Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41809 Publications

Saturable absorption mode-locking based on intersubband transitions in quantum wells at 2 μm

Yang, K.; Ruf, H.; Neuhaus, J.; Dekorsy, T.; Villas-Boas Grimm, C.; Helm, M.; Heumann, E.; Huber, G.; Biermann, K.; Künzel, H.

Abstract

Saturable absorption mode-locking based on intersubband transitions in quantum wells at 2 μm.

Keywords: intersubband; laser; mode locking

  • Lecture (Conference)
    CLEO Europe, 14.-19.06.2009, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12905


Investigation of the Formation of Fe-filled Carbon Nanotubes

Reuther, H.; Müller, C.; Leonhardt, A.; Kutz, M. C.

Abstract

The formation of Fe-filled carbon nanotubes by thermal decomposition of ferrocene combined with a Fe-catalyst-nanostructuring on an oxidized Si substrate is investigated in the temperature range of 1015 – 1200 K. The optimal growth conditions for aligned and homogeneous carbon nanotubes are found at 1100 K. Mössbauer spectroscopy (both in transmission geometry and CEMS) was used to analyze and quantify the different formed Fe-phases. In general, a-Fe, g-Fe and Fe3C are found to form within the carbon nanotubes. Depending on the growth conditions their fractions vary strongly. Moreover, an alignment of the a-Fe in the tubes could be detected.

  • Open Access Logo Journal of Physics: Conference Series 217(2010), 012098
  • Poster
    International Conference on the Applications of the Mössbauer Effect, 19.-24.07.2009, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-12904


Kaons and Antikaons in Nuclear Matter: AA vs. pA Collisions

Schade, H.

Abstract

Kaons and Antikaons in Nuclear Matter: AA vs. pA Collisions

  • Lecture (Conference)
    Gemeinsame DPG Frühjahrstagung mit der European Physical Society (EuNPC) Frühjahrstagung 2009, 18.03.2009, Bochum, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12903


Transport model calculations for HADES

Schade, H.

Abstract

Transport model calculations for HADES

  • Lecture (others)
    WIP, 30.01.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12902


Transport Models for Heavy-Ion Collisions

Schade, H.

Abstract

Transport Models for Heavy-Ion Collisions

  • Lecture (Conference)
    ENLITE 2009, 03.04.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12901


Comparative investigation of the limiting solution species [U(CO3)5]6- and the crystal structure of Na6[U(CO3)5]•12H2O

Hennig, C.; Ikeda-Ohno, A.; Emmerling, F.; Kraus, W.; Bernhard, G.

Abstract

The coordination of the limiting U(IV) carbonate species in aqueous solution was investigated by comparing its structure parameters with those of the complex preserved in a crystal structure. The solution species was obtained in a aqueous solution of 0.05 M U(IV) and 1 M NaHCO3. Single crystals of Na6[U(CO3)5]•12H2O were obtained directly from this mother solution. The U(IV) carbonate complex in the crystal structure was identified as [U(CO3)5]6 anionic complex. This monomeric complex forms a network with charge compensating Na+ cations and H2O ligands. The interatomic distances around the U(IV) coordination polyhedron show average distances of U-O = 2.461(8) Å, U-C = 2.912(4) Å and U-Odist = 4.164(6) Å. U L3edge EXAFS spectra were collected from the solid Na6[U(CO3)5]•12H2O and the corresponding solution. In both samples, the first shell of the Fourier transforms (FTs) revealed ten oxygen atoms at an average distance of 2.450.02 Å, the second shell originates from five carbon atoms with a U-C distance of 2.910.02 Å, and the third shell was fit with single and multiple scattering paths of the distal oxygen at 4.170.02 Å. These data indicate the identity of the [U(CO3)5]6 complex in solid and solution state. The high negative charge of the [U(CO3)5]6 anion is compensated by Na+ cations. In solid state the Na+ cations form a bridging network between the [U(CO3)5]6 units, while in liquid state they seem to be located closer at the anionic complex. The average metal-oxygen distances of the coordination polyhedron show a linear correlation to the radius contraction of the neighbour actinide(IV) ions and indicate the equivalence of the [An(CO3)5]6 coordination within the series of thorium, uranium, neptunium and plutonium.

Keywords: U(IV) carbonate species; EXAFS; XRD

Permalink: https://www.hzdr.de/publications/Publ-12900


Double photoexcitation of 2p and 4f electrons in curium

Hennig, C.; Skanthakumar, S.; Soderholm, L.

Abstract

The L3-edge x-ray absorption spectrum of the aqua trivalent Cm ion in aqueous solution exhibits a double photoexcitation involving 2p and 4f electrons. The sharp resonance structure of the multielectron excitation reveals a shake-up process at 508.110 eV. The data indicate a monotonic increase of the [2p4f] excitation energy between elements of sixth period (Au, Hg, Pb, and Bi) and the early actinides (Th, Pa, U, Np, Pu, Am and Cm).

Keywords: Curium; EXAFS; multielectron excitation

Permalink: https://www.hzdr.de/publications/Publ-12899


Proceedings of the 16th International Conference on Ion Beam Modification of Materials

Möller, W.; Rauschenbach, B.; (Editors)

Abstract

It is our pleasure to publish the Proceedings of the 16th International Conference on Ion Beam Modification of Materials (IBMM 2008), which was held at the Lecture Hall Centre of the Technische Universität at Dresden, Germany, from August 31 to September 5, 2008, under the common organization by the Forschungszentrum Dresden-Rossendorf, Dresden, Germany and the Leibniz-Institut für Oberflächenmodifizierung, Leipzig, Germany.
The biannual IBMM International Conference Series looks back on a 30-years history starting in 1978, being considered as the major international forum to present and discuss recent results in ion-related materials research and to point into the future of the field. It assembles physicists, chemists, material scientists and engineers from all over the world and along the whole chain from basic research to industrial production.

  • Book (Editorship)
    Amsterdam: Elsevier B.V. in Nuclear Instruments and Methods in Physics Research B, 2009
    544 Seiten

Permalink: https://www.hzdr.de/publications/Publ-12898


A Comparative Complexation Study on Np(V) Interactions with Bacterial Cell Wall Compartments and Bioligands Secreted by Microbes

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

Abstract

Microorganisms, microbial components, biopolymers and bioligands secreted by microbes have a great potential to influence the behavior of actinides in the environment. Functional groups provided by both lipopolysaccharide (LPS: main part of the cell wall of Gram-negative bacteria), and peptidoglycan (PG: main part of the cell wall of Gram-positive bacteria) are very effective in complexing uranium(VI) over a wide pH range (2.0 to 9.0) [1, 2]. The main functionalities for uranyl binding are phosphoryl and carboxyl groups of LPS and carboxyl groups of PG. The aerobic soil bacterium Pseudomonas fluorescens (CCUG 32456 A) isolated from the aquifers at the Äspö Hard Rock Laboratory, Sweden secretes pyoverdins. These unique bioligands have a high potential to bind uranium(VI) and curium(III) mainly due to their hydroxamate and catecholate functionalities [3, 4]. However, the interaction of neptunium(V) with both microbial cell wall components (LPS, PG) and secreted bioligands (PYO) are unknown. To address this lack, we thus present findings regarding the complexation of neptunium(V) with LPS, PG, and P. fluorescens (CCUG 32456) pyoverdins (PYO) obtained using near-infrared (NIR) absorption spectroscopy.
The spectrophotometric titrations of the Np(V)-LPS system showed a dominant neptunyl(V) coordination to phosphoryl groups between pH 4 and 8 followed by hydroxyl interactions in the alkaline pH range. A very low affinity of Np(V) to interact with the carboxyl groups of PG was measured. Strong Np(V)-pyoverdin species of the type MxLyHz could be identified from the spectrophotometric titrations. Remarkable was that the influence of Np(V)-pyoverdin species could already be detected under equimolar conditions.
Estimates are possible, on the basis of the determined stability constants, if neptunium(V) prefers to interact with the microbial cell wall (LPS), with biopolymers (PG) or with the secreted pyoverdin bioligands (PYO). The calculations were performed using nearly equimolar conditions of Np(V) and functional groups of the biosystems. More than 80% of all Np(V) is bound to pyoverdin species at pH 8 compared to ~37% bound to LPS and less than 1% bound to PG. This shows both the high affinity of neptunium(V) to bioligands containing hydroxamate and catecholate groups and the importance of indirect interaction processes between neptunium(V) and bioligands secreted by resident microbes.

[1] A. Barkleit, H. Moll, G. Bernhard, Dalton Trans. 2879-2886 (2008).
[2] A. Barkleit, H. Moll, G. Bernhard, Dalton Trans. published online: DOI 10.1039/b818702a (2009).
[3] H. Moll, M. Glorius, G. Bernhard, A. Johnsson, K. Pedersen, M. Schäfer, H. Budzikiewicz, Geomicrobiol. J. 25, 157-166 (2008).
[4] H. Moll, A. Johnsson, M. Schäfer, K. Pedersen, H. Budzikiewicz, G. Bernhard, Biometals 21, 219-228 (2008).

This work was funded by the BMWi under contract number: 02E9985.

Keywords: Neptunium; NIR; Spectroscopy; Bioligands; Pyoverdins; LPS; PG; Complexation

  • Contribution to proceedings
    4th Asia-Pacific Symposium on Radiochemistry (APSORC' 09), 29.11.-04.12.2009, Napa, California, USA
  • Lecture (Conference)
    4th Asia-Pacific Symposium on Radiochemistry (APSORC' 09), 29.11.-04.12.2009, Napa, California, USA

Permalink: https://www.hzdr.de/publications/Publ-12897


Wie man schwarze Löcher füttert - Theorien und Experimente zur Magnetorotationsinstabilität

Stefani, F.

Abstract

Seit langem ist bekannt, dass die Magnetfelder von Planeten, Sternen und Galaxien durch den hydromagnetischen Dynamoeffekt erzeugt werden. Weniger bekannt ist die erstaunlich aktive Rolle, die Magnetfelder in der kosmischen Strukturbildung spielen. So sind die hohen Wachstumsraten von Sternen und Schwarzen Löchern nur erklärbar, wenn die Akkretionsscheiben, aus denen sie gefüttert werden, turbulent sind und damit Drehimpuls effektiv nach außen transportieren können. Die Ursache dieser Turbulenz liegt in der destabilisierenden Wirkung von Magnetfeldern auf rotierende Strömungen, die als Magnetorotationsinstabilität (MRI) bezeichnet wird. Der Vortrag gibt eine kurze Einführung in die Theorien zur Entstehung und Wirkung kosmischer Magnetfelder. Im Mittelpunkt stehen aber die Flüssigmetall-Experimente der letzten zehn Jahre, in denen Dynamoeffekt bzw. MRI untersucht worden sind, insbesondere das PROMISE-Experiment am Forschungszentrum Dresden-Rossendorf.

  • Invited lecture (Conferences)
    Physikalisches Kolloquium, 23.06.2009, Ilmenau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12895


The influence of bottom oxide thickness on the extraction of the trap energy distribution in SONOS (silicon-oxide-nitride-oxide-silicon) structures

Bernert, K.; Oestreich, C.; Bollmann, J.; Mikolajick, T.

Abstract

The charge retention characteristics of SONOS (silicon-oxide-nitride-oxide-silicon) nonvolatile memory cells at elevated temperatures were investigated. Assuming the thermal excitation model to be the dominant charge loss mechanism, the trap energy distribution in the nitride was determined. We present an improved model which includes the influence of subsequent tunneling of the charge carriers through the bottom oxide after being thermally emitted into the conduction band of the silicon nitride. The trap energy distribution was evaluated from samples with different bottom oxide thicknesses. Using this model it was found that the detected trap energy distribution is nearly identical despite the different tunneling probabilities from the various bottom oxide thicknesses.

Keywords: SONOS memory devices; defect levels; trap energy distribution; silicon nitride

Permalink: https://www.hzdr.de/publications/Publ-12894


SIMS measurement of oxygen content in gamma-TiAl single crystals and polycrystalline alloys with Nb addition

Oswald, S.; Hermanna, R.; Schmidt, B.

Abstract

The oxygen content of binary Ti45Al55 and ternary Ti44Al52Nb4 single crystals and polycrystalline alloys
was quantified with secondary ion mass spectrometry (SIMS) using Cs+ primary ions. The SIMS measurements
were calibrated with respect to concentration and depth scale using oxygen implanted samples.
The measurements revealed considerably lower oxygen content in the ternary alloy indicating a protecting
impact of the Nb addition in grain boundaries against oxygen contamination. The relative strong
surface oxide layer thickness of the investigated samples was determined to about 1µm.

Keywords: Ti aluminides; Single crystals; Impurities

Permalink: https://www.hzdr.de/publications/Publ-12893


Boundary condition for Ginzburg-Landau theory of superconducting layers

Kolacek, J.; Lipavský, P.; Morawetz, K.; Brandt, E. H.

Abstract

Electrostatic charging changes the critical temperature of superconducting thin layers. To understand the basic mechanism, it is possible to use the Ginzburg-Landau theory with the boundary condition derived by de Gennes from the BCS theory. Here we show that a similar boundary condition can be obtained from the principle of minimum free energy.
We compare the two boundary conditions and use the Budd-Vannimenus theorem as a test of approximations.

  • Physical Review B 79(2009), 174510-1-174510-6

Permalink: https://www.hzdr.de/publications/Publ-12892


Magnetic measurements as a sensitive tool for studying dehydrogenation processes in hydrogen storage materials

Menendez, E.; Garroni, S.; Lopez Ortega, A.; Estrader, M.; Liedke, M. O.; Fassbender, J.; Solsona, P.; Surinach, S.; Baro, M. D.; Nogues, J.

Abstract

Magnetic characterization is shown to be a highly effective, nondestructive, and commonly available method to accurately assess dehydrogenation temperatures and further clarify the reaction mechanisms during dehydrogenation in systems with superconducting or ferromagnetic constituents. As examples, the dehydrogenation temperature of NaBH4 in a nanostructured NaBH4/MgH2 system and the dehydrogenation process of nanostructured Mg2CoH5, based on the superconducting and ferromagnetic properties of MO, and Co, respectively, are determined.

Keywords: hydrogen storage; superconductivity; ball-milling; nanocrystals; SQUID

  • Journal of Physical Chemistry C 114(2010)39, 16818-16822

Permalink: https://www.hzdr.de/publications/Publ-12891


Conserving T-matrix theory of superconductivity

Sopik, B.; Lipavský, P.; Männel, M.; Morawetz, K.

Abstract

A selfconsistent T-matrix theory of many-Fermion systems is proposed. In the normal state the theory agrees with the Galitskii-Feynmann approximation, in the superconducting state it has the form of the renormalized Kadanoff-Martin approximation. The two-particle propagator satisfies the Baym-Kadanoff symmetry condition which guarantees that the theory conserves the number of particles, momentum and energy. The theory is developed for retarded interactions leading to the Eliashberg theory in the approximation of a single pairing channel.

Permalink: https://www.hzdr.de/publications/Publ-12890


Hydrogen micro-kinetics in titanium under mechanical stress studied by ion beam analysis

Wang, T. S.; Lv, H. Y.; Grambole, D.; Yang, Z.; Peng, H. B.; Han, Y. C.

Abstract

Hydrogen (H) is continuously produced by the large dose fast neutron irradiation on fusion reactor material. The concentration, diffusion and evolution of H in the structure material may cause H-embrittlement. Ion beam analysis is one of the most useful methods for studying the micro-kinetics of H in solids. In this work, the H-distribution in titanium (Ti) has been studied by resonance nuclear reaction analysis (resonance-NRA) and micro-elastic recoil detection analysis (micro-ERDA). The evolution of H-depth-profile in titanium samples has been studied versus the change of normal stress. Evident H diffusion has been observed, while a normal stress is changed in the range of 107-963 MPa. The H diffusion is related to the concentration of H in samples.

Permalink: https://www.hzdr.de/publications/Publ-12889


Self-organized ripple patterns by ion erosion - experiment, theory, and application

Keller, A.; Facsko, S.; Möller, W.

Abstract

It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. These ripple structures have been found on a large variety of materials, including semiconductors, metals, and insulators. The formation and early evolution of the ripple patterns can be described 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.
This talk will provide an overview of ion-induced pattern formation and summarize the theoretical basics. Recent experimental results on the evolution of nanoscale ripple patterns on silicon surfaces during high-fluence ion sputtering will be presented and compared to the predictions of different continuum models. In addition, promising applications of nanorippled substrates as templates in thin film growth will be discussed.

  • Lecture (others)
    Seminar, 16.06.2009, Wien, Austria

Permalink: https://www.hzdr.de/publications/Publ-12888


Photoluminescence enhancement in Si+ implanted PMMA

Tsvetkova, T.; Balabanov, S.; Avramov, L.; Borisova, E.; Angelov, I.; Sinning, S.; Bischoff, L.

Abstract

Silicon ion implantation effects on the optical and photoluminescence (PL) properties of polymethylmethacrylate (PMMA) have been studied. Low-energy ion implantation (E = 30-50 keV) was carried out over a range of different ion fluences (D = 10(13)-10(17) cm(-2)). Visible PL and optical transmission spectra in the range (330-800 nm) have been measured. The existing visible range PL emission in the unimplanted PMMA samples is clearly affected by the Si+ ion implantation and the observed modification effect of photoluminescence enhancement (PLE) is essentially dependent on the implantation fluence. For certain fluences, dependent on the ion energy, the overall amplitude of the PL emission has a several times (similar to 5 times) increase. Optical absorption also gradually increases with the fluence.

Keywords: Si -implantation; PMMA; Photoluminescence

Permalink: https://www.hzdr.de/publications/Publ-12887


The correlation between mechanical stress, thermal shift and refractive index in HfO2, Nb2O5, Ta2O5 and SiO2 layers and its relation to the layer porosity

Stenzel, O.; Wilbrandt, S.; Kaiser, N.; Vinnichenko, M.; Munnik, F.; Kolitsch, A.; Chuvilin, A.; Kaiser, U.; Ebert, J.; Jakobs, S.; Kaless, A.; Wüthrich, S.; Treichel, O.; Wunderlich, B.; Bitzer, M.; Grössl, M.

Abstract

We present extended experimental material about optical and mechanical properties of oxide optical coating materials, deposited by electron beam evaporation, ion and plasma ion assisted evaporation, sputtering and ion plating. A clear correlation between these experimental data is established and understood as being caused by the different degree of the porosity of the films. This assumption has been verified by investigation of the layer structure and accompanying simulations of the effect of porosity on refractive index, layer stress and thermal shift. As a practical conclusion, we find that a certain pore fraction in the films is essential in order to get a valuable balance between optical and mechanical coating properties.

Keywords: metal oxide films; electron beam evaporation; ion and plasma assisted evaporation; magnetron sputtering; ion plating; high-refractive index; low extinction; mechanical properties

Permalink: https://www.hzdr.de/publications/Publ-12886


Sorption properties of the NaBH4/MgH2 system: dehydrogenation mechanism and pathway

Garroni, S.; Menendez, E.; Lopez Ortega, A.; Estrader, M.; Milanese, C.; Nolis, P.; Nogues, J.; Surinach, S.; Baro, M. D.

Abstract

Nanostructured NaBH4/MgH2 composites have established themselves as promising materials for hydrogen storage applications due to their high gravimetric capacity, large hydrogen volumetric density and rather low dehydrogenation temperature compared to that one corresponding to the single compounds. Actually, further research on the NaBH4/MgH2 system could lead to an enhanced understanding of more complex reactive hydride composites, such as Ca(BH4)2/MgH2 or LiBH4/MgH2.

As-received NaBH4 and MgH2 powders were mixed, in a 2 to 1 molar ratio (2NaBH4/MgH2) and ball-milled to obtain nanostructured composites. The milling processes were carried out for diverse times, under Ar atmosphere, in a Spex mill with a ball-to-powder mass ratio of 10:1.

In-situ synchrotron x-ray powder diffraction indicates that the dehydrogenation process starts at around 210 C, with the desorption of the MgH2 to Mg, and rpoceeds with the chemical dismutation of NaBH4 in NaH and a possible intermediate specie, such as Na2B12H12. In fact, solid-NMR seems to confirm the existence of the transitional compound. However, the temperature onset of the dehydrogenation process of the NaBH4 counterpart has not yet been fully elucidated and, since it is difficutls to establish from either x-ray diffraction or thermogravimetric analyiss, magnetic hcaracterization is proposed as an alternative technique, which takes advantage of the superconducting nature of the MgB2 phase, to further study dehydrogenation processes.

Keywords: hydrogen storage; XRD; magnetic characterization; ball-milling

  • Lecture (Conference)
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-12885


Verfahren zur Bewegungskorrektur

van den Hoff, J.

  • Invited lecture (Conferences)
    19. Jahrestagung der Gesellschaft für Nuklearmedizin Sachsens, 19.-20.06.2009, Nimbschen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12884


Neue Radiotracer für die Tumorbildgebung

Pietzsch, J.

  • Invited lecture (Conferences)
    19. Jahrestagung der Gesellschaft für Nuklearmedizin Sachsens, 19.-20.06.2009, Nimbschen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12883


Onkologische Pharmazie versus Radiopharmazie

Steinbach, J.

  • Invited lecture (Conferences)
    Onkologisch-pharmazeutischer Fachkongress, 12.-13.06.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12882


Labelling of bio-macromolecules: Challenge in radiolabelling for radiopharmacy

Steinbach, J.

Abstract

Over the last two decades, radiolabeled antibodies and peptides have been introduced in research and in clinical application of nuclear medicine. Such substances are utilized for tumor targeting as radiotracers and for therapeutic purposes as well. Labelling of such substances with PET radionuclides such as F-18 offers the chance of introduction the label without drastic changes of the molecular properties in conjunction with highest image quality, i.e. high diagnostic value. Radiometal-labeled bioactive substances offer both: The possibility of diagnostics and therapeutic intervention as well. However, the labelling procedure is a considerable alteration of the molecules radiopharmacological properties. This is due to the need of introducing a chelating moiety to bind the radiometals kinetically and thermodynamically inert. Beside this geometric impact, the labelling conditions are of highest importance. Whereas peptides may withstand rather drastic conditions, proteins e.g. antibodies need ambient labelling conditions such as aqueous solution, room temperature, near physiological pH. Furthermore, various proteins tend to coagulate in the presence of heavy metals as radio-copper.
The talk will present such results of scientific investigations at the Institute of Radiopharmacy during the last five years. This involves the application of established methods such as the use of [18F]SFB (N-succinimidyl-4-[18F]fluorobenzoate) for labelling of biomolecules, the development of alternative labelling agents/prosthetic groups as well as current efforts to establish methods for pre- and postlabelling with radiometals. All these investigations are directed to corresponding applications with biomolecules and bioactive compounds, respectively.

  • Invited lecture (Conferences)
    16th Biennial Congress of the György Hevesy Hungarian Society of Nuclear Medicine (MONT), 02.-04.07.2009, Debrecen, Hungary
  • Open Access Logo Abstract in refereed journal
    Nuclear Medicine Review 12(2009)1, 31
    ISSN: 1506-9680

Permalink: https://www.hzdr.de/publications/Publ-12881


18F-Radiotracer: Von der Grundlagenchemie zur Anwendungsrelevanz

Steinbach, J.

  • Invited lecture (Conferences)
    Pharmazeutisch-lebensmittelchemisches Kolloquium, Westfälische Wilhelms-Universität Münster, 23.09.2009, Münster, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12880


Electromagnetic flow control during solidification of AlSi-alloys using time-modulated AC magnetic fields

Räbiger, D.; Nikrityuk, P. A.; Leonhardt, M.; Eckert, S.; Eckert, K.

Abstract

This paper considers the directional solidification of Al-Si alloys from a water cooled copper chill. Melt stirring during solidification has been realised by utilising time-modulated AC magnetic fields in two different variants: (1) an RMF applied in form of a pulse sequence with a periodic inversion of the direction of rotation between two consecutive pulses and (2) a combination of rotating (RMF) and travelling magnetic fields (TMF), whereas both fields are implemented subsequently in form of rectangular pulses. Our results demonstrate that the melt agitation using modulated magnetic fields offers a considerable potential for a well-aimed modification of casting properties by an effective control of the flow field, but, this goal requires an optimisation of the magnetic field onfiguration with respect to the particular solidification parameters.

Keywords: electromagnetic melt stirring; rotating magnetic field (RMF); travelling magnetic field (TMF); solidification; grain refinement

  • Contribution to proceedings
    EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany, pp. 624-627
  • Lecture (Conference)
    EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12879


Comparison of the structural developments in the C:Ni films grown by ion beam sputtering and pulsed filtered cathodic vacuum arc

Abrasonis, G.; Kovacs, G. J.; Ryves, L.; Mücklich, A.; Krause, M.; Munnik, F.; Oates, T. W. H.; Bilek, M. M. M.; Kolitsch, A.; Möller, V.

Abstract

he structure of C:Ni nanocomposite thin films grown by ion beam sputtering (IBS) and pulsed filtered cathodic vacuum arc (PFCVA) is compared. The films were grown in the temperature (T) and Ni concentration ranges of RT-500C and 7-40 at.%, respectively. The composition of the films and elemental depth profiles were determined by elastic recoil detection analysis (ERDA). The morphology and phase composition were investigated by transmission electron microscopy and x-ray diffraction, respectively. Independent of the growth method the Ni dispersed phase is carbidic for T<=300C and mostly fcc metallic at higher deposition temperatures. In the C:Ni films grown by IBS the transition from globular towards columnar growth occurs at 200

  • Lecture (Conference)
    E-MRS 2009 Spring Meeting,, 08.-12.06.2009, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-12878


Grain refinement in Al-Si Alloys by inoculation and electromagnetic stirring

Räbiger, D.; Metan, V.; Leonhardt, M.; Eigenfeld, K.; Eckert, S.

Abstract

The present study concerns the directional solidification of grain-refined and non-refined AlSi7 alloys under the influence of a travelling magnetic field (TMF). An upwards travelling field has been applied to provide a forced convection within the solidifying melt. The formation of a fine equiaxed structure is favoured by both the addition of grain refining AlTi5B1-particles and electromagnetic stirring as well, whereas the addition of grain refiners into the melt appears to be more efficient for achieving a reduction of the mean grain size. A minimum grain size has been observed of the electromagnetic agitation of a grain-refined alloy. A melt stirring by a sufficiently high magnetic field provides a homogeneous grain size distribution in the sample volume.

Keywords: grain refinement; solidification; electromagnetic stirring; travelling magnetic field (TMF)

  • Contribution to proceedings
    EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany, pp. 334-337
  • Poster
    EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12877


Liquid metal flow in a cylinder during the spin-up of a rotating magnetic field

Räbiger, D.; Eckert, S.; Gerbeth, G.

Abstract

This experimental study is concerned with the secondary meridional flow during the time if the fluid spins up from rest. A cylindrical cavity with an aspect ratio of unity is filled with liquid metal and suddenly exposed to an azimuthal body force generated by a rotating magnetic field (RMF). Vertical profiles of the axial velocity have been measured by means of the ultrasound Doppler velocimetry. Our experimental results show an excellent agreement with recently published numerical results with respect to the laminar spin-up and the onset of linear three-dimensional instabilities in RMFdriven flows.

Keywords: spin-up; rotating magnetic field (RMF); time-modulated RMF

  • Contribution to proceedings
    EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany, pp. 69-72
  • Lecture (Conference)
    EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12876


Quantitative ion beam analysis of ultra thin films with magnetic spectrometers using heavy MeV ions

Kosmata, M.; Grötzschel, R.; Munnik, F.; Vieluf, M.; Möller, W.

Abstract

The aim of a combination of magnetic spectrometers with ion beam analysis techniques is to measure concentration profiles in thin layers with sub-nanometer depth resolution. For these measurements heavy ions from a MV-ion accelerator are directed to the sample. Scattered primary ions or ejected recoil atoms are detected and energy analysed under forward angles. The depth resolution depends directly on the energy resolution of the spectrometer. High energy resolution can only be obtained using magnetic particle spectrometers, where the energy measurement is transformed into a position measurement at the focal plane.
The depth scale is provided by the stopping power of energetic heavy ions moving in matter. The yet produced data are only valid for dynamic charge state equilibrium due to electron loss and capture along the ion trajectory. In the case of ultra thin layers the path length of the particles are too short to achieve this equilibrium. Since magnetic spectrometers separate particles with identical energy but different charge states, it is necessary to consider charge state dependent stopping cross sections for quantitative data analysis. Here only very few data are available in the literature.
In this work, we introduce quantitative ion beam analysis of ultra thin films with magnetic spectrometers.
1. the Quadruple-Quadrupole-Dipole-Sextupole spectrometer “Little John” to measure concentration profiles and charge state distribution of light ions.
2. The Browne-Buechner spectrometer, which is designed to measure samples with heavy atoms.

Keywords: magnetic spectrometer; ion beam analysis; concentration profile; thin layer; high resolution; nonequilibrium charge state; QQDS; Little John

  • Invited lecture (Conferences)
    5th International Workshop on High-Resolution Depth Profiling, 15.-19.11.2009, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-12875


Ionenstrahlanalyse ultradünner Schichten mit Nanometertiefenauflösung

Kosmata, M.; Grambole, D.; Grötzschel, R.; Möller, W.; Munnik, F.; Neelmeijer, C.; Vieluf, M.

Abstract

Die quantitative Elementanalytik von Schichten und Schichtabfolgen im Dickenbereich weniger Nanometer ist in den letzten Jahren in den Fokus aktueller Forschung gerückt. Im Mittelpunkt dieser materialwissenschaftlichen Fragestellungen steht die Bestimmung von Tiefenverteilungen von Elementen in dünnen Schichten, die durch spezielle Abscheideverfahren oder nachfolgende Prozessschritte wie Temperung erzielt werden, aber auch der Nachweis unbeabsichtigter Kontamination in den Schichten. Daraus können Informationen im Hinblick auf gezielte Materialentwicklung gewonnen werden und die Qualität bestehender Prozessführungen lässt sich bewerten.
Die meisten konventionellen (nicht nuklearen) Analyseverfahren sind zur Quantifizierung ihrer Ergebnisse in der Regel auf Referenzmaterialien (gleicher Matrix) angewiesen. Im Gegensatz dazu kann die Ionenstrahlanalyse (ion beam analysis, IBA) standardfrei betrieben werden. Der physikalische Prozess, auf der alle Methoden der IBA beruhen, ist die binäre Wechselwirkung von MeV-Ionen mit den Atomkernen in den Schichten. Diese Wechselwirkung, elastische Streuung oder Kernreaktion, ist einfach und genau beschreibbar; kollektive Matrixeffekte treten dabei nicht auf.
Am Ionenstrahlzentrum des Forschungszentrums Dresden-Rossendorf kommen hauptsächlich drei Analysemethoden zur Anwendung:
• Kernreaktionsanalyse (Nuclear Reaction Analysis, NRA) zum tiefenabhängigen Nachweis von Wasserstoff über die resonante Kernreaktion 1H(15N,αγ)12C*
• Rutherford-Rückstreuspektrometrie (Rutherford Backscattering Spectrometry, RBS) insbesondere zur Detektion von Elementen mit Ordnungszahlen Z > 14
• Detektion elastisch rückgestossener Atome (Elastic Recoil Detection Analysis, ERDA) zum Nachweis leichter Elemente mit Z = 2-14 (He-Si)
Die zur Messung ultradünner Schichten mit RBS und ERDA erforderliche Tiefenauflösung (< 1 nm) kann mit Teilchenspektrometern mit höchster Energieauflösung erreicht werden.
.

Keywords: Nanometer; subnanometer; ultradünn; ultra dünn; ultra thin; standardfrei; Ionenstrahlanalyse; ion beam analysis; IBA; Kernreaktionsanalyse; muclear reaction analysis; NRA; Wasserstoff; Wasserstoffnachweis; 1H(15N; αγ)12C; Rutherford-Rückstreuspektrometrie; Rutherford Backscattering Spectrometry; RBS; Elastic Recoil Detection Analysis; ERDA; Tiefenauflösung; Spektrometer; Massenspektrometer; QQDS; Little John; Browne Buechner

  • Lecture (Conference)
    15. Tagung Festkörperanalytik, 12.-16.07.2009, Chemnitz, Deutschland
  • Poster
    15. Tagung Festkörperanalytik, 12.-16.07.2009, Chemnitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-12874


Release of light elements from ultra thin films during high resolution depth profiling using heavy ion ERDA

Kosmata, M.; Grötzschel, R.; Munnik, F.; Vieluf, M.; Möller, W.

Abstract

The modified QQDS magnetic spectrometer “Little John” [1] at the Forschungszentrum Dresden-Rossendorf is aimed to measure concentration profiles of light elements in thin layers with sub-nanometre depth resolution by Elastic Recoil Detection Analysis (ERDA). Of particular interest are various ultra thin films of metal oxides, nitrides and of carbon compounds. For these measurements heavy ions from the 5 MV-Tandem accelerator are directed to the sample. The ejected recoil atoms are detected and their energy is analysed under forward angles (15°, 30°, 45°, or 60°). Due to the low solid angle of the QQDS spectrometer of about 0.5 msr rather high fluences of initial heavy ions have to be applied. Therefore, special care must be taken to minimize layer deterioration and decomposition by preferential release of elements from the film. To identify optimum measurement conditions and perform final corrections for quantification of high resolution results, we studied the release of oxygen as a function of beam fluence. Thus, different oxides have been irradiated with Cl-, Cu- and I-ions in the energy range from 15 to 40 MeV. We could validate the earlier reported [2] dependency of oxygen loss on
• angle of incidence
• kind and energy of incoming ion
• stopping power
• layer thickness
for SiO2. Similar results have been yet found for La2O3. Further experiments on materials relevant for microelectronics as e.g. high k-dielectrics as HfO2 or ZrO2 are foreseen for the very near future and, thus, will be presented.

References: [1] H.J. Gils et al., Nucl. Instr. and Meth. A276 (1989) 151. [2] W.M. Arnoldbik et al., Nucl. Inst. and Meth. B203 (2003) 151.
.

Keywords: magnetic spectrometer; thin layers; thin films; high depth resolution; ERDA; elastic recoil detection; Little John; QQDS; quantification; release of oxygen; irradiation; electronic sputtering

  • Poster
    19th International Conference on Ion Beam Analysis, 07.-11.09.2009, Cambridge, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-12873


CONCAST: A liquid metal model for continuous steel casting

Timmel, K.; Eckert, S.; Gerbeth, G.; Claussner, J.; Schlenk, R.; Voigtländer, J.

Abstract

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows being relevant for metallurgical applications. In this paper we present the new experimental facility CONCAST for modeling the continuous casting process of steel by using the low melting point alloy SnBi. The facility operates at temperatures of 200°C-400°C. Main parameters of the facility and dimensions of the test sections will be shown. The resultant possibilities with respect to flow investigations in tundish, submerged entry
nozzle and mould will be discussed.

Keywords: continuous casting; liquid metal model; flow investigation

  • Poster
    6th International Conference on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, Deutschland
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, Deutschland, 251-254

Permalink: https://www.hzdr.de/publications/Publ-12872


Flow investigations in an isothermal liquid metal model of the continuous casting process

Timmel, K.; Galindo, V.; Miao, X.; Eckert, S.; Gerbeth, G.

Abstract

The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. First experimental results will be presented which have been obtained using a small-scale experimental set-up with the room temperature alloy GaInSn. Measurements of the liquid flow in the mold will be compared with accompanying numerical calculations. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the submerged entry nozzle (SEN) has been studied.

Keywords: continuous casting; liquid metal model; flow measurement; ultrasound doppler velocimetry; electromagnetic brake

  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, Deutschland
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, Deutschland, 231-234

Permalink: https://www.hzdr.de/publications/Publ-12871


Fluorine-18 radiolabeling of native and oxidized proteins: An important tool in the pathophysiologists’ toolbox

Pietzsch, J.; Wuest, F.

Abstract

The systematic development and improvement of a methodology for mild radiolabeling of both native and modified proteins with the short-lived positron emitter fluorine-18 (18F) under physiological conditions is reported. The presented methodology is an attractive alternative to protein and lipoprotein radiolabeling methods using iodine or metal radionuclides and, particularly, can be applied for functional characterization of both native and oxidized protein species in vivo by means of positron emission tomography (PET).

  • Chimica Oggi - Chemistry Today 27(2009), 12-14

Permalink: https://www.hzdr.de/publications/Publ-12869


Sorption of Np(V) and Np(IV) onto kaolinite: Effects of pH, ionic strength, carbonate and humic acid

Schmeide, K.; Bernhard, G.

Abstract

The sorption of Np(V) and Np(IV) onto kaolinite has been studied in the absence and presence of humic acid (HA) in a series of batch equilibrium experiments under different experimental conditions: [Np]0: 1.0x10-6 or 1.0x10-5 M, [HA]0: 0 or 50 mg/L, I: 0.01 or 0.1 M NaClO4, solid to liquid ratio: 4 g/L, pH: 6-11, anaerobic or aerobic conditions.
The results showed that the Np(V) sorption onto kaolinite is effected by solution pH, ionic strength, Np concentration, presence of carbonate and HA. In the absence of carbonate, the Np(V) uptake increased with pH up to ~ 96% at pH 11. HA further increased the Np(V) sorption between pH 6 and 9 but decreased the Np(V) sorption between pH 9 and 11. In the presence of carbonate, the Np(V) sorption increased with pH and reached a maximum of 54% between pH 8.5 and 9. At higher pH values, the Np(V) sorption decreased due to the presence of dissolved neptunyl carbonate species with a higher negative charge that were not sorbed onto the kaolinite surface which is negatively charged in this pH range. HA again decreased the Np(V) uptake in the near-neutral to alkaline pH range due to formation of aqueous neptunyl humate complexes. The decrease of the initial Np(V) concentration from 1.0x10-5 M to 1.0x10-6 M led to a shift of the Np(V) adsorption edge to lower pH values. A higher ionic strength increased the Np(V) uptake onto kaolinite in the presence of carbonate but had no effect on Np(V) uptake in the absence of carbonate.
To the best of the author`s knowledge, the sorption of Np(IV) onto kaolinite in the presence of HA was studied the first time. For this, a synthetic HA with pronounced reducing properties was applied. This HA effectively reduced Np(V) to Np(IV) and stabilized the tetravalent oxidation state during sorption experiments over a wide pH range. The Np(IV) uptake onto kaolinite is strongly effected by HA. Especially in the near-neutral pH range the Np(IV) uptake was found to be very low in the presence of HA which was attributed to the strong Np(IV) humate complexation in solution.
Thus, depending on the prevailing geochemical conditions, HA has an immobilizing as well as a mobilizing effect on Np(V). In case of Np(IV), the mobilizing effect predominates.

Keywords: Neptunium; Adsorption; Tetravalent; Humic matter; Clay; Kaolinite

Permalink: https://www.hzdr.de/publications/Publ-12868


Resonant enhancement of second order sideband generation for intraexcitonic transitions in GaAs/AlGaAs multiple quantum wells

Wagner, M.; Schneider, H.; Winnerl, S.; Helm, M.; Roch, T.; Andrews, A. M.; Schartner, S.; Strasser, G.

Abstract

We present an experimental study on efficient second order sideband generation in symmetric undoped GaAs/AlGaAs multiple quantum wells. A near-infrared laser tuned to excitonic interband transitions is mixed with an in-plane polarized terahertz beam from a free-electron laser. The terahertz beam is tuned either to the intraexcitonic heavy-hole 1s-2p transition or to the interexcitonic heavy-hole light-hole transition. We find strong evidence that the intraexcitonic transition is of paramount influence on n=+-2 sideband generation, leading to an order-of-magnitude resonant enhancement of the conversion efficiency up to 0.1% at low temperature. At room temperature, the efficiency drops only by a factor of 7 for low terahertz powers.

Keywords: THz sidebands; nonlinear mixing; free-electron laser; FEL

Involved research facilities

  • F-ELBE

Permalink: https://www.hzdr.de/publications/Publ-12867


High-resolution gas-oil two-phase flow visualization with a capacitance wire-mesh sensor

Da Silva, M. J.; Thiele, S.; Abdulkareem, L.; Azzopardi, B. J.; Hampel, U.

Abstract

The application of a novel wire-mesh sensor based on electrical capacitance (permittivity) measurements for the investigation of gas-oil two-phase flow in a vertical pipe of 67 mm diameter under industrial operating conditions is reported in this article. The employed wire-mesh sensor can be operated at up to 5,000 frames per second acquisition speed and at a spatial resolution of 2.8 mm. By varying gas and liquid flow rates different flow patterns, such as bubbly, slug and churn flow, were produced and investigated. From the images of gas void fraction distribution quantitative flow structure information, such as time series of cross-sectional void fraction, radial void fraction profiles and bubble size distributions, was extracted by special image processing algorithms.

Keywords: wire-mesh sensor; phase distribution; two-phase flow; flow visualization; void fraction

Permalink: https://www.hzdr.de/publications/Publ-12866


Bedeutung von Experimenten für die Reaktorsicherheit

Teschendorff, V.; Glaeser, H.; Kliem, S.

Abstract

Experimente waren von Beginn der Reaktortechnik an bis heute Grundlage der Sicherheit und können auch durch weiterentwickelte Rechenmethoden nicht vollständig ersetzt werden. Der Weiterbetrieb unserer laufenden Reaktoren muss von aktiver Sicherheitsforschung begleitet werden, die Experimente mit innovativer Messtechnik einschließt. Der Wirksamkeitsnachweis passiver Sicherheitseinrichtungen bei Gen-III Reaktoren basiert auf spezifischen Experimenten. Neue Experimente zur Sicherheit von Gen-IV-Reaktoren sind parallel zum Design durchzuführen. Deutsche Versuchsanlagen sind unverzichtbar zum Kompetenzerhalt und als Beitrag im internationalen Verbund.

  • Invited lecture (Conferences)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
    Tagungsband der Jahrestagung Kerntechnik 2009; Fachsitzung: Thermohydraulische Experimente für Reaktoren der Generation II - III, Berlin: INFORUM GmbH
  • atw - International Journal for Nuclear Power 55(2010)03, 163-173
    ISSN: 1431-5254

Permalink: https://www.hzdr.de/publications/Publ-12865


Ultra fast electron beam x-ray CT scanner for two phase flow measurement

Fischer, F.; Hampel, U.

Abstract

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

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
  • atw - International Journal for Nuclear Power (2009)7, 461-464

Permalink: https://www.hzdr.de/publications/Publ-12864


Correlation between morphology and bonding structure in titanium oxide films produced by reactive pulsed magnetron sputtering

Gago, R.; Redondo-Cubero, A.; Vinnichenko, M.; Jiménez, I.; Czigány, Z.; Vázquez, L.

Abstract

Titanium dioxide (TiO2) thin films have been grown by reactive pulsed magnetron sputtering (PMS) under different O2 partial pressures in an O2/Ar atmosphere. The films were analyzed by Rutherford backscattering spectrometry (RBS), spectroscopic ellipsometry (SE), atomic force microscopy (AFM), X-ray absorption near edge structure (XANES), grazingincidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). RBS shows that stoichiometric TiO2 films are obtained even at low O2 fraction in the process gas (O2/Ar > 0.05). The formation of mixed or dominant amorphous, rutile and anatase atomic arrangements during PMS has been assessed by XANES and GIXRD as a function of the O2 partial pressure. Further, a clear structural evolution with film thickness (derived by SE) has been detected by AFM and TEM, its dynamics driven by the O2 availability in the gas. Interestingly, this evolution leads to a correlation between the surface morphology and the relative content of the rutile phase, resulting in a nanoscale lateral modulation of the surface properties. Growth experiments varying substrate temperature and bias voltage have been also conducted for further control over the film evolution and to deepen in the growth mechanisms.

Keywords: reactive pulsed magnetron sputtering; TiO2; rutile; anataze

  • Poster
    EMRS Spring Meeting 2009, 08.-12.06.2009, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-12863


Optical and magnetic properties of indium oxides implanted with Cr

Scarlat, C.; Zhou, S.; Vinnichenko, M.; Kolitsch, A.; Bürger, D.; Fassbender, J.; Potzger, K.; Shalimov, A.; Grenzer, J.; Helm, M.; Schmidt, H.

Abstract

Dilute magnetic oxides are expected to play a key role in the development of electronics using the electron spin rather than its charge as information carrier. Indium oxide (IO), a transparent conductive material, is of potential interest for spintronics [1] due to its unique combination of magnetic, electrical, and optical properties. Highly oxygen deficient Cr:IO co-evaporated films revealed ferromagnetism [2]. In present work, we report the post-growth treatment effect on the structural, electrical, magnetic, and optical properties of Cr-implanted IO films. Cr is chosen as a dopant because of its large magnetic moment in the ionic state, and its antiferomagnetic nature in the bulk, ruling out the extrinsic origin of the ferromagnetism if Cr metal segregation occurs. It is non-trivial to form any ferromagnetic secondary phase of Cr oxide. Polycrystalline and amorphous, ca. 300 nm thick IO films were grown on SiO2/Si substrates using reactive pulsed magnetron sputtering and then implanted with Cr+ ions (1, 2, 3, 4 and 5 at% of Cr). The implantation energy was 120 keV. The magnetic-field dependence of magnetization of 2%Cr:IO showed a weak ferromagnetic behavior at 5K. A reasonable model for the Cr implanted IO films has been developed to extract optical constants from spectroscopic ellipsometry data below 3 eV. [1] C. Scarlat et al., Proceedings IBMM 2008, August 31- September 05, 2008, Dresden, Germany [2] J. Philip et al., Nature materials 5, 298 (2006).

  • Poster
    E-MRS 2009 Spring Meeting, 08.-12.06.2009, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-12862


Ultrasound Doppler array measurement system for two-dimensional flow investigations in liquid metals

Franke, S.; Büttner, L.; Czarske, J.; Räbiger, D.; Eckert, S.

Abstract

This paper presents a specific ultrasound Doppler measurement system for investigations of the velocity field in electromagnetically driven liquid metal flows. Two orthogonally arranged ultrasound sensor line arrays facilitate a two-dimensional measurement of two velocity components (2d/2c) within a square area of 70 x 70 mm². The line array elements are controlled by a specific multiplex mode to achieve both a high spatial and a high temporal resolution. The sensor design, the control electronics and the mode of operation of the measurement system are described. Preliminary results of velocity measurements in a liquid metal flow driven by a rotating magnetic field (RMF) are presented.

Keywords: Liquid metal; flow measurement; Ultrasound Doppler method; Sensor array

  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland, 978-3-936104-65-3, 411-414

Permalink: https://www.hzdr.de/publications/Publ-12861


Impact of wetting on velocity measurements in liquid metal flows

Eckert, S.; Buchenau, D.; Gerbeth, G.; Stefani, F.; Weiß, F.-P.; Wondrak, T.

Abstract

Flow measurements are an important issue to ensure the safe and reliable operation of liquid metal systems. In many cases the measuring apparatus is influenced by the wetting between the metal melt to be measured and the sensor or the inner wall of the fluid vessel. In this presentation we report about specific experiences obtained from laboratory experiments using different measuring techniques in various liquid metal flows.

Keywords: Liquid metal; Wetting; Flow measurement; Ultrasound Doppler Method; Electromagnetic flow meter; Inductive flow tomography

  • Lecture (Conference)
    3rd International Seminar "Coolants and Innovative Reactor Technologies", 06.-07.07.2009, Aix-en-Provence, France

Permalink: https://www.hzdr.de/publications/Publ-12860


Micro-ERDA measurements of hydrogen distribution in natural Pd–Pt compounds

Munnik, F.; Cabral, A. R.; Lehmann, B.

Abstract

Micro-ERDA is a unique technique for the measurement of the 2.5D distribution of hydrogen. In this work, this technique is applied to geological samples and in particular Pd–Pt-containing compounds found at the Serra Pelada Au–Pd–Pt deposit. This deposit triggered the most spectacular gold rush in the Amazon region of Brazil in recent history. The sample material is especially important because it represents a novel mineralization style of platinum-group elements.
The sample material was taken from a drill core, filled with resin since it was porous rock, cut and polished. The samples were analysed by simultaneous measurements of PIXE and ERDA with the Dresden-Rossendorf Nuclear Microprobe using a 2 MeV He ion beam. The angle of incidence between beam and sample surface was 15°. The PIXE maps were used to locate the areas of interest because the exact beam position on the target is very critical with this incidence angle. PIXE was also used to determine the matrix composition that is needed for the stopping power calculation in the ERDA analysis.
The results of the measurements and its interpretation are presented. The measurements confirm the presence of hydrogen in the Pd–Pt compounds (either as hydroxide, or hydrated oxide), so far only suspected, and help to better understand the formation process of Pd–Pt mineralization in oxic near-surface environments.

  • Poster
    19th International Conference on Ion Beam Analysis, 07.-11.09.2009, Cambridge, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-12859


Investigation of luminescence properties of dendritic ligands, molecular clips and flavylium salts by time resolved spectroscopy

Raditzky, B.

Abstract

Photochemical and photophysical characterization of novel supramolecular host compounds: Dendritic cyclams, molecular clips and flavylium salts. Result overview of working group collaborations within the COST Action D31.

  • Poster
    COST Action D31 4th Workshop, 28.-30.05.2009, Warszawa, Poland

Permalink: https://www.hzdr.de/publications/Publ-12858


NanoFoto - Neue Wege zur verwertungsorientierten Netzwerkbildung in der Nanobiotechnologie (Schlussbericht)

Raff, J.; Günther, T.; Marquard, A.; Kutschke, S.; Pollmann, K.; Roos, S.; Hofinger, J.; Meyer, A.

Abstract

Wissenschaftliches Ziel des Vorhabens ist die Entwicklung von fotokatalytisch aktiven Verbundmaterialien zum Abbau von organischen Verbindungen (z. B. Arzneistoffen) in Wasser. Diese Verbundmaterialien beruhen auf der Beschichtung von Trägermaterialien mit ZnO/TiO2-Nanopartikeln, die mit Hilfe von selbstorganisierenden bakteriellen Hüllproteinen (S-Layern) als Matrix hergestellt werden. Vorgesehen sind ein Up-Scaling der Biomasseproduktion, Entwicklung und Optimierung von Syntheseverfahren von ZnO-Nanopartikeln, Beschichtung von Trägermaterialien mit ZnO-Nanopartikeln, katalytische Tests. Durch die Beteiligung der Firmen Namos GmbH und UMEX GmbH wird die Überführung der Nanokatalysatoren in eine technische Nutzung vorbereitet, eine kontinuierliche Biomassegewinnung etabliert und optimiert. Weiteres Ziel des Vorhabens ist die Bildung eines verwertungsorientierten Netzwerks.

  • Other report
    Dresden: Schlussbericht, BMBF-Vorhaben 01SF0717 2009, 2009
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-12857


Dynamic surface barrier effects on hydrogen storage capacity in Mg-Ni films

Wirth, E.; Munnik, F.; Pranevicius, L. L.; Milcius, D.

Abstract

Hydrogen distribution profiles in Mg-Ni films deposited on quartz substrate by the magnetron-sputter co-deposition of Mg and Ni atoms have been investigated after hydrogenation at 8 x 105 Pa hydrogen pressure at temperatures 210,230 and 250 degrees C during 1, 3,6 and 72 h using elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA) methods. Oxygen distribution profiles in the near-surface region have been measured by ERDA. It is shown that hydrogen storage capacity decreases as hydrogenation temperature increases from 210 to 250 degrees C for fixed hydrogenation duration and changes not monotonously as function of hydrogenation time for a fixed temperature. To explain variations of storage capacity as function of hydrogenation temperature and time, the structural film changes have been studied by X-ray diffraction technique, and surface topography was analysed using scanning electron microscopy. We suggest that registered results may be explained on the basis of assumption about the dynamic properties of surfaces which modify the hydrogen uptake mechanism.

Permalink: https://www.hzdr.de/publications/Publ-12856


Ion implantation enhanced formation of 3C-SiC grains at the SiO2/Si interface after annealing in CO gas

Pécz, B.; Stoemenos, J.; Voelskow, M.; Skorupa, W.; Dobos, L.; Pongrácz, A.; Battistig, G.

Abstract

Silicon carbide with its hexagonal and cubic polytypes is one of the wide band-gap semiconductors used for high temperature applications. Obviously the growth of cubic SiC on Si would be very advantageous, because very large, high quality substrates would then be available at relatively low cost.

Keywords: 3C-SiC formation of carbide; ion implantation; annealing in CO

  • Contribution to proceedings
    16th International Conference on Microscopy of Semiconducting Materials, 17.03.2009, Oxford, United Kingdom
    Ion implantation enhanced formation of 3C-SiC grains at the SiO2/Si interface after annealing in CO gas
  • Open Access Logo Journal of Physics: Conference Series 209(2010), 012045-1-012045-2
    DOI: 10.1088/1742-6596/209/1/012045
    Cited 1 times in Scopus

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Permalink: https://www.hzdr.de/publications/Publ-12855


Crossbeam processing for nano-structures on SOI substrates

Bischoff, L.; Schmidt, B.; Lange, H.; Donzev, D.

Abstract

The further miniaturization of silicon nanomechanical structures in combination with the highly developed microelectronic technology at the micro- and nanometer level will lead to a new generation of nano-electro-mechanical systems (NEMS). A modern technique to fabricate such three-dimensional structures is the combination of high-concentration p-type doping of silicon by high resolution writing implantation using a focused ion beam (FIB) and subsequent anisotropic and selective wet chemical etching. FIB-patterned and chemically etched 3D Si structures with nanoscale thickness and width have been fabricated using 30 keV Ga+ ion implantation (CANION 31Mplus and NVision40) followed by an anisotropic etching in KOH/H2O solution on Silicon-On-Insulator (SOI) substrates. This technology is combined with classical microelectronic techniques, like lithography and broad beam implantation working on a 4 inch wafer to increase the fabrication efficiency especially for the contact areas. Design, performance and fabrication considerations to achieve freestanding Si structures, like nanowires (NW) and -bridges are discussed and some typical structures are shown. Static electrical measurements are demonstrated among others a nano-thermometer, which reveal a broad spectrum in the field of sensor applications. To reduce the resistance the amorphous Si-NWs were covered by electron beam assisted deposition of a 30 nm Platinum film. The dynamic behaviour like resonance frequency was determined by AC excitation and laser interferometer measurements.

Keywords: FIB; etching; SOI wafer; nanowire; NEMS

  • Lecture (others)
    4. FIB-Workshop, Focused Ion Beams in Research, Science and Technology, 29.-30.06.2009, Halle/Saale, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12854


Alloy Liquid Metal Ion Source for Carbon Focused Ion Beams

Mazarov, P.; Wieck, A. D.; Bischoff, L.; Pilz, W.

Abstract

An aluminium-carbon-cerium alloy Liquid Metal Ion Source (AlCCe LMIS) is presented for generating of focused ion beams of carbon ions as well as ionized clusters with a size of 2, 4 and 8 atoms. Emission current dependent measurements were carried out of the mass spectra and energy spread of all species, but focused to the carbon monomer ions and clusters. A FWHM of the energy distribution was determined to be 6.5 eV for the monomer carbon ion and 14 eV for the light clusters at an emission current of 5 µA. The source showed a good beam performance after inserting in a mass separated focused ion beam (FIB) system. Applications to graphene structures, organic matter and other carbon containing materials are promising tasks of the new carbon containing alloy LMIS.

Keywords: Carbon alloy LMIS; mass spectra; energy spread; FIB

  • Journal of Vacuum Science & Technology B 27(2009)6, L47-L49

Permalink: https://www.hzdr.de/publications/Publ-12853


Comparison of different tools to study gas-liquid flow

Abdulkareem, L. A.; Hernandez-Perez, V.; Azzopardi, B. J.; Sharaf, S.; Thiele, S.; Da Silva, M. J.

Abstract

In an effort to obtain a comprehensive knowledge of gas-liquid flows, in this paper the use of different tools available at the University of Nottingham to study gas-liquid flow in pipes is presented, followed by a comparison of the instrumentation performance. Air-silicone oil is used as the working mixture. The tools are capacitance wire mesh sensor (WMS), electrical capacitance tomography (ECT), capacitance probes and computational fluid dynamics (CFD) modelling. This is supplemented by illustrations of the sort of information that have been obtained. In general the agreement in the comparison is fairly good. However, it is observed that the WMS provides a better spatial resolution than ECT (with a first order reconstruction method) and is excellent for measurement of bubbly flow parameters.

Keywords: Wire-mesh; ECT; capacitance; CFD

  • Contribution to proceedings
    7th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 28.06.-03.07.2009, Krakow, Poland
    Proceedings of ExHFT-7, Krakow: AGH University of Science and Technology Press, 978-83-7464-235-4, 785-792
  • Lecture (Conference)
    7th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 28.06.-03.07.2009, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-12852


Interrogation of gas/oil flow in a vertical pipe using two tomographic techniques

Abdulkareem, L. A.; J. Azzopardi, B.; Thiele, S.; Hunt, A.; Da Silva, M. J.

Abstract

In the design of wells and risers it is important to understand the behaviour of the gas/liquid flows. The very complex nature of the interface between the phases can make observations very difficult with interfaces near the wall obscuring the phenomena occurring at the pipe centre. Here, two tomographic techniques are applied to the flow in a 67 mm internal diameter vertical pipe. One is Electrical Capacitance Tomography (ECT) electrode system driven by Tomoflow electronic and employs two rings of eight electrodes each mount on the outside of the non-conducting pipe wall. Measurement of the capacitance between each electrode pair in a ring yield matrices of data which can yield time varying cross-sectionally resolved gas fraction and velocities data. The other technique, usually known as the Wire Mesh Sensor (WMS) approach developed at Forschungszentrum Rossendorf-Dresden, which had been previously applied and used in a two-phase flow facility at Nottingham for air/water, was used. In the present experiments a new, capacitance based version has been utilised. This employs two arrays of 24 wires stretched along regularly spaced chords. The second array is a few millimetres downstream of the first and positioned orthogonally to it. One array acts as the exciter and the other as the detector. Each exciter wire is pulsed in turn and the signal reaching every detector wire is monitored. The entire cross section is sampled at 1 kHz. Simultaneous measurements were made with the two techniques for gas superficial velocities of 0.05 – 4.7 m/s and liquid superficial velocities of 0 – 0.7 m/s with air and a silicone oil as the fluids. Bubble, slug and churn flows were identified from the characteristic signatures of the Probability Density Functions of the cross-sectionally averaged void fraction. Three-dimensional gas fraction data can be extracted. In addition, the detailed shape of individual large bubbles has been extracted. The output of both instruments show clearly that the shapes of the large bubbles in slug flow are distinctly different from the smooth bullet-shaped objects observed in smaller diameter pipes and which are sketched in text books. In this larger diameter pipe, the interface is much more disturbed. They might be described as wrinkled. In addition, flow can be classified according to the sizes of bubbles present. Distributions of bubble sizes are presented and the fractions of gas flowing in different bubble sizes classes quantified.

Keywords: Two-phase flow; wire-mesh sensor; electrical capacitance tomography; flow visualization

  • Contribution to proceedings
    OMAE 2009, 31.05.-05.06.2009, Honolulu, USA
    Proceedings of the ASME 28th International Conference on Ocean, Offshore and Arctic Engineering, 79840
  • Lecture (Conference)
    28th International Conference on Ocean, Offshore and Arctic Engineering, 31.05.-05.06.2009, Honolulu, USA

Permalink: https://www.hzdr.de/publications/Publ-12851


Wire-mesh sensors for fast visualization of multiphase flows

Da Silva, M. J.; Thiele, S.; Schleicher, E.; Hampel, U.

Abstract

Wire-mesh sensors are flow imaging devices and allow for high spatial and high temporal resolution visualization of phase fraction (e.g. gas void fraction or liquid holdup) distribution of multiphase flow. This type of sensor has been successfully employed to investigate a number of single phase and two-phase flow phenomena in the past. In this contribution, an overview about the operation principle of wire-mesh sensors along with the signal and image processing procedures to obtain physical flow parameters from the electrical measured signals is given. Besides describing the state of the art of wire-mesh sensor technology, the latest development of a temperature wire-mesh sensor is depicted in detail.

Keywords: wire-mesh sensor; flow visualization; multiphase flow; temperature; void fraction

  • Contribution to proceedings
    What Where When Multi-dimensional Advances for Industrial Process Monitoring, 23.-24.06.2009, Leeds, United Kingdom
    Proceedings of W3MDM 2009, 98-108
  • Poster
    What Where When Multi-dimensional Advances for Industrial Process Monitoring, 23.-24.06.2009, Leeds, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-12850


Charge storage properties and electroluminescence in silicon nanocrystals fabricated by ion beam mixing of gate oxide/silicon interfaces

Schmidt, B.; Heinig, K.-H.; Beyer, V.

Abstract

The present contribution addresses the Si nanocrystal formation by a non-conventional ion beam synthesis approach of ion beam mixing of SiO2/Si interfaces in thin gate oxides, with special emphasis on well-controlled size and position tailoring as well as on their application in non-volatile nanocrystal memories and in light emitting field-effect transistors. The Si nanocrystal MOSFETs were fabricated as nMOSFET devices and their electrical characteristics have been evaluated in terms of write/erase voltage, duration of the programming time, endurance and retention for different ion irradiation and annealing conditions. For the investigation of the light emitting characteristics of the same nMOSFETs an AC voltage was applied to the gate in order to inject charges of both polarities into the nanocrystals leading to the formation of excitons there. They recombine under emission of a photon, whereas the emitted wavelength is a function of the nanocrystal size. AC voltage and frequency dependent electroluminescence spectra in the wavelength region of 400-1000 nm were recorded for different annealing conditions.

Keywords: Ion beam mixing of interfaces; silicon nanocrystal; non-volatile memory; light-emitting MOSFET; electroluminesence

  • Contribution to proceedings
    10th International Symposium on Sputtering and Plasma Processes (ISSP 2009), 08.-10.07.2009, Kanazawa, Japan
    Proceedings of the 10th International Symposium on Sputtering and Plasma Processes -ISSP 2009-, Ishikawa, Japan: Eiji Kusano, Kanazawa Institute of Technology, ISSN 0917-2440, 52-56

Permalink: https://www.hzdr.de/publications/Publ-12849


The Analysis of Uranium Binding Form with Mineral Phases by Time- resolved Laser-induced Fluorescence Spectroscopy

Baumann, N.

Abstract

Uranium migration is mainly occurred when mobile uranium species from rock piles and old mines are washed by surface water. It is necessary to study the pathway, the species, and the amount of migrating uranium compounds. The objective of this research is to investigate the interactions between solid mineral phases and mobile uranium species such as sorption, precipitation and forming secondary uranium minerals by time-resolved laser-induced fluorescence spectroscopy (TRLFS). This technique has shown to be able to detect a trace amount of uranium (VI) species in both solution and solid phases. TRLFS delivers a fluorescence signal with characteristic features related to the concentration and speciation of fluorescent species in the sample. These features include, the positions of the peak maxima, and characteristic lifetimes of the signals. Results show fluorescent signals of absorbed uranium species on gibbsite and muscovite surfaces. The spectroscopic signatures of these uranium (VI) minerals are useful in identifying uranium (VI) species as colloids, thin coatings on rocks, minor components in soils, or alteration products of nuclear waste.

Keywords: Uranium mining; uranium (VI); time-resolved laser-induced fluorescence spectroscopy

  • Contribution to proceedings
    11th Conference on Nuclear Science and Technology, 02.-03.07.2009, Bangkok, Thailand

Permalink: https://www.hzdr.de/publications/Publ-12848


Ultrafast Cross-Sectional Imaging of Gas-Particle Flow in a Fluidized Bed

Bieberle, M.; Fischer, F.; Schleicher, E.; Koch, D.; Menz, H.-J.; Mayer, H.-G.; Hampel, U.

Abstract

Ultrafast electron beam X-ray computed tomography is used to visualise the gas-solids distribution inside an experimental fluidized bed at frame rates of 5000 s-1.

Keywords: fluidized bed; ultrafast X-ray computed tomography

Permalink: https://www.hzdr.de/publications/Publ-12847


Synthesis and radiopharmacological investigation of 3-[4’-[18F]fluorobenzylidenyl]-indolin-2-one as possible tyrosine kinase inhibitor

Knieß, T.; Bergmann, R.; Kuchar, M.; Steinbach, J.; Wüst, F.

Abstract

The radiosynthesis and radiopharmacological evaluation of 3-[4’-[18F]fluorobenzylidenyl]-indolin-2-one, a derivative of tyrosine kinase inhibitor SU5416, is described. The radiosynthesis was accomplished by Knoevenagel condensation of 4-[18F]fluorobenzaldehyde with oxindole in a remotely controlled synthesis module. The reaction conditions were optimized through screening the influence of different bases on the radiochemical yield. The radiotracer was obtained after a two-step labelling procedure in 4% decay-corrected radiochemical yield at a specific activity of 48-61 GBq/µmol within 90 min. The radiochemical purity after semi-preparative HPLC purification exceeded 98%.
The biodistribution was studied in Wistar rats. After distribution the radiotracer was rapidly accumulated in the adrenals, liver and kidneys, however, it was cleared from these and the most other organs. Only the adipose tissue remained the activity over 60 min. Unexpected high transient uptake was observed in the brain, pancreas, heart and lung. The fast clearance of 3-[4’-[18F]fluorobenzylidenyl]-indolin-2-one was caused by excretion, approximately one half each was renal and biliary excreted and the other part cleared by metabolic processes. In arterial blood plasma two more polar metabolites were found by radio-HPLC. After 20 min post injection, only 12% of intact radiotracer has been detected. Consequently, in small animal PET studies with FaDu tumour bearing mice no specific uptake in the tumours could be observed.

Keywords: Positron emission tomography (PET); 4-[18F]fluorbenzaldehyde; tyrosine kinase inhibitor; Knoevenagel condensation; SU5416

Permalink: https://www.hzdr.de/publications/Publ-12846


Two Coordination Modes of Bidentate Aminopyrazine Ligands in Cubane-type Cluster Complex Re4Te4Cl8(C4N3H4)4 . 2DMF

Efremova, O. A.; Mironov, Y. V.; Pietzsch, H.-J.; Stephan, H.; Perrin, C.; Fedorov, V. E.

Abstract

A new cubane-type cluster complex Re4Te4Cl4(C4H4N3)4 . 2DMF has been synthesized by reaction of Re4Te4Cl8(TeCl2)4 with 2-aminopyrazine C4H5N3 in DMF. The crystal structure of compound has been solved by X-ray single crystal diffraction method. Crystal data for Re4Te4Cl4(C4N3H4)4 . 2DMF: a = 22.8718(16) A ° , b = 8.5936(7) A ° , c = 20.5720(17) A ° , ß° = 106.493(2), V = 3877.1(5) A ° 3, R1 = 0.0466, Rw(F2) = 0.1191. In the complex bidentate aminopyrazine ligands are coordinated in two different types, namely, two of four aminopyrazine ligands bind to a single rhenium atom, and each of two other ligands is coordinated as bridge between two rhenium atoms.

Keywords: Cubane Re4 cluster; 2-Aminopyrazine; Synthesis; Crystal structure

Permalink: https://www.hzdr.de/publications/Publ-12845


Development of bispidine derivatives containing targeting vector molecules and fluorescent labels

Fähnemann, S.

  • Lecture (Conference)
    6th SUPRAPHONE Meeting, 04.-07.06.2009, Jyväskylä, Finland

Permalink: https://www.hzdr.de/publications/Publ-12844


Molecular Imaging Modalities for Tumor Visualization

Stephan, H.; Bergmann, R.

  • Lecture (Conference)
    6th SUPRAPHONE Meeting, 04.-07.06.2009, Jyväskylä, Finland

Permalink: https://www.hzdr.de/publications/Publ-12843


Toward Bio-Inspired Photoadressable Supramolecular Systems. Synthesis, Light-Emission, Dynamics, Biomedical Application: A Final Report

Stephan, H.

  • Lecture (Conference)
    4th Annual COST-D31 Workshop, 28.-30.05.2009, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-12842


Dual-plane ultrafast limited-angle electron beam x-ray tomography

Bieberle, M.; Schleicher, E.; Fischer, F.; Koch, D.; Menz, H.-J.; Mayer, H.-G.; Hampel, U.

Abstract

Electron beam x-ray tomography is an imaging technique, which can provide cross-sectional images of an object of interest with about 1 mm spatial resolution at frame rates of up to 10,000 frames per second. As a non-intrusive method it is especially suited for studying multiphase flows. For this purpose we devised an experimental limited-angle scan setup which utilizes linear beam deflection to generate radiographic projections. This setup was employed in the study of gas-liquid flow in an experimental flow loop operated at different liquid and gas flow rates. Electron-beam tomography images were compared with image data of a wire-mesh sensor. The latter is a fast, but intrusive imaging device, which is commonly used in gas-liquid flow imaging and achieves comparable frame rates but at lower spatial resolution. As a novelty we implemented a dual-plane limited-angle electron beam x-ray tomography which allows us to gain information about the phase velocities using cross-correlation data analysis.

Keywords: electron beam x-ray CT; limited-angle CT; wire-mesh sensor; two-phase flow

Permalink: https://www.hzdr.de/publications/Publ-12841


X-ray visualisation of bubble formation and bubble motion in liquid metals

Boden, S.; Eckert, S.; Gerbeth, G.; Simonnet, M.; Anderhuber, M.; Gardin, P.

Abstract

The real-time digital X-ray radioscopy has been used to visualise the liquid metal two-phase flow in a GaInSn melt in a flat container with a rectangular cross-section. Argon bubbles were injected through single orifices at the side-walls of the fluid vessel. X-ray images were acquired with a frame rate of 22.3 Hz. Exposure times of 5 ms deliver instantaneous snapshots of the flow structure. Quantitative values of the mean bubble size, bubble velocity, bubble distribution and bubble trajectory were obtained from the X-ray data. It was shown for the liquid metal case that the wetting conditions at the gas injector significantly affect the size of the detaching gas bubbles.

Keywords: liquid metal two-phase flow; nozzle wetting; X-ray visualisation

  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland, 387-390
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12840


X-ray visualisation of solidifying GaIn-alloys in the presence of melt convection

Boden, S.; Willers, B.; Eckert, S.; Gerbeth, G.

Abstract

X-ray radioscopic methods enable the in-situ real-time observation of solidification processes in metal alloys with a spatial resolution of a few microns. Visualisation of bottom up directional solidification of a Ga-25wt%In binary metal alloy contained in a capillary slit container was conducted. The solidification is obviously affected by natural thermosolutal melt flow patterns. Externally forced melt convection was superimposed by means of a magnetic stirrer in form of a rotating wheel equipped with permanent magnets. The electromagnetic flow provokes a considerable redistribution of the solutal boundary layers around the solidifying dendrites, and influences therewith the formation of the microstructure.

Keywords: directional solidification; melt convection; forced flow; X-ray visualisation

  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland, 261-264
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12839


Binding Form of Uranium in Environmental Relevant Waters, Studied by Laser Spectroscopic Methods

Bernhard, G.; Geipel, G.

Abstract
  • wird nachgereicht
  • Invited lecture (Conferences)
    Freiberger Forschungsforum 2009 (60. Berg- und Hüttenmännischer Tag), 19.06.2009, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12838


Laser Spectroscopy of Highly Charged Ions at Storage Rings

Winters, D. F. A.; Geppert, C.; Sánchez, R.; Nörtershäuser, W.; Kühl, T.; Zielbauer, B.; Ursescu, D.; Schramm, U.; Bussmann, M.; Birkl, G.; Walther, T.; Hannen, V.; Weinheimer, C.; Stöhlker, T.

Abstract

Heavy highly charged ions (HCI) are the simplest few-body systems and the strongest laboratory sources of electromagnetic fields. These ions thus uniquely enable one to probe the effects of quantum electrodynamics and relativity at strong fields, and to verify corresponding theoretical predictions. The impact of these strong fields on the atomic structure can, however, still only be measured by very accurate techniques, such as laser spectroscopy. Unfortunately, the required experimental conditions (e.g. for the HCI to remain in their charge-state) are severe, and the relevant spectroscopic transitions of the ions cannot be directly probed by standard laser systems. In storage rings, such as the experimental storage ring (ESR) of GSI in Darmstadt, the conditions are excellent: a high intensity ion beam, which can also be cooled, traverses the ultra-high vacuum (10−11 mbar) beamline with a revolution frequency of about a MHz. There are thus many ion-photon interactions, and corresponding fluorescence yields are sufficient. The kinetic energy of the ions can be varied over a large range, and the Dopplershift be used to boost the transitions into the laser accessible regime. The future Facility for Antiproton and Ion Research (FAIR) will provide even more possibilities. The Stored Particle Atomic Research Collaboration (SPARC) therefore developed a broad research programme [1]. For example, at the new experimental storage ring (NESR), it is planned to determine QED effects in strong fields via laser spectroscopy of the 1s and 2s hyperfine structure in H- and Li-like ions, respectively [2]. For this purpose, radioactive nuclei or even chains of isotopes can be used to disentangle QED and nuclear effects. In addition, by means of optical pumping with lasers (via the hyperfine structure), spin-polarised ion beams will be produced for e.g. parity non-conservation studies. The high-energy laser PHELIX will generate x-rays which, combined with HCI in the new ESR, enable studies of 2s−2p transitions in high-Z few-electron systems for accurate tests of atomic structure theory in the strong field regime. In the SIS300, laser cooling - the only possible cooling method at these high energies - of Li-like heavy ions is planned [3].
[1] Th. Stöhlker et al., Nucl. Instr. Meth. Phys. Res. B 261 (2007) 234.
[2] D.F.A. Winters et al., Can. J. Phys. 85 (2007) 403.
[3] H. Backe, Hyp. Int. 171 (2007) 93.

Keywords: highly charged ions; laser; laser spectroscopy; atomic structure; laser cooling; HCI; ESR; QED

  • Poster
    PEARL 2009 - Physics at EBITS and Advanced Research Light Sources, 06.-09.05.2009, Dublin City University, Glasnevin, Dublin, Ireland

Permalink: https://www.hzdr.de/publications/Publ-12837


Towards Optical Control over the Lowest Nuclear Excited State in 229Th

Thirolf, P. G.; Habs, D.; Bussmann, M.; Maier, H. J.; Neumayr, J. B.; Schätz, T.; Schmitz, H.; Schreiber, J.; Szerypo, J.; Trepl, L.; Wirth, H.-F.

Abstract

The MLL IonCatcher buffer gas cell facility forms the key component of our experimental efforts to study the isomeric ground state transition of the lowest nuclear excited state in 229mTh at 7.6(5) eV as described in the 2007 annual report [1]. There the goal is to exploit the unique properties of this lowest excited nuclear state with its unprecedented narrow relative linewidth of about 10−21 for metrology as well as for fundamental physics studies such as a potential time dependence of fundamental constants like the fine structure constant ). Using the gas cell as an 'isomer generator' from the – decay of 233U, the production of the 229Th isomers can be decoupled from the fluorescence decay of the isomeric first excited state in 229mTh, thus avoiding any background contaminations from atomic or conversion processes.

Keywords: ion; buffer gas cooling; isomeric state; th229; laser cooling; laser spectroscopy; gas cell

  • Contribution to external collection
    in: Annual Report of the Maier-Leibnitz-Laboratorium der Universität und der Technischen Universität München, MLL, Am Coulombwall 6, D-85748 Garching: Maier-Leibnitz-Laboratorium (MLL), 2009, 16-17

Permalink: https://www.hzdr.de/publications/Publ-12836


Application of contactless inductive flow tomography to the continuous casting process

Wondrak, T.; Galindo, V.; Gerbeth, G.; Gundrum, T.; Stefani, F.; Timmel, K.

Abstract

The contactless inductive flow tomography (CIFT) is a method for reconstructing the velocity field in electrically conducting melts from externally measured induced magnetic fields. One of its possible applications is the velocity reconstruction in the continuous casting process. In this paper, we apply this method to the flow field in a small model of a continuous casting mould. It is shown that the flow structure in general, and the jet position and the intensity in particular, can be reliably determined.

Keywords: continuous casting; industrial tomography; liquid metal flow measurement

  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM), 19.-23.10.2009, Dresden, Deutschland
    Application of contactless inductive flow tomography to the continuous casting process, pp. 395-398
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM), 19.-23.10.2009, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12835


Recent progress on contactless inductive flow tomography

Wondrak, T.; Stefani, F.; Gundrum, T.; Gerbeth, G.

Abstract

The contactless inductive flow tomography (CIFT) is a technique to reconstruct the velocity in electrically conducting melts using magnetic fields. One of its application could be the velocity reconstruction in the mould of the continuous casting process. In this paper, we present the numerical investigation and first measurements of the induced magnetic field taken in our lab on a small model of a continuous casting mould.

Keywords: Inverse Problems; Industrial tomography; Liquid metal flow measurement; continuous casting

  • Contribution to proceedings
    80th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM), 09.-13.2.2009, Gdansk, Poland
  • Lecture (Conference)
    80th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM), 09.-13.2.2009, Gdansk, Poland

Permalink: https://www.hzdr.de/publications/Publ-12834


Some methodological improvements of the contactless inductive flow tomography

Wondrak, T.; Stefani, F.; Gundrum, T.; Gerbeth, G.

Abstract

The goal of contactless inductive flow tomography (CIFT) is the velocity reconstruction in electrically
conducting melts which are used in many metallurgical and crystal growth applications. In this paper,
we discuss some recent methodological improvements of this method, in particular the automatic
search for an optimum regularisation parameter and the amended treatment of the boundary integrals.

Keywords: inverse problems; industrial tomography; liquid metal flow measurement

  • International Journal of Applied Electromagnetics and Mechanics 30(2009)3-4, 255-264

Permalink: https://www.hzdr.de/publications/Publ-12833


CFD simulations of GIDROPRESS mixing facility experiments

Höhne, T.; Rohde, U.; Melideo, D.; Moretti, F.; D’Auria, F.; Shishov, A.; Lisenkov, E.

Abstract

Extensive analytical work:

  • 65 pre-test calculations
  • 45 post-test calculations
Comparison of all code results against exp data
Main findings:
  • 3rd Group (steady pump operation + tracer injection)
  • Perturbation morphology correctly described
  • Quantitative discrepancies (degree of mixing)
  • Can be handled by proper accuracy and uncertainty evaluation

2nd Group (tracer slug + onset of NC)

  • Crucial role played by density effects

Keywords: CFD; VVER-1000

  • Lecture (Conference)
    Working Group C and G of AER, 11.-12.06.2009, Tengelic, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-12832


Temperature control design for a high-resolution gamma ray tomography detector

Bieberle, A.; Schleicher, E.; Hampel, U.

Abstract

In this paper a thermal control design for a high-resolution gamma ray computed tomography (CT) detector is presented. It accounts for the generation of heat produced by active electronic components as well as heat transfer from external heat sources. The development and implementation of this feature was motivated by stringent requirements for measurement accuracy at thermal hydraulic test facilities where ambient thermal conditions are constantly changing. As a first step the thermal behaviour of the existing tomography detector was analysed, critical components were identified and different approaches for heat removal were tested. Eventually, an improved thermal detector design was elaborated and a controlled active cooling system implemented. Performance tests proved its effectiveness and accuracy improvement.

Keywords: gamma ray tomography; temperature control

  • Review of Scientific Instruments 81(2010), 014702

Permalink: https://www.hzdr.de/publications/Publ-12831


Mikrostruktur und mechanische Eigenschaften der RDB-Stähle JRQ und JFL in Abhängigkeit von der Bestrahlung mit Neutronen

Altstadt, E.; Ulbricht, A.; Viehrig, H.-W.; Zurbuchen, C.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2009
    FZD\FWS\2009\02
    0032 Seiten
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-12830


IAEA coordinated research project on master curve approach to monitor fracture toughness of RPV steels: final results of an analytical round robin exercise to support constraint effects

Scibetta, M.; Altstadt, E.; Sang, L. B.; Callejas, R. H.; Miura, N.; Onizawa, K.; Paffumi, E.; Serrano, M.; Tatar, L.; Yin, S.

Abstract

There is strong interest from the nuclear industry to use the precracked Charpy single-edge notched bend, SE(B), specimen (PCVN) to enable determination of the reference temperature, T0, with reactor pressure vessel surveillance specimens. Unfortunately, for many different ferritic steels, tests with the PCVN specimen (10x10x55 mm) have resulted in T0 temperatures up to 25°C lower than T0 values obtained using data from compact, C(T), specimens. This difference in T0 reference temperature has often been designated a specimen bias effect, and the primary focus for explaining this effect is loss of constraint in the PCVN specimen. The International Atomic Energy Agency has developed a three-part coordinated research project (CRP) to evaluate various issues associated with the fracture toughness Master Curve for application to light-water reactor pressure vessels. One part of the CRP is focused on the issue of test specimen geometry effects, with emphasis on the PCVN bias. This topic area was organized in two parts, an experimental part and an analytical part with a view towards each part complementing the other. Within the analytical part, elastic plastic finite element methods are extensively used in order to access local stress and strain information that is the basic ingredient for most of the micro-models of cleavage fracture developed to date.

In the framework of the international qualification and acceptance of such a tool for actual loss of constraint prediction, the validation of such tool is of prime importance. Therefore, a round robin exercise has been proposed and performed by ten laboratories from nine different countries. The round robin focuses on the modeling of realistic three-dimensional geometries containing shallow and deep crack.

This round robin has been useful to qualify different finite element codes and to identify possible errors in the input file. The round robin demonstrates that errors in the input file can be easily introduced. Some remaining differences cannot be attributed to one particular finite element code or to actual errors. Those differences are attributed to the so called "user effect" which can only be reduced through in depth discussion and deep understanding of each finite element code.

Independently of the used code and of relatively small user effect differences, it is found that shallow crack specimens are more sensitive to loss of constraint than deep crack specimens for a given specimen size. The difference in terms of reference temperature between the two geometries is evaluated to be about 40 °C. For a deep crack, loss of constraint is identified to appear at M values around 200. This value is larger than the one specified in current standard (M = 30). Increasing the M value to 200 will jeopardize the use of PCVN for the nuclear industry on the other hand bias introduced by M value of 30 is acceptable.

Keywords: Fracture toughness; Bermin model; local approach; numerical fracture mechanics; constraint

  • Contribution to proceedings
    2009 ASME Pressure Vessels and Piping Conference (PVP2009), 13.-17.07.2009, Prague, Czech Republic
    Proceedings of the 2009 ASME Pressure Vessels and Piping Conference

Permalink: https://www.hzdr.de/publications/Publ-12829


Ultrafast electron beam tomography

Hampel, U.

Abstract

Since its invention in the 1970th computed tomography (CT) has become an indispensable diagnostic tool in medicine. CT scanning using X-rays was the first clinical tomographic imaging technique which was later complemented by tomographic imaging modalities based on other physical principles, such as magnetic resonance imaging (MRI), positron emission tomography (PET) and single photon emission tomography (SPECT). Today, medical radiology is still the primary application field of computed tomography, but meanwhile this imaging technology has diverted also into other fields of science and engineering, for instance non-destructive testing, flow measurement and small animal imaging.

Keywords: electron beam tomography; computed tomography

  • Contribution to external collection
    Krzysztof Iniewski: Semiconductor Radiation Detection Systems, Boca Raton: CRC Press, Taylor & Francis Group, 2010, 978-1-4398-0385-1, 263-280

Permalink: https://www.hzdr.de/publications/Publ-12828


Process tomography with electron beams

Hampel, U.; Fischer, F.

Abstract

Electron beams are versatile tools for material processing and imaging applications. Tomography with a scanned electron beam has already been proposed and realized more than 20 years ago with the cardiac electron beam CT. Though electron beam technology is somewhat intricate and complex the potentials of this technology regarding multiphase flow and process imaging are large. With the commissioning of a dedicated flow tomography scanner based on electron beam tomography our group now starts to use this technology for high-speed flow visualization in practical applications. One example is the study of gas-liquid mixture flows, which is an important flow type in nuclear and chemical engineering. Here we give an introduction into the measurement technology and discuss future prospects in scanner design and applications.

Keywords: computed tomography; electron beam tomography; process tomography

  • Contribution to proceedings
    What, Where, When: Multi-dimensional Advances for Industrial Process Monitoring International Symposium, 23.-24.06.2009, Leeds, UK
    Proceedings, Paper #5
  • Lecture (Conference)
    What, Where, When: Multi-dimensional Advances for Industrial Process Monitoring International Symposium, 23.-24.06.2009, Leeds, UK

Permalink: https://www.hzdr.de/publications/Publ-12827


Ultra high speed electron beam tomography for flow measurement and small animal imaging

Hampel, U.; Fischer, F.

Abstract

We introduce ultra high speed electron beam tomography as a new imaging tool for multiphase flow measurement and small animal imaging. The technique is based on imaging with X-rays produced by a rapidly scanned electron beam instead of a mechanically rotating source-detector compound. The scanner device ROFEX was developed manufactured and commissioned recently at FZD and allows scanning of objects with up to 7.000 frames per second speed and 1 mm spatial resolution. Application examples from multiphase flow measurement and small animal imaging are presented. Multiphase flow imaging mainly benefits from fast scanning which is impossible with any other imaging technology at this temporal and spatial resolution. Small animal imaging with ultra fast electron beam CT, however, is still in its beginning. Here higher spatial resolution and 3D imaging is needed.

Keywords: computed tomography; electron beam CT; X-ray CT; ultra fast imaging

  • Contribution to proceedings
    2009 IEEE International Workshop on Imaging Systems and Techniques (IST 2009), 11.-12.05.2009, Shenzhen, China
    Proceedings of IEEE International Workshop on Imaging Systems and Techniques 2009 (IST 2009): IEEE Publishing, 978-1-4244-3483-1, 1-5
  • Invited lecture (Conferences)
    2009 IEEE International Workshop on Imaging Systems and Techniques (IST 2009), 11.-12.05.2009, Shenzhen, China

Permalink: https://www.hzdr.de/publications/Publ-12826


Self-assembly of neutral hexanuclear circular copper(II) meso-helicates: topological control by sulfate ions

Tanh Jeazet, H.; Gloe, K.; Doert, T.; Kataeva, O.; Jaeger, A.; Geipel, G.; Bernhard, G.; Büchner, B.; Gloe, K.

Abstract

Bis-pyridylimine ligands with different linking elements are capable of forming unique hexanuclear circular Cu(II) mesohelicates; the self-assembly is controlled by coordination of sulfate ions to the metal centres.

  • Chemical Communications 46(2010), 1359-7345(2010)46:14;1-L
    ISSN: 1359-7345

Permalink: https://www.hzdr.de/publications/Publ-12825


Biogeochemical changes induced in uranium mining waste pile samples by uranyl nitrate treatments under anaerobic conditions

Geissler, A.; Merroun, M.; Geipel, G.; Reuther, H.; Selenska-Pobell, S.

Abstract

Response of the subsurface soil bacterial community of a uranium mining waste pile to treatments with uranyl nitrate over different periods of time was studied under anaerobic conditions. The fate of the added U(VI) without supplementation with electron donors was investigated as well. By using 16S rRNA gene retrieval, we demonstrated that incubation with uranyl nitrate for 4 weeks resulted in a strong reduction in and even disappearance of some of the most predominant bacterial groups of the original sample. Instead, a strong proliferation of denitrifying and uranium-resistant populations of Rahnella spp. from Gammaproteobacteria and of Firmicutes occurred. After longer incubations for 14 weeks with uranyl nitrate, bacterial diversity increased and populations intrinsic to the untreated samples such as Bacteroidetes and Deltaproteobacteria propagated and replaced the above-mentioned uranium-resistant groups. This indicated that U(VI) was immobilized. Mössbauer spectroscopic analysis revealed an increased Fe(III) reduction by increasing the incubation time from four to 14 weeks. This result signified that Fe(III) was used as an electron acceptor by the bacterial community established at the later stages of the treatment. X-ray absorption spectroscopic analysis demonstrated that no detectable amounts of U(VI) were reduced to U(IV) in the time frames of the performed experiments. The reason for this observation is possibly due to the low level of electron donors in the studied oligotrophic environment. Time-resolved laser-induced fluorescence spectroscopic analysis demonstrated that most of the added U(VI) was bound by organic or inorganic phosphate phases both of biotic origin.

Permalink: https://www.hzdr.de/publications/Publ-12824


Numerical and experimental results on Lorentz force driven flows during electrodeposition of copper in homogeneous magnetic fields

Mutschke, G.; Schäfer, P.; Weier, T.; Bund, A.; Fröhlich, J.

Abstract

Lorentz forces due to external magnetic fields are well known to force electrolyte flow and thereby to influence mass transport in electrochemical reactions. To achieve a quantitative understanding of this so called “MHD effect” and maybe to tailor it, it is crucial to study the magnetically driven convection in as much detail as possible. The present work aims to further clarify the role of magnetically forced convection during copper electrolysis in cuboid cells with vertical wall electrodes. Homogeneous magnetic fields of different directions are investigated. This paper presents results of threedimensional numerical simulations which are compared with new and detailed three-dimensional PIV measurements of the electrolyte flow. The influence of the convection on integral quantities as the limiting current is discussed.

Keywords: Lorentz force; magnetoelectrochemistry; PIV

  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, BRD
  • Contribution to proceedings
    6th Int. Conf. on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, BRD, 461-464

Permalink: https://www.hzdr.de/publications/Publ-12823


13C-detection for sputtering investigations

Khan, S. A.; Tripathi, A.; Gerlach, J. W.; Grambole, D.; Toulemonde, M.; Assmann, W.

Abstract

The measurement of sputtering yields for Carbon and angular distributions of sputtered C-particles is often hindered by hydrocarbon contaminations at the sample surface. In order to overcome this problem, 13C-enriched samples can be used, provided a 13C-sensitive detection method is available. For sputtering yield determination we have measured the thickness decrease of a thin 13C-layer on Si by ERDA, where 12C and 13C can be separated by their kinematic energy difference. A pre-condition is an energy resolution below 1%, which makes a position sensitive detector for kinematic correction of different recoil an-gles necessary. A high energy resolution and sensitivity is required, if sputtered 13C-particles have to be detected on a catcher foil to determine the angular distribution, as sputtered 13C and contamination 12C particles are of the same order. Our ERDA-detector fulfills this requirement having a solid angle of 6.2 msr and 2-dim position sensitivity. The result of the catcher analysis is compared to TOF-SIMS with very high mass resolution and NRA using 13C(p,gamma) or 13C(d,p)-reactions. With these techniques, a new attempt has been made to measure the energy distribution of sputtered particles by covering the sputter target with very thin layers of 13C.

  • Contribution to proceedings
    19th Ion Beam Analysis Conference, 07.-11.09.2009, Cambridge, UK
    Abstract book, 201
  • Poster
    19th Ion Beam Analysis Conference, 07.-11.09.2009, Cambridge, UK

Permalink: https://www.hzdr.de/publications/Publ-12822


Experimental two-phase flow measurements using two-plane limited-angle electron beam x-ray CT and wire-mesh sensor

Bieberle, M.; Hampel, U.; Schleicher, E.; Fischer, F.; Koch, D.; Mayer, H.-G.; Menz, H.-J.

Abstract

Reliable measurements form the basis for the understanding and modelling of two-phase flows. However, it is quite challenging to develop measurement techniques which achieve high spatial resolution and high temporal resolution at the same time. Electron beam x-ray CT is one technique, which provides cross-sectional images of an object of interest with about 1 mm spatial resolution at frame rates of up to 10,000 frames per second without influencing the flow. The method introduced here utilizes linear beam deflection which limits the angular range of the CT projections. With this method, we scanned a gas-liquid flow in an experimental flow loop operated at different liquid and gas flow rates. Electron-beam x-ray CT data was reconstructed and results compared with measurements of a wire-mesh sensor. The latter is a well-known intrusive measurement technique, which achieves comparable frame rates but at lower spatial resolution. As a novelty we implemented two-plane limited-angle electron beam x-ray tomography and are thus able to gain information about the phase velocities using cross-correlation data analysis Gas phase velocity information is a decisive parameter for accurate quantitative gas bubble size and gas fraction determination and is often missed in transmission tomography measurements.

Keywords: electron beam x-ray CT; limited-angle CT; wire-mesh sensor; two-phase flow

  • Contribution to proceedings
    3rd International Workshop on Process Tomography (IWPT-3), 15.-17.04.2009, Tokyo, Japan
    IWPT 3, Nr 77
  • Lecture (Conference)
    3rd International Workshop on Process Tomography (IWPT-3), 15.-17.04.2009, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-12821


Lorentz force driven rotating flows in electrochemical systems

Weier, T.; Gerbeth, G.

Abstract
Lorentz forces are in almost all cases an inevitable consequence, when electrochemical reactions are performed under the influence of a magnetic field. The reason for this fact is that it is quite difficult to actually guarantee parallelism of magnetic and electric fields everywhere in the electrochemical cell.
The current contribution focuses on cases which are essentially axial symmetric. While the main parts of the electric and magnetic fields are parallel to the axis, an azimuthal Lorentz force is generated by radial components of either the electric or the magnetic field. The Lorentz force acting in circumferential direction drives primarily azimuthal flows. However, pressure differences due to these primary flows as well as the nonuniform Lorentz force density distribution itself give rise to secondary flows which, together with the primary flow, can lead to complex and sometimes unexpected flow patterns. The matter is complicated even more by the action of buoyancy originating from the density changes of the electrolyte solution due to the electrode reactions. Since the flow, i.e. the momentum transfer, determines mass transfer to a good extend electrochemical reactions under mass transfer control are usually influenced by magnetic fields. This fact has been known for a long time and is often referred to as “MHD–effect” in the electrochemical literature. However, often the seeming simplicity suggested by this term is misleading since, as denoted above, the Lorentz force driven flow is frequently rich in features [1].
We use particle image velocimetry (PIV) as well as synthetic schlieren, i.e. background oriented schlieren (BOS), to study velocity and concentration gradient fields in electrochemical cells. On the basis of these measurements, the flow in the cells and its consequences for the concentration distributions and the reactions are discussed. Examples include the retainment of buoyant electrolyte near circular electrodes as described in [2], the reversal of the secondary flow direction depending on the electrode radius [3] and the interplay of gravity and Lorentz forces in cylindrical cells with horizontal electrodes.
References
[1] Mutschke G, Cierpka C, Weier T, Eckert K, Mühlenhoff S and Bund A. ECS Transactions 13, 16, 9 (2008).
[2] Weier T, Eckert K, M¨uhlenhoff S, Cierpka C, Bund A and Uhlemann M. Electrochem Comm 9, 2479 (2007).
[3] Cierpka C, Weier T, Gerbeth G, Uhlemann M and Eckert K. J Solid State Electrochem 11, 687 (2007).

Keywords: Lorentz force; magnetoelectrochemistry; PIV; BOS

  • Lecture (Conference)
    International Conference on Magneto Science, 26.-29.10.2009, Nijmegen, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-12820


Numerical and experimental results on copper electrolysis in homogeneous and inhomogeneous magnetic fields

Mutschke, G.; Weier, T.; Schäfer, P.; Hess, A.; Bund, A.; Fröhlich, J.

Abstract
Lorentz forces due to external magnetic fields are well known to force electrolyte flow and thereby to influence mass transport in electrochemical reactions. To achieve a quantitative understanding of this so called “MHD-effect” and maybe to tailor it, it is crucial to study the magneti-cally forced convection in as much detail as possible.
The present work aims to further clarify the role of magnetically forced convection during copper electrolysis in cuboid cells with vertical wall electrodes. Both, homogeneous and inhomogeneous magnetic fields of different directions are investigated. Substantial differences in the convection forced arise from the fact that only the rotational part of the Lorentz force drives additional convection [1]. In case of homogeneous magnetic fields, this results in characteristic horizontal counter-rotating flow in the top and the bottom region of the cells (see Fig. 1) [2]. Inhomogeneous magnetic fields characterized by a constant gradient in a certain direction give rise to simpler convection patterns as the Lorentz force possesses a natural rotational part. This way, tailored electrolyte stirring throughout the cell can easily begenerated.
The presentation will summarize recent results of numerical simulations combined with detailed experimental PIV measurements of the electrolyte flow. The influence of the forced convection on the limiting current, the vertical density stratification and the vertical distribution of the current density at the cathode will be discussed.
Acknowledgment: We are very grateful to C. Cierpka for contributing to the initial DP-PIV setup. This work was supported by Deutsche Forschungsgemeinschaft in frame of the collaborative research center SFB 609 "Electromagnetic flow control in metallurgy, crystal growth and electrochemistry"
References
[1] G. Mutschke, A. Bund, Electrochem. Comm. 10 (2008) 597-601.
[2] G. Mutschke, C. Cierpka, T. Weier, K. Eckert, S. Mühlenhoff, A. Bund, Trans. Electrochem. Soc. 13 (16) (2008) 9-13.

Keywords: Lorentz force; magnetoelectrochemistry; PIV; electrolysis

  • Lecture (Conference)
    International Conference on Magneto Science, 26.-29.10.2009, Nijmegen, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-12819


Numerical and experimental results on copper electrolysis in homogeneous and inhomogeneous magnetic fields

Mutschke, G.; Schäfer, P.; Weier, T.; Hess, A.; Bund, A.; Fröhlich, J.

Abstract
Lorentz forces due to external magnetic fields are well known to force electrolyte flow and thereby to influence mass transport in electrochemical reactions. To achieve a quantitative understanding of this so called “MHD-effect” and maybe to tailor it, it is crucial to study the magnetically forced convection in as much detail as possible.
The present work aims to further clarify the role of magnetically forced convection during copper electrolysis in cuboid cells with vertical wall electrodes. Both, homogeneous and inhomogeneous magnetic fields of different directions are investigated. Substantial differences in the convection forced arise from the fact that only the rotational part of the Lorentz force drives additional convection [1]. In case of homogeneous magnetic fields, this results in characteristic horizontal counter-rotating flow in the top and the bottom region of the cells [2]. Inhomogeneous magnetic fields characterized by a constant gradient in a certain direction give rise to simpler convection patterns as the Lorentz force possesses a natural rotational part. This way, electrolyte stirring throughout the cell can be generated (see Figs. 1 and 2).
The presentation will summarize recent results of numerical simulations combined with detailed experimental PIV measurements of the electrolyte flow. The influence of the forced convection on the limiting current, the vertical density stratification and the vertical distribution of the current density at the cathode will be discussed.
Acknowledgment: This work was supported by Deutsche Forschungsgemeinschaft in frame of the collaborative research center SFB 609 "Electromagnetic flow control in metallurgy, crystal growth and electrochemistry"
[1] G. Mutschke, A. Bund, Electrochem. Comm. 10 (2008) 597-601.
[2] G. Mutschke, C. Cierpka, T. Weier, K. Eckert, S. Mühlenhoff, A. Bund, Trans. Electrochem. Soc. 13 (16) (2008) 9-13.

Keywords: Lorentz force; magnetoelectrochemistry; copper electrolysis

  • Poster
    216th Meeting of the Electrochemical Society, 04.-09.10.2009, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-12818


Nano-Biotechnologie für den Umweltschutz: Neue photokatalytisch aktive Verbundmaterialien zur Eliminierung von pharmazeutischen Reststoffen (NanoPharm)

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

Abstract

Vorstellung des NanoPharm-Verbund-Vorhabens

  • Lecture (others)
    Antragsgespräch "NanoPharm", Projektträger Jülich, Forschungszentrum Jülich, 23.06.2009, Jülich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12817


Radioökologische Forschungsarbeiten als Ausgangspunkt für die Entwicklung innovativer Materialien für die Umwelttechnik

Raff, J.

Abstract

Im Zuge radioökologischer Untersuchungen wurden besondere „surface –layer“ (S-Layer)-Proteine von Uranabfallhaldenisolaten entdeckt, die zum Teil gegenüber S-Layer-Proteine anderer Bakterien eine deutlich erhöhte Metallbindungskapazität und eine besonders hohe Stabilität aufweisen. Diese Eigenschaften sind im Falle der Haldenisolate auf deren Funktion als selektiver Filter für toxische Metalle zurückzuführen. S-Layer-Proteine allgemein besitzen die Fähigkeit an Grenz- und Oberflächen sowie in Suspension zu hoch geordneten einlagigen Schichten zu rekristallisieren und lassen sich deshalb hervorragend zur Beschichtung verschiedener Träger wie z. B. Glas, Keramik und Silizium verwenden. Aus diesem Grund erlauben gerade die S-Layer der Haldenisolate die Herstellung besonders stabiler Beschichtungen. Derartige Schichten können als selektive Bindungsmatrix zur Filterung von Wasser, zur Funktionalisierung von Trägermaterialien für die Herstellung sensorischer Schichten oder als Template zur Erzeugung und Immobilisierung von (foto)katalytisch aktiven Nanopartikeln verwendet werden. Die Entwicklung entsprechender Materialien ist Gegenstand aktueller Forschungsarbeiten am Institut für Radiochemie des Forschungszentrums Dresden-Rossendorf und wird im Rahmen des Vortrags vorgestellt.

  • Lecture (others)
    Umweltkolloquium, Studiengang Chemieingenieurwesen, Hochschule für Technik und Wirtschaft Dresden (FH), 22.10.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12816


Radiohaloes in feldspar group minerals

Krickl, R.; Götze, J.; Grambole, D.; Nasdala, L.; Kaindl, R.

Abstract

External irradiation of minerals with alpha-particles emitted from radionuclide bearing inclusions may lead to significant alteration of the physical and chemical properties of the host material. These altered regions are commonly referred to as radiohaloes. In the vast majority of reported cases, haloes can be detected using an optical microscope, because they show significantly changed optical absorption and birefringence behaviour in comparison to the unaltered host (e.g. Paul Ramdohr (1960): Geol. Rundschau, 49, 253-263). However, there are minerals which commonly show no change in optical absorption upon alpha-irradiation. One well known example is quartz, where radiohaloes can only be revealed by cathodoluminescence (CL) imaging, as they show an intensified, orange emission (e.g. Jens Götze, Michael Plötze, Dirk Habermann (2001): Mineral Petrol, 71, 225-250). In the course of CL-studies on radiohaloes in quartz (Robert Krickl, Lutz Nasdala, Jens Götze, Dieter Grambole, Richard Wirth (2008): Eur J Mineral, 20, 517- 522), hitherto unreported alpha-induced alteration effects in alkali-feldspars and plagioclases were discovered and characterised.
In contrast to quartz, the newly discovered “negative CL-haloes” in feldspars exhibit a lower emission intensity as compared to the unaltered host. Cathodoluminescence spectra show, that this decrease is mainly caused by a strong intensity loss of bands attributed to the O– / 2 27Al centre. In some cases a new, probably radiogenic band at ~570–600 nm can be observed.
Radiohaloes in feldspars seem to be quite common and were detected in a number of rocks from different localities. Haloes are not only found around radioactive inclusions but also along cracks, indicating the former circulation of radionuclide bearing solutions. The radioactive origin of the reported features is confirmed by several observations: Haloes are only found at the contact zones to radionuclide bearing phases like for example monazite. Measured outer radii of haloes (and sometimes rings within haloes) are in very good agreement with penetration depths of natural alpha-particles calculated by Monte-Carlo-simulations. Finally, micro-Raman spectroscopic investigations indicate the presence of structural damage which increases with decreasing distance from the radionuclide bearing inclusion, thus correlating with the presumed point defect density distribution in radiohaloes. Amorphised regions within haloes are rare, though they exist in some cases. Glassy feldspar seems to be unstable against secondary alteration and is most often found to be recrystallised and chemically altered. Evidence on different resistance against secondary alteration within different feldspar minerals will be discussed.
The results on natural radiohaloes are confirmed by artificial irradiation experiments: Implantation of a sanidine single crystal with 8.8 MeV He2+ ions (corresponding to alpha-particles produced in the decay of 212Po) results in analogous decrease in CL-intensity, showing systematic dependence on irradiation dose. Raman spectroscopic investigations show significant broadening of vibrational bands, indicating significant disturbance of the short range order in the crystal structure. However, crystalline long range order seems to be preserved up to doses of 1016 He2+/cm2. The measured extent of broadening correlates very well with calculated point defect distribution curves resulting from Monte-Carlo-simulations. In the case of natural and artificial alpha-irradiation no change in optical absorption could be detected. However, irradiation with electrons and gamma-rays resulted in a markedly yellow-brown colouration of the same sample material that was subjected to He-implantation. For these treatments obviously induce different effects, they are not adequate methods to simulate alpha-particle haloes in these minerals.

  • Lecture (Conference)
    Jahrestagung der Deutschen Mineralogischen Gesellschaft, 13.-16.09.2009, Halle, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12815


The role of ferromagnetic impellers in the VKS dynamo experiment

Giesecke, A.; Stefani, F.; Gerbeth, G.

Abstract

In the Cadarache von-Karman-Sodium (VKS) experiment a flow of liquid sodium is driven by two counterrotating impellers located at the top and the bottom of a cylindrical vessel. Dynamo action is obtained at a critical magnetic Reynolds number Rm_c=32. Striking property of the self-generated field is the high degree of axisymmetry. Furthermore, dynamo action is obtained only with impellers made of soft iron with a relative permeability of the order of mu_r ~ 100...1000. So far, no satisfying explanation is available that explains the failure of field generation when using steel impellers. Therefore, the role of the ferromagnetic material to obtain a dynamo, appears to be a critical issue and deserves further experimental and numerical investigations.

Numerical simulations of the kinematic induction equation have been carried out in a cylindrical domain that resembles the VKS setup. In case of a prescribed axisymmetric velocity distribution the resulting magnetic field is always determined by an azimuthal m=1 -- mode. Axisymmetric fields can be obtained applying a (localized) alpha-effect that might arise from the induction action of radially oriented helical outflow trapped between the impeller blades. However, it turns out, that the amplitude of alpha, which is necessary to generate an axisymmetric field, is far above realistic values. Therefore, a simple alpha-omega-model can be ruled out as the single explanation for the dynamo mechanism in the VKS experiment. Additional support of dynamo action stems from the presence of a high permeability domain within the cylindrical domain. In numerical simulations with a non-uniform permeability distribution that resembles the shape of the impeller disk (including the flow driving blades) the axisymmetric field mode is significantly enhanced, whereas the first non-axisymmetric mode remains nearly unaffected. To circumvent the restrictions of Cowling's theorem, still an alpha-effect is required for a growing axisymmetric field. However, the necessary magnitude of alpha is significantly reduced.

Alternatively, the implications of intermittent non-axisymmetric velocity disturbances are considered as they have been found in water experiments in form of azimuthal drifting equatorial vortices. Resonance effects -- so called swing excitations -- provide a strong increment of the field growthrate if the vortex drift motion proceeds phase synchronous with the drift of a non-axisymmetric magnetic field. However, a careful controlling of the dynamical behavior of vortices and/or the magnetic field would be required to benefit from this effect in a dynamo experiment.

Keywords: dynamo; VKS; experiment; alpha-effect; simulations; induction; permeability

  • Lecture (Conference)
    Natural Dynamos, 30.08.-05.09.2009, Stará Lesná, Slovakia
  • Open Access Logo Abstract in refereed journal
    Contributions to Geophysics and Geodesy (2009)39, 83-84
    ISSN: 1335-2806

Permalink: https://www.hzdr.de/publications/Publ-12814


Visualisierung von Mehrphasenströmungen in der Verfahrenstechnik

Kryk, H.; Hampel, U.

Abstract

Ein Arbeitsgebiet des Instituts für Sicherheitsforschung des FZD ist die Untersuchung transienter Mehrphasenströmungen in kern- und verfahrenstechnischen Anlagen. Das längerfristige Ziel der Untersuchungen besteht dabei in der Entwicklung theoretischer Modelle für grundlegende Phänomene in dreidimensionalen und transienten Mehrphasensystemen. Sowohl die Modellerarbeitung als auch die Validierung der Programme ist nur in enger Anbindung an das Experiment möglich. Dazu wurden innovative schnelle, hochauflösende und robuste Messverfahren, wie Gittersensoren, Nadelsonden und tomographische Methoden entwickelt, die neben der Strömungsvisualisierung der Ermittlung charakteristischer Parameter der Mehrphasenströmung, wie z. B. Phasenanteile, Geschwindigkeiten und Blasengrößenverteilungen dienen. Die entsprechenden Messgeräte kommen sowohl für Strömungsuntersuchungen im eigenen Hause (z. B. an der Versuchsanlage TOPFLOW) als auch für Messungen im Kundenauftrag zum Einsatz. Strömungssensoren für den Einsatz als Prozessmesstechnik, wie Gittersensoren und Nadelsonden, werden darüber hinaus auf Kundenwunsch gefertigt. Der Vortrag gibt eine Übersicht über die Messprinzipien und die technischen Daten der Mehrphasenmesstechnik und präsentiert Einsatzbeispiele und Ergebnisse aus den Bereichen der chemischen und der Energie-Verfahrenstechnik.

Keywords: Multiphase Flow; Needle Probe; Wire-mesh Sensor; X-ray Tomography; Gamma-Tomography

  • Lecture (Conference)
    ACHEMA 2009, 29. Internationaler Ausstellungskongress für Chemische Technik, Umweltschutz und Biotechnologie, 11.-15.05.2009, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12813


Spin-dependent transport in hard superparamagnetic C:Ni nanocomposites

Zhou, S.; Abrasonis, G.; Mücklich, A.; Potzger, K.; Fassbender, J.; Helm, M.; Schmidt, H.

Abstract

Structural, magnetic, and magneto-transport properties in C:Ni (30 at.%) nanocomposite films grown by ion beam cosputtering at 500 °C are investigated by means of transmission electron microscopy, superconducting quantum interference device magnetometry and electrical transport measurements. The C:Ni film shows a superparamagnetic behavior with a large coercivity field of 250 Oe at 5 K compared with bulk Ni metals. Anomalous Hall effect is observed in C:Ni nanocomposites, which is attributed to the scattering of spin-polarized carriers by the magnetic Ni nanoparticles in the carbon matrix.

Permalink: https://www.hzdr.de/publications/Publ-12812


Tribological Effects of Plasma Immersion Ion Implantation Heating Treatments on Ti-6Al-4V Alloy

Mello, C. B.; Ueda, M.; Silva, M. M.; Reuther, H.; Pichon, L.; Lepienski, C. M.

Abstract

In order to achieve improved surface in components with high reliability required by the tool or metallurgical industries by means of plasma immersion ion implantation (PIII), it is necessary to obtain quite thick treated layers with reasonable thickness uniformity. One effective way to achieve such a thick nitrogen-rich layer in Ti–6Al–4V alloy is to run PIII process in high temperatures of about 800°C. In these experiments, we heated the sample-holder and subjected the Ti–6Al–4V samples to nitrogen glow discharge PIII with relatively low peak voltages (5 kV). We also treated the Ti–6Al–4V samples by the traditional PIII method, increasing slowly the high voltage pulse intensities, and at the end of processing, reaching temperatures of up to 350°C. These modes of treatments were compared with respect to nitrogen implantation profiles, tribological and mechanical properties. Nitrogen profiles measured by AES showed that auxiliary heating leads to richer and deeper layers. The best results were obtained for the samples treated for 4 h that, after 25,000 cycles in unlubricated pin-on-disk test, presented very small wear (reduction of 89%). In spite of friction coefficient being higher in the beginning of the test, probably due to the increase of the average roughness (Rms) in the surface of the treated material, it decreases when the rough surface wears away, due to the reduction of frictional force necessary to slide the pin on the sample. The material treated at 800°C presents high wear resistance, which is desired in this alloy, that normally possesses excellent mechanical properties, however, poor tribological properties.

  • Wear 267(2009), 867-873
  • Lecture (Conference)
    17th International Conference on Wear of Materials, 19.-23.04.2009, Las Vegas, USA

Permalink: https://www.hzdr.de/publications/Publ-12811


Bioinspired Materials for Nanotechnology

Raff, J.

Abstract

Bacterial S-layers are highly ordered paracrystalline protein polymers on the surface of many bacteria. During a long evolutionary process of billions of years, S-layers have been optimized as simple system to form regular lattices with different functions by self-assembly. Solutions of S-layer proteins can be used for the simple coating of a broad spectrum of different materials e.g. glas, silicon and ceramics with a mono-molecular protein layer. The well defined arrangement of different functional groups effects the selective binding of several metals or can be used for the regular immobilization of bio-functional molecules. Furthermore S-layers or S-layer coatings can be used as template for the controlled formation and immobilization of nano-particles. S-layer proteins are therefore very prospective for different bio- and nanotechnological applications, like the selective removal of metals, the production of noble metal catalysts and photo-catalysts and the development of sensory layers.

  • Invited lecture (Conferences)
    7th International Nanotechnology Symposium Nanofair 2009, 26.-29.05.2009, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12810


Uranabfallhalden als Fundgrube für Technologie-Innovationen

Raff, J.

Abstract

Wie überall auf der Erde leben auch in den Böden und Sickerwässer der Hinterlassenschaften des ehemaligen Uranerzbergbaus zahlreiche Bakterien. Um in einer solchen Umgebung trotz des Vorkommens verschiedener giftiger Elemente wie zum Beispiel Uran, Kupfer, Nickel und Arsen überleben zu können, bedarf es ganz besonderer Fähigkeiten.
Am Beispiel der bakteriellen Hüllproteinschichten (S-Layer) wird im Vortrag gezeigt, wie sich Bakterien vor negativen Umwelteinflüssen schützen können und wie man sich dies, im Sinne einer Entwicklung neuer innovativer Materialien, zu Nutze machen kann.

  • Lecture (others)
    Tag des offenen Labors, 09.05.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12809


Advanced Bio-composite Materials for Water Treatment

Raff, J.

Abstract
  • wird nachgereicht
  • Lecture (Conference)
    60. Berg- und Hüttenmännischer Tag, 17.-19.06.2009, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12808


PT quantum mechanics and some of its underlying mathematics

Günther, U.

Abstract

In 1998, 1999 it was shown by Bender and collaborators that there are certain classes of Hamiltonians which at a first glance seem not selfadjoint in Hilbert spaces, but which nevertheless are having real spectra. Examples are Hamiltonians of the type H=p2+x2(ix)μ. For parameters μ ∈ [0,1] these Hamiltonians have positive real eigenvalues with square integrable eigenfunctions defined over the real line. It was found that the reality of the eigenvalues was connected with an underlying PT-symmetry of the Hamiltonians and their eigenfunctions, i.e. the systems are in a sector of unbroken PT-symmetry. There exist other sectors like μ ∈ (-1,0) where this PT-symmetry is spontaneously broken: although the Hamiltonian remains PT-symmetric, part of its eigenfunctions loose PT-symmetry and the corresponding eigenvalues are coming in complex conjugate pairs. A PT phase transition occurs at μ=-0.
It turns out that the PT-symmetry of the Hamiltonian H induces a natural indefinite metric structure in Hilbert space and that H, instead of being selfadjoint in a usual Hilbert space (with positive definite metric), is selfadjoint in a generalized Hilbert space with an indefinite metric --- a so called Krein space. Similar to time-like, space-like and light-like vectors in Minkowski space a Krein space has elements of positive and negative type as well as neutral (isotropic) elements. Moreover in analogy to passing via Wick-rotation from Minkowski space to Euclidian space, in the sector of exact PT-symmetry there exists an operator which allows to pass from a Krein space description of the system to a description in a Hilbert space with a highly nontrivial metric operator. At the PT phase transition point this operator becomes singular and the corresponding mapping breaks down.
In the talk, on an introductory level, some of the basic structures of PT-symmetric quantum mechanics and their relation to corresponding Krein-space setups are sketched. For gaining some rough intuition, the facts are illustrated by simple matrix models. The richness of the systems is demonstrated on the simple example of a PT-symmetric two-mode Bose-Hubbard model and the geometry of a PT-symmetric brachistochrone setup.

Keywords: PT quantum mechanics; PT-symmetry; non-Hermitian operators; Krein space; indefinite metric; phase transition; quantum brachistochrone; Bose-Hubbard model

  • Invited lecture (Conferences)
    seminar at the Graduate School of Fundamental Physics; Institute of Physics; Heidelberg University, 04.06.2009, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12807


Neptunium(V) complexation by natural pyoverdins and related model compounds

Moll, H.; Johnsson, A.; Schäfer, M.; Glorius, M.; Pedersen, K.; Budzikiewicz, H.; Bernhard, G.

Abstract

The aerobic soil bacterium Pseudomonas fluorescens (CCUG 32456 A) isolated from the aquifers at the Äspö Hard Rock Laboratory, Sweden secretes pyoverdin-type siderophores. These unique bioligands have a high potential to bind uranium(VI) and curium(III) mainly due to their hydroxamate and catecholate functionalities [1, 2]. However, the interaction of neptunium(V) with pyoverdin-type siderophores is still unknown. In general, Np(V) interactions with natural bioligands are poorly understood. To address this lack, we thus present findings regarding the speciation of the neptunyl cation with pyoverdins in aqueous solution using near-infrared (NIR) absorption spectroscopy over a wide pH range. Np(V)-pyoverdin species of the type MxLyHz could be identified from the spectrophotometric titrations. Remarkable was that the influence of neptunium(V)-pyoverdin species could already be detected under equimolar conditions. The stability constants of these strong neptunyl(V)-bioligand complexes and their individual spectroscopic properties are reported. NIR absorption spectroscopy shows that the Np(V)-pyoverdin species cause a strong red shift of the characteristic NpO2+ absorption band at 980 to 1000 nm. The findings of our Np(V) speciation study with pyoverdins and selected model compounds indicate a stronger affinity of Np(V) to the catechol functionality of the pyoverdin molecules in contrast to for instance their hydroxamate groups.

[1] H. Moll, M. Glorius, G. Bernhard, A. Johnsson, K. Pedersen, M. Schäfer, H. Budzikiewicz, Geomicrobiol. J. 25, 157-166 (2008).
[2] H. Moll, A. Johnsson, M. Schäfer, K. Pedersen, H. Budzikiewicz, G. Bernhard, BioMetals 21, 219-228 (2008).

Keywords: Neptunium(V); Pyoverdin; NIR absorption spectroscopy; Speciation

  • Contribution to proceedings
    12th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere, 20.-25.09.2009, Kennewick, Washington, USA
  • Lecture (Conference)
    12th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA
  • Radiochimica Acta 98(2010), 571-576
    DOI: 10.1524/ract.2010.1755
    Cited 8 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-12806


Nachrechnung der Leistungsparameter eines Sicherheitsventils mit ANSYS CFX

Moncalvo, D.; Friedel, L.; Jörgensen, B.; Höhne, T.

Abstract

Der Einfluss der Gitterfeinheit und der des Turbulenzmodells sind hier bezüglich der Wiedergabegenauigkeit von Luftmassenströmen in zwei kleinen Sicherheitsventilen bei Abblasedrücken zwischen 4 und 40 bar untersucht worden. Die Ergebnisse zeigen, dass für beide Ventile die Gitterfeinheit der entscheidende Faktor und die Auswahl des Turbulenzmodells eher zweitrangig ist.

Keywords: CFD; Sicherheitsventil

Permalink: https://www.hzdr.de/publications/Publ-12805


Einfluss von Glutathion auf das Komplexbildungs- und Redoxverhalten von Uran(VI)

Frost, L.

Abstract

Ziel dieser Diplomarbeit war es, die Wechselwirkung des Glutathions mit dem Uranylion zu untersuchen. Die Stabilitätskonstante des Komplexes zwischen dem Uranylion und Glutathion bei pH 7,4 sollte unter Verwendung der UV/VIS-Spektroskopie und der zeitaufgelösten Laserfluoreszenzspektroskopie bestimmt werden. Außerdem sollten über eine Derivatisierung des Glutathions dessen spektroskopische Eigenschaften verbessert und die Komplexierung des Uranylions durch das erzeugte Derivat untersucht werden. Ferner war zu untersuchen, ob Glutathion unter geeigneten Bedingungen das Uranylion bei pH 7,4 direkt reduzieren kann.
Die Bestimmung der Stabilitätskonstante des Komplexes zwischen dem Uranylion und Glutathion wurde mittels UV/VIS-Spektroskopie zu 38,70 ± 0,15 (Mittelwert mit Standardfehler) bestimmt. Unter Anwendung der zeitaufgelösten Laserfluoreszenzspektroskopie konnte die Bildungskonstante des 1:1-Uranyl-Glutathion-Komplexes zu 38,65 ± 0,02 berechnet und somit bestätigt werden.
Auch die Derivatisierung des Glutathions gelang mit der Bildung des Glutathion-Pyruvat-S-Konjugats, welches im UV/VIS-Bereich gut absorbiert. Die Bildungskonstante des Komplexes zwischen dem erzeugten Konjugat und dem Uranylion wurde zu > 38,85 ± 0,08 mittels UV/VIS-Spektroskopie bestimmt. Eine zweite Derivatisierung des Glutathions mit Monobromobiman zum fluoreszierenden Glutathion-Biman-Konjugat wurde durchgeführt. Die Komplexierung des Uranylions durch das Glutathion-Biman-Konjugat wurde mittels fs-Laserfluoreszenzspektroskopie untersucht und die Stabilitätskonstante dieses Komplexes zu > 38,96 ± 0,02 bestimmt. Da bei der Untersuchung der Glutathionderivate trotz Blockierung der Thiolgruppe des Glutathions eine starke Komplexierung festgestellt wurde, kann eine signifikante Beteiligung der SH-Gruppe an der Koordination ausgeschlossen werden.
Die Untersuchung des Redoxverhaltens des U(VI) in Gegenwart von Glutathion mit Hilfe der Laser-induzierten photoakustischen Spektroskopie zeigte, dass in vitro bei pH 7,4 keine Reduktion zum Uran(IV) erfolgt. Ein Redoxprozess würde eine Reduzierung der Konzentration des freien Uranyls und somit eine Veränderung der Komplexstabilitätskonstante bewirken. Da keine Reduktion festgestellt wurde, ist keine Korrektur der ermittelten Konstanten nötig.

  • Other report
    TU Dresden: Diplomarbeit (Studiengang Chemie), 2009
    63 Seiten

Permalink: https://www.hzdr.de/publications/Publ-12804


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