Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34118 Publications

The photon-scattering facility at the superconducting electron accelerator ELBE

Schwengner, R.; Beyer, R.; Dönau, F.; Grosse, E.; Hartmann, A.; Junghans, A. R.; Mallion, S.; Rusev, G.; Schilling, K. D.; Schulze, W.; Wagner, A.

A new facility for the production of polarised bremsstrahlung has been built
at the superconducting electron accelerator ELBE of the Forschungszentrum
Rossendorf. The bremsstrahlung facility and the setup for photon-scattering
experiments are designed such that the background radiation due to scattering
of photons and production of neutrons is minimised. The sensitive setup in
connection with electron energies up to 20 MeV and average currents up to 1 mA
delivered by the ELBE accelerator enables novel experiments using
photon-induced reactions. First results of photon-scattering experiments are
presented.

Keywords: superconducting electron accelerator; polarised bremsstrahlung; photon scattering

  • Nuclear Instruments and Methods in Physics Research A 555(2005), 211-219

Permalink: https://www.hzdr.de/publications/Publ-7536
Publ.-Id: 7536


Fullerene-like arrangements in carbon nitride thin films grown by direct ion beam sputtering

Gago, R.; Abrasonis, G.; Mücklich, A.; Möller, W.; Czigany, Z.; Radnoczi, G.

Carbon nitride (CNx) thin films were grown by direct N-2/Ar ion beam sputtering of a graphite target at moderate substrate temperatures (300-750 K). The resulting microstructure of the films was studied by high-resolution transmission electron microscopy. The images showed the presence of curved basal planes in fullerenelike arrangements. The achievement and evolution of these microstructural features are discussed in terms of nitrogen incorporation, film-forming flux, and ion bombardment effects, thus adding to the understanding of the formation mechanisms of curved graphitic structures in CNx materials. (C) 2005 American Institute of Physics.

  • Applied Physics Letters 87(2005)7, 71901

Permalink: https://www.hzdr.de/publications/Publ-7535
Publ.-Id: 7535


Extreme habitats as reservoir for unusual bacterial strains: Perspectives for bioremediation and nanotechnology

Merroun, M.

Microorganisms can mobilise radionuclides/metals through autotrophic and heterotrophic leaching, chelation by microbial metabolites and siderophores, and methylation, which can result in volatilisation. Conversely, immobilisation can result from sorption to cell components or exopolymers, intracellular sequestration or precipitation as insoluble organic and inorganic compounds. In this talk, we will present the last results about the spectroscopic and microscopic characterization of interaction mechanisms between radionuclides and bacterial strains isolated from extreme habitats, including uranium mining waste piles. Some of the isolated strains could be used as templates for the formation of metallic nanoparticles (Pd, Au).

  • Invited lecture (Conferences)
    Civil Engineering Department, 01.07.2005, Sheffield, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-7534
Publ.-Id: 7534


Urankontamination durch Erzbergbau und Aufarbeitung

Bernhard, G.

Ausgehend von der Hintergrundkonzentration in den Eintrag von Uran in geochemische und biologische Systeme, wird über die Bestimmung der Speziation des Urans in kontaminierten Wässern, die aus dem ehemaligen Uranerzbergbau resultieren, berichtet.

  • Invited lecture (Conferences)
    Uran-Statusseminar, 21.07.2005, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-7533
Publ.-Id: 7533


188Re(III) Mixed-ligand Complexes: Stability Studies and Labeling of Biomolecules

Schiller, E.; Seifert, S.; Tisato, F.; Refosco, F.; Kraus, W.; Spies, H.; Pietzsch, H.-J.

Trigonal-bipyramidal Re(III) complexes with tetra-dentate/monodetate NS3/P ‘4+1’-coordination are inter-esting agents for the development of rhenium-188 com-plexes for potential therapeutic application. In order to understand relationships between the structure of rhenium-188 ‘4+1’ complexes and their in vitro stability we synthesized a series of rhenium model complexes 1, 2 and determined their stability in human plasma.
The complexes were prepared as described in [1] using various combinations of NS3 derivatives and mono-dentate phosphorus(III) ligands.
Since instability in aqueous solution always leads to the formation of perrhenate, we determined the amount of perrhenate formed after 1h, 24 h and 48 by TLC.
By means of physico-chemical parameters of the corres-ponding non-radioactive rhenium complexes we tried to find factors which may govern the formation of complexes showing high in vitro stability.
Finally, the most stable representative 3 was studied in 188Re labeling experiments with a phosphine-arginine-tyrosine model conjugate using the water-soluble N-hydroxysulfosuccinimidyl ester of the monodentate phosphine.

  • Poster
    „Radiotracers for In vivo Assessment of Biological Function New Directions“, 22.-23.04.2005, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-7532
Publ.-Id: 7532


Analysen zur Kühlmittelvermischung und zum Kernverhalten bei unterstellter Borverdünnung in Druckwasserreaktoren

Weiß, F.-P.; Kliem, S.

Bor ist ein starker Absorber für thermische Neutronen und wird dem Kühlmittel von DWR zugesetzt, um die Überschussreaktivität des Reaktorkerns zu kompensieren. Die unbeabsichtigte Verringerung der Borkonzentration, die sog. Borverdünnung, im Kern hat deshalb eine Reaktivitätserhöhung zur Folge und könnte im Extremfall die Rekritikalität des abgeschalteten Reaktors nach sich ziehen.

  • Invited lecture (Conferences)
    Kolloquium des Institutes für Kern- und Energietechnik des FZ Karlsruhe, 28.06.2005, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-7531
Publ.-Id: 7531


The Synthesis of Novel „4+1” Tc(III)/Re(III) Mixed-ligand Complexes with a Dendritic Modified Monodentate Ligand

Gniazdowska, E.; Stephan, H.; Pietzsch, H.-J.

Inert, so-called “4+1” trigonal-bipyramidal coordinated mixed–ligand complexes of the trivalent technetium and rhenium with tetradentate and monodentate ligands proved to be more stable than the pentavalent “3+1” mixed–ligand complexes with the (M=O)3+ core. They have appeared not to undergo a substitution in vivo with SH groups of such species as cysteine or glutathione [1].
In the presented paper we describe the synthesis of novel 99mTc(III) and 188Re(III) complexes containing the tripodal chelator 2,2’,2’’-nitrilotris(ethanethiol), NS3, and a dendritic modified monodentate isocyanide, CN-R(den). The reaction course was monitored with TLC and the radiochemical purity was monitored by HPLC. As a reference compound we have synthesized also the non-radioactive rhenium(III) complex which has been characterized by elemental analysis, IR, MS, 1H and 13C NMR.

  • Poster
    4th National Conference on Radiochemistry and Nucler Chemistry, 09.-11.05.2005, Kraków-Przegorzały, Poland

Permalink: https://www.hzdr.de/publications/Publ-7530
Publ.-Id: 7530


{2-Carboxy-2-{bis[(2-thiolato-_S)ethyl]amino-_N}ethanthiolato-_S} (triphenylphosphin-_P)rhenium(III)

Schiller, E.; Kraus, W.; Reck, G.; Spies, H.; Pietzsch, H.-J.

The title compound, [Re(C7H12NO2S3)(C18H15P)]center dot C3H6O, crystallizes from a solution in chloroform - acetone - cyclohexane with enantiomers disordered equally over each molecular site. Hydrogen bonds between the carboxyl groups form dimers in the crystal structure.

Keywords: COMPLEXES; THERAPY; RE-188

  • Open Access Logo Acta Crystallographica Section E 61(2005), M1373-M1375

Permalink: https://www.hzdr.de/publications/Publ-7529
Publ.-Id: 7529


A new molecular mechanics force field for the design of oxotechnetium(V) and oxorhenium(V) radiopharmaceuticals

Comba, P.; Daubinet, A.; Martin, B.; Pietzsch, H.-J.; Stephan, H.

Force field parameters for the modeling of oxotechnetium(V) and oxorhenium(V) complexes with amine, amide, imine, carboxylate and thiolate donors have been derived and optimized with 131 published solid state structures. An automated procedure, based on a simplex algorithm, was used to optimize the 35 sets of metal-dependent structural parameters for each metal ion. These were introduced into the established MOMEC97 force field. The application of the new force field in the prediction of a novel radio-pharmaceutical’s structure was successful; the predicted structures of the two isomers compared well with the corresponding crystal structures obtained (RMS around the metal core: 0.153 and 0.035 Å, respectively).

  • Journal of Organometallic Chemistry 691(2006)11, 2495-2502

Permalink: https://www.hzdr.de/publications/Publ-7528
Publ.-Id: 7528


A model of low-frequency rotating magnetic field with a weak axial gradient

Priede, J.; Gerbeth, G.

We introduce a model of rotating magnetic field with a weak axial gradient which approximates the field generated by a slightly conical and sufficiently long inductor. The axial variation of the free-space field is assumed to be weak and its amplitude is approximated by the first linear term of expansion in a power series of the axial coordinate. This allows us to obtain an analytic solution for the azimuthal harmonics of the induced scalar electric potential and the azimuthal driving force in a cylinder of finite length. The results are verified by comparison with a numerical solution obtained by a Chebyshev-tau method.

  • Magnetohydrodynamics 41(2005)2, 189-198

Permalink: https://www.hzdr.de/publications/Publ-7526
Publ.-Id: 7526


A novel rhenium chelate system derived from dimercaptosuccinic acid for the selective labeling of biomolecules

Heinrich, T.; Kraus, W.; Pietzsch, H.-J.; Smuda, C.; Spies, H.

This work is part of efforts to develop chelating agents for stable binding and easy conjugation of rhenium-188 to biologically interesting structures. Starting from the well-known high in vivo stability of [188ReO(DMSA)2]- we want to exploit this coordination system for the design of 188ReO(V) chelates which are stable towards re-oxidation to perrhenate and towards ligand exchange under all conditions of radiopharmaceutical procedures and applications. Therefor a new type of tetradentate ligand has been synthesized by bridging two molecules of N,N’-diisobutyl-2,3-dimercaptosuccinamide with N-(3-aminopropyl)propane-1,3-diamine. The resulting stereoisomeric tetrathiolato S4 ligand of the composition (iBu)2N(O)C-C(SH)-C(SH)-C(O)NH-(CH2)3–NH-(CH2)3–NHC(O)-C(SH)-C(SH)-C(O)N(iBu)2 forms anionic five-coordinated oxorhenium(V) complexes by ligand exchange reaction of NBu4[ReOCl4] in methanol. Without addition of base the compounds will be isolated as “betain”, [ReO(S4)], with the protonated nitrogen of the bridge as internal “counter ion”. Two representatives have been fully characterized both in solid and solution states and found to adopt the expected square-pyramidal coordination geometry. The equatorial plane is formed by four thiolate sulfur atoms, whereas the oxygen occupies the apical position. The orientation of the metal oxo group is exo in relation to the carbamido groups in both isomers. Both complexes are stereoisomeric regarding the junction of the triamine chain.

  • Inorganic Chemistry 44(2005)26, 9930-9937

Permalink: https://www.hzdr.de/publications/Publ-7525
Publ.-Id: 7525


Einfluss von Wasserstoff auf die Zähigkeit von bestrahlten Reaktordruckbehälterstählen

Uhlemann, M.; Müller, G.; Ulbricht, A.; Böhmert, J.

Das Projekt liefert einen Beitrag zum Kenntnisstand der Wirkung von Bestrah-lung und Umgebungseinflüssen auf den Reaktordruckbehälter und dient zur Aufrechterhaltung eines hohen Sicherheitsstandards. Bis heute ist der Me-chanismus der Versprödung von RDB-Stählen nicht vollständig verstanden. Gesichert ist die Wirkung des Neutronenfeldes auf die Zähigkeitsabnahme von RDB Stählen. Zunehmend wird aber ein synergistischer Effekt zwischen Wasserstoff und den durch Bestrahlung erzeugten nanodispersen Strukturde-fekten diskutiert.
Ziel des Projektes war es eine experimentellen Nachweis über die Wechsel-wirkung von Wasserstoff und den bestrahlungsbedingten Strukturdefekten zu erbringen, den möglichen Einfluss auf die Zähigkeitsabnahme von RDB Stäh-len zu untersuchen und Unterschiede im Verhalten gegenüber dem unbe-strahlten Zustand auszuweisen.
Zur Untersuchung des Einflusses von Wasserstoff auf das Zähigkeitsverhal-ten von Reaktordruckbehälterstählen wurden einachsige Zugversuche bei verschiedenen Dehnraten an unbestrahlten und bestrahlten, wasserstoffvor- und in-situ beladenen Proben bei Raumtemperatur und 250°C durchgeführt. Die Bestimmung der mechanischen Eigenschaften wurde durch fraktografi-sche Untersuchungen der Bruchflächen ergänzt.
Mit SANS-Untersuchungen, der Analyse von Wasserstoffgehalten und Ther-modesorptions-untersuchungen wurde geprüft, ob Strahlendefekte als Haft-stellen für Wasserstoff wirksam werden.
Es konnte gezeigt werden, dass die Empfindlichkeit gegenüber Wasserstoff-versprödung von der chemischen Zusammensetzung des RDB-Stahles, der Fluenz bis zu der bestrahlt wurde, der Bestrahlungstemperatur und der Art der gebildeten Strahlendefekte bestimmt wird. Eine verstärkte Anfälligkeit ge-genüber Wasserstoffversprödung wird bei RT, in-situ Wasserstoffbeladung und langsamen Dehnraten sowie geringen Bestrahlungstemperaturen beo-bachtet. Bei 250°C ist eine Versprödung durch Wasserstoff nicht mehr nach-weisbar. Aus den Ergebnissen ist abzuleiten, dass bestrahlungsinduzierte De-fekte keine bevorzugten Plätze für eine höhere Aufenthaltswahrscheinlichkeit für Wasserstoff unter Betriebstemperaturen von RDB darstellen. Sie sind so-mit keine internen Quellen für Wasserstoff. Bei Betriebstemperaturen ist des-halb nicht mit einer erhöhten Versprödungsanfälligkeit zur zu rechnen. Durch die höheren Festigkeiten der bestrahlten Stähle steigt aber allgemein die Empfindlichkeit gegenüber Wasserstoffversprödung.
Der Integritätsnachweis von RDB’s außerhalb des Leistungsbetriebes unter Wasserstoffwirkung ist deshalb noch zu erbringen.

Keywords: diffusivity; hydrogen embrittlement; mechanical properties; reaktor pressure vessel steels; solubility; SANS

  • Invited lecture (Conferences)
    55. Sitzung des RSK-Ausschusses „Druckführende Komponenten und Werkstoffe“, 05.-06.07.2005, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-7524
Publ.-Id: 7524


Spectroscopic ellipsometry study of the role of the annealing time on nickel induced crystallization of a-Si

Pereira, L.; Águas, H.; Beckers, M.; Martins, R. M. S.; Fortunato, E.; Martins, R.

wird nachgereicht

  • Lecture (Conference)
    21st International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 21), 04.-09.09.2005, -, Portugal

Permalink: https://www.hzdr.de/publications/Publ-7523
Publ.-Id: 7523


Octahedral rhenium cluster complexes with inner organic ligands: synthesis, structure and properties of [Re6Q8(3,5-Me2PzH)6]Br2·2(3,5-Me2PzH) (Q = S, Se)

Mironov, Y.; Bryleva, K.; Shestopalova, M.; Yarovoia, S.; Fedorova, V.; Spies, H.; Pietzsch, H.-J.; Stephan, H.; Geipel, G.; Bernhard, G.; Kraus, W.

Two new octahedral cluster complexes – [Re6S8(3,5-Me2PzH)6]Br2·2(3,5-Me2PzH) (1) and [Re6Se8(3,5-Me2PzH)6]Br2·2(3,5-Me2PzH) (2), where 3,5-Me2PzH is 3,5-dimethyl-pyrazole, have been synthesized using reaction of rhenium chalcobromide complexes Cs4[Re6S8Br6]·2H2O and Cs3[Re6Se8Br6]·H2O respectively with molten 3,5-dimethylpyrazole. Both compounds synthesized were characterised by X-ray single-crystal diffraction and chemical analysis, IR and luminescent spectra.

  • Inorganica Chimica Acta (2006)359, 1129-1134

Permalink: https://www.hzdr.de/publications/Publ-7522
Publ.-Id: 7522


Synthesis and biodistribution of an 18F-labelled resveratrol derivative for small animal positron emission tomography (PET)

Gester, S.; Wüst, F.; Pawelke, B.; Bergmann, R.; Pietzsch, J.

Resveratrol (3,4',5-trihydroxy-trans-stilbene) is a naturally occurring phytoalexin and polyphenol existing in grapes and various other plants, and one of the best known 'nutriceuticals' . It shows a multiplicity of beneficial biological effects, particularly, by attenuating atherogenic, inflammatory, and carcinogenic processes. However, despite convincing evidence from experimental and clinical studies, data concerning the role of resveratrol and other members of the large polyphenols family for human health is still a matter of debate. One reason for this is the lack of suitable sensitive and specific methods, which would allow direct assessment of biodistribution, biokinetics, and the metabolic fate of these compounds in vivo. The unique features of positron emission tomography (PET) as a non-invasive in vivo imaging methodology in combination with suitable PET radiotracers have great promise to assess quantitative information on physiological effects of polyphenols in vivo. Herein we describe the radiosynthesis of an 18F-labelled resveratrol derivative, 3,5-dihydroxy-4'-[18F]fluoro-trans-stilbene ([ 18 F]-1), using the Horner-Wadsworth-Emmons reaction as a novel radiolabelling technique in PET radiochemistry for subsequent functional imaging of polyphenol metabolism in vivo. In a typical "three-step/one-pot reaction, 18F-labelled resveratrol derivative [ 18 F]-1 could be synthesized within 120-130 min including HPLC separation at a specific radioactivity of about 90 GBq/mumol. The radiochemical yield was about 9% (decay-corrected) related to [18F]fluoride and the radiochemical purity exceeded 97%. First radiopharmacological evaluation included measurement of biodistribution ex vivo and positron emission tomography (PET) studies in vivo after intravenous application of [ 18 F]-1 in male Wistar rats using a dedicated small animal PET camera with very high spatial resolution. Concordantly with data on bioavailability and metabolism of native resveratrol from the literature, these investigations revealed an extensive uptake and metabolism in the liver and kidney, respectively, of [ 18 F]-1. This study represents the first investigation of polyphenols in vivo by means of PET.

Keywords: Polyphenols; Resveratrol; [18F]Fluorobenzaldehyde; Horner-Wadsworth-Emmons reaction; Positron emission tomography (PET)

Permalink: https://www.hzdr.de/publications/Publ-7521
Publ.-Id: 7521


Aspects of positron emission tomography (PET) radiochemistry as relevant for food chemistry

Wüst, F.

Positron emission tomography (PET) is a medical imaging technique using compounds labelled with short-lived positron emitting radioisotopes to obtain functional information of physiological, biochemical and pharmacological processes in vivo. The need to understand the potential link between the ingestion of individual dietary agents and the effect of health promotion or health risk requires the exact metabolic characterization of food ingredients in vivo. This exciting but rather new research field of PET would provide new insights and perspectives on food chemistry by assessing quantitative information on pharmocokinetics and pharmacodynamics of food ingredients and dietary agents. To fully exploit PET technology in food chemistry appropriately radiolabelled compounds as relevant for food sciences are needed. The most widely used short-lived positron emitters are 11C (t1/2 = 20.4 min) and 18F (t1/2 = 109.8 min). Longer-lived radioisotopes are available by using 76Br (t1/2 = 16.2 h) and 124I (t1/2 = 4.12 d). The present review article tries to discuss some aspects for the radiolabelling of food ingredients and dietary agents either by means of isotopic labelling with 11C or via prosthetic group labelling approaches using the positron emitting halogens 18F, 76Br and 124I.

Keywords: Positron emission tomography; Radiolabelling; Prosthetic group

Permalink: https://www.hzdr.de/publications/Publ-7520
Publ.-Id: 7520


Dramatic effect of the tridentate ligand on the stability of Tc-99m "3+1" oxo complexes bearing arylpiperazine derivatives

Fernandes, C.; Correia, D. G.; Gano, L.; Santos, I.; Seifert, S.; Syhre, R.; Bergmann, R.; Spies, H.

Mixed - ligand model complexes of general formula [Tc-99m(O)(kappa(3) -SPh)(kappa(1)-SPh))] [X = O (1a), S (2a)] were prepared in a one-step procedure from [(TcO4-)-Tc-99m] using stannous chloride as reducing agent. Stability studies and challenge experiments with glutathione showed that complex 2a presented promising features for pursuing animal studies. The activity in the brain (% dose injected/organ) at 5 min (0.14% +/- 0.03) and 120 min (0.11% +/- 0.02) pi encouraged the synthesis of several mixed-ligand "3 + 1" oxo complexes of general formula [M(O)(kappa(3)-PNS)(kappa(1)-SL))] (M = Tc-99m, 3a-6a, Re, 3-6), in which the tridentate ligand is the heterofunctionalized phosphine 2-(diphenylphosphanyl)-N-(2-thioethyl)benzamide (PNS) and the co-ligands are different arylpiperazine derivatives (HSL1-HSL4). The Tc-99m complexes have been characterized by comparison of their retention times in the HPLC chromatogram (gamma-detection) with the retention times of the analogous Re complexes (UV detection at 254 nm). The 99mTc complexes, obtained with radiochemical purity higher than 95%, after HPLC purification, are stable in saline, 0.01 M PBS (pH 7.4), rat plasma (4 h, 37 degrees C), and glutathione (10 mM solutions, 2h, 37 degrees C). Binding affinity and selectivity for 5-HT1A receptors (relative to the 5-HT2A receptor) were determined, complex 5 demonstrating the best values (IC50 for the 5-HT1A 2.35 +/- 0.02 nM; competitor 5-HT2A 372 +/- 11 nM). Biodistribution and stability studies in mice indicated a preferred hepatobiliary excretion, a high in vivo stability, but a poor brain uptake.

Keywords: SMALL-MOLECULE RADIOPHARMACEUTICALS; DONOR ATOM SET; OXORHENIUM(V) COMPLEXES; 5-HT1A RECEPTORS; IMAGING AGENTS; IN-VIVO; RADIOLIGANDS; REACTIVITY

  • Bioconjugate Chemistry 16(2005)3, 660-668

Permalink: https://www.hzdr.de/publications/Publ-7519
Publ.-Id: 7519


Flow structure during steam condensation in sub-cooled water in a large vertical pipe using wire-mesh sensors

Prasser, H.-M.; Beyer, M.; Carl, H.; Gregor, S.; Schütz, P.; Weiss, F.-P.

The structure of a steam-water flow in a vertical pipe of 195.3 mm inner diameter was studied using novel wire-mesh sensors for high-pressure / high-temperature operation (max. 7 MPa / 286 °C). Tests were carried out at pressures of 1 and 2 MPa under nearly adiabatic conditions as well as with slightly sub-cooled water. The evolution of radial gas fraction profiles and bubble-size distributions along the pipe in a high-pressure steam-water flow was measured for the first time. The experimental data allow to correlate the intensity of steam condensation in contact with sub-cooled water with the structure of the interfacial area and the bubble size distribution, which is very important for the model development.

Keywords: bubbly flow; phase transfer; bubble size distribution; vertical pipe

  • Contribution to proceedings
    4th International Conference on transport phenomena in multiphase systems, 26.-30.06.2005, Gdansk, Poland
    Proceedings of HEAT-2005, 433-438

Permalink: https://www.hzdr.de/publications/Publ-7518
Publ.-Id: 7518


Novel surface layer protein genes in Bacillus sphaericus associated with unusual insertion elements

Pollmann, K.; Raff, J.; Schnorpfeil, M.; Radeva, G.; Selenska-Pobell, S.

The surface layer (S-layer) protein genes of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 and of its relative B. sphaericus NCTC 9602 were analyzed. The almost identical N-termini of both S-layer proteins possess a unique structure, comprising three Nterminal S-layer homologous domains (SLH). The central parts of the proteins share a high homology and are related to the S-layer proteins of B. sphaericus CCM 2177 and P-1. In contrast, the C-terminal parts of the studied S-layer proteins differ significantly between each other. Surprisingly, the C-terminal part of the S-layer protein of JG-A12 shares a high identity with that of the S-layer protein of B. sphaericus CCM 2177. In both strains the chromosomal S-layer protein genes were followed by a newly identified putative insertion element comprising three ORFs, which encode a putative transposase, a putative integrase/recombinase, a putative protein containing a DNA binding helix turn helix motif, and the S-layer protein-like gene copies sllA (9602) or sllB (JG-A12). Interestingly, both studied B. sphaericus strains were found to contain an additional, plasmid located and silent S-layer protein gene possessing the same sequence as sllA and sllB. The primary structures of the corresponding putative proteins are almost identical in both strains. The N-terminal and central parts of these S-layer proteins share a high identity with those of the chromosomally encoded functional S-layer proteins. Their C-terminal parts, however, differ significantly. These results strongly suggest that the S-layer protein genes have evolved via horizontal transfer of genetic information followed by DNA rearrangements mediated by mobile elements.

Permalink: https://www.hzdr.de/publications/Publ-7517
Publ.-Id: 7517


Metal binding by bacteria from uranium mining waste piles and its technological applications

Pollmann, K.; Raff, J.; Merroun, M.; Fahmy, K.; Selenska-Pobell, S.

Uranium mining waste piles, heavily polluted with radionuclides and other toxic metals, are a reservoir for bacteria that have evolved special strategies to survive in these extreme environments. Understanding the mechanisms of bacterial adaptation may enable the development of novel bioremediation strategies and other technological applications. Cell isolates of Bacillus sphaericus JG-A12 from a uranium mining waste pile in Germany are able to accumulate high amounts of toxic metals such as U, Cu, Pb, Al, and Cd as well as precious metals. Some of these metals, i.e. U, Cu, Pd(II), Pt(II) and Au(III), are also bound by the highly orderd paracrystalline proteinaceous surface layer (S-layer) that envelopes the cells of this strain. These special capabilities of the cells and the S-layer proteins of B. sphaericus JG-A12 are highly interesting for the clean-up of uranium contaminated waste waters, for the recovery of precious metals from electronic wastes, and for the production of metal nanoclusters. The fabricated nanoparticles are promising for the development of novel catalysts. This work reviews the molecular biology of the S-layer of the strain JG-A12 and the S-layer dependent interactions of the bacterial cells with metals. It presents future perspectives for their application in bioremediation and nanotechnology.

Keywords: Uranium mining waste piles; Bacillus sphaericus; S-layer; bioremediation; biocers; metal nanoclusters

Permalink: https://www.hzdr.de/publications/Publ-7516
Publ.-Id: 7516


Characterization of L Amino Acid Transporter 1 (LAT1) for 3-O-Methyl-6-18F-Fluoro-L-DOPA (OMFD) in Tumor Cells and Tumor Tissues

Haase, C.; Oswald, J.; Pietzsch, J.; Bergmann, R.

18F-labeled amino acids represent a promising class of imaging agents in tumors visualized by means of positron emission tomography (PET). Because of the high uptake it is still problematic to clear differentiate between tumors and inflammation.
The high enrichment in tumor tissues assumed the uptake of the tracer via a tumor-specific amino acid transporter, which is not or different expressed in inflammatory cells suggesting a different endowment of neutral amino acids. As previously shown, L-type amino acid transporter 1 (LAT1) is playing a key role because of its high up-regulation in malignant tumors. For the functional expression of LAT1 a single membrane-spanning protein, the heavy chain of 4F2 antigen (4F2hc), essentially forms a heterodimeric complex via disulfide bonds.
The present study investigated the amino acid transport mechanism of LAT1 for 3-O-methyl-6-18F-Fluoro-L-DOPA (OMFD), a novel 18F-labeled phenylalanine derivative, into tumor cells.
For molecular characterisation of L-type amino acid transporters focusing on the LAT1-4F2hc subtype we used two different tumor cells like FaDu (squamous cell carcinoma)/HT29 (colorectal adenocarcinoma) and tumor bearing mice performing quantitative RT-PCR, Western-Blot, and immunhistochemistry. In vitro uptake assays with HT29 and FaDu were performed with OMFD under physiological amino acid concentrations.
OMFD demonstrated a saturable and sodium- and energy-independent accumulation in vitro in different tumor cell lines, suggesting its uptake to be mediated exclusively by sodium-independent LAT1.
Our data emphasize the relevance of OMFD as a PET tracer for imaging of specific amino acid transport via LAT1 in tumors. Furthermore, the identification and characterization of tumor specific amino acid transporters like LAT1 will be a helpful tool for therapeutic implications. The inhibition of LAT1 activity in tumor cells could be effective in the inhibition of tumor cell growth by depriving tumor cells of essential amino acids, too.

Keywords: LAT1; OMFD; PET; tumor

  • Poster
    Fourth Annual Meeting of the Society for Molecular Imaging, 07.-10.09.2005, Köln, Deutschland
  • Abstract in refereed journal
    Molecular Imaging 4(2005)3, 285

Permalink: https://www.hzdr.de/publications/Publ-7515
Publ.-Id: 7515


Experimental hypoxia as potent stimulus for radiotracer uptake in vitro: comparison of different primary endothelial cells

Oswald, J.; Haase, C.; Wüst, F.; Bergmann, R.

Hypoxia is a common feature of various human tumor entities. Hypoxic tumor tissue can be studied by nuclear medicine imaging techniques like PET and SPECT. In this study we analyzed in vitro the influence of experimental hypoxia on the radiotracer uptake of various primary endothelial cells, which play an essential part in tumor angiogenesis.
Experimental hypoxia was induced by cultivating cells for 24 hours in presence of 2% oxygen in a special incubator (Gasboy C40, Labotect). Cellular uptake of [99mTc]MIBI, [18F]MISO and [18F]FDG was determined after one or four hours incubation and measured after cell lysis with a gamma counter Cobra II (Perkin Elmer). Radiotracer uptake was normalized to the cell protein. Three types of primary endothelial cells were used: human umbilical vein endothelial cells (HUVEC), human dermal microvascular endothelial cells (HDMEC) and human aortic endothelial cells (HAEC) as well as the two tumor cell lines, being FaDu (squamous cell carcinoma) and HT29 (colorectal adenocarcinoma), respectively. Cellular expression of hypoxia-inducible factor-1a (HIF-1a) and vascular endothelial growth factor (VEGF) was monitored with quantitative PCR (RotorGene 2000).
In our experiments we found that under hypoxic conditions the uptake of [99Tc]MIBI was decreased in all cell types. The uptake of the hypoxia-specific radiotracer [18F]MISO was slightly increased in all primary endothelial cell types. Furthermore, primary endothelial cells incorporated significant higher amounts of [18F]FDG under experimental hypoxic conditions in comparison to normoxic conditions. Especially HDMECs showed a marked response to hypoxia with an approximately two-fold higher [18F]FDG uptake. Also HUVECs and HAECs responded to experimental hypoxia, whereas tumor cell lines FaDu and HT29 showed only moderate increase of [18F]FDG uptake under hypoxic conditions.
We conclude that experimental hypoxia represents a much higher stimulus for primary endothelial cells than for cultivated tumor cells to accumulate [18F]FDG and also to incorporate [18F]MISO in vitro. Our data emphasize the relevance of endothelial cells as one important part of the tumor micromilieu and stimulate further studies on the different patterns of radiotracer uptake in neoplastic or neovascularized lesions.

Keywords: Hypoxia; Endothel; PET Tracer

  • Poster
    Fourth Annual Meeting of Molecular Imaging, 07.-10.09.2005, Köln, Deutschland
  • Abstract in refereed journal
    Molecular Imaging 4(2005)3, 301

Permalink: https://www.hzdr.de/publications/Publ-7514
Publ.-Id: 7514


Human primary endothelial cells incorporate increased levels of [18F]FDG under hypoxic conditions

Oswald, J.; Haase, C.; Wüst, F.; Bergmann, R.

Aim:
Hypoxia is a common feature of various human tumor entities and the enhanced uptake of specific radiotracers in hypoxic tissues can be visualized by means of positron emission tomography (PET). In this study we analyzed the influence of experimental hypoxia on the [18F]FDG uptake of various primary endothelial cells and tumor cell lines.
Material and Methods:
Experimental hypoxia was induced by cultivating cells for 24 hours in presence of 2% oxygen in a special incubator (Gasboy C40, Labotect). Cellular [18F]FDG uptake was determined after one hour incubation and measured after cell lysis with a Cobra II spectrometer (Packard). [18F]FDG uptake was correlated to protein concentration. Three types of primary endothelial cells were used: human umbilical cord endothelial cells (HUVEC), human dermal microvascular endothelial cells (HDMEC) and human aortic endothelial cells (HAEC) as well as the two tumor cell lines, being FaDu (squamous cell carcinoma) and HT29 (colorectal adenocarcinoma), respectively.
Results:
In our experiments we found that primary endothelial cells incorporate significant higher amounts of [18F]FDG under experimental hypoxic conditions in comparison to normoxic conditions. Especially HDMECs showed a marked response to hypoxia with an approximately two-fold higher [18F]FDG uptake. Also HUVECs and HAECs responded to experimental hypoxia, whereas tumor cell lines FaDu and HT29 showed only moderate increase of [18F]FDG uptake under hypoxic conditions.
Conclusion:
Experimental hypoxia represents a much higher stimulus for primary endothelial cells than for cultivated tumor cells to incorporate [18F]FDG. Our data emphasize the relevance of endothelial cells as one important part of the tumor micromilieu and stimulate further studies on the different patterns of radiotracer uptake in neoplastic or neovascularized lesions.

  • Lecture (Conference)
    Annual Congress of the European Association of Nuclear Medicine, 15.-19.10.2005, Istanbul, Turkey
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 32(2005)Suppl. 1, S44

Permalink: https://www.hzdr.de/publications/Publ-7513
Publ.-Id: 7513


The Becin hoard – Analysis of the ancient silver coins

Schreiner, M.; Mäder, M.; Bidaud, E.; Zich, W.; Uhlir, K.; Grambole, D.; Herrmann, F.; Alram, M.

During the archaeological work in summer 2000 a spectacular hoard of silver coins could be excavated at the medieval site Becin, next to Ephesos / Turkey. This hoard, whose total weight amounted to approximately 30 kg, includes about 60.000 Islamic coins as well as 830 European coins and represents the largest finding of coins ever made in Turkey. One of the most outstanding features of the Becin hoard is the fact that almost all mint places recorded for the Ottoman Empire and all rulers of the second half of the 16th century up to the beginning of the 17th century are represented in this treasure. Thus, the numismatic evaluation and the material analysis of the coins will provide a general insight in the monetary and economic history of the Ottoman Empire in this time.
In a first step of the investigations a collection of 450 samples was analyzed quantitatively. Photon, electron and proton induced X-ray analysis provide complementary information on the chemical composition of the coins. Using EDXRF, the content of both the major constituent Ag and the minor elements Cu and Pb were determined. The advantage of SEM/EDX is the ability to analyze small areas of the cross-sections. Finally, PIXE measurements were carried out in order to characterize also the trace elements, like Au, Bi, Fe, Ni. The initial results show on the one hand an arrangement in different groups of coins concerning their chemical composition. On the other hand the findings illustrate frequent devaluations in the fineness of the silver coins described in the Ottoman written sources.

  • Poster
    17th International Conference on Ion Beam Analysis, 26.06.-01.07.2005, Sevilla, Spain

Permalink: https://www.hzdr.de/publications/Publ-7512
Publ.-Id: 7512


Hydrogen as origin of compressive intrinsic stress in hydrogenated amorphous silicon: the contribution of clustered forms

Pantchev, B.; Danesh, P.; Schmidt, B.

The role of hydrogen in hydrogenated amorphous silicon (a-Si:H) has been studied from the viewpoint of its specific contribution to mechanical stress in the material. Hydrogen ion implantation has been used to increase the hydrogen concentration. In order to distinguish the effect of the changed hydrogen concentration/bonding configuration from the accompanying implantation-induced defects, a-Si:H samples with corresponding number of displacements have been studied, created using proper doses of silicon ion implantation. The experimental results have shown that it is the silicon-bonded hydrogen that essentially affects the stress, as the major contribution has its clustered bonding configuration.

Keywords: a-Si:H; hydrogen ion implantation; NRA-; FTIR-and stress measurements

  • Applied Physics Letters 87(2005)2, 23104

Permalink: https://www.hzdr.de/publications/Publ-7511
Publ.-Id: 7511


Highly stable metal complexes with tuneable transport properties

Stephan, H.

wird nachgereicht

  • Lecture (Conference)
    2nd SUPRAPHONE Meeting, 05.-07.05.2005, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7510
Publ.-Id: 7510


Cyclam-core PAMAM dendrimers having sugar moieties as terminal groups

Röhrich, A.

wird nachgereicht

  • Lecture (Conference)
    2nd SUPRAPHONE Meeting, 05.-07.05.2005, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7509
Publ.-Id: 7509


Synthesis and characterization of novel bispidine derivatives and their copper(II) complexes

Juran, S.

wird nachgereicht

  • Lecture (Conference)
    2nd SUPRAPHONE Meeting, 05.-07.05.2005, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7508
Publ.-Id: 7508


Determination of association constants by distribution studies

Bomkamp, M.; Stephan, H.; Waldvogel, S.

wird nachgereicht

  • Poster
    2nd SUPRAPHONE Meeting, 05.-07.05.2005, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7507
Publ.-Id: 7507


Hindered E4 decay of the 12+ yrast trap in 52Fe

Gadea, A.; Lenzi, S. M.; Napoli, D. R.; Axiotis, M.; Ur, C. A.; Martinez-Pinedo, G.; Gorska, M.; Roeckl, E.; Caurier, E.; Nowacki, F.; de Angelis, G.; Batist, L.; Borcea, R.; Brandolini, F.; Cano-Ott, D.; Döring, J.; Fahlander, C.; Farnea, E.; Gawe, H.; Hellström, M.; Janas, Z.; Kirchner, R.; La Commara, M.; Mazzocchi, C.; Nacher, E.; Plettner, C.; Plochocki, A.; Rubio, B.; Schmidt, K.; Schwengner, R.; Tain, J. L.; Zylicz, J.

The γ decay of the 12+ yrast trap in 52Fe has been measured for the first time. The two E4 γ-branches to the 8+ states are hindered with respect to other B(E4) reduced transition probabilities measured in the f 7/2 schel. The interpretation of the data is given in the full pf shell model framework, comparing the results obtained with different residual interactions. It is shown that measurements of hexadecapole transition probabilities constitute a powerful tool in discriminationg the correct configurration of the involved wavefunctions.

  • Physics Letters B 619(2005), 88-94

Permalink: https://www.hzdr.de/publications/Publ-7506
Publ.-Id: 7506


Sorption von Uran (VI) an Phyllit

Zorn, T.; Arnold, T.; Bernhard, G.; Nitsche, H.

Die Sorption von Uran (VI) an das komplexe Gestein Phyllit wurde gründlich untersucht. Dominierender Prozess der Sorption ist die Bindung an das Sekundärmaterial Ferrihydrit. Anhand der gewonnenen experimentellen Daten gelang die Bestimmung von Oberflächenkomplexbildungskonstanten für die mineralischen Bestandteile Quarz, Muskovit, Albit und Chlorit. Diese log K-Werte können in chemischen Transportprogrammen Verwendung finden.

Keywords: Analytik; Uran; Sorption; Komplexbildungskonstanten; Phyllit; chemischer Transport

  • Vom Wasser 2(2005)103, 20-21

Permalink: https://www.hzdr.de/publications/Publ-7505
Publ.-Id: 7505


Untersuchungen zur Entfernung organischer Wasserinhaltsstoffe mit Ionenaustauschern

Schumann, T.

Diese Arbeit beschäftigt sich mit der Entfernung von organischen Stoffen aus Wässern durch Anionenaustauscher. Dabei werden C-14-markierte Modellsubstanzen eingesetzt. Die Aufnahme von Durchbruchskurven erfolgt bei verschiedenen Bedingungen (Variation von Beladungstemperatur, Salzgehalt und Organikakonzentration).

Keywords: ion exchange; organics; water

  • Lecture (others)
    Seminar "Entfernung organischer Stoffe aus Wässern durch Ionenaustauscher", 29.06.2005, Zittau, Germany

Permalink: https://www.hzdr.de/publications/Publ-7504
Publ.-Id: 7504


Hexadentate bispidine ligands with pyridine and imidazole groups

Schubert, R.; Juran, S.; Stephan, H.; Geipel, G.; Comba, P.; Kerscher, M.; Kraus, W.

wird nachgereicht

  • Poster
    2nd SUPRAPHONE Meeting, 05.-07.05.2005, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7503
Publ.-Id: 7503


Homogenisation of the melting depth in SiC on Si structures during flash lamp irradiation

Voelskow, M.; Smith, M.; Skorupa, W.; Mc Mahon, R.

Flash lamp annealing of heteroepitaxial silicon carbide on silicon structures involves melting the silicon below the SiC layer but the facetted nature of the liquid-solid interface leads to unacceptable surface roughness. This paper describes a method of controlling melting by using a melt stop created at a controlled depth below the Si / SiC interface by implanting a high dose of carbon, which significantly increases the silicon melting temperature. Results confirm the effectiveness of the technique in reducing roughness.

Keywords: FLASiC; flash lamp annealing; implantation; 3C-SiC

  • Applied Physics Letters 87(2005), 241901

Permalink: https://www.hzdr.de/publications/Publ-7502
Publ.-Id: 7502


Electromagnetically-driven convection during solidification: Heat and mass transfer in solidifying Pb-Sn melts

Nikritjuk, P. A.; Eckert, K.; Eckert, S.; Willers, B.

Swirling flows generated by the application of a rotating magnetic field (RMF) during the solidification significantly modify the heat and mass transport in the melt. Their enormous potential to modify the microstructure is known since long but was systematically studied only recently [1,2]. However, the understanding of flow field driven by the RMF in the solidifying melt and the corresponding temperature and concentration distributions is far from being complete. By means of a combination of experiments and numerical simulations important relations shall be established.
To calculate the flow field we use a code based on the SIMPLE algorithm which has been carefully validated on the isothermal problem of the RMF-driven acceleration of a melt from rest [3,4]. The solidification is treated by using a mixture-theory-model following Voller et al. [Int. J. Heat Mass Transfer 32 (1989), 1719]. The geometry studied is a Pb-Sn melt in a cylindrical cavity directionally solidified from below. The simulations cover Taylor numbers, Ta, up to 2*106 where Ta determines the magnitude of the bulk flow.
The solidification in the RMF depends on the degree of development of the forced convection (spin-up problem). The flow fields belonging to characteristic stages are discussed. Generally, the RMF significantly modifies the solidification as soon as the average flow velocity of the meridional flow becomes comparable or larger as the velocity of the solidification front. We discuss the impact of the flow on heat transfer in the melt thereby providing a detailed comparison of experimental and numerical date with respect to cooling rates and temperature gradients. Emphasis is given to the temperature gradients in vicinity of the solidication front which are hardly accessible in experiments. Their tendency with growing Ta is examined and linked with the accelerated onset of the transition from columnar to equiaxed growth (CET) found in the experiments [2]. Furthermore the macrosegregation to be expected in the RMF case are discussed.

Keywords: solidification; convection; rotating magnetic field; cooling rate; temperature gradient; macrosegregation

  • Lecture (Conference)
    EUROMAT 2005, 05.-08.09.05, Praha, Czech Republik

Permalink: https://www.hzdr.de/publications/Publ-7501
Publ.-Id: 7501


Electromagnetically-driven convection during solidification: velocity field and impact on the microstructure of Pb-Sn ingots

Eckert, S.; Willers, B.; Nikritjuk, P. A.; Eckert, K.; Michel, U.

The application of time varying magnetic fields can be considered as an effective tool to organize a well-defined flow structure in the liquid phase affecting the nucleation and solidification parameters. Main goal of our activities is to elucidate a strategy to control the microstructure of castings by an optimal combination of magnetic field intensity, field frequency and cooling rate. The development of fine, globular grains is preferred. Structures containing textured columnar grains and zones of macrosegregation should be avoided.
Solidification experiments as well as numerical simulations were carried out dealing with Pb Sn alloys solidified directionally from a water cooled copper chill. A rotating magnetic field (RMF) was chosen for melt agitation, because the essential features of an RMF-driven flow have already been intensively investigated for the isothermal case. The magnitude of the bulk flow in the melt generated by the RMF varies with the magnetic Taylor number Ta. The forced convection causes distinct modifications of the temperature and concentration field such as a reduction of the temperature gradient ahead of the solidification front. Without electromagnetic stirring the alloy solidifies solely in form of dendrites aligned parallel to the heat flow direction. In contrast, a transition from a columnar to an equiaxed growth (CET) is observed if the solidifying ingot is exposed to an RMF. The position of the CET is shifted towards the bottom of the casting by increasing the Ta number. The CET was found to occur for a cooling rate of about 0.4 K/s and temperature gradients in the range between 0.6 and 1.0 K/mm
The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow during solidification. Our results show that the velocity profiles undergo distinct modifications during solidification indicating the occurrence of more sophisticated flow patterns as known from the isothermal case. Furthermore, the UDV data allow an assessment of the current position of the columnar solidification front.

Keywords: solidification; dendritic growth; columnar-to-equiaxed transition; convection; rotating magnetic field

  • Poster
    EUROMAT 2005, 05.-08.09.05, Prague, Czech Republik

Permalink: https://www.hzdr.de/publications/Publ-7500
Publ.-Id: 7500


The influence of an external DC magnetic field on the behaviour of bubble driven liquid metal flows

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

Bubble driven flows have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenize the physical and chemical properties of the melt or to refine the melt. For such gas-liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way.
Compared to the numerous experimental studies on the movement of bubbles in transparent liquids , especially in water, the number of publications dealing with gas bubbles rising in liquid metals is comparatively small. The shortage of suitable measuring techniques can be considered as one reason for the slow progress in the investigations of gas-liquid metal flows. Powerful optical methods are obviously not available for measurements in liquid metals. The majority of measurements in liquid metal two-phase flows published until now was obtained using local conductivity probes, hot wire anemometer or optical fiber probes to determine quantities such as void fraction, bubble and liquid velocity or the bubble size. However, measurements with any local probe disturb the flow in a significant way, especially if the structures to be investigated reach dimensions comparable to the probes. In the case of opaque liquids the application of acoustic or ultrasonic sensors offers a possibility to get information about the flow structure and bubble quantities. We applied the Ultrasound Doppler Velocimetry (UDV) for measurements of the velocity structure in liquid metal bubbly flows. Because of the ability to work non-invasively in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications.
In our experiments we investigated the consequence of an application of a DC magnetic field on both the bubble and the liquid velocity. The motion of single argon bubbles rising in GaInSn were analyzed in terms of the terminal velocity, the drag coefficient, the oscillation frequency of the bubble velocity and the Strouhal number. Because the gas bubble is electrically non-conducting, it does not experience the effect of the electromagnetic force directly. However, the bubble behaviour is influenced by the magnetically induced modifications in the liquid flow structure around the bubble. The measurements reveal a distinct effect of the magnetic field on the bubble velocity as well as the bubble wake. The magnetic field application leads to a mitigation of the horizontal components of the bubble velocity resulting in a more rectilinear bubble path. A restructuring of the entire flow field can be observed if a bubble plume is exposed to a DC magnetic field. As a result of the interaction between magnetic field and liquid flow electric currents were induced inside the liquid causing a damping of the flow by Joule dissipation. However, a characteristic feature of the electromagnetic dissipation is the anisotropy. Thus, the application of a transverse field leads not only to a general damping of the flow, but also favours the occurrence of vortices aligned parallel to the magnetic field direction.

Keywords: liquid metal; bubbles; magnetic fields; UDV

  • Invited lecture (Conferences)
    MULTIMET, Workshop on Multiphase Flows in Metallurgy, 28.-30.09.05, Praha, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-7499
Publ.-Id: 7499


Die Welt der Bakterien – eine Fundgrube für die Bionik

Raff, J.

Bakterien sind winzig klein, sehr leistungsfähig und es gibt keinen noch so extremen Lebensraum, den sie nicht besiedeln könnten. Als wahre Alleskönner liefern sie der Bionik (Verbindung aus Biologie und Technik) viele neue Impulse. Am Beispiel faszinierender Hüllstrukturen verschiedener Bakterien wird dies exemplarisch aufgezeigt.

  • Lecture (others)
    Lange Nacht der Wissenschaften 2005, 01.07.2005, Dresden, Germany
  • Lecture (others)
    Tag der offenen Tür, 24.09.2005, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-7498
Publ.-Id: 7498


Theoretical study on reaction paths of formation and decay of 1D nanostructures

Heinig, K.-H.; Röntzsch, L.

Nanowires have fascinating properties. Also the kind and strength of driving forces for their structural evolution differ from macroscopic systems, thus opening new routes for their synthesis. And, with respect to interface energy, nanowires are unstable, during their decay new selforganized 1D structures evolve.
This presentation summarizes reaction pathways of the formation and decay of 1D nanostructures predicted by atomistic computer simulations. It will be shown that nanowire synthesis by phase separation from supersaturated 1D traces relies on different time scales of different processes involved: (i) phase separation is faster than long-range diffusion, thus, initially small nanodroplets form. (ii) Short-range diffusion is fast, thus, lateron the minority phase is concentrated/unified to a wire (ripening, coalescence). (iii) On a long time scale, the wire lowers its surface energy by peristaltic undulations and decays finally into large droplets (Rayleigh instability). Each process can be governed in order to fabricated functional structures. For instance, crosspoints of nanowires accelerates the wire instability locally, which leads to a nanodot separated by nm gaps from the four nanowires. Such a Si structure embedded in SiO2 might operate as a room temperature single electron transistor.

Keywords: Nanowire; Reation pathway; Kinetic Monte-Carlo; Ion Beam Synthesis

  • Lecture (Conference)
    DPG Jahrestagung, 04.-09.03.2005, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-7497
Publ.-Id: 7497


Atomistic Computer Simulations on Ion Beam Synthesis and Decay of CoSi2 Nanowires

Röntzsch, L.; Heinig, K.-H.

Nanowires (NWs) and chains of nanocrystals (NCs) embedded in dielectrics or semiconductors are intensively studied regarding their potential application in nanoelectronics. CoSi2 nanostructures in Si are particularly interesting because of the full compatibility of CoSi2 with CMOS technology.
Here, we present predictive atomistic computer simulations on the ion beam synthesis of CoSi2 NWs in Si and their decay into chains of CoSi2 NCs which are applicable as plasmon waveguides. In order to simulate the Co implantation, the binary collision codes TRIDYN and TRIM were adapted to the particular experimental situation of a finely-focused Co ion beam of 50nm in width. The resulting 3D implantation profile serves as input for a kinetic lattice Monte-Carlo code by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are described. From an evolutionary viewpoint, NW synthesis and decay proceed on different time scales. The NW decay into a NC chain (Rayleigh instability) is driven by the minimization of interfacial free energy. In this regard, it will be demonstrated that the orientation of the Co implantation profile to the single crystalline Si matrix influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the CoSi2(111)/Si(111) interface, driving faceting forces may occur which accelerate the NW decay into a NC chain.

Keywords: Nanowire; Ion Beam Synthesis; Kinetic Monte-Carlo

  • Poster
    DPG Jahrestagung, 04.-09.03.2005, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-7496
Publ.-Id: 7496


Atomistic Computer Simulations on Synthesis and Stability of Single-crystalline Nanowires

Röntzsch, L.; Heinig, K.-H.

An abstract was not required.

Keywords: Nanowires; Stability; Kinetic Monte-Carlo

  • Lecture (others)
    Annual Meeting of the DFG Priority Program 1165: Nanowires and Nanotubes, 02.-04.05.2005, Fulda, Germany
  • Poster
    Annual Meeting of the DFG Priority Program 1165: Nanowires and Nanotubes, 02.-04.05.2005, Fulda, Germany

Permalink: https://www.hzdr.de/publications/Publ-7495
Publ.-Id: 7495


Ion Beam Synthesis of CoSi2 Nanowires in Si and Their Stability -– Predictions of Atomistic Computer Simulations

Röntzsch, L.; Heinig, K.-H.

Nanowires (NWs) and chains of nanocrystals (NCs) embedded in dielectrics or semiconductors are intensively studied for photonic and nanoelectronic applications. In this respect, CoSi2 NWs and NC chains are of particular interest because of their full CMOS compatibility, the low damping of surface plasmons at the CoSi2-Si interface, and the transparency of Si at the plasmon frequency.
Here, we present results of atomistic computer simulations which describe the ion beam synthesis of CoSi2 NWs in Si and their thermally activated decay into chains of CoSi2 NCs. The Co implantation is simulated with the binary collision codes TRIDYN and TRIM adapted to the particular experimental situation of a finely focused Co ion beam of a few tens of nanometers in width. The resulting 3D implantation profile serves as input for a kinetic lattice Monte-Carlo code by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are described. From an evolutionary viewpoint, NW synthesis proceeds on a shorter time scale than its decay. The NW decay into a NC chain (Rayleigh instability) is driven by the minimization of interfacial free energy. Moreover, we demonstrate that the orientation of the Co implantation profile to the single crystalline Si matrix strongly influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the CoSi2(111)-Si(111) interface, driving faceting forces may occur which accelerate the NW decay into a NC chain. Thus, intentional misalignment between the focused Co ion beam and the Si substrate is suggested as way to a controlled decay of the ion beam synthesized CoSi2 NW into a chain of monodisperse and equidistant CoSi2 NCs.

Keywords: CoSi2; Nanowires; Stability; Kinetic Monte-Carlo

  • Poster
    E-MRS spring meeting 2005, 31.05.-03.06.2005, Strausbourg, France

Permalink: https://www.hzdr.de/publications/Publ-7494
Publ.-Id: 7494


Ion Beam Synthesis of CoSi2 Nanowires in Si and their Stability - Predictions of Atomistic Computer Simulations

Röntzsch, L.; Heinig, K.-H.

An abstract was not required.

Keywords: Nanowire; Stability; Ion Beam Synthesis

  • Poster
    25th GIF Meeting: Nanotubes and Nanowires, 20.-23.06.2005, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-7493
Publ.-Id: 7493


Modification of the near surface layer of carbon steels with intense argon and nitrogen plasma pulses

Sartowska, B.; Piekoszewski, J.; Walis, L.; Szymczyk, W.; Stanislawski, J.; Nowicki, L.; Ratajczak, R.; Kopcewicz, M.; Kalinowska, J.; Barcz, M.; Prokert, F.; (Editors)

Series of carbon steels with various contents of carbon were irradiated with high intensity 5-6 J cm-2, short (µs range) nitrogen and argon plasma pulses. In all samples the near surface layer of the thickness in µm range was melted. The paper reports the results of investigation of changes induced by such treatment. The identified phases, profiles of retained nitrogen concentration, microhardness and wear resistance of the modified layer are presented and discussed.

Keywords: intense pulsed plasma beams; paramagnetic phases; expanded austenite; SEM; SIMS; CEMS; GXRD

  • Vacuum 78(2005)2-4, 181-186

Permalink: https://www.hzdr.de/publications/Publ-7492
Publ.-Id: 7492


Superconductivity of MgB2 thin films prepared by ion implantation and pulsed plasma treatment

Piekoszewski, J.; Kempinski, W.; Andrzejewski, B.; Trybula, Z.; Piekara-Sady, L.; Kaszynski, J.; Stankowski, J.; Werner, Z.; Richter, E.; Prokert, F.; Stanislawski, J.; Barlak, M.

The experiments to synthesize thin MgB2 inter-metallic compound with the use of ion implantation and plasma pulse treatment are presented. Mg was implanted with 3e18 cm-2 of 80 keV and 5e18 cm-2 of 100 keV B+ ions and next treated with hydrogen and argon plasma pulses of duration of about 1 mu s and fluence between 2 and 4 J/cm2. Superconducting properties were examined by magnetically modulated microwave absorption (MMMA), magnetic moment and electrical conductivity measurements. The structural properties of the implanted and pulse-treated samples were examined by the X-ray diffraction (XRD) and Rutherford backscattering (RBS) methods. The main result consists in observation of MMMA hysteresis loop demonstrating the existence of superconducting regions with T-c as high as 32 K. However, the zero-resistance effect has not been obtained due to incomplete global connectivity between the superconducting regions.

Keywords: MgB2 thin films; ion implantation; pulsed plasma treatment

  • Vacuum 78(2005)2-4, 123-129

Permalink: https://www.hzdr.de/publications/Publ-7491
Publ.-Id: 7491


Deterministic and Monte Carlo neutron transport calculation for Greifswald-1 and comparison with ex-vessel measurement data

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

Neutron and gamma field functionals were studied by means of deterministic Sn and stochastic Monte Carlo calculations and by neutron activation measurements that were carried out in the ex-vessel cavity of the VVER-440 reactor Greifswald-1. The paper presents and analyses the results. The influence of different numbers of energy groups for the description of the cross sections is pointed out. A good agreement was found both between the results of deterministic and Monte Carlo calculation and between numerical and measurement results.

Keywords: VVER reactors; neutron-gamma transport calculations; Sn method; Monte Carlo method; ex-vessel reactor cavity; neutron activation measurements

  • Lecture (Conference)
    12 th International Symposium on Reactor Dosimetry, 08.-13.05.2005, Gatlinburg, United States
  • Journal of ASTM International 3(2006)4
  • Contribution to proceedings
    12 th International Symposium on Reactor Dosimetry, 08.-13.05.2005, Gatlinburg, United States
    Reactor Dosimetry: 12th International Symposium, West Conshohocken: ASTM, 978-0-8031-3412-6

Permalink: https://www.hzdr.de/publications/Publ-7490
Publ.-Id: 7490


Laser-Induced Fluorescence Spectroscopy

Geipel, G.

Laser-Induced spectroscopic methods were often used in actinide chemistry as tool to study the speciation of these elements in aquatic environments. The main goal of the application of time-resolved laser-induced fluorescence spectroscopy (TRLFS) and laser-induced photoacoustic spectroscopy (LIPAS) is to achieve detection limits of the actinide species as low as possible or in concentration ranges expected under environmental conditions.
With laser sources can it is possible to provide any wavelength from the near UV to the NIR (Near Infrared) wavelength range. The development of tunable solid-state lasers overcame some disadvantages of the dye laser systems as short tunable wavelength range and the use of hazardous chemicals. The application of low temperatures for samples measured with fluorescence spectroscopic methods brought effort especially in the detection of carbonate species.
In this contribution the focus will be mainly on the fluorescence spectroscopy of lower actinides, as it is not possible to include all literature in this field.

Keywords: Laser-induced spectroscopy; Fluorescence; Solid state

  • Contribution to external collection
    R. Vij: The Handbook of Solid State Spectroscopy, Heidelberg: Springer Verlag, 2006, 978-0-387-32497-5

Permalink: https://www.hzdr.de/publications/Publ-7489
Publ.-Id: 7489


Light emission and charge trapping in Er-doped silicon dioxide films containing silicon nanocrystals - art. no. 151914

Nazarov, A.; Sun, J.; Skorupa, W.; Yankov, R.; Osiyuk, I.; Tjagulskii, I.; Lysenko, V.; Gebel, T.

The processes of electro- (EL) and photoluminescence (PL) and charge trapping in Er-implanted SiO2 containing silicon nanoclusters have been studied. It is shown that in Er-doped SiO2 with an excess of silicon nanoclusters of 10 at. %, a strong energy transfer from silicon nanoclusters results in a ten-fold increase of the PL peak at 1540 nm from Er luminescent centers, whereas the EL is strongly quenched by the excess silicon nanoclusters. It is further shown that the implantation of Er creates in the oxide positive charge traps with a giant cross section (σ(h0) > 10(-13) cm(2)). Introducing subsequent silicon nanocrystals in the oxide leads to the formation of negative charge traps of a giant cross section (σ(e0) > 10(-13) cm(2)). The possible reason for the EL quenching in the Er-doped SiO2 by silicon nanoclusters is discussed. (C) 2005 American Institute of Physics.

  • Applied Physics Letters 86(2005)15, 51914

Permalink: https://www.hzdr.de/publications/Publ-7488
Publ.-Id: 7488


SIMS measurements of oxygen content in the Nd2Fe14B phase

Oswald, S.; Mazilu, I.; Fahler, S.; Gruner, W.; Hermann, R.; Loser, W.; Filip, O.; Wendrock, H.; Schultz, L.; Schmidt, B.; Rodewald, W.

The oxygen concentration in Nd-Fe-B alloy was determined with secondary ion mass spectrometry (SIMS) using Cs+-ions. The SIMS measurements were calibrated with oxygen-implanted single crystals. The depth profile of Nd2Fe14B single crystals displays a 0.5 μ m thick surface layer with elevated oxygen concentration which can be distinguished from the matrix with an oxygen content c(O) = 0.006± 0.002 at%. Polycrystalline samples can exceed this value by far and are sensitive to processing parameters and sample handling. SIMS measurements revealed the oxygen content of the Nd2Fe14B phase considerably lower than the total oxygen content of Nd-Fe-B samples. © 2004 Elsevier B.V. All rights reserved.

  • Journal of Magnetism and Magnetic Materials 290(2005)2, 1249-1242

Permalink: https://www.hzdr.de/publications/Publ-7487
Publ.-Id: 7487


Characterisation and comparison of Cm(III) and Eu(III) complexed with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine using EXAFS, TRFLS, and quantum chemical methods

Denecke, M. A.; Rossberg, A.; Panak, P. J.; Weigl, M.; Schimmelpfennig, B.; Geist, A.

The complexation of Cm(III) and Eu(III) with n-C3H7-BTP in non-aqueous organic solution was studied with extended X-ray absorption spectroscopy. Bond lengths are the same in both complexes. Quantum chemical calculations performed at different levels support this finding. On the other hand, the Cm•(n-C3H7-BTP)3 complex is formed at much lower metal-to-ligand concentration ratio than the Eu•(n-C3H7-BTP)3 complex, as shown by time-resolved laser-induced fluorescence spectroscopy. This is in good agreement with n-C3H7-BTP’s high selectivity for trivalent actinides over lanthanides in liquid-liquid extraction.

Keywords: in Publikation noch nicht angegeben

  • Inorganic Chemistry 44(2005), 8418-8425

Permalink: https://www.hzdr.de/publications/Publ-7486
Publ.-Id: 7486


Experimental results on the fluid flow in an electromagnetically driven metallic melt

Cramer, A.; Varshney, K.; Zhang, C.

Electromagnetic processing comprises the influence of Lorentz forces in the molten state. Whereas the action of static magnetic fields is solely damping in most cases, alternating fields offer the potentiality of active control mechanisms such as pumping, stirring, homogenization, and the like. Among the latter, various field types have to be distinguished based on the number of poles and geometric arrangement. Neither for one type, and more than ever for a combination thereof, might the resulting flow tagged well known.
Numerous, often non-validated numerical simulations overwhelm the few experiments done on liquid metals. In the present work, the ultrasonic Doppler velocimetry (UDV) and local potential probes have been employed to study the flow of an alloy in single-phase, traveling, and rotating fields. The area-wide results conveyed by the UDV technique will be presented as flow visualization whereas potential probe measurements may answer questions of more quantitative nature regarding turbulence characteristics.

Keywords: Fluid flow; Liquid metal; Measuring techniques; Magnetohydrodynamics

  • Contribution to proceedings
    Electromagnetics in Materials Processing, Electromagnetic Stirring, Levitation, and Forming, 25.-28.09.2005, Pittsburgh, PA, United States, pp. 41-52
  • Lecture (Conference)
    Materials Science & Technology, 25.-28.09.2005, Pittsburgh, PA, United States

Permalink: https://www.hzdr.de/publications/Publ-7485
Publ.-Id: 7485


Random coincidences during in-beam PET measurements at microbunched therapeutic ion beams

Parodi, K.; Crespo, P.; Eickhoff, H.; Haberer, T.; Pawelke, J.; Schardt, D.; Enghardt, W.

At the experimental carbon ion tumour therapy facility at GSI Darmstadt, in-beam positron emissions tomography (PET) is used to monitor the dose delivery precision. A dual head positron camera has been assembled from commercial detector components in order to measure the β+-activity, induced by the irradiation, simultaneously to the dose application. Despite the positive clinical impact, the image quality is limited by the low counting statistics, orders of magnitude below that in standart PET applications to nuclear medicine. This paper investigates the origin for the noisy acquisition during particle extraction from the synchrottron of GSI. The results demonstrate the failure of standard random correction techniques due to a γ-ray background correlated in time with the carbon ion beam microstructure. This prevents the use of data acquired during beam extraction for imaging. The loss of counting statistics is expected to rise further at the future hospital-based facility at Heidelberg, due to a more efficient utilisation of the accelerator resulting in shorter beam pauses and a reduced treatment time. In respect, this paper provides the basis for a new data acquísition concept tailored to the unconventional application of in-beam PET imaging to therapy monitoring at radiofrequency pulsed radiation sources.

Keywords: Positron emission tomography; Random correction; Carbon ion therapy

  • Nuclear Instruments and Methods in Physics Research A 545(2005), 446-458

Permalink: https://www.hzdr.de/publications/Publ-7484
Publ.-Id: 7484


Flow control and propulsion in weak conductors

Weier, T.; Shatrov, V.; Gerbeth, G.

The subjects of electromagnetic flow control and ship propulsion are reviewed, and possibilities for further developments are sketched.

  • Magnetohydrodynamics - Historical Evolution and Trends (2007), 295-312

Permalink: https://www.hzdr.de/publications/Publ-7483
Publ.-Id: 7483


Velocity measurement techniques for liquid metal flows

Eckert, S.; Cramer, A.; Gerbeth, G.

The possibilities for local velocity measurements in liquid metal flows are reviewed. Special emphasis is put on local potential probes and the ultrasonic velocimetry.

  • Magnetohydrodynamics - Historical Evolution and Trends Berlin(2006), 275-294

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Permalink: https://www.hzdr.de/publications/Publ-7482
Publ.-Id: 7482


Gefahrenpotenziale bei Grignard-Reaktionen - Sichere Betriebsführung durch Online-Monitoring

Kryk, H.; Hessel, G.; Schmitt, W.; Tefera, N.

Ausgehend von den physikochemischen Grundlagen der Grignard-Chemie werden Einflussfaktoren für eine sichere Prozessführung beschrieben. Bei Grignard-Synthesen tritt das größte Gefahrenpotential in der ersten Reaktionsstufe, der Herstellung der Grignard-Reagenz, auf. Insbesondere muss das Anspringen der Reaktion bei einer unzulässig großen Akkumulation von organischem Halogenid verhindert werden, wenn keine ausreichende, schnell wirksam werdende Kühlleistungsreserve vorhanden ist.
Vor der Überführung einer neuen Grignard-Synthese in den großtechnischen Maßstab sollten umfassende Untersuchungen der Grignard-Reaktionsstufe in Laborreaktoren durchgeführt werden. Mit Hilfe isothermer und adiabatischer kalorimetrischer Messungen konnten die wichtigsten Prozessparameter, wie molare Reaktionsenthalpie, adiabatische Temperaturerhöhung, Induktionszeit, Anstiegsgeschwindigkeit der Wärmeleistung und Dauer der Startphase, ermittelt werden. Sie sind notwendig, um die maximal zulässige Akkumulation des organischen Halogenids für die verfügbare Kühlleistung der Produktionsanlage bestimmen zu können.
Die Untersuchungen zeigten, dass gleiche Werte der molaren Reaktionsenthalpie sowohl bei isothermer als auch adiabatischer Kalorimetrie gemessen wurden. Als Ursache für die gemessenen größeren Enthalpiewerte während der isotherme Startreaktionsphase konnten noch vorhandene Wasser-Restmengen identifiziert werden, die infolge ihrer exothermen Folgereaktion mit der gebildeten Grignard-Reagenz einen zusätzlichen Wärmebeitrag lieferten. Eine Temperaturabhängigkeit der molaren Reaktionsenthalpie konnte im Temperaturbereich von 25°C bis 120°C nicht festgestellt werden.
Um subjektive Fehleinschätzungen des Anspringens der Grignard-Reaktion zu vermeiden, wurden die Anwendungsmöglichkeiten verschiedener Messmethoden zur Online-Überwachung getestet. Mit der in situ-Infrarotspektroskopie ließ sich das Anspringen der Grignard-Reaktion eindeutig und empfindlich detektieren. Ebenso könnte das spätere Einschlafen der Reaktion infolge zudosierter oder eindringender Verunreinigungen erkannt werden. Das Leistungsvermögen der Stoff- und Energiebilanzen als Methode zur Online-Überwachung konnte sowohl für die Startphase als auch für die Hauptreaktionsphase im Vergleich mit der Infrarotspektroskopie nachgewiesen werden. Die Wärmebilanzierung liefert eine viel versprechende Alternative zur in situ-Infrarotspektroskopie für den Einsatz an Produktionsanlagen, weil sie mit einer ausreichend empfindlichen Betriebsmesstechnik realisiert werden kann, quasi im Echtzeitbetrieb arbeitet und wesentlich kostengünstiger ist. Der Vorteil der in situ-Infrarotspektroskopie ist die parallele Online-Messung von störenden Wasseranteilen im Reaktionsmedium. Beispielsweise könnte das Nichtstarten der Grignard-Reaktion aufgrund von zu großen Wasserrestmengen in der Mehrzweckanlage erkannt werden. Durch geeignete Sicherheitsmaßnahmen und Sicherheitsverriegelungen sollte die Überdosierung von organischem Halogenid und das Eindringen stark exothermer Verunreinigungen (wie z. B. Wasser) während der ersten Grignard-Reaktionsstufe unbedingt verhindert werden. Aus Sicherheitsgründen sollte Wasser durch Öl als Kühlmedium möglichst ersetzt werden.

  • Technische Überwachung 46(2005)7/8, 41-47

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Permalink: https://www.hzdr.de/publications/Publ-7481
Publ.-Id: 7481


Diffusion of Humic Acid in Clay

Mibus, J.

The impact of organic matter on the migration of actinides in argillaceous media is relevant for the risk assessment of future nuclear waste repositories. The diffusion of a 14C-labelled synthetic humic acid in compacted Georgia kaolinite and its influence on the uranium(VI) migration was studied.
The migration of humic acid in clay is governed by diffusion. The colloidal properties of humic acid result in a size exclusion from small pores. Thus the accessible pore space decreases and the tortuosity of the diffusion path increases compared to a conservative tracer. Furthermore, the compacted clay filters large humic colloids. Both effects restrict the diffusive flux of humic acid in the clay.
Diffusion experiments on the time scale of several weeks could not demonstrate a humic colloid-borne migration of uranium(VI) in the clay system. The competition of the humate and surface binding sites for uranium as well as the kinetics and reversibility of the complexation govern the actinide migration in this system.

Keywords: Diffusion; Adsorption; Humic Acid; Kaolinite; Uranium

  • Invited lecture (Conferences)
    Institutsseminar, 21.06.2005, Villigen-PSI, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-7480
Publ.-Id: 7480


Near-field optical mapping of the ion-implanted patternsfabricated in amorphous silicon carbide

Tsvetkova, T.; Takahashi, S.; Zayats, A.; Dawson, P.; Turner, R.; Bischoff, L.; Angelov, O.; Dimova-Malinovska, D.

We propose scanning near-field optical microscopy as a novel technique for characterizing the ion-implanted patterns fabricated in amorphous silicon carbide (a-SiC:H). Different patterns have been fabricated in a-SiC:H films with a focused Ga+-ion beam system and examined with scanning near-field optical microscopy and atomic force microscopy. Although a considerable thickness change (thinning tendency) has been observed in the ion-irradiated areas, the near-field measurements confirm increases of optical absorption in these areas. The observed values of the optical contrast modulation are sufficient to justify the efficiency of the method for optical data recording using focused ion beams.

Keywords: Amorphous silicon carbide (a-SiC:H); Scanning near-field optical microscopy (SNOM); Focused ion beams (FIB); Highdensity optical data storage

  • Vacuum 79(2005), 94-99

Permalink: https://www.hzdr.de/publications/Publ-7479
Publ.-Id: 7479


Fabrication of nano-scale optical patterns in amorphous silicon carbide with focused ion beam writing

Tsvetkova, T.; Takahashi, S.; Zayats, A.; Dawson, P.; Turner, R.; Bischoff, L.; Angelov, O.; Dimova-Malinovska, D.

Optical patterns as small as 200nm width have been fabricated in a thin film of amorphous silicon carbide (a–SiC:H)using a focused ion beam microscope, (FIB). Because of the low electric conductivity of a–SiC:H, the diameter of the writing ion beam is broadened by the effect of surface charging which was overcome by depositing a thin layer of gold onto the a–SiC:H film. The topographic and optical contrasts of the patterned thin films have been mapped with
scanning near-field optical microscopy. The optical contrast corresponding to nanostructures is 0.2 with an overall increase of the optical density contrast of 0.5 in the irradiated areas. The results of the fabrication of patterns created with FIB on aluminium-coated a-SiC:H films are also briefly presented.

Keywords: Amorphous silicon carbide (a–SiC:H); Focused ion beam; Scanning near-field optical microscopy (SNOM); Nano-scale, optical data storage

  • Vacuum 79(2005), 100-105
  • Lecture (Conference)
    Vth International Symposium on Ion Implantation and other Applications of Ions and Electrons, 14.-17.06.2004, Kazimierz Dolny, Poland

Permalink: https://www.hzdr.de/publications/Publ-7478
Publ.-Id: 7478


A transient electrical model of charging for Ge nanocrystal containing gate oxides

Beyer, V.; von Borany, J.; Klimenkov, M.

The write performance of a multidot memory is investigated in MOS (metal-oxide-semiconductor) capacitors. The oxide of the MOS structure on p-type Si contains a layer of ion beam synthesized Ge nanocrystals (NC's) very close to the Si/SiO2 interface. This structure is modeled in a floating gate-like approach, where the NC's are considered as individual storage nodes and charged by direct tunneling of holes. Quantum confinement and Coulomb blockade effects of small Ge NC's (1-6 nm) are discussed and found to be negligible for the present structure. A close agreement between the calculated write characteristics and experimental data clearly confirms the validity of the model. From the simulation results it is predicted that a flatband voltage shift ΔVfb = -1V could be gathered with programming times tprog < 1µs. The write parameters (pulse voltage and duration) for a given ΔVfb value are mainly determined by the distance of the NCs' to the substrate.

Keywords: nanocrystals; MOS; Ge; memory; quantum confinement; Coulomb blockade

Permalink: https://www.hzdr.de/publications/Publ-7476
Publ.-Id: 7476


Influence of the substrate bias on the size and thermal stability of grains in magnetron-sputtered nanocrystalline Ag films

Almtoft, K.; Bottiger, J.; Chevallier, J.; Schell, N.; Martins, R.

The nanostructural evolution during heat treatments of DC magnetron-sputtered Ag films, deposited at room temperature at different substrate bias voltages, was experimentally studied. A growth chamber equipped with a magnetron and Kapton windows for in-situ x-ray diffraction was mounted on a six circle goniometer at a synchrotron beam line. Bragg-Brentano x-ray diffraction was used to monitor the (111) Bragg peak during thermal annealing of the Ag films. In addition, to investigate the <111> fiber texture one-dimensional pole figures were measured ex situ. The thermal stability of the nanostructure was sensitively dependent on the substrate bias voltage. Increasing the bias voltage resulted in significantly lower rates of grain growth, which we ascribe mainly to the formation of Ar bubbles. Furthermore, the grain size in the as-deposited films decreased with increasing bias voltage while the width of the one-dimensional pole figures increased.

Keywords: deposition by sputtering; crystal growth and orientation (texture development); in-situ XRD; nanophase materials : Ag

  • Journal of Materials Research 20(2005)4, 1071-1080

Permalink: https://www.hzdr.de/publications/Publ-7475
Publ.-Id: 7475


Migration Case Studies and the Implications of Humic Substances for the Radiological Performance Assessment of Radioactive Waste Repositories

Bryan, N. D.; Bernhard, G.; Geipel, G.; Heise, K. H.; Schmeide, K.; Benes, P.

Abstract wird nachgereicht

Keywords: Humic acid; fulvic acid; case study

  • Contribution to external collection
    G. Buckau: Humic Substances in Performance Assessment of Nuclear Waste Disposal: Actinide and Iodine Migration, Forschungszentrum Karlsruhe: Wissenschaftliche Berichte FZKA 7070, 2005, 81-114

Permalink: https://www.hzdr.de/publications/Publ-7474
Publ.-Id: 7474


Measurements and Monte Carlo calculations of gamma and neutron flux spectra inside and behind iron/steel/water configurations

Boehmer, B.; Konheiser, J.; Noack, K.; Rogov, A.; Stephan, I.; Hansen, W.; Hinke, D.; Unholzer, S.; Grantz, M.; Mehner, H.-C.

Gamma and neutron flux spectra were measured inside and behind various combined iron, steel and water slabs, which were set up in the radial beams of the zero-power training and research reactors AKR of the Technical University Dresden and ZLFR of the University of Applied Sciences Zittau/Görlitz. The measurements were carried out with a liquid NE-213 scintillation spectrometer in the energy ranges 0.23-10 MeV for photons and 1-20 MeV for neutrons. These experiments were simulated with help of the Monte Carlo transport codes MCNP-4C2 and TRAMO. With MCNP the energy point-wise representation of the nuclear data from ENDF/B-VI library, release 8, was used but with TRAMO effective group cross sections prepared by means of NJOY from the same data library. The paper describes the experiments and calculations and exemplarily presents and compares some results.

Keywords: Neutron/Gamma flux spectra; NE-213 scintillation spectrometer; neutron/gamma transport calculations; Monte Carlo method; MCNP; TRAMO

  • Lecture (Conference)
    12th International Symposium on Reactor Dosimetry, 08.-13.05.2005, Gatlinburg, United States
  • Journal of ASTM International 3(2006)8
  • Contribution to proceedings
    12 th International Symposium on Reactor Dosimetry, 08.-13.05.2005, Gatlinburg, United States
    Reactor Dosimetry: 12th International Symposium, West Conshohocken: ASTM, 978-0-8031-3412-6

Permalink: https://www.hzdr.de/publications/Publ-7473
Publ.-Id: 7473


Bloactivity of titanium following sodium plasma immersion ion implantation and deposition

Maitz, M. F.; Poon, R. W. Y.; Liu, X. Y.; Pham, M. T.; Chu, P. K.

Bio-activation of titanium surface by Na plasma immersion ion implantation and deposition (Pllf&D) is illustrated by precipitation of calcium phosphate and cell culture. The bioactivity of the plasma-implanted titanium is compared to that of the untreated. Na beam-line implanted and NaOH-treated titanium samples. Our data show that the samples can be classified into two groups: non-bioactive (untreated titanium and beam-line Na implanted titanium) and bioactive (Na-PIII&D and NaOH-treated titanium). None of the four types of surfaces exhibited major cell toxicity as determined by lactate dehydrogenase (LDH) release. However. the LDH release was higher oil the more bioactive PIII and NaOH-treated surfaces. From a morphological point of view, cell adherence on the NaOH-treated titanium is the best. On the other hand, the cell activity and protein production were higher on the non-bioactive surfaces. The high alkaline phosphatase activity per cell Suggests that the active surfa! ces support an osteogenic differentiation of the bone marrow cells at the expense of lower proliferation. The use of Na-PIII&D provides an environmentally cleaner technology to improve the bioactivity of Ti compared to conventional wet chemical processes. The technique is also particularly useful for the uniform and conformal treatment of medical implants that typically possess an irregular shape and are difficult to treat by conventional ion beam techniques. (c) 2005 Elsevier Ltd. All rights reserved.

  • Biomaterials 26(2005)27, 5465-5473

Permalink: https://www.hzdr.de/publications/Publ-7472
Publ.-Id: 7472


Observation of longitudinal optical-transverse optical splitting for E-symmetry phonons in Te by coherent phonon spectroscopy

Misochko, O. V.; Lebedev, M. V.; Dekorsy, T.

We report on the fermosecond time-resolved detection of coherent phonons in single-crystal tellurium. For different crystallographic faces a detection scheme is employed which is sensitive to the anisotropic part of the Raman tensor. In this scheme we observe all three Raman allowed phonons, i.e. one of A(1) and two of E symmetry. Furthermore, for both doubly degenerate E-symmetry modes obtained from different crystallographic faces, longitudinal optical-transverse optical splitting is observed. In addition, we show that even in the low fluence regime the frequency of the fully symmetric phonon in Te is chirped and that it demonstrates an anomalous dependence on the pump fluence.

  • Journal of Physics: Condensed Matter 17(2005)19, 3015-3023

Permalink: https://www.hzdr.de/publications/Publ-7471
Publ.-Id: 7471


Verification of geometrical perturbation calculations for the pulsed fast reactor IBR-2

Noack, K.; Rogov, A.; Shabalin, E.

The IBR-2 is a small fast reactor with plutonium oxide fuel and liquid sodium cooling. A ro-tating two-reflector system periodically closes and opens a non-reflected side of the reactor and leads it through the prompt super critical state in a time of about 500 microseconds. During this time a burst of fast neutrons is generated in the core of the reactor, which spreads out through moderators. Channels lead the neutrons to measurement instruments.
Certain reactivity parameters of the rotating reflector system determine essential parameters of the reactor as a pulsed neutron source. Just now a new reflector system, the so-called PO-3, has been installed. For this reason the important reactivity effects of the reflector were newly calcu-lated with help of the MCNP-4C2 code. The contribution presents numerical results, which were obtained in different ways and compares results of calculations and measurements. The special in-terest consisted in studying the effect of neglecting the fission source effect, as assumed by the PERT option of the code, on the calculation results. The comparison of numerical with measure-ment results showed agreements in some cases but also considerable discrepancies, which could not yet be explained. Therefore, no final conclusion on the applicability of the PERT method for the calculation of total and displacement reactivity effects of the rotating reflector system of the IBR-2 reactor could be drawn.

Keywords: Pulsed fast reactor IBR-2; reactivity effect; geometrical perturbation; MCNP calculations

  • Contribution to proceedings
    Monte Carlo 2005 Topical Meeting, 17.-21.04.2005, Chattanooga, United States, 0 89448 695 0

Permalink: https://www.hzdr.de/publications/Publ-7470
Publ.-Id: 7470


Two-dimensional numerical simulations of Marangoni-Bénard instabilities during liquid-liquid mass transfer in a vertical gap

Grahn, A.

2D simulations of isothermal liquid-liquid mass transfer subject to surface tension and buoyancy driven hydrodynamic instabilities have been carried out. Simulation is based on the numerical solution of two-dimensional equations of momentum and mass transport, using a combination of finite difference and finite volume methods. Two different cases have been considered: (1) buoyancy stable mass transfer, only surface tension driven convection occurs; (2) surface tension driven instability superseeded by buoyant convection. The faster attenuation of mass transfer coefficients in buoyancy stable situations is attributed to the merging of convection cells leading to a reduction in the number of renewal zones along the interface. Concentration profiles next to the interface reveal the diffusional nature of the mass transfer.

Keywords: Marangoni Instability; Rayleigh-Bénard Instability; Interfacial Convection; Mass Transfer; Momentum Transfer; Simulation

Permalink: https://www.hzdr.de/publications/Publ-7469
Publ.-Id: 7469


Two recipies to stabilize the substrate melting in FLASiC structures

Voelskow, M.; Mücklich, A.; Stoemenos, J.; Skorupa, W.

It could be shown that both, the introduction of a melt stop layer as well as the introduction of a layer with reduced melting temperature are usefull methods for the homogenisation of the melting depth at the bulk silicon surface in FLASIC structures.

Keywords: Flash lamp annealing silicon carbide

  • Lecture (others)
    Program Seminar of the Institute of ion beam physics and material research Rossendorf, 13.-15.06.2005, Schmochtitz, BRD

Permalink: https://www.hzdr.de/publications/Publ-7466
Publ.-Id: 7466


Entwicklung von neuartigen, stabilen und anpassbaren Rhenium-Komplexen mit verbrückten Dimercaptobernsteinsäure-Chelatbildnern

Heinrich, T.

Wir wollen auf diese Weise äußerst stabile Stabile Komplexe darstellen in denen Re perfekt eingekapselt ist. Ein aktives Zentrum in der Brücke soll eine gerichtete WW zum Re ausbilden und die Komplexe zusätzlich stabilisieren.

  • Lecture (others)
    1. Zittauer Doktorandentag, 01.06.2005, Zittau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7465
Publ.-Id: 7465


CFD-simulation of thermalhydraulic benchmark v1000ct –2

Höhne, T.; Bieder, U.; Kolev, N.

CFD pre-calculations have been performed for the themalhydraulic benchmark V1000CT-2.
The numerical grid model was generated with the grid generator IC4C (ICEM-CFD) and the preprocessor CFX-5 and contains 4.7 Mio. tetrahedral elements.The output of the Best Practice Guidelines for optimizing the numerical studies in different reactor types was used in the numerical simulation. The agreement with the Kozloduy experiment at the core inlet is very good. The results show a clear sector formation of the affected loop at the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.4%.

Keywords: PWR; CFD; Coolant Mixing

  • Lecture (Conference)
    OECD/DOE/CEA VVER-1000 Coolant Transient Benchmark - Third Workshop, 03.-07.04.2005, Garching, Germany

Permalink: https://www.hzdr.de/publications/Publ-7464
Publ.-Id: 7464


CFD-simulation of coolant transient benchmark v1000ct –1, exercise 3 using results of Dyn3d/Athlet coupled code calculation

Höhne, T.

Transient CFD calculations have been performed for the thermal-hydraulic benchmark V1000CT-1, exercise 3
The numerical grid model was generated with the grid generator IC4C (ICEM-CFD) and the preprocessor CFX-5 and contains 4.7 Mio. tetrahedral elements. The output of the Best Practice Guidelines for optimizing the numerical studies in different reactor types was used in the numerical simulation. Data from a coupled code calculation with DYN3D/ATHLET were used as inlet boundary conditions. 4 different Mixing Scalars were utilized to obtain information about the contribution of each loop during the transient. The results show a clear sector formation of the affected loops at the downcomer and core inlet. At the beginning of the start-up of loop 3 the sectors of loop 1,2,4 cover a bigger area.

Keywords: PWR; CFD; DYN3D; ATHLET; Coolant Mixing

  • Lecture (Conference)
    OECD/DOE/CEA VVER-1000 Coolant Transient Benchmark - Third Workshop, 03.-07.04.2005, Garching, Germany

Permalink: https://www.hzdr.de/publications/Publ-7463
Publ.-Id: 7463


Experimental investigation and CFD simulation of an air/water flow in a horizontal channel

Höhne, T.

The plug flow was simulated with a transient CFD simulation in the horizontal channel using time dependent inlet boundary conditions. The qualitative structure of the simulated slug front and tail are similar to the experiment, while the slug length is increasing in the calculation and remains constant in the experiment. The slug propagation velocities are in good agreement.

Keywords: slug flow; horizontal channel; CFD

  • Lecture (Conference)
    Multiphase Flows: Simulation, Experiment and Applications, 31.05.-03.06.2005, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-7462
Publ.-Id: 7462


The European project FLOMIX-R: Fluid mixing and flow distribution inthe reactor circuit - Final summary report

Rohde, U.; Höhne, T.; Kliem, S.; Scheuerer, M.; Hemström, B.; Toppila, T.; Dury, T.; Klepac, J.; Remis, J.; Mühlbauer, P.; Vyskocil, L.; Farkas, I.; Aszodi, A.; Boros, I.; Lycklama A. Nijeholt, J.-A.

The project was aimed at describing the mixing phenomena relevant for both safety analysis, particularly in steam line break and boron dilution scenarios, and mixing phenomena of interest for economical operation and the structural integrity. Measurement data from a set of mixing experiments, gained by using advanced measurement techniques with enhanced resolution in time and space help to improve the basic understanding of turbulent mixing and to provide data for Computational Fluid Dynamics (CFD) code validation. Slug mixing tests simulating the start-up of the first main circulation pump are performed with two 1:5 scaled facilities: The Rossendorf coolant mixing model ROCOM and the VATTENFALL test facility, modelling a German Konvoi type and a Westinghouse type three-loop PWR, respectively. Additional data on slug mixing in a VVER-1000 type reactor gained at a 1:5 scaled metal mock-up at EDO Gidropress are provided. Experimental results on mixing of fluids with density differences obtained at ROCOM and the FORTUM PTS test facility are made available.
Concerning mixing phenomena of interest for operational issues and thermal fatigue, flow distribution data available from commissioning tests (Sizewell-B for PWRs, Loviisa and Paks for VVERs) are used together with the data from the ROCOM facility as a basis for the flow distribution studies. The test matrix on flow distribution and steady state mixing performed at ROCOM comprises experiments with various combinations of running pumps and various mass flow rates in the working loops.
Computational fluid dynamics calculations are accomplished for selected experiments with two different CFD codes (CFX-5, FLUENT). Best practice guidelines (BPG) are applied in all CFD work when choosing computational grid, time step, turbulence models, modelling of internal geometry, boundary conditions, numerical schemes and convergence criteria. The BPG contain a set of systematic procedures for quantifying and reducing numerical errors. The knowledge of these numerical errors is a prerequisite for the proper judgement of model errors. The strategy of code validation based on the BPG and a matrix of CFD code validation calculations have been elaborated. Besides of the benchmark cases, additional experiments were calculated by new partners and observers, joining the project later.
Based on the “best practice solutions”, conclusions on the applicability of CFD for turbulent mixing problems in PWR were drawn and recommendations on CFD modelling were given. The high importance of proper grid generation was outlined. In general, second order discretization schemes should be used to minimise numerical diffusion. First order schemes can provide physically wrong results. With optimised “production meshes” reasonable results were obtained, but due to the complex geometry of the flow domains, no fully grid independent solutions were achieved. Therefore, with respect to turbulence models, no final conclusions can be given. However, first order turbulence models like K-e or SST K-w are suitable for momentum driven slug mixing. For buoyancy driven mixing (PTS scenarios), Reynolds stress models provide better results.

Keywords: turbulent mixing; flow distribution; nuclear reactors; experimental data base; computational fluid dynamics; best practice guidelines

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-432 2005
    ISSN: 1437-322X

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The European project FLOMIX-R: Description of the experimental and numerical studies of flow distribution in the reactor primary circuit(Final report on WP 3)

Toppila, T.; Höhne, T.; Kliem, S.; Elter, J.; Remis, J.; Klepac, J.; Farkas, I.; Aszodi, A.; Boros, I.

The flow distribution in the primary circuit of the pressurized water reactor was studied with experiments and Computational Fluid Dynamics (CFD) simulations. The main focus was on the flow field and mixing in the downcomer of the pressure vessel: how the different factors like the orientation of operating loops, the total loop flow rate and the asymmetry of the loop flow rates affect the outcome. In addition to the flow field studies the overall applicability of CFD methods for primary circuit thermal-hydraulic analysis was evaluated based on the CFD simulations of the mixing experiments of the ROCOM (Rossendorf Coolant Mixing Model) test facility and the mixing experiments of the Paks NPP.
The experimental part of the work in work package 3 included series of steady state mixing experiments with the ROCOM test facility and the publication of results of Paks VVER-440 NPP thermal mixing experiments. The ROCOM test facility models a 4-loop KONVOI type reactor. In the steady-state mixing experiments the velocity field in the downcomer was measured using laser Doppler anemometry and the concentration of the tracer solution fed from one loop was measured at the downcomer and at the core inlet plane. The varied parameters were the number and orientation of the operating loops, the total flow rate and the (asymmetric) flow rate of individual loops.
The Paks NPP thermal mixing experiments took place during commissioning tests of replaced steam generator safety valves in 1987-1989. It was assumed that in the reactor vessels of Paks VVER-440 NPP equipped with six loops the mixing of the coolant is not ideal. For the realistic determination of the active core inlet temperature field for the transients and accidents associated with different level temperature asymmetry a set of mixing factors were determined. Based on data from the online core monitoring system and a separate mathematical model the mixing factors for loop flows at the core inlet were determined.

In the numerical simulation part of the work package 3 the detailed measurements of ROCOM tests were used for the validation of CFD methods for primary circuit studies. The selected steady state mixing experiments were simulated with CFD codes CFX-4, CFX-5 and FLUENT. The velocity field in the downcomer and the mixing of the scalar were compared between CFD simulations and experiments. The CFD simulations of full scale PWR included the simulation of Paks VVER-440 mixing experiment and the simulation of Loviisa VVER-440 downcomer flow field. In the simulations of Paks experiments the experimental and simulated concentration field at the core inlet were compared and conclusions made concerning the results overall and the VVER-440 specific geometry modelling aspects like how to model the perforated elliptic bottom plate and what is the effect of the cold leg bends to the flow field entering to the downcomer. With Loviisa simulations the qualitative comparison was made against the original commissioning experiments but the emphasis was on the CFD method validation and testing.

The overall conclusion concerning the CFD modelling of the flow field and mixing in the PWR primary circuit could be that the current computation capacity and physical models also in commercial codes is beginning to be sufficient for simulations giving reliable and useful results for many real primary circuit applications. However the misuse of CFD methods is easy, and the general as well as the nuclear power specific modelling guidelines should be followed when the CFD simulations are made.

Keywords: fluid mixing; flow distribution; velocity filed; nuclear power plant; commissioning experiments; experimental data base; computational fluid dynamics

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-431 2005
    ISSN: 1437-322X

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Publ.-Id: 7460


The European project FLOMIX-R: Description of the slug mixing and buoyancy related experiments at the different test facilities(Final report on WP 2)

Rohde, U.; Kliem, S.; Hemström, B.; Toppila, T.; Bezrukov, Y.

The goal of the work described in this report was the experimental investigation of the mixing of coolant with different quality (temperature, boron concentration) in nuclear reactors on the way from the cold leg through the downcomer and lower plenum to the core inlet in a systematic way. The obtained data were used for the clarification of the mixing mechanisms and form a data basis for the validation of computational fluid dynamics (CFD) codes.
For these purposes, experiments on slug mixing have been performed at two test facilities, modelling different reactor types in scale 1:5, the Rossendorf and Vattenfall test facilities. The corresponding accident scenario is the start-up of first main coolant pump (MCP) after formation of a slug of lower borated water during the reflux-condenser mode phase of a small break loss of coolant accident (LOCA). The matrices for the experiments were elaborated on the basis of the key phenomena, being responsible for the coolant mixing during pump start-up. Slug mixing tests have also been performed at the VVER-1000 facility of EDO Gidropress to meet the specifics of this reactor type.
The mixing of slugs of water of different quality is also very important for pre-stressed thermal shock (PTS) situations. In emergency core cooling (ECC) situations after a LOCA, cold ECC water is injected into the hot water in the cold leg and downcomer. Due to the large temperature differences, thermal shocks are induced at the reactor pressure vessel (RPV) wall. Temperature distributions near the wall and temperature gradients in time are important to be known for the assessment of thermal stresses.
One of the important phenomena in connection with PTS is thermal stratification, a flow condition with a vertical temperature profile in a horizontal pipe. Due to the fluctuating character of the flow, this may cause thermal fatigue in the pipe. Besides of thermal fatigue, a single thermal shock can also be relevant for structural integrity, if it is large enough, especially in the case, that the brittle fracture temperature of the RPV material is reduced due to radiation embrittlement. Therefore, additional to the investigations of slug mixing during re-start of coolant circulation, the mixing of slugs or streams of water with higher density with the ambient fluid in the RPV was investigated. The aim of these investigations was to study the process of turbulent mixing under the influence of buoyancy forces caused by the temperature differences. Heat transfer to the wall and thermal conductivity in the wall material have not been considered.
Experiments on density driven mixing were carried out at the Rossendorf and the Fortum PTS facilities.

Keywords: turbulent mixing; slug mixing; boron dilution; buoyancy controled mixing; pressurised thermal shock; nuclear reactors; experimental data base

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-430 2005
    ISSN: 1437-322X

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Publ.-Id: 7459


Axial RF power input into photocathode electron guns

Janssen, D.; Volkov, V.; Bluem, H. P.; Todd, A. M. M.

We discuss the coaxial power input in normal and superconducting RF (SRF) photoinjector cavities. Upstream coaxial power input has been previously used at the PITZ facility where the output beam tube is an intrinsic part of the coaxial transmission line into the gun. In this paper, we describe coaxial coupling from the cathode side of the gun. For normal conducting RF guns, in addition to the advantage from symmetric coupling, an emittance compensation solenoid can now be positioned close to the gun cavity to deliver optimal transverse emittance. Beam dynamics calculations demonstrate 0.8 mm-mrad at 1 nC in X-band. For an SRF gun, we present a design for coaxial input around the cathode using a superconducting coupling cell. This cell matches the external quality factor of the gun for different beam powers and there is no RF loss associated with the axial gap of the cathode. The heat input into the coaxial feed and the surface field of the coupler are discussed. For a 1.3 GHz half-cell gun cavity with stored energy of 6.6 J, a 2.5 MeV electron beam can be delivered with a peak accelerating field of 50 MV/m. At 10 mA, the external Q is 2.1 x 106 and the coaxial line power loss that must be cooled is 28 W.

  • Lecture (Conference)
    PAC Particle Accelerator Conference 2005, 16.-21.05.2005, Knoxville, TN, USA
  • Contribution to proceedings
    Particle Accelerator Conference 2005, 16.-20.05.2005, Knoxville, Tennessee, USA
    Proceedings of 2005 Particle Accelerator Conference, MOPB011, ISBN 0-7803-8860-7, 743-745

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Publ.-Id: 7458


Third order spectral branch points in Krein space related setups: PT-symmetric matrix toy model, MHD α²-dynamo, and extended Squire equation

Günther, U.; Stefani, F.

The spectra of self-adjoint operators in Krein spaces are known to possess real sectors as well as sectors of pair-wise complex conjugate eigenvalues. Transitions from one spectral sector to the other are a rather generic feature and they usually occur at exceptional points of square root branching type. For certain parameter configurations two or more such exceptional points may happen to coalesce and to form a higher order branch point. We study the coalescence of two square root branch points semi-analytically for a PT-symmetric 4×4 matrix toy model and illustrate numerically its occurrence in the spectrum of the 2×2 operator matrix of the magnetohydrodynamic α²-dynamo and of an extended version of the hydrodynamic Squire equation.

Keywords: non-Hermitian operators; discrete symmetries; Krein space; level crossings; branch points; Jordan structure; MHD dynamo; Squire equation

Permalink: https://www.hzdr.de/publications/Publ-7457
Publ.-Id: 7457


Dynamo experiments

Gailitis, A.; Lielausis, O.; Gerbeth, G.; Stefani, F.

The long history of laboratory experiments on homogeneous dynamo action is delineated. It is worked out what sort of insight can be expected from experiments, and what not. Special focus is laid on the principle and the main results of the Riga dynamo experiment which is shown to represent a genuine hydromagnetic dynamo with a non-trivial saturation mechanism that relies mainly on the fluidity of the electrically conducting medium.

  • Magnetohydrodynamics - Historical Evolution and Trends Berlin(2006), 37-54

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Publ.-Id: 7456


Response of drinking-water reservoir ecosystems to decreased acidic atmospheric deposition in central Europe II. Signs of biological recovery

Meybohm, A.; Ulrich, K.-U.

Strongly decreasing atmospheric emissions and acidic depositions during the 1990s have caused a chemical reversal from acidification in several drinking-water reservoirs of the Ore Mountains, SE Germany. Responses of phytoplankton, zooplankton, and fish stock were studied in five reservoirs and in enclosure scale where a water body of 1,200 m3 was experimentally neutralized by application of a new buffering substance. Three months after this treatment, the dominating chrysophytes and dinoflagellates were substituted by diatoms and cryptomonades. The colonization by acidic-sensitive species of green algae, cryptomonades, rotifers, and Cladocera (e.g. Bosmina longirostris) is explained by the occurrence of dormant stages or by survival of individuals in very low abundances. In conformity with the enclosure experiment, three reservoirs showed significantly (p<0.01) falling trends of chlorophyll a and phytoplankton biovolume, mainly due to the decline of dinoflagellates. Picoplankton and diatoms slightly increased in two reservoirs. The zooplankton biocoenosis was dominated by rotifers and small cladocera, the genus Daphnia was still lacking. Two reservoirs were re-colonized by zooplanktivorous fish populations of either perch (Perca fluviatilis) or sunbleak (Leucaspius delineatus). The latter exhibited extremely high fluctuating abundance and biomass and even suffered from a population crash. This natural mortality was caused by limited food supply. Hence, severe top-down control may delay the recovery of bigger zooplankton species like daphnids. Fishery management comprising the introduction of predatory fishes could help to control zooplanktivorous fish populations and to prevent their mass mortality.

Keywords: acidification reversal; enclosure experiment; fish stock; phytoplankton; recovery; reservoir ecosystem; zooplankton

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Publ.-Id: 7455


The usefulness of radiotracers to make the body biochemically transparent

Johannsen, B.

Radioactive isotopes are uniquely applicable to observe reactions or circuits of reactions at the molecular level without disturbing the system being studied. The advent of molecular imaging modalities, particularly positron emission tomography (PET), is a major breakthrough for the visualisation and quantitative assessment of cellular and molecular processes occurring in living tissues. The recent development of animal PET scanners that offers 2-mm resolution and is tailored to laboratory rodents, has made a further great impact on in vivo biochemistry. With these live-imaging modalities at hand, radiotracer-based technologies allow to look directly at biochemical distribution and interaction processes. Tremendous progress made in radiotracer chemistry, primarily in carbon-11 and fluorine-18 radiochemistry, and in the design of imaging devices strengthens the usefulness of radiotracers in nuclear medicine and drug research and development and opens exciting opportunities for new applications, e.g. in food science.

Keywords: Radiotracer; Positron emission tomographie; Molecular imaging

Permalink: https://www.hzdr.de/publications/Publ-7454
Publ.-Id: 7454


Control of properties and structure of ZnO thin films by a wide variation of oxygenpressure during reactive magnetron deposition and by post-deposition annealing

Vinnichenko, M.; Poperenko, L.; Lebyedyeva, T.; Shpylovyy, P.; Shevchenko, N.; Rogozin, A.; Sudovtsova, V.; Kolitsch, A.; Möller, W.

Due to recent progress in crystal growth and unique optical and electrical properties ZnO becomes a prospective material for use in optoelectronic devices. ZnO thin films have been prepared at unheated glass substrates by reactive DC magnetron sputtering. The oxygen fraction in Ar + O2 gas mixture was varied from 0 to approximately 83%. The films have been characterized by spectroscopic ellipsometry (SE), atomic force microscopy (AFM) and X-ray diffraction (XRD). The dielectric function of ZnO layers was parameterized using Drude-Lorentz oscillator. As shown by SE, the dielectric functions of the films prepared at low oxygen fraction are characteristic for cermet materials (mixture of oxide and metal particles). XRD confirms the presence of both ZnO and metallic Zn phases in these films. The layers produced at high oxygen fractions (above 60%) are insulating and their dielectric functions can be reasonably described by Lorentz oscillator alone. Importantly, that the latter films are polycrystalline with pronounced (002) type texture even at a thickness of only 50 nm. The XRD results point to a high mechanical stress in these films that can be related to the bombardment by negative oxygen ions during the film growth.
ZnO films prepared at medium oxygen fraction of 48% were annealed in vacuum at about 340 °C for 1.5 hour with in situ control of optical properties by SE and resistivity by two point probe measurement. The influence of the structural ordering during annealing on the refractive index is higher than the free electron density variation. An enhancement of the film resistivity at the final annealing stage (last 40 min) with concomitant decrease of the free electron concentration could be an indication of the acceptor-like defect formation.

Keywords: ZnO; reactive DC magnetron sputering; spectroscopic ellipsometry; optical properties

  • Poster
    European Materials Research Society Spring Meeting (E-MRS), Symposium G: ZnO and related materials, 31.05.-03.06.2005, Strasbourg, France

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Publ.-Id: 7453


Near-infrared intersubband transitions in InGaAs–AlAs–InAlAs double quantum wells

Semtsiv, M.; Ziegler, M.; Masselink, W. T.; Georgiev, N.; Dekorsy, T.; Helm, M.

Intersubband optical transitions at short wavelengths in strain-compensated In0.70Ga0.30As—AlAs double quantum wells are investigated by means of mid-infrared absorption. Trade-offs between achieving a high transition energy and a large oscillator strength of the two highest-energy intersubband transitions using our strain-compensation approach are analyzed as a function of the widths of the two wells. Two design strategies leading to relatively strong intersubband optical transitions at 800 meV, 1.55 µm, are described and the corresponding structures grown using gas-source molecular-beam epitaxy on (001)InP are investigated. The strongest intersubband transitions obtained experimentally are generally between 300 and 600 meV, 2–4 µm. Significant oscillator strength, however, also extends out to 800 meV, 1.55 µm.

Keywords: intersubband transition; quantum well; infrared

Permalink: https://www.hzdr.de/publications/Publ-7452
Publ.-Id: 7452


Biocere mit spezifischer Metallbindungsaktivität

Raff, J.

Thema: Entwicklung und Testung einer neuen Klasse hybrider keramischen Funktionswerkstoffe (Biocere), die als schwermetallbindende Filtermaterialien oder als Immobilisierungsmatrix für lebende Zellen in der Umwelt- und Biotechnologie genutzt werden können.

  • Other report
    Abschlussbericht zum DFG-Förderprojekt SE 671/7-2: Berichtszeitraum: 01.10.2002 - 30.09.2004, 2005
    35 Seiten

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Publ.-Id: 7451


Spatial dynamics of MSRE

Krepel, J.; Rohde, U.; Grundmann, U.; Weiss, F.-P.

The paper report about spatial dynamics studies of the Molten Salt Reactors (MSR). MSR is one of the concepts considered within the 'Generation IV International Forum'. The graphite-moderated channel type MSR based on the previous Oak Ridge National Laboratory (ORNL) research is considered.
The physical models and numerical solution procedures used in the dynamics code DYN3D-MSR are described. The most relevant peculiarities in MSR dynamics are the delayed neutrons precursors drift with the flowing fuel and the direct release of fission energy into the fuel-coolant salt. The code is based on the in-house developed code DYN3D for Light Water Reactor, which solves two-group neutron diffusion equations by the help of a nodal expansion method. The same method for prompt neutron kinetics is used in DYN3D-MSR, but the appropriate models for the delayed neutrons and for the thermal-hydraulic have been integrated.
The code has been validated against experimental data gained from the Molten Salt Reactor Experiment (MSRE), performed in the ORNL. After successful validation, the code DYN3D-MSR was applied to the analysis of several hypothetical transients typical for liquid fuel systems. Particularly, a prompt reactivity insertion modeling a control rod ejection accident was analyzed. By performing these analyses, the DYN3D-MSR code has been shown to be an effective tool for MSR dynamics studies.

Keywords: MSR; MSRE; spatial; dynamics; 3D; molten; salt; reactor

  • Lecture (Conference)
    ICONE 13 - 13th International Conference on Nuclear Engineering, 16.-20.05.2005, Beijing, China
  • Contribution to proceedings
    13th International Conference on Nuclear Engineering, 16.-20.05.2005, Beijing, China
    Proceedings of 13th International Conference on Nuclear Engineering

Permalink: https://www.hzdr.de/publications/Publ-7449
Publ.-Id: 7449


Annual Report 2004 - Institute of Nuclear and Hadron Physics

Enghardt, W.; Fahmy, K.; Grosse, E.; Kämpfer, B.; Schneidereit, C.; Wagner, A.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-423 2005
    ISSN: 1437-322X

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Publ.-Id: 7448


The influence of a poly-Si intermediate layer on the crystallization behaviour of Ni-Ti SMA magnetron sputtered thin films

Martins, R. M. S.; Braz Fernandez, F. M.; Silva, R. J. C.; Pereira, R. J. C.; Gordo, P. R.; Maneira, M. J. P.; Beckers, M.; Mücklich, A.; Schell, N.

Ni-Ti thin films as-sputtered are amorphous if the substrate is not intentionally heated during deposition. Therefore, these films have to be heat-treated to induce crystallization in order to exhibit the shape memory effect. Several films have been prepared by dc magnetron sputtering and then studied concerning the influence of the type of substrate (single crystal Si, polycrystalline Si) on the crystallization kinetics and the final structure. The structural development of the films during crystallization (at a constant temperature of 430°C) has been studied by X-ray diffraction in grazing incidence geometry (GID) off-plane at a synchrotron radiation beamline. These experiments allow to establish a correlation between the deposition conditions and the kinetics of crystallization. For films deposited at an electrode distance of 70 mm on a Si(100) substrate, a longer crystallization time is needed compared with films obtained at 40 mm, for otherwise fixed deposition parameters. The analysis of the nucleation kinetics by using the Kolmogorov-Johson-Mehl-Avrami equation lead to exponents between 2.6 and 3. The presence of an intermediate layer of poly-Si drastically enhances the crystallization process. Additionally, ex-situ annealing of identical samples at 500°C during 1 hour and complementary characterization of the structure and morphology of the films by Cross-sectional Transmission Electron Microscopy (XTEM) and Selected Area Electron Diffraction (SAED) were performed. The temperature dependence of the electrical resistivity was measured, identifying the phase transformation temperature ranges. An increase of the overall resistivity with the precipitation of Ni4Ti3 has been detected. Results obtained by X-ray reflectometry (XRR) and GID suggest that during crystallization excess nickel is driven into an amorphous region ahead of the crystal/amorphous interface, thus leading to a higher concentration of Ni at the surface and further precipitation of Ni4Ti3. t the shape memory effect. Several films have been prepared by dc magnetron sputtering and then studied concerning the influence of the type of substrate (single crystal Si, polycrystalline Si) on the crystallization kinetics and the final structure. The structural development of the films during crystallization (at a constant temperature of 430°C) has been studied by X-ray diffraction in grazing incidence geometry (GID) off-plane at a synchrotron radiation beamline. These experiments allow to establish a correlation between the deposition conditions and the kinetics of crystallization. For films deposited at an electrode distance of 70 mm on a Si(100) substrate, a longer crystallization time is needed compared with films obtained at 40 mm, for otherwise fixed deposition parameters. The analysis of the nucleation kinetics by using the Kolmogorov-Johson-Mehl-Avrami equation lead to exponents between 2.6 and 3. The presence of an intermediate layer of poly-Si drastically enhances the crystallization process. Additionally, ex-situ annealing of identical samples at 500°C during 1 hour and complementary characterization of the structure and morphology of the films by Cross-sectional Transmission Electron Microscopy (XTEM) and Selected Area Electron Diffraction (SAED) were performed. The temperature dependence of the electrical resistivity was measured, identifying the phase transformation temperature ranges. An increase of the overall resistivity with the precipitation of Ni4Ti3 has been detected. Results obtained by X-ray reflectometry (XRR) and GID suggest that during crystallization excess nickel is driven into an amorphous region ahead of the crystal/amorphous interface, thus leading to a higher concentration of Ni at the surface and further precipitation of Ni4Ti3.

Keywords: Deposition by sputtering, X-ray diffraction; Structure and morphology; thickness; crystalline orientation and texture

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Publ.-Id: 7447


A comparative study of the electrical properties of heavily Al implanted, single crystalline and nanocrystalline SiC

Heera, V.; Madhusoodanan, K. N.; Skorupa, W.; Dubois, C.; Romanus, H.

The electrical properties of heavily Al doped single and nanocrystalline 4H-SiC layers on semi-insulating 4H-SiC substrate, prepared by multi-energy, high-fluence Al implantation and subsequent furnace annealing, are investigated by sheet resistance and Hall effect measurements. Ion beam induced crystallization is used to prepare the nanocrystalline SiC layers. The doping levels are chosen around the solid solubility limit of 2x1020 cm-3 in the range from 5x1019 to 1.5x1021 cm-3. The comparison of the results shows that heavily Al doped single crystalline SiC layers have superior conduction properties. The lowest resistivities measured at room temperature are 0.07 Ohm-cm and 0.8 Ohm-cm for the single crystalline and nanocrystalline samples, respectively. Recent results on enhanced Al acceptor activation in nanocrystalline SiC cannot be confirmed. There is an upper limit for the hole concentration in the nanocrystalline samples independent of the Al supersaturation level in the as-implanted state due to outdiffusion of Al in excess to the solid solubility limit during annealing. In contrast to the nanocrystalline SiC layers the as-implanted Al profile in single crystalline material remains stable after annealing even for concentrations above the solid solubility limit. Therefore, in single crystalline material efficient impurity band conduction due to strongly interacting acceptors can be achieved in the range of supersaturation. For lower doping levels impurity band conduction is more effective in nanocrystalline SiC.

Keywords: SiC; nanocrystalline; p-type doping; ion implantation; Hall effect

  • Journal of Applied Physics 99(2006)15, 123716-1-123716-8

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Publ.-Id: 7446


Atomistic study of intrinsic defects in Germanium

Geßner, H.; Posselt, M.

Since high-k insulators appear more and more to be preferable to SiO2 in semiconductor technology, Ge is again becoming of increasing interest, since its carrier mobility is higher than that of Si. Atomistic simulations are a powerful tool to investigate atomic-level physics and to get a better understanding of the processes during the technological steps in integrated electronic device manufacturing.
In the present work different interatomic potentials for Ge are evaluated with respect to their accuracy in describing the structure and energetics as well as the migration of point defects. A number of parameterizations of the Stillinger-Weber (SW) potential and one Tersoff type potential were tested.
The formation energies for different configurations of the interstitial are calculated. Also the formation energy of the vacancy and the bond defect are estimated. It can be shown that the extended 110-dumbbell configuration is the interstitial with the lowest formation energy for most SW parameter sets. In the Tersoff case the tetrahedral interstitial shows the lowest formation energy. For the SW-type potentials the vacancy shows a strong inward-distortion, whereas for the Tersoff potential it shows a slight outwards-distortion.
In recent ab-initio calculations the 110 dumbbell has been found to be the most stable interstitial structure. This is in qualitative agreement with the results for most SW parameter sets, although these calculations predict the extended dumbbell configuration as the interstitial with the lowest formation energy. For the SW parameter sets of W. Yu (model B) and Nordlund, the formation energy of this dumbbell is also in qualitative agreement with the ab-initio result. The formation energy of the vacancy obtained with these SW parameter sets is nearly equal to the ab-initio result. The observed inwards relaxation of the atoms around the vacancy is also found by ab-initio calculations. However, the details of the lattice distortion near the vacancy and the interstitial differ from those predicted by ab-initio calculations.
For the reasons mentioned above, the SW parameter sets of Nordlund et al. and W. Yu et al. are selected for migration investigations. In both cases the vacancy mobility strongly dominates interstitial mobility. Some investigations are also performed with the Tersoff potential, where the vacancy shows a very low mobility.
The results are used to estimate the self-diffusion coefficient. With the SW approach it is shown that self-diffusion in Ge is mediated by vacancies. This stands in good agreement with experimental data. However, the calculated migration energy (2.2 eV) is less than the measured value (3.09 eV). With the Tersoff potential an interstitial dominated mechanism is found. Therefore the Tersoff potential cannot be considered useful for a study of point defect and self-diffusion in Ge.

Keywords: defects; computer simulation; germanium

  • Poster
    E-MRS 2005 Spring Meeting, 31.05.-03.06.2005, Strasbourg, France

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Publ.-Id: 7445


Simulation of phase transfer in case of bubbly steam-water flow along a large vertical pipe

Lucas, D.; Prasser, H.-M.

Detailed experimental data obtained at the TOPFLOW facility for steam-water vertical pipe flow were used to test the complex interaction of local bubble distributions, bubble size distributions and local heat and mass transfer. Steam is injected into sub-cooled water and condenses during the upwards flow. The model considers a large number of bubble classes (50). This allows the investigation of the influence of the bubble size distribution. The results of the simulations show a good agreement with the experimental data. The condensation process is clearly slower, if large bubbles are injected (4 mm holes). Also bubble break-up has a strong influence on the condensation process because of the change of the interfacial area. Some unsureness arises from the unknown interfacial area for large bubbles and possible uncertainties of the heat transfer coefficient.

Keywords: bubbly flow; phase transfer; bubble size distribution; vertical pipe flow

  • Contribution to proceedings
    4th International Conference on transport phenomena in multiphase systems, 26.-30.06.2005, Gdansk, Poland
    Proceedings, Gdansk, Poland: IFFM Publishers, 83-88237-90-X, 345-350
  • Lecture (Conference)
    4th International Conference on transport phenomena in multiphase systems, 26.-30.06.2005, Gdansk, Poland

Permalink: https://www.hzdr.de/publications/Publ-7444
Publ.-Id: 7444


Simulation of bubble condensation with a multi-bubble size class model

Lucas, D.; Prasser, H.-M.

Experimental data obtained at the TOPFLOW facility for steam-water vertical pipe flow were used to test the complex interaction of local bubble distributions, bubble size distributions and local heat and mass transfer. Steam is injected into sub-cooled water and condenses during the upwards flow. The model considers a large number of bubble classes (50). This allows the investigation of the influence of the bubble size distribution. The results of the simulations show a good agreement with the experimental data. The condensation process clearly depends on the initial bubble size. Also bubble break-up has a strong influence on the condensation process because of the change of the interfacial area.

Keywords: bubbly flow; phase transfer; bubble size distribution; vertical pipe flow; condensation

  • Lecture (Conference)
    Workshop on Multi-Phase Flow: Simulation, Experiment and Application, Rossendorf, 31 May - 3 June 20, 31.05.-03.06.2005, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-7443
Publ.-Id: 7443


Experimental investigation of rotating magnetic field driven flow by highly sensitive potential probe measurements

Cramer, A.; Gundrum, T.; Varshney, K.; Gerbeth, G.

Electric potential difference probes (PDP) are mostly applied on laboratory scale to measure local velocities in electrically conducting media. Their principle of operation is based on Ohms law. In the absence of electric currents, and provided a proper orthogonal arrangement, the voltage drop measured between the two electrodes is proportional to the fluids velocity. The measuring magnetic field may be applied globally or by a small permanent magnet at the very tip of the Sensor (VIVES--probe). A typical probe as described in the original work has an electrode spacing of 5 mm while using relatively large CoSm magnets. Because the electrodes are usually mounted on the side of the magnet where the field is weaker, the authors were limited to measure velocities down to 1 cm/s at U =1 mV. They specified a sensitivity of 1 mm/s.

Along with progress in analog electronics, results have recently been published by (GELFGAT) who reported on an increased sensitivity of almost an order of magnitude even for a smaller probe. As stated by the the authors, all measurements were conducted at least five times comprising 200 readings, each. From this averaging it becomes obvious that turbulence measurements have not been possible. The subject of this investigation was the flow driven by a rotating magnetic field (RMF), which may be characterised by the aspect ratio and the magnetic Taylor number.

In the present paper, it is described how the applicable range of PDPs regarding sensitivity can be increased further by about two orders of magnitude. An extremely low-noise preamplifier served as a basis of a multistage measuring chain consisting of another two amplifiers and steep
Butterworth filters. For the differential signal processing required for such small voltages as a few nanovolt it was vital to provide a proper common mode rejection throughout the whole instrumental chain. Since acquisition of velocity fluctuations does not allow any averaging or even the use of integrating amplifiers, potential sources of statistical errors had to be avoided. In particular, the electromagnetic noise was countered by a sophisticated wiring scheme. Systematic errors such as thermoelectric currents are detrimental to the measurement of very small mean velocities. Meticulously avoiding both temperature differences and gradients of Seebeck coefficients, it was possible to reduce thermoelectrical voltages below the velocity signal level.

RMF-driven flows comprise a secondary recirculation in the meridional plane. According to theory, the change-over from a Stokes regime to a laminar boundary one of the primary swirl takes place at a Taylor number of approx. 1000, accompanied by a change of the linear scaling (velocity versus Taylor number) to a power 2/3 characteristic. A sensitivity of 0.01 mm/s permitted to safely determine mean velocities for Taylor numbers commencing with 31.

Besides sensitivity and accuracy, measurements of turbulent velocity fluctuations put a severe
restriction on the size of the sensor in order to resolve all scales of potentially significant vortices. The high sensitivity described above was achieved substantially by state of the art analog instrumentation while the dimensions of the probe were quite small. Having an induction
of 75 mT at the tips of the electrodes, their spacing of 1 mm delivered a signal of 180 nV per cm/s, only. Nevertheless, the performance of the measuring chain allowed for the acquisition of
velocity fluctuations even in the transitional regime slightly above the critical Taylor number. The wavenumber spectra calculated via Taylors hypothesis were well resolved up to the end of the inertial range and showed a steep decrease with an exponent less than 4.

  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    Proceedings 2(2005), 337-340
  • Poster
    Joint 15th Riga and 6th PAMIR Interantional Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia

Permalink: https://www.hzdr.de/publications/Publ-7442
Publ.-Id: 7442


Float-zone crystal growth with a novel melt flow control

Priede, J.; Gerbeth, G.; Hermann, R.; Behr, G.

We consider the growth of single crystals by the floating-zone method using a radio frequency (RF) heating magnetic field. The quality of the grown crystals, especially of complicated intermetallic compounds, strongly depends on the growth conditions, particularly on the shape of the solidification front. To obtain single crystals of high physical and chemical precision, a convex to the melt growth interface is desirable. The shape of the solid-liquid interface can strongly be influenced by the convective heat transport in the melt. The major mechanism driving the melt flow is the electromagnetic force due to the RF-heating. This force drives a melt flow directed radially inwards at mid-height of the floating zone. Favourable growth conditions, however, would require the flow to be directed away from the solidification front at the axis of symmetry and, respectively, to be directed against it at the free surface of the floating zone. This flow can be generated by an electromagnetic force directed along the free surface towards the solidification front.
We developed the solution of a two-phase stirrer which allows a flexible control of the melt motion. This stirrer basically consists in an additional coil superimposed to the primary induction coil. The additional coil is not connected to any power supply, but it is part of a secondary circuit with adjustable capacitor and resistance. The current in the secondary coil is solely induced by the primary coil. In that way, an electromagnetic pump is created. Its intensity and resulting flow direction can easily be adjusted to the process needs. The flexible system parameter are the location and distance of the secondary coil with respect to the primary one, and the capacitor and resistance of the secondary circuit.
We present numerical and experimental results for the melt flow and temperature fields resulting from the influence of such a two-phase stirrer. Ni-based single crystals as well as various intermetallic compounds have been grown, and the obtained results are discussed in relation to the provided flow control.

  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    2(2005), 189-192

Permalink: https://www.hzdr.de/publications/Publ-7441
Publ.-Id: 7441


On magnetohydrodynamic drag reduction and its efficiency

Shatrov, V.; Gerbeth, G.

Recently various drag reduction techniques were studied numerically and experimentally in many papers. Among others there is the subtopic of magnetohydrodynamic (MHD) drag reduction where the Lorentz force is used for the purpose of drag reduction in an electrically conducting fluid. In many recently published papers permanent magnets and high electric current densities are used in order to achieve reasonable Lorentz forces. This choice, however, immediately leads to a low efficiency.
We consider a plane channel as the flow configuration. Here, the fully developed turbulent channel flow is homogeneous in the streamwise and spanwise directions, thus, periodic boundary conditions can be applied in these directions. This simplifies the numerical solution of the problem significantly. We present the results of direct numerical simulations of turbulent channel flow drag reduction using electromagnetic forces. The Lorentz force is created by the interaction of a permanent magnetic field and an electric current from electrodes placed on the bottom wall surface. Two various electromagnetic field cases are considered. In the first case an oscillating electric current and a permanent magnetic field create a spanwise oscillating Lorentz force, whereas in the second case a stationary electric current and a permanent magnetic field create a steady streamwise force.
The reason of the low MHD drag reduction efficiency by a spanwise oscillating Lorentz force, as obtained up to now in literature, is explained. The main result of our work is that using a load factor k ~ 1 leads to a significant efficiency improvement for all considered cases. The efficiency increases when the load factor is close to its optimum value. We show that the time oscillating spanwise Lorentz force reduces the skin-friction drag. The full drag is also reduced, the efficiency is increased by 100 times but is still much less than 1. In this case, the skin-friction drag may be strongly reduced at a very small load factor k < 1, but not the full drag.
The application of the streamwise Lorentz force leads to a much more effective drag reduction if we consider the drag as a full force applied to the body. The skin-friction drag increases but the full drag may be reduced to the zero value with a good efficiency.

  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    1(2005), 149-152
  • Poster
    Joint 15th Riga and 6th PAMIR Interantional Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
  • Magnetohydrodynamics 42(2006)2/3, 181-186

Permalink: https://www.hzdr.de/publications/Publ-7440
Publ.-Id: 7440


Fluid flow analysis and vertical gradient freeze crystal growth in a traveling magnetic field

Lantzsch, R.; Galindo, V.; Grants, I.; Pätzold, O.; Gerbeth, G.; Stelter, M.; Cröll, A.

The Traveling Magnetic Field (TMF) is a versatile tool to control the flow in an electrically conducting fluid. It introduces a mainly axial Lorentz force into the fluid which leads to meridional flow patterns. Applying the TMF to the Vertical Gradient Freeze (VGF) growth of semiconductor single crystals, the heat and mass transport in the melt can be tailored for growth under optimised flow conditions to improve crystal properties and/or growth yield.
In this paper we present experimental and numerical results on the TMF driven flow in an isothermal model fluid as well as in a VGF melt. The field is created by an equally spaced set-up of six coils of 36 windings each. Induction and frequency can be varied between 0-5 mT and 50-400 Hz, respectively.
Model experiments were carried out at about 20°C with the traveling field applied to InGaSn melts in cylindrical, non-conducting vessels of different diameters. Axial velocity profiles were measured by means of the Ultrasonic Doppler Velocimetry (UDV) method. The basic flow was investigated as a function of the aspect ratio and of the non-dimensional forcing and screening parameters with the focus on the transition from laminar to time-dependent convection. For comparison, numerical calculations were performed using advanced, highly accurate spectral methods as well as commercial codes.
For the growth experiments a VGF furnace was equipped with the TMF set-up. The maximum temperature of the furnace is about 1300°C and crystals with a diameter up to three inches can be grown. Ga doped germanium single crystals were grown under the influence of the field and without field. The TMF impact on the thermal field in the melt was studied on the basis of natural or artificially induced dopant striations which characterise the solid-liquid interface and, thus, the local temperature field. The transition to instationary melt flow which is indicated by the appearance of regular striation patterns in the crystal, was investigated by increasing the TMF forcing parameter intentionally during growth. Numerical results came from a quasi-2D simulation of the melt flow using the commercial code CrysVun++. A global, thermal model of the VGF furnace has been developed for this purpose.

  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    2(2005), 197-200
  • Magnetohydrodynamics 42(2006)4, 445-449

Permalink: https://www.hzdr.de/publications/Publ-7439
Publ.-Id: 7439


Formation of Highly Mobile Di-Interstitials During Ion Implantation

Posselt, M.

Atomistic computer simulations show that the metastable defect structure formed immediately after ion bombardment of silicon does not only consist of isolated mono-vacancies and mono-interstitials but also of more complex defects. Amongst them a small percentage of very mobile di-interstitials is found. The structure and energetics of these defects as well as their migration are investigated in more detail, and the results are compared with literature data. Mobile and immobile di-interstitial configurations are found. The migration mechanism shows a pronounced dependence on the temperature. The di-interstitial diffusivity and the self-diffusion coefficient per defect are calculated. The di-interstitial migrates much faster than the mono-interstitial.
The high mobility of the di-interstitials and the fact that they can be already formed during the ion bombardment may have implications for the current understanding of many experimental results obtained in the last decade, in particular for the explanation of the implantation-induced migration of interstitial-like defects at room temperature.

Keywords: defects; computer simulation; silicon

  • Poster
    E-MRS 2005 Spring Meeting, 31.05.-03.06.2005, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-7438
Publ.-Id: 7438


Nitrogen recoil chromium implantation into SAE 1020 steel by means of ion beam or plasma immersion ion implantation

Gomes, G. F.; Ueda, M.; Reuther, H.; Richter, E.; Beloto, A. F.

As an effort to improve the corrosion behavior of the mild steel under work conditions, we attempted to produce a high chromium content layer on its surface by applying the recoil implantation process. After polishing, SAE 1020 construction steel samples were covered with chromium and then bombarded with ions. As recoil bombarding atom, we used nitrogen, a light mass specimen. Recoil atoms were applied either by ion beam (IB) accelerator or by plasma immersion ion implantation (PIII) method. Samples treated by the PIII process showed better results, presenting a thicker layer of high Cr content, as measured by Auger electron spectroscopy (AES).

  • Surface & Coatings Technology 196(2005)1-3, 275-278

Permalink: https://www.hzdr.de/publications/Publ-7437
Publ.-Id: 7437


Electro-vortex flows in shallow liquid metal layers

Kolesnichenko, I.; Khripchenko, S.; Buchenau, D.; Gerbeth, G.

We investigate different kinds of electro-vortex flows generated in a shallow layer of liquid metal. The metal flow is driven by an externally applied electrical current which interacts with its own magnetic field. Due to symmetry this interaction alone causes not yet a flow as the Lorentz force is purely irrotational. If, however, ferromagnetic C-cores or yokes are applied, the magnetic field distribution is modified and a flow driving action results. An electro-vortex flow occurs with several eddies in this MHD-layer. In the stable case, for some range of electrical current values, these eddies are held in permanent position. The unstable case is characterized by an oscillation of the eddies, which are moving in the plane of the layer. One of the reasons to perform this study is related with the occurrence of similar unstable processes in some devices used for metallurgical purposes including the flat MHD-layer considered here. We have investigated this flow by experimental and numerical methods.
We applied the ultrasound Doppler velocimetry which allows us to measure velocity profiles in non-transparent media. The oxide particles of this alloy were acting as good tracers for ultrasound measurements and allowed us to obtain the time-dependences of the velocity profiles. At higher electrical currents, the profiles showed large-scale low-frequency oscillations. Various types of flows are distinguished depending on the location of the ferromagnetic C-core.
The mathematical model of the processes was based on the MHD-equations, which have been modified using a thin-layer approximation. The numerical calculations support the results obtained in experiments, and showed the behavior of the velocity field with the moving of the eddies.

  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    1(2005), 199-202
  • Poster
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia

Permalink: https://www.hzdr.de/publications/Publ-7435
Publ.-Id: 7435


Review of the results of the KaoS Collaboration

Förster, A.; Böttcher, I.; Dohrmann, F.; Förster, A.; Grosse, E.; Koczon, P.; Kohlmeyer, B.; Lang, S.; Laue, F.; Menzel, M.; Naumann, L.; Oeschler, H.; Ploskon, M.; Pühlhofer, F.; Scheinast, W.; Schmah, A.; Schuck, T.; Schwab, E.; Senger, P.; Shin, Y.; Ströbele, H.; Sturm, C.; Uhlig, F.; Walus, W.; Wagner, A.

The production of K+ and of K- mesons in heavy-ion collisions at beam energies of 1 to 2 A GeV has systematically been investigated with the kaon spectrometer KaoS. The ratio of the K+ production excitation function for Au+Au and for C+C reactions increases with decreasing beam energy, which is expected for a soft nuclear equation-of-state. A comprehensive study of the K+ and of the K- emission as a function of the size of the collision system, of the collision centrality, of the kaon energy, and of the polar emission angle has been performed. The K-/K+ ratio is found to be nearly constant as a function of the collision centrality and can be explained by the dominance of strangeness exchange. On the other hand, the spectral slopes and the polar emission patterns are different for K- and for K+. Furthermore the azimuthal distribution of the particle emission has been investigated. K+ mesons and pions are emitted preferentially perpendicular to the reaction plane as well in Au+Au as in Ni+Ni collisions. In contrast for K- mesons in Ni+Ni reactions an in-plane flow was observed for the first time at these incident energies.

  • Journal of Physics G 31(2005), 693-700

Permalink: https://www.hzdr.de/publications/Publ-7434
Publ.-Id: 7434


11C-C bond formation by palladium-mediated cross-coupling of alkenylzirconocenes with [11C]methyl iodide

Berndt, M.; Wüst, F.

The prenyl group is known as an important structural building block in natural and medicinal products. The isotopic substitution of one of the two methyl groups with a [11C]methyl group would provide an access to a large number of interesting 11C-labelled compounds. Here we report a strategy for the synthesis of 11C-labelled prenyl group-containing derivatives starting from methyl-substituted alkynes (1) via a novel 11C-C bond forming reaction. A commonly employed strategy to form a,a’-disubstituted alkenes comprises the formation of alkenylzirconocenes by the syn-insertion of a C-C triple bond into the Zr-H bond of Schwartz reagent [Cp2Zr(H)Cl] followed by metal-mediated C-C bond formation with electrophiles under retention of the configuration of the C-C douple bond [1,2].
In principle the formation of alkenylzirconocenes by syn-addition of Schwartz reagent onto disubstituted alkynes (1) leads to a mixture of regioisomers 2 and 2’. However, treatment of an excess of Schwartz reagent favors the formation of the sterically less hindered isomer 2. Transmetalation with transition metal complexes M(PPh3)4 and conversion with [11C]MeI leads to compound 4.

Keywords: 11C-C bond formation; [11C]MeI; alkenyl-zirconium complexes

  • Lecture (Conference)
    International Symposium on Radiopharmaceutical Chemistry (ISRC 2005), 24.-28.06.2005, Iowa City, Iowa, USA
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 48(2005), S24

Permalink: https://www.hzdr.de/publications/Publ-7432
Publ.-Id: 7432


Synthesis and characterization of [18F]MCl-322 as a potential PET radiotracer for imaging the dopamine transporter

Wüst, F.; Neumeyer, J.; Bergmann, R.; Kretzschmar, M.; van den Hoff, J.

The fluoroethyl ester-containing phenyltropane derivative MCL-322 was shown to display high affinity to the dopamine transporter (DAT) (Ki = 2.3 nM). The binding affinities (Ki values) for the serotonin transporter and norepinephrine transporter were determined to be 5.1 nM and 280 nM, respectively [1]. The high binding affinities and selectivities of MCL-322 make the corresponding 18F-labelled compound an attractive PET radioligand for imaging DAT in brain tissue. Here, we report on the radiosynthesis of [18F]MCL-322 and its radiopharmacological characterization involving biodistribution, autoradiography and small animal PET studies.

Keywords: [18F]MCL-322; dopamine transporter (DAT); PET

  • Poster
    International Symposium on Radiopharmaceutical Chemistry (IRSC 2005), 24.-28.06.2005, Iowa City, Iowa, USA
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 48(2005), S204

Permalink: https://www.hzdr.de/publications/Publ-7431
Publ.-Id: 7431


Aspects of 6-[18F]fluoro-F-DOPA preparation: experiences with chloroform as a substitute solvent for Freon 11

Füchtner, F.; Zessin, J.; Wüst, F.

An increasing number of PET centers is using 6-[18F]fluoro-L-DOPA ([18F]FDOPA) to study presynaptic dopamine metabolism in vivo.
Currently the electrophilic radiofluoro-destannylation reaction of N-Boc-3,4-di(Boc-O)-6-trimethylstannyl-L-phenylalanine ethyl ester with [18F]F2 has emerged as the preparation method of choice for the reliable and reproducible radiosynthesis of [18F]FDOPA (1-5).
Up to now the radiofluorination step of the trimethyltin precursor is carried out in trichlorofluoromethan (CFCl3, Freon 11) as the solvent. De Vries et al. (4) have reported Freon 11 as the superior solvent to provide the highest radiochemical yields for the radiofluorination step. The authors also have investigated the possibility to substitute Freon 11 with other solvents. They observed considerable losses of radioactivity (61-71%) during the evaporation step of the solvents (e.g. chloroform and acetonitrile). They discussed this finding with the formation of volatile radiofluorine compounds originating from the reaction of [18F]F2 gas with the solvents.
For Freon 11 is hardly available in Europe for environmental protection reasons, we investigated the possibility of substituting Freon 11 with chloroform. In contrast to (4) we use 5 M HCl for protecting group hydrolysis. The acid is added directly after the radiofluorination step and the solvent was evaporated at 130°C. First results with chloroform also show increased losses of radioactivity in comparison to Freon 11. However, we found that the rate of radioactivity loss depends on the quality of the chloroform used. The radioactivity losses using chloroform stabilised with ethanol were in the range of 25%, whereas the amylene stabilised chloroform gave losses of 40%. In contrast, using deuterated chloroform (CDCl3) for NMR analysis purposes stabilised with silver no significant losses of radioactivity were observed in comparison with Freon 11. We conclude that no competitive radiofluorination of the solvent chloroform, neither CHCl3 nor CDCl3, with [18F]F2 occures. Instead of that the observed radioactivity losses can be explained by the radiofluorination of stabilisers present in CHCl3.The non-decay-corrected total yield for [18F]FDOPA preparation using Freon 11 as the solvent is 17% (n = 26). Using CDCl3 (silver stabilised) instead of CFCl3 the average non-decay-corrected total yield is slightly higher, being 20% (n = 17).
The use of CDCl3 has further advantages:
- easy handling (boiling point = 61°C) and unlimited availability,
- better environmental protection properties,
- the radiofluoro-destannylation reaction can be carried out at temperatures above freezing-point
The results of our investigations indicate the possibility to substitute Freon 11 with CDCl3 stabilised with silver.

Keywords: [18F]FDOPA preparation; substitution of Freon 11; chloroform

  • Poster
    International Symposium on Radiopharmaceutical Chemistry (IRSC 2005), 24.-28.06.2005, Iowa City, Iowa, USA
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 48(2005), S211

Permalink: https://www.hzdr.de/publications/Publ-7430
Publ.-Id: 7430


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