Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31735 Publications
Angular-dependent specific heat of the fully organic superconductor β′′-(ET)2SF5CH2CF2SO3 - evidence for an FFLO phase
Beyer, R.; Schlueter, J. A.; Wosnitza, J.;
Since 1964 predicted, there is no clear-cut experimental proof of the existence of a field-induced superconducting state with finite center of mass momentum (q \neq 0) [1]. In 2007, Lortz et al. reported thermodynamic evidence for a FFLO state in κ-(ET)2Cu(NCS)2 [2], where ET stands for bisethylenedithio-tetrathiafulvalene. They found an emerging sharp double-peak structure in the specific heat, indicating first-order phase transitions at high magnetic fields applied parallel to the superconducting ET layers. Expecting similar novel results for β′′-(ET)2SF5CH2CF2SO3, we performed high-resolution specific-heat measurements for different orientations with very fine steps around perfect parallel alignment. In conclusion, we found an upturn in the field-temperature phase diagram of the superconducting phase beyond the Pauli-Clogston limit and we could observe a double-peak structure above 9.4 Tesla but only by tilting the field 0.2 degree out of the ET sheets.
  • Lecture (Conference)
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17017 - Permalink


ESR studies of the quasi-2D antiferromagnet Cu(Pz)2(ClO4)2
Ozerov, M.; Wosnitza, J.; Čižmár, E.; Xiao, F.; Turnbull, M. M.; Landee, C. P.; Zvyagin, S. A.;
We report systematic high-field electron spin resonance (ESR) studies of the quasi-two-dimensional spin- ½ Heisenberg antiferromagnet Cu(pz)2(ClO4)2 (pz denotes pyrazine or C4H4N2). The linewidth and resonance-field temperature dependences of the ESR absorptions in this compound were investigated in the frequency range from 85 to 416 GHz in magnetic fields up to 16 T. A pronounced ESR linewidth anomaly was revealed in the vicinity of TN. This anomaly reflects enhanced critical fluctuations in this compound at the 3D ordering. The experiment revealed a significant change in the linewidth behavior for magnetic fields above 7 T, whose origin will be discussed.
  • Poster
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17016 - Permalink


Tantalum incorporation in TiO2 based transparent conductive thin films
Neubert, M.; Vinnichenko, M.; Cornelius, S.; Kolitsch, A.;
The growing number of applications of transparent electrodes in optoelectronic devices drives the need for novel cost-efficient transparent conductive materials. The epitaxial films of TiO2 doped with Nb or Ta show electrical resistivity values comparable to those of the best In2O3:Sn and ZnO:Al films. However, it is still challenging to achieve low electrical resistivity in polycrystalline TiO2-based films. In order to address this problem, we studied the films formed on glass substrates without heating by DC magnetron sputtering of reduced TiO2:Ta ceramic targets followed by vacuum annealing. It was crucial to use a plasma feedback system in order to enable a fine tuning of the oxygen supply into Ar and O2 gas mixture during the growth. This approach yielded the films with optical transittance above 85%, electrical resistivity in the range of 10-3  cm and free electron mobility of 8 cm²/Vs. The electrical activation of Ta dopant was above 60% that is substantially higher than that of Al in ZnO.
Keywords: TCO TiO2 titania Ta tantalum transparent conductive oxide
  • Lecture (Conference)
    DPG-Frühjahrstagung, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17015 - Permalink


Investigations on optimization of accident management measures following a station blackout accident in a VVER-1000 pressurized water reactor
Tusheva, P.; Schaefer, F.; Kliem, S.;
The reactor safety issues are of primary importance for preserving the health of the population and ensuring no release of radioactivity and fission products into the environment. A part of the nuclear research focuses on improvement of the safety of existing nuclear power plants. Studies, research and efforts are a continuing process at improving the safety and reliability of existing and newly developed nuclear power plants at prevention of a core melt accident.

Station blackout (loss of AC power supply) is one of the dominant accidents taken into consideration at performing accident analysis. In case of multiple failures of safety systems it leads to a severe accident. To prevent an accident to turn into a severe one or to mitigate the consequences, accident management measures must be performed. The present paper outlines possibilities for application and optimization of accident management measures following a station blackout accident. Assessed is the behaviour of the nuclear power plant during a station blackout accident without accident management measures and with application of primary/secondary side oriented accident management measures. Discussed are the possibilities for operators’ intervention and the influence of the performed accident management measures on the course of the accident. Special attention has been paid to the effectiveness of the passive feeding and physical phenomena having an influence on the system behaviour.

The performed simulations show that the effectiveness of the secondary side feeding procedure can be limited due to an early evaporation or flashing effects in the feed water system. The analyzed cases show that the effectiveness of the accident management measures strongly depends on the initiation criteria applied for depressurization of the reactor coolant system.
Keywords: SBO, nuclear power plant behaviour, accident management, accident management measures, passive feeding, flashing effects
  • Contribution to proceedings
    International Congress on Advances in Nuclear Power Plants (ICAPP'12), 24.-28.06.2012, Chicago, USA
  • Lecture (Conference)
    International Congress on Advances in Nuclear Power Plants (ICAPP'12), 24.-28.06.2012, Chicago, USA

Publ.-Id: 17014 - Permalink


Radial solidification of Al-Si alloys in the presence of a rotating magnetic field
Travnikov, V.; Nikrityuk, P. A.; Eckert, K.; Räbiger, D.; Odenbach, S.; Eckert, S.;
We study the flow during the radial solidification of an Al-7wt pct Si melt inside a cylindrical cavity with cooled side walls which is placed in a rotating magnetic field (RMF). The solidification process is simulated by means of a continuum model which is implemented in a code which solves the axisymmetric Navier-Stokes equations. qwe first analyz the start-up of the buoyancy-driven convection driven by the radial heat flux in absence of the RMF. We show that the initial large vortex breaks up into three smaller ones. The resulting radial temperature profiles are compared with experimental data. Second, we study how the vortex structure is modified by the application of small RMF's.
Keywords: solidification, Al-Si alloys, convection, rotating magnetic field
  • Lecture (Conference)
    Modeling of Casting, Welding and Advanced Solidification Processes 2012 (MCWASP XIII), 17.-22.06.2012, Schladming, Österreich
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 33(2012), 012048
    DOI: 10.1088/1757-899X/33/1/012048

Publ.-Id: 17013 - Permalink


Ultraschall-Array-Geschwindigkeitsmesssystem zur Untersuchung komplexer Flüssigmetallströmungen
Czarske, J.; Büttner, L.; Nauber, R.; Burger, M.; Pätzold, O.; Eckert, S.;
Schmelzen von Metallen und Halbleitern besitzen eine hohe industrielle Bedeutung. Als wichtigste Beispiele sind die Stahlherstellung und die Kristallzüchtung zu nennen. Bei allen Prozessen haben die in den Schmelzen auftretenden Strömungsverhältnisse eine großen Einfluss auf die Qualität des Endproduktes. Aufgrund ihrer hohen elektrischen Leitfähigkeit bietet sich die interessante Möglichkeit, diese Strömungen aktiv durch magnetische Felder zu beeinflussen. Da numerische Simulationen komplexe Strömungszustände oftmals nicht zuverlässig nachbilden können, besteht ein großer Bedarf an hochauflösenden Messverfahren. Aufgrund der opaken Fluide sind Ultraschallmesstechniken sehr gut geeignet. Allerdings weisen die aus der Medizintechnik verfügbaren tomographischen Verfahren keine ausreichenden Messeigenschaften, insbesondere für instationäre Strömungen, auf. Vorgestellt wird ein neuartiges Ultraschall-Messsystem, das mit dem Einsatz segmentierter Wandler und deren weitgehendem Parallelbetrieb erstsmals sowohl eine hohe Zeit- als auch eine hohe Ortsauflösung ermöglicht.
Keywords: Messtechnik, Strömungsmessung, Flüssigmetall, Ultraschall-Doppler Methode
  • Lecture (Conference)
    Workshop "Messtechnische Anwendungen von Ultraschall", 18.-20.06.2012, Drübeck, Deutschland

Publ.-Id: 17012 - Permalink


LMFR instrumentation development
Eckert, S.; Buchenau, D.; Gerbeth, G.; Stefani, F.; Wondrak, T.;
The safe and reliable operation of liquid metal systems requires corresponding measuring systems and control units, both for the liquid metal single-phase flow as well as for bubble-laden liquid metal two-phase flows. However, velocity measurements in opaque liquid metal flows still represent a challenging task as commercial measuring systems are not available for such fluids.
The paper reports on established methods and new developments in the field of measuring techniques for liquid metal flows. The presentation is focussed on measurements of the flow rate and the local velocity field as well as on the characterization of liquid metal two-phase flows. During the last two decades considerable effort was spent by miscellaneous researcher groups to provide new solutions for measurements of flow fields in liquid metals. This paper intends to summarize different approaches and tempts to account on perspectives, particularly in view of some recent developments (ultrasonic techniques, magnetic tomography).
Keywords: liquid metal cooled fast reactor, instrumentation, flow rate measurements, velocity measurements, inductive tomography, ultrasound Doppler method
  • Lecture (Conference)
    International Workshop on Innovative Nuclear Reactors, 17.-20.04.2012, Pisa, Italy

Publ.-Id: 17011 - Permalink


Two concepts of introducing thin-film superconductivity in Ge and Si by use of Ga-ion implantation
Skrotzki, R.; Herrmannsdörfer, T.; Fiedler, J.; Heera, V.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Helm, M.; Wosnitza, J.;
We report on two unconventional routes of embedding superconducting nanolayers in a semiconducting environment. Ion implantation and subsequent annealing have been used for preparation of superconducting thin-films of Ga-doped germanium (Ge:Ga) [1] as well as 10 nm thin amorphous Ga-rich layers in silicon (Si:Ga) [2]. Structural investigations by means of XTEM, EDX, RBS/C, and SIMS have been performed in addition to low-temperature electrical transport and magnetization measurements. Regarding Ge:Ga, we unravel the evolution of Tc with charge-charrier concentration while for Si:Ga recently implemented microstructuring renders critical-current densities or more than 50 kA/cm2. Combined with a superconducting onset at around 10 K, this calls for onchip application in novel heterostructured devices.
  • Poster
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17010 - Permalink


Ultrasound investigations of intrinsic and extrinsic nonstationary field-driven processes in spin ice
Erfanifam, S.; Zherlitsyn, S.; Wosnitza, J.; Moessner, R.; Petrenko, O. A.; Balakrishnan, G.; Zvyagin, A. A.;
The elastic properties of spin-ice material Dy2Ti2O7 has been studied for different longitudinal and transverse acoustic-modes in a temperature range from 20 mK to 300 K and magnetic fields applied along various crystallographic directions. The sound velocity and the sound attenuation exhibit a number of anomalies versus magnetic field at temperatures below the ”freezing” temperature of approximately 500 mK. Most notable are peaks in the sound velocity, which exhibit two distinct regimes: an intrinsic (extrinsic) one in which the data collapse for different field-sweep rates when plotted as function of field strength (time). The intrinsic regime involves the release of Zeeman energy from spins, the extrinsic one, transfer of energy out of the sample. Additionally a sharp drop in the sound velocity can be seen at B = 1.25 T. This can indicate a 1st-order phase transition from the low-density to the high-density monopole state. We discuss our observations in context of the emergent quasiparticles which govern the low-temperature dynamics of the spin-ice.
  • Poster
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17009 - Permalink


High field magnetism and magnetoacoustics in UCu0.95Ge
Zvyagin, A. A.; Yasin, S.; Skourski, Y.; Andreev, A. V.; Zherlitsyn, S.; Wosnitza, J.;
Studies of magnetic and magneto-acoustic characteristics of the intermetallic compound UCu0.95Ge with antiferromagnetic ground state have been performed on single crystals in pulsed magnetic fields up to 64 T applied along the main axes. Along the a axis, a first-order phase transition has been observed at 61 T. For the field applied along the c axis, the first-order phase transition occurs at a much lower magnetic field (38 T). In both directions, the magnetization trends to saturate at 1.35 µB per formula unit. These field-induced transitions as well as the spontaneous transition at the magnetic ordering at TN = 48 K are accompanied by pronounced anomalies in the sound velocity and sound attenuation. The field-temperature phase diagrams are constructed for both directions of the magnetic field. The results of our theoretical analysis within the framework of the mean-field approximation qualitatively agree with the observed behavior of magnetic and magneto-acoustic characteristics of UCu0.95Ge.

Publ.-Id: 17008 - Permalink


Numerical modeling of bubble-driven liquid metal flows with external static magnetic field
Miao, X.; Lucas, D.; Ren, Z.; Eckert, S.; Gerbeth, G.;
Three-dimensional numerical simulations are presented considering the impact of a steady magnetic field on a bubble-driven liquid metal flow inside a cylinder. The injection of moderate gas flow rates through a single orifice at the bottom of the fluid vessel results in the formation of a bubble plume. The magnetic field is applied in either vertical or horizontal direction. The calculations were performed by means of the commercial software package CFX using the Euler-Euler multiphase model and the RANS-SST turbulence model. The non-isotropic nature of MHD turbulence was taken into account by specific modifications of the turbulence model. The numerical models are validated with recent experimental results (Zhang et al., 2007b). The comparison between the numerical simulations and the experimental findings shows a good agreement. The calculations are able to reproduce a striking feature of a horizontal magnetic field found in the range of moderate Hartmann numbers revealing that such a steady transverse magnetic field may destabilize the flow and cause distinct oscillations of the liquid velocity.
Keywords: Liquid metal, Bubble-driven flow, DC magnetic field, Multiphase model

Publ.-Id: 17007 - Permalink


An optimized protocol for the radiosynthesis of (–)-[F-18]flubatine permits its application as a new PET radioligand for neuroimaging of alpha4beta2-nAChRs
Fischer, S.; Hiller, A.; Hoepping, A.; Smits, R.; Funke, U.; Sabri, O.; Steinbach, J.; Brust, P.;
Objectives:
The alpha4beta2 subtype of nicotinic acetylcholine receptors (nAChRs) is involved in various neurodegenerative diseases. (–)-[F-18]flubatine is a new and promising PET tracer for neuroimaging of alpha4beta2-nAChRs and is currently investigated in a first study in humans. The original radiosynthesis of (–)-[F-18]flubatine was based on the bromo precursor and afforded the product in low yields (~2-3%). Here we present a new high yield radiosynthesis strategy based on an optimised leaving group/ protecting group assembly.

Methods:
A small library of precursors was synthesized containing –Cl, –NO2 and trimethylammonium (TMA) triflate and iodide as leaving groups and ethylcarbamate, Fmoc, Trityl, as well as Boc as protecting groups. [F-18]flubatine, was prepared via a two-step radiosynthesis. In the first step the nucleophilic radiofluorination was investigated. The radiolabelled product was then deprotected to yield the final radiotracer.

Results:
The best radiochemical results were obtained with a TMA iodide precursor containing a Bocprotecting group. Radiolabelling afforded the protected product in yields of 90±5%, with a RCY 70±5% (n=25) and a specific activity >350 GBq/Hmol. The complete deprotection of the Boc-PG succeeded with 1M HCl at 90°C within 5 min. TMA iodide precursors with other PGs led to lower labelling yields and several by-products after deprotection. Analytical and semipreparative HPLC separation protocols were developed using RP18-AQ phases and (–)-[F-18]flubatine was isolated in very high purity. The final product is stable in diluted HCl, NaOH and K2CO3 solutions as well as under physiological conditions.

Conclusions:
An optimized radiosynthesis of (–)-[F-18]flubatine was developed which will allow for an easy and automated radiotracer production applicable for human studies.

Research Support:
The project was supported by the German Federal Ministry of Education and Research (01EZ0820).
  • Lecture (Conference)
    SNM 2012 Annual Meeting, 09.-13.06.2012, Miami, Florida, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 53(2012)1, 130

Publ.-Id: 17006 - Permalink


THz-range free-electron laser ESR sprectroscopy: techniques and applications in high magnetic fields
Ozerov, M.;
  • Poster
    503. WE-Heraeus-Seminar on Free-Electron Lasers: from Fundamentals to Applications, 11.-13.04.2012, Bad Honnef, Deutschland

Publ.-Id: 17005 - Permalink


Wann ist denn das passiert? – Ko(s)mische Strahlung und einstürzende Berge
Merchel, S.;
eingeladener Vortrag ohne Abstract
Keywords: accelerator mass spectrometry, geomorphology
  • Lecture (others)
    TU Dresden, Ringvorlesung im Studium generale / öffentliche Vorträge, Sommersemester 2012, 19.04.2012, Dresden, Deutschland

Publ.-Id: 17004 - Permalink


Spatially-resolved analysis of natural minerals as carriers of high-tech metals and Rare Earth Elements: comparison of EPMA, PIXE and Sy-µXRF
Michalak, P. P.; Munnik, F.; Radtke, M.; Buzanich, G.; Reinholz, U.; Riesemeier, H.; Merchel, S.; Renno, A. D.;
The assessment of supply risk of high technology elements requires quality assurance of their natural carriers such as ores. One path to achieve this goal is through the use of reference materials (RMs). Providing reliable data on elemental concentrations at the µg/g level and on their spatial distribution is achieved by employing spatially-resolved micro-analytical methods.
In order to produce synthetic RMs with optimized chemical composition, three natural mineral analogues (sanidine, pyrite, columbite) have been tested for chemical homogeneity with three methods based on X-ray detection: EPMA (Electron Probe Micro Analyzer), Sy-µXRF (Synchrotron radiation-induced X-ray Fluorescence) and PIXE. EPMA analyses were carried out at the TU Bergakademie Freiberg using an accelerating voltage of 20 keV and a beam size of 2 µm. Sy-µXRF measurements were performed at the hard X-ray beamline “BAMline” at the synchrotron facility BESSY in Berlin. Samples were exposed in atmosphere to monochromatic X-rays of 20 keV focused with a compound refractive lens to 3x3 µm2 or 5x7.4 µm2. PIXE data were obtained using a 3 MeV proton beam of about 5x5 µm2 from a 3 MV tandem accelerator at the HZDR, Dresden.
Quantitative (EPMA, PIXE) and qualitative (Sy-µXRF) elemental distribution maps have been obtained for major, minor and trace elements for each scan. At least five trace elements were detected in each of the matrices, showing irregular distribution patterns. Compared to PIXE, Sy-µXRF spectra were characterized by lower peak to background ratios, thus, better detection limits could be achieved and more trace elements identified, such as Ge and Pb in sanidine, Mn and Ti in columbite, and Zn and Se in pyrite.
Compared to EPMA and PIXE, only Sy-µXRF seems to be thorough and robust enough for swift homogeneity testing for trace elements distribution in light, medium-heavy matrices, thus, proving to be an invaluable method in quality assurance of synthetic candidate RMs.
Keywords: ion beam analysis, reference materials, PIXE, XRF, synchrotron
  • Poster
    13th International Conference on Nuclear Microprobe Technology & Applications (ICNMTA), 22.-27.07.2012, Lisbon, Portugal

Publ.-Id: 17003 - Permalink


Switching voltages and back-hopping in magnetic tunnel junctions with different geometries
Bernert, K.; Sluka, V.; Fowley, C.; Fassbender, J.ORC; Deac, A. M.
A spin-polarized current flowing through a ferromagnet can exert a torque on the local magnetization [1,2]. This phenomenon is currently intensively investigated due to its potential application in magnetic random access memory (MRAM) or in telecommunication devices. Presently, the structure of choice for spin-torque devices includes a magnetic tunnel junction (MTJ) with an MgO barrier, due to their large magnetoresistance signals. However, a key step towards the practical implementation as MRAM elements is the reduction of the critical voltages, in order to keep the size of the selection transistor down and compete with existing technologies [3]. In addition, magnetic tunnel junctions also exhibit a somewhat obscure behaviour referred to as ‘back-hopping’, whereby reliable switching to the desired state is achieved for applied voltages of the order of the critical voltage, but a larger applied bias induces a telegraph-noise behaviour [4, 5]. Back-hopping is characteristic for MTJs, as it has not been observed in metallic multilayers, and poses concerns for designing industrially-competitive MRAM devices.

We evaluate the switching voltages and their temperature dependence by analytically and numerically solving the modified Landau-Lifshitz-Gilbert equation which includes both Slonczewski-like (in-plane) and field-like (out-of-plane) torque terms for different geometries. Its quadratic dependence on the applied voltage [6] translates into a more complex correlation between the critical bias and the external field, altering the shape of the phase diagram. It also explains back-hopping at a large bias for specific geometries, in agreement with experimental results.

References:
[1] J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996)
[2] L. Berger, Phys. Rev. B 54, 9359 (1996)
[3] Z. Diao et al., J. Phys. D: Cond. Mat. 19, 165209 (2007)
[4] J. Z. Sun, J. Appl. Phys. 105, 07D109 (2009)
[5] T. Min et al., J. Appl. Phys. 105, 07D126 (2009)
[6] C. Heiliger and M. Stiles, Phys. Rev. Lett. 100, 186805 (2008)
Keywords: spin-transfer torque, magnetic tunnel junction, magnetic random access memory
  • Invited lecture (Conferences)
    Third Nordic Workshop on Spintronics and Nanomagnetism (NordicSpin 2012), 22.-25.04.2012, Varberg, Sweden
  • Invited lecture (Conferences)
    Spin Caloritronics 4, 02.-06.06.2012, Sendai, Japan
  • Invited lecture (Conferences)
    Magnetism and Magnetic Nanomaterials, MMN’2012, 04.-06.09.2012, Bourmedes, Algeria

Publ.-Id: 17002 - Permalink


Injection and detection of spin in a semiconductor by tunneling via interface states
Jansen, R.; Deac, A. M.; Saito, H.; Yuasa, S.;
Injection and detection of spin accumulation in a semiconductor having localized states at the interface is evaluated. Spin transport from a ferromagnetic contact by sequential, two-step tunneling via interface states is treated not in itself, but in parallelwith direct tunneling. The spin accumulation dμch induced in the semiconductor channel is not suppressed, as previously argued, but genuinely enhanced by the additional spin current via interface states. Spin detection with a ferromagnetic contact yields a weighted average of dμch and the spin accumulation dμls in the localized states. In the regime where dμls/dμch is largest, the detected spin signal is insensitive to dμls and the ferromagnet probes the spin accumulation in the semiconductor channel.
Keywords: semiconductor, spin injection, spin detection, interface states

Publ.-Id: 17001 - Permalink


Probing Electron-Induced Bond Cleavage at the Single-Molecule Level Using DNA Origami Templates
Keller, A.; Bald, I.; Rotaru, A.; Cauët, E.; Gothelf, K. V.; Besenbacher, F.;
Low-energy electrons (LEEs) play an important role in nanolithography, atmospheric chemistry, and DNA radiation damage. Previously, the cleavage of specific chemical bonds triggered by LEEs has been demonstrated in a variety of small organic molecules such as halogenated benzenes and DNA nucleobases. Here we present a strategy that allows for the first time to visualize the electron-induced dissociation of single chemical bonds within complex, but well-defined self-assembled DNA nanostructures. We employ atomic force microscopy to image and quantify LEE-induced bond dissociations within specifically designed oligonucleotide targets that are attached to DNA origami templates. In this way, we use a highly selective approach to compare the efficiency of the electron-induced dissociation of a single disulfide bond with the more complex cleavage of the DNA backbone within a TT dinucleotide sequence. This novel technique enables the fast and parallel determination of DNA strand break yields with unprecedented control over the DNA’s primary and secondary structure. Thus the detailed investigation of DNA radiation damage in its most natural environment, e.g., DNA nucleosomes constituting the chromatin, now becomes feasible.
Keywords: DNA origami, Low-energy electrons, Atomic force microscopy, DNA radiation damage, ab initio calculations
  • ACS Nano 6(2012)5, 4392-4399
    DOI: 10.1021/nn3010747
  • Poster
    Electron Controlled Chemical Lithography 2012 Meeting, 18.-22.05.2012, Stykkishólmur, Iceland

Publ.-Id: 17000 - Permalink


Applocation of new closure models for bubble coalescence and breakup to steam-water vertical pipe flow
Liao, Y.; Lucas, D.; Krepper, E.;
The new closure models for bubble coalescence and breakup proposed in our previous work (Liao and Lucas, 2011) are tested in the case of condensing steam-water pipe flows. Steady-state CFD calculations are performed with the commercial CFD solver CFX12.1. The predicted evolution of cross-section averaged bubble size distribution and gas volume fraction along the pipe is compared with the measured one provided by the TOPFLOW facility (Lucas et al., 2010). It is shown that for cases with small initial bubble size and low gas volume fraction, bubble coalescence and breakup is nearly negligible and the change of bubble size is mainly due to condensation. Nevertheless, with the increase of initial bubble size or gas volume fraction bubble coalescence and breakup become important phenomena. The performance of the new closure models and the standard ones available in CFX is investigated for two examples of such a case. It is shown that both sets of the models give an overestimation of breakup rate, especially the standard ones. Furthermore, the results are found to be dependent sensitively on the inlet liquid temperatures, which might exceed the accuracy of the measurements. In addition, inter-phase heat transfer models have a significant impact on the results.
Keywords: condensation, steam-water, sub-cooling, coalescence and breakup, interphase heat transfer
  • Open Access LogoContribution to proceedings
    CFD4NRS-4 - The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology - OECD/NEA and IAEA Workshop, 10.-12.09.2012, Daejeon, Korea
    Proceedings of CFD4NRS - 4
  • Lecture (Conference)
    CFD4NRS-4 - The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology - OECD/NEA and IAEA Workshop, 10.-12.09.2012, Daejeon, Korea
  • Nuclear Engineering and Design 279(2014), 126-136
    DOI: 10.1016/j.nucengdes.2014.02.015

Publ.-Id: 16999 - Permalink


Electromagnetic dipole strength of 136Ba below the neutron separation energy
Massarczyk, R.; Schwengner, R.; Dönau, F.; Litvinova, E.; Rusev, G.; Beyer, R.; Hannaske, R.; Junghans, A. R.; Kempe, M.; Kelley, J. H.; Kögler, T.; Kosev, K.; Kwan, E.; Marta, M.; Matic, A.; Nair, C.; Raut, R.; Schilling, K. D.; Schramm, G.; Stach, D.; Tonchev, A. P.; Tornow, W.; Trompler, E.; Yakorev, D.; Wagner, A.;
The electromagnetic dipole strength of the nucleus 136Ba has been investigated at two facilities. At the bremsstrahlung facility at the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf, two measurements were performed with electron energies of 7.0 and 11.4 MeV. Photon scattering on the same nucleus has been investigated at the HI$gS facility of the Triangle Universities Nuclear Laboratory.
The GEANT4 code has been used to determine detector response and non-nuclear scattered events. Thus it is possible to account for the dipole strength in the quasi-continuum of unresolvable transitions. A statistical code was used to simulate inelastic transitions and to determine the branching ratios of transitions to the ground-state. The resulting photo-absorption cross section is compared to QRPA and RQTBA calculations.
Keywords: Photon scattering, nuclear spectroscopy, nuclear structure, gamma strength function

Publ.-Id: 16998 - Permalink


Superconducting Gallium implanted Germanium
Fiedler, J.; Heera, V.;
Superconductivity in doped semiconductors is of increasing interest in both, fundamental research and applied physics. We report on superconducting Ge layers fabricated by Ga ion implantation and subse-quent flash lamp annealing. A brief introduction to alternative preparation methods and the physics of superconducting semiconductors is given, too. The microstructure of and the electrical transport in the Ga doped Ge layers are investigated in detail. Finally, it is demonstrated that increasing the Ga concentration and the thermal budget of annealing leads to Ga segregation. In this case superconducting properties similar to that of amorphous Ga films are obtained.
Keywords: carrier density; clusters; cover layer; diffusion; dopant; flash lamp annealing; gallium; germanium; Hall; implantation; metal-insulator-transition; nanocrystalline; oxygen; rapid thermal annealing; resistance; sem-iconductor; superconducting; surface
  • Book chapter
    Heidemarie Schmidt, Wolfgang Skorupa: Subsecond Annealing of Advanced Materials: Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Springer Series in Materials Science), Switzerland: Springer, 2014, 978-3-319-03130-9, 57-78
    DOI: 10.1007/978-3-319-03131-6_4

Publ.-Id: 16997 - Permalink


Ridge waveguide lasers in Nd:GGG crystals produced by swift carbon ion irradiation and femtosecond laser ablation
Jia, Y.; Dong, N.; Chen, F.; de Aldana, J. R. V.; Akhmadaliev, S.; Zhou, S.;
We report on the fabrication of ridge waveguide in Nd:GGG crystal by using swift C5+ ion irradiation and femtosecond laser ablation. At room temperature continuous wave laser oscillation at wavelength of ~1063 nm has been realized through the optical pump at 808 nm with a slope efficiency of 41.8% and the pump threshold is 71.6 mW.
Keywords: Integrated optics devices, Laser materials processing, Waveguides

Publ.-Id: 16996 - Permalink


AMS within Eurogenesis: Nanodiamonds and SN-signatures
Wallner, A.; Feige, J.; Fifield, K.; Korschinek, G.; Melber, K.; Merchel, S.; Ott, U.; Paul, M.; Rugel, G.; Steier, P.; Tims, S.; Vockenhuber, C.;
CoDustMas is a Collaborative Research Project (CRP) of Eurogenesis, one of the EUROCORES programmes of the European Science Foundation. This international network aims at understanding the crucial role that supernovae (SNe) play in the formation of cosmic dust. Specifically, this CRP will study the synthesis of dust grains in core-collapse supernovae; isotopic signatures in dust grains; and mixing, evolution and transport of dust in supernova remnants.
Applying accelerator mass spectrometry (AMS) two aspects are tackled. First, the measurement of trace element isotope ratios in presolar nanodiamonds isolated from primitive meteorites, e.g. the ratios of Pt isotopes to extract r-process nucleosynthesis signatures. Recent results demonstrate the applicability of AMS for determining stable Pt isotope signatures in diamonds extracted from Allende. These AMS data may indicate a small 198Pt anomaly; its significance and new approaches will be discussed.
The second aspect relates to the search for live SN-produced radionuclides in terrestrial deep-sea archives. In particular, the focus is on isotopes with half-lives of the order of million years. We continue this search by investigating, with high time resolution, two deep-sea sediment cores from the Indian Ocean for a possible signal of the SN-candidates 26Al, 53Mn, 60Fe, and potentially 244Pu.
Keywords: accelerator mass sepctrometry, AMS, Pt, supernova, radionuclide
  • Lecture (Conference)
    XII International Symposium on Nuclei in the Cosmos, 05.-10.08.2012, Cairns, Australia

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Publ.-Id: 16995 - Permalink


Dipole Strength in 86Kr up to Neutron Separation
Massarczyk, R.; Schwengner, R.; Junghans, A. R.; Wagner, A.;
For the rst time a high-pressure gas target has been investigated at the bremsstrahlung facility at the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf. The experiment was carried out at electron beam energies of 7 and 12MeV in order to study dipole excitations up to an energy region up to the neutron separation. The talk will present data analysis and simulations methods of the experiments in Rossendorf. GEANT4 simulations were performed to subtract the atomic background from the measured spectrum and deduce the intensity of the resonantly scattered gamma-rays. Also the response functions for the high-purity germanium detectors were simulated by GEANT4, which allows us to deduce the intensity of unresolvable peaks due to decreasing level-spacing. Considering also the transitions from states in the quasicontinuum, simulations of gamma-ray cascades were carried out with a new code to estimate branching ratios. As a result the photoabsorption cross section obtained from transitions to the ground state is calculated. The data will be presented in the context of further photon-scattering experiments performed in Rossendorf on the stable isotopes at the closed neutron shell N = 50.
Keywords: Photon scattering, nuclear spectroscopy, nuclear structure, gamma strength function
  • Lecture (Conference)
    3rd Workshop on Level Density and Gamma Strength, 23.-27.05.2011, Oslo, Norway

Publ.-Id: 16994 - Permalink


Cross-Section Measurements of the 86Kr(gamma,n) Reaction to Probe the s-Process Branching at 85Kr
Raut, R.; Banu, A.; Iliadis, C.; Kelley, J. H.; Rusev, G.; Schwengner, R.; Tonchev, A. P.; Tornow, W.;
For the first time, cross-section measurements were carried out for the 86 Kr(gamma,n) reaction in order to probe the s-process branching point nucleus 85Kr. The branching point nuclei in the s-process path are of importance in testing and constraining the nucleosynthesis models. Cross-section measurement for the photoneutron reaction on the neighbouring stable isotope is carried out to deduce the aforesaid neutron capture cross-section, as has been adopted in the present case of 85Kr branching point. The cross-section results from the 86 Kr(gamma,n) reaction were compared with the statistical model calculations using TALYS code.
Keywords: Monoenergetic gamma rays, photodisintegration, neutron detection, cross section, s-process, waiting point, statistical models.

Publ.-Id: 16991 - Permalink


Study of hadron properties in cold nuclear matter with HADES
Tlusty, P.; Agakishiev, G.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Cabanelas, P.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Huck, P.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Krása, A.; Krizek, F.; Kuc, H.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.;
Results of a study of dielectron and pion production in p + Nb collisions at incident proton beam energy 3.5 GeV are presented. The data are taken by the High Acceptance Di-Electron Spectrometer (HADES) at GSI Darmstadt.
The dielectron invariant mass distributions are compared to data from elementary p+p reactions at the same beam energy. At this energy above the light vector meson production threshold, the omega peak is clearly identified. The collected statistics and high acceptance for pair momenta within the interval 50-2000 MeV/c allow for a study of momentum dependence of the omega yield and spectral shape. The strongest medium modification in the line shape is expected for low momenta mesons decaying inside the nuclear matter. Comparing the measured p+Nb data with the p+p reference experiment results, the signifficant change in yield of low momenta dielectron pairs in the vector meson mass region is observed.
Data on charged pi meson emission, which are related to neutral pions representing a dominant contribution to the dielectron yield, are shown as well. They contribute to the results from systematic studies of the pion production in the proton-nucleus collisions, which point to a transition of the pion source from simple NN collisions to emission of thermalized pions from a fireball, when increasing the atomic number of the target nucleus. The data also serve as a reliable tool for normalization of the dielectron data.
  • Open Access LogoProceedings of Science (2012), Pos(Bormio2012)019

Publ.-Id: 16990 - Permalink


Detection of Laser-accelerated ions at the DRACO laser
Kraft, S.;
In the last years, the detection schemes for laser-accelerated ion beams had to be developed much further. In the beginning, experiments where mainly performed on laser facilities with a few shots a day and online diagnostics such as film stacks where sufficient in order to characterize the ion beam. Nowadays many experiments are carried out at high power lasers with repetition rates on the order of 10 Hz and thus the need of on line detectors has grown significantly.
In this talk, the ion accelerator at the 100 TW laser DRACO in Dresden are described. Already implemented detectors such as MCPs and scintillators as well as desirable devices for future measurements are described.
  • Invited lecture (Conferences)
    Industry meets Academia: Beam Monitoring Instrumentation and Quality Assurance, 10.-11.11.2011, Darmstadt, Deutschland

Publ.-Id: 16989 - Permalink


20 kW Upgrade of the ELBE 1.3 GHz CW RF-System with BRUKER 10kW Solid State Amplifiers
Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.;
Summary:
With the expansion of the radiation source ELBE, a centre for high power radiation sources is being built between 2009 and 2014 at the Helmholtz Zentrum Dresden Rossendorf. One part of this program is to increase the beam current of the ELBE LINAC. In January 2012 each of the 10kW CW klystrons used to operate the superconducting cavities of ELBE since 2001 had been replaced by a pair of 10kW solid state amplifiers.The talk gives an overview on the new RF-system of ELBE and its performance.
Keywords: Superconducting LINAC, 1.3GHz RF-System, Solid State RF-Power Amplifiers, 10kW RF Power, 10 kW RF SSPA, Turnkey SSPA, ELBE-RF System, ELBE-UPGRADE, HSQ
  • Lecture (others)
    Eingeladener Vortrag KEK Tsukuba/Japan, 17.04.2012, KEK, Tsukuba, Japan

Publ.-Id: 16988 - Permalink


Present and future laser driven proton therapy program in Dresden
Kraft, S.;
  • Lecture (Conference)
    Coulomb ’11: Optical Acceleration of Ions and Perspective for Biomedicine, 04.-05.11.2011, Bologna, Italien

Publ.-Id: 16987 - Permalink


Nanocavity formation and hardness increase by dual ion beam irradiation of oxide dispersion strengthened FeCrAl alloy
Kögler, R.; Anwand, W.; Richter, A.; Butterling, M.; Ou, X.; Wagner, A.; Chen, C.-L.;
Open volume defects generated by ion implantation into oxide dispersion strengthened (ODS) alloy and the related hardness were investigated by positron annihilation spectroscopy and nanoindentation measurements, respectively. Synchronized dual beam implantation of Fe and He ions was performed at room temperature and at moderately enhanced temperature of 300°C. For room temperature implantation a significant hardness increase after irradiation is observed which is more distinctive in heat treated than in as-received ODS alloy. There is also a difference between the simultaneous and sequential implantation mode as the hardening effect for the simultaneously implanted ODS alloy is stronger than for sequential implantation.
The comparison of hardness profiles and of the corresponding open volume profiles shows a qualitative agreement between the open volume defects generated on the nanoscopic scale and the macroscopic hardness characteristics.
Open volume defects are drastically reduced for performing the simultaneous dual beam irradiation at 300°C which is a more realistic temperature under application aspects. Few remaining defects are clusters of 3-4 vacancies in connection with Y oxide nanoparticles. These defects completely disappear in a shallow layer at the surface. The results are in agreement with hardness measurements showing little hardness increase after irradiation at 300°C.
Suitable characteristics of ODS alloy for nuclear applications and the close correlation between He-related open volume defects and the hardness characteristics are verified.
Keywords: Radiation hardness, ion implantation, ODS alloy, positron annihilation spectrometry, nanointendation

Publ.-Id: 16986 - Permalink


Ansätze zur Bestimmung heterogener Diffusionsparameter auf Bohrkernskala mit Hilfe von Na-22-PET-Diffusionsmessungen und Modellsimulationen
Kulenkampff, J.; Schikora, J.; Zakhnini, A.; Gründig, M.; Lippmann-Pipke, J.;
  • Lecture (others)
    2. Actinidenverbundtreffen "Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen", 03.-04.04.2012, Köln, Deutschland

Publ.-Id: 16985 - Permalink


Für den Laboreinsatz optimierte Kalibrationsmethode für pH-Elektroden bei hohen Ionenstärken
Fritsch, K.;
Eine vereinfachte Auswertemethode für die Elektrodenkalibration bei hohen Ionenstärken unter Beachtung der Kw-Korrektur wird vorgestellt.
Keywords: pH measurements, electrode calibration, high ionic strength
  • Lecture (others)
    2. Workshop des Verbundprojekts „Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen“, 04.04.12, Köln, Deutschland

Publ.-Id: 16984 - Permalink


Monte Carlo simulations of GeoPET experiments: 3D images of tracer distributions (18F, 124I and 58Co) in Opalinus Clay, anhydrite and quartz
Zakhnini, A.; Kulenkampff, J.; Sauerzapf, S.; Pietrzyk, U.; Lippmann-Pipke, J.;
Understanding conservative flow and reactive tracer transport processes in soils and rock formations requires quantitative visualization methods in 3D+t. After a decade of research and development we established the GeoPET as a non-destructive method with unrivalled sensitivity and selectivity, without physical and chemical impact, and with due spatial and temporal resolution by applying Positron Emission Tomography (PET), a nuclear medicine imaging method, to dense rock material. Requirements for reaching the physical limit of image resolution of nearly 1 mm are a high-resolution PET- camera, like our ClearPET scanner (Raytest), and appropriate correction methods for scatter and attenuation of 511 keV - photons in the dense geological material, which are by far more significant than in human and small animal body tissue (water).
Here we present data from Monte Carlo simulations, considering all involved nuclear physical processes of the measurement with the ClearPET-system, that allows us to quantify the sensitivity of the method and the scatter fractions in geological media as function of material (quartz, Opalinus clay and anhydrite compared to water), PET isotope (18F, 58Co and 124I), and system parameters. Comparison of simulated data with measured images indicates the limits of the method and provides procedures for image quality improvement, including a scatter correction method by subtracting projections of simulated scattered coincidences from experimental data sets prior to image reconstruction with an iterative reconstruction process.
Keywords: Monte Carlo Simulation, PET, radiotracer, radiation, process monitoring

Publ.-Id: 16983 - Permalink


Magnetic Frustration in a Quantum Spin Chain: The Case of Linarite PbCuSO4(OH)2
Willenberg, B.; Schäpers, M.; Rule, K. C.; Süllow, S.; Reehuis, M.; Ryll, H.; Klemke, B.; Kiefer, K.; Schottenhamel, W.; Büchner, B.; Ouladdiaf, B.; Uhlarz, M.; Beyer, R.; Wosnitza, J.; Wolter, A. U. B.;
We present a combined neutron diffraction and bulk thermodynamic study of the natural mineral linarite PbCuSO4(OH)2, this way establishing the nature of the ground-state magnetic order. An incommensurate magnetic ordering with a propagation vector k = (0, 0.186, 1/2) was found below TN = 2.8 K in a zero magnetic field. The analysis of the neutron diffraction data yields an elliptical helical structure, where one component (0.638 µB) is in the monoclinic ac plane forming an angle with the a axis of 27(2)°, while the other component (0.833 µB) points along the b axis. From a detailed thermodynamic study of bulk linarite in magnetic fields up to 12 T, applied along the chain direction, a very rich magnetic phase diagram is established, with multiple field-induced phases, and possibly short-range-order effects occurring in high fields. Our data establish linarite as a model compound of the frustrated one-dimensional spin chain, with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions. Long-range magnetic order is brought about by interchain coupling 1 order of magnitude smaller than the intrachain coupling.

Publ.-Id: 16981 - Permalink


Vorstellung und Bewertung des Beitrags zur Erreichung des Meilensteins im Projekt Nanopharm
Vogel, M.;
Vorstellung der wissenschaftlichen Arbeiten und erzielten Ergebnisse im Projekt NanoPharm - Teilprojekt: Herstellung und Charakterisierung von photokatalytischen S-Layer Nanokompositen, welche zur Erreichung des Meilensteins beitragen.
  • Lecture (others)
    Meilenstein-Treffen zum Projekt Nanopharm, 19.04.2012, Köthen, Deutschland

Publ.-Id: 16979 - Permalink


Untersuchung der 40Ca(alpha,gamma)44Ti-Reaktion bei E_alpha ~ 3.5 MeV
Schmidt, K.; Akhmadaliev, C.; Anders, M.; Bemmerer, D.; Boretzky, K.; Caciolli, A.; Dietz, M.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Hannaske, R.; Junghans, A.; Marta, M.; Menzel, M.-L.; Schwengner, R.; Szücs, T.; Wagner, A.; Yakorev, D.; Zuber, K.;
Das radioaktive Nuklid Titan-44 wird Modellrechnungen zufolge in Kernkollaps-Supernovae erzeugt. Die Gammastrahlung aus seinem Zerfall kann als Werkzeug zum Test von Supernova-Modellen genutzt werden, weil sie zumindest für einen Supernova-Überrest durch satellitengestützte Gamma-Teleskope nachweisbar ist. Zur Interpretation dieser Messungen ist eine genaue Kenntnis der Kernreaktionsraten für die Erzeugung und Zerstörung von Titan-44 erforderlich. Die 40Ca(alpha,gamma)44Ti-Reaktion dominiert die Erzeugung von Titan-44. Ihre Rate wird je nach Temperatur von mehreren Resonanzen dominiert. Die Stärken der Resonanzen bei 3.5 - 3.7 MeV alpha-Energie werden am Dresdner 3MV Tandetron sowohl mittels in-beam Gamma-Spektrometrie als auch durch eine Aktivierungsmessung im Felsenkeller-Niederniveaumesslabor bestimmt. Gefördert von der EU (FP7-SPIRIT 227012) und der DFG (BE 4100/2-1).
Keywords: Titan-44, 44Ti, 40Ca(alpha,gamma)44Ti, 40Ca(a,g)44Ti, Kernkollaps-Supernovae, Supernova, Kernreaktionsraten, Resonanzstärken, Gamma-Spektrometrie, Felsenkeller-Niederniveaumesslabor
  • Lecture (Conference)
    DPG Frühjahrstagung 2012, 19.-23.03.2012, Mainz, Deutschland

Publ.-Id: 16978 - Permalink


Towards a study of the 22Ne(p,g)23Na reaction at LUNA
Menzel, M.-L.; Bemmerer, D.;
The 22Ne(p,g)23Na reaction takes part in the so called neon-sodium-cycle of hydrogen burning. This cycle is important at higher temperature than those experienced in the sun and plays a role in explosive hydrogen burning in an astrophysical nova. In addition, this reaction possibly depletes the supply of 22Ne in the accreting white dwarf preceeding a supernova of type Ia. The rate of this reaction depends on the strengths of several resonances in the energy range of the LUNA 0.4 MV accelerator which have never been observed in direct experiments. A related study is under preparation at LUNA. The poster will show the experimental set-up and planned measurement strategy.
Keywords: 22 Neon, 23 Natrium, LUNA
  • Poster
    Heraeus-Seminar on Astrophysics with modern small-scale accelerators, 06.-10.02.2012, Bad Honnef, Deutschland
  • Lecture (Conference)
    Heraeus-Seminar on Astrophysics with modern small-scale accelerators, 06.-10.02.2012, Bad Honnef, Deutschland

Publ.-Id: 16977 - Permalink


Late Pleistocene glaciation in the Gissar Range, Tajikistan, based on 10Be surface exposure dating
Zech, R.; Röhringer, I.; Sosin, P.; Kabgov, H.; Akhmadaliev, S.; Merchel, S.; Zech, W.;
Mountain glaciers are sensitive indicators for climate change, mainly summer temperature and precipitation. Glacial chronologies from Central Asia have therefore been suggested to provide valuable information about past changes in temperature, as well as precipitation and related changes in atmospheric circulation. However, available age control is still sparse. Here we present a glacial chronology for the Gissar Range, Tajikistan, based on thirteen 10Be surface exposure ages. Prominent moraine lobes document glacial advances in phase with the global last glacial maximum (LGM) during marine isotope stage (MIS) 2. Rapid and significant deglaciation occurred already at ~20 ka as inferred from recessional stages. An older and slightly more extensive glaciation could be dated to MIS 4, whereas the timing of the most extensive glaciation remains speculative. In contrast to the glacial chronologies from the nearby, more arid Pamir and Tien Shan, where MIS 3 and MIS 5 moraines likely document past periods with increased precipitation, glaciers in the more humid Gissar Range predominantly recorded past changes in temperature and summer insolation.
Keywords: cosmogenic nuclides; Quaternary; paleoclimate; Central Asia; accelerator mass spectrometry

Publ.-Id: 16976 - Permalink


Electronic andmagneticstudiesof k-(BEDT-TTF)2Hg(SCN)2Cl
Yasin, S.; Rose, E.; Drichko, N.; Dressel, M.; Schlueter, J. A.; Zhilyaeva, E. I.; Torunova, S.; Lyubovskaya, R. N.;
DC resistivity and electron spin resonance (ESR) measurements have been performed on the two-dimensionalorganicconductor k-(BEDT-TTF)2Hg(SCN)2Cl. Due to electronic correlations, the compound undergoes a transition from a metallic to an insulating state at TMI= 34 K.The ESR parameters exhibit a drastic change below Tafm=27K that evidences a magnetic phase transition. Int his low-temperature state, we observe the characteristics of antiferromagnetic resonances in the angular dependence of the g-value.

Publ.-Id: 16975 - Permalink


In-plane interdot carrier transfer in InAs/GaAs quantum dots
Bhattacharyya, J.; Zybell, S.; Winnerl, S.; Helm, M.; Hopkinson, M.; Wilson, L. R.; Schneider, H.;
Using time resolved photoluminescence (PL) quenching measurements, we investigated inplane carrier transfer in InAs/GaAs self-assembled quantum dots (QDs). THz pulses from a free-electron laser tuned to the intersublevel transition energy were used to excite carriers to higher levels causing quenching in the PL. These carriers could either fall back to the lower energy states and recombine or get transferred to adjacent QDs. The relaxation of the carriers was directly reflected in the recovery of the PL signal. Comparing measurements from two samples, we found that the redistribution of carriers into the neighbouring QDs is the dominant mechanism of carrier relaxation. The data were fitted using a rate equation model to estimate the PL recovery time which we attribute to the interdot carrier transfer time.
Keywords: Quantum dots, Photoluminescence, Free electron laser

Publ.-Id: 16974 - Permalink


On the safety evaluation methodology applied in Germany after the Fukushima event
Merk, B.; Kliem, S.;
The presentation gives an overview on the safety evaluation methodology applied in Germany after the Fukushima event. The general idea of the used evaluation methodology is described. The different evaluation topics based on natural and civilization caused threats will be discussed. Additionally, the new postulated incidents for the safety evaluation are presented. Conclusions are drawn on the applicability of the methodology, originally derived for light water reactors, to fast reactors.
Keywords: Reactor Safety, Fukushima
  • Open Access LogoContribution to proceedings
    Technical Meeting on Impact of the Fukushima Event on Current and Future Fast Reactor (FR) Designs, 19.-23.03.2012, Dresden, Deutschland: Reproduced by the IAEA
  • Lecture (Conference)
    Technical Meeting on Impact of the Fukushima Event on Current and Future Fast Reactor (FR) Designs, 19.-23.03.2012, Dresden, Deutschland

Publ.-Id: 16973 - Permalink


Subcriticality determination in accelerator driven systems (ADS)
Merk, B.;
Different current and planned experiments (MUSE, YALINA, Guinevere) are designed to study the zero power neutron physical behavior of accelerator driven systems (ADS). The detailed analysis of the kinetic space-time behavior of the neutron flux is important for the evaluation of these ADS experiments. Current analysis for all these experiments is based on the standard methods - Sjöstrand method and Slope method – both based on the point kinetics equations. The point kinetics equations are developed from different approximations to the transport equation. Nevertheless, all these partial differential equations of the transport equation are solved by the separation of space and time to derive the point kinetics equations. The separation of space and time does not provide useful results for cases with strongly space-time dependent external source like it appears during the shutdown of the external neutron source. In recent years, two big projects have been launched to solve the problem of sub-criticality determination in ADS experiments and for the future during ADS operation. In the 6th European Framework program in the integrated project EUROTRANS, the domain 2, ECATS has been dedicated to ADS experiments and the analysis methods for the experiments. In the same time frame, the IAEA has launched the coordinated research project: ”Analytical and Experimental Benchmark Analyses of Accelerator Driven Systems (ADS)”. Different correction methods based on Monte Carlo Results for the YALINA-Booster system have been derived for the Sjöstrand method as well as for the Slope method in EUROTRANS/ ECATS. Good results have been achieved with this correction method for the analysis of the detectors in the thermal zone. Nevertheless, there is still a problem existing in the fast zone which is the really important zone, since the follow up experiment GUINEVERE and the foreseen facility MHYRRA will be a pure fast system. The results for the analysis of the fast zone of YALINA-Booser are still not convincing, even with the use of correction factors. Good results, but once more only for the thermal and the reflector positions, have been shown in the IAEA CRP by the US American group, especially. These results rely on the use of correction factors form deterministic calculations. The conclusion of the IAEA meeting suggests for further activities, maybe a further CRP among others, the following two topics: “Online Reactivity Monitoring and Control of Sub-critical System”; and “Determination of Sub-criticality Level and Uncertainties Analyses”.
Keywords: ADS, Subcriticality determinaiton, EUROTRANS, YALINA
  • Open Access LogoContribution to proceedings
    Technical Meeting to Identify innovative fast neutron systems development gaps, 29.02.-02.03.2012, Wien, Österreich: Reproduced by the IAEA
  • Lecture (Conference)
    Technical Meeting to Identify innovative fast neutron systems development gaps, 29.02.-02.03.2012, Wien, Österreich

Publ.-Id: 16972 - Permalink


Core/system modeling and simulation: state-of-the-art, R&D needs and new ideas
Merk, B.;
Especially in Europe, the status of the core and system simulation is an essential point for the licensing of future nuclear reactor plants. In the light water reactor (LWR) technology, the development of modern coupled thermal hydraulics/neutronics simulation tools has undergone a rapid development in the late 90ies and during the first years of the new century. The simulation standard in LWR is described with a detailed view into the available codes and methods including the calculation chain for the coupled thermal hydraulics/neutronics steady state core analysis. Further on, the simulation capabilities for the load following and for the transient analysis in LWR cores are discussed. The overview will be closed with a description of the coupled simulations for the core integrated into the whole reactor system using the core simulators together with the system simulation codes for the description of transients which are induced or influenced by the primary or even the secondary system.
The current capabilities for the simulation of the core and system behavior of fast reactors in steady state as well as during transients are discussed in comparison with the described state-of-the-art in LWR to demonstrate the currently available possibilities and to define the development demand.
Advantage in the development of simulation codes for fast reactors can be taken from the state-of-the-art available in LWR technology. Conclusions are drawn about the required extensions needed to make the LWR code systems usable for fast reactor simulation. Two code systems under development and validation are presented to give an insight into the newest advances in the topic. The major point in the future for these works is the validation of the extended codes. For his topic, an outlook is given to the IAEA CRP on the EBR-II benchmark proposed by the Argonne National Lab., which is a good opportunity for the code validation.
Keywords: DYN3D, Fast Reactor, Simulation
  • Open Access LogoContribution to proceedings
    Technical Meeting to Identify innovative fast neutron systems development gaps, 29.02.-02.03.2012, Wien, Österreich: Reproduced by the IAEA
  • Lecture (Conference)
    Technical Meeting to Identify innovative fast neutron systems development gaps, 29.02.-02.03.2012, Wien, Österreich

Publ.-Id: 16971 - Permalink


Direct measurement of the d(alpha,gamma)6Li cross-section at astrophysical energies
Anders, M.; The LUNA collaboration;
Standard Big Bang nucleosynthesis predicts a very low abundance of the minor lithium isotope 6Li, which is instead believed to be produced by cosmic rays over time. However, recently 6Li has been detected in very old metal-poor stars, leading to the question whether its Big Bang production might be stronger than believed. The key reaction for 6Li production in the Big Bang is d(alpha,gamma)6Li. Using the deep underground LUNA 400 kV accelerator at the Gran Sasso Laboratory in Italy, a direct measurement of the cross section is underway. The contribution will report on this experiment, collected data, methods to analyze them, and preliminary results.
Keywords: Big Bang, nucleosynthesis, LUNA, Gran Sasso, underground
  • Lecture (Conference)
    496. WE-Heraeus-Seminar "Astrophysics with modern small-scale accelerators", 06.-10.02.2012, Bad Honnef, Deutschland

Publ.-Id: 16970 - Permalink


Initial tests of Silicon Photomultipliers for NeuLAND
Reinhardt, T.; Wagner, A.; Bemmerer, D.;
Initial tests of KETEK 3*3mm^2 SiPM's are presented, for the readout of BC408 scintillator material.
Keywords: Photosensors SiPM neutron detectors FAIR nuclear astrophysics photon readout photomultiplier tube geiger mode photodiode avalanche photodiode
  • Lecture (Conference)
    NUPNET NEDENSAA (NEutron DEtector developments for Nuclear Structure, Astrophysics and Applications) kick-off meeting, 15.-17.02.2012, Madrid, Spanien

Publ.-Id: 16969 - Permalink


Presentation of NEDENSAA working package 4: Photosensors
Bemmerer, D.;
The plans for working package 4 (photosensors) within the NUPNET NEDENSAA project are reviewed, with a focus on planned efforts at TU Dresden, Uppsala, and INFN.
Keywords: Photosensors SiPM neutron detectors FAIR nuclear astrophysics photon readout photomultiplier tube geiger mode photodiode avalanche photodiode
  • Invited lecture (Conferences)
    NUPNET NEDENSAA (NEutron DEtector developments for Nuclear Structure, Astrophysics and Applications) kick-off meeting, 15.-17.02.2012, Madrid, Spanien

Publ.-Id: 16968 - Permalink


NeuLAND time of flight detector for 0.2-1.0 GeV neutrons
Bemmerer, D.;
The goals and design of the future NeuLAND detector at FAIR are presented.
Keywords: NeuLAND time of flight neutron detector FAIR nuclear astrophysics r-process radioactive ion beam
  • Invited lecture (Conferences)
    NUPNET NEDENSAA (NEutron DEtector developments for Nuclear Structure, Astrophysics and Applications) kick-off meeting, 15.-17.02.2012, Madrid, Spanien

Publ.-Id: 16967 - Permalink


Study of the 2H(alpha,gamma)6Li nuclear reaction producing 6Li in standard big bang nucleosynthesis
Bemmerer, D.; Gustavino, C.; Anders, M.;
The 2H(alpha,gamma)6Li reaction dominates the production of lithium-6 in standard big bang nucleosynthesis. Due to its exceedingly low cross section, this reaction has never been studied experimentally at the relevant energies, and consequently the adopted reaction rate depends on uncertain extrapolations. A direct study of the 2H(alpha,gamma)6Li cross section is currently underway at the LUNA 400 kV accelerator, located deep underground in the Gran Sasso laboratory, Italy. The expected data lie directly at big-bang energies. It is hoped that they help constrain non-standard lithium-6 production scenarios, by putting the standard Big Bang production on a solid experimental footing.
Keywords: LUNA underground nuclear astrophysics, Felsenkeller, Big Bang nucleosynthesis, hydrogen burning, nucleosynthesis
  • Poster
    Lithium in the Cosmos, 27.-29.02.2012, Paris, Frankreich
  • Open Access LogoMemorie della Societa Astronomica Italiana 22(2012)Suppl., 181

Publ.-Id: 16966 - Permalink


Experimental study of the 2H(α,γ)6Li reaction and other recent progress at LUNA
Bemmerer, D.;
In addition to the well-known 7Li problem of Big Bang nucleosynthesis, observations of 6Li in very metal poor stars hint at a possible Big Bang Li problem. Network calculations show that the 2H(𝛼,𝛾)6Li reaction dominates 6Li production in the Big Bang, but there are no direct experimental data on this reaction at relevant energies. An experiment on this reaction is underway at the 400kV underground accelerator LUNA in Gran Sasso/Italy, and preliminary data will be shown. In addition, recent LUNA work on the 15 N(p,𝛾)16O, 17O(p,𝛾)18 F, and 25Mg(p,𝛾)26Al reactions and a planned 22Ne(p,𝛾)23Na study will be briefly discussed, and an outlook will be given.
Keywords: LUNA underground nuclear astrophysics, Felsenkeller, Big Bang nucleosynthesis, hydrogen burning, nucleosynthesis
  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 19.-23.03.2012, Mainz, Deutschland

Publ.-Id: 16965 - Permalink


The Dresden Felsenkeller: A shallow underground option for accelerator-based nuclear astrophysics
Bemmerer, D.;
The status and perspectives for a possible accelerator in the shallow underground facility Felsenkeller in Dresden is reviewed.
Keywords: Underground laboratory, small accelerator, LUNA, Felsenkeller, astrophysics, nucleosynthesis, solar abundance problem, big bang nucleosynthesis
  • Invited lecture (Conferences)
    Workshop on Nuclear Astrophysics at the Canfranc Underground Laboratory, 22.-23.03.2012, Canfranc, Spanien

Publ.-Id: 16964 - Permalink


Underground laboratories
Bemmerer, D.;
The status and future of underground laboratories for nuclear astrophysics are reviewed
Keywords: Underground laboratory, small accelerator, LUNA, Felsenkeller, astrophysics, nucleosynthesis, solar abundance problem, big bang nucleosynthesis
  • Invited lecture (Conferences)
    496. Wilhelm und Else Heraeus - Seminar „Astrophysics with modern small-scale accelerators“, 06.-10.02.2012, Bad Honnef, Deutschland

Publ.-Id: 16963 - Permalink


Insider 5 / 2012
Weigl, A.;
Mitarbeiterzeitung des HZDR
Keywords: HZDR in-house paper
  • Communication & Media Relations
    Mitarbeiterzeitung 05.04.2012
    12 Seiten

Publ.-Id: 16962 - Permalink


Hexanuclear actinide(IV) carboxylates formed by competition between ligation and hydrolysis
Hennig, C.; Takao, S.; Takao, K.; Weiss, S.; Kraus, W.; Emmerling, F.; Meyer, M.; Scheinost, A. C.;
Tetravalent actinides show a strong tendency toward hydrolysis already at low pH. Below the onset of hydrolysis they commonly form monomeric complexes with carboxylate ligands. As the pH reaches the hydrolysis limit, olation and oxolation occur as competing reactions. We observed under these circumstances the formation of several well-defined hexanuclear carboxylate complexes. Recent thermodynamic studies suffer from the lack of structural information on such solution species. EXAFS spectroscopy is well suited to gain this information and has been applied to study U(IV), Th(IV), Np(IV) and Pu(IV) carboxylates and amino-carboxylates in aqueous solution and solid state. A comparison with the corresponding single crystal data supports the structure analysis of the solution species. We found that the carboxylic group acts as terminating ligand and stabilizes nanosized hexanuclear clusters in solution as well as in solid state. It is important to note that this reaction prevents the formation of hydrolysis products as well as the formation of An(IV) hydrous oxide colloids.
Keywords: EXAFS, tetravalent actinides, carboxylate, aminocarboxylate
  • Lecture (Conference)
    15th International Conference on X-ray Absorption Fine Structure (XAFS15), 22.-28.7.2012, Beijing, China

Publ.-Id: 16961 - Permalink


Investigation of the dynamics of magnetic Vortices in trilayer systems
Banholzer, A.; Wintz, S.; Bunce, C.; Strahe, T.; Körner, M.; Erbe, A.; Puzic, A.; Raabe, J.; Quitmann, C.; Lenz, K.; Fassbender, J.ORC
Magnetic Vortices are of great interest for storage media for quite a while. Different control methods are used to manipulate them. We now use scanning transmission x-ray microscopy (STXM) to image the magnetic configurations within the different layer of a trilayer system of Cobalt/Copper/Permalloy. The dominant coupling mechanisms here are the magneto-dipolar interaction and interlayer exchange coupling. The corresponding behaviors of the magnetization configurations in a static magnetic field, as well as in an oscillating magnetic field, are investigated. The emerging movement of the core can be tuned with the amplitude and frequency of the field. The interactions of the two cores and their individually resonance frequencies are studied. This implies the corresponding resistance changes within different configurations at different magnetic fields and currents as well as the shifting of the core.
Keywords: vortex, trilayer, STXM
  • Poster
    DPG-Frühjahrstagung, 27.03.2012, Berlin, Deutschland

Publ.-Id: 16960 - Permalink


Biodistribution of radioactively labelled nanoparticles in the mouse
Holzhausen, C.; Mundhenk, L.; Gröger, D.; Licha, K.; Rainer, H.; Abram, U.; Gemeinhardt, I.; Schnorr, J.; Donat, C.; Gruber, A.;
Introduction
Fluorochromatic labeling of organic nanoparticles is often used to investigate their biodistribution in animal models. However, this technique is descriptive in nature and does not allow for signal quantification. Furthermore, fluorochromatic labeling changes chemical and physical properties and is therefore thought to change the distribution characteristics of nanoscaled particles. We therefore hypothesized that radioactive labeling facilitates a quantifiable determination of the biodistribution of nanoparticles.

Material and Methods
47 NMRI-mice received 35S- labeled, 7 ± 1,5 nm sized dendritic Polyglycerol Sulfate (dPGS) or unlabelled dPGS intravenously or subcutaneously. Radioactivity from tissues at different times up to 21 days was analyzed by surface-counts, autoradiography, liquid-scintillation, imager-survey and histological photoemulsion.

Results
Radioactivity measurements allowed for a tissue- and time-dependent quantification of the labelled dPGS. Radioactively-labelled dPGS were still quantifiable in liver and spleen after 21 days following intravenous injection. Subcutaneous application resulted in a similar but delayed distribution kinetic.

Discussion
The biodistribution of dPGS was quantitatively determined by all methods used for radioactivity testing. This approach should provide an innovative, sensitive and adaptable method to detect nanoparticles without changing their biorelevant properties.
  • Lecture (Conference)
    ESVP-ECVP-ESTP-Meeting 2011, 07.-10.09.2011, Uppsala, Schweden
  • Abstract in refereed journal
    Journal of Comparative Pathology 146(2012)1, 52
    DOI: 10.1016/j.jcpa.2011.11.028

Publ.-Id: 16958 - Permalink


Extrinsically controlled spin relaxation in NiFe thin films induced by a periodic scattering potential
Körner, M.; Lenz, K.; Banholzer, A.; Grebing, J.; Barsukov, I.; Römer, F. M.; Lindner, J.; Farle, M.; Fassbender, J.ORC
The spin relaxation process of thin Ni80Fe20 (Py) films is influenced by introducing a periodic scattering potential using ion beam techniques. These potentials can be created in two ways: (i) by Cr+ implantation into the surface of the Py film, using a lithographically defined mask. (ii) by using nanometer scale periodically modulated substrates (ripple) that change the morphology of the Py film grown on top [2].
The magnetic damping contributions are determined by frequencydependent ferromagnetic resonance measurements using a vector network analyzer. For both sample systems we find several strongly enhanced linewidth peaks over a wide frequency range. By varying the scattering potential, the frequency positions of the damping peaks are preselectable.
This work is supported by DFG grant FA 314/6-1 and SFB 491.
[1] I. Barsukov et al., Phys. Rev. B 84, 140410(R) (2011).
[2] J. Fassbender et al., New Journal of Physics 11, 125002 (2009).
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16957 - Permalink


Insights on the U(VI) Speciation with Bacterial Isolates from Äspö and Mont Terri
Lütke, L.; Moll, H.; Bachvarova, V.; Selenska-Pobell, S.; Bernhard, G.;
In this study we examined the impact of two microbial representatives from actually discussed potential geological formations for nuclear waste storage on the U(VI) speciation. Pseudomonas fluorescens CCUG 32456A isolated from the granitic aquifers at the Äspö Hard Rock Laboratory, Sweden, and a novel strain of the genus Paenibacillus from clay samples of the Mont Terri Rock Laboratory, Switzerland, which we have recently isolated and been able to cultivate, were investigated. To assess the U(VI) interaction with surface functional groups of theses strains, potentiometric titration in combination with time-resolved laser-induced fluorescence spectroscopy (TRLFS) were applied. Based on the stability constants of U(VI) complexes with the bacterial surface functional groups U(VI) species distributions in presence of both strains in dependence on the pH were calculated. The differences in the U(VI) speciation with both strains and the influencing factors will be discussed in detail.
Keywords: uranium, P. fluorescens, Paenibacillus sp. nov., potentiometric titration, TRLFS
  • Contribution to proceedings
    International Symposium on Metal Complexes (ISMEC2012), 18.-22.06.2012, Lisbon, Portugal
    Acta of the International Symposia on Metal Complexes
  • Lecture (Conference)
    International Symposium on Metal Complexes (ISMEC) 2012, 18.-22.06.2012, Lisbon, Portugal

Publ.-Id: 16956 - Permalink


Insider 4/2011
Weigl, A.;
Mitarbeiterzeitung des HZDR
Keywords: in-house journal of HZDR
  • Communication & Media Relations
    Mitarbeiterzeitung 16.12.2011
    4 Seiten

Publ.-Id: 16955 - Permalink


Insider 3/2011
Weigl, A.; Schmiedel, S.;
Mitarbeiterzeitung des HZDR
Keywords: in-house journal of HZDR
  • Communication & Media Relations
    Mitarbeiterzeitung 28.10.2011
    10 Seiten

Publ.-Id: 16954 - Permalink


Transition between turbulent magnetically driven flow states in a Rayleigh-Bénard cell
Grants, I.; Gerbeth, G.;
Transition between turbulent flow regimes is studied experimentally in a cylinder of liquid mercury heated from below under the influence of a rotating magnetic field. The latter creates a rotating flow which almost completely suppresses the temperature fluctuation near horizontal boundaries at a much lower angular velocity than a simple mechanical rotation. Our experiment confirms that this effect persists in the deep turbulent range to Grashof numbers as high as about 10^9. An intermediate range is observed for Gr > 2 × 10^8 with the temperature fluctuation suppressed in the core but near the sidewall. This is explained by turbulent friction replacing the Coriolis force as the leading retarding force. The linear instability of a simplified model is studied numerically. The model considers a base flow consisting of a uniform rotation and a formally independent uniform meridional flow in a cylinder with an adverse vertical temperature gradient. The model shows that the bulk meridional flow being itself much slower than the rotation is able to delay the Rayleigh-Bénard instability.
Keywords: Rayleigh-Bénard, Transition to turbulent flow, magnetically driven flow

Publ.-Id: 16953 - Permalink


3D Profile-Based Approach to Proteome-Wide Discovery of Novel Human Chemokines
Tomczak, A.; Sontheimer, J.; Drechsel, D.; Hausdorf, R.; Gentzel, M.; Shevchenko, A.; Eichler, S.; Fahmy, K.; Buchholz, F.; Pisabarro, M. T.;
Chemokines are small secreted proteins with important roles in immune responses. They consist of a conserved three-dimensional (3D) structure, so-called IL8-like chemokine fold, which is supported by disulfide bridges characteristic of this protein family. Sequence- and profile-based computational methods have been proficient in discovering novel chemokines by making use of their sequence-conserved cysteine patterns. However, it has been recently shown that some chemokines escaped annotation by these methods due to low sequence similarity to known chemokines and to different arrangement of cysteines in sequence and in 3D. Innovative methods overcoming the limitations of current techniques may allow the discovery of new remote homologs in the still functionally uncharacterized fraction of the human genome.
We report a novel computational approach for proteome-wide identification of remote homologs of the chemokine family that uses fold recognition techniques in combination with a scaffold-based automatic mapping of disulfide bonds to define a 3D profile of the chemokine protein family. By applying our methodology to all currently uncharacterized human protein sequences, we have discovered two novel proteins that, without having significant sequence similarity to known chemokines or characteristic cysteine patterns, show strong structural resemblance to known anti-HIV chemokines. Detailed computational analysis and experimental structural investigations based on mass spectrometry and circular dichroism support our structural predictions and highlight several other chemokine-like features. The results obtained support their functional annotation as putative novel chemokines and encourage further experimental characterization.
The identification of remote homologs of human chemokines may provide new insights into the molecular mechanisms causing pathologies such as cancer or AIDS, and may contribute to the development of novel treatments. Besides, the genome-wide applicability of our methodology based on 3D protein family profiles may open up new possibilities for improving and accelerating protein function annotation processes.
Keywords: G protei-coupled receptor circular dichroism

Publ.-Id: 16952 - Permalink


S-layer proteins as possible immobilization matrix for photocatalysts – OH radical scavenging capacity and protein stability
Schmoock, C.; Börnick, H.; Vogel, M.; Lehmann, F.; Kutschke, S.; Raff, J.; Dittmar, T.; Worch, E.;
Supported nanostructured photocatalysts were improved by using novel biohybrid materials based on bacterial S-layer proteins. Within the development of advanced photocatalytic materials supported with bacterial S-layer proteins, the OH radical scavenging capacity of suspended S-layer proteins in a photocatalytic system was determined with 2.39 × 105 (mg protein)−1 s−1 using tertiary butanol OH radical assay. Furthermore, applying the photocatalyst in suspension, S-layer proteins inhibit the photocatalytic process by covering the ZnO nanoparticles. This effect is related to the protein concentration and can be described by a saturation function. S-layer proteins were not conspicuously damaged, such as fragmentation, by photocatalytic treatment. Only a slight cross-linking was visible by gel electrophoresis. For future use, immobilized S-layer proteins will be utilized in significantly lower amounts. Therefore the inhibition by covering particles and the relatively low scavenging capacity will not strongly affect the OH radical yield of the final composite. These findings were also confirmed by degradation experiments with diclofenac. Based on these findings it can be concluded that the implementation of nanoscaled biocomposite materials using S-layer proteins for the preparation of multi-functional coatings for photocatalytic applications is promising.
Keywords: OH radicals; S-layer protein; Scavenger capacity; Photocatalysis; Advanced materials

Publ.-Id: 16951 - Permalink


Mechanical and ellipsometry measurements of thin TiN layer prepared by PIII
Abd El-Rahman, A. M.; Raaif, M.; Mohamed, S.; Kolitsch, A.;
Titanium nitrides have good mechanical, biomedical and optical properties, therefore they are used to harden and protect cutting and sliding surfaces and as a non-toxic exterior for bio-medical applications. Nitrogen plasma immersion implantation (Pill), in which the diffusion of nitrogen from low pressure r.f. plasma is combined with the implantation of nitrogen ions at energies up to 30 kV, is an effective tool for nitriding titanium and titanium alloys. In this work, samples of pure titanium were nitrided by Pill at different negative high voltage pulses. The properties and the characteristics of the processed samples were evaluated using X-ray diffraction (XRD), Auger electron spectroscopy (AES), ball-on-disk type tribometer, surface profilemeter, and ellipsometry measurements. The results show that, the wear resistance of the untreated sample in comparison to the PIII treated samples is extremely poor and the friction coefficient for the PIII treated samples is decrease!
d to the half value in comparison to the untreated titanium, this attributed to the formation of the solid solution titanium alpha-Ti(N) and the cubic TiN phases. Ellipsometric measurements were carried out on the PIII treated samples at different negative high voltage pulses. A three layers model was used to fit the calculated data to the experimental ellipsometric spectra. The thickness, surface roughness and refractive index increase with increasing the negative high voltage pulses. The refractive index at 550 nm increases from 1.83 to 2.09 as the negative high voltage pulses increases from 10 to 30 kV.
Keywords: PIII, TiN, ellipsometry

Publ.-Id: 16950 - Permalink


Copper and silver ion implantation of aluminium oxide-blasted titanium surfaces: proliferative response of osteoblasts and antibacterial effects
Fiedler, J.; Kolitsch, A.; Kleffner, B.; Henke, D.; Stenger, S.; Brenner, R.;
Implant infection still represents a major clinical problem in orthopedic surgery. We therefore tested the in vitro biocompatibility and antibacterial effects of copper (Cu)- and silver (Ag)-ion implantation. Discs of a commonly used titanium alloy (Ti6AlV4) with an aluminium oxide-blasted surface were treated by Cu- or Ag-ion implantation with different dosage regimen (ranging from 1e15-17 ions cm(-2) at energies of 2-20 keV). The samples were seeded with primary human osteoblasts and cell attachment and proliferation was analyzed by an MTT-assay. In comparison to the reference titanium alloy there was no difference in the number of attached viable cells after two days. After seven days the number of viable cells was increased for Cu with 1e17 ions cm(-2) at 2 and 5 keV, and for Ag with 1e16 ions cm(-2) at 5 keV while it was reduced for the highest amount of Ag deposition (1e17 ions cm(-2) at 20 key). Antibacterial effects on S.aureus and E.coli were marginal for the studied dosages of Cu but clearly present for Ag with 1e16 ions cm(-2) at 2 and 5 keV and 1e17 ions cm(-2) at 20 keV. These results indicate that Ag-ion implantation may be a promising methodological approach for antibacterial functionalization of titanium implants.
Keywords: ion implantation, orthopedic surgery, antibacterial effects

Downloads:

Publ.-Id: 16949 - Permalink


The Specific Value of Early Stage Mining Projects: Are Common Valuation Methods Appropriate?
Marakulina, P.; Klossek, A.;
Taking into account the recent worldwide strive for raw materials, the emergence of start-ups in the mining sector for rare metals, and tendencies of financial and strategic investors to invest in such companies, the paper critically evaluates the suitability of common methods widely used to valuate mining projects and start-ups. Building on the deficiencies of single methods to capture the specificities of rare earth junior mining companies, which are assumed to be single-project companies, the paper suggests using a combined approach including discounted cash flow, real options, and multipliers methods. Compared to the value obtained by using singular methods, the resulting specific value is argued to better reflect the value of a specific company and project, respectively, within the rare earth junior mining industry.
Keywords: Early Stage Mining Project, Valuation Method, Rare Earths
  • Lecture (Conference)
    12th Annual Conference of the European Academy of Management - EURAM 2012, 06.-08.06.2012, Rotterdam, Niederlande

Publ.-Id: 16948 - Permalink


Nuclear waste management: Current research at ROBL/ESRF
Scheinost, A. C.;
X-ray absorption spectroscopy (XAS) is well suited to investigate trace amounts of target elements in a variety of matrices, which makes it the method of choice for the investigation of radionuclides in the framework of nuclear waste management. With the Rossendorf Beamline at ESRF (ROBL), a dedicated XAS station for radionuclide research is available, licensed to investigate actinides from throrium to californium with activities up to 185 MBq. In this talk, I will give an overview on nuclear waste related research performed at ROBL, encompassing waste disposal as well as waste reduction.
Keywords: XAFS EXAFS XANES nuclear waste synchrotron
  • Invited lecture (Conferences)
    Expert Panel: Industry’s needs for advanced characterisation, by neutron and synchrotron X-ray techniques, of materials for civil nuclear power, 03.-04.04.2012, Grenoble, France

Publ.-Id: 16947 - Permalink


High-field magnetism and magneto-acoustics in UCo2Si2
Yasin, S.; Andreev, A. V.; Skourski, Y.; Zherlitsyn, S.; Wosnitza, J.;
We report results of magnetization and magneto-acoustic studies on a UCo2Si2 single crystal in high magnetic fields. This compound orders antiferromagnetically at the Néel temperature TN = 83 K and shows at low temperatures a first-order metamagnetic transition (MT) at 45 T with very small hysteresis (µ0ΔHcr = 0.16 T) to a ferrimagnetic state seen as a sharp jump in the magnetization when the magnetic field is applied along the c direction. The magnetization curve measured along the a axis shows no transition and is linear up to 60 T. The acoustic properties exhibit drastic anomalies in the vicinity of both magnetic phase transitions; the spontaneous and the field-induced one. At TN, a pronounced change in the sound velocity Δv/v accompanied with a peak in the attenuation Δα has been observed. Whereas Δα only shows a very sharp peak at the MT, Δv/v displays a more complicated behavior; it has a non-monotonous temperature evolution with maximum effects at 30 K, which can be due to the transition changing from first to second order. Our results enabled us to map the phase diagram of UCo2Si2 in fields applied along the c axis. We discuss our observations in relation to the magnetism on the U site and the magnetoelastic interaction in this material. *Part of this work was supported by EuroMagNET under the EU contract No. 228043.
  • Lecture (Conference)
    Frühjahrstagung der DPG, 26.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16946 - Permalink


Direct observation of the superconducting energy-gap opening in the optical conductivity spectra of LuNi2B2C
Fischer, T.; Pronin, A. V.; Stehr, D.; Wosnitza, J.; Niemeier, T.; Holzapfel, B.;
At frequencies between 100 GHz and 2.5 THz, we have accurately measured the complex transmission coefficient of LuNi2B2C films on MgO substrates using two different setups: a time-domain terahertz spectrometer and a setup based on backward-wave oscillators. For the first time, the development of the superconducting energy gap is directly observed in the optical spectra. From the measured data, we have calculated the optical conductivity and the penetration depth. We have compared the results with the BCS theory, and found an additional absorption at low frequencies. The origin of this absorption may be related to the complex gap structure of the compound with possible nodes. Theoretical calculations are currently under way. Part of this work has been supported by EuroMagNET, EU contract 228043.
  • Poster
    Frühjahrstagung der DPG, 26.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16945 - Permalink


Characterization of superparamagnetic nanoparticles for bone-tissue engineering
Uhlarz, M.; Herrmannsdörfer, T.; de Santis, R.; Sandri, M.; Tampieri, A.; Figallo, E.; D’Alessandro, T.; Keshari-Samal, S.; Rischitor, G.; Collaboration Magister;
Currently, large bone or cartilage defects are stabilized by massivelyinvasive surgery. The permanent implants used for this purpose are either metallic prostheses, or body tissue taken elsewhere from the patient. In a novel tissue-engineering approach, autologous tissue regeneration is guided by implanted magnetic scaffolds under external magnetic field. These scaffolds attract superparamagnetic Fe3O4 (magnetite) nanoparticles tagged with Vascular Endothelial Growth Factor (VEGF) molecules. Release of the growth-factor molecules at the scaffold (optionally triggered by ac-field induced hyperthermia) attracts autologous chondrocytes and osteoblasts, which build up fresh bone and cartilage tissue. We report on the magnetic characterization of several biocompatible and biodegradable materials that might serve as scaffold materials.
This project is supported by the European Union’s FP7-Cooperation Programme through the MAGISTER project (Magnetic Scaffolds for in-vivo Tissue Engineering), Large Collaborative Project FP7 - 21468.
  • Poster
    Frühjahrstagung der DPG, 26.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16944 - Permalink


Fermi-surface change in Yb-doped CeCoIn5
Polyakov, A.; Ignatchik, O.; Bergk, B.; Bianchi, A. D.; Blackburn, S.; Prevost, B.; Cote, M.; Seyfarth, G.; Hurt, D.; Fisk, Z.; Goodrich, R. G.; Richter, M.; Sheikin, I.; Wosnitza, J.;
The evolution of the band-structure parameters of Ce1−xYbxCoIn5 was studied as a function of Yb doping by systematic de Haas–van Alphen (dHvA) measurements. We found only a small change of the dHvA frequencies and effective masses of CeCoIn5 for a low Yb concentrations (x =0.1). A drastic change of the Fermi surface appears for high dilution, i.e., for x ≥0.55. The experimentally observed Fermisurface topology of YbCoIn5 is in perfect agreement with the calculated band structure. For small x, the effective masses remain strongly renormalized, whereas for ≥0.55 the masses are reduced dramatically.
  • Poster
    Frühjahrstagung der DPG, 26.-29.03.2012, Berlin, Deutschland

Publ.-Id: 16943 - Permalink


Experimental data on vertical air-water pipe flow obtained by ultrafast electron beam X-ray tomography measurements
Lucas, D.; Banowski, M.; Hoppe, D.; Beyer, M.; Szalinski, L.; Barthel, F.; Hampel, U.;
The qualification of CFD codes for two-phase flows requires reliable experimental data with high resolution in space and time. Especially data on the transient structure of the interface is required. Bubble sizes play an important role for the evolution of the flow along the flow path. Vertical pipe flow is suitable for model development and validation because of the well-defined boundary conditions and the possibility to observe the evolution of the flow along the pipe. In nuclear reactor safety research often flows with high void fraction have to be considered. Since optical measuring methods fail for such dense flows intrusive techniques as needle tip probes or wire-mesh sensors are frequently used. Due to the intrusive effect these techniques can be applied only for a limited range of flow conditions. This paper presents first quantitative results of measurements done in upwards vertical pipe flows with air-water and steam-water systems using the new non-intrusive ultrafast electron beam tomography.
Keywords: two-phase, CFD, bubble, X-ray, tomography, experiment, database, pipe flow
  • Contribution to proceedings
    CFD4NRS-4, The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology, 10.-12.09.2012, Daejeon, Korea
  • Lecture (Conference)
    CFD4NRS-4, The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology, 10.-12.09.2012, Daejeon, Korea

Publ.-Id: 16942 - Permalink


Variations of structure and magnetic properties in UTGe hydrides (T = late transition metal)
Adamska, A. M.; Havela, L.; Skourski, Y.; Andreev, A. V.;
Hydrogenation of UTGe compounds results in formation of stable alpha- and beta-hydrides, and modification of the crystal structure and magnetic properties. TC = 3 K of UCoGe increases up to 50 K in beta-hydrides and TC = 9.5 K of URhGe up to 17 K in alpha-hydrides. The type of magnetic order is changed in UNiGe-H and UIrGe-H. The observed effects are attributed to the increased U-U spacing in the hydrides.

Publ.-Id: 16941 - Permalink


Pronounced first-order metamagnetic transition in the paramagnetic heavy-fermion system CeTiGe
Deppe, M.; Lausberg, S.; Weickert, F.; Brando, M.; Skourski, Y.; Caroca-Canales, N.; Geibel, C.; Steglich, F.;
We report on the observation of large, steplike anomalies in the magnetization (ΔM = 0.74 μB/Ce), in the magnetostriction (Δl/l0 = 2.0 × 10−3), and in the magnetoresistance in polycrystals of the paramagnetic heavyfermion system CeTiGe at a critical magnetic field μ0Hc ≈ 12 T at low temperatures. The size of these anomalies is much larger than those reported for the prototypical heavy-fermion metamagnet CeRu2Si2. Furthermore, hysteresis between increasing and decreasing field data indicate a real thermodynamic, first-order type of phase transition, in contrast to the crossover reported for CeRu2Si2. Analysis of the resistivity data shows a pronounced decrease of the electronic quasiparticle mass across Hc. These results establish CeTiGe as a rare metamagnetic Kondo-lattice system, with an exceptionally large, metamagnetic transition of first-order type at a moderate field.

Publ.-Id: 16940 - Permalink


Field-induced phases in UPt2Si2
Schulze Grachtrup, D.; Bleckmann, M.; Willenberg, B.; Süllow, S.; Bartkowiak, M.; Skourski, Y.; Rakoto, H.; Sheikin, I.; Mydosh, J. A.;
The tetragonal compound UPt2Si2 has been characterized as a moderately mass-enhanced system with an antiferromagnetic (AFM) ground state below TN = 32 K. Here, we present an extensive study of the behavior in high magnetic fields.We have performed pulsed field magnetization and static field resistivity measurements on single crystalline samples UPt2Si2. Along the crystallographic a axis, at low temperatures, we find a metamagnetic-like transition in fields of the order 40 T, possibly indicating a first-order transition. Along the crystallographic c axis, in magnetic fields of B ≥ 24 T, we find distinct anomalies in both properties. From our analysis of the data we can distinguish new high-field phases above the AFM ground state. We discuss the emergence of these new phases in the context of Fermi surface effects and the possible occurrence of a Lifshitz or electronic topological transition, this in contrast to previous modelings of UPt2Si2 based on crystal electric field effects.

Publ.-Id: 16939 - Permalink


Decorated Shastry-Sutherland lattice in the spin-1/2 magnet CdCu2(BO3)2
Janson, O.; Rousochatzakis, I.; Tsirlin, A. A.; Richter, J.; Skourski, Y.; Rosner, H.;
We report the microscopic magnetic model for the spin-1/2 Heisenberg system CdCu2(BO3)2, one of the few quantum magnets showing the 1/2-magnetization plateau. Recent neutron diffraction experiments on this compound [M. Hase et al., Phys. Rev. B 80, 104405 (2009)] evidenced long-range magnetic order, inconsistent with the previously suggested phenomenological magnetic model of isolated dimers and spin chains. Based on extensive density functional theory band structure calculations, exact diagonalizations, quantum Monte Carlo simulations, third-order perturbation theory as well as high-field magnetization measurements, we find that the magnetic properties of CdCu2(BO3)2 are accounted for by a frustrated quasi-2D magnetic model featuring four inequivalent exchange couplings: the leading antiferromagnetic coupling Jd within the structural Cu2O6 dimers, two interdimer couplings Jt1 and Jt2, forming magnetic tetramers, and a ferromagnetic coupling Jit between the tetramers. Based on comparison to the experimental data, we evaluate the ratios of the leading couplings Jd : Jt1 : Jt2 : Jit = 1 : 0.20 : 0.45 : −0.30, with Jd of about 178 K. The inequivalence of Jt1 and Jt2 largely lifts the frustration and triggers long-range antiferromagnetic ordering. The proposed model accounts correctly for the different magnetic moments localized on structurally inequivalent Cu atoms in the ground-state magnetic configuration. We extensively analyze the magnetic properties of this model, including a detailed description of the magnetically ordered ground state and its evolution in magnetic field with particular emphasis on the 1/2-magnetization plateau. Our results establish remarkable analogies to the Shastry-Sutherland model of SrCu2(BO3)2, and characterize the closely related CdCu2(BO3)2 as a material realization for the spin-1/2 decorated anisotropic Shastry-Sutherland lattice.

Publ.-Id: 16938 - Permalink


Dissipation in Non-Kramers Doublet of PrMg3
Araki, K.; Goto, T.; Mitsumoto, K.; Nemoto, Y.; Akatsu, M.; Suzuki, H. S.; Tanida, H.; Takagi, S.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.;
The low-temperature ultrasonic dispersion in the transverse (C11 - C12)/2 mode of PrMg3 with the non-Kramers-doublet ground state has been investigated in temperatures down to 20 mK. The dispersion is caused by a thermally activated motions characterized by an Arrhenius-type relaxation time of τ = τ0 exp(E/kBT) with low activation energy, E = 500 mK, and slow attempt time, τ0 = 8.5 x 10-10) s. The coupling of the electric quadrupoles of the non-Kramers-doublet ground state to transverse lattice vibrations leads to a vibronic ground state with dissipation. The vibronic state in PrMg3 releases the entropy of kB ln 2 with lowering temperature across the activation energy. A Kondo-like singlet state due to the binding of the non-Kramers doublet to the lattice vibrations appears at low temperatures far below the activation energy.

Publ.-Id: 16937 - Permalink


Magnetic properties of a GdMn6Sn6 single crystal
Gorbunov, D. I.; Kuz’Min, M. D.; Uhlírová, K.; Zácek, M.; Richter, M.; Skourski, Y.; Andreev, A. V.;
The magnetization of a GdMn6Sn6 single crystal has been measured in static magnetic fields up to 14 T as well as in pulsed fields up to 60 T. The easy magnetization direction has been confirmed to lie in the basal plane of the hexagonal crystal, the anisotropy within the plane being negligible. However, our data do not corroborate the earlier assertion that GdMn6Sn6 is a collinear ferrimagnet. This disagrees with the observed field dependence of magnetization along the easy direction as well as with the temperature dependence of spontaneous magnetization. A way out of the contradiction is to admit that GdMn6Sn6 has a more complex, non-collinear magnetic structure

Publ.-Id: 16936 - Permalink


Chitin-based Renewable Materials from Marine ponges for Uranium Adsorption
Schleuter, D.; Günther, A.; Paasch, S.; Ehrlich, H.; Kljajic, Z.; Hanke, T.; Bernhard, G.; Brunner, E.;
Chitin is known to adsorb various metals. Therefore, chitin containing materials are taken into consideration as filter materials for contaminated waters. Marine sponges of the order Verongida form three-dimensional networks of fibrous chitin, which can easily be extracted. In the hydrated state, these networks are flexible, mechanically stable and can be cut or pressed into any desired form. Here, we show for the first time that chitin-based networks of sponge origin are useful for effective uranium adsorption. They adsorb U(VI) from solution with a higher sorption capacity than many other chitinous sorbents from fungal biomass. Solid-state NMR, infrared and Raman spectroscopy indicated that the U(VI) is bound to the chitin by weak interactions such as hydrogen bonds. 90 % of the U(VI) could be desorbed using diluted hydrochloric acid. Uranium adsorption and desorption did not result in any destruction of the chitin material.
Keywords: Sponge, chitin, uranium, adsorption

Publ.-Id: 16935 - Permalink


Detailed study of the de Haas-van Alphen effect in the Shubnikov state of LuNi2B2C
Bergk, B.; Drechsler, S. L.; Canfield, P. C.; Wosnitza, J.;
We present de Haas-van Alphen (dHvA) measurements in the normal and in the superconducting state of LuNi2B2C. Inside the superconducting state, we observe quantum oscillations of a spherical Fermi-surface sheet in all crystallographic directions. Apart from the field region close to the phase transition where a strong peak effect hampers the analysis of the dHvA signal, the additional damping of the quantum oscillations inside the superconducting state is much smaller than expected from theory. For the magnetic field aligned along the [100] direction, three different dHvA frequencies are visible in the superconducting state. In particular, the orbit related to a cushion-like Fermi surface does not show any additional damping at and below the upper critical field contrary to theoretical expectations of simple effective one-band theories. Consequently, the superconducting gap on this Fermi-surface sheet can only evolve at lower fields than the observed bulk critical field, Bc2 ≈ 8 T, which clearly points to a Fermi-surface-sheet-dependent gap opening in LuNi2B2C.

Publ.-Id: 16934 - Permalink


Superconductor-insulator transition controlled by annealing in Ga implanted Si
Heera, V.; Fiedler, J.; Voelskow, M.; Mücklich, A.; Skrotzki, R.; Herrmannsdörfer, T.; Skorupa, W.;
Heavily Ga implanted Si nanolayers covered with a thin SiO2 layer exhibit a superconductor-insulator transition in dependence on annealing conditions. The transition characteristics resemble those of ultrathin quench-condensed metal films although the implanted layer differs clearly in composition, width, and nanostructure. This implies a general physical mechanism for the superconductor-insulator transition in thin, disordered layers which is supposed to be a quantum phase transition between dual states - the superconducting and the superinsulating one. The existence of a critical resistance for the phase transition is confirmed.
Keywords: Ga implantation, Ga doped Si, rapid thermal annealing (RTA), superconductor-insulator transition, Hall effect, critical resistance

Publ.-Id: 16933 - Permalink


High Efficiency 10 J Diode Pumped Cryogenic Gas Cooled Yb:YAG Multi-Slab Amplifier
Banerjee, S.; Ertel, K.; Mason, P.; Phillips, J.; Siebold, M.; Loeser, M.; Hernandez-Gomez, C.; Collier, J.;
We report on the first demonstration of a diode pumped, gas cooled, cryogenic multi-slab Yb:YAG amplifier. The performance was characterised over a temperature range from 88 K to 175 K. A maximum small-signal single-pass longitudinal gain of 11.0 was measured at 88 K. When amplifying ns-pulses, recorded output energies were 10.1 J at 1 Hz in a 4-pass extraction geometry and 6.4 J at 10 Hz in a 3-pass setup, corresponding to optical-to-optical conversion efficiencies of 21 % and 16 %, respectively. To our knowledge, this represents the highest pulse energy so far obtained from a cryo-cooled Yb-laser and the highest efficiency from a multi-J DPSSL system.
Keywords: Lasers, solid-state; Laser amplifiers; Lasers, pulsed; Lasers, ytterbium.
  • Optics Letters 37(2012)12, 2175-2177

Publ.-Id: 16932 - Permalink


Experimental databases on two-phase vertical pipe flows with and without phase transfer obtained at the TOPFLOW-DN200 test section
Lucas, D.; Beyer, M.; Szalinski, L.; Krepper, E.;
A comprehensive CFD-grade database on two-phase vertical pipe flow was established during the last years. The experiments were done at the test section "Variable Gas Injection" which is part of the TOPFLOW facility. Data are available on adiabatic air-water flows, condensing steam-water flows and boiling flows. In case of condensing flow steam was injected into sub-cooled water, while boiling was obtained by pressure relief. The measurements and the available databases are presented.
Keywords: two-phase, multiphase, CFD, bubble, pipe flow
  • Lecture (Conference)
    20th Meeting of the German CFD Network, 07.-08.03.2012, Garching, Germany

Publ.-Id: 16931 - Permalink


Numerical simulations of counter current flow experiments using a morphology detection algorithm
Höhne, T.; Darlianto, D.;
Problem: Different models necessary for dispersed particles and separated continuous phases (interfacial drag etc.)
Aim: To simulate the CCFL phenomenon in a hot leg of PWR on the basis of the flow morphologies and physics.
Counter current flow was successfully simulated in the Hot Leg Channel
A new surface drag model inside the morphology detection algorithm AIAD was introduced, it further improves the physics
The qualitative structure of the flow morphology is similar to the one observed in the experiment (slug flow regime).
The calculated quantitative CCFL characteristics & water levels inside the hot leg channel were in an agreement with the experiments.
CFD calculations of 1:1 scaled UPTF CCFL experiments show very promizing results
The effect of turbulence parameters near the free surface has to be studied in future
Validation of the AIAD model is going on – Official release of the AIAD framework in CFX is on the way
Keywords: CFD, CCFL, AIAD, CFX, PWR, Hot Leg
  • Lecture (Conference)
    German CFD Network Meeting, 07.-08.03.2012, Garching, Deutschland

Publ.-Id: 16930 - Permalink


CFD analysis on the NUPEC PWR Subchannel and Bundle Test (PSBT)
Krepper, E.; Rzehak, R.;
The presentation shows CFD calculations of the void distribution tests of the PSBT benchmark using ANSYS CFX-12.1. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncertainties in several model parameters. It is then shown that the measured cross sectionally averaged values can be reproduced well with a single set of calibrated model parameters for different tests cases. For the reproduction of patterns of void distribution cross sections attention has to be focussed on the modelling of turbulence in the narrow channel. Only a turbulence model with the capability to resolve turbulent secondary flows is able to reproduce at least qualitatively the observed void distribution patterns.
Keywords: CFD, wall boiling, CFX, PSBT benchmark, rod bundle, two phase flow, turbulence
  • Lecture (Conference)
    20th Meeting of the CFD Network, 07.-08.03.2012, Garching, Gemany

Publ.-Id: 16929 - Permalink


Insights on the Uranium(VI) Speciation with Pseudomonas fluorescens on a Molecular Level
Lütke, L.; Moll, H.; Bernhard, G.;
Microorganisms have a great potential to bind and thus transport actinides in the environment. Thus microbes indigenous to designated nuclear waste disposal sites have to be investigated regarding their interaction mechanisms with soluble actinyl ions when assessing the safety of a planned repository. This paper presents results on the pH-dependent sorption of U(VI) onto Pseudomonas fluorescens isolated from the granitic rock aquifers at Äspö Hard Rock Laboratory, Sweden. To characterize the U(VI) interaction on a molecular level, potentiometric titration in combination with time-resolved laser-induced fluorescence spectroscopy (TRLFS) were applied. This paper as a result is one of the very few sources which provide stability constants of U(VI) complexed by cell surface functional groups. In addition the bacteria-mediated liberation of inorganic phosphate in dependence on [U(VI)] at different pHs was studied to judge the influence of phosphate release on U(VI) mobilization. The results demonstrate that in the acidic pH range U(VI) is bound by the cells mainly via protonated phosphoryl and carboxylic sites. The complexation by carboxylic groups can be observed over a wide pH range up to around pH 7. At neutral pH fully deprotonated phosphoryl groups are mainly responsible for U(VI) binding. U(VI) can be bound by P. fluorescens with relatively high thermodynamic stability.
Keywords: Uranium, Pseudomonas fluorescens, Äspö, Complexation, Potentiometric Titration, Time-resolved Laser-induced Fluorescence Spectroscopy

Publ.-Id: 16928 - Permalink


The pp->nK+Σ+ reaction at 2.95 GeV/c
Abdel-Bary, M.; Abdel-Samad, S.; Brinkmann, K.-T.; Clement, H.; Doroshkevich, E.; Dshemuchadse, S.; Erhardt, A.; Eyrich, W.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Georgi, J.; Gillitzer, A.; Hesselbarth, D.; Jakob, B.; Karsch, L.; Kilian, K.; Koch, H.; Kreß, J.; Kuhlmann, E.; Marcello, S.; Marwinski, S.; Mauro, S.; Michel, P.; Möller, K.; Morsch, H. P.; Naumann, L.; Paul, N.; Plettner, C.; Richter, M.; Ritman, J.; Roderburg, E.; Schamlott, A.; Schönmeier, P.; Schroeder, W.; Schulte-Wissermann, M.; Sefzick, T.; Stinzing, F.; Steinke, M.; Sun, G. Y.; Teufel, A.; Wagner, G. J.; Wagner, M.; Wenzel, R.; Wilms, A.; Wintz, P.;
The total cross-section of the pp → nK+Σ+ reaction was measured at COSY using a proton beam with a momentum of p beam = 2.95 GeV/c, corresponding to an excess energy of ε = 129 MeV. The neutron detector COSYnus was added to the time-of-flight spectrometer COSY-TOF which tracks charged primary and secondary particles. Thus a complete reconstruction of the exit channel was feasible by exploiting for both neutron and kaon their time and direction of flight as well as the decay of the Σ+-hyperon into a neutral and a charged particle. The cross-section was determined to be between σ = 2.0 and 5.9 μb with 68% confidence. The experimental data published so far by various groups for this reaction are assessed as a whole. We conclude that either the theoretical models lack some important aspect of the reaction mechanism if one takes the experimental data at face value, or the experimental data are inconsistent and therefore theoretical descriptions must fail.

Publ.-Id: 16927 - Permalink


Benchmark simulations on TOPFLOW-PTS experiments
Apanasevich, P.; Coste, P.; Heib, C.; Niceno, B.;
The EU NURISP project (Nuclear Reactor Integrated Simulation Project) continued to improve the CFD modelling for two-phase PTS situations. For this purpose, two reference cases from the TOPFLOW-PTS experimental programme were defined: one for steady air-water and one for steady steam-water flow. The numerical simulations of the reference experiments were done using three different CFD codes: NEPTUNE_CFD, ANSYS FLUENT and ANSYS CFX. Due to technical and time constraints, three different meshes have been used with the three codes. In the air-water test, there is a temperature gradient only in the region upstream from the ECC injection point. ANSYS CFX predicted the temperature in the ECC upstream region well, while NEPTUNE_CFD and ANSYS FLUENT considerably underestimated the temperature there. In the NEPTUNE_CFD computation, a stratified flow was found in the ECC line, contrary to the experimental observation and causing higher velocity of jet, thus influencing the mixing in this area. In the ECC downstream and in the dowmcomer the fluids are well mixed. All the codes managed to predict this prefectly mixed temperature well. From the steam-water pre-test simulations, we could see that only NEPTUNE_CFD and ANSYS CFX predicted a thermal stratification at the entrance into the downcomer. The results of the steam-water test could not be validated due to lack of the experimental data. In the downcomer, NEPTUNE_CFD and ANSYS FLUENT predicted a homogeneous temperature which is very close to the saturated temperature. ANSYS CFX calculated an inhomogeneous temperature there which is considerably lower than in NEPTUNE_CFD and ANSYS FLUENT cases. Moreover, in the ANSYS CFX simulation we could see a downward flowing cold-water plume in the downcomer.
Keywords: Pressurized Thermal Shock, Direct Contact Condensation, TOPFLOW-PTS experiments, CFD
  • Lecture (Conference)
    The 2nd NURISP General Seminar, 02.-03.04.2012, Karlsruhe, Deutschland

Publ.-Id: 16926 - Permalink


NURISP work package 2.1: Pressurized Thermal Shock
Lucas, D.; Apanasevich, P.; Niceno, B.; Heib, C.; Coste, P.; Boucker, M.; Raynauld, C.; Lakehal, J.; Tiselj, I.; Scheuerer, M.; Bestion, D.;
The first part of this presentaion gives an brief overview of the activities done in the Work Package W2.1 of the NURISP SP2 subproject (Thermal Hydraulic). In the second part dicusses conclusions and recommendations for future modelling work.
Keywords: CFD, two-phase flow, PTS
  • Lecture (Conference)
    2nd NURISP General Seminar, 02.-03.04.2012, Karlsruhe, Germany

Publ.-Id: 16925 - Permalink


The Fukushima reactor accident - Reasons, background and consequences
Kliem, S.; Schäfer, F.; Tusheva, P.;
The presentation gives an overview on the course of the accident and discusses the resaons and consequences.
  • Invited lecture (Conferences)
    International Seminar Series of the Universitas Gadjah Mada, 30.01.-03.02.2012, Yogyakarta, Indonesia

Publ.-Id: 16924 - Permalink


Research on reactor physics for the enhancement of the safety of nuclear reactors
Kliem, S.;
The presentation gives an introduction to the reactor safety research at HZDR with a special emphasis to the in-house reactor dynamics code DYN3D.
  • Invited lecture (Conferences)
    International Seminar Series of the Universitas Gadjah Mada, 30.01.-03.03.2012, Yogyakarta, Indonesia

Publ.-Id: 16923 - Permalink


CFD analysis of a void distribution benchmark of the NUPEC PSBT tests: model calibration and influence of turbulence modelling
Krepper, E.; Rzehak, R.;
The paper presents CFD calculations of the void distribution tests of the PSBT benchmark using ANSYS CFX-12.1. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncertainties in several model parameters. It is then shown that the measured cross sectionally averaged values can be reproduced well with a single set of calibrated model parameters for different tests cases. For the reproduction of patterns of void distribution cross sections attention has to be focussed on the modelling of turbulence in the narrow channel. Only a turbulence model with the capability to resolve turbulent secondary flows is able to reproduce at least qualitatively the observed void distribution patterns.
Keywords: CFD, wall boiling, CFX, PSBT benchmark, rod bundle, two phase flow, turbulence

Publ.-Id: 16922 - Permalink


ROCOM experiments on boron dilution conducted within the NRG/EdF Project – Scenario 2
Kliem, S.; Franz, R.;
In the frame of the project ordered by NRG Petten (Purchase order: NRG-P2144963) experiments on two boron dilution scenarios have to be conducted at the ROCOM test facility.
Both scenarios are based on a hypothetical boron dilution accident following a SBLOCA in a PWR. A slug of unborated coolant has been accumulated in one of the loops. The re-established natural circulation drives the slug towards the reactor pressure vessel (RPV). In the vessel the slug mixes with the coolant of the downcomer and with the emergency core cooling water (ECC) which is injected into two other loops (Scenario 1) or into the loop with the slug (Scenario 2).
The boundary conditions on loop flow rates and temperature (density) differences are based on corresponding experiments at the PKL test facility operated by AREVA (Hertlein, 2003) and are described in the technical annex being a part of the project order (Kliem, 2010).
The well-proven wire-mesh sensor technology developed by HZDR over the last years is used to quantify the mixing of the slug and the ECC water on the way from the loops to the core inlet plane.
This report gives an overview about the ROCOM test facility and describes the experimental results on the second scenario. The results on the first scenario have been summarized in an earlier report (Kliem, 2011).
  • Article, self-published (no contribution to HZDR-Annual report)
    Helmholtz-Zentrum Rossendorf 2012
    HZDR\FWO\2012\01
    58 Seiten

Publ.-Id: 16921 - Permalink


Tailoring of magnetism in Pt/Co/Pt ultrathin films by ion irradiation
Maziewski, A.; Mazalski, P.; Kurant, Z.; Liedke, M.; McCord, J.; Fassbender, J.ORC; Ferre, J.; Mougin, A.; Wawro, A.; Baczewski, L.; Rogalev, A.; Wilhelm, F.; Gemming, T.
Magnetization orientation in Ga+-irradiated Pt/Co(d(Co))/Pt ultrathin films can be changed in a controlled way by adjusting the ion fluence, F. Two-dimensional (d(Co), F) diagrams of magnetic and magneto-optical properties have been derived. Distinct out-of-plane magnetic anisotropy states with enhanced magneto-optical effects were evidenced for specific (d(Co), F) values. This rich behavior originates from two competing mechanisms: intermixing of Co and Pt atoms at the interfaces and the formation of ordered CoPt alloy phases with high magnetic anisotropy. The irradiation-induced effects open novel routes for both tailoring thin-film magnetic and magneto-optical properties and patterning of magnetic nanostructures.

Publ.-Id: 16920 - Permalink


Determination of 41Ca with LSC and AMS: method development, modifications and applications
Hampe, D.; Gleisberg, B.; Akhmadaliev, S.; Rugel, G.; Merchel, S.;
Despite the emission of only low-energy Auger electrons (ca. 3.6 keV) and the difficulty of obtaining a certified standard, LSC determinations are still reasonable options for a radioanalytical laboratory involved in nuclear installation decommission. Besides accelerator mass spectrometry (AMS), being the most sensitive analytical technique not only for 41Ca, is gaining increasingly broader accessibility and applicability.
Herein, we present a radiochemical separation procedure developed for 41Ca determination with LSC and AMS in varying materials (i.e. water, concrete, sediment, soil, and biota). The radioanalytical isolation consists of anion exchange and extraction chromatography as well as carbonate precipitation and recrystallization from organic solvents. Thereby, interfering radionuclides as 55Fe, 60Co, 152Eu, U or actinides are removed with decontamination factors of 102-104. Quench curves for determining the measurement efficiency are generated with a 41Ca solution gained from the 41Ca/40Ca certified reference material ERM-AE701. In routine application the procedure is characterized by chemical yields of 25-80%, measurement efficiencies of 1-10% and detection limits of 0.05 Bq g-1 ash and 0.3 Bq l-1. Aliquot solutions of LSC can be easily converted into CaF2-AMS-targets by successive oxalate and fluoride precipitation. Pros and cons for both measurement techniques are addressed based on 41Ca results from LSC and AMS for the same material.
Keywords: 41Ca, radiochemical separation, liquid scintillation counting (LSC), accelerator mass spectrometry (AMS), method comparison

Publ.-Id: 16919 - Permalink


EXAFS investigation on U(VI) immobilization in hardened cement paste: Influence of experimental conditions on speciation
Macé, N.; Wieland, E.; Dähn, R.; Tits, J.; Scheinost, A. C.;
Extended X-ray absorption fine structure (EXAFS) spec-troscopy has been used to investigate the coordination envi-ronment of U(VI) in cementitious materials. The EXAFS measurements were carried out on U(VI)-doped samples prepared under varying conditions, such as samples from sorption, hydration and diffusion experiments, and using different cementitious materials, such as crushed hydrated hardened cement paste (HCP) and calcium silicate hydrates (C-S-H). The samples had U(VI) loadings ranging between 1 700 µg/g to 45 000 µg/g. Applying principal component analysis (PCA) on 13 EXAFS spectra (each spectra corre-sponding to a minimum of 5 different scans) of the low loading samples, we obtained one single species indicating a similar U(VI) coordination environment for both HCP and C-S-H samples. This result confirms that C-S-H phases control the uptake of U(VI) in the complex cement matrix. The radial structure of this species is similar to a U(VI) surface complex or to U(VI) in uranyl silicate minerals (two axial O atoms at 1.82 ± 0.02 Å; four equatorial O atoms at 2.25 ± 0.01 Å; one Si atom at 3.10 ± 0.03 Å). At high U(VI) loading, PCA revealed a second U(VI) species, with a radial structure similar to that of U(VI) in calcium uranate (two axial O atoms at 1.94 ± 0.04 Å; five equatorial O at-oms at 2.26 ± 0.01 Å; four Ca atoms at 3.69 ± 0.05 Å and five U atoms at 3.85 ± 0.04 Å).
This study suggest that, at low U(VI) loading, U(VI) is bound to C-S-H phases in HCP while at high U(VI) load-ing, the immobilization of U(VI) in cementitious materials is mainly controlled by the precipitation of a calcium uran-ate-type phase.
Keywords: cement nuclear waste uranium exafs

Publ.-Id: 16918 - Permalink


PET Quantification Of 18F-Flubatine Binding To Nicotinic alpha4beta2 acetylcholine receptors in Human Brains
Becker, G.; Wilke, S.; Schönknecht, P.; Patt, M.; Luthardt, J.; Hesse, S.; Wagenknecht, G.; Höpping, A.; Brust, P.; Sabri, O.;
Objectives: Nicotinic alpha4beta2 acetylcholine receptors (nAChR) are an important target for diagnostic neuroimaging because of their involvement in Alzheimer's disease (AD) and Parkinson's disease. Using 2-[18F]F-A85380 PET a significant decline in alpha4beta2-nAChRs in early AD-patients which correlated to loss of cognitive function was shown (1, 2). However, this tracer was not suited to be used as a biomarker for early AD-diagnosis in a routine clinical set-up because of its unfavourable slow kinetic. Here we used the new radiotracer 18F-Flubatine (18F-NCFHEB) with significantly improved brain uptake, receptor affinity and selectivity (3). nAChR-parameters were determined by full kinetic modeling and the validity of the practically useful tissue ratio and tissue to plasma ratio as receptor parameters was evaluated.

Methods: After intravenous administration of ~370 MBq 18F-Flubatine, the PET brain imaging was performed in 20 healthy controls (HC, age 70.6±4.6) using an ECAT EXACT HR+ system in 3D-acquisition mode. 23 frames were acquired from 0-90 min post injection and motion corrected with SPM2. Kinetic modeling using a 1-tissue compartment model (1TCM) with arterial input-function was applied to the volume of interest (VOI) based tissue-activity curves (TACs) generated for 29 brain regions (anatomically defined via MRI co-registration). Model-based receptor parameters used were the total distribution volume (VT) and the distribution volume ratio (DVR) (reference: posterior corpus callosum). In addition the standardized uptake value ratio (SUVR) (50-70 min) as approximation of the DVR and the tissue- to plasma-concentration ratio (TTPR) (70-90 min) as approximation of VT were used as non model-based receptor parameters.

Results: TACs of all 29 regions could be described adequately with the 1TCM and all kinetic parameters could be reliably estimated from 90 min PET data. VT increased as expected with receptor density. Corpus callosum (VT: 5.68±1.01), frontal (9.18±0.59), parietal (9.10±0.61), pons (11.10±0.86), thalamus (25.03±3.33). Mean TTPR values in frontal and parietal cortices were 2% higher than the corresponding VT values but 7% lower in the thalamus. There was a strong linear correlation between the two sets of TTPR and VT values (r2 = 0.98, p < 10-4) (Fig. 1A). As VT, DVR increased with receptor density. Frontal (DVR: 1.66±0.27), parietal (1.64±0.27), pons (2.01±0.35), thalamus (4.52±0.87). Mean SUVR values in frontal and parietal cortices were very similar to mean DVR values (difference <0.1%) but 15 % lower in the thalamus. However there was a strong linear correlation between the SUVR and DVR values (r2 = 0.97, p < 10-4) (Fig. 1B).

Conclusions: For18F-Flubatine the receptor parameters TTPR and SUVR in cortical regions are in good agreement with corresponding parameters computed by full kinetic modeling. For unbiased estimates of TTPR and SUVR in the thalamus the use of a bolus/infusion scheme for tracer application should be considered.

References: 1. O. Sabri, ..P. Brust: Acetylcholine receptors in dementia and mild cognitive impairment. Eur J Nucl Med Mol Imaging 2008; 35 (Suppl. 1): 30-45.
2. K. Kendziorra, ..O. Sabri: Decreased cerebral 4ß2 nicotinic acetylcholine receptors in living patients with mild cognitive impairment and Alzheimer's disease assessed with positron emission tomography. Eur J Nucl Med Mol Imaging 2010; 38: 515-525.
3. P. Brust, ..O. Sabri: In-vivo measurement of nicotinic acetylcholine receptors with [18F]norchloro-fluoro-homoepibatidine (NCFHEB). Synapse 2008; 62: 205-218.
  • Poster
    The 9th International Symposium on Functional Neuroreceptor Mapping of the Living Brain (NRM12), 09.-11.08.2012, Baltimore, USA
  • Abstract in refereed journal
    Journal of Cerebral Blood Flow and Metabolism 32(2012), 172-173
    DOI: 10.1038/jcbfm.2012.80

Publ.-Id: 16916 - Permalink


First in man study with the new radioligand F-18-Flubatine to image alpha4beta2 cerebral nicotinic acetylcholine receptors (nAChRs) in early Alzheimer's disease (AD) with PET
Sabri, O.; Wilke, S.; Gräf, S.; Lengler, U.; Gertz, H. J.; Schönknecht, P.; Habermann, B.; Becker, G.; Luthardt, J.; Patt, M.; Kendziorra, K.; Meyer, P.; Hesse, S.; Barthel, H.; Steinbach, J.; Wagenknecht, G.; Höpping, A.; Hegerl, U.; Brust, P.;
Ziel/Aim: Using F-18-A85380 (2FA) PET we recently demonstrated significant cerebral nAChR declines in early AD which correlated significantly with the loss of cognitive function (1-2). However, 2FA is not well suited in clinical routine use because of slow kinetics, acquisition times up to 7 hours, and limited nAChR selectivity. Thus, we developed the new tracer F-18-Flubatine, an epibatidine derivative without toxicity in humans formerly named as F-18-NCFHEB (3) and report here on the worldwide first human Flubatine-PET results. Methodik/Methods: 16 mild AD patients (NINCDS-ADRDA, age 74.4±6.6, MMSE 23.7±2.8) and 11 age-matched healthy controls (HCs, MMSE 28.5±0.9), all nonsmokers and nave for central acting medication, underwent Flubatine-PET (370 MBq, 3D-acquisition, ECAT Exact HR+). Dynamic 0-270min p.i. scans were acquired and corrected for motion (SPM2). Kinetic modeling was applied to 29 brain VOI-based tissue-activity curves (VOIs defined on individual MRI) using a one-tissue compartment model with measured arterial input function. Total distribution volume (DV) and binding potential (BP, reference region: corpus callosum) were used to characterize specific binding. Ergebnisse/Results: Image quality of Flubatine scans was clearly superior to 2FA, and a 20 minutes scan already adequate for visual analysis. All 29 regions were well described with one-tissue compartment. PET data acquired over only 90 minutes were sufficient to estimate all kinetic parameters precisely indicating a fast receptor binding kinetic (much faster than for 2FA). DVs in HCs increase as expected with receptor density: Corpus callosum (DV: 4.81±0.32), posterior cingulate (8.92±0.66), temporal (9.03±0.44), pons (11.00±1.19), thalamus (24.32±2.96). The AD patients showed extensive BP reductions in frontal, parietal, temporal, anterior and posterior cingulate cortices, caudate, and midbrain (all p<0.05) compared to HCs. There was significant correlation between nAChR reductions and cognitive declines in posterior cingulate, parietal, and temporal cortices, as well as in pons and cerebellum (p<0.05, all r> 0.41). Schlussfolgerungen/Conclusions: Due to the significant shorter acquisition time and superior image quality Flubatine appears to be a much more valuable tracer than 2FA to image nAChRs in humans. Early AD patients show significant declines of nAChRs in brain regions typically affected by AD pathology which correlate well with the corresponding cognitive declines. These results indicate that Flubatine-PET has a great potential as a biomarker for early AD diagnosis. Literatur/References: (1) Sabri et al. Eur J Nucl Med Mol Imaging 2008; 35 (Suppl. 1): 30-45
(2) Kendziorra et al., Eur J Nucl Med Mol Imaging 2011; 38: 515-525
(3) Brust et al. Synapse 2008; 62: 205-218
This trial is granted by the German Federal Ministry of Education and Research (BMBF-Nr. 01EZ0820)
  • Lecture (Conference)
    NuklearMedizin 2012, 25.-28.04.2012, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), V77

Publ.-Id: 16915 - Permalink


Complexation of Eu(III) with Borates
Schott, J.; Barkleit, A.; Acker, M.; Brendler, V.; Bernhard, G.;
Borates are ubiquitous compounds in the environment (rocks, soils, natural waters) and are used in many applications. Thus, there are many sources for the release of borates in the environment. Another aspect is the occurrence of borates in salt formations, which is important concerning the search of a proper nuclear waste repository.
But although there is a relevance of borates the Ln(III)/An(III)-borate system is investigated insufficiently.
The investigations concentrated on the complexation between Eu(III) and borates in aqueous solution. First results show a small influence of borates on the Eu(III) speciation.
Keywords: Europium(III), borates, complexation
  • Lecture (Conference)
    BMWi-Verbundprojekttreffen „Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen“, 03.-04.04.2012, Köln, Germany

Publ.-Id: 16914 - Permalink


The Sorption of Eu(III) on Opalinus Clay at elevated Temperatures and in Presence of Organics
Schott, J.; Acker, M.; Barkleit, A.; Brendler, V.; Bernhard, G.;
Presently, argillaceous rock formations are under investigation as potential host rocks for nuclear waste repositories. In addition to the diffusion the sorption of radionuclides on mineral phases is an important physicochemical process in a nuclear waste repository in the case of a water inleakage. Concerning the required long-term safety and risk assessment of the storage of high-level radioactive waste the understanding of these processes is essential. The investigations concentrated on the sorption of Eu(III) on OPA under realistic OPA pore water conditions (medium: pH 7.6; ionic strength 0.4 mol•L-1; presence of chloride, sulfate, carbonate) up to 50°C. In addition to the temperature dependent investigations the influence of tartrate and citrate (representatives of NOM) on the Eu(III) sorption was studied.
The sorption is characterized by a very strong binding of Eu(III) to the clay surface and a significant temperature dependency. With rising temperature the Rd value rises, showing that the Eu(III) sorption increases. In the presence of tartrate or citrate the Eu(III) sorption decreases with rising ligand concentration.
Keywords: Europium(III), sorption, Opalinus Clay, temperature, citrate, tartrate
  • Contribution to proceedings
    Workshop "Kompetenzerhaltung in der Kerntechnik", 23.-24.05.2012, Stuttgart, Germany
    Proceedings des Workshops "Kompetenzerhaltung in der Kerntechnik"
  • Lecture (Conference)
    The Sorption of Eu(III) on Opalinus Clay at elevated Temperatures and in Presence of Organics, 23.-24.05.2012, Stuttgart, Germany

Publ.-Id: 16913 - Permalink


Filtration and Catalytic Reaction in Trickle Beds: The Use of Solid Foam Guard Beds To Mitigate Fines Plugging
Wardag, A. R. K.; Hamidipour, M.; Schubert, M.; Edouard, D.; Larachi, F.;
The sensitivity of catalytic reactions to concurrent filtration and fines deposition in trickle-bed reactors (TBRs) was assessed by means of the catalytic hydrogenation of alpha-methylstyrene from kaolin-kerosene suspension flows. A negative correlation between catalytic conversion and the specific deposit of the bed resulted from the extra mass-transfer step that built up on the collectors in the course of filtration. The severity of the evolving extra mass-transfer step was sensitive to deposit compaction resulting from higher gas superficial velocities. Furthermore, irreversible catalyst activity losses were observed after catalyst cleanup and were ascribed to irretrievable active sites by catalyst intraparticle fines trapping. Fines accumulation in the catalyst bed was notably reduced by means of high-porosity solid-foam modules used as guard filters and placed upstream of, and adjacent to, the trickle bed. Hydrodynamic studies were carried out with alumina and silicon c!
arbide solid foams to assess their role on the distribution of suspension and the reduction of specific deposit and pressure drop in trickle beds. It was found that the foam capture efficiency critically depended on the open connectivity of foam cells and the physicochemical nature of foam materials. The numbering up of foam modules led to reduced overall specific deposits of the beds and pressure drops, foreseeing a prospect for prolonging the hydrotreatment TBR lifetime, using solid foam as guard beds.
  • Industrial & Engineering Chemistry Research 51(2012)4, 1729-1740
    DOI: 10.1021/ie200955v

Publ.-Id: 16912 - Permalink


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