Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Spin-strain coupling in NiCl2-4SC(NH2)2
Chiatti, O.; Sytcheva, A.; Wosnitza, J.; Zherlitsyn, S.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.;
We report results of sound-velocity and sound-attenuation measurements in the quantum S = 1 spin-chain magnet NiCl2-4SC(NH2)2, in magnetic fields up to 18 T. This material is discussed in the context of Bose-Einstein condensation of magnons. The longitudinal c33 acoustic mode, which has a propagation direction along the spin chains, shows pronounced spin-lattice effects. This mode demonstrates a softening in the vicinity of the field-induced antiferromagnetic ordering (below T = 1.2 K), accompanied by an energy dissipation in the acoustic wave. A broad maximum has been observed in the temperature dependence of the sound velocity at 44 K. The low-temperature sound-velocity and sound-attenuation behavior is subject to fluctuations of Ni spin degrees of freedom resulting in frequency-dependent effects. The B − T phase diagram obtained from the ultrasonic measurements is compared with results extracted from other experimental investigations. The ultrasonic results are analyzed with a theory based on exchange-striction spin-phonon coupling.
  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Deutschland

Publ.-Id: 11567 - Permalink


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

Publ.-Id: 11566 - Permalink


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

Publ.-Id: 11565 - Permalink


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

Publ.-Id: 11564 - Permalink


Magnetic properties of the Haldane-gap material NENB
Cizmar, E.; Ozerov, M.; Ignatchik, O.; Papageorgiou, T. P.; Wosnitza, J.; Zvyagin, S. A.; Krzystek, J.; Zhou, Z.; Landee, C. P.; Landry, B. R.; Turnbull, M. M.; Wikaira, J. L.;
Results of magnetization and high-field ESR studies of the new spin- 1 Haldane-chain material [Ni(C2H8N2)2NO2](BF4) (NENB) are reported. A definite signature of the Haldane state in NENB was obtained. From the analysis of the frequency-field dependence of magnetic excitations in NENB, the spin-Hamiltonian parameters were cal-
culated, yielding Δ/kB = 17.4 K, gk = 2.14, D/kB = 7.5 K, and |E/kB| = 0.7 K for the Haldane gap, g factor. and the crystal-field anisotropy, respectively. The presence of fractional S = 1/2 chain-end states, revealed by ESR and magnetization measurements, is found to be responsible for spin-glass-freezing effects. In addition, extra states in the excitation spectrum of NENB have been observed in the vicinity of the Haldane gap, whose origin is discussed.
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11563 - Permalink


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

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

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Publ.-Id: 11562 - Permalink


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

Publ.-Id: 11561 - Permalink


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

Publ.-Id: 11560 - Permalink


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

Publ.-Id: 11559 - Permalink


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

Publ.-Id: 11558 - Permalink


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

Publ.-Id: 11557 - Permalink


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

Publ.-Id: 11556 - Permalink


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

Publ.-Id: 11555 - Permalink


On the modelling of bubble entrainment by impinging jets in CFD-simulations
Schmidtke, M.; Lucas, D.;
This contribution presents different approaches for the modeling of air entrainment under water by plunging jets in CFD codes. In simulations which include the full length of the jet and its environment, the process of bubble generation can not be resolved due to computational limitations. This is why the air entrainment has to be modeled in meso-scale simulations. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. In the impinging jet configuration, the air is a continuous phase above the water level but bubbly below the water level. Various drag models are implemented in the CFD solver CFX11 and their influence on the gas void fraction below the water level is discussed. The algebraic interface area density (AIAD) model applies a drag coefficient for bubbles and a different drag coefficient for the free surface. If the AIAD model is used for the simulation of impinging jets, the gas entrainment depends on the free parameters included in this model. The calculated gas entrainment can be adapted via these parameters. Therefore, an advanced AIAD approach could be used in future for the implementation of models (e.g. correlations) for the gas entrainment.
Keywords: jet, entrainment, bubble, plunging, impinging, free surfase, bubble, area density
  • Contribution to proceedings
    XCFD4NRS, Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
    On the modelling of bubble entrainment by impinging jets in CFD-simulations
  • Poster
    XCFD4NRS, Experiments and CFD Code Applications to Nuclear Reaktor Safety, 10.-12.09.2008, Grenoble, France

Publ.-Id: 11554 - Permalink


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

Publ.-Id: 11553 - Permalink


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

Publ.-Id: 11552 - Permalink


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

Publ.-Id: 11551 - Permalink


The Naimark dilated PT-symmetric brachistochrone
Günther, U.; Samsonov, B.;
The quantum mechanical brachistochrone system with PT-symmetric Hamiltonian is Naimark dilated and reinterpreted as subsystem of a Hermitian system in a higher-dimensional Hilbert space. This opens a way to a direct experimental implementation of the recently hypothesized PT-symmetric ultra-fast brachistochrone regime of [C. M. Bender et al, Phys. Rev. Lett. {\bf 98}, 040403 (2007)] in an entangled two-spin system.
Keywords: PT-symmetric quantum mechanics, brachistochrone, minimal passage time, entangled states, qubits, spin systems, polarized photons, quantum information theory, Naimark dilation, positive operator valued measure, POVM, exceptional point

Publ.-Id: 11550 - Permalink


Spectral distribution of UV range diffuse reflectivity for Si+ ion implanted polymers
Balabanov, S.; Tsvetkova, T.; Borisova, E.; Avramov, L.; Bischoff, L.;
The analysis of the UV range spectral characteristics can supply additional
information on the formed sub-surface buried layer with implanted dopants. The near-surface
layer (50÷150 nm) of bulk polymer samples have been implanted with silicon (Si+) ions at low
energies (E=30 keV) and a wide range of ion doses (D=1.1013 ÷ 1,2.1017 cm-2). The studied
polymer materials were: ultra-high-molecular-weight polyethylene (UHMWPE), poly-methylmetacrylate
(PMMA) and poly-tetra-fluor-ethylene (PTFE). The diffuse optical reflectivity
spectra Rd = f(λ) of the ion implanted samples have been measured in the UV range (λ =
220÷350 nm). In this paper the dose dependences of the size and sign of the diffuse optical
reflectivity changes ΔRd = f(D) have been analysed.
Keywords: polymers; implantation; spectral distribution; UV-range

Publ.-Id: 11549 - Permalink


Dose dependence of visible range diffuse reflectivity for Si+ and C+ ion implanted polymers
Balabanov, S.; Tsvetkova, T.; Borisova, E.; Avramov, L.; Bischoff, L.;
Detailed insight into the near-surface area of the ion beam modified polymer is supplied by the measured diffuse reflectivity spectra. The near-surface layer (50÷150 nm) of bulk polymer samples have been implanted with silicon (Si+) and carbon (C+) ions at low energies (E=30 keV) and a wide range of ion doses (D=5.1012-2.1017 cm-2). The polymer materials studied were: ultra-high-molecular-weight polyethylene (UHMWPE), poly-propylene (PP), and poly-tetra-fluor-ethylene (PTFE). The diffuse optical reflectivity spectra Rd = f(λ) of the implanted samples have been measured in the visible range (λ=400÷830 nm). In this paper the dose dependences of the size and sign of the diffuse reflectivity changes ΔRd=f(D) have been analyzed.
Keywords: polymers; implantation; dose dependence; reflectivity

Publ.-Id: 11548 - Permalink


In-beam PET at high-energy photons
Möckel, D.;
Presentation about the application of in-beam PET for high-energy photons
  • Lecture (others)
    OncoRay - Seminar, 03.06.2008, Dresden, Deutschland

Publ.-Id: 11547 - Permalink


Commissioning and Test Results of the Superconducting RF Gun at ELBE
Teichert, J.; Arnold, A.; Büchner, A.; Büttig, H.; Janssen, D.; Justus, M.; Kamps, T.; Klemz, G.; Lehnert, U.; Matheisen, A.; Michel, P.; Murcek, P.; Schurig, R.; Staats, G.; Staufenbiel, F.; Xiang, R.; Will, I.;
  • Lecture (Conference)
    Sixth PHIN Collaboration Meeting, 17.-18.07.2008, Lecce, Italy
  • Lecture (Conference)
    Seventh PHIN Collaboration Meeting, 02.-03.12.2008, Geneva, Switzerland

Publ.-Id: 11546 - Permalink


Materialforschung für sichere Kernkraftwerke
Altstadt, E.;
Es wird ein Überblick zu den Aspekten der Materialsicherheit in der Kerntechnik gegeben. Im Mittelpunkt der Betrachtungen steht der Reaktordruckbehälter von Leichtwasserreaktoren. Im FZD angwendete Methoden zur experimentellen Mikrostrukturanalyse, zur Modellierung von strahleninduzierten Defekten mit Ratentheorie und zur bruchmechanischen Analyse werden erläutert.
Keywords: Small angel neutron scattering, rate theory, fracture mechanical analysis, reactor pressure vessel
  • Invited lecture (Conferences)
    Werkstofftechnisches Kolloquium der Technischen Universität Darmstadt, 12.06.2008, Darmstadt, Deutschland

Publ.-Id: 11545 - Permalink


Multiphase flows in industrial applications - experiments and CFD simulations
Höhne, T.;
The last decade has seen an increasing use of three-dimensional Computational Fluid Dynamics (CFD) codes to predict steady state and transient flows in industrial applications because a number of important phenomena such as slugging, pressurized thermal shocks, coolant mixing, and thermal striping cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution. CFD codes contain models for simulating turbulence, heat transfer, multi-phase flows, and chemical reactions. Such models must be validated before they can be used with sufficient confidence in industrial applications. The necessary validation is performed by comparing model results against measured data. The multipurpose thermalhydraulic test facility TOPFLOW was designed at FZD to investigate stationary and transient phenomena in two-phase flows with the purpose of development and validation of models used in CFD codes. In addition, for the experimental investigation of horizontal two phase flows, different non pressurized channels and the Hot Leg Model in a pressure chamber were built and the experimental results compared with numerical simulations. Our partner for CFD code qualification is ANSYS CFX. Based on this partnership physical models which are developed are implemented into the code and thus contribute to the code qualification.
Keywords: CFD, FZD, Multiphase flow, TOPFLOW
  • Invited lecture (Conferences)
    CFD OIL2008 - 3d Encontro Latino-Americano de CFD Aplicado à Indústria de Petróleo, 18.-19.08.2008, Rio de Janeiro, Brasil
  • Contribution to proceedings
    CFD OIL2008 - 3d Encontro Latino-Americano de CFD Aplicado à Indústria de Petróleo, 18.-19.08.2008, Rio de Janeiro, Brasil
    CD-ROM, Webpage

Publ.-Id: 11544 - Permalink


An Analytical Approximation Solution for a Time-Dependent Neutron Transport Problem with External Source and Delayed Neutron Production
Merk, B.;
This work presents the development of an analytical approximation solution for a space-time-dependent neutron transport problem in a one-dimensional system consisting of a homogenized medium with a central external source with Green functions. The delayed neutron production is implemented with the multiple-scale expansion method. Qualitative results for a given system are analyzed and an example of the use for the analysis of accelerator-driven systems is given.
Keywords: Time dependet neutron transport, Accelerator driven system, Experimental analysis, Green's funtion expansion
  • Nuclear Science and Engineering 161(2009)1, 49-67

Publ.-Id: 11543 - Permalink


CFD-simulation of the VVER thermal hydraulic benchmark V1000CT–2 using ANSYS CFX
Höhne, T.;
Plant measured data from VVER-1000 coolant mixing experiments were used within the OECD/NEA and AER coupled code benchmarks for light water reactors to test and validate CFD codes. The task is to compare the various calculations with measured data, using specified boundary conditions and core power distributions. The experiments, which are provided for CFD validation, include single loop cooling down or heating-up by disturbing the heat transfer in the steam generator (SG) through the steam valves at low reactor power in the range of 5-14% and with all main coolant pumps (MCP) in operation. They were conducted during the plant commissioning phase at Kozloduy-6, Bulgaria and Kalinin-1, 2, Russia. CFD calculations have been performed for the thermal hydraulic benchmark V1000CT-2 using ANSYS CFX. The numerical grid model was generated with the grid generator ICEM-CFD and contains 4.7 Mio. tetrahedral elements. The Best Practice Guidelines (BPG) in using CFD in Nuclear Reactor Safety Applications has been used. Different advanced turbulence models were utilized in the numerical simulation. The best agreement with the Kozloduy heating-up experiment at the core inlet shows the Detached Eddy Simulation (DES). The results show a clear sector formation of the affected loop at the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.3%. Uncertainties are still the estimation and interpolation of experimental values at the core outlet to the core inlet.
Keywords: CFD, Coolant Mixing, PWR

Publ.-Id: 11542 - Permalink


The ELBE Superconducting Photoinjector
Teichert, J.; Arnold, A.; Janssen, D.; Murcek, P.; Staufenbiel, F.; Xiang, R.; Kamps, T.; Klemz, G.; Will, I.;

Publ.-Id: 11541 - Permalink


QCD quasiparticle model with collective modes and Landau damping
Schulze, R.;
extrapolation of lattice QCD to large baryon densities, e.g. CBM@FAIR; QPM with ImΠi ≠ 0, plasmons and plasminos from HTL; Is the small -T region accessible? Improvement of previous models?
  • Lecture (Conference)
    Hadrons@FAIR, 25.-27.06.2008, Frankfurt, Deutschland

Publ.-Id: 11540 - Permalink


Finite Density QCD Sum Rules for D Meson, Nucleon and Light Vector Mesons
Thomas, R.;
In-Medium Modification of Hadrons: w, N, D
QCD Sum Rules
Four-Quark Condensates
  • Lecture (Conference)
    Hadrons@FAIR, 25.-27.06.2008, Frankfurt, Deutschland

Publ.-Id: 11539 - Permalink


The Radiation Source ELBE at the Forschungszentrum Dresden-Rossendorf
Michel, P.;
A superconducting Electron Linac with high Brilliance and low Emittance (ELBE) which provides an average beam current of 1 mA with maximum beam energy of 36 MeV was constructed in the Forschungszentrum Dresden-Rossendorf, Germany. The electron beam is used to generate infrared light (Free Electron Lasers), MeV-Bremsstrahlung, X-rays (electron channelling), fast neutrons and positrons. The ELBE secondary beams are used for a wide range of basic research like semiconductor physics, nuclear astrophysics and radio biological investigations. The technical setup of the accelerator and secondary beam generation will be explained and some representative application examples will be demonstrated. ELBE runs in routine user operation since 2004 with stepwise commissioning of the secondary radiation targets.
  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Deutschland
  • Contribution to proceedings
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Deutschland
    Nuclear Science Symposium, N48-5

Publ.-Id: 11538 - Permalink


CFD-Modellierung von Vermischungsvorgängen in Druckwasserreaktoren in Anwesenheit von Dichtegradienten
Vaibar, R.; Rohde, U.; Höhne, T.;
In der Reaktorsicherheitsforschung sind auftriebsgetriebene Strömungen von Relevanz für Störfall-szenarien mit Verdünnung der Borkonzentration und für thermische Schockbelastungen des Reak-tordruckbehälters. In der numerischen Simulation der Strömungen werden neben der Berücksichtigung der Auftriebskräfte Quell- und Korrekturterme in die Bilanzgleichungen für die turbulente Energie und die turbulente Dissipation eingeführt. Es wurden erweiterte Modelle entwickelt, in die zusätzliche Gleichungen für die Turbulenzgrößen „turbulenter Massenstrom“ und „Dichtevarianz“ eingehen. Die Modelle wurden in den CFD-Code ANSYS-CFX implementiert.
Die Validierung der Modelle erfolgte an einem speziellen Versuchsaufbau (VeMix-Versuchsanlage), mit Einspeisung von Fluid höherer Dichte in eine Vorlage. Als Kriterien für die Validierung wurde der Umschlag zwischen impulsdominiertem Strömungsregime mit vertikalem Jet oder ein vertikales Absinken bei Dominanz von Dichteeffekten herangezogen sowie lokale Konzentrationsmessungen mit Hilfe eines speziell entwickelten Leitfähigkeits-Gittersensors. Eine Verbesserung der Simulation dichtedominierter Vermischungsprozesse mit den erweiterten Turbulenzmodellen konnte allerdings nicht nachgewiesen werden, da die Unterschiede zwischen den Rechnungen mit verschiedenen Turbulenzmodellen zu gering sind. Andererseits konnte jedoch die Simulation der Stratifikation von Fluiden unterschiedlicher Dichte im kalten Strang einer Reaktoranlage deutlich verbessert werden. Anhand der Nachrechnung von Ver-suchen am geometrisch ähnlichen Reaktor-Strömungsmodell ROCOM wurde gezeigt, dass diese Stratifikation von bedeutendem Einfluss auf die Vermischung und somit letztendlich auch auf die Temperatur- bzw. Borkonzentrationsverteilung innerhalb des Reaktordruckbehälters ist. Sie lässt sich nur korrekt simulieren, wenn ausreichend große Abschnitte des kalten Stranges mit modelliert werden. Somit konnte doch eine bessere Vorhersagegenauigkeit der Simulation der Vermischung erreicht werden.

In reactor safety research, buoyancy driven flows are of relevance for boron dilution accidents or pressurised thermal shock scenarios. Concerning the numerical simulation of these flows, besides of the consideration of buoyancy forces, source and correction terms are introduced into the balance equations for the turbulent energy and its dissipation rate. Within the project, extended turbulence models have been developed by introducing additional balance equations for the turbulent quantities “turbulent mass flow” and “density variance”. The models have been implemented into the computati-onal fluid dynamics code ANSYS-CFX.
The validation of the models was performed against tests at a special experimental set-up, the VeMix facility, were fluid of higher density was injected into a vertical test section filled with lighter fluid. As validation criteria the switching-over between a momentum controlled mixing pattern with a horizontal jet and buoyancy driven mixing with vertical sinking down of the heavier fluid was used. Additionally, measurement data gained from an especially developed conductivity wire mesh sensor were used. However, an improvement of the modelling of buoyancy driven mixing by use of the extended models could not be shown, because the differences between calculations with the different models were not relevant. On the other hand, the modelling of the stratification of fluids with different density in the cold leg of a reactor primary circuit could be significantly improved. It has been shown on calculations of experi-ments at the ROCOM mixing test facility, a scaled model of a real reactor plant, that this stratification is relevant as a boundary condition for the mixing process inside the reactor pressure vessel. It can be correctly simulated only if sufficient large parts of the cold legs are included in the modelling. On this way, an improvement of the accuracy of the prediction of mixing processes was achieved.
Keywords: Boron dilution, Pressurised Thermal Shock, coolant mixing, buoyancy forces, turbulence models, validation
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-500 2008

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Publ.-Id: 11537 - Permalink


Entwicklung einer Transportnäherung für das reaktordynamische Rechenprogramm DYN3D
Grundmann, U.; Beckert, C.;
Es wurde eine SP3-Transportmethode entwickelt, die neutronenkinetische Rechnungen für die Kerne von Leichtwasserreaktoren mit höherer Genauigkeit als die gegenwärtig in der Kernauslegung angewandten Standardmethoden auf Basis der Zweigruppendiffusionsnäherung er-laubt. Eine Verbesserung der Genauigkeit von Abbrandrechnungen und der Berechnung von Tran-sienten ist für heterogene Kerne notwendig, in denen neben UO2-Brennelementen auch Mischoxyd – Brennelemente eingesetzt werden.
In einem ersten Schritt wird die in dem Rechenprogramm DYN3D verwendete Zweigruppendiffusi-onsmethode auf viele Energiegruppen erweitert. Auf der Basis von Untersuchungen zu einer optima-len Gruppenstruktur wird die Verwendung von 8-10 Energiegruppen der Neutronen als optimal erach-tet. Das Verfahren wurde anhand von stationären und transienten Rechnungen für das OECD/NEA und US NRC PWR MOX/UO2 Core Transient Benchmark verifiziert.
In den nächsten Schritten erfolgte die Entwicklung und Implementierung einer SP3-Näherung in DYN3D. Dabei besteht die Möglichkeit, ein feineres Gitter im BE zu benutzen. Das Verfahren wurde zunächst durch pinweise Berechnung stationärer Zustände des obigen Benchmarks verifiziert.
Untersuchungen für das Benchmarkproblem zeigen, dass das Verhältniss des 2-ten Momentes zum 0-ten Moment des Flusses klein ist. Die beiden SP3-Gleichungen können deshalb separat in iterativer Weise gelöst werden. Dies reduziert den benötigten Speicherplatz und erfordert weniger CPU-Zeit. Dieses vereinfachte Verfahren wurde deshalb ebenfalls in das Programm implementiert. Es wird ge-zeigt, dass mit diesem Verfahren eine vergleichbare Genauigkeit erreicht wird. Stabweise Rechnun-gen mit 4, 8 und 16 Energiegrupppen wurden für einen stationären Zustand des Benchmarks durch-geführt. Eine 3-dimensionale Aufgabe des Benchmarks mit Rückkopplung und Vollleistung wurde mit dem optimierten SP3-Verfahren gerechnet.

A SP3 transport approximation was developed for neutron kinetic calculations of cores of light water reactors with a higher accuracy than the present standard methods of core design based on the two group diffusion approximation. An improvement of accuracy for burnup and transient calculations is required for cores loaded with UO2 and MOX fuel assemblies.
In the first step, the two group diffusion method applied in the computer code DYN3D was extended to an arbitrary number of groups. Investigations for an optimal group structure have shown that a number of 8 to 10 energy groups of neutrons seems to be reasonable. The multi-group technique was verified for steady states and transients of the OECD/NEA und US NRC PWR MOX/UO2 Core Tran-sient Benchmark.
In the next steps, a SP3-approximation was developed and implemented into DYN3D. The possibility of using finer meshes inside the fuel assemblies is involved in this method. The technique was veri-fied by pinwise calculations for steady states of the above mentioned benchmark.
The investigations to the benchmark problem have shown that ratio of the 2nd moment of flux to the 0th moment is small. Therefore the two coupled SP3 equations can be solved separately in an iterative way. The required computer memory and the CPU time can be reduced by this technique. This sim-pler method was also implemented in the code. It is shown that the reached accuracy is comparable to accuracy of the original technique. Pinwise calculations with 4, 8 and 16 energy groups were per-formed for a steady state of this benchmark. A three-dimensional problem of the benchmark at full power and with feedback was calculated with the optimized SP3 technique. The optimized method was used for the time integration of the transient SP3 equations. The pinwise calculation of a control rod ejection was tested for a simple system and the results were compared with the diffusion solution.
Keywords: reactor physics, neutron kinetics, diffusion approximation, neutron transport, SP3 method, code vali-dation, MOX fuel, benchmarking
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-497 2008

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Publ.-Id: 11536 - Permalink


Multipole mixing ratios of transitions in 11B
Rusev, G.; Tonchev, A. P.; Schwengner, R.; Sun, C.; Tornow, W.; Wu, Y. K.;
The mixing ratios for M1 and E2 radiation for transitions in 11B have been determined by measuring the azimuthal asymmetry of the radiation emitted from levels populated by resonant absorption of polarized photons. The photon-scattering experiments were carried out at the FreeElectron Laser Laboratory at Duke University using nearly monoenergetic and linearly polarized photon beams. The mixing ratios were deduced from a comparison of the measured azimuthal asymmetries with calculations for the angular distribution of mixed transitions.
Keywords: Photon scattering, monochromatic photons, FEL, gamma-ray spectroscopy, multipole mixing ratios.

Publ.-Id: 11535 - Permalink


Validation of CFD Codes and Applications in Nuclear Industry
Höhne, T.; Krepper, E.; Vallee, C.;
The last decade has seen an increasing use of three-dimensional CFD codes to predict steady state and transient flows in nuclear reactors.

The reason for the increased use of multidimensional CFD methods is that a number of important phenomena such as pressurized thermal shocks, boron mixing and thermal striping cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.

CFD codes contain empirical models for simulating turbulence, heat transfer, multi-phase flows, and chemical reactions. Such models must be validated before they can be used with sufficient confidence in NRS (Nuclear Reactor Safety) applications.
CFD simulations are shown with an emphasis on validation in areas such as: heat transfer, buoyancy, multi-phase flows, natural circulation, turbulent mixing, and complex geometries. These topics are related to NRS-relevant issues such as: pressurized thermal shocks, boron dilution, hydrogen distribution, sub-cooled boiling etc.
Keywords: CFD
  • Invited lecture (Conferences)
    16th International Conference on Nuclear Engineering ICONE16, 11.-15.05.2008, Orlando, USA

Publ.-Id: 11534 - Permalink


Deep sub-threshold production of Xi(1321) hyperons in collisions of Ar+KCl at 1.76 AGeV
Kotte, R.;
Deep sub-threshold production of Xi(1321) hyperons in collisions of Ar+KCl at 1.76 AGeV
  • Lecture (Conference)
    HADES Collaboration Meeting XIX, 01.-05.07.2008, Darmstadt, Deutschland

Publ.-Id: 11533 - Permalink


New Events display
Wüstenfeld, J.; Wendisch, C.;
The HADES Eventdisplay
  • Lecture (Conference)
    HADES Collaboration Meeting XIX, 01.-05.07.2008, Darmstadt, Deutschland

Publ.-Id: 11532 - Permalink


Parametrization of pp and pn bremsstrahlung for PLUTO
Kaehlitz, P.; Zhou, P.;
Parametrization of pp and pn bremsstrahlung for PLUTO
  • Lecture (Conference)
    HADES Collaboration Meeting XIX, 01.-05.07.2008, Darmstadt, Deutschland

Publ.-Id: 11531 - Permalink


Timeschedule for the MDC DAQ upgrade
Wüstenfeld, J.;
Activities towards the mounting of the MDC DAQ upgrade parts
  • Lecture (Conference)
    HADES Collaboration Meeting XIX, 01.-05.07.2008, Darmstadt, Deutschland

Publ.-Id: 11530 - Permalink


MDC Front End Electronics
Wüstenfeld, J.;
Current status regarding MDC FEE and how to equip the plane I chambers
  • Lecture (Conference)
    HADES Collaboration Meeting XIX, 01.-05.07.2008, Darmstadt, Deutschland

Publ.-Id: 11529 - Permalink


Status of MDC-I
Naumann, L.;
Status of MDC-I ...
  • Lecture (Conference)
    HADES Collaboration Meeting XIX, 01.-05.07.2008, Darmstadt, Deutschland

Publ.-Id: 11528 - Permalink


Virtual Bremsstrahlung in NN collisions
Kämpfer, B.;
  • Invited lecture (Conferences)
    HADES Kollaborations Meeting, 04.07.2008, Darmstadt, Deutschland

Publ.-Id: 11527 - Permalink


Exclusive charm production in pp collisions at √s <~ 15GeV
Titov, A. I.; Kämpfer, B.;
We discuss the open charm production in peripheral reactions pp → YcYc and pp → McMc, where Yc and Mc stand for Lambda^+_c, Sigma^+_c and D,D∗, respectively, at √s <~ 15 GeV, which corresponds to the energy range of FAIR. Our consideration is based on the topological decomposition of the planar quark and diquark diagrams which allows to estimate consistently meson and baryon exchange trajectories and energy scale parameters as well. The spin dependance is determined by the effective interaction of lowest exchanged resonance. Unknown parameters are fixed by an independent analysis of open strangeness production in pp → YY and pp → KK reactions and of SU(4) symmetry. We present the corresponding cross sections and longitudinal double-spin asymmetries for exclusive binary reactions with open charm mesons and baryons in the final state. The polarization observables have a non-trivial t and s dependence which is sensitive to details of the open charm production mechanism.

Publ.-Id: 11526 - Permalink


Unfolding of higher order exceptional points in a PT-symmetric Bose-Hubbard model
Graefe, E.-M.; Günther, U.; Korsch, H.-J.; Niederle, A.;
The physics of the PT-symmetric two-mode Bose-Hubbard model is discussed in detail. Special emphasis is laid on the unfolding of higher-order exceptional points (EPs) and on a detailed presentation of the Newton polygon technique. It is shown that the latter can be considered as a highly efficient tool for the unfolding analysis of higher-order roots in any polynomial equation.
Keywords: PT-symmetric quantum mechanics, Bose-Enstein condensate, Bose-Hubbard model, spectral singularity, exceptional point, Newton polygon technique, Puiseux-Newton technique, higher-order polynomial equation
  • Invited lecture (Conferences)
    Quantum Physics with Non-Hermitian Operators (PHHQP VII), 29.06.-11.07.2008, Benasque, Spain

Publ.-Id: 11525 - Permalink


Generalized measurements and non-Hermitian quantum mechanics
Samsonov, B.; Günther, U.;
The basics of the theory of generalized quantum measurements is briefly discussed. Starting from positive operator valued measures (POVMs) (as generalization of decompositions of unity in terms of orthogonal projectors) it is demonstrated how to associate the POVMs in a natural way with the nonorthogonal eigenvectors of non-Hermitian operators with non-degenerate real spectrum. This approach allows for a self-consistent treatment of the non-Hermitian operators connected with a state discrimination technique for their non-orthogonal eigenvectors and the definition of a probabilistic content of corresponding generalized measurement procedures. The technique is applied to the brachistochrone problem of PT-symmetric quantum mechanics (PTSQM) in a measurement frame with Hermitian Hamiltonian and non-Hermitian generalized spin-type observables. The Naimark dilation (extension) technique for POVMs is briefly sketched.
Keywords: quantum mechanics, non-Hermitian operators, positive operator valued measure, POVM, PT-symmetric quantum mechanics, brachistochrone, Naimark dilation, Naimark extension
  • Invited lecture (Conferences)
    Quantum Physics with Non-Hermitian Operators (PHHQP VII), 29.06.-11.07.2008, Benasque, Spain

Publ.-Id: 11524 - Permalink


Technologieplattform S-Layer
Raff, J.;
Der Vortrag dient der Vorstellung abgeschlossener, laufender und geplanter Forschungsarbeiten zum Thema bakterielle S-Layer-Proteine. Insbesondere werden dabei aktuelle Arbeiten zur Herstellung fotokatalytisch aktiver Nanopartikel zur Eliminierung von Arzneimittelrückständen aus Wasser vorgestellt.
  • Lecture (others)
    Koordinierungstreffen mit dem Institut für Wasserchemie der TU Dresden, 16.06.2008, Dresden, Deutschland

Publ.-Id: 11523 - Permalink


Photokatalytische Spaltung von Diclofenac mit an S-Layer gebundenen ZnO/TiO2-Nanopartikeln
Marquard, A.;
wird nachgereicht
  • Lecture (others)
    Seminar NF-Gruppe, 16.06.2008, Dresden, Deutschland

Publ.-Id: 11522 - Permalink


Multifunktionale Biokompositschichten zur Eliminierung von Arneimittelrückständen aus Wasser
Raff, J.; Marquard, A.; Pollmann, K.;
Nach der Verabreichung von Arzneimitteln werden vom menschlichen Körper bis zu 95% des wirkstoffs unverändert ausgeschieden und können über das Abwasser in den Wasserkreislauf gelangen. In den weitaus meisten Fällen werden die Wirkstoffe jedoch schnell abgebaut oder die Wirkstoffkonzentrationen sind derart gering, dass keine akute Gefährdung für die Umwelt und die menschliche Gesundheit besteht. Dennoch weisen einige wenige Stoffe in umweltrelevanten Konzentrationen negative Langzeiteffekte auf. Dazu gehört zum Beispiel das schwer abbaubare und in der Umwelt nachweisbare Schmerzmittel Diclofenac. Aufgrund der niedrigen Konzentrationen ist es mit konventionellen Verfahren sehr aufwendig, derartige Stoffe aus dem Wasser zu entfernen. Abhilfe können hier alternative Verfahren schaffen. Mittels hoch geordnetet bakterieller Hüllproteine können in enfacher Art und Weise verschiedenste nanostrukturierte fotokatalytisch aktive Schichten auf der Basis von ZnO und TiO2-Nanocluster hergestellt werden und durch Bindung an oder Einbettung in silikatische Träger immobilisiert werden...
  • Lecture (Conference)
    Bremer Colloquium Produktionsintegrierte Wasser-/Abwassertechnik, 22.-23.09.2008, Bremen, Germany
  • Contribution to proceedings
    Bremer Colloquium Produktionsintegrierte Wasser-/Abwassertechnik, 22.-23.09.2008, Bremen, Germany
    Proceedings of the Bremer Colloquium Produktionsintegrierte Wasser-/Abwassertechnik

Publ.-Id: 11521 - Permalink


Multifunctional multilayer-systems based on bacterial surface layers (S-layers)
Pollmann, K.;
Projektvorstellung
  • Lecture (others)
    Workshop zum DFG-Schwerpunktprogramm "Biomimetic Materials Research", 07.07.2008, Potsdam, Deutschland

Publ.-Id: 11520 - Permalink


Magnetic order by C-ion implantation into Mn5Si3 and Mn5Ge3 and its laterial modification
Suergers, C.; Joshi, N.; Potzger, K.; Strache, T.; Moeller, W.; Fischer, G.; von Loehneysen, H.;
Ferromagnetic Mn5Si3C0.8 and Mn5Ge3C0.8 films with Curie temperatures TC well above room temperature are obtained by 12C+-ion implantation in antiferromagnetic Mn5Si3 or ferromagnetic Mn5Ge3. Patterning of the films with a gold mesh serving as a stencil mask during implantation allows a lateral modification of magnetic order creating ferromagnetic regions of high-TC Mn5Ge3C0.8 which are embedded in low-TC Mn5Ge3. This provides a procedure for the fabrication of magnetoelectronic hybrid-devices comprised of different magnetic phases.
Keywords: magnetic semiconductors, ion implantation, silicides
  • Applied Physics Letters 93(2008), 062503

Publ.-Id: 11519 - Permalink


Non-DMS related ferromagnetism in transition metal doped zinc oxide
Potzger, K.; Zhou, S.;
We review pitfalls in recent efforts to make a conventional semiconductor, namely ZnO, ferromagnetic by means of doping with transition metal ions. Since the solubility of those elements is rather low, formation of secondary phases and the creation of defects upon low temperature processing can lead to unwanted magnetic effects. Among others, ion implantation is a method of doping, which is highly suited for the investigation of those effects. By focussing mainly on Fe, Co or Ni implanted ZnO single crystals we show that there are manifold sources for ferromagnetism in this material which can easily be confused with the formation of a ferromagnetic diluted magnetic semiconductor (DMS). We will focus on metallic as well as oxide precipitates and the difficulties of their identification. Moreover, we will try to clarify the role of lattice disorder or point defects upon development of ferromagnetic properties.
Keywords: ZnO, ion implantation, DMS
  • Physica Status Solidi (B) 246(2009)6, 1147-1167

Publ.-Id: 11518 - Permalink


Fe valence state of Sr2FeMoO6 probed by x-ray absorption spectroscopy: the sample age matters
Kuepper, K.; Raekers, M.; Taubitz, C.; Hesse, H.; Neumann, M.; Young, A. T.; Piamonteze, C.; Bondino, F.; Prince, K. C.;
Recent studies of the magnetic properties of Sr2FeMoO6, a half metallic double perovskite showing large magneto resistance effects at room temperature, by means of site specific x-ray absorption spectroscopy (XAS) have led to very different results concerning the Fe valence state. We present a detailed study of a Sr2FeMoO6 polycrystalline sample, which has been probed by means of XAS and XMCD over several years. We find a mixed valent Fe2+, Fe3+ state, which shifts towards Fe3+ with time. An understanding of such a chemical change is of importance for potential applications of Sr2FeMoO6 and related transition metal oxides.
Keywords: Sr2FeMoO6, double perovskite, tunneling magneto resistance, x-ray absorption spectroscopy, x-ray magnetic circular dichroism, full multiplet calculations
  • Journal of Applied Physics 104(2008)3, 036103

Publ.-Id: 11516 - Permalink


Selected vector-meson decay-distributions in reactions of polarized photons with protons
Titov, A. I.; Kämpfer, B.;
We develop a formalism for studying vector meson (V ) photo-production at the proton (p) with polarized photons, ~γp ! V p, through an analysis of the decay distribution in the channel V ! π0γ. We show that this decay distribution differs noticeably from the distributions of purely hadronic decays, like φ ! K+K−, ω ! π0π+π−. Formulas for the decay distributions are presented which are suitable for data analysis and interpretation.

Publ.-Id: 11515 - Permalink


In-beam measurements of the HADES-TOF RPC wall
Blanco, A.; Cabanelas, P.; Belver, D.; Castro, E.; Diaz, J.; Fonte, P.; Gil, A.; Gonzalez-Diaz, D.; Heinz, T.; Koenig, W.; Lopes, L.; Muentz, C.; Palka, M.; Pietraszko, J.; Rustamov, A.; Schwab, E.; Sobolev, Y.; Tarantola, A.; Teilab, K.; Traxler, M.; Trebacz, R.; Yurevich, S.; Garzon, J. A.; Wuestenfeld, J.;
A full size prototype of the new inner HADES-TOF wall based on Resistive Plate Chambers (RPCs) was mounted and exposed to secondaries from C reactions on Be and Nb targets at 2 AGeV kinetic energy and typical HADES particle fluxes. The tested sextant is constituted by 187 individual 4-gap glass-aluminium shielded RPC cells distributed in three columns and two layers, covering an area of 1.26 m2.
An average timing resolution of 73 ps σ was measured with 99% intrinsic efficiency, on a random location, and moderate timing tails, along with an average longitudinal position resolution of 7.7 mmσ, in the range from a few Hz/cm2 up to 80 Hz/cm2 without noticeable degradation of performance. Aditionally, the atching efficiency was estimated using the tracking system of HADES, yielding an average value of 97.5%.

Publ.-Id: 11513 - Permalink


Electroproduction of phi mesons
Titov, A.;
Electroproduction of phi mesons
  • Invited lecture (Conferences)
    Donnersberg Workshop 2008, 31.03.-03.04.2008, Donnersberg, Deutschland

Publ.-Id: 11512 - Permalink


Strangeness Electroproduction
Dohrmann, F.;
Strangeness Electroproduction
  • Invited lecture (Conferences)
    Donnersberg Workshop 2008 A1 Collaboration, 31.03.-03.04.2008, Donnersberg, Deutschland

Publ.-Id: 11510 - Permalink


Attenuation correction of four dimensional (4D) PET using phase-correlated 4D-computed tomography
Pönisch, F.; Richter, C.; Just, U.; Enghardt, W.;
The image quality in a conventional positron emission tomography (PET)/computed tomography (CT) scanner is degraded by respiratory motion because of erroneous attenuation correction when three-dimensional image acquisition is used. To overcome this problem, time-resolved data acquisition (4D) is required. For this, a Siemens Biograph 16 PET/CT scanner has been modified and its normal capability has been extended to a true 4D-PET/4D-CT imaging device including phase-correlated attenuation correction. To verify the correct functionality of this device, experiments on a respiratory motion phantom that allowed movement in two dimensions have been performed. The measurements showed good spatial correlation as well as good time synchronization between the PET and CT data. Furthermore, the motion pattern of the phantom and the shape of the activity distribution have been examined, and the volume of the reconstructed PET images has been analyzed. The results demonstrate the feasibility of such a procedure, and we therefore recommend that 4D-PET data should be reconstructed using 4D-CT data, which can be acquired on the same machine.
  • Physics in Medicine and Biology 53(2008), N259-N268

Publ.-Id: 11509 - Permalink


Diagonal and Off-Diagonal Susceptibilities as Diagnostics of the QCD Phase Diagram: A Quasiparticle Perspective
Bluhm, M.;
Diagonal and Off-Diagonal Susceptibilities as Diagnostics of the QCD Phase Diagram: A Quasiparticle Perspective
  • Lecture (Conference)
    Hadrons@FAIR, 25.-27.06.2008, Frankfurt, Deutschland

Publ.-Id: 11508 - Permalink


Diagonal and Off-Diagonal Susceptibilities in a Quasiparticle Model of the Quark-Gluon Plasma
Bluhm, M.;
Diagonal and Off-Diagonal Susceptibilities in a Quasiparticle Model of the Quark-Gluon Plasma
  • Lecture (Conference)
    DPG Frühjahrstagung, 10.-14.03.2008, Darmstadt, Deutschland

Publ.-Id: 11507 - Permalink


QCD Equation of State
Bluhm, M.;
QCD Equation of State
  • Poster
    Quark-Matter 2008, 04.-10.02.2008, Jaipur, India

Publ.-Id: 11506 - Permalink


Tumortherapie mit Ionenstrahlen
Enghardt, W.;
Motivation für neue Therapiestrahlen etc.
  • Lecture (others)
    Seminarvortrag Institut für Optik und Quantenelektronik, 11.06.2008, Jena, Deutschland

Publ.-Id: 11505 - Permalink


Hochpräzisions-Strahlentherapie von Tumoren
Enghardt, W.;
Die Wechselwirkung ionisierender Strahlung mit (belebter) Materie etc.
  • Lecture (others)
    Urania Seniorenakademie, 25.06.2008, Bernau, Deutschland

Publ.-Id: 11504 - Permalink


Umsetzung biologisch adaptierter Bestrahlungspläne
Enghardt, W.;
Umsetzung biologisch adaptierter Bestrahlungspläne
  • Invited lecture (Conferences)
    DEGRO ÖGRO 2008, 03.05.2008, Wien, Österreich

Publ.-Id: 11502 - Permalink


Erste dosimetrische und strahlenbiologische Experimente an Laser-beschleunigten Elektronenstrahlen
Enghardt, W.;
Laser-Beschleuniger für die Strahlentherapie etc.
  • Lecture (others)
    Radioonkologisches Kolloquium, 02.04.2008, München, Deutschland

Publ.-Id: 11501 - Permalink


Medizinische Anwendung laserbeschleunigter Teilchenstrahlen in der Krebstherapie
Enghardt, W.;
Strahlentherapie - Einführung, Tumortherapie mit Ionenstrahlen, Beschleuniger und Therapiestrahlführung, Laserbeschleuniger für die Krebtherapie
  • Invited lecture (Conferences)
    Festveranstaltung zum Tag im Land der Ideen 2008, 08.03.2008, Jena, Deutschland

Publ.-Id: 11500 - Permalink


Konzeption der medizinischen Strahlführung bei Laser getriebenen Therapiebeschleunigern
Enghardt, W.;
Konventionelle Partikel-Strahlführungen,, Strahführungen für Laser-Beschleuniger, Strahlungs-Quelltherme (DAP 3.1), Konzeption der Therapie-Strahlführung (DAP 3.2), Sekundäre Untergrundstrahlung (DAP 3.3)
  • Lecture (others)
    Verbundprojekt-Treffen "onCOOPtics", 07.03.2008, Jena, Deutschland

Publ.-Id: 11499 - Permalink


Medical Radiation Sciences
Enghardt, W.;
Medical Radiation Sciences
  • Lecture (others)
    Weiterbildender Masterstudiengang "Medical Radiation Sciences", 29.01.2008, Dresden, Deutschland

Publ.-Id: 11498 - Permalink


Dosimetry and radiobiology at ultrashortly pulsed, laser accelerated electron beams
Enghardt, W.;
Lase particle acceleration, the irradiation device, dosimetry, cell irradiation, direct effects of ultrashortly pulsed beams, conclusions
  • Invited lecture (Conferences)
    CERRO, 24.01.2008, Les Menuires, France

Publ.-Id: 11497 - Permalink


Stand der experimentellen Arbeiten im Rahmen des TOPFLOW-II Projekts
Beyer, M.; Vallee, C.; Fischer, F.; Danciu, D.-V.; Schütz, P.; Pietruske, H.; Lucas, D.; Carl, H.;
Im Vortrag wird der aktuelle Stand der experimentellen Arbeiten, die im Rahmen des TOPFLOW-II Projektes notwendig sind, ausführlich erläutert. Hauptaufgabe dieses wissenschaftlichen Projektes ist die Bereitstellung von qualitativ hochwertigen Daten zur Modellierung von Strömungsphänomenen im CFD Code und deren Validierung.
Nach einer kurzen Vorstellung der TOPFLOW Versuchsanlage werden die erzielten Ergebnisse der Dampf/Wasser-Experimente im Modell eines heißen Stranges eines Konvoi Druckwasserreaktors erörtert. Danach folgt die Beschreibung der zur Vorbereitung der Kondensations- und Druckentlastungsexperimente in einer vertikalen Teststrecke durchgeführten Arbeiten. Hierbei wird besonders auf den Versuchsaufbau und die Spezialmesstechnik (Thermoelementlanze, Doppel-Thermonadelsonden, Hochtemperatur-Gittersensoren) eingegangen. Des Weiteren wird der schnelle Röntgentomograph als nichtinvasives Messverfahren zur Erfassung der Strömungsformen in einem vertikalen DN50 Ti-Rohr vorgestellt und die Anwendung dieses Scanners bei der Durchführung von Experimenten mit auf- bzw. abwärtsgerichteten Strömungen beschrieben.
Zusätzlich zu diesen Arbeiten beinhaltet das TOPFLOW-II Projekt Kondensationsversuche an freien Oberflächen und an einem Wasserstrahl sowie Experimente zum Blasenmitriss beim Auftreffen eines Wasserstrahls auf eine freie Wasseroberfläche. Zu diesem Thema werden Aufbau und Ziele eines kleinskaligen Vorversuches sowie die anlagentechnischen Erweiterungen zum Durchführen derartiger Experimente im TOPFLOW-Drucktank vorgestellt. Abschließend werden kurz die Ergebnisse einer umfangreichen Luft/Wasser-Versuchsserie mit optimierten Randbedingungen zur Validierung der Blasenkoaleszenz- und fragmentationsmodelle im CFD-Code erläutert.
Keywords: CFD, TOPFLOW, two-phase flow, steam-water flow, wire-mesh sensor, ultra-fast X-ray tomograph, vertical test section, stratified flow, condensation, evaporation
  • Lecture (Conference)
    CFD im Containment / CFD für Zweiphasenströmungen (Meilstein-Workshop Sommer 2008), 16.07.2008, Stuttgart, Deutschland

Publ.-Id: 11495 - Permalink


Anisotropic scaling of ion-induced ripple morphologies on Si
Keller, A.; Facsko, S.; Möller, W.; Peverini, L.; Kozhevnikov, I. V.;
It is well known that oblique low and medium energy (typically 0.1 - 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. The ripples produced in this way are oriented either parallel or normal to the projection of the ion beam and their wavelength scales with ion energy. These structures were found on a large variety of materials, such as semiconductors, metals, and insulating surfaces [1].

The formation of the ripple patterns can be qualitatively explained by continuum models like the Bradley-Harper model [2] which attributes the formation of regular patterns as resulting from the interplay between roughening due to sputter erosion and smoothing by surface diffusion. A surface instability is induced by the curvature dependence of the sputter yield, as the local erosion rate is higher in depressions than on elevations. This leads to an amplification of initial surface modulations and, therefore, to roughening of the surface. The resulting linear continuum equation is able to reproduce the formation and early evolution of the ripple patterns [2]. However, at longer times nonlinear terms have to be taken into account, leading to nonlinear models based on the Kuramoto-Sivashinsky equation [3].

In this work, Grazing Incidence Small Angle X-ray Scattering (GISAXS) has been used to study the evolution of Si(100) surfaces in-situ during oblique sub-keV ion sputtering. The sputtering has been performed with 500 eV Ar ions at incident angles ranging from 65° to 70°. The observed surface morphologies are dominated by nanoscale ripple patterns at short lateral distances but exhibit kinetic roughening at larger scales. The dynamic scaling properties of the surfaces have been analyzed by evaluating the one-dimensional power spectral density (PSD) functions in the direction normal and parallel to the ripples, respectively, which are extracted from the recorded scattering diagrams. A transition from anisotropic to isotropic scaling is observed with increasing incident angle. In addition, the ripples exhibit wavelength coarsening which is only slightly affected by the angle of incidence.


REFERENCES

[1] Chan, W.L. and Chason, E. Making waves: Kinetic processes controlling surface evolution during low energy ion sputtering, J. Appl. Phys. 101, 121301 (2007).
[2] Bradley, R.M. and Harper, J.M.E. Theory of ripple topography induced by ion bombardment, J. Vac. Sci. Technol. A 5, 2390 (1988).
[3] Makeev, M.A., Cuerno, R. and Barabási, A.-L. Morphology of ion-sputtered surfaces, Nucl. Inst. Meth. Phys. Res. B 197, 185 (2002).
  • Lecture (Conference)
    NanoSteps - Self-organized nanostructures on crystal surfaces, 30.06.-12.07.2008, Cargèse, France

Publ.-Id: 11494 - Permalink


Simulation von Experimenten am Heißstrangmodell der TOPFLOW-Anlage
Höhne, T.;
Stratified two-phase flow regimes can occur
-in the main cooling lines of Pressurized Water Reactors (PWR)
-Chemical plants
-Oil pipelines
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 the system due to the strong oscillating pressure levels formed behind the liquid slugs as well as the mechanical momentum of the slugs.
State of the art:
1D system codes validated, but:
geometry and scale dependent
no access to local parameters

CFD codes for application in multiphase flows:
the investigation of the feasibility of numerical prediction of stratified two phase flow with existing multiphase flow models in ANSYS CFX
to prove the understanding of the general fluid dynamic mechanism
to identify the critical parameters (like e.g. slug length, frequency and propagation velocity, pressure drop, CCFL)
to improve the multiphase flow modeling (interfacial momentum transfer, turbulence at the free surface et.)
experimental data required for the validation
Keywords: hot leg, CFD, stratified flow
  • Invited lecture (Conferences)
    Workshop Strömungssimulation, 25.09.2008, Dresden-Rossendorf, Germany

Publ.-Id: 11493 - Permalink


Electron Beam Diagnostics for a Superconducting Radio Frequency Photoelectron Injector
Kamps, T.; Boehlick, D.; Dirsat, M.; Lipka, D.; Quast, T.; Rudolph, J.; Schenk, M.; Arnold, A.; Staufenbiel, F.; Teichert, J.; Will, I.; Klemz, G.;
A superconducting radio frequency photo-electron injector (SRF injector)is currently under construction by a collaboration of BESSY, DESY, FZD and MBI. The project aims at the design and setup of a continuous-wave SRF injector including a diagnostics beamline for the ELBE FEL and to address R&D issues on low emittance injectors for future light sources such as the BESSY FEL. Of critical importance for the injector performance is the control of the electron beam parameters. For this reason a compact diagnostics beamline is under development serving a multitude of operation settings. In this paper the layout and the rationale of the diagnostics beamline is described. Furthermore detailed information on specific components is given, together with results from laboratory tests and data taking.
  • Review of Scientific Instruments 79(2008), 093301

Publ.-Id: 11492 - Permalink


Rückgewinnung von Neptunium aus Probelösungen zur radioökologischen Forschung
Knobel, M.; Wagner, M.;
Beitrag zum 10. Sächsischen Landeswettbewerb zur Umsetzung der Agenda21 in der beruflichen Ausbildung, 2007/2008

Das Ziel dieser Arbeit besteht in der Auswahl geeigneter Trennverfahren, Abtrennung und Rückgewinnung des Neptuniums aus einer Vielzahl verschiedener nicht charakterisierbarer Lösungen und Feststoffe unter Beachtung strahlenschutz-technischer Aspekte, der Charakterisierung der zurückgewonnenen Neptuniumlösung sowie der Erstellung einer Vorschrift für die Rückgewinnung.
  • Other report
    Dresden: FZD, 2008
    28 Seiten
  • Poster
    10. Sächsischer Landeswettbewerb zur Umsetzung der Agenda 21 in der beruflichen Ausbildung 2007/2008, 07.07.2008, Dresden, Deutschland

Publ.-Id: 11491 - Permalink


Uranium(VI) Uptake by Calcium Silicate Hydrates
Tits, J.; Macé, N.; Eilzer, M.; Geipel, G.; Wieland, E.;
Batch sorption studies show strong retention of U(VI) by C-S-H phases
U(VI) retention by C-S-H phases may be controlled by the formation of a Ca-U(VI) solid-solution
TRLFS studies indicate the presence of sorbed U(VI) species in an uranate-like coordination environment at high loadings and sorbed U(VI) species in an Ca-UO2-silicate-like coordination environment at low loadings.
  • Poster
    Goldschmidt 2008, 13.-18.07.2008, Vancouver, Canada
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 72(2008)12, A948

Publ.-Id: 11490 - Permalink


Commissioning of the Diagnostics Beamline for the SRF Photoinjector Project at Rossendorf
Kamps, T.; Böhlick, D.; Dirsat, M.; Quast, T.; Rudolph, J.; Schenk, M.; Arnold, A.; Michel, P.; Staufenbiel, F.; Teichert, J.; Will, I.;
A superconducting radio frequency photo electron injector (SRF injector) has been developed by a collaboration of BESSY, DESY, FZD and MBI and is in operation since late 2007. After the initial commissioning in late 2007 with a Copper photocathode a Caesium-Telluride cathode was installed early 2008 to allow for high charge production. The longitudinal and transverse electron beam parameters are measured in a compact diagnostics beamline. This paper describes results from beam commissioning of the main diagnostic tools. Special emphasis is given on the bunch length measurement system for the 15 ps FWHM electron bunches. The system is based on the conversion of the electron pulses into radiation pulses by Cherenkov radiation. These radiation pulses are transported in a novel fully-reflective, relay imaging optical beamline to a streak camera, where the temporal properties of the pulses are measured. Results from beam measurements at 2pC (Copper cathode) and 1nC (Cesium-Telluride cathode) bunch charge are presented and discussed.
  • Poster
    11th biennial European Particle Accelerator Conference, EPAC'08, 23.-27.06.2008, Genoa, Italy
  • Contribution to proceedings
    11th biennial European Particle Accelerator Conference, EPAC'08, 23.-27.06.2008, Genoa, Italy
    Proceedings of the EPAC'08, 1158

Publ.-Id: 11489 - Permalink


First Operation Results of the Superconducting Photoinjector at ELBE
Teichert, J.; Arnold, A.; Buechner, A.; Buettig, H.; Janssen, D.; Lehnert, U.; Michel, P.; Murcek, P.; Schurig, R.; Staats, G.; Staufenbiel, F.; Xiang, R.; Kamps, T.; Matheisen, A.; Klemz, G.; Will, I.;
In November 2007 the first electron beam was generated from the superconducting RF photo electron gun installed at the ELBE linear accelerator facility. The injector together with a sophisticated laser system and a diagnostic beam line were developed and constructed within a collaboration of BESSY, DESY, MBI and FZD. Delivering a CW beam with up to 1 mA average current, a significant improvement of the beam quality like an increase of the bunch charge up to 1 nC and a reduced transverse emittance will be obtained. After the cool-down of the cryostat the RF properties of the 3½-cell niobium cavity like pass band mode frequencies, unloaded quality factor versus accelerating gradient, Lorentz force detuning, and He pressure influence were measured. The first beam was extracted of a Cu photo cathode using a 262 nm UV laser system with a repetition rate of 100 kHz and about 0.4 W laser power. Later, caesium telluride photo cathodes will be applied. The installed diagnostics allow beam current, energy, energy spread, transverse emittance and bunch length measurements of the beam. The results of these measurements and the operational experiences with the gun will be presented.
  • Poster
    11th biennial European Particle Accelerator Conference, EPAC'08, 23.-27.06.2008, Genoa, Italy

Publ.-Id: 11488 - Permalink


Nano-structures for sensors on SOI by writing FIB implantation and subsequent anisotropic wet chemical etching
Bischoff, L.; Schmidt, B.; Lange, H.; Donzev, D.;
Nanowires, nanocantilevers and nanobridges will be important components for future micro- and nanoelectronic devices as well as for nano-electro-mechanical systems (NEMS).
A modern technique to fabricate three-dimensional (3D) nanostructures is the combination of high-concentration p-type doping of silicon by writing implantation using a focused ion beam (FIB) with subsequent wet chemical anisotropic and selective etching. Free-standing FIB-patterned and chemically etched 3D Si structures with nanoscale thickness and width have been fabricated on 4 inch Silicon-On-Insulator (SOI) substrates using 30 keV Ga+ ion implantation and subsequent anisotropic etching in KOH/H2O solution. This technology is combined with classical microelectronic processing steps of photolithographic patterning and broad beam ion implantation to position and integrate 3D nanostructures into current technological platforms and therefore to increase the fabrication efficiency. Design, performance and fabrication considerations to achieve free-standing Si structures, like wires, bridges and cantilevers are discussed and some typical examples are shown. Static and dynamic electrical measurements are presented, including I-V characteristics and displacements after AC excitation.
The temperature dependence of the electrical resistance of nanostructures is demonstrated, which reveal, for example, the applications as nanowire thermal sensors.
Keywords: Nanostructures, FIB, anisotropic wet chemical etching; 3D-nanostructures; sensor; displacement
  • Lecture (Conference)
    16th International Conference on Ion Beam Modification of Materials (IBMM 08), 30.08.-05.09.2008, Dresden, Deutschland
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1372-1375

Publ.-Id: 11487 - Permalink


Nachrechnung eines Vollhub-Feder-Sicherheitsventils mit ANSYS CFX
Höhne, T.; Moncalvo, D.; Friedel, L.; Jörgensen, B.;
Sicherheitsventile schützen druckbeaufschlagte Räume oder Druckbehälter (z. B. Dampfkessel, Druckbehälter, Rohrleitungen, Transportbehälter) vor einem unzulässigen 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 verwendet, wenn der Druck in einem Druckbehälter den zulässigen Betriebsdruck bei vorhersehbaren Störungen um mehr als 10 % übersteigen kann. Bei richtiger Dimensionierung 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 bei Auslegungsberechnungen, Optimierungen und Sicherheitsanalysen von Sicherheitsventilen helfen. Um Leistungsparameter zu studieren, wurden Experi-mente am Institut für Strömungsmechanik der Technischen Universität Hamburg-Harburg (TUHH) für die CFD-Code-Validierung genutzt. Durch die konstante Weiterentwicklung der Numerik bzw. der physikalischen Modelle ist es nun möglich, die relativ komplexen Strömungsvorgänge in einem Sicherheitsventil (Jets, Umströmung von Hindernissen, Strömungsseparation, Stagnationsgebiete, Zonen mit hohen Ma-Zahlen) zu simulieren.
Mit dem ANSYS CFX-Code erfolgten Nachrechnungen von Durchsatzparametern eines LESER-Sicherheitsventils auf einem numerischen Gitter von einer Million Hexaederzellen (Abb. 1). Am Ein- bzw. Austritt des Strömungsgebietes wurden Druckrandbedingungen definiert. Die Turbulenzmodellierung erfolgte unter Nutzung des k-ε und k-ω basierten SST-Modellansatzes. Eine sehr gute Übereinstimmung zwischen Messung und CFD-Rechnung ist für die Durchsatzkennlinien der Charakteristiken für die Medien Luft bzw. Wasser bis 5 bar Stagnationsdruck erreicht worden, es existierte jedoch eine systematische Abweichung bei Luft im Falle hoher Ansprechdrücke (über 20 bar) durch Realgasverhalten und das Auftreten hoher Ma-Zahlen. CFD-Rechnungen mit Luft/Wasser-Zweiphasengemischen bei 5 - 9 bar Überdruck und 79 - 93 % Gasanteil ergaben realistische Durchsatzraten. Hierbei wurde das monodisperse Modell des homogenen Euler-Euler-Ansatzes für Zweiphasengemische genutzt. Weitere numerische Untersuchungen, insbesondere das Verhalten von 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
  • Contribution to proceedings
    9. Fachtagung "Anlagen-, Arbeits- und Umweltsicherheit", 06.-07.11.2008, Köthen, Deutschland
  • Lecture (Conference)
    9. Fachtagung "Anlagen-, Arbeits- und Umweltsicherheit", 06.-07.11.2008, Köthen, Deutschland
  • Forschung im Ingenieurwesen - Engineering Research 73(2009)2, 99-103
    DOI: DOI: 10.1007/s10010-009-0096-1

Publ.-Id: 11486 - Permalink


Quercetin and other flavonoids bind to actin and affect its biological activity
Gutzeit, H.-O.; Boehl, M.; Pfennig, F.; Richter, S.; Tietze, S.; Sokoll, A.; Madathil, S.; Fahmy, K.; Apostolakis, J.;
In a screen for flavonoid target proteins we identified actin as a quercetin-binding protein. This interaction was studied using fluorescence and infrared spectroscopy and compared with the binding parameters of related flavonoids. The biological relevance of the flavonoid/actin interaction in the cytoplasm and the nucleus was assayed using an actin polymerization and a transcription assay, respectively. While some flavonols inhibit actin functions, the structurally related epigallocatechin tends to promote actin functions in the chosen in vitro assays. Furthermore, cellular test systems were used to evaluate the biological consequences of the flavonoid/actin interaction. The flavonoid – induced conformational changes of actin were analyzed by infrared spectroscopy. The obtained data and in silico docking studies gave further insights into possible modes of protein-ligand interactions and helped to understand the molecular basis of the observed biological effects.
Keywords: flavonoids, FTIR-spectroscopy, docking
  • Contribution to proceedings
    32nd FEBS Congress, 07.-12.07.2007, Vienna, Austria
    Abstracts of the 32nd FEBS Congress, England: Wiley-Blackwell, 236-236

Publ.-Id: 11485 - Permalink


CFD validation against slug mixing experiment
Moretti, F.; Melideo, D.; Del Nevo, A.; D’Auria, F.; Höhne, T.; Lisenkov, E.;
A commercial CFD code was applied, for validation purposes, to the simulation of a slug mixing experiment carried out at OKB “Gidropress” scaled facility in the framework of a TACIS project: “Development of safety analysis capabilities for VVER-1000 transients involving spatial variations of coolant properties (temperature or boron concentration) at core inlet”. Such experimental model reproduces a VVER-1000 nuclear reactor and is aimed at investigating the in-vessel mixing phenomena. The addressed experiment involves the start-up of one of the four reactor coolant pumps (the other three remaining idle), and the presence of a tracer slug on the starting loop, which is thus transported to the reactor pressure vessel where it mixes with the clear water. Such conditions may occur in a boron dilution scenario, hence the relevance of the addressed phenomena for the nuclear reactor safety.
Both a pre-test and a post-test CFD simulation of the mentioned experiment were performed, which differ in the definition of the boundary conditions (based either on nominal quantities or on measured quantities, respectively). The numerical results are qualitatively and quantitatively analyzed and compared against the measured data in terms of space and time tracer distribution at the core inlet. The improvement of the results due to the optimization of the boundary conditions is evidenced, and a quantification of the simulation accuracy is proposed.
Keywords: CFD, Validation, Slug, Mixing, Experiment

Publ.-Id: 11483 - Permalink


Deep level defects in a nitrogen-implanted ZnO homogeneous p-n junction
Gu, Q.; Ling, C.; Brauer, G.; Anwand, W.; Skorupa, W.; Hsu, Y.; Djurisic, A.; Zhu, C.; Fung, S.; Lu, L.;
Nitrogen ions were implanted into undoped melt grown ZnO single crystals. A light-emitting p-n junction was subsequently formed by postimplantation annealing in air. Deep level transient spectroscopy was used to investigate deep level defects induced by N+ implantation and the effect of air annealing. The N+ implantation enhanced the electron trap at E-C-(0.31 +/- 0.01) eV (E3) and introduced another one at E-C-(0.95 +/- 0.02) eV (D1), which were removed after annealing at 900 and 750 degrees C, respectively. Another trap D2 (E-a = 0.17 +/- 0.01 eV) was formed after the 750 degrees C annealing and persisted at 1200 degrees C.
  • Applied Physics Letters 92(2008)22, 222109

Publ.-Id: 11482 - Permalink


CFD post test calculation of pressurized air / water TOPFLOW hotleg experiments
Höhne, T.; Vallée, C.; Beyer, M.;
Stratified two-phase flow regimes can occur
-in the main cooling lines of Pressurized Water Reactors (PWR)
-Chemical plants
-Oil pipelines
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 the system due to the strong oscillating pressure levels formed behind the liquid slugs as well as the mechanical momentum of the slugs.
State of the art:
1D system codes validated, but:
geometry and scale dependant
no access to local parameters

CFD codes for application in multiphase flows:
the investigation of the feasibility of numerical prediction of stratified two phase flow with existing multiphase flow models in ANSYS CFX
to prove the understanding of the general fluid dynamic mechanism
to identify the critical parameters (like e.g. slug length, frequency and propagation velocity, pressure drop, CCFL)
to improve the multiphase flow modeling (interfacial momentum transfer, turbulence at the free surface et.)
experimental data required for the validation
Keywords: slug flow, Hot leg, CFD, stratified flow
  • Lecture (Conference)
    6th Workshop Multiphase Flows Simulation, Experiment and Application, 24.-26.06.2008, Dresden, Deutschland

Publ.-Id: 11481 - Permalink


Dielectron Production in 12C + 12C Collisions at 1 GeV/u and the Solution to the DLS Puzzle
Pachmayer, Y. C.; Dohrmann, F.; Grosse, E.; Kanaki, K.; Kaempfer, B.; Kotte, R.; Naumann, L.; Sadovsky, A.; Wüstenfeld, J.; Zhou, P.; Hades Collaboration;
The production of e+e− pairs in 12C + 12C collisions at 1 GeV/u was investigated with the HADES experiment at GSI, Darmstadt. In the invariant-mass region 0.15GeV/c2 Mee 0.5GeV/c2 the measured pair yield shows a strong excess above the contribution expected from hadron decays after freeze-out. The data are in good agreement with the results of the former DLS experiment for the same system and energy.

Publ.-Id: 11480 - Permalink


Chapter 7 - Growth Mechanisms and Structure of Fullerene-like Carbon-based Thin Films: Superelastic Materials for Tribological Applications, in Fullerene Research Advances
Gago, R.; Abrasonis, G.; Jimenez, I.; Möller, W.;
In this chapter we review our findings on the bonding structure and growth mechanisms of carbon-based thin solid films with fullerene-like (FL) microstructure. The so-called FL arrangements arise from the curvature and cross-linking of basal planes in graphitic-like structures, partially resembling that of molecular fullerenes. This three-dimensional superstructure takes advantage of the strength of planar pi bonds in sp2 hybrids and confers the material interesting mechanical properties, such as high hardness, high elastic recovery, low-friction and wear-resistance. These properties can be tailored by controlling the curvature, size and connectivity of the FL arrangements, making these materials promising coatings for tribological applications. We have focused our interest mostly on carbon nitride (CNx) since nitrogen promotes the formation of FL arrangements at low substrate temperatures and they are emerging over pure carbon coatings in tribological applications such as protective overcoats in magnetic hard disks. We address structural issues such as origin of plane curvature, nature of the cross-linking sites and sp2 clustering, together with growth mechanisms based on the role of film-forming precursors, chemical re-sputtering or concurrent ion assistance during growth.
  • Contribution to external collection
    Carl N. Kramer: Fullerene Research Advances, New York, USA: Nova Science Publishers, 2007, 1-60021-824-5, 145-181

Publ.-Id: 11479 - Permalink


Origin of ferromagnetism in iron implanted rutile single crystals
Talut, G.; Reuther, H.; Grenzer, J.; Zhou, S.;
57Fe doped titanium oxide monocrystals, prepared by ion implantation at different temperatures and subsequent thermal treatment, were characterized by conversion electron Mössbauer spectroscopy, synchrotron radiation x-ray diffraction and superconducting quantum interference device magnetometry. After implantation at 240 K and room temperature Fe is present in divalent state. Upon annealing in high vacuum Fe2+ is reduced to metallic Fe, while during annealing on air Fe2+ is oxidized to Fe3+. After implantation at 623 K most iron is in metallic state. During annealing on air Fe is gradually oxidized from Fe2+ to Fe3+.
Depending on preparation conditions and thermal treatment the role of different nanosized secondary phases is discussed in terms of their influence on the magnetic properties of Fe:TiO2. α-Fe nanoparticles are found to be responsible for ferromagnetism observed in TiO2.
Keywords: conversion electron Mössbauer cpectroscopy (CEMS), diluted magnetic semiconductor (DMS), Fe doping of Ti oxide, ion beam implantation
  • Contribution to proceedings
    International Symposium on the Industrial Applications of the Mössbauer Effect, 17.-22.08.2008, Budapest, Hungary
    Hyperfine Interactions: Springer
  • Poster
    International Symposium on the Industrial Applications of the Mössbauer Effect, 17.-22.08.2008, Budapest, Hungary

Publ.-Id: 11478 - Permalink


Digitale Signalverarbeitung von Bariumfluorid- und Germaniumdetektorsignalen am nELBE-Experiment
Hannaske, R.; Beyer, R.; Dammrau, A.; Grosse, E.; Junghans, A.; Wagner, A.;
Am supraleitenden Elektronen-Linearbeschleuniger ELBE des Forschungszentrums Dresden-Rossendorf induzieren Elektronen in einem Radiator aus flüssigem Blei (γ,n)-Reaktionen und erzeugen Neutronen mit Energien von 50 keV bis 10 MeV [1,2] zur Messung Neutronen-induzierter Reaktionen mit einer Energieauflösung von besser als 1 % (bei 1 MeV) [3]. Die Bestimmung der Wirkungsquerschnitte von (n,γ)- oder (n,n'γ)-Reaktionen dient hierbei der Transmutationsforschung, der nuklearen Astrophysik sowie Anwendungen für Fusions- und Spaltreaktoren. Zum Nachweis der Photonen aus Neutronen-induzierten Reaktionen ist das Target von 42 Bariumfluorid-Szintillationsdetektoren umgeben, die 80 % des gesamten Raumwinkels abdecken.
Ein Hochgeschwindigkeitsabtastsystem (2 GS/s, 10 bit Auflösung) wurde in Betrieb genommen und bezüglich Energie- und Zeitauflösung charakterisiert. Erste Resultate zur digitalen Pulsformanalyse werden vorgestellt.
[1] E.Altstadt, et al., Ann. Nucl. Energy 34, 36 (2007)
[2] J.Klug, et al., Nucl. Instr. Meth. A 577, 641 (2007)
[3] R.Beyer, et al., Nucl. Instr. Meth. A 575, 449 (2007)
* gefördert durch EU-FP6 / EFNUDAT
  • Lecture (Conference)
    DPG-Frühjahrstagung, 14.03.2008, Darmstadt, Deutschland

Publ.-Id: 11477 - Permalink


Sächsische Forschung im Herzen Europas: Zu Ursprüngen und Befindlichkeiten
Skorupa, W.;
Es werden Ausführungen zur aktuellen Forschungslandschaft in Sachsen mit Ausrichtung auf Aktivitäten am Forschungszentrum Dresden-Rossendorf gemacht.
  • Invited lecture (Conferences)
    Treffen des Bundesausschusses der FDP zu Fragen der Technologie, 05.07.2008, Dresden, Deutschland

Publ.-Id: 11476 - Permalink


Enhanced Hot Electron Localization and Heating in High-Contrast Ultra-Intense Laser Irradiation of Sharp Micro-Cone Targets
Rassuchine, J.; D’Humières, E.; Baton, S. D.; Guillou, P.; Koenig, M.; Fuchs, J.; Audebert, P.; Kodama, R.; Nakatsutsumi, M.; Ozaki, N.; Batani, D.; Morace, A.; Redaelli, R.; Gremillet, L.; Rousseaux, C.; Dorchies, F.; Fourment, C.; Santos, J. J.; Adams, J.; Korgan, G.; Malekos, S.; Hansen, S. B.; Shepherd, R.; Flippo, K.; Gaillard, S.; Sentoku, Y.; Cowan, T. E.;
We report experiments demonstrating enhanced coupling efficiencies employing high contrast laser irradiation of nano-fabricated conical targets. Peak temperatures near 200 eV are observed with modest laser energy (10 J), revealing similarities in hot electron localization and material heating to reduced mass targets. Collisional particle-in-cell simulations attribute this enhancement to self-generated resistive magnetic fields forming within the cone wall, which effectively confine the energetic electrons to heat a reduced volume at the cone tip.
  • Physical Review E 79(2009)3, 036408

Publ.-Id: 11475 - Permalink


Electrons in Strong Laser Fields: Compton Backscattering
Seipt, D.;
  • Invited lecture (Conferences)
    Ultra High-Intensity Laser Nuclear/Particle Physics, 23.-27.06.2008, Trento, Italy

Publ.-Id: 11474 - Permalink


Non-linear theory of deformable superconductors
Lipavský, P.; Morawetz, K.; Kolácek, J.; Brandt, E. H.;
The interaction of the superconducting condensate with deformations of the crystal lattice is formulated assuming the electrostatic potential to be of Bernoulli type and the effect of strain on material parameters. In the isotropic approximation it is shown that within the Ginzburg-Landau theory both contributions can be recast into the local but non-linear interaction term of the free energy.
Keywords: 74.20.De, % Phenomenological theories (two-fluid, % Ginzburg-Landau, etc.) 74.25.Ld, % Mechanical and acoustical properties, elasticity, % and ultrasonic attenuation %74.25.Qt, % Vortex lattices, flux pinning, flux creep 74.81.-g% Inhomogeneous superconductors % and superconducting systems
  • Physical Review B 78(2008), 174516-1-174516-7

Publ.-Id: 11472 - Permalink


Generation of Stable, Low-Divergence Electron Beams by Laser Wakefield Acceleration in a Steady-State-Flow Gas Cell
Osterhoff, J.; Popp, A.; Major, Z.; Marx, B.; Rowlands-Rees, T. P.; Fuchs, M.; Geissler, M.; Hörlein, R.; Hidding, B.; Becker, S.; Peralta, E. A.; Schramm, U.; Grüner, F.; Habs, D.; Krausz, F.; Hooker, S. M.; Karsch, S.;
Laser-driven, quasi-monoenergetic electron beams of up to ~200 MeV in energy have been observed from steady-state-flow gas cells. These beams emitted within a low-divergence cone of 2.1± 0.5 mrad FWHM display unprecedented shot-to-shot stability in energy (2.5% RMS), pointing (1.4 mrad RMS) and charge (16% RMS) owing to a highly reproducible gas-density profile within the interaction volume. Laser-wakefield acceleration in gas cells of this type provides a simple and reliable source of relativistic electrons potentially suitable for applications such as the production of XUV-undulator radiation.
Keywords: Stable electron acceleration in gas cells, relativistic laser plasma PACS numbers: 52.38.Kd, 52.38.Hb, 41.75.Jv

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Publ.-Id: 11471 - Permalink


Results of a modified PROMISE experiment
Stefani, F.; Gerbeth, G.; Gundrum, T.; Hollerbach, R.; Rüdiger, G.; Szklarski, J.;
The PROMISE experiment relies on the fact that the critical Reynolds number for the appearance of the magnetorotational instability (MRI) in liquid metal flows drastically decreases when the purely axial magnetic field is replaced by a helical one. We report the results of a modified version of this experiments in which the radial electrical boundary conditions are changed. Special focus is laid on the role of the radial jet region where the two Ekman vortices from the top and the bottom meet each other.
  • Astronomische Nachrichten 329(2008)7, 652-658

Publ.-Id: 11470 - Permalink


Magnetohydrodynamic experiments on cosmic magnetic fields
Stefani, F.; Gailitis, A.; Gerbeth, G.;
It is widely 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 both effects in liquid metal experiments. In 1999, magnetic field self-excitation was observed in the large scale liquid sodium facilities in Riga and Karlsruhe. Recently, self-excitation was also obtained in the French "von Karmann sodium" (VKS) experiment. An MRI-like mode was found on the background of a turbulent spherical Couette flow at the University of Maryland. Evidence for MRI as the first instability of an hydrodynamically stable flow was obtained in the "Potsdam Rossendorf Magnetic Instability Experiment" (PROMISE). In this review, the history of dynamo and MRI related experiments is delineated, and some directions of future work are discussed.
  • Zeitschrift für Angewandte Mathematik und Mechanik 88(2008)12, 930-954

Publ.-Id: 11469 - Permalink


History and results of the Riga dynamo experiments
Gailitis, A.; Gerbeth, G.; Gundrum, T.; Lielausis, O.; Platacis, E.; Stefani, F.;
On 11 November 1999, a self-exciting magnetic eigenfield was detected for the first time in the Riga liquid sodium dynamo experiment. We report on the long history leading to this event, and on the subsequent experimental campaigns which provided a wealth of data on the kinematic and the saturated regime of this dynamo. The present state of the theoretical understanding of both regimes is delineated, and some comparisons with other laboratory dynamo experiments are made.
  • Comptes Rendus Physique 9(2008), 721-728

Publ.-Id: 11468 - Permalink


Führungsverhalten als Einflussfaktor auf Qualität und Effektivität in kleinen und mittleren Unternehmen in Deutschland und in der Slowakei
Kozikova, O.;
Das Hauptthema der vorgelegten Dissertation betrifft das Führungsverhalten als Einflussfaktor auf Qualität und Effektivität in kleinen und mittleren Unternehmen, die im Rahmen der Untersuchung zufällig in Deutschland und in der Slowakei angesprochen wurden. In diesem Zusammenhang wurde die Führungssituation zwischen beiden Ländern verglichen. Obwohl der Titel der Arbeit nur kleine und mittlere Unternehmen behandelt, wurde die Führungssituation auch in einigen großen Unternehmen, Forschungszentren und Einrichtungen der Staatsverwaltung bzw. im öffentlichen Dienst untersucht, um die Richtung der Führung auch in diesen Organisationen festzustellen und diese Tendenz mit der in kleinen und mittleren Unternehmen zu vergleichen. Die vorgelegte Dissertation mit 29 Abbildungen, 79 Diagrammen und 15 Tabellen konzentriert sich im Wesentlichen auf zwei Hauptteile – Theorie und Praxis. Neben dem Inhaltsverzeichnis befinden sich Verzeichnisse aller Abbildungen, Diagrammen und Tabellen sowie alle in der Arbeit verwendeten Abkürzungen vor der Theorie. Der theoretische Teil umfasst die ersten vier Kapitel. In der Einführung wird eine kurze Übersicht über die Dissertation mit ihren einzelnen Kapiteln gegeben. Im zweiten Kapitel wird die Recherche über die Ergebnisse einiger Studien bzw. Dissertationen dargestellt, um auf die Bedeutung des Themas, mit der sich diese Dissertation beschäftigt, hinzuweisen. Das Ziel der Dissertation und die Methode zur Aufbereitung des praktischen Teils werden im dritten Kapitel beschrieben. Bestandteil dieses Kapitels ist zugleich die Beschreibung der Befragung mittels Fragebogen, durch die die Untersuchung durchgeführt wurde. Vorliegende theoretische Kenntnisse aus der Literatur werden im vierten Kapitel dargestellt. Der praktische Teil der vorgelegten Dissertation beginnt mit dem fünften Kapitel. Hier wird die Bearbeitung der entwickelten Fragebogen beschrieben und die daraus abgeleiteten Ergebnisse dargestellt. Die Auswertung aller erhobenen Daten, deren Darstellung in grafischer Form sowie deren Interpretationen sind Inhalt des sechsten Kapitels. Der Vergleich der Situation in Deutschland und der Slowakei erfolgt im siebten Kapitel. Der praktische Teil wird durch die Zusammenfassung und den Ausblick im achten Kapitel abgeschlossen. Anschließend an den Untersuchungsteil ist das Verzeichnis aller verwendeten Literaturquellen angegeben. Zur Dissertationsarbeit gehört auch der Anhang (233 S.), der wegen seines großen Umfanges (1194 S.) nur einen kleinen Teil des Verfahrens, durch das die ganze Dissertationsarbeit bearbeitet wurde, darstellt.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    Dissertationsarbeit, Fakultät für Werkstoffe und Technologien Trnava
    223 Seiten

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Publ.-Id: 11467 - Permalink


Pygmy dipole strength in 90Zr
Schwengner, R.; Rusev, G.; Tsoneva, N.; Benouaret, N.; Beyer, R.; Erhard, M.; Grosse, E.; Junghans, A. R.; Klug, J.; Kosev, K.; Lenske, H.; Nair, C.; Schilling, K. D.; Wagner, A.;
The dipole response of the N=50 nucleus {90}Zr was studied in photon-scattering experiments at the electron linear accelerator ELBE with bremsstrahlung produced at kinetic electron energies of 7.9, 9.0, and 13.2 MeV.
We identified 190 levels up to an excitation energy of 12.9 MeV. Statistical methods were applied in order to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. In this way we derived the photoabsorption cross section up to the neutron-separation energy. This cross section matches well the photoabsorption cross section obtained from (\gamma,n) data and thus provides information about the extension of the dipole-strength distribution towards energies below the neutron-separation energy. An enhancement of E1 strength has been found in the range of 6 MeV to 11 MeV. Calculations within the framework of the Quasi-Particle-Phonon Model ascribe this strength to a vibration of the excessive neutrons against the N = Z neutron-proton core, giving rise to a pygmy dipole resonance.
Keywords: Nuclear Structure, statistical nuclear physics, photon scattering, QRPA, QPM

Publ.-Id: 11466 - Permalink


Thomson scattering at the ELBE linac - status and perspectives
Schramm, U.;
Invited talk on the status of the Thomson scattering experiment at ELBE
Keywords: Thomsons scattering, ELBE
  • Invited lecture (Conferences)
    ECT* Workshop on Ultra High-Intensity Laser Nuclear and Particle Physics, 23.-27.6.2008, Trento, Italy

Publ.-Id: 11465 - Permalink


Few-Cycle-Laser-Driven Electron Acceleration
Schmid, K.; Veisz, L.; Tavella, F.; Benavides, S.; Tautz, R.; Herrmann, D.; Buck, A.; Hidding, B.; Marcinkevicius, A.; Schramm, U.; Geissler, M.; Meyer-Ter-Vehn, J.; Habs, D.; Krausz, F.;
Laser-driven plasma waves were proposed as compact electron accelerators [1] owing to their ability to produce longitudinal accelerating ¯elds several orders of magnitude higher than those attainable in conventional accelerators. A promising implementation relies on "broken" plasma waves driven by a laser pulse shorter than half the plasma period [2]. In the absence of intense laser pulses of the required duration, previous experiments [3] - [13] drew on longer (several-10-fs) driver pulses. Under these circumstances, monoenergetic electron acceleration is preceded by a nonlinear interaction of the laser pulse with the relativistic plasma [14], which shortens its duration into the required domain. Longer-than-optimal driver pulses compromise e±ciency as well as reproducibility, and result in copious amounts of low-energy electrons accompanying the monoenergetic emission with an exponentially-decaying spectrum, forming a "thermal" background.
Here, we report the first electron accelerator based on high-density plasma waves driven with laser pulses ¯tting in one half of the plasma period. Direct excitation of a broken plasma wave permits monoenergetic electron acceleration virtually free of thermal background for the first time. In our experiments, 5-terawatt, 8-femtosecond laser pulses yield electron bunches up to energies of 25 MeV.
The dramatically reduced °ux of low-energy electrons as compared to earlier experiments also manifests itself in a strongly-reduced secondary radiation emerging from the accelerator and o®ers the potential for enhancing e±ciency and stability with more intense driver pulses.
Keywords: Laser plasma electron acceleration, few cycle laser pulses, bubble regime

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Publ.-Id: 11464 - Permalink


Nanoskalige Biokompositmaterialien zur Eliminierung von Arzneimittelrückständen
Raff, J.; Pollmann, K.;
Bis zu 95 % der verabreichten Wirkstoffe von Arzneimitteln werden vom menschlichen Körper wieder ausgeschieden und gelangen über das Abwasser in den Wasserkreislauf. Für gewöhnlich sind die Wirkstoffkonzentrationen sehr gering und werden schnell abgebaut. In einzelnen Fällen handelt es sich jedoch um schwer abbaubare Verbindungen, die in größeren Mengen anfallen und bei denen bereits eine negative Langzeitwirkung umweltrelevanter Konzentrationen auf die Fischgesundheit nachgewiesen wurde. Ein Beispiel dafür ist der Wirkstoff Diclofenac. Derzeit ist kein kostengünstiges Verfahren verfügbar, mit dem derartige Stoffe aus dem Wasser entfernt werden können. Neuartige nanostrukturierte Biokompositmaterialien auf der Basis bakterieller Hüllproteinschichten, sogenannte S-Layer, können hier Abhilfe schaffen. Alle bakteriellen Hüllproteine besitzen die Fähigkeit, an Grenz- und Oberflächen monolagige hochgeordnete Schichten mit zum Teil hoher Stabilität auszubilden. Diese Eigenschaften in Kombination mit der hohen Metallbindungskapazität der Hüllproteine mancher Naturisolate ermöglicht die einfache Herstellung verschiedener dotierter und nicht dotierter Edelmetall- und Metalloxidnanocluster mit hoher katalytischer und fotokatalytischer Aktivität. Ziel ist die Herstellung fotokatalytisch aktiver Biokompositschichten, die bereits bei Tageslicht eine ausreichende hohe Aktivität besitzen, um die Spaltung organischer Reststoffe zu bewirken. Dieses Projekt wird vom Bundesministerium für Bildung und Forschung gefördert.
  • Poster
    Biotechnica 2008, 07.-09.10.2008, Hannover, Deutschland

Publ.-Id: 11463 - Permalink


Probing 3d-4f exchange interactions by high-field magnetization measurements
Skourski, Y.; Kuz’Min, M.; Müller, K.-H.; Wosnitza, J.;
In a 4f-3d ferrimagnet the molecular field (a net value expressing the relevant exchange interactions) can be determined from high-field magnetization measurements. If the field is high enough, it breaks the ferrimagnetic ground state and drives the system towards ferromagnetic order via non-collinear intermediate phases. Magnetization curves of Er2Fe17 singe crystal have been measured along the [100] and [001] crystallographic directions in magnetic fields up to 50 Tesla. An unfixed sample, free to rotate, was measured as well. The magnetization measured along the easy magnetization direction shows jumps at 37.5 and 44 Tesla. The first jump was used for the determination of the molecular field (66.4 Tesla). This agrees with the data for the unfixed sample where a kink in the magnetization at 33.5 Tesla yields a molecular field of 65.7 Tesla. The obtained values are in a good agreement with literature data.
  • Lecture (Conference)
    Physics of Magnetism ´08, 24.-27.06.2008, Poznan, Poland
  • Open Access LogoActa Physica Polonica A 115(2009), 178

Publ.-Id: 11462 - Permalink


Observation of dendritic growth and fragmentation in Ga-In alloys by X-ray radioscopy
Boden, S.; Willers, B.; Eckert, S.; Gerbeth, G.;
Capabilities of the X-ray attenuation contrast radioscopy were utilised to provide a real-time diagnostic technique for observations of dendritic growth and fragmentation during solidification of a Ga-30wt%In alloy. The solidification process was visualised by means of a microfocus X-ray tube providing shadow radiographs at spatial resolutions of about 10 µm. Experiments have been carried out to solidify the Ga-In alloy unidirectional either starting from the bottom or the top of the specimen. The first case is significantly affected by solutal convection, which governs a redistribution of solute concentration. A detachment of dendrite side arms, which is unambiguously caused by melt flow, was not observed. Dendritic fragmentation occurs during the solidification in the reverse top-down direction. Variations of the applied cooling rate excited a transition from a columnar to an equiaxed dendritic growth (CET).
Keywords: solidification, X-ray radioscopy, dendrite growth, dendrite fragmentation
  • International Journal of Cast Metals Research 22(2009), 30-33

Publ.-Id: 11461 - Permalink


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