

Figuren/Figures:

4-[18F]Fluoro-N-methyl-N-(prop-2-ynyl)benzenesulfonamide

Referenzen/Refrences:
1 Marik, J.; Sutcliffe, J.L. Tetrahedron Lett., 2006, 47, 6681.
2 Ramenda, T.; Bergmann, R.; Wuest, F. Lett. Drug Des. Discovery, 2007, 4, 279.
3 Glaser, M.; Arstad, E. Bioconjugate Chem., 2007, 18, 989.
4 Li, Z.-B.; Wu, Z.; Chen, K.; Chin, F.T.; Chen, X. Bioconjugate Chem., 2007, 18, 1987.

  • Lecture (others)
    16. Arbeitstagung der AG Radiochemie/Radiopharmazie, 25.-27.09.2008, Münster, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11620
Publ.-Id: 11620


3-D magnetic field effects during metal electrodeposition In cuboid cells

Mutschke, G.; Cierpka, C.; Weier, T.; Eckert, K.; Mühlenhoff, S.; Bund, A.

In electrochemical reactions, Lorentz forces due to external homogeneous magnetic fields may lead to increased mass transfer as additional convection is caused (MHD effect). A careful analysis shows that often a three-dimensional modeling of this effect is necessary. We will present numerical simulations of copper electrolysis in cuboid cells under the influence of homogeneous magnetic fields of different directions in the limiting current regime. The found complex interplay of natural and magnetically driven convection is compared with recent experimental results.

Keywords: Electrodeposition; Magnetic Field; Magneto-Electrolysis; Numerical Simulations; PIV

  • Lecture (Conference)
    7th PAMIR International Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu'ile de Giens, Frankreich
  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu'ile de Giens, Frankreich, 273-277

Permalink: https://www.hzdr.de/publications/Publ-11619
Publ.-Id: 11619


X-ray absorption and X-ray scattering - two complementary techniques to determine the coordination of solution species

Hennig, C.

The intention of the presentation is to compare the experimental observations with X-ray absorption and X-ray scattering to determine the coordination of solution species. EXAFS is an element selective technique and allows to identify the direct coordinated ligands. Distances above 4 Ae are often difficult to detect, even if it concerns heavy atoms. X-ray scattering detects all scattering pairs in a solution. The difference technique allows to select specific ions and makes X-ray scattering is especially sensitive to heavy scatterers in distances above 4 Ae.

Keywords: X-ray scattering; X-ray absorption

  • Invited lecture (Conferences)
    Invited lecture, 5.8.2008, Leuven, Belgium

Permalink: https://www.hzdr.de/publications/Publ-11618
Publ.-Id: 11618


RPV weld material investigations of a VVER-440 NPP

Rindelhardt, U.; Viehrig, H.-W.; Schuhknecht, J.; Konheiser, J.

The Greifswald NPP was operated between 1973 and 1990. The units are of Russian WWER-440-230 type. In autumn 2005 the first trepans (diameter 120 mm) were taken from the unit 1 of this NPP. The RPV of this unit was annealed after 14 years of operation, followed by two additional years of operation.
The paper describes the results of weld metal investigations. The trepan originates from the RPV core weld exposed with the highest neutron flux. The neutron dosimetry was based on Monte Carlo fluence calculations as well as retrospective Nb dosimetry. The maximum fluence for E>0.5 MeV was determined to be 4*1019 neutron/cm2, and the maximum gamma fluence was found to be 1.7*1020 gamma/cm2 for E>1 MeV. A decrease of 60% through the thickness of the RPV was found.
The key part of the material testing was aimed on 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. It could be shown that the Master Curve approach as adopted in E1921 is applicable to the investigated original RPV weld metal. The weld metal located in a distance of about 22 mm from the inner surface of the RPV wall yielded a T0 of 50°C which is about 40K higher than T0 close to the inner surface. This outcome is important for the assessment of results retrieved from so called boat samples taken directly from the RPV surface after the recovery annealing. It shows that boat samples do not mandatory represent the material with the lowest toughness.

Keywords: Neutron dosimetry; neutron embrittlement; VVER-440; reactor pressure vessel

  • Lecture (Conference)
    10th International Conference "Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment", 06.-10.10.2008, St. Petersburg, Russia
  • Contribution to proceedings
    10th International Conference "Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment", 06.-10.10.2008, St. Petersburg, Russia
    The 10th Interntional Conference (Conference CD), St. Petersburg: PROMETEY

Permalink: https://www.hzdr.de/publications/Publ-11616
Publ.-Id: 11616


Probing nanoscale inhomogeneities in transition metal oxides with ultrafast mid-infrared spectroscopy

Prasankumar, R. P.; Lee, H. J.; Okamura, H.; Imai, H.; Shimakawa, Y.; Kubo, Y.; Zvyagin, S.; Kamenev, K.; Balakrishnan, G.; Paulf, D. M.; Trugman, S. A.; Taylor, A. J.; Averitt, R. D.

Transition metal oxides are a rich area of investigation for experimentalists and theorists alike due to their coupling of multiple degrees of freedom with similar interaction strengths. This complexity leads to intrinsic phase inhomogeneities that are believed to play a significant role in the fascinating phenomena observed in these systems. We use ultrafast mid-infrared spectroscopy to probe quasiparticle dynamics in the colossal magnetoresistive oxides, Nd0.5Sr0.5MnO3 and Tl2Mn2O7. Our results demonstrate for the first time that ultrafast spectroscopy is sensitive to the presence of nanoscale phase inhomogeneities, strongly indicating the universality of phase coexistence in complex transition metal oxides.

  • Physica B 403(2008)5-9, 1401-1403

Permalink: https://www.hzdr.de/publications/Publ-11615
Publ.-Id: 11615


ESR excitations in the BEC candidate DTN: what can we learn from that?

Zvyagin, S.

NiCl2-4SC(NH2)2 (known as DTN) is a quantum S = 1 chain system with strong easy-plane anisotropy that is regarded as a new candidate for the Bose-Einstein condensation (BEC) of magnons, with critical fields Bc1 = 2.1 T, Bc2 = 12.6 T (defined at T = 0). Tuneable-frequency Electron Spin Resonance (ESR) studies of magnetic excitations in DTN in fields up to 25 T are presented. Based on analysis of the single-magnon excitation mode observed in the high-field spin-polarized phase at temperatures above Tc (Tc ≤ 1.2 K) and previous experimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set of spin-Hamiltonian parameters is obtained. Our results yield D = 8.9 K, Jc = 2.2 K, and Ja,b = 0.18 K for the anisotropy, intrachain, and interchain exchange interactions, respectively. These values are used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Furthermore, we present a systematic study of the low-energy excitation spectrum of DTN in the field-induced magnetically ordered phase (which has been regarded as the magnon BEC phase) at temperatures down to 0.45 K. We argue that two gapped modes observed in the experiment can be consistently interpreted within a four-sublattice antiferromagnet model with a finite interaction between two tetragonal subsystems and unbroken axial symmetry. The physically simplest scenario would correspond to the isotropic “corner-center” exchange. Since the exchange interaction within each sublattice is antiferromagnetic, the system in the BEC phase is supposed to be highly frustrated, and then its mean-field ground state at B > Bc1 should be infinitely degenerate. Our observations are of crucial importance for the interpretation of the field-induced ordering in DTN in terms of the BEC of magnons.

  • Lecture (Conference)
    Workshop Highly Frustrated Magnets, 02.-05.03.2008, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-11614
Publ.-Id: 11614


Excitation spectrum and magnetic properties of the Haldane-gap material NENB

Zvyagin, S.; Cizmar, E.; Ozerov, M.; Ignatchik, O.; Papageorgiou, T.; Wosnitza, J.; Krzystek, J.; Zhou, Z.; Wikaira, J. L.; Landee, C. P.; Thurnbull, M.

Results of high-field ESR and magnetization studies of the new
spin-1 Haldane-chain material [Ni(C2H8N2)2NO2](BF4) (NENB) are reported. A definite signature of the Haldane state in NENB was obtained. From the analysis of the frequency-field dependence of magnetic excitations in NENB, the spin-Hamiltonian parameters were calculated, yielding \Delta/k_{B} = 17.4~K, g_{\parallel}=2.14, D/k_{B}=7.5~K, and |E/k_{B}|=0.7~K for the Haldane gap, g factor and the crystal-field anisotropy constants, respectively. The presence of fractional S=1/2 chain-end states, revealed by ESR and magnetization measurements, is found to be responsible for spin-glass freezing effects. In addition, extra states in the excitation spectrum of NENB have been observed in the vicinity of the Haldane gap, which origin is discussed.

  • Lecture (Conference)
    2008 APS March Meeting, 10.-14.03.2008, New Orleans, USA

Permalink: https://www.hzdr.de/publications/Publ-11613
Publ.-Id: 11613


QCD Sum Rules for D Mesons at Finite Density

Hilger, T.

QCD Sum Rules for D Mesons at Finite Density

  • Lecture (others)
    Helmholtz International Summer School - Dense Matter in Heavy Ion Collisions and Astrophysics, 21.07.2008, Dubna, Russia

Permalink: https://www.hzdr.de/publications/Publ-11612
Publ.-Id: 11612


Simulation of defects and composition after Ga+ irradiation of ultrathin Pt/Co/Pt film

Liedke, B.; Facsko, S.; Fassbender, J.; Heinig, K.-H.; Möller, W.; Jaworowicz, J.; Ferre, J.; Maziewski, A.; Vernier, N.

Theoretical studies of the collision intermixing and defects creation processes of irradiated ultrathin Pt/Co/Pt films by 30 keV Ga+ are presented. First, in order to investigate the influence of the Ga ions, with ion fluence ranging between 1014 and 5·1016 ions/cm, on the composition of the film and the sputtering yield TRIDYN simulation is employed. Second, the relaxation of defects created during irradiation is estimated by means of the Lattice Kinetic Monte Carlo Ising model, which is subsequently applied after each collision cascade. According to our theoretical results ion fluence has a strong impact on the erosion velocity and intermixing processes that take place at the interface. Due to the nuclear energy losses of the implanted ions, changes in the material composition at the interface and the spin reorientation transition from the in-plane to out-of-plane magnetization state is observed. Moreover, the so-called swelling effect, which originates from the strain relaxation of the irradiated films, gives rise to an increase of the magnetic anisotropy. However, the strain relaxation can be strongly non-uniform in the implanted square area providing a mixture of patches with in-plane or out-of-plane anisotropy. Experimentally observed irradiation induced phenomena is fairly well described in the frame of our simulations.

Keywords: magnetism; ion irradiation; simulations; Monte Carlo

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

Permalink: https://www.hzdr.de/publications/Publ-11611
Publ.-Id: 11611


Fe nanoparticles embedded in MgO crystals

Shalimov, A.; Potzger, K.; Talut, G.; Geiger, D.; Reuther, H.; Zhou, S.; Baetz, C.; Misiuk, A.; Fassbender, J.

Iron nanoparticles embedded in MgO single crystals were synthesized by high temperature Fe+ implantation with energy of 100 keV and fluences varying from 3×10E16 to 3×10E17 ions/cm-2. Complex investigations of structural and magnetic properties of Fe nanoparticles have been performed using magnetometry, x-ray diffraction, electron microscopy and Moessbauer spectroscopy, as well as theoretical modeling of magnetization of bistable magnetic systems.
It has been found that at the low implantation fluences superparamagnetic Fe nanoparticles were created that finally were attributed to alpha-Fe coexisting with non-magnetic gamma-Fe, while implantation with high fluences causes formation of ferromagnetic alpha-Fe particles. Post implantation annealing at 800 ºC in high vacuum results in size increase of the gamma-Fe particle’s simultaneously reducing internal lattice strain. Annealing at 800 ºC under 1 GPa hydrostatic pressure limits dimension of superparamagnetic nanoparticles significantly increasing their concentration.
Theoretical simulations of irreversible magnetization processes, performed within the framework of generalized Preisach model, show a strong correlation between the spontaneous magnetization, coercive field and dimension of nanoparticles. The model allows us to define the anisotropy effects and thermal fluctuation effects, which provides the detailed description of temperature behavior of magnetization.

Keywords: magnetism; ion implantation; nanoparticle; Fe

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

Permalink: https://www.hzdr.de/publications/Publ-11610
Publ.-Id: 11610


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