Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33407 Publications

Structure investigation of uranium in aqueous solution under reduced conditions

Hennig, C.
The presentation refers to the application of a spectroelectrochemical cell for X-ray absorption spectroscopy to structure investigations under reduced conditions. The spectro-electrochemical cell will be used at the Rossendorf Beamline in Grenoble/France.
Keywords: Actinides, XAFS, Rossendorf beamline
  • Invited lecture (Conferences)
    Research Reactor Institute, Kyoto University, 19.01.2006, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-8119
Publ.-Id: 8119


X-ray absorption spectroscopy as tool for speciation and structure analysis of actinides in solution

Hennig, C.
The contribution comprises an introduction in X-ray absorption spectroscopy and several typical examples of speciation and structure analysis. XAFS sectroscopy is a appropriate method to study structure sequences of solution species.
Keywords: XAFS, actinides, ROBL beamline
  • Invited lecture (Conferences)
    Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 17.01.2006, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-8118
Publ.-Id: 8118


Entwicklung eines 3D Neutronentransportcodes auf der Basis der Ray-Tracing-Methode und Untersuchungen zur Aufbereitung effektiver Gruppenquerschnitte für heterogene LWR-Zellen

Beckert, C.; Rohde, U.
Standardmäßig erfolgt die Datenaufbereitung der Neutronenwirkungsquerschnitte für Reaktorkernrechnungen mit 2D-Zellcodes. Ziel dieser Arbeit war es, einen 3D-Zellcode zu entwickeln, mit diesem Code 3D-Effekte zu untersuchen und die Notwendigkeit einer 3D-Datenaufbereitung der Neutronenwirkungsquerschnitte zu bewerten. Zur Berechnung des Neutronentransports wurde die Methode der Erststoßwahrscheinlichkeiten, die mit der Ray-Tracing-Methode berechnet werden, gewählt. Die mathematischen Algorithmen wurden in den 2D/3D-Zellcode TransRay umgesetzt. Für den Geometrieteil des Programms wurde das Geometriemodul eines Monte-Carlo-Codes genutzt. Das Ray-Tracing wurde auf Grund der hohen Rechenzeiten parallelisiert. Das Programm TransRay wurde an 2D-Testaufgaben verifiziert.
Für einen Druckwasser-Referenzreaktor wurden folgende 3D-Probleme untersucht: Ein teilweise eingetauchter Regelstab und Void (bzw. Moderator mit geringerer Dichte) um einen Brennstab als Modell einer Dampfblase. Alle Probleme wurden zum Vergleich auch mit den Programmen HELIOS (2D) und MCNP (3D) nachgerechnet. Die Abhängigkeit des Multiplikationsfaktors und der gemittelten Zweigruppenquerschnitte von der Eintauchtiefe des Regelstabes bzw. von der Höhe der Dampfblase wurden untersucht. Die 3D berechneten Zweigruppenquerschnitte wurden mit drei üblichen Näherungen verglichen: linearer Interpolation, Interpolation mit Flusswichtung und Homogenisierung. Am 3D-Problem des Regelstabes zeigte sich, dass die Interpolation mit Flusswichtung eine gute Näherung ist. Demnach ist hier eine 3D-Datenaufbereitung nicht notwendig. Beim Testfall des einzelnen Brennstabs, der von Void (bzw. Moderator geringerer Dichte) umgeben ist, erwiesen sich die drei Näherungen für die Zweigruppenquerschnitte als unzureichend. Demnach ist eine 3D-Datenaufbereitung notwendig. Die einzelne Brennstabzelle mit Void kann als der Grenzfall eines Reaktors angesehen werden, in dem sich eine Phasengrenzfläche herausgebildet hat.
Keywords: Reactor physics, calculational methods, neutron transport, transport methods, Monte Carlo method, ray tracing, cross sections, cell calculation, absorber rod, void
  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-446 2006

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Permalink: https://www.hzdr.de/publications/Publ-8117
Publ.-Id: 8117


Annealing of the indium tin oxide films with an electrical current

Rogozin, A.; Shevchenko, N.; Vinnichenko, M.; Seidel, M.; Kolitsch, A.; Möller, W.
Indium tin oxide (ITO) films were grown by reactive middle frequency magnetron sputtering. Postdeposition annealing of transparent and conductive ITO films was performed with an electrical current in vacuum and air. The electrical power released by the current into the film during annealing was maintained at a constant level. The film structure and properties were characterized in situ by synchrotron produced X-ray diffraction, spectroscopic ellipsometry and resistance measurements.
The XRD data demonstrate transformation of the as-deposited amorphous film structure in to
crystalline during annealing. The films annealed in vacuum show two-stage decrease in the film resistance: first in amorphous state and second during crystallization. Increasing the electrical power of annealing hastens the onset of the second stage and reduces its total time. Resistance of the films annealed in air have three-stage behaviour: the resistance decreases at the beginning, then it starts to increase and finally, it decreases again. The experimental results are discussed in the terms of oxygen vacancy generation and tin donor activation.
Comparison of these results with data obtained during annealing of the indium oxide film without tin doping demonstrates significance of tin donor activation on the film resistance during crystallization process.
The mass analysis of the gas fractions escaping the ITO film during subsequent annealing in vacuum of the samples annealed already in air and vacuum was carried out. It is established that the samples annealed in air contain approximately one order of magnitude higher amount of water in comparison to the samples annealed in vacuum. This result shows that the water absorption deteriorates the improvement of the film resistance during annealing in air.
Keywords: ITO, annealing, electric current, film resistivity
  • Poster
    13th International Congress on Thin Films; 8th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures, 19.-23.06.2005, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-8116
Publ.-Id: 8116


Mass dependence of nuclear isotopic temperature for binary and ternary fission.

Andronenko, M. N.; Andronenko, L. N.; Neubert, W.
Method of Temperature Distributions based on isotope thermometers has been suggested and applied to determine nuclear temperatures related to spontaneous and neutron induced fission process. Binary and ternary fission modes show a pronounced difference for the mean temperature. Target mass dependence of nuclear temperatures is in agreement for both modes of fission process but in contradiction to one for high energy fragmentation.
Keywords: will be included
  • Other report
    Gatchina, Russia: Preprint St. Petersburg Nuclear Physics Institute, PN PI - 2643, 2005
    21 Seiten

Permalink: https://www.hzdr.de/publications/Publ-8115
Publ.-Id: 8115


Improved Monte Carlo Methods with Application to Borehole Logging Simulations

Legrady, D.
Monte Carlo simulation is the most accurate method in general for nuclear particle transport calculations. The convergence properties are, however, often outstandingly poor. The efficiency can be enhanced by replacing the simulation by a statistically equivalent calculation by modifying the sampling algorithms by so-called variance reduction techniques. One way of achieving such aim is the adjoint Monte Carlo method, where particle interactions are simulated in reverse. The Midway Monte Carlo method combines a regular Monte Carlo forward simulation with an adjoint one on a virtual surface separating source and detector resulting in an enhanced convergence rate. The coupling of forward and ajoint calculations is a statistically evaluation of a bilinear surface integral of the radiation current and the adjoint function in every phase-space variable.
This doctorate thesis develops and applies the time dependent form of the Midway Monte Carlo method to a pulsed neutron-photon oil well logging tool. Full analysis is given on the accuracy and convergence properties of the coupling possibilities and of the efficiency increase for such an application. Additionally, the theoretical framework of the adjoint simulation of scintillation detectors (Pulse Height tallies) has been developed.
The thesis concludes that the Midway Monte Carlo method delivers a user-friendly general variance reduction tool with high efficiency improvement, moreover the application of conventional variance reduction techniques can further enhance the efficiency. On the downside the reliability of the delivered answer and confidence intervals are often poor for time dependent simulations. Also, the method requires high computer memory capacity for the current standards.
Keywords: Monte Carlo, Midway, Adjoint, Well logging, Borehole logging, pulse height, neutron, photon, time dependent
  • Book (Editorship)
    (Signatur: 518.2/4/1:1) Delft: Delft University Press, 2005
    140 Seiten
    ISBN: 90-407-2614-0

Permalink: https://www.hzdr.de/publications/Publ-8114
Publ.-Id: 8114


Potential energy retention of slow highly charged Ar-Ions into solid surfaces -a calorimetric measurement-

Kost, D.; Facsko, S.; Keller, A.; Grötzschel, R.; Möller, W.
Highly charged ions (HCIs) carry a large amount of potential energy, which is defined as the sum of the binding energies of all electrons that are removed from the atom. In the case of low velocities of the ions this energy can exceed the kinetic energy of the ions. Retaining such a large energy in a very small surface area of typically about 1-10nm^2 and in a very short interaction time of typically 5-10 fs an enormous power flux of 10^13 W/cm^2 is given. Here the mechanisms of energy dissipation are not completely understood yet. A fraction of energy is released by emission of electrons and photons, the other part is retained in the surface. Micro-calorimetric techniques provide some advantages for the measurement of the energy retention. We used this technique to determine the fraction of the retained potential energy in collisions of argon ions of charge states from Ar+ to Ar9+ with atomically clean surfaces of Si. We measured values between 0.7 and 0.8 for the fraction of the retained energy. This values are compared with earlier measurements on a copper surface. The potential energy retention coefficient for silicon is about three times larger than in case of the copper surface.
  • Lecture (Conference)
    25th Brandt-Richie Workshop on Particle Penetration Phenomena and Excitations of Solids: Electronic Interactions at Surfaces, 10.-13.04.2005, Gainesville, USA

Permalink: https://www.hzdr.de/publications/Publ-8113
Publ.-Id: 8113


Magnetic domains and magnetization reversal of ion-induced magnetically patterned RKKY-coupled Ni81Fe19/Ru/Co90Fe10 films

Kuepper, K.; Fassbender, J.ORC; Bischoff, L.; Mattheis, R.; Fischer, P.
Pure magnetic patterning by means of ion beam irradiation of magnetic thin films and multilayers result often from a post deposition local modification of the interface structure with only minor effects on the film topography. In the study presented here a 60 keV fine focused Co ion beam was used to change the coupling in a Ni81Fe19/Ru/Co90Fe10 structure from antiferromagnetic to ferromagnetic on a micron scale. Thereby an artificial structure with locally varying interlayer exchange coupling and therefore magnetization alignment is produced. High-resolution fullfield x-ray microscopy is used to determine the magnetic domain configuration during the magnetization reversal process locally and layer resolved dueto the element specific contrast in circular x-ray dichroism. In the magnetically patterned structure there is in addition to the locally varying interlayer exchange coupling across the Ru layer also the direct exchange coupling within each ferromagnetic layer present. Therefore the magnetization reversal behaviour of the irradiated stripes is largely influenced by the surrounding magnetic film.
Keywords: magnetic patterning, ion irradiation, x-ray magnetic circular dichroism (XMCD), x-ray microscopy
  • Poster
    ALS Users' Meeting 2005, 20.-22.10.2005, Berkeley, USA
  • Poster
    364. WE-Heraeus-Seminar Nanoscale Magnets - Top down meets Bottom up, 04.-06.01.2006, Bad Honnef, Germany
  • Poster
    DPG - spring meeting of the Division Condensed Matter, 26.-31.03.2006, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-8110
Publ.-Id: 8110


Plasma-immersion ion-implanted nitinol surface with depressed nickel concentration for implants in blood

Maitz, M.; Shevchenko, N.
Ion implantation into nitinol had been shown previously to decrease the surface nickel concentration of this alloy and produce a titanium oxide layer. Nothing is known yet about the blood compatibility of this surface and the suitability for implants in the blood vessels, like vascular stents. Nickel depletion of superelastic nitinol was obtained by oxygen or helium plasma-immersion ion implantation. The latter leads to the formation of a nickel-poor titanium-oxide surface with a nanoporous structure, which was used for comparison. Fibrinogen adsorption and conformation changes, blood platelet adhesion, and contact activation of the blood clotting cascade have been checked as in vitro parameters of blood compatibility; metabolic activity and release of cytokines IL-6 and IL-8 from cultured endothelial cells on these surfaces give information about the reaction of the blood vessel wall. The oxygen-ion-implanted nitinol surface adsorbed less fibrinogen on its surface and activated the contact system less than the untreated nitinol surface, but conformation changes of fibrinogen were higher on the oxygen-implanted nitinol. No difference between initial and oxygen-implanted nitinol was found for the platelet adherence, endothelial cell activity, or cytokine release. The nanoporous, helium-implanted nitinol behaved worse than the initial one in most aspects. Oxygen-ion implantation is seen as a useful method to decrease the nickel concentration in the surface of nitinol for cardiovascular applications.
Keywords: nitinol, ion implantation, nickel depletion, titanium oxide, blood compatibility
  • Journal of Biomedical Materials Research Part A 76A(2006)2, 356-365

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Permalink: https://www.hzdr.de/publications/Publ-8109
Publ.-Id: 8109


Oxygen implanted NiTi surfaces for biomedical application

Shevchenko, N.; Richter, E.; Maitz, M. F.; Möller, W.
no abstract delivered from author
Keywords: PIII, biomedical, NiTi, surface
  • Poster
    8th International Workshop on Plasma Based Ion Implantation and Deposition, 18.-22.09.2005, Chengdu, China

Permalink: https://www.hzdr.de/publications/Publ-8108
Publ.-Id: 8108


Structure and properties of oxygen implanted NiTi surfaces

Shevchenko, N.; Richter, E.; Pham, M.-T.; Maitz, M. F.
The memory shape and superelastic NiTi alloy for biomedical implants and devices has the drawback of the high nickel concentration of 50 at%. Plasma immersion ion implantation (PIII) for improved corrosion resistance and surface nickel depletion of NiTi has been suggested. In the recent work it could be shown that oxygen PII implantation (ion energy of 20 keV and fluence of 1e17 – 1e18 cm-2) can reduce the Ni concentration in 50-100 nm surface layers to concentration below 1 at%. This effect is combined with a Ni enriched layer below the Ni depleted surface layer, what suggests a reactive process as mechanism. Grazing incidence X-ray diffraction analysis revealed the formation of rutile TiO2 phase in the surface layer and perhaps Ni4Ti3 in the Ni enriched layer. The effect of ion fluence and implantation temperature on element profiles, phase composition, layers thickness has been systematically investigated.
The nickel depleted TiO2 layer prevents corrosion and out-diffusion of Ni ions. The oxygen ion implanted NiTi surface had a superior blood compatibility in vitro compared to untreated NiTi.
Keywords: Nitinol, PIII, oxide layer, surface properties
  • Poster
    13th International Congress on Thin Films /8th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures, 19.-23.06.2005, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-8107
Publ.-Id: 8107


Real-time investigations of ITO film structure evolution during annealing

Shevchenko, N.; Rogozin, A.; Vinnichenko, M.; Cantelli, V.; Kolitsch, A.; Möller, W.
The real-time in-situ evolution of the ITO film structure during annealing was continuously investigated by synchrotron X-ray diffraction at ROssendorf Beam Line (ROBL), which is located at the European Synchrotron Radiation Facility in Grenoble, France. The amorphous ITO films are produced by reactive pulsed middle frequency dual magnetron sputtering on the Si substrates covered with SiO2. The post-deposition annealing in vacuum of ITO samples was carried out with the ROBL UHV annealing chamber equipped with a hemispherical Be dome at two annealing modes: termal annealing (at constant temperature within the range of 200 - 240 °C) and annealing with an electrical current (at constant electrical power within the range of 1.25 – 2.0 W). In both experiments the resistivity behavior of the ITO film was monitored in situ by the four point probe technique or direct electrical measurement.
The evolution of XRD peaks of crystalline In2O3 phase with annealing time was shown. The time dependence of XRD peak integral intensity has the typical S-like shape. Using the Kolmogorov–Avrami–Johnson–Mehl equation for the dependence of the crystalline fraction on the annealing time, the kinetic parameters of crystallization process were determined. The value of kinetic exponent n is within the range of 2-3 for the thermal annealing and within the range of 1-2 for the annealing with an electrical current. The activation energy for the crystallisation at thermal annealing was found as 1.5 +/- 0.2 eV, whereas the activation energy at electrical current annealing was determined as 0.8 +/- 0.1 eV. It could be suggested that an electrical current stimulates the crystallization process.
Keywords: ITO, in-situ XRD, crystallization, activation energy
  • Lecture (Conference)
    13th International Congress on Thin Films /8th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures, 19.-23.06.2005, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-8106
Publ.-Id: 8106


Optimized List-Mode Acquisition and Data Processing Procedures for ACS2 Based PET Systems

Langner, J.; Bühler, P.; Just, U.; Pötzsch, C.; Will, E.; van den Hoff, J.
PET systems using the acquisition control system version 2 (ACS2), e.g. the ECAT Exact HR PET scanner series, offer a rather restricted list-mode functionality. For instance, typical transfers of acquisition data consume a considerable amount of time. This represents a severe obstacle to the utilization of potential advantages of listmode acquisition. In our study, we have developed hardware and software solutions which do not only allow for the integration of list-mode into routine procedures, but also improve the overall runtime stability of the system.
We show that our methods are able to speed up the transfer of the acquired data to the image reconstruction and processing workstations by a factor of up to 140. We discuss how this improvement allows for the integration of list-mode-based post-processing methods such as an event-driven movement correction into the data processing environment, and how list-mode is able to improve the
overall flexibility of PET investigations in general. Furthermore, we show that our methods are also attractive for conventional histogram-mode acquisition, due to the improved stability of the ACS2 system.
Keywords: Dynamic data acquisition, list mode, data processing, ACS2, ECAT Exact HR+, positron emission tomography
  • Zeitschrift für Medizinische Physik 16(2006)1, 75-82
    DOI: 10.1078/0939-3889-00294
  • Poster
    IEEE Medical Imaging Conference 2006, 29.10.-04.11.2006, San Diego, USA

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Permalink: https://www.hzdr.de/publications/Publ-8105
Publ.-Id: 8105


Structural evolution on thermal cycling in Ti-rich NiTi SMA

Paula, A. S.; Canejo, J. P. H. G.; Schell, N.; Braz Fernandes, F. M.
Shape-memory alloys (SMA) represent a class of metallic materials that has the capability of recovering a previously defined initial shape when subjected to an adequate thermomechanical treatment. Annealing of a Ti-rich Ni–Ti alloy has been followed by in situ high temperature diffraction in order to register the texture as well as the microstrain/microstress evolution. This type of study is relevant to the envisaged applications, because the type of preferential orientation and the corresponding anisotropic response of the material conditions contributes to the success of the SMA application. In the present study we have tested the feasibility of high temperature pole figures determination at ROBL (BM20) at the ESRF, and we have shown that there is a relation between the preferential orientation changing and the structural evolution taking place during annealing.
Keywords: Keywords: Shape-memory alloy; Texture; In situ high temperature X-ray diffraction
  • Nuclear Instruments and Methods in Physics Research B 238(2005)1-4, 111-114

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Permalink: https://www.hzdr.de/publications/Publ-8104
Publ.-Id: 8104


Porous surface of NiTi alloy produced by plasma ion implantation

Shevchenko, N.; Muecklich, A.; Richter, E.; Maitz, M. F.
For several applications a nanoporous surface layer of titanium oxide on titanium or NiTi is desired, e.g. for surface-increase for catalytical or electrochemical applications, or as carrier in a drug release system. This application requires interconnected pores with the size in the same order of magnitude as the drug molecule, few nanometers. A possibility to produce such a nanoporous structure is seen in the high dose ion implantation of a non reactive gas, which aggregates to nano-bubbles. To our knowledge this type of treatment has not yet been done with the superelastic or memory shape NiTi alloy.
Helium ion implantation of the NiTi and Ti samples was performed by means of plasma immersion ion implantation at following parameters: ion energy of 20 keV, ion fluence of ~1e18 cm -2, substrate temperature (100 – 400 °C). The implanted layers were examined by elastic recoil detection analysis, Auger electron spectroscopy, grazing incidence X-ray diffraction analysis, atomic force microscopy and transmission electron microscopy.
The He+-implanted region of NiTi samples contains a Ni depleted surface layer of TiOx, a Ni enriched zone with fine Ni4Ti3 crystallites and a nanoporous amorphous layer. Structure and morphology of these layers after etching in 1% HF acid were studied in order to characterize a deeper porous layer. An influence of implantation temperature on Ni transport from surface to the deeper layers and nanoporous layer formation are discussed.
Keywords: NiTi, nanoporous, surface, PIII
  • Poster
    European Materials Research Society Spring Meeting (E-MRS), 31.05.-03.06.2005, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-8103
Publ.-Id: 8103


Structural in situ studies of shape memory alloy (SMA) Ni–Ti thin films

Martins, R. M. S.; Schell, N.; Silva, R. J. C.; Braz Fernandes, F. M.
Ni–Ti SMA thin films formed by sputtering have been attracting great interest as powerful actuators in microelectromechanical systems (MEMS) such as micro-valves, micro-fluidic pumps and micro-manipulators. Successful implementation of Ni–Ti micro-actuators requires a good understanding of the relationship among processing, microstructure and properties of Ni–Ti thin films. At the ROssendorf BeamLine (ROBL-CRG) at ESRF, we carried out a series of experiments that clearly illustrate the benefit of in situ studies, not only during annealing, but also during sputtering. The in situ sputtering experiments during film growth were performed using a magnetron sputter deposition chamber installed into the six-circle diffractometer of the materials research station. This facility allowed us to follow, almost in ‘‘real time’’, the structural evolution of the deposited thin films as a consequence of changing deposition parameters.
Keywords: Keywords: Structure and morphology; Deposition by sputtering; In situ X-ray diffraction
  • Nuclear Instruments and Methods in Physics Research B 238(2005)1-4, 319-322

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Permalink: https://www.hzdr.de/publications/Publ-8102
Publ.-Id: 8102


Determination of absolute defect concentrations forsaturated positron trapping – deformed polycrystalline Ni as a case study

Krause-Rehberg, R.; Bondarenko, V.; Thiele, E.; Klemm, R.; Schell, N.
Positrons may be used in many cases to determine defect densities of vacancies and dislocations. In case of saturated positron trapping, i.e. all positrons are getting trapped, only a lower-limit estimation can be given. However, a combination of positron back-diffusion measurements using a monoenergetic positron beam in combination with conventional lifetime spectroscopy can be used to overcome the problem of saturated positron trapping. As a case study, this combination was used for the determination of dislocation densities in polycrystalline nickel samples of highly varying dislocation density. Saturated positron trapping into dislocations and small voids was observed. The total positron trapping rate was calculated from the positron diffusion length obtained by back-diffusion experiments. The trapping rates of the two defects were finally obtained using the decomposition of lifetime spectra. The results were found in good agreement with those determined by the analysis of synchrotron Bragg-diffraction profiles, measured on the same set of samples. From the comparison of both techniques, the positron trapping coefficient was found to be ldisl = 3.9 ± 0.3 cm2/s for a high density of dislocations in Ni.
Keywords: Keywords: Positron annihilation; VEPAS; Dislocation density; Nickel; Specific trapping rate; Bragg-diffraction profiles
  • Nuclear Instruments and Methods in Physics Research B 240(2005)3, 719-725

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Permalink: https://www.hzdr.de/publications/Publ-8101
Publ.-Id: 8101


Investigation of the formation and phase transitionof Ge and Co nanoparticles in a SiO2 matrix

Cantelli, V.; von Borany, J.; Mücklich, A.; Schell, N.
The evolution of ion beam synthesized Co and Ge nanoclusters into a SiO2 matrix during annealing processes has been investigated by X-ray diffraction and transmission electron microscopy. Remarkable differences have been found between Ge and Co clusters behaviour. For Ge implanted SiO2 films, a clear influence of near-surface Ge oxidation and nanoclusters melting has been established. Annealing at temperatures around 1000 C leads to the formation of small (diameter 5 nm) nanocrystals. Classical Ostwald ripening mainly drives the clusters thermodynamical growth. On the contrary, for Co-implanted SiO2 films, a jump-like transition in nanoclusters evolution has been established at about 800 °C. A homogenous distribution of small (diameter 4 nm) amorphous clusters is transformed into a bimodal clusters profile, characterised by large (diameter between 20 and 40 nm) nanocrystals near the surface and a region of smaller clusters (diameter 7 nm) in depth. During Co nanoclusters formation the influence of nanoclusters melting can be neglected.
PACS: 81.07.Bc; 61.10.Eq; 68.37.Lp; 66.30.Pa
Keywords: Keywords: Nanoclusters; Ion-beam synthesis; Cobalt; Germanium; Silicon dioxide
  • Nuclear Instruments and Methods in Physics Research B 238(2005)1-4, 268-271

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Permalink: https://www.hzdr.de/publications/Publ-8100
Publ.-Id: 8100


Novel and Efficient Preparation of Precursor [188Re(OH2)3(CO)3]+ for the Labeling of Biomolecules

Park, S. H.; Seifert, S.; Pietzsch, H.-J.
A novel and efficient method for preparing 188Re(I) tricarbonyl precursor [188Re(OH2)3(CO)3]+ has been developed by reacting [188Re]perrhenate with Schibli’s kit in the presence of borohydride exchange resin (BER) as a reducing agent and an anion scavanger. The precursor was produced in more than 97% yield by reacting a solution of tetrahydroborate exchange resin (BER, 3 mg), borane-ammonia (BH3âNH3, 3 mg), and potassium boranocarbonate (K2[H3BCO2], 3 mg) in 0.9% saline with a solution of sodium perrhenate (Na188ReO4) with up to 50 MBq and concentrated phosphoric acid (85%, 7 íL) at 60 °C for 15 min. HPLC and TLC revealed 0% unreacted [188Re]-perrhenate ion and <3% of colloidal 188ReO2. Since the precursor is produced with high radiochemical purity and labeling efficiency under the milder conditions than those required for the conventional reducing agents, the latter can be replaced.
  • Bioconjugate Chemistry 17(2006), 223-225

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Permalink: https://www.hzdr.de/publications/Publ-8099
Publ.-Id: 8099


Synthesis of Azolyl Carboximidamides as Ligands for Zn(II) andCu(II): Application of the Zn(II) Complexes as Catalysts for theCopolymerization of Carbon Dioxide and Epoxides

Walther, M.; Wermann, K.; Lutsche, M.; Günther, W.; Görls, H.; Anders, E.
A series of novel S,N-heterocyclic (thiazolyl) substituted carboximidamides 3 and 4 was synthesized in yields up to 82% from specific triazinium salts 1 and primary or secondary amines 2 which additionally bear pyridine or imidazole units. These carboximidamides are used as tailor-made ligands for the complexation of Cu(II) and Zn(II). The coordination behavior of 3 and 4 and the properties of the resulting metal complexes are affected a significant extent especially by the nature of these amine substituents. The most important structural feature of the novel complexes is that the ligation of the metal cations is achieved by a 1,3,5-triazapentadienyl anion system, compare the X-ray structure of the model complex Cu-4d. Analogous Zn(II) complexes 5, 6a, 6b, 6c, 7a, and 7b were obtained from carboximidamides 3, 4a, 4b, 4c, 4d, and 4e after reaction with diethylzinc. Interestingly, these Zn(II) complexes possess an intrinsic activity to catalyze the copolymerization of cyclohexene oxide and carbon dioxide to give polycarbonates 15 (TON up to 113; Turn Over Number: moles of substrate 14 consumed per moles of zinc. Molecular weights: up to 206â103 Da). Contaminations of 15 by polyethers are produced only in remarkably small amounts.
  • Journal of Organic Chemistry 71(2006)4, 1399-1406

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Permalink: https://www.hzdr.de/publications/Publ-8098
Publ.-Id: 8098


Real time in situ diagnostics of PVD growth using synchrotron radiation

Andreasen, K. P.; Bøttiger, J.; Chevallier, J.; Schell, N.
For specific applications of hard coatings, the microstructure (or nanostructure) has to be tailored for optimum performance. This requires information about the mechanisms of growth and the connection between the microstructure and the deposition parameters. In order to obtain this knowledge, in situ real time growth studies of magnetron-sputtered thin films were carried out. A growth chamber, equipped with two magnetrons and Kapton windows for X-ray diffraction and reflectivity, was mounted on a six-circle goniometer at a synchrotron beam line at ESRF in Grenoble. As an example, X-ray diffraction measurements were carried out in situ during growth of TiN to follow the development of the microstructure. Recrystallization was identified as the mechanism which controlled the development of texture. The driving force for these texture changes arose from minimalization of the sum of the surface energy and the strain energy of the individual grains. As another example, the heteroepitaxial growth of TiN on MgO(001) was studied. Bragg–Brentano as well as grazing-incidence in-plane wide angle scattering was used to establish the pseudomorphic growth of TiN to the underlying MgO(001). Using real-time specular X-ray reflectivity, layer-by-layer growth was observed, with the surface roughening decreasing with an increase in the deposition temperature. The growth of nanocrystalline Au was also investigated. Among the results we found that changes in the (111) fiber texture arose from grain rotations.
Keywords: Keywords: In situ diagnostics; X-ray diffraction; Magnetron; Gold; Titanium nitride; Nanostructure
  • Surface & Coatings Technology 200(2005), 1-6

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Permalink: https://www.hzdr.de/publications/Publ-8096
Publ.-Id: 8096


A Low Energy Ion Beam Line for Highly Charged Ions

Zschornack, G.; Landgraf, S.; Großmann, F.; Kentsch, U.; Ovsyannikov, V. P.; Schmidt, M.; Ullmann, F.
An ion beam line is presented, which is designed to study the interaction of highly charged ions with matter, especially solid surfaces. The highly charged ions are produced in a room temperature electron beam ion trap, the Dresden EBIT. This device delivers bare nuclei up to elements with an atomic number of about 28, and neon-like ions up to about Z=80. After leaving the trap the ion beam containing several neighbouring ion charge states passes through standard ion optics elements before entering an analysing magnet for separating a certain ion charge state. In a following deceleration unit, which will be integrated soon, the ions can be slowed down to a definite kinetic energy of a few eV. The characteristic of the HCI beam is presented, combined with ion extraction spectra of selected elements detected by a Faraday cup after passing through an analysing magnet.
Keywords: Highly Charged Ions, Electron Beam Ion Trap
  • Vacuum 78(2005)2-4, 319-323

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Permalink: https://www.hzdr.de/publications/Publ-8095
Publ.-Id: 8095


Experimente zur CFD-Validierung für horizontale Zweiphasen-Strömungen

Vallee, C.
Zur Weiterentwicklung und Validierung von CFD-Codes bei Zweiphasen-Strömungen wurden am Forschungszentrum Rossendorf zwei horizontale Luft/Wasser-Strömungskanäle aufgebaut. Die Teststrecken, mit unterschiedlichem rechteckigen Querschnitt, wurden für den Einsatz optischer Messverfahren aus Acrylglas konstruiert. Die Versuche fanden bei Umgebungsdruck und -temperatur statt.

Die erste Anlage wurde für Vorversuche genutzt: An dieser konnte die Instrumentierung getestet und weiterentwickelt werden. Es wurden optische Messungen mit einer Hochgeschwindigkeitskamera durchgeführt und mit dynamischen Druckmessungen synchronisiert. Aus den entstandenen Bildsequenzen wurde die Phasengrenzfläche durch eigenentwickelte Algorithmen ermittelt. Außerdem wurden Geschwindigkeitsfelder in einem Schwall mit PIV (Particle Image Velocimetry) gemessen.

Der zweite Testkanal profitierte von den Erfahrungen an der ersten Anlage: Seine Konstruktion wurde für die Validierung von CFD-Codes optimiert. Eine spezielle Einlaufkomponente sorgt für definierte und konstante Randbedingungen am Eintritt. Zudem kann die Kanallänge bis auf 14 m erweitert werden. Es werden erste qualitative Ergebnisse gezeigt, so zum Beispiel Visualisierungen verschiedener Strömungsformen.
Keywords: Horizontal two-phase flow, Slug flow, High-speed video observations, Image processing, PIV
  • Invited lecture (Conferences)
    Seminar des Lehrstuhl für Thermodynamik, 09.01.2006, Garching, München, Germany

Permalink: https://www.hzdr.de/publications/Publ-8094
Publ.-Id: 8094


Magic matching in semiconductor heterojunctions

Pecz, B.; Barna, Á.; Heera, V.; Skorupa, W.
Matching of m crystal planes of a grown layer to n planes of the substrate is observed in many cases, when the difference in the lattice parameters is large. This kind of magic matching is explained by coincidence planes. Two examples are shown in this paper. SiC grains perfectly oriented to the substrate were prepared by high temperature ion implantation of Si into natural diamond. Considering the (111) lattice planes and the cases, when 5 planes of SiC match to 6 planes in diamond, or 4 planes of SiC match to 5 planes in diamond, the misfit is reduced to about 2% in both cases having opposite signs. High resolution images taken at the SiC/diamond interface were investigated and both of the above mentioned domains were found. When we consider the regular distribution of the above two domains, i.e. matching of 9 SiC lattice planes to 11 diamond planes a misfit value below 0.1% is obtained. This explains how the ion beam synthesised SiC can grow epitaxially despite the huge difference in lattice parameters. GaN synthesised in GaAs by ion implantation is presented as another example where magic matching of 5:4 reduces the misfit to 0.8%. That value is low enough to be compensated by elastic deformation of the lattice, therefore the insertion of another domain is not needed.
Keywords: ion beam synthesis, heteroeptitaxy, SiC-diamond, GaAs-GaN, lattice matching, XTEM
  • Lecture (Conference)
    14th International Conference on Microscopy of Semiconducting Materials- MSMXIV, 11.-14.04.2005, Oxford, U. K.
  • Contribution to proceedings
    Microscopy of Semiconducting Materials, 11.-14.04.2005, Oxford, UK
    Proceedings of the 14th Conference, Berlin, Heidelberg, New York: Springer, 3-540-31914-X, 159-162

Permalink: https://www.hzdr.de/publications/Publ-8093
Publ.-Id: 8093


Dependence of the linewidth of planar electron channeling radiation on the thickness of the diamond crystal

Azadegan, B.; Wagner, W.; Pawelke, J.
Measurements of (110) planar channeling radiation have been performed at the radiation source ELBE at electron energies of 14.6, 17, 30 and 34 MeV using diamond crystals of thickness 42.5, 102, 168 and 500 micrometers. The influence of different line-broadening mechanisms on the spectral shape of radiation from the 1 - 0 transition has been investigated. The analysis bases on fitting a convolution of the intrinsic Lorentz-like line shape with a Gaussian-like multiple-scattering distribution to the measured spectra. The asymmetry parameter involved relates to the standard deviation of the multiple-scattering angle under channeling condition. Its dependence on the crystal thickness at channeling was found to be weaker than for nonchanneled particles. The deduced coherence lengths show no significant dependence on the electron energy.
Keywords: planar channeling radiation, linewidth, diamond, coherence length
  • Physical Review B 74(2006), 045209-1

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Publ.-Id: 8092


Untersuchung der Verschiebung der bakteriellen Populationen in mit U(VI) inokulierten Bodenproben einer Uranabfallhalde mittels direkter molekularer Analysen

Tschikov, J.
wird nachgereicht
  • Other report
    Hochschule Anhalt: Köthen, 2005
    45 Seiten

Permalink: https://www.hzdr.de/publications/Publ-8091
Publ.-Id: 8091


"Böttger Stoneware" - Authentic or Not?

Neelmeijer, C.; Mäder, M.; Pietsch, U.; Ulbricht, H.; Walcha, H.-M.
The so-called "Böttger Stoneware", red porcelain invented by Böttger in the early 18th century, represents an independent development of high technological standard. In comparison to other ceramics Böttger stoneware is characterized by a high material density, consequently greater hardness and suitability for surface polishing. Hence museums show growing interest in obtaining objective criteria based on non-destructive methods of stoneware material analysis. In the present work the possibility of characteristic "fingerprints" for the different provenance of stoneware is tested by making use of ion beam analysis at the external proton beam, i.e. a proton beam on air.
Keywords: ceramics, Böttger, stoneware, material analysis, fingerprints, ion beam analysis, PIXE
  • Contribution to external collection
    Dagmar Hülsenberg: Ehrenfried Walther von Tschirnhaus Gesamtausgabe, Beiband, Leipzig: Sächsische Akademie der Wissenschaften zu Leipzig, 2003, 3-515-08464-9, 29-33

Permalink: https://www.hzdr.de/publications/Publ-8090
Publ.-Id: 8090


Schätze im Protonenlicht

Neelmeijer, C.; Mäder, M.
Glas kann korrodieren wie Metall. Wenngleich die Prozesse andersartig sind, das Resultat ist identisch. Umgebungsbedingte chemische Reaktionen zerstören die Materialien. Schadstellen an wertvollen Gemälden lassen sich restauratorisch festigen und ergänzen, für Unikate aus Glas besteht diese Chance nicht. Der Erhaltungszustand von Glasoberflächen kann bestenfalls eingefroren werden. Voraussetzung dafür ist, dass man ihn kennt und dass es möglich ist, die potentielle Gefahr umweltbedingter Schädigung für das einzelne Glasobjekt objektiv einzuschätzen. Selbst unter dem Schutz von Klimaanlagen in den Museen altern die Schätze aus Glas. Einige hochkarätische Pretiosen befinden sich heute bereits in einem außerordentlich kritischen Zustand. Das Schadensbild reicht von Trübung über feine Haarrisse und großflächige Rissnetze bis zur Schuppenbildung, der Ablösung von Glasschichten und den Verlust von Farbfassungen. Viele Objekte erscheinen, visuell beurteilt, heute noch in recht gutem Erhaltungszustand. Genau hier setzt die Entwicklung unserer präventiven Untersuchungsmethode ein, in Analogie zur lebensrettenden Krebsfrüherkennung bei Patienten. Ohne Probenahme gelingt es mittels zerstörungsfreier Materialanalyse solche Gläser aufzufinden, deren Zusammensetzung für Glaskorrosion kritisch ist. Für diese empfehlen wir dem Museum vorsorgliche Erhaltungsmaßnahmen.
Keywords: Glass, museum, deterioration, non-destructive analysis, PIGE, PIXE, RBS
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-398 März 2004, 62-71

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Permalink: https://www.hzdr.de/publications/Publ-8089
Publ.-Id: 8089


Preventive ion beam inspection of glass treasures

Neelmeijer, C.; Mäder, M.
Art objects made of glass may undergo deterioration when exposed to environmental stress. Even in air conditioned museums, susceptible glass surfaces may decompose. Thus, their transparency is reduced and initial tiny surface cracks may result in irreplaceable loss of glass. Degradation takes place via ion exchange reactions between the silicate network and the humidity of the ambient atmosphere. Endangered glass objects in important collections should be studied using non-destructive analytical methods. In this regard, the advantage of ion beam analysis by simultaneous Particle Induced Gamma-ray Emission (PIGE), Particle Induced X-ray Emission (PIXE) and Rutherford Backscattering Spectrometry (RBS) in a non-vacuum facility is demonstrated. This paper is concerned with both the current condition of the glass surface and the composition of the bulk of the glass. The result of such ion beam examination enables the scientist to recommend suitable storage conditions. In addition, the non-destructive study provides scientists studying art objects with means of objective material identification, enabling them to reach conclusions with respect to particular glass technologies or proveniences.
Keywords: Glass, museum, deterioration, non-destructive analysis, ion beam analysis, PIGE, PIXE, RBS
  • Contribution to external collection
    Annemie Adriaens, Christian Degrini, JoAnn Cassar: Benefits of non-destructive analytical techniques for conservation, Brussels: COST Office, 2005, 92-898-0010-0, 99-108

Permalink: https://www.hzdr.de/publications/Publ-8088
Publ.-Id: 8088


IBA of iridescent Art Nouveau glass - comparative studies

Mäder, M.; Jembrih-Simbürger, D.; Neelmeijer, C.; Schreiner, M.
Simultaneous PIXE, PIGE, and RBS in air were employed to characterise the surface structure of iridescent Art Nouveau glass artefacts produced around 1900 by Tiffany, USA and Loetz, Austria. Using PIXE and PIGE, the chemical composition of the bulk glass and the overlays was determined in a non-destructive manner. Furthermore, the combination of PIXE and RBS enabled the layer structure of the analysed glasses (bulk, overlays, and iridescent layers) and the thicknesses of the thin layers in the near-surface domain to be determined. The measurement and evaluation procedure is demonstrated on blue iridescent glass fragments of Tiffany and Loetz by way of example. The initial results showing similarities but also differences in the layered glass structure of Tiffany and Loetz objects are presented.
Keywords: Ion beam analysis (IBA); Proton induced X-ray emission (PIXE); Proton induced γ-ray emission (PIGE); Rutherford backscattering spectrometry (RBS); Iridescent Art Nouveau glass; Tiffany; Loetz
  • Nuclear Instruments and Methods in Physics Research B 239(2005), 107-113

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Publ.-Id: 8087


Three-dimensional modeling of EXAFS spectral mixtures by combining Monte-Carlo Simulations and Target Transformation Factor Analysis

Rossberg, A.; Scheinost, A.
wird nachgereicht
  • Poster
    15th Users Meeting, 08.-11.02.2005, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-8086
Publ.-Id: 8086


Wavelet analysis of EXAFS Data

Funke, H.; Chukalina, M.; Hennig, C.; Rossberg, A.; Scheinost, A.
wird nachgereicht
  • Poster
    15th Users Meeting, 08.-11.02.2005, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-8085
Publ.-Id: 8085


The Rossendorf Beamline for Actinide Research

Scheinost, A.
wird nachgereicht
  • Lecture (others)
    CEA, 11.05.2005, Valduc, France

Permalink: https://www.hzdr.de/publications/Publ-8084
Publ.-Id: 8084


Coolant mixing studies of natural circulation flows at the ROCOM test facility using ANSYS CFX

Höhne, T.; Kliem, S.
Coolant mixing in the cold leg, downcomer and the lower plenum of pressurized water reactors is an important phenomenon mitigating the reactivity insertion into the core. Therefore, mixing of the de-borated slugs with the ambient coolant in the reactor pressure vessel was investigated at the ROCOM mixing test facility. The Rossendorf Coolant Mixing Model (ROCOM) was constructed for the investigation of coolant mixing in PWR. The ROCOM facility has four loops each with an individually con¬trol¬led pump. This allows to per¬form tests in a wide range of PWR flow conditions from natural con¬vec¬tion flow up to forced con¬vec¬tion flow at nominal flow rates including flow ramps. ROCOM is operated with wa¬ter at ambient tem¬pe¬ra¬tures because the re¬ac¬tor pressure ves¬sel (RPV) mock-up and its internals are made of perspex. The model has a linear scale 1:5 to the prototype, the water inventory in the loops is kept in scale 1:125 and the traveling time of the coolant is identical to the original reactor.

Thermal hydraulics analyses showed, that weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive safety injection. After refilling of the primary circuit, natural circulation in the stagnant loops can re-establish simultaneously and the de-borated slugs are shifted towards the reactor pressure vessel (RPV). In the ROCOM experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied. During inherent dilution the slug could have a higher temperature and a lower density. Additionally the boron content influences the fluid density. In ROCOM this density difference is adjusted by the addition of ethyl alcohol. The acquisition of the concentration fields is performed with high spatial and temporal resolution mea¬sure¬ments of the tracer con¬¬¬centration.

Experiments with 0 up to 2% density differences between the de-borated slugs and the ambient coolant were used to validate the CFD software ANSYS CFX. A Reynolds stress turbulence model was employed and a hybrid mesh consisting of 3.6 million nodes and 6.4 million elements was used. The Best Practice Guidelines were applied to ensure the quality of the calculations. In the calculations, the High-Resolution discretisation scheme of ANSYS CFX was used to discretize the convective terms in the model equations. A second-order implicit scheme was utilized to approximate the transient terms. The time step size was set to 0.1 s. The ethyl alcohol water, which had a lower density, was applied as a tracer. It was modelled with the multi-component model of ANSYS CFX. The ethyl alcohol water was modelled as a component with different density and viscosity compared to water.

Depending on the degree of density differences the experiments and CFD calculations show a more or less intense stratification in the cold leg and downcomer. The ANSYS CFX calculations show a good qualitative agreement with the data. At some local positions differences in the predicted and measured concentration fields occur. The obtained experimental and numerical results can be used for further studies of the core behaviour using coupled thermo-hydraulic and neutron-kinetic code systems.
Keywords: CFD, ROCOM, boron dilution, PWR
  • Contribution to proceedings
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS), 05.-09.09.2006, Garching, Germany
  • Lecture (Conference)
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS), 05.-09.09.2006, Garching, Germany

Permalink: https://www.hzdr.de/publications/Publ-8083
Publ.-Id: 8083


Neural correlates of anosognosia for cognitive impairment in Alzheimer's disease.

Salmon, E.; Perani, D.; Herholz, K.; Marique, P.; Kalbe, E.; Holthoff, V.; Delbeuck, X.; Beuthien-Baumann, B.; Pelati, O.; Lespagnard, S.; Collette, F.; Garraux, G.
We explored the neural substrate of anosognosia for cognitive impairment in Alzheimer's disease (AD). Two hundred nine patients with mild to moderate dementia and their caregivers assessed patients' cognitive impairment by answering a structured questionnaire. Subjects rated 13 cognitive domains as not impaired or associated with mild, moderate, severe, or very severe difficulties, and a sum score was calculated. Two measures of anosognosia were derived. A patient's self assessment, unconfounded by objective measurements of cognitive deficits such as dementia severity and episodic memory impairment, provided an estimate of impaired self-evaluative judgment about cognition in AD. Impaired self-evaluation was related to a decrease in brain metabolism measured with 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) in orbital prefrontal cortex and in medial temporal structures. In a cognitive model of anosognosia, medial temporal dysfunction might impair a comparison mechanism between current information on cognition and personal knowledge. Hypoactivity in orbitofrontal cortex may not allow AD patients to update the qualitative judgment associated with their impaired cognitive abilities. Caregivers perceived greater cognitive impairments than patients did. The discrepancy score between caregiver's and patient's evaluations, an other measure of anosognosia, was negatively related to metabolic activity located in the temporoparietal junction, consistent with an impairment of self-referential processes and perspective taking in AD.
Keywords: dementia • neuroimaging • cognition • awareness • evaluation • self • perspective taking • beliefs • confabulation

Permalink: https://www.hzdr.de/publications/Publ-8082
Publ.-Id: 8082


Surface Passivation of Silicon Solar Cells by Amorphous Silicon/Silicon Nitride Dual Layers

Bentzen, A.; Ulyashin, A.; Suphellen, A.; Sauar, E.; Grambole, D.; Wright, D. N.; Marstein, E. S.; Svensson, B. G.; Holt, A.
We have investigated surface passivation of silicon by a dual structure consisting of a hydrogenated amorphous silicon thin film capped by a silicon nitride anti-reflection layer, both layers deposited by plasma enhanced chemical vapor deposition. The results show that a synergetic effect on the surface passivation properties is obtained from such a dual structure. Moreover, we find that the surface passivation can be significantly enhanced after a short anneal for temperatures up to about 500 °C, whereas anneals at higher temperatures result in degradation of the passivation properties. From nuclear reaction analyses of the as-deposited and annealed structures, the enhanced surface passivation experienced after annealing is indicated to be due to hydrogen release from the structure towards the silicon substrate, possibly followed by a redistribution of hydrogen and subsequent passivation of silicon dangling bonds in the sub-interface region.
Keywords: Surface Passivation, Amorphous Silicon, Silicon Solar Cells
  • Contribution to proceedings
    15th International Photovoltaic Science and Engineering Conference (PVSEC-15), 10.-15.10.2005, Shanghai, China, 316-317

Permalink: https://www.hzdr.de/publications/Publ-8081
Publ.-Id: 8081


Experimental investigation and CFD simulation of horizontal stratified two-phase flow phenomena

Vallee, C.; Höhne, T.; Prasser, H.-M.; Sühnel, T.
For the investigation of stratified two-phase flow, two horizontal channels with rectangular cross-section were built at Forschungszentrum Rossendorf. The channels allow the investigation of air/water co-current flows, especially the slug behaviour, at atmospheric pressure and room temperature. The test-sections are made of acrylic glass, so that optical techniques, like high-speed video observation or particle image velocimetry (PIV), can be applied for measurements. The rectangular cross-section was chosen to provide better observation possibilities. Moreover, dynamic pressure measurements were performed and synchronised with the high-speed camera system.

CFD post test simulations of stratified flows were performed using the code ANSYS-CFX. The Euler-Euler two fluid model with the free surface option was applied on grids of minimum 400'000 control volumes. The turbulence was modelled separately for each phase using the k-ω based shear stress transport (SST) turbulence model. The results compare very well in terms of slug formation, velocity, and breaking. The qualitative agreement between calculation and experiment is encouraging and shows that CFD can be a useful tool in studying horizontal two-phase flow.
Keywords: Horizontal two-phase flow, Slug flow, High-speed video observations, Image processing, PIV, CFD
  • Contribution to proceedings
    CFD4NRS - Benchmarking of CFD Codes for Application to Nuclear Reactor Safety, 05.-07.09.2006, Garching, München, Germany
    Paper A6-31
  • Lecture (Conference)
    CFD4NRS - Benchmarking of CFD Codes for Application to Nuclear Reactor Safety, 05.-07.09.2006, Garching, München, Germany
  • Nuclear Engineering and Design 238(2008), 637-646
    DOI: 10.1016/j.nucengdes.2007.02.051

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Permalink: https://www.hzdr.de/publications/Publ-8080
Publ.-Id: 8080


Heterogeneity of brain glucose metabolism in mild cognitive impairment and clinical progression to Alzheimer disease

Anchisi, D.; Borroni, B.; Franceschi, M.; Kerrouche, N.; Kalbe, E.; Beuthien-Baumann, B.; Cappa, S.; Lenz, O.; Ludecke, S.; Marconi, A.; Mielke, R.; Ortelli, P.; Padovani, A.; Pelati, O.; Pupi, A.; Scarpini, E.; Weisenback, S.; Herholz, K.; Salmon, E.; Holthoff, V.; Sorbi, S.; Fazio, F.; Perani, D.
BACKGROUND: Subjects with amnesic mild cognitive impairment (aMCI) may include patients at high risk for progression to Alzheimer disease (AD) and a population with different underlying pathologic conditions. OBJECTIVE: To evaluate the potential roles of positron emission tomography with fluorodeoxyglucose F 18 (18FDG-PET) and memory scores in identifying subjects with aMCI and in predicting progression to dementia.
DESIGN, SETTING, AND PATIENTS: Sixty-seven patients at European centers for neurologic and AD care who were diagnosed as having aMCI each underwent an extensive clinical and neuropsychological examination and an 18FDG-PET study. Forty-eight subjects were followed up periodically for at least 1 year, and progression to dementia was evaluated.

MAIN OUTCOME MEASURES: Brain glucose metabolism and memory scores. RESULTS: Fourteen subjects with aMCI who converted to AD within 1 year showed bilateral hypometabolism in the inferior parietal, posterior cingulate, and medial temporal cortex. Subjects with "stable" aMCI presented with hypometabolism in the dorsolateral frontal cortex. The severity of memory impairment, as evaluated by the California Verbal Learning Test-Long Delay Free Recall scores, correlated with the following brain metabolic patterns: scores less than 7 were associated with a typical 18FDG-PET AD pattern, and scores of 7 or higher were associated with hypometabolism in the dorsolateral frontal cortex and no progression to AD. CONCLUSION: These data provide evidence for clinical and functional heterogeneity among subjects with aMCI and suggest that 18FDG-PET findings combined with memory scores may be useful in predicting short-term conversion to AD.
  • Archives of Neurology 62(2005)11, 1728-1733

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Permalink: https://www.hzdr.de/publications/Publ-8079
Publ.-Id: 8079


Pressure vessel investigations of the former Greifswald NPP: Fluence calculations and Nb based fluence measurements

Rindelhardt, U.; Konheiser, J.; Viehrig, H.-W.; Gleisberg, B.
Pressure vessel integrity assessment after long-term service irradiation is commonly based on surveillance program results. Radiation loading, metallurgical and environmental histories, however, can differ between surveillance and RPV materials. Therefore, the investigation of RPV material from decommissioned NPPs offers the unique opportunity to evaluate the real toughness response. A chance is given now through the investigation of material from the decommissioned Greifswald NPP (VVER-440/230) to evaluate the state of a standard RPV design and to assess the quality of prediction rules and assessment tools.

The operation of the four Greifswald units was finished in 1991 after 12 – 15 years of operation. In autumn 2005 the first trepans (diameter 120 mm) were gained from the unit 1 of this NPP. A new drilling machine was developed and adopted to the actual plant conditions. The drilling machine allows the following remote controlled actions:

• Labeling the position and orientation of the trepan
• Drilling the trepan and ejection of the trepan into the RPV
• Closing the hole in the RPV

Details of the trepanning procedure will be given.

Fluence calculations using the code TRAMO were based on pin-wise time dependent neutron sources and an updated nuclear data base (ENDF/B-VI release 8). The neutron and gamma fluence spectra were determined at the trepan positions. The different loading schemes of unit 1 (standard, with 4 or 6 dummy assemblies) were taken into account. The fluences after the annealing procedure (after cycle 13) were separately determined. The statistical error of the integral fluence values (E > 0.5 MeV) was estimated to be smaller than 1%. The comparison between the calculated fluences and experimental values (determined from excore fluence monitors applied during the 12th cycle) showed a good agreement.
The integral neutron fluence at the inner RPV wall near the critical weld was found to 4.64* 10^18 n*cm-2. The maximum fluence at the RPV is 50 % higher. In addition, it could be shown that the fluence at the designated reference positions can be neglected (3 orders of magnitude smaller). The gamma fluence was calculated to 1.9 *10^20 photons* cm-2 at the critical weld with a similar axial distribution.

The experimental determination of the neutron fluence was based on Niobium activity measurements. The RPV material contains Niobium as trace element. The analysis of the Nb-content is carried out by ICP-MS (inductive coupled plasma mass spectrometry) after dissolution of the material sample. The radiochemical isolation of Nb was done by anion exchange separation. During this separation all other elements of the sample were removed. Finally Nb is stripped from the column. The radiochemical separation is accompanied by determination of the chemical yield of Nb using the above mentioned ICP-MS method.
The measurement of the 93mNb activity is realized by Liquid Scintillation Spectrometry (LSC). A detection efficiency of 91 % was achieved.
Keywords: reactor pressure vessel, NPP, neutron embrittlement, reactor dosimetry
  • Lecture (Conference)
    14th International Conference On Nuclear Energy, 17.-20.07.2006, Miami, United States
  • Contribution to proceedings
    14th International Conference on Nuclear Engineering (ICONE 14), 17.-20.07.2006, Miami, United States
    Proceedings, 0-7918-3783-1, 89578

Permalink: https://www.hzdr.de/publications/Publ-8078
Publ.-Id: 8078


Retrospective dosimetry of Greifswald VVER 440 RPV: Fluence calculations and Nb based fluence measurements

Rindelhardt, U.; Konheiser, J.; Viehrig, H.-W.; Gleisberg, B.
The operation of the four Greifswald units (VVER-440/230) finished in 1991 after 12 – 15 years of operation. The investigation of RPV material from the decommissioned Greifswald NPP offers the possibility to evaluate the state of the standard RPV design and to assess the quality of prediction rules and assessment tools. The different operation conditions (irradiated, annealed, and re-irradiated) are a special advantage of the research program.
In autumn 2005 the first trepans (diameter 120 mm) were gained from the unit 1 of this NPP. A new drilling machine was developed and adopted to the actual plant conditions. The drilling machine allows the following remote controlled actions:

• Labeling the position and orientation of the trepan
• Drilling the trepan and ejection of the trepan into the RPV
• Closing the hole in the RPV

Details of the trepanning procedure will be given.
Fluence calculations using the code TRAMO were based on pin-wise time dependent neutron sources and an updated nuclear data base (ENDF/B-VI release 8). The neutron and gamma fluence spectra were determined at the trepan positions. The integral neutron fluence at the inner RPV wall near the critical weld was found to 4.64* 10^18 n*cm-2. The maximum fluence at the RPV is 50 % higher. In addition, it could be shown that the fluence at the designated reference positions can be neglected (3 orders of magnitude smaller). The gamma fluence was calculated to 1.9 *10^20 photons* cm-2 at the critical weld with a similar axial distribution.
The experimental determination of the neutron fluence was based on Niobium activity measurements. The RPV material contains Niobium as trace element. The analysis of the Nb-content is carried out by ICP-MS (inductive coupled plasma mass spectrometry) after dissolution of the material sample. The radiochemical isolation of Nb was done by an anion exchange column. By this separation all other elements were removed.
The measurement of the 93mNb activity is realized by Liquid Scintillation Spectrometry (LSC). Parallel the chemical yield is determined by the above mentioned ICP-MS method.
Keywords: Neutron embrittlement, Greifswald NPP, RPV dosimetry
  • Lecture (Conference)
    9th International Conference on Material Issues inIN Design, Manufactoringand Operation Peration of Nuclear Power Plants Equipment, 05.-09.06.2006, St. Petersburg, Russia
  • Contribution to proceedings
    9th International Conference on Material Issues in Design, Manufactoringand Operation Peration of Nuclear Power Plants Equipment, 06.-09.06.2006, St. Petersburg, Russia
    Proceedings, 241-247

Permalink: https://www.hzdr.de/publications/Publ-8077
Publ.-Id: 8077


Positron emission tomography in food sciences

Pietzsch, J.; van den Hoff, J.
kein Abstract verfügbar

Permalink: https://www.hzdr.de/publications/Publ-8076
Publ.-Id: 8076


Morphology of surfaces bombarded with highly charged ions

Facsko, S.; Kost, D.; Keller, A.; Möller, W.
The morphology of surfaces after erosion by ion sputtering show very different char-acteristics depending on the ion beam parameters and the material properties. The surface exposed to the ion beam can turn atomically smooth, stochastically or self-affine rough, or can evolve towards regular self-organised patterns, like periodic rip-ples or hexagonally ordered dots [1,2,3]. The structures of these patterns have small sizes in the range of 10 to 100 nm and show a high degree of ordering. Therefore, they have attracted strong interest recently as possible candidates for quantum struc-tures or as templates for deposition or etching processes [3,4].
On materials whose surface turns amorphous during the ion erosion the formation of the periodic patterns relies on at least two interplaying processes: roughening of the surface due to the local variation of sputtering yield and smoothing via diffusion proc-esses [5]. Therefore, the surface morphology depends strongly on the details of the energy deposition by the incoming ions and on the details of the surface diffusion.
At the atomic level, the atomic sputtering, the creation of surface defects, and the influence of the ion beam on surface diffusion processes play a decisive role for the morphology evolution. In the case of single charged ions, the energy deposition is mainly dissipated kinetically in a collision cascade which leads finally to the emission of the sputtered atoms and the creation of defects.
Multiple or highly charged ions carry in addition to their kinetic energy also “potential” energy which is the sum of the ionization energies for getting the higher charge state. Thus, a second energy deposition process takes place, i.e. the release of the poten-tial energy. This dissipation process is mainly electronic and takes place at the direct impact of the ions with the surface. For slow ions at high charge states the potential energy can exceed the kinetic energy thus dominating the ion-solid interaction. It has been demonstrated that at least 30% of the potential energy is retained in the surface and can induce electronic sputtering in the case of insulators [6,7].
We present first investigations of the effect of the potential energy deposition on the surface morphology of insulators and semiconductors. Special emphasis will be given on the characterisation of single ion impacts and the effect of the additional potential energy deposition on self-organised patterns.
Keywords: Highly Charged Ions, Ion Sputtering, Surface Morphology
  • Invited lecture (Conferences)
    348. WE-Heraeus-Seminar: Ions at Surfaces, Patterns and Processes, 19.-23.06.2005, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-8075
Publ.-Id: 8075


Interaction of Highly Charged Ions with the Surface of Insulators

Facsko, S.; Kost, D.; Keller, A.; Möller, W.; Pesic, Z.; Stolterfoht, N.
The interaction of highly charged ions (HCIs) with surfaces has been the subject of in-tense scientific research in the last years. Special attention was paid to the interaction with the surface of metals, where the formation of hollow atoms and their relaxation dynamics has been studied in detail [1]. From theses studies the interaction scenario for metal surfaces has been revealed and found to be consistent with the classical-over-barrier-model [2]. In contrast, the study of the interaction of HCIs with insulating surfaces is not as complete and still lacks some understanding [3].
The main differences between metals and insulators can be found in the higher work function, the lower density of electrons in the conduction band, and the much lower conduc-tivity. Therefore, the microscopic and macroscopic charging of insulating surfaces, which constitutes an important part of the interaction mechanisms, makes these studies difficult. Different methods can be used to overcome this difficulty. Using thin layers of a deposited material is one of the possibilities and will be presented here for the interaction of highly charged Ne ions with the SiO2 surface. Secondary electron emission from these layers and the calorimetric determination of the potential energy retention in these layers will be compared to results on Au surfaces.
In addition, the main aspects of the interaction of HCIs with insulating surfaces will be reviewed briefly. By means of the emission of x-rays and secondary electrons the formation and relaxation of hollow atoms above insulating surfaces will be discussed. Furthermore, the more applicative aspects of the interaction of HCIs with insulators like potential sputtering and single ion induced surface tracks and modifications will be covered.
Keywords: Highly Charged Ions, Insulator Surfaces, Electron Spectroscopy, Calorimetry
  • Invited lecture (Conferences)
    3rd Conference on Elementary Processes in Atomic Systems (CEPAS), 31.08.-2.09.2005, Miskolc, Hungary
  • Radiation Physics and Chemistry 76(2007)3, 387-391

Permalink: https://www.hzdr.de/publications/Publ-8074
Publ.-Id: 8074


Self-Organized Ordered Nanostructures by Ion Beam Sputtering

Facsko, S.; Rossbach, S.; Keller, A.; Gago, R.; Möller, W.
There is a high demand of lateral structures with dimensions from some nanometers to tens of nanometers in the fields of electronics, magnetic storage, and biology. This has triggered research activities in self-organization and self-assembling mechanisms for their fabrication which can successfully complement the classical methods of lithography. These self-organization processes, classified as “bottom-up” approaches, in contrast to the “top-down” approaches of lithography, will join more and more the nanotechnology.
In the series of self-organized processes for the fabrication of nanostructures the pattern formation during ion erosion of surfaces has attracted much interest in the last years. In the continuous sput-tering process, induced by the bombardment with low-energy ions, periodic surface patterns ap-pear in form of ripples under off-normal incidence or regular arrays of hexagonally ordered dots at normal incidence. The dimension of the patterns is related to the size of the typical collision cascade and lies in the range of ten to tens of nanometers, depending primary on ion energy, inci-dence angle, and surface temperature. The self-organization mechanism relies on the interplay between a surface instability caused by the sputtering and surface diffusion processes. Regular ripple and dot morphologies have been produced in this way on very different materials including semiconductors, and metals, demonstrating the universality of this mechanism.
Keywords: Ion Sputtering, Nanostructures, Quantum Dots
  • Invited lecture (Conferences)
    Joint Meeting of the German Vacuum Society (DVG) and the Polish Vacuum Society (PTP), 26.-29.10.2005, Krakow, Polen

Permalink: https://www.hzdr.de/publications/Publ-8073
Publ.-Id: 8073


How to increase the MHD drag reduction efficiency for turbulent flows

Shatrov, V.; Gerbeth, G.
Recently, permanent magnets and high electric current densities are often used to achieve reasonable Lorentz forces for a magnetohydrodynamic (MHD) flow control. This choice, however, usually leads to a low energetic efficiency for the flow control of seawater. We present results of direct numerical simulations of turbulent channel flow drag reduction using electromagnetic forces. The Lorentz force is created by a permanent magnetic field and an electric current from electrodes placed at the bottom wall. We consider the two cases of a spanwise oscillating force and a streamwise steady force. The main result is that a significant efficiency improvement is possible if load factors k ~ 1 are used. 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 strongly reduced with a good efficiency.
  • Lecture (Conference)
    Whither Turbulence Prediction and Control, 26.-29.03.2006, Seoul, Korea
  • Contribution to proceedings
    Whither Turbulence Prediction and Control, 26.-29.03.2006, Seoul, Korea
    Proceedings, 80-81

Permalink: https://www.hzdr.de/publications/Publ-8072
Publ.-Id: 8072


Synthesis of cobalt-disilicide nanowires using fine-focused ion beam

Akhmadaliev, C.; Schmidt, B.; Bischoff, L.
No abstract required
Keywords: CoSi2,FIB, nanowires, ion beam synthesis
  • Lecture (others)
    DFG Priority Program 1165 Workshop: Nanowires and Nanotubes, 04.-09.09.2005, Kleinwalsertal, Germany

Permalink: https://www.hzdr.de/publications/Publ-8071
Publ.-Id: 8071


Focused ion beam synthesis of CoSi2 nanowires

Akhmadaliev, C.; Bischoff, L.; Schmidt, B.
No abstract required
Keywords: FIB, ion beam synthesis, nanowires, CoSi2
  • Lecture (others)
    342. WE-Heraeus Seminar "Science and Technology of Inorganic Nanowires", 13.-16.02.2005, Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-8070
Publ.-Id: 8070


Quantum well infrared photodetectors: Physics and applications

Schneider, H.
This seminar talk reports on the physics and applications of quantum well infrared photodetectors.
Keywords: infrared, photodetector, intersubband, QWIP
  • Lecture (others)
    Seminarvortrag, 12.01.2006, TU Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-8069
Publ.-Id: 8069


FIB ion implantation into Si for CoSi2 nanowire growth

Schmidt, B.; Akhmadaliev, C.; Bischoff, L.
No abstract required
Keywords: CoSi2, ion beam synthesis, FIB, nanowires
  • Lecture (others)
    Annual Meeting of the DFG Priority Program 1165: Nanowires and Nanotubes, 02.-04.04.2005, Fulda, Germany

Permalink: https://www.hzdr.de/publications/Publ-8068
Publ.-Id: 8068


Thin highly sensitive piezoresitive cantilevers - implantation technology

Schmidt, B.
No abstract required
Keywords: Low energy ion implantation, RTA annealing, boron depth profiles
  • Lecture (others)
    EU-IP 515739: Technology for the production of massively parallel intelligent cantilever- probe platforms for nanoscale analysis and synthesis, PRONANO WP1 Technical Meeting, 28.-29.11.2005, Kassel, Germany

Permalink: https://www.hzdr.de/publications/Publ-8067
Publ.-Id: 8067


Resistivity of boron implanted p++ and piezoresistor layers

Zier, M.; Schmidt, B.
No abstract required
Keywords: shallow pn-junction, sheet resistance, piezresistors
  • Lecture (others)
    EU-IP 515739: Technology for the production of massively parallel intelligent cantilever- probe platforms for nanoscale analysis and synthesis, PRONANO WP1 Technical Meeting, 28.-29.11.2005, Kassel, Germany

Permalink: https://www.hzdr.de/publications/Publ-8066
Publ.-Id: 8066


Quantum well infrared photodetectors: quantum structures for high-performance thermal imaging

Schneider, H.; Maier, T.; Fleissner, J.; Walther, M.; Koidl, P.; Weimann, G.; Cabanski, W.; Finck, M.; Menger, P.; Rode, W.; Ziegler, J.
Intersubband transitions in GaAs/AlGaAs heterostructures are increasingly used in cameras for the thermal infrared regime. An excellent thermal resolution has been achieved in particular in the 8 - 12 µm spectral range. We report on the basic properties of these quantum well infrared photodetectors (QWIPs) and on the properties of cameras based on these devices in comparison to other detector materials. Finally we address a few applications for which QWIPs are the material of choice.
Keywords: thermal imaging, intersubband, infrared, QWIP
  • Invited lecture (Conferences)
    International Symposium on Advanced Electronics for Future Generations - “Secure-Life Electronics” for Quality Life and Society, 11.-12.10.2005, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-8065
Publ.-Id: 8065


Thin highly sensitive piezoresitive cantilevers - fabrication of ultra-shallow pn-junctions

Schmidt, B.; Zier, M.
No abstract required
Keywords: boron implantation, low energy implantation, RTA annealing, piezoresistors, SIMS profiles
  • Lecture (others)
    EU-IP 515739: Technology for the production of massively parallel intelligent cantilever- probe platforms for nanoscale analysis and synthesism, PRONANO Meeting, Vienna, 18.-19.10.2005, Vienna, Austria

Permalink: https://www.hzdr.de/publications/Publ-8064
Publ.-Id: 8064


Thin highly sensitve pizoresistive cantilevers - fabrication of ultra-shallow pn-junctions

Schmidt, B.
No abstract required
Keywords: Low-energy ion implantation, ultra-shallow boron layers, piezorestistors
  • Lecture (others)
    EU-IP 515739: Technology for the production of massively parallel intelligent cantilever- probe platforms for nanoscale analysis and synthesis, Kick-Off Meeting, 19.-20.04.2005, Erlangen, Germany

Permalink: https://www.hzdr.de/publications/Publ-8063
Publ.-Id: 8063


Ion beam synthesis of CoSi2 for nanoscale interconnects

Schmidt, B.
No abstract was required
Keywords: CoSi2, nanowares, nanochains, ion beam synthesis, FIB
  • Lecture (others)
    Seminar INFINEON Dresden, 16.12.2005, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-8062
Publ.-Id: 8062


Ionenstrahltechnik und Nano-Technologie

Schmidt, B.
No abstract was required
Keywords: Ion implantation, ion beam synthesis, nanoparticles, nanowires
  • Lecture (others)
    URANIA Vortragszentrum e.V. Dresden, 14.10.2005, Rossendorf, Germany

Permalink: https://www.hzdr.de/publications/Publ-8061
Publ.-Id: 8061


Ion beam synthesis of CoSi2 for nano-interconnects

Schmidt, B.
No abstract was required
Keywords: Ion beam synthesis, Fib, Co++-implantation, nanowires
  • Lecture (others)
    Seminar FhG Center of Nanotechnology Dresden, 13.10.2005, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-8060
Publ.-Id: 8060


Was können Ionenstrahlen in der Nanotechnologie bewirken?

Schmidt, B.
No abstract was required
Keywords: Ion beam synthesis, nanostructures, nanocrystals, nanowires
  • Lecture (others)
    Sonderseminar Universität der Bundeswehr, 06.10.2005, München-Neubiberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-8059
Publ.-Id: 8059


Nano-Technologie - Materialien für die Zukunft

Schmidt, B.
No abstract was required
Keywords: Nanotechnology, Nanostructures, Nanodots, Nanowires, Ion beam synthesis, FIB
  • Lecture (others)
    Lange Nacht der Wissenschaften, 01.07.2005, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-8058
Publ.-Id: 8058


Correlation of structural and physical properties of metastable Fe-Cr phases

Gorbunov, A.; Levin, A. A.; Meyer, D. C.; Bischoff, L.; Eckert, D.; Köhler, B.; Mertig, M.; Weissbach, T.; Wieser, E.; Pompe, W.
This paper contributes to the studies of physical properties of metastable Fe-Cr phases which have been discovered recently in the thin films deposited from the hyperthermal Fe and Cr particle beams. The electrical resistance and the magnetic remanence are correlated with the crystallographic parameters and phase composition of the samples. It is demonstrated that the focused ion-beam induced phase transformation in the unusual metastable Fe-Cr alloys can be used for the fabrication of ferromagnetic arrays.
Keywords: metastable Fe-Cr phases, ferromagnetic arrays, FIB
  • Crystal Research and Technology 40(2005), 106

Permalink: https://www.hzdr.de/publications/Publ-8057
Publ.-Id: 8057


Präparation und Charakterisierung von Strukturen für die Nanotechnologie

Schmidt, B.
No abstract was required
Keywords: Nanocrystals, Nanowires, FIB, Ion beam synthesis
  • Lecture (others)
    Sonderseminar im Rahmen des Graduiertenkollegs, 27.06.2005, Rostock, Germany

Permalink: https://www.hzdr.de/publications/Publ-8056
Publ.-Id: 8056


Nano-Technologie

Schmidt, B.
No abstract was required
Keywords: Nanotechnology, Nanocrystals, Nanowires, Ion beam Synthesis, FIB
  • Lecture (others)
    Lehrerfortbildungsseminar Rossendorf, 12.02.2005, Forschungszentrum Rossendorf, Germany

Permalink: https://www.hzdr.de/publications/Publ-8055
Publ.-Id: 8055


Ionenstrahlanalytik an den Rossendorfer Beschleunigern

Grötzschel, R.; Grambole, D.; Güttler, D.; Herrmann, F.; Kreißig, U.; Neelmeijer, C.
Das Ionenstrahllabor des Forschungszentrums Rossendorf als Teil des Institutes für Ionenstrahlphysik und Materialforschung betreibt Materialanalytik mit MeV Ionenstrahlen an 3 Beschleunigern, dem 5 MV Tandem, dem 3 MV Tandetron und dem 2 MV van de Graaff-Beschleuniger.
Insgesamt sind für diese Arbeiten 12 Experimentierplätze installiert, mit denen alle ionenstrahlanalytischen Techniken in hoher Qualität zur Verfügung stehen.
Neben Standardtechniken wie RBS/channeling, ERDA, PIXE und NRA, die wegen spezifischer Vorteile inzwischen unverzichtbar zum Instrumentarium der physikalischen Dünnschicht- Charakterisierung gehören, werden Verfahren eingesetzt und weiterentwickelt, die von hoher Relevanz bei der Entwicklung moderne funktioneller Schichten und deren Abscheidung sind.
Dazu gehört vor allem die quantitative Analytik von Oberflächen und ultradünnen Schichten mit Tiefenauflösungen im sub-nm – Bereich durch den Einsatz von Magnetspektrometern für die hochauflösende Teilchenspektrometrie. Begleitet wird diese methodische Entwicklung von Grundlagenarbeiten zur Abbremsung und zum Ladungsaustausch von leichten Schwerionen in Festkörpern.
Eine andere Richtung wird verfolgt bei der in situ – Ionenstrahlanalytik transienter Prozesse in „Echtzeit“, also während eines Prozessverlaufes.
Im Vortrag werden nach einer kurzen Vorstellung des Ionenstrahllabors die Arbeiten zur Höchstauflösung vorgestellt und ein in situ-Experiment zur Targetvergiftung beim reaktiven Magnetronsputtern beschrieben.
  • Invited lecture (Conferences)
    Zukunftsperspektiven und Anwendungen von Ionenstrahlen, 17.10.2005, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-8054
Publ.-Id: 8054


Nano-Drähte durch Ionenbeschuss

Schmidt, B.; Bischoff, L.; Akhmadaliev, C.; Heinig, K.-H.
Die fortschreitende Miniaturisierung mikroelektronischer Strukturen sowie deren Kombination mit optischen, mechanischen oder magnetischen Komponenten erfordern laufend neue physikalische und technologische Ansätze. Im Forschungszentrum Rossendorf wird im Rahmen von zwei Projekten, getragen von der Deutschen Forschungsgemeinschaft (DFG), intensiv an der Entwicklung und Untersuchung von Nanostrukturen für die Elektronik der Zukunft gearbeitet. So beschäftigt sich das FZR-Institut für Ionenstrahlphysik und Materialforschung u. a. mit der reproduzierbaren Herstellung von maßgeschneiderten Nano-Drähten, die möglichst passfähig zur herkömmlichen Silizium-Techologie sein sollen.

Die Herstellung dieser Drähte beruht auf der Ionenstrahlsynthese, schematisch in Abb. 2 dargestellt. Hierzu werden feine Linien von Cobalt-Ionen mit dem Fokussierten Ionenstrahl (FIB; Focussed Ion Beam) in ein Silizium-Substrat bei erhöhten Temperaturen implantiert und in einem folgenden Ausheilprozess zu einem Cobaltdisilizid-Draht (CoSi2) synthetisiert. Dabei wird die Kombination zweier wesentlicher Aspekte ausgenutzt. Zum einen wird der geringe Drahtdurchmesser durch die hohe Fokussierbarkeit des FIB auf kleiner als 50 Nanometer erreicht, auch als „top-down“-Ansatz bezeichnet. Zum anderen führen selbst-organisierende Prozesse, der „bottom-up“-Ansatz, zu einer weiteren Konzentration der implantierten Cobalt-Verteilung. Dies ermöglicht die Synthese von Nanostrukturen mit einem Durchmesser von 10 bis 20 Nanometer.

Der Schwerpunkt der Arbeiten konzentriert sich zunächst auf das zur Mikroelektronik-Technologie kompatible Cobaltdisilizid. Dieses Material ist metallisch, weist eine sehr gute Leitfähigkeit auf und ist hinsichtlich der Gitterstruktur der des Siliziums sehr ähnlich. Die ersten Ergebnisse sind vielversprechend, nun gilt es, die Reproduzierbarkeit sowie die genaue „Platzierung“ der Drähte im Material zu gewährleisten. Auf dem Weg hin zu neuen Nano-Bauelementen für die Mikroelektronik ist also noch viel zu tun.
Keywords: nano-wire, CoSi2, ion beam synthesis
  • Dresdner Transferbrief 2(2005), 13-13

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Permalink: https://www.hzdr.de/publications/Publ-8053
Publ.-Id: 8053


Metabolite analysis in positron emission tomography studies: examples from food sciences

Pawelke, B.
Substances of various chemical structures can be labelled with appropriate positron emitting isotopes and applied as tracer compounds in PET examinations. Using dynamic data acquisition protocols, time-activity curves of radioactivity uptake in organs can be derived and the measurements of tissue tracer concentrations can be translated into quantitative values of tissue function. However, analysis of metabolites of these tracers regarding their nature and distribution in the living organism is an essential need for the quantitative analysis of PET measurements. In addition, metabolite analysis contributes to the interpretation of the images obtained as well as to the identification of pathological changes in metabolic pathways. This paper reports on representative examples of radiolabelled compounds which might be of importance in food science (e.g., amino acids, polyphenols, and model compounds for advanced glycation end products (AGEs)). Typical procedures of analysis (radio-HPLC, radio-TLC) including pre-analytical sample preparation are described. Specific challenges of the method, e.g., trace amounts of radiolabelled compounds and the influence of the often very short half-lives of positron-emitting nuclides used are highlighted. Representative results of analyses of plasma, urine, and tissue samples are presented and discussed in terms of the metabolic fate of the tracers.
Keywords: Positron emission tomography – Metabolite analysis – Tracer – Amino acids – Advanced glycation endproducts – Polyphenols

Permalink: https://www.hzdr.de/publications/Publ-8052
Publ.-Id: 8052


Small animal positron emission tomography in food sciences

Bergmann, R.; Pietzsch, J.
Positron emission tomography (PET) is a 3-dimensional imaging technique that has undergone tremendous developments during the last decade. Non-invasive tracing of molecular pathways in vivo is the key capability of PET. It has become an important tool in the diagnosis of human diseases as well as in biomedical and pharmaceutical research. In contrast to other imaging modalities, radiotracer concentrations can be determined quantitatively. By application of appropriate tracer kinetic models, the rate constants of numerous different biological processes can be determined. Rapid progress in PET radiochemistry has significantly increased the number of biologically important molecules labelled with PET nuclides to target a broader range of physiologic, metabolic, and molecular pathways. Progress in PET physics and technology strongly contributed to better scanners and image processing. In this context, dedicated high resolution scanners for dynamic PET studies in small laboratory animals are now available. These developments represent the driving force for the expansion of PET methodology into new areas of life sciences including food sciences. Small animal PET has a high potential to depict physiologic processes like absorption, distribution, metabolism, elimination and interactions of biologically significant substances, including nutrients, ‘nutriceuticals’, functional food ingredients, and foodborne toxicants. Based on present data, potential applications of small animal PET in food sciences are discussed.
Keywords: Positron emission tomography – Food sciences – Small animal PET scanners – PET tracer

Permalink: https://www.hzdr.de/publications/Publ-8051
Publ.-Id: 8051


Principles of quantitative positron emission tomography

van den Hoff, J.
The central distinguishing feature of positron emission tomography (PET) is its ability to investigate quantitatively regional cellular and molecular transport processes in vivo with good spatial resolution. This review wants to provide a concise overview of the established principles underlying quantitative data evaluations of the acquired PET images. Especially, the compartment modelling framework is discussed on which virtually all quantification methods utilized in PET are based. The aim of the review is twofold: first, to provide the reader with an idea of the theoretical framework and mathematical tools and second, to enable an intuitive grasp of the possibilities and limitations of a quantitative approach to PET data evaluation. This should facilitate an understanding of how PET measurements translate into quantities such as regional blood flow, volume of distribution, and metabolic rates of specific substrates.
Keywords: Positron emission tomography – PET – Tracer kinetics – Compartment modelling

Permalink: https://www.hzdr.de/publications/Publ-8050
Publ.-Id: 8050


Ge/Si quantum dot nanostructures grown with low-energy ion beam-assisted epitaxy

Dvurechenskii, A. V.; Smagina, J. V.; Groetzschel, R.; Zinovyev, V. A.; Armbrister, V. A.; Novikov, P. L.; Teys, S. A.; Gutakovskii, A. K.
Scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED) experiments were performed to study growth modes induced by hyperthermal Ge+ ion action during molecular beam epitaxy (MBE) of Ge on Si(100). The continuous and pulsed ion beams were used. These studies have shown that ion beam bombardment during heteroepitaxy leads to decrease in critical film thickness for transition from two-dimensional (2D) to three-dimensional (3D) growth modes, enhancement of 3D island density, and narrowing of island size distribution, as compared with conventional MBE experiments. Moreover, it was found that ion beam assists the transition from hut- to dome-shaped Ge islands on Si(100). The crystal perfection of Ge/Si structures with Ge islands embedded in Si was analyzed by Rutherford backscattering/channeling technique,(RBS) and transmission electron microscopy (TEM). The studies of Si/Ge/Si(100) structures indicated defect-free Ge nanopaticles and Si layers for the initial stage of heteroepitaxy (five monolayers of Ge) in pulsed ion beam action growth mode at 350 degrees C. Continuous ion beam irradiation was found to induce dislocations around Ge clusters. The results of kinetic Monte Carlo (KMC) simulation have shown that two mechanisms of ion beam action can be responsible for stimulation of 2D-3D transition: (1) surface defect generation by ion impacts, and (2) enhancement of surface diffusion.
Keywords: ion beam-assisted epitaxy; nanoparticles; self-assembling effects
  • Surface & Coatings Technology 196(2005)1-3, 25-29

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Permalink: https://www.hzdr.de/publications/Publ-8049
Publ.-Id: 8049


Analysis of PF surfaces and interfaces using nuclear analytical methods

Mackova, A.; Grötzschel, R.; Nekvindova, P.; Spirkova, J.; Svorcik, V.; Zemek, J.
The application of nuclear analytical methods on surface and interface study is presented. Two topics are included in the presentation - polymer-metal interaction studies and study of single-crystalline structures using RBS-channeling method. Diffusion of Ag atoms in polyethyleneterephtalate (PET) was studied using Rutherford Backscattering Spectroscopy (RBS) and Elastic Recoil Detection Analysis (ERDA). The samples were prepared by deposition of Ag thin layers on polymer surface using CVD and diode sputtering techniques. Faster diffusion of Ag atoms was observed from non-compact Ag layers prepared by diode sputtering than from those prepared by CVD technique. The samples of erbium doped lithium niobate (Er:LiNbO3) were prepared by standard Czochralski method and treated by Annealed Proton Exchange (APE) procedure to create planar wave-guide for further optical application. The position of Er atoms in the crystal lattice of pristine and APE treated Er:LiNbO3 samples were studied by Rutherford Backscattering Spectrometry (RBS)-channeling method. The Er3+ ion position in the pristine and the APE treated Er:LiNbO3 samples are compared.
Keywords: DIFFUSION; LINBO3
  • Open Access Logo Acta Physica Slovaca 55(2005)3, 323-329

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Permalink: https://www.hzdr.de/publications/Publ-8048
Publ.-Id: 8048


Comparison of crystal lattice changes caused by APE treatment of Er : LiNbO3 and by localised Er doping into LiNbO3 obtained by RBS-channeling and XRD analysis

Mackova, A.; Spirkova, J.; Nekvindova, P.; Salavcova, L.; Groetzschel, R.; Eichhorn, F.
Lithium niobate containing erbium (Er:LiNbO3), which is often used as non-linear optical material, was studied by Rutherford backscattering spectroscopy (RBS)-channeling analysis and X-ray diffraction (XRD). The Er3+ doping was done by both bulk doping and by localised doping. The studied samples were virgin Er:LiNbO3 wafers, and annealed proton exchange (APE) treated wafers in order to increase the refractive index in the surface layer and to create the planar optical waveguides. Moreover, erbium ions were introduced into the surface of pure LiNbO3 wafers by Er-moderate temperature localised doping. The APE:Er:LiNbO3 samples showed modifications of the crystal lattice compared to the virgin Er:LiNbO3; the Er localised doping samples even exhibited the tendency to form an amorphous surface layer in which the Er ions were incorporated.
Keywords: RBS-channeling; XRD; APE : Er : LiNbO3
  • Nuclear Instruments and Methods in Physics Research B 240(2005)1-2, 391-394

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Permalink: https://www.hzdr.de/publications/Publ-8047
Publ.-Id: 8047


Optical and transport nonlinearities in quantum well infrared photodetectors

Schneider, H.; Maier, T.; Schönbein, C.; Koidl, P.; Walther, M.; Liu, H. C.
Nonlinear behavior in quantum well infrared photodetectors (QWIPs) can be classified into nonlinearities associated with transport effects, such as quantum well depletion or photocurrent saturation induced by the emitter barrier, and nonlinearities induced by nonlinear absorption.
After giving a short overview on the different nonlinearities occurring in QWIPs and related device structures, we will concentrate on two particular phenomena. First, it is well known that the photoconductivity in n-type GaAs/AlGaAs QWIPs exhibits negative differential behavior, and that this negative differential photoconductivity gives rise to electric field domains. We have analyzed the spatial distribution of electric field domains induced by negative differential photoconductivity in a 50-period QWIP. We found evidence of two different domain configurations, with the high-field domain and the low-field domain, respectively, adjacent to the emitter contact. Second, we report on two-photon detection based on nonlinear absorption between subbands in quantum wells. Resonantly enhanced nonlinear absorption, six orders of magnitude higher as compared to typical bulk semiconductors, leads to a threshold power density for quadratic detection as low as 0.1 W/cm2, and femtosecond time resolution. The approach enables dynamical characterization of the optical light field of infrared emitters via autocorrelation measurements. We also demonstrate the use of this technique to investigate inter- and intra-subband scattering times.
Keywords: infrared, photodetector, intersubband, QWIP
  • Invited lecture (Conferences)
    8-th International Conference on Intersubband Transitions in Quantum Wells, 11.-16.09.2005, Cape Cod, MA, USA

Permalink: https://www.hzdr.de/publications/Publ-8046
Publ.-Id: 8046


Influence of Al on the growth of NiSi2 on Si(001)

Allenstein, F.; Budzinski, L.; Hirsch, D.; Mogilatenko, A.; Beddies, G.; Groetzschel, R.; Hinneberg, H.
Thin films of different atomic ratios of nickel and aluminium were deposited on Si(001)-wafers by magnetron cosputtering. The content of deposited nickel complies to layer thickness of about 20 nm, After deposition the samples were annealed between 500 and 900 degrees C in steps of 100 degree using rapid thermal annealing (RTA) in N-2 ambient. RBS, SEM, TEM, XRD, AES and sheet resistance measurements were performed to characterize the grown thin films.
  • Microelectronic Engineering 82(2005)3-4, 474-478

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-8045
Publ.-Id: 8045


Nine Years Experience in Routine Operation and Maintenance of the Rossendorf CYCLONE 18/9 Facility

Preusche, S.; Füchtner, F.; Roß, H.; Wüst, F.
kein Abstract verfügbar
  • Contribution to proceedings
    CYCLONE 18/9 & 10/5 User Community, 5. Workshop, 01.-04.05.2005, Montreal, Canada
    5th IBA C18/9 C10/5 PET Cyclotron Users Meeting

Permalink: https://www.hzdr.de/publications/Publ-8044
Publ.-Id: 8044


Production of 86Y and 56Co at the Rossendorf CYCLOTRONE 18/9

Preusche, S.; Wüst, F.; Schilling, K.-D.; Roß, H.; Dohn, N.
kein Abstract verfügbar
  • Poster
    CYCLONE 18/9 & 10/5 User Community, 5. Workshop, 01.-04.05.2005, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-8043
Publ.-Id: 8043


The Rossendorf Solid Target System

Preusche, S.; Roß, H.; Dohn, N.; Wüst, F.; Steinbach, J.
kein Abstract verfügbar
  • Lecture (Conference)
    CYCLONE 18/9 & 10/5 User Community, 5. Workshop, 01.-04.05.2005, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-8042
Publ.-Id: 8042


Field profile measurement and tuning of the 3½ cell SRF-gun

Arnold, A.; Büttig, H.; Janssen, D.; Teichert, J.; Murcek, P.
kein Abstract vorhanden
  • Poster
    1st Annual EUROFEL Workshop 2005, 07.-09.11.2005, Orsay, France

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-8041
Publ.-Id: 8041


Bioverteilung und Metabolisierung des 18F-markierten Amadori-Produktes Fructoselysin

Hultsch, C.; Hellwig, M.; Bergmann, R.; Henle, T.
Ziel:
Amadore-Produkte (1-Amino-1-desoxy-2-ketosen) werden in der Frühphase der sogenannten Maillard-Reaktion zwischen reduzierenden Zuckern und primären Aminen in Lebensmitteln bei der zubereitung oder Lagerung sowie in vivo gebildet. Täglich werden etwa 1 g Amadori-Produkte mit der nahrung aufgenommem [1]. Jedoch ist nur der Verbleib von ca. 5% dieser Verbindungen bislang bekannt. Die ernährungsphysiologischen Konsequenzen, die sich aus der Aufnahme dieser Verbindungen ergeben, sind weitestgehend ungeklärt. Ziel dieser Arbeit war es daher, Bioverteilung und eventuelle Metabolisierungsreaktionen des Amadori-Produktes Fructoselysin auch vor dem Hintergrund der kürzlich entdeckten Fructosamin-3-Kinasen [2] zu untersuchen.

Methodik:
Fructoselysin wurde mit N-Succinimidyl-4-[18F]-Fluorbenzonat zum [18F]fluorbenzoylierten Fructoselysin (FB-FL) umgesetzt. Dieses wurde mit Organhomogenaten (Herz, Hirn, Leber, Milz, Niere, Pankreas), Vollblut, Plasma und Vollblutlysat von männlichen Wistar-Ratten inkubiert. Dabei wurde der Einfluss von ATP und 1-Desoxy-1-morpholino-fructose (DMF), einem spezifischen Inhibitor der Fructosamin-3-Kinase, auf die Umsetzung des FB-FL untersucht. Weiterhin erfolgte die Messung der Bioverteilung un der in vivo-Stabilität.

Ergebnisse:
Weder in den untersuchten Organhomogenaten noch im Vollblut oder Plasma fand eine Umsetzung des FB-FL statt. Nur im Vollblutlysat konnte die Bildung eines Umwandlungsproduktes m1 beobachtet werden. Diese Umsetzung konnte durch die Zugabe von ATP beschleunigt und durch Zugabe von DMF gehemmt werden.Die Inkubation von m1 mit alkalischer Phosphatase führte zu einem vollständigen Abbau. Bei m1 handelt es sich damit voraussichtlich um ein Phosphatester, gebildet durch eine Fructosamin-3-Kinase. Bei der Messung der Bioverteilung nach intravenöser Applikation kam es zu einer schnellen Aufnahme des Präparates in die Niere. 30% der injizierten Dosis waren auch 60 min nach Applikation noch dort zu finden. Auch in den in vivo-Untersuchungen konnte m1 als Metabolit gefunden werden. Der Anteil an unverändertem FB-FL betrug 60 min p.i. im Blut 90%, im Urin 92% und in den Nieren 16%.

Schlussfolgerungen:
Es konnte gezeigt werden, dass FB-FL ein Substrat der Fructosamin-3-Kinase ist. Trotz des Wirkens dieses Enzyms wurden 60 min p.i. fast die Hälfte des applizierten FB-FL nahezu unverändert in den Urin ausgeschieden. Somit bleibt der größte Teil des Lysins, welches bei der Zubereitung bzw. Lagerung von Nahrungsmitteln fructosyliert wird, für den Körper nicht nutzbar.

Literatur:
[1] Henle T. AGEs in foods: Do they play a role in uremia? Kidney Int Sppl. 2003;84:145-147.
[2] Delpierre G, Vanstapel F, Stroobant V, van Schaftingen E Conversion of a synthetic fructosamine into 3-phospho derivative in human erythrocytes. Biochem J. 2000;352:835-839
  • Lecture (others)
    13. Arbeitstreffen AG Radiochemie/Radiopharmazie, 06.-08.10.2005, Seefeld, Österreich, 06.-08.10.2005, Seefeld, Austria

Permalink: https://www.hzdr.de/publications/Publ-8038
Publ.-Id: 8038


Rhenium-188-Komplexe verbrückter DMSA-Derivate: Stabilitätsbetrachtungen in vitro und in vivo

Heinrich, T.; Kraus, W.; Pietzsch, H.-J.; Seifert, S.; Jentschel, C.; Faltin, I.; Pawelke, B.; Bergmann, R.; Spies, H.; Johannsen, B.
Ziel:
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.

Methodik:
Dieser Typ tetradentater Liganden wurde durch Überbrückung zweier DMSA-Moleküle mittels einer Alkylentriaminkette dargestellt. An Hand eines Modellkomplexes wurden die auftretenden Isomerien geklärt. In vitro und in vivo Stabilitätsuntersuchungen wurden für verschiedene dieser 188Re(V)OS4-Komplexe durchgeführt. Weitere funktionalisierte Liganden wurden dargestellt.

Ergebnisse:
Kopplungsfähige Derivate erlauben die Bindung an terminale Aminogruppen von Modellpeptiden. 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.

Ausblick:
Hydrophile Derivate werden bezüglich Kopplung an Biomoleküle getestet. Stabilitätsuntersuchungen der Konjugate mit therapierelevanten Aktivitätsdosen werden sich anschließen.
  • Lecture (others)
    13. Arbeitstreffen der AG Radiochemie/Radiopharmazie, 06.-08.10.2005, Seefeld, Austria

Permalink: https://www.hzdr.de/publications/Publ-8037
Publ.-Id: 8037


Erfahrungen zur Herstellung von [11C]CH3I unter Berücksichtigung langer Transportleitungen zwischen Zyklotron und Synthesemodul

Rode, K.; Knieß, T.; Wüst, F.
Ziel:
[11C]CH3I sind wichtige Markierungsbausteine in der 11C-Chemie. Für ihre Synthese und ihre Verwendung in verschiedenen Methylierungsreaktionen sind automatisierte Synthesemodule entwickelt worden. Hier vergleichen wir die Herstellung von [11C]CH3I über die Iodierung von [11C]CH4 in der Gasphase. Die erzielten radiochemischen Ausbeuten und spezifischen Radioaktivitäten sollen unter Berücksichtigung der besonderen Rossendorfer Infrastruktur (500 m Distanz zwischen Zyklotron und Synthesemodul) diskutiert werden.

Methodik:
Beim klassischen nasschemischen Verfahren wurde das im Zyklotron hergestellte [11C]CO2 in einem 11C-Synthesemodul (Nuclear Interface) zu [11C]CH3I und [11C]CH3OTf umgesetzt und für die N-Methylierung eines Piperazinderivates verwendet. Ein GE TRACERlab Fx C Synthesemodul wurde für die Konversion von [11C]CO2 in [11C]CH4 und die weitere Umwandlung in [11C]CH3I bzw. [11C]CH3OTf genutzt.

Ergebnisse:
Die N-Methylierung des Piperazinderivates mit [11C]CH3OTf im Nuclear Interface 11C-Synthesemodul ergab radiochemische Ausbeuten von 40-60% und spezifische Radioaktivitäten von bis zu 30 GBq/µmol. Die Reaktion in dem GE TRACERlab Fx C Synthesemodul lieferte radiochemische Ausbeuten von 30-40% und nur geringe spezifische Radioaktivitäten von 5-10 GBq/µmol.

Schlußfolgerungen:
Überraschenderweise konnten mit dem nasschemischen Verfahren höhere radiochemische Ausbeuten und bessere spezifische Aktivitäten erzielt werden. Das gezielte Ausfrieren von [11C]CO2 vor der Reduktion mit LiAlH4 im Nuclear Interface Synthesemodul ist von Vorteil, um Bestandteile des Targetgases, wie z.B. O2, zu entfernen.
Dagegen wurden mit dem GE TRACERlab Fx C Synthesemodul schlechtere spezifische Aktivitäten erreicht, was neben der langen Targetleitung auf folgende Ursachen zurückzuführen ist:
- Reduktion von Targetgasbestandteilen durch den Ni-Katalysator zu kaltem CH4
Dieses Problem konnte durch eine niedrigere Reduktionstemperatur und durch Verwendung von weniger reaktiven Ni teilweise gelöst werden. Die geringere Aktivität des Ni-Katalysators bedingt aber eine Verschlechterung der CH4-Konversion.
- Die eingesetzten hochreaktiven Ni-Katalysatoren verwenden Al2O3/SiO2 als Träger-material. Dieses Trägermaterial stellt eine potentielle Quelle für Kohlenstoffkontaminationen dar.
Eine Verbesserung der spezifischen Radioaktivität könnte durch das vorherige Ausfrieren von [11C]CO2 oder durch die direkte Verwendung vom im Zyklotron hergestellten [11C]CH4 erzielt werden.

Literatur:
Knieß, T. et al., Annual Report 2004, FZR-424, p. 33
  • Lecture (others)
    13. Arbeitstreffen der AG Radiochemie/Radiopharmazie, 06.-08.10.2005, Seefeld, Austria

Permalink: https://www.hzdr.de/publications/Publ-8036
Publ.-Id: 8036


SANS investigation of neutron-irradiated RPV steels with special emphasis on Ni effect

Ulbricht, A.; Bergner, F.; Pranzas, K. P.
The SANS experiment is aimed at studying the influence of neutron fluence and Ni content on irradiation-induced changes of the microstructure of WWER 1000-type reactor pressure vessel (RPV) steel. A feature of this material is a high Ni content (> 1 wt.-%) in comparison with other RPV steels. Specimens from two WWER 1000 steels with different composition, one single neutron fluence each, were analysed in a previous investigation. It turned out that:
There is a monomodal size distribution of irradiation-induced defects with an average radius of about 1 nm.
The total volume fraction of defects is significantly higher than for WWER 440 steels, which had been investigated before in more detail also by other groups.
  • Contribution to external collection
    A. Schreyer, J. Vollbrandt, R. Willumeit: GeNF - Experimental Reports 2005, GKSS 2006/4, Geesthacht: GKSS Forschungszentrum Geesthacht GmbH, 2006, 107-108

Permalink: https://www.hzdr.de/publications/Publ-8035
Publ.-Id: 8035


Small-angle scattering applied to post-irradiation annealing of neutron-irradiated pressure vessel steels

Ulbricht, A.; Bergner, F.; Heinemann, A.
The aim of the present investigation is to contribute to the understanding of cluster dissolution after isochronal post-irradiation annealing treatments (annealing time: 10 h) at stepwise increasing levels of temperature.
  • Poster
    BENSC User's Meeting 2005, 22.-23.09.2005, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-8034
Publ.-Id: 8034


Microstructural analysis by means of Small-angle neutron scattering

Ulbricht, A.; Bergner, F.
The aim of the present talk is to contribute small-angle neutron scattering (SANS) data to the experimental database. We have shown that SANS measurements for irradiated and annealed RPV steels provide additional information on the dissolution behaviour of irradiation-induced clusters particularly useful for modelling the long term evolution of clusters. A SANS experiment in December 2005 is devoted to the investigation of VVER 1000 steel in two fluences and Fe-Ni alloys.
  • Lecture (others)
    Second Plenary Meeting RPV & Internals - Physics Modelling, 17.-19.10.2005, Saclay, France

Permalink: https://www.hzdr.de/publications/Publ-8033
Publ.-Id: 8033


Microstructural analysis of WWER RPV materials with Small-angle neutron scattering

Ulbricht, A.; Bergner, F.
The aim of the present talk is to contribute small-angle neutron scattering (SANS) data on irradiated VVER steels to the experimental database.
  • Lecture (others)
    Perfect meeting on VVER materials, 13.-14.06.2005, Bratislava, Slovakia

Permalink: https://www.hzdr.de/publications/Publ-8032
Publ.-Id: 8032


Detecting irradiation induced damage in RPV steels by SANS

Ulbricht, A.; Bergner, F.
The aim of the present talk is to contribute small-angle neutron scattering (SANS) data to the experimental database. Some preliminary conclusions can be drawn from the comparison of SANS data for the materials selected within the workpackage WPII-3. SANS allows for the determination of the size distribution of irradiation-induced clusters and, in particular, for the calculation of mean radius and volume fraction. The mean radius was found to be constant (about 1 nm) and independent of the material under the present experimental conditions. The volume fraction turned out to depend on irradiation conditions and chemical composition of the material. Additional partial information on the composition of clusters is implied in the A-ratio.
  • Lecture (others)
    First Plenary Meeting RPV & Internals - Physics Modelling, 19.-21.01.2005, Manchester, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-8031
Publ.-Id: 8031


Dyslipidämien beim metabolischem Syndrom: Glykierte LDL und Atherogenese

Pietzsch, J.
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Symposium Metabolisches Syndrom 2005, 19.11.2005, Radebeul, Germany

Permalink: https://www.hzdr.de/publications/Publ-8030
Publ.-Id: 8030


Pathophysiologie der Fettstoffwechselstörungen

Pietzsch, J.
kein Abstract verfügbar
  • Invited lecture (Conferences)
    40. Jahrestagung der Deutschen Diabetes Gesellschaft, 04.-07.05.2005, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-8029
Publ.-Id: 8029


Assessment of catabolism of glycated and glycoxidized LDL in vivo: insights of small animal positron emission tomography (PET) studies

Pietzsch, J.; Hoppmann, S.; Bergmann, R.; Steiniger, B.; van den Hoff, J.
kein Abstract verfügbar
  • Abstract in refereed journal
    Diabetologia 48(2005)Suppl 1, A416
  • Lecture (Conference)
    41st Annual Meeting of the European Association for the Study of Diabetes (EASD), 10.-15.09.2005, Athens, Greece

Permalink: https://www.hzdr.de/publications/Publ-8028
Publ.-Id: 8028


Catabolism of Hypochlorite-modified low density lipoprotein (LDL) in vivo: insights from small animal positron emission tomography studies

Hoppmann, S.; Steiniger, B.; Pietzsch, J.
kein Abstract verfügbar
  • Poster
    5th European Life Science Organisation (ELSO), 03.-06.09.2005, Dresden, Deutschland
  • Contribution to proceedings
    5th European Life Science Organisation (ELSO), 03.-06.09.2005, Dresden, Deutschland
    Proceedings of the 5th European Life Science Organisation (ELSO), 230

Permalink: https://www.hzdr.de/publications/Publ-8027
Publ.-Id: 8027


Radiolabeling of human apolipoproteins using SH-reactive 18F-labeling agents: a potential approach for characterization and differentiation of metabolism of native and modified lipoproteins by small animal positron emission tomography (PET) in vivo

Pietzsch, J.; Berndt, M.; Wüst, F.; van den Hoff, J.
Oxidative modification of LDL is regarded as a crucial event in atherogenesis. Data concerning the role of circulating oxidized LDL (oxLDL) in the development of atherosclerosis are scarce. One reason for this is the shortage of methods for direct assessment of metabolism of oxLDL in vivo. We report a new methodology for labeling of both native LDL (nLDL) and oxLDL with the positron emitter fluorine-18 (18F; t½=109.7 min) by conjugation with SH-reactive N-[6-(4-[18F]fluorobenzylidene)-aminooxyhexyl]maleimide ([18F]MHAA) and the use of 18F-labeled LDL particles in dynamic PET studies in male Kyoto-Wistar rats. For labeling experiments, pools of chemically and biochemically well characterized human nLDL and oxLDL (modified by hemin/H2O2) particles, respectively, were used. Radiosynthesis of [18F]MHAA started with the preparation of [18F]fluorobenzaldehyde. In a one-pot procedure N-(6-aminooxyhexyl)maleimide was added to the generated aldehyde and after-wards [18F]MHAA was isolated by HPLC. Preparation of [18F]MHAA was achieved within 70 min with radiochemical yields of 34±5% (corrected for decay) and purity of >96%. [18F]MHAA was shown to react efficiently and selectively with SH-groups of various peptides and proteins under mild conditions. LDL labeling with [18F]MHAA resulted in radiochemical yields of 20±10% (corrected for decay) and specific radioactivity of 150-300 GBq/µmol. Radiolabeling of nLDL and oxLDL using [18F]MHAA caused neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality in vitro, respectively. The method was evaluated with respect to uptake of 18F-labeled LDL in human hepatoma cells (HepG2) and monocytes/macrophages (THP-1), respectively. Biodistribution studies in rats revealed high in vivo stability for the 18F-labeled LDL. The metabolic fate of the 18F-labeled LDL in vivo was delineated by dynamic PET studies using a dedicated small animal tomograph (spatial resolution of <2 mm). Data were compared to former studies using the NH2-reactive 18F-labeling agent N-succinimidyl-4-[18F]fluorobenzoate. In conclusion, 18F-labeling of LDL and the use of small animal PET provide a valuable tool for mapping sites of both nLDL and oxLDL metabolism in animal models in vivo.
  • Abstract in refereed journal
    Amino Acids 29(2005)1, 18-19
    DOI: 10.1007/s00726-005-0220-y
  • Invited lecture (Conferences)
    9th International Congress on Proteins and Amino Acids, 08.-12.08.2005, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-8025
Publ.-Id: 8025


Rate theory modelling of neutron irradiation induced cluster formation in RPV steels and iron based alloys

Bergner, F.; Gokhman, A. R.; Ulbricht, A.
A method allowing the cluster-matrix interaction to be introduced into the rate theory approach to cluster evolution in neutron-irradiated RPV steels and model alloys has been established. Corresponding FORTRAN code has been generated. Adjustment of the model parameters by means of comparison with experimentally obtained size distributions of radiation-induced clusters shows that cluster-matrix interaction is an important factor. In ongoing work the effect of solute enrichment and coherency between clusters and matrix should be considered.
  • Lecture (others)
    First Plenary Meeting RPV & Internals - Physics Modelling, 19.-21.01.2005, Manchester, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-8024
Publ.-Id: 8024


Isolation, characterization, and U(VI)-immobilizing potential of bacterial strains from uranium contaminated environments

Merroun, M.; Rossberg, A.; Hennig, C.; Selenska-Pobell, S.
Uranium is a long-living radionuclide that represents ecological and human health hazards. The mining and processing of uranium during the last decades for nuclear fuel and nuclear weapon production resulted in generation of significant amounts of radioactive waste. It is critical that the uranium in these wastes has to be effectively immobilized and removed away in order to prevent ground water contamination. Microbial biosorption of U(VI) was proposed as one of the methods for uranium immobilization. In this paper, we describe the isolation of bacterial strains from water and soil samples collected from different uranium contaminated environments. Phylogenetic analysis of these strains revealed that they are related to Stenotrophomonas maltophilia, Bacillus sphaericus, Microbacterium oxydans, Pseudomonas rhodesiae etc. As estimated by using ICP-MS these natural isolates possess a high ability to accumulate uranium and other heavy metals such as Cd, Pb, Ni and Ag. The bacterial uranium tolerance was studied using flow cytometry techniques. X-ray absorption near-edge structure analysis showed that the cells of these strains precipitate U(VI) as autunite-like phase (inorganic uranyl phosphate phase) at pH 4.5, probably due to the release of the inorganic phosphate from the cells. However, at pH 2 the uranium bonding was consistent with the formation of complexes with organic bound phosphate of the cell surface. These results are in agreement with those found by infrared measurements.Transmission electron microscope and energy dispersive X-ray analysis showed strain-specific extracellular and/or intracellular uranium accumulation to varying degrees.
  • Contribution to proceedings
    Biometals 2004, 03.-05.09.2004, Garmisch-Partenkirchen, Germany

Permalink: https://www.hzdr.de/publications/Publ-8023
Publ.-Id: 8023


Long term evolution of radiation induced damage - FZR contribution to rate theory

Bergner, F.; Gokhman, A. R.; Altstadt, E.
A coupled rate theory model of defect evolution and Cu clustering was introduced as a basis for the rate theory upgrade with coherency and solute content of clusters. The coupling is essentially due to the operation of Cu clusters as vacancy sinks. The model was transferred to FORTRAN code and calibrated using results of small-angle neutron scattering (SANS) experiments for a Cu-enriched (0.42% Cu) iron model alloy irradiated up to two neutron fluences. Extensions of the model to take into account size dependent cluster composition are proposed.
  • Lecture (others)
    Second Plenary Meeting RPV & Internals - Physics Modelling, 17.-18.10.2005, Saclay, France

Permalink: https://www.hzdr.de/publications/Publ-8022
Publ.-Id: 8022


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 (positive lift force coefficient) or to increase the initial disturbances (negative lift force coefficient). The feedback mechanism was 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. Recently two different groups confirmed the stability criteria experimentally.
Keywords: bubble column, linear stabiliy analysis, bubbly flow, homogeneous flow
  • Contribution to proceedings
    7th German/Japanese Symposium on Bubble Columns, 20.-23.05.2006, Goslar, Germany
  • Lecture (Conference)
    7th German/Japanese Symposium on Bubble Columns, 20.-23.05.2006, Goslar, Germany

Permalink: https://www.hzdr.de/publications/Publ-8021
Publ.-Id: 8021


Analysis of the LR-0 benchmark results (WP-3 Final Report)

Böhmer, B.
The lecture gives an overview over the final results of REDOS Work Package 3 (Analytical area - Analysis of calculated and measured data, conclusions).
For a VVER-1000 Mock-up and two VVER-440 Mock-ups and for all positions, where measurements had been carried out, neutron-gamma transport calculations were performed independently by the project participants using deterministic and/or stochastic codes and associated nuclear data libraries, mostly based on ENDF/B-VI. The calculated with different codes and laboratories neutron and gamma flux integrals, DPA-rates and spectra were compared with each other and with experimental values. Seven institutions from 5 countries (Bulgaria, Czech Republic, Germany, Hungary and Spain) delivered calculation results for the VVER-1000 Mock-up, six institutions from 4 countries performed calculations for one or both VVER-440 Mock-ups. More than eight different calculational schemes were used, covering the most important methods used for pressure vessel dosimetry and shielding. The codes used were the stochastic codes MCNP and TRAMO and the deterministic codes ANISN/DORT and TORT. They were associated with different data libraries and data preparation schemes. The BUGLE 47n/20g group structure was used for comparisons of calculated spectra as well as for comparison with experimental spectra. The comparison of the different calculation results showed considerable discrepancies for the calculation of absolute flux spectra normalized to one source neutron per second in the core for thermal neutrons and photons. The attenuation coefficients and spectra related to the spectrum in a special point had slightly lower discrepancies. The measured spectra and attenuation coefficient agree in most cases with the calculated values within the limits of experimental and calculational errors. Considerable discrepancies are found for the gamma to neutron relation at the outer surface of the barrel. The neutron attenuation through the RPV tends to be calculated too small. The uncertainties of the calculations were evaluated on the basis of the dispersion of the participants results, of the discrepancies between calculated and measured results and of the scattering of results obtained with different data libraries and data treatment procedures.
Keywords: neutron-gamma transport calculations, VVER-1000 Mock-up, VVER-440 Mock-up, neutron and gamma flux spectra, flux integrals, DPA-rates
  • Invited lecture (Conferences)
    Final REDOS Meeting, 14.-15.10.2004, Madrid, Spain

Permalink: https://www.hzdr.de/publications/Publ-8020
Publ.-Id: 8020


Reactor dosimetry: accurate determination and benchmarking of radiation field parameter, relevant for pressure vessel monitoring (REDOS) - REDOS Final Report

Ballesteros, A.; Jardí, X.; Böhmer, B.; Konheiser, J.; OšMera, B.; Kyncl, J.; Keresztúri, A.; Hordosy, G.; Ilieva, K.; Belousov, S.; Kirilova, D.; Mitev, M.; Petrov, B.; Acosta, B.; Smutný, V.; Polke, E.; Zaritsky, S.; Töre, C.; Ortego, P.
The REDOS project aims to improve reactor dosimetry for radiation embrittlement monitoring of the reactor pressure vessel (RPV) steels. Benchmarking, as well as combined experimental and computational techniques, have been used. Specific objectives were the improvement of the neutron-gamma calculation methodologies through the LR-0 engineering benchmarks for WWER-1000 and WWER-440 reactor types, and the accurate determination of radiation field parameters in the vicinity and over the thickness of the RPV.
A review of the available experimental reactor dosimetry data of Kozloduy Units 1, 4, 5 was performed, and attenuation coefficients through the vessel wall were calculated. Existing data for the WWER-440 and WWER-1000 Mock-ups were reviewed and the preparatory work for subsequent measurement and experimental data analysis was carried out. Measurements of the space-energy distribution of the mixed neutron-gamma field in the WWER-1000 model over the RPV simulator were performed. The most important improvements in the experimental techniques used were the multiparameter spectrometer and a new low noise precise monitoring system in the LR-0 research reactor, developed for this type of measurements. For the WWER-1000 Mock-up and the two WWER-440 Mock-ups and for all positions, where measurements had been performed, neutron-gamma transport calculations were carried out independently by the participants using deterministic and/or stochastic codes and associated nuclear data libraries, mostly based on ENDF/BVI. The calculated neutron and gamma flux integrals, DPA-rates and spectra were compared with each other and with experimental values. Seven institutions from 5 countries (Bulgaria, Czech Republic, Germany, Hungary and Spain) delivered calculation results for the WWER-1000 Mock-up, six institutions from 4 countries performed calculations for one or both WWER-440 Mock-ups. More than eight different calculational schemes were used, covering the most important methods used for pressure vessel dosimetry and shielding. The codes used were the stochastic codes MCNP and TRAMO and the deterministic codes ANISN/DORT and TORT. They were associated with different data libraries and data preparation schemes. The BUGLE 47n/20g group structure was used for comparisons of calculated spectra as well as for comparison with experimental spectra. Results of RPV attenuation calculations for WWER-440s and WWER-1000s were obtained. A comparison between Western and Eastern attenuation determination approaches was carried out. The neutron/fluence (E>0.5 MeV) wall attenuation for WWER-440 and WWER-1000 RPVs is slower than the dpa attenuation. This means that fluence above 0.5 MeV is more conservative approach than the use of dpa. Another task performed was the application/extrapolation of the WWER mock-ups results to power reactors. The attenuation through the RPV of the neutron flux/fluence with energy above 0.5 MeV was determined. The relative difference value does not exceed 10% for WWER-440. The relative difference value does not exceed 10% for WWER-1000 too, except at the position behind the RPV wall.
Keywords: Radiation embrittlement, reactor pressure vessel, VVER-1000, VVER-440, LR-0, reactor mock-up, neutron-gamma calculation, radiation field parameters, photon and neutron spectra measurements, stilbene scintillator, multiparameter spectrometer
  • Other report
    JRC Petten: AMES Report n.17, EUR 21771 EN, 2005
    63 Seiten

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Publ.-Id: 8019


Structure and pH-Sensitivity of the Transmembrane Segment 3 of Rhodopsin

Madathil, S.; Furlinski, G.; Fahmy, K.
Activation of G protein-coupled receptors (GPCRs) originates in ligand-induced protein conformational changes that are transmitted to the cytosolic receptor surface. In the photoreceptor rhodopsin, and possibly other rhodopsin-like GPCRs, protonation of a carboxylic acid in the conserved E(D)RY motif at the cytosolic end of transmembrane helix 3 (TM3) is coupled to receptor activation. Here, we have investigated the structure of synthetic peptides derived from rhodopsin TM3. Polarized FTIR-spectroscopy reveals a helical structure of a 31-mer TM3 peptide reconstituted into PC vesicles with a large tilt of 40-50° of the helical axis relative to the membrane normal. Helical structure is also observed for the TM3 peptide in detergent micelles and depends on pH especially in the C-terminal sequence. In addition, the fluorescence emission of the single tyrosine of the D(E)RY motif in the TM3 peptide exhibits a pronounced pH sensitivity that is abolished when Glu is replaced by Gln demonstrating that protonation of the conserved Glu side chain affects the structure in the environment of the D(E)RY motif of TM3. The pH-regulation of the C-terminal TM3 structure may be an intrinsic feature of the E(D)RY motif in other class I receptors allowing the coupling of protonation and conformation of membrane-exposed residues in full length GPCRs.
Keywords: G protein-coupled receptor, FTIR-spectroscopy, membrane protein, peptide, secondary structure

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Publ.-Id: 8018


Light-ion production in the interaction of 96 MeV neutrons with oxygen

Tippawan, U.; Pomp, S.; Atac, A.; Bergenwall, B.; Blomgren, J.; Dangtip, S.; Hildebrand, A.; Johansson, C.; Klug, J.; Mermod, P.; Nilsson, L.; Österlund, M.; Olsson, N.; Prokofiev, A.; Nadel-Turonski, P.; Corcalciuc, V.; Koning, A.
Double-differential cross sections for light-ion (p, d, t, He-3 and alpha) production in oxygen, induced by 96 MeV neutrons are reported. Energy spectra are measured at eight laboratory angles from 20 to 160 degrees in steps of 20 degrees. Procedures for data taking and data reduction are presented. Deduced energy-differential and production cross sections are reported. Experimental cross sections are compared to theoretical reaction model calculations and experimental data at lower neutron energies in the literature.
Keywords: Neutron scattering, light-ion production, reaction cross sections
  • Physical Review C 73(2006), 034611

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Publ.-Id: 8017


Reversals in a nutshell

Stefani, F.; Gerbeth, G.; Günther, U.
An appropriate theory of Earth's magnetic field reversals has to explain a number of observations:

The first observation concerns the different time scales relevant in the process. The very polarity transition takes only about 5 kyr which is much shorter than the typical interval between reversals (varying between 200 kyr in the present and some tens of Myr during superchrons). In between these two time scales there lies the so-called inhibition time (approximately 40 kyr) during which a follow-up reversal is very unlikely. A second remarkable feature of reversals is their typical asymmetric (saw-toothed) shape with a slow decay and a fast recovery of the opposite field. A third, although controversially discussed hypothesis points to a correlation of the interval time between reversals and the magnetic field amplitude. A fourth observation concerns the bimodal distribution of the virtual dipole moment that has been observed with two peaks at about 4 x 1022 A m2 and at about twice that value.

Using a paradigmatic mean-field dynamo model with a spherically symmetric helical turbulence parameter alpha which is quenched by the magnetic energy and disturbed by additional noise we attribute all these reversal features to the magnetic field dynamics in the vicinity of an exceptional point of the spectrum of the non-selfadjoint dynamo operator (Phys. Rev. Lett. 94 (2005), 184506).

A weakness of this reversal model is the apparent necessity to fine-tune the magnetic Reynolds number and/or the radial profile alpha(r)in order to adjust the operator spectrum in an appropriate way. It can be shown, however, that this fine-tuning is not necessary in the case of higher supercriticality of the dynamo (arxiv.org/abs/physics/0509118). For increasing magnetic Reynolds number there is a strong tendency for the exceptional point and the associated local maximum to move close to the zero growth rate line were the indicated reversal scenario can be actualized.

Special focus is also laid on the astonishing similarities between numerically computed time series and paleomagnetic observations from the last five reversals (arxiv.org/abs/physics/0601011).
  • Open Access Logo Abstract in refereed journal
    Geophysical Research Abstracts 8(2006), 03265

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Publ.-Id: 8016


Influence of colloids produced by the weathering of rock material on uranium(VI) behaviour

Zänker, H.; Weiß, S.
There is a mechanism of secondary mineral colloid generation straight at the water-rock interfaces by the weathering of the rock material. It is of importance in the unsaturated zone as for instance in mine waste rock piles. Here we demonstrate the influence of iron-rich colloids generated by this mechanism on the behaviour of uranium(VI). The weathering of phyllite from an abandoned uranium mine in waters poor in cations and anions (“rainwater”) was simulated. The colloids produced by the weathering of this phyllite were able to keep large fractions (up to 90 %) of the uranium(VI) in a colloid-borne form in the pH region of 5.0 to 7.5. In the absence of colloids, this U(VI)) would have been truly dissolved in this pH region. The consequences of this colloid influence on uranyl speciation in natural oxic waters depend on the specific conditions in a geological environment. In a mine waste rock pile both, situations where the iron-rich colloids increase U(VI) mobility by preventing UO22+ attachment at interfaces and situations where the colloids immobilize U(VI) by scavenging, colloid aggregation, colloid deposition, formation of crusts etc., are possible
Keywords: Colloids, Weathering, Transport of Uranium(VI), Mine waste rock piles
  • Lecture (Conference)
    36th Journées des Actinides, 01.-04.04.2006, Oxford, Great Britain

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Publ.-Id: 8014


Test of the photocathode cooling system of the 3½ cell SRF gun

Staufenbiel, F.; Büttig, H.; Evtushenko, P.; Janssen, D.; Lehnert, U.; Michel, P.; Möller, K.; Schneider, C.; Schurig, R.; Teichert, J.; Xiang, R.; Stephan, J.; Lehmann, W.-D.; Kamps, T.; Lipka, D.; Will, I.; Volkov, V.
This paper presents results of the photocathode cooling system test of the 3½ cell SRF gun at the Forschungszentrum Rossendorf. The SRF gun will produce short electron pulses with high bunch charges and low transverse emittance. The requirement for the superconducting electron linear accelerator in Rossendorf (ELBE) is to provide a low emittance electron beam up to 1mA current and 9.5 MeV energy. Additionally, it will easily operate in continuous wave (cw) mode because of the low RF power losses in the superconducting material. Therefore, the normal conducting copper cathode must be cooled by liquid nitrogen in order to preserve the temperature of the cavity at 2.2 K. The estimated power input from the RF field into the cathode could be more than 10 W [1]. First results of temperature measurements of the photo cathode respectively from the cooling system at a heat load up to 30 W are presented.
  • Physica C 441(2006)1-2, 216-219

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