Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Wavelet analysis of EXAFS data
Funke, H.; Chukalina, M.; Scheinost, A.;
- wird nachgereicht
  • Lecture (others)
    Seminarvortrag, 17.03.2005, Zürich, Switzerland

Publ.-Id: 7278 - Permalink


Isotopically resolved residues frorn the fragmentation of projectiles with largely different N/Z - the isospin-thermometer method
Henzlova, D.; Audouin, L.; Benlliure, J.; Botvina, A.; Boudard, A.; Casarejos, E.; Ducret, J.; Enqvist, T.; Got, L.; Heinz, A.; Henzl, V.; Junghans, A.; Jurado, B.; Kelic, A.; Krasa, A.; Kurtukian, T.; Leray, S.; Napolitani, P.; Ordonez, M.; Pereira, J.; Pleskac, R.; Rejmund, F.; Ricciardi, M.; Schmidt, K.; Schmitt, C.; Stephan, C.; Villagrasa, C.; Volant, C.; Wagner, A.; Yordanov, O.;
The mean N-over-Z (Z) ratio of residues produced in the fragmentation of Xe-136 (N/Z = 1.519), Xe-124 (N/Z = 1.296) in comparison with Fe-56 (N/Z = 1.154) is investigated over the full range of Z. The final residues from the Xe-136 projectile keep a memory on the initial N/Z. The idea to trace back the excitation energy of the fragment entering evaporation via direct exploration of the N/Z evolution in the evaporation process is investigated and applied to the data. The freeze-out temperature is deduced, which is consistent with the investigations of light and intermediate-mass fragments (IMF) in other experiments.
  • Nuclear Physics A 749(2005), 110c-113c

Publ.-Id: 7277 - Permalink


Investigation of the creation of Fe nanoparticles in MgO by ion beam synthesis
Reuther, H.; Potzger, K.; Zhou, S.; Mücklich, A.; Eichhorn, F.;
Recently, the investigation of metallic nanoparticles embedded in dielectric oxides has become a topic in magnetic data storage development. Especially the creation of high density data storage devices due to ion beam synthesis of magnetically, highly anisotropic FePt nanoparticles in sapphire yielded promising results. On the other hand, pure Fe-nanoparticles have been created in sapphire, Y-stabilized ZrO2 or MgO. The motivation for the latter includes the search for magneto-optically active surfaces as well as pronounced magnetoresistance.
For doping MgO single crystals with Fe, ion implantation is a promising technique. First extensive studies were performed by Perez et al. who investigated the annealing behaviour of samples implanted with different doses of 57Fe at different energies with conversion electron Mössbauer spectroscopy (CEMS) [1]. They obtained up to 20 % of the implanted iron atoms in a-Fe precipitates while the remaining Fe-atoms were found to be in different Fe2+ and Fe3+ charge states.

In this paper, we propose a method for the creation of large fractions of a-Fe nanoparticles (up to 60%). MgO(001) single crystals were implanted with of 6x1016 cm-2 ions of the Mössbauer isotope 57Fe at 100 keV. The implantation temperature was varied from room temperature up to 800 °C. Moreover, post annealing was investigated. Samples were characterized by CEMS, RBS, TEM and XRD. We found that the temperature during the implantation plays the important role for the formation of the Fe0 state while post annealing results in the preferential formation of Fe oxidation states, mainly Fe3+ states. The largest fraction of iron with Fe0 state was obtained at implantation temperatures between 600 and 800 °C.

[1] A. Perez, G. Marest, B.D. Sawicka, J.A. Sawicki, T. Tyliszczak, Phys. Rev. B, 28, 1227 (1983)
  • Lecture (Conference)
    International Conference on the Applications of the Mössbauer Effect, 05.-09.09.2005, Montpellier, France

Publ.-Id: 7276 - Permalink


Efficient silicon based light emitters
Helm, M.; Sun, J. M.; Potfajova, J.; Dekorsy, T.; Schmidt, B.; Skorupa, W.;
Recent progress on electrically driven silicon based light emitters is reviewed, with emphasis on our work on light emitting pn diodes (LED) and MOS devices doped with rare-earth elements. The LEDs were fabricated by high-dose boron implantation, producing nanoscale modifications in the material. The electroluminescence (EL) efficiency increases with temperature, reaching 0.1% (wall plug efficiency) at room temperature for optimized conditions. Such devices were integrated into a microcavity. In the MOS devices the oxide was implanted with various rare-earth elements, resulting in strong EL in the visible (Tb) and ultraviolet (Gd). External quantum efficiencies in excess of 10% are reported.
Keywords: silicon, light emitting diode, electroluminescence, rare earth, microcavity
  • Microelectronics Journal 36(2005), 957-962

Publ.-Id: 7275 - Permalink


Efficient silicon based light emitters
Helm, M.;
Recently remarkable progress has occurred in the variety and efficiency of silicon based light emitters, based on Si pn junctions, Si MOS structures doped with rare earth elements, or containing Si nanoclusters. I will present our work in some of these areas.

We have fabricated Si light emitting diodes (LED) by high-dose boron implantation into n-type Si. The free-exciton electroluminescence (EL) increases with temperature, reaching wall-plug efficiencies of more than 0.1% at room temperature. A model which is based on excitons localized near nanoscale boron doping spikes can explain the EL dependence on current and temperature. We have integrated such structures into a microcavity with a buried metallic CoSi2 bottom mirror and a Si/SiO2 Bragg mirror on top. This resonant-cavity LED exhibits significant spectral narrowing, consistent with the quality of the cavity.

We also have fabricated light emitting Si MOS structures which were implanted with various rare-earth elements, from the well known Er3+ emitting at the telecom wavelength of 1.54 microns, to Gd3+, which emits in the deep UV at 316 nm. This is, to our knowledge, the first Si based UV light emitter, with many potential applications in areas such as bio-sensing.
Keywords: silicon, light emitting diode, rare earth, electroluminescence, microcavity
  • Invited lecture (Conferences)
    4th Workshop on Semiconductor Nanodevices and Nanostructured Materials (NANOSEMIMAT-4), 09.-13.03.2005, Sao Pedro, SP, Brazil

Publ.-Id: 7274 - Permalink


Krein space related physics: PT-symmetric Quantum Mechanics, MHD α²-dynamos, planar Couette flows, ...
Günther, U.; Stefani, F.; Znojil, M.;
Operator theoretic structures are discussed which underlie PT-symmetric Quantum Mechanics (PTSQM), the spherically symmetric α²-dynamo of magnetohydrodynamics (MHD) and the plane Couette flow of hydrodynamics (described by the Squire equation). Mathematically, the three types of models are closely related as spectral problems in Krein spaces − Hilbert spaces with an indefinite metric structure.
In contrast to the purely real spectrum of self-adjoint operators in "usual" Hilbert spaces, the spectrum of self-adjoint operators in Krein spaces consists, in general, of two types of spectral sectors: sectors with purely real eigenvalues and other sectors with pairwise complex conjugate eigenvalues. Transitions between different sectors occur at exceptional points of square root branching type. Knowing the boundaries of the sectors in parameter space one would know, e.g., the boundaries of the physical sectors of PTSQM (with exact/unbroken PT-symmetry) or of the oscillatory regimes of α²-dynamos.
The underlying Krein space related structure of the different physical setups indicates a possible fruitful interplay of these models in handling their technical and conceptual aspects on a unified footing. We make some aspects of such an interplay explicit and demonstrate its usefulness on the example of a PT-symmetric interpolation model and the Squire equation of hydrodynamics. This allows us to gain a deeper insight into the specifics of the Herbst limit.

The talk is based on material from math-ph/0501069 (which is to appear in J. Math. Phys.) and extends it.
Keywords: MHD dynamos, PT-symmetric Quantum Mechanics, Squire equation, Krein spaces, exceptional points, Herbst limit
  • Invited lecture (Conferences)
    3rd International Workshop on Pseudo-Hermitian Hamiltonians in Quantum Physics, 20.-22.06.2005, Istanbul, Turkey

Publ.-Id: 7273 - Permalink


Diffusion von Huminstoffkolloiden im Laborsystem Kaolinit-Wasser
Sachs, S.; Mibus, J.;
Abstract wird nachgereicht.
Keywords: Huminstoffe, Kolloide, Ton, Migration, Diffusion
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Migration von Actiniden im System Ton, Huminstoff, Aquifer", 04.-05.04.2005, München, Germany

Publ.-Id: 7272 - Permalink


Inherent Dilution: Qualification of TRIO_U on a ROCOM experiment
Bieder, U.; Höhne, T.;
In this report, a generic test case concerning the “heterogeneous inherent dilution during a small break LOCA” is analyzed. During the heat transfer phase of a small break in the primary circuit, vapour, which is formed in the core region, can condense in the steam generator tubes what yields pure, unborated water. Under certain conditions, in particular in the absence of natural circulation, this pure water can accumulate in the steam generator and/or the U form intermediate leg. When the natural circulation starts, the pure water can be transported into the reactor pressure vessel with the possible risk of a criticality accident.

For the validation of Trio_U to the application to such accidents, a generic ROCOM experiment with a constant flow rate in one loop in the magnitude of natural circulation and 10% density difference between ECC and loop water was analysed. The following results have been concluded:

The Trio_U calculation shows a good agreement with the experiment, provided that the exact ROCOM geometry is used.
The LES approach led not only to a good qualitative representation of the experiment, but also a good quantitative accordance. This is true for the two tested sub-grid models, the Smagorinsky model and the WALE model.
It seems that the WALE model treats more correctly the injection phase and the formation of the cold plume in the upper downcomer region. However, the detected azimuthal displacement of the cold plume with the WALE model can lead to errors in the prediction of the core region which is affected by the injection.
The Smagorinsky model seems to underestimate the mixing phenomena during the injection phase. However, the location of the cold plume at the lower end of the downcomer was better predicted than with the WALE model
The transient of the tracer concentrations in the downcomer has been calculated on one hand for the 1:5 KONVOI geometry and on the other hand for the ROCOM geometry. The comparison of these results has shown the importance of using very precise CAD data when applying CFD.
Keywords: ROCOM, TRIO_U, inherent dilution, boron mixing, turbulence, LES, CFD
  • Other report
    Grenoble: CEA/DEN/GRE/DER/SSTH/LMDL-2004-029, 2005
    29 Seiten

Publ.-Id: 7271 - Permalink


Quantification of iron minerals formed during aging of iron-containing colloids
Reuther, H.; Ulrich, K.-U.;
Due to their large specific surface area and high sorption affinity, iron-containing colloids are capable to remove dissolved contaminants from solution and to retard their migration by the water path. In a pH range near to the point of zero charge, the low electrostatic stability favors agglomeration and sedimentation of such colloids, enabling their retention (e.g., by the formation of crusts). Freshly formed iron-rich colloids mainly consist of metastable iron phases such as schwertmannite or ferrihydrite. X-ray diffraction is not sensitive enough to quantify these phases because of small particle size (< 50 nm) and/or poor structural order. Aging of these metastable phases to more crystalline Fe minerals such as goethite or hematite may have consequences on the fate of the adsorbed contaminants. The modification of surface binding sites and of steric mineral properties by the recrystallization process may cause either desorption of the contaminants from the surface, or allow their incorporation into the lattice.

Our research focuses on the mobility of uranium during the flooding process of abandoned uranium mines in East Germany. The aim is to study the behavior of uranium during the aging process of iron-rich colloids which have scavenged uranium. Information on the speciation of uranium and its migration in the vicinity of such mines is crucial for hazard prognosis.
It is thus necessary to identify and to quantify precisely the transformation of iron phases into more crystalline Fe minerals by chemical analysis. Mössbauer spectroscopy is a powerful tool to discriminate the expected minerals goethite, hematite and ferrihydrite. In mixtures, fractions < 5 % can be separated without difficulties. We used Mössbauer spectroscopy at room temperature to identify the aging products. Transmission spectra of calibration standards of ferrihydrite, goethite, hematite and mixtures of defined ratios were compared with spectra of the iron-containing colloids. This enabled us to characterize the aging process.
  • Contribution to proceedings
    International Conference on Applications of Mössbauer Effect, 05.-09.09.2005, Montpellier, France
  • Poster
    International Conference on Applications of Mössbauer Effect, 05.-09.09.2005, Montpellier, France

Publ.-Id: 7269 - Permalink


Complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses
Vulpius, D.; Geipel, G.; Baraniak, L.; Bernhard, G.;
The complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid (vanillic acid) was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses using the fluorescence properties of 4-hydroxy-3-methoxybenzoic acid. A 2:1 complex of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid was found. The stability constant of this complex was determined to be log β210 = 7.33 ± 0.10 at an ionic strength of 0.1 mol/l (NaClO4) and at 21 °C. The determination of the stability constant required an investigation of the excited-state proton transfer of 4-hydroxy-3-methoxybenzoic acid over the whole pH range. It was realized that 4-hydroxy-3-methoxybenzoic acid undergoes excited-state reactions only at pH values below 5. At pH values above 5 stability constants can be determined without kinetic calculation of the proton transfer.
Keywords: Neptunium, 4-Hydroxy-3-methoxybenzoic acid, Complex formation, Time-resolved laser-induced fluorescence spectroscopy, Excited-state proton transfer

Publ.-Id: 7268 - Permalink


Multiple implantations into Si: influence of the implantation sequence on ion range profiles
Posselt, M.; Mäder, M.; Lebedev, A.; Grötzschel, R.;
In successive implantations of p- and/or n-dopants the implantation sequence may affect the ion range distributions. This is demonstrated for two consecutive implantations into the [001] channel direction: (i) 35 keV B followed by 50 keV As and (ii) 50 keV As followed by 35 keV B. The defects formed in the first implantation cause enhanced dechanneling of the subsequently implanted ions and, therefore, influence the shape of the range distributions in the second implantation step. The experimental range profiles can be reproduced very well by atomistic computer simulations which take into account damage accumulation or dynamic annealing during a single implantation step as well as the influence of the defects formed by the preceding implantation steps.
Keywords: ion implantation, channeling, radiation damage, computer simulation
  • Applied Physics Letters 87(2005), 043109

Publ.-Id: 7267 - Permalink


5. Workshop "Measurement Techniques for Steady and Transient Multiphase Flows"
Prasser, H.-M.; (Editor)
The Forschungszentrum Rossendorf (FZR) carries on a series of workshops on Measurement Techniques for Steady and Transient Multiphase Flows with the support of the following organisations: DECHEMA / Gesellschaft für Chemische Technik und Biotechnologie e.V., Kerntechnische Gesellschaft e. V. (KTG), Technical Group on Thermal and Fluiddynamics and Local Section of Saxony, Institute of Process Technique, Process Automation, and Measuring Technique (IPM) at the University of Applied Sciences Zittau/Görlitz and the TELETRONIC GmbH in Rossendorf. The first workshop was held in 1997 and had the character of a national event. International participation started for the first time in the 2000 edition of the workshops series.

The main aim of this workshops series is to discuss recent developments and future tendencies in the field of high-resolution measuring techniques used to characterise two-phase or multi-phase flow fields. Examples are measurements of the gas-liquid interface, the characterisation of its structure and its evolution in the field of gas-liquid flows and measurements of size, shape and velocity of individual particles of the disperse phase (bubbles, droplets etc.) and their dynamics. The efforts in the measure-ments field correspond to the needs of the development of three-dimensional computational fluid-dynamics (CFD) models and computer codes. High-resolution data is necessary both for the development of geometry independent constitutive equations describing the interaction of the different phases taking part in the flow and for the validation of the CFD codes against experiments. Moreover, modern tendencies in instrumentation for industrial applications are discussed.
Keywords: multiphase flow, measurement instrumentation, workshop, transient flow
  • Book (Editorship)
    Dresden: Forschungszentrum Rossendorf, 2002
    99 Seiten

Publ.-Id: 7266 - Permalink


EXAFS-Untersuchungen am System U(VI)-Huminsäure-Kaolinit und aktuelle Ergebnisse zur U(VI)-Sorption am Kaolinit
Krepelova, A.;
Abstract wird nachgereicht
  • Lecture (others)
    Workshop des Verbundprojekts Migration von Actiniden im System Ton, Huminstoff, Aquifer, 04.-05.04.2005, München, Germany

Publ.-Id: 7265 - Permalink


Die Koordination von Actiniden in wässriger Lösung - Untersuchungen mit EXAFS-Spektroskopie
Hennig, C.;
eingeladener Institutsvortrag
  • Invited lecture (Conferences)
    Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, 19.4.2005, Leipzig, Germany

Publ.-Id: 7264 - Permalink


Uncertainty and sensitivity analysis for the modeling of a start-up experiment in a VVER-1000 reactor
Kliem, S.; Mittag, S.; Weiß, F.-P.; Langenbuch, S.;
The transition from the application of conservative models to the use of best-estimate models raises the question about the uncertainty of the obtained results. This question becomes especially important, if the best-estimate models should be used for safety analyses in the field of nuclear engineering. Different methodologies were developed to assess the uncertainty of the calculation results of computer simulation codes. One of them is the methodology developed by Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) which uses the statistical code package SUSA.

In the frame of the recently finished EU FP5 funded research project VALCO, that methodology was extended and successfully applied to different coupled code systems, including the uncertainty analysis for neutronics. These code systems consist of a thermal hydraulic system code and a 3D neutron kinetic core model. One of the code systems applied was ATHLET coupled with the Rossendorf kinetics code DYN3D. Two real transients at NPPs with VVER-type reactors documented within the VALCO project were selected for analyses. One was a test with the switching-off of one of two main feed water pumps at the VVER-1000 Balakovo-4 NPP. Based on the relevant physical processes in the transients, a list of possible sources of uncertainties was compiled. Besides control parameters like control rod movement and thermal hydraulic parameters like secondary side pressure, mass flow rates, pressurizer sprayer and heater performance, different neutron kinetic parameters were included into the list of possible sources of uncertainties. Sets of input data with statistical variation of the relevant parameter values were generated for a large number of runs of the coupled code.

The SUSA package was used to make a statistical analysis of the result parameters from the output data of the calculations. Time-dependent rank correlation coefficients were calculated showing the influence of the varied parameters on the output parameter under investigation. The most interesting output parameters are the physical parameters for which experimental data are available. The calculation results allowed also the determination of time-dependent tolerance intervals for given coverage and confidence. The comparison of the experimental data, the (best-estimate) reference solution and the tolerance intervals showed how the agreement between experiment and calculation could be quantified. In most of the cases the tolerance intervals include the experimental curves. A compiled list of the most important input parameters based on the rank correlation coefficients shows, which input parameters and models are responsible for the deviations. This list gives indications for further model improvements and code developments.
  • Lecture (Conference)
    4th International Conference: Safety Assurance of Nuclear Power Plants with WWER", 23.-26.05.2005, Podolsk, Russia
  • Contribution to proceedings
    4th International Conference: Safety Assurance of Nuclear Power Plants with WWER", 23.-26.05.2005, Podolsk, Russia
    Proceedings CD-ROM

Publ.-Id: 7263 - Permalink


Fluid mixing and flow distribution in the reactor circuit (FLOMIX-R)
Rohde, U.; Höhne, T.; Kliem, S.; Hemström, B.; Scheuerer, M.; Dury, T.; Remis, J.; Muhlbauer, P.; Toth, I.; Elter, J.; Bezrukov, Y.; Toppila, T.; Lillington, J.;
The coolant mixing in PWR is an issue relevant for reactor safety, but of importance also for the optimisation of normal reactor operation. In the case of boron dilution accidents, the coolant mixing is the only effective mitigative mechanism against severe consequences of the accident. The degree of mixing determines the thermal and, therefore, mechanical load of the reactor pressure vessel wall.

Within the European project FLOMIX-R, an unique experimental data base on coolant mixing in PWRs has been created. Experiments on coolant mixing have been performed at three European mixing test facilities representing different types of reactors. Additionally, slug mixing data from the FSUE EDO Gidropress VVER-1000 mock-up have been made available. Mixing under steady-state flow conditions, slug mixing during the start-up of the first main coolant pump and mixing of cold emergency core cooling (ECC) water have been investigated. Moreover, measurement data from a real VVER-440 reactor plant (NPP Paks in Hungary) have been made available.

The measurement data base was used for the validation of computational fluid dynamics (CFD) codes. Calculations were performed for selected tests from the data base using the CFD codes CFX and FLUENT. For quality assurance in the CFD code validation, so-called Best Practice Guidelines (BPG) have been applied. The BPG require a minimization of numerical errors and solution errors by systematic grid and time step refinement and sensitivity tests on the impact of uncertainties in the boundary conditions, before the effect of different physical models can be assessed. The applicability of various turbulence modeling techniques was studied for transient and steady state flow.

The paper gives on overview on the experimental data base and on first, preliminary conclusions from the CFD code validation.
Keywords: pressurised water reactor, boron dilution, turbulent mixing, measurement data, computational fluid dynamics, code validation, best practice guidelines
  • Lecture (Conference)
    The 4-th International Conference "Safety Assurance of NPP with WWER", 23.-25.05.2005, Podolsk, Russia
  • Contribution to proceedings
    4th Scientific and Technical Conference "Safety Assurance of NPP with WWER", 23.-26.05.2005, Podolsk, Russia

Publ.-Id: 7262 - Permalink


Measurement data base on fluid mixing and flow distribution in the reactor circuit
Rohde, U.; Kliem, S.; Höhne, T.; Prasser, H.-M.; Hemström, B.; Toppila, T.; Elter, J.; Bezrukov, Y.; Scheuerer, M.;
Experimental investigations on coolant mixing in Pressurised Water Reactors (PWR) have been performed within the EC project FLOMIX-R. The project was aimed at describing the mixing phenomena relevant for both safety analysis, particularly in steam line break and boron dilution scenarios, and mixing phenomena of interest for economical operation and the structural integrity. Measurement data from a set of mixing experiments have been gained by using advanced measurement techniques with enhanced resolution in time and space. Slug mixing tests simulating the start-up of the first main circulation pump are performed with three 1:5 scaled facilities: the Rossendorf Coolant Mixing model ROCOM, the Vattenfall test facility and a metal mock-up of VVER-1000 type reactor at EDO Gidropress. Experimental results on buoyancy driven mixing of fluids with density differences have been obtained at ROCOM and the Fortum PTS test facility. In generic experiments with injection of water with higher density performed at ROCOM, transition between momentum driven mixing as it is typical for pump start-up scenarios, and buoyancy driven mixing was found. The Froude number was identified as a proper transition criterion. Measurement data available from NPP Paks VVER-440 type reactor commissioning tests together with data from the ROCOM facility are used as a basis for the flow distribution studies. Alltogether, a unique data base has been created to be used for the validation of Computational Fluid Dynamics (CFD) codes for the application to turbulent mixing in nuclear reactors.
Keywords: turbulent mixing, boron dilution, pre-stressed thermal shock, computational fluid dynamics, numerical simulation, measurement data base, pressurised water reactor
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
  • Contribution to proceedings
    11th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 02.-06.10.2005, Avignon, France, 2-9516195-0-2

Publ.-Id: 7261 - Permalink


Interaction of Actinides with the Predominant Indigenous Bacteria in Äspö Aquifer - Interactions of Selected Actinides U(VI), Cm(III), Np(V) and Pu(VI) with Desulfovibrio äspöensis
Moll, H.; Merroun, M.; Stumpf, T.; Rossberg, A.; Geipel, G.; Selenska-Pobell, S.; Bernhard, G.;
Sulfate-reducing bacteria (SRB) frequently occur in the deep granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden. The new SRB strain Desulfovibrio äspöensis could be iso-lated. The objective of this project was to explore the basic interaction mechanisms of uranium, curium, neptunium and plutonium with cells of D. äspöensis DSM 10631T.
The cells of D. äspöensis were successfully cultivated under anaerobic conditions as well in an optimized bicarbonate-buffered mineral medium as on solid medium at 22 °C. To study the interaction of D. äspöensis with the actinides, the cells were grown to the mid-exponential phase (four days). The collected biomass was usually 1.0±0.2 gdry weight/L. The purity of the used bacterial cultures was verified using microscopic techniques and by applying the Amplified Ribosomal DNA Restriction Enzyme Analysis (ARDREA).
The interaction experiments with the actinides showed that the cells are able to remove all four actinides from the surrounding solution. The amount of removed actinide and the interaction mechanism varied among the different actinides.
The main U(VI) removal occurred after the first 24 h. The contact time, pH and [U(VI)]initial influence the U removal efficiency. The presence of uranium caused a damaging of the cell membranes. TEM revealed an accumulation of U inside the bacterial cell. D. äspöensis are able to form U(IV). A complex interaction mechanism takes place consisting of biosorption, bioreduction and bioaccumulation.
Neptunium interacts in a similar way. The experimental findings are indicating a stronger interaction with uranium compared to neptunium.
The results obtained with 242Pu indicate the ability of the cells of D. äspöensis to accumulate and to reduce Pu(VI) from a solution containing Pu(VI) and Pu(IV)-polymers.
In the case of curium at a much lower metal concentration of 3x10-7 M, a pure biosorption of Cm(III) on the cell envelope forming an inner-sphere surface complex most likely with organic phosphate groups was detected.
To summarize, the strength of the interaction of D. äspöensis with the selected actinides at pH 5 and actinide concentrations ≥ 10 mg/L ([Cm] 0.07 mg/L) follows the pattern: Cm > U > Pu >> Np.
Keywords: Uranium, Neptunium, Curium, Plutonium, Bacteria, Desulfovibrio äspöensis, TRLFS, LIPAS, XAS, XANES, EXAFS, TEM/EDX, Microbial Interactions, Surface Complexation, Biosorption, Bioreduction, Bioaccumulation, Microbiology, Cultivation, Liquid-liquid Extraction, Absorptionsspectroscopy
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-422 2005
  • Other report
    Dresden: Final Report, BMWA Project No. 02 E9491, 2005
    60 Seiten

Downloads:

Publ.-Id: 7260 - Permalink


Annual Report 2004 - Institute of Safety Research
Weiss, F. P.; Rindelhardt, U.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-420 2005

Downloads:

Publ.-Id: 7258 - Permalink


Annual report 2004 - Institute of Radiochemistry
Bernhard, G.; Foerstendorf, H.; Mibus, J.; Richter, A.; Ulrich, K.-U.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-419 2005

Downloads:

Publ.-Id: 7257 - Permalink


A simple mean-field model of polarity reversals
Stefani, F.; Gerbeth, G.;
The Earth magnetic field undergoes polarity reversals with a mean reversal rate that varies from zero during the supercrons to 4-5 per Myr in the present. Typically, these reversals have an asymmetric, saw-toothed shape. Recently, a bimodal distribution of the dipole moment has been observed with two peaks at about 4 x 10^22 (Am)^2 and at about twice that value. In an attempt to identify the basic mechanism of such reversals, we study a mean-field dynamo model with a spherically symmetric helical turbulence parameter alpha which is quenched by the magnetic energy and disturbed by additional noise. The basic features of geomagnetic polarity reversals are shown to be generic consequences of the dynamo action in the vicinity of branching points of the spectrum of the dynamo operator where two real eigenvalues coalesce and continue as complex conjugated pair of eigenvalues. The model yields long periods of constant polarity which are interrupted by asymmtric polarity reversals. In certain parameter regions, it exhibits a bimodal field distribution, and it gives a natural explanation of the correlation between polarity persistence time and field strength. Typical features of coherence resonance are identified in the dependence of the polarity persistence time on the noise.
  • Lecture (Conference)
    EGU General Assembly 2005, 24.-29.04.2005, Wien, Austria
  • Open Access LogoAbstract in refereed journal
    Geophysical Research Abstracts 7(2005), 07307

Publ.-Id: 7256 - Permalink


Modellierung von Luftblasen als Rotationsellipsoide anhand paarweiser ebener Projektionen
Hoppe, D.; Zaruba, A.; Prasser, H.-M.;
Eine in ruhendem Wasser aufsteigende Luftblase wird parallel zur Wasseroberfläche in zwei zueinander senkrechte horizontale Richtungen parallel projiziert. Diese beiden Projektionen werden zunächst als Ellipsen approximiert. Anhand der Ellipsen wird die Blase dann als Rotationsellipsoid modelliert. Das Rotationsellipsoid eignet sich zur Analyse des Verhaltens von Blasen auf ihrem Weg durch das Wasser. Dies wird an einem Ensemble schraubenartig aufsteigender Blasen verdeutlicht.

An air bubble rising in resting water is imaged by a parallel projection in two perpendicular horizontal directions. Initially, these two projections are approximated by ellipses. In the next step, the bubble is modelled as a spheroid matching the ellipses. The resulting spheroid is suitable to analyse the orientation of the symmetry axis of the bubble during its propagation through the liquid phase. The capabilities of the method is illustrated on an ensemble of bubbles rising on a helical trajectory.
Keywords: Luftblase, Ellipsenfit, Rotationsellipsoid Bubble, Ellipsenfit, Spheroid
  • Technisches Messen 2(2006), 103-108

Publ.-Id: 7255 - Permalink


Characterization of a SiC/SiC composite by X-ray diffraction, atomic force microscopy and positron spectroscopies
Brauer, G.; Anwand, W.; Eichhorn, F.; Skorupa, W.; Hofer, C.; Teichert, C.; Kuriplach, J.; Cizek, J.; Prochazka, I.; Coleman, P. G.; Nozawa, T.; Kohyama, A.;
A SiC/SiC composite is characterized by X-ray diffraction, atomic force microscopy, and various positron spectroscopies (slow positron implantation, positron lifetime, re-emission). It is found that beside its main constituent 3C-SiC the composite still must contain some graphite. In order to better interpret the experimental findings of the composite, a pyrolytic graphite sample was also investigated by slow positron implantation and positron lifetime spectroscopies. In addition, theoretical calculations of positron properties of graphite are presented.
Keywords: SiC/SiC composite, graphite, X-ray diffraction, atomic force microscopy, slow-positron spectroscopy, positron lifetime, positron affinity, positron re-emission
  • Invited lecture (Conferences)
    10th International conference on slow positron beam techniques for solids and surfaces, 19.-25.03.2005, Doha, Qatar
  • Applied Surface Science 252(2006), 3342-3351

Publ.-Id: 7254 - Permalink


Evidence of a low quartz structure at the SiO2/Si interface from coincidence Doppler broadening spectroscopy
Brauer, G.; Becvar, F.; Anwand, W.; Skorupa, W.;
Results from coincidence Doppler broadening measurements on various Si samples and Brazilian quartz having low quartz structure are presented with the aim to give further strong evidence for the existence of a low quartz structure, but not Si divacancies, at the SiO2/Si interface.
Keywords: slow-positron spectroscopy, coincidence Doppler broadening, silicon, Brazilian quartz, silicon divacancy, SiO2/Si interface
  • Lecture (Conference)
    10th International conference on slow positron beam techniques for solids and surfaces, 19.-25.03.2005, Doha, Qatar
  • Applied Surface Science (2007)

Publ.-Id: 7253 - Permalink


Three-dimensional modeling of EXAFS spectral mixtures by combining Monte Carlo Simulations and Target Transformation Factor Analysis
Rossberg, A.; Scheinost, A. C.;
We developed a new method for the three-dimensional modeling of Extended X-ray Absorption Fine Structure (EXAFS) spectra, which is suited to extract the local structure of aqueous metal complexes from spectral mixtures of several components. The new method combines two techniques: Monte Carlo simulation and Target Transformation Factor Analysis (TFA). Monte Carlo simulation is used to create random arrangements between the X-ray absorbing metal ion and the ligand atoms, and to calculate the theoretical EXAFS spectrum of each arrangement. The theoretical EXAFS spectrum is then introduced as test spectrum in the TFA procedure, in order to test whether the test spectrum is likely a component of the spectral mixtures or not. This coupled procedure is repeated, until the error in the test spectrum is minimized. The new method is thus able to isolate and refine the structure of complexes from spectral mixtures and to determine their relative concentrations, based solely on an estimate of the ligand structure. The performance of the proposed method was validated using uranium LIII-edge EXAFS spectra of binary mixtures of two uranium(VI) 3,4-dihydoxy benzoic acid complexes.
Keywords: EXAFS, Complexation, Speciation, Factor Analysis, Monte Carlo

Publ.-Id: 7252 - Permalink


Superconductivity at Ultralow Temperatures and its Interplay with Nuclear Magnetism
Herrmannsdörfer, T.; Pobell, F.;
In this article we will describe experiments at microkelvin temperatures which were performed to give - at least partly - answers to the following questions:

a. will all nonmagnetic metals become superconducting if refrigerated to low enough temperatures,
b. what is the impact of the weakest version of magnetism, nuclear magnetism, on superconductivity.

a. The first question has intrigued low temperature physicists since the discovery of superconductivity by H. Kamerlingh-Onnes in 1911. He wrote already in 1913 “There is left little doubt that if Au and Pt could be obtained absolutely pure, they could also pass into the superconducting state at helium temperatures”. And in 1929 W. Meissner wrote “At present it does not seem unlikely that, opposite to former expectations, all metals will become superconducting at low enough temperature”. One can pose the question in more general terms: “Is the electron-phonon interaction or another possible pairing mechanism in all metals strong enough so that they will eventually become superconducting, if this transition is not hindered by other phenomena, like magnetic properties?” After all, somehow the conduction electrons have to get rid of their entropy when approaching absolute zero, and one way is a transition to a superconducting state.

Looking at the periodic system of the elements, one realizes that superconductivity is rather the rule than the exception. Most metallic elements become superconducting if they show no magnetic order like some 3d- and 4f-elements. Even most insulators, like S or O, if forced into a metallic state by high pressure, eventually enter the superconducting state. When we started our research, there were only two small “islands” in the periodic system of the elements where metals had shown neither a superconducting nor a magnetic transition: some alkali and alkaline-earth metals and the noble and platinum metals (Cu, Ag, Au, Rh, Pd, Pt).

b. Superconductivity in its simplest version - s-wave, singlet pairing of conduction electrons mediated by electron-phonon interaction - is counteracted by magnetic interactions. This has been well demonstrated by the depression of the superconducting transition temperature when magnetic impurities are introduced. The large variety of “magnetic interactions” has varying impacts on superconductivity. The clearest demonstration of its detrimental impact is the vanishing of the superconducting state when a superconducting metal enters a ferromagnetic state. This was demonstrated in 1977 by Matthias et al. for ErRh4B4 and by Ishikawa and Fischer for HoMo8S8.

The weakest known version of magnetism is caused by the interaction of nuclear magnetic moments. Hence, it was a natural question to investigate the impact of nuclear ferromagnetism on superconductivity. This investigation became possible when we had observed a nuclear ferromagnetic transition of the superconductor AuIn2 at 35 µK in 1994. The results of the investigation of the interplay between nuclear ferromagnetism and superconductivity in AuIn2 - some of it are not yet understood - will be described in Sect. 5. Further investigations of the impact of nuclear paramagnetism in AuAl2, Al, Sn, AuIn2, In, Rh, as well as TiH2+x on superconductivity are discussed in Sect. 6. In Sect. 7, a first study of the interplay of hyperfine enhanced nuclear magnetism and superconductivity is presented. Eventually, in Sect. 8, we will summarize our results.

The experiments described in this article have been performed at the Forschungszentrum (formerly: Kernforschungsanlage) Jülich and at the University of Bayreuth
  • Contribution to external collection
    in: Frontiers in Superconducting Materials, Heidelberg: Springer Verlag, 2005, 71

Publ.-Id: 7251 - Permalink


High-intensity terahertz radiation from a microstructured large-area photoconductor
Dreyhaupt, A.; Winnerl, S.; Dekorsy, T.; Helm, M.;
We present a planar large-area photoconducting emitter for impulsive generation of terahertz (THz) radiation. The device consists of an interdigitated electrode metal-semiconductor-metal (MSM) structure which is masked by a second metallization layer isolated from the MSM electrodes. The second layer blocks optical excitation in every second period of the MSM finger structure. Hence charge carriers are excited only in those periods of the MSM structure which exhibit a unidirectional electric field. Constructive interference of the THz emission from accelerated carriers leads to THz electric field amplitudes up to 85 V/cm when excited with fs optical pulses from a Ti:sapphire oscillator with an average power of 100 mW at a bias voltage of 65 V applied to the MSM structure. The proposed device structure has a large potential for large-area high-power THz emitters.

Publ.-Id: 7250 - Permalink


11B-NMR studies of weakly ferromagnetic BaB6
Mushkolaj, S.; Gavilano, J. L.; Rau, D.; Ott, H. R.; Bianchi, A.; Fisk, Z.;
BaB6 is a weakly ferromagnetic material with a Curie temperature TC well above room temperature. From the results of d.c. magnetization measurements on single crystalline BaB6, the saturation magnetization at low temperatures is 8\times 10-4(\mu B/f.u.), in line with other weak ferromagnets of the hexaboride series. The 11B-NMR spectra measured on a collection of single crystals of BaB6 yield a quadrupolar frequency of 472 KHz, in good agreement with calculated field gradients for this type of materials. The central 11B-NMR transition consists of two partially resolved signals, where the frequency displacement between them is of the order of 10 KHz. One of the signals exhibits a positive, the other a negative frequency shift, both of the order of 50 ppm. Between 7 K and room temperature these shifts do not vary with temperature. The temperature dependence of the spin-lattice relaxation rate T1-1(T) at the B sites is similar to that of other alkaline-earth hexaborides.
  • Open Access LogoActa Physica Polonica B 34(2003)22, 1537-1537

Publ.-Id: 7249 - Permalink


NMR studies of YbB6
Gavilano, J. L.; Mushkolaj, S.; Rau, D.; Ott, H. R.; Bianchi, A.; Fisk, Z.;
We report results of DC-magnetization and 11B-NMR measurements on single crystalline YbB6. The magnetization data at temperatures between 4 and 300 K reveal weak ferromagnetic order with a TC>300 K. It involves very small ordered moments, of the order of 0.002 µB/f.u., representing only a small fraction of the effective paramagnetic moment per formula unit that is indicated by the magnetic susceptibility. The latter can be accounted for by assuming that 2% of all the Yb atoms adopt the Yb+3 configuration. Since almost all the Yb ions adopt the divalent configuration one expects YbB6 to be a poor metal.
Keywords: NMR; Magnetism; Hexaborides
  • Physica B 329-333(2003)Part II, 570-571

Publ.-Id: 7248 - Permalink


Atomistic simulation of defects in Si: migration of di- and tri-interstitials
Posselt, M.;
The state-of-the-art interpretation of physical processes during post-implantation annealing, such as defect evolution, transient-enhanced dopant diffusion and dopant activation, assumes that ion implantation produces only single vacancies and self-interstitials, and that these are the only mobile intrinsic defects. Theoretical investigations show that both assumptions may be not correct. The talk presents results of comprehensive atomistic simulations on the properties of di- and tri-interstitials. It is focused on the migration of these defects and on the atomic mechanisms of the defect diffusion. The results of the atomistic simulations are compared with experimental data. The fact that the simulations predict a high di-interstitial mobility may lead to a re-interpretation of some experimental results.
Keywords: intrinsic defects, silicon, computer simulation
  • Lecture (others)
    43. Arbeitskreis Punktdefekte, 02.-03.03.2005, Dresden, Deutschland

Publ.-Id: 7247 - Permalink


Low-temperature thermal conductivity of CaB6 and EuB6
Gianno, K.; Sologubenko, A. V.; Ott, H. R.; Bianchi, A. D.; Fisk, Z.;
The thermal conductivities of stoichiometric CaB6, vacancy-doped Ca1-B6, and EuB6have been measured between 6 and 300 K. All our data may be rather well described across the entire temperature regime covered on the basis of a Debye-type relaxation-time approximation and by assuming the concurring influence of various scattering channels on the mean free path of the phonons. An unusual and strong resonance in the scattering rate of the phonons of all investigated materials is attributed to a strong interaction between acoustic itinerant and localized modes, the latter arising from oscillations of the metal cations around their equilibrium position.
  • Journal of Physics: Condensed Matter 15(2003)40, 6739-6748

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Publ.-Id: 7246 - Permalink


Possible Fulde-Ferrell-Larkin-Ovchinnikov superconducting state in CeCoIn5
Bianchi, A.; Movshovich, R.; Capan, C.; Pagliuso, P. G.; Sarrao, J. L.;
We report observation of the specific heat anomaly within the superconducting state of the heavy fermion CeCoIn5. It appears in the vicinity of the superconducting critical field Hc2, where the superconducting transition changes from second to first order, above 10 T for H || [1 1 0] and H || [1 0 0], and above 4.7 T for H || [0 0 1], and at temperatures on the order of 0.1Tc. We interpret the anomaly within the superconducting state as a signature of a Fulde–Ferrell–Larkin–Ovchinnikov FFLO inhomogeneous superconducting state.
Keywords: FFLO; Heavy fermion; Superconductivity; Unconventional; Inhomogeneous superconducting state

Publ.-Id: 7245 - Permalink


FFLO superconducting state in CeCoIn5
Bianchi, A.; Movshovich, R.; Capan, C.; Lacerda, A.; Pagliuso, P. G.; Sarrao, J. L.;
We present specific heat data for the heavy fermion superconductor CeCoIn5 close to the upper critical field Hc2 for magnetic fields applied along the [1 0 0] crystallographic axis. For fields above 10 T, the superconducting phase transition becomes first-order. In the same field range, we observe a second specific heat anomaly within the superconducting state, which we attribute to a Fulde–Ferrell–Larkin–Ovchinnikov state.
Keywords: Heavy fermion superconductors; Superconductivity phase diagrams; Magnetic field-dependent specific heat
  • Journal of Magnetism and Magnetic Materials 272-76(2004), 140-141

Publ.-Id: 7244 - Permalink


Electron-spin domains - Magnetic enhancement of superconductivity
Movshovich, R.; Bianchi, A.; Capan, C.; Jaime, M.; Goodrich, R. G.;
Magnetic enhancement of superconductivity
  • Nature (2004)427, 802-802

Publ.-Id: 7243 - Permalink


First-order transition from a Kondo insulator to a ferromagnetic metal in single crystalline FeSi1-xGex
Yeo, S.; Nakatsuji, S.; Bianchi, A. D.; Schlottmann, P.; Fisk, Z.; Balicas, L.; Stampe, P.; Kennedy, R. J.;
The phase diagram of FeSi1-xGex, obtained from magnetic, thermal, and transport measurements on single crystals, shows a discontinuous transition from Kondo insulator to ferromagnetic metal with x at a critical concentration, xc ≈ 0.25. The gap of the insulating phase strongly decreases with x. The specific heat γ coefficient appears to track the density of states of a Kondo insulator. The phase diagram is consistent with an insulator-metal transition induced by a reduction of the hybridization with x in conjunction with disorder on the Si=Ge ligand site
  • Physical Review Letters 91(2003)046401, 1-4
    DOI: 10.1103

Publ.-Id: 7242 - Permalink


Possible Fulde-Ferrell-Larkin-Ovchinnikov superconducting state in CeCoIn5
Bianchi, A.; Movshovich, R.; Capan, C.; Pagliuso, P. G.; Sarrao, J. L.;
We report specific heat measurements of the heavy fermion superconductor CeCoIn5 in the vicinity of
the superconducting critical field Hc2, with magnetic fields in the [110], [100], and [001] directions, and at temperatures down to 50 mK. The superconducting phase transition changes from second to first
order for fields above 10 T for H ║ [110] and H ║ [100]. In the same range of magnetic fields, we observe
a second specific heat anomaly within the superconducting state. We interpret this anomaly as a
signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting state. We obtain similar results for H ║ [100], with the FFLO state occupying a smaller part of the phase
diagram.

Publ.-Id: 7241 - Permalink


Avoided antiferromagnetic order and quantum critical point in CeCoIn5
Bianchi, A.; Movshovich, R.; Vekhter, I.; Pagliuso, P. G.; Sarrao, J. L.;
We measured the specific heat and resistivity of heavy fermion CeCoIn5 between the superconducting critical field c2 = 5 T and 9 T, with the field in the [001] direction, and at temperatures down to 50 mK. At 5 T the data show a non-Fermi liquid (NFL) behavior down to the lowest temperatures. At the field above 8 T the data exhibit a crossover from the Fermi liquid to a non-Fermi liquid behavior. We analyzed the scaling properties of the specific heat and compared both the resistivity and the specific heat with the predictions of a spin-fluctuation theory. Our analysis leads us to suggest that the NFL behavior is due to incipient antiferromagnetism (AFM) in CeCoIn5 with the quantum critical point in the vicinity of Hc2. Below Hc2 the AFM phase which competes with the paramagnetic ground state is superseded by the superconducting transition.
  • Physical Review Letters 91(2003)257001, 1-4
    DOI: 10.1103

Publ.-Id: 7240 - Permalink


Magneto-optical Kerr effect in Eu1-xCaxB6
Caimi, G.; Broderick, S.; Ott, H. R.; Degiorgi, L.; Bianchi, A. D.; Fisk, Z.;
We have measured the magneto-optical Kerr rotation of ferromagnetic Eu1-xCaxB6 with x=0.2 and 0.4, as well as of YbB6 serving as the nonmagnetic reference material. As previously for EuB6, we could identify a feature at 1 eV in the Kerr response which is related with electronic transitions involving the localized 4 f electron states. The absence of this feature in the data for YbB6 confirms the relevance of the partially occupied 4 f states in shaping the magneto-optical features of Eu-based hexaborides. Disorder by Ca-doping broadens the itinerant charge carrier contribution to the magneto-optical spectra.
  • Physical Review B 69(2004)012406, 1-4
    DOI: 10.1103

Publ.-Id: 7239 - Permalink


Optical evidence for a spin-filter effect in the charge transport of Eu0.6Ca0.4B6
Perucchi, A.; Caimi, G.; Ott, H. R.; Degiorgi, L.; Bianchi, A. D.; Fisk, Z.;
We have measured the optical reflectivity R(ω) of Eu0.6Ca0.4B6 as a function of temperature (T) between 1.5 and 300 K and in external magnetic fields (H) up to 7 T. R(ω) increases with decreasing T and increasing H field, but the plasma edge feature does not exhibit the sharp onset and steep slope that is observed in EuB6. The analysis of the H-field dependence of the low-T optical conductivity confirms the previously observed exponential decrease of the electrical resistivity upon increasing bulk magnetization at constant T. The individual exponential magnetization dependences of the plasma frequency and scattering rate are also extracted from the optical data.
  • Physical Review Letters 92(2004)067401, 1-4
    DOI: 10.1103

Publ.-Id: 7238 - Permalink


Weak ferromagnetism in CaB6
Bennett, M. C.; van Lierop, J.; Berkeley, E. M.; Mansfield, J. F.; Henderson, C.; Aronson, M. C.; Young, D. P.; Bianchi, A.; Fisk, Z.; Balakirev, F.; Lacerda, A.;
We have combined the results of magnetization and Hall effect measurements to conclude that the ferromagnetic moments of lightly doped CaB6 samples display no systematic variation with electron doping level.
Removal of the surface with acid etching substantially reduces the measured moment, although the Hall constant and resistivity are unaffected, indicating that the ferromagnetism largely resides on and near the sample surface. Electron microprobe experiments reveal that Fe and Ni are found at the edges of facets and growth steps, and on other surface features introduced during growth. Our results indicate that the weak ferromagnetism previously reported in undoped CaB6 is most likely of extrinsic origin.
  • Physical Review B 69(2004)132407, 1-4
    DOI: 10.1103

Publ.-Id: 7237 - Permalink


Transport and thermodynamic properties of Sr3Ru2O7 near the quantum critical point
Zhou, Z. X.; Mccall, S.; Alexander, C. S.; Crow, J. E.; Schlottmann, P.; Bianchi, A.; Capan, C.; Movshovich, R.; Kim, K. H.; Jaime, M.; Harrison, N.; Haas, M. K.; Cava, R. J.; Cao, G.;
The specific heat and electrical resistivity of Sr3Ru2O7 single crystals are measured in several magnetic
fields applied along the c axis for temperatures below 2 K and at fields up to 17 T. Near the critical metamagnetic
field at B1*~7.8 T, the electronic specific heat divided by temperature increases logarithmically as the
temperature decreases, over a large range of T, before saturating below a certain T* (which is sample dependent),
indicating a crossover from a non-Fermi liquid (NFL) region dominated by quantum critical fluctuations
to a Fermi liquid (FL) region. This crossover from a NFL to a FL state is also observed in the resistivity data
near the critical metamagnetic field for Ic and Bc. The coefficient of electronic specific heat, γ, plotted as a
function of field shows two peaks, consistent with the two metamagnetic transitions observed in magnetization
and magnetic torque measurements. At the lowest temperatures, a Schottky-like upturn with decreasing temperature
is observed. The coefficient of the Schottky anomaly exhibits a field dependence similar to that of γ,
implying an influence by the electrons near the Fermi surface on the Schottky level splitting.
  • Physical Review B 69(2004)140409, 1-4
    DOI: 10.1103

Publ.-Id: 7236 - Permalink


Anisotropy of Thermal Conductivity and Possible Signature of the Fulde-Ferrell-Larkin-Ovchinnikov state in CeCoIn5
Capan, C.; Bianchi, A.; Movshovich, R.; Christianson, A. D.; Malinowski, A.; Hundley, M. F.; Lacerda, A.; Pagliuso, P. G.; Sarrao, J. L.;
We have measured the thermal conductivity of the heavy-fermion superconductor CeCoIn5 in the vicinity of the upper critical field, with the magnetic field perpendicular to the c axis. Thermal conductivity displays a discontinuous jump at the superconducting phase boundary below critical temperature T0≈1 K, indicating a change from a second- to first-order transition and confirming the recent results of specific heat measurements on CeCoIn5. In addition, the thermal conductivity data as a function of field display a kink at a field Hk below the superconducting critical field, which closely coincides with the recently discovered anomaly in specific heat, tentatively identified with the appearance of the spatially inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state. Our results indicate that the thermal conductivity is enhanced within the FFLO state, and call for further theoretical investigations of the order parameter’s real-space structure (and, in particular, the structure of vortices) and of the thermal transport within the inhomogeneous FFLO state.
  • Physical Review B 70(2004)134513, 1-7
    DOI: 10.1103

Publ.-Id: 7235 - Permalink


Percolation and the Colossal Magnetoresistance of Eu-Based Hexaboride
Wigger, G. A.; Beeli, C.; Felder, E.; Ott, H. R.; Bianchi, A. D.; Fisk, Z.;
Upon substituting Ca for Eu in the local-moment ferromagnet EuB6, the Curie temperature TC
decreases substantially with increasing dilution of the magnetic sublattice and is completely suppressed
for x ≤0:3. The Ca substitution leads to significant changes of the electronic properties across the
EuxCa1-xB6 series. Electron microscopy data for x ≈ 0.27 indicate a phase separation into Eu- and
Ca-rich clusters of 5 to 10 nm diameter, leading to percolation-type phenomena in the electrical
transport properties. The related critical concentration xp is approximately 0.3. For x ≈ 0.27, we
observe colossal negative magnetoresistance effects at low temperatures, similar in magnitude as those
reported for manganese oxides.
  • Physical Review Letters 93(2004)147203, 1-4
    DOI: 10.1103

Publ.-Id: 7234 - Permalink


Non-Fermi Liquid behavior in CeIrI5 near a metamagnetic transition
Capan, C.; Bianchi, A.; Ronning, F.; Lacerda, A.; Thompson, J. D.; Pagliuso, P. G.; Sarrao, J. L.; Movshovich, R.;
We present a specific heat and resistivity study of CeIrIn5 in magnetic fields up to 17 T and temperature down to 50 mK. Both quantities were measured with the magnetic field parallel to the c axis (H║[001]) and within the a-b plane (H┴[001]). Non-Fermi-liquid (NFL) behavior develops above 12 T for H║[001]. The Fermi-liquid state is much more robust for H║[001] and is suppressed only moderately at the highest applied field. Based on the observed trends and the proximity to a metamagnetic phase transition, which exists at fields above 25 T for H║[001], we suggest that the observed NFL behavior in CeIrIn5 is a consequence of a metamagnetic quantum critical point.
  • Physical Review B 70(2004)180502, 1-4
    DOI: 10.1103

Publ.-Id: 7233 - Permalink


First Results from SHIP Experiment
Bagryansky, P. A.; Anikeev, A. V.; Ivanov, A. A.; Lizunov, A. A.; Maximov, V. V.; Murakhtin, S. V.; Stepanov, D. N.; Noack, K.; Prikhodko, V. V.; Solomakhin, A. L.;
At present, the GDT facility of the Budker Institute of Nuclear Physics Novosibirsk is being upgraded. The first stage of the upgrade is the Synthesized Hot Ion Plasmoid (SHIP) experiment. It aims, on the one hand, at the investigation of plasmas the parameters of which are expected to appear in the region of high neutron production in a GDT based fusion neutron source as proposed by the Budker Institute and, on the other hand, at the investigation of plasmas the parameters of which have never been achieved before in magnetic mirrors.
The experiment is performed in a small mirror section which is installed at the end of one side of GDT. The magnetic field on axis is in the range of 0.5-20 Tesla and the mirror ratio is 1.2-1.4. The mirror is filled with background plasma streaming in from the central cell. This plasma component is maxwellized and has an electron temperature of about 100 eV. Two neutral beam injectors perpendicularly inject a total current of about 50 Atom Amperes of deuterium neutrals with an energy of 20 keV
as a pulse with a duration of about 1 ms. Ionization of the beams generates the high-energy ion component. The device has been equipped with several diagnostic methods which are successfully used in GDT experiments.
The paper presents first results of plasma parameter measurements in the SHIP experiment.
Keywords: gas dynamik trap, magnetic mirror, GDT facility, SHIP experiment, neutral beam injection, plasma diagnostic
  • Contribution to proceedings
    5th Int. Conf. on Open Magnetic Systems for Plasma Confinement,, 05.-09.07.2004, Novosibirsk, Russia
    Open Magnetic Systems for Plasma Confinement, Dexter, Michigan: Beljan Ltd.
  • Lecture (Conference)
    5th Int. Conference on Open Magnetic Systems for Plasma Confinement, 05.-09.07.2004, Novosibirsk, Russia
  • Fusion Science and Technology 47(2005)1T, 59-62

Publ.-Id: 7229 - Permalink


Magnetic domain structure of micro-patterned PtMn/CoFe exchange bias bilayers
Liedke, M. O.; Potzger, K.; Hillebrands, B.; McCord, J.; Rickart, M.; Freitas, P.; Fassbender, J.ORC
Using magnetron sputter deposition a number of glass/Ta 7nm/PtMn 20nm/CoFe 4nm/Ta 4nm samples with large exchange bias field were prepared for magnetic pattering investigations. By means of optical lithography and physical etching several patterns with decreasing lateral sizes of either the elements or the spacing between the elements were prepared. The largest square is 50 x 50 µm2 and the smallest only 1 µm2. The separating lines range from 10 µm to 2 µm width. The magnetic characterization of the samples was done by VSM and MOKE. Kerr microscopy and MFM investigations in an applied magnetic field have been performed in order to get a deeper understanding of the domain pattern. All images show a monodomain magnetization state in zero magnetic field. The shape of the structure itself dose not influence the magnetization direction. The shape anisotropy contribution is thus smaller than the unidirectional anisotropy given by the exchange bias. In addition 5 keV He+ ion irradiation was used to decrease exchange bias field value and thereby modify the ratio between unidirectional and shape anisotropy. The magnetic domain structure is investigated as a function of this ratio.
Keywords: magnetism, exchange bias, magnetization reversal, magnetic force microscopy, Kerr microscopy, magnetic patterning
  • Poster
    The European Conference on Physics of Magnetism'05, 24.-27.06.2005, Poznan, Poland

Publ.-Id: 7228 - Permalink


Velocity measurements and concentration field visualizations in natural convection copper electrolysis under magnetic field influence
Weier, T.; Hüller, J.; Gerbeth, G.; Weiss, F.-P.;
The effect of magnetic fields on momentum and mass transfer in electrochemical processes has been studied by means of Digital Particle Image Velocimetry (DPIV), shadowgraphy and mean current
density measurements.

Chronoamperometric copper electrolysis was carried out in a small electrolytic cell (29x46x6 mm) made mainly from PMMA. The sidewalls forming the vertical electrodes consist of thin copper plates behind
which permanent magnets could be fixed. The Lorentz force generated from the faradaic currents and the permanent magnets field has been always parallel to the electrodes. Depending on the orientation of the magnets, downwards or upwards directed Lorentz forces could be generated.

The moderate magnetic field of permanent magnets placed behind the electrodes, although its action is limited to the vicinity of the electrodes, is able to promote convection in the whole cell. Flow
structures measured by DPIV compare very well with the patterns of the concentration field given by shadography. Steady state limiting current densities as well as initially instationary current density
values can be explained by the corresponding velocity measurements. It will be shown that the interplay of Lorentz and buoyancy forces is substantial for the resulting flow structure.
  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia

Publ.-Id: 7227 - Permalink


Status of the GDT Experiment and Future Plans
Abdrashitov, A.; Abdrashitov, G.; Anikeev, A.; Bagryansky, P.; Beklemishev, A.; Deichuli, P.; Ivanov, A.; Korepanov, S.; Maximov, V.; Murakhtin, S.; Lizunov, A.; Prikhodko, V.; Kapitonov, V.; Kolmogorov, V.; Khilchenko, A.; Mishagin, V.; Savkin, V.; Shoukajev, A.; Shulzhenko, G.; Solomakhin, A.; Sorokin, A.; Stepanov, D.; Stupishin, N.; Tsidulko, Y.; Zouev, A.; Noack, K.; Fiksel, G.; Den Hartog, D.;
In recent experiments, on-axis transverse beta exceeding 0.4 in the fast ion turning points near the end mirrors has been achieved in the GDT experiment with 4 MW injection of 15-17 keV deuterium neutral beams at the center of the device. Neither enhanced transverse losses of the plasma nor anomalies in the fast ion scattering and slowing down were observed. The measured beta value is close to that needed in the versions of the GDT based 14 MeV neutron source. At the same time, the electron
temperature for given injection power and pulse duration is limited to 100-130 eV. Its further increase is planned after upgrading the injection system and increasing the magnetic field at the center of the device up to 0.3 T. The upgrade of the injection system assumes that the neutral beam power incident on the plasma will be increased up to 9-10 MW and the pulse duration is extended from 1.2 to 5 ms. According to the results
of numerical simulations, for the extended pulse duration
a plasma steady state will be achieved with electron temperature of 250-320 eV depending upon the assumptions on the transverse energy loss rate. Future experiments at the GDT upgrade are discussed in the paper.
Keywords: gasdynamic trap, GDT experiment, neutral beam injection, transverse plasma beta, fusion, neutron source
  • Lecture (Conference)
    5th Internationale Conference on Open Magnetic Systems for Plasma Confinement, 05.-09.07.2004, Novosibirsk, Russia
  • Contribution to proceedings
    5th Internationale Conference on Open Magnetic Systems for Plasma Confinement,, 05.-09.07.2004, Novosibirsk, Russia
    Status of the GDT Experiment and Future Plans, Dexter: Beljan Ltd.
  • Fusion Science and Technology 47(2005)1T, 27-34

Publ.-Id: 7226 - Permalink


Irreversible magnetization deep in the vortex-liquid state of a 2D superconductor at high magnetic fields
Maniv, T.; Zhuravlev, V.; Wosnitza, J.; Hagel, J.;
The remarkable phenomenon of weak magnetization hysteresis loops, observed recently deep in the vortex-liquid state of a nearly two-dimensional (:213) superconductor at low temperatures and high magnetic fields, is shown to reflect the existence of an unusual vortex-liquid state, consisting of collectively pinned crystallites of easily sliding vortex chains.
Keywords: Vortices, Lattices, Systems
  • Journal of Physics: Condensed Matter 16(2004)41, 429-435

Publ.-Id: 7225 - Permalink


Fermi-surface reconstruction close to a pressure-induced metal-insulator transition
Wosnitza, J.; Hagel, J.; Stockert, O.; Pfleiderer, C.; Schlueter, J. A.; Mohtasham, J.; Gard, G. L.;
We report on a detailed investigation of the pressure-dependent structural and electronic properties close to the pres-sure-induced metal-insulator transition of the quasi-two-dimensional organic superconductor beta"-(BEDT-TTF)2SF5CH2CF2SO3, where BEDT-TTF stand for bisethylenedithio-tetrathiafulvalene (or ET for short). Although the pressure-dependent hysteresis of the metal-insulator transition suggests a structural origin, no major crystallo-graphic modifications could be detected by neutron-scattering experiments. Shubnikov-de Haas (SdH) experiments, on the other hand, show that a reconstructed band structure precedes the phase transition to the insulating state. A new SdH frequency with a rather small effective mass appears.
Keywords: organic superconductors; band structure; metal-insulator transition
  • Journal de Physique IV 114(2004), 277-281

Publ.-Id: 7223 - Permalink


Transport properties of CeBiPt in magnetic fields up to 60 T
Wosnitza, J.; Hagel, J.; Kozlova, N.; Eckert, D.; Müller, K.-H.; Mielke, C. H.; Goll, G.; Yoshino, T.; Takabatake, T.;
Electrical-transport measurements of the semimetal CeBiPt in magnetic fields up to 60 T reveal a drastic change of the electronic band structure. The oscillating Shubnikov-de Haas signal vanishes above about 25 T although the quantum limit is not yet reached. Above this field the magneto resistance rises strongly independent of angle and temperature. These unique features are caused by the Cc 4f electrons as evidenced by the absence of any unconventional behavior in the sister compound LaBiPt.
Keywords: Shubnikov-de Haas effect, Fermi-surface studies, magnetoresistance, CeBiPt, LaBiPt
  • Physica B 346-347(2004), 127-131

Publ.-Id: 7222 - Permalink


Neutron-proton pairing in rotating N similar to Z nuclei: dominance of the isovector component
Afanasjev, A.; Frauendorf, S.;
Theoretical calculations of rotating N approximate to Z nuclei with A = 58 - 80 within the cranked Nilsson+Strutinsky approach, cranked relativistic mean field and cranked relativistic Hartree+Bogoliubov theories show good agreement with experiment. They point on the presence of the isovector t = 1 np-pairing, but do not show any indications of the isoscalar t = 0 np-pairing.
  • Nuclear Physics A 746(2004), 575C-578C

Publ.-Id: 7221 - Permalink


Shell stabilization and the survival of heavy compound nuclei
Heinz, A.; Schmidt, K.; Junghans, A.;
Knowledge of the influence of nuclear shell structure on the survival probability of heavy compound nuclei against fission is important for a quantitative understanding of the production rates of spherical super-heavy elements (SHE). Fission probabilities of N = 126 isotones beyond astatine can be used as test cases for the production of spherical super-heavy elements, as those isotones possess a strong shell correction energy and are highly fissile. Here, we report on two new experimental approaches which probe the effect of the closed neutron shell at N = 126 on the competition between fission and particle evaporation using projectile fragmentation and electromagnetic-induced fission of radioactive beams. We conclude that these nuclei lose at least a great part of their stability against fission at low excitation energies and angular momenta-mostly due to the influence of collective contributions in the level density. Implications on the production of spherical SHE will be!
discussed.
  • Nuclear Physics A 746(2004), 483C-486C

Publ.-Id: 7220 - Permalink


New determination of the Be-7(p,gamma)B-8 S-factor
Junghans, A.; Mohrmann, E.; Snover, K.; Et, A.;
We present new measurements of the Be-7(p,gamma)B-8 cross section from (E) over bar (cm) = 116 to 2460 keV. Our new measurements lead to S-17(0) = 22.1 +/- 0.6(expt) +/- 0.6(theor) eV b based on data from (E) over bar (cm) = 116 to 362 keV, where the central value is based on the theory of Descouvemont and Baye. We compare our results to other S-17(0) values extracted from both direct (Be-7(p, gamma)B-8) and indirect (Coulomb dissociation and heavy-ion reaction) measurements, and show that the results of these 3 types of experiments are not mutually compatible. We recommend a "best" value, S-17(0) = 21.4 +/- 0.5(expt) +/- 0.6(theor) eV b, based on the mean of all modern direct measurements below the 1(+) resonance.
  • Nuclear Physics A 746(2004), 210C-214C

Publ.-Id: 7219 - Permalink


Optical characterization of beta-FeSi2 layers formed by ion beam synthesis
Ayache, R.; Bouabellou, A.; Richter, E.;
Thin beta-FeSi2 layers have been prepared by ion beam synthesis (IBS) on (111)Si substrates. The obtained samples have been characterized by means of infrared and Raman spectroscopies. The infrared (IR) transmittance spectra show the absorption at 310 cm(-1) as an indication of the initial nucleation of beta-FeSi2 precipitates during the implantation of iron into silicon substrate. The main feature of the photoluminescence (PL) measurements at 12 K in the beta-FeSi2/(111)Si samples annealed at 850 degreesC for 90 min is an intense peak localized at 0.811 eV. This peak is assigned to optical radiative transitions intrinsic to beta-FeSi2. (C) 2004 Elsevier Ltd. All rights reserved.
  • Materials Science in Semiconductor Processing 7(2004)4-6, 463-466

Publ.-Id: 7218 - Permalink


Mesoscopic dots as collective terahertz oscillators
Metzner, C.; Stehr, D.;
Electrons confined in a flat semiconductor quantum dot with a parabolic in-plane potential act like a collective many-particle oscillator under coherent intraband excitation. We investigate theoretically the properties of these oscillators under a simultaneous scale transformation of the lateral dimensions and the electron occupation number. As the lateral size increases from a few nm (typical for self-assembled dots) to the mesoscopic regime, the physics of the system is changing qualitatively: Quantization effects gradually lose importance against Coulomb interactions and eventually the electron lake in a mesoscopic dot resembles a classical Wigner liquid. This parabolically confined "Wigner lake" behaves to the outside like a form-elastic "superparticle" of high charge. It can be coherently controlled by THz dipole radiation just like a single electron, but with reduced Brownian diffusion in the phonon heat bath. We propose a flexible method to fabricate single mesoscopic!
dots of a controlled shape, Coulomb-coupled groups of dots, and almost arbitrary potential landscapes, using current semiconductor technology. As a first example, the collective modes of two Coulomb-coupled superparticles in neighboring dots are calculated. Also, we consider the possibility of steering a superparticle with shaped laser pulses to follow any complex two-dimensional orbit.
  • Physical Review B 7019(2004)19, 5433-5433

Publ.-Id: 7217 - Permalink


Numerical investigation of transition control in low conductive fluids
Albrecht, T.; Grundmann, R.; Mutschke, G.; Gerbeth, G.;
We investigate numerically the transition to turbulence in a flat-plate boundary layer controlled by electromagnetic forces. The fluid considered is incompressible, Newtonian and low conductive. Similar to boundary layer suction, when applying a steady, wall-parallel, and streamwise orientated Lorentz force, (as suggested by Gailitis and Lielausis [1] in the early 1960s) the Blasius velocity profile is transformed to an exponential one gaining a critical Reynolds number which is increased by two orders of magnitude.

Two and three dimensional direct numerical simulation (DNS) of both linear and nonlinear stages of the transition process were performed, as well as alinear stability analysis (LSA) of the calculated intermediate velocity profiles. DNS and preliminary LSA results confirm the expected increased stability of the controlled flow. Depending on Lorentz force strength transition to turbulence is delayed or even stopped. Suprisingly, both DNS and LSA results suggest interesting stability characteristics of the intermediate velocity profiles.

In DNS, to initiate transition, small amplitude disturbances are introduced by means of an oscillating body force within a small region near the inflow boundary, forming Tollmien-Schlichting waves (TSW) which grow and decay in uncontrolled case corresponging to linear stability theory. When applying Lorentz force, TSW of all investigated frequencies 0.4 <= F+ <= 3.75 are damped within the computational domain extending over 900 times the inflow displacement thickness d1i. Reynolds number, based on d1i, is 360. The decay rate based on the maximum rms value in wall-normal direction of the streamwise velocity component, is maximum in a region near the onset of control and decreases as the velocity profile approaches the exponential state. This observation could suggest that in the intermediate region there are profiles more stable than the exponential one, although we are aware that from these decay rates one cannot conclude directly the stability of a velocity profile, notably its critical reynolds number. However, our assumption is confirmed by preliminary LSA results where critical Reynolds numbers of intermediate profiles are found to be larger than for the exponential profile.

By three dimensional DNS we show that transition to turbulence can be stopped even in it's late stage. While the evolution of Lambda vorticies from former two dimensional TSW remains almost unchanged, the emerge of Omega vorticies is supressed with increasing Lorentz force strength, thus relaminarizing the flow.

[1] A. Gailitis, O. Lielausis: On a possibility to reduce the hydrodynamic resistance of a plate in an electrolyte. Applied Magnetohydrodynamics, Reports of the Physics Institute Riga, Vol. 12, pp. 143-146, 1961
Keywords: Fluid Mechanics, Magnetohydrodynamics, Stability, Transition, Control
  • Poster
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
    1(2005), 145-148

Publ.-Id: 7216 - Permalink


Rossendorf Beamline at ESRF: Biannual Report 2003/2004
Scheinost, A. C.; Schell, N.; (Editors) Keywords: EXAFS Synchrotron diffraction x-ray absorption spectroscopy radiochemistry actinides materials sciences
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-418 2005

Downloads:

Publ.-Id: 7215 - Permalink


TRIDYN simulation of target poisoning in reactive sputtering
Rosén, D.; Katardjiev, I.; Berg, S.; Möller, W.;
During reactive sputter deposition, target "poisoning", i.e. the formation of a compound layer at the target surface, may reduce the sputter erosion rate substantially and thereby represent a major limitation to achieve high deposition rates. In order to investigate the formation of the poisoned layer, the TRIDYN program has been employed to simulate the processes that take place at the target surface during sputtering at ion energies which are typical for a magnetron discharge, in a typical gas mixture of Ar with a small (<10%) addition of a reactive gas (e.g. oxygen). The bulk of the sputtering results from Ar ion bombardment, while the reactive gas ions contribute to compound formation due to implantation into the subsurface layer. In addition, reactive gas molecules are adsorbed on the surface and react with target metal atoms to add to the formation of the compound layer. Thus, both chemisorption and ion implantation of energetic reactive ions are the two main mechanism! s for the formation of the poisoned layer.TRIDYN simulations have been performed at varying reactive ion to total ion flux ratio, and at varying ion to reactive neutral flux ratio, for fluences which are sufficiently large to achieve a stationary deposition/erosion balance. The results illustrate that the two mechanisms will generate almost identical shapes of the poisoned layer. They also demonstrate the significance of recoil implantation from the chemisorbed layer for the formation of the compound layer. In agreement with experimental findings, the calculated sputter erosion rate of the target is predicted to decrease monotonically as the partial pressure of the reactive gas increases. The shape of the sputter erosion curve hardly changes between conditions dominated by ion implantation or chemisorption. We therefore conclude that ion implantation basically acts as an additional source of reactive atoms to the target surface.
  • Nuclear Instruments and Methods in Physics Research B 228(2005), 193-197

Publ.-Id: 7214 - Permalink


Fate of U(VI) Added to a U Mining Waste Sample and the Resulting Changes in the Indigenous Bacterial Community
Geissler, A.; Scheinost, A.; Selenska-Pobell, S.;
Background
Bacteria play an important role in biogeochemical transformations and migration of uranium (U) in nature. In order to understand how U(VI) interacts with natural bacterial communities of U mining waste piles a series of microcosm experiments was performed.
Methods
Several portions of a solid sample collected from the U mining waste pile near the city of Johanngeorgenstadt in Germany were supplemented with different amounts of U(VI), starting from the original 40 mg U/kg up to 300 mg/kg.
The solubility of the U originally present and of the added U was assessed by selective sequential extraction (SSE). The composition of bacterial communities present in the original and in the supplemented with U samples was analyzed applying 16S rDNA retrieval by using 43F and 1404R degenerated primers.
Results
SSE analysis demonstrated that in the original sample the main part of uranium was strongly bound in mineral phases. The bacterial community of this sample was predominated by Alphaproteobacteria and by representatives of Holophaga /Acidobacterium phylum.
The bacterial community structure of the sample was noticeable changed by increasing its U content to 100 mg/kg . No Holophaga/Acidobacterium and only a few representatives of Alphaproteobacteria were retrieved in this sample. Instead, a large number of sequences of mainly Gamma-Pseudomonas, and of Arthrobacter sp. were found. The propagation of several populations of Deltaproteobacteria and especially of Geobacter sp. was induced in the sample as well. After 4 weeks of incubation, most of the U added to this sample was still only weakly complexed.
The bacterial community structure of the most contaminated sample, containing 300 mg U/kg, differed significantly from the two samples described above and depended on the aeration conditions during the incubation. In this sample the number of 16S rDNA sequences representing Cytophaga/Flavobacterium /Bacteroides group was extremely high. Arthrobacter sp. populations were also identified but not as strongly predominant.
Conclusions
The addition of U(VI) to a low contaminated U mining waste sample induces significant shifting in the indigenous bacterial populations. The effect of the added U(VI)seems to depend on its amount and on the redox conditions.
  • Contribution to proceedings
    ISSM 05 + ISEB XVII, 14.-19.08.2005, Jackson Hole, Wyoming, United States
  • Lecture (Conference)
    ISSM 05 + ISEB XVII, 14.-19.08.2005, Jackson Hole, Wyoming, United States

Publ.-Id: 7213 - Permalink


Microbial Diversity and Activity in Waters of a Siberian Monitoring Well at the Deep-Bore-Hole Radioactive Waste Disposal Site TOMSK-7
Nedelkova, M.; Merroun, M.; Selenska-Pobell, S.;
Background
Microorganisms strongly influence the migration of radionuclides in the environment. For this reason analysis of natural bacterial and archaeal communities near radioactive wastes deposition sites is of great importance for risk assessments. In this study diversity was studied of the microorganisms indigenous for a monitoring well near the radioactive waste injection site Tomst-7 in Siberia. In addition, interactions of several bacterial isolates from this site with uranium and other metals was investigated.
Methods
Microbial diversity was studied applying the 16S rDNA7F-1513F for bacteria and 16S rDNA21f-958R for archaea. The diversity of the autotrophic bacteria was estimated by direct analysis of different RubisCO gene forms. Oligotrophic bacteria were cultured in low nutrient R2A medium. Interactions of the cultured bacterial isolates with U, Ni, Pb, As, and other metals were studied by using ICP-MS, flow cytometry and X-ray spectroscopic analyses.
Results
Our analyses demonstrated presence of a large number of diverse bacterial and archaeal groups at a depth of about 300m at the Siberian depository site Tomsk-7 where the radioactive wastes were injected. The most predominant bacterial populations were those of Betaproteobacteria mainly from the Rhodocyclus group, of Citophaga/Flavo-bacterium/Bacteroides, and of several novel “Cyanobacteria-like” groups. The RubisCO approach confirmed the Betaproteobacterial predominance in the samples studied.
Bacterial isolates were cultured from the samples belonging to Sphingomonas sp., Brevundimonas sp., Methylobacter sp., and a large microdiverse group of Actinobacteria closely related to Microbacterium oxydans. They tolerated U and other heavy metals in a species- and even strain-specific way. EXAFS analyses demonstrated that the isolates of Microbacterium sp. and of Sphingomonas sp. are complexing U(VI) at pH 4.5 via phosphorus (P) in a form of meta-autunite. The latter was connected to the liberation of inorganic phosphate by these strains due to their exo-phosphatase activity. At lower pH values the U is bound to organic phosphate residues.
Conclusions
The environment around the radioactive waste injection site Tomsk-7 possesses a large variety of microorganisms with a potential to bind and possibly transport radionuclides.
  • Contribution to proceedings
    ISSM 05 + ISEB XVII, 14.-19.08.2005, Jackson Hole, Wyoming, United States
  • Lecture (Conference)
    ISSM 05 + ISEB XVII, 14.-19.08.2005, Jackson Hole, Wyoming, United States

Publ.-Id: 7212 - Permalink


Anomalous behaviors of E-1/E-2 deep level defects in 6H silicon carbide
Chen, X.; Ling, C.; Gong, M.; Fung, S.; Beling, C.; Brauer, G.; Anwand, W.; Skorupa, W.;
Deep level defects E1/E2 were observed in He-implanted, 0.3 and 1.7 MeV electron-irradiated n-type 6H-SiC. Similar to others' results, the behaviors of E-1 and E-2 (like the peak intensity ratio, the annealing behaviors or the introduction rates) often varied from sample to sample. This anomalous result is not expected of E-1/E-2 being usually considered arising from the same defect located at the cubic and hexagonal sites respectively. The present study shows that this anomaly is due to another DLTS peak overlapping with the E-1/E-2. The activation energy and the capture cross section of this defect are E-C-0.31 eV and sigma similar to 8 x 10(-11) cm(2), respectively.
Keywords: Deep level transient spectroscopy, silicon carbide, electron irradiation
  • Applied Physics Letters 86(2005)3, 31903-31903

Publ.-Id: 7211 - Permalink


Experimental results on the effect of wall-parallel Lorentz forces on lift and drag of hydrofoils
Weier, T.; Gerbeth, G.;
Lorentz forces on the suction side flow of NACA 0015 and PTL IV hydrofoils is investigated experimentally. Emphasis is placed on separation control. Steady as well as time periodic Lorentz forces will be discussed. Their effect is compared mainly in respect of the attainable increase of the maximum lift and in terms of power consumption.
  • Lecture (Conference)
    2nd International Symposium on Seawater Drag Reduction, 23.-26.05.2005, Busan, South Korea
  • Contribution to proceedings
    2nd International Symposium on Seawater Drag Reduction, 23.-26.05.2005, Busan, South Korea
    Proceedings, 267-281

Publ.-Id: 7210 - Permalink


From short-wavelength quantum cascade lasers to impulsive THz emitters
Helm, M.;
I will discuss two recent advances related to semiconductor light sources in the infrared and THz regions. One example is a quantum cascade laser operating at a wavelength shorter than 4 microns above room temperature with high peak power. It is based on strained InGaAs/InAlAs on InP, with the addition of high barriers of pure AlAs for better confinement and strain compensation. In a novel few-cycle THz emitter we try to combine the advantages of the high electric bias field in photoconductive antennas with a large active area. This is achieved with an interdigitated electrode structure, partially covered in order to mask one field polarity. As a result no destructive interference of the emitted THz wave occurs, which allows upscaling of the device area.
Keywords: quantum cascade lasers, THz emitters
  • Lecture (others)
    Seminarvortrag bei THALES Research & Technology, 24.02.2005, Orsay, France

Publ.-Id: 7209 - Permalink


Recent developments at the Dresden High Magnetic Field Laboratory
Herrmannsdörfer, T.;
Recent developments at the Dresden High Magnetic Field Laboratory
  • Lecture (Conference)
    3rd Workshop on High Field Techniques of the High Field Labs of Toulouse, Nijmegen and Dresden, 18.09.2004, Toulouse, France

Publ.-Id: 7208 - Permalink


The Dresden High Field Project
Herrmannsdörfer, T.;
We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.
Keywords: Dresden High Field Project
  • Invited lecture (Conferences)
    14. Edgar Lüscher Seminar, 03.02.2003, Serneus, Schweiz

Publ.-Id: 7205 - Permalink


Synthesis and radiopharmacological evaluation of 2´-(4-fluorophenyl)-21-[18F]fluoro-20-oxo-11β,17α-dihydroxy-pregn-4-eno[3,2-c]pyrazole as potential glucocorticoid receptor ligand for positron emission tomography (PET)
Wüst, F.; Knieß, T.; Kretzschmar, M.; Bergmann, R.;
The radiosynthesis and the radiopharmacological evaluation of pyrazolo steroid 2´-(4-fluorophenyl)-21-[18F]fluoro-20-oxo-11β,17α-dihydroxy-pregn-4-eno[3,2-c]pyrazole [18F]-2 is described. The radiolabeling was accomplished in 3 - 4 % decay-corrected radiochemical yield within 80 min at an specific radioactivity of 0.8-1.2 Ci/μmol. Biodistribution studies in male Wistar rats showed an initial brain uptake of 0.25 ± 0.03 % ID/g after 5 min, which remained constant over 60 min. The radiopharmacological evaluation of compound [18F]-2 was completed with autoradiography using rat brain sections and micro-PET imaging.
Keywords: Positron emission tomography; Glucocorticoid receptor; Radiolabeling
  • Bioorganic & Medicinal Chemistry Letters 15(2005), 1303-1306

Publ.-Id: 7204 - Permalink


High Field Lab Dresden, progresses
Herrmannsdörfer, T.; Krug, H.;
Further developments for the Dresden High Field Laboratory
  • Lecture (Conference)
    2nd Workshop on High Field Techniques of the High Field Labs of Toulouse, Nijmegen and Dresden, 24.01.2003, Nijmegen, Niederlande

Publ.-Id: 7203 - Permalink


Survey on finite element software with "multiple physics options"
Herrmannsdörfer, T.;
In order to design and optimize pulsed field coils, their current leads, and in particular their reinforcement, we currently test commercial Finite Element software of various suppliers. We concentrate on these programs which have implemented so called "multiphysics modules" which are able to solve combined problems as they typically occur in high field techniques: e.g. calculation of the magnetic field from a current distribution along with the resulting Lorentz forces, stresses, dislocations etc.. In detail, we focus on the programs ANSYS, ANSOFT, as well as FEMLAB. We like to give a brief survey of their usefulness, perspectives, and last but not least, of their cost.
Keywords: Novel Multiphysics Finite Element Software
  • Lecture (Conference)
    1st Workshop on High Field Techniques of the High Field Labs of Toulouse, Nijmegen and Dresden, 21.06.2002, Dresden, Deutschland

Publ.-Id: 7201 - Permalink


High Field Lab Dresden, building
Herrmannsdörfer, T.;
In the frame of the high field project Dresden, a new building to be constructed at the research center Rossendorf is in its design phase. The HLD building will be located near the IR-free electron lasers of the superconducting linear accelerator ELBE in order to provide the possibility of IR spectroscopy in high pulsed magnetic fields. Following the present plans, five magnet cells for pulsed magnets, preparation rooms, a lab for superconducting magnets and four labs for accompanying experiments are located around a central room which houses the capacitor bank. In addition, a workshop, stores, and a technical section on one side, as well as the offices for stuff and guests and a control room on the other side are located in separate sections. We present the plans emphasising the ability and the safety items in order to get your feedback.
Keywords: High Field Lab Dresden
  • Lecture (Conference)
    1st Workshop on High Field Techniques of the High Field Labs of Toulouse, Nijmegen and Dresden, 21.06.2002, Dresden, Deutschland

Publ.-Id: 7200 - Permalink


Synthesis and biological evaluation of S-[11C]methylated mercaptoimidazolde piperazinyl derivatives as potential radioligands for imaging 5-HT1A receptors by positron emission tomography (PET)
Garcia, R.; Xavier, C.; Paulo, A.; Santos, I.; Knieß, T.; Bergmann, R.; Wüst, F.;
The novel 2-mercaptoimidazolde derivatives, 1-[4-((2-methoxyphenyl)-1-piperazinyl)-butyl]-2-mercaptoimidazolde (3) and methyl[4-((2-methoxyphenyl)-1-piperazinyl))butyl] (2-mercapto-1-methylimidazol-5-yl)methanamide (8), were efficiently labelled with 11C through methylation of the thioketone function with [11C]methyl iodide. The resulting radioligands 1-[4-((2-methoxyphenyl)-1-piperazinyl))butyl]-2-thio[11C]-methylimidazole ([11C]9) and methyl [4-((2-methoxyphenyl)-1-piperazinyl))butyl] (2-thio[11C]methyl-1-methylimidazol-5-yl)-methanamide ([11C]10) were synthesized in radiochemical yields of 20 - 30 % (decay-corrected, related to [11C]CO2) at a specific radioactivity of 0.2-0.4 Ci/μmol within 40-45 min including HPLC-purification. The radiochemical purity exceeded 99 %. The reference compounds 9 and 10 were tested in a competitive receptor binding assay to determine their affinity toward the 5-HT1A recptor. Both compounds exhibit excellent sub-nanomolar affinities (IC50 = 0.576 ± 0.008 nM (9); IC50 = 0.86 ± 0.02 nM (10)) for the 5-HT1A receptor while displaying a high selectivity towards the 5-HT2A subtype of receptors (IC50 > 480 nM). By contrast, compound 9 also shows substantial binding for the alpha-adrenergic receptor (IC50 = 3.00 ± 0.02 nM) when compared with compound 10 (IC50 = 54.5 ± 0.6 nM). Preliminary biodistribution studies in rats showed an initial brain uptake of 1.14 ± 0.11 and 0.37 ± 0.04 % ID/g after 5 min, which decreased to 0.18 ± 0.04 and 0.16 ± 0.01 % ID/g after 60 min for compounds [11C]9 and [11C]10, respectively. For both compounds, the cerebellum and rest of the brain uptake are very similar at the different time points. Unlike [11C]9, the radioligand [11C]10 has significant uptake and retention in the adrenal glands. Due to their washout from the brain compounds [11C]9 and [11C]10 seem not to be good condidates as radioligands for imaging 5-HT1A receptors by PET.
Keywords: carbon-11; mercaptoimidazoles, piperazines; 5-HT1A receptors, positron emission tomography
  • Journal of Labelled Compounds and Radiopharmaceuticals 48(2005), 301-315

Publ.-Id: 7198 - Permalink


Research at High Magnetic Fields in Europe, the New Facility in Dresden
Herrmannsdörfer, T.;

In nature, the magnetic field acts as a fundamental thermodynamic property like temperature or pressure. For this, the magnetic field plays a decisive role in many facets of nature, and in consequence, is of importance in several natural sciences. In particular, the understanding of magnetic properties of matter and the interplay of magnetism with other quantities is a challenging field of research. Under extreme conditions, like low temperatures, high pressures, and high magnetic fields, new interesting properties of matter can appear and the understanding of materials properties can crucially be gained.

Further, the manifold magnetic effects in nature and in particular the magnetic properties of matter are a rich source for technological innovations. Historically, there is an immense number of inventions like the compass, electro motor, generator, relay, magnetic brake, levitating train, nuclear magnetic resonance tomograph, hard disk drive, magneto-electric random access memory. Nowadays, in transport, energy production, medicine, communication, data storage, and other areas of daily live, magnetic systems, components, and properties are used in a large variety.

In the last decades, the application of high magnetic fields became a powerful research tool. Especially in solid state physics important discoveries like the integer quantum Hall and fractional quantum Hall effect, both honoured with the Physics Nobel Prize, are based on experiments in very high magnetic fields.

In order to establish a large modern user facility with unique experimental possibilities for science in high magnetic fields and in order to provide an easy access for the high field community in Europe, the Dresden High Field Project has been created. Since 2003 this facility is under construction. In this paper, we give a snapshot on the status and some recent achievements in the course of the project. The Dresden High Field Laboratory for nondestructive pulsed magnetic fields up to 100 T will open its doors as a user facility in January 2007.

Keywords: High Magnetic Fields, Pulsed Fields, Experiments in High Magnetic Fields, User Facility, Megagauss
  • Invited lecture (Conferences)
    12. Internationale Konferenz für Materialwissenschaften und Technologie (Co Mat Tech 2004), 14.-15.10.2004, Trnava, Slovakia

Publ.-Id: 7197 - Permalink


The new high magnetic field laboratory at Dresden-Rossendorf
Herrmannsdörfer, T.;
A new facility for experiments in pulsed high magnetic fields is under construction at the Forschungszentrum Rossendorf in Dresden, Germany. Its heart will be a modular 50 MJ / 24 kV capacitor bank in a new laboratory. In order to offer a wide spectrum of experimental possibilities, pulsed field coils are planned in the parameter range 60 T, 50 mm, 1s to 100 T, 20 mm, 0.01 s for maximum field, bore, and pulse duration. Experience in the construction of the pulsed capacitive power supply as well as in the experimental equipment has been gained from a pilot laboratory at the IFW since 1999. The pulsed magnets will be complemented by commercial superconducting magnets for dc fields up to 20 T. Besides many other experimental possibilities, as a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible in pulsed fields by connecting the pulsed field lab to the new free-electron-lasers of the neighbouring superconducting electron linear accelerator ELBE of the FZR.
The laboratory building will be completed in 2004. The 50 MJ power supply can be partly used in 2005 and will be fully operational by 2006. First pulsed test coils have already been built and will be tested in 2004 by the 1.44 MJ / 24 kV pilot power supply manufactured at FZR. The user coils as well as the experimental equipment will be installed in 2006, so that the facility can open its doors as a user laboratory in 2007.

* The HLD project has been jointly submitted for funding by the FZR, the Leibniz-Institut für Festkörper- und Werkstoffforschung IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the Technische Universität Dresden. It is jointly funded for installation by the Bundesministerium für Bildung und Forschung of Germany and the Sächsische Ministerium für Wissenschaft und Kunst in the years 2003 to 2006.
Keywords: High Magnetic Fields, Pulsed Fields, Experiments in High Magnetic Fields, User Facility, Megagauss
  • Lecture (Conference)
    Joint European Magnetic Symposium, 05.-10.09.2004, Dresden, Deutschland

Publ.-Id: 7196 - Permalink


Van Vleck Paramagnets in High Magnetic Fields
Herrmannsdörfer, T.;
We present measurements of the dc magnetization M(B) of van Vleck paramagnets, e.g. PrNi5, at high magnetic fields up to B = 60 T. At low fields up to 10 T, we observe magnetizations which increase linearly with the applied field. Beyond 10 T, the magnetizations start to become nonlinear as the result of the shifts of the energy levels of the crystalline electrical field (CEF) states of the 4f-Pr3+ electrons through the external field. A significant change of slope of the magnetization M(B) as well as of the corresponding susceptibility dM/dB occurs in PrNi5 at B = 20 T which can be explained by a level crossing of the two lowest singlet CEF states. We compare our data to calculations from a point charge model.
  • Poster
    RHMF, 20.-23.07.2003, Toulouse, Frankreich

Publ.-Id: 7195 - Permalink


The Dresden High Field Project
Herrmannsdörfer, T.;
We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.
  • Poster
    RHMF, 20.-23.07.2003, Toulouse, Frankreich

Publ.-Id: 7194 - Permalink


The Pulsed High Magnetic Field Facility in Dresden
Herrmannsdörfer, T.;
We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.
  • Invited lecture (Conferences)
    Symposium „Materials under extreme conditions“ während der 67. Physikertagung der DPG, 24.-28.03.2003, Dresden, Deutschland

Publ.-Id: 7193 - Permalink


The impact of hyperfine interaction on Cooper pair breaking
Herrmannsdörfer, T.;
Since the first experimental finding of a competition between nuclear magnetism and superconductivity in the nuclear ferromagnet AuIn2, investigations have been extended to Al, Sn, Rh, In, AuAl2, and very recently to Pr1-xLaxTe. The experiments have demonstrated that the contribution of nuclear magnetism to Cooper pair breaking is a common phenomenon. Even in a system with tiny nuclear magnetic moments (e.g. Sn), a reduction of the critical field Bc(T) has been detected at ultralow temperatures. In more detail, the observed influences of nuclear magnetism on superconductivity vary strongly with the size of hyperfine coupling, ranging between a tiny reduction of Bc(T) in the case of weak hyperfine coupling (AuAl2) and the complete destruction of superconductivity in the opposite case of strongly coupled and hyperfine enhanced nuclear spin systems (e.g. Pr0.50La0.50Te). The hyperfine interaction appeares to be the dominant mechanism for the nuclear magnetic contribution to Cooper pair breaking.
  • Poster
    International Conference on Ultralow Temperature Physics, 28.-31.08.2002, Kanazawa, Japan

Publ.-Id: 7192 - Permalink


Anomalous properties of the heavy fermion compound CeCu6 at ultralow temperatures
Herrmannsdörfer, T.;
In the course of our investigation of the heavy fermion compound CeCu6,
we have recently performed measurements of the heat capacity as well as elastic neutron diffraction down to ultralow temperatures. In the last decade, various groups have investigated this compound by means of susceptibility, magnetization, nuclear quadrupole resonance, and thermal expansion as well. There is a strong evidence for a magnetic ordering transition at about 2.5 mK. Here we like to present our latest heat capacity data taken at 0.1 mK ≤ T ≤ 100 K as well as neutron diffraction data taken down to 15 mK. These results give further
hints for magnetic correlation effects in CeCu6.
  • Poster
    International Conference on Ultralow Temperature Physics, 28.-31.08.2002, Kanazawa, Japan

Publ.-Id: 7191 - Permalink


Hyperfine Enhanced Nuclear Antiferromagnetism in PrS, PrTe, and PrBi
Herrmannsdörfer, T.;
We have investigated the strongly correlated electronic and nuclear magnetic properties of the cubic Van Vleck paramagnets PrS, PrTe, and PrBi by means of SQUID magnetometry at 2 K≤T≤300 K as well as ac susceptometry at ultralow temperatures, 0.06 mK≤T ≤100 mK. We observe magnetic ordering transitions of the hyperfine enhanced magnetic moments of the 141Pr nuclei in all three compounds. Our ac susceptibility data taken at ultralow temperatures point to antiferromagnetic ground states. The observed Neel temperatures, TN(PrS, PrTe, PrBi) = 0.09, 0.60, 1.20 mK, scale with the size of the Van Vleck susceptiblity and related hyperfine enhancement factor respectively. The nuclear fcc spin-5\2 antiferromagnets PrS, PrTe, and PrBi are promising candidates for interesting spin structures. Currently we use the metallurgical possibility to substitute Pr by La and Pb in these compounds in order to study the multiple interplay between electronic magnetism, nuclear magnetism, superconductivity (e.g. in Pr1-xLaxTe), and semiconductivity (e.g. in Pr1-xPbxTe).
  • Invited lecture (Conferences)
    International Conference on Ultralow Temperature Physics, 28.-31.08.2002, Kanazawa, Japan

Publ.-Id: 7190 - Permalink


First finding of reentrant superconductivity driven by hyperfine interaction
Herrmannsdörfer, T.;
Compared to magnetically doped superconductors described by the theory of Abrikosov and Gorkov, electronic singlet ground state systems can have a much larger critical concentration of magnetic impurities, following the model of Keller and Fulde. The recent study of the superconducting Van Vleck paramagnet La{1-x}PrxTe revealed a critical Pr{3+} concentration x close above 0.50. Surprisingly, in La{0.50}Pr{0.50}Te the superconducting state with Tc = 0.20 K appeares not to be stable down to zero temperature. Instead, a reentrant transition to the normal state likely caused by the hyperfine enhanced magnetic moments of the {141}Pr nuclei occurs at about 0.02 K. Although these moments are not in a magnetically ordered ground state at T = 0.02 K, their contribution to Cooper pair breaking seems to be even stronger than of ferromagnetically ordered but non enhanced nuclear moments in type-I superconducting AuIn2.
  • Poster
    23rd International Conference on Low Temperature Physics, 20.-27.08.2002, Hiroshima, Japan

Publ.-Id: 7189 - Permalink


First observation of superconductivity in LaCu6 and possible applications
Herrmannsdörfer, T.;
We have measured the ac susceptibility and resistivity of highly pure samples of the intermetallic compound LaCu6 down to ultralow temperatures. We have prepared the samples by arc melting of stoichiometric amounts of 99.99\% La and 99.9999\% Cu in a water-cooled copper crucible under Ar protective atmosphere and analysed them by x-ray diffraction and SQUID magnetometry. At T≤Tc = 0.16 K we observe a superconducting transition. Due to the manifold physical properties of isostructural ReCu6 compounds (e.g. RE = Ce: heavy fermion system, RE = Pr: hyperfine enhanced nuclear spin system, RE = Nd: electronic antiferromagnet), numerous studies of interplay phenomena may become possible in the quasibinary compounds RE1-xLaxCu6, respectively.
  • Poster
    23rd International Conference on Low Temperature Physics, 20.-27.08.2002, Hiroshima, Japan

Publ.-Id: 7188 - Permalink


The quantum functional intermetallic compound Pr1-x-yLaxPbyTe
Herrmannsdörfer, T.;

The intermetallic compound Pr1-x-yLaxPbyTe shows a wide spectrum of physical phenomena*. Depending on the metallurgical composition as function of x and y, the compound changes its behaviour from nuclear magnetic order to super- or semiconductivity. In addition, there are interesting interplay effects between these ground state phenomena. In consequence, Pr1-x-yLaxPbyTe may serve as an interesting candidate for studies on quantum computing. In this talk, experimental results taken in a wide range of temperature, 0.1 mK ≤ T ≤ 300 K, are presented. Further, effects which arise through the application of high magnetic fields are discussed.

* Whereas several rare earth tellurides undergo magnetic order, in PrTe the crystal electrical field splitting with a singlet ground state leads to Van Vleck paramagnetism. However, the nuclear magnetic moments of Pr are hyperfine enhanced as well as strongly coupled to the conduction electrons in PrTe. In consequence the effective nuclear magnetic moments order antiferromagnetically at 0.6 mK. LaTe is a superconductor with Tc = 5.7 K. The singlet ground state of the Pr ions in Pr1-xLaxTe lead to a large critical Pr concentration x = 0.5 for Cooper pair breaking. Finally, PbTe is a narrow band semiconductor.

Keywords: Quantum Computing, Hyperfine enhanced nuclear magnetism, Quantum functional materials, High Fields, Low Temperature
  • Invited lecture (Conferences)
    InternationalConference on QTSM-QFS, 21.11.2004, Seoul, South Korea

Publ.-Id: 7187 - Permalink


Bewertung der Nachhaltigkeit heutiger Technologien der Stromerzeugung - Aggregation der Indikatoren -
Weiß, F.-P.;
Die Internationale Länderkommission Kerntechnik (ILK) hat 2004 eine Stellungnahme zur Bewertung der Nachhaltigkeit der Kernenergie und anderer Technologien zur Stromerzeugung vorgelegt.
Die Bewertung beruht u.a. auf der Quantifizierung von Indikatoren, wie etwa die Produktionskosten oder die CO-2-Emission, die verschiedene Nachhaltigkeitsaspekte charakterisieren und der Aggregation dieser Indikatoren zu einem einzigen Nachhaltigkeitskennwert für jede der betrachteten Energieoptionen.
Die Aggregation kann beispielsweise über den Totalkostenansatz oder mit Hilfe der Multikriteriellen Entscheidungsanalyse (MCDA) erfolgen. Die beiden Verfahren führen in der Regel zu unterschiedlicher Nachhaltigkeitsbewertung. Dies liegt zum einen daran, dass einige der Indikatoren finanziell nicht fassbar sind und deshalb im Totalkostenansatz nicht berücksichtigt werden. Zum anderen sind bei der Aggregation mit Hilfe der MCDA Wichtungsfaktoren für Einzelindikatoren und die "Nachhaltigkeitssäulen" Wirtschaft, Umwelt, Gesellschaft festzulegen. Bislang stehen keine Leitlinien für die Fixierung dieser Gewichtungen zur Vefügung. Der Vortrag stellt die genannten Aggregationsverfahren vor und diskuiterit dann Vor- und Nachteile.
  • Invited lecture (Conferences)
    Internationaler ILK-Workshop, 23.02.2005, Frankfurt/Main, Germany

Publ.-Id: 7186 - Permalink


The new user facility for high magnetic fields in Dresden, Germany
Herrmannsdörfer, T.;

A new facility for experiments in pulsed high magnetic fields (HLD*) is under construction at the Forschungszentrum Rossendorf (FZR) in Dresden, Germany. In order to offer a wide spectrum of experimental capabilities at HLD, pulsed field coils are planned in the parameter range 60 T, 50 mm, 1s to 100 T, 20 mm, 0.01 s for maximum field, bore, and pulse duration. These magnets will be energized by a modular 50 MJ / 24 kV / 600 kA capacitor bank. The pulsed magnets will be complemented by commercial superconducting magnets for dc fields up to 20 T. Besides many other experimental capabilities, as a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible in pulsed fields by connecting the pulsed field lab with the new free-electron-lasers of the neighbouring superconducting electron linear accelerator ELBE of the FZR.
Since 1999, we have gained experience in a pilot project by building a 1.0 MJ / 10 kV / 61 T high field laboratory. Funded since 2003, we have already completed our laboratory building and machineshop. In addition, we have planned and started to assemble the 50 MJ power supply which can be partly used in 2005 and will be fully operational by 2006. First pulsed test coils have already been built and tested using a 1.44 MJ / 24 kV / 37 kA pilot power supply manufactured at FZR. Currently we are starting to order our experimental equipment. Together with the user coils, this equipment will be mainly installed and put into operation during 2006. We are planning to open the doors of our laboratory to users in 2007.

* The HLD project has been jointly submitted for funding by the Forschungszentrum Rossendorf FZR, the Leibniz Institute for Solid State and Materials Research Dresden, the Max Planck Institute for Chemical Physics of Solids, the Max Planck Institute for the Physics of Complex Systems, and the Institute for Solid State Physics of the Dresden Technical University in 1998. It is jointly funded for installation by the Federal Ministry of Education and Research of Germany and the Saxon Ministry of Science and the Fine Arts.

Keywords: High Magnetic Fields, Pulsed Fields, Experiments in High Magnetic Fields, User Facility, Megagauss
  • Invited lecture (Conferences)
    Workshop on the latest Developments in MTNBS, 19.11.2004, Seoul, South Korea

Publ.-Id: 7185 - Permalink


The Dresden High Field Project
Herrmannsdörfer, T.;

A new facility for experiments in pulsed high magnetic fields up to 1 MegaGauss is under construction at the Forschungszentrum Rossendorf (FZR) in Dresden, Germany. In order to provide a wide spectrum of experimental possibilities, pulsed field coils are planned in the parameter range 60 T, 50 mm, 1s to 100 T, 20 mm, 0.01 s for maximum field, bore, and pulse duration. These field coils will be energized by a modular 50 MJ / 24 kV capacitor bank. Experience in the construction of the pulsed capacitive power supply as well as in the experimental equipment has been gained from a pilot laboratory at the Leibniz-Institut für Festkörper- und Werkstoffforschung, Dresden (IFW) since 1999. The pulsed magnets will be complemented by commercial superconducting magnets for dc fields up to 20 T. Besides many other experimental possibilities, as a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 μm will be possible in pulsed fields by connecting the pulsed field lab to the new free-electron-lasers of the neighbouring superconducting electron linear accelerator ELBE of the FZR.
The laboratory building and a workshop hall for coil fabrication will be completed in 2004. The 50 MJ pulsed power supply which is under construction can be partly used in 2005 and will be fully operational by 2006. First pulsed test coils have already been built and will be tested in 2004 by the 1.44 MJ / 24 kV / 40 kA pilot power supply manufactured at FZR. The user coils as well as the experimental equipment will be installed in 2006, so that the facility should open its doors as a user laboratory in 2007.

* The HLD project has been jointly submitted for funding by the Forschungszentrum Rossendorf (FZR), the Leibniz-Institut für Festkörper- und Werkstoffforschung (IFW), the Max-Planck-Institut für chemische Physik fester Stoffe (MPI-CPFS), the Max-Planck-Institut für Physik komplexer Systeme (MP-PKS), and the Institut für Angewandte Physik of the Technische Universität Dresden (TU-DD). It is jointly funded for installation by the Bundesministerium für Bildung und Forschung of Germany and the Sächsische Ministerium für Wissenschaft und Kunst in the years 2003 to 2006.

Keywords: High Magnetic Fields, Pulsed Fields, Experiments in High Magnetic Fields, User Facility, Megagauss
  • Lecture (Conference)
    10. Megagauss-Konferenz MGX, 20.07.2004, Berlin, Deutschland

Publ.-Id: 7184 - Permalink


Estimation of field amplitudes during the operation of the 1.5 cell photoelectron RF gun of the PITZ collaboration
Janssen, D.;
The present paper discuss the posibility to obtain information about the field flatness of a 1.5 cell normal conducting RF gun cavity during the running of the gun. By measurements of the microwave network parameters at room temperature and by measurement of the passband frequencies in the running regime of the gun it is possible to estimate the perturbation of field flatness, caused by an inhomogeneous temperature distribution.
  • Other report
    Hamburg: DESY, 2005
    7 Seiten

Publ.-Id: 7183 - Permalink


[11C]SMe-ADAM, an imaging agent for the brain serotonin transporter: Synthesis, pharmacological characterization and microPET studies in rats
Zessin, J.; Deuther-Conrad, W.; Kretzschmar, M.; Wüst, F.; Pawelke, B.; Brust, P.; Steinbach, J.; Bergmann, R.;
N,N-Dimethyl-2-(2-amino-4-methylthiophenylthio)benzylamine (SMe-ADAM, 1) was found to be a highly potent and selective inhibitor of the serotonin transporter (SERT). This compound was labelled with carbon-11 by methylation of the S-desmethyl precursor 10 with [11C]methyl iodide to obtain the potential positron emission tomography radiotracer [11C]SMe-ADAM. Radiochemical yield was 27  5 % and the specific radioactivity was 26 – 40 GBq/µmol at the end of synthesis . Ex vivo and in vivo biodistribution experiments in rats demonstrated a rapid accumulation of the radiotracer in brain regions known to be rich in SERT, such as the thalamus/hypothalamus region (3.59 ± 0.41 %ID/g at 5 min after injection). This is the highest brain uptake ever reported for this type of radiotracer in rats. The specific uptake reached a thalamus to cerebellum ratio of 6.74 ± 0.95 at 60 min post injection. The [11C]SMe-ADAM uptake in the thalamus was significantly decreased by pre-treatment with fluoxetine to 45 ± 9 % of the control values. Furthermore, no metabolites of [11C]SMe-ADAM could be detected in the SERT rich regions of the rat brain. It is concluded that [11C]SMe-ADAM may be a suitable PET ligand for SERT imaging in the living brain.
Keywords: [11C]SMe-ADAM, [11C]methyl iodide, serotonin transporter, microPET
  • Nuclear Medicine and Biology 33(2006)1, 53-63

Publ.-Id: 7181 - Permalink


Motion of single gas bubbles rising in a liquid metal exposed to a DC magnetic field
Zhang, C.; Eckert, S.; Gerbeth, G.;
The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC magnetic field was examined. The magnetic field lines were aligned either in longitudinal or in transverse direction. The magnetic field strength was chosen up to 0.3 T corresponding to magnetic interaction parameters N of 1.5. The experiments were carried out in the following parameter range: 2500 < Re < 5500, 2 < Eo < 7, Mo = 2.4e-13. The liquid metal was in a cylindrical container at rest. The Ultrasound Doppler Velocimetry (UDV) was applied to determine bubble and liquid velocities simultaneously. The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. Within the present interaction number range (N < 2), the applied magnetic field can either increase or decrease the bubble drag coefficient depending on the bubble size and the magnetic interaction parameter. Moreover, significant modifications of the bubble wake structure were observed. Raising of the magnetic field strength causes an enlargement of the eddy structures in the wake. In case of the longitudinal magnetic field the Strouhal number St decreases with increasing magnetic interaction parameter.
Keywords: Single bubble, Liquid metal, Magnetic field, Terminal velocity, Drag coefficient, Bubble wake, Ultrasound Doppler Velocimetry
  • Poster
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
    1(2005), 195-198

Publ.-Id: 7178 - Permalink


Flow structures during solidification of metallic alloys affected by a rotating magnetic field
Willers, B.; Nikritjuk, P. A.; Eckert, K.; Eckert, S.;
In order to improve the microstructure of casting ingots a rotating magnetic field (RMF) is widely used to stir the liquid phase during solidification. Usually, the interaction between the solidification process and the RMF driven flow has been discussed only in terms of the flow pattern well-known from the laminar, isothermal case being a superposition of a primary swirling flow in azimuthal direction and a secondary flow occurring as a double vortex in the r-z plane. Effects arising from the propagation of the solidification front, the extension of the mush zone or the spin-up of the flow at higher cooling rates are almost not taken into account. We present experimental and numerical investigations concerning the influence of a RMF driven flow on the momentum, heat and mass transfer within a binary Sn-Pb alloys solidified directionally.
Solidification experiments were carried out using a Sn-15wt%Pb alloy in a cylindrical mold positioned on a water-cooled copper chill. The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow during solidification. The temperature field was monitored using thermocouples. The set-up was enclosed by an inductor providing the RMF. The Taylor numbers Ta were varied between 10e5 and 10e8.
The continuum formulation based model has been adopted for numerical simulations using the following assumptions: all transport properties, such as thermal and electrical conductivity or viscosity, are assumed to be constant; the density of solid phase equals the density of liquid phase; the phases are in local thermodynamic equilibrium; the velocity of solid phase in the upper part of the mushy zone is equal to the velocity of the liquid phase. The mushy region is modeled using a mixture viscosity formulation. The Lorentz force in the Navier-Stokes equation has been calculated by means of an analytical solution for the time-averaged Lorentz force for a finite cylinder. The resulting set of eqiuations is discretized by an implicit finite-volume, finite-difference based method, and solved by using the SIMPLE algorithm.
Our results show that the velocity field undergoes distinct modifications during solidification indicating the occurrence of more sophisticated flow patterns as known from the isothermal case.
Keywords: solidification, Pb-Sn alloy, Fluid flow, Electromagnetic stirring, Rotating magnetic field
  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
    Proceedings 2(2005), 269-272

Publ.-Id: 7177 - Permalink


Synthesis and Binding Properties of Dendritic Oxybathophenanthroline Ligands towards Copper(II)
Stephan, H.; Geipel, G.; Bernhard, G.; Comba, P.; Rajaraman, G.; Hahn, U.; Vögtle, F.;
Dendritic oxybathophenanthroline ligands (generation 0 to 3) have been synthesized by treatment of 4,7-bis(4´-hydroxyphenyl)-1,10-phenanthroline with the corresponding Fréchet-type dendrons carrying a benzylic bromide function at the focal point. The complexation of copper(II) has been studied by liquid-liquid extraction using the radioisotope 64Cu and time-resolved laser-induced fluorescence (TRLFS) measurements in organic media proving the formation of 1:3 complexes (Cu : dendritic ligand). The stability of the copper complexes is mainly determined by the 1,10-phenanthroline core element. The stability constants of the 1:3 complexes were found to be in the order of log K ~ 16 in CHCl3. On the other hand, increasing generation of the dendritic Fréchet-type branches leads to enhanced shielding of the copper ion from the environment. Additional information about this behaviour was obtained by the fluorescence lifetimes which are much less influenced upon addition of copper(II) salt to solutions of the higher generation ligands.

Publ.-Id: 7176 - Permalink


A study on the mixing behaviour of different density liquids in a stirred tank reactor by passive and reactive tracers
Hessel, G.; Hristov, H. V.; Kryk, H.; Prasser, H.-M.; Schmitt, W.;
Mixing in stirred vessels of different density liquids is common operation in the process industry. The hydrodynamic behaviour of such a system could be crucial for the overall process performance. The aim of this work is to numerically predict the dynamics of the mixing process of initially stratified system of two different density liquids. Stratified conditions could occur in the stirred vessel, especially in the case of impeller malfunctioning, i.e. impeller breakdown. This effect might prove to be of significant importance, particularly in the case of reacting liquids for large-scale reactors operating in the industry.
The CFD analyses were performed for a non-baffled stirred vessel reactor, mechanically agitated by the Pfaudler impeller. The two main cases of passive and reactive tracer mixing behaviour were numerically predicted by the means of the CFD software CFX 5.7. In both cases the system of two miscible liquids with different densities was dynamically predicted in 3D from an initially stratified to a complete mixing condition. The full 3D simulation was applied in order to capture the flow instabilities associated with the impeller blade passage, especially pronounced in the first few seconds after the impeller start. In order to study the effect of the free surface deformation on the mixing process, the gas phase was also involved into the system via the free surface model. The different density liquids were comprised into the liquid phase by the means of the multicomponent model. In the case of the reactive tracer mixing, the alkali was diluted in the lighter liquid. The simulations were performed on different grids in order to obtain grid independent results.
The accuracy of the numerical simulations was evaluated experimentally using video visualisation technique. The lighter (alcoholic) coloured component and the heavier (water) transparent one which were initially stratified were brought into motion by the rotating impeller. In the case of the passive tracer mixing, the alcoholic phase was coloured by blue dye whereas in the case of the reactive mixing a phenolphthalein indicator was applied. The mixing process was captured by a digital camcorder and subsequently the images were digitally processed. The mixing of different initial lighter phase concentrations was visually investigated to obtain the colour calibration curve. The numerical predictions were evaluated against several locations, close to vessel central line and wall, for which the optical distortion was minimal.
  • Lecture (Conference)
    GVC/DECHEMA Jahrestagung, 06.-08.09.2005, Wiesbaden, Germany
  • Abstract in refereed journal
    Chemie Ingenieur Technik 77(2005)8, 1057-1058

Publ.-Id: 7175 - Permalink


Untersuchungen zur sicheren Prozessführung von Grignard-Reaktionen
Hessel, G.; Kryk, H.; Schmitt, W.; Tefera, N.;
Die Grignard-Chemie erlebt eine Renaissance bei der industriellen Herstellung neuer pharmazeutischer Wirkstoffe, Lebensmitteladditive und Feinchemikalien. Sicherheitsprobleme können aufgrund der sehr großen Exothermie und der hohen Reaktivität der Grignard-Reagenz beim Scale-up in den großtechnischen Maßstab auftreten. Die Hauptgefahrenquelle ist das spontane Starten der Grignard-Reaktion, wenn bereits eine kritische Menge an organischem Halogenid akkumuliert ist, und dann die durchgehende Startreaktion durch den starken Druckanstieg zur Stofffreisetzung führt. Die genaue Bestimmung der reaktionstechnischen Prozessparameter zur Auslegung des Kühlsystems für das Produktions-Betriebsregime wird an einem ge-schlossenen Reaktionskalorimeter mit integriertem in-situ FTIR-Spektrometer für eine industrielle Grignard-Reaktion beschrieben. Weiterhin werden Möglichkeiten zur Detektion des Reaktionsstarts und zur Verfolgung der Halogenid-Akkumulation vorgestellt. Durch den Einsatz der in-situ FTIR-Spektroskopie läßt sich einerseits der Re-aktionsstart eindeutig detektieren, andererseits können sowohl der Verbrauch des organischen Halogenids als auch der Aufbau der Grignard-Reagenz in Echtzeit überwacht werden. Neben den Online-Konzentrationsmessungen können an einem geschlossenen Rührkesselreaktor auch die steilen Anstiege der Reaktortemperatur und des Druckes sowie die Wärmebilanz zum Nachweis des Reaktionsstarts genutzt werden. Durch Online-Konzentrationsmessungen und/oder Wärmebilanzmessungen ist es außerdem möglich, das Einschlafen der Hauptreaktion durch Verunreinigungen zu erkennen und das spätere Wiederstarten zu verhindern. Darüber hinaus konnte nachgewiesen werden, daß im geschlossenen Reaktionskalorimeter die reaktionstechnischen Parameter, wie Induktionszeit, Dauer des Startprozesses und Reaktionsenthalpie, wesentlich genauer als im offenen Reaktor gemessenen werden können. Ferner werden Untersuchungen dieser Grignard-Reaktion im adiabatischen Reaktionskalorimeter (PhiTecII) diskutiert, das auch zur Dimensionierung von Notentlastungssystemen dienen kann.
  • Lecture (Conference)
    GVC/DECHEMA Jahrestagung 2005, 06.-08.09.2005, Wiesbaden, Germany
  • Abstract in refereed journal
    Chemie Ingenieur Technik 77(2005)8, 1123-1123

Publ.-Id: 7174 - Permalink


The influence of the density difference on the mixing process in mechanically agitated reactor
Hessel, G.; Hristov, H. V.; Kryk, H.; Prasser, H.-M.; Schmitt, W.;
A non-baffled stirred vessel reactor was investigated computationally with CFX-5 numerical package. The mixing of two miscible liquids with different densities was dynamically predicted from an initially stratified to a complete mixing condition. Although for a non-baffled vessel an axi-symmetric behaviour can be expected, the process was regarded as three dimensional in order to demonstrate the local instabilities associated with the blade passage. Additionally, the gas phase was involved into the simulations to investigate the effect of the free surface deformation on the mixing process. The two-phase gas-liquid interactions were modelled using the free surface model. The different density liquids were comprised into the liquid phase by the means of the multicomponent model. The grid elements size was kept relatively low because of the dynamic behaviour of the liquid surface central vortex. Furthermore, the available turbulence models were considered to obtain the closest possible match with the experimental observations. In such a way, the stirred vessel hydrodynamics was dynamically calculated in 3-D in order to study the effect of the density difference.
The numerical simulations were evaluated experimentally using video visualisation technique. The lighter (alcoholic) coloured component and the heavier (water) transparent one, which were initially stratified, were brought into motion by the means of the rotating impeller and the mixing process was captured by digital camcorder and subsequently the images were digitally processed. Several points, close to vessel central line and wall, for which the optical distortion was minimal were considered for evaluation of the numerical predictions.
The hydrodynamics of the above described system is of particular concern for many chemical and biochemical reactions engineered to take place in stirred vessel reactor. Although the initial conditions were to some extend idealised in order to avoid some complications raised by the presence on an injection, the studies showed strong influence on the density difference on the homogenisation. Such so called idealised conditions, however, also might occur in the stirred vessel, especially in the case of impeller malfunctioning. In case of impeller stoppage, i.e. breakdown, different density liquids present in the vessel might get stratified. This effect might prove to be of significant importance, especially in the case of reacting liquids for large-scale reactors operating in the industry.
  • Contribution to proceedings
    Conference on Computational Fluid Dynamics in Chemical Reaction Engineering IV, 19.-24.06.2005, Barga, Italy
    CD-ROM
  • Lecture (Conference)
    Conference on Computational Fluid Dynamics in Chemical Reaction Engineering IV, 19.-24.06.2005, Barga, Italy

Publ.-Id: 7173 - Permalink


Sonne in der Schule: Betriebsergebnisse aus den Programmen in Bayern, Sachsen und Norddeutschland
Becker, G.; Schiebelsberger, B.; Rindelhardt, U.; Weber, W.;
Seit 10 Jahren wird in Deutschland das Programm "Sonne in der Schule" durchgeführt. An mehr als 1000 Schulen wurden dabei netzgekoppelte Photovoltaik-Anlagen errichtet. Im Beitrag werden die erreichten Betriebsergebnisse dieser Anlagen dargestellt. Darüber hinaus wird auf die Nutzung der Anlagen im Unterricht eingegangen.
Keywords: Photovoltaik-Anlagen
  • Poster
    20. Symposium Photovoltaische Solarenergie, 09.-11.03.2005, Staffelstein, Deutschland
  • Contribution to proceedings
    20. Symposium Photovoltaische Solarenergie, 09.-11.03.2005, Staffelstein, Germany

Publ.-Id: 7172 - Permalink


Athermal germanium migration in strained silicon layers during junction formation with solid-phase epitaxial regrowth
Vandervorst, W.; Janssens, T.; Brijs, B.; Delhougne, R.; Loo, R.; Caymax, M.; Pawlak, B. J.; Posselt, M.;
The formation of a thin strained Si layer on top of a strain-relaxed SiGe buffer is a recent approach to improve the drive current of complementary metal-oxide-semiconductor devices by inducing strain within the transistor channel. At the same time, advanced process technologies require junction formation processes with minimal diffusion and very high dopant activation. Solid-phase epitaxial regrowth is a low temperature process based on preamorphization and subsequent regrowth leading to highly activated and shallow junctions. In this letter, we investigate the stability of the thin strained Si layer, during solid-phase epitaxial regrowth process by monitoring the Ge redistribution/strain after the preamorphization step (without any anneal) and after the thermal regrowth process.
Keywords: strained silicon, germanium, silicon germanium, junction formation, athermal migration
  • Applied Physics Letters 86(2005), 081915

Publ.-Id: 7168 - Permalink


Wire-mesh sensors and tomography methods developed by FZR
Prasser, H.-M.;
The Institute of Safety Research of the Forschungszentrum Rossendorf, Germany, has developed electrode-mesh sensors, which allow the measurement of the electrical conductivity distribution in a flow duct. This can be used either for the detection of the gaseous phase in a gas-liquid flow or for mixing studies in single phase flow, when the components have different electric conductivities. Due to the high measuring rate each bubble is mapped in several successive instantaneous frames. This allows to obtain bubble size distributions as well as bubble-size resolved gas fraction profiles beside the visualisation and the calculation of profiles of the time-averaged void fraction. The sensor is widely used to study the evolution of the flow pattern in an upwards air-water flow. The experiments aim at closure equations describing forces acting on bubbles as well as coalescence and fragmentation frequencies for the implementation in CFD-codes. Some other prominent examples of the application of wire-mesh sensors were given, like (1) boiling water reactor stability studies, (2) the visualization of cavitation at fast-acting cut-off valves, (3) the visualization of the flow structure behind a closing globe valve, and finally (4) mixing studies in single-phase flow at the ROCOM test facility in Rossendorf, which are aimed at the mixing of deborated slugs during boron dilution transients.

Second subject of the paper is radiation tomography. A gamma-tomography setup for imaging a periodically changing density field is described. It is based on a time-resolved acquisition of the detector signals. It was used to visualize the gas fraction distribution within the impeller of an axial turbo-pump operating at about 1500 rpm, that delivered a gas-liquid mixture, as well as to a hydraulic clutch (coupling). In the field of X-ray tomography, the status of the development of an ultra-fast system based on a scanning electron beam is presented. An electron beam is linearly deflected over a tungsten target with a frequency of 1 kHz. X-rays generated by the traveling focus penetrate the object and arrive at a detector line placed behind the object. The detectors are read-out with a sufficiently high speed in order to obtain projections of the density distribution in different projecting directions, which change thanks to the scanning. First results showing tomographic image sequences of a phantom consisting of small spheres kept in arbitrary motion in a cylindrical test box will be presented. Moving spheres of 3 mm diameter with cylindrical holes of 1 mm diameter were resolved at a framing rate of 1 kHz.
Keywords: Wire-mesh sensor, X-ray tomography, gamma tomography, gas-liquid flow
  • Invited lecture (Conferences)
    Seminar, 29.11.2004, Darmstadt, Germany

Publ.-Id: 7167 - Permalink


Irrtümer über Kernenergie
Prasser, H.-M.;
Der Vortrag plädiert für einen Mix aus Atomenergie und erneuerbaren Energien, um die Versorgung für die Zukunft sicher zu stellen. Kernkraftwerke sind ebenso wirtschaftlich, wie heute die Energiegewinnung aus fossilen Brennstoffen, jedoch mit wesentlich geringeren Stoffströmen verbunden: Der Ertrag aus der Spaltung von einem Kilogramm Uran 235 oder Plutonium 239 entspricht dem aus der Verbrennung von rund 2800 Tonnen Steinkohle. Dies ist die Stärke der Kernenergie, denn dadurch ist sie die einzige Primärenergiequelle, bei der die Abfälle vollständig erfasst und geordnet entsorgt werden können. Unrealistisch ist die Vorstellung, Deutschland könne seinen Energiebedarf bis 2050 zur Hälfte aus regenerativen Quellen decken. Speichermöglichkeiten sind begrenzt, weshalb bei idealen Witterungsbedingungen Überkapazitäten auftreten würden, die nicht verwertet werden könnten. Bei einer Flaute oder bedecktem Himmel wiederum müsste Strom importiert oder beispielsweise aus fossilen Kraftwerken eingespeist werden. Beides würde den ohnehin schon hohen Strompreis aus diesen Quellen in unvertretbare Höhen treiben. Weiterhin betrachtet werden die Verfügbarkeit von Spaltmaterial, der erreichte Stand bei der Sicherheit der Kernkraftwerke sowie die Endlagerproblematik.
Keywords: nuclear energy, energy strategy, nuclear safety, nuclear waste disposal, nuclear fuel
  • Lecture (others)
    Thematischer Abend, 19.11.2004, Darmstadt, Germany

Publ.-Id: 7166 - Permalink


Kernkraft - eine Energiequelle der Zukunft - auch für Deutschland
Prasser, H.-M.;
Gefährlich, riskant, umweltschädigend, gesundheitsschädlich, unverantwortbar, unwirtschaftlich, unsozial, nicht nachhaltig - das sind Adjektive, mit der die Nutzung der Kernenergie zur Stromversorgung häufig belegt wird. Tatsächlich tragen die Kernkraftwerke jedoch stabil zur kostengünstigen Stromversorgung bei. In Deutschland haben sie einen Anteil von 30 %, in einigen Ländern mehr. Unter dem Eindruck spürbar anwachsender Brennstoffpreise bei den fossilen Energieträgern und immer deutlicher werdender Folgen der Klimaveränderungen mehren sich die Stimmen, die eine Renaissance der Kernenergie für notwendig halten. In einer solchen Situation ist es wichtig, die Potenzen der Energiegewinnung durch Kernspaltung zu kennen und die wichtigsten Behauptungen der Kernenergiegegner kritisch zu hinterfragen. Speziell für Deutschland wird ein Blick auf die gängigen Konzeptionen zur Energiestrategie der nächsten 50 Jahre geworfen. Letztendlich wird der Schluss gezogen, dass langfristig ein Umsteuern auf einen Mix aus nuklearen und regenerativen Energiequellen erfolgen muss, um zu einer nachhaltigen und ökonomisch, sozial und ökologisch vertretbaren Energieversorgung zu gelangen.
Keywords: nuclear energy, sustainability, energy strategy, acceptance of nuclear energy
  • Lecture (others)
    Industrieclub Sachsen, 05.10.2004, Dresden, Schloss Eckberg, Germany

Publ.-Id: 7165 - Permalink


Turbulent dispersion of bubbles in poly-dispersed gas-liquid flows in a vertical pipe
Shi, J.-M.; Burns, A.; Prasser, H.-M.;
The turbulence of the liquid phase has a signi cant dispersion e ect on the migration of bubbles in a vertical ow. Based on a double averaging approach and by adopting the Favre averaged velocity, a generalized model, called the Favre Averaged Drag (FAD) Model, was developed for the turbulent dispersion force for Eulerian simulations of multiphase ows [Burns et al., 2004]. The model formulation was originally derived from the instant Eulerian model equations as a result of the correlation between the inter phase drag and the volume fractions. In this work, a new model derivation from the two-way coupled Lagrangian formulation is provided. This derivation makes the sense of the double averaging approach straightforward. Moreover, the new derivation provides a theoretical foundation for applying the FAD model to the Lagrangian solver, which will signi cantly increase the computational e ciency. We also provide validation and evaluation for this model by numerical and experimental investigations of bubbly ows in a vertical pipe. The experimental data were obtained by using the wire-mesh sensor technique. The computations were carried out by applying poly-dispersed models. The emphasis is to examine the model applicability under various ow conditions including bubbly ows with a wall peak and a core peak of the gas volume fraction, ows in the transition region between them, and in the nely dispersed ow regime. The e ect of the drag force model on the turbulent dispersion force was also examined.
Keywords: Turbulent dispersion force, non-drag force model, bubbly flow, CFD
  • Contribution to proceedings
    13th International Conference on Nuclear Engineering, 15.-20.05.2005, Beijing, China

Publ.-Id: 7163 - Permalink


DYN1D-MSR dynamics code for molten salt reactors
Krepel, J.; Rohde, U.; Grundmann, U.; Weiss, F.-P.;
This paper reports about the DYN1D-MSR code development and dynamics studies of the molten salt reactors (MSR) – one of the ‘Generation IV International Forum’ concepts. In this forum the graphite-moderated channel type MSR based on the previous Oak Ridge National Laboratory research is considered.
The liquid molten salt serves as a fuel and coolant, simultaneously and causes two physical peculiarities: the fission energy is released predominantly directly into the coolant and the delayed neutrons precursors are drifted by the fuel flow. The drift causes the spread of delayed neutrons distribution to the non-core parts of primary circuit and it can lead to a reactivity loss or gain in the case of fuel flow acceleration or deceleration, respectively. Therefore, specific 3D tool based on in house code DYN3D was developed in FZR. The code DYN3D-MSR is based on the solution of two-group neutron diffusion equation by the help of a nodal expansion method and it includes models of delayed neutrons drift and specific MSR heat release distribution.
In this paper the development and verification of 1D version DYN1D-MSR of the code is described. The code has been validated with the experimental data gained from the molten salt reactor experiment performed in the Oak Ridge and after the validation it was applied to several typical transients (overcooling of fuel at the core inlet, reactivity insertion, and the fuel pump trip).
Keywords: MSR, Molten, Salt, Reactor, Dynamics, DYN3D, DYN1D-MSR, liquid, fuel

Publ.-Id: 7162 - Permalink


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