Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Without submitted and only approved publications
Only approved publications

31745 Publications
Two-photon photocurrent autocorrelation using intersubband transitions at nearly-resonant excitation
Schneider, H.; Maier, T.; Liu, H. C.; Walther, M.;
We investigate nonlinear mid-infrared detection via two-photon transitions involving two bound subbands and one continuum resonance in an n-type multiple quantum well. By varying the excitation energy, we have tuned the two-photon transition from resonant, yielding optimum resonant enhancement with a real intermediate state, to nearly-resonant, with a virtual but resonantly enhanced intermediate state. For autocorrelation purposes, the latter configuration improves time resolution whilst partially retaining a resonant enhancement of the two-photon transition strength.
Keywords: intersubband transition, multiple quantum well, two-photon excitation, mid-infrared detector, ultrafast spectroscopy
  • Open Access LogoOptics Express 16(2008)3, 1523-1528

Publ.-Id: 10912 - Permalink


Experimental investigation and CFD simulation of the behaviour of mineral wool in the reactor sump
Krepper, E.; Cartland-Glover, G.; Grahn, A.; Weiss, F.-P.; Alt, S.; Hampel, R.; Kästner, W.; Seeliger, A.;
The investigation of insulation debris generation, transport and sedimentation becomes important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core cooling systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems.
Open questions of generic interest are the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow and the particle load on strainers and corresponding pressure drop. A joint research project on such questions is being performed in cooperation between the University of Applied Sciences Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow and the development of CFD models for its description. While the experiments are performed at the University at Zittau/Görlitz, the theoretical modeling efforts are concentrated at Forschungszentrum Dresden-Rossendorf.
In the current paper the basic concepts for CFD modeling are described and feasibility studies including the conceptual design of the experiments are presented.
Keywords: CFD, two-fluid approach, fiber flows
  • Contribution to proceedings
    16th International Conference on Nuclear Engineering, ICONE-16, 11.-15.05.2008, Orlando, Florida, USA
  • Lecture (Conference)
    16th International Conference on Nuclear Engineering, ICONE-16, 11.-15.05.2008, Orlando, Florida, USA

Publ.-Id: 10911 - Permalink


Development of segmented straws for very high-rate capability coordinate detector
Davkov, K.; Davkov, V.; Geyer, R.; Gusakov, Y. V.; Kekelidze, G. D.; Myalkovskiy, V. V.; Naumann, L.; Peshekhonov, D. V.; Peshekhonov, V. D.; Savenkov, A. A.; Tikhomirov, V. O.; Viryasov, K. S.;
To reduce the occupancy of the large-size coordinate detectors, the high-granularity straw tracking chamber has been designed and tested. The main tasks were to improve the detector granularity and provide the best value of the detector radiation thickness. We have developed the techniques of the multiple anode production, assembling of the segmented straws and the low-mass readout by means of flat cable. Testing of the constructed prototypes has shown that these techniques can be applied to build the high-granularity straw detectors.
Keywords: Straw-drift chamber; Tracking detector; High granularity; Small occupancy

Publ.-Id: 10910 - Permalink


Review of available data for validation of nuresim two-phase CFD software applied to CHF investigations
Bestion, D.; Anglart, H.; Carraghiaur, D.; Péturaud, P.; Smith, B.; Andreani, M.; Niceno, B.; Krepper, E.; Lucas, D.; Moretti, F.; Galassi, M. C.; Macek, J.; Vyskocil, L.; Koncar, B.; Hazi, G.;
The NURESIM Integrated Project of the 6th European Framework Program was envisaged to initiate the development of the next-generation common European Standard Software Platform for simulating nuclear reactors. The overall objective of NURESIM Thermalhydraulic sub-project is to improve the understanding and the predictive capabilities of the simulation tools for key two-phase flow thermal-hydraulic processes such as the Critical Heat Flux (CHF). A multi-scale analysis of reactor thermalhydraulics is envisaged and two-phase CFD is developed to allow some zoom on local processes when the resolution of system codes is not sufficient.
Current industrial methods for CHF mainly use the sub-channel analysis and empirical CHF correlations based on large scale experiments having the real geometry of the reactor assembly. The NURESIM-TH activities regarding CHF aim at using two-phase CFD as a tool for understanding boiling flow processes, in order to subsequently help new fuel assembly design and to develop better CHF predictions in both PWR and BWR. A “Local Predictive Approach” may be envisaged for the long term where CHF empirical correlations would be based on local T/H parameters provided by CFD.
This paper presents a review of existing experimental data bases which can be used for validation of the two-phase CFD application to Critical Heat Flux (CHF) investigations with respect to nuclear reactors. The phenomenology of DNB and Dry-Out are detailed identifying all basic flow processes which require a specific modeling in CFD tool. The resulting program of work is given and the current state of the art of the modeling is presented.
Keywords: Critical heat flux, experimenbtal data, CFD simulation

Publ.-Id: 10909 - Permalink


An overview of the Pressurized Thermal Shock issue in the context of the NURESIM project
Lucas, D.; Bestion, D.; Bodèle, E.; Scheuerer, M.; D’Auria, F.; Mazzini, D.; Smith, B.; Tiselj, I.; Martin, A.; Lakehal, D.; Seynhaeve, J.-M.; Kyrki-Rajamäki, R.; Ilvonen, M.; Macek, J.; Coste, P.;
This paper reports activities regarding the simulation of Pressurized Thermal Shock (PTS) performed within the European Integrated Project NURESIM. Some Loss of Coolant Accident (LOCA) scenarios for Pressurized Water Reactors (PWR) may cause Emergency Core Coolant injection into the cold leg and thus lead to PTS situations. They imply the formation of temperature gradients in the thick vessel walls with consequent localized stresses and the potential for propagation of possible flaws present in the material. The present paper, in the area of fluid dynamics, focuses on the study of two-phase conditions that are potentially at the origin of PTS. It summarizes recent advances in the understanding of the two-phase phenomena occurring within the geometric region of the nuclear reactor, i.e. the cold leg and the downcomer, where the ‘PTS fluid-dynamics’ is relevant. Available experimental data for validation of two-phase CFD simulation tools are reviewed and the capabilities of such tools to capture each basic phenomenon are discussed. Key conclusions show that several two phase flow sub-phenomena are involved and can individually be simulated at least at a qualitative level, but the capability to simulate their interaction and the overall system performance is still limited. In the near term, one may envisage a simplified treatment of two-phase PTS transients by neglecting some effects which are not yet well controlled, leading to slightly conservative predictions.
Keywords: PTS, CFD, Nuclear reactor simulation

Publ.-Id: 10908 - Permalink


Simulations of DEBORA data with CFX
Krepper, E.;
In the DEBORA experiments subcooled boiling is investigated heating up Dichlorodifluoromethane (R12) in a side wall heated tube. Radial profiles for gas volume fraction, gas velocity, liquid temperatures and bubble sizes were measured at the end of the heated length. This enables the validation not only of the wall boiling model but also of the models for liquid/gas momentum, heat and mass transfers.
The report describes the model simulating the wall boiling preliminary implemented in CFX-11 which is also implemented in the NEPTUNE code. These approaches are based on the proposal of Kurul and Podowski (1990). Specific model developments concerning the near wall phenomena are described in the report. Furthermore the momentum exchange models used in the CFX simulations are described.
The same parameters for the model correlations adjusted for water/steam flow were applied simulating the fluid R12. To investigate the influence on the results, essential boiling model parameters were varied and the sensitivity of the results is shown. The need of further model development and of further experiments can be confirmed. The validation applying for the different models shows the state and the limits of the present modelling.
The simulations are intended for the comparison to other CFD models e.g. to the NURESIM-CFD platform.
Keywords: Two phase flow, CFD, subcooled boiling, drag forces, non drag forces, experimente, model validation
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    NURESIM-SP2-TH-D2.2.3.2 (Jauary 2008)
    37 Seiten

Publ.-Id: 10907 - Permalink


Fracture Mechanics Characterisation of the WWER-440 Reactor Pressure Vessel Core Welding Seam
Viehrig, H.-W.; Schuhknecht, J.;
The Master Curve (MC) approach as standardised in the ASTM Standard Test Method E 1921-05 was applied on weld metal of the reactor pressure vessel (RPV) core welding seam of Greifswald Unit 8 RPV. Charpy size SE(B) specimens from 13 locations equally spaced over the thickness of the welding seam were tested. The specimens are TL and TS orientation.
The fracture toughness values measured on the SE(B) specimens with both orientations follow the course of the Master Curve. Nearly all values lie within the fracture toughness curves for 5% and 95% fracture probability. There is a strong variation of the reference temperature T0 though the thickness of the welding seam, which can be explained with structural differences. The scatter is more pronounced for the TS SE(B) specimens. It can be shown that specimens with TL and TS orientation in the welding seam have a differentiating and integrating behaviour, respectively.
Keywords: reactor pressure vessel, multilayer welding seam, specimen orientation, structure, fracture toughness, Master Curve approach, reference temperature, integrity assessment of base metal from the Greifswald Unit 8 RPV show large scatter

Publ.-Id: 10906 - Permalink


Fullerene-like alloyed carbon films
Abrasonis, G.;
The synthesis, structure and properties of fullerene-like alloyed carbon films are reviewed. The term fullerene-like describes extended structures consisting of curved basal planes, which are stacked perpendicular to the basal planes. Fullerene-like structures can be observed in layered materials like graphitic carbon, carbon nitride, hexagonal boron nitride or tungsten disulfide. They can be characterized by extension, curvature and cross-linking of basal planes. Their structure results in an exceptional combination of mechanical properties such as high hardness, high elastic recovery, high wear resistance and low coefficient of friction.

In carbon based fullerene-like structures, these properties result from stiff (sigma pi)-bonds within the basal graphitic planes, fullerene-like structure assuring the presence of their 3D network due to the curvature and cross-linking. The fullerene-like structure of pure carbon can be further stabilized by alloying with nitrogen. Different nitrogen incorporation routes result in different local carbon-nitrogen bonding arrangements which then determine the extension, curvature and cross-linking of basal planes. Since both elements – carbon and nitrogen – can form sp1, sp2 and sp3 bonds, the nanostructure is determined by the relative concentration of local chemical environments such as nitrile-like, pyridine-like or graphite-substitutional. The former two configurations are terminating, thus hindering the extension of basal planes The latter induces buckling in the planes due to stabilization of pentagon rings or due to the difference between C-N and C-C bonds which locally shrinks the network.

An alternative way to produce fullerene-like structures is carbon alloying with metallic elements. The metal atoms segregate into the nanoparticles which act as catalytic sites for the six-fold-ring clustering of carbon atoms. Different metal incorporation routes determine the shape of metal nanoparticles ranging from completely spherical to nanorod-like. This significantly affects the graphitization of carbon as the so-formed graphitic planes follow the boundaries of the metal nanoparticles resulting in partially wrapped metal nanocolumns or completely encapsulated metal nanoparticles. These fullerene-like nanostructures might be used for applications as low-friction, self-lubrication, wear resistant coatings, as 2D network of tunnel junctions, as nanocontainers for foreign materials, or for encapsulation of ferromagnetic nanoparticles in non-magnetic media.
  • Invited lecture (Conferences)
    Fifteenth International Summer School on Vacuum, Electron and Ion Technologies, 17.-21.09.2007, Sozopol, Bulgaria

Publ.-Id: 10905 - Permalink


CFD calculation of new TOPFLOW hot leg experiments
Höhne, T.;
Usually, the slug flow regime is characterized by an acceleration of the gaseous phase and by the transition of fast liquid slugs, which carry a significant amount of liquid with high kinetic energy. It is potentially hazardous to the structure of a system due to the strong oscillating pressure levels formed behind the liquid slugs as well as the mechanical momentum of the slugs. Because slug flow cannot be predicted with the required accuracy and spatial resolution by the one-dimensional system codes, the stratified flows are increasingly modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated. The recent improvements of the multiphase flow modelling in the ANSYS CFX code make it now possible to simulate these mechanisms in detail. In order to validate existing and further developed multiphase flow models, high-resolution measurement data is needed in time and also in space.

Thanks to the optical access of the test channels built at Forschungszentrum Dresden-Rossendorf, it is possible to study detailed local stratified air/water flow phenomena. These experimental results give an important input for two-phase flow CFD model validation (i.e. interfacial momentum transfer, turbulent profiles of each phase). For the experimental investigation of co-current air/water flows, the HAWAC (Horizontal Air/Water Channel) was built (Fig. 1). Its inlet device provides defined inlet boundary conditions for code comparison. The channel allows in particular the study of air/water slug flow under atmospheric pressure. A flow pattern map (Fig. 2) was arranged constructed on the basis of a visual observation of the flow structure at different combinations of the gas and liquid superficial velocities. Parallel to the experiments, CFD calculations were carried out. A picture sequence recorded during slug flow was compared with the equivalent CFD simulation made (Figs. 3 and 4). The two-fluid model was applied with a special turbulence damping procedure at the free surface. An Algebraic Interfacial Area Density (AIAD) model on the basis of the implemented mixture model was introduced, which allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value.

The behaviour of slug generation and propagation at the experimental setup was qualitatively reproduced by the simulation, while local deviations require a continuation of the work. The creation of small instabilities due to pressure surge or an increase of interfacial momentum should be analysed in the future. Furthermore, experiments like pressure and velocity measurements are planned and will allow quantitative comparisons, also at other superficial velocities.
Keywords: hot leg, TOPFLOW, CFD
  • Lecture (others)
    13th Meeting, 23.-24.01.2008, Großhartpenning, Deutschland

Publ.-Id: 10903 - Permalink


Experimental and numerical modeling of transition matrix from momentum to buoyancy-driven flow in a pressurized water reactor
Höhne, T.; Kliem, S.; Vaibar, R.;
The influence of density differences on the mixing of the primary loop inventory and the Emergency Core Cooling (ECC) water in the cold leg and downcomer of a Pressurised Water Reactor (PWR) was analyzed at the ROssendorf COolant Mixing (ROCOM) test facility. This paper presents a matrix of ROCOM experiments in which water with the same or higher density was injected into a cold leg of the reactor model with already established natural circulation conditions at different low mass flow rates. Wire-mesh sensors measuring the concentration of a tracer in the injected water were installed in the cold leg, upper and lower part of the downcomer. A transition matrix from momentum to buoyancy-driven flow experiments was selected for validation of the CFD software ANSYS CFX. A mesh with 4 million control volumes was used for the calculations. The turbulence models usually applied in such cases assume that turbulence is isotropic, whilst buoyancy actually induces anisotropy. Thus, in this paper, higher order turbulence models have been developed which take into account for that anisotropy. Buoyancy generated source and dissipation terms were proposed and introduced into the balance equations for the turbulent kinetic energy. The results of the experiments and of the numerical calculations show that mixing strongly depends on buoyancy effects: At higher mass flow rates (close to nominal conditions) the injected slug propagates in the circumferential direction around the core barrel. Buoyancy effects reduce this circumferential propagation with lower mass flow rates and/or higher density differences. The ECC water falls in an almost vertical path and reaches the lower downcomer sensor directly below the inlet nozzle. Therefore, density effects play an important role during natural convection with ECC injection in PWR and should be also considered in Pressurized Thermal Shock (PTS) scenarios. ANSYS CFX was able to predict the observed flow patterns and mixing phenomena quite well.
Keywords: CFD, ROCOM, BUOYANCY-DRIVEN FLOW, PWR
  • Contribution to proceedings
    16th International Conference on Nuclear Engineering ICONE16, 11.-15.05.2008, Orlando, USA
    CD_ROM, 48490
  • Lecture (Conference)
    16th International Conference on Nuclear Engineering ICONE16, 11.-15.05.2008, Orlando, USA
  • Journal of Engineering for Gas Turbines and Power - Transactions of the ASME 131(2009)1, 012906
    DOI: DOI: 10.1115/1.2983137

Publ.-Id: 10902 - Permalink


Analysis of safety valve characteristics using measurements and CFD simulations
Höhne, T.; Moncalvo, D.;
In order to study valve characteristics, experiments of the Institut für Strömungsmechanik at the Technical University Hamburg-Haburg (TUHH) were used to validate the CFD-code ANSYS CFX. Due to the constant improvement of the physical models and numerics of the code it is now possible to simulate very complex flows through valves. This includes phenomena like jets, flow around obstacles, flow separation effects, stagnant regions and partly zones with high mach numbers. The geometric details of the safety valve internals have a strong influence on the flow field. Therefore, an exact representation of the inlet region, the seat and disc region and the shape of the valve body were necessary. The computational grid contains one million nodes. For code validation purposes experiments were taken with different fluids and mixtures and the influence of the different hubs was studied. In all cases a good agreement between measurements and numerical results could be achieved with existing models of the CFD code.
Keywords: safety valve, CFD
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Germany
    CD_ROM, paper 0249
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Germany

Publ.-Id: 10901 - Permalink


Modelling
van den Hoff, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    XX. Winterschule für Medizinische Physik, 25.-29.02.2008, Pichl, Austria

Publ.-Id: 10900 - Permalink


Quantitative Verfahren in der Positronen-Emissions-Tomographie
van den Hoff, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Bildgebung des Herzens - Workshop zur biomedizinischen Bildgebung, 18.02.2008, Würzburg, Germany

Publ.-Id: 10899 - Permalink


Visualization of branch points in PT-symmetric waveguides
Klaiman, S.; Günther, U.; Moiseyev, N.;
The visualization of an exceptional point in a PT-symmetric directional coupler (DC) is demonstrated. In such a system the exceptional point can be probed by varying only a single parameter. Using the Rayleigh-Schrödinger perturbation theory we prove that the spectrum is real as long as the radius of convergence has not been reached. We also show how one can use a PT-symmetric DC to measure the radius of convergence for non PT-symmetric structures. For such systems the physical meaning of the rather mathematical term `radius of convergence´ is exemplified.

Publ.-Id: 10897 - Permalink


Neuartige Lichtemitter und Nanosonden für zukünftige Optoelektronik und Nanotechnologie
Helm, M.;
Nach einem kurzen Überblick über die Forschung an meinem Institut möchte ich zwei Themengebiete näher diskutieren:
(1) Lichtemitter auf Basis von Silizium MOS Strukturen als möglicher Weg zu einer integrierten Silizium-Optoelektronik
(2) Infrarot-Nahfeldmikroskopie als Methode zur Untersuchung von oberflächennahen Nanostrukturen, hier demonstriert an ferroelektrischen Domänen in BaTiO3.
Keywords: Silizium Lichtemitter, Infrarot Nahfeldmikroskopie
  • Lecture (others)
    Seminarvortrag an der TU Wien, 05.12.2007, Wien, Austria

Publ.-Id: 10896 - Permalink


Quantitative Chemical Speciation in Environmental Systems: Statistical Approaches to EXAFS
Scheinost, A.;
- wird nachgereicht
  • Invited lecture (Conferences)
    School on Synchrotron X-ray and IR Methods Focusing on Environmental Sciences, 21.-23.01.2008, Karlsruhe, Deutschland

Publ.-Id: 10895 - Permalink


Short time thermal processing: From electronics via photonics to pipe organs of the 17th century
Skorupa, W.;
There is a clear and increasing interest in short time thermal processing far below one second, i.e. the lower limit of RTP (Rapid Thermal Processing) called spike annealing. It is the world of preocessing in the millisecond or nanosecond range. This was driven by the need of suppressing the so-called Transient Enhanced Diffusion in advanced boron-implanted shallow pn-junctions in the front-end silicon chip technology. Meanwhile the interest in flash lamp annealing (FLA) in the millisecond range spread out into other fields related to silicon technology and beyond. This paper reports shortly about the restart in flash lamp annealing of the Rossendorf group in collaboration with the Mattson group and further on recent experiments regarding shallow junction engineering in germanium, annealing of ITO layers on glass and plastic foil to form an conductive layer as well as investigations which we did during the last years in the field of wide band gap semiconductor materials (SiC, ZnO). Moreover recent achievements in the field of silicon-based light emission basing on Metal-Oxide-Semiconductor Light Emitting Devices will be reported. Finally it will be demonstrated that the basic principle of short time thermal processing, i.e. surface heating on a colder bulk, features also advantages regarding the casting of lead sheets to produce organ pipes in the spirit of the 17th century.
Keywords: millisecond processing, flash lamp annealing, silicon, germanium, indium tin oxide, silicon carbide, ziic oxide, photonics, light emission, electroluminescence, wafer stress.
  • Materials Science Forum 573-574(2008), 417-428
  • Invited lecture (Conferences)
    Mattson International Technology Seminar, 07.05.2008, Maritim Hotel Ulm, Deutschland
  • Invited lecture (Conferences)
    23. Nutzertreffen Kurzzeittemperung, 08.05.2008, Erlangen, Deutschland
  • Invited lecture (Conferences)
    VII-th International Conference on Ion Implantation and Other Applications of Ions and Electrons, 16.-19.06.2008, Kazimierz Dolny, Polen

Publ.-Id: 10894 - Permalink


Realistische Simulation von Reaktivitätsstörfällen mit gekoppelten neutronenkinetisch-thermohydraulischen Systemcodes - Abschlussbericht
Kliem, S.;
Der gekoppelte Programmkomplex DYN3D/ATHLET wurde im Rahmen der Arbeiten zum Projekt weiterentwickelt. Dabei wurde das in der externen Kopplung von DYN3D und ATHLET verfügbare Modell für die Beschreibung der Kühlmittelvermischung auf weitere Szenarien erweitert und in die anderen beiden Kopplungsoptionen implementiert. Des Weiteren wurde ein spezielles Modell zur Vermeidung der numerischen Diffusion beim Bortransport innerhalb des Reaktorkerns, das für DYN3D entwickelt worden war, in das Thermohydraulikprogramm ATHLET übertragen.
Für die Analyse von heterogenen Borverdünnungsstörfällen wurde eine Methodik bestehend aus stationären und transienten Rechnungen entwickelt. Durch die Implementierung des o.g. Modells zur realistischen Beschreibung der Kühlmittelvermischung in den gekoppelten Programmkomplex DYN3D/ATHLET war es möglich, eine neue Qualität in der Analyse von Borverdünnungsstörfällen zu erreichen. Die Methodik wurde auf zwei verschiedene Borverdünnungsstörfalle angewandt. Wesentliches Ergebnis ist, dass entsprechend den Rechenergebnissen selbst bei Vorgabe einer aus konservativen Abschätzungen stammenden maximalen Pfropfengröße für beide Szenarien die Integrität des Brennstoffs nicht gefährdet ist. Die entsprechenden Studien zeigten die großen Reserven, die beim konsequenten Abbau von Konservativitäten freigesetzt werden können. Der entscheidende Beitrag zu diesem Abbau ist dabei auf die realistische Modellierung der Vermischung der deborierten Pfropfen innerhalb des Reaktordruckbehälters zurückzuführen. Von Vorteil erwies sich hier der Einsatz der verschiedenen Kopplungsoptionen. Die damit verbundene Anwendung unterschiedlicher Thermohydraulikmodelle auf ein und dieselbe Störfalltransiente erhöht das Vertrauen in die erzielten Ergebnisse.
Die Untersuchungen zur Borverdünnung während des Nachkühlbetriebes wurden in einem gesonderten Bericht ausführlich dargestellt. Dieser Bericht wird derzeit im Rahmen eines Genehmigungsverfahrens eingesetzt.
Erstmals wurde das Programm DYN3D/ATHLET auf eine ATWS-Transiente angewandt. Am Beispiel der Transiente: „Ausfall der Hauptspeisewasserversorgung“ wurde der Einfluss verschiedener thermohydraulischer und neutronenkinetischer Randbedingungen auf die Ergebnisse untersucht. Der wichtigste Sicherheitsparameter bei der betrachteten Transiente ist der Druck im Primärkreislauf. Im Bereich der thermohydraulischen Variationen hat die Effektivität der Entlastungs- und Sicherheitsventile den größten Einfluss auf diesen Parameter. Der berechnete Maximaldruck hängt auch stark von der Kernbeladung ab. So wurde gezeigt, dass mit Erhöhung der Anzahl der MOX-Brennelemente das berechnete Druckmaximum deutlich niedriger ausfällt. Weiterhin wurden die Rückkopplungsparameter einer generischen Kernbeladung einer statistischen Unsicherheits- und Sensitivitätsanalyse unterzogen, in deren Verlauf 100 Variationsrechnungen durchgeführt wurden. Diese Analyse ergab, dass dabei bei identischer relativer Variationsbreite der Rückkopplungskoeffizient der Moderatordichte einen doppelt so großen Einfluss auf den berechneten Maximaldruck hat wie der Koeffizient der Brennstofftemperatur.
Mit dem Programmkomplex DYN3D/ATHLET steht ein anwendungsbereites Werkzeug mit einer breiten Validierungsbasis für die Analyse von Störfällen zur Verfügung, in denen die enge Kopplung von Neutronenkinetik und Thermohydraulik unter Berücksichtigung des Einflusses der Anlagenkomponenten von Bedeutung ist. Es kann für konkrete Nachweisrechnungen einschließlich der Quantifizierung von Unsicherheiten auf Basis deterministischer oder statistischer Ansätze eingesetzt werden.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    FZD\FWS\2007\11
    113 Seiten

Publ.-Id: 10893 - Permalink


Science at the new Dresden High Magnetic Field Laboratory
Wosnitza, J.;
hat nicht vorgelegen
  • Invited lecture (Conferences)
    International Conference on Magnetic Materials (ICMM-2007), 11.-16.12.2007, Kolkata, India

Publ.-Id: 10892 - Permalink


Die Jagd nach dem Feldrekord: Forschung in hohen Magnetfeldern
Wosnitza, J.;
hat nicht vorgelegen
  • Invited lecture (Conferences)
    Physikalisches Kolloquium der Universität Frankfurt, 05.12.2007, Frankfurt/ M., Germany

Publ.-Id: 10891 - Permalink


Comparison of the americium(III), neptunium(V) and uranium(VI) sorption onto kaolinite in the absence and presence of humic acid
Schmeide, K.; Krepelova, A.; Sachs, S.; Bernhard, G.;
We studied the sorption of Am(III), Np(V) and U(VI) onto kaolinite under aerobic and anaerobic conditions as a function of pH, ionic strength and actinide concentration in a series of batch equilibrium experiments. These actinides were selected as representatives of actinides in different oxidation states. Furthermore, we studied the influence of humic acid on the actinide sorption.
Keywords: americium, neptunium, uranium, sorption, humic acid, trivalent, pentavalent, hexavalent
  • Lecture (Conference)
    2nd International Nuclear Chemistry Congress, 13.-18.04.2008, Cancún, Mexico
  • Contribution to proceedings
    2nd International Nuclear Chemistry Congress, 13.-18.04.2008, Cancún, Mexico

Publ.-Id: 10890 - Permalink


Sorption of U(VI) onto an artificial humic substance-kaolinite-associate
Sachs, S.; Bernhard, G.;
An artificial humic substance-kaolinite-associate was synthesized as a model substance for natural clays containing organic matter in clay formations, soils, and sediments. The U(VI) sorption onto this model substance was studied in batch experiments as a function of pH and compared to the U(VI) sorption onto kaolinite in absence and presence of separately added humic acid (HA).
The humic substance-kaolinite-associate has a TOC content of 4.9 mg/g. It was found that the humic matter associated with kaolinite exhibits an immobilizing as well as an mobilizing effect on U(VI). Between pH 3 and 5, humic matter causes an increase in the U(VI) sorption onto kaolinite, whereas at pH above 5 the release of humic matter from the associate in the solution and the formation of dissolved uranyl humate complexes reduces the U(VI) sorption. The U(VI) sorption onto the synthetic humic substance-kaolinite-associate differs from that of U(VI) in the system U(VI)-HA-kaolinite with comparable amounts of separately added HA. Separately added HA causes a stronger mobilizing effect on U(VI) than humic matter present in the humic substance-kaolinite-associate. This can be attributed to structural and functional dissimilarities of the humic substances.
Keywords: Uranium, Sorption, Clay, Kaolinite, Humic matter

Publ.-Id: 10889 - Permalink


Determination of structural components, e.g. exopolymeric substances (EPS) within biofilms and their effect on the immobilisation of actinides (U) - Determination of pH, Eh, and dissolved oxygen and their influence on the actinide speciation
Krawczyk-Bärsch, E.; Arnold, T.; Großmann, K.;
Fluorescent uranium(V) and uranium(VI) particles were observed for the first time in vivo by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach in a living multispecies biofilm grown on biotite plates. Anaysis of amplified 16S rRNA fragments and fluorescence in situ hybridization were used to characterize the biofilm communities. 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 biofilms. Concentration profiles of oxygen versus biofilm depths were measured in the biofilms by electrochemical microsensors with a tip diameter of 10µm. A motor-driven micromanipulator was used for moving downwards through the biofilm in 20 or 50µm steps. The microsensor results clearly showed that the vertical profiles of the O2 concentration within the biofilms are affected by the presence as well as by the concentration of U(VI) in the culture media. In the absence of uranium the O2 concentration in the well aerated biofilm decreased slightly. In contrast, O2 concentrations in the biofilms, which were exposed to different concentrations of uranium, decreased with increasing uranium concentration.
Keywords: biofilm, uranium, oxygen microsensors
  • Lecture (Conference)
    3rd Semi-Annual RTDC-2 meeting of FUNMIG, 26.08.2007, München, Deutschland

Publ.-Id: 10888 - Permalink


WnSm-Clusters: Possible Building Blocks for New Nanomaterials?
Westhäuser, W.; Mangler, T.; Fischer, T.; Gemming, S.; Seifert, G.; Ganteför, G.;
Since bulk WS2 forms layered structures similar to bulk graphite, this material might also built up stable cage-like fullerene structures. Large graphite-like structures (multiwall fullerenes, nanotubes) have been found in TEM experiments, but so far no anorganic fullerenes have been detected in the size regime of C60. Thus, we started a search for WS2 fullerenes by combining gas phase and deposition experiments. In the gas phase, we identified a variety of different structures (nanowires, nanoplatelets) in the size regime up to 30 metal atoms [1-3]. To investigate the suitability as building blocks, in a first attempt small size-selected WnSm-clusters were soft-landed on Ag- and Si substrates at ultrahigh vacuum conditions. These samples were analysed via HREELS and XPS. The HREELS spectra are different for the different cluster sizes indicating that these clusters survived the soft landing on the substrate and do not coalesce to bulk-like structures.
[1] S. Gemming, J. Tamuliene, G. Seifert, N. Bertram, Y.D. Kim, and G. Ganteför, Appl. Phys. 82, 161 (2006)
[2] N. Bertram, Y.D. Kim, G. Ganteför, Q. Sun, P. Jena, J. Tamuliene, and G. Seifert, Chem. Phys. Lett. 396, 341 (2004)
[3] N. Bertram, J. Cordes, Y.D. Kim, G. Ganteför, S. Gemming, and G. Seifert, Chem. Phys. Lett. 418, 36 (2006)
Keywords: MoS2, WS2, sulfide, nanostructures, DFT, density-functional
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 10885 - Permalink


Modelling a nanoscale ferroic OFET
Gemming, S.; Enyashin, A. N.; Seifert, G.; Eng, L. M.;
The present study describes an approach for the scale-bridging modelling of ferroic materials as functional elements in micro- and nanoelectronic devices. Ferroic materials are characterised by temperature-dependent complex ordering phenomena of the internal magnetic, electronic, and structural degrees of freedom with several involved length and time scales. Hence, the modelling of such compounds is not straighforward, but relies on a combination of electronic-structure-based methods like ab-initio and density-functional schemes with classical particle-based approaches given by Monte-Carlo simulations with Ising, lattice-gas, or Heisenberg Hamiltonians, which incorporate material-specific parameters both from theory and experiment. The interplay of those methods is demonstrated for device concepts based on electroceramic materials like ferroelectrics and multiferroics, whose functionality is closely related with their propensity towards structural and magnetic polymorphism. In the present case, such scale-bridging techniques are employed to aid the development of an organic field effect transistor on a ferroelectric substrate generated by the self-assembly of field-sensitive molecules on the surfaces of ferroic oxides.
Keywords: OFET, ferroic, multi-scale, DFT, density-functional, Monte-Carlo
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 10884 - Permalink


Point defects in germanium - theory and experiment
Gemming, S.; Wündisch, C.; Posselt, M.;
The functionality of standard silicon-based semiconductor devices is achieved by careful point defect engineering, hence tremendous efforts have been made to arrive at a quantitative understanding of the underlying interactions. Germanium has distinct advantages over silicon, for instance the lower energy gap between occupied and empty electronic states and the resultant lower carrier injection barriers. However, point defect engineering in germanium has not yet reached a level of sophistication comparable with the one in silicon. Thus, both theoretical and experimental investigations were carried out to study the interaction of point defects in germanium.
Conductivity measurements of phosphorus-implanted germanium indicate that not all dopant atoms are electronically active. Therefore density-functional calculations were carried out to study the properties of Ge vacancies, substitutional phosphorus defects and their interaction. Stable defect clusters are obtained, and in the limit of high dopant concentration an electrically inactive form of the P dopant is predicted.
Keywords: germanium, doping, phosphorus, DFT, density-functional
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 10883 - Permalink


A Hybrid Modelling Approach for the Structural Evolution of Surfaces
Gemming, S.; Kundin, J.; Radke De Cuba, M.; Yu, C.-J.; Emmerich, H.;
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. A particle-based Ising-type approach with a Metropolis-Monte-Carlo kinetics additionally provides 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 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 is calculated by the phase-field method. Several growth modes are distinguished: 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.
Keywords: Burton-Cabrera-Frank, Hybrid model, Monte-Carlo, phase-field, vicinal, nucleation
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 10882 - Permalink


DFT for the Actinides
Tsushima, S.;
no abstract for this publication
Keywords: DFT, actinide
  • Lecture (others)
    internal ROBL seminar, 13.3.2007, Grenoble, France

Publ.-Id: 10881 - Permalink


Hydration of U(VI,V) and Np(VI) Ions Revisited
Tsushima, S.;
no abstract for this publication
Keywords: hydration, actinide, DFT
  • Poster
    17th ESRF User's Meeting, 05.-8.2.2007, Grenoble, France

Publ.-Id: 10880 - Permalink


Quantum Chemical Calculations of U(VI) Aquo and Sulfato complexes
Tsushima, S.;
no abstract for this publication
Keywords: quantum chemistry, EXAFS
  • Invited lecture (Conferences)
    GRK Symposium "Speciation of Radionuclides in the Environment", 21.09.2006, Mainz, Germany

Publ.-Id: 10879 - Permalink


Thermochromatographic Studies of Plutonium Oxides
Hübener, S.; Taut, S.; Vahle, A.; Bernhard, G.; Fanghänel, T.;
Trace amounts of oxidic plutonium species were studied by thermochromatography in silica glass columns in comparison to oxidic species of Th, Pa, U, Np, and Am. Humid oxygen was used as reactive admixture to the carrier gas helium. The thermochromatographic behavior of plutonium provides evidence for the oxidation of Pu(IV) to Pu(VI) with humid oxygen. The gas chromatographic transport of U, Np, and Pu is governed by the surface reaction
MO2(OH)2(g) = MO3(ads) + H2O(g)
with M = U, Np, and Pu in the hexavalent state and competitive reactions of the actinide oxides with silica to nonvolatile compounds or solid solutions. There is good agreement with earlier volatility studies and the reported oxidation of PuO2 with water. The oxidation to PuO4 as claimed by Domanov could not be confirmed.
Keywords: Plutonium oxides, thermochromatography, oxidation, volatility

Publ.-Id: 10878 - Permalink


Influence of uranium (VI) on the metabolic activity of stable multispecies biofilms studied by oxygen microsensors and fluorescence microscopy
Krawczyk-Bärsch, E.; Arnold, T.; Großmann, K.; Hofmann, S.; Wobus, A.;
The effect of uranium added in ecologically relevant concentrations (1×10-5 M and 1×10-6 M) to stable multispecies biofilms was studied by electrochemical oxygen microsensors with tip diameters of 10 µm and by confocal laser fluorescence microscopy (CLSM). The microsensor profile measurements in the stable multispecies biofilms exposed to uranium showed that the oxygen concentration decreased faster with increasing biofilm depth compared to the uranium free biofilms. In the uranium containing biofilms, the oxygen consumption, calculated from the steady-state microprofiles, showed high consumption rates of up to 68 nmol cm-3s-1 in the top layer (0 - 70 µm) and much lower consumption rates in the lower zone of the biofilms. Staining experiments with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4,6-diamidino-2-phenylindole (DAPI) confirmed the high respiratory activities of the bacteria in the upper layer. Analysis of the amplified 16S rRNA gene fragments showed that the addition of uranium in ecological relevant concentrations did not change the bacterial diversity in the stable multispecies biofilms and is therefore not responsible for the different oxygen profiles in the biofilms. The fast decrease in the oxygen concentrations in the biofilm profiles showed that the bacteria in the top region of the biofilms, i.e. the metabolically most active biofilms zone, battle the toxic effects of aqueous uranium with an increased respiratory activity. This increased respiratory activity results in O2 depleted zones closer to the biofilm air interface which triggers redox processes leading to a precipitation of uranium(IV) solids and consequently to a removal of uranium from the aqueous phase.

Publ.-Id: 10876 - Permalink


Bacteria-based nanoscaled materials
Selenska-Pobell, S.;
- wird nachgereicht
  • Invited lecture (Conferences)
    Institut für Neue Materialien GmbH, 23.02.2007, Saarbrücken, Germany

Publ.-Id: 10875 - Permalink


Novel S-layer supported Pd bionanocatalysts
Selenska-Pobell, S.;
- wird nachgereicht
  • Invited lecture (Conferences)
    Institute of Molecular Biology, 26.09.2007, Sofia, Bulgaria

Publ.-Id: 10874 - Permalink


Biogeochemical changes in uranium wastes induced by increased U(VI) and nitrate concentrations
Selenska-Pobell, S.;
- wird nachgereicht
  • Invited lecture (Conferences)
    Institute of Microbiology, 02.11.2007, Prague, Czech Republic

Publ.-Id: 10872 - Permalink


Boden-Pflanzen Transfer von U(VI) - Anwendung mikroskopischer und spektroskopischer Methoden zur Charakterisierung der chemischen Speziation
Günther, A.;
Darstellung von ausgewählten Methoden zur Bestimmung der chemischen Speziation von Uran(IV) im System Boden-Pflanze
  • Lecture (Conference)
    Workshop "Uran in Böden", 04.12.2007, Freiberg, Germany

Publ.-Id: 10871 - Permalink


Increased metabolic activity in biofilms caused by uranium: A microsensor study
Krawczyk-Bärsch, E.; Arnold, T.; Großmann, K.; Wobux, A.; Diessner, S.;
- wird nachgereicht
  • Poster
    ISEB 18 - International Symposia on Environmental Biogeochemistry, 11.-16.11.2007, Taupo, New Zealand

Publ.-Id: 10870 - Permalink


Curvature effects of nitrogen on graphitic sheets: Structures and energetics
Mandumpal, J.; Gemming, S.; Seifert, G.;
A correlation of the nitrogen concentration on graphitic sheets with structural deformations is presented using the density functional based tight binding method (DFTB). Graphite sheets of various sizes were doped by nitrogen at different sites; either a local deviation from planarity or negative curvature is obtained. In addition, we derive a formula for constructing two sets of isomer series namely methylene cyclopentadiene and benzene to study nitrogen's role in positive curvature formation. Comparing these structures, the exact energy difference to convert a fully hexagonal network to a pentagon centered hexagonal network can be predicted systematically for infinitely large structures. (c) 2007 Elsevier B.V. All rights reserved.
Keywords: CNX THIN-FILMS; CARBON-NITRIDE; FULLERENES; DEPOSITION; STABILITY
  • Chemical Physics Letters 447(2007)(1-3), 115-120

Publ.-Id: 10869 - Permalink


Intersubband relaxation dynamics in narrow InGaAs/AlAsSb quantum well structures studied by femtosecond pump-probe spectroscopy
Tribuzy, C. V.-B.; Ohser, S.; Winnerl, S.; Grenzer, J.; Schneider, H.; Helm, M.; Neuhaus, J.; Dekorsy, T.; Biermann, K.; Künzel, H.;
Intersubband transitions (ISBT) in semiconductor quantum wells have been attracting much attention for infrared optoelectronic device applications such as quantum cascade lasers and quantum well infrared detectors. There is also considerable interest to extend ISBT to short wavelengths (< 2 μm), for devices applications such as fast switching and modulators, due to ultrafast intersubband relaxation in the picosecond and subpicosecond regime. Therefore attentions were driven to heterosystem with large conduction band offsets (> 1 eV).
On the other hand, to achieve short wavelengths thin quantum wells (< 3 nm) are required, where the first excited state inside the QW may lie higher than some state related to indirect valleys. Examples for such material systems are strained InGaAs/AlAs or lattice matched InGaAs/AlAsSb, both grown on InP.
We have studied the intersubband relaxation dynamics in multi QWs of both material systems by femtosecond pump-probe measurements using an optical parametric oscillator. By the transient transmission as a function of the pump-probe delay we observe that some long living states are present in our systems, showing that more than two levels might be involved in the relaxation dynamics. This can be caused by transfer of electrons to X- or L-states in the QWs or the barriers. To investigate the origin of such long living states and the involved relaxation time constants, we have studied samples with different QW thicknesses, containing doping impurities localized either inside the QW or at the barriers. The experimental results are compared to simulations based on rate equations.
Keywords: Intersubband relaxation, InGaAs/AlAsSb quantum wells
  • Poster
    28th International Conference on the Physics of Semiconductors (ICPS-28), 24.-28.07.2006, Wien, Österreich
  • Contribution to proceedings
    28th International Conference on the Physics of Semiconductors (ICPS-28), 24.-28.07.2006, Wien, Österreich
    AIP Conf. Proc. 893, 473 (2007)

Publ.-Id: 10868 - Permalink


Liquid metal Taylor-Couette experiment on the magnetorotational instability
Gundrum, T.; Stefani, F.; Gerbeth, G.; Szklarski, J.; Ruediger, G.; Hollerbach, R.;
The magnetorotational instability (MRI) plays an essential role in the formation of stars and black holes. By destabilizing hydrodynamically stable Keplerian flows, the MRI triggers turbulence and enables outward transport of angular momentum in accretion discs which is necessary for the mass accumulation of central objects.
In order to examine the MRI we applied helical magnetic fields to a Taylor-Couette experiment with the liquid alloy GaInSn [1,2,3]. The low velocities of the liquid metal in the experiment are measured using an ultrasonic Doppler velocimeter.
The results show typical predicted features of MRI at Reynolds numbers of the order 1000 and Hartmann numbers of the order 10. Particular focus is laid on new results with an improved experiment in which split end caps are used to minimize the effect of Ekman pumping.
Keywords: MRI
  • Lecture (Conference)
    6th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 09.-11.09.2008, Praha, Czech Republic
  • Contribution to proceedings
    6th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 09.-11.09.2008, Praha, Czech Republic
    Proceedings of the 6th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, Praque, Czech Republic: Czech Technical University in Praque, 978-80-87117-05-7, 65-68

Publ.-Id: 10867 - Permalink


Severe accident analysis for VVER-1000/V-320 for a station blackout accident scenario with ASTEC V1.3.0
Tusheva, P.; Reinke, N.; Hurtado, A.; Schäfer, F.;
This paper presents the results from a severe accident analysis performed with ASTEC V1.3.0 code for a nuclear power plant with a VVER-1000/V-320 reactor. The purpose of this analysis is to assess the ASTEC code behaviour in modelling of main severe accident phenomena in the primary and secondary circuit arising during a hypothetical severe accident. The performed analyses cover a station blackout (SBO) sequence with passive safety injection systems (hydro-accumulators), in order to investigate the capabilities of ASTEC to model the physical phenomena during the in-vessel phase of such a transient.

An investigation on a SBO scenario with primary side depressurization has been carried out. The code results show delayed RPV failure by depressurization of the primary side, as slowing the core damage would allow more time for systems to be recovered to mitigate or terminate the accident. This would give more time and different possibilities for operator interventions.
Keywords: astec, severe accident analysis, SBO, accident management measures
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Germany

Publ.-Id: 10866 - Permalink


P0609-Erhöhung der Oxidationsbeständigkeit von TiAl-Legierungen durch die kombinierte Implantation von Fluor und Silizium
Schütze, M.; Donchev, A.; Yankov, R.; Richter, E.;
Die kombinierte Implantation von Fluor und Silizium in die Werkstoffoberfläche von TiAl-Legierungen kann deren Oxidationsbestähigkeit im Temperaturbereich von 750 bis 1100°C an Luft gegenüber unbehandelten TiAl-Legierungen deutlich erhöhen. Die Implantation kann durch verschiedene Verfahren, einmal die Beamline-Ionenimplantation (BLII) oder die Plasma-lmmersion-Ionenimplantation(PlII,PI3), erfolgen. Entgegen dem bisherigen Kenntnisstand, wo nur reine Halogene imlantiert wurden, lassen sich durch die Kombination von Fluor und Silizium bessere Ergebnisse als bei reiner Fluorimplantation erzielen.
  • Patent
    DE 10 2006 043 436 B3 - 29 Nov 2007

Publ.-Id: 10865 - Permalink


Hydrophilic oxybathophenanthroline ligands: Synthesis and copper(II) complexation
Stephan, H.; Juran, S.; Born, K.; Comba, P.; Geipel, G.; Hahn, U.; Werner, N.; Vögtle, F.;
Hydrophilic oxybathophenanthroline dendrons (generation 1 to 3) have been synthesized by treatment of 4,7-bis(4´-hydroxyphenyl)-1,10-phenanthroline with the corresponding bromo-functionalized etheraryl branching units containing triethylene glycol monomethyl end groups. Radiotracer experiments using 64Cu prove the rapid formation of stable copper(II) complexes in aqueous solution. These 64Cu complexes remain unchanged even upon addition of a high excess of glutathion as competing ligand, thus demonstrating the high stability of the formed copper(II) complexes. Electronic and EPR spectroscopy indicate the formation of [Cu(L)2(OH2)2]2+ (L = Ligand) complexes in aqueous solution, confirmed by time-resolved laser fluorescence spectroscopy and supported by molecular mechanics modeling.

Publ.-Id: 10864 - Permalink


Synthesis of modified pyrimidine bases and positive impact of the chemically reactive substituents on their in vitro antiproliferative activity
Noll, S.; Kralj, M.; Suman, L.; Stephan, H.; Piantanida, I.;
The antiproliferative activity screening on human tumor cell lines of a series of modified uracil and cytosine bases as well as some corresponding acyclonucleotides, and comparison of structure-activity relationship revealed the importance of chemical reactivity of the substituent attached to the C5-position of uracil for the activity of studied compounds. Namely, the results obtained for the most active compounds, 5-(chloroacetylamino)uracil (2) and its acyclic sugar analogue 18, suggest that formation of a covalent bond between reactive substituent and several possible targets within the thymidylate synthase mechanism (sulphur of the cysteine residue, basic part of the enzyme, N,N-methylene tetrahydrofolate or its reactive iminium forms) is the most probable mode of action. In addition, novel C5-substituted uracil derivative 6 (5-[bis-(2-p-methoxybenzylthioethyl)amine]-acetylaminouracil) exhibited high antiproliferative activity against HeLa and MiaPaCa-2 cell lines, by an as yet unknown mechanism.
  • European Journal of Medicinal Chemistry 44(2009), 1172-1179
    DOI: 10.1016/j.ejmech

Publ.-Id: 10862 - Permalink


Junction formation in Ge by ion implantation
Satta, A.; Simoen, E.; van Daele, B.; Clarysse, T.; Nicholas, G.; Vandervorst, W.; Anwand, W.; Skorupa, W.; Peaker, T.; Markevich, V.;
Ion implantation in Ge is studied at energies and doses relevant for application to advanced modern devices, such as CMOS transistors. Shallow donors like P typically have high diffusivity and low activity in view of the formation of shallow, low-resistance junctions. Similarly to the Si case, co-doping with non-dopant elements (N in this study) and advanced annealing techniques, such as FLA annealing, can provide a viable route to significantly improve the trade-off of n-type Ge junctions.
Residual implant-induced defectivity, which can be a source of enhanced diffusion and generation currents in Ge diodes, seems to remain up to temperatures (≥ 500 oC) important for activation of dopants in Ge.
However, once the thermal budget is optimized for implant damage removal, the Ge diode leakage may be dominated by surface generation currents, due to a high density of surface states, not efficiently reduced by current passivation schemes.
Keywords: ion implantation, shallow junctions, germanium, flash lamp annealing, rapid thermal annealingphosphorus, co-doping, nitrogen, electrical activation, diodes, leakage current
  • Contribution to proceedings
    International Workshop on INSIGHT in Semiconductor Device Fabrication, Metrology and Modeling (INSIGHT-2007), 06.-09.05.2007, Napa, USA
    Proceedings INSIGHT-2007 Workshop, 297-308
  • Invited lecture (Conferences)
    International Workshop on INSIGHT in Semiconductor Device Fabrication, Metrology and Modeling (INSIGHT-2007), 06.-09.05.2007, Napa, USA

Publ.-Id: 10860 - Permalink


Meyer-Neldel rule in ZnO
Schmidt, H.; Wiebe, M.; Dittes, B.; Grundmann, M.;
Seventy years ago Meyer and Neldel investigated four polycrystalline n-type conducting ZnO rods [W. Meyer and H. Neldel, Z. Tech. Phys. (Leipzig) 12, 588 (1937)]. The specific conductivity increased exponentially with temperature. A linear relationship between the thermal activation energy for the specific conductivity and the logarithm of the prefactor was observed. Since then thermally activated processes revealing this behavior are said to follow the Meyer-Neldel (MN) rule. We show that the emission of charge carriers from deep electron traps in ZnO follows the MN rule with the isokinetic temperature amounting to 226±4 K.

Publ.-Id: 10859 - Permalink


Short time thermal processing of materials - beyond electronics and photonics to pipe organ materials
Skorupa, W.;
There is a clear and increasing interest in short time thermal processing far below one second, i.e. the lower limit of RTP (Rapid Thermal Processing) called spike annealing. It is the world of preocessing in the millisecond or nanosecond range. This was recently driven by the need of suppressing the so-called Transient Enhanced Diffusion in advanced boron-implanted shallow pn-junctions in the front-end silicon chip technology. Meanwhile the interest in flash lamp annealing (FLA) in the millisecond range spread out into other fields related to silicon technology and beyond. This talk reports shortly about the restart in flash lamp annealing of the Rossendorf group in collaboration with other groups and further on recent experiments regarding shallow junction engineering in germanium, annealing of ITO layers on glass and plastic foil to form an conductive layer as well as investigations which we did during the last years in the field of wide band gap semiconductor materials (SiC, ZnO). Moreover recent achievements in the field of silicon-based light emission basing on Metal-Oxide-Semiconductor Light Emitting Devices will be reported. Finally it will be demonstrated that short time thermal processing features also advantages regarding the casting of lead sheets to produce organ pipes in the spirit of the 17th century - as a completely different world of materials processing!
Keywords: short time annealing, flash lamp annealing, transient enhanced diffusion, silicon-based light emission, shallow junction engineering, germanium, silicon, silicon carbide, zinc oxide, indium tin oxide, lead casting, pipe organ materials
  • Invited lecture (Conferences)
    Seminarvortrag am Max Planck Institut für Mikrostrukturphysik, 05.12.2007, Halle/Saale, Germany

Publ.-Id: 10858 - Permalink


Investigations of biochemical interactions of actinides with microorganisms and plants.
Reitz, T.; Geissler, A.; Merroun, M. L.; Selenska-Pobell, S.; et all;
This presentation show an overview about the research at the IRC, in particular about the investigations of the biochemical interactions of actinides with microorganisms and plants.
  • Lecture (others)
    2nd phD Seminar, 26.-28.09.2007, Rabenberg, Germany

Publ.-Id: 10857 - Permalink


Changes in archaeal community of a uranium mining waste pile induced by treatments with uranyl or sodium nitrate.
Reitz, T.; Geissler, A.; Merroun, M. L.; Selenska-Pobell, S.;
Changes in the archaeal community of a uranium mining waste pile, called Haberland caused by the addition of uranyl or sodium nitrate were investigated by using the 16S rRNA gene retrieval. The natural archaeal diversity in studied environment was limited to only a few lineages of mesophilic Crenarchaeota, predominantly of subgroup 1.1a. Addition of and subsequent incubation with uranyl nitrate for 4 weeks resulted in a significant shifting of the archaeal populations to the soil/sediment cluster 1.1b of Crenarchaeota. The proliferation of the latter populations occurred independently of the amount of the added uranium and the aeration conditions during the incubation. The same shifting of the archaeal populations was also observed in the parallel control samples which were supplemented with sodium nitrate.
Efforts to culture members of the 1.1b Crenarchaeota resulted in their enrichment together with representatives of Firmicutes, mainly of Clostridium spp. Clostridia can effectively interact with uranium and they can also fermentatively reduce nitrate to ammonium. Because an ammonia oxidizing activity was deduced on the basis of meta-genomic analyses of the closest relative to the stimulated in our case 1.1b populations, we speculate that the clostridia possibly supply the crenarchaeal members of the recovered synergetic consortium with ammonia.
  • Poster
    BAGECO 9 - 9th Symposium on Bacterial Genetics and Ecology, 23.-27.07.2007, Wernigerode, Germany

Publ.-Id: 10856 - Permalink


Crenarchaeota 1.1b and Firmicutes consortium recovered from a uranyl nitrate treated uranium waste sample and its possible role against the toxicity of uranium.
Reitz, T.; Geissler, A.; Merroun, M. L.; Selenska-Pobell, S.;
Supplementations of a sample collected from a depleted uranium mining waste pile with uranyl nitrate induced significant changes in microbial community structure during the first four weeks of incubation. At the latter stages of the treatment, however, the initial composition of the community, indigenous for the untreated samples and consisting mostly of uranium sensitive populations, started to set up. This indicates that the added uranium was no longer bio-available, possibly due to the interactions of the induced at the first stages of the treatment uranium resistant populations with the added radionuclide. Studies on archaeal diversity demonstrated a strong shifting from the subgroup 1.1a to the subgroup 1.1b of the mesophilic soil Crenarchaeota within the first four weeks of the incubations.
Our efforts to cultivate representatives of this crenarchaeal group on specific enrichment media from the sample treated with uranyl nitrate under anaerobic (corresponding to the natural) conditions, resulted in the recovery of a consortium consisting of the mentioned 1.1b Crenarchaeota mixed with populations of Firmicutes, mainly of Clostridium spp. Clostridia can effectively interact with uranium and they can also fermentatively reduce nitrate to ammonium. Because an ammonia oxidizing activity was deduced on the basis of meta-genomic analyses for the closest relative to the stimulated in our case 1.1b populations, we speculate that the clostridia possibly supply the crenarchaeal members of the recovered synergetic consortium with ammonia. In addition, a Paenibacillus sp. isolate was cultivated from this consortium and its interactions with uranium were studied by using TEM and EDX analyses.
  • Poster
    Jahrestagung der Vereinigung für Allgemeine und Angewandte Mikrobiologie (VAAM), 01.-04.04.2007, Osnabrück, Germany

Publ.-Id: 10855 - Permalink


Interactions of U(VI) with members of a microbial consortium recovered from a uranium mining waste pile.
Reitz, T.; Geissler, A.; Merroun, M. L.; Selenska-Pobell, S.;
Treatments of a soil sample from a uranium mining waste pile with uranyl nitrate led to a shifting in the crenarchaeal populations from subgroup 1.1a to 1.1b. Efforts to culture members of these Crenarchaeota resulted in an enrichment of a mixed microbial consortium consisting of representatives of 1.1b Crenarchaeota and Firmicutes.
In this study interactions of U(VI) with a pure culture of Paenibacillus sp. JG35+U4-B1 isolated from the mentioned consortium were studied by using a combination of wet chemistry and microscopic methods. Preliminary analyses on U sorption showed that the Paenibacillus strain studied accumulated up to 85 mg U/g dry biomass from a solution with an initial uranium concentration of 120 mg U/l. Live/Dead cell staining indicated that less than 10% of the U-treated cells were viable. Transmission electron microscope (TEM) analyses showed that the cells of the isolated strain accumulated uranium intracellularly as needle-like fibrils, and also at the cell surface. Energy dispersive X-ray (EDX) analysis of these U accumulates demonstrated the presence of U and P indicating that in both cases the phosphate groups are, probably, the main functional binding sites for U(VI).
Efforts to culture other strains from the mentioned consortium and especially of the yet to be cultured 1.1b-Crenarchaeota are in progress in our laboratory. Because our results indicated that these archaeal populations are strongly induced by the addition of U(VI) the study of these organisms is of importance for understanding the natural behavior of U in soils and also for remediation of contaminated sites.
  • Lecture (Conference)
    37ièmes Journées des Actinides, 27.03.2007, Sesimbra, Portugal

Publ.-Id: 10854 - Permalink


Experimental studies and CFD calculations for buoyancy driven mixing phenomena
Da Silva, M. J.; Thiele, S.; Höhne, T.; Vaibar, R.; Hampel, U.;
Buoyancy driven flow is found in many engineering application such as the mixing of fluids with different densities. In nuclear reactor safety the mixing of borated and deborated water is a critical issue that needs investigation, assessment and prediction. Recent progress in computer hardware and numerical techniques has made it viable to predict these mixing patterns using CFD codes. However, as CFD codes contain more or less empirical models it is necessary to validate the predicted results using experimental data. Therefore, a combined numerical and experimental study of buoyant mixing processes has been performed. A newly developed planar sensor was applied to experimentally investigate the mixing process. Validation experiments were performed in the VeMix test facility, which show typical vertical and horizontal flow pattern under different flow regimes. The data from the planar sensor of mixing behavior and velocity fields were used for the validation of the simulation results. Comparisons of the experimental results with the corresponding simulations show similar flow patterns and typical periodic behavior.
Keywords: CFD, validation, buoyancy-driven flow, planar array sensor, image processing
  • Contribution to proceedings
    XCFD4NRS, Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France, MIX-02
  • Lecture (Conference)
    XCFD4NRS, Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France

Publ.-Id: 10853 - Permalink


An 86Y-Labeled Mirror-Image Oligonucleotide: Influence of Y-DOTA Isomers on the Biodistribution in Rats
Schlesinger, J.; Közle, I.; Bergmann, R.; Tamburini, S.; Bolzati, C.; Tisato, F.; Noll, B.; Klussmann, S.; Vonhoff, S.; Wüst, F.; Pietzsch, H.-J.; Steinbach, J.;
A mirror-image oligonucleotide (L-RNA) was radiolabeled with the positron emitting radionuclide 86Y (t1/2 = 14.7 h) via the bifunctional chelator approach. DOTA-modification of the L-RNA (sequence: 5’-Aminohexyl UGA CUG ACU GAC-3’; MW 3975) was performed using (S)-p-SCN-bz-DOTA.

86Y radiolabeling of the DOTA-bz-L-RNA produced more than one species as evidenced by HPLC radiometric detection. For the identification of the 86Y-labeled L-RNA the structural analogue ‘cold’ precursor [Y((S)-p-NH2-bz-DOTA)]- was synthesized. Two coordination isomers were separated via HPLC adopting the square antiprismatic (SAP) and the twisted square antiprismatic (TSAP) geometry, respectively. Their stereochemical configuration in the solution state was assessed by NMR and circular
dichroism spectroscopy. Both [Y((S)-p-NH2-bz-DOTA)]- isomers were converted into isothiocyanate derivatives [Y((S)-p-SCN-bz-DOTA)]- and conjugated to the L-RNA. The identity of the [86Y-DOTA-bz]-L-RNA species was finally established by comparison of the radiometric (86Y) and UV-visible (‘cold’ Y) chromatographic profiles.

Biodistribution studies in Wistar rats showed minor changes in the biodistribution profile of the [86Y((S)-p-NH2-bz-DOTA)]- complex isomers, while no significant differences where observed for the [86Y-DOTA-bz]-L-RNA isomers. High renal excretions were found for the [86Y((S)-p-NH2-bz-DOTA)]- complex isomers as well as for the L-RNA isomers.
  • Bioconjugate Chemistry 19(2008), 928-939
    DOI: 10.1021/bc700453h
  • Lecture (Conference)
    Turku PET Symposium New Targets in Molecular Imaging, 24.-27.05.2008, Turku, Finland
  • Contribution to proceedings
    Turku PET Symposium New Targets in Molecular Imaging, 24.-27.05.2008, Turku, Finland
    Abstracts of the XI Turku PET Symposium, Kaarina, Finland: Painola, 978-951-29-3563-5, 11

Publ.-Id: 10851 - Permalink


Double-electron excitations in L3-edge X-ray absorption spectra of Actinides
Hennig, C.;
Multielectron excitations are well known in absorption spectra of noble gases. There, the absorption signal is not affected from neighbored atoms that cause the extended X-ray absorption fine structure (EXAFS). Although EXAFS oscillations often cover these features, they have been revealed also in the spectra of liquids and solids. For the first time, this effect has been observed for actinides.
Keywords: Actinides, EXAFS, 2p4f double electron excitation
  • Poster
    17th ESRF Users Meeting, 07.02.2007, Grenoble, France

Publ.-Id: 10850 - Permalink


Spectroscopic investigation of uranium solution species
Hennig, C.;
The concept of in situ measurements in a spectro-electrochemical cell for XAFS measurements is presented.
Keywords: EXAFS, UV-vis, U(IV), U(V), U(VI)
  • Invited lecture (Conferences)
    CEA, Laboratoire de Reconnaissance Ionique et Chimie de Coordination, 08.06.2007, Grenoble, France

Publ.-Id: 10849 - Permalink


Die Koordination von Uran-Spezies in Loesungen - Eine Analyse mit EXAFS Spektroskopie
Hennig, C.;
Der Vortrag gibt eine kurze Einfuehrung in die experimentellen Moeglichkeiten und Besonderheiten der EXAFS Spektroskopie. Im Weiteren werden umweltelevante Probleme der Urankontamination im ehemaligen Bergbaugebiet der Wismut anhand spektroskopischer Analysen von umweltrelevanten Modellsystemen diskutiert.
Keywords: EXAFS, ehemaliger Uranbergbau
  • Invited lecture (Conferences)
    Bundesanstalt fuer Materialforschung und -pruefung, 05.06.2007, Berlin, Germany

Publ.-Id: 10848 - Permalink


The structure of actinides in solution - An investigation with XAFS spectroscopy
Hennig, C.;
Outline of this poesentation
1. Motivation.
2. Theory.
3. Experimental conditions
4. Comparison between EXAFS and XRD.
5. Electronic transitions in EXAFS and UV-vis.
6. U(VI) and U(IV) in aq. and nonaq. cloride media.
7. Sulfate coordination of aq. Th(IV), U(IV), U(VI), Pa(V),Np(IV), Np(V), and Np(VI) media.
8. Conclusion
Keywords: EXAFS, XRD, UV-vis, Actinides, Coordination, Speciation
  • Invited lecture (Conferences)
    Workshop on Structural Chemistry of Actinide and Lanthanide Inorganic Compounds, 29.09.-01.10.2007, Tsarskoe Selo, St. Petersburg, Russia

Publ.-Id: 10847 - Permalink


Investigation of actinides in solution under controlled redox conditions
Hennig, C.; Ikeda, A.; Rossberg, A.; Funke, H.; Scheinost, H.;
The results from the research activities of the last 5 years have been presented. This concerns the development and application of a spectro-electrochemical cell for in situ investigations of speciation and coordination of actinides in solution.
Keywords: actinides, EXAFS, electrochemistry
  • Lecture (others)
    ESRF Beamline Review Panel Meeting, 06.-07.11.2007, Grenoble, France

Publ.-Id: 10846 - Permalink


Complex structure and species distribution of U(VI) cloride in aqueous and nonaqueous solutions
Hennig, C.;
New spectroscopic techniques by combining UVvis and EXAFS will be discussed applied to the samples mentioned in the title.
Keywords: UVvis EXAFS uranium
  • Lecture (others)
    Institute de Physique Nucleaire, Groupe de Radiochemie, 13.12.2007, Paris-Orsay, France

Publ.-Id: 10845 - Permalink


Dynamoeffekt und Magnetorotationsinstabilität: Kosmische Magnetfelder im Laborexperiment
Stefani, F.;
Im Vortrag wird herausgearbeitet, dass kosmische Magnetfelder einerseits durch den hydromagnetischen Dynamoeffekt erzeugt werden und andererseits vermittels der Magnetorotationsinstabilität eine fundamentale Rolle in der kosmischen Strukturbildung spielen. Die Laborexperimente zum Dynamoeffekt in Riga, Karlsruhe und Cadarache sowie das PROMISE-Experiment zur Magnetorotationsinstabilität werden detailliert behandelt.
  • Invited lecture (Conferences)
    Lehrstuhlseminar Magnetofluiddynamik, TU Dresden, 05.12.2007, Dresden, Germany

Publ.-Id: 10844 - Permalink


Crystallographically oriented Fe nanocrystals formed in Fe-implanted TiO2
Zhou, S.; Potzger, K.; Talut, G.; Shalimov, A.; Grenzer, J.; Skorupa, W.; Helm, M.; Fassbender, J.ORC; Cizmar, E.; Zvyagin, S. A.; Wosnitza, J.
A comprehensive characterization of the structural and magnetic properties of Fe-implanted rutile TiO2(110) is presented. Fe and FeTiO3 (Ilmenite) nanocrystals (NCs) are identified by synchrotron-radiation X-ray diffraction. The majority of Fe NCs are crystallographically oriented with respect to the matrix following the relation Fe(001)[010]kTiO2(110)[110]. Post-annealing induced the out-diffusion of Fe and the growth of FeTiO3 at the cost of Fe NCs. Mössbauer spectroscopy and SQUID magnetometry reveal the corresponding evolution of magnetic properties, i.e. magnetization, and superparamagnetic blocking temperature. We unambiguously identify Fe NCs as the origin of the ferromagnetism. These Fe NCs possess a uniaxial in-plane magnetic anisotropy, such that the two Fe[100] axes are inequivalent.
Keywords: TiO2, Ferromagnetism, Nanocrystals

Publ.-Id: 10843 - Permalink


Structural and magnetic properties of Tb implanted ZnO single crystals
Zhou, S.; Potzger, K.; Mücklich, A.; Eichhorn, F.; Helm, M.; Skorupa, W.; Fassbender, J.ORC
ZnO single crystals have been implanted with Tb ions. For an atomic concentration of 1.5 %, annealing at 823 K leads to an increase of the saturation magnetization per implanted Tb ion up to 1.8 mu_B at room temperature. Structural investigations revealed no secondary phase formation, but the out-diffusion of Tb. No significant evidence is found for Tb substituting Zn sites neither in the as-implanted nor annealed samples. However, indications for the existence of a small amount of Tb nanoclusters however have been found using magnetization vs. temperature measurements. The ferromagnetic properties disappear completely upon annealing at 1023 K. This behavior is related to the formation of oxide complexes or nanoparticles.
Keywords: ZnO, rare earth, diluted magnetic semiconductors

Publ.-Id: 10842 - Permalink


Complexation of Curium(III) with Hydroxamic Acids Investigated by Time-Resolved Laser-Induced Fluorescence Spectroscopy
Glorius, M.; Moll, H.; Bernhard, G.;
The unknown complex formation of Cm(III) with two hydroxamic acids, salicylhydroxamic (SHA) and benzohydroxamic acid (BHA) was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Hydroxamate containing chelating substances have the potential to enhance the solubility and mobility of metals and radionuclides by forming complexes. We explored the fluorescence properties, lifetimes and individual fluorescence emission spectra of the formed Cm(III) hydroxamate species. In both Cm(III)-hydroxamic acid systems a 1: 1 and a 1:2 complex of the type MpLqHr could be identified from the fluorescence emission spectra having peak maxima at 600 and 609 nm, respectively. An indirect excitation mechanism of the Cm(III) fluorescence was observed in the presence of the hydroxamic acids. Consistent stability constants were determined by using either indirect or direct excitation mode of the Cm(III) fluorescence. In the Cm(III)-SHA system, the stability constants are log β111 = 16.52 0.14 and log β121 = 24.09 0.62. The complex formation constants of the Cm(III)-BHA species results to log β110 = 6.52 0.19 and log β120 = 11.60 0.50. The stability constants were compared to those of natural pyoverdins.
Keywords: Cm(III); Complexation; TRLFS; Hydroxamic acids

Publ.-Id: 10841 - Permalink


Initial stages in the metal-dusting process on alloy 800
Röhnert, D.; Phillipp, F.; Reuther, H.; Weber, T.; Wessel, E.; Schütze, M.;
The initial stages of the metal-dusting process on Alloy 800 at 620 degrees C were investigated by light optical microscopy, RAMAN spectroscopy, atomic-force microscopy, Auger electron spectroscopy, transmission-electron microscopy and electron back-scatter diffraction. As it turned out the incubation period for metal-dusting is characterized by simultaneous formation of a heterogeneously growing oxide scale and deposition of carbon. The material surface shows different tarnish colors depending on the substrate-grain orientation with different susceptibility to the beginning of metal-dusting attack. "Low-index" grains were not attacked within the times investigated while the other grain orientations showed pitting. Carbon is evidently incorporated into the oxide scale from the very beginning of exposure with different intensities depending on the underlying substrate-grain orientation leading to differences in the tarnish colors. As a consequence carbides are formed even underneath "dense" oxide layers. Evidently metal-dusting attack starts at positions of the oxide scale where "higher carbon concentrations" are present.
  • Oxidation of Metals 68(2007), 271-293

Publ.-Id: 10840 - Permalink


Recent achievement on actinide chemistry at FZD: Short introduction about electrochemical and structural study of uranium and neptunium in solution.
Ikeda, A.;
Understanding the electrochemical and complexation behavior of actinides in solution is very fundamental for the assessment of environmental impact on the geological disposal of radioactive wastes, such as predicting the migration behavior of these nuclides in the geosphere. Especially, uranium(U) and neptunium(Np) are some of the important nuclides for this kind of research.Therefore, in order to investigate the electrochemical and complexation properties of U and Np, cyclic voltammetry (CV), electrolysis, and X-ray absorption measurements were carried out in various types of aqueous- and nonaqueous solutions. In this presentation, some remarkable results are introduced and discussed to draw a general conclusion about the electro- and complexation chemistry of U and Np in solution.
Keywords: uranium, neptunium, electrochemistry, complex, solution, cyclic voltammetry, electrolysis, XAFS
  • Invited lecture (Conferences)
    Internal seminar at the Synchrotron Radiation Research Center, Japan Atomic Energy Agency, 29.11.2007, SPring-8, Hyogo, Japan

Publ.-Id: 10839 - Permalink


Time-resolved semiconductor spectroscopy in the mid-infrared and Terahertz regimes
Schneider, H.;
This talk will focus on several research topics exploiting our free-electron (FEL) and modelocked Ti:Sapphire lasers to investigate semiconductor nanostructures. Pump-probe spectroscopy and two-photon detection is used for time-resolved investigations of intersubband transitions in quantum wells and for FEL pulse diagnostics. Terahertz emitters based on interdigitated metal stripe arrays will also be discussed.
  • Lecture (others)
    Seminarvortrag, 30.11.2007, Palaiseau, France

Publ.-Id: 10838 - Permalink


Positronen-Emissions-Tomographie (PET) - von der Chemie radioaktiv markierter Verbindungen bis zu deren Herstellung für die klinische Praxis
Knieß, T.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Reihe der hochschuloffenen Kolloquien des FB MachinenBau/Verfahrenstechnik, Studiengang Chemieingenieurwesen der HTW Dresden, 06.12.2007, Dresden, Germany

Publ.-Id: 10837 - Permalink


Projective Hilbert space structures at exceptional points and Krein space related boost deformations of Bloch spheres
Günther, U.; Rotter, I.; Samsonov, B.;
Simple non-Hermitian quantum mechanical matrix toy models are considered in the parameter space vicinity of Jordan-block structures of their Hamiltonians and corresponding exceptional points of their spectra. In the first part of the talk, the operator (matrix) perturbation schemes related to root-vector expansions and expansions in terms of eigenvectors for diagonal spectral decompositions are projectively unified and shown to live on different affine charts of a dimensionally extended projective Hilbert space. The monodromy properties (geometric or Berry phases) of the eigenvectors in the parameter space vicinities of spectral branch points (exceptional points) are briefly discussed.

In the second part of the talk, it is demonstrated that the recently proposed PT-symmetric quantum brachistochrone solution [C. Bender et al, Phys. Rev. Lett. {\bf 98}, (2007), 040403, quant-ph/0609032] has its origin in a mapping artifact of the PT-symmetric 2×2 matrix Hamiltonian in the vicinity of an exceptional point. Over the brachistochrone solution the mapping between the PT-symmetric Hamiltonian as self-adjoint operator in a Krein space and its associated Hermitian Hamiltonian as self-adjoint operator in a Hilbert space becomes singular and yields the physical artifact of a vanishing passage time between orthogonal states. The geometrical aspects of this mapping are clarified with the help of a related hyperbolic Möbius transformation (contraction/dilation boost) of the Bloch (Riemann) sphere of the qubit eigenstates of the 2×2 matrix model.
The controversial discussion on the physics of the brachistochrone solution is briefly commented and a possible resolution of the apparent inconsistencies is sketched.

partially based on:
J. Phys. A 40 (2007) 8815-8833; arXiv:0704.1291 [math-ph].
arXiv:0709.0483 [quant-ph].
Keywords: non-Hermitian Hamiltonian, PT-symmetric Quantum Mechanics, Jordan block, exceptional point, projective Hilbert space, geometric phase, quantum brachistochrone, Bloch sphere, Möbius transformation, hyperbolic dilation-contraction mapping
  • Invited lecture (Conferences)
    7th Workshop Operator Theory in Krein Spaces and Spectral Analysis, 13.-16.12.2007, Berlin, Germany

Publ.-Id: 10836 - Permalink


Flüssigmetallströmung unter dem Einfluß eines elektromagnetischen Wanderfeldes bei der Kristallzüchtung nach der VGF-Methode - Numerische Simulation und Modell-Experimente -
Galindo, V.; Grants, I.; Lantzsch, R.; Pätzold, O.; Gerbeth, G.; Zhang, C.;
Die Strömung einer Flüssigmetall-Legierung unter dem Einfluß eines externen elektromagnetischen Wanderfeldes wurde untersucht mit besonderen Augemerk auf die Abhängigkeit von der Feld-Frequenz.
Keywords: crystal growth, traveling magnetic fields
  • Lecture (Conference)
    Workshop Strömungssimulation, 30.11.2007, Dresden, Germany

Publ.-Id: 10834 - Permalink


Use of a traveling magnetic field in VGF growth: flow reversal and resulting dopant distribution
Grants, I.; Gerbeth, G.;
The melt flow in a model of a vertical gradient freeze facility under the action of a traveling magnetic field (TMF) is studied numerically. The radial temperature gradient over a concave solidification interface drives a radially converging flow which may cause an undesirable dopant concentration peak on the axis. We study the characteristics of such a flow for parameters beyond the previously reported linear regime. An upward directed TMF induces a body force which counteracts buoyancy. We report conditions under which the TMF reverses the flow direction for a wide parameter range. These conditions depend primarily on the product of the thermal gradient and the interface deflection. The simulation of the dopant transport demonstrates that the concentration peak disappears as soon as the flow direction changes.
  • Journal of Crystal Growth 310(2008), 3699-3705

Publ.-Id: 10831 - Permalink


Magnetohydrodynamic experiments on cosmic magnetic fields
Stefani, F.;
It is well known that cosmic magnetic fields, including the fields of planets, stars, and galaxies, are produced by the hydromagnetic dynamo effect in moving electrically conducting fluids. It is less well known that cosmic magnetic fields play also an active role in cosmic structure formation by enabling outward transport of angular momentum in accretion disks via the magnetorotational instability (MRI). Considerable theoretical and computational progress has been made in understanding both processes. In addition to this, the last ten years have seen tremendous efforts in studying these effects in the laboratory. In 1999, magnetic field self-excitation was observed in the large scale liquid sodium facilities in Riga and Karlsruhe. Recently, self-excitation was also observed in the French "von Karman sodium" (VKS) experiment, although with the help of iron propellers which complicates the interpretation of the results. The magnetorotational instability was recently observed in the ''Potsdam Rossendorf Magnetic Instability Experiment'' (PROMISE). In the talk, the history of dynamo and MRI experiments is delineated, and some interesting directions of future work are discussed.
  • Invited lecture (Conferences)
    79th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM 2008), 31.03.-04.04.2008, Bremen, Germany

Publ.-Id: 10830 - Permalink


Homotopic deformations of the Arnold tongue patterns in the MHD α2-dynamo spectrum
Günther, U.; Kirillov, O.;
The spectrum of an MHD α2-dynamo has been studied under perturbations of the α-profile as well as under smooth changes of the boundary conditions (BCs). Basic ingredient was a set of analytically (exactly) calculable bi-orthogonal eigenfunctions for constant α-profiles α0=const. These eigenfunctions have been used as input for both perturbative and numerical Galerkin (weighted residual) analyses with BCs imposed on them as one-parameter homotopic family which smoothly interpolates between idealized (Dirichlet) BCs and physically realistic (Robin) BCs.

For constant α-profiles the spectrum is purely real and depending on the BCs it changes from a spectral mesh (living as line structure on the doubly ruled surface of a hyperbolic paraboloid) into a countably infinite set of parabolic branches. Under inhomogeneous perturbations of the α-profile the spectrum deforms in such a way that complex spectral sectors form from a subset of intersection points of the spectral mesh. With increasing perturbation strength these complex sectors widen and have the well known form of partially merging Arnold tongues. Explicit analytical approximations are derived for the Arnold tongues. Technically the approximations are based on the perturbation theory of multiple eigenvalues applied to the double eigenvalues (diabolical points) at the nodes of the spectral mesh. A detailed analysis is presented of the interplay of inhomogeneous α-perturbations and homotopic BC deformations with the formation of a wealth of Arnold tongues and partially invariant spectral branch patterns. A good correspondence between the numerical and the perturbative approaches is observed.
Keywords: MHD dynamo, non-selfadjoint operator, bi-orthogonal eigenfunctions, spectral analysis, perturbation theory, homotopic deformation family, Arnold tongue, spectral mesh, diabolical point, ruled surface
  • Lecture (Conference)
    79th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM-2008), 31.03.-04.04.2008, Bremen, Germany

Publ.-Id: 10829 - Permalink


Binding form of ingested uranium in human urine
Bernhard, G.; Geipel, G.; Steudtner, R.;
The dominant reasons for the increase in uranium emitted to the environment arise from the use of uranium as a fuel for the generation of nuclear energy and as a basic material for nuclear weapons production, which also includes the use of depleted uranium metal in armor piercing ammunition.
Keywords: urine, ingested uranium
  • Contribution to proceedings
    2nd International Nuclear Chemistry Congress, 13.-18.04.2008, Cancun, Mexico
  • Lecture (Conference)
    2nd International Nuclear Chemistry Congress, 13.-18.04.2008, Cancun, Mexico

Publ.-Id: 10828 - Permalink


Implementation of a pressure drop model for the CFD simulation of clogged containment sump strainers
Grahn, A.; Krepper, E.; Alt, S.; Kästner, W.; Weiß, F.-P.; Hampel, R.;
In the present article a combination of a semi-empirical flow equation and a material equation is proposed that allows to calculate the pressure drop in beds composed of compressible, fibrous media. The model has been successfully implemented as an extension to the general-purpose CFD code ANSYS-CFX. Its capability to simulate the transient pressure drop build-up at non-uniformly loaded strainers in arbitrary three-dimensional geometries is demonstrated using a step-like flow geometry with a horizontally embedded strainer plate. It will be shown that the increasing pressure drop at the strainer has a rectifying effect on the flow field. The model could as well be implemented into system codes for nuclear reactor and containment simulation. Thus, existing system codes might be enabled for use in the risk assessment of loss-of-coolant accidents.
Keywords: safetety analysis, containment sump, strainer clogging, loss-of-coolant accident, pressure drop, cfd
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Germany
    Implementation of a pressure drop model for the CFD simulation of clogged containment sump strainers
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Germany

Publ.-Id: 10827 - Permalink


THEREDA – Ein Beitrag zur Langzeitsicherheit von Endlagern nuklearer und nichtnuklearer Abfälle
Altmaier, M.; Brendler, V.; Hagemann, S.; Herbert, H.-J.; Kienzler, B.; Marquardt, C. M.; Moog, H. C.; Neck, V.; Richter, A.; Voigt, W.; Wilhelm, S.;
Im Rahmen von Langzeitsicherheitsanalysen für deutsche Endlager radioaktiver bzw. Untertagedeponien chemotoxischer Abfälle sowie weiterer Einsatzfelder (Altlastensanierung) wird eine einheitliche und umfassende thermodynamische Referenzdatenbasis dringend benötigt. Der ehemalige „Arbeitskreis Thermodynamische Standarddatenbasis“ (ATS) hatte sich die Aufgabe gestellt eine solche Datenbasis zu realisieren. Die Aktivitäten des ATS werden seit Juli 2006 in dem Projektverbund "THEREDA" (Thermodynamische Referenzdatenbasis) von BMBF, BMWi und BfS zunächst für 3 Jahre gefördert. THEREDA setzt sich aktuell aus fünf Partnerinstitutionen zusammen, die im Wesentlichen die deutschen Forschungsinstitutionen auf dem Gebiet der Endlagersicherheitsforschung repräsentieren. THEREDA soll die Transparenz und Belastbarkeit der Sicherheitsanalysen in Deutschland entscheidend verbessern und stellt erstmalig eine konsistente thermodynamische Datensätze für alle in Deutschland diskutierten Endlageroptionen und Wirtsgesteine bereit. Für jede thermodynamische Größe werden anhand eindeutig definierter Evaluierungskriterien Qualitätsstufen angegeben, mit Hilfe derer Anwender Daten, entsprechend der jeweiligen spezifischen Problemstellungen, gezielt einbeziehen oder ausschließen können. Für fehlende thermodynamische Daten werden im Rahmen von THEREDA begründete Schätzwerte ermittelt, sodass Modellrechnungen zur Sicherheitsanalyse in Zukunft auf einer deutlich breiteren Datenbasis durchgeführt werden können. Die Datenbasis wird in einer Datenbank zentral verwaltet und Anwendern über das Internet frei und unentgeltlich verfügbar sein. Importformate, um THEREDA in die gängigsten Modellierungscodes (EQ3/6, PHREEQC, Geochemist’s Workbench, CHEMAPP, usw.) überführen zu können, werden ebenfalls unentgeltlich zur Verfügung gestellt.
  • atw - International Journal for Nuclear Power 53(2008)4, 249-253

Publ.-Id: 10825 - Permalink


Influence of the Time of Flight Information on the Reconstruction of In-Beam PET Data
Shakirin, G.; Crespo, P.; Braess, H.; Enghardt, W.;
At the heavy ion therapy facility at the Gesellschaft für Schwerionenforschung Darmstadt, Germany, an in-beam PET scanner is operated for quality assurance monitoring simultaneously to the therapeutic irradiation. The PET scanner, which is completely integrated into the treatment facility, registers the annihilation γ - rays following the decay of minor amounts of β+ radioactive nuclei produced via nuclear reactions between the ions of the therapeutic beam and the atomic nuclei of the irradiated tissue. From a comparison of the reconstructed activity distributions with those predicted from the treatment plan, deviations between the prescribed and the applied dose distributions can be detected. We investigate how reconstruction of in-beam PET data can profit from the time of flight (TOF) information taking into account specific issues of in-beam PET system, namely, a very low counting statistics and the dual head geometry of the PET scanner which results in missing ray sums in certain directions. We simulated β+-activity distributions based on real treatment plans and generated events measured with a timing resolution 1.2 ns FWHM. We further reconstructed the data via list mode MLEM algorithm and via randomly filled subsets expectation maximization (RFS-EM) algorithm (a modification of OSEM adapted for in-beam PET). Two irradiation situations were evaluated: a relatively small field in the head and neck region (clivus chondrosarcoma) and a large field in the pelvic region (prostate carcinoma). Root mean square error is reduced by 20 % for head and neck field and by 36 % for pelvic field for TOF included reconstructions. Also a significant reduction of specific reconstruction artifacts (in particular, elongation of the images caused by the dual head geometry of the scanner) is observed in TOF included reconstructions versus non-TOF ones for both irradiation cases.
Keywords: in-beam PET, reconstruction, time-of-flight, TOF, MLEM, OSEM
  • Poster
    2007 Nuclear Science Symposium & Medical Imaging Conference, 27.10.-03.11.2007, Honolulu, Hawaii, USA
  • Contribution to proceedings
    2007 Nuclear Science Symposium & Medical Imaging Conference, 27.10.-03.11.2007, Honolulu, Hawaii, USA
    Conference Record. 2007 IEEE Nuclear Science Symposium & Medical Imaging Conference: IEEE, 1-4244-0923-3

Publ.-Id: 10824 - Permalink


Two mononuclear Tc complexes: [2,2′-(3-phenylpropylimino)- and [2,2′-(propylimino)-bis(ethanethiolato)](4-methoxybenzenethiolato)-oxidotechnetate(V)
Emmerling, F.; Kraus, W.; Noll, B.; Noll, S.; Pietzsch, H.-J.;
The molecular structures of the two mononuclear title complexes, namely (4-methoxybenzene-thiolato-κS)oxido-[2.2′-(3-phenylpropylimino)bis(ethanethiolato)-κ3S,N,S′]technetium(V), [Tc(C14H21NS2)(C7H7OS)O], (I), and (4-methoxybenzenethiolato- κS)oxido[2, 2′-(propylimino)-bis(ethanethiolato) -κ3S,N,S′]technetium(V) [Tc(C7H15NS2)(C7H7OS)O], (II), exhibit the same coordination environment for the central Tc atoms. The atoms are five-coordinated (TcNOS3) with a square-pyramidal geometry comprising a tridentate 2.2′-(3-phenylpropylimino)bis(ethanethiolate) or 2, 2′-(propylimino)-bis(ethanethiolate) ligand, a 4-methoxybenzenethiolate ligand and an additional oxide O atom. Intermolecular C–H …O and C–H...S hydrogen bonds between the monomeric units result in two-dimensional layers with a parallel arrangement.

Publ.-Id: 10823 - Permalink


Determination of charge state in Co- and Mn-doped ZnO films
Markó, D.; Potzger, K.; Küpper, K.; Xu, Q.; Zhou, S.; Schmidt, H.; Fassbender, J.ORC; Lorenz, M.; Arenholz, E.; Denlinger, J. D.
We have investigated Co- and Mn-alloyed ZnO films grown by pulsed laser deposition (PLD) on a-plane sapphire substrates. X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements have been performed at beamline 8.0.1 and beamline 6.3.1 at the Advanced Light Source in Berkeley, USA. From XAS spectra, recorded in both total electron yield and total fluorescence yield mode, the valence states of Mn and Co have been determined. No ferromagnetic properties have been observed by means of XMCD at 20 K at the L2,3-absorption edges of Mn and Co, respectively. This observation agrees with the purely paramagnetic response of those Co- and Mn-alloyed ZnO films from SQUID magnetometry and Hall effect measurements.
Keywords: ZnO, magnetic semiconductor, XAS, XMCD
  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 10822 - Permalink


Study of dielectron production in C+C collisions at 1 AGeV
Agakichiev, G.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Bassini, R.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Bortolotti, A.; Boyard, J. L.; Braun-Munziger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kajetanowicz, M.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krasa, A.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lapidus, K.; Lopes, L.; Maier, L.; Mangiarotti, A.; Marin, J.; Markert, J.; Metag, V.; Michalska, B.; Mishra, D.; Moriniere, E.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, J.; Otwinowski, J.; Pachmayer, Y.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Perez Cavalcanti, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Schroeder, C.; Schwab, E.; Simon, R. S.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Taranenko, A.; Teilab, K.; Tlusty, P.; Toia, A.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Weber, M.; Wen, H.; Wisniovski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.; Zumbruch, P.;
The emission of e+e- pairs from C+C collisions at an incident energy of 1 GeV per nucleon has been investigated. The measured production probabilities, spanning from the pi0-Dalitz to the rho/omega invariant-mass region, display a strong excess above the cocktail of standard hadronic sources. The bombarding-energy dependence of this excess is found to scale like pion production, rather than like eta production. The data are in good agreement with results obtained in the former DLS experiment.

Publ.-Id: 10821 - Permalink


Elementary Collisions with HADES
Froehlich, I.; Pietraszko, J.; Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Boehmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Froehlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhaeuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kaempfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krizek, F.; Kruecken, R.; Kuehn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lopes, L.; Maier, L.; Mangiarotti, A.; Marin, J.; Markert, J.; Metag, V.; Michalska, B.; Mishra, D.; Moriniere, E.; Mousa, J.; Muentz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palk! A, M.; Pechenov, V.; Pechenova, O.; Cavalcanti, T. P.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Simon, R.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Wen, H.; Wisniowski, M.; Wojcik, T.; Wuestenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zumbruch, P.;
The "High Acceptance DiElectron Spectrometer" (HADES) at GSI, Darmstadt, is investigating the production of e+e- pairs in A+A, p+A and N+N collisions. The latter programm allows for the reconstruction of individual sources. This strategy will be roughly outlined in this contribution and preliminary pp/pn data is shown.
  • Open Access LogoContribution to proceedings
    MENU2007 11th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon, 10.-14.09.2007, Jülich, Germany
    http://www.slac.stanford.edu/econf Proceedings of MENU 2007 - 11th International conference on Meson-Nucleon Physics and the Structure of the Nucleon, 105-110
  • European Physical Journal A (2007)
  • Contribution to WWW
    arXiv: 0712.1505 [nucl-ex]: http://arxiv.org/pdf/0712.1505.pdf

Publ.-Id: 10820 - Permalink


Polyhedral Surface Approximation of Non-Convex Voxel Sets through the Modification of Convex Hulls
Schulz, H.;
In this paper we want to introduce an algorithm for the creation of polyhedral approximations for objects represented as strongly connected sets of voxels in three-dimensional binary images. The algorithm generates the convex hull of a given object and modifies the hull afterwards by recursive repetitions of generating convex hulls of subsets of the given voxel set or subsets of the background voxels. The result of this method is a polyhedron which separates object voxels from background voxels. The objects processed by this algorithm and also the background voxel components inside the convex hull of the objects are restricted to have genus 0.
Keywords: Digital Geometry, Convex Hull, Surface Approximation, Abstract Polyhedron
  • Contribution to proceedings
    12th International Workshop on Combinatorial Image Analysis, 07.-09.04.2008, Buffalo, NY, USA
    Combinatorial Image Analysis

Publ.-Id: 10819 - Permalink


Autonomous planar conductivity array sensor for fast liquid distribution imaging in a fluid coupling
Da Silva, M. J.; Lu, Y.; Sühnel, T.; Schleicher, E.; Thiele, S.; Kernchen, R.; Diele, K.-H.; Hampel, U.;
In this paper, we introduce a new autonomous planar array sensor based on the measurements of electrical conductivity which has been applied to the visualization of fluid distributions inside a fluid coupling during normal operation. The sensor is composed of approximately 1000 interdigital sensing structures which are used to measure the two-dimensional electrical conductivity distribution at the sensors’s surface with a fast multiplexed probing-sensing scheme at up to 10 kHz frame rate. Two such sensors where used to measure dynamic two-phase flow patterns in a fluid coupling at full operation at 790 rpm rotational speed. Therefore, the sensors were mounted on the pressure-side and the suction-side walls of a blade channel inside a test coupling. The whole measurement system is supplied by a battery and controlled via wireless link, thus being fully autonomous, which enable sensor and electronics to rotate together with the coupling.
Keywords: planar sensor, interdigital electrodes, conductivity measurement, flow measurement, fluid coupling, turbo machinery

Publ.-Id: 10817 - Permalink


A fast way to measure phase fractions in multiphase flow
Ondrey, G. S.;
A new measuring technique for the fast measurement of phase fractions in multiphase flow is presented.
Keywords: wire-mesh sensor, capacitance, multiphase flow
  • Chemical Engineering 114(2007)12, 16

Publ.-Id: 10816 - Permalink


Betriebserfahrungen mit PV-Megawattanlagen in Mitteldeutschland
Rindelhardt, U.;
Im Vortrag werden Auslegung und Betriebsergebnisse von 7 PV-Megawatt-Anlagen in Mitteldeutschland beschrieben.Die Module der meisten Anlagen haben eine feste, nach Süden ausgerichtete Orientierung, während eine Anlage mit zwei-achsig nachgeführten Trackern ausgerüstet ist. In allen Anlagen wurden poly- oder monokristalline Solarzellen verwendet. Es kamen sowohl Zentralwechselrichter als auch String-Wechselrichter zum Einsatz. Bei vergleichbaren Einstrahlungsbedingungen wurden Erträge zwischen 950 und 1080 kWh/kW erreicht, die Anlage mit nachgeführten Modulen übertraf diese Erträge erheblich. Durch Detailanalysen der Anlagenerträge wurden vermeidbare Quellen von Mindererträgen identifiziert.
Keywords: Solar radiation, grid connected PV systems, performance
  • Invited lecture (Conferences)
    Institutsseminar, 26.02.2008, Hameln-Emmerthal, Germany

Publ.-Id: 10815 - Permalink


Perspektiven der Kernenergie - Herausforderungen und Möglichkeiten
Rindelhardt, U.;
Ausgehend von der bisherigen Entwicklung wird der derzeitige Stand der Kernenergienutzung auf der Basis der Kernspaltung vorgestellt. Vertieft wird auf die Brennstoffausnutzung in modernen Kernkraftwerken eingegangen. Die Hauptmerkmale der KKW der 3. Generation und der in Entwicklung befindlichen 4. Generation werden dargestellt.Ein besonderes Gewicht liegt auf der Darstellung der Rolle von schnellen Brutreaktoren. Abschließend wird das Problem der Endlagerung und aktueller Alternativen (Transmutation) erörtert.
Keywords: nuclear power, safety, nuclear fuel cycle
  • Lecture (others)
    Mitgliederversammlung VDE-Bezirksverein Chemnitz, 17.01.2008, Zwickau, Germany

Publ.-Id: 10814 - Permalink


Numerical prediction of horizontal stratified flows
Höhne, T.; Vallee, C.;
Usually, the slug flow regime is characterized by an acceleration of the gaseous phase and by the transition of fast liquid slugs, which carry a significant amount of liquid with high kinetic energy. It is potentially hazardous to the structure of a system due to the strong oscillating pressure levels formed behind the liquid slugs as well as the mechanical momentum of the slugs. Because slug flow cannot be predicted with the required accuracy and spatial resolution by the one-dimensional system codes, the stratified flows are increasingly modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated. The recent improvements of the multiphase flow modelling in the ANSYS CFX code make it now possible to simulate these mechanisms in detail. In order to validate existing and further developed multiphase flow models, high-resolution measurement data is needed in time and also in space.

Thanks to the optical access of the test channels built at Forschungszentrum Dresden-Rossendorf, it is possible to study detailed local stratified air/water flow phenomena. These experimental results give an important input for two-phase flow CFD model validation (i.e. interfacial momentum transfer, turbulent profiles of each phase). For the experimental investigation of co-current air/water flows, the HAWAC (Horizontal Air/Water Channel) was built (Fig. 1). Its inlet device provides defined inlet boundary conditions for code comparison. The channel allows in particular the study of air/water slug flow under atmospheric pressure. A flow pattern map (Fig. 2) was arranged constructed on the basis of a visual observation of the flow structure at different combinations of the gas and liquid superficial velocities. Parallel to the experiments, CFD calculations were carried out. A picture sequence recorded during slug flow was compared with the equivalent CFD simulation made (Figs. 3 and 4). The two-fluid model was applied with a special turbulence damping procedure at the free surface. An Algebraic Interfacial Area Density (AIAD) model on the basis of the implemented mixture model was introduced, which allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value.

The behaviour of slug generation and propagation at the experimental setup was qualitatively reproduced by the simulation, while local deviations require a continuation of the work. The creation of small instabilities due to pressure surge or an increase of interfacial momentum should be analysed in the future. Furthermore, experiments like pressure and velocity measurements are planned and will allow quantitative comparisons, also at other superficial velocities.

Keywords: horizontal flow, CFD, slug flow, flow pattern, HAWAC
  • Contribution to proceedings
    6th International Conference on COMPUTATIONAL FLUID DYNAMICS in the Oil & Gas, Metallurgical and Process Industries, 10.-12.06.2008, Trondheim, Norway
    CD_ROM, paper 08-12
  • Lecture (Conference)
    6th International Conference on COMPUTATIONAL FLUID DYNAMICS in the Oil & Gas, Metallurgical and Process Industries, 10.-12.06.2008, Trondheim, Norway

Publ.-Id: 10813 - Permalink


Simulation von Vermischungsvorgängen
Höhne, T.; Kliem, S.;
Buoyancy driven mixing was investigated under simulated natural circulation conditions at the test facility ROCOM.
Experiments with density differences between the ECC water (higher density) resp. the de-borated slugs (lower density) and the ambient coolant was used to validate the CFD software CFX.
A Reynolds stress turbulence model was employed to model the effects of turbulence on the mean flow.
Hybrid meshes consisting at least of 2 million nodes and 4 million elements were used.
The experiment and CFD calculations show in both cases significant mixing effects due to the density differences.
The ANSYS CFX calculations show a good qualitative agreement with the data. At some local positions differences in the predicted and measured concentration fields occur.
Keywords: Boron Dilution, Coolant Mixing, ROCOM, CFD
  • Invited lecture (Conferences)
    Workshop Strömungssimulation, 30.11.2007, Dresden, Germany

Publ.-Id: 10812 - Permalink


Nachrechnung von experimentell bestimmten Leistungsparametern eines Vollhub-Feder-Sicherheitsventils mit ANSYS CFX
Höhne, T.; Moncalvo, D.;
Sicherheitsventile schützen druckbeaufschlagte Räume oder Druckbehälter (z. B. Dampfkessel, Druckbehälter, Rohrleitungen, Transportbehälter) vor einem unzuläs-sigen Druckanstieg, der zu einer Schädigung des angeschlossenen Druckgerätes führen kann. Sicherheitsventile leiten bei Überschreiten des Ansprechdruckes Gase, Dämpfe oder Flüssigkeiten in die Atmosphäre ab. Das Sicherheitsventil wird verwen-det, wenn der Druck in einem Druckbehälter den zulässigen Betriebsdruck bei vor-hersehbaren Störungen um mehr als 10 % übersteigen kann. Bei richtiger Dimensio-nierung des Sicherheitsventils bleibt der Druckaufbau beherrschbar. Nach dem Ansprechen des Sicherheitsventils und Abbau des zu hohen Druckes durch Abblasen in die Umgebung oder über eine Rohrleitung schließt das Ventil wieder und die Anlage kann weiter betrieben werden.
Numerische Strömungs-berechnungsprogramme (CFD-Codes) können helfen, die Leistung von Sicherheitsventilen zu verbessern. Um Leistungsparameter zu studie-ren, wurden Experimente am Institut für Strömungsmechanik der Technischen Universität Hamburg-Haburg (TUHH) für die CFD-Codevalidierung genutzt. Durch die konstante Weiterentwicklung der Numerik bzw. der physikalischen Modelle ist es nun möglich, die relativ komplexen Strömungsvorgänge eines Sicherheitsventils (Jets, Umströmung von Hindernissen, Strömungsseparation, Stagnationsgebiete, Zonen mit hohen Ma-Zahlen) zu simulieren.
Mit dem ANSYS CFX-Code wurden Nachrechnungen von Durchsatzparametern ei-nes Leser Sicherheitsventils mit einem Gitter von 1 Million Hexaeder Zellen vorge-stellt (Abb. 1). Druckrandbedingungen wurden am Ein- und Austritt des Strömungs-gebietes definiert. Die Turbulenz wurde mit dem k-ε und k-ω basierten SST-Modell berechnet. Sehr gute Übereinstimmung wurde bei den Durchsatzkennlinien der Cha-rakteristiken für Luft und Wasser bis 5 bar Stagnationsdruck erzielt, es existierte je-doch eine systematische Abweichung bei Luft im Falle hoher Ansprechdrücke (über 20 bar) durch Realgasverhalten und das Auftreten hohe Ma-Zahlen. CFD-Rechnungen mit Luft/Wasser-Zweiphasengemischen bei 5-9 bar Überdruck und 70-95% Gasanteil ergaben realistische Durchsatzraten. Hierbei wurde das monodisper-se Partikelmodell des homogenen Euler-Euler-Ansatzes für Zweiphasengemische genutzt. Weitere Untersuchungen, insbesondere das Verhalten bei Stoffgemischen (Glukoselösung) bzw. der Einfluss des Hubs des Sicherheitsventils (Stellung des Ventiltellers zwischen Sitz und maximaler Öffnung) auf den Durchsatz im Vergleich mit Experimenten werden vorgestellt.
Keywords: Safety Valve, CFD
  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachausschüsse Computational Fluid Dynamics, Gasreinigung, Mechanische Flüssigkeitsabtrennung und Grenzflächenbestimmte Systeme und Prozesse, 18.-20.02.2008, Wiesbaden, Germany
  • Contribution to proceedings
    Jahrestreffen der ProcessNet-Fachausschüsse Computational Fluid Dynamics, Gasreinigung, Mechanische Flüssigkeitsabtrennung und Grenzflächenbestimmte Systeme und Prozesse, 18.-20.02.2008, Wiesbaden, Germany
    CD-ROM

Publ.-Id: 10811 - Permalink


Experimental and numerical prediction of horizontal stratified flows using the HAWAC facility
Höhne, T.; Vallee, C.;
Slug flow is potentially hazardous to the structure of the system due to the strong oscillating pressure levels formed behind the liquid slugs. It is usually characterized by an acceleration of the gaseous phase and by the transition of fast liquid slugs, which carry out a significant amount of liquid with high kinetic energy. For the experimental investigation of air/water flows, a horizontal channel with rectangular cross-section was build at Forschungszentrum Dresden-Rossendorf (FZD). Experimental data were used to check the feasibility to predict the slugging phenomenon with the existing multiphase flow models build in ANSYS CFX. Further it is of interest to prove the understanding of the general fluid dynamic mechanism leading to slug flow and to identify the critical parameters affecting the main slug flow parameters (like e.g. slug length, frequency and propagation velocity; pressure drop).
A selected co-current test run that was carried out at a superficial water velocity of 0.69 m /s and a superficial air velocity of 2.2 m /s at ambient pressure and temperature conditions was analyzed using the software package ANSYS CFX. At these conditions, a slug flow is generated. For free surface simulations, the inhomogeneous multiphase model was used, where the gaseous and liquid phases can be partially mixed in certain areas of the flow domain. In this case the local phase demixing after a gas entrainment is controlled by buoyancy and interphase drag and is not hindered by the phase interface separating the two fluids. A further decision has to be made regarding the applied fluid morphology and interphase drag law for the multiphase flow. The fluid-dependent shear stress transport (SST) turbulence models were selected for each phase. Damping of turbulent diffusion at the interface has been considered. The k-ω based SST model accounts for the transport of the turbulent shear stress and gives highly accurate predictions of the onset and the amount of flow separation under adverse pressure gradients. The tail of the calculated slug and the flow behind it is in good agreement with the experiment. The entrainment of small bubbles in front of the slug could not be observed in the calculation. However, the front wave rolls over and breaks. It is created due to the high air velocity. In contrast to the measurement, the slug period is increasing with the time in the calculation. This could be a result of different amount of water in the channel at the beginning of experiment and CFD simulation. While in the simulation, the liquid phase covers 78% of the channel, it represents about 70% at the beginning of the experiment. Furthermore, in the experiment, this value is also reduced by a first slug which carries a significant amount of water out of the channel. This first slug could not be simulated. The behavior of slug propagation at the experimental setup was qualitatively reproduced, while quantitative deviations require a continuation of the work.
As some uncertainties were noticed at the inlet of this channel, the HAWAC (Horizontal Air/Water Channel) with well defined inlet boundary conditions dedicated to co-current flows was built. A picture sequence recorded during slug flow was compared with the equivalent CFD simulation made with the code ANSYS CFX. The two-fluid model was applied with a special free surface treatment. Due to an interfacial momentum transfer, it was possible to generate slugs based on instabilities. The behaviour of slug generation and propagation at the experimental setup was qualitatively reproduced, while deviations require a continuation of the work. The creation of small instabilities due to pressure surge or an increase of interfacial momentum should be analysed in the future. Furthermore, experiments like pressure and velocity measurements are planned and will allow quantitative comparisons, also at other superficial velocities.
Keywords: CFD, flow pattern, stratified flow, slug flow
  • Invited lecture (Conferences)
    ANSYS Conference & 25th CADFEM Users’ Meeting, 21.-23.11.2007, Dresden, Germany
  • Contribution to proceedings
    ANSYS Conference & 25th CADFEM Users’ Meeting, 21.-23.11.2007, Dresden, Germany
    CD-ROM, paper 679

Publ.-Id: 10810 - Permalink


Rare-earth implanted Y2O3 thin films
Peeva, A.; Dikovska, A. O.; Atanasov, P. A.; Jime´Nez De Castro, M.; Skorupa, W.;
Thin Er, Yb co–doped Y2O3 films were grown by pulsed laser deposition from ceramic target. Subsequent ion implantation with 1.1 MeV Er+
ions to a fluence of 6 x 10E14 at/cm2 at room temperature was performed in order to modify the structure of the as-deposited films. The as-depositedfilms have a polycrystalline column-like structure. Ion implantation induces defects into the as-deposited films. After annealing at 900 8C for 1 h inoxygen atmosphere, the films recrystallize in roundly shaped grain-like structure with grain size of about 100 nm. The Er3+ photoluminescence response was obtained for all the films by excitation through cross-relaxation of Yb3+ ions. The IR emission spectrum, consisting of two narrow peaks at 1415 and 1514 nm, differs from the typical spectra of Er-doped materials. The VIS emission spectrum observed in as-deposited films does not appear after implantation and subsequent 900 8C annealing.
Keywords: Rare-earth, erbium, ion implantation, thin films; Y2O3; Pulsed Laser Deposition

Publ.-Id: 10809 - Permalink


Investigation of flow development of co-current gas-liquid vertical slug flow
Kaji, R.; Azzopardi, B. J.; Lucas, D.;
Void fraction, Taylor bubble/liquid slug length, and slug frequency are parameters essential to understand the structure of slug flow. In the present study, these parameters were extracted from the time series of cross-sectionally averaged void fraction obtained from two vertical facilities having similar internal pipe diameter but significantly different axial lengths; 51.2mm/3.5m and 52.3mm/9m. To investigate the effect of flow development on slug characteristics measurements were carried out at several axial locations from the mixing section for both facilities. For slug frequency, a new correlation including the effect of the axial length has been proposed and assessed using previously published data.
Keywords: slug flow, vertical pipe, flow structure, flow development, frequency

Publ.-Id: 10807 - Permalink


Search of the origin of ferromagnetism in DMS
Talut, G.; Reuther, H.; Stromberg, F.; Zhou, S.; Potzger, K.; Grenzer, J.; Mücklich, A.; Eichhorn, F.;
Transition metal doped wide band gap semiconductors like GaN, ZnO and TiO2 are promising candidates to be diluted magnetic semiconductors (DMS) with Curie temperatures (Tc) above room temperature (RT). In most of the studies reported in literature the presence of metallic precipitates could not be excluded and may play an important role in the discussion of the origin of the ferromagnetism.
Hence, one of the main obstacles while creating a DMS is the formation of secondary phases. The detection of those is very problematic too.
Since solubility limits for the doping atoms, especially in GaN, are rather low, non-equilibrium doping techniques like low temperature film growth or ion implantation are commonly used.
Ion implantation gives the possibility of doping at different temperatures and with high dopand concentrations but is always connected with lattice damage of the target material. Subsequent annealing in a time scale of some minutes mostly results in phase separation. Combining ion implantation with faster techniques, i.e. rapid thermal annealing or flash lamp annealing, leads to a diluted state while the crystallinity of the target material can be partially restored.
Sample sets were implanted with 57Fe ions and concentrations up to 18 at. % and subsequently annealed at different temperatures and time scales.
Conversion electron Mössbauer spectroscopy (CEMS), superconducting quantum interference device (SQUID), x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and Rutherford backscattering spectroscopy (RBS) were used to characterize the (micro)-structure, magnetic response and radiation damage of specimens as well as the charge state and site location of Fe. The origin of ferromagnetism is discussed on base of these results.
Keywords: DMS, Ferromagnetism, GaN, TiO2
  • Invited lecture (Conferences)
    Condensed Matter Seminar, University of Central Florida, 12.11.2007, Orlando, Florida, USA

Publ.-Id: 10806 - Permalink


Entwicklung und Validierung des Druckstoßprogramms DYVPRO Mod. 3
Neuhaus, T.; Schaffrath, A.; Ronneberger, R.; Altstadt, E.;
Druckstöße entstehen in Rohrleitungssystemen immer dann, wenn ein Fluid (z.B. eine Flüssigkeit oder ein Gas) durch das plötzliche Öffnen oder Schließen einer Armatur, die Änderung der Drehzahl einer Pumpe, in Folge von Rohrleitungsbrüchen usw. beschleunigt oder abgebremst wird. Hierbei entstehen Druckwellen, die erhöhte Innendrücke verbunden mit mechanischen Spannungen in den Rohrleitungswänden sowie zeitabhängige axiale Kräfte auf Rohrleitungen und deren Halterungen hervorrufen können. Durch Reflexionen der Druckwellen können Unterdrücke entstehen, die bei Unterschreiten des lokalen Sättigungsdrucks zur Bildung von Dampfblasen (Kavitation) führen können. Bei dem Zusammenfall der Dampfblasen können weitere, sekundäre Druckstöße auftreten, die die primären Druckwellen überlagern. Die Ausbreitungsgeschwindigkeit von Druckwellen hängt zum einen von den Eigenschaften des Fluids (speziell dessen Kompressibilität und Dichte) und zum anderen von den mechanischen Eigenschaften des Rohrleitungssystems (Elastizitätsmodul und Querkontraktionszahl) sowie dessen Geometrie (Durchmesser des Rohrs und Wanddicke) ab. Druckstöße sind oftmals die Ursache für Beschädigungen an Rohrleitungen und Rohrleitungshalterungen und stellen daher für viele verfahrenstechnische Anlagen ein Problem dar.

Die TÜV NORD SysTec GmbH & Co. KG beschäftigt sich seit vielen Jahren mit der Berechnung von Druckstößen in Kraftwerken und speziell in Kernkraftwerken. Hierzu hat sie das Druckstoßprogramm DYVRO entwickelt und qualifiziert. Der vorliegende Beitrag be¬schreibt die nun hinsichtlich des verwendeten partiellen Differentialgleichungssystems und der eingesetzten Numerik überarbeitete Programmversion DYVRO Mod. 3 und deren Validierung anhand repräsentativer Experimente (u.a. anhand des Simpson-Experiments sowie anhand eines Versuches an der Cold Water Hammer Test Facility). Die Ergebnisse der Validierungsrechnungen werden anschließend mit eigenen oder fremden Rechnungen mit Systemcodes (hier ATHLET und RELAP) sowie dem Druckstoßprogramm WAHA verglichen. Bei diesen Vergleichen werden u.a. die Ergebnisse des im 5. EU-Rahmenprogramm geförderten Forschungsvorhabens WAHALOADS mit einbezogen. Die Vergleiche zeigen eine sehr gute Übereinstimmung der Rechenergebnisse von DYVRO mit den Experimenten sowie den Ergebnissen des WAHA-Codes. Die Ergebnisse der Druckstoßcodes WAHA und DYVRO sind – sowohl im einphasigen als auch im zweiphasigen Bereich - deutlich besser als die der Systemcodes. Unsere Analysen belegen, dass DYVRO Mod. 3 dem aktuellen Stand von Wissenschaft und Technik entspricht.
Keywords: water hammer, pipe line, fluid dynamics, pressure wave
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Germany

Publ.-Id: 10805 - Permalink


(4-Methoxybenzenethiolato-κS)oxido-[2,2’-propylimino)-bis(ethanethiolato)- κ3S,N,S’]rhenium(V)
Kraus, W.; Emmerling, F.; Noll, B.; Noll, S.; Pietzsch, H.-J.;
The central Re atom of the mononuclear title complex, [Re(C8H18NS2)(C6H4OS)O], is five-coordinate (ReNOS3) with a square-pyramidal geometry comprising a tridentate 2,2 0-(propylimino)diethanethiolate ligand, a 4-methoxybenzenethiolate ligand and a doubly-bonded O atom.

Publ.-Id: 10804 - Permalink


Nachweis solarer Neutrinooszillationen an SNO
Wagner, A.;
Das Sudbury Neutrino Observatory wird vorgestellt, die Daten zur Flavour-Zusammensetzung des solaren Neutrinoflusses interpretiert und Schlüsse auf Neutrinooszillationen gezogen.
  • Invited lecture (Conferences)
    Vortrag an Fachbereich Physik der Technischen Universität Darmstadt, 31.10.2007, Darmstadt, Germany

Publ.-Id: 10803 - Permalink


The spectrum of a non-Hermitian two-mode Bose-Hubbard system
Graefe, E.-M.; Günther, U.; Niederle, A.; Korsch, H. J.;
We study an N-particle, two-mode Bose-Hubbard system, modelling a Bose-Einstein condensate in a double-well potential. By introducing effective complex energies to the modes we describe a coupling to a continuum. The eigenvalues of the resulting non-Hermitian matrix model are in general complex where the imaginary parts (resonance widths) describe the decay rate into the continuum. In dependence on the system parameters, the eigenvalues show intricate patterns of avoided and real crossings, as well as characteristic bifurcations. In the present talk the effect of the interplay between the particle interaction and the non-Hermiticity on characteristic features of the spectrum is analysed and its peculiarities are clarified by perturbational methods.
Keywords: Bose-Einstein condensate, Bose-Hubbard system, non-Hermitian matrix model, perturbation theory, exceptional point, spectral bifurcation
  • Lecture (Conference)
    DPG Frühjahrstagung, 10.-14.03.2008, Darmstadt, Germany

Publ.-Id: 10802 - Permalink


Reduzierung des Out-of-Field-of-View Einflusses auf die Event-basierte Bewegungskorrektur von Hirnuntersuchungen in der PET
Langner, J.;
Ziel/Aim:
Event-basierte Bewegungskorrekturverfahren erlauben durch räumliche Transformation jedes Koinzidenzereignisses auf einer line-of-response (LOR) eine exakte Korrektur von Patientenbewegungen in der PET. Die Integration dieser komplexen Verfahren in die klinische Routine setzt jedoch ein Bewegungsverfolgungssystem (Motion-Tracking) sowie einen vollautomatischen Verarbeitungsablauf voraus. Ein Schritt hierbei ist die Korrektur des Out-of-Field-of-View (OutFOV) Effektes. Bei diesem Effekt kommt es dazu, dass LORs zeitweise ausserhalb des FOV transformiert und somit nicht in den Emissions-Sinogrammen erfasst werden. Durch entsprechende Normierung der unterbewerteten Bins wird versucht, dies auszugleichen. Werden die Korrekturfaktoren jedoch zu groß, kommt es zu Bildartefakten, welche u.a. die quantitative Auswertung beeinträchtigen. Ziel dieser Arbeit war die Minimierung des OutFOV Einflusses und die Integration der Methode in einen automatisierten Untersuchungsablauf, welcher den Einsatz im klinischen Umfeld ermöglicht.

Methodik/Methods:
Meist wird bei event-basierter Korrektur ein einzelner Referenzzeitpunkt für alle Teilabschnitte (Frames) einer dynamischen Aufnahme benutzt – üblicherweise der Startzeitpunkt der Untersuchung. Ein solches Vorgehen führt jedoch i.a. zu den angesprochenen hohen statistischen Unsicherheiten bei der Normierung der OutFOV-Counts. Durch Analyse der Bewegungsdaten, wird für jeden Frame eine
Häufigkeitsverteilung der relativen Patientenbewegung erstellt. Anhand dieser werden optimale Zeitpunkte ermittelt, an denen die Normierungsfaktoren minimal sind. Diese Referenzpositionen erlauben es, jeden Frame einzeln mit ebenfalls räumlich angepassten Transmissionsdaten zu rekonstruieren. Die daraus resultierenden Bildvolumina werden abschließend auf eine gemeinsame
Orientierung transformiert. Hierbei wird die aus den Bewegungsdaten bekannte Orientierung der Bildvolumina zu den Referenzzeitpunkten genutzt.

Ergebnisse/Results:
Die Nutzung für jeden Frame angepasster Referenzzeitpunkte reduziert die OutFOV- Korrekturfaktoren erheblich und gewährleistet eine hinreichende Messstatistik für alle LORs im Gesichtsfeld des Tomographen. Die bewegungskorrigierten Bilddaten sind infolgedessen frei von den erwähnten Artefakten.

Schlussfolgerungen/Conclusions:
Es konnte gezeigt werden, dass durch die Einführung optimierter Referenzpositionen ein wichtiger limitierender Faktor der event-basierten Bewegungskorrektur eliminiert werden kann. Dies zeigt sich auch bei der Auswertung von klinischen Daten, wo das Verfahren in der Lage ist, bewegungsfreie sowie nunmehr quantitativ auswertbare Datensätze zu erzeugen. Nach Kombination dieser Methode mit bereits etablierten Methoden zeigt dies die Machtbarkeit einer klinischen Nutzung einer event-basierten Bewegungskorrektur und deren Potenzial.
  • Abstract in refereed journal
    Nuklearmedizin 47(2008)2, A59
  • Lecture (Conference)
    46. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 23.-26.04.2008, Leipzig, Germany

Publ.-Id: 10801 - Permalink


Helical MRI in MHD Taylor-Couette flow
Szklarski, J.;
Magnetorotational Instability (MRI) is believed to be one of the most important instabilities on astrophysical scales. However, it is very difficult to observe it in a laboratory experiment. One possibility is to use a Taylor-Couette setup (a flow between two concentric rotating cylinders) where a liquid metal alloy is used. Problems arise since such metals are characterized by very small magnetic Prandtl number and consequently vast rotation rates are necessary. In the PROMISE experiment a special helical configuration of the applied magnetic field was used in order to dramatically reduce rotation rates. We present numerical simulations and relate it to experimental results confirming the existence of MRI of this type.
  • Lecture (Conference)
    10th MHD Days, 26.-29.11.2007, Garching, Germany

Publ.-Id: 10800 - Permalink


Untersuchungen zur Kontrastabhängigkeit des untergrundbereinigten Schwellwertes bei der Volumenbestimmung in der PET
Dittrich, S.;
Ziel/Aim:
Bei der quantitativen Bewertung dreidimensionaler Strukturen (VOIs) innerhalb von PET-Bildvolumen wurde in (1) auch nach Untergrundsubtraktion eine Abhängigkeit des relativen Schwellwertes vom Bildkontrast nachgewiesen, welche aus theoretischer Sicht unerwartet ist. Für ein Verständnis dieser Abhängigkeit soll in der vorliegenden Arbeit der Einfluss verschiedener Faktoren wie Auflösung und Streukorrektur genauer untersucht werden. Es soll zudem ein effizientes Kalibrierungsverfahren entwickelt werden, welches für eine korrekte Volumenbestimmung bei einem automatischen Schwellwertverfahren notwendig wird.

Methodik/Methods:
Es wurden PET-Volumendatensätze mit unterschiedlichen Bildkontrasten ausgewertet, welche sowohl aus Phantommessungen als auch aus Monte Carlo Simulationen mit dem Programmpaket GATE (2) gewonnen wurden. Für die im rekonstruierten Bildvolumen dargestellten Kugeln wurde der Schwellwert, der zur bekannten wahren Objektgröße führt, bestimmt. Aus Least Squares Fits unter Nutzung des analytischen Ausdrucks für die Faltung der Objektfunktion (Aktivitätsverteilung) mit der Point Spread Function (PSF) wurden ferner die rekonstruierte Auflösung und die Kugelradien ermittelt.

Ergebnisse/Results:
Die aus den gemessenen Daten erhaltene Abhängigkeit des untergrundbereinigten, relativen Schwellwertes vom Bildkontrast konnte mit den simulierten Bilddaten bestätigt werden. Mit abnehmender Auflösung wird der relative Schwellwert zunehmend unabhängig vom Kontrast. Die aus den Least Squares Fits ermittelten Radien waren stets kleiner als die wahren Kugelradien. Diese scheinbare Reduktion der Objektgröße wies ebenfalls eine Abhängigkeit vom Bildkontrast auf, aus der sich wiederum der Zusammenhang zwischen relativen Schwellwert und Kontrast ableiten lässt. Dadurch konnte eine Kalibrierungsvorschrift für automatische Schwellwertverfahren entwickelt werden.

Schlussfolgerungen/Conclusions:
Für eine präzise Volumenbestimmung mittels automatischer Schwellwertanalyse in der PET muss auch nach erfolgter Untergrundsubtraktion die Kontrastabhängigkeit des relativen Schwellwertes beachtet werden. Die beobachtete Abhängigkeit konnte über eine Radiusreduktion erklärt werden, woraus eine allgemeine Kalibrierungsvorschrift für die Volumenbestimmung mit automatischen
Schwellwertverfahren entwickelt wurde.

Literatur/References:
(1) C. Pötzsch; F. Hofheinz; J. van den Hoff; Minimierung der Inter-Observer-Variabilität bei volumetrischen Auswertungen von onkologischen Ganzkörperstudien in der PET; Nuklearmedizin (2005) 44 p. A16
(2) S. Jan; G. Santin; D. Strul et al.; GATE: a simulation toolkit for PET and SPECT; Phys. Med. Biol. 49 (2004) 4543
  • Abstract in refereed journal
    Nuklearmedizin 47(2008)2, A58
  • Lecture (Conference)
    46. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 23.-26.04.2008, Leipzig, Germany

Publ.-Id: 10799 - Permalink


Multimere Neurotensin-Liganden: Synthese, Komplexbildung gegenüber Kupfer(II) und Affinität zum Neurotensin-Rezeptor 1
Stephan, H.; Röhrich, A.; Noll, S.; Bergmann, R.; Pietzsch, J.; Steinbach, J.;
Neben den eingeführten Radionukliden Tc-99m, Re-188 und Y-90 rücken Radionuklide wie Cu-64 und Cu-67 zunehmend in das Interesse für Diagnostik und Therapie von Tumor- und Stoffwechselerkrankungen. In Verbindung mit multifunktionale Liganden eröffnet dies einen neuen Zugang zu spezifischen Radiopharmaka und zwar vor allem dann, wenn die Verkapslung radioaktiver Metallnuklide im Kern topologisch so gelingt, dass diese unter physiologischen Bedingungen kinetisch und thermodynamisch stabil fixiert sind. Eine Modifizierung der Ligandstruktur mit Biomolekülen - wie Zucker oder Peptide - erlaubt dann die Einstellung definierter Löslichkeits- und selektiver Bindungseigenschaften. Ziel ist die Entwicklung metabolisch stabiler, radioaktiv markierter Neurotensin-Konjugate für die Tumordiagnostik und –therapie
  • Lecture (Conference)
    46. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 23.-26.04.2008, Leipzig, Germany
  • Abstract in refereed journal
    Nuklearmedizin 47(2008)2, A82

Publ.-Id: 10798 - Permalink


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