Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32337 Publications
Favorable Conditions of Θ+ Formation in γD Reaction
Titov, A.; Kämpfer, B.; Daté, S.; Ohashi, Y.;
We show that a Θ+ signal may appear in the [γD, pK−] missing mass distribution in inclusive γD → pK−X reaction when the pK− pair is knocked out in the forward direction and its invariant mass is close to the mass of Λ(1520). We show that the conditions of the recent CLAS experiment reduce the Θ+ formation probability making it difficult to extract a Θ+ peak from the data.
  • Open Access LogoProgress of Theoretical Physics 168(2007), 86-89

Publ.-Id: 11244 - Permalink


Dynamo action and magnetorotational instability: cosmic magnetism in the liquid metal lab
Stefani, F.;
It is widely known that cosmic magnetic fields are produced by the hydromagnetic dynamo effect. Yet it is less well known that cosmic magnetic fields play an active role in cosmic structure formation by means of the magnetorotational instability (MRI). The last ten years have seen tremendous efforts in studying both effects in the laboratory. In 1999, magnetic field self-excitation was observed nearly simultaneously in the liquid sodium facilities in Riga and Karlsruhe. Recently, self-excitation was also obtained in the French "von Karman sodium" (VKS) experiment, although with the help of iron propellers. The helical MRI was recently studied in the ''Potsdam Rossendorf Magnetic Instability Experiment'' (PROMISE), and an improved version of this experiment (PROMISE 2) has provided sharper transitions between stable and unstable regimes. In the talk, the history of dynamo and MRI experiments is delineated, and some interesting directions of future work are discussed.
  • Invited lecture (Conferences)
    MHD fundamentals, from liquid-metals to astrophysics, 14.-16.04.2008, Bruxelles, Belgium

Publ.-Id: 11243 - Permalink


Plastic foils as primary hydrogen standards for nuclear reaction analysis
Rudolph, W.; Bauer, C.; Brankoff, K.; Grambole, D.; Grotzschel, R.; Heiser, C.; Herrmann, F.;
Plastic materials like polypropylene, polyester (Mylar) and polycarbonate (Lexan or Makrofol E) contain large amounts of hydrogen and their compositions are well known. However, these materials are not stable during ion bombardment. Using the 1H(15N,αγ)12C and 1H(19F, αγ)16O nuclear resonance reaction at energies EN = 6.50 MeV and EF = 6.83 MeV, respectively, we have investigated the behaviour of plastic foils during 15N and 19F ion bombardment. By means of a rotating sample holder low current densities of 1–2 nA/cm² and large irradiated foil areas of up to 10 cm² were realized. Under these measuring conditions the γ-ray yields change only slightly and the initial yields, which correspond to the known compositions of the foils, can be determined with good accuracy. In this way the plastic foils can be used as primary standards for hydrogen content calibration. The method was employed to calibrate an a-Si(H) reference target.
  • Nuclear Instruments and Methods in Physics Research B 15(1986), 508-511

Publ.-Id: 11242 - Permalink


Void measurement in boiling water reactor rod bundles using high resolution gamma ray tomography
Bieberle, A.; Hoppe, D.; Zippe, C.; Schleicher, E.; Tschofen, M.; Suehnel, T.; Zimmermann, W.; Hampel, U.;
We present a high resolution gamma ray computed tomography (CT) system for the measurement of the void distribution in sub-channels in an electrically heated fuel rod bundle at the thermal hydraulic test loop KATHY (AREVA NP GmbH, Germany). This measurement system generates cross-sectional void fraction profiles through the pressure vessel for true-to-scale fuel rod bundles operating under typical nuclear reaction conditions and in steady state. Measurements are non-invasive, thus the two-phase flow in the bundle is not influenced. The gamma ray computed tomography system consists of a collimated 137Cs isotopic source, a gamma radiation detector arc including 320 single elements and a pulse processing unit. The average spatial resolution of the CT system is about 3 mm in plane and 8 mm axial. The thermal design of the detector arc is optimised to keep the temperature of internal components constant under changing environmental conditions. A specially developed gantry was constructed to realise vertical positioning and continuous rotation of the CT system. To determine the void fraction distribution a two-point calibration method is used. Here, data sets at zero and one hundred percent void fraction are required. The non-superposed slice image is generated using the filtered back projection reconstruction algorithm.
Keywords: high resolution gamma ray tomography, void fraction determination
  • Contribution to proceedings
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.08, Grenoble, France
    PaperNo BOI-06
  • Lecture (Conference)
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.08, Grenoble, Frankreich

Publ.-Id: 11241 - Permalink


Eta-prime meson production in nucleon-nucleon collisions near the threshold
Kaptari, L. P.; Kämpfer, B.;
The production of eta' mesons in the reactions pp to ppeta' and pn to pn eta' at threshold-near energies is analyzed within a covariant effective meson-nucleon theory. The description of cross section and angular distributions of the available data in this kinematical region in the pp channel is accomplished by including meson currents and nucleon currents with the resonances S_{11}(1650), P_{11}(1710) and P_{13}(1720). Predictions for the pn channel are given. The di-electron production from subsequent eta' Dalitz decay eta' to gamma gamma^* to gamma e^+e^- is also calculated and numerical results are presented for intermediate energy and kinematics of possible experiments with HADES, CLAS and KEK-PS.

Publ.-Id: 11240 - Permalink


Investigating the ESBWR stability with experimental and numerical tools: a comparative study
Rohde, M.; Marcel, C. P.; Manera, A.; van der Hagen, T. H. J. J.; Shiralkar, B.;
In this work, the stability of the Economic Simplified Boiling Water Reactor (ESBWR) has been studied by using a Freon-134a based experimental facility (GENESIS) and two system codes, being ATHLET 2.0a and (to a lesser extent) TRACG. During setting up the GENESIS facility and the numerical calculations, a great effort has been made to approximate the ESBWR system as accurate as possible.
In general, it was found that a sufficient margin to instability exists regarding the ESBWRs nominal point. In addition, a comparison was made between the numerical and experimental results for both the thermal-hydraulic system and the reactor system. Deviations were found between the numerical and experimental results, in spite of the close similarity between the GENESIS facility and the definition of the ESBWR system in the system code. This result shows that predictions regarding real nuclear reactors, based on modeled systems, should be taken with care.

Publ.-Id: 11239 - Permalink


Quantum well infrared photodetector array development and applications
Schneider, H.;
Quantum well infrared photodetector (QWIP) technology has opened up new opportunities to realize focal plane arrays (FPA) for high-performance thermal imaging [1]. High thermal and spatial resolution, low 1/f noise, low fixed-pattern noise, and high pixel operability makes QWIP FPAs appropriate for many applications. Due to their narrow absorption bands with relative spectral widths of the order of 10%, QWIPs are particularly suitable for thermal imaging applications involving several atmospheric transmission bands or several colors within the same band. In this talk, I will report on the development of QWIP structures optimized for thermal imaging applications and on the performance of QWIP cameras which were jointly realized by the Fraunhofer-Institute for Applied Solid State Physics (Freiburg, Germany) and AIM Infrarot-Module GmbH (Heilbronn, Germany). Besides imagers for the 8 – 12 micron long-wavelength infrared (LWIR) and 3 – 5 micron mid-wavelength infrared (MWIR) regimes, a LWIR/MWIR dual-band QWIP FPA will also be discussed.
[1] H. Schneider and H. C. Liu, Quantum Well Infrared Photodetectors: Physics and Applications, ISBN 3540363238, Springer Series in Optical Sciences Vol. 126, 2007.
Keywords: quantum well infrared photodetector, QWIP
  • Lecture (others)
    Seminarvortrag, Shanghai Institute of Technical Physics, Chinese Academy of Science, 24.03.2008, Shanghai, China
  • Lecture (others)
    Seminarvortrag, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Science, 27.03.2008, Suzhou, China
  • Lecture (others)
    Seminarvortrag, Institute of Semiconductors, Chinese Academy of Science, 02.04.2008, Beijing, China

Publ.-Id: 11238 - Permalink


TEM, SANS and PAS applied to neutron-irradiated pure Fe
Hernández Mayoral, M.; Bergner, F.; Almazouzi, A.; Lambrecht, M.;
Irradiation-induced microstructural features in pure Fe were investigated by a triple of methods: TEM, SANS and PAS. In the talk it will be analyzed, if and how the features detected by the individual techniques reflect themselves in the output of each other method. This information is used in order to derive a coherent picture of irradiation damage in pure Fe.
  • Lecture (Conference)
    14th Meeting of the International Group on Radiation Damage Mechanisms (IGRDM-14), 20.-25.04.2008, Pittsburgh, United States

Publ.-Id: 11237 - Permalink


Flux dependence of cluster formation in neutron irradiated weld material
Bergner, F.; Ulbricht, A.; Hein, H.;
SANS results for an RPV weld material irradiated at two different neutron fluxes up to the same neutron fluence will be presented. We have observed a remarkable effect of flux on the size of irradiation-induced clusters. A rate theory model is applied in order to give a tentative explanation for the findings. Interestingly, the mechanical properties do not show a corresponding flux effect. The results will be faced with observations for another RPV steel exhibiting a different behaviour.
  • Lecture (Conference)
    14th Meeting of the International Group on Radiation Damage Mechanisms (IGRDM-14), 20.-25.04.2008, Pittsburgh, USA

Publ.-Id: 11236 - Permalink


Double photoexcitation involving 2p and 4f electrons in L3-edge x-ray absorption spectra of protactinium
Hennig, C.; Le Naour, C.; Den Auwer, C.;
The L3-edge x-ray absorption spectrum of Pa(V) fluoride in aqueous solution show clear evidence for the double photoexcitation involving 2p and 4f electrons. A comparison with the [2p4f] double-electron excitations observed in the L3-edge x-ray absorption spectra of other actinides (thorium, uranium, neptunium, plutonium and americium) indicates a monotonic increase of the excitation energy. The sharp edge-like structure of the multielectron excitation reveals the origin of a shake-up channel.
Keywords: [2p4f] double-electron excitation, protactinium

Publ.-Id: 11235 - Permalink


Experiments on slug mixing under natural circulation conditions at the ROCOM test facility using high resolution measurement technique and numerical modeling
Kliem, S.; Höhne, T.; Rohde, U.; Weiß, F.-P.;
ROCOM is a four-loop test facility for the investigation of coolant mixing in the primary circuit of pressurized water reactors. Recently, a new sensor was developed for an improved visualisation and quantification of the coolant mixing in the downcomer. This new sensor spans a dense measuring grid and covers nearly the whole downcomer. In the presented work, special emphasis was given to the comparison of the data of this sensor with the results of calculations using the CFD code ANSYS CFX. A coolant mixing experiment during natural circulation conditions has been conducted. The underlying scenario of this experiment is based on a boron dilution scenario following a SBLOCA event. The corresponding CFD code solution has been obtained using the Best Practice Guidelines. All main effects observed in the measurement are described by the calculation. The detailed comparison reveals that the calculation underestimates the coolant mixing inside the reactor pressure vessel.
The measurement data, boundary conditions of the experiment and facility geometry can be made available to other CFD code users for benchmarking.
  • Lecture (Conference)
    XCFD4NRS - Experiments and CFD Codes Application to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
  • Contribution to proceedings
    XCFD4NRS - Experiments and CFD Codes Application to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, Frankreich
    Proceedings of the XCFD4NRS - Experiments and CFD Codes Application to Nuclear Reactor Safety, CDROM
  • Nuclear Engineering and Design 240(2010)9, 2271-2280
    DOI: doi:10.1016/j.nucengdes.2009.11.015

Publ.-Id: 11234 - Permalink


Advanced two-phase flow measurement techniques at Research Centre Dresden-Rossendorf - sensors, systems and applications
Hampel, U.;
Understanding and modelling of two-phase flow is a key issue in nuclear engineering and in many other engineering fields. The Research Centre Dresden-Rossendorf is, amongst others, engaged in safety research for nuclear light water reactors and performs combined experimental and theoretical work on two-phase flow phenomena. In the frame of this work considerable effort has been spent in the past to develop innovative two-phase flow measuring techniques. Special focus has been given to imaging techniques which are able to resolve phase distributions at high temporal and spatial resolution. The presentation introduces the most advanced of these techniques, including different types of wire-mesh sensors, gamma ray tomography and ultra fast electron beam tomography and discusses application of such techniques and systems in basic research as well as industrial applications.
Keywords: Two-phase flow, flow measurement
  • Invited lecture (Conferences)
    Meeting der Industrial Tomography Systems Ltd., 01.04.2008, Manchester, UK
  • Invited lecture (Conferences)
    Frontier Seminar at Institute of Particle Science and Engineering, Leeds University, 2.4.2008, Leeds, UK
  • Invited lecture (Conferences)
    Research Seminar, School of Chemical, Environmental and Mining Engineering, Nottinhgam University, 3.4.2008, Nottingham, UK
  • Invited lecture (Conferences)
    Research Seminar, Nuclear Physics Group, Positron Imaging Centre, Birmingham University, 4.3.2008, Birmingham, UK

Publ.-Id: 11233 - Permalink


Recent progress in ultra fast electron beam X-ray computed tomography
Hampel, U.; Fischer, F.; Bieberle, M.; Schleicher, E.;
A new ultra fast electron beam X-ray CT scanner has been developed, implemented and tested in different applications. It consists, amongst other components, of an electron beam unit with 10 kHz scanning capability and 1 mm focal spot size and a 240 element circular CZT detector arc. The system is capable to produce slice images at up to 7 kHz frame rate of moderately absorbing objects with maximum 120 mm diameter. The paper introduces the scanner and first results for two-phase flow measurements in a bubble column and a fluidized bed.
Keywords: ultra fast electron beam ray tomography, two-phase flow
  • Contribution to proceedings
    5th International Symposium on Process Tomography, 25.-26.08.2008, Zakopane, Poland
    Proceedings of the 5th International Symposium on Process Tomography, Paper No. PT08_cr11
  • Lecture (Conference)
    5th International Symposium on Process Tomography, 25.-26.08.2008, Zakopane, Poland

Publ.-Id: 11232 - Permalink


Wire-mesh and X-ray microtomography studies of flow patterns in the mixing chamber of an effervescent atomizer
Otahal, J.; Boden, S.; Schleicher, E.; Beyer, M.; Jícha, M.; Hampel, U.;
We performed wire-mesh and X-ray micro¬tomography studies of the two-phase flow in the mixing chamber of an effervescent atomizer. Flow patterns in the mixing chamber can be revealed by the miniature wire mesh sensor with a temporal resolution of 10 kHz whereas microtomography provides accurate and high-resolution axial-radial gas fraction profiles. The paper describes both measurement techniques and first results of experimental investigation.
Keywords: Two-phase flow, wire mesh sensor, X-ray microtomography
  • Contribution to proceedings
    5th International Symposium on Process Tomography, 25.-26.08.2008, Zakopane, Poland
    Proceedings of the 5th International Symposium on Process Tomography, Paper No. PT08_cr8
  • Lecture (Conference)
    5th International Symposium on Process Tomography, 25.-26.08.2008, Zakopane, Poland

Publ.-Id: 11231 - Permalink


Ultra fast scanned electron beam X-ray CT for two-phase flow measurement
Hampel, U.; Fischer, F.; Schleicher, E.; Hoppe, D.;
We developed an ultra fast X-ray CT scanner based on scanned electron beam technology. The new device enables ultra fast two-dimensional phase fraction imaging in flow cross-sections at frame rates up to 7 kHz. As an example flow measurement in a 60 mm diameter bubble column is presented.
Keywords: Electron beam CT, X-ray CT, multiphase flow imaging
  • Contribution to proceedings
    CT2008: TOMOGRAPHY CONFLUENCE - An International Conference on the Applications of Computerized Tomography, 15.-17.02.2008, Kanpur, India
    AIP Conference Proceedings 1050: American Institute of Physics, 978-0-7354-0578-3, 144-150
  • Invited lecture (Conferences)
    CT2008: TOMOGRAPHY CONFLUENCE - An International Conference on the Applications of Computerized Tomography, 15.-17.02.2008, Kanpur, India

Publ.-Id: 11230 - Permalink


High resolution gamma ray tomography and its application to multiphase flow measurement
Hampel, U.; Bieberle, A.; Schleicher, E.; Hoppe, D.; Zippe, C.;
Gamma ray tomography is a valuable tool for multiphase flow analysis in different areas of process, nuclear and mechanical engineering. Here, we introduce the design of a high resolution gamma ray tomography scanner and discuss two application examples from different technical fields.
Keywords: gamma ray tomography, multiphase flow imaging
  • Contribution to proceedings
    CT2008: TOMOGRAPHY CONFLUENCE - An International Conference on the Applications of Computerized Tomography, 15.-17.02.2008, Kanpur, India
    AIP Conference Proceedings 1050: American Institute of Physics, 978-0-7354-0578-3, 138-143
  • Invited lecture (Conferences)
    CT2008: TOMOGRAPHY CONFLUENCE - An International Conference on the Applications of Computerized Tomography, 15.-17.02.2008, Kanpur, India

Publ.-Id: 11229 - Permalink


Solidification of metal alloys under the influence of pulse-modulated magnetic fields
Nikrityuk, P. A.; Räbiger, D.; Eckert, K.; Eckert, S.; Gerbeth, G.;
Alternating current (AC) magnetic fields are commonly used in industrial practice for melt stirring. The requirements arising from the particular metallurgical or casting operation can be manifold. For instance, the electromagnetic stirring is applied to provide an efficient mixing of metallic melts, to control the flow at the mold region in the continuous casting process or to achieve a purposeful alteration of the microstructure of casting ingots.
In the present study we introduce a novel type of electromagnetic stirring using a pulse-modulated rotating magnetic field (RMF). Capabilities of this approach are exemplarily demonstrated for controlling the melt flow during the unidirectional solidification of an Al-7wt%Si alloy. Two variants have been examined. Firstly, we use a succession of pulses that always have the same rotational direction (RMF-PSCD). Secondly, we use an RMF pulse sequence of alternating direction (RMF-PSAD). The latter method is related to a periodic inversion of the sense of rotation between two consecutive pulses. The characteristic period of the inversion for RMF-PSAD and of the pulses for RMF-PSCD is derivable from the spin-up dynamics of a continuously applied RMF.
Numerical and experimental investigations of different configurations applying an RMF either continuously or in form of RMF-PSAD and RMF-PSCD reveal the development of different flow pattern. It was found that the application the time-modulated RMF with suitable modulation frequencies delivers a homogeneous, equiaxed microstructure. Typical segregation pattern or flow-induced gas porosity usually arising from a continuous RMF application can be avoided with the new stirring methods. Essential features of the interplay between the electromagnetically-driven melt flow and solidification parameters such as temperature and mixture mass concentration of Si are discussed. Our results demonstrate that the success of the presented RMF-PSAD technique requires a precise tuning of the magnetic field parameter with respect to the material properties of the alloy, the geometry of the casting or process parameters like the cooling rate.
Keywords: solidification, Al alloys, electromagnetic stirring, pulse-modulated magnetic fields, macrosegregation
  • Poster
    7th PAMIR International Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
  • Contribution to proceedings
    7th PAMIR International Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France, 879-884

Publ.-Id: 11228 - Permalink


Bubble-driven liquid metal flows influenced by miscellaneous magnetic fields
Zhang, C.; Eckert, S.; Gerbeth, G.;
Bubble driven flows have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenize the physical and chemical properties of the melt or to refine the melt. For such gas-liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way.
Compared to the numerous experimental studies on the movement of bubbles in transparent liquids, especially in water, the number of publications dealing with gas bubbles rising in liquid metals is comparatively small. The shortage of suitable measuring techniques can be considered as one reason for the slow progress in the investigations of gas-liquid metal flows. We applied the Ultrasound Doppler Velocimetry (UDV) for measurements of the velocity structure in liquid metal bubbly flows. Because of the ability to work non-invasively in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications. In the range of small or moderate void fractions the UDV technique delivers both the bubble and the liquid velocity.
Keywords: bubble plume, magnetic fields, velocity measurements, Ultrasound Doppler method
  • Lecture (Conference)
    7th PAMIR International Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
  • Contribution to proceedings
    7th PAMIR International Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France, 363-368

Publ.-Id: 11227 - Permalink


Benchmark database on the evolution of two-phase flows in a vertical pipe
Lucas, D.; Beyer, M.; Kussin, J.; Schütz, P.;
Basing on many years of experience a new extensive high quality database was obtained for stationary upward air-water flows in a vertical pipe with an inner diameter of 195.3 mm using the wire-mesh sensor technology. During the experiments the sensor was always mounted on the top of the test section while the distance between gas injection and measuring plane was varied to up to 18 different L/D by using gas injection chambers at different vertical positions. The gas was injected via holes in the pipe wall. In this new test series the pressure was kept at 0.25 MPa (absolute) at the location of the active gas injection while the temperature was constant at 30°C +- 1K. The experiments were done for 48 combinations of air and water superficial velocities varying from 0.04 m/s to 1.6 m/s for water and 0.0025 m/s to 3.2 m/s for air. From the raw data time averaged data as: radial gas volume fraction profiles, bubble size distributions, radial volume fraction profiles decomposed according to the bubble size and the radial profiles of the gas velocity were calculated. All data were checked regarding their consistency. They are characterized by a high resolution in space what makes them suitable for the development and validation of CFD-grade closure models, e.g. for bubble forces and coalescence and break-up. It is also an ideal base to validate CFD approaches for poly-dispersed flow. For this reason it is proposed to use the database as a benchmark for modelling poly-dispersed flows.
Keywords: multiphase flow, bubbly flow, churn turbulent flow, annular flow, bubble size, pipe flow
  • Contribution to proceedings
    XCFD4NRS, Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France, BOI-001
  • Lecture (Conference)
    XCFD4NRS, Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
  • Nuclear Engineering and Design 240(2010), 2338-2346
    DOI: 10.1016/j.nucengdes.2009.11.010

Publ.-Id: 11226 - Permalink


A hybrid finite volume - boundary element method (FV-BEM) for the numerical solution of the kinematic induction equation
Giesecke, A.; Stefani, F.; Gerbeth, G.;
The experimental realization of dynamo excitation has demonstrated the relevance of boundary conditions and material properties for a self-sustaining dynamo. The consideration of conductivity or permeability inhomogeneities requires a flexible numerical method that utilizes a local discretization scheme. A fast and accurate approach is provided by the constraint transport (CT) approach, a well known realization of a finite volume (FV) method that intrinsically maintains the solenoidal character of the magnetic field. The
problem of laboratory boundary conditions is treated by the boundary element method (BEM) which in combination with the FV scheme offers the flexibility of a local discretization with a stringent treatment of insulating magnetic boundary conditions.

Test simulations reproduce key results of the induction effects of a von-Karman-like flow and demonstrate the applicability and reliability of the approach.

Current examinations investigate the dynamo process presented by Busse & Wicht (1992, GaFD, 64, 135-144) who showed that a constant flow over a conducting material that exhibits a sinusoidal variation of the conductivity is already sufficient to generate a dynamo.
  • Lecture (Conference)
    MHD fundamentals, from liquid-metals to astrophysics, 14.-16.04.2008, Brussels, Belgium

Publ.-Id: 11225 - Permalink


Coexistence of localized and delocalized f-electrons in α-YbPdSn from thermodynamic and transport measurements
Görlach, T.; Putselyk, S.; Hamann, A.; Tomanic, T.; Uhlarz, M.; Schappacher, F. M.; Pöttgen, R.; von Löhneysen, H.;
We report the specific heat, magnetic susceptibility, and magnetization as well as resistivity of hexagonal α-YbPdSn polycrystals down to temperatures T of 50 mK and fields up to 12 T. In the susceptibility χ(T), several different temperature regimes can be distinguished. For 300 K>T>170 K, a Curie-Weiss-like behavior is obtained with the effective moments close to that of Yb>sup>3+. The large Weiss temperature ΘH≈150 K and the leveling off of χ toward low T are indicative of valence fluctuations. Around 30 K, crystal-field excitations manifest themselves in features of χ(T) and the resistivity ρ(T). For 5 K>T>0.2 K, a Curie-Weiss behavior with µeff=1.27µB/Yb atom and ΘL=0.41 K is found, signaling the occupation of the lowest crystal-field doublet. A sharp maximum in χ(T) and in the specific heat C(T) indicates antiferromagnetic ordering at 250 mK. The specific-heat peak develops into a broadened Schottky anomaly in moderate magnetic fields. The sizable linear specific-heat coefficient γ=68 mJ/mole K2 is attributed to valence fluctuations. Likewise, the magnetization at 10 and 2.3 K measured up to 12 T can be decomposed into a contribution of delocalized electrons and localized magnetic moments. The data can be consistently interpreted in terms of a two-fluid model with ~6% localized and ~94% delocalized moments derived from (nearly) trivalent Yb.
  • Physical Review B 76(2007), 205112

Publ.-Id: 11224 - Permalink


Spin dynamics of NiCl2-4SC(NH2)2 in the field-induced ordered phase
Zvyagin, S.; Wosnitza, J.; Kolezhuk, A. K.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.; Glazkov, V. N.; Sosin, S. S.; Smirnov, A. I.;
NiCl2-4SC(NH2)2 (known as DTN) is a spin-1 material with a strong single-ion anisotropy that is regarded as a new candidate for Bose-Einstein condensation (BEC) of spin degrees of freedom. We present a systematic study of the low-energy excitation spectrum of DTN in the field-induced magnetically ordered phase by means of high-field electron spin resonance measurements at temperatures down to 0.45 K. We argue that two gapped modes observed in the experiment can be consistently interpreted within a four-sublattice antiferromagnet model with a finite interaction between two tetragonal subsystems and unbroken axial symmetry. The latter is crucial for the interpretation of the field-induced ordering in DTN in terms of BEC.
  • Physical Review B 77(2008), 092413

Publ.-Id: 11223 - Permalink


An easy mechanical way to create ferromagnetic defective ZnO
Potzger, K.; Zhou, S.; Grenzer, J.; Helm, M.; Fassbender, J.ORC
We present an experiment for the creation of unconventional ferromagnetism in pure ZnO powder by application of mechanical force. The ferromagnetism is related to flake like structures in planar compressed pieces of the powder with easy axis in the plane. It is associated with defect creation and disappears upon annealing in oxygen. Besides cluster formation, such defects might be one of the non-intrinsic origins of ferromagnetism in transition metal doped ZnO.
Keywords: ZnO, Intendation, diluted magnetic semiconductors
  • Applied Physics Letters 92(2008), 182504

Publ.-Id: 11222 - Permalink


Large carbon-isotope shift of Tc in boron-doped diamond
Dubrovinskaia, N.; Dubrovinsky, L.; Papageorgiou, T.; Bosak, A.; Krisch, M.; Braun, H. F.; Wosnitza, J.;
We report the carbon-isotope effect for boron-doped diamond (BDD). Resistive as well as specific-heat measurements reveal a 0.2 K shift in the superconducting transition temperature Tc between BDDs containing 13C and 12C. This is more than two times larger than could be expected from the mass difference by the use of the simple BCS formula in case the phenomenon is related to electron-phonon mediated superconductivity in BDD.
  • Applied Physics Letters 92(2008), 132506

Publ.-Id: 11221 - Permalink


Uranium(VI) Complexation with Pyoverdins and Related Model Compounds Studied by EXAFS
Moll, H.; Glorius, M.; Roßberg, A.; Bernhard, G.;
Synchrotron-based EXAFS spectroscopy is a powerful technique to obtain structural information on radionuclide bioligand species in solution. As an example pyoverdin-type siderophores are a unique class of bioligands, with a high potential to dissolve, bind, and thus transport uranium in the environment. Pyoverdins are secreted from fluorescent Pseudomonas species which are ubiquitous soil bacteria. The functional groups of the pyoverdin molecule, LH4, participating in metal binding are the catechol group of the chromophore and two ligand sites in the peptide chain, i.e., one or two hydroxamate groups and one or two -hydroxy acid moieties [1]. The formation of complexes of UO22+ with pyoverdins released by the groundwater bacterium Pseudomonas fluorescens (CCUG 32456) isolated at a depth of 70 m in the Äspö Hard Rock Laboratory, Sweden, was investigated in our previous study [2]. Two UO22+-P. fluorescens pyoverdin species, UO2LH2 and UO2LH-, could be distinguished on the basis of UV-vis spectroscopy and fs-TRLFS.

Little structural information is available regarding the U(VI) pyoverdin species formed in aqueous solutions. We therefore performed U LIII-edge EXAFS measurements of test solutions containing 5x10-4 or 0.001 M UO22+ and pyoverdins or related model compounds at an ionic strength of 0.1 M NaClO4. The pH was varied between 2 and 8 depending on the bioligand. EXAFS measurements were carried out on the Rossendorf Beamline (ROBL) BM20 at the ESRF [3]. The samples were measured at room temperature using a water-cooled Si(111) double-crystal monochromator in channel cut mode (5-35 keV). The spectra were collected either in fluorescence mode using a 13-element Ge solid-state detector or in transmission mode using Ar filled ionization chambers. The model compounds simulate the hydroxamate function (simple hydroxamate and a trihydroxamate compound) and the chromophore of the pyoverdin molecule. The obtained structural information for the axial and equatorial oxygen atoms surrounding the uranium atom will be presented. Estimations of the near order surrounding of uranyl in pyoverdin complexes are based on the comparison with those found in uranium(VI) model ligand species.
Keywords: Uranyl, pyoverdins, bioligands, EXAFS
  • Contribution to proceedings
    Actinide XAS 2008, 15.-17.07.2008, Saint-Aubin, France
  • Lecture (Conference)
    Actinide XAS 2008, 15.-17.07.2008, Saint-Aubin, France

Publ.-Id: 11220 - Permalink


Annual Report 2007 - Institute of Ion Beam Physics and Materials Research
von Borany, J.; Heera, V.; Helm, M.; Möller, W.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-493 2008

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Publ.-Id: 11219 - Permalink


CFD-modeling and Experiments of insulation debris transport phenomena in water flow
Krepper, E.; Cartland-Glover, G.; Grahn, A.; Weiss, F.-P.; Alt, S.; Hampel, R.; Kästner, W.; Seeliger, A.;
The investigation of insulation debris generation, transport and sedimentation becomes important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core cooling systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems.
Open questions of generic interest are the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow and the particle load on strainers and corresponding pressure drop. A joint research project on such questions is being performed in cooperation between the University of Applied Sciences Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow and the development of CFD models for its description. While the experiments are performed at the University at Zittau/Görlitz, the theoretical modeling efforts are concentrated at Forschungszentrum Dresden-Rossendorf.
In the current paper the basic concepts for CFD modeling are described and feasibility studies including the conceptual design of the experiments are presented.
Keywords: CFD, two-fluid approach, fiber flows, experiments
  • Contribution to proceedings
    XCFD4RS Experiments and CFD Codes Application to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
  • Lecture (Conference)
    XCFD4RS Experiments and CFD Codes Application to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France

Publ.-Id: 11218 - Permalink


Heat and charge transport in YNi2B2C and HoNi2B2C single crystals
Schneider, M.; Gladun, A.; Kreyssig, A.; Wosnitza, J.; Petzold, V.; Rosner, H.; Behr, G.; Souptel, D.; Müller, K.-H.; Drechsler, S.-L.; Fuchs, G.;
For a systematic investigation of the heat- and charge-transport properties of YNi2B2C and HoNi2B2C, single-crystal measurements of the electrical resistivity, the thermal conductivity, and the thermoelectric power were performed on the same samples. For HoNi2B2C, a local maximum of the Lorenz number at 20 K is evidently connected with the occurrence of magnetic fluctuations well above the ordering temperature. For the in-plane thermal conductivity, a kink near the superconducting transition was observed, consistent with an anisotropic gap or a multiband description. For both investigated borocarbides, the electrical resistance is isotropic. In contrast, the thermal conductivity shows a pronounced anisotropy. The thermoelectric power exhibits a minor anisotropy and can be well described by electron-diffusion and phonon-drag contributions over a wide temperature range. Based on an analysis of full-potential local-orbital calculations, a strong influence of the boron z position on the thermoelectric power has been
revealed.
  • Journal of Physics: Condensed Matter 20(2008), 175221

Publ.-Id: 11217 - Permalink


Radiosynthesis of novel 18F-labelled derivatives of indiplon as potential GABAA receptor imaging tracers for PET
Fischer, S.; Hiller, A.; Scheunemann, M.; Deuther-Conrad, W.; Hoepping, A.; Diekers, M.; Wegner, F.; Brust, P.; Steinbach, J.;
The involvement of gamma amino butyric acid (GABA) receptors in a variety of neurological and psychiatric diseases has promoted the development and use of radiolabelled benzodiazepines (BZ) for brain imaging by PET. However, these radioligands are unable to distinguish between the various subtypes of GABAA receptors. Novel non-BZ such as the pyrazolo-pyrimidine indiplon proved to be selective for the alpha1-subunit of the GABAA receptor. Here, we describe the syntheses of four novel 18F-labelled indiplon derivatives. Radiosyntheses were performed via n.c.a. 18F-nucleophilic substitution starting from the tosyl, bromo, and 4-nitrobenzoyl precursors to obtain fluorine substituted N-alkylamide side chain derivatives of indiplon, followed by multistep purification using semi-preparative high-performance liquid chromatography and solid phase extraction. Tosyl and bromo precursors were converted into 18F-labelled indiplon derivatives with good and reproducible radiochemical yield (RCY) (35–70%, decay corrected), high radiochemical purity (>/= 98.5%), and high specific activity ( > 150 GBq/lmol). By contrast, a low RCY (5–10%) and specific activity (10–15 GBq/lmol) were achieved for the 4-nitrobenzoyl precursor.
Keywords: GABAA receptor; 18F-labelled indiplon derivatives; PET
  • Journal of Labelled Compounds and Radiopharmaceuticals 51(2008), 123-131
    DOI: 10.1002/jlcr.1473

Publ.-Id: 11216 - Permalink


New chelating agents for copper(II): emerging opportunities for the application in nuclear medicine
Stephan, H.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Institutskolloquium, Ruhr Universität Bochum, Lehrstuhl für Anorganische Chemie, 11.04.2008, Bochum, Germany

Publ.-Id: 11215 - Permalink


Design und Synthese mehrfunktionaler Liganden zur Entwicklung von radioaktiven Kupferkomplexen für Diagnostik und Therapie
Stephan, H.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Institutskolloquium, Universität Bonn, Institut für Organische Chemie und Biochemie, 10.04.2008, Bonn, Germany

Publ.-Id: 11214 - Permalink


Uranium Speciation - from mineral to water
Geipel, G.; Bernhard, G.;
Following the possible transport of uranium under environmental conditions we may start with the weathering of uranium compounds in the soil or in a mining waste rock pile. The seepage water contains about 2 mg/L uranium and the speciation is mainly influenced be the formation of the dicalcium-uranyl-tricarbonate species. The input of these seepage water leads to a dilution of the uranium by about three orders of magnitude. Using the cryogenic technique in TRLFS we could also determine the uranium speciation in the river water nearby the former uranium mining area. The uranium concentration was about 2 µg/L uranium and in the river water mainly uranyl-tricarbonate species are formed.
Despite this uranium can migrate down to the groundwater. In this case uranium may come back to the food chain by the production of mineral waters. We have studied the uranium speciation in several German mineral waters with uranium concentrations between 50 ng/L and 5 µg/L. In agreement with speciation calculations the sparkling and the calcium poor waters contain uranium as uranyl-tricarbonate species, whereas the non-sparkling waters if they are rich in calcium show clearly the formation of the dicalcium-uranyl-tricarbonate species. Using cryogenic TRLFS the detection limit for uranium species was estimated to be about 50 ng/L. Additionally a Hungarian medicinical water shows a uranium concentration of 150 µg/L. Due to the high mineralisation of this water also the dicalcium-uranyl-tricarbonate species was determined.
Summarizing it can be concluded that the most natural waters contain uranium as tri-carbonate species. According to investigations of these uranium species are less hazardous than phosphate and citrate species.
Keywords: Uranium, Speciation, Depleted
  • Invited lecture (Conferences)
    Institutsseminar, 28.05.2008, Prag, Tschechische Republik

Publ.-Id: 11213 - Permalink


Uranium Speciation - from mineral phases to mineral waters
Geipel, G.; Bernhard, G.;
Uranium in the environment is ubiquitous. Nevertheless human activities as uranium mining and milling, use of uranium in nuclear power production and as penetrating ammunitions as well as the distribution of uranium with fertilizers lead to an increase of the uranium content in the environment.
Especially the uranium ammunition can generate locally high concentrations of uranium in the environment.
Weathering processes of the uranium metal lead in a first step to the formation of uranium minerals1. Depending on the composition of the soil the formation of several types of minerals can be estimated. Especially the content of phosphate from fertilizers and the aluminium from soil components are involved in the mineral formation.
By use of time-resolved laser-induced fluorescence spectroscopy (TRLFS) the mineral type can be determined without any destruction. A large database of luminescence spectra, obtained from uranium minerals of the collection of the Technical University Mining Academy Freiberg, enables us to identify the formed uranium mineral2. In the experiment, described in (1) we found that mainly the mineral sabugalite was formed. Other experiments with pure calcium and phosphate containing solution lead to the formation of the mineral meta-autunite3.
In a second step the formed minerals than undergo further weathering processes, forming dissolved uranium species.
In the former uranium mining areas of eastern Germany we could discover a new dissolved uranium carbonate species4,5. However, the uranium concentration of about 2 mg/L in these mining related waters is relatively high. Nevertheless the carbonate and calcium concentration are high enough to form a very stable dicalcium-uranyl-tricarbonate species. This species is of great importance, as its existence explains the uranium migration at the Hanford site6.
In addition to the calcium species it can be stated that also the other alkaline earth elements form this type of alkaline earth uranyl carbonate species7,8,910.
Following the uranium migration in the soil we could detect in the experiments that mainly carbonate species are formed. The pure carbonate species do not show any luminescence properties at room temperature. Therefore the samples have to be frozen to temperatures below 220 K11, in order to minimize the dynamic quench effect of the carbonate anion. This increases also the luminescence intensity and the luminescence lifetime of all carbonate containing species.
Nevertheless, in one case of the soil experiment also hydroxo species were found. This may be connected to a non-equilibrium with atmospheric CO2 in this column.
Following the possible transport of uranium under environmental conditions we may start with the weathering of uranium compounds in the soil or in a mining waste rock pile. The seepage water contains about 2 mg/L uranium and the speciation is mainly influenced be the formation of the dicalcium-uranyl-tricarbonate species. The input of these seepage water leads to a dilution of the uranium by about three orders of magnitude. Using the cryogenic technique in TRLFS12 we could also determine the uranium speciation in the river water nearby the former uranium mining area. The uranium concentration was about 2 µg/L uranium and in the river water mainly uranyl-tricarbonate species are formed.
Keywords: Uranium, Speciation
  • Contribution to proceedings
    2nd International Nuclear Chemistry Congress, 13.-18.04.2008, Cancun, Mexico
  • Lecture (Conference)
    2nd International Nuclear Chemistry Congress, 13.-18.04.2008, Cancun, Mexico
  • Contribution to external collection
    Broder J. Merkel, Andrea Hasche-Berger: Uranium, Mining and Hydrogeology, Berlin: Springer Verlag, 2008, 978-3-540-87745-5, 599-601
  • Lecture (Conference)
    5th International Conference Uranium Mining and Hydrogeology (UMH V), 14.-18.09.2008, Freiberg, Germany

Publ.-Id: 11212 - Permalink


High cluster formation tendency in Co implanted ZnO
Potzger, K.; Kuepper, K.; Xu, Q.; Zhou, S.; Schmidt, H.; Helm, M.; Fassbender, J.ORC
ZnO(0001) single crystals have been implant-doped with maximum 5 atomic % of Co at low temperatures. While as-implanted crystals do not show ferromagnetic properties, post implantation annealing leads to the transformation of the implanted Co ions into small metallic clusters giving rise to a pronounced hysteresis upon magnetization reversal. The dispersed Co ions are in 2+ oxidation state. Positive magneto-resistance could be observed at low temperatures.
Keywords: zno, ion implantation, diluted magnetic semiconductors
  • Journal of Applied Physics 104(2008)2, 23510

Publ.-Id: 11211 - Permalink


Resonant Ring Test Bench for Warm Window and Coupler Tests at ELBE.
Staats, G.; Buechner, A.; Buettig, H.; Michel, P.; Schurig, R.; Teichert, J.; Winter, A.;
A new coupler test bench based on a resonant ring has been built at ELBE in Dresden-Rossendorf to run warm window as well as coupler tests with RF power up to 190 kW (warm window tests up to 250kW) in CW operation. The ring is driven by a 10 kW klystron. This test bench also includes liquid nitrogen cooling of the ceramic cold window of the RF-coupler which allows testing under almost real conditions. A special waveguide to coupler transition was designed to match couplers with different antenna tips. At the beginning with the test bench it was possible to test the warm windows used at ELBE. It has been shown that the used warm windows are usable up to 70kW of CW-RF power with additional air cooling, much more than the 10kW CW used at ELBE. After this test the coupler used at the ELBE cryomodules was tested, in CW operation a power level of about 20kW was reached. More tests are in program and in near future some improvements are planned.
  • Lecture (Conference)
    Fifth CW and High Average Power RF Workshop, 25.-28.03.2008, Geneva, Switzerland

Publ.-Id: 11210 - Permalink


Summary of the OECD VVER-1000 MSLB benchmark results
Kolev, N.; Donov, J.; Spasov, I.; Royer, E.; Höhne, T.;
Recent coupled code benchmarks have identified coolant mixing in the reactor vessel as an unresolved issue in the analysis of complex plant transients with reactivity insertion. This issue was one of the main topics in Phase 2 of the recently completed OECD VVER-1000 Coolant Transient Benchmark (V1000CT-2). Exercise 1 of this benchmark is a VVER-1000 V320 vessel mixing problem based on a steam generator isolation experiment at Kozloduy-6 in Bulgaria. Plant data are available for code validation. The validated codes can be used to calculate asymmetric MSLB transients involving similar mixing patterns. A variety of mixing models were tested including multi-1D with cross flow, coarse 3D and fine CFD.
This presentation summarizes a comparison of six submitted CFD results for the V1000CT-2 Exercise 1. The results were obtained with a specified CAD model of the real vessel geometry. Five participants used a solution region from vessel inlet to the core inlet. FZK solved the benchmark for the whole pressure vessel. The comparison is code-to-code and code to experiment. The results show good overall agreement with the experiment and between the codes as well as specific features depending on the turbulence model.
  • Lecture (Conference)
    Annual Meeting of the AER Working Group D, 31.03.-01.04.2008, Garching, Germany

Publ.-Id: 11209 - Permalink


A PWR boron dilution benchmark
Kliem, S.;
The presentation describes the outline, assumptions and preliminary results of a boron dilution benchmark for pressurized water reactors. In this benchmark the neutron kinetic code DYN3D in combination with three different thermal hydraulic models has been used. Besides the own thermal hydraulic model of DYN3D, models based on the ATHLET and the RELAP5 code were created. The calculations were carried out for a generic PWR core for the subcritical hot zero power state at beginning of an equilibrium cycle. All control rods except the most effective one are inserted into the core. The deboration scenario is based on the start-up of the first main coolant pump with a slug of deborated coolant in the loop. Time dependent core inlet distribution of the boron concentration used as boundary condition for the calculations is based on corresponding experiments at the coolant mixing test facility ROCOM.
Stationary core calculations for the initial state show an excellent agreement between the three calculations. The influence of the different thermal hydraulic models reveals after the return to power. The deboration front causes in all three cases a super-prompt overcriticality jump. The time and the height of the first power peak depend on the ability of the codes to suppress the numerical diffusion of the deboration front. DYN3D and DYN3D/RELAP5 shows with about 30000 MW a considerably lower value than the 53000 MW of DYN3D/ATHLET. This difference has also an influence on the maximum cladding temperature. DYN3D/ATHLET shows with nearly 300 °C the highest value, what is still far from safety relevant conditions.
  • Lecture (Conference)
    Annual Meeting of the AER Working Group D, 31.03.-01.04.2008, Garching, Germany

Publ.-Id: 11208 - Permalink


Second dynamic AER benchmark – new results
Kliem, S.;
The presentation describes the new results obtained for the asymmetric control rod ejection benchmark defined in the frame of the co-operation inside the AER.
  • Lecture (Conference)
    Annual Meeting of the AER Working Group D, 31.03.-01.04.2008, Garching, Germany

Publ.-Id: 11207 - Permalink


CW Operation of the Superconducting LINAC "ELBE"
Buettig, H.; Arnold, A.; Buechner, A.; Gabriel, F.; Justus, M.; Lehnert, U.; Michel, P.; Schneider, C.; Schurig, R.; Staats, G.; Teichert, J.;
The superconducting CW-LINAC of the Radiation Source ELBE, based on 1.3 GHz-TESLA cavities, has been operational since 2001. An overview of the ELBE facility and of the RF-system of the superconducting CW-LINAC are presented. It is reported on different improvements on RF components to ensure stable operation of this user facility and on experience gathered during 7 years of CW- operation.
  • Lecture (Conference)
    Fifth CW and High Average Power RF Workshop 2008, 25.-28.03.2008, Geneva, Switzerland

Publ.-Id: 11206 - Permalink


The impact of turbulent flow on the solidification of metal alloys driven by a rotating magnetic field
Nikrityuk, P. A.; Eckert, K.; Eckert, S.;
The paper presents a study concerning the impact of a turbulent, rotating melt flow on the macrosegregation and the shape of the mushy zone during unidirectional solidification of an Al-7wt%Si alloy. The flow is generated by applying a rotating magnetic field (RMF). Direct numerical simulations (DNS) were performed to study the weakly turbulent flow. The transient heat and mass transfer were simulated using a standard mixture model (Bennon and Incropera, 1987). The treatment of the fluid flow in the mushy zone requires the use of permeability and mixture viscosity models, which also allow for consideration of both columnar and equiaxed solidification. Our results demonstrate that in the case of columnar solidification the Ekman pumping effect causes the development of a Si-enriched liquid channel along the rotational axis . The Taylor-Goertler vortices, which appear randomly along the side wall of the cylinder, amplify the solute transport from the wall to the axis intermittently in the upper part of the mushy zone. This effect leads to a wavy shape of the mushy zone and segregation in the form of a fir tree with a distinct accumulation of silicon along the axis of the cylinder. Moreover, we propose strategies to avoid macrosegregation by using a pulse-modulated rotating magnetic field.
Keywords: solidification, rotating magnetic field, turbulent flow, macrosegregation
  • Lecture (Conference)
    2nd International Conference on Advances in Solidification Processes, 17.-22.06.2008, Leoben, Austria
  • International Journal of Cast Metals Research 22(2009)No 1-4, 236-239

Publ.-Id: 11205 - Permalink


CFD approaches for modeling bubble entrainment by an impinging jet
Schmidtke, M.; Lucas, D.;
This contribution presents different approaches for the modeling of air entrainment under water by a plunging jet. Since the generation of bubbles happens on a scale which is smaller than the bubbles, this process cannot be resolved in meso-scale simulations, which include the full length of the jet and its environment. This is why the air entrainment has to be modeled in meso-scale simulations.
In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. For example the air is a continuous phase above the water level but bubbly below the water level. Various drag models are tested and their influence on the gas void fraction below the water level is discussed.
As a first approach the air is modelled as dispersed phase everywhere in the domain. This causes an air entrainment which is obviously determined by numerical effects. Thus, this approach is not suitable for the implementation of a physical model for gas entrainment. The algebraic interface area density (AIAD) model applies a drag coefficient for bubbles and a different drag coefficient for the free surface. If the AIAD model is used for the simulation of impinging jets, the gas entrainment depends on the free parameters included in this model. The calculated gas entrainment can be adapted via these parameters. Therefore, an advanced AIAD approach could be used in future for the implementation of models (e.g. correlations) for the gas entrainment.

Publ.-Id: 11204 - Permalink


Multi-Vendor Enterprise Storage-Lösungen erfolgreich integrieren
Konrad, U.;
Eingeladener Vortrag der Computerwoche Fachkonferenz: Data Center up-to-date 08 - virtualisieren, konsolidieren, outsourcen
Es wird ein Anwendervortrag gehalten, der Fokus liegt auf folgenden Schwerpunkten:
- IT-Profil des Forschungszentrums Dresden-Rossendorf
- Enterprise Storagelösungen
- Virtualisierung im Speichernetzwerk
- Einsatz von Filesystemen
- Lebenszyklus eines Storagesystems
Ein wesentlicher Punkt des Vortrages ist die Beschreibung der am FZD geschaffenen Lösung mit in-band Virtualisierung des Speichers im Netzwerk über spezielle Appliances sowie die Auswertung der Erfahrungen dazu.
Keywords: information technology, data center, enterprise storage solutions, in-band virtualization, SAN, file systems, computerwoche
  • Invited lecture (Conferences)
    Data Center up-to-date 08 - virtualisieren, konsolidieren, outsourcen, 10.04.2008, Frankfurt am Main, Germany

Publ.-Id: 11203 - Permalink


Velocity measurements in liquid metal flows using the Ultrasonic Doppler Method: examples and perspectives
Eckert, S.; Gerbeth, G.;
The Ultrasound Doppler Velocimetry (UDV) is a non-intrusive technique to measure velocities of liquid flows. Because of the ability to work in opaque fluids and to deliver complete velocity profiles in real time it becomes very attractive for liquid metal applications. But, in case of hot metallic melts the user is confronted with a number of specific problems: First of all the application of the ultrasonic transducers is usually restricted to maximum temperatures of about 150°C. The transmission of a sufficient amount of ultrasonic energy from the transducer to the fluid has to be guaranteed. Here, the acoustic coupling and the wetting conditions have to be considered as important issues. Moreover, the flow has to be seeded with reflecting particles to obtain Doppler signals from the fluid.
In this presentation various applications of UDV in liquid metal flows will be shown to demonstrate the capabilities and current restrictions of this technique. For instance, we consider single- and multi-transducer arrangements for flow mapping or present velocity measurements obtained during the solidification of a metallic melt. Besides the determination of velocity profiles in the liquid phase the UDV data allow for an assessment of the current position of the solidification front, too. Specific problems arising in the context of UDV measurements in liquid metal experiments will be discussed.
Keywords: Ultrasonic Doppler velocimetry, velocity measurements, liquid metals, electromagnetic stirring
  • Invited lecture (Conferences)
    6th. International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 09.-11.09.2008, Praha, Czech Republic
  • Contribution to proceedings
    6th. International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 09.-11.09.2008, Praha, Czech Republic, 1-6

Publ.-Id: 11202 - Permalink


Application of the Ultrasound Doppler method for velocity measurements in an electromagnetically-stirred liquid metal
Räbiger, D.; Eckert, S.; Gerbeth, G.;
Alternating current (AC) magnetic fields are commonly used in industrial practice for melt stirring. The requirements arising from the particular metallurgical or casting operation can be manifold. For instance, the electromagnetic stirring is applied to provide an efficient mixing of metallic melts, to control the flow at the mold region in the continuous casting process or to achieve a purposeful alteration of the microstructure of casting ingots. However, a purposeful practice of melt stirring requires suitable flow measurements which deliver a detailed knowledge of the magnetic field impact on the flow pattern.
This experimental study considers the transient liquid metal flow which is generated inside a cylindrical container by discontinuously applying a rotating magnetic field (RMF). The focus is on the fluid motion arising from the impulsive spin-up from the resting state, a single pulse or a sequence of RMF pulses. The ultrasonic Doppler velocimetry (UDV) has been used to determine profiles of the fluid velocity in the ternary alloy GaInSn. The azimuthal and vertical velocity components have been measured allowing for an analysis of both the primary, swirling flow and the secondary flow in the radial-meridional plane. The experimental results show an excellent agreement with recently published numerical results. The investigations reveal that the recirculating flow in the radial- meridional plane undergoes characteristic oscillations. Periodic reversals of the meridional flow direction can be observed for a specific length of the RMF pulses.
Our results demonstrate that the utilisation of a time-modulated rotating magnetic field (RMF) offers a considerable potential to provide optimal flow pattern for an efficient melt mixing. For instance, such tailored methods of electromagnetic stirring can be applied during the solidification of metal alloys, where a well-aimed modification of casting properties is achieved by controlling the melt flow in the bulk and adjacent to the solidification front.
Keywords: Ultrasonic Doppler velocimetry, velocity measurements, liquid metal, modulated magnetic fields
  • Lecture (Conference)
    6th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 09.-11.09.2008, Praha, Czech Republic
  • Contribution to proceedings
    6th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 09.-11.09.2008, Praha, Czech Republic, 143-146

Publ.-Id: 11201 - Permalink


Thermophysical properties of Al-Cu liquid alloys
Plevachuk, Y.; Sklyarchuk, V.; Yakymovych, A.; Eckert, S.; Willers, B.;
Considerable effort is permanently directed to optimise methods and facilities for material processing technologies like melting, refining or casting of metallic alloys. The main goals are an improvement of the final product quality, an enhancement of the process efficiency and an economical consumption of resources and energy. Nowadays it is impossible to imagine such optimisation without performing numerical simulations and a corresponding physical modelling. However, the accuracy of the predictions depends sensitively on the availability of precise and trustworthy data concerning the thermophysical properties of the alloys under consideration. The development of new workable aluminium-based light alloys is a key issue in current materials science. Al-Cu alloys, for instance AlCu4TiMg (A356), are the most utilized casting alloys in the aluminium industry. The distinctive characteristics of these alloys are low density, high melting temperature, good thermal conductivity and excellent oxidation resistance.
In this work, thermophysical properties (density, viscosity and electrical conductivity) of liquid Al96Cu4, Al80Cu20, Al70Cu30, and AlCu4TiMg (wt.%) alloys have been measured in a wide temperature range from the melting point up to 1200 K. Corresponding fit relations have been derived for the density, the dynamic viscosity and the electrical conductivity. All properties are compared to available literature data. An increase of a copper content raises gradually the density and the dynamic viscosity of aluminium suggesting a short-range order in the liquid state. According to the density and viscosity data, no substantial structure rearrangement takes place with admixtures. At the same time, the electrical conductivity results demonstrate that small additions of copper slightly raise the conductivity of liquid Al, while further increase of a copper content decreases predictably the conductivity values.
Keywords: aluminium alloys, density, viscosity, electrical conductivity
  • Poster
    11th International Conference on Aluminium Alloys, 22.-26.09.2008, Aachen, Germany
  • Contribution to proceedings
    11th International Conference on Aluminium Alloys, 22.-26.09.2008, Aachen, Germany, 1359-1360

Publ.-Id: 11200 - Permalink


Solidification of aluminium alloys under the influence of modulated magnetic fields
Eckert, S.; Willers, B.; Räbiger, D.; Dong, J.; Nikrityuk, P. A.; Eckert, K.;
AC magnetic fields are used in industrial practice for melt stirring. The requirements are manifold for miscellaneous metallurgical operations or casting technologies, mainly the magnetic field application should provide an efficient mixing of the melt in order to achieve homogeneous distributions of solute and/or temperature. The rotary stirring during solidification has been proved to be a striking method to achieve a purposeful alteration of the microstructure of casting ingots, such as a distinct grain refining or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET). Solidification experiments as well as numerical simulations were carried out considering the directional solidification of Al-Si alloys from a water cooled copper chill. A modulated rotating magnetic field (RMF) was applied for melt agitation. Thermocouples were used to measure the temperature field during solidification. The velocity field in the liquid phase was determined by means of Ultrasound Doppler velocimetry (UDV). The comparison between numerical simulations and solidification experiments delivered a good agreement. Our results demonstrate that the modulated magnetic field enables an effective control of the flow field and the structure of the solidified samples.
Keywords: solidification, aluminium alloys, electromagnetic stirring, modulated magnetic fields, macrosegregation
  • Lecture (Conference)
    11th International Conference on Aluminium Alloys, 22.-26.09.2008, Aachen, Germany
  • Contribution to proceedings
    11th International Conference on Aluminium Alloys, 22.-26.09.2008, Aachen, Germany, 497-502

Publ.-Id: 11199 - Permalink


Use of time-modulated AC magnetic fields for melt flow control during unidirectional solidification
Eckert, S.; Räbiger, D.; Willers, B.; Nikrityuk, P. A.; Eckert, K.;
The rotary stirring during solidification has been proved to be a striking method for achieving a purposeful alteration of the microstructure of casting ingots, such as grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET). However, the imposition of a rotating magnetic field (RMF) also causes problems like the occurrence of typical segregation pattern or a deflection of the upper free surface leading to surface defects or the entrainment of gas. A permanent radial inward flow along the solidification front is responsible for the transport of solute to the axis of the ingot resulting in typical freckle segregation pattern in form of vertical channels filled with alloy of eutectic composition. We present a new innovative method of electromagnetic stirring using a modulated RMF which offers a considerable potential for a well-aimed modification of casting properties. This paper considers the directional solidification of Al-Si alloys from a water cooled copper chill. Modulated AC magnetic fields were applied for melt agitation. The comparison between numerical simulations and solidification experiments delivered a good agreement. Our results demonstrate that the modulated magnetic field enables an effective control of the flow field and the structure of the solidified samples.
Keywords: solidification, electromagnetic stirring, rotating magnetic field, modulated AC magnetic fields, macrosegregation
  • Lecture (Conference)
    Second International Conference on Advances in Solidification Processes, 17.-20.06.2008, Leoben, Austria
  • International Journal of Cast Metals Research 22(2009), 78-81

Publ.-Id: 11198 - Permalink


Observation of melt flow effects on dendritic growth of Ga-In alloys by X-ray radioscopy
Boden, S.; Eckert, S.; Willers, B.; Gerbeth, G.;
Capabilities of the X-ray attenuation contrast radioscopy were utilized to provide a real-time diagnostic technique for observations of dendritic growth and the melt flow during solidification of a Ga-30wt%In alloy. The solidification process was visualised using a microfocus X-ray tube. The X-ray facility provided shadow radiographs at spatial resolutions of about 10 µm and frame repetition rates up to 25 Hz. We used the optical flow approach to derive information about the velocity field ahead of the solidification front and in the mushy zone from the observed displacement of the brightness patterns appearing during the X-ray image sequence. Experiments have been carried out to solidify the Ga-In alloy unidirectionally either starting from the bottom or the top of the specimen. The first case is significantly affected by solutal convection. Buoyancy-driven flow patterns were found at length scales being larger than the length scales of the solidifying microstructure. A strong coupling between convection and dendritic growth became apparent via flow-induced modifications of the concentration profile in the liquid. Dendritic fragmentation can be observed during the solidification in the reverse top-down direction. Variations of the applied cooling rate evoked a transition from a columnar to an equiaxed dendritic growth (CET).
Keywords: solidification, X-ray radioscopy, dendritic growth, dendrite fragmentation
  • Lecture (Conference)
    Second International Conference on Advances in Solidification Processes, 17.-20.06.2008, Leoben, Austria

Publ.-Id: 11197 - Permalink


Shear flow compositions on the Galerkin piano: A unified theory for instabilities, strange attractors, statistical mechanics and attractor control
Noack, B. R.; Schlegel, M.; Pastoor, M.; Luchtenburg, M.; Mutschke, G.; Morzynski, M.; Comte, P.; Tadmor, G.; Ahlborn, B.;
A well-tuned Galerkin melody about fluid flows requires a piano with the right keys (called modes, e.g. POD), musical notes (physics resolution), an audience (observer), and a composer (control law) in case the music shall be changed. Here, we briefly review new key enablers for these tasks. Then, a finite-time thermodynamics is proposed bridging fluid mechanics disciplines and theoretical physics treasures. This formalism opens the path to fully nonlinear attractor control, as required for turbulence manipulation in experimental demonstrators. Presented studies include shear flows with simple to complex dynamics.
Keywords: Galerkin method, POD, control, shear flow, instabilities, finite-time thermodynamics
  • Invited lecture (Conferences)
    Workshop Industrial applications of low-order models based on proper orthogonal decomposition, 31.03.-02.04.2008, Bordeaux, France

Publ.-Id: 11196 - Permalink


Ion irradiation induced sub-100nm ferromagnetic patterns
Liedke, M. O.; Strache, T.; Fassbender, J.ORC; Möller, W.; Menéndez, E.; Sort, J.; Gemming, T.; Weber, A.; Heyderman, L. J.; Rao, K. V.; Deevi, S. C.; Nogués, J.
Focus ion beam (FIB) patterning of Fe60Al40 provides the potential to create arrays of microscopic ferromagnetic regions embedded in a paramagnetic matrix. As the consequence of low fluence irradiation such a method does not affect the surface roughness. Due to the ion damage distribution the phase transition from the chemically ordered B2-phase to the chemically disordered, ferromagnetic A2-phase is setup. The magnetic phase transformation is studied as a function of noble gases mass and is directly related to the number of displacements per atom (dpa) during ion irradiation. In case of heavy ions (Ar+, Kr+ or Xe+) the phase transformation originates purely from ballistic nature of the disordering process. For light ions (He+, Ne+) the disordering conditions deviates from the former case. The bulk vacancy diffusion from dilute collision cascades, that leads to a partial recovery of the thermodynamically favored B2-phase, plays a major role. Furthermore, by means of moderately high temperature annealing (about 900 K) the paramagnetic phase is completely recovered due to the annealing-induced atomic reordering. Therefore, local ion irradiation may lead to a novel type of patterned recording media free from tribological and exchange coupling effects.
Keywords: focus ion beam, irradiation, phase transition, defects, magnetic pattering
  • Lecture (Conference)
    The European Conference PHYSICS OF MAGNETISM 2008, 24.-27.06.2008, Poznan, Poland

Publ.-Id: 11195 - Permalink


Spectroscopic THz near-field microscope
von Ribbeck, H.-G.; Brehm, M.; van der Weide, D. W.; Winnerl, S.; Drachenko, O.; Helm, M.; Keilmann, F.;
We demonstrate a scattering-type scanning near-field optical microscope (s-SNOM) with broadband THz illumination. A cantilevered W tip is used in tapping AFM mode. The direct scattering spectrum is obtained and optimized by asynchronous optical sampling (ASOPS), while near-field scattering is observed by using a space-domain delay stage and harmonic demodulation of the detector signal. True near-field interaction is determined from the approach behavior of the tip to Au samples. Scattering spectra of differently doped Si are presented.
Keywords: terahertz, SNOM
  • Open Access LogoOptics Express 16(2008), 3430-3438

Publ.-Id: 11194 - Permalink


BACOPP-D - An etoposide-free dose-escalated polychemotherapy regimen in advanced Hodgkin Lymphoma
Naumann, R.; Wetzko, K.; Haenel, A.; Friedrichsen, K.; Zschuppe, E.; Schmidt, H.; Dawel, M.; Beuthien-Baumann, B.; Scbwanebeck, U.; Ehninger, G.; Haenel, M.;
Introduction:
The development of the escalated BEACOPP regimen let to an improved outcome in patients with advanced Hodgkin Lymphoma (HD9 study of the GHSG). However, the application of high dose etoposide (cumulative 4,8 g/m2 per 8 cycles) seems to be associated with an increased incidence of secondary MDS and AML, respectively. Therefore, the aim of our multicenter pilot study was to evaluate the efficacy and toxicity of the etoposide free as well as dose intensified BACOPP-D protocol.

Methods:
Since May 2000 a total of 115 patients with Hodgkin Lymphoma (HL) stage IIB, III, and IV were treated with BACOPP-D which included cyclophosphamide 1250 mg/m2 (d1), adriamycin 25 mg/m2 (d1+2), dacarbazine 250 mg/m2 (d1-3), procarbazine 100 mg/m2 (d1-7), prednisolone 40 mg/m2 (d1-14), bleomycin 10 mg/m2 (d8) and vincristine 1,4 mg/m2 (maximum 2 mg, d8) at three-weekly intervals with granulocyte colony-stimulating factor (G-CSF). A consolidating involved field radiation (30 Gy) was performed only in patients who achieved less than CR following chemotherapy. Post-treatment follow-up included PET imaging.

Results:
Until now 97 patients (median age 35 years, range 17-65; 61 male, 36 female) are assessable for toxicity and treatment outcome. We analyzed the acute toxicity for 728 cycles of BACOPP-D. CTC/WHO grade III/IV haematological toxicities per patient were observed as follows: leukopenia 93%, anemia 39%, and thrombocytopenia 33%. CTC grade III/IV non-haematological side effects included documented infection (4%) and lung toxicity (one patient). A total of 85 patients (88%) achieved complete remission, 9 patients (9%) achieved partial remission, three patients (3%) had progressive disease. At a median observation time of 39 months (0,9-77 months), five patients have relapsed, and nine deaths were documented (4 HL-specific and 3 treatment related deaths, 1 death due to ruptured Meckel diverticulum with peritonitis, one 65 year-old woman died in CR following myocardial infarction). One patient developed a second neoplasia (hypopharyngeal carcinoma in an alcoholic). The overall survival and freedom from treatment failure rates at 39 months were 91% and 85%, respectively. FDG-PET scans after BACOPP-D chemotherapy were performed in 68 of 97 patients. PET scans revealed no increased FDG uptake in 48/68 patients (71%), in 20 patients (29%) increased FDG uptake was detected. In the group of patients with increased FDG uptake, one patient developed progressive disease and four patients relapsed. In the group with PET-negative findings no patient relapsed.

Diskussion:
BACOPP-D regimen appears as a feasible and effective treatment which induced a complete morphologic and metabolic remission in a high proportion of patients with advanced HL. The treatment was associated with moderate acute toxicity. No secondary AML or MDS occurred until now.

Footnotes

Disclosure: No relevant conflicts of interest to declare.
  • Poster
    ASH 49th Annual Meeting, 08.-11.12.2007, Atlanta/Georgia, USA
  • Abstract in refereed journal
    BLOOD 110(2007)11, 685A

Publ.-Id: 11193 - Permalink


Das neue Urheberrecht seit 1.1.2008, Dokumentenbereitstellung, SUBITO, EZB - Erfahrungen aus der Praxis
Reschke, E.;
Die Umsetzung des neuen Urheberechts für den Bereich der Dokumentenbereitstellung durch Bibliotheken ist äußerst problematisch. Die Einschränkungen der Verfügbarkeit elektronischer Lieferungen bedingen umfangreiche Schulungen des Bibliothekspersonals, Informationen der Bibliotheksbenutzer, zusätzlichen Bearbeitungsaufwand der Bestellungen und Bestelleingangs- und Rechnungsverwaltung und wesentlichen finanziellen Mehraufwand. Im Vortrag wird am Beispiel des Subito-Rahmenvertrages auf die aktuellen Probleme eingegangen.
  • Lecture (others)
    Treffen des Arbeitskreises Spezialbibliotheken Dresden, 02.04.2008, Dresden, Germany

Publ.-Id: 11192 - Permalink


Wire mesh sensor studies in a vertical pipe
Azzopardi, B.; Hernandez Perez, V.; Kaji, R.; Da Silva, M. J.; Beyer, M.; Hampel, U.;
A Wire Mesh Sensor system has been employed on a vertical 67 mm diameter pipe up which air and water mixtures flow. This enables an examination of the flow to be carried out at several levels of complexity. The measuring system provides time and cross-sectionally resolved information about the spatial distribution of the phases. The information can be used to obtain space and time averaged void fractions, radial profiles of time averaged void fraction and cross-sectional averaged time series of void fraction. This last yields Probability Density Function information as well as other statistical information. It also yields data of the frequency of periodic structures within the flow. More powerfully, the fully resolved data can give deep insights into the structure of the gas/liquid interface. A hitherto unreported structure has been seen in churn flow which could be linked to the wisps in wispy-annular flow.
Keywords: wire-mesh sensor, pipe flow, wispy-annular flow
  • Contribution to proceedings
    Fifth International Conference on Transport Phenomena In Multiphase Systems, HEAT 2008, 30.06.-03.07.2008, Bialystok, Poland
    Proceedings of the 5th International Conference on Transport Phenomena in Multiphase Systems, HEAT 2008, 405-412
  • Lecture (Conference)
    Fifth International Conference on Transport Phenomena In Multiphase Systems, HEAT 2008, 30.06.-03.07.2008, Bialystok, Poland

Publ.-Id: 11191 - Permalink


Spectral shaping of laser generated proton beams
Pfotenhauer, S. M.; Jäckel, O.; Sachtleben, A.; Polz, J.; Ziegler, W.; Schlenvoigt, H.-P.; Amthor, K.-U.; Kaluza, M. C.; Ledingham, K. W. D.; Sauerbrey, R.; Gibbon, P.; Robinson, A. P. L.; Schwoerer, H.;
The rapid progress in the field of laser particle acceleration has stimulated a debate about the promising perspectives of laser based ion beam sources. For a long time, the beams produced exhibited quasi-thermal spectra. Recent proof-of-principle experiments demonstrated that ion beams with narrow energy distribution can be generated from special target geometries. However, the achieved spectra were strongly limited in terms of monochromacity and reproducibility. We show that microstructured targets can be used to reliably produce protons with monoenergetic spectra above 2 MeV with less than 10% energy spread. Detailed investigations of the effects of laser ablation on the target resulted in a significant improvement of the reproducibility. Based on statistical analysis, we derive a scaling law between proton peak position and laser energy, underlining the suitability of this method for future applications. Both the quality of the spectra and the scaling law are well reproduced by numerical simulations.
Keywords: perspectives of laser; proof-of-principle experiments; ion beams with narrow energy distribution can be generated from special target geometries microstructured targets can be used to reliably produce protons with monoenergetic spectra above 2 MeV with less than 10% energy spread; derive a scaling law between proton peak position and laser energy
  • Open Access LogoNew Journal of Physics 10(2008), 033034

Publ.-Id: 11190 - Permalink


Shielding and Fuel Storage Calculations for GUINEVERE
Noack, K.; Rindelhardt, U.; Rogov, A.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-490 2008

Downloads:

Publ.-Id: 11189 - Permalink


Annual Report 2007 - Institute of Radiochemistry
Bernhard, G.; Foerstendorf, H.; Richter, A.; Viehweger, K.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-489 2008

Downloads:

Publ.-Id: 11188 - Permalink


Defect studies of ZnO single crystals electrochemically doped with hydrogen
Cizek, J.; Zaludova, N.; Vlach, M.; Danis, S.; Kuriplach, J.; Prochazka, I.; Brauer, G.; Anwand, W.; Grambole, D.; Skorupa, W.; Gemma, R.; Kirchheim, R.; Pundt, A.;
Various defect studies of hydrothermally grown (0001) oriented ZnO crystals electrochemically doped with hydrogen are presented. The hydrogen content in the crystals is determined by nuclear reaction analysis and it is found that already 0.3 at. % H exists in chemically bound form in the virgin ZnO crystals. A single positron lifetime of 182 ps is detected in the virgin crystals and attributed to saturated positron trapping at Zn vacancies surrounded by hydrogen atoms. It is demonstrated that a very high amount of hydrogen (up to similar to 30 at. %) can be introduced into the crystals by electrochemical doping. More than half of this amount is chemically bound, i.e., incorporated into the ZnO crystal lattice. This drastic increase of the hydrogen concentration is of marginal impact on the measured positron lifetime, whereas a contribution of positrons annihilated by electrons belonging to O-H bonds formed in the hydrogen doped crystal is found in coincidence Doppler broaden!
ing spectra. The formation of hexagonal shape pyramids on the surface of the hydrogen doped crystals by optical microscopy is observed and discussed.
  • Journal of Applied Physics 103(2008)5, 053508

Publ.-Id: 11187 - Permalink


In-beam PET measurement of 7Li3+ irradiation induced beta+-activity
Priegnitz, M.; Möckel, D.; Parodi, K.; Sommerer, F.; Fiedler, F.; Enghardt, W.;
At present positron emission tomography (PET) is the only feasible method of an in situ and non-invasive monitoring of patient irradiation with ions. At the experimental carbon ion treatment facility of the Gesellschaft für Schwerionenforschung (GSI) Darmstadt an in-beam PET scanner has been integrated into the treatment site and lead to a considerable quality improvement of the therapy. Thus, it is highly desirable to extend in-beam PET also to other therapeutic relevant ions which requires an extensive knowledge on the spatial distribution of generated positron emitters. Therefore, by means of the in-beam PET scanner at GSI the beta+-activity induced by 7Li3+ ions has been investigated for the first time. Targets of PMMA, water, graphite and polyethylene were irradiated with monoenergetic, pencil-like beams of 7Li3+ with energies between 129.1 AMeV and 205.3 AMeV and intensities ranging from 3.0 e7 to 1.9 e8 ions s-1. This paper presents the measured beta+-activity profiles as well as depth dependent thick target yields which have been deduced from the experimental data. The beta+-activity induced by 7Li ions was found to be a factor of 1.9 higher than the one induced by 12C ions at the same physical dose and particle range.
  • Physics in Medicine and Biology 53(2008), 4443-4453

Publ.-Id: 11184 - Permalink


Implementation of temperature control into a high resolution gamma ray detector for tomography applications
Bieberle, A.; Bärtling, Y.; Fleischer, A.; Sühnel, T.; Zimmermann, W.; Schleicher, E.; Hampel, U.;
In this paper the development of a new thermal design for a high resolution gamma ray computed tomography detector is presented. The new design has become necessary due to stringent requirements on count rate accuracy under varying thermal conditions at thermal hydraulic test loops. The components of the existing tomography detector have been analysed with respect to their thermal response and a new arrangement has been devised that is optimized with respect to efficient heat conduction from internal as well as external heat sources to a cooling circuit.
Keywords: gamma ray tomography, temperature control
  • Contribution to proceedings
    5th International Symposium on Process Tomography, 25.-26.08.08, Zakopane, Poland
    PaperNo PT08_cr12
  • Poster
    5th International Symposium on Process Tomography, 25.-26.08.08, Zakopane, Polen

Publ.-Id: 11183 - Permalink


Simulation of buble coalescence in bubble column using the least-squares method
Zhu, Z.; Patruno, L. E.; Dorao, C. A.; Lucas, D.; Jakobsen, H. A.;
The population balance equation (PBE) has been combined with a steady-state gas phase momentum equation to model the operation of an air-water bubble column. Instead of solving a bubble number density constitutive equation, a population balance equation with coalescence term has been solved. The system of equations has been linearized by successive iteration and solved by the least-squares method with high accuracy and fast convergence. The bubble size distribution along the column axis has been investigated and compared to the corresponding experimental data, showing good agreement.
Keywords: bubble, coalescence, population balance
  • Contribution to proceedings
    11th International Conference on Multiphase Flow in Industrial Plant (MFIP'08), 07.-10.09.2008, Palermo, Italy, 643-650

Publ.-Id: 11182 - Permalink


Kinematic simulation of dynamo action with a hybrid boundary-element/finite-volume method.
Giesecke, A.; Stefani, F.; Gerbeth, G.;
The experimental realization of dynamo excitation as well as theoretical and numerical examinations of the induction equation have shown the relevance of boundary conditions for a self-sustaining dynamo. Within the interior of a field producing domain geometric constraints or varying material properties (e.g. electrical conductivity of the container walls or localized high-permeability material) might also play a role. Combining a grid based finite volume approach with the boundary element method in a hybrid FV-BEM scheme offers the flexibility of a local discretization with a stringent treatment of insulating magnetic boundary conditions in almost arbitrary geometries at comparatively low costs. Kinematic simulations of dynamo action generated by a well known prescribed mean flow demonstrate the reliability of the approach.


Future examinations are intended to understand the behavior of the VKS-dynamo experiment where the field producing flow is driven by ferrous propell lers and the induction effects of conductivity/permeability inhomogeneities might provide the required conditions for the measured dynamo characteristics.
Keywords: kinematic dynamo, boundary element method, numerical simulations, induction equation
  • Magnetohydrodynamics 44(2008)3, 237-252

Publ.-Id: 11181 - Permalink


Contactless inductive flow tomography: theory, experiments, perspectives
Wondrak, T.; Gundrum, T.; Stefani, F.; Gerbeth, G.;
The velocity field of a propeller-driven liquid metal flow is reconstructed by a contactless inductive flow tomography (CIFT). A robust reconstruction of large scale velocity fields is already achieved by applying the external magnetic field in two orthogonal directions. The results of this technique are shown to be in satisfactory agreement with ultrasonic measurements.
Keywords: Inverse Problems, Industrial tomography, Liquid metal flow measurement
  • Contribution to proceedings
    The 10th Workshop on Optimization and Inverse Problems in Electromagnetism (OIPE 2008), 14.-17.09.2008, Ilmenau, Germany, 75-76
  • Lecture (Conference)
    The 10th Workshop on Optimization and Inverse Problems in Electromagnetism (OIPE 2008), 14.-17.09.2008, Ilmenau, Deutschland

Publ.-Id: 11180 - Permalink


Uranium speciation after contact with plant cells
Geipel, G.; Viehweger, K.; Bernhard, G.;
Uranium is an ubiqutous element. Besides this depleted uranium amunition as well as uranium mining and milling and manifold other use of uranium leads to an increase of uranium contamination in the environment.
Application of laser-induced and time-resolved methods allow the direct determination of uranium speciation at extremely low concentrations. This behaviour can be directly observed due to the properties extraorbitant luminescence properties of uranium-(VI). Contact of dissolved uranium with living cells at ambient conditions changes dramatically the uranium speciation.
Some examples fluorescence properties of uranium species relevant to the environment are shown. The change of this speciation can be observed then due to a change in luminescence properties. Besides of several organic phosphate binding forms although other uranium species were found as uranium bond to phenolic and thiol groups. Some of them do not emit any luminescence at room temperature. Nevertheless low temperature measurements allow the assignment of species not fluorescing at room temperature, due to strong dynamic quench effects of H2O molecules and COO- groups.
Keywords: Uranium, speciation, plants
  • Contribution to proceedings
    BioMetals 2008, 14.-18.7.2008, Santiago de Compostela, Spain
  • Lecture (Conference)
    BioMetals 2008, 14.-18.07.2008, Santiago de Compostela, Spain
  • Contribution to proceedings
    The 48th Annual American Society for Cell Biology Annual Meeting, 13.-17.12.2008, San Francisco, USA

Publ.-Id: 11179 - Permalink


Extracellular defence reactions of rape cells caused by uranium exposure
Viehweger, K.; Geipel, G.;
Uranium is a widespread radioactive toxic heavy metal, released into the biosphere mostly by military purposes and nuclear industry. It is taken up by plant root systems and its chemical toxicity is much more dangerous than the radiological. Thus cell suspensions of rape (Brassica napus) revealed specific extracellular defence reactions after uranium exposure. These include characteristic pH-shifts of the culture medium caused by contact with the heavy metal. At the same time a transient release of fluorescent compounds from the cells occurred. These phytoalexins probably belong to the widespread group of flavonoids detected by HPLC and thin layer chromatography (TLC). They are able to interact with uranium and hence can protect the cell against heavy metal poisoning. To gain an insight in these interactions time-resolved laser-induced fluorescence spectroscopy (TRLFS) was performed. Further investigations are under way to identify intracellular defence mechanisms, e.g. spatial patterns of a possible cytoplasmic pH-shift, the formation of proteins possessing thiol groups (phytochelatins), respectively.
Keywords: Plant cells, uranium
  • Contribution to proceedings
    Biometals 2008, 14.-18.7.2008, Santiago de Compostela, Spain
  • Lecture (Conference)
    5th International Conference Uranium Mining and Hydrogeology (UMH V), 14.-18.09.2008, Freiberg, Germany
  • Contribution to external collection
    Broder J. Merkel, Andrea Hasche-Berger: Uranium, Mining and Hydrogeology, Berlin: Springer Verlag, 2008, 978-3-540-87745-5, 691-691

Publ.-Id: 11178 - Permalink


Excitation spectrum and magnetic properties of the new Haldane-gap material NENB
Zvyagin, S.; Cizmar, E.; Ozerov, M.; Ignatchik, O.; Papageorgiou, T.; Wosnitza, J.; Krzystek, J.; Zhou, Z.; Wikaira, J. L.; Landee, C. P.; Thurnbull, M. M.;
Results of high-field ESR and magnetization studies of the new spin-1 Haldane-chain material [Ni(C2H8N2)2NO2](BF4) (NENB) are reported. A definite signature of the Haldane state in NENB was obtained. From the analysis of the frequency-field dependence of magnetic excitations in NENB, the spin-Hamiltonian parameters were calculated, yielding Δ/kB = 17.4 K, gk = 2.14, D/kB = 7.5 K, and |E/kB| = 0.7 K for the Haldane gap, g factor and the crystal-field anisotropy constants, respectively. The presence of fractional S = 1/2 chain-end states, revealed by ESR and magnetization measurements, is found to be responsible for spin-glass freezing effects. In addition, extra states in the excitation spectrum of NENB have been observed in the vicinity of the Haldane gap, which
origin is discussed.
  • Lecture (Conference)
    APS March Meeting, 08.-14.03.2008, New Orleans, USA

Publ.-Id: 11177 - Permalink


Growth and study of LuNi2B2C single crystals
Köhler, A.; Behr, G.; Bergk, B.; Fuchs, G.; Nenkov, K.; Wosnitza, J.;
Rare earth-nickel-borocarbides have attracted much interest in the last years because the compounds show the interplay of superconductivity and magnetic ordering. LuNi2B2C can be considered as non-magnetic reference system of such magnetic borocarbides as HoNi2B2C in which superconducting and antiferromagnetic ordering temperatures, Tc and TN, are similar.
So far, LuNi2B2C crystals were only prepared by a flux method. For growing larger crystals we used an optical floating zone (FZ) technique, which already was successful in crystal growth of other RNi2B2C (R = Y,Tb,Ho,Tm,Er) compounds. In the case of LuNi2B2C, the primary crystallization field is far from the stoichiometric composition, and adjacent to the properitectic LuB2C2 phase field an extended region of LuNiBC occurs. Systematic studies of polycrystalline samples revealed that samples with nominal compositions LuNi5B3.5C and LuNi5B3C0.5 are free of the properitectic LuB2C2 and LuNiBC phases.
Thus in the FZ crystal growth experiments we used a molten zone which corresponds to these compositions. From the grown LuNi2B2C rods single crystalline pieces have been prepared to investigate Fermi surface peculiarities by magnetoresistance measurements and to study the electronic band structure.
  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11176 - Permalink


Evidence for an Fulde-Ferrell-Larkin-Ovchinnikov state in a layered organic superconductor
Bergk, B.; Böttger, P. H. M.; Lortz, R.; Wang, Y.; Demuer, A.; Sheikin, I.; Zwicknagl, G.; Nakazawa, Y.; Wosnitza, J.;
We present specific heat and torque-magnetization data of the layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 in high magnetic fields up to 28 T and at low temperatures down to 1.5 K. The magnetic field was aligned perfectly parallel to the superconducting planes of the sample. In that orientation and at low temperatures the upper critical field, Bc2, gets close to the Pauli limit which is about 21 T. But instead of the expected saturation at this field value we observe an upturn of Bc2 towards low temperatures. This comes along with a change of the order of the phase transition from second order to first order. In addition, another first-order phase transition appears below Bc2 in the superconducting state. These features strongly point to the formation of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in the state above the Pauli limit. Our results are in line with the behaviour predicted for FFLO states in two-dimensional systems.
  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11175 - Permalink


Anomalous critical behavior at the antiferromagnetic phase of YbRh2Si2
Krellner, C.; Hartmann, S.; Pikul, A.; Oeschler, N.; Geibel, C.; Wosnitza, J.; Steglich, F.;
Quantum phase transitions are one of the important topics in the understanding of condensed matter. These transitions are driven by quantum fluctuations in contrast to classical phase transitions which are accompanied by thermal fluctuations. Recently, the heavy fermion system YbRh2Si2 was intensively studied, because it is a clean and stoichiometric metal situated on the magnetic side (TN = 72 mK), but very close to a quantum critical point, which can be crossed by applying a tiny magnetic field. Therefore, this system presents both an antiferromagnetic phase transition driven by thermal fluctuations as well as pronounced quantum fluctuations due to the vicinity to the quantum phase transition. In this contribution, we show accurate measurements of the specific heat C around TN on a single crystal of highest quality (RRR ~ 150). We observe a very sharp peak at TN with absolute values as high as C/T = 8 J/molK2. A detailed analysis of the critical exponent α around TN reveals α = 0.37 which differs significantly from those of the conventional universality classes in the Landau theory α < 0.11. We will discuss in detail the analysis and possible mechanism.
  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11174 - Permalink


Observation of two-magnon bound states in the spin-1 anisotropic Heisenberg antiferromagnetic chain system NiCl2-4SC(NH2)2
Zvyagin, S. A.; Batista, C. D.; Krzystek, J.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.; Wosnitza, J.;
Results of systematic tunable-frequency ESR studies of the spin dynamics in NiCl2-4SC(NH2)2 (known as DTN), a gapped S = 1 chain system with easy-plane anisotropy dominating over the exchange coupling (large-D chain), are presented. We have obtained direct evidence for two-magnon bound states, predicted for S = 1 large-D spin chains in the fully spin-polarized (FSP) phase. The frequency–field dependence of the corresponding excitations was calculated using the set of parameters obtained earlier [S.A. Zvyagin, et al., Phys. Rev. Lett. 98 (2007) 047205]. Very good agreement between the calculations and the experiment was obtained. It is argued that the observation of transitions from the ground to two-magnon bound states might indicate a more complex picture of magnetic interactions in DTN, involving a finite in-plane anisotropy.
  • Physica B 403(2008), 1497-1499

Publ.-Id: 11173 - Permalink


Possible magnetic-field-induced Lifshitz transition in CeBiPt
Wosnitza, J.; Goll, G.; Bartkowiak, M.; Bergk, B.; Bianchi, A. D.; von Löhneysen, H.; Yoshino, T.; Takabatake, T.;
We report on resistance and Hall-effect measurements of the half-Heusler compound CeBiPt in pulsed magnetic fields up to 70 T. The band structure of the semimetal CeBiPt depends highly sensitively on temperature, magnetic field, and stoichiometry. This is reflected by the observed sample-dependent threshold fields above which the Shubnikov–de Haas signal disappears and at which clear changes of the Hall coefficient occur.
  • Physica B 403(2008), 1219-1221

Publ.-Id: 11172 - Permalink


Magnetic properties of the Haldane-gap material [Ni(C2H8N2)2NO2](BF4)
Cizmár, E.; Ozerov, M.; Ignatchik, O.; Papageorgiou, T. P.; Wosnitza, J.; Zvyagin, S. A.; Krzystek, J.; Zhou, Z.; Landee, C. P.; Landry, B. R.; Turnbull, M. M.; Wikaira, J. L.;
Abstract. Results of magnetization and high-field electron spin resonance (ESR) studies of the new spin-1 Haldane-chain material [Ni(C2H8N2)2NO2] (BF4) (NENB) are reported. A definite signature of the Haldane state in NENB was obtained. From the analysis of the frequency–field dependence of magnetic excitations in NENB, the spin-Hamiltonian parameters were calculated, yielding ∆/kB = 17.4 K, g = 2.14, D/kB = 7.5K and |E/kB| = 0.7K for the Haldane gap, g factor and the crystal-field anisotropy constants, respectively. The presence of fractional S = 1/2 chain-end states, revealed by ESR and magnetization measurements, is found to be responsible for spin-glass freezing effects. In addition, extra states in the excitation spectrum of NENB have been observed in the vicinity of the Haldane gap; their origin is discussed.
  • Open Access LogoNew Journal of Physics 10(2008), 033008

Publ.-Id: 11171 - Permalink


Sources for ferromagnetism in ion implanted ZnO
Potzger, K.; Zhou, S.;
The combination of magnetic and semiconducting properties in oxides is currently one of most popular fields in materials research. Besides the expected gain of knowledge about basic physics, such materials have a large application potential in spin electronics. We present a summary of our results on transition metal doping of ZnO single crystals and thin films by means of ion implantation. We found that none of the samples investigated represents a diluted magnetic semiconductor as predicted by theory [1]. The observed ferromagnetism mainly originates from secondary phase formation (metals or inverted spinel ferrites). We highlight the suppression of secondary phase formation by means of deliberately lowering the crystalline quality prior to the doping. Moreover, bombardment with transition metal ions leads to defects which create weak ferromagnetism without participation of the transition metal implanted. We discuss the possibility that such defects are also responsible for ferromagnetism observed in transition metal doped ZnO thin films. Thus, interpretations of ferromagnetic DMS reported in the past are often misleading.

[1] K. Sato and H. Katayama-Yoshida, Physica E 10, 251 (2001).
Keywords: ion implantation, zno, DMS
  • Lecture (Conference)
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-5.9.2008, Dresden, Germany

Publ.-Id: 11170 - Permalink


Design of non-destructive pulsed magnets at the Dresden High Magnetic Field Laboratory
Zherlitsyn, S.;
The Dresden High Magnetic Field Laboratory (HLD) is a user facility which provides external users with the possibility of performing diverse experiments in pulsed magnetic field. Various experimental techniques, such as electrical transport, magnetization, ultrasound and magnetic-resonance measurements are available or are under installation at the HLD. A particular feature of the laboratory is a nearby free-electron laser facility which enables high-field infrared spectroscopy in pulsed magnetic fields [1].
A 50 MJ modular capacitor bank with a maximum charging voltage of 24 kV is in operation at the HLD. This capacitor bank allows to energize independently up to four sub-coils in multi-coil configurations and the energy pulses can be switched to five experimental cells. A program of the non-destructive pulsed magnets for the HLD includes a wide spectrum of coils designed for energies between 1 and 46 MJ, magnetic fields of 60 – 100 T, pulse durations of 10 - 1000 ms, and magnet bores in the range from 20 to 40 mm. In order to fulfill this program the necessary infrastructure accounting for the technical and technological aspects of pulsed-magnet design and fabrication has been established at the HLD. A pulsed-magnet core design has been developed [2]. In spite of the strong external mechanical support, our magnets are designed in a compact way which is suitable both for a mono-coil and a multi-coil configuration. With this design we are trying to achieve higher fields with longer pulse duration and high field homogeneity as well as to provide adequate space inside the magnet for the experimental installations. Important issues of the pulsed-magnet design are numerical simulations of the magnet performance. Both analytical approaches and finite-element analysis are used for these simulations.
Currently a number of 60 T /1.44 MJ and 70 T /8.5 MJ pulsed-magnets are available for external users and for in-house research [3]. A fabrication of a 60 T /43 MJ “long pulse” mono-coil is near to completion. A few double-coil prototypes have been designed, constructed and tested in frame of our 100 T project. Using the test results some improvements have been implemented in the multi-coil configuration. New double-coil prototypes targeting magnetic field above 90 T are under construction now.
  • Invited lecture (Conferences)
    Pioneering High Fields Symposium, 18.-19.03.2008, Tallahassee, USA

Publ.-Id: 11169 - Permalink


Simulation study on electron beam X-ray CT arrangements for two-phase flow measurements
Bieberle, M.; Schleicher, E.; Hampel, U.;
Recently, we presented a limited-angle computed tomography approach that utilises a scanned electron beam X-ray source to produce multiple projections of an object. From these projections cross sectional images of the object are reconstructed by application of iterative reconstruction algorithms. Experiments with different kinds of two-phase flows proved that this approach is capable to recover the in-plane phase structure of the flow at scan rates of up to 10,000 frames per second and to reach an in-plane resolution of 1 mm. However, there are also some problems associated with this approach. One is the occurrence of limited-angle artefacts due to the limited number of views. Another problem is that no information about the volumetric structure of a multiphase flow can be obtained without knowing phase velocities. Both problems are addressed in this article. By means of a simulation study on software phantoms we evaluated different limited-angle scanning geometries with respect to their capability to suppress limited-angle artefacts. Secondly, we propose and evaluate a multi-slice limited-angle technique which allows to recover phase velocities and reconstruction of volumetric flow data. For the studies we employed a software phantom modelling bubbly two-phase flow in a pipe.
Keywords: electron beam x-ray CT
  • Measurement Science and Technology 19(2008)9, 094003

Publ.-Id: 11168 - Permalink


Keynote lecture: Biogeochemistry of iron and interacting metals in soils
Scheinost, A. C.; Charlet, L.;
Iron is the 4th most abundant element in the Earth’s crust and in soils; its bioavailability is often limited, however, because the Fe(III) oxides and hydroxides forming at oxic, non-acidic conditions are characterized by a very low solubility. Due to their nanoparticulate size and surface properties, the vividly colored soil Fe oxides and oxihydroxides strongly sorb oxyanions as well as metal cations, hence also limit the bioavailability of other nutrients, micronutrients and toxic metals.
In contrast, microbial reduction of Fe(III) to Fe(II) drastically increases Fe solubility and bioavailability, and may release associated nutrients and toxic metals. The Fe-mediated electron cycles are often driving the redox cycles of other redox-sensitive metals, among them micronutrients and toxic metals like Se and U.
Processes like seasonal fluctuations of ground water levels, enhanced O2 diffusion along soil macropores, rhizosphere biochemistry or mineral surface-catalyzed redox processes may produce redox fronts at various spatial and temporal scales, which in turn produce complex spatial and temporal patterns of nutrient and toxin bioavailabilities.
Keywords: Iron, geochemistry, redox
  • Invited lecture (Conferences)
    13th International Symposium on Iron Nutrition and Interactions in Plants, 03.-07.07.2006, Montpellier, France

Publ.-Id: 11167 - Permalink


XAS study of Am2Zr2O7 pyrochlore - Evolution under alpha self-irradiation
Martin, P.; Belin, R.; Valenza, P.; Scheinost, A. C.;
Management of long-lived nuclear wastes is, after safety, the main issue of nuclear industry, both in terms of scientific challenge as well as public acceptance. Among the different options that have been envisioned and explored for minor actinides over the past thirty years, two alternatives currently remain: long term disposal in a safe repository or “burning” of nuclear wastes in a so-called transmutation process. Materials selected for such applications have to meet the following criteria: high incorporation of actinides, good structural and chemical stability, low thermal dilatation, and resistance to radiation.
Among the various ceramics envisaged, zirconia based pyrochlore oxides of composition An2Zr2O7 (An=actinide) appear to be ideal candidates. Results obtained with lanthanide pyrochlores submitted to ion-beam irradiation show that Zr-based pyrochlores, unlike Ti-based, remain crystalline with a transition from the pyrochlore to a defect fluorite structure [1]. The ordered pyrochlore belongs to the Fd-3m space group and is a superstructure of the ideal defect fluorite structure (Fm-3m) with exactly twice the lattice constant. In the pyrochlore structure, the coordination shell of Am cations (8 (2+6) oxygen atoms) is distinct from that of Zr cations (6 oxygen atoms), whereas the second coordination shell (cation-cation) is the same for both cations (6xAm+6xZr at the same distance). The structural phase transition from pyrochlore to defective fluorite involves the randomization of the oxygen atoms into the anionic and vacant positions of the pyrochlore structure. In the ideal fluorine defect structure, the Am and Zr cations share the same position and thus have the same local environment: a first coordination shell consisting of 7 oxygen atoms at the same distance and the same second coordination shell as observed in the pyrochlore structure.
The objective of this study was to investigate the radiation tolerance of Zr-pyrochlore during a more realistic experiment using alpha emitting 241Am as structural component.
Keywords: Transmutation, XAFS, pyrochlore, Zircon, Americium
  • Lecture (Conference)
    Actinide-XAS 2008, 15.-17.07.2008, Saint Aubin, France

Publ.-Id: 11166 - Permalink


On the effect of spatial discretization in LWR calculations with HELIOS 1.9
Merk, B.;
The differences arising in the neutron flux distribution due to different spatial discretization are demonstrated. These differences in the flux distribution cause significant changes in the kinf value. An evaluation of the kinf value for the case of infinitely fine discretization is made. The influence of the discretization on the calculation of homogenized few group cross sections which are forwarded to the 3D full core calculations is investigated. The consequences on the calculation time are discussed
Keywords: Spatial Discretization, Neutron Transport, HELIOS, Collision Probabilities, Flat-Flux-Approximation
  • Lecture (others)
    Studsvik User Group Meeting 2008, 09.-11.04.2008, Budapest, Hungary

Publ.-Id: 11165 - Permalink


Tidal waves and spatial symmetry
Frauendorf, S.;
Tidal waves and spatial symmetry
  • Invited lecture (Conferences)
    Gordon Research Conference on Nuclear Chemistry, 03.-08.06.2007, New London, NH, USA

Publ.-Id: 11164 - Permalink


Symmetries and collective nuclear excitations
Frauendorf, S.;
Symmetries and collective nuclear excitations
  • Lecture (Conference)
    Workshop on Present and Future Exotics in Nuclear Physics, 28.-29.02.2008, Copenhagen, Danmark

Publ.-Id: 11163 - Permalink


Emergence of phases with size
Frauendorf, S.;
  • Invited lecture (Conferences)
    Kolloqium, 02.10.2007, Dresden, Germany

Publ.-Id: 11162 - Permalink


Role of P2 purinergic receptors in synaptic transmission under normoxic and ischaemic conditions in the CA1 region of rat hippocampal slices
Coppi, E.; Pugliese, A. M.; Stephan, H.; Müller, C. E.; Pedata, F.;
The role of ATP and its stable analogue ATPγS [adenosine-5′-o-(3-thio)triphosphate] was studied in rat hippocampal neurotransmission under normoxic conditions and during oxygen and glucose deprivation (OGD). Field excitatory postsynaptic potentials (fEPSPs) from the dendriticlayer or population spikes (PSs) from the soma were extracellularly recorded in the CA1 area of the rat hippocampus. Exogenous application of ATP or ATPγS reduced fEPSP and PS amplitudes. In both cases the inhibitory effect was blocked by the selective A1 adenosine receptor antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine) and was potentiated by different ecto-ATPase inhibitors: ARL 67156 (6-N,N-diethyl-D-β,γ-dibromomethylene), BGO 136 (1-hydroxynaphthalene-3,6-disulfonate) and PV4 [hexapotassium dihydrogen monotitanoun-decatungstocobaltate(II) tridecahydrate, K6H2[TiW11CoO40]•13H2O]. ATPγSmediated inhibition was reduced by the P2 antagonist suramin [8-(3-benzamido-4-methylbenzamido)naphthalene-1,3,5-trisulfonate] at the somatic level and by other P2 blockers, PPADS (pyridoxalphosphate-6-azophenyl-2′, 4′-disulfonate) and MRS 2179 (2′-deoxy-N6-methyladenosine 3′,5′-bisphosphate), at the dendritic level. After removal of both P2 agonists, a persistent increase in evoked synaptic responses was recorded both at the dendritic and somatic levels. This effect was prevented in the presence of different P2 antagonists. A 7-min OGD induced tissue anoxic depolarization and was invariably followed by irreversible loss of fEPSP. PPADS, suramin, MRS2179 or BBG (brilliant blue G) significantly prevented the irreversible failure of neurotransmission induced by 7-min OGD. Furthermore, in the presence of these P2 antagonists, the development of anoxic depolarization was blocked or significantly delayed. Our results indicate that P2 receptors modulate CA1 synaptic transmission under normoxic conditions by eliciting both inhibitory and excitatory effects. In the same brain region, P2 receptor stimulation plays a deleterious role during a severe OGD insult.

Publ.-Id: 11161 - Permalink


Heart-shaped nuclei: Condensation of rotational-aligned octupole phonons
Frauendorf, S.;
The strong octupole correlations in the mass region A approximate to 226 are interpreted as rotation-induced condensation of octupole phonons having their angular momentum aligned with the rotational axis. Discrete phonon energy and parity conservation generate oscillations of the energy difference between the lowest rotational bands with positive and negative parity. Anharmonicities tend to synchronize the rotation of the condensate and the quadrupole shape of the nucleus forming a rotating heart shape.
  • Physical Review C 77(2008), 021304

Publ.-Id: 11160 - Permalink


Fast Intraband Capture and Relaxation in InAs/GaAs Self-Assembled Quantum Dots
Zibik, E. A.; Menzel, S.; Aivaliotis, P.; Carpenter, B. A.; Cockburn, J. W.; Skolnick, M. S.; Wilson, L. R.; Grange, T.; Ferreira, R.; Bastard, G.; Stehr, D.; Winnerl, S.; Helm, M.; Steer, M. J.; Hopkinson, M.;
Electron capture and relaxation processes in n-type InAs/GaAs quantum dots were investigated using mid-infrared degenerated pump-probe spectroscopy. Fast (~4 ps - 10 ps) intraband relaxation/capture times were measured even in the absence of electron-hole scattering.
  • Lecture (Conference)
    Conference on Lasers & Electro-Optics 2007, 06.-11.05.2007, Baltimore, USA
  • Contribution to proceedings
    Conference on Lasers & Electro-Optics 2007, 06.-11.05.2007, Baltimore, USA
    CLEO/QELS & PhAST Technical Digest CD-ROM 2007

Publ.-Id: 11159 - Permalink


On the consequences of a lifetime extension on the accumulated Plutonium mass in Germany
Merk, B.;
The Plutonium production in the German reactor park under the actual political guidelines is studied. The influence of different options (once-through scenario, single and double MOX recycling scenario) on the residual Plutonium masses are analysed and compared to a close to reality scenario. Additionally an insight into the consequences of a postulated lifetime extension on the residual Plutonium mass is given and the Plutonium reduction and the change of the Plutonium composition due to double recycling are demonstrated. An outlook is given on the consequences of a lifetime extension for 10 years on the UOX fuel, the Plutonium and the Minor Actinide masses and compared to the additional amount of electricity produced due to the lifetime extension.
Keywords: Lifetime Extension, Cycle Studies, Plutonium Management, MOX Fuel
  • Contribution to proceedings
    Actinide and Fission Product Partitioning and Transmutation Tenth Information Exchange Meeting, 06.-10.10.2008, Mito, Japan
  • Poster
    Actinide and Fission Product Partitioning and Transmutation Tenth Information Exchange Meeting, 06.-10.10.2008, Mito, Japan

Publ.-Id: 11158 - Permalink


An analytical solution for a simple time dependent neutron transport problem: Shut down of the external source
Merk, B.;
An analytical solution for the shut down of an external source in a homogeneous subcritical reactor problem is developed. The problem is described through an approximation of the Boltzmann Transport equation, the Telegrapher's or time dependent P1 equation. The analytical solution to the problem is expressed in terms of a Green's function expansion. The differences between the solution for the Telegrapher's equation and the diffusion equation without separation of space and time are discussed.
Keywords: Telegrapher's equation, Neutron Transport, Space-Time Dependent Transport, Accelerator Driven Systems
  • Contribution to proceedings
    Actinide and Fission Product Partitioning and Transmutation Tenth Information Exchange Meeting, 06.-10.10.2008, Mito, Japan
    Actinide and Fission Product Partitioning and Transmutation: Nuclear Energy Agency
  • Poster
    Actinide and Fission Product Partitioning and Transmutation Tenth Information Exchange Meetin, 06.-10.10.2008, Mito, Japan

Publ.-Id: 11157 - Permalink


The dance of the Domains: Excitations in Magnetic Microstructures Studied by X-ray Microscopy
Raabe, J.; Buess, M.; Kuepper, K.; Fassbender, J.ORC; Quitmann, C.
Micron sized magnetic thin film structures have interesting magnetic properties. By adjusting size, shape, and material they can form a multitude of magnetic domain patterns. They consist of homogenously magnetized domains, which are separated by domain walls and magnetic vortices forming at the intersections of the domain walls. We study the static and dynamic magnetic properties of such thin film structures. For this we use synchrotron based Photo Emission Electron Microscopy (PEEM). By combining the naturally pulsed time structure of the synchrotron light with magnetic field pulses to the sample, we are able to study magnetization dynamics with a time resolution of tfwhm<100ps. This allows quantitative analysis of the excitations in such particles which can in turn be compared to simulations based on the Landau-Lifshitz-Gilbert equation. We start with simple discs or squares, where three modes connected to the homogenously magnetized domains, the domain walls and the vortex exist. From there we move to more complex objects. For instance, in a rectangular platelet a configuration containing a stable combination of vortices and an antivortex can be created. Such a single cross-tie wall can be understood as being a coupled micromagnetic system with three static solitons. We report on its magnetization dynamics including the vortex-antivortex interactions. The spectrum of eigenmodes is investigated as well as the effect of different vortex core orientations. We show that the vortex dynamics can be used to identify the core configuration which is not directly accessible to x-ray microscopy because of its limited spatial resolution. In the second part we will briefly show the current capabilities for magnetic imaging of the Scanning Transmission X-ray Microscope (STXM) at the PolLux Beamline of the Swiss Light Source as a complementary x-ray based technique.
Keywords: magnetism, magnetic domains, time-resolved, x-ray microscopy
  • Lecture (Conference)
    MRS Spring Meeting 2008, Symposium: Advances and Applications of Surface Electron Microscopy, 24.-28.03.2008, San Francisco, USA

Publ.-Id: 11156 - Permalink


The development of intersubband semiconductor light sources: from MOSFETs to Quantum Cascade Lasers
Helm, M.;
I will present a short history of intersubband light emission from semiconductor quantum structures, starting with MOSFETs in 1976 and culminating with the invention of the quantum cascade laser in 1994. I will discuss the underlying physics and present some highlight achievements.
Nowadays these lasers span a wavelength range between 2.8 and 250 microns, which is nearly two spectral decades.
Keywords: intersubband, quantum cascade laser
  • Lecture (others)
    Seminarvortrag am Institute for Laser Engeineering, Osaka University, 17.03.2008, Osaka, Japan

Publ.-Id: 11155 - Permalink


THz physics at the Research Center Dresden-Rossendorf: from scalable antennas to free-electron laser based near-field microscopy
Helm, M.;
I will discuss two quite different activities, (1) novel scalable THz antennas for time-domain spectroscopy and (2) near field microscopy using a free-electron laser.
We have developed photoconductive antennas based on an interdigitated, scalable design, which combines the advantages of large-aperture emitters and usual antennas, yet without their respective drawbacks. I will discuss their use as THz emitters as well as detectors.
In our institute we have an IR/THz free-electron laser. After describing this facility, I will present some results from using this high-power source for near-field imaging of ferroelectric domains in BaTiO3.

Keywords: Terahertz, antenna, near-field microscopy, free electron laser
  • Lecture (others)
    Seminar am Institute for Laser Engineering, Osaka University, 05.03.2008, Osaka, Japan

Publ.-Id: 11154 - Permalink


Pump-probe studies of electron dynamics in quantum wells and superlattices
Helm, M.;
After introducing the infrared/THz free-electron laser (FEL) facility at the Research Center Dresden-Rossendorf, I will discuss some pump-probe experiments to study the electron relaxation dynamics in superlattices. Both one-color, but also two-color experiments have been performed using the FEL, and, in addition, THz radiation generated by optical rectification in GaSe as the probe beam. In the second part of my talk I will discuss the intersubband dynamics in thin InGaAs/AlAsSb quantum wells, which are important for short-wavelength quantum cascade lasers. These experiments were performed using a femtosecond OPO system and yield information on the relevance of intervalley scattering.
Keywords: pump-probe, quantum well, superalttice, infrared, free-electron laser
  • Lecture (others)
    Seminarvortrag am Institute of Industrial Science, Tokyo University, 27.02.2008, Tokyo, Japan
  • Lecture (others)
    Seminarvortrag am Research Institute of Electrical Communication (RIEC), Tohoku University, 14.03.2008, Sendai, Japan

Publ.-Id: 11153 - Permalink


Reaktivitätsmessungen am WWER-440 des KKW Paks mittels Incore-Rhodiumdetektoren
Maletti, R.; Stein, H.; Hoppe, D.; Beier, M.; Jozsa, I.; Horvath, C.;
Im Beitrag wird über die Nutzung von Incore-Signalen für Reaktivitätsmessungen zur Bestimmung wichtiger reaktorphysikalischer Parameter wie differentielle Stabwirksamkeit oder Leistungskoeffizient berichtet. Aus der Diskussion von Mess- und Rechenergebnissen folgt, dass für den Zeitraum der Durchführung der Messungen am Block 3 des KKW Paks der Reaktivitätseffekt bei Störungsmessungen mit den Ionisationskammern offensichtlich deutlich unterschätzt wird.
Keywords: Paks-3 reactor, reactivity measurements, in core instruments, self-powered neutron detectors, control rod worths, power coefficient
  • Kernenergie 34(1991)6, 253-260

Publ.-Id: 11152 - Permalink


Dynamische Reaktivitätsstörungsmessungen an Leistungsreaktoren mittels prompt ansprechender Elektronenemissionsdetektoren
Maletti, R.; Seidenkranz, T.; Stein, H.;
Erstmals werden prompt ansprechende Elektronenemissionsdetektoren mit Cobalt- bzw. Platin-Emitter für die Anwendung der Methode der Reaktivitätsstörungsmessungen im Leistungsbereich des Reaktors WWER-70 des KKW Rheinsberg eingesetzt. Dadurch lässt sich der experimentelle Aufwand für die Durchführung der Reaktivitätsmessungen senken und die Genauigkeit der ermittelten Reaktivitätskoeffizienten erhöhen. Störungsmessungen wurden auch bei sehr kleiner Reaktorleistung, d. h. im rückkopplungsfreien Reaktorzustand, durchgeführt. Die experimentellen Resultate bestätigen die theoretischen Modellvorstellungen zur Ortskorrektion bei rückkopplungsfreien Zuständen.
Keywords: Rheinsberg akw1 reactor, reactor kinetics, reactivity coefficients, self-powered neutron detectors, space dependence
  • Kernenergie 32(1989)11, 437-441

Publ.-Id: 11151 - Permalink


Evaluation of Intergrated (F-18)fluoro-DOPA-PET/CT for identification of focal forms of congenital hyperinsulinism (CHI)
Blankenstein, O.; Mohnike, W.; Hussain, K.; Barthlen, W.; Koch, M.; Füchtner, F.; Strom, T.; Mohnike, K.; Grueters, A.;
kein Abstract verfügbar
  • Lecture (Conference)
    10th European Congress of Endocrinology, 03.-07.05.2008, Berlin, Germany
  • Abstract in refereed journal
    European Journal of Pediatrics 167(2008)3, 363

Publ.-Id: 11150 - Permalink


On the influence of spatial discretization in LWR-burnup calculations with HELIOS 1.9 – part II: mixed oxide (MOX) fuel
Merk, B.;
Cell- and burnup calculations are the fundament for all deterministic static and transient 3D full core calculations for different operational states of the reactor. The arising differences in the integral transport solution (neutron flux and kinf) for different discretization strategies over the burnup of mixed oxide (MOX) fuel due to different spatial discretization are demonstrated. The influence of different discretization strategies on the calculation of homogenized few group cross sections which are forwarded to the 3D full core calculations is investigated and on the calculation time is evaluated. The differences between UOX and MOX fuel are discussed.
Keywords: Cell- and Lattice calculation, cross section preparation, HELIOS, Discretization, Brunp calculation, Mixed Oxide Fuel
  • Annals of Nuclear Energy 36(2009), 168-182

Publ.-Id: 11149 - Permalink


On the influence of spatial discretization in LWR-burnup calculations with HELIOS 1.9 – part I: Uranium oxide (UOX) fuel
Merk, B.;
Cell- and burnup calculations are the fundament for all deterministic static and transient 3D full core calculations for different operational states of the reactor. The spatial discretization used for the cell- and burnup calculations influences the results for the used integral transport solutions significantly. The arising differences in the neutron flux distribution for different discretization strategies over the burnup of Uranium oxide (UOX) fuel due to different spatial discretization are demonstrated. These differences in the flux distribution cause significant changes in the kinf value. The influence of different discretization strategies on the calculation of homogenized few group cross sections which are forwarded to the 3D full core calculations is investigated The influence of the discretization strategies on the calculation time is evaluated.
Keywords: Cell- and Lattice calculation, cross section preparation, HELIOS, Discretization, Burnup calculation
  • Annals of Nuclear Energy 36(2009), 151-167

Publ.-Id: 11148 - Permalink


Nano Composit Materialien fuer Flugzeit RPC Detektoren
Wuestenfeld, J.;
The talk presents recent results from our investigations of new nanocomposite materials for the construction of resistive plate counters. This counters are forseen as timing detectors for the upcomming Compressed Baryonic Matter (CBM) experiment at FAIR. These tests where performed at the electron beam of ELBE.
Keywords: RPC, nano composite materials, ELBE
  • Lecture (Conference)
    DPG Frühjahrstagung des AMOP und der Fachverbände Hadronen und Kerne, Umweltphysik 2008, 10.-14.03.2008, Darmstadt, Germany

Publ.-Id: 11146 - Permalink


Application of CFD codes in nuclear reactor safety analysis
Rohde, U.; Höhne, T.; Krepper, E.; Kliem, S.;
The last decade has seen an increasing use of computational fluid dynamics codes (CFD) to predict steady state and transient flows in nuclear reactors. The reason for the increased use of CFD methods is that a number of phenomena important for the assessment of the safety of nuclear reactors such as pressurized thermal shocks, boron mixing, thermal striping and sub-cooled boiling cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.

CFD codes are characterized by the fact that the underlying equations are implemented in a clearly more detailed way in comparison to the one-dimensional system codes. Nevertheless, these codes contain empirical models for simulating turbulence, heat transfer, multi-phase flows, and chemical reactions. Such models must be validated before they can be used with sufficient confidence in Nuclear Reactor Safety (NRS) applications.

CFD validation simulations are shown in areas such as: heat transfer, buoyancy, multi-phase flows, natural circulation, turbulent mixing, and complex geometries. These topics are related to the above mentioned NRS-relevant issues.

The following topical issues will be discussed in the presentation:

1. Coolant Mixing (Boron Dilution Transient)
2. Coolant Mixing (Pressurized Thermal Shock)
3. Debris Transport Phenomena in multidimensional water flow
4. Sub-cooled boiling - Application to fuel rod bundle safety assessment

The material presented has been prepared by FZD partly under the sponsorship by the European Commission, the German Government (BMWA) and the VGB PowerTech e.V.
Keywords: CFD, NRS
  • Invited lecture (Conferences)
    TOPSAFE 2008, 01.-03.10.2008, Dubrovnik, Kroatia
  • Contribution to proceedings
    TOPSAFE 2008, 01.-03.10.2008, Dubrovnik, Kroatia
    CD-ROM. paper 099
  • Open Access LogoScience and Technology of Nuclear Installations 2010(2010), Article ID 198758
    DOI: doi:10.1155/2010/198758

Publ.-Id: 11145 - Permalink


CFD simulations of Gidropress mixing facility experiments in the framework of TACIS project R2.02/02
Höhne, T.; Rohde, U.; Melideo, D.; Moretti, F.; D’Auria, F.; Shishov, A.; Lisenkov, E.;
The main objective for the quantification of the fluid mixing in the downcomer and the lower plenum is the demonstration of the safety of the nuclear plant during non-symmetrical transients. This concerns two main topics: The risk of fragile brittle of the Reactor Pressure Vessel (RPV) during Pressurized Thermal Shock (PTS) transients and the risk of core reactivity excursion during non-symmetrical transient such as Main Steam Line Breaks (MSLB) or Boron Dilution Transients (BDT). The corresponding fluid mixing scenarios are studied in the 1:5 scaled VVER-1000 reactor model at OKB “Gidropress” in the framework of a TACIS project: “Development of safety analysis capabilities for VVER-1000 transients involving spatial variations of coolant properties (temperature or boron concentration) at core inlet”.

An extensive experimental program was running, studying different flow conditions in the reactor mock up, like the start of the 1st coolant pump or natural circulation conditions with density differences of the primary coolant. Pre and post test CFD simulations were carried out for code validation and for a deeper understanding of the flow and mixing behavior in the VVER-1000 reactor also in the future of the project. The 3-D computational fluid dynamics (CFD) codes provide an effective tool for mixing calculations. The CFD-Code used was ANSYS CFX. The geometric details of the construction internals inside the RPV have a strong influence on the flow field and on the mixing. Therefore, an exact representation of the inlet region, the spacer in the downcomer, the elliptical perforated plate and the complicated structures in the lower plenum was necessary. All parts of the lower plenum structures were modeled in detail. The final computational grid contained 6.5 Million nodes. Results of selected experiments and corresponding CFD calculations will be described and discussed in the paper and conclusions will be drawn.
Keywords: CFD, VVER-1000, Coolant Mixing
  • Contribution to proceedings
    TOPSAFE 2008, 01.-03.10.2008, Dubrovnik, Kroatia
    CD-ROM, paper 063
  • Lecture (Conference)
    TOPSAFE 2008, 01.-03.10.2008, Dubrovnik, Kroatia

Publ.-Id: 11144 - Permalink


RPC development for CBM @ FZD
Wuestenfeld, J.;
The talk presents recent results from our investigations of new nanocomposite materials for the construction of resistive plate counters. This counters are forseen as timing detectors for the upcomming Compressed Baryonic Matter (CBM) experiment at FAIR. These tests where performed at the electron beam of ELBE.
Keywords: RPC, nano composite materials, ELBE
  • Lecture (Conference)
    11th CBM Collaboration Meeting of the CBM Experiment at FAIR, 26.-29.02.2008, GSI, Darmstadt, Deutschland

Publ.-Id: 11143 - Permalink


Complexation study of europium(III) and curium(III) with urea in aqueous solution investigated by time-resolved laser-induced fluorescence spectroscopy
Heller, A.; Barkleit, A.; Bernhard, G.; Ackermann, J.-U.;
The complex formation of europium(III) and curium(III) with urea in aqueous solution has been studied at I = 0.1 M (NaClO4), room temperature and trace metal concentrations in the pH-range of 1 to 8 at various ligand concentrations using time-resolved laser-fluorescence spectroscopy. While for curium(III) the luminescence maximum is red shifted upon complexation, in case of europium(III) emission wavelengths remain unaltered but a significant change in peak splitting occurs. Both heavy metals form weak inner sphere complexes of the formulae ML3+ with urea, which are stable till pH 6 but easily repressed by metal hydroxide formation. Stability constants were determined to be logß110 = -0.10 ± 0.07 for europium(III) and -0.80 ± 0.23 for curium(III).
Keywords: curium(III), europium(III), urea, complexation, TRLFS, heavy metal speciation
  • Inorganica Chimica Acta 362(2009)4, 1215-1222

Publ.-Id: 11142 - Permalink


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