Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39515 Publications

Gas/liquid flow in large risers

Omebere-Iyari, N. K.; Azzopardi, B. J.; Lucas, D.; Beyer, M.; Prasser, H.-M.

Although, most of the work reported on two-phase flows are limited to small pipe diameters, two-phase flow in large risers are increasingly being encountered in the petroleum and nuclear industries. In the present work, a wire mesh sensor was employed to obtain void fraction and bubble size distribution data and visualizations of steam/water flow in a large vertical pipe (194mm in diameter) at 46bar. For comparison purposes, measurements were made at similar phase velocities and physical properties to the data of Omebere-Iyari et al. (2007), which is for nitrogen/naphtha flow in a similar-sized riser. There exist significant differences between both sets of data. Churn-turbulent flow is observed in the present work instead of slug flow, and this differs from the intermittent and semi-annular flow patterns reported by Omebere-Iyari et al. (2007). The mean void fraction of the nitrogen/naphtha data is higher than that of the present steam/water data due to the differences in composition in the liquid phases. Furthermore, core peak distributions are observed for the present work in contrast to the flatter profiles predicted for the data of Omebere-Iyari et al. (2007) using a power law relationship.

Keywords: two phase flow; large diameter; vertical pipe; high pressure; wire-mesh sensor; void fraction

Publ.-Id: 10574

Electromagnetic processing of materials

Ren, Z.; Gerbeth, G.

A brief description is given of the subject of EPM and, in particular, the Chinese-German cooperation program in this field.

  • Steel Research International 78(2007), 371-372

Publ.-Id: 10573

Abteilung Magnetohydrodynamik des Forschungszentrums Dresden-Rossendorf

Gerbeth, G.

Die Arbeiten und Methoden der in der Abteilung durchgeführten Forschungen zur MHD werden vorgestellt.

  • Elektrowärme International (2007)3, 187-189

Publ.-Id: 10572

Melting-Solidification process InN Pb-Bi melts

Sklyarchuk, V.; Plevachuk, Y.; Gerbeth, G.; Eckert, S.

Electrical conductivity, s(T), and thermoelectric power, S(T), of liquid Pb-Bi alloys of eutectic and near eutectic compositions were investigated in the “melting-solidification” temperature region. The revealed discrepancies between the heating and cooling s(T) and S(T) curves as well as a hysteresis observed in course of heating-cooling cycles suggest a metastable microheterogeneous structure of the Pb-Bi melts. A solidification mechanism is proposed.

  • Open Access Logo Journal of Physics: Conference Series 79(2007), 012019

Publ.-Id: 10571

Investigation of the behaviour of mineral wool in the reactor sump

Weiss, F.-P.; Alt, S.; Cartland-Glover, G.; Grahn, A.; Hampel, R.; Kästner, W.; Krepper, E.; Seeliger, A.

The investigation of insulation debris generation, transport and sedimentation becomes more important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core coolant 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 for example the particle load on strainers and corresponding pressure drop, the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow. A joint research project on such questions is being performed in cooperation with the University of Applied Sciences Zittau/Görlitz. The project deals with the experimental investigation and the development of CFD models for the description of particle transport phenomena in coolant flow. While the experiments are performed at the University in Zittau, the theoretical work is concentrated at Forschungszentrum Dresden-Rossendorf.

  • Invited lecture (Conferences)
    Quadripartite Meeting on Sump Screen Blockage, 17.-18.10.2007, Erlangen, Germany

Publ.-Id: 10568

Practical calculation of bubble column flow with CFX-11

Frank, T.; Lifante, C.; Krepper, E.

The lesson 6 of the "Short Course on Multiphase Flow Modelling" describes the practical simulation of the flow in a bubble column. The necessiy of the correct simulation of the momentum exchange between the phases is shown comparing different results with experiments.

Keywords: CFD; two fluid model; dispersed gaseous phase; drag bubble forces; non drag bubble forces; bubble column

  • Invited lecture (Conferences)
    5th Joint FZD & ANSYS Workshop & Short Course on Multiphase Flows: Simulation, Experiment & Application, 25.-27.04.2007, Dresden, Germany

Publ.-Id: 10566

Interfacial heat and mass tansfer models

Krepper, E.; Scheuerer, G.

The lesson 4 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of mass and energy exchange between the phases based on the two fluid model approach. After the basic principles the lesson describes the simulation of subcooled boiling and the simulation of cavitation processes.

Keywords: CFD; Two fluid model; heat transfer; mass transfer; boiling; cavitation

  • Invited lecture (Conferences)
    5th Joint FZD & ANSYS Workshop & Short Course on Multiphase Flows: Simulation, Experiment & Application, 25.04.2007, Dresden, Germany

Publ.-Id: 10565

CFD simulation of the two-phase flow around an obstacle applying an inhomogeneous multiple bubble size class approach

Krepper, E.; Lucas, D.; Prasser, H.-M.; Beyer, M.; Frank, T.

In recent years in close cooperation with ANSYS/CFX a population balance model was developed to simulate multiphase flow with higher gas volume fraction. Several dispersed gaseous phases are modeled having a distinct velocity field. Bubble fragmentation and coalescence is simulated by decades of gaseous sub-size mass fractions, which are assigned to the few dispersed gaseous phases. This approach was called “inhomogeneous MUSIG model” and enables the simulation of bubble size dependent bubble forces.
The presentation reports the basic principles and the application of the model approach to simulate a TOPFLOW experiment, in which a complex three dimensional flow field was measured. A half moon shaped obstacle was arranged in the DN200 test section and the two phase flow field was analysed by a wire mesh sensor.
Applying this approach a more deep understanding of the flow structure is possible. To improve the quantitative accuracy further developments particularly of the models describing bubble fragmentation and coalescence are necessary.

Keywords: CFD; multi-fluid model; poly-disperse phase; population balance; gas-liquid; model validation

  • Lecture (Conference)
    5th Joint FZD & ANSYS Workshop & Short Course on Multiphase Flows: Simulation, Experiment & Application, 25.-27.04.2007, Dresden, Germany

Publ.-Id: 10564

Formation of superconducting regions of MgB2 by implantation of magnesium ions into boron substrate followed by intense pulsed plasma treatment

Piekoszewski, J.; Kempinski, W.; Andrzejewski, B.; Trybula, Z.; Kaszynski, J.; Stankowski, J.; Stanislawski, J.; Barlak, M.; Jagielski, J.; Werner, Z.; Grotzschel, R.; Richter, E.

Mg ion implantation into boron substrates followed by pulsed Ar plasma treatment was used to form MgB2 compound. Rutherford Backscattering (RBS) analysis of the best samples revealed that the ratio of atomic concentration of Mg to B atoms could be close to the stoichiometry of MgB2 in the range of about 100 nm beneath the surface. Results of magnetically modulated microwave absorption (MMMA), magnetic moment and electrical conductivity measurements indicate the presence of superconductive grains with critical temperature T-c=25 K. A gradual onset of microscopic percolation is inferred starting from 15 K although no full percolation has been reached.

  • Surface & Coatings Technology 201(2007)19-20, 8175-8179

Publ.-Id: 10562

Superconducting and electrical properties of Mg-B structures formed by implantation of magnesium Ions into the bulk boron followed by pulse plasma treatment

Piekoszewski, J.; Kempinski, W.; Barlak, M.; Kaszynski, J.; Stanislawski, J.; Anduejewski, B.; Werner, Z.; Plekara-Sady, L.; Richter, E.; Stankowskic, J.; Grotzschel, R.; Lo, S.

Superconducting regions of magnesium diboride (MgB2) on magnesium substrate were formed by the combined methods of ion implantation and transient annealing using three different ion fluences and three different energy density of Ar plasma pulses. The samples were characterized by Rutherford back scattering (RBS) and superconductivity detection techniques. The results of these characterizations are presented and discussed. The highest critical temperature observed T-C = 33.8 K.

  • Vacuum 81(2007)10, 1398-1402

Publ.-Id: 10561

Two-Phase flow pattern in the mixing chamber of an effervescent atomizer

Otáhal, J.; Sühnel, T.; Beyer, M.; Jícha, M.

This paper deals with an experimental study of the two-phase flow in the mixing chamber of an effervescent atomizer. Not only do operational conditions and media properties affect the process of effervescent atomization but also the pattern (quality) of the two-phase flow. Therefore, it is necessary to describe the phenomena associated with the mixing process. Two-phase flow structure was investigated in a mixing chamber with an inner diameter of 8 mm. During the experiment, the effervescent nozzle was operated in the air pressure range of 1 to 0.5 MPa and mass GLR (Gas-to-liquid- ratio) was between 1 and 25%. Mass flow rates of water ranged from 5 up to 50 g•s-1. Since optical measurement techniques fail to provide sufficient quantitative information on the flow structure at higher GLR we applied the conductivity wire-mesh sensor technology to this problem. Therefore, a new miniature wire-mesh sensor for small-diameter tubes was developed. The measuring principle of this sensor is based on the measurement of electrical conductivity in the crossing points of a wire mesh. Due this principle we used a conductive liquid (deionized water). The two-phase flow in the chamber is highly unstable and the wire-mesh sensor provides also data for an evaluation of two-phase flow pulsation.

Keywords: wire-mesh sensor; effervescent atomization; two-phase flow; mixing process

  • Poster
    Experimental fluid mechanics 2007, 28.-30.11.2007, Liberec, Czech Republik

Publ.-Id: 10560

Two-photon photocurrent spectroscopy of electron intersubband relaxation and dephasing in quantum wells

Schneider, H.; Maier, T.; Walther, M.; Liu, H. C.

Resonantly enhanced nonlinear absorption between conduction subbands in InGaAs/AlGaAs quantum wells induces a two-photon photocurrent under femtosecond excitation, which is exploited to determine electron intersubband relaxation and dephasing times. The approach allows us to study systematically the dependence of these time constants on structural parameters, including carrier density and modulation/well doping, and to discriminate between different scattering processes.

Keywords: two-photon transition; intersubband absorption; semiconductor quantum well; InGaAs/AlGaAs; femtosecond infrared spectroscopy

Publ.-Id: 10559

Intelligente Radiometallkomplexe für Diagnostik und Therapie

Stephan, H.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Knauer Jubiläumstreffen zur Chromatographie, 01.10.2007, Berlin, Germany

Publ.-Id: 10558

Ion Beam Synthesis of Nanoclusters and Nanowires by FIB

Bischoff, L.

During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and derived an exceedingly importance with the development of the nano-technology. For special purposes like writing ion implantation for doping or ion beam synthesis (IBS) in the µm- as well as in the nm-range without any lithographic steps ion species other than gallium become more and more relevant. Therefore mass separated FIB systems equipped with alloy liquid metal ion sources (LMIS) play an increasing role.
A Co-FIB obtained from a Co36Nd64 alloy LMIS was applied for the IBS at elevated sample temperatures and subsequent annealing for the fabrication CoSi2 nano-structures down to 20 nm on Si(111) and Si(100) substrates. The combination of FIB implantation (top-down approach) and self organization processes during IBS (bottom-up approach) can provide a spatial reduction of the FIB implanted structures. A second investigated process is the defect induced formation of CoSi2 nanoparticles and nanowires using other ions than cobalt in the FIB, focused down to a spot diameter less than 30 nm at room temperature. The source for Co atoms for the NW growth was a 10 nm thin Co film evaporated onto the rear side of the wafer. The FIB irradiation of Nd, Ga, Si and Au ions and doses of 1015-1017 cm-2 creates a broad spectrum of defects in the substrate. Subsequent annealing leads amongst others to the formation of rod-like extended {311}-defects, which act as a prime source of transient enhanced diffusion of impurities in silicon. Also these defects can dissolve and form other rod-like defects always aligned to the (110) direction with a diameter of 10 – 20 nm and a length of some hundred nm. The heat treatment (1000°C, 30 min, N2) leads to a gettering of cobalt atoms in these defects followed by a CoSi2 formation through Ostwald ripening which stabilizes the origin of the defect rods. The obtained crystalline CoSi2 nanowires showed a diameter of 10 – 30 nm and a length up to some ten micrometer always aligned along the (110) orientations independent of the FIB writing direction with respect to the wafer orientation. These structures were studied by SEM/EDX and AFM analysis as well as by electrical characterization after contacting with W-pads, fabricated by FIB MO-CVD [1].
Furthermore, the high resolution mass separated Rossendorf FIB system, equipped with a CANION 31Mplus column (Orsay Physics) and a Ga liquid metal ion source (LMIS) as well as with different alloy LMIS (CoNd, AuSi, etc.) was used to fabricate other nanostructures.

[1] C. Akhmadaliev, B. Schmidt and L. Bischoff, Appl. Phys. Lett. 89 (2006) 223129

Keywords: Focused Ion Beam; nanostructures; nanowires; CoSi2

  • Lecture (others)
    Indian Association for the Cultivation of Science, 01.10.2007, Kolkatta, India

Publ.-Id: 10557

Three-dimensional analysis of macroporosity distributions in polyolefin particles using X-ray microtomography

Boden, S.; Hampel, U.; Bieberle, M.; Weickert, G.

We applied X-ray microtomography (XMT) to determine the macroporosity distribution in polypropylene macroparticles extracted from a gas phase polymerisation process. Different specimens were scanned with a laboratory XMT setup comprising a microfocus X-ray source and an X-ray image intensifier. The XMT technique provides comprehensive three dimensional data volumes representing the local X-ray attenuation in voxels of 5.3 μm x 5.3 μm x 5.3 μm size. After 3D image reconstruction with the Feldkamp algorithm the resulting volume data were processed with histogram based binarisation, connectivity check and volume rendering algorithms. From the resulting 3D images void size distributions in different radial regions of the particles were computed. This enables characterisation of the particles regarding their morphology and elucidation of the effect of given process conditions on morphogenesis.

Keywords: polyolefin macroparticles; X-ray microtomography

Publ.-Id: 10556

The two-step gamma cascade method as a tool for studying photon strength functions of intermediate-weight and heavy nuclei

Becvar, F.; Honzatko, J.; Krticka, M.; Pasic, S.; Rusev, G.; Tomandl, I.

The method of two-step c cascades following the thermal neutron capture is described. An example of two-step cascade data from measurements with 162Dy target is given together with interpretation of these data in terms of scissors-mode resonances built on excited levels in 163Dy. With the aim of verifying the correctness of the method results of benchmark testing measurements with a 56Fe target are compared with the outcome of the GEANT3 simulations.

Keywords: Photon strenght functions; Scissors mode; Two-step gamma cascades; Nuclear levels

Publ.-Id: 10555

Ripple structures at top surfaces and underlying crystalline layers induced by ion beam erosion in silicon

Grenzer, J.; Mücklich, A.; Grigorian, S.; Biermanns, A.; Chini, T. K.; Sanyal, M. K.; Pietsch, U.

Ion beam implantation is one of the major technologies in the semiconductor industry. Although there have been a lot of technological applications there is relatively little known about the structural changes of semiconductors after ion beam implantation. Of particular interest is the creation of lateral nanostructures using different methods of ion beam implantation. One method is to exploit the phenomenon of self-organization during the Ar+ implantation using an oblique ion beam bombarding the sample surface. This results in the growth of the periodic wavelike or ripple like morphology which is produced as a result of the interplay between a roughening process caused by the ion beam erosion (sputtering) of surface and a smoothening process caused by thermal or ion-beam-induced surface diffusion. At least the developing surface structures can be well described in terms of the Bradley-Harper model and respective extensions. Lot of investigations is going on to understand the formation of such nano-structures but mostly looking on the top surface. However, the ion energy dissipation takes place below the surface. Thus the investigation of the interface between the almost amorphous top layer and the underlying crystalline material is important for the understanding of pattern formation.
Detailed studies on the ion induced ripple formation on Si have revealed that they appear only in a limited range of incident angles. The ripple wavelength appears to be linearly dependent on the ion energy and varies in between several nm and hundreds of nm when the ion energy changes from 0.5 to 100 keV. If the ion beam energy was increased up to the 100keV range one-dimensional ripple structures on Si (100) surfaces with wave lengths up to the micro meter range have been observed.Recent investigations using TEM and depth resolved X-ray diffraction methods discovered that the ripples at the surface are followed by a nearly sinusoidal shaped buried interface between the strongly damaged, not completely amorphous near-surface region and the crystalline material. Depending on the chosen energy and the irradiation dose the “amorphous” layer could be reach a thickness of 100nm and corresponds fairly well to the end of range distance of implanted ions.

Keywords: ion beam induced ripples; semiconductor; X-ray diffraction

  • Lecture (Conference)
    12th International Conference on Defects-Recognition, Imaging and Physics in Semiconductors (DRIP), 09.-13.09.2007, Berlin, Germany

Publ.-Id: 10554

Radioaktiv markierte Humanserumalbumin-Mikrosphären zur nuklearmedizinischen Tumortherapie

Schiller, E.; Bergmann, R.; Pietzsch, J.; Noll, B.; Sterger, A.; Johannsen, B.; Wunderlich, G.; Pietzsch, H.-J.


Gegenstand der Arbeiten war die In-vitro- und In-vivo-Charakterisierung von radioaktiv beladenen Humanserumalbumin-Mikrosphären (HSAM). Ziel war dabei die Bewertung der Partikel hinsichtlich ihrer Eignung zur radiotherapeutischen Behandlung von Krebserkrankungen der Leber.


An vorgefertigte HSAM (3 Chargen mit unterschiedlicher Oberflächenrauigkeit; mittlerer Durchmesser 25 µm) wurden oberflächlich DOTA-Chelatoren kovalent gebunden. Anschließend erfolgte die Markierung mit Y-86, indem die DOTA-HSAM in einer Lösung des Radionuklides suspendiert wurden. Die In-Vitro-Charakterisierung der markierten Partikel erfolgte durch Inkubation in Humanplasma und Challenge mit DTPA. Die In-vivo-Stabilität der Y-86-DOTA-HSAM wurde bestimmt durch Bioverteilungsstudien in gesunden Wistarratten. Nach intravenöser Applikation der Y-86 markierten Partikel kommt es zum vollständigen Trapping der Mikrosphären in der Lunge, die in useren Untersuchungen als Zielorgan diente. Aus dem Verschwinden der Radioaktivität aus der Lunge können Rückschlüsse auf die Stabilität der Markierung und damit verbunden auf die Stabilität der HSA-Partikel gezogen werden.


DOTA konnte in Form eines Isothiocyanat-Derviates an Oberflächenaminogruppen der HSAM gebunden werden. Unter optimierten Bedingungen enthielten 1 mg Mikrosphären 2 x 10-7 mol DOTA. Die Markierung der Partikel mit Y-86 gelang in hohen reproduzierbaren Ausbeuten (96 ± 1 %, n = 7) nach 15minütigem Schütteln der suspendierten DOTA-HSAM in Acetatpuffer (pH = 6,5). Die markierten Mikrosphären zeigten hohe Stabilität in Humanplasma und in Anwesenheit von DTPA. Bei den Bioverteilungsstudien fanden wir große Unterschiede zwischen den einzelnen Mikrosphärenchargen mit unterschiedlicher Oberflächenrauigkeit. Partikel mit glatter Oberfläche zeigten die höchste Stabilität. Hier war das Aktivitätsniveau in der Lunge über 48 Stunden annähernd konstant.


Die Kopplung von Chelatoren an die Oberfläche von HSAM stellt eine einfache Strategie zu deren Beladung mit Radionukliden dar. Aufgrund ihrer höheren In-Vivo-Stabilität sind Partikel mit glatter Oberfläche besser für radiotherapeutische Anwendungen geeignet als raue Mikrosphären.

  • Lecture (others)
    15. Arbeitstagung der AG Radiochemie/Radiopharmazie, 27.-29.09.2007, Morschach, Switzerland

Publ.-Id: 10553

PET/CT demonstrates increased myocardial FDG uptake following irradiation therapy

Zöphel, K.; Hölzel, C.; Dawel, M.; Hölscher, T.; Evers, C.; Kotzerke, J.

Late myocardial damage induced by radiotherapy has become an important issue in radio-oncology since several studies have demonstrated increased incidence of cardiovascular disease following radiotherapy.

Publ.-Id: 10552

Prospective profit by using modulated magnetic fields during unidirectional solidification of metal alloys

Eckert, S.; Nikrityuk, P. A.; Willers, B.; Räbiger, D.; Eckert, K.; Gerbeth, G.

AC magnetic fields are used in industrial practice for melt stirring. The requirements are manifold for miscellaneous metallurgical operations or casting technologies, mainly the magnetic field application should provide an efficient mixing of the melt in order to achieve homogeneous distributions of solute and/or temperature. Applications of different magnetic fields (rotating, traveling, pulsating and combinations thereof) are connected with the occurrence of a more or less symptomatic flow pattern. Various forms of electromagnetic stirring have been studied in our laboratory. Here we consider exclusively the use of a rotating magnetic field (RMF), which has already become widespread in industrial practice. For instance, the rotary stirring during solidification has been proved to be a striking method in order to achieve a purposeful alteration of the microstructure of casting ingots, such as a distinct grain refining or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET). However, the imposition of an RMF on a metal column also causes problems like the occurrence of typical segregation pattern or a deflection of the upper free surface leading to surface defects or the entrainment of gas. The RMF application provides a permanent radial inward flow along the solidification front. Such flow is responsible for the transport of solute to the axis of the ingot resulting in typical freckle segregation pattern in form of vertical channels filled with alloy of eutectic composition. In this paper we present a new innovative method of electromagnetic stirring using a modulated RMF which offers a considerable potential for a well-aimed modification of casting properties
Solidification experiments as well as numerical simulations were carried out considering the directional solidification of Pb Sn alloys from a water-cooled copper chill. A modulated rotating magnetic field (RMF) was applied for melt agitation. Thermocouples were used to measure the temperature field during solidification. The velocity field in the liquid phase was determined by means of Ultrasound Doppler velocimetry (UDV). Our numerical model is based on the classical mixture formulation. To calculate the viscosity in the mushy region the model proposed by Roplekar and Dantzig (2001) was implemented into the code. The comparison between numerical simulations and solidification experiments delivered a good agreement. Our results demonstrate the modulation magnetic field enables an effective control of the flow field and the structure of the solidified samples. Modifications of the grain structure and macrosegregation effects are discussed with respect to the details of the flow field.

Keywords: solidification; convection; electromagnetic stirring; macrosegregation

  • Lecture (Conference)
    3rd Sino-German Workshop 2007, 16.-19.10.2007, Shanghai, China

Publ.-Id: 10551

Effect of various magnetic fields on a liquid metal bubble plume

Zhang, C.; Eckert, S.; Gerbeth, G.

Bubble driven flows have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenize the physical and chemical properties of the melt or to refine the melt. For such gas-liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contact-less way.
Compared to the numerous experimental studies on the movement of bubbles in transparent liquids, especially in water, the number of publications dealing with gas bubbles rising in liquid metals is comparatively small. The shortage of suitable measuring techniques can be considered as one reason for the slow progress in the investigations of gas-liquid metal flows. We applied the Ultrasound Doppler Velocimetry (UDV) for measurements of the velocity structure in liquid metal bubbly flows. Because of the ability to work non-invasively in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications.
In our experiments we investigated the consequence of an application of a DC magnetic field on both the bubble and the liquid velocity. The motion of single argon bubbles rising in GaInSn were analyzed in terms of the terminal velocity, the drag coefficient, the oscillation frequency of the bubble velocity and the Strouhal number. Because the gas bubble is electrically non-conducting, it does not experience the effect of the electromagnetic force directly. However, the bubble behaviour is influenced by the magnetically induced modifications in the liquid flow structure around the bubble. The measurements reveal a distinct effect of the magnetic field on the bubble velocity as well as the bubble wake. The magnetic field application leads to a mitigation of the horizontal components of the bubble velocity resulting in a more rectilinear bubble path. A restructuring of the entire flow field can be observed if a bubble plume is exposed to a DC magnetic field. As a result of the interaction between magnetic field and liquid flow electric currents were induced inside the liquid causing a damping of the flow by Joule dissipation. However, a characteristic feature of the electromagnetic dissipation is the anisotropy. Thus, the application of a transverse field leads not only to a general damping of the flow, but also favours the occurrence of vortices aligned parallel to the magnetic field direction.
Our investigations focus on the use of AC magnetic fields, too. Velocity measurements in a liquid metal bubble plume demonstrated that the application of a travelling magnetic field (TMF) can lead to completely new flow structures in the liquid phase. This fact offers new perspectives regarding the control of the heat and mass transfer in liquid metal bubble plumes. For instance, reversals of the mean flow direction can be organised. Moreover, the formation of dead flow regions at the bottom of the fluid vessel was prevented. Therefore, the use of AC magnetic fields could be an efficient tool to considerably reduce the mixing time of refining operations.

Keywords: single bubble; bubble plume; magnetic fields; MHD tturbulence

  • Lecture (Conference)
    3rd Sino-German Workshop 2007, 16.-19.10.2007, Shanghai, China

Publ.-Id: 10550

FIB Anwendungen mit Legierungs-Flüssigmetall-Ionenquellen

Bischoff, L.

Die Erweiterung eines Fokussierten Ionenstrahles (FIB) mit einem Massenseparator (ExB Filter) wird vorgestellt, wodurch Legierungs-Flüssigmetallionenquellen eingesetzt werden können, die eine ganze Reihe von anderen Ionnarten als Gallium bereitstellen können. Die Herstellung solcher Quellen wird gezeigt und anhand ausgewählter Beispiele näher erläutert. Die Massenspektren sowie die Besonderheiten der Handhabung der Ionenoptik werden diskutiert. Anwendungsbeispiele, wie effektives Ionenzerstäuben (sputtern) durch schwere Ionen wie Gold, die Implantation von verschiedenen Spezies zur lokalen Änderung magnetischer oder elektrischer Eigenschaften sowie die Ionenstrahlsynthese von CoSi2 – Nanostrukturen unterstützen das wachsende Interesse an massenseparierten FIB Anlagen in Forschung und Industrie.

Keywords: alloy liquid metal ion sources; FIB; ExB filter; applications

  • Invited lecture (Conferences)
    Crossbeam Workshop, 24.-25.10.2007, Halle/Saale, Germany

Publ.-Id: 10549


Bischoff, L.

Der Begriff “Nanostrukturen” wird definiert und anhand von Beispielen erläutert. Speziell eingegangen wird auf Methoden der Herstellung von Nanostrukturen wie Nanodrähten und Nanocluster mit dem Fokussierten Ionenstrahl (FIB), die im Forschungszentrum Dresden-Rossendorf praktiziert werden. Die Ionenstrahlsynthese von CoSi2 Nanostrukturen wird präsentiert und erläutert. Weiterin wird die 3D Nanostrukturherstellung mittels FIB Implantation und anschließender anisotroper naßchemischer Ätzung gezeigt und an Beispielen demonstriert.

Keywords: nanostructures; focused ion beam nanowires; nanocluster; anisotropic wet chemical etching

  • Invited lecture (Conferences)
    VDE YoungNet Convention 2007, 15.10.07, Dresden, Germany

Publ.-Id: 10548

Metal contamination detection in nickel induced crystallized silicon by spectroscopic ellipsometry

Pereira, L.; Aguas, H.; Beckers, M.; Martins, R. M. S.; Fortunato, E.

The metal (Ni) contamination on crystallized silicon obtained by metal induced crystallizaion (MIC) was estimated by Spectroscopic Ellipsometry (SE) using a new simulation approach. The method employs the addition of Ni as reference for a Bruggeman Effektive Medium Approximation (BEMA) to simulate the optical response of the crystallized silicon.
Samples with different initial metal/silicon ratios were annealed and crystallized. Besides determining thickness, surface roughness and crystalline fraction, this new approach using SE has shown to be sensible to changes on the initial metal thickness used on the crystallization process being able of determining in a quick and non destructive way the Ni concentration inside MIC poly-Si films.
The effectiveness of the obtained results was confirmed by RBS. An accurate determination of the initial Ni thickness that is deposited onto the amorphous silicon prior to crystallization is not possible using a quartz oscillator due to the very low quantity of evaporated materials. A better relation between defferent metal amounts present inside the crystallized films can be obtained by integratingthe Ni distribution in the RBS spectra. The obtained values are proportional to the Ni volume fraction determined by SE ellipsometry proves to be sensible to a metal volume fraction as low as 0.24%, corresponding to an initial Ni average thickness of 0.05 nm.

  • Journal of Non-Crystalline Solids 354(2008)19-25, 2319-2323

Publ.-Id: 10546

Reconstruction of the 3D velocity field of the two-phase bubbly flow around a half moon obstacle using wire-mesh sensor data

Al Issa, S.; Beyer, M.; Prasser, H.-M.; Frank, T.

The TOPFLOW facility at Forschungszentrum Dresden-Rossendorf (FZD) is used to investigate two-phase upward flows in 50 mm diameter and 200 mm dia meter pipes. The facility enables conducting Experiments with air-water and steam-water flows for temperature range of 35-280 °C and pressure range of 1-70 bar. The test pipes are equipped with a wire -mesh sensor, which is a conductivity-based void fraction sensor developed by FZD. It provides void fraction measurements in a matrix of 64×64 points and a measuring frequency of 2.5 kHz. CFD models have to demonstrate their validity in geometries, where phenomena like flow separation, recirculation regions, stagnation points, free jet formation and similar are present. In the experiment described in this paper the flow around an asymmetric, half-moon shaped obstacle put into the large vertical test section of TOPFLOW is studied. In order to obtain information in three dimensions, the obstacle was traversed along the pipe axis. In this way, it was possible to record 2D void fraction distributions at different distances upstream and downstream of the obstacle using a stationary wire-mesh sensor. The fact that the high resolution data supplied by the sensor contains information on all individual bubbles that cross the measuring plane gives the opportunity to extract more detailed information on the flow structure. In particular, from the transit time of bubbles through the sensor plane approximate axial profiles of the liquid velocity were obtained. The lateral movement of the 2D image of bubbles in the measuring plane during their passage was evaluated to reconstruct 2D velocity fields in the environment of the obstacle. In this way, a full three-dimensional vector field of the velocity was provided for code validation. The paper presents the methods of data evaluation, an assessment of the obtained accuracy of the velocity estimation, experimental results and a comp arison to the results of CFD calculations.

Keywords: 3D velocity field; two-phase flows; obstacle; CFD

  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 10545

Synthese und biologische Evaluierung eines 11C-markierten Cyclooxygenase-2 (COX-2) Inhibitors

Knieß, T.; Wüst, F.; Bergmann, R.; Pietzsch, J.


Cyclooxygenase-2 (COX-2) ist ein Enzym das hauptsächlich bei Entzündungen freigesetzt wird, jedoch ist eine Überexpression von COX-2 auch im Zusammenhang mit verschiedenen Tumorerkrankungen beobachtet worden [1]. Obwohl in der Literatur die Markierung von COX-2 Inhibitoren mit PET-Radioisotopen mehrfach beschrieben worden ist [2-5], existieren bis heute wenig Untersuchungen über das Potential dieser Substanzen zur Tumordarstellung mittels PET. Wir berichten über die Radiosynthese sowie erste Ergebnisse der radiopharmakologischen und biologischen Evaluierung von 1-(4-[11C]Methoxyphenyl)-2-(4-methylsulfonyl)-1-cyclopenten als 11C-markierter COX-2 Inhibitor.


Die Radiomarkierung wurde als eine 11C-Methylierungsreaktion des entsprechenden Desmethyl-Präkursors mit [11C]CH3I in DMF in einem TRACERLab FXC Synthesizer® durchgeführt. Studien zur Bioverteilung wurden an der Wistar-Ratte und Kleintier-PET Untersuchungen an HT-29 tumortragenden Mäusen mittels eines micro-PET®P4 Scanners durchgeführt.


Die Radiomarkierung des Präkursors 1-(4-Hydroxyphenyl)-2-(4-methylsulfonyl)-1-cyclopenten mit [11C]CH3I erfolgte 3 Minuten bei 60°C in DMF/wässriger NaOH (siehe Abb.). Nach semi-preparativer HPLC Reinigung und Festphasenextraktion wurde der 11C-markierte COX-2 Inhibitor in 12-14% zerfallskorrigierter radiochemischer Ausbeute mit einer spezifischen Aktivität von 30-40 GBq/µmol (EOS) in radiochem. Reinheit >97% isoliert. Bioverteilungsexperimente zeigten eine Anreicherung des [11C]-COX-2 Inhibitors in der Leber, den Nebennieren und braunem Fettgewebe von 0.6 - 0.8+/-0.1 %ID/g. In Kleintier-PET Untersuchungen an HT-29 tumortragenden Mäusen wurde ein Tumor/Muskel Verhältnis von 1.7+/-0.2 1h p.i.. bestimmt.


Erste radiopharmakologische Untersuchungen zeigen eine Anreicherung des 11C-markierten COX-2 Inhibitors am HT-29 Tumor. Aufgrund der hohen Lipophilie der Verbindung (logP=4.2) erfolgt ebenfalls eine Akkumulation in fettreichem Gewebe mit dem Ergebnis einer hohen unspezifischer Bindung. Weitere Experimente an verstärkt COX-2 exprimierenden Zellen sowie blocking/non-blocking Studien sind geplant.


[1] E. F.J. De Vries, Current Pharmaceutical Design 12 (2006) 3847-3856.
[2] E.F.J. De Vries, J. Nucl. Med. 44 (2003) 1700-1706.
[3] T.J. Mc Carthy, J. Nucl. Med. 43 (2002) 117-124.
[4] V.J. Majo, Bioorg. Chem. Lett. 15 (2005) 4268-4271.
[5] T. Toyokuni, Bioorg. Chem. Lett. 15 (2005) 4499-4702.

  • Lecture (others)
    15. Arbeitstreffen der AG Radiochemie/Radiopharmazie, 27.-29.09.2007, Morschach, Switzerland

Publ.-Id: 10544

Superconducting RF Gun cavities for large bunch charges

Volkov, V.; Floettmann, K.; Janssen, D.

The first electron beam of an RF gun with a 3.5 cell superconducting cavity is expected in July 2007 in FZD. This cavity has been designed for small bunch charges. In this paper we present the design of a similar cavity and of 1.5 cell gun cavities for large bunch charges. For a charge of 2.5 nC, which is the design value of the BESSY-FEL, and a bunch length of 21 ps a projected transverse emittance less then 1 πμ has been obtained (without thermal emittance).

  • Contribution to proceedings
    Particle Accelerator Conference 07 (22nd PAC Conference), 25.-29.06.2007, Albuquerque, New Mexico
    Proceedings of PAC 2007, 1-4244-0917-9/07, 4150-4152

Publ.-Id: 10542

First Experiences with the FIR-FEL at ELBE

Lehnert, U.; Michel, P.; Seidel, W.; Staats, G.; Teichert, J.; Wünsch, R.

We show the design and the parameters of operation of the long-wavelength (U100) FEL at ELBE. First lasing has been shown in August, 2006. Since then, the laser has undergone thorough commissioning and is available for user experiments since fall, 2006. Besides in-house users the IR beam is available to external users in the FELBE (FEL@ELBE) program witch is a part of the integrated activity on synchrotron and free electron laser science in the EU. At the beginning of 2007 lasing in the full designed wavelength range from 20 µm to 200 µm was demonstrated. The laser power typically reaches several Watts in cw operation but drops for very long wavelengths depending on the size of the used out-coupling hole. However, there exists a serious problem with small gaps in the wavelength spectrum. We attribute this behaviour to the transmission characteristics of the overmoded partial waveguide used from the undulator entrance to the first mirror.

  • Poster
    29th International Free Electron Laser Conference FEL 2007, 26.-31.08.2007, Novosibirsk, Russia
  • Open Access Logo Contribution to proceedings
    29th International Free Electron Laser Conference FEL 2007, 26.-31.08.2007, Novosibirsk, Russia
    Proceedings of FEL 2007


Publ.-Id: 10541

Infrared Radiation and Bremsstrahlung at ELBE

Michel, P.

The radiation source ELBE (Electron Linac of high Brilliance and low Emittance) at Forschungszentrum Dresden-Rossendorf is based on a superconducting linac that produces a high power continuous wave (cw) electron beam up to 40 MeV and 1 mA. Electron beams with variable bunch charges up to 80 pC and variable repetition rates up to 260 MHz are produced using a pulsed thermionic DC gun followed by a two-stage RF bunching system. Two cryomodules each containing two 9-cell RF-cavities (1.3 GHz) accelerate the electrons to about 40 MeV. The linac is used to drive two free-electron lasers producing infrared radiation from 3 to 200 microns wavelength. Additionally, from several conversion targets, MeV-bremsstrahlung (< 20 MeV) and X-rays (10-100 keV) from electron channelling are generated. Presently facilities for neutron and positron beams are commissioned at ELBE. The superconducting RF accelerator technology used, details of the machine instrumentation and several kinds of electron beam diagnosis will be described. In particular the generation of Infrared radiation and Bremsstrahlung and some examples of their applications will be discussed.

  • Invited lecture (Conferences)
    3. Türkischer Beschleuniger Kongress, 17.-19.09.2007, Bodrum, Türkey

Publ.-Id: 10540

Reconstruction of the Field Distribution by Measuring the Fundamental Passband Frequencies of the Rossendorf SRF-Gun Cavity

Arnold, A.; Büttig, H.; Jannsen, D.; Lehnert, U.; Michel, P.; Möller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Teichert, J.; Xiang, R.; Matheisen, A.; Horst, B. V. D.; Stephan, J.; Lehmann, W.-D.; Kamps, T.; Volkov, V.

In contrast to the TESLA cavities the shapes and the mechanical stiffness of the four SRF-Gun cells differ from each other. Furthermore the axis field to achieve a “flat” surface field over all cells has a profile of 60% in the first and 100% in the TESLA like cells, respectively. Due to the different mechanical properties one tuner for the half cell and one for the three TESLA cells are assembled. Both of them are equipped to manipulate the field of the cavity during the adjustment of the tuner bias and later during operation. Hence it is very important to determine the fields inside the cleaned and closed cavity.
The poster presents a method that provides the field profile by measuring the passband frequencies based on the well known equivalent circuit for cell coupled cavities. At least one complete field and frequency measurement prior the last cleaning is necessary. The comparison with real measured values demonstrates the accuracy of the predicted field distribution within a range of 2%.

  • Poster
    13th International Workshop on RF Superconductivity (SRF2007), 14.-19.10.2007, Peking, China
  • Contribution to proceedings
    13th International Workshop on RF Superconductivity (SRF2007), 14.-19.10.2007, Peking, China
    Reconstruction of the Field Distribution by Measuring the Fundamental Passband Frequencies of the Rossendorf SRF-Gun Cavity, 689-691


Publ.-Id: 10539

A high-brightness SRF photo injector for FEL light sources

Arnold, A.; Büttig, H.; Janssen, D.; Lehnert, U.; Michel, P.; Möller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Teichert, J.; Xiang, R.; Kamps, T.; Lipka, D.; Marhauser, F.; Klemz, G.; Will, I.; Lehmann, W. D.; Stephan, J.; Volkov, V.

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 photo guns 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 right photocathode type, its life time and possible cavity contamination, the difficulty of coupling high-average power into the gun, and beam excitation of higher order cavity modes. But in combination with SRF linacs, the SRF guns will be the best solution for high average currents. Continuous wave operation is simple to achieve. Thus, several R&D projects of SRF-gun have been launched.
The talk will give an overview of the progress of the SRF photoinjector development. In detail, the technical concept, performance, and status of the Rossendorf superconducting rf gun project, a collaboration of BESSY, DESY, MBI and FZD, will be presented. Main design parameters of this SRF gun are a final electron energy of 9.5 MeV, an average current of 1 mA, 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 full cells with TESLA geometry, a specially designed half-cell in which the photo cathode is placed, and a choke filter in order to prevent rf losses at the cathode side of the cavity. The photocathode with a Cs2Te photoemission layer is normal-conducting and are 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, a titanium He tank with two-phase supply tube. A heater pot in the He input port will be used for He level control. The 10-kW fundamental power coupler is adopted from the ELBE cryomodule. The gun will be installed at the ELBE superconducting linear accelerator. 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.

Keywords: Superconductivity; Radio Frequency, Photoelectron Injector; SRF Gun; Cavity; Laser

  • Invited lecture (Conferences)
    International Workshop on Frontiers in FEL Physics and Related Topics, 08.-14.09.2007, Elba Island-La Biodola, Tuscany, Italy


Publ.-Id: 10538

Syntheses and spectroscopic characterization of uranium(VI) silicate minerals

Lehmann, S.; Geipel, G.; Foerstendorf, H.; Bernhard, G.

In this study, the secondary uranium(VI) silicate minerals boltwoodite, sodium boltwoodite and uranophane were synthesized. Sodium boltwoodite was successfully obtained following a new reaction procedure. Their analytical characterization was carried out by means of inductively coupled plasma mass spectrometry and atomic absorption spectroscopy, scanning electron microscopy, X-ray powder diffraction, differential thermal analysis combined with thermogravimetry and infrared spectroscopy. Furthermore, the fluorescence behaviour was measured using time-resolved laser fluorescence spectroscopy. Herewith, the fluorescence properties of the three silicious uranyl phases were determined at room temperature.

Keywords: uranium(VI); silicate; minerals; spectroscopy; TRLFS

Publ.-Id: 10537

Measurement of fluid distributions in a rotating fluid coupling using high resolution gamma ray tomography

Hampel, U.; Hoppe, D.; Bieberle, A.; Kernchen, R.; Diele, K.-H.; Schleicher, E.; Da Silva, M. J.; Zippe, C.

Gamma ray tomography has been used to visualize fluid distributions in a rotating fluid test coupling at different operation points. The gamma ray CT system comprises a Cs-137 isotopic source and a high resolution gamma ray detector. By means of an angle synchronized tomographic data acquisition technique we were able to produce sharp two-dimensional slice images of the fluid distribution inside the coupling at full pump rotation of up to 780 rpm and lower turbine speeds. Three-dimensional images have been synthesized from different scans along the coupling axis. The data has been used to assess the hydraulic behavior of the fluid coupling and greatly improves our understanding of the flow structure development and its implications on torque transfer in such a device.

Keywords: gamma ray tomography; fluid coupling; two-phase flow measurement

Publ.-Id: 10536

Channeling radiation X-ray source at ELBE

Wagner, W.; Pawelke, J.; Azadegan, B.; Sobiella, M.; Steiner, J.

An intense channeling radiation X-ray source installed at ELBE is presented.

Keywords: channeling radiation; X-rays

  • Poster
    VII International Symposium "RREPS-07" Radiation from Relativistic Electrons in Periodic Structures, 24.-28.09.2007, Prague, Czech Republic
  • Poster
    International Conference on Charged and Neutral Particles Channeling Phenomena (Channeling 2008), 25.10.-01.11.2008, Erice, Sicily, Italy

Publ.-Id: 10535

Laser-Teilchenbeschleunigung: (1) Heller wirds schneller, (2) relativistische Optik

U. Schramm; R. Sauerbrey; D. Rathje

Heller wird's scheller
Richtet man intensives Laserlicht auf Materie, so werden geladene Teilchen freigesetzt und auf hohe Energien beschleunigt. Für eine kontrollierte Laser-Teilchenbeschleunigung sind zwar noch einige technologische Hürden zu meistern, erste Anwendungen in der Medizin sind aber absehbar.
Relativistische Optik
Wenn das intensive Licht moderner Hochleistungskurzpulslaser mit Materie in Wechselwirkung tritt, reichen die Gesetze der klassischen Optik zur Beschreibung nicht mehr aus. Vielmehr muss man sich der relativistischen Optik zuwenden, deren Effekte auch zur Beschleunigung von Teilchen genutzt werden können.

Keywords: relativistic optics; laser particle acceleration; tutorial

Publ.-Id: 10534

Microstructure of nitrogen implanted stainless steel after wear experiment

Manova, D.; Hirsch, D.; Richter, E.; Mandl, S.; Neumann, H.; Rauschenbach, B.

Outstanding wear resistance of austenitic stainless steel after nitrogen insertion and formation of expanded austenite in the temperature range below 420 degrees C is a well established phenomena. However, detailed information on the wear mechanism for the modified surfaces is still missing. This paper presents the results of wear experiments performed in a dry oscillating geometry against a WC ball (diameter 3 mm, load 3 N), together with metallographic investigations of the resulting cross-sections, both with and without nitriding. Comparisons with calculated stress distributions indicate that those nitrided samples showing a specific wear reduction by a factor of about 100 were subjected to a combination of stress maxima within the surface layer and below the layer in the bulk material.

  • Surface & Coatings Technology 201(2007)19-20, 8329-8333

Publ.-Id: 10533

Combining DFT calculations , EXAFS, IR, and UV-vis spectroscopy

Tsushima, S.

no abstract for this publication

Keywords: DFT; EXAFS

  • Invited lecture (Conferences)
    ACTINET workshop "How can we improve coupling theoretical chemistry with X-ray absorption spectroscopy?", 11.-12.10.2007, Avignon, France

Publ.-Id: 10531

Interaction of uranium(VI) with lipopolysaccharide

Barkleit, A.; Moll, H.; Bernhard, G.

Bacteria have a great influence on the migration behaviour of heavy metals in the environment. Lipopolysaccharides form the main part of the outer membrane of Gram-negative bacteria. We investigated the interaction of the uranyl cation (UO22+) with lipopolysaccharide (LPS) from Pseudomonas aeruginosa by using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy (TRLFS) over a wide pH and concentration range. Generally, LPS consists of a high density of different functionalities for metal binding such as carboxyl, phosphoryl, amino and hydroxyl groups. The dissociation constants and corresponding site densities of these functional groups were determined using potentiometric titration. The combination of both methods, potentiometry and TRLFS, show that at an excess of LPS uranyl phosphoryl coordination dominates, whereas at a slight deficit on LPS compared to uranyl, carboxyl groups also become important for uranyl coordination. The stability constants of one uranyl carboxyl complex and three different uranyl phosphoryl complexes and the luminescence properties of the phosphoryl complexes are reported.

Keywords: Uranyl; complexation; time-resolved laser-induced fluorescence spectroscopy; TRLFS; LPS

Publ.-Id: 10530

Evolution of ion induced ripple patterns on silicon surfaces

Keller, A.; Facsko, S.; Möller, W.

It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. The ripples produced in this way are oriented either parallel or normal to the projection of the ion beam and their wavelength scales with ion energy. These structures were found on a large variety of materials, such as semiconductors, metals, and insulating surfaces [1]. The formation and early evolution of the ripple patterns can be qualitatively reproduced by a linear continuum equation derived by Bradley and Harper [2]. However, at longer times nonlinear terms have to be taken into account, leading to nonlinear models based on the Kuramoto-Sivashinsky equation [3].
In this work, we studied the evolution of ion induced ripple patterns on Si(100) during sputtering at sub-keV energies by means of ex-situ AFM. At a certain stage of the evolution, larger corrugations appear and superpose the ripple pattern. With increasing time, these corrugations get more pronounced until they become the dominating feature of the surface. The morphology of the surface was characterized by determining the dynamic scaling exponents in direction normal and parallel to the ripples. Different scaling behavior is found for the ripples and the corrugations, respectively.
In order to gain better understanding of the evolution of the surface morphology, simulations of the damped Kuramoto-Sivshinsky equation [4] were performed, finding good qualitative agreement. Quantitatively, however, the simulations fail to reproduce the experimentally observed scaling behavior.

[1] U. Valbusa et al., J. Phys.: Condens. Matter 14 (2002), 8153
[2] R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6 (1988), 2390
[3] M. A. Makeev et al., Nucl. Inst. Meth. Phys. Res. B 197 (2002), 185
[4] S. Facsko et al., Phys. Rev. B 69 (2004), 153412

  • Lecture (Conference)
    Nanopatterning via Ions, Photon beam and Epitaxy, 23.-27.09.2007, Sestri Levante, Italy

Publ.-Id: 10529

The effect of irradiation-induced damage on the hardening embrittlement of RPV steels

Lambrecht, M.; Almazouzi, A.; Hernandez Mayoral, M.; Gomez Briceno, D.; Meslin, E.; Barbu, A.; Pareige, P.; Radiguet, B.; Bergner, F.; Ulbricht, A.

The effect of irradiation-induced damage on the hardening of RPV steels is evaluated on the basis of SANS, TEM, PAS and TAP applied to Fe-based model alloys. Composition (especially Cu, Mn and Ni) and neutron dose of these alloys were systematically varied. The applied methods were utilized in order to separate the contributions to the irradiation-induced yield stress increase caused by different type of defects including dislocation loops, vacancy-type clusters, Cu-rich precipitates and Ni/Mn-rich precipitates.

  • Poster
    International School on Modelling of Irradiation Damage (ISMID), 01.-05.10.2007, Rochehaut sur Semois, Belgium

Publ.-Id: 10528

Novel photocatalytic nanomaterials for environmental purposes based on bacterial cells and S-layer proteins

Raff, J.; Pollmann, K.; Scholz, A.

  • wird nachgereicht
  • Poster
    1st International Workshop Aquatic Nanosciences and Nanotechnology, 09.-11.12.2007, Wien, Austria

Publ.-Id: 10527

Cathodoluminescence of Ion-Implanted Silica Layers

Salh, R.; Fitting-Kourkoutis, L.; Schmidt, B.; Fitting, H.-J.

Scanning electron microscopy (SEM) and cathodoluminescence (CL) in combination with scanning transmission electron microscopy (STEM) have been used to investigate thermally grown amorphous silicon dioxide layers implanted isoelectronically with group IV ions (C+, Si+, Ge+, Sn+, Pb+) as well as with group VI ions (O+, S+, Se+).

Keywords: ion implanted SiO2; SEM; CL; STEM

  • Microscopy and Microanalysis 13(2007)Suppl. 3, 328-329

Publ.-Id: 10526

Fabrication of self-assembled L10 ordered FePt nanoislands by conventional DC magnetron sputtering

Cantelli, V.; von Borany, J.; Grenzer, J.

L10 ordered c-axis oriented FePt thin films belong to the most promising ferromagnetic materials for future magnetic storage media. The layer coercivity can be significantly improved if changing from a homogeneous to granular film morphology, or even to arrays of FePt nanoislands.
This contribution describes the formation of self-assembled FePt nanoislands by conventional DC magnetron sputtering deposition on single-crystalline Si(001) or amorphous SiO2/Si substrates. The deposition was performed with substrate temperature of 320 °C and a working pressure of 0.4 Pa. In these conditions the deposition rate for FePt is about 0.4 Å/s, leading to an equivalent film thickness of 6 nm. An ultra thin Ag buffer layer, deposited in the same working conditions but with a deposition rate of about 1 Å/s, that, because of its nanoparticulate morphology, is supporting the islands formation.
The well-separated FePt islands exhibit a quite regular size of typical 20 – 30 nm, for both employed substrates. X-ray diffraction analysis reveals the existence of L10 ordered FePt phase. However, it is noteworthy that the islands formation is obtained both for crystalline and amorphous substrate which is of significant practical relevance. The enhanced coercivity of patterned FePt films with respect to homogeneous FePt layers has been confirmed by SQUID measurements. The formation of the nanoisland structure is discussed in terms of the adatom surface mobility, the influence of energetic ions and the ratio of surface to stress-energy during thin film deposition.

Keywords: FePt; nanoislands; Dc amgnetron sputtering; XRD

  • Poster
    International Conference on Nanoscale Magnetism - ICNM-2007, 25.-29.06.2007, Istanbul, Turkey

Publ.-Id: 10525

Generation and detection of THz radiation with scalable antennas based on GaAs substrates with different carrier lifetimes

Winnerl, S.; Peter, F.; Dreyhaupt, A.; Zimmermann, B.; Wagner, M.; Schneider, H.; Helm, M.; Köhler, K.

We report on scalable photoconductive antennas for both emission and detection of THz radiation. The concept yields THz emitters with high efficiencies for the conversion of near infrared into far infrared radiation and provides detectors which do not require tight focusing of both the THz beam and the near infrared gating beam. GaAs substrates implanted with dual energy implants of N+ and As+ ions of various doses are compared with semi-insulating and low-temperature-grown GaAs. We discuss which material properties are desirable for emitters and detectors and identify which material is optimal as either emitter or detector substrate. Best results for detectors are found for implanted samples with doses in the 1013 cm-2 range for GaAs:N and for LT-GaAs. Best emitters for typical excitation conditions with a Ti:sapphire oscillator system are based on SI-GaAs

Keywords: Terahertz; photoconductive antenna; ion implantation

  • IEEE Journal of Selected Topics in Quantum Electronics 14(2008), 449-457

Publ.-Id: 10524

Air/water counter-current flow experiments in a model of the hot leg of a pressurised water reactor

Vallee, C.; Deendarlianto; Beyer, M.; Lucas, D.; Carl, H.

Different scenarios of small break Loss of Coolant Accident (LOCA) for pressurised water reactors (PWR) lead to the reflux-condenser mode in which steam enters the hot leg from the reactor pressure vessel (RPV) and condenses in the steam generator. A part of the condensate flows back towards the RPV in counter current to the steam. During the reflux-condenser mode, a counter-current flow limitation (CCFL) must be prevented because this would limit the core cooling. The simulation of CCFL conditions, which is dominated by 3D effects, requires the use of a computational fluid dynamics (CFD) approach. These methods are not yet mature and have to be validated before they can be applied to nuclear reactor safety. Therefore, dedicated experimental data is needed with high resolution in space and time.

In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, the "hot leg model" was built at Forschungszentrum Dresden-Rossendorf (FZD). This setup is devoted to optical measurement techniques, therefore, a flat test-section design was chosen with a width of 50 mm. The test-section outlines represent the hot leg of a German Konvoi PWR at a scale of 1:3, which corresponds to a channel height of 250 mm in the straight part of the hot leg. The test-section is mounted between two separators, one simulating the reactor pressure vessel and the other is connected to the steam generator inlet chamber. This allows to perform co-current as well as counter-current flow experiments. Moreover, the hot leg model is built in the pressure vessel of the TOPFLOW facility of FZD, which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the vessel. Therefore, the test section can be designed with thin materials and equipped with big size windows like in the hot leg model.

The presented air/water experiments focus on the flow structure observed in the region of the riser and of the steam generator inlet chamber at room temperature and pressures up to 5 bars. The performed high-speed observations show the evolution of the stratified interface and the distribution of the two-phase mixture (droplet and bubbles). Counter-current flow limitation, or the onset of flooding, was found by analysing the water levels measured in the separators. A confrontation with the images indicates that the initiation of flooding coincides with the formation of slug flow. Furthermore, the CCFL data was compared with similar experiments and empirical correlations available in the literature. The agreement of the CCFL curve is good and indicate that the data is relevant for CFD validation purposes. The zero penetration was found at lower values of the Wallis parameter than in most of the previous work, which can be attributed to the rectangular geometry of the hot leg model.

Keywords: hot leg; pressurised water reactor; PWR; two-phase flow; counter-current flow; counter-current flow limitation; CCFL

  • Contribution to proceedings
    ICONE 16 - International Conference on Nuclear Engineering, 11.-15.05.2008, Orlando, Florida, USA
    Paper ICONE16-48374
  • Lecture (Conference)
    ICONE 16 - International Conference on Nuclear Engineering, 11.-15.05.2008, Orlando, Florida, USA
  • Journal of Engineering for Gas Turbines and Power - Transactions of the ASME 131(2009)2, 022905
    DOI: 10.1115/1.3043816
    Cited 11 times in Scopus

Publ.-Id: 10523

Structure and lattice location of Ge implanted 4H-SiC

Kups, T.; Tonisch, K.; Voelskow, M.; Skorupa, W.; Konkin, A. L.; Pezoldt, J.

Pseudomorphic 4H-(Si1-xC1-y)Gex+y solid solutions were formed by ion implantation at 600°C and subsequent rapid thermal annealing if the implantation dose is kept below 10%. At higher doses and subsequent annealing 3C-SiC inclusion and SiGe precipitates are formed. Transmission electron microscopy investigations accompanied with “atomic location by channeling enhanced microanalysis” of the annealed samples revealed an increasing Si lattice site incorporation of Ge.

Keywords: ion implantation; solid solution; germanium; TEM; HXRD; EPR

  • Lecture (Conference)
    ICSCRM2007 - International Conference on Silicon Carbide and Related Materials 2007, 14.-19.10.2007, Otsu, Japan
  • Materials Science Forum 600-603(2009), 623-626

Publ.-Id: 10522

High intensity capillary gas ion source for accelerator applications

Akhmadaliev, S.; Bischoff, L.

An ion source based on the field ionization of a gas flowing out from a small capillary was developed and investigated. The source consists of a metallic nozzle with a small hole of 5-20 µm in diameter and the tip radius of about 20-50 µm, a tungsten needle inside the nozzle, and an extractor. If the nozzle is sharp enough the ion source can also operate without a tungsten tip. The gas was introduced into the nozzle under the pressure of 0.1-1 bar leading to the rest gas pressure near the source in the vacuum chamber in the range of 10-4 - 10 -5 mbar. Also liquids can be ionized in the ion source. Argon, helium, nitrogen and organic liquids like alcohol and acetone were used for measurements. I-V characteristics of the source, energy distributions and mass spectra of the emitted ions were investigated in a test stage. An emission current up to several hundreds of µA could be emitted, corresponding to current densities up to 20-50 A/cm 2.
The ion source shows a long term stable operation with noble gases (several days) in the vacuum test stage. This source can be used for high and low energy micro-beams as well as in focused ion beam systems. In combination with a charge-exchange canal it can be also applied in tandem accelerators.

Keywords: Gas ion source

  • Poster
    ECAART9 - 9th European Conference on Accelerators in Applied Research and Technology, 03.-07.09.2007, Florence, Italy

Publ.-Id: 10521

Selenite Retention by Iron Oxy-Hydroxides: Role of Adsorption, Reduction and Dissolution/Co-Precipitation

Missana, T.; Alonso, U.; Scheinost, A. C.; Granizo, N.; García-Gutiérrez, M.

Goethite and magnetite are naturally occurring iron oxides with very different properties in terms of microstructure, surface area and water solubility. In addition, the presence of FeII in magnetite can be of importance in the retention of redox-sensitive radionuclides if reduction reactions are triggered. The study of the radionuclide retention made in parallel with both oxides is of great help to get insight on the underlying mechanisms.
Selenite (SeO32-) sorption onto goethite and magnetite was investigated by batch experiments and XAS techniques to evaluate the role played by adsorption, reduction and dissolution/co-precipitation processes. Sorption was studied as a function of the pH (2-10), ionic strength, solid to liquid ratio and Se concentration (1•10-10 – 10-3 M), both under oxic and anoxic conditions.
Sorption onto both oxides was independent on the ionic strength and decreased when the pH increased but the shape of the sorption edges was not totally comparable.
Under oxic conditions, the results obtained for goethite were very similar to those previously obtained by other authors, and all the goethite data could be simulated considering the formation of inner-sphere complexes between selenite and the iron oxide surface sites (SOH). By contrast, the sorption edges of selenite on magnetite presented features that could not be fit considering the same simple model.
XANES analysis performed on samples obtained at different pH, discarded that these “anomalies” were the consequence of selenite reduction at the magnetite surface or of precipitation of metallic selenium.
To explain the experimental sorption results in magnetite it was necessary to account for the oxide dissolution at acidic pH, the formation of iron-selenite aqueous species and their complexation with SOH sites, apart from the formation of inner-sphere complexes between selenite and the iron oxide surface sites. In addition, at higher selenite concentration (>1•10-4 M) and pH< 5-6 the precipitation of ferric selenite was observed to be the dominating retention process, in agreement with EXAFS analyses.
The sorption behaviour on magnetite was similar under oxic and anoxic conditions. With goethite, increased sorption at very acidic pH was observed under anoxic conditions. This fact can be explained by the increase of goethite solubility when the pCO2 decreases, as reported in the literature.
These results evidenced the importance of dissolution and co-precipitation processes in the iron oxides/selenite systems.

  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 71-71

Publ.-Id: 10519

Sorption of U(VI) on Multiwall Carbon Nanotubes

Schierz, A.; Zaenker, H.; Bernhard, G.

Carbon nanotubes (CNTs) are attracting the attention of many scientists due to their unique structural, mechanical, electronic, chemical and biological properties [1]. Large efforts have been attended to improving their synthesis, determining their structure, measuring their properties and finding applications.
The oxidation process is of great importance for CNT application, since it is necessary for CNT purification and functionalization [2]. Acid treatment was recommended as a method of purification [2]: it removes the non-fullerene components and converts the metal catalyst to a more soluble form. Additionally the oxidation causes chemical and/or structural changes on CNTs, which modify their properties.
Due to their hollow and nanosized structure the use of CNTs as adsorbent for pollutants such as dioxin, Cd2+, Pb2+, Am3+ [3, 4, 5] for environmental remediation purposes has been considered. Li et al. [2003] reported that HNO3 oxidized CNTs show a higher sorption capacity for heavy metal ions compared with other adsorbents such as activated carbon. These studies suggested that CNTs may be a promising adsorbent for use in environmental protection. The high cost of CNTs still limits their practical use.
This study is aimed at gaining information on both the properties of the CNTs as a potential adsorbent material in water purification and the behavior of the CNTs as potential carriers of pollutants in the case of their accidental release to the environment. Two aspects are considered: the changes in surface properties after acid treatment and the influence of acid treatment on the sorption of U(VI).
Different methods (FT-IR, SEM, BET, potentiometric titration) were used to study surface properties of Multi Wall CNTs after acid treatment with HNO3/H2SO4. We observed that the acid treatment has a significant effect on the surface properties but not on the morphology of the CNTs.
In this work we report the first data on CNTs as an adsorbent for U(VI) removal. The acid treatment has a great impact on the adsorption capacity of CNTs for U(VI) at different pH values. The sorption capacity of the modified CNTs increases by almost one order of magnitude due to the modification. Under the given conditions, precipitation of U(VI) from solution could be excluded, i.e. the major adsorption mechanism is obviously surface complexation of the uranyl ion. It is well known that U(VI) forms strong complexes with carboxylic groups [6] which have been identified as the major functional surface groups of our modified CNTs.
Investigations into the effect of acid treatment of CNTs on their dispersibility in aqueous solutions simulating natural ground and surface water as well as the transport behavior of CNTs in porous media are underway.

Reference: [1] Tasis et al. 2006, Chem. Rev., 106, 1105; [2] Chiang et al. 2001, J. Phys. Chem. B, 105, 1157; [3] Long and Yang 2001, J. Am. Chem. Soc., 123, 2058; [4] Li et al. 2003, Carbon, 41, 1057; [5] Wang et al. 2005, Environ. Sci. Technol., 39, 2856; [6] Moll et al. 2003, Radiochim. Acta, 91, 11.

Keywords: Carbon nanotubes; manufactured nanoparticles; surface properties

  • Lecture (Conference)
    1st International Workshop Aquatic Nanoscience & Nanotechnology, 09.-11.12.2007, Wien, Austria

Publ.-Id: 10518

Elastic properties and electronic structure of vanadium silicides - a density functional investigation

Thieme, M. B.; Gemming, S.

Vanadium and silicon form several binary compounds; the most well characterized structures have the compositions V:Si= 3:1, 5:3, 6:5, 1:2. Spin-polarized density functional band-structure calculations with the PAW-method have been carried out for the stable binary compounds in the system Si-V. As many rare earth and early transition metals belong to the class of refractory materials, the study focuses on the ground state structures and their stabilities determining the elastic properties. The magnetic properties were investigated, as well, because structurally related Si-Mn compounds exhibit magnetism. As result, all investigated silicides are refractory, hard, metallic materials and no magnetism can be found in the ground state

Publ.-Id: 10517

Ni implanted ZnO single crystals: correlation between nanoparticle formation and defect structure

Zhou, S.; Potzger, K.; Kuepper, K.; Grenzer, J.; Helm, M.; Arenholz, E.; Denlinger, J. D.; Fassbender, J.

We show that metallic secondary phase formation inside ZnO(0001) single crystals implant-doped with Ni at an atomic concentration of 5 % can be suppressed. All the Ni ions are in 2+ valence state after mild post-annealing. The suppression is achieved by means of annealing of the crystals in high vacuum prior to implantation and is correlated with structural defects of the ZnO single crystals. The observed ferromagnetic properties of the pre-annealed crystals degrade at ambient temperature within several days.

Keywords: DMS; ZnO

  • Journal of Applied Physics 103(2008), 043901

Publ.-Id: 10516

Nanocluster evolution in Ge+ ion implanted Ta2O5 layers

Peeva, A.; Kalitzova, M.; Beshkov, G.; Zollo, G.; Vitali, G.; Skorupa, W.

Ion implantation-induced nanoclusters were synthesized in reactive sputtered Ta2O5 films by Ge+ implantation and subsequent annealing. The effects of ion fluence and post-implantation thermal treatment on the kinetics of the nanoclustering were investigated. Ge+ ions with energy of 40 keV and fluences of 5 × 1015, 1 × 1016 and 5 × 1016 cm− 2 were implanted in the Ta2O5 layers at room temperature. The samples were thermally treated by rapid thermal annealing in vacuum at 700 °C and 1000 °C for 30, 60 and 180 s. Structural studies of all samples were done by Cross-sectional Transmission Electron Microscopy in diffraction and phase contrast mode. Under optimized conditions (high implantation fluence, subsequent annealing) nanoclusters are formed around the projected ion range of the implanted Ge+ ions. The structure of the implanted Ta2O5 matrix changes from amorphous to orthorhombic when the annealing was performed at 1000 °C. Although the Ta2O5 matrix crystallizes, no evidence is obtained for crystallization of the embedded nanoclusters even after annealing at 1000 °C.

Keywords: ion implantation; nanocluster; tantalum oxide; germanium; crystallization; cross-sectional transmission electron microscopy

Publ.-Id: 10515

Silicon-based MOS light emitters using rare earth implantation

Skorupa, W.

An overview on recent results regarding ion beam processing for silicon-based light emission using rare earths is presented

Keywords: rare earths; ion implantation; silicon-based light emission

  • Invited lecture (Conferences)
    Silicon to Light & Light to Silicon - Materials, Characterisation and Applications, 09.-10.07.2007, Halle, Germany

Publ.-Id: 10514

A new casting technique for the restoration of lead pipes in old organs

Skorupa, W.; Rossner, M.; Neelmeijer, C.; Eichhorn, F.; von Borany, J.; Werner, H.; Eule, A.-C.; Schucknecht, T.; Klemm, V.; Rafaja, D.

We have developed a new casting technique basing on old recipes from the 17. and 18. century to restaurate old lead pipes as well as to produce new pipes approaching the quality of the old ones. Materials studies of old and new metal probes were performed by metallography, scanning electron microscopy, and x-ray diffraction analysis. Different casting variants as well as the influence of hammering the casted metal plates onto the microstructure were investigated. Moreover we investigated by PIXE (Proton induced X-ray Emission) the residuals of old glue on the old pipes which remaining from tin foil adornment. In this manner we positioned the pipe directly in front of an external ion beam and analysed it without cutting pieces away from the metal pipe.

Keywords: lead casting; organ pipes; PIXE; metallography; scanning electron microscopy; x-ray diffraction analysis

  • Lecture (Conference)
    E-MRS 2007 Spring Meeting, Workshop: Science & Technology of Cultural heritage Materials : Art conservation and Restoration, 28.05.-01.06.2007, Strasbourg, France

Publ.-Id: 10513

Echtzeit-in-situ-Messung der Oberflächenbelegung einer Magnetron-Kathode bei der reaktiven Sputter-Abscheidung

Güttler, D.

Reactive Sputtering is a widely used technique in processing of thin compound films. Such films can be sputtered from metal targets, which are comparatively cost efficient. Also the fact that sputtering from metal targets can ccur in the dc mode reduces the cost of the sputtering equipment. To keep the deposition process stable, its necessary to know the effects of target poisoning including its hyteresis behavior. The aim of this work was to nvestigate the evolution of reactive gas coverage on a titanium magnetron target surface, by real time, in-situ ion beam analysis during magnetron sputtering. A cylindrical 2 inch magnetron was used for reactive sputtering of TiN. It was operated in an Ar/N2 gas mixture at achamber pressure of about 3∙10-3 mbar. The argon/nitrogen flux ratio was variated between 0 and 20%. The nitrogen concentration on the target was determinated using the 14N(d, α)12C, nuclear reaction at a deuterium beam energy of 1.8 MeV. Depending on the adjusted nitrogen flow the target incorporation varies between 0 and about 1∙1016 N∙cm-2. Further the expected hysteresis behaviour ofnitrogen partial pressure, target voltage and nitrogen concentration at increasing/decreasing nitrogen gas flow is confirmed. The lateral distribution of nitrogen was measured across the diameter of target surface. In the zone of higher erosion (the "race track") the nitrogen concentration is 50% lower than in the middle or the edge of the target. A deposition zone in the center of the target could not be detected. By increasing the nitrogen flow into the chamber a saturation in nitrogen content in the target was found at an Ar/N2 flow ratio of about 10%. Assuming nitrogen implantation with a depth of 2.5 nm under the influence of typical target voltage during magnetron sputtering, this saturation is at a concentration value where stoichiomtric TiN is formed. Within the precision of the measurements, a mobile fraction of nitrogen could not determined. The concentration in the target remains unchanged after switching off the magnetron.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-411 2004
    ISSN: 1437-322X


Publ.-Id: 10512

Formation of metallic clusters in oxide insulators by means of ion beam mixing

Talut, G.; Potzger, K.; Mücklich, A.; Zhou, S.

The intermixing and near-interface cluster formation of Pt and FePt thin flms deposited on different oxide surfaces by means of Pt+ ion irradiation and subsequent annealing was investigated. Irradiated as well as post-annealed samples were investigated using high resolution transmission electron microscopy (HRTEM). In MgO and Y:ZrO2 covered with Pt, crystalline clusters with mean size of 2 nm and 3.5 nm were found after the Pt+ irradiation with 8x10^15 cm^-2 and 2x10^16 cm^-2 and subsequent annealing, respectively. In MgO samples covered with FePt, clusters with mean size of 1 nm and 2 nm were found after the Pt+ irradiation with 8x10^15 and 2x10^16 cm^-2 and subsequent annealing, respectively. In Y:ZrO2 samples covered with FePt, clusters up to 5 nm in size were found after the Pt+ irradiation with 2x10^16 cm^-2 and subsequent annealing. In LaAlO3 the irradiation was accompanied by a full amorphization of the host matrix and appearance of embedded clusters of different sizes. The determination of the lattice constant and thus the kind of the clusters in samples covered by FePt was hindered due to strong deviation of the electron beam by the ferromagnetic FePt.

Keywords: FePt; nanocluster; ion beam mixing

  • Journal of Applied Physics 103(2008)7, 07D505
  • Lecture (Conference)
    52nd Conference on Magnetism and Magnetic Materials, 05.-09.11.2007, Tampa, USA

Publ.-Id: 10511

Radiation stability of WWER RPV cladding materials

Gillemot, F.; Horvath, M.; Uri, G.; Fekete, T.; Houndeffo, E.; Acosta, B.; Debarberis, L.; Viehrig, H.-W.

A study investigating the WWER-440/213 reactor pressure vessel (RPV) cladding properties and their degradation due to neutron irradiation has been recently completed under an Hungarian National Government funded project "Evaluation of the lifetime of NPP structural materials". This has been carried out in co-operation with European partners and the key results from this project are presented in this paper. The RPV cladding, designed primarily to protect the RPV ferritic steel from primary water corrosion, also has structural integrity functions. The clad is made of a thin layer of austenitic steel with good ductility and toughness that offers additional robustness to the vessel. The degradation of the properties of the cladding material needs to be carefully assessed in order to properly consider the cladding as a relevant element in the global RPV integrity assessment. By taking into account the cladding it is possible to gain safety margins. This is an important result since it has a direct impact on the global lifetime evaluation of the RPV as well as avoiding the adoption of other very expensive and less effective mitigation methods.

Keywords: reactor pressure vessel; cladding; integrity assessment

  • International Journal of Pressure Vessels and Piping 84(2007)8

Publ.-Id: 10510

Time-resolved semiconductor spectroscopy at FZD

Schneider, H.

Es existiert kein Abstract.

  • Lecture (others)
    Seminar, 07.09.2007, Nottingham, UK

Publ.-Id: 10509

Quadratic autocorrelation and photocurrent saturation study in two-photon QWIPs

Schneider, H.; Drachenko, O.; Winnerl, S.; Helm, M.; Walther, M.

Using the free-electron laser facility FELBE, we have studied the influence of the intensity on the quadratic autocorrelation measured with two-photon quantum well infrared photodetectors (QWIP). At high illumination powers, the shape of the autocorrelation trace is affected by photocurrent saturation of the two-photon QWIP. We describe the saturation mechanism by different analytical models taking account of the photocurrent nonlinearity in analogy to linear QWIPs and give conditions where true quadratic behavior can be observed.

Keywords: quantum well infrared photodetector; QWIP; two-photon absorption; photocurrent saturation; free-electron laser; GaAs/AlGaAs

  • Lecture (Conference)
    The Ninth International Conference on Intersubband Transitions in Quantum Wells, 09.-14.09.2007, Ambleside, Cumbria, UK

Publ.-Id: 10508

A novel method for characterizing relativistic electron beams in a harsh laser-plasma environment

Hidding, B.; Pretzler, G.; Clever, M.; Brandl, F.; Zamponi, F.; Lübcke, A.; Kämpfer, T.; Uschmann, I.; Förster, E.; Schramm, U.; Sauerbrey, R.; Kroupp, E.; Veisz, L.; Schmid, K.; Benavides, S.; Karsch, S.

Particle pulses generated by laser-plasma interaction are characterized by ultrashort duration, high particle density, and sometimes a very strong accompanying electromagnetic pulse (EMP). Therefore, beam diagnostics different from those known from classical particle accelerators such as synchrotrons or linacs are required. Easy to use single-shot techniques are favored, which must be insensitive towards the EMP and associated stray light of all frequencies, taking into account the comparably low repetition rates and which, at the same time, allow for usage in very space-limited environments. Various measurement techniques are discussed here, and a space-saving method to determine several important properties of laser-generated electron bunches simultaneously is presented. The method is based on experimental results of electron-sensitive imaging plate stacks and combines these with Monte Carlo-type ray-tracing calculations, yielding a comprehensive picture of the properties of particle beams. The total charge, the energy spectrum, and the divergence can be derived simultaneously for a single bunch.

Keywords: PACS: 52.38.Kd; 41.75.Jv; 52.35.Mw


Publ.-Id: 10507

Miniature magnetic devices for laser-based, table-top free-electron lasers

Eichner, T.; Grüner, F.; Becker, S.; Fuchs, M.; Habs, D.; Weingartner, R.; Schramm, U.; Backe, H.; Kunz, P.; Lauth, W.

Truly table-top sized radiation sources based on compact laser-plasma accelerators require compact and strong focusing devices and efficient short-period undulators. Complementing our recent theoretical work on the feasibility of a table-top FEL, we here present the design and successful experimental characterizations of a 5 mm period length undulator and miniature quadrupole magnets with field gradients of the order of 500  T/m.

Keywords: PACS: 41.85.Lc; 41.60.Cr; 41.75.Jv; 52.38.Kd; magnet design; FEL

Publ.-Id: 10506

Flash-lamp annealing of semiconductor materials - Applications and process models

Mcmahon, R. A.; Smith, M. P.; Seffen, K. A.; Voelskow, M.; Anwand, W.; Skorupa, W.

Flash-lamp annealing (FLA) oil a millisecond time scale has been shown to be a promising tool in the preparation of high-quality semiconducting materials. The process imposes time varying through-thickness temperature profiles on the substrates being processed, and consequently thermal stresses. A combined thermal and optical model has been developed to predict the substrate temperature distribution and this model has been linked to a structural Model to compute stresses and deflections The paper shows how these models can be used to explore process conditions in flash lamp annealing; with particular regard to the annealing of ion implants in silicon and the crystallization of amorphous silicon layers on glass substrates.

Keywords: flash lamp; pulse annealing; thermal model; optical model; temperature profiles; stress

  • Vacuum 81(2007)10, 1301-1305
    DOI: 10.1016/j.vacuum.2007.01.033
    Cited 46 times in Scopus
  • Contribution to proceedings
    VI Int. Conf. Ion Implantation and other Applications of Ions and Electrons, 26.-29.09.2006, Lublin, Poland
    Proceedings of the VI Int. Conf. Ion Implantation and other Applications of Ions and Electrons

Publ.-Id: 10505

Design considerations for table-top, laser-based VUV and X-ray free electron lasers

Grüner, F.; Becker, S.; Schramm, U.; Eichner, T.; Fuchs, M.; Weingartner, R.; Habs, D.; Meyer-Ter-Vehn, J.; Geissler, M.; Ferrario, M.; Serafini, L.; van der Geer, B.; Backe, H.; Reiche, S.; Lauth, W.

Abstract A recent breakthrough in laser-plasma accelerators, based upon ultrashort high-intensity lasers, demonstrated the generation of quasi-monoenergetic GeV-electrons. With future Petawatt lasers ultra-high beam currents of ∼100 kA in ∼10 fs can be expected, allowing for drastic reduction in the undulator length of free-electron-lasers (FELs). We present a discussion of the key aspects of a table-top FEL design, including energy loss and chirps induced by space-charge and wakefields. These effects become important for an optimized table-top FEL operation. A first proof-of-principle VUV case is considered as well as a table-top X-ray-FEL which may also open a brilliant light source for new methods in clinical diagnostics.

Keywords: FEL, laser acceleration, PACS 41.60.Cr; 52.38.Kd


Publ.-Id: 10504

Plasmons, plasminos and Landau damping in a quasiparticle model of the quark-gluon plasma

Schulze, R.; Bluhm, M.; Kämpfer, B.

A phenomenological quasiparticle model is surveyed for 2+1 quark flavors and compared with recent lattice QCD results. Emphasis is devoted to the effects of plasmons, plasminos and Landau damping. It is shown that thermodynamic bulk quantities, known at zero chemical potential, can uniquely be mapped towards nonzero chemical potential by means of a thermodynamic consistency condition and a stationarity condition.

Keywords: QCD; quasiparticle; model; plasmon; plasmino; plasmons; plasminos; quark; gluon; plasma; Landau; damping; characteristics

Publ.-Id: 10503

Investigation of acceptor states in ZnO by junction DLTS

von Wenckstern, H.; Pickenhain, R.; Schmidt, H.; Brandt, M.; Biehne, G.; Lorenz, M.; Grundmann, M.; Brauer, G.

We have realized a p-type ZnO surface layer by N+ ion implantation of a high quality ZnO wafer and subsequent annealing. The conduction type of this surface layer was revealed by scanning capacitance microscopy. Rectifying current–voltage characteristics for processed devices were coherent with the existence of an internal pn junction. Deep donor- and acceptor-like defects were investigated by junction deep level transient spectroscopy. The donor-like levels correspond to those commonly observed for E1 and E3 defects. The acceptor states resolved have thermal activation energies of about 150 meV and 280 meV, respectively.

  • Superlattices and Microstructures 42(2007), 14-20

Publ.-Id: 10502

Coordination of a uranium(IV) sulfate monomer in an aqueous solution and in the solid state

Hennig, C.; Kraus, W.; Emmerling, F.; Ikeda, A.; Scheinost, A.

Uranium(IV) sulfate in an aqueous solution and the solid state has been investigated with extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD). The coordination polyhedron comprises monodentate sulfate, bidentate sulfate, and water molecules. The coordination modes of sulfate in solution have been determined from the U-S distances with EXAFS. The U-S distance of 3.67 +/- 0.02 angstrom indicates monodentate sulfate, and the U-S distance of 3.08 +/- 0.02 A indicates bidentate c oordination. The obtained sulfur coordination numbers of a solution with a SO4 (2-)]/[U4+] ratio of 40 suggest species with compositions of, [U(SO4,bid)(2)(SO4,(mon))(2)center dot nH(2)O](4-) and [U(SO4,bid)(3) (SO4,(mon))(2)center dot mH(2)O](6-). Charge-compensating countercations or ion pairing with Na+ and NH4+ could not be detected with EXAFS. One of the solution species, [U(SO4)(5)H2O!
(4.5)[U(SO4)(5 center dot)H2O]center dot H2O [space group P (1) over bar, a = 9.4995(16) angstrom, b = 9.8903(16) angstrom, c = 12.744(2) angstrom, alpha = 93,669(2)degrees, beta = 103.846(2)degrees,gamma = 109.339(2)degrees] has been determined by single-crystal XRD. Two monomeric uranium(IV) sulfate complexes and three sodium units are linked in alternating rows and form a one-dimensoinal ribbon structure parallel to the a axis.

Keywords: EXAFS; XRD; single crystal structure; U(IV) sulfate

  • Inorganic Chemistry 47(2008)5, 1634-1638

Publ.-Id: 10501

Dissolution of UO2, UO3 and of some lanthanide oxides in BumimTf2N: effect of acid and water and formation of UO2(NO3)3−

Billard, I.; Gaillard, C.; Hennig, C.

UO2, UO3, Nd2O3, Eu2O3 and Pr6O11 powders were successfully dissolved in the ionic liquid
1-methyl-3-butyl-imidazolium bistriflimide (BumimTf2N) with the help of small amounts of HNO3.
The uranyl species have been characterised through UV-vis and EXAFS spectroscopies. The uranium
dissolution leads to the formation of UO2(NO3)3−, even in the presence of water. The kinetics of UO2
dissolution/oxidation is intricate, due to the transient existence of NO2−, which is absent in the case of
the UO3 dissolution, occurring with no change in the oxidation state of U.

Keywords: EXAFS; UV-Vis; UO2; UO3; ionic liquids

Publ.-Id: 10500

CFD studies on boron dilution scenarios in VVER type reactors - use of best practice guidelines

Höhne, T.

The main objective for the quantification of the fluid mixing in the downcomer and the lower plenum is the demonstration of the safety of the nuclear plant during non-symmetrical transients.

This concerns two main topics: The risk of fragile brittle of the Reactor Pressure Vessel (RPV) during Pressurized Thermal Shock (PTS) transients and the risk of core reactivity excursion during non-symmetrical transient such as Main Steam Line Breaks (MSLB) or Boron Dilution Transients (BDT).

These scenarios are studied in the 1:5 scaled VVER-1000 reactor model at OKB “Gidropress” in the framework of a TACIS project: “Development of safety analysis capabilities for VVER-1000 transients involving spatial variations of coolant properties (temperature or boron concentration) at core inlet”.

Keywords: CFD; Boron DIlution; Coolant Mixing

  • Invited lecture (Conferences)
    COVERS/ WP3 Training, 09.10.2007, Dresden-Rossendorf, Germany

Publ.-Id: 10499

Spatial discretization in LWR cell calculations with HELIOS 1.9: influence on kinf and flux distribution

Merk, B.; Koch, R.

Cell calculations are the fundament for all deterministic static and transient 3D full core calculations. The spatial discretization used for the cell calculations influences the results for these transport solutions significantly. The arising differences in the neutron flux distribution due to different spatial discretization are demonstrated. These differences in the flux distribution cause significant changes in the kinf value. Different optimized schemes for economic cell calculations are developed.

Keywords: Spatial Discretization; Neutron Transport; HELIOS; Collision Probabilities; Flat-Flux-Approximation

  • Lecture (Conference)
    ENS TOPSAFE 2008, 01.-03.10.2008, Dubrovnik, Croatia
  • Contribution to proceedings
    ENS TOPSAFE 2008, 01.-03.10.2008, Dubrovnik, Croatia
    Book of Abstracts with Proceedings CD, ISBN 978-92-95064-06-5, A1-067

Publ.-Id: 10498

Two-Scale Modeling of Adsorption Processes at Structured Surfaces

de Cuba, M. R.; Kundin, J.; Emmerich, H.; Gemming, S.

We present a hybrid algorithm for the simulation of vicinal surface growth which combines a lattice gas Ising model with a phase-field model. The molecular behavior of individual adatoms is resolved by the kinetic Monte-Carlo (KMC) generated dynamics of the anisotropic Ising model. The microstructure dynamics on the vicinal surface are calculated using the phase-field method. Therefore adsorption processes on two different scales are described. In addition to step-flow growth the hybrid algorithm describes nucleation processes on the terraces which lead to an epitaxial layer-by-layer growth controlled by temperature and by deposition rate. The method is faster than pure KMC simulation and can take into account the stochastic processes in a comparable way.

Keywords: hybdir model; phase-field; Monte Carlo; vicinal surface

Publ.-Id: 10495

Star-shaped Oligobenzoates: Non-Conventional Mesogens Forming Columnar Helical Mesophases

Lehmann, M.; Jahr, M.; Donnio, B.; Graf, R.; Gemming, S.; Popov, I.

Star-shaped mesogens with a phloroglucinol or a trimesic acid core and oligobenzoate arms with up to five repaeting units have been synthesised. These non-conventional mesogens possess various columnar mesophases over a broad temperature range. The liquid crystal phases are characterised by optical microscopy, differential scanning calorimetry, X-ray diffraction, dilatometry and Solid State NMR spectroscopy. Beside a high temperature hexagonal columnar phase, the columnar structures transform to higher ordered, undulated columns in a body-centered orthorhombic unit cell at low temperatures. A model of E-shaped folded conformers helically displaced along the columns is proposed. Helical preorganisation in the hexagonal phase precedes the transition to the low temperature phases. Space-filling and nano-segregation compete in the self-organisation process, thus aliphatic chains and polar oligobenzoate scaffold are not perfectly separated for these star-shaped mesogens.

Keywords: star-shaped mesogens; liquid crystals; columnar; mesophase; semi-empirical modelling

Publ.-Id: 10494

A superconducting RF photo-injector for operation at the ELBE linear accelerator

Teichert, J.; Arnold, A.; Büttig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Moeller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Xiang, R.; Stephan, J.; Lehmann, W.-D.; Kamps, T.; Klemz, G.; Will, I.; Lipka, D.; Matheisen, A.; Horst, B. V. D.; vom Stein, P.; Volkov, V.

For the ELBE superconducting linear accelerator at FZD a radiofrequency photoelectron injector with a superconducting cavity (SRF gun) is under development. The SRF gun combines the excellent beam quality which can be delivered by RF photoinjectors with the possibility of continuous wave operation. The superconducting niobium cavity of the injector consists of 3½ cells and contains a Cs2Te photocathode which is normal-conducting and cooled by liquid nitrogen. The RF frequency of the cavity is 1.3 GHz. The final electron energy will be about 9.5 MeV and the average electron current will be 1 mA. In the past years the SRF photo injector has been designed and fabricated. Several critical subsystems have been tested. For the cavity, the results of the RF measurements will be shown. An UV driver laser system has been developed which fulfils the different requirements (77 pC @ 13 MHz, 1 nC @ 500 kHz) for the future operation at ELBE. A photo cathode preparation system was developed and installed. The equipment is now in operation and the first series of Cs2Te photo cathodes have been produced.

  • Open Access Logo Contribution to proceedings
    29th International Free Electron Laser Conference, 26.-31.08.2007, Novosibirsk, Russia
    Proceedings of FEL 2007: JACoW


Publ.-Id: 10493

A Hybrid Method for the Structural Evolution of Stepped Surfaces

Gemming, S.; Emmerich, H.; Radke De Cuba, M.; Kundin, J.

The Burton-Cabrera-Frank (BCF) model describes the structural evolution of vicinal surfaces in terms of an incoming particle flux and concentration-dependent desorption and surface diffusion terms. A continuum formulation of the BCF scheme given by a phase-field implementation for the moving-boundary problem yields the long-term evolution of the step structure during a step-flow growth mode. Phenomena like step bunching or meandering are well covered by such an approach, but the nucleation of additional structures is not. A particle-based Ising-type approach with a Metropolis-Monte-Carlo kinetics provides such nucleation processes in a temperature-controlled manner and on a shorter time and length scale.

We have integrated both approaches in a hybrid algorithm, which describes adsorption, nucleation, and structure evolution processes at solid-liquid and solid-gas interfaces on both time and length scales. The short-term nucleation from individual adatoms or molecules is resolved by the Monte-Carlo generated dynamics of an anisotropic Ising model, whose interaction parameters stem from first-principles calculations. The long-term microstructure dynamics on the vicinal surface is calculated using the phase-field method. Several growth modes are distinguished by the present scheme: In addition to step-flow growth the nucleation processes on the terraces can lead to roughening or an epitaxial layer-by-layer growth controlled by temperature and by flux. This hybrid algorithm has been applied to the decoration of structured crystalline surfaces with optically active molecules and to the coverage of glass surfaces with inhibitor molecules, which suppress glass corrosion.

Keywords: vicinal surface; hybrid model; Monte-Carlo; phase field; Burton-Cabrera-Frank

  • Lecture (Conference)
    Euromat 2007, 10.-14.09.2007, Nürnberg, Germany

Publ.-Id: 10492

From Clusters to Wires - DFT investigations of molybdenum sulfide nanostructures

Gemming, S.; Seifert, G.; Enyashin, A.; Popov, I.; Tamuliene, J.

The dependence of morphology and composition in molybdenum sulfide nanostructures was investigated by density-functional-based calculations. Sulfur-rich compounds preferentially form two-dimensional platelet structures, which can accomodate a large extent of excess sulfur atoms along the platelet edges. Compounds which are understoichiometric in sulfur, i.e., with a negative sulfur extent, contain a metalloid molybdenum core structure, which is stabilised by Mo-Mo metal bonds and decorated by sulfur atoms. Small species of this type are polyhedral clusters, which grow into nanowires with increasing atom number. Close to the bulk stoichiometry of Mo:S = 1:2 larger polyhedral and partially hollow clusters are obtained, which exhibit an octahedral shape at system sizes of up to a few thousands of atoms and finally grow into spherical fullerenes at even larger sizes.

Keywords: molybdenum sulfide; nanostructures; first-principles

  • Invited lecture (Conferences)
    iNANO-Seminar, 08.08.2007, Aarhus, Denmark

Publ.-Id: 10491

Bacterial surface layers (S-layers) as building blocks for nanocomposites

Pollmann, K.; Raff, J.; Fahmy, K.; von Ny, J.; Grenzer, J.; Herrmannsdörfer, T.

Nanoscaled materials comprised of organic and inorganic components are becoming more and more important in nanotechnology due to the diversity of applications. The use of self-assembling organic systems as part of such a hybrid material, serving as template for the fabrication of arrays of inorganic nanoparticles, is an attractive approach for the development of new materials. Especially the proteinaceous bacterial surface layers (S-layers) that envelop bacterial cells are attractive for fabricating and patterning of nanostructures. These proteins are composed of protein monomers with the ability to self-assemble into two-dimensional arrays. The regular distributed pores of these paracrystalline arrays work as binding sites for various metals and offer ideal structures for the formation of regular distributed metallic nanoclusters of a defined size (15). Such arrays are very attractive for technical applications ranging from the development of novel catalysts to biomedical applications, development of innovative filter materials, the programmed assembly of nanometre scale electronic devices, and optical industry (7, 9). Another approach is the embedding of S-layer proteins into ceramics thus producing metal binding functionalized nanocomposites (12).
Our current work focuses on the synthesis and characterization of different S-layer templated inorganic nanoclusters. Due to quantum size effects nanosized grains often exhibit changed physical and chemical properties in comparison to bulk material. We demonstrate the fabrication of catalytic active nanoparticles such as ZnO. The photocatalytic properties of ZnO-particles are interesting for their application as nanoscaled catalytic material, i.e. for the degradation of pharmaceutical residues that are released in environment.

  • Contribution to proceedings
    Nanofair 2008, 11.-12.03.2008, Dresden, Germany
  • Poster
    Nanofair 2008, 11.-12.03.2008, Dresden, Germany

Publ.-Id: 10490

Effect of As incorporation on ZnO film structure and dielectric function

Vinnichenko, M.; Rogozin, A.; Shevchenko, N.; Kolitsch, A.; Moeller, W.

Understanding the process of defect formation due to impurity incorporation is crucial for the control of electrical and optical properties of ZnO. The influence of As doping of ZnO on the film structure and properties is much less understood than the effect of N or Al incorporation. Therefore, this study is aimed at investigation of the ZnO film structure and dielectric function modification by doping with As. Two approaches to As incorporation have been used. In the first, the film has been deposited onto Al2O3 (0001) substrate by reactive pulsed magnetron sputtering of a Zn-As target at a temperature of 450 °C, thereby providing an As concentration of 2.0 at % in the layer. In the second approach, epitaxial films of ZnO deposited by the same method on Al2O3 (0001) substrate at 550 °C have been implanted with As+ ions (energy 300 keV) to provide the same As concentration. The film thickness has been adjusted to rule out any ion-beam intermixing effects at the ZnO/Al2O3 (0001) interface. The As concentration has been determined by particle induced X-ray emission, whereas film structure has been characterized by X-ray diffraction (XRD). Spectrscopic ellipsometry measurements have yielded the dielectric function of the films, as well as their thickness and roughness. The results have been compared with the structure and the optical properties of undoped ZnO.
Reactive pulsed magnetron sputtering of Zn target produces ZnO epitaxial layers with single-domain in-plane ordering and strong c-axis texture (rocking curve width of 0.37°). In contrast, ZnO:As layers are in nanostructured state as indicated by the broad peak at 34.2° on the XRD patterns. The doped layers also show much lower degree of in-plane ordering than the undoped films. XRD measurements suggest stronger ZnO structure modification due to the As+ ion implantation than to As incorporation during magnetron sputtering, although the impurity concentration is the same in both cases. The pole figure measurements show that the recrystallization of ZnO films heavily damaged by ion bombardment leads to a much more pronounced in-plane and off-plane textures of the samples annealed at 750-950 °C. The annealing also decreases film thickness which points to evaporation of the damaged layer [1]. The crystalline quality of the annealed ZnO is only slightly lower than that of the epitaxial undoped ZnO. Spectroscopic ellipsometry shows that the dielectric function in the spectral range around the band gap is sensitive to the crystalline quality of the films. The increased defect density in the doped layers broadens the oscillator used for the dielectric function parameterization. The band gap of the doped layers increases compared with that of the undoped ones.

[1] V.A. Coleman, H.H. Tan, C. Jagadish, S.O. Kucheyev, and J. Zou, Appl. Phys. Lett. 87, 231912 (2005).

Keywords: ZnO films; reactive magnetron sputtering; spectroscopic ellipsometry; x-ray diffraction

  • Poster
    13th International Conference on II-VI Compounds, 10.-14.09.2007, Jeju, Korea

Publ.-Id: 10489

Phylogenetic Analysis and In Situ Identification of Bacteria Community Composition in Uranium Contaminated Soil.

Diessner, S.; Wobus, A.; Huth, C.; Großmann, K.; Arnold, T.; Röske, I.

wird nachgereicht

Keywords: wird nachgereicht

  • Poster
    18th International Symposium on Environmental Biogeochemistry - ISEB XVIII, 11.-16.11.2007, Taupo, New Zealand

Publ.-Id: 10488

Two-color pump-probe spectroscopy of electron dynamics in doped superlattices

Wagner, M.; Stehr, D.; Winnerl, S.; Helm, M.; Andrews, M.; Roch, T.; Strasser, G.

With respect to their dynamics semiconductor superlattices (SL) have been much less investigated than other heterostructures like quantum wells. We have already reported on single-color pump-probe measurements on doped superlattices where we could observe the interminiband relaxation and subsequent cooling of the heated electron distribution in the lower miniband of a SL after excitation to the upper one [1]. However, superlattices have a broad absorption range so that excitation at a special k-value in the mini-Brillouin zone influences the electron distribution over the entire zone. Therefore we have performed two-color pump-probe measurements on three doped superlattices to investigate the intraminiband dynamics.
We employed infrared pulses from the free-electron laser FELBE at the Forschungszentrum Dresden-Rossendorf as the pump beam and synchronized broadband THz pulses generated by optical rectification in GaSe as the probe beam. The three GaAs/AlGaAs superlattices had nearly the same doping concentration but different miniband widths of 10 meV, 22 meV and 45 meV, which is smaller or larger, respectively, than the optical phonon energy of 36 meV.
We have first analyzed the cooling behavior. At low temperature, electrons were excited to the upper miniband by the FEL pulse at the zone center of the superlattice mini-Brillouin zone and the interminiband transition was probed at the zone edge. The excited electrons relax back to the ground miniband where they heat up the electronic distribution. A higher temperature leads to more absorption at the zone edge low energy transition. Therefore we found an induced absorption signal after excitation, which decays when the electronic distribution cools down. In the superlattice structures with miniband widths below the optical phonon energy we measured cooling times of 40-50 ps for pump intensities higher than 20 MW/cm². For smaller pump intensities the time constants rose up to 200 ps. The sample with the miniband width of 45 meV showed a much shorter cooling time of 3.5 ps, nearly independent of the pump intensity. This can be explained by the new relaxation channel through polar optical phonons.
Additionally we performed room temperature measurements where the lower miniband is already occupied at the zone edge so that no induced absorption should be observed. In fact we measured a positive transmission change which decays in a few picoseconds in all samples. This can be attributed to a relaxation process in the lower miniband where the electrons at the zone edge relax to the miniband center, which is depleted of electrons by the pump pulse.
[1] D. Stehr et al., Appl. Phys. Lett. 88, 151108 (2006)

Keywords: two-color pump-probe; superlattice; electron dynamics; intraminiband; cooling

  • Poster
    The Ninth International Conference on Intersubband Transitions in Quantum Wells, 09.-14.09.2007, Ambleside, United Kingdom

Publ.-Id: 10487

A finite-time thermodynamics of unsteady shear flows

Noack, B. R.; Schlegel, M.; Ahlborn, B.; Mutschke, G.; Morzynski, M.; Compte, P.; Tadmor, G.

A finite-time thermodynamics (FTT) formalism (Andresen, Salamon \& Berry 1977) is proposed to compute the mean flow and fluctuation levels of unsteady, incompressible, shear flows. That formalism yields a definition for a thermodynamic degree of freedom of the velocity fluctuation as well as conditions for local thermal equilibrium. In general, the dynamics of unsteady flow is shown to be in partial thermal equilibrium, a state governed by finite time scales of energy transfer. The FTT model has been successfully applied to shear flows with simple to complex dynamics, e.g. vortex shedding and homogenous shear turbulence.

Keywords: Thermodynamics; Turbulence

  • Lecture (Conference)
    60th Annual Meeting of the Divison of Fluid Dynamics, 18.-20.11.2007, Salt Lake City, Utah, USA

Publ.-Id: 10484

A finite-time thermodynamics of unsteady fluid flows

Noack, B. R.; Schlegel, M.; Ahlborn, B.; Mutschke, G.; Morzynski, M.; Comte, P.; Tadmor, G.

Turbulent fluid has often been conceptualized as a transient thermodynamic phase. Here, a finite-time thermodynamics (FTT) formalism (Andresen, Salamon & Berry 1977) is proposed to compute mean flow and fluctuation levels of unsteady incompressible flows. The proposed formalism builds upon the Galerkin model framework which simplifies a continuum 3D fluid motion into a finite-dimensional phase-space dynamics and subsequently, into a thermodynamics energy problem. The Galerkin model consists of a velocity field expansion in terms of flow configuration dependent modes and of a dynamical system describing the temporal evolution of the mode coefficients. Each mode may be considered as a wave, parameterized by a wave number and frequency. In our FTT formalism, the mode is treated as one thermodynamic degree of freedom, characterized by an energy level. The dynamical system approaches local thermal equilibrium where each mode has the same energy if it is governed only by internal (triadic) mode interactions. However, in the generic case of unsteady flows, the full system approaches only partial thermal equilibrium with unequal energy levels due to strongly mode-dependent external interactions. In these interactions, large-scale modes typically gain energy from the mean flow while small-scale modes loose energy to the heat bath. The energy flow cascade from large to small scales is thus a finite-time transition phenomenon. The FTT model is first illustrated by a traveling wave governed by a 1D Burgers equation. It is then applied to two flow benchmarks: the relatively simple laminar vortex shedding which is dominated by 2 eigenmodes, and the homogeneous shear turbulence which has been modeled with 1459 modes.

Keywords: Nonequilibrium and irreversible thermodynamics; Nonlinear dynamics and chaos; Dynamical systems approaches; Statistical theories and models; Flow control; Turbulence control; Turbulent flows; Isotropic turbulence; homogeneous turbulence; Instability of shear flows

  • Journal of Non-Equilibrium Thermodynamics 33(2008)2, 103-148

Publ.-Id: 10483

Identification of Fluorescent U(V) and U(VI) Microparticles in a Multispecies Biofilm by Confocal Laser Scanning Microscopy and Fluorescence Spectroscopy.

Grossmann, K.; Arnold, T.; Krawczyk-Bärsch, E.; Diessner, S.; Wobus, A.

A combined approach of laser fluorescence spectroscopy and confocal laser scanning microscopy was used to study in vivo fluorescent particles in living multispecies biofilms which were exposed to 10-5 M and 5×10-6 M uranium, respectively. These particles ranged between 1 and 7 µm in width and up to 20 µm in length and were located at the bottom and at the edges of biofilms colonies.
Analysis of the amplified 16S rRNA gene fragments have shown that the biofilm consisted of members of the alpha-, beta-, and, gamma-subgroup of Proteobacteria, as well as of representatives of Actinobacteria, Firmicutes, and Bacteroidetes. Restriction fragment length polymorphism (RFLP) screening and cloning of selected clones indicated a similar composition of the microbial communities in biofilm reactors with and without U addition. Both clone libraries were dominated by sequences affiliated to the alpha-subgroup of Proteobacteria. Fluorescence in situ hybridization (FISH) with group specific probes indicated a slightly higher coverage of the uranium contaminated biofilm by cells affiliated with the beta-Proteobacteria. Beta-Proteobacteria are recognized for their ability to reduce uranium in the presence of nitrate. However, an enrichment of additional bacteria known for their ability to reduce U(VI) did not become apparent, neither by 16S rRNA gene retrieval nor by the FISH technique. From both techniques it can be concluded that the multispecies biofilms grown without and with uranium addition were very similar regarding their microbial composition.
Laser fluorescence spectroscopy was used to identify these particles. The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415-475 nm, indicative for uranium-(V), or in the range of 480-560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium-(VI) were simultaneously observed in the biofilms. These uranium particles were attributed for uranium(VI) to biologically mediated precipitation and for uranium(V) to redox processes taking place within the biofilm. The detection of uranium(V) in a multispecies biofilm was interpreted as a short-lived intermediate of the uranium(VI) to uranium-(IV) redox reaction. Its presence clearly documents that the uranium(VI) reduction is not a two electron step but that only one electron is involved.

Keywords: uranium(V); uranium(VI); biofilm; Laser fluorescence spectroscopy; Confocal laser scanning microscopy

  • Poster
    18th International Symposium on Environmental Biogeochemistry at the Extremes - ISEB XVIII, 11.-16.11.2007, Taupo, New Zealand
  • Contribution to proceedings
    18th International Symposium on Environmental Biogeochemistry at the Extremes - ISEB XVIII, 11.-16.11.2007, Taupo, New Zealand

Publ.-Id: 10482

Validation of the multiple velocity multiple size group (CFX10.0 N x M MUSIG) model for polydispersed multiphase flows

Shi, J.-M.; Rohde, U.; Prasser, H.-M.

To simulate dispersed two-phase flows CFD tools for predicting the local particle number density and the size distribution are required. These quantities do not only have a significant effect on rates of mixing, heterogeneous chemical reaction rates or interfacial heat and mass transfers, but also a direct relevance to the hydrodynamics of the total system, such as the flow pattern and flow regime. The Multiple Size Group (MUSIG) model available in the commercial codes CFX-4 and CFX-5 was developed for this purpose. Mathematically, this model is based on the population balance method and the two-fluid modeling approach. The dispersed phase is divided into N size classes. In order to reduce the computational cost, all size groups are assumed to share the same velocity field. This model allows to use a sufficient number of particle size groups required for the coalescence and breakup calculation. Nevertheless, the assumption also restricts its applicability to homogeneous dispersed flows. We refer to the CFX MUSIG model mentioned above as the homogeneous model, which fails to predict the correct phase distribution when heterogeneous particle motion becomes important. In many flows the non-drag forces play an essential role with respect to the bubble motion. Especially, the lift force acting on large deformed bubbles, which is dominated by the asymmetrical wake, has a direction opposite to the shear induced lift force on a small bubble. This bubble separation cannot be predicted by the homogeneous MUSIG model. In order to overcome this shortcoming we developed an efficient inhomogeneous MUSIG model in cooperation with ANSYS CFX. A novel multiple velocity multiple size group model, which incorporates the population balance equation into the multi-fluid modeling framework, was proposed. The validation of this new model is discussed in this report.

Keywords: Bubbly flow; momentum transfer; bubble forces; multi bubble size group modelling

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-487 2007
    ISSN: 1437-322X


Publ.-Id: 10481

Turbulent dispersion of bubbles in poly-dispersed gas-liquid flows in a vertical pipe

Shi, J.-M.; Rohde, U.; Prasser, H.-M.

Turbulence dispersion is a phenomenon of practical importance in many multiphase flow systems. It has a strong effect on the distribution of the dispersed phase. Physically, this phenomenon is a result of interactions between individual particles of the dispersed phase and the continuous phase turbulence eddies. In a Lagrangian simulation, a particle-eddy interaction sub-model can be introduced and the effect of turbulence dispersion is automatically accounted for during particle tracking. Nevertheless, tracking of particleturbulence interaction is extremely expensive for the small time steps required. For this reason, the Lagrangian method is restricted to small-scale dilute flow problems. In contrast, the Eulerian approach based on the continuum modeling of the dispersed phase is more efficient for densely laden flows. In the Eulerian frame, the effect of turbulence dispersion appears as a turbulent diffusion term in the scalar transport equations and the so-called turbulent dispersion force in the momentum equations. The former vanishes if the Favre (mass-weighted) averaged velocity is adopted for the transport equation system. The latter is actually the total account of the turbulence effect on the interfacial forces. In many cases, only the fluctuating effect of the drag force is important. Therefore, many models available in the literature only consider the drag contribution. A new, more general derivation of the FAD (Favre Averaged Drag) model in the multi-fluid modeling framework is presented and validated in this report.

Keywords: Bubbly flow; momentum transfer; bubble forces; turbulent dispersion force; Favre averaging

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-487 2007
    ISSN: 1437-322X


Publ.-Id: 10480

CFD models for polydispersed bubbly flows

Lucas, D.; Krepper, E.

Many flow regimes in Nuclear Reactor Safety Research are characterized by multiphase flows, with one phase being a continuous liquid and the other phase consisting of gas or vapour of the liquid phase. In dependence on the void fraction of the gaseous phase the flow regimes e.g. in vertical pipes are varying from bubbly flows with low and higher volume fraction of bubbles to slug flow, churn turbulent flow, annular flow and finally to droplet flow. In the regime of bubbly and slug flow the multiphase flow shows a spectrum of different bubble sizes. While disperse bubbly flows with low gas volume fraction are mostly mono-disperse, an increase of the gas volume fraction leads to a broader bubble size distribution due to breakup and coalescence of bubbles. Bubbles of different sizes are subject to lateral migration due to forces acting in lateral direction different from the main drag force direction. The bubble lift force was found to change the sign dependent on the bubble size. Consequently this lateral migration leads to a de-mixing of small and large bubbles and to further coalescence of large bubbles migrating towards the pipe center into even larger Taylor bubbles or slugs. An adequate modeling has to consider all these phenomena. A Multi Bubble Size Class Test Solver has been developed to investigate these effects and test the influence of different model approaches. Basing on the results of these investigations a generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework has been proposed and was finally implemented into the CFD code CFX. Within this model the dispersed gaseous phase is divided into N inhomogeneous velocity groups (phases) and each of these groups is subdivided into Mj bubble size classes. Bubble breakup and coalescence processes between all bubble size classes Mj are taken into account by appropriate models. The inhomogeneous MUSIG model has been validated against experimental data from the TOPFLOW test facility.

Keywords: Bubbly Flow; CFD; Bubble Forces; Coalescence; Breakup; Pipe Flow

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-486 2007
    ISSN: 1437-322X


Publ.-Id: 10479

Experimental investigation and CFD simulation of slug flow in horizontal channels

Vallée, C.; Höhne, T.; Prasser, H.-M.; Sühnel, T.

For the investigation of stratified two-phase flow, two horizontal channels with rectangular cross-section were built at Forschungszentrum Dresden-Rossendorf (FZD). The channels allow the investigation of air/water co-current flows, especially the slug behaviour, at atmospheric pressure and room temperature. The test-sections are made of acrylic glass, so that optical techniques, like high-speed video observation or particle image velocimetry (PIV), can be applied for measurements. The rectangular cross-section was chosen to provide better observation possibilities. Moreover, dynamic pressure measurements were performed and synchronised with the high-speed camera system. CFD post-test simulations of stratified flows were performed using the code ANSYS CFX. The Euler-Euler two fluid model with the free surface option was applied on grids of minimum 4∙105 control volumes. The turbulence was modelled separately for each phase using the k-ω based shear stress transport (SST) turbulence model. The results compare well in terms of slug formation, velocity, and breaking. The qualitative agreement between calculation and experiment is encouraging and shows that CFD can be a useful tool in studying horizontal two-phase flow.
Furthermore, CFD pre-test calculations were done to show the possibility of slug flow generation in a real geometry and at relevant parameters for nuclear reactor safety. The simulation was performed on a flat model representing the hot-leg of the German Konvoi-reactor, with water and saturated steam at 50 bar and 263.9°C. The results of the CFD-calculation show wave generation in the horizontal part of the hot-leg which grow to slugs in the region of the bend.

Keywords: horizontal two-phase flow; interfacial area; slug flow

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-485 2007
    ISSN: 1437-322X


Publ.-Id: 10478

Experimentelle Untersuchung von geschichteten Luft/Wasser Strömungen in einem horizontalen Kanal

Vallée, C.; Prasser, H.-M.; Sühnel, T.

Für die Untersuchung von Luft/Wasser-Strömungen wurde ein horizontaler Acrylglas-Kanal mit rechteckigem Querschnitt gebaut. Der Kanal ermöglicht Gleich- und Gegenstrom-Versuche bei Atmosphärendruck, insbesondere die Untersuchung der Schwallströmung.
Es wurden optische Messungen mit einer Hochgeschwindigkeits-Kamera durchgeführt, die durch synchronisierte dynamische Druckmessungen ergänzt wurden. Für die Analyse der Bilder wurde eine Methode zur Erfassung der Phasengrenze entwickelt und diese anhand möglicher Anwendungen getestet. Die Druckmessungen zeigten, dass der Druck bei Schwallströmungen um einige Kilopascal ansteigt und wieder abfällt, sobald der Schwall aus dem Kanal austritt. Zudem wurden Geschwindigkeiten in der flüssigen Phase mittels nicht invasiver Verfahren gemessen. Das durchschnittliche Geschwindigkeits-Profil am Kanaleintritt wurde mit Ultraschall-Köpfen bestimmt. Die Ermittlung des Geschwindigkeitsfeldes in einem Schwall erfolgte mit PIV (Particle Image Velocimetry).

Keywords: dynamic pressure measurement; horizontal two-phase flow; optical high-speed observation; image processing; PIV (Particle Image Velocimetry); interfacial area; slug flow

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-484 2007
    ISSN: 1437-322X


Publ.-Id: 10477

Experiments on two-phase flow in a vertical tube with a moveable obstacle

Prasser, H.-M.; Beyer, M.; Carl, H.; Al Issa, S.; Schütz, P.; Pietruske, H.

A novel technique to study the two-phase flow field around an asymmetric diaphragm in a vertical pipe is presented, that enables producing data for CFD code validation in complex geometries. Main feature is a translocation of the diaphragm to scan the 3D void field with a stationary wire-mesh sensor. Besides the measurement of time-averaged void fraction fields, a novel data evaluation method was developed to extract estimated liquid velocity profiles from the wire-mesh sensor data. The flow around an obstacle of the chosen geometry has many topological similarities with complex flow situations in bends, T-junctions, valves, safety valves and other components of power plant equipment and flow phenomena like curved stream lines, which form significant angles with the gravity vector, flow separation at sharp edges and recirculation zones in their wake are present. In order to assess the quality of the CFD code and their underlying multiphase flow and turbulence models pre-test calculations by ANSYS CFX 10.0 were carried out. A comparison between the calculation results and the experimental data shows a good agreement in term of all significant qualitative details of the void fraction and liquid velocity distributions. Furthermore, the report contains a method to assess the lateral components of bubble velocities in the form of a basic theoretical description and visualisation examples. The plots show the deviation of the flow around the obstacle in term of vectors represented the average velocities of the instantaneous cross-sections of all bubbles in the time interval when they pass the measuring plane. A detailed uncertainty analyse of the velocity assessments concludes the presented report. It includes remarks about the comparison with a second method for calculating bubble velocity profiles – the cross-correlation. In addition, this chapter gives an overview about the influence of acceleration and deceleration effects on the velocity estimation.

Keywords: Two-Phase Flow; Gas bubbles; Gas volume fraction distribution; velocity fields

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-483 2007
    ISSN: 1437-322X


Publ.-Id: 10476

Experiments on upwards gas/liquid flow in vertical pipes

Prasser, H.-M.; Beyer, M.; Carl, H.; Manera, A.; Schütz, H.; Pietruske, P.

Two-phase flow experiments at vertical pipes are much suitable for studying the action of different constitutive relations characterizing the momentum exchange at the gas/liquid interface as well as the dynamic behaviour of the gas/liquid interface itself. The flow can be observed in its movement along the pipe and, in particular, within the shear field close to the pipe wall over a considerable vertical distance and, consequently, over a comparatively long time without the immediate separation of gas and liquid characteristic for horizontal flows.
Wire-mesh sensors, which were the working horse in the described experiments, supplied sequences of instantaneous two-dimensional gas fraction distributions with a high-resolution in space and time. This allows to derive from the data not only void fraction and bubble velocity profiles, but also bubble size distributions, bubble-size resolved radial gas fraction profiles as well as the axial evolution of these distributions. An interfacial surface reconstruction algorithm was developed in order to extract the extension of interfacial area from the wire-mesh sensor data. The sensors were upgraded to withstand parameters that are close to nuclear reactor conditions. Most of the experiments were performed for both air/water flow at ambient pressure and steam/water flow of up to 6.5 MPa at identical combinations of the gas and liquid superficial velocities. This offers excellent conditions for studying the influence of the fluid properties.

Keywords: Two-Phase Flow; Gas bubbles; Gas volume fraction distribution; velocity fields

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-482 2007
    ISSN: 1437-322X


Publ.-Id: 10475

Construction and execution of experiments at the multi-purpose thermal hydraulic test facility TOPFLOW for generic investigations of two-phase flows and the development and validation of CFD codes - Final report

Prasser, H.-M.; Lucas, D.; Beyer, M.; Vallée, C.; Krepper, E.; Höhne, T.; Manera, A.; Carl, H.; Pietruske, H.; Schütz, P.; Al Issa, S.; Zaruba, A.; Shi, J.-M.; Weiß, F.-P.

The works aimed at the further development and validation of models for CFD codes. For this reason, the new thermal-hydraulic test facility TOPFLOW was erected and equipped with wire-mesh sensors with high spatial and time resolution. Vertical test sections with nominal diameters of DN50 and DN200 operating with air-water as well as steam-water two-phase flows provided results on the evaluation of flow patterns, on the be¬haviour of the interfacial area as well as on interfacial momentum and heat transfer. The validation of the CFD-code for complex geometries was carried out using 3D void fraction and velocity distributions obtained in an experiment with an asymmetric obstacle in the large DN200 test section. With respect to free surface flows, stratified co- and counter-current flows as well as slug flows were studied in two horizontal test channels made from acrylic glass. Post-test calculations of these experiments succeeded in predicting the slug formation process.
Corresponding to the main goal of the project, the experimental data was used for the model development. For vertical flows, the emphasis was put on lateral bubble forces (e.g. lift force). Different constitutive laws were tested using a Multi Bubble Size Class Test Solver that has been developed for this purpose. Basing on the results a generalized inhomogeneous Multiple Size Group (MUSIG) Model has been proposed and implemented into the CFD code CFX (ANSYS). Validation calculations with the new code resulted in the conclusion that particularly the models for bubble coalescence and fragmentation need further optimisation.
Studies of single effects, like the assessment of turbulent dissipation in a bubbly flow and the analysis of trajectories of single bubbles near the wall, supplied other important results of the project.

Keywords: Two-phase flow; 3D-void fraction distribution; 3D-velocity distribution; CFD-simulation

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-481 2007
    ISSN: 1437-322X


Publ.-Id: 10474

Aufbau und Durchführung von Experimenten an der Mehrzweck-Thermohydraulikversuchsanlage TOPFLOW für generische Untersuchungen von Zweiphasenströmungen und die Weiterentwicklung und Validierung von CFD-Codes - Abschlussbericht

Prasser, H.-M.; Lucas, D.; Beyer, M.; Vallée, C.; Krepper, E.; Höhne, T.; Manera, A.; Carl, H.; Pietruske, H.; Schütz, P.; Zaruba, A.; Al Issa, S.; Shi, J.-M.; Weiß, F.-P.

Ziel der Arbeiten war die Weiterentwicklung und Validierung von Modellen in CFD-Codes. Hierzu wurde am FZD die thermohydraulische Versuchsanlage TOPFLOW aufgebaut und mit räumlich und zeitlich hochauflösenden Gittersensoren ausgestattet. Vertikale Teststrecken mit Nenndurchmessern von DN50 bzw. DN200 für Luft/Wasser- sowie Dampf/Wasser-Strömungen lieferten Ergebnisse zur Entwicklung von Strömungsformen, zum Verhalten der Zwischenphasengrenzfläche sowie zum Wärme- und Impulsaustausch zwischen den Phasen. Die Validierung des CFD-Codes in komplexen Geometrien erfolgte anhand von 3D Gasgehalts- und Geschwindigkeitsfeldern, die bei Umströmung eines asymmetrischen Hindernisses auftreten, das in der Teststrecke DN200 eingebaut war. Im Hinblick auf Strömungen mit freier Oberfläche untersuchte das FZD in zwei horizontalen Acrylglas-Kanälen geschichtete Zweiphasenströmungen im Gleich- bzw. Gegenstrom sowie Schwallströmungen. Bei den Nachrechnungen dieser Versuche gelang die Simulation der Schwallentstehung.
Entsprechend des Projektziels wurden die experimentellen Ergebnisse zur Modellentwicklung genutzt. Bei vertikalen Strömungen stand die Wirkung der lateralen Blasenkräfte (z. B. Liftkraft) im Vordergrund. Zum Test unterschiedlicher Modellansätze wurde hierzu ein Mehrblasenklassen-Testsolver entwickelt und genutzt. Darauf aufbauend wurde ein neues Konzept für ein Mehrblasenklassenmodell, das Inhomogene MUSIG Modell erarbeitet und in den kommerziellen CFD Code CFX (ANSYS) implementiert. Bei Validierungsrechnungen zeigte sich, dass vor allem die Blasenkoaleszenz- und –zerfallsmodelle weiter optimiert werden müssen. Untersuchungen zu Einzeleffekten, wie z. B. die Abschätzung von Turbulenzkoeffizienten und die Analyse der Trajektoren von Einzelblasen in unmittelbarer Wandnähe, lieferten weitere wichtige Ergebnisse des Projekts.

Keywords: Two-phase flow; 3D-void fraction distribution; 3D-velocity distribution; CFD-simulation

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-480 2007
    ISSN: 1437-322X


Publ.-Id: 10473

Localized proton magnetic resonance spectroscopy of lipids in adipose tissue at high spatial resolution in mice in vivo

Strobel, K.; van den Hoff, J.; Pietzsch, J.

We describe a localized proton magnetic resonance spectroscopy (1H-MRS) method for in vivo measurement of lipid composition in very small voxels
(1.5 mm x 1.5 mm x 1.5 mm) in adipose tissue in mice. The method uses localized point resolved spectroscopy (PRESS) to collect 1H-spectra from voxels in intra-abdominal white adipose tissue (WAT) and brown adipose tissue (BAT) deposits. Nonlinear least squares fits of the spectra in the frequency domain allow for accurate calculation of the relative amount of saturated, monounsaturated, and polyunsaturated fatty acids.
All spectral data are corrected for spin-spin relaxation. The data show BAT of NMRI mice to be significantly different from BAT of NMRI nu/nu mice in all aspects except for the fraction of monounsaturated fatty acids; for WAT only the fraction of monounsaturated fatty acids is different. BAT and WAT of NMRI mice differ in the amount of saturated and diunsaturated fatty acids. This method provides a potential tool for studying lipid metabolism in small animal models of disease during initiation, progression and manifestation of obesity-related disorders in vivo.

Our results clearly demonstrate that localized 1H-MRS of adipose tissue in vivo is possible at high spatial resolution with voxel sizes down to 3.4 ml.

Publ.-Id: 10472

Hydrogen interaction with vacancies in electron irradiated niobium

Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.; Gemma, R.; Nikitin, E.; Kirchheim, R.; Pundt, A.

Defect studies of Nb irradiated with 10 MeV electrons were performed in the present work by means of positron annihilation spectroscopy. The lattice defects were characterized by positron lifetime spectroscopy. Moreover, defect depth profiles were studied by slow positron implantation spectroscopy. The experimental investigations were accompanied by first principles theoretical calculations of positron parameters. It was found that irradiation-induced vacancies in Nb specimens are surrounded by H, which causes a shortening of the lifetime of trapped positrons. The influence of a Pd and Cr over-layer on the H concentration in the Nb specimens was examined.

  • Invited lecture (Conferences)
    37th Polish Seminar on Positron Annihilation, 03.-07.09.2007, Ladek Zdroj, Poland
  • Open Access Logo Acta Physica Polonica A 113(2008), 1293-1299

Publ.-Id: 10471

Characterization of ZnO by positron annihilation

Brauer, G.

  • Invited lecture (Conferences)
    37th Polish Seminar on Positron Annihilation, 03.-07.09.2007, Ladek Zdroj, Poland

Publ.-Id: 10470

A microsensor study on the O2 consumption in a U(VI) contaminated multispecies biofilm

Krawczyk-Bärsch, E.; Großmann, K.; Arnold, T.; Wobus, A.; Diessner, S.

Multispecies biofilms were cultured in annular rotating biofilm reactors and subsequently exposed to U(VI) in ecological relevant concentration (5×10-5 M and 5×10-6 M). Such concentrations are comparable with uranium concentrations typically found in seepage waters of uranium tailings, e.g. in Saxony/Germany. The resulting response of the microbial biofilm community to the added U(VI) was then studied by electrochemical oxygen microsensors with tip diameters of 10 µm and by staining methods using the fluorogenic redox indicator 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and the DNA-binding fluochrome 4,6-diamidino-2-phenylindole (DAPI) in combination with confocal laser scanning microscopy (CLSM). The visualized ratio of CTC-formazan to DAPI intensity was used as an indication of the specific respiratory activity within the biofilms. In addition, 16S rDNA analysis and fluorescence in situ hybridization (FISH) investigations were carried out to study the effect of added uranium on the bacterial diversity.

The microsensor measurements revealed that the oxygen concentration in the multispecies biofilms exposed to uranium decreased faster with increasing biofilm depths in comparison to the uranium free biofilms. Analyses of the amplified 16S rDNA gene fragments showed that the addition of uranium induced no changes to the bacterial diversity in the multispecies biofilms. However, the analyses clearly indicated that a stable multispecies biofilms had developed. The metabolic activity, determined by CTC measurements increased in the upper layers of the biofilms by the addition of the uranium shown by faster oxygen consumptions. This indicates that the bacteria in the biofilms battle the toxic effects of aqueous uranium with an increased metabolic activity proven by the increased CTC activity and in particular by faster oxygen consumption in the biofilm profiles.

  • Contribution to proceedings
    6. Jenaer Sanierungskolloquium, 04.-05.10.2007, Jena, Germany
  • Poster
    6. Jenaer Sanierungskolloquium, 04.-05.10.2007, Jena, Germany

Publ.-Id: 10469

Reduktion von Uran(VI) durch Glucose

Gründig, I.

... Die Untersuchungsergebnisse sind von grundlegender Bedeutung für Aussagen zur Mobilität dieser nuklide in der Geo- und Biosphäre, denn in wässrigen Sysstemen sind besonders die Actinide in verschiedenen Oxidationsstufen stabil und sie bilden eine Reihe von Komplexen mit anorganischen und organischen Liganden. Durch den sehr niedrigen Konzentrationsbereich, der teilweise durch die geringe Löslichkeit der Actiniden verursacht wird, weisen Datenbanken oft große Lücken und Unsicherheiten auf. Diese gelten vor allem für die unter natürlichen reduzierenden Bedingungen stabilen, niedrigen Oxidationsstufen dieser Elemente.
Die meisten erforschten Reduktionsvorgänge verschiedener Actinide liegen im sauren pH-Bereich, die neutralen beziehungsweise basischen pH-Bereiche wurden selten betrachtet. Dabei spielen auch diese pH-Werte eine wichtige Rolle für die Weiterentwicklung thermodynamischer Datenbanken, da diese Datensätze eine entscheidende Voraussetzung zu Aussagen für die Langzeitsicherheit von nuklearen Endlager und Sanierungsvorhaben der Altlasten des Uranerzbergbaus bilden.
Ziel dieser Arbeit war es, die Reduktion von U(VI) mit dem Bioliganden Glucose in dem pH-Bereich vier bis neun zu erforschen.

  • Other report
    Praktikumsbericht: Dresden: Hochschule für Technik und Wirtschaft, 2007
    55 Seiten

Publ.-Id: 10466

Air/water flow experiments in the hot leg model of the TOPFLOW facility

Vallee, C.; Deendarlianto; Lucas, D.; Beyer, M.; Pietruske, H.

The presentation gives an overview about the air/water experiments performed in the hot leg model built in the pressure vessel of the TOPFLOW facility.
These experiments were conducted in a flat test-section representing a model of the hot leg of a pressurised water reactor. The region of the elbow and of the steam generator inlet chamber are equipped with glass side walls in order to allow high-speed video observations of the two-phase flow in this region. Three types of experiments were performed: co-current flow experiments, steady counter-current flow experiments and counter-current flow limitation (CCFL) experiments. The test procedures, detailed test matrices and selected examples of the measured data are presented. Furthermore, an analysis of the CCFL experiments is shown, including a comparison with similar experiments and empirical correlations available in the literature.
In the next future, the acquired data will be treated to allow the validation of CFD codes.

Keywords: hot leg; pressurised water reactor; PWR; two-phase flow; counter-current flow; counter-current flow limitation; CCFL

  • Lecture (others)
    10th Meeting of the German CFD Network, 17.-18.09.2007, Garching, Germany

Publ.-Id: 10465

Post Mortem Investigations of the NPP Greifswald WWER-440 Reactor Pressure Vessels

Viehrig, H.-W.; Rindelhardt, U.; Schuhknecht, J.

The investigation of reactor pressure vessel (RPV) materials from decommissioned NPPs offers the unique opportunity to scrutinize the irradiation behaviour under real conditions. Trepans taken from the whole RPV wall enable a comprehensive material characterisation. The paper describes the trepanning technology applied to the decommissioned WWER-440/230 RPVs of the Greifswald NPP. The Greifswald RPVs represent different material conditions such as irradiated, irradiated and recovery annealed and irradiated, recovery annealed and re-irradiated. The working program is focussed on the characterisation of the RPV steels (base and weld metal) through the RPV wall. The key part of the testing is aimed at 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. In a first step the material of the core welding seam was investigated. 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 represent the material with the lowest toughness.

Keywords: reactor pressure vessel steels; fracture toughness; Master Curve; nuclear reactor pressure vessel integrity assessment

  • Contribution to proceedings
    33. MPA-Seminar Werkstoff- und Bauteilverhalten in der Energie- und Anlagentechnik, 11.-12.10.2007, Stuttgart, Germany
    Proceedings 33. MPA-Seminar "Werkstoff- & Bauteilverhalten in Energie- & Anlagentechnik", Stuttgart: Materialprüfungsanstalt Universität Stuttgart, 4-1-4-9

Publ.-Id: 10464

Surface roughness evolution and growth mechanism of carbon films from hyperthermal species

Lifshitz, Y.; Edrei, R.; Hoffman, A.; Grossman, E.; Lempert, G. D.; Berthold, J.; Schultrich, B.; Jäger, H. U.

The roughness evolution of carbon films deposited from hyperthermal species was investigated by AFM. 10 eV C deposition at normal incidence angle starts with formation of 10 nm high islands followed by continuous, sp2 rich films at larger doses with essentially the same feature height and film roughness. 40 eV C deposition at normal incidence angle (0°) forms sp3 rich, atomically smooth films, which become sp2 rich and rough at oblique angles (≥60°). The limitations of currently available molecular dynamic simulations prevent their use to describe the island formation during 10 eV C bombardment. Dedicated calculations probing the effect of incidence angle on 40 eV C deposition exhibit similar trends to the experimental data i.e. decrease of the sp3 fraction and increase of the roughness with increasing incidence angle. The results are in accord with the “subplantation” scheme, linking roughness and sp2 bonding to surface entrapment. Implications on recent works discussing growth mechanisms or surface smoothening are given.

Keywords: DLC; Amorphous carbon; Growth; Surface roughness; Subplantation; AFM

  • Diamond and Related Materials 16(2007), 1771-1776
  • Invited lecture (Conferences)
    6th Specialists Meeting on Amorphous Carbon (SMAC 2006), 10.-13.09.2006, Heraclion, Crete, Greece

Publ.-Id: 10463

In-medium modification and decay asymmetry of omega mesons in cold nuclear matter

Titov, A. I.; Kämpfer, B.

We discuss an asymmetry of the decay omega -> e+ e- in nuclear matter with respect to the electron and positron energies. This asymmetry is sensitive to the properties of the omega meson self-energy and, in particular, it has a non-trivial dependence on the omega energy and momentum. Therefore, this asymmetry may serve as a powerful tool in studying the properties of the omega meson in the nuclear medium.

Keywords: omega meson in nuclear matter; decay asymmetry

Publ.-Id: 10462

Asymptotic methods for spherically symmetric MHD α2-dynamos

Günther, U.; Kirillov, O.

We consider two models of spherically-symmetric MHD α2-dynamos; one with idealized boundary conditions (BCs); and one with physically realistic BCs. As it has been shown in our previous work, the eigenvalues λ of a model with idealized BCs and constant α-profile α0 are linear functions of α0 and form a mesh in the (α0, λ)-plane. The nodes of the spectral mesh correspond to double-degenerate eigenvalues of algebraic and geometric multiplicity 2 (diabolical points). It was found that perturbations of the constant α-profile lead to a resonant unfolding of the diabolical points with selection rules of the resonant unfolding defined by the Fourier coefficients of the perturbations. In the present contribution we present new exact results on the spectrum of the model with physically realistic BCs and constant α. For non-degenerate (simple) eigenvalues perturbation gradients are found at any particular α0. We briefly discuss the spectral behavior of the α2-dynamo operator over a family of homotopic deformations of the BCs between idealized ones and physically realistic ones. Furthermore, we demonstrate that although the spectral singularities are lifted, a memory about their locations remains deeply imprinted in the homotopic family of spectral deformations due to a hidden underlying invariance.

Keywords: MHD dynamo; diabolical point; perturbation theory; boundary conditions; homotopy; deformation; gradient technique; resonance pattern

  • Open Access Logo Proceedings in Applied Mathematics and Mechanics 7(2007)1, 4140023-4140024
    DOI: 10.1002/pamm.200700964
    ISSN: 1617-7061

Publ.-Id: 10460

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