Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
„risk management and the European Market Infrastructure Regulation (emir)”
Stiller, D.; Dammert, C.; Joehnk, P.;
  • Invited lecture (Conferences)
    International Doctoral Seminar 2013, 13.-15.05.2013, Dubrovnik, Croatia

Publ.-Id: 18791 - Permalink

The impact of electromagnetic stirring on grain refinement and the mechanical properties of AlSi alloys
Räbiger, D.; Krößig, C.; Eckert, S.; Gerbeth, G.;
The adjustment of fine grain morphologies has been approved to be a crucial issue for improving characteristics and properties of cast and wrought aluminium alloys. Several methods are known to achieve grain refinement in solidification processes: add-on of grain refiners, rapid cooling conditions, mechanical or electromagnetic stirring, or ultrasonic treatment.
AC magnetic fields provide a contactless method to control the flow inside a liquid metal and the grain size of the solidified ingot. However, the imposition of a rotating (RMF) or a travelling magnetic field (TMF) also causes problems like the occurrence of typical segregation pattern or a deflection of the upper free surface. Previous investigations considered the use of time-modulated rotating magnetic field to control the heat and mass transfer at the solidification front to avoid segregation effects.
This present study examines the directional solidification of AlSi7 alloys from a water cooled copper chill. A rotating magnetic field are used to agitate the melt. Different magnetic field intensities and time-modulated magnetic fields were considered to show the impact of diverse flow conditions on the resulting mechanical properties. The solidified structure was reviewed in comparison to an unaffected solidified ingot. Measurements of the phase distribution, the grain size, the hardness and the tensile strength were realized. Our results reveal the potential of magnetic fields to control the grain size, the formation of segregation freckles and the mechanical properties. In particular, time–modulated rotating fields demonstrated their capability to homogenize both the grain size distribution and the corresponding mechanical properties.
Keywords: grain refinement, mechanical properties, tailored magnetic field
  • Poster
    3rd International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining, 20.-23.05.2013, Hanasaari, Finnland

Publ.-Id: 18790 - Permalink

"after the Crisis: lessons learned? Responsibility and ethics of managers in large companies"
Joehnk, P.;
Verantwortung und Moral der Manager in großen Unternehmen
  • Lecture (Conference)
    International Doctoral Seminar 2013, 13.-15.05.2013, Dubrovnik, Croatia

Publ.-Id: 18789 - Permalink

pK+Λ final state: towards the extraction of the ppK contribution
Fabbietti, L.; Agakishiev, G.; Behnke, C.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Blume, C.; Böhmer, M.; Cabanelas, P.; Chernenko, S.; Dritsa, C.; Dybczak, A.; Epple, E.; Fateev, O.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garz´On, J. A.; Gill, K.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Harabasz, S.; Hennino, T.; Höhne, C.; Holzmann, R.; Huck, P.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Krasa, A.; Krebs, E.; Krizek, F.; Kuc, H.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Rehnisch, L.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.;
The reaction p(@3.5GeV) + p -> p + Λ + K+ can be studied to search for the existence of kaonic bound states like ppK− leading to this final state. This effort has been motivated by the assumption that in p+p collisions the (1405) resonance can act as a doorway to the formation of the kaonic bound states. The status of this analysis within the HADES collaboration, with particular emphasis on the comparison to simulations, is shown in this work and the deviation method utilized by the DISTO collaboration in a similar analysis is discussed. The outcome suggests the employment of a partial wave analysis to disentangle the different contributions to the measured pK+Λ final state.

Publ.-Id: 18787 - Permalink

Magnetic field controlled floating-zone single crystal growth of intermetallic compounds
Herrmann, R.; Gerbeth, G.; Priede, J.;
Radio-frequency (RF) floating zone single crystal growth is an important technique for the preparation of single bulk crystals. The advantage of the floating-zone method is the crucible-free growth of single crystals of reactive materials with high melting points. The strong heat diffusion on the surface, as well as the melt convection in the molten zone due to induction heating, often leads to an undesired solid-liquid interface geometry with a concave (towards the solid phase) outer rim. These concave parts aggravate the single crystal growth over the full cross-section. A two-phase stirrer was developed at IFW Dresden in order to avoid the problems connected with these concave parts. It acts as a magnetic field pump and changes the typical double vortex structure to a single roll structure, thus pushing hot melt into the regions where the concave parts may arise. The current in the secondary coil is induced by the primary coil, and the capacitor and the resistance of the secondary circuit are adjusted to get a stable 90 degree phase-shift between the coil currents. Single crystal growth of industrial relevant RuAl and TiAl intermetallic compounds was performed based on the material parameters and using the adjusted two-phase stirrer. Very recently, the magnetic system was applied to the crystal growth of biocompatible TiNb alloys and antiferromagnetic Heusler MnSi compounds.

Publ.-Id: 18786 - Permalink

Silicon nanodot Formation and self-ordering under bombardment with heavy Bi3 ions
Böttger, R.; Heinig, K.-H.; Bischoff, L.; Liedke, B.; Hübner, R.; Pilz, W.;
Si nanodots of high density and hexagonal short-range order are observed upon normal-incidence bombardment of hot, crystalline Si with Bi3+ ions having a kinetic energy of a few tens of keV. The heights of nanodots are comparable to their widths of ~20 nm. The implanted Bi accumulates in tiny Bi nanocrystals in a thin Si top layer which is amorphous due to implantation damage. Light and heavy ions up to Xe cause smoothing of surfaces, but Bi3+ ions considered here have a much higher mass. Atomistic simulations prove that each Bi3+ impact deposits an extremely high energy density resulting in a several nanometer large melt pool, which resolidifies within a few hundreds of picoseconds. Experiments confirm that dot patterns form only if the deposited energy density exceeds the threshold for melting. Comparing monatomic and polyatomic Bi ion irradiation, Bi–Si phase separation and preferential ion erosion are ruled out as driving forces of pattern formation. A model based on capillary forces in the melt pool explains the pattern formation consistently.
Keywords: silicon, polyatomic ions, melting, nanodots, ion bombardment

Publ.-Id: 18785 - Permalink

High-Speed PIXE – schnelle Multielementanalyse mit Ionenstrahlen
Ziegenrücker, R.; Hanf, D.; Gutzmer, J.; Ihle, S.; Merchel, S.; Renno, A. D.; Rugel, G.; Scharf, O.; Buchriegler, J.;
Das Helmholtz-Institut Freiberg für Ressourcentechnolgie (HIF @ HZDR) entwickelt unter dem Schlagwort „Ressourcenanalytik“ neue Analysemethoden, um Technologien zur Erkundung, Gewinnung, Nutzung und dem Recycling von Rohstoffen entlang der Wertschöpfungskette zu bewerten und zu verbessern. Eines dieser neuen Verfahren ist eine weltweit unikale High-Speed PIXE, das ist die schnelle ortsaufgelöste Teilchen-induzierte Röntgenemissionspektrometrie (PIXE = Particle-Induced X-ray Emission). Mittels High-Speed PIXE wird die elementare Zusammensetzung großformatiger Erzproben in kurzer Zeit (min-h) quantitativ bestimmt. Neben den für die Ressourcentechnologie wichtigen geologischen und aufbereitungstechnischen Proben, sind Materialanalysen möglich und bei entsprechender Probenvorbereitung, da die Messung im Vakuum erfolgt, auch biologische oder medizinische Proben analysierbar.
Im Gegensatz zur Elektronen-induzierten EDX (EDX = Energy dispersive X-ray spectrometry) wird die spezifische Röntgenstrahlung bei der PIXE mit Protonen angeregt. Ein 6 MV Tandem-Teilchenbeschleuniger[1] erzeugt Protonen mit einer Energie von 4,2 MeV. Der 2 bis 3 mm große Teilchenstrahl wird anschließend aufgeweitet und regt simultan alle Atome über einer Probenfläche von 12x12 mm² an. Die dabei entstehende Röntgenstrahlung ist für die enthaltenen Elemente charakteristisch und kann quantitativ ausgewertet werden. Für die ortsaufgelöste Detektion wird eine sogenannte Röntgenfarbkamera SLcam®[2] verwendet, bestehend aus einer speziellen Röntgenkapillaroptik, die am IFG (IFG = Institut for Scientific Instruments) in Berlin entwickelt wurde in Verbindung mit einer pnCCD der Firma PNSensor. Der Detektorchip dieser Kamera ist aus 69696 48x48 µm² großen Pixeln aufgebaut, die alle ein komplettes energieaufgelöstes Röntgenspektrum messen können.
In der Abbildung sind mit der High-Speed PIXE gemessene Element-verteilungsbilder mit einer lateralen Ortsauflösung von 50 µm (bis ~10 µm möglich) dargestellt; links kumulativ alle Röntgenphotonen und rechts nur die K-alpha- und K-beta-Linien von As. Im Moment können alle Elemente ab Mg und zukünftig sogar ab B mit elementspezifischen Nachweisgrenzen bis in den µg/g-Bereich detektiert werden.

[1] S. Akhmadaliev et al., Nucl. Instr. Meth. B 294 2013, doi:10.1016/j.nimb.2012.01.053
[2] O. Scharf et al., Analyt. Chem. 83 2011, doi: 10.1021/ac102811p
Keywords: High-Speed PIXE, multi-element analysis, particle-induced X-ray emission, X-ray colorcam, X-ray-optics
  • Poster
    Wissenschaftsforum Chemie 2013, 01.-04.09.2013, Darmstadt, Deutschland

Publ.-Id: 18784 - Permalink

Synthesis and radiopharmacological characterisation of a fluorine-18 labelled azadipeptide nitrile as potential PET Tracer for in vivo imaging of cysteine cathepsins
Löser, R.; Bergmann, R.; Frizler, M.; Mosch, B.; Dombrowski, L.; Kuchar, M.; Steinbach, J.; Gütschow, M.; Pietzsch, J.;
A fluorinated cathepsin inhibitor based on the azadipeptide nitrile chemotype was prepared and selected for PET tracer development owing to its high affinity for the oncologically relevant cathepsins L, S, K and B. Labelling with fluorine-18 was accomplished in an efficient and reliable two-step, one-pot radiosynthesis using 2-[18F]fluoroethyl nosylate as prosthetic agent. The pharmacokinetic properties of the resulting radiotracer compound were studied in vitro, ex vivo and in vivo in normal rats by radiometabolite analysis and small animal positron emission tomography (PET). These investigations revealed the rapid conjugate formation of the tracer with glutathione in the blood associated with a slow blood clearance. The potential of the developed 18F-labelled probe to image tumour-associated cathepsin activity was investigated by dynamic small-animal PET imaging in nude mice bearing tumours derived from the human NCI-H292 lung carcinoma cell line. Computational analysis of the obtained image data indicated the time-dependent accumulation of the radiotracer in the tumours. The expression of the target enzymes in the tumours was confirmed by immunohistochemistry using specific antibodies. This indicates that azadipeptide nitriles have the potential to target thiol-dependent cathepsins in vivo despite their disadvantageous pharmacokinetics.
Keywords: cathepsins, glutathione, molecular imaging, small animal positron emission tomography, tumour-associated proteolysis

Publ.-Id: 18783 - Permalink

Use of 3-[18F]fluoropropanesulfonyl chloride as prosthetic agent for the radiolabelling of amines: Investigation of precursor molecules, labelling conditions and enzymatic stability of the corresponding sulfonamides
Löser, R.; Fischer, S.; Hiller, A.; Köckerling, M.; Funke, U.; Maisonial, A.; Brust, P.; Steinbach, J.;
3-[18F]fluoropropanesulfonyl chloride, a recently proposed prosthetic agent for fluorine-18 labelling, was prepared in a two-step radiosynthesis via 3-[18F]fluoropropyl thiocyanate as intermediate. Two benzenesulfonate-based radiolabelling precursors were prepared by various routes. Comparing the reactivities of 3-thiocyanatopropyl nosylate and the corresponding tosylate towards [18F]fluoride the former proved to be superior accounting for labelling yields of up to 85%. Conditions for a reliable transformation of 3-[18F]fluoropropyl thiocyanate to the corresponding sulfonyl chloride with the potential for automation have been identified. The reaction of 3-[18F]fluoropropanesulfonyl chloride with eight different aliphatic and aromatic amines was investigated and the identity of the resulting 18F-labelled sulfonamides was confirmed chromatographically by comparison with their non-radioactive counterparts. Even for weakly nucleophilic amines such as 4-nitroaniline the desired radiolabelled sulfonamides were accessible in satisfactory yields owing to systematic variation of the reaction conditions. With respect to the application of the 18F-fluoropropansulfonyl group to the labelling of compounds relevant as imaging agents for positron emission tomography (PET), the stability of N-(4-fluorophenyl)-3-fluoropropanesulfonamide against degradation catalyzed by carboxylesterase was investigated and compared to that of the analogous fluoroacetamide.
Keywords: fluorine-18, hydrolytic metabolism, prosthetic groups, radiochemistry, sulfonamides

Publ.-Id: 18782 - Permalink

Experimental Study of the 22Ne(p,γ)23Na Reaction and its Implications for Novae Scenarios
Menzel, M.-L.;
The 22Ne(p,γ)23Na reaction belongs to the catalytic neon-sodium cycle and has an important role in the explosive hydrogen burning. The neon-sodium cycle takes place at temperatures of T = 0:1 - 0:5GK and is assumed to occur in different astrophysical systems: e.g. in novae, in super novae of type Ia and during the shell-burning of red giant branch stars.

The implications of 22Ne(p,γ)23Na and the neon-sodium cycle in a nova scenario have been studied by using the nuclear network code libnucnet at GSI in Darmstadt. A nova is an outburst of matter in a binary system consisting of a white dwarf and a red giant star. It is therefore a representative phenomenon for explosive hydrogen burning. For the calculation of the nucleosynthesis during the nova outburst, the code libnucnet requires the initial mass composition of the novae partners, the temperature and density proles of the nova explosion and the thermonuclear reaction rates of the participating reactions. In the following, the code determined the ow and the nal atomic abundance in the neon-sodium cycle during the entire nova process. Additionally, the in uence of the temperature prole of the novae outburst as well as the thermonuclear reaction rate of the 22Ne(p,γ)23Na reaction on the nal atomic abundance in the outburst has been studied.

A characteristic measure for the reactions in astrophysical environments is the thermonuclear reaction rate. The reaction rate of 22Ne(p,γ)23Na has still strong uncertainties in the temperature range of T = 0:03-0:3 GK. These uncertainties are based on insucient upper limits of the resonance strengths as well as the possible existence of tentative states that are populated in the energy range of Elabp = 30 - 300 keV. The research presented in this thesis is dedicated to the experimental study of the 22Ne(p,γ)23Na reaction for an improved determination of the thermonuclear reaction rate. Furthermore, the implications of 22Ne(p,γ)23Na and the neon-sodium-cycle in novae scenarios are discussed. The data taking has been performed at the Laboratori Nazionali del Gran Sasso, Italy. This laboratory provides the LUNA facility (Laboratory for Underground Nuclear Astrophysics) for the measurement of small reaction cross sections. The LUNA facility includes a 400 kV ion accelerator, a windowless gas target system and a HPGe-detector. Based on the measurements of the 22Ne(p,γ)23Na reaction at LUNA, upper limits for the strengths of ve isolated resonances in the energy range of Elabp = 150 - 340 keV have been determined.

For the nuclear resonance at Elabres = 186 keV, a positive resonance strength has been measured for the rst time in literature.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-034 2013
    ISSN: 2191-8708


Publ.-Id: 18781 - Permalink

Strömungsprofilmessungen mittels PIV-Verfahren an einem Stabbündel
Franz, R.; Dominguez-Ontiveiro, E.; Barth, T.; Drapeau-Martin, S.; Hampel, U.;
Umströmte Rohr- bzw. Stabbündel sind als Übertrager von Wärmeenergie in einem breiten Spektrum von Anwendungsgebieten zu finden. Beispiele sind Heizkörper, Kühlaggregate, Heizpatronen, industrielle Wärmetauscher und Brennelemente in Kernreaktoren. Für jede dieser Anwendungen besteht die Anforderung, die Wärmeübertragung an den Wärmeübertragerflächen zu optimieren. Dabei besteht eine enge Kopplung zwischen Wärmetransport und Strömungsstruktur. Eine besonders effiziente Form der Wärmeübertragung ist die Verdampfung. Diese wird unter anderem bei Brennelementen in Druckwasserreaktoren genutzt. Hier siedet das Kühlwasser an der Brennstaboberfläche. Durch Kondensation der Dampfblasen in der unterkühlten Kernströmung wird die Wärme dann effizient in die Flüssigphase übertragen. Durch die hohe Verdampfungsenthalpie des Wassers wird beim Strömungssieden ein viel höherer Wärmestrom in das Kühlwasser übertragen, als bei rein einphasig-konvektivem Wärmetransport. Sicherheitstechnisch relevant für Brennelemente in Leichtwasserreaktoren ist der Übergang vom Blasensieden zum Filmsieden (kritischer Wärmestrom). Dieser muss unter allen Umständen vermieden werden, um die Integrität der Brennstabhüllen zu gewährleisten, die bei Überschreiten der kritischen Heizflächenbelastung aufschmelzen bzw. reißen können. Aus diesem Grund werden im Rahmen eines vom Bundesministerium für Bildung und Forschung geförderten Projektes (Förderkennzeichen 02NUK010A) numerische Strömungsberechnungsmodelle entwickelt, die bei der Beschreibung und numerischen Behandlung der Siedephänomene helfen sollen. Zur Validierung dieser Modelle anhand von Experimenten wurde ein Strömungskanal konstruiert, in dem ein vertikales Stabbündel von einem Kältemittel (RC318) aufwärtig durchströmt wird. Der Versuchsstand ist so konzipiert, dass ein optischer und messtechnischer Zugang zu den umströmten Einbauten gegeben ist. Damit sind Messungen in Zweiphasenströmungen ebenso möglich, wie Untersuchungen zur einphasigen Durchströmung. Für später erfolgende Zweiphasen-Experimente mit Stabbeheizung wurden zunächst Voruntersuchungen zur einphasigen Durchströmungen durchgeführt, welche insbesondere Aufschluss über die Homogenität der Strömung in den Unterkanälen sowie die Existenz von Querströmungen geben sollten. Als Messverfahren dafür wurde die Particle Image Velocimetry (PIV) ausgewählt, welche es ermöglicht, zweidimensionale Strömungsfelder aufzuzeichnen. Die experimentellen Studien erfolgten am Optical Multi-Phase Flow Research Laboratory des Nuclear Engineering Department der Texas A&M University in College Station, USA.
Die Untersuchungen wurden für drei Volumenstromraten durchgeführt. Der vorliegende Bericht umfasst die Beschreibung des Versuchsstandes und der Messmethodik, eine Vorstellung des Auswerteverfahrens und relevanter Ergebnisse sowie eine Fehlerbetrachtung.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-033 2013
    ISSN: 2191-8708


Publ.-Id: 18780 - Permalink

Entwicklung und Validierung von Modellen für Blasenkoaleszenz und -zerfall
Liao, Y.; Lucas, D.;
Ein neues, verallgemeinertes Modell für Blasenkoaleszenz und –zerfall wurde entwickelt. Es basiert auf physikalischen Überlegungen und berücksichtigt verschiedene Mechanismen, die zu Blasenkoaleszenz und –zerfall führen können. In einer ausführlichen Literaturrecherche wurden zunächst die verfügbaren Modelle zusammengestellt und analysiert. Es zeigte sich, dass viele widersprüchliche Modelle veröffentlicht wurden. Keins dieser Modelle erlaubt die Vorhersage der Entwicklung der Blasengrößenverteilungen entlang einer Rohrströmung für einen breiten Bereich an Kombinationen von Volumenströmen der Gas- und der Flüssigphase.
Das neue Modell wurde ausführlich in einem vereinfachten Testsolver untersucht. Dieser erfasst zwar nicht alle Einzelheiten einer sich entlang des Rohres entwickelten Strömungen, erlaubt aber im Gegensatz zu den CFD-Simulationen eine Vielzahl von Variationsrechnungen zur Untersuchung des Einflusses einzelner Größen und Modelle. Koaleszenz und Zerfall kann nicht getrennt von anderen Phänomenen und Modellen, die diese widerspiegeln, betrachtet werden. Es bestehen enge Wechselwirkungen mit der Turbulenz der Flüssigphase und dem Impulsaustausch zwischen den Phasen. Da die Dissipationsrate der turbulenten kinetischen Energie ein direkter Eingangsparameter für das neue Modell ist, wurde die Turbulenzmodellierung besonders genau untersucht.
Zur Validierung des Modells wurde eine TOPFLOW-Experimentalserie zur Luft-Wasser-Strömungen in einem 8 m langen DN200-Rohr genutzt. Die Daten zeichnen sich durch eine hohe Qualität aus und wurden im Rahmen des TOPFLOW-IIVorhabens mit dem Ziel eine Grundlage für die hier vorgestellten Arbeiten zu liefern, gewonnen. Die Vorhersage der Entwicklung der Blasengrößenverteilung entlang des Rohrs konnte im Vergleich zu den bisherigen Standardmodellen für Blasenkoaleszenz und -zerfall in CFX deutlich verbessert werden. Einige quantitative Abweichungen bleiben aber bestehen.
Die vollständigen Modellgleichungen sowie eine Implementierung über „User-FORTRAN“ in CFX stehen zur Verfügung und können für weitere Arbeiten zur Simulation polydisperser Blasenströmungen genutzt werden.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-032 2013
    ISSN: 2191-8708


Publ.-Id: 18779 - Permalink

Annual Report 2012 - Institute of Ion Beam Physics and Materials Research
Cordeiro, A. L.; Fassbender, J.ORC; Heera, V.; Helm, M.
In 2012 the HZDR, and in consequence also the Institute of Ion Beam Physics and Materials Research (IIM) including its Ion Beam Center (IBC), has undergone a scientific evaluation. The evaluation committee composed of the Scientific Advisory Board and numerous external experts in our field of research concluded that “the overall quality of the scientific work is excellent”, that “there are an impressive number of young scientists working enthusiastically on a variety of high-level projects” and that “the choice of these projects represents a clear underlying strategy and vision”. We feel honored and are proud that the external view on our scientific achievements is that extraordinary. In view of this outstanding result we would like to express our gratitude to all our staff members for their commitment and efforts!
In the past year, we continued our integration into the Helmholtz Association of German Research Centers (HGF) with our Institute mostly active in the research area “Matter”, but also involved in a number of activities in the research area “Energy”. In this respect, many consultations were held with the Helmholtz centers contributing to common research areas to precisely define the role we will play in the newly established HGF program “From Matter to Materials and Life” (see schematic below). Our IBC has been recognized as a large-scale user facility for ion beam analysis and modification of materials, i.e., specializing on materials science. In particular, the IBC plays a prominent role in the recently approved Helmholtz Energy Materials Characterization Platform (HEMCP), which mainly concentrates on the development of dedicated analytical tools for the characterization of materials required for future energy technologies. The successes achieved by the IBC allows us to invest 7200 k€ to further improve and strengthen the ion beam capabilities at the Institute. In addition to this infrastructure-related grant, we were also successful in our funding application for the establishment of the International Helmholtz Research School for Nanoelectronic Networks (IHRS NANONET), aiming at promoting the next generation of leading scientists in the field of nanoelectronics. The IHRS NANONET is coordinated by our Institute and offers a well-structured PhD program to outstanding students of all nationalities with emphasis on interdisciplinary research and comprehensive training in technical and professional skills.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-031 2013
    ISSN: 2191-8708


Publ.-Id: 18778 - Permalink

Annual Report 2012 - Institute of Resource Ecology
Brendler, V.; Foerstendorf, H.; Bok, F.; Richter, A.; (Editors)
The Institute of Resource Ecology (IRE) is one of the currently eight institutes of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The research activities are fully integrated into the program “Nuclear Safety Research” of the Helmholtz Association and focused on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors”. With the integration of the division of “Reactor Safety” from the former “Institute of Safety Research” nuclear research at HZDR is now mainly concentrated within this institute.
In addition, various activities have been started investigating chemical and environmental aspects of processing and recycling of strategic metals, namely rare earth elements. Here, a knowledge transfer from the nuclear to the non-nuclear community, branching thermodynamics and spectroscopy, has been established. This also strengthens links to the recently established “Helmholtz-Institute Freiberg for Resource Technology”.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-030 2013
    ISSN: 2191-8708


Publ.-Id: 18777 - Permalink

Nanomaterialien – Einsatz in der Tumordiagnostik und Therapie
Stephan, H.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Kolloquium, Hochschule Zittau/Görlitz (FH), 08.05.2013, Zittau, Deutschland

Publ.-Id: 18776 - Permalink

Tumor imaging using copper-64 labeled peptides
Stephan, H.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Seminar, Beijing Normal University, College of Chemistry, 19.04.2013, Beijing, China

Publ.-Id: 18775 - Permalink

Instrument V4: Topic 1 - SANS investigation of irradiation-induced defects in RPV steels; Topic 2 - Characterization of nanoparticles in ODS Fe-Cr model alloys
Ulbricht, A.;
Topic 1: Hardening combined with embrittlement of the reactor pressure vessel (RPV) due to the neutron irradiation during the operation of a nuclear power plant is one of the most safety-relevant phenomena. So far, design and safe operation have mainly relied on a predominantly empirical approach based on long-term irradiation programs in test reactors as well as on mechanical testing in specialized hot cells. However, the physical mechanism of radiation damage is not yet understood in detail. The microstructure that arise in RPV steels, primarily as a consequence of radiation-enhanced diffusion and defect clustering, are extremely fine-scaled, i.e. in magnitude of few nanometers. Among the experimental methods capable of detecting and characterizing irradiation-induced clusters small-angle neutron scattering is the only technique allowing a statistically representative size distribution of clusters to be calculated.
The measurements carried out on the instrument V4 have contributed to the understanding of the
• cluster formation under different irradiation conditions (temperature, neutron fluence and flux),
• effect of impurities and alloying elements on the formation of irradiation-induced clusters,
• cluster dissolution and/or coarsening after post-irradiation annealing treatments,
• reirradiation behaviour of materials.
The instrument V4 is particularly suitable for such kind of investigations because of the special equipment – an evacuated sample environment with electromagnet and a 14 position sample changer. This allows measurements with low background noise particularly important for the detection of very small scatterers such as irradiation-induced clusters.

Topic 2: Ferritic-martensitic chromium steels are candidate materials for future application in both Gen-IV fission and fusion technology. In order to improve irradiation-creep properties and to reduce detrimental helium effects oxide-dispersion strengthened (ODS) variants of these steels are of prime interest. Due to the complex microstructures of these ODS steels there is a multitude of hardening features, such as Y2O3 particles, carbides and alpha'-phase particles, that may also affect the brittle-to-ductile transition. Therefore, the fabrication and characterization of dedicated model alloys is an important means in order to separate individual effects and to improve mechanistic understanding.
The quality of the ODS material produced by means of a special procedure of powder metallurgy was checked and characteristics of ODS nanoparticles were determined by SANS.
Keywords: Small-angle neutron scattering, irradiation-induced cluster, reactor pressure vessel steel, Fe-Cr alloy, ODS, nanoparticle
  • Invited lecture (Conferences)
    Review of Neutron Scattering Instruments at BER II, 07.-08.05.2013, Berlin, Deutschland

Publ.-Id: 18774 - Permalink

Short note on the hydrolysis and complexation of neptunium(IV) in HEPES solution
Dahou, S.; Hennig, C.; Moisy, P.; Petit, S.; Scheinost, A. C.; Subra, G.; Vidaud, C.; Den Auwer, C.;
The speciation of actinides in environmental or biological media is often difficult to assess because it involves complex media. We would like to report here on the properties of Np(IV) cation in the well known biological HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) buffer medium. HEPES has been targeted because the possibility to use this biological buffer in actinide toxicological studies presents several advantages although the possible effects of concentrated HEPES medium on the hydrolysis of the actinides (in particular at oxidation state +IV) has not been studied yet. A combination of spectrophotometric and EXAFS measurements at the Np L III edge shows that stable hydrolyzed neptunium(IV) clusters are obtained between pH 2.5 and 4. In a second step, in order to better understand the reactivity of these hydrolysis species formed in HEPES, the effect of a strong chelating ligands such as the hydroxamic acid (HA) or desferrioxamine (DFO) siderophores has been also investigated using spectrophotometry and EXAFS. Upon addition of HA or DFO, the hydrolyzed clusters of Np(IV) are unstable and monomeric complexes are formed and yield Np environments that are very similar to that of crystallized Pu-DFOE complex [Al(H2 O)6 ][Pu(DFE)(H2 O)3 ]2 (CF3 SO3 )5 ·10H2 O reported in the literature.
Keywords: Neptunium HEPAS EXAFS

Publ.-Id: 18773 - Permalink

Comparison of simulations with PHITS and HIBRAC with experimental data in the context of particle therapy monitoring
Rohling, H.; Sihver, L.; Priegnitz, M.; Enghardt, W.; Fiedler, F.;
Therapeutic irradiation with protons and ions is advantageous over radiotherapy with photons due to its favorable dose deposition. Additionally, ion beams provide a higher Relative Biological Effectiveness (RBE) than photons. For this reason an improved treatment of deep seated tumors is achieved and normal tissue is spared. However, small deviations from the treatment plan can have a large impact on the dose distribution. Therefore, a monitoring is required to assure the quality of the treatment. Particle Therapy Positron-Emission-Tomography (PT-PET) is the only clinically proven method which provides a non-invasive monitoring of dose delivery. It makes use of the ß+-activity produced by nuclear fragmentation during irradiation. In order to evaluate these PT-PET-measurements, simulations of the ß+-activity are necessary. Therefore, it is essential to know the yields of the ß+-emitting nuclides at every position of the beam path as exact as possible. We evaluated the 3D Monte-Carlo simulation tool PHITS (version 2.30) and the 1D deterministic simulation tool HIBRAC with respect to the production of ß+-emitting nuclides. The yields of the most important ß+-emitting nuclides for carbon, lithium, helium, and proton beams have been calculated. The results were then compared to experimental data obtained at GSI Helmholtzzentrum für Schwerionenforschung Darmstadt, Germany. GEANT4 simulations provide an additional benchmark. For PHITS the impact of different nuclear reaction models, total cross section models and evaporation models on the ß+-emitter production has been studied. In general, PHITS underestimates the yields of positron-emitters and cannot compete with GEANT4 so far. The ß+-emitters calculated with an extended HIBRAC code were in good agreement with the experimental data for carbon and proton beams and comparable to the GEANT4 results. Considering the simulation results and its speed compared with 3D Monte-Carlo tools, HIBRAC is a good candidate for the implementation in clinical routine PT PET.
Keywords: Simulation, Particle Therapy PET, PHITS, HIBRAC
  • Poster
    HITSRS2013 - Heavy Ion in Therapy and Space Radiation Symposium 2013, 15.-18.05.2013, Chiba, Japan
  • Open Access LogoAbstract in refereed journal
    Journal of Radiation Research 55 suppl1(2014), i43-i44
    DOI: 10.1093/jrr/rrt151

Publ.-Id: 18772 - Permalink

Titel der Publikation Test RODARE
Schmeißer, N.ORC; Konrad, U.ORC; Test, R.ORC
Abstract* (30001 Byte)
ASCII/ ANSI/ Unicode (UTF-8) kopierbar über Zwischenablage
Enthält der Abstract keine HTML-Zeilenumbrüche, werden ASCII-Umbrüche als solche interpretiert.
in der Sprache der Publikation, ggf. zusätzlich in Englisch
Keywords: Keyword1, Keyword2,Keyword3 Keyword4, Keyword5
  • Lecture (others)
    Test-Veranstaltung, 07.05.2019, HZDR, Germany, Dresden
    Test: DOI: 10.14278/rodare.248


Publ.-Id: 18770 - Permalink

Flüssigmetallbatterien als stationäre Speicher
Weier, T.; Weber, N.; Stefani, F.; Galindo, V.; Seilmayer, M.;
Flüssigmetallbatterien, d.h. elektrochemische Hochtemperaturbatterien mit vollständig flüssigem Inventar, werden derzeit als preiswerte Regelenergiespeicher diskutiert. Das ursprünglich auf kleinere Zellen als Bestandteil thermisch regenerierbarer Systeme gerichtete Konzept soll auf Zellen mit Grundflächen im Quadratmeterbereich übertragen werden.

Eine elektrochemische Zelle mit vollständig flüssigem Inventar hat eine Reihe von Vorteilen: bei gut abgestimmten Dichten von Elektrolyt und aktiven Materialien ist die Batterie selbstassemblierend, eine stabile Dichteschichtung bildet sich aus. Die strukturlosen (flüssigen) Elektroden sind für Alterungserscheinungen unanfällig, versprechen somit gute Zyklierbarkeit, die Kinetik an den flüssig-flüssig Phasengrenzen und die Diffusionsprozesse sind vergleichsweise schnell, was hohe Stromdichten ermöglicht. Als aktive Materialien können breit und ökonomisch verfügbare Ausgangsstoffe eingesetzt werden. Natrium-Schwefel und Natrium-Nickelchlorid Zellen teilen eine Reihe der obengenannten Vorteile, erfordern wegen der komplexen Konstruktion jedoch ein beträchtliches Investitionsvolumen. Die Ausnutzung positiver Skaleneffekte ist ein wichtiges Mittel zur Kostensenkung und die einfache Skalierbarkeit eine der grundlegenden Annahmen bei der Entwicklung von Flüssigmetallbatterien.

Hohe Stromdichten und große Phasengrenzflächen resultieren jedoch in erheblichen Zellströmen. Diese generieren Magnetfelder und mithin beträchtliche elektromagnetische Kräfte. Das flüssige Inventar der Zelle kann auf diese elektromagnetischen Einwirkungen mit Instabilitäten reagieren. Eine dieser Instabilitäten ist die Tayler-Instabilität. Sie führt zu einer starken Strömung im Zellvolumen, die in der Lage ist, die Dichteschichtung zu destabilisieren. In der Folge käme es zu einem Direktkontakt der Elektroden und einem Versagen der Zelle. Der Tayler-Instabilität lässt sich durch konstruktive Maßnahmen begegnen, die in der Lage sind, die gewünschte Skalierbarkeit zu gewährleisten.
Keywords: liquid metal battery, Tayler instability, magnetohydrodynamics
  • Poster
    2.Dresdner Konferenz "Zukunft Energie", 28.-29.05.2013, Dresden, Deutschland

Publ.-Id: 18768 - Permalink

Fluid dynamic aspects of large liquid metal batteries
Weier, T.; Weber, N.; Stefani, F.; Galindo, V.; Seilmayer, M.;
Liquid metal batteries (LMBs) are currently discussed as a means to provide economic grid-scale energy storage. LMBs are all-liquid electrochemical cells, typically containing an alkali metal as the negative, and a metal or half metal as the positive electrode. Due to their different densities, both metals form distinct horizontal layers separated by a molten salt with a density in between those of both metals. The molten salt acts as the electrolyte. Evidently, LMBs need elevated temperatures to function. However, they have a number of distinct advantages as, to name a few, self-assembly, ease of construction and scalability, high current densities, and potentially very long cycle life.
Due to the completely liquid inventory and the high total cell currents, fluid dynamics plays an important role for the operation of LMBs. We will focus on the occurrence and prevention of fluid dynamic instabilities in LMBs, especially the current driven Tayler instability (TI). Since the density differences between negative electrode and molten salt are typically small, fluid dynamic instabilities can provoke mixing of electrode and electrolyte material leading to an internal shorting of the cell. Both experimental as well as numerical results will be presented and discussed in relation to cell design and choice of active materials.
Keywords: liquid metal battery, Tayler instability, magnetohydrodynamics
  • Lecture (Conference)
    3rd International Conference on Energy Process Engineering, 03.-06.06.2013, Frankfurt am Main, Deutschland
  • Contribution to proceedings
    3rd International Conference on Energy Process Engineering, 03.-06.06.2013, Frankfurt am Main, Deutschland
    Proceedings of the 3rd International Conference on Energy Process Engineering

Publ.-Id: 18767 - Permalink

Theory of thermoelectric transport in layered structures
Hinsche, N. F.; Yavorsky, B. Y.; Mertig, I.; Zahn, P.;
The thermoelectric transport properties of layered structures are analyzed by means of first-principles calculations and semi-classical Boltzmann theory. The electronic structure of the systems was calculated by means of a fully relativistic screened Korringa-Kohn-Rostoker Greens function method. The transport properties along in-plane and cross-plane direction were obtained within the relaxation time approximation of the Boltzmann theory.
We studied the change in thermoelectric properties due to symmetry breaking in Si and Si/Ge heterostructures. The anisotropy of the electrical conductivity, the thermopower and the resulting power factor are studied in dependence on doping level, temperature, and strain in [001] and [111] direction. Our results show that tetragonal [1] and rhombohedral [2] distortions have a strong influence on the thermoelectric transport properties.
Furthermore, we investigated the influence of strain and lattice period in Bi2Te3/Sb2Te3-heterostructures which show a remarkable enhancement of the thermoelectric figure of merit compared to the bulk materials [3]. To identify the physical origin, we studied the influence of composition, interfacial strain, and doping in detail. In addition, insights on the Lorenz function, the electronic contribution to the thermal conductivity, and the resulting figure of merit are given [4,5].


[1] N. F. Hinsche, I. Mertig, and P. Zahn, J. Phys.: Cond. Matt. 23, 295502 (2011)
[2] N. F. Hinsche, I. Mertig, and P. Zahn, Thermoelectric transport in strained Si and Si/Ge heterostructures, J. Phys.: Cond. Mat. 24, 275501 (2012)
[3] R. Venkatasubramanian, E. Siivola, T. Colpitts, and B. O’Quinn, Nature 413, 597 (2001)
[4] N. F. Hinsche, B. Yu. Yavorsky, M. Gradhand, M. Czerner, M. Winkler, J. König, H. Böttner, I. Mertig, and P. Zahn, Thermoelectric transport in Bi2Te3/Sb2Te3 superlattices, Phys. Rev. B 86, 085323 (2012)
[5] N. F. Hinsche, I. Mertig, and P. Zahn, Lorenz function of Bi2Te3/Sb2Te3 superlattices, J. Electronic Materials, 10.1007/s11664-012-2279-z (DOI) (2012)
Keywords: Thermo-electric transport, power factor, Seebeck coefficient, electrical conductivity, thermal conductivity, electronic contribution to thermal conductivity, figure of merit, multilayer, strain, Bi2Te3/Sb2Te3, Si(100), Si(111), Si/Ge(111)
  • Invited lecture (Conferences)
    529. WE-Heraeus-Seminar - Thermal transport at the nanoscale, 07.-10.04.2013, Bad Honnef, Deutschland

Publ.-Id: 18766 - Permalink

Spin Nernst Angle: Definition and qualitative Estimate for Cu Alloys
Zahn, P.; Gemming, S.;
The spin Nernst effect describes the occurrence of a spin current perpendicular to an applied thermal gradient and the spin quantization axis in a non-magnetic material. To quantify the effect, the spin Nernst angle will be defined in a more general way than in ref. [1]. This allows for a clear separation of the transverse spin current into two opposite contributions proportional to the spin Hall angle and the spin Nernst angle, respectively. Qualitative trends for Cu alloys with 3d, 4d, and 5d defects extending a resonant scattering model by Fert and Levy [2] will be presented.

The work was supported by the Initiative and Networking Fund of the German Helmholtz Association, Helmholtz Virtual Institute MEMRIOX (VH-VI-442).

[1] K. Tauber et al., Phys. Rev. Lett. 109, 026601 (2012)

[2] A. Fert and P.M. Levy, Phys. Rev. Lett. 106, 157208 (2011)
Keywords: Spin-Nernst-effect, spin-caloric, thermo-electric, alloys, defect scattering, spin-orbit coupling, spin-dependent transport phenomena
  • Lecture (Conference)
    DPG Frühjahrstagung, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18765 - Permalink

The “quiete Goldschmidt” - a mechanochemical, thermoanalytical, and spectroscopic study of selected steps of the aluminothermic reaction
Stößer, R.; Feist, M.; Willgeroth, C.; Emmerling, F.; Menzel, M.; Reuther, H.;
The Goldschmidt reaction (2 Al + α-Fe2O3) was investigated both under mechanical and thermal activation by employing a combination of analytical methods such as ESR and Mössbauer spectroscopies, magnetic susceptibility, X-ray powder diffraction (XRD), and thermal analysis (TA). Both the mechanical treatment and the TA runs under air caused the reaction conditions of “quiete redox reactions” due to a retarding effect and enabled a reaction study in a “slow motion mode”. This allowed to establish distinct partial steps of the integral reaction process depending on the intensity of the mechanical impact, the educt composition, the gas phase composition, and, finally, the thermal excitation in the TA runs.

Publ.-Id: 18764 - Permalink

Mössbauer-spectroscopic study of the effect of He+ irradiation on model Fe-Cr alloys
Dubiel, S. M.; Cieslak, J.; Reuther, H.;
Effect of 25 keV He ion irradiation on three model Fe100−xCrx alloys (x = 5.8, 10.75 and 15.15) was investigated by means of the conversion electron Mössbauer spectroscopy. A short-range ordering (SRO) parameter concerning a distribution of Cr atoms within the first-two neighbour shells, <α12>, for all three non-irradiated samples was positive, hence indicative of ordering, yet its amplitude, hence the degree of ordering, was decreasing with x. For the samples irradiated to the dose of 1.2·1017 He+/cm2 (7.5 dpa) <α12 > was unaffected for x = 5.8 and 10.75 but its value was negative for x = 15.15 i.e. an irradiation-induced inversion of the SRO-parameter occurred.
Keywords: Mösbauer spectroscopy; Fe–Cr alloys; Short-range ordering; He ion irradiation

Publ.-Id: 18763 - Permalink

Cross-Section Measurements of the 86Kr(gamma,n) Reaction to Probe the s-Process Branching at 85Kr
Raut, R.; Tonchev, A. P.; Rusev, G.; Tornow, W.; Iliadis, C.; Lugaro, M.; Buntain, J.; Goriely, S.; Kelley, J. H.; Schwengner, R.; Banu, A.; Tsoneva, N.;
We have carried out, for the first time, photodisintegration cross-section measurements on 86Kr using monoenergetic photon beams ranging from the neutron separation energy, Sn = 9.86 MeV, to 13 MeV. We combine our experimental 86Kr(,n)85Kr cross section with results from our recent 86Kr(gamma,gamma) measurement below the neutron separation energy to obtain the complete nuclear dipole response of 86Kr. The new experimental information is used to predict the neutron capture cross section of 85Kr, an important branching point nucleus on the abundance flow path during s-process nucleosynthesis. Our new and more precise 85Kr(n,)86Kr cross section allow us to consider models of asymptotic giant branch (AGB) stars. We find that models of mass smaller than the sun mass, where the 13 C neutron source burns convectively rather than radiatively, represent a possible solution for explaining the highest 86Kr/82Kr ratios observed in meteoritic stardust SiC grains.
Keywords: photodissociation, monoenergetic gamma rays, neutron detection, (gamma,n) cross section, s-process branching point.

Publ.-Id: 18762 - Permalink

Experimental and numerical study of flow in a precessing cylinder
Albrecht, T.; Gundrum, T.; Stefani, F.;
Precession has long been discussed as a complementary energy source for homogeneous dynamo action. To that end, DRESDYN, a large scale, precession driven dynamo experiment, is currently in advanced planning stage at Helmholtz-Zentrum Dresden-Rossendorf. DRESDYN will consist of a variable axis, precessing cylinder of approximately 2m diameter filled with liquid sodium.

Preliminary studies using a 1:6 scale water experiment are currently performed, focussing on laminar-turbulent transition characteristics. A sudden jump in the motor's mesured electrical power suggests transition to occur at a precession rate of $\Gamma = 0.06$. We also conduct Direct Numerical Simulations, although, for the time being, limited to a Reynolds number Re = O(6000), which is ten times smaller than in the water experiment.

At the conference, we will introduce the planned setup of DRESDYN and show first experimental and numerical results for the 1:6 water model.
Keywords: precession, cylinder, DNS, water experiments, DRESDYN
  • Lecture (Conference)
    Bifurcations and Instabilities in Fluid Dynamics 2013, 08.-11.07.2013, Haifa, Israel

Publ.-Id: 18761 - Permalink

Bubble-driven liquid metal flows under the influence of AC magnetic fields
Vogt, T.; Zhang, C.; Andruszkiewicz, A.; Eckert, K.; Odenbach, S.; Eckert, S.; Gerbeth, G.;
Mixing of liquid metals is an important issue in many industrial applications. In metallurgy, gas-bubbles are injected into furnaces, ladles or similar melt containing transfer vessels in order to homogenize the melt and their physical and chemical parameters. We present two experimental studies where a mixing enhancement in a gas-stirred ladle is achieved by the use of AC magnetic fields.
  • Lecture (Conference)
    The International Symposium on Electromagnetic Flow Control in Metallurgy, Crystal Growth and Electrochemistry, 25.-27.03.2013, Dresden, Deutschland

Publ.-Id: 18760 - Permalink

Transient Taylor-Görtler vortex flow in a spinning liquid metal
Vogt, T.; Grants, I.; Räbiger, D.; Eckert, S.; Gerbeth, G.;
This paper is concerned with a liquid metal flow driven by a rotating magnetic field inside a stationary cylinder. We consider especially the secondary meridional flow during the time when the fluid spins up from rest.
Therefore, we filled a Perspex cylinder with the aspect ratio A=H0/D0=2 with the eutectic alloy GaInSn, which is liquid at room temperature. The filled cylinder is placed concentrically in the magnetic induction system PERM at the Helmholtz-Zentrum Dresden-Rossendorf. The PERM stirrer is equipped with six coils, arranged as pole pairs in order to create a rotating magnetic field with field strength up to 17 mT. The magnetic field frequency was fixed to 50 Hz. The developing flow is investigated experimentally and by direct numerical simulations. The fluid velocities are measured non-intrusively using the ultrasound Doppler velocimetry.
Evolving instabilities in the form of Taylor–Görtler vortices have been observed just above the instability threshold (Ta > 1.5*Tacr). They evolve from local spots near midplane that quickly spread around the whole circumference of the cylinder to form closed rings. Subsequently, the central TG-vortex ring is advected by the secondary flow towards the top or bottom of the vessel. In some cases, the central vortex pair is observed to remain stable at half height of the vessel for a long time. The rotational symmetry may survive over a distinct time even if a first Taylor–Görtler vortex pair has been formed as closed rings along the cylinder perimeter. The transition to a three dimensional flow in the side layers results from the advection or a precession and splitting of the Taylor–Görtler vortex rings. The predictable behaviour of the Taylor–Görtler vortices disappears with increasing magnetic field strength. The numerical simulations agree very well with the flow measurements.
Keywords: Transition, Tayler-Görtler, Vortices
  • Lecture (Conference)
    Bifurcations & Instabilities in Fluid Dynamics - 4th International Symposium, 08.-11.07.2013, Haifa, Israel

Publ.-Id: 18759 - Permalink

Persistent Current Reduction in Metal-Semiconductor FETs With a ZnCoO Channel in an External Magnetic Field
Kaspar, T.; Fiedler, J.; Skorupa, I.; Bürger, D.; Mücklich, A.; Fritzsche, M.; Schmidt, O. G.; Schmidt, H.;
Transparent metal-semiconductor field-effect transistors (MESFETs) with a ZnCoO channel have been fabricated by pulsed laser deposition on c-plane sapphire substrates at a temperature of 550 degrees C. The paramagnetic properties have been confirmed by magnetotransport measurements on undepleted ZnCoO films without Schottky gate contacts.
The Au/AgxO Schottky gate contacts were processed by optical lithography and metallization. Below 50 K, the MESFET characteristics are persistently changed from a low resistance state (LRS) to high resistance state by an external magnetic field. The MESFET can be switched back into the LRS only by heating it up to room temperature.
Keywords: metal-semiconductor field-effect transistor

Publ.-Id: 18758 - Permalink

Electromagnetic flow control in poor conductors
Albrecht, T.; Stiller, J.; Metzkes, H.; Weier, T.; Gerbeth, G.;
Lorentz force-based flow control in materials with low electrical conductivity has a long history back to the first half of the 19th century. This review will focus on developments during the last two decades, collecting results from numerical simulations and laboratory experiments. Typically, the actuators consist of permanent magnets and electrodes flush-mounted with the surface, generating Lorentz forces in the fluid layers adjacent to the wall. We will discuss the application of Lorentz forces to reduce friction drag in turbulent boundary layers and to delay boundary layer transition. The control of separated flows and shear layers is another key aspect of the review. Energetic efficiency, one of the main criteria for flow control, and its relation to typical operating conditions will be analyzed as well. Lorentz forces can be successfully used to control a broad range of flow phenomena and are a versatile tool for basic fluid dynamics research. However their current applicability in large scale systems is hampered by the low electrical to mechanical efficiency intrinsic to actuators based on the magnetic fields delivered by today’s permanent magnets.
Keywords: EMHD, flow control, boundary layer control, separation control, transition control

Publ.-Id: 18757 - Permalink

Deriving forces from 2D velocity field measurements
Albrecht, T.; Del Campo, V.; Weier, T.; Metzkes, H.; Stiller, J.;
We discuss how to derive a force or a force density from a measured velocity field. The first part focuses on the integral force a fluid exerts on a body, e.g. lift and drag on an airfoil. Obtaining the correct pressure is crucial; however, it cannot be measured within the flow non-intrusively. Using numerical and experimental test cases, we compare the accuracy achievable with three methods: pressure reconstruction from velocity fields via (1) the differential momentum equation, or (2) the Poisson equation, furthermore, (3) Noca’s momentum equation [Noca, JFS 13(5), 1999], which does not require pressure explicitly. The latter gives the best results for the lift, whereas the first or second approach should be used for the drag. The second part deals with obtaining the distribution of a body force density generated by an actuator. Using a stream function ansatz, we obtain a Laplace equation that allows us to compute the solenoidal part of the force distribution; however, the irrotational part is lost. Furthermore, the wall pressure must be known. We validate this approach using numerical data from a wall jet flow in a rectangular box, driven by a fictitious, solenoidal body force. Reconstructing the force distribution yields an error of less than 10−2 for most of the domain.
Keywords: PIV, force measurement

Publ.-Id: 18756 - Permalink

Synthesis of multi trace element doped Fe0.6Mn0.4Ta2O6 tantalite reference crystals by Czochralski method
Michalak, P.-P.; Uecker, R.; Galazka, Z.; Munnik, F.; Renno, A. D.; Merchel, S.;
Quality assurance of natural raw materials (e.g. ores) with beam-based microanalytical methods requires a proper set of homogeneous, matrix-matched reference materials (RMs) doped with trace elements relevant to resource technology applications. Natural minerals usually exhibit chemical heterogeneity at μg/g sampling masses and are unsuitable as RMs for in-situ chemical microanalysis. On the other hand, available synthetic RMs (e.g. glasses, pressed pellets) fail to satisfy matrix-match criterion.
A novel strategy has been established to obtaining such RMs through the synthesis of multi trace element doped phases that would be subsequently tested for chemical and structural homogeneity with both microscopic and spectroscopic spatially-resolved microanalytical methods.
A dark brown tantalite crystal from the melt of composition Fe0.6Mn0.4Ta2O6 has been grown by the conventional Czochralski method (melting point of about 1600°C) with the use of an Ir crucible and a protective atmosphere consisting of 85% Ar, 10% CO2 and 5% CO. The growth rate of 1 mm/h and rotation rate of 10 rpm were applied. The boule was 17 mm in diameter and 30 mm in length (Fig. 1). Standard mineralogical thin sections were prepared for chemical analysis.
Back-scatter Electrons imaging (BSE) was implemented to check for the presence of impurities and other phases within the crystal. Electron Probe Microanalysis (EPMA) and Particle Induced X-ray Emission (PIXE) were used to determine the composition and homogeneity of the crystal. Compositional maps were prepared for each element for each method. As shown in Fig. 2 both BSE-EPMA and PIXE consistently proved stoichiometric composition of the crystal what is in agreement with stoichiometric composition of the melt. EPMA and PIXE compositional maps showed homogenous lateral distribution of all constituents of the crystal (Fig. 3).
The obtained tantalite phase turned out to be homogenous and stable. A matrix of the same stoichiometry will be used in further experiments – synthesis of tantalite crystals doped with different sets of technological trace elements - Sc, Ti; Y, Zr, W; La, Ce, Nd – each at concentration of 0.01 wt%.
Fig. 2
Mg wt% Ca wt% Fe wt% Mn wt% Ta wt% O wt% Total
EPMA 0.000048 0.00013 5.94 4.29 70.38 18.51 99.13
PIXE b.d. b.d. 6.44 4.08 70.98 18.50 100.00
b.d.= below limit of detection
Fig. 1 Tantalite boule
Fig. 3 PIXE Fe-Kα intensity distribution map
Keywords: IBA, reference material, EPMA, PIXE
  • Poster
    17th International Conference on Crystal Growth and Epitaxy (ICCGE-17), 11.-16.08.2013, Warszawa, Polska

Publ.-Id: 18755 - Permalink

‘Freiberg Strategy’ for obtaining matrix-matched reference materials for resource-related microanalytical methods technology
Michalak, P.-P.; Renno, A. D.; Merchel, S.; Munnik, F.; Gutzmer, J.; Uecker, R.; Galazka, Z.; Heller, H.-P.; Radtke, M.; Reinholz, U.;
Quality assurance of natural raw materials (e.g. ores) requires thorough studies on concentration and spatial distribution patterns of technologically relevant trace elements within the mineral matrix at the microscale. Obtaining such a goal is yet only possible with the use of beam-based microanalytical methods and a proper set of homogeneous, matrix-matched reference materials (RMs) doped with trace elements relevant to resource technology.
Natural minerals usually exhibit chemical heterogeneity at μg/g sampling masses and are unsuitable as RMs for in-situ chemical microanalysis. On the other hand, available synthetic RMs (e.g. glasses, pressed pellets) fail to satisfy matrix-match criterion.
A collaboration involving several German scientific institutions centered around TU Bergakademie Freiberg proposed a novel strategy for obtaining such RMs through the synthesis of multi trace element doped mineral matrices subsequently tested for chemical and structural homogeneity with both microscopic and spectroscopic (RMs-dependent and absolute) microanalytical methods.
Three mineral matrices vital to resource technology applications – pyrite, tantalite and feldspar – have been synthesized using flux method, Czochralski method and alkoxide-based sol-gel synthesis, respectively and doped with various sets of technologically important trace elements at the concentration range found in corresponding natural minerals. Their spatial chemical micro-homogeneity has been investigated using light and electron microscopy as well as RMs–dependent (EPMA, LA-ICP-MS) and absolute (PIXE, PIGE) analytical methods.
Quantitative and qualitative elemental spatial distribution maps have been obtained for major and trace elements for each matrix. Homogeneity of the matrices was evaluated using petrologically sensitive statistical analysis.
Established homogeneity testing protocol will be employed in the next stages of the project.
Keywords: reference material, microhomogeneity, pyrite, tantalite, feldspar, IBA, PIXE, PIGE
  • Poster
    Goldschmidt 2013, 25.-30.08.2013, Firenze, Italia

Publ.-Id: 18754 - Permalink

The surface reactions of U(VI) on γ-Al2O3 - In situ spectroscopic evaluation of the transition from sorption complexation to surface precipitation
Müller, K.; Foerstendorf, H.; Brendler, V.; Rossberg, A.; Stolze, K.; Gröschel, A.;
The surface reactions of U(VI) on γ-Al2O3 were comprehensively investigated by a combined approach of in situ vibrational spectroscopy and X-ray absorption spectroscopy. The focus was set to micromolar U(VI) concentrations and a variety of sorption parameters which are relevant to most environmental scenarios, such as pH, ionic strength, different aluminum oxides, and solid-to-liquid ratios. Time-resolved IR spectroscopic sorption experiments at the alumina-water interface evidence the formation of three different species as a function of surface loading: a monomeric carbonate surface complex, an oligomeric surface complex, and a surface precipitate. EXAFS experiments of batch sorption samples different in their U(VI) surface loading, provided consistent results. Aluminum oxides and oxyhydroxides represent an essential structural component of many minerals and play a decisive role in regulating the mobility of contaminants in rocks and soils. Thus, the results presented in this study are of interest for the assessment of water contamination characterized by near neutral solutions. Additionally, the molecular-scale knowledge of the sorption reactions occurring at the water-alumina interface substantiates basic thermodynamic ideas of the formation and transition of surface complexes from sorption of monomers and oligomers to surface precipitation.
Keywords: ATR FT-IR spectroscopy, EXAFS spectroscopy, time-resolved, alumina, uranium

Publ.-Id: 18753 - Permalink

77Se-NMR spectroscopic investigations on aqueous selenium speciation at higher temperatures and in the presence of divalent metal ions
Kretzschmar, J.; Jordan, N.; Brendler, E.;
The radioactive isotope selenium-79 is a long-lived fission product found in nuclear waste. Due to its half-life of 327,000 years, it is expected to be one of the important isotopes contributing to the potential radiation dose of nuclear waste underground repositories. High level and long-lived radioactive waste increases the temperature in the vicinity of the waste disposal site for at least 10,000 years. Thus, it is important to understand to what extent this temperature increase influences the aqueous speciation of the selenium itself and, hence, its sorption behaviour onto mineral phases.
With respect to the redox properties of selenium with its four main oxidation states (-II, ±0, +IV, +VI), the speciation may become quite complex depending on the prevailing environmental conditions.
The spin ½ nucleus of the inactive isotope Se-77 is well suited to be directly observed by NMR spectroscopy. This method provides a valuable tool for the discrimination of oxidation and protonation states of selenium compounds because of the high structural sensitivity of the selenium nucleus to its electronic environment. Thus, changes in speciation due to elevated temperatures or interactions with metal ions can be investigated.
The spectra clearly demonstrate that the aqueous speciation of Se(VI) is not changed within the investigated temperature range (20 °C – 60 °C). However, the interaction of selenium oxyanions with Ca2+ and Mg2+ can be tracked by changes in the selenium chemical shifts. These findings serve as reference data for further investigations addressing the mobility and the sorption behaviour in the presence of ubiquitous metal ions.
Keywords: selenium, aqueous speciation, NMR spectroscopy, nuclear safety research
  • Poster
    EURACT-NMR Workshop 2013, 17.-19.07.2013, Karlsruhe, Deutschland

Publ.-Id: 18752 - Permalink

Model experiments for the Czochralski crystal growth technique
Cramer, A.; Pal, J.; Gerbeth, G.;
A lot of the physical and the numerical modeling of Czochralski crystal growth is done on the generic Rayleigh-B´enard system. To better approximate the conditions in a Czochralski puller, the influences of a rounded crucible bottom, deviations of the thermal boundary conditions from the generic case, crucible and/or crystal rotation, and the influence of magnetic fields are often studied separately. The present contribution reviews some of these topics while concentrating on studies of the flow and related temperature fluctuations in systems where a rotating magnetic field (RMF) was applied.
The three-dimensional convective patterns and the resulting temperature fluctuations will be discussed both for the mere buoyant case and for the application of an RMF. It is shown that a system between a Rayleigh-Benard and a more realistic configuration, which is still cylindrical but whose surface is partially covered by a crystal model, behaves much the same as a Rayleigh-Benard system. An RMF can be used to damp the temperature fluctuations. Secondly, a more Czochralski-like system is examined. It turns out that the RMF does not provide the desired damping of the temperature fluctutions in the parameter range considered.

Publ.-Id: 18751 - Permalink

A new solver for magnetohydrodynamic flow simulations
Weber, N.; Galindo, V.; Stefani, F.; Weier, T.;
Numerical schemes for magnetized rotating flows often attempt to solve the induction equation directly. Due to numerical difficulties, this approach is limited to magnetic Prandtl numbers larger than 0.01, i.e., four orders of magnitude above the values typical for liquid metals. This makes a direct comparison of numerical results with liquid metal experiments difficult. Here we present an alternative approach based on a finite volume scheme for the Navier-Stokes and the Poisson equation describing the electric potential combined with a magnetic field calculation via Biot-Savart’s law. Using this integro-differential formulation, it is possible to circumvent the magnetic Prandtl number limitation mentioned above. First, we will discuss the implementation of this method in the framework of the open source library OpenFOAM. Second, calculations of the Tayler instability (TI), a kink-type current-driven instability, will be presented and compared to the data from a recent liquid metal TI experiment (Seilmayer et al., 2012). The computations faithfully reproduce the experimentally findings. Then, we will elaborate on further details of the TI in liquid metals, as the influence of the aspect ratio on the critical current, transient helical states, and possible implications for large-scale liquid metal batteries.
Keywords: OpenFOAM Tayler instability
  • Poster
    18th International Couette-Taylor Workshop, 24.-26.06.2013, Twente, Niederlande

Publ.-Id: 18750 - Permalink

Liquid metal flows driven by rotating and travelling magnetic fields
Stiller, J.; Koal, K.; Nagel, W. E.; Pal, J.; Cramer, A.;
Alternating magnetic fields provide a comfortable means for non-intrusive flow control in conductive fluids. However, despite a long history of applications in metallurgy and crystal growth, detailed investigation of the practically important transitional and turbulent flow regimes has become possible only in the last dozen years. The present review gives an overview of this topic with focus on recent experimental and numerical studies of the flow driven by rotating and traveling magnetic fields. We discuss the three-dimensional, instantaneous flow structure as well as the resulting average transport properties for a broad range of parameters, including the superposition of both field types. In addition to the ideal case, the effect of a misalignment of the field with respect to the container axis will be considered, too.

Publ.-Id: 18749 - Permalink

Bildgebende Messverfahren für die Prozess- und Strömungsaufklärung in der Verfahrenstechnik
Hampel, U.;
Verfahrenstechnische Prozesse sind zumeist mit mehrphasigen Stoffströmungen verbunden. Die Analyse und Vermessung solcher Mehrphasenströmungen ebenso wie räumlicher Verteilungen von Prozessparametern erfordern fortgeschrittene Mess- und Bildgebungsverfahren. Im Fokus des Interesses stehen dabei vor allem tomographische Bildgebungsverfahren, die heute bereits in der Medizin und in der zerstörungsfreien Prüfung verbreitet sind. Diese müssen allerdings an die oft vielfältigen Anwendungsbedingungen in der Verfahrenstechnik angepasst werden. Typische Probleme sind die optische und akustische Intransparenz von Stoffgemischen, hohe Betriebsdrücke, Temperaturen und aggressive Medien in Prozessanlagen und prozessnahen Versuchsständen sowie die bei vielen bekannten Messverfahren oft zu geringe zeitliche Auflösung bei der Untersuchung transienter Vorgänge. Der Beitrag gibt einen Überblick über neuere Entwicklungen im Bereich der Bildgebungsverfahren für Mehrphasenströmungen und erläutert deren Grundprinzipien und Anwendung.
Keywords: Bildgebende Messverfahren, Strömungsmesstechnik, Computertomographie, Mehrphasenströmungen, Verfahrenstechnik
  • Jubiläumsband 60 Jahre Dresdner Verfahrenstechnik (2013)

Publ.-Id: 18748 - Permalink

The production of K+K- pairs in proton-proton collisions below the φ meson threshold
Ye, Q. J.; Hartmann, M.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Gao, H.; Gebel, R.; Hejny, V.; Kacharava, A.; Lorentz, B.; Mchedlishvili, D.; Merzliakov, S.; Mielke, M.; Mikirtytchiants, S.; Ohm, H.; Papenbrock, M.; Polyanskiy, A.; Serdyuk, V.; Stein, H. J.; Ströher, H.; Trusov, S.; Valdau, Y.; Wilkin, C.; Wüstner, P.;
The pp -> ppK+K- reaction was measured below the phi threshold at a beam energy of 2.568 GeV using the COSY-ANKE magnetic spectrometer. By assuming that the four-body phase space is distorted only by the product of two-body final state interactions, fits to a variety of one-dimensional distributions permit the evaluation of differential and total cross sections. The shapes of the distributions in the Kp and Kpp invariant masses are reproduced only if the K-p interaction is even stronger than that found at higher energy. The cusp effect in the K+K- distribution at the K0K0bar threshold is much more clear and some evidence is also found for coupling between the K-p and K0bar n channels. However, the energy dependence of the total cross section cannot be reproduced by considering only a simple product of such pair-wise final state interactions.

Publ.-Id: 18747 - Permalink

Konzeption eines Experimentaufbaus zum Studium der Magneto-Rotationsinstabilität und der Tayler-Instabilität
Zscharschuch, J.;
Auf der Grundlage eines methodisch konstruktiven Vorgehens wird die Suche nach Prinziplösungen für die Umsetzung eines Experimentaufbaus zum Studium der Magneto-Rotationsinstabilität und der Tayler-Instabilität beschrieben. Einer Kurzvorstellung des Zieles dieser Arbeit und des Experimentes folgt eine Übersicht artverwandter Experimente in der Magnetohydrodynamik. Der Fokus ist dabei auf Gestaltung und Funktion gerichtet. Ein Überblick zu den physikalischen Grundlagen und fluiddynamischen Phänomenen schließt sich an, bevor detailliert auf die angewandte Konstruktionsmethodik eingegangen wird. Anhand der Anforderungen zum Aufbau des Experimentes wird eine zweckdienliche Abstraktion zur technischen Hauptaufgabe durchgeführt. Schrittweise werden dadurch Flussbilder und darauf aufbauend Funktionsstrukturen abgeleitet. Ausgehend davon werden danach einzelne Funktionsgruppen näher betrachtet und Lösungskonzepte entwickelt. Mittels eines Vergleichs der Konzepte wird eine Vorzugsvariante gefunden. Eine Darstellung der Prinziplösung liegt als Ergebnis vor und bietet für den nachfolgenden Entwurfs- und Ausarbeitungsprozess die Basis.
Keywords: Fluiddynamik, Magnetohydrodynamik, Tayler-Instabilität, Magneto-rotationsinstabilität
  • Bachelor thesis
    HTW Berlin, 2013
    86 Seiten

Publ.-Id: 18746 - Permalink

Anti-tumor effects of peptide hormone analogs in pheochromocytoma cell lines and preclinical tumor imaging
Ullrich, M.; Ziegler, C. G.; Bergmann, R.; Pietzsch, J.; Ehrhart-Bornstein, M.; Schally, A. V.; Eisenhofer, G.; Bornstein, S. R.;
Pheochromocytoma (PHEO) is a rare but potentially lethal neuroendocrine tumor arising from catecholamine producing chromaffin cells. Available treatment strategies are limited and, if the tumor has metastasized, not very effective. The abundant expression of peptide hormone receptors on endocrine tumor cells allows specific targeting by highly effective anti-tumor peptide analogs. The present study focuses on the preclinical evaluation of potential therapies in the treatment of pheochromocytoma targeting peptide hormone receptors.

Design and method
Our in vitro evaluation of peptide hormone receptor expression on the mouse pheochromocytoma (MPC) cell line and a more malignant mouse tumor tissue-derived (MTT) cell line was based on RT-PCR and immunohistological analysis. Based on these data, we evaluated the effects of cytotoxic peptide hormone analogs on cell viability, apoptosis and necrosis on MPC and MTT cells. For in vivo studies, we established a subcutaneous mouse model of MPC-derived PHEO and multimodal tumor imaging using PET, MRI, and CT, fluorescence and bioluminescence.

Results and conclusions
Our data reveal significant anti-tumor effects mediated by the cytotoxic peptide hormone analogs AN-162 and AN-238 targeting somatostatin receptor 2 (sst2), by the antagonist Cetrorelix and the cytotoxic analog AN-152 targeting luteinizing hormone-releasing hormone receptor (LHRH-R) as well as by the antagonist MIA-602 targeting growth hormone-releasing hormone receptors (GHRH-R) on MPC cells. Similar anti-tumor effects were evidenced for AN-152 and MIA-602 also on the more aggressive MTT cells. Using our newly established mouse model, we were able to visualize the growth of MPC cell-derived subcutaneous pheochromocytomas in vivo by multimodal molecular imaging including SSTR2 PET. Additionally, ex vivo tumor characterization demonstrated unaltered peptide hormone receptor expression during in vivo tumor growth in mice.
Our current investigation provides strong evidence for a possible future treatment of malignant pheochromocytoma using targeted peptide hormone receptor therapy.
  • Lecture (Conference)
    17th International AEK Cancer Congress, 20.-22.03.2013, Heidelberg, Deutschland
  • Contribution to proceedings
    17th International AEK Cancer Congress, 20.-22.03.2013, Heidelberg, Deutschland
    Congress Program and Abstracts: 17th International AEK Cancer Congress, Deutsche Krebsgesellschaft - Abteilung Experimentelle Krebsforschung. DKG. Heidelberg, 12

Publ.-Id: 18745 - Permalink

Anti-tumor effects of peptide hormone analogs in pheochromocytoma
Ullrich, M.; Ziegler, C. G.; Bergmann, R.; Pietzsch, J.; Ehrhart-Bornstein, M.; Schally, A. V.; Eisenhofer, G.; Bornstein, S. R.;
Pheochromocytoma (PHEO) is a rare but potentially lethal neuroendocrine tumor arising from catecholamine producing chromaffin cells of the adrenal medulla. Especially for malignant pheochromoytoma the available treatment strategies are not very effective. Peptide hormone receptors are abundantly expressed on endocrine tumor cells and can be specifically targeted by highly effective anti-tumor peptide analogs. Our actual study focuses on the preclinical evaluation of potential peptide hormone receptor therapies for the treatment of pheochromocytoma.

Design and method
In our in vitro studies we evaluated peptide hormone receptor expression on a neuroendocrine tumors relevant mouse pheochromocytoma (MPC) cell line and a thereof established more malignant mouse tumor tissue-derived (MTT) cell line based on RT-PCR and immunohistological analysis. We also measured the effects of cytotoxic peptide hormone analogs on cell viability, apoptosis and necrosis on MPC and MTT cells. Furthermore, for our in vivo studies we established a subcutaneous mouse model of PHEO for optimization of multimodal tumor imaging using PET, MRI, and CT, fluorescence and bioluminescence imaging.

Results and conclusions
We could demonstrate significant anti-tumor effects mediated by the cytotoxic peptide hormone analogs AN-162 and AN-238 targeting somatostatin receptor 2 (sst2), by the antagonist Cetrorelix and cytotoxic analog AN-152 targeting luteinizing hormone-releasing hormone receptor (LHRH-R) as well as by the antagonist MIA-602 targeting growth hormone-releasing hormone receptors (GHRH-R) on MPC cells. Furthermore, similar anti-tumor effects were evidenced also for AN-152 and MIA-602 on more aggressive MTT cells. In our mouse model we were able to visualize tumor growth of MPC cell-derived subcutaneous pheochromocytomas in vivo by fluorescence imaging. Ex vivo tumor characterization demonstrated that peptide hormone receptors are still expressed during tumor growth in mice.
Our current investigation provides strong evidence for the usefulness of targeted peptide hormone receptor therapy for a possible future treatment of malignant pheochromocytoma.
  • Poster
    Fourth International Symposium on Adrenal Cancer, 22.-23.02.2013, Paris, France
  • Contribution to proceedings
    Fourth International Symposium on Adrenal Cancer, 22.-23.02.2013, Paris, France
    Fourth International Symposium on Adrenal Cancer: Final Program. European Science Foundation, Paris: European Science Foundation, 27

Publ.-Id: 18744 - Permalink

Novel therapeutic strategies for the treatment of pheochromocytoma
Ziegler, C. G.; Eisenhofer, G.; Ullrich, M.; Bergmann, R.; Pietzsch, J.; Schally, A. V.; Ehrhart-Bornstein, M.; Bornstein, S. R.;
Pheochromocytoma is a rare but potentially lethal chromaffin cell tumor. The prognosis for malignant pheochromocytoma is particularly poor and there are currently no effective treatments. Interestingly, peptide hormone receptors are frequently overexpressed on endocrine tumor cells and can be specifically targeted by highly effective anti-tumor peptide analogs. Our actual study focuses on two endocrinologically relevant mouse pheochromocytoma cell lines, one more malignant and one more benign one as well as on mouse models of pheochromocytoma, which our group currently establishes.
First, we could demonstrate significant anti-tumor effects mediated by cytotoxic somatostatin analogs AN-162 and AN-238, by LHRH antagonist Cetrorelix and cytotoxic LHRH analog AN-152 as well as by GHRH antagonist MIA-602 targeting their respective receptors on mouse pheochromocytoma cells (MPC). Furthermore, similar anti-tumor effects were evidenced also for AN-152 and MIA-602 on more aggressive tumor tissue-derived (MTT) cells.
Second, we established a subcutaneous mouse model of pheochromocytoma for optimization of parametric tumor imaging in vivo. Tumor volume, morphology, metabolic activity and peptide receptors are evaluated using PET/MR and PET/CT imaging as well as fluorescence and bioluminescence imaging after injection of mCherry or luciferase transduced MPC cell lines. Furthermore, we are establishing an intravenous mouse model of pheochromocytoma to test the most effective peptide analogs in vivo. Ex vivo characterization of mouse pheochromocytomas demonstrated that peptide hormone receptors are still expressed during tumor growth in mice.
Altogether, our current investigation provides further evidence for the usefulness of targeted peptide hormone receptor therapy as a potential new option for future treatment of malignant pheochromocytoma
  • Lecture (Conference)
    56. Symposium der Deutschen Gesellschaft für Endokrinologie, 13.-16.03.2013, Düsseldorf, Deutschland
  • Abstract in refereed journal
    Experimental and Clinical Endocrinology & Diabetes 121(2013), OP5_32b
    DOI: 10.1055/s-0033-1336641

Publ.-Id: 18743 - Permalink

Novel aspects on the irradiation of HOPG surfaces with slow highly charged ions
Ritter, R.; Shen, Q.; Wilhelm, R. A.; Heller, R.; Ginzel, R.; Crespo López-Urrutia, J. R.; Facsko, S.; Teichert, C.; Aumayr, F.;
As a continuation of our previous work, we present new results regarding the interaction of slow highly charged ions with HOPG. Lateral atomic force microscopy measurements with calibrated cantilevers were performed to investigate in more detail the locally enhanced friction at ion impact sites, which has been reported earlier. For very high charge states, apart from ever-present changes in frictional and electronic properties, we find evidence for true topographic surface modifications (hillocks). In complementary studies, we have investigated these structures regarding their conductivity by employing high-resolution conductive atomic force microscopy. In addition, we demonstrate the possibility to etch ion-induced surface structures by thermal annealing.
Keywords: HOPG; Highly charged ions; Nanostructuring; AFM; STM; Friction

Publ.-Id: 18742 - Permalink

Di-pion and di-electron production in NN reactions with HADES at 1.25GeV incident beam energy
Kuc, H.; Agakishiev, G.; Behnke, C.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Blume, C.; Böhmer, M.; Cabanelas, P.; Chernenko, S.; Dritsa, C.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gill, K.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Harabasz, S.; Hennino, T.; Höhne, C.; Holzmann, R.; Huck, P.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Krása, A.; Krebs, E.; Krizek, F.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Rehnisch, L.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.;
Significant isospin effects are observed by the HADES collaboration in inclusive dilepton production channels in the pp and quasi free np experiments at 1.25 GeV kinetic beam energy. Triggered by this observation, analyses of several exclusive channels within either dilepton or pion production have been started to shed more light on the possible explanations. Furthermore, the exclusive p+p production in np and pp collisions provide tests for a consistent description of double pion production in different isospin states, which is necessary to understand contributions of the double Δ(1232) and N*(1440) production. This is also important in the context of the recent results from the WASA collaboration on the ABC effect with reference to a d* dibaryon resonance in isospin 0 channel.
  • Open Access LogoProceedings of Science (2013), PoS(BORMIO2013)060

Publ.-Id: 18741 - Permalink

Radiolabeling of modified recombinant epidermal growth factor (EGF) by Huisgen-Click reaction for multimodal imaging and therapy of tumors
Pietzsch, D.; Pretze, M.; Mamat, C.; Mosch, B.; Steinbach, J.; Pietzsch, J.;
The epidermal growth factor receptor (EGFR) plays a critical role in epithelial tumors and, therefore, is a promising target for both tumor imaging and therapy. In order to develop novel EGFR-targeted radiotracers/radiotherapeutics the present work aims at synthesis of structurally modified recombinant EGF. One strategy implies incorporation of azidohomoalanine instead of methionine using supplementation-based incorporation by E. coli. Consequently, the biomolecule can be labeled site-selectively by Click reaction (Huisgen 1,3-dipolar cycloaddition) with fluorescence and radiolabeled building blocks, respectively.

Method and Results
The EGF gene motif was successfully ligated into vectors containing either a GST-tag or His6-tag. Resulting plasmids were transformed into methionine-auxotrophic E. coli (B834(DE3)pLysS), protein synthesis under addition of azidohomoalanine and protein purification were established. Purification of the GST fusion protein only resulted in the unmodified protein, but not in the azido-functionalized protein. In contrast, purification of His6-tagged azido-functionalized EGF was successfully established. This could be demonstrated by reaction with various alkynylated fluorescent dyes. Moreover, the modified EGF was radiolabeled with 1-(but-3-inyl)-4-(3-[18F]fluoropropyl)piperazine ([18F]BFP) as the alkyne with a radiochemical yield of about 0.5 % using Click reaction. First cell binding studies of [18F]BFP-labeled EGF demonstrated cellular association in EGFR-overexpressing A431 human epidermoid carcinoma cells. Cellular uptake amounted to about 25 % of injected dose/mg protein after 1 hour at 37°C.

Ongoing work focuses on the optimization of site-selective radiolabeling of EGF by Click reaction with higher radiochemical yield and specific activity. Afterwards, the radiolabeled protein will be radiopharmacologically tested concerning its properties as potential radiotracer.
  • Poster
    7th Conference on Recombinant Protein Production, 06.-08.03.2013, Laupheim, Deutschland
  • Contribution to proceedings
    7th Conference on Recombinant Protein Production., 06.-08.03.2013, Laupheim, Deutschland
    Programme & Abstracts. European Federation of Biotechnology, 104

Publ.-Id: 18740 - Permalink

Design, synthesis and surface engineering of ultrasmall iron oxide nanoparticles for cancer imaging
Pombo Garcia, K.; Zarschler, K.; Stephan, H.; Steinbach, J.;
There is currently a great interest in the application of nanoparticles for molecular imaging. This results in the development of both, organic and inorganic nanoparticles functionalized in a way that radionuclides, targeting ligands, and different biopolymers can be attached in order to provide an imaging signal. Ultrasmall superparamagnetic iron oxide (Fe3O4) nanoparticles (USPIOs) are one of the most widely studied nanomaterials. USPIOs possess unique magnetic properties that make them attractive candidates as advanced biomedical materials (1).
Furthermore, the biocompatibility of USPIOs makes them suitable to be used as multifunctional agents. They can serve as contrast agents for clinical use in magnetic resonance imaging (MRI), positron emission tomography (PET) and optical imaging (OI) (2).
This work aims at the development of new nanotracers based on USPIOs coated with a biodegradable polymer that are also decorated with agents for radiochemical and/or fluorescence imaging and Epidermal Growth Factor Receptor-specific ligands as targeting units (3).
The production of hydrophobic USPIOs has been achieved using thermal decomposition and monodisperse nanocrystals within a size of 4-5 nm were observed with Transmission electron microscopy (TEM) (4). The main limitation of using USPIOs for in vivo applications is their instability in water. Different biocompatible polymers such as polyvinylalcohol and polyacrylic acid have been tested for the hydrophilic coating of the iron oxide core to make them stable in aqueous solution (5). After an intensive physicochemical characterization including studies of their stability in water and several buffers, carboxymethyl polyvinyl alcohol (CMPVA) was chosen as the most suitable coating agent for the surface modification of USPIOs (6). The stability of the CMPVA-coated USPIOs was studied using Dynamic Light Scattering (DLS, Zetasizer/ Malvern).
Our first goal was to engineer and functionalize the surface of the hydrophilic USPIOs. This included the attachment of a fluorescent label to the shell. This enabled the USPIOs to be suitable for fluorescence imaging. Furthermore, preliminary radiolabeling studies (64Cu) have been undertaken using USPIOs decorated with functional copper chelating agents, such as NOTA. Radio-HPLC and Radio-TLC have been applied to get information about the labelling efficiency and stability of the 64Cu-labeled USPIOs.
From our point of view, the generated nanoparticles possess promising features as novel imaging agents for in vivo cancer diagnostics.

1. Barreto, J.A., et al. Advanced Materials, 23(12): p. H18-H40, 2011.
2. Laurent, S., et al., Chemical Reviews, 108(6): p. 2064-211, 2008.
3. Li, Z., et al., The FASEB Journal, 19(14): p. 1978-1985, 2005..
4. Park, J., et al., Nat Mater, 3(12): p. 891-895, 2004.
5. Zhang, F., et al., Small, 7(22): p. 3113-3127, 2011.
6. Liong, M., et al., Advanced Materials, 22(45): p. 5168-5172, 2010.
  • Lecture (Conference)
    6th International Symposium on the Separation and Characterization of Natural and Synthetic Macromolecules (SCM-6), 06.-08.02.2013, Dresden, Deutschland

Publ.-Id: 18739 - Permalink

Single-domain antibodies as targeting moieties for nanomaterial-based cancer imaging
Witecy, S.; Zarschler, K.; Zscheppang, K.; Cordes, N.; Stephan, H.;
kein Abstract verfügbar
  • Poster
    OncoRay-Retreat 2013, 07.-08.03.2013, Dresden-Rossendorf, Deutschland

Publ.-Id: 18738 - Permalink

Surface morphology and interface chemistry under ion irradiation - simultaneous atomistic simulation of collisional and thermal kinetics
Liedke, B.; Heinig, K.-H.; Möller, W.;
A novel program package has been developed which allows for the simultaneous treatment of atomistic kinetics in collision cascades caused by energetic ion impacts and thermally activated relaxation and diffusion. In this 3D program named TRIDER (TRansport of Ions in matter with DEfect R}elaxation) the collision cascades treated in the framework of the Binary Collision Approximation has been combined with kinetic lattice Monte-Carlo simulations of the atomistic relaxation and diffusion. TRIDER simulations allow a more realistic description of ion-induced surface patterning because subsurface defect kinetics can be included in the simulations, which is demonstrated for low-energy Ar+ ion irradiation of silicon. The deeper understanding of ion beam mixing of bimetal interfaces can also be achieved: it is shown that the conventional Gaussian mixing profile is changed substantially for immiscible metals due to precipitation and for chemically active metals due to formation of intermetallics of different stoichiometry.
Keywords: Monte-Carlo; KMC; BCA; TRIM; TRIDYN; TRIDER; ripple formation ; surface modification; large scale simulation; ion beam irradiation

Publ.-Id: 18737 - Permalink

Synthesis and characterization of silicon nanoparticles
Licciardello, N.; Hsu, C.-W.; Hunoldt, S.; Viehweger, K.; Stephan, H.; de Cola, L.;
kein Abstract verfügbar
  • Poster
    3rd International Conference on Multifunctional, Hybrid and Nanomaterials, 03.-07.03.2013, Sorrento, Italy

Publ.-Id: 18736 - Permalink

Production of large volume, strongly magnetized laser-produced plasmas by use of pulsed external magnetic fields
Albertazzi, B.; Béard, J.; Ciardi, A.; Vinci, T.; Albrecht, J.; Billette, J.; Burris-Mog, T.; Chen, S. N.; Da Silva, D.; Dittrich, S.; Herrmannsdörfer, T.; Hirardin, B.; Kroll, F.; Nakatsutsumi, M.; Nitsche, S.; Riconda, C.; Romagnagni, L.; Schlenvoigt, H.-P.; Simond, S.; Veuillot, E.; Cowan, T. E.; Portugall, O.; Pépin, H.; Fuchs, J.;
The production of strongly magnetized laser plasmas, of interest for laboratory astrophysics and inertial confinement fusion studies, is presented. This is achieved by coupling a 16 kV pulse-power system. This is achieved by coupling a 16 kV pulse-power system, which generates a magnetic field by means of a split coil, with the ELFIE laser facility at Ecole Polytechnique. In order to influence the plasma dynamics in a significant manner, the system can generate, repetitively and without debris, high amplitude magnetic fields (40 T) in a manner compatible with a high-energy laser environment. A description of the system and preliminary results demonstrating the possibility to magnetically collimate plasma jets are given.

Publ.-Id: 18735 - Permalink

Proton induced dielectron radiation off Nb: Pt and Y distributions
Lorenz, M.; Weber, M.; Agakishiev, G.; Behnke, C.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Dohrmann, F.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Lalik, R.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.;
Following our recent letter [1] on inclusive e+e− pair production in proton induced reactions at Ekin = 3.5 GeV on the nucleus Nb, we present here in addition the transverse and rapidity distributions for various e+e− invariant mass bins and compare them to reference data measured in p+p reactions.

Publ.-Id: 18734 - Permalink

Reduction and immobilization processes of contaminants (Se, Tc, Pu) by Fe(II)-bearing minerals
Scheinost, A. C.;
Fe(II)-bearing phases are naturally occuring in most anoxic aquifers, and form also at the surface of corroding steel containers under typical nuclear waste repository conditions. Due to their ability to reduce metal and metalloid contaminants, they are expected to play a key role for the migration behaviour of a wide range of radionuclides, including actinides and fission products. Using X-ray absorption spectroscopy as main tool, we have studied reaction end products, mechanisms and kinetics of redox processes at a range of water/mineral interfaces, including magnetite, green rust, mackinawite, chukanovite, and Fe2+-sorbed clays, but also in more redox-inert systems like cement.
Our results show that the electron transport within mineral structures and at the surface is controlling the extent and the kinetics of multi-electron redox reactions.
Keywords: XAFS XANES Redox
  • Invited lecture (Conferences)
    Chemical and Radiochemical Processes in the Environment, 17.05.2013, Nice, France
  • Invited lecture (Conferences)
    Institutsseminar am Institut für Radioökologie und Strahlenschutz der Universität Hannover, 16.05.2013, Hannover, Germany

Publ.-Id: 18733 - Permalink

Is plutonium being incorporated by magnetite under anoxic conditions?
Dumas, T.; Fellhauer, D.; Gaona, X.; Altmaier, M.; Scheinost, A. C.;
Magnetite, which forms under anoxic conditions on the surface of corroding steel containers, is able to reduce a range of elements, including radionuclides of high relevance in the context of nuclear waste disposal, e.g. Se, Tc, U, Np, Pu [1]. Aqueous Pu(V) is rapidly reduced by nanoparticulate magnetite to Pu(III), which then forms stable, tridentate sorption complexes on the {111} faces of magnetite [2]. Trivalent lanthanides have been shown to substitute for Fe(III) in magnetite, although their ionic radii are about 1.4 times larger than that of Fe(III) (1.15-1.17 vs. 0.79 Å in six-fold coordination) [3]. To investigate if such an incorporation is also possible for Pu(III) with a similar ionic radius as the lanthanides, we conducted coprecipitation experiments with two Pu loadings of 1000 and 3500 ppm. UV-VIS spectroscopy showed an immediate reduction of Pu(V) to Pu(III) in the initial Fe(II)/Fe(III) chloride solution. After formation of the black magnetite precipitate, Pu(III) concentration in solution was below 10-9 M. X-ray Absorption Near-Edge Structure (XANES) spectroscopy confirmed the trivalent oxidation state of solid phase-associated Pu. Extended X-ray Absorption Fine-Structure (EXAFS) spectroscopy was then used to investigate the molecular structure of incorporated Pu(III) in the fresh precipitate as well as after Fe(II)-induced aging [4]. The EXAFS spectra revealed two different spectral components. The first component represents the tridentate Pu(III) sorption complex also observed during sorption experiments. The second component represents Pu(III) in a highly distorted magnetite Oh site. The proportion of the incorporated Pu(III) decreased from about 75% to 40% with Fe(II)-induced aging, while the proportion of sorbed Pu(III) increased correspondingly. Our results suggest, therefore, that Pu can be incorporated by magnetite, but will convert to sorbed species on the long time scales relevant for nuclear waste disposal.

[1] Scheinost et al. (2008) J. Contam. Hydrol. 102, 228-245. [2] Kirsch et al. (2011), Environ. Sci. Technol. 45, 7267–7274. [3] Moon et al. (2007) Extremophiles 11, 859-867. [4] Boland et al. (2011) Environ. Sci. Technol. 45, 1327-1333.
Keywords: XAFS XANES Plutonium Redox magnetite
  • Lecture (Conference)
    Goldschmidt 2013, 25.-30.08.2013, Firenze, Italy
  • Invited lecture (Conferences)
    248th ACS National Meeting, 10.-14.08.2014, San Francisco, USA

Publ.-Id: 18732 - Permalink

Interaction of plutonium with magnetite under anoxic conditions: Reduction, surface complexation, and structural incorporation
Scheinost, A. C.; Kirsch, R.; Dumas, T.; Fellhauer, D.; Gaona, X.; Altmaier, M.;
For the redox-reactive fission products and actinides Se, Tc, U, and Np, it is assumed that the strongly reducing conditions in deep underground, anoxic nuclear waste repositories will reduce their mobility, since their lower-oxidation states commonly form solids of very low solubility. This is not necessarily the case for Pu, where the hexa- and pentavalent aquo-complexes prevalent at higher pe are replaced at lower pe by a tetravalent solid of low solubility, PuO2, but also by a trivalent aquocomplex at lower pH (Fig. 1) [1, 2]. Since the predominance field of Pu(III)aq overlaps with that obtained for the Fe(II)/Fe(III) redox couple as aqueous species or in equilibrium with Fe(II)-bearing minerals [3], one should assume that Pu(III) exists under anoxic nuclear waste conditions, where Fe(II) sources are provided by corroding steel containers and Fe(II)-bearing clays used as confinement, as well as by geogenic minerals. Although some studies have previously reported on trivalent lanthanides, little is known on the retention mechanisms of the trivalent Pu aquo complex by minerals, with implications for the safety case of nuclear waste repositories.
Keywords: Plutonium Redox XAFS XANES magnetite
  • Invited lecture (Conferences)
    Actinides2013, 21.-26.07.2013, Karlsruhe, Deutschland

Publ.-Id: 18731 - Permalink

Recent trends in malignant melanoma biomarker research
Pietzsch, J.; Tandler, N.; Mosch, B.;
Melanoma is the most malignant type of all skin neoplasms. Although current clinical, morphologic, pathologic, and biochemical methods provide insights into disease behavior and outcome, melanoma is still an unpredictable disease. Once in an advanced stage, it remains a fatal neoplasm with scarce therapeutic options. Therefore, significant efforts still need to be made in finding suitable biomarkers that could aid or improve its early diagnosis, its correct staging, the discrimination of other pathological conditions as well as indicate patients’ prognosis or the most appropriate therapeutic regimes. On the other hand, well-defined diagnostic markers are necessary to avoid the apparent overdiagnosis of melanoma.
  • Clinical Laboratory International 37(2013), 6-8

Publ.-Id: 18730 - Permalink

4-[18F]Fluoro-N-methyl-N-(propyl-2-yn-1-yl)benzenesulfonamide ([18F]F-SA): a versatile building block for labeling of peptides, proteins and oligonucleotides with fluorine-18 via Cu(I)-mediated click chemistry
Ramenda, T.; Steinbach, J.; Wuest, F.;
Cu(I)-mediated [3+2]cycloaddition between azides and alkynes has evolved into a valuable bioconjugation tool in radiopharmaceutical chemistry. We have developed a simple, convenient and reliable radiosynthesis of 4-[18F]fluoro-N-methyl-N-(propyl-2-yn-1-yl)benzenesulfonamide ([18F]FSA) as a novel aromatic sulfonamide-based click chemistry building block. [18F]F-SA could be prepared in a remotely controlled synthesis unit in 32 ± 5 % decay-corrected radiochemical yield in a total synthesis time of 80 min. The determined lipophilicity of [18F]F-SA (logP = 1.7) allows handling of the radiotracer in aqueous solutions. The versatility of [18F]F-SA as click chemistry building blockwas demonstrated by the labeling of a model peptide (phosphopeptide), protein (HSA), and oligonucleotide (L-RNA). The obtained radiochemical yields were 77 % (phosphopeptide), 55–60 %(HSA), and 25 %(L-RNA), respectively. Despite the recent emergence of a multitude of highly innovative novel bioconjugation methods for 18F labeling of biopolymers, Cu(I)-mediated click chemistry with [18F]F-SA represents a reliable, robust and efficient radiolabeling technique for peptides, proteins, and oligonucleotides with the short-lived positron emitter 18F.
Keywords: Cu(I)-mediated click chemistry ; Fluorine-18; Peptides; Proteins; Oligonucleotides; Positron emission tomography (PET)

Publ.-Id: 18729 - Permalink

Uranyl-Halide Complexation in N,N-Dimethylformamide: Halide Coordination Trend Manifests Hardness of [UO2]2+
Takao, K.; Takao, S.; Ikeda, Y.; Bernhard, G.; Hennig, C.;
Complexation of [UO2]2+ with Cl−, Br−, and I− in N,N-dimethylformamide (DMF) was studied by UV-vis absorption spectroscopy and extended X-ray absorption fine structure (EXAFS) to clearly differentiate halide coordination strengths to [UO2]2+. In the Cl− system, it was clarified that the Cl− coordination to [UO2]2+ in DMF proceeds almost quantitatively. The coordination number of Cl− increases up to 4 with increasing its total concentration, i.e., the limiting complex is [UO2Cl4]2−. Logarithmic gross stability constants of [UO2Clx]2−x (x = 1-4) were evaluated as log 1 = 9.67, log 2 = 15.49, log 3 = 19.89, and log 4 = 24.63 from UV-vis titration experiment. The EXAFS results well demonstrated not only the Cl− coordination, but also the DMF solvation in the equatorial plane of [UO2]2+. The similar experiments were also performed for the Br− and I− systems. As a result, the Br− coordination to [UO2]2+ stops at the second step, i.e., only [UO2Br]+ and UO2Br2 were observed. The molecular structure of each occurring species was confirmed by EXAFS. The evaluated log x of [UO2Brx]2−x (x = 1, 2) are 3.45 and 5.42, respectively. The much smaller log x than those of [UO2Clx]2−x indicates that Br− is much weaker ligand to [UO2]2+ than Cl−. The EXAFS experiments revealed that the presence of I− in the test solution does not modify any coordination structure around [UO2]2+. Thus, I− does not form any stable [UO2]2+ complexes in DMF. Consequently, the stability of the halido complexes of [UO2]2+ in DMF is exactly in line with the hardness order of halides. This trend clearly manifests the hardness of [UO2]2+.
Keywords: EXAFS, UV-Vis, Uranium, Halides

Publ.-Id: 18728 - Permalink

Crystal structure and solution species of Ce(III) and Ce(IV) formates-from mononuclear to hexanuclear complexes
Hennig, C.; Ikeda-Ohno, A.; Kraus, W.; Weiss, S.; Pattison, P.; Emerich, H.; Abdala, P.; Scheinost, A.;
Cerium(III) and cerium(IV) form both formate complexes. However, their species in aqueous solution and the solid-state structures are surprisingly different. The species in aqueous solutions were investigated with Ce K-edge EXAFS spectroscopy. Ce(III) formate shows only mononuclear complexes, which is in agreement with the predicted mononuclear species of Ce(HCOO)2+ and Ce(HCOO)2+. In contrast, Ce(IV) formate forms in aqueous solution a stable hexanuclear complex of [Ce6(μ3-O)4(μ3-OH)4(HCOO)x(NO3)y]12-x-y. The structural differences reflect the different influence of hydrolysis, which is weak for Ce(III) and strong for Ce(IV). Hydrolysis of Ce(IV) ions causes initial polymerization while complexation through HCOO- results in 12 chelate rings stabilizing the hexanuclear Ce(IV) complex.
Crystals were grown from the above mentioned solutions. Two crystal structures of Ce(IV) formate were determined. Both form a hexanuclear complex with a [Ce6(µ3-O)4(µ3-OH)4]12+ core in aqueous HNO3 / HCOOH solution. The pH titration with NaOH resulted in a structure with the composition [Ce6(µ3-O)4(µ3-OH)4(HCOO)10(NO3)2(H2O)3] (H2O)9.5, while the pH adjustment with NH3 resulted in [Ce6(µ3-O)4(µ3-OH)4(HCOO)10(NO3)4] (NO3)3(NH3)3(H2O)5. Furthermore, the crystal structure of Ce(III) formate, Ce(HCOO)3, was determined. The coordination polyhedron is a tricapped trigonal prism which is formed exclusively by nine HCOO- ligands. The hexanuclear Ce(IV) formate species from aqueous solution is widely preserved in the crystal structure, whereas the mononuclear solution species of Ce(III) formate undergoes a polymerization during the crystallization process.
Keywords: EXAFS, XRD, aqueous solution, Ce(III), Ce(IV), formate

Publ.-Id: 18727 - Permalink

Formation of actinide(IV) carboxylate complexes in aqueous solution – the unexpected predominance of hexanuclear species
Hennig, C.; Takao, K.; Takao, S.; Weiss, S.; Kraus, W.; Emerling, F.; Scheinost, A.;
Tetravalent actinides form strong complexes with carboxyl containing ligands. Such complexes play an important role in technological processes as well as biological and environmental systems. The aqueous chemistry of such complexes is therefore of wide interest. So far, most of the thermodynamic data of actinide(IV) carboxylates are estimated assuming mononuclear solution species (see for example [1]). We applied comprehensive spectroscopic studies (EXAFS, UV-Vis-NIR spectroscopy and X-ray diffraction) to estimate the complex structure of actinide(IV) carboxylates with different actinides (Th4+, U4+ and Np4+) and carboxylates (RCOO–; R = H, CH3, CHR’NH2; R’ = H, CH3, CH2SH) in aqueous solution and solid state [2-4]. These studies show clearly that in all of the investigated systems hexanuclear complexes appear, which become predominant with increasing metal and ligand concentration as well as increasing pH, and comprise finally often close to 100% of the species distribution. The aim of our studies was to investigate the complex structure, stability constants, and the mechanism of complex formation.
Keywords: EXAFS, XRD, UV-Vis, Actinides, carboxyl groups
  • Poster
    Actinides 2013, 21.-26.07.2013, Karlsruhe, Deutschland

Publ.-Id: 18726 - Permalink

Colorimetric As (V) Detection Based on S-Layer Functionalized Gold Nanoparticles
Lakatos, M.; Matys, S.; Raff, J.; Pompe, W.;
Herein, we present simple and rapid colorimetric and UV/VIS spectroscopic methods for detecting anionic arsenic (V) complexes in aqueous media. The methods exploit the aggregation of S-layer-functionalized spherical gold nanoparticles of sizes between 20 and 50 nm in the presence of arsenic species. The gold nanoparticles were functionalized with oligomers of the S-layer protein of Lysinibacillus sphaericus JG-A12. The aggregation of the nanoparticles results in a color change from burgundy-red for widely dispersed nanoparticles to blue for aggregated nanoparticles. A detailed signal analysis was achieved by measuring the shift of the particle plasmon resonance signal with UV/VIS spectroscopy. To further improve signal sensitivity, the influence of larger nanoparticles was tested. In the case of 50 nm gold nanoparticles, a concentration of the anionic arsenic (V) complex lower than 24 ppb was detectable.
Keywords: arsenic, colorimetric, nanoparticle, S-layer, detection

Publ.-Id: 18724 - Permalink

Dual time point based quantification of metabolic uptake rates in 18F-FDG PET
van den Hoff, J.; Hofheinz, F.; Oehme, L.; Schramm, G.; Langner, J.; Beuthien-Baumann, B.; Steinbach, J.; Kotzerke, J.;
Assessment of dual time point (DTP) positron emission tomography was carried out with the aim of a quantitative determination of Km, the metabolic uptake rate of [18F]fluorodeoxyglucose as a measure of glucose consumption.

Starting from the Patlak equation, it is shown that Km?mt/ca0 + Vr/?a, where mt is the secant slope of the tissue response function between the dual time point measurements centered at t=t0. ca0=ca(t0) denotes arterial tracer concentration, Vr is an estimate of the Patlak intercept, and ?a is the time constant of the ca(t) decrease. We compared the theoretical predictions with the observed relation between Ks=mt/ca0 and km in a group of nine patients with liver metastases of colorectal cancer for which dynamic scans were available, and Km was derived from conventional Patlak analysis. derived from conventional Patlak analysis. Twenty- two lesion regions of interest (ROIs) were evaluated. ca(t) was determined from a three-dimensional ROI in the aorta. Furthermore, the correlation between Km and late standard uptake value (SUV) as well as retention index was investigated. Additionally, feasibility of the approach was demonstrated in a whole-body investigation.

Patlak analysis yielded a mean Vr of Vr = 0.53?0.08 ml/ml. The patient averaged ?a was 99?23 min. Linear regression between Patlak-derived Km and DTP-derived Ks according to Ks = b ? Km + a yielded b = 0.98 ? 0.05 and a = -0.0054 ? 0.0013 ml/min/ml (r = 0.98) in full accordance with the theoretical predictions b = 1 and a ? -Vr=?a Ks exhibits better correlation with Km than late SUV and retention index, respectively. K(c)s = Ks + Vr=?a is proposed as a quantitative estimator of Km which is independent of patient weight, scan time, and scanner calibration.

Quantification of Km from dual time point measurements compatible with clinical routine is feasible. The proposed approach eliminates the issues of static SUV and conventional DTP imaging regarding influence of chosen scanning times and inter-study variability of the input function. Ks and K(c)s exhibit improved stability and better correlation with the true Km. These properties might prove especially relevant in the context of radiation treatment planning and therapy response control.

Publ.-Id: 18723 - Permalink

Anti-tumor effects of peptide analogues targeting neuropeptide hormone receptors on mouse pheochromocytoma cells
Ziegler, C. G.; Eisenhofer, G.; Schally, A. V.; Gebauer, L.; Gondek, K.; Ullrich, M.; Qin, N.; Bergmann, R.; Pietzsch, J.; Ehrhart-Bornstein, M.; Bornstein, S. R.;
Pheochromocytoma is a rare but potentially lethal chromaffin cell tumor with currently no effective treatment. Peptide hormone receptors are frequently overexpressed on endocrine tumor cells and can be specifically targeted by various anti-tumor peptide analogs. The present study carried out on mouse pheochromocytoma cells (MPCs) and a more aggressive mouse tumor tissue-derived (MTT) cell line revealed that these cells are characterized by pronounced expression of the somatostatin receptor 2 (sst2), growth hormone-releasing hormone (GHRH) receptor and the luteinizing hormone-releasing hormone (LHRH) receptor. We further demonstrated significant anti-tumor effects mediated by cytotoxic somatostatin analogs, AN-162 and AN-238, by LHRH antagonist, Cetrorelix, by the cytotoxic LHRH analog, AN-152, and by recently developed GHRH antagonist, MIA-602, on MPC and for AN-152 and MIA-602 on MTT cells. Studies of novel anti-tumor compounds on these mouse cell lines serve as an important basis for mouse models of metastatic pheochromocytoma, which we are currently establishing.

Publ.-Id: 18721 - Permalink

Matching the 20 kW SSPA to ELBE
Büttig, H.; Arnold, A.;
In January 2012 the 10 kW CW klystrons (CPI VKL7811St) used to operate the superconducting cavities of ELBE since 2001 have been replaced by pairs of 10 kW solid state amplifiers (SSPA) providing 20 kW RF power per cavity. The paper reviews the procedures and the problems during commissioning the new RF system.
Keywords: LINAC RF, Commissioning Linac RF-system, ELBE RF system
  • Lecture (Conference)
    ARD Workshop “Pushing the ELBE CW RF-system to high average beam current”, 14.-15.03.2013, Dresden, Deutschland

Publ.-Id: 18719 - Permalink

Substitution of the Klystrons by Solid State Power Amplifiers (SSPA) at ELBE
Büttig, H.;
In January 2012 the 10 kW CW klystrons (CPI VKL7811St) used to operate the superconducting cavities of ELBE since 2001 have been replaced by pairs of 10 kW solid state amplifiers (SSPA) providing 20 kW RF power per cavity. The paper gives an overview on the activities and the problems during high power CW operation.
Keywords: ELBE RF-system, 1.3GHz SSPA, SC-LINAC RF Power Generation
  • Lecture (Conference)
    ARD Workshop “Pushing the ELBE CW RF-system to high average beam current”, 14.-15.03.2013, Dresden, Deutschland

Publ.-Id: 18718 - Permalink

Design and Performance of the Upgraded ELBE RF-System Based on Solid State Amplifiers
Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.;
With the expansion of the radiation source ELBE, a centre for high power radiation sources is being built until 2014 at the Helmholtz Zentrum Dresden Rossendorf. One part of this program is to double the beam current of the ELBE LINAC. In January 2012 the 10 kW CW klystrons, used to operate the superconducting cavities of ELBE since 2001, had been replaced by a pair of 10 kW solid state amplifiers. The paper gives an overview on the activities around this project and the first experience with the new RF-system.
Keywords: ELBE RF system, Superconducting LINAC RF, 1.3 GHz Solid State Power Amplifiers, Solid State Poer Amplifiers for Particle Accelerators
  • Invited lecture (Conferences)
    TIARA Workshop on RF Power Generation for Accelerators, 17.-19.06.2013, Uppsala, Schweden

Publ.-Id: 18717 - Permalink

Effective Spin Meron Pairs In Ferromagnetic Multilayers
Wintz, S.; Bunce, C.; Neudert, A.; Körner, M.; Strache, T.; Buhl, M.; Erbe, A.; Gemming, S.; Raabe, J.; Quitmann, C.; Fassbender, J.ORC
We report on pairs of diverging/converging spin vortices in Co/Rh/Ni81Fe19 trilayer disks. The lateral magnetization distribution of these effective spin merons is imaged directly by means of element-selective x-ray microscopy. By this method, both the divergence and circulation states of the individual layers are identified as antisymmetric. Reversal measurements on corresponding continuous films reveal that biquadratic interlayer exchange coupling is the origin for the formation of effective meron pairs. Furthermore, their three-dimensional magnetization structure is determined by micromagnetic simulations. Interestingly, the magnetic induction follows a kind of flux-closing torus. This toroidal topology enforces a symmetry break, which ties the core polarities to the divergence configuration.
Keywords: spin, texture, vortex, meron, topology
  • Lecture (Conference)
    Joint European Magnetic Symposia 2013, 25.-30.08.2013, Rhodos, Griechenland

Publ.-Id: 18716 - Permalink

Commisioning of the upgraded superconducting linac ELBE
Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.;
In January 2012 the 10 kW CW klystrons (CPI VKL7811St) used to operate the superconducting cavities of ELBE since 2001 have been replaced by pairs of 10 kW solid state amplifiers (SSPA) providing 20 kW RF power per cavity. The paper gives an overview on the activities and the problems during high power CW operation.
Keywords: Linac-RF, SSPA, High power solid state RF amplifiers, Accelerator RF systems, Superconducting Linac RF, CW Linac RF
  • Open Access LogoContribution to proceedings
    4th International Particle Accelerator Conference, IPAC13, 12.-17.05.2013, Shanghai, China
    IPAC2013-Proceedings , Paper WEPME007, page 2935, Geneva: JACoW, 2935
  • Poster
    4th International Particle Accelerator Conference, IPAC13, 12.-17.05.2013, Shanghai, China

Publ.-Id: 18715 - Permalink

X-ray diffraction studies during magnetron co-sputtering of Ni-Ti shape memory alloy films
Martins, R. M. S.; Schell, N.; Mahesh, K. K.; Silva, R. J. C.; Braz Fernandes, F. M.;
The study of Ni-Ti shape memory alloy films is of great technological interest for applications in the field of microengineering. They can work as sensors and actuators at the same time. However, there are still important issues unresolved like formation of film crystallographic orientation and its control. Films exhibiting the two-way shape memory effect are also required.
A two-magnetron sputter deposition chamber mounted into the six-circle diffractometer of the Rossendorf Beamline at the European Synchrotron Radiation Facility was used for the processing of Ni-Ti films. The in-situ x-ray diffraction studies enabled to identify the different steps of the structural evolution during film growth.
Deposition conditions leading to Ni-Ti films mainly containing grains with (100) or (110) planes of the B2 phase parallel to the film surface were successfully defined. This is an important achievement since texture has a strong influence on the extent of the strain recovery. The deposition of films with a “two-way” actuation (films with a combination of superelasticity and shape memory characteristics) was also achieved. It will allow the development of smaller devices since no consideration has to be paid to a resetting spring.
Keywords: Shape Memory Alloy; Ni-Ti; Deposition by sputtering; In-situ X-ray diffraction; Texture development.
  • Open Access LogoCiência & Tecnologia dos Materiais 24(2012)3/4, 161-169

Publ.-Id: 18714 - Permalink

Ein neuartiges Konzept zur Berechnung der Positronenemitter-Ausbeuten für die Reichweiteverifikation bei der Partikeltherapie mittels PET
Priegnitz, M.; Enghardt, W.; Laube, K.; Fiedler, F.;
no abstract available
  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 18.-21.09.2013, Köln, Deutschland
  • Open Access LogoContribution to proceedings
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 18.-21.09.2013, Köln, Deutschland
    Medizinische Physik - Abstractband, 978-3-9816002-1-6, 119-121

Publ.-Id: 18713 - Permalink

Flashing evaporation under different pressure levels
Liao, Y.; Lucas, D.; Krepper, E.; Rzehak, R.;
Flashing evaporation of water inside a vertical pipe under four different system pressures is investigated by mono-dispersed CFD simulations. Phase change is assumed to be caused only by thermal heat transfer. The available thermal energy decreases rapidly with the increase of pressure level. Under low-pressure conditions, the maximum steam volume fraction is over-predicted, while an overestimation is observed in high-pressure cases. The possible explanation for the deviation is that bubble growth during the evaporation is especially significant in low-pressure cases, which reduces the evaporation rate but is not considered in the simulation. Furthermore, as the system pressure increases the contribution of nucleation to the total steam generation rate becomes large, which is confirmed by the experimental data. In addition, the effect of pressure on the critical bubble diameter that succeeds in starting flashing as well as the nucleation mechanism is discussed.
Keywords: Flashing; Nucleation; Thermal Energy; Vertical Pipe Flow; Pressure Effect

Publ.-Id: 18712 - Permalink

Time-resolved spectroscopy on intraband Landau-level transitions in graphene
Mittendorff, M.; Winnerl, S.; Orlita, M.; Potemski, M.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.;
The linear dispersion for electrons in graphene leads to a non-equidistant Landau-level (LL) spectrum. This enables one to investigate single Landau-level transitions by resonant pump-probe experiments. So far, however, only the quasi-continuum of high-index LL states has been studied in near-infrared pump-probe experiments. Here we report on terahertz pump-probe measurements at a fixed photon energy of 14 meV, where the free-electron laser FELBE at Dresden-Rossendorf served as radiation source. The magnetic field was varied between 0 T and 7 T. For these measurements we used a sample with 50 layers of graphene, which were epitaxially grown on the C-face of silicon carbide. While the interface layers are highly doped, the major part of the layers is quasi neutral with a Fermi energy in the range of ~10 meV.
At a magnetic field of 0.165 T the photon energy of 14 meV becomes resonant with the inter-LL transition LL-1(0) -> LL0(1). The amplitude of the pump-probe signal is increased by roughly a factor of 4 compared to zero field. Only the quasi neutral layers contribute to this signal, since the first LL is fully occupied for the interface layers with a higher doping. Surprisingly a decreased relaxation time is observed on resonance. We will discuss how the contribution of the LL-1 -> LL0 and LL0 -> LL1 and Auger-type processes lead to a unique relaxation scenario. At higher magnetic fields higher intraband LL transitions can be tuned into resonance (LLn -> LLn+1, n=1,2,3,…). The observed pump-probe signals then stem from these transitions in the interface layers, where the elevated Fermi energy ensures that the ground state LL is populated. With increasing magnetic field both amplitude and decay time constants vary non-monotonically. In the magnetic field region around 3 T negative pump-probe signals occur. The main features observed in the experiments are explained by a model for the electron temperature after optical excitation, which describes the absorption in the layers via the Kubo formalism and takes into account the doping level of the interface layers. The doping levels agree well with values previously obtained from pump-probe experiments without magnetic field.
Keywords: Landau quantization, relaxation dynamics, pump-probe spectroscopy, magnetic field
  • Lecture (Conference)
    Graphene Week 2013, 02.-07.06.2013, Chemnitz, Deutschland

Publ.-Id: 18711 - Permalink

THz spectroscopy of optically excited InGaAs quantum wells in the high charge-carrier density regime
Schmidt, J.; Teich, M.; Wagner, M.; Winnerl, S.; Stehr, D.; Schneider, H.; Helm, M.;
In this work we study the THz transmission of a 40 nm wide undoped In0.1Ga0.9As quantum well (QW) under optical excitation. Carriers are photoexcited by a near-infrared (NIR) fs pulse and probed in the frequency range from 0.1 to 3 THz by electro-optic sampling using the modified setup of Ref. [1]. The THz pulse is focused on a side facet of the QW sample such that the THz electric field is mostly polarized perpendicular to the QW layer. Fig. 1a depicts the THz field transients for modulated (signal) and un-modulated (reference) NIR excitation. The presence of the carriers which were photoinjected several ps prior to the THz pulse creates a large amount of THz signatures in the QW. Our present goal is to disentangle the various possible contributions to the THz signal: electron intersubband, heavy-hole intersubband, 1s-2p intraexciton and free-carrier absorption. In addition we search for a Fano-like behavior, similar as has been observed in narrower QWs in the mid infrared [2], which is supposed to arise from the interplay between the intersubband absorption and the purely reactive ponderomotive contribution. The different phase of the associated dielectric functions results in a (non-quantum like) interference between these two polarizations, which is only visible in the differential transmission but not in the absorption. We will also report experiments where we use wavelength tuning of the near-infrared pulse using an optical parametric amplifier in order to selectively pump optically either into the barrier or into the QW. Polarization resolved measurements are underway which should help us to reveal the various contributions.
[1] M. Wagner et. al. , Appl. Phys. Lett. 99, 131109 (2011).
[2] D. Golde, M. Wagner et. al., PRL 102, 127403 (2009).
Keywords: quantum well, THz time domain, photoexcitation
  • Poster
    OTST 2013: International Workshop on Optical Terahertz Science and Technology 2013, 01.-05.04.2013, Kyoto, Japan

Publ.-Id: 18710 - Permalink

Terahertz nonlinear optics of excitons in quantum wells: the Autler-Townes effect and beyond
Helm, M.; Teich, M.; Wagner, M.; Winnerl, S.; Schneider, H.; Klettke, A. C.; Chatterjee, S.; Kira, M.; Koch, S. W.; Keywords: terahertz, nonlinear optics, Autler-Townes effect, excitons
  • Invited lecture (Conferences)
    International Workshop on Optical Terahertz Science and Technology (OTST 2013), 01.-05.04.2013, Kyoto, Japan

Publ.-Id: 18709 - Permalink

How does a free-electron laser work and why is it useful in the THz range ?
Helm, M.; Keywords: free-electron laser, terahertz
  • Lecture (others)
    Terahertz Seminar (invited talk), 30.03.2013, Osaka, Japan

Publ.-Id: 18708 - Permalink

THz spectroscopy of semiconductor nanostructures with the free electron laser
Helm, M.; Keywords: terahertz, free electron laser, semiconductor nanostructures
  • Lecture (others)
    TeraNano Student Seminar (invited talk), 02.-03.03.2013, Würzburg, Deutschland

Publ.-Id: 18707 - Permalink

PIC and GPUs - About my Work at HZDR
Hübl, A.;
Presentation of my scientific CV, laser-electron theory at HZDR and the work on PIConGPU.
Keywords: picongpu, epp, ist, lisboa, GPGPU
  • Invited lecture (Conferences)
    Meeting of the extreme plasma physics team of the Group for Lasers and Plasmas of the Instituto de Plasmas e Fusão Nuclear at Instituto Superior Técnico., 12.10.2012, Lisboa, Portugal

Publ.-Id: 18706 - Permalink

PIConGPU - Validations, Enhancements and Recent Draco Sims
Hübl, A.; Bussmann, M.; Burau, H.; Widera, R.; Steiniger, K.; Berninger, F.; Pausch, R.; Buikstra, L.; Debus, A.; Kluge, T.; Irman, A.; Jochmann, A.; Couperus, J. P.; Schmitt, F.; Höhnig, W.; Juckeland, G.;
Presentation of recent feature enhancements and physical Validations of PIConGPU. We presented laser dispersion test, radiation tests and thermal plasma tests, added new numerical shemes for the PIC cycle and performed HPC simulations for the recent laser-electron experiment at draco, performed by A. Irman et al.
Keywords: PIConGPU, GPGPU, CUDA, numerics, draco, simulation
  • Lecture (others)
    Meeting of Laser Particle Acceleration Division at the Institute for Radiation Physics, 01.08.2012, Dresden, Deutschland

Publ.-Id: 18705 - Permalink

EPP/IPFN Annual Report 2012 (Contribution)
Hübl, A.; EPP team of GoLP at IST (Lisboa);
Contribution to the Annual Report 2012 of EPP/IPFN at Instituto Superior Técnico (Lisboa).
Keywords: annual report 2012, ist, epp, lisboa
  • Open Access LogoContribution to external collection
    in: Annual Report 2012 of EPP/IPFN, Lisboa: Instituto Superior Técnico, 2015

Publ.-Id: 18704 - Permalink

Measurement of spin observables in the quasi-free np -> {pp}sπ reaction at 353 MeV
Dymov, S.; Shmakova, V.; Azaryan, T.; Barsov, S.; Baru, V.; Benati, P.; Chiladze, D.; Dzyuba, A.; Engels, R.; Gaisser, M.; Gebel, R.; Grigoryev, K.; Goslawski, P.; Guidoboni, G.; Hartmann, M.; Kacharava, A.; Kamerdzhiev, V.; Khoukaz, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Kurbatov, V.; Lehrach, A.; Lenisa, P.; Lensky, V.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Maier, R.; Mchedlishvili, D.; Merzliakov, S.; Mielke, M.; Mikirtychyants, M.; Mikirtytchiants, S.; Nioradze, M.; Oellers, D.; Ohm, H.; Polyanskiy, A.; Papenbrock, M.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Seyfarth, H.; Steffens, E.; Stein, H. J.; Stockhorst, H.; Ströher, H.; Tabidze, M.; Trusov, S.; Tsirkov, D.; Uzikov, Y.; Valdau, Y.; Weidemann, C.; Wilkin, C.; Wüstner, P.; Ye, Q. J.; Zhabitsky, M.;
The transverse spin correlations Ax,x and Ay,y have been measured in the ~d~p ! pspec{pp}sπ−reaction at COSY-ANKE at 353 MeV per nucleon. Here {pp}s denotes a proton-proton pair with low excitation energy, which is dominantly in the 1S0 state. By measuring three protons in the final state it was possible to extract events where there was a spectator proton pspec so that the reaction could be interpreted in terms of quasi-free ~n ~p ! {pp}sπ−. The proton analyzing power in this reaction was also deduced from this data set by averaging over the polarization of the deuteron beam. The values of Apy were shown to be consistent with a refined analysis of our earlier results obtained with a polarized proton incident on a deuterium target. Taking these data in combination with our earlier measurements of the differential cross sections and analyzing powers in the ~pp ! {pp}s π0 reaction, a more robust partial wave decomposition was achieved. Three different acceptable solutions were found and the only way of resolving this ambiguity without further theoretical input would be through a measurement of the mixed spin-correlation parameter Ax,z.

Publ.-Id: 18703 - Permalink

Accelerated Codes and Charges
Hübl, A.;
Final talk about the results of the cooperation/internship at Instituto Superior Técnico (IST) in 2012/13.
A new method for charged beam loading in particle-in-cell simulations was presented. Furthermore, side-topics like the creation of a Raspberry Pi (ARM) cluster, the development of a dependency analyser for fortran modules for parallel builds, a GPU vs CPU benchmark, the development of a transversal resolution criteria for gaussian laser beams and a Thrust-Fortran binding were presented.
Keywords: beam loading, cooperation, internship, fortran parallel make, raspberry pi, arm, cluster, thrust, transversal resolution gaussian laser beam
  • Lecture (others)
    Final talk with results of the cooperation, 20.02.2013, Lisboa, Portugal

Publ.-Id: 18702 - Permalink

PIConGPU - Physics Validation for Laser Plasma and Astrophysics Plasma Simulations
Hübl, A.; Burau, H.; Helm, A.; Widera, R.; Debus, A.; Kluge, T.; Couperus, J. P.; Irman, A.; Bussmann, M.; Schramm, U.; Cowan, T.; Schmitt, F.; Juckeland, G.; Nagel, W.;
PIConGPU is a highly-scalable implementation of the fully relativistic electromagnetic particle-in-cell algorithm for GPGPUs. It allows for fast simulations of laser plasma interaction and astrophysical plasmas.
We present several physics validation results, allowing reliable checks during development stages of the code. Furthermore, we show applications in astrophysical scenarios and in laser wakefield acceleration experiments for next generation electron accelerators.
Keywords: particle-in-cell, PIConGPU, CUDA, GPGPU, laser-electron acceleration, laser-plasma interaction, underdense plasma, numerics, HPC, cluster, instabilities, astro physics
  • Poster
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18701 - Permalink

Spin Torque Generated Magnetic Droplet Solitons
Mohseni, S. M.; Sani, S. R.; Persson, J.; Anh Nguyen, T. N.; Chung, S.; Pogoryelov, Y.; Muduli, P. K.; Iacocca, E.; Eklund, A.; Dumas, R. K.; Bonetti, S.; Deac, A.; Hoefer, M. A.; Åkerman, J.;
Dissipative solitons have been reported in a wide range of nonlinear systems, but the observation of their magnetic analog has been experimentally challenging. Using spin transfer torque underneath a nanocontact on a magnetic thin film with perpendicular magnetic anisotropy (PMA), we have observed the generation of dissipative magnetic droplet solitons and report on their rich dynamical properties. Micromagnetic simulations identify a wide range of automodulation frequencies, including droplet oscillatory motion, droplet "spinning," and droplet "breather" states. The droplet can be controlled by using both current and magnetic fields and is expected to have applications in spintronics, magnonics, and PMA-based domain-wall devices.
Keywords: spin-transfer torque, droplet soliton, magnetic nanostructure

Publ.-Id: 18700 - Permalink

Weighted Poisson cells as models for random convex polytopes
Ballani, F.; van den Boogaart, K. G.;
We introduce a parametric family for random convex polytopes in Rd which allows for an easy generation of samples for further use, e. g., as random particles in materials modelling and simulation. The basic idea consists in weighting the Poisson cell, which is the typical cell of the stationary and isotropic Poisson hyperplane tessellation, by suitable geometric characteristics. Since this approach results in an exponential family, parameters can be efficiently estimated by maximum likelihood. This work has been motivated by the desire for a flexible model for random convex particles as can be found in many composite materials such as concrete or refractory castables.
Keywords: Random polygon, Random polyhedron , Poisson cell, Crofton cell, Exponential family, Gibbs distribution

Publ.-Id: 18699 - Permalink

Superconducting layers in Si – a new approach for Quantum-bits?
Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Voelskow, M.; Hübner, R.; Philipp, P.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.;
With the observation of superconductivity at ambient pressure conditions in B doped Si in 2006 [1] and Ga doped Ge [2] the group-IV semiconductors become of interest for future information processing technologies like quantum computing.
To achieve the high doping levels needed for superconductivity non-equilibrium doping techniques like gas immersion laser doping or ion implantation and short term annealing are needed. Only the latter one is fully compatible to standard microelectronic technology. In a new approach we implanted a Ga concentration up to 11 at.% through a 30 nm SiO2 cover layer into commercial Si and Ge wafers [3-6]. During annealing a thin superconducting Ga-rich nanolayer is formed at the SiO2/semiconductor interface. These layers show promising superconducting properties (TC = 7 K, BC < 8 T, jC < 50 kA/cm2).
Detailed microstructural investigations by means of XTEM and RBS/C will be discussed. Recent results show the adjustability of the superconducting properties. We are able to produce superconducting microstructures having a width of 3 µm and used the FIB to implement a Josephson junction as key element for a prospective SQUID.
[1] E. Bustarret et al., Nature 444 (2006) 465
[2] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102 (2009) 217003
[3] R. Skrotzki et al., Appl. Phys. Lett. 97 (2010) 192505
[4] J. Fiedler et al., Phys. Rev. B 83 (2011) 214504
[5] J. Fiedler et al., Phys. Rev. B 85 (2012) 134530
[6] V. Heera et al., Appl. Phys. Lett. 100 (2012) 262602
  • Lecture (Conference)
    E-MRS 2013 Spring Meeting (Ausgezeichnet mit dem "Young Scientist Award" - Symposium J), 27.-31.05.2013, Strasbourg, Frankreich

Publ.-Id: 18698 - Permalink

Insights into the Biodiversity of salt sumps in the Asse II salt mine, Germany
Zirnstein, I.; Arnold, T.;
The former salt mine (1908-1964) Asse II, Germany is a final disposal site of radioactive waste. It is composed of salt rocks, which are approximately 250 million years old. A number of salt sumps exist in the Asse II, which were so far not microbiologically characterized. In this study, cultivation-independent methods, e.g. pyrosequencing, were applied to identify the microbial diversity in these unique salt sump habitats.
In this study, a total of 3.168 sequences, divided in 314 operational taxonomic units (OTUs), representing bacterial and archaeal groups from the underground Asse II salt mine. The class halobacteria (Euryarchaeota) predominates the archaeal community, representing 99.5% of all sequences. The least abundant sequences were represented by Thermoprotei (Crenarchaeota) and Methanobacteria (Euryarchaeota).
In addition, halophilic bacteria have been detected in the salt sumps of the underground Asse II mine. A total of 8 phyla of bacteria were identified by 16S rRNA sequence analyzes. The dominating phylum are Firmicutes (e.g. Bacilli, Halocella, Filifactor, Veillonella) with ~51% of all detected bacterial sequences, followed by Proteobacteria (Marinobacter, Hyphomicrobium, Methylophilus, Pseudomonas, Sphingomonas) with ~19%.
This study identified for the first time extreme halophilic bacteria and archaea in the underground salt sumps of the Asse II environment. For generating a final disposal site, not only geological, chemical or physical, but also microbiological aspects are important to consider.
Keywords: extreme environment, halophilic microorganisms, 16S rDNA, pyrosequencing, salt rock, Asse
  • Lecture (Conference)
    Actinide and Brine Chemistry in a Salt Repository Workshop (III), 15.-17.04.2013, Santa Fe (NM), USA

Publ.-Id: 18697 - Permalink

Thermally assisted all-optical helicity dependent magnetic switching in amorphous Fe100-xTbx alloy films.
Hassdenteufel, A.; Hebler, B.; Schubert, C.; Liebig, A.; Teich, M.; Helm, M.; Aeschlimann, M.; Albrecht, M.; Bratschitsch, R.;
All-optical switching (AOS) in ferrimagnetic Fe100−x Tbx alloys is presented. AOS is witnessed below, above, and in samples without a magnetic compensation point. It is found that AOS is associated with laser heating up to the Curie temperature and intimately linked to a low remanent sample magnetization. Above a threshold magnetization of 220 emu cm−3 helicity dependent AOS is replaced by pure thermal demagnetization.
Keywords: all optical switching, magnetic switching, ferrimagnetism

Publ.-Id: 18696 - Permalink

Particle-Mesh-Methods on Next Generation Supercomputers
Bussmann, M.;
In the coming years supercomputers will have millions of compute cores.
It is estimated that the computing power will grow by a factor of 1000 in the coming years while the memory will only grow by a factor of 10.
This means that at optimum codes can be 100 times faster than before.
I will show that such codes exist today and both allow and require online visualization and interaction with the user.
Based on the example of particle-mesh methods I will present the most important techniques on how to write optimum codes.
Keywords: particlemesh, gpu, exaflop
  • Invited lecture (Conferences)
    Seminar, Center of Excellence for Computational Fluid Dynamics, 12.04.2013, Warszawa, Polska

Publ.-Id: 18695 - Permalink

Free-electron laser spectroscopy of exciton dynamics in GaAs quantum wells
Zybell, S.; Bhattacharyya, J.; Winnerl, S.; Helm, M.; Schneider, H.;
Intraband excitation of optically injected carriers using strong mid-infrared or THz pulses provides interesting opportunities to study carrier and exciton dynamics in semiconductor quantum wells (QW). In particular, owing to the odd parity of the dipole operator, such intraband excitation transfers excitons located in radiative states into dark (or interband-forbidden) states as long as the symmetry of the QW ensures parity conservation. This property yields spectroscopic access to specific dark states, giving rise to resonant enhancement of intraband absorption as well as suppression of the photoluminescence (PL), and allows us to investigate associated dynamical processes.
We will report on time-resolved PL studies, where we investigate the dynamics of excitons and electron-hole plasma subsequent to pulsed irradiation using the free-electron laser (FEL) at the Helmholtz-Zentrum Dresden-Rossendorf. The FEL is tuned into resonance with, respectively, intraexcitonic and intersubband transitions. Specifically, Figs. 1(a)-(b) demonstrate the effect of FEL excitation of radiative excitons in resonance with the 1s-2p transition, located at 9 meV for 8.2 nm wide high-quality QWs (sample 1). Besides quenching and recovery of the 1s PL, the salient feature in Fig. 1(b) is the appearance of PL originating from the 2s exciton. As direct excitation from 1s into 2s is dipole forbidden, the latter has to be the consequence of rapid scattering from the 2p into the 2s state, which nicely confirms earlier theoretical predictions. This 2s PL is specific for resonant 1s-2p excitation and just seen in high-quality quantum wells. Figs. 1(c) and (d) show PL transients for FEL excitation at 173 meV, in resonance with the electron intersubband transition for 6 nm wide GaAs QWs (sample 2). Typically, the PL recovery after the FEL pulse obeys the same time constant as the initial PL formation after NIR excitation, and its value after recovery exceeds the reference value since the population transferred into nonradiative states eventually returns into the radiative ones, such that the time-integrated PL emission is conserved.
Keywords: Exciton dynamics, semiconductor quantum wells, time-resolved photoluminescence, free-electron laser
  • Poster
    OTST 2013 - International Workshop on Optical Terahertz Science and Technology 2013, 01.-05.04.2013, Kyoto, Japan

Publ.-Id: 18692 - Permalink

Microorganisms in flooded underground uranium mines of East Germany
Gagell, C.; Arnold, T.;
After the German reunification the Wismut GmbH, formerly the 3rd largest U producer of the world, started to remediate the legacies of their U mining activities. As part of the remediation strategy the pit body was flooded to induce reductive processes. Although flooding of the mines Pöhla and Schlema-Alberoda was already finished about ten years ago, the mine water still contains elevated concentrations of toxic metals such as U, As and Ra. Thus, expensive and long-lasting monitoring and waste water treatment is required. Since microorganisms can influence the toxicity of metals directly or indirectly, one alternative approach is to use them for bioremediation. Here, the diversity of the indigenous microbial community of the mine water from Pöhla and Schlema-Alberoda is reported. Bacteria as well as Archaea were analyzed by state-of-the-art pyrosequencing of the 16S rRNA gene. Mine water samples were either filtrated or harvested from a flow cell. For the filtrated Pöhla mine water, the Pöhla flow cell, the filtrated Schlema mine water, and the Schlema flow cell 485, 697, 325 and 527 sequences, respectively, were divided into 98, 189, 188 and 89 operational taxonomical units (OTUs), respectively, belonging mainly to Bacteria. The bacterial sequences from the Pöhla mine were classified into Proteobacteria, Verrumicrobia, Bacteriodetes, WS3, Chloroflexi, Firmicutes, Acidobacteria, SR1, Actinobacteria, Spirochaetes and OD1. For the Schlema mine Proteobacteria, Acidobacteria, WS3, Bacteriodetes, Chloroflexi, SR1, Chlorobi, TM7 and Acinobacteria were found. The dominant bacterial phylum in all samples are the Proteobacteria. Higher bacterial diversities were observed in flow cells in comparison with filtrated waters. A dataset of 15786, 17872, 11404, 7780 sequences revealed 639, 643, 769 and 455 OTUs, respectively, mainly for Archaea of the filtrated Pöhla mine water, the Pöhla flow cell, the filtrated Schlema mine water and the Schlema flow cell, respectively. The archaeal sequences of the Pöhla as well as the Schlema mine water belong to the class of Methanobacteria, Thermoprotei, Methanomicrobia, Thermoplasmata and Halobacteria.
  • Contribution to proceedings
    Goldschmidt 2013, 25.-30.08.2013, Florenz, Italien

Publ.-Id: 18691 - Permalink

Observation of Forbidden Exciton Transitions Mediated by Coulomb Interactions in Photoexcited Semiconductor Quantum Wells
Rice, W. D.; Kono, J.; Zybell, S.; Winnerl, S.; Bhattacharyya, J.; Schneider, H.; Helm, M.; Ewers, B.; Chernikov, A.; Chatterjee, S.; Khitrova, G.; Gibbs, H. M.; Schneebeli, L.; Breddermann, B.; Kira, M.; Koch, S.;
We use terahertz pulses to induce resonant transitions between the eigenstates of optically generated exciton populations in a high-quality semiconductor quantum well sample. Monitoring the excitonic photoluminescence, we observe transient quenching of the 1s exciton emission, which we attribute to the terahertz-induced 1s-to-2p excitation. Simultaneously, a pronounced enhancement of the 2s exciton emission is observed, despite the 1s-to-2s transition being dipole forbidden. A microscopic many-body theory explains the experimental observations as a Coulomb-scattering mixing of the 2s and 2p states, yielding an effective terahertz transition between the 1s and 2s populations.
Keywords: THz spectroscopy, time-resolved photoluminescence, interexcitonic transitions, semiconductor quantum wells, microscopic many-body theory, Coulomb-scattering mixing

Publ.-Id: 18690 - Permalink

Sorption and desorption processes of U(VI) on iron (hydr)oxide phases
Foerstendorf, H.; Heim, K.; Jordan, N.;
In this comparative study, the surface speciation of uranium(VI) on ferrihydrite (Fh) and maghemite (Mh) were investigated by vibrational spectroscopy. The experimental setup allows the monitoring of the surface processes at the water-solid interface in real time with a time resolution in the subminute time range. The performance of the experiments under inert gas atmosphere and under ambient conditions provides further insight into the molecular events of the binary and ternary sorption systems, respectively.
The spectra clearly demonstrate a characteristic surface speciation in dependence of the solid phase. On Fh, the formation of ternary inner sphere complexes are observed as it was derived earlier [1]. In addtion, the time-resolved spectra reveal the change of the surface speciation of atmospherically derived carbonate upon U(VI) sorption [2].
From the sorption experiments on Mh, outer sphere complexation of the uranyl ion can be derived. In ambient atmosphere, contributions of carbonate ions to the U(VI) surface speciation on Mh can not be ruled out.

[1] Ulrich et al. (2006) Geochim. Cosmochim. Acta 70, 5469-5487. [2] Foerstendorf et al. (2012) J. Colloid Interface Sci. 377, 299-306.
  • Lecture (Conference)
    Goldschmidt 2013, 25.-30.08.2013, Florence, Italy
  • Open Access LogoAbstract in refereed journal
    Mineralogical Magazine 77(2013)5, 1098-1098
    DOI: 10.1180/minmag.2013.077.5.6

Publ.-Id: 18689 - Permalink

Formation of Se(0) nanoparticles by Azospirillum brasilense
Steudtner, R.; Maffert, A.; Vogel, M.; Franzen, C.; Scheinost, A. C.;
In the present study we investigated the reduction of SeO32− by Azospirillum brasilense. The formation of fairly soluble Se(0) nano-particles during this process might be of interest for both bioremediation of Se-contaminated sites and for nanobiotechnology. After A.brasilense being exposed to Se(IV), the bacterial growth continued subsequent to a prolonged lag-phase. After a cultivation time of 3 days, a clearly reddish staining of the sample was observed and a bright red precipitate occurred, indicating the formation of Se(0) nano-particles. The SEM-EDX spectra derived from the nano-spheres indicated that they mainly consist of selenium. In addition, only 10 % of the initial Se(IV) concentrations was recoverd in culture media by means of HG-AAS, indicating a Se(IV) removal from the media. The isolated and resuspended Se(0) nanoparticles showed a long time stability of some hours, which is sufficient for the PCS and the zeta potential measurements. In contrast, Se(0) chemically formed by reduction with hydroxylamine solution produced amorphous aggregates with a rapid sedimentation behavior. The PCS measurement and the SEM imaging of the Se(0) particles showed a particle size distribution between 100 and 300 nm with an averaged particle diameter of 200 nm. The isoelectric point of Se(0) particles was found at pH 2.8 ± 0.2. The preference of forming Se(0) particles with a negative charge agree very well with the literature [1].

[1] Dhanjal & Cameotra (2010) Microb. Cell Fact. 9,1-11.
Keywords: Selen, Redox reaction, HG-AAS, SEM-EDX, PCS, Zeta potential
  • Contribution to proceedings
    Goldschmidt 2013, 25.-30.08.2013, Florence, Italy

Publ.-Id: 18688 - Permalink

Retention of selenate at the water-mineral interface in the context of salt dome repositories
Franzen, C.; Hering, D.; Jordan, N.;
One major process controlling the mobility and bioavailability of selenium, a long-lived fission product found in nuclear waste, is the adsorption onto mineral surfaces of both the engineered and geological barrier. In this context, it is important to understand to what extent this sorption is influenced particularly by characteristic parameters as expected in deep underground repositories for high level and long-lived radioactive waste. These parameters include inter alia the presence of different background salts which are important with regard to salt domes as potential repositories.
In the present study, a combination of macroscopic sorption experiments, electrophoretic mobility and in-situ ATR FT-IR spectroscopy measurements was used to study the interaction of selenate with aged γ-Al2O3 in the presence of NaCl and MgCl2. From in-situ ATR FT-IR spectra, a change in the symmetry of the aqueous tetrahedral selenate anion can be derived evidencing the formation of a surface complex on γ-Al2O3. From batch experiments, we observe a dependence of selenate sorption on the ionic strength and composition of the electrolyte. Additionally, the sorption generally decreases with increasing pH. However, in the presence of 0.1 M MgCl2, the sorption increased again at a pH above 9.5.
The isoelectric point (pHIEP) of γ-Al2O3 is located at pH 9.6 for low NaCl background electrolyte concentration (I = 0.1 M). The increase of ionic strength (up to I = 1 M) results in a decrease of the zeta potential for both the acidic and alkaline pH range. However, in the alkaline range the decrease of the zeta potential is more pronounced. Additionally, we observe that the pHIEP is shifted to more alkaline values and finally no charge reversal is observed. In the presence 0.1 M MgCl2, the surface charge of γ-Al2O3 is positive throughout the studied pH range (3-11). Above pH 10, a sharp potential decrease occurs due to Mg(OH)2 precipitation. The impact of the varied parameters on the sorption of selenate in the alkaline pH range will be verified in detail.
Keywords: sorption, selenate, gamma-al2O3
  • Poster
    Goldschmidt 2013, 25.-30.08.2013, Florence, Italy
  • Mineralogical Magazine 77(2013)5, 1107-1107
    DOI: 10.1180/minmag.2013.077.5.6

Publ.-Id: 18687 - Permalink

Sorption of uranium and neptunium onto diorite from Äspö HRL
Schmeide, K.; Gürtler, S.; Müller, K.; Steudtner, R.; Joseph, C.; Bok, F.; Brendler, V.;
The retention behavior of the crystalline rock diorite from the Äspö Hard Rock Laboratory (HRL, Sweden) towards the redox-sensitive actinides U and Np was studied by means of batch sorption experiments. The influence of various parameters, such as grain size (0.063 – 0.2 mm, 0.5 – 1 mm, 1 – 2 mm), temperature (25 and 10°C), atmosphere and sorption time (5 to 108 days) was studied using a synthetic Äspö groundwater (pH 7.8, I = 0.178 M) as background electrolyte. For U(VI), sorption isotherms were recorded (5x10−9 M to 7x10−5 M). Distribution coefficients, Kd values, were determined.
Keywords: uranium, neptunium, sorption, reduction, diorite
  • Lecture (Conference)
    Goldschmidt 2013, 25.-30.08.2013, Florence, Italy
  • Open Access LogoAbstract in refereed journal
    Mineralogical Magazine 77(2013)5, 2155-2155
    DOI: 10.1180/minmag.2013.077.5.19

Publ.-Id: 18686 - Permalink

THz free-electron laser spectroscopy of zero- and two-dimensional semiconductors
Schneider, H.;
There is no abstract.
  • Invited lecture (Conferences)
    6th Annual Meeting, Deutsches THz-Zentrum e.V., ISL Saint-Louis, 25.-26.02.2013, Saint-Louis, Frankreich

Publ.-Id: 18685 - Permalink

Mid-infrared and terahertz free-electron laser spectroscopy of zero- and two-dimensional semiconductors
Schneider, H.; Winnerl, S.; Helm, M.;
The free-electron laser (FEL) facility FELBE in Dresden provides unique opportunities to advance our knowledge on the interaction of intense mid-infrared and terahertz fields with materials and devices. Its nearly transform-limited ps pulses, which can also be combined with synchronous ps or fs pulses from near-infared tabletop lasers, represent a versatile radiation source for novel experiments, which is also available to external users. This talk reviews some of our recent experimental studies, which are also representative for advanced measurement techniques at FELBE.
In high-quality semiconductor quantum wells, time-resolved photoluminescence allows us to investigate the dynamics of excitons, i.e. two-dimensional, hydrogen-like electron-hole quasiatoms. In particular, applying time-delayed FEL pulses tuned to the intra-excitonic 1s-2p transition (at 9 meV for an 8 nm wide GaAs/AlGaAs quantum well), we have studied the population transfer between the 2p and 2s exciton states. Moreover, strong terahertz pumping in resonance with the 1s-2p transition results in a characteristic splitting (Rabi splitting) of the 1s exciton state, which is a manifestation of the intra-excitonic Autler-Townes effect [1].
In semiconductor quantum dots, resonant excitation between s, p and d sublevels in these zero-dimensional atom-like nanostructures is shown to produce an absorption contrast in aperture-less scattering scanning near-field optical microscopy (s-SNOM). This effect allows us to obtain functional s-SNOM images with deep sub-wavelength resolution, where far-infrared absorption by single electrons produces sufficient contrast to map individual quantum dots [2].
In graphene, FEL-based pump-probe spectroscopy has shown evidence of different relaxation times for excitation energies above and below those of the optical phonons, as well as a transition from induced transmission (bleaching) to induced absorption if the photon energy becomes smaller than twice the Fermi energy [3]. In particular, the latter observation is indicative for interesting potential applications of this two-dimensional semiconductor material, e.g. as an electro-optical modulator.
[1] J. Wagner et al., Phys. Rev. Lett. 105, 167401 (2010)
[2] R. Jacob et al., Nano Lett. 12, 4336–4340 (2012))
[3] S. Winnerl et al., Phys. Rev. Lett. 107, 237401 (2011)
  • Lecture (Conference)
    41st Freiburg Infrared Colloquium, 26.-27.02.2013, Freiburg, Deutschland

Publ.-Id: 18684 - Permalink

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