Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31738 Publications
Thermal evolution of defects in undoped zinc oxide grown by pulsed laser deposition
Wang, Z.; Su, S.; Ling, F. C. C.; Anwand, W.; Wagner, A.;
Undoped ZnO films are grown by pulsed laser deposition on c-plane sapphire with different Oxygen pressures. Thermal evolutions of defects in the ZnO films are studied by secondary ion mass spectroscopy (SIMS), Raman spectroscopy, and positron annihilation spectroscopy (PAS), and with the electrical properties characterized by the room temperature Hall measurement. Oxygen deficient defect related Raman lines 560 cm^-1 and 584 cm^-1 are identified and their origins are discussed. Thermal annealing induces extensive Zn out-diffusion at the ZnO/sapphire interface and leaves out Zn-vacancy in the ZnO film. Two types of Zn-vacancy related defects with different microstructures are identified in the films. One of them dominates in the samples grown without oxygen. Annealing the sample grown without oxygen or growing the samples in oxygen would favor the Zn-vacancy with another microstructure, and this Zn-vacancy defect persists after 1100 °C annealing.
Keywords: undoped ZnO films, Raman spectroscopy, positron annihilation, green luminescence

Publ.-Id: 20678 - Permalink


Nature of red luminescence band in research-grade ZnO single crystals: A “self-activated” configurational transition
Chen, Y. N.; Xu, S. J.; Zheng, C. C.; Ning, J. Q.; Ling, F. C. C.; Anwand, W.; Brauer, G.; Skorupa, W.;
By implanting Zn+ ions into research-grade intentionally undoped ZnO single crystal for facilitating Zn interstitials (Zni) and O vacancies (VO) which is revealed by precise X-Ray diffraction rocking curves, we observe an apparent broad red luminescence band with a nearly perfect Gaussian lineshape. This red luminescence band has the zero phonon line at ~2.4 eV and shows distinctive lattice temperature dependence which is well interpreted with the configurational coordinate model. It also shows a low “kick out” thermal energy and small thermal quenching energy. A “selfactivated” optical transition between a shallow donor and the defect center of Zni-VO complex or VZnVO di-vacancies is proposed to be responsible for the red luminescence band. Accompanied with the optical transition, large lattice relaxation simultaneously occurs around the center, as indicated by the generation of multiphonons.
Keywords: ZnO, Zn Implantation, red luminescence, Zn interstitials, O vacancies

Publ.-Id: 20677 - Permalink


Quantification of brittle-ductile failure behavior of ferritic reactor pressure vessel steels using the Small-Punch-Test and micromechanical damage models
Linse, T.; Kuna, M.; Viehrig, H.-W.;
Two German ferritic pressure vessel steels are examined in the brittle to ductile transition regime as a function of temperature and irradiation.The experiments are done by a miniaturized Small-Punch-Test in hot cells within the temperature range of -185 °C up to 70 °C. From the load–displacement curve of the SPT,the yield curves and parameters of both a non-local GURSON-TVERGAARD-NEEDLEMAN ductile damage model and a modified BEREMIN model are identified. The influence of temperature and irradiation on the model parameters is analyzed. All parameters are verified by comparison with results from standard test methods. The parameters, identified from SPT, are used to simulate the failure behavior in standard fracture mechanics specimens.In the uppershelf, the non-local GTN-model is applied to simulate crack resistance curves,from where the fracture toughness data could be successfully predicted. In the lower shelf, the WEIBULL-stress of the specimens was computed to find out the statistics of fracture toughness values.Finally, the modified BEREMIN model and the non-local ductile damage model were combined to evaluate the failure of fracture specimens in the brittle-ductile transition region.This way, an acceptable agreement with Master-Curve data for non-irradiated steels could be achieved in the whole temperature range.
Keywords: Non-local ductiledamagemodel, Beremin-Model, Small-Punch-Test, Brittle-ductile transition

Publ.-Id: 20676 - Permalink


Numerical simulations of two-phase stratified turbulent flow in a channel
Apanasevich, P.; Lucas, D.; Sato, Y.; Ničeno, B.;
The main goal of the current research project is numerical investigation of steam condensation on a subcooled water interface. The Direct Numerical (DNS) and Large Eddy Simulation (LES) methods are used to study physical mechanisms determining the interfacial heat and mass transfer. The paper presents a part of this work that deals with the evaluation of the Sub-Grid Scale (SGS) modeling within the LES framework. For that purpose two simulations of a stratified turbulent counter-current steam-water flow in a channel were conducted using the Wall-Adapting Local Eddy-Viscosity (WALE) SGS model. To exclude the phase change and to focus on the turbulence in the vicinity of the interface, both phases were assumed to be at saturation tem-perature. The simulations have shown that the variation of the WALE model constant has a significant influence on the mean velocity and velocity fluctuations and should be calibrated using the DNS data. It was also shown that the deformable steam-water interface has a strong damping effect on the near-interfacial turbulent field in the liquid phase.
Keywords: Computational fluid dynamics, free surface flows, large eddy simulation, turbulent flows
  • Contribution to proceedings
    2nd International Symposium on Multiscale Multiphase Process Engineering (MMPE2014), 24.-27.09.2014, Hamburg, Deutschland
    2nd International Symposium on Multiscale Multiphase Process Engineering
  • Poster
    2nd International Symposium on Multiscale Multiphase Process Engineering (MMPE2014), 24.-27.09.2014, Hamburg, Deutschland

Publ.-Id: 20673 - Permalink


Isobar separation of 93Zr and 93Nb at 24MeV with a new multi-anode ionization chamber
Martschini, M.; Buchriegler, J.; Collon, P.; Kutschera, W.; Lachner, J.; Lu, W.; Priller, A.; Steier, P.; Golser, R.;
93Zr with a half-life of 1.6 Ma is produced with high yield in nuclear fission, and thus should be present as a natural or anthropogenic trace isotope in all compartments of the general environment. This isotope would immediately find numerous applications, however, its detection at sufficiently low levels has not yet been achieved. AMS measurements of 93Zr suffer from the interference of the stable isobar 93Nb. At the Vienna Environmental Research Accelerator VERA a new multi-anode ionization chamber was built. It is optimized for isobar separation in the medium mass range and is based on the experience from AMS experiments of 36Cl at our 3MV-facility. The design provides high flexibility in anode configuration and detector geometry. After validating the excellent energy resolution of the detector with 36Cl, it was recently used to study Iron-Nickel and Zirconium-Niobium-Molybdenum isobar separation. To our surprise, the separation of 94Zr (Z=40) from 94Mo (Z=42) was found to be much better than that of 58Fe (Z=26) from 58Ni (Z=28), despite the significantly larger deltaZ/Z of the latter pair. This clearly contradicts results from SRIM-simulations and suggests that differences in the stopping behavior may unexpectedly favor identification of 93Zr. At 24 MeV particle energy, a 93Nb (Z=41) suppression factor of 1000 was achieved based on a 93Zr spectrum obtained by interpolation between experimental spectra from the two neighboring stable isotopes 92Zr and 94Zr. Assuming realistic numbers for chemical Niobium reduction, a detection level of 93Zr/Zr below 10^9 seems feasible.
Keywords: accelerator mass spectrometry, isobar separation, isobar suppression, anthropogenic trace isotope, VERA, SRIM, Niobium, Zirconium
  • Lecture (Conference)
    AMS-13 The Thirteenth International Conference on Accelerator Mass Spectrometry, 24.-29.08.2014, Aix en Provence, France

Publ.-Id: 20672 - Permalink


Investigations on the Discrimination of Nuclear Reactor Core State Changes by the external Gamma Radiation Field
Brachem, C.; Konheiser, J.; Hampel, U.;
Monte Carlo Simulations have been carried out to estimate the gamma radiation distributions outside the reactor pressure vessel of a generic pressurized water reactor for a set of simplified accident-like reactor states.
This is done as a first step towards the development of a non-invasive core monitoring system for light water reactors.
The results show a change in the shape of the gamma ray distributions for decreasing coolant levels as well as a vast increase in flux for corium accumulating inside the lower head.
Keywords: gamma radiation, Monte Carlo simulation, PWR, accident
  • Lecture (Conference)
    46th Annual Meeting on Nuclear Technology, 05.-07.05.2014, Berlin, Germany

Publ.-Id: 20671 - Permalink


The Gamma Radiation emitted by a PWR Core under severe Accident Conditions
Brachem, C.; Konheiser, J.; Hampel, U.;
The gamma radiation emitted by a nuclear reactor core might contain information about the reactor state. This information may be used in a monitoring system for severe accidents.
The Technische Universit¨at Dresden and the Zittau/G¨orlitz University of Applied Sciences are currently carrying out feasibility studies for the development of such a system in a collaborative effort. As one part of such feasibility studies we performed Monte Carlo simulations on a simplified model of a generic pressurized water reactor. For a set of states which represent scenarios of a coolant level decrease and core melt, the gamma radiation distribution outside the reactor pressure vessel has been computed.
The results are presented in this paper.
They indicate that different coolant levels yield different gamma radiation distributions, and that an accumulation of corium inside the lower head is detectable from the outside.
Keywords: gamma radiation, Monte Carlo simulation, PWR, accident
  • Lecture (Conference)
    22nd International Conference on Nuclear Engineering (ICONE22), 07.-11.07.2014, Prague, Czech Republic
  • Contribution to proceedings
    22nd International Conference on Nuclear Engineering (ICONE22), 07.-11.07.2014, Prague, Czech Republic
    Proceedings of the 22nd International Conference on Nuclear Engineering, ICONE22

Publ.-Id: 20670 - Permalink


Development of a Joule-class Yb:YAG amplifier and its implementation in a CPA system generating 1TW pulses
Wandt, C.; Klingebiel, S.; Keppler, S.; Hornung, M.; Loeser, M.; Siebold, M.; Skrobol, C.; Kessel, A.; Trushin, S. A.; Major, Z.; Hein, J.; Kaluza, M. C.; Krausz, F.; Karsch, S.;
In this paper the development and implementation of a novel amplifier setup as an additional stage for the CPA pump laser of the Petawatt Field Synthesizer, currently developed at the Max-Planck-Institute of Quantum Optics, is resented. This amplifier design comprises 20 relay-imaged passes through the active medium which are arranged in rotational symmetry. As the gain material, an in-house-developed Yb:YAG active-mirror is used. With this setup, stretched 4 ns seed pulses are amplified to output energies exceeding 1 J with repetition rates of up to 2 Hz. Furthermore, a spectral bandwidth of 3.5nm (FWHM) is maintained during amplification and the compression of the pulses down to their Fourier-limit of 740 fs is achieved. To the best of our knowledge, this is the first demonstration of 1TW pulses generated via CPA in diode-pumped Yb:YAG.

Publ.-Id: 20669 - Permalink


Sponge-like Si-SiO2 nanocomposite for PV applications
Liedke, B.; Heinig, K.-H.; Friedrich, D.; Schmidt, B.; Mücklich, A.; Keles, U.; Bulutay, C.;
The aim of this talk is to explain method of fabrication, modification and optimization of Sponge-like Si-SiO2 nanocomposite.
It consists of Si embedded in SiO2 fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide SiOx≈1. Thermal treatment using rapid thermal processing and oven annealing requires annealing times of few tens of sec. up to few tens of min. However, in a thin film technology the phase separation of SiOx at high temperatures requires a very rapid thermal processing of few tens of ms in order to avoid substrate damage.
Here, the structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography and atom probe tomography, which revealed a percolated Si morphology. This is in excellent agreement with atomistic simulations using kinetic Monte-Carlo method. Depending on the annealing time and temperature a feature size in the range of 2...5 nm was found, which is small enough for band gap widening due to quantum confinement.
We show that the favorable properties of Si-SiO2 nanocomposite, e.g. quantum size effect and percolated morphology, make it a suitable material for PV absorber.
Keywords: sponge-like nanocomposite, SiOx, photovoltaic, absorber, phase separation, band-gap engineering
  • Lecture (others)
    Seminar an der TU Bergakademie Freiberg, 15.07.2014, Freiberg, Germany

Publ.-Id: 20668 - Permalink


Optimization of magnetic amplification by flow constraints in turbulent liquid sodium
Nornberg, M. D.; Taylor, N. Z.; Forest, C. B.; Rahbarnia, K.; Kaplan, E.;
Direct measurements of the vector turbulent emf in a driven two-vortex flow of liquid sodium were performed in the Madison Dynamo Experiment [K. Rahbarnia et al., Astrophys. J. 759, 80 (2012)]. The measured turbulent emf is anti-parallel with the mean current and is almost entirely described by an enhanced resistivity, which increases the threshold for a kinematic dynamo. We have demonstrated that this enhanced resistivity can be mitigated by eliminating the largest-scale eddies through the introduction of baffles. By tailoring the flow to reduce large-scale components and control the helical pitch, we have reduced the power required to drive the impellers, doubled the magnetic flux generated by differential rotation, and increased the decay time of externally applied magnetic fields. Despite these improvements, the flows remain sub-critical to the dynamo instability due to the reemergence of turbulent fluctuations at high flow speeds.
Keywords: Magnetic fields, Magnetic field measurements, Rotating flows, Diffusion, Flow Instabilities

Publ.-Id: 20666 - Permalink


Stand-alone modelling of the high burnup structure formation and burst release during design basis accidents
Holt, L.; Schubert, A.; van de Laar, J.; van Uffelen, P.;
In the first part of the paper, experimental results for the Xe depletion in the matrix of high burn-up fuel are analysed from the High Burnup Rim Project (HBRP). The influence of the burn-up and irradiation temperature on the Xe concentration was investigated using a multi-physics approach involving various simulation tools. The temperature influence was accounted for by means of the temperature dependent effective burn-up. Good agreement was found between the modelled temperature threshold of the effective burn-up and the experimental temperature threshold between un- and restructured fuel in the HBRP. However, a systematic difference was observed between the onset burn-up derived from the Xe measurements in highly enriched discs such as those of HBRP and the corresponding values derived from irradiated Light Water Reactor fuel rods and reported in the open literature. A sensitivity study identified the neutron flux spectrum and the fission product yields as the main reasons for the observed differences.

In the second part of the paper, we present a new model for dealing with release of fission gas from nuclear fuel containing a high burnup structure (HBS) during design basis accidents such as loss of coolant accident. The fission gas release from the HBS during an accident is assumed to be caused by crack formation. The empirical model is developed on the basis of out-of-pile annealing tests carried out with samples from HBRP discs irradiated in Halden, and then subsequently applied to an integral in-pile test in IFA-650. In addition to the comparison with the experimental data, the new model is also compared with some models available in the open literature. Finally, from the discussion we also outline the experimental and modelling work needed for further model refinements.
  • Contribution to proceedings
    Enlarged Halden Programme Group Meeting, 07.-12.09.2014, Røros, Norway

Publ.-Id: 20665 - Permalink


Stabilität des Hypoxietracers [18F]-FMISO während sequentieller PET-Untersuchungen bei Patienten mit radiochemotherapierten HNO-Tumoren und Korrelation von funktionellen Tumor-Subvolumina zur Rezidivlokalisation
Zschaeck, S.; Haase, R.; Zöphel, K.; Abolmaali, N.; Perrin, R.; Kotzerke, J.; Steinbach, J.; Zips, D.; Krause, M.; Baumann, M.;
Fragestellung.
Untersucht wurde die Verteilung der Aktivitätskonzentration des Hypoxietracers FMISO in sequentiellen PET-Untersuchungen bei Patienten mit primär radiochemotherapierten Kopf-Hals-Tumoren. Patienten mit residueller Hypoxie während der zweiten Behandlungswoche erleiden fast immer ein Lokalrezidiv im Hochdosis-Bereich. Zur Erhöhung der Strahlendosis werden unter anderem FMISO-PET-basiert adaptierte Dosisverschreibungen (Dose-painting) diskutiert. Für eine erste Plausibilitätsprüfung dieses Ansatzes wurde die Stabilität der FMISO-Verteilung und die Lokalisation von Lokalrezidiven mit, während der Therapie erfassten, PET-Parametern untersucht.
Methodik.
Von 25 Patienten, die während der primären Radiochemotherapie sequentielle FMISO Aufnahmen erhielten (FMISO1 vor Therapie, FMISO2 in der ersten, FMISO3 in der zweiten und FMISO4 in der fünften Woche) zeigten 12 eine ausgeprägte residuelle Hypoxie (bestimmt als TBRmax>1,9). Sechs dieser Patienten hatten ein auswertbares Lokalrezidiv (2 x in der CT und 4 x in der FDG-PET-CT). Die Rezidivbildgebung und darauf basierende Konturen wurden auf die FMISO- und FDG PET-Untersuchungen vor Therapie fusioniert und die PET-Konturen auf ein Überlappen überprüft.
Ergebnis.
Die wiederholten FMISO-PET-Untersuchungen während der Radiochemotherapie zeigten ein sehr heterogenes volumetrisches Verhalten der hypoxischen Subvolumina zu Beginn der Therapie. In der FMISO4-Bildgebung war nur noch selten Hypoxie nachzuweisen. Trotz der Größenvariationen innerhalb der ersten beiden Wochen war die Überlappung der sequentiellen Sub-Volumina ausgeprägt, bestimmt als mittlerer Dice-Index von 62% zwischen FMISO1 und FMISO2 und 58% zwischen FMISO2 und FMISO3. Die Lokalisation des Aktivitäts-Hot-Spots SUVmax zeigte demgegenüber dramatische Veränderungen, der mittlere Abstand betrug zwischen FMISO2 und FMISO3 13,5
mm. Die vorhandenen, registrierten Rezidive zeigten sowohl ein Überlappen mit dem initialen FDG-PET, als auch mit FMISO1 und FMISO3 (medianer Dice-Index 27, 24 und 28%). Zur Überprüfung ob es wirklich eine reproduzierbare und stabile FMISO-PET-positive Region gibt, die sich zur Dosiseskalation eignet, wurden die überlappenden Konturen verschiedener FDG und FMISO-Konturen zu einer gemeinsamen Kontur zusammengefasst (FDG, FMISO1, FMISO3). Nur in 2 Fällen trat das Rezidiv in der so eingegrenzten Region auf.
Schlussfolgerung.
Die FMISO-Verteilung variiert während der ersten beiden Therapiewochen erheblich, es erfolgt jedoch keine komplette Verschiebung des hypoxischen Subvolumens sondern eine unterschiedlich ausgeprägte Volumenveränderung. Die Überlappung der FMISO-PET-basierten Subvolumina mit dem Lokalrezidiv stärken die Hypothese, dass radioresistente Zellen in diesen Regionen das Rezidiv verursachen können. Die Variabilität des SUVmax und die geringe Rate an Rezidiven innerhalb einer reproduzierbar abgrenzbaren FDG und FMISO aviden Region sprechen jedoch gegen eine, rein voxelbasierte, Dosisverschreibung.
  • Poster
    20. Jahrestagung der Deutschen Gesellschaft für Radioonkologie (DEGRO), 03.-06.07.2014, Düsseldorf, D
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 190(2014)Suppl. 1, 52

Publ.-Id: 20664 - Permalink


Spin dynamics in triangular-lattice antiferromagnets Cs2CuBr4 and Cs2CuCl4: high-field ESR studies
Zvyagin, S.;
A spin-1/2 Heisenberg antiferromagnet (AF) on a triangular lattice is the paradigmatic model in quantum magnetism, which was intensively studied. In spite of numerous theoretical studies (which predict a rich variety of grounds states, ranging from a gapless spin liquid to Néel order), many important details of the phase diagram of triangular-lattice AFs remain controversial or even missing. In order to test the theory experimentally, a precise information on the spin-Hamiltonian parameters for the materials of interest is highly demanded. Here, we present results of high-field electron spin resonance (ESR) studies of spin-1/2 Heisenberg AFs Cs2CuCl4 and Cs2CuBr4 with distorted triangular-lattice structures in magnetic fields up to 50 T [1]. In the magnetically saturated phase (H>Hsat), quantum fluctuations are fully suppressed, and the spin dynamics is defined by ordinary magnons. This allows us to accurately describe the magnetic excitation spectra in both materials and, using the harmonic spin-wave theory, to determine their exchange parameters. The viability of the proposed method was first proven by applying it to Cs2CuCl4, revealing good agreement with inelastic neutron-scattering results. For the isostructural Cs2CuBr4 we obtain J/kB=14.9(7) K, J'/kB=6.1(3) K, [J'/J~0.41], providing exact and conclusive information on the exchange coupling parameters in this frustrated spin system. The approach has a broader impact and can be potentially used for any quantum magnet with reduced (e.g., by the staggered Dzyaloshinskii-Moriya interaction) translational symmetry, resulting, as predicted, in emergence of a new exchange mode above Hsat
  • Invited lecture (Conferences)
    Fifth Workshop on Current Trends in Molecular and Nanoscale Magnetism, 26.-29.05.2014, Larnaca, Cyprus

Publ.-Id: 20662 - Permalink


Site-selective TRLFS of Eu(III) doped rare earth phosphates for conditioning of radioactive wastes
Huittinen, N.; Arinicheva, Y.; Holthausen, J.; Holliday, K.; Neumeier, S.; Stumpf, T.;
Crystalline ceramic materials show promise as potential waste forms for immobilization of high-level radioactive wastes. Rare earth (RE) phosphate ceramics have been found to be extremely stable over geological time scales and they show good tolerance to high radiation doses. These ceramics are able to incorporate radionuclides in well-defined atomic positions within the crystal lattice up to high (~25%) loadings, which will reduce the volume of waste in the radionuclide conditioning process. The dehydrated RE phosphates are known to crystallize in two distinct structures, depending on the ionic radius of the cation: the larger lanthanides from La3+ to Gd3+ crystallize in the nine-fold coordinated monazite structure, while the smaller lanthanides such as Lu3+ form eight-fold coordinated xenotime structures.
Structural information on the radionuclide substitution in these RE phophates can be obtained by site-selective time-resolved laser fluorescence spectroscopy (TRLFS). In our previous work we studied the structural incorporation of Eu(III), taken as an analogue for the long-lived trivalent actinides Pu(III), Am(III) and Cm(III) found in spent nuclear fuel, in the monazite LaPO4. Eu3+ was found to incorporate on the La3+ site in LaPO4 as expected, despite slight discrepancies between the ionic radii of the host and dopant cations.
In the present work we study synthetic Eu(III) doped LaPO4, GdPO4, and LuPO4, as well as mixtures thereof, to investigate the influence of the ionic radius and crystalline structure on Eu(III) substitution in the ceramic material. Results on Eu(III) substitution in the monazite and xenotime materials will be presented and influences of the ionic radii on Eu(III) substitution within the host cation sites will be discussed.
  • Poster
    Goldschmidt 2014, 08.-13.06.2014, Sacramento, USA

Publ.-Id: 20661 - Permalink


Experimentelle Untersuchungen zur Ablagerung und Remobilisierung von Aerosolpartikeln in turbulenten Strömungen
Barth, T.;
Im Rahmen dieser Dissertation werden eine Serie von Grundlagenexperimenten zur Ablagerung (Deposition) und Remobilisierung (Resuspension) von Aerosolpartikeln in turbulenten Strömungen beschrieben. Die Kernmotivation stellt die Quelltermanalyse von Druckentlastungsstörfällen von Hochtemperaturreaktoren (HTR) dar. Im Primärkreislauf früherer HTR-Forschungsanlagen wurden größere Mengen an radiologisch belastetem Graphitstaub gefunden. Dieser Staub scheint größtenteils durch Abrieb zwischen den graphitischen Kernstrukturen entstanden zu sein und verteilte sich während des fortlaufenden Reaktorbetriebs über sämtliche Oberflächen des Primärkreislaufs. Während eines Druckentlastungsstörfalls kann dieser Staub durch die Gasströmung remobilisiert und aus dem Primärkreislauf ausgetragen werden. Eine Quelltermanalyse solch eines Störfallszenarios erfordert die Kenntnis über die Menge und die räumliche Verteilung des Staubs, die radiologische Belastung sowie das Remobilisierungsverhalten in Bezug auf die zu erwartenden Strömungstransienten. Nach dem heutigen Stand von Wissenschaft und Technik kann die räumlich-zeitliche Verteilung des Staubs im Primärkreislauf für stationären Reaktorbetrieb unter Verwendung eindimensionaler Systemcodes abgeschätzt werden. Jedoch ist unbekannt, welcher Anteil des Staubinventars durch die Gasströmung remobilisiert und aus dem Primärkreislauf ausgetragen werden würde.
Zur systematischen Untersuchung des Staubtransportverhaltens in turbulenten Strömungen wurden zwei kleinskalige Versuchsanlagen entwickelt und eine Serie von Depositions- und Resuspensionsexperimenten durchgeführt. Die partikelbeladene Strömung in der Heißgasumgebung des HTR-Primärkreislaufs wurde über die Verwendung von Ähnlichkeitskennzahlen auf eine Luftströmung bei Umgebungsbedingungen herunterskaliert. Die Strömung und die Partikel wurden mittels hochauflösender, bildgebender und nichtinvasiver Messverfahren räumlich und zeitlich vermessen, um eine umfangreiche Datenbasis für die Analyse der Partikeltransportprozesse zu erstellen. Inhaltlich lassen sich die durchgeführten Untersuchungen in drei Teile gliedern. Der erste Teil besteht aus zwei Studien über die Deposition und Resuspension monodisperser, sphärischer Einzelpartikel in einer ungestörten, horizontalen Kanalströmung. Die systematische Variation experimenteller Randbedingungen wie der Partikelgröße, der Oberflächenrauheit und der Strömungsgeschwindigkeit ermöglichte die Quantifizierung der einzelnen Einflussgrößen. Im zweiten und dritten Teil der Dissertation wurden die Deposition und Resuspension einer mehrschichtigen Ablagerung (Partikel-Multilayer) zwischen periodischen Stufen und in einer Kugelschüttung untersucht, um die komplexe Interaktion zwischen der turbulenten Strömung und der Multilayer-Ablagerung weiter zu erforschen.
Die gewonnenen Erkenntnisse leisten einen Beitrag für die Quelltermanalyse des Staubtransports im HTR-Primärkreislauf und können für die Weiterentwicklung numerischer Strömungssimulationen des Partikeltransports in turbulenten Strömungen verwendet werden.
Keywords: turbulent flows, aerosol particle, deposition, resuspension, high temperature reactor
  • Doctoral thesis
    TU Dresden, 2014
    Mentor: Prof. Dr.-Ing. habil. Uwe Hampel
    155 Seiten

Publ.-Id: 20660 - Permalink


Development of substrate-based radiotracers for imaging of tumour-associated lysyl oxidase activity by positron emission tomography
Kuchar, M.; Bergmann, R.; Wodtke, R.; Mosch, B.; Lenk, J.; Steinbach, J.; Pietzsch, J.; Löser, R.;
kein Abstract verfügbar
  • Poster
    23rd Biennial Congress of the European Association for Cancer Research (EACR), 05.-08.07.2014, München, D
  • Abstract in refereed journal
    European Journal of Cancer 50(2014)Suppl. 5, S204

Publ.-Id: 20659 - Permalink


EphB4 negatively regulates blood vessel network formation and perfusion in human A375 melanoma xenografts
Neuber, C.; Hofheinz, F.; Bergmann, R.; Meister, S.; Steinbach, J.; Mosch, B.; Pietzsch, J.;
kein Abstract verfügbar
  • Poster
    23rd Biennial Congress of the European Association for Cancer Research (EACR), 05.-08.07.2014, München, D
  • Abstract in refereed journal
    European Journal of Cancer 50(2014)Suppl. 5, S62-S63

Publ.-Id: 20658 - Permalink


A novel animal model of phaeochromocytoma for preclinical therapy evaluation
Ullrich, M.; Bergmann, R.; Pietzsch, J.; Cartellieri, M.; Peitzsch, M.; Eisenhofer, G.; Bornstein, S. R.; Ziegler, C. G.;
kein Abstract verfügbar
  • Poster
    23rd Biennial Congress of the European Association for Cancer Research (EACR), 05.-08.07.2014, München, D
  • Abstract in refereed journal
    European Journal of Cancer 50(2014)Suppl. 5, S53

Publ.-Id: 20657 - Permalink


Role of extracellular S100A4 in stimulation of melanoma cells crossing the blood-brain barrier in vitro and in vivo
Herwig, N.; Wolf, S.; Haase-Kohn, C.; Steinbach, J.; Pietzsch, J.;
kein Abstract verfügbar
  • Poster
    23rd Biennial Congress of the European Association for Cancer Research (EACR), 05.-08.07.2014, München, D
  • Abstract in refereed journal
    European Journal of Cancer 50(2014)Suppl. 5, S49

Publ.-Id: 20656 - Permalink


Effect of notch acuity on the apparent fracture toughness
Schindler, H.-J.; Kalkhof, D.; Viehrig, H.-W.;
The fracture behaviour of a component or specimen that contains a sharp notch is governed essentially by the same theoretical relations known from cracks. The blunt notch root only causes an increase of the resistance against crack initiation, which depends on the fracture mechanism. In the present paper, the relation between fracture toughness and notch toughness is investigated by simple analytical models. The derived formulas were compared with experimental results obtained from fracture toughness tests on RPV-steel 24 NiCrMo 3-7 at various temperatures. 1T-CT- and 0.4T-SEB-specimens that contained a sharp notch with a root radius of 0.06 mm introduced by spark erosion (EDM) instead of the standard fatigue crack were used. The predictions were found to agree well with the experimental data. The effect of the notch radius on fracture toughness is most pronounced in the brittle to ductile transition regime, where fracture toughness can be characterized by the master curve and the corresponding reference temperature T0 according to ASTM E1921. Accordingly, the effect of the notch radius can be quantified by a shift of T0. Since the shape of the transition curve depends on the notch radius, the procedure of ASTM E1921 to determine T0 is not applicable. An alternative is suggested. As limiting cases, ductile tearing and brittle fracture are also considered.
Keywords: Ductile to brittle transition, reference temperature, notch, toughness, root radius, ferritic steel

Publ.-Id: 20654 - Permalink


Uniaxial anisotropy and its manipulation in amorphous Co68Fe24Zr8 thin films
Fu, Y.; Barsukov, I.; Meckenstock, R.; Lindner, J.; Zhai, Y.; Hjörvarsson, B.; Farle, M.;
We have proven that the growth of Co68Fe24Zr 8 layers under external field yields a uniaxial anisotropy, defined by the direction of the field. No magnetic coupling is present between Co 68Fe24Zr8 layers when separated by a 3nm of Al70Zr30. The anisotropy axis can therefore be manipulated at will and the direction can be tailored, layer by layer in multilayers, by the choice of the direction of the applied field during growth. The g-factor (2.13) and the anisotropy constant, obtained from ferromagnetic resonance, support the existence of short-range order. The relation between the temperature dependences of magnetic anisotropy and magnetization are partially captured by Callen-Callen power law.

Publ.-Id: 20653 - Permalink


Strong Auger scattering in Landau-quantized graphene investigated by infrared pump-probe experiments
Mittendorff, M.; Wendler, F.; Malic, E.; Knorr, A.; Orlita, M.; Potemski, M.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.; Winnerl, S.;
The non-equidistant Landau-level (LL) spectrum of graphene enables the investigation of the carrier dynamics of distinct LL transitions. We present pump-probe measurements on multilayer epitaxial graphene, complemented by microscopic modelling. The free-electron laser (FEL) FELBE served as radiation source at a wavelength of 16.5 µm, which corresponds to a photon energy of 75 meV. At a magnetic field of 4.2 T, the photon energy gets resonant with the energetically degenerate LL transitions LL-1 → LL0 and LL0 → LL1. Circularly polarized radiation allows one to address one of these transitions selectively.
Besides a strong increase of the pump-probe signal at 4.2 T, we observe a complex set of pump-probe signals for all four combinations of pump and probe polarization. For contrarily polarized pump and probe radiation, one would expect negative pump-probe signals, as the initial state of the probed transition is populated (pump: σ+; probe: σ-) or the final state of the probe gets depopulated.
Our measurements show the counterintuitive result of positive pump-probe signals for the case of σ+-polarized pump radiation. The experimental findings are well described by microscopic calculations based on the density matrix formalism, which helped to reveal the origin of this behavior.
Keywords: Landau quantization; relaxation dynamics; graphene
  • Lecture (Conference)
    High Magnetic Fields in Semiconductor Physics, 03.-08.08.2014, Panama City Beach, USA

Publ.-Id: 20652 - Permalink


Kurzzeitspektroskopie: Kürzeste Laserpulse für Materialuntersuchungen
Mittendorff, M.;
Mit Hilfe der Kurzzeitspektroskopie ist es möglich die Ladungsträgerdynamik in unterschiedlichen Materialsystemen direkt zu untersuchen. Bei sog. „Pump-Probe-Messungen“ werden z.B. Ladungsträger oder Moleküle mit einem sehr intensiven, aber auch sehr kurzen Laserpuls angeregt. Ein zweiter, wesentlich schwächerer Puls wird verwendet um die verursachte Änderung zu messen. Durch eine zeitliche Verschiebung des zweiten Pulses kann gemessen werden, wie lange das System braucht um die Energie wieder abzugeben. Eine einfache Skizze eines Aufbaus für Pump-Probe-Messungen, sowie ein Beispiel für das Ergebnis einer Messung sind in Abb. 1 gezeigt. Diese Untersuchungen sind beispielsweise besonders wichtig zur Entwicklung und Optimierung elektro-optischer Bauelemente wie z. B. Detektoren oder optische Modulatoren.
Die erreichbare zeitliche Auflösung bei diesen Messungen hängt im Wesentlichen von der Pulsdauer des Lasersystems ab. In diesem Vortrag werden verschieden Lasersysteme zur Erzeugung ultra-kurzer Laserpulse in einem breiten Spektralbereich vom nahen bis zum fernen Infrarot vorgestellt (800 nm – 250 µm). Zu jedem vorgestellten System wird als Beispiel eine Messung der Ladungsträgerdynamik in Graphen gezeigt, das aus einem zweidimensionalen Gitter aus Kohlenstoffatomen besteht. Dieses relativ neue Material, für dessen Untersuchung der Nobelpreis für Physik 2010 verliehen wurde, ist neben der Verwendung in der Elektronik speziell für Anwendungen in der Optoelektronik interessant. Durch die Verwendung verschiedener Wellenlängen können in diesem Material unterschiedliche physikalische Effekte untersucht werden.
  • Lecture (others)
    2. Fortbildungsveranstaltung zu Optotechnik und Bildverarbeitung, 27.06.2014, Darmstadt, Deutschland

Publ.-Id: 20651 - Permalink


Radiobiological response to ultra-short pulsed megavoltage electron beams of ultra-high pulse dose rate
Beyreuther, E.; Karsch, L.; Laschinsky, L.; Lessmann, E.; Naumburger, D.; Oppelt, M.; Richter, C.; Schürer, M.; Woithe, J.; Pawelke, J.;
Purpose: In line with the long-term aim of establishing the laser based particle acceleration for future medical application the radiobiological consequences of electron delivery with the typical ultra-short pulses of ultra-high pulse dose rate have to be investigated.
Materials and methods: The radiation source ELBE (Electron Linac for beams with high Brilliance and low Emittance) was used to mimic the quasi-continuous electron beam of a clinical linear accelerator (LINAC) and to deliver electron pulses at the ultra-high pulse dose rate of 10^10 Gy min-1 either at the low frequency of a laser accelerator or at 13 MHz avoiding effects of prolonged dose delivery. The impact of pulse structure was analysed by clonogenic survival assay and by the number of residual DNA double-strand breaks remaining 24 h after irradiation of two human squamous cell carcinoma lines of differing radiosensitivity.
Results: The radiation response of both cell lines was found to be independent from electron pulse structure for the two endpoints under investigation.
Conclusions: The results reveal, that ultra-high pulse dose rate of 10^10 Gy min-1 and the low repetition rate of laser accelerated electrons have no additional influence on the radiobiological effectiveness of megavoltage electrons.
Keywords: pulsed electron treatment, laser particle acceleration, ultra-high pulse dose rate, in vitro dose response

Publ.-Id: 20650 - Permalink


Microscopic Description of Intraband Absorption in Graphene: The Occurrence of Transient Negative Differential Transmission
Kadi, F.; Winzer, T.; Malic, E.; Knorr, A.; Göttfert, F.; Mittendorff, M.; Winnerl, S.; Helm, M.;
We present a microscopic explanation of the controversially discussed transient negative differential transmission observed in degenerate optical pump-probe measurements in graphene. Our approach is based on the density matrix formalism allowing a time- and momentum-resolved study of carrier-light, carrier-carrier, and carrier-phonon interaction on microscopic footing. We show that phonon-assisted optical intraband transitions give rise to transient absorption in the optically excited hot carrier system counteracting pure absorption bleaching of interband transitions. While interband transition bleaching is relevant in the first hundreds of fs after the excitation, intraband absorption sets in at later times. In particular, in the low excitation regime, these intraband absorption processes prevail over the absorption bleaching resulting in a zero crossing of the differential transmission. Our findings are in good qualitative agreement with recent experimental pump-probe studies.
Keywords: graphene, carrier-dynamics, ultrafast spectroscopy

Publ.-Id: 20649 - Permalink


Magnetization reversal in Co zigzag nanocolumns grown by glancing angle deposition
Buchta, K.; Lewandowski, M.; Bischoff, L.; Synoradzki, K.; Błaszyk, M.; Toliński, T.; Luciński, T.;
A Co zigzag nanocolumn sample was grown by glancing angle deposition using molecular beam epitaxy. A structural study was carried out using scanning electron microscopy and the magnetic properties and the magnetoresistance were investigated at room temperature. Each zigzag consisted of six arms tilted with respect to each other by approx. 60°, had a club-like shape, diameter in the range of 20-100 nm, a single arm length of about 150 nm and a total height of approx. 370 nm. The magnetization hard axis was observed for the magnetic field oriented parallel to the zigzag long axis and the easy axis for the field oriented perpendicular to the long axis. The system exhibited very high maximum coercivity values, which could find potential applications. The angular dependences of the coercive field and the remanent to saturation magnetization ratio, as well as magnetoresistance curves, indicated the presence of curling magnetization reversal mode.
Keywords: Glancing Angle Deposition; Magnetization Reversal Mechanisms; Magnetic Anisotropy; Magnetic Properties; Zigzag Nanostructures; Sculptured Thin Films

Publ.-Id: 20648 - Permalink


A Survivin-XIAP regulates Complexity of the Signaling Molecules FAK and Aktl Radiation Sensitivity as well as Motility of Colorectal Tumor Cells
Hehlgans, S.; Petraki, C.; Cordes, N.; Oppermann, J.; Rodel, C.; Rodel, F.;
kein Abstract vorhanden
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 35-35

Publ.-Id: 20647 - Permalink


Effect of EGF Receptor and beta 1-Integrin Inhibition on the Radiosensitivity three dimensions growing colorectal Cancer cells / Einfluss von EGF Rezeptor und β1-Integrin Hemmung auf die Strahlenempfindlichkeit dreidimensional wachsender kolorektaler Karzinomzellen
Poschau, M.; Zscheppang, K.; Cordes, N.;
kein Abstract vorhanden
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 44-44

Publ.-Id: 20646 - Permalink


Pharmacological Inhibition of Focal Adhesion Kinase affects Cell Survival and Cell death but not Radiosensitivity of human Glioblastoma Cells / Pharmakologische Hemmung der Fokalen Adhäsionskinase beeinflusst Zellüberleben und Zelltod aber nicht Strahlenempfindlichkeit von humanen Glioblastomzellen
Sagerer, A.; Storch, K.; Cordes, N.;
kein Abstract vorhanden
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 190(2014)Suppl. 1, 35-35

Publ.-Id: 20645 - Permalink


Fractionated radiotherapy and cetuximab: EGFR amplification and histological markers as potential biomarkers / Fraktionierte Bestrahlung und Cetuximab: EGFR-Amplifikation und histologische Marker als potenzielle Biomarker
Gurtner, K.; Thurow, C.; Koi, L.; Yaromina, A.; Eicheler, W.; Baumann, M.; Krause, M.;
kein Abstract vorhanden
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 27-27

Publ.-Id: 20644 - Permalink


Effects of a Combined Radio (chemo) therapy and HMG-CoA Reductase-Inhibition in Patients with Head-and-neck-Cancer / Effekte einer kombinierten Radio(chemo)therapie und HMG-CoAReduktase-Inhibition bei Patienten mit Kopf-Hals-Tumoren
Ebert, N.; Thiele, C.; Gurtner, K.; Dorr, W.; Lock, S.; Baumann, M.; Krause, M.;
kein Abstract vorhanden
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 144-144

Publ.-Id: 20643 - Permalink


Influence of Chromatin Condensation on cellular Radiosensitivity in three dimensions growing human Tumor Cells / Einfluss der Chromatinkondensierung auf die zelluläre Strahlenempfindlichkeit dreidimensional wachsender humaner Tumorzellen
Storch, K.; Borgmann, K.; Eke, I.; Krause, M.; Becker, K.; Schrock, E.; Cordes, N.;
kein Abstract vorhanden
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 45-45

Publ.-Id: 20642 - Permalink


Radiation sensitization of human squamous by alpha3 integrin Inhibition / Strahlensensibilisierung humaner Plattenepithelkarzinomzellen durch alpha3 Integrin Hemmung
Steglich, A.; Eke, I.; Vehlow, A.; Cordes, N.;
kein Abstract vorhanden
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 22-22

Publ.-Id: 20641 - Permalink


The LIM only Protein FHL2 modulates the MAPK Signal Pathways and influences the Radiation Sensitivity of growing 3D Pancreatic Carcinoma Cells / Das LIM only Protein FHL2 moduliert MAPK Signalwege und beeinflusst die Strahlenempfindlichkeit von 3D wachsenden Pankreaskarzinomzellen
Zienert, E.; Eke, I.; Cordes, N.;
kein Abstract vorhanden
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 14-15

Publ.-Id: 20640 - Permalink


From a non-magnet to a ferromagnet: Mn implantation into different TiO2 structures
Yildirim, O.; Cornelius, S.; Butterling, M.; Anwand, W.; Wagner, A.; Smekhova, A.; Baehtz, C.; Potzger, K.;
As one of the most promising candidates for a diluted magnetic oxide material for spintronic and magneto optic applications, transition metal (TM) doped titanium dioxide (TiO2) has been extensively studied for last two decades. Up to date room temperature ferromagnetism (RTFM) has been reported for different types of TM dopants and also different types of preparation methods, such as ion implantation [1] or magnetron sputtering [2]. There is an ongoing debate on the origin of the ferromagnetic properties of TiO2, whether RTFM arises from unwanted clustering of the TM atoms, magnetic contamination from sample handling or the desired substitution of Ti by the TM dopants.
We have investigated Mn implanted TiO2 films with respect to the effect of the crystalline structure of the pristine film on the magnetic properties of the doped films. The films were prepared by DC magnetron sputtering using a high purity oxygen deficient ceramic TiO2-x target in Ar/O2 atmosphere. SrTiO3 (100) single crystals were used as substrates. In order to achieve different structures of TiO2, namely amorphous, polycrystalline anatase and epitaxial anatase, different substrate temperatures and post-growth annealing were applied. The as-prepared TiO2 samples have been implanted with Mn ions of 30 keV to 190 keV kinetic energy and variable fluence resulting in a homogenous Mn concentration of 5 at.% within a 150 nm thin layer below the film surface.
The structural changes upon implantation were followed by means of X-ray diffraction (XRD) measurements. Comparison of the diffraction patterns indicates ion-induced damage in the epitaxial film and the formation of Mn containing secondary phases in the polycrystalline material. Depth resolved defect concentration profiles of as-grown and Mn implanted films were determined by means positron annihilation spectroscopy (PAS) measurements based on Doppler broadening spectroscopy. Magnetometry measurements of Mn implanted films reveal ferromagnetism for amorphous and polycrystalline films whereas paramagnetism is observed for epitaxial films. The local environments of implanted Mn ions in different TiO2 structures were probed by X-ray absorption spectroscopy (XAS) in fluorescence mode.
In summary, we have found a significant influence of the as-grown film structure on the magnetic properties of Mn:TiO2. During the presentation the PAS and XAS data will be discussed with respect to the presence of defects and secondary phases in the Mn doped TiO2 films.
  • Lecture (Conference)
    Moscow International Symposium on Magnetism MISM-2014, 29.06.-03.07.2014, Moscow, Russia
  • Lecture (Conference)
    The 59th Annual Magnetism and Magnetic Materials (MMM) Conference, 03.-07.11.2014, Honolulu, Hawaii, United States of America

Publ.-Id: 20639 - Permalink


Angular dependent ferromagnetic resonance analysis in a single micron sized cobalt stripe
Schoeppner, C.; Wagner, K.; Stienen, S.; Meckenstock, R.; Farle, M.; Narkowicz, R.; Suter, D.; Lindner, J.;
We demonstrate how planar microresonators (PMRs) can be utilized to investigate the angular dependent magnetic resonance response of single magnetic nanostructures. In contrast to alternative detection schemes like electrical or optical detection, the PMR approach provides a classical means of investigating the high frequency dynamics of single magnetic entities, enabling the use of well-established analysis methods of ferromagnetic resonance (FMR) spectroscopy. To demonstrate the performance of the PMR-based FMR setup for angular dependent measurements, we investigate the microwave excited magnons in a single Co stripe of 5x1x0.02 µm^3 and compare the results to micromagnetic simulations. The evolution of excited magnons under rotation of one individual stripe with respect to a static magnetic field is investigated. Besides quasi uniform excitations, we observe magneto-static as well as localized excitations. We find a strong influence of inhomogeneous dynamic and static demagnetizing fields for all modes.

Publ.-Id: 20638 - Permalink


Efficiency determination of resistive plate chambers for fast quasi-monoenergetic neutrons
Röder, M.; Elekes, Z.; Aumann, T.; Bemmerer, D.; Boretzky, K.; Caesar, C.; Cowan, T. E.; Hehner, J.; Heil, M.; Kempe, M.; Maroussov, V.; Nusair, O.; Prokofiev, A. V.; Reifarth, R.; Sobiella, M.; Stach, D.; Wagner, A.; Yakorev, D.; Zilges, A.; Zuber, K.; for the R3B Collaboration;
Composite detectors made of stainless-steel converters and multigap resistive plate chambers have been irradiated with quasi-monoenergetic neutrons with a peak energy of 175 MeV. The neutron detection efficiency has been determined using two different methods. The data are in agreement with the output of Monte Carlo simulations. The simulations are then extended to study the response of a hypothetical array made of these detectors to energetic neutrons from a radioactive ion beam experiment.

Publ.-Id: 20637 - Permalink


Nanofiltration of uranium-contaminated water – focus on separation mechanisms
Hoyer, M.; Haseneder, R.; Steudtner, R.; Brendler, V.; Repke, J.-U.;
Nanofiltration offers new perspectives for the treatment of mine drainage from former uranium mines, e.g. in East Germany. In this study the perfor-mance of various commercial nanofiltration membranes for a real mine water sample was determined experimentally and modelled. Experimental data is key to membrane selection and is necessary to validate modelling results. Mathematical modelling offers deeper insights into the interaction of uranium species with solid surfaces which also has the potential to extrapolate to other research fields.
  • Contribution to proceedings
    Uranium Mining and Hydrogeology 2014, 21.-25.09.2014, Freiberg, Germany

Publ.-Id: 20633 - Permalink


Interfacial heat transfer models for flashing flows: a review
Liao, Y.; Lucas, D.;
An extensive literature review on existing models for interfacial heat transfer in flashing of pure liquids was carried out. It reveals that recent numerical simulations rely still on empirical closures. A correlation in terms of the Jakob number, Reynolds number and Prandtl number might be the most promising one. However, all the validation against experiment is limited to single spherical droplet or bubble. For large deformed bubbles and high void fractions, there are still no direct validation due to the lack of experimental data and complicated intervening physics. Improvement regarding the effect of bubble interaction, interfacial morphology and turbulence is necessary.
Keywords: Flashing flow, Heat transfer, Models, Review
  • Contribution to proceedings
    13th international conference Multiphase Flow in Industrial Plant, 17.-19.09.2014, Genova, Italy
  • Lecture (Conference)
    13th international conference Multiphase Flow in Industrial Plant, 17.-19.09.2014, Genova, Italy

Publ.-Id: 20632 - Permalink


Assessment of CFD predictive capacity for flash boiling
Liao, Y.; Lucas, D.; Krepper, E.; Rzehak, R.;
Flash boiling of water inside a converging-diverging nozzle and a vertical pipe under pressure release transients is investigated. Some representative assumptions and simplifications encountered in the literature are assessed. It is shown that a fully non-equilibrium model with two velocity fields and two temperature fields should be applied. Non-drag forces are necessary to predict the lateral distribution of bubbles, which is usually non-uniform. For large bubbles (dg>1mm), bubble translation has a significant contribution to the interphase heat transfer, and thus heat conduction would give a significant under-prediction. The most important point in the assessment of these interphase exchange closures is to have a reliable prediction of bubble size. On this topic there is still much to do, since a realistic modelling of bubble number density transport is still missing. Great efforts need to be invested in the development of generally applicable closure models for nucleation, bubble growth, coalescence and breakup, etc.
Keywords: CFD, Flash boiling, phase change, heat transfer
  • Contribution to proceedings
    CFD4NRS-5, 09.-11.09.2014, Zürich, Schweiz
  • Lecture (Conference)
    CFD4NRS-5, 09.-11.09.2014, Zürich, Schweiz

Publ.-Id: 20631 - Permalink


CFD simulations on TOPFLOW-PTS tests
Apanasevich, P.; Coste, P.; Merigoux, N.;
Pressurized Thermal Shock (PTS) has been identified as one of the most important industrial needs related to nuclear reactor safety. The PTS analysis is required to assure the integrity of the Reactor Pressure Vessel (RPV) throughout the reactor life. One important part of the PTS analysis is the thermal hydraulic analysis which must predict the local temperature fields experienced by the structural parts of the cold leg and especially of the RPV wall close to the cold leg nozzle. Such results are applied as the input data for further structural analyses. Several scenarios that describe what could occur in Small Break Loss Of Coolant Accidents (SB-LOCA) result in an Emergency Core Cooling (ECC) water injection into the cold leg of a Pressurized Water Reactor (PWR). The cold water mixes there with the hot coolant, which is present in the primary circuit. The mixture flows to the downcomer where further mixing of the fluids takes place. Single-phase as well as two-phase PTS situations have to be considered. In case of two-phase PTS situations the water level in the RPV has dropped down to or below the height of the cold leg nozzle, which leads to a partially filled or totally uncovered cold leg. Pressurized Thermal Shock implies the occurrence of thermal loads on the Reactor Pressure Vessel wall. In order to predict thermal gradients in the structural components of the Reactor Pressure Vessel (RPV) wall, knowledge of transient temperature distribution in the downcomer is needed. The prediction of the temperature distribution requires reliable Computational Fluid Dynamic simulations. The CFD models should be able to model the complex mixing processes taking place in the cold leg and the downcomer of the reactor pressure vessel (IAEA, 2001; Lucas et al., 2008, 2009).

In the framework of the NURESAFE project attempts have been made to continue improvement and validation of CFD modeling for two-phase PTS situations. The NEPTUNE_CFD, ANSYS CFX and TransAT codes are used in the project for PTS investigations. A CFD benchmark test on a reference TOPFLOW-PTS steam-water experiment is a part of these activities within the project.
Keywords: TOPFLOW-PTS experiments, direct contact condensation, CFD
  • Lecture (Conference)
    NURESAFE 1st Open Seminar, 16.-17.06.2014, Budapest, Hungary

Publ.-Id: 20630 - Permalink


Ge(1-x)Sn(x) alloys synthesized by ion implantation and pulsed laser melting
Gao, K.; Prucnal, S.; Huebner, R.; Baehtz, C.; Skorupa, I.; Wang, Y.; Skorupa, W.; Helm, M.; Zhou, S.;
The tunable bandgap and the high carrier mobility of Ge(1-x)Sn(x) alloys stimulate a large effort for bandgap and strain engineering for Ge based materials using silicon compatible technology. In this letter we present the fabrication of highly mismatched Ge(1-x)Sn(x) alloys by ion implantation and pulsed laser melting with Sn concentration ranging from 0.5 at. % up to 1.5 at. %. According to the structural investigations, the formed Ge(1-x)Sn(x) alloys are monocrystalline with high Sn-incorporation rate. The shrinkage of the bandgap of Ge(1-x)Sn(x) alloys with increasing Sn content is proven by the red-shift of the E1 and E1+Δ1 critical points in spectroscopic ellipsometry. Our investigation provides a chip technology compatible route to prepare high quality monocrystalline Ge(1-x)Sn(x) alloys.
Keywords: Ge(1-x)Sn(x) alloys, ion implantation, pulsed laser melting

Publ.-Id: 20629 - Permalink


Uncertainties in the fluence determination in the surveillance samples of VVER-440
Konheiser, J.; Grahn, A.; Borodkin, P.; Borodkin, G.;
The reactor pressure vessel (RPV) represents one of the most important safety components in a nuclear power plant. Therefore, surveillance specimen (SS) programs for the RPV material exist to deliver a reliable assessment of RPV residual lifetime. This report will present neutron fluence calculations for SS. These calculations were carried out by the codes TRAMO and DORT [1, 2]. This study was accompanied by ex-vessel neutron dosimetry experiments at Kola NPP. The main neutron activation monitoring reactions were Fe-54(n,p)Mn-54 and Ni-58(n,p)Co-85. Good agreement was found between the deterministic and stochastic calculation results and between the calculations and the ex-vessel measurements. The different influences on the monitors were studied. In order to exclude the possible healing effects of the samples due to excessive temperatures, the heat release in the surveillance specimens was determined based on the calculated gamma fluences. Under comparatively realistic conditions, the heating was up to 6 K.
Keywords: VVER440, reactor pressure vessel, surveillance specimen, activation monitors, Fe-54(n,p)Mn-54, Ni-58(n,p)Co-85
  • Lecture (Conference)
    Fifteenth International Symposium on Reactor Dosimetry, 18.-23.05.2014, Aix-en-Provence, France
  • Open Access LogoContribution to proceedings
    Fifteenth International Symposium on Reactor Dosimetry, 18.-23.05.2014, Aix-en-Provence, France
    EPJ Web of Conferences, Les Ulis Cedex: EDP Sciences, 978-2-7598-1929-4
    DOI: 10.1051/epjconf/201610602006

Publ.-Id: 20627 - Permalink


Assessment of the best N3− donors in preparation of [M(N)(PNP)]-based (M = 99mTc-; 188Re) target-specific radiopharmaceuticals: Comparison among succinic dihydrazide (SDH), N-methyl-S-methyl dithiocarbazate (HDTCZ) and PEGylated N-methyl-S-methyl dithiocarbazate (HO2C-PEG600-DTCZ)
Carta, D.; Jentschel, C.; Thieme, S.; Salvarese, N.; Morellato, N.; Refosco, F.; Ruzza, P.; Bergmann, R.; Pietzsch, H.-J.; Bolzati, C.;
Succinic dihydrazide (SDH), N-methyl-S-methyl dithiocarbazate (HDTCZ) and PEGylated N-methyl-S-methyl dithiocarbazate (HO2C-PEG600-DTCZ) are nitrido nitrogen atom donors employed for the preparation of nitride [M(N)]‐complexes (M = 99mTc and 188Re).
This study aims to compare the capability and the efficiency of these three N3− group donors, in the preparation of [M(N)PNP]-based target-specific compounds (M = 99mTc, 188Re; PNP = aminodiphosphine). For this purpose, three different kit formulations (SDH kit; HO2C-PEG600-DTCZ kit; HDTCZ kit) were assembled and used in the preparation of [M(N)(cys~)(PNP3)]0/+ complexes (cys~ = cysteine derivate ligands).
For each formulation, the radiochemical yield (RCY) of the [M(N)(~cys)(PNP3)] compounds, was determined by HPLC. The deviation of the percentage of RCY, due to changes in concentration of the N3− donors and of the
exchanging ligand, was determined.
For 99mTc, data clearly show that HDTCZ is the most efficient donor of N3−; however, SDH is the most suitable nitrido nitrogen atom donor for the preparation of [99mTc(N)(PNP)]-based target-specific agents with high specific activity. When HO2C-PEG600-DTCZ or HDTCZ are used in N3− donation, high amounts of the exchanging ligand (10−4 M) were required for the formation of the final complex in acceptable yield.
The possibility to usemicrogram amounts of HDTCZ also in [188Re(N)] preparation (0.050 mg) reduces its ability to compete in ligand exchange reactions, minimizing the quantity of chelators required to obtain the final complex in high yield. This finding can be exploit for increasing the radiolabeling efficiency in [188Re(N)]-radiopharmaceutical preparations compared to the previously reported HDTCZ-based procedure, notwithstanding a purification process could be necessary to improve the specific activity of the complexes.
Keywords: Rhenium; Technetium; 188Re; Diphosphinoamines; Peptide; Therapy

Publ.-Id: 20626 - Permalink


Influence of riboflavin on the reduction of radionuclides by Shewanella oneidenis MR-1
Cherkouk, A.; Law, G. T. W.; Rizoulis, A.; Law, K.; Renshaw, J. C.; Morris, K.; Livens, F. R.; Lloyd, J. R.;
Uranium (as UO22+), technetium (as TcO4-) and neptunium (as NpO2+) are highly mobile radionuclides that can be reduced enzymatically by a range of anaerobic and facultatively anaerobic microorganisms, including Shewanella oneidensis MR-1, to poorly soluble analogues. The redox chemistry of Pu is more complicated, but the dominant oxidation state in most environments is poorly soluble Pu(IV), which can be reduced to the potentially more soluble Pu(III), which could enhance migration of Pu in the environment. Recently it was shown that flavins (riboflavin and flavin mononucleotide (FMN)) secreted by Shewanella oneidensis MR-1 can act as electron shuttles, promoting anoxic growth coupled to the accelerated reduction of poorly-crystalline Fe(III) oxides. Here we studied the role of riboflavin in mediating the reduction of radionuclides in cultures of Shewanella oneidensis MR-1. Our results demonstrate that the addition of 10 µM riboflavin enhances the reduction rate of Tc(VII) to Tc(IV) and Np(V) to Np(IV), but has no significant influence on the reduction rate of U(VI) by Shewanella oneidensis MR-1. The presence of riboflavin also accelerated Pu(IV) reduction, demonstrated by an increase in the percentage of Pu(IV) reduced to Pu(III), with and without riboflavin present (17 and 3%, respectively). Thus riboflavin can act as an extracellular electron shuttle to enhance rates of Tc(VII), Np(V) and Pu(IV) reduction, and may therefore play a role in controlling the oxidation state of key redox active actinides and fission products in natural and engineered environments. These results also suggest that the addition of riboflavin could be used to accelerate the bioremediation of radionuclide-contaminated environments.

Publ.-Id: 20625 - Permalink


Scalable, interactive 3D in-situ visualization of large-scale Simulations
Pausch, R.; Schneider, B.; Hettmanczyk, D.; Burau, H.; Huebl, A.; Schmitt, F.; Widera, R.; Grottel, S.; Gumhold, S.; Bussmann, M.;
We present scalable, in-situ visualization of large-scale plasma simulations that allows for remote live visualization. We discuss the GPU rendering implementation, its interface to the simulation, scalable image composition on large clusters and the use of low-power visualisation clients attached to a server located at the HPC system. Such a setup challenges current HPC visualization paradigms and will potentially allow for explorative simulation surveys of large parameter spaces with strongly reduced storage footprint.
Keywords: in-situ visualization, PIConGPU, live visualization, GPU, HPC
  • Lecture (Conference)
    Workshop Programming of Heterogeneous Systems in Physics, 14.-15.07.2014, Jena, Deutschland

Publ.-Id: 20624 - Permalink


Computing Angularly-resolved Far Field Emission Spectra in Particle-in-cell Codes using GPUs
Pausch, R.; Burau, H.; Bussmann, M.; Couperus, J. P.; Cowan, T.; Debus, A.; Huebl, A.; Irman, A.; Köhler, A.; Schramm, U.; Steiniger, K.; Widera, R.;
Angularly resolved far field radiation spectra computed from the Lienard Wiechert Potentials of accelerated electrons give information on the microscopic particle dynamics. We present recent results using our many-GPU, fully relativistic 3D3V particle-in-cell code PIConGPU for which we have developed fully synthetic radiation diagnostics that is capable of computing angularly-resolved radiation spectra of more than 10^10 electrons for several hundred to a thousand wavelengths and directions in a single simulation in less than a day on large-scale supercomputers. With such a technique it is possible to use precision spectroscopic methods for understanding the dynamics of electron acceleration in scenarios where other diagnostics fail. We present studies on laser-driven wakefield acceleration and astrophysical jet dynamics to underline the power of this new technique.
Keywords: far field radiation spectra, Lienard Wiechert potentials, PIConGPU, many-GPU, synthetic radiation diagnostics
  • Poster
    5th International Particle Accelerator Conference (IPAC 2014), 15.-20.06.2014, Dresden, Deutschland
  • Contribution to proceedings
    5th International Particle Accelerator Conference (IPAC 2014), 15.-20.06.2014, Dresden, Deutschland
    Proceedings of IPAC2014, 978-3-95450-132-8, MOPRI069

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Publ.-Id: 20623 - Permalink


Charakterisierung von anisotropen Magnetowiderstandseffekten in Nanostrukturen aus Permalloy und Eisenaluminium
Warnatz, T.;
Magnetic field induced resistance effects are used in digital storage media - like hard- disk read heads [1]. To produce commercial devices it is of utmost importance to understand and tune the effect. The ion beam induced change of ferromagnetic or paramagnetic effects is known since 1986 [2,3]. However, most of the research was done on bulk material. Due to the increasing miniaturization of digital storage devices it is essential to investigate also the behavior in thin films. Taking into account that a commercial use of the devices is favored, it was focused on easy and reproducible sample geometries. The aim of this thesis was to produce, tune and character- ize magnetic field induced resistance changes in thin films of permalloy and iron-aluminum. Af- terwards, the results have been used to create well-defined nanostructures with potential giant magnetoresistance effects. It is shown, that magnetoresistance effects can be created (iron- aluminum) or reduced (permalloy) by ion beam irradiation. The measurements were performed by a self-programmed LabVIEW program with a precise four-terminal sensing setup at low tempera- tures and with a variable magnetic field up to 2.5 T. The variation of the angle between current flow and the magnetic field as well as measurements at different temperatures led to a very good understanding of the occurring phenomena.
Keywords: FeAl, anisotropic magnetoresistance
  • Bachelor thesis
    Westsächsische Hochschule Zwickau, 2013

Publ.-Id: 20622 - Permalink


Herstellung und Charakterisierung eines Spinventils zur Untersuchung der Spindiffusionslänge von FeAl
Liersch, V.;
Spintronic devices hold great potential for future applilcations in information technology. In this work, the design and fabrication of a lateral spin valve for investigating the spin diffusion length of paramagnetic Fe60Al40 will be discussed. Samples were prepared by defining polycrystalline circuits using electron beam lithography, thin film deposition, and lift-off processing. The developed sample layout allows for both local and non-local measurement routines. Cobalt was employed as ferromagnetic polarizing material, while aluminium holds for reference measurements of the spin diffusion length. The determination of the so far unknown spin diffusion length of paramagnetic Fe60Al40 shall then be performed by detecting resistance changes at different temperatures and for different polarizer distances. Highly sensitive electric transport measurements were carried out in a so-called probe station, which allows for achieving very low temperatures via liquid He cooling. Additionally, paramagnetic ferromagnetic heterostructures were investigated with respect to possible giant magneto resistance effects.
Keywords: FeAl, spin valve, spin diffusion length
  • Bachelor thesis
    Westsächsische Hochschule Zwickau, 2014

Publ.-Id: 20621 - Permalink


Transverse Emittance Compensation for the Rossendorf SRF GUN II
Vennekate, H.; Lu, P.; Arnold, A.; Murcek, P.; Teichert, J.; Xiang, R.; Kneisel, P.; Kamps, T.;
Superconducting RF particle sources combine the advantages of normal conducting RF sources and high duty cycle non-RF sources. The Rossendorf SRF gun was the first to demonstrate this injecting electrons into the ELBE accelerator at 13MHz. Recently, a new 3-1/2-gun cavity has been prepared at Jefferson Lab for its use in an updated injector which is expected to increase the electron energy from 2:4 to 7:5 MeV. Along with this new cavity, a new gun cryostat has been introduced. It combines several minor updates to the setup with the installation of a superconducting solenoid right at the exit of the gun, compensating the emittance growth of the electron bunch at an early stage. Hereby, the results of the commissioning of the new cryostat including the solenoid are concluded and compared to the prior concept of using a normal conducting solenoid outside the cryostat. As it is of great importance to this subject, studies of the magnetic shielding are going to be presented as well.
Keywords: SRF, superconducting radio frequency, injector, Rossendorf SRF Gun, ELBE, emittance
  • Open Access LogoContribution to proceedings
    5th International Particle Accelerator Conference (IPAC'14), 15.-20.06.2014, Dresden, Deutschland
    Proceedings of IPAC2014, JACoW, 978-3-95450-132-8, TUPRI015

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Publ.-Id: 20620 - Permalink


Simulation d ́écoulement multiphasique couplé aux effets magnétiques des batteries à métaux liquides
Barry, L.;
Le stockage d’énergie électrique devient une nécessité avec le développement des énergies renouvelables en Allemagne. Dans cette perspective un nouveau type de batterie, composée de trois phases de métal liquide maintenues à plus de 500°C, semble prometteur pour une future utilisation. Cependant ces batteries sont le siège d’instabilités qui peuvent mener à un mélange non voulu des trois phases liquides. Ce projet étudie une instabilité particulière appelée instabilité de Tayler, et cherchera à savoir si celle-ci peut mener à une destruction de la batterie. Pour cela, un nouveau solveur numérique est utilisé, combinant à la fois les lois de l’électromagnétique et de la mécanique des fluides. Des simulations seront lancées à partir de diverses conditions initiales, et nous verrons qu’il est en effet possible d’arriver à une destruction de la batterie, sous réserves de conditions initiales particulières.
Keywords: Tayler instability, liquid metal battery, multiphase simulation, OpenFOAM
  • Master thesis
    Arts et Métiers Paristech Bordeaux-Talence, 2014
    Mentor: Azita Ahmadi, Tom Weier

Publ.-Id: 20619 - Permalink


Experimental evidence for nonaxisymmetric magnetorotational instability in a rotating liquid metal exposed to an azimuthal magnetic field
Seilmayer, M.; Galindo, V.; Gerbeth, G.; Gundrum, T.; Stefani, F.; Gellert, M.; Rüdiger, G.; Schultz, M.; Hollerbach, R.;
The azimuthal version of the magnetorotational instability (MRI) is a nonaxisymmetric instability of a hydrodynamically stable differentially rotating flow under the influence of a purely or predominantly azimuthal magnetic field. It may be of considerable importance for destabilizing accretion disks, and plays a central role in the concept of the MRI dynamo. We report the results of a liquid metal Taylor-Couette experiment that shows the occurrence of an azimuthal MRI in the expected range of Hartmann numbers.

Publ.-Id: 20618 - Permalink


Magnetic fields in space: phenomena and related lab experiments
Stefani, F.;
The magnetic fields of cosmic bodies are generated by the homogeneous dynamo effect in moving electrically conducting fluids. Cosmic magnetic fields also play an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. In 1999 the threshold of magnetic-field self-excitation was exceeded in the two liquid sodium experiments in Riga and Karlsruhe. Since 2006, the Cadarache dynamo experiment has successfully reproduced many features of geophysical interest such as reversals and excursions. In the same year, the helical version of the magnetorotational instability was observed in the PROMISE facility in Dresden-Rossendorf.
The lecture gives an overview about liquid metal experiments on dynamo action and magnetically triggered instabilities, and it concludes with an overview about future experiments, including a precession driven dynamo and a large-scale Tayler-Couette experiment to be set-up in the framework of the DRESDYN project.
  • Invited lecture (Conferences)
    Space trips summer school on thermo-acoustic and space technologies, 17.-20.06.2014, Riga, Latvia

Publ.-Id: 20617 - Permalink


The azimuthal MRI in experiment: confirmations and surprises
Stefani, F.;
The azimuthal magnetorotational instability (AMRI) may be of considerable importance for destabilizing accretion disks and plays also a central role in the concept of the MRI dynamo. We report the results of a liquid metal Taylor-Couette experiment that shows the occurrence of an azimuthal MRI in the expected range of Hartmann numbers. We also discuss some peculiarities of the experimental results which are connected with the slight symmetry breaking of the applied magnetic field.
  • Invited lecture (Conferences)
    General Meeting of the Max Planck/Princeton Center for Plasma Physics, 28.06.-01.07.2014, Berlin, Germany

Publ.-Id: 20616 - Permalink


Simulation of the ELBE SRF Gun II
Lu, P.; Arnold, A.; Lehnert, U.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.;
By combining the code of ASTRA and elegant in a user-friendly interface, a simulation tool is developed for the ELBE SRF Gun II. The photoelectric emission and first acceleration to several MeV in the gun cavity are simulated by ASTRA with a 1D Model, where the space charge effect is considered. The dependence of the beam quality on key parameters is studied, and a compromised optimization for a 77 pC beam is used for further elegant simulation of the beam transport through a dogleg and ELBE Linacs. Proper settings of the magnets and RF phases are the main targets of improving the beam quality. Up to now the best simulation result is an electron bunch with the energy of 47 MeV, energy spread of 66 keV, bunch length of 0.35 ps and transverse emittance of 1.9 μm and 2.7 μm in the two perpendicular directions.
  • Open Access LogoContribution to proceedings
    IPAC2014 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Germany
    Proceedings of IPAC2014, MOPRI023

Publ.-Id: 20615 - Permalink


Dynamo action and related magnetic instabilities in the liquid metal lab
Stefani, F.;
Magnetic fields of cosmic bodies are generated by the hydromagnetic dynamo effect in moving electrically conducting fluids, such as liquid metals or plasmas. Once produced, cosmic magnetic fields are able to act back on moving fluids. This back-reaction may have dramatic consequences for cosmic structure formation, with the magnetorotational instability (MRI) in accretions disks as the most prominent example. Considerable theoretical and computational progress has been made in understanding both the dynamo effect as well as magnetically triggered flow instabilities. Complementary to this, the last fifteen years have seen much effort in studying both effects in liquid metal experiments.
In the talk, we summarize the history of these experiments, discuss their main results and their limitations, and give an outlook on future activities. As for dynamo action, we focus on the Riga, Karlsruhe and Cadarache experiments, and discuss the present status of a large-scale precession-driven dynamo experiment to be set-up in the framework of the DRESDYN project. As for magnetically triggered instabilities, we review the recent experiments on the helical and azimuthal versions of the MRI, as well as on the current-driven Tayler instability (TI). After discussing the astrophysical relevance of those basically induction-less instabilities, we motivate the set-up of a large-scale liquid sodium experiment for studying the continuous transition to the standard version of MRI.
  • Invited lecture (Conferences)
    EUROMECH Colloquium 561: Dimensionality of Turbulence, 19.-21.05.2014, Coventry, United Kingdom

Publ.-Id: 20614 - Permalink


Liquid metal experiments on dynamo action and related magnetic instabilities
Stefani, F.;
The magnetic fields of planets, stars and galaxies are generated by self-excitation in moving electrically conducting fluids. Once produced, cosmic magnetic fields can play an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. For a long time, both effects, i.e. hydromagnetic dynamo action and the magnetorotational instability, have been the subject of purely theoretical investigations. This situation changed in 1999 when the threshold of magnetic-field self-excitation was exceeded in the two liquid sodium experiments in Riga and Karlsruhe. Since 2006, the Cadarache dynamo experiment has successfully reproduced many features of geophysical interest such as reversals and excursions. In the same year, the helical version of the magnetorotational instability was observed in the PROMISE facility in Dresden-Rossendorf. The lecture gives an overview about liquid metal experiments on dynamo action and magnetically triggered instabilities, it asks for the lessons they have taught us about real cosmic dynamos and accretion disks, and it concludes with an overview about future experiments, including a precession driven dynamo and a large-scale Tayler-Couette experiment to be set-up in the framework of the DRESDYN project.
  • Invited lecture (Conferences)
    LSTM Fluid Mechanics Seminar, 07.02.2014, Erlangen, Germany

Publ.-Id: 20613 - Permalink


Properties of oxide nanoclusters in ODS ferritic steels: A combined DFT and Metropolis Monte Carlo simulation study
Devaraj, M.; Posselt, M.;
The main structural characteristic of Oxide Dispersion Strengthened (ODS) Fe-Cr alloys is the finely dispersed distribution of nm-size clusters that may contain O, Y, and Ti. Many details of the structure and composition of these nanoclusters are not yet fully understood. Numerous experiments demonstrated that number and size of the nanoclusters do not change significantly when ODS alloys are exposed to high dose irradiation and/or high temperatures. Furthermore, it was shown that the fine dispersion of the nanoclusters prevents recrystallization, i.e. the increase of grain size, which usually occurs at elevated temperatures. The extraordinary properties of the nanoclusters are deemed to be the cause of the superior high-temperature creep strength and the high radiation resistance of the ODS Fe-Cr alloys. Therefore, these materials are promising candidates for applications as structural materials in extreme environments, i.e. at high temperature and intense particle irradiation, such as in advanced nuclear fission and fusion reactors.
In this work a multiscale modeling approach is developed and successfully applied to interpret a large number of experimental data on the properties of nanoclusters in the ODS Fe-Cr alloys. Extensive first-principle calculations on embedded clusters containing few O, Y, Ti, and Cr atoms as well as vacancies are performed to obtain interaction parameters to be applied in Metropolis Monte Carlo simulations, within the framework of a rigid lattice model. A novel description using both pair and triple parameters is shown to be more precise than the commonly used pair parameterization. Simulated annealing provides comprehensive data on the energetics, structure and stoichiometry of nm-size clusters at . The results are fully consistent with the experimental finding of negligible coarsening and a high dispersion of the clusters, with the observation that the presence of Ti reduces the cluster size, and with the reported radiation tolerance of the clusters. In alloys without vacancies clusters show a planar structure, whereas the presence of vacancies leads to three-dimensional configurations. Additionally, Metropolis Monte Carlo simulations are carried out at high temperature in order to investigate the dependence of nanocluster composition on temperature. A good agreement between the existing experimental data on the ratios (Y+Ti):O, Y:Ti, (Y+Cr):O, and Y:Cr, and the simulation results is found. In some cases it is even possible to draw the conclusion that the respective alloys contained a certain amount of vacancies, or that the clusters analyzed were frozen-in high-temperature configurations. The comparison of experimental data with those obtained by simulations demonstrates that the assumption of nanoclusters which are coherent with the bcc lattice of the Fe-Cr matrix leads to reasonable results.
Keywords: ODS ferritic alloys, DFT, Monte Carlo simulation
  • Lecture (Conference)
    2nd International Workshop on ODS Materials, 26.-27.06.2014, Dresden, Germany

Publ.-Id: 20612 - Permalink


Fluorinated phosphodiesterase 10A inhibitors with a potential use as 18F-labeled imaging agents
Wagner, S.; Scheunemann, M.; Egerland, U.; Hoefgen, N.; Brust, P.;
Phosphodiesterases (PDEs) are a class of enzymes heavily involved in cellular signaling by inactivating the second messenger cAMP and cGMP. So far, 11 different PDE families are known, of which one, the dual substrate enzyme PDE10A is abundantly expressed in a particular brain region, the striatum. Since it is thought to be involved in the pathomechanism of schizophrenia, PDE10A inhibition represents a novel approach in the treatment of this disease. In-vivo imaging via positron emission tomography (PET) of PDE10A would allow investigating the enzyme and its expression in neuropathological processes.
Recently, 1 arylimidazo[1,5a]quinoxalines have been reported as potent and selective PDE10A inhibitors.1 Considering the potential use of these inhibitors as 18F-labeled imaging agents fluorinated PDE10A inhibitors based on 1-arylimidazo[1,5a]quinoxaline as lead structure have been synthesized.
The imidazo[1,5a]quinoxaline key structure was synthesized from 2,6-difluoroaniline over 7 steps in an total yield of 8%. Using the palladium catalyzed Suzuki-coupling different substituted 2-fluoropyridine boronic acids could be linked to brominated imidazo[1,5a]quinoxalines. This divergent step allows a quick and easy variation. Moreover 2-fluoropyridines could be introduced at two positions of the aromatic system.
The inhibitory potency of these compounds was tested towards human, recombinant PDE10A and other PDE families. All inhibitors showed a high affinity for PDE10A with moderate to good selectivity versus other PDEs.
Currently the most selective inhibitor is under further investigation to be developed as PET tracer.

[1] Malamas et. al. J. Med. Chem. 2011,54, 7621-7638.
  • Poster
    ORCHEM 2014, 15.-17.09.2014, Weimar, Deutschland

Publ.-Id: 20611 - Permalink


Liquid phase epitaxy of Ge(1-x)Sn(x) alloy using ion-implantation and pulsed laser melting
Gao, K.; Prucnal, S.; Huebner, R.; Skorupa, W.; Helm, M.; Zhou, S.;
Group IV semiconductor alloys have drawn substantial attention for their potential applications in optoelectronic devices capable of integration with the existing Si IC circuitry. Single crystalline Ge1-xSnx alloys are promising for electronic and optical applications in virtue of their high carrier mobility. In this contribution we present the fabrication of Ge1-xSnx by ion-implantation and pulsed laser melting (PLM). Sn was implanted into commercial Ge wafers to form 0.2 µm thick layers with different atomic concentrations from 0.5 % 3.0 %. The as-implanted Ge layer becomes amorphous due to the bombardment of Sn ions with high kinetic energy. The regrowth of the Ge1-xSnx layer after PLM and the lattice expansion were confirmed by X-ray diffraction and micro-Raman spectroscopy. Field emission scanning electron microscopy was applied to determine the surface morphology. High resolution transmission electron microscopy and Rutherford backscattering and channeling analysis confirmed the monocrystalline structure of the Ge1-xSnx layer. Our investigation provides an efficient technique to prepare high quality monocrystalline Ge1-xSnx alloys.
Keywords: GeSn, ion implantation, pulsed laser melting
  • Lecture (Conference)
    E-MRS 2014 SPRING MEETING, 26.05.-01.08.2014, Lille, France

Publ.-Id: 20610 - Permalink


Photoluminescence from GaAs(1-x)N(x) dilute nitride achieved by nitrogen-implantation and flash lamp annealing
Gao, K.; Prucnal, S.; Huebner, R.; Skorupa, W.; Helm, M.; Zhou, S.;
Nitrogen atoms are isoelectronic substituents for arsenic in GaAs. A small amount of nitrogen doping can lead to a pronounced bandgap reduction. Therefore nitrogen-doping can be applied as a powerful technique to modify GaAs based materials for long wavelength optoelectronic devices. In this contribution we present the fabrication of dilute nitride material GaAs1-xNx by nitrogen-implantation and flash lamp annealing (FLA). N was implanted in to the commercial GaAs wafer to form a 0.2 ?m thick layer with atomic concentration of about 0.76 % and 0.38 %. The as-implanted GaAs layer becomes amorphous due to the bombardment of nitrogen ions with high kinetic energy. The GaAs1-xNx layer with compressive strain is epitaxially regrown on GaAs during FLA treatment as confirmed by X-ray diffraction and micro-Raman spectroscopy. In the meantime the bandgap shrinkage is proven by photoluminescence spectroscopy. Based on the redshift of the GaAs1-xNx near band-edge emission, up to 60 % of the implanted N atoms are successfully incorporated into the lattice after FLA. According to our investigation, ion-implantation followed by ultrashort flash lamp treatment, which is quite efficient and low-cost, exhibits a promising prospect on bandgap engineering of GaAs based semiconductors.
Keywords: GaAsN, ion implantation, flash lamp annealing
  • Poster
    E-MRS 2014 SPRING MEETING, 26.05.-01.08.2014, Lille, France

Publ.-Id: 20609 - Permalink


Spatiotemporal process monitoring of conservative and reactive tracer transport in a synthetic soil column
Kulenkampff, J.; Stoll, M.; Enzmann, F.; Gründig, M.; Mansel, A.; Lippmann-Pipke, J.;
Transport and retardation of chemical species in soils as observed by input-output approaches are commonly interpreted by process simulations and break-through curve (BTC) fitting. Positron emission tomography (PET) provides a direct quantitative spatiotemporal (4D) visualization method for the propagation of compounds labelled with a PET-tracer at intermediate resolution and molecular sensitivity (Kulenkampff et al. 2013).
In the framework of SPP 1315, we conducted transport experiments on an artificial soil column with both reactive and conservative tracers, which were monitored with sequential PET imaging. The soil column used (l: 94.5 mm, d: 40 mm; composition: 94% sand, 5% illite, 1% goethite; porosity: 29%) was prepared under CO2-atmosphere and structurally characterized by µCT imaging as widely homogeneous. For the conservative tracer experiment, 5 mL 0.001 M NaNO3 + 0.01 M [18F]KF was flown through the equilibrated column. For the reactive species experiment, 64Cu was produced at the Leipzig cyclotron by the nuclear reaction 64Ni(p,n)64Cu and separation by ion exchange. 5 mL of 0.0008 M [64Cu]Cu(MCPA)2 was produced from 2 mL 64Cu2+ in 0.1 M HNO3, 1 mg Cu(NO3)2•3H2O and 2 mg MCPA in synthetic pore water. The labeled solution was adjusted to pH 5 and flown through the column, which had no former contact with MCPA and had been preconditioned for 4 days with synthetic pore water at pH 5. In both experiments the flow rate was 0.1 ml/min.
In the conservative experiment, the break-through occurred after 140 min, and – in spite of the homogeneous packing of the column – the tracer propagation observed with PET showed a preferential flow field towards the rim of the sample. The reactive [64Cu]Cu(MCPA)2 pulse was strongly retarded with a break-through of the activity after 66 h. Fig. 1 shows a snapshot of both experiments after 110 min.
Preferential and superficial transport, commonly ignored in input-output approaches, controls the effective volume and reactive internal surface area, and thus impacts interpretation and inverse numerical modelling of BTCs. Such effects can be assessed and quantified with PET process tomography, especially when the pore structure is heterogeneously altered by microbial activity.

Reference
Kulenkampff, J., Gründig, M., Korn, N., Zakhnini, A., Barth, T., Lippmann-Pipke, J., 2013. Application of high-resolution positron-emission-tomography for quantitative spatiotemporal process monitoring in dense material. http://www.isipt.org/world-congress/7/902.html.
Keywords: reactive transport, column experiments, tomography, PET, preferential flow
  • Lecture (Conference)
    International Symposium 2014 Biogeochemical Interfaces in Soil: Towards a Comprehensive and Mechanistic Understanding of Soil Functions, 06.-08.10.2014, Leipzig, Deutschland

Publ.-Id: 20608 - Permalink


Formation and photoluminescence of GaAs(1-x)N(x) dilute nitride achieved by N-implantation and flash lamp annealing
Gao, K.; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, S.;
In this paper we present the fabrication of dilute nitride semiconductor GaAs(1-x)N(x) by nitrogen-ion-implantation and flash lamp annealing (FLA). N was implanted into the GaAs wafers with atomic concentration of about ximp1=0.38% and ximp2=0.76%. The GaAs1-xNx layer is regrown on GaAs during FLA treatment in a solid phase epitaxy process. Room temperature near band-edge photoluminescence (PL) has been observed from the FLA treated GaAs(1-x)N(x) samples. According to the redshift of the near band-edge PL peak, up to 80% and 44% of the implanted N atoms have been incorporated into the lattice by FLA for ximp1=0.38% and ximp2=0.76%, respectively. Our investigation shows that ion implantation followed by ultrashort flash lamp treatment, which allows for large scale production, exhibits a promising prospect on bandgap engineering of GaAs based semiconductors.
Keywords: GaAs(1-x)N(x), ion implantation, flash lamp annealing, photoluminescence

Publ.-Id: 20607 - Permalink


Process tomography of diffusion, using PET, to evaluate anisotropy and heterogeneity
Kulenkampff, J.; Gründig, M.; Zakhnini, A.; Lippmann-Pipke, J.;
Anisotropy, compositional and structural heterogeneity of clays cause considerable deviations from homogeneous diffusion, in particular direction dependent transport rates and preferred transport zones. Conventional diffusion experiments, treating the sample as homogeneous black box in a concentration gradient, are interminable and inappropriate to elucidate these spatial effects. In contrast, tomographic imaging methods are capable both to shorten the required observation time and to reveal space-dependent variations of the diffusion process.
Here we applied positron-emission-tomography (PET) as quantitative spatiotemporal imaging method with perfect characteristics for non-destructive diffusion process observations. We adopted this nuclear medical imaging method and developed its geoscientific applicability in the past ten years [1-3]. GeoPET visualizes the concentration of certain positron-emitting radiotracers in opaque media with ultimate sensitivity (picomoles) and reasonable resolution (1 mm) on the laboratory scale (100 mm). For diffusion experiments longer living nuclides are applicable, like 58Co (T1/2=70.86 d) and 22Na (T1/2=2.603 a), and we have to consider the higher density of our specimens, which causes attenuation and scattering of the radiation [4].
GeoPET revealed spatial particularities in diffusion experiments that have been conducted on Opalinus clay samples of different sizes, as well as on other rock types. Applying the Comsol Optimization Module, we derived anisotropic diffusion parameters from the tomograms [5, 6].


References

1. Richter, M., et al., Radiochimica Acta 93, 643-651, 2005.
2. Gründig, M., et al., Applied Geochemistry 22, 2334-2343, 2007.
3. Kulenkampff, J., et al., Physics and Chemistry of the Earth 33, 937-942, 2008.
4. Zakhnini, A., et al., Computers and Geosciences 57 183-196, 2013.
5. Schikora, J., Dresden Technical University, Diploma thesis, 2012.
6. Kulenkampff, J., et al. Clays in Natural and Engineered Barriers for Radioactive Waste Confinement (O/11B/2), 2012. Montpellier, France.
Keywords: diffusion, clay, tomography, pet
  • Lecture (Conference)
    7th Mid-European Clay Conference, 16.-19.09.2014, Dresden, Deutschland
  • Clay Minerals 50(2015), 369-375
    DOI: 10.1180/claymin.2015.050.3.09

Publ.-Id: 20606 - Permalink


Influence of substrate on resistive switching behavior of YMnO3 films in bottom-top contact configuration
Bogusz, A.; Blaschke, D.; Skorupa, I.; Scholz, A.; Bürger, D.; Schmidt, O. G.; Schmidt, H.;
The influence of the bottom electrode/substrate on the resistive switching behavior of YMnO3 thin films was investigated. Unipolar resistive switching was observed when Pt/Ti/SiO2/Si and Pt/Al2O3 were employed as a bottom electrode/substrate. YMnO3 deposited on a SrTiO3 doped with Nb exhibits bipolar resistive switching characteristics. It was shown that the use of different substrate materials has got a decisive impact on the YMnO3 microstructure and current-voltage characteristics.
  • Contribution to proceedings
    12th International Conference on Solid-State and Integrated Circuit Technology (ICSICT 2014), 29.-31.10.2014, Guilin, China
    Proceedings of ICSICT-2014: IEEE, 978-1-4799-3296-2
    DOI: 10.1109/ICSICT.2014.7021530
  • Lecture (Conference)
    12th International Conference on Solid-State and Integrated Circuit Technology (ICSICT 2014), 28.-31.10.2014, Guilin, China

Publ.-Id: 20605 - Permalink


Nanoscale Transport Phenomena
Erbe, A.; Gemming, S.;
The miniaturization and concurrent diversification of functional devices is one of the key technology drivers in science and technology. Following the ITRS roadmap the length scales of functional elements have shrunk to the nanoscale, permitting comparison between controlled experiments and a realistic, scale-adapted modeling of their physical properties.
In this presentation we show studies of transport properties in nanoscale systems, such as electrical current transport through single molecules, magnetic nanoparticles, and nanowires in experiment and simulation. Our results open possible routes towards new functional devices on the molecular and nanometer scale using effects like light-induced switching of single molecules or charging of single electrons to magnetic single electron transistors. Future integration of these nanostructures into micronsize electrical circuits requires structuring techniques, which form contacts by using combinations of self-assembly and top-down approaches. We demonstrate charge transport through self-organized structures and their placement on large electrodes.
Keywords: nanoscale transport, molecular electronics, charge transport, density-functional theory, functional oxides, nanocomposite materials
  • Lecture (others)
    Abengoa Research Seminar, 20.05.2014, Sevilla, Spanien

Publ.-Id: 20604 - Permalink


Kleinste Strukturen ganz groß – Forschung mit Großgeräten
Gemming, S.;
allg. Vorstellung der Forschungsanagen am HZDR
Keywords: -
  • Lecture (others)
    Seniorenkolleg der TU Chemnitz, 27.05.2014, Chemnitz, Deutschland

Publ.-Id: 20603 - Permalink


Selbstorganisation – Wie kommt das Muster auf die Oberfläche?
Gemming, S.;
Muster auf Oberflächen können sich durch eine Vielzahl verschiedener Mechanismen ausbilden. Regelmäßige mikro- und nanoskalige Muster für mobile elektronische Geräte lassen sich zum Beispiel nach vorgegebenen Vorlagen durch aktive top-down Strukturierungsverfahren wie Lithographie oder Drucken erzeugen.

Aus der Natur ist demgegenüber spontane Musterbildung unter Gleichgewichtsbedingungen bekannt, wenn ordnende Wechselwirkungen mit entropischen Faktoren erfolgreich konkurrieren. Induzierte Musterbildung durch Einwirkung externer Faktoren wie den Ionenstrahl ergänzt die Palette möglicher Wege zur Bildung geordneter Oberflächenstrukturen.

Strukturelle Muster finden sich auf verschiedensten Längen- und Zeitskalen von der dreidimensionalen Anordnung von Materie in Galaxien bis hin zur Dekoration von Sensor- oder Katalysatoroberflächen mit Atomen und Molekülen. Gerade die Mustererkennung auf molekularer Ebene bildet die Basis vieler biologischer Prozesse. Darauf basierende Ansätze wie die DNA-Origami-Technik versprechen eine gezielte Strukturierung größerer, technologisch relevanter Oberflächen aus kleinen molekularen Bausteinen. Selbstorganisation auf atomarer Ebene treibt dagegen die Ausbildung von meso- und nanoskopischen Strukturen wie Quantenpunkten, Rippeln oder Nanokompositen durch Ionenstrahlerosion oder ionenstrahlgestützte Abscheidung. Hierbei ist die Strukturierung gekoppelt an das Entstehen funktionaler Muster, wie man sie auch bei Materialien beobachtet, in denen sich am Ordnungs-Unordnungs-Übergang Domänen spontaner Magnetisierung oder spontaner elektrischer Polarisation ausbilden. Einige Beispiele aus der aktuellen Materialforschung sollen verdeutlichen, dass die Musterbildung jenseits des rein Dekorativen eine Vielzahl fundamentaler Aspekte der Physik berührt.
Keywords: Musterbildung, crystal structure, space groups, frieze groupd, rod groups
  • Invited lecture (Conferences)
    Workshop Nanostrukturbildung, 15.04.2013, Dresden, Deutschland
  • Lecture (others)
    Physikalisches Kolloquium, 17.04.2013, Chemnitz, Deutschland

Publ.-Id: 20602 - Permalink


Strontium titanate: An all-in-one rechargeable energy storage material
Hanzig, J.; Zschornak, M.; Nentwich, M.; Hanzig, F.; Gemming, S.; Leisegang, T.; Meyer, D. C.;
Redistribution of oxygen vacancies in a strontium titanate single crystal is caused by an external electric field. We present electrical measurements during and directly after electroformation, showing that intrinsic defect separation establishes a non-equilibrium state in the transition metal oxide accompanied by an electromotive force. A comprehensive thermodynamic deduction in terms of theoretical energy and entropy calculations indicate an exergonic electrochemical reaction after the electric field is switched off. Based on that driving force the experimental and theoretical proof of concept of an all-in-one rechargeable SrTiO3 single crystal energy storage is reported here.
Keywords: Solid state energy storage; Transition metal oxides; Defects; Density functional theory

Publ.-Id: 20601 - Permalink


Probing a crystal's short-range structure and local orbitals by Resonant X-ray Diffraction methods
Zschornak, M.; Richter, C.; Nentwich, M.; Stöcker, H.; Gemming, S.; Meyer, D. C.;
Diffraction Anomalous Fine Structure (DAFS) combines the long-range, crystallographic sensitivity of X-ray diffraction with the short-range sensitivity of X-ray Absorption Spectroscopy (XAS). In comparison to other spectroscopic methods, DAFS can additionally distinguish phases of different translational symmetry by choice of momentum transfer, or isolate spectra from chemically identical atoms on various Wyckoff sites of a crystal's structure using crystallographic weights. The Anisotropy of Anomalous Scattering (AAS) extends the concept of isotropically scattering atoms to a more general case, where the atom's scattering characteristics depend on the polarization as well as the wavevector of the incident and scattered X-rays. These can be written as tensors that reflect the local site symmetries of the resonant atom. Forbidden Reflection Near-Edge Diffraction (FRED) is an elegant way to measure AAS by using reflections that are extinguished in the special case of isotropically scattering atoms. They can only be observed due to the non-isotropic contributions at photon energies in the vicinity of an absorption edge where electronic transitions occur. Combining the site selectivity of DAFS with the information accessible through AAS allows probing the short-range order and local orbitals of selected atoms in a crystal structure of a chosen phase. The present condensed review gives a brief overview on the pioneer work, the theory and sensitivities as well as selected recent applications of these powerful and promising Resonant X-ray Diffraction (RXD) methods. Additionally, some recent work of the authors is included exemplarily for the model structure rutile TiO2 presenting the progress in measurement and interpretation.
Keywords: diffraction anomalous fine structure; anisotropic anomalous scattering; resonant elastic X-ray scattering; forbidden reflection near-edge diffraction

Publ.-Id: 20600 - Permalink


Investigation of contaminated soil
Richter, C.; Fahmy, K.;
Investigation of microbial growth in natural minerals using the TAM Air 3 channel calorimeter.
  • Lecture (Conference)
    ISBC Meeting, Lund 2014, 03.06.2014, Lund, Schweden

Publ.-Id: 20599 - Permalink


Single-crystalline Ga- and In- based compound semiconductor nanocrystals in Si by ion implantation and short time flash lamp annealing
Wutzler, R.; Rebohle, L.; Prucnal, S.; Bregolin, F.; Hübner, R.; Helm, M.; Skorupa, W.;
The integration of III-V compound semiconductors into silicon is a substantial research field for the progress of micro- and optoelectronic device technology. We fabricated various III-V compound semiconductor nanocrystals (NCs) in Si and SOI substrates by sequential high fluence ion beam implantation and ultra-short flash lamp annealing (FLA). Single-crystalline GaAs, GaP, GaSb, InAs, InP and InSb NCs were grown by liquid phase epitaxy during FLA. Additionally, precise positioning of NCs was achieved by using a lithographically patterned aluminum mask layer for ion implantation.

The characterization of the NCs was performed by using Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and Rutherford Backscattering (RBS). Raman measurements confirmed the formation of III-V NCs. AFM and SEM were used to control surface morphology and to investigate the lateral NC distribution. RBS monitored the distribution of the implanted ions. TEM images show distinct, single-crystalline NCs of various shapes. The shape and size of the NCs varies from large domes over small spherical precipitates to conical and pyramidal nanostructures depending on the processing conditions.
Keywords: Ion Implantation, Flash Lamp Annealing, III-V Integration, SOI
  • Lecture (Conference)
    X-th International Conference Ion Implantation and other Applications of Ions and Electrons, 23.-26.06.2014, Kazimierz Dolny, Poland

Publ.-Id: 20598 - Permalink


In-situ spectroscopic characterization of Np(V) sorption complexes at manganese and iron oxide surfaces
Müller, K.; Rossberg, A.; Simon, B.; Berger, J.;
Neptunium (Np) is one of the most important components of nuclear waste to consider for the long-term safety assessment of nuclear waste repositories, due to the increasing enrichment, the long half-life and the high toxicity of Np-237. Hence, great attention is attracted to its geochemistry [1]. Among the various geochemical reactions, the molecular processes occurring at the solid-water interface, e.g. sorption onto mineral phases, surface precipitation, and colloid formation strongly affect the migration behavior of the radioactive contaminant in the environment [2]. Thus, various components of geological materials, such as manganese and iron oxides and hydroxides play an important role in regulating the mobility of actinides in aquifers, due to their widespread environmental presence, high sorption capacity and tendency to form coatings on mineral surfaces [3]. In recent years, the sorption behavior of Np(V), the most relevant oxidation state under ambient conditions, onto iron oxides was mainly studied by macroscopic experiments [4]. Manganese oxides were rarely investigated [5]. For a better understanding of the molecular events occurring at the mineral’s surfaces, ATR FT-IR spectroscopy is a useful tool for the in-situ identification of surface species [5]. In addition, time-resolved measurements provide kinetic information on the surface reactions. Complementary information on molecule structure and atomic environment can be elucidated from EXAFS spectroscopy.

In this work, Np(V) sorption on the oxyhydroxides of Fe and Mn is investigated comprehensively by combining in-situ ATR FT-IR and EXAFS spectroscopy under a variety of environmentally relevant sorption conditions. As an example, upon sorption of micromolar Np(V) on Fe2O3, a band observed at 789 cm−1 is assigned to the antisymmetric stretching vibrational mode (ν3) of the neptunyl ion (Fig.1). The IR spectrum obtained at equal conditions in an aqueous solution shows the absorption of ν3(NpVO2) at 818 cm−1 [6]. The red shift of ν3 to 789 cm−1 upon sorption can be assigned to an inner-sphere sorption complex. Kinetic experiments have shown that only one sorption complex was formed independent from Np(V) loading. Furthermore, no impact of ionic strength (1- 10−4 M NaCl) and pH (≤ 10) on the sorbed species was found. By EXAFS structural analysis of batch samples the surface complex was further characterized being a binary edge-sharing Np(V) sorption species (Fig.2). From a comparison of Np(V) surface complexation on different mineral oxides of iron, manganese, silicon and titanium a very similar sorption behavior was elucidated.


[1] Kaszuba, J.P. et al. (1999) Environ. Sci. Technol. 33, 4427-4433.
[2] O'Day, P.A. (1999) Rev. Geophys. 37, 249-274.
[3] Tochiyama, O. et al. (1996) Radiochim. Acta 73, 191-198.
[4] Li, D. et al. (2012) J. Hazard. Mater. 243, 1-18.
[5] Wilk, P. A. et al. (2005) Environ. Sci. Technol. 39, 2608-2615.
[6] Müller, K. et al. (2009) Environ. Sci. Techn. 43, 7665-7670.
[7] Blake, R. L.et al. (1966) Am. Mineral. 51, 123-129
  • Poster
    International workshop on Advanced Techniques in Actinide Spectroscopy (ATAS 2014), 03.-07.11.2014, Dresden, Deutschland

Publ.-Id: 20597 - Permalink


Aligning 1D and 2D axial symmetric transport simulations with observations: consequences for the reactive transport
Lippmann-Pipke, J.; Stuhlfauth, C.; Lippold, H.; Kulenkampff, J.; Enzmann, F.;
With 1D and axial symmetric 2D finite element simulations of tracer transport in porous media columns, we conducted systematic studies of increasing heterogeneity on the resulting break-through curves (BTC).

While preferential flow can still have comparably little effect on the BTC of non-reactive tracer substances, for strongly adsorbing tracer preferential flow can significantly shift the break-through towards earlier arrival times by reducing the reactive surface area.

Motivation for conducting this systematic simulation study is our unique GeoPET method (Positron Emission Tomography) that allows the visualization of the spatio-temporal tracer distribution in geologic media (Richter et al., 2000; Gründig et al., 2007; Kulenkampff et al., 2008). The real complexity of thus directly observed flow fields is always surprising. Even for non-reactive tracers quantitative transport simulations typically remain a challenge due to the need for detailed knowledge of hydrodynamic parameter values in 3D with a certain critical spatial resolution.

Here we show simulation results obtained by the COMSOL Multiphysics code coupled with PHREEQC (Wissmeier and Barry, 2011) and compare them with measurement results (BTC) from reactive transport (herbicide MCPA on goethite/sand). CD-MUSIC adsorption model parameter were obtained from Kersten et al., (2014). The underlying structural heterogeneity of the simulated column experiments reflects preferential flow along the column boundaries caused by locally elevated permeability in otherwise homogeneous sand packing as verified by the GeoPET images from both conservative and reactive tracer experiments.

References
Gründig, M., Richter, M., Seese, A. and Sabri, O., 2007. Tomographic radiotracer studies of the spatial distribution of heterogeneous geochemical transport processes. Applied Geochemistry, 22: 2334-2343.
Kersten, M., Tunega, D., Georgieva, I. and Vlasova, N., 2014. Surface complexation modeling of herbicide adsorption by goethite: 1. 4-chloro-2-methylphenoxyacetic acid (MCPA). Environmental Science & Technology, submitted.
Kulenkampff, J., Gründig, M., Richter, M. and Enzmann, F., 2008. Evaluation of positron emission tomography for visualisation of migration processes in geomaterials. Physics and Chemistry of the Earth, 33: 937-942.
Richter, M., Gründig, M. and Butz, T., 2000. Tomographische Radiotracerverfahren zur Untersuchung von Transport- und Sorptionsprozessen in geologischen Schichten. Zeitschrift für Angewandte Geologie, 46(2): 101.
Wissmeier, L. and Barry, D.A., 2011. Simulation tool for variably saturated flow with comprehensive geochemical reactions in two- and three-dimensional domains. Environmental Modelling & Software, 26(2): 210-218.
  • Poster
    International Symposium of the German Priority Programme SPP 1315 Biogeochemical Interfaces in Soil - Towards a Comprehensive and Mechanistic Understanding of Soil Functions, 06.-08.10.2014, Leipzig, Deutschland

Publ.-Id: 20595 - Permalink


Imaging of α7 nicotinic acetylcholine receptors in brain and cerebral vasculature of juvenile pigs with [18F]NS14490
Rötering, S.; Deuther-Conrad, W.; Cumming, P.; Donat, C. K.; Scheunemann, M.; Fischer, S.; Xiong, G.; Steinbach, J.; Peters, D.; Sabri, O.; Bucerius, J.; Brust, P.;
Background: The α7 nicotinic acetylcholine receptor (nAChR) is an important molecular target in neuropsychiatry and oncology. Development of applicable highly-specific radiotracers has been challenging due to comparably low protein expression. To identify novel ligands as candidates for positron emission tomography (PET), a library of diazabicyclononane compounds was screened regarding affinity and specificity towards α7 nAChRs. From these, [18F]NS14490 has been shown to yield reliable results in organ distribution studies; however, dynamic PET investigations required the establishment of an automated radiosynthesis.

Methods: Automated radiosynthesis of [18F]NS14490 has been performed by [18F]fluoroalkylation of the tosylate precursor in the TRACERlabTM FX-N synthesis module. After optimization, the radiochemical yield of [18F]NS14490 was consistently ~35% and the total synthesis time was about 90 min. The radiotracer was prepared with >92% radiochemical purity, and the specific activity at the end of the synthesis was 226 ± 68 GBq µmol-1. PET measurements were performed in young pigs to investigate the metabolic stability and cerebral binding of [18F]NS14490 without and with administration of the α7 nAChR partial agonist NS6740 in baseline and blocking conditions.

Results: The total distribution volume relative to the metabolite-corrected arterial input was 3.5-4.0 mL g-1 throughout telencephalon, and was reduced to 2.6 in animals treated with NS6740. Assuming complete blockade, this displacement indicated a binding potential (BPND) of approximately 0.5 in brain of living pigs. In addition, evidence for specific binding in major brain arteries has been obtained.

Conclusion: [18F]NS14490 is not only comparable to other preclinically investigated PET radiotracers for imaging of α7 nAChR in brain but could besides be a potential PET radiotracer for imaging of α7 nAChR in vulnerable plaques of diseased vessels.
Keywords: Alpha7 nicotinic acetylcholine receptors; Alzheimer´s disease; Blood-brain barrier; Cancer; Diazabicyclononane; Metabolism; PET; Stroke

Publ.-Id: 20594 - Permalink


Recent improvement of Cs2Te photocathodes at HZDR
Xiang, R.; Arnold, A.; Michel, P.; Murcek, P.; Teichert, J.; Lu, P.; Vennekate, H.;
The ELBE SRF gun has been successfully operated for the radiation source at HZDR. To achieve higher current and lower beam emittance, a new niobium cavity with superconducting solenoid and a new 13 MHz laser have been recently developed. Meanwhile, better photocathodes with high quantum efficiency are urgently in demand. In this work we improve the present Cs2Te preparation system for cleaner environment and more precise stoichiometric control than before. A new mask is designed to prevent cesium pollution of the cathode body. Instead of Kapton only alumina ceramics are used for isolation, and the cathode plugs are degassed at higher temperature. New evaporators are produced for an accurate deposition rate. Furthermore, the cathode transfer system is improved for a better vacuum condition.
Keywords: SRF gun, high current, low beam emittance, Cs2Te photocathode
  • Open Access LogoContribution to proceedings
    5th International Particle Accelerator Conference (IPAC’14), 15.-20.06.2014, Dresden, Germany
    Proceedings of IPAC'14, MOPRI025
  • Poster
    the 5th International Particle Accelerator Conference (IPAC’14), 15.-20.06.2014, Dresden, Germany

Publ.-Id: 20593 - Permalink


PET Imaging of the α4β2* Nicotinic Acetylcholine Receptors in Alzheimer's Disease
Sabri, O.; Meyer, P. M.; Gertz, H.-J.; Brust, P.; Barthel, H.; Hesse, S.;
Alzheimer's disease (AD) is a progressive neurodegenerative disease and the most common form of dementia in the elderly. The subunits α4 and β2 of the nicotinic acetylcholine receptors (α4β2*-nAChRs) are widely abundant throughout the human Brain and play an important role as neuromodulators in different neuronal systems. They are particularly important for cognitive functions and the loss of α4β2*-nAChRs, especially in cholinergic neurons may underlie memory loss in AD. Postmortem autoradiographic and immunohistochemical studies identified cortical and subcortical reductions in α4β2*-nAChR binding in patients with AD. Recently, the α4β2*-nAChR-specific PET and SPECT tracers 2-[18F]FA-85380 (2-FA) and 5-[123I]IA-85380 (5-IA) were developed enabling to study the α4β2*nAChR availability in the living human brain. With such specific radioligands, α4β2*-nAChR binding and its association to cognitive symptoms can be quantitatively determined in patients with AD and mild cognitive impairment (MCI). Initial results show that α4β2*-nAChR availability is reduced in AD but also in amnestic MCI patients who progressed into AD. Hence, the prediction of conversion from MCI to AD seems to be feasible, and therefore, quantitative assessment of α4β2*-nAChR binding using 2-FA-PET or 5-IA-SPECT might become an early biomarker of mental dysfunction in AD. However, the devvelopment of new α4β2*-nAChR PET radioligands characterized by faster kinetics, higher receptor affinity and selectivity is needed and currently underway.
  • Book chapter
    Rudi, A.J.O.; Dierckx, A.; Otte, E. F.J.; de Vries, A.; van Waarde: PET and SPECT in Neurology, Berlin, Heidelberg: Springer, 2014, 978-3-642-54307-4, 255-269
    DOI: 10.1007/978-3-642-54307-4_11

Publ.-Id: 20592 - Permalink


NEA-GaAs (Cs, O) Photocathodes for the ELBE SRF gun
Xiang, R.; Arnold, A.; Michel, P.; Murcek, P.; Teichert, J.; Lu, P.; Vennekate, H.;
At HZDR a preparation chamber for NEA-GaAs (Cs,O) has been built and tested. GaAs is the next photocathode material for the ELBE SRF gun, which has been successfully operated with Cs2Te photocathode in last years. GaAs photocathodes are advantageous because of their high quantum efficiency (QE) with visible light and the extensive experiences of their use in DC guns. Furthermore, GaAs photocathodes provide the possibility to realize a polarized SRF gun in the future. In this presentation we will introduce the new preparation system and the first results of the GaAs tests. The new transfer system under construction will be also presented.
Keywords: NEA-GaAs (Cs,O), SRF gun, photocathode
  • Open Access LogoContribution to proceedings
    5th International Particle Accelerator Conference (IPAC’14), 15.-20.06.2014, Dresden, Germany
    Proceedings of IPAC'14, MOPRI024
  • Poster
    the 5th International Particle Accelerator Conference (IPAC’14), 15.-20.06.2014, Dresden, Germany

Publ.-Id: 20591 - Permalink


Surface nanostructuring by ion-induced localized plasma expansion in zinc oxide
El-Said, A. S.; Moslem, W. M.; Djebli, M.;
Creation of hillock-like nanostructures on the surface of zinc oxide single crystals by irradiation with slow highly charged ions is reported. At constant kinetic energy, the nanostructures were only observed after irradiation with ions of potential energies above a threshold between 19.1 keV and 23.3 keV. The size of the nanostructures increases as a function of potential energy. A plasma expansion approach is used to explain the nanostructures creation. The calculations showed that the surface nanostructures became taller with the increase of ionic temperature. The influence of charged cluster formation and the relevance of their polarity are discussed.
Keywords: Surface Nanostructuring; highly charged ions; Zinc oxide; plasma expansion

Publ.-Id: 20590 - Permalink


Commissioning and First RF Results of the Second 3.5 Cell Rossendorf SRF Gun
Arnold, A.; Lu, P.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.; Kneisel, P.;
As in 2007 the first 3.5 cell superconducting radio frequency (SRF) gun was taken into operation at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), it turned out that the specified performance to realize an electron energy gain of 9.4 MeV (E_peak=50 MV/m @ Q_0=1e10) has not been achieved. Instead, the resonator of the gun was limited by field emission to about one third of these values and the measured beam parameters remained significantly below the expectations. However, to demonstrate the full potential of this new electron source for the ELBE LINAC, a second and slightly modified SRF gun was developed and built in collaboration with Thomas Jefferson National Accelerator Facility (TJNAF). We will report on commissioning and first results of this new SRF gun. This includes in particular the characterization of the most important RF properties of the cavity as well as their comparison with previous vertical test results.
Keywords: superconducting radio frequency, SRF gun, cavity
  • Poster
    5th International Particle Accelerator Conference (IPAC’14), 15.-20.06.2014, Dresden, Deutschland

Publ.-Id: 20589 - Permalink


Investigation of Cryomodules for the Mainz Energy-recovering Superconducting Accelerator MESA
Schlander, F.; Aulenbacher, K.; Heine, R.; Simon, D.; Arnold, A.;
For the multiturn accelerator MESA it is planned to employ superconducting technology for the main linac, which is supposed to provide an energy gain of 50 MeV per turn. As continuous wave operation is mandatory for the experiments, it is important to minimise the cryogenic losses, hence to find cavities and the corresponding cryomodule meeting the framework conditions for the accelerator. The findings and the current statuts will be reported.
Keywords: superconducting technology, linac, cryomodule
  • Open Access LogoContribution to proceedings
    5th International Particle Accelerator Conference IPAC’14, 15.-20.06.2014, Dresden, Deutschland
    Proceedings of IPAC'14
  • Poster
    5th International Particle Accelerator Conference IPAC’14, 15.-20.06.2014, Dresden, Deutschland

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Publ.-Id: 20588 - Permalink


The CBM Time-of-Flight wall - A conceptual design
Deppner, I.; Herrmann, N.; Akindinov, A.; Bartos, D.; Balaceanu, A.; Belogurov, S.; Cao, P.; Caragheorgheopol, G.; Chen, H.; Ciobanu, M.; Constantin, F.; Deng, Z.; Deppe, H.; Duta, V.; Flemming, H.; Frühauf, J.; Gebelein, J.; Heidel, K.; Hildenbrand, K.; Kebschull, U.; Kiš, M.; Kiselev, S.; Koch, K.; Koczon, P.; Kotte, R.; Laso Garcia, A.; Lehrbach, J.; Li, C.; Loizeau, P.-A.; Malkevich, D.; Manz, S.; Naumann, L.; Nedosekin, A.; Niebur, W.; Oancea, A.; Petris, M.; Petrovici, M.; Plotnikov, V.; Prokudin, M.; Radulescu, L.; Shao, M.; Simion, V.; Simon, C.; Sultanov, R.; Sun, Y.; Tang, Z.; Wang, J.; Wang, Y.; Wüstenfeld, J.; Xiang, C.; Xu, N.; Zhang, Y.; Zhou, D.; Zhu, X.;
Charged hadron identification in the Compressed Baryonic Matter experiment (CBM) is realized via the Time-of-Flight method [1]. For this purpose the CBM-ToF collaboration designed a Time-of-Flight wall composed of Multi-gap Resistive Plate Chambers (MRPCs). Due to the high interaction rate in CBM of 10 MHz the key challenge is the development of high rate MRPCs above 25 kHz/cm² which become possible after the development of low resistive glass with extremely good quality. In this article we present the actual conceptual design of the ToF-wall which is subdivided in three parts namely the outer wall, the inner wall and the forward zone that are discussed in detail.

Publ.-Id: 20587 - Permalink


New experimental upper limit of the electron-proton spin-flip cross-section
Oellers, D.; Weidemann, C.; Lenisa, P.; Meyer, H. O.; Rathmann, F.; Trusov, S.; Augustyniak, W.; Bagdasarian, Z.; Barion, L.; Barsov, S.; Bechstedt, U.; Bertelli, S.; Carassiti, V.; Chiladze, D.; Ciullo, G.; Contalbrigo, M.; Dalpiaz, P. F.; Dymov, S.; Engels, R.; Gaisser, M.; Gebel, R.; Goslawski, P.; Grigoriev, K.; Guidoboni, G.; Kacharava, A.; Khoukaz, A.; Kulikov, A.; Kleines, H.; Langenberg, G.; Lehrach, A.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Maier, R.; Marianski, B.; Martin, S.; Mchedlishvili, D.; Merzliakov, S.; Meshkov, I. N.; Mielke, M.; Mikirtychiants, M.; Mikirtychiants, S.; Nass, A.; Nikolaev, N.; Nioradze, M.; Papenbrock, M.; Pappalardo, L.; Pesce, A.; Prasuhn, D.; Sarkadi, J.; Schleichert, R.; Smirnov, A.; Seyfarth, H.; Statera, M.; Steffens, E.; Stein, H. J.; Stockhorst, H.; Ströher, H.; Tabidze, M.; Tagliente, G.; Thörngren Engblom, P.; Trzcinski, A.; Valdau, Y.; Vasiliev, A.; Wüstner, P.; Zupranski, P.;
In a previous publication, measurements of the depolarization of a stored proton beam by interaction with a co-propagating unpolarized electron beam at low relative energy have been presented and an upper limit of about 3 ×107 b for the electron-proton spin-flip cross-section was determined. A refined analysis presented in this paper reduces the previous upper limit by a factor of three by the introduction of a new procedure that also makes use of non-identified particles.

Publ.-Id: 20586 - Permalink


Different Countermeasures of Electron Amplification in the Photocathode Unit
Tafa Tulu, E.; van Rienen, U.; Arnold, A.;
Superconducting radio frequency (SRF) structures may be subjected to electron multipacting (MP). The electrons emitted from one of the structure’s wall under certain conditions are accelerated by the RF field, thereby they may impact the wall again based on the field pattern in the structure. Accordingly the number of electrons increases exponentially caused by secondary electron emission. The latter depends on the secondary emission coefficient of the surface material and the electron trajectory in the device under study. This phenomenon limits the accelerating gradient in the cavity, moreover, it might cause an impair of RF components and distortion of the RF signal. Therefore, there should be an efficient countermeasure to suppress MP in order to boost the performance of the SRF gun. In this paper, three techniques of suppression of MP from the vicinity of the cathode, such as DC-bias, geometric modification and the microstructure of the cathode's surface, in the Rossendorf SRF gun are presented. The simulation has been done using CST Microwave Studio® and CST Particle Studio®. Eventually, the efficient suppression method would be chosen for this particular case.
Keywords: SRF gun, multipacting, electron source
  • Open Access LogoContribution to proceedings
    5th International Particle Accelerator Conference IPAC’14, 15.-20.06.2014, Dresden, Deutschland
    Different Countermeasures of Electron Amplification in the Photocathode Unit
  • Poster
    5th International Particle Accelerator Conference IPAC’14, 15.-20.06.2014, Dresden, Deutschland

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Publ.-Id: 20585 - Permalink


Defects and localized states in silica layers implanted with lead ions
Zatsepin, A. F.; Fitting, H.-J.; Buntov, E. A.; Pustovarov, V. A.; Schmidt, B.;
The luminescence of silica films and glasses implanted with Pb+ ions was studied by means of time-resolved photoluminescence spectroscopy under synchrotron excitation. The ion-modified silica layers are "metal- dielectrics" composites the oxide part of which is represented by amorphous micro-heterogeneous phase with variable Pb2+ions. Two groups of emission centers are identified: such as: (1) radiation-induced oxygen-deficient centers (ODCs) and non-bridging oxygen atoms (NBOs) in the SiO2 matrix and (2) localized electronic states (LS) of the amorphous lead-silicate phase
Keywords: Lead ion implantation; Metal-dielectric composites; Photoluminescence excitation; Silica; UV-vis-photoluminescence

Publ.-Id: 20584 - Permalink


Simulation Study of a Combined Pair Production - Compton Camera for In-Vivo Dosimetry During Therapeutic Proton Irradiation
Rohling, H.; Golnik, C.; Enghardt, W.; Hueso-González, F.; Kormoll, T.; Müller, A.; Pausch, G.; Fiedler, F.;
Proton and light ion beams are applied to the therapeutic irradiation of cancer patients due to the favorable dose deposition of these particles in tissue. By means of accelerated ions, a high dose can be accurately deposited in the tumor while normal tissue is spared. Since minor changes in the patient’s tissue along the beam path can compromise the success of the treatment, an in-vivo monitoring of the dose deposition is highly desired. Cameras detecting the prompt gamma-rays emitted during therapy are under investigation for this purpose. Due to the energy spectrum of prompt gamma-rays with a range between a few keV and several MeV, it is reasonable to consider the utilization of electron-positron pair production events to reconstruct the origin of these prompt photons. We evaluated if a pair production camera could be suitable in this context by means of Monte-Carlo simulations. Modelling of the pair production events taking place in a prototype detector dedicated to Compton imaging were performed. We analyzed the efficiency of the detector system regarding pair production and Compton events. The most crucial property of this pair production camera is the angular resolution. The results of this work indicate that the spatial resolution of a pair production camera is, for principal reasons, insufficient for an application to range assessment in particle therapy. Furthermore, the efficiency of the pair production camera under study is one magnitude lower than the efficiency of the Setup applied to the detection of Compton events.
Keywords: Pair production camera, Compton camera, in-vivo dosimetry, Particle therapy

Publ.-Id: 20583 - Permalink


APPL proteins modulate DNA repair and radiation survival of pancreatic carcinoma cells by regulating ATM
Hennig, J.; Mcshane, M.; Cordes, N.; Eke, I.;
Despite intensive multimodal therapies, the overall survival rate of patients with ductal adenocarcinoma of the pancreas is still poor. The chemo- and radioresistance mechanisms of this tumor entity remain to be determined in order to develop novel treatment strategies. In cancer, endocytosis and membrane trafficking proteins are known to be utilized and they also critically regulate essential cell functions like survival and proliferation. On the basis of these data, we evaluated the role of the endosomal proteins adaptor proteins containing pleckstrin homology domain, phosphotyrosine binding domain and a leucine zipper motif (APPL) 1 and 2 for the radioresistance of pancreatic carcinoma cells. Here, we show that APPL2 expression in pancreatic cancer cells is upregulated after irradiation and that depletion of APPL proteins by small interfering RNA (siRNA) significantly reduced radiation survival in parallel to impairing DNA double strand break (DSB) repair. In addition, APPL knockdown diminished radiogenic hyperphosphorylation of ataxia telangiectasia mutated (ATM). Activated ATM and APPL1 were also shown to interact after irradiation, suggesting that APPL has a more direct role in the phosphorylation of ATM. Double targeting of APPL proteins and ATM caused similar radiosensitization and concomitant DSB repair perturbation to that observed after depletion of single proteins, indicating that ATM is the central modulator of APPL-mediated effects on radiosensitivity and DNA repair. These data strongly suggest that endosomal APPL proteins contribute to the DNA damage response. Whether targeting of APPL proteins is beneficial for the survival of patients with pancreatic adenocarcinoma remains to be elucidated.

Publ.-Id: 20581 - Permalink


EGFR-Mediated Chromatin Condensation Protects KRAS-Mutant Cancer Cells against Ionizing Radiation
Wang, M.; Kern, A.; Hulskotter, M.; Greninger, P.; Singh, A.; Pan, Y.; Chowdhury, D.; Krause, M.; Baumann, M.; Benes, C.; Efstathiou, J.; Settleman, J.; Willers, H.;
Therapeutics that target the epidermal growth factor receptor (EGFR) can enhance the cytotoxic effects of ionizing radiation (IR). However, predictive genomic biomarkers of this radiosensitization have remained elusive. By screening 40 non-small cell lung cancer cell (NSCLC) lines, we established a surprising positive correlation between the presence of a KRAS mutation and radiosensitization by the EGFR inhibitors erlotinib and cetuximab. EGFR signaling in KRAS-mutant NSCLC cells promotes chromatin condensation in vitro and in vivo, thereby restricting the number of DNA double-strand breaks (DSB) produced by a given dose of IR.
Chromatin condensation in interphase cells is characterized by an unexpected mitosis-like colocalization of serine 10 phosphorylation and lysine 9 trimethylation on histone H3. Aurora B promotes this process in a manner that is codependent upon EGFR and protein kinase C alpha (PKC alpha). PKC alpha, in addition to MEK/ERK signaling, is required for the suppression of DSB-inducible premature senescence by EGFR. Blockade of autophagy results in a mutant KRAS-dependent senescence-to-apoptosis switch in cancer cells treated with IR and erlotinib. In conclusion, we identify EGFR as a molecular target to overcome a novel mechanism of radioresistance in KRAS-mutant tumor cells, which stands in contrast to the unresponsiveness of KRAS-mutant cancers to EGFR-directed agents in monotherapy. Our findings may reposition EGFR-targeted agents for combination with DSB-inducing therapies in KRAS-mutant NSCLC. Cancer Res; 74(10); 2825-34. (C) 2014 AACR.

Publ.-Id: 20580 - Permalink


Bispidine dioxotetraaza macrocycles: a new class of bispidines for 64Cu PET imaging
Comba, P.; Kubeil, M.; Pietzsch, J.; Rudolf, H.; Stephan, H.; Zarschler, K.;
The three new dioxo-tetraazamacrocyclic ligands with a fused, very rigid bispidine (3,7-diazabicyclo[3.3.1]nonane) group connecting the two tertiary amine donors, and ethyl, propyl, or benzene groups connecting the two amide donors are highly preorganized and lead to very stable, uncharged CuII complexes. Solution spectroscopy and solid state structures indicate that these are square pyramidal with a solvent molecule occupying the apical position. Cyclic voltammetry defines a reversible CuIII/II couple and a strongly negative irreversible CuII/I couple (ca. −2 V vs Fc/Fc+), indicating that the CuII complexes are very stable in solution. This is supported by superoxide dismutase (SOD) and human serum challenge experiments as well as the biodistribution, which all show that the benzene-based ligand has the highest in vitro and in vivo stability and that this was expected on the basis of the macrocycle ring size and shape and the highest degree of preorganization. This ligand is easy to functionalize for a possible coupling to biological vector molecules and/or fluorescence markers for PET (positron emission tomography) and multimodal imaging (i.e., PET and optical imaging).

Publ.-Id: 20579 - Permalink


Evaluation of Novel Fluorescence Probes for Conjugation Purposes Using the Traceless Staudinger Ligation
Wodtke, R.; König, J.; Pigorsch, A.; Köckerling, M.; Mamat, C.;
A robust and versatile method for the synthesis of various azide, alkyne and phosphane functionalized coumarin derivatives from the corresponding 7-amino and 7-hydroxy analogs for an application in bioorthogonal conjugation and labeling reactions like the Staudinger Ligation or the Huisgen-Click reaction is presented. Further, the convenient preparation of modified coumarins was performed and subsequent regio–/chemoselective labeling reactions delivered the desired biologically active derivatives in high yields. These new compounds may thus constitute attractive scaffolds for designing novel fluorescence building blocks for various challenging biolabeling applications.

Publ.-Id: 20578 - Permalink


Uranium Redox processes – initiated by plant cells
Geipel, G.; Viehweger, K.;
Recently we have shown that uranium can be taken up by plant cells. Fractionation studies showed that the uranium was present in nearly all cell compartments. Nevertheless, luminescence measurements showed that the speciation of the uranium in the several cell compartments differs from each other.
One of the major remaining questions concerns to the ways of uranium uptake. Recently published work [1, 2] proposed that the uranium uptake is influenced by the iron uptake. As it is known that the iron uptake occurs via reduction of the iron(III) into iron(II), we conclude that uranium uptake should also by accompanied by a redox process.
From electrochemical point of view the formation of uranium(V) is a reversible process and the redox potential uranium(VI)/uranium(V) is of the same order as the redox potential iron(III)/iron(II) (values for acidic solution).
The evaluation of Laser-Induced Photoacoustic Spectra (LIPAS) in the wavelength range 620 nm to 680 nm gave evidence for the formation of both reduced oxidation states in the media studied. The uranium(V) is assigned to an absorption at around 637 nm, while uranium(IV) absorbs light at ~660 nm.
Keywords: Uranium, oxidation states, redox process, plant cells
  • Contribution to proceedings
    International Workshop on Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, Rossendorf, Deutschland
    Advanced Techniques in Actinide Spectrooscopy (ATAS 2014) Abstract Book, Dresden-Rossendorf: HZDR-054

Publ.-Id: 20577 - Permalink


Radiofluorination and first radiopharmacological characterization of a SWLAY peptide-based ligand targeting EphA2
Pretze, M.; Mosch, B.; Bergmann, R.; Steinbach, J.; Pietzsch, J.; Mamat, C.;
Peptides labeled with short-lived positron-emitting radionuclides are of considerable interest as probes for molecular imaging by positron emission tomography (PET). Herein, the regioselective and convenient radiofluorination of a biologically relevant alkyne-modified SWLAY peptide bound on solid support with the radiolabeling building block 1-(3-azidopropyl)-4-(3-fluoropropyl)piperazine ([18F]AFP) is described.
The desired 18F-peptide could be prepared in a total synthesis time of 140 min including the removal of the catalytic copper species and was obtained with a RCY of 7–13% and a RCP > 98%. The method’s feasibility for a robust and bioorthogonal radiolabeling via the 1,3-dipolar Huisgen cycloaddition was demonstrated. Preliminary radiopharmacological studies regarding the metabolic stability of the peptides in cell culture supernatants and rat plasma were accomplished as well as the cellular association of the 18F-peptide in EphA2-overexpressing human melanoma cells in vitro. Furthermore, an initial in vivo PET experiment was performed which showed a fast metabolism of the novel 18F-peptide followed by an accumulation in the kidneys, followed by elimination into the bladder.
  • Journal of Labelled Compounds and Radiopharmaceuticals 57(2014), 660-665
    DOI: 10.1002/jlcr.3237

Publ.-Id: 20576 - Permalink


Development of New PET Tracers for Clinical Use: Challenges and Problems
Brust, P.;
Es ist kein Abstract vorhanden.
  • Invited lecture (Conferences)
    4. Dresdner Workshop "Molekulare Bildgebung in den Lebenswissenschaften", 26.06.2014, Rossendorf, Deutschland

Publ.-Id: 20575 - Permalink


Aufbereitung von [18O]Wasser für die Produktion und Verwendung von [18F]Fluorid
Rötering, S.; Franke, K.; Zessin, J.; Brust, P.; Füchtner, F.; Fischer, S.; Steinbach, J.;
Ziel/Aim:
Bestrahltes [18O]H2O kann nach Aufbereitung erneut für Bestrahlungen eingesetzt werden1. Wir berichten über einen einfachen Aufbereitungsprozess und eine genaue Charakterisierung des [18O]H2O.

Methodik/Methods:
1 l bestrahltes [18O]Wasser mit 396 mg l–1 Ethanol und 44 mg l–1 Aceton sowie Ionen im g-l–1-Bereich wurde in unterschiedlichen Ansätzen zur Oxidation der organischen Lösungsmittel mit KMnO4/NaOH bei 50°C bzw. mit UV-Strahlung1 (254 nm, 1 W) behandelt. Anschließend erfolgte eine Vakuumdestillation. Nach genauer Charakterisierung mit Gas- und Ionenchromatographie Pyknometrie wurde das gewonnene Wasser in einem Nirta®Fluor - Target an einem Cylcone®18/9 (IBA, Belgien) bestrahlt und die Produktionsaktivitäten mit denen von (verdünntem) [18O]Originalwasser verglichen. Das produzierte [18F]Fluorid wurde für die Entwicklung von Radiosynthesen und für standardisierte Herstellungsverfahren eingesetzt.
Für einen Vergleich der beiden Oxidationsmethoden wurde [16O]H2O mit Methanol, Ethanol, Aceton und Acetonitril kontaminiert und entsprechend aufbereitet.

Ergebnisse/Results:
Mit beiden Oxidationsmethoden wurden die organischen Lösungsmittel innerhalb von max. 2 Tagen unter einen Grenzwert von 50 mg l–1 abgebaut. Nach der Vakuumdestillation zeichneten sich die einzelnen Chargen durch übereinstimmende 18O-Anreicherungen sowie geringe Ionengehalte aus. Der Vergleich der Produktionsaktivitäten zeigt eine Übereinstimmung zu verdünntem Originalwasser. Die Verwendung des [18F]F– in radiochemischen Umsetzungen war erfolgreich.


Abbildung 1: Produktionsaktivitäten mit aufbereitetem Wasser und verdünntem Originalwasser
Die Aufbereitung von Modelllösungen mit [16O]H2O ergab, dass Acetonitril durch KMnO4/NaOH defakto nicht abgebaut wird. Es wurden für beide Methoden ≥97% des eingesetzten Wassers gewonnen.

Schlussfolgerungen/Conclusions:
Die Ergebnisse zeigen einen zuverlässigen, nahezu verlustfreien Aufbereitungsprozess von bestrahltem [18O]H2O. Dies ermöglicht einen ökonomisch sinnvollen Gebrauch von [18O]H2O.

Referenzen/References:
[1] Gebrauchsmuster DE 29504388 U1 (15.03.95), Forschungszentrum Jülich GmbH
  • Lecture (Conference)
    22. Jahrestagung der AGRR 2014, 11.-13.09.2014, Mainz, Deutschland

Publ.-Id: 20574 - Permalink


Proinflammatory human 6-sulfo LacNAc-positive dendritic cells accumulate in intestinal acute graft-versus-host disease
Sommer, U.; Larsson, B.; Tuve, S.; Wehner, R.; Zimmermann, N.; Kramer, M.; Kloß, A.; Günther, C.; Babatz, J.; Schmelz, R.; Brückner, S.; Schetelig, J.; Bornhäuser, M.; Schäkel, K.; Bachmann, M. P.; Aust, D.; Baretton, G.; Schmitz, M.;
kein Abstract verfügbar
Keywords: Acute graft versus host disease; b-sulfo LacNAc positive; Dendritic cells; Proinflammatory

Publ.-Id: 20573 - Permalink


Combined measurement of tumor perfusion and glucose metabolism for improved tumor characterization in advanced cervical carcinoma: A PET/CT pilot study using [15O]water and [18F]fluorodeoxyglucose
Apostolova, I.; Hofheinz, F.; Buchert, R.; Steffen, I. G.; Michel, R.; Rosner, C.; Prasad, V.; Köhler, C.; Derlin, T.; Brenner, W.; Marnitz, S.;
Background and purpose:
The aim of this pilot study was (1) to evaluate the combination of [18F]fluorodeoxyglucose (FDG) and [ 15O]water for detection of flow-metabolism mismatch in advanced cervical carcinomas, i.e., increased glycolysis at low blood flow, as a possible parameter for prediction of response to treatment, and (2) to propose a method for automated quantification of its spatial extent.
Patients and methods:
The study retrospectively included 10 women with advanced cervical carcinoma in whom PET with both FDG and [15O]water had been performed prior to therapy. The metabolically active tumor volume was delineated automatically in the FDG images. For computation of the regional blood flow in the tumor, a recovery corrected image-derived arterial input function was used. A tumor voxel was classified as mismatched when the voxel SUV of FDG was larger than the median tumor SUV and the voxel perfusion (K1) was smaller than the median perfusion. The absolute mismatch volume (aMMV) was defined as the volume of all mismatched voxels in ml, and the relative mismatch volume (rMMV) as the ratio of the aMMV to the metabolic tumor volume in percent.
Results:
The tumors were quite heterogeneous with respect to both FDG uptake and perfusion. The aMMV clustered into 2 groups: "large aMMV" ∈10 ml in 40∈% of patients and "small aMMV" 5 ml in 60∈% of patients. The rMMV ranged from 12.7-24.9∈%. There was no correlation between rMMV and metabolic tumor volume. There was a tendency (p∈=∈0.126) for an association between rMMV and histological grading, rMMV being about 20∈% higher in G3 than in G2 tumors. rMMV did not correlate with SUV or perfusion.
Conclusion:
These results suggest that combined PET with FDG and [15O]water allows detection and quantitative characterization of flow-metabolism mismatch in advanced cervical carcinomas.
Keywords: Positron emission tomography; Prognosis; Uterine cervical carcinoma

Publ.-Id: 20572 - Permalink


64Cu-labeling of dendritic polyglycerol derivatives for biodistribution studies
Pant, K.; Steinbach, J.; Stephan, H.; Gröger, D.; Nowag, S.; Haag, R.;
Dendritic polyglycerols (dPG) and polyglycerol sulfates (dPGS) are promising compounds for biomedical applications due to their easy synthesis and high biocompatibility. Dendritic polyglycerol sulfate shows strong anti-inflammatory
properties [1, 2] which makes it a promising agent for diagnostic and therapeutic applications [3].

Information about the biodistribution and the metabolism of dendritic polyglycerol derivatives in living systems are quite scarce. In order to obtain quantitative information about the biodistribution of dPGS in vivo, methods like positron emission tomography (PET) will be applied. Among the metal-based positron emitting radionuclides, 64Cu is one of the most intensively evaluated isotopes. Incorporation of 64Cu into dPG/dPGS derivatives requires the use of chelate ligands capable of tightly binding the radionuclide.

Herein, we report the conjugation of bifunctional chelating agents (BFCA), based on bis(2-pyridylmethyl)triazacyclononane (DMPTACN) [4], on the dPG/dPGS scaffold. The structure of DMPTACN allows for the introduction of linker groups, such as carboxylic acids, maleimides or isothiocyanates, thereby facilitating coupling to the dendritic polyglycerol derivatives that contain amino and mercapto surface groups. 64Cu-labeling experiments and studies of the stability of the resulting radiocopper complexes in the presence of human serum or the competing ligand EDTA will be discussed.

References:
[1] H. Türk et al., Bioconjugate Chem. 2004, 15, 162.
[2] J. Dernedde et al., PNAS 2010, 117, 19679.
[3] K. Licha et al., Bioconjugate Chem. 2011, 22, 2453.
[4] G. Gasser et al., Bioconjugate Chem.2008, 19, 719.
  • Poster
    GDCh-Wissenschaftsforum Chemie 2013, 01.-04.09.2013, Darmstadt, Deutschland

Publ.-Id: 20571 - Permalink


Magnetic dipole strength in 128Xe and 134Xe in the spin-flip resonance region
Massarczyk, R.; Rusev, G.; Schwengner, R.; Dönau, F.; Bhatia, C.; Gooden, M. E.; Kelley, J. H.; Tonchev, A. P.; Tornow, W.;
The magnetic dipole strength in the energy region of the spin-flip resonance has been investigated in {128}Xe and {134}Xe using quasi-monoenergetic and linearly polarized gamma-ray beams at the HI gamma S facility in Durham, USA. Absorption cross sections were deduced for the electric and magnetic Dipole distributions separately for various intervals of excitation energy, including the strength of states in the unresolved quasi-continuum. Spin-flip like resonance structures were found in the magnetic dipole strength distribution around an excitation energy of 8 MeV. The E1 strength distributions deduced from the present experiments are compatible with the data of an experiment using bremsstrahlung that are based on simulations of statistical gamma-ray cascades. The experimental E1 and M1 strengths are compared with phenomenological approximations and with deformed-basis quasiparticle-random-phase-approximation predictions.
Keywords: Photon scattering, nuclear resonance fluorescence, polarized $\gamma$-ray beams, electric and magnetic dipole strength functions, nuclear deformation, quasiparticle-random-phase-approximation

Publ.-Id: 20570 - Permalink


64Cu-labelling and biodistribution of dendritic polyglycerol derivatives
Pant, K.; Stephan, H.; Bergmann, R.; Steinbach, J.; Gröger, D.; Haag, R.;
Dendritic polyglycerols are highly biocompatible polymers which can be synthesized on a multi gram scale in a one-pot synthesis. The properties of these derivatives can be influenced by using various surface groups, such as sulfates, carbonates, phosphates etc. Some derivatives have been already known for inflammation and bone targeting [1]. Dendritic polyglycerol sulfates (dPGS) are promising candidates to be applied as anti-inflammation and anti-coagulation agents [2]. The presence of amine surface groups in dPGS derivatives allows the attachment of various fluorescence tags and/or radiolabels. Fluorescence imaging using near IR probes visualizes a specific accumulation of dendritic polyglycerol sulfates (dPGS) in inflamed lesions [3]. With respect to radioactive labelling, 35S-labelled dPGS amines have been prepared. This allows ex vivo experiments using autoradiography[4]. However, there is a need of detailed information about bio-distribution and pharmacokinetic properties for dendritic polyglycerol derivatives.

For this reason, appropriate imaging techniques should be applied to achieve reliable information about the bio-distribution and the metabolic fate of these macromolecules in vivo. Nuclear imaging, especially positron emission tomography (PET) is known to be one of the most reliable techniques to follow the fate of substances in vivo and to examine the biological and pathological processes considering the small dose requirement of the radiolabelled substances to diminish the pharmacological effects. 64Cu has suitable decay characteristics that allow for PET imaging and a variety of bifunctional chelator agents (BFCAs) are available for attachment to dendritic polyglycerol derivatives using appropriate anchor groups.

Herein, we report the synthesis, radiolabelling and biodistribution studies of the dPGS scaffolds using BFCAs on the basis of 1,4,7-triazacyclononane with various functional end groups (carboxylic, maleimide, isothiocyanate groups) for easy bioconjugation onto the dPGS scaffolds (amine/mercapto surface groups). 64Cu-labeling experiments confirmed rapid CuII complex formation under mild conditions. The stability of the 64Cu radiolabelled conjugates has been studied in the presence of competing ligands, human serum and super oxide dismutase (SOD)[5] For stability studies in the presence of human serum and SOD, two complementary in vitro assays have been applied. Small animal PET studies with 64Cu-labelled dPGS derivatives in male Wistar rats have been performed and discussed.
  • Poster
    Biodendrimer 2014, 4th International Symposium on Biomedical Applications of Dendrimers, 18.-20.06.2014, Lugano, Schweiz

Publ.-Id: 20569 - Permalink


Carbon redistribution and precipitation in high temperature ion-implanted strained Si/SiGe/Si multi-layered structures
Gaiduk, P. I.; Lundsgaard Hansen, J.; Larsen, A. N.; Korolik, O. V.; Bregolin, F. L.; Skorupa, W.;
We report on the segregation of carbon atoms and structural transformations in strained multilayered Si/SiGe/Si structures after molecular-beam epitaxial (MBE) growth, carbon ion implantation and thermal treatment at different conditions. The idea behind this study was that due to their specific strain distribution, pseudomorphic layers of Si/SiGe promote spatial separation of vacancies and interstitials followed by segregation of foreign dopant atoms. High temperature ion implantation was used for injection of carbon atoms as well as point defects in the strained layers. The defects were investigated by transmission electron microscopy (TEM), dopant depth profiles by secondary-ion-mass spectrometry (SIMS), and optical properties by Raman scattering measurements. Based on SIMS data we demonstrate anomalous redistribution of the implanted carbon atoms around the strained SiGe/Si layers which results in their accumulation on the Si side and depletion on the SiGe side of the structure. The TEM study demonstrates formation of plate-like defects, stacking faults and thin carbon-precipitated flakes distributed along the Si/SiGe interfaces. Raman spectra reveal peaks at 1600 and 2700 cm -1 which might be associated with carbon-related phases. The concept of strain-enhanced separation of point defects and dopant precipitation is discussed.
Keywords: Carbon redistribution; Defects; Precipitates; Si-SiGe heterostructures; Voids

Publ.-Id: 20568 - Permalink


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