Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32609 Publications
Untersuchungen mittels PET bei onkologischen Fragestellungen
van den Hoff, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Workshop: Einsatz der PET in der Bestahlungsplanung, 11.-12.03.2005, Homburg/Saar, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-8552
Publ.-Id: 8552


Annual Report 2005 - Institute of Nuclear and Hadron Physics
Enghardt, W.; Fahmy, K.; Grosse, E.; Kämpfer, B.; Schneidereit, C.; Wagner, A.; Wünsch, R.; (Editors)
Preface
The Forschungszentrum Rossendorf (FZR) at Dresden is a multidisciplinary research center within the Wissenschafts-Gemeinschaft G. W. Leibniz (WGL), one of the German agencies for extra-university research. The center is active in investigations on the structure of matter as well as in the life sciences and in environmental research. The Institute of Nuclear and Hadron Physics (IKH) within the FZR avails for its research the coupling of radiation to matter in subatomic dimensions as well as to tissue, to cells, and to their components. Its research in the field of Subatomic Physics is part of the FZR-program Structure of Matter and its investigations concerning the interaction of Biostructures and Radiation contribute to the bf Life Science program of the FZR. In this field the IKH exploits possibilities for transfer and introduction of experimental and theoretical techniques from particle and nuclear physics to projects in radiobiology and biophysics. Much of this kind of interdisciplinary transfer is connected to the Radiation Source ELBE at the FZR. With its superconducting accelerator for relativistic electrons this large installation provides photons in the wide wavelength range from fm to mm - i.e. bremsstrahlung for the investigation of photonuclear processes, hard X-rays for radiobiological and other studies and infrared light for research on the structural dynamics of biomolecules. The investigation of radiation-induced processes not only dominates the projects in nuclear astrophysics as pursued at ELBE, it also is a central theme of the experimental and theoretical research performed by the IKH in close connection to the heavy ion synchrotron SIS and the upcoming FAIR facility at Darmstadt. ELBE also will deliver compact bunches of secondary neutrons and fission fragments; both offer new possibilities in laboratory studies related to the cosmic breeding of the chemical elements thus complementing the astrophysics-motivated studies with bremsstrahlung photons...
  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-442 2006

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Permalink: https://www.hzdr.de/publications/Publ-8551
Publ.-Id: 8551


CFD simulations and X-ray measurements of the local gas hold-up in a stirred tank reactor agitated by a gas-inducing turbine
Hristov, H. V.; Boden, S.; Hampel, U.; Kryk, H.; Schmitt, W.; Hessel, G.;
The experimental and the numerically studies were applied to a non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine. The dispersion of air as gas phase into isopropanol as liquid phase at room temperature under different stirrer speeds was investigated. The X-Ray cone beam tomography measurements were taken at five different stirrer speeds with thresholds of 50 rpm starting from 1000 rpm at which the gas inducement occurs for the given operating conditions.
The cone-beam type X-Ray tomography is a potential method to measure the phase-distributions in stirred vessels. Three-dimensional information can be gathered within only one tomographic scan. The reconstruction of a rotationally symmetric distribution-field is even possible from a single radiographic image. Such an experimental approach was carefully examined and applied to obtain the quantitative measurements of gas-fraction profiles in a stirred tank reactor. Additionally, a moving slit technique was adapted to estimate the inherent scattered radiation offset, which emerges while un-collimated x-rays penetrate the fluid-filled tank. An additional reference measurement was introduced and used to remove beam hardening artefacts. An absolute quantification was possible due to the knowledge of the ratio of the fluids and the reference-materials x-ray absorption coefficients. Phantom-measurements inside the vessel were conducted for performance evaluation. A systematic measurement error of less then 1.5% absolute gas fraction for local gas fractions up to 30% was achieved while maintaining a spatial resolution of better then 1 mm.
The computational fluid dynamics analyses of the stirred tank reactor were performed in 3D with CFX 10.0 numerical software. Five steady state simulations, at stirrer speeds corresponding to the ones at which the measurements were performed, were conducted to be compared with the experimental observations. The tetrahedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer described by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid and the liquid phase as continuous fluid. Different turbulence models and their suitability were considered in the simulations.
  • Lecture (Conference)
    ANSYS-FZR Multiphase Flow: Simulation, Experiment and Application, 26.-29.06.2006, Dresden, Germany
  • Contribution to proceedings
    ANSYS-FZR Multiphase Flow: Simulation, Experiment and Application, 26.-29.06.2006, Dresden, Deutschland
    Proceedings, CD-ROM

Permalink: https://www.hzdr.de/publications/Publ-8550
Publ.-Id: 8550


Experimental and numerical assessment of the phase distribution in a stirred tank reactor agitated by a gas-inducing turbine
Hristov, H. V.; Boden, S.; Hampel, U.; Kryk, H.; Schmitt, W.; Hessel, G.;
Over the last century two-phase flow mixing, engineered to take place in mechani-cally agitated tank reactors, has become one of the most common operations in the industry. Traditionally the gas-phase is supplied via a single pipe or a ring sparger mounted beneath the rotating impeller. The gas-inducing impellers provide an alter-native gas injection, in which case the gas is fed directly in the stirrer region.
A non-baffled laboratory-scale tank reactor mechanically agitated by a gas inducing turbine was experimentally and numerically studied. Above a certain impeller speed, at the investigated experimental conditions, the stirrer becomes able to induce gas and consequently disperse it into the bulk liquid phase. The two-phase system under examination comprises air as gas phase into isopropanol as liquid phase at room temperature. The gas-phase distribution was assessed at five different impeller speeds starting from 1000 rpm, at which gas inducement occurs.
The cone-beam type X-Ray tomography, which can provide three-dimensional infor-mation on the gas-phase distribution, was employed to experimentally study the two-phase system. The reconstruction of a rotationally symmetric distribution-field is pos-sible from a single radiographic image. Such an experimental approach was applied to obtain the quantitative measurements of gas-fraction profiles. Additionally, a mov-ing slit technique was adapted to estimate the inherent scattered radiation offset, which emerges while un-collimated X-rays penetrate the fluid-filled tank. An addi-tional reference measurement was introduced and used to remove beam hardening artefacts. An absolute quantification was possible due to the knowledge of the ratio of the fluids and the reference-materials X-ray absorption coefficients. Phantom-measurements inside the vessel were conducted for performance evaluation.
The computational fluid dynamics analyses of the stirred tank reactor were performed with CFX 10.0 numerical software. The numerical predictions at 1000 rpm used pre-vious simulation results at lower impeller speed as an initial guess. Starting from 1000rpm, five simulations were performed at stirrer speed thresholds of 50 rpm to be compared with X-Ray cone beam tomography experimental observations. The tetra-hedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer de-scribed by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid with a mean diame-ter of 1 mm and the liquid phase as continuous fluid.
The results demonstrate the X-Ray cone beam tomography and the CFD capabilities to capture the two-phase flow in detail, which can provide valuable information for the industry. In particular the special gas phase distribution can have a crucial impact on the reactor performance. This can be in detail predicted by the computational fluid dynamic software, which can prove to be an essential tool for the reactor optimisation and scale-up.
  • Poster
    DECHEMA 2006 - GVC/DECHEMA-Jahrestagungen 2006, Rhein-Main-Hallen, Wiesbaden, 26.-28.09.2006, Wiesbaden, Germany
  • Abstract in refereed journal
    Chemie Ingenieur Technik 78(2006)9, 1274

Permalink: https://www.hzdr.de/publications/Publ-8549
Publ.-Id: 8549


Contactless electromagnetic induction flowmeter based on phase shift measurements
Priede, J.; Buchenau, D.; Gerbeth, G.;
This study is concerned with a conceptual design of a new contactless AC induction flowmeter for liquid metal flows. The basic idea is to make use of the fact that the fluid flow disturbs not only the amplitude but also the phase distribution of an applied AC magnetic field. The goal is to consider the possibility of using the fluid flow induced phase shift of an AC magnetic field to measure the flow rate. In order to figure out the basic characteristics of such a flowmeter we consider several simple theoretical models where the liquid flow is approximated by a solid body motion. Based on these ideas a laboratory model of such a flowmeter has been built and tested at a liquid metal flow.
  • Contribution to proceedings
    EPM 2006, 23.-27.10.2006, Sendai, Japan
    Proceedings, Tokyo: The Iron and Steel Institute of Japan, 4-930980-55-0 C3057, 735-740
  • Lecture (Conference)
    EPM 2006, 23.-27.10.2006, Sendai, Japan

Permalink: https://www.hzdr.de/publications/Publ-8548
Publ.-Id: 8548


Hyperon production in the channel pp→K+Λp near the reaction threshold
Abd El-Samad, S.; Bilger, R.; Böhm, A.; Brinkmann, K.-T.; Clement, H.; Dshemuchadse, S.; Eyrich, W.; Erhardt, A.; Fanara, C.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Geyer, R.; Hauffe, J.; Hassan, A.; Herrmann, P.; Hesselbarth, D.; Jakob, B.; Kilian, K.; Koch, H.; Kress, J.; Kuhlmann, E.; Marcello, S.; Marwinski, S.; Metzger, A.; Michel, P.; Möller, K.; Morsch, H. P.; Naumann, L.; Roderburg, E.; Schamlott, A.; Schönmeier, P.; Schulte-Wissermann, M.; Schroeder, W.; Steinke, M.; Stinzing, F.; Sun, G. Y.; Wächter, J.; Wagner, G. J.; Wagner, M.; Wilms, A.; Wirth, S.; Zielinski, U.;
Hyperon production in the threshold region was studied in the reaction pp→K+Λp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at three different beam momenta pbeam=2.59, 2.68 and 2.85 GeV/c (corresponding to excess energies of var epsilon=85, 115 and 171 MeV). Total cross-sections were deduced to be 7.4±0.5 μb, 8.6±0.6 μb and 16.5±0.4 μb, respectively. Differential observables including Dalitz plots were obtained. From the investigation of the Dalitz plot at pbeam=2.85 GeV/c a dominant contribution of the Nasterisk operator(1650)-resonance to the reaction mechanism was found. In addition the pΛ-final-state interaction turned out to have a significant influence on the Dalitz plot distribution even 171 MeV above threshold.
Keywords: Associated strangeness production; Total cross-section; Angular distribution; Dalitz plot
  • Physics Letters B 632(2006)1, 27-34

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Permalink: https://www.hzdr.de/publications/Publ-8547
Publ.-Id: 8547


Complex formation of uranium(VI) with the amino acids L-glycine and L-cysteine: A fluorescence emission and UV-vis absorption study
Günther, A.; Geipel, G.; Bernhard, G.;
The complexation of uranium(VI) with the amino acid L-glycine and L-cysteine has been investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and UV-vis spectroscopy at low pH range. The identified 1:1 and 1:2 uranyl-L-glycine complexes fluoresce and have similar absorbance properties. In contrast to the glycine system, uranyl forms with L-cysteine two different non-fluorescent 1:1 complexes showing individual absorbance properties under the given experimental conditions.The corresponding complex formation constants were calculated using the spectroscopic data.
Keywords: uranium, complexation, amino acid, TRLFS, UV-vis spectroscopy
  • Polyhedron 26(2007), 59-65

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Permalink: https://www.hzdr.de/publications/Publ-8546
Publ.-Id: 8546


Effect of an external magnetic field on the flow in a liquid metal bubble plume
Zhang, C.; Eckert, S.; Gerbeth, G.;
Bubble driven flows have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenize the physical and chemical properties of the melt or to refine the melt. For such gas-liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way.
Compared to the numerous experimental studies on the movement of bubbles in transparent liquids, especially in water, the number of publications dealing with gas bubbles rising in liquid metals is comparatively small. The shortage of suitable measuring techniques can be considered as one reason for the slow progress in the investigations of gas-liquid metal flows. We applied the Ultrasound Doppler Velocimetry (UDV) for measurements of the velocity structure in liquid metal bubbly flows. Because of the ability to work non-invasively in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications. In the range of small or moderate void fractions the UDV technique delivers both the bubble and the liquid velocity.
In our experiments we investigated the consequences of an application of both DC and AC magnetic fields on the velocity field of bubble plumes. A restructuring of the entire flow field can be observed if a bubble plume is exposed to a DC magnetic field. The application of a transverse field leads not only to a general damping of the flow, but also favours the occurrence of vortices aligned parallel to the magnetic field direction. AC magnetic fields can be applied to generate flow structures being different from the recirculating flow known from classical bubble plumes. A tailoring of the flow using magnetic fields obviously allows a control of the heat and mass transfer in bubble plumes.
Keywords: bubble plume, DC magnetic field, AC travelling magnetic field, electromagnetic stirring, velocity measurements, ultrasound Doppler technique
  • Lecture (Conference)
    CHISA 2006, 27.-31.08.2006, Praha, Czech Republic
  • Contribution to proceedings
    17th International Congress of Chemical and Process Engineering, CHISA 2006, 27.-31.08.2006, Praha, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-8545
Publ.-Id: 8545


Upper limits on resonance contributions to proton-proton elastic scattering in the c.m. mass range 2.05-2.85 GeV/c^2
Rohdjeß, H.; Altmeier, M.; Bauer, F.; Bisplinghoff, J.; Bollmann, R.; Büßer, K.; Busch, M.; Diehl, O.; Dohrmann, F.; Engelhardt, H.-P.; Ernst, J.; Eversheim, P. D.; Eyser, K. O.; Felden, O.; Gebel, R.; Groß, A.; Groß-Hardt, R.; Hinterberger, F.; Langkau, R.; Lindlein, J.; Maier, R.; Mosel, F.; Prasuhn, D.; von Rossen, P.; Scheid, H.; Schulz-Rojahn, F.; Schwandt, F.; Schwarz, V.; Scobel, W.; Trelle, H.-J.; Ulbrich, K.; Weise, E.; Wellinghausen, A.; Woller, K.; Ziegler, R.;
Recently published excitation functions in proton-proton (pp) elastic scattering observables in the laboratory energy range 0.5-2.5GeV provide an excellent data base to establish firm upper limits on the elasticities ηel = Γel/Γtot of possible isovector resonant contributions to the nucleon-nucleon (NN) system. Such contributions have been predicted to arise from dibaryonic states, with c.m. masses between 2.1-2.9GeV/c2, but have not been confirmed experimentally. A method to determine quantitatively the maximum value of ηel compatible with experimental data is presented. We use energy-dependent phase shift fits to the pp data base to model the non-resonant interaction. Based upon the differential cross-section data measured by the EDDA Collaboration an unbiased statistical test is constructed to obtain upper limits on ηel, that exclude larger values with a 99% confidence level. Results in the c.m. mass range 2.05-2.85GeV/c2 and total widths of 10-100MeV/c2 in the partial waves 1S0, 1D2, 3P0, 3P1, and 3F3 are presented and discussed.
Keywords: PACS. 25.40.Cm Elastic proton scattering - 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 14.20.Pt Dibaryons - 11.80.Et Partial-wave analysis

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Permalink: https://www.hzdr.de/publications/Publ-8544
Publ.-Id: 8544


Determining beam parameters in a storage ring with a cylindrical hodoscope using elastic proton–proton scattering
Rohdjeß, H.; Albers, D.; Bisplinghoff, J.; Bollmann, R.; Büßer, K.; Diehl, O.; Dohrmann, F.; Engelhardt, H.-P.; Eversheim, P. D.; Gasthuber, M.; Greiff, J.; Groß, A.; Groß-Hardt, R.; Hinterberger, F.; Igelbrink, M.; Langkau, R.; Maier, R.; Mosel, F.; Müller, M.; Münstermann, M.; Prasuhn, D.; von Rossen, P.; Scheid, H.; Schirm, N.; Schwandt, F.; Scobel, W.; Trelle, H. J.; Wellinghausen, A.; Wiedmann, W.; Woller, K.; Ziegler, R.;
The EDDA-detector at the cooler-synchrotron COSY/Jülich has been operated with an internal CH2 fiber target to measure proton–proton elastic scattering differential cross-sections. For data analysis knowledge of beam parameters, like position, width and angle, are indispensable. We have developed a method to obtain these values with high precision from the azimuthal and polar angles of the ejectiles only, by exploiting the coplanarity of the two final-state protons with the beam and the kinematic correlation. The formalism is described and results for beam parameters obtained during beam acceleration are given.
Keywords: Vertex reconstruction; Fiber target; Elastic proton–proton scattering; Storage ring

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Permalink: https://www.hzdr.de/publications/Publ-8543
Publ.-Id: 8543


Radiation damage of polypropylene fiber targets in storage rings
Rohdjeß, H.; Albers, D.; Bisplinghoff, J.; Bollmann, R.; Büßer, K.; Diehl, O.; Dohrmann, F.; Engelhardt, H.-P.; Eversheim, P. D.; Greiff, J.; Groß, A.; Groß-Hardt, R.; Hinterberger, F.; Igelbrink, M.; Langkau, R.; Maier, R.; Mosel, F.; Müller, M.; Münstermann, M.; Prasuhn, D.; von Rossen, P.; Scheid, H.; Schirm, N.; Schwandt, F.; Scobel, W.; Trelle, H. J.; Wellinghausen, A.; Wiedmann, W.; Woller, K.; Ziegler, R.;
Thin polypropylene fibers have been used for internal experiments in storage rings as an option for hydrogen targets. The change of the hydrogen content due to the radiation dose applied by the circulating proton beam has been investigated in the range 1 × 106–2 × 108 Gy at beam momenta of 1.5–3 GeV/c by comparing the elastic pp-scattering yield to that from inelastic p-carbon reactions. It is found that the loss of hydrogen as a function of applied dose receives contributions from a fast and a slow component.
Keywords: Radiation damage; Polypropylene; Fiber target; Elastic proton–proton scattering; Storage ring

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Permalink: https://www.hzdr.de/publications/Publ-8542
Publ.-Id: 8542


Determination of the flow structure in bubble-driven liquid metal flows using ultrasound Doppler method
Zhang, C.; Eckert, S.; Gerbeth, G.;
The ultrasound Doppler velocimetry (UDV) was validated for its capability to measure both gas and liquid velocities in transparent as well as opaque two-phase flows. A special threshold method has been tested successfully for processing of UDV data acquired from bubble-driven flows. Our experimental work presented here is focused on the influence of a transverse static magnetic field on a bubble plume in a cylindrical vessel. The liquid flow field has been measured by means of the ultrasound Doppler velocimetry. Despite the well-known damping effect of a DC magnetic field, it was observed, that the application of a moderate magnetic field may also cause an intensification of the liquid recirculation. The global flow field was found to be dominated by quasi-two-dimensional large scale vortex structures, whose axes are parallel aligned with the magnetic field direction. Therefore, the time-averaged flow field shows a distinct anisotropy. Local recirculating zones are found in the meridional plane perpendicular to the magnetic field lines, while velocity distributions become more uniform in the other plane parallel to the magnetic field.
Keywords: bubble plume, liquid metal, magnetic field, ultrasound Doppler velocimetry
  • Lecture (Conference)
    5th International Symposium on Ultrasound Doppler Methods (ISUD), 12.-14.09.2006, Zürich, Swizerland
  • Contribution to proceedings
    ISUD5, 5th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics, 12.-14.09.2006, Zürich, Swizerland
    Proceedings: ETH Zürich, 51-54

Permalink: https://www.hzdr.de/publications/Publ-8541
Publ.-Id: 8541


Electron beam monitoring for channeling radiation measurements
Neubert, W.; Azadegan, B.; Enghardt, W.; Heidel, K.; Pawelke, J.; Wagner, W.;
A secondary emission monitor and an auxiliary Faraday cup necessary for calibration purposes have been constructed and installed at the radiation physics beam line of the electron accelerator ELBE. These devices are to be applied for the precise beam-current monitoring in measurements of channeling radiation. Miscellaneous simulations of underlying interactions of the beam electrons with the target material as well as with the materials of the monitor equipment have been performed to optimize the design and to evaluate possible correction factors inherent to transmission monitoring.
Keywords: electron beam monitor, secondary electrons, channeling radiation
  • Nuclear Instruments and Methods in Physics Research B 254(2007), 319-328

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Permalink: https://www.hzdr.de/publications/Publ-8540
Publ.-Id: 8540


Magnetic turbulence in the Riga dynamo experiment
Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Stefani, F.;
The Riga dynamo experiment demonstrates that a strong enough and appropriately directed flow of a fluid electroconductor generates a magnetic field very similar as the Earth and other celestial bodies do. Two 100 kW motors are driving a propeller which forces molten sodium to circulate inside an annular vessel, a part of which is located in the basement of the sodium lab. The sodium flow is directed by two thin coaxial electroconducting cylindrical partition walls. In the central channel sodium is swirling down from the propeller. In the coaxial counter-flow channel the flow is raising straight up to the propeller. In an outer part of the vessel the sodium is at rest, it serves only for better electric boundary conditions. Depending on sodium temperature at a propeller speed of 1800-2000 rpm (flow-rate about 0.6 qm/s) the zero state for the magnetic field is becoming unstable and a field appears seemingly from nothing. The magnetic field values are recovered from coil voltage records by means of Fast Fourier processing. For finer spectral resolution two small coils were inserted alternately in a narrow channel tip penetrating deep inside the central flow. Examples for recorded signals and FFT processed fields are presented.
  • Invited lecture (Conferences)
    Workshop: Modelling MHD Turbulence: Application to Planetary and Stellar Dynamos, 27.-30.06.2006, Boulder, United States

Permalink: https://www.hzdr.de/publications/Publ-8539
Publ.-Id: 8539


Some aspects of a Krein space related perturbation theory for MHD α²-dynamos and the resonant unfolding of diabolical points
Kirillov, O.; Günther, U.;
The spectrum of the spherically symmetric α²-dynamo is studied in the case of idealized boundary conditions. Starting from the exact analytical solutions of models with constant α-profiles a perturbation theory and a Galerkin technique are developed in a Krein-space approach. With the help of these tools a very pronounced α-resonance pattern is found in the deformations of the spectral mesh as well as in the unfolding of the diabolical points located at the nodes of this mesh. Non-oscillatory as well as oscillatory dynamo regimes are obtained. A Fourier component based estimation technique is developed for obtaining the critical α-profiles at which the eigenvalues enter the right spectral half-plane with non-vanishing imaginary components (at which overcritical oscillatory dynamo regimes form). Finally, Fréchet derivative (gradient) based methods are developed, suitable for further numerical investigations of Krein-space related setups like MHD α²-dynamos or models of PT-symmetric quantum mechanics.
Keywords: Krein space, MHD dynamo, diabolical point, exceptional point, spectral deformation, perturbation theory, resonance, Galerkin method
  • Lecture (Conference)
    International Summer School and Workshop "Operator algebras, operator theory and applications" (WOAT 2006), Satellite conference to the International Congress of Mathematicians, Madrid 2006, 01.-05.09.2006, Madrid, Portugal

Permalink: https://www.hzdr.de/publications/Publ-8538
Publ.-Id: 8538


New results on the spectrum of the MHD α²-dynamo and on Jordan algebra related canonical structures of PT-symmetric matrices
Günther, U.; Kirillov, O.;
The talk consists of two parts.

The results reported in the first part concern some unexpected properties of the spectrum of the α²-dynamo operator. In a work from February 2006 we investigated the unfolding of diabolical points in the spectrum of a dynamo operator with idealized boundary conditions (BCs). Similar to the Hamiltonians of PT-symmetric Quantum Mechanics this operator is selfadjoint in a Krein space. For constant α-profiles α₀ its spectrum λ[α₀] forms a mesh-like structure in the (α₀,Re λ)-plane with diabolical points (degeneration points of geometric and algebraic multiplicity two) at the nodes of the mesh. Under inhomogeneous perturbations of the α-profile the spectral mesh undergoes deformations which are accompanied by a resonant unfolding of the diabolical points. It was shown that each Fourier component of an α-profile α(x) induces a selective unfolding of diabolical points located on a specific parabola in the (α₀,Re λ)-plane. In recent research we extended this analysis to dynamo operators with realistic boundary conditions. Unexpectedly, it was found that the parabolas related to the resonant unfolding of diabolical points in models with idealized BCs coincide exactly with the spectral branches of dynamo operators with realistic BCs. We discuss some first aspects of the underlying mechanism responsible for this coincidence and indicate some of its possible implications.

In the second part of the talk, canonical representations of Jordan normal forms of PT-symmetric matrices are presented. These canonical representations are derived with the help of Jordan-algebra based conjugations which map Jordan blocks and Jordan chains into corresponding explicitly PT-symmetric matrices and their eigenvectors and associated vectors.
Keywords: Krein space, MHD dynamo, PT-symmetric Quantum Mechanics, diabolical point, resonance, Jordan algebra, Jordan normal form
  • Lecture (Conference)
    5th International Workshop on pseudo-Hermitian Hamiltonians in Quantum Physics, 03.-08.07.2006, Bologna, Italy

Permalink: https://www.hzdr.de/publications/Publ-8537
Publ.-Id: 8537


Transitional and weakly turbulent flow in a rotating magnetic field
Stiller, J.; Frana, K.; Cramer, A.;
The early stage of the turbulent flow driven by a rotating magnetic field is studied via direct numerical simulations and electric potential measurements for the case of a cyindrical geometry. The numerical results show that the undisturbed flow remains stable up to the linear stability limit, wheras small perturbations may initiate nonlinear transition at subcritical Taylor numbers. The observed instabilities occur randomly as isolated pairs of Taylor-Görtler vortices, which grow from spots to long tubes until they are dissipated in the lid boundary layers. At 7.5 times the critical Taylor number, the flow is governed by large-scale 3D fluctuations and may be characterized as weakly turbulent. Taylor-Görtler vortices provide the major turbulence mechanism, apart from oscillations of the rotation axis. As the vortices tend to align with the azimuthal direction, they result in a locally two-dimensional turbulence pattern.
  • Physics of Fluids 18(2006), 074105

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Permalink: https://www.hzdr.de/publications/Publ-8536
Publ.-Id: 8536


Container-less melt extraction of metallic fibres
Cramer, A.; Priede, J.; Galindo, V.; Andersen, O.; Kostmann, C.;
A method for the production of metallic fibres is proposed that uses melt extraction from a pending molten edge at the lower end of a metal sheet. Melting the sheet at its edge rather than between the two opposing branches of the inductor is achieved by a tailoring of the induction heating magnetic field. The basic feature of the configuration is the same direction of the electric current in both branches of the inductor. A proper choice of geometry, electrical conductivities of both extraction and substrate material, and the frequency of the alternating magnetic field have proven to be essential for the extraction process. Melting a platinum sheet at the edge and extraction of fibres only 20 micron in effective cross-section from a tin sheet were successfully demonstrated in model experiments.
  • Contribution to proceedings
    EPM 2006, 23.-27.10.2006, Sendai, Japan
    Processing of Materials (EPM2006), Proceedings, Tokyo: The Iron and Steel Institute of Japan, 4-93 980-55-0 C3057, 335-340
  • Lecture (Conference)
    EPM 2006, 23.-27.10.2006, Sendai, Japan

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Permalink: https://www.hzdr.de/publications/Publ-8535
Publ.-Id: 8535


Positron lifetimes in ZnO single crystals
Brauer, G.; Kuriplach, J.; Cizek, J.; Anwand, W.; Melikhova, O.; Prochazka, I.; Skorupa, W.;
Analysis of positron lifetime data for ZnO single crystals suggests that four well-separated lifetime levels exist between those for the bulk and the Zn vacancy. Due to the hydrothermal growth conditions of most ZnO single crystals studied so far, it is postulated that a hydrogen-defect interaction could be responsible for this finding.
Keywords: ZnO, positron lifetime, vacancy defects, hydrogen-defect interaction
  • Invited lecture (Conferences)
    VIth International Conference "Ion implantation and other applications of ions and electrons", 26.-29.06.2006, Kazimierz Dolny, Polen

Permalink: https://www.hzdr.de/publications/Publ-8534
Publ.-Id: 8534


Positron lifetimes in ZnO single crystals
Brauer, G.; Kuriplach, J.; Cizek, J.; Anwand, W.; Melikhova, O.; Prochazka, I.; Skorupa, W.;
Analysis of positron lifetime data for ZnO single crystals suggests that four well-separated lifetime levels exist between those for the bulk and the Zn vacancy. Due to the hydrothermal growth conditions of most ZnO single crystals studied so far, it is postulated that a hydrogen-defect interaction could be responsible for this finding.
Keywords: ZnO, positron lifetime, vacancy defects, hydrogen-defect interaction
  • Vacuum 81(2007), 1314-1318

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Permalink: https://www.hzdr.de/publications/Publ-8531
Publ.-Id: 8531


Indentation response of single-crystal GaAs in the nano-, micro-, and macroregime
Bergner, F.; Schaper, M.; Hammer, R.; Jurisch, M.; Kleinwechter, A.; Chudoba, T.;
Fabrication, handling and processing of wafers of intrinsically brittle and anisotropic single-crystalline GaAs require a high level of control of the material’s response to different loading conditions. The present work is focused on the response to hardness indentation. A short overview on the behaviour of (100) GaAs wafers in several doping conditions over a wide range of indentation loads from nano-indentation up to macro-indentation including sharp and blunt indenters is given. Special attention is paid to the pop-in effect in depth-sensing nano-indentation, to the anisotropy of indentation-induced radial crack formation and to the material’s crack resistance obtained from the indentation fracture mechanics approach. We have observed that, under certain conditions, the frequency of formation of radial cracks is essentially different for the two in-plane <110> directions. This observation is attributed to the occurrence of two different kinds of dislocations and to the lack of inversion symmetry. The effect turns out to be closely related to a left-right asymmetry in the material removal caused by wire sawing. This insight has paved the way to the optimization of the process of wire sawing of GaAs single crystals.

Permalink: https://www.hzdr.de/publications/Publ-8530
Publ.-Id: 8530


Atomistic simulation of interstitial cluster migration in silicon
Posselt, M.;
The state-of-the-art interpretation of physical processes during post-implantation annealing, such as defect evolution and transient-enhanced boron diffusion assumes that ion implantation produces a supersaturation of single vacancies and self-interstitials. They are supposed to be mobile and may recombine or may form immobile clusters. On the other hand, atomistic simulations demonstrated that implantation may generate not only single vacancies and self-interstitials but also more complex defects. Furthermore, recent theoretical studies showed that small interstitial clusters may be mobile as well. The present work gives an overview on the latter investigations. Due to the complex structure of the interstitial clusters, methods based on the estimation of migration barriers by considering the potential energy surface at 0 K are hardly applicable. Molecular dynamics (MD) simulations must be used to get a thorough understanding of the migration mechanisms. Ab-initio MD simulations are presently not practicable since they require a tremendous computational effort. Therefore atomic-level MD simulations are applied. The diffusivity of the small interstitial clusters, the self-diffusion coefficient per defect, and the corresponding effective migration barriers are determined. The implications of the present results for the explanation of experiments on post-implantation annealing and on room-temperature migration of implantation-induced self-interstitial defects are discussed.
Keywords: defects, diffusion, silicon, atomistic simulation, interstitial clusters
  • Invited lecture (Conferences)
    E-MRS IUMRS ICEM Spring Meeting 2006, 29.05.-02.06.2006, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-8529
Publ.-Id: 8529


Equilibrium concentration and diffusivity of vacancies in Ge: An atomistic study with an improved interatomic potential
Gessner, H.; Posselt, M.;
An improved Stillinger-Weber-type potential for Ge is developed by adjusting the three-body parameters in such a manner that lattice parameter and cohesive energy are preserved, and the elastic constants and the melting point are reproduced satisfactorily. The dependence of the equilibrium concentration and the diffusivity of vacancies on the temperature as well as the contribution of vacancies to self-diffusion are determined by atomistic simulations and by thermodynamic considerations. The calculations are performed in the temperature range between 600 and 1100 K. The enthalpies and entropies for formation and migration are estimated. Similar investigations are performed for self-interstitials in order to check whether their contribution to self-diffusion in Ge can be neglected, as shown experimentally. Finally, the self-diffusion coefficient and the equilibrium concentration of vacancies are compared with experimental data from the literature.
Keywords: defects, diffusion, germanium, computer simulation
  • Poster
    E-MRS IUMRS ICEM 2006 Spring Meeting, 29.05.-02.06.2006, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-8528
Publ.-Id: 8528


Dose rate and temperature dependence of ion-beam-induced defect evolution in germanium
Posselt, M.; Bischoff, L.; Grambole, D.; Herrmann, F.; Grötzschel, R.;
To investigate the effect of dose rate and irradiation temperature on defect evolution in germanium during the ion implantation process a focused ion beam system is used. Channeling implantation of Ga is performed at two very different dose rates (3.5x1011 and 1.6x1019 cm-2s-1), at two temperatures (RT and 250 0C), and at five different doses, ranging from 5x1012 to 5x1014 cm-2. The depth distributions of Ga and of the implantation damage are determined by SIMS and micro-RBS/C, respectively. The shape of the measured range and damage profiles is strongly influenced by the dose rate and the implantation temperature. These results are explained by the competition between damage buildup and dynamic annealing during the ion bombardment. For the two implantation temperatures considered, the time scale for intracascade defect relaxation can be estimated. The measured Ga depth profiles can be reproduced by atomistic computer simulations using a phenomenological model to describe the probability that an implanted ion collides with a target atom of a damaged region in dependence on the total nuclear energy deposition per target atom.
Keywords: ion implantation, damage, defects, germanium
  • Lecture (Conference)
    E-MRS IUMRS ICEM Spring Meeting 2006, 29.05.-02.06.2006, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-8527
Publ.-Id: 8527


Phase distribution in a stirred tank reactor mechanically agitated by gas-inducing turbine
Hristov, H. V.; Boden, S.; Hampel, U.; Kryk, H.; Schmitt, W.; Hessel, G.;
The experimental and the numerically studies were applied to a non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine. The dispersion of air as gas phase into isopropanol as liquid phase at room temperature under different stirrer speeds was investigated. The X-Ray cone beam tomography measurements were taken at five different stirrer speeds with thresholds of 50 rpm starting from 1000 rpm at which the gas inducement occurs for the given operating conditions.
Cone-beam type X-ray computed tomography is a potential method to measure three-dimensional phase distributions in vessels. An example for that is the measurement of gas profiles in stirred chemical reactors. However, there are considerable difficulties for accurate quantitative measurements, for instance of average gas fraction in a fluid, due to beam hardening and radiation scattering effects. We have developed a suitable measurement setup as well as calibration and software correction methods to achieve a highly accurate void fraction measurement.
The computational fluid dynamics analyses of the stirred tank reactor were performed in 3D with CFX 10.0 numerical software. Five steady state simulations, at stirrer speeds corresponding to the ones at which the measurements were performed, were conducted to be compared with the experimental observations. The tetrahedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer described by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid and the liquid phase as continuous fluid. Different turbulence models and their suitability were considered in the simulations.
  • Lecture (others)
    VDI-GVC-Fachausschusssitzung "Mehrphasenströmungen" und "Computational Fluid Dynamics", 01.-03.03.2006, Überlingen, Germany

Permalink: https://www.hzdr.de/publications/Publ-8526
Publ.-Id: 8526


Low-lying E1, M1, and E2 strength distributions in 124,126,128,129,130,131,132,134,136Xe:Systematic photon scattering experiments in the mass region of a nuclear shape or phase transition
von Garrel, H.; von Brentano, P.; Fransen, C.; Friessner, G.; Hollmann, N.; Jolie, J.; Käppeler, F.; Käubler, L.; Kneissl, U.; Kohstall, C.; Kostov, L.; Linnemann, A.; Mücher, D.; Pietralla, N.; Pitz, H. H.; Rusev, G.; Scheck, M.; Schilling, K. D.; Scholl, C.; Schwengner, R.; Stedile, F.; Walter, S.; Werner, V.; Wisshak, K.;
Systematic nuclear resonance fluorescence (NRF) experiments on all nine stable (seven even-even and two odd-mass) Xe isotopes have been performed at the bremsstrahlung facility of the 4.3-MV Stuttgart Dynamitron accelerator. For the first time thin-walled, high-pressure gas targets (about 70 bar) with highly enriched target material were used in NRF experiments. Precise excitation energies, transition strengths, spins, and decay branching ratios were obtained for numerous states, most of them previously unknown.
The systematics of the observed E 1 two-phonon excitations (2+,3-) and M1 excitations to 1+ mixed-symmetry states in the even-even isotopes are discussed with respect to the new critical point symmetry E(5). The fragmentation of these fundamental dipole excitation modes in the odd-mass isotopes 129,131 Xe is shown and discussed. In the even-even nuclei several low-lying E2 excitations were observed.
Keywords: Nuclear structure, nuclear spectroscopy, photon scattering.

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Permalink: https://www.hzdr.de/publications/Publ-8525
Publ.-Id: 8525


18F-labelling, cellular uptake and biodistribution of novel acyclic purine nucleosides for monitoring HSV1-tk based gene therapy
Oswald, J.; Noll, S.; Bergmann, R.; Noll, B.;
Aim
Suicide gene therapy utilizing herpes simplex virus type 1 thymidine kinase gene (HSV1-tk) requires careful monitoring of the successful transfection. 18F-labelled nucleoside analoga, especially acyclic nucleosides such as 9-[(3-[18F]fluoro-1-hydroxy-2-propoxy)methyl]guanine ([18F]FHPG) and 9-[(4-[18F]fluoro)-3-hydroxymethylbutyl]guanine ([18F]FHBG) are currently used as PET tracers for monitoring and quantification of HSV1-tk expression. To improve the tracer properties, two new precursors have been synthesized by introduction of bromine in order to get the new substrates 8-bromo-9-[(3-[18F]fluoro-1-hydroxy-2-propoxy)methyl]guanine ([18F]FHBrPG) and 8-bromo-9-[(4-[18F]fluoro)-3-hydroxymethylbutyl]guanine ([18F]FHBrBG) for monitoring gene expression of HSV1-tk.

Materials and methods
The precursors as well as the nonradioactive reference compounds were prepared by introduction a p-toluenesulphonyl leaving group and trityl protecting groups into the brominated derivatives of ganciclovir and penciclovir. In a further step the precursors reacted with a K[18F]F kryptofix complex to trityl-protected intermediates. Then, the protecting groups were removed by heating in methanolic acetic acid solution. Both tracers were purified by RP HPLC separation. The identity of the tracers with the nonradioactive reference compounds was proved by HPLC. The in vitro uptake of all compounds was evaluated in a glioblastoma cell line stably transfected with the HSV1-tk gene and in the respective non-transfected cell line. The biodistribution and biokinetics of the radiotracers have been studied in mice and rats by small animal PET.

Results
The radiochemical yield of the 18F-tracers amounts to 10-15% (decay corrected) after a synthesis time of 85 95 min, the radiochemical purity was > 98%. The average specific activity was 19 GBq/µmol at the end of synthesis. Cell-uptake studies were carried out with both the brominated and the non-brominated derivatives of ganciclovir and penciclovir as standards. The relative cellular uptake (ratio HSV-tk-positive/controls) was 12.4±4.5 after 1 h of incubation with [18F]FHBrBG. In contrast, the uptake ratio of the other tracers [18F]FHBrPG (1.7±0.4), [18F]FHBG (4.0±2.3) and [18F]FHPG (1.6±0.3) was significantly lower than that of [18F]FHBrBG. Renal elimination was the main route of tracer clearance from the body, however with increasing lipophilicity of the tracers, increasing amounts were also eliminated through liver and bile into the intestine.

Conclusions
The novel tracer [18F]FHBrBG showed a superior uptake in HSV1-tk transfected cells compared to the clinically tested PET-tracer [18F]FHBG. Therefore [18F]FHBrBG appears to be a novel tracer for an improved monitoring of HSV1-tk based gene therapy approaches with PET.
  • Lecture (Conference)
    EANM'06 Annual Congress of the European Association of Nuclear Medicine, 30.09.-04.10.2006, Athens, Greece
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 33(2006)Suppl. 2, 624

Permalink: https://www.hzdr.de/publications/Publ-8524
Publ.-Id: 8524


Expression of VEGF and VEGF receptors and radiotracer uptake in tumor cells and primary endothelial cells under experimental hypoxia
Oswald, J.; Treite, F.; Haase, C.; Bergmann, R.; Schwenzer, B.; Pietzsch, J.;
Aim:
Vascular-endothelial growth factor (VEGF) is expressed in response to various stimuli like hypoxia and plays a key role in tumor angiogenesis. In this study we analyzed the influence of experimental hypoxia on the upregulation of VEGF and its receptors in primary endothelial cells and tumor cell lines. Furthermore we quantified the uptake of radiotracers in these cells in response to experimental hypoxia in vitro.
Material and Methods:
Three types of primary endothelial cells were used: human umbilical vein endothelial cells (HUVEC), human dermal microvascular endothelial cells (HDMEC) and human aortic endothelial cells (HAEC) as well as the two tumor cell lines FaDu (squamous cell carcinoma) and HT-29 (colorectal adenocarcinoma), respectively. Experimental hypoxia was induced by cultivating cells for 24 to 72 hours in presence of <1% oxygen in a special incubator (Gasboy C40, Labotect). Expression of VEGF, and of the VEGF receptors FLT-1, KDR, FLT-4 and neuropilin 1 and 2 were quantified with quantitative PCR (Realplex, Eppendorf). Cellular uptake of [99mTc]sestamibi, [18F]FDG, and [18F]F-misonidazole was determined after one to four hours incubation and measured after cell lysis with a Cobra II gamma counter (Packard).
Results:
After 48 h of experimental hypoxia all cell lines showed a significant upregulation of VEGF expression. VEGF receptors FLT-1, KDR and FLT-4 were expressed in endothelial cells but absent in tumor cells. Cellular uptake of [99mTc]sestamibi was reduced under hypoxic conditions in all cell lines. Furthermore, we found that primary endothelial cells incorporated significantly higher amounts of [18F]FDG under experimental hypoxic conditions in comparison to normoxic conditions.
When compared to normoxia [18F]FDG uptake after 48h hypoxia was increased 4.3-fold in HUVECs, 3.4-fold in HDMECs, and 3.5-fold in HAECs. These values were substantially higher than the values for the tumor cells FaDu (1.9-fold) and HT-29 (2.1-fold).
Conclusion:
Our data show VEGF to be a suitable indicator for enhanced oxygen demand in both tumor and endothelial cells in vitro. Moreover, the results emphasize the particular relevance of endothelial cells as one important part of the tumor micromilieu.
  • Lecture (Conference)
    EANM'06 Annual Congress of the European Association of Nuclear Medicine, 30.09.-04.10.2006, Athens, Greece
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 33(2006)Suppl. 2, 661

Permalink: https://www.hzdr.de/publications/Publ-8523
Publ.-Id: 8523


Central depression in nuclear density and its consequences for the shell structure of superheavy nuclei
Afanasjev, A. V.; Frauendorf, S.;
The influence of the central depression in the density distribution of spherical superheavy nuclei on the shell structure is studied within the relativistic mean-field theory. A large depression leads to the shell gaps at the proton Z = 120 and neutron N = 172 numbers, whereas a flatter density distribution favors N = 184 and leads to the appearance of a Z = 126 shell gap and to the decrease of the size of the Z = 120 shell gap. The correlations between the magic shell gaps and the magnitude of the central depression are discussed for relativistic and nonrelativistic mean field theories.
  • Physical Review C 71(2005), 024308

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Publ.-Id: 8522


Description of rotating N=Z nuclei in terms of isovector pairing
Afanasjev, A. V.; Frauendorf, S.;
A systematic investigation of the rotating N=Z even-even nuclei in the mass A=68-80 region has been performed within the frameworks of the cranked relativistic mean field, cranked relativistic Hartree-Bogoliubov theories, and cranked Nilsson-Strutinsky approach. Most of the experimental data are well accounted for in the calculations. The present study suggests the presence of strong isovector np pair field at low spin, whose strength is defined by the isospin symmetry. At high spin, the isovector pair field is destroyed and the data are well described by the calculations assuming zero pairing. No clear evidence for the existence of the isoscalar t=0 np pairing has been obtained in the present investigation performed at the mean field level.
  • Physical Review C 71(2005), 064318

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Publ.-Id: 8521


Reappearance of the pairing correlations at finite temperature
Sheikh, J. A.; Palit, R.; Frauendorf, S.;
Rotational and deformation dependence of isovector and isoscalar pairing correlations at finite temperature are studied in an exactly solvable cranked deformed shell model Hamiltonian. It is shown that isovector pairing correlations, as expected, decrease with increasing deformation and the isoscalar pairing correlations remain constant at temperature, T=0. However, it is observed that at finite temperature both isovector and isoscalar pairing correlations are enhanced with increasing deformation. It is also demonstrated that the pair correlations, which are quenched at T=0 and high rotational frequency reappear at finite temperature. The changes in the individual multipole pairing fields as a function of rotation and deformation are analyzed in detail.
  • Physical Review C 72(2005), 041301

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Publ.-Id: 8520


Superdeformation and hyperdeformation in the 108Cd nucleus
Afanasjev, A. V.; Frauendorf, S.;
Superdeformation and hyperdeformation in 108Cd have been studied for the first time within the framework of the fully self-consistent cranked mean-field theory, namely, cranked relativistic mean-field theory. The structure of observed superdeformed bands 1 and 2 have been analyzed in detail. The bumps seen in their dynamic moments of inertia are explained as arising from unpaired band crossings. This is contrary to an explanation given earlier within the framework of the projected shell model. It was also concluded that this nucleus is not a doubly magic superdeformed nucleus.
  • Physical Review C 72(2005), 031301

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Publ.-Id: 8519


Investigation of antimagnetic rotation in light Cadmium nuclei: 106,108Cd
Simons, A. J.; Wadsworth, R.; Jenkins, D. G.;
The lifetimes of excited states belonging to the lowest lying positive-parity bands in 106,108Cd have been measured using the Doppler-shift attenuation method. The resulting B(E2) transition rates show a significant decrease with increasing spin in 106Cd, whereas in 108Cd there is tentative evidence for a similar effect. The results are compared with cranking and semiclassical model calculations, which indicate that the structures have the properties expected from an "antimagnetic" rotational band resulting from the coupling of g9/2 proton holes to aligned pairs of h11/2 and g7/2 neutron particles.
  • Physical Review C 72(2005)2, 024318

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Publ.-Id: 8517


Low-energy cross section of the 7Be(p,gamma)8B solar fusion reaction from the Coulomb dissociation of 8B
Schümann, F.; Typel, S.; Hammache, F.; Sümmerer, K.; Uhlig, F.; Böttcher, I.; Cortina, D.; Förster, A.; Gai, M.; Geissel, H.; Greife, U.; Grosse, E.; Iwasa, N.; Koczon, P.; Kohlmeyer, B.; Kulessa, R.; Kumagai, H.; Kurz, N.; Menzel, M.; Motobayashi, T.; Oeschler, H.; Ozawa, A.; Ploskon, M.; Prokopowicz, W.; Schwab, E.; Senger, P.; Strieder, F.; Sturm, C.; Zhi-Yu, S.; Surowka, G.; Wagner, A.; Walus, W.;
An exclusive measurement of the Coulomb breakup of 8B into 7Be+p at 254A MeV was used to infer the low-energy 7Be(p,gamma)8B cross section. The radioactive 8B beam was produced by projectile fragmentation of 350A MeV 12C and separated with the FRagment Separator (FRS) at Gesellschaft für Schwerionenforschung in Darmstadt, Germany. The Coulomb-breakup products were momentum-analyzed in the KaoS magnetic spectrometer; particular emphasis was placed on the angular correlations of the breakup particles. These correlations demonstrate clearly that E1 multipolarity dominates within the angular cuts selected for the analysis. The deduced astrophysical S17 factors exhibit good agreement with the most recent direct 7Be(p,gamma)8B measurements. By using the energy dependence of S17 according to the recently refined cluster model for 8B of P. Descouvemont [Phys. Rev. C 70, 065802 (2004)], we extract a zero-energy S factor of S17(0)=20.6±0.8(stat)±1.2(syst) eV b. These errors do not include the uncertainty of the theoretical model to extrapolate to zero relative energy, estimated by Descouvemont to be about 5%.
Keywords: Coulomb breakup 7Be radioactive 8B beam S17 S-factor

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Permalink: https://www.hzdr.de/publications/Publ-8513
Publ.-Id: 8513


Three models of Krein-space related physics: PT-symmetric Quantum Mechanics, Squire equation and the MHD α²-dynamo
Günther, U.; Kirillov, O.; Stefani, F.;
PT-symmetric Quantum Mechanics, the Squire equation of hydrodynamics and the spherically symmetric α²-dynamo of magnetohydrodynamics (MHD) can be structurally linked and treated in a unified way as spectral problems in Krein spaces. We demonstrate their interrelation explicitly and provide examples for specific parameter dependencies of their spectra. Special emphasis is laid on the physical relevance of transitions between real and complex spectral branches in connection with phase transitions between sectors of exact PT-symmetry and spontaneously broken PT-symmetry in Quantum Mechanics as well as with possible polarity reversals of dynamo maintained magnetic fields of planets. We briefly comment on third order spectral branch points with geometric multiplicity one and algebraic multiplicity three as well as on a dynamo related resonant unfolding of diabolical points (spectral intersection points of geometric and algebraic multiplicity two).

Based on:
[1] U. Günther and F. Stefani, J. Math. Phys. 44, (2003), 3097-3111, math-ph/0208012.
[2] U. Günther, F. Stefani and G. Gerbeth, Czech. J. Phys. 54, (2004), 1075-1090, math-ph/0407015.
[3] U. Günther, F. Stefani and M. Znojil, J. Math. Phys. 46, (2005), 063504, math-ph/0501069.
[4] U. Günther and F. Stefani, Czech. J. Phys. 55, (2005), 1099-1106, math-ph/0506021.
[5] U. Günther and O. Kirillov, J. Phys. A: Math. General (2006), in press, math-ph/0602013.
Keywords: operator theory, Krein space, PT-symmetric Quantum Mechanics, dynamo theory, Squire equation, spectral branch points, diabolical points, phase transition, perturbation theory, resonances
  • Lecture (Conference)
    The Seventeenth International Workshop on Operator Theory and Applications (IWOTA 2006), 31.07.-03.08.2006, Seoul, South Korea

Permalink: https://www.hzdr.de/publications/Publ-8511
Publ.-Id: 8511


Perspectives of contactless inductive flow tomography
Stefani, F.; Gundrum, T.; Gerbeth, G.; Xu, M.;
The flow of an electrically conducting fluid exposed to an externally applied magnetic field leads to induced currents and hence to induced magnetic fields. These induced fields can be measured in the exterior of the fluid. The application of different external magnetic fields and the measurement of the corresponding induced magnetic fields allows to reconstruct the basic features of the velocity field of the melt. The principle of such a “Contactless Inductive Flow Tomography” (CIFT) is delineated, and a prototype experiment with a propeller driven flow of the eutectic alloy GaInSn is presented. The areas of application of CIFT, its limitations, and possible further developments are discussed.
  • Contribution to proceedings
    EPM 2006, The 5th International Symposium on Electromagnetic Processing of Materials, 23.-27.10.2006, Sendai, Japan
    Proceedings, Tokyo: The Iron and Steel Institute of Japan, 4-930980-55-0 C3057, 745-750
  • Lecture (Conference)
    EPM 2006, The 5th International Symposium on Electromagnetic Processing of Materials, 23.-27.10.2006, Sendai, Japan

Permalink: https://www.hzdr.de/publications/Publ-8510
Publ.-Id: 8510


Environmental Soil Chemistry with Synchrotron Methods: Linking Space, Time, Biology and Hydrology
Scheinost, A.;
- wird nachgereicht
  • Invited lecture (Conferences)
    Lecture at the Institute of Environmental Technology - CTM, 23.05.2006, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-8509
Publ.-Id: 8509


Requirements on the HLD-Grid
Kunicke, M.; Herrmannsdörfer, T.;
In 2007 the Dresden High Magnetic Field Laboratory (HLD) [1] will come into operation. This collective project of five institutes located in Dresden will used by the high field community in Europe. The IT tasks concerning the shared use of the experimental facilities should be solved using Grid technologies. The report describes the requirements on the HLD-Grid.
Keywords: Grid, shared use, experimental facility, High Magnetic Field Laboratory
  • Lecture (Conference)
    Distributed computing and Grid technologies in science and education GRID'2006, 26.-30.06.2006, Dubna, Russia
  • Contribution to proceedings
    Distributed Computing and Grid-Technologies in Science and Education GRID'2006, 26.-30.06.2006, Dubna, Russia
    Proceedings of the Second International Conference Distributed Computing and Grid-Technologies in Science and Education, 5-9530-0138-X, 113-116

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Publ.-Id: 8508


Hydrodynamic phenomena in the downcomer during flow rate transients in the primary circuit of a PWR
Cartland Glover, G. M.; Höhne, T.; Kliem, S.; Rohde, U.; Weiss, F.-P.; Prasser, H.-M.;
Mixing phenomena observed when the flow rate in a single loop of the primary circuit is changed can influence the operation of Pressurized Water Reactor (PWR) by inducing local gradients of boron concentration or coolant temperature. Analysis of one-dimensional Laser Doppler Anemometry measurements during the start-up and shutdown of pump on a single loop of the ROCOM test facility has been performed. The effect of a step change and a ramped change in the flow rate on the axial and azimuthal velocities was examined. Numerical simulations were also performed for the step change in the flow rate that gave quantitative agreement with the axial velocities. Phenomenological agreement was made on the turbulent kinetic energy; however, observed values were a factor of 10 less than the turbulent kinetic energy derived from the measurements.

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Publ.-Id: 8507


X-ray studies of ultra-thin Si wafers for mirror application
Sass, J.; Mazur, K.; Surma, B.; Eichhorn, F.; Litwin, D.; Galas, J.; Sitarek, S.;
The ultra-thin 2” diameter silicon (111)-H(1x1) wafer appeared to be a promising material for a mirror focusing He-atom beam in a scanning atom microscope. To increase achievable at present resolution from 1.5 µm to a sub-micron range the 50 µm thick (111) silicon wafer with shape thickness variation better than +-1 µm and 0.05° precision of miscut value is necessary. The purpose of this paper was to adapt X-ray measurements to control the miscut value with high precision for the 50 µm thick silicon wafers as well as to control the deviation of the wafer surface from ideal flat plane by measurements of low-angle reflection using X-ray high resolution diffractometer (HRXRD). The crucial point was the construction of a stress-free ultra-thin wafer holder. The precision of 0.01° miscut value was obtained. The deviation of the surface from the ideal flat surface obtained but X-ray measurements were compared with the one estimated from optical (confocal) method. A satisfactory good conformity between both methods has been observed.
Keywords: x-ray reflectometry, confocal microscopy, ultra-thin Si wafers
  • Poster
    EMRS Spring Meeting, 29.05.-03.06.2006, Nice, France
  • Nuclear Instruments and Methods in Physics Research B 253(2006), 236-240

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Publ.-Id: 8506


The investigation of the chemical composition profile and the lateral homogeneity of AIIIBV quantum wells
Gaca, J.; Wojcik, M.; Turos, A.; Strupinski, W.; Jasik, A.; Zynek, J.; Kosiel, K.; Eichhorn, F.; Prokert, F.;
The chemical composition and interplanar spacing profiles as well the lateral homogeneity of AIIIBV heterostructures containing a highly strained In(x)Ga(1-x)As layer were investigated. The heterostructures grown by metallorganic chemical vapor deposition were chracterized by means of high resolution x-ray diffractometry, x-ray reflectometry and Rutherford backscattering. In order to analyze the experimental results an algorithm for calculating the x-ray profiles based on the Darwin diffraction theory has been worked out. The developed method was applied to find out: the dependence of the growth rate and the interface profiles of the highly strained In(x)Ga(1-x)As layer on the deposition time to supervise the growth process of a resonant cavity enhanced photodiode heterostructure for which a highly strained In(x)Ga(1-x)As layer is an essential part.
Keywords: AIIIBV, highly strained heterostructures, high resolution x-ray diffractometry, x-ray reflectometry, Rutherford backscattering
  • Contribution to external collection
    in: Materialy Elektroniczne (Reports of the ITME Warsaw) Nr. 1/4, Warsaw: ITME Warsaw, 2005, 5-42

Permalink: https://www.hzdr.de/publications/Publ-8505
Publ.-Id: 8505


Synthesis and structural aspects of pyridine- and imidazole-functionalised bispidines
Stephan, H.; Juran, S.; Emmerling, F.; Kraus, W.;
Bispidines (bispidine = 3,7-diazabicyclo[3.3.1]-nonane) show unique complexation properties towards transition metals. The high thermodynamic stability of the complexes of these structurally reinforced ligands with Cu(II) offers the possibility to apply such complexes for diagnostic and therapeutic purposes (64/67Cu). Furthermore, the bispidine structure opens suitable chemical approaches to introduce bio-molecules onto the skeleton, an important feature in view of the targeting of such complexes.
We want to present the synthesis and the coordinating properties of novel hexadentate bispidine derivatives having pyridine and/or imidazole units as donor groups. Cu(II) complexes of some bispidines have been isolated and the structures were solved by X-ray single crystal diffraction. As shown in the following figure, the copper(II) complex of the hexadentate bis(amine)tetrakis(pyridine) bispidine ligand L is six-coordinate having a distorted octahedral structure. It is evident from this structure that the copper(II) ion is almost completely shielded from the environment resulting in a very high stability against exogenous competing ligands.
Preliminary labelling experiments of bispidine ligands with 64/67Cu indicate the rapid formation of stable complexes under mild conditions.
  • Lecture (Conference)
    37. International Conference on Coordination Chemistry, 13.-18.08.2006, Cape Town, South Africa
  • Abstract in refereed journal
    International Conference on Coordination Chemistry (2006), 51

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Publ.-Id: 8504


Polyoxotungstates as potent inhibitors for ecto-nucleotidases
Emmerling, F.; Kraus, W.; Iqbal, J.; Müller, C.; Röllich, A.; Stephan, H.;
The particular structural features of transition metal oxygen anion clusters cause a rapidly expanding scientific as well as practical interest for these compounds, e.g. applications in areas including catalysis, materials chemistry and biochemistry. In the past decade, especially polyoxometalates (POMs) based on V(V), Mo(VI) and W(VI) were found as attractive candidates for medical applications. Such polynuclear metal compounds show unique transport properties into cells, and may act as antiviral and antitumoral agents.
We want to report the enzyme inhibition behaviour of the polyoxotungstates [W12O39]6- (1), [W12PO40]3- (2), [Ti2W10PO40]7- (3), [TiW11CoO40]8- (4), [Co4(H2O)2(W9PO34)2]10- (5), and [NaSb9W21O86]18- (6) towards the ecto-nucleotidases NTPDase 1, 2 and 3.
The polyoxotungstates (3) and (4) have been characterised by single X-ray diffraction showing the typical Keggin structure.
All of the polyoxotungstates investigated are potent inhibitors of the NTPDases 1-3 with Ki values between 0.14 and 29 µM.
  • Poster
    37. International Conference on Coordination Chemistry, 13.-18.08.2006, Cape Town, South Africa
  • Abstract in refereed journal
    International Conference on Coordination Chemistry (2006), 317

Permalink: https://www.hzdr.de/publications/Publ-8503
Publ.-Id: 8503


Excess vacancies in high energy ion implanted SiGe
Kögler, R.; Peeva, A.; Mücklich, A.; Kutznetsov, A.; Christensen, J. S.; Svensson, B. G.; Skorupa, W.;
Excess vacancies generated by high energy implantation with 1.2 MeV Si+ and 2 MeV Ge+ ions in SiGe were investigated after rapid thermal annealing at 900 °C. Excess vacancies were probed by decoration with Cu and measuring the Cu profile by secondary ion mass spectrometry. Cross section transmission electron microscopy of cleaved specimen enabled us to visualize nanocavities resulting from agglomeration of excess vacancies. The ion-induced damage in SiGe increases with increasing Ge fraction of the alloy. The amorphization threshold decreases and the extension of a buried amorphous layer increases for given implantation and annealing conditions.
In contrast to ballistic simulations of excess defect generation where perfect local self-annihilation is assumed the concentrations of excess vacancies and excess interstitials in SiGe increase with increasing Ge fraction. The main contribution to the high excess vacancy concentration in SiGe was found to result from the inefficient recombination of vacancies and interstitials. The widely used +1 model describing the ion-induced damage in Si is not valid for SiGe.
Keywords: Ion implantation, SiGe, Excess vacancies, Defects
  • Journal of Applied Physics 101(2007), 033508-033508
    DOI: 10.1063/1.2433122
  • Poster
    15th International Conference on Ion Beam Modification of Materials (IBMM2006), 18.-22.09.2006, Taormina, Italy

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Publ.-Id: 8502


Synthesis and biological evaluation of a new type of 99mTechnetium-labeled fatty acid for myocardial metabolism imaging
Walther, M.; Jung, C.; Bergmann, R.; Pietzsch, J.; Rode, K.; Fahmy, K.; Mirtschink, P.; Stehr, S.; Heintz, A.; Wunderlich, G.; Kraus, W.; Pietzsch, H.-J.; Kropp, J.; Deussen, A.; Spies, H.;
Technetium-labeled fatty acids intended for myocardial metabolism imaging and the respective rhenium model complexes were synthesized according to the “4+1” mixed-ligand approach and investigated in vitro and in vivo. The non-radioactive rhenium model complexes were characterized by NMR, IR, EA and the geometrical impact of the chelate unit on the integrity of the fatty acid head structure was determined by single crystal X-ray analyses. To estimate the diagnostic value of the 99mTc-labeled fatty acids the compounds were investigated in experiments in vitro and in biodistribution studies using male Wistar rats. The new fatty acid tracers contain the metal core in the oxidation states +3, well-wrapped in a trigonal-bipyramidal coordination moiety which is attached at the ω-position of a fatty acid chain. This structural feature is considered to be a good imitate of the well-established iodinated phenyl fatty acids. High heart extraction in perfused heart studies (up to 26% ID) and noticeable heart uptake of the 99mTc tracers in vivo being in the order of 2% ID/g at 5 min p.i., accompanied by a good heart to blood ratio of 8, confirms that the new Tc-compounds are suitable as fatty acid tracer.
  • Bioconjugate Chemistry 18(2007), 216-230

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Publ.-Id: 8501


Synthesis of a new rhenium labeled fatty acids and their 99mTechnetium analogues for myocardial metabolism imaging
Walther, M.; Bergmann, R.; Pietzsch, J.; Rode, K.; Mirtschink, P.; Stehr, S.; Heintz, A.; Wunderlich, G.; Kraus, W.; Pietzsch, H.-J.; Deussen, A.;
Rhenium model complexes and the respective Technetium-labeled fatty acids for myocardial metabolism imaging, were synthesized according to the “4+1” mixed-ligand approach and investigated in vitro and in vivo. The non-radioactive rhenium model complexes were characterized by NMR, IR, EA and the geometrical impact of the chelate unit on the integrity of the fatty acid structure was determined by X-ray analyses. The new fatty acid tracers contain the metal core in the oxidation states +3, well-wrapped in a trigonal-bipyramidal coordination moiety which is attached at the ω-position of a fatty acid chain as isocyano ligand in the case A. The compounds of group B contain the fatty acid moitie coupled on the tetradentate ligand. High heart extraction in perfused heart studies (up to 26% ID) and noticeable heart uptake of the 99mTc tracers in vivo (using male Wistar rats) being in the order of 2% ID/g at 5min p.i. accompanied by a good heart to blood ratio of 8, confirms the target comparability.
  • Poster
    3rd International Symposium on Bioorganometallic Chemistry (ISBOMC’06), 05.-08.07.2006, Milan, Italy

Permalink: https://www.hzdr.de/publications/Publ-8500
Publ.-Id: 8500


Untersuchung elektromagnetischer Strömungsbeeinflussung in elektrisch leitfähigen Fluiden mit Hilfe von 2d2k/1d3k-Ultraschall-Doppler-Array-Techniken
Lenz, M.; Shirai, K.; Büttner, L.; Csarske, J.; Eckert, S.; Gerbeth, G.;
Die elektromagnetische Strömungsbeeinflussung spielt eine wichtige Rolle in der metallischen Werkstofftechnik. Wichtige potentielle Anwendungsgebiete sind Strömungsoptimierungen für die Herstellung einkristalliner Halbleiterkristalle (450 mm Siliziumwafer) und die Optimierung von Stahlgussprozessen.
Zur Validierung der numerischen Strömungssimulationen verwendet man häufig ein Wassermodell des zugehörigen Prozesses. Dieses ermöglicht prinzipiell den Einsatz von Laserverfahren zur Strömungsvermessung, spiegelt jedoch wegen der unterschiedlichen Eigenschaften von Metallen und Wasser die physikalische Realität nur unzureichend wider.
Zur Strömungsmessung in Metallschmelzen bedient man sich daher häufig der Ultraschall-Messtechnik unter Ausnutzung des Doppler-Effektes. Die Messaufbauten ermöglichen in der Regel die Messung einer Geschwindigkeitskomponente entlang einer Linie.
Zukünftige Messaufgaben wie beispielsweise die Vermessung inkohärenter Strömungsfelder können mit den vorhandenen Messgeräten nicht realisiert werden. Das liegt im wesentlichen an der fehlenden zeitlichen Auflösung der Messsysteme und der langsamen Traversierung.
Der Vortrag präsentiert aktuelle Ergebnisse bei Ultraschallmessungen in der Metallurgie. Dabei wird vorgestellt, wie die Erhöhung der zeitlichen Auflösung und damit die Messung instationärer Felder erreicht werden kann. Beschrieben werden dabei grundsätzliche Erwägungen hinsichtlich der Wandler-Geometrie und des Schallfeldes, Probleme bei der Schallanregung in der Flüssigkeit und Elemente der Signalverarbeitung. Die erreichbare maximale zeitliche und örtliche Auflösung wird theoretisch und experimentell dargelegt.
Keywords: Electromagnetic flow control, Ultrasound Doppler velocimetry, Ultrasound array technique, Flow imaging
  • Lecture (Conference)
    14. Fachtagung “Lasermethoden in der Strömungsmesstechnik",”GALA2006, 05.-07.09.06, Braunschweig, Germany
  • Contribution to proceedings
    GALA-Fachtagung: Lasermethoden in der Strömungsmesstechnik, 05.-07.09.06, Braunschweig, Germany
    Lasermethoden in der Strömungsmesstechnik 14(2006), 3-98056 13-3-X, 5.1-5.9

Permalink: https://www.hzdr.de/publications/Publ-8499
Publ.-Id: 8499


Electromagnetic flow control in casting and metallurgical processing
Eckert, S.; Galindo, V.; Gerbeth, G.; Willers, B.; Zhang, C.;
Es wird ein Überblick über die Möglichkeiten der elektromagnetischen Strömungskontrolle für Anwendungen in der Giessereitechnik und in der Metallurgie gegeben, namentlich zur Kontrolle der Formfüllung beim Feinguß, zur elektromagnetischen Beeinflussung der Strömungsstruktur in Flüssigmetall-Zweiphasenströmungen sowie bei der Erstarrung von Legierungen unter Magnetfeldeinfluß. Insbesondere wird auf die Bedeutung von Modellexperimenten mit metallischen Modellschmelzen hingewiesen, die einen wesentlichen Beitrag zum Verständnis der Strömungs-vorgänge in praxisrelevanten Anordnungen liefern können. Betrachtet man für die industriellen Anwendungen realistische Parameterbereiche liefern diese Wassermodelle liefern allerdings oft falsche Ergebnisse und sind völlig wertlos für Untersuchungen zur elektromagnetischen Strömungskontrolle.
Keywords: electromagnetic flow control, investment casting, bubble plume, solidification
  • Poster
    MCWASP Conference, Modeling of Casting, Welding and Advanced Solidification Processes XI, 29.05.-02.06.06, Opio, France

Permalink: https://www.hzdr.de/publications/Publ-8498
Publ.-Id: 8498


Myocardial extraction and subcellular distribution of new types of technetium-labeled fatty acids
Mirtschink, P.; Stehr, S. N.; Heintz, A.; Pexa, A.; Wunderlich, G.; Walther, M.; Pietzsch, H.-J.; Spies, H.; Jung, C.; Kraus, W.; Kropp, J.; Deussen, A.;
SPECT- images performed with radiolabeled fatty acids (FA) allow detailed studies about the heart function, because flow and metabolism are represented. Up to now, only 123iodinated FA are available for myocardial viability diagnostics in some parts of the world, but the application is limited due to serious disadvantages: first, the expensive production of pure 123I requires a cyclotron and second, the radiolabeled FA compounds must be purchased by outside vendors which resulted in disproportional costs and logistical problems. 99mTc, has ideal physical properties for SPECT-imaging (Eγ-= 140 keV), a short half- life of 6 h, and is available through a 99Mo/99mTc generator whenever needed. The development of 99mTc- labeled FA has been a goal of various research groups in the past. Despite many different approaches, no appropriate 99mTc compound with similar myocardial extraction properties as found with BMIPP and DMIPP is available to date. Most previous work in this field has focused on radiometal coordination by use of a polar tetradentate N2S2 chelate with a central oxometal(V) core. We concentrated on the development and experimental evaluation of alternative coordination moieties according to the ‘4+1’ mixed ligand approach to create newly technetium labeled FA with an improved myocardial profile. In the ‘4+1’ donor atom arrangement, 99mTc is coordinated by both a tetradentae ligand and by a monodentate bearing the FA moiety. This system is rather lipophilic and show high stability towards, e.g. challenging SH-agents. While the conventional ‘4+1’ 99mTc FA are built on in the sequence Tc-chelate, alkyl chain (a), carboxyl group (c) ->(Tc-a-c) we also developed and investigated some compounds with a new design according to the sequence carboxyl group (c), alkyl chain, Tc chelate, lipophilic tail (lt) -> (c – a – Tc – lt), transferring the 99mTc chelate from the end- to a more central position of the compound.
  • Lecture (Conference)
    ESRR'06 - European Symposium on Radiopharmacy and Radiopharmaceuticals, 30.03.-02.04.2006, Lucca, Italy
  • Abstract in refereed journal
    Quarterly Journal of Nuclear Medicine and Molecular Imaging 50(2006)Suppl 1, 20-21

Permalink: https://www.hzdr.de/publications/Publ-8497
Publ.-Id: 8497


Experimental and numerical studies of void fraction distribution in rectangular bubble columns
Krepper, E.; Reddy Vanga, B. N.; Zaruba, A.; Prasser, H.-M.; Lopez De Bertodano, M.;
Bubbly flow is encountered in a wide variety of industrial applications ranging from flows in nuclear reactors to process flows in chemical reactors. The presence of a second phase, recirculating flow, instabilities of the gas plume and turbulence, complicate the hydrodynamics of bubble column reactors.
This paper describes experimental and numerical results obtained in a rectangular bubble column 0.1 m wide and 0.02 m in depth. The bubble column was operated in the dispersed bubbly flow regime with gas superficial velocities up to 0.02 m/s. Images obtained from a high speed camera were used to observe the general flow pattern and have been processed to calculate bubble velocities, bubble turbulence parameters and bubble size distributions. Gas disengagement technique was used to obtain the volume averaged gas fraction over a range of superficial gas velocities. A wire mesh sensor was applied, to measure the local volume fraction at two different height positions. Numerical calculations were performed with an Eulerian-Eulerian two-fluid model approach using the commercial code CFX.
The paper details the effect of various two-fluid model interfacial momentum transfer terms on the numerical results. The inclusion of a lift force was found to be necessary to obtain a global circulation pattern and local void distribution that was consistent with the experimental measurements. The nature of the drag force formulation was found to have significant effect on the quantitative volume averaged void fraction predictions.
Keywords: Bubble column, experiments, wire mesh sensor, high speed video camera CFD, drag bubble forces, non-drag bubble forces

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Publ.-Id: 8496


Reconstruction and Corrections in In-Beam PET
Shakirin, G.;
The talk was given during the Siemens In-Beam PET workshop 9-10 May 2006 at OnkoRay, Dresden. The achievements and issues in reconstruction procedure of in-beam PET data were discussed
Keywords: in-beam PET, reconstruction
  • Lecture (Conference)
    Scientific Workshop - In-Beam PET, 09.-10.05.2006, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-8495
Publ.-Id: 8495


PET and photon therapy
Möckel, D.;
Challenges for in-beam PET at hard photon beams
Keywords: In-beam PET, hard photons
  • Lecture (Conference)
    Scientific Workshop for In-Beam PET, 09.-10.05.2006, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-8494
Publ.-Id: 8494


Mikrostrukurelle Mechanismen der Strahlenversprödung
Altstadt, E.; Böhmert, J.; Ulbricht, A.; Borodin, V. A.; Ganchenkova, M.; Voskoboinikov, R.;
Gegenstand des Vorhabens im Rahmen der WTZ mit Russland ist die Versprödung des Reaktordruckbehälters infolge der Strahlenbelastung mit schnellen Neutronen im kernnahen Bereich.
Um den Einfluss von bestrahlungsinduzierten Gitterdefekten auf die mechanischen Eigenschaften zu ermitteln, wurden analytische Berechnungen zum Einfluss von Hindernissen auf die Beweglichkeit von Versetzungen und damit auf die Ausbildung einer plastischen Zone an der Rissspitze durchgeführt. Es wird demonstriert, dass sich die an der Rissspitze entstehenden Versetzungen an dem Hindernis (bestrahlungsinduzierte Punktdefekte) aufstauen. In Abhängigkeit der Rissbelastung KI und der Entfernung des Hindernisses von der Rissspitze werden die Versetzungsdichte und das durch den Versetzungsstau verursachte Spannungsfeld berechnet.
Mit Hilfe von Experimenten zur Neutronenkleinwinkelstreuung (SANS – small angle neutron scattering) an verschiedenen WWER-Stählen und Modelllegierungen wurden Größenverteilungen und die Volumenanteile der strahleninduzierten Defekte für verschiedene Bestrahlungszustände (Fluenzen, Bestrahlungstemperaturen) ermittelt. Es wurde gezeigt, dass sich die strahleninduzierte Werkstoffschädigung durch Wärmebehandlung weitgehend wieder ausheilen lässt. Nach der thermischen Ausheilung ist der Werkstoff bei erneuter Bestrahlung weniger anfällig für strahleninduzierte Defekte. Die Ergebnisse der SANS-Untersuchungen wurden mit der Änderung der mechanischen Eigenschaften (Härte, Streckgrenze und Sprödbruchübergangstemperatur) korreliert.
Mit der kinetischen Gitter-Monte-Carlo-Methode wurden numerische Sensitivitätsstudien zum Einfluss des Cu-Gehalts auf die Stabilität von Defekt-Clustern durchgeführt. Die Berechnungen zeigen, dass die Anwesenheit von Cu-Atomen zur Bildung von langlebigen Defekten führt. Dabei werden Leerstellen in Cu/Leerstellen-Cluster eingefangen. Leerstellen in reinem Eisen sind bei Bestrahlungstemperaturen von 270 °C dagegen nicht stabil, die Lebensdauer liegt zwischen 0.01 s und 1 s. Die kritische Cu-Konzentration, ab welcher stabile Defekte entstehen, beträgt ca. 0.1 Masseprozent.
Keywords: Reactor pressure vessel, Irradiation induced embrittlement, Small angle neutron scattering, Defect cluster, Dislocation, Monte Carlo Simulation, VVER reactors
  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-452 2006

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Publ.-Id: 8493


Primary photoluminescence in as-neutron (electron)-irradiated n-type 6H-SiC
Zhong, Z. Q.; Wu, D. X.; Gong, M.; Wang, O.; Shi, S. L.; Xu, S. J.; Chen, X. D.; Ling, C. C.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Skorupa, W.;
Low-temperature photoluminescence spectroscopy has revealed a series of features labeled S1, S2, S3 in n-type 6H-SiC after neutron and electron irradiation. Thermal annealing studies showed that the defects S1, S2, S3 disappeared at 500 °C. However, the well-known D1 center was only detected
for annealing temperatures over 700 °C. This experimental observation not only indicated that the defects S1, S2, S3 were a set of primary defects and the D1 center was a kind of secondary defect, but also showed that the D1 center and the E1, E2 observed using deep level transient spectroscopy
might not be the same type of defects arising from the same physical origin.

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Publ.-Id: 8492


Study of the solubility of amorphous and crystalline uranium dioxide by combined spectroscopic methods
Opel, K.; Weiß, S.; Hübener, S.; Zänker, H.; Bernhard, G.;
Colloid formation and solubility of U(IV) in acidic HClO4/NaClO4 solutions are investigated by coulometric titration. Quantification of traces of U(VI) by laser fluorescence spectroscopy proves that the tetravalent state of uranium had been maintained. Laser-induced breakdown detection (LIBD) is applied for the detection of traces of uranium colloids as the pH is increased. The pH values at the onset of colloid formation are used for thermodynamic calculations aimed at determining the solubility products Ksp0 of crystalline and amorphous uranium dioxides. The particle size of the colloids determined by means of LIBD is taken into account since it influences the solubility product. The results indicate the formation of crystalline UO2(cr) at low pH ~ 1 (log Ksp0 = 59.6 ± 1.0) whereas the amorphous hydrous oxide UO2·xH2O(am) is formed at pH ~ 3 (log Ksp0 = -54.4 ± 1.0). Measurements by EXAFS, XRD and REM confirm the occurrence of these different modifications. The obtained solubility products fit well in the known series of solubility products of the other tetravalent actinides.
Keywords: Uranium dioxide, solubility product, colloids, laser-induced breakdown detection
  • Radiochimica Acta 95(2007)3, 143-149

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Publ.-Id: 8491


Photovoltaic plants in Saxony: Development, status and perspectives
Rindelhardt, U.; Schlegel, H.-J.;
Purpose
The development and the perspectives of photovoltaic plants (PVP) in Saxony will be described. The development reflects the effects of the different funding instruments as well as the technical progress which has been made during the past 15 years.

Funding as accelerator
The first large step in the PVP installation in Saxony was done with the German 1000-Roofs-Program between 1991 and 1995. In the frame of this program the first 150 PVP were installed with a total power of 450 kW (see Fig.1). A new high light was set when the 100.000-Roofs-Program came into force. More than 450 PVP with a total power of 1,5 MW were connected to the grid. With the EEG (Renewable Energy Act) this development was continued. Starting with 2004 also Megawatt PVP were put into operation, the PVP Espenhain (5 MW power) belongs also today to the world largest PVP.

Technical development
The first PVPs reflect the technical level of the early nineties. The power was limited to 5 kW, and the DC-voltage was restricted to 140 V. Beginning with the year 2000 the mean power of the PVP has been clearly increased. Sonny Boy is the dominating inverter type (with a share of more than 50 %), but the module types vary strongly. An increase in the mean module power has been certainly observed.

Some operation results
A mean annual yield of 750 kWh/kW was found for the first generation of PVP, which was influenced by the low quality of some module types. New systematic monitoring programs were started in 2000. These investigations allowed the evaluation of new built PVP (yields up to 1000 kWh/KW, Fig. 2), but also the long time behaviour of the older PVP could be observed (Figs. 3 and 4).

Conclusions
The development generally confirms the politically decisions for PV funding in Germany. It could be proofed, that new PVPs in Saxony with optimal design and components, respectively, can generate up to 950 kWh/kW in an "average" year.
Keywords: PV plants, Saxony
  • Contribution to proceedings
    21th European Photovoltaic Solar Energy Conference and Exhibition, 04.-08.09.2006, Dresden, Germany
    Proceedings, ISBN 3-936338-20-5, 2719-2722
  • Poster
    21th European Photovoltaic Solar Energy Conference and Exhibition, 04.-08.09.2006, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-8490
Publ.-Id: 8490


Irradiance maps applied for the performance assessment of PV-Systems- a case study for the German federal state of Saxony
Beyer, H. G.; Drews, A.; Rindelhardt, U.;
For the estimation of the expected annual energy gain and the month by month check of the system performance, methods based on irradiance maps published by weather services, both general or dedicated to solar energy application, are in use. Examples for this type of information for Germany are annual and monthly irradiance maps published by the German weather service DWD or the data bank of hourly irradiance data with continuous spatial coverage prepared by the University of Oldenburg and offered as commercial service by the company Meteocontrol. The DWD maps are derived from both, satellite images and ground measurements and are given with a spatial resolution of 1km x 1km. The Oldenburg data bank is basically derived from satellite data only (resolution ~ 5km x 5km), although an option for amelioration by ground station data exists.
To assess the validity of these data sets for the aforementioned tasks, a case study for a region covering the German federal state of Saxony is performed, using data for the years 2004-2005.
Saxony is characterised by a wide variety of topographical features, ranging from flat relief to highly structured mountainous terrain. For this region an independent high quality ground data set given by a dense network operated for agro-meteorological purposes is available. An assessment of the end use accuracy of the irradiance data can by done via a set of monthly yield data of grid connected PVsystems.
The comparison of information on radiation sums is on one hand performed by the monthly analysis of the bias and the rms-error for the data bank versus the ground station data. On the other hand, the quality of the information on the spatial structure of the radiation field that is extractable from the data banks is analysed via the inspection of the a co- and cross-variograms.
For the assessment of the end use accuracy of the data, procedures to derive an estimation of the system yield from irradiance data as developed by the PVSAT2 project are applied for the Oldenburg data set.
A first impression of the reliability of the map data is given by the inter comparison of the annual maps for the year 2004. This shows deviations of up to 40 kWh/m², which presents an relative error of about 4%. Besides a systematic bias of about 20 kWh/m² in favour the Oldenburg data, remarkable differences in the spatial structure of the irradiance field concerning the homogeneity/inhomogeneity within some regions occur.
Thus, to pin down the reliability of the content of the maps it has to be compared to the ground data.
For the Oldenburg data it can be stated that even having a quite low bias for each station on an annual scale, monthly sums can deviate by up to 40%, especially for the winter months. This finding is coherent with the results of the PVSAT project, indicating the general increase of the uncertainties of satellite based estimates in months with low radiation sums.
Concerning the annual end use accuracy, a typical deviation of ? 5% for the estimated annual energy gain of a set PV-systems - chosen for their excellent yield figures - can be stated. Regarding the fact, that the system simulation is base on data sheet information rather than system specific parameters, this result is quite satisfactory. However, as expected remarkable relative deviation for the winter
months are hidden by these annual figures which are dominated by the PV gain in the summer months.
Using the respective results of for sets of both 2004 and 2005 general conclusions on the uncertainties connected to the use of state of the art irradiance information in view of PV application can be draw.
Keywords: photovoltaic, system performance, irradiance maps
  • Contribution to proceedings
    21th European Photovoltaoc Solar Energy Conference and Exhibition, 04.-08.09.2006, Dresden, Germany
    Proceedings, 3-936338-20-5, 2756-2760
  • Poster
    21th European Photovoltaic Solar Energy Conference and Exhibition, 04.-08.09.2006, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-8489
Publ.-Id: 8489


Amorphisation at heterophase interfaces
Gemming, S.; Enyashin, A.; Schreiber, M.;
Heterophase interfaces are boundaries, which join two material types with different physical and chemical nature. Therefore, heterophase interfaces can exhibit a large variety of geometric morphologies ranging from atomically sharp boundaries to gradient materials, in which an interface-specific phase is formed, which provides a continuous change of the structural parameters and thus reduces elastic strains and deformations.

In addition, also the electronic properties of the two materials may be different, e.g. at boundaries between an electronically conducting metal and a semiconductor or an insulating material. Due to the deviations in the electronic structure, various bonding mechanisms are observed, which span the range from weakly interacting systems to boundaries with strong, directed bonding and further to reactively bonding systems which exhibit a new phase at the interface. Thus, both elastic and electronic factors may contribute to the formation of a new, often amorphous phase at the interface. Numerical simulations based on electronic structure theory are an efficient tool to distinguish and quantify these different influence factors, and massively parallel computers nowadays provide the required numerical power to tackle structurally more demanding systems. Here, this power has been exploited by the parallelisation over an optimised set of integration points, which split the solution of the Kohn-Sham equations into a set of matrix equations with equal matrix sizes. In this way, the analysis and prediction of material properties at the nanoscale has become feasible.
Keywords: interface, wetting, density-functional, electronic structure, silicon, Si, titanium, Ti
  • Contribution to external collection
    Karl Heinz Hoffmann, Arnd Meyer: Parallel Algorithms and Cluster Computing - Lecture Notes in Computational Science and Engineering, Berlin - Heidelberg - New York: Springer, 2006, 3-540-33539-0, 235-254

Permalink: https://www.hzdr.de/publications/Publ-8488
Publ.-Id: 8488


Li-doped Mo6S6 nanowires: elastic and electronic properties
Gemming, S.; Seifert, G.; Vilfan, I.;
Isolated and crystalline Mo6S6 nanowires, doped with Li to form Li2Mo6S6, are investigated with the density-functional techniques. We find that Li atoms "decorate" individual wires at the S-coordinated sites and occupy the interstitial positions between 3 S atoms in crystalline nanowires.
Doping with Li changes the lattice constants by less than 0.1 Angstrom, but it decreases the modulus of elasticity along the wire axis in the crystalline form. Doping raises the Fermi energy but retains the strongly uniaxial metallic character of nanowires, attributed to the Mo(4d) electrons.
Keywords: Nanowires, mechanical properties, electronic properties, density functional theory

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C28 fullerites - structure, electronic properties and intercalates
Enyashin, A.; Gemming, S.; Heine, T.; Seifert, G.; Zhechkov, L.;
Mechanical and electronic properties of hypothetical carbon nanostructures, on the basis of C28 building blocks, hyperdiamond and hyperlonsdaleite, have been investigated by DFT-based methods. The low mass density and large internal surface suggest applications as catalyst, nanosieve and ga storage material. We estimate the active volume accessible by H2. Special emphasis is given to tune the properties by endo- and exohedral intercalation with Zn, Ti, and K. While endohedral intercalation with Zn does not affect the overall structure, endohedral Ti intercalation has different consequences on the structural stability of the two allotropes. Exohedral intercalation with K leads to an ionic fullerite phase with metallic conductivity.
Keywords: fullerenes, intercalates, hydrogen storage, electronic structure
  • Physical Chemistry Chemical Physics 8(2006)28, 063AN

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Investigations on the stability of the flow characteristics in a bubble column
Lucas, D.; Krepper, E.; Prasser, H.-M.; Manera, A.;
The role of the lift force for the stability of the homogeneous flow regime in a bubble column is investigated. Instabilities caused by the lift force may be one important reason for the transition from homogeneous to heterogeneous bubble column. The lift force acts on rising bubbles in lateral direction, when gradients of the liquid velocity are present. Such gradients may result from circulation cells in the bubble column as well as from local disturbances. Depending on the sign of the lift force such local disturbances in a homogeneous flow may be damped or enhanced. The corresponding feedback mechanism was analysed by means of a linear stability analyses. In the result criteria for stability were obtained for mono-dispersed flow, for a with two bubble size groups and finally with some additional approximations also for the case of N bubble size groups or a given bubble size distribution. In a next step the effects were investigated by CFD calculations. The obtained criteria for stability fit well together with the observed effects in CFD simulations. Recently two different groups confirmed the stability criteria experimentally.
Keywords: Bubble column, stabilty, lift force, CFD
  • Chemical Engineering & Technology 29(2006)9, 1066-1072

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The electrical properties of heavily Al-implanted, nanocrystalline and single crystalline SiC layers
Heera, V.; Madhusoodanan, K. N.; Skorupa, W.; Dubois, C.; Romanus, H.;
The electrical properties of heavily Al doped (5x1019 – 1.5x1021 cm-3) single and nanocrystalline 4H-SiC layers on semi-insulating 4H-SiC substrate, prepared by multi-energy, high-fluence Al implantation and subsequent furnace annealing, are investigated by sheet resistance and Hall effect measurements. The reliability of recent results on enhanced acceptor activation in heavily Al doped, nanocrystalline SiC on conductive substrate is evaluated by direct comparison with doped SiC layers on semi-insulating substrate.
Keywords: SiC, p-type doping, Hall effect measurement
  • Poster
    SiC Rundgespräch 2006, 17.-18.07.2006, Kloster Banz, Staffelstein, Deutschland

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Publ.-Id: 8483


The integral equation approach to kinematic dynamo theory and its application to dynamo experiments in cylindrical geometry
Xu, M.; Stefani, F.; Gerbeth, G.;
The conventional magnetic induction equation that governs hydromagnetic dynamo action is transformed to an equivalent integral equation system. An advantage of this approach is that the computational domain is restricted to the region occupied by the electrically conducting fluid and to its boundary. This integral equation approach is applied to simulate kinematic dynamos within cylindrical geometry including the von Karman sodium (VKS) experiment and the Riga dynamo experiment. A modified version of this approach is utilized to investigate magnetic induction effects under the influence of externally applied magnetic fields. The computed induced magnetic fields for the VKS experiment show a satisfactory agreement with the experimental results.
  • Contribution to proceedings
    ECCOMAS CFD 2006, European Conference on Computational Fluid Dynamics, 05.-08.09.2006, Egmond aan Zee, The Netherlands
    Proceedings paper 497, Delft: TU Delft, 90-9020970-0
  • Journal of Computational Physics 227(2008), 8130-8144

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Publ.-Id: 8482


Reducing the impurity incorporation from residual gas by ion bombardment during high vacuum magnetron sputtering
Rosen, J.; Widenkvist, E.; Larsson, K.; Kreissig, U.; Mraz, S.; Martinez, C.; Music, D.; Schneider, J. M.;
The influence of ion energy on the hydrogen incorporation has been investigated for alumina thin films, deposited by reactive magnetron sputtering in an Ar/O2/H2O environment. Ar+ with an average kinetic energy of ~5 eV was determined to be the dominating species in the plasma. The films were analyzed with x-ray diffraction, x-ray photoelectron spectroscopy, and elastic recoil detection analysis, demonstrating evidence for amorphous films with stoichiometric O/Al ratio. As the substrate bias potential was increased from –15 V (floating potential) to –100 V, the hydrogen content decreased by ~70%, from 9.1 to 2.8 at.%. Based on ab initio calculations, these results may be understood by thermodynamic principles, where a supply of energy enables surface diffusion, H2 formation, and desorption [Rosén et al., J. Phys.: Condens. Matter 17, L137 (2005)]. These findings are of importance for the understanding of the correlation between ion energy and film composition and also show a pathway to reduce impurity incorporation during film growth in a high vacuum ambient.
Keywords: Magnetron sputtering; thin films; impurities; hydrogen
  • Applied Physics Letters 88(2006), 191905

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Publ.-Id: 8481


Intense terahertz radiation from a large-area photoconductive device.
Dreyhaupt, A.; Winnerl, S.; Dekorsy, T.; Helm, M.;
We present an approach of photoconductive terahertz (THz) generation providing a broad bandwidth and exceptional electric field amplitude. A large-area interdigitated two-electrode structure is applied to a GaAs substrate to offer high electric fields. Photocarriers excited by a Ti:Sapphire oscillator laser with MHz repetition rate are accelerated there, yielding an intense THz output. An appropriate binary mask covers every second electrode interval and carriers are excited in uniform electric field areas only. Hence contrary carrier acceleration and destructive interference is avoided. Due to the periodic nature of the electrode structure, the size of the excitation spot on the photoconductive THz emitter can be varied. This results in a THz beam of variable divergence. By electro-optic sampling the THz radiation is detected and characteristic properties of the THz source are measured. For an excitation spot diameter of about 300 μm, which corresponds to the central wavelength of the THz pulses, the THz generation is most efficient. THz radiation with an average power of 145 µW is generated with an efficiency of 2 × 10^-4 for the conversion from NIR to THz power. Furthermore, the THz radiation has excellent focusing properties. A Gaussian beam profile with a diameter (FWHM) of less than 1.4 of the central wavelength of the THz pulses is found. The THz field amplitude in the center of the focused THz beam is 1.5 kV/cm, which is almost one order of magnitude more of what is achieved with conventional semi-large aperture photoconductive emitters and a similar excitation spot diameter. Exceptionally large signal-to-noise ratios are achieved by modulating the bias voltage in the kHz range and using lock-in technique. We suggest that the THz power can be further improved by a sufficient cooling system, e.g. water cooling. Furthermore the use of LT GaAs instead of semiinsulating GaAs can result in larger THz bandwidth.
Keywords: optical, infrared (IR) spectroscopy, photoconductivity
  • Lecture (Conference)
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-8480
Publ.-Id: 8480


The flow structure of a bubble-driven liquid metal jet in a horizontal magnetic field
Zhang, C.; Eckert, S.; Gerbeth, G.;
Static magnetic fields are known to be suitable for damping mean flow and turbulent motion in an electrically conducting liquid. In this paper, an experimental study is presented considering the influence of a horizontal magnetic field on a bubble-driven flow of a liquid metal. The investigation is focused on the liquid circulation inside a liquid metal column driven by a central jet produced by gas injection. The fluid vessel has a circular cross section and electrically insulating walls. Low gas flow rates were applied resulting in a plume of separated bubbles rising inside a spot around the cylinder axis. This axisymmetric configuration is exposed to a horizontal magnetic field. We present detailed experimental data describing the spatial as well as the temporal structure of the velocity field. Measurements of the vertical and the radial velocity component, respectively, were performed using the ultrasound Doppler velocimetry (UDV) allowing for the first time a complete mapping of the liquid velocity distribution for a bubble-driven liquid metal flow. The magnetic field considerably modified the global and local properties of the flow field compared to an ordinary bubble plume. In the parameter range considered here we did not find a prior flow suppression, but, in fact, a restructuring of the convective motion. The original axisymmetric flow field became anisotropic with respect to the direction of the magnetic field lines. An upwards flow dominated in a plane parallel to the magnetic field, whereas the recirculating motion was enforced in the orthogonal plane. Contrary to usual expectations, the application of a moderate magnetic field (100 < Ha < 400, 1 < N < 10) destabilizes the global flow and gives rise to transient, oscillating flow pattern with predominant frequencies.
Keywords: Gas-liquid flow, Bubble plume, Liquid metal, MHD turbulence, UDV velocity measurement
  • Journal of Fluid Mechanics 575(2007), 57-82

Permalink: https://www.hzdr.de/publications/Publ-8479
Publ.-Id: 8479


Nonmagnetic to magnetic nanostructures via ion irradiation
Dev, B. N.; Bera, S.; Satpati, B.; Goswami, D. K.; Bhattacharjee, K.; Satyam, P. V.; Yamashita, K.; Liedke, M. O.; Potzger, K.; Fassbender, J.ORC; Eichhorn, F.; Grötzschel, R.
A Pt/C multilayer stack (15 layer-pairs) with Fe impurities was prepared on a glass substrate by the ion sputtering technique. Ion irradiation effects on this multilayer were studied following irradiation with 2 MeV Au ions at fluences from 1 · 1014 to 1 · 1015 ions/ cm2. Irradiation induced atomic displacements in such multilayers have been earlier analyzed by a combined X-ray standing wave (XSW) and X-ray reflectivity (XRR) technique with a depth resolution better than 0.2 nm [S.K. Ghose, B.N. Dev, Phys. Rev. B 63 (2001) 245409; S.K. Ghose, D.K. Goswami, B. Rout, B.N. Dev, G. Kuri, G. Materlik, Appl. Phys. Lett. 79 (2001) 467]. Using the combined XSW-XRR technique ion beam induced preferential movement of Fe from C- to Pt-layers has been detected. At the highest ion fluence Pt layers (containing Fe) break into nanoparticles apparently surrounded by C. Grazing incidence X-ray diffraction (GIXRD) measurements indicate the formation of FePt particles in the irradiated multilayer samples. Results of magnetic force microscopy (MFM) and magneto-optical Kerr effect (MOKE) measurements reveal that while the virgin sample hardly shows any magnetism, the irradiated samples show a soft ferromagnetism with an increasing coercive field with increasing ion fluence. Use of focused ion beam to fabricate ferromagnetic nanodots and their possible uses in spin electronics are discussed.
Keywords: magnetism, ion irradiation
  • Microelectronic Engineering 83(2006), 1721

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Secondary structure and Pd(II) coordination in S-layer proteins from Bacillus sphaericus studied by infrared and X-ray absorption spectroscopy
Fahmy, K.; Merroun, M.; Pollmann, K.; Raff, J.; Savchuk, O.; Hennig, C.; Selenska-Pobell, S.;
The S-layer of Bacillus sphaericus strain JG-A12, isolated from a uranium-mining site, exhibits a high metal-binding capacity, indicating that it may provide a protective function by preventing the cellular uptake of heavy metals and radionuclides. This property has allowed the use of this and other S-layers as self-assembling organic templates for the synthesis of nano-sized heavy metal cluster arrays. However, little is known about the molecular basis of the metal protein interactions and their impact on secondary structure. We have studied the secondary structure, protein stability, and Pd(II) coordination in S-layers from the B. sphaericus strains JG-A12 and NCTC 9602 to elucidate the molecular basis of their biological function and of the metal nanocluster growth. Fourier-transform IR-spectroscopy reveals similar secondary structures, containing ~35 % -sheets and little helical structure. pH-induced IR absorption changes of the side chain carboxylates evidence a remarkably low pK < 3 in both strains and a structural stabilisation when Pd(II) is bound. The COO--stretching absorptions reveal a predominant Pd(II)-coordination by chelation / bridging by Asp and Glu residues. This agrees with XANES and EXAFS data revealing oxygens as coordinating atoms to Pd(II). The additional participation of nitrogen is assigned to side chains rather than to the peptide backbone. The topology of nitrogen- and carboxyl-bearing side chains appears to mediate heavy metal-binding binding to the large number of Asp and Glu in both S-layers at particularly low pH as an adaptation to the environment from which the strain JG-A12 has been isolated. These side chains are thus prime targets for the design of engineered S-layer-based nanoclusters.
Keywords: metal binding, FTIR, XANES, EXAFS, nanocluster

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Publ.-Id: 8477


Investigation of chemical and grain boundary effects in highly ordered Sr2FeMoO6: XPS and Mössbauer studies
Raekers, M.; Kuepper, K.; Hesse, H.; Balasz, I.; Deac, I. G.; Constantinescu, S.; Burzo, E.; Valeanu, M.; Neumann, M.;
We have studied the oxidation states of Fe and Mo and the presence of grain boundaries in the magneto resistive (MR) compounds Sr2FeMoO6 by means of x-ray photoelectron spectroscopy (XPS), Mössbauer spectroscopy and electrical resistivity measurements. XPS of the Mo 3d and Fe 3s core levels is indicating a mixed valence state involving around 30% Fe3+- Mo5+ and 70% Fe2+- Mo6+ states. Mössbauer studies confirm the presence of a valence fluctuation state and an essential amount of grain boundaries in the present Sr2FeMoO6 crystals. Resistivities and magnetoresistance studies evidenced strong grain boundary effects.
Keywords: Sr2FeMoO6, Double perovskite, Magnetoresistance, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, Electrical resistivity
  • Journal of Optoelectronics and Advanced Materials 8(2006)2, 455-460

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Publ.-Id: 8476


Prediction of the evolution of the dispersed phase in bubbly flow problems
Dorao, C. A.; Lucas, D.; Jakobsen, H. A.;
For modeling multi-phase where the disperse phase play a major role for determining the flow structure and inter phase transfer quantities, the size distribution of the particles has to be considered. This can be done by extension of the mass balance equation to a population balance equation. In this work, a least squares spectral method is tested for predicting the evolution of the disperse phase in a vertical two phases bubbly flow. The least squares spectral method consists in minimizing the L2 norm of the residual over the simulation domain. The results are compared with experimental data obtain for two different initial bubble distribution.
Keywords: Two Phase Flow; Vertical Pipe Flow, Bubbly Flow, Population; Balance Equation; Least Squares Spectral Method

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Ion beam induced magnetic property modifications
Fassbender, J.ORC
In recent years the tailoring of magnetic properties by means of ion irradiation techniques has become fashionable. Since the magnetic properties of magnetic multilayers depend sensitively on the mutual interfaces a modification of these interfaces by light ion irradiation leads to a local modification of the magnetic anisotropy, the exchange bias or the interlayer exchange coupling [1]. As an example it will be demonstrated that ion irradiation in an applied magnetic field allows to set the uniaxial anisotropy direction on a micrometer scale in the case of soft magnetic alloys [2]. However, in order to modify the structural and magnetic properties not only light ion irradiation but also ion implantation doping can be used. If, for example, Cr is implanted in thin Permalloy films the Curie temperature and the saturation magnetization can be reduced, which consecutively leads to a decrease of the magnetic anisotropy and an increase of the magnetic damping behavior [3]. The formation of magnetically dead layers at the interfaces to buffer and cap layers can be investigated using Ni implantation [4].
In an alternative route to design magnetic properties periodically modulated substrates are employed. These modulated substrates are created by means of low energy ion erosion. A ripple structure with a typical periodicity of 30 – 50 nm and a ripple height of about 2 nm is created on a Si substrate. Subsequently deposited Permalloy films exhibit a uniaxial anisotropy which is about a factor of 20 larger than conventionally prepared films. If exchange bias bilayers are deposited the interplay between the unidirectional and the ripple-induced uniaxial anisotropy contributions can be investigated.


[1] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
[2] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
[3] J. Fassbender, J. von Borany, A. Mücklich, K. Potzger, W. Möller, J. McCord, L. Schultz, R. Mattheis, Phys. Rev. B, in press.
[4] J. Fassbender, J. McCord, Appl. Phys. Lett., in press.
Keywords: magnetism, magnetic properties, ion irradiation, ion implantation, ripples
  • Lecture (others)
    Seminarvortrag, 06.06.2006, Halle, Deutschland
  • Lecture (others)
    Seminarvortrag Universitaet Goettingen, 08.12.2006, Goettingen, Deutschland
  • Invited lecture (Conferences)
    Workshop on "Ion beam processing and magnetic properties of semiconductors", 13.02.2007, Leuven, Belgien

Permalink: https://www.hzdr.de/publications/Publ-8474
Publ.-Id: 8474


Tailoring magnetic properties by ion beams
Fassbender, J.ORC
In recent years the tailoring of magnetic properties by means of ion irradiation techniques has become fashionable. Since the magnetic properties of magnetic multilayers depend sensitively on the mutual interfaces a modification of these interfaces by light ion irradiation leads to a local modification of the magnetic anisotropy, the exchange bias or the interlayer exchange coupling [1]. As an example it will be demonstrated that ion irradiation in an applied magnetic field allows to set the uniaxial anisotropy direction on a micrometer scale in the case of soft magnetic alloys [2]. However, in order to modify the structural and magnetic properties not only light ion irradiation but also ion implantation doping can be used. If, for example, Cr is implanted in thin Permalloy films the Curie temperature and the saturation magnetization can be reduced, which consecutively leads to a decrease of the magnetic anisotropy and an increase of the magnetic damping behavior [3]. The formation of magnetically dead layers at the interfaces to buffer and cap layers can be investigated using Ni implantation [4].
In an alternative route to design magnetic properties periodically modulated substrates are employed. These modulated substrates are created by means of low energy ion erosion. A ripple structure with a typical periodicity of 30 – 50 nm and a ripple height of about 2 nm is created on a Si substrate. Subsequently deposited Permalloy films exhibit a uniaxial anisotropy which is about a factor of 20 larger than conventionally prepared films. If exchange bias bilayers are deposited the interplay between the unidirectional and the ripple-induced uniaxial anisotropy contributions can be investigated.


[1] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
[2] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
[3] J. Fassbender, J. von Borany, A. Mücklich, K. Potzger, W. Möller, J. McCord, L. Schultz, R. Mattheis, Phys. Rev. B, in press.
[4] J. Fassbender, J. McCord, Appl. Phys. Lett., in press.
Keywords: magnetism, magnetic properties, ion irradiation, ion implantation, ripples
  • Lecture (Conference)
    Ionenstrahlphysik und Nanotechnologie, 16.-17.05.2006, Berlin, Deutschland

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Publ.-Id: 8473


Comparative characterization of differently grown ZnO single crystals by positron annihilation and Hall effect
Brauer, G.; Anwand, W.; Skorupa, W.; Kuriplach, J.; Melikhova, O.; Cizek, J.; Prochazka, I.; Moisson, C.; von Wenckstern, H.; Schmidt, H.; Lorenz, M.; Grundmann, M.;
High quality ZnO single crystals of dimensions 10 x 10 x 0.3 mm3, grown either using a pressurized melt or a hydrothermal growth approach, have been investigated in their as-received state and are compared regarding their properties revealed by positron annihilation and Hall effect measurements. By positron annihilation performed at room temperature it is found that the pressurized melt grown crystals contain a certain amount of Zn+O divacancies but no Zn vacancies are detected, whereas the hydrothermally grown crystals contain a dominating defect yet unknown in its structure but maybe connected to the Zn vacancy. Furthermore, the influence of an additional refined chemical-mechanical polishing of the crystal surface by a special procedure on the depth distribution of vacancy-type defects is demonstrated. Hall measurements, performed in the temperature range 20 – 325 K, showed that the crystal growth method has a strong influence on the carrier mobility, and the estimated acceptor densities also differ significantly in both types of crystal.
Keywords: zinc oxide, point defects, positron annihilation, Hall effect
  • Contribution to proceedings
    E-MRS 2006 Spring Meeting, 29.05.-02.06.2006, Nice, France
    Superlattices and Microstructures: Elsevier
  • Lecture (Conference)
    E-MRS 2006 Spring Meeting, 29.06.-02.07.2006, Nice, France
  • Superlattices and Microstructures 42(2007), 259-264

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Tetrabutylammonium bis(2-amidobenzenethiolato-k2S,N)oxorhenate(V)
Gniazdowska, E.; Kraus, W.; Emmerling, F.; Spies, H.; Stephan, H.;
Bu4N[ReO(abt)2] was obtained via the precursor Bu4N[ReOCl4], its conversion into an ethylene glycol complex as an intermediate and subsequent ligand exchange by H2abt to form the tetrabutylammonium salt of the abt complex in 62 % yield. Elemental analysis, mass, NMR and IR spectra confirm the composition Bu4N[ReO(abt)2]. The crystal structure contains well separated ReO(NHC6H4S)2 anions and Bu4N+ counter cations. The coordinationgeometry of Re is distorted square pyramidal, with an apical Re O bond length of 1.676(5)A°.The dihedral angle between the two benzene rings is 33.75(1)°. These values do not differ
much from those of the corresponding Tc compound.

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Publ.-Id: 8471


Nanowire transformation into long-range-ordered nanocluster chains controlled by thermocapillarity
Röntzsch, L.; Heinig, K.-H.;
Capillarity-driven surface-free-energy minimization may lead to morphological changes of nanowires (NWs), e.g. their decay into chains of nanoclusters (NCs) by the Rayleigh instability. At the nano-scale, such capillary effects are more pronounced than in macroscopic systems due to the large surface-to-volume ratio. However, the capillary-driven NW decay is subject to increasing fluctuations with decreasing dimensions. This might prevent the formation of NC chains with long-range order which is needed for potential applications (e.g. in nanophotonics as light guides). We predict a novel method to fabricate long-range-ordered NC chains by decay of NWs under the control of an external temperature field. The prediction is based on the temperature dependence of surface tension causing thermocapillary effects. Surface tension gradients trigger atomic migration from hot to cold regions. Thus, long-range-order of NC chains may be achieved by a weak periodic temperature field along the NW. Such a temp. profile might be realized by a standing surface-plasmon-polariton wave. Here, a feasibility evaluation of the prediction will be presented which is based on computer experiments. The NW decay with and without external temperature fields was examined by kinetic Monte Carlo simulations. Just a small, symmetry-breaking periodic temperature field is needed to control long-range-order. In practice, the field must be stronger than thermally induced fluctuations along the NW, as is discussed.
Keywords: nanowire, Rayleigh instability, thermocapillarity, external field, long-range order, atomistic computer simulation
  • Poster
    EMRS Spring Meeting, 29.05.-02.06.2006, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-8470
Publ.-Id: 8470


Nanowire synthesis with focused ion beams: predictive atomistic simulations on the fabrication of functional nanowire structures
Röntzsch, L.; Heinig, K.-H.;
Nanowires (NWs) play an important role as basic components of electronic and photonic devices, such as interconnects or surface-plasmon propagators. Here, theoretical studies are presented on reaction pathways of the CMOS-compatible fabrication of metal silicide or semiconductor nanowires (NWs) by focused ion beam (FIB) implantation and subsequent thermal annealing. On realistic time and length scales, the simulation of the whole process is divided into two steps: (i) The spatio-temporal evolution of FIB implantation profiles is calculated by a new computer code including dynamical target changes, local ion erosion etc. The FIB implantation along a straight trace leads to a local and surface-near supersaturation in the substrate. (ii) Post-implantation annealing causes NW formation by self-organization, which is described theoretically by kinetic Monte Carlo simulations. It is demonstrated that the evolution of the FIB implantation profile proceeds in three well-separated stages: (1) Phase separation by nucleation and growth, (2) NW formation by coalescence of nanoclusters, (3) NW surface smoothening. After this evolution, a NW diameter which is several times smaller than the width of the FIB implantation trace (some tens of nanometers) is found. Likewise, components for functional devices involving several NWs, like T- or X-junctions, can be obtained by crossing different FIB traces.
Keywords: nanowire, focused ion beam, ion beam synthesis, computer simualtion, phase separation, self-organization
  • Poster
    EMRS Spring Meeting, 29.05.-02.06.2006, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-8469
Publ.-Id: 8469


Atomistic Structure of Grain Boundaries determined by first-principles Calculations and Quantitative HRTEM
Gemming, T.; Nufer, S.; Gemming, S.; Kurtz, W.; Marinopoulos, A. G.; Fabris, S.; Elsässer, C.; Rühle, M.;
A combination of transmission electron microscopy (TEM) and local density-functional theory (LDFT) is employed to analyze the microscopic structure of the rhombohedral (-1012) and the prismatic Sigma-3 (10-10) twin interfaces in alpha-alumina. LDFT provides interface energies, atomic and electronic structures for competing structure models. With high-resolution TEM the atomic structure at the interface is imaged quantitatively along two orthogonal zone axes. Electron energy loss spectroscopy in TEM yields the interfacial electronic structure with nano-scale spatial resolution. All experiments confirm the theoretically preferred model for each of the two grain boundaries quantitatively.
Keywords: interface, grain boundary, density-functional theory, DFT, calculation, electronic structure, atomic structure
  • Contribution to proceedings
    DFTEM 2006 - bringing together two communities International Conference on Density Functional Theory and Transmission Electron Microscopy, 21.-23.04.2006, Wien, Austria, Wien: Editio Amici/Physicae et chimicae solidorum amici, 3-902548-00-2, 142-145
  • Poster
    DFTEM 2006 - bringing together two communitites International Conference on Density Functional Theory and Transmission Electron Microscopy, 21.-23.04.2006, Wien, Österreich

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Publ.-Id: 8468


Inductionless magnetorotational instability in a Taylor-Couette flow with a helical magnetic field
Priede, J.; Grants, I.; Gerbeth, G.;
We consider the magnetorotational instability (MRI) of a hydrodynamically stable Taylor-Couette flow with a helical external magnetic field in the inductionless approximation defined by a zero magnetic Prandtl number (Pm=0). This leads to a considerable simplification of the problem eventually containing only hydrodynamic variables. First, we point out that the energy of any perturbation growing in the presence of magnetic field has to grow faster without the field. This is a paradox because the base flow is stable without the magnetic while it is unstable in the presence of a helical magnetic field without being modified by the latter as it has been found recently by Hollerbach and Rüdiger (Phys. Rev. Lett. {95}, 124501, 2005). We revisit this problem by using a Chebyshev collocation method to calculate the eigenvalue spectrum of the linearized problem. In this way, we confirm that MRI with helical magnetic field indeed works in the inductionless limit where the destabilization effect appears as an effective shift of the Rayleigh line. Second, we integrate the linearized equations in time to study the transient behavior of small amplitude perturbations, thus showing that the energy arguments are correct as well. However, there is no real contradiction between both facts. The linear stability theory predicts the asymptotic development of an arbitrary small-amplitude perturbation, while the energy stability theory yields the instant growth rate of any particular perturbation, but it does not account for the evolution of this perturbation. Thus, although switching off the magnetic field instantly increases the energy growth rate, in the same time the critical perturbation ceases to be an eigenmode without the magnetic field. Consequently, this perturbation is transformed with time and so looses its ability to extract energy from the base flow necessary for the growth.
  • Physical Review E 75(2007), 047303

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Publ.-Id: 8467


Synthesis of 18F-labelled biphenyls via Suzuki cross-coupling with 4-[18F]fluoroiodobenzene
Steiniger, B.; Wüst, F.;
The SUZUKI reaction of organoboron compounds with 4-[18F]fluoroiodobenzene has been developed as a novel radiolabelling technique in 18F chemistry. The cross-coupling reaction of p-tolylboronic acid with 4-[18F]fluoroiodobenzene was used to screen different palladium complexes, bases and solvents. Optimised reaction conditions (Pd2(dba)3, Cs2CO3, acetonitrile, 60 °C for 5 minutes) were further applied to the synthesis of various 18F-labelled biphenyls bearing different functional groups. The reaction proceeded in excellent radiochemical yields of up to 94 % within 5 min while showing good compatibility to many functional groups.
  • Journal of Labelled Compounds and Radiopharmaceuticals 49(2006), 817-827
    DOI: 10.1002/jlcr

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Publ.-Id: 8466


Simulation of positron distributions for carbon and proton beams
Fiedler, F.;
Challenges for further development in in-beam PET
Keywords: in-beam PET
  • Lecture (Conference)
    Scientific Workshop for In-Beam PET, 09.-10.05.2006, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-8465
Publ.-Id: 8465


Predictive process simulation of the FIB-based fabrication of metallic nanoparticle waveguides
Röntzsch, L.; Heinig, K.-H.;
Chains of metallic nanoparticles may be applied as surface-plasmonpolariton (SPP) waveguides. Moreover, nanoparticle waveguide structures with small bend radii, e.g. L-turns or beam splitting T-junctions, are of technological interest. In this contribution, we present reaction pathways of the fabrication of 1D metallic nanostructures by focused metal ion implantation and subsequent thermal treatment. Nanowires (NWs) as well as structures consisting of metallic nanoparticle chains were found. The search for reaction pathways was performed by kinetic Monte Carlo simulations including realistic focused ion beam (FIB) implantation profiles which were determined by spatially dependent dynamic ion range calculations. During annealing, buried NWs and more complex structures (e.g. T- or X-junctions) form that are embedded in the matrix along the FIB implantation trace. The diameter of the synthesized NWs is about five times smaller than the width of the FIB implantation trace. The dominating driving force of NW formation is a free energy gain by phase separation and by reduction of high interface curvatures. During longterm thermal annealing, NWs disintegrate into regular chains of nanodots because of the built-up of long-wavelength interface undulations (Rayleigh instability). Crosses, corners or ends of NWs are subject to a preferential disintegration. Thus, by choosing appropriate geometries and implantation conditions, SPP waveguides based on multiple nanodot chains, e.g. L-turns, X- or T-junctions, might be fabricated by FIB implantation. The simulations were performed for focused Co ion implantation into Si since CoSi2 might be a metallic waveguide material with several advantages: monocrystalline embedding into c-Si with coherent (and defect-free) interfaces, CMOS-compatibility, and surface plasmon resonance in the infrared where Si is transparent.
Keywords: focused ion beam, ion beam synthesis, CoSi2, kinetic Monte Carlo simulation, nanowire, waveguide, surface plasmon polaritons, phase separation
  • Poster
    MRS Spring Meeting, 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-8463
Publ.-Id: 8463


Focused-ion-beam-based synthesis of semiconductor nanowires and functional structures – an atomistic computer simulation study
Röntzsch, L.; Heinig, K.-H.;
We present reaction pathways of a novel method of semiconductor nanowire (NW) fabrication using a focused ion beam (FIB). This investigation is based on kinetic Monte Carlo simulations including realistic FIB implantation profiles which were determined by spatially dependent dynamic ion range calculations. A focused implantation of Si or Ge ions into SiO2 along a straight trace leads to local supersaturation of the implanted species in the dielectric substrate. During post-implantation annealing, semiconductor NWs embedded in the dielectric matrix form along the FIB implantation trace. Even complex structures involving several NWs, e.g. T- or X-junctions, may be obtained. The dominating driving force of NW formation is a free energy gain by phase separation and by reduction of high interface curvatures. The diameter of the synthesized NWs is about five times smaller than the width of the FIB implantation trace. During long-term thermal annealing, NWs disintegrate into regular chains of nanodots because of the built-up of long-wavelength interface undulations (Rayleigh instability). Crosses, corners or ends of NWs are subject to a preferential disintegration. Thus, structures suitable for single-electron-transistors may be realized where an isolated nanocluster is located in a tunnel distance from several NW contacts. Moreover, multi-gate NW field effect transistors may be fabricated by crossing FIB traces of different ion fluences.
Keywords: focused ion beam, ion beam synthesis, kinetic Monte Carlo simulation, nanowire, Rayleigh instability
  • Poster
    MRS Spring Meeting, 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-8462
Publ.-Id: 8462


Search for reaction pathways of a CMOS-compatible fabrication of nanofluidic channels by means of atomistic computer simulations
Röntzsch, L.; Heinig, K.-H.;
Nanofluidic devices are going to play an important role in miniaturization, automation and parallelization of chemical, biological, or medical systems. At present, the fabrication of microfluidic channel networks requires a large number of sophisticated processing steps. For "lab on a chip" devices, CMOS compatibility is desired in the fabrication process, additionally. In this contribution, we present potential reaction pathways of a nonconventional, however, CMOS-compatible fabrication method of nanofluidic channels and channel networks. The reaction pathways are predicted by Monte Carlo simulations which atomistically describe the evolution of a sample configuration during a thermal treatment. Referring to the "empty space-in-silicon" formation technique (T. Sato et al., Jnp. J. Appl. Phys. 43 (2003) 12.), a Si-(100) substrate is assumed which contains isolated trenches that are arranged in a line. This approach is modified by using trenches of different depths and diameters. During thermal treatment in a low-pressure hydrogen atmosphere, migration of surface atoms leads to an overall surface minimization. Thin trenches decouple quickly from the wafer surface forming buried voids. In a self-organizing manner, neighboring voids may coalesce and, thus, they construct a buried channel. Due to their lower surface-to-volume ratio, thick trenches are more stable. They remain in contact with the wafer surface and, therefore, they may act as vertical supply and drain pipes for the buried channels. In addition, the simulations predict the formation of elementary nanochannel networks such as T-junctions, X-junctions, or Hfilters. The channel surface of the whole active layer can be transformed into SiO2 by postfabrication oxidation.
Keywords: fluidics, silicon on nothing, channels, whormholes, fabrication, surface diffusion, Rayleigh instability
  • Poster
    MRS Spring Meeting, 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-8461
Publ.-Id: 8461


Size and position control of chains or arrays of nanoparticles by surface-plasmon-polariton-induced thermocapillarity
Röntzsch, L.; Heinig, K.-H.;
Surface free energy minimization, driven by capillary forces, may lead to morphological changes of wires (e.g. disintegration into a droplet chain which is known as Rayleigh instability) and layers (dewetting). At nano-scale dimensions, capillary effects are much more pronounced than in macroscopic systems due to the large surface-to-volume ratio. On the other hand, capillary-driven self-organization processes are subject to increasing fluctuation with decreasing dimensions, which mostly prevent the formation of regular structures with long-range order. In this contribution, we predict by means of atomistic Monte Carlo simulations a novel method to fabricate size- and position controlled 1D- and 2D-patterns of nanoparticles. Our prediction rests on the temperature dependence of surface tension – the origin of the wellknown thermocapillarity. Uncompensated forces occur due to surface temperature gradients. These forces may have considerable impact in the nanoworld, thus, leading to material transport and structure formation on short time and length scales. A surface tension gradient (also responsible for the Marangoni effect) triggers the biased migration of atoms from hot to cold regions by surface diffusion. A periodic temperature gradient on the surface of a wire or a layer may be achieved by a surface-plasmon-polariton (SPP) wave or even by a SPP wave interference pattern. For SPP excitations with long wavelengths (e.g. by a CO2 laser), sufficiently strong steady-state temperature gradients may be produced. However, pulsed operation might be necessary for shorter wavelengths. We predict by kinetic Monte Carlo simulations that the regularity of nanodroplet chains, that form during a self-organized disintegration of nanowires, might be considerably improved by SPPs. If the SPP wavelength is commensurable with the inherent Rayleigh wavelength of the nanowire disintegration, the SPP-induced temperature undulations control the Rayleigh instability. Thus, a regular and long-range order in nanodroplet size and position may be achieved. Similarly, this principle may be used for the fabrication of regular and long-range 2D nanodroplet patterns, if interference patterns of SPP waves on thin layers are achieved.
Keywords: Thermocapillarity, Rayleigh instability, nanowire, dewetting, patterning, surface plasmon polariton, kinetic Monte Carlo simulation
  • Lecture (Conference)
    MRS Spring Metting, 17.-21.04.2006, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-8460
Publ.-Id: 8460


On the stability of the boundary layer subject to a wall-parallel Lorentz force
Albrecht, T.; Grundmann, R.; Mutschke, G.; Gerbeth, G.;
The stability of a transitional boundary layer controlled by a wall-parallel, streamwise oriented Lorentz force is investigated by means of direct numerical simulation. Damping of Tollmien-Schlichting waves is observed already at weak control amplitudes.
For a particular control amplitude, similar to homogeneous suction, the initial Blasius layer evolves towards an exponential velocity profile of strongly enhanced stability. Here, intermediate velocity profiles are found to have linear stability properties superior to that of the asymptotic exponential profile. Additional 3-D simulations support the 2-D results as Lorentz force control clearly damps the coherent structures of the transitional flow.
Keywords: MHD, Control, Boundary Layer, DNS, linear stability analysis
  • Physics of Fluids 18(2006), 098103

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Publ.-Id: 8459


CFD-simulation of thermalhydraulic benchmark V1000CT2 - analysis with advanced turbulence models
Höhne, T.;
CFD calculations have been performed for the themalhydraulic benchmark V1000CT-2
The numerical grid model was generated with the grid generator IC4C (ICEM-CFD) and the preprocessor ANSYS CFX and contains 4.7 Mio. tetrahedral elements
Different advanced turbulence models were used in the numerical simulation
The best agreement with the Kozloduy experiment at the core inlet shows the DES simulation. Strong fluctuations occur in the downcomer of the RPV.
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%
Keywords: PWR, VVER-1000, CFD
  • Lecture (Conference)
    V1000CT4 Workshop, 24.-29.04.2006, Pisa, Italy
  • Contribution to proceedings
    V1000CT4 Workshop, 24.-29.04.2006, Pisa, Italy

Permalink: https://www.hzdr.de/publications/Publ-8458
Publ.-Id: 8458


Elektromagnetische Strömungskontrolle mit wandparallelen Lorentzkräften in schwach leitfähigen Fluiden
Weier, T.;
Die vorliegende Arbeit widmet sich der, vorwiegend experimentellen, Untersuchung der Wirkung wandparalleler Lorentzkräfte in Strömungsrichtung auf Grenzschichtprofile und Körperumströmungen. Die Themen
- Beeinflussung der Grenzschicht an ebenen Platten mit stationären Lorentzkräften
- Kontrolle von Strömungsablösungen an Zylindern und symmetrischen Profilen mit stationären Lorentzkräften
- Beeinflussung von Zylindernachläufen und abgelösten Tragflügelumströmungen mit zeitlich periodischen Lorentzkräften
werden behandelt.
Keywords: Lorentz force, boundary layer control, separation control, active flow control
  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-454 2006

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Annual Report 2005 - Institute of Radiopharmacy
Steinbach, J.; Seifert, S.; (Editors)
kein Abstract verfügbar
  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-449 2006

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Publ.-Id: 8456


Investigation of FIB assisted CoSi2 nanowire growth
Bischoff, L.; Schmidt, B.; Akhmadaliev, C.; Mücklich, A.;
The ion beam synthesis process of CoSi2 by writing stoichiometric ion implantation and subsequent annealing has been studied. For this a Focused Ion Beam (FIB), equipped with a Co36Nd64 alloy liquid metal ion source, was applied. Si(1 0 0) and (1 1 1) wafers were implanted with 60 keV Co2+ ions in the dose range of 2 × 1016–2 × 1017 cm−2. The implantation parameters, like pixel dwell time, relaxation time, dose rate as well as the pixel overlapping factor were investigated. During subsequent annealing CoSi2 nanostructures with dimensions down to 10 nm have been achieved. To investigate the silicide formation more in detail the annealing process was done in situ in a transmission electron microscope (TEM) on a pre-dimpled and FIB implanted samples of a Si(1 1 1). The formation of the cobalt silicide nano-crystals was monitored by plane-view TEM imaging during a 30 min heat treatment at 600 °C in vacuum.
Keywords: Focused ion beam; Cobaltdisilicide; Ion beam synthesis; Nanowire
  • Microelectronic Engineering 83(2006)4-9, 800-803

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Publ.-Id: 8455


Actinides in Biosystems - Complexation Studies with Relevant Bioligands
Glorius, M.; Moll, H.; Bernhard, G.;
Biosystems such as microorganisms, plants, algae’s etc. are influencing for instance the migration of actinides in the environment. It is important to include these processes in the risk assessment of potential high level nuclear waste disposal sites and other affected areas. In general, the overall interaction process of actinides with microbes can be divided into a) direct interaction path ways such as biosorption, bioaccumulation and biotransformation/bioreduction and b) indirect interaction paths such as complexation with released bioligands. The potential of microbes to mobilize actinides by means of the formed bioligands is less investigated.

Our approach is focused on the investigation of selected bioligands having relevant functionalities for a better understanding of the complex actinide interaction processes in biological systems on a molecular level. To achieve this goal a variety of spectroscopic techniques such as time-resolved laser fluorescence spectroscopy (TRLFS) and/or absorption spectroscopy in the ultraviolet-visible-near infrared (UV-vis-NIR) wavelength range will be applied depending on the nature of the actinide element and the bioligand.
This poster gives an overview about our ongoing research in this area by taking three examples: complex formation of curium(III) with adenosine 5’-triphosphate (ATP) [1], curium(III) and amino acids of different functionalities [2], and uranium interactions with molecules containing hydroxamate groups [3].
We want to use this workshop in order to try to answer the question: How can theory help to interpret our experimental results obtained by using spectroscopic methods especially in exploring the structure of the respective aqueous actinide species?

[1] H. Moll, G. Geipel, G. Bernhard, Inorg. Chim. Acta 358 (2005) 2275.
[2] H. Moll, G. Bernhard, Inorg. Chim. Acta (2006) submitted.
[3] M. Glorius, H. Moll, G. Bernhard, manuscript in preparation.

This work was funded by the BMWA under contract number 02E9985.
Keywords: actinides, biosystems, complexation, TRLFS, UV-Vis spectroscopy
  • Poster
    ThUL-Actinet School, 15.-20.05.2006, Lille, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-8453
Publ.-Id: 8453


New TRLFS Laboratory at the CTU in Prague
John, J.; Filipská, H.; Cernochová, K.; Benes, P.; Geipel, G.; Kubecek, V.; Semelová, M.; Bocan, J.;
Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is a unique method for direct actinide and lanthanide speciation at low concentrations that is increasingly used for the study of various chemical aspects of actinides and lanthanides in solutions, suspensions or on solid surfaces namely in the framework of environmental studies or problems related to nuclear fuel reprocessing and waste disposals. Early in this year, construction and equipment of a new TRLFS laboratory was finished at the Czech Technical University in Prague, Czech Republic, in collaboration and under the support of Institute of Radiochemistry, Forschungszentrum Rossendorf, Germany. The new set-up comprises:
− Vibrant 355 II (Opotec) tunable laser with optical parametric oscillator, basic range 410 2400 nm, pumped at 355 nm with a Brilliant Nd:YAG pulse laser with SHG 532 nm and THG-355 nm modules and an additional FHG 266 nm module. Independent outlets for 355 nm and 266 nm laser beams. A UV 3 module extends the range down to 355 nm. Variable repetition frequency up to 10 Hz with the lengths of the laser pulse 6-8 ns.
− Cuvette Holder Flash 200 with Temperature Controller TC 101 (Quantum Northwest) and the necessary optical elements for signal collection and focussing.
− MS257 (Oriel) monochromator/spectrograph with 4 gratings (150 l/mm 190 800 nm, blaze 300 nm; 300 l/mm 250-1150 nm, blaze 500 nm; 600 l/mm 280 1200 nm, blaze 500 nm; 1200 l/mm 280-1600 nm, blaze 500 nm), with micrometrically adjustable aperture and optical fibre outlet. The main parameters are: outlet focal length 257,4 mm, resolution 0,1 nm, precision ± 0,1 nm, repeatability ± 0,028 nm.
− iStar 720 (Andor) DH720i-18F-03 intensified CCD camera designed for low-light spectroscopy applications requiring fast gating. The CCD sensor has spectral range of 180-850 nm and it includes a digital delay generator built into the head - the minimum optical gate is 1.6 ns.
Results of the first measurements obtained in the new laboratory for a standard UO22+ – SO42– system will be presented. The future research plans include:
− study of uranium complexation with humic substances,
− study of actinides bonding onto solid surfaces,
− actinides and lanthanides complexation with novel extraction and/or complexing agents relevant for spent nuclear fuel reprocessing or operational decontamination, respectively.
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7
  • Czechoslovak Journal of Physics 56(2006), D565-D568

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Publ.-Id: 8452


Ferromagnetic ZnFe2O4 synthesized by Fe implantation into ZnO
Zhou, S.; Potzger, K.; Reuther, H.; Mücklich, A.; Eichhorn, F.; Schell, N.; Skorupa, W.; Helm, M.; Fassbender, J.ORC
Bulk Zinc ferrite (ZnFe2O4) is known to possess a normal spinel structure and is an antiferromagnetic material. However, ferri- or ferro- magnetism has been observed in nanosized ZnFe2O4, which raised the current interest of ZnFe2O4 nanoparticles [1-3]. In this work, crystalline ZnFe2O4 was synthesized by Fe implantation into ZnO at 623 K, following a post thermal annealing. In the as-implanted ZnO sample, a fraction of Fe is in metallic state, and is responsible for the magnetic property. An annealing at 823 K enhanced the Fe particle formation, but Fe nanoparticles were oxidized after an annealing at 1070 K. A further annealing at 1070 K for 3.5 h induced the formation of ZnFe2O4. ZnFe2O4 was identified by x-ray diffraction, transmission electron microscopy and indirectly by room temperature conversion electron Mössbauer spectroscopy. The magnetic property was investigated by superconducting quantum interference device (SQUID) magnetometry (Fig. 1). At 5 K, the sample shows a hysteric loop upon magnetization reversal with a high coecivity of around 400 Oe. The magnetization also was measured as a function of temperature with zero field cooling and field cooling protocol. The zero field cooling curve exhibits a maximum magnetization at a temperature of around 26 K, indicating a nanoparticle magnetic characteristic. The ferromagnetism of ZnFe2O4 can be explained by a partially inverted spinel structure, where Fe ions migrate from octahedral B sites (Fe3+) to tetrahedral A sites (Fe2+), and a strong A-B superexchange interaction produces the ferromagnetic coupling [1-3].

[1] Z. H. Zhou, et al, Appl. Phys. Lett. 79, 3167 (2001).
[2] G. F. Goya, et al, J. Phys.: Condens. Matter 15, 641 (2003).
[3] J. H. Shim, et al, Appl. Phys. Lett. 86, 082503 (2005).
Keywords: Zinc ferrite; Ferromagnetism; Ion implantation; ZnO
  • Poster
    The 4th International Conference on Physics and Applications of Spin Related Phenomena in Semiconductors, 15.-18.08.2006, Sendai, Japan

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Publ.-Id: 8451


Mn-silicide nanoparticles formed inside Si using ion implantation
Zhou, S.; Potzger, K.; Zhang, G.; Mücklich, A.; Eichhorn, F.; Grötzschel, R.; Schmidt, B.; Skorupa, W.; Helm, M.; Fassbender, J.ORC
300 keV Mn was implanted into p-Si with a fluence of 1*10ˆ15/cm2, 1*10ˆ16/cm2 and 5*10ˆ16/cm2, respectively, at 620 K. The samples were annealed at 1070 K in N2 ambient for 5 min by rapid thermal annealing. Rutherford backscattering/channeling, transmission electron microscopy and X-ray diraction were applied for structural characterization. Mnsilicide nanoparticles were formed with the size of 5 nm already in the asimplanted samples and grew up to around 30 nm after annealing. Moreover no significant evidence is found for Mn substituting Si sites either in as-implanted or annealed samples. The virgin samples already show a ferromagnetic like behavior, and the moment is slightly increased after implantation (1*10ˆ16/cm2) and annealing by around 0.5 Bohr magneton per Mn. Therefore, the majority of Mn ions formed Mn-silicides, and some are diluted in Si matrix and develop into ferromagnetic coupling. These effects have to be properly considered for the design of Si-based diluted magnetic semiconductors.
[1] M. Bolduc, C. Awo-Aouda, A. Stollenwerk, M. B. Huang, F. G. Ramos, G. Agnello, and V. P. LaBella Phys. Rev. B 71, 033302 (2005).
  • Poster
    DPG Frühjahrstagung 2006, 27.-31.03.2006, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-8449
Publ.-Id: 8449


Carbon ion implantation into aluminium: Mechanical and tribological properties
Foerster, C. E.; Da, S. S. L. R.; Fitz, T.; Dekorsy, T.; Prokert, F.; Kreissig, U.; Richter, E.; Möller, W.; Lepienski, C. M.; Siqueira, C. J. D.;
Aluminium, carbide nucleation and growing kinetics is correlated to the mechanical properties (hardness and elastic modulus), and to the friction coefficients as a function of carbon ion implantation parameters on aluminium. The microstructure of the modified surface was studied by: a) Elastic Recoil Detection Analysis (ERDA), b) Grazing Incidence X-ray Diffraction analysis (GIXRD) and c) Raman spectroscopy. Hardness and elastic modulus profiles were measured by instrumented nanoindentation technique. Pin-on-disc technique in reciprocal scratch mode was employed to obtain the friction coefficient profile. For low carbon fluences (<= 2 x 10(17) C+ cm(-2)) small size (approximate to 4 nm) embedded Al4C3 precipitates were produced. Higher carbon fluences create an amorphous-like structure. Implantations performed at high substrate temperatures can produce big size precipitate (approximate to 40 nm). Surface hardness increases as a function of carbon fluence resulting in values !
of about 6 GPa (20 times Al bulk value). The hardening mechanisms are associated with dislocations to precipitates bowing and/or cutting processes. Implantation parameters ruled the mechanical properties. Tribological responses are more difficult to correlate to the ion implantations conditions. However, wear is reduced when highly disordered C-C cluster are present.
Keywords: aluminium, Carbon ion implantation, hardness, tribology
  • Surface & Coatings Technology 200(2006)18-19, 5210-5219

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Determination and evolution of tunneling distances in Ge nanocrystal based memories
Beyer, V.; von Borany, J.; Klimenkov, M.;
A Ge nanocrystal layer embedded in thin SiO2 was prepared by ion beam synthesis in direct-tunneling distance to the Si substrate. The write performance was investigated in metal-oxide-semiconductor capacitors by means of capacitance measurements. With the experimental data and calculations using a floating-gate-like approach, the distribution of the tunneling oxide thickness dtox can be obtained in high precision confirmed by high-angle annular dark-field scanning transmission electron microscopy imaging. The evolution of dtox during heat treatment is discussed in terms of Ostwald ripening; i.e., dtox increases with annealing time.
Keywords: memory, MOS, nanocrystal, Germanium
  • Applied Physics Letters 89(2006), 193505

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Ferromagnetic Gd-implanted ZnO single crystals
Zhou, S.; Potzger, K.; Eichhorn, F.; Helm, M.; Skorupa, W.; Mücklich, A.; Fassbender, J.ORC; Herrmannsdörfer, T.; Bianchi, A.
In order to introduce ferromagnetic properties, ZnO single crystals have been implanted with Gd ions at 180 keV ion energy and two different fluences. Magnetization reversal hysteresis loops have been recorded using a superconducting quantum interference device. The virgin ZnO shows a pure diamagnetic behaviour. Besides the diamagnetic background, weak ferromagnetism has been observed for the as-implanted films. Post-implantation annealing greatly improved the magnetism. For a fluence of 5x10ˆ15 Gd/cm2, post implantation annealing at 820K in vacuum leads to an increase of the saturation moment up to 1.8 Bohr magneton per Gd at exactly 300 K thus excluding Gd, ZnGd or Gd2O3 secondary phases to be formed. The increase of the saturation moment can be explained along with changes in resistivity due to the annealing reported elsewhere. Moreover magnetic domains were observed up to 2 microns by atomic/magnetic force microscope, which again evidenced the formation of diluted magnetic semiconductor.
[1]K. Potzger et al, submitted to J. Appl. Phys. (2005).
[2]S. O. Kucheyev et al. J. Appl. Phys. 93, 2972 (2003).
  • Lecture (Conference)
    DPG Frühjahrstagung 2006, 27.-31.03.2006, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-8446
Publ.-Id: 8446


Hemocompatibility of low-friction boron-carbon-nitrogen containing coatings
Maitz, M.; Gago, R.; Abendroth, B.; Camero, M.; Caretti, I.; Kreissig, U.;
Mechanical heart valves are exposed to extreme mechanical demands, which require a surface showing not only nonhaemostatic properties, but also wear resistance and low friction. As alternative to different forms of amorphous carbon (a-C), so-called diamondlike carbon (DLC), the suitability of boron carbonitride (BCN) coatings is tested here for hemocompatible coatings. They have similar mechanical properties like a-C surfaces, but superior chemical stability at ferrous substrates or counterparts. BCN films with different nitrogen content were compared with hydrogenated a-C films regarding their mechanical properties, surface energy, adsorption of albumin and fibrinogen, blood platelet adherence, and activation of the contact system of the clotting cascade and kinin system. Similar mechanical properties and biological response have been found in the BCN films with respect to a-C, indicating the potential of these coatings for biomedical applications. The increase in the cryst!
allinity and tribological properties of the BCN samples with a higher incorporation of N was also followed by a lower protein adsorption and low activation of the contact system, but an increased adherence of thrombocytes. (c) 2005 Wiley Periodicals, Inc.
  • Journal of Biomedical Materials Research Part B 77B(2006), 179-187

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Wettability and biocompatibility of nitrogen-doped hydrogenated amorphous carbon films: Effect of nitrogen
Yang, P.; Huang, N.; Leng, Y.; Yao, Z.; Zhou, H.; Maitz, M.; Leng, Y.; Chu, P.;
Amorphous carbon films have been applied in biomedical fields as potential biocompatible materials with wettability that can be adjusted by doping with other elements, including F, Si, Ti, O and N. In this study, nitrogen-doped hydrogenated amorphous carbon (a-C:H:N) films were deposited by PIII-D using C2H2 + N-2 gas mixtures. The biocompatibility and anti-thrombotic properties of the films were assessed in vitro. The surface morphology and surface wettability of the films were characterized using atomic force microscopy (AFM) and a contact angle method. The results show no cytotoxicity for all films, and films with appropriate nitrogen doping possess much better endothelial cell growth and anti-thrombotic properties. (c) 2005 Elsevier B.V. All rights reserved.
  • Nuclear Instruments and Methods in Physics Research B 242(2006), 22-25

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Speciation of actinides
Geipel, G.;
Actinides under environmental conditions can be found in a sub-µ-molar to the lower millimolar concentration range. However, the direct detection of species under these conditions with conventional spectroscopic techniques is not possible.
By application of very intense light sources, as are available with the different laser systems the excitation of traces of actinides ions becomes possible. Several ions of actinides possess outstanding spectroscopic properties which allow the detection of species also in the lowest concentration range.
For the non-invasive detection of species in solution especially the laser-induced photoacoustic spectroscopy (LIPAS) and in the case of fluorescing species the time-resolved laser-induced fluorescence spectroscopy (TRLFS) are method of first choice. LIPAS is a very sensitive method for absorption spectroscopy and can be applied therefore for all non-fluorescent systems. Compared to conventional UV-VIS spectroscopy up to three orders of magnitude lower detection limits can be achieved. TRLFS is only applicable in systems where the deexcitation takes place via radiative processes with emission of photons. In the series of the lower actinides here the systems containing protactinium(IV), uranium(IV) and uranium(VI) as well as americium(III) and curium(III) have to be named. Due to the extremely high quantum efficiency of curium(III) ions concentrations down to 10-11 mol/L can be observed be TRLFS. On the other hand organic ligands as humic substances are ubiquitous in the nature. The interaction of such compounds with actinides can also studied using the fluorescence properties of the organic ligand. A brief overview for these methods will be given.
Examples for the application of the laser-induced spectroscopic methods we be given. At first examples for the spectroscopy and detection of uranium species in natural waters from mining related to drinking waters will be shown. As special case the determination pure uranyl carbonate species, which are non-fluorescent at room temperature, will be shown. Also the interaction with sulfate, phosphate and arsenate will be touched on. The application of LIPAS will be shown especially for the uranium(IV) phosphate and arsenate systems. As uranium(IV) shows also fluorescence properties some problems with the detection of these species will be summarized. Studies of the interaction of curium and americium with several ligands will also shortly summarized.
Polyelectrolytic organic macromolecules, like humic substances, are important complexing agents towards actinide metal ions. Due to these properties humic substances are possible carriers for the migration of actinides in the environment. The study of the high molecular compounds is very complex. Therefore the investigation of simple model ligands would give a more detailed description of the binding behavior of humic substances. Especially the different bonding of carboxylic and phenolic group and the discrimination between them is of interest to get more detailed information about the complex formation. To study the complex formation of actinides with such organic ligands the TRLFS with ultrashort excitation pulses is a very suitable method.
Keywords: Laser-induced spectroscopy, actinides, organid ligands
  • Invited lecture (Conferences)
    Selected topics on nuclear methods for non-nuclear applications, 27.-30.09.2006, Varna, Bulgaria

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Publ.-Id: 8443


Microscopic theory of impurity states in coupled quantum wells and superlattices
Stehr, D.; Helm, M.; Metzner, C.; Wanke, M. C.;
We present a theory of impurity states in quantum wells and superlattices which treats the confining heterostructure potential and the random impurity potential on the same footing. The relevant 3D Hamiltonian is diagonalized exactly in the low-doping regime. The results are used to calculate infrared absorption spectra which contain contributions of impurity and intersubband transitions. We mainly discuss the excited impurity states, which are pinned to higher subbands and are resonant states in the continuum. After a detailed analysis of a coupled quantum well system, we study the transition to a superlattice. In particular, we are able to reproduce existing experimental data on a quadruple quantum well, which had not been understood in the past.
  • Physical Review B 7408(2006)8, 511

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Permalink: https://www.hzdr.de/publications/Publ-8442
Publ.-Id: 8442


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