Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Crossbeam processing for nano-structures on SOI substrates
Bischoff, L.; Schmidt, B.; Lange, H.; Donzev, D.;
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

Publ.-Id: 12854 - Permalink


Alloy Liquid Metal Ion Source for Carbon Focused Ion Beams
Mazarov, P.; Wieck, A. D.; Bischoff, L.; Pilz, W.;
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

Publ.-Id: 12853 - Permalink


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.;
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

Publ.-Id: 12852 - Permalink


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.;
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

Publ.-Id: 12851 - Permalink


Wire-mesh sensors for fast visualization of multiphase flows
Da Silva, M. J.; Thiele, S.; Schleicher, E.; Hampel, U.;
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

Publ.-Id: 12850 - Permalink


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.;
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

Publ.-Id: 12849 - Permalink


The Analysis of Uranium Binding Form with Mineral Phases by Time- resolved Laser-induced Fluorescence Spectroscopy
Baumann, N.;
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

Publ.-Id: 12848 - Permalink


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.;
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

Publ.-Id: 12847 - Permalink


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.;
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

Publ.-Id: 12846 - Permalink


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.;
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

Publ.-Id: 12845 - Permalink


Development of bispidine derivatives containing targeting vector molecules and fluorescent labels
Fähnemann, S.;
kein Abstract verfügbar
  • Lecture (Conference)
    6th SUPRAPHONE Meeting, 04.-07.06.2009, Jyväskylä, Finland

Publ.-Id: 12844 - Permalink


Molecular Imaging Modalities for Tumor Visualization
Stephan, H.; Bergmann, R.;
kein Abstract verfügbar
  • Lecture (Conference)
    6th SUPRAPHONE Meeting, 04.-07.06.2009, Jyväskylä, Finland

Publ.-Id: 12843 - Permalink


Toward Bio-Inspired Photoadressable Supramolecular Systems. Synthesis, Light-Emission, Dynamics, Biomedical Application: A Final Report
Stephan, H.;
kein Abstract verfügbar
  • Lecture (Conference)
    4th Annual COST-D31 Workshop, 28.-30.05.2009, Warsaw, Poland

Publ.-Id: 12842 - Permalink


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.;
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

Publ.-Id: 12841 - Permalink


X-ray visualisation of bubble formation and bubble motion in liquid metals
Boden, S.; Eckert, S.; Gerbeth, G.; Simonnet, M.; Anderhuber, M.; Gardin, P.;
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

Publ.-Id: 12840 - Permalink


X-ray visualisation of solidifying GaIn-alloys in the presence of melt convection
Boden, S.; Willers, B.; Eckert, S.; Gerbeth, G.;
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

Publ.-Id: 12839 - Permalink


Binding Form of Uranium in Environmental Relevant Waters, Studied by Laser Spectroscopic Methods
Bernhard, G.; Geipel, G.;
- wird nachgereicht
  • Invited lecture (Conferences)
    Freiberger Forschungsforum 2009 (60. Berg- und Hüttenmännischer Tag), 19.06.2009, Freiberg, Deutschland

Publ.-Id: 12838 - Permalink


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.;
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

Publ.-Id: 12837 - Permalink


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.;
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

Publ.-Id: 12836 - Permalink


Application of contactless inductive flow tomography to the continuous casting process
Wondrak, T.; Galindo, V.; Gerbeth, G.; Gundrum, T.; Stefani, F.; Timmel, K.;
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

Publ.-Id: 12835 - Permalink


Recent progress on contactless inductive flow tomography
Wondrak, T.; Stefani, F.; Gundrum, T.; Gerbeth, G.;
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

Publ.-Id: 12834 - Permalink


Some methodological improvements of the contactless inductive flow tomography
Wondrak, T.; Stefani, F.; Gundrum, T.; Gerbeth, G.;
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

Publ.-Id: 12833 - Permalink


CFD simulations of GIDROPRESS mixing facility experiments
Höhne, T.; Rohde, U.; Melideo, D.; Moretti, F.; D’Auria, F.; Shishov, A.; Lisenkov, E.;
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

Publ.-Id: 12832 - Permalink


Temperature control design for a high-resolution gamma ray tomography detector
Bieberle, A.; Schleicher, E.; Hampel, U.;
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

Publ.-Id: 12831 - Permalink


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.;
kein Abstract, da vertraulich
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2009
    FZD\FWS\2009\02
    0032 Seiten

Publ.-Id: 12830 - Permalink


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.;
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

Publ.-Id: 12829 - Permalink


Ultrafast electron beam tomography
Hampel, U.;
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

Publ.-Id: 12828 - Permalink


Process tomography with electron beams
Hampel, U.; Fischer, F.;
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

Publ.-Id: 12827 - Permalink


Ultra high speed electron beam tomography for flow measurement and small animal imaging
Hampel, U.; Fischer, F.;
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

Publ.-Id: 12826 - Permalink


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.;
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

Publ.-Id: 12825 - Permalink


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.;
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.

Publ.-Id: 12824 - Permalink


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.;
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

Publ.-Id: 12823 - Permalink


13C-detection for sputtering investigations
Khan, S. A.; Tripathi, A.; Gerlach, J. W.; Grambole, D.; Toulemonde, M.; Assmann, W.;
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

Publ.-Id: 12822 - Permalink


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.;
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: 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

Publ.-Id: 12821 - Permalink


Lorentz force driven rotating flows in electrochemical systems
Weier, T.; Gerbeth, G.;
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

Publ.-Id: 12820 - Permalink


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.;
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

Publ.-Id: 12819 - Permalink


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.;
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

Publ.-Id: 12818 - Permalink


Nano-Biotechnologie für den Umweltschutz: Neue photokatalytisch aktive Verbundmaterialien zur Eliminierung von pharmazeutischen Reststoffen (NanoPharm)
Raff, J.; Pollmann, K.; Meyer, A.;
Vorstellung des NanoPharm-Verbund-Vorhabens
  • Lecture (others)
    Antragsgespräch "NanoPharm", Projektträger Jülich, Forschungszentrum Jülich, 23.06.2009, Jülich, Deutschland

Publ.-Id: 12817 - Permalink


Radioökologische Forschungsarbeiten als Ausgangspunkt für die Entwicklung innovativer Materialien für die Umwelttechnik
Raff, J.;
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

Publ.-Id: 12816 - Permalink


Radiohaloes in feldspar group minerals
Krickl, R.; Götze, J.; Grambole, D.; Nasdala, L.; Kaindl, R.;
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

Publ.-Id: 12815 - Permalink


The role of ferromagnetic impellers in the VKS dynamo experiment
Giesecke, A.; Stefani, F.; Gerbeth, G.;
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 LogoAbstract in refereed journal
    Contributions to Geophysics and Geodesy (2009)39, 83-84

Publ.-Id: 12814 - Permalink


Visualisierung von Mehrphasenströmungen in der Verfahrenstechnik
Kryk, H.; Hampel, U.;
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

Publ.-Id: 12813 - Permalink


Spin-dependent transport in hard superparamagnetic C:Ni nanocomposites
Zhou, S.; Abrasonis, G.; Mücklich, A.; Potzger, K.; Fassbender, J.ORC; Helm, M.; Schmidt, H.
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.

Publ.-Id: 12812 - Permalink


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.;
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

Publ.-Id: 12811 - Permalink


Bioinspired Materials for Nanotechnology
Raff, J.;
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

Publ.-Id: 12810 - Permalink


Uranabfallhalden als Fundgrube für Technologie-Innovationen
Raff, J.;
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

Publ.-Id: 12809 - Permalink


Advanced Bio-composite Materials for Water Treatment
Raff, J.;
- wird nachgereicht
  • Lecture (Conference)
    60. Berg- und Hüttenmännischer Tag, 17.-19.06.2009, Freiberg, Deutschland

Publ.-Id: 12808 - Permalink


PT quantum mechanics and some of its underlying mathematics
Günther, U.;
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

Publ.-Id: 12807 - Permalink


Neptunium(V) complexation by natural pyoverdins and related model compounds
Moll, H.; Johnsson, A.; Schäfer, M.; Glorius, M.; Pedersen, K.; Budzikiewicz, H.; Bernhard, G.;
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

Publ.-Id: 12806 - Permalink


Nachrechnung der Leistungsparameter eines Sicherheitsventils mit ANSYS CFX
Moncalvo, D.; Friedel, L.; Jörgensen, B.; Höhne, T.;
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

Publ.-Id: 12805 - Permalink


Einfluss von Glutathion auf das Komplexbildungs- und Redoxverhalten von Uran(VI)
Frost, L.;
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

Publ.-Id: 12804 - Permalink


Modeling of the evolution of bubbly flows along a large vertical pipe with new coalescence and breakup model
Liao, Y.; Lucas, D.;
In today’s technology, air-water bubbly flows occur in a wide range of industrial applications. The evolution of bubble size as well as the transition of flow pattern has a significant relevance to the design, safety analysis and performance of a two-phase process. For the capture of bubble size evolution in a poly-dispersed flow, coalescence and breakup models have been found to be the weakest points.
Based on an extensive literature study on breakup and coalescence models available for fluid particles, a new basis model was proposed in this work, which considers coalescence and breakup due to different mechanisms, including coalescence due to turbulence, laminar shear, wake entrainment and eddy capture, and breakup due to turbulent fluctuation, laminar shear and interfacial slip velocity.
For the first step, the basis model was implemented into a home-made 1D Test Solver, which is developed specially for bubbly flows along a round vertical pipe and has an obvious advantage of high computational efficiency. For the purpose of CFD model development and validation, with aid of the multipurpose TOPFLOW (Transient twO Phase FLOW) facility, a comprehensive high-quality databank was established for the evolution of air-water and steam-water mixtures along a round vertical pipe. The new coalescence and breakup model was validated against the air-water bubbly flow data.
Simulation results showed that at relatively low superficial gas velocities, the initial bubble size was small and had a narrow distribution, and coalescence dominates the bubble size evolution; with the increase in the superficial gas velocity, large bubbles appear near injection position, and result in a much wider bubble size distribution, and breakup became predominant. In between is a transition status. On the other hand, the radial air volume fraction was redistributed from the injection position at wall to the whole cross section, and the stable peak remains near the wall for small bubbles while large bubbles migrating towards the pipe centre. According to the work of Tomiyama and his coworker, this different radial migration behavior of small and large bubbles is the effect of lift non-drag force.
The comparison of simulation results with experimental data showed encouraging agreements, which affirmed the feasibility and capability of the basis model and indicated also requirements for adjustments and improvements. At the next step, the basis model will be adjusted in the ANSYS – CFX code.
Keywords: air-water mixture, bubbly flow, bubble size distribution, radial gas volume fraction, new model, coalescence and breakup
  • Invited lecture (Conferences)
    47th European Two-phase Flow Group Meeting 2009, 1st Joint ETPFG-EFCE Multi-phase Meeting 2009, 03.-06.06.2009, Bled, Slovenia

Publ.-Id: 12803 - Permalink


Coordination environment of [UO2Br4]2- in ionic liquids and crystal structure of [Bmim]2[UO2Br4]
Sornein, M. O.; Mendes, M.; Cannes, C.; Le Naour, C.; Nockemann, P.; van Hecke, K.; van Meervelt, L.; Berthet, J. C.; Hennig, C.;
The complex formed by the reaction of the uranyl ion, UO22+, with bromide ions in the ionic liquids 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][Tf2N]) and methyl-tributylammonium bis(trifluoromethylsulfonyl)imide ([MeBu3N][Tf2N]) has been investigated by UV–Vis and U LIII-edge EXAFS spectroscopy and compared to the crystal structure of [Bmim]2[UO2Br4]. The solid state reveals a classical tetragonal bipyramid geometry for [UO2Br4]2 with hydrogen bonds between the Bmim+ and the coordinated bromides. The UV–Vis spectroscopy reveals the quantitative formation of [UO2Br4]2- when a stoichiometric amount of bromide ions is added to UO2(CF3SO3)2 in both Tf2N-based ionic liquids. The absorption spectrum also suggests a D4h symmetry for [UO2Br4]2- in ionic liquids, as previously observed for the [UO2Cl4]2- congener. EXAFS analysis supports this conclusion and demonstrates that the [UO2Br4]2- coordination polyhedron is maintained in the ionic liquids without any coordinating solvent or water molecules. The mean U–O and U–Br distances in the solutions, determined by EXAFS, are, respectively, 1.766(2) and 2.821(2) Å in [Bmim][Tf2N], and, respectively, 1.768(2) and 2.827(2) Å, in [MeBu3N][Tf2N]. Similar results are obtained in both ionic liquids indicating no significant influence of the ionic liquid cation either on the complexation reaction or on the structure of the uranyl species.
Keywords: Uranium Tetrabromide complex Ionic liquid EXAFS Single crystal structure UV–Vis spectroscopy

Publ.-Id: 12802 - Permalink


Advanced multiphase flow measurement techniques at FZD
Da Silva, M. J.;
Multiphase flow, the simultaneous stream in a pipe or vessel of two or more physically distinct and immiscible substances, is present in many industry branches. The correct understanding and modeling of such flows is a key issue for safety and efficiency aspects of processes and plants where they occur. In this presentation, state-of-the-art measuring techniques for investigation of multiphase flows are presented which have been developed or are under investigation at FZD. Special focus has been given to imaging techniques which are able to resolve phase distributions at high temporal and spatial resolution, including different types of wire-mesh sensors and our newest development: the ultra fast electron beam tomograph. Furthermore, some application examples of such techniques in research and industry are presented and discussed.
Keywords: measurement techniques, flow visualization, multiphase flow, tomography, wire-mesh sensors
  • Invited lecture (Conferences)
    30th Advisory Board Meeting of Tulsa University Separation Tecnology Projects, 12.-13.05.2009, Houston, USA

Publ.-Id: 12801 - Permalink


Comparison between electrical capacitance tomography and wire mesh sensor output for air/silicone oil flow in a vertical pipe
Azzopardi, B. J.; Abdulkareem, L. A.; Zhao, D.; Thiele, S.; Da Silva, M. J.; Beyer, M.; Hunt, A.;
Two tomographic techniques have been applied simultaneously to the flow of air and silicone oil in 67 mm internal diameter vertical pipe. A twin plane Electrical Capacitance Tomgraphy (ECT) electrode system driven by Tomoflow electronics was positioned below a new Capacitance Wire Mesh Sensor (WMS) system. The former used 8 electrodes round the pipe in each plane, the latter employed two arrays of 24 evenly spaced wires stretched over the pipe cross section. The ECT measurement was
triggered from the WMS electronics. High speed videos were also taken simultaneously through the transparent pipe wall. Gas superficial velocities of 0.05 to 5.5 m/s and liquid superficial velocities of 0 to 0.7 m/s were studied. These gave bubbly, slug and churn flow in the pipe. The outputs of the two techniques have been compared at a number of levels. At its most basic, the time averaged crosssectionally averaged void fractions were compared. They showed excellent agreement. At the next level, the time series of the cross-sectionally averaged void fraction were considered directly and through their variations in amplitude and frequency space. Examples of Probability Density Functions are presented. Radial variations of the void fraction were also considered. Thereafter the shapes of the large bubbles and the velocities of periodic structures are presented.
Keywords: Gas, liquid, vertical pipe, tomography, comparison
  • Contribution to proceedings
    3rd International Workshop on Process Tomography, 17.-19.04.2009, Tokyo, Japan
    Proceedings of 3rd International Workshop on Process Tomography
  • Lecture (Conference)
    3rd International Workshop on Process Tomography, 17.-19.04.2009, Tokyo, Japan
  • Industrial & Engineering Chemistry Research 49(2010), 8805-8811
    DOI: 10.1021/ie901949z

Publ.-Id: 12800 - Permalink


Capacitance wire mesh sensor and electrical capacitance tomography study of trickle-bed reactor hydrodynamics
Matusiak, B.; Da Silva, M. J.; Grudzien, K.; Hampel, U.;
Trickle-bed reactors are widely used for a number of different applications in chemical, biochemical and waste treatment industry. Knowledge of liquid distribution and holdup in such reactors is required to better understand their operation and thus to enhance efficiency of processes. The objective of this work was a comparative analysis of the usability of a wire-mesh sensor and Electrical Capacitance Tomography (ECT) for the measurement of liquid distribution and holdup in a trickle-bed reactor model. Thus, a wire-mesh sensor with 2 x 16 wires, operated with a newly developed capacitance-measuring electronics was mounted in the trickle-bed reactor model with inner diameter of 0.1 m. Further, an ECT sensor containing 12 internal electrodes of 50 mm length was mounted above the wire-mesh sensor. The reactor model was randomly packed with a commercial porous Al2O3 catalyst support. Isopropanol was fed into the reactor from the different inlets located at the top of the test facility. In this way, different liquid distributions were obtained and monitored. For each condition, we compared integral liquid holdups and liquid distribution profiles from wire-mesh and ECT systems. Obtained results are in good agreement between both modalities.
Keywords: wire-mesh sensor; ECT; trickle bed; flow visualization
  • Contribution to proceedings
    3rd International Workshop on Process Tomography, 17.-19.04.2009, Tokyo, Japan
    Proceedings of 3rd International Workshop on Process Tomography
  • Lecture (Conference)
    3rd International Workshop on Process Tomography, 17.-19.04.2009, Tokyo, Japan

Publ.-Id: 12799 - Permalink


Advanced wire-mesh sensor technology for fast flow imaging
Da Silva, M. J.; Schleicher, E.; Hampel, U.;
Wire-mesh sensors are flow imaging devices which are able to generate images of cross-sectional phase distribution at high spatial and temporal resolution. In this paper, we introduce a novel general concept of advanced wire-mesh sensors for the measurement of other physical quantity than phase fractions. The main idea is to provide the wire crossings with miniature transducers which convert a physical quantity into electrical impedance which is in turn measured by the sensor. The multiplexed probing-sensing scheme of wire-mesh sensor is used to readout the transducers. As a first example we developed a temperature wire-mesh sensor. The crossing points are provided with miniature PT1000 resistors. Thus the sensor is able to twodimensionally map the temperature distribution in a crosssection. First results are presented and discussed.
Keywords: Wire-mesh sensor; flow visualization; temperature profile, resistance thermometer
  • Contribution to proceedings
    2009 IEEE International Workshop on Imaging Systems & Techniques, 11.-12.05.2009, Shenzhen, China
    Proceedings of IEEE International Workshop on Imaging Systems & Techniques 2009: IEEE, 978-1-4244-3483-1, 253-256
  • Lecture (Conference)
    2009 IEEE International Workshop on Imaging Systems & Techniques, 11.-12.05.2009, Shenzhen, China

Publ.-Id: 12798 - Permalink


Formation of iron-rich natural nanoparticles by the weathering of rock materials
Zänker, H.; Weiß, S.;
The formation of colloidal nanoparticles during the weathering of Fe(II)-containing mass rock material was investigated by exposing ground phyllite to Milli-Q water (a simulation of “rain water”). Secondary mineral colloids of 101 to 102 nm were detected in significant concentrations (cf. [1]). At pH of about 8.5, the solution concentration of these colloids reached up to 10 mg/L (however, acidification to pH 4.0 prevented the formation of the colloids). The mineralogical composition of the secondary mineral colloids is assumed to be a mixture of ferrihydrite, manganese oxyhydroxides, aluminosilicates, amorphous Al(OH)3 and possibly further components. The colloids were stable in solution over longer periods of time (at least several weeks).
Direct formation of iron-containing secondary mineral colloids at the rock-water interface by the weathering of rock is an alternative to the well-known mechanism of colloid formation in the bulk of water bodies by mixing of different waters or by aeration of anoxic waters [2-4]. This direct mechanism is of relevance for colloid production during the weathering of freshly crushed rock in the unsaturated zone as for instance crushed rock in gravel heaps or mine waste rock piles.
The properties (particle size, chemical composition) of the nanoparticles produced in the weathering experiments and their influence on the behaviour of an environmental contaminant (hexavalent uranium) were investigated. It was shown that the colloids are able to keep large fractions of the U(VI) (in our case up to 90%) in a colloid-borne form.

[1] H. Zänker, G. Hüttig, T. Arnold and H. Nitsche, Aquatic Geochem. 12 (2006) 299.
[2] L. E. Schemel, B. A. Kimball and K. E. Bencala. ppl. Geochem. 15 (2000) 1003.
[3] A. B. Sullivan and J. I. Drever, Appl. Geochem. 16 (2001) 1663.
[4] A. Wolthoorn, E.J.H. Temminghoff, W.H. van Riemsdijk, Appl. Geochem. 19 (2004) 1391.
Keywords: Colloids, nanoparticles, weathering, rock, phyllite, uranium
  • Lecture (Conference)
    4th International Conference on the Environmental Effects of Nanoparticles and Nanomaterials, 06.-09.09.2009, Wien, Österreich

Publ.-Id: 12797 - Permalink


Spectroscopic study and surface complexation modeling of Np(V) sorption on montmorillonite
Reich, T.; Amayri, S.; Dierking, S.; Baeyens, B.; Dähn, R.; Bradbury, M. H.; Scheinost, A. C.;
The sorption of Np(V) on Na-montmorillonite (STx-1) has been studied in the absence of inorganic carbon and under air-equilibrated conditions. Batch experiments were performed with 0.1 and 0.01 M NaClO4 as background electrolyte, 8 × 10-12 and 9 × 10-6 M Np(V), and 3 ≤ pH ≤ 10. At pH > 8 the presence of inorganic carbon has a strong influence on the sorption behavior of Np(V) due to the formation of aqueous Np(V) complexes with carbonate. Neptunium LIII-edge extended X-ray absorption fine structure (EXAFS) measurements on Np(V)/montmorillonite samples with Np(V) loadings in the range of 0.3-3.5 μmol/g have been performed to determine the local structure of Np at the solid-liquid interface. Wet paste samples were prepared at pH 9.0 and 9.5 in the absence and presence of inorganic carbon. The EXAFS spectra of samples prepared under ambient air conditions (pCO2 = 10-3.5 atm) revealed the formation of Np(V)-carbonate complexes at the montmorillonite surface.
The results of the batch experiments obtained under CO2-free conditions could be modeled using the two site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) model described in [1]. For modeling the sorption behavior of Np(V) on montmorillonite in the air-equilibrated system, the aqueous complexation of Np(V) with carbonate [2] was included and the following additional surface complexation reaction was required: ≡SOH + NpO2 + + CO3 2- ⇔ ≡SONpO2CO3 2- + H+. This study, combining batch experiments, spectroscopic measurements, and surface complexation modeling contributes towards a better understanding of the sorption of neptunium in the near field (bentonite) and far field (argillaceous rocks) of nuclear waste repositories.

[1] M.H. Bradbury, B. Baeyens, Modelling the sorption of Mn(II), Co(II), Ni(II), Zn(II),
Cd(II), Eu(III), Am(III), Sn(IV), Th(IV), Np(V) and U(VI) on montmorillonite: Linear free
energy relationships and estimates of surface binding constants for some selected heavy metals
and actinides, Geochim. Cosmochim. Acta 69, 875-892, 2005.
[2] Chemical Thermodynamics of Neptunium and Plutonium, (Eds. J. Fuger et al.) Elsevier,
Amsterdam 2001.
Keywords: Np EXAFS montmorillonite surface complexation modeling
  • Poster
    Migration ´09 - 12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 12796 - Permalink


Zerstörungsfreie Analyse an Unikaten
Neelmeijer, C.;
Kunstwerke sind Unikate und oft morbide Patienten. Das Material, woraus sie bestehen und das Klima, in dem sie aufbewahrt werden, bestimmen ihr Wohlbefinden. Die Oberfläche von Kunstwerken aus Glas, zum Beispiel, kann „rosten“ wie Metall. Wenn das Glasobjekt matt und rissig erscheint, kommt Abhilfe schon sehr spät. Chemische Reaktionen über lange Zeit führen möglicherweise zu Veränderungen der Farben von Gemälden, auch Kolorierungen. Präventive Konservierung ist dringend angezeigt, Vorsorge also. Entscheidend dafür ist die Früherkennung solcher Vorgänge, besser noch die Voraussage möglicher Schadensbilder. Hierzu dient die zerstörungsfreie Materialanalyse. Das kann der Protonenstrahl an Luft im Zusammenspiel mit empfindlicher Messtechnik. Am Beispiel Glas, aber auch an Gemälden, Zeichnungen, Tinten auf Urkunden gibt die Präsentation Antworten auf die typischen Fragen von Konservatoren, Restauratoren und Kunstwissenschaftlern: Wie gefährdet ist das Kunstwerk - welche Technologien hat der Künstler verwandt, um bestimmte ästhetische Eindrücke zu erlangen – gibt es Anzeichen für eine Kopie anstelle des Originals?
Die Gastvorlesung schafft eine Brücke zwischen den künftigen Betreuern einmaliger Stücke in Museen und dem wissenschaftlichen Potenzial am Ionenstrahl des FZD.
Keywords: art objects, non-destructive analysis, ion beam analysis, IBA, PIXE, PIGE, RBS
  • Lecture (others)
    Gastvorlesung, 23.02.2007, Dresden, BRD

Publ.-Id: 12795 - Permalink


Zerstörungsfreie Materialanalyse an Kunstwerken
Neelmeijer, C.;
Kunstwerke sind Unikate, unwiederbringliche Zeugen vergangener Zeit. Ähnlich wie Patienten können sie erkranken, unterliegen der Alterung und bedürfen der Pflege. Das Material, woraus sie bestehen und das Klima, in dem sie aufbewahrt werden, bestimmen ihr Wohlbefinden. Die Oberfläche von Kunstwerken aus Glas, zum Beispiel, kann „rosten“ wie Metall. Wenn das Glasobjekt matt und rissig erscheint, kommt Abhilfe schon sehr spät. Präventive Konservierung heißt das Zauberwort, Vorsorge also. Entscheidend dafür ist die Früherkennung von Veränderungen besser noch die Einschätzung möglicher Schädigungen. Dazu dient die zerstörungsfreie Materialanalyse. Das kann der Protonenstrahl an Luft im Zusammenspiel mit empfindlicher Messtechnik. Am Beispiel Glas, aber auch an Gemälden, Zeichnungen, Tinten auf Urkunden gibt die Präsentation Antworten auf die typischen Fragen von Restauratoren und Kunstwissenschaftlern: Wie gefährdet ist das Kunstwerk, welche Technologien hat der Künstler verwandt um bestimmte ästhetische Eindrücke zu erlangen, gibt es Anzeichen für eine Kopie anstelle des Originals?
Keywords: art objects, non-destructive analysis, ion-beam analysis, glass, porcelain, metal, painting
  • Lecture (others)
    Gastvorlesung, 24.02.2009, HfBK Dresden, BRD

Publ.-Id: 12794 - Permalink


ELNES study of chemical solution deposited SrO(SrTiO3)(n) Ruddlesden-Popper films: Experiment and simulation
Riedl, T.; Gemming, T.; Weissbach, T.; Seifert, G.; Gutmann, E.; Zschornak, M.; Meyer, D. C.; Gemming, S.;
This article analyzes electron energy-loss near-edge fine structures of the SrO(SrTiO3)n=1 Ruddlesden-Popper system and of the parent compounds SrTiO3 and SrO by comparison with calculations. For that, the fine structures have been experimentally recorded of Ruddlesden-Popper films deposited by the sol-gel method. Moreover, extensive density-functional theory (FPLO code) a computations have been performed. It is shown that the appearance and shape of the experimental O-K and Ti-L2,3 fine structure features result from the crystallography-dependent electronic structure of the investigated oxides, which display technologically interesting dielectric as well as lattice-structural properties.
Keywords: Ruddlesden-Popper phases, oxides, functional oxides, functional material, DFT, EELS

Publ.-Id: 12793 - Permalink


High-Resolution Depth Profiling of thin high-k layers by means of HRBS
Vieluf, M.; Grötzschel, R.; Neelmeijer, C.; Kosmata, M.; Teichert, S.;
The increasing interest in new high-k materials in MOS technology enforces the development of new analytical techniques to characterize the depth dependent elemental composition in ultrathin layers of such materials. The well established methods of ion beam materials analysis (IBA) as Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Spectrometry (ERDA) can also provide depth profiles of elements and isotopes with subnanometer depth resolution. These techniques base upon the binary elastic nuclear scattering with well known cross sections and are therefore absolutely quantitative and standard-free. The high energy resolution necessary for high depth resolution is achieved using magnetic spectrometers.
We have installed a magnetic spectrometer of the Browne-Buechner-type at the 3 MV Tandetron accelerator of the FZD, which can provide a wide variety of MeV ions both for RBS and for ERDA. To minimise deterioration of the layers due to electronic sputtering during the measurements we implemented a multi-pad position sensitive detector (PSD) in the experimental setup to increase the solid angle and reduce the measurement time. This type of detector gives also the information needed for kinematical corrections. In this poster we describe the high-resolution spectrometer with the improved detector system and show the recent results.
Keywords: RBS Rutherford Backscattering Spectrometry, HR-RBS High Resolution Rutherford Backscattering Spectrometry, Dielectrica, High-k Materials, Sub-Nanometer
  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 26.02.2008, Berlin, Deutschland

Publ.-Id: 12792 - Permalink


Dichtefunktional-Studie zu Domänengrenzen in BiFeO3
Gemming, S.; Lubk, A.; Lichte, H.; Spaldin, N. A.;
Domain boundaries in ferroic materials deviate from the bulk in both the structural and electronic properties. Their presence in the material influences the total energy of the system, the band structure and the magnetic and electric polarization. We report on a Density Functional Theory (DFT) approach within the Local Density Approximation on domain boundaries in multiferroic BiFeO3 (space group: R3c). Our model systems consist of the experimentally observed 71deg, 109deg and 180deg domain walls. The calculations were performed within the DFT software VASP, incorporating standard pseudopotentials and a plane wave basis set. A complete electronic and ionic relaxation of the model structures has been performed to yield details of the charge and structure modulation at the boundary including the deformation of the Fe-centered oxygen octahedron, the formation of electric dipole layers leading to a jump in the electrostatic potential, band gap narrowing and a domain wall dependent modification of the small ferromagnetic effect present in BiFeO3.
Keywords: bismuth ferrite, multiferroic, ferroic, DFT
  • Lecture (Conference)
    17. Jahrestagung der Deutschen Gesellschaft für Kristallographie, 09.-12.02.2009, Hannover, Deutschland

Publ.-Id: 12791 - Permalink


First principle calculations of domain boundaries in multiferroic BiFeO3
Lubk, A.; Spaldin, N.; Gemming, S.; Lichte, H.;
Domain boundaries in ferroic materials deviate from the bulk in both the structural and electronic properties. Their presence in the material influences the total energy of the system, the band structure and the magnetic and electric polarization. We report on a Density Functional Theory (DFT) approach within the Local Density Approximation on domain boundaries in multiferroic BiFeO3 (space group: R3c). Our model systems consist of the experimentally observed 71 degree, 109 degree and 180 degree domain walls. The calculations were performed within the DFT software VASP, incorporating standard pseudopotentials and a plane wave basis set. A complete electronic and ionic relaxation of the model structures has been performed to yield details of the charge and structure modulation at the boundary including the deformation of the Fe-centered oxygen octahedron, the formation of electric dipole layers leading to a jump in the electrostatic potential, band gap narrowing and a domain wall dependent modification of the small ferromagnetic effect present in BiFeO3.
Keywords: bismuth ferrite, multiferroic, ferroic, DFT
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12790 - Permalink


DFT-study of the adsorption of organic molecules on low-index titanium dioxide surfaces
Luschtinetz, R.; Enyashin, A. N.; Milek, T.; Frenzel, J.; Gemming, S.; Seifert, G.;
The adsorption of small (bio-)organic molecules on clean, low-index TiO2 surfaces has been investigated by density-functional based tightbinding calculations with the goal to rationalise the propensity of such molecules to self-assemble into row-like structures or two-dimensionally ordered patches. The systems studied range from phosphonic acids to the nucleotide cytidin monophosphate adsorbed on TiO2 anatase(101) and rutile(110) surfaces. We studied the geometries and adsorption energies of several adsorption models and obtain several possible adsorption structures that can be present on the specific TiO2 surfaces with comparable probability. For the pure phosphonic acids the preferable coordination is exclusively bidentate with similar adsorption energies but several different geometries. Monodentate and tridentate arrangements have significantly smaller adsorption energies and tend to relax towards the bidentate coordination. Despite the different steric situation, cytidin monophosphate exhibits exactly the same trends as phosphonic acids with bidentate coordination via a combination of oxo, alkoxy and hydroxyl groups.
Keywords: self-assembly, SAM, TiO2, rutile, anatase, surface, DFT, calculation
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12789 - Permalink


A structure-induced metal-insulator transition in thin MoS nanowires
Popov, I.; Seifert, G.; Gemming, S.;
Transition metal chalcohalides MX2 can form a wealth of diverse nanostructures, which range from large octahedral and fullerene-like hollow clusters and cylindrical nanotubes close to the nominal composition M:X = 1:2 to smaller, two-dimensional platelet-shaped clusters under sulfur excess and to one-dimensionally elongated nanowires under sulfur-deficient conditions. All of those structures exhibit specific electronic properties that differ from the ones of the pure bulk and open up a large application spectrum, that includes the lubricant aspect, but extends to catalysis and electronic transport. One-dimensionally delocalized electronic states provide the basis for the higher activity, reactivity and conductivity in such nanostructures. One-dimensional MX wires are composed of a central metallic wire coated by a sulfur and/or halide shell. They exhibit a very high structural regularity, hence, ballistic conductivity may be obtained in such structures. DFT calculations showed that wires can act as electromechanical switches, because they undergo a symmetry-dependent metal-insulator transition upon twisting [Nano Lett.,10.1021/nl801456f; Nano Lett., 2008, 8, 3928-3931].
Keywords: molybdenum sulfide, conduction, conductivity, nanowire, ballistic
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12788 - Permalink


Structural and DFT studies on YFeMnO5
Weißbach, T.; Lubk, A.; Leisegang, T.; Führlich, T.; Wunderlich, F.; Souptel, D.; Behr, G.; Chaplygin, I.; Seifert, G.; Meyer, D. C.; Gemming, S.;
Ferromagnetic and ferroelectric oxides of composition REMn2O5 have become known for exhibiting a coupling between those properties. On substitution of Fe in YMn2−xFexO5, the crystal structure is conserved, but the magnetic structure changes and the ferroelectricity disappears. X-ray diffraction measurements on a series of powders with different Fe content were employed to inspect the crystal structure whereas extended X-ray absorption fine structure measurements were done to identify the iron substitution site. Density functional theory calculations of the electronic structure for YMnFeO5 were carried out using the experimentally determined crystal structure data and the FPLO-5 program. Different magnetic structures are studied to determine the type of interaction between the magnetic ions.
Keywords: ferroic oxides, multiferroics, yttrium manganese iron oxide
  • Poster
    Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12787 - Permalink


Design of a neutrally buoyant self-powered multi-parameter sensor for data logging in flow applications
Thiele, S.; Schöne, S.; Voigt, F.; Da Silva, M. J.; Hampel, U.;
In many industrial processes the measurement and monitoring of process parameters is hampered by limited access to the process itself. This is especially true for large vessels, such as large size tanks, reactors, fermenters, etc. State of the art instrumentation is commonly applied locally and spatially resolved parameter measurement is either not feasible or too expensive. For the measurement of process parameters in a stirred fermentation biogas reactor we developed the concept of neutrally buoyant self-powered sensor particles. The prototype sensor performs logging of temperature, absolute pressure and 3D-acceleration data using appropriate commercial miniature sensors, a low power microcontroller and associated EEPROM modules integrated in a robust capsule which gives a balance between buoyancy and gravitation with respect to the liquid process substrate. In an initial test of the developed prototype its autonomous operation has been successfully proved showing feasibility for future application in a biogas reactor.
Keywords: autonomous sensing, multi-parameter logging, neutrally buoyant sensor particle
  • Lecture (Conference)
    IEEE SENSORS 2009 Conference, 25.-28.10.2009, Christchurch, New Zealand
  • Contribution to proceedings
    IEEE Sensors 2009 Conference, 25.-28.10.2009, Christchurch, New Zealand
    IEEE Sensors 2009 Conference, Sensors 2009, 978-1-4244-5335-1

Publ.-Id: 12786 - Permalink


Electronic properties of defects in SrTiO3 - theory and experiments
Weißbach, T.; Riedl, T.; Gemming, T.; Gemming, S.; Zschornak, M.; Gutmann, E.; Stöcker, H.; Leisegang, T.; Meyer, D. C.;
SrTiO3 is a commercially available wafer material e.g. for the integration of oxide superconductors or microwave filter applications. The electric properties of SrTiO3 are routinely modified by doping with additional elements such as Nb. A targeted defect engineering may, however, achieve similar or superior results, while remaining in the ternary system (Sr,Ti,O), i.e. without the need for extrinsic doping. Material characterization methods able to distinguish such defects in particular are needed. In the present study we combine all-electron first-principles calculations with electron energy loss and X-ray absorption spectroscopy to study the electronic properties of SrTiO3-related oxygen deficient compounds. In particular, such changes of the SrTiO3 core-level spectra are studied, which occur if O vacancies accumulate in SrTiO3, or if excess SrO(001) planes are inserted to form Ruddlesden-Popper-type compounds.
Keywords: Ruddlesden-Popper phases, EELS, DFT, SrTiO3, strontium titanate
  • Lecture (Conference)
    DPG-Frühjahrstagung, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12785 - Permalink


Nanoscale Magnetic Lithography on FeAl alloys by ion irradiation and nanoindentation
Sort, J.; Menendez, E.; Varea, A.; Pi, F.; Surinach, S.; Baro, M. D.; Nogues, J.;
Nanoindentation and local ion irradiation (i.e., focused ion beam or broad beam irradiation through shadow masks, such as alumina templates or PMMA masks) are shown to be effective methods to generate periodic arrays of sub-micron ferromagnetic dots at the surface of paramagnetic Fe60Al40 alloys (both in the form of sheets and thin films). The fabricated entities exhibit a variety of magnetic properties depending on their size and shape. Remarkably, in some cases, the magnetic anisotropy of the dots is oriented perpendicular to the film plane. Furthermore, the ferromagnetic properties of the patterned structures can be removed by annealing at sufficiently high temperatures, thus evidencing the reversible character of this novel magnetic lithography procedure.
Keywords: magnetism, ion irradiation, binary alloy, ordering, nanoscale, patterning
  • Invited lecture (Conferences)
    ICAM International Conference on Advanced Materials, 20.-25.09.2009, Rio de Janeiro, Brasilien

Publ.-Id: 12784 - Permalink


Modelling electronic and transport properties in ferroic devices
Gemming, S.;
In nanostructured materials spatial confinement effects lead to structure-dependent modifications of the bulk transport properties. In part, such modifications can be accounted for by a classical master equation approach for the transport of the different charge carrier species. The rather large quantity of parameters, which enter such an approach, can more or less easily be adjusted to the dimensional characteristics and the electronic settings of the system as well as to temperature effects. On the other hand, a microscopically more detailed and mostly parameter-free picture is obtained from a quantum-mechanical treatment on the basis of the density-functional theory. An extension by a Green's function formalism allows the determination and analysis of electronic transport through contacted nanostructures. Examples will be given to demonstrate the applicability of the different approaches for dissipative and hopping transport through a regular array of nanostructures, for a mechanically triggered metal-insulator transition in nanowires, and for the enhanced conductivity at multiferroic domain walls.
Keywords: bismuth ferrite, molybdenum sulfide, transport, hopping, ballistic, shuttling
  • Invited lecture (Conferences)
    Fraunhofer IWM - Seminarreihe zur Materialforschung, 13.02.2009, Freiburg, Brsg., Deutschland

Publ.-Id: 12783 - Permalink


Unusual transport phenomena in nanostructured materials
Gemming, S.;
In nanostructured materials spatial confinement effects lead to structure-dependent modifications of the bulk transport properties. In part, such modifications can be accounted for by a classical master equation approach for the transport of the different charge carrier species. The rather large quantity of parameters, which enter such an approach, can more or less easily be adjusted to the dimensional characteristics and the electronic settings of the system as well as to temperature effects. On the other hand, a microscopically more detailed and mostly parameter-free picture is obtained from a quantum-mechanical treatment on the basis of the density-functional theory. An extension by a Green's function formalism allows the determination and analysis of electronic transport through contacted nanostructures. Examples will be given to demonstrate the applicability of the different approaches for dissipative and hopping transport through a regular array of nanostructures, for a mechanically triggered metal-insulator transition in nanowires, and for the enhanced conductivity at multiferroic domain walls.
Keywords: transport, bismuth ferrite, molybdenum sulfide, hopping, shuttling
  • Invited lecture (Conferences)
    nanoSeminar, 05.02.2009, Dresden, Deutschland

Publ.-Id: 12782 - Permalink


Designing miniature wires for small-scale electronics
Popov, I.; Seifert, G.; Gemming, S.;
The last few decades have seen an amazing miniaturization of silicon microelectronics, to the extent that modern transistors are approaching quantum limits. Further miniaturization requires novel materials with a well-defined atomic structure that allows information to be processed and stored with a small and uniform number of charge carriers. Nanostructured materials have attracted the attention of researchers because they promise both improved processing and energy efficiency.
Keywords: nanowires, molybdenum sulfide, electronic transport

Publ.-Id: 12781 - Permalink


Quantitative analysis of corroded coins with four non-destructive X-ray methods
Wolff, T.; Denker, A.; Hahn, O.; Merchel, S.; Radtke, M.; Reinholz, U.;
To check the general quality of our analytical results, we started an intercomparison between four more or less common non-destructive X-ray based methods:
• low energy particle induced X-ray emission with protons of 2 MeV (PIXE)
• high energy particle induced X-ray emission with protons of 68 MeV (HE-PIXE)
• X-ray fluorescence with a portable device (µ-XRF)
• synchrotron-induced X-ray fluorescence (SY-XRF)
As test objects we selected six Roman coins with corrosion layers of different occurrence. Each coin was analyzed at three locations: original surface, surface with fully removed and partially removed corrosion layer, respectively.
We used two different external beam set-ups for PIXE: A “classical” one at a 2 MV tandem accelerator (BAM) and a high-energy one at the Helmholtz-Zentrum Berlin. The low-energy proton beam was extracted into air through a thin polyimide window (8 µm thick) and focused by a magnetic quadrupole doublet followed by a carbon aperture (Ø=0.7 mm). X-rays were energy dispersively measured by a Si(Li) detector [1]. There are some advantages in using higher energy protons [2] over low-energy ones: The protons can penetrate more deeply the material and the excitation probability for K-lines of heavy elements is bigger, resulting in better detection limits for those elements. At our set-up the beam is extracted into air via a thin Kapton foil and the X-ray signals are collected by a HPGe (resolution: 180 eV at 5.9 keV). Measurement times were 200 s. The data evaluation was done using the Guelph PIXE software GUPIX.
SY-XRF was performed at the hard X-ray beamline BAMline at BESSY. We analysed the Roman coins by our typical set-up [3]: A Si(111) Double-Crystal-Monochromator (DCM), and a W/Si Double-Multilayer-Monochromator (DMM) were used to produce a monochromatic X-ray beam of 32 keV. Signals were collected by a Si(Li) detector.
Last but not least, a mobile XRF-device equipped with a Mo-X-ray tube (30 W) and a polycapillary (spot size: 70 µm) was used to check to which extent a method that could in principal analyse objects in the field or in the collections can keep up with the three stationary (and more expensive) methods.
The four different methods produced tolerable to horrendous differences of quantitative results. Some discrepancies can be e.g. explained by variations of the analysed volume. For instance, a possible inhomogeneity of the sample will differently influence analytical results, if one changes the spot-size and penetration depth. The influence of the corrosion layer on the obtained concentrations also depends on the analytical depth of each method. Quantification procedures for each method should be adapted to these effects.
References: [1] I. Reiche et al., X-Ray Spectrom. 34 (2005) 42. [2] A. Denker et al., X-Ray Spectrom. 34 (2005) 376. [3] H. Riesemeier et al., X-Ray Spectrom. 34 (2005) 160.
Keywords: PIXE, SY-XRF, µ-XRF, intercomparison
  • Poster
    19th International Conference on Ion Beam Analysis, 07.-11.09.2009, Cambridge, UK

Publ.-Id: 12780 - Permalink


The QQDS magnetic spectrometer “Little John” for High Resolution Depth Profiling
Kosmata, M.; Grötzschel, R.; Hanf, D.; Munnik, F.; Akhmadaliev, C.; Vieluf, M.; Möller, W.;
The aim of the modified magnetic spectrometer “Little John” [1] is to measure concentration profiles of light elements in thin layers with sub-nanometer depth resolution by Elastic Recoil Detection Analysis (ERDA). For these measurements heavy ions from the Rossendorf 5-MV-Tandem accelerator are directed to the sample. The 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 resolutions can 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 available data of which assume a dynamic charge state equilibrium due to electron loss and capture along the ion trajectory. In the case of ultrathin 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 an experimental setup at “Little John” for charge state distribution measurements of light heavy ions and present first results.

References: [1] H.J. Gils, J. Buschmann, S. Zagromski, J. Krisch and H. Rebel, Nucl. Instr. and Meth. A276 (1989), p. 151.
.
Keywords: magnetic spectrometer, thin layers, high depth resolution, ERDA, elastic recoil detection, charge state distribution, charge state dependent stopping cross section, Little John, QQDS
  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 06.-08.04.2009, Jena, Deutschland

Publ.-Id: 12779 - Permalink


The French accelerator mass spectrometry facility ASTER: Improved performance and developments
Arnold, M.; Merchel, S.; Bourlès, D. L.; Braucher, R.; Benedetti, L.; Finkel, R. C.; Aumaître, G.; Gottdang, A.; Klein, M.;
A new 5 MV tandem accelerator has been installed at the Centre Européen de Recherche et d’Enseignement des Géosciences de l’Environnement (CEREGE). The machine is fully dedicated to accelerator mass spectrometry (AMS) in applied research like environmental and Earth sciences. For 10Be and 36Cl the troublesome isobar suppression is maintained by nuclear charge dependent energy loss in an absorber foil, subsequent energy selection by a 35° electrostatic deflector followed by a 30° vertical magnet, and final separation of the rare isotope in a high-resolution, 4-anode (ΔE1, ΔE2, ΔE3, E-final) gas ionisation chamber [1].

Since the acceptance test in March 2007, we have successfully established routine measurement conditions for the long-lived cosmogenic radionuclides 10Be and 26Al. Using 9Be carrier derived in our laboratory from phenakite crystals originating from a deep mine, we determined a background-level as low as 1.5x10-16 (10Be/9Be) [2]. Considerable time has been spent to investigate reasons for variability of ion currents and background. We have performed cross-calibrations for 26Al and 41Ca and took part into international round-robin exercises of 10Be and 36Cl to establish quality assurance at ASTER. For 41Ca (extracted as CaF3-) and 129I, background levels are in the range of 2x10-14. The original Cs-sputter ion source SO110 [3], that produced sample-to-sample cross-contamination at the ‰-level and unacceptable long-term memory effects for volatile elements as chlorine or iodine, had been continuously replaced by a number of newly developed versions enhancing the performance step by step. Under optimum conditions, i.e. using exclusively low-level standards (36Cl/Cl=1.4x10-13) for calibration and cathode material containing the lowest isobar (36S) concentrations, the 36Cl background can reach 3x10-16 (36Cl/35Cl). The total transmission varies from 2% for 36Cl with the post-stripping absorber foil to 38% for 26Al.

The main focus of applications of ASTER is on geological and environmental topics with the broad goal of using isotopic techniques to help understand the timing and rates of processes in the earth system. Work so far has included reconstruction of past climate, determination of the rate and timing of seismic activity, volcanic eruptions and rock falls.

References: [1] M.G. Klein et al., Nucl. Instr. and Meth. B 266 (2008) 1828. [2] S. Merchel et al., Nucl. Instr. and Meth. B 266 (2008) 4921. [3] M.G. Klein et al., Nucl. Instr. and Meth. B 249 (2006) 764.

Acknowledgments: This work was partially funded by CRONUS-EU (Marie-Curie Action, 6th FP #511927).
Keywords: accelerator mass spectrometry, AMS, terrestrial cosmogenic nuclides
  • Poster
    19th International Conference on Ion Beam Analysis, 07.-11.09.2009, Cambridge, UK

Publ.-Id: 12778 - Permalink


Bakterielle S-Layer als Strukturelemente für die Nanobiotechnologie
Raff, J.;
Eine der großen Herausforderungen in den Nanowissenschaften ist die reproduzierbare und einfache Herstellung nanoskaliger Strukturen mit neuen Eigenschaften für technische Anwendungen. Hier kann die Biologie einen wichtigen Beitrag leisten. So besitzen 70% aller bekannten Bakterien und Archaeen parakristalline Zellwandschichten, so genannte S-Layer, als äußerste Zellwandkomponente. Diese nanoskaligen Proteingitter können sehr unterschiedliche Funktionen übernehmen wie zum Beispiel als Schutzschicht, sie können für die Formgebung notwendig sein, als Molekularsieb wirken oder aber als Ionen- und Molekülfalle dienen. Die intrinsische Eigenschaft der Proteinuntereinheiten als monomolekulare Schicht in Suspension, an Grenz- und zahlreichen Oberflächen zu assemblieren, machen diese Proteine äußerst interessant für die einfache Herstellung multifunktionaler Oberflächenbeschichtungen. Auf Grund der sehr guten Metall-bindenden Eigenschaften und der höhere Stabilität gegenüber chemischen Einflüssen sind die S-Layer verschiedener Uranabfallhaldenisolate besonders gut zur Herstellung stabiler metallischer und halbleitender Nanopartikel und Nanostrukturen geeignet. Der Vortrag gibt einen Überblick über die Möglichkeiten und Grenzen der technischen Anwendung bakterieller S-Layer-Proteine und stellt die aktuelle Arbeiten des Instituts für Radiochemie dazu vor.
Keywords: Nanobiotechnologie, S-Layer
  • Invited lecture (Conferences)
    Forschungsseminar, Institut für Physikalische Chemie, TU Dresden, 19.05.2009, Dresden, Deutschland

Publ.-Id: 12777 - Permalink


Enhanced dipole strength below particle threshold
Schwengner, R.;
Dipole-strength functions up to the neutron-separation energies Sn of the N=50 isotones 88Sr, 89Y, 90Zr, and the even-mass Mo isotopes from 92Mo to 100Mo have been studied in photon-scattering experiments using the bremsstrahlung facility at the superconducting electron accelerator ELBE of the Forschungszentrum Dresden-Rossendorf.
To estimate the distribution of inelastic transitions from high-lying levels at high level density to low-lying levels, simulations of gamma-ray cascades were performed. On the basis of these simulations intensities of inelastic transitions were subtracted from the experimental intensity distributions, including the resolved peaks as well as a continuous part formed by unresolved transitions, and the intensities of elastic transitions to the ground state were corrected for their branching ratios. The photoabsorption cross sections obtained in this novel way are combined with (gamma,n) and (gamma,p) data and give detailed information about the dipole-strength functions in the energy range from about 4 MeV up to the giant dipole resonance (GDR). In all nuclides extra strength in excess to simple Lorentzian-like approximations of the tail of the GDR is found in the energy range from about 5 MeV up to about the respective particle thresholds. Calculations in the framework of the quasiparticle-random-phase approximation (QRPA) underestimate the dipole strength at low energy because they do not take into account the coupling of two-quasiparticle to multi-quasiparticle excitations. A new approach is presented that calculates the dipole strength for nuclei with shape fluctuations by combining the interacting boson model (IBA) with QRPA. Based on the slow shape dynamics and the fast dipole vibrations an Instantaneous Shape Sampling (ISS) is performed that describes the photoabsorption at a fixed shape with QRPA with probabilities given by IBA. The ISS-QRPA improves the description of the experimental photoabsorption cross sections.
Keywords: Nuclear structure, gamma-ray spectroscopy, bremsstrahlung, photon scattering, gamma-ray strength functions, photoabsorption cross section, quasiparticle-random-phase approximation, interacting boson model.
  • Lecture (Conference)
    2nd Workshop on Level Density and Gamma Strength, 11.-15.05.2009, Oslo, Norwegen

Publ.-Id: 12776 - Permalink


Nanometrologie für die Nanoelektronik
Helm, M.;
no abastract available
Keywords: Nanometrologie
  • Lecture (others)
    Cool Silicon, 06.05.2009, Dresden, Deutschland

Publ.-Id: 12775 - Permalink


The 4D Naimark dilated PT brachistochrone as 2D Hermitian brachistochrone
Günther, U.;
After a brief exposition of the Naimark dilated PT brachistochrone [PRL 101, 230404 (2008)] evidence is provided that the dilation (doubling of the Hilbert space dimension) preserves the brachistochrone features of the model. The dilated PT brachistochrone in 4D-Hilbert space behaves as an effective Hermitian brachistochrone in the 2D subspace spanned by the 4D initial and final states.
Keywords: PT quantum mechanics, non-Hermitian Hamiltonian, Naimark dilation, quantum brachistochrone, dilation invariants
  • Invited lecture (Conferences)
    Analytic and algebraic methods V, 27.-28.05.2009, Prague, Czech Republic

Publ.-Id: 12774 - Permalink


Measurement of low-mass e+e- pair production in 1 and 2 AGeV C-C collisions with HADES
Sudol, M.; Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Bielcik, J.; Blanco, A.; Bortolotti, A.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Chernenko, S.; Christ, T.; Coniglione, R.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Duran, I.; Dybczak, A.; Eberl, T.; Fabietti, L.; Fateev, O.; Ferreira-Marques, R.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krasa, A.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lapidus, K.; Lopes, L.; Lorenz, M.; Maier, L.; Maiolino, C.; Mangiarotti, A.; Marin, J.; Markert, J.; Metag, V.; Michalska, B.; Michel, D.; Moriniere, E.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Perez Cavalcanti, T.; Piatelli, P.; Pietraszko, J.; Pospisil, V.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sapienza, P.; Schmah, A.; Schröder, C.; Schwab, E.; Simon, R.; Smolyankin, V.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.; Zumbruch, P.;
HADES is a secondary generation experiment operated at GSI Darmstadt with the main goal to study dielectron production in proton, pion and heavy ion induced reactions. The first part of the HADES mission is to reinvestigate the puzzling pair excess measured by the DLS collaboration in C+C and Ca+Ca collisions at 1A GeV. For this purpose dedicated measurements with the C+C system at 1 and 2 A GeV were performed. The pair excess above a cocktail of free hadronic decays has been extracted and compared to the one measured by DLS. Furthermore, the excess is confronted with predictions of various model calculations.

Publ.-Id: 12773 - Permalink


Mid-frequency deposition of a-C:H films using five different precursors
Peter, S.; Günther, M.; Hauschild, D.; Grambole, D.; Richter, F.;
The plasma enhanced chemical vapour deposition of amorphous hydrogenated carbon films from pulsed discharges with frequencies in the range from 50 kHz to 250 kHz was investigated. A Pinnacle Plus+ generator (Advanced Energy Ind., Inc.) was used to power the discharges in the so called mid-frequency range. Five different hydrocarbons (acetylene C2H2, 2-methylpropene/isobutylene C4H8, cyclopentene C5H8, toluene C7H8 and cycolheptatriene C7H8) were probed as film growth precursors. The a-C:H films deposited in a parallel plate reactor were characterised for their thickness/deposition rate (profilometer), hardness (nanoindentation with Berkovich indentor) and hydrogen content (nuclear reaction analysis, NRA). The measurement of neutral reaction products in the gas phase was performed with quadrupole mass spectrometry. The formation of stable, higher molecular hydrocarbons, that means cyclic ring compounds and polyacetylenes, was detected in all precursor plasmas. The hydrogen concentration in the films varied between 20 atomic-% and 37 atomic-%. It is roughly in inverse proportion to the hardness. The film with the highest hardness of 25 GPa was formed at a deposition rate of 0.8 µm/h in the C2H2 discharge at the lowest investigated pressure of 2 Pa. With increasing molecular mass of the precursor mostly weaker films were deposited. Relatively high values of both deposition rate and hardness were achieved using the precursor isobutylene: a hardness of 21 GPa combined with a deposition rate of 4.1 µm/h. But, as an over-all trend the a-C:H hardness decreases with increasing deposition rate.
  • Lecture (Conference)
    4-th Symposium on Vacuum based Science and Technology in conjunction with 8-th Annual Meeting of German Vacuum Society (DVG), 21.-23.09.2009, Koszalin- Kołobrzeg, Poland

Publ.-Id: 12772 - Permalink


Studies on multigap resistive plate chamber prototypes for the new NeuLAND detector at the R3B experiment at FAIR
Elvers, M.; Aumann, T.; Bemmerer, D.; Boretzky, K.; Endres, J.; Hehner, J.; Heil, M.; Kratz, J. V.; Prokopowicz, W.; Reifarth, R.; Rossi, D.; Schrieder, G.; Stach, D.; Wagner, A.; Yakorev, D.; Zilges, A.;
The NeuLAND detector is part of the R3B experiment at FAIR and will detect neutrons between 0.2 and 1 GeV. The high energy neutrons are converted to charged particles, mainly protons, which are detected by Multigap Resistive Plate Chambers (MRPC). For the detector, a time resolution of σt < 100 ps and a position resolution of σx,y,z ≈ 1 cm is required for given flight paths in the range from 10 to 35 m. An active area of 2 × 2 m2 of the neutron detector at a distance of 12.5 m to the target will match the angular acceptance of ±80 mrad for the neutrons defined by the gap of the superconducting dipole magnet. The salient features of the prototypes will be described, as well as electrical measurements and studies with cosmic rays.
Keywords: MRPC, NeuLAND, R3B, Multigap resistive plate chambers, neutron detector, cosmic rays
  • Lecture (Conference)
    Frühjahrstagung des DPG - Fachverbands Hadronen und Kerne and European Nuclear Phyisics Conference (EuNPC), 16.-20.03.2009, Bochum, Deutschland

Publ.-Id: 12771 - Permalink


Timing measurements at ELBE on multigap resistive plate chamber prototypes for NeuLAND
Yakorev, D.; Aumann, T.; Bemmerer, D.; Boretzky, K.; Cowan, T.; Elvers, M.; Hehner, J.; Heil, M.; Kratz, J. V.; Prokopowicz, W.; Reifarth, R.; Rossi, D.; Schrieder, G.; Stach, D.; Wagner, A.; Zilges, A.;
The NeuLAND detector for fast neutrons (0.2-1\,GeV) at the R3B experiment at FAIR aims for high time and spatial resolutions ($\sigma_{\rm t}$$<$100\,ps, $\sigma_{\rm x,y,z}$$<$1\,cm). The detector will consist of about 60 sequences of a stacked structure from iron converter material and multigap resistive plate chambers (MRPC's). The secondary charged particles stemming from hadronic interactions of the high energetic neutrons in the converter will be detected in the MRPC's, with excellent timing properties. As part of the ongoing development of the NeuLAND detector, MRPC prototypes designed for this application have been studied at the superconducting electron linac ELBE in Dresden with its picosecond time structure. The ELBE experiments show that the prototypes studied so far have efficiency $\geq$90\% for minimum ionizing particles in a 2x2 gap structure and fulfill the called for time resolution. --- Supported by BMBF (06DR134I) and GSI (FuE DR-GROS).
Keywords: MRPC, NeuLAND, R3B, multigap resistive plate chamber, ELBE
  • Lecture (Conference)
    Frühjahrstagung des DPG - Fachverbands Hadronen und Kerne and European Nuclear Phyisics Conference (EuNPC), 16.-20.03.2009, Bochum, Deutschland

Publ.-Id: 12770 - Permalink


MRPC prototyping for NeuLAND
Bemmerer, D.; Heidel, K.; Kempe, M.; Sobiella, M.; Stach, D.; Wagner, A.; Yakorev, D.; Boretzky, K.; Caesar, C.; Hehner, J.; Heil, M.; Schrieder, G.; Prokopowicz, W.; Elvers, M.; Zilges, A.; Datta Pramanik, U.;
I review the status of the prototyping effort for multigap resistive plate chamber (MRPC) based neutron detectors for the NeuLAND detector at FAIR. Several MRPC prototypes have been built at FZD Dresden and at GSI Darmstadt. They have been tested using the picosecond time structure of the ELBE electron beam facility at FZD Dresden, Germany. All detectors display the called for time resolution of sigma < 100 ps at > 90% efficiency for 30 MeV electrons. The cross-talk issue is still under investigation. Preliminary data obtained using the new single-electron mode of operation at ELBE are also shown here.
Keywords: MRPC, NeuLAND, R3B, FAIR, neutron, multigap resistive plate chamber, large area neutron detector
  • Lecture (Conference)
    R3B collaboration meeting on technical issues, 27.-30.04.2009, Darmstadt, Deutschland

Publ.-Id: 12769 - Permalink


Grain size control in Al-Si Alloys by grain refinement and electromagnetic stirring
Metan, V.; Eigenfeld, K.; Räbiger, D.; Leonhardt, M.; Eckert, S.;
The present study concerns the directional solidification of grain-refined and non-refined AlSi7 alloys under the influence of a travelling magnetic field (TMF). Upwards and downwards travelling fields have 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, but, gives rise to the formation of segregation zones.
Keywords: Al-Si alloy, Directional solidification, Grain refinement, Electromagnetic stirring, Travelling magnetic field (TMF), Grain size
  • Journal of Alloys and Compounds 487(2009)1-2, 163-172

Publ.-Id: 12768 - Permalink


Magnetfelder kontrollieren Erstarrungsprozesse bei Metalllegierungen
Eckert, S.; Schue, A.;
In der Arbeitsgruppe Magnetohydrodynamik am Forschungszentrum Dresden-Rossendorf (FZD) werden die komplexen Wechselwirkungen zwischen elektrisch leitfähigen Flüssigkeiten und magnetischen Feldern untersucht, um Strömungsverhalten und Erstarrungsprozesse flüssiger Metalllegierungen kontrolliert zu steuern. Ziel sind optimierte Produktionsprozesse für die Gießereitechnik. Zur Analyse der metallischen Mikrogefüge setzen die Wissenschaftler ein automatisiertes System aus High-end-Mikroskop und PowerMosaic-Bildaufnahme ein, das große Probenoberflächen in hochaufgelösten Einzelbildern abrastert und ein präzises Gesamtbild für quantitative Auswertungen liefert.
Keywords: metal alloys, solidification, electromagnetic stirring, microstructure
  • Giesserei-Praxis 4(2009), 135-138

Publ.-Id: 12767 - Permalink


Some recent developments in the field of liquid metal measuring techniques and instrumentation
Eckert, S.; Buchenau, D.; Gerbeth, G.; Stefani, F.; Weiss, F.-P.;
Liquid metal cooling or liquid metal targets belong to innovative reactor concepts such as the sodium cooled fast breeder reactor or the lead-bismuth target in a transmutation system. The safe and reliable operation of liquid metal systems requires corresponding measuring systems and control units, both for the liquid metal single-phase flow as well as for gas bubble liquid metal two-phase flows. We report on some recent developments in this field.
Integral flow rate measurements are an important issue. We describe two new, fully contactless electromagnetic solutions and related test measurements at available sodium and lead loops. One of the sensors is of particular interest since its operation does not depend on the electrical conductivity of the liquid metal, hence it is independent on the melt temperature.
A development of the past decade is the local velocity measurement by application of the Ultrasound Doppler Velocimetry (UDV). It provides the velocity profile along the ultrasonic beam, and has the capability to work even through some channel wall. We report on measurements in liquid sodium at 150°C. For higher temperatures, an integrated ultrasonic sensor with an acoustic wave-guide has been developed to overcome the limitation of ultrasonic transducers to temperatures lower than 200°C. This sensor can presently be applied at maximum temperatures up to 700°C. Stable and robust measurements have been performed in various PbBi flows in our laboratory at FZD as well as at the THESYS loop of the KALLA laboratory of Forschungszentrum Karlsruhe, Germany (FZK). We will present experimental results obtained in a PbBi bubbly flow at 250...300°C. Argon bubbles were injected through a single orifice in a cylindrical container filled with stagnant PbBi. Velocity profiles were measured in the bubble plume. At the THESYS loop of FZK, stable velocity profiles were measured in a round tube of diameter 60 mm during a period of about 72 hours at temperatures between 180°C and 350°C.
Further, we report on the development of a contactless magnetic tomography of the mean flow in liquid metals. This method gives the full three-dimensional mean velocity distribution in a liquid metal volume. Results from a laboratory demonstration experiment will be presented.
Keywords: liquid metal cooled reactors, electromagnetic flow meter, ultrasound Doppler velocimetry, magnetic flow tomography
  • Lecture (Conference)
    International Conference on Fast Reactors and Related Fuel Cycles (FR09), 07.-11.12.2009, Kyoto, Japan
  • Contribution to proceedings
    International Conference on Fast Reactors and Related Fuel Cycles (FR09), 07.-11.12.2009, Kyoto, Japan

Publ.-Id: 12766 - Permalink


Bremsstrahlung and related items
Kämpfer, B.;
Bremsstrahlung and related items
  • Invited lecture (Conferences)
    RNM Workshop, 14.05.2009, Darmstadt, Deutschland

Publ.-Id: 12765 - Permalink


A differentiation of the affinity of uranium(VI) to phosphate and carboxylic groups in native phosvitin studied by ATR FT-IR spectroscopy
Li, B.; Raff, J.; Bernhard, G.; Foerstendorf, H.;
The toxicity of the uranium to the living organisms is because of its heavy metal characteristic. Proteins, the fundamental component of all living cells and the key to their metabolism, undergo conformational changes upon the heavy metal complexation, thus loss their proper cellular function. In this study, phosvitin, a highly water soluble 34 kDa protein containing roughly 35 phosphate groups and 29 carboxylic residues1, is chosen as an ideal model system for the spectroscopic investigation of the interaction of U(VI) with proteins allowing the differentiation between the U(VI)-phosphate and U(VI)-carboxylic complexation. For this purpose, two different U(VI) concentrations (10−4 M and 10−5 M) are set up at pH 4 with various amounts of phosvitin to acquire complexes with different U(VI)/phosphate group ratios. The aqueous solutions were investigated by ATR FT-IR spectroscopy. For the very first time, soluble protein U(VI) complexes are achieved in aqueous solution providing spectral evidence for U(VI) complexation by the unequivocal identification of the νas(UO22+) mode. The spectra of the soluble complex show that at a low U(VI)/phosphate ratio (1:10.2) U(VI) preferentially binds to the phosphate groups. Interestingly, the νas(UO22+) mode is found at 905 cm−1 which is bathochromic shifted about 60 cm−1 compared to the free uranyl ion2 reflecting a strong coordination to several phosphate groups. With increasing U(VI)/phosphate ratio, U(VI) complexation to carboxylic groups is observed by a hypsochromic shift of the νas(UO22+) mode and characteristic bands of the νs(COO−) and νas(COO−) modes. At a higher U(VI)/phosphate ratio (10:1), complexation between U(VI) and carboxylic groups becomes dominant. From the observed frequency of this mode (925 cm−1) a typical bidental complexation to U(VI) by carboxylic group can be assumed3. In order to reduce the impact of the carboxylic groups on the U(VI) binding, phosvitin is modified using EDC. After subsequent incubation with 10−3 M U(VI) in aqueous solution at pH 4, the obtained IR spectra of the precipitated U(VI)-protein complex confirm this assumption.
Keywords: Phosvitin, U(VI), ATR FT-IR, phosphate groups, carboxylic groups.
  • Poster
    European Conference on the Spectroscopy of Biological Molecules 2009, 28.08.-02.09.2009, Palermo, Italy

Publ.-Id: 12764 - Permalink


Single Pt/Co(0.5 nm)/Pt Nano-discs: Beyond the Coherent Spin Reversal Model and thermal stability
Adam, J.-P.; Rohart, S.; Jamet, J.-P.; Mougin, A.; Ferre, J.; Bernas, H.; Faini, G.; Fassbender, J.ORC
The dynamics of the magnetization reversal in single Pt/Co(0.5 nm)/Pt nano-discs with diameter 130 nm, fabricated by an He+ ion irradiation is investigated. They exhibit a very narrow distribution of small switching fields and a perpendicular magnetic anisotropy. In spite of the small involved magnetic volume, their dynamics cannot be interpreted within the usual Néel-Braun prediction developed and verified for uniform spin reversal in spherical nano-particles. Non-coherent magnetization reversal proceeds here by fast nucleation at nanodot borders and rather slow wall motion towards their center. Dynamics are perfectly accounted from a refined confined droplet model, involving the wall energy rather than the anisotropy energy. In counterpart, the blocking temperature for these nanodiscs is well described by the Néel-Braun model.
Keywords: magnetism, ion irradiation, switching field, magnetic anisotropy, dynamics, Neel model
  • Journal of the Magnetics Society of Japan (JSMJ) 33(2009), 498

Publ.-Id: 12763 - Permalink


Chitin-based scaffolds are an integral part of the skeleton of the marine demosponge Ianthella basta
Brunner, E.; Ehrlich, H.; Schupp, P.; Hedrich, R.; Hunoldt, S.; Kammer, M.; Machill, S.; Paasch, S.; Bazhenov, V. V.; Kurek, D. V.; Arnold, T.; Brockmann, S.; Ruhnow, M.; Born, R.;
The skeleton of demosponges such as Ianthella basta is known to be a composite material formed from organic constituents, mostly collagenous proteins (spongin). Here, we show for the first time that a filigree, chitin-based scaffold is an integral constituent of the skeleton of I. basta. These chitin-based scaffolds can be isolated from the sponge skeletons using an extraction and purification technique based on the treatment with alkaline solutions. Solidstate 13C NMR, Raman, and FTIR spectroscopy as well as chitinase digestion reveal that the extracted material indeed consists of chitin. The morphology of the extracted material has been determined by light and electron microscopy. It consists of cross-linked chitin fibers of ca. 40 – 100 nm diameter forming a micro-structured network. The overall shape of this network closely resembles the shape of the integer sponge skeleton. For the first time, solidstate 13C NMR spectroscopy is used to characterize chitin from the skeleton of a marine sponge on a molecular level. The 13C NMR signals of the chitin-based scaffolds are relatively broad indicating a high amount of disordered chitin, possibly in the form of surface-exposed molecules. X-ray diffraction shows that the scaffolds extracted from I. basta are indeed lowly crystalline and consist of loosely packed chitin with large surfaces. The spectroscopic signature of these chitin-based scaffolds is closer to that of alpha-chitin than beta-chitin.
Keywords: Sponges, chitin, skeleton, solid-state NMR spectroscopy, optical spectroscopy, X-ray diffraction
  • Journal of Structural Biology 168(2009)3, 539-547

Publ.-Id: 12762 - Permalink


Sorption of Th(IV) onto Iron Corrosion Products: EXAFS Study
Seco, F.; Hennig, C.; de Pablo, J.; Rovira, M.; Rojo, I.; Marti, V.; Gimenez, J.; Duro, L.; Grive, M.; Bruno, J.;
Long-term performance assessment of nuclear waste repositories is affected by the ability of the outer barrier systems to retain radionuclides after possible corrosive leakage of waste containers. The mobility of the radionuclides released from the spent fuel depends strongly on the processes that take place in the backfill material. The interaction of steel corrosion products and radionuclides is part of such a scenario. In this work, the sorption of Th(IV) onto 2-line-ferrihydrite (FeOOH center dot H2O) and magnetite (Fe3O4), used as models for steel corrosion products, has been studied using EXAFS spectroscopy. Sorption samples were prepared in 0.1 M NaClO4 solutions at acidic pH (initial pH values in the range 3.0-4.2) either from undersaturation and supersaturation conditions with respect to amorphous ThO2. Two oxygen subshells, one at 2.37 angstrom and another at 2.54 angstrom, were observed in the first hydration sphere of Th in the case of the ferrihydrite samples.
Th-Fe distances for the different ferrihydrite samples are similar to 3.60 angstrom. These results indicate a corner sharing surface complex of Th(IV) ion onto the ferrihydrite surface where the Th atom shares one 0 atom with each of two coordinated octahedra. The longer Th-O distance accounts for coordinated water molecules. No significant changes in the structural environment of Th in terms of coordination numbers and distances were detected as a function of Th(IV) concentration. Magnetite samples sorbing Th(IV) also showed also a strong distortion of the 0 shell, but in contrast to ferrihydrite, two types of nearest Fe atoms were detected at 3.50 angstrom and 3.70 angstrom. These results indicate that Th(IV) ion sorbs onto the magnetite surface as bidentate-corner sharing arrangements to [FeO6] octahedra and [FeO4] tetrahedra.

Publ.-Id: 12761 - Permalink


Nukleare Endlager - was die Radiochemie dazu beiträgt
Nebelung, C.;
Die prinzipiellen Lagerungsmöglichkeiten für radioaktiven Abfall wurden mit den in Deutschland vorhandenen Lagern verglichen. Stand und Planung der möglichen Endlager wurde erläutert. Es wurden die technischen Anforderungen an ein sicheres Endlager beschrieben um Sicherheit für Mensch und Umwelt zu gewährleisten. Wichtige Prozesse der Schadstoffausbreitung wie Rückhaltung (Sorption, Ausfällung, Kristalleinbau), Mobilisierung (Anlagerung an Kolloide, Bildung stabiler in Wasser gelöster Verbindungen, Auflösung) und Diffusion durch Festgestein wurden beschrieben. Ausgewählte Arbeiten aus dem Institut für Endlager in Salz, Ton und Granit wurden vorgestellt, sowie die Möglichkeiten der Sorptionsdatenbank RES3T.
Keywords: Nukleare Endlager, Sicherheitsanforderungen, Zwischenlager Ahaus, Endlager Konrad, Endlager Gorleben, Sorption, Ausfällung, Salzton, Salzbeton, Kaolinit, Bentonit, Granit, Sorptionsdatenbank, Sorptionsmodellierung
  • Lecture (others)
    Tag des offenen Labors 2009, 09.05.2009, Dresden, Deutschland

Publ.-Id: 12760 - Permalink


Microstructure at the water lipid protein interface controls conformational switching mechanisms in the conserved D(E)RY motif of G-protein coupled receptors
Eichler, S.; Madathil, S.; Fahmy, K.;
G-Protein coupled receptors (GPCRs) play a fundamental role in many physiological processes due to their ability to switch between different structures upon activation. The prototypical GPCR rhodopsin serves as a model to study molecular switching mechanisms. Upon photoisomerization of the chromophore retinal, protonation of a glutamic acid (Glu 134) in the highly conserved D(E)RY motif at the cytosolic end of transmembrane helix 3 (TM3) leads to breakage of an ionic lock which stabilizes the inactive state [1]. Due to the low dielectricity of the lipidic environment, side chain charges and their neutralization contribute to the energetics of conformational transitions much more than in a purely aqueous environment. Our aim is to elucidate the functional implication of lipid protein interactions and microstructure at the water lipid protein interface in controlling protein conformation. We have studied synthetic peptides derived from rhodopsin TM3 by fluorescence spectroscopy at different pH in a hydrophobic environment. In [2] pH dependency of FRET between Trp at the cytosolic side of a TM3-derived peptide and DANSYL-PE was used as a monitor for helix motion. The observed pH dependency argues for stabilization of the protonated state by lipid protein interactions. In addition, we studied a TM3-derived peptide with a Trp probe shifted into the hydrophobic region. This peptide showed a red-shifted emission maximum of Trp, indicative of water accessibility. Moreover, at low pH the red-shift was less pronounced supporting the hypothesis that the neutralized Glu134 repels water and in general provides a pH-regulated hydration site. We conclude that microstructure at the water lipid protein interface and lipid protein interaction play a key role in the switching mechanism of GPCRs. The predominance of these local interactions which are not strictly dependent on intramolecular contacts to specific amino acids reconciles the highly conserved proton uptake at the D(E)RY motif in GPCR activation on the one hand and the diverse ligand specificity of class-A GPCRs on the other hand.
References
[1] J. A. Ballesteros, A. D. Jensen, G. Liapakis, S. G.F. Rasmussen, L. Shi, U. Gether, J. A. Javitch, J. Biol. Chem. 276, 29171-29177 (2001)
[2] S. Madathil, G. Furlinski, K.Fahmy, Biopolymers 82, 329-333 (2006).
Keywords: G-protein coupled receptor, GPCR, D(E)RY motif, lipid protein interaction, water lipid protein interface
  • Poster
    XIII European Conference on the Spectroscopy of Biological Molecules, 28.08.-02.09.2009, Palermo, Italia

Publ.-Id: 12759 - Permalink


Inferring parameters of the geodynamo from temporal reversal characteristics
Stefani, F.; Fischer, M.; Gerbeth, G.; Giesecke, A.;
One of the most prominent features of Earth's magnetic field reversals is their asymmetric shape which includes a slow decay of the initial dipole and a fast recreation of the reversed dipole. This relaxation-oscillation-like behaviour can result from a simple mean-field dynamo model in its highly supercritical regime. The same model can also explain the deviation of paleomagnetic reversal sequences from Poisson statistics, as well as the stochastic resonance phenomenon with the Milankovitch cycle of the Earth's orbit eccentricity. Encouraged by this agreement, we utilize those three temporal reversal characteristics to constrain the most essential parameters of the geodynamo, among them the effective (turbulent) magnetic diffusivity, the degree of supercriticality, and the relative strength of the periodic forcing. Using a downhill simplex method we obtain an optimized dynamo model that yields reversal characteristics which are in surprising correspondence with paleomagnetic data.
  • Lecture (others)
    Natural Dynamos, 30.08.-05.09.2009, Stara Lesna, Slovakia
  • Open Access LogoAbstract in refereed journal
    Contributions to Geophysics and Geodesy 39(2009), 31-31

Publ.-Id: 12758 - Permalink


Liquid metal experiments on the magnetorotational instability in a Taylor-Couette flow
Stefani, F.; Gerbeth, G.; Gundrum, T.; Hollerbach, R.; Priede, J.; Rüdiger, G.; Szklarski, J.;
The magnetorotational instability (MRI) is known to play a key role in the formation of stars and black holes by triggering turbulence in hydrodynamically stable Keplerian accretion discs. As discussed recently, it might also play a role in the angular momentum transport in the Earth's outer core. We report the experimental demonstration of this instability in a Taylor-Couette flow under the influence of a helical magnetic field. Special focus is laid on a new version of this experiment in which the Ekman pumping is strongly reduced by using split end-caps.
  • Lecture (Conference)
    Natural dynamos, 30.08.-05.09.2009, Stara Lesna, Slovakia
  • Open Access LogoAbstract in refereed journal
    Contributions to Geophysics and Geodesy 39(2009), 90-90

Publ.-Id: 12757 - Permalink


Experiments on the helical magnetorotational instability in a Taylor-Couette flow with reduced Ekman pumping
Gundrum, T.; Gerbeth, G.; Stefani, F.; Hollerbach, R.; Priede, J.; Rüdiger, G.; Szklarski, J.;
The magnetorotational instability (MRI) is believed to play a key role in the formation of stars and black holes by triggering turbulence in hydrodynamically stable Keplerian accretion discs. Although the MRI had been discovered by Velikhov as early as 1959, its key role for the understanding of accretion disks was revealed only in 1991 by Balbus and Hawley. While thousands of papers have been written on the astrophysical relevance of MRI since that time, experimental work on MRI is still rare.
In 2004, Sisan et al. had observed a new coupled mode of velocity and magnetic field perturbations in a spherical Couette flow, whose parameter dependencies resemble those of the MRI. However, the background flow in this experiment was already fully turbulent so that the original goal to investigate MRI as the first instability on an otherwise stable flow could not be met. Another MRI experiment, on the basis of a short Taylor-Couette flow, is presently pursued at Princeton University.
Both experiments are carried out with a purely axial magnetic field being applied. In this standard MRI (SMRI) configuration, the governing parameters for the onset of the instability are the magnetic Reynolds number and the Lundquist number. Surprisingly, by adding an azimuthal magnetic field to the axial magnetic field, the governing role is taken over by the hydrodynamic Reynolds number and the Hartmann number. Consequently, this helical MRI (HMRI) can be observed with much less experimental effort than the SMRI.
In previous experiments at the facility PROMISE (Potsdam ROssendorf Magnetic InStability Experiment), the HMRI was observed in a liquid metal Taylor-Couette flow at moderate Reynolds and Hartmann numbers. However, the observation of this HMRI was disrupted by a significant Ekman pumping driven by solid end-caps that confined the instability only to a part of the Taylor-Couette cell. We present the observation of the HMRI in an improved Taylor-Couette setup in which the Ekman pumping is strongly reduced by using split end-caps. The HMRI wave, which now spreads over the whole height of the cell, appears much sharper and in better agreement with numerical predictions. By analyzing various parameter dependencies we conclude that the observed HMRI represents a self-sustained global instability rather than a noise-sustained convective one.
  • Lecture (Conference)
    16th Couette-Taylor Workshop, 09.-11.09.2009, Princeton, USA

Publ.-Id: 12756 - Permalink


Generation of axisymmetric modes in cylindrical kinematic mean-field dynamos of VKS type
Giesecke, A.; Nore, C.; Plunian, F.; Laguerre, R.; Ribeiro, A.; Stefani, F.; Gerbeth, G.; Leorat, J.; Guermond, J.-L.;
In an attempt to understand why the dominating magnetic field observed in the von-K\'arm\'an-Sodium (VKS) dynamo experiment is axisymmetric, we investigate in the present paper the ability of mean field models to generate axisymmetric eigenmodes in cylindrical geometries. An $\alpha$-effect is added to the induction equation and we identify reasonable and necessary properties of the $\alpha$ distribution so that axisymmetric eigenmodes are generated. The parametric study is done with two different simulation codes. We find that simple distributions of $\alpha$-effect, either concentrated in the disk neighbourhood or occupying the bulk of the flow, require unrealistically large values of the parameter $\alpha$ to explain the VKS observations.
Keywords: Dynamo experiments; Induction equation; Kinematic simulations; alpha-effect

Publ.-Id: 12755 - Permalink


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