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39515 Publications

Theoretical study on reaction paths of formation and decay of 1D nanostructures

Heinig, K.-H.; Röntzsch, L.

Nanowires have fascinating properties. Also the kind and strength of driving forces for their structural evolution differ from macroscopic systems, thus opening new routes for their synthesis. And, with respect to interface energy, nanowires are unstable, during their decay new selforganized 1D structures evolve.
This presentation summarizes reaction pathways of the formation and decay of 1D nanostructures predicted by atomistic computer simulations. It will be shown that nanowire synthesis by phase separation from supersaturated 1D traces relies on different time scales of different processes involved: (i) phase separation is faster than long-range diffusion, thus, initially small nanodroplets form. (ii) Short-range diffusion is fast, thus, lateron the minority phase is concentrated/unified to a wire (ripening, coalescence). (iii) On a long time scale, the wire lowers its surface energy by peristaltic undulations and decays finally into large droplets (Rayleigh instability). Each process can be governed in order to fabricated functional structures. For instance, crosspoints of nanowires accelerates the wire instability locally, which leads to a nanodot separated by nm gaps from the four nanowires. Such a Si structure embedded in SiO2 might operate as a room temperature single electron transistor.

Keywords: Nanowire; Reation pathway; Kinetic Monte-Carlo; Ion Beam Synthesis

  • Lecture (Conference)
    DPG Jahrestagung, 04.-09.03.2005, Berlin, Germany

Publ.-Id: 7497

Atomistic Computer Simulations on Ion Beam Synthesis and Decay of CoSi2 Nanowires

Röntzsch, L.; Heinig, K.-H.

Nanowires (NWs) and chains of nanocrystals (NCs) embedded in dielectrics or semiconductors are intensively studied regarding their potential application in nanoelectronics. CoSi2 nanostructures in Si are particularly interesting because of the full compatibility of CoSi2 with CMOS technology.
Here, we present predictive atomistic computer simulations on the ion beam synthesis of CoSi2 NWs in Si and their decay into chains of CoSi2 NCs which are applicable as plasmon waveguides. In order to simulate the Co implantation, the binary collision codes TRIDYN and TRIM were adapted to the particular experimental situation of a finely-focused Co ion beam of 50nm in width. The resulting 3D implantation profile serves as input for a kinetic lattice Monte-Carlo code by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are described. From an evolutionary viewpoint, NW synthesis and decay proceed on different time scales. The NW decay into a NC chain (Rayleigh instability) is driven by the minimization of interfacial free energy. In this regard, it will be demonstrated that the orientation of the Co implantation profile to the single crystalline Si matrix influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the CoSi2(111)/Si(111) interface, driving faceting forces may occur which accelerate the NW decay into a NC chain.

Keywords: Nanowire; Ion Beam Synthesis; Kinetic Monte-Carlo

  • Poster
    DPG Jahrestagung, 04.-09.03.2005, Berlin, Germany

Publ.-Id: 7496

Atomistic Computer Simulations on Synthesis and Stability of Single-crystalline Nanowires

Röntzsch, L.; Heinig, K.-H.

An abstract was not required.

Keywords: Nanowires; Stability; Kinetic Monte-Carlo

  • Lecture (others)
    Annual Meeting of the DFG Priority Program 1165: Nanowires and Nanotubes, 02.-04.05.2005, Fulda, Germany
  • Poster
    Annual Meeting of the DFG Priority Program 1165: Nanowires and Nanotubes, 02.-04.05.2005, Fulda, Germany

Publ.-Id: 7495

Ion Beam Synthesis of CoSi2 Nanowires in Si and Their Stability -– Predictions of Atomistic Computer Simulations

Röntzsch, L.; Heinig, K.-H.

Nanowires (NWs) and chains of nanocrystals (NCs) embedded in dielectrics or semiconductors are intensively studied for photonic and nanoelectronic applications. In this respect, CoSi2 NWs and NC chains are of particular interest because of their full CMOS compatibility, the low damping of surface plasmons at the CoSi2-Si interface, and the transparency of Si at the plasmon frequency.
Here, we present results of atomistic computer simulations which describe the ion beam synthesis of CoSi2 NWs in Si and their thermally activated decay into chains of CoSi2 NCs. The Co implantation is simulated with the binary collision codes TRIDYN and TRIM adapted to the particular experimental situation of a finely focused Co ion beam of a few tens of nanometers in width. The resulting 3D implantation profile serves as input for a kinetic lattice Monte-Carlo code by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are described. From an evolutionary viewpoint, NW synthesis proceeds on a shorter time scale than its decay. The NW decay into a NC chain (Rayleigh instability) is driven by the minimization of interfacial free energy. Moreover, we demonstrate that the orientation of the Co implantation profile to the single crystalline Si matrix strongly influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the CoSi2(111)-Si(111) interface, driving faceting forces may occur which accelerate the NW decay into a NC chain. Thus, intentional misalignment between the focused Co ion beam and the Si substrate is suggested as way to a controlled decay of the ion beam synthesized CoSi2 NW into a chain of monodisperse and equidistant CoSi2 NCs.

Keywords: CoSi2; Nanowires; Stability; Kinetic Monte-Carlo

  • Poster
    E-MRS spring meeting 2005, 31.05.-03.06.2005, Strausbourg, France

Publ.-Id: 7494

Ion Beam Synthesis of CoSi2 Nanowires in Si and their Stability - Predictions of Atomistic Computer Simulations

Röntzsch, L.; Heinig, K.-H.

An abstract was not required.

Keywords: Nanowire; Stability; Ion Beam Synthesis

  • Poster
    25th GIF Meeting: Nanotubes and Nanowires, 20.-23.06.2005, Dresden, Germany

Publ.-Id: 7493

Modification of the near surface layer of carbon steels with intense argon and nitrogen plasma pulses

Sartowska, B.; Piekoszewski, J.; Walis, L.; Szymczyk, W.; Stanislawski, J.; Nowicki, L.; Ratajczak, R.; Kopcewicz, M.; Kalinowska, J.; Barcz, M.; Prokert, F.; (Editors)

Series of carbon steels with various contents of carbon were irradiated with high intensity 5-6 J cm-2, short (µs range) nitrogen and argon plasma pulses. In all samples the near surface layer of the thickness in µm range was melted. The paper reports the results of investigation of changes induced by such treatment. The identified phases, profiles of retained nitrogen concentration, microhardness and wear resistance of the modified layer are presented and discussed.

Keywords: intense pulsed plasma beams; paramagnetic phases; expanded austenite; SEM; SIMS; CEMS; GXRD

  • Vacuum 78(2005)2-4, 181-186

Publ.-Id: 7492

Superconductivity of MgB2 thin films prepared by ion implantation and pulsed plasma treatment

Piekoszewski, J.; Kempinski, W.; Andrzejewski, B.; Trybula, Z.; Piekara-Sady, L.; Kaszynski, J.; Stankowski, J.; Werner, Z.; Richter, E.; Prokert, F.; Stanislawski, J.; Barlak, M.

The experiments to synthesize thin MgB2 inter-metallic compound with the use of ion implantation and plasma pulse treatment are presented. Mg was implanted with 3e18 cm-2 of 80 keV and 5e18 cm-2 of 100 keV B+ ions and next treated with hydrogen and argon plasma pulses of duration of about 1 mu s and fluence between 2 and 4 J/cm2. Superconducting properties were examined by magnetically modulated microwave absorption (MMMA), magnetic moment and electrical conductivity measurements. The structural properties of the implanted and pulse-treated samples were examined by the X-ray diffraction (XRD) and Rutherford backscattering (RBS) methods. The main result consists in observation of MMMA hysteresis loop demonstrating the existence of superconducting regions with T-c as high as 32 K. However, the zero-resistance effect has not been obtained due to incomplete global connectivity between the superconducting regions.

Keywords: MgB2 thin films; ion implantation; pulsed plasma treatment

  • Vacuum 78(2005)2-4, 123-129

Publ.-Id: 7491

Deterministic and Monte Carlo neutron transport calculation for Greifswald-1 and comparison with ex-vessel measurement data

Borodkin, G.; Khrennikov, N.; Böhmer, B.; Noack, K.; Konheiser, J.

Neutron and gamma field functionals were studied by means of deterministic Sn and stochastic Monte Carlo calculations and by neutron activation measurements that were carried out in the ex-vessel cavity of the VVER-440 reactor Greifswald-1. The paper presents and analyses the results. The influence of different numbers of energy groups for the description of the cross sections is pointed out. A good agreement was found both between the results of deterministic and Monte Carlo calculation and between numerical and measurement results.

Keywords: VVER reactors; neutron-gamma transport calculations; Sn method; Monte Carlo method; ex-vessel reactor cavity; neutron activation measurements

  • Lecture (Conference)
    12 th International Symposium on Reactor Dosimetry, 08.-13.05.2005, Gatlinburg, United States
  • Journal of ASTM International 3(2006)4
  • Contribution to proceedings
    12 th International Symposium on Reactor Dosimetry, 08.-13.05.2005, Gatlinburg, United States
    Reactor Dosimetry: 12th International Symposium, West Conshohocken: ASTM, 978-0-8031-3412-6

Publ.-Id: 7490

Laser-Induced Fluorescence Spectroscopy

Geipel, G.

Laser-Induced spectroscopic methods were often used in actinide chemistry as tool to study the speciation of these elements in aquatic environments. The main goal of the application of time-resolved laser-induced fluorescence spectroscopy (TRLFS) and laser-induced photoacoustic spectroscopy (LIPAS) is to achieve detection limits of the actinide species as low as possible or in concentration ranges expected under environmental conditions.
With laser sources can it is possible to provide any wavelength from the near UV to the NIR (Near Infrared) wavelength range. The development of tunable solid-state lasers overcame some disadvantages of the dye laser systems as short tunable wavelength range and the use of hazardous chemicals. The application of low temperatures for samples measured with fluorescence spectroscopic methods brought effort especially in the detection of carbonate species.
In this contribution the focus will be mainly on the fluorescence spectroscopy of lower actinides, as it is not possible to include all literature in this field.

Keywords: Laser-induced spectroscopy; Fluorescence; Solid state

  • Contribution to external collection
    R. Vij: The Handbook of Solid State Spectroscopy, Heidelberg: Springer Verlag, 2006, 978-0-387-32497-5

Publ.-Id: 7489

Light emission and charge trapping in Er-doped silicon dioxide films containing silicon nanocrystals - art. no. 151914

Nazarov, A.; Sun, J.; Skorupa, W.; Yankov, R.; Osiyuk, I.; Tjagulskii, I.; Lysenko, V.; Gebel, T.

The processes of electro- (EL) and photoluminescence (PL) and charge trapping in Er-implanted SiO2 containing silicon nanoclusters have been studied. It is shown that in Er-doped SiO2 with an excess of silicon nanoclusters of 10 at. %, a strong energy transfer from silicon nanoclusters results in a ten-fold increase of the PL peak at 1540 nm from Er luminescent centers, whereas the EL is strongly quenched by the excess silicon nanoclusters. It is further shown that the implantation of Er creates in the oxide positive charge traps with a giant cross section (σ(h0) > 10(-13) cm(2)). Introducing subsequent silicon nanocrystals in the oxide leads to the formation of negative charge traps of a giant cross section (σ(e0) > 10(-13) cm(2)). The possible reason for the EL quenching in the Er-doped SiO2 by silicon nanoclusters is discussed. (C) 2005 American Institute of Physics.

  • Applied Physics Letters 86(2005)15, 51914
    ISSN: 0003-6951

Publ.-Id: 7488

SIMS measurements of oxygen content in the Nd2Fe14B phase

Oswald, S.; Mazilu, I.; Fahler, S.; Gruner, W.; Hermann, R.; Loser, W.; Filip, O.; Wendrock, H.; Schultz, L.; Schmidt, B.; Rodewald, W.

The oxygen concentration in Nd-Fe-B alloy was determined with secondary ion mass spectrometry (SIMS) using Cs+-ions. The SIMS measurements were calibrated with oxygen-implanted single crystals. The depth profile of Nd2Fe14B single crystals displays a 0.5 μ m thick surface layer with elevated oxygen concentration which can be distinguished from the matrix with an oxygen content c(O) = 0.006± 0.002 at%. Polycrystalline samples can exceed this value by far and are sensitive to processing parameters and sample handling. SIMS measurements revealed the oxygen content of the Nd2Fe14B phase considerably lower than the total oxygen content of Nd-Fe-B samples. © 2004 Elsevier B.V. All rights reserved.

  • Journal of Magnetism and Magnetic Materials 290(2005)2, 1249-1242

Publ.-Id: 7487

Characterisation and comparison of Cm(III) and Eu(III) complexed with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine using EXAFS, TRFLS, and quantum chemical methods

Denecke, M. A.; Rossberg, A.; Panak, P. J.; Weigl, M.; Schimmelpfennig, B.; Geist, A.

The complexation of Cm(III) and Eu(III) with n-C3H7-BTP in non-aqueous organic solution was studied with extended X-ray absorption spectroscopy. Bond lengths are the same in both complexes. Quantum chemical calculations performed at different levels support this finding. On the other hand, the Cm•(n-C3H7-BTP)3 complex is formed at much lower metal-to-ligand concentration ratio than the Eu•(n-C3H7-BTP)3 complex, as shown by time-resolved laser-induced fluorescence spectroscopy. This is in good agreement with n-C3H7-BTP’s high selectivity for trivalent actinides over lanthanides in liquid-liquid extraction.

Keywords: in Publikation noch nicht angegeben

  • Inorganic Chemistry 44(2005), 8418-8425
    ISSN: 0020-1669

Publ.-Id: 7486

Experimental results on the fluid flow in an electromagnetically driven metallic melt

Cramer, A.; Varshney, K.; Zhang, C.

Electromagnetic processing comprises the influence of Lorentz forces in the molten state. Whereas the action of static magnetic fields is solely damping in most cases, alternating fields offer the potentiality of active control mechanisms such as pumping, stirring, homogenization, and the like. Among the latter, various field types have to be distinguished based on the number of poles and geometric arrangement. Neither for one type, and more than ever for a combination thereof, might the resulting flow tagged well known.
Numerous, often non-validated numerical simulations overwhelm the few experiments done on liquid metals. In the present work, the ultrasonic Doppler velocimetry (UDV) and local potential probes have been employed to study the flow of an alloy in single-phase, traveling, and rotating fields. The area-wide results conveyed by the UDV technique will be presented as flow visualization whereas potential probe measurements may answer questions of more quantitative nature regarding turbulence characteristics.

Keywords: Fluid flow; Liquid metal; Measuring techniques; Magnetohydrodynamics

  • Contribution to proceedings
    Electromagnetics in Materials Processing, Electromagnetic Stirring, Levitation, and Forming, 25.-28.09.2005, Pittsburgh, PA, United States, pp. 41-52
  • Lecture (Conference)
    Materials Science & Technology, 25.-28.09.2005, Pittsburgh, PA, United States

Publ.-Id: 7485

Random coincidences during in-beam PET measurements at microbunched therapeutic ion beams

Parodi, K.; Crespo, P.; Eickhoff, H.; Haberer, T.; Pawelke, J.; Schardt, D.; Enghardt, W.

At the experimental carbon ion tumour therapy facility at GSI Darmstadt, in-beam positron emissions tomography (PET) is used to monitor the dose delivery precision. A dual head positron camera has been assembled from commercial detector components in order to measure the β+-activity, induced by the irradiation, simultaneously to the dose application. Despite the positive clinical impact, the image quality is limited by the low counting statistics, orders of magnitude below that in standart PET applications to nuclear medicine. This paper investigates the origin for the noisy acquisition during particle extraction from the synchrottron of GSI. The results demonstrate the failure of standard random correction techniques due to a γ-ray background correlated in time with the carbon ion beam microstructure. This prevents the use of data acquired during beam extraction for imaging. The loss of counting statistics is expected to rise further at the future hospital-based facility at Heidelberg, due to a more efficient utilisation of the accelerator resulting in shorter beam pauses and a reduced treatment time. In respect, this paper provides the basis for a new data acquísition concept tailored to the unconventional application of in-beam PET imaging to therapy monitoring at radiofrequency pulsed radiation sources.

Keywords: Positron emission tomography; Random correction; Carbon ion therapy

  • Nuclear Instruments and Methods in Physics Research A 545(2005), 446-458

Publ.-Id: 7484

Flow control and propulsion in weak conductors

Weier, T.; Shatrov, V.; Gerbeth, G.

The subjects of electromagnetic flow control and ship propulsion are reviewed, and possibilities for further developments are sketched.

  • Magnetohydrodynamics - Historical Evolution and Trends (2007), 295-312

Publ.-Id: 7483

Velocity measurement techniques for liquid metal flows

Eckert, S.; Cramer, A.; Gerbeth, G.

The possibilities for local velocity measurements in liquid metal flows are reviewed. Special emphasis is put on local potential probes and the ultrasonic velocimetry.

  • Magnetohydrodynamics - Historical Evolution and Trends Berlin(2006), 275-294


Publ.-Id: 7482

Gefahrenpotenziale bei Grignard-Reaktionen - Sichere Betriebsführung durch Online-Monitoring

Kryk, H.; Hessel, G.; Schmitt, W.; Tefera, N.

Ausgehend von den physikochemischen Grundlagen der Grignard-Chemie werden Einflussfaktoren für eine sichere Prozessführung beschrieben. Bei Grignard-Synthesen tritt das größte Gefahrenpotential in der ersten Reaktionsstufe, der Herstellung der Grignard-Reagenz, auf. Insbesondere muss das Anspringen der Reaktion bei einer unzulässig großen Akkumulation von organischem Halogenid verhindert werden, wenn keine ausreichende, schnell wirksam werdende Kühlleistungsreserve vorhanden ist.
Vor der Überführung einer neuen Grignard-Synthese in den großtechnischen Maßstab sollten umfassende Untersuchungen der Grignard-Reaktionsstufe in Laborreaktoren durchgeführt werden. Mit Hilfe isothermer und adiabatischer kalorimetrischer Messungen konnten die wichtigsten Prozessparameter, wie molare Reaktionsenthalpie, adiabatische Temperaturerhöhung, Induktionszeit, Anstiegsgeschwindigkeit der Wärmeleistung und Dauer der Startphase, ermittelt werden. Sie sind notwendig, um die maximal zulässige Akkumulation des organischen Halogenids für die verfügbare Kühlleistung der Produktionsanlage bestimmen zu können.
Die Untersuchungen zeigten, dass gleiche Werte der molaren Reaktionsenthalpie sowohl bei isothermer als auch adiabatischer Kalorimetrie gemessen wurden. Als Ursache für die gemessenen größeren Enthalpiewerte während der isotherme Startreaktionsphase konnten noch vorhandene Wasser-Restmengen identifiziert werden, die infolge ihrer exothermen Folgereaktion mit der gebildeten Grignard-Reagenz einen zusätzlichen Wärmebeitrag lieferten. Eine Temperaturabhängigkeit der molaren Reaktionsenthalpie konnte im Temperaturbereich von 25°C bis 120°C nicht festgestellt werden.
Um subjektive Fehleinschätzungen des Anspringens der Grignard-Reaktion zu vermeiden, wurden die Anwendungsmöglichkeiten verschiedener Messmethoden zur Online-Überwachung getestet. Mit der in situ-Infrarotspektroskopie ließ sich das Anspringen der Grignard-Reaktion eindeutig und empfindlich detektieren. Ebenso könnte das spätere Einschlafen der Reaktion infolge zudosierter oder eindringender Verunreinigungen erkannt werden. Das Leistungsvermögen der Stoff- und Energiebilanzen als Methode zur Online-Überwachung konnte sowohl für die Startphase als auch für die Hauptreaktionsphase im Vergleich mit der Infrarotspektroskopie nachgewiesen werden. Die Wärmebilanzierung liefert eine viel versprechende Alternative zur in situ-Infrarotspektroskopie für den Einsatz an Produktionsanlagen, weil sie mit einer ausreichend empfindlichen Betriebsmesstechnik realisiert werden kann, quasi im Echtzeitbetrieb arbeitet und wesentlich kostengünstiger ist. Der Vorteil der in situ-Infrarotspektroskopie ist die parallele Online-Messung von störenden Wasseranteilen im Reaktionsmedium. Beispielsweise könnte das Nichtstarten der Grignard-Reaktion aufgrund von zu großen Wasserrestmengen in der Mehrzweckanlage erkannt werden. Durch geeignete Sicherheitsmaßnahmen und Sicherheitsverriegelungen sollte die Überdosierung von organischem Halogenid und das Eindringen stark exothermer Verunreinigungen (wie z. B. Wasser) während der ersten Grignard-Reaktionsstufe unbedingt verhindert werden. Aus Sicherheitsgründen sollte Wasser durch Öl als Kühlmedium möglichst ersetzt werden.

  • Technische Überwachung 46(2005)7/8, 41-47


Publ.-Id: 7481

Diffusion of Humic Acid in Clay

Mibus, J.

The impact of organic matter on the migration of actinides in argillaceous media is relevant for the risk assessment of future nuclear waste repositories. The diffusion of a 14C-labelled synthetic humic acid in compacted Georgia kaolinite and its influence on the uranium(VI) migration was studied.
The migration of humic acid in clay is governed by diffusion. The colloidal properties of humic acid result in a size exclusion from small pores. Thus the accessible pore space decreases and the tortuosity of the diffusion path increases compared to a conservative tracer. Furthermore, the compacted clay filters large humic colloids. Both effects restrict the diffusive flux of humic acid in the clay.
Diffusion experiments on the time scale of several weeks could not demonstrate a humic colloid-borne migration of uranium(VI) in the clay system. The competition of the humate and surface binding sites for uranium as well as the kinetics and reversibility of the complexation govern the actinide migration in this system.

Keywords: Diffusion; Adsorption; Humic Acid; Kaolinite; Uranium

  • Invited lecture (Conferences)
    Institutsseminar, 21.06.2005, Villigen-PSI, Switzerland

Publ.-Id: 7480

Near-field optical mapping of the ion-implanted patternsfabricated in amorphous silicon carbide

Tsvetkova, T.; Takahashi, S.; Zayats, A.; Dawson, P.; Turner, R.; Bischoff, L.; Angelov, O.; Dimova-Malinovska, D.

We propose scanning near-field optical microscopy as a novel technique for characterizing the ion-implanted patterns fabricated in amorphous silicon carbide (a-SiC:H). Different patterns have been fabricated in a-SiC:H films with a focused Ga+-ion beam system and examined with scanning near-field optical microscopy and atomic force microscopy. Although a considerable thickness change (thinning tendency) has been observed in the ion-irradiated areas, the near-field measurements confirm increases of optical absorption in these areas. The observed values of the optical contrast modulation are sufficient to justify the efficiency of the method for optical data recording using focused ion beams.

Keywords: Amorphous silicon carbide (a-SiC:H); Scanning near-field optical microscopy (SNOM); Focused ion beams (FIB); Highdensity optical data storage

  • Vacuum 79(2005), 94-99

Publ.-Id: 7479

Fabrication of nano-scale optical patterns in amorphous silicon carbide with focused ion beam writing

Tsvetkova, T.; Takahashi, S.; Zayats, A.; Dawson, P.; Turner, R.; Bischoff, L.; Angelov, O.; Dimova-Malinovska, D.

Optical patterns as small as 200nm width have been fabricated in a thin film of amorphous silicon carbide (a–SiC:H)using a focused ion beam microscope, (FIB). Because of the low electric conductivity of a–SiC:H, the diameter of the writing ion beam is broadened by the effect of surface charging which was overcome by depositing a thin layer of gold onto the a–SiC:H film. The topographic and optical contrasts of the patterned thin films have been mapped with
scanning near-field optical microscopy. The optical contrast corresponding to nanostructures is 0.2 with an overall increase of the optical density contrast of 0.5 in the irradiated areas. The results of the fabrication of patterns created with FIB on aluminium-coated a-SiC:H films are also briefly presented.

Keywords: Amorphous silicon carbide (a–SiC:H); Focused ion beam; Scanning near-field optical microscopy (SNOM); Nano-scale, optical data storage

  • Vacuum 79(2005), 100-105
  • Lecture (Conference)
    Vth International Symposium on Ion Implantation and other Applications of Ions and Electrons, 14.-17.06.2004, Kazimierz Dolny, Poland

Publ.-Id: 7478

A transient electrical model of charging for Ge nanocrystal containing gate oxides

Beyer, V.; von Borany, J.; Klimenkov, M.

The write performance of a multidot memory is investigated in MOS (metal-oxide-semiconductor) capacitors. The oxide of the MOS structure on p-type Si contains a layer of ion beam synthesized Ge nanocrystals (NC's) very close to the Si/SiO2 interface. This structure is modeled in a floating gate-like approach, where the NC's are considered as individual storage nodes and charged by direct tunneling of holes. Quantum confinement and Coulomb blockade effects of small Ge NC's (1-6 nm) are discussed and found to be negligible for the present structure. A close agreement between the calculated write characteristics and experimental data clearly confirms the validity of the model. From the simulation results it is predicted that a flatband voltage shift ΔVfb = -1V could be gathered with programming times tprog < 1µs. The write parameters (pulse voltage and duration) for a given ΔVfb value are mainly determined by the distance of the NCs' to the substrate.

Keywords: nanocrystals; MOS; Ge; memory; quantum confinement; Coulomb blockade

Publ.-Id: 7476

Influence of the substrate bias on the size and thermal stability of grains in magnetron-sputtered nanocrystalline Ag films

Almtoft, K.; Bottiger, J.; Chevallier, J.; Schell, N.; Martins, R.

The nanostructural evolution during heat treatments of DC magnetron-sputtered Ag films, deposited at room temperature at different substrate bias voltages, was experimentally studied. A growth chamber equipped with a magnetron and Kapton windows for in-situ x-ray diffraction was mounted on a six circle goniometer at a synchrotron beam line. Bragg-Brentano x-ray diffraction was used to monitor the (111) Bragg peak during thermal annealing of the Ag films. In addition, to investigate the <111> fiber texture one-dimensional pole figures were measured ex situ. The thermal stability of the nanostructure was sensitively dependent on the substrate bias voltage. Increasing the bias voltage resulted in significantly lower rates of grain growth, which we ascribe mainly to the formation of Ar bubbles. Furthermore, the grain size in the as-deposited films decreased with increasing bias voltage while the width of the one-dimensional pole figures increased.

Keywords: deposition by sputtering; crystal growth and orientation (texture development); in-situ XRD; nanophase materials : Ag

  • Journal of Materials Research 20(2005)4, 1071-1080
    ISSN: 0884-2914

Publ.-Id: 7475

Migration Case Studies and the Implications of Humic Substances for the Radiological Performance Assessment of Radioactive Waste Repositories

Bryan, N. D.; Bernhard, G.; Geipel, G.; Heise, K. H.; Schmeide, K.; Benes, P.

Abstract wird nachgereicht

Keywords: Humic acid; fulvic acid; case study

  • Contribution to external collection
    G. Buckau: Humic Substances in Performance Assessment of Nuclear Waste Disposal: Actinide and Iodine Migration, Forschungszentrum Karlsruhe: Wissenschaftliche Berichte FZKA 7070, 2005, 81-114

Publ.-Id: 7474

Measurements and Monte Carlo calculations of gamma and neutron flux spectra inside and behind iron/steel/water configurations

Boehmer, B.; Konheiser, J.; Noack, K.; Rogov, A.; Stephan, I.; Hansen, W.; Hinke, D.; Unholzer, S.; Grantz, M.; Mehner, H.-C.

Gamma and neutron flux spectra were measured inside and behind various combined iron, steel and water slabs, which were set up in the radial beams of the zero-power training and research reactors AKR of the Technical University Dresden and ZLFR of the University of Applied Sciences Zittau/Görlitz. The measurements were carried out with a liquid NE-213 scintillation spectrometer in the energy ranges 0.23-10 MeV for photons and 1-20 MeV for neutrons. These experiments were simulated with help of the Monte Carlo transport codes MCNP-4C2 and TRAMO. With MCNP the energy point-wise representation of the nuclear data from ENDF/B-VI library, release 8, was used but with TRAMO effective group cross sections prepared by means of NJOY from the same data library. The paper describes the experiments and calculations and exemplarily presents and compares some results.

Keywords: Neutron/Gamma flux spectra; NE-213 scintillation spectrometer; neutron/gamma transport calculations; Monte Carlo method; MCNP; TRAMO

  • Lecture (Conference)
    12th International Symposium on Reactor Dosimetry, 08.-13.05.2005, Gatlinburg, United States
  • Journal of ASTM International 3(2006)8
  • Contribution to proceedings
    12 th International Symposium on Reactor Dosimetry, 08.-13.05.2005, Gatlinburg, United States
    Reactor Dosimetry: 12th International Symposium, West Conshohocken: ASTM, 978-0-8031-3412-6

Publ.-Id: 7473

Bloactivity of titanium following sodium plasma immersion ion implantation and deposition

Maitz, M. F.; Poon, R. W. Y.; Liu, X. Y.; Pham, M. T.; Chu, P. K.

Bio-activation of titanium surface by Na plasma immersion ion implantation and deposition (Pllf&D) is illustrated by precipitation of calcium phosphate and cell culture. The bioactivity of the plasma-implanted titanium is compared to that of the untreated. Na beam-line implanted and NaOH-treated titanium samples. Our data show that the samples can be classified into two groups: non-bioactive (untreated titanium and beam-line Na implanted titanium) and bioactive (Na-PIII&D and NaOH-treated titanium). None of the four types of surfaces exhibited major cell toxicity as determined by lactate dehydrogenase (LDH) release. However. the LDH release was higher oil the more bioactive PIII and NaOH-treated surfaces. From a morphological point of view, cell adherence on the NaOH-treated titanium is the best. On the other hand, the cell activity and protein production were higher on the non-bioactive surfaces. The high alkaline phosphatase activity per cell Suggests that the active surfa! ces support an osteogenic differentiation of the bone marrow cells at the expense of lower proliferation. The use of Na-PIII&D provides an environmentally cleaner technology to improve the bioactivity of Ti compared to conventional wet chemical processes. The technique is also particularly useful for the uniform and conformal treatment of medical implants that typically possess an irregular shape and are difficult to treat by conventional ion beam techniques. (c) 2005 Elsevier Ltd. All rights reserved.

  • Biomaterials 26(2005)27, 5465-5473
    ISSN: 0142-9612

Publ.-Id: 7472

Observation of longitudinal optical-transverse optical splitting for E-symmetry phonons in Te by coherent phonon spectroscopy

Misochko, O. V.; Lebedev, M. V.; Dekorsy, T.

We report on the fermosecond time-resolved detection of coherent phonons in single-crystal tellurium. For different crystallographic faces a detection scheme is employed which is sensitive to the anisotropic part of the Raman tensor. In this scheme we observe all three Raman allowed phonons, i.e. one of A(1) and two of E symmetry. Furthermore, for both doubly degenerate E-symmetry modes obtained from different crystallographic faces, longitudinal optical-transverse optical splitting is observed. In addition, we show that even in the low fluence regime the frequency of the fully symmetric phonon in Te is chirped and that it demonstrates an anomalous dependence on the pump fluence.

  • Journal of Physics: Condensed Matter 17(2005)19, 3015-3023
    ISSN: 0953-8984

Publ.-Id: 7471

Verification of geometrical perturbation calculations for the pulsed fast reactor IBR-2

Noack, K.; Rogov, A.; Shabalin, E.

The IBR-2 is a small fast reactor with plutonium oxide fuel and liquid sodium cooling. A ro-tating two-reflector system periodically closes and opens a non-reflected side of the reactor and leads it through the prompt super critical state in a time of about 500 microseconds. During this time a burst of fast neutrons is generated in the core of the reactor, which spreads out through moderators. Channels lead the neutrons to measurement instruments.
Certain reactivity parameters of the rotating reflector system determine essential parameters of the reactor as a pulsed neutron source. Just now a new reflector system, the so-called PO-3, has been installed. For this reason the important reactivity effects of the reflector were newly calcu-lated with help of the MCNP-4C2 code. The contribution presents numerical results, which were obtained in different ways and compares results of calculations and measurements. The special in-terest consisted in studying the effect of neglecting the fission source effect, as assumed by the PERT option of the code, on the calculation results. The comparison of numerical with measure-ment results showed agreements in some cases but also considerable discrepancies, which could not yet be explained. Therefore, no final conclusion on the applicability of the PERT method for the calculation of total and displacement reactivity effects of the rotating reflector system of the IBR-2 reactor could be drawn.

Keywords: Pulsed fast reactor IBR-2; reactivity effect; geometrical perturbation; MCNP calculations

  • Contribution to proceedings
    Monte Carlo 2005 Topical Meeting, 17.-21.04.2005, Chattanooga, United States, 0 89448 695 0

Publ.-Id: 7470

Two-dimensional numerical simulations of Marangoni-Bénard instabilities during liquid-liquid mass transfer in a vertical gap

Grahn, A.

2D simulations of isothermal liquid-liquid mass transfer subject to surface tension and buoyancy driven hydrodynamic instabilities have been carried out. Simulation is based on the numerical solution of two-dimensional equations of momentum and mass transport, using a combination of finite difference and finite volume methods. Two different cases have been considered: (1) buoyancy stable mass transfer, only surface tension driven convection occurs; (2) surface tension driven instability superseeded by buoyant convection. The faster attenuation of mass transfer coefficients in buoyancy stable situations is attributed to the merging of convection cells leading to a reduction in the number of renewal zones along the interface. Concentration profiles next to the interface reveal the diffusional nature of the mass transfer.

Keywords: Marangoni Instability; Rayleigh-Bénard Instability; Interfacial Convection; Mass Transfer; Momentum Transfer; Simulation

Publ.-Id: 7469

Two recipies to stabilize the substrate melting in FLASiC structures

Voelskow, M.; Mücklich, A.; Stoemenos, J.; Skorupa, W.

It could be shown that both, the introduction of a melt stop layer as well as the introduction of a layer with reduced melting temperature are usefull methods for the homogenisation of the melting depth at the bulk silicon surface in FLASIC structures.

Keywords: Flash lamp annealing silicon carbide

  • Lecture (others)
    Program Seminar of the Institute of ion beam physics and material research Rossendorf, 13.-15.06.2005, Schmochtitz, BRD

Publ.-Id: 7466

Entwicklung von neuartigen, stabilen und anpassbaren Rhenium-Komplexen mit verbrückten Dimercaptobernsteinsäure-Chelatbildnern

Heinrich, T.

Wir wollen auf diese Weise äußerst stabile Stabile Komplexe darstellen in denen Re perfekt eingekapselt ist. Ein aktives Zentrum in der Brücke soll eine gerichtete WW zum Re ausbilden und die Komplexe zusätzlich stabilisieren.

  • Lecture (others)
    1. Zittauer Doktorandentag, 01.06.2005, Zittau, Deutschland

Publ.-Id: 7465

CFD-simulation of thermalhydraulic benchmark v1000ct –2

Höhne, T.; Bieder, U.; Kolev, N.

CFD pre-calculations have been performed for the themalhydraulic benchmark V1000CT-2.
The numerical grid model was generated with the grid generator IC4C (ICEM-CFD) and the preprocessor CFX-5 and contains 4.7 Mio. tetrahedral elements.The output of the Best Practice Guidelines for optimizing the numerical studies in different reactor types was used in the numerical simulation. The agreement with the Kozloduy experiment at the core inlet is very good. The results show a clear sector formation of the affected loop at the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.4%.

Keywords: PWR; CFD; Coolant Mixing

  • Lecture (Conference)
    OECD/DOE/CEA VVER-1000 Coolant Transient Benchmark - Third Workshop, 03.-07.04.2005, Garching, Germany

Publ.-Id: 7464

CFD-simulation of coolant transient benchmark v1000ct –1, exercise 3 using results of Dyn3d/Athlet coupled code calculation

Höhne, T.

Transient CFD calculations have been performed for the thermal-hydraulic benchmark V1000CT-1, exercise 3
The numerical grid model was generated with the grid generator IC4C (ICEM-CFD) and the preprocessor CFX-5 and contains 4.7 Mio. tetrahedral elements. The output of the Best Practice Guidelines for optimizing the numerical studies in different reactor types was used in the numerical simulation. Data from a coupled code calculation with DYN3D/ATHLET were used as inlet boundary conditions. 4 different Mixing Scalars were utilized to obtain information about the contribution of each loop during the transient. The results show a clear sector formation of the affected loops at the downcomer and core inlet. At the beginning of the start-up of loop 3 the sectors of loop 1,2,4 cover a bigger area.

Keywords: PWR; CFD; DYN3D; ATHLET; Coolant Mixing

  • Lecture (Conference)
    OECD/DOE/CEA VVER-1000 Coolant Transient Benchmark - Third Workshop, 03.-07.04.2005, Garching, Germany

Publ.-Id: 7463

Experimental investigation and CFD simulation of an air/water flow in a horizontal channel

Höhne, T.

The plug flow was simulated with a transient CFD simulation in the horizontal channel using time dependent inlet boundary conditions. The qualitative structure of the simulated slug front and tail are similar to the experiment, while the slug length is increasing in the calculation and remains constant in the experiment. The slug propagation velocities are in good agreement.

Keywords: slug flow; horizontal channel; CFD

  • Lecture (Conference)
    Multiphase Flows: Simulation, Experiment and Applications, 31.05.-03.06.2005, Dresden, Germany

Publ.-Id: 7462

The European project FLOMIX-R: Fluid mixing and flow distribution inthe reactor circuit - Final summary report

Rohde, U.; Höhne, T.; Kliem, S.; Scheuerer, M.; Hemström, B.; Toppila, T.; Dury, T.; Klepac, J.; Remis, J.; Mühlbauer, P.; Vyskocil, L.; Farkas, I.; Aszodi, A.; Boros, I.; Lycklama A. Nijeholt, J.-A.

The project was aimed at describing the mixing phenomena relevant for both safety analysis, particularly in steam line break and boron dilution scenarios, and mixing phenomena of interest for economical operation and the structural integrity. Measurement data from a set of mixing experiments, gained by using advanced measurement techniques with enhanced resolution in time and space help to improve the basic understanding of turbulent mixing and to provide data for Computational Fluid Dynamics (CFD) code validation. Slug mixing tests simulating the start-up of the first main circulation pump are performed with two 1:5 scaled facilities: The Rossendorf coolant mixing model ROCOM and the VATTENFALL test facility, modelling a German Konvoi type and a Westinghouse type three-loop PWR, respectively. Additional data on slug mixing in a VVER-1000 type reactor gained at a 1:5 scaled metal mock-up at EDO Gidropress are provided. Experimental results on mixing of fluids with density differences obtained at ROCOM and the FORTUM PTS test facility are made available.
Concerning mixing phenomena of interest for operational issues and thermal fatigue, flow distribution data available from commissioning tests (Sizewell-B for PWRs, Loviisa and Paks for VVERs) are used together with the data from the ROCOM facility as a basis for the flow distribution studies. The test matrix on flow distribution and steady state mixing performed at ROCOM comprises experiments with various combinations of running pumps and various mass flow rates in the working loops.
Computational fluid dynamics calculations are accomplished for selected experiments with two different CFD codes (CFX-5, FLUENT). Best practice guidelines (BPG) are applied in all CFD work when choosing computational grid, time step, turbulence models, modelling of internal geometry, boundary conditions, numerical schemes and convergence criteria. The BPG contain a set of systematic procedures for quantifying and reducing numerical errors. The knowledge of these numerical errors is a prerequisite for the proper judgement of model errors. The strategy of code validation based on the BPG and a matrix of CFD code validation calculations have been elaborated. Besides of the benchmark cases, additional experiments were calculated by new partners and observers, joining the project later.
Based on the “best practice solutions”, conclusions on the applicability of CFD for turbulent mixing problems in PWR were drawn and recommendations on CFD modelling were given. The high importance of proper grid generation was outlined. In general, second order discretization schemes should be used to minimise numerical diffusion. First order schemes can provide physically wrong results. With optimised “production meshes” reasonable results were obtained, but due to the complex geometry of the flow domains, no fully grid independent solutions were achieved. Therefore, with respect to turbulence models, no final conclusions can be given. However, first order turbulence models like K-e or SST K-w are suitable for momentum driven slug mixing. For buoyancy driven mixing (PTS scenarios), Reynolds stress models provide better results.

Keywords: turbulent mixing; flow distribution; nuclear reactors; experimental data base; computational fluid dynamics; best practice guidelines

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-432 2005
    ISSN: 1437-322X


Publ.-Id: 7461

The European project FLOMIX-R: Description of the experimental and numerical studies of flow distribution in the reactor primary circuit(Final report on WP 3)

Toppila, T.; Höhne, T.; Kliem, S.; Elter, J.; Remis, J.; Klepac, J.; Farkas, I.; Aszodi, A.; Boros, I.

The flow distribution in the primary circuit of the pressurized water reactor was studied with experiments and Computational Fluid Dynamics (CFD) simulations. The main focus was on the flow field and mixing in the downcomer of the pressure vessel: how the different factors like the orientation of operating loops, the total loop flow rate and the asymmetry of the loop flow rates affect the outcome. In addition to the flow field studies the overall applicability of CFD methods for primary circuit thermal-hydraulic analysis was evaluated based on the CFD simulations of the mixing experiments of the ROCOM (Rossendorf Coolant Mixing Model) test facility and the mixing experiments of the Paks NPP.
The experimental part of the work in work package 3 included series of steady state mixing experiments with the ROCOM test facility and the publication of results of Paks VVER-440 NPP thermal mixing experiments. The ROCOM test facility models a 4-loop KONVOI type reactor. In the steady-state mixing experiments the velocity field in the downcomer was measured using laser Doppler anemometry and the concentration of the tracer solution fed from one loop was measured at the downcomer and at the core inlet plane. The varied parameters were the number and orientation of the operating loops, the total flow rate and the (asymmetric) flow rate of individual loops.
The Paks NPP thermal mixing experiments took place during commissioning tests of replaced steam generator safety valves in 1987-1989. It was assumed that in the reactor vessels of Paks VVER-440 NPP equipped with six loops the mixing of the coolant is not ideal. For the realistic determination of the active core inlet temperature field for the transients and accidents associated with different level temperature asymmetry a set of mixing factors were determined. Based on data from the online core monitoring system and a separate mathematical model the mixing factors for loop flows at the core inlet were determined.

In the numerical simulation part of the work package 3 the detailed measurements of ROCOM tests were used for the validation of CFD methods for primary circuit studies. The selected steady state mixing experiments were simulated with CFD codes CFX-4, CFX-5 and FLUENT. The velocity field in the downcomer and the mixing of the scalar were compared between CFD simulations and experiments. The CFD simulations of full scale PWR included the simulation of Paks VVER-440 mixing experiment and the simulation of Loviisa VVER-440 downcomer flow field. In the simulations of Paks experiments the experimental and simulated concentration field at the core inlet were compared and conclusions made concerning the results overall and the VVER-440 specific geometry modelling aspects like how to model the perforated elliptic bottom plate and what is the effect of the cold leg bends to the flow field entering to the downcomer. With Loviisa simulations the qualitative comparison was made against the original commissioning experiments but the emphasis was on the CFD method validation and testing.

The overall conclusion concerning the CFD modelling of the flow field and mixing in the PWR primary circuit could be that the current computation capacity and physical models also in commercial codes is beginning to be sufficient for simulations giving reliable and useful results for many real primary circuit applications. However the misuse of CFD methods is easy, and the general as well as the nuclear power specific modelling guidelines should be followed when the CFD simulations are made.

Keywords: fluid mixing; flow distribution; velocity filed; nuclear power plant; commissioning experiments; experimental data base; computational fluid dynamics

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-431 2005
    ISSN: 1437-322X


Publ.-Id: 7460

The European project FLOMIX-R: Description of the slug mixing and buoyancy related experiments at the different test facilities(Final report on WP 2)

Rohde, U.; Kliem, S.; Hemström, B.; Toppila, T.; Bezrukov, Y.

The goal of the work described in this report was the experimental investigation of the mixing of coolant with different quality (temperature, boron concentration) in nuclear reactors on the way from the cold leg through the downcomer and lower plenum to the core inlet in a systematic way. The obtained data were used for the clarification of the mixing mechanisms and form a data basis for the validation of computational fluid dynamics (CFD) codes.
For these purposes, experiments on slug mixing have been performed at two test facilities, modelling different reactor types in scale 1:5, the Rossendorf and Vattenfall test facilities. The corresponding accident scenario is the start-up of first main coolant pump (MCP) after formation of a slug of lower borated water during the reflux-condenser mode phase of a small break loss of coolant accident (LOCA). The matrices for the experiments were elaborated on the basis of the key phenomena, being responsible for the coolant mixing during pump start-up. Slug mixing tests have also been performed at the VVER-1000 facility of EDO Gidropress to meet the specifics of this reactor type.
The mixing of slugs of water of different quality is also very important for pre-stressed thermal shock (PTS) situations. In emergency core cooling (ECC) situations after a LOCA, cold ECC water is injected into the hot water in the cold leg and downcomer. Due to the large temperature differences, thermal shocks are induced at the reactor pressure vessel (RPV) wall. Temperature distributions near the wall and temperature gradients in time are important to be known for the assessment of thermal stresses.
One of the important phenomena in connection with PTS is thermal stratification, a flow condition with a vertical temperature profile in a horizontal pipe. Due to the fluctuating character of the flow, this may cause thermal fatigue in the pipe. Besides of thermal fatigue, a single thermal shock can also be relevant for structural integrity, if it is large enough, especially in the case, that the brittle fracture temperature of the RPV material is reduced due to radiation embrittlement. Therefore, additional to the investigations of slug mixing during re-start of coolant circulation, the mixing of slugs or streams of water with higher density with the ambient fluid in the RPV was investigated. The aim of these investigations was to study the process of turbulent mixing under the influence of buoyancy forces caused by the temperature differences. Heat transfer to the wall and thermal conductivity in the wall material have not been considered.
Experiments on density driven mixing were carried out at the Rossendorf and the Fortum PTS facilities.

Keywords: turbulent mixing; slug mixing; boron dilution; buoyancy controled mixing; pressurised thermal shock; nuclear reactors; experimental data base

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-430 2005
    ISSN: 1437-322X


Publ.-Id: 7459

Axial RF power input into photocathode electron guns

Janssen, D.; Volkov, V.; Bluem, H. P.; Todd, A. M. M.

We discuss the coaxial power input in normal and superconducting RF (SRF) photoinjector cavities. Upstream coaxial power input has been previously used at the PITZ facility where the output beam tube is an intrinsic part of the coaxial transmission line into the gun. In this paper, we describe coaxial coupling from the cathode side of the gun. For normal conducting RF guns, in addition to the advantage from symmetric coupling, an emittance compensation solenoid can now be positioned close to the gun cavity to deliver optimal transverse emittance. Beam dynamics calculations demonstrate 0.8 mm-mrad at 1 nC in X-band. For an SRF gun, we present a design for coaxial input around the cathode using a superconducting coupling cell. This cell matches the external quality factor of the gun for different beam powers and there is no RF loss associated with the axial gap of the cathode. The heat input into the coaxial feed and the surface field of the coupler are discussed. For a 1.3 GHz half-cell gun cavity with stored energy of 6.6 J, a 2.5 MeV electron beam can be delivered with a peak accelerating field of 50 MV/m. At 10 mA, the external Q is 2.1 x 106 and the coaxial line power loss that must be cooled is 28 W.

  • Lecture (Conference)
    PAC Particle Accelerator Conference 2005, 16.-21.05.2005, Knoxville, TN, USA
  • Contribution to proceedings
    Particle Accelerator Conference 2005, 16.-20.05.2005, Knoxville, Tennessee, USA
    Proceedings of 2005 Particle Accelerator Conference, MOPB011, ISBN 0-7803-8860-7, 743-745

Publ.-Id: 7458

Third order spectral branch points in Krein space related setups: PT-symmetric matrix toy model, MHD α²-dynamo, and extended Squire equation

Günther, U.; Stefani, F.

The spectra of self-adjoint operators in Krein spaces are known to possess real sectors as well as sectors of pair-wise complex conjugate eigenvalues. Transitions from one spectral sector to the other are a rather generic feature and they usually occur at exceptional points of square root branching type. For certain parameter configurations two or more such exceptional points may happen to coalesce and to form a higher order branch point. We study the coalescence of two square root branch points semi-analytically for a PT-symmetric 4×4 matrix toy model and illustrate numerically its occurrence in the spectrum of the 2×2 operator matrix of the magnetohydrodynamic α²-dynamo and of an extended version of the hydrodynamic Squire equation.

Keywords: non-Hermitian operators; discrete symmetries; Krein space; level crossings; branch points; Jordan structure; MHD dynamo; Squire equation

Publ.-Id: 7457

Dynamo experiments

Gailitis, A.; Lielausis, O.; Gerbeth, G.; Stefani, F.

The long history of laboratory experiments on homogeneous dynamo action is delineated. It is worked out what sort of insight can be expected from experiments, and what not. Special focus is laid on the principle and the main results of the Riga dynamo experiment which is shown to represent a genuine hydromagnetic dynamo with a non-trivial saturation mechanism that relies mainly on the fluidity of the electrically conducting medium.

  • Magnetohydrodynamics - Historical Evolution and Trends Berlin(2006), 37-54


Publ.-Id: 7456

Response of drinking-water reservoir ecosystems to decreased acidic atmospheric deposition in central Europe II. Signs of biological recovery

Meybohm, A.; Ulrich, K.-U.

Strongly decreasing atmospheric emissions and acidic depositions during the 1990s have caused a chemical reversal from acidification in several drinking-water reservoirs of the Ore Mountains, SE Germany. Responses of phytoplankton, zooplankton, and fish stock were studied in five reservoirs and in enclosure scale where a water body of 1,200 m3 was experimentally neutralized by application of a new buffering substance. Three months after this treatment, the dominating chrysophytes and dinoflagellates were substituted by diatoms and cryptomonades. The colonization by acidic-sensitive species of green algae, cryptomonades, rotifers, and Cladocera (e.g. Bosmina longirostris) is explained by the occurrence of dormant stages or by survival of individuals in very low abundances. In conformity with the enclosure experiment, three reservoirs showed significantly (p<0.01) falling trends of chlorophyll a and phytoplankton biovolume, mainly due to the decline of dinoflagellates. Picoplankton and diatoms slightly increased in two reservoirs. The zooplankton biocoenosis was dominated by rotifers and small cladocera, the genus Daphnia was still lacking. Two reservoirs were re-colonized by zooplanktivorous fish populations of either perch (Perca fluviatilis) or sunbleak (Leucaspius delineatus). The latter exhibited extremely high fluctuating abundance and biomass and even suffered from a population crash. This natural mortality was caused by limited food supply. Hence, severe top-down control may delay the recovery of bigger zooplankton species like daphnids. Fishery management comprising the introduction of predatory fishes could help to control zooplanktivorous fish populations and to prevent their mass mortality.

Keywords: acidification reversal; enclosure experiment; fish stock; phytoplankton; recovery; reservoir ecosystem; zooplankton

Publ.-Id: 7455

The usefulness of radiotracers to make the body biochemically transparent

Johannsen, B.

Radioactive isotopes are uniquely applicable to observe reactions or circuits of reactions at the molecular level without disturbing the system being studied. The advent of molecular imaging modalities, particularly positron emission tomography (PET), is a major breakthrough for the visualisation and quantitative assessment of cellular and molecular processes occurring in living tissues. The recent development of animal PET scanners that offers 2-mm resolution and is tailored to laboratory rodents, has made a further great impact on in vivo biochemistry. With these live-imaging modalities at hand, radiotracer-based technologies allow to look directly at biochemical distribution and interaction processes. Tremendous progress made in radiotracer chemistry, primarily in carbon-11 and fluorine-18 radiochemistry, and in the design of imaging devices strengthens the usefulness of radiotracers in nuclear medicine and drug research and development and opens exciting opportunities for new applications, e.g. in food science.

Keywords: Radiotracer; Positron emission tomographie; Molecular imaging

Publ.-Id: 7454

Control of properties and structure of ZnO thin films by a wide variation of oxygenpressure during reactive magnetron deposition and by post-deposition annealing

Vinnichenko, M.; Poperenko, L.; Lebyedyeva, T.; Shpylovyy, P.; Shevchenko, N.; Rogozin, A.; Sudovtsova, V.; Kolitsch, A.; Möller, W.

Due to recent progress in crystal growth and unique optical and electrical properties ZnO becomes a prospective material for use in optoelectronic devices. ZnO thin films have been prepared at unheated glass substrates by reactive DC magnetron sputtering. The oxygen fraction in Ar + O2 gas mixture was varied from 0 to approximately 83%. The films have been characterized by spectroscopic ellipsometry (SE), atomic force microscopy (AFM) and X-ray diffraction (XRD). The dielectric function of ZnO layers was parameterized using Drude-Lorentz oscillator. As shown by SE, the dielectric functions of the films prepared at low oxygen fraction are characteristic for cermet materials (mixture of oxide and metal particles). XRD confirms the presence of both ZnO and metallic Zn phases in these films. The layers produced at high oxygen fractions (above 60%) are insulating and their dielectric functions can be reasonably described by Lorentz oscillator alone. Importantly, that the latter films are polycrystalline with pronounced (002) type texture even at a thickness of only 50 nm. The XRD results point to a high mechanical stress in these films that can be related to the bombardment by negative oxygen ions during the film growth.
ZnO films prepared at medium oxygen fraction of 48% were annealed in vacuum at about 340 °C for 1.5 hour with in situ control of optical properties by SE and resistivity by two point probe measurement. The influence of the structural ordering during annealing on the refractive index is higher than the free electron density variation. An enhancement of the film resistivity at the final annealing stage (last 40 min) with concomitant decrease of the free electron concentration could be an indication of the acceptor-like defect formation.

Keywords: ZnO; reactive DC magnetron sputering; spectroscopic ellipsometry; optical properties

  • Poster
    European Materials Research Society Spring Meeting (E-MRS), Symposium G: ZnO and related materials, 31.05.-03.06.2005, Strasbourg, France

Publ.-Id: 7453

Near-infrared intersubband transitions in InGaAs–AlAs–InAlAs double quantum wells

Semtsiv, M.; Ziegler, M.; Masselink, W. T.; Georgiev, N.; Dekorsy, T.; Helm, M.

Intersubband optical transitions at short wavelengths in strain-compensated In0.70Ga0.30As—AlAs double quantum wells are investigated by means of mid-infrared absorption. Trade-offs between achieving a high transition energy and a large oscillator strength of the two highest-energy intersubband transitions using our strain-compensation approach are analyzed as a function of the widths of the two wells. Two design strategies leading to relatively strong intersubband optical transitions at 800 meV, 1.55 µm, are described and the corresponding structures grown using gas-source molecular-beam epitaxy on (001)InP are investigated. The strongest intersubband transitions obtained experimentally are generally between 300 and 600 meV, 2–4 µm. Significant oscillator strength, however, also extends out to 800 meV, 1.55 µm.

Keywords: intersubband transition; quantum well; infrared

Publ.-Id: 7452

Biocere mit spezifischer Metallbindungsaktivität

Raff, J.

Thema: Entwicklung und Testung einer neuen Klasse hybrider keramischen Funktionswerkstoffe (Biocere), die als schwermetallbindende Filtermaterialien oder als Immobilisierungsmatrix für lebende Zellen in der Umwelt- und Biotechnologie genutzt werden können.

  • Other report
    Abschlussbericht zum DFG-Förderprojekt SE 671/7-2: Berichtszeitraum: 01.10.2002 - 30.09.2004, 2005
    35 Seiten

Publ.-Id: 7451

Spatial dynamics of MSRE

Krepel, J.; Rohde, U.; Grundmann, U.; Weiss, F.-P.

The paper report about spatial dynamics studies of the Molten Salt Reactors (MSR). MSR is one of the concepts considered within the 'Generation IV International Forum'. The graphite-moderated channel type MSR based on the previous Oak Ridge National Laboratory (ORNL) research is considered.
The physical models and numerical solution procedures used in the dynamics code DYN3D-MSR are described. The most relevant peculiarities in MSR dynamics are the delayed neutrons precursors drift with the flowing fuel and the direct release of fission energy into the fuel-coolant salt. The code is based on the in-house developed code DYN3D for Light Water Reactor, which solves two-group neutron diffusion equations by the help of a nodal expansion method. The same method for prompt neutron kinetics is used in DYN3D-MSR, but the appropriate models for the delayed neutrons and for the thermal-hydraulic have been integrated.
The code has been validated against experimental data gained from the Molten Salt Reactor Experiment (MSRE), performed in the ORNL. After successful validation, the code DYN3D-MSR was applied to the analysis of several hypothetical transients typical for liquid fuel systems. Particularly, a prompt reactivity insertion modeling a control rod ejection accident was analyzed. By performing these analyses, the DYN3D-MSR code has been shown to be an effective tool for MSR dynamics studies.

Keywords: MSR; MSRE; spatial; dynamics; 3D; molten; salt; reactor

  • Lecture (Conference)
    ICONE 13 - 13th International Conference on Nuclear Engineering, 16.-20.05.2005, Beijing, China
  • Contribution to proceedings
    13th International Conference on Nuclear Engineering, 16.-20.05.2005, Beijing, China
    Proceedings of 13th International Conference on Nuclear Engineering

Publ.-Id: 7449

Annual Report 2004 - Institute of Nuclear and Hadron Physics

Enghardt, W.; Fahmy, K.; Grosse, E.; Kämpfer, B.; Schneidereit, C.; Wagner, A.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-423 2005
    ISSN: 1437-322X


Publ.-Id: 7448

The influence of a poly-Si intermediate layer on the crystallization behaviour of Ni-Ti SMA magnetron sputtered thin films

Martins, R. M. S.; Braz Fernandez, F. M.; Silva, R. J. C.; Pereira, R. J. C.; Gordo, P. R.; Maneira, M. J. P.; Beckers, M.; Mücklich, A.; Schell, N.

Ni-Ti thin films as-sputtered are amorphous if the substrate is not intentionally heated during deposition. Therefore, these films have to be heat-treated to induce crystallization in order to exhibit the shape memory effect. Several films have been prepared by dc magnetron sputtering and then studied concerning the influence of the type of substrate (single crystal Si, polycrystalline Si) on the crystallization kinetics and the final structure. The structural development of the films during crystallization (at a constant temperature of 430°C) has been studied by X-ray diffraction in grazing incidence geometry (GID) off-plane at a synchrotron radiation beamline. These experiments allow to establish a correlation between the deposition conditions and the kinetics of crystallization. For films deposited at an electrode distance of 70 mm on a Si(100) substrate, a longer crystallization time is needed compared with films obtained at 40 mm, for otherwise fixed deposition parameters. The analysis of the nucleation kinetics by using the Kolmogorov-Johson-Mehl-Avrami equation lead to exponents between 2.6 and 3. The presence of an intermediate layer of poly-Si drastically enhances the crystallization process. Additionally, ex-situ annealing of identical samples at 500°C during 1 hour and complementary characterization of the structure and morphology of the films by Cross-sectional Transmission Electron Microscopy (XTEM) and Selected Area Electron Diffraction (SAED) were performed. The temperature dependence of the electrical resistivity was measured, identifying the phase transformation temperature ranges. An increase of the overall resistivity with the precipitation of Ni4Ti3 has been detected. Results obtained by X-ray reflectometry (XRR) and GID suggest that during crystallization excess nickel is driven into an amorphous region ahead of the crystal/amorphous interface, thus leading to a higher concentration of Ni at the surface and further precipitation of Ni4Ti3. t the shape memory effect. Several films have been prepared by dc magnetron sputtering and then studied concerning the influence of the type of substrate (single crystal Si, polycrystalline Si) on the crystallization kinetics and the final structure. The structural development of the films during crystallization (at a constant temperature of 430°C) has been studied by X-ray diffraction in grazing incidence geometry (GID) off-plane at a synchrotron radiation beamline. These experiments allow to establish a correlation between the deposition conditions and the kinetics of crystallization. For films deposited at an electrode distance of 70 mm on a Si(100) substrate, a longer crystallization time is needed compared with films obtained at 40 mm, for otherwise fixed deposition parameters. The analysis of the nucleation kinetics by using the Kolmogorov-Johson-Mehl-Avrami equation lead to exponents between 2.6 and 3. The presence of an intermediate layer of poly-Si drastically enhances the crystallization process. Additionally, ex-situ annealing of identical samples at 500°C during 1 hour and complementary characterization of the structure and morphology of the films by Cross-sectional Transmission Electron Microscopy (XTEM) and Selected Area Electron Diffraction (SAED) were performed. The temperature dependence of the electrical resistivity was measured, identifying the phase transformation temperature ranges. An increase of the overall resistivity with the precipitation of Ni4Ti3 has been detected. Results obtained by X-ray reflectometry (XRR) and GID suggest that during crystallization excess nickel is driven into an amorphous region ahead of the crystal/amorphous interface, thus leading to a higher concentration of Ni at the surface and further precipitation of Ni4Ti3.

Keywords: Deposition by sputtering, X-ray diffraction; Structure and morphology; thickness; crystalline orientation and texture

Publ.-Id: 7447

A comparative study of the electrical properties of heavily Al implanted, single crystalline and nanocrystalline SiC

Heera, V.; Madhusoodanan, K. N.; Skorupa, W.; Dubois, C.; Romanus, H.

The electrical properties of heavily Al doped single and nanocrystalline 4H-SiC layers on semi-insulating 4H-SiC substrate, prepared by multi-energy, high-fluence Al implantation and subsequent furnace annealing, are investigated by sheet resistance and Hall effect measurements. Ion beam induced crystallization is used to prepare the nanocrystalline SiC layers. The doping levels are chosen around the solid solubility limit of 2x1020 cm-3 in the range from 5x1019 to 1.5x1021 cm-3. The comparison of the results shows that heavily Al doped single crystalline SiC layers have superior conduction properties. The lowest resistivities measured at room temperature are 0.07 Ohm-cm and 0.8 Ohm-cm for the single crystalline and nanocrystalline samples, respectively. Recent results on enhanced Al acceptor activation in nanocrystalline SiC cannot be confirmed. There is an upper limit for the hole concentration in the nanocrystalline samples independent of the Al supersaturation level in the as-implanted state due to outdiffusion of Al in excess to the solid solubility limit during annealing. In contrast to the nanocrystalline SiC layers the as-implanted Al profile in single crystalline material remains stable after annealing even for concentrations above the solid solubility limit. Therefore, in single crystalline material efficient impurity band conduction due to strongly interacting acceptors can be achieved in the range of supersaturation. For lower doping levels impurity band conduction is more effective in nanocrystalline SiC.

Keywords: SiC; nanocrystalline; p-type doping; ion implantation; Hall effect

  • Journal of Applied Physics 99(2006)15, 123716-1-123716-8


Publ.-Id: 7446

Atomistic study of intrinsic defects in Germanium

Geßner, H.; Posselt, M.

Since high-k insulators appear more and more to be preferable to SiO2 in semiconductor technology, Ge is again becoming of increasing interest, since its carrier mobility is higher than that of Si. Atomistic simulations are a powerful tool to investigate atomic-level physics and to get a better understanding of the processes during the technological steps in integrated electronic device manufacturing.
In the present work different interatomic potentials for Ge are evaluated with respect to their accuracy in describing the structure and energetics as well as the migration of point defects. A number of parameterizations of the Stillinger-Weber (SW) potential and one Tersoff type potential were tested.
The formation energies for different configurations of the interstitial are calculated. Also the formation energy of the vacancy and the bond defect are estimated. It can be shown that the extended 110-dumbbell configuration is the interstitial with the lowest formation energy for most SW parameter sets. In the Tersoff case the tetrahedral interstitial shows the lowest formation energy. For the SW-type potentials the vacancy shows a strong inward-distortion, whereas for the Tersoff potential it shows a slight outwards-distortion.
In recent ab-initio calculations the 110 dumbbell has been found to be the most stable interstitial structure. This is in qualitative agreement with the results for most SW parameter sets, although these calculations predict the extended dumbbell configuration as the interstitial with the lowest formation energy. For the SW parameter sets of W. Yu (model B) and Nordlund, the formation energy of this dumbbell is also in qualitative agreement with the ab-initio result. The formation energy of the vacancy obtained with these SW parameter sets is nearly equal to the ab-initio result. The observed inwards relaxation of the atoms around the vacancy is also found by ab-initio calculations. However, the details of the lattice distortion near the vacancy and the interstitial differ from those predicted by ab-initio calculations.
For the reasons mentioned above, the SW parameter sets of Nordlund et al. and W. Yu et al. are selected for migration investigations. In both cases the vacancy mobility strongly dominates interstitial mobility. Some investigations are also performed with the Tersoff potential, where the vacancy shows a very low mobility.
The results are used to estimate the self-diffusion coefficient. With the SW approach it is shown that self-diffusion in Ge is mediated by vacancies. This stands in good agreement with experimental data. However, the calculated migration energy (2.2 eV) is less than the measured value (3.09 eV). With the Tersoff potential an interstitial dominated mechanism is found. Therefore the Tersoff potential cannot be considered useful for a study of point defect and self-diffusion in Ge.

Keywords: defects; computer simulation; germanium

  • Poster
    E-MRS 2005 Spring Meeting, 31.05.-03.06.2005, Strasbourg, France

Publ.-Id: 7445

Simulation of phase transfer in case of bubbly steam-water flow along a large vertical pipe

Lucas, D.; Prasser, H.-M.

Detailed experimental data obtained at the TOPFLOW facility for steam-water vertical pipe flow were used to test the complex interaction of local bubble distributions, bubble size distributions and local heat and mass transfer. Steam is injected into sub-cooled water and condenses during the upwards flow. The model considers a large number of bubble classes (50). This allows the investigation of the influence of the bubble size distribution. The results of the simulations show a good agreement with the experimental data. The condensation process is clearly slower, if large bubbles are injected (4 mm holes). Also bubble break-up has a strong influence on the condensation process because of the change of the interfacial area. Some unsureness arises from the unknown interfacial area for large bubbles and possible uncertainties of the heat transfer coefficient.

Keywords: bubbly flow; phase transfer; bubble size distribution; vertical pipe flow

  • Contribution to proceedings
    4th International Conference on transport phenomena in multiphase systems, 26.-30.06.2005, Gdansk, Poland
    Proceedings, Gdansk, Poland: IFFM Publishers, 83-88237-90-X, 345-350
  • Lecture (Conference)
    4th International Conference on transport phenomena in multiphase systems, 26.-30.06.2005, Gdansk, Poland

Publ.-Id: 7444

Simulation of bubble condensation with a multi-bubble size class model

Lucas, D.; Prasser, H.-M.

Experimental data obtained at the TOPFLOW facility for steam-water vertical pipe flow were used to test the complex interaction of local bubble distributions, bubble size distributions and local heat and mass transfer. Steam is injected into sub-cooled water and condenses during the upwards flow. The model considers a large number of bubble classes (50). This allows the investigation of the influence of the bubble size distribution. The results of the simulations show a good agreement with the experimental data. The condensation process clearly depends on the initial bubble size. Also bubble break-up has a strong influence on the condensation process because of the change of the interfacial area.

Keywords: bubbly flow; phase transfer; bubble size distribution; vertical pipe flow; condensation

  • Lecture (Conference)
    Workshop on Multi-Phase Flow: Simulation, Experiment and Application, Rossendorf, 31 May - 3 June 20, 31.05.-03.06.2005, Dresden, Germany

Publ.-Id: 7443

Experimental investigation of rotating magnetic field driven flow by highly sensitive potential probe measurements

Cramer, A.; Gundrum, T.; Varshney, K.; Gerbeth, G.

Electric potential difference probes (PDP) are mostly applied on laboratory scale to measure local velocities in electrically conducting media. Their principle of operation is based on Ohms law. In the absence of electric currents, and provided a proper orthogonal arrangement, the voltage drop measured between the two electrodes is proportional to the fluids velocity. The measuring magnetic field may be applied globally or by a small permanent magnet at the very tip of the Sensor (VIVES--probe). A typical probe as described in the original work has an electrode spacing of 5 mm while using relatively large CoSm magnets. Because the electrodes are usually mounted on the side of the magnet where the field is weaker, the authors were limited to measure velocities down to 1 cm/s at U =1 mV. They specified a sensitivity of 1 mm/s.

Along with progress in analog electronics, results have recently been published by (GELFGAT) who reported on an increased sensitivity of almost an order of magnitude even for a smaller probe. As stated by the the authors, all measurements were conducted at least five times comprising 200 readings, each. From this averaging it becomes obvious that turbulence measurements have not been possible. The subject of this investigation was the flow driven by a rotating magnetic field (RMF), which may be characterised by the aspect ratio and the magnetic Taylor number.

In the present paper, it is described how the applicable range of PDPs regarding sensitivity can be increased further by about two orders of magnitude. An extremely low-noise preamplifier served as a basis of a multistage measuring chain consisting of another two amplifiers and steep
Butterworth filters. For the differential signal processing required for such small voltages as a few nanovolt it was vital to provide a proper common mode rejection throughout the whole instrumental chain. Since acquisition of velocity fluctuations does not allow any averaging or even the use of integrating amplifiers, potential sources of statistical errors had to be avoided. In particular, the electromagnetic noise was countered by a sophisticated wiring scheme. Systematic errors such as thermoelectric currents are detrimental to the measurement of very small mean velocities. Meticulously avoiding both temperature differences and gradients of Seebeck coefficients, it was possible to reduce thermoelectrical voltages below the velocity signal level.

RMF-driven flows comprise a secondary recirculation in the meridional plane. According to theory, the change-over from a Stokes regime to a laminar boundary one of the primary swirl takes place at a Taylor number of approx. 1000, accompanied by a change of the linear scaling (velocity versus Taylor number) to a power 2/3 characteristic. A sensitivity of 0.01 mm/s permitted to safely determine mean velocities for Taylor numbers commencing with 31.

Besides sensitivity and accuracy, measurements of turbulent velocity fluctuations put a severe
restriction on the size of the sensor in order to resolve all scales of potentially significant vortices. The high sensitivity described above was achieved substantially by state of the art analog instrumentation while the dimensions of the probe were quite small. Having an induction
of 75 mT at the tips of the electrodes, their spacing of 1 mm delivered a signal of 180 nV per cm/s, only. Nevertheless, the performance of the measuring chain allowed for the acquisition of
velocity fluctuations even in the transitional regime slightly above the critical Taylor number. The wavenumber spectra calculated via Taylors hypothesis were well resolved up to the end of the inertial range and showed a steep decrease with an exponent less than 4.

  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    Proceedings 2(2005), 337-340
  • Poster
    Joint 15th Riga and 6th PAMIR Interantional Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia

Publ.-Id: 7442

Float-zone crystal growth with a novel melt flow control

Priede, J.; Gerbeth, G.; Hermann, R.; Behr, G.

We consider the growth of single crystals by the floating-zone method using a radio frequency (RF) heating magnetic field. The quality of the grown crystals, especially of complicated intermetallic compounds, strongly depends on the growth conditions, particularly on the shape of the solidification front. To obtain single crystals of high physical and chemical precision, a convex to the melt growth interface is desirable. The shape of the solid-liquid interface can strongly be influenced by the convective heat transport in the melt. The major mechanism driving the melt flow is the electromagnetic force due to the RF-heating. This force drives a melt flow directed radially inwards at mid-height of the floating zone. Favourable growth conditions, however, would require the flow to be directed away from the solidification front at the axis of symmetry and, respectively, to be directed against it at the free surface of the floating zone. This flow can be generated by an electromagnetic force directed along the free surface towards the solidification front.
We developed the solution of a two-phase stirrer which allows a flexible control of the melt motion. This stirrer basically consists in an additional coil superimposed to the primary induction coil. The additional coil is not connected to any power supply, but it is part of a secondary circuit with adjustable capacitor and resistance. The current in the secondary coil is solely induced by the primary coil. In that way, an electromagnetic pump is created. Its intensity and resulting flow direction can easily be adjusted to the process needs. The flexible system parameter are the location and distance of the secondary coil with respect to the primary one, and the capacitor and resistance of the secondary circuit.
We present numerical and experimental results for the melt flow and temperature fields resulting from the influence of such a two-phase stirrer. Ni-based single crystals as well as various intermetallic compounds have been grown, and the obtained results are discussed in relation to the provided flow control.

  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    2(2005), 189-192

Publ.-Id: 7441

On magnetohydrodynamic drag reduction and its efficiency

Shatrov, V.; Gerbeth, G.

Recently various drag reduction techniques were studied numerically and experimentally in many papers. Among others there is the subtopic of magnetohydrodynamic (MHD) drag reduction where the Lorentz force is used for the purpose of drag reduction in an electrically conducting fluid. In many recently published papers permanent magnets and high electric current densities are used in order to achieve reasonable Lorentz forces. This choice, however, immediately leads to a low efficiency.
We consider a plane channel as the flow configuration. Here, the fully developed turbulent channel flow is homogeneous in the streamwise and spanwise directions, thus, periodic boundary conditions can be applied in these directions. This simplifies the numerical solution of the problem significantly. We present the results of direct numerical simulations of turbulent channel flow drag reduction using electromagnetic forces. The Lorentz force is created by the interaction of a permanent magnetic field and an electric current from electrodes placed on the bottom wall surface. Two various electromagnetic field cases are considered. In the first case an oscillating electric current and a permanent magnetic field create a spanwise oscillating Lorentz force, whereas in the second case a stationary electric current and a permanent magnetic field create a steady streamwise force.
The reason of the low MHD drag reduction efficiency by a spanwise oscillating Lorentz force, as obtained up to now in literature, is explained. The main result of our work is that using a load factor k ~ 1 leads to a significant efficiency improvement for all considered cases. The efficiency increases when the load factor is close to its optimum value. We show that the time oscillating spanwise Lorentz force reduces the skin-friction drag. The full drag is also reduced, the efficiency is increased by 100 times but is still much less than 1. In this case, the skin-friction drag may be strongly reduced at a very small load factor k < 1, but not the full drag.
The application of the streamwise Lorentz force leads to a much more effective drag reduction if we consider the drag as a full force applied to the body. The skin-friction drag increases but the full drag may be reduced to the zero value with a good efficiency.

  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    1(2005), 149-152
  • Poster
    Joint 15th Riga and 6th PAMIR Interantional Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
  • Magnetohydrodynamics 42(2006)2/3, 181-186

Publ.-Id: 7440

Fluid flow analysis and vertical gradient freeze crystal growth in a traveling magnetic field

Lantzsch, R.; Galindo, V.; Grants, I.; Pätzold, O.; Gerbeth, G.; Stelter, M.; Cröll, A.

The Traveling Magnetic Field (TMF) is a versatile tool to control the flow in an electrically conducting fluid. It introduces a mainly axial Lorentz force into the fluid which leads to meridional flow patterns. Applying the TMF to the Vertical Gradient Freeze (VGF) growth of semiconductor single crystals, the heat and mass transport in the melt can be tailored for growth under optimised flow conditions to improve crystal properties and/or growth yield.
In this paper we present experimental and numerical results on the TMF driven flow in an isothermal model fluid as well as in a VGF melt. The field is created by an equally spaced set-up of six coils of 36 windings each. Induction and frequency can be varied between 0-5 mT and 50-400 Hz, respectively.
Model experiments were carried out at about 20°C with the traveling field applied to InGaSn melts in cylindrical, non-conducting vessels of different diameters. Axial velocity profiles were measured by means of the Ultrasonic Doppler Velocimetry (UDV) method. The basic flow was investigated as a function of the aspect ratio and of the non-dimensional forcing and screening parameters with the focus on the transition from laminar to time-dependent convection. For comparison, numerical calculations were performed using advanced, highly accurate spectral methods as well as commercial codes.
For the growth experiments a VGF furnace was equipped with the TMF set-up. The maximum temperature of the furnace is about 1300°C and crystals with a diameter up to three inches can be grown. Ga doped germanium single crystals were grown under the influence of the field and without field. The TMF impact on the thermal field in the melt was studied on the basis of natural or artificially induced dopant striations which characterise the solid-liquid interface and, thus, the local temperature field. The transition to instationary melt flow which is indicated by the appearance of regular striation patterns in the crystal, was investigated by increasing the TMF forcing parameter intentionally during growth. Numerical results came from a quasi-2D simulation of the melt flow using the commercial code CrysVun++. A global, thermal model of the VGF furnace has been developed for this purpose.

  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    2(2005), 197-200
  • Magnetohydrodynamics 42(2006)4, 445-449

Publ.-Id: 7439

Formation of Highly Mobile Di-Interstitials During Ion Implantation

Posselt, M.

Atomistic computer simulations show that the metastable defect structure formed immediately after ion bombardment of silicon does not only consist of isolated mono-vacancies and mono-interstitials but also of more complex defects. Amongst them a small percentage of very mobile di-interstitials is found. The structure and energetics of these defects as well as their migration are investigated in more detail, and the results are compared with literature data. Mobile and immobile di-interstitial configurations are found. The migration mechanism shows a pronounced dependence on the temperature. The di-interstitial diffusivity and the self-diffusion coefficient per defect are calculated. The di-interstitial migrates much faster than the mono-interstitial.
The high mobility of the di-interstitials and the fact that they can be already formed during the ion bombardment may have implications for the current understanding of many experimental results obtained in the last decade, in particular for the explanation of the implantation-induced migration of interstitial-like defects at room temperature.

Keywords: defects; computer simulation; silicon

  • Poster
    E-MRS 2005 Spring Meeting, 31.05.-03.06.2005, Strasbourg, France

Publ.-Id: 7438

Nitrogen recoil chromium implantation into SAE 1020 steel by means of ion beam or plasma immersion ion implantation

Gomes, G. F.; Ueda, M.; Reuther, H.; Richter, E.; Beloto, A. F.

As an effort to improve the corrosion behavior of the mild steel under work conditions, we attempted to produce a high chromium content layer on its surface by applying the recoil implantation process. After polishing, SAE 1020 construction steel samples were covered with chromium and then bombarded with ions. As recoil bombarding atom, we used nitrogen, a light mass specimen. Recoil atoms were applied either by ion beam (IB) accelerator or by plasma immersion ion implantation (PIII) method. Samples treated by the PIII process showed better results, presenting a thicker layer of high Cr content, as measured by Auger electron spectroscopy (AES).

  • Surface & Coatings Technology 196(2005)1-3, 275-278

Publ.-Id: 7437

Electro-vortex flows in shallow liquid metal layers

Kolesnichenko, I.; Khripchenko, S.; Buchenau, D.; Gerbeth, G.

We investigate different kinds of electro-vortex flows generated in a shallow layer of liquid metal. The metal flow is driven by an externally applied electrical current which interacts with its own magnetic field. Due to symmetry this interaction alone causes not yet a flow as the Lorentz force is purely irrotational. If, however, ferromagnetic C-cores or yokes are applied, the magnetic field distribution is modified and a flow driving action results. An electro-vortex flow occurs with several eddies in this MHD-layer. In the stable case, for some range of electrical current values, these eddies are held in permanent position. The unstable case is characterized by an oscillation of the eddies, which are moving in the plane of the layer. One of the reasons to perform this study is related with the occurrence of similar unstable processes in some devices used for metallurgical purposes including the flat MHD-layer considered here. We have investigated this flow by experimental and numerical methods.
We applied the ultrasound Doppler velocimetry which allows us to measure velocity profiles in non-transparent media. The oxide particles of this alloy were acting as good tracers for ultrasound measurements and allowed us to obtain the time-dependences of the velocity profiles. At higher electrical currents, the profiles showed large-scale low-frequency oscillations. Various types of flows are distinguished depending on the location of the ferromagnetic C-core.
The mathematical model of the processes was based on the MHD-equations, which have been modified using a thin-layer approximation. The numerical calculations support the results obtained in experiments, and showed the behavior of the velocity field with the moving of the eddies.

  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    1(2005), 199-202
  • Poster
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia

Publ.-Id: 7435

Review of the results of the KaoS Collaboration

Förster, A.; Böttcher, I.; Dohrmann, F.; Förster, A.; Grosse, E.; Koczon, P.; Kohlmeyer, B.; Lang, S.; Laue, F.; Menzel, M.; Naumann, L.; Oeschler, H.; Ploskon, M.; Pühlhofer, F.; Scheinast, W.; Schmah, A.; Schuck, T.; Schwab, E.; Senger, P.; Shin, Y.; Ströbele, H.; Sturm, C.; Uhlig, F.; Walus, W.; Wagner, A.

The production of K+ and of K- mesons in heavy-ion collisions at beam energies of 1 to 2 A GeV has systematically been investigated with the kaon spectrometer KaoS. The ratio of the K+ production excitation function for Au+Au and for C+C reactions increases with decreasing beam energy, which is expected for a soft nuclear equation-of-state. A comprehensive study of the K+ and of the K- emission as a function of the size of the collision system, of the collision centrality, of the kaon energy, and of the polar emission angle has been performed. The K-/K+ ratio is found to be nearly constant as a function of the collision centrality and can be explained by the dominance of strangeness exchange. On the other hand, the spectral slopes and the polar emission patterns are different for K- and for K+. Furthermore the azimuthal distribution of the particle emission has been investigated. K+ mesons and pions are emitted preferentially perpendicular to the reaction plane as well in Au+Au as in Ni+Ni collisions. In contrast for K- mesons in Ni+Ni reactions an in-plane flow was observed for the first time at these incident energies.

  • Journal of Physics G - Nuclear and Particle Physics 31(2005), 693-700

Publ.-Id: 7434

11C-C bond formation by palladium-mediated cross-coupling of alkenylzirconocenes with [11C]methyl iodide

Berndt, M.; Wüst, F.

The prenyl group is known as an important structural building block in natural and medicinal products. The isotopic substitution of one of the two methyl groups with a [11C]methyl group would provide an access to a large number of interesting 11C-labelled compounds. Here we report a strategy for the synthesis of 11C-labelled prenyl group-containing derivatives starting from methyl-substituted alkynes (1) via a novel 11C-C bond forming reaction. A commonly employed strategy to form a,a’-disubstituted alkenes comprises the formation of alkenylzirconocenes by the syn-insertion of a C-C triple bond into the Zr-H bond of Schwartz reagent [Cp2Zr(H)Cl] followed by metal-mediated C-C bond formation with electrophiles under retention of the configuration of the C-C douple bond [1,2].
In principle the formation of alkenylzirconocenes by syn-addition of Schwartz reagent onto disubstituted alkynes (1) leads to a mixture of regioisomers 2 and 2’. However, treatment of an excess of Schwartz reagent favors the formation of the sterically less hindered isomer 2. Transmetalation with transition metal complexes M(PPh3)4 and conversion with [11C]MeI leads to compound 4.

Keywords: 11C-C bond formation; [11C]MeI; alkenyl-zirconium complexes

  • Lecture (Conference)
    International Symposium on Radiopharmaceutical Chemistry (ISRC 2005), 24.-28.06.2005, Iowa City, Iowa, USA
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 48(2005), S24

Publ.-Id: 7432

Synthesis and characterization of [18F]MCl-322 as a potential PET radiotracer for imaging the dopamine transporter

Wüst, F.; Neumeyer, J.; Bergmann, R.; Kretzschmar, M.; van den Hoff, J.

The fluoroethyl ester-containing phenyltropane derivative MCL-322 was shown to display high affinity to the dopamine transporter (DAT) (Ki = 2.3 nM). The binding affinities (Ki values) for the serotonin transporter and norepinephrine transporter were determined to be 5.1 nM and 280 nM, respectively [1]. The high binding affinities and selectivities of MCL-322 make the corresponding 18F-labelled compound an attractive PET radioligand for imaging DAT in brain tissue. Here, we report on the radiosynthesis of [18F]MCL-322 and its radiopharmacological characterization involving biodistribution, autoradiography and small animal PET studies.

Keywords: [18F]MCL-322; dopamine transporter (DAT); PET

  • Poster
    International Symposium on Radiopharmaceutical Chemistry (IRSC 2005), 24.-28.06.2005, Iowa City, Iowa, USA
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 48(2005), S204

Publ.-Id: 7431

Aspects of 6-[18F]fluoro-F-DOPA preparation: experiences with chloroform as a substitute solvent for Freon 11

Füchtner, F.; Zessin, J.; Wüst, F.

An increasing number of PET centers is using 6-[18F]fluoro-L-DOPA ([18F]FDOPA) to study presynaptic dopamine metabolism in vivo.
Currently the electrophilic radiofluoro-destannylation reaction of N-Boc-3,4-di(Boc-O)-6-trimethylstannyl-L-phenylalanine ethyl ester with [18F]F2 has emerged as the preparation method of choice for the reliable and reproducible radiosynthesis of [18F]FDOPA (1-5).
Up to now the radiofluorination step of the trimethyltin precursor is carried out in trichlorofluoromethan (CFCl3, Freon 11) as the solvent. De Vries et al. (4) have reported Freon 11 as the superior solvent to provide the highest radiochemical yields for the radiofluorination step. The authors also have investigated the possibility to substitute Freon 11 with other solvents. They observed considerable losses of radioactivity (61-71%) during the evaporation step of the solvents (e.g. chloroform and acetonitrile). They discussed this finding with the formation of volatile radiofluorine compounds originating from the reaction of [18F]F2 gas with the solvents.
For Freon 11 is hardly available in Europe for environmental protection reasons, we investigated the possibility of substituting Freon 11 with chloroform. In contrast to (4) we use 5 M HCl for protecting group hydrolysis. The acid is added directly after the radiofluorination step and the solvent was evaporated at 130°C. First results with chloroform also show increased losses of radioactivity in comparison to Freon 11. However, we found that the rate of radioactivity loss depends on the quality of the chloroform used. The radioactivity losses using chloroform stabilised with ethanol were in the range of 25%, whereas the amylene stabilised chloroform gave losses of 40%. In contrast, using deuterated chloroform (CDCl3) for NMR analysis purposes stabilised with silver no significant losses of radioactivity were observed in comparison with Freon 11. We conclude that no competitive radiofluorination of the solvent chloroform, neither CHCl3 nor CDCl3, with [18F]F2 occures. Instead of that the observed radioactivity losses can be explained by the radiofluorination of stabilisers present in CHCl3.The non-decay-corrected total yield for [18F]FDOPA preparation using Freon 11 as the solvent is 17% (n = 26). Using CDCl3 (silver stabilised) instead of CFCl3 the average non-decay-corrected total yield is slightly higher, being 20% (n = 17).
The use of CDCl3 has further advantages:

  • easy handling (boiling point = 61°C) and unlimited availability,
  • better environmental protection properties,
  • the radiofluoro-destannylation reaction can be carried out at temperatures above freezing-point
The results of our investigations indicate the possibility to substitute Freon 11 with CDCl3 stabilised with silver.

Keywords: [18F]FDOPA preparation; substitution of Freon 11; chloroform

  • Poster
    International Symposium on Radiopharmaceutical Chemistry (IRSC 2005), 24.-28.06.2005, Iowa City, Iowa, USA
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 48(2005), S211

Publ.-Id: 7430

Synthesis and evaluation of [11C]AL-438 as a nonsteroidal glucocorticoid recepter ligand for imaging of brain glucocorticoid receptors

Wüst, F.; Knieß, T.; Pietzsch, J.; Bergmann, R.

AIMS: Corticosteroids are implicated in neuropsychiatric disorders such as severe depression and anxiety. This work investigates the usefulness of nonsteroidal glucocorticoid receptor (GR) ligand [11C]AL-438 as PET ligand for imaging of brain GRs.
METHODS: [11C]AL-438 was synthesised by methylation of the corresponding O-desmethyl labelling precursor with [11C]MeI. Radiopharmacological characterisation of [11C]AL-438 was performed in Wistar rats using biodistribution studies, ex vivo autoradiography and small animal PET studies.
RESULTS: [11C]MeI was trapped in a DMF solution containing the O-desmethyl labelling precursor and NaOH as the base. The methylation reaction was accomplished within 5 min at 100°C. The total synthesis time including HPLC-purification was 40-45 min. [11C]AL-438 was obtained in radiochemical yields of 30-40% (decay-corrected) at a specific radioactivity of 15 to 20 GBq/µmol at the end of the synthesis. The radiochemical purity of [11C]AL-438 exceeded 98%.
Biodistribution studies in rats demonstrated a brain uptake of 1.6 ± 0.4% ID/g after 5 min p.i., which decreased to 0.6 ± 0.1% ID/g after 60 min. Brain to blood ratios at 5 min and 60 min p.i. were 3.0 and 1.0, respectively. The pituitary and adrenals as major GR-containing peripheral organs showed uptake of 2.4 ± 0.5% ID/g and 7.5 ± 1.5% ID/g after 5 min and of 1.8 ± 1.0% ID/g and 3.8 ± 0.6% ID/g after 60 min, respectively. The uptake in the pituitary and adrenals could not be reduced significantly by pretreatment with 10 mg/kg of corticosterone.
Ex vivo autoradiographic studies of [11C]AL-438 on rat brain 5 min after i.v. administration showed specific accumulation of radioactivity in regions rich of GR, such as hypothalamus and various nuclei of thalamus. CONCLUSION: The biodistribution and the brain autoradiographic data of [11C]AL-438 correlated with the expected pattern of GRs in rodents.

  • Lecture (Conference)
    X Turku PET Symposium, 28.-31.05.2005, Turku, Finland

Publ.-Id: 7429

Alternating layers of vacancy-type and interstitial-type defects in Ge ion implanted silicon

Kögler, R.; Peeva, A.; Mücklich, A.; Eichhorn, F.; Skorupa, W.

The defect structure of Ge-implanted and annealed silicon was investigated. Based on the observation of both, interstitial- and vacancy-type defects, a stacked structure of layers of vacancy and interstitial clusters was detected. These defects form a substructure within the basic dual structure consisting of a vacancy-dominated and an interstitial-dominated region. The appearance of cavities (vacancy clusters) in the interstitial-dominated region indicates significant vacancy–vacancy clustering beside the vacancy–interstitial recombination. Clustering of vacancies and interstitials prevents the vacancy–interstitial recombination. The observed defect structure is in contrast to the widely accepted +1 model which predicts the complete recombination of ion-generated vacancies and interstitials. The limits of the +1 model are discussed.

Keywords: Ion implantation; defects; +1 model; Si

  • Applied Physics Letters 88(2006)10, 1918

Publ.-Id: 7428

Recursively coupled thermal and mechanical FEM-analysis of lower plenum creep failure experiments

Willschütz, H.-G.; Altstadt, E.; Sehgal, B. R.; Weiss, F.-P.

Postulating an unlikely core melt down accident for a light water reactor (LWR), the possible failure mode of the reactor pressure vessel (RPV) and its failure time have to be investigated for a determination of the load conditions for subsequent containment analyses. Worldwide several experiments have been performed in this field accompanied with material properties evaluation, theoretical, and numerical work.
At the Institute of Safety Research of the FZR a finite element model (FEM) has been devel-oped simulating the thermal processes and the viscoplastic behaviour of the vessel wall. An advanced model for creep and material damage has been established and has been validated using experimental data. The thermal and the mechanical calculations are sequentially and recursively coupled. The model is capable of evaluating fracture time and fracture position of a vessel with an internally heated melt pool.
The model was applied to pre- and post test calculations for the FOREVER test series repre-senting the lower head RPV of a pressurized water reactor (PWR) in the geometrical scale of 1:10. These experiments were performed at the Royal Institute of Technology in Stockholm. In this paper the differences between the results of a simple coupled and a recursive coupled FE-simulation are highlighted. Due to the thermal expansion at the beginning and the accu-mulating creep strain later on the shape of the melt pool and of the vessel wall are changing. Despite of the fact that these relative small geometrical changes take place relatively slowly over time, the effect on the temperature field is rather significant concerning the mechanical material behavior and the resulting failure time. Assuming the same loading conditions, the change in the predicted failure time between the simple and the recursive coupled model is in the order of magnitude of the total failure time of the simple model. The comparison with results from the FOREVER-experiments shows that the recursive coupled model is closer to reality than the one-way coupled model.

Keywords: experimental investigation of a severe accident with core melt down; recursively coupled thermal and mechanical FE-model; sensitivity analysis of different approaches

Publ.-Id: 7427

Bioadsorción de Cr, Pb, Co, Mn, La y Ni por biomasa húmeda de una bacteria marina perteneciente a las Pseudomonadaceas

Gonzalez-Munoz, M.; Morcillo, F.; Linares, C.; Martinez-Ruiz, F.; Merroun, M.; Arias, J.

La polución de aguas por metales pesados es un serio problema ambiental, siendo las principales fuentes de esta contaminación las aguas procedentes de industrias metalúrgicas y mineras. A diferencia de otros contaminantes, una característica preocupante de los metales pesados es la tendencia a persistir indefinidamente en el ambiente, circulando a través de la cadena trófica y acumulándose eventualmente en los organismos superiores.

La búsqueda de soluciones a este tipo de problemas ha hecho que en las dos últimas décadas se haya incrementado notablemente la investigación en relación al potencial biotecnológico de los microorganismos para su eliminación, teniendo en cuenta la capacidad de la biomasa microbiana para concentrarlos y removerlos. Para el tratamiento de aguas dulces se ha ensayado biomasa procedente de bacterias, hongos y algas. No obstante, para el de aguas marinas, si bien hay abundante bibliografía sobre la utilización de algas, apenas hay referencias sobre la utilización de bacterias, por lo que ha parecido de interés realizar una investigación sobre la capacidad de bioadsorción de metales pesados por una cepa bacteriana marina.

Esta comunicación presenta los resultados preliminares obtenidos trabajando con una bacteria aislada de aguas someras del Mar de Alborán, denominada MAH1. Esta cepa bacteriana que crece bien en medios de cultivo comunes y produce abundante cantidad de EPS, presenta la capacidad de desarrollarse en un rango de temperaturas de 2 a 47ºC y a concentraciones de NaCl de 0,6 a 20%. Los ensayos realizados con ella han tenido una doble finalidad: probar, en condiciones estándar, la capacidad de bioadsorción de cromo, plomo, lantano, cobalto, níquel y manganeso y determinar, mediante obresvación con microcopio electronico de transmisión, la localización celular de los metales bioadsorbidos. Los ensayos de bioadsorción se han realizado con biomasa húmeda obtenida en fase exponencial de crecimiento y con soluciones de los metales a concentración 0,5 mM en agua mili- Q y pH 4,5. Los resultados obtenidos indican una buena adsorcion para el cromo y para el plomo (0,91 y 0,78 mmol/gr de biomasa seca, respectivamente), y menor para el resto de los metales ensayados (lantano 0,08 mmol/gr; cobalto 0,1 mmol/gr; manganeso 0,063 mmol/gr y níquel 0,14 mmol/gr). La localización celular de los metales bioadsorbidos ha sido: Pb y Cr, en la pared celular, La en el EPS y los restantes, intracelularmente.

Estos resultados indican que se trata de una bacteria que puede ser buen candidato para desarrollar sistemas de tratamiento de aguas marinas contaminadas por metales pesados, más aún si se tiene en cuenta que son preliminares y que no se han optimizado las condiciones para la bioadsorción de cada metal.

  • Poster
    XX Congress of the Spanish Society of Microbiology, 19.-22.09.05, Cáceres, Spain

Publ.-Id: 7426

Unusual insertion elements probably involved in the evolution of the S-Layer protein genes of B.sphaericus

Pollmann, K.; Raff, J.; Selenska-Pobell, S.

Unusual, S-layer-like gene carrying, mobile elements were localized on the chromosomes of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 and of the closely related strain Bacillus sphaericus NCTC 9602 in the vicinity of the functional S-layer genes. Each of the two almost identical elements designated ISBsph1 (strain 9602) and ISBsph2 (strain JG-A12) possess four ORFs which encode a putative integrase /recombinase, a putative XRE-family like protein containing a DNA binding helix turn helix motif, and a S-layer-like gene copy. Interestingly, the S-layer-like gene copies of the two IS elements are analogous to the coding parts of the previously described plasmid-located, identical between each other, and siltent S-layer genes of the two strains. In the case of the strain JG-A12, however, the ISBsph2 borne s-layer-like gene is truncated.
Comparative analyses of the functional, of the plasmid-located, and of the IS-element-specific S-layer genes of the above mentioned two strains between each other and with the S-layer genes of the other Bacillus sphaericus strains studied up to date revealed that all functional S-layer genes possess mosaic structure and share regions with very high identitiy which are surrounded by regions possessing very low or almost no identity.
Our results strongly suggest that the functional S-layer protein genes in Bacillus sphaericus have evolved via horizontal transfer of genetic information followed by rearrangements which were mediated by mobile elements.
The primary structure of the functional S-layer of the uranium mining waste isolage JG-A12 and in particular its higher capability in comparison to the other S-layers to bind uranium and other metals indicate that the environmental stress factors played an important role in the evolution of its gene.

  • Lecture (Conference)
    BAGECO-8, 26.-29.06.05, Lyon, France

Publ.-Id: 7425

Fate of U(VI) added to a U mining waste pile sample and the resulting changes in the indigenous microbial community

Geissler, A.; Scheinost, A.; Selenska-Pobell, S.

Interactions of U(VI) with the indigenous bacterial and archael communities of the uranium mining waste pile Johanngeorgestadt in Germany were studied. For this several portions of one sample with a natural content of 40 mg U/kg were supplemented with 60 mg U/kg and 260 mg U/kg in form of uranyl nitrate. Part of the most contaminated portion was additionally incubated under anaerobic conditions. Bothe, selective sequential extraction (SSE) and X-ray absorption spectroscopic analyses, indicated that added U(VI) was bound as uranyl by inner-sphere sorption complexes. No reduction of U(VI) to U(IV) was observed even by the anaerobic treatment.
Analyses of the constructed 16S rRNA gene clone libraries of the untreated and of the U(VI)-supplemented samples revealed changes in the bacterial and in the archaeal parts of the natural microbial community. In the untreated sample the bacterial community was predominated by Alphaproteobacteria and Holophaga/Acidobacterium members. The number of the latter was strongly reduced by increasing the uranium content up to 100 mg U/kg. Instead, a large number of sequences were found representing Gamma-Pseudomonas spp., Arthrobacter ssp. (Actinobacteria) as well as Geobacter spp. (Deltaproteobacteria). The most contaminated portion containing approximately 300 mg U/kg was predominated by represenatives of Cytophaga/Flavobacterium/Bacteroides group. The anaerobic treatment of this sample induced also proliferation of Alpha- and Gammaproteobacteria in it.
The archaeal populations in the original waste sample were rather diverse, whereas the supplemented with U samples wee strongly predominated by a few particular Grenarchaeota species.
Our results indicate that the addition of U(VI) to a low contaminated uranium mining waste sample induces significant shifting in the indigenous microbial populations in dependence on the amount of U(VI) and the redox conditions.

  • Poster
    BAGECO-8, 26.-29.06.05, Lyon, Frankreich

Publ.-Id: 7424

Stability constants evaluated by fluorescence spectroscopy for metal complexes

Geipel, G.

It could be shown that dendritic compounds show the same complex stoichiometry in non-water and water soluble forms. The stability constants in both solution sytems are comparable. As a consequence this demonstrates the possible use of such compounds in for complexation of metal ions aquatic systems.
As the fluorescence decay times change with the concentration of the added metal ion two effects have to be discussed: Dynamic fluorescence quenching, excited state reactions of the ligand. In case of dynamic fluorescence quenching a linear relationship between the concentration of the quencher and the ratio of the fluorescence decay time without and with quencher should be observed.

  • Lecture (Conference)
    2nd Supraphone Meeting Dresden 2005, 05.-07.05.05, Dresden, Germany

Publ.-Id: 7423

Some Aspects of Actinide Speciation by Laser Induced Spectroscopy

Geipel, G.


During the past decade many studies on speciation of actinides in natural and artificial environments have been done. High demands on the sensitivity in speciation of actinides lead to the development of advanced detection methods. This is connected with intensive use of laser systems as excitation source. Laser can provide any wavelength from the near UV to the NIR (Near Infrared) wavelength range. The development of tunable solid-state lasers overcame some disadvantages of dye laser systems. The application of low temperatures for samples measured with fluorescence spectroscopic methods brought effort in the detection of carbonate species. The availability of modern femtosecond laser systems in combination with ICCD (Intensified Charge Coupled Device) cameras gave the possibility to exploit the fluorescence properties of aromatic organic compounds for the study of their interaction with actinides, especially non-fluorescent metal ions.
The fluorescence of some tetravalent actinides as Pa(IV) and U(IV) in aquatic systems was described firstly. The speciation of actinides in arsenate and several carbonate systems was investigated. The interaction with ligands from life sciences as ATP (adenosine triphosphate) and sugar phosphates became more and more important. Also studies of the speciation of actinides in plants and microorganism cannot be neglected.
In the solid state the speciation of uranium(VI) in several natural and synthetic minerals has been studied as well as the behaviour of depleted uranium in the environment. The interaction of actinides with rock materials and minerals as well as their uptake is also of common interest in actinide chemistry. Especially the sorption and inclusion of Cm into several minerals lead to an improvement in knowledge of minor components in solids.
It is not possible to give a complete overview on the literature about the laser-induced spectroscopy of actinides. The restricted length of this contribution allows only a relatively small and personally influenced selection.

Keywords: Actinides; spectroscopy; laser; fluorescence; photoacoustic

Publ.-Id: 7421

Nitrogen Incorporation In Carbon Nitride Films Produced By Direct And Dual Ion Beam Sputtering

Abrasonis, G.; Gago, R.; Jimenez, I.; Kreissig, U.; Kolitsch, A.; Möller, W.

Carbon (C) and carbon nitride (CNx) films were grown on Si(100) substrates by direct ion beam sputtering (IBS) of a carbon target at different substrate temperatures (RT-450°C) and Ar/N2 sputtering gas mixtures. Additionally, the effect of concurrent nitrogen ion assistance during the growth of CNx films by IBS was also investigated. The samples were analyzed by elastic recoil detection analysis (ERDA) and x-ray near edge absorption spectroscopy (XANES). ERDA results showed that significant nitrogen amount (up to 20 at. %) was incorporated in the films, without any other nitrogen source but the N2-containing sputtering gas. The nitrogen concentration is proportional to the N2 content in the sputtering beam and no saturation limit is reached under the present working conditions. The film areal density derived from ERDA revealed a decrease in the amount of deposited material at increasing the growth temperature, with a correlation between the C and N losses. XANES results indicate that N atoms are efficiently incorporated into the carbon network and can be found in different bonding environments, such as pyridine-like, nitrile-like, graphite-like, and embedded N2 molecules. The contribution of molecular and pyridine-like nitrogen decreases when the temperature increases while the contribution of the nitrile-like nitrogen increases. The concurrent nitrogen ion assistance resulted in the significant increase of the nitrogen content in the film but it induced a further reduction of the deposited material. Additionally, the assisting ions inhibited the formation of the nitrile-like configurations while promoting nitrogen environments in graphite-like positions. The nitrogen incorporation and release mechanisms are discussed in terms of film growth precursors, ion bombardment effects and chemical sputtering.

Keywords: Ion beam sputtering; Dual ion beam deposition; Carbon nitride; Thin film; Growth mechanisms; X-ray near edge absorption spectroscopy

  • Journal of Applied Physics 98(2005)7, 074907-1-074907-8
    ISSN: 0021-8979

Publ.-Id: 7418

Plutonium(III) complexation by humic substances studied by X-ray absorption fine structure spectroscopy

Schmeide, K.; Reich, T.; Sachs, S.; Bernhard, G.

We determined structural parameters for the near-neighbor surrounding of plutonium(III) in complexes with humic and fulvic acids at pH 1 and for the purpose of comparison also for the plutonium(III) aquo ion by means of X-ray absorption fine structure (XAFS) spectroscopy. It could be shown that in the complexes with humic substances as well as in the Pu3+ aquo ion sample the trivalent oxidation state of plutonium was stable within the time of the experiment. In the humate and fulvate complexes, the plutonium(III) is surrounded by about 8 oxygen atoms with an average Pu-O distance of 2.48 ± 0.02 Å. The structural parameters determined for plutonium(III) humate and fulvate complexes were compared to structural parameters of plutonium(III) and plutonium(IV) aquo ions given in the literature.

Keywords: Plutonium; Trivalent; Humic acid; Fulvic acid; Aquo ion; Structure; XANES; EXAFS

  • Inorganica Chimica Acta 359(2006)1, 237-242

Publ.-Id: 7417

Observation of different azimuthal emission patterns for K+ and of K- mesons in Heavy Ion Collisions at 1-2 AGeV

Uhlig, F.; Foerster, A.; Boettcher, I.; Debowski, M.; Dohrmann, F.; Grosse, E.; Koczon, P.; Kohlmeyer, B.; Laue, F.; Menzel, M.; Naumann, L.; Oeschler, H.; Scheinast, W.; Schwab, E.; Senger, P.; Shin, Y.; Stroebele, H.; Sturm, C.; Surowka, G.; Wagner, A.; Walus, W.

Azimuthal distributions of pi+, K+ and K- mesons have been measured in Au+Au reactions at 1.5 AGeV and Ni+Ni reactions at 1.93 AGeV. In semi-central collisions at midrapidity, pi+ and K+ mesons are emitted preferentially perpendicular to the reaction plane in both collision systems. In contrast for K- mesons in Ni+Ni reactions an in-plane elliptic flow was observed for the first time at these incident energies.

Publ.-Id: 7416

Ion Beam Analysis and Computer Simulation of Damage Accumulation in Nitrogen Implanted 6H-SiC: Effects of Channeling

Zolnai, Z.; Ster, A.; Khánh, N. Q.; Kótai, E.; Posselt, M.; Battistig, G.; Lohner, T.; Gyulai, J.

500 keV nitrogen implantations at different tilt angles (0o, 0.5o, 1.2o, 1.6o, 4o) with respect to the c-axis of 6H-SiC were carried out. Radiation damage distributions have been investigated by Backscattering Spectrometry combined with channeling technique (BS/C) using 3550 keV 4He+ ion beam. A comparative simultaneous evaluation of the damage depth distributions in the Si and C sublattices of 6H-SiC led to a correction factor of 0.8 in the electronic stopping power of 4He+ ions along <0001> channel. Full-cascade Crystal-TRIM simulations with the same set of damage accumulation model parameters could reconstruct the measured shapes and heights of damage distributions for all implantation tilt angles. Secondary defect generation effects in addition to the primary point defect accumulation were assumed in the analysis.

Keywords: Silicon Carbide; Channeling; Electronic Stopping Power; Radiation Defects; Backscattering Spectrometry; Computer Simulation

  • Materials Science Forum 483-485(2005), 637-640

Publ.-Id: 7415

Response of drinking-water reservoir ecosystems to decreased acidic atmospheric deposition in SE Germany: Trends of chemical reversal

Ulrich, K.-U.; Paul, L.; Meybohm, A.

This study evaluates chemical trends of seven acidified reservoirs and 22 tributaries in the Erzgebirge from 1993 to 2003. About 85% of these waters showed significantly (p < 0.05) declining concentrations of protons (−69%), nitrate (−41%), sulfate (−27%), and reactive aluminum (−50% on average). This reversal is attributed to the intense reduction of industrial SO2 and NOx emissions from formerly high levels, which declined by 99% and 82% in the German–Czech border region between 1993 and 1999. The deposition rates of protons and sulfur decreased by 70–90%. Since 1993, the dry deposition of total inorganic nitrogen diminished to a minor degree, but the wet deposition remained unchanged. The surface waters reflect a substantial decrease in Al exchange processes, a release of sulfur previously stored in soils, and an uptake of nitrate by forest vegetation. The latter effect may be supported by soil protection liming which contributed to the chemical reversal in almost 20% of the study waters.

Keywords: Acid deposition; Hydrochemical trend; Recovery; Reservoir ecosystem; Forest soil liming

Publ.-Id: 7413

Efficient electroluminescence from rare-earth implanted SiO2 metal-oxide-semiconductor structures

Sun, J. M.; Skorupa, W.; Dekorsy, T.; Helm, M.

The IR, green, and UV electroluminescence from rare-earth (Er, Tb, and Gd) implanted SiO2 MOS devices is studied, exhibiting quantum efficiencies comparable to III-V light emitting diodes.

Keywords: Electroluminescence rare earth; ion implantation; silicon dioxide

  • Lecture (others)
    2005 2nd International Conference on Group IV Photonics, 21.9.2005, Antwerp, Belgium

Publ.-Id: 7412

Defect engineering in ion beam synthesis of SiC and SiO2 in Si

Kögler, R.; Mücklich, A.; Kaschny, J. R.; Reuther, H.; Eichhorn, F.; Hutter, H.; Skorupa, W.

Different methods of defect engineering are applied in this study for ion beam synthesis of a buried layer of SiC and SiO2 in Si. The initial state of phase formation is investigated by implantation of relatively low ion fluences. He-induced cavities and Si ion implantation generated excess vacancies are intentionally introduced in the Si substrate in order to act as trapping centers for C and O atoms and to accommodate volume expansion due to SiC and SiO2 phase formation. Especially the simultaneous dual implantation is shown to be an effective method to achieve better results from ion beam synthesis at implantation temperatures above 400oC. For SiC synthesis it is the only successful way to introduce vacancy defects. The “in situ” generation of vacancies during implantation increases the amount of SiC nanoclusters and improves crystal quality of Si in the case of SiO2 synthesis. Also the pre-deposition of He-induced cavities is clearly advantageous for the formation of a narrow SiO2 layer. Moreover, in-diffusion of O by surface oxidation can substitute a certain fraction of the O ion fluence necessary to obtain a buried homogeneous SiO2 layer.
The results show that defect engineering for SiC and SiO2 synthesis is working. However, the implementation of a single action is not sufficient to achieve a significant improvement of ion beam synthesis. Only an optimized combination of the different versions of defect engineering can bring about pronounced better results.

Keywords: Ion Implantation; Ion Beam Synthesis; SiC; SiO2; Excess Vacancies; Cavities

  • Solid State Phenomena 108-109(2005), 321-326

Publ.-Id: 7411

Radioaktiv markierte Magnetit-Nanoteilchen mit einer DMSA-Hülle

Stephan, H.; Steinbach, J.; Buske, N.

Die „Nanopartikel-Zell-Chirurgie“ unter Ausnutzung der Partikelstrahlung von Radionukliden trägt ein großes Potential für die adjuvante Krebstherapie in sich, sofern es gelingt, das entsprechende Radiotherapeutikum im Tumor selektiv zu deponieren und dort eine letale Strahlendosis unter weitgehender Schonung gesunden Gewebes zu erreichen, so dass die Zelle in ihrer Gesamtheit untergeht. In diesem Zusammenhang gewinnen magnetische Kern/Hüll-Nanoteilchen an Bedeutung. Durch zielgerichtete Modifizierung können auf der Oberfläche von magnetischen Ferrit-Nanoteilchen spezielle Haftgruppen zur stabilen Fixierung von Radionukliden angebracht werden. Diese radioaktiv markierten Nanoteilchen können dann durch geeignete Magnetfelder an Tumoren fixiert werden. Bedeutendes Zukunftspotential ist außerdem im zusätzlichen, selektiven Targeting der radioaktiv markierten, magnetischen Nanoteilchen durch Einführung von zielsuchenden Strukturen - wie Antikörper oder spezifische Peptide - in die Hülle der Nanopartikel gegeben.
Für erste Untersuchungen zur radioaktiven Markierung wurden Magnetit-Teilchen mit einem mittleren Kerndurchmesser von 10 nm ausgewählt, die eine DMSA-Hüllschicht tragen. DMSA bildet mit Technetium(V) und Rhenium(V) sehr stabile Komplexe, die eine quadratisch-pyramidale Koordinationsgeometrie aufweisen (s. Abb. 1).
Die Markierung von DMSA mit den therapeutisch relevanten Radionukliden 186Re und 188Re liefert die entsprechenden radioaktiven Komplexe in hoher Ausbeute, wobei in der Regel bei Temperaturen von 100°C gearbeitet wird. Für die eingesetzten DMSA-umhüllten magnetischen Nanoteilchen konnten bei Raumtemperatur Markierungs-ausbeuten bis zu 70% für das Generatornuklid 188Re erzielt werden, wobei das Radionuklid mindestens 24 h stabil an diesen Teilchen gebunden bleibt.

  • Contribution to proceedings
    2. Workshop über Molekulare Bildgebung und magnetische Nanopartikel, 17.-18.06.2005, Jena, Deutschland, 103-104
  • Poster
    2. Workshop über Molekulare Bildgebung und magnetische Nanopartikel, 17.-18.06.2005, Jena, Deutschland

Publ.-Id: 7410

188Re(III)-EDTA - a Multipurpose Starting Material for the Preparation of Relevant 188Re Complexes under Mild Conditions

Seifert, S.; Pietzsch, H.-J.

An easy and gentle method for the preparation of 188Re(V) complexes with bidentate and tetradentate ligands is described starting from the precursor complex 188Re(III)-EDTA. That complex is prepared at room temperature in acidic solution and reacts by a combined re-oxidation/ligand exchange reaction with appropriate ligands like DMSA or ECD (DMSA = dimercapto succinic acid, ECD = L,L-ethylene dicysteine diethyl ester) or en and cyclam (en = ethylene diamine, cyclam = 1,4,8,11-tetraazacyclotetradecane) to the 188Re(V)-oxo- and dioxocomplexes, respectively. The chelates were unambiguously identified by chromatographic comparison with spectroscopically characterised samples or known 99mTc-kit reconstitutions. The reaction succeeds under mild conditions (room temperature, short time, neutral or weak basic solutions) with high yields and has potential for labelling of sensitive biomolecules with 188Re.

Keywords: 188Re(V) Complexes; Ligands; Re-oxidation

  • Applied Radiation and Isotopes 64(2006), 223-227

Publ.-Id: 7409

Atomistische Computersimulation ionenstrahlinduzierter Prozesse: Implantation, Defektbildung, Defektmigration

Posselt, M.

Abstract is not available.

Keywords: ion-beam-induced processes; atomistic computer simulation

  • Lecture (others)
    eingeladener Vortrag, Leibniz-Institut für Oberflächenmodifizierung, Leipzig, 19.05.2005, Leipzig, Germany

Publ.-Id: 7408

Optimization of the metal/silicon ratio on nickel assisted crystallization of amorphous silicon

Pereira, L.; Beckers, M.; Martins, R. M. S.; Fortunato, E.; Martins, R.

The aim of this work is to optimize the metal/silicon ratio on nickel metal induced crystallization of silicon. For this purpose amorphous silicon layers with 80, 125 and 220 nm thick were used on the top of which 0.5 nm of Ni was deposited and annealed during the required time to full crystallize the a-Si. The data show that the 80 nm a-Si layer reaches a crystalline fraction of 95.7% (as detected by spectroscopic ellipsometry) after annealed for only 2 hours. No significant structural improvement is detected by ellipsometry neither by XRD when annealing the films for longer times. However, on 125 nm thick samples, after annealing for 2 hours the crystalline fraction is only 59.7%, reaching a similar value to the one with 80 nm only after 5 hours, with a crystalline fraction of 92.2%. Here again no significant improvements were achieved by using longer annealing times. Finally, the 220 nm thick a-Si sample is completely crystallized only after 10 hours annealing. These data clear suggest that the crystallization of thicker a-Si layers requires thicker Ni films to be effective for short annealing times. A direct dependence of the crystallization time on the metal/silicon ratio was observed and estimated.

  • Contribution to proceedings
    MRS Spring Meeting, 28.04.-01.05.2005, San Francisco, U.S.A.
    Materials Research Society Symposium Proceedings 869, D2.5.1

Publ.-Id: 7407

Spectroscopic characterization of gold nanoparticles formed by cells and S-layer protein of Bacillus sphaericus JG-A12

Merroun, M.; Rossberg, A.; Hennig, C.; Scheinost, A.; Selenska-Pobell, S.

The strain Bacillus sphaericus JG-A12, isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, is capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from uranium waste waters. The cells of this strain are enveloped by a surface layer protein (S-layer). The highly regular structure of this S-layer with many pores of identical size offers good binding sites for different kinds of molecules and provides nucleation sites for the formation of metal nanoclusters or minerals. In this study we demonstrate that B. sphaericus JG-A12 cells and their purified S-layer protein were capable to reduce Au to metallic nanoclusters in the presence of reducing agents such as molecular H2. The gold nanoparticles were regularly distributed and sized according to the pores of the protein lattice. The metallic nature of the clusters was confirmed by different techniques such as extended X-ray absorption fine structure (EXAFS) spectroscopy, X-ray absorption near edge (XANES) spectroscopy, UV-vis spectroscopy and X-ray powder diffraction (XRD). The size of the gold nanoparticles was estimated to be almost 1 nm. Our results demonstrate that B. sphaericus JG-A12 can be used to prepare gold nanoparticles tailor-made for industrial applications

Publ.-Id: 7405

„Rossendorfer Beiträge zur Flutung von Gruben des Uranbergbaus – Über den Einfluss des Grubenholzes auf das Verhalten von Kontaminanten im Flutungswasser“

Baraniak, L.; Abraham, A.

Der Prozess des natürlichen Grubenholzabbaus in gefluteten Bergwerken führt zu stark reduzierenden Bedingungen im Grubenwasser. Dies hat Konsequenzen für Kontaminanten im Flutungswasser. Insbesondere gelöstes Uran und Arsen könnten reduktiv ausgeschieden werden. Um die künftigen Redoxbedingungen im Grubenwasser zu charakterisieren, wurde das Wasser eines Hochmoors im Erzgebirge in dieser Hinsicht als nahezu gleich gearteter Fall untersucht. Das Redoxpotential im Moorwasser, gemessen mit einer Platinelektrode, sank von der Oberfläche bis in einen Meter Tiefe von etwa 600 mV auf -100 mV. Aus der Tiefenwasseranalyse und der Untersuchung des Sumpfgases, das aus dem Moorgrund extrahiert wurde, errechnete sich ein Redoxpotential von -119  5 mV. Charakteristisch für das stark reduzierende Milieu ist das Auftreten von Methan und Schwefelwasserstoff im Sumpfgas. Aus der Kenntnis dieses Zustands kann für die künftige Situation in der gefluteten Grube hergeleitet werden, dass Uran(VI) und Arsen(V) im Laufe der Zeit reduziert werden und als Uran(IV)-hydroxid und Arsen(III)-sulfid ausgeschieden werden. Durch diesen natürlichen Reinigungsprozess wird die Gefahr der Ausbreitung im unterirdischen Wasserleiter, der als Reservoir für die Trinkwasserversorgung dient, gebannt. Das Hochmoor kann in diesem Sinne als natürliches Analogon zur gefluteten Grube betrachtet werden.

  • Lecture (others)
    Veranstaltung, 12.05.2005, Zwickau, Germany

Publ.-Id: 7404

Uncertainty analyses of coupled thermal hydraulic/neutron kinetic code calculations

Kliem, S.; Langenbuch, S.; Weiß, F.-P.

The transition from the application of conservative models to the use of best-estimate models raises the question about the uncertainty of the obtained results. This question becomes especially important, if the best-estimate models should be used for safety analyses in the field of nuclear engineering. Different methodologies were developed to assess the uncertainty of the calculation results of computer simulation codes. One of them is the methodology developed by Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) which uses the statistical code package SUSA. In the past, this methodology was applied to the calculation results of the advanced thermal hydraulic system code ATHLET. In the frame of the recently finished EU FP5 funded research project VALCO, that methodology was extended and successfully applied to different coupled code systems, including the uncertainty analysis for neutronics. These code systems consist of a thermal hydraulic system code and a 3D neutron kinetic core model. Six different working groups applying different coupled code systems performed calculations. The involved system codes were ATHLET and SMABRE. They were used for the calculations together with the 3D neutron kinetic core models DYN3D, KIKO3D, BIPR8 and HEXTRAN.
Two real transients at NPPs with VVER-type reactors documented within the VALCO project were selected for analyses. One was the load drop of one of two turbines to house load level at the Loviisa-1 NPP (VVER-440), the second was a test with the switching-off of one of two main feed water pumps at the VVER-1000 Balakovo-4 NPP. Based on the relevant physical processes in both transients, lists of possible sources of uncertainties were compiled. They are specific for the two transients. Besides control parameters like control rod movement and thermal hydraulic parameters like secondary side pressure, mass flow rates, pressurizer sprayer and heater performance, different neutron kinetic parameters were included into the list of possible sources of uncertainties. These are the burn-up state of the core, the control rod efficiency for different control rod groups and the coefficients for Doppler and moderator density feed back. By use of the SUSA package, sets of input data with statistical variation of the relevant parameter values were generated for a large number of runs of the coupled codes for each transient.
Time-dependent rank correlation coefficients were calculated showing the influence of the varied parameters on the output parameter under investigation. The most interesting output parameters are the physical parameters for which experimental data are available. First of all, these are the core power, upper plenum pressure, core outlet and loop temperatures. The calculation results allowed also the determination of time-dependent tolerance intervals for given coverage and confidence. The comparison of the experimental data, the (best-estimate) reference solution and the tolerance intervals showed how the agreement between experiment and calculation could be quantified. In most of the cases the tolerance intervals include the experimental curves. A compiled list of the most important input parameters based on the rank correlation coefficients shows, which input parameters and models are responsible for the deviations. This list gives indications for further model improvements and code developments.

  • Invited lecture (Conferences)
    Annual Meeting on Nuclear Technology 2005; Fachsitzung: Neuere Methoden im Nachweisverfahren bei Störfallanalyse, 10.-12.05.2005, Nürnberg, Germany
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2005, 10.-12.05.2005, Nürnberg, Germany
    Proceedings der Fachsitzung: Neuere Methoden im Nachweisverfahren bei Störfallanalysen, Berlin: INFORUM GmbH, 79-105

Publ.-Id: 7401

Linear stability analysis for the effect of the lift force in a bubble column

Lucas, D.; Prasser, H.-M.; Manera, A.

The role of the lift force for the stability of a homogeneous bubble column is investigated. Instabilities caused by the lift force may be one important reason for the transition from homogeneous to heterogeneous bubble column. The lift force acts on rising bubbles in lateral direction, when gradients of the liquid velocity are present. Non-uniform liquid velocity fields may be induced, if the gas fraction is not equally distributed, e.g. caused by local disturbances. For regions with locally increased gas volume fraction the liquid is accelerated in upwards direction and following a gradient of the liquid velocity occurs. This causes a lateral redistribution of the gas bubbles. Depending on the sign of the lift force coefficient this can act to smooth the spatial bubble distribution or to increase the initial disturbances. It is obvious, that a positive lift coefficient stabilizes the flow, while a negative coefficient leads to unstable gas fraction distributions, and thus it favours the appearance of a heterogeneous bubble column regime. According to the well know correlation obtained by Tomiyama, the lift force coefficient is positive for small bubbles (for air-water at ambient conditions for bubbles with an equivalent diameter < 5.8 mm) and change to negative values for large bubbles. Thus this mechanism may be a possible explanation for the experimentally observed ‘pure heterogeneous’ regime, which occurs when large bubbles are injected. In this case the bubble column is heterogeneous also for small gas volume flow rates.
The above mentioned is feedback mechanism is studied by the means of a linear stability analysis. In addition to the lift force, the turbulent dispersion force is considered, which has always a stabilizing effect, i.e. it partially compensates the destabilisation induced by a negative lift coefficient. The stability analysis for a mono-dispersed system nevertheless showed, that influence of the lift force is much larger, compared to the influence of the turbulent dispersion force, if only bubble induced turbulence is considered. Thus the stability condition is practically the positive sign of the lift force coefficient. The analysis was then extended to two bubbles classes - one being small enough to have a positive lift force coefficient, the other being large enough to have a negative coefficient. The result of the analysis is a condition for the minimum fraction of small bubbles needed for stability. Finally a generalized criterion for N bubble classes and for a continuous bubble size distribution is given.

Keywords: bubble columns; bubble; stability modelling; lift force; turbulence

  • Lecture (Conference)
    43rd European Two-Phase Flow Group Meeting, 11 - 13 May 2005, Prague, Czech Republic, 11.-13.05.2005, Praha, Czech Republic

Publ.-Id: 7400

Homogenisation of the melting depth in FLASiC material

Voelskow, M.

It could be shown that both, the introduction of a melt stop layer in any depth behind the Si / SiC interface and the installation of a surface layer, decreasing the silicon melting temperature, are usefull methods to homogenize the melting depth in the bulk silicon.

Keywords: flash lamp; pulse annealing; silicon carbide

  • Lecture (others)
    FLASiC Meeting, 15.-16.10.2004, Ilmenau, BRD

Publ.-Id: 7399

Homogenisation of the melting depth in FLASiC structures

Voelskow, M.

It could be shown that both, the introduction of a melt stop layer in any depth behind the Si / SiC interface and the installation of a surface layer, decreasing the silicon melting temperature, are usefull methods to homogenize the melting depth in the bulk silicon.

Keywords: flash lamp; pulse annealing; silicon carbide

  • Contribution to proceedings
    HeT-SiC-05, 26.04.-01.05.2005, Krippen, BRD
    FZR-433, Dresden: Forschungszentrum Rossendorf, 27-30

Publ.-Id: 7398

Entwicklung von Rhenium-188-Komplexen basierend auf neuartigen, sich von Dimercaptobernsteinsäure (DMSA) ableitenden Chelatoren, geeignet zur Bindung an Biomoleküle

Heinrich, T.; Kraus, W.; Pietzsch, H.-J.; Seifert, S.; Spies, H.; Johannsen, B.

Diese Arbeit ist Teil unserer Bemühungen, Chelatbildner zur stabilen und unkomplizierten Bindung von Rhenium-188 an biologische interessante Strukturen zu entwickeln. Aufgrund der hohen in vivo Stabilität von [188ReO(DMSA)2]- (1) soll dieses Koordinationssystem zum Design von neuen 188ReO(V) Chelaten, die bezüglich Reoxidation zu Perrhenat und Ligandenaustausch unter allen Bedingungen radiopharmazeutischer Anwendungen stabil sind, ausgenutzt werden. Dieser neuartige Typ tetradentater Liganden wurde durch Überbrückung zweier DMSA-Moleküle mittels einer Alkylentriaminkette dargestellt. Durch Ligandenaustauschreaktionen von NBu4[ReOCl4] in Methanol liefert der stereoisomere Tetrathiolato-S4-Ligand 1 die fünffach koordinierten Oxo-Rhenium(V) Komplexe 2 (exo-cis) und 3 (exo-trans). Ohne Zusatz von Base werden die Verbindungen als Betain, [ReO(S4)], isoliert. Der protonierte Stickstoff der Brücke dient als internes Gegenion. Röntgenstrukturbestimmungen bieder Isomeren zeigen die quadratisch pyramidale Koordinationsgeometrie des ReOS4. Die Orientierung des Metall-oxo core ist exo bezüglich der Carbamidgruppen in beiden Isomeren.
Der aktivierte BFC 4 ermöglicht die Kupplung an terminale Aminogruppen von Biomolekülen. Nichtradioaktive Modelladukte mit Tripeptiden wurden mittels Electrospray Massenspektrometrie identifiziert. Die Re-188-Markierungen verlaufen schnell, in guten Ausbeuten und unter milden Bedingungen. Daher bieten diese neuartigen ReOS4-Komplexe einen weiteren Zugang zu stabilen Rhenium-188-Radiotherapeutika.

  • Lecture (Conference)
    Gesellschaft Deutscher Chemiker - Jahrestagung, 11.-14.09.2005, Düsseldorf, Deutschland
  • Contribution to proceedings
    GDCH-Jahrestagung 2005: Chemie schafft neue Strukturen, 11.-14.09.2005, Düsseldorf, Deutschland
    Kurzreferate, 504

Publ.-Id: 7397

CoSi2 nanostructures by writing FIB ion beam synthesis

Akhmadaliev, C.; Bischoff, L.; Schmidt, B.

A mass separated focused ion beam (FIB) is a very useful tool to fabricate nanostructures by writing implantation within an ion beam synthesis process. In these investigations the IMSA-OrsayPhysics FIB, equipped with a Co36Nd64 alloy liquid metal ion source, was applied. Si(100) and (111) wafers were implanted with 60 keV Co++ ions in the dose range of 2E16 to 2E17 cm-2. Implantation parameters were investigated, like pixel dwell time, relaxation time (time between two cycles), dose rate as well as the pixel overlapping factor. The subsequent annealing was done in a two step process, namely 600°C for 60 minutes and 1000°C for 30 minutes in a N2 ambient. The results obtained by SEM investigations in terms of continuous nanowire structures following the <110> direction and interrupted CoSi2 pattern in the <100> direction show a clear dependence on the time scale as well as the scanning mode of the irradiation. Structure sizes as small as 10 nm are demonstrated. The formation of CoSi2 nanostructures is explained by precipitation, Ostwald ripening and coarsening leading to a shrinking of the initial implanted profile.

Keywords: Focused ion beam; Cobalt disilicide; Ion beam synthesis; Nanowire

  • Materials Science and Engineering C 26(2006), 818-821

Publ.-Id: 7396

Validierung von Software-Komponenten zur Voraussage der strahleninduzierten Schädigung von RDB-Stahl

Bergner, F.

Gegenstand des Vortrags sind der aktuelle Stand der Wissenschaft und Technik, eigene Vorarbeiten sowie die Darlegung einer Projektskizze zur Modellierung der bestrahlungsinduzierten Schädigung von RDB-Stählen.

  • Lecture (others)
    Sitzung des Projektkomitees Komponentenverhalten, 21.02.2005, Dresden, Germany

Publ.-Id: 7395

Modelling of the evolution of vacancy clusters in neutron-irradiated iron

Gokhman, A.; Bergner, F.; Ulbricht, A.

There is experimental evidence for the formation of stable nm-sized vacancy clusters (VC) in low-copper iron alloys irradiated with fast neutrons under in-service conditions of reactor pressure vessels (RPVs) (BÖHMERT et al. 2001, CUMBLIDGE et al. 2003). Modelling of the evolution of VCs in pure iron under neutron irradiation is both of fundamental interest and of practical importance, because vacancies and VCs (even if not present after long-term irradiation) may play an intermediary role in the formation of Cu-rich clusters in RPV steels resulting in an irradiation-induced degradation of mechanical properties. In the present investigation we apply rate theory (RT) to simulate the evolution of VCs in pure bcc iron. Similar work was reported by ODETTE (1998) and HARDOUIN DUPARC et al. (2002). ODETTE (1998) directly solved the master equation with clustering of self-interstitial atoms (SIAs) neglected. HARDOUIN DUPARC et al. (2002) considered both planar SIA clusters and planar VCs and transformed the master equation into a Fokker-Planck equation, which may be a problem at small cluster sizes. The objective of the present investigation is to introduce the effect of lattice relaxation into the framework of ODETTE’s approach. The model can be adjusted in such a way that both volume fraction and mean size of irradiation-induced vacancy clusters measured by means of SANS are reproduced. The values of the specific surface energy of clusters and the dislocation density needed to adjust the model are reasonable estimates for the alloy under investigation. The expectation that the surface energies for the two dose rates considered should agree is fulfilled more closely, if cluster-matrix interaction is taken into account.

Keywords: Reactor pressure vessel steel; neutron irradiation; rate theory

  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany
    CD-ROM, 634-640
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany

Publ.-Id: 7394

188Re(III)-„4+1“-Mixed-ligand Complexes: Stability Studies and Labeling of Biomolecules

Schiller, E.; Seifert, S.; Tisato, F.; Refosco, F.; Kraus, W.; Spies, H.; Heinrich, T.; Pietzsch, H.-J.

In oder to understand relationships between the structure of rhenium-188 '4+1' complexes and their in vitro stability we synthesized a series of rhenium model complexes and determined their stability in human plasma. Rhenium-188 '4+1' complexes were synthesized using different monodentate phosphorus(III) ligands, including both lipophilic and hydrophilic tertiary phosphines and phosphites (188Re1-3) and unsubstituted tetradentate ligands and substituted NS3 ligands bearing a carboxyl group or an isopropyl amide were used as chelators (188Re4-6). As instability in aqueous solution leads always to perrhenate, the amount of 188ReO4- formed after 1h, 24 h and 48 h was determined by TLC. According to our findings 188Re4 was of sufficient stability and therefore used for further investigations. We tried to find out which physico-chemical parameter of the corresponding non-radioactive rhenium complexes Re1-6 may govern the formation of complexes of high in vitro stability. The water-soluble N-hydroxysulfosuccinimidyl activated ester 1 is a useful compound for the conjugation of exclusively water soluble biomolecules. Rhenium-188 labeling of the phosphine-arginine-tyrosine conjugate 2 as model compound was carried out using a labile 188Re(III)-EDTA intermediate. Based on this procedure peptides and proteins shall by labeld and tested in vivo.

Keywords: rhenium-188; "4+1"-complexes; bioconjugation; targeted radiotherapy

  • Poster
    International Symposium on Radiopharmaceutical Chemistry (ISRC 2005), 24.-28.06.2005, Iowa City, Iowa, USA
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 48(2005), S232

Publ.-Id: 7393

Darstellung und Charakterisierung von Nanopartikeln auf der Basis von [Ti2W10PO40]7- und Chitosan

Meißner, T.; Richter, W.; Stephan, H.; Zänker, H.; Kraus, W.

Polyoxometallate (POMs) gewinnen zunehmend an Bedeutung im Hinblick auf eine Anwendung in der Medizin [1]. Aufgrund ihrer bekannten antiviralen und antitumoralen Eigenschaften werden insbesondere Clusterverbindungen auf der Basis von Polyoxomolybdaten, -wolframaten sowie -vanadaten intensiv untersucht. Eigenschaften wie hohe Stabilität, geringe Toxizität, hohe Wirksamkeit und eine steuerbare Bioverteilung sind für eine Anwendung von POMs in der Medizin von besonderem Interesse. In diesem Zusammenhang ergeben sich durch Modifizierung der POMs mit organischen Verbindungen vielfältige Möglichkeiten. Besonders aussichtsreich erscheint die Anwendung von Kern/Hüll-Nanoteilchen mit einem Durchmesser von < 100 nm. So ergibt sich im Vergleich zu freien Clusterverbindungen eine höhere antitumorale Aktivität, wenn mit Stärke umhüllte nanometergroße Teilchen eingesetzt werden [2].
Unsere Untersuchungen haben gezeigt, dass die Darstellung von hydrolytisch stabilen Nanoteilchen auf der Basis von Polyoxowolframaten mit dem Biopolymer Chitosan möglich ist. Durch Vermischen von wässrigen Lösungen der Clusterverbindung K7[Ti2W10PO40] und einem Chitosanderivat (Mr ~ 10.000 g/mol) erhält man nanometergroße Assoziate. Diese Nanopartikeln weisen eine definierte Stöchiometrie (~ 5 Clustermoleküle/Molekül Chitosan) auf und die Teilchengröße liegt im Bereich von etwa 40 nm bis 400 nm, wobei der überwiegende Anteil <100 nm ist. Erste Untersuchungen zur Aufnahme in Tumorzelllinien haben ergeben, dass die Assoziate von K7[Ti2W10PO40] mit Chitosan im Vergleich zum freien Polywolframat deutlich besser aufgenommen werden.

[1] J. T. Rhule, C. L. Hill, D. A. Judd, R. F. Schinazi, Chem. Rev. 1999 99, 327.
[2] X. H. Wang, J. F. Liu, M. T. Pope, Dalton Trans. 2003, 957.

  • Poster
    GVC/DECHEMA-Jahrestagung 2005, 06.-08.09.2005, Wiesbaden, Deutschland
  • Abstract in refereed journal
    Chemie Ingenieur Technik (2005)77, 1227

Publ.-Id: 7392

Development of Rhenium-188 Complexes Based on Novel Chelators Derived from Dimercaptosuccinic Acid (DMSA) Suitable for easy Linking of Biomolecules

Heinrich, T.; Kraus, W.; Pietzsch, H.-J.; Smuda, C.; Seifert, S.; Spies, H.

This work is part of our efforts to develop chelating agents for stable binding and easy conjugation of rhenium-188 to biologically interesting structures. Keeping in mind the high in vivo stability of [188ReO(DMSA)2]- (1) we want to exploit this coordination system for the design of 188ReO(V) chelates which are stable towards re-oxidation to perrhenate and towards ligand exchange under all conditions of radiopharmaceutical procedures and applications.
The new type of tetradentate ligand has been synthesized by bridging two molecules of dimercaptosuccinic acid (DMSA) with an alkylene triamine chain. The resulting stereo-isomeric tetrathiolato S4 ligand 1 forms five-coordinate oxorhenium(V) complexes 2 (exo-cis) and 3 (exo-trans) by ligand exchange reaction of NBu4[ReOCl4] in methanol. Without addition of base the compounds will be isolated as “betain”, [ReO(S4)], with the protonated nitrogen of the bridge as internal “counter ion”. X-ray crystal structure determination of both stereoisomeric forms reveals the square-pyramidal coordination geometry of the ReOS4 core. The orientation of the metal-oxo core is exo in relation to the carbamido groups in both isomers.
The activated BFCA 4 enables easy linking of biomolecules containing a terminal amino group. Prototypic model conjugates with tripeptides have been identified in non-radioactive form by electrospray mass spectrometry.
The Re-188 labelling procedure runs fast, in good yields and under mild conditions, making the new complexes interesting as a further access to stable rhenium-188 radiotherapeutics.

  • Poster
    International Symposium on Radiopharmaceutical Chemistry (ISRC 2005), 24.-28.06.2005, Iowa City, Iowa, USA
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 48(2005), S234

Publ.-Id: 7391

Messung der regionalen Hirnfunktion bei spezifischen neuropsychiatrischen Symptomen der frühen Demenz vom Alzheimertyp

Holthoff, V.; Beuthien-Baumann, B.; Meyer, S.; Pöttrich, K.; Kalbe, E.; Sorbi, S.; Herholz, K.

Ziel: Das klinische Bild der Demenz vom Alzheimer (DAT) wird im Erkrankungsverlauf durch kognitive Einbußen und neuropsychiatrische Auffälligkeiten geprägt. Im Rahmen einer europäischen Multizenterstudie mit Positronen-Emissions-Tomographie (PET) zur Frühdiagnostik der DAT (NEST-DD), sind wir erstmalig der Frage nachgegangen, ob neuropsychiatrischen Symptomen spezifische zerebrale Funktionsstörungen zugrunde liegen könnten.

Methodik: Patienten mit einer beginnenden DAT (NINCDS/ADRDA; n0173; MMSE: 21.2±4.0; Alter: 70.6±8.24) unterzogen sich einer ausführlichen klinischen und neuropsychologischen Untersuchung sowie einer Glukosestoffwechselmessung mittels PET. Die neuropsychiatrischen Symptome wurden mittels standardisierter Fragen an die betreuenden Angehörigen erhoben (Neuropsychiatric Inventory, NPI). Es wurden Einschätzungen zum Vorliegen von Apathie, Depression, Angst, Erregtheit, Euphorie, Wahn, Halluzinationen, Enthemmung, Reizbarkeit und abnormaen motorischen Verhalten erhoben. Die Datenanalyse erfolgte bei den Patienten, die an einer isolierten neuropsychiatrischen Störung klinischer Relevanz litten (NPI-item > 4 Punkte) und wurden mit den Patienten ohne neuropsychiatrische Symptome verglichen (NPI-item < 0 Punkte). Die statistische Auswertung der PET-Bilder erfolgte mittels des interaktiven Programms SPM99 (Statistical Parametric Imaging), nach Normalisierung der einezelnen Studien auf den anatomischen Atlas nach Talairach und einer pixel-basierten statistischen Auswertung (p>0,05; korrigiert).

Ergebnisse: Insgesamt 37 Patienten wiesen keine neuropsychiatrischen Auffälligkeiten auf und dienten als Kontrollgruppe. Drei Patientengruppen konnten untersucht werden: mit klinisch relevanter Apathie (n=20), Depression (n=12) und Angst (n=12). Patienten mit klinisch relevanter Apathie wiesen eine signifikante regionale Stoffwechselminderung im orbitofrontalen Kortex auf. Depressive Patienten zeigten eine signifikante regionale Stoffwechselminderung im dorsolateralen Präfrontalkortex, während bei Patienten mit Angst eine Minderung im ventrolateralen Präfrontalkortex nachgewiesen werden konnte.

Schlussfolgerung: Diese Ergebnisse sprechen dafür, dass bei der frühen DAT den neuropsychiatrischen Auffälligkeiten Apathie, Depression und Angst unterschiedliche regionale Funktionsstörungen im Frontalkortex zugrunde liegen, die sich zum von den Hirnregionen unterscheiden, die mit den kognitiven Einbussen korrelieren.

  • Lecture (Conference)
    Gemeinsame Jahrestagung der Deutschen, Österreichischen und Schweizerischen Gesellschaft für Nuklearmedizin, 27.-30.04.2005, Basel, Schweiz
  • Abstract in refereed journal
    Nuklearmedizin 44(2005), A30

Publ.-Id: 7390

Regrowth mechanisms in flash lamp processing of heteroepitaxial SiC on silicon substrates

Smith, M.; Mcmahon, R.; Voelskow, M.; Skorupa, W.; Stoemenos, J.

The use of 3C-SiC wafers for device fabrication has been restricted by the high defect density in the substrates. Flash lamp annealing (the FLASiC process) has been shown to reduce the defect density in 3C-SiC by at least an order of magnitude. This process involves melting a layer of silicon in contact with the 3C-SiC layer on a time scale of milliseconds and the subsequent regrowth of the SiC layer by liquid phase epitaxy. This paper shows how the transport of carbon in the liquid silicon is determined by the structure of the starting substrate and process conditions. The movement of carbon controls the dissolution and regrowth of the SiC and determines the morphology of the regrown film.

Keywords: flash lamp; pulse annealing; SiC; silicon carbide; regrowth

  • Journal of Crystal Growth 277(2005)1-4, 162-169

Publ.-Id: 7389

Fast user guided segmentation and quantification of volumes in 3-d datasets

Pötzsch, C.; Hofheinz, F.; van den Hoff, J.

Positron emissions tomography studies typically contain serveral hundred tomographic images, which have to be analyzed to derive informations such as the volume of target structures (e.g. tumors). Available programs do not offer the necessary functionality because evaluation is limited to processing of individual tomographic images.

We present a newly developed tool for easy and fast evaluation of regions of interest in a volume orientated way. Examples of typical applications to microPET studies are presented.

To achive the aim the following key functionality was defined and implemented: For acceptance the tool should offer an easy and fast way of navigation through the three dimensional volumes. For that purpose three views are available, an orthogonal view, a multiple plane view and a maximum intensity projection view.

Interesting regions are enclosed by user defined masks to exclude regions of high activity background. A threshold guided automatic delineaction of interesting structures as well as an automatic segmentions of the thresholded data is used to find the target structures. These detected volumes of interest are delineated in realtime in all available views (including, especially, the maximum projection view) with a separate colormap for visual control through the operator. For each detected region the volume and parameters characterizing the tracer accumulation (maximum, minimum, mean, standard deviation, etc.) are provide. For post processing and archiving an export (XML and ASCII) as well as printing of these statistical values is possible.

  • Poster
    Annual Conference of the Academy of Molecular Imaging, 18.-23.03.2005, Orlando, Florida, USA
  • Abstract in refereed journal
    Molecular Imaging and Biology 7(2005)2, 152

Publ.-Id: 7388

Automatic coregistration of whole-body positron emission tomography images using piece-wise rigid body transformations

Hofheinz, F.; Pötzsch, C.; van den Hoff, J.

The coregistration of whole body PET images runs into certain problems. On the one hand if one uses non-rigid transformatin the validity of the data might be compromised. On the other hand if one uses only rigid body transformations, it is hardly possible to take all details of the images into account. We developed a method that circumvents this problem by using piecewise rigid body transformation.

This method evaluates the alignment of the images by the correlation of intensities and the mutual information of the data. The best transformation parameters are searched for by a modified conjugate gradient method.

The complete functionality is implemented in form of a libarary, which might be linked to an application. A command line and graphical user interface is provided. This program allows to define several areas in the images on which a separate coregistration is performed. All areas can be viewed in the same transformed image. The regions in between are interpolated by a Fermi box for each area in order to keep as much of the original information as possible.

The user interaction is reduced to a minimum, besides the coregistration areas only some information about the image content used for optimization and acceleration might be provided. However, the method will lead to improved alignment even without this additional information.

We will present the method as well as result for the different fields of application, e.g. follow up studies or dynamical studies.

  • Poster
    Annual Conference of the Academy of Molecular Imaging, 18.-23.03.2005, Orlando, Florida, USA
  • Abstract in refereed journal
    Molecular Imaging and Biology 7(2005)2, 134

Publ.-Id: 7387

Integration von erweiterten Visualisierungsoptionen in ein System zur quantitativen Auswertung von 3D PET-Datensätzen bei onkologischen Fragestellungen

Pötzsch, C.; Hofheinz, F.; van den Hoff, J.

Ziel: In (1) wurde bereits ein Auswertesystem vorgestellt, welches zur Eingrenzung, Analyse und quantitativen Auswertung dreidimensionaler Strukturen (VOIs) innerhalb von PET-Bildvolumen dient. Im Rahmen eines fortdauernden Projektes zur verbesserten quantitatischen volumetrischen Auswertung in 3D PET Daten wurden zusätzliche Module entwickelt, um die Visualisierung und interaktive Befundung zu verbessern

Methodik: Um dem Anwender bessere Auswertemöglichkeiten zu bieten, wurden zwei zusätzliche Ansichten der Volumen geschaffen. Die erste ist ein Überblick über alle Schichten ("Multipe Planes View") einer zu spezifizierenden Ansicht (Transaxial, Coronar, Sagittal). Die zweite Ansicht stellt eine rotierende Maximum Intensität Projektion (MIPS) bereit. Hierbei besteht die Möglichkeit, alternativ zur ungewichteten Maximum Projektion eine frei wählbare Abstandsgewichtung entlang der jeweiligen Projektionsrichtung vorzunehmen, um die bei der MIPS mögliche Abschirmung interner Strukturen, z. B. im Gehirn, zu verhindern.

Ergebnisse: Da in beiden neuen Ansichten die VOIs in Echtzeit und mit Hilfe eienr zweiten Farbtabelle eingeblendet werden, behält der Anwender auch hier einen Überblick übe die bereits ausgewerteten Volumina. Insbesondere die Abgrenzung der Volumina in der MIPS mittels einer zweiten Farbtafel erleichtert die Demonstration und Dokumentation von Befunden. Zusätzlich bleiben in der Multiple Plane Ansicht alle Funktionalitäten wie Masken setzen und die VOI-Detektion erhalten. Die Gaußsche Gewichtung der Intensitäten in der MIPS Ansicht schafft die Möglichkeit, heiße Bereiche, wie zum Beispiel den Cortex, auszublenden. In allen drei Ansichten besteht die Möglichkeit, Entfernungen zu messen, um Aussagen über Größen oder Abstände treffen zu können. Zur Dokumentation wurde ein Bilderexport (PNG, JPG, etc) mit verschiedenen Enstellmöglichkeiten und eine Druckfunktion für alle drei Ansichten implementiert.

Schlussfolgerungen: Die Erweiterung der Software um fehlende Funktionalitäten erlaubt die Integration des Softwarepaketes in den Routinebetrieb. In weiteren Entwicklungen soll die Möglichkeit geschaffen werden, mehrere PET-Studien zu koregistrieren und einmal erzeugte VOIs auf diese abzubilden. Dadurch sollen Aussagen über den Therapieerfolg in Follow Up Studien vereinfacht werden.

  • Poster
    Gemeinsame Jahrestagung d. Deutschen,Österreichischen u. Schweizerischen Gesell. f. Nuklearmedizin, 27.-30.04.2005, Basel, Schweiz
  • Abstract in refereed journal
    Nuklearmedizin 44(2005), A162

Publ.-Id: 7386

Entwicklung von Methoden zum beschleunigten Zugriff auf Akquisitionsdaten ACS2-basierter PET-Scanner

Langner, J.; Pötzsch, C.; Bühler, P.; van den Hoff, J.

Ziel: ACS2-basierte PET-Scanner wie der weit verbreitete ECAT HR+ unterliegen auf Grund von Hardwarelimitationen nicht nur einigen allgemein bekannten Stabilitätsproblemen, sondern auch der Problematik, dass ein Netzwerkzugriff auf die akquirierten Daten nur mit 0,5 MB/s möglich ist. Besonders bei der Verarbeitung von Listmodedaten, z. B. bei einer event-basierten Bewegungskorrektur, ist dies nicht tolerierbar und behindert die Überführung dieser Methoden in die Routine in erheblichem Makße (1). Unsere Studie greift dies auf und soll am Beispiel des ECAT HR+ überprüfen, inwieweit die Entwicklung von hard- und softwarenahen Methoden die Stabilität des ACS2 verbessern, vor allem aber den Zugriff auf die Daten wesentlich beschleunigen kann.

Methodik: Beim ACS werden die akquirierten Daten über einen SCSI-2 Bus auf eine Festplatte abgespeichert. Dieser Bustyp bietet eine Höchstgeschwindigkeit von 10 MB/s, wobei er jedoch bei einer Datenübertragung per Netzwerk durch die Limitationen des ACS2 kaum an sein Limit gerät. Um dies zu verbessern, wurde das ACS2 mit einem von zwei getrennten Hostanschlüssen eines SCSI-RAID System verbunden. Ferner wurde ein auf Linux basierender Rechner an den zweiten Anschluss angeschlossen, um beide Rechnersystemen einen physischen Zugriff auf das RAID System zu ermöglichen. Im Rahmen einer Softwareentwicklung wurde dann das vom ACS2 verwendete Dateisystem auf Linux portiert, um von dort aus auf die Daten zugreifen zu können. Um einen transparenten Zugriff auf die Daten zu erhalten und diese unmittelbar nach jeder Messung vom ACS2 auf die Akquisitionsworkstatin zu verschieben, wurden Shellskripte in Messprotokolle des PET-Scanners integriert.

Ergebnisse: Durch den Einsatz eines Ultra1 60 SCSI-RAID Systems konnten mit Hilfe eines parallel betriebenen Linux-Rechners beträchtliche Geschwindigkeitenszuwächse erzielt werden. Im Gegensatz zu der vormals auf 0,5 MB/s limitierten Methode, ist es nun möglich, mit einer Transferrate von 70 MB/s die Akquisitionsdaten zu übertragen bzw. Zugriff darauf zu erhalten.

Schlussfolgerungen: Durch die erzielte Geschwindigkeitssteigerung konnte ein langjähriger Limitationsfaktor beim akquirieren großer Datenmengen mit ACS2-basierten PET-Scannern eliminiert werden. Die entwickleten Methoden erlauben es nun, im vertretbaren Zeitrahmen Zugriff auf die Akquisitionsdaten zu erhalten und dsind darüber hinaus in der Lage, den wie verbreiteten Stabilitätsproblemen des ACS2 entgegenzuwirken.

  • Poster
    Gemeinsame Jahrestagung d. Deutschen,Österreichischen u. Schweizerischen Gesell. f. Nuklearmedizin, 27.-30.04.2005, Basel, Schweiz
  • Abstract in refereed journal
    Nuklearmedizin 44(2005), A161

Publ.-Id: 7385

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