Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31738 Publications
Correlation of structural and physical properties of metastable Fe-Cr phases
Gorbunov, A.; Levin, A. A.; Meyer, D. C.; Bischoff, L.; Eckert, D.; Köhler, B.; Mertig, M.; Weissbach, T.; Wieser, E.; Pompe, W.;
This paper contributes to the studies of physical properties of metastable Fe-Cr phases which have been discovered recently in the thin films deposited from the hyperthermal Fe and Cr particle beams. The electrical resistance and the magnetic remanence are correlated with the crystallographic parameters and phase composition of the samples. It is demonstrated that the focused ion-beam induced phase transformation in the unusual metastable Fe-Cr alloys can be used for the fabrication of ferromagnetic arrays.
Keywords: metastable Fe-Cr phases, ferromagnetic arrays, FIB
  • Crystal Research and Technology 40(2005), 106

Publ.-Id: 8057 - Permalink


Präparation und Charakterisierung von Strukturen für die Nanotechnologie
Schmidt, B.;
No abstract was required
Keywords: Nanocrystals, Nanowires, FIB, Ion beam synthesis
  • Lecture (others)
    Sonderseminar im Rahmen des Graduiertenkollegs, 27.06.2005, Rostock, Germany

Publ.-Id: 8056 - Permalink


Nano-Technologie
Schmidt, B.;
No abstract was required
Keywords: Nanotechnology, Nanocrystals, Nanowires, Ion beam Synthesis, FIB
  • Lecture (others)
    Lehrerfortbildungsseminar Rossendorf, 12.02.2005, Forschungszentrum Rossendorf, Germany

Publ.-Id: 8055 - Permalink


Ionenstrahlanalytik an den Rossendorfer Beschleunigern
Grötzschel, R.; Grambole, D.; Güttler, D.; Herrmann, F.; Kreißig, U.; Neelmeijer, C.;
Das Ionenstrahllabor des Forschungszentrums Rossendorf als Teil des Institutes für Ionenstrahlphysik und Materialforschung betreibt Materialanalytik mit MeV Ionenstrahlen an 3 Beschleunigern, dem 5 MV Tandem, dem 3 MV Tandetron und dem 2 MV van de Graaff-Beschleuniger.
Insgesamt sind für diese Arbeiten 12 Experimentierplätze installiert, mit denen alle ionenstrahlanalytischen Techniken in hoher Qualität zur Verfügung stehen.
Neben Standardtechniken wie RBS/channeling, ERDA, PIXE und NRA, die wegen spezifischer Vorteile inzwischen unverzichtbar zum Instrumentarium der physikalischen Dünnschicht- Charakterisierung gehören, werden Verfahren eingesetzt und weiterentwickelt, die von hoher Relevanz bei der Entwicklung moderne funktioneller Schichten und deren Abscheidung sind.
Dazu gehört vor allem die quantitative Analytik von Oberflächen und ultradünnen Schichten mit Tiefenauflösungen im sub-nm – Bereich durch den Einsatz von Magnetspektrometern für die hochauflösende Teilchenspektrometrie. Begleitet wird diese methodische Entwicklung von Grundlagenarbeiten zur Abbremsung und zum Ladungsaustausch von leichten Schwerionen in Festkörpern.
Eine andere Richtung wird verfolgt bei der in situ – Ionenstrahlanalytik transienter Prozesse in „Echtzeit“, also während eines Prozessverlaufes.
Im Vortrag werden nach einer kurzen Vorstellung des Ionenstrahllabors die Arbeiten zur Höchstauflösung vorgestellt und ein in situ-Experiment zur Targetvergiftung beim reaktiven Magnetronsputtern beschrieben.
  • Invited lecture (Conferences)
    Zukunftsperspektiven und Anwendungen von Ionenstrahlen, 17.10.2005, Berlin, Deutschland

Publ.-Id: 8054 - Permalink


Nano-Drähte durch Ionenbeschuss
Schmidt, B.; Bischoff, L.; Akhmadaliev, C.; Heinig, K.-H.;
Die fortschreitende Miniaturisierung mikroelektronischer Strukturen sowie deren Kombination mit optischen, mechanischen oder magnetischen Komponenten erfordern laufend neue physikalische und technologische Ansätze. Im Forschungszentrum Rossendorf wird im Rahmen von zwei Projekten, getragen von der Deutschen Forschungsgemeinschaft (DFG), intensiv an der Entwicklung und Untersuchung von Nanostrukturen für die Elektronik der Zukunft gearbeitet. So beschäftigt sich das FZR-Institut für Ionenstrahlphysik und Materialforschung u. a. mit der reproduzierbaren Herstellung von maßgeschneiderten Nano-Drähten, die möglichst passfähig zur herkömmlichen Silizium-Techologie sein sollen.

Die Herstellung dieser Drähte beruht auf der Ionenstrahlsynthese, schematisch in Abb. 2 dargestellt. Hierzu werden feine Linien von Cobalt-Ionen mit dem Fokussierten Ionenstrahl (FIB; Focussed Ion Beam) in ein Silizium-Substrat bei erhöhten Temperaturen implantiert und in einem folgenden Ausheilprozess zu einem Cobaltdisilizid-Draht (CoSi2) synthetisiert. Dabei wird die Kombination zweier wesentlicher Aspekte ausgenutzt. Zum einen wird der geringe Drahtdurchmesser durch die hohe Fokussierbarkeit des FIB auf kleiner als 50 Nanometer erreicht, auch als „top-down“-Ansatz bezeichnet. Zum anderen führen selbst-organisierende Prozesse, der „bottom-up“-Ansatz, zu einer weiteren Konzentration der implantierten Cobalt-Verteilung. Dies ermöglicht die Synthese von Nanostrukturen mit einem Durchmesser von 10 bis 20 Nanometer.

Der Schwerpunkt der Arbeiten konzentriert sich zunächst auf das zur Mikroelektronik-Technologie kompatible Cobaltdisilizid. Dieses Material ist metallisch, weist eine sehr gute Leitfähigkeit auf und ist hinsichtlich der Gitterstruktur der des Siliziums sehr ähnlich. Die ersten Ergebnisse sind vielversprechend, nun gilt es, die Reproduzierbarkeit sowie die genaue „Platzierung“ der Drähte im Material zu gewährleisten. Auf dem Weg hin zu neuen Nano-Bauelementen für die Mikroelektronik ist also noch viel zu tun.
Keywords: nano-wire, CoSi2, ion beam synthesis
  • Dresdner Transferbrief 2(2005), 13-13

Publ.-Id: 8053 - Permalink


Metabolite analysis in positron emission tomography studies: examples from food sciences
Pawelke, B.;
Substances of various chemical structures can be labelled with appropriate positron emitting isotopes and applied as tracer compounds in PET examinations. Using dynamic data acquisition protocols, time-activity curves of radioactivity uptake in organs can be derived and the measurements of tissue tracer concentrations can be translated into quantitative values of tissue function. However, analysis of metabolites of these tracers regarding their nature and distribution in the living organism is an essential need for the quantitative analysis of PET measurements. In addition, metabolite analysis contributes to the interpretation of the images obtained as well as to the identification of pathological changes in metabolic pathways. This paper reports on representative examples of radiolabelled compounds which might be of importance in food science (e.g., amino acids, polyphenols, and model compounds for advanced glycation end products (AGEs)). Typical procedures of analysis (radio-HPLC, radio-TLC) including pre-analytical sample preparation are described. Specific challenges of the method, e.g., trace amounts of radiolabelled compounds and the influence of the often very short half-lives of positron-emitting nuclides used are highlighted. Representative results of analyses of plasma, urine, and tissue samples are presented and discussed in terms of the metabolic fate of the tracers.
Keywords: Positron emission tomography – Metabolite analysis – Tracer – Amino acids – Advanced glycation endproducts – Polyphenols

Publ.-Id: 8052 - Permalink


Small animal positron emission tomography in food sciences
Bergmann, R.; Pietzsch, J.;
Positron emission tomography (PET) is a 3-dimensional imaging technique that has undergone tremendous developments during the last decade. Non-invasive tracing of molecular pathways in vivo is the key capability of PET. It has become an important tool in the diagnosis of human diseases as well as in biomedical and pharmaceutical research. In contrast to other imaging modalities, radiotracer concentrations can be determined quantitatively. By application of appropriate tracer kinetic models, the rate constants of numerous different biological processes can be determined. Rapid progress in PET radiochemistry has significantly increased the number of biologically important molecules labelled with PET nuclides to target a broader range of physiologic, metabolic, and molecular pathways. Progress in PET physics and technology strongly contributed to better scanners and image processing. In this context, dedicated high resolution scanners for dynamic PET studies in small laboratory animals are now available. These developments represent the driving force for the expansion of PET methodology into new areas of life sciences including food sciences. Small animal PET has a high potential to depict physiologic processes like absorption, distribution, metabolism, elimination and interactions of biologically significant substances, including nutrients, ‘nutriceuticals’, functional food ingredients, and foodborne toxicants. Based on present data, potential applications of small animal PET in food sciences are discussed.
Keywords: Positron emission tomography – Food sciences – Small animal PET scanners – PET tracer

Publ.-Id: 8051 - Permalink


Principles of quantitative positron emission tomography
van den Hoff, J.;
The central distinguishing feature of positron emission tomography (PET) is its ability to investigate quantitatively regional cellular and molecular transport processes in vivo with good spatial resolution. This review wants to provide a concise overview of the established principles underlying quantitative data evaluations of the acquired PET images. Especially, the compartment modelling framework is discussed on which virtually all quantification methods utilized in PET are based. The aim of the review is twofold: first, to provide the reader with an idea of the theoretical framework and mathematical tools and second, to enable an intuitive grasp of the possibilities and limitations of a quantitative approach to PET data evaluation. This should facilitate an understanding of how PET measurements translate into quantities such as regional blood flow, volume of distribution, and metabolic rates of specific substrates.
Keywords: Positron emission tomography – PET – Tracer kinetics – Compartment modelling

Publ.-Id: 8050 - Permalink


Ge/Si quantum dot nanostructures grown with low-energy ion beam-assisted epitaxy
Dvurechenskii, A. V.; Smagina, J. V.; Groetzschel, R.; Zinovyev, V. A.; Armbrister, V. A.; Novikov, P. L.; Teys, S. A.; Gutakovskii, A. K.;
Scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED) experiments were performed to study growth modes induced by hyperthermal Ge+ ion action during molecular beam epitaxy (MBE) of Ge on Si(100). The continuous and pulsed ion beams were used. These studies have shown that ion beam bombardment during heteroepitaxy leads to decrease in critical film thickness for transition from two-dimensional (2D) to three-dimensional (3D) growth modes, enhancement of 3D island density, and narrowing of island size distribution, as compared with conventional MBE experiments. Moreover, it was found that ion beam assists the transition from hut- to dome-shaped Ge islands on Si(100). The crystal perfection of Ge/Si structures with Ge islands embedded in Si was analyzed by Rutherford backscattering/channeling technique,(RBS) and transmission electron microscopy (TEM). The studies of Si/Ge/Si(100) structures indicated defect-free Ge nanopaticles and Si layers for the initial stage of heteroepitaxy (five monolayers of Ge) in pulsed ion beam action growth mode at 350 degrees C. Continuous ion beam irradiation was found to induce dislocations around Ge clusters. The results of kinetic Monte Carlo (KMC) simulation have shown that two mechanisms of ion beam action can be responsible for stimulation of 2D-3D transition: (1) surface defect generation by ion impacts, and (2) enhancement of surface diffusion.
Keywords: ion beam-assisted epitaxy; nanoparticles; self-assembling effects
  • Surface & Coatings Technology 196(2005)1-3, 25-29

Publ.-Id: 8049 - Permalink


Analysis of PF surfaces and interfaces using nuclear analytical methods
Mackova, A.; Grötzschel, R.; Nekvindova, P.; Spirkova, J.; Svorcik, V.; Zemek, J.;
The application of nuclear analytical methods on surface and interface study is presented. Two topics are included in the presentation - polymer-metal interaction studies and study of single-crystalline structures using RBS-channeling method. Diffusion of Ag atoms in polyethyleneterephtalate (PET) was studied using Rutherford Backscattering Spectroscopy (RBS) and Elastic Recoil Detection Analysis (ERDA). The samples were prepared by deposition of Ag thin layers on polymer surface using CVD and diode sputtering techniques. Faster diffusion of Ag atoms was observed from non-compact Ag layers prepared by diode sputtering than from those prepared by CVD technique. The samples of erbium doped lithium niobate (Er:LiNbO3) were prepared by standard Czochralski method and treated by Annealed Proton Exchange (APE) procedure to create planar wave-guide for further optical application. The position of Er atoms in the crystal lattice of pristine and APE treated Er:LiNbO3 samples were studied by Rutherford Backscattering Spectrometry (RBS)-channeling method. The Er3+ ion position in the pristine and the APE treated Er:LiNbO3 samples are compared.
Keywords: DIFFUSION; LINBO3
  • Open Access LogoActa Physica Slovaca 55(2005)3, 323-329

Publ.-Id: 8048 - Permalink


Comparison of crystal lattice changes caused by APE treatment of Er : LiNbO3 and by localised Er doping into LiNbO3 obtained by RBS-channeling and XRD analysis
Mackova, A.; Spirkova, J.; Nekvindova, P.; Salavcova, L.; Groetzschel, R.; Eichhorn, F.;
Lithium niobate containing erbium (Er:LiNbO3), which is often used as non-linear optical material, was studied by Rutherford backscattering spectroscopy (RBS)-channeling analysis and X-ray diffraction (XRD). The Er3+ doping was done by both bulk doping and by localised doping. The studied samples were virgin Er:LiNbO3 wafers, and annealed proton exchange (APE) treated wafers in order to increase the refractive index in the surface layer and to create the planar optical waveguides. Moreover, erbium ions were introduced into the surface of pure LiNbO3 wafers by Er-moderate temperature localised doping. The APE:Er:LiNbO3 samples showed modifications of the crystal lattice compared to the virgin Er:LiNbO3; the Er localised doping samples even exhibited the tendency to form an amorphous surface layer in which the Er ions were incorporated.
Keywords: RBS-channeling; XRD; APE : Er : LiNbO3
  • Nuclear Instruments and Methods in Physics Research B 240(2005)1-2, 391-394

Publ.-Id: 8047 - Permalink


Optical and transport nonlinearities in quantum well infrared photodetectors
Schneider, H.; Maier, T.; Schönbein, C.; Koidl, P.; Walther, M.; Liu, H. C.;
Nonlinear behavior in quantum well infrared photodetectors (QWIPs) can be classified into nonlinearities associated with transport effects, such as quantum well depletion or photocurrent saturation induced by the emitter barrier, and nonlinearities induced by nonlinear absorption.
After giving a short overview on the different nonlinearities occurring in QWIPs and related device structures, we will concentrate on two particular phenomena. First, it is well known that the photoconductivity in n-type GaAs/AlGaAs QWIPs exhibits negative differential behavior, and that this negative differential photoconductivity gives rise to electric field domains. We have analyzed the spatial distribution of electric field domains induced by negative differential photoconductivity in a 50-period QWIP. We found evidence of two different domain configurations, with the high-field domain and the low-field domain, respectively, adjacent to the emitter contact. Second, we report on two-photon detection based on nonlinear absorption between subbands in quantum wells. Resonantly enhanced nonlinear absorption, six orders of magnitude higher as compared to typical bulk semiconductors, leads to a threshold power density for quadratic detection as low as 0.1 W/cm2, and femtosecond time resolution. The approach enables dynamical characterization of the optical light field of infrared emitters via autocorrelation measurements. We also demonstrate the use of this technique to investigate inter- and intra-subband scattering times.
Keywords: infrared, photodetector, intersubband, QWIP
  • Invited lecture (Conferences)
    8-th International Conference on Intersubband Transitions in Quantum Wells, 11.-16.09.2005, Cape Cod, MA, USA

Publ.-Id: 8046 - Permalink


Influence of Al on the growth of NiSi2 on Si(001)
Allenstein, F.; Budzinski, L.; Hirsch, D.; Mogilatenko, A.; Beddies, G.; Groetzschel, R.; Hinneberg, H.;
Thin films of different atomic ratios of nickel and aluminium were deposited on Si(001)-wafers by magnetron cosputtering. The content of deposited nickel complies to layer thickness of about 20 nm, After deposition the samples were annealed between 500 and 900 degrees C in steps of 100 degree using rapid thermal annealing (RTA) in N-2 ambient. RBS, SEM, TEM, XRD, AES and sheet resistance measurements were performed to characterize the grown thin films.
  • Microelectronic Engineering 82(2005)3-4, 474-478

Publ.-Id: 8045 - Permalink


Nine Years Experience in Routine Operation and Maintenance of the Rossendorf CYCLONE 18/9 Facility
Preusche, S.; Füchtner, F.; Roß, H.; Wüst, F.;
kein Abstract verfügbar
  • Contribution to proceedings
    CYCLONE 18/9 & 10/5 User Community, 5. Workshop, 01.-04.05.2005, Montreal, Canada
    5th IBA C18/9 C10/5 PET Cyclotron Users Meeting

Publ.-Id: 8044 - Permalink


Production of 86Y and 56Co at the Rossendorf CYCLOTRONE 18/9
Preusche, S.; Wüst, F.; Schilling, K.-D.; Roß, H.; Dohn, N.;
kein Abstract verfügbar
  • Poster
    CYCLONE 18/9 & 10/5 User Community, 5. Workshop, 01.-04.05.2005, Montreal, Canada

Publ.-Id: 8043 - Permalink


The Rossendorf Solid Target System
Preusche, S.; Roß, H.; Dohn, N.; Wüst, F.; Steinbach, J.;
kein Abstract verfügbar
  • Lecture (Conference)
    CYCLONE 18/9 & 10/5 User Community, 5. Workshop, 01.-04.05.2005, Montreal, Canada

Publ.-Id: 8042 - Permalink


Field profile measurement and tuning of the 3½ cell SRF-gun
Arnold, A.; Büttig, H.; Janssen, D.; Teichert, J.; Murcek, P.;
kein Abstract vorhanden
  • Poster
    1st Annual EUROFEL Workshop 2005, 07.-09.11.2005, Orsay, France

Downloads:

Publ.-Id: 8041 - Permalink


Bioverteilung und Metabolisierung des 18F-markierten Amadori-Produktes Fructoselysin
Hultsch, C.; Hellwig, M.; Bergmann, R.; Henle, T.;
Ziel:
Amadore-Produkte (1-Amino-1-desoxy-2-ketosen) werden in der Frühphase der sogenannten Maillard-Reaktion zwischen reduzierenden Zuckern und primären Aminen in Lebensmitteln bei der zubereitung oder Lagerung sowie in vivo gebildet. Täglich werden etwa 1 g Amadori-Produkte mit der nahrung aufgenommem [1]. Jedoch ist nur der Verbleib von ca. 5% dieser Verbindungen bislang bekannt. Die ernährungsphysiologischen Konsequenzen, die sich aus der Aufnahme dieser Verbindungen ergeben, sind weitestgehend ungeklärt. Ziel dieser Arbeit war es daher, Bioverteilung und eventuelle Metabolisierungsreaktionen des Amadori-Produktes Fructoselysin auch vor dem Hintergrund der kürzlich entdeckten Fructosamin-3-Kinasen [2] zu untersuchen.

Methodik:
Fructoselysin wurde mit N-Succinimidyl-4-[18F]-Fluorbenzonat zum [18F]fluorbenzoylierten Fructoselysin (FB-FL) umgesetzt. Dieses wurde mit Organhomogenaten (Herz, Hirn, Leber, Milz, Niere, Pankreas), Vollblut, Plasma und Vollblutlysat von männlichen Wistar-Ratten inkubiert. Dabei wurde der Einfluss von ATP und 1-Desoxy-1-morpholino-fructose (DMF), einem spezifischen Inhibitor der Fructosamin-3-Kinase, auf die Umsetzung des FB-FL untersucht. Weiterhin erfolgte die Messung der Bioverteilung un der in vivo-Stabilität.

Ergebnisse:
Weder in den untersuchten Organhomogenaten noch im Vollblut oder Plasma fand eine Umsetzung des FB-FL statt. Nur im Vollblutlysat konnte die Bildung eines Umwandlungsproduktes m1 beobachtet werden. Diese Umsetzung konnte durch die Zugabe von ATP beschleunigt und durch Zugabe von DMF gehemmt werden.Die Inkubation von m1 mit alkalischer Phosphatase führte zu einem vollständigen Abbau. Bei m1 handelt es sich damit voraussichtlich um ein Phosphatester, gebildet durch eine Fructosamin-3-Kinase. Bei der Messung der Bioverteilung nach intravenöser Applikation kam es zu einer schnellen Aufnahme des Präparates in die Niere. 30% der injizierten Dosis waren auch 60 min nach Applikation noch dort zu finden. Auch in den in vivo-Untersuchungen konnte m1 als Metabolit gefunden werden. Der Anteil an unverändertem FB-FL betrug 60 min p.i. im Blut 90%, im Urin 92% und in den Nieren 16%.

Schlussfolgerungen:
Es konnte gezeigt werden, dass FB-FL ein Substrat der Fructosamin-3-Kinase ist. Trotz des Wirkens dieses Enzyms wurden 60 min p.i. fast die Hälfte des applizierten FB-FL nahezu unverändert in den Urin ausgeschieden. Somit bleibt der größte Teil des Lysins, welches bei der Zubereitung bzw. Lagerung von Nahrungsmitteln fructosyliert wird, für den Körper nicht nutzbar.

Literatur:
[1] Henle T. AGEs in foods: Do they play a role in uremia? Kidney Int Sppl. 2003;84:145-147.
[2] Delpierre G, Vanstapel F, Stroobant V, van Schaftingen E Conversion of a synthetic fructosamine into 3-phospho derivative in human erythrocytes. Biochem J. 2000;352:835-839
  • Lecture (others)
    13. Arbeitstreffen AG Radiochemie/Radiopharmazie, 06.-08.10.2005, Seefeld, Österreich, 06.-08.10.2005, Seefeld, Austria

Publ.-Id: 8038 - Permalink


Rhenium-188-Komplexe verbrückter DMSA-Derivate: Stabilitätsbetrachtungen in vitro und in vivo
Heinrich, T.; Kraus, W.; Pietzsch, H.-J.; Seifert, S.; Jentschel, C.; Faltin, I.; Pawelke, B.; Bergmann, R.; Spies, H.; Johannsen, B.;
Ziel:
Diese Arbeit ist Teil unserer Bemühungen, Chelatbildner zur stabilen und unkomplizierten Bindung von Rhenium-188 an biologische interessante Strukturen zu entwickeln. Aufgrund der hohen in vivo Stabilität von [188ReO(DMSA)2]- (1) soll dieses Koordinationssystem zum Design von neuen 188ReO(V) Chelaten, die bezüglich Reoxidation zu Perrhenat und Ligandenaustausch unter allen Bedingungen radiopharmazeutischer Anwendungen stabil sind, ausgenutzt werden.

Methodik:
Dieser Typ tetradentater Liganden wurde durch Überbrückung zweier DMSA-Moleküle mittels einer Alkylentriaminkette dargestellt. An Hand eines Modellkomplexes wurden die auftretenden Isomerien geklärt. In vitro und in vivo Stabilitätsuntersuchungen wurden für verschiedene dieser 188Re(V)OS4-Komplexe durchgeführt. Weitere funktionalisierte Liganden wurden dargestellt.

Ergebnisse:
Kopplungsfähige Derivate erlauben die Bindung an terminale Aminogruppen von Modellpeptiden. Die Re-188-Markierungen verlaufen schnell, in guten Ausbeuten und unter milden Bedingungen. Daher bieten diese neuartigen ReOS4-Komplexe einen weiteren Zugang zu stabilen Rhenium-188-Radiotherapeutika.

Ausblick:
Hydrophile Derivate werden bezüglich Kopplung an Biomoleküle getestet. Stabilitätsuntersuchungen der Konjugate mit therapierelevanten Aktivitätsdosen werden sich anschließen.
  • Lecture (others)
    13. Arbeitstreffen der AG Radiochemie/Radiopharmazie, 06.-08.10.2005, Seefeld, Austria

Publ.-Id: 8037 - Permalink


Erfahrungen zur Herstellung von [11C]CH3I unter Berücksichtigung langer Transportleitungen zwischen Zyklotron und Synthesemodul
Rode, K.; Knieß, T.; Wüst, F.;
Ziel:
[11C]CH3I sind wichtige Markierungsbausteine in der 11C-Chemie. Für ihre Synthese und ihre Verwendung in verschiedenen Methylierungsreaktionen sind automatisierte Synthesemodule entwickelt worden. Hier vergleichen wir die Herstellung von [11C]CH3I über die Iodierung von [11C]CH4 in der Gasphase. Die erzielten radiochemischen Ausbeuten und spezifischen Radioaktivitäten sollen unter Berücksichtigung der besonderen Rossendorfer Infrastruktur (500 m Distanz zwischen Zyklotron und Synthesemodul) diskutiert werden.

Methodik:
Beim klassischen nasschemischen Verfahren wurde das im Zyklotron hergestellte [11C]CO2 in einem 11C-Synthesemodul (Nuclear Interface) zu [11C]CH3I und [11C]CH3OTf umgesetzt und für die N-Methylierung eines Piperazinderivates verwendet. Ein GE TRACERlab Fx C Synthesemodul wurde für die Konversion von [11C]CO2 in [11C]CH4 und die weitere Umwandlung in [11C]CH3I bzw. [11C]CH3OTf genutzt.

Ergebnisse:
Die N-Methylierung des Piperazinderivates mit [11C]CH3OTf im Nuclear Interface 11C-Synthesemodul ergab radiochemische Ausbeuten von 40-60% und spezifische Radioaktivitäten von bis zu 30 GBq/µmol. Die Reaktion in dem GE TRACERlab Fx C Synthesemodul lieferte radiochemische Ausbeuten von 30-40% und nur geringe spezifische Radioaktivitäten von 5-10 GBq/µmol.

Schlußfolgerungen:
Überraschenderweise konnten mit dem nasschemischen Verfahren höhere radiochemische Ausbeuten und bessere spezifische Aktivitäten erzielt werden. Das gezielte Ausfrieren von [11C]CO2 vor der Reduktion mit LiAlH4 im Nuclear Interface Synthesemodul ist von Vorteil, um Bestandteile des Targetgases, wie z.B. O2, zu entfernen.
Dagegen wurden mit dem GE TRACERlab Fx C Synthesemodul schlechtere spezifische Aktivitäten erreicht, was neben der langen Targetleitung auf folgende Ursachen zurückzuführen ist:
- Reduktion von Targetgasbestandteilen durch den Ni-Katalysator zu kaltem CH4
Dieses Problem konnte durch eine niedrigere Reduktionstemperatur und durch Verwendung von weniger reaktiven Ni teilweise gelöst werden. Die geringere Aktivität des Ni-Katalysators bedingt aber eine Verschlechterung der CH4-Konversion.
- Die eingesetzten hochreaktiven Ni-Katalysatoren verwenden Al2O3/SiO2 als Träger-material. Dieses Trägermaterial stellt eine potentielle Quelle für Kohlenstoffkontaminationen dar.
Eine Verbesserung der spezifischen Radioaktivität könnte durch das vorherige Ausfrieren von [11C]CO2 oder durch die direkte Verwendung vom im Zyklotron hergestellten [11C]CH4 erzielt werden.

Literatur:
Knieß, T. et al., Annual Report 2004, FZR-424, p. 33
  • Lecture (others)
    13. Arbeitstreffen der AG Radiochemie/Radiopharmazie, 06.-08.10.2005, Seefeld, Austria

Publ.-Id: 8036 - Permalink


SANS investigation of neutron-irradiated RPV steels with special emphasis on Ni effect
Ulbricht, A.; Bergner, F.; Pranzas, K. P.;
The SANS experiment is aimed at studying the influence of neutron fluence and Ni content on irradiation-induced changes of the microstructure of WWER 1000-type reactor pressure vessel (RPV) steel. A feature of this material is a high Ni content (> 1 wt.-%) in comparison with other RPV steels. Specimens from two WWER 1000 steels with different composition, one single neutron fluence each, were analysed in a previous investigation. It turned out that:
There is a monomodal size distribution of irradiation-induced defects with an average radius of about 1 nm.
The total volume fraction of defects is significantly higher than for WWER 440 steels, which had been investigated before in more detail also by other groups.
  • Contribution to external collection
    A. Schreyer, J. Vollbrandt, R. Willumeit: GeNF - Experimental Reports 2005, GKSS 2006/4, Geesthacht: GKSS Forschungszentrum Geesthacht GmbH, 2006, 107-108

Publ.-Id: 8035 - Permalink


Small-angle scattering applied to post-irradiation annealing of neutron-irradiated pressure vessel steels
Ulbricht, A.; Bergner, F.; Heinemann, A.;
The aim of the present investigation is to contribute to the understanding of cluster dissolution after isochronal post-irradiation annealing treatments (annealing time: 10 h) at stepwise increasing levels of temperature.
  • Poster
    BENSC User's Meeting 2005, 22.-23.09.2005, Berlin, Germany

Publ.-Id: 8034 - Permalink


Microstructural analysis by means of Small-angle neutron scattering
Ulbricht, A.; Bergner, F.;
The aim of the present talk is to contribute small-angle neutron scattering (SANS) data to the experimental database. We have shown that SANS measurements for irradiated and annealed RPV steels provide additional information on the dissolution behaviour of irradiation-induced clusters particularly useful for modelling the long term evolution of clusters. A SANS experiment in December 2005 is devoted to the investigation of VVER 1000 steel in two fluences and Fe-Ni alloys.
  • Lecture (others)
    Second Plenary Meeting RPV & Internals - Physics Modelling, 17.-19.10.2005, Saclay, France

Publ.-Id: 8033 - Permalink


Microstructural analysis of WWER RPV materials with Small-angle neutron scattering
Ulbricht, A.; Bergner, F.;
The aim of the present talk is to contribute small-angle neutron scattering (SANS) data on irradiated VVER steels to the experimental database.
  • Lecture (others)
    Perfect meeting on VVER materials, 13.-14.06.2005, Bratislava, Slovakia

Publ.-Id: 8032 - Permalink


Detecting irradiation induced damage in RPV steels by SANS
Ulbricht, A.; Bergner, F.;
The aim of the present talk is to contribute small-angle neutron scattering (SANS) data to the experimental database. Some preliminary conclusions can be drawn from the comparison of SANS data for the materials selected within the workpackage WPII-3. SANS allows for the determination of the size distribution of irradiation-induced clusters and, in particular, for the calculation of mean radius and volume fraction. The mean radius was found to be constant (about 1 nm) and independent of the material under the present experimental conditions. The volume fraction turned out to depend on irradiation conditions and chemical composition of the material. Additional partial information on the composition of clusters is implied in the A-ratio.
  • Lecture (others)
    First Plenary Meeting RPV & Internals - Physics Modelling, 19.-21.01.2005, Manchester, Great Britain

Publ.-Id: 8031 - Permalink


Dyslipidämien beim metabolischem Syndrom: Glykierte LDL und Atherogenese
Pietzsch, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Symposium Metabolisches Syndrom 2005, 19.11.2005, Radebeul, Germany

Publ.-Id: 8030 - Permalink


Pathophysiologie der Fettstoffwechselstörungen
Pietzsch, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    40. Jahrestagung der Deutschen Diabetes Gesellschaft, 04.-07.05.2005, Berlin, Germany

Publ.-Id: 8029 - Permalink


Assessment of catabolism of glycated and glycoxidized LDL in vivo: insights of small animal positron emission tomography (PET) studies
Pietzsch, J.; Hoppmann, S.; Bergmann, R.; Steiniger, B.; van den Hoff, J.;
kein Abstract verfügbar
  • Abstract in refereed journal
    Diabetologia 48(2005)Suppl 1, A416
  • Lecture (Conference)
    41st Annual Meeting of the European Association for the Study of Diabetes (EASD), 10.-15.09.2005, Athens, Greece

Publ.-Id: 8028 - Permalink


Catabolism of Hypochlorite-modified low density lipoprotein (LDL) in vivo: insights from small animal positron emission tomography studies
Hoppmann, S.; Steiniger, B.; Pietzsch, J.;
kein Abstract verfügbar
  • Poster
    5th European Life Science Organisation (ELSO), 03.-06.09.2005, Dresden, Deutschland
  • Contribution to proceedings
    5th European Life Science Organisation (ELSO), 03.-06.09.2005, Dresden, Deutschland
    Proceedings of the 5th European Life Science Organisation (ELSO), 230

Publ.-Id: 8027 - Permalink


Radiolabeling of human apolipoproteins using SH-reactive 18F-labeling agents: a potential approach for characterization and differentiation of metabolism of native and modified lipoproteins by small animal positron emission tomography (PET) in vivo
Pietzsch, J.; Berndt, M.; Wüst, F.; van den Hoff, J.;
Oxidative modification of LDL is regarded as a crucial event in atherogenesis. Data concerning the role of circulating oxidized LDL (oxLDL) in the development of atherosclerosis are scarce. One reason for this is the shortage of methods for direct assessment of metabolism of oxLDL in vivo. We report a new methodology for labeling of both native LDL (nLDL) and oxLDL with the positron emitter fluorine-18 (18F; t½=109.7 min) by conjugation with SH-reactive N-[6-(4-[18F]fluorobenzylidene)-aminooxyhexyl]maleimide ([18F]MHAA) and the use of 18F-labeled LDL particles in dynamic PET studies in male Kyoto-Wistar rats. For labeling experiments, pools of chemically and biochemically well characterized human nLDL and oxLDL (modified by hemin/H2O2) particles, respectively, were used. Radiosynthesis of [18F]MHAA started with the preparation of [18F]fluorobenzaldehyde. In a one-pot procedure N-(6-aminooxyhexyl)maleimide was added to the generated aldehyde and after-wards [18F]MHAA was isolated by HPLC. Preparation of [18F]MHAA was achieved within 70 min with radiochemical yields of 34±5% (corrected for decay) and purity of >96%. [18F]MHAA was shown to react efficiently and selectively with SH-groups of various peptides and proteins under mild conditions. LDL labeling with [18F]MHAA resulted in radiochemical yields of 20±10% (corrected for decay) and specific radioactivity of 150-300 GBq/µmol. Radiolabeling of nLDL and oxLDL using [18F]MHAA caused neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality in vitro, respectively. The method was evaluated with respect to uptake of 18F-labeled LDL in human hepatoma cells (HepG2) and monocytes/macrophages (THP-1), respectively. Biodistribution studies in rats revealed high in vivo stability for the 18F-labeled LDL. The metabolic fate of the 18F-labeled LDL in vivo was delineated by dynamic PET studies using a dedicated small animal tomograph (spatial resolution of <2 mm). Data were compared to former studies using the NH2-reactive 18F-labeling agent N-succinimidyl-4-[18F]fluorobenzoate. In conclusion, 18F-labeling of LDL and the use of small animal PET provide a valuable tool for mapping sites of both nLDL and oxLDL metabolism in animal models in vivo.
  • Abstract in refereed journal
    Amino Acids 29(2005)1, 18-19
    DOI: 10.1007/s00726-005-0220-y
  • Invited lecture (Conferences)
    9th International Congress on Proteins and Amino Acids, 08.-12.08.2005, Wien, Österreich

Publ.-Id: 8025 - Permalink


Rate theory modelling of neutron irradiation induced cluster formation in RPV steels and iron based alloys
Bergner, F.; Gokhman, A. R.; Ulbricht, A.;
A method allowing the cluster-matrix interaction to be introduced into the rate theory approach to cluster evolution in neutron-irradiated RPV steels and model alloys has been established. Corresponding FORTRAN code has been generated. Adjustment of the model parameters by means of comparison with experimentally obtained size distributions of radiation-induced clusters shows that cluster-matrix interaction is an important factor. In ongoing work the effect of solute enrichment and coherency between clusters and matrix should be considered.
  • Lecture (others)
    First Plenary Meeting RPV & Internals - Physics Modelling, 19.-21.01.2005, Manchester, Great Britain

Publ.-Id: 8024 - Permalink


Isolation, characterization, and U(VI)-immobilizing potential of bacterial strains from uranium contaminated environments
Merroun, M.; Rossberg, A.; Hennig, C.; Selenska-Pobell, S.;
Uranium is a long-living radionuclide that represents ecological and human health hazards. The mining and processing of uranium during the last decades for nuclear fuel and nuclear weapon production resulted in generation of significant amounts of radioactive waste. It is critical that the uranium in these wastes has to be effectively immobilized and removed away in order to prevent ground water contamination. Microbial biosorption of U(VI) was proposed as one of the methods for uranium immobilization. In this paper, we describe the isolation of bacterial strains from water and soil samples collected from different uranium contaminated environments. Phylogenetic analysis of these strains revealed that they are related to Stenotrophomonas maltophilia, Bacillus sphaericus, Microbacterium oxydans, Pseudomonas rhodesiae etc. As estimated by using ICP-MS these natural isolates possess a high ability to accumulate uranium and other heavy metals such as Cd, Pb, Ni and Ag. The bacterial uranium tolerance was studied using flow cytometry techniques. X-ray absorption near-edge structure analysis showed that the cells of these strains precipitate U(VI) as autunite-like phase (inorganic uranyl phosphate phase) at pH 4.5, probably due to the release of the inorganic phosphate from the cells. However, at pH 2 the uranium bonding was consistent with the formation of complexes with organic bound phosphate of the cell surface. These results are in agreement with those found by infrared measurements.Transmission electron microscope and energy dispersive X-ray analysis showed strain-specific extracellular and/or intracellular uranium accumulation to varying degrees.
  • Contribution to proceedings
    Biometals 2004, 03.-05.09.2004, Garmisch-Partenkirchen, Germany

Publ.-Id: 8023 - Permalink


Long term evolution of radiation induced damage - FZR contribution to rate theory
Bergner, F.; Gokhman, A. R.; Altstadt, E.;
A coupled rate theory model of defect evolution and Cu clustering was introduced as a basis for the rate theory upgrade with coherency and solute content of clusters. The coupling is essentially due to the operation of Cu clusters as vacancy sinks. The model was transferred to FORTRAN code and calibrated using results of small-angle neutron scattering (SANS) experiments for a Cu-enriched (0.42% Cu) iron model alloy irradiated up to two neutron fluences. Extensions of the model to take into account size dependent cluster composition are proposed.
  • Lecture (others)
    Second Plenary Meeting RPV & Internals - Physics Modelling, 17.-18.10.2005, Saclay, France

Publ.-Id: 8022 - Permalink


Linear stability analysis for the effect of the lift force in a bubble column
Lucas, D.; Prasser, H.-M.; Manera, A.;
The role of the lift force for the stability of a homogeneous bubble column is investigated. Instabilities caused by the lift force may be one important reason for the transition from homogeneous to heterogeneous bubble column. The lift force acts on rising bubbles in lateral direction, when gradients of the liquid velocity are present. Non-uniform liquid velocity fields may be induced if the gas fraction is not equally distributed, e.g. caused by local disturbances. For regions with locally increased gas volume fraction the liquid is accelerated in upwards direction and following a gradient of the liquid velocity occurs. This causes a lateral redistribution of the gas bubbles. Depending on the sign of the lift force coefficient this can act to smooth the spatial bubble distribution (positive lift force coefficient) or to increase the initial disturbances (negative lift force coefficient). The feedback mechanism was studied by the means of a linear stability analysis. In addition to the lift force, the turbulent dispersion force is considered, which has always a stabilizing effect, i.e. it partially compensates the destabilisation induced by a negative lift coefficient. The stability analysis for a mono-dispersed system nevertheless showed, that influence of the lift force is much larger, compared to the influence of the turbulent dispersion force, if only bubble induced turbulence is considered. Thus the stability condition is practically the positive sign of the lift force coefficient. The analysis was then extended to two bubbles classes - one being small enough to have a positive lift force coefficient, the other being large enough to have a negative coefficient. The result of the analysis is a condition for the minimum fraction of small bubbles needed for stability. Finally a generalized criterion for N bubble classes and for a continuous bubble size distribution is given. Recently two different groups confirmed the stability criteria experimentally.
Keywords: bubble column, linear stabiliy analysis, bubbly flow, homogeneous flow
  • Contribution to proceedings
    7th German/Japanese Symposium on Bubble Columns, 20.-23.05.2006, Goslar, Germany
  • Lecture (Conference)
    7th German/Japanese Symposium on Bubble Columns, 20.-23.05.2006, Goslar, Germany

Publ.-Id: 8021 - Permalink


Analysis of the LR-0 benchmark results (WP-3 Final Report)
Böhmer, B.;
The lecture gives an overview over the final results of REDOS Work Package 3 (Analytical area - Analysis of calculated and measured data, conclusions).
For a VVER-1000 Mock-up and two VVER-440 Mock-ups and for all positions, where measurements had been carried out, neutron-gamma transport calculations were performed independently by the project participants using deterministic and/or stochastic codes and associated nuclear data libraries, mostly based on ENDF/B-VI. The calculated with different codes and laboratories neutron and gamma flux integrals, DPA-rates and spectra were compared with each other and with experimental values. Seven institutions from 5 countries (Bulgaria, Czech Republic, Germany, Hungary and Spain) delivered calculation results for the VVER-1000 Mock-up, six institutions from 4 countries performed calculations for one or both VVER-440 Mock-ups. More than eight different calculational schemes were used, covering the most important methods used for pressure vessel dosimetry and shielding. The codes used were the stochastic codes MCNP and TRAMO and the deterministic codes ANISN/DORT and TORT. They were associated with different data libraries and data preparation schemes. The BUGLE 47n/20g group structure was used for comparisons of calculated spectra as well as for comparison with experimental spectra. The comparison of the different calculation results showed considerable discrepancies for the calculation of absolute flux spectra normalized to one source neutron per second in the core for thermal neutrons and photons. The attenuation coefficients and spectra related to the spectrum in a special point had slightly lower discrepancies. The measured spectra and attenuation coefficient agree in most cases with the calculated values within the limits of experimental and calculational errors. Considerable discrepancies are found for the gamma to neutron relation at the outer surface of the barrel. The neutron attenuation through the RPV tends to be calculated too small. The uncertainties of the calculations were evaluated on the basis of the dispersion of the participants results, of the discrepancies between calculated and measured results and of the scattering of results obtained with different data libraries and data treatment procedures.
Keywords: neutron-gamma transport calculations, VVER-1000 Mock-up, VVER-440 Mock-up, neutron and gamma flux spectra, flux integrals, DPA-rates
  • Invited lecture (Conferences)
    Final REDOS Meeting, 14.-15.10.2004, Madrid, Spain

Publ.-Id: 8020 - Permalink


Reactor dosimetry: accurate determination and benchmarking of radiation field parameter, relevant for pressure vessel monitoring (REDOS) - REDOS Final Report
Ballesteros, A.; Jardí, X.; Böhmer, B.; Konheiser, J.; OšMera, B.; Kyncl, J.; Keresztúri, A.; Hordosy, G.; Ilieva, K.; Belousov, S.; Kirilova, D.; Mitev, M.; Petrov, B.; Acosta, B.; Smutný, V.; Polke, E.; Zaritsky, S.; Töre, C.; Ortego, P.;
The REDOS project aims to improve reactor dosimetry for radiation embrittlement monitoring of the reactor pressure vessel (RPV) steels. Benchmarking, as well as combined experimental and computational techniques, have been used. Specific objectives were the improvement of the neutron-gamma calculation methodologies through the LR-0 engineering benchmarks for WWER-1000 and WWER-440 reactor types, and the accurate determination of radiation field parameters in the vicinity and over the thickness of the RPV.
A review of the available experimental reactor dosimetry data of Kozloduy Units 1, 4, 5 was performed, and attenuation coefficients through the vessel wall were calculated. Existing data for the WWER-440 and WWER-1000 Mock-ups were reviewed and the preparatory work for subsequent measurement and experimental data analysis was carried out. Measurements of the space-energy distribution of the mixed neutron-gamma field in the WWER-1000 model over the RPV simulator were performed. The most important improvements in the experimental techniques used were the multiparameter spectrometer and a new low noise precise monitoring system in the LR-0 research reactor, developed for this type of measurements. For the WWER-1000 Mock-up and the two WWER-440 Mock-ups and for all positions, where measurements had been performed, neutron-gamma transport calculations were carried out independently by the participants using deterministic and/or stochastic codes and associated nuclear data libraries, mostly based on ENDF/BVI. The calculated neutron and gamma flux integrals, DPA-rates and spectra were compared with each other and with experimental values. Seven institutions from 5 countries (Bulgaria, Czech Republic, Germany, Hungary and Spain) delivered calculation results for the WWER-1000 Mock-up, six institutions from 4 countries performed calculations for one or both WWER-440 Mock-ups. More than eight different calculational schemes were used, covering the most important methods used for pressure vessel dosimetry and shielding. The codes used were the stochastic codes MCNP and TRAMO and the deterministic codes ANISN/DORT and TORT. They were associated with different data libraries and data preparation schemes. The BUGLE 47n/20g group structure was used for comparisons of calculated spectra as well as for comparison with experimental spectra. Results of RPV attenuation calculations for WWER-440s and WWER-1000s were obtained. A comparison between Western and Eastern attenuation determination approaches was carried out. The neutron/fluence (E>0.5 MeV) wall attenuation for WWER-440 and WWER-1000 RPVs is slower than the dpa attenuation. This means that fluence above 0.5 MeV is more conservative approach than the use of dpa. Another task performed was the application/extrapolation of the WWER mock-ups results to power reactors. The attenuation through the RPV of the neutron flux/fluence with energy above 0.5 MeV was determined. The relative difference value does not exceed 10% for WWER-440. The relative difference value does not exceed 10% for WWER-1000 too, except at the position behind the RPV wall.
Keywords: Radiation embrittlement, reactor pressure vessel, VVER-1000, VVER-440, LR-0, reactor mock-up, neutron-gamma calculation, radiation field parameters, photon and neutron spectra measurements, stilbene scintillator, multiparameter spectrometer
  • Other report
    JRC Petten: AMES Report n.17, EUR 21771 EN, 2005
    63 Seiten

Publ.-Id: 8019 - Permalink


Structure and pH-Sensitivity of the Transmembrane Segment 3 of Rhodopsin
Madathil, S.; Furlinski, G.; Fahmy, K.;
Activation of G protein-coupled receptors (GPCRs) originates in ligand-induced protein conformational changes that are transmitted to the cytosolic receptor surface. In the photoreceptor rhodopsin, and possibly other rhodopsin-like GPCRs, protonation of a carboxylic acid in the conserved E(D)RY motif at the cytosolic end of transmembrane helix 3 (TM3) is coupled to receptor activation. Here, we have investigated the structure of synthetic peptides derived from rhodopsin TM3. Polarized FTIR-spectroscopy reveals a helical structure of a 31-mer TM3 peptide reconstituted into PC vesicles with a large tilt of 40-50° of the helical axis relative to the membrane normal. Helical structure is also observed for the TM3 peptide in detergent micelles and depends on pH especially in the C-terminal sequence. In addition, the fluorescence emission of the single tyrosine of the D(E)RY motif in the TM3 peptide exhibits a pronounced pH sensitivity that is abolished when Glu is replaced by Gln demonstrating that protonation of the conserved Glu side chain affects the structure in the environment of the D(E)RY motif of TM3. The pH-regulation of the C-terminal TM3 structure may be an intrinsic feature of the E(D)RY motif in other class I receptors allowing the coupling of protonation and conformation of membrane-exposed residues in full length GPCRs.
Keywords: G protein-coupled receptor, FTIR-spectroscopy, membrane protein, peptide, secondary structure

Publ.-Id: 8018 - Permalink


Light-ion production in the interaction of 96 MeV neutrons with oxygen
Tippawan, U.; Pomp, S.; Atac, A.; Bergenwall, B.; Blomgren, J.; Dangtip, S.; Hildebrand, A.; Johansson, C.; Klug, J.; Mermod, P.; Nilsson, L.; Österlund, M.; Olsson, N.; Prokofiev, A.; Nadel-Turonski, P.; Corcalciuc, V.; Koning, A.;
Double-differential cross sections for light-ion (p, d, t, He-3 and alpha) production in oxygen, induced by 96 MeV neutrons are reported. Energy spectra are measured at eight laboratory angles from 20 to 160 degrees in steps of 20 degrees. Procedures for data taking and data reduction are presented. Deduced energy-differential and production cross sections are reported. Experimental cross sections are compared to theoretical reaction model calculations and experimental data at lower neutron energies in the literature.
Keywords: Neutron scattering, light-ion production, reaction cross sections
  • Physical Review C 73(2006), 034611

Publ.-Id: 8017 - Permalink


Reversals in a nutshell
Stefani, F.; Gerbeth, G.; Günther, U.;
An appropriate theory of Earth's magnetic field reversals has to explain a number of observations:

The first observation concerns the different time scales relevant in the process. The very polarity transition takes only about 5 kyr which is much shorter than the typical interval between reversals (varying between 200 kyr in the present and some tens of Myr during superchrons). In between these two time scales there lies the so-called inhibition time (approximately 40 kyr) during which a follow-up reversal is very unlikely. A second remarkable feature of reversals is their typical asymmetric (saw-toothed) shape with a slow decay and a fast recovery of the opposite field. A third, although controversially discussed hypothesis points to a correlation of the interval time between reversals and the magnetic field amplitude. A fourth observation concerns the bimodal distribution of the virtual dipole moment that has been observed with two peaks at about 4 x 1022 A m2 and at about twice that value.

Using a paradigmatic mean-field dynamo model with a spherically symmetric helical turbulence parameter alpha which is quenched by the magnetic energy and disturbed by additional noise we attribute all these reversal features to the magnetic field dynamics in the vicinity of an exceptional point of the spectrum of the non-selfadjoint dynamo operator (Phys. Rev. Lett. 94 (2005), 184506).

A weakness of this reversal model is the apparent necessity to fine-tune the magnetic Reynolds number and/or the radial profile alpha(r)in order to adjust the operator spectrum in an appropriate way. It can be shown, however, that this fine-tuning is not necessary in the case of higher supercriticality of the dynamo (arxiv.org/abs/physics/0509118). For increasing magnetic Reynolds number there is a strong tendency for the exceptional point and the associated local maximum to move close to the zero growth rate line were the indicated reversal scenario can be actualized.

Special focus is also laid on the astonishing similarities between numerically computed time series and paleomagnetic observations from the last five reversals (arxiv.org/abs/physics/0601011).
  • Open Access LogoAbstract in refereed journal
    Geophysical Research Abstracts 8(2006), 03265

Publ.-Id: 8016 - Permalink


Influence of colloids produced by the weathering of rock material on uranium(VI) behaviour
Zänker, H.; Weiß, S.;
There is a mechanism of secondary mineral colloid generation straight at the water-rock interfaces by the weathering of the rock material. It is of importance in the unsaturated zone as for instance in mine waste rock piles. Here we demonstrate the influence of iron-rich colloids generated by this mechanism on the behaviour of uranium(VI). The weathering of phyllite from an abandoned uranium mine in waters poor in cations and anions (“rainwater”) was simulated. The colloids produced by the weathering of this phyllite were able to keep large fractions (up to 90 %) of the uranium(VI) in a colloid-borne form in the pH region of 5.0 to 7.5. In the absence of colloids, this U(VI)) would have been truly dissolved in this pH region. The consequences of this colloid influence on uranyl speciation in natural oxic waters depend on the specific conditions in a geological environment. In a mine waste rock pile both, situations where the iron-rich colloids increase U(VI) mobility by preventing UO22+ attachment at interfaces and situations where the colloids immobilize U(VI) by scavenging, colloid aggregation, colloid deposition, formation of crusts etc., are possible
Keywords: Colloids, Weathering, Transport of Uranium(VI), Mine waste rock piles
  • Lecture (Conference)
    36th Journées des Actinides, 01.-04.04.2006, Oxford, Great Britain

Publ.-Id: 8014 - Permalink


Test of the photocathode cooling system of the 3½ cell SRF gun
Staufenbiel, F.; Büttig, H.; Evtushenko, P.; Janssen, D.; Lehnert, U.; Michel, P.; Möller, K.; Schneider, C.; Schurig, R.; Teichert, J.; Xiang, R.; Stephan, J.; Lehmann, W.-D.; Kamps, T.; Lipka, D.; Will, I.; Volkov, V.;
This paper presents results of the photocathode cooling system test of the 3½ cell SRF gun at the Forschungszentrum Rossendorf. The SRF gun will produce short electron pulses with high bunch charges and low transverse emittance. The requirement for the superconducting electron linear accelerator in Rossendorf (ELBE) is to provide a low emittance electron beam up to 1mA current and 9.5 MeV energy. Additionally, it will easily operate in continuous wave (cw) mode because of the low RF power losses in the superconducting material. Therefore, the normal conducting copper cathode must be cooled by liquid nitrogen in order to preserve the temperature of the cavity at 2.2 K. The estimated power input from the RF field into the cathode could be more than 10 W [1]. First results of temperature measurements of the photo cathode respectively from the cooling system at a heat load up to 30 W are presented.
  • Physica C 441(2006)1-2, 216-219

Publ.-Id: 8013 - Permalink


Efficient Determination of Optimal Regularization Parameter for Inverse Problem in EXAFS Spectroscopy
Kunicke, M.; Kaminsky, I. Y.; Babanov, Y. A.; Funke, H.;
This paper presents a method for choosing the optimal regularization parameter in EXAFS analysis based on the L-curve-criterion without any external pa-rameter. The L-curve is a log-log plot of the norm of regularized solution ver-sus the norm of the corresponding residual norm. The optimal regularization parameter is chosen as a maximum of the L curve curvature. We apply this method in two experimental cases: crystalline Cu with well-known structure and aqua-ion Cm+3 with unknown structure. The optimal regularization pa-rameter leads to a stable solution with a good convergence of the iterative process
  • Physica Scripta T115(2005), 237-239

Downloads:

Publ.-Id: 8011 - Permalink


SANS response of VVER440-type weld material after neutron irradiation, post-irradiation annealing and reirradiation
Ulbricht, A.; Bergner, F.; Böhmert, J.; Valo, M.; Mathon, M.-H.; Heinemann, A.;
We present the first small angle neutron scattering (SANS) study of neutron irradiated, annealed and reirradiated VVER440-type reactor pressure vessel weld material. The SANS results are analyzed in terms of the size distribution of irradiation-induced defect/solute atom clusters and of the ratio of total and nuclear scattering intensity in a saturation magnetic field (A-ratio). The measured A-ratio is compared with calculations performed for the cluster composition reported by Pareige et al. [Phil. Mag. 85 (2005) 429-441] for a similar weld material investigated by means of three-dimensional atom probe tomography. The observed deviation between both estimates and possible reasons for the discrepancy are discussed. Special emphasis is placed on the differences between the materials response to the original irradiation and to reirradiation after annealing. We have observed that reirradiation-induced clusters are different in composition and their formation saturates at a lower volume fraction than in the case of the original irradiation.

Publ.-Id: 8010 - Permalink


Water hammer induced by fast acting valves - experimental studies at Pilot Plant Pipework
Dudlik, A.; Prasser, H.-M.; Apostolidis, A.; Bergant, A.;
Water hammer and inertia-driven cavitation hammer phenomena caused by the activation of fast acting valves were studied in a pipeline test facility at Fraunhofer UMSICHT in the context of the EURATOM project WAHALoads. The main goal of the project is the prediction of the loads on equipment and support structures. The presented experiments tackle some scenarios typical for power plants and supply material for the code validation with regard to the modelling of both thermal hydraulic effects and fluid-structure interaction. The test facility Pilot Plant Pipework (PPP) representing an approximately 230 m long experimental pipeline was upgraded in order to allow experiments at system pressures of up to 30 bar at maximum temperatures of about 180 °C. The test rig was furthermore equipped with a test segment that simulates a piping system and the associated supports typical for a (nuclear) power plant. For a better understanding of thermal hydraulic processes during cavitation behind the fast acting valve, novel instrumentation was applied. Wire mesh sensors as well as local void probes were equipped with integrated micro-thermocouples and used for the local instantaneous measurement of both void fractions and fluid temperature. The fast temperature measurement combined with the instantaneous detection of the passage of the gas-liquid interface measurement reveals insights into the condensation heat transfer controlling the speed of the void collapse in case of a condensational water hammer.
Keywords: two-phase flow, water hammer, void collapse, fast acting valve, fluid column separation
  • Multiphase Science and Technology 20(2008), 239-263

Publ.-Id: 8009 - Permalink


Spontaneous water hammers in a steam line in case of cold water ingress
Prasser, H.-M.; Ezsöl, G.; Baranyai, G.;
Some of the accident scenarios discussed for VVER-440 reactors assume an overfeed of the secondary side of the steam generators by water coming either from the primary side or from the feed water system. This may happen, for example, in case of a leakage from the primary to the secondary side as well as during earthquakes and may lead to a water ingress into the main steam-lines, where condensation induced water hammer may be the consequence. The present work was initiated to study this phenomenon experimentally. For this purpose the PMK-2 test facility of KFKI-AEKI Budapest, an integral thermo- hydraulic model of a VVER-440 / W213, was extended by a steam-line model, which is equipped with a novel two-phase flow instru-mentation as well as fast pressure and strain-gauge transducers. The applied mesh sensor de-veloped by Forschungszentrum Rossendorf allows a visualisation of the transient flow section during the water hammers. Local void probes detect the propagation of slugs along the pipe. The applied new kind of probe is equipped with micro-thermocouples to provide local instan-taneous temperature measurements beside the phase detection. This allows to assess tempera-ture gradients at the boundary between water and steam. The paper describes test facility and new instrumentation. The results of the first tests are presented and discussed. The work is part of the WAHALoads project, which was performed within the 5th EU framework programme.
Keywords: pressurized water reactor, main steam line, two-phase flow, water hammer, void collapse
  • Multiphase Science and Technology 20(2008), 239-263

Publ.-Id: 8008 - Permalink


Profile of a photoconductive THz Emitter excited by an amplified laser system
Peter, F.; Winnerl, S.; Dreyhaupt, A.; Schneider, H.; Helm, M.;
We present a large photoconductive THz emitter[1] consisting of two interdigitated metallization layers on a semi-insulating GaAs substrate.
The photoexcited carriers are unidirectional accelerated by a bias voltage providing an electric field. This leads to a subsequent emission of THz radiation. The second metallization inhibits the optical excitation in every second period of the electrode structure in order to prevent destructive interference. We analyse the spatial profile of such an emitter excited with unfocused fs optical pulses from an Ti:sapphire amplifier with an average power of 60mW at a 1kHz repetition rate. The resulting THz beam has a bandwidth from 0.1 THz to 4 THz and a field amplitude of up to 6kV/cm (Ubias = 30V ). The focussed THz spot was mapped out and analyzed with respect to the frequency. A strong increase of the beam diameter with decreasing frequency was found. Saturation behavior was observed by changing the excitation density.
[1] A. Dreyhaupt, S.Winnerl, T.Dekorsy, and M.Helm, Appl. Phys 86,
121114 (2005)
  • Poster
    DPG-Frühjahrstagung, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8007 - Permalink


Gas-liquid flow around an obstacle in a vertical pipe - experiments and cfd simulation
Prasser, H.-M.; Frank, T.; Beyer, M.; Carl, H.; Pietruske, H.; Schütz, P.;
In the frame of the TOPFLOW project, vertical pipe flow is experimentally studied in order to develop and validate models for bubble forces as well as for bubble coalescence and fragmentation in a gas-liquid two-phase flow. The advantage of TOPFLOW [1] consists in the combination of (1) a large scale of the test channel with (2) a wide operational range both in terms of the superficial velocities and the system pressure and finally (3) the availability of an instrumentation that is capable in resolving structures of the gas-liquid interface, namely the wire-mesh sensors.
After a large number of experiments in plain vertical pipes, which are the basis of the development for a multi-bubble size model for ANSYS CFX 10.0, the large test section with a nominal diameter of DN200 was used to study the flow field around an asymmetric obstacle. This is an ideal test case for the CFD code validation, since the obstacle creates a pro-nounced three-dimensional two-phase flow field. Curved stream lines, which form significant angles with the gravity vector, a recirculation zone in the wake and a flow separation at the edge of the obstacle are phenomena widespread in real industrial components and installations. Recently, test series were performed with an air-water flow at ambient conditions as well as with a steam-water mixture at a saturation pressure of 6.5 MPa. Before the experiments were commissioned, an ANSYS CFX 10.0 pre-test calculation was carried out for one of the experimental tests, which resulted in a good agreement with the experiment in terms of all significant qualitative details of the void fraction and velocity distributions.
Keywords: Two-phase flow, computational fluid dynamics, wire-mesh sensor, flow structure
  • Lecture (Conference)
    Annual Meeting of Nuclear Technology, 16.-18.05.2006, Aachen, Germany

Publ.-Id: 8006 - Permalink


Steam-water experiments at high pressure to study the structure of the gas-liquid interface in a large vertical pipe
Prasser, H.-M.; Beyer, M.; Carl, H.; Pietruske, H.; Schütz, P.; Weiß, F.-P.;
In the frame of the TOPFLOW project, vertical pipe flow is experimentally studied in order to develop and validate models for bubble forces as well as for bubble coalescence and fragmentation in a gas-liquid two-phase flow. The advantage of TOPFLOW consists in the combination of (1) a large scale of the test channel with (2) a wide operational range both in terms of the superficial velocities and the system pressure and finally (3) the availability of an instrumentation that is ca-pable in resolving structures of the gas-liquid interface, namely the wire-mesh sensors. Results are presented for tests with steam-water mixture at a saturation pressure of up to 6.5 MPa. The measured radial gas fraction profiles and bubble size distributions show in detail the influence of the fluid properties to the flow structure and its evolution along the flow path when compared to earlier results obtained at identical superficial velocities in an air-water flow. The results from the high-pressure tests are of particular interest for the validation of CFD codes for an application in the field of nuclear reactor safety. A significant influence of the physical properties to the flow structure was found: the steam-water flow at high pressure compared to the air water flow under ambient conditions shows less tendency to develop large bubbles and a bimodal bubble size distribution but is characterised by larger bubble sizes in the region of the small bubble peak.
Keywords: two-phase flow, steam-water flow, wire-mesh sensor, flow pattern
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology, 10.-12.05.2005, Nürnberg, Germany, 98-101

Publ.-Id: 8005 - Permalink


Radiokupferverbindungen für die nuklearmedizinische Diagnostik und Therapie: Stand und Perspektiven
Stephan, H.;
Das Interesse an der Entwicklung von Radiopharmaka auf der Basis von Radiometallen wird durch eine Reihe von Faktoren wie zunehmende Verfügbarkeit der Nuklide (Generatoren, Zyklotron), einfache Markierung von Liganden und wachsende Anwendungsmöglichkeiten in klinischen Zentren gestärkt. In Abhängigkeit von den kernphysikalischen Eigenschaften der Radiometallnuklide ergeben sich Einsatzmöglichkeiten in der nuklearmedizinischen Diagnostik und Therapie.
Für Kupfer stehen eine Reihe von Radionukliden zur Verfügung, die einen diagnostischen und therapeutischen Einsatz erlauben. Es werden verschiedene Anwendungsmöglichkeiten diskutiert und eigene Arbeiten zur Entwicklung neuer Chelatsysteme vorgestellt. Das betrifft sechszähnige Chelate auf der Basis des Bispidins (3,7-Diazabicyclo[3.3.1]nonan) sowie dendritische Liganden.
  • Invited lecture (Conferences)
    Institutskolloquium, Bergakademie TU Freiberg, Institut für Organische Chemie, 02.02.2006, Freiberg, Germany

Publ.-Id: 8004 - Permalink


Influence of the pipe diameter on the structure of the gas-liquid interface in a vertical two-phase pipe flow
Prasser, H.-M.; Beyer, M.; Böttger, A.; Carl, H.; Lucas, D.; Schaffrath, A.; Schütz, P.; Weiß, F.-P.; Zschau, J.;
Air-water two-phase flow tests in a large vertical pipe of 194.1 mm inner diameter are reported. Close to the outlet of a 9 m tall test section two wire-mesh sensors are installed that deliver instantaneous void fraction distributions over the entire cross section with a resolution of 3 mm and 2500 Hz used for fast flow visualization. Void-fraction profiles, gas velocity profiles and bubble size distributions were obtained. A comparison to a small pipe of 52.3 mm inner diameter (DN50) revealed significant scaling effects. Here, the increase of the air flow rate leads to a transition from bubbly via slug to churn turbulent flow. This is accompanied by an appearance of a second peak in the bubble size distribution. A similar behavior was found in the large pipe, though the large bubbles have a significantly larger diameter at identical superficial velocities, the peak is less high but wider. These bubbles move more freely in the large pipe and show more deformations. Shapes of such large bubbles were characterized in three dimensions. They can rather be complicated and far from ideal Taylor bubbles. Also the small bubble fraction tends to bigger sizes in the large pipe.
Keywords: two-phase flow, flow pattern, bubble size
  • Nuclear Technology 152(2005)1, 3-22

Publ.-Id: 8003 - Permalink


Influence of U(VI) and nitrate on microbial communities of uranium mining wastes
Geissler, A.; Reitz, T.; Tschikov, S.; Selenska-Pobell, S.;
Changes in the structure of the microbial community of a soil sample from the uranium mining waste pile Haberland near the town Johanngeorgenstadt in Germany were investigated after addition and incubation with uranyl or sodium nitrate. For this purpose a sample with a natural uranium content of 26 mg/kg was treated with uranyl and sodium nitrate solutions (pH 4.0) and incubated under aerobic and anaerobic conditions for different periods of time. Afterwards total DNA was extracted from both treated and untreated samples, 16S rRNA gene fragments were amplified by PCR using primers specific for the domains of Bacteria or Archaea and then cloned. The predominant microbial populations were identified by restriction fragment length polymorphism and their 16S rRNA genes were sequenced and phylogenetically affiliated. The 16S rRNA gene retrieval revealed that representatives of Acidobacteria and of Alphaproteobacteria were dominating the bacterial community of the untreated sample. The increasing of the uranium content up to 100 mg/kg with a subsequent incubation for four weeks under aerobic conditions stimulated a propagation of Pseudomonas spp., Arthrobacter spp., and Geobacter spp. In a parallel sample supplemented with sodium nitrate under the same conditions mainly denitrifying and nitrate reducing populations of Actinobacteria and of Bacteroidetes were induced. In another sample, which was longer incubated (14 weeks) even with a higher uranium content, U-sensitive Bacteroidetes and alphaproteobacterial populations were predominant. The latter indicates that at that later stages of incubation the added U(VI) was not anymore bioavailable. In a parallel sample incubated under anaerobic conditions mainly Betaproteobacteria were stimulated. Additionally, some sequences closely related to Clostridium spp. were found in the anaerobic sample.
Archaeal diversity in the uranyl and sodium nitrate treated samples decreased in comparison to the untreated sample. All retrieved archaeal sequences were closely related to representatives of Crenarchaeota.
Our results represent the first cultivation-independent analysis of changes in the structure of a natural microbial community of a particular environment induced by the addition of uranyl or sodium nitrate.
  • Contribution to proceedings
    Annual Conference of the Association for General und Applied Micobiology, 19.-22.03.2006, Jena, Germany
    Abstract in Procceding: Biospektrum Sonderausgabe 2006 Elsevier, 69
  • Lecture (Conference)
    Annual Conference of the Association for General und Applied Micobiology, 19.-22.03.2006, Jena, Germany

Publ.-Id: 8002 - Permalink


PET online for protons and ions
Parodi, K.; Haberer, T.; Pönisch, F.; Enghardt, W.;
Positron emission tomography (PET) is currently the only technically feasible method for invivo, non-invasive monitoring of the precision of the dose delivery in highly conformal ion therapy. Online (in-situ) implementation offers the attractive advantages to detect the significant contribution from short-lived emitters e.g. 15O, reduce image degradation due to perfusion and acquire data in treatment position. To date, clinical applications of online PET have been limited to the concluded trial of range verification with radioactive isotopes prior to stable ion irradiation at Lawrence Berkeley Laboratory (LBL), USA, and the ongoing routine monitoring of stable carbon ion irradiation at the Gesellschaft für Schwerionenforschung Darmstadt (GSI), Germany. The rapidly growing number of proton therapy facilities is stimulating the research on the applicability of PET monitoring to protons. However, due to instrumentation restrictions and costs, most of the former and ongoing studies were carried out offline at remote, conventional PET scanners. Extensive in-beam phantom experiments with proton beams were recently finished at GSI using the available dedicated, unique online tomographic positron camera. The main results, providing novel insight and supporting the applicability and usefulness of online PET for proton therapy monitoring, will be reported.
Keywords: in-beam PET, protons, ions
  • Contribution to proceedings
    HCPBM 10th workshop on Heavy Charged Particles in Biology and Medicine, 15.-19.6.2005, Oropa, Italy, 119-123
  • Invited lecture (Conferences)
    HCPBM 10th workshop on Heavy Charged Particles in Biology and Medicine, 15.-19.6.2005, Oropa, Italy

Publ.-Id: 8000 - Permalink


Superconductivity at ultralow temperatures and its interplay with nuclear magnetism
Herrmannsdörfer, T.;
The search for superconductivity in platinum as well as studies of the interplay of superconductivity and nuclear magnetism will be reviewed. The pair breaking mechanism between nuclear magnetic moments and Cooper pairs will be described.
Keywords: interplay of superconductivity and nuclear magnetism, superconductivity in platinum
  • Lecture (others)
    Forschungsseminar Elektronische Festkörpereigenschaften, 15.11.2005, Dresden, Deutschland

Publ.-Id: 7999 - Permalink


Intersubband relaxation dynamics in narrow InGaAs/AlAsSb and InGaAs/AlAs quantum well structures using pump-probe spectroscopy
Tribuzy, C. V.-B.; Ohser, S.; Neuhaus, J.; Dekorsy, T.; Winnerl, S.; Schneider, H.; Helm, M.; Biermann, K.; Künzel, H.; Semtsiv, M. P.; Masselink, W. T.;
Intersubband (ISB) transitions in semiconductor quantum wells (QWs) can be employed for various mid-infrared optoelectronic devices. Presently there is strong interest to extend the available wavelength range into the near infrared, by using materials with a large conduction band offset. To achieve such short wavelengths thin QWs are required, where the first excited state inside the QW may lie higher than some state related to indirect valleys. Examples for such material systems are strained InGaAs/AlAs or lattice matched InGaAs/AlAsSb, both grown on InP. We have studied the ISB relaxation dynamics in multi QWs of both material systems by femtosecond pump-probe measurements. The transient transmission as a function of the pump-probe delay does not show a single-exponential decay, indicating a more complicated relaxation dynamics. This can be caused by transfer of electrons to X- or L- states in the QWs or the barriers. We will show results on samples with different QW thicknesses and compare them to simulations based on rate equations.
  • Lecture (Conference)
    DPG Frühjahrstagung, Fachverband Halbleiterphysik, 27.-31.03.2006, Dresden, Deutschalnd

Publ.-Id: 7998 - Permalink


LDL isolated from subjects with impaired glucose tolerance increases the expression of CD36 and PPAR-gamma in macrophages
Graessler, J.; Westendorf, T.; Kopprasch, S.; Pietzsch, J.;
Kein Abstract verfügbar
  • Lecture (Conference)
    The Metabolic Syndrome - a postprandial disease. Satellite Symposium of the 1st International Congress on "Prediabetes and the Metabolic Syndrome", 16.-18.04.2005, Dresden, Deutschland
  • Abstract in refereed journal
    Diabetes und Stoffwechsel (2005)Suppl. 1, 31-32

Publ.-Id: 7997 - Permalink


Elektroenergiebereitstellung
U., R.; Th., S.; J., Z.;
Im Kapitel Elektroenergiebereitstellung werden die verschiedenen Techniken zur Stromerzeugung dargestellt. Diese umfassen neben den konventionellen Wärmekraftwerken auch Kernkraftwerke, Wasserkraftwerke und Kraftwerke zur Wandlung erneuerbarer Energien.
Keywords: Kraftwerk, Kernkraftwerk, Wasserkraftwerk, Windenergieanlage, Biomassekraftwerk
  • Contribution to external collection
    W. Schufft: Taschenbuch der Elektrischen Energietechnik, München: Hanser-Verlag, 2007, 978-3-446-40475-5

Publ.-Id: 7996 - Permalink


Biodistribution and catabolism of 18F-labelled isopeptide N (varepsilon)-(gamma-glutamyl)-L-lysine
Hultsch, C.; Bergmann, R.; Pawelke, B.; Pietzsch, J.; Wüst, F.; Johannsen, B.; Henle, T.;
Isopeptide bonds between the varepsilon-amino group of lysine and the gamma-carboxamide group of glutamine are formed during strong heating of pure proteins or, more important, by enzymatic reaction mediated by transglutaminases. Despite the wide use of a microbial transglutaminase in food biotechnology, up to now little is known about the metabolic fate of the isopeptide N(varepsilon)-(gamma-glutamyl)-L-lysine. In the present study, N-succinimidyl-4-[18F]fluorobenzoate was used to modify N(varepsilon)-(gamma-glutamyl)-L-lysine at each of its two alpha-amino groups, resulting in the 4-[18F]fluorobenzoylated derivatives, for which biodistribution, catabolism, and elimination were investigated in male Wistar rats. A significant different biochemical behavior of the two labelled isopeptides was observed in terms of in vitro stability, in vivo metabolism as well as biodistribution. The results suggest that the metabolic fate of isopeptides is likely to be dependent on how they are reabsorbed - free or peptide bound.

Publ.-Id: 7995 - Permalink


Catabolism of native and oxidized low density lipoproteins (LDL): in vivo insights from small animal positron emission tomography studies
Pietzsch, J.; Bergmann, R.; Wüst, F.; Pawelke, B.; Hultsch, C.; van den Hoff, J.;
The human organism is exposed to numerous processes that generate reactive oxygen species (ROS). ROS may directly or indirectly cause oxidative modification and damage of proteins. Protein oxidation is regarded as a crucial event in the pathogenesis of various diseases ranging from rheumatoid arthritis to Alzheimer's disease and atherosclerosis. As a representative example, oxidation of low density lipoprotein (LDL) is regarded as a crucial event in atherogenesis. Data concerning the role of circulating oxidized LDL (oxLDL) in the development and outcome of diseases are scarce. One reason for this is the shortage of methods for direct assessment of the metabolic fate of circulating oxLDL in vivo. We present an improved methodology based on the radiolabelling of apoB-100 of native LDL (nLDL) and oxLDL, respectively, with the positron emitter fluorine-18 (18F) by conjugation with N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). Radiolabelling of both nLDL and oxLDL using [18F]SFB causes neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality, respectively, in vitro. The method was further evaluated with respect to the radiopharmacological properties of both [18F]fluorobenzoylated nLDL and oxLDL by biodistribution studies in male Wistar rats. The metabolic fate of [18F]fluorobenzoylated nLDL and oxLDL in rats in vivo was further delineated by dynamic positron emission tomography (PET) using a dedicated small animal tomograph (spatial resolution of 2 mm). From this study we conclude that the use of [18F]FB-labelled LDL particles is an attractive alternative to, e.g., LDL iodination methods, and is of value to characterize and to discriminate the kinetics and the metabolic fate of nLDL and oxLDL in small animals in vivo.

Publ.-Id: 7992 - Permalink


Efficient terahertz radiation of a large-area photoconductive device
Dreyhaupt, A.; Winnerl, S.; Dekorsy, T.; Helm, M.;
Photoconductive emitters are an attractive way for impulsive generation of THz radiation. There are two main categories, namely large-aperture emitters and interdigitated electrodes coupled to antennas. Large-aperture emitters have the advantage of a high active volume, while interdigitated structures provide high electric fields for efficient acceleration of photogenerated carriers. We present a large-aperture emitter consisting of a interdigitated metal-semiconductor-metal (MSM) structure, which combines both advantages. A second metallization layer, which is electrically insulated from the first one, blocks the optical excitation in every second period of the MSM structure, resulting in an unidirectional acceleration of carriers in the device. Focussing fs optical pulses with an average power of 100 mW from a Ti:sapphire oscillator on the emitter lead to THz field amplitudes of up to 85 V/cm (Ubias = 65 V). Excitation with unfocussed radiation from a 1 kHz repetition rate Ti:sapphire amplifier system (average power 10 mW) provided THz field amplitudes of 6 kV/cm (Ubias = 23 V). In case of the excitation with the Ti:sapphire amplifier system a pronounced nonlinear behavior of the THz field amplitude with respect to both the excitation density and the bias electric field was observed.
  • Lecture (Conference)
    DPG Frühjahrstagung, Fachverband Halbleiterphysik, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 7991 - Permalink


Glucose-Induced Enhancement of Hemin-Catalyzed LDL Oxidation In Vitro and In Vivo
Julius, U.; Pietzsch, J.;
Growing evidence indicates that oxidative modification of low-density lipoprotein (LDL) is increased in diabetes mellitus; however, the mechanism(s) of this phenomenon is still unclear. Gamma-Glutamyl semialdehyde (gammaGSA) is a product of hemin (Fe3+-protoporphyrin IX)-catalyzed oxidation of apolipoprotein B-100 (apoB- 100) proline and arginine residues. On reduction, gammaGSA forms 5-hydroxy-2-aminovaleric acid (HAVA). This report describes the application of sensitive HAVA assay, to characterize gammaGSA formation in LDL under normo- and hyperglycemic conditions, both in vitro and in vivo. In vitro studies revealed that apoB-100 proline and arginine residues are not oxidized to HAVA by HOCl or the myeloperoxidase/hydrogen peroxide (H2O2) oxidation system. Cu2+, Cu2+/H2O2, and Fe2+ induced only minor HAVA formation. In contrast, the hemin oxidation system appeared reactive toward LDL apoB-100 proline and arginine residues. The resulting significant HAVA formation was specifically inhibited by a redox-inert ferric iron chelator. Glucose further enhanced hemin-induced increase in relative electrophoretic mobility of LDL and apoB-100 HAVAformation. In vivo we observed elevated concentrations of HAVA in LDL apoB-100 in patients with impaired glucose tolerance and with manifest diabetes mellitus. In conclusion, glucose promotes iron-mediated oxidation of apoB- 100 proline and arginine residues via a superoxide-dependent mechanism, thus rendering the LDL particles more atherogenic. The findings (a) identify a potential mechanism of enhanced atherogenesis in subjects with diabetes mellitus and (b) support the value of HAVA as a specific marker of LDL apoB-100 oxidation.
  • Antioxidants and Redox Signaling 7(2005)11-12, 1507-1512

Publ.-Id: 7990 - Permalink


Scattering scanning near-field optical microscopy on anisotropic dielectrics using a free-electron laser light source
Schneider, S.; Seidel, J.; Grafström, S.; Loppacher, C.; Cebula, M.; Eng, L. M.; Winnerl, S.; Stehr, D.; Helm, M.;
Scattering scanning near- field optical microscopy (s-SNOM) is based on the interaction between an optically scattering nano-particle (AFM tip) and a dielectric sample. The size of the scatterer defines the optical resolution of the microscope, which is on the order of a few nanometers. On that scale, the optically anisotropic properties of most samples have to be taken into account [1]. To examine the influence of optical anisotropy on the scattering signal, we excite a ferroelectric sample close to its phonon resonance in the mid infrared regime. As the precisely tunable light source at infrared wavelengths we used a free electron laser (FEL). We have measured the near-field signal at several wavelengths while scanning the sample, as well as the tip-sample distance dependence of the scattered light signal for the 1st, 2nd, and 3rd harmonic signal. The anisotropy is revealed for different sample orientations. Not only are we presenting the first tunable IR near-field measurements on ferroelectric lithium niobate and barium titanate single crystals, but furthermore are our measurements in excellent accordance with recent calculations of optical anisotropy in such systems [1].
[1] S. Schneider, et al., Phys. Rev. B 71, 115418 (2005)
  • Lecture (Conference)
    DPG Frühjahrstagung, Fachverband Oberflächenphysik, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 7989 - Permalink


Intersubband transitions in GaP-AlP heterostructures for infrared applications
Semtsiv, M. P.; Masselink, W. T.; Georgiev, N.; Dekorsy, T.; Helm, M.;
not available
Keywords: intersubband absorption, infrared, quantum well
  • Lecture (Conference)
    12 Int. Conf. on Narrow Gap Semiconductors (NGS-12), 03.-07.07.2005, Toulouse, France
  • Institute of Physics Conference Series 187(2006), 209

Publ.-Id: 7988 - Permalink


Intersubband absorption in GaP-AlP multiple quantum wells
Semtsiv, M. P.; Masselink, W. T.; Georgiev, N.; Dekorsy, T.; Helm, M.;
not available
Keywords: intersubbadn absorption, quantum well, infrared
  • Lecture (Conference)
    8th Int. Conf. on Intersubband Transitions in Quantum Wells (ITQW 2005), 11.-16.09.2005, Cape Cod, MA, USA

Publ.-Id: 7987 - Permalink


Impurity states in quantum wells and superlattices and their influence in the intersubband absorption spectra
Stehr, D.; Metzner, C.; Helm, M.; Roch, T.; Strasser, G.;
Intersubband absorption in quantum wells (QW) and superlattices usually requires the presence of doping atoms, inevitably giving rise to disorder by randomly distributed hydrogenic impurity states (Coulomb potentials). It has been shown that in particular the 1s-2pz transition plays the role of an impurity-shifted intersubband transition, clearly observed in superlattices at low temperature, but recently also in isolated quantum wells.
In an attempt to understand the inter-miniband absorption spectra in doped superlattices on a more profound level than the usual variational approach for the impurity states, we have performed numerical calculations of the absorption spectra, by exactly diagonalizing the fully three-dimensional Schrödinger equation for a certain number of N coupled QWs (N=1..20), in an areal sheet of 100 x 100 nm2. The impurities are placed in the middle of each QW, but randomly distributed in the xy plane. The resulting energy levels and wave functions are used to calculate the absorption spectra.
For the case of a single QW the well known results for a quasi 2D impurity are reproduced, in particular the 2pz state (or 2p0, i.e. m=0) lies just below the second subband. More interesting is the double QW. Here it turns out that each subband level gets “its own” m=0 type impurity level, all of which can be optically reached from the 1s ground state.
It is now most interesting to observe how this evolves into a superlattice (SL). We find that, at low temperature, there remain two absorption peaks even at low doping, when only the 1s ground state is occupied: the transition to the 2pz-type excited state, just below the second miniband, but also a transition to an impurity state pinned to the top of the second miniband (and a weaker continuum in between). This result requires re-interpretation of data reported in the past: at low temperature and low doping, the high-energy peak in the SL absorption spectrum is not the miniband transition at kz=0, but an impurity transition to the state near the top of the excited miniband. This also explains a hitherto not understood behavior: the high-energy peak does not disappear, when the SL is driven through the metal-insulator transition by a magnetic field into the insulating regime, when only the impurity states are occupied, but the miniband states are empty. This is the first calculation which treats quantum well and random impurity potential on the same footing. At higher doping, screening and impurity band formation sets in, and the resulting Mott transition can be treated by the same method.
Keywords: intersubband transition, superlattice, impurity states, infrared
  • Lecture (Conference)
    8th Int. Conf. on Intersubband Transitions in Quantum Wells (ITQW 2005), 11.-16.09.2005, Cape Cod, MA,, USA

Publ.-Id: 7986 - Permalink


Solidification of SnPb and AlSi alloys in a rotating magnetic field
Willers, B.; Eckert, S.; Dong, J.;
Many references from the cast metal literature consider the application of sonic vibrations, mechanical or electromagnetic stirring as a tool to promote the formation of fine, equiaxed grains during solidification. 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. Once a flow occurs in the liquid melt during solidification, nucleation and grain growth are mainly governed by the convective transport of heat and solute. The consequences on the structure of solidified ingots are widely discussed in the literature. So it is known, that the application of mechanical or electromagnetic stirring promotes the formation of fine, equiaxed grains [1-4].
In this paper experimental and numerical investigations will be presented concerning the influence of a flow driven by a rotating magnetic field (RMF) on the momentum, heat and mass transfer within binary Sn-Pb alloys solidified directionally. Solidification experiments were carried out considering the directional solidification of Pb Sn and Al-Si alloys from a water cooled copper chill. A rotating magnetic field (RMF) was applied for melt agitation. Thermocouples were used to measure the temperature field during solidification. Profiles of the velocity in the liquid phase were determined by means of Ultrasound Doppler velocimetry (UDV) [5].
Our results show that the forced convection influences significantly the concentration as well as the temperature profile ahead of the solidification front. The convective transport of solute reduces the thickness of the solutal boundary layer and increases the constitutional supercooling. The RMF-application provokes a distinct grain refinement for all considered alloy compositions and equiaxed growth has shown to be encouraged. A flow effect can be supposed both on the presence of nuclei in the melt and suitable conditions allowing them to grow in competition with the columnar front.
  • Lecture (others)
    2nd Sino-German Workshop on EPM, 16.-19.10.2005, Dresden, Germany

Publ.-Id: 7985 - Permalink


Influence of melt convection on the microstructure of Nd-Fe-B- alloys
Hermann, R.; Filip, O.; Biswas, K.; Gerbeth, G.; Priede, J.;
The solidification process and the resulting microstructure of Nd-Fe-B alloys in consideration of melt convection has been investigated experimentally with a specially designed forced crucible rotation technique. Samples were subjected to well-defined forced rotation and vibration, respectively, during induction heating and solidification. A concerted microstructure evolution is possible by enhancement or suppression of the melt convection. As a result, the microstructure pattern, mainly the volume fraction of the soft magnetic -Fe phase, vary strongly with the strength of the internal flow motion. A distinct reduction of the -Fe volume fraction in samples with strong melt rotation was observed by measuring the magnetic moment. Moreover, the melt flow was studied numerically taking into account the coupled heat and fluid flow fields. Furthermore, a new category of experiment has been started where a tailored magnetic field was applied in order to study the microstructure evolution due to an enhancement or suppression of the melt convection by additional alternating magnetic fields.
  • Lecture (Conference)
    2nd Sino-German Workshop on EPM, 16.-19.10.2005, Dresden, Germany

Publ.-Id: 7984 - Permalink


Experimental studies of bubble-driven liquid metal flows in a static magnetic field
Zhang, C.; Eckert, S.; 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.
  • Lecture (Conference)
    2nd Sino-German Workshop on EPM, 16.-19.10.2005, Dresden, Germany

Publ.-Id: 7983 - Permalink


Electromagnetic flow control for casting and metallurgical applications: Model experiments and measuring techniques
Eckert, S.; Cramer, A.; Galindo, V.; Gerbeth, G.; Willers, B.;
The contactless handling of electrically conducting liquids by the application of magnetic fields makes this technology attractive for many industrial applications. The possibility to superimpose different kind of fields allows to generate a variety of flow structures being beneficial, for instance, to control the heat and mass transfer.
The further optimization of liquid metal flows in industrial technologies requires experimental data of the flow field to understand the process and the consequences of an intervention using electromagnetic fields. Numerical simulations alone are often of limited value. Realizing this situation, the motivation arises to perform laboratory studies using cold liquid metals as a model of realistic processes. The main feature of such cold (temperatures up to about 300°C) liquid metal models is the availability of measuring techniques allowing to analyse the local transport phenomena with a sufficient resolution. Some applications using the ultrasound Doppler velocimetry (UDV) will be presented showing the capability of this technique to measure velocity profiles in liquid metal flows. Note that water models of liquid metal processes are only meaningful if the melt flow Reynolds number represents the only determining parameter of the transport processes under consideration, which is seldom the case for real casting processes. As soon as temperature gradients, free-surface phenomena, two-phase flows or electromagnetic phenomena play a role, the water model is always of very limited value.
Some examples for model experiments will be presented showing the flow modelling of an investment casting process of aluminium alloys, the electromagnetic stirring of liquid metals and the solidification of metallic alloys affected by time-dependant magnetic fields, respectively.
  • Lecture (Conference)
    2nd Sino-German Workshop on EPM, 16.-19.10.2005, Dresden, Germany

Publ.-Id: 7982 - Permalink


A novel role for [18F]FDG: Synthesis and application of a [18F]FDG-based prosthetic group for peptide and protein labeling
Berndt, M.; Pietzsch, J.; Bergmann, R.; Wüst, F.;
Objectives: The routine 18F labeling of biomacromolecules like peptides and proteins should involve simple and efficient radiolabeling methods based on readily available prosthetic groups. 2-[18F]Fluoro-2-deoxy-D-glucose ([18F]FDG) as the most important PET radiotracer is available in almost every PET center. However, there are only very few examples using [18F]FDG as a building block for the radiosynthesis of 18F-labeled compounds.
The present study describes the use of [18F]FDG as a 18F building block for the convenient single-step synthesis of thiol-reactive prosthetic group [18F]FDG-maleimidehexyloxime ([18F]FDG-MHO). The potential of this novel [18F]FDG-based prosthetic group was evaluated by the reaction with thiol group-containing biomacro-molecules.

Methods: The reaction was performed using a 0.9% NaCl solution of [18F]FDG and N-(6-aminoxyhexyl)maleimide in 80% ethanol. The mixture was heated at 100°C in a sealed vial for 15 min. Then, ethanol was evaporated and [18F]FDG-MHO was purified by HPLC. Conjugation of [18F]FDG-MHO to thiol groups was investigated by the reaction with the tripeptide glutathione and the protein Annexin-V.

Results: [18F]FDG-MHO was obtained in 45-69 % radiochemical yield after HPLC purification in a total synthesis time of 50 min. The use of [18F]FDG-MHO as a selective thiol-reactive reagent was first exemplified using various concentrations of glutathione. The reaction was monitored by radio-TLC. At glutathione concentrations ranging from 30 µmol to <100 pmol we found complete consumption of the labeling agent. The application of [18F]FDG-MHO was further investigated by the conjugation to Annexin-V that contains one accessible cysteine side chain. Radiolabeling yields of up to 80% (based upon [18F]FDG-MHO) could be achieved.

Conclusion: The thiol-reactive prosthetic group [18F]FDG-MHO derived from readily available [18F]FDG has been developed. The labeling experiments using glutathione as a model peptide and Annexin-V as protein indicate that [18F]FDG-MHO can be used for the mild and selective 18F labeling of thiol group-containing biomacro-molecules like peptides and proteins.
  • Abstract in refereed journal
    Journal of Nuclear Medicine 47(2006)Suppl. 1, 29P
  • Lecture (Conference)
    53rd Annual Meeting of the Society of Nuclear Medicine, 03.-07.06.2006, San Diego, USA

Publ.-Id: 7981 - Permalink


Radiometallverbindungen für nuklearmedizinische Anwendungen
Stephan, H.; Noll, S.;
Das Interesse an der Entwicklung von Radiopharmaka auf der Basis von Radiometallen wird durch eine Reihe von Faktoren wie zunehmende Verfügbarkeit der Nuklide (Generatoren, Zyklotron), einfache Markierung von Liganden und wachsende Anwendungsmöglichkeiten in klinischen Zentren gestärkt. In Abhängigkeit von den kernphysikalischen Eigenschaften der Radiometallnuklide ergeben sich Einsatzmöglichkeiten in der nuklearmedizinischen Diagnostik und Therapie.
Unsere Untersuchungen konzentrieren sich auf die Radionuklide 64/67Cu und 188Re. Es werden neue Chelatsysteme, die über einen zielsuchenden und einen komplexbildenden Teil für metallische Radionuklide verfügen, vorgestellt. Das betrifft insbesondere sechszähnige Chelate auf der Basis des Bispidins (3,7-Diazabicyclo[3.3.1]nonan) und dendritische Liganden. Als zielsuchende Biomoleküle können prinzipiell Antikörper, spezifische Peptide oder Aptamere eingebaut werden. Möglichkeiten der radioaktiven Markierung von Nukleinsäurebausteinen werden diskutiert.
  • Invited lecture (Conferences)
    Institutskolloquium, 20.02.2006, Bonn, Germany

Publ.-Id: 7980 - Permalink


Nachrechnung der Leistungsparameter des Vollhub-Feder –Sicherheitsventils Leser Type 441 mit CFX-10
Höhne, T.;
Nachrechnung von Durchsatzparametern eines Leser Sicherheitsventils mit CFX-10
Gitter: 1 Million Hexaeder Zellen
CFX-Rechnungen mit Standard-Eingabedatensatz:
-Druckrandbedingung Eintritt und Austritt, Subdomain für Wasser und Luft
Sehr gute Übereinstimmung bei allen Durchsatzkennlinien, aber:
-systematische Abweichung bei Luft im Falle hoher Ansprechdrücke durch Realgasverhalten u. hohe Ma-Zahlen
CFX-Rechnung mit Zweiphasengemisch bei 2 bar Überdruck, 1 mm Blasendurchmesser, 4% Gasanteil, monodispers
-Erhöhnung des Volumenanteils der Gasphase in Abhängigkeit von Druckabsenkung konnte abgebildet werden
-Vergleich mit Experimenten
Keywords: Sicherheitsventil, CFD
  • Lecture (others)
    DECHEMA/GVC-Arbeitsausschuß “Sicherheitsgerechtes Auslegen von Chemieapparaten“ 60. Sitzung am 30.11./01.12.2005 im DECHEMA-Haus, 30.11.2005, Frankfurt am Main, Germany

Publ.-Id: 7979 - Permalink


Superconductivity and magnetism at lowest temperatures, highest magnetic fields, and in smallest structures
Herrmannsdörfer, T.;
Research at extreme material conditions can lead to new scientific knowledge. As an example, experiments at low temperatures and high magnetic fields have improved the understanding of matter dramatically in the last century. Nowadays, we dispose of the technology to reach ultralow temperatures, highest magnetic fields and even to produce material structures on length scales on which the geometrical size dominates physical properties. In this talk, research examples on superconducting nanogranular metals, quantum functional intermetallic compounds, nuclear magnetic superconductors, as well as magnetic high temperature superconductors will be presented. In addition, magnetic cooling technology and the non-destructive generation of highest pulsed magnetic fields will be briefly introduced along with facilities, e.g. the new Dresden High Magnetic Field Laboratory (HLD)*.

*HLD is a new large scale facility for the generation of pulsed magnetic fields up to 100 T which is under construction during 2003 to 2006 and which will open its doors for users in early 2007.
Keywords: Research at ultralow temperaturtes and highest magnetic fields, superconductivity in granular matter, interplay of magnetism and superconductivity, superconductivity in platinum
  • Invited lecture (Conferences)
    Kolloquium, Forschungszentrum Karlsruhe, 27.-28.11.2005, Karlsruhe, Deutschland

Publ.-Id: 7978 - Permalink


Magnetism and superconductivity of compacted micro- and nanogranular Platinum
Herrmannsdörfer, T.;
Compared to their bulk counterparts, micro- and nanogranular materials can reveal a diverse physical appearance. In particular, their magnetic and superconducting behaviour can be drastically influenced. As a prominent example, the superconductivity of compacted granular Pt will be presented.
Pt has been cooled down to an equilibrium temperature of phonons, electrons and nuclear magnetic moments of 1.5 µK, lower than all other materials so far [1]. However, superconductivity has not been observed in bulk Pt. Surprisingly, superconductivity occurs in compacted microgranular Pt [2]. The weakened impurity magnetism in powdered Pt (spin glass behaviour at mK temperatures) may play the crucial role in adjusting the balance between electron-phonon interaction and competing magnetic interactions. As a proof, we have also investigated Pt powders with a higher impurity content observing lower Tc values. In addition, low frequency phonons from the Pt surface could influence the electron-phonon interaction. In further investigated nanoscale Pt powders, the superconducting transition temperature is about 20 times larger than detected in the micrometer sized grains [3].

[1] W. Wendler, T. Herrmannsdörfer, S. Rehmann, F. Pobell, Europhys. Lett. 38, 619 (1997)
[2] R. König, A. Schindler, T. Herrmannsdörfer, Phys. Rev. Lett. 82, 4528 (1999)
[3] A. Schindler et al., Europhys. Lett. 58, 885 (2002)
  • Invited lecture (Conferences)
    International Conference on Quantum Transport, 03.-05.07.2005, Bologna, Italy

Publ.-Id: 7977 - Permalink


The quantum-functional properties of Pr(1-x-y)La(x)Pb(y)Te
Herrmannsdörfer, T.; Bianchi, A.; Papageorgiou, T. P.; Wosnitza, J.;
The intermetallic compound Pr(1-x-y)La(x)Pb(y)Te shows a wide spectrum of physical phenomena. Depending on the metallurgical composition as function of x and y, the compound changes its behavior from nuclear magnetic order to super- or semiconductivity. In addition, there are interesting interplay effects between these ground states. In consequence, Pr(1-x-y)La(x)Pb(y)Te may serve as an interesting material for quantum-computing applications. In this contribution, we focus on our recent investigation of the magnetic properties of Pr(1-y)Pb(y)Te. We present data of the magnetisation taken at 1.8 K < T < 350 K for various compositions y = 0, 90, 99, 99.9 %, i.e. turning the system from a van Vleck paramagnet, y = 0, into a doped semiconductor, y = 99.9 %.
Keywords: hyperfine enhanced nuclear magnetism, magnetic semiconductors, quantum computing
  • Invited lecture (Conferences)
    24th International Conference on Low Temperature Physics, 10.-17.07.2005, Orlando, USA

Publ.-Id: 7976 - Permalink


The quantum functional intermetallic compound Pr(1-x-y)La(x)Pb(y)Te
Herrmannsdörfer, T.;
The intermetallic compound Pr(1-x-y)La(x)Pb(y)Te shows a wide spectrum of physical phenomena. Depending on the metallurgical composition, the compound changes its behaviour from hyperfine enhanced nuclear magnetic order to super- or semiconductivity. In addition, there are interesting interplay effects between these ground state phenomena. In consequence, Pr(1-x-y)La(x)Pb(y)Te may
serve as an interesting quantum functional compound for quantum computing experiments. In this paper, the hyperfine enhanced nuclear magnetic and superconducting properties are pointed out.
Keywords: hyperfine enhanced nuclear magnetism, interplay of superconductivity and magnetism, quantum computing

Publ.-Id: 7975 - Permalink


Die Berechnung gepulster Magnetfeldspulen mittels der Methode der Finiten Elemente
Herrmannsdörfer, T.; Zherlitsyn, S.; Wosnitza, J.;
Die phänomenologischen Grundlagen und prinzipiellen Gesetzmäßigkeiten zur Berechnung von Feldern und Kräften in Magnetfeldspulen wurden bereits vor 185 Jahren von Hans Christian Oersted, André Marie Ampère, Jean-Baptiste Biot, Felix Savart und anderen geschaffen. Seit etwa 130 Jahren können elektromagnetische Fragestellungen nach Einführung der Maxwellschen Gleichungen umfassend bearbeitet werden. Man könnte daher annehmen, dass Magnetfeldspulen, die uns zudem in sämtlichen Bereichen des täglichen Lebens wie bei der Energieerzeugung, dem Transport, der Unterhaltungselektronik, der Datenverarbeitung oder der Medizintechnik als vertraute technische Komponenten begegnen, kaum mehr als ingenieurtechnische oder physikalische Herausforderung betrachtet werden können. Insbesondere scheinen die Möglichkeiten grenzenlos zu sein, seit die Supraleitertechnik selbst spektakuläre Dauerstromspulen für z.B. Kernspin-Tomographen oder Fusionsexperimente ermöglicht. Dennoch kann die Berechnung von Magnetfeldspulen eine wissenschaftliche Herausforderung darstellen. Dies gilt z.B. für Spulen sehr hoher Feldhomogenität und Feldstabilität, insbesondere aber für Spulen besonders hoher Feldstärke.
Keywords: high magnetic fields, coil design, finite element modelling
  • Physikjournal 4(2005)6, 90-91

Publ.-Id: 7974 - Permalink


Effects of excitation wave form on an electromagnetically forced separated flow
Weier, T.; Cierpka, C.; Gerbeth, G.;
Experimental results on separation control by time periodic Lorentz forces are reported for hydrofoils in the Reynolds number range 10^4 - 10^5. Force measurements reveal that in a small frequency around the most effective excitation frequency control authority is a function of the peak momentum input. The vorticity distribution derived from phase averaged laser doppler anemometry shows different vortical structures for excitation with varying wave forms. The effect of the excitation wave form on the attainable lift gain is interpreted as resulting from these different vortex structures.
Keywords: flow control, separation control, Lorentz force
  • Lecture (Conference)
    European Drag Reduction and Flow Control Meeting, 10.-14.04.2006, Ischia, Italy
  • Contribution to proceedings
    European Drag Reduction and Flow Control Meeting, 10.-13.04.2006, Ischia, Italy

Publ.-Id: 7973 - Permalink


Description of 3D calculations of decay heat and thermal hydraulic equations
Grundmann, U.;
The decay heat model implemented in the three-dimensional core model DYN3D is described. The equations solved in DYN3D for transport of the coolant and the heat conduction in the fuel rods are presented. The solution scheme is outlined.
Keywords: decay heat nuclear reactor transient caslculation thermal hydraulics coolant flow heat transfer heat conduction fuel temperature
  • Invited lecture (Conferences)
    IAEA Workshop on “Neutronic Analyses of BNPP-1 Reactor Core. Task 7.8 of IRA4035", 10.-14.10.2005, Wien, Österreich

Publ.-Id: 7972 - Permalink


Overview on space-time core calculationsfor VVER reactors
Grundmann, U.;
Transient analyses for VVER reactors performed with the computer code DYN3D are described. The decay heat after the shutdown of a VVER-440 is considered. A Xenon oscillation transient in a VVER-1000 is presented. The results for control rod ejections and control rod withdrawal in VVER-440 and VVER-1000 reactors are shown. A boron dilution transient in a VVER-440 by using the coolant mixing model of DYN3D is presented.
Keywords: VVER reactors transients analyses three-dimensional core model feedback reactivities
  • Invited lecture (Conferences)
    IAEA Workshop on “Neutronic Analyses of BNPP-1 Reactor Core. Task 7.8 of IRA4035”, 10.-14.10.2005, Wien, Austria

Publ.-Id: 7971 - Permalink


Experimental investigation of the flow in a bubble column
Zaruba, A.;
Computational Fluid Dynamics (CFD) models for two-phase flows always require closure relations representing the nature of the forces acting at the interface between the participating phases. This is vital for the modelling of momentum transfer term. In case of a gas-liquid flow, it is expressed in terms of forces acting on bubbles. The present study uses instantaneous high-speed video observations of the bubble motion to validate models for the interfacial forces.
The turbulent diffusion coefficient of the gaseous phase is obtained by a statistical evaluation of the movement of bubbles in a swarm, which is affected by the turbulence of the liquid phase. After the bubble trajectories were identified, the lateral displacement of bubbles was statistically analysed by constructing probability density functions. The dispersion coefficients of the standard distributions were found to grow proportionally to the square-root of the time. This supports the assumption of a diffusion model for the lateral displacement. Deviations from the linear dependency were identified to be the result of deterministic oscillatory motions of the rising bubbles.
Another objective is objective is to demonstrate the capabilities of the high-speed stereo-imaging technique to study the single (isolated) bubble dynamics in a vertical bubble column. The reconstruction algorithm of the 3D bubble trajectories from the stereo images of the bubble projection is presented. The bubble size, shape, orientation as well as bubble aspect ratio are investigated.
The first results of experiments on bubble motion in a vary narrow flat bubble column (width-100 mm, depth-8 mm, height – 600 mm) obtained for the validation of numerical predictions achieved using DNS-based analyses (Wörner et al. FZK) are presented. Results of high-speed video measurements of bubble parameters (bubble shape, size, rising velocity etc.) as well as PIV measurements of velocity of the liquid phase are discussed.
Keywords: Bubble column, CFD, interfacial forces, PIV
  • Invited lecture (Conferences)
    Seminar, 24.11.2005, Karlsruhe, Germany

Publ.-Id: 7970 - Permalink


Comparisons of DYN3D results with the reference solution of the AER-FCM-101 benchmark
Grundmann, U.;
The configuration of the reactor core used in the steady-state AER-FCM-101 benchmark is described. The results of different options of the DYN3D code are compared with the reference solution.
Keywords: reactor core benchmarks reference solution code validation nodal methods steady state
  • Invited lecture (Conferences)
    IAEA Workshop on “Neutronic Analyses of BNPP-1 Reactor Core. Task 7.8 of IRA4035”, 10.-14.10.2005, Wien, Austria

Publ.-Id: 7969 - Permalink


Molekulare Analysen von metallbindenden S-Layer-Proteinen
Pollmann, K.;
wird nachgereicht
  • Lecture (others)
    FZR - FSU Jena Workshop, 27.-28.07.2005, Dresden, Germany

Publ.-Id: 7966 - Permalink


Characterization of the Bacillus isolates from the uranium mining waste pile Haberlandhalde
Regenhardt, D.;
wird nachgereicht
  • Lecture (others)
    FZR - FSU Jena Workshop, 27.-28.07.2005, Dresden, Germany

Publ.-Id: 7965 - Permalink


Untersuchung des Einflusses von U(VI) auf die Struktur der natürlichen bakteriellen Gemeinschaft in einer Bodenprobe einer Uranabfallhalde
Geissler, A.;
wird nachgereicht
  • Lecture (others)
    FZR - FSU Jena Workshop, 27.-28.07.2005, Dresden, Germany

Publ.-Id: 7964 - Permalink


Optimum excitation conditions for the generation of high-electric-field THz radiation from an oscillator-driven photoconductive device
Dreyhaupt, A.; Winnerl, S.; Helm, M.; Dekorsy, T.;
We report on impulsive generation of terahertz (THz) radiation with more than 1.5 kV/cm field amplitude at MHz repetition rates, using an interdigitated photoconducting device. The approach provides an average THz power of 190 µW corresponding to an optical-to-THz conversion efficiency of 2.5 × 10-4. Optimum conditions are achieved when the excitation spot size is on the order of the THz wavelength.
  • Optics Letters 31(2006)10, 1546-1548

Publ.-Id: 7963 - Permalink


Jahresüberblick: Technische Entwicklungen, Nutzung, Erfolgsbilanz, ACTINET
Scheinost, A.; Claussner, J.; Dienel, S.; Funke, H.; Hennig, C.; Oehme, W.; Proehl, D.; Rossberg, A.; Strauch, U.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7961 - Permalink


XAS Characterization of metallic nanoparticles formed by cells and S-layer of Bacillus sphaericus JG-A12
Merroun, M.; Pollmann, K.; Raff, J.; Rossberg, A.; Hennig, C.; Scheinost, A.; Selenska-Pobell, S.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7960 - Permalink


Uranyl Minerals - special features of EXAFS spectra at 10-30 K
Funke, H.; Hennig, C.; Rossberg, A.; Scheinost, A.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7958 - Permalink


EXAFS-Untersuchungen am System U(VI)-Kaolinit-Huminsäure
Krepelova, A.; Sachs, S.; Reich, T.; Rossberg, A.; Bernhard, G.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7957 - Permalink


Müssen die Sorptionskomplexe von Uran(VI) an Ferrihydrit revidiert werden? II. Strukturaufklärung und spektroskopischer Nachweis mittels Monte Carlo Simulation und Faktoranalyse von EXAFS-Spektren
Rossberg, A.; Ulrich, K.-U.; Scheinost, A.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7956 - Permalink


Strukturanalyse von U(VI), U(IV) und Th(IV) Sulfato-Komplexen in wässriger Lösung
Hennig, C.; Schmeide, K.;
wird nachgereicht
  • Lecture (others)
    ROBL-Radiochemie Workshop, 07.12.2005, Dresden, Germany

Publ.-Id: 7955 - Permalink


Size and structure of the Au nanoclusters formed on Cells and S-layer of Bacillus sphaericus JG-A12
Merroun, M.;
Cells and S-layer sheets of B. sphaericus JG-A12 were used as templates for the deposition of metallic gold nanoclusters using dimethyl amino borane (DMAB) as reducing agent . Gold LIII-edge XAS measurements confirmed the formation of Au(0) nanoclusters in both cases. In this Talk, the preliminary results on the size and the structure of the Au nanoclusters deposited on cells and S-layer protein of B. sphaericus JG-A12 will be presented.
  • Lecture (others)
    SMWK-Projekttreffen, 16.12.2005, Dresden, Germany

Publ.-Id: 7954 - Permalink


Microbial diversity in ground water at the deep-well monitoring site SI5 of the radioactive waste depository Tomske-7, Siberia, Russia
Nedelkova, M.;
Microbial diversity was studied in ground waters collected from a monitoring well at the radioactive waste depository Tomsk-7, Siberia, Russia, applying the 16S rDNA retrieval. The results demonstrated dominance of Betaproteobacteria, Bacteroidetes, and a novel “Cyanobacteria-like” group. The archaeal populations are represented by methanogens and three distinct clusters of Crenarchaeota. The autotrophic bacterial diversity was estimated via the RubisCO approach and the results confirm the dominance of Betaproteobacteria. Oligotrophic bacteria, from the groups of Alphaproteobacteria and Actinobacteria were isolated from the studied site. The strains tolerate relatively high concentration of different heavy metals and interact effectively with uranium. EXAFS analysis demonstrated that they immobilize U(VI) at pH 4.5 extracellularly in a form of meta-autunite. At pH 2 the U was bound by the organic phosphate residues of the cells. The environment around the radioactive waste repository site Tomsk-7 possesses microorganisms with a potential to bind and transport radionuclides.
  • Other report
    Bergakademie Freiberg: Doktorarbeit (Studiengang Chemie), 2005
    60 Seiten

Publ.-Id: 7953 - Permalink


Changing physical parameters to gain more information from EXAFS spectroscopy
Hennig, C.;
The contribution splits into three parts. (1) Theory and experiment of polarization dependent EXAFS at the U L1 and U L3 edge will be compared. (2) The effect of the temperature on the EXAFS Debye-Waller factor will be analyzed. (3) In-situ EXAFS experiments with changing electrochemical potential will be presented.
  • Lecture (others)
    CEA, 11.05.2005, Valduc, France

Publ.-Id: 7952 - Permalink


Speciation of uranium in environmental relevant compartments II
Bernhard, G.;
In the past, the chemistry of uranium was focused on its mining and milling for production of high pure uranium compounds as initial matter of reactor fuel elements for energy production and breeding of plutonium for weapons production. In this sense, the recovery of uranium and plutonium from the used reactor fuel elements was also technical realized. The increasing input into bio-sphere by uranium mining and milling and industrial processes like production of cement, fossil fuels, and fertilizers has led to the realization of the importance of environmental chemistry of uranium. Starting from uranium content in geo-and bio-systems, about the chemical behavior - the speciation of uranium - is reported in selected environmental compartments like seepage water, bacteria, and plants. The results obtained
by various spectroscopic methods show that the speciation of uranium is dominated in surface waters by uranyl carbonate complex in opposite to the speciation in bacteria and p! lants. In these compartments the speciation is dominated by binding of uranium on carboxylic and phosphorous containing functional groups.
  • Landbauforschung Volkenrode 55(2005), 139-148

Publ.-Id: 7951 - Permalink


Changes in microbial community structure induced by addition of U(VI) to uranium mining waste samples
Geissler, A.; Reitz, T.; Tschikov, J.; Selenska-Pobell, S.;
Microorganisms are involved in biogeochemical transformations and migration of uranium in the environment. In order to study the influence of U(VI) on natural bacterial and archaeal communities, a soil sample collected from the uranium mining waste pile Haberland near the town of Johanngeorgenstadt was treated with different amounts of uranyl or sodium nitrate as a control. The samples were incubated for different periods of time and at different aeration conditions and their microbial communities were analyzed by the 16S rDNA retrieval using bacteria- and archaea-specific primers. Bacterial community of the untreated sample was predominated by Alphaproteobacteria and Acidobacteria. The increasing of the uranium content up to 100 mg U/kg with a subsequent incubation for four weeks under aerobic conditions stimulated a propagation of Pseudomonas spp., Arthrobacter spp. and Geobacter spp. Treatment of a parallel sample with sodium nitrate under the same conditions induced a strong propagation of denitrifying and nitrate reducing populations of Actinobacteria and of Bacteroidetes. After a longer incubation of fourteen weeks even in most contaminated samples containing 300 mg U/kg U-sensitive Bacteroidetes and alphaproteobacterial populations were stimulated. In parallel samples incubated under anaerobic conditions mainly Betaproteobacteria were identified. Archaeal diversity of the uranyl and sodium nitrate treated samples was significantly lower than in untreated samples and only sequences related to Crenarchaeotea were found. Our results demonstrate for the first time changes in the structure of a natural microbial community induced by incubation with uranyl nitrate for different periods of time and at different aeration conditions.
  • Contribution to proceedings
    VAAM-Jahrestagung, 19.-22.03.2006, Jena, Germany
  • Lecture (Conference)
    VAAM-Jahrestagung, 19.03.-22.06.2006, Jena, Germany

Publ.-Id: 7950 - Permalink


Spatial distribution and speciation of lead around corroding bullets in a shooting range soil studied by micro-X-ray fluorescence and absorption spectroscopy
Vantelon, D.; Lanzirotti, A.; Scheinost, A.; Kretzschmar, R.;
wird nachgereicht
  • Environmental Science & Technology 39(2005), 4808-4815

Publ.-Id: 7949 - Permalink


Chemical Heterogeneity of Organic Soil Colloids Investigated by Scanning Transmission X-ray Microscopy and C-1s NEXAFS Microspectroscopy
Schumacher, M.; Christl, I.; Scheinost, A.; Jacobsen, C.; Kretzschmar, R.;
Colloid release and deposition in soils and sorption of inorganic and organic pollutants to soil colloids are strongly influenced by the composition and chemical heterogeneity of colloidal soil particles. To investigate the chemical heterogeneity of organic soil colloids at the particle scale, we used synchrotron scanning transmission X-ray microscopy (STXM) and C-1s near-edge X-ray absorption fine structure (NEXAFS) spectroscopy on 49 individual particles isolated from the surface horizons of three forest soils. Stacks of 130 images of each particle were collected at different X-ray energies between 280 and 310 eV. From these image arrays, NEXAFS spectra were obtained for each pixel and analyzed by principle component analysis and cluster analysis (PCA-CA) to characterize the intraparticle heterogeneity of the organic components. The results demonstrate that the organic matter associated with water-dispersible soil colloids is chemically heterogeneous at the single-particle scale. PCA-CA identified at least two distinct regions within single particles. However, the spectral variations between these regions were much smaller than the variations of averaged NEXAFS spectra representing different particles from the same soil horizon, implying that interparticle heterogeneity is much larger than intraparticle heterogeneity. Especially the contents of aromatic and carboxyl carbon exhibited a large variability. Overall, the NEXAFS spectra of water-dispersible soil colloids were similar to the NEXAFS spectrum of the humic acid fraction, but differed clearly from the fulvic acid and dissolved organic matter fractions extracted from the same soil horizon using conventional techniques.
  • Environmental Science & Technology 39(2005), 9094-9100

Publ.-Id: 7948 - Permalink


Linking Monte-Carlo Simulation and Target Transformation Factor Analysis: A novel tool for the EXAFS analysis of mixtures
Rossberg, A.; Scheinost, A.;
wird nachgereicht
  • Physica Scripta T115(2005), 912-914

Publ.-Id: 7947 - Permalink


Neptunium uptake by serum transferring
Llorens, I.; Den Auwer, C.; Moisy, P.; Ansoborlo, E.; Vidaud, C.; Funke, H.;
wird nachgereicht
  • FEBS journal 272(2005), 1739-1744

Publ.-Id: 7946 - Permalink


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