Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf
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42029 Publications
Crystalline Ge surface nanopatterns by erosion with heavy Bi-dimer and trimer ions
Bischoff, L.; Heinig, K.-H.; Schmidt, B.; Facsko, S.; Pilz, W.
Abstract
Two features of our heavy-ion-irradiation-induced surface patterns differ drastically from patterns formed on Ge with ions so far: The surface remains crystalline as proven by Raman measurements, and the dots and ripples heights equal their wavelengths (aspect ratio ~1).
The self-organisation of these very regular, high-amplitude dot and ripple patterns on (001)Ge has been found under bombardment with heavy ions of bismuth dimers and trimers. The Bi2
+, Bi3
+ and Bi3
++ ions are formed in a Liquid Metal Ion Source, they were accelerated, focused and scanned by a Focused Ion Beam system. 30 kV acceleration voltage and up to 1017 ions/cm2 have been used.
In the ion impact angle range from normal to ~30° incidence, hexagonal patterns of dots with ~30 nm diameter and ~40 nm height are found. Using a Bi monomer ion beam having the same atomic energy and fluence like the dimer and trimer beams, an amorphous Ge nanosponge is found. In the incidence range from 30° to 60° Bi3
++ ions smoothen the Ge surface, whereas we found for 60° to 80° and more grazing incidence ripples and shingles perpendicular to the beam, respectively.
The Bi3
++ ions are 16 times heavier than Ar+ ions, and still 5 times heavier than Xe+ ions. This high ion mass leads to a patterning mechanism different from the Bradley-Harper model, which becomes strikingly apparent by the crystalline Ge surface. An identified threshold of this new patterning mode could help to understand the mechanism: The ion-impact-induced deposition of energy per volume (as estimated by SRIM) must exceed a value which coincides with the energy needed for melting. Thus, Bi segregation during melt pool resolidification and the 5% volume difference between molten and solid Ge can cause the observed Bi separation and Ge patterning, respectively. A consistent, qualitative model will be discussed.
Keywords: Bi- LMIS; FIB; cluster beam; surface structures
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Invited lecture (Conferences)
21th International Conference on the Application of Accelerators in Research and Industry CAARI 2010, 08.-13.08.2010, Fort Worth, USA
Permalink: https://www.hzdr.de/publications/Publ-13870
ESTRAL - Realistic Integration of Sorption Processes in Transport Programs for Long-term Safety Analysis
Stockmann, M.; Brendler, V.; Klemm, K.; Noseck, U.
Abstract
In safety assessments for radioactive waste repositories in deep geological formations the host formation and/or the sedimentary overburden might act as a barrier, since sorption on mineral surfaces of the sediments can retard the transport of many radionuclides. So far, the retention of radionuclides has been described in respective computer programs by temporally constant distribution coefficients.
A coupling of reactive transport programs with a full geochemistry code is currently not practical due to the high computing costs for the calculation of large model areas and very long time scales as required in long-term safety analysis. Therefore, the present study develops and implements a different methodology to extend the existing 3D transport program r3t [FEI 04] towards a more realistic description of the radionuclide migration under temporal variable geochemical conditions. Such changes might be caused in a sedimentary overburden by a marine transgression or the thawing of permafrost.
Keywords: Safety assessment; repository; radionuclide sorption; "smart Kd"-values
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Lecture (Conference)
Jahrestagung Kerntechnik, Workshop "Kompetenzerhaltung in der Kerntechnik", 04.-06.05.2010, Berlin, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13869
Role of the soft-iron impellers in the french von-Karman-Sodium (VKS) dynamo experiment
Giesecke, A.; Stefani, F.; Gerbeth, G.
Abstract
not available
not available
Keywords: dynamo; mhd; vks
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Contribution to HZDR-Annual report
Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-541 November 2010, 59-64
ISSN: 1437-322X
Permalink: https://www.hzdr.de/publications/Publ-13868
Experimentelle Untersuchungen zur Korrosionschemie und zum Anlagerungsverhalten von Korrosionsprodukten
Kryk, H.; Hoffmann, W.; Hessel, G.
Abstract
Zur Aufrechterhaltung der Kernkühlung bei Kühlmittelverluststörfällen (KMV) in Leichtwasserreaktoren wird das aus dem Leck im Primärkreislauf austretende Kühlwasser im Reaktorsumpf gesammelt und über Notkühlpumpen in den Kühlkreislauf zurückgeführt. Auf der Saugseite der Notkühlpumpen befinden sich Sumpfsiebe zur Rückhaltung von im Kühlwasser suspendierten Fremdstoffen. Im Fokus von Arbeiten zur Gewährleistung einer gesicherten Kernkühlung bei KMV-Störfällen steht seit Jahren die Erforschung von Transport- und Verblockungsprozessen von Isoliermaterialfasern im Reaktorsumpf bzw. an entsprechenden Rückhaltevorrichtungen. Im Verlauf eines KMV-Störfalles können neben dem Isoliermaterial weitere Feststoffe im Kühlwasser sowohl das Verblockungsverhalten an den Sumpfsieben als auch die Wasserchemie beeinflussen. Speziell der Langzeitkontakt des Leckwasserstrahls mit feuerverzinkten Lichtgitterrosten kann zur Bildung löslicher und partikelförmiger Korrosionsprodukte führen. Im Rahmen eines vom BMWi geförderten Forschungsvorhabens soll der Einfluss derartiger Korrosionsprozesse auf die chemische Zusammensetzung des Kühlwassers und auf das Sumpfsieb-Verstopfungsverhalten untersucht werden. Ziel ist die Unterstützung der Modellierung für eine konsistente Strömungssimulation von KMV-Störfällen unter Einbeziehung von chemischen Langzeiteffekten.
Neben grundlegenden Aussagen zur Korrosionschemie verzinkter Stahloberflächen und Einflussfaktoren auf die Korrosionsprozesse beinhaltet der Vortrag die geplanten Versuchsstrategien und die darauf aufbauenden Auslegungskriterien für die am FZD zu errichtenden Versuchsanlagen für korrosionschemische Experimente unter störfallspezifischen Bedingungen. Weiterhin wird die Mess- und Analysentechnik für die Untersuchung der Korrosionsvorgänge vorgestellt und diskutiert.
Keywords: loss-of-coolant accident; light water reactor; sump strainer; corrosion; hot-dip galvanized steel
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Lecture (Conference)
BMWi-Fachkolloquium Isolationsmaterialbelastete Kühlmittelströmung, 03.-04.03.2009, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13867
Radiosynthesis and radiopharmacological evaluation of cyclin-dependent kinase 4 (Cdk4) inhibitors
Koehler, L.; Graf, F.; Bergmann, R.; Steinbach, J.; Pietzsch, J.; Wuest, F.
Abstract
Tumor cells are characterized by their loss of growth control resulting from alterations in regulating pathways of the cell cycle, such as a deregulated cyclin-dependent kinase (Cdk) activity and/or Cdk expression. Appropriately radiolabeled Cdk4 inhibitors are discussed as promising molecular probes for imaging cell proliferation processes and tumor visualization by PET. This work describes the design, synthesis and radiopharmacological evaluation of two 124I-labeled Cdk4 inhibitors as potential radiotracers for imaging of Cdk4 in vivo. Treatment of a solution containing labeling precursors with [124I]NaI gave radiolabeled Cdk4 inhibitors [124I]CKIA and [124I]CKIB in radiochemical yields of up to 35%. 124I-labeled radiotracers [124I]CKIA and [124I]CKIB were used in cell uptake studies as well as biodistribution studies in Wistar rats and small-animal PET in tumor-bearing mice. In vitro radiotracer uptake studies in adherent tumor cells using [124I]CKIA showed substantial uptake in HT-29 and FaDu cells (750850 %ID/mg protein [124I]CKIA and 9001000 %ID/mg protein [124I]CKIB) after 1 h at 37 °C. Biodistribution of [124I]CKIA and [124I]CKIB showed rapid blood clearance of radioactivity and an accumulation as well as metabolization in the liver. Both radiotracers were administered intravenously to mouse FaDu xenograft tumor model and imaging studies were performed on a small-animal PET scanner. Both imaging techniques showed only little uptake of both radiotracers in the FaDu tumor xenografts.
Keywords: Iodine-124; Cell cycle; Cyclin-dependent kinase 4 inhibitor; Positron emission tomography (PET)
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European Journal of Medicinal Chemistry 45(2010), 727-737
DOI: 10.1016/j.ejmech.2009.11.020
Cited 21 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13866
Proceedings of the 6th International Conference on Electromagnetic Processing of Materials (EPM 2009)
Gerbeth, G.; Eckert, S.; Fautrelle, Y.; (Editors)
Abstract
Electromagnetic Processing of Materials (EPM) relates to all branches of materials processing where some benefit could be attained from an electromagnetic influence on the process. This covers traditional areas such as liquid metal processing, metal casting and solidification, induction heating, but also crystal growth from the melt, plasma processes, etc. The series of EPM conferences was initiated in 1994 by S. Asai (Japan) and M. Garnier (France).
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Book (Editorship)
Dresden: Eigenverlag Forschungszentrum Dresden-Rossendorf, 2009
903 Seiten
ISBN: 978-3-936104-65-3
Permalink: https://www.hzdr.de/publications/Publ-13865
Superconductivity in thin-film germanium in the temperature regime around 1 K
Herrmannsdörfer, T.; Skrotzki, R.; Heera, V.; Ignatchik, O.; Uhlarz, M.; Mücklich, A.; Posselt, M.; Schmidt, B.; Heinig, K.-H.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Helm, M.; Wosnitza, J.
Abstract
We report recent discoveries of superconductivity in p-type-doped germanium which has been fabricated by implantation of gallium ions into near-intrinsic cubic Ge. Depending on the detailed preparation and annealing conditions, we demonstrate that superconductivity can be generated and tailored in thin p-doped layers of the Ge host. By carefully adjusting the annealing parameters, we have been able to raise the onset temperature of superconductivity to about 1.4 K at a Ga peak concentration of ∼10 at.%. This progress and the large in-plane critical magnetic field of about the size of the ChandrasekharClogston limit makes thin-film Ga-doped Ge (Ge:Ga) even more attractive for technological applications. There might be particular interest to utilize on-chip thin-film superconductivity in a semiconducting environment as our preparation method of Ge:Ga is fully compatible with state-of-the-art semiconductor processing used nowadays for the mass production of logic circuits. After its finding in Si and diamond, our work adds another unexpected observation of superconductivity in doped elemental semiconductors and in one of the few remaining islands of the periodic table of elements on which superconductivity has not been found so far.
Involved research facilities
- Ion Beam Center DOI: 10.17815/jlsrf-3-159
Related publications
- DOI: 10.17815/jlsrf-3-159 is cited by this (Id 13864) publication
- Superconductor Science and Technology 23(2010), 034007
Permalink: https://www.hzdr.de/publications/Publ-13864
Scavenger receptors are associated with cellular interactions of S100A12 in vitro and in vivo
Hoppmann, S.; Steinbach, J.; Pietzsch, J.
Abstract
Increased plasma levels of S100 proteins and interaction of S100 proteins with receptor for advanced glycation end products (RAGE) have been associated with a number of disease states, including chronic inflammatory processes and atherosclerosis. However, data concerning the role of circulating S100 proteins in these pathologies in vivo are scarce and, furthermore, it is currently not known whether RAGE is the sole receptor for extracellular S100 proteins in vivo. We report a novel methodology using recombinant human S100 proteins radiolabelled with fluorine-18, particularly, 18F-S100A12, in receptor binding studies and cellular association studies in vitro, and in dynamic small animal positron emission tomography (PET) studies in rats in vivo. Association to both human aortic endothelial cells and macrophages revealed specific binding of 18F-S100A12 to RAGE, but, furthermore, provides evidence for interaction of 18F-S100A12 to various scavenger receptors (SR). PET data showed temporary association of 18F-S100A12 with tissues overexpressing RAGE (e.g., lung), and, moreover, accumulation of 18F-S100A12 in tissues enriched in cells overexpressing SR (e.g., liver and spleen). Blockade of overall SR interaction by maleylated BSA (malBSA) clearly shows diminished in vivo association of 18F-S100A12 to these tissues as well as a significant increment of the mean plasma residence time of 18F-S100A12 (4.8 ± 0.4 h vs. 2.3 ± 0.3 h). The present approach first demonstrates that besides RAGE also scavenger receptors contribute to distribution, tissue association and elimination of circulating proinflammatory S100A12.
Keywords: Maleylated bovine serum albumin; Receptor for advanced glycation endproducts (RAGE); S100 proteins/calgranulins; Scavenger receptors; Small animal positron emission tomography (PET)
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International Journal of Biochemistry & Cell Biology 42(2010), 651-661
DOI: 10.1016/j.biocel.2009.12.010
Cited 26 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13863
Magnetic properties of the quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6
Cizmar, E.; Zvyagin, S. A.; Beyer, R.; Uhlarz, M.; Ozerov, M.; Skourski, Y.; Manson, J. L.; Schlueter, J. A.; Wosnitza, J.
Abstract
We report on high-field magnetization, specific heat, and electron-spin-resonance (ESR) studies of the quasi-two-dimensional spin- 1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6. The frequency-field diagram of ESR modes below TN = 4.38 K is described in the frame of the mean-field theory, confirming a collinear magnetic structure with an easy-plane anisotropy. The obtained results allowed us to determine the anisotropy/exchange interaction ratio, A/J = 0.003, and the upper limit for the interplane/intraplane exchange interaction ratio, J´ /J = 1/ 16. It is argued that despite the onset of three-dimensional long-range magnetic ordering the magnetic properties of this material (including high-magnetic-field magnetization and nonmonotonic field dependence of the Néel temperature) are strongly affected by two-dimensional spin correlations.
- Physical Review B 81(2010), 064422
Permalink: https://www.hzdr.de/publications/Publ-13862
A Star-Shaped Heteronuclear CrIIIMnII3 Species and Its Precise Electronic and Magnetic Structure: Spin Frustration Studied by X-Ray Spectroscopic, Magnetic, and Theoretical Methods
Prinz, M.; Kuepper, K.; Taubitz, C.; Raekers, M.; Khanra, S.; Biswas, B.; Weyhermüller, T.; Uhlarz, M.; Wosnitza, J.; Schnack, J.; Postnikov, A. V.; Schröder, C.; George, S. J.; Neumann, M.; Chaudhuri, P.
Abstract
Molecular magnets incorporate transition-metal ions with organic groups providing a bridge to mediate magnetic exchange interactions between the ions. Among them are star-shaped molecules in which antiferromagnetic couplings between the central and peripheral atoms are predominantly present. Those configurations lead to an appreciable spin moment in the nonfrustrated ground state. In spite of its topologically simple magnetic structure, the [CrIIIMnII
3(PyA)6Cl3] (CrMn3) molecule, in which PyA represents the monoanion of syn-pyridine-2-aldoxime, exhibits nontrivial magnetic properties, which emerge from the combined action of single-ion anisotropy and frustration. In the present work, we elucidate the underlying electronic and magnetic properties of the heteronuclear, spin-frustrated CrMn3 molecule by applying X-ray magnetic circular dichroism (XMCD), as well as magnetization measurements in high magnetic fields, density functional theory, and ligand-field multiplet calculations. Quantum-model calculations based on a Heisenberg Hamiltonian augmented with local anisotropic terms enable us not only to improve the accuracy of the exchange interactions but also to determine the dominant local anisotropies. A discussion of the various spin Hamiltonian parameters not only leads to a validation of our element selective transition metal L edge XMCD spin moments at a magnetic field of 5 T and a temperature of 5 K but also allows us to monitor an interesting effect of anisotropy and frustration of the manganese and chromium ions.
- Inorganic Chemistry 49(2010), 2093-2102
Permalink: https://www.hzdr.de/publications/Publ-13861
Magnetic excitations of the gapped quantum spin dimer antiferromagnet Sr3Cr2O8
Quintero-Castro, D. L.; Lake, B.; Wheeler, E. M.; Islam, A. T. M. N.; Guidi, T.; Rule, K. C.; Izaola, Z.; Russina, M.; Kiefer, K.; Skourski, Y.
Abstract
dimers by the dominant antiferromagnetic intrabilayer coupling. The dimers are coupled three dimensionally by frustrated interdimer interactions. A structural distortion from hexagonal to monoclinic leads to orbital order and lifts the frustration giving rise to spatially anisotropic exchange interactions. We have grown large single crystals of Sr3Cr2O8 and have performed DC susceptibility, high-field magnetization and inelastic neutron scattering measurements. The neutron scattering experiments reveal three gapped and dispersive singlet to triplet modes arising from the three twinned domains that form below the transition thus confirming the picture of orbital ordering. The exchange interactions are extracted by comparing the data to a random phase approximation model and the dimer coupling is found to be J0 = 5.551(9) meV, while the ratio of interdimer to intradimer exchange constants is J´/J0 = 0.64(2). The results are compared to those for other gapped magnets.
- Physical Review B 81(2010), 014415
Permalink: https://www.hzdr.de/publications/Publ-13860
High-Field ESR in Spin Systems with Competing Magnetic Interactions
Zvyagin, S.
Abstract
In my talk I will present a short review of our recent high-field Electron Spin Resonance (ESR) studies of spin systems with competing magnetic interactions. This topic will cover Antiferromagnetic Resonance in the multiferroic hexagonal antiferro-magnet YMnO3, ESR in the anisotropic triangular antiferromagnet Cs2CuBr4, and organic spin-1/2 chain systems [Cu(C4H4N2)(NO3)2 and (C6H9N2)CuCl3], in which an additional frustration term originates either from interchain or next-nearest-neighbor exchange interactions. A brief introduction into the recent development of the high-field ESR program at the High Magnetic Field Laboratory in Dresden will be also given.
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Invited lecture (Conferences)
HFM R, Magnetic Resonance in highly frustrated magnetic systems, 01.-04.02.2010, Kranjska Gora, Slovenia
Permalink: https://www.hzdr.de/publications/Publ-13859
Räumlich hochauflösende Computertomografie mit Gammastrahlung zur Untersuchung von Mehrphasenströmungen
Bieberle, A.
Abstract
Multiphase flows denote flowing mixtures of different fluids, solids and gases, such as oil, water and air. A phase is defined in a thermo dynamical sense as a physically homo-geneous portion of a material. Multiphase flows are to be found in many industrial proc-esses and plants, for instance in oil production, chemical reactors, energy production or driving systems. In many cases, process efficiency as well as safety is directly coupled with the flow behaviour inside industrial facilities. Therefore, there was and is a strong development of invasive and non-invasive measuring and imaging techniques with the aim to improve our understanding of physical flow phenomena and achieve flow optimi-sation and control wherever necessary. Furthermore, flow measurement technology plays an important role in the derivation of physical models for flow simulation with so called CFD (computational fluid dynamics) codes.
Computed tomography (CT) is a non invasive imaging technique that produces non superimposed cross sectional images using analytical, algebraic or statistical reconstruc-tion algorithms. Radiation based transmission tomography therefore employs a radiation source, such as a nuclide or an X-ray source, and a spatially resolving radiation detec-tor. Such as measurement system must acquire radioscopic projections from different angular positions, which can be accomplished either by rotating it around the object of investigation or by rotation of the object itself. In industrial applications nuclide sources with photon energies higher than 500 keV are often used. Such radiation can penetrate metal housings and still gives sufficient contrast between the phases that have to be analysed.
In this work, a new high resolution gamma radiation computed tomography system that uses a 137Cs source was developed. The design and the electronic parts were carefully developed for the application in harsh industrial environments (e.g. temperature and humidity variation as well as electrical and magnetic fields respectively) and high meas-urement accuracy. The spatial resolution of the detector arc is about 2 mm, the stop-ping efficiency for gamma photons with 662 keV energy is about 75% and the deviation of measuring repetition is lower than 1%. The detector arc operates in pulse mode al-lowing excluding scattered gamma photons to a certain degree from the measurement by a pulse height discriminator stage. The developed measurement system was success-fully applied in industrial and laboratory measurement campaigns, for instance meas-urements on an electrically heated rod bundle, a fluid coupling and a chemical reactor. Due to the quantum limitations of the radiation source and slow rotation of the heavy scanner elements the developed gamma radiation computed tomography system can only be used for time-averaged flow measurement with integration times in the range of one minute or more. However, within the frame of this work an extension of the system to the measurement of rapidly rotating fluid distributions is shown. Here, the principle of angle-resolved data acquisition has been implemented which was highly challenging for this type of high resolution radiation detector from an electronic point of view. The developed gamma ray tomography system is not only valuable for flow measurement but has a much wider application range, such as high-energy non-destructive testing of materials and components, such as castings, vehicle constructions or palaeontological objects.
Keywords: Hochauflösende Computertomographie; Gammastrahlung
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Book (Authorship)
Dresden: TUDPress, 2009
122 Seiten
Permalink: https://www.hzdr.de/publications/Publ-13858
Nanoindentation and transmission electron microscopy of ion-irradiated iron-chromium alloys
Heintze, C.
Abstract
Ion irradiations combined with nanoindentation provide a means to characterize irradiation damage in a wide range of irradiation temperature and fluence. Nanoindentation results are reported for Fe-2.5at%Cr, Fe9at%Cr and Fe-12.5at%Cr irradiated at 300°C up to 1 and 10 dpa. The effect of Cr content and fluence are discussed. Hardening features were characterized by means of transmission electron microscopy. The ion-induced damage is compared with the damage created by neutron irradiation for the same alloys.
Keywords: ion-irradiation; nanoindentation; TEM; irradiation hardening; iron base alloys
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Lecture (Conference)
Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Deutschland - atw - International Journal for Nuclear Power 7(2010), 479-481
Permalink: https://www.hzdr.de/publications/Publ-13857
Bildrekonstruktion für die ultraschnelle Limited-Angle-Röntgen-Computertomographie von Zweiphasenströmungen
Bieberle, M.
Abstract
Messtechnik für Mehrphasenströmungen steht heutzutage verstärkt im Fokus der Forschung, da Mehrphasenströmungen einerseits maßgeblich die Sicherheit und Effizienz vieler industrieller Prozesse beeinflussen und andererseits - aufgrund der erhöhten Rechenleistung heutiger Computer - zentrales Thema bei der Entwicklung verbesserter Strömungsmodelle für Simulationscodes sind. Die ultraschnelle Röntgen-Computertomographie ist ein neuartiges Messverfahren, das erstmalig eine nicht-invasive sowie zeitlich und räumlich hochauflösende Abbildung von transienten Mehrphasenströmungen erlaubt. Die zu Grunde liegende Limited-Angle-Anordnung stellt dabei besondere Anforderungen an die Bildrekonstruktion, da ein Teil der hierfür benötigten Projektionsinformationen fehlt.
Kernthema dieser Ausgabe der Reihe "Dresdner Beiträge zur zerstörungsfreien Prüftechnik" ist die Entwicklung eines Bildrekonstruktionsalgorithmus', der in der Lage ist, fehlende Projektionsinformationen durch a-priori-Informationen über das Untersuchungsobjekt auszugleichen und somit die Ausprägung von Bildartefakten stark zu reduzieren. Der auf Basis der Level-Set-Methode entwickelte Algorithmus erreicht dieses Ziel durch die Rekonstruktion von Phasengrenzflächen anstelle von Dichteverteilungen. Gleichzeitig umfasst er einen Glättungseffekt, der eine Minimierung des durch die kurzen Messintervalle hervorgerufenen Rauschens bewirkt. Die ultraschnelle Röntgen-Computertomographie sowie der neu entwickelte Level-Set-Rekonstruktionsalgorithmus wurden an diversen Zweiphasenströmungsexperimenten erprobt. Zudem wurde das Messsystems erfolgreich für die Zweiebenen- und Volumentomographie erweitert.
Keywords: X-ray; tomography; ultrafast; image reconstruction; level-set method
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Book (Authorship)
Dresden: TUDpress, 2010
142 Seiten
Permalink: https://www.hzdr.de/publications/Publ-13856
Nanocrystalline Electroplated Cu-Ni: Metallic Thin Films with Enhanced Mechanical Properties and Tunable Magnetic Behavior
Pellicer, E.; Varea, A.; Pane, S.; Nelson, B. J.; Menendez, E.; Estrader, M.; Surinach, S.; Baro, M. D.; Nogues, J.; Sort, J.
Abstract
Nanocrystalline 3mm thick Cu1xNix (0.45 < x < 0.87) films are electrodeposited galvanostatically onto Cu/Ti/Si (100) substrates, from a citrate- and sulphate-based bath containing sodium lauryl sulphate and saccharine as additives. The films exhibit large values of reduced Youngs modulus (173 < Er < 192 GPa) and hardness (6.4 < H < 8.2 GPa), both of which can be tailored by varying the alloy composition. The outstanding mechanical properties of these metallic films can be ascribed to their nanocrystalline nature - as evidenced by X-ray diffraction, transmission electron microscopy, and atomic force microscopy - along with the occurrence of stacking faults and the concomitant formation of intragranular nanotwins during film growth. Due to their nanocrystalline character, these films also show very low surface roughness (root mean square deviation of around 2 nm). Furthermore, tunable magnetic properties, including a transition from paramagnetic to ferromagnetic behavior, are observed when the Ni percentage is increased. This combination of properties, together with the simplicity of the fabrication method, makes this system attractive for widespread technological applications, including hard metallic coatings or magnetic micro/nano-electromechanical devices.
Keywords: magnetism; Ni; magnetic properties; mechanical properties; nanocrystalline
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Advanced Functional Materials (2010)20, 1-9
DOI: 10.1002/adfm.200901732
Cited 105 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13855
Experimental investigation of the flow in a continuous casting mould under the influence of a transverse DC magnetic field
Timmel, K.; Eckert, S.; Gerbeth, G.
Abstract
This paper describes laboratory experiments aimed at investigations of flow structures and related transport processes in the continuous casting mould under the influence of an external DC magnetic field. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. Experimental results will be presented which have been obtained using a physical model operating with the room temperature alloy GaInSn. 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 up to Hartmann numbers of about 400. The effect of the magnetic field on the flow structure turned out to be rather complex. The flow measurements do not manifest a smooth braking effect which would be expected as an overall damping of the flow velocity and the related fluctuations all-over the mould volume. Variations of the wall conductivity showed a striking impact on the resulting flow structures. The experiments provide a substantial data base for the validation of respective numerical simulations.
Keywords: continuous casting; mould flow; electromagnetic brake; flow measurements; ultrasonic Doppler velocimetry
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Metallurgical and Materials Transactions B 42(2011), 68-80
DOI: 10.1007/s11663-010-9458-1
Cited 98 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13854
Evidence for a novel high-field superconductry state in layered organic superconductors
Wosnitza, J.
Abstract
In the so-called FFLO state, named after Fulde, Ferrell, Larkin, and Ovchinnikov, the super-conducting state can survive even at high magnetic fields above the Pauli paramagnetic limit. The quasi-two-dimensional (2D) organic superconductors have been suggested as good can-didates for exhibiting the FFLO state. When applying the magnetic field exactly parallel to the conducting layers the orbital pair breaking is greatly suppressed and the Pauli limit is reached. We performed high-resolution specific-heat and torque-magnetization experiments in magnetic fields up to 32 T for such 2D organic superconductors. In a very narrow angular region close to parallel-field orientation we observe additional anomalies below the upper critical field sig-naling the existence of an additional superconducting phase. The specific-heat data for kappa-(BEDT-TTF)2Cu(NCS)2 with Tc = 9.1 K show that the superconducting transition becomes first order for fields above 21 T indicating that the Pauli limit is reached. Below about 3 K, the upper critical field increases sharply and a second first-order transition appears within the superconducting phase. These results are corroborated by magnetic-torque data which allowed to follow the phase diagram to lower temperatures and higher fields. Our results give strong evidence for the realization of the FFLO state in organic superconductors.
Work done in cooperation with R. Lortz, B. Bergk, Y. Wang, A. Demuer, I. Sheikin, G. Zwicknagl, and Y. Nakazawa.
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Invited lecture (Conferences)
International Symposium on "Novel states in correlated condensed matter - from model systems to real materials", 02.-04.03.2010, Berlin, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13853
Ceramics high rate timing RPC
Naumann, L.; Stach, D.; Kotte, R.; Wüstenfeld, J.
Abstract
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, whose volume resitivity can be tuned in the production process over five orders of magnitude. The detector prototype has been tested with single electrons of 32MeV. It shows an all-time high rate capability for electron fluxes up to 5·10 5s−1cm−2.
Keywords: RPC; Rate capability; Ceramics composite; Bulk resistivity; Detection efficiency; Time resolution
Involved research facilities
- Radiation Source ELBE DOI: 10.17815/jlsrf-2-58
Related publications
- DOI: 10.17815/jlsrf-2-58 is cited by this (Id 13852) publication
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Nuclear Instruments and Methods in Physics Research A 628(2011), 138-141
DOI: 10.1016/j.nima.2010.06.302
Cited 21 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13852
The 14N(p,gamma )15O reaction studied at high energy
Marta, M.
Abstract
The 14N(p,gamma)15O reaction is the bottleneck of the carbon-nitrogen-oxygen (CNO) cycle. Recent studies of this reaction have been performed in the low energy range E < 500 keV. However, also data at higher energy are necessary to extrapolate the S-factor down to the energy range of astrophysical interest. Up to now, only one set of data froman experiment performed in 1987 extends up to 2.5MeV. A new study has been carried out at the high-current FZD Tandetron in Dresden, in the energy region from 0.6 to 2.5MeV. The astrophysics motivations, setup and on-going analysis are presented.
Keywords: CNO cycle; solar neutrinos; capture reaction; gamma-ray spectroscopy
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Contribution to proceedings
Fifth European Summer School on Experimental Nuclear Astrophysics, 20.-27.09.2009, Santa Tecla, Sicilia, Italy
AIP Conference Proceedings, Vol. 1213: American Institute of Physics, 978-0-7354-0756-5, 222-224
Permalink: https://www.hzdr.de/publications/Publ-13851
Capture of planktonic microbial diversity in fractures by long-term monitoring of flowing boreholes, Evander Basin, South Africa
Davidson, M. M.; Silver, B. J.; Onstott, T. C.; Moser, D. P.; Gihring, T. M.; Pratt, L. M.; Boice, E. A.; Sherwood Lollar, B.; Lippmann-Pipke, J.; Pfiffner, S. M.; Kieft, T. L.; Seymore, W.; Ralston, C.
Abstract
The diversity of planktonic microorganisms in fluids from a group of flowing subterranean boreholes was monitored from the day they were drilled to as long as three and a half months after drilling as they drained into Evander Au mine. Geochemical analyses of the water, characterization of microbial communities by phospholipids fatty acid (PLFA) and DNA sequence analyses, and calculations of free energy flux indicated thatmine-introduced microbial contaminants, dominated by β and γ Proteobacteria, Cenarchaeaceae and Candidatus Nitrososphaera, were flushed from the boreholes and replaced by fracture water derived microbial communities dominated by Firmicutes, Methanosarcinalesand Thermoproteaceaea. The fracture water was a mixture of paleometeoric water and 2.0 Ga old, diagenetically altered, hydrothermal fluid. The C and H isotopic data for C1−4 indicated that the CH4 was primarily abiogenic in origin although ∼35–50% of it might have originated from microbial methanogenesis. Noble gas analyses yielded estimated residence times of some 10 million years for the fracture water, which is estimated to represent a capture cross-section of 0.25–0.50 km2. The 16S rRNA and dsrAB gene sequences indicated that the indigenous bacterial communities were predominantly comprised of sulfate reducers belonging to the genera Desulfotomaculum, Candiditus Desulforudis and Desulfofustis. The sulfur isotopic analyses of sulfate and sulfide yielded fractionation delta-34S values ranging from 16 to 22% consistent with microbial sulfate reduction.Thermodynamic analyses indicate that methanogenic reactions are inhibited by the high partial pressure of abiogenic CH4 and that sulfate-reducing reactions are more favorable, which is consistent with the abundance of 16S rRNA genes belonging to known sulfate reducing bacteria. Supplemental materials are available for this article. Go to the publisher’s online edition of Geomicrobiology Journal to view the free supplemental files.
Keywords: 16S rRNAphylogeny; dsrAB; sulfate reduction; methanogenesis; isotope geochemistry
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Geomicrobiology Journal 28(2011)4, 275-300
DOI: 10.1080/01490451.2010.499928
Cited 28 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13850
Evidence for reduced collectivity around the neutron mid-shell in the stable even-mass Sn isotopes from new lifetime measurements
Jungclaus, A.; Walker, J.; Leske, J.; Speidel, K.-H.; Stuchbery, A. E.; East, M.; Boutachkov, P.; Cederkäll, J.; Doornenbal, P.; Egido, J. L.; Ekström, A.; Gerl, J.; Gernhäuser, R.; Goel, N.; Gorska, M.; Kojouharov, I.; Maier-Komor, P.; Modamio, V.; Naqvi, F.; Pietralla, N.; Pietri, S.; Prokopowicz, W.; Schaffner, H.; Schwengner, R.; Wollersheim, H.-J.
Abstract
Precise measurements of the lifetimes of the first excited 2+ states in the stable even Sn isotopes 112-124Sn have been performed using the Doppler shift attenuation (DSA) technique. For the isotopes 112Sn, 114Sn and 116Sn the B(E2) transition strengths deduced from the measured lifetimes are in severe disagreement with the previously reported values and indicate a minimum at N = 66. The observed deviation from a maximum at mid-shell is attributed to the obstructive effect of the s1/2 neutron orbital in generating collectivity when being close to the Fermi level.
Keywords: Nuclear structure; gamma-ray spectroscopy; level lifeftimes
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Physics Letters B 695(2011), 110-114
DOI: 10.1016/j.physletb.2010.11.012
Cited 63 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13849
Dilepton Production at SIS Energies with HADES
Holzmann, R.; Balanda, A.; Bassini, R.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Hennino, T.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Maiolino, C.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, D.; Mishra, D.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.
Abstract
One of the main goals of the HADES experiment is to achieve a detailed understanding of dielectron emission from hadronic systems at moderate bombarding energies. Results obtained on electron pair production in elementary N+N collisions pave the way to a better understanding of the origin of the pair excess seen in heavy-ion collisions. This puzzling excess, reported first by the former DLS experiment, is now being investigated systematically by HADES.
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Nuclear Physics A 834(2010), 298c-302c
DOI: 10.1016/j.nuclphysa.2010.01.003
Cited 1 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13848
High depth resolution analysis of elemental depth distributions in nanocoatings
Neelmeijer, C.; Vieluf, M.; Kosmata, M.; Munnik, F.
Abstract
Elemental depth distributions in thin films and near surface regions can be obtained with Ion Beam Analysis (IBA) techniques using MeV ions. Depth profiling of films of a few nanometres thickness as well as multilayer arrangements in the nanometre scale is possible with high resolution (HR) spectrometers. At the research centre in Dresden-Rossendorf, two systems are available for high depth resolution analysis, one for medium to heavy elements (Z > 13) using elastic scattering of ions at the target atoms and one for light elements (Z < 14) detecting atoms ejected from the sample (recoils). In both cases, an energy resolution of about 1 is obtained using magnetic spectrometers which allow sub-nanometre depth resolution and, thus, the characteristics of thin film interfaces. Advantages and limits of HR-depth profiling are presented. As an example, atomic layer deposition (ALD) of the high-k material ZrO2 has been examined on two different underlayers, i.e. SiO2 or TiN. From the HR-spectrum it is deduced that fifteen ALD cycles result in 1.5 nm ZrO2 (3.8 ● 1015 Zr/cm²) on the SiO2 surface. In more detail simulation and measured energy distribution of C-ions, scattered on the Zr atoms, are in excellent agreement if ZrO2 layer thickness fluctuation is taken into account. The latter can be obtained by considering surface roughness obtained from AFM measurements. The mentioned agreement of measured and simulated HR-spectra proves that there is no diffusion of Zr atoms into the SiO2. In a second example ten ALD cycles of ZrO2 on TiN were studied. Obviously, the TiN underlay causes two effects as visible in the corresponding HR-spectrum: First, the broad low energy tail of the Zr energy distribution can not be verified by ZrO2 layer thickness variations. Thus, TiN certainly induces Zr diffusion which takes place probably preferentially along grain boundaries of the titanium nitride. Estimated diffusion depths extend up to 3 nm. Secondly, only ten ALD cycles are enough to deposit 4.1 ● 1015 Zr/cm2 on this backing. This finding supports the interpretation of stimulated Zr grain boundary diffusion into TiN. The last example presents a nanometre multilayer arrangement of Al/Cu/FePt on SiO2. HR measurements are demonstrated for various elements and their corresponding interfaces in different depths.
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Poster
2nd International Conference on Functional Nanocoatings, 28.-31.03.2010, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-13847
Convectional controlled crystal-melt interface using two-phase radio-frequency electromagnetic heating
Hermann, R.; Gerbeth, G.; Priede, J.; Krauze, A.; Behr, G.; Buchner, B.
Abstract
The radio frequency floating-zone growth of massive intermetallic single crystals is very often unsuccessful due to an unfavourable solid-liquid interface geometry enclosing concave fringes. This interface depends on the flow in the molten zone. A tailored magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt flow ranging from intense inwards to outwards flows. Depending on the phase shift between the two induction coils, a transition from a double vortex structure to a single vortex structure to a single vortex structure is created at a preferable phase shift of 90° this change in the flow field has a significant influence on the shape of the solid-liquid interface. Due to their attractive properties for high temperature applications such as high melting temperature, low density, high modulus and good oxidation resistance, the magnetic system was applied to the crystal growth of TiAl alloys.
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Journal of Materials Science (2010)45, 2228-2232
DOI: 10.1007/s10853-009-4117-0
Cited 4 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13846
Improving proton acceleration with circularly polarized intense laser pulse by radial confinement with heavy ions
Huang, L. G.; Lei, A. L.; Bin, J. H.; Bai, Y.; Yu, W.; Yu, M. Y.; Cowan, T. E.
Abstract
Energetic proton acceleration from interaction of intense short circularly polarized laser pulse with a sandwich target is investigated using two-dimensional particle-in-cell simulation. The sandwich target consists of a hydrogen-plasma layer surrounded by carbon-plasma layers. It is found that the transverse electric fields generated at the plasma layer interfaces efficiently confine the longitudinally accelerated protons to within the hydrogen-plasma layer such that they are collimated and have smaller energy spread compared with a pure proton layer target. The proton energy spectrum can be controlled by adjusting the target parameters, in particular the width of the hydrogen-plasma layer and the density of the carbon-plasma layer.
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Physics of Plasmas 17(2010), 013106
DOI: 10.1063/1.3302536
ISSN: 1070-664X
Cited 4 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13845
Enhanced Isochoric Heating from Fast Electrons Produced by High-Contrast, Relativistic-Intensity Laser Pulses
Perez, F.; Gremillet, L.; Koenig, M.; Baton, S. D.; Audebert, P.; Chahid, M.; Rousseaux, C.; Drouin, M.; Lefebvre, E.; Vinci, T.; Rassuchine, J.; Cowan, T.; Gaillard, S. A.; Flippo, K. A.; Shepherd, R.
Abstract
Thin, mass-limited targets composed of V/Cu/Al layers with diameters ranging from 50 to 300 μm have been isochorically heated by a 300 fs laser pulse delivering up to 10 J at 2×1019 W/cm2 irradiance. Detailed spectral analysis of the Cu x-ray emission indicates that the highest temperatures, of the order of 100 eV, have been reached when irradiating the smallest targets with a high-contrast, frequency-doubled pulse despite a reduced laser energy. Collisional particle-in-cell simulations confirm the detrimental influence of the preformed plasma on the bulk target heating.
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Physical Review Letters 104(2010), 085001
DOI: 10.1103/PhysRevLett.104.085001
Cited 52 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13844
Cold quarks stars from hot lattice QCD
Schulze, R.; Kämpfer, B.
Abstract
At small net baryon densities ab initio lattice QCD provides valuable information on the finite-temperature equation of state of strongly interacting matter. Our phenomenological quasiparticle model provides a means to map such lattice results to regions relevant for future heavy-ion experiments at large baryon density; even the cool equation of state can be inferred to address the issue of quark stars. We report on (i) the side conditions (charge neutrality, beta equilibrium) in mapping latest lattice QCD results to large baryon density and (ii) scaling properties of emerging strange quark stars.
Keywords: lattice qcd htl quasiparticle model quark stars
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Lecture (Conference)
Strongly Interacting Matter under Extreme Conditions, 17.-23.01.2010, Hirschegg, Österreich
Permalink: https://www.hzdr.de/publications/Publ-13843
Temporal pulse control of a multi-10TW diode-pumped Yb:Glass laser
Hornung, M.; Boedefeld, R.; Siebold, M.; Kessler, A.; Schnepp, M.; Wachs, R.; Saevert, A.; Podleska, S.; Keppler, S.; Hein, J.; Kaluza, M.
Abstract
At the Institute of Optics and Quantum Electronics in Jena, Germany, the currently most powerful diodepumped solid-state laser system with 25-TW peak power POLARIS is in operation. In this paper we give an overview about the dispersion management of the chirped pulse amplification in order to minimize the pulse duration and thus to maximize the intensity available for experiments. A detailed description of the stretcher and compressor design with a novel alignment routine is given as well as measurements for the pulse duration and the temporal contrast. The far field measurement of the beam focussed by an off-axis parabola yields a nearly diffraction limited focal spot.
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Applied Physics B 101(2010), 93-102
DOI: 10.1007/s00340-010-3952-7
Cited 52 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13842
Original version or not: PIXE-RBS testing of a Meissen porcelain box
Neelmeijer, C.; Roscher, R.
Abstract
Introduction: The valuation of an artistic object depends decisively on its complete originality. Regarding the 18th century snuffbox, made from Meissen Porcelain, restorers ask the following question: Are both the base body but also the hinged cover originals?
Visual discrepancies concerning especially the shade of porcelain glazing raised doubts. In addition, the onglaze decorations show slight differences in colour and flow. Assured non-destructive materials analysis was in demand to clarify the problem.
External Ion Beam Analysis: The 4-MeV proton beam used in atmosphere and PIXE (Particle Induced X-Ray Emission) simultaneously with RBS (Rutherford Backscattering Spectrometry) for analysis [1,2] proved ideal to get convincing answers. Visible marks due to the beam spot (1 mm2) on the highly sensitive porcelain were avoided by using only 200 pA beam intensity and 30 s irradiation time.
Similarities and differences:
Ornamental painting. The ancient Meissen onglaze colour palette is well-known since decades [3]. In conformity with [3] the artist used the pigment copper green for leaves of trees painted on both bottom and cover (point a). However, the green colourant of the cover contains Co and Zn, not obtained in the X-ray spectrum from the bottom. According to [3] Meissen copper green was made from Cu or brass, an alloy of Cu and Zn, which are both reduced to ashes. The addition of Co is mentioned [3] for getting special shaded green paint. Whether or not such characteristic differences are also present in the case of the crimson clothes can not be revealed. Indeed, the PIXE spec-trum taken from the pink gown on the cover (b) shows signals from Au, to be characteristic for purple [3]. Corresponding low-intensity Au-peaks cannot be identified for the pink skirt painted on the bottom. This is because of the superimposed high-intensity Pb L lines due to another type of glazing.
Porcelain glazing. The bottom comprises comparatively thick lead containing glazing, hence intense Pb-L signals are found in the PIXE spectrum.
The number of lead atoms inside the glazing of the cover (c) is much lower. The latter gets reflected also by comparing Pb-Lγ in the presented PIXE spectra taken from the green leaves painted on glazing. Moreover, RBS taken from pure glazing of the cover makes clear that the few Pb atoms are situated on the glazing surface. This is understandable when supposing Pb to originate from a surface polishing process using Pb containing polish agent. The discussed difference in glazing of cover and bottom and especially the considerable Pb-content of the latter, assumable to be bond as lead oxide, clarifies the apparent discrepancies of shades.
Unfortunately, unglazed positions had not been avail-able for getting compositions of the porcelain body.
Conclusions: Cover and base body of the porcelain box can not be related to one and the same workmanship. The cover was certainly later on replaced or it represents completely a later additive. Despite of differences regarding the green pigments of porcelain paints used on bottom and cover, the box fit the typical Meissen onglaze colour technology. Therefore, the question - original version or not - must be answered by the statement: Certainly not, but there is no doubt concerning original Meissen handcraft.
References: [1] Neelmeijer C. et al. NIMB 118 (1996) 338-345. [2] Neelmeijer C. and Mäder M. NIMB 189 (2002) 293-302. [3] Mields M., Kerami-sche Zeitschrift 8 (1963) 453-459.
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Lecture (Conference)
Workshop Ionenstrahlphysik, 29.-31.03.2010, FZD, Germany
Permalink: https://www.hzdr.de/publications/Publ-13841
Effect of temperature on the retention of 2 keV Cs+ ions in Si
Wilde, C.; Möller, W.; Neidhardt, J.
Abstract
Introduction: Cesium is a commonly used species for SIMS, because it provides a high negative secondary ion yield. For more quantitative modeling of the secondary ion yield during SIMS the precise knowledge of the amount of Cs retained in the near surface region is vital. Its equilibrium concentration can be theoretically described by the implantation process and the material removal by (self) sputtering. However, the experimentally determined concentrations of Cs ions retained in Si [1] are lower than that predicted by TRIDYN or by the model of Schulz and Wittmaack [2]. This indicates more complex interaction of chemical (compound formation) or physical nature (texture), which is not described by the given models. The chemical incorporation of residual gas is thought to be a possible reason (e. g. [3]). Therefore, an IBA set-up including RBS and ERD for simultaneous in-vacuo detection of Cs and O in Si was developed to analyze the incorporation of oxygen during Cs sputtering as a function of sample temperature in order to draw conclusion of their activation threshold.
Results: Fig. 1 shows the saturation of Cs in Si at room temperature. The temporal development is consistent with the model of implantation and self sputter-ing. Regardless the low partial pressure of oxygen, there is also a strong correlation between Cs and O indicating ion induced incorporation pathways on top of the natural oxide on the untreated Si surface.
Fig. 2 shows the steady state areal densities for Cs and O as a function of temperature. Two discrete steady state regimes for Cs are observed at high (> 500°C) and low (< 250°C) temperatures with an transition, where the steady state areal density de-creases almost linearly by a factor of four. The O concentration behaves congruently, while the deviation at temperatures > 600°C might be attributed to thermal oxidation.
Conclusion: Even though no significant influence on the physical conditions of the sputtering processes are expected within the temperature range, the Cs areal density shows two discrete regimes, which, interestingly, correlate closely to the amount of O incorporated from residual gas even at base pressures below 10-7 mbar. The reported recrystallisation by rapid thermal annealing with an app. 10% increase of sputter yield shown by Anderson [4] for Ar in Ge seems to be much to small to explain this strong de-crease of steady state Cs concentration. Instead overlying chemical processes are thought to play a major role, e. g. the Cs enhanced formation of mixed oxides (e. g. Cs2O shown by Michel et al. [5]) can impact sputtering yields and/or thermally desorb in the ob-served temperature range under UHV conditions. The precise nature remains unclear up to now and follow-up experiments at different O partial pressures might provide further insights.
References: [1] Gnaser H. NIMB 267 (2009) 28082816. [2] Schulz F. and Wittmaack K. Ra-diat. Eff. 29 (1976) 31-40. [3] Berghmans B. and Van-dervorst W. J. Appl. Phys. 106 (2009), 033509. [4] Anderson G. S. J. Appl. Phys. 38 (1967) 1607-1611. [5] Michel E. G. et al. Phys. Rev. B 38 (1988) 13999-13406.
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Poster
Workshop Ionenstrahlphysik, 29.-31.03.2010, FZD, Germany
Permalink: https://www.hzdr.de/publications/Publ-13840
Bacterial diversity in opalinus clay samples collected from the Mont Terri Laboratory in April 2009 as estimated by cultivation and direct molecular approaches
Buchvarova, V.; Geissler, A.; Selenska, S.
Abstract
Bacterial diversity in unperturbed opalinus clay samples was studied by using a molecular approach based on DNA recovery via direct cell lysis, PCR amplification of 16S rRNA gene fragments, cloning, RFLP typing and consequent sequence analyses. Two highly predominant bacterial groups, each including almost one third of the analysed clones, were found. The first group was represented by proteobacterial clones; 70 % of them were affiliated with Acidovorax (Betaproteobacteria). The second numerically predominant group consisted of representatives of several various Clostridium subgroups (Firmicutes). One additional, third predominant group included about 14 % of the studied clones and was affiliated with Bacteroidetes. About one quarter of the analysed 16S rDNA clones possessed individual RFLP types, which indicated the presence in the studied bacterial community of highly diverse bacterial groups in low numbers.
The amount of total DNA, recovered from a parallel opalinus clay sample supplemented with R2A medium and incubated under sterile and anaerobic conditions, was significantly higher. This is an indication of microbial growth. By using the above described 16S rRNA gene retrieval we were able to demonstrate that the stimulated bacterial community in the R2A treated samples was strongly shifted and predominated by two main groups of Firmicutes: Paenibacillus sp. (about the half of the studied clones) and Sporomusa sp. belonging to one non-pathogenic sub-group of Clostridiales (about 42 % of the clones). Interestingly, none of these two bacterial populations was dominant in the unperturbed opalinus clay samples. Moreover, the three times lower number of individual 16S rRNA gene fragments in the clone library of the R2A treated sample then in the untreated one indicates that natural bacterial diversity in the opalinus clay was masked by the selectively induced by the medium two groups of heterotrophic bacteria. The latter was confirmed by the results of our cultivation experiments: up to date three groups of bacterial isolates were cultivated from the R2A treated samples. The first and most predominant group was affiliated with the non-pathogenic Clostridium species, Sporomusa silvacetica, the second - with Paenibacillus wynnii, and the third - with another non-pathogenic Clostridium, namely Clostridium bowmanii. The interactions of some of these isolates with uranium and other radionuclides are planed to be studied.
Additionally, we will analyse the influence of U(VI) on natural bacterial diversity in the opalinus clay samples. Efforts to stimulate the growth of other specific bacterial groups such as sulphate reducers and metal reducers in the opalinus clay samples are in progress.
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Lecture (others)
Mont Terri Meeting, 08.-09.03.2010, Paris, France
Permalink: https://www.hzdr.de/publications/Publ-13838
Factor analysis and sequential extraction unveil geochemical processes relevant for trace metal distributions in fluvial sediments of a pyrite mining area, China
Liu, J.; Chen, Y.; Wang, J.; Qi, J.; Wang, C.; Lippold, H.; Lippmann-Pipke, J.
Abstract
Four fluvial sediment cores were geochemically analysed for their major elements and for their trace metal contents and represent a sensitive environmental record for heavy metal contamination in a pyrite mining area, Pearl River Basin, South China. While an identification of depositional and post-depositional processes is not possible by means of the vertical profiles of the trace metal contents alone, factor analysis uncovers four main factors that control trace metal distributions in the sediment cores. After analysing the geochemical fractions of heavy metals by a sequential extraction procedure, these four factors could be explained as (i) complexation with organic matter in the sediment (As, Cu, Ni and Zn), (ii) weathering processes by iron reduction and oxidation (Pb, Mo and Cr), (iii) weathering by Mn reduction and oxidation (Tl and Co) and (iv) binding effects of sulphur in the sediment or physical transport of pyrite tailings (Zn). The environmental evaluation by geoaccumulation indices and enrichment factors reveals that the studied sediment cores are significantly contaminated and enriched with As, Tl, Pb and Zn. The risk assessment code additionally suggests low to medium risk of these studied heavy metals on the whole.
Keywords: Trace metal contamination; Factor analysis; Geoaccumulation index; Fluvial sediment; Mining area
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Carbonates and Evaporites 25(2010)1, 51-63
DOI: 10.1007/s13146-010-0007-4
ISSN: 0891-2556
Cited 16 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13837
Mid-frequency deposition of a-C:H films using five different precursors
Peter, S.; Günther, M.; Hauschild, D.; Grambole, D.; Richter, F.
Abstract
The plasma-enhanced chemical vapour deposition (PECVD) of amorphous hydrogenated carbon films from pulsed discharges with frequencies in the range from 50 kHz to 250 kHz was investigated. Five different hydrocarbons (acetylene C2H2, isobutene C4H8, cyclopentene C5H8, toluene C7H8 and cycloheptatriene C7H8) were probed as film growth precursors. In addition, two types of pulse-generators with somewhat different waveforms were used to power the discharges in the so called mid-frequency range. The a-C:H films deposited in a parallel-plate reactor were characterised for their thickness/deposition rate, hardness and hydrogen content. The hydrogen concentration in the films varied between 19 at.-% and 37 at.-%. With the substrate temperature held constant, it is roughly in inverse proportion to the hardness. The film with the highest hardness of 25 GPa was formed at a deposition rate of 0.8 μm/h in the C2H2 discharge at the lowest investigated pressure of 2 Pa. With increasing molecular mass of the precursor mostly weaker films were deposited. Relatively high values of both deposition rate and hardness were achieved using the precursor isobutene: a hardness of 21 GPa combined with a deposition rate of 4.1 μm/h. From the probed precursors, isobutene is also most advantageous for a-C:H deposition at higher pressures (up to 50 Pa investigated). But, as an over-all trend, the a-C:H hardness decreases with increasing deposition rate.
Keywords: Diamond-like carbon; a-C:H; PECVD; Pulsed discharge; Precursor
- Vacuum 84(2010), 958-961
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Permalink: https://www.hzdr.de/publications/Publ-13836
Analyse ultradünner Schichten und deren Grenzflächen mit Nanometertiefenauflösung
Kosmata, M.; Munnik, F.; Neelmeijer, C.; Heller, R.; Vieluf, M.; Merchel, S.; Möller, W.
Abstract
Die quantitative Elementanalytik von Schichten und Schichtabfolgen im Dickenbereich weniger Nanometer ist in den letzten Jahren von steigender technologischer Relevanz geworden und somit im Fokus der aktuellen Forschung. Im Mittelpunkt dieser materialwissenschaftlichen Fragestellungen steht die Bestimmung von Tiefenverteilungen von Elementen in dünnen Schichten, die durch sequentielle Abscheideverfahren oder nachfolgende Prozessschritte wie Temperung erzielt werden, aber auch der Nachweis unbeabsichtigter Kontamination. Daraus können Informationen im Hinblick auf gezielte Materialentwicklung gewonnen werden und die Qualität bestehender Prozessführungen lässt sich bewerten.
Die meisten konventionellen Analyseverfahren wie z. B. Sekundärionenmassen-spektrometrie (SIMS) sind zur Quantifizierung ihrer Ergebnisse in der Regel auf Referenzmaterialien (gleicher Matrix) angewiesen. Im Gegensatz dazu kann die Ionenstrahlanalyse (ion beam analysis, IBA) standardfrei betrieben werden. Der physikalische Prozess, auf der fast alle Methoden der IBA beruhen, ist die binäre Wechselwirkung von MeV-Ionen mit den Atomkernen in den Schichten. Diese Wechselwirkung, elastische Streuung oder Kernreaktion, ist einfach und genau beschreibbar; kollektive Matrixeffekte treten dabei nicht auf.
Am Ionenstrahlzentrum des FZD kommen hauptsächlich drei Analysemethoden zur Anwendung:
Kernreaktionsanalyse (Nuclear Reaction Analysis, NRA) zum tiefenabhängigen Nachweis von Wasserstoff über die resonante Kernreaktion 1H(15N,αγ)12C
Rutherford-Rückstreuspektrometrie (Rutherford Backscattering Spectrometry, RBS) insbesondere zur Detektion von Elementen mit Ordnungszahlen Z > 14
Elastische Rückstreuanalyse (Elastic Recoil Detection, ERD) zum Nachweis leichter Elemente mit Z = 2-14 (He-Si)
Die zur Messung ultradünner Schichten mit RBS und ERD erforderliche Tiefenauflösung (< 1 nm) kann mit Teilchenspektrometern mit höchster Energieauflösung erreicht werden.
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Lecture (others)
seminar an der TU Dresden, 25,02,2010, TU Dresden Institut für Halbleiter - und Mikrosyst, Germany
Permalink: https://www.hzdr.de/publications/Publ-13835
Novel U(VI) Complexes of Bis(2-hydroxyaryl)imine Ligands: Synthesis, Structural Characterization, and Extraction Studies.
Tanh Jeazet, H. B.; Doert, T.; Gloe, K.; Tsushima, S.; Geipel, G.; Gloe, K.; Bernhard, G.
Abstract
The coordination chemistry of uranium in different oxidation states has recently generated much attention due to several reasons. The most important reason is the separation of U(VI) present in radioactive waste, but also the effects of U(VI) on our environment are of great interest.[1] The extraction and separation of U(VI) and other actinides, especially the separation from lanthanides, is most difficult due to their similar chemical behavior.[2] However, the introduction of soft heteroatoms, as imine nitrogen, in the ligand systems could be used as a tool for more selective and effective binding and extraction. We have synthesized and characterized some novel U(VI) complexes using multidentate Schiff base ligands. Structures of these complexes were characterized by X-ray crystallography and DFT calculations. It is the intention of this work to determine not only the structure of these complexes but also the extraction ability of the ligands towards U(VI) and Eu(III).
Keywords: Extraction study; radioactive waste; schiff base; uranium
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Poster
GDCh-Wissenschaftsforum Chemie, 30.08.-02.09.2009, Frankfurt am Main, Germany
Permalink: https://www.hzdr.de/publications/Publ-13834
Geochemical study of different-aged mining dump materials in the Freiberg mining district, Germany
Stockmann, M.; Hirsch, D.; Lippmann-Pipke, J.; Kupsch, H.
Abstract
Historical mining dumps are useful archives for the investigation of weathering processes. The objective of this study was to investigate the weathering behavior of waste-rock material derived from the 800 years old silver ore mining in Freiberg, Germany. For identify time-dependent weathering indices, dumped material of four dumps of different ages and corresponding rock was examined regarding the geochemical composition. The dumped material is characterized by high contents of heavy metal containing sulfidic ores, such as pyrite, arsenopyrite, sphalerite and galena. Acid mine drainage (AMD) is produced by the oxidative weathering of the sulfide minerals and causes the increased dissolving of soluble metals with increasing age of dumps. As a result of these weathering processes, a clear depletion of chalcophile elements in the older dump material (800 years) compared to the youngest dump (100 years) was observed. In the soil horizons downstream the dumps, high quantities of heavy metals (e.g., up to 12000 ppm As, 3300 ppm Pb, 640 ppm Zn), mainly adsorbed on organic matter, were determined and indicate a time-dependent element transfer from the dumps into their surrounding soils.
Keywords: Waste-rock dumps; Heavy metals; Weathering; Mobilization; Adsorption
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Environmental Earth Sciences 68(2013)4, 1153-1168
Online First (2012) DOI: 10.1007/s12665-012-1817-6
Cited 11 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13833
Scaling of proton energies in ultrashort pulse laser plasma acceleration
Zeil, K.; Kraft, S.; Bock, S.; Bussmann, M.; Cowan, T.; Kluge, T.; Metzkes, J.; Richter, T.; Sauerbrey, R.; Schramm, U.
Abstract
This paper presents a systematic investigation of an ultrashort pulse laser acceleration of protons that yields unprecedented maximum proton energies of 17MeV at a table-top Ti:sapphire laser power level of 100TW. For plain fewmicron- thick foil targets, a linear scaling of the maximum proton energy with laser power is observed and this is attributed to the short acceleration period close to the target rear surface. Although excellent laser pulse contrast was available, slight deformations of the target rear were found to lead to a predictable shift of the direction of the energetic proton emission away from the target normal that could be used for better discrimination of the low-energy part of the spectrum.
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New Journal of Physics 12(2010), 045015
DOI: 10.1088/1367-2630/12/4/045015
Cited 198 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13832
Magnetization Dynamics of Coupled Vortices
Wintz, S.; Puzic, A.; Strache, T.; Koerner, M.; Bunce, C.; Marko, D.; Grebing, J.; Fritzsche, M.; Moench, I.; Mattheis, R.; Erbe, A.; Raabe, J.; Quitmann, C.; Fassbender, J.
Abstract
We report on the layer-resolved imaging of the magnetization dynamics of vortices in different coupling states. The study is performed using time-resolved magnetic soft x-ray microscopy. Magnetic vortices confined into micron-sized trilayer stacks offer a unique opportunity to study the coupling of magnetic moments on the nanoscopic scale. Antiferromagnetically (AFM) coupled vortices can be created within cobalt-IL-permalloy stacks, if the material of the nonmagnetic interlayer (IL) is chosen properly, with the thickness corresponding to the first antiferromagnetic maximum of the interlayer-exchange-coupling (IEC). It is known that the strength, as well as the orientation of the IEC can be modified by noble gas ion irradiation. A controlled neon irradiation of such structures leads to a successive reorientation of the IEC and eventually AFM coupled vortices can be transformed into ferromagnetically (FM) coupled ones. The response of a vortex to an alternating magnetic field depends crucially on the specific orientation of its in-plane magnetization curling (circulation) and the direction of the out-of- plane vortex core (polarization). This holds true especially for the gyrotropic mode, which corresponds to an orbiting of the core around its equilibrium position. The cores in the individual layers of a strictly FM coupled vortex pair show an in-phase motion that is similar to that of a single layer vortex. However, in the case of a vortex pair with AFM coupled in-plane magnetization an inverse sense of gyration can be detected, with highly elliptical trajectories of the individual cores. Furthermore, independent vortex core switching processes were observed in the individual layers of a vortex pair with FM coupled circulation.
Keywords: magnetism; dynamics; vortex; coupling; interlayer-exchange; x-ray microscopy; XMCD
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Poster
MML 2010 - IEEE 7th International Symposium on Magnetic Multilayers, 19.-24.09.2010, Berkeley, USA
Permalink: https://www.hzdr.de/publications/Publ-13831
Determining the radial pair distribution function from X-ray absorption spectra by use of the Landweber iteration method
Rossberg, A.; Funke, H.
Abstract
The Landweber iteration approach is used to construct the radial pair distribution function (RPDF) from an X-ray absorption (EXAFS) spectrum. The physical motivation for the presented investigation is the possibility to also reconstruct asymmetric RPDFs from the EXAFS spectra. From the methodical point of view the shell fit analysis in the case of complicated spectra would be much more eased if the RPDF for the first shell(s) are computed precisely and independently. The RPDF, as a solution of the fundamental EXAFS integral equation, is examined for theoretical examples, and a detailed noise analysis is performed. As a real example the EXAFS spectrum of curium(III) hydrate is evaluated in a stable way without supplementary conditions by the proposed iteration, i.e. by a recursive application of the EXAFS kernel.
Keywords: EXAFS; pair distribution function; Fredholm integral equation; Landweber iteration
- Journal of Synchrotron Radiation 17(2010), 280-288
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Invited lecture (Conferences)
ACTINET-I3 workshop, Coupling XAS and theoretical chemistry for heavy atoms, 23.-24.07.2010, Avignon, France
Permalink: https://www.hzdr.de/publications/Publ-13830
Obsidian homogeneity study for provenancing using Ion Beam- and Neutron Activation Analysis
Eder, F.; Neelmeijer, C.; Bichler, M.; Merchel, S.
Abstract
Obsidian is a natural volcanic glass, which was one of the most appreciated materials of ancient man for cutting tools and has been found in many locations far away from any natural source. Reliable provenancing can provide evidence of contacts over certain distances and information about exchange patterns and mobility of prehistoric people.
The application of analytical methods can assist to solve the problem of obsidian provenancing by means of its highly specific chemical composition, the chemical fingerprint. Ion Beam Analysis (IBA) measurements, combining Particle Induced X-ray Emission (PIXE), Particle Induced Gamma-ray Emission (PIGE) and Rutherford Backscattering Spectrometry (RBS), are frequently used because of their high sensitivity and the non-destructive external beam mode [1-5]. Our studies have been carried out using the 4 MeV proton beam in-air of the 5 MV Tandem accelerator of the FZD. For comparative reasons and in order to obtain additional information, all obsidian samples were analysed by Neutron Activation Analysis (NAA) at the Atominstitut in Vienna, where previous investigations of volcanic rocks and glasses have been performed successfully [6-8].
Obsidian is generally described as a relatively homogeneous material [9]. Therefore, samples from the obsidian source Demenegakion (Milos, Greece) have been analysed in order to check the actual variation range of their chemical compositions. Special attention was paid to banded obsidians to clarify, if these bands show differences in the chemical composition or if these changes in the optical properties are related to inclusions of gas bubbles, microphenocrysts or similar features without significant compositional influence. Furthermore, both the influence of the surface quality and alteration by weathering has been studied.
This study is part of a joint project to apply selected analytical methods, in particular IBA, NAA and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS), to reveal a maximum of compositional differences between (geological) samples of obsidian sources available in Europe. This knowledge is essential to decide, which least invasive analytical method should be chosen for the analysis of a specific archaeological artefact, on a case by case basis.
References: [1] Bugoi R. and Neelmeijer C. NIMB 226 (2004) 136-146. [2] Mäder M. et al. NIMB 239 (2005) 107-113. [3] Mäder M. and Neelmeijer C. NIMB 226 (2204) 110-118. [4] Jembrih D. et al. NIMB 181 (2001) 698-702. [5] Mäder M. et al. NIMB 136-138 (1998) 863-868. [6] Steinhauser G. et al. Appl. Geochem. 21 (2006) 1362-1375. [7] Steinhauser G. et al. Appl. Radiat. Isot. 65 (2007) 488-503. [8] Saminger S. et al. J. Radioanal. Nucl. Chem. 245 (2000) 375-383. [9] Pollard A.M. and Heron C. (2008) Archaeological chemistry Royal Society of Chemistry, Cambridge 8081 [2nd edition].
Keywords: archaeometry; RBS; PIXE; PIGE
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Poster
12th International Conference on Particle Induced X-ray Emission and its Analytical Applications (PIXE), University of Surrey, 27.06.-02.07.2010, Surrey, GB
Permalink: https://www.hzdr.de/publications/Publ-13829
Electromagnetic control of local temperature gradients in a Czochralski crystal growth model
Pal, J.; Cramer, A.; Gerbeth, G.
Abstract
This experimental work is concerned with optimisation of the Czochralski crystal growth process. With respect to the shape of the solidication front and the related mono-crystalline growth, the ratio of the horizontal and the vertical temperature gradient at the triple point liquid-solid atmosphere is thought of being a crucial magnitude, which desirably should be in the order of unity. A liquid metal model experiment was therefore build that allows studying this ratio under the influence of magnetic elds applied to the melt.
Keywords: Czochralski crystal growth; Stirring; Convection
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Lecture (Conference)
81st Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM), 22.-26.03.2010, Karlsruhe, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13828
Kunstwerke - zerstörungsfreie Materialanalyse
Neelmeijer, C.
Abstract
Kunstwerke sind Unikate, unwiederbringliche Zeugen vergangener Zeit. Ähnlich wie Patienten können sie erkranken, unterliegen der Alterung und bedürfen der Pflege. Das Material, woraus sie bestehen und das Klima, in dem sie aufbewahrt werden, bestimmen ihr Wohlbefinden. Die Oberfläche von Kunstwerken aus Glas, zum Beispiel, kann rosten wie Metall. Wenn das Glasobjekt matt und rissig erscheint, kommt Abhilfe schon sehr spät. Präventive Konservierung heißt das Zauberwort, Vorsorge also. Entscheidend dafür ist die Früherkennung von Veränderungen besser noch die Einschätzung möglicher Schädigungen. Dazu dient die zerstörungsfreie Materialanalyse. Das kann der Protonenstrahl an Luft im Zusammenspiel mit empfindlicher Messtechnik. Am Beispiel Glas, aber auch an Gemälden, Zeichnungen, Tinten auf Urkunden gibt die Präsentation Antworten auf die typischen Fragen von Restauratoren und Kunstwissenschaftlern: Wie gefährdet ist das Kunstwerk, welche Technologien hat der Künstler verwandt um bestimmte ästhetische Eindrücke zu erlangen, gibt es Anzeichen für eine Kopie anstelle des Originals?
Keywords: art objects; non-destructive analysis; ion-beam analysis; glass; porcelain; metal; painting
Involved research facilities
- Ion Beam Center DOI: 10.17815/jlsrf-3-159
Related publications
- DOI: 10.17815/jlsrf-3-159 is cited by this (Id 13827) publication
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Lecture (others)
Vorlesung, 24.02.2010, Dresden, BRD
Permalink: https://www.hzdr.de/publications/Publ-13827
Laser-Teilchenbeschleuniger
Bussmann, M.; Kluge, T.; Gaillard, S.; Flippo, K.; Schramm, U.; Cowan, T. E.
Abstract
Weltrekord in Protonenbeschleunigung mit Licht: Schnelle Protonen sind zum Beispiel für die Krebstherapie notwendig. Nicht immer kann man dabei an große Beschleunigeranlagen gehen. Forschern gelingt nun neue Bestmarke bei der Laser-Beschleunigung dieser Teilchen.
In der Bestrahlungstherapie von Tumoren spielen schnelle Teilchen eine wichtige Rolle. So können Strahlen schneller Protonen genutzt werden um Augenkrebs zu bekämpfen. Die Erzeugung solcher hochenergetischer Partikelstrahlen ist jedoch nicht nur in großen Beschleunigeranlagen möglich.
Man kann auch Laserlicht nutzen um Protonen und andere geladene Teilchen extrem zu beschleunigen. Dazu wird die Wechselwirkung des Lasers mit einem Materietarget, also einem materiellen Zielobjekt, genutzt. Dabei werden mikroskopischen Längenskalen sehr große Feldstärken erzeugt.
In einem kürzlich vorgestellten Versuch wurde ein neuer Rekordwert für diese Art von Teilchenbeschleunigung erzielt. Einem Forscherteam, an dem mehrere US-amerikanische Universitäten und Forschungseinrichtungen und das Forschungszentrum Dresden-Rossendorf (FZD) beteiligt sind, gelang es, einen Protonenstrahl mit einer Energie von 67 MeV (Megaelektronvolt) zu erzeugen.
Das entspricht der Energie, die ein Elektron oder ein Proton aufnähme, würde es mit einer Spannung von 67 Millionen Volt beschleunigt. Zum Vergleich: An Synchrotron-Beschleunigern wie etwa dam BESSY in Berlin oder PETRA III in Hamburg werden Energien erreicht, die etwa hundert bis tausend mal so groß sind.
Möglich wird die Teilchenbeschleunigung mit Licht durch die hohe Energiedichte moderner Hochleistungs-Kurzpuls-Laser. Trifft ein Puls aus einer solchen Quelle auf Materie, werden die Elektronen derartig stark beschleunigt, dass sie sich von ihren Atomrümpfen lösen.
Ein Plasma entsteht. Die endliche Ausdehnung des Lichtpulses sorgt nun dafür, dass die Elektronen nicht nur quer zur Ausbreitungsrichtung des Lasers beschleunigt werden, wie man das auch bei weniger intensivem Licht beobachtet.
Statt dessen tritt, nach dem der Puls durch die Materie gewandert ist, eine Plasmawelle aus zurückschwingenden Elektronen auf, die auch eine Komponente in Laserausbreitungsrichtung enthält.
Keywords: laser acceleration; cone target; particle-in-cell; pic; simulation; proton energy; high-energy; laser; plasma; record
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Contribution to WWW
"Welt der Physik"-Podcast mit Dr. Jens Kube und einem Interview mit Dr. Michael Bussmann (Projektgruppe Laser-Teilchenbeschleunigung am Forschungszentrum Dresden-Rossendorf).: http://www.youtube.com/WeltDerPhysik#p/u/0/FEnuw2yh7Gc
Permalink: https://www.hzdr.de/publications/Publ-13826
Laser-Teilchenbeschleunigung
Bussmann, M.; Kluge, T.; Gaillard, S.; Flippo, K.; Cowan, T. E.; Schramm, U.
Abstract
Podcast zum Rekord für laser-beschleunigte Protonen von Kegeltargets.
Keywords: laser particle acceleration; particle-in-cell simulation; pic; proton; high energy; cone target; record; pizza-top
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Contribution to WWW
Welt der Physik Podcast "Laser-Teilchenbeschleunigung": http://www.weltderphysik.de/intern/upload/podcast/WeltDerPhysik043.mp3
Permalink: https://www.hzdr.de/publications/Publ-13825
Laser creates record-breaking protons
Cartlidge, E.; Flippo, K.; Gaillard, S.; Bussmann, M.; Kluge, T.
Abstract
An international group of physicists working at the Los Alamos Laboratory in the US has used a laser to generate 67.5 MeV protons the highest-energy protons yet produced in this way. Their work points the way to new laser-based devices for proton therapy, which would be far smaller and cheaper than existing particle-accelerator sources.
Keywords: cone target; proton acceleration; laser; plasma; trident; high-energy; record
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Contribution to WWW
IOP Physics World News: http://physicsworld.com/cws/article/news/40902
Permalink: https://www.hzdr.de/publications/Publ-13824
Record proton energies from laser acceleration with cone targets
Kluge, T.; Gaillard, S. A.; Bussmann, M.; Gall, B.; Gautier, D. C.; Geissel, M.; Kraft, S. D.; Lockard, T.; Offermann, D.; Schollmeier, M.; Sentoku, Y.; Schramm, U.; Zeil, K.; Cowan, T. E.; Flippo, K.
Abstract
High-Energy, short-pulse lasers can be used to accelerate ion beams. Laser-driven acceleration promises to provide very compact ion sources suitable for a variety of applications such as ion beam tumor therapy.
Up until recently, however, the ion energies observed in experiments were too low to be useful for treating tumors.
Using a novel target design, we have broken a long-lasting record for maximum proton energy measured in a laser acceleration experiment, reaching for the first time proton energies suitable for radiation therapy of intraocular tumors.
We present realistic particle-in-cell simulations of the laser interacting with the target that can explain the increase in energy seen in our experiment. The results from these simulations will help to improve the target design, paving the way towards even higher proton energies.
Keywords: cone target; laser; proton acceleration; high-energy; particle-in-cell; simulation; pic; grazing incidence; electron acceleration; cone wall; pizza-top
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Poster
NIC-SYMPOSIUM 2010, 24.-25.2.2010, Forschungszentrum Jülich, Deutscland
Permalink: https://www.hzdr.de/publications/Publ-13823
Laser Cooling of relativistic Ion Beams Prospects for high-energy Storage Rings
Bussmann, M.; Schramm, U.; Winters, D. F. A.; Wen, W.; Walther, T.; Birkl, G.; Nörtershäuser, W.; Novotny, C.; Geppert, C.; Kühl, T.; Kozhuharov, C.; Nolden, F.; Dimopoulou, C.; Steck, M.; Stöhlker, T.
Abstract
We present the setup for a new beam time on laser cooling of relativistic C3+ ion beams at the Experimental Storage Ring at GSI.
With laser cooling it becomes possible to reach very small relative momentum spread down to dp/p=10-7 even at high-energy storage rings.
With new laser sources and new optical diagnostics it will become possible to detect the onset of beam ordering expected for ultra-cold ion beams.
Keywords: laser cooling; ion beam; relativistic; strong coupling; optical diagnostics; laser sources
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Poster
SNI 2010, 24.-26.02.2010, Berlin, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13822
Simulating Laser Particle Acceleration on a Cluster of GPU Nodes
Bussmann, M.; Burau, H.; Widera, R.; Hönig, W.; Schmitt, F.; Juckeland, G.; Debus, A.; Kluge, T.; Schramm, U.; Cowan, T. E.; Sauerbrey, R.
Abstract
We present the particle-in-cell code PIConGPU. This fully-relativistic plasma code utilizes the computational power of graphic processing units.
We show that it scales well even on a cluster of GPU-enhanced nodes, by interleaving the communication between the GPU and CPU and the inter-node communication with the local computation steps.
Keywords: GPU; particle-in-cell; latency; communication algorithm; laser; plasma; acceleration; simulation; graphic cards; pic
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Invited lecture (Conferences)
The State of Affairs of GPU Computing in HPC, 09.02.2010, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13821
P0804 Skalierbare Terahertz-Antennen, ihre Herstellung und Verwendung
Winnerl, S.; Schneider, H.; Dreyhaupt, A.; Peter, F.; Helm, M.
Abstract
Mit der Erfindung wird eine Klasse von Bauelementen beschrieben, die es erlauben, beliebige Moden (definiert als räumliche Verteilung der elektrischen Feldstärke der Strahlung) von Terahertz-Wellen elementar zu erzeugen und in optimaler Weise, d. h. unter bestmöglicher Anpassung der Detektorgeometrie an die Mode, zu detektieren. Diese Freiheit bei der Erzeugung von Moden ist von grundlegendem Interesse für neue Anwendungen auf dem Gebiet der Terahertz-Strahlung und bringt große Vorteile bei Systemen, die Terahertz-Wellenleiter nutzen. Diese Terahertz-Emitter und -Detektoren zeichnen sich durch ihre Skalierbarkeit aus, so dass in den Emittern hohe Beschleunigungsfelder bei geringer Beschleunigungsspannung über große Flächen realisiert werden können. Damit wird der Betrieb vereinfacht und die Effizienz erhöht.
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Patent
DE102008023991A1 03.12.2009 -
Patent
EP2120291 31.12.2009
Permalink: https://www.hzdr.de/publications/Publ-13820
P0810 - Silizium-basierter Lichtermitter auf SOI-Substraten
Rebohle, L.; Skorupa, W.
Abstract
Die Erfindung beschreibt einen Si-basierten Lichtemitter, der aus einem frontseitigen Metallkontakt, einer dielektrischen Schutzschicht sowie einer Lumineszenzzentren enthaltenden SiO2-Schicht auf Silizium besteht, und derart auf SOI prozessiert wurde, dass er vorwiegend seitlich abstrahlt und sein Licht in eine Wellenleiterstruktur eingekoppelt werden kann.
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Patent
DE102008037225A1 25.02.2010
Permalink: https://www.hzdr.de/publications/Publ-13818
Effects of specimen size, initial crack acuity and test temperature on the master curve reference temperature
Viehrig, H.-W.; Zurbuchen, C.; Schindler, H.-J.; Kalkhof, D.
Abstract
This paper reports the investigation of different variables viz. specimen size, specimen geometry, crack to length ratio a/W and the sharpness of the initial crack on the Master Curve reference temperature T0. The investigations were performed on 1T-C(T) and SE(B) specimens with different thicknesses. The specimens were machined from a sections of a RPV forged ring of steel 22 NiMoCr 3 7 of the not commissioned German pressurized water reactor Biblis C.
It was found that SE(B) specimens with different sizes (specimen thickness B=0.4T, 0.8T, 1.6T, 3.2T, fatigue pre-cracked to a/W=0.5 and 20% side-grooved) have comparable T0, but with a trend to lower T0 as the size decreases. T0 is dependent on specimen type. T0 of 0.4T-SE(B) specimens is 86.1°C, 15 K below the T0 = 70.1°C of 1T-C(T) specimens. Specimens with a/W=0.3 and a/W=0.5 crack length ratios yield comparable T0. The T0 of EDM notched specimens lies 41 to 54 K below the T0 of fatigue pre-cracked specimens. This effect is observed for different specimen sizes (0.4T and 0.8T), in both SE(B) and C(T) specimen types and with different crack length ratios (a/W=0.5 and 0.3). The paper presents a first evaluation of data obtained within a larger research project. A more detailed scientific analysis of the data will follow.
Keywords: reactor pressure vessel steel; fracture toughness; Master Curve; compact tension specimen; single edge specimen; specimen size; fatigue crack; electroerosive notch; constraint
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Contribution to proceedings
18th European Conference on Fracture, 30.08.-03.09.2010, Dresden, Germany
Proceedings of the 18th European Conference on Fracture: 18th European Conference on Fracture -
Lecture (Conference)
18th European Conference on Fracture, 30.08.-03.09.2010, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-13817
Flow stability in magnetically manipulated vertical gradient freeze
Grants, I.; Klyukin, A.; Gerbeth, G.
Abstract
Instability of magnetically driven flow in a vertical cylinder is considered in presence of a stable thermal stratification. The magnetic body force is induced by either a travelling or a rotating magnetic field. The problem models vertical gradient freeze semiconductor crystal growth of medium or large size.
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Contribution to proceedings
6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland, pp. 869-872 -
Poster
6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13816
Model experiments on the melt flow driven by a two-phase inductor
Pedchenko, A.; Bojarevics, A.; Priede, J.; Gerbeth, G.; Hermann, R.
Abstract
The action of a two-phase inductor on the melt in a cylindrical cavity is investigated by corresponding velocity measurements in a GaInSn melt using ultrasonic Doppler velocimetry as well as local potential probes. The transition from a typical double vortex to a single toroidal vortex is shown depending on the phase shift between the two inductors.
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Contribution to proceedings
6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland, pp. 131-134 -
Lecture (Conference)
6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13815
Marginally turbulent MHD flow in a square duct
Shatrov, V.; Gerbeth, G.
Abstract
Direct numerical simulation of turbulent flow in a straight square duct was performed in the spanwise magnetic field. Without magnetic field the turbulence can be maintained for values of the bulk Reynolds number above approximately Re = 1077 [1]. In the magnetohydrodynamic case that minimal value of the bulk Reynolds number increases with the Hartmann number. For example the flow is laminar at Re = 3000 when the Hartmann number is larger than approximately Ha = 12.3 and the flow is turbulent when the Hartmann number is equal all smaller than Ha = 12.15. The secondary mean flow structure is analyzed.
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Contribution to proceedings
6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland, pp. 123-126 -
Poster
6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13814
Single crystal growth of intermetallic compounds by a two-phase RF floating zone method
Hermann, R.; Behr, G.; Gerbeth, G.; Priede, J.; Guguschev, C.; Krauze, A.; Büchner, B.
Abstract
The radio frequency floating-zone growth of massive intermetallic single crystals very often fails due to an unfavourable solid-liquid interface geometry enclosing concave fringes. This interface depends on the flow in the molten zone. A tailored magnetic two-phase stirrer system has been developed enabling to control the melt flow ranging from intense inwards to outwards flows. Depending on the phase shift between the two induction coils, a transition from a double vortex structure to a single vortex structure is created at a preferable phase shift of 90°. This change in the flow field has a significant influence on the shape of the solid-liquid interface. The magnetic system was applied to the crystal growth of TiAl alloys. The segregation behaviour was studied and the experimental results were compared to samples grown with the common optical floating-zone technique.
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Contribution to proceedings
6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland, pp. 849-852 -
Lecture (Conference)
6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13813
Comparison of numerical and experimental flow data from a liquid-metal model of a continuous casting mould
Maiwald, A.; Timmel, K.; Schwarze, R.; Gerbeth, G.
Abstract
Detailed knowledge of the flow fields in continuous casting moulds is of major importance, e.g., for the steel and the copper industry. Because there are only limited possibilities for measurements at real plant mould flows, model experiments and numerical simulations have been extensively used in the past for the inspection of mould flows. However, most data which are available in the literature are obtained at water model experiments, and most validation studies are based on those data sets. Recently, a new liquid-metal model of a continuous casting mould has been installed at the Forschungszentrum Dresden-Rossendorf. The facility allows for the first time flow measurements in liquid metal mould flows. The paper presents a first comparison of the experimental data with results from a numerical model of the mould flow. The numerical grid includes the submerged entry nozzle (SEN) and the mould. Simulations are performed with boundary conditions which fit to the operating parameters of the experiment. The Reynolds number based on the mean velocity and the hydraulic diameter of the SEN ports is about 4 x 104, the Reynolds number based on the mean velocity and the hydraulic diameter of the mould cross section area is about 3 x 103. The numerical model is based on the Reynolds-averaged Navier-Stokes (RANS) equations.
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Contribution to proceedings
6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland, pp. 239-242 -
Lecture (Conference)
6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13812
Conductivity in DFT
Gemming, S.
Abstract
In nanostructured materials spatial confinement effects lead to structure-dependent modifications of the bulk transport properties. In part, such modifications can be accounted for by a classical master equation approach for the transport of the different charge carrier species. The rather large quantity of parameters, which enter such an approach, can more or less easily be adjusted to the dimensional characteristics and the electronic settings of the system as well as to temperature effects. On the other hand, a microscopically more detailed and mostly parameter-free picture is obtained from a quantum-mechanical treatment on the basis of the density-functional theory. An extension by a Green's function formalism allows the determination and analysis of electronic transport through contacted nanostructures. Examples will be given to demonstrate the applicability of the different approaches for dissipative and hopping transport through a regular array of nanostructures, for a mechanically triggered metal-insulator transition in nanowires, and for the enhanced conductivity at multiferroic domain walls.
Keywords: DFT; conductivity
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Lecture (Conference)
Wilhelm-und-Else-Heraeus Physics School on Density Functional Theory and its Applications in Crystallography, 07.-11.02.2010, Aachen, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13811
Density-functional theory within multi-scale modelling
Gemming, S.
Abstract
Modeling the changes in materials during everyday use requires a thorough understanding of processes on length and time scales which span several orders of magnitude. Standard simulation techniques are commonly restricted to much smaller ranges in length and time, thus a method hierarchy is desirable to join the virtues of approaches at different scales and employ this synergy for a scale-adapted description of modifications which materials undergo during processing and use. Electronic interactions including optical, magnetic and transport phenomena range at the shortest, the nanoscopic time and length scales. Their proper description provides the basis for more average meso- and macro-scale quantities, thus a precise nano-scale modelling provides the basis for a detailed and quantitative understanding of the macroscopic material piece. Density-functional theory is a computationally efficient numerical tool which provides fast access to the ground-state electronic properties and perturbation expansions yield also observables for more complex physical interactions. Determination of relevant processes at the atomistic scale and suitable averaging then yields input parameters for more meso-/macro-scale particel-based or continuum approaches.
Keywords: multiscale modelling; density functional theory; DFT
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Lecture (Conference)
Wilhelm-und-Else-Heraeus Physics School on Density Functional Theory and its Applications in Crystallography, 07.-11.02.2010, Aachen, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13810
DNS and LES of separation control using oscillating Lorentz forces
Albrecht, T.; Marlow, F.; Metzkes, H.; Stiller, J.
Abstract
The separated flow around an inclined flat plate at a Reynolds number 10↑4 has been computed using Direct Numerical and Large Eddy Simulation. A Lorentz force oscillates near the leading edge to reduce the separated flow region and increase the lift coefficient. Since no theory on relevant spanwise length scales of this flow is known to the authors, different mesh sizes have been investigated. Lift and drag coefficients seem to converge for ratio of spanwise length to chord ≥ 0.3. Although a comparison with PIV measurements is already quite satisfactory, simulation time should be extended to allow for more reliable statistics.
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Lecture (Conference)
6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland -
Contribution to proceedings
6th International Conference on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, Deutschland, pp. 688-691
Permalink: https://www.hzdr.de/publications/Publ-13809
Dosimetric characterization of laser-accelerated particles
Richter, C.
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Lecture (others)
5th Meeting of the Scientific Advisory Board of OncoRay, 04.03.2010, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13808
Auf dem Weg zu systematischen radiobiologischen Experimenten mit laserbeschleunigten Protonen: Entwicklung, Charakterisierung und Einsatz eines integrierten Dosimetrie- und Zellbestrahlungssystems
Richter, C.; Akhmadaliev, S.; Beyreuther, E.; Dammene, Y.; Karsch, L.; Laschinsky, L.; Leßmann, E.; Naumburger, D.; Schürer, M.; Sobiella, M.; Weber, A.; Pawelke, J.; Baumann, M.
Abstract
Abstract too long (9790) - is not allowed from system
Keywords: laser; radiooncology; cell irradiation; laser particle acceleration
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Lecture (Conference)
19. Symposium - Experimentelle Strahlentherapie und Klinische Strahlenbiologie, 04.-06.03.2010, Dresden, Deutschland - Experimentelle Strahlentherapie und klinische Strahlenbiologie 19(2010), 192-195
Permalink: https://www.hzdr.de/publications/Publ-13807
Development of Diode-pumped lasers for ultra-high peak-power
Röser, F.; Siebold, M.; Loeser, M.; Kroll, F.; Schramm, U.; Sauerbrey, R.
Abstract
100J-class diode-pumped lasers (HEC-DPSSLs)
Laser materials
Spectroscopic & thermo-mech. properties
Optical Quality
PW-Laser development @ FZD
Applications
Laser electron acceleration
Laser ion acceleration
Keywords: HEC-DPSSL; diode; pumped; solid; state; laser; PW project
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Lecture (others)
PS&A Seminar Series, 04.02.2010, Livermore, CA, USA
Permalink: https://www.hzdr.de/publications/Publ-13806
Optical absorption, luminescence, and electron paramagnetic resonance (EPR) spectroscopy of crystalline to metamict zircon: Evidence for formation of uranyl, manganese, and other optically active centers
Kempe, U.; Thomas, S.-M.; Geipel, G.; Thomas, R.; Plötze, M.; Böttcher, R.; Grambole, G.; Hoentsch, J.; Trinkler, M.
Abstract
wird nachgereicht
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American Mineralogist 95(2010), 335-347
DOI: 10.2138/am.2010.3248
Cited 17 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13805
Untersuchungen zum Einfluss von Huminsäuren auf die Migration von Actiniden in der Umwelt
Sachs, S.
Abstract
Huminsäuren (HS), ubiquitär vorkommende organische Makromoleküle, spielen eine wichtige Rolle in geochemischen Wechselwirkungsprozessen von Metallionen. HS sind löslich im pH-Bereich natürlicher Wässer und zeigen die Fähigkeit Metallionen zu komplexieren und Kolloide zu bilden. Außerdem sind HS durch ein ausgeprägtes Redoxverhalten charakterisiert. Aufgrund dieser Eigenschaften können HS die Speziation und somit auch den Transport von Metallionen, z. B. Actinidionen, in der Umwelt beeinflussen. Detaillierte Kenntnisse der geochemischen Wechselwirkungsprozesse von HS mit Actiniden sind z. B. für Langzeitsicherheitsanalysen für zukünftige Endlager hochradioaktiver Abfälle sowie zur Sanierung kontaminierter Flächen und Einrichtungen des ehemaligen Uranbergbaus erforderlich.
Im Vortrag werden am Beispiel von Uran detaillierte Untersuchungen zur Komplexierung von Actiniden mit HS vorgestellt. Der Einfluss der Uran-HS-Komplexierung auf die Uranspeziation wird anhand von Speziationsdiagrammen diskutiert. Weiterhin wird anhand von Ergebnissen aus Sorptions- und Transportuntersuchungen der mögliche Einfluss von HS auf Immobilisierung und Migration von Uran im Tongestein diskutiert und mit anderen Actiniden verglichen.
Keywords: Humic acid; uranium; complexation; speciation; migration; sorption; environment; clay; actinides
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Invited lecture (Conferences)
Umwelttechnisches Fachseminar "Wissenschaft&Praxis" des Instituts für Verfahrensentwicklung, Torf- und Naturstoff-Forschung (iTN), 31.03.2010, Zittau, Germany
Permalink: https://www.hzdr.de/publications/Publ-13804
Saturation of the filament density of ultrashort intense laser pulses in air
Henin, S.; Petit, Y.; Kasparian, J.; Wolf, J.-P.; Jochmann, A.; Kraft, S. D.; Bock, S.; Schramm, U.; Sauerbrey, R.; Nakaema, W. M.; Stelmaszczyk, K.; Rohwetter, P.; Wöste, L.; Soulez, C.-L.; Mauger, S.; Bergé, L.; Skupin, S.
Abstract
We experimentally and numerically characterize multiple filamentation of laser pulses with incident intensities of a few TW/cm2. Propagating 100 TW laser pulses over 42 m in air, we observe a new propagation regime where the filament density saturates. As also evidenced by numerical simulations in the same intensity range, the total number of filaments is governed by geometric constraints and mutual interactions among filaments rather than by the available power in the beam.
Keywords: High power laser propagation in air; filamentation; multiple filamentation
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Applied Physics B 100(2010), 77
DOI: 10.1007/s00340-010-3941-x
Cited 40 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13803
Chemical bonds and formation process of actinide(IV) oligomers and colloids
Hennig, C.; Takao, K.; Takao, S.; Ikeda-Ohno, A.; Banerjee, D.; Weiss, S.; Zaenker, H.; Kraus, W.; Emmerling, F.; Scheinost, A. C.
Abstract
Tetravalent actinides show a strong tendency towards hydrolysis followed by the formation of oligomers and colloids. This formation process was investigated on Th(IV), U(IV) and Np(IV) species with EXAFS, LIBD, XPS, HEXS, UV-Vis, NMR and XRD. We investigated the involved chemical bonds, the local structure and structure development as well as the formation mechanism.
We observed that the oligomerization of tetravalent actinides was limited by the presence of chelating ligands. The presence of carboxylic acids, for example, resulted in hexanuclear complexes [1]. Such polynuclear species consist of a framework made of oxo and hydroxo bonds which is terminated by chelating carboxylic acids. In absence of such terminating ligands, the polymerization often continues until stable colloids are formed [2]. This formation process is kinetically hindered due to several reasons related with (a) the limited number of OH groups in the An(OH)n4-n precursor and (b) terminating water molecules. The polymerization comprises of olation and oxolation processes. At a later stage, the initially amorphous structure of the colloides undergoes an ordering process during which hydroxo groups are systematically replaced by oxo groups. Zeta potential measurements indicated that the colloidal particles carry positive charge at acidic pH and negative charge at alkaline pH. We found that silicate is able to stabilize such colloids at near-neutral pH through modification of the inner structure and by influencing the electrostatic repulsion caused by an enhanced negative surface charge.
UV/Vis, EXAFS spectroscopy and light scattering proved to be sensitive tools to differentiate between hydolysis species, oligomers and colloids.
[1] Takao et al. (2009) Eur. J. Inorg. Chem. 32, 4771-4775.
[2] Ikeda-Ohno et al. (2009) Inorg. Chem. 48, 7201-7210.
Keywords: UV/Vis; EXAFS; light scattering; hydolysis species; oligomers; colloids
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Abstract in refereed journal
Geochimica et Cosmochimica Acta 74(2010), A400-A400 -
Lecture (Conference)
Goldschmidt Conference, 13.-18.06.2010, Knoxville, USA
Permalink: https://www.hzdr.de/publications/Publ-13802
Homogeneity study for obsidian provenancing by ion beam analysis
Eder, F.; Neelmeijer, C.; Bichler, M.; Merchel, S.
Abstract
Obsidian is a natural volcanic glass which was one of the most appreciated materials by of ancient man for cutting tools and has been found by researchers in many locations, far away from any natural source. Reliable provenancing can provide evidence of contacts over a certain distance and information about exchange patterns and mobility of prehistoric people.
The application of analytical methods can solve the problem of obsidian provenancing by means of its highly specific chemical composition, the chemical fingerprint. Combined external Ion Beam Analysis (IBA) measurements, consisting of Proton Induced X-ray Emission (PIXE), Proton Induced Gamma-ray Emission (PIGE) and Rutherford Backscattering Spectrometry (RBS), are frequently used due to the high sensitivity and the non-destructive beam mode. Our study has been carried out at the 5 MV Tandem accelerator of the Ion Beam Centre of FZD, where a number of quantitative glass analyses has been performed simultaneously with all three external ion beam techniques [1-5].
Obsidian usually exhibits a very uniform appear-ance and is generally described as a relatively homogeneous material. Banded obsidians can be observed also, and the question was raised, if these bands are caused by differences in the chemical composition or if these changes in the optical properties are related to inclusions of clouds of gas bubbles, microphenocrysts or similar features without significant compositional influence. Therefore, a systematic investigation of a banded obsidian sample from Demengakion (Milos, Greece) has been carried out in order to check the actual variation range of the chemical composition. (Fig. 1).
To investigate the influence of different preparation techniques on the analytical results, we produced an obsidian in-house reference sample (Fig. 2). This specimen originates from the highly homogeneous obsidian source Hrafntinnuhryggur (Iceland) and features three different surfaces: natural fracture, ground finish (1200 diamond lap) and polished [6].
This study is part of a project which aim is to apply selected analytical methods, in particular IBA, Neutron Activation Analysis (NAA) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), to detect a maximum of compositional differences between easily available samples of the natural obsidian sources in Europe. This knowledge should enable to decide, which least invasive analytical method should be chosen for the analysis of a specific archaeological artefact, on a case by case basis.
References: [1] Bugoi R. and Neelmeijer C. NIMB 226 (2004) 136146. [2] Mäder M. et al. NIMB 239 (2005) 107-113. [3] Mäder M. and Neelmeijer C. NIMB 226 (2004) 110118. [4] Jembrih D. et al. NIMB 181 (2001) 698702. [5] Mäder M. et al. NIMB 136-138 (1998) 863868. [6] Tuffen H. and Castro J. M. Journal of Volcanology and Geothermal Research 185 (2009) 352366.
Keywords: archeometry; RBS; PIXE; PIGE
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Poster
Ionenstrahlphysik-Workshop 2010, 29.-31.03.2010, Dresden-Rossendorf, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13801
Landweber-EXAFS structural analysis of aqueous polynuclear U(VI) complexes with tartaric acid
Rossberg, A.; Lucks, C.; Tsushima, S.; Scheinost, A. C.
Abstract
In coordination chemistry, an open question is if the structure of an aqueous metal complex is equal to the structure of its solid form. While the structure of the solid can usually be determined with great reliability and precision by XRD, determination of the structure in solution by EXAFS may be much more biased. An intrinsic problem of EXAFS shell fitting is that the radial pair distribution function (RPDF) is approximated by Gaussians functions imitating the coordination shells. Different combinations of shells can yield different structures with similar fit quality, thereby making the structural solution non-unique. Even the so-called F-test often does not allow obtaining a unique solution.
Therefore, we developed two methods which enable the direct calculation of the RPDF and the spatial structure of metal complexes in solution. Solely based on the FEFF scattering theory, the Landweber inverse method [1] yields the RPDF for the aqueous bi- and tri-nuclear U(VI)-tartaric acid complexes without predefined assumptions about the form of the RPDF. With this information and density functional theory (DFT) calculations, the spatial structures of the complexes are refined by Monte Carlo Target Transformation Factor Analysis [2], which also include the calculation of higher order scattering events. Using this combinatorial structural analysis, we were able to show that in the (UO2)3(H-1Tar)3(OH)25- complex a central equatorial oxygen atom at a radial U-O distance of 2.22 Å connects the three uranium atoms symmetrically. Consequently, the formula of the aqueous complex corresponds to its stoichiometric equivalent (UO2)3(mue3-O)(H-1Tar)35-.
[1] Rossberg & Funke (2010), J. Synchr. Rad. 17, 280-288.
[2] Rossberg et al. (2005), Anal. Bioanal. Chem. 383, 56-66.
Keywords: Landweber iteration; EXAFS; uranium; tartaric acid; aqueous; complexes; radial pair distribution function
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Abstract in refereed journal
Geochimica et Cosmochimica Acta 74 Suppl.1(2010)12, A884 -
Poster
Goldschmidt 2010, 13.-18.06.2010, Knoxville, USA
Permalink: https://www.hzdr.de/publications/Publ-13800
Ion Beam Analysis at FZD: Achievements and Perspectives
Munnik, F.; Heller, R.
Abstract
There are many applications for which it is important to know the composition of surface layers and even to know the composition as a function of depth. Such information is needed for (ultra) shallow implantation profiles and the damage caused by implantation, diffusion barriers for IC technology, interface mixing in IBAD processing, multilayers for X-ray mirrors, magnetic multilayer structures, etc.
Ion Beam Analysis (IBA) can provide answers through a variety of methods for the compositional analysis of surface layers. In this presentation, the principles of (IBA) are presented with the emphasis on those methods useful for materials science like Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA). The possibilities of analysis with our equipment is shown by means of examples of applications.
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Lecture (others)
Materials Science Seminar, 19.01.2010, Dresden, Germany
Permalink: https://www.hzdr.de/publications/Publ-13799
Autonomous sensor particle for parameter tracking in large vessels
Thiele, S.; Da Silva, M. J.; Hampel, U.
Abstract
We developed a neutrally buoyant self-powered sensor particle for the measurement of spatially distributed process parameters in large vessels. One intended application is the measurement of flow parameters in stirred fermentation biogas reactors. The prototype sensor particle is a robust and neutrally buoyant capsule with integrated measurement electronics which performs logging of temperature, absolute pressure (immersion depth) and 3D-acceleration data. In an initial flow experiment the autonomous operation of the developed prototype was successfully proven, showing feasibility for future application in fermentation reactors and other industrial processes.
Keywords: Autonomous Sensing; Parameter Tracking; Multi-Parameter Measurement; Neutral Buoyancy; Sensor Particle
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Measurement Science and Technology 21(2010)8
DOI: 10.1088/0957-0233/21/8/085201
Cited 13 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13798
Reaction of Pu(III) and (V) with magnetite and mackinawite: a XANES/EXAFS investigation
Kirsch, R.; Fellhauer, D.; Altmaier, M.; Neck, V.; Rossberg, A.; Charlet, L.; Scheinost, A. C.
Abstract
Plutonium is the major transuranium actinide in nuclear waste and a highly toxic environmental contaminant. As iron(II) minerals are ubiquitous and known to reduce a range of metal(loid)s, including As, Cr, Se, Pu and Np, through surface-mediated redox reactions, we investigated here the reactivity of magnetite (Fe3O4) and mackinawite (FeS) towards Pu(III) and (V) using XAFS to analyse the oxidation state and molecular structure of the reaction products.
Experimental Conditions
Mineral syntheses and reactions were carried out under anoxic conditions in N2 or Ar glove-boxes. Fe3O4 and FeS were reacted for 40 days in 0.1 M NaCl with Pu (1x10-5M) at approx. pH 8. 242Pu was added as electrolytically prepared Pu(V) to Fe3O4 and FeS, and as Pu(III) to Fe3O4.
Results and Discussion
The spectra obtained from tri- and pentavalent Pu reacted with magnetite are nearly identical; shell fitting yielded a Pu-O distance of 2.50 Å, indicative of Pu(III). Using Monte Carlo modeling of the EXAFS spectra (MC) [1], we were able to unequivocally identify a distinct Pu(III) surface complex wherein Pu(III) is connected via three oxygen atoms to three edge-sharing FeO6-octahedra of the Fe3O4 {111} face. This result is in disagreement with [2], where in the absence of spectroscopic methods Pu(IV) had been determined as the oxidation state resulting from reduction of Pu(V) by magnetite under anoxic conditions. After reaction of Pu(V) with mackinawite, Pu(IV) was identified as the prevalent Pu oxidation state by both XANES and EXAFS shell fitting. The EXAFS spectrum closely ressembles that of PuO2 solids and colloids. Our study demonstrates that under reducing conditions in geological environments both Pu(IV) and Pu(III) species may be relevant and migration as eigen-colloids or adsorbed species may play an important role in controlling Pu mobility.
Keywords: Plutonium; XAFS; XANES; EXAFS; magnetite; mackinawite; redox reaction; surface complex
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Abstract in refereed journal
Geochimica et Cosmochimica Acta 74 Suppl.1(2010)12, A520
ISSN: 0016-7037
Permalink: https://www.hzdr.de/publications/Publ-13796
Measurement of the hydrogen concentration in indium oxide tubular nanostructures
Voelskow, M.; Grambole, D.; Skorupa, W.; Kanjilal, A.; Kumar, M.; Chatterjee, R.; Milikisiyants, S.; Lakshmi, K. V.; Singh, J. P.
Abstract
Hydrogen is ubiquitous and it is often difficult to remove hydrogen from synthesis of nano-materials. Therefore, studying interaction of hydrogen with metals and semiconductors is of immense interest owing to the development of efficient materials for the storage of hydrogen and gas-sensing devices.
Keywords: Hydrogen; indium oxide; nuclear methods
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Poster
Workshop Ionenstrahlphysik, 29.-31.03.2010, Dresden, BRD
Permalink: https://www.hzdr.de/publications/Publ-13795
Photon Counting System for Time-resolved Experiments in Multibunch Mode
Puzic, A.; Korhonen, T.; Kalantari, B.; Raabe, J.; Quitmann, C.; Juellig, P.; Bommer, L.; Goll, D.; Schuetz, G.; Wintz, S.; Strache, T.; Koerner, M.; Marko, D.; Bunce, C.; Fassbender, J.
Abstract
Photon Counting System for Time-resolved Experiments in Multibunch Mode
Keywords: photon counting; synchrotron radiation; multibunch; time-resolved; magnetic imaging
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Synchrotron Radiation News 23(2010)2, 26-32
DOI: 10.1080/08940881003702056
Cited 19 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13794
Spektroskopische Bestimmung der Bindungsform von Europium(III) und Curium(III) im menschlichen Urin
Heller, A.; Barkleit, A.; Bernhard, G.; Ackermann, J.-U.
Abstract
Das Institut für Radiochemie des Forschungszentrums Dresden-Rossendorf e.V. beschäftigt sich mit der Aufklärung des Schicksals von radioaktiven Schwermetallen in der Umwelt. Hierzu werden u. a. sowohl die Bindung an natürlich vorkommende Liganden untersucht, als auch die komplexeren Wechselwirkungen in Pflanzen- und Bakterienzellen oder in Biofluiden. Die vorgestellte Promotionsarbeit befasst sich dabei mit der spektroskopischen Aufklärung der Bindungsform von Curium(III) und Europium(III) in natürlichem, menschlichem Urin.
Curium und Europium sind zwei f-Elemente, deren Metabolismus im Biosystem bis heute nicht vollständig geklärt ist. Da Curium innerhalb des Kernbrennstoffzyklus gebildet wird und nur radioaktive Isotope aufweist, stellt es im Falle einer Kontamination oder unfallbedingter Freisetzung in die Umwelt eine ernste Gefahr für die Gesundheit dar. Um mögliche Dekontaminationsmittel zu erforschen, müssen daher sein Metabolismus und die Bindungsform in Biofluiden bekannt sein. Im Gegensatz dazu ist Europium nicht radioaktiv und gewinnt in der Medizin immer mehr an Bedeutung als Bestandteil von Kontrastmitteln in der bildgebenden Diagnostik. Trotz seiner wachsenden Applikation ist auch der Metabolismus dieses Metalls bisher unbekannt. Beide Elemente weisen ähnliche Eigenschaften auf, da sie in Form ihrer dreiwertigen Ionen vergleichbare Elektronenkonfigurationen besitzen. Aufgrund seiner besseren Handhabbarkeit wird Europium daher oft als Analogon für Curium verwendet. Darüber hinaus zeigen beide Elemente einzigartige Fluoreszenzeigenschaften. Dies erlaubt Untersuchungen mittels (zeitaufgelöster) laserinduzierter Fluoreszenzspektroskopie im Spurenkonzentrationsbereich.
Urin ist das Hauptausscheidungsmedium im menschlichen Körper und besteht zu über 90 % aus Harnstoff. Mögliche Reaktionen mit dieser Matrixkomponente wurden daher zuerst untersucht. Weitere biologisch relevante, organische Liganden, deren Komplexbildungsvermögen gegenüber Curium(III) und Europium(III) ebenfalls untersucht wurde, sind Citronensäure und Aminosäuren. Die Ergebnisse zeigen, dass die Komplexirung mit Harnstoff vernachlässigbar gering ist und Aminosäuren bei physiologisch relevanten pH-Werten ebenfalls nur schwache Komplexe bilden. Demgegenüber bildet Citronensäure starke Komplexe mit beiden Metallen.
Erste Aufnahmen von Lumineszenzspektren natürlicher, menschlicher Urinproben, die in vitro mit einem der beiden Elemente versetzt wurden, zeigen, dass bei niedrigeren pH-Werten Komplexe mit Citronensäure dominieren. Im Gegensatz dazu scheinen bei höheren pH-Werten Komplexe mit anorganischen Liganden, vorzuherrschen.
Keywords: Eu(III); Cm(III); Biofluide; Komplexierung; TRLFS; Speziation von Schwermetallen
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Lecture (others)
Umweltkolloquium, 01.04.2010, Dresden, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13793
Relaxation dynamics in graphene investigated in the mid- and far-infrared spectral range
Winnerl, S.; Helm, M.; Malic, E.; Knorr, A.
Abstract
We describe experiments and microscopic modelling based on density matrix theory to study the relaxation dynamics in graphene. Experiments using the free-electron laser at FZD include also experiments in magnetic fields which will show how Landau quantization can quench relaxation channels.
Keywords: graphene; relaxation dynamics
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Poster
Begutachtungskolloquium zum Schwerpunktprogram "Graphen" der DFG, 21.-22.01.2010, Bad Honnef, Germany
Permalink: https://www.hzdr.de/publications/Publ-13792
Large Scale and Small Scale Terahertz Sources for Spectroscopy
Winnerl, S.
Abstract
We present FELBE, the free-electron laser at FZD and discuss time-resloved experiemnts using its radiation. Furthermore we discuss tabletop terahertz sources based on surface emitters and scalable photoconductive emitters.
Keywords: Terahertz; free-electron laser; photoconductive emitter
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Lecture (others)
Seminarvortrag in der Gruppe von K. von Klitzing, 21.12.2009, Stuttgart, Germany
Permalink: https://www.hzdr.de/publications/Publ-13791
Efficiency, energy, and power scaling of diode-pumped, short-pulse laser amplifiers using Yb-doped gain media
Siebold, M.; Loeser, M.; Koerner, J.; Wolf, M.; Hein, J.; Wandt, C.; Klingebiel, S.; Karsch, S.; Schramm, U.
Abstract
We present a novel approach to overcome efficiency limitations of nanosecond lasers based on Yb-doped materials. Furthermore, we introduce a combination of bulk and thin-disk design for power scaling of diode-pumped lasers.
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Lecture (Conference)
Advanced Solid-State Photonics (ASSP), 31.01.-03.02.2010, San Diego, USA -
Contribution to proceedings
Advanced Solid-State Photonics (ASSP), 31.01.-03.02.2010, San Diego, USA
Efficiency, Energy, and Power Scaling of Diode-Pumped, Short-Pulse Laser Ampliers Using Yb-Doped Gain Media: OSA Technical Digest Series, AWB19
Permalink: https://www.hzdr.de/publications/Publ-13790
Humic acid model substances with pronounced redox functionality for the study of environmentally relevant interaction processes of metal ions in the presence of humic acid
Sachs, S.; Bernhard, G.
Abstract
Humic acid (HA) model substances with pronounced redox functionality were synthesized by oxidation of hydroquinone or catechol in the presence of glycine or glutamic acid and characterized concerning their elemental, structural and functional properties. In order to characterize the redox properties of the synthetic products, formal redox potentials and Fe(III) reducing capacities were determined and compared to purified Aldrich HA (AHA). Furthermore, the reduction of U(VI) in the presence of HA was studied.
The synthetic products show elemental, functional and structural properties comparable to natural HA, however, they are characterized by high amounts of phenolic/acidic OH groups. Furthermore, the synthetic HA show significantly higher reducing capacities for Fe3+ and [Fe(CN)6]3- at pH 3.0 and at pH 9.2, respectively, than AHA. The highest reducing capacities were obtained for HA Cat-Gly, an oxidation product from catechol and glycine, which is characterized by the lowest formal redox potential of all studied HA. Indications for a slight reduction of U(VI) in the presence of HA were observed, whereby, HA Cat-Gly exhibits again the highest reducing capacity. Using modified HA with blocked phenolic/acidic OH groups the importance of these functional groups for the redox behavior of HA was confirmed.
Synthetic HA with pronounced redox functionality can be used to study the redox behavior of HA and the redox stability of metal ions in the presence of HA and furthermore, to stabilize redox-sensitive metal ions against oxidation in complexation and transport studies with HA. This contributes to a better understanding of interaction processes of metal ions with humic substances in soils, sediments and waters.
Keywords: Humic acid; humic acid model substances; synthesis; characterization; redox behavior; redox potential; reducing capacity; iron(III); uranium(VI)
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Geoderma 162(2011), 132-140
DOI: 10.1016/j.geoderma.2011.01.012
Cited 30 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13789
Degradation of cover SiO2 on Ge during Ga implantation
Fiedler, J.; Heera, V.; Bischoff, L.; Facsko, S.; Heinig, K.-H.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Voelskow, M.; Wündisch, C.; Skorupa, W.; Gobsch, G.
Abstract
Germanium is currently considered as a potential replacement for silicon devices [1]. The formation of heavily doped, shallow junctions in Ge by ion im-plantation and appropriate annealing techniques is under investigation [2, 3]. In contrast to Si the Ge surface is severely affected by irradiation damage. Im-plantation into the uncovered Ge surface leads to sur-face roughening and even porous layers [3]. Therefore, the Ge surface must be protected by a thin cover layer, which is commonly a sputtered SiO2-layer between 10 and 30 nm. This cover layer remains on the Ge sample also during annealing. For light dopants like B or P this oxide layer remains stable and smooth. However, with increasing ion mass and fluence surface erosion and oxide degradation can occur. A relatively heavy ion of interest is Ga [3]. It is a shallow acceptor with a high solid solubility in Ge. We studied the effect of Ga im-plantation through a SiO2 cover layer.
Keywords: doping of germanium; cover SiO2; Ga implantation; surface degradation
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Poster
Workshop Ionenstrahlphysik, 29.-31.03.2010, Dresden-Rossendorf, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13788
Non-termination of yrast bands at maximum configuration spin in 73Kr
Steinhardt, T.; Eberth, J.; Thelen, O.; Schnare, H.; Schwengner, R.; Plettner, C.; Käubler, L.; Dönau, F.; Algora, A.; de Angelis, G.; Gadea, A.; Napoli, D. R.; Hausmann, M.; Jungclaus, A.; Lieb, K. P.; Müller, G. A.; Jenkins, D. G.; Wadsworth, R.; Wilson, A. N.
Abstract
High-spin states in 73Kr were studied at the XTU tandem accelerator of the Laboratori Nazionali di Legnaro using the reaction 40Ca(40 Ca,2pn) at a beam energy of 185 MeV. Gamma rays were detected with the EUROBALL spectrometer. Particle detection enabled us to identify the reaction channel leading to 73Kr. The yrast bands of positive and negative parity were established up to probable spins of 61/2+ and 63/2- , respectively. The energies of the two identified bands agree well with the predictions of the configuration-dependent Cranked Nilsson-Strutinsky approximation and indicate that the nucleus remains collective up to the maximum spins of the respective high-spin configurations. The positive-parity band represents one of the rare cases where band non-termination at the highest spin of the configuration could be established experimentally.
Keywords: Nuclear structure; gamma-ray spectroscopy; particle detection; EUROBALL; Cranked Nilsson-Strutinsky calculations
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Physical Review C 81(2010), 054307
DOI: 10.1103/PhysRevC.81.054307
Cited 4 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13787
Two models of PT Quantum Mechanics and their behavior in the vicinity of spectral singularities
Günther, U.; Samsonov, B.; Rotter, I.; Graefe, E.-M.; Korsch, H.-J.; Niederle, A.
Abstract
The last ten years witnessed a strong research activity into so called PT Quantum Mechanics (PTQM) --- a Quantum Mechanics whose Hamiltonians are allowed to be non-Hermitian but PT-symmetric. In general, PTQM has sectors of exact PT-symmetry with purely real energy spectrum as well as sectors of spontaneously broken PT-symmetry with pairwise complex conjugate energy branches. Sectors of exact PT-symmetry can be isomorphically mapped into models of conventional (von Neumann) Quantum Mechanics (possibly of highly nonlocal type). Sectors of spontaneously broken PT-symmetry might have realizations as certain effective quantum systems. Varying the coupling parameters of PTQM models the corresponding quantum system can undergo phase transitions from exact PT symmetry to spontaneously broken PT-symmetry. Such PT phase transitions are associated with branch points (exceptional points) of the energy spectrum --- so called spectral singularities.
In the talk two PTQM models and their behavior in the vicinity of spectral singularities will be discussed.
In the first part of the talk, I will report on the quantum brachistochrone problem for PTQM, i.e. the problem of finding a PT-symmetric Hamiltonian which minimizes the time needed for evolving a given initial state into a predefined final state (e.g. for a spin-flip). This problem was solved by Bender, Brody, Jones and Meister in 2007. It turned out that in PTQM the evolution time for a spin flip can be tended toward zero so that the Aharonov-Anandan lower bound on the evolution time for Hermitian systems would be violated --- a kind of "quantum wormhole" effect. In 2007 we showed that this effect occurs in the vicinity of a PT phase transition (a spectral singularity). A still open problem at that time was a possible scheme for an experimental realization, because one somehow would have to switch between PTQM and experimental setups based on conventional QM. In [Phys. Rev. Lett. 101, 230404, 2008] we solved this switching problem by embedding the PTQM brachistochrone into a higher dimensional Hilbert space. In this way we found a realization of the PTQM brachistochrone evolution as a special kind of tuned unitary evolution in a highly asymmetrically entangled two-qubit setup --- which in principle might be realized experimentally in the nearest future.
The second part of the talk will be devoted to a non-Hermitian PT-symmetric two-mode Bose Hubbard model which might describe e.g. a BEC in a double-well potential with additional well-balanced gain-loss couplings. The main focus is laid on the unfolding of the higher-order spectral singularities typical for this kind of models. A perturbative Newton polygon technique allows us to qualitatively explain the numerically obtained branching behavior of the energy spectrum. It turns out that the Hessenberg type of the effective coupling matrix is responsible for the special Galois structure of the occurring eigenvalue rings in the complex energy plane.
Keywords: PT quantum mechanics; spectral singularity; exceptional point; quantum brachistochrone; spin flip; Naimark dilation; two-qubit state; Bose Hubbard model; Bose Einstein condensate; Newton polygon technique; Galois structure; eigenvalue ring; singularity unfolding; Hessenberg type
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Lecture (Conference)
Many-Body Open Quantum Systems: From Atomic Nuclei to Quantum Dots, 22.-26.02.2010, Trento, Italy
Permalink: https://www.hzdr.de/publications/Publ-13786
XPS and XAS investigation of Sb(V) reduction on mackinawite: Effect of pH and surface loading
Banerjee, D.; Kirsch, R.; Scheinost, A. C.
Abstract
Sb exists in nature in a wide range of oxidation states and can be a potential hazardous contaminant depending on its speciation and reactivity. In this study we employed cryogenic-XPS and XAS techniques in order to understand the reduction of SbV at the surface of mackinawite (FeS) as a function of pH and surface loading.
Experimental Conditions
Nanoparticulate, Mackinawite samples were prepared and stored as suspensions under strictly anoxic conditions (~ 1 ppmv O2) in a Jacomex glovebox. Sorption experiments at pH 5 and pH 8 with increasing Sb concentrations (0.1, 0.3, 0.6, 0.8 mM) were also conducted in the same glovebox under anoxic conditions [1, 2]. X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) measurements were conducted on frozen wet pastes of reacted mackinawite samples.
Results and Discussion
Sb3d XPS spectra of reacted sample series at pH 5 revealed presence of increasing amounts of SbIII at the surface suggesting that the rate of reduction of SbV was directly proportional to surface loading. Corresponding Fe 2p ans S 2p spectra of the same samples showed significant increase in the proportion of FeIII species and presence of S0 at the surface. However, the proportion of S0 remained constant suggesting that Fe is the dominant redox partner in this sytem. At pH 8, presence of SbIII was only observed at higher surface loadings indicating that adsorption and redox processes both occur at much slower rate compared to that at pH 5. In addition, increased contribution of surface monosulfide group at pH 5 suggest that Sb is most likely bound to S atoms at the surface, which was confirmed by Sb K-edge EXAFS spectra. In contrast, at pH 8, such increase in surface monosulfide contributions are absent, suggesting Sb is most likely bound to O atoms at the surface.
Keywords: XPS; mackinawite; redox processes; surface loading; EXAFS
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Lecture (Conference)
Goldschmidt 2010, 13.-18.06.2010, Knoxville, USA -
Abstract in refereed journal
Geochimica et Cosmochimica Acta 74(2010)11, A47-A47
Permalink: https://www.hzdr.de/publications/Publ-13785
N-Doped Photocatalytic Titania Thin Films on Active Polymer Substrates
Tavares, C. J.; Marques, S. M.; Lanceros-Méndez, S.; Rebouta, L.; Alves, E.; Barradas, N. P.; Munnik, F.; Girardeau, T.; Riviére, J.-P.
Abstract
Active polymer substrates have found their way in the semiconductor industry as a base layer for flexible electronics, as well as in sensor and actuator applications. The optimum performance of these systems may be affected by dirt adsorbed on its surface, which can also originate mechanisms for the degradation of the polymer. Titanium dioxide (titania) semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron sputtering on one of the most applied and investigated electroactive polymer: poly(vinilidene fluoride), PVDF In order to increase the photocatalytic efficiency of the titania coatings, a reduction of the semiconductor band-gap has been attempted by using a nitrogen doping. Rutherford Backscattering Spectroscopy was used in order to assess the composition of the titania thin films, whereas Heavy Ion Elastic Recoil Detection Analysis provided the evaluation of the doping level of nitrogen. X-ray Photoelectron Spectroscopy provided valu!
able information about the cation-anion binding within the semiconductor lattice. The photocatalytic performance of the titania films have been characterized by decomposing an organic dye illuminated with combined UV/visible light.
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Journal of Nanoscience and Nanotechnology 10(2010), 1072-1077
DOI: 10.1166/jnn.2010.1868
Cited 13 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13784
P0805 Erhöhung der Hochtemperaturoxidationsbeständigkeit von TiAl-Legierungen und daraus bestehenden Bauteilen durch Pl3
Kolitsch, A.; Yankov, R.; Donchev, A.; Schütze, M.
Abstract
Die Plasma-Immersion-Ionen-Implantation (Pl3) von Fluor, das aus z. B. einem CH2F2-Plasma generiert wurde, in die Oberfläche von TiAl-Bauteilen kann deren Oxidationsbeständigkeit im Temperaturbereich von 700 bis 1100°C an trockener und feuchter Luft oder anderen oxidierenden Atmosphären auch unter Temperaturwechselbeanspruchung gegenüber unbehandelten TiAl-Legierungen deutlich erhöhen. Entgegen dem bisherigen Kenntnisstand, wo nur die reinen Halogene verwendet wurden, lässt sich durch Verwendung von z. B. Difluormethan oder Tetrafluorkohlenstoff ein deutlich vereinfachter Ionen-Implantationsprozess durchführen als bei reiner Fluorimplantation, ohne eine Beeinträchtigung des positiven Fluoreffekts zu erzielen. Das Fluor wird in kontrollierbaren Mengen in die Oberflächenrandzone von TiAl-Bauteilen implantiert, wo es seinen positiven Effekt auf den Oxidationswiderstand entfaltet.
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Patent
DE102008028990A1: Offenlegung-11.01.2010; Erteilung-08.10.2013
Permalink: https://www.hzdr.de/publications/Publ-13783
P0809 Vorrichtung und Verfahren zur Auswertung einer Aktivitätsverteilung sowie Bestrahlungsanlage
Rietzel, E.; Bert, C.; Parodi, K.; Enghardt, W.
Abstract
Die Erfindung betrifft eine Vorrichtung zur Auswertung einer in einem bewegten Zielobjekt auftretenden Aktivitätsverteilung, welche durch einen mit einer Bestrahlungseinrichtung erzeugten Strahl erzeugbar ist, aufweisend:
- einen Positronen-Emissions-Tomographen, welcher ausgebildet ist zum Aufzeichnen von durch den Strahl im Zielobjekt erzeugten Photonen und zur Erzeugung von Messdaten, welche Entstehungsorte der Photonen repräsentieren,
- eine Bewegungserfassungseinrichtung, welche ausgebildet ist, ein Bewegungssignal zu erzeugen, das die Bewegung des Zielobjekts repräsentiert,
- eine Auswertungseinheit, welche ausgebildet ist, die Entstehungsorte der gemessenen Photonen zu Positionen im Zielobjekt unter Verwendung des Bewegungssignals zuzuordnen, wodurch eine räumliche Charakteristik der tatsächlich im Zielobjekt erzeugten Aktivitätsverteilung über die durch den Strahl erzeugten Photonen auswertbar ist, sowie eine Bestrahlungsanlage und ein Verfahren, in welchen eine derartige Vorrichtung eingesetzt wird.
-
Patent
DE 102008036478 A1 - 11.01.2010 -
Patent
Anmeldung: WO 2010015358 A1 2010/02/11
Permalink: https://www.hzdr.de/publications/Publ-13782
Ions and X-rays: Unique partners for accurate stopping power determination of 15N ions in Si for hydrogen depth profiling
Zier, M.; Reinholz, U.; Riesemeier, H.; Radtke, M.; Munnik, F.
Abstract
In many areas of material sciences hydrogen analysis is of particular importance. For example, hydrogen is most abundant as impurity in thin-film materials - depending on the deposition process - and has great influence on the chemical, physical and electrical properties of many materials. Therefore, it is necessary to monitor the H-concentration by depth profiling. Best-suited methods for depth-resolved hydrogen analysis are ion beam techniques such as elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA). In principle, both methods can be performed as primary - reference material free - methods.
The most common method, NRA, makes use of the 6385 keV resonance of the 1H(15N,αγ)12C nuclear reaction. The correct quantification of the depth scale in the measured hydrogen profiles essentially relies on accurate stopping power values, i.e. any imperfection in the stopping power values is influencing all H-values provided by NRA. For the determination of the accurate stopping power of ~6.4 MeV 15N ions in hydrogen-containing amorphous Si-layers (a-Si:H), we have, therefore, combined NRA with X-ray reflectometry (XRR), also a primary method.
The samples are prepared by magnetron sputtering of a-Si in an Ar/H2-atmosphere on a Cr-layer, which is needed as contrast material for XRR. The energy loss in the layers is measured by NRA at FZD. The layer thickness, density and roughness are determined by XRR using synchrotron radiation. XRR measurements were performed at the electron storage ring BESSY at the hard X-ray beamline BAMline. The beam was monochromatised to 10 keV using a Si [111]-double-crystal monochromator. The reflected photons of the θ-2θ-scans from the 6-circle goniometer are counted by a scintillation detector and a photodiode, respectively. Data analysis is performed by the IMD 4.1 software package.
The unique combination of results from NRA and XRR allows the accurate calculation of the mass stopping power independent of the density of the material. Our preliminary results show significant discrepancies in the order of 15-20% to the commonly used stopping powers calculated by the well accepted SRIM program (version 2006). These discrepancies have to be considered, if transforming the energy loss scale to a depth scale in hydrogen profiles. Thus, further work for confirmation is absolutely needed.
Acknowledgments: The help of D. Grambole and S. Merchel (FZD) is greatly appreciated.
Keywords: Stopping power; hydrogen depth profiling; NRA; XRR; synchrotron radiation
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Poster
Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten (SNI2010), 24.-26.02.2010, Berlin, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13781
GDCh Arbeitskreis Analytik mit Radionukliden und Hochleistungsstrahlenquellen
Eberhardt, K.; Henkelmann, R.; Merchel, S.; Denecke, M. A.
Abstract
Der Arbeitskreis Analytik mit Radionukliden und Hochleistungsstrahlenquellen (ARH) wird gemeinsam von den GDCh-Fachgruppen Nuklearchemie, Analytische Chemie, Makromolekulare Chemie, Festkörperchemie und Materialforschung und der Wöhler-Vereinigung für Anorganische Chemie getragen. Der ARH Vorstand setzt sich aus Synchrotron-, Neutronen- und Ionen-Experten zusammen und steht hiermit in direktem Bezug zum SNI2010. Der Arbeitskreis setzt sich die Förderung und den Einsatz von Radionukliden zur Qualitätssicherung von Analysenverfahren und die Analytik mit Großgeräten zum Ziel. Zurzeit strebt der ARH-Vorstand insbesondere eine Vertiefung von Kontakten zu anderen wissenschaftlichen Vereinigungen wie dem Komitee für Synchrotronstrahlung (KFS) und dem Komitee Forschung mit nuklearen Sonden und Ionenstrahlen (KFSI) an. Ein weiterer Schwerpunkt ist die (Fort-)Bildung sowie der Wissenstransfer und der Erfahrungsaustausch in Form von wissenschaftlichen Tagungen und Seminaren. Zum Beispiel finden das 23. SAAGAS (Seminar Aktivierungsanalyse und Gammaspektroskopie) im September 2009 und der Workshop Ionenstrahlphysik im März 2010 in Dresden statt. In dieser Posterpräsentation werden der Arbeitskreis ARH, seine Arbeitsschwerpunkte und Ziele sowie zukünftige
Aktivitäten dargestellt.
Keywords: nuclear analytics; synchrotron radiation; neutrons; ion accelerator
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Poster
Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten (SNI2010), 24.-26.02.2010, Berlin, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13780
Ungeduldige Wissenschaftler: Bestimmung langlebiger Radionuklide mittels Beschleunigermassenspektrometrie (AMS)
Merchel, S.
Abstract
Das Forschungszentrum Dresden-Rossendorf (FZD) erweitert diesen Sommer sein Portfolio um eine weitere hochsensitive analytische Methode: die Beschleunigermassenspektrometrie (accelerator mass spectrometry, AMS). Die AMS ermöglicht insbesondere die Bestimmung langlebiger Radionuklide mit Halbwertszeiten im Bereich von ka bis Ma.
Entgegen der sonst allgemein üblichen Zerfallszählung warten die ungeduldigen AMS-Wissenschaftler dabei nicht auf den Zerfall des Radionuklids und die Detektion des durch den Zerfall emittierten Teilchens bzw. der Strahlung. Vielmehr werden die noch nicht zerfallenen Radionuklide wesentlich effizienter massenspektrometrisch bestimmt. Die AMS besitzt allerdings gegenüber der konventionellen Massenspektrometrie den Vorteil, dass sie Störsignale, hervorgerufen von Molekülionen oder Ionen ähnlicher Masse, insbesondere Isobare, effektiver unterdrücken kann. Die AMS liefert somit weitaus niedrigere Nachweisgrenzen als die konventionellen Methoden.
Im Gegensatz zu den in Deutschland und Europa gängigen niederenergetischen AMS-Anlagen, die sich hauptsächlich auf die Bestimmung des Radiokohlenstoffs (14C) spezialisiert haben, wird die AMS-Anlage des FZD - DREAMS (DREsden AMS) - als erste moderne Anlage in der EU mit einer Terminalspannung von 6 MV betrieben werden. Sie ist somit prädestiniert zur effizienten und hochempfindlichen Analyse der Radionuklide 10Be, 26Al, 36Cl, 41Ca und 129I (t1/2=0,1-15,7 Ma).
Die Einführung der AMS wird die interne Vernetzung der FZD-Forschungsaktivitäten im Bereich Materialforschung, Strahlenphysik, Radiochemie und Radiopharmazie vorantreiben. Darüber hinaus wird die AMS aber auch externen Nutzern zur Verfügung stehen. Die möglichen Arbeitsgebiete sind vielfach und multidisziplinär. So haben die instrumentellen Weiterentwicklungen auf dem Gebiet der AMS, die Anwendungsfelder der Methode stark ausgeweitet. Die anfänglich bevorzugt untersuchten Proben aus der Kosmochemie, Astrophysik und Kernreaktionsdaten, werden zunehmend von Proben aus den Bereichen Strahlenschutz, Nuklearsicherheit, Nuklearentsorgung, Radioökologie, Phytologie, Ernährungswissenschaften, Toxikologie und Pharmakologie verdrängt.
Zudem hat die AMS vor allem in den Geo- und Umweltwissenschaften in den letzten Jahren an Bedeutung gewonnen. Mittels kosmogener Radionuklide können relativ plötzlich aufgetretene prähistorische Ereignisse wie Vulkanausbrüche, Bergstürze, Tsunamis, Meteoriteneinschläge und Erdbeben datiert werden. Die Quantifizierung von geomorphologischen Vorgängen wie Erosion und Flusseinschnitte über lange Zeiträume, sowie hydrogeologische Studien sind ebenfalls möglich. Mittels der Datierung von Gletscher-bewegungen und Untersuchungen an Eisbohrkernen können zudem Klimaveränderungen rekonstruiert und Klimamodelle für die Zukunft validiert werden.
Nach dem Motto Ready for dreams for DREAMS sehen wir gespannt den neuen AMS-Möglichkeiten am FZD und den damit verbundenen interdisziplinären Kooperationen, vor allen Dingen auch im Bereich der Helmholtz-Gemeinschaft, entgegen.
Keywords: cosmogenic radionuclides; TCN; AMS; accelerator mass spectrometry
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Lecture (others)
Glaziologie-Seminar, Alfred-Wegener-Institut für Polar- und Meeresforschung, 18.02.2010, Bremerhaven, Deutschland
Permalink: https://www.hzdr.de/publications/Publ-13779
Linear and non-linear stability of a thermally stratified magnetically driven rotating flow in a cylinder
Grants, I.; Gerbeth, G.
Abstract
The stability of a thermally stratified liquid metal flow is considered numerically. The flow is driven by the rotating magnetic field in a cylinder heated from above and cooled from below. The stable thermal stratification turns out to destabilise the flow. This is explained by the fact that a stable stratification suppresses the secondary meridional flow, thus indirectly enhancing the primary rotation. The instability in the form of Taylor-Görtler rolls is consequently promoted. It is known from earlier studies that these rolls can be only excited by finite disturbances in the isothermal flow. A sufficiently strong thermal stratification transforms this non-linear bypass instability into a linear one reducing, thus, the critical value of the magnetic driving force. A weaker temperature gradient delays the linear instability but makes the bypass transition more likely. We quantify the non-normal and non-linear components of this transition by direct numerical simulation of the flow response to noise.
It is observed that the flow sensitivity to finite disturbances increases considerably under the action of a stable thermal stratification. The capabilities of the random forcing approach to identify disconnected coherent states in a general case are discussed.
- Physical Review E 82(2010), 016314
Permalink: https://www.hzdr.de/publications/Publ-13778
Stellarator-Mirror Based Fusion Driven Fission Reactor
Moiseenko, V.; Noack, K.; Agren, O.
Abstract
The version of fusion driven system (FDS), a sub-critical fast fission assembly with a fusion plasma neutron source, theoretically investigated here is based on a stellarator with a small mirror part. In the magnetic well of the mirror part, fusion reactions occur from collision of an RF heated hot ion component (tritium), with high perpendicular energy with cold background plasma ions. The hot ions are assumed to be trapped in the magnetic mirror part. The stellarator part which connects to the mirror part provides confinement for the bulk (deuterium) plasma. Calculations based on a power balance analysis indicate the possibility to achieve a net electric power output with a compact FDS device. For representative thermal power output of a power plant (P (th) a parts per thousand P (fis) = 0.5-2 GW) the computed electric Q-factor is in the range Q (el) = 8-14, which indicates high efficiency of the FDS scheme.
- Journal of Fusion Energy 29(2010)1, 65-69
Permalink: https://www.hzdr.de/publications/Publ-13777
Filamentous E. coli induced by heterologous expression of surface layer proteins
Lederer, F.; Günther, T.; Raff, J.; Pollmann, K.
Abstract
Bacterial envelope proteins, so called surface layers (S-layer) are widely spread paracrystalline surface structures which coat the cells of lots of bacterial strains and as universal attribute of all archaea. They are mostly composed of protein monomers which form via self-assembling high regular two dimensional arrays on the cells as well as on surfaces and interfaces after their isolation. The S-layer proteins we investigate are from bacterial strains recovered from the uranium mining waste pile Haberland in Saxony, Germany. Their special S-layer proteins selectively bind uranium and protect the cells from its toxicity. These special S-layer characteristics make them interesting for many technological applications such as filter materials, biosensors, as functional surfaces, or for example as drug containers.
In order to produce surface layer proteins in a high efficient way a heterologous expression in Escherichia coli is essential. In our study, the S-layer-like protein SllB of Lysinibacillus sphaericus JG-A12 was expressed in E. coli Bl21 (DE3). Noteworthy, recombinant protein production resulted in a high stability of the cells against mechanical and chemical treatment. These unusual cells were analyzed by light microscopy, AFM and TEM.
All methods demonstrated a total changed cell morphology. The cells formed long filaments in the beginning of the exponential growth stage and started to form 5-200 µm long tube like transparent structures at the end of the exponential growth stage, which contained E. coli single cells. These tube-like structures were isolated and analyzed by SDS-PAGE, N-terminal sequencing and infra red spectroscopy. The analyses showed that the tube-like structures consist of outer membrane associated with recombinant surface layer proteins. These findings point to a disordered cell division. However, the underlying mechanisms of these morphological changes are not known and will be analyzed in future. Investigations of supernatant proteins and proteins of periplasmic space in combination with enzyme assays demonstrate a transport of recombinant proteins that is not caused by cell damage. The long filaments, in combination with high expression level, good growth and high stability make these unusual E. coli cells interesting for biotechnological applications. In addition, these results cast a new light on one of the best studied microorganisms.
Keywords: Escherichia coli; S-layer proteins; Outer membrane; tube-like structures
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Poster
Bacterial Cell Surfaces, 27.06.-02.07.2010, New London, NH, USA
Permalink: https://www.hzdr.de/publications/Publ-13776
Future perspectives at SIS-100 with HADES-at-FAIR
Fröhlich, I.
Abstract
Currently, the HADES spectrometer undergoes un upgrade program to be prepared for measurements at the upcoming SIS-100 synchrotron at FAIR. We describe the current status of the HADES di-electron measurments at the SIS-18 and our future plans for SIS-100.
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Contribution to proceedings
xLVII International Winter Meeting on Nuclear Physics, 01.02.2010, Bologna, Italien
Conference Proceedings Vol. 99 -
Invited lecture (Conferences)
47th International Winter Meeting on Nuclear Physics, 26.-30.01.2009, Bormio, Italy -
Contribution to WWW
arXiv:0906.0091v2 [nucl-ex]
Permalink: https://www.hzdr.de/publications/Publ-13775
Scanning Probe Microscopy-based Characterization of ZnO Nanorods
Teichert, C.; Hou, Y.; Beinik, I.; Chen, X.; Hsu, Y. F.; Djurisic, A. B.; Anwand, W.; Brauer, G.
Abstract
Abstract-We apply scanning probe microscopy (SPM) to study the morphology and electrical properties of vertical zinc oxide nanorods grown by hydrothermal methods on silicon substrates. It is demonstrated that against the intuition SPM techniques can indeed be used to study such fragile high-aspect ratio semiconductor nanorods. Atomic-force microscopy (AFM) operating in tapping mode yields - via the analysis of the height histograms calculated from AFM images - easy access to the height fluctuations in the nanorod ensemble. High-resolution AFM images reveal the three-dimensional shape of the nanorods including transition facets between the (0001) top terrace and the {10-10} side facets. Further, we were able to acquire currentvoltage curves of individual nanorods by conductive atomic force microscopy (CAFM) operating in contact mode.
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Lecture (Conference)
IEEE International nanoElectronics Conference (INEC 2010), 03.-08.01.2010, Hong Kong, China
Permalink: https://www.hzdr.de/publications/Publ-13774
Defect studies of nanocrystalline zirconia powders and sintered ceramics
Cizek, J.; Melikhzova, O.; Prochazka, I.; Kuriplach, J.; Kuzel, R.; Brauer, G.; Anwand, W.; Konstantinova, T. E.; Danilenko, I. A.
Abstract
The main objective of the present paper is to communicate a study of defects behavior in zirconia-based nanomaterialspressure-compacted yttria-stabilized zirconia (YSZ) nanopowders with different contents of Y2O3 and ceramics obtained by sintering the YZS nanopowders. In addition, YZS single crystals were also investigated. Positron annihilation techniques including positron lifetime and coincidence Doppler broadening with a conventional positron source and Doppler broadening experiments on a monoenergetic positron beam were involved in this study as the principal tools. These techniques were supplemented with transmission electron microscopy and x-ray diffraction observations. In order to get better support of the experimental data interpretation, the state-of-art theoretical calculations of positron parameters were performed for the perfect ZrO2 lattice and selected defect configurations in the YSZ. Theoretical calculations have indicated that neither the oxygen vacancies nor their neutral complexes with substitutional yttrium atoms are capable of positron trapping. On the other hand, the zirconium vacancies are deep positron traps and obviously are responsible for the saturated positron trapping observed in the YSZ single crystals. In the compacted YSZ nanopowders, a majority of positrons is trapped either in the vacancylike defects situated in the negative space-charge layers along grain boundaries (τ1≈185 ps) or in vacancy clusters at intersections of grain boundaries (τ2≈370 ps). The intensity ratio I2/I1 was found to be correlated with the mean grain size d as I2/I1∼d−2. A small fraction of positrons (≈10%) form positronium in large pores (τ3≈2 ns, τ4≈30 ns). A significant grain growth during sintering of the YSZ nanopowders above 1000 °C was observed.
Involved research facilities
- P-ELBE
- Physical Review B 81(2010), 024116
Permalink: https://www.hzdr.de/publications/Publ-13773
Nature of vacancy complexes associated with hydrogen ion-induced splitting of bulk GaN
Moutanabbir, O.; Scholz, R.; Gösele, U.; Guittoum, A.; Jungmann, M.; Butterling, M.; Krause-Rehberg, R.; Anwand, W.; Egger, W.; Sperr, P.
Abstract
We present a detailed study of the thermal evolution of H ion-induced vacancy related complexes and voids in bulk GaN implanted under ion-cut condition. By using transmission electron microscopy, we found that the damaged band in as-implanted GaN is decorated with a high density of nanobubbles of ~1-2 nm in diameter. Variable energy Doppler broadening spectroscopy showed that this band contains vacancy clusters and voids. In addition to vacancy clusters, the presence of VGa, VGa-H2, and VGaVN complexes was evidenced by pulsed low energy positron lifetime spectroscopy. Subtle changes upon annealing in these vacancy complexes were also investigated. As a general trend, a growth in open volume defects is detected in parallel to an increase in both size and density of nanobubbles. The observed vacancy complexes appear to be stable during annealing. However, for temperatures above 450ºC, unusually large lifetimes were measured. These lifetimes are attributed to the formation of positronium in GaN. Our finding contradicts the prevalent belief that the formation of postronium is not possible in a semiconductor. Based on the Tao-Eldrup model, the lattice opening during thermal annealing was quantified. We found that a wall spacing of 0.4 nm is induced by annealing at 600ºC. The role of these complexes in the sub-surface microcraking is discussed.
Keywords: GaN; hydrogen ion-induced splitting; thermal evolution of H ion-induced vacancy related complexes and voids; TEM; PAS
Involved research facilities
- P-ELBE
- Physical Review B 81(2010), 115205
Permalink: https://www.hzdr.de/publications/Publ-13772
Contactless inductive flow tomography for a model of continuous steel casting
Wondrak, T.; Galindo, V.; Gerbeth, G.; Gundrum, T.; Stefani, F.; Timmel, K.
Abstract
The contactless inductive flow tomography (CIFT) aims at reconstructing the velocity field in electrically conducting melts from externally measured induced magnetic fields. One of its possible applications is the velocity reconstruction in the continuous casting process. In this paper, we apply this method to the flow field in a small model (containing approximately 1.4 liters of the eutectic alloy GaInSn) of a mould for thin slab casting. It is shown that the flow structure in general, and the jet position and intensity in particular, can be reliably determined from magnetic field data using only a modest number (in the order of 5) of sensors.
- Measurement Science and Technology 21(2010), 045402
Permalink: https://www.hzdr.de/publications/Publ-13771
Determination of Uranium Speciation in Aqueous Samples by Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS)
Bernhard, G.; Geipel, G.
Abstract
wird nachgereicht
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Contribution to external collection
Lahiri, Susanta: Advanced Trace Analysis, New Delhi: Narosa Publishing House, 2010, 978-81-8487-029-9, 127-147
Permalink: https://www.hzdr.de/publications/Publ-13770
Effects of posture on regional pulmonary blood flow in rats as measured by PET
Richter, T.; Bergmann, R.; Pietzsch, J.; Közle, I.; Hofheinz, F.; Schiller, E.; Ragaller, M.; van den Hoff, J.
Abstract
Using small animal PET with 68Ga-radiolabeled human albumin microspheres (Ga-68-microspheres), we investigated the effect of posture on regional pulmonary blood flow (PBF) in normal rats. This in vivo method is noninvasive and quantitative, and it allows for repeated longitudinal measurements. The purpose of the experiment was to quantify spatial differences in PBF in small animals in different postures. Two studies were performed in anesthetized, spontaneously breathing Wistar rats. Study 1 was designed to determine PBF in the prone and supine positions. Ga-68-microspheres were given to five prone and eight supine animals. We found that PBF increased in dorsal regions of supine animals (0.75) more than in prone animals (0.70; P = 0.037), according to a steeper vertical gradient of flow in supine than in prone animals. No differences in spatial heterogeneity were detected. Study 2 was designed to determine the effects of tissue distribution on PBF measurements. Because microspheres remained fixed in the lung, PET was performed on animals in the position in which they received Ga-68-microsphere injections and thereafter in the opposite posture. The distribution of PBF showed a preference for dorsal regions in both positions, but the distribution was dependent on the position during administration of the microspheres. We conclude that PET using Ga-68-microspheres can detect and quantify regional PBF in animals as small as the rat. PBF distributions differed between the prone and supine postures and were influenced by the distribution of lung tissue within the thorax.
Keywords: pulmonary blood flow; positron emission tomography; 68Ga radiolabel; human serum albumin microspheres; prone position; supine position; small animal
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Journal of Applied Physiology 108(2010), 422-429
DOI: 10.1152/japplphysiol.91257.2008
Cited 21 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13769
Comment on "Developing DCE-CT to Quantify Intra-Tumor Heterogeneity in Breast Tumors With Differing Angiogenic Phenotype"
Abramyuk, A.; Wolf, G.; Hietschold, V.; Haberland, U.; van den Hoff, J.; Abolmaali, N.
Abstract
In our comment some essential issues concerning determination of arterial input function (AIF), cardiac and respiratory related motion artifacts, contrast agent application and compartmental model fitting done by Cao et al., 2009 are discussed.
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IEEE Transactions on Medical Imaging 29(2010)4, 1088-1092
DOI: 10.1109/TMI.2009.2031780
Cited 1 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-13768
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