Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Photoluminescence of Si+ and C+ implanted polymers

Tsvetkova, T.; Balabanov, S.; Avramov, L.; Borisova, E.; Angelov, I.; Bischoff, L.

Visible photo luminescence (PL) of ion implanted polymers was studied. Different polymer materials were used for the purpose: polypropylene (PP), poly-tetrafluor-ethylene (Teflon), ultra-high-molecular-weight-polyethylene (UHMWPE) and UHMWPE+Bi. Ion implantation with Si+ and C+ was performed at energies of 30 keV with doses in the range 1013 – 1017 cm−2. The results show that a PL enhancement (PLE) effect may occur for some polymer materials if proper implantation energy and doses are employed, the effect in the case of some polymer materials implanted with Si+ and C+ being considerable. While the effect is observed for all doses of C+ implanted in UHMWPE, PLE is only observed for the lowest dose of Si+ (D=1×1015 cm−2) implanted in Teflon, the further dose increase resulting in PL quenching only, presumably due to processes of structural degradation The appearance of ultra-violet (UV) range PL in the case of Si+ implanted UHMWPE could be originating from the formation of Si-related new defect sites, but more data are needed to explore this effect further into the deeper UV range (λ<350 nm).

Keywords: photo luminescence; polymers; implantation

  • Lecture (Conference)
    16th Int. Summer School on Vacuum, Electron and ion Technologies VEIT2009, 28.09.-02.10.2009, Sunny Beach, Bulgaria
  • Open Access Logo Journal of Physics: Conference Series 223(2010), 012033_1-012033_5
    DOI: doi:10.1088/1742-6596/223/1/012033

Publ.-Id: 14113

Dynamics of magnetic objects and ultra-fast phase transitions in RhFe

Quitmann, C.; Raabe, J.; Puzic, A.; Wintz, S.; Fassbender, J.; Marriager, S.; Ingold, G.; Johnson, S.; Beaud, P.; Feidenhans'L, R.; Pressacco, F.; Back, C.

In the first part we report on progress in measuring and understanding the dynamics of mesoscopic magnetic objects. These are studied in a scanning transmission x-ray microscope (STXM) which provides information about the space- and time resolved magnetization. We study individual objects, arrays and multilayer samples. The multilayer samples are of particular interest because the coupling between the layers can be tuned from anti-ferromagnetic to ferromagnetic using ion-beam irradiation. In a second part we present results on the unusual magnetic phase transition in RhFe taking place above room temperature. Here an anti-ferromagnetic low-temperature phase changes to a ferromagnetic high-temperature phase. This phase transition can be initiated using an ultra-fast laser pulse. We have studied the evolution of the crystal lattice in this transition using a pump-probe scheme. The pump-pulse is a fs laser pulse, the probe pulse is an x-ray pulse (width ~200 fs) produced by laser slicing of the stored electron beam. The data provide quantitative information about the time evolution of the lattice constants and the domain sizes. These data can be compared to optical MOKE data which measure the time dependant magnetization.

Keywords: mesoscopic magnetic objects; ultrafast RhFe phase transition; magnetization dynamics; domain imaging; x-ray microscopy

  • Invited lecture (Conferences)
    International Workshop on X-Ray spectroscopy of Magnetic Solids (XRMS10), 10.-11.06.2010, Oxfordshire, United Kingdom

Publ.-Id: 14112

Advanced emitters and detectors for terahertz time-domain spectroscopy

Peter, F.

The idea of terahertz-time-domain spectroscopy (THz-TDS) is to exploit a single cycle, spectrally broad THz radiation pulse to gain insight into the response of matter. Photoconductive devices and nonlinear crystals are utilized in both the generation as well as the coherent detection of THz radiation. The relatively high cost and the complexity of commonly used titanium-sapphire lasers hinder a more widespread use of pulsed THz systems for commercial applications. Er-doped femtosecond fiber lasers operating at 1.55 μm could offer a viable alternative. In this thesis nonlinear crystals and photoconductive emitters are discussed for excitation in the near infrared (NIR) window of between 800 nm to 1550 nm. The main focus of this thesis is a detailed study of substrate materials for an interdigitated photoconductive antenna. Photoconductive antennas with microstructured electrodes provide high electric acceleration fields at moderate voltages because of small electrode separations. The scalability of these devices allows for large active areas in the mm^2 range, which are sufficient for excitation at large optical powers. In comparison with conventional emitter structures, these antennas have more favourable characteristics regarding THz power, spectral properties, and ease of handling. Depending on the utilized substrate material, photoconductive antennas can then be operated using different excitation wavelengths. By employing substrates with short carrier trapping times these antennas can be operated as THz-detectors. Moreover the design of electrode structures for generating radially and azimuthally polarized THz waves are presented. A second topic deals with the signal analysis and signal interpretation of THz pulses transmitted through several material systems. These experiments show the potential for tomographic and spectroscopic applications. The third part deals with THz emission by frequency mixing in nonlinear organic and inorganic crystals. Hereby the focus is on polaritonic phase matching in GaAs. Furthermore, indications of THz tunability by the excitation wavelength were found by utilizing waveguide structures. However, the observed tuning range is much lower then theoretically predicted. Specific reasons for this are discussed.

Keywords: infrared spectroscopy; terahertz; photoconductive devices; nonlinear optics

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-538 2010
    ISSN: 1437-322X


Publ.-Id: 14111

Field and stress induced twin boundary motion in NiMnGa

Neudert, A.; Lai, Y. W.; Schäfer, R.; McCord, J.

Twin boundaries in NiMnGa can be moved by applying either magnetic fields or mechanical stresses, which favour one of the two variants next to the twin boundary. We have used polarized light microscopy to study the two different ways of twin boundary motion in bulk NiMnGa. By placing magnetic indicator films on top of the sample surface we were able to detect the magnetic domain structure of the sample. Without the indicator films, the different variants can be seen by using polarized light illumination.
We found qualitative differences in the resulting magnetic state after a twin boundary has been moved by magnetic field or mechanical stress. By applying a magnetic field along the easy axis of one variant this variant is magnetically saturated and upon reducing the magnetic field the domain state consists of wide anti-parallel domains with 180° domain walls. Moving the twin boundary by applying mechanical stress results in a different domain state. Here the magnetization rotates by about 90° as the twin boundary passes through the area and we found the domain state to consist mainly of smaller patchy domains. The domain state with wide anti-parallel domains can be reached by demagnetizing the sample in an ac magnetic field. This suggests that the magnetic state after stress induced twin boundary motion is not in its global energy minima but rather trapped in a higher energy state

Keywords: magnetic shape memory alloy; field induced twin boundary motion; stress induced twin boundary motion; magnetization process

  • Lecture (Conference)
    EMRS Strasbourg, 07.06.2010, Strasbourg, France

Publ.-Id: 14110

Twin boundary motion in NiMnGa upon pulsed field excitation

Neudert, A.; Lai, Y. W.; McCord, J.

We studied the motion of twin boundaries in NiMnGa shape memory alloy bulk samples using time-resolved optical polarisation microscopy. The sample was excited by pulsed magnetic fields with variable rise-time. The restoring force to reset the sample, necessary for stroboscopic imaging, was set by applying mechanical stress along the long axis of the bulk sample perpendicular to the magnetic field. Upon decreasing the rise-time from 10 to 1 ms we found an increase of the twin boundary motion. This dependency of the actuation range on the pulsed field rise-time can be used in actuation devices to improve the magnetic field-induced strain by changing the field rise-time without having to change the repetition rate of the magnetic field.

Keywords: magnetic shape memory alloy; twin boundary motion

  • Poster
    Actuator 2010 Bremen, 14.-16.06.2010, Bremen, Deutschland
  • Contribution to proceedings
    Actuator 2010, 15.06.2010, Bremen, Germany
    Actuator 2010 Conference Proceedings, 978-3-933339-13-3

Publ.-Id: 14109

Systematics of central heavy ion collisions in the 1A GeV regime

Reisdorf, W.; Andronic, A.; Averbeck, R.; Benabderrahmane, M. L.; Hartmann, O. N.; Herrmann, N.; Hildenbrand, K. D.; Kang, T. I.; Kim, Y. J.; Kis, M.; Koczon, P.; Kress, T.; Leifels, Y.; Merschmeyer, M.; Piasecki, K.; Schuettauf, A.; Stockmeier, M.; Barret, V.; Basrak, Z.; Bastid, N.; Caplar, R.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasik, P.; Grishkin, Y.; Hong, B.; Kecskemeti, J.; Kirejczyk, M.; Korolija, M.; Kotte, R.; Lebedev, A.; Lopez, X.; Matulewicz, T.; Neubert, W.; Petrovici, M.; Rami, F.; Ryu, M. S.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Stoicea, G.; Tyminski, Z.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z. G.; Xu, H. S.; Yushmanov, I.; Zhilin, A.

Using the large acceptance apparatus FOPI, we study central collisions in the reactions (energies in A GeV are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 58Ni+58Ni (0.15, 0.25, 0.4), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0, 1.5), 129Xe+CsI (0.15, 0.25, 0.4), 197Au+197Au (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include cluster multiplicities, longitudinal and transverse rapidity distributions and stopping, and radial flow. The data are compared to earlier data where possible and to transport model simulations.

Publ.-Id: 14108

Energy dependence of the pp -> K(+)n Sigma(+) reaction close to threshold

Valdau, Y.; Barsov, S.; Buscher, M.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Hartmann, M.; Kacharava, A.; Keshelashvili, I.; Khoukaz, A.; Koptev, V.; Kulessa, P.; Merzliakov, S.; Mielke, M.; Mikirtychiants, S.; Nekipelov, M.; Ohm, H.; Papenbrock, M.; Rathmann, F.; Serdyuk, V.; Stroher, H.; Trusov, S.; Wilkin, C.

Production of the Sigma(+) hyperon through the pp -> K(+)n Sigma(+) reaction has been investigated at four energies close to threshold, 1.826, 1.920, 1.958, and 2.020 GeV. At low energies, correlated K+pi(+) pairs can only originate from Sigma(+) production so their measurement allows the total cross section for the reaction to be determined. The results obtained are completely consistent with the values extracted from the study of the K+-proton correlation spectra obtained in the same experiment. These spectra, as well as the inclusive K+ momentum distributions, also provide conservative upper limits on Sigma(+) production rates. The measurements show a Sigma(+) production cross section that varies roughly like phase space, and, in particular, none of the three experimental approaches used supports the anomalously high, near-threshold pp -> K(+)n Sigma(+) total cross section previously reported [T. Rozek et al., Phys. Lett. B 643, 251 (2006)].

Publ.-Id: 14107

The microstructure of neutron-irradiated Fe-Cr alloys: A small-angle neutron scattering study

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

The effect of Cr on the microstructures of neutron-irradiated Fe-Cr alloys is not yet known in all details including types, sizes, concentrations and compositions of irradiation-induced features on the nanoscale. Such details are needed in order to develop and validate models devoted to the long-term evolution of microstructures. Among other techniques, small-angle neutron scattering (SANS) can contribute to this task. Results obtained for a set of Fe-Cr alloys of Cr levels of 2.5, 5, 9 and 12.5 at%, irradiated at 300°C up to neutron exposures of 0.6 and 1.5 dpa are reported. We have found that the incoherent magnetic scattering of the unirradiated alloys exhibits a systematic variation with the Cr content and that there is an irradiation-induced increase of the coherent magnetic scattering for each of the irradiated conditions. The effect of Cr on size and type of irradiation-induced scatterers is discussed.

Publ.-Id: 14106

Small-angle neutron scattering investigation of as-irradiated, annealed and reirradiated reactor pressure vessel weld material of decommissioned reactor

Ulbricht, A.; Altstadt, E.; Bergner, F.; Viehrig, H.-W.; Keiderling, U.

Small-angle neutron scattering (SANS) was applied to characterize the microstructure of weld material taken from the reactor pressure vessel (RPV) of the decommissioned VVER440(230)-type nuclear power plant (NPP) Greifswald, units 1, 2 and 4. The welding seam of highest neutron exposure of unit 1 was subject to a large-scale annealing treatment in 1988 after about 11.5 effective years of operation. The same type of annealing was applied to unit 2 in 1990 after about 11 effective years of operation. After final decommissioning of NPP Greifswald in 1990, RPV material was left in the reirradiated condition (unit 1), in the as-annealed condition (unit 2) and in the as-irradiated condition (unit 4). Trepans of material from the highly irradiated RPV welds of these units have recently become available for examination. The results of the SANS investigation are reported and compared with published results obtained for asirradiated, post-irradiation annealed and reirradiated surveillance material of the same type. We have found general agreement indicating in particular the formation of irradiation-induced Cu-enriched clusters and efficient recovery as a result of the largescale annealing treatments. The only essential difference was observed for the ratio of magnetic and nuclear scattering indicating differences of the cluster composition for the RPV wall and surveillance material.

Publ.-Id: 14105

SANS investigation of RPV weld material from the decommissioned NPP Greifswald

Bergner, F.; Ulbricht, A.; Viehrig, H.-W.; Keiderling, U.

Nuclear plant operators must demonstrate that the structural integrity of a nuclear reactor pressure vessel (RPV) is assured during routine operations or under postulated accident conditions. The aging of the RPV steels is monitored with surveillance program results or predicted by trend curves. Embrittlement forecast with trend curves and surveillance specimens may not reflect the reality. Accordingly, the most realistic evaluation of the toughness response of RPV material to irradiation is done directly on RPV wall samples from decommissioned nuclear power plants (NPP). Such a unique opportunity is now offered with material from the decommissioned Greifswald NPP. The four Greifswald NPP units representing the first generation of WWER-440/V-230 reactors were shut down in 1990 after 11–17 years of operation. Material from RPVs in three different conditions is available: Unit 1 is irradiated, annealed and reirradiated. Unit 2 is irradiated and annealed. Unit 4 is in the as-irradiated condition. Small-angle neutron scattering (SANS) was applied in order to characterize the microstructure of weld material taken from the core-belt regions of Units 1, 2 and 4. Furthermore, material from Unit 4 exposed to post-irradiation annealing corresponding to the large-scale annealings of Units 1 and 2 was also investigated. The results of the SANS experiments are reported and compared with mechanical properties as well as results obtained for surveillance material of the same type.

  • Lecture (Conference)
    E-MRS 2010 Spring Meeting, 06.-11.06.2010, Strasbourg, Frankreich

Publ.-Id: 14104

Microstructure of oxide dispersion strengthened Eurofer and iron–chromium alloys investigated by means of small-angle neutron scattering and transmission electron microscopy

Heintze, C.; Bergner, F.; Ulbricht, A.; Hernandez-Mayoral, M.; Keiderling, U.; Lindau, R.; Weißgärber, T.

Oxide dispersion strengthening of ferritic/martensitic chromium steels is a promising route for the extension of the range of operation temperatures for nuclear applications. The investigation of dedicated model alloys is an important means in order to separate individual effects contributing to the mechanical behaviour under irradiation and to improve mechanistic understanding. A powder metallurgy route based on spark plasma sintering was applied to fabricate oxide dispersion strengthened (ODS) Fe9Cr model materials. These materials along with Eurofer97 and ODS-Eurofer were investigated by means of small-angle neutron scattering (SANS) and TEM. For Fe9Cr–0.6 wt.%Y2O3, TEM results indicate a peak radius of the size distribution of Y2O3 particles of 4.2 nm with radii ranging up to 15 nm, and a volume fraction of 0.7%, whereas SANS indicates a peak radius of 3.8 nm and a volume fraction of 0.6%. It was found that the non-ODS Fe9Cr and Eurofer97 are suitable reference materials for ODS-Fe9Cr and ODS-Eurofer, respectively, and that the ODS-Fe9Cr variants are suitable model materials for the separated investigation of irradiation-Y2O3 particle interaction effects.

Publ.-Id: 14103

Microstructure and properties of Fe-Cr and ODS-Fe-Cr model alloys

Heintze, C.; Bergner, F.; Ulbricht, A.; Weißgärber, T.

In order to explore the effects of Cr and dispersion strengthening on microstructure and properties, two sets of Fe-Cr-based alloys were investigated. The binary Fe-Cr alloys were obtained by means of furnace melting of industrial pure Fe and Cr [Matijasevic, JNM 377 (2008) 147]. Cr levels are in the range from 2.4 to 11.6 wt%. The ODS-Fe-9wt%Cr alloys were produced by spark plasma sintering starting from industrial elemental powders of Fe and Cr and two different qualities of Y2O3 powder [Franke, Diploma Thesis, TUB Freiberg, 2009]. Milling time (5, 10 and 20 hours) and ODS fraction (0, 0.3 and 0.6%) were varied. For part of the ODS-Fe-Cr alloys an additional HIP treatment was performed in order to reduce porosity. Several techniques including small-angle neutron scattering (SANS) were applied in order to characterize the microstructure of the alloys. Sound velocity measurements, nanoindentation, tensile testing and impact testing were applied in order to characterize the mechanical behaviour. The effects of Cr and ODS on microstructure and properties are reported. Using SANS a significant increase of the scattering cross sections was found in comparison with the respective non-ODS variant. The reconstructed size distribution indicates the presence of ODS particles in the size range from 2 to 20 nm. Significant effects of both Cr content and disperion strengthening on the polycrystalline elastic properties and nanohardness were also observed.

  • Poster
    E-MRS 2010 Spring Meeting, 06.-11.06.2010, Strasbourg, Frankreich

Publ.-Id: 14102

Np(V) reduction by humic acids - Impact of sulfur functionalities of humic acids

Schmeide, K.; Sachs, S.; Bernhard, G.

The migration behavior of actinide contaminants is influenced by humic substances (fulvic acids and humic acids (HA)) due to their complexing and redox properties and their ability to form colloids. The redox activity of humic substances is attributed to the reversible hydroquinone/quinone redox couple with semiquinone-type free radicals as significant electron donor/acceptor intermediate species and furthermore, to the oxidation of phenolic OH groups to phenoxy radicals. Also nitrogen and sulfur containing functional groups of HA are discussed as redox-active groups. While sulfur functional groups of HA have not been studied as reducing agents toward actinides like U, Np or Pu so far, organic compounds containing sulfur in the reduced form as thiol groups (R-SH) were found to reduce Np(VI).
In the present work, the influence of sulfur functional groups of HA on their capability to reduce Np(V) in aqueous solution has been studied. For this, HA model substances type M1-S with different sulfur contents (1.9, 3.9, 6.9 wt.%) were applied. Reduced sulfur species, such as thiols, dialkylsulfides and/or disulfides, were determined as the dominating sulfur functionalities in the HA. Their Np(V) reduction behavior was studied in comparison to a sulfur-free HA type M1.
At pH 5.0, the Np(V) reduction strongly increases with increasing content of reduced sulfur functional groups of the HA. That means that the sulfur functionalities contribute to the reduction capability of HA at pH 5.0. In contrast to this, at pH 7.0 and 9.0, the sulfur functionalities of HA have only a slight influence on the Np(V) reduction (not shown). This implies that the contribution of the sulfur functionalities to the reduction capability of HA toward Np(V) depends on pH value.

Keywords: Neptunium; tetravalent; humic acid; redox-active groups

  • Contribution to proceedings
    Plutonium Futures - The Science 2010, 19.-23.09.2010, Keystone, Colorado, USA
  • Poster
    Plutonium Futures - The Science 2010, 19.-23.09.2010, Keystone, Colorado, USA

Publ.-Id: 14101

Calculation of the operation mode of the emergency condenser (EC) of the INKA test facility with ATHLET

Willschütz, H.-G.; Leyer, S.; Krüssenberg, A.-K.; Schäfer, F.

The KERENA(TM) boiling water reactor (BWR) is a proven further developed design, based on Gundremmingen NPP and the whole accumulated German BWR operating experience. Especially for the passive safety systems, which are described in the paper more in detail, not only an experimental testing and validation is needed, but also thermal-hydraulic system codes have to be qualified, to be able to consider the mostly gravity driven 3D-flow phenomena correctly. Since in some countries the code ATHLET is well established, it is useful to prove its capabilities or to enhance the capabilities, if necessary. Therefore the FZD in co-operation with E.ON and AREVA is performing a model development and calculations for code validation with help of test results from INKA test facility (INtegral test facility in KArlstein, Germany). The paper gives an introduction into condensation phenomena and describes the condensation models applicable for a special heat removal system driven by natural circulation, it presents a detailed description of the ATHLET-model for the emergency condenser and first results from an estimation of the heat removal power.

Keywords: KERENA; INKA; ATHLET; Emergency Condenser

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology (Jahrestagung Kerntechnik), 04.-06.05.2010, Berlin, Deutschland
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology (Jahrestagung Kerntechnik), 04.-06.05.2010, Berlin, Deutschland
    Jahrestagung Kerntechnik - Annual Meeting on Nuclear Technology, 04.-06. Mai 2010

Publ.-Id: 14100

Operation of a 10kW@1,3GHz Solid State Amplifier at the Superconducting LINAC ELBE

Büttig, H.; Martinache, L.; Dupire, P.; Gonella, O.; Ilijev, J.; Weiss, M.; Michel, P.; Staats, G.; Schurig, R.

The prototype of a "tunk key" 10kW@1.3GHz solid state power amplifier, designed and built by Bruker BioSpin Wissembourg/France has been tested at the superconducting linac ELBE in the Research Center Dresden-Rossendorf. The talk gives an overview on the design, its RF-parameters and the first 8-week period of test and operation at the superconducting CW-linac ELBE.

Keywords: Solid State Power Amplifier 1,3GHZ; LINAC RF-SSA; 1,3GHz PA; 10kW Turn-key PA; Transistor PA 10kW at 1,3GHz

  • Lecture (Conference)
    6th Workshop on CW and High Average Power RF ( CWRF 2010), 04.-07.05.2010, Barcelona, Espagna

Publ.-Id: 14099

Magnetic domain compensation effect on the magneto-dynamic response of ferromagnetic elements

Patschureck, C.; Kaltofen, R.; Mönch, I.; Schäfer, R.; Schultz, L.; McCord, J.

Tuning ferromagnetic resonance frequencies in soft ferromagnetic films relies on the possibility to tailor the uniaxial anisotropy of the film material. A systematic change of anisotropy field, being the solely changing material property, was achieved by preparing Ni81Fe19/Co60Fe20B20 multilayers. We show that in patterned films deviations from the regular Landau domain pattern occur, which compensate magnetic anisotropy effects and thereby lead to a precessional frequency independent of anisotropy. The results manifest the significance of even small changes in the magnetic domain structure over magnetic anisotropy adjustments for the optimization of the magneto-dynamic response in mesoscopic thin film elements.

Keywords: magnetization dynamics; magnetic domains

Publ.-Id: 14098

The short range order of ions in clay minerals: Sm3+ coordination

Sobolev, O.; Cuello, G. J.; Scheinost, A. C.; Johnson, M. R.; Nikitenko, S.; Le Forestier, L.; Brendle, J.; Charlet, L.

Experimental techniques as neutron diffraction with isotopic substitution, extended X-ray absorption fine structure spectroscopy and quasielastic neutron scattering, in combination with molecular dynamics simulations, are usually applied to the study of non-crystalline solids, but they are also very useful for the study of complex systems, where the short range order provides an insight of its structure and dynamics. Here they are used in the study of the coordination of the Sm3+ in the interlayer of hydrated synthetic montmorillonite and hectorite. The neutron diffraction results indicate that not all O atoms in the first coordination shell of the Sm3+ belong to water molecules, supporting the formation of the Sm3+ innersphere complex. On the other hand, the other techniques suggest that the adsorbed Sm3+ cations form outersphere complexes with the clay surface. The hypothesis making compatible all results is that there are different Sm species adsorbed in the clay interlayer: a part of Sm is in the Sm3+ cationic form, forming outer-sphere adsorption complexes, another part is hydrolyzed and present in the interlayer space as Sm(OH)2+, Sm(OH)+ 2 or Sm(OH)03 species. The latter are more hydrophobic than Sm3+ cations and can be dehydrated and are able to stick to the clay surface.

Keywords: Lanthanide; clay; neutron; simulation; EXAFS

  • Physica Status Solidi (C) 208(2011), 2293-2298
    DOI: 10.1002/pssa.201000311
  • Invited lecture (Conferences)
    10th International Workshop on Non-Crystalline Solids, 21.-23.04.2010, Barcelona, Spain

Publ.-Id: 14097

Roadmap der chemischen Reaktionstechnik

Schubert, M.; u. a.

Der Vorstand der ProcessNet-Fachsektion Reaktionstechnik hatte sich im Februar 2009 entschlossen, für das Fachgebiet der Chemischen Reaktionstechnik eine Roadmap zu erstellen. Im September 2009 wurde ein etwa 10-köpfiges Vorbereitungskomitee installiert, das sich der Aufgabe annahm. Es erfolgte im Mitteilungsblatt der Fachsektion (Info-Brief Nr. 4, September 2009) ein Gliederungsvorschlag und ein Aufruf an alle Mitglieder, zu den einzelnen Gliederungspunkten beizutragen. Auf dieser Basis entstand die hier vorliegende Roadmap.
Zweck der Roadmap ist es, die aktuellen Arbeitsgebiete der Chemischen Reaktionstechnik zu benennen, den Forschungsbedarf zu konkretisieren und über Fallstudien zu illustrieren. Sie ist dabei ein lebendes Dokument, das einer regelmäßigen Aktualisierung bedarf.
Die Roadmap der ProcessNet-Fachsektion Reaktionstechnik soll nicht der Abschottung zu anderen Disziplinen wie der Katalyse oder der Prozessintensivierung dienen, sondern vielmehr als Wegweiser für Kooperationen. In diesem Zusammenhang sei auf andere existierende Roadmaps und Positionspapiere hingewiesen wie die "Roadmap der deutschen Katalyseforschung" der Deutschen Gesellschaft für Katalyse, die jüngst in ihrer dritten überarbeiteten Auflage erschienen ist, das Positionspaper "Prozessintensivierung - eine Standortbestimmung" der ProcessNet-Fachsektion Prozessintensivierung sowie das Positionspapier "Energieversorgung der Zukunft", das von den führenden nationalen Chemieorganisationen gemeinsam erarbeitet wurde. Auf europäischer Ebene sei insbesondere auf die "European Roadmap for Process Intensification" des EUROPIC1a und die "Roadmap for 21st Century Chemical Engineering" der IChemE1 hingewiesen und auf internationaler Ebene auf die "Vision 2020 - Reaction Engineering Roadmap" der AIChE2. Wir wünschen allen Lesern eine anregende Lektüre, freuen uns über Anregungen und Kommentare und hoffen, dass die Roadmap viele neue Impulse für die Forschung auf dem Gebiet der Reaktionstechnik liefert.

  • Roadmap der chemischen Reaktionstechnik 1(2010)

Publ.-Id: 14096

Magnetization reversal and artificial domains in hybrid magnetic materials

Fassbender, J.; Strache, T.; Fritzsche, M.; McCord, J.; Basitz, M.; Mcvitie, S.

Ion irradiation and implantation allows for a focussed materials modification in the range of a few nm only [1-3]. The modification of physical properties is especially effective, if interface effects in multilayer systems or ordering phenomena in binary alloys are considered. An addi¬tional degree of freedom can be exploited by a periodic patterning of the physical properties circumventing a topographic patterning in the conventional sense. Hybrid magnetic materials are created. Their integral magnetic properties are mainly governed by the shape and arrangement of the individual areas and cannot be considered as a simple superposition of the magnetic properties of modified and unmodified areas. The interactions between both areas and hence the length scales on which the magnetic properties are modified play a key role for their overall behaviour. For a review see Refs. 4 and 5. One of the major challenges is to exploit the scaling limits of this kind of structures and the appearance of an effective medium type material. These questions are addressed by high-resolution Lorentz microscopy imaging.

This work was supported by DFG grant no. FA 314/3-1 and DAAD.

[1] J. Fassbender et al., New J. Phys. 11, 125002 (2009).
[2] E. Menendez et al., Small 5, 229 (2009).
[3] J. McCord et al., Adv. Mater. 20, 2090 (2008).
[4] J. Fassbender and J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).
[5] J. Fassbender et al., J. Phys. D: Appl. Phys. 37, R179 (2004).

Keywords: magnetism; magnetic domains; domain imaging; ion irradiation; hybrid materials

  • Invited lecture (Conferences)
    IEEE 7th International Symposium on Metallic Multilayers (MML 2010), 19.-24.09.2010, Berkeley, USA

Publ.-Id: 14095

Ion-erosion-induced pattern as templates for layers with magnetic anisotropy and coupling

Fassbender, J.; Liedke, M. O.; Körner, M.; Markó, D.; Lenz, K.; Facsko, S.

Ion-erosion-induced ripples are perfect template systems to systematically investigate the influence of a periodic surface modulation on magnetic properties like magnetic anisotropy in the case of single magnetic films or interlayer exchange coupling in the case of multilayer systems. One of the key advantages of these ripples is that their periodicity can easily be varied in the range between 20 and 60 nm. This matches exactly the range where magnetic properties can be affected by a surface modulation. Two different examples will be discussed: i.) ripple-induced magnetic anisotropies in soft magnetic Permalloy films [1,2] and ii.) the appearance of roughness induced magnetic coupling, e.g. Neel coupling, in multilayer systems [3]. In both cases a significant influence of the surface and interface modulation on the magnetic properties is observed, which drastically depends on the ripple periodicity itself.

[1] M.O. Liedke et al., Phys. Rev. B 75, 220407 (2007).
[2] J. Fassbender et al. New J. Phys. 11, 125002 (2009).
[3] M. Körner et al., Phys. Rev. B 80, 214401 (2009).

Keywords: magnetism; ion erosion; length scales; ripples; magnetic anisotropy; coupling

  • Invited lecture (Conferences)
    Joint European Magnetics Symposium JEMS 2010, Symposium “Surfaces and Interfaces of Magnetic Thin Films”, 23.-28.08.2010, Krakau, Polen

Publ.-Id: 14094

Nanomagnets - created and tailored by ions

Fassbender, J.; Strache, T.; Marko, D.; Wintz, S.; Lenz, K.; Keller, A.; Facsko, S.; McCord, J.

The potential of ion irradiation and ion implantation for the formation of new nanoscale magnetic materials will be reviewed.

Keywords: magnetism; ion irradiation; ion implantation; lithography; hybrid materials

  • Invited lecture (Conferences)
    6th Nanoscience and Nanotechnology Conference, 15.-18.06.2010, Izmir, Türkei

Publ.-Id: 14093

Experimental modelling of the continuous casting process:The LIMMCAST-Program

Timmel, K.; Eckert, S.; Gerbeth, G.

There are only few and locally restricted measurement data existing about the flow in a continuous casting mould and the influence of a magnetic field on the steel flow therein. This is related to the extremely harsh environmental conditions and the opaqueness of the media in the real steel casting process, so that there is nearly no measurement technique applicable. To overcome this lack of knowledge, there were build two experimental facilities at the FZD, working with low melting point alloys. The Ultrasonic Doppler Velocimetry (UDV) can be used for flow monitoring in the mould at these models. The resulting experimental data will be very valuable for the validation of numerical simulations.
Mainly, the two experimental facilities will be presented in the paper. Additionally, first results will be shown, which were obtained at the small scale experiment. It is shown, that the flow structures, like the emerging jet flow from the submerged entry nozzle and the recirculation zones, can be adequately resolved with the UDV-technique. Further the influence of a DC-magnetic field in the function as a electro-magnetic brake was studied. One result was, that a DC-magnetic field may give rise to non-steady, non-isotropic large-scale flow perturbations.

Keywords: continuous casting; liquid metal model; magnetic field; mould flow; Ultrasound Doppler Method

  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-541 November 2010, 53-58
    ISSN: 1437-322X


Publ.-Id: 14092

Dynamo action in heterogenous domains

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

From the technically point of view the realisation of dynamo action in the laboratory is a demanding task because it requires magnetic Reynolds numbers of the order of 10...100. In order to reach such values in experiments, materials with high relative magnetic permeabilities have been utilized (Lowes & Wilkinson, von Karman Sodium dynamo).

The modification of the induction process by material properties is examined by means of simulations of the kinematic induction equation in hetrogenous domains where disk like assemblies with high conductivity and/or high permeability are introduced in a cylindrical volume filled with liquid sodium.

Both material properties not only lead to a decrease of the effective magnetic Reynolds number but also result in a quite distinct geometric structure of the final eigenmode. Furthermore, high permeability material even if localized in a small volume like the soft iron impellers in the VKS dynamo, essentially determines the field generation process and is reponsible for the selection of the dominating azimuthal dynamo mode.

Keywords: dynamo; kinematic induction equation; heterogenous material coefficients; permeability

  • Lecture (Conference)
    The 8th AIMS Conference on Dynamical Systems, Differential Equations and Applications, 25.-28.05.2010, Dresden, Deutschland

Publ.-Id: 14091

Influence of humic acids on the actinide migration in the environment: Suitable humic acid model substances and their application

Sachs, S.; Bernhard, G.

Humic acids (HA) are soluble in the pH range of natural water, possess the ability for complex and colloid formation and show redox properties that can impact the redox state of metal ions. Therefore, HA can influence the speciation of metal ions, e.g., actinides, and thus, their migration in the environment. Knowledge of the impact of HA on the actinide migration is required for the long-term risk assessment for potential nuclear waste repositories in deep geological environments. The complex nature of HA complicates the description of their interaction with metal ions. Thus, there are a lot of difficulties in the thermodynamic description of the geochemical interaction processes of HA. A more basic understanding of the interaction processes of HA can be obtained by model investigations with model ligands representing building blocks of HA as well as with specific HA model substances. These should be characterized by similar operational and chemical properties, a more defined functionality, and a higher homogeneity compared to natural HA. Furthermore, they should offer the possibility for specific variations of functional and structural properties and for the stable isotopic labeling (e.g., 13C, 14C, 15N) of the HA structure. Model substances which achieve these requirements can be applied to study the interaction behavior of HA with metal ions in detail and to study the fate of HA in sorption and migration experiments. This work focuses on selected types of HA model substances, their synthesis and characterization in comparison to natural HA. Their use in geochemical studies will be shortly discussed.

Keywords: Humic acids; model substances; actinides; migration; complexation; environment; sorption; reduction; redox behavior; labeling

  • Contribution to proceedings
    Second International Conference on Application of Radiotracers in Chemical, Environmental and Biological Sciences, ARCEBS-10, 07.-13.11.2010, Kolkata, India
    Application of Radiotracers in Chemical, Environmental and Biological Sciences, Vol. 3, S. Lahiri, M. Maiti, S.K. Das (Editors), 286-288
  • Lecture (Conference)
    Second International Conference on Application of Radiotracers in Chemical, Environmental and Biological Sciences, ARCEBS-10, 07.-13.11.2010, Kolkata, India

Publ.-Id: 14090

Experimentelle Untersuchung der Flüssigmetallströmung im Stranggussprozess unter Einfluss eines DC – Magnetfeldes

Timmel, K.; Eckert, S.; Gerbeth, G.

Zur Untersuchung der Magnetfeldwirkung auf die Stahlströmung im kontinuierlichen Stranggussverfahren wurden Experimente an einem verkleinerten Flüssigmetallmodell durchgeführt. Als Modellfluid wurde dabei eine bei Raumtemperatur flüssige Legierung, bestehend aus Gallium, Indium und Zinn, gewählt. Die Kokillenströmung wurde am Modell mittels der Ultraschall-Doppler-Methode ausgemessen. Die Anordnung von 10 Sensoren ermöglichte die zweidimensionale Aufzeichnung der horizontalen Geschwindigkeiten in der Kokille.
Basierend auf dem Konzept der Elektromagnetischen Bremse wurde ein DC-Magnetfeld im Bereich der stärksten Strömungen an die Kokille angelegt. Die Messungen mittels Ultraschall zeigen deutlich die aus dem Tauchrohr austretende Strahlströmung als auch das zeitliche Verhalten der Strömung im untersuchten Gebiet. Bei Anwesenheit des DC-Magnetfeldes verändert sich sowohl Lage als auch die Form des Flüssigmetalljets. Des Weiteren sind Gebiete mit verstärkter Rezirkulation direkt ober- und unterhalb des Jets zu beobachten. Ein weiteres, wichtiges Ergebnis dieser Messungen ist, dass das Magnetfeld unerwünschte Oszillationen in der Strömung anregen kann.
Die Kombination eines Flüssigmetallmodels, eines DC-Magnetfeldes und der Ultraschall-Doppler-Methode ist ein wichtiges Element bei der Untersuchung des Stranggussprozesses. Damit können wertvolle und bisher nur rudimentär vorhandene experimentelle Daten über den Einfluss elektromagnetische Felder auf die Strömung in der Kokille gewonnen werden, die auch für die Validierung numerischer Modell von Bedeutung sind.

Keywords: continuous casting; mould flow; liquid metal model; magnetic field; Ultrasound Doppler Method

  • Lecture (Conference)
    Symposium zur Simulation metallurgischer Strömungen an österreichischen und deutschen Universitäten, 16.-18.06.2010, Kirnitzschtal, Deutschland

Publ.-Id: 14089

Plutonium Redox Behavior in Aqueous Solutions and on Nanocrystalline Iron Phases

Fellhauer, D.; Kirsch, R.; Altmaier, M.; Neck, V.; Scheinost, A. C.; Wiss, T.; Charlet, L.; Fanghänel, T.

The redox behavior of Pu in aqueous solution is of particular interest for the disposal of nuclear waste in deep geological formations. Iron minerals are widespread in the environment and can be formed inside a repository by corrosion of steel canisters or construction materials. Their interaction with actinides and impact on redox chemistry needs to be understood for reliable performance assessment calculations.
The sorption and redox behavior of aqueous Pu(III) and Pu(V) in presence of synthetic nanocrystalline iron mineral suspensions and in homogeneous redox buffer solutions is investigated using a combination of classical wet chemistry methods and advanced spectroscopy (XANES, EXAFS). The impact of the redox conditions (pH + EH) in solution / suspension on the oxidation state distribution of Pu is studied by comparing the results to thermodynamic model calculations.

Keywords: thermodynamics; redox; interfaces; Pu; XANES; EXAFS; Fe oxides

  • Lecture (Conference)
    Plutonium Futures 2010, 19.-23.09.2010, Keystone, Colorado, USA

Publ.-Id: 14088

Study of americium and plutonium chemistry in Mixed OXide fuel

Martin, P.; Belin, R.; Robisson, A. C.; Scheinost, A. C.

The aim of this work is to follow the chemistry of uranium, plutonium and americium, and in particular their oxidation states, in MOX samples sintered under different oxygen potentials. To address this issue, X-ray Absorption Spectroscopy (XAS) is the ideally suited as it allows the quantitative determination of oxidation states for each cation using X-ray Absorption Near Edge Structure (XANES) and to outline potential discrepancies in actinide local environments using Extended X-ray Absorption Fine Structure (EXAFS) [3].
MOX samples with the following composition (U0.750Pu0.246Am0.004)O2-x, were manufactured at the LEFCA facility at CEA Cadarache (France). The process used is based on a direct co-milling of the oxides and leads to a homogeneous plutonium distribution [4]. Pellets were sintered at 1700°C under controlled atmosphere (moist Ar/5% H2) to obtain the following O/M ratios: 1.94, 1.97 and 2.00. These values were confirmed by thermogravimetric analysis.
XAS spectra at uranium, plutonium and americium LII,III edges were collected at the ROssendorf Beamline (ROBL) of the European Synchrotron Radiation Facility (Grenoble, France). XRD and thermogravimetric measurements were performed at the LEFCA facility.

Keywords: EXAFS; XANES; americium; plutonium; oxides

  • Lecture (Conference)
    Plutonium Futures 2010, 19.-23.09.2010, Keystone, Colorado, USA

Publ.-Id: 14087

Ultraschnelle Röntgen-Computertomographie für die Untersuchung von Zweiphasenströmungen

Bieberle, M.; Fischer, F.; Hampel, U.

Die ultraschnelle Röntgen-Computertomographie ist ein bildgebendes Verfahren, das am FZD für die Untersuchung von Strömungsprozessen qualifiziert wurde und auf dem Gebiet der Prozessdiagnostik zunehmend an Bedeutung gewinnt. In dem Vortrag werden das Messsystem sowie Ergebnisse von Strömungsexperimenten präsentiert sowie Ansätze für einer Weiterentwicklung des Messverfahrens aufgezeigt.

Keywords: x-ray; computed tomograpy; two-phase flows; imaging

  • Lecture (others)
    Kolloquium des Lehrstuhls für Magnetofluiddynamik, 19.05.2010, Dresden, Deutschland

Publ.-Id: 14086

Lasergetriebene Strahlungsquellen

Bussmann, M.

Eine Einführung in neuartige Strahlungsquellen am FZD für Schüler des Schott-Gymnasiums Jena

Keywords: laser; particle; acceleration; advanced; radiation; source; thomson; x-ray; elbe; draco; petawatt

  • Lecture (others)
    Besuch durch Schüler des Schott-Gymnasiums Jena, 24.03.2010, Dresden, Deutschland

Publ.-Id: 14085

Simulation of Advanced Radiation Sources at FZD

Bussmann, M.; Debus, A.; Kluge, T.; Schramm, U.; Cowan, T. E.; Sauerbrey, R.

We present an overview of the simulation work done at the Laser Particle Acceleration Group at the Institute of Radiation Physics. We show that with highly-parallel computing codes it is possible to perform realistic simulations of laser ion acceleration, laser-electron acceleration and Thomson scattering.

Keywords: laser; particle; acceleration; electron; ion; x-ray; thomson; scattering; wakefield; cone; target; simualtion; particle-in-cell; pic; gpu

  • Invited lecture (Conferences)
    Kick-Off Workshop: Atomic, Molecular, and Plasma Physics within PNI, 15.-16.04.2010, Hamburg, Deutschland

Publ.-Id: 14084

Illuminating Matter Bit by Bit – Computer-Experiments on Laser-Matter Interaction

Bussmann, M.; Kluge, T.; Debus, A.; Schramm, U.; Cowan, T. E.

The interaction of high-intensity, ultra-short laser pulses with matter is based on the well-understood physics of classical electromagnetics. In order to design, analyse and optimize laser-driven radiation sources, understanding the microscopic dynamics of electrons and ions interacting with strong laser fields is vital. These complex dynamics are both hard to resolve in experiment and hard to describe by analytic models. Here, realistic simulations based on the fundamental physical laws which govern the interaction can provide new and valuable insights. So-called computer experiments can bridge the gap between experiment and analytic theory and thus advance our understanding of the underlying plasma dynamics. Today, newest high performance computing technology makes it possible to incorporate all relevant physical processes in the simulation. With this, detailed modelling of experiments has entered the stage and will guide the way to new laser-driven radiation sources.

Keywords: laser; particle; electron; ion; simulation; x-ray; thomson; scattering; particle-in-cell; pic; molecular dynamics; fluid; hydrodynamic; vlasov

  • Lecture (others)
    Theory Seminar Series in FZD, 22.04.2010, Dresden, Deutschland

Publ.-Id: 14083

Research on Advanced Radiation Sources at FZD

Bussmann, M.; Debus, A.; Kluge, T.; Schramm, U.; Cowan, T. E.

At FZD the combination of ultra-short high-power Lasers and ultra-brilliant electron accelerators allows to provide unique sources for ions, electrons and photons. In combination, these sources will allow to probe the structure of matter in a new way, from applications in material science, the detection of strong magnetic fields, as a tool to study short-time-scale plasma dynamics and as a possible future source for medical applications. This talk presents some of the recent results and developments at FZD concerning new targets for ion beams, short-pulse x-ray sources and intense electron beams.

Keywords: fzd; laser; particle; acceleration; pump-probe; x-ray; radiation; sources; advanced; novel; applications; draco; petawatt; elbe; electron; ion; beam

  • Lecture (others)
    Institutsseminar (Kolloquium) IKTP TU Dresden, 22.04.2010, Dresden, Deutschland

Publ.-Id: 14082

Electron bunch length measurements from laser-accelerated electrons using single-shot THz time-domain interferometry

Debus, A.; Bussmann, M.; Schramm, U.; Sauerbrey, R.; Karsch, S.

Laser-plasma wakefield based electron accelerators are expected to deliver ultrashort electron bunches with unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment. We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5J, 45fs, 800nm laser and a ZnTe-based electro-optical setup we demonstrate the duration of laser-accelerated, quasi-monoenergetic electron bunches at a best fit of 32fs (FWHM) with a 90% upper confidence level of 38fs.

Keywords: laser; plasma; wakefield; electron; bunch; acceleration; duration; measurement; terahertz; electro-optical; crystal; mono-energetic; ultra-short; wavelength; single-shot

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) 2010, 08.-12.03.2010, Hannover, Deutschland

Publ.-Id: 14081

Platinum-H in presolar nanodiamond

Ott, U.; Merchel, S.; Melber, K.; Wallner, A.

Introduction: Among the presolar grains in meteorites, nanodiamonds are still the most enigmatic. Partly this is due their small size, which would render results from single grain analyses - even if they were possible – of limited value. Another reason is the low abundance of trace elements [1]. In acid resistant residues that also contain “impurities” of presolar silicon carbide, the trace element pattern is dominated by the SiC contribution for many elements, in particular in the REE range [2]. The most distinctive isotopic patterns linking the diamonds to a supernova have been observed in the noble gases, in particular xenon [3, 4]. This has been supplemented by large effects observed in tellurium [5], and smaller not so telling effects in a few other elements (Sr, Ba, Pd: [6, 7]).
Experimental: We have been continuing our search for isotopic effects in platinum. As in [8], we use accelerator mass spectrometry, which eliminates molecular interferences, a problem encountered in our multi-grain multi-element study by ICP-MS [2]. AMS is also able in principle to distinguish between true isobars, but this has not been necessary in our case. Ignoring low-abundant 190Pt and 192Pt, the only interfering isobars are at masses 196 and 198 from volatile Hg, which is not present in the beam when using negative ions. Measurements were performed at the Vienna Environmental Research Accelerator (VERA) [9] using similar methods as in our previous work at TU Munich [8]. VERA has recently been optimized for heavy ion detection, resulting in improved precision and background suppression.
Results: We observed enhancements in 198Pt/195Pt by ~6% in two diamond residues from Allende, AKL and AMW, which were prepared by different dissolution techniques [8]. Analyses were run in two different analytical sessions and the effect was reproduced. Variations in other isotopic ratios were within analytical uncertainty, and no anomaly could be identified in a third Allende diamond sample.
Interpretation: Enhanced 198Pt/195Pt is predicted by both the neutron burst model [10] and the rapid r-process separation scenario [11]. However, the latter also predicts a strong negative anomaly in 194Pt/195Pt, which is not observed. Thus, the Pt results seem to favor the neutron burst model. This is in contrast to the situation in tellurium (and xenon, to some extent) and adds to the enigma of the nanodiamonds.
References: [1] Lewis R. S. et al. 1991. Meteoritics 26:363-364. [2] Yin Q.-Z. et al. 2006. Astrophysical Journal 647:676-684. [3] Lewis R. S. et al. 1987. Nature 326:160-162. [4] Huss G. R. & Lewis R. S. 1994. Meteoritics 29:791-810. [5] Richter S. et al. 1998. Nature 391:261-263. [6] Lewis R. S. et al. 1991. 22nd Lunar and Planetary Science Conference. pp. 807-808. [7] Maas R. et al. 2001. Meteoritics & Planetary Science 36:849-858. [8] Merchel S. et al. 2003. Geochimica et Cosmochimica Acta 67:4949-4960. [9] Wallner A. 2010. Nuclear Instruments and Methods in Physics Research B268: 1277-1282. [10] Meyer B.S. et al. 2000. Astrophysical Journal Letters 540:L49-L52. [11] Ott U. 1996. Astrophysical Journal 463:344-348.

Keywords: accelerator mass spectrometry; AMS; strophysics; presolar; nanodiamonds

Publ.-Id: 14080

On the phase formation of sputtered hafnium oxide and oxynitride films

Sarakinos, K.; Music, D.; Mráz, S.; To Baben, M.; Jiang, K.; Nahif, F.; Braun, A.; Zilkens, C.; Konstantinidis, S.; Munnik, F.; Schneider, J. M.

Hafnium oxynitride films are deposited from a Hf target employing direct current magnetron sputtering in an Ar-O2-N2 atmosphere. It is shown that the presence of N2 allows for the stabilization of the transition zone between the metallic and the compound sputtering mode enabling deposition of films at well defined conditions of target coverage by varying the O2 partial pressure. Plasma analysis reveals that this experimental strategy facilitates control over the flux of the O- ions which are generated at the oxidized target surface and accelerated by the negative target potential towards the growing film. An arrangement that enables film growth without O- ion bombardment is also implemented. Moreover, stabilization of the transition sputtering zone and control of the O- ion flux without N2 addition is achieved employing high power pulse magnetron sputtering. Structural characterization of the deposited films unambiguously proves that the phase formation of hafnium oxide and hafnium oxynitride films with the crystal structure of HfO2 is independent from the O- bombardment conditions. Experimental and theoretical data indicate that the presence of vacancies and/or the substitution of O by N atoms in the non-metal sublattice favor the formation of the cubic and/or the tetragonal HfO2 crystal structure at the expense of the monoclinic HfO2 one.

  • Journal of Applied Physics 108(2010)1, 014904

Publ.-Id: 14079

Three-Dimensional Cell Growth Confers Radioresistance by Chromatin Density Modification

Storch, K.; Eke, I.; Borgmann, K.; Krause, M.; Richter, C.; Becker, K.; Schröck, E.; Cordes, N.

Cell shape and architecture are determined by cell-extracellular matrix interactions and have profound effects on cellular behavior, chromatin condensation, and tumor cell resistance to radiotherapy and chemotherapy. To evaluate the role of chromatin condensation for radiation cell survival, tumor cells grown in three-dimensional (3D) cell cultures as xenografts and monolayer cell cultures were compared. Here, we show that increased levels of heterochromatin in 3D cell cultures characterized by histone H3 deacetylation and induced heterochromatin protein 1α expression result in increased radiation survival and reduced numbers of DNA double strand breaks (DSB) and lethal chromosome aberrations. Intriguingly, euchromatin to heterochromatin–associated DSBs were equally distributed in irradiated 3D cell cultures and xenograft tumors, whereas irradiated monolayer cultures showed a 2:1 euchromatin to heterochromatin DSB distribution. Depletion of histone deacetylase (HDAC) 1/2/4 or application of the class I/II pharmacologic HDAC inhibitor LBH589 induced moderate or strong chromatin decondensation, respectively, which was translated into cell line–dependent radiosensitization and, in case of LBH589, into an increased number of DSBs. Neither growth conditions nor HDAC modifications significantly affected the radiation-induced phosphorylation of the important DNA repair protein ataxia telangiectasia mutated. Our data show an interrelation between cell morphology and cellular radiosensitivity essentially based on chromatin organization. Understanding the molecular mechanisms by which chromatin structure influences the processing of radiation-induced DNA lesions is of high relevance for normal tissue protection and optimization of cancer therapy.


Publ.-Id: 14078

Nitrogen at the Si-nanocrystal / SiO2 interface and its influence on luminescence and interface defects

Hiller, D.; Götze, S.; Munnik, F.; Jivanescu, M.; Gerlach, J. W.; Vogt, J.; Pippel, E.; Zakharov, N.; Stesmans, A.; Zacharias, M.

The influence of the high temperature annealing ambient (N2 or Ar) on size controlled Si nanocrystals (NCs) in SiO2 ranging from ~2 to ~6 nm has been investigated in detail. Generally, N2 annealing is beneficial as the dangling bond density (Pb-defects at the NC/SiO2 interface) is about half accompanied by a doubled PL intensity. The N-related PL blueshift was found to be pronounced only for the small NCs whereas it appears to be insignificant for larger NCs. The origin of this N-blueshift was previously attributed to NC growth suppression by the presence of N. However, no evidence for this assumption is found by time-resolved PL, as the luminescence decay times are similar despite considerable N-blueshift. The exact location of the N incorporated during annealing was investigated by ToF-SIMS and ESR: Besides the distinct N-enrichment in the NC-layer, the K0-center (•Si≡N3) was detected indicating the formation of an interfacial N layer at the NC/SiO2 interface. ERD analysis enabled the quantification of the incorporated N as well as the excess Si. Combined with TEM analysis (determination of NC size) the calculation of the NC-density per superlattice layer and the thickness of the interfacial N-layer were achieved. It turns out that ~ 5×1014 N-atoms cm-2 exist at the NC, which is well in accordance to the optimum value of the bulk Si/SiO2 interface. These results support our recently suggested explanation for the N-blueshift that is based on the influence of the polarity of the surface terminating groups on the bandgap of the NC.

Publ.-Id: 14077

The sorption of U(VI), Np(V) and Se(VI) onto surfaces of selected metal oxidesstudied by in situ vibrational spectroscopy

Müller, K.; Meusel, T.; Foerstendorf, H.; Brendler, V.; Bernhard, G.; Lefèvre, G.

The migration behavior of actinides and other radioactive contaminants in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at liquid-solid interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI), neptunium(V) and selenium(VI) at environmentally relevant mineral – water interfaces of oxides of titania, alumina, silica, iron, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy.
Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.

  • Lecture (others)
    Seminar at the Institut de Physique Nucléaire, Division de Recherche Radiochemie., 10.05.2010, Orsay, France

Publ.-Id: 14076

High-rate timing RPC with ceramics electrodes

Naumann, L.; Kotte, R.; Stach, D.; Wüstenfeld, J.

A resistive plate counter for timing purposes in the high-rate environment of the Compressed Baryonic Matter Experiment has been developed at the Forschungszentrum Dresden-Rossendorf. The detector electrodes are made of a ceramics composite.
Detector tests have been performed with minimum ionizing single electrons, delivered by the electron accelerator ELBE with a time accuracy of few picoseconds. The ceramics RPC shows an all-time high-rate capability for electron fluxes up to 2.7x10E5 /s/cm².

Keywords: RPC; Rate capability; Ceramics composite; Bulk resistivity; Detection efficiency; Time resolution

Publ.-Id: 14075

Numerical simulation of air-water counter-current two-phase flow in a model of the hot-leg of a pressurized water reactor (PWR)

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

In order to validate newly developed multiphase flow models in the code ANSYS CFX, a CFD simulation of the counter-current two-phase flow of 1/3rd scale model of the hot leg of a German Konvoi Pressurized Water Reactor with rectangular cross section was performed. A selected air-water Counter-current flow limitation (CCFL) experiment of Forschungszentrum Dresden-Rossendorf (FZD) at 0.153 MPa and room temperature was simulated with three-dimensional two-fluid Euler-Euler models of computer code CFX 12.0 (ANSYS CFX). The calculation was carried out in fully transient manner using a gas/liquid inhomogeneous multiphase flow model coupled with a shear stress transport (SST) turbulence model. In the simulation, the drag coefficient was approached by the Algebraic Interfacial Area Density (AIAD) model. The results indicated that quantitative agreement of the CCFL characteristics between calculation and experimental data was obtained. Next, a comparison with the high-speed video observations shows also a good qualitative agreement.

Keywords: Numerical simulation; Computational fluid dynamic; Counter-current flow limitation (CCFL); Pressurized water reactor (PWR); Algebraic interfacial area density (AIAD) model

  • Contribution to proceedings
    7th International Conference on Multiphase Flow (ICMF 2010), 30.05.-04.06.2010, Tampa, USA
    Proceeding of the 7th International Conference on Multiphase Flow
  • Lecture (Conference)
    7th International Conference on Multiphase Flow (ICMF 2010), 30.05.-04.06.2010, Tampa, USA

Publ.-Id: 14074

Modeling the spectral history in the depletion of a PWR core.

Bilodid, I.

Codes for reactor core calculations use few-group cross sections (XS) which depend on local burnup, given in terms of the energy produced per fuel mass (MWd/kgHM). However, a certain burnup value can be reached under different spectral conditions depending on moderator density and other local parameters. Neglecting these spectral effects, i.e. applying the summary-burnup value only, can cause considerable errors in the calculated power density.
This paper describes a way to take into account spectral-history effects. It is shown that the respective XS correction linearly depends on the actual Pu-239 concentration. The applicability of the method was proved not only for usual uranium oxide fuel, but also for mixed uranium/plutonium oxide (MOX) and fuel assemblies with burnable absorber. The code DYN3D was extended by new subroutines which calculate the actual distribution of Pu-239 in the core and apply a spectral-history correction for the XS.

Keywords: cross section library; history effects; spectral history; burnup; DYN3D

  • Contribution to proceedings
    18th International Conference on Nuclear Engineering (ICONE18), 17.-21.05.2010, Xi'an, China
    Proceedings of the 18th International Conference on Nuclear Engineering (ICONE18) May 17-21, 2010 • Xi’an, China
  • Poster
    18th International Conference on Nuclear Engineering (ICONE18), 17.-21.05.2010, Xi'an, China
  • Lecture (Conference)
    18th International Conference on Nuclear Engineering (ICONE18), 17.-21.05.2010, Xi'an, China

Publ.-Id: 14073

Cumulative minor loop growth in Co/Pt- and Co/Pd-multilayers

Berger, A.; Mangin, S.; McCord, J.; Hellwig, O.; Fullerton, E. E.

The behavior of minor hysteresis loops in perpendicular anisotropy [Co/Pt]- and [Co/Pd]-multilayers has been investigated. Upon applying a succession of identical magnetic field cycles, we observe a very substantial cumulative growth of the minor loop area. For the [Co/Pt] multilayers this effect only saturates near complete magnetization reversal, while the behavior is slightly more limited for [Co/Pd] multilayers. We also find this cumulative growth to occur even if the minor loop field cycles are made asymmetric by means of a positive bias field. The cumulative behavior persists up to a sample dependent threshold value above which this effect disappears. In all samples, the cumulative minor loop growth is correlated with a small reduction of the maximum magnetization value in each cycle. Magneto-optical Kerr microscopy studies correlate the minor-loop growth with the memory and cumulative expansion of lateral domain cycling. All experimental observations can be consistently explained as an accumulation of small nucleation domains that aid subsequent reversals and facilitate the cumulative minor loop growth.

Publ.-Id: 14072

Gas phase chemical studies of superheavy elements using the Dubna gas-filled recoil separator – Stopping range determination

Wittwer, D.; Abdullin, F. S.; Aksenov, N. V.; Albin, Y. V.; Bozhikov, G. A.; Dmitriev, S. N.; Dressler, R.; Eichler, R.; Gäggeler, H. W.; Henderson, R. A.; Hübener, S.; Kenneally, J. M.; Lebedev, V. Y.; Lobanov, Y. V.; Moody, K. J.; Oganessian, Y. T.; Petrushkin, O. V.; Polyakov, A. N.; Piguet, D.; Rasmussen, P.; Sagaidak, R. N.; Serov, A.; Shirokovsky, I. V.; Shaughnessy, D. A.; Shishkin, S. V.; Sukhov, A. M.; Stoyer, M. A.; Stoyer, N. J.; Tereshatov, E. E.; Tsyganov, Y. S.; Utyonkov, V. K.; Vostokin, G. K.; Wegrzecki, M.; Wilk, P. A.

Currently, gas phase chemistry experiments with heaviest elements are usually performed with the gasjet technique with the disadvantage that all reaction products are collected in a gas-filled thermalisation chamber adjacent to the target. The incorporation of a physical preseparation device between target and collection chamber opens up the perspective to perform new chemical studies. But this approach requires detailed knowledge of the stopping force (STF) of the heaviest elements in various materials. Measurements of the energy loss of mercury (Hg), radon (Rn), and nobelium (No) in Mylar and argon (Ar) were performed at low kinetic energies of around (40–270) keV per nucleon. The experimentally obtained values were compared with STF calculations of the commonly used program for calculating stopping and ranges of ions in matter (SRIM). Using the obtained data points an extrapolation of the STF up to element 114, eka-lead, in the same stopping media was carried out. These estimations were applied to design and to perform a first chemical experiment with a superheavy element behind a physical preseparator using the nuclear fusion reaction 244Pu(48Ca; 3n)289114. One decay chain assigned to an atom of 285112, the adecay product of 289114, was observed.

Publ.-Id: 14071

De Haas-van Alphen (dHvA) study of the isostructural compounds YbCoIn5 and LuCoIn5

Polyakov, A.; Ignatchik, O.; Bartkowiak, M.; Bianchi, A.; Prevost, B.; Seyfarth, G.; Fisk, Z.; Hurt, D.; Goodrich, R. G.; Choi, E. S.; Wosnitza, J.

The intermetallic compounds RIn3 and RTIn5 (R = rare earth, T = transition metal) have attracted great interest for their large variety of anomalous ground states. Among these are the well-known heavy-fermion superconductors CeCoIn5 and CeIrIn5. We present here a dHvA study of YbCoIn5 and LuCoIn5, performed by use of a capacitive torque cantilever technique at temperatures down to 0.4 K in magnetic fields up to 13 T. In addition, one single crystal of LuCoIn5 has been measured in magnetic field up to 34 T. Besides their angular-dependent Fermi-surface topologies, we have also determined the effective masses of the different bands by following the temperature-dependent amplitude changes of the dHvA oscillations. A large number of different dHvA frequencies has been observed for the main crystallographic directions. In contrast to CeCoIn5 and CeIrIn5, the cyclotron effective masses for these compounds are in the range from 0.7 to 2.0 m0.

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 14070

Magnetic measurements on Tb5Ge3

Haase, A.; Doerr, M.; Bartkowiak, M.; Daou, R.; Skourski, Y.; Rotter, M.; Uhlarz, M.

Tb5Ge3 is a weak antiferromagnet, which orders at 83 K. It crystallizes in Mn5Si3-type hexagonal structure with two different positions for the Tb3+ ions. The hexagonal ab-plane is the easy plane of magnetization. Magnetization and magnetostriction measurements have been done on a single crystal in static fields up to 30 T and in pulsed fields up to 50 T. In addition to the antiferromagnetic phase, three more phases were found in fields in the ab-plane at low temperatures. Surprisingly, the measurements along the b-axis do not resemble the a-axis properties which indicates an anisotropy in the hexagonal plane. Initial model calculations reveal the anisotropy of the magnetic exchange, which is dominant over the crystal electric field effect, as cause. The hard c-axis shows only one phase transition at 5 T followed by a nearly linear magnetization and magnetostriction slope which is attributed to a steady-going rotation of the moment.

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM)2010, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 14069

Field-Induced Phase Transitions in UIrGe Probed by Ultrasound Measurements

Yasin, S.; Andreev, A. V.; Wosnitza, J.; Zherlitsyn, S.

es hat kein Abstract vorgelegen.

  • Poster
    40èmes Journées des Actinides & 2nd Workshop on Actinide Targets, 27.03.-01.04.2010, Genf, Schweiz

Publ.-Id: 14068

Superconducting Phase Diagram of Rh17S15

Uhlarz, M.; Ignatchik, O.; Wosnitza, J.; Daou, R.; Doerr, M.; Haase, A.; Naren, H. R.; Thamizhavel, A.; Ramakrishnan, S.

Rh17S15 is a 4d-electron metal which becomes superconducting below Tc = 5.4 K at zero field. The upper critical field is 19.2 T at T = 0.07 K. Above Tc, Rh17S15 is a paramagnet. The crystallographic structure (Pm3m) of Rh17S15 features a nearest-neighbor Rh-Rh distance even less than in elementary (fcc) Rh, possibly resulting in a high density of 4d-electron states at the Fermi level. Using a polycrystalline sample, we measured the specific heat, resistivity, magnetization, and magnetostriction in fields up to 14 T as well as the magnetic susceptibility in fields up to 20 T. Our data allow us to present the complete superconducting phase diagram. The assumption of narrow 4d band states (and thus of strong electronic correlations not providing magnetic correlations) is supported by the moderately enhanced electronic contribution to the specific heat of 107 mJ/molK2 and favors the existence of a strong superconducting interaction. Together with the remarkably high upper critical field (exceeding the Pauli limit by a factor of two), our findings make Rh17S15 a likely candidate for unconventional superconductivity.

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 14067

Calorimetric investigations of HoNi2B2C

Beyer, R.; Herrmannsdoerfer, T.; Ignatchik, O.; Canfield, P.; Wosnitza, J.

The rare-earth nickel borocarbides show an intriguing competition between magnetism and superconductivity. For HoNi2B2C, this leads to a rich phase diagram with superconducting and magnetic phase transitions. Besides these competing electronic interactions, also the nuclear magnetic moment of Holmium may influence the superconducting state due to an expected strong hyperfine-enhanced nuclear polarization. In order to study this in more detail, we performed high-resolution specific-heat measurements by use of a continuous relaxation-time method. While the superconducting transition at about 8 K results in a very small, but resolvable specific-heat jump, at lower temperatures there are at least three independent magnetic-ordering transitions. One of these shows a lambda-like anomaly with a small hysteresis indicating a first-order phase transition. Additionally, the increasing specific heat below 1 K can be taken as evidence for a pronounced hyperfine contribution.

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 14066

High-field metamagnetism in UCo2Si2

Skourski, Y.; Andreev, A. V.; Wosnitza, J.

es hat kein Abstract vorgelegen

  • Poster
    40èmes Journées des Actinides & 2nd Workshop on Actinide Targets, 27.03.-01.04.2010, Genf, Schweiz

Publ.-Id: 14065

Interaction of point defects with impurities in the Si–SiO2 system and its influence on the properties of the interface

Kropman, D.; Mellikov, E.; Öpik, A.; Lott, K.; Kärner, T.; Heinmaa, I.; Laas, T.; Medvid, A.; Skorupa, W.; Prucnal, S.; Rebohle, L.; Zvyagin, S.; Cizmar, E.; Ozerov, M.; Wosnitza, J.

The results of investigations of the point defect generation, redistribution and interaction with impurities in the Si–SiO2 system during the process of its formation by means of electron paramagnetic resonance (EPR) and nucleus magnetic resonance (NMR) techniques are presented. The type and density of the point defect that are generated in the Si surface layer during thermal oxidation depend on the oxidation condition: temperature, cooling rate, oxidation time, and impurity content. The interaction between the point defects with extended defects and impurities affects the properties of the Si–SiO2 interface. The influence of the point defects may be diminished and the interface properties improved by an appropriate choice of the oxidation conditions. The difference between the interface properties of n- and p-type wafers may be connected with the different position of the Fermi level at the interface and different point defects density in the volume near the interface.

  • Thin Solid Films 518(2010), 2374-2376

Publ.-Id: 14064

Electronic structure and magnetic properties of the spin-gap compound Cu2(PO3)2CH2: Magnetic versus structural dimers

Schmitt, M.; Gippius, A. A.; Okhotnikov, K. S.; Schnelle, W.; Koch, K.; Janson, O.; Liu, W.; Huang, Y.-H.; Skourski, Y.; Weickert, F.; Baenitz, M.; Rosner, H.

A joint experimental and theoretical investigation of the spin 1/2 system Cu2(PO3)2CH2 suggests a description of this compound as coupled alternating antiferromagnetic Heisenberg chains. Magnetic susceptibility, specific heat, nuclear magnetic resonance, nuclear quadrupole resonance, and high-field magnetization measurements evidence a spin gap of about 25 K. Surprisingly, the leading antiferromagnetic exchange of about 75 K can be assigned by density-functional band-structure calculations to a coupling between the structural Cu2O6 dimers, whereas the coupling within these dimers is strongly reduced due to sizable ferromagnetic contributions. The coupling within the structural dimers competes with a number of long-range couplings. The present available experimental data can be consistently described in a scenario of coupled alternating chains. The proposed model should be considered as a minimal model for an appropriate description of this compound.

Publ.-Id: 14063

High-field magnetization study of a Tm2Co17 single crystal

Andreev, A. V.; Kuzmin, M. D.; Narumi, Y.; Skourski, Y.; Kudrevatykh, N. V.; Kindo, K.; de Boer, F. R.; Wosnitza, J.

Tm2Co17 is a ferrimagnet with TC = 1170 K and, at 4.2 K, has a spontaneous magnetic moment Ms =13.4 muB/ f.u. Magnetization curves were measured on a Tm2Co17 single crystal along the principal axes in pulsed magnetic fields up to 70 T at 4.2 K. The curve along the easy [001] direction exhibits a distinct anomaly at mu0Hcr = 39 T, where the magnetization exhibits a stepwise rise from Ms to Mflip = 40.6 muB/ f.u. The observed transition from the ferrimagnetic ground state (with Ms = 17muCo − 2muTm) to a saturated spin-flip state with parallel orientation of the sublattice moments and Mflip = 17muCo + 2muTm is unusual for 3d-4f intermetallics because it does not proceed via an intermediate angled-sublattice state. Rather, a collinear remagnetization of the Tm sublattice takes place: as the applied magnetic field grows, the Tm moments disorder at first, reaching a fully disordered paramagnetic state at H = Hcr, then they order magnetically in the opposite sense.

  • Physical Review B 81(2010), 134429

Publ.-Id: 14062

Optical Floating-Zone Growth of Large Single Crystal of Spin Half Dimer Sr3Cr2O8

Nazmul Islam, A. T. M.; Quintero-Castro, D.; Lake, B.; Siemensmeyer, K.; Kiefer, K.; Skourski, Y.; Herrmannsdörfer, T.

Large single crystals (∼6 mm in diameter and 35-50 mm in length) of spin dimer system Sr3Cr2O8 have been grown in a four-mirror type optical floating-zone furnace under different atmospheres. Single crystals were characterized by polarized optical microscopy, energy dispersive X-ray analysis, X-ray powder diffraction, X-ray, and neutron Laue measurements, etc. Crystals were grown under an optimized growth atmosphere of flowing (6-8 L/min) synthetic air found to be free of any impurities and excellent in quality. Characteristics of the magnetic susceptibility and magnetization along different crystallographic axes are also shown.

  • Crystal Growth & Design 10(2010), 465-468

Publ.-Id: 14061

Theory of Unusual Superconducting Phase Transitions in Heavy Fermion Metals at High Magnetic Fields

Zhuravlev, V.; Maniv, T.; Wosnitza, J.

We present a non-perturbative theory of paramagnetically-driven superconducting (SC) phase transitions in heavy-fermion metals, which reliably determines their stable SC phases, treats properly the corresponding finite jumps of the order parameter, and can account for unusual features reported recently for this type of materials. It is found that for quasi-2D heavy-fermion metals, such as CeCoIn5, at high magnetic fields oriented perpendicular to the highly conducting planes, the effect of the Fulde-Ferrel (FF) modulation is too weak to prevent a direct first-order phase transition from the normal to the uniform SC state. For 3D heavy-fermion metals, such as URu2Si2, the FF modulation stabilizes, under a decreasing magnetic field, a non-uniform SC state via a second-order phase transition from the normal state. However, at a slightly lower field the modulated phase becomes unstable, transforming to a uniform SC state via a first-order transition.

  • Journal of Low Temperature Physics 159(2010), 138-142

Publ.-Id: 14060

Lattice Instabilities in the Frustrated Magnet CdCr2O4: An Ultrasonic Study

Zherlitsyn, S.; Chiatti, O.; Sytcheva, A.; Wosnitza, J.; Bhattacharjee, S.; Moessner, R.; Zhitomirsky, M.; Lemmens, P.; Tsurkan, V.; Loidl, A.

We report results on ultrasound studies of the frustrated magnet CdCr2O4. This compound demonstrates an antiferromagnetic ordering at TN = 7.8 K and a metamagnetic phase transition at 28 T followed by a wide magnetization plateau with one half of the full moment of S = 3/2 of Cr3+ ions. A longitudinal acoustic mode in the [111] crystallographic direction exhibits pronounced effects both in the temperature and magnetic-field dependencies. Pulsed-field measurements show a drastic change in the sound velocity just below and above the 1/2 magnetization plateau. Our results suggest a large spin-strain coupling and give evidence for a pronounced interplay between spin and lattice degrees of freedom in CdCr2O4.

  • Journal of Low Temperature Physics 159(2010), 134-137

Publ.-Id: 14059

Magneto-Acoustic Properties of UCuGe Single Crystal

Yasin, S.; Andreev, A. V.; Sytcheva, A.; Zherlitsyn, S.; Wosnitza, J.

Abstract We report on results of sound velocity and sound-attenuation measurements performed on the antiferromagnetic (TN = 48 K) UCuGe. The measurements have been done on a UCuGe single crystal at different frequencies for longitudinal ultrasound waves propagating along the [001] direction in static (up to 18 T) and pulsed (up to 60 T) magnetic fields applied along the same direction. The temperature dependences of the sound velocity and attenuation display a pronounced anomaly at TN, which is evidence for a strong magneto-elastic interaction. The pulse-field measurements at 4.2 K show a minimum in the sound velocity followed by a jump-like anomaly at 37 T, and another kink-like anomaly at 48–49 T. These anomalies are due to field-induced spin rearrangements as measured in magnetization studies. In the paramagnetic state (T > TN), both acoustic characteristics show large frequency-dependent changes revealing the presence of an unusual relaxation mechanism which might be due to vacancy dynamics.

  • Journal of Low Temperature Physics 159(2010), 105-108

Publ.-Id: 14058

Resonance strengths in the 14N(p, gamma)15O and 15N(p, alpha gamma)12C reactions

Marta, M.; Trompler, E.; Bemmerer, D.; Beyer, R.; Broggini, C.; Caciolli, A.; Erhard, M.; Fülöp, Z.; Grosse, E.; Gyürky, G.; Hannaske, R.; Junghans, A. R.; Menegazzo, R.; Nair, C.; Schwengner, R.; Szücs, T.; Vezzù, S.; Wagner, A.; Yakorev, D.

The 14N(p,gamma)15O reaction is the slowest reaction of the carbon-nitrogen-oxygen cycle of hydrogen burning in stars. As a consequence, it determines the rate of the cycle. The 15N(p, alpha gamma)12C reaction is frequently used in inverse kinematics for hydrogen depth profiling in materials. The 14N(p,gamma)15O and 15N(p, alpha gamma)12C reactions have been studied simultaneously, using titanium nitride targets of natural isotopic composition and a proton beam. The strengths of the resonances at Ep = 1058 keV in 14N(p,gamma)15O and at Ep = 897 and 430 keV in 15N(p, alpha gamma)12C have been determined with improved precision, relative to the well-known resonance at Ep = 278 keV in 14N(p,gamma)15O. The new recommended values are omega gamma = 0.353 ± 0.018, 362 ± 20, and 21.9 ± 1.0 eV for their respective strengths. In addition, the branching ratios for the decay of the Ep = 1058 keV resonance in 14N(p,gamma)15O have been redetermined. The data reported here should facilitate future studies of off-resonant capture in the 14N(p,gamma)15O reaction that are needed for an improved R-matrix extrapolation of the cross section. In addition, the data on the 430 keV resonance in 15N(p, alpha gamma)12C may be useful for hydrogen depth profiling.

Keywords: Nuclear astrophysics; CNO cycle; Tandetron; TiN solid target; hydrogen depth profiling

Publ.-Id: 14056

Development of an inline multiphase flow metering sensor

Springer, R.; Schubert, M.; Hampel, U.

Measurement of multiphase flow rates, for example in gas-liquid two-phase flow, is a challenging issue in many industrial applications. While current solutions are based on upstream phase separation or combination of different methods (e.g. densitometry and Venturi tube flow meter), the target of our new sensor is to allow an inline measurement of multiphase flow rates at lower cost and space requirements. Starting with flow rate measurements in gas-liquid systems, the sensor principle is to subdivide the gas-liquid flow into partial streams of alternating gas and liquid fractions (also called Taylor flow) in a grid of small tubes. This allows contactless instantaneous phase detection and time-resolved detection of subsequent phase transitions using a capacitance sensing principle based only on the dielectric properties of the flu-ids. The sensor design will be discussed in detail, a prototype introduced and simulation and experimental results presented. Further, application requirements and limitations of the measurement principle will be discussed. The performance of the multiphase flow meter was evaluated from experiments in a gas-liquid flow loop.
Multiphase flows, whether wanted or not, are encountered in very different industrial areas, e.g. oil explo-ration, fueling of petrol or in milk floats, chemical production units, etc. However, they have in common, that they often require quantitative measurement or at least qualitative detection of multiple phases. Con-ventional measurement systems typically require expensive phase separation units to allow the applica-tion of well-established single phase measurement equipment. Alternatively, transmission-based systems that are costly and require stringent safety regulations may be combined with measurement devices that reveal mixture velocity by cross-correlation methods. However, measurement accuracy decreases clearly if the flow deviates from a-priori assumed well-defined regimes and if phases separate locally. To summarize, economic and space saving sensor concepts would be highly appreciated.
The development of the new sensor concept makes use of preferable flow conditions (superficial gas and liquid flow rates), such as the Taylor flow regime, which allows sharp discrimination of phase transitions at intermitted liquid and gas fractions. As a preliminary study such gas-liquid flow scenarios were ob-served in a transparent sensor model using a high speed camera (see Fig. 1). Important design specifications for a high functionality of the sensor concept (prevention of micro bubbles or single-phase formations) were derived. Furthermore, characteristic flow behavior was studied and findings of earlier studies confirmed.
At Taylor flow conditions, phase transition can be detected at two positions with an axial offset (see Fig. 2) and velocity of the corresponding fraction can be determined by cross-correlation. As a detection principle we use local capacitance measurement due to its conceptual simplicity and capability of discriminating many different fluids. An optimized electrode configuration was chosen by performing field simulations on the fluid layers. (see Fig. 3)

Keywords: multiphase flow; Taylor flow; gas; liquid; oil exploration; fueling; chemical production

  • Poster
    IEEE Sensors 2010 Conference, 01.-04.11.2010, Waikoloa, Hawaii

Publ.-Id: 14055

Eighteenth-Century Meissen Porcelain reference data obtained by proton-beam analysis (PIXE-PIGE)

Neelmeijer, C.; Pietsch, U.; Ulbricht, H.

Prior to their restoration, the porcelain bodies of broken pieces from 31 authentic Meissen objects of the early 18th century were investigated by proton-beam analysis. Attention was paid so that the proton beam probed only the bare porcelain paste areas of fractures. Thus, contributions to the measured X-ray and γ-ray spectra from adjacent surface glaze were prevented. The chemical compositions, obtained by simultaneous detection of elements with Z ≥ 13 (X-rays) and lighter elements Z ≤ 14 (γ-rays), represent rather consistent mixtures of paste ingredients. This result highlights the durable recipes and raw materials used in early Meissen porcelain production in the years 1725–50. Mean concentration values of element oxides, deduced from the detailed measurements, prove suitable for use as a database for Meissen porcelain paste identification. Material authentication of intact objects, without access to the bare porcelain body, is demonstrated by inspection of the white glaze. Unique museum objects are examined in atmosphere and without sampling. A low proton-beam intensity and a short irradiation time ensure non-destructive analysis. Simultaneous radiation and backscattered particle detection allow complete composition analysis, using the established ion beam techniques of particle-induced X-ray emission (PIXE), particle-induced gamma-ray emission (PIGE) and Rutherford backscattering spectrometry (RBS).

Keywords: Porcelain; chemical analysis; Ion beam Analysis; PIXE; PIGE

Publ.-Id: 14054

Deuteron breakup pd → {pp}sn with forward emission of a fast 1S0 diproton

Dymov, S.; Komarov, V.; Macharashvili, G.; Uzikov, Y.; Azarian, T.; Imambekov, O.; Kulikov, A.; Kurbatov, V.; Merzliakov, S.; Zalikhanov, B.; Zhuravlev, N.; Büscher, M.; Hartmann, M.; Hejny, V.; Kacharava, A.; Nekipelov, M.; Ohm, H.; Rathmann, F.; Seyfarth, H.; Stein, H. J.; Ströher, H.; Khoukaz, A.; Mersmann, T.; Rausmann, T.; Barsov, S.; Mikirtychiants, S.; Kämpfer, B.; Kulessa, P.; Nioradse, M.; Trusov, S.; Yaschenko, S.

The deuteron breakup reaction pd→{pp}sn, where {pp}s is a fast proton pair emitted in forward direction with small excitation energy Epp<3  MeV, has been studied at proton beam energies of 0.5–2.0  GeV using the ANKE spectrometer at COSY-Jülich. The differential c.m. cross sections are measured in complete kinematics and provide angular distributions of the neutron emission angle in the range θn=168°–180°, the dependence on beam energy at θn=180°, angular distributions of the direction of the proton in the pp rest frame, and distributions of the excitation energy Epp of the proton pair. The obtained data are analyzed on the basis of theoretical models previously developed for the pd→dp process in a similar kinematics and properly modified for the diproton channel in pd→{pp}sn. It is shown that the measured observables are highly sensitive to the short-range part of the nucleon-nucleon interaction.

Publ.-Id: 14053

LUNA: Nuclear Astrophysics Deep Underground

Broggini, C.; Bemmerer, D.; Guglielmetti, A.; Menegazzo, R.

Nuclear astrophysics strives for a comprehensive picture of the nuclear reactions responsible for synthesizing the chemical elements and for powering the stellar evolution engine. Deep underground in the Gran Sasso laboratory the cross sections of the key reactions of the proton-proton chain and of the Carbon-Nitrogen-Oxygen (CNO) cycle have been measured right down to the energies of astrophysical interest. The salient features of underground nuclear astrophysics are summarized here. The main results obtained by LUNA in the last twenty years are reviewed, and their influence on the comprehension of the properties of the neutrino, of the Sun and of the Universe itself are discussed. Future directions of underground nuclear astrophysics towards the study of helium and carbon burning and of stellar neutron sources in stars are pointed out.

Publ.-Id: 14052

Time-dependent changes of Zinc speciation in four soils contaminated with zincite or sphalerite

Voegelin, A.; Jacquat, O.; Pfister, S.; Barmettler, K.; Scheinost, A. C.; Kretzschmar, R.

The speciation of Zn in contaminated soils depends on soil pH, clay content, and other soil properties. However, it is currently unclear how the type of Zn-bearing contaminant itself influences the Zn species newly formed in soils upon contamination. Therefore, we conducted a soil incubation study in which four soils (pH 4.2 to 7.7) were spiked either with ZnO (zincite) or ZnS (sphalerite) to a total Zn concentration of 2000 mg/kg and then incubated under aerated conditions near field capacity. The extractability and speciation of Zn were assessed after 1, 2, and 4 years of incubation using extractions with 0.01 M CaCl2 and Zn K-edge X-ray absorption fine structure (XAFS) spectroscopy, respectively. ZnO was dissolved most rapidly in the acidic soils, and in all soils more than 90% of the added ZnO were dissolved after four years. Fast dissolution of ZnO presumably results in elevated pH and high local Zn concentrations around dissolving ZnO particles, favoring the formation of Zn-LDH, and to a lesser degree Zn-phyllosilicates besides adsorbed Zn species. In contrast, ZnS dissolved much more slowly, reaching only 25 to 97% of the added ZnS after four years, with lower dissolution rates in the acidic soils. The resulting Zn speciation after 4 years was markedly different, with Zn-LDH only occurring in the neutral and alkaline soils. In both cases, adsorbed Zn was mainly octahedrally coordinated Zn bound as outer-sphere complex or Zn bound to HIM in the acidic soils, whereas tetrahedrally coordinated Zn sorbed as inner-sphere complex was found to be more important at higher soil pH. These results show that the type of Zn-bearing contaminant and its influence on local chemical conditions in addition to bulk soil properties control the types of Zn species forming in contaminated soil.

Keywords: XAS; zinc; soil; sphalerite; zincite

Publ.-Id: 14051

PuCrO3 compound: synthesis, structural and thermodynamic studies

Pieragnoli, A.; Belin, R. C.; Cécilia, G.; Léchelle, J.; Martin, P. M.; Valenza, P. J.; Richaud, J. C.; Reynaud, M.; Scheinost, A. C.

The synthesis of PuCrO3 compound starting from metallic or sesquioxide chromium and PuO2 powder mixtures in stoichiometric ratios has been studied at different temperatures under atmospheres with a varying oxygen potential (Ar, Ar + 5% H2, Ar + 5% H2 + 850 ppm H2O). The structure of the polycrystalline perovskite compound PuCrO3 was investigated by X-ray powder pattern fitting. A Rietveld analysis was performed using the computer program JANA 2000. PuCrO3 crystallizes in the orthorhombic space group Pbnm with a = 543±2 Å, b = 549±2 Å and c = 771±2 Å. A XAS study gave oxidation states +III for both chromium and plutonium. The heat capacity of PuCrO3 was measured by means of a differential scanning calorimeter (DSC) in the temperature range of 373–1373 K. Debye temperature as well as electronic defect energies have been fitted from these measurements. Enthalpy increment, entropy and free energy function of PuCrO3 have been calculated from the measured heat capacity and estimated data as a function of temperature.

Keywords: PuO2; PuCrO3; Rietveld; XAS

  • Lecture (Conference)
    Nuclear Materials 2010 Conference, 04.-07.10.2010, Karlsruhe, Germany

Publ.-Id: 14050

Evaluation of periodic operation of a trickle-bed reactor based on empirical modelling

Brzić, D.; Schubert, M.; Häring, H.; Lange, R.; Petkovska, M.

In this paper we propose a new procedure for fast evaluation of the potential of periodic operations in trickle-bed reactors, based on empirical modeling. Step response experiments, with different input amplitudes, were performed on a laboratory trickle-bed reactor, in order to derive a simple nonlinear dynamic model. α-methylstyrene (AMS) hydrogenation was used as a test reaction and the feed AMS concentration was used as the modulated input. An empirical nonlinear model was postulated and used for simulation of periodic operations. The simulation of a periodic operation with sinusoidal modulation of the inlet AMS concentration with 40 % amplitude resulted with up to 35% higher time averaged conversion than the corresponding steady-state one.

Publ.-Id: 14049

Gammatomographie zur Messung mittlerer Voidgehalte am KATHY-Versuchsstand - Messkampagne 2009 -

Hoppe, D.

Die in diesem Bericht dokumentierten Ergebnisse sind vertraulich.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2010
    129 Seiten
    ISSN: 1437-322X

Publ.-Id: 14048

Measurement technique developments for LBE flows

Buchenau, D.; Eckert, S.; Gerbeth, G.; Stieglitz, R.; Dierckx, M.

We report on the development of measurements techniques for flows in lead-bismuth eutectic alloys (LBE). This paper covers the test results of newly developed contact-less flow rate sensors as well as the development and test of the LIDAR technique for operational free surface level detection. The flow rate sensors are based on the flow-induced disturbance of an externally applied AC magnetic field which manifests itself by a modified amplitude or a modified phase of the AC field. Another concept of a force-free contactless flow meter uses a single cylindrical permanent magnet. The electromagnetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation. The operation of those sensors has been demonstrated at liquid metal test loops for which comparative flow rate measurements are available, as well as at the LBE loops THESYS at KIT and WEBEXPIR at SCK-CEN. For the level detection a commercial LIDAR system was successfully tested at the WEBEXPIR facility in Mol and the THEADES loop in Karlsruhe.

Keywords: Liquid metal; LBE; Phase-shift sensor; EMFM; Rotating magnet; LIDAR

  • Journal of Nuclear Materials 415(2011)3, 396-403

Publ.-Id: 14047

Investigation of the flow field in a liquid metal continuous casting model

Eckert, S.; Gerbeth, G.; Miao, X.; Stefani, F.; Timmel, K.; Wondrak, T.

In this paper we present the new experimental facility LIMMCAST for modeling the continuous casting process of steel by using the low melting point alloy SnBi. The facility operates at temperatures of 200°C-400°C. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. First experimental results will be presented which have been obtained using a small-scale preliminary set-up with the room temperature alloy GaInSn. Measurements of the liquid flow in the mold will be compared with accompanying numerical calculations. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the submerged entry nozzle (SEN) has been studied.

Keywords: continuous casting; mould flow; liquid metal model; flow measurements; electromagnetic brake

  • Invited lecture (Conferences)
    The 6th Japan-France Seminar on Electromagnetic Processing of Materials, 19.-22.05.2010, Hakone, Japan
  • Contribution to proceedings
    The 6th Japan-France Seminar on Electromagnetic Processing of Materials, 19.-22.05.2010, Hakone, Japan
    Electromagnetic Processing of Materials - Development of New Fields and Applications, 1-10

Publ.-Id: 14046

Luminescence spectroscopy characterization of uranium(VI) at low temperature

Steudtner, R.; Günther, A.; Geipel, G.; Bernhard, G.; Brendler, V.

Cryogenic techniques in laser spectroscopy are currently used in scanning tunnelling microscopy (STM) and single molecule spectroscopy. Recently such cryogenic devices have also been adapted to time resolved laser-induced fluorescence spectroscopy (TRLFS) systems applied to uranium. We used TRLFS at low temperatures (cryo-TRLFS) as an experimental technique to investigate the uranium(VI) complexation with a variety of organic ligands (glucose, citric acid, oxalic acid). For the first time, luminescence properties were determined for a uranium(VI) glucose complex [1], uranium(VI) citrate [2] and uranium(VI) oxalate [2] species by cryo-TRLFS at 153 K. The emission signals are bathochromic shifted in comparison to the emission maxima of the uncomplexed uranyl(VI) cation. Using the spectroscopic data, the corresponding complex formation constants were calculated. This is a great improvement towards TRLFS measurements at room temperature, where emission signals of the complex species are not detectable. Our TRLFS investigation at low temperature opens up new possibilities for the determination of complex formation constants since interfering quenching effects often encountered at room temperature condition are suppressed. In addition we used cryo-TRLFS technique for studying uranium(VI) speciation in natural samples. The uranium(VI) speciation in urine and in mineral water [3] could be thus investigated. Samples with an uranium concentration of < 0.1 μg/L could be analyzed unproblematically. The complexation of uranium(VI) with carbonate in commercial mineral waters could be verified. In urine, it was found that the uranium(VI) speciation strongly depends on the pH, with the latter varied between 5 and 7 as observed in human samples. Up to pH value of 6 the uranium(VI) speciation is defined mostly by organic ligands. At higher pH the uranium(VI) speciation should be dominated by inorganic phosphate complexes or carbonate complexes. The fluorescence spectroscopic analysis showed a mixture of complexation by citrate and phosphate at lower pH (< 6) and at higher pH (> 6) an dominance of complexation by carbonate. This results are in a very good correspondence with model calculation of the uranium(VI) speciation in urine.

Keywords: uranium(VI); glucose; citric acid; oxalic acid; urine; mineral water; cryo-TRLFS

  • Lecture (Conference)
    3rd EuCheMS Chemistry Congress, 29.08.-02.09.2010, Nürnberg, Deutschland

Publ.-Id: 14045

Enhancement of ferromagnetism in Ni-implanted HfO2 dielectric thin films

Sharma, M. K.; Kanjilal, A.; Voelskow, M.; Kanjilal, D.; Chatterjee, R.

We report thermal annealing and 100 MeV Si8+ swift heavy ion irradiation effects on the structural and magnetic properties of Ni-implanted HfO2 thin films. At low Ni doping concentration (1%), HfO2 thin films show ferromagnetic behavior. We clearly demonstrate the cluster free nature of our film using cross-sectional high resolution transmission microscopy and magnetization vs. temperature data. Rutherford backscattering spectrometry is used to estimate the film thickness and to establish that Ni-ions are placed in the HfO2 matrix. By comparing the results for the annealed and swift heavy ion irradiated samples, it is concluded that the enhancement in magnetic signal is closely related to the dispersion/diffusion of implanted Ni and defect creation such as oxygen vacancies. The results of magnetic force microscopy supported the observation of room temperature ferromagnetism in Ni-implanted HfO2 films.

Keywords: Ferromagnetism; Ion-implantation; Rutherford backscattering spectrometry; Sputtering; Hafnium dioxide

Publ.-Id: 14044

Simulating the bioavailability of carbon nanotubes

Gemming, S.; Seifert, G.; Enyashin, A. N.

Carbon nanotubes (CNTs) are structurally well-defined, chemically inert and electrically conducting or semi-conducting fibers which have extensively been explored for medical applications as active components such as antibacterial agents or electric conductors, as templates for cell growth, drugs and magnetic probes or as sensors. Recently, the enhanced antibacterial activity of dispersed single-wall CNTs was successfully related to the piercing of the bacterial cell membranes by the CNTs [1]. Solution-spun composite fibers from CNTs and DNA have proven their suitability as electrically conducting scaffolds, which target muscle or nerve repair [2]. Regularly aligned CNTs are efficient and inert templates for the growth and proliferation of human osteoblasts [3]. Cancer treatment relies on the ability of CNTs to specifically deliver anti-cancer agents and on the hyperthermal effect induced by magnetically doped CNTs in an oscillating magnetic field [4] CNT-based sensors exhibit an exceptional specificity for measuring electronic properties of small biological structures [5]. Here we focus on the functionalization of CNTs by DNA molecules; we present an analysis of the nanoscale CNT-DNA interactions and the immobilization of such aggregates on oxidic surfaces.

Materials and Methods
Carbon nanotubes embedded in single-stranded DNA (CNT@DNA) were investigated by self-consistent density-functional-based tight-binding calculations (DFTB). A phenomenological model for the stability was derived, which gives the CNT-DNA interaction energy as a function of the nanotube radii and the number of DNA chains [6]. To study anchoring such aggregates on scaffold materials we analyze the interactions which bond the nucleotide to oxidized surfaces by DFTB calculations [7].

Results and Discussion
Single CNTs are readily complexed by DNA, but for CNT bundles an essential energy gain is only obtained, if multiple DNA chains wrap around the tubes. Hence, the destruction of the CNT bundles, e.g. by sonication, can promote the CNT@DNA complex formation. Pyrimidine-based homopolymeric DNA more effectively wraps the CNT, whereas purine-based DNA exhibits a larger radius selectivity. The CNT-DNA interaction is not a genuine van-der-Waals interaction. The electronic structure of most aggregates is close to a superposition of the electronic states of the “free” DNA and CNT fragments. However, within a small structural window there exist several very strongly bonding systems which are characterized by combined electronic states. Hence, magic matching occurs in conjunction with a remarkable charge transfer (Fig. 1).
While the DNA-CNT interaction involves the aromatic part of the DNA immobilization of suchsystems on oxidic surfaces occurs mainly via the phosphate group. The preferred anchoring on titania and alumina [7,8] relies on bonding two oxygen atoms of the phosphate group to the surface by esterification. The resulting structures are stable against solvatation.

Keywords: DNA; CNT; carbon nanotubes; DFTB; DFT

  • Invited lecture (Conferences)
    12th International and Interdisciplinary NRW Symposium Biomaterials and Biomechanics, 17.-19.03.2010, Essen, Deutschland

Publ.-Id: 14043

Electronic structure and magnetism in YFeMnO5

Weißbach, T.; Leisegang, T.; Lubk, A.; Meyer, D. C.; Gemming, S.

YFeMnO5 crystallizes in the structure type of the orthorhombic RMn2O5 class of oxides. These show a series of antiferromagnetic phases with propagation vectors (1/2-δ, 0, 1/4+є) below TN ≈ 45 K. For several of these phases, magnetism coexists with ferroelectricity. In YFeMnO5, only one commensurable ferrimagnetic phase was found below TN = 165 K, and ferroelectricity is absent. We apply crystallographic and quantum chemical methods to compare the Fe-substituted and the mangenese-only compounds. Diffraction experiments show slight displacements of the atom sites with increasing Fe content. The largest effects are related to crystal-field repulsion acting on the local metal 3d orbitals. The interaction between the magnetic metal ions is studied using DFT calculations starting with a bias magnetization of the atoms.

Keywords: magnetism; ferroicity; multiferroic; manganite; DFT; XRay; Heisenberg; Ising

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 14042

Polarization dependent Diffraction Anomalous Fine Structure of rutile TiO2 001 and 111 reflections

Zschornak, M.; Richter, C.; Stöcker, H.; Leisegang, T.; Gemming, S.; Meyer, D. C.

Energy and polarization dependent Diffraction Anomalous Fine Structure (DAFS) also known as Anisotropic Anomalous Scattering (AAS) can be employed in addition to X-ray Absorption Fine Structure (XAFS) to study electronic transitions from core states to unoccupied states. Here, we present results from resonant X-ray diffraction experiments on TiO2 rutile, space group (136) P42/mnm. For this model structure, site symmetry information was extracted from determination of the structure factor tensor by refining elements of Ti atomic scattering factor tensors. Influences of oxygen vacancies on the anomalous scattering contributions have been studied on a series of rutile wafers of different oxygen concentration. Samples investigated were 10 × 10 × 1 mm3 single crystal wafers and experiments were carried out at DESY/HASYLAB beamlines C and E2 using a Si (111) double crystal monochromator in the vicinity of the Ti-K absorption edge. Considered reflections include the ‘forbidden’ 001 and allowed 111 reflection.

Keywords: diffraction; DAFS; anomalous fine-structure; TiO2; rutile; XAFS; X-ray Absorption Fine Structure

  • Lecture (Conference)
    DPG-Frühjahrstagung, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 14041

DFT modelling of SrO(SrTiO3)n Ruddlesden-Popper surfaces

Zschornak, M.; Gutmann, E.; Weißbach, T.; Leisegang, T.; Meyer, D. C.; Gemming, S.

Strontium titanate (SrTiO3) is an oxide crystallizing with cubic perovskite-type of structure that exhibits a high tunability of dielectric, electric, mechanical and optical properties by means of defects. Apart from dopants, also intrinsic oxygen vacancies or ordered stacking faults, e.g. Ruddlesden-Popper (RP) phases SrO(SrTiO3)n, may influence these properties.
We have investigated the surface energy, relaxation and electronic properties of such RP surfaces up to n = 3 in comparison to ’pure’ SrTiO3 by means of density-functional theory for ⟨ 001⟩ and ⟨ 100⟩ directions and with all possible perfect crystal terminations. We find a significant influence of the surface-near SrO-OSr stacking fault on surface energies and rumpling. Migrating surface states decrease the band gap of TiO2 terminations but all terminations show insulating character. A detailed discussion of surface-near relaxations will be presented.

Keywords: SrTiO3; STO; Strontium titanate; Ruddlesden-Popper; DFT; surface

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 14040

Spectroscopic and Theoretical Investigations on Pd(II) and Pt(II) Dithiocarbamates

Wenisch, R.; Forrer, D.; Gross, S.; Casarin, M.; Montagner, D.; Vittadini, A.; Helm, M.; Tondello, E.; Gemming, S.

In coordination chemistry, the nature and strength of the metal-ligand interaction has attracted much interest. Metal-sulfur complexes, in particular in comparison with their oxygen-based analogues, are intriguing as the sulfur atoms are polarized more easily. The use of specifically tailored sulfur-based ligands allows for tuning the complex functional properties. Among them, electronic properties are very sensitive to changes in the sulfur coordination sphere, suggesting potential uses as molecular switches in optoelectronic devices. Metal dithiocarbamates [R2NCS2]lM have been extensively studied by IR and UV-vis. spectroscopy, ESR and to a limited extent XPS and UPS. Here, we present experimental and theoretical studies investigating the electronic properties of a series of dithiocarbamates of Pd(II) and Pt(II): the pyrrolidine-based one and the 1-pyrrolidinecarbodithioate methyl ester (PyDTM). MX2(PyDTM) (M=Pt/Pd; X=Cl/Br) were analyzed by XPS and by FT-IR spectroscopy. DFT calculations yielded details on the electronic structure and allowed for unambiguous assignment of the IR spectral features. Ionization energies were evaluated with the asymptotically correct LB94 potential and the two components ZORA.

Keywords: molecular aggregates; cis-Platin; optical spectroscopy; ESR; DFT; cis-Palladium; IR

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Dresden, Deutschland

Publ.-Id: 14039

The influence of helium and ODS on the irradiation-induced hardening of Eurofer97 at 300°C

Heintze, C.; Bergner, F.; Koegler, R.; Lindau, R.

The influence of helium on the mechanical properties of reduced-activation ferritic/martensitic Cr-steels under fusion-relevant irradiation conditions is still a concern. While the fact that He can influence the mechanical properties is well established [1,2], the underlying mechanisms are not fully understood [1,2]. In this work the effect of He and displacements per atom (dpa) on the irradiation-induced hardening of Eurofer97 at 300°C was studied. Self-ion irradiation was applied to simulate the neutron-irradiation-induced damage. Helium was implanted prior to (pre-implantation), simultaneously (dual-beam irradiation) or following the (post-implantation) self-ion irradiation to investigate the He effect. Nanoindentation was used in order to characterize the damage layer. Under the present conditions (300°C, 1 dpa, 10 appmHe) the observed hardening increased in the following order: single-beam Fe-ion irradiation/pre-implantation < simultaneous implantation < post-implantation. We conclude, that there is a significant interaction between damage and He.
Additionally, Eurofer97 and ODS-Eurofer were irradiated with Fe ions up to 1 and 10 dpa to study the effect of the oxide particles on the irradiation-induced hardening. We have found a higher irradiation-induced hardening at 1 dpa for ODS-Eurofer but a steeper hardness increase per dpa up to 10 dpa for Eurofer97.

Keywords: Nanoindentation; Dual-beam irradiation; ODS; Eurofer

  • Contribution to proceedings
    CIMTEC 2010, 5th Forum on New Materials, 13.-18.06.2010, Montecatini Terme, Italia
    5th Forum on Materials Part B: Trans Tech Publications Ltd, 124-129
  • Poster
    CIMTEC 2010, 5th Forum on New Materials, 13.-18.06.2010, Montecatini Terme, Italia

Publ.-Id: 14038

Influence of N*-resonances on hyperon production in the channel pp --> K+ Lambda p at 2.95, 3.20 and 3.30 GeV/c beam momentum

Cosy-Tof-Collaboration; Abd El-Samad, S.; Michel, P.; Möller, K.; Naumann, L.; Schamlott, A.

Hyperon production in the threshold region was studied in the reaction pp -> K+ Lambda p using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at the three different beam momenta of pbeam = 2.95, 3.20 and 3.30GeV/c, corresponding to excess energies of epsilon = 204, 285 and 316MeV, respectively. Total cross-sections were deduced for the three beam momenta to be 23.9 ± 0.8 ± 2.0 μb, 28.4 ± 1.3 ± 2.2 μb and 35.0 ± 1.3 ± 3.0 μb. Differential observables including Dalitz plots were obtained. The analysis of the Dalitz plots reveals a strong influence of the N(1650)-resonance at pbeam = 2.95GeV/c, whereas for the higher momenta an increasing relative contribution of the N(1710)- and/or of the N(1720)- resonance was observed. In addition, the p Lambda-final-state interaction turned out to have a significant influence on the Dalitz plot distribution

Keywords: Associated strangeness production; Total cross-section; Dalitz plot

  • Physics Letters B 688(2010), 142

Publ.-Id: 14037

Submarine hydrothermal activity and gold-rich mineralization at Brothers Volcano, Kermadec Arc, New Zealand.

de Ro; Massoth, G. J.; Butterfield, D. A.; Christenson, B. W.; Ishibashi, J.; Ditchburn, R. G.; Hannington, M. D.; Brathwaite, R. L.; Lupton, J. E.; Kamenetsky, V. S.; Graham, I. J.; Zellmer, G. F.; Dziak, R. P.; Embley, R. W.; Dekov, V. M.; Munnik, F.; Lahr, J.; Evans, L. J.; Takai, K.

Brothers volcano, of the Kermadec intraoceanic arc, is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world. It has two distinct vent fields, known as the NW caldera and cone sites, whose geology, permeability, vent fluid compositions, mineralogy and ore forming conditions are in stark contrast to each other. The NW caldera site strikes for ~600 m in a SW-NE direction with chimneys occurring over a ~145 m depth interval, between ~1,690 and 1,545 m. At least 100 dead and active sulfide chimney spires occur in this field, as seen during manned submersible dives, and are typically 2-3 m in height, although locally reach 6-7 m. Their ages fall into three groups: 0-4 years (at time of sampling), 23 and 35 years old. The chimneys typically occur near the base of individual fault-controlled benches on the caldera wall, striking in lines orthogonal to the slopes. More rare are massive sulfide crusts up to 2-3 m thick. Two main types of chimney predominate: Cu-rich chimneys (with parts up to 28.5 wt.% Cu) and more commonly, Zn-rich chimneys (up to 43.8 wt.% Zn). Geochemical results indicate a "magmatic" suite of elements associated with the Cu mineralization, including up to 91 ppm Au, and an ‘epithermal’ suite of elements with the dominant Zn-rich chimneys. The cone site comprises the Upper cone site atop the summit of the recent (main) dacite cone, and the Lower cone site that straddles the summit of an older, smaller, more degraded dacite cone on the NE flank of the main cone. Huge volumes of diffuse venting are seen at the Lower cone site, in complete contrast to venting at both the Upper cone and NW caldera sites. Individual vents are marked by low relief (≤0.5 m) mounds comprised predominately of native sulfur with bacterial mats. Vent fluids of the NW caldera field are focused, hot (≤300°C), acidic (pH ≥ 2.8), metal-rich and relatively gas-poor. Calculated end-member fluids from various NW caldera vents indicate phase-separation has occurred with Cl values ranging from 93% to 137% seawater values. By contrast, vent fluids for the cone site are diffuse, noticeably cooler (≤122°C), very acidic (to pH = 1.86), relatively metal-poor and very gas-rich. Higher-than-seawater values of SO4 and Mg in the cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water/rock interactions. Three year old Fe-oxide crusts covering the main cone summit appear to have formed from Fe-rich brines. Evidence for magmatic contributions to the hydrothermal system at Brothers includes: high concentrations of dissolved CO2 (e.g., 206 mM/kg at the cone site), high CO2/3He values, negative δD and δ18OH2O values for vent fluids, negative δ34S values for sulfides (to -4.6‰), sulfur (to -10.2‰) and δ15N2 (to -3.5‰), vent fluid pH values to -1.9 and mineral assemblages of chalcopyrite, bornite, chalcocite, covelllite and euhedral grains of hematite. Changing physio-chemical conditions at the Brothers hydrothermal system, and especially the cone site, occur over months to hundreds of years, as shown by interlayed Cu/Au- and Zn-rich zones in chimneys, variable fluid and isotopic compositions between vents, similar shifts in 3He/4He values for both cone and NW caldera sites, and overprinting of "magmatic" mineral assemblages by water/rock dominated ones. Metals, especially Cu and possibly Au, may be entering the hydrothermal system via the dissolution of metal-rich glasses. They are then transported rapidly up into the system via magmatic volatiles utilizing vertical (~2.5 km long), narrow (~300 m diameter) "pipes", consistent with evidence of vent fluids forming at higher than hydrostatic pressures, at relatively shallow depths. The NW caldera and cone sites are considered to represent stages along a continuum between magmatic-hydrothermal and water/rock-dominated end-members.

Publ.-Id: 14036

Modellexperimente mit Flüssigmetallen

Gundrum, T.; Kretzschmar, N.; Leege, K.-W.; Stefani, F.; Timmel, K.; Wondrak, T.; Gerbeth, G.; Herbrand, F.

Eine Übersicht über das Forschungszentrum und die Abteilung Magnetohydrodynamik soll die Zuhörer auf die Aufgaben für die Prozessautomation in der Forschung einstimmen. Die Prozessautomation bei Modellexperimenten mit Flüssigmetallen ist mannigfaltig und weicht durch die Versuchsanordnung stark von einer industriellen Prozessautomation ab. Hardwareseitig werden PC's und ADSP Systeme eingesetzt. Angepasst an vorhandenes Know-How werden die Systeme mit Fortran, C++, LabView und AdBasic programmiert. Anhand des Rigaer Dynamo Experimentes, der kontaklosen Strömungstomografie (CIFT) und der Strangguss-Modellanlage (LIMMCAST) wird der Herangehensweise und Ergebnisse erleutert.


  • Invited lecture (Conferences)
    5. Technologietag Prozessautomation, 06.05.2010, Chemnitz, Deutschland

Publ.-Id: 14035

Correlation of structure and conductance in nanowires and nanotubes

Gemming, S.

In nanostructured materials spatial confinement effects lead to structure-dependent deviations from the bulk transport properties. Such modifications may in part be accounted for by classical transport simulations, but a microscopically more detailed and mostly parameter-free picture is obtained from quantum-mechanical density-functional theory (DFT). DFT calculations yield the atom arrangement and electronic structure of nanotubes and nanowires in the electronic ground state. Additionally, an extension by a Green’s function formalism leads to the determination and analysis of electronic transport through contacted nanostructures. A combination of both approaches allows to correlate structural and transport properties of nanostructures. The applicability of this approach will be demonstrated for a mechanically triggered metal-insulator transition in nanowires.
Kibsgaard et al. Nano Lett 8 (2008) 3928; [2] Popov et al. Nano Lett 8 (2008) 4093.

Keywords: nanotubes; nanowires; crystallography; DFT; transition metal chalcogenides; MoS; molybdenum sulfide

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 14034

Modeling the morphogenesis of brine channels in sea ice

Kutschan, B.; Morawetz, K.; Gemming, S.

Brine channels are formed in sea ice under certain constraints and represent a habitat of different microorganisms. The complex system depends on a number of various quantities as salinity, density, pH-value or temperature. Each quantity governs the process of brine channel formation. There exists a strong link between bulk salinity and the presence of brine drainage channels in growing ice with respect to both the horizontal and vertical planes. We develop a suitable phenomenological model for the formation of brine channels both referring to the Ginzburg-Landau-theory of phase transitions as well as to the chemical basis of morphogenesis according to Turing. It is possible to conclude from the critical wavenumber on the size of the structure and the critical parameters. The theoretically deduced transition rates have the same magnitude as the experimental values. The model creates channels of similar size as observed experimentally. An extension of the model towards channels with different sizes is possible. The microstructure of ice determines the albedo feedback and plays therefore an important role for large-scale global circulation models (GCMs).

Keywords: structure formation; differential equations; Landau; brine channels; reaction-diffusion system

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland
  • Physical Review E 81(2010), 036106
    DOI: 10.1103/PhysRevE.81.036106
  • Poster
    DPG Frühjahrstagung, 26.03.-30.06.2012, Berlin, Deutschland

Publ.-Id: 14033

Low-temperature modelling for degenerate and frustrated Heisenberg systems with anisotropy

Gemming, S.; Schreiber, M.; Kunze, T.; Numazawa, S.

Thermodynamic equilibration of complex systems like spin glasses or (degenerate) anisotropic spin crystals by numerical methods can be challenging due to the presence of multiple minima on the potential energy surface. This problem becomes pronounced especially at low temperature, where the system remains mainly in few states. We employ the anisotropic Heisenberg model in two dimensions to simulate and analyze the domain formation and the domain structure of multiferroic oxides. In particular, we discuss various techniques to improve the low-temperature equilibration behavior by means of a trigonal antiferromagnet with single-ion anisotropy. Furthermore, we present a localized sampling method for the Metropolis algorithm, which increases the acceptance ratio significantly.

Keywords: Monte-Carlo; Heisenberg; frustrated magnetism; Metropolis; importance sampling; multiferroics

  • Poster
    Perspectives in Highly Frustrated Magnetism, 19.-23.04.2010, Dresden, Deutschland

Publ.-Id: 14032

Systematic study of the pp -> pp omega reaction

Abdel-Bary, M.; Abdel-Samad, S.; Brinkmann, K.; Clement, H.; Dietrich, J.; Doroshkevich, E.; Dshemuchadse, S.; Ehrhardt, K.; Erhardt, A.; Eyrich, W.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Gast, W.; Gillitzer, A.; Gottwald, J.; Jager, H.; Jakob, B.; Jakel, R.; Karsch, L.; Kilian, K.; Koch, H.; Krapp, M.; Kress, J.; Kuhlmann, E.; Lehmann, A.; Marcello, S.; Mauro, S.; Michel, P.; Moller, K.; Morsch, H.; Naumann, L.; Paul, N.; Pizzolotto, C.; Plettner, C.; Reimann, S.; Richter, M.; Ritman, J.; Roderburg, E.; Schamlott, A.; Schonmeier, P.; Schroeder, W.; Schulte-Wissermann, M.; Sefzick, T.; Steinke, M.; Sun, G.; Teufel, A.; Ullrich, W.; Wagner, G.; Wagner, M.; Wenzel, R.; Wilms, A.; Wintz, P.; Wustner, P.; Zupranski, P.

A systematic study of the production of omega-mesons in proton-proton-collisions was carried out in a kinematically complete experiment at three excess energies (epsilon= 92, 128, 173 MeV). Both protons were detected using the large-acceptance COSY-TOF spectrometer at an external beam line at the Cooler Synchrotron COSY at Forschungszentrum J¨ulich. The total cross section, angular distributions of both omega-mesons and protons were measured and presented in various reference frames such as the overall CMS, helicity and Jackson frame. In addition, the orientation of the omega-spin and invariant mass spectra were determined. We observe !-production to take place dominantly in Ss and Sp final states at epsilon = 92, 128 MeV and, additionally, in Sd at epsilon = 173 MeV. No obvious indication of resonant omega-production via N*- resonances was found, as proton angular distributions are almost isotropic and invariant mass spectra are compatible with phase space distributions. A dominant role of 3P1 and 1S0 initial partial waves for omega-production was concluded from the orientation of the decay plane of the !-meson. Although the Jackson angle distributions in the omega-p-Jackson frame are anisotropic we argue that this is not an indication of a resonance but rather a kinematical effect reflecting the anisotropy of the omega angular distribution. The helicity angle distribution in the omega-p-helicity frame shows an anisotropy which probably reflects effects of the omega angular momenta in the final state; this observable may be, in addition to the orientation of the omega decay plane, the most sensitive one to judge the validity of theoretical descriptions of the production process.

Keywords: Nucleon-nucleon interactions; Polarization in interactions and scattering; Other mesons with S=C=0, mass < 2.5 GeV; Nuclear reactions involving few-nucleon systems; Other reactions above meson production thresholds (energies > 400 MeV)

  • European Physical Journal A 44(2010), 7

Publ.-Id: 14031

Cobalt(II) "Scorpionate" Complexes as Models for Cobalt-Substituted Zinc Enzymes: Electronic Structure Investigation by High-Frequency and -Field Electron Paramagnetic Resonance Spectroscopy

Krzystek, J.; Swenson, D. C.; Zvyagin, S. A.; Smirnov, D.; Ozarowski, A.; Telser, J.

A series of complexes of formula Tp(R,R')CoL, where Tp(R,R'-) = hydrotris(3-R,5-R'-pyrazol-1-yl)borate ("scorpionate") anion (R = tert-butyl, R' = H, Me, 2'-thienyl (Tn), L = Cl-, NCS-, NCO-, N-3(-)), has been characterized by electronic absorption spectroscopy in the visible and near-infrared (near-IR) region and by high-frequency and -field electron paramagnetic resonance (HFEPR). Reported here are also crystal structures of seven members of the series that have not been reported previously: R' = H, L = NCO-, N-3(-); R' = Me, L = Cl-, NCS-, NCO-, N-3(-); R' = Tn, L = Cl-, NCS-. These include a structure for Tp(t-Bu,me)CoCl different from that previously reported. All of the investigated complexes contain a four-coordinate cobalt(II) ion (3d(7)) with approximate C-3v point group symmetry about the metal ion and exhibit an S = 3/2 high-spin ground state. The use of HFEPR allows extraction of the full set of intrinsic S = 3/2 spin Hamiltonian parameters (D, E, and g values)!The axial zero-field splitting parameter, D, for all investigated Tp(R,R')CoL complexes is always positive, a fact not easily determined by other methods. However, the magnitude of this parameter varies widely: 2.4 cm(-1)<= D<= 12.7 cm(-1), indicating the extreme sensitivity of this parameter to environment. The spin Hamiltonian parameters are combined with estimates of 3d energy levels based on the visible-near-IR spectra to yield ligand-field parameters for these complexes following the angular overlap model (AOM). This description of electronic structure and bonding in pseudotetrahedral cobalt(II) complexes can enhance the understanding of similar sites in metalloproteins, specifically cobalt-substituted zinc enzymes.

  • Journal of the American Chemical Society 132(2010)14, 5241-5253

Publ.-Id: 14030

Defects in a nitrogen-implanted ZnO thin film

Schmidt, M.; Ellguth, M.; Schmidt, F.; Lüder, T.; von Wenckstern, H.; Pickenhain, R.; Grundmann, M.; Brauer, G.; Skorupa, W.

Defects in a nitrogen implanted and thermally annealed zinc oxide thin film (n-type conducting) and reference samples were studied. Space charge regions realised by fabrication of semitransparent palladium Schottky contacts enabled the application of capacitance spectroscopic methods and photo - current measurements. We report on the formation of a deep level, in the following labelled TN1. It is 580 meV below the conduction band edge, probably related to nitrogen, and must be distinguished from the well known intrinsic deep level E4 at almost equal energetical depth. Capacitance measurements in combination with optical excitation, conducted at different temperatures, as well as photo-current measurements revealed the existence of two states approximately 60 meV and 100 meV above the valence band edge for the nitrogen implanted sample. These states cause an acceptor compensation degree larger than 0.9. The thermal emission of holes from these states into the valence band was observed by optical deep level transient spectroscopy.

  • Physica Status Solidi (B) 247(2010)5, 1220-1226

Publ.-Id: 14029

Numerical and experimental modelling of various MHD induction pumps

Khripchenko, S.; Khalilov, R.; Kolesnichenko, I.; Denisov, S.; Galindo, V.; Gerbeth, G.

This paper considers three variants of MHD induction pumps a centrifugal magnetovortex pump, a transformer type pump with magnetic asymmetry and a travelling field pump All these pumps have a flat channel placed between the poles of one or several ferromagnetic cores inducing an alternating magnetic field directed normally to the channel plane To describe electromagnetic forces generated in the pump channel, a mathematical model is proposed The results of numerical and physical experiments ale presented.

Keywords: mhd induction pumps

  • Magnetohydrodynamics 46(2010)1, 85-97

Publ.-Id: 14028

Ion beam induced ferromagnetism in semiconductors

Potzger, K.

Recently, research on diluted magnetic semiconductors (DMS) became very popular due to their large potential in future spintronics devices like spin valves or current-induced magnetic switches. Mostly, transition metal doped classical semiconductors like Si, Ge or GaAs as well as oxides have been investigated. The research faces, however, serious difficulties due to the appearance of tiny magnetic secondary phases, spinodal decomposition or magnetically active defects in the semiconductor induced by the implantation/oversaturation. It was found that those effects lead to ferromagnetic as well as magneto-transport properties which, by mistake, could be interpreted as intrinsic DMS. In this paper, I will focus on the discussion of pitfalls during magnetic and structural analysis, especially on element-specific analysis methods for the identification of the source of the ferromagnetic signal. Moreover, possibilities to overcome those difficulties will be presented.

Keywords: diluted magnetic semiconductors; ion implantation

  • Invited lecture (Conferences)
    International Conference on Nanoscale Magnetism ICNM-2010, 28.09.-02.10.2010, Istanbul, Türkei
  • Invited lecture (Conferences)
    VIII-th International Conference ION 2010, 14.-17.06.2010, Kazimierz Dolny, Polen
  • Invited lecture (Conferences)
    17th International Conference on Ion Beam Modification of Materials (IBMM), 22.-27.08.2010, Montreal, Kanada

Publ.-Id: 14027

Untersuchung von Redoxprozessen von Uranyl-Verbindungen mit Flavonoiden

Drewitz, S.

Durch den Uranbergbau entstanden in Sachsen und Thüringen eine Vielzahl von Gruben, Abfallhalden und Absetzanlagen, aus denen beispielsweise über Sickerwasser das Schwermetall in die Umwelt gelangen konnte. Böden wurden kontaminiert und das Actinoid kann von Pflanzen aufgenommen werden. Um Erkenntnisse über die Migration und Wirkung des Urans gewinnen zu können, ist es notwendig die Wechselwirkung mit einzelnen Pflanzenstoffen zu untersuchen.
Im Mittelpunkt dieser Arbeit stand die Untersuchung von in vitro-Wechselwirkungen des in Pflanzen weitverbreiteten Flavonoids Quercetin mit Uranverbindungen. Insbesondere sollte überprüft werden, ob eine Reduktion des Uranyl zu Uran(IV) stattfindet. Im Allgemeinen besitzt vierwertiges Uran gegenüber dem sechswertigen Uran eine sehr geringe Löslichkeit, dies führt zu einer Immobilisierung des Urans.
Zur Charakterisierung des Reduktionsvermögens wurde das Redoxpotential des Polyphenols in Abhängigkeit vom pH-Wert in dem für die nachfolgenden Versuche verwendeten Lösungsmittel (50 % Methanol) bestimmt. Hierbei wurde ein linearer Zusammenhang zwischen pH 3,3 und 8,3 festgestellt: E = (-69 ± 3) mV * pH + (616 ± 7) mV bestimmt gegen Silber-Silberchlorid-Elektrode. Somit weist Quercetin bei steigendem pH-Wert ein zunehmendes Reduktionsvermögen auf.
Es erfolgte zudem die Bestimmung der Stabilitätskonstante des Komplexes zwischen Uran(IV) und Quercetin bei einem pH-Wert von 5,8 in 50 % Methanol im carbonatfreien System unter Inertgasbedingungen (Modellkomplexierung). Die Stabilitätskonstante wurde mittels UV/Vis-Spektroskopie zu log10β1:3:1 = 20,36 ± 0,18 bestimmt. Durch diese starke Komplexbildung wird auch die Löslichkeit der sonst schwerer löslichen Uran(IV)-Spezies erhöht. Dieser Komplex ist zudem stabiler als der Uranyl-Quercetin-Komplex (log10β1:3:1 = 13,8 [1]). Dies bedeutet, dass durch die Komplexbildung eine Erhöhung des Redoxpotentials des Redoxpaares U(VI)│U(IV) vorliegt und somit bei der Koordination des Uranyls mit Quercetin eine Reduktion des Metall-Ions leichter möglich ist.
Es galt weiterhin zu prüfen, ob ein Redoxprozess zwischen Quercetin und Uranyl in vitro bei pH 5,8 bzw. pH 7,0 in 50 % Methanol unter Inertgasbedingungen stattfindet. Eine Reduktion des Uranyl-Ions führt zur Bildung von Uran(IV), der stabilsten reduzierten Oxidationsstufe des Urans. Vierwertiges Uran konnte mittels laserinduzierter photoakustischer Spektroskopie (LIPAS), durch die Komplexbildung mit Arsenazo III bzw. durch die Extraktion mit 2-Thenoyltrifluoraceton (TTA) nachgewiesen werden. Es wurde mithilfe der genannten Methoden bestimmt, dass der Umsatz von Uranyl zu Uran(IV) durch das Reduktionsmittel Quercetin im Prozentbereich liegt.

[1] Viehweger, K. & Geipel, G. (2009) Report FZD-511 p. 41

Keywords: flavonoids; quercetin; uranium(IV); uranyl; reduction

  • Other report
    TU Dresden: Wissenschaftliche Abschlussarbeit (Studiengang Lebensmittelchemie), 2010
    74 Seiten

Publ.-Id: 14026

Microstructure, electrical, magnetic, and extraordinary Hall effect studies in Ni:SiO2 nanogranular films synthesized by atom beam sputtering

Kumar, H.; Gosh, S.; Bürger, D.; Zhou, S.; Kabiraj, D.; Avasthi, D. K.; Grötzschel, R.; Schmidt, H.

In this work we report on the synthesis of Ni:SiO2 nanogranular films with different metal fraction 0.10 < x < 0.68 and a homogeneous distribution of Ni particles by atom beam sputtering technique and on the study of their microstructure, electrical transport, magnetic properties, and on the observation of extraordinary Hall effect (EHE). Films with the Ni fraction x above percolation threshold x > 0.58 > xp as revealed by resistivity versus temperature measurements have a large Ni particle size, pronounced ferromagnetic characteristics, and appreciable extraordinary Hall resistivity at 300 K. Furthermore, films above percolation have a relatively low, nearly temperature independent Ohmic resistivity smaller than 10E−3 Ohm cm and may be useful for Hall sensor applications. On the other hand, films below percolation threshold x < 0.54 < xp have a small Ni particle size, superparamagnetic behavior, and do not show EHE at 300 K. However, at 5 K all films show ferromagnetic characteristics with an enhanced EHE.

  • Journal of Applied Physics 107(2010)11, 113913

Publ.-Id: 14025

Cluster spin glass behavior in Bi(Fe0.95Co0.05)O3

Xu, Q.; Zhou, S.; Wu, D.; Uhlarz, M.; Tang, Y.; Potzger, K.; Xu, M.; Schmidt, H.

The static and time-dependent magnetic properties of Bi(Fe0.95Co0.05)O3 have been investigated by dc and ac magnetization measurements. Cluster spin glass has been confirmed to be the ground state due to the frustration of the interaction between the ferromagnetic clusters by canted antiferromagnetically arranged Fe spins (Tc > 350 K) and by ferrimagnetically arranged Co and Fe spins (Tc ~ 250 K). Two freezing temperatures Tf of about 260 K and 100 K have been clearly identified from the abrupt change in magnetization relaxation. The higher Tf is related to the canted antiferromagnetically arranged Fe spins, and the lower Tf is related to the ferrimagnetically arranged Co and Fe spins. The cluster spin glass behavior with two freezing temperatures has been confirmed by ac susceptibility measurements.

Publ.-Id: 14024

The importance of hole concentration in establishing carrier-mediated ferromagnetism in Mn doped Ge

Zhou, S.; Bürger, D.; Skorupa, W.; Oesterlin, P.; Helm, M.; Schmidt, H.

In the present work, we have prepared Mn-doped Ge using different annealing approaches after Mn ion implantation, and obtained samples with hole concentrations ranging from 1018 to 2.1$\times$1020 cm-3, the latter being the highest reported so far. Based on the magneto-transport properties of Mn doped Ge, we argue that the hole concentration is a decisive parameter in establishing carrier-mediated ferromagnetism in magnetic Ge.

Keywords: Diluted magnetic semiconductor; Ge; ion implantation

Publ.-Id: 14023

Hysteresis in the magnetotransport of manganese-doped germanium: Evidence for carrier-mediated ferromagnetism

Zhou, S.; Bürger, D.; Mücklich, A.; Baumgart, C.; Skorupa, W.; Timm, C.; Oesterlin, P.; Helm, M.; Schmidt, H.

We report the fabrication of Ge:Mn ferromagnetic semiconductors by Mn-ion implantation into Ge followed by pulsed laser annealing. Benefiting from the short time annealing, the hole concentration in Mn-implanted Ge has been increased by two orders of magnitude from 1018 to over 1020 cm−3. Likely due to the high hole concentration, we observe that the longitudinal and Hall resistances exhibit the same hysteresis as the magnetization, which is usually considered as a sign of carrier-mediated ferromagnetism.

Keywords: Diluted magnetic semiconductor; Ge; Ion implantation

Publ.-Id: 14022

New high-spin isomer and quasiparticle-vibration coupling in 187Ir

Modamio, V.; Jungclaus, A.; Algora, A.; Bazzacco, D.; Escrig, D.; Fraile, L. M.; Lenzi, S.; Marginean, N.; Martinez, T.; Napoli, D. R.; Schwengner, R.; Ur, C. A.

The nucleus 187 Ir has been populated up to high spin using the reaction 186 W(7 Li, 6n) at a beam energy of 59 MeV. A comprehensive extension of its level scheme has been proposed comprising 116 newly established excited states connected by 194 transitions which have been observed for the first time. All known rotational bands have been extended up to higher spin and in particular the band crossing region of the h9/2 band has been revised. A number of new intrinsic high-K states has been identified and for some of them multi-quasiparticle configurations have been tentatively assigned. The three-quasiparticle state with spin 29/2- and an excitation energy of 2487 keV is isomeric with a half-live of T1/2 = 1.8(5) µs. On top of this state a rich level scheme reaching up to spin (59/2-) and excitation energies around 7 MeV has been established. Of particular interest is a new structure built on the 31/2-, maximum spin three-quasiparticle state with {11/2-[505]} {11/2+[615],9/2+[624]} configuration at 2755 keV. Arguments have been presented which indicate a vibrational character of these states similar to the proposed vibration-plus-quasiparticle coupling suggested for the structure built on the 11/2- h11/2 proton 1qp state.

Keywords: nuclear structure; gamma-ray spectroscopy; high-spin isomer; vibration-particle coupling

Publ.-Id: 14021

Anwendung zeitmodulierter AC-Magnetfelder zur Strömungskontrolle in metallischen Schmelzen

Räbiger, D.; Eckert, S.; Gerbeth, G.

In dieser Arbeit wird die Wirkung des elektromagnetischen Rührens der Restschmelze bei der gerichteten Erstarrung einer Al-Si-Legierung untersucht. Dabei werden neue Methoden zum elektromagnetischen Rühren unter Nutzung eines zeitlich modulierten rotierenden Magnetfeldes (RMF) und eines wandernden Magnetfeldes (TMF) vorgestellt. Beim elektromagnetischen Rühren mit kontinuierlich wirkenden Feldern treten oft strömungsinduzierte Entmischungen im Gefüge auf. Mit der Strategie der Nutzung zeitmodulierter Felder sollen diese bekannten Nachteile vermieden werden. Die Ergebnisse zeigen, dass das Rühren unter Anwendung eines modulierten magnetischen Feldes Möglichkeiten zur effizienten Kontrolle des Strömungsfeldes vor der Erstarrungsfront bietet.

Keywords: Flow control; Electromagnetic stirring; liquid metal

  • Lecture (Conference)
    Symposion zur Simulation metallurgischer Strömungsprozesse an österreichischen und deutschen Universitäten, 16.-19.06.2010, Kirnitzschtal, Deutschland

Publ.-Id: 14020

Anwendung zeitmodulierter AC-Magnetfelder zum Rühren metallischer Schmelzen während der Erstarrung einer Al-Si-Legierung

Räbiger, D.; Leonhardt, M.; Eckert, S.; Gerbeth, G.

Der Einsatz elektromagnetischer Felder zum Rühren metallischer Schmelzen stellt eine elegante Möglichkeit einer völlig kontaktlosen Strömungskontrolle in erstarrenden Metalllegierungen dar, wobei die Strömungsintensität über die elektrischen Regelgrößen Strom und Frequenz gesteuert werden kann.
Trotz der nachweislichen Verbesserung der Gefügeeigenschaften, wie Kornfeinung und Vergrößerung des equiaxialen Erstarrungsbereiches durch eine intensive Strömung im Bereich der Erstarrungsfront, ist der Einsatz des elektromagnetischen Rührens auch problembehaftet, da die Strömung negative Auswirkungen wie strömungsinduzierte Porosität oder Gefügeinhomogenitäten (z.B. weiße Bänder beim Stahlguss) hervorrufen kann. Diese Nachteile erschweren eine industrielle Anwendung des Verfahrens im Strangguss.
Der Einsatz maßgeschneiderter, zeitmodulierter Magnetfelder bietet die Perspektive, die oben genannten, nachteiligen Effekte zu vermeiden. Mit dem Konzept der maßgeschneiderten Magnetfelder werden geeignete Strömungen erzeugt, welche die für die Herausbildung vorteilhafter Gefüge notwendigen Temperatur- und Konzentrationsfelder in der erstarrenden Schmelze liefern. Dies erfordert jedoch ein genaues Verständnis der Wechselwirkung von Magnetfeld, induzierter Strömung und Erstarrungsvorgang.
In diesem Vortrag wird die Wirkung des elektromagnetischen Rührens der Restschmelze mittels zeitmodulierter Magnetfelder bei der gerichteten Erstarrung einer binären Al-Si-Legierung untersucht. Für eine erfolgreiche Anwendung dieses Verfahrens sind geeignete Kombinationen der Magnetfeldparameter zu ermitteln. Zu diesem Zweck wurden Strömungsmessungen in einer isothermen Modellschmelze unter dem Einfluss modulierter Magnetfelder durchgeführt. Aufbauend auf den gewonnenen Erkenntnissen zur zeitlichen Entwicklung der Strömungsstruktur wurden geeignete Strategien für eine gezielte Beeinflussung der Gefügemerkmale durch den Einsatz maßgeschneiderter Magnetfelder abgeleitet. Die Erstarrungsversuche demonstrieren, dass es möglich ist, mit Hilfe zeitmodulierter magnetischer Felder korngefeinte, equiaxiale Gefüge unter Vermeidung der Herausbildung makroskopischer Gefügeinhomogenitäten herzustellen.
Die Ergebnisse veranschaulichen das große Potenzial des elektromagnetischen Rührens zur Verbesserung der Materialeigenschaften der erstarrten Struktur und einer Optimierung der Prozesskontrolle.

Keywords: Al-Si alloy; Electromagnetic stirring; Rotating magnetic field; Solidification; Columnar to equiaxed transition (CET); Grain refinement

  • Lecture (Conference)
    Tagung Stranggiessen, 15.-17.11.2010, Neu-Ulm, Deutschland
  • Contribution to proceedings
    Tagung Stranggiessen, 15.-17.11.2010, Neu-Ulm, Deutschland
    Stranggießen, Frankfurt: Werkstoff-Informationsgesellschaft mbH, 978-3-88355-384-9, 163-168

Publ.-Id: 14019

Terahertz free-electron lasers and their applications for the spectroscopy of solids

Helm, M.

In free-electron lasers (FEL) optical gain and stimulated emission are provided by relativistic electrons, wiggling through a periodic magnetic-field arrangement. Since the emitted wavelength only depends on the energy of the electrons and the magnetic field strength, an in principle arbitrary lasing wavelength may be achieved. Thus FELs are mostly used in spectral ranges, where conventional lasers with reasonably high power hardly exist. This is true, among others, for the long-wavelength infrared and terahertz (THz) range and represents the motivation to build such bulky THz sources.

Here I will discuss the operation principle of an FEL and then describe the THz FEL at FZD in Dresden. This FEL, called FELBE, was first operated in 2004 and covers now a wavelength range of nearly two spectral decades (3-300 µm or 1-100 THz). The key feature which distinguishes FELBE from other FEL user facilities is the possibility of delivering a continuous train of (micro)pulses, made possible by the superconducting accelerator cavities. The FEL thus provides picosecond optical pulses at a repetition rate of 13 MHz.

In order to pinpoint interesting scientific experiments using the FEL, one has to focus on its unique features, which are high peak power (up to 1 MW), high average power (tens of Watts), and short pulses (1-20 ps, depending on the wavelength). These features lend themselves to nonlinear optical experiments, near-field microscopy, and time resolved pump-probe studies, respectively. I will present experiments belonging to each of these three classes, namely

(1) pumping the intra-excitonic 1s-2p transition in semiconductor quantum wells, which leads to THz sideband generation and the observation of the AC Stark effect;
(2) near-field micro-spectroscopy of ferroelectrics, which allows imaging of ferroelectric domains in BaTiO3 purely due to their optical contrast resulting from a slight anisotropy of the dielectric function;
(3) carrier relaxation in semiconductor quantum dots. Here the relaxation time varies by three orders of magnitude (2 ps to 1.5 ns), if the energy level spacing is changed by only a factor of two (30 meV to 15 meV).

Keywords: free electron laser; spectroscopy; terahertz

  • Invited lecture (Conferences)
    THz radiation: generation, detection and applications (Heraeus Seminar), 18.-21.04.2010, Bad Honnef, Deutschland

Publ.-Id: 14018

Impulsive terahertz radiation with high electric fields from an amplifier-driven large-area photoconductive antenna

Beck, M.; Schäfer, H.; Klatt, G.; Demsar, J.; Winnerl, S.; Helm, M.; Dekorsy, T.

We report on the generation of impulsive terahertz (THz) radiation with 36 kV/cm vacuum electric field (1.5 mW average thermal power) at 250 kHz repetition rate and a high NIR-to-THz conversion efficiency of 2×10−3. This is achieved by photoexciting biased large-area photoconductive emitter with NIR fs pulses of μJ pulse energy. We demonstrate focussing of the THz beam by tailoring the pulse front of the exciting laser beam without any focussing element for the THz beam. A high dynamic range of 104 signal-to-noise is obtained with an amplifier based system.

Publ.-Id: 14017

Biosorption of U(VI) by the green algae Chlorella vulgaris in dependence of pH value and cell activity

Vogel, M.; Günther, A.; Rossberg, A.; Li, B.; Bernhard, G.; Raff, J.

Biosorption of uranium(VI) by the green alga Chlorella vulgaris was studied at varying uranium concentrations from 5 µM to 1 mM, and in the environmentally relevant pH range of 4.4 to 7.0. Living cells bind in a 0.1 mM uranium solution at pH 4.4 within 5 min 14.3 ± 5.5 mg U/g dry biomass and dead cells 28.3 ± 0.6 mg U/g dry biomass which corresponds to 45% and 90% of total uranium in solution, respectively. During 96 h of incubation with uranium initially living cells died off and with 26.6 ± 2.1 mg U/g dry biomass bound similar amounts of uranium compared to dead cells, binding 27.0 ± 0.7 mg U/g dry biomass. In both cases, these amounts correspond to around 85 % of the initially applied uranium. Interestingly, at a lower and more environmentally relevant uranium concentration of 5 µM, living cells firstly bind with 1.3±0.2 mg U/g dry biomass to 1.4±0.1 mg U/g dry biomass almost all uranium within the first 5 min of incubation. But then algal cells again mobilize up to 80% of the bound uranium during ongoing incubation in the time from 48 h to 96 h. The release of metabolism related substances is suggested to cause this mobilization of uranium. As potential leachates for algal-bound uranium oxalate, citrate and ATP were tested and found to be able to mobilize more than 50% of the algal-bound uranium within 24 h. Differences in complexation of uranium by active and inactive algae cells were investigated with a combination of time-resolved laser-induced fluorescence spectroscopy (TRLFS), extended X-ray absorption fine structure (EXAFS) spectroscopy and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Obtained results demonstrated an involvement of carboxylic and organic/inorganic phosphate groups in the uranium complexation with varying contributions dependent on cell status, uranium concentration and pH.

Keywords: sorption; uranium(VI); green algae; TRLFS; EXAFS; ATR-FTIR

Publ.-Id: 14016

Development of a generalized coalescence and breakup closure for the inhomogeneous MUSIG model

Liao, Y.; Lucas, D.; Krepper, E.; Schmidtke, M.

In the present study we propose new coalescence and breakup closures for the inhomogeneous MUltiple bubble Size Group (MUSIG) model. The major purpose is to consider bubble coalescence and breakup due to different mechanisms in turbulent gas-liquid mixtures and to develop a generally applicable constitutive model for CFD applications. For bubble coalescence the new model includes coalescence due to turbulence, laminar shear, wake entrainment and eddy capture. Bubble breakup mechanisms encompass turbulent fluctuation, laminar shear and interfacial slip velocity. The new model was implemented in the commercial CFD software (CFX-12.0) and applied to the case of turbulent air-water mixtures in a large vertical pipe (DN200). Simulation results for the evolution of bubble size distributions were compared to the standard closure model of Luo and Svendsen (1996), Prince and Blanch (1990) as well as the experimental data of TOPFLOW test facility. Better prediction is accomplished by the proposed new model.

Keywords: new coalescence and breakup closures; the inhomogeneous MUSIG model; upward pipe flow; TOPFLOW facility

Publ.-Id: 14015

Influence of two-phase turbulence models on the bubble coalescence and breakup behavior in bubbly pipe flow

Liao, Y.; Lucas, D.; Krepper, E.

In poly-disperse bubbly flows, bubble coalescence and breakup are important local events, which determines the evolution of the flow as well as the transition to slug flow. On the other hand side, the characterization of bubble coalescence and breakup is still one weak point in the CFD simulation of poly-disperse bubbly flows, since the transferability of available models is limited. A generalized model was proposed in our previous work, which takes into account all mechanisms of interest for bubble coalescence and breakup. Turbulence is one major mechanism in a turbulent bubbly flow. In other word, the performance of models for bubble coalescence and breakup relies on the accuracy of turbulence modeling. However, two-phase turbulence modeling is still one open issue.

In the current work, air-water bubbly flow in a vertical pipe (DN200) was investigated. The experimental data were obtained from the TOPFLOW test facility at the Forschungszentrum Dresden-Rossendorf (FZD). The inhomogeneous MUSIG approach in CFD code CFX with a new closure model for bubble coalescence and breakup was used for the simulation. Influence of various two-phase turbulence models was studied. The results of bubble size distribution, radial gas volume fraction, air/water axial velocity, Sauter mean bubble diameter as well as turbulent parameters were compared for each model.
In general, a good agreement with the experimental data has been achieved. The new model for bubble coalescence and breakup was shown as capable of predicting the flow evolution. The influence of two-phase turbulence modeling is considerable. Bubble-induced turbulence can be modeled by additional source term for turbulence transport equations instead of additional viscosity term.

Keywords: Poly-disperse bubbly flow; New model for bubble coalescence and breakup; Two-phase turbulence modeling

  • Contribution to proceedings
    The 8th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-8), 10.-14.10.2010, Shanghai, China
  • Lecture (Conference)
    The 8th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-8), 10.-14.10.2010, Shanghai, China

Publ.-Id: 14014

Validierung von Software-Komponenten zur Voraussage der strahleninduzierten Schädigung von RDB-Stahl

Bergner, F.; Birkenheuer, U.; Ulbricht, A.

Die skalenübergreifende Modellierung der strahleninduzierten Schädigung von RDB-Stahl von den Primärschäden auf der atomaren Skala bis zu den Änderungen der mechanischen Eigenschaften auf der Makroskala trägt wesentlich zu einem ver¬besserten Verständnis des Phänomens der Neutronenversprödung bei. Sie kann sich zukünftig zu einem Bestandteil der Sicherheitsbewertung des RDB entwickeln. Der gewählte zweistufige Modellierungsansatz beruht auf der Kopplung eines ratentheoretischen Moduls zur Voraussage der Größenverteilung der strahlen¬induzierten Defekt-Fremdatom-Cluster mit einem Härtungs-Modul zur Voraussage der strahleninduzierten Streckgrenzenerhöhung. Gegenstand der Untersuchungen sind die Weiterentwicklung und Validierung entsprechender Software-Komponenten. Die Validierung erfolgt durch Gegenüberstellung der Berechnungsergebnisse mit Resultaten von Neutronenkleinwinkelstreumessungen und Zugversuchen an neutronenbestrahlten RDB-Stählen.

Der entwickelte ratentheoretische Modul ermöglicht es, die Größe, Konzentration und Zusammensetzung gemischter Cu-Leerstellen-Cluster über die für RDB-Stähle relevanten Größenbereiche von bis zu 10000 Atomen und Zeitbereiche von bis zu mehreren 10 Jahren zu verfolgen. Die Verbindung der Ratentheorie zur Härtungs¬modellierung beruht auf der Übergabe von berechneten mittleren Hindernis¬abständen und -stärken. Die Validierung der numerischen Werkzeuge hat ergeben, dass wesentliche Tendenzen der strahleninduzierten Streckgrenzenerhöhung von Cu-haltigen und Cu-armen RDB-Stählen richtig wiedergegeben werden. Erste Ansätze zur Erfassung des Einflusses des Legierungselements Nickel im Rahmen der Ratentheorie und der Härtungsmodellierung wurden verwirklicht.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-533 2010
    ISSN: 1437-322X


Publ.-Id: 14013

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