Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31742 Publications
Correlated electron systems at high magnetic fields
Wosnitza, J.;
High magnetic fields are one of the most powerful tools available to scientists for the study, modification, and control of the state of matter. The application of magnetic fields, therefore, has become a commonly used instrument for condensed-matter physics. For the observation of many phenomena very high magnetic fields are essential. Consequently, the demand for the highest possible magnetic-field strengths is increasing. At the Dresden High Magnetic Field Laboratory (HLD), that has just opened its doors for external users, pulsed magnetic fields up to 70 T are available and the ambitious goal of reaching 100 T has been set. Here, I will present the current status of the HLD and discuss some scientific results recently obtained at high magnetic fields. This covers e.g. the clear thermodynamic evidence for the existence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in a layered organic superconductor, the magnetic-field-induced change of the electronic band structure in the metal CeBiPt, and finally the determination of the band- and angle-resolved superconducting coupling strength in a borocarbide superconductor.
  • Invited lecture (Conferences)
    1st Bilateral Estonian-German Workshop Strong Nonlinear Vibronic and Electronic Interactions in Solids, 30.04.-02.05.2008, Tartu, Estonia

Publ.-Id: 11654 - Permalink

An insight into what superconducts in polycrystalline boron-doped diamonds based on investigations of microstructure
Dubrovinskaia, N.; Wirth, R.; Wosnitza, J.; Papageorgiou, T.; Braun, H. F.; Miyajima, N.; Dubrovinsky, L.;
The discovery of superconductivity in polycrystalline boron-doped diamond (BDD) synthesized under high pressure and high temperatures [Ekimov, et al. (2004) Nature 428:542–545] has raised a number of questions on the origin of the superconducting state. It was suggested that the heavy boron doping of diamond eventually leads to superconductivity. To justify such statements more detailed information on the microstructure of the composite materials and on the exact boron content in the diamond grains is needed. For that we used high-resolution transmission electron microscopy and electron energy loss spectroscopy. For the studied superconducting BDD samples synthesized at high pressures and high temperatures the diamond grain sizes are ≈1–2 µm with a boron content between 0.2 (2) and 0.5 (1) at %. The grains are separated by 10- to 20-nm-thick layers and triangular-shaped pockets of predominantly (at least 95 at %) amorphous boron. These results render superconductivity caused by the heavy boron doping in diamond highly unlikely.
  • Proceedings of the National Academy of Sciences of the United States of America 105(2008)33, 11619-11622

Publ.-Id: 11653 - Permalink

Characterization of ZnO Nanostructures: A Challenge to Positron Annihilation Spectroscopy and other Methods
Brauer, G.; Anwand, W.; Grambole, D.; Egger, W.; Sperr, P.; Beynik, I.; Hofer, C.; Teichert, C.; Kuriplach, J.; Lang, J.; Zviagin, S.; Cizmar, E.; Ling, C. C.; Hsu, Y. F.; Xi, Y. Y.; Djurisic, A. B.; Skorupa, W.;
ZnO is of considerable interest for optoelectronic device applications due to its wide band gap and high exciton binding energy. In spite of decades of study and recent progress in research on ZnO properties, there remained unresolved controversies which are mainly related to native defects formed during crystal growth. Positron annihilation spectroscopy (PAS) is among the methods to tackle this structural issue [1, 2].
ZnO nanostructures, like e.g. nanorods [3] and tetrapods [4], are of special interest for device applications [5, 6]. However, their characterization remains an ongoing challenge.
This talk intends to review our recent efforts and latest achievements in this direction. Results obtained will comprise PAS in the form of Slow Positron Implantation Spectroscopy (SPIS) and Pulsed Low Energy Positron Lifetime Spectroscopy (PLEPS), Nuclear Reaction Analysis (NRA), Atomic Force Microscopy (AFM), conductive AFM (C-AFM), Nuclear Magnetic Resonance (NMR), Electron Spin Resonance (ESR), Photoluminescence (PL) spectroscopy, and latest theoretical investigations of structure-related and positron properties of selected defects.
The fundamental importance of a relationship between fabrication conditions, native defect formation, and resulting optical and electronic properties is demonstrated by getting either inferior (nanorods) or significantly improved (tetrapods) optical properties compared to single crystal samples, depending on the nanostructure fabrication method.
  • Invited lecture (Conferences)
    XVth International Conference on Positron Annihilation (ICPA-15), 18.-23.01.2009, Kolkata, India

Publ.-Id: 11652 - Permalink

Activities towards p-Type Doping of ZnO
Brauer, G.; Kuriplach, J.; Djurisic, C. C.; Ling, A. B.;
Zinc oxide (ZnO) is an interesting and promising semiconductor material for many potential applications, e.g. in opto-electronics and for sensor devices. However, its p-type doping represents a challenging problem, and the physical reasons of its mostly n-type conductivity are not perfectly clear at present.
Firstly, efforts to achieve p-type conductivity by ion implantation are reviewed, and the creation of a p-n junction by N+ ion implantation with post-implantation annealing is discussed.
Secondly, ways to achieve p-type ZnO nanorods by various growth conditions are presented. Their characterization by electrical, optical and positron annihilation spectroscopy methods will also be included.
Third, the preparation of Schottky contacts on ZnO with the surface pre-treatments of hydrogen peroxide is mentioned in some detail as this is a demand of the device formation process.
Finally, the possible incorporation of hydrogen and nitrogen into structural defects, which can act as trapping sites for positrons, is discussed. This will be discussed in the context of positron experimental and theoretical results and estimated H and N contents in a selected variety of ZnO materials.
  • Invited lecture (Conferences)
    8th International Conference on Position Sensitive Detectors (PSD 2008), 01.-05.09.2008, Prague, Czech Republic
  • Open Access LogoJournal of Physics: Conference Series 265(2011), 012002
    DOI: 10.1088/1742-6596/265/1/012002

Publ.-Id: 11651 - Permalink

Secondary Structure and Compliance of a Predicted Flexible Domain in Kinesin-1 Necessary for Co-operation of Motors
Crevenna, A. H.; Madathil, S.; Cohen, D. N.; Wagenbach, M.; Fahmy, K.; Howard, J.;
While the mechanism by which a kinesin-1 molecule moves individually along a microtubule is quite well understood, the way that many kinesin-1 motor proteins bound to the same cargo move together along a microtubule is not. We have identified a 60-aa-long domain, termed Hinge 1, in kinesin-1 from Drosophila melanogaster that is located between the coiled coils of the neck and stalk domains. Its deletion reduces microtubule gliding speed in multiple–motor assays but not single-motor assays. Hinge 1 thus facilitates the co-operation of motors by preventing them from impeding each other. We have addressed the structural basis for this phenomenon. Video-microscopy of single microtubule-bound full-length motors reveals the sporadic occurrence of high compliance states alternating with longer-lived low compliance states. Deletion of Hinge 1 abolishes transitions to the high compliance state. Based on FTIR, CD, and fluorescence spectroscopy of Hinge 1 peptides, we propose that the low compliance states correspond to an unexpected structured organization of the central Hinge 1 region, whereas the high-compliance state corresponds to the loss of that structure. We hypothesize that strain accumulated during multiple-kinesin motility populates the high compliance state by unfolding helical secondary structure in the central Hinge 1 domain flanked by unordered regions, thereby preventing the motors from interfering with each other in multiple-motor situations.
Keywords: Gliding assay, single-molecule assay, torsional elasticity, protein flexibility, microtubule, spectroscopy

Publ.-Id: 11650 - Permalink

Interplay between Kondo-like behavior and short-range antiferromagnetism in EuCu2Si2 single crystals
Cao, C. D.; Klingeler, R.; Leps, N.; Vinzelberg, H.; Kataev, V.; Muranyi, F.; Tristan, N.; Teresiak, A.; Zhou, S.; Löser, W.; Behr, G.; Büchner, B.;
The static and dynamic magnetic properties, electrical resistivity, specific heat, and magnetoresistance have been studied in EuCu2Si2 single crystals grown by a floating zone method. The magnetic susceptibility exhibits a considerable anisotropy and a steep rise below 10 K for external fields parallel to the c axis but with no evident magnetic ordering in the temperature range of 2–350 K. The data imply a gradual change in the Eu valence as a function of temperature. Electron spin resonance (ESR) measurements reveal a sizeable fraction of stable Eu2+ magnetic moments that interact with conduction electrons and develop quasistatic antiferromagnetic correlations on the ESR timescale. The electrical resistivity and specific heat demonstrate the presence of spin fluctuations and Kondo-like behavior, which apparently competes with the antiferromagnetic order. The analysis of experimental data enables to conclude that the remarkable diversity of the physical properties of EuCu2Si2 results from the variation of lattice parameters as well as of local crystal chemistry as a consequence of the particular preparation route employed for the growth of single crystals and polycrystals.

Publ.-Id: 11649 - Permalink

Arsenic doped zinc oxide
Volbers, N.; Lautenschläger, S.; Leichtweiss, T.; Laufer, A.; Graubner, S.; Meyer, B. K.; Potzger, K.; Zhou, S.;
As-doping of zinc oxide has been approached by ion implantation and chemical vapor deposition. The effect of thermal annealing on the implanted samples has been investigated by using secondary ion mass spectrometry and Rutherford backscattering/channeling geometry. The crystal damage, the distribution of the arsenic, the diffusion of impurities, and the formation of secondary phases is discussed. For the thin films grown by vapor deposition, the composition has been determined with regard to the growth parameters. The bonding state of arsenic was investigated for both series of samples using x-ray photoelectron spectroscopy.
Keywords: ZnO, Doping

Publ.-Id: 11648 - Permalink

Electron beam CT – a potential tool for small animal imaging ?
Hampel, U.; Fischer, F.; Bergmann, R.;
Electron beam CT has until today been exclusively used in cardiac imaging of human beings. As a high cost diagnostic tool with frame rates in the range of 20 Hz it has so far not been considered for small animal imaging. With recent progress in technology an application in this field becomes feasible. Especially perfusion imaging for heart and other organs using iodine based contrast agents may be a target of interest for electron beam CT. We present a small volume ultra fast electron beam CT scanner which was originally developed for process tomography applications and with it preliminary results of a small animal study showing visualization of heart motion and perfusion in a rat. We further discuss the potential of this new technology and novel technological principles which allow fast 3D electron beam imaging of small animals. Included in the discussion is an assessment of radiation effects.
Keywords: electron beam tomography, small animal imaging
  • Lecture (Conference)
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
    IEEE NSS/MIC/RTSD Conference Record

Publ.-Id: 11647 - Permalink

Application of CdTe and CZT detectors in ultra fast electron beam X-ray tomography
Hampel, U.; Fischer, F.;
Ultra fast electron beam tomography has been developed as a novel tool for visualisation of fast processes. As in medical electron beam CT this technique is based on the generation of images from radiographs produced with a rapidly scanned electron beam. Thereby an electron beam of sufficiently high power (typically UB=150kV, power up to 10 kW) is scanned across a circular metal target producing X-rays in a small focal spot. With the rotation of the spot around an object radiographs from different viewing angles are produced and subsequently reconstructed to slice images. A fast electron beam scanner at FZD operates with beam sweeping of up to 7 kHz, producing up to 7000 images per second. The X-ray detector used in this device consists of 240 room temperature semiconductor elements operated in current mode. Photon flux at the detector is rather high, being >10^11 ph/s. The detector is sampled with 1 MHz frequency. It is known, that high flux current mode operation poses problems for semiconductor detectors made of CZT and CdTe due to polarization effects and decay time in the few hundred ns range. We have compared both types of detectors regarding their suitability in such an application. The presentation will give an overview on these results and furthermore give an introduction of this new fast imaging technique.
Keywords: electron beam tomography, CdTe detector, CZT detector
  • Invited lecture (Conferences)
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    IEEE - Workshop on X-Ray Micro Imaging of Materials, Devices, and Organisms, 22.-24.10.2008, Dresden, Germany
    IEEE NSS/MIC/RTSD Conference Record

Publ.-Id: 11646 - Permalink

Ultra fast electron beam X-ray tomography at FZD
Hampel, U.;
The presentation gives an overview on recent developments in ultra fast electron beam X-ray tomography for process applications. Principles of this new tomographic imaging modality are discussed along with applications in flow measurement. A focus is given on potential extension of the technology towards high power electron beam CT using DC electron LINAC.
Keywords: electron beam tomography
  • Invited lecture (Conferences)
    Electron Beam Tomography Meeting at BUDKERS Institute Novosibirsk, 02.09.2008, Novosibirsk, Russia

Publ.-Id: 11644 - Permalink

Computed tomography methods in flow measurement
Hampel, U.;
The lecture introduces computerized tomography as applied in process and flow diagnostics. In many indutrial fields multiphase flows play a key role in efficiency and safety aspects of indiustrial plants and processes. In the lecture principles of tomographic imaging modalities, such as electrical tomography, gamma and X-ray tomography, electron beam tomography, PET and PEPT are discussed along with exemplary applications in oil industry, chemical industry, nuclear engineering and other industrial and scientific fields.
Keywords: computed tomography, process tomography, multi-phase flow
  • Invited lecture (Conferences)
    FZD Lectures, 07.07.2008, Dresden, Germany

Publ.-Id: 11643 - Permalink

Self-organized metallic nanoparticle and nanowire arrays from ion-sputtered silicon templates
Oates, T. W. H.; Keller, A.; Noda, S.; Facsko, S.;
We demonstrate a production method for self-organized arrays of metal nanoparticles and aligned nanowires. Ion beam-sputtered Si/SiO2 substrates are used as templates for metallic vapor deposition, forming aligned arrays of 5–20 nm silver and cobalt nanoparticles with a period of 35 nm. The 20 nm diameter cobalt nanowires with lengths in excess of a micrometer are produced under appropriate conditions. All processing steps can be integrated into a single vacuum chamber and performed in a matter of minutes at mild temperatures. This inherently scalable technique can be extended to a range of substrate materials, array patterns, and nanoparticle materials.

Publ.-Id: 11642 - Permalink

Electromagnetic excitation of separated flows: Coherent structures and mean flow features
Weier, T.; Cierpka, C.; Gerbeth, G.;
Flow separation and its control is a persistent topic of fluid dynamic research with large technological importance. Since the early 1990s, separation control by periodic addition of momentum, now commonly termed “active flow control”, has been a subject of intense research. Its main advantage compared to steady actuation is that a control goal, e.g. a specific lift increase, can typically be attained by orders of magnitude smaller momentum input . The significant actuation parameters are mainly the time averaged momentum input and the normalized excitation frequency.
The present lectures discusses the applicability of electromagnetic forces to control separated flows. Simultaneous time resolved force measurements and flow fields obtained by Particle Image Velocimetry on a NACA 0015 are presented. The effects of momentum coefficient, exciatation frequency and -wave-form on the coherent structures and the resulting mean flow are discussed.
Keywords: active flow control, Lorentz force, coherent structures
  • Lecture (Conference)
    European Drag Reduction and Flow Control Meeting (EDRFCM 2008), 08.-11.09.2008, Ostritz - St. Marienthal, Germany

Publ.-Id: 11641 - Permalink

Efficient oxygen gettering in Si by co-implantation of hydrogen and helium
Ou, X.; Koegler, R.; Mücklich, A.; Skorupa, W.; Möller, W.; Wang, X.; Gerlach, J. W.; Rauschenbach, B.;
Hydrogen pre-implantation performed in addition to helium implantation efficiently shrinks the width of the gettering layer in Si and increases the empty volume fraction as well as the internal surface area per unit volume. The gettering efficiency for oxygen is significantly enhanced compared to the single helium implantation, and the helium implantation dose can be strongly reduced. The gas-filled bubble layer induced by the co-implantation of hydrogen and helium has the highest gettering efficiency for the oxygen accumulation. Direct evidence for oxygen gettering at the internal wall of the cavity is demonstrated by cross-sectional transmission electron microscopy (XTEM).
Keywords: ion implantation, gettering, oxygen, helium, hydrogen, silicon, SIMOX

Publ.-Id: 11640 - Permalink

Time-resolved semiconductor spectroscopy in the mid-infrared and Terahertz regimes
Schneider, H.;
This talk will focus on several research topics exploiting our free-electron (FEL) and modelocked Ti:Sapphire lasers to investigate semiconductor nanostructures. Pump-probe spectroscopy and two-photon detection is used for time-resolved investigations of intersubband transitions in semiconductor quantum wells and for FEL pulse diagnostics, respectively. Terahertz emitters based on interdigitated metal stripe arrays will also be discussed.
  • Lecture (others)
    Seminar, Bhabha Atomic Research Centre, Mumbai, India, 07.08.2008, Mumbai, India

Publ.-Id: 11639 - Permalink

Tutorial on Intersubband Devices: Quantum Cascade Laser
Schneider, H.;
There is no abstract.
  • Invited lecture (Conferences)
    Optoschool 2008, 27.07.-02.08.2008, Mumbai, India

Publ.-Id: 11638 - Permalink

Tutorial on Intersubband Devices: Quantum Well Infrared Photodetectors
Schneider, H.;
There is no abstract.
  • Invited lecture (Conferences)
    Optoschool 2008, 27.07.-02.08.2008, Mumbai, India

Publ.-Id: 11637 - Permalink

Room-temperature mid-infrared two-photon photodetector
Schneider, H.; Liu, H. C.; Winnerl, S.; Drachenko, O.; Helm, M.; Faist, J.;
We report on a two-photon detector based on resonantly enhanced nonlinear absorption between subbands in InGaAs/InAlAs quantum wells and demonstrate its use as a quadratic autocorrelator for mid-infrared pulses. Modified device design allows for device operation at room temperature, which is crucial for applications in practical systems.
Keywords: Quantum well intersubband photodetector, two-photon transition, quadratic autocorrelation, InGaAs/AlGaAs

Publ.-Id: 11636 - Permalink

Experimental observation of swirl accumulation in a magnetically driven flow
Grants, I.; Zhang, C.; Eckert, S.; Gerbeth, G.;
Independent poloidal and azimuthal body forces are induced in a liquid metal cylinder by traveling and rotating magnetic fields of different frequencies, respectively. The bulk axial and azimuthal velocities are measured by the ultrasound Doppler method. Particle image velocimetry is used to observe the upper free surface velocity distribution. The transition from the poloidal to the azimuthal body force governed regime occurs at a fixed ratio of the respective force magnitude of around 100. This transition is marked by a formation of a concentrated vortex revealing several similarities to intense atmospheric vortices. The vortex structure is controlled by a relatively weak azimuthal force while the poloidal one holds the main control over the top speed of the top speed of the swirl is mainly governed by the poloidal one. Under a certain force ratio the average axial velocity changes its direction in the vortex core resembling the subsidence in an eye of a tropical cyclone or a large tornado. Multiple moving vortices encircle the vortex core in this regime.
  • Journal of Fluid Mechanics 616(2008), 135-152

Publ.-Id: 11635 - Permalink

Two phase flow 1D turbulence model for poly disperse upward flow in a vertical pipe
Al Issa, S.; Lucas, D.;
A 1D test solver was developed in recent years for the modeling of two phase bubbly flow in pipe geometry. The solver considers number of bubble classes and calculates bubble-size resolved void fraction profiles in radial direction. A successful implementation was achieved regarding bubble forces models (non-drag forces). Discrepancies appeared when coalescence and breakup rates are significant. These rates depend upon local turbulent values, which are possible reason for shortcomings in calculating coalescence and breakup rates. Originally the test solver is equipped by Sato model (Sato et al. 1981) which accounts for turbulence via shear- and bubble-induced viscosities calculated out of empirical correlations. One-equation for the turbulent kinetic energy was considered. In order to improve the local values of turbulence parameters the existing turbulence model was replaced by two-equation turbulence model. The new model accounts for the bubble-induced turbulence via source term taken from literature. Comparisons between new and old turbulence modeling against experimental data showed better agreement of the new model. The experiments covered wide range of water and air superficial velocities for upward bubbly flow in two pipe’s diameters: 50 mm and 200 mm. Main feature of new calculations is providing values of turbulence parameters for application in coalescence and breakup models. A comparison with CFX 5.7 calculations in 50 mm pipe showed better calculation results when applying the source term. An implementation of the source term into CFX calculations is planned.
Keywords: Poly-disperse, bubbly Flow, bubble-induced turbulence, CFD
  • Nuclear Engineering and Design 239(2009)10, 1933-1943

Publ.-Id: 11634 - Permalink

Effect of melt convection on microstructure evolution of Nd-Fe-B and Ti-Al peritectic alloys
Hermann, R.; Gerbeth, G.; Biswas, K.; Filip, O.; Shatrov, V.; Priede, J.;
The influence of melt convection on the microstructure during solidification of peritectic Nd-Fe-B and Ti-Al alloys has been investigated. Since the magnetic and mechanical properties of these technical relevant materials depend strongly on the microstructure and especially on the volume fraction of the properitectic phase, such investigation is of growing scientific interest. On the basis of numerical simulation of melt convection modes in an inductively heated metallic melt, novel techniques for the modification of the melt convection were developed. This is the forced rotation technique and a modified floating-zone facility equipped with a special designed double coil system enabling the application of additional magnetic fields. The forced rotation technique where the crucible rotates with well defined frequencies leads in accordance to numerical simulation to a strong reduction of the melt convection in dependence on the frequency. The volume fraction of the soft magnetic α-Fe phase could be drastically reduced in comparison to a common induction melting accompanied by a simultaneous reduction of the secondary dendritic arm spacing. The floating-zone facility with the patented double coil system allows the tailoring of the melt convection in a wide range from motion at rest to strong stirring. The microstructure of the investigated Ti-Al alloy changed from dendritic to globulitic morphology under strong stirring whereas the volume fraction of the properitectic phase increases with increasing stirring. The mechanical properties show a significant increased plastic deformation of the samples solidified under strong stirring. The possible reason of the change in morphology is explained as a result of spherical growth under forced convection. The study of the influence of melt convection on the microstructure formation of peritectic alloys showed the feasibility of tailoring the microstructure and the resulting alloy properties by customized melt convection using magnetic fields.
Keywords: Melt convection, Peritectic solidification, Nd-Fe-B alloys, Ti-Al alloys
  • Contribution to external collection
    D.Herlach: Phase transformations in multicomponent melts, Weinheim: Wiley-VCH, 2008, 245-261

Publ.-Id: 11633 - Permalink

Noble gas retention in the target during rotating cylindrical magnetron sputtering
Mahieu, S.; Leroy, W. P.; Depla, D.; Schreiber, S.; Moeller, W.;
A rotating cylindrical magnetron with a Ti target was sputtered in pure Xe or in a mixture of Xe and N2. The atomic composition of the target surface during sputtering has been investigated by in situ Rutherford backscattering spectrometry. The noble gas atomic ratio at the target surface is around 3.4% or 9.8% for sputtering in pure Xe and with 10% N2 addition, respectively. Energy resolved mass spectrometry reveals that some of the implanted Xe atoms are sputtered from the target. A radiation enhanced diffusion/detrapping/sputtering mechanism is proposed to model the flux of noble gas leaving the target during sputtering
  • Applied Physics Letters 93(2008), 061501-1-061501-3

Publ.-Id: 11632 - Permalink

Boundary layer in the MRI experiment PROMISE
Szklarski, J.; Gerbeth, G.;
One of the most convenient approaches to observe experimentally the magnetorotational instability (MRI) is to use a magnetized Taylor-Couette setup. The flow of liquid metal between two rotating, concentric cylinders can become unstable in the presence of an external magnetic field. One of the issues which should be addressed when designing such an experiment is the influence of plates enclosing the cylinders from the top and the bottom. In this paper we discuss properties of the boundary layer which arises near these plates. Our primary concern is the importance of this layer in the MRI experiment PROMISE.
  • Astronomische Nachrichten 329(2008)7, 667-674

Publ.-Id: 11631 - Permalink

Hexadentate bispidine radiocopper complexes: emerging opportunities for the application in nuclear medicine
Stephan, H.; Juran, S.; Walther, M.; Bergmann, R.; Steinbach, J.; Comba, P.;
The advantageous properties of numerous 3,7-diazabicyclo[3.3.1]nonane (bispidine) derivatives have attracted much attention and caused intensive research efforts in different directions. An attractive goal represents the development of target-specific radiopharmaceuticals. For this purpose, bifunctional chelating agents are needed which have to show fast metal complexation kinetics, form complexes with high in vitro and in vivo stability and contain a group that can be linked to biomolecules. In this regard, hexadentate bispidines 1 – 3 containing pyridine units in C2, C4, N3, and N7 position have been shown to rapidly form stable radiocopper (such as 64Cu and 67Cu) complexes. Furthermore, the carboxylic groups of ligand 3 provide the possibility for coupling bio-molecules.
  • Lecture (Conference)
    2nd EuCheMS Chemistry Congress, 16.-20.09.2008, Torino, Italy

Publ.-Id: 11630 - Permalink

Radioaktive Substanzen helfen beim Suchen und Zerstören von Tumoren
Stephan, H.;
Beim Aufspüren von Tumoren und deren Metastasen hat die Positronen-Emissions-Tomographie (PET) entscheidende Fortschritte gebracht. Mit speziellen radioaktiven Substanzen lassen sich Tumore viel früher finden als mit anderen bildgebenden Verfahren. Die PET-Bilder geben – oft in Kombination mit anderen Verfahren wie Computertomographie (CT) oder Magnetresonanztomographie (MRT) – die notwendigen Informationen für eine chirurgische oder externe strahlentherapeutische Behandlung von Tumorerkrankungen. Ihre Grenzen findet die externe Bestrahlung häufig bei der metastasierenden Erkrankung, wobei Tumorzellen über Blut oder Körperflüssigkeit abgeschwemmt werden und an neuen Orten weiter wachsen. In diesen Fällen muss die Behandlungsmethode systemisch sein, d.h. die Tumortherapeutika müssen über die Blutbahnen zu den (zum Teil nicht sichtbaren) Metastasen gelangen. Dies ist bisher der Chemotherapie vorbehalten. Mit Mitteln der internen Radionuklidtherapie sollen künftig die Heilungserfolge insbesondere bei der Bekämpfung solcher Metastasen verbessert werden.
  • Lecture (others)
    Lange Nacht der Wissenschaften, 04.07.2008, Dresden, Deutschland
  • Lecture (others)
    Jobbörse FH Zittau/Görlitz, 24.11.2010, Zittau, D

Publ.-Id: 11629 - Permalink

New versatile bifunctional chelating agents for developing copper radiopharmaceuticals
Stephan, H.;
Radiopharmaceuticals based on metallic radionuclides, such as 64/67Cu, 99mTc, 186/188Re and 86/90Y, are often used for diagnostic and therapeutic purposes. These nuclides are usually enveloped in organic ligands, such as heteromacrocyclic systems. To be effective, the ligands have to show fast metal complexation kinetics, form complexes with high in vitro and in vivo stability and contain a group that can be linked to biomolecules. In this regard, we are developing new ligand scaffolds for copper radionuclides which satisfy these requirements. Ligands – based on hexadentate 3,7-diazabicyclo[3.3.1]nonane I (bispidine) and bis(2-pyridylmethyl) triazacyclononane (DMPTACN) II – are discussed. These derivatives allow the introduction of linker groups, such as carboxylic acids, maleinimide or isothiocyanate, thereby facilitating coupling of targeting molecules.
  • Lecture (others)
    COST BM0607 Action WG Meeting, 24.-25.06.2008, Krakow, Polen

Publ.-Id: 11628 - Permalink

Fracture mechanics characterisation of the WWER-440 reactor pressure vessel beltline welding seam of Greifswald Unit 8
Viehrig, H.-W.; Schuhknecht, J.;
WWER-440 second generation (V-213) reactor pressure vessels (RPV) were produced by IZHORA in Russia and by SKODA in the former Czechoslovakia. The surveillance Charpy-V and fracture mechanics SE(B) specimens of both producers have different orientations. The main difference is the crack extension direction which is through the RPV thickness and circumferential for ISHORA and SKODA RPV, respectively. In particular for the investigation of weld metal from multilayer submerged welding seams the crack extension direction is of importance. Depending on the crack extension direction in the specimen there are different welding beads or a uniform structure along the crack front. The specimen orientation becomes more important when the fracture toughness of the weld metal is directly determined on surveillance specimens according to the Master Curve (MC) approach as standardised in the ASTM Standard Test Method E1921. This approach was applied on weld metal of the RPV beltline welding seam of Greifswald Unit 8 RPV. Charpy size SE(B) specimens from 13 locations equally spaced over the thickness of the welding seam were tested. The specimens are in TL and TS orientation.
The fracture toughness values measured on the SE(B) specimens with both orientations follow the course of the MC. Nearly all values lie within the fracture toughness curves for 5% and 95% fracture probability. There is a strong variation of the reference temperature T0 though the thickness of the welding seam, which can be explained with structural differences. The scatter is more pronounced for the TS SE(B) specimens. It can be shown that specimens with TS and TL orientation in the welding seam have a differentiating and integrating behaviour, respectively. The statistical assumptions behind the MC approach are valid for both specimen orientations even if the structure is not uniform along the crack front. By comparison crack extension, JR, curves measured on SE(B) specimens with TL and TS orientation show only minor differences within the mean variation.
Keywords: reactor pressure vessel steel, welding seam, surveillance programme, specimen orientation, fracture toughness, Master Curve concept
  • Lecture (Conference)
    34th MPA-Seminar and VGB-Symposium "Materials and Components Behaviour in Energy & Plant Technology", 09.-10.10.2008, Stuttgart, Deutschland
  • Contribution to proceedings
    34th MPA-Seminar and VGB-Symposium "Materials and Components Behaviour in Energy & Plant Technology", 09.-10.10.2008, Stuttgart, Deutschland
    Proceedings 34th MPA-Seminar and VGB-Symposium "Materials and Components Behaviour in Energy & Plant Technology", Stuttgart: MPA Stuttgart

Publ.-Id: 11627 - Permalink

Effects of Neutron Irradiation on Positron and Micro-Vickers Hardness of Fe-Cu Model Alloys and Reactor Pressure Vessel Steel
Hempel, A.; Hasegawa, M.; Brauer, G.; Plazaola, F.; Saneyasu, M.; Tang, Z.;
  • Contribution to proceedings
    Ninth International Symposium on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, 01.-05.08.1999, Newport Beach, United States
    Proceedings of the Ninth International Symposium on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, 0-87339-475-5, 835-843

Publ.-Id: 11626 - Permalink

3-(4-(6-Fluoroalkoxy-3,4-dihydroisoquinolin-2(1H)-yl)cyclohexyl)-1H-indole-5-carbonitriles for SERT imaging: chemical synthesis, evaluation in vitro and radiofluorination
Funke, U.; Fischer, S.; Hiller, A.; Scheunemann, M.; Deuther-Conrad, W.; Brust, P.; Steinbach, J.;
Aminocyclohexyl indoles bind with high affinity and specificity toward the serotonin transporter (SERT). Based on this structural lead, we designed fluoroalkoxydihydroisoquinoline-cyclohexyl indole carbonitriles for future application as 18F-labeled tracers for SERT imaging by PET. Six compounds, three pairs of cis- and trans-isomer derivatives, respectively, were synthesized and evaluated in vitro. The chemistry of the new compounds, their affinity and specificity data, the general route to the phenolic precursor for labeling, and the successful 18F-fluoroalkylation of one pair of compounds are described herein.
Keywords: Serotonin transporter; PET; Indole carbonitriles; Affinity; Radiolabeling; Fluorine-18

Publ.-Id: 11625 - Permalink

Synthesis and radioiodination of two Cdk4 inhibitors.
Köhler, L.; Graf, F.; Pietzsch, J.; Steinbach, J.; Wüst, F.;
Accurate cell proliferation is depending on the correct execution of the cell cycle. The cell cycle is controlled and coordinated by various enzymes and proteins like cyclins, cyclin-dependent kinases (Cdk) and cyclin-dependent kinase inhibitors (Cki). Many tumors show dysregulated Cdk activity and/or Cdk expression, and in 80 % of tumors the cell cycle relevant Cdk4-D1/INK4/pRb/E2F signal cascade is altered. Hence, appropriately radiolabeled Cdk4 inhibitors may be promising molecular probes for imaging cell proliferation processes and tumor visualization by PET. This work describes the design and synthesis of two 124I-labeled Cdk4 inhibitors 8-cyclopentyl-6-[124I]iodo-5-methyl-2-(4-piperazin-1-yl-phenylamino)-8H-pyrido[2,3-d]pyrimidin-7-one ([124I]CKIA) and 8-cyclopentyl-6-[124I]iodo-5-methyl-2-(5-(piperazin-1-yl)pyridin-2-ylamino)-8H-pyrido[2,3-d]pyrimidin-7-one ([124I]CKIB) (figure) as potential radiotracers for imaging Cdk4 expression in vivo.

Reference substances and labeling precursors were prepared with minor modifications according to the chemistry described by Barvian et al.1 and VanderWel et al.2. The trimethylstannane compounds CKIAP and CKIBP as labeling precursors for the radioiodination reaction with I-124 were prepared in a multi-step synthesis sequence. Radioiodination was achieved by regioselective destannylation reaction under mild conditions using [124I]NaI and Chloramine-T or Iodogen as oxidizing agents. Treatment of a solution (50 µl) containing CKIAP (5 mg/ml) with [124I]NaI (36 MBq) in Iodogen precoated tubes afforded 12 MBq (34 %, decay-corrected) of [124I]CKIA, including HPLC purification. The optimal reaction conditions for the [124I]CKIA synthesis were applied to the synthesis of [124I]CKIB. Starting from a 50 µl solution of CKIBP (5 mg/ml) and [124I]NaI (29 MBq), compound [124I]CKIB was obtained in a 34 % decay-corrected radiochemical yield, including HPLC purification. Both compounds were isolated in radiochemical purity exceeding 95 % and high chemical purity. The specific activities were determined to be 20 GBq/µmol and 4 GBq/µmol, respectively. The lipophilicity (logP) was experimentally measured. The logP value was 2.77 ± 0.13 for [124I]CKIA and 1.99 ± 0.03 for [124I]CKIB.

The radiosynthesis of two 124I-labeled Cdk4 inhibitors has been developed. Both radiotracers were obtained in reproducible radiochemical yields and purity enabling further radiopharmacological characterization aimed at imaging Cdk4 expression by means of PET.

1 : Barvian, M.; Boschelli, D. H.; Cossrow, J.; Dobrusin, E.; Fattaey, A.; Fritsch, A.; Fry, D.; Harvey, P.; Keller, P.; Garrett, M.; La, F.; Leopold, W.; McNamara, D.; Quin, M.; Trumpp-Kallmeyer, S.; Toogood, P.; Wu, Z. P.; Zhang, E. L. Journal of Medicinal Chemistry, 2000, 43, 4606-4616.
2 : VanderWel, S. N.; Harvey, P. J.; McNamara, D. J.; Repine, J. T.; Keller, P. R.; Quin, J.; Booth, R. J.; Elliott, W. L.; Dobrusin, E. M.; Fry, D. W.; Toogood, P. L. Journal of Medicinal Chemistry, 2005, 48, 2371-2387.
  • Lecture (others)
    16. Arbeitstagung der AG Radiochemie/Radiopharmazie, 25.-27.09.2008, Münster, Deutschland

Publ.-Id: 11624 - Permalink

Biological, biochemical and radiopharmacological properties of two Cdk4 inhibitors.
Graf, F.; Köhler, L.; Wüst, F.; Mosch, B.; Pietzsch, J.;
The aim of our study was the biological, biochemical and radiopharmacological characterization of a known Cdk4 inhibitor CKIA, a derivative compound CKIB and their corresponding iodine-124 radiolabeled compounds in different tumor cell lines. Further we wanted to prove the hypothesis that potent Cdk4 inhibitors, which are interesting for cancer therapy are also suitable as radiotracers for imaging of cell proliferation processes in vivo and tumor visualization by positron emission tomography (PET).

Cell growth and cell cycle studies were performed in human tumor cell lines HT-29 (colon carcinoma), FaDu (head- and neck squamous cell carcinoma), and THP-1 (acute monocytic leukemia). Cdk4 specific pRb phosphorylation at Ser780 was analyzed in cell lysates by western blotting. mRNA expression of the pRb affected genes E2F-1 and PCNA was measured with quantitative real-time RT-PCR. Radiotracer uptake studies were performed using iodine-124 radiolabeled CKIA ([124I]CKIA) or CKIB ([124I]CKIB).

Tumor cell growth studies indicate a significantly reduced cell proliferation in all cell lines after 48 h of treatment with 0.1 (< 50%) and 1 µM (< 25%) CKIA. This effect is confirmed by cell cycle studies. Already 24 h after incubation with CKIA the percentage of tumor cells in G1 phase showed a concentration dependent increment up to 90%. pRb phosphorylation is decreased three- to tenfold after 24 h of treatment with 0.1 and 1 µM CKIA in all cell lines. Furthermore, a substantial downregulation of E2F-1 and PCNA mRNA expression could be demonstrated. In vitro radiotracer uptake studies in adherent tumor cells using [124I]CKIA (As = 20 GBq/µmol) showed a substantial uptake in HT-29 (1,649±117 %ID/mg protein) and FaDu cells (1,033±84 %ID/mg protein) after 2 h at 37°C. At 4°C an obvious lower uptake was detectable in both cell lines (258±30 %ID/mg protein in HT-29, 169±14 %ID/mg protein in FaDu).
Further, a new compound derived from CKIA was studied. CKIB shows similar effects on cell growth and cell cycle distribution. After 48 h of treatment with CKIB cell proliferation was reduced by 36% (0.1 µM) or 62% (1 µM) in HT-29 cells. Over 90% of HT-29 cells in G1 phase were obtained after 24 h of incubation with 1 µM CKIB. Results of pRb phosphorylation and both E2F-1 and PCNA mRNA expression analyses suggest a downregulation after 24 h of incubation with 1 µM CKIB in the tumor cells. In vitro studies with [124I]CKIB (As = 3.5 GBq/µmol) demonstrate a radiotracer uptake of 904±43 %ID/mg protein in HT-29 and 856±45 %ID/mg protein in FaDu cells after 2 h at 37°C. Radiotracer uptake at 4°C is substantially lower.

In conclusion, our data demonstrate a definite and specific inhibition of tumor cell proliferation after incubation with CKIA and CKIB due to an arrest of tumor cells in G1 phase as a result of Cdk4-cyclin D/ pRb/ E2F pathway inhibition. The radiotracer uptake of [124I]CKIA and [124I]CKIB observed in human tumor cells are a promising prerequisite for in vivo biodistribution and imaging studies by PET to further support our hypothesis that radiolabeled CKIA and corresponding compounds are suitable tracers for visualization of tumors using PET.

  • Lecture (others)
    16. Arbeitstagung der AG Radiochemie/Radiopharmazie, 25.-27.09.2008, Münster, Deutschland

Publ.-Id: 11623 - Permalink

Pyridinhaltige Liganden des 1,4,7-Triazacyclononans (TACN): Neue bifunktionelle Kupferchelatoren
Ruffani, A.; Stephan, H.; Fähnemann, S.; Steinbach, J.;
Ziel der Arbeit ist die Entwicklung von bifunktionellen Markierungsbausteinen für eine milde und selektive radioaktive Markierung von Proteinen mit dem Positronenstrahler Kupfer-64. In diesem Zusammenhang sind pyridinhaltige Derivate des 1,4,7-Triazacyclononans 1 besonders geeignet, weil sie sehr stabile Kupfer(II)-Komplexe bilden sowie eine schnelle Komplexbildungskinetik aufweisen. Erste Untersuchungen zeigen, dass Komplexe von Kupfer-64 mit Verbindung 2 sowie einem entsprechenden Peptidkonjugat auf der Basis eines stabilisierten Bombesinfragments BBN(7-14) eine hohe in vitro und in vivo Stabilität besitzen.[1]

Das maleinimidhaltige Derivat 3 wurde durch Peptidkupplung mittels HBTU in Anwesenheit der Hünigbase DIPEA aus der Carbonsäure 2 und Aminoethylmaleinimid synthetisiert. Ein weiterer vielseitig einsetzbarer Synthesebaustein wurde durch Umsetzung von 1 mit einem Boc-geschützden Phenylendiamin-Derivat erhalten. Durch Abspaltung der Schutzgruppe wird das freie Amin 4 gebildet, das durch Behandlung mit Thiophosgen in das Isothiocyanat 5 überführt werden kann. Maleinimid-Derivate 6 mit unterschiedlicher aliphatischer Spacerlänge sind durch Amidkupplung von 4 mit Aktivester-Maleinimid-Derivaten zugänglich.

Markierungsstudien des Maleinimids 3 mit Kupfer-64 weisen auf eine sehr schnelle Komplexbildungskinetik unter physiologischen Bedingungen hin. Wie Untersuchungen mit dem Modellpeptid Glutathion zeigen, bindet dieser Markierungsbaustein sehr effektiv an Thiolgruppen.

Bifunktionelle Liganden auf der Basis von pyridinhaltigen TACN-Derivaten können unter milden Bedingungen effektiv mit Kupfer-64 markiert werden. Sie sind vielfältig modifizierbar. Damit eignen sie sich zur schonenden Konjugation an Biomoleküle mit unterschiedlichen funktionellen Gruppen.

[1] G. Gasser et al., Bioconjugate Chem. 2008, 19, 719-730.
  • Lecture (others)
    16. Arbeitstagung der AG Radiochemie/Radiopharmazie, 25.-27.09.2008, Münster, Deutschland

Publ.-Id: 11622 - Permalink

Entwicklung eines Pretargeting-Ansatzes unter Nutzung radioaktiv markierter L Oligonukleotide
Förster, C.; Schlesinger, J.; Közle, I.; Bergmann, R.; Walther, M.; Pietzsch, H.-J.; Steinbach, J.;
Gegenstand der Forschungsarbeiten ist die systematische Entwicklung eines geeigneten Pretargeting-Modells für die Endoradionuklidtherapie unter Verwendung komplementärer L konfigurierter Oligonukleotide (L ON). Ziel dabei ist die Bewertung der in vivo Hybridisierungseigenschaften hinsichtlich ihrer Eignung zur radiodiagnostischen und -therapeutischen Verwendung bei Tumorerkrankungen.

Modifizierte 12- und 17-basige L-RNAs wurden mit DOTA-Derivaten funktionalisiert und im Anschluss mit den PET-Nukliden 68Ga und 86Y markiert. Die Hybridisierung wurde u. a. in Rattenvollblut in Abhängigkeit von der Konzentration untersucht. Weiterhin wurden die Bioverteilung sowie Metabolitenuntersuchungen in männlichen Wistar Ratten durchgeführt (1).
Als Modellsystem dienen DOTA-modifizierte Human Serum Albumin Mikrosphären (HSAM, Durchmesser 20 30 μm). Nach intravenöser Applikation dieser Partikel kommt es auf Grund ihrer Größe zum vollständigen Trapping der Mikrosphären in der Lunge (2, siehe Abb. 1). Analog zu diesen Untersuchungen ist geplant, diese Partikel mit L-ON zu modifizieren und somit eine in vivo Hybridisierung in der Lunge zu ermöglichen. Mit Hilfe dieses Ansatzes wäre man in der Lage, quantitative Beurteilungen des in vivo Hybridisierungsverhaltens komplementärer L-ON vorzunehmen. Zunächst erfolgen in vitro Tests, um das Hybridisierungspotenzial der auf der HSAM-Oberfläche präsentierten L ON zu verifizieren. Zudem wurde eine erste in vivo Untersuchung mittels Kleintier-PET und Urinanalyse durch aufeinander folgende intravenöse Verabreichung von L ON-HSAM-Konjugaten und der komplementären, radioaktiv markierten RNA Stränge vorgenommen.

Die in Abbildung 2 dargestellten Ergebnisse unter Verwendung eines [86Y]Y-DOTA-17mers sind exemplarisch für die Bioverteilung der 86Y markierten L-ON. Bereits 5 min p. i. wurden 16 ± 5 % der injizierten Dosis renal ausgeschieden sowie 20 ± 2 % in der Niere akkumuliert (zum Vergleich zeigte ein 12mer eine renale Ausscheidung nach 5 min von nahezu 82 % ID). Nach 60 min sank die im Tier verbleibende Aktivitätsmenge auf 26 ± 2 %. Es lagen keine signifikanten Akkumulationen in anderen Organen vor (1). Die hohe in vivo Stabilität konnte anhand der Metabolitenanalyse nachgewiesen werden. 60 Minuten p. i. konnten im Urin 80 % und im Nierenhomogenat 81 % der vorliegenden markierten Substanz dem intakten 17mer zugeordnet werden. Konzentrationsabhängige Untersuchungen in Rattenvollblut ergaben eine maximale Hybridisierung bei einem Stoffmengenverhältnis von 1:1.
Aufgrund der vorteilhafteren Ergebnisse in Bezug auf biologische Verfügbarkeit und Hybridstabilität werden die nachfolgende Modellansätze mit 17-basigen L ON durchgeführt. Die kovalente Verknüpfung der RNA über eine Amid- oder Thioharnstoffbindung mit unbehandelten sowie DOTA-modifizierten HSAM ist auf Grund der Vielzahl an Amino- und Carboxylgruppen auf der Oberfläche der Partikel (elektrostatische Wechselwirkungen und starke Wasserstoffbrückenbindungen zwischen den Oligonukleotiden und HSAM) unter den bisher getesteten Bedingungen nur in geringen Ausbeuten möglich. Erste in vitro Hybridisierungstests ergaben positive Ergebnisse, wobei die entstandenen Hybride an der HSAM-Oberfläche lokalisiert sind. Bei einer in vivo Untersuchung wurde jedoch im Urin 45 % der vorhandenen Aktivitätsmenge den entstandenen Hybriden zugeordnet. Um das Problem der Adsorption von L ON auf der Partikeloberfläche zu lösen, werden die HSAM in weiteren Untersuchungen zuerst mit hydrophoben Reagenzien modifiziert, um eine kovalente Bindung zu gewährleisten. Als alternativer Ansatz werden zurzeit carboxylfunktionalisierte Polystyren-Mikrosphären analog modifiziert und untersucht. Zudem wird daran gearbeitet, die rasche renale Ausscheidung sowie die hohe Nierenakkumulation zu verringern. .....
  • Lecture (others)
    16. Arbeitstagung der AG Radiochemie/Radiopharmazie, 25.-27.09.2008, Münster, Deutschland

Publ.-Id: 11621 - Permalink

4-[18F]Fluoro-N-methyl-N-(prop-2-ynyl)benzenesulfonamide: A novel prosthetic group for click chemistry with peptides and proteins
Ramenda, T.; Knieß, T.; Steinbach, J.; Wüst, F.;
The radiolabeling of peptides or proteins with the short-lived positron emitter 18F requires rapid and mild reaction conditions to maintain the structural and functional integrity of these bioactive compounds. Over the last two years several approaches have been published focused on the application of copper(I)-mediated 1,3-dipolar [3+2]cycloaddition of azides and alkynes for labeling peptides with 18F.1-4 The peptides were functionalized with an azide- or alkyne group to be reacted with an appropriately 18F-labeled azide or alkyne, respectively. In this work we report on the radiosynthesis and application of a novel 18F-labeled prosthetic group based upon a sulfonamide backbone suitable for click chemistry applications using azide-functionalized phosphopeptide and human serum albumin (HSA).

Two labeling precursors containing different leaving groups (nitro- and trimethylammoniumtriflate) and the reference substance were prepared by the reaction of N-methylpropargylamine with the corresponding sulfonic acid chlorides. Radiofluorination was performed in a single step. Different purification procedures have been developed including solid phase extraction and semi-preparative HPLC. The peptide and the protein were modified with an azide linker. Cycloaddition reactions were carried out in the presence of copper(I) salts in combination with different copper-chelating ligand systems.

The radiolabeled sulfonamide can be obtained in radiochemical yields of 23 % (decay corrected) in high radiochemical purity of >99 % after HPLC purification within 89 min. First promising results in labeling a phosphopeptide and a protein (HSA) could be achieved.

The novel prosthetic group for peptide and protein labeling with 18F via click chemistry can be prepared in reasonable radiochemical yields and high radiochemical purity. Moreover, for the first time click chemistry was successfully applied to the 18F labeling of a a phosphopeptide and a protein.



1 Marik, J.; Sutcliffe, J.L. Tetrahedron Lett., 2006, 47, 6681.
2 Ramenda, T.; Bergmann, R.; Wuest, F. Lett. Drug Des. Discovery, 2007, 4, 279.
3 Glaser, M.; Arstad, E. Bioconjugate Chem., 2007, 18, 989.
4 Li, Z.-B.; Wu, Z.; Chen, K.; Chin, F.T.; Chen, X. Bioconjugate Chem., 2007, 18, 1987.
  • Lecture (others)
    16. Arbeitstagung der AG Radiochemie/Radiopharmazie, 25.-27.09.2008, Münster, Deutschland

Publ.-Id: 11620 - Permalink

3-D magnetic field effects during metal electrodeposition In cuboid cells
Mutschke, G.; Cierpka, C.; Weier, T.; Eckert, K.; Mühlenhoff, S.; Bund, A.;
In electrochemical reactions, Lorentz forces due to external homogeneous magnetic fields may lead to increased mass transfer as additional convection is caused (MHD effect). A careful analysis shows that often a three-dimensional modeling of this effect is necessary. We will present numerical simulations of copper electrolysis in cuboid cells under the influence of homogeneous magnetic fields of different directions in the limiting current regime. The found complex interplay of natural and magnetically driven convection is compared with recent experimental results.
Keywords: Electrodeposition, Magnetic Field, Magneto-Electrolysis, Numerical Simulations, PIV
  • Lecture (Conference)
    7th PAMIR International Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu'ile de Giens, Frankreich
  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu'ile de Giens, Frankreich, 273-277

Publ.-Id: 11619 - Permalink

X-ray absorption and X-ray scattering - two complementary techniques to determine the coordination of solution species
Hennig, C.;
The intention of the presentation is to compare the experimental observations with X-ray absorption and X-ray scattering to determine the coordination of solution species. EXAFS is an element selective technique and allows to identify the direct coordinated ligands. Distances above 4 Ae are often difficult to detect, even if it concerns heavy atoms. X-ray scattering detects all scattering pairs in a solution. The difference technique allows to select specific ions and makes X-ray scattering is especially sensitive to heavy scatterers in distances above 4 Ae.
Keywords: X-ray scattering, X-ray absorption
  • Invited lecture (Conferences)
    Invited lecture, 5.8.2008, Leuven, Belgium

Publ.-Id: 11618 - Permalink

RPV weld material investigations of a VVER-440 NPP
Rindelhardt, U.; Viehrig, H.-W.; Schuhknecht, J.; Konheiser, J.;
The Greifswald NPP was operated between 1973 and 1990. The units are of Russian WWER-440-230 type. In autumn 2005 the first trepans (diameter 120 mm) were taken from the unit 1 of this NPP. The RPV of this unit was annealed after 14 years of operation, followed by two additional years of operation.
The paper describes the results of weld metal investigations. The trepan originates from the RPV core weld exposed with the highest neutron flux. The neutron dosimetry was based on Monte Carlo fluence calculations as well as retrospective Nb dosimetry. The maximum fluence for E>0.5 MeV was determined to be 4*1019 neutron/cm2, and the maximum gamma fluence was found to be 1.7*1020 gamma/cm2 for E>1 MeV. A decrease of 60% through the thickness of the RPV was found.
The key part of the material testing was aimed on the determination of the reference temperature T0 following the ASTM Test Standard E1921-05 to determine the fracture toughness of the RPV steel in different thickness locations. It could be shown that the Master Curve approach as adopted in E1921 is applicable to the investigated original RPV weld metal. The weld metal located in a distance of about 22 mm from the inner surface of the RPV wall yielded a T0 of 50°C which is about 40K higher than T0 close to the inner surface. This outcome is important for the assessment of results retrieved from so called boat samples taken directly from the RPV surface after the recovery annealing. It shows that boat samples do not mandatory represent the material with the lowest toughness.
Keywords: Neutron dosimetry, neutron embrittlement, VVER-440, reactor pressure vessel
  • Lecture (Conference)
    10th International Conference "Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment", 06.-10.10.2008, St. Petersburg, Russia
  • Contribution to proceedings
    10th International Conference "Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment", 06.-10.10.2008, St. Petersburg, Russia
    The 10th Interntional Conference (Conference CD), St. Petersburg: PROMETEY

Publ.-Id: 11616 - Permalink

Probing nanoscale inhomogeneities in transition metal oxides with ultrafast mid-infrared spectroscopy
Prasankumar, R. P.; Lee, H. J.; Okamura, H.; Imai, H.; Shimakawa, Y.; Kubo, Y.; Zvyagin, S.; Kamenev, K.; Balakrishnan, G.; Paulf, D. M.; Trugman, S. A.; Taylor, A. J.; Averitt, R. D.;
Transition metal oxides are a rich area of investigation for experimentalists and theorists alike due to their coupling of multiple degrees of freedom with similar interaction strengths. This complexity leads to intrinsic phase inhomogeneities that are believed to play a significant role in the fascinating phenomena observed in these systems. We use ultrafast mid-infrared spectroscopy to probe quasiparticle dynamics in the colossal magnetoresistive oxides, Nd0.5Sr0.5MnO3 and Tl2Mn2O7. Our results demonstrate for the first time that ultrafast spectroscopy is sensitive to the presence of nanoscale phase inhomogeneities, strongly indicating the universality of phase coexistence in complex transition metal oxides.
  • Physica B 403(2008)5-9, 1401-1403

Publ.-Id: 11615 - Permalink

ESR excitations in the BEC candidate DTN: what can we learn from that?
Zvyagin, S.;
NiCl2-4SC(NH2)2 (known as DTN) is a quantum S = 1 chain system with strong easy-plane anisotropy that is regarded as a new candidate for the Bose-Einstein condensation (BEC) of magnons, with critical fields Bc1 = 2.1 T, Bc2 = 12.6 T (defined at T = 0). Tuneable-frequency Electron Spin Resonance (ESR) studies of magnetic excitations in DTN in fields up to 25 T are presented. Based on analysis of the single-magnon excitation mode observed in the high-field spin-polarized phase at temperatures above Tc (Tc ≤ 1.2 K) and previous experimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set of spin-Hamiltonian parameters is obtained. Our results yield D = 8.9 K, Jc = 2.2 K, and Ja,b = 0.18 K for the anisotropy, intrachain, and interchain exchange interactions, respectively. These values are used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Furthermore, we present a systematic study of the low-energy excitation spectrum of DTN in the field-induced magnetically ordered phase (which has been regarded as the magnon BEC phase) 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 physically simplest scenario would correspond to the isotropic “corner-center” exchange. Since the exchange interaction within each sublattice is antiferromagnetic, the system in the BEC phase is supposed to be highly frustrated, and then its mean-field ground state at B > Bc1 should be infinitely degenerate. Our observations are of crucial importance for the interpretation of the field-induced ordering in DTN in terms of the BEC of magnons.
  • Lecture (Conference)
    Workshop Highly Frustrated Magnets, 02.-05.03.2008, Grenoble, France

Publ.-Id: 11614 - Permalink

Excitation spectrum and magnetic properties of the 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.;
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 \Delta/k_{B} = 17.4~K, g_{\parallel}=2.14, D/k_{B}=7.5~K, and |E/k_{B}|=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)
    2008 APS March Meeting, 10.-14.03.2008, New Orleans, USA

Publ.-Id: 11613 - Permalink

QCD Sum Rules for D Mesons at Finite Density
Hilger, T.;
QCD Sum Rules for D Mesons at Finite Density
  • Lecture (others)
    Helmholtz International Summer School - Dense Matter in Heavy Ion Collisions and Astrophysics, 21.07.2008, Dubna, Russia

Publ.-Id: 11612 - Permalink

Simulation of defects and composition after Ga+ irradiation of ultrathin Pt/Co/Pt film
Liedke, B.; Facsko, S.; Fassbender, J.ORC; Heinig, K.-H.; Möller, W.; Jaworowicz, J.; Ferre, J.; Maziewski, A.; Vernier, N.
Theoretical studies of the collision intermixing and defects creation processes of irradiated ultrathin Pt/Co/Pt films by 30 keV Ga+ are presented. First, in order to investigate the influence of the Ga ions, with ion fluence ranging between 1014 and 5·1016 ions/cm, on the composition of the film and the sputtering yield TRIDYN simulation is employed. Second, the relaxation of defects created during irradiation is estimated by means of the Lattice Kinetic Monte Carlo Ising model, which is subsequently applied after each collision cascade. According to our theoretical results ion fluence has a strong impact on the erosion velocity and intermixing processes that take place at the interface. Due to the nuclear energy losses of the implanted ions, changes in the material composition at the interface and the spin reorientation transition from the in-plane to out-of-plane magnetization state is observed. Moreover, the so-called swelling effect, which originates from the strain relaxation of the irradiated films, gives rise to an increase of the magnetic anisotropy. However, the strain relaxation can be strongly non-uniform in the implanted square area providing a mixture of patches with in-plane or out-of-plane anisotropy. Experimentally observed irradiation induced phenomena is fairly well described in the frame of our simulations.
Keywords: magnetism, ion irradiation, simulations, Monte Carlo
  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11611 - Permalink

Fe nanoparticles embedded in MgO crystals
Shalimov, A.; Potzger, K.; Talut, G.; Geiger, D.; Reuther, H.; Zhou, S.; Baetz, C.; Misiuk, A.; Fassbender, J.ORC
Iron nanoparticles embedded in MgO single crystals were synthesized by high temperature Fe+ implantation with energy of 100 keV and fluences varying from 3×10E16 to 3×10E17 ions/cm-2. Complex investigations of structural and magnetic properties of Fe nanoparticles have been performed using magnetometry, x-ray diffraction, electron microscopy and Moessbauer spectroscopy, as well as theoretical modeling of magnetization of bistable magnetic systems.
It has been found that at the low implantation fluences superparamagnetic Fe nanoparticles were created that finally were attributed to alpha-Fe coexisting with non-magnetic gamma-Fe, while implantation with high fluences causes formation of ferromagnetic alpha-Fe particles. Post implantation annealing at 800 ºC in high vacuum results in size increase of the gamma-Fe particle’s simultaneously reducing internal lattice strain. Annealing at 800 ºC under 1 GPa hydrostatic pressure limits dimension of superparamagnetic nanoparticles significantly increasing their concentration.
Theoretical simulations of irreversible magnetization processes, performed within the framework of generalized Preisach model, show a strong correlation between the spontaneous magnetization, coercive field and dimension of nanoparticles. The model allows us to define the anisotropy effects and thermal fluctuation effects, which provides the detailed description of temperature behavior of magnetization.
Keywords: magnetism, ion implantation, nanoparticle, Fe
  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland

Publ.-Id: 11610 - Permalink

Untwinning of alloyed nanoparticles via intermediate amorphization
Järvi, T. T.; Pohl, D.; Albe, K.; Rellinghaus, B.; Schultz, L.; Fassbender, J.ORC; Kuronen, A.; Nordlund, K.
Recent experimental evidence shows that multiply twinned CuAu and FePt nanoparticles transform to single crystalline morphology under helium irradiation with keV energies [1,2]. The untwinning is rather unexpected, since it is widely accepted that under the given conditions only Frenkel pairs are formed, which do not affect the stability of twin boundaries.
We present molecular dynamics simulations revealing that the mechanism behind the transformation is based on intermediate amorphization of the particles. By comparing with irradiation simulations of elemental nanoparticles, published previously [3], as well as alloyed bulk samples and surface cascades, we show that this transformation route is only present in alloyed particles. Moreover, the observed amorphization is more efficient for twinned than single- crystalline particles, explaining, together with fast recrystallization kinetics, the observed untwinning.

[1] Dmitrieva et al., J. Appl. Phys. 97 (2005) 10N112
[2] Järvi T. T., Pohl D., et al., unpublished
[3] T. T. Järvi et al., J. Appl. Phys. 102 (2007) 124304
Keywords: magnetism, ion irradiation, binary alloys, nanoparticle, FePt
  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11609 - Permalink

The influence of ion irradiation on the structure of binary nanoparticles
Pohl, D.; Järvi, T. T.; Mohn, E.; Fassbender, J.ORC; Albe, K.; Schultz, L.; Rellinghaus, B.
FePt and CuAu nanoparticles with a narrow size distribution and a diameter of about 5 nm are prepared through inert gas condensation. Since as-deposited particles usually exhibit the metastable disordered A1 phase we have investigated, how ion irradiation influences the phase stability of various crystal motifs such as icosahedral or decahedral multiply twinned structures.
Ion irradiation leads to the creation of vacancies within the particles and thereby enhances the bulk diffusion of their constituents. In the present study, gas-phase prepared single crystalline and multiply twinned FePt and CuAu nanoparticles are irradiated with ions of different noble gases and different energy. It is shown that the He+ ion irradiation promotes the de-twinning of the binary nanoparticles and the formation of single crystalline A1 phase particles. A comparison of the experiments on CuAu nanoparticles with the results of molecular dynamic simulations will be presented. The effect of the energy difference between the different morphologies for both the ordered and disordered structures is discussed.
Keywords: magnetism, ion irradiation, binary alloys, FePt, nanoparticle
  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland

Publ.-Id: 11608 - Permalink

Precision study of ground state capture in the 14N(p,gamma )15O reaction
Marta, M.; Bemmerer, D.; Bonetti, R.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Confortola, F.; Conti, E.; Costantini, H.; Elekes, Z.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gyürky, G.; Gustavino, C.; Imbriani, G.; Junker, M.; Lemut, A.; Limata, B.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.;
The rate of the hydrogen-burning carbon-nitrogen-oxygen (CNO) cycle is controlled by the slowest process, 14N(p,gamma)15O, which proceeds by capture to the ground and several excited states in 15O. Previous extrapolations for the ground state contribution disagreed by a factor of 2, corresponding to 15% uncertainty in the total astrophysical S-factor. A new experiment on ground state capture has been carried out at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator deep underground in the Gran Sasso facility in Italy. Systematic corrections have been reduced considerably with respect to previous work by using a Clover detector and by adopting a relative analysis. The previous discrepancy has been resolved, and ground state capture no longer dominates the uncertainty of the total S-factor. The present data make it possible to use solar CNO neutrinos to measure the metallicity at the center of the Sun.
Keywords: nuclear astrophysics, LUNA, CNO cycle, solar neutrinos, Clover segmented detector
  • Poster
    10th International Symposium on Nuclei in the Cosmos, 27.07.-01.08.2008, Mackinac Island, Michigan, USA

Publ.-Id: 11607 - Permalink

Precision study of the 14N(p, gamma)15O reaction at LUNA
Marta, M.; Bemmerer, D.; Kunz, R.; Rolfs, C.; Strieder, F.; Trautvetter, H.-P.;
The rate of the hydrogen-burning CNO cycle is controlled by the slowest reaction, 14N(p,gamma)15O. 15-30% of the total cross section are contributed by radiative capture to the ground state in 15O. Previous extrapolated S-factors for this ground state contribution disagree by a factor 2. The precision of those previous studies had been limited by a sizable true coincidence summing correction. In a new experiment using a segmented Clover detector deep underground at LUNA, the summing correction has been reduced by a factor 30, so existing R-matrix fits can now be precisely tested. The present data enable a direct measurement of the metallicity at the center of the Sun by detecting solar CNO neutrinos, for example at Borexino.
Keywords: nuclear astrophysics, CNO cycle, solar neutrinos, Clover segmented detector
  • Lecture (Conference)
    DPG Frühjahrstagung des AMOP und der Fachverbände Hadronen und Kerne, Umweltphysik, 10.-14.03.2008, Darmstadt, Deutschland

Publ.-Id: 11606 - Permalink

Instantaneous-shape sampling for calculation of the electromagnetic dipole strength in transitional nuclei
Zhang, S.; Bentley, I.; Brant, S.; Dönau, F.; Frauendorf, S.; Kämpfer, B.; Schwengner, R.; Wagner, A.;
Electromagnetic dipole absorption cross sections of transitional nuclei with large-amplitude shape fluctuations are calculated in a microscopic way by introducing the concept of instantaneous-shape sampling, which is based on slow shape dynamics as compared with fast dipole vibrations. The dipole strength is calculated by means of the quasiparticle random-phase approximation (QRPA) for the instantaneous shapes, the probability of which is obtained by means of the interacting boson approximation. The calculations agree well with the experimental photoabsorption cross sections near the nucleon emission threshold, but they underestimate it at low energies. The cumulative cross sections for the region below the threshold are a factor of 2 too low.
Keywords: nuclear models, deformation, electromagnetic strength

Publ.-Id: 11605 - Permalink

Direct nanoscale magnetic patterning in FeAl alloys by means of ion irradiation
Menendez, E.; Sort, J.; Liedke, M. O.; Strache, T.; Fassbender, J.ORC; Möller, W.; Gemming, T.; Weber, A.; Heydermann, L. J.; Surinach, S.; Deevi, S. C.; Rao, K. V.; Sommerlatte, J.; Nielsch, K.; Baro, M. D.; Nogues, J.
Fe60Al40 (at. %) alloys show an interesting combination of magnetic and structural properties, where atomically ordered Fe60Al40 (B2-structure) is paramagnetic at room temperature, whereas disorder Fe60Al40 (i.e., atomically intermixed, A2-structure) becomes ferromagnetic [1]. The transformation from paramagnetic B2-phase to the ferromagnetic A2-phase can be accomplished by means of homogeneous ion irradiation procedures. The irradiation induced transformation depends on the irradiation dose and the type of ions [2]. Furthermore, local ion irradiation procedures (i.e., focused ion beam or ion irradiation through masks) have been also used in order to fabricate periodic arrays of ferromagnetic structures embedded in a paramagnetic matrix [3]. Patterned polymer layers defined by electron beam lithography and porous alumina templates were used as masks. While the e-beam lithography allows for a careful design of the patterns, alumina templates lead to fast processing of very large areas. Importantly, due to the low fluences used, this method does not induce any roughening of the surface, leading to topographically featureless magnetic dots. The fabricated entities exhibit a range of magnetic properties depending on the size and shape, which were investigated by means of magneto-optical Kerr effect magnetometry, while the local character of the induced ferromagnetism was examined by magnetic force microscopy. The smallest dots (sub-50 nm in size) exhibit coercivities in the range of HC  500 Oe and a large squareness, MR/MS  1 (see Fig. 1). Interestingly, when the patterned sheets are annealed at sufficiently high temperatures, the ferromagnetic properties are removed due to the annealing-induced atomic reordering. Hence, these methods may lead to a novel type of patterned recording media free from tribological and exchange coupling effects. Moreover, these approaches can be easily extrapolated to a variety of other systems exhibiting disorder-induced magnetism.

[1] J. Nogués et al., Phys. Rev. B 74, 024407 (2006)
[2] J. Fassbender et al., Phys. Rev. B 77, 174430 (2008)
[3] E. Menéndez, (2008) submitted
Keywords: magnetism, ion irradiation, focused ion beam, modification, intermetallics, binary alloys
  • Invited lecture (Conferences)
    Trends in Nanotechnology, TNT 2008, 01.-05.09.2008, Oviedo, Spanien

Publ.-Id: 11604 - Permalink

Beispielhafte Wasserkraftnutzung an der Saale: Entwicklung, Stand und Perspektiven
Rindelhardt, U.;
Nach 1990 erlebte die Wasserkraftnutzung in Thüringen und Sachsen-Anhalt eine Renaissance. 20 neue WKA mit einer Leistung von mehr als 20 MW entstanden bisher an den vorhandenen Wehren mit teilweise interessanten technischen Lösungen. Die mögliche jährliche Stromerzeugung dieser Anlagen liegt bei 70 GWh. Die Kaplan-Turbine dominiert bei den Neubauten eindeutig, wobei sowohl Schacht- als auch Rohrturbinen zum Einsatz kommen. Technisch bemerkenswert sind die überströmten WKA in Jena sowie die PIT-Turbine in der mit 2 MW größten neu errichteten Anlage in Calbe. Nur an wenigen Anlagen ist noch Bedienungspersonal erforderlich, an einigen Standorten ist die Zukunft teils denkmalgeschützter, heute nicht mehr genutzte Gebäude offen.

Mit dem erreichten beachtlichen Stand ist das technische Wasserkraftpotenzial der Saale noch nicht erschöpft. Unterhalb der Saalekaskade hat die Saale in Thüringen insgesamt ein Gefälle von 110 m, und in Sachsen-Anhalt zwischen Bad Kösen und Calbe beträgt das Gefälle etwa 63 m. Die bisher genutzten Fallhöhen in den genannten Bereichen liegen bei 33 m in Thüringen und bei knapp 29 m in Sachsen-Anhalt. In Sachsen-Anhalt laufen derzeit Vorbereitungen zum Bau von weiteren WKA (etwa 4-5 MW) an bisher nicht bzw. nur zum Teil genutzten Wehren, wodurch sich die genutzte Fallhöhe um etwa 10 m erhöhen kann. Im Zusammenhang mit dem geplanten Bau des Tornitz-Kanals an der Saalemündung ist keine weitere Wasserkraftnutzung vorgesehen. In Thüringen ist die Perspektive wegen des erfolgten Rückbaus von 2 Wehren (Saalfeld und Kunitz) weniger günstig. Nur an 2 noch bestehenden Wehren ist eine Wasserkraftnutzung denkbar (etwa 0,5 MW).

Insgesamt sind die Rahmenbedingungen für den Wasserkraftausbau in Deutschland in den letzen Jahren deutlich ungünstiger geworden. Die EU-WRRL und ihre Untersetzung in nationalen Gesetzen bzw. Vorschriften führten praktisch zu einem Baustopp für neue Wehre sowie zu hohen Anforderungen an die Restwassermenge bei Ausleitungskraftwerken. Unter diesen Bedingungen ist ein weiterer Ausbau der Wasserkraftnutzung trotz ihrer unbestreitbaren Vorteile und der jüngsten Modifizierungen im EEG kaum realisierbar.
Keywords: renewable energy, small hydro power
  • Lecture (Conference)
    Dresdner Wasserbaukolloquium 2009, 12.-13.03.2009, Dresden, Deutschland
  • Contribution to proceedings
    Dresdner Wasserbaukolloquium 2009, 12.-13.03.2009, Dresden, Deutschland
    Dresdner Wasserbauliche Mitteilungen Heft 39: Wasserkraftnutzung im Zeichen des Klimawandels, Dresden: Selbstverlag TU Dresden, 978-3-86780-101-0, 163-172

Publ.-Id: 11603 - Permalink

Weld material investigations of a VVER-440 reactor pressure vessel: Results from the first trepan taken from the former Greifswald NPP
Rindelhardt, U.; Viehrig, H.-W.; Konheiser, J.; Schuhknecht, J.;
Between 1973 and 1990 4 units of the Russian NPP type WWER-440/230 were operated in Greifswald (former East Germany). Material probes from the pressure vessels were gained in the frame of the ongoing decommissioning procedure. The investigations of this material started with material from the circumferential core weld of unit 1.
Firstly this paper presents results of the RPV fluence calculations depending on different loading schemes and on the axial weld position based on the Monte Carlo code TRAMO. The results show, that the use of the dummy assemblies reduces the flux by a factor of 2 – 5 depending on the azimuthal position. The circumferential core weld (SN0.1.4) received a fluence of 2.4•1019 neutrons/cm² at the inner surface, it decreases to 0.8•1019 neutrons/cm² at the outer surface.
The material investigations were done using a trepan from the circumferential core weld. The reference temperature T0 was calculated with the measured fracture toughness values, KJc, at brittle failure of the specimen. The KJc values show a remarkable scatter The highest T0 was about 50°C at a distance of 22 mm from the inner surface of the weld The Charpy transition temperature TT41J estimated with results of sub size specimens after the recovery annealing was confirmed by the testing of standard Charpy V-notch specimens.
The VERLIFE procedure prepared for the integrity assessment of WWER RPV was applied on the measured results. The VERLIFE lower bound curve indexed with the SINTAP reference temperature RTT0SINTAP envelops the KJc values. Therefore for a conservative integrity assessment the fracture toughness curve indexed with a RT representing the brittle fraction of a dataset of measured KJc values has to be applied.
Keywords: neutron dosimetry, neutron embrittlement, reactor pressure vessel
  • Journal of Engineering for Gas Turbines and Power - Transactions of the ASME 131(2009), 22904
    DOI: 10.1115/1.3032461

Publ.-Id: 11602 - Permalink

Combined xenolith and receiver function study, western Bohemian Massif, central Europe
Kämpf, H.; Heuer, B.; Mrlina, J.; Reuther, H.;
The occurrence of strong negative phases at 7,5s Ps delay, may indicate body of partial melt at ca. 65km depth beneath
western Bohemian Massif (see Figure below). To test the hypothesis, we studied 2 suites of lithospheric
mantle xenoliths, different in age (P-T-fO2, petrophysical, geochemical and isotope [Sr, Nd, Pb] constraints). The
xenoliths from 25 Ma old volcanics are spinel lherzolithes. The suite from 0.3 Ma old volcanics represent cumulates,
porous fragments of magmatic veins or porous wehrlites. These samples are strongly altered by mantle metasomatism
(changes of fO2, geochemical constraints, density/porosity).
  • Geochimica et Cosmochimica Acta 72(2008)12, A447
  • Lecture (Conference)
    Goldschmidt Conference 2008, 13.-18.07.2008, Vancouver, Kanada

Publ.-Id: 11601 - Permalink

On the effectiveness of ion range determination from in-beam PET data
Fiedler, F.; Shakirin, G.; Crespo, P.; Braess, H.; Skowron, J.; Kunath, D.; Pönisch, F.; Pawelke, J.; Enghardt, W.;
At present, in-beam positron emission tomography (PET) is the only method for in vivo and in situ range verification in ion therapy. At the GSI Helmholtzzentrum f¨ur Schwerionenforschung GmbH (GSI) Darmstadt, Germany, a unique in-beam PET installation has been operated from 1997 until the shut down of the carbon ion therapy facility in 2008. Therapeutic irradiation by means of 12C ion beams of more than 400 patients have been monitored. In this paper a first quantitative study on the accuracy of the inbeam PET method to detect range deviations between planned and applied treatment in clinically relevant situations using simulations based on clinical data is presented. Patient treatment plans were used for performing simulations of positron emitter distributions. For each patient a range difference of ±6mm in water was applied and compared to simulations without any changes. The comparisons were performed manually by six experienced evaluators for data of 81 patients. The number of patients required for the study was calculated using the outcome of a pilot study. The results indicate a sensitivity of (91±3)% and a specificity of (96 ± 2)% for detecting an overrange, a reduced range is recognized with a sensitivity of (92±3)% and a specificity of (96±2)%. The positive and the negative predictive value of this method are 94% and 87%, respectively. The interobserver coefficient of variation is between 3 and 8%. The in-beam PET method demonstrated a high sensitivity and specificity forthe detection of range deviations. As the range is a most indicative factor of deviations in the dose delivery, the promising results shown in this paper confirm the in-beam PET method as an appropriate tool for monitoring ion therapy.
Keywords: in-beam PET, ion therapy

Publ.-Id: 11600 - Permalink

Simulation of postulated accidents in pressurized water reactors using coupled 3D neutron kinetic/thermal hydraulic code systems
Kliem, S.; Rohde, U.; Weiss, F.-P.;
Coupled code systems consisting of 3D neutron kinetics in combination with advanced thermal hydraulic plant models have been developed for an improved analysis of the whole reactor system. At Forschungszentrum Dresden-Rossendorf, the 3D neutron kinetic core model DYN3D, developed in house, was coupled with the advanced thermal hydraulic system code ATHLET of the German Gesellschaft für Anlagen- und Reaktorsicherheit.
Analyses of a hypothetical boron dilution event were carried out using that coupled code system. For that purpose a validated coolant mixing model was implemented into the code. Transient calculations for the bounding scenario of the start-up of one main coolant pump with the maximum size of a deborated slug showed a significant reactivity insertion and over-criticality. However, according to the calculations, even an over-criticality of about 2 $ did not lead to safety-relevant consequences. The power excursion is mitigated and stopped by fuel temperature feedback.
Anticipated transients without SCRAM are a second application area of the coupled code systems. In such transients with a postulated failure of the control rod insertion, the core power behavior is determined exclusively by the neutron kinetic feedback of the fuel and the moderator. The DYN3D/ATHLET code was used to investigate the influence of the core loading on the safety parameters during the transient: “Loss of main feedwater at running main coolant pumps”. It was shown that the variation of the number of mixed oxide (MOX) fuel elements in the reactor core has a remarkable influence on the fuel temperature and the moderator density feedback, which influences through the core power the primary coolant pressure. Increasing the number of MOX fuel elements decreases the calculated pressure maximum.
  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany

Publ.-Id: 11598 - Permalink

Nature of defects formed in neutron-irradiated Fe-Cr model alloys
Ulbricht, A.; Heintze, C.; Bergner, F.; Eckerlebe, H.;
Reduced activation ferritic-martensitic (RAFM) Cr-steels are candidate materials for future applications in fusion and generation IV fission research and technology. Previous SANS experiments for this class of materials indicated defects on the nanometer size scale to be formed as a result of neutron irradiation. The experiment was devoted to the investigation of Eurofer97, which is in the focus of current coordinated European research activities, and related Fe-Cr model alloys. The investigation of binary Fe-Cr alloys will significantly contribute to the understanding of the behaviour of more complex alloys.
Keywords: SANS, Fe-Cr alloy, Eurofer97, radiation defects
  • Other report
    Geesthacht: GeNF-Experimental Report 2007, Eds. P. K. Pranzas, A. Schreyer, R. Willumeit, GKSS Forschungszentrum, 2008
    2 Seiten

Publ.-Id: 11597 - Permalink

Application of Positron Emission Tomography for Radiotherapy Monitoring
Shakirin, G.; Fiedler, F.; Laube, K.; Möckel, D.; Parodi, K.; Pawelke, J.; Priegnitz, M.; Enghardt, W.;
Positron emission tomography (PET) is used for independent monitoring of dose delivery in ion therapy. An in-beam PET scanner registers the annihilation γ-rays following the decay of minor amounts of β+ radioactive nuclei, which are produced via nuclear reactions between the ions of the therapeutic beam and the atomic nuclei of the irradiated tissue. From a comparison of the reconstructed activity distributions with those predicted from the treatment plan, deviations between the prescribed and the applied dose distributions can be detected. In-beam PET, therefore, allows to verify the physical beam model used in the treatment planning, to detect patient dislocations and density changes in the irradiated tissue. Treatment of more than 400 patients has been monitored by means of in-beam PET at Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany. The in-beam PET method demonstrated a positive clinical impact as in vivo, in situ, non-invasive technique for independent monitoring of dose application.
Keywords: in-beam PET, radiotherapy monitoring
  • Invited lecture (Conferences)
    20th International Conference on the Application of Accelerators in Research and Industry, 09.-15.08.2008, Fort Worth, TX, USA

Publ.-Id: 11596 - Permalink

Development of the high-field ESR facility at the Dresden High Magnetic Field Laboratory (HLD)
Zvyagin, S. A.; Cismar, E.; Ozerov, M.; Pronin, A.; Wosnitza, J.;
In this presentation I will talk about recent developments of the high-field Electron Spin Resonance facility at the Dresden High Magnetic Field Laboratory (HLD), Forschungszentrum Dresden–Rossendorf. A unique feature of the facility is a combination of an extraordinary broad frequency range, 9 GHz – 100 THz (achieved by use of a number of tunable-frequency radiation sources, including MVNA, BWOs and FEL) and high magnetic fields (70 T and 16 T, produced by pulsed and superconducting magnets, respectively). The talk will be illustrated by recent results obtained in-house (including the study of the excitation spectrum in the spin-1/2 chain system (6MAP)CuCl3, the spin-ladder material BPCB, and others), as well as by results of international collaborations (including the collaboration with the National Institute of Chemical Physics and Biophysics, Tallinn, Estonia)
  • Invited lecture (Conferences)
    1st Bilateral Estonian-German Workshop, Strong Nonlinear Vibronic and Electronic Interactions in Solids, 30.04.-02.05.2008, Tartu, Estonia

Publ.-Id: 11595 - Permalink

High-field ESR in low-dimensional spin systems
Zvyagin, S. A.;
Here, I present results of our recent tunable-frequency high-field Electron Spin Resonance (ESR) studies of two low-dimensional quantum spin systems. The first one, copper pyrimidine dinitrate, is an S=1/2 antiferromagnetic chain material with alternating g-tensor and the Dzyaloshinskii-Moriya interaction, which exhibits a field-induced gap Δ. Employing ESR technique, the gap was observed directly.1 Experimental data are sufficiently detailed to make an accurate comparison with predictions based on the sine-Gordon quantum-field theory. Signatures of three breather branches and a soliton are identified. In addition, the temperature and field dependences of ESR parameters in the perturbative spinon regime (T > Δ/kB) are studied.2 Excellent agreement with theory is found. The second material, NiCl2-4SC(NH2)2 (known as DTN) is a quantum S = 1 chain system with strong easy-plane anisotropy that is regarded as a new candidate for the field-induced Bose-Einstein condensation (BEC) of spin degrees of freedom. Employing ESR, we were able to accurately estimate parameters of the spin-Hamiltonian, to study the frequency-field dependence of two-magnon bound-state excitations 3 (predicted by theory and observed in DTN for the first time), and to investigate the magnetic excitation spectrum in DTN in the field-induced ordered phase.4 Supported in part by NHFMF (through NSF and DOE) and DFG.
  • Invited lecture (Conferences)
    50th Annual Rocky Mountain Conference on Analytical Chemistry, 27.-31.07.2008, Breckenridge, Colorado, USA

Publ.-Id: 11594 - Permalink

Anisotropic many-body effects in nonmagnetic borocarbides
Bergk, B.; Petzold, V.; Rosner, H.; Drechsler, S.-L.; Bartkowiak, M.; Ignatchik, O.; Canfield, P. C.; Wosnitza, J.;
We present de Haas{van Alphen measurements of the nonmagnetic borocarbide superconductors LuNi2B2C and YNi2B2C. The measurements have been performed by use of the torque method in high magnetic fields up to 32 T and at temperatures down to 50 mK. The Fermi-surface cross sections are extracted from the magnetic quantum oscillations in the normal state. In accordance with previous investigations we find a complex band structure with dfferent open and closed Fermi-surface sheets. From the temperature dependence of the oscillations amplitude the effective mass of the single bands can be determined. We observe sizeable and anisotropic enhancements of the effective masses compared to full-potential-localorbital calculations which is due to anisotropic many-body interactions.
  • Poster
    25th International Conference on Low Temperature Physics (LT25), 06.-13.08.2008, Amsterdam, The Netherlands

Publ.-Id: 11593 - Permalink

Superconductivity of p-Type Doped Ge
Herrmannsdörfer, T.; Ignatchik, O.; Wosnitza, J.; Heera, V.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Skorupa, W.; Voelskow, M.;
We report the first observation of superconductivity in heavily p-type doped Germanium at ambient-pressure conditions. Using Ga as dopant, we have produced a series of GeGax samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga concentrations up to 14%, i.e. a doping level which is clearly larger than the solubility limit and not accessible to any other method so far. Transport measurements reveal superconducting transitions with Tc up to 0.39 K. In more detail, we observe a strong dependence of the superconducting critical parameters on the annealing conditions. Further, we find a strong anisotropy of the superconducting critical field re ecting the two-dimensional character of the superconducting state in the thin GeGax layer having an effective depth of only 20 nm. We find critical magnetic in-plane fields even larger than the Pauli-Clogston limit. After its finding in Si and diamond, our work adds another unexpected observation of superconductivity in doped elemental semiconductors.
  • Poster
    LT25 (25th International Conference on Low Temperature Physics), 06.-13.08.2008, Amsterdam, The Netherlands

Publ.-Id: 11592 - Permalink

Low-temperature excitation spectrum in the BEC candidate DTN: an ESR study
Zvyagin, S. A.; 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 quantum S = 1 system with an easy-plane anisotropy dominating over the exchange interaction and exhibiting a field-induced low-temperature ordering with critical fields Bc1=2.1 T and Bc2=12.6 T. A systematic study of the low-energy excitation spectrum of DTN in the field-induced magnetically ordered phase at temperatures down to 0.45 K and frequencies down to 25 GHz is presented. It is argued that two gapped modes observed in the experiment can be consistently interpreted within a four-sublattice antiferromagnet model with a weak isotropic corner-center interaction of magnetic ions in the body-centered tetragonal lattice with unbroken axial symmetry.1 The latter is of particular importance, being a necessary prerequisite for the interpretion of the antiferromagnetic ordering in DTN in terms of the Bose-Einstein condensation of the spin degrees of freedom
  • Poster
    25th International Conference on Low Temperature Physics (LT25), 06.-13.08.2008, Amsterdam, The Netherlands

Publ.-Id: 11591 - Permalink

Magnetic properties of Zn-doped Haldane-gap material NENB
Cizmar, E.; Ozerov, M.; Ignatchik, O.; Papageorgiou, T. P.; Wosnitza, J.; Zvyagina, S. A.; Krzystek, J.; Zhou, Z.; Landee, C. P.; Landry, B. R.; Turnbull, M. M.; Wikaira, J. L.;
Experimental studies of magnetic susceptibility and electron-spin resonance (ESR) properties of the spin-1 Haldane-chain material [Ni(C2H8N2)2NO2](BF4) (NENB) doped with non-magnetic Zn-ions in a range up to 5% are reported. The presence of fractional S = 1/2 chain-end states, revealed by ESR and susceptibility measurements in nominally pure single crystals of NENB, is found to be responsible for spin-glass freezing effects. Higher doping ratio of Zn-ions suppresses the spin-glass behaviour by creating shorter and isolated chain fragments. The effect of non-magnetic doping on the lineshape of ESR spectra of fractional S = 1/2 chain-end states is discussed.
  • Poster
    25th International Conference on Low Temperature Physics (LT25), 06.-13.08.2008, Amsterdam, The Netherlands

Publ.-Id: 11590 - Permalink

Ultrasonic Investigation of NiCl2-4SC(NH2)2
Chiatti, O.; Zherlitsyn, S.; Sytcheva, A.; Wosnitza, J.; Zvyagin, A. A.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.;
We report results of ultrasonic investigations of the quantum S = 1 spin-chain magnet NiCl2-4SC(NH2)2 (DTN), in magnetic fields up to 18 T and temperatures down to 0.3 K. A field H along the c axis induces a transition into an antiferromagnetic phase with Tmax N ≈ 1:2 K. Accordingly, at T = 0 there are two quantum critical points at ~ 2:1 T and at ~ 12:6 T. The acoustic c33 mode, propagating along the spin chains, shows a pronounced softening close to the phase transition, accompanied by energy dissipation of the sound-wave. The H - T phase diagram obtained from our measurements is compared with results from other experimental investigations, and the low temperature acoustic anomalies are traced up to T > TN. We suggest a model where the main contribution to the spin-lattice interactions arises from the exchange- striction coupling within one-dimensional spin chains, and find a good qualitative agreement with the experimental data from the disordered phase.
  • Poster
    25th International Conference on Low Temperature Physics (LT25), 06.-13.08.2008, Amsterdam, The Netherlands

Publ.-Id: 11589 - Permalink

Magnetic properties of the S = 1/2 Heisenberg spin-chain material (6MAP)CuCl3
Ozerov, M.; Cizmar, E.; Zvyagin, S. A.; Wosnitza, J.; Xiao, F.; Landee, C.; Turnbull, M.;
We report on the magnetic properties of the S = 1/2 Heisenberg spin-chain material (6MAP)CuCl3. The magnetic susceptibility exhibits a pronounced maximum at T ≈ 70 K, which is a signature of low-dimensional magnetic interactions in (6MAP)CuCl3, following by a pronounced Curie-like behavior at low temperatures. In order to understand the nature of low-temperature magnetic interactions, the excitation spectrum of (6MAP)CuCl3 is probed using the electron spin resonance (ESR) technique. The angular dependence of the g-factor clearly indicates the existence of two magnetically non-equivalent sites of Cu-ions in neighboring chains. The ESR signal exhibits a significant linebroadening with decreasing temperature (starting at approximately 30 K), accompanied by a pronounced shift of the g-factor. The observed features can be explained by enhanced short-range-order spin correlations when approaching the long-range ordering at low temperature. Our suggestion is confirmed by the observation of a lowtemperature (T ~ 2.3 K) anomaly in the specific heat. The anomaly measured in field up to 14 T does not exhibit any significant dependence on the applied magnetic field.
  • Poster
    25th international conference on Low Temperature Physics (LT25), 06.-13.08.2008, Amsterdam, The Netherlands

Publ.-Id: 11587 - Permalink

Observation of the antiferromagnetic resonance in the Ho-subsystem in multiferroic HoMnO3
Zvyagin, S. A.; Ozerov, M.; Cizmar, E.; Wosnitza, J.; Zhou, H. D.; Wiebe, C. R.;
Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic orders. Among hexagonal magnanites, the largest magnetoelectric effect was found in HoMnO3, which is ferroelectric below Tc = 875 K and antiferromagnetically ordered below TMn N = 75 K (Mn-subsystem). In addition, at THo N ~ 5 K the Ho-subsystem undergoes a transition into antiferromagnetically ordered state. The coupling between ferroelectric and antiferromagnetic order parameters in HoMnO3 has not been yet unambiguously explained, revealing the importance of geometrical frustrations and a complex interplay between Ho and Mn magnetic subsystems. Here, the magnetic excitation spectrum in high-quality single-crystalline samples of HoMnO3 was probed by means of X-band (9.3 GHz) electron spin resonance spectroscopy. A relatively strong absorption was found below 5 K, which corresponds to the temperature of the magnetic ordering of the Ho-subsystem. The observed mode exhibits very pronounced anisotropic behavior and can be interpreted as excitations within the antiferromagnetically ordered Ho-subsystem.
  • Lecture (Conference)
    Highly Frustrated Magnetism 2008, 07.-12.09.2008, Braunschweig, Germany

Publ.-Id: 11586 - Permalink

CFD modelling of polydispersed bubbly two phase flow around an obstacle
Krepper, E.; Beyer, M.; Frank, T.; Lucas, D.; Prasser, H.-M.;
A population balance model (the Inhomogeneous MUSIG model) has recently been developed in close cooperation between ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into the CFD-Code CFX (Krepper et al. 2005, Frank et al. 2005, Krepper et al. 2007). The current paper presents a brief description of the model principles. The capabilities of this model are discussed via the example of a bubbly flow around a half-moon shaped obstacle arranged in a 200 mm pipe. In applying the Inhomogeneous MUSIG approach, a deeper understanding of the flow structures is possible and the model allows effects of poly-dispersion to be investigated. For the complex flow around the obstacle, the general structure of the flow was well reproduced in the simulations. This test case demonstrates the complicated interplay between size dependent bubble migration and the effects of bubble coalescence and break-up on real flows. The closure models that characterize the bubble forces responsible for the simulation of bubble migration show agreement with the experimental observations. However, clear deviations occur for bubble coalescence and fragmentation. The models applied here, which describe bubble fragmentation and coalescence could be proved as a weakness in the validity of numerous CFD analyses of vertical upward two-phase pipe flow. Further work on this topic is under way.
Keywords: bubbly flow, CFD, non-drag forces, bubble breakup, bubble coalescence, population balance, code validation

Publ.-Id: 11585 - Permalink

Magnet technology and experimental technique at the Dresden High Magnetic Field Laboratory
Scurschii, J.;
  • Invited lecture (Conferences)
    Seminar am "International Laboratory of High Magnetic Fields and Low Temperatures", 23.06.2008, Wroclaw, Poland

Publ.-Id: 11584 - Permalink

Coil design for magnetic pulse applications
Herrmannsdörfer, T.;
The generation of high magnetic fields for scientific and industrial applications, in particular those techniques which meet critical limits of field strength, coil heating, and mechanical stress as well, require a careful design and modelling. In order to describe the mutual dependences of the electrical, thermodynamical, and mechanical processes in such systems in a reasonable way, the use of multi-physics modules of finite-element software packages becomes more and more relevant. Here, the designs based on finite-element simulations of pulsed magnetic-field coils for industrial applications as well as of their pulsed-power supplies for the generation of electrical-current pulses are presented.

  • Invited lecture (Conferences)
    Join Forces - The 1st Technical Conference on MP Welding and Forming, 03.07.2008, München, Deutschland

Publ.-Id: 11583 - Permalink

Terahertz and infrared spectroscopy of superconductors
Pronin, A.;
In the talk, results of experimental investigations of terahertz and infrared electrodynamics of different families of superconductors will be reviewed. In the conventional BCS-superconductors, a pronounced gap feature dominates the terahertz response below Tc. In the cuprates, entering into the superconducting state is accompanied by developing of a narrow zero-frequency centered mode in the real part of the in-plane complex conductivity. In the multi-gap superconductors (such as MgB2), opening of the gap on each sheet of the Fermi surface contributes to the changes of dynamic complex conductivity.
A particular stress will be given on electron-doped cuprates, the electrodynamical response of which was found to have a remarkable dependence on the doping level. Significant changes in the gap anisotropy or even in the gap symmetry may account for this dependence.
The majority of the experiments have been performed on a home-made spectrometer, which utilizes backward-wave oscillators as sources of coherent and frequency-tunable terahertz radiation. An interferometer arrangement of the spectrometer has allowed both, amplitude and phase shift measurements, thus permitting direct (without using the Kramers-Kronig relations) determination of the optical constants.
  • Invited lecture (Conferences)
    Seminar bei BESSY, 30.06.2008, Berlin, Deutschland

Publ.-Id: 11582 - Permalink

Simultaneous measurement of magnetization and magnetostriciton in 50 T pulsed high magnetic fields
Doerr, M.; Lorenz, W.; Neupert, T.; Loewenhaupt, M.; Kozlova, N. V.; Freudenberger, J.; Bartkowiak, M.; Kampert, E.; Rotter, M.;
To simultaneously perform magnetization and magnetostriction measurements in high magnetic fields, a miniaturized device was developed that combines an inductive magnetometer with a capacitive dilatometer and, therefore, it is called “dilamagmeter.” This combination of magnetic and magnetoelastic investigations is a new step to a complex understanding of solid state properties. The whole system can be mounted in a 12 mm clear bore of any cryostat usually used in nondestructive pulsed high field magnets. The sensitivity of both methods is about 10−5 Am2 for magnetization and 10−5 relative changes in length for striction measurements. Measurements on a GdSi single crystal, which are corrected by the background signal of the experimental setup, agree well with the results of steady field experiments. All test measurements, which are up until now performed in the temperature range of 4–100 K, confirm the perfect usability and high stability in pulsed fields up to 50 T with a pulse duration of 10 ms. © 2008 American Institute of Physics.
  • Review of Scientific Instruments 79(2008), 063902

Publ.-Id: 11581 - Permalink

Excitation hierarchy of the spin-1 large-D system NiCl2-4SC(NH2)2
Zvyagin, S. A.; Wosnitza, J.; Batista, C. D.; Krzystek, J.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.; Tsukamoto, M.; Kawashima, N.;
NiCl2-4SC(NH2)2 (known as DTN) is an S = 1 chain system with the easy-plane anisotropy dominating over the exchange interaction (so-called large-D system) and a new candidate for studying the fieldinduced Bose-Einstein condensation of magnons. The excitation spectrum of DTN has been investigated by means of tunable-frequency ESR technique in fields up to 25 T. Based on analysis of the magnon excitation spectrum, a revised set of spin-Hamiltonian parameters was obtained. These values were used to calculate the AFM phase boundary, low-temperature magnetization and the frequency-field dependence of two-magnon bound-state excitations, predicted by theory and observed in DTN for the first time. Excellent quantitative agreement with experimental data was obtained. Published in Phys. Rev. Lett. 98, 047205 (2007).
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Deutschland

Publ.-Id: 11580 - Permalink

CeRu2Si2 and Quantum Critical Metamagnetism?
Weickert, F.; Gegenwart, P.; Garst, M.; Steglich, F.;
CeRu2Si2 is a well-known prototypical heavy fermion system and shows a sudden strong increase in the magnetization M and the sample length ΔL for magnetic fields parallel to the crystallographic c-direction at around 7.8 T. These anomalies occur below 4K and sharpen with decreasing temperatures, but no features for a first order phase transition are observed down to 15mK. We report new thermal expansion α, magnetostriction λ and specific heat C/T measurements, which have been made in mT magnetic field steps around the metamagnetic crossover down to 15mK on very pure single crystals. The results show hints for the existence of a quantum critical endpoint in CeRu2Si2 and were compared with an extended model of metamagnetic quantum criticality, which was first introduced by Millis et al. in 2002.
  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Deutschland

Publ.-Id: 11579 - Permalink

Experimental and numerical investigation of temperature stratification phenomena during heating-up processes of fluids in passive cooling systems
Krepper, E.; Beyer, M.;
In modern designs of nuclear reactors often natural circulation is used as a passive mechanism for heat removal. In the concepts the heat is removed from the reactor and transported into a large pool. Examples are the pressure suppression pool (wet-well) of the ESBWR, the in-containment refuelling water storage tank of the AP-1000, the pool of the emergency condenser of the SWR-1000 and the gravity driven water pool of the AHWR.
In large pools temperature stratification can compromise the heat transfer process. Generation of steam might lead to an increase of the flow velocities, to a mixing of liquids having different temperatures and to a disappearance of temperature stratification. At the corresponding temperatures steam is released from the pool into the containment and influences the increase of the containment pressure. Under conditions of strong temperature stratification compared to a homogeneous temperature distribution, the fluid at the top of the pool much earlier reaches the saturation temperature. The evaporation starts much earlier resulting in an earlier the pressure increase in the containment.
In the presentation both experiments and numerical CFD simulations are reported to investigate the capability of actual CFD modeling this task.
Keywords: passive safety systems, large pools, natural circulation, experiments, CFD
  • Lecture (Conference)
    Multiphase Flow: Simulation, Experiment and Application, 24.-26.06.08, Dresden, Germany

Publ.-Id: 11578 - Permalink

Calorimetric evidence for a Fulde-Ferrell-Larkin-Ovchinnikov superconducting state in the layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2
Wosnitza, J.;
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    The 63rd Calorimetry Conference (CALCON 2008), 02.-06.07.2008, Jersey City, New Jersey, USA

Publ.-Id: 11577 - Permalink

Experimental investigation and CFD simulation of insulation debris transport phenomena in water flow
Krepper, E.; Cartland-Glover, G.; Grahn, A.; 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 presentation 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
  • Lecture (Conference)
    Multiphase Flow: Simulation, Experiment and Application, 24.-26.06.08, Dresden, Germany

Publ.-Id: 11576 - Permalink

Stretching the limits - Research at High Magnetic Fields
Bartkowiak, M.;
es hat kein Abstrakt vorgelegen
  • Invited lecture (Conferences)
    Seminar des Max-Planck-Instituts für Festkörperforschung, 11.07.2008, Stuttgart, Deutschland

Publ.-Id: 11575 - Permalink

Numerical and experimental investigation of temperature stratification phenomena during heating up processes of fluids in large pools
Krepper, E.;
In modern designs of nuclear reactors often natural circulation is used as a passive mechanism for heat removal. In the concepts the heat is removed from the reactor and transported into a large pool. Examples are the pressure suppression pool (wet-well) of the ESBWR, the in-containment refuelling water storage tank of the AP-1000, the pool of the emergency condenser of the SWR-1000 and the gravity driven water pool of the AHWR.

In large pools temperature stratification can compromise the heat transfer process. Generation of steam might lead to an increase of the flow velocities, to a mixing of liquids having different temperatures and to a disappearance of temperature stratification. At the corresponding temperatures steam is released from the pool into the containment and influences the increase of the containment pressure. Under conditions of strong temperature stratification compared to a homogeneous temperature distribution, the fluid at the top of the pool much earlier reaches the saturation temperature. The evaporation starts much earlier resulting in an earlier the pressure increase in the containment.

In the presentation both experiments and numerical CFD simulations are reported to investigate the capability of actual CFD modeling this task.
Keywords: passive safety systems, large pools, natural circulation, experiments, CFD
  • Lecture (Conference)
    International Workshop on Thermal-Hydraulics of Innovative Reactor and Transmutation Systems – THIRS, 14.04.08, Karlsruhe, Germany

Publ.-Id: 11574 - Permalink

A high-brightness SRF photoelectron injector for FEL light sources
Arnold, A.; Büttig, H.; Janssen, D.; Kamps, T.; Klemz, G.; Lehmann, W. D.; Lehnert, U.; Lipka, D.; Marhauser, F.; Michel, P.; Möller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Stephan, J.; Teichert, J.; Volkov, V.; Will, I.; Xiang, R.;
Most of the proposed electron accelerator projects for future FELs, ERLs or 4th generation light sources require electron beams with an unprecedented combination of high brightness, low emittance, and high average current. In all projects photoguns will be applied: DC-photoguns, normal conducting RF-photoguns (NC-guns), and superconducting RF photoguns (SRF-guns). While the concepts of DC- and NC-guns are well proofed, the SRF-gun development still possesses a high risk. Challenges are the design of the superconducting cavity, the choice of the photocathode type, its life time, a possible cavity contamination, the difficulty of coupling high average power into the gun, and, finally, the risk of beam excitation of higher-order cavity modes. In combination with SRF linacs, the SRF-guns seem to be the best solution for high average currents. Several R&D projects of SRF-gun have been launched. In this paper, we will give an overview of the progress of the SRF photoinjector development. In detail, the technical concept, the performance and the status of the Dresden Rossendorf SRF-gun project, a collaboration of BESSY, DESY, MBI and FZD, will be presented. The main design parameters of this SRF-gun are the final electron energy of 9.5 MeV, 1 mA average current, and transverse normalized emittances (rms) of 1 mm mrad at 77 pC and 2.5 mm mrad at 1 nC bunch charge. The 1.3 GHz cavity consists of three TESLA-shaped cells, a specially designed half-cell where the photocathode is placed and a choke filter in order to prevent RF losses at the cathode side. The normal-conducting photocathode with a Cs2Te photoemission layer is cooled by liquid nitrogen. The SRF-gun cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid nitrogen-cooled thermal shield and a titanium He tank with a two-phase supply tube. The 10 kW fundamental power coupler is adopted from the ELBE cryomodule. In a first commissioning and test period the gun will be operated in parallel to the accelerator. A diagnostic beamline will allow beam parameter measurement and further optimization of the SRF-gun. In a final step, the gun will be connected to the ELBE superconducting linear accelerator to deliver an improved electron beam to the user labs.
Keywords: Superconductivity; Radio frequency; Photoelectron injector; SRF-gun; Cavity; Laser
  • Nuclear Instruments and Methods in Physics Research A 593(2008), 57-62


Publ.-Id: 11573 - Permalink

Quasiparticle model for the quark-gluon plasma: equation of state near T-c
Bluhm, M.; Kämpfer, B.;
We test the quark mass dependence implemented in the quasiparticle dispersion relations of our quasiparticle model for the QCD equation of state by comparing with recently available lattice QCD data near Tc employing almost physical quark masses. In addition, we emphasize the capability of our model to successfully describe lattice QCD results for imaginary chemical potential and to analytically continue the latter to real chemical potential.

Publ.-Id: 11572 - Permalink

Magnetic field reversals in nature, experiments and simulations
Giesecke, A.; Stefani, F.; Gerbeth, G.;
From paleomagnetic observations, numerical simulations and -- meanwhile -- also experiments, it appears that reversing dynamos are a quite common phenomenon.
Long time series of mean field simulations adopting Earth-like parameters yield reversal sequences whose statistical behavior is comparable to the Earth.
Recent hints for a reversing experimental dynamo give reason for the examination of a cylindrical dynamo with simulations that are especially suited to the experimental conditions.
This requires a numerical scheme that is able to treat insulating boundary conditions and material properties like permeability and/or conductivity jumps.
Preliminary calculations including a high permeability zone show a slight reduction of the critical Reynolds number.
In future simulations permeability jumps will be increased and an alpha-effect describing the inductive action of turbulence will be included.
Keywords: Reversals, Geodynamo, Simulations
  • Lecture (Conference)
    ICTAM2008 - International Congress of Theoretical and Applied Mechanics, 25.-29.08.2008, Adelaide, Australia
  • Contribution to proceedings
    ICTAM2008 - International Congress of Theoretical and Applied Mechanics, 25.08.-29.09.2008, Adelaide, Australien, 978-0-9805142-1-6

Publ.-Id: 11571 - Permalink

Dielectron spectroscopy at 1–2 AGeV with HADES
Spataro, S.; Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; González-Díaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krása, A.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lapidus, K.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Marín, J.; Markert, J.; Metag, V.; Micel, J.; Michalska, B.; Mishra, D.; Morinière, E.; Mousa, J.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pérez Cavalcanti, T.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Simon, R.; Sobolev, Y. G.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Wen, H.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zumbruch, P. Z. P.;
The HADES spectrometer at GSI (Darmstadt) is investigating the e+e- pair production in p+p, p+A and A+A collisions. In this contribution we would like to highlight the physics motivations and the experiments performed so far, focusing mainly on the first results coming form 12C+12C collisions at 1 and 2 AGeV, and on preliminary results from p+p/d+p collisions at 1.25 AGeV.

Publ.-Id: 11570 - Permalink

Measurement of the in-medium K0 inclusive cross section in pi- -induced reactions at 1.15 GeV/c
Benabderrahmane, M. L.; Herrmann, N.; Wisniewski, K.; Kecskemeti, J.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Buehler, P.; Cargnelli, M.; Caplar, R.; Cordier, E.; Deppner, I.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fabbietti, L.; Fodor, Z.; Gasik, P.; Gasparic, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kienle, P.; Kirejczyk, M.; Kim, Y. J.; Kis, M.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Lopez, X.; Manko, V.; Marton, J.; Mangiarotti, A.; Merschmeyer, M.; Matulewicz, T.; Petrovici, M.; Piasecki, K.; Rami, F.; Reischl, A.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schuttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Suzuki, K.; Tyminski, Z.; Widmann, E.; Xiao, Z. G.; Yamazaki, T.; Yushmanov, I.; Zhang, X. Y.; Zhilin, A.; Zmeskal, J.; Bratkovskaya, E.; Cassing, W.;
The K0 meson production by pi- mesons of 1.15 GeV/c momentum on various nuclear targets was measured with the FOPI spectrometer at the SIS accelerator of GSI. Inclusive production cross-sections and the momentum distributions of K0 mesons are compared to the elementary production cross-sections and to QMC and HSD model predictions. The results point to modifications of the elementary reactions amplitudes inside nuclei and to the existence of a repulsive KN potential of about 20 MeV at normal nuclear matter density.

Publ.-Id: 11569 - Permalink

Magnetic and superconducting properties of metal and oxide nanoclusters on biological templates
Walter, C.; Bartkowiak, M.; Ignatchik, O.; Herrmannsdörfer, T.; Wosnitza, J.; Merroun, M.; Pollmann, K.; Raff, J.; Selenska-Pobell, S.;
Nanogranular materials will play an important role in future technologies due to their exciting magnetic and superconducting properties that differ strongly from their bulk counterparts. In this study, we have focused on metal and oxide nanoclusters that have been deposited on a biological template, a self-assembling surface layer (S-layer) of Bacillus sphaericus JG-A12 which is composed of identical monomers. We present data of Pd, Pb, and Fe3O4 nanograins with sizes of 2, 19, and 13 nm respectively. The magnetization data obtained for the palladium clusters demonstrate that the Stoner enhancement factor of the d conduction-electron susceptibility is clearly reduced compared to the one of bulk Pd. For the Pb nanograins we have investigated the superconducting B-T phase diagram and encountered a superconducting critical field of the size of several Tesla which is strongly enhanced in comparison to the corresponding critical magnetic field of 0.09 T for bulk Pb. Last but not least we investigated the superparamagnetic properties of Fe3O4 nanograins and have found a magnetic anomaly at 30 K. Here, we present magnetization data taken by SQUID magnetometry as well as experimental results of dielectric measurements.
  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Deutschland

Publ.-Id: 11568 - Permalink

Spin-strain coupling in NiCl2-4SC(NH2)2
Chiatti, O.; Sytcheva, A.; Wosnitza, J.; Zherlitsyn, S.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.;
We report results of sound-velocity and sound-attenuation measurements in the quantum S = 1 spin-chain magnet NiCl2-4SC(NH2)2, in magnetic fields up to 18 T. This material is discussed in the context of Bose-Einstein condensation of magnons. The longitudinal c33 acoustic mode, which has a propagation direction along the spin chains, shows pronounced spin-lattice effects. This mode demonstrates a softening in the vicinity of the field-induced antiferromagnetic ordering (below T = 1.2 K), accompanied by an energy dissipation in the acoustic wave. A broad maximum has been observed in the temperature dependence of the sound velocity at 44 K. The low-temperature sound-velocity and sound-attenuation behavior is subject to fluctuations of Ni spin degrees of freedom resulting in frequency-dependent effects. The B − T phase diagram obtained from the ultrasonic measurements is compared with results extracted from other experimental investigations. The ultrasonic results are analyzed with a theory based on exchange-striction spin-phonon coupling.
  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Deutschland

Publ.-Id: 11567 - Permalink

Dynamic scaling at MIT in yttrium hydride switchable mirrors
Pronin, A. V.; Romijn, I. G.; Brom, H. B.; Hoekstra, A. F. T.; Wosnitza, J.;
Yttrium hydride demonstrates a remarkable transition of its electronic and optical properties upon change of hydrogen concentration: a thin YHx film can be continuously and reversibly brought from a shiny metal at x = 2 to a transparent dielectric at x = 3, by changing pressure of the surrounding hydrogen gas [1]. It has been showed that the metal-insulator transition (MIT) could be neatly passed under constant hydrogen pressure by changing the carrier doping via ultraviolet illumination at low temperatures [2]. Pronounced electron-electron interactions are posited to lead to the opening of a large optical gap. The established scaling laws of the conductivity with temperature and doping [2] are strong indications for the quantum nature of the metalinsulator transition in YHx. To shed more light on the quantum nature of the MIT, the frequency dependence of conductivity is very informative. In an extensive frequency range, frequency ! and temperature T will influence the conductivity in a similar way, which will lead to a so-called !/T -scaling behaviour. In this talk results on the optical conductivity in the sub-terahertz regime will be presented.
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Deutschland

Publ.-Id: 11566 - Permalink

Magnetic properties of the spin-1/2 chain material (6MAP)CuCl3
Ozerov, M.; Cizmar, E.; Zvyagin, S.; Landee, C.; Turnbull, M.; Wosnitza, J.;
Recently, low-dimensional spin systems have received a considerable amount of attention due to their relevance to numerous quantum phenomena such as quantum criticality problems, spin-Peierls transitions, etc. Here we report on magnetization, electron paramagnetic resonance (EPR) and specific-heat measurements of the spin-1/2 Heisenberg antiferromagnetic chain material (6MAP)CuCl3. Magnetization data measured at 0.1 T exhibit a maximum at about 70 K, indicating the low-dimensional character of the magnetic interactions. The data are in a good agreement with the temperature dependence of the resonance peak intensity measured at 73 GHz. At low temperatures (T < 25 K) the EPR linewidth drastically increases, indicating a possible enhancement of 3D short-range-order correlations. Such behavior is consistent with a broad maximum in the specific heat observed at about 1.5 K, which can be interpreted in terms of 3D magnetic ordering. In addition, we present results of room-temperature X-band EPR measurements of (6MAP)CuCl3, including angular dependence of the g-factor and of the resonance linewidth.
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Deutschland

Publ.-Id: 11565 - Permalink

Magnetic ordering in organic transition-metal compounds
Huang, L.; Beyer, R.; Papageorgiou, T.; Ignatchik, O.; Herrmannsdörfer, T.; Wosnitza, J.; Gemming, S.; Manson, J.; Schlueter, J.;
The magnetic properties of metalorganic compounds attract much attention as their structural and electronic exchange dimensionality can vary between one and three. Here, we present data of representatives which exhibit magnetic ordering and have been recently investigated by means of magnetometry and calorimetry. In the quasi-cubic compound [Cu(HF2)(pyz)2]BF4, we have observed an antiferromagnetic (AF) ordered phase occurring at TN = 1.6K and a rich magnetic phase diagram up to 14 T as well. Above TN, the specific heat of that compound is in reasonable agreement with the predictions of the model for a s = 1/2 2D square lattice quantum Heisenberg AF describing the in-plane exchange via the Cu−F −H−F −Cu bonds. In the quasi- 1D compound Mn(glycine)(H2O)2Cl2 which is structurally arranged in helical chains, we have observed an unexpected 3D AF ordering at TN = 0.84 K, both in the results of the heat capacity and ac susceptibility. Probably, the 3D exchange is mediated by hydrogen bonds between the chains in addition to Mn−O−Mn bonds along the chains.
  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Deutschland

Publ.-Id: 11564 - Permalink

Magnetic properties of the Haldane-gap material NENB
Cizmar, 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.;
Results of magnetization and high-field 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 cal-
culated, 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, 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, whose origin is discussed.
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11563 - Permalink

Untersuchung der Dynamik fluider Partikel auf Basis der Volume of Fluid Methode
Schmidtke, M.;
Die in dieser Arbeit vorgestellten Simulationen aufsteigender fluider Partikel wurden mit dem CFD-Programm FS3D durchgeführt, welches auf der Volume-of-Fluid (VoF) Methode basiert. Die Validierung des Codes erfolgt durch Vergleich der numerischen Lösungen für schleichende Strömungen mit analytischen Lösungen, wobei eine gute Übereinstimmung festgestellt wird.
Im ersten Teil der Dissertation werden Simulationen für den freien Aufstieg von Öltropfen in Wasser mit experimentellen Beobachtungen hinsichtlich der Aufstiegsgeschwindigkeit, der Tropfenform und der Bewegungsbahn verglichen. Die Aufstiegsgeschwindigkeiten und Widerstandsbeiwerte sind vergleichbar, die simulierten Tropfen sind jedoch deutlich flacher. Dieser Unterschied kann durch Verunreinigungen der Grenzfläche im Experiment verursacht sein. Der Übergang von einem gradlinigen Aufstieg zu zickzack-förmigen Aufstiegsbahnen kann mit Hilfe der Simulationen auf Instabilitäten im Nachlauf der Blasen zurückgeführt werden, die zu einer periodischen Wirbelablösung führen.
Im zweiten Teil der Dissertation wird der Aufstieg von Blasen in linearen Scherströmungen untersucht. Steigen die Blasen in einer vertikalen Scherströmung auf, so beobachtet man eine seitliche Migration. Diese seitliche Migration der Blasen wird durch die sogenannte Liftkraft verursacht, deren Vorzeichen und Betrag von der Blasengröße und den Stoffeigenschaften der Flüssigkeit abhängt. Die Simulationen zeigen, daß das Vorzeichen der Liftkraft für eher sphärische Blasen durch den Bernoulli-Effekt erklärt werden kann. An stark deformierten Blasen hingegen wirkt die Liftkraft in umgekehrter Richtung. Dieses Phänomen tritt auch in den Simulationen auf.
Verschiedene Hypothesen für die Ursache dieses Phänomens werden überprüft. Die bekannteste experimentelle Korrelation für die Liftkraft von Tomiyama u.a. (2002) wird durch Simulation von realen Flüssigkeiten mit bekannten Stoffeigenschaften wie auch von Modellfluiden mit willkürlichen Stoffeigenschaften validiert und weitgehend bestätigt. Die Lift-Korrelation hat demnach hinsichtlich der Stoffeigenschaften der Flüssigkeit einen größeren Geltungsbereich, als bisher experimentell überprüft wurde.

The simulations presented in this thesis were performed with the CFD code FS3D which is based on the Volume of Fluid method. The code is validated using analytical solutions for creeping flows and a good agreement is observed between simulation and analytical solution.
In the first part of the thesis, the free rise of oil drops in water is simulated and compared with experimental observations. The results show that the rising velocities and the drag coefficients are similar in both cases, but the simulated drops are flatter (more oblate). This difference may be caused by impurities of the particle surface (surfactants) in the experiments. The simulations show that the transition from rectilinear to periodic trajectories is caused by instabilities in the wake, which lead to a periodic vortex shedding.
In the second part of the thesis, the rise of bubbles in linear shear flows is investigated. If bubbles rise in a vertical shear flow, a lateral migration can be observed. This migration is caused by the so called lift force. Sign and magnitude of the lift force depend on the size of the bubble and the material properties of the liquid. The simulation results show that the sign of the lift force on spherical bubbles can be explained by the Bernoulli effect. However, the lift force on more distorted bubbles acts in the opposite direction. This phenomenon can also be observed in the simulation. In this work several hypotheses for the reason of this phenomenon are checked. Furthermore, most common correlation for the lift force (developed by Tomiyama et al. in 2002) is validated for fluids of known material and model fluids with arbitrary material data. The correlation is valid in a wider range of fluid material properties than proved experimentally up to now.
Keywords: fluid particle, bubble, drop, volume of fluid, DNS, oil, lift force, VoF, CFD
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-502 2008


Publ.-Id: 11562 - Permalink

Science at the Dresden High Magnetic Field Laboratory
Wosnitza, J.; Herrmannsdörfer, T.; Skourski, Y.; Zherlitsyn, S.; Zvyagin, S. A.; Drachenko, O.; Schneider, H.; Helm, M.;
Since the beginning of 2007 the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden = HLD) has opened as a user facility offering access to world-unique experimental infrastructure in pulsed-field magnets. Some of the available user magnets, reaching up to 70 T, and experimental techniques are reported. The brilliant light of a next-door free-electron-laser source allows dedicated high-field infrared spectroscopy. First scientific results obtained in pulsed magnetic fields are highlighted.

Publ.-Id: 11561 - Permalink

Recent Developments At The Dresden High Magnetic Field Laboratory
Wosnitza, J.; Bianchi, A. D.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S.;
The recent progress made at and the status quo of the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden = HLD) is reported. This laboratory, pres-ently under construction at the research center (Forschungszentrum) Dresden-Rossendorf, is planned to open as user facility in 2007 offering access to various pulsed-field magnets. Besides introducing the installed capacitive energy supply at the HLD, the pulsed-magnet designs are discussed in some detail. The experimental techniques that are routinely running at the HLD and the additional ones being set up, are summarized. First scientific results are highlighted.
  • Contribution to proceedings
    2006 International Conference on Megagauss Magnetic Field Generation and Related Topics, 05.-10.11.2006, Santa Fe, USA
    Proceedings of the 2006 International Conference on Megagauss Magnetic Field Generation and Related Topics, Piscataway: IEEE, 978-1-4244-2061-2, 197-206

Publ.-Id: 11560 - Permalink

Hochfeste Leitermaterialien auf Kupfer-Basis: quo vadis?
Freudenberger, J.; Botcharova, E.; Gaganov, A.; Lyubimova, J.; Schultz, L.; Witte, H.; Jones, H.; Herrmannsdörfer, T.; Zherlitsyn, S.; Wosnitza, J.; Givord, D.; Barthem, V. M. T. S.; Boettcher, R.-D.; Hannemann, K.;
Leitermaterialien mit besonderen mechanischen Eigenschaften werden in vielen wissenschafts- und anwendungsorientierten Bereichen eingesetzt. Diese Leiter werden gezielt auf ihre Eigenschaften optimiert, um eine bestmögliche Funktionalität der Werkstoffe zu erreichen. Daher stellen diese auf ihre Anwendung zugeschnittenen Leiter oft eine Schlüsselkomponente des Systems, in dem sie eingesetzt sind, dar. Dieser Beitrag zeigt gegenwärtige und zukünftige Anwendungen der am IFW Dresden entwickelten hochfesten Leitermaterialien auf Kupfer-Basis auf.
  • Metall 62(2008)3, 35-37

Publ.-Id: 11559 - Permalink

Anisotropic Multiband Many-Body Interactions in LuNi2B2C
Bergk, B.; Petzold, V.; Rosner, H.; Drechsler, S.-L.; Bartkowiak, M.; Ignatchik, O.; Bianchi, A. D.; Sheikin, I.; Canfield, P. C.; Wosnitza, J.;
We present a comprehensive de Haas–van Alphen study on the nonmagnetic borocarbide superconductor LuNi2B2C. The analysis of the angular-dependent effective masses for different bands in combination with full-potential density functional calculations allowed us to determine the massenhancement factors, λ, for the different electronic bands and their wave-vector dependences. Our data clearly show the anisotropic multiband character of the superconductivity in LuNi2B2C.
  • Physical Review Letters 100(2008), 257004

Publ.-Id: 11558 - Permalink

Determining anisotropy constants from a first-order magnetization process in Tb2Fe17
Kuz’Min, M. D.; Skourski, Y.; Skokov, K. P.; Müller, K.-H.; Gutfleisch, O.;
The critical parameters of a first-order magnetization process, Hcr and mcr, are used to determine the anisotropy constants K1 and K2 of Tb2Fe17 in the temperature range between 5 and 300 K. Both anisotropy constants are proportional to the critical field Hcr (times spontaneous magnetization), whereas their ratio is independent of Hcr and depends solely on the dimensionless reduced critical magnetization mcr. The employed method of determining K1 and K2 is complementary to the classical Sucksmith–Thompson technique, which is inapplicable in the case of a first-order magnetization process.
  • Physical Review B 77(2008), 132411

Publ.-Id: 11557 - Permalink

A literature review of theoretical models for drop and bubble breakup in turbulent dispersions
Liao, Y.; Lucas, D.;
This paper presents a literature review on mechanisms and models for the breakage of bubbles and drops (fluid particles) in turbulent dispersions. For the mechanisms, four categories are summarized, namely, turbulence fluctuation, viscous shear stress, shearing-off process and interfacial instability. The models for breakup frequency and daughter size distribution available in literature are reviewed thoroughly. The development and limitation of the existing models are studied and possible improvements are proposed.
Keywords: Population balance equation, Size distribution, Breakup mechanisms, Breakup frequency, Daughter size distribution
  • Chemical Engineering Science 64(2009)15, 3389-3406

Publ.-Id: 11556 - Permalink

Finite-element simulation and performance of pulsed magnets
Skourski, Y.; Herrmannsdörfer, T.; Sytcheva, A.; Wosnitza, J.; Wustmann, B.; Zherlitsyn, S.;
The design of a high-energy pulsed magnet is a challenging task and usually implies substantial calculation efforts. As the maximum stress is located in the mid-plane of the magnet, this region is usually the only focus of analysis. For that a number of well-established algorithms are available. However, the coil performance is governed not exclusively by the mid-plane. Therefore, it is important to simulate the whole coil behavior. Here we report on a simulation approach used among others at the Hochfeld-Magnetlabor Dresden (HLD). Assuming axial symmetry of the coil, the cross section of the magnet is modeled by finite elements. We illustrate this simulation technique for an 8.5 MJ 70 Tesla mono-coil and a 46 MJ double-coil magnet designed at the HLD.
  • IEEE Transactions on Applied Superconductivity 18(2008)2, 608-611

Publ.-Id: 11555 - Permalink

On the modelling of bubble entrainment by impinging jets in CFD-simulations
Schmidtke, M.; Lucas, D.;
This contribution presents different approaches for the modeling of air entrainment under water by plunging jets in CFD codes. In simulations which include the full length of the jet and its environment, the process of bubble generation can not be resolved due to computational limitations. 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. In the impinging jet configuration, the air is a continuous phase above the water level but bubbly below the water level. Various drag models are implemented in the CFD solver CFX11 and their influence on the gas void fraction below the water level is discussed. 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.
Keywords: jet, entrainment, bubble, plunging, impinging, free surfase, bubble, area density
  • Contribution to proceedings
    XCFD4NRS, Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
    On the modelling of bubble entrainment by impinging jets in CFD-simulations
  • Poster
    XCFD4NRS, Experiments and CFD Code Applications to Nuclear Reaktor Safety, 10.-12.09.2008, Grenoble, France

Publ.-Id: 11554 - Permalink

Rapid cooling methods for pulsed magnets
Frings, P.; Witte, H.; Jones, H.; Béard, J.; Herrmannsdoerfer, T.;
Pulsed magnets are generally evaluated and compared in terms of the magnetic field they can achieve in combination with a bore size. However, in practice another criterion is equally important: the waiting time for a researcher in between two consecutive shots. The cooling time of pulsed magnets can range from a few minutes up to several hours, depending on coil size and desired field. Using simulations and measurements several options to reduce the cool down time are compared in this paper. One of the discussed methods is now routinely in use at the Laboratoire National des Champs Magnetiques Pulses (LNCMP) in Toulouse.
  • IEEE Transactions on Applied Superconductivity 18(2008)2, 612-615

Publ.-Id: 11553 - Permalink

Pressurized Thermal Shock (PTS) in the European project NURESIM
Lucas, D.;
The presentation summarizes the activities regarding the simulation of Pressurized Thermal Shock (PTS) performed within the European Integrated Project NURESIM. Some Loss of Coolant Accident (LOCA) scenarios for Pressurized Water Reactors (PWR) may lead to PTS situations. They imply the formation of temperature gradients in the thick vessel walls with consequent localized stresses and the potential for propagation of possible flaws present in the material. Current generation PWR (including the Russian VVER types), are primarily affected by the phenomenon which is investigated within three broad areas: material damage originated by irradiation, thermal-hydraulics (including single and two-phase flow conditions in the region of the ‘shock’) and structural mechanics with main reference to fracture mechanics. The present paper, in the area of thermal-hydraulics, focuses on the study of two-phase conditions that are potentially at the origin of PTS. Within the above context, the paper summarizes recent advances in the understanding of the two-phase phenomena occurring within the geometric region of the nuclear reactor, i.e. the cold leg and the downcomer, where the ‘PTS fluid-dynamics’ is relevant. Available experimental data for validation of two-phase CFD simulation tools are reviewed and the capabilities of such tools to capture each basic phenomenon are discussed. Key conclusions show that several two phase mechanisms (or sub-phenomena) are involved and can individually be simulated at least at a qualitative level, but the capability to simulate their interaction and the overall system performance (case of two phase flow) is presently not available.
Keywords: PTS, CFD, two-phase flow
  • Lecture (Conference)
    14th Meeting of the German CFD Network, 17.07.2008, Stuttgart, Deutschland

Publ.-Id: 11552 - Permalink

Entwicklung und Validierung von Modellen für Zweiphasenströmungen
Lucas, D.; Beyer, M.; Vallee, C.; Krepper, E.; Höhne, T.; Al Issa, S.; Liao, Y.;
Es wird eine Übersicht über den aktuellen Status der vom BMWi gefördeten Projekte "TOPFLOW-Experimente, Modellentwicklung und Validierung von CFD-Codes für Wasser-Dampf-Strömungen mit Phasenübergang " und "Entwicklung und Validierung von Modellen für Blasenkoaleszenz und –zerfall " gegeben.
  • Lecture (Conference)
    Meilenstein-Workshop zu vom BMWi geförderten Projekten der Reaktorsicherheitsforschung, 16.07.2008, Stuttgart, Deutschland

Publ.-Id: 11551 - Permalink

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