Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31742 Publications
Observation of melt flow effects and dendritic growth during directional solidification of Ga-In alloys by X-ray radioscopy
Boden, S.; Willers, B.; Eckert, S.; Gerbeth, G.;
Capabilities of the X-ray attenuation contrast radioscopy were used to provide a real-time diagnostic technique for the observations of dendritic growth and the melt flow during directional solidification of a Ga-30wt%In alloy. The metal alloy was contained in the 150 µm wide gap between the two quartz glass plates of a solidification cell. The solidification process was visualised using a microfocus X-ray radioscopy setup. At typical frame repetition rates of one frame per second, the experimental assembly enables both the observation of the evolution of the dendritic network at length scales of several micrometers as well as the simultaneous observation of the melt convection at nearly millimeter length scale. The Optical Flow approach was used to derive information about the velocity field ahead of the solidification front and in the mushy zone from the observed displacement of the brightness patterns between consecutively acquired X-ray image frames. Growth rates of single primary dendrite trunks were obtained by means of a tip tracking algorithm. Therewith, aspects of the complex interaction mechanisms between melt flow and dendritic growth have been elucidated. Experiments have been carried out to solidify the Ga-In alloy unidirectionally either starting from the bottom or the top of the specimen. The first case is significantly affected by solutal convection. Dendritic fragmentation can be observed during the solidification in the reverse top-down direction.
  • Lecture (Conference)
    IEEE 2008 - Workshop on X-Ray Micro Imaging of Materials, Devices, and Organisms, 22.-24.10.2008, Dresden, Germany

Publ.-Id: 11757 - Permalink


Identification of Yrast high-K intrinsic states in 188Os
Modamio, V.; Jungclaus, A.; Podolyak, Z.; Shi, Y.; Xu, F. R.; Algora, A.; Bazzacco, D.; Escrig, D.; Fraile, L. M.; Lenzi, S.; Marginean, N.; Martinez, T.; Napoli, D. R.; Schwengner, R.; Ur, C. A.;
The high-spin structure of the Z=76 nucleus 188 Os has been studied using the incomplete fusion reaction 7 Li +186 W. A K = 10+ band has been established up to spin (24+ ) and its crossing with the ground state band studied. In addition, intrinsic high-K states have been identified and on top of two of them, K = 7- and K = 10- , regular bands have been observed. The K =16+ and K =18+ states are Yrast while the K =14+ level lies only 33 keV above the Yrast line and decays with a low reduced hindrance of f < 1.3 to the ground state band (K=14). The results are discussed by means of a systematic comparison with the even-even neighbouring nucleus 186 Os. Configurationconstrained multi-quasiparticle potential-energy-surface calculations have been performed in order to identify the configurations of multi-quasiparticle states.
Keywords: Nuclear structure, gamma-ray spectroscopy, high-spin states, potential-energy-surface calculations.

Publ.-Id: 11756 - Permalink


Influence of electron irradiation on hydrothermally grown zinc oxide single crystals
Lu, L. W.; So, C. K.; Zhu, C. Y.; Gu, Q. L.; Li, C. J.; Fung, S.; Brauer, G.; Anwand, W.; Skorupa, W.; Ling, C. C.;
The resistivity of hydrothermally grown ZnO single crystals increased from similar to 10(3) Omega cm to similar to 10(6) Omega cm after 1.8 MeV electron irradiation with a fluence of similar to 10(16) cm(-2), and to similar to 10(9) Omega cm as the fluence increased to similar to 10(18) cm(-2). Defects in samples were studied by thermally stimulated current (TSC) spectroscopy and positron lifetime spectroscopy (PLS). After the electron irradiation with a fluence of 10(18) cm(-2), the normalized TSC signal increased by a factor of similar to 100. A Zn vacancy was also introduced by the electron irradiation, though with a concentration lower than expected. After annealing in air at 400 degrees C, the resistivity and the deep traps concentrations recovered to the levels of the as-grown sample, and the Zn vacancy was removed.
  • Semiconductor Science and Technology 23(2008)9, 095028

Publ.-Id: 11754 - Permalink


Development of an ultra fast scanned electron beam X-ray CT
Fischer, F.; Hoppe, D.; Bieberle, M.; Schleicher, E.; Hampel, U.; Mattausch, G.; Flaske, H.; Bartel, R.;
Electron beam X-ray CT is a promising technique for a fast measurement of multiphase flows with frame rates of at least 1000 images per second. Thus, X-ray tomography in principle gives quantitatively accurate images of the flow at high resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement application we devised and built a fast scanned electron beam X-ray tomography scanner. The heart of the scanner is a medium power electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current. The system further comprises all the typical components of an electron beam device, such as beam adjustment, beam focussing and beam deflection unit and the vacuum system. X-ray radiation is produced on a circular tungsten target that is water cooled. For X-ray detection we use a fast circular CZT detector comprising 240 elements of 1.5 mm x 1.5 mm active pixel area. The photonic converters are connected to a state-of-the-art detector electronics with gain selectable amplifiers, fully parallel analogue-to-digital conversion and online data storage within a 4 GB dynamic RAM. The whole system is controlled by an industrial PC via LabVIEW.
Keywords: Keywords Ultra fast X-ray CT, multi phase flow measurement, scanned electron beam CT
  • Lecture (Conference)
    5th World Congress on Industrial Process Tomography, 03.-06.09.07, Bergen, Norway
  • Contribution to proceedings
    5th World Congress on Industrial Process Tomography, 03.-06.09.07, Bergen, Norwegen

Publ.-Id: 11753 - Permalink


An ultra fast electron beam x-ray tomography scanner
Fischer, F.; Hoppe, D.; Schleicher, E.; Mattausch, G.; Flaske, H.; Bartel, R.; Hampel, U.;
This paper introduces the design of an ultra fast x-ray tomography scanner based on electron beam technology. The scanner has been developed for two-phase flow studies where frame rates of 1 kHz and higher are required. Its functional principle is similar to that of the electron beam x-ray CT scanners used in cardiac imaging. Thus, the scanner comprises an electron beam generator with a fast beam deflection unit, a semicircular x-ray production target made of tungsten alloy and a circular x-ray detector consisting of 240 CZT elements with 1.5 mm × 1.5 mm × 1.5 mm size each. The design is optimized with respect to ultra fast imaging of smaller flow vessels, such as pipes or laboratory-scale chemical reactors. In that way, the scanner is capable of scanning flow cross-sections at a speed of a few thousand frames per second which is sufficient to capture flows of a few meters per second velocity.
Keywords: electron beam tomography, x-ray tomography, multiphase flow measurement

Publ.-Id: 11751 - Permalink


Fracture mechanical investigation of a thermo shock scenario for a VVER-440 RPV
Altstadt, E.; Abendroth, M.;
The paper describes the modelling and evaluation of a pressurized thermal shock (PTS) scenario in a VVER-440 reactor pressure vessel due to an emergency cooling. An axially oriented semi-elliptical crack is assumed to be located in the core welding seam. Two variants of fracture mechanical evaluation are performed: the analysis of a sub-cladding crack and of a surface crack. Three-dimensional finite element (FE) models are used to compute the global transient temperature and stress-strain fields. By using a three-dimensional submodel, which includes the crack, the local crack stress-strain field is obtained. Within the subsequent postprocessing using the J integral technique the stress intensity factors KI along the crack front are obtained. The FE results are compared to analytical calculations proposed in the VERLIFE code. The stress intensity factors are compared to the fracture toughness curve of the weld material.
Keywords: Fracture mechanichs, thermal shock, crack, reactor pressure vessel
  • Contribution to proceedings
    34. MPA-Seminar, 09.-10.10.2008, Stuttgart, Deutschland
    34. MPA-Seminar “Werkstoff- & Bauteilverhalten in der Energie- & Anlagentechnik”

Publ.-Id: 11750 - Permalink


Interactions of microorganisms with U(VI).
Reitz, T.; Merroun, M. L.; Selenska-Pobell, S.;
The release of uranium into the environment is a subject of great public concern due to the chemical and radiological toxicity of this radionuclide. For the development of effective remediation strategies and reliable risk assessment, consolidated knowledge about the uranium behavior in contaminated sites is necessary. Beside the interactions with inorganic soil components, an important role in the migration behavior of uranium play the naturally occurring microorganisms. A high number of studies were dedicated to elucidate the bacterial processes responsible for the binding of uranium. However, little is known about the processes implicated in the complexation of this radionuclide by representatives of the second microbial domain of life, the “Archaea”. The objective of the present work was to investigate whether the structural differences between the cell surfaces of representatives of archaea and bacteria influence the cellular localization and the molecular environment of U(VI) bound by the two kinds of organisms. For this, Transmission Electron Microscopy (TEM), Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS), and X-ray Absorption Spectroscopy (XAS) were used.
  • Poster
    3rd PhD Seminar of the Forschungszentrum Dresden/Rossendorf, 27.-29.08.2008, Limbach, Deutschland

Publ.-Id: 11749 - Permalink


Interactions of Paenibacillus sp. JG-TB8 and Sulfolobus acidocaldarius with U(VI)
Reitz, T.; Merroun, M. L.; Selenska-Pobell, S.;
Microorganisms are interacting in multiple ways with radionuclides. A high number of studies were dedicated to elucidate the bacterial mechanisms of uranium binding. However, little is known about the complexation of this radionuclide by representatives of archaea. The objective of the present work was to investigate whether the structural differences between the cell walls of archaea and bacteria influence the cellular localization and the molecular environment of U(VI) bound by the two kinds of organisms. For this, Transmission Electron Microscopy (TEM), Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS), and X-ray Absorption Spectroscopy (XAS) were used
  • Poster
    12th International Symposium on Microbial Ecology, 17.-22.08.2008, Cairns, Australien

Publ.-Id: 11748 - Permalink


Uranium biomineralization by uranium mining waste isolates: a multidisciplinary approach study
Merroun, M.; Hennig, C.; Selenska-Pobell, S.;
- wird nachgereicht
  • Contribution to external collection
    Broder J. Merkel, Andrea Hasche-Berger: Uranium, Mining and Hydrogeology, Berlin: Springer Verlag, 2008, 978-3-540-87745-5, 723-723

Publ.-Id: 11747 - Permalink


Dipole strength in 89Y up to the neutron-separation energy
Benouaret, N.; Schwengner, R.; Rusev, G.; Dönau, F.; Beyer, R.; Erhard, M.; Grosse, E.; Junghans, A. R.; Kosev, K.; Nair, C.; Schilling, K. D.; Wagner, A.; Bendjaballah, N.;
Photoexcitation of the N = 50 nucleus 89Y has been performed at the bremsstrahlung facility at the superconducting electron accelerator ELBE at electron energies of E = 9.5 MeV and 13.2 MeV. About 250 levels up to the neutron-separation energy were identified. Statistical methods were applied to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section derived in this way up to the neutron-separation energy is combined with the photoabsorption cross section obtained from (gamma,n) data and provides information about the extension of the giant dipole resonance toward energies below the neutron-separation energy. An enhancement of E1 strength has been found in the range from about 6 MeV to 11 MeV. The experimental photoabsorption cross sections of 89Y and of the neighboring N = 50 isotones 88Sr and 90Zr are compared with predictions of the quasiparticle-random-phase approximation.
Keywords: Nuclear structure, photon scattering, gamma-ray strength functions, absorption cross sections, random-phase-approximation.

Publ.-Id: 11746 - Permalink


Begleitende Untersuchungen zur Pilotierung eines Verfahrens zur elektrochemischen Aufbereitung saurer Wässer aus Tagebaurestseen / 3. Zwischenbericht
Kryk, H.; Schubert, M.; Hessel, G.;
Das vom VKTA entwickelte elektrochemische Verfahren zur Aufbereitung schwefelsaurer Wässer aus Tagebau-Restseen (RODOSAN®) befindet sich zurzeit in der Phase der Pilotierung. Hierzu wurde vom VKTA im Gebiet des Lausitzer Braunkohlen-Tagebaureviers eine Grubenwasserreinigungs-Pilotanlage errichtet. Durch das FZD wurden prozessbegleitende Untersuchungen sowohl zur Optimierung des Elektolyseprozesses als auch zur Aufbereitung der Koppelprodukte durchgeführt.
Schwerpunkte waren experimentelle Untersuchungen zum Einfluss des Elektrolyseprozesses (Gasblasenbildung) auf die Verweilzeitverteilung der Flüssigkeit im Katodenraum unter Verwendung der laserinduzierten Fluoreszenz (LIF). Dazu wurde die Strömung im Katodenraum der Elektrolysezelle bei laufender Elektrolyse unter Anwendung verschiedener Stromdichten untersucht. Die Messungen stellen eine informative Basis zur Optimierung der Strömungsstruktur in der Zelle dar.
Im Mittelpunkt des Projektes stand weiterhin eine Machbarkeitsstudie zur Abtrennung des Koppelproduktes Ammoniumperoxodisulfat aus der Anolyt-Lösung. Hierzu wurden thermodynamische Kristallisationsparameter ermittelt und Verfahrensvorschläge für die großtechnische Koppelproduktaufbereitung erarbeitet. Ziel ist die optimale Verwertung der beim Elektrolyseprozess entstehenden Koppelprodukte zur Erhöhung der Wirtschaftlichkeit des Gesamtverfahrens.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\04
    0069 Seiten

Publ.-Id: 11745 - Permalink


Begleitende Untersuchungen zur Pilotierungeines Verfahrens zur elektrochemischen Aufbereitung saurer Wässer aus Tagebaurestseen / 2. Zwischenbericht
Kryk, H.; Schubert, M.; Hessel, G.;
Das vom VKTA entwickelte elektrochemische Verfahren zur Aufbereitung schwefelsaurer Wässer aus Tagebau-Restseen (RODOSAN®) befindet sich zurzeit in der Phase der Pilotierung. Hierzu wurde vom VKTA im Gebiet des Lausitzer Braunkohlen-Tagebaureviers eine Grubenwasserreinigungs-Pilotanlage errichtet. Durch das FZD wurden prozessbegleitende Untersuchungen sowohl zur Optimierung des Elektolyseprozesses als auch zur Aufbereitung der Koppelprodukte durchgeführt.
Schwerpunkte waren experimentelle Untersuchungen zum Einfluss des Abstandgitters, der beweglichen Membran sowie der Volumenströme auf die Verweilzeitverteilung der Flüssigkeit im Katodenraum unter Verwendung der laserinduzierten Fluoreszenz (LIF). Außerdem gibt die Visualisierung durch die Verwendung fluoreszierender Tracer Informationen über Strömungsasymmetrien durch die Einlassgeometrie, das Abstandsgitter sowie den Aufbau der Zelle. Dazu wurde die Strömung im Katodenraum der Elektrolysezelle in unterschiedlichen Konfigurationen untersucht. Die Messungen stellen eine informative Basis zur Optimierung der Strömungsstruktur in der Zelle dar. Ziel der Untersuchung war, das Verweilzeitverhalten besser zu charakterisieren und damit Rückschlüsse auf das Elektrolyseergebnis ziehen zu können.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\01
    0042 Seiten

Publ.-Id: 11744 - Permalink


Melt flows in combined rotating and traveling magnetic fields
Gerbeth, G.; Grants, I.; Zhang, C.; Eckert, S.;
The liquid metal flow in a cylinder driven by poloidal and azimuthal magnetic body forces is studied experimentally. For this purpose we apply the ultrasound Doppler velocimetry in the bulk and a particle image velocimetry on the free surface. The body forces are generated by axial traveling and rotating magnetic fields of considerably different frequencies. The transition between poloidal to azimuthal force governed states proceeds in two intermediate stages. At first, a pronounced swirl enhancement and concentration is observed. As the azimuthal forcing is further increased the axial vorticity accumulates on a ring inside of which the poloidal flow changes its direction. This transition occurs at a surprisingly low azimuthal forcing of just about one per cent of its poloidal counterpart. The two characteristic velocity components, in turn, have comparable magnitude. The disproportionality of both force strengths is, thus, a consequence of a considerably higher hydraulic resistance for the poloidal flow. The observed swirl concentration during the regime change is explained by the phenomenon of vortex stretching.
  • Lecture (Conference)
    79th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM2008), 02.-04.04.2008, Bremen, Germany

Publ.-Id: 11743 - Permalink


On the efficiency of MHD drag reduction
Shatrov, V.; Gerbeth, G.;
Recently, permanent magnets and high electric current densities are often used to achieve reasonable Lorentz forces for a magnetohydrodynamic (MHD) flow control. This choice, however, usually leads to a low energetic efficiency for the flow control of seawater. We present results of direct numerical simulations of turbulent channel flow drag reduction using electromagnetic forces. The Lorentz force is created by a permanent magnetic field and an electric current from electrodes placed at the bottom wall. The investigations are restricted to the two cases of a spanwise oscillating force and a streamwise steady force. The lecture to be presented extends the results recently published by the authors.
  • Lecture (Conference)
    European Drag Reduction and Flow Control Meeting, 08.-11.09.2008, Ostritz, Germany

Publ.-Id: 11742 - Permalink


Tridiagonal factorization algorithm for Chebyshev-tau method with an exponential coordinate mapping
Priede, J.; Grants, I.; Gerbeth, G.;
Spectral numerical methods, which involve seeking the solution in terms of a series of known, smooth functions such as, for example, Chebyshev polynomials, are well known in Computational Fluid Mechanics for their superior accuracy. However, the practical use of spectral methods depends critically on the efficiency of algorithms for solution of the resulting systems of algebraic equations. Spectral methods often yield systems of linear equations with dense matrices whose solution may be considerably less cost efficient in comparison to the band matrices resulting from finite element or finite difference techniques. Exception is the Chebyshev-tau method which combined with the recurrence relations for derivatives of Chebyshev polynomials results in tri- and penta-diagonal matrices for approximation of second derivative operators in Cartesian and polar coordinates, respectively.
In the present study we derive a similar reduction to a tridiagonal matrix for a Chebyshev-tau approximation of the second derivative operator in a transformed coordinatemapping a semi-infinite domain which is useful for the numerical solution of boundary layer equations. This approach combined with FFT results in a cost-efficient and accurate algorithm for a direct numerical simulation of boundary layer flows. Application of this algorithm is demonstrated for a turbulent Hartmann-layer flow of an electrically conducting liquid in a transverse magnetic field.
  • Lecture (Conference)
    8th World Congress on Computational Mechanics (WCCM8), 01.-05.07.2008, Venice, Italy

Publ.-Id: 11741 - Permalink


Linear stability analysis of an alternating magnetic field driven flow in a spinning container
Gerbeth, G.; Shatrov, V.; Hermann, R.;
We present a numerical analysis of the free surface liquid metal flow driven by an alternating (AC) magnetic field in a spinning cylindrical container. The axysimmetric flow structure is analyzed for various values of the magnetohydrodynamic interaction parameter N and the Ekman number E. The governing hydrodynamic equations are solved by a spectral collocation method. The alternating magnetic field distribution is found by a boundary-integral method. The electromagnetic and hydrodynamic fields are fully coupled via the shape of the liquid free surface. The upper free boundary was found simultaneously with the flow by a Newton method. It is found that in all considered parameter ranges the flow contains four main toroidal eddies. This is caused by the non-uniformity of the magnetic field near the edges of the liquid volume. The interaction parameter N controls the intensity of the flow. The additional container spinning leads to a deformation of the flow structure. At Ekman number E < 1 ´ 10-2 the meridional flow is reduced. The secondary azimuthal flow has its maximum in the Ekman number range of E ~ 10-3 - 10-2, at smaller Ekman number the azimuthal flow is suppressed too.
The three-dimensional stability analysis of the flow showed that the spinning leads mainly to a destabilization of the base flow. Only at very small Ekman numbers E the flow in the spinning container is more stable than in the non-spinning case. The instability at large Ekman numbers is of oscillatory type and the most unstable azimuthal wave number is m = 3. At smaller Ekman numbers the azimuthal wave number increased to m = 5, m = 6, etc. At E < 2.1 ´ 10-4 the most unstable wave number is m = 16. Except the narrow Ekman number range of 1.935 ´ 10-2 < E < 2.376 ´ 10-2 where the instability is of oscillatory type, at all other values of Ekman number E < 4.6136 ´ 10-2 the instability is of steady type.
  • Lecture (Conference)
    8th World Congress on Computational Mechanics (WCCM8), 01.-05.07.2008, Venice, Italy

Publ.-Id: 11740 - Permalink


The flow around an electromagnetically self-propelled sphere
Shatrov, V.; Gerbeth, G.;
We present a numerical analysis of the flow behind an electromagnetically self-propelled sphere. Two cases are considered. In the first part the sphere contains the electromagnetic coil system which creates a traveling magnetic field on the sphere surface. The control parameter of the problem is the interaction parameter N of the traveling field. For a given value of N the sphere moves in an electrically conducting fluid with some velocity, which defines the corresponding Reynolds number. It is found that in the self-propelled regime when the hydrodynamic drag force and the electromagnetic thrust force balance each other, the flow behind the sphere has a much smaller separation bubble than in the absence of the Lorentz force. The size of the separation bubble depends from the distribution of the electromagnetic field near the sphere surface and the value of the interaction parameter N. Vortex separation can be fully suppressed. We study the linear stability of the axisymmetric flow. It is found that the 3D instability occurs at much larger Reynolds numbers than in the absence of the Lorentz force. For the unstable 2D flow case we calculated a full 3D flow behind the sphere. It is found that even in this unstable case the drag of the sphere can be smaller than the drag of the sphere without Lorentz force.
In the second part we studied a so-called conductive system. The sphere contains a system of sectioned electrodes on the surface and a coil system inside. The Lorentz force is three-dimensional now and the flow behind the sphere is three-dimensional too, due to the 3D Lorentz forcing. We calculated the 3D flow behind a sphere in the self-propelled regime and found that the drag can be significantly reduced. We consider the energy consumption due to the drag reduction as well.
  • Lecture (Conference)
    8th World Congress on Computational Mechanics (WCCM8), 01.-05.07.2008, Venice, Italy

Publ.-Id: 11739 - Permalink


Morphology and structure of C:Co, C:V and C:Cu nanocomposite films
Berndt, M.; Abrasonis, G.; Krause, M.; Mücklich, A.; Munnik, F.; Kolitsch, A.; Möller, W.;
The influence of transition metals (TM) type on the encapsulating carbon (C) medium during the growth of C:TM composite films is investigated. The C:V(~30 at.%), C:Co(~30 at.%) and C:Cu (~30 at. %) thin films have been grown by ion beam co-sputtering in the temperature range of RT-500°C. The films have been investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy at two excitation wavelengths (532 nm and 632 nm). For comparison reasons, pure carbon films have been grown in the same temperature range.
XRD reveals that the nanoparticles in C:V and C:Cu films are in carbidic and metallic state over the whole temperature range of this study, respectively. In contrast, in C:Co films a phase transition from carbide phase, present for growth temperatures of RT-300°C, to the metallic phase above 300°C occurs. According to the TEM observations, cobalt or cobalt carbide nanoparticles embedded in a carbon matrix have an elongated shape in the direction of the thin film growth with both length and diameter increasing with growth temperature (the latter from 2 up to 5 nm). However, in C:V films the nanoparticles exhibit globular shapes with diameters of ~ 2 nm at RT, which only slightly increases with temperature. Raman spectroscopy shows that all three metals enhance 6-fold ring clustering of the carbon phase independent of the nanoparticle type, size, shape and phase.
Keywords: carbon, transition metal, sputter deposition, transmission electron microscopy, raman spectroscopy
  • Lecture (Conference)
    Eleventh International Conference on Plasma Surface Engineering, 15.-19.09.2008, Garmisch-Partenkirchen, Germany
  • Plasma Processes and Polymers 6(2009)Suppl., S902-S906

Publ.-Id: 11738 - Permalink


Some new results on liquid metal measuring techniques and instrumentation
Gerbeth, G.; Eckert, S.; Weiss, F.-P.;
Liquid metal cooling or liquid metal targets belong to innovative reactor concepts such as the sodium cooled fast breeder reactor or the lead-bismuth target in a transmutation system. The safe and reliable operation of liquid metal systems requires corresponding measuring systems and control units, both for the liquid metal single-phase flow as well as for gas bubble liquid metal two-phase flows. We report on some recent developments in this field. Integral flow rate measurements are an important issue. We describe two new, fully contactless electromagnetic solutions and related test measurements at available sodium and lead loops. One of the sensors is of particular interest since its operation does not depend on the electrical conductivity of the liquid metal, hence it is independent on the melt temperature. A development of the past decade is the local velocity measurement by application of the Ultrasound Doppler Velocimetry (UDV). It provides the velocity profile along the ultrasonic beam, and has the capability to work even through some channel wall. We report on measurements in liquid sodium at 150°C. For higher temperatures, an integrated ultrasonic sensor with an acoustic wave-guide has been developed to overcome the limitation of ultrasonic transducers to temperatures lower than 200°C. This sensor can presently be applied at maximum temperatures up to 1000°C. Stable and robust measurements have been performed in various PbBi flows in our laboratory at FZD as well as at the THESYS loop of the KALLA laboratory of Forschungszentrum Karlsruhe (FZK). We will present experimental results obtained in a PbBi bubbly flow at 250...300°C. Argon bubbles were injected through a single orifice in a cylindrical container filled with stagnant PbBi. Velocity profiles were measured in the bubble plume. At the THESYS loop of FZK, stable velocity profiles were measured in a round tube of diameter 60 mm during a period of about 72 hours at temperatures between 180°C and 350°C. Further, we report on the development of a contactless magnetic tomography of the mean flow in liquid metals. This method gives the full three-dimensional mean velocity distribution in a liquid metal volume. Results from a laboratory demonstration experiment will be presented. Finally, a heat exchanger design will be presented working with an intermediate liquid metal in order to avoid the possible contact between a hot liquid metal and cooling water. It is installed at FZD at a lead loop where liquid lead of up to 500°C circulates. The room temperature liquid alloy GaInSn is used as intermediate melt, the heat flux is controlled by regulating the height of this melt in a gap separating the flowing lead from the cooling water.
  • Lecture (Conference)
    THIRS Workshop, 14.-16.04.2008, Karlsruhe, Germany

Publ.-Id: 11737 - Permalink


Auswirkungen von verschiedenen Brennstoffzyklusoptionen auf die anfallenden Aktinidenmengen im deutschen Reaktorpark
Merk, B.; Broeders, C. H. M.;
On the basis of the legally stipulated total volume of electricity to be generated in Germany an estimate is given of the amounts of residues arising from reactor operation in terms of spent uranium fuel, plutonium, and minor actinides. Various idealized scenarios are considered as limiting criteria and compared with a realistic scenario in an attempt to show the impacts of various fuel cycle options on the remaining plant life. The case of plutonium reduction by using mixed oxide (MOX) fuels is analyzed in particular. While consistent direct disposal at the end of plant life leaves approx. 160 t of plutonium (upper bound), this quantity can be reduced by some 40 t merely by recycling once. Recycling twice could reduce the amount of plutonium by nearly 60 t (lower bound). Present boundary conditions already reduce the remaining amount of plutonium by some 17 t, which level could be raised to something close to the possible value of 40 t by resuming reprocessing. An additiona!
l scenario considered are the impacts on actinide production of plant life extension for all scenarios as a basis for future discussions of the kind already going on in other countries.
Keywords: Lifetime Extension, Cycle Studies, Plutonium Management, MOX Fuel
  • atw - International Journal for Nuclear Power 53(2008)6, 404-412

Publ.-Id: 11736 - Permalink


Magnetfelder optimieren Metalllegierungen: Forschen für das optimale Gefüge
Schue, A.; Eckert, S.;
In der Arbeitsgruppe Magnetohydrodynamik am Forschungszentrum Dresden-Rossendorf (FZD) werden Wechselwirkungen zwischen elektrisch leitfähigen Flüssigkeiten und magnetischen Feldern eingesetzt, um Strömungsverhalten und Erstarrungsprozesse flüssiger Metalllegierungen kontrolliert zu steuern. Ziel sind optimierte Produktionsprozesse für die Gießereitechnik. Zur Analyse setzt man ein System aus High-End-Mikroskop und Power-Mosaic-Bildaufnahme ein, das große Probenoberflächen in hochaufgelösten Einzelbildern abrastert und ein präzises Gesamtbild für quantitative Auswertungen liefert.
Keywords: metal alloys, solidification, electromagnetic stirring, microstructure
  • Quality Engineering (2008)10, 47-49

Publ.-Id: 11735 - Permalink


Improvement of structural, electronic, and magnetic properties of Co2MnSi thin films by He+-irradiation
Gaier, O.; Hamrle, J.; Hillebrands, B.; Kallmayer, M.; Pörsch, P.; Schönhense, G.; Elmers, H. J.; Fassbender, J.ORC; Gloskovskii, A.; Jenkins, C. A.; Felser, C.; Ikenaga, E.; Sakuraba, Y.; Tsunegi, S.; Oogane, M.; Ando, Y.
The influence of 30 keV He+ ion irradiation on structural, electronic and magnetic properties of Co2MnSi thin films with B2 order was investigated. It was found, that irradiation with light ions can improve the local chemical order. This provokes changes of the electronic structure and elementspecific magnetization towards the bulk properties of the well-ordered Co2MnSi Heusler compound with L21 structure.
Keywords: magnetism, ion irradiation, Heusler alloy, ordering, chemical order

Publ.-Id: 11734 - Permalink


A literature review on mechanisms and models for the coalescence process of fluid particles
Liao, Y.; Lucas, D.;
This paper presents a literature review on mechanisms and models for the coalescence process of fluid particles (bubbles and drops). For the mechanisms, five categories are summarized, namely, turbulence fluctuation, viscous shear stress, capture in turbulent eddies, buoyancy and wake interaction. Models for the collision frequency and coalescence efficiency of bubbles or drops in turbulent liquid are reviewed thoroughly. The development and limitation of the existing models are studied and possible improvements are proposed.
Keywords: Population balance equation; Bubble size distribution; Coalescence mechanisms; Coalescence models

Publ.-Id: 11733 - Permalink


Analysis of scattered radiation cross-talk in a high-resolution gamma ray tomography detector with GATE Monte-Carlo simulation
Kiessling, N.; Bieberle, A.; Hampel, U.;
Limited energy resolution in scintillation type gamma ray detectors leads to systematic errors in photon counting because the pulse height discrimination stages cannot accurately discriminate interactions with full respectively partial deposition of isotopic emission energy. The resulting error is a systematic positive count rate offset originating from erroneously counted scattered photons. The origin of scattering may be the detector itself (scintillation crystals and other construction material) as well as components of the setup, including the object of investigation. In this article results of a simulation study are presented which was carried out to assess the role of different design parameters for the count rate accuracy of a high resolution gamma ray detector used for transmission tomography. Thereby the simulation software Geant4 Application for Emission Tomography (GATE) was used. As a target parameter we evaluated the radiation cross-talk, which is the amount of erroneously counted interactions from photons which have undergone Compton scattering in neighbouring crystals. For the given detector design it was found that cross-talk obtained from the simulated data is in good agreement with experimentally determined cross-talk. It could further be shown by virtual detector design changes that radiation cross-talk can be reduced only to a degree that would still require additional software correction measures, such as scattering correction algorithms, if quantitative accuracy it demanded.
Keywords: GATE, Monte-Carlo simulation, scintillation detector, gamma ray tomography

Publ.-Id: 11732 - Permalink


Numerical study of the turbulent two-phase flow in a steel mould
Miao, X.; Galindo, V.; Gerbeth, G.; Ren, Z.;
Magnetic fields are an attractive contactless possibility in order to influence the liquid steel flow in the mould of the continuous casting process. In slab casting, argon bubbles are commonly introduced through the submerged entry nozzle into the liquid steel in order to reduce nozzle clogging. However, argon gas bubbles are very influential on the upper recirculation zone. Argon gas bubbles give rise to the entrapment of mould flux while bursting out at the free surface between the molten steel and the mould flux. On the other hand, several reports show that argon gas bubbles ascend near the nozzle due to their buoyancy, and such ascending argon bubbles induce an upstream of the molten steel. Thus, argon gas bubbling is thought to be able to affect the flow pattern of molten steel and subsequently exert an influence on the initial solidification in the meniscus region. Therefore, it is essential not only to prevent the steel defects which are caused by both the entrainment of mould flux and the gas bubbles, but to control the two-roll flow pattern. In our presentation, a multi-phase model is adopted to simulate the effect of argon gas bubbles on the flow pattern in the slab mould compared with water model experiments. The calculations show that argon gas bubbling increases the probability of an asymmetric instability and even unbalances the two-roll flow pattern in the slab mould.
Keywords: magnetic control, continuous casting
  • Lecture (Conference)
    8th. World Congress on Computational Mechanics (WCCM8) / 5th. European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2008), 30.06.-04.07.2008, Venice, Italy

Publ.-Id: 11731 - Permalink


Detailed Analysis Concerning the Biodistribution and Metabolism of Human Calcitonin-Derived Cell-Penetrating Peptides
Neundorf, I.; Rennert, R.; Franke, J.; Közle, I.; Bergmann, R.;
The interest in using small peptides for therapeutic and diagnostic in vivo applications is based on several advantageous features such as good penetration into tissues and rapid clearance from the body. Because of their size, they can easily be synthesized chemically. The recently discovered cell-penetrating peptides (CPP) and among them CPP derived from the native peptide hormone human calcitonin (hCT) could meet these requirements.
Therefore, they are nowadays widely used as delivery vectors for a variety of bioactive molecules. However, the knowledge about the distribution and metabolism of CPP in vivo is very limited. Hence, evaluation of the pharmacological features of any promising peptide is a crucial challenge in its development process. Herein, we studied the in vivo radiopharmacology of 68Ga radiolabeled DOTA-modified, hCT-derived CPP in rats using small animal PET. Furthermore, the arterial blood at different time points and urine were analyzed for radiometabolites. It was shown that D-amino acid modifications of the sequence hCT(9-32) resulted in an increased in vivo stability and lower retention in the kidney cortex of this peptide.

Publ.-Id: 11730 - Permalink


Photothermal measurements of Al+ - and Al+/N+ implanted 6H-SiC
Pezoldt, J.; Teichert, G.; Panknin, D.; Voelskow, M.;
Thermal wave measurements on 6H-SiC with a particular emphasis on Al+ and Al+/N+ implanted 6H-SiC was carried out. The 6H-SiC wafers were implanted at different substrate temperatures.
Keywords: SiC implantation thermal wave measurement
  • Contribution to proceedings
    Third International Workshop on Nondestructive Testing and Computer Simulations in Science and Engineering, 07.-11.06.1999, St. Petersburg, Russia
    Proceedings of the Third International Workshop on Nondestructive Testing and Computer Simulations in Science and Engineering, ISSN:0277-786X ( print )

Publ.-Id: 11729 - Permalink


Model experiments on macroscopic thermoelectromagnetic convection
Zhang, X.; Cramer, A.; Lange, A.; Gerbeth, G.;
Thermoelectromagnetic convection (TEMC) in a generic configuration is studied experimentally. The experimental results demonstrate that even a moderate temperature gradient can produce distinct convection. When the magnet was positioned close to an isothermal wall with its direction of magnetization parallel to , a relatively stable vortex developed throughout the whole container. Moving the magnet to the center led to a modified distribution of the magnetic field, while, in turn, altered the flow topology into four-vortex structure. Numerical results support the experimental findings.
Keywords: Thermoelectromagnetic Convection, Thermoelectric Power, Temperature Gradient, Container
  • Contribution to proceedings
    7th PAMIR International Conference on fundamental and applied MHD, 08.-12.09.2008, Presqu'Île de Giens, France, 495-499
  • Poster
    7th PAMIR International Conference on fundamental and applied MHD, 08.-12.09.2008, Presqu'Île de Giens, France

Publ.-Id: 11728 - Permalink


Develompent of a modeling approach for bubble entrainment
Schmidtke, M.; Lucas, D.;
This final report presents the work done for the numerical prediction of the plunging jet configuration including the air entrainment below the surface by the jet. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. For example the air is a continuous phase above the water level but bubbly below the water level. Various drag models are tested and their influence on the gas void fraction below the water level is discussed. For the quantification of the gas entrainment and for the description of the plume geometry diverse measures are developed. The results of simulations are compared with experimental correlations and are discussed with respect to physical plausibility, e.g. in terms of mass conservation, bubble entrainment and the penetration depth of the gas plume below the water level.
If the gas is treated as dispersed phase everywhere in the domain and the grace drag law is applied, the gas entrainment is overestimated substantially. The algebraic interface area density (AIAD) model applies a drag coefficient for bubbles and a drag coefficient for the free surface. If the AIAD model is used for the simulation of impinging jets, the gas entrainment depends on the free surface drag coefficient. The gas entrainment can be controlled (tuned) via this parameter. So the AIAD approach can be used in future for the implementation of models (e.g. correlations) for the gas entrainment, since the physical details of the bubble generation generally can not be resolved in Euler-Euler simulations of large multiphase configurations.
Keywords: bubble, entrainment, jet, plunging, impinging, interface area density, AIAD, ECC, PTS
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    NURESIM-SP2-TH-D2.1.3.2
    0026 Seiten

Publ.-Id: 11727 - Permalink


Impedance sensors for fast multiphase flow measurement and imaging
Da Silva, M. J.;
In this work, the use of electrical impedance techniques for multiphase flow measurement has been investigated. Three different impedance sensor systems to quantify and monitor multiphase flows have been developed, implemented and metrologically evaluated. The first one is a complex permittivity needle probe which can detect the phases of a multiphase flow at its probe tip by simultaneous measurement of the electrical conductivity and permittivity at up to 20 kHz repetition rate. Two-dimensional images of the phase distribution in pipe cross section can be obtained by the newly developed capacitance wire-mesh sensor. The sensor is able to discriminate fluids with different relative permittivity (dielectric constant) values in a multiphase flow and achieves frame frequencies of up to 10,000 frames per second. The third sensor introduced in this thesis is a planar array sensor which can be employed to visualize fluid distributions along the surface of objects and near-wall flows. The planar sensor can be mounted onto the wall of pipes or vessels and thus has a minimal influence on the flow. It can be operated by a conductivity-based as well as permittivity-based electronics at imaging speeds of up to 10,000 frames/s. All three sensor modalities have been employed in different flow applications which are discussed in this thesis. The main contribution of this research work to the field of multiphase flow measurement technology is therefore the development, characterization and application of new sensors based on electrical impedance measurement. All sensors present high-speed capability and two of them allow for imaging phase fraction distributions. The sensors are furthermore very robust and can thus easily be employed in a number of multiphase flow applications in research and industry.
Keywords: impedance sensors, multiphase flow, flow imaging, tomography
  • Book (Authorship)
    Dresden: TUDpress, 2008
    154 Seiten

Downloads:

Publ.-Id: 11725 - Permalink


SIMS investigation of Gex(4H-SiC)1-x solid solutions synthesized by Ge-ion implantation up to x=0.2
Peyre, H.; Pezoldt, J.; Voelskow, M.; Skorupa, W.; Camassel, J.;
Ge-ion implantation in SiC is of interest for fundamental damage studies and hetero-junction device applications. For instance, a thin Ge-implanted layer has already been used as base for hetero-structure bipolar transistors [5]. Germanium is also a widely used solvent in VLS (Vapor-Liquid-Solid) growth technology and shedding more light on the incorporation of Ge in the SiC lattice is of interest [6]. Recently, high dose / high temperature ion-implantations have been done in 4H-SiC samples which, when investigated by RBS (Rutherford Backscattering Spectroscopy) techniques, suggested that up to 50% of the initial dose could be lost for targeted concentrations in the range of 10 to 20%. In this work we present a comparative investigation of the Ge concentration distributions carried out by SIMS and RBS and highlight the effects affecting the depth distribution and measurement results.
Keywords: SiC Ge Ion implantation SIMS RBS
  • Lecture (Conference)
    7th European Conference on Silicon Carbide and Related Materials, 07.-11.09.2008, Barcelona, Spain
  • Materials Science Forum 615-617(2009), 465-468

Publ.-Id: 11724 - Permalink


Meson and di-electron production with HADES
Fröhlich, I.; Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; González-Díaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krása, A.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lapidus, K.; Lopes, L.; Maier, L.; Mangiarotti, A.; Marín, J.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Mishra, D.; Morinière, E.; Mousa, J.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pérez Cavalcanti, T.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Simon, R.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Wen, H.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.; Zumbruch, P.;
The HADES experiment, installed at GSI, Darmstadt, measures di-electron production in A+A, p/pi+N and p/pi+A collisions. Here, the pi0 and eta Dalitz decays have been reconstructed in the exclusive p+p reaction at 2.2 GeV to form a reference cocktail for long-lived di-electron sources. In the C+C reaction at 1 and 2 GeV/u, these long-lived sources have been subtracted from the measured inclusive e+e- yield to exhibit the signal from the early phase of the collision. The results suggest that resonances play an important role in dense nuclear matter.
  • Contribution to proceedings
    MESON2008, 10th International Workshop On Meson Production, Properties And Interaction, 06.-10.06.2008, Cracow, Poland
    Int. J. Mod. Phys. A 24 (2009) 317-326, Singapore: World Scientific Publ., ISSN: 0217-751X
  • Contribution to WWW
    arXiv:0809.2764: http://de.arxiv.org/abs/0809.2764

Publ.-Id: 11723 - Permalink


Epitaxial 3C-SiC nanocrystal formation at the SiO2/Si interface after carbon implantation and annealing in CO atmosphere
Voelskow, M.; Pécz, B.; Stoemenos, J.; Skorupa, W.;
High quality 3C-SiC nanocrystallites were epitaxially formed on a single crystalline Si surface covered by a 150 nm thick SiO2 capping layer after low dose carbon implantation and subsequent high temperature annealing in CO atmosphere. Carbon implantation is used to introduce nucleation sites by forming silicon-carbon clusters at the SiO2/Si interface facilitating the growth of 3C-SiC nanocrystallites.
Keywords: nanocrystallites 3C-SiC carbon implantation
  • Poster
    IBMM 08 - 16th International Conference on ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1364-1367

Publ.-Id: 11722 - Permalink


Nanometer-thick SGOI structures produced by Ge+ ion implantation of SiO2 film and subsequent hydrogen transfer of Si layer
Tyschenko, I. E.; Voelskow, M.; Cherkov, A. G.; Popov, V. P.;
Strong decrease in the carrier mobility of the nanometer-thick silicon films imposes a limitation on the application of silicon-on-insulator (SOI) structures in the current silicon planar CMOS technology. The formation of SiGe-heterostructures-on-insulator (SGOI) is a way to increase the hole mobility in the nanometer-scale layers. In this work, we present the results on the interface mediated endotaxial growth of nanometer-thick Ge film from the Ge+-ion implanted SiO2 layer of the SOI structure
Keywords: SOI SiGe SGOI Ge implantation
  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1277-1280

Publ.-Id: 11721 - Permalink


Comparative simulations of bubble entrainment cases with NURESIM_CFD and CFX-11
Schmidtke, M.; Lucas, D.;
This progress report presents the work done for the numerical prediction of the plunging jet configuration. A study case is simulated with both the NURESIM_CFD_1.0.5 code and with CFX-11 and the results for the gas entrainment near the jet are compared. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. For example the air is a continuous phase above the water level but bubbly below the water level. In this study the SIMMER model is applied for the drag. This model assumes bubbly flow where the gas void fraction is low and droplets in air, where the gas void fraction is high. The influence of the drag model and particle diameters for droplets and bubbles on the gas entrainment is studied.
For the drag, the Grace law (constant drag coefficient) and the Schiller Naumann law are tested. The particle diameter also has an influence on the drag. A variation of the drag force does not have an obvious effect on the gas entrainment in the simulations performed with the SIMMER model. The gas entrainment is overestimated in all simulations and there is no free parameter inside the SIMMER model which allows an adjustment of the entrainment in the simulation.
Keywords: Bubble entrainment, jet, impinging, plunging, PTS, ECC
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    NURESIM-SP2-TH-D2.1.3.3
    12 Seiten

Publ.-Id: 11720 - Permalink


Endotaxial growth of InSb nanocrystals at the bonding interface of the In+ and Sb+ ion implanted SOI structure
Tyschenko, I. E.; Voelskow, M.; Cherkov, A. G.; Popov, V. P.;
The formation of heterostructures-on-insulator is a way to increase the carrier mobility in the nanometer-scale layers. The electron mobility in InSb is about 50 times higher than that in bulk silicon. The formation of Si/InSb on insulator heterostructures may provide an increase of effective electron mobility in the nanometer scale SOI films. In this work, we present the results on the interface mediated endotaxial growth of InSb nanocrystalline phase at the Si/SiO2 bonding interface of silicon-on-insulator (SOI) structure.
Keywords: SOI mobility InSb heterostructures
  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1360-1363

Publ.-Id: 11719 - Permalink


Controlled localised melting in silicon by high dose germanium implantation and flash lamp annealing
Voelskow, M.; Pezoldt, J.; Kups, T.; Skorupa, W.;
The annealing of semiconductor surfaces via pulsed laser melting has been practised since the 70 ' s. During the process a thin surface layer is molten up to a depth of mkm and recrystallises, after the pulse is over, epitaxially on the non molten substrat.
Depending on the segregation coefficient of additionally admixed atoms completely different doping profiles can be achieved. Typical for all pulse irradiation techniques is, that the melting process starts near the surface. The aim of the present work is to overcome this phenomen and to force a buried melting by large area flash lamp irradiation using an additional Ge admixture. The addition of Germanium locally leads to a reduction of the silicon melting temperature so that separated melting in the bulk of silicon can be observed. During cooling down of the sample the buried liquid layer recrystallises epitaxially on the non molten bulk material and for the case of additional doping of the layer special profiles can be observed. Ion implantation at high doses and high energies was used to produce structures with a buried germanium enriched layer. The pulse irradiation was performed at the Rossendorf flash lamp apparatus using intense light pulses with a duration of 20 ms from a field of Xe flash tubes. The energy density at the sample surface was varied within wide limits. For the determination of the Ge profiles after the flash lamp irradiation the RBS technique was used. The microstructure of the recrystallised films was observed by cross sectional TEM. It could be shown that buried melting takes place whereby the width of the molten zone depends on the energy density. Deep facetted melting, typical for virgin silicon material, was not observed.
Keywords: flash lamp annealing buried melting germanium RBS TEM
  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1269-1272

Publ.-Id: 11718 - Permalink


Gamma flashes from relativistic electron-positron plasma droplets
Mustafa, G. M.; Kämpfer, B.;
Ultra-intense lasers are expected to produce, in near future, relativistic electron-positron plasma droplets. Considering the local photon production rate in complete leading order in quantum electrodynamics (QED), we point out that these droplets are interesting sources of gamma ray flashes.

Publ.-Id: 11717 - Permalink


Synthesis of a precursor for an alumina ceramic reinforced by zirconium dioxide from inorganic compounds in the presence of urea
Zharnylskaya, A. L.; Volkhin, V. V.; Shcherban, M. G.; Reuter, H.;
Samples of a precursor for an alumina ceramic reinforced by zirconium dioxide were synthesized. The samples have a uniform structure and are characterized by high ratios of the tetragonal and monoclinic modifications of ZrO2, tlm, after a thermal treatment (1250 degrees C). The structure of samples in the system Al2O3-ZrO2 is formed under conditions favorable for deposition of products of hydrolysis of Al(III) ions on the surface of ZrO2 sol particles in decomposition of urea. The coating of ZrO2 sol particles by products of hydrolysis of Al(III) salts was confirmed by electrophoresis. The size distribution of particles of the in?dividual ZrO2 sol was determined by small-angle X-ray scattering. The structure of the products formed in thermal treatment of samples of mixed oxides Al2O3-ZrO2 was characterized by X-ray phase analysis and scanning electron microscopy. The porosity and specific surface area of a thermally treated sample was determined by measuring nitrogen absorpt!
  • Russian Journal of Applied Chemistry 81(2008)7, 1147-1152

Publ.-Id: 11716 - Permalink


Force-free and contactless electromagnetic flow rate sensors
Priede, J.; Buchenau, D.; Gerbeth, G.;
We present a novel design of flowmeter using a single cylindrical permanent magnet magnetized perpendicularly to its axis about which it can freely rotate, and placed close the duct with liquid metal flow. The electromagetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation. However, the equilibrium rotation rate, which attained at vanishing net electromagnetic torque on the magnet, depends only on the flowrate and geometry of the system while it is independent of the electromagnetic torque itself. A laboratory model of a such flowmeter has been built and tested at a liquid metal flow.
Keywords: flowmeter
  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 815-819
  • Poster
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Publ.-Id: 11715 - Permalink


Experimental study of traveling magnetic field driven instability in a thermally stratified liquid gallium cylinder
Klyukin, A.; Grants, I.; Gerbeth, G.;
A liquid gallium cylinder is subject to a stable vertical thermal stratification (hot top and cold bottom) and an upward traveling magnetic field (TMF). The instability, which arises due to the combined action of magnetic field and temperature gradient, is investigated experimentally.
  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 627-631
  • Poster
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Publ.-Id: 11714 - Permalink


Nonstationary electrovortex flows in a long shallow channel with conducting fluid
Kolesnichenko, I.; Khripchenko, S.; Buchenau, D.; Gerbeth, G.;
This paper describes our investigations into the generation of the electro-vortex flow of a conducting fluid in a plane long layer in the unstable regime. In the context of the present problem we consider the velocity field and the amplitude and frequency of velocity oscillations of this flow. The pressure drop in the channel with inclined ferromagnetic plates induced by both the direct and alternating electrical currents is studied. The obtained results can be used in developing metallurgical devices having the maximum possible stability of the flow-rate.
  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 369-373
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Publ.-Id: 11713 - Permalink


Helical magnetorotational instability in a TaylorCouette flow
Priede, J.; Gerbeth, G.;
We analyze numerically 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. The Chebyshev collocation method is used to calculate the eigenvalue spectrum for small amplitude perturbations. Besides the convective instability threshold also an absolute one is found implying that this type of MRI might be experimentally observable in a system of sufficiently large but finite axial extension.
Keywords: magnetorotational instability
  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 251-255
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Publ.-Id: 11712 - Permalink


Vertical Gradient Freeze growth in a combined magnetic AC/DC field
Pätzold, O.; Lantzsch, R.; Grants, I.; Stelter, M.; Gerbeth, G.;
The Vertical Gradient Freeze (VGF) method is an important technology for the melt growth of bulk compound semiconductors. The structural perfection of the crystals and the distribution of dopants in the material are closely connected to the conditions of heat and mass transport in the liquid phase. The application of external magnetic fields allows for tailoring the melt flow and, hence, gives the possibility to optimize the quality of the crystals and the yield of the growth process.
In this paper experimental and numerical results are presented, showing the influence of a combined traveling magnetic field (TMF) and steady axial magnetic field (DC) on the VGF growth of semiconducting GaAs and Ge single crystals. The quality of the crystals is characterized in terms of the interface deflection, axial/radial macrosegregation and microsegregation. The numerical simulations of the VGF growth are performed using the commercial code CrysMAS. The TMF melt flow and its influence on the interface deflection as well as the resulting local v. Mises stress are calculated on the basis of a global thermal model of the equipment.
Keywords: Vertical Gradient Freeze, crystal growth, traveling magnetic field
  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 633-635
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Publ.-Id: 11711 - Permalink


An alternating magnetic field driven flow in a spinning cylindrical container and its three-dimensional linear stability analysis
Shatrov, V.; Gerbeth, G.; Hermann, R.;
We present a numerical analysis of the free surface liquid metal flow and its three-dimensional linear stability. The flow is driven by an alternating magnetic field in a spinning cylindrical container. The electromagnetic and hydrodynamic fields are fully coupled via the shape of the liquid free surface.
Keywords: free surface liquid metal flow, three-dimensional linear stability
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 525-529

Publ.-Id: 11710 - Permalink


Numerical modeling of the growth of small-diameter intermetallic compound crystals by a two-phase RF floating zone method
Krauze, A.; Priede, J.; Hermann, R.; Gerbeth, G.;
We model numerically the growth of small–diameter single crystals of intermetallic compounds by the floating zone technique using two-phase radio-frequency (RF) electromagnetic heating. An axisymmetric quasi-stationary numerical model is implemented as several coupled computer programs for modeling electromagnetic fields, heat source and force density distributions, heat transfer, and turbulent melt flow. The results of model calculations are presented for the growth of Ni crystals of 2 mm in diameter. It is found that the stable molten zone exists in a very narrow range of inductor currents.
Keywords: crystal growth, electromagnetic heating, floating zone technique
  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 851-855
  • Poster
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Publ.-Id: 11709 - Permalink


Interfacial heat and mass tansfer models
Krepper, E.; Scheuerer, G.;
The lesson 4 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of mass and energy exchange between the phases based on the two fluid model approach. After the basic principles the lesson describes the simulation of subcooled boiling and the simulation of cavitation processes.
Keywords: CFD, Two fluid model, heat transfer, mass transfer, boiling, cavitation
  • Invited lecture (Conferences)
    6th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 24.-26.06.2008, Dresden, Germany

Publ.-Id: 11708 - Permalink


Practical calculation of bubble column flow with CFX-11
Frank, T.; Lifante, C.; Krepper, E.;
The lesson 6 of the "Short Course on Multiphase Flow Modelling" describes the practical simulation of the flow in a bubble column. The necessiy of the correct simulation of the momentum exchange between the phases is shown comparing different results with experiments.
Keywords: CFD, two fluid model, dispersed gaseous phase, drag bubble forces, non drag bubble forces, bubble column
  • Invited lecture (Conferences)
    6th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 24.-26.06.2008, Dresden, Germany

Publ.-Id: 11707 - Permalink


Finite-time thermodynamics of shear flows - modelling attractors of simple to complex dynamics
Schlegel, M.; Noack, B.; Ahlborn, B.; Mutschke, G.; Morzynski, M.; Comte, P.; Tadmor, G.;
A finite-time thermodynamics formalism is proposed to compute mean flow and fluctuation levels of unsteady incompressible flows. The formalism builds upon a Galerkin model framework (see Noack et al., J. Noneqilib. Thermodyn. 33 (2008) 103-148) and is applied to a periodic vortex shedding regime behind a circular cylinder, homogeneous shear turbulence and the Burgers equation.
Keywords: finite-time thermodynamics, Galerkin methods, turbulence.
  • Poster
    Dynamics Days Europe 2008, 25.-29.08.2008, Delft, Netherlands

Publ.-Id: 11706 - Permalink


Periodically modulated surfaces and interfaces: Introducing artificial length scales to tailor magnetic properties
Fassbender, J.ORC; Liedke, M. O.; Strache, T.; Marko, D.; Lenz, K.; Keller, A.; Facsko, S.; Tibus, S.; Springer, F.; Albrecht, M.; Rohrmann, H.
In thin magnetic films different intrinsic length scales affect the magnetic properties, e.g., the exchange correlation length determined by the exchange constant and the anisotropy of the material or the grain size of polycrystalline materials determined mainly by the growth conditions and substrates used. In the latter case also the intergranular coupling influences the magnetic properties.

Introducing an artificial extrinsic length scale in the range 10 – 100 nm allows an additional degree of freedom to tailor the overall magnetic properties of the material of choice. This length scale is established by means of low energy ion erosion of semiconductor surfaces which lead to a periodically modulated surface (ripple structure). The periodicity and amplitude can easily be varied by means of the ion erosion parameters [1]. Hence upon thin film deposition modulated surfaces and interfaces of the magnetic films result.

Two different examples will be discussed. i) Induced magnetic anisotropies in soft magnetic films deposited on rippled substrates [2]. The microscopic origin can be extrinsic, due to dipolar stray fields, as well as intrinsic, due to spin-orbit coupling phenomena at monoatomic steps. The relative contribution of both microscopic effects to the macroscopically measurable material properties depend sensitively on the introduced ripple wavelength and amplitude. ii) Magnetic properties of hard magnetic CoCrPt-SiO2 perpendicular recording media [3]. Due to a combination of deposition on a modulated surface and post-deposition ion irradiation a predefined number of grains can be exchange coupled to act as one magnetic entity required for bit patterned media. The physical mechanisms will be discussed.

Support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged.

[1] S. Facsko, H. Kurz, T. Dekorsy, Energy dependence of quantum dot formation by ion sputtering, Phys. Rev. B 63, 165329 (2001).
[2] M. O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mücklich, S. Facsko, J. Fassbender, Induced anisotropies in exchange-coupled systems on rippled substrates, Phys. Rev. B 75, 220407(R) (2007).
[3] T. Strache, S. Tibus, F. Springer, H. Rohrmann, M. Albrecht, J. Fassbender, Tuning coercivity in CoCrPt-SiO2 hard disk material, OR15-4, International Conference on Ion Beam Modification of Materials, IBMM08, 31.08.-05.09.2008, Dresden, Germany
Keywords: magnetism, ion erosion, ion irradiation, modulated surfaces, MBE, intergranular coupling, induced anisotropies
  • Lecture (others)
    Seminar, National Institute of Standards and Technology, 03.11.2008, Boulder, USA
  • Invited lecture (Conferences)
    2nd International Conference on Physics at Surfaces and Interfaces, 23.-27.02.2009, Puri, Orissa, Indien
  • Lecture (others)
    Seminar, Institut für Physik, TU Ilmenau, 30.10.2008, Ilmenau, Deutschland
  • Invited lecture (Conferences)
    Symposium "Ion Beams and Nano-Engineering", MRS Spring Meeting, 13.-17.04.2009, San Francisco, USA

Publ.-Id: 11705 - Permalink


Application of GATE to detector optimisation in transmission gamma ray tomography
Hampel, U.; Kiessling, N.; Bieberle, A.;
We present results of a simulation study on the role of different design parameters for the count rate accuracy of a high resolution gamma ray detector used for transmission tomography. The considered gamma ray tomography system is operated with a Cs-137 isotopic source and a special detector composing 320 single elements, made of LYSO scintillators coupled to APD. Typically, energy resolution of the detector elements (geometry 2mm x 2mm x 24mm) is limited to about 25% which leads to erroneous counting of photons which have been Compton scattered before detection in other parts of the detector and the object. This introduces a linearity error into the tomographic data which leads to artefacts and errors in the reconstructed images. We therefore performed a theoretical analysis with the GATE simulation software. Simulation of the count rate error for the existing configuration shows good agreement with measured detector cross-talk. In the following we assessed different virtual design changes regarding crystal geometry, separation, shielding and arrangement. Results show that further increase in accuracy is possible.
Keywords: Monte Carlo simulation, GATE, scattered radiation, radiation cross-talk, gamma ray tomography
  • Lecture (Conference)
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
    IEEE NSS/MIC/RTSD Conference Record

Publ.-Id: 11704 - Permalink


Ultra fast electron beam X-ray computed tomography for two-phase flow measurement
Fischer, F.; Hampel, U.;
Electron beam X-ray CT is a new technique for a fast measurement of multiphase flows with frame rates of 1000 images per second and more. It gives, in principle, quantitatively accurate images of the flow at high spatial resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated by X-rays. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement studies we devised and built a fast scanned electron beam X-ray tomography scanner. The scanner consists of an electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current, with the required electron optics for beam adjustment, beam focussing and beam deflection unit and a fast circular CZT detector comprising 240 elements of 1.5 mm x 1.5 mm x 1.5 mm active pixel
area. X-ray radiation is produced on a circular water cooled tungsten target The CT system achieves up to 7000 frames per second with a spatial resolution of 1 millimetre. First two-phase flow experiments have been carried out on gas-water flows in bubble columns. On the basis of these data we developed image processing algorithms which enable to extract information on bubble shapes, bubble size distributions and interfacial area density distribution. Further, a vertical test section made of titanium alloy has been installed at the TOPFLOW facility and will be used in the future to study the evolution of two-phase gas-water pipe flow at high pressures and temperatures.
Keywords: Two-phase flow, electron beam tomography, CFD code validation
  • Contribution to proceedings
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
    Proceedings of XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety
  • Lecture (Conference)
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 12.09.2008, Grenoble, France

Publ.-Id: 11703 - Permalink


Quadratic detection and autocorrelation measurements with two-photon quantum well infrared photodetectors
Schneider, H.; Winnerl, S.; Liu, H. C.; Drachenko, O.; Helm, M.; Walther, M.; Faist, J.;
The two-photon quantum well infrared photodetector (QWIP) comprises three equidistant subbands, two of which are bound in the quantum well, and the third state in the continuum. This results in a resonantly enhanced optical nonlinearity, which is by six orders of magnitude stronger than in usual semiconductors. In addition, temporal resolution is only limited by the sub-ps intrinsic time constants of the quantum wells, namely the intersubband relaxation time and the dephasing time of the intersubband polarization. Both properties make this device very promising for quadratic autocorrelation measurements of pulsed mid-infrared sources, including modelocked quantum cascade lasers, radiation obtained by nonlinear optical frequency conversion, and free-electron lasers (FEL).
We have performed autocorrelation measurements of ps optical pulses from the free-electron laser (FEL) facility FELBE at the Forschungszentrum Rossendorf. Using a rapid-scan autocorrelation scheme at a scan frequency of 20 Hz, high-quality quadratic autocorrelation traces are obtained, yielding ratios close to the theoretically expected value of 8:1 between zero delay and large delay for interferometric autocorrelation, and 3:1 for intensity autocorrelation. Thus, two-photon QWIPs provide an excellent new approach to online pulse monitoring of the FEL. In addition, we have investigated the saturation mechanism of the photocurrent signal, which is due to internal space charges generated in the detector. We will also report on room temperature operation of two-photon QWIPs.
Keywords: quantum well infrared photodetector, two-photon absorption, intersubband transition, quadratic autocorrelation, GaAs/AlGaAs
  • Lecture (Conference)
    9th International Conference on Mid-Infrared Optoelectronics: Materials and Devices (MIOMD-IX), 07.-11.09.2008, Freiburg, Deutschland

Publ.-Id: 11702 - Permalink


Spannungs- und Ermüdungsanalyse für den Sicherheitsbehälter des KKW Krümmel
Altstadt, E.;
Es handelt sich um einen vertraulichen Bericht, kein Abstract.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\07

Publ.-Id: 11701 - Permalink


Spannungs- und Ermüdungsanalyse für die RDB-Einbauten des KKW Krümmel
Altstadt, E.; Werner, M.;
Es handelt sich um einen vertraulichen Bericht, kein Abstract.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\06

Publ.-Id: 11700 - Permalink


Spannungs- und Ermüdungsanalyse für den RDB-Boden des Kernkraftwerks Krümmel
Altstadt, E.;
Es handelt sich um einen vertraulichen Bericht, kein Abstract.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\05

Publ.-Id: 11699 - Permalink


In-beam Positron Emission Tomography for Ion Therapy Monitoring
Fiedler, F.; Laube, K.; Möckel, D.; Parodi, K.; Pawelke, J.; Priegnitz, M.; Shakirin, G.; Enghardt, W.;
Due to the special characteristics of ion beams and delicate treatment situations, i.e. in close vicinity to organs at risk, a three-dimensional, in-vivo and in-situ monitoring of the dose delivery is highly desirable. At present, in-beam PET is the only method meeting these requirements. An in-beam PET system has been implemented for clinical application at the carbon ion therapy facility of the Gesellschaft für Schwerionenforschung (GSI) Darmstadt. So far, more than 400 patients have been monitored with this system. It could be demonstrated that this PET technique is capable of assessing relevant parameters for quality assurance of carbon ion therapy, measuring the particle range in tissue, the position of the irradiated volume with respect to anatomical landmarks, and estimating local deviations between the planned and applied dose. In-beam PET has become a tool providing valuable clinical feedback.
The implementation of the in-beam PET system at the medical beamline at GSI will be described. Clinical results will be shown with examples. Furthermore, the application of in-beam PET for protons, 3-He, 7-Li and 16-O shows promising results and will be presented.
Keywords: in-beam PET, ion therapy
  • Invited lecture (Conferences)
    IGRT Vienna 2008 - Visions and Perspectives in Image Guided Radiation Oncology, 24.-26.09.2008, Wien, Österreich

Publ.-Id: 11698 - Permalink


From multiply twinned to fcc nanoparticles via irradiation-induced transient amorphization
Järvi, T. T.; Pohl, D.; Albe, K.; Rellinghaus, B.; Schultz, L.; Fassbender, J.ORC; Kuronen, A.; Nordlund, K.
We present experimental evidence for structural trransformation of multiply twinned CuAu nanoparticles to single crystalline morphology by 0.5 keV helium irradiation. This finding is unexpected as the stability of twin boundaries should not be affected by ion-beam induced Frenkel pairs. Molecular dynamics simulations reveal, however, a new transformation mechanism based on transient amorphization of the particle. By comparing with irradiation simulations of elemental nanoparticles, as well as alloyed bulk samples and surface cascades, we show that this transformation route is only present in alloyed particles. Moreover, the observed amorphization is more efficient for twinned than single-crystalline particles. This, together with the fast recrystallization kinetics in CuAu, explains the experimentally observed untwinning process.
Keywords: ion irradiation, nanoparticles, binary alloys, structural transformation, ordered phases

Publ.-Id: 11697 - Permalink


The effect of ion irradiation and annealing on exchange spring magnets
Fassbender, J.ORC; Grenzer, J.; Roshchupkina, O.; Choi, Y.; Jiang, J. S.; Bader, S. D.
It is demonstrated that both the nucleation field and the irreversible switching field of Sm2Co7/Fe exchange spring bilayers is decreased by means of 10 keV He ion irradiation. The reduction is attributed to interfacial mixing and irradiation induced softening of the hard magnetic layer. By lowering the energy to 0.8 keV the ions do not penetrate the hard magnetic layer and consequently no softening is observed. However, although irradiation induced interfacial mixing is still present it is not large enough to create a graded interface layer and the nucleation field decreases. In contrast conventional annealing under appropriate conditions leads to an increase of the nucleation field. This distinct discrepancy can be explained by detailed investigation of the layer structure by x-ray reflectivity measurements.
Keywords: magnetism, ion irradiation, exchange spring, hard magnets

Publ.-Id: 11696 - Permalink


Simulation analysis of the spatial sensitivity of a wire-mesh sensor
Thiele, S.; Da Silva, M. J.; Wagner, M.; Hampel, U.;
The wire-mesh sensor is an imaging instrument which is able to generate cross-sectional phase distribution images with high spatial and temporal resolutions, thus being very well suitable for the investigation of multiphase flows. It has successfully been used in several research and industrial applications. In this article, we present the results of the precise simulation analysis of the spatial sensitivity of this device, which support further developments of the image data processing.
Keywords: wire-mesh sensor, spatial sensitivity, numerical field simulation
  • Contribution to proceedings
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Germany
    EUROSENSORS XXII, Duesseldorf: Verein Deutscher Ingenieure e.V. (VDI), 978-3-00-025217-4, 157-160
  • Poster
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Germany

Publ.-Id: 11695 - Permalink


Intraminiband relaxation in doped GaAs/AlGaAs superlattices studied by two-color infrared pump-probe experiments
Stehr, D.; Wagner, M.; Schneider, H.; Helm, M.; Andrews, A. M.; Roch, T.; Strasser, G.;
no abstract available
Keywords: superlattice, free electron laser, infrared
  • Poster
    29th International Conference on the Physics of Semiconductors, 27.07.-01.08.2008, Rio de Janeiro, Brazil

Publ.-Id: 11694 - Permalink


Intersubband relaxation and dephasing in narrow InGaAs/AlAsSb quantum well structures
Villas-Boas Grimm, C.; Pfau, C.; Ohser, S.; Winnerl, S.; Schneider, H.; Helm, M.; Biermann, K.; Künzel, H.;
no abstract available
Keywords: intersubband, quantum wells, infrared, dephasing
  • Poster
    29th International Conference on the Physics of Semiconductors, 27.07.-01.08.2008, Rio de Janeiro, Brazil

Publ.-Id: 11693 - Permalink


Structural identification of thioarsenates and their differentiation from thioarsenites by EXAFS
Suess, E.; Scheinost, A. C.; Bostick, B. C.; Merkel, B. J.; Wallschlaeger, D.; Planer-Friedrich, B.;
Thioarsenic complexes play an important role in regulating arsenic solubility, mobility, and toxicity in sulfidic systems. Despite their importance, there is little consensus on their thermodynamic properties and structural identification. A major focus of current research is the unambiguous identification of the members of the two homologue series of monomeric thioarsenic species that are conceptually postulated to exist under sulfidic conditions, (oxy)thioarsenites and (oxy)thioarsenates. Here we report the unambiguous identification of synthetic mono-, di, and tetrathioarsenate using a combination of X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). As-O and As-S coordination numbers confirmed the structure as the expected mono-, di- and tetrathioarsenate compounds. The As-O bond distances of 1.69 to 1.70 $\AA$ are comparable with those stated for arsenates, and are easily distinguishable from those for arsenites at 1.78 $\AA$. The As-S distances in our standard materials with 2.17 $\AA$ are clearly shorter than those published for arsenite-sulfide minerals with 2.24 to 2.34 $\AA$. As expected, no As-O bonding was determined in tetrahedral tetrathioarsenate, which is fully coordinated to S. As the extent of thiol complexation increases, the position of the absorption-edge shifts systematically and linearly towards lower energies compared to that of arsenate. The structural data for the individual solid and liquid samples, measured at room temperature or at 15 K, did not show obvious differences, suggesting that the aqueous complexes have similar structures as the XRD-identified solids and are stable in natural waters. An interesting observation was made during the titration of the liquid tetrathioarsenate from pH 6 to 3. Below neutral pH, the absorption edge shifted to lower energies by $\sim$2 eV concomitant with an increase of the As-S bond length to 2.28 $\AA$ at pH 3, comparable with those of orpiment and indicative of either thioarsenites (which have been reported to exist in arsenite-sulfide-containing solutions) or colloidal orpiment. As for thioarsenates, the observed complexes also show a linear trend together with arsenite and orpiment, clearly distinguishable from the arsenate-based line. The present data demonstrate that it is possible to differentiate thioarsenates from thioarsenites by XAS. Combined with other recent studies, these data indicate that thioarsenates can be formed in sulfidic solutions under a broad range of conditions.
Keywords: arsenic arsenite arsenate EXAFS
  • Poster
    2008 AGU Fall Meeting, 15.-19.12.2008, San Francisco, USA

Publ.-Id: 11692 - Permalink


High energy Xe+ ion beam induced rippled patterns on silicon
Hanisch, A.; Grenzer, J.; Facsko, S.; Biermanns, A.; Pietsch, U.; Metzger, T. H.; Carbone, G.;
Under certain conditions ion beam bombardment on semiconductor surfaces leads to well-defined morphological structures in the nanoscale range caused by a self-organization process. Due to the ion impact as a start the surface-adjacent layer is amorphized before a periodical wave-like rippled structure on the surface as well as at the amorphous-crystalline interface is developed. So far we found that the ripple wavelength linearly scales with the ion energy in a range of 5 to 70 keV (50 to 300 nm). Furthermore, we try to evaluate the ripple patterns from the point of homogeneity and uniformity. Therefore, we defined a quality factor for the amplitude and a correlation length for the wavelength to characterize the structures over a larger scale. We used a routine to extract the ripple amplitude from the Atomic Force Microscopy (AFM) images. In order to determine the correlation length we prosecuted Grazing Incidence Small Angle X-Ray Scattering (GISAXS) measurements.
Also, we asked for the mechanisms behind the formation of ripples. The investigation of the amorphous-crystalline interface gives a first hint. The subsurface structure has been identified by both Transmission Electron Microscopy (TEM) and Rutherford backscattering (RBS). Applying two different ion types for the formation of rippled patterns we could identify clear differences in the structure of the amorphous layer.
Keywords: nanopatterns, ripples, self-organization
  • Poster
    IBMM 2008 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.08, Dresden, Deutschland

Publ.-Id: 11691 - Permalink


Magnetic and transport properties of Cu1.05Cr0.89 Mg0.05O2 and Cu0.96Cr0.95 Mg0.05Mn0.04O2 films
Xu, Q.; Schmidt, H.; Zhou, S.; Potzger, K.; Helm, M.; Hochmuth, H.; Lorenz, M.; Meinecke, C.; Grundmann, M.;
We prepared conductive, polycrystalline or amorphous Cu1.05Cr0.89 Mg0.05O2 films on a-plane sapphire substrates by pulsed laser deposition under different O2 partial pressure and substrate temperature. Hall measurements were performed to study the majority carrier type in these films. Polycrystalline Cu1.05Cr0.89 Mg0.05O2 is n-type conducting at 290 K, while in amorphous Cu1.05Cr0.89 Mg0.05O2 the type of majority charge carriers changes from electrons to holes at around 270 K. Interestingly, the structure has little influence on the magnetic properties of the films. A clear antiferromagnetic to paramagnetic transition was observed in both polycrystalline and amorphous Cu1.05Cr0.89 Mg0.05O2 films at 25 K. Similar electrical properties to Cu1.05Cr0.89 Mg0.05O2 film were observed for Cu0.96Cr0.95 Mg0.05Mn0.04O2 in dependence on the structure, while only paramagnetic without antiferromagnetic ordering was observed down to 5 K. Large negative magnetoresistance of 27% at 20 K was observed at 6 T in amorphous Cu1.05Cr0.89 Mg0.05O2 film.
Keywords: Oxide semiconductor; Hall effect; Magnetic properties; Magnetoresistance

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Publ.-Id: 11690 - Permalink


Simulation of a nano-scale magnetic switch
Pankoke, V.; Gemming, S.;
We used ab-initio methods in the LDA with pseudo potentials and a plane wave basis to simulate the growth of thin palladium films on the piezo electric oxide PMN (Pb(Mg/Nb)O3). It is known that the palladium ground state is similar to the ground state of ferromagnetic nickel. A magnetic switch of nano-scale dimension might be possible if the palladium ground-state can be forced to get also ferromagnetic. The piezo electric property of PMN oxides can be used to achieve this by an expansion of the lattice constant. First calculations on bulk-Pd with all-electron and pseudo-potential methods lead to different results with respect to the magnetic ground state, but it seems, that the projector augmented wave method PAW describes the magnetism correctly. In PAW calculations pure fcc-palladium films remain non-magnetic during expansion, but a doping with cobalt can help to induce a magnetic state.
Keywords: Magnetism, magnetic transition, film growth
  • Lecture (Conference)
    Junior Euromat 2008, 14.-18.07.2008, Lausanne, Schwitzerland

Publ.-Id: 11689 - Permalink


Evolution of ripple morphologies on silicon during sub-keV ion sputtering
Keller, A.; Facsko, S.; Peverini, L.; Kozhevnikov, I. V.; Möller, W.;
It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces may lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. The ripples produced in this way are oriented either parallel or normal to the projection of the ion beam and their wavelength scales with ion energy. These structures have been found on a large variety of materials, such as semiconductors, metals, and insulating surfaces. The formation and early evolution of the ripple patterns can be qualitatively reproduced by a linear continuum equation derived by Bradley and Harper. At longer times, however, nonlinear terms have to be taken into account leading to nonlinear models based on the Kuramoto-Sivashinsky equation.
The evolution of Si(100) surfaces during oblique sub-keV ion sputtering has been studied in-situ and ex-situ by means of surface sensitive X-ray techniques, namely X-ray Reflectivity and Grazing Incidence Small Angle X-ray Scattering (GISAXS), and atomic force microscopy, respectively. The observed morphologies are dominated by nanoscale ripples at short lateral scales but exhibit kinetic roughening at larger distances. The roughening of the surface is found to depend strongly on the angle of incidence and even small changes of only 2° lead to very different roughening dynamics. The obtained experimental results will be compared to predictions of different nonlinear continuum models of ion erosion.
  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11688 - Permalink


Ferromagnetic structurally disordered ZnO implanted with Co ions
Potzger, K.; Zhou, S.; Xu, Q.; Shalimov, A.; Groetzschel, R.; Schmidt, H.; Muecklich, A.; Helm, M.; Fassbender, J.ORC
We present superparamagnetic clusters of highly disordered Zn-Co-O created by high fluence Co ion implantation into ZnO (0001) single crystals at low temperatures. This secondary phase cannot be detected by x-ray diffraction but by high-resolution transmission electron microscopy. In contrast to many other secondary phases it shows anomalous Hall effect and thus is a candidate for magneto-electronics applications.
Keywords: ZnO, diluted magnetic semiconductors, ion implantation
  • Applied Physics Letters 93(2008)23, 232504

Publ.-Id: 11687 - Permalink


The Rossendorf Beamline at ESRF: the next 10 years of actinide XAFS
Scheinost, A. C.; Funke, H.; Hennig, C.; Rossberg, A.; Banerjee, D.; Hesse, M.;
The Rossendorf Beamline as a dedicated X-ray absorption spectroscopy station for actinide research is in operation since 1998. It has served for hundreds of experiments in the past 10 years, ranging from Materials Science to Aquatic and Environmental Chemistry of actinides and other radionuclides. A short overview on research highlights will be given, including the current extensive work on redox processes.
The beamline’s strength is built on the high reliability and flux of the ESRF, which allows to run samples even at very low concentrations of a few ppm, and on the long experience with actinide EXAFS. After 10 years of operation, the beamline is ready to take the next step in order to further lower the concentration limits of XAFS and to extend the array of methods to -XRF, -XAFS and XRD. Essential optical components will be replaced parallel to the upgrade of the ESRF to increase the photon flux by about one order of magnitude to 1012 photons/sec on the sample, and to prepare the microfocus. Additional modifications like easily exchangeable monochromator crystals, additional mirror coatings and a routine quick-XAFS mode will widen the experimental possibilities without sacrificing the user friendly operation of the beamline.
These changes are planned for 2010, and will be installed and commissioned with little loss of beamtime. This is especially important, since the Rossendorf Beamline will continue to provide its facilities to the actinide community within the ACTINET network, in addition to the routine beamtime application paths via ESRF and FZD collaborations.
An overview on the current status of operation modes, technical details, access conditions and user support with advanced data analysis methods is presented, by updating earlier information and summarizing the features most important for prospective users.
Keywords: XAFS actinides synchrotron
  • Invited lecture (Conferences)
    Actinide-XAS 2008, 15.-17.07.2008, Saint Aubin, France

Publ.-Id: 11686 - Permalink


SANS investigation of irradiation-induced phase separation in binary Fe-Cr-alloys
Ulbricht, A.; Bergner, F.; Heintze, C.; Eckerlebe, H.;
Ferritic-martensitic chromium steels are candidate materials for future applications in both Gen-IV and fusion technology. Investigations of related binary Fe-Cr alloys will significantly contribute to the understanding of the behaviour of more complex alloys. The presented SANS results are focused on a Fe-9at.% Cr alloy neutron-irradiated up to a dose of 1.5 displacements per atom (dpa).
We have observed a pronounced increase of scattering intensities for two different irradiation conditions at scattering vectors Q > 0.2 nm-1 for both magnetic (figure (a)) and nuclear scattering. The reason for the increased intensities are irradiation-induced clusters with size distributions presented in figure (b). The A-ratio is about 2.8 for both irradiation conditions. This value is far from a value of 1.45 corresponding to nanovoids as scattering objects. This indicates that the irradiation-induced clusters are different from pure nanovoids and must contain Cr-atoms with the same or very similar average composition for both irradiation conditions. These clusters are interpreted as alpha’-phase. The volume fraction of clusters of this type increases slightly with neutron dose.
Keywords: SANS, irradiation-induced cluster, Fe-Cr alloy
  • Poster
    Deutsche Neutronenstreutagung 2008, 15.-17.09.2008, Garching, Deutschland

Publ.-Id: 11685 - Permalink


Influence of carbonate complexation on the sorption of U(VI) on montmorillonite
Marques Fernandes, M.; Dähn, R.; Baeyens, B.; Scheinost, A.; Bradbury, M. H.;
Clay minerals play an important role in the retention/retardation of radio-contaminants in the near- and far-fields of a radioactive waste repository. Identifying and quantifying the radionuclide sorption processes occurring at clay/solution interface over a representative range of relevant conditions is indispensable for performance assessment.
Next to hydroxide ions, carbonate is the predominant inorganic ligand in most natural groundwaters and clay porewaters. Actinides are known to form very strong carbonate complexes in solution, which could potentially decrease the metal ion sorption and thus increase the migration rates of actinides. The aim of this study is:
To apply Extended X-Ray Absorbtion Spectroscopy to verify whether or not U(VI)-carbonato ternary complexes form at the montmorillonite surface

The macroscopic sorption data show a significant influence of dissolved carbonate on the sorption of U(VI)) on Na-montmorillonite.
Structural data obtained by EXAFS show unambiguously that U(VI) forms inner-sphere complexes at the montmorillonite surface (splitting of the Oeq shell, Si and Fe shell).
No difference is observed in the absence and the presence of carbonate (no C shell ~ 2.90 Å [1], no Odist shell), indicating that no U(VI)-carbonato ternary complexes
form at the montmorillonite surface.
Keywords: EXAFS Uranium Sorption Montmorillonite Carbonate
  • Poster
    Actinide-XAS 2008, 15.-17.07.2008, Saint Aubin, France

Publ.-Id: 11684 - Permalink


Bacterial cell walls - Promoters and inhibitors of mineral nucleation
Behrends, T.; Scheinost, A.; Shaw, S.; Benning, L.; van Cappellen, P.;
Formation of minerals at the Earth’s surface can often be directly or indirectly assigned to the activity of microorganisms. Regarding a direct effect, several examples of microbially controlled, extracellular precipitation of minerals have been reported, which typically involve the enrichment of metal ions at the bacterial surface. However, sorption of metal ions to microbial cell walls might also inhibit mineral formation. Here, we present two examples in which interactions between metal ions and bacterial cell walls interfere with the formation of mineral although a promoting effect could be anticipated: the formation of UO2 as a consequence of microbial U reduction and the formation of Mn oxides in the presence of a Mn oxidizing organism. Microbial reduction of U(VI) to U(IV) is expected to result in the precipitation of solid UO2 at neutral pH.
However, EXAFS analyses of samples from incubation experiments with the organism Shewanella putrefaciens revealed that enzymatic reduction of U(VI) did not instantaneously lead to the formation of an UO2 precipitate but that U(IV) was monomerically associated with the bacterial cells. Indications were obtained that U(IV) in this form is very susceptible for reoxidation.
The kinetics of Mn(II) oxidation with and without the organism Pseudomonas putida were studied at pH 7.5 and 8.5.
The rates of Mn2+(aq) consumption in the presence of bacteria were similar at both pH values although the rates of abiotic Mn oxidation, determined in the absence of bacteria, were higher at pH 8.5. XANES analyses showed that the removal of Mn(II) from solution by the bacteria at pH 8.5 was, in contrast to pH 7.5, not caused by Mn oxidation. Consequently, not only enzymatic Mn(II) oxidation but also the abiotic oxidation were inhibited at pH 8.5 in the presence of bacteria. Possible mechanisms for the removal of dissolved Mn(II) by the bacteria and the inhibition of the abiotic oxidation at pH 8.5 will be discussed.
Keywords: Uranium EXAFS Redox Shewanella Mn oxides
  • Lecture (Conference)
    Goldschmidt 2008, 13.-18.07.2008, Vancouver, Canada
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 72(2008)12, A68

Publ.-Id: 11683 - Permalink


X-ray photoelectron and absorption spectroscopy investigation of Se-IV and Sb-V reduction by mackinawite
Banerjee, D.; Kirsch, R.; Scheinost, A. C.;
Both Se and Sb exist in nature in a wide range of oxidation states and can be potential hazardous contaminants depending on their speciation and reactivity. While Se typically occurs as oxyanions (SeO3-2 and SeO4-2) in oxic conditions, it can be reduced by FeII containing minerals such as mackinawite (FeS) to Se0 and Se–II [1, 2]. Similarly, Sb occurs in several oxidations states (-III, 0, III, V) and is shown to strongly adsorb to Fe oxide minerals as Sb(OH)6 - and subsequently reduced to the more mobile form Sb(OH)3(aq) [3]. In this study we employed cryogenic-XPS and XAS techniques in order to understand the redox processes involving SeIV and SbV at the surface of mackinawite.
Fe 2p XPS spectrum of pure mackinawite surface revealed presence of both FeII-S and FeIII-S species and the proportion of the latter increased when reacted to SeIV suggesting oxidation of surface FeII. In addition, presence of elemental S at the surface of the reacted sample suggested oxidation of sulfur as well. Corresponding Se K-edge XANES spectra of the reacted sample confirmed reduction of Se with the formation of FeSe. These results suggest that Se reduction is coupled to both S-II/S0 and FeII/FeIII redox half reactions.
Sb 3d spectrum of the reacted sample revealed that SbV was completely reduced to SbIII at the surface of mackinawite.
However, the S 2p spectrum of the reacted sample remained largely unchanged except for a slight increase in surface monosulfide content. This suggests that in contrast to the SeIVmackinawite system, S did not take part in the redox reaction involving SbV. The Fe 2p spectrum, however, showed a distinct shoulder of FeIII-species indicating oxidation of surface FeII. Corresponding Sb K-edge EXAFS of the reacted sample confirmed that the SbIII was coordinated to three sulfur atoms at a distance of 2.5 Å as in Sb2S3, which most likely explains the slight increase in the surface monosulfide content in the S 2p spectrum.
These results demonstrate the importance of surface mediated redox reactions in controlling the fate of toxic
contaminats such as Se and Sb in soil and groundwater.
[1] Charlet et al. (2007) GCA 71, 5731-5749. [2] Scheinost & Charlet (2008) ES&T, online. [3] Scheinost et al. (2006) GCA 70, 3299-3312.
Keywords: XPS XAFS selenium antimony Se Sb redox
  • Lecture (Conference)
    Goldschmidt 2008, 13.-18.07.2008, Vancouver, Canada
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 72(2008)12, A51

Publ.-Id: 11682 - Permalink


EXAFS investigation of U(VI) speciation in cementitious materials
Macé, N.; Harfouche, M.; Dähn, R.; Tits, J.; Scheinost, A.; Wieland, E.;
Cement in the Swiss radioactive waste management program is used as a waste matrix for the long-lived intermediate-level waste (ILW) disposal, where Uranium is an important radionuclide. Calcium Silicate Hydrates (C-S-H) are one of the major components of Hardened Cement Paste (HCP). In such a context, the understanding of Uranium uptake processes occurring in cementitious materials is necessary.

U(VI) uptake by C-S-H (CaO/SiO2 = 1.07) in Artificial Cement pore-Water (ACW) and HCP has been investigated using X-Ray Absorption Spectroscopy (XAS) technique in order to determine the chemical environment of sorbed and precipitated U(VI) species in cementitious matrices.

Phase X (CaUO4(H2O)x) and a uranophane ([Ca(H3O)2](UO2)2(SiO4)2(H2O)3) have been chosen as relevant reference compounds.

Similar coordination environment of U(VI) taken up by C-S-H and HCP
U(VI) sorbed species  a-uranophane-like structure
U(VI) precipitated species  phase-X-like structure
No split equatorial shell is observed
Complementary informations are expected using Time-Resolved Laser Fluorescence spectroscopy (TRLFS)
Keywords: Uranium cement EXAFS
  • Poster
    Actinide-XAS 2008, 15.-17.07.2008, Saint Aubin, France

Publ.-Id: 11681 - Permalink


Kinematic dynamos in cylindrical geometry
Giesecke, A.; Stefani, F.; Gerbeth, G.;
In order to understand the results of recent dynamo experiments, the behavior of kinematic dynamos in cylindrical geometries is analyzed. Simulations are performed applying a hybrid finite volume/boundary element method that allows a stringent treatment of insulating boundary conditions.

A suitable prescribed velocity field, either analytic or -- more realistic -- from measurement data from water experiments, leads to dynamo action, and a strong influence of boundary conditions and additional (stagnant) fluid layers around the active domain is observed.

An additional source term for dynamo action exists in case of a spatially varying conductivity distribution. A very simple set-up -- serving as a proof of concept -- is given by a steady axial flow in an infinite cylinder with inhomogenous container walls. Such a configuration is sufficient for dynamo action, however, the critical Reynolds number might be too large for the realisation in a simple laboratory-sized experiment.

Similiar effects appear in case of permeability inhomogenities, where increased gradients might also lead to a significant reduction of the critical Reynolds number.
Keywords: Dynamo Boundary Conditions Simulations
  • Lecture (Conference)
    EURO MHD 2008, 23.-26.09.2008, Nice, France

Publ.-Id: 11680 - Permalink


Electromagnetic stirring with superimposed travelling and rotating magnetic fields
Cramer, A.; Pal, J.; Gerbeth, G.;
Flow visualization and velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating and a travelling magnetic field. The combination of both fields, which is not necessarily a linear superposition, may give rise to an inherent three-dimensional constituent of the electromagnetic force distribution. As the Lorentz force may also become time-dependent, a quite intense mixing of metallic melts is achievable.
Keywords: Electromagnetic processing of materials, liquid metal flow, combined magnetic fields, stirring
  • Electrical Review (2008)11, 144-148

Publ.-Id: 11679 - Permalink


Balance-based real-time monitoring – a tool to improve safety and efficiency of batch and semi-batch processes
Kryk, H.; Hessel, G.;
In the fine chemical and pharmaceutical industry, batch and semi-batch processes are mostly used to produce special chemicals in small amounts. The behaviour of such strongly exothermic processes in stirred tank reactors is characterised by instationarity, non-linearity and a large number of influences which may affect the process safety and efficiency as well. Especially in multi purpose plants, such complex processes are usually controlled by conventional process variables, such as temperatures, pressures, dosing rates etc., but without any knowledge of the crucial parameters of a chemical reaction, the concentration profiles of reactants, products and intermediates. Thus, even experienced operators have difficulties to distinguish allowable from undesired process deviations and to identify the cause of process trends.
Therefore, it is of vital importance to establish industrially applicable methods for an objective detection of the actual process state and for alerting the operators in case of undesired process deviations. To avoid the use of expensive and fragile on-line analytics, a real-time monitoring approach based on adaptive energy and mass balances was developed, and related monitoring systems were tested at pilot scale and industrial applications as well.
Especially, if such a real-time monitoring approach is used as an integral part of a batch information management system (BIMS), the additional data could contribute to the enhancement of the process knowledge as a basis for continuative process optimisation. The additional process information provided by real-time monitoring systems enables application of advanced control strategies up to the point of a safety-oriented fully automated control of complex exothermic batch and semi-batch processes.
  • Invited lecture (Conferences)
    9th International Conference and Exhibition on The Scale-Up of Chemical Processes, 15.-17.09.2008, Rome, Italy
  • Contribution to proceedings
    9th International Conference and Exhibition on The Scale-Up of Chemical Processes, 15.-17.09.2008, Rome, Italy
    Conference Proceedings, Scale-up of Chemical Processes

Publ.-Id: 11678 - Permalink


X-ray spectroscopic and magnetic investigation of C : Ni nanocomposite films grown by ion beam cosputtering
Abrasonis, G.; Scheinost, A. C.; Zhou, S.; Torres, R.; Gago, R.; Jimenez, I.; Kuepper, K.; Potzger, K.; Krause, M.; Kolitsch, A.; Moller, W.; Bartkowski, S.; Neumann, M.; Gareev, R. R.;
The nearest-neighbor coordination and electronic structure in C:Ni(∼30 at.%) nanocomposite films grown by ion beam cosputtering in the temperature range of room temperatue (RT) to 500 °C are investigated by the means of extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS). The obtained results are correlated with the composite nanostructure published elsewhere and magnetic properties determined by the means of X-ray magnetic circular dichroism (XMCD) and superconducting quantum interference device (SQUID) magnetometry. A combined use of EXAFS, XANES, and XPS shows that a carbidic Ni phase exhibiting only local atomic ordering is formed at low growth temperatures (e200 °C), while ordered carbidic Ni phase forms at ∼300 °C. Further increase in growth temperature results in the formation of face-centered cubic (fcc) Ni with a high degree of crystallinity. On the other hand, Ni incorporation strongly promotes the formation of carbon structures with the prominent peak in C K-edge XANES spectra positioned at 288.5 eV in the whole growth temperature range. The magnetic measurements show no magnetic response for the films grown at RT to 200 °C, superparamagnetic behavior for the film grown at 500 °C with >90% of the Ni atoms in metallic state, and a weak magnetic response for the film grown at 300 °C, indicating the presence of Ni-rich regions within carbon containing Ni nanoparticles with ∼3% of Ni atoms in metallic state.
  • Journal of Physical Chemistry C 112(2008), 12628-12637

Publ.-Id: 11677 - Permalink


Qualification of simulation tools for two-phase flows
Lucas, D.;
According to the state of the art nuclear safety analyses related to thermohydraulics are mostly done using so-called system codes. Such one-dimensional codes base on empirical or semi-empirical correlations, which are generally geometry dependent and valid only within a limited range of scales. In principle the validation of such codes requires experimental data obtained for the same geometries, similar scales and flow conditions. In the past such codes were validated and successfully applied to many relevant flow situations. But the transferability to differing flow situations as well as the reliability for flows with pronounced 3D effects as they are observed e.g. in Reactor Pressure Vessel (RPV) is questionably. For this reason there is an interest to apply beside system codes also Computational Fluid Dynamics (CFD) codes for special analyses in future. Presently CFD codes are frequently used in practical applications for single phase flows, e.g. in automobile or aviation industries. Two-phase flow simulations using CFD codes are not yet mature due to the complex interactions between the phases. Closure models are needed to describe mass, momentum and energy transfer between the phases. Such models should consider only local flow parameters, i.e. correlations available for system codes cannot be transferred in general for the use in CFD codes. Such models have to be developed and validated basing on new experimental data with high resolution in space and time. Examples are poly-dispersed bubbly flows which require a multi bubble size modelling or models for separated flows in horizontal or near horizontal channels. TOPFLOW is a unique thermal hydraulic test facility for such two-phase flow studies. Experiments can be carried out for air-water or steam-water two phase flows at pressures up to 7 MPa. For steam production up to 4 MW heating power are available. The TOPFLOW facility is currently prepared for different types of flow experiments in vertical test sections and a large pressure chamber. Unique measurement devices, such as high-pressure wire-mesh sensors and an X-ray scanner are available. They provide CFD like data, which means data in high resolution in space and time. The lecture gives a general overview on the CFD model development and validation for two-phase flows, which is illustrated on the examples of poly-dispersed bubbly flows and Pressurized Thermal Shock (PTS). The experimental capabilities of the TOPFLOW facility and the applied measuring techniques are discussed.
Keywords: CFD, two-phase flow, modelling, experiment, polydispersed flow
  • Invited lecture (Conferences)
    Frédéric Joliot/Otto Hahn Summer School on Nuclear Reactors: "Physics, Fuels, and Systems", 20.-29.08.2008, Aix-en-Provence, France
  • Contribution to proceedings
    Frédéric Joliot/Otto Hahn Summer School on Nuclear Reactors: "Physics, Fuels, and Systems", 20.-29.08.2008, Aix-en-Provence, France
    Lecture notes of the 2008 Frédéric JOLIOT & Otto HAHN Summer School

Publ.-Id: 11676 - Permalink


Von PROMISE 1 zu PROMISE 2: Helikale MRI im Laborexperiment
Stefani, F.;
Die Magneto-Rotationsinstabilität (MRI) ist verantwortlich für Turbulenz und Drehimpulstransport in kosmischen Akkretionsscheiben und ermöglicht damit das Wachstum von Sternen und Schwarzen Löchern. Im Vortrag wird das PROMISE-Experiment vorgestellt, mit dem die helikale Variante der MRI erstmalig nachgewiesen worden ist.
  • Invited lecture (Conferences)
    Kolloquium "10000 MHD-Tage in Potsdam", 01.09.2008, Potsdam, Germany

Publ.-Id: 11675 - Permalink


Site-specific substitution of Fe in YFexMn2-xO5: X-ray investigations and DFT
Weißbach, T.; Führlich, T.; Wunderlich, F.; Leisegang, T.; Dshemuchadse, J.; Rother, A.; Souptel, D.; Behr, G.; Chaplygin, I.; Seifert, G.; Gemming, S.; Meyer, D. C.;
YMnFeO5 is a ferrimagnet below 165 K [1]. Its crystal structure is derived from that of the ferromagnetic and low-temperature ferroelectric YMn2O5 by occupation of the Mn position possessing pyramidal oxygen environment with Fe; the other Mn site is coordinated by oxygen in an octahedral manner. Powder samples for x = 0, 0.25, 0.5, 1 [2] were inspected by X-ray powder diffraction and EXAFS, single crystals (x = 0.07, 0.25) by single-crystal X-ray diffraction methods. The structure data show a significant displacement of Fe within the oxygen pyramid, while the Mn position remains nearly constant with respect to the surrounding oxygen atoms. All-electron density-functional calculations in the LSDA+U approximation for the x = 1 compound [3] are in good agreement with the collinear, commensurate ferrimagnetic ordering of the magnetic moments as proposed in [1]. [1] Munoz, A. et al., Chem. Mater. 16, 4087 (2004); [2] all materials prepared by D. Souptel at IFW Dresden; [3] FPLO: Koepernik, K. et al., Phys. Rev. B 59, 1743 (1999).
Keywords: ferrimagnet, magnet, multiferroic, manganite, density functional, DFT, X-ray, EXAFS
  • Poster
    16th International Conference on Solid Compounds of Transition Elements (SCTE2008), 26.-31.07.2008, Dresden, Deutschland

Publ.-Id: 11674 - Permalink


Evolution of the crystal structure of YMn2-xFexO5 due to substitution of iron for manganese
Weißbach, T.; Wunderlich, F.; Führlich, T.; Dshemuchadse, J.; Souptel, D.; Behr, G.; Gemming, S.; Meyer, D. C.;
YMnFeO5 is a ferrimagnet below 165 K [1]. Its crystal structure is derived from that of the ferromagnetic and low-temperature ferroelectric YMn2O5 by occupation of the Mn position possessing pyramidal oxygen environment with Fe; the other Mn site is coordinated by oxygen in an octahedral manner. Powder samples for x = 0, 0.25, 0.5, 1 [2] were inspected by X-ray powder diffraction and EXAFS, single crystals (x = 0.07, 0.25) by single-crystal X-ray diffraction methods. The structure data show a significant displacement of Fe within the oxygen pyramid, while the Mn position remains nearly constant with respect to the surrounding oxygen atoms. All-electron density-functional calculations in the LSDA+U approximation for the x = 1 compound [3] are in good agreement with the collinear, commensurate ferrimagnetic ordering of the magnetic moments as proposed in [1]. [1] Munoz, A. et al., Chem. Mater. 16, 4087 (2004); [2] all materials prepared by D. Souptel at IFW Dresden; [3] FPLO: Koepernik, K. et al., Phys. Rev. B 59, 1743 (1999).
Keywords: ferrimagnet, magnetic, multiferroic, DFT, density functional, X-ray, EXAFS, functional oxide
  • Poster
    16. Jahrestagung der Deutschen Gesellschaft für Kristallographie, 03.-06.03.2008, Erlangen, Deutschland

Publ.-Id: 11673 - Permalink


Evolution of the crystal structure of YMn2-xFexO5 due to iron doping and DFT calculations for the x = 1 compound
Weißbach, T.; Souptel, D.; Behr, G.; Führlich, T.; Wunderlich, F.; Meyer, D. C.; Gemming, S.;
YMnFeO5 is a ferrimagnet below 165 K [1]. Its crystal structure is derived from that of the ferromagnetic and low-temperature ferroelectric YMn2O5 by occupation of the Mn position possessing pyramidal oxygen environment with Fe; the other Mn site is coordinated by oxygen in an octahedral manner. Powder samples for x = 0, 0.25, 0.5, 1 [2] were inspected by X-ray powder diffraction and EXAFS, single crystals (x = 0.07, 0.25) by single-crystal X-ray diffraction methods. The structure data show a significant displacement of Fe within the oxygen pyramid, while the Mn position remains nearly constant with respect to the surrounding oxygen atoms. All-electron density-functional calculations in the LSDA+U approximation for the x = 1 compound [3] are in good agreement with the collinear, commensurate ferrimagnetic ordering of the magnetic moments as proposed in [1].
[1] Munoz, A. et al., Chem. Mater. 16, 4087 (2004);
[2] all materials prepared by D. Souptel at IFW Dresden;
[3] FPLO: Koepernik, K. et al., Phys. Rev. B 59, 1743 (1999)
Keywords: magnetism, multiferroic, ferrimagnet, calculation, DFT, density-functional, EXAFS, X-Ray
  • Poster
    72. Jahrestagung der Deutschen Physikalischen Gesellschaft (DPG) und DPG-Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Deutschland

Publ.-Id: 11672 - Permalink


The helical magnetorotational instability in cylindrical Taylor--Couette flow
Hollerbach, R.; Stefani, F.; Gerbeth, G.; Gundrum, T.; Rüdiger, G.;
We present new results from the PROMISE experiment, consisting of a GaInSn alloy confined between differentially rotating cylinders, in the presence of a combined axial and azimuthal (helical) magnetic field. The apparatus has been upgraded to incorporate split-ring end-plates, thereby reducing end-effects. The resulting traveling-wave disturbances are in good agreement with theoretical predictions for the onset of the helical magnetorotational instability.
  • Lecture (Conference)
    XXII International Congress of Theoretical and Applied Mechanics, 24.-29.08.2008, Adelaide, Australia
  • Contribution to proceedings
    XXII International Congress of Theoretical and Applied Mechanics, 24.-29.08.2008, Adelaide, Australia
    Proceedings of the XXII International Congress of Theoretical and Applied Mechanics, Adelaide: IUTAM, 978-0-9805142-1-6, 11858

Publ.-Id: 11671 - Permalink


(Multi-)ferroic domain walls - a combined ab-initio and microscopical investigation
Rother, A.; Gemming, S.; Geiger, D.; Spaldin, N.;
Interest in magnetoelectric multiferroic materials has increased exponentially over the last ten years, with considerable effort devoted both to combining magnetism and ferroelectricity in a single phase material and in obtaining magnetoelectric coupling between the two phenomena. Progress has been made on both front and a rich array of fundamental phenomena have been revealed in prototypical multiferroics such as bismuth ferrite, BiFeO3. Here we describe a new and previously unanticipated functionality: the observation – using conductive atomic force microscopy – of room temperature electronic conductivity at ferroelectric domain walls in BiFeO3. We explore the origin of the observed conductivity using high resolution transmission electron microscopy and first-principles density functional computations. Our results suggest the possibility of exploiting domain walls as a functional component in novel applications.
Keywords: multiferroic, ferroelectric, bismuth ferrate, domain, domain wall, functional material
  • Poster
    14th European Microscopy Conference (EMC 2008), 31.08.-05.09.2008, Aachen, Deutschland

Publ.-Id: 11670 - Permalink


Spin Manipulation in Co-Doped ZnO
Xu, Q.; Hartmann, L.; Zhou, S.; Mcklich, A.; Helm, M.; Biehne, G.; Hochmuth, H.; Lorenz, M.; Grundmann, M.; Schmidt, H.;
We report the clearly observed tunneling magnetoresistance at 5 K in magnetic tunnel junctions with Co-doped ZnO as a bottom ferromagnetic electrode and Co as a top ferromagnetic electrode prepared by pulsed laser deposition. Spin-polarized electrons were injected from Co-doped ZnO to the crystallized Al2O3 and tunnelled through the amorphous Al2O3 barrier. Our studies demonstrate the spin polarization in Co-doped ZnO and its possible application in future ZnO-based spintronics devices.
Keywords: ZnO, Diluted magnetic semiconductor, Tunneling magnetoresistance

Publ.-Id: 11669 - Permalink


57Fe and 119Sn CEMS Study of SnO2 Films Implanted with 57Fe
Nomura, K.; Rykov, A.; Iio, S.; Hirose, Y.; Hasegawa, I.; Reuther, H.;
The origin of magnetic interactions in Diluted Magnetic Semiconductors (DMS) is attracting a great attention as a basic problem on magnetism[1-2]. This subject is still an issue of controversy. In all of these works, the observed ferromagnetism has been attributed to interactions between the magnetic impurities, but the main source has never been associated to magnetically ordered defects. We have reported the different types of magnetic source in case of Fe doped SnO2 powder [3], and the phonon density of states of rutile type structures [4]. Defects in DMS can also contribute to saturation magnetization. Here we have made the thin films of SnO2 implanted with 57Fe and characterized them by 57Fe and 119Sn conversion electron Mössbauer spectrometry (CEMS).
  • Poster
    International Symposium on the Industrial Applications of the Mössbauer Effect (ISIAME'08), 17.-22.08.2008, Budapest, Ungarn

Publ.-Id: 11668 - Permalink


Mössbauer Spectroscopy as a Tool to Explore Diluted Magnetic Semiconductors
Reuther, H.;
Worldwide, semiconductor spin transfer electronics (spintronics) is of strongly increasing interest. To realize such materials polarized carriers can be injected from a ferromagnetic metal into a diluted magnetic semiconductor (DMS). DMS are “conventional” semiconductors doped with transition metal or rare-earth ions which are diluted within the host matrix and ferromagnetically aligned via an indirect magnetic coupling.

Wide band gap semiconductors like GaN, ZnO, or TiO2 are promising candidates. Doping could be performed by Mn, V, Fe, Co or Ni with concentrations in the range of some %. In the case of 57Fe as doping ion, Mössbauer spectroscopy can be used to investigate how it is built in the host matrix. The 57Fe ion acts both as doping and probe.

In the present study, a survey about Mössbauer spectroscopy as a tool to explore such materials is given. It is very useful however it is insufficient for a full characterization. Other techniques like transmission electron microscopy, Zero-field-cooled/field-cooled SQUID measurements or X-ray diffraction are necessary as complementary methods.
  • Invited lecture (Conferences)
    International Symposium on the Industrial Applications of the Mössbauer Effect (ISIAME'08), 17.-22.08.2008, Budapest, Ungarn

Publ.-Id: 11667 - Permalink


Swift-heavy-ion-induced shaping of spherical Ge nanoparticles into disks and rods
Schmidt, B.; Heinig, K.-H.; Mücklich, A.; Akhmadaliev, C.;
The work reports on experimental features and theoretical studies of swift-heavy-ion-induced shaping of Ge nanospheres into disks. A stack of alternating Ge and SiO2 layers was sputtered on an oxidized Si wafer. The Ge layer thicknesses varied from 2.5 to 7.5 nm. Thermal treatment above the melting temperature of Ge transformed each Ge layer into a layer of Ge nanospheres. With growing Ge layer thickness the mean diameter increases from 8 to 37 nm. Irradiation with low fluences (~1014cm-2) of 38 MeV I7+ shaped medium-sized Ge nanospheres into disks, whereas smaller ones became rod-like and larger ones remained unchanged. At higher fluences, the larger Ge nanospheres shrink due to Ge loss and shape into disks too. A new model is presented and atomistic Monte-Carlo simulations are shown which describe the shaping evolution and the size thresholds for shaping quantitatively. The volume change of Ge upon melting has been identified as driving force.
Keywords: heavy ion irradiation, ion beam shaping, nanoparticles
  • Lecture (Conference)
    16th International Conference on Ion Beam Modification of Materials (IBMM 2008), 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1345-1348
    DOI: 10.1016/j.nimb.2009.01.062

Publ.-Id: 11666 - Permalink


Photodisintegration studies on 92Mo and 144Sm
Nair, C.; Junghans, A. R.; Erhard, M.; Bemmerer, D.; Beyer, R.; Grosse, E.; Klug, J.; Kosev, K.; Rusev, G.; Schilling, K. D.; Schwengner, R.; Wagner, A.;
In burning stellar environments like supernova explosions, the temperatures are high enough for the production of heavy neutron deficient nuclei, the so-called p-nuclei. These are thought to be produced in such explosive scenarios either through chains of photodisintegration reactions on heavy seed nuclei. The modelling of the nucleosynthesis for the p-nuclei is mainly based on statistical model calculations. In this context, the knowledge of the experimental cross sections for the prediction of the p-nuclei abundances is of crucial importance and to forward in this direction we have started and experimental program at the bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden-Rossendorf . Photodisintegration measurements on the astrophysically relevant p-nuclei 92Mo and 144Sm have been performed via photoactivation technique with bremsstrahlung end-point energies from 10.0 to 16.5 MeV. In particular the (gamma,alpha) reactions of the mentioned nuclei were studied for the first time at different endpoint energies above and close to the threshold. The bremsstrahlung facility and the experimental area are deigned so as to facilitate the studies under optimized background conditions. To probe the fascinating investigations on short-lived nuclei a new pneumatic delivery system has been built recently. First experiments on the short-lived decays following the reaction 144Sm(gamma,n) is discussed. The activation yields from all measurements are compared with calculations using cross sections from recent Hauser-Feshbach models .
Keywords: photodisintegration, bremsstrahlung
  • Lecture (Conference)
    10th Symposium on the Nuclei in Cosmos, 27.07.-01.08.2008, Mackinac Island, Michigan, USA

Publ.-Id: 11665 - Permalink


Ion-irradiation-induced damage of steels characterized by means of nanoindentation
Heintze, C.; Recknagel, C.; Bergner, F.; Hernández-Mayoral, M.; Kolitsch, A.;
Self-ion irradiation was used to simulate the damage caused by fast neutrons in the austenitic stainless steel SS 304 SA, the ferritic/martensitic steel Eurofer’97 and a Fe-9at%Cr model alloy. The irradiation-induced hardness change in the damage layer was evaluated by means of nanoindentation. Three-step irradiations were performed at room temperature and 300°C up to 1 and 10dpa. An irradiation-induced hardness change was shown for all materials. No influence of irradiation temperature could be resolved. Irradiation-induced hardening exhibits different fluence dependencies in Eurofer’97 and Fe-9at%Cr. While the data indicate a saturation-like behaviour for Fe-9at%Cr, a monotonous increase of hardness with fluence up to 10dpa was found for Eurofer’97.
Keywords: self-ion irradiation, nanoindentation, irradiation hardening, iron base alloys
  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1505-1508

Publ.-Id: 11664 - Permalink


Terahertz emission from a large-area GaInAsN emitter
Peter, F.; Winnerl, S.; Schneider, H.; Helm, M.; Köhler, K.;
A large-area interdigitated terahertz (THz) emitter based on molecular-beam epitaxy grown GaInAsN with an additional AlGaAs heterostructure is investigated as THz source for excitation wavelengths between 1.1 and 1.5 µm. The optical and electrical properties of the emitter material exhibit absorption up to a wavelength of 1.5 µm and have a resistivity of 550 kΩ cm. Terahertz waves were detected by electro-optical sampling with a bandwidth exceeding 2 THz. Best performance is found for excitation wavelengths below 1.35 µm. Furthermore the emission properties for several excitation powers are investigated showing a linear increase of THz emission.
Keywords: TERAHERTZ, SPECTROSCOPY, ANTENNAS, BEAMS

Publ.-Id: 11663 - Permalink


RTA and FLA of ultra-shallow implanted layers in Ge
Wündisch, C.; Posselt, M.; Anwand, W.; Schmidt, B.; Mücklich, A.; Skorupa, W.; Clarysse, T.; Simoen, E.;
The formation of ultra-shallow n+ layers by P or As implantation and subsequent rapid thermal annealing (RTA) or flash-lamp annealing (FLA) is investigated. The focus is on diffusion and activation of dopants. RTA leads to considerable broadening of the shallow as-implanted profiles by concentration-dependent diffusion. In contrast, FLA does not cause any diffusion and is therefore a promising method for producing ultra-shallow n+p junctions in Ge. Under present annealing conditions RTA yields maximum activation levels of about 1.1E19 and 6.5E18 for P and As, respectively. The maximum activation achieved by FLA is about 4.0E19 and 2.1E19 for P and As, respectively. Possible mechanisms for diffusion and deactivation of dopants are discussed.
Keywords: Germanium, ion implantation, annealing, electrical doping, diffusion, activation
  • Contribution to proceedings
    16th IEEE International Conference on Advanced Thermal Processing of Semiconductors (IEEE RTP 2008), 30.09.-03.10.2008, Las Vegas, NV, USA
    Proceedings of the 16th IEEE International Conference on Advanced Thermal Processing of Semiconductors, RTP 2008, September 30- October 3, 2008, Las Vegas, NV, USA, Piscataway, NJ: IEEE, 978-1-4244-1950-0, 245-249
  • Lecture (Conference)
    16th IEEE International Conference on Advanced Thermal Processing of Semiconductors (IEEE RTP 2008), 30.09.-03.10.2008, Las Vegas, NV, USA

Publ.-Id: 11662 - Permalink


Precision study of ground state capture in the 14N(p,gamma)15O reaction
Marta, M.; Formicola, A.; Gyurky, G.; Bemmerer, D.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Elekes, Z.; Fulop, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Imbriani, G.; Junker, M.; Kunz, R.; Lemut, A.; Limata, B.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Romano, M.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.; Vomiero, A.;
The rate of the hydrogen-burning carbon-nitrogen-oxygen (CNO) cycle is controlled by the slowest process, 14N(p,gamma)15O, which proceeds by capture to the ground and several excited states in 15O. Previous extrapolations for the ground state contribution disagreed by a factor 2, corresponding to 15% uncertainty in the total astrophysical S-factor. At the Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator placed deep underground in the Gran Sasso facility in Italy, a new experiment on ground state capture has been carried out at 317.8, 334.4, and 353.3 keV center-of-mass energy. Systematic corrections have been reduced considerably with respect to previous studies by using a Clover detector and by adopting a relative analysis. The previous discrepancy has been resolved, and ground state capture no longer dominates the uncertainty of the total S-factor.
Keywords: Nuclear astrophysics, solar neutrinos, CNO cycle, radiative capture, in-beam gamma-spectrometry, underground, Gran Sasso, R-matrix, Clover detector

Publ.-Id: 11661 - Permalink


Nano-Biotechnologie für den Umweltschutz: Entwicklung neuer fotokatalytisch aktiver Verbundmaterialien
Pollmann, K.; Raff, J.;
wird nachgereicht
  • Lecture (Conference)
    DECHEMA-Workshop zur Fördermaßnahme NanoNature des BMBF, 26.08.2008, Frankfurt, Deutschland
  • Poster
    DECHEMA-Workshop zur Fördermaßnahme NanoNature des BMBF, 26.08.2008, Frankfurt, Deutschland

Publ.-Id: 11660 - Permalink


Metal removal and recovery by bacteria-based biocomposites
Raff, J.;
Bacteria are simply organized, but apart from that and their small size they are an unbelievable complex and a highly efficient group of creatures. Some are able to thrive at the most forbidding, uninviting places on Earth, for example in hot springs, in the perpetual ice, in the deep sea or in deserts. For production of energy they can use different kinds of organic and inorganic matter or sun light. Furthermore, they successfully conquer also any other habitats, even so an environment is highly contaminated with toxic substances, like organic solvents, heavy metals and radionuclides. Adaptation and detoxification mechanisms allow them to resist high concentrations of toxic elements without getting sustainably affected. These mechanisms are very prospective for the development of innovative remediation strategies and for other biotechnical applications [1-6].
Within the radio-ecological research on the interaction of bacteria with actinides many reference strains and isolates were investigated for their interaction with heavy metals and radionuclides [7-11]. The studied bacteria possess different strategies to handle high metal concentrations in their environment. Namely, via an immobilization of the metals by biosorption, bioaccumulation inside the cell, biomineralization and biotransformation. In principle, all mentioned strategies are suitable for the development of new materials for bioremediation techniques and the removal of metals. In respect of the development of metal selective and reusable filter materials, several Bacillus and Lysinibacillus isolates from a uranium mining waste pile were preferentially investigated. The cells bind selectively and reversibly uranium on their surface. Furthermore the analyses results in the identification of new so called surface layer (S-layer) proteins, forming the outermost structure on many bacteria. This S-layers are able to bind and detain toxic heavy metals while essential ones may pass. To take advantage of this intelligence intact cells, spores and the S-layer proteins of the bacteria were immobilized in sol-gel ceramics [11, 12] and used for metal binding experiments. Ongoing experiments include also the production of biofilm based materials and the protein immobilization on conventional carriers. Especially the S-layer proteins not only bind heavy metals very selectively but also some precious metals. The superior aim is the development of metal selective filter materials for the removal of heavy metals and in future for the recovery of precious metals from aqueous solutions.

Ackowledgements
We gratefully acknowledge support by the DFG (Biocere, SE 671/1-2) and the BMWi/PTJ (BIOREM, 03EGSSN014).

References
[1] L. Hendrickx and M Mergeay (2007), Curr Opin Microbiol 10(3), 231-237
[2] R. Margesin and F. Schinner F. (2001), Appl Microbiol Biotechnol. 56(5-6) 650-663
[3] G. Antranikian (2005), Adv Biochem Eng Biotechnol, 96, 219-262
[4] M. Kalin et al. (2005), J Environ Radioact. 78(2),151-177
[5] B. Volesky and Z.R. Holan (1995), Biotechnol. Prog. 11, 235-250
[6] J. Raff and S. Selenska-Pobell (2006), Nuclear Engineering International 51(619) 34-36
[7] M. Merroun et al. (2005) Appl. Environ. Microbiol. 71(9): 5532-5543
[8] M. Merroun et al. (2006) Radiochimica Acta 94, 723-729
[9] H. Moll et al. (2008) BioMetals 21, 219-228
[10] H. Moll et al. (2006) Radiochimica Acta 94(2006), 815-824
[11] J. Raff et al. (2003), Chem. Mater. 15, 240-244
[12] K. Pollmann et al. (2006), Biotechn. Adv. 24 (1), 58-68
  • Lecture (Conference)
    Max Bergmann Symposium 08 on Molecular Designed Biological coatings, 04.-06.11.2008, Dresden, Deutschland

Publ.-Id: 11659 - Permalink


Polyhedral Approximation and Practical Convex Hull Algorithm for Certain Classes of Voxel Sets
Schulz, H.;
In this paper we introduce an algorithm for the creation of polyhedral approximations for certain kinds of digital objects in a three-dimensional space. The objects are sets of voxels represented as strongly connected subsets of an abstract cell complex. The proposed algorithm generates the convex hull of a given object and modifies the hull afterwards by recursive repetitions of generating convex hulls of subsets of the given voxel set or subsets of the background voxels. The result of this method is a polyhedron which separates object voxels from background voxels. The objects processed by this algorithm and also the background voxel components inside the convex hull of the objects are restricted to have genus 0. The second aim of this paper is to present some practical improvements to the discussed convex hull algorithm to reduce computation time.
Keywords: digital geometry, convex hull, abstract cell complex, abstract polyhedron, surface approximation

Publ.-Id: 11658 - Permalink


Bacterial surface layers proteins: self-organizing biomolecules as building blocks for nanostructured materials
Pollmann, K.; Raff, J.; Günther, T.; Fahmy, K.;
Surface layer proteins (S-layers) form the outer sheet around the cells of many primitive microorganisms. They form two-dimensional paracrystalline arrays with repeating units on the scale of a few nanometers (10-9 m). We have established their utilization as a technology platform for innovative materials. The S-layer of Lysinibacillus sphaericus JG-A12 isolated from a uranium waste pile has been shown to exhibit highly ordered binding sites for various metals such as Pt, Pd, Au, suitable for the formation of regularly distributed nanoclusters of defined sizes. Such bioinorganic materials possess a great potential for the development of novel catalysts, new biomedical and bio¬analytical applications, the assembly of nanometer-scaled electronic devices, optical industry, and storage media. At the Institutes of Radiation Physics, Ion-beam Physics and Materials Research, and the Dresden High Magnetic Field Laboratory, the structure of such nanoparticles and their physical properties are currently analyzed in an interdisciplinary approach.
Keywords: S-layer, bioremidiation, spectroscopy, metal binding
  • Contribution to proceedings
    11th Vietnamese-German Seminar on Physics and Engineering, 31.03.-05.04.2008, Nha Trang, Vietnam
    Proceedings of the Eleventh Vietnamese-German Seminar on Physics and Engineering, Hanoi: Hanoi University

Publ.-Id: 11657 - Permalink


Measurement of the electrical conductivity of Pb-Bi alloys in the melting-solidification region
Plevachuk, Y.; Sklyarchuk, V.; Eckert, S.; Gerbeth, G.;
The electrical conductivity of Pb-Bi alloys of eutectic and near eutectic compositions was investigated in the melting-solidification temperature region. The revealed discrepancies between the heating and cooling curves as well as a hysteresis observed in course of heating-cooling cycles suggest a metastable microheteregenous structure of the Pb-Bi melts.
Keywords: Pb-Bi alloys, electrical conductivity, eutectic transformation
  • Journal of Nuclear Materials 376(2008), 363-365

Publ.-Id: 11656 - Permalink


Gold nanoparticle tips for optical field confinement in infrared scattering near-field optical microscopy
Wenzel, M. T.; Härtling, T.; Olk, P.; Kehr, S. C.; Grafström, S.; Winnerl, S.; Helm, M.; Eng, L. M.;
We report on the implementation of metal nanoparticles as probes for scattering and apertureless near-field optical investigations in the mid-infrared (mid-IR) spectral regime. At these wavelengths, an efficient electric-field confinement is necessary and achieved here through a gold metal nanoparticle of 80 nm in diameter (Au80-MNP) acting as the optical antenna. The Au80-MNP is attached to a standard AFM cantilever used as the spatial manipulator. When approached to a sample surface while being illuminated with an infrared beam, the Au80-MNP produces a considerably improved spatial confinement of the electric field compared to an ordinary scattering AFM tip. We demonstrate here the confinement normal to the sample surface by making use of a sample-induced phonon polariton resonance in a ferroelectric lithium niobate sample. Our experimental findings are in very good agreement with the quasistatic dipole model and show improved optical resolution via well-selected antenna particles.
  • Open Access LogoOptics Express 16(2008), 12302-12312

Publ.-Id: 11655 - Permalink


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