Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Analysis of hydrogen passivation by sputtered silicon nitride
Catoir, J.; Grisshammer, M.; Wolke, W.; Preu, R.; Trassl, R.; Grambole, D.;
An important parameter for a good bulk passivation of silicon solar cells is the hydrogen content of the silicon nitride anti reflexion layer [1,2]. Several studies [3,4] show that the hydrogen diffuses during the silicon nitride (SiN:H) deposion and the contact formation process into the bulk of the solar cell and passivates impurities and defects. In this work we present some results showing the benefit of an optimal hydrogen rate and a plasma pretreatment of the SiN especially for the bulk passivation. Additionally Nuclear Reaction Resonance Analysis measurements and effusion measurements were carried out for a better understanding of the hydrogen diffusion in the silicon nitride and at the boundary layer.
  • Poster
    23th European Photovoltaic Solar Energy Conference and Exhibition, 01.-05.09.2008, Valencia, Spain
  • Contribution to proceedings
    23th European Photovoltaic Solar Energy Conference and Exhibition, 01.-05.09.2008, Valencia, Spain
    Proceedings of the 23th European Photovoltaic Solar Energy Conference and Exhibition, 1530-1533

Publ.-Id: 11444 - Permalink


New sub-\mu s isomers in 125,127,129Sn and isomer systematics of 124-130 Sn
Lozeva, R. L.; Simpson, G. S.; Grawe, H.; Neyens, G.; Atanasova, L. A.; Balabanski, D. L.; Bazzacco, D.; Becker, F.; Bednarczyk, P.; Benzoni, G.; Blasi, N.; Blazhev, A.; Bracco, A.; Brandau, C.; Caceres, L.; Camera, F.; Chamoli, S. K.; Crespi, F. C. L.; Daugas, J.-M.; Detistov, P.; de Rydt, M.; Doornenbal, P.; Fahlander, C.; Farnea, E.; Georgiev, G.; Gerl, J.; Gladnishki, K. A.; Gorska, M.; Grebosz, J.; Hass, M.; Hoischen, R.; Ilie, G.; Ionescu-Bujor, M.; Iordachescu, A.; Jolie, J.; Jungclaus, A.; Kmiecik, M.; Kojouharov, I.; Kurz, N.; Lakshmi, S. P.; Lo Bianco, G.; Mallion, S.; Maj, A.; Montanari, D.; Perru, O.; Pfützner, M.; Pietri, S.; Pinston, J. A.; Podolyak, Z.; Prokopowicz, W.; Rudolph, D.; Rusev, G.; Saitoh, T. R.; Saltarelli, A.; Schaffner, H.; Schwengner, R.; Tashenov, S.; Turzo, K.; Valiente-Dobon, J. J.; Vermeulen, N.; Walker, J.; Werner-Malento, E.; Wieland, O.; Wollersheim, H.-J.;
New sub-\mu s isomers have been observed in the neutron-rich Sn isotopes. 125,127,129Sn nuclei have been produced in a relativistic fission reaction of 238U on a 9Be target at 750 A MeV and by the fragmentation of 136Xe at 600 A MeV populating high-spin yrast states. In addition to the already known \mu s isomers, three new ones -1 with sub-\mu s half-lives have been observed. These yrast isomers are the high-spin members
of the \nu (d_3/2^-1 h_11/2^-2 ) and \nu h_11/2 ^-n, seniority v = 3 multiplets leading to isomeric (23/2+) and (27/2-) states, respectively. Added to the already known 19/2+ \mu s isomers in this region the current work completes the systematic information of neutron-hole excitations toward the filling of the last h_11/2 orbital a t N = 82.
The results are discussed in the framework of state-of-the -art shell-model calculations using realistic interactions.
Keywords: Nuclear structure, isomers, radioactive ion beams, shell model.

Publ.-Id: 11443 - Permalink


New Insights into the Formation of Radiohaloes: Effects of Artificial Alpha–Irradiation on Cordierite
Krickl, R.; Nasdala, L.; Wildner, M.; Grambole, D.;
Radiohaloes showing a markedly altered light absorption behaviour caused by the action of alpha particles are found in a number of minerals, surrounding radioactive inclusions (Ramdohr, 1960). In order to shed light on the processes of radiohalo formation, a study on artificially produced analogues of natural radiohaloes was conducted: Oriented cordierite crystals were implanted with 8.8 MeV He2+ ions, which corresponds to the highest alpha energy commonly encountered in nature. The irradiated areas are characterised by yellow colouration, which is strongly polarised parallel to the crystallographic c axis. Optical absorption spectra show that the colour is mainly caused by the low-wavelength slope of an intense absorption band in the ultraviolet region. Furthermore, the relative changes of metal–metal charge transfer and d–d band intensities as compared to the un-irradiated host reveal significant oxidation of the Fe2+ ions in the cordierite structure.
Monte Carlo simulations show that the observed alteration depth of ~48 µm is in very good agreement with the calculated ranges of the injected particles. However, total intensity and radial intensity distribution of the radio-induced absorption change with increasing irradiation dose. The colouration intensity increases up to doses of 1014 He2+/cm² but fades at higher doses, i.e. a radio-induced colouration reversal is observed.
The change in colour is accompanied by structural damage, caused by the impact of the He2+ ions: Raman spectra show increased broadening of vibrational bands when approaching the penetration depth of the injected particles, indicating a decrease of the short range order due to the accumulation of point defects. However, no indication of amorphisation was observed in cordierite irradiated with up to 1016 He2+/cm². This seems to be in apparent contrast to He-irradiated α-quartz where local amorphisation was detected after implantation with only 1015 He2+/cm² (Krickl et al., 2008).
Furthermore, Raman and infrared spectroscopic investigations yield evidence for a radiochemical transformation of molecular species incorporated in the structural channels of the cordierite structure. Especially the transformation CO2→CO, which was also found in natural radiohaloes, was reproduced artificially and experimentally confirmed. The presence of CO in cordierite may therefore not only be caused by reducing conditions during formation (Khomenko & Langer, 2005) but also by the action of radioactivity.

References
Khomenko VM, Langer K (2005) Carbon oxides in cordierite channels: Determination of CO2 isotopic species and CO by single crystal IR spectroscopy. Am Mineral 90: 1913-1917
Krickl R, Nasdala L, Götze J, Grambole D, Wirth R (2008) Alpha-irradiation effects in SiO2. Eur J Mineral 20 (accepted)
Ramdohr P (1960) Neue Beobachtungen an radioaktiven Höfen in verschiedenen Mineralien mit kritischen Bemerkungen zur Auswertung der Höfe zur Altersbestimmung. Geol Rundschau 49: 253-263
  • Lecture (Conference)
    86th Annual Meeting of the German Mineralogical Society, 14.-17.09.2008, Berlin, Germany

Publ.-Id: 11442 - Permalink


Plasma-Based Ion Implantation Treatments Under Industrially Relevant Conditions
Ueda, M.; Wei, R.; Reuther, H.;
Industrially relevant PIII conditions were applied to H13 and CrNiMo 316 steel as well as in CrCoMo and Ti6Al4V metal alloys. Typically, nitrogen ions were implanted at peak voltages of 10 to 15 kV, 50 to 80 (s pulse durations, and 1 to 2 kHz frequencies, for treatment times of 1 to12h. Case thicknesses of more than 20 μm were achieved in treated H13 steel which resulted in reduced friction and wear. For CrNiMo steel, a wear reduction of as high as 160 times was obtained besides a significant reduction of the coefficient of friction. Much thinner modified layer was obtained for Ti6Al4V but sufficient for an important improvement of the surface hardness.
  • Solid State Phenomena 107(2005), 31-36

Publ.-Id: 11441 - Permalink


In vitro and in vivo evaluation of 64Cu-labeled bispidine ligands
Juran, S.;
Introduction:
The synthesis, characterization and evaluation of novel hexadentate bispidine derivatives containing pyridine and/or imidazole units as donor groups are presented. Bispidine ligands (bispidine = 3,7-diazabicyclo[3.3.1]-nonane) show unique complexation behaviour towards transition metals [1,2]. The high thermodynamic stability of the complexes of these structurally reinforced ligands with Cu(II) offers the possibility to apply such complexes for diagnostic (64Cu) and therapeutic (67Cu) purposes [3]. Moreover the bispidine structure opens suitable chemical approaches to connect bio-molecules onto the skeleton, an important feature in view of the targeting of such complexes.

Experimental:
The ligands were prepared by two consecutive Mannich condensations according to the known procedure [1]. Cyclic voltammetry (CV) measurements were recorded on a BAS 100B instrument with a standard three-electrode cell (glassy carbon electrode, AgNO3/Ag reference electrode, Pt wire with auxiliary electrode) at 25 °C in degassed water in an Ar atmosphere. Bispidines were labelled with 67Cu using 67CuCl2. To 200 µl of the ligand solution (10-4 M ligand in 0.05 M MES/NaOH buffer, pH = 5.4) 250 kBq of 67CuCl2 were added. 67Cu-labelling yields were studied by TLC using RP18 TLC plates which were developed in acetonitrile /water (0.1%TFA) = 4/1.

Results and Discussion:
CV measurements were performed in order to estimate the stability of the copper(II) bispidine complexes. Strongly negative redox potentials were found for all compounds investigated indicating the high stability of the Cu(II) complexes [2]. Labelling experiments of the new bispidines with 67Cu and 64Cu indicate the rapid formation of radiocopper complexes under mild conditions in almost quantitatively yields.

Conclusion:
The radiocopper complexes were found to be stable in the presence of a high excess of competing ligands, and showed a high in vitro stability in rat plasma up to 24 h. Studies on the bioconjugation of the bispidine 64Cu complexes are now in progress.

Acknowledgement:
Roger Schibli (Paul Scherrer Institute, Villigen, Switzerland) is gratefully acknowledged for providing copper-67.

[1] P. Comba, W. Schiek, Coord. Chem. Rev. 2003, 238-239, 21-29.
[2] C. Bleiholder et al. Inorg. Chem. 2005, 44, 8145-8155.
[3] M. J. Welch, C. S. Redvanly, Eds., Handbook of Radiopharmaceuticals: Radiochemistry and Applications, J. Wiley & Sons, Chichester, 2003
  • Lecture (Conference)
    15th Workshop "The Synthesis and Applications of Isotopes and Isotopically Labelled Compounds", 12.-13.06.2008, Bad Soden, Deutschland

Publ.-Id: 11440 - Permalink


Controlled transport and focusing of laser-accelerated protons with miniature magnetic devices
Schollmeier, M.; Becker, S.; Geißel, M.; Flippo, K. A.; Blazevic, A.; Gaillard, S. A.; Cort Gautier, D.; Grüner, F.; Harres, K.; Kimmel, M.; Nürnberg, F.; Rambo, P.; Schramm, U.; Schreiber, J.; Schütrumpf, J.; Schwarz, J.; Tahir, N. A.; Atherton, B.; Habs, D.; Hegelich, B. M.; Roth, M.;
This letter demonstrates the transporting and focusing of laser-accelerated 14 MeV protons by permanent magnet mini quadrupole lenses providing field gradients as high as 500 T/m. The approach is highly reproducible and predictable, leading to a focal spot of (286 × 173) μm full width at half maximum 50 cm behind the source. It decouples the relativistic laser-proton acceleration from the beam transport, paving the way to optimize both separately. The collimation and the subsequent energy selection obtained is perfectly applicable for upcoming high-energy high-repetition rate laser systems.
Keywords: Laser ion acceleration, beam focusing, permanent magnets, miniature magnetic lenses PACS numbers: 41.75.Jv,52.38.Kd,41.85.Lc,52.59.-f

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Publ.-Id: 11439 - Permalink


ALD of YF3 thin films from TiF4 and Y(thd)3 precursors
Pilvi, T.; Puukilainen, E.; Munnik, F.; Leskelä, M.; Ritala, M.;
Yttrium fluoride is a dielectric material with good light transmittance between ultraviolet (UV) and infrared (IR) range of wavelengths. In this paper we introduce the first use of atomic layer deposition (ALD) process of YF3 thin films. The films were grown at 175–325 °C. Y(thd)3 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) was used as a cation source and TiF4 as a fluorine precursor. YF3 film growth characteristics as well as structural, optical, and electrical properties were studied. Different methods, such as spectrophotometry, X-ray diffractometry, scanning electron microscopy, atomic force microscopy, and elastic recoil detection analysis were applied to characterize the films. Electrical properties were analyzed from Al/YF3/indium-tin-oxide capacitor structures at room temperature. The growth rates of the films were between 1.1 and 1.7 Å/cycle. The films grown below 225 °C were amorphous, otherwise they were polycrystalline. Permittivities of the films were around 6. The surface roughness of the YF3 films increased with the deposition temperatures. The refractive indices were 1.51–1.59 (at λ = 580 nm), and high light transmittance was achieved from UV to IR region with the sample grown at 300 °C.
Keywords: Atomic layer deposition (ALD), Yttrium fluoride (YF3), Optical materials, Thin films.

Publ.-Id: 11437 - Permalink


Applications of cavity transverse modes in accelerators
Janssen, D.; Volkov, V.;
Different applications of TE modes in accelerator physics are discussed. In this discussion, the Fourier transform of the squared axial component of magnetic field, Bz2(z), plays an important role. If it turns to be zero, the RF field-particle energy transfer is negligible and the focal length of the TE mode lens is phase independent. Such RF lens focuses continuous beams just as a solenoid. In order to compensate spherical aberrations and emittance growth caused by field nonlinearities of a focusing solenoid, the RF focusing is used also even if the beam space charge is taken into account. If the transform has its maximum, excitations of TE mode resonances and electron beam self-focussing are possible. Furthermore, the RF field of the TE mode can be used to expand the radial acceptance of a FEL for the THz region.
  • Open Access LogoPhysical Review Special Topics - Accelerators and Beams 11(2008), 061302

Publ.-Id: 11436 - Permalink


Beam Diagnostics around the ELBE LINAC at FZD
Schurig, R.; Buechner, A.; Buettig, H.; Gabriel, F.; Jainsch, R.; Justus, M.; Lehnert, U.; Michel, P.; Proehl, D.; Schneider, C.; Teichert, J.;
The ELBE linear electron accelerator (LINAC) was put into operation in 2001. It now consists of a thermionic injector and two superconducting modules, each employing two niobium 9 cell TESLA type cavities. The LINAC is capable of accelerating 1 mA up to 40 MeV. The electron beam is used to generate various types of secondary radiation (IR, Bremsstrahlung, x-rays) and particle beams (neutrons, positrons). Being a multi purpose machine with high demands on beam precision and stability and given the high average cw beam power, sophisticated beam instrumentation and machine protection systems had to be developed. Systems and methods to measure beam position, -loss, -energy and -current, energy spread, bunch length and emittance are described in this paper.
  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Deutschland

Publ.-Id: 11435 - Permalink


The ELBE Free-Electron Lasers – a user facility for the mid- to far infrared
Lehnert, U.; Michel, P.; Seidel, W.; Teichert, J.; Wünsch, R.;
The Radiation Source ELBE at the Forschungszentrum Dresden-Rossendorf in is centered around a superconducting Electron Linear accelerator of high Brilliance and low Emittance (ELBE), constructed to deliver a CW electron beam with up to 1 mA beam current at 40 MeV. The electron beam is used to generate various kinds of secondary radiation, mainly to drive free-electron lasers in the infrared.

First lasing of the mid-IR free-electron laser (U27) at ELBE was achieved in May, 2004. Since then, using electron beam energies from 15 to 35 MeV infrared radiation from 3 to 22 µm wavelength has been produced. At all wavelengths below 20 µm a CW optical power higher than 1 W can be produced with an electron beam of 50 pC bunch charge. The optical pulse width at its minimum was measured to 0.9 ps at 11 µm and could be increased to 4 ps by detuning the optical cavity. The optical bandwidth was in all cases close to the Fourier limit.

In August, 2006 the long-wavelength (U100) FEL was installed and lasing was achieved within a few hours from first beam injection. Equipped with a partially waveguided resonator this FEL covers a range of wavelengths from 20 µm to above 230 µm. Its output power reaches some 10 watts in CW operation.

Since 2005, the FEL is operated as a user facility, being open to users worldwide, provided their scientific proposals have been favorably evaluated by the panel responsible for distribution of beam time. Under the name "FELBE" the facility is a member of the EC funded "Integrating Activity on Synchrotron and Free Electron Laser Science (IA-SFS)", which comprises most synchrotron and FEL facilities in Europe and provides financial support to users from the EC and associated states. A unique scientific opportunity is opened with the beamline coupling the ELBE FELs to the Dresden High Magnetic Field Laboratory allowing magneto-optical experiments with IR and THz radiation under fields that will reach 100 T in the near future.
  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Deutschland

Publ.-Id: 11434 - Permalink


New Structures for High Resolution THz-Imaging in Medical Applications
Staats, G.; Schade, U.;
In the past years new methods for medical and biochemical imaging and microspectroscopy in the THz-range were developed. Naturally in imaging and also in microspectroscopy high spatial resolutions are requested. This is contrary to the relatively long wavelengths in the THz-range and has been lead to nearfield microscopy methods with resolution in the sub-wavelength range. For this method special structures, called coupling structures, are needed to focus the incident Gaussian beam or free space mode on a probe, as shown at Figure 1. At the beginning cones are used for this purpose. This was connected with high transmission losses due the sub-wavelength-regime and the evanescent wave propagation inside the cones.
In a first step invented by Keilmann et al [1] the transmission losses are lowered using a wire in the centre of the cone. With this method it is possible to transform the incident wave in a TEM (transversal electro-magnetic) wave without lower cut-off fre-quency.
  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Deutschland

Publ.-Id: 11433 - Permalink


Investigation and improvement of beam stability at the ELBE FEL's
Michel, P.; Justus, M.; Lehnert, U.; Schurig, R.; Teichert, J.;
At the radiation source ELBE in the Forschungszentrum Dresden-Rossendorf two free electron lasers (3-20 µm and 20-230 µm) are in routine user operation for a wide range of IR experiments for some years. The lasers are driven by a superconducting RF Linac which permits the generation of a cw-beam with high average beam power. For many experiments the frequency and power stability of the laser beam is of outstanding importance. Therefore studies on fluctuations and drifts in different time scales (from µs to hours) were accomplished and possible causes for these instabilities were investigated. To improve the long and short term stability we developed and implemented active feed back controls for electron energy and thus laser wavelength and out-coupled IR-beam power at ELBE.
  • Lecture (Conference)
    30th International Free Electron Laser Conference, 24.-29.08.2008, Gyeongbuk, Republic of Korea

Publ.-Id: 11432 - Permalink


Initial Commissioning Experience with the Superconducting RF Photoinjector at ELBE
Teichert, J.; Arnold, A.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schamlott, A.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Xiang, R.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.;
A radio frequency photo injector with a superconducting acceleration cavity (SRF gun) for installation at the Radiation Source ELBE was developed within a collaboration of BESSY, DESY, FZD, and MBI. The aim of the project is to improve the electron beam quality and to extend the parameter range of the ELBE accelerator. Especially the bunch charge will be increased up to 1 nC and the transverse emittance will be reduced to 1 - 3 mm mrad. At present, the thermionic injector at ELBE delivers bunches of 77 pC at about 8 mm mrad. Furthermore, the SRF gun together with its diagnostic beam line is an excellent test bench for extended studies and improvements of this new and promising injector type. The gun cryostat, the electron diagnostic beamline, and the driver laser with optical beamline were installed in summer and fall 2007. In November the first beam was produced. It will be reported on the experience gained at the first phase of commissioning. Results of rf and beam parameter measurements with Cu and Cs2Te photo cathodes will be presented.
  • Invited lecture (Conferences)
    30th International Free Electron Laser Conference, 24.-29.08.2008, Gyeongju, Republic of Korea
  • Contribution to proceedings
    30th International Free Electron Laser Conference, 24.-29.08.2008, Gyeongju, Republic of Korea
    Proceedings of the FEL2008, 467-472

Publ.-Id: 11431 - Permalink


A surface structural model for ferrihydrite II: Adsorption of uranyl and carbonate
Hiemstra, T.; van Riemsdijk, W. H.; Rossberg, A.; Ulrich, K.-U.;
A multisite surface complexation (MUSIC) model for ferrihydrite has been developed. The surface structure and composition are described for ferrihydrite in terms of site densities, molar mass, bulk density and reactive surface area, all linked to ion binding and surface charge development. Singly coordinated surface groups dominate the surface of ferrihydrite. These groups are present in two structural configurations, each linked to different surface patches. The configurations either form bidentate complexes by edge sharing coordination or form double-corner complexes. Both types of configurations react differently in terms of binding of ions such as uranyl and carbonate.
The adsorption of uranyl (UO22+) on ferrihydrite has been evaluated with the Charge Distribution (CD) model. Modeling shows that uranyl forms bidentate innersphere complexes at binding sites that do not react with carbonate ions. This observation is used to develop a surface structural model for ferrihydrite. Uranyl is bound by singly coordinated surface groups present at particular edges of Fe-octahedrons of ferrihydrite while another set of singly coordinated surface groups may form double-corner bidentate complexes with for instance carbonate ions. The uranyl surface speciation strongly changes in the presence of carbonate due to the specific adsorption of carbonate ions as well as the formation of ternary uranyl-carbonate surface complexes. The CD model reveals the formation of a uranyl-triscarbonato surface complex, i.e. ≡ (UO2)(CO3)34-, particularly present in systems with a high pH and carbonate concentration. This finding remarkably differs from results from previous interpretations made in literature. The presence of this surface species agrees quantitatively with a recent interpretation of EXAFS data (Rossberg et al. 2008). In the specific case of a high pH value, but at low carbonate level, as can be prepared in CO2-closed systems, the model suggests the presence of a ternary uranyl-monocarbonato complex. The binding mode (type A or type B complex) is uncertain. At high uranyl concentrations, uranyl will polymerize at the surface of ferrihydrite. The differences and similarities in U(VI) adsorption behavior of goethite and ferrihydrite is discussed from a structural point of view.
Keywords: uranium, uranyl, carbonate, triscarbonato, HFO, ferrihydrite, goethite, hematite, iron, oxide, EXAFS, FTIR, edge, double-corner, adsorption, surface, competition, CD model, MUSIC model.
  • Geochimica et Cosmochimica Acta 73(2009)15, 4437-4451

Publ.-Id: 11430 - Permalink


Identification of uranyl surface complexes on ferrihydrite: Advanced EXAFS data analysis and CD-MUSIC modeling
Rossberg, A.; Ulrich, K.-U.; Weiss, S.; Tsushima, S.; Hiemstra, T.; Scheinost, A. C.;
Previous spectroscopic research suggested that uranium(VI) adsorption to iron oxides is dominated by ternary uranyl-carbonato surface complexes across an unexpectedly wide pH range. Formation of such complexes would have significant impact on the sorption behavior and mobility of uranium in aqueous environments. We therefore re-investigated the identity and structural coordination of uranyl sorption complexes using a combination of U LIII-edge Extended X-ray Absorption Fine-Structure (EXAFS) spectroscopy and Iterative Transformation Factor Analysis, which enhances the resolution in comparison to conventional EXAFS analysis. A range of conditions (pH, CO2 partial pressure, ionic strength) made it possible to quantify the variations in surface speciation. In the resulting set of spectral data (N=11), the variance is explained by only two components, which represent two structurally different types of surface complexes: (1) a binary uranyl surface complex with a bidentate coordination to edges of Fe(O,OH)6 octahedra, and (2) a uranyl triscarbonato surface complex where one carbonate ion bridges uranyl to the surface. This ternary type B complex differs from a type A complex where uranyl is directly attached to surface atoms, and carbonate is bridged by uranyl to the surface. Both surface complexes agree qualitatively and quantitatively with predictions by a charge distribution (CD) model. According to this model, the edge-sharing uranyl complex has equatorial ligands (–OH2, -OH or one -CO3 group) that point away from the surface. The monodentate uranyl triscarbonato surface complex (type B) is relevant only at high pH and elevated pCO2. At these conditions, however, it is responsible for significant uranyl sorption, whereas standard models would predict only weak sorption. This paper presents the first spectroscopic evidence of this ternary surface complex, which has significant implications for the immobilization of uranyl in carbonate-rich aqueous environments.
Keywords: uranyl, carbonate, sorption, surface complexation, ferrihydrite, EXAFS, X-ray absorption spectroscopy, factor analysis, VARIMAX , CD model
  • Environmental Science & Technology 43(2009)5, 1400-1406
  • Lecture (Conference)
    12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 20.-25.09.2009, Kennewick,, USA

Publ.-Id: 11428 - Permalink


Beam Stabilization at the ELBE electron accelerator and the FELBE infrared user facility
Jainsch, R.; Proehl, D.; Seidel, W.; Lehnert, U.; Justus, M.; Gabriel, F.; Michel, P.;
Abstract. The high current SRF electron accelerator facility ELBE started user operation at the Bremsstrahlung facility in 2003, followed straight-line by channelling X-rays and the infrared FEL laboratories. Since then, automated beam stabilization in terms of energy, intensity and also trajectory became a clear necessity for a number of experiments carried out. This contribution describes observed instabilities of the electron beam and the infrared beam at FELBE and alludes to their certain or possible sources. For slow (mHz) beam energy drift compensation, a dispersion based feedback loop was developed and implemented, using strip line beam position monitors and the accelerating RF gradient. Further, the IR beam intensity is measured by a newly developed scatter wire detector system and stabilized via the electron beam current up to the few Hz range. Control theory aspects used to design both solutions are shown, also their implementation into the existing ELBE control landscape and performance characteristics.
  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Deutschland

Publ.-Id: 11427 - Permalink


The New Superconducting RF Photoinjector at the ELBE Linac
Teichert, J.; Arnold, A.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schamlott, A.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Xiang, R.; Kamps, T.; Rudolph, J.; Schenk, M.; Matheisen, A.; Klemz, G.; Will, I.; vom Stein, P.;
Most of the proposed electron accelerator projects for future FELs, ERLs, or 4th generation light sources require electron beams with an unprecedented combination of high-brightness, low emittance and high average current. For that reason existing electron injectors must be considerably improved or new injector concepts developed. One very promising approach represents the superconducting radio frequency photoinjector (SRF gun). This injector type combines the advantages of a conventional photoelectron injector with that of superconducting acceleration, i.e. the very low RF losses and simple continuous wave operation. Within a collaboration of BESSY, DESY, FZD and MBI a SRF gun was developed and installed at the FZD for operation at the ELBE superconducting linear accelerator. In November the first beam was produced. First commissioning results have been collected. Besides an improvement of beam quality and parameter range the SRF gun serves as a test bench for further development, evaluation and optimization since it is the first injector of its type which is operating at an accelerator worldwide.
  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Deutschland
  • Contribution to proceedings
    The IEEE Nuclear Science Symposium and Medical Imaging Conference, Conference Record 3066, 19.-25.10.2008, Dresden, Deutschland

Publ.-Id: 11426 - Permalink


It's a matter of cores
Raabe, J.; Quitmann, C.; Buess, M.; Kuepper, K.; Fassbender, J.ORC
Using time-resolved X-ray microscopy, it is possible to get an insight into the dynamics of magnetic micro- and nanostructures. A fascinating property of micro-magnetism comes from the possibility to control the domain and vortex configuration through the sample's shape and size. For instance, in a rectangular platelet a configuration containing a stable combinatio of vortices and an antivortex can be created. Such a single crosstie wall contains three vortex cores that can each point either up or down resulting in a total of 2^3 (=eight) configurations only distinguishable when their dynamics are investigated.
Keywords: magnetism, magnetization dynamics, PEEM, vortex, antivortex, synchrotron
  • Contribution to external collection
    Scott Capper, Fribourg: PSI Scientific Report 2007, Villigen: Paul Scherrer Institut, 2008, ISSN 1662-1719, 12

Publ.-Id: 11425 - Permalink


LIF based hydrodynamic studies in pilot-scale electrolytic cells
Kryk, H.; Schubert, M.; Hessel, G.; Hristov, H. V.; Friedrich, H.-J.;
Carrying out electrochemical processes at high efficiency would require having optimal hydrodynamic conditions of the electrolyte liquids within the cell, forcing high mass transfer rates of the relevant components at the electrodes as well as through the membrane. Hence, the electrolyte residence time distribution (RTD) in the individual compartments is one of the key issues, affecting the performance. For the investigation of RTD and spatially resolved velocity profiles at different compartment levels of technical electrolytic cells, a new laser induced fluorescence (LIF) visualization method has been developed. Back-mixing effects of the electrolytes are quantified by axial dispersion coefficients using adequate dispersion models. Among the description of the measurement setup, the contribution mainly discusses the effects of liquid flow rate, spacer grids and pressure conditions in the compartments as well as the effect of gas evolution on RTD. The measurements provide an informative basis for optimization of the flow textures that diverge from expected symmetric flows. The aim of the research is to get a better understanding regarding the RTD behaviour and to draw conclusions on the cell behaviour as basis for optimization of the cell design as well as of the process parameters. Moreover, the experimental results can prove to be useful to evaluate modelling and simulation of hydrodynamics using CFD methods which is also shown by means of selected examples.
  • Abstract in refereed journal
    Chemie Ingenieur Technik 80(2008)9, 1314-1314
  • Poster
    ProcessNet Jahrestagung, 07.-09.10.2008, Karlsruhe, Germany

Publ.-Id: 11424 - Permalink


Nuclear Astrophysics At LUNA: Status And Perspectives
Prati, P.; Bemmerer, D.; Bonetti, R.; Broggini, C.; Corvisiero, P.; Confortola, F.; Conti, E.; Costantini, H.; Elekes, Z.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gyürky, G.; Gustavino, C.; Imbriani, G.; Junker, M.; Lemut, A.; Limata, B.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; Roca, V.; Rolfs, C.; Alvarez, C. R.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.;
The talk will be mainly devoted to the measurement of the cross section of the 3He(alpha,gamma)7Be reaction which belongs to the p-p chain. Actually, solar neutrino fluxes depend both on astrophysical and on nuclear physics inputs, namely on the cross sections of the reactions responsible for neutrino production inside the Solar core. While the flux of solar 8B neutrinos has been recently measured at Superkamiokande with a 3.5% uncertainty and a precise measurement of 7Be neutrino flux is foreseen in the next future, the predicted fluxes are still affected by larger errors. The largest nuclear physics uncertainty to determine the fluxes of 8B and 7Be neutrinos comes from the 3He(alpha,gamma)7Be reaction. The uncertainty on its S-factor is due to an average discrepancy in results obtained using two different experimental approaches: the detection of the delayed gamma rays from 7Be decay and the measurement of the prompt gamma emission. The LUNA Collaboration has performed a new high precision experiment with both techniques at the same time. Thanks to the low background conditions of the Gran Sasso LUNA accelerator facility, the cross section has been measured down to 93 keV, the lowest interaction energy ever reached. The S-factors from the two methods do not show any discrepancy within the experimental errors. An extrapolated S(0) = 0.560±0.017 keV barn is obtained. Moreover, branching ratios between the two prompt gamma -transitions have been measured with 3\u20138% accuracy. Recently, the LUNA Collaboration has presented to the Scientific Board of Gran Sasso Laboratory its experimental program for the next five years based on the existing 400 kV accelerator facility. A Letter of Intent addressing the possibility to install a 3 MV machine at Gran Sasso has also been submitted to the Board. The LUNA scientific programs with both the 400 kV and 3 MV accelerator facilities will be illustrated in the final part of the talk.
  • Contribution to proceedings
    International Conference on Frontiers in Nuclear Structure, Astrophysics and Reactions, 10.-14.09.2007, Crete, Greece
    AIP Conference Proceedings Volume 1012: American Institute of Physics, 305-312

Publ.-Id: 11423 - Permalink


Rhenium and technetium complexes bearing quinazoline derivatives: progress towards a 99mTc biomarker for EGFR-TK imaging
Fernandes, C.; Santos, I. C.; Santos, I.; Pietzsch, H.-J.; Künstler, J.-U.; Kraus, W.; Rey, A.; Margaritis, N.; Bourkoula, A.; Chiotellis, A.; Paravatou-Petsotase, M.; Pirmettis, I.;
The quinazoline derivatives (3-chloro-4-fluorophenyl)quinazoline-4,6-diamine (2) and (3-bromophenyl)quinazoline-4,6-diamine (3) were labelled with 99mTc using the “4 + 1” mixed-ligand system [Tc(NS3)(CN-R)] and the tricarbonyl moiety fac-[Tc(CO)3]+. In the “4 + 1” approach the technetium(III) is stabilized by a monodentate isocyanide bearing a quinazoline fragment (L1, L2) and by the tetradentate tripodal ligand tris(2-mercaptoethyl)-amine (NS3). In the “4 + 1” approach, 99mTc-labelling was performed in a two-step procedure, the complexes [Tc(NS3)(L1)] (7a) and [Tc(NS3)(L2)] (8a) being obtained in about 50–70% yield. In the tricarbonyl approach, the fac-[Tc(CO)3]+ unit is anchored by two different monoanionic chelators bearing the quinazoline derivatives (3-chloro-4-fluorophenyl)quinazoline-4,6-diamine (2) and (3-bromophenyl)quinazoline-4,6-diamine (3). Both chelators have a N2O donor atom set, but one contains a pyrazolyl ring (L5H) and the other contains a pyridine unit (L6H). In both cases the conjugation of the quinazoline to the chelator was done through the secondary amine of the potentially tridentate and monoanionic chelators, the corresponding 99mTc-complexes (10a, 11a) being obtained in quantitative yield. The identities of the 99mTc-labelled quinazolines (7a, 8a, 10a, 11a) were confirmed by comparison with the HPLC profiles of the analogous Re compounds (7, 8, 10, 11). All these Re complexes were characterized by NMR and IR spectroscopy, elemental analysis and in some cases by MS and X-ray diffraction analysis. In vitro studies indicate that the quinazoline fragments, after conjugation to the cyano group (L1, L2) or to the pyrazolyl containing chelator (L5H), as well as the corresponding Re complexes (7, 8, 10) inhibit significantly the EGFR autophosphorylation and also inhibit A431 cell growth. These two effects were also found for the pyridine-containing chelator (L6H) and corresponding Re complex (11), although to a lesser extent.

Publ.-Id: 11422 - Permalink


Sternentwicklung und Elementsynthese
Wagner, A.;
Sternentwicklung und Elementsynthese
  • Lecture (others)
    Hauptseminar Kosmologie, TU Dresden, 13.06.2007, Dresden, Deutschland

Publ.-Id: 11421 - Permalink


Nuclear Physics in Astrophysics: Where do the chemical elements come from?
Wagner, A.;
  • Lecture (others)
    FZD Lecture, Forschungszentrum Dresden-Rossendorf, 13.06.2007, Dresden, Deutschland

Publ.-Id: 11420 - Permalink


Effect of substrate temperature on Al-doping of ZnO films
Vinnichenko, M.; Gago, R.; Rogozin, A.; Shevchenko, N.; Cornelius, S.; Jimenez, I.; Kolitsch, A.; Möller, W.;
Al-doping of ZnO is routinely used to create transparent electrodes, although the mechanisms of incorporation and electrical activation of the doping impurity are not well understood. In order to have a deeper insight into these processes, polycrystalline ZnO and ZnO:Al films were grown by reactive pulsed magnetron sputtering of Zn and Zn:Al targets, respectively. The substrate temperatures (Ts) were spanning in the 40-580 °C range. The films were characterized by spectroscopic ellipsometry, Hall effect measurements, X-ray diffraction (XRD) and X-ray absorption near edge spectroscopy (XANES). The electrical resistivity of ZnO:Al films shows a clear minimum at Ts=350 °C, which correlates with a maximum in crystallinity (grain size). The lower resistivity is due to the increased density and mobility of free electrons according to the Hall effect measurements. At Ts>350 °C, the ZnO:Al film crystallinity significantly deteriorates, while the crystallinity of undoped ZnO films grown at identical conditions always improves by increasing Ts. XANES results show that the poorer film crystallinity and higher resistivity at high Ts can be related to AlOx segregation. Further, the electrical properties correlate with changes in the O(1s) absorption edge, whereas the Zn(2p) edge shows no modification with respect to undoped ZnO films. This result suggests that the Al incorporation increases charge carrier density due to oxygen vacancy formation in ZnO lattice.
Keywords: Al-doped ZnO, reactive pulsed magnetron sputtering, film structure, electrical properties, optical properties
  • Lecture (Conference)
    E-MRS 2008 Spring Meeting, 26.-30.05.08, Strasbourg, France

Publ.-Id: 11419 - Permalink


Salty neutrinos from the sun
Wagner, A.;
  • Lecture (others)
    Astrophysical Journal Club, FZD, 05.12.2007, Dresden, Deutschland

Publ.-Id: 11418 - Permalink


Digitizer Data Acquisition at nELBE
Wagner, A.;
Works on modern methods using fast neutrons for research related to the transmutation of nuclear waste
  • Lecture (others)
    FZD Lectures, Forschungszentrum Dresden-Rossendorf, 14.02.2008, Dresden, Deutschland

Publ.-Id: 11417 - Permalink


Kerne und Sterne
Wagner, A.;
Kerne und Sterne - Vom Urknall, der Entstehung der chemischen Elemente und Experimenten im FZD
  • Lecture (others)
    Besuch des Albert-Schweizer-Gymnasiums Erfurt, 29.05.2008, Erfurt, Deutschland

Publ.-Id: 11415 - Permalink


Investigation of planar electron channeling radiation generated in quartz single crystals
Azadegan, B.; Grigoryan, L. S.; Pawelke, J.; Wagner, W.;
Measurements of planar channeling radiation generated in a variety of crystallographic planes of a quartz single crystal have been performed at the radiation source ELBE at electron energies of 17, 25 and 32 MeV. The quantum theory of channeling radiation has been applied for the interpretation of the observed spectra. Planar continuum potentials, transverse electron states, transition energies and line widths have been calculated. Taking the population dynamics of states during channeling into account, spectral distributions of the channeling radiation could be simulated, which reveal a good quantitative agreement with the measured spectra.
Keywords: channeling radiation, quartz single crystal
  • Journal of Physics B 41(2008), 235101

Publ.-Id: 11414 - Permalink


LUNA and the neutrinos from the Sun
Bemmerer, D.;
Nuclear reactions that generate energy and synthesize elements take place inside the stars in a relatively narrow energy window: the Gamowpeak. The extremely low value of the cross-section inside the Gamowpeak has always prevented its measurement in a laboratory at the Earth's surface, where the signal to background ratio is too small because of cosmic ray interactions. In order to explore this new domain of nuclear astrophysics LUNA (Laboratory for Underground Nuclear Astrophysics) started in 1991 its activity by installing a 50 kV electrostatic accelerator underground at the GranSassoLaboratory in central Italy, followed in the year 2000 by a 400 kV one. LUNA still remains the only underground accelerator facility existing in the world. In the seminar I will describe the main
contributions given by LUNA to the study of the pp-chain and the CNO cycle in the Sun, in particular to the precise determination of the solar neutrino spectrum.
  • Invited lecture (Conferences)
    DESY-Seminar, 10.06.2008, Hamburg, Deutschland
  • Invited lecture (Conferences)
    Seminar des DESY-Zeuthen, 11.06.2008, Zeuthen, Deutschland
  • Lecture (others)
    TU Berlin, Seminar Nukleare Astrophysik, 03.11.2008, Berlin, Deutschland

Publ.-Id: 11413 - Permalink


RPC Prototype Development
Bemmerer, D.; Yakorev, D.; Stach, D.; Wagner, A.;
The NeuLAND detector at FAIR is designed to detect neutrons of up to 1 GeV kinetic energy with high efficiency. It consists of a layered structure of iron converter material and MRPC units to detect the secondary charged particles. The talk reports on the status of the MRPC prototyping effort for NeuLAND at Forschungszentrum Dresden-Rossendorf.
  • Lecture (Conference)
    Joint R3B/EXL/ELISe Collaboration Meeting on Technical Issues, 21.-24.04.2008, Darmstadt, Deutschland

Publ.-Id: 11412 - Permalink


Irradiation-induced copper precipitation in the FeCu system including vacancy absorption: the V3C model
Birkenheuer, U.; Bergner, F.; Ulbricht, A.;
Rate theory (RT) simulations for two different FeCu model alloys, Fe-0.1%Cu and Fe-0.3%Cu, are reported which have been performed in conjunction with small angle neutron scattering (SANS) experiments for samples neutron-irradiated at four different neutron doses. The newly developed Vacancy Coupled Copper Clustering (V3C) model is introduced and it is demonstrated what with only two fit parameters the whole set of sixteen independent experimental data points could be reproduced. It is also shown that our V3C model allows (in contrast to the RT models discussed in the literature) assessing the chemical composition of the mixed copper-vacancies clusters which are formed, especially in the Fe-0.1%Cu alloy. The experimental trends could be reproduced this way without any re-calibration of the V3C model.
Keywords: rate theory, neutron irradiation, FeCu model alloys, SANS experiments, mixed copper-vacancy clusters
  • Poster
    Final PERFECT Workshop (a project within the 6th European framework program, FP6), 16.-19-06.2008, Moret sur Loing, France

Publ.-Id: 11411 - Permalink


Terahertz-Strahlung auf der Basis beschleunigter Ladungsträger in GaAs
Dreyhaupt, A.;
kein Abstract vorhanden
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-498 2008

Downloads:

Publ.-Id: 11410 - Permalink


SANS results of neutron-irradiated VVER-1000 RPV steels and model alloys
Ulbricht, A.; Bergner, F.;
The aim of the present poster is to contribute small-angle neutron scattering (SANS) data to the experimental database of the integrated project PERFECT. The results serve as database for model validation. The nature of irradiation-induced features in Fe-3wt%Ni was investigated and compared with results for commercially pure Fe. We have observed a three times larger volume fraction of irradiation-induced scatterers for the Fe-Ni alloy than for pure Fe. For VVER-1000 RPV steels matrix damage is the dominant feature in the case of low Cu level, but Cu-rich precipitates significantly contribute for Cu-enriched steels.
Keywords: Small-angle neutron scattering, radiation defects, RPV steel, Fe-Ni alloy
  • Poster
    Final PERFECT Workshop, 16.-19.06.2008, Moret sur Loing, France

Publ.-Id: 11409 - Permalink


Improving the Oxidation Resistance of TiAl-Alloys with Fluorine
Donchev, A.; Richter, E.; Schütze, M.; Yankov, R.;
The technical TiAl-alloy gamma-MET (Ti-46.5Al-4(Cr, Nb, Ta, B)) was oxidised thermocyclically (24h-cycle-test) at 900 degrees C in wet and dry air. In this paper results of untreated and fluorine treated TiAl-samples are presented. Their oxidation behaviour will be shown. Several methods were used to apply the halogens to the surface, e.g. beamline ion implantation, spraying of or dipping into a halogen containing liquid. A pure protective alumina scale was found, e.g. after treatment with a fluorine containing polymer and thermocyclic oxidation up to 1 year at 900 degrees C in laboratory air. On the other side thick fast growing and non-protective mixed oxide scales were found on the untreated samples.
Keywords: intermetallics; oxidation; metallography; halogen effect; titanium aluminides

Publ.-Id: 11407 - Permalink


Human S100A12: a novel key player in inflammation?
Pietzsch, J.; Hoppmann, S.;
Abstract S100A12 is a member of the S100 family of EF-hand calcium-binding proteins. Human S100A12 is predominantly expressed and secreted by neutrophil granulocytes and, therefore, has been assigned to the S100 protein subfamily of calgranulins or myeloid-related proteins. Intracellular S100A12 exists as an anti-parallel homodimer and upon calcium-dependent activation interacts with target proteins to regulate cellular functions. Extracellular S100A12 exists majorily as homodimer and hexamer, respectively, and shows cytokine-like characteristics. It is part of the innate immune response and linked to certain autoimmune reactions. Human S100A12 is markedly overexpressed in inflammatory compartments, and elevated serum levels of S100A12 are found in patients suffering from various inflammatory, neurodegenerative, metabolic, and neoplastic disorders. In this regard, interaction of calcium-activated S100A12 with the multiligand receptor for advanced glycation endproducts (RAGE) and its soluble form (sRAGE) plays a central pathogenetic role. Recent clinical evidence suggests a high potential of S100A12 as a sensitive and specific diagnostic marker of localized inflammatory processes.
Keywords: Calcium-binding proteins - Canonical EF-hand - Copper-binding proteins - Damage-associated molecular pattern molecules - Inflammatory diseases - Pseudo EF-hand - Receptor for advanced glycation endproducts - Soluble RAGE

Publ.-Id: 11406 - Permalink


Systematic comparison of two novel thiol-reactive prosthetic groups for 18F labeling of peptides and proteins with the acylation agent succinimidyl-4-[18F]fluorobenzoate [18F]SFB
Wüst, F.; Köhler, L.; Berndt, M.; Pietzsch, J.;
A systematic comparison of 4-[18F]fluorobenzaldehyde-O-(2-{2-[2-(pyrrol-2,5-dione-1-yl)ethoxy]-ethoxy}-ethyl)oxime ([18F]FBOM) and 4-[18F]fluorobenzaldehyde-O-[6-(2,5-dioxo-2,5-dihydro-pyrrol-1-yl)-hexyl]oxime ([18F]FBAM) as prosthetic groups for the mild and efficient 18F labeling of cysteine-containing peptides and proteins with the amine-group reactive acylation agent, succinimidyl-4-[18F]fluorobenzoate ([18F]SFB), is described. All three prosthetic groups were prepared in a remotely controlled synthesis module. Synthesis of [18F]FBOM and [18F]FBAM was accomplished via oxime formation through reaction of appropriate aminooxy-functionalized labeling precursors with 4-[18F]fluorobenzaldehyde. The obtained radiochemical yields were 19% ([18F]FBOM) and 29% ([18F]FBAM), respectively. Radiolabeling involving [18SUP>F]FBAM and [18F]FBOM was exemplified by the reaction with cysteine-containing tripeptide glutathione (GSH), a cysteine-containing dimeric neurotensin derivative, and human native low-density lipoprotein (nLDL) as model compounds. Radiolabeling with the acylation agent [18F]SFB was carried out using a dimeric neurotensin derivative and nLDL. Both thiol-group reactive prosthetic groups show significantly better labeling efficiencies for the peptides in comparison with the acylation agent [18F]SFB. The obtained results demonstrate that [18F]FBOM is especially suited for the labeling of hydrophilic cysteine-containing peptides, whereas [18F]FBAM shows superior labeling performance for higher molecular weight compounds as exemplified for nLDL apolipoprotein constituents. However, the acylation agent [18F]SFB is the preferred prosthetic group for labeling nLDL under physiological conditions.
Keywords: 18F-labeled prosthetic groups - Peptides - LDL - Apolipoproteins - Positron emission tomography (PET)
  • Amino Acids 36(2009), 283-295

Publ.-Id: 11405 - Permalink


Effects of pioglitazone and/or simvastatin on low density lipoprotein subfractions in non-diabetic patients with high cardiovascular risk: A sub-analysis from the PIOSTAT study
Leonhardt, W.; Pfützner, A.; Müller, J.; Pietzsch, J.; Forst, T.; Karagiannis, E.; Lübben, G.; Hanefeld, M.;
Background
We analyzed the efficacy and possible synergistic actions of pioglitazone and simvastatin monotherapy versus their combination on LDL subfractions from a subpopulation from the PIOSTAT three-arm randomized controlled trial. PPARγ agonists, such as pioglitazone, improve insulin sensitivity and glycemic control and appear to lower the concentration of atherogenic small dense LDL particles. Insulin resistance frequently occurs in non-diabetic patients with cardiovascular disease. Statins, such as simvastatin, reduce cardiovascular events by lowering LDL-C. So far, only scarce information exists for comparative efficacy and possible synergistic effects of combination therapy on LDL subfractions, cholesterol particle load, and particle number of atherogenic small dense LDL.

Methods
125 non-diabetic patients with high cardiovascular risk were randomized to therapy with pioglitazone 45 mg/day, simvastatin 40 mg/day, or the combination of both, for 12 weeks. In the present sub-study, LDL subfractions from 88 patients were separated by very-fast ultracentrifugation.

Results
Simvastatin monotherapy significantly reduced cholesterol and triglyceride concentrations in IDL, LDL1, and LDL2. The lipid concentrations and lipid loads in LDL3 remained unchanged. By contrast, treatment with pioglitazone reduced the cholesterol concentration in LDL3 (density 1.040–1.066 kg/l) from 0.38 to 0.31 mmol/l (p = 0.0004) and of the cholesterol load per particle from 1058 to 934 mol/mol (p = 0.0149). Even greater reductions of cholesterol in LDL3 were observed with the combination of pioglitazone and simvastatin: from 0.38 to 0.29 mmol/l (p = 0.0006) and from 1021 to 903 mol/mol (p = 0.0011), respectively. In addition, combination therapy reduced the particle number of LDL3 from 356 to 316 nmol/l (p = 0.0074).

Conclusions
Simvastatin preferentially lowered LDL1 and LDL2 subfractions, whereas pioglitazone reduced LDL3 cholesterol and cholesterol load. In addition, the combination reduced the LDL3 particle number. Thus, our data suggest a synergistic action of pioglitazone and simvastatin on atherogenicity of small dense LDL particles.

Publ.-Id: 11404 - Permalink


Impact of imatinib mesylate on bone remodeling in the growing skeleton of juvenile mice
Boehme, J.; Bergmann, R.; Fischer, R.; Mosch, B.; Pietzsch, J.; Bornhäuser, M.; Gasser, J. A.; Suttorp, M.;
kein Abstract verfügbar
  • Lecture (Conference)
    6th International Workshop for Musculoskeletal and Neuronal Interactions, 08.-11.05.2008, Köln, Deutschland
  • Contribution to proceedings
    Proceedings of the 6th International Workshop for Musculoskeletal and Neuronal Interactions, 08.-11.05.2008, Köln, Deutschland

Publ.-Id: 11403 - Permalink


Scavenger receptors are involved in phagocyte adhesion to endothelial cells stimulated by oxidized and glycoxidized LDL
Kopprasch, S.; Pietzsch, J.; Bornstein, S. R.; Graessler, J.;
kein Abstract verfügbar
  • Abstract in refereed journal
    Atherosclerosis 9(2008), 52
    DOI: 10.1016/S1567-5688(08)70205-8
  • Poster
    77th Congress of the European Atherosclerosis Society, 26.-29.04.2008, Istanbul, Turkey

Publ.-Id: 11402 - Permalink


Modulation of adrenocortical aldosterone and cortisol synthesis by in vitro oxidized low density lipoprotein
Kopprasch, S.; Ansurudeen, I.; Graessler, J.; Bornstein, S. R.; Pietzsch, J.;
Objectives:
Oxidative stress is of critical importance in the pathogenesis of endocrinopathies. Since cholesterol serves as a major source of steroid hormone synthesis we investigated the effect of hypochlorite-modified low density lipoprotein (LDL) on aldosterone and cortisol release from human adrenocortical NCI-H295R cells.

Methods:
Native LDL obtained from healthy volunteers was oxidized to varying degrees by sodium hypochlorite. The resulting modified LDL was biochemically characterized by gas chromatography–mass spectrometry (GC–MS) analysis. Human NCI-H295R cells were cultured in DMEM/F12. Aldosterone release in supernatants was measured by RIA and cortisol secretion was determined by competitive luminometric assay.

Results:
Incubation of LDL with sodium hypochlorite resulted in increasing concentrations of the apolipoprotein B-100 oxidation markers HAVA, HACA, and 3-chlorotyrosine in dependence on the degree of oxidation. Incubation of adrenocortical cells with 10–100 μg/ml native or oxidized LDL for 24 h stimulated hormone release dose-dependently up to 3-fold. Subsequent stimulation of NCI-H295R cells with the physiological stimulus angiotensin II induced an additional hormone secretion up to 2.9-fold in LDL-pretreated samples. Compared to native LDL, oxidized LDL induced a smaller stimulation of hormone secretion that decreased with increasing degree of oxidation.

Conclusion:
Oxidation of LDL may contribute to endocrine dysfunction by decreasing adrenocortical aldosterone and cortisol release.
  • Poster
    10th European Congress of Endocrinology, 03.-07.05.2008, Berlin, Deutschland
  • Abstract in refereed journal
    Endocrine Abstracts 16(2008), P27

Publ.-Id: 11401 - Permalink


Cluster dynamics simulation of mixed Cu-vacancy clusters in a neutron-irradiated Fe-Cu alloy
Gokhman, A. R.; Bergner, F.;
The binary Fe-Cu system as a model system for Cu-containing reactor pressure vessel steels under neutron irradiation was studied by means of cluster dynamics simulations. In these simulations the evolution of the size distribution and composition of mixed Cu-vacancy clusters in the Fe matrix is described. We have found that the kinetics of copper rich precipitates under neutron irradiation is described correctly, if the Cu-rich clusters are considered as traps as well as emitters of single vacancies. The results are compared with SANS experiments on a binary Fe-Cu model alloy reported in the literature. The assumption on the constant composition of copper rich precipitates after the cascade stage was checked.
Keywords: Cluster dynamics, Iron-copper alloy, Neutron irradiation
  • Contribution to external collection
    J.W.P. Schmelzer, G. Röpke, V.B. Priezzhev: Nucleation Theory and Applications, Dubna: JINR, 2008, 978-5-9530-0199-1, 319-325

Publ.-Id: 11400 - Permalink


A microscopic examination of nanosized mixed Ni-Al hydroxide surface precipitates on pyrophyllite
Livi, K. J. T.; Senesi, G.; Scheinost, A. C.; Sparks, D. L.;
The nature of Ni-hydroxide precipitates on pyrophyllite were re-examined by analytical electron microscopy (AEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), powder X-ray diffraction (PXRD) and X-ray absorption fine structure XAFS. Analytical analysis of precipitates shows that the precipitate contains about 20% Al. High resolution TEM imaging showed that the precipitate was amorphous and PXRD failed to find any crystalline peaks associated with crystalline Ni-Al layered double-hydroxide (LDH) or α-Ni(OH)2. These results confirm the conclusion from XAFS spectroscopic data that Al co-precipitates with Ni on Al-rich substrates to form Ni-Al hydroxide (LDH) surface precipitates. However, the HRTEM data clarifies that although the bonding environment of the precipitate is like that of Ni-Al LDH, no long range ordering of the structure exists. The study illustrates the need for TEM observations to complement XAFS data and the potential importance of amorphous materials in environmental settings.
Keywords: Layered double hydroxides (LDH) EXAFS HR-TEM
  • Environmental Science & Technology 43(2009)5, 1299-1304

Publ.-Id: 11399 - Permalink


Cluster dynamics study of the binary systems in neutron irradiated iron alloys
Gokhman, A.; Bergner, F.; Birkenheuer, U.;
Two binary systems are studied in neutron irradiated alloys by cluster dynamics. They are the coupling copper-vacancy system in high content copper-iron alloy and VVER steel and vacancy-interstitial system in commercial pure iron. It is found that the kinetics of copper rich precipitates under neutron irradiation is described correct if they are considered as the sinks as well as emitters of the single vacancies. Long-time behavior of the free vacancies, free interstitials and vacancies clusters and interstitial clusters in pure iron under neutron irradiation is governed by the surface limited regime of kinetics.
Keywords: Cluster dynamics, High copper-iron alloy, pure iron, Neutron irradiation
  • Lecture (Conference)
    Workshop Nucleation Theory and Applications, 12.-20.04.2008, Dubna, Russia

Publ.-Id: 11398 - Permalink


Determining role of Krein signature for 3D Arnold tongues of oscillatory dynamos
Kirillov, O.; Günther, U.; Stefani, F.;
Using a homotopic family of boundary eigenvalue problems for the mean-field α2-dynamo with helical turbulence parameter α(r)=α0+γΔα(r) and homotopy parameter β ∈[0,1], we show that the underlying network of diabolical points for Dirichlet (idealized, β=0) boundary conditions substantially determines the choreography of eigenvalues and thus the character of the dynamo instability for Robin (physically realistic, β=1) boundary conditions. In the (α0,β,γ)-space the Arnold tongues of oscillatory solutions at β=1 end up at the diabolical points for β=0. In the vicinity of the diabolical points the space orientation of the 3D tongues, which are cones in first-order approximation, is determined by the Krein signature of the modes involved in the diabolical crossings at the apexes of the cones. The Krein space induced geometry of the resonance zones explains the subtleties in finding α-profiles leading to spectral exceptional points, which are important ingredients in recent theories of polarity reversals of the geomagnetic field.
Keywords: oscillatory MHD dynamo, geomagnetic field reversals, exceptional points, Arnold's tongues, perturbation theory, Krein space

Publ.-Id: 11397 - Permalink


A time dependent analytical approximation solution for a pulsed source problem: P1 transport versus diffusion
Merk, B.;
An analytical solution for a pulse of an external source in a homogeneous subcritical reactor problem is developed. The problem is described through an approximation of the Boltzmann Transport equation, the Telegrapher's or time dependent P1 equation. The analytical solution to the problem is expressed in terms of a Green's function expansion. The differences between the solution for the Telegrapher's equation and the diffusion equation without separation of space and time are discussed
Keywords: Telegrapher's equation, Neutron Transport, Space-Time Dependent Transport, Accelerator Driven Systems, Pulsed Source
  • Lecture (Conference)
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Deutschland
  • Contribution to proceedings
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Deutschland
    IEEE Conference Record, 978-1-4244-2715-4

Publ.-Id: 11396 - Permalink


Stable Mode‐Locked Pulses from Mid‐Infrared Quantum Cascade Lasers
Wang, C. Y.; Kuznetsova, L.; Diehl, L.; Kärtner, F.; Belkin, M.; Schneider, H.; Liu, H. C.; Capasso, F.;
We report direct evidence of active mode‐locking of quantum cascade lasers from second‐order interferometric autocorrelation measurements with a non‐linear quantum well infrared photodetector. A FWHM of 3ps was deduced for the stable train of pulses.
Keywords: quantum cascade laser, QCL, modelocking, QWIP, autocorrelation
  • Lecture (Conference)
    Conference on Lasers and Electro-Optics, Quantum Electronics and Laser Science Conference, 04.-09.05.2008, San Jose, United States

Publ.-Id: 11395 - Permalink


Methods for an Automatic Analysis of Motion Tracking Data in PET
Langner, J.; Oehme, L.; Pötzsch, C.; Dittrich, S.; Beuthien-Baumann, B.; van den Hoff, J.;
Due to the constantly improving spatial resolution of PET systems, patient motion increasingly limits the achievable image quality in PET. Especially for tracer kinetic analysis in dynamic PET, as well as for the analysis of small spatial regions of interests (ROI), patient motion represents a severe obstacle. Therefore, different methods for the tracking and correction of patient movement have been investigated in the past. Generally, suitable motion threshold values have to be deduced from the motion data to identify significant motion and to reduce the amount of computation time for motion compensation methods. Therefore, an objective analysis of the motion data has to be performed. Motion data is usually provided in the form of three translations along, and three rotations around, the coordinate axes. These raw parameters, however, proof to be unsuited for a direct assessment of the magnitude of 3D motion. Rather, it is necessary to execute the spatial transformations defined by the six parameters for each point within the ROI. Therefore, we developed procedures for an automated analysis of motion tracking data which address these problems. The raw motion data from the tracking device is automatically processed via methods based on the 'R' statistics toolkit. Parameters are calculated for the general stability of the motion tracking. Furthermore, the translation and rotation parameters are analysed and graphically displayed. Time dependent transformation matrices relative to the acquisition start are also calculated. For the quantitative analysis of head motion, we translate the motion information onto the surface of a virtual sphere with a diameter comparable to that of a human brain (~20 cm). By transforming each point of a grid on the sphere with the available motion parameters, the 3D-Euclidean distance of each grid point from its original position is calculated. If the distance of any of these points exceeds a certain threshold (~3 mm), the motion is considered to be significant.
Furthermore, a target ROI (e.g. the striatum) can be specified. This analysis allows the objective identification of all time points where significant motion occurred. This enables optimised settings for motion correction algorithms, notably avoiding time intensive redundant computations.
Furthermore, this data enables an intuitive quality control by providing pseudo 3D plots of the motion on the reference sphere. Finally, a report page is provided yielding summary information concerning the areas of largest/smallest motion as well as an automatic motion score of the study as a feedback for the physicians.
  • Poster
    EANM'08, Annual Congress of the European Association of Nuclear Medicine, 11.-15.10.2008, München, Deutschland
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 35(2008), S333
    DOI: 10.1007/s00259-008-0896-9

Publ.-Id: 11394 - Permalink


Cell cycle regulating kinase Cdk4 as a potential target for tumour visualisation in vivo
Treite, F.; Köhler, L.; Mosch, B.; Pietzsch, J.;
Aim
Loss of growth control in tumour cells is a result of alterations in regulatory pathways of the cell cycle, in particular, the cyclin-dependent kinase (Cdk)/retinoblastoma (pRb)/E2F cascade. Inhibition of this G1/S transition regulating pathway using, e.g., selective Cdk4 inhibitors provides a promising approach for cancer treatment.
We hypothesise that potent Cdk4 inhibitors are suitable for imaging of cell proliferation processes and tumour visualisation by PET in vivo. Therefore, biological, biochemical, and radiopharmacological characteristics of a selected Cdk4 inhibitor (CKIA, 8-Cyclopentyl-6-iodo-5-methyl-2-(4-piperazin-1-yl-phenylamino)-8H-pyrido[2,3-d]pyrimidin-7-one) was examined.

Materials & Methods
Cell growth and cell cycle studies were performed in human tumour cell lines (HT-29, FaDu, THP-1). Cdk4 specific pRb phosphorylation at Ser780 was analysed in cell lysates by western blotting. mRNA expression of the pRb affected genes E2F-1 and PCNA was measured with quantitative RT-PCR. Further, cell uptake studies were performed using iodine-124 radiolabelled CKIA ([124I]CKIA).

Results
Tumour cell growth studies indicate a significantly reduced cell proliferation in all cell lines after 48 h of treatment with 0.1 (< 50%) and 1 µM (< 15%) CKIA. This effect is confirmed by cell cycle studies. Already 24 h after incubation with CKIA the percentage of tumour cells in G1 phase showed a concentration dependent increment up to 90%. pRb phosphorylation is decreased three- to tenfold after 24 h of treatment with 0.1 and 1 µM CKIA in all cell lines. Further, a downregulation of E2F-1 and PCNA mRNA expression could be demonstrated.
Preliminary experiments with [124I]CKIA indicate an adequate stability of this compound in various buffers (pH 4.2, 7.4, 9.0), cell culture media, and rodent plasma samples. In vitro cell uptake studies in adherent tumour cells using [124I]CKIA showed a substantial uptake in HT-29 (1,649±117 %ID/mg protein) and FaDu cells (1,033±84 %ID/mg protein) after 2 h at 37°C.

Conclusion
Our data demonstrate a definite and specific inhibition of tumour cell proliferation when incubating with CKIA due to an arrest of tumour cells in G1 phase. The repression of G1 progression is achieved by CKIA induced inhibition of the Cdk4/pRb/E2F pathway. The stability of [124I]CKIA in physiological buffers and plasma, and the cell uptake observed in human tumour cells are a promising prerequisite for in vivo biodistribution and imaging studies to further support our hypothesis that radiolabelled CKIA and corresponding compounds are suitable tracers for visualisation of tumours using PET.
  • Poster
    EANM'08, Annual Congress of the European Association of Nuclear Medicine, 11.-15.10.2008, München, Deutschland
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 35(2008), S325
    DOI: 10.1007/s00259-008-0896-9

Publ.-Id: 11393 - Permalink


PECVD-ONO: A New Deposited Firing Stable Rear Surface Passivation Layer Systemfor Crystalline Silicon Solar Cells
Hofmann, M.; Kambor, S.; Schmidt, C.; Grambole, D.; Rentsch, J.; Glunz, S. W.; Preu, R.;
A novel plasma-enhanced chemical vapour deposited (PECVD) stack layer system consisting of a-SiOx:H, a-SiNx:H, and a-SiOx:H is presented for silicon solar cell rear side passivation. Surface recombination velocities below 60 cm/s (after firing) and below 30 cm/s (after forming gas anneal) were achieved. Solar cell precursors without front and rear metallisation showed implied open-circuit voltages Voc values extracted fromquasi-steady-state photoconductance (QSSPC) measurements above 680mV. Fully finished solar cells with up to 20.0% energy conversion efficiency are presented. A fit of the cell’s internal quantum efficiency using software tool PC1D and a comparison to a full-area aluminium-back surface field (Al-BSF) and thermal SiO2 is shown. PECVDONO was found to be clearly superior to Al-BSF. A separation of recombination at the metallised and the passivated area at the solar cell’s rear is presented using the equations of Fischer and Kray. Nuclear reaction analysis (NRA) has been used to evaluate the hydrogen depth profile of the passivation layer system at different stages.

Publ.-Id: 11392 - Permalink


A novel embedding technique for multimodality imaging of xenotransplanted tumor models
Strobel, K.; Meister, S.; Bergmann, R.; van den Hoff, J.; Pietzsch, J.;
Introduction
Multimodality imaging (magnetic resonance imaging and spectroscopy (MRI/MRS), positron emission tomography (PET), computer tomography (CT), and autoradiography) of xenotransplanted or syngene tumors on the legs of mice requires the solving of two main problems:
a) the magnetic field inhomogeneity in the tumor periphery caused by the transition of the magnetic field from tissue to the surrounding air, which makes MRS in the tumor periphery difficult or impossible and
b) reproducible positioning for subsequent histological sectioning of the separated tumor.

The aim of the present study was to find an embedding of tumors to solve these two problems simultaneously.

Materials and Methods
Phantom studies were performed using balloons filled with a water/ethanol mixture. Animal experiments were performed using 7-14-week-old NMRI mice. We used a 7 Tesla magnetic resonance tomograph. Chemical shift imaging (CSI) was performed to detect magnetic field inhomogeneities. For phantom embedding, three different materials were used: i) alginate, ii) gelatin, and iii) a mixture (“dough”) of wheat flour, sodium chloride, and potassium aluminum sulfate dodecahydrate. For tissue/tumor embedding alginate was used. The animals were placed in an animal bed including position markers which are visible in MR, PET, and CT images. Prior to histological sectioning the embedded phantoms and tumors were shock frozen in liquid nitrogen.

Results
The easy handling of alginate was superior to that of gelatin and dough. Gelatin disrupted during freezing and did not yield improvement of magnetic field homogeneity. Dough showed improvement of magnetic field homogeneity, but was not completely frozen and therefore not suitable. Alginate showed improvement of magnetic field homogeneity. Also histological sectioning after freezing succeeded very well. Therefore, we selected alginate for tumor embedding. The embedding with alginate showed a significant improvement of the full width at half maximum (FWHM) of the water peak in the peripheral rim of the tumor in comparison to the FWHM of the spectra without embedding (21+/-8 Hz vs. 54+/-29 Hz).


Discussion and conclusion
Our investigation showed that alginate exhibits the properties needed for multimodality investigations with MRS and histological sectioning simultaneously, namely easy handling, magnetic field homogeneity, and the consistency required for histological sectioning. Freezing immediately after imaging, especially after PET imaging is necessary, to avoid dislocation of radioactivity before and after sectioning.
  • Poster
    ESMRMB 25. Annual Scientific Meeting, European Society for Magnetic Resonance in Medicine and Biology, 02.-04.10.2008, Valencia, Spain
  • Abstract in refereed journal
    Magnetic Resonance Materials in Physics, Biology and Medicine 21(2008)Suppl. 1, 267

Publ.-Id: 11391 - Permalink


Real-time evolution of electrical properties and structure of indium oxide and indium tin oxide during crystallization
Rogozin, A.; Vinnichenko, M.; Shevchenko, N.; Kreissig, U.; Kolitsch, A.; Möller, W.;
Indium oxide and tin-doped indium oxide amorphous films grown by pulsed reactive magnetron sputtering were annealed in vacuum. The film structure and properties were studied using in-situ X-ray diffraction, spectroscopic ellipsometry, elastic recoil detection analysis and four point probe measurements. The electrical properties of the indium oxide film change mainly before the crystallization outset. In contrast, the crystallization of tin-doped indium oxide caused a resistivity decrease due to Sn donor activation with an estimated efficiency of 40%.
Keywords: indium oxide, tin-doped indium oxide, annealing, in situ characterization

Publ.-Id: 11390 - Permalink


Factors affecting the specific activity of [18F]fluoride from a [18O]water target
Füchtner, F.; Preusche, S.; Mäding, P.; Zessin, J.; Steinbach, J.;
Aim:
Characterisation of the influence of different polymeric tube materials of a water target system, used for the production of 18F activity, on the specific activity of radiotracers.

Material, methods:
Target water samples taken from different locations of the 18F water target system of a Cyclone® 18/9 cyclotron, equipped with Teflon® (PTFE) or polypropylene (PP) tubes, were analyzed for non-radioactive [19F]fluoride content. [19F]Fluoride content was measured by ion chromatography (IC20, Dinoex) with suppressed conductivity detection. Both the ion chromatographic results and the amount of 18F activity produced were used for the calculation of the specific activity (SA) of [18F]fluoride at the start of the labelling synthesis. To check these results, the SA of the labelled receptor ligand [18F]ZK811460 was also determined by using the different tubing materials.

Results:
Dose-exposed PTFE tubes of the target dispensing (loading) system were identified to be a major source of [19F]fluoride contamination.

Conclusion:
By replacing PTFE tubes of the target dispensing system with PP tubes, the content of 19F was reduced considerably resulting in an increase of SA of the radiotracer [18F]ZK811460 by factor of two.
Keywords: Production of 18F, [18F]fluoride, [19F]fluoride, specific activity, [18O]water target

Publ.-Id: 11389 - Permalink


PET-CT after 50-60 Gy in NSCLC as a means of planning dose escalation
Gillham, C.; Zips, D.; Pönisch, F.; Evers, C.; Abolmaali, N.; Zöphel, K.; Steinbach, J.; Kotzerke, J.; Herrmann, T.; Baumann, M.;
kein Abstract verfügbar
  • Poster
    6th Annual BTOG (British Thoracic Oncology Group) Meeting 2008, 23.-25.01.2008, Dublin, Ireland
  • Abstract in refereed journal
    Lung Cancer 60(2008)94, S30

Publ.-Id: 11388 - Permalink


Field-focusing imaging sensor for visualization of multiphase flows
Da Silva, M. J.; Thiele, S.; Schleicher, E.; Hampel, U.;
We introduce a novel sensor modality for imaging of multiphase flows based on capacitance measurements. The basic idea of the new approach is to place a multitude of electrodes at two opposing walls of a vessel whereby the walls are parallel and each plane of electrodes are positioned perpendicular to each other. This arrangement combined with a special excitation-sensing scheme realizes a focusing of the electrical field in a given region of the interrogating volume allowing images to be generated.
Keywords: multiphase flow, flow visualization, capacitance measurement
  • Contribution to proceedings
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Germany
    Proceedings of EUROSENSORS XXII, Duesseldorf: VDI, 978-3-00-025217-4, 736-739
  • Lecture (Conference)
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Germany

Publ.-Id: 11387 - Permalink


Creation of Nanohillocks on CaF2 Surfaces by Single Slow Highly Charged Ions
El-Said, A. S.; Heller, R.; Meissl, W.; Ritter, R.; Facsko, S.; Lemell, C.; Solleder, B.; Gebeshuber, I. C.; Betz, G.; Toulemonde, M.; Möller, W.; Burgdörfer, J.; Aumayr, F.;
Upon impact on a solid surface, the potential energy stored in slow highly charged ions is primarily deposited into the electronic system of the target. By decelerating the projectile ions to kinetic energies as low as 150 q eV, we find first unambiguous experimental evidence that potential energy alone is sufficient to cause permanent nanosized hillocks on the (111) surface of a CaF2 single crystal. Our investigations reveal a surprisingly sharp and well-defined threshold of potential energy for hillock
formation which can be linked to a solid-liquid phase transition.
Keywords: Highly Charged Ions
  • Physical Review Letters 100(2008)23, 237601

Publ.-Id: 11386 - Permalink


Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika - Verbundprojekt "Actinidenmigration im natürlichen Tongestein"
Bernhard, G.;
- wird nachgereicht
  • Lecture (others)
    8. Projektstatusgespräch zur Forschungsförderung zur Entsorgung gefährlicher Abfälle in tiefen geologischen Formationen, 06.-07.05.2008, Karlsruhe, Deutschland

Publ.-Id: 11385 - Permalink


Bacterial surface layers (S-layers) as building blocks for photocatalytic nanocomposites
Pollmann, K.; Raff, J.; Marquard, A.; Scholz, A.;
Nanoscaled materials comprised of organic and inorganic components are becoming more and more important in nanotechnology due to the diversity of applications. Self-assembling organic systems as part of such a hybrid material can be used as template for the fabrication of arrays of inorganic nanoparticles. Especially the proteinaceous bacterial surface layers (S-layers) that envelop bacterial cells are attractive for fabricating and patterning of nanostructures. These proteins are composed of protein monomers with the ability to self-assemble into two-dimensional arrays. The regular distributed pores of these paracrystalline arrays work as binding sites for various metals and offer ideal structures for the formation of regular distributed metallic nanoclusters of a defined size [1]. Such arrays are very attractive for technical applications ranging from the development of novel catalysts to biomedical applications, the programmed assembly of nanometre scale electronic devices, and optical industry [2]. Another approach is the embedding of S-layer proteins into ceramics thus producing metal binding functionalized nanocomposites [3].
Here we present the synthesis and characterization of S-layer templated ZnO-nanoclusters of a size of 16 nm. The photocatalytic properties of ZnO-particles are interesting for the application as nanoscaled catalytic material. We used these nanoparticles for photocatalytic degradation of the parmaceutical Diclofenac at a wavelength of 365 nm. The widespread occurrence of pharmaceutical residues such as Diclofenac in the environment has been reported in numerous investigations [4], thus establishing these compounds as a new class of pollutants. Therefore, the need of novel technologies for removal of these compounds has become evident. Our future work will concentrate on the development of photocatalytic active nanocomposites by the use of S-Layer produced ZnO-particles.
  • Poster
    NanoBioEurope2008, 09.-13.06.2008, Barcelona, Spain
  • Contribution to proceedings
    NanoBioEurope2008, 09.-13.06.2008, Barcelona, Spain

Publ.-Id: 11384 - Permalink


The Impact of Microorganisms on the Behaviour of Actinides in Natural Environments
Selenska-Pobell, S.;
The behaviour of uranium and other actinides in the environment is strongly influenced by a broad range of biogeochemical factors and also by their own, often very complex chemistry. The major biotic factors in the radioactively polluted environments are the unicellular prokaryotic microorganisms (bacteria and archaea) which, in contrast to the other forms of life on Earth, possess fascinating robustness to these extremely harsh and life-unfriendly surroundings. Microorganisms have developed very effective protection mechanisms against radionuclides and other heavy metals which are based on their ability for oxidative or reductive biotransformations, bioaccumulation, and/or biomineralization of these toxic elements (1 - 3).
...
  • Invited lecture (Conferences)
    Actinide XAS 2008, 15.-17.07.2008, Soleil, France

Publ.-Id: 11382 - Permalink


Coordination of U(IV) and U(VI) sulfate hydrate in aqueous solution
Hennig, C.; Tsushima, S.; Brendler, V.; Ikeda, A.; Scheinost, A. C.; Bernhard, G.;
Sulfuric acid has been used to perform in situ leaching of uranium ore at several sites in the world, among them in Königstein/Germany. The remaining leaching solvents cause questions concerning their environmental problems. The actual thermodynamic data, describing the species distribution in aqueous solution, are not sufficient because typical leaching solutions easily exceed the limit of ionic strengths where conventional models provide trustful results. The application of spectroscopic techniques may help to provide the required data. Therefore, the coordination of U(IV) and U(VI) sulfate in aqueous solutions with high ionic strengths has been recently investigated by several spectroscopic techniques (mainly EXAFS) combined with XRD studies and DFT calculations. The observed results expand the actual knowledge of the aquatic chemistry which is based mainly on thermodynamic data. The recent results are summarized in this contribution.
  • Lecture (Conference)
    5th International Conference Uranium Mining and Hydrogeology, 14.-18.09.2008, Freiberg, Germany
  • Contribution to external collection
    Broder J. Merkel, Andrea Hasche-Berger: Uranium, Mining and Hydrogeology, Berlin: Springer Verlag, 2008, 978-3-540-87745-5, 603-613

Publ.-Id: 11381 - Permalink


A new database on upwards air-water flow in a large pipe
Lucas, D.; Beyer, M.; Kussin, J.; Schütz, P.;
A new database for stationary upward air-water flows in a vertical pipe with an inner diameter of 195.3 mm using the wire-mesh sensor technology is presented. During the experiments the sensor was always mounted on the top of the test section while the distance between gas injection and measuring plane was varied to up to 18 different L/D by using gas injection chambers at different vertical positions. The gas was injected via holes in the pipe wall. The pressure was kept at 0.25 MPa (absolute) at the location of the active gas injection while the temperature was constant at 30°C +-1K. This procedure exactly represents the evolution of the flow along the pipe, as it would be observed for an injection at a constant height position and a shifting of the measurement plane. The experiments were done for 48 combinations of air and water superficial velocities varying from 0.04 m/s to 1.6 m/s for water and 0.0025 m/s to 3.2 m/s for air. From the raw data time averaged data as: radial gas volume fraction profiles, bubble size distributions, radial volume fraction profiles decomposed according to the bubble size and the radial profiles of the gas velocity were calculated. All data were checked regarding their plausibility. They are characterized by a high resolution in space what makes them suitable for the development and validation of closure models for CFD-codes (e.g. for models on bubble forces or on coalescence and break-up) as well as for the test and validation of approaches for poly-dispersed flow.
Keywords: multiphase flow, bubbly flow, churn turbulent flow, annular flow, bubble size, pipe flow
  • Lecture (Conference)
    46th European Two-Phase Flow Group Meeting, 28.-30.05.2008, Pisa, Italy

Publ.-Id: 11380 - Permalink


Magnetization dynamics of Landau structures: tuning the response of mesoscopic magnetic objects using defects
Kuepper, K.; Wintz, S.; Raabe, J.; Buess, M.; Akhmadaliev, C.; Bischoff, L.; Quitmann, C.; Fassbender, J.ORC
Magnetic vortex cores are interacting with and can be annihilated by artificial defects, such as holes. We report the imaging of the magnetic excitation spectrum in presence of holes, fabricated by focussed ion beam milling, in the magnetic domains, domain walls, and the center of Landau structures by means of x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM). Due to the very high lateral and temporal resolution the magnetization dynamics, which is characteristic for the vortex-hole interaction, is investigated in detail. We find that the vortex as well as domain walls can be trapped by small holes. As a consequence the frequency vortex gyrotropic motion is enhanced with a significant lower amplitude in case of non centric holes in domain walls. Non centric holes in domains lead to no frequency shift, but a higher amplitude of the vortex gyration due to attractive vortex-hole interaction. The experimental results are compared to micromagnetic simulations.
Keywords: magnetism, magnetization dynamics, vortex, defects, magnetic domain, XMCD, simulations

Publ.-Id: 11379 - Permalink


Controlled generation of ferromagnetic martensite from paramagnetic austenite in AISI 316L austenitic stainless steel
Menendez, E.; Sort, J.; Liedke, M. O.; Fassbender, J.ORC; Surinach, S.; Baro, M. D.; Nogues, J.
The strain-induced austenite (gamma) to martensite (alpha') transformation in AISI 316L austenitic stainless steel, either in powders or bulk specimens, has been investigated. The phase transformation is accomplished by means of either ball milling processes (in powders) –dynamic approach– or by uniaxial compression tests (in bulk specimens) –quasi-static approach–. Remarkably, an increase of the strain rate causes opposite effects in each case: (i) it increases the amount of transformed alpha' in ball milling procedures, but (ii) it decreases the amount of alpha' in pressed samples. Both the microstructural changes (e.g., crystallite size refinement, microstrains or type of stacking faults) in the parent gamma phase and the role of the concomitant temperature rise during deformation seem to be responsible for these opposite trends. Furthermore, the results show the correlation between the gamma to alpha' phase transformation and the development of magnetism and enhanced hardness.
Keywords: phase transformation, steel, strain, ball milling, compression

Publ.-Id: 11378 - Permalink


Surface energy and magnetocapacitance of superconductors under electric field bias
Morawetz, K.; Lipavsky, P.; Kolacek, J.; Brandt, E. H.;
A superconducting layer exposed to a perpendicular electric field and a parallel magnetic field is considered within the Ginzburg-Landau (GL) approach. The GL equation is solved near the surface and the surface energy is calculated. The nucleation critical field of superconducting state at the surface depends on the magnetic and electric fields. Special consideration is paid to the induced magnetic-field effect cause d by diamagnetic surface currents. The latter effect is strongly dependent on the thickness of the sample . The effective inverse capacitance determines the effective penetration depth. It is found that the capacitance exhibits a jump at the surface critical field. An experiment is suggested for determining the change in the effective capacitance of the layer.
Keywords: Superconducting surfaces, magneto-capacitance

Publ.-Id: 11377 - Permalink


Atomistic simulation of amorphous germanium
Gabriel, A.; Posselt, M.;
Electrical doping of Ge is usually performed by ion implantation and subsequent annealing. In many cases ion bombardment leads to formation of an amorphous layer. During annealing the layer recrystallizes by solid-phase epitaxial regrowth. In order to investigate this process by classical molecular dynamics simulations, first of all amorphous Ge with realistic properties must be prepared. This is the subject of the present work. The atomistic simulations use the Stillinger-Weber interatomic potential with a parameter set that yields correct or reasonable structural, thermodynamic and defect properties of diamond-structure Ge. In the first simulation step liquid Ge is prepared. Then, the system is cooled down slowly to 300 K using the method of Luedtke and Landman which was applied to simulate amorphous silicon. Finally, an equilibration at 300 K and zero pressure is performed. The characterization of amorphous Ge obtained in this manner includes density and cohesive energy, radial distribution function and static structure factor, coordination number, bond-angle distribution, distribution of interatomic distances as well as melting temperature and heat of fusion. The simulation results show very good agreement with experimental data and are consistent with previous theoretical investigations.
Keywords: amorphous Germanium, atomistic simulation
  • Poster
    E-MRS 2008 Spring Meeting, Symposium J: Beyond Silicon Technology: Materials and Devices for Post-Si CMOS, 26.-30.05.2008, Strasbourg, France
  • Poster
    9th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2008), 12.-17.10.2008, Beijing, China

Publ.-Id: 11376 - Permalink


Molecular dynamics simulation of solid phase epitaxial regrowth of amorphous Ge layers
Gabriel, A.; Posselt, M.;
In Ge the regrowth of an amorphous layer formed by ion implantation occurs in a similar manner as in Si, namely by solid phase epitaxy. In most cases this process takes place in the very first stage of annealing before dopant diffusion and activation. In the present work the solid phase epitaxial regrowth (SPER) is investigated by classical molecular dynamics simulations. The Stillinger-Weber interatomic potential is used with an adapted parameter set that yields correct or reasonable structural, thermodynamic and defect properties of diamond-structure Ge. First of all a realistic atomic system with an amorphous-crystalline interface which is nearly parallel to a {100} plane is prepared and characterized. The properties of the simulated amorphous Ge are compared with experimental and theoretical data and a very good agreement is found. Then, the system is heated to a given temperature and the regrowth of the amorphous layer is monitored by different methods including visualization and statistical analysis. Regrowth velocities are calculated for a wide temperature range and the effective migration barrier is determined. The results are compared to experimental data from literature. During SPER the evolution of the roughness and the morphology of the amorphous-crystalline interface are investigated. In order to improve the physical understanding of SPER the rearrangement of atoms at the amorphous-crystalline interface is studied in detail.
Keywords: Germanium, atomistic simulation, solid phase epitaxy
  • Lecture (Conference)
    E-MRS 2008 Spring Meeting, Symposium J: Beyond Silicon Technology: Materials and Devices for Post-Si CMOS, 26.-30.05.2008, Strasbourg, France
  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM 2008), 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11375 - Permalink


n+ doping of Ge by P or As implantation and flash-lamp annealing
Wündisch, C.; Posselt, M.; Anwand, W.; Schmidt, B.; Grötzschel, R.; Mücklich, A.; Skorupa, W.; Simoen, E.; Clarysse, T.; Satta, A.; Hortenbach, H.; Möller, A.; Pelzing, P.;
The increasing interest in Ge as a high mobility substrate has led to numerous investigations on shallow junction formation by ion beam processing. It has been shown that p+ doping yields junctions with the required properties whereas the formation of n+ junctions is complicated by the high diffusivity and the low solubility of the dopants.
The present work is focused on the application of flash-lamp annealing to the formation of shallow n+ layers since this method has the potential of good dopant activation while dopant diffusion is suppressed. Shallow layers with high concentrations of P or As are formed by ion implantation. Then the samples are pre-heated at relatively low temperatures (e.g. 400 °C, for 240 s) in order to achieve the regrowth of the amorphous layer formed during implantation. Subsequently, flash-lamp annealing is performed at 800 and 900 °C, for 0.84, 3 and 20 ms. RBS/C is applied to monitor the regrowth of the amorphous layer. Selected samples are studied by XTEM in order to search for precipitates and end-of-range defects. The depth distributions of P and As are measured by SIMS. The sheet resistance of the shallow n+ layer is obtained by the variable probe spacing method. Spreading resistance profiling is applied to determine the carrier depth profile. Results on phosphorus show that dopant diffusion only occurs at 900 °C for 20 ms whereas the maximum activation is in the order of 4-6x1019 cm-3.
Keywords: Germanium, n-doping, ion implantation, annealing
  • Lecture (Conference)
    E-MRS 2008 Spring Meeting, Symposium J: Beyond Silicon Technology: Materials and Devices for Post-Si CMOS, 26.-30.05.2008, Strasbourg, France
  • Lecture (Conference)
    16th International Conference on Ion Beam Modification of Materials (IBMM 2008), 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11374 - Permalink


Atomistic simulation of solid phase epitaxial regrowth in Si: A critical review
Posselt, M.;
During ultra-shallow junction formation, pre-amorphization or dopant implantation may lead to the formation of an amorphous (a-)layer. In the first stage of annealing the solid phase epitaxial regrowth (SPER) of the a-layer takes place. During SPER, redistribution of the dopants occurs, and they are incorporated into crystalline Si (c-Si), either substitutionally or within clusters containing dopant atoms, self-interstitials (Is) and/or vacancies. The SPER process leaves beyond the original a/c interface the end-of-range (EOR) damage which contains an excess of Is. During further annealing, free Is are emitted from the EOR damage and diffuse towards the surface. In this period the diffusion of dopants is considerably enhanced. It is highly desirable to obtain the initial conditions for calculations of dopant diffusion and activation, i.e. the fractions of dopants on substitutional sites and in clusters as well as the cluster morphology, from atomistic simulations of SPER. This work gives a critical review of previous simulations that are based on classical molecular dynamics. It is shown that even for pure Si the experimental regrowth rates cannot be reproduced reasonably well. The main cause for the disagreement is the inaccuracy of the interatomic potentials used. Proposals for physically-based improvements are discussed. They are based on a better description of the amorphous phase using a modified potential, without changing the well-established potential for c-Si.
Keywords: silicon, atomistic simulation, solid phase epitaxy
  • Lecture (Conference)
    E-MRS 2008 Spring Meeting, Symposium I: Front-end junction and contact formation in future Silicon/Germanium based devices, 26.-30.05.2008, Strasbourg, France

Publ.-Id: 11373 - Permalink


Neutron dosimetry study in the region of the support structure of a VVER-1000 type reactor
Borodkin, G.; Khrennikov, N.; Konheiser, J.; Noack, K.;
The support structure of a reactor pressure vessel experiences a high mechanical stress during reactor operations. In addition, supposed accident conditions and ferritic steel properties result in a low limiting value for the ductile-to-brittle transition temperature and, therefore, a low maximal irradiation load is permitted for this region compared with others. In case of a VVER-1000 reactor, the same applies to weld #5, which is closely above the support structure. The Russian Reactor Operation Rules lay down that profound analyses of the components integrity have to be regularly done if the neutron fluence above the neutron energy of 0.5 MeV must be expected to accumulate a value greater than 1·1018 n/cm2 during the projected operation time of forty years. Therefore, it was necessary to reliably clarify whether this area of the pressure vessel falls into the category of permanent inspection or not. To this end, highly precise fluence calculations were carried out. Applied codes and nuclear data sets were verified by special neutron activiation measurements, which were done just in the near neighborhood of the support structure and of weld #5. The calculation results show that in certain subareas of both construction elements the neutron fluence will exceed the limiting value if the reactor is nominally operated during the projected life-time.
Keywords: reactor, dosimetry, neutron, fluence, support, VVER-1000, TRAMO, DORT, synthesis method
  • Lecture (Conference)
    13th International Symposium on reactor Dosimetry, 25.-31.05.2008, Alkmaar, Netherlands
  • Contribution to proceedings
    13th International Symposium on Reactor Dosimetry, 25.-31.05.2008, Alkmaar, Netherlands
    Reactor Dosimetry State of the Art 2008, New Jersey London Singapore: World Scientific Publishing Co. Pte. Ltd., 13 978-981-4271-10-3, 688-699

Publ.-Id: 11372 - Permalink


Neutron dosimetry on the full-core first generation VVER-440 aimed at reactor support structure load evaluation
Borodkin, P.; Borodkin, G.; Khrennikov, N.; Konheiser, J.; Noack, K.;
Reactor support structures (RSS), especially ferritic steel wall of water tank, of VVER-440 of first generation are non-restorable reactor equipment and their lifetime may restrict plant-life at whole. All operated Russian first generation VVER-440 have a reduced core with dummy assemblies except reactor of Unit 4 of Novovoronezh NPP. In comparison with other reactors, the full-core loading scheme of this reactor provides the highest neutron fluence on the reactor pressure vessel (RPV) and RSS accumulated over design service-life and its prolongation. The radiation load parameters on the RPV and RSS resulted from this core loading scheme should be evaluated by means of precise calculations and validated by ex-vessel neutron dosimetry to provide the reliable assessment of embrittlement parameters of these reactor components. The results of different types of calculations and their comparison with measured data have been analyzed in this paper. The calculational analysis of RSS fluence rate variation in dependence on core loading scheme, including standard and low leakage core as well as dummy assemblies, has been presented in paper.
Keywords: reactor, dosimetry, neutron, fluence, support, VVER-440, TRAMO, DORT, synthesis method
  • Lecture (Conference)
    13th International Symposium on Reactor Dosimetry, 25.-31.05.2008, Alkmaar, Netherlands
  • Contribution to proceedings
    13th International Symposium on Reactor Dosimetry, 25.-31.05.2008, Alkmaar, Netherlands
    Reactor Dosimetry State of the Art 2008, New Jersey London Singapore: World Scientific Publishing Co. Pte. Ltd., 13 978-981-4271-10-3, 300-309

Publ.-Id: 11371 - Permalink


Investigation of the beltline welding seam of the Greifswald WWER-440 unit 1 reactor pressure vessel
Viehrig, H.-W.; Schuhknecht, J.; Rindelhardt, U.; Weiss, F.-P.;
The investigation of reactor pressure vessel (RPV) materials from decommissioned NPPs offers the unique opportunity to scrutinize the irradiation behaviour under real conditions. Material samples taken from the RPV wall enable a comprehensive material characterisation. The paper describes the investigation of trepans taken from the decommissioned WWER-440 1st generation RPVs of the Greifswald NPP. The Greifswald RPVs represent different material conditions such as irradiated (I), irradiated and recovery annealed (IA) and irradiated, recovery annealed and re-irradiated (IAI). The working program is focussed on the characterisation of the RPV steels (base and weld metal) through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the ASTM Test Standard E1921-05 to determine the fracture toughness of the RPV steel in different thickness locations.
In a first step the trepan taken from the RPV Greifswald Unit 1 containing the X-butt multilayer submerged welding seam located in the beltline region was investigated. This welding seam represents the IAI condition. It is shown that the Master Curve approach as adopted in ASTM E1921 is applicable to the investigated original WWER-440 weld metal. The evaluated T0 varies through the thickness of the welding seam. After an initial increase of T0 from 10°C at the inner surface to 49°C at 22 mm distance from it, T0 again decreases to 41°C at a distance of 70 mm, finally increasing again to maximum 20°C towards the outer RPV wall. The lowest T0 value was measured in the root region of the welding seam representing a uniform fine grain ferritic structure. Beyond the welding root T0 shows a wavelike behaviour with a span of about 50 K. The highest T0 of the weld seam was not measured at the inner wall surface. This is important for the assessment of ductile-to-brittle temperatures measured on sub size Charpy specimens made of weld metal compact samples removed from the inner RPV wall. Our findings imply that these samples do not represent the most conservative condition. Nevertheless, the Charpy transition temperature TT41J estimated with results of sub size specimens after the recovery annealing was confirmed by the testing of standard Charpy V-notch specimens.
Keywords: Russian WWER-type reactor, reactor pressure vessel steel, weld metal, trepans, fracture toughness, Master Curve
  • Journal of ASTM International 6(2009)5
  • Lecture (Conference)
    24th Symposium on Effects of Radiation on Nuclear Materials and the Nuclear Fuel Cycle, 24.-26.06.2008, Denver, United States

Publ.-Id: 11370 - Permalink


Homotopic Arnold tongues deformation of the MHD α2-dynamo
Günther, U.; Kirillov, O.;
We consider a mean-field α2-dynamo with helical turbulence parameter α(r)=α0+γΔα(r) and a boundary homotopy with parameter β ∈[0,1] interpolating between Dirichlet (idealized, β=0) and Robin (physically realistic, β=1) boundary conditions. It is shown that the zones of oscillatory solutions at β=1 end up at the diabolical points for β=0 under the homotopic deformation. The underlying network of the diabolical points for β=0 substantially determines the choreography of eigenvalues and thus the character of the dynamo instability for β=1. Using perturbation theory we derive the first-order approximations to the resonance (Arnold's) tongues in the (α0,β,γ)-space, which turn out to be cones in the vicinity of the diabolical points, selected by the Fourier coefficients of Δα(r). The space orientation of the 3D tongues is determined by the Krein signature of the modes involved in the diabolical crossings at the apexes of the cones. The Krein space induced geometry of the resonance zones explains the subtleties in finding α-profiles leading to oscillatory dynamos, and it explicitly predicts the locations of the spectral exceptional points, which are important ingredients in the recent theories of polarity reversals of the geomagnetic field.
Keywords: MHD dynamo, operator theory, Krein space, exceptional point, diabolical point, perturbation theory, spectral mesh, homotopy, Arnold tongue, field reversal

Publ.-Id: 11369 - Permalink


Quantum Chemical Calculations of the Redox Potential of the Pu(VII)/Pu(VIII) Couple
Tsushima, S.;
The redox potential of the Pu(VII)/Pu(VIII) couple was studied by density functional theory calculations. The spin-orbit effect was corrected at the CASSCF level. The redox potential (relative to the standard hydrogen potential) of the Pu(VII)/Pu(VIII) couple in alkaline solution was found to vary from 4.36 to 1.06 V depending on the number of Pu-O oxo bonds, coordination numbers, and coordination modes. The redox potential drops substantially as the number of Pu-O oxo bonds increases. Pu(VIII) may be synthesized in strong alkaline solution assuming that both Pu(VII) and Pu(VIII) exist in penta-oxo form, PuVIIO5OH4- and PuVIIIO5OH3-, respectively. The Mulliken population of Pu in Pu(VII) and Pu(VIII) complexes are very similar, suggesting that the spin-orbit effect is rather small in Pu(VII) complexes and that when Pu(VII) is oxidized to Pu(VIII) the electron is stripped mainly from the ligand. Consequently, Pu(VIII) is in an unstable oxidation state and easily reduced back to Pu(VII) by the solvent water molecules. In acidic medium, the Pu(VII)/Pu(VIII) redox potential is too high to get the Pu(VIII) valence state.

Publ.-Id: 11368 - Permalink


A hybrid finite volume -- boundary element method (FV-BEM) for the numerical solution of the kinematic induction equation.
Giesecke, A.; Stefani, F.; Gerbeth, G.;
The experimental realization of dynamo excitation as well as theoretical and numerical examinations of the induction equation have shown the relevance of boundary conditions and material properties for a self-sustaining dynamo.

Laboratory (insulating) boundary conditions in non-spherical geometry, in general, are treated by elaborated schemes (e.g. solving of the Laplace equation in an extended domain) or by simplifying approximations (pseudo vacuum, vanishing tangential field).

Rather precise results for the numerical solution of the kinematic induction equation are provided by the integral equation approach which also considers insulating boundary conditions exactly.

However, the application possibilities are limited because of enormous computational resources that are required by this method.
In particular in the context of inverse problems -- e.g. estimation of the velocity structure from measurements of induced electric and/or magnetic fields -- solving the forward model turned out to be the most time consuming part.

Therefore, a more flexible approach utilizing a local discretization like the constraint transport (CT) method as a well known realization of a finite volume scheme (FV) is adopted for solving the induction equation. The CT-scheme ensures a fast, robust and accurate solution of the kinematic dynamo problem and intrinsically maintains the solenoidal character of the magnetic field.
Within the framework of the finite volume scheme insulator boundary conditions are treated by a modified integral equation procedure,
commonly known as the boundary element method (BEM).

On the boundaries the magnetic flux density B can be expressed as the gradient of a scalar potential B=-\nabla \Phi, where Phi is
described by a Laplace equation: $\Delta Phi = 0$. Integrating the Laplace equation only on the boundaries requires less computational
power than the full integral equation approach.

Combining both methods in a hybrid FV-BEM scheme offers the flexibility of a local discretization with a stringent treatment of insulating magnetic boundary conditions in almost arbitrary geometries.

The fast and easy to handle algorithm exhibits further advantages when considering spatial varying material properties like electrical conductivity of container walls or localized high-permeability material. Discontinuities of material coefficients are treated within the framework of the FV-BEM scheme under utilization of appropriate averaging procedures for the permeability/conductivity on the contact interfaces which ensures that the corresponding jump conditions for the magnetic flux density B and/or the electric field E are fulfilled.

Several test computations with prescribed alpha-effect or velocity distribution reproduce well known key results and demonstrate the applicability and reliability of the approach. Future examinations are intended to understand the behavior of the VKS-dynamo experiment where the field producing flow is driven by ferrous propellers and the dynamo mechanism probably is strongly influenced by this high permeability material. Indeed, preliminary results including ferromagnetic material inside the computational domain show a certain reduction in the critical magnetic Reynolds number Rm=LV/eta but, up till now, they cannot explain the dominating axisymmetric field mode that is observed in the experiment. Other applications of the hybrid scheme may also be important for the
evaluation of forthcoming dynamo experiments for which a precise knowledge of the critical magnetic Reynolds number is essential. Finally, the method is of interest for the treatment of inverse problems in industrial applications like estimation of the liquid metal flow in continuous casting from measurements of induced magnetic fields via contactless inductive flow tomography.
Keywords: induction equation, boundary conditions, permeability discontinuity, computing methods
  • Lecture (Conference)
    8th. World Congress on Computational Mechanics (WCCM8) / 5th. European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2008), 29.06.-04.07.2008, Venedig, Italy

Publ.-Id: 11367 - Permalink


Aqueous Suspensions of Carbon Nanotubes: Surface Oxidation, Colloidal Stability and Uranium Sorption
Schierz, A.; Zänker, H.;
Our study is aimed at gaining information on the behaviour of carbon nanotubes (CNTs) as potential carriers of pollutants in the case of accidental CNT release to the environment and on the properties of CNTs as a potential adsorbent material in water purification. The effects of acid treatment of CNTs on (i) the surface properties, (ii) the colloidal stability and (iii) heavy metal sorption are investigated, the latter being exemplified by uranium(VI) sorption. There is a pronounced influence of surface treatment on the behaviour of the CNTs in aqueous suspension. Results showed that the acid treatment increases the amount of acidic surface groups on the CNTs. Acid treatment has a great impact on the colloidal stability of the CNTs and on their adsorption capacity for U(VI). Furthermore, pristine CNT colloids can be stabilised by the addition of humic acid.
Keywords: carbon nanotube, surface oxidation, uranium, sorption, colloidal stability

Publ.-Id: 11366 - Permalink


Fraktografische Untersuchungen an unbestrahlten und bestrahlten Reaktordruckbehälterstählen
Müller, G.;
Der Druckbehälter eines Kernkraftwerkes ist von herausragender sicherheitstechnischer Bedeutung. Während des Betriebes eines Kernkraftwerkes kommt es zur Verschlechterung der mechanischen Eigenschaften des Reaktordruckbehälterstahls infolge der Strahlenbelastung - das Material altert.
Das Institut für Sicherheitsforschung im Forschungszentrum Dresden – Rossendorf besitzt die Kompetenz, mikrostrukturelle und bruchmechanische Untersuchungen an bestrahlten Werkstoffen durchzuführen sowie die thermomechanische Beanspruchung von Bauteilen zu bestimmen mit dem Ziel, die Integrität von Reaktorkomponenten zu beurteilen.
Bei der bruchmechanischen Charakterisierung des Zähigkeitsverhaltens der Reak-tordruckbehälterstähle werden dynamische und quasistatische Kennwerte ermittelt und unter Anwendung statistischer Methoden nach dem Master-Curve-Konzept ausgewertet. Die fraktografischen Untersuchungen der Bruchflächen der geprüften Pro-ben mit dem Rasterelektronenmikroskop dienen zusätzlich der Interpretation und Absicherung der ermittelten Bruchzähigkeitswerte. Insbesondere die Charakterisierung der Bruchtypen, der Rissfrontverlauf, die Ausbildung einer Stretchzone, Rissinitiierungspunkte sowie Besonderheiten auf der Bruchfläche stehen im Mittelpunkt der des Interesses. Da bestrahlte oder radioaktiv kontaminierte Proben nicht unmittelbar im REM untersucht werden können, kommt hierfür eine speziell entwickelte Abdrucktechnik zur Anwendung. Die Abdrücke sind kontaminationsfrei und detailgenau, die Methode muss in einer Heißen Zelle praktikabel sein.
Für die REM- und EDX- Untersuchungen wird ein Zeiss EVO 50 mit einem Bruker Leichtelement-X-Flash-Detektor 4010 verwendet.
  • Invited lecture (Conferences)
    Multi Purpose SEM User Meeting 2008, 02.-03.06.2008, Jena, Deutschland

Publ.-Id: 11365 - Permalink


The tunable-frequency ESR as a tool to study magnetic excitations in highly-correlated spin systems
Zvyagin, S. A.;
es hat kein Abstrakt vorgelegen.
  • Invited lecture (Conferences)
    Annual Meeting at the Grenoble High Magnetic Field Laboratory, 13.-17.05.2008, Grenoble, Frankreich

Publ.-Id: 11364 - Permalink


Neuartige Impedanzsensoren für die Visualisierung von Mehrphasenströmungen
Da Silva, M. J.; Hampel, U.;
In diesem Beitrag werden zwei neuartige, bildgebende Messverfahren zur Untersuchung von Mehrphasenströmungen vorgestellt. Beide Messverfahren basieren auf der mehrkanaligen Messung der elektrischen Impedanz eines strömenden Fluides. Sie sind in der Lage, zeitlich und räumlich hoch aufgelöste Bilder der Phasenverteilung einer Mehrphasenströmung zu erzeugen. Weiterhin werden im Beitrag die neuen Sensoren messtechnisch bewertet (Messgenauigkeit, Zeitverhalten, etc.) und es werden ausgewählte Beispiele aus der Strömungsdiagnostik präsentiert.
Keywords: multiphase flow, electrical impedance, flow visualization
  • Contribution to proceedings
    XXII. Messtechnisches Symposium, 11.-13.09.2008, Dresden, Germany
    Tagungsband XXII. Messtechnisches Symposium, Aachen: Shaker, 978-3-8322-7506-8, 25-34
  • Lecture (Conference)
    XXII. Messtechnisches Symposium, 11.-13.09.2008, Dresden, Germany

Publ.-Id: 11363 - Permalink


Synthesis and spectroscopic analysis of uranyl sugar complexes
Steudtner, R.;
The bonding of uranium with glucose and alpha cyclodextrin were investigated by time resolved laser fluorescence spectroscopy (TRLFS), attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) and confocal laser scanning microscopy (CLSM). Two different uranyl-sugar complexes could be synthesized. Both complexes show a strong fluorescence signal by excitation with 266 nm. The emission maxima were detected at 497 nm for the uranyl-glucose complex and 494 nm for the uranyl-alpha-cyclodextrin complex respectively. The time resolved investigations show a fluorescence lifetime of 36 µs for the uranyl-glucose complex and 37 µs for the uranyl-alpha-cyclodextrin complex.
Keywords: Uranyl, Sugar, TRLFS, ATR-FTIR, CLSM
  • Lecture (Conference)
    5th SUPRAPHONE/4th WG Meeting COST D31, 29.-31.05.2008, Prague, Czech Republic

Publ.-Id: 11362 - Permalink


Thermophysical properties of Al-Cu and Al-Si liquid alloys
Plevachuk, Y.; Sklyarchuk, V.; Yakymovych, A.; Gerbeth, G.; Eckert, S.; Willers, B.; Eigenfeld, K.;
New workable aluminium-based light alloys are a key issue in current materials science. Al-Cu alloys, for instance AlCu4TiMg (A356), are the most utilized casting alloys in the aluminium industry. The distinctive characteristics of these alloys are low density, high melting temperature, good thermal conductivity and excellent oxidation resistance. Al-Cu alloys are ubiquitous in technical applications: they are the main components for screw machine products, truck frames, aircraft structures, jet engine impellers and aircraft engine cylinder heads. Moreover, binary Al-Cu alloys are in the focus of numerous, academic studies which are especially concerned with solidification processes and consider for instance, the columnar-to equiaxed transition, the formation of macrosegregation zones, the visualization of the dendritic growth, the impact of melt convection or the application of electromagnetic stirring. The solidification process of a liquid alloy has a profound impact on the structure and properties of the solid material. Therefore, the knowledge of the physical properties of the molten alloys prior to solidification becomes very important for the development of materials with predetermined characteristics.
Aluminium alloy castings have achieved wide usage in automobile, aerospace and other applications because of their high strength to weight ratio. Al–Si–Mg alloys, a group of heat treatable cast Al–Si alloys, exhibit good castability and corrosion resistance in addition to high strength to weight ratio. However, the pursuit of high quality castings with consistent mechanical properties depends upon the proper processing of the alloy, including grain refinement, modification and precipitation heat treatment, etc.
Among all physical properties, the structure-sensitive characteristics of the liquid phase play a prominent role. The density is directly related to the atomic structure and potential short range order of the liquid; on the other hand, it is a fundamental quantity for all technological applications, since it determines fundamental non-dimensional parameters characterising the fluid flow, such as the Reynolds or the Rayleigh number. Reliable information about the structural heterogeneity of the melt can be also obtained from studies considering the temperature dependence of the electrical conductivity and the viscosity. The knowledge of the viscosity is of particular importance considering the relationship between melt convection and solidification.
In that paper we present data of the thermophysical properties of Al-Cu liquid alloys (Al96Cu4, Al80Cu20, Al70Cu30, and AlCu4TiMg in wt.%) and Al-Si liquid alloys (AlSi7, AlSi7Mg, AlSi8Cu3), namely density, viscosity and electrical conductivity. The measurements cover a wide temperature range above the liquidus. The anomalies with respect to the concentration dependence of the electrical conductivity in some Al-Cu alloys are explained in terms of the s–d hybridization model. A comparison with data and scaling relations available in literature is given.
  • Lecture (Conference)
    18th European Conference on Thermophysical Properties, 01.-04.09.2008, Pau, France

Publ.-Id: 11361 - Permalink


Capacitance planar array sensor for fast multiphase flow imaging
Thiele, S.; Da Silva, M. J.; Hampel, U.;
In this paper, we introduce a novel planar array sensor based on electrical capacitance (permittivity) measurements to visualize flows of multiphase mixtures along the surface of objects. The prototype sensor is formed by 32 × 32 interdigital sensing structures. It can be mounted onto the wall of pipes or vessels and thus has minimal influence on the flow. An associated electronics measures the capacitance of the fluid at each sensing structure in a multiplexed manner at high sampling rate. This way, images of the fluid distribution are produced. The electronics is able to generate up to 15,000 images per second. Results of system evaluation and results of two exemplary flow experiments are presented and discussed.
Keywords: interdigital electrodes, permittivity measurement, flow visualization, multiphase flow

Publ.-Id: 11360 - Permalink


The origin of the Energy-Dose window in SIMOX processing and defect engeneering
Ou, X.; Kögler, R.; Skorupa, W.; Möller, W.; Wang, X.; Rauschenbach, B.;
The excess of implantation-induced point defects controls the oxygen redistribution in silicon during a high-temperature treatment such as in SIMOX (Separation-by-IMplanted-Oxygen). The Energy-Dose window for the formation of a perfect homogeneous and planar buried oxide layer is caused by excess point defects. Quantitative relations are given between the distribution of the initially generated excess defects and the finally formed oxide layer. Different methods of defect engineering by vacancy introduction via He implantation are discussed.
Keywords: Implantation defects, SIMOX, Cavities, Silicon, Oxygen
  • Lecture (Conference)
    European Materials Research Society Conference, 25.-30.05.2008, Strasbourg, France

Publ.-Id: 11359 - Permalink


The role of implantation-induced point defects for the redistribution of oxygen in silicon at high-temperature processing
Kögler, R.; Ou, X.; Skorupa, W.; Möller, W.;
The excess of implantation-induced point defects controls the oxygen redistribution in silicon during a high-temperature treatment such as in SIMOX (Separation-by-IMplanted-Oxygen). The Energy-Dose window for the formation of a perfect homogeneous and planar buried oxide layer is caused by excess point defects. Quantitative relations are given between the distribution of the initially generated excess defects and the finally formed oxide layer. Moreover, implantation-induced defects can explain the depth positions of different oxide precipitate layers and of silicon islands inside the oxide layer. Other defects, e.g. dislocations, which form during thermal treatment, can relocate the Energy-Dose window towards lower oxygen dose.
Keywords: Implantation defects, SIMOX, Silicon, Oxygen

Publ.-Id: 11358 - Permalink


Binding properties between ferroic oxides and metals
Pankoke, V.; Gemming, S.;
The structural parameters and the electronic structure of palladium films with different thickness on the piezo-electric ceramic PbMg{1/3}Nb{2/3}O3 (PMN) were studied. The calculations were performed using density functional theory in the local density approximation. Binding properties were examined via total energies differences and densities of states for the different metal/ceramic interfaces.
The Pd films are located on top of the O atoms of the NbO_2 terminated (100) PMN surface and have an fcc structure as the bulk Pd.
Local bonding at the interface can be characterized in terms of overlapping electron densities of the contributing atoms. Furthermore the rearrangement of the electron density at the interface is discussed.
Keywords: PMN, Pd , interfaces, thin films
  • European Physical Journal B 67(2009)1, 57-62

Publ.-Id: 11357 - Permalink


Radioaktiv markierte Kern-Hüll-Nanopartikel auf der Basis von Stärke-umhülltem Magnetit
Matterna, M.;
kein Abstract verfügbar
  • Lecture (others)
    Seminar, Universität Jena, Institut für Diagnostische und Interventionelle Radiologie, 14.04.2008, Jena, Deutschland

Publ.-Id: 11356 - Permalink


Diagnostik und Therapie mit radioaktiven Substanzen
Stephan, H.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Hochschule Zittau/Görlitz (FH), 22.05.2008, Zittau, Deutschland

Publ.-Id: 11355 - Permalink


18F-radiolabeled S100 proteins as potential probes for molecular imaging of inflammatory processes in vivo
Hoppmann, S.; Richter, S.; Pietzsch, J.;
Interaction of certain extracellular S100 proteins with the receptor for advanced glycation endproducts (RAGE) is considered to play a crucial role in various inflammatory diseases. However, data concerning the interaction of circulating S100 proteins with RAGE in inflammatory processes in vivo are scarce. One reason is the shortage of suitable radiotracer methods. To address this question, we report a novel methodology using recombinant human S100A1, S100B, and S100A12 for radiolabeling with the positron emitter fluorine-18 (18F) and the use of 18F-S100 proteins in cell association assays in vitro and in dynamic small animal positron emission tomography (PET) studies in Wistar rats in vivo. Human S100 proteins were cloned in the bacterial expression vector pGEX-6P-1, expressed in E. coli BL21, and purified. Purified S100 proteins were radiolabeled with N-succinimidyl-4-[18F]fluorobenzoate. Cellular association studies in human THP-1 macrophages and human aortic endothelial cells (HAEC) showed specific binding of all 18F-S100 proteins to the non-internalizing RAGE as confirmed by inhibitory effects exerted either by other RAGE ligands, e.g., glycated LDL, or by soluble RAGE. Of interest, uptake of 18F-S100 proteins in THP-1 and HAEC mediated by various scavenger receptors was observed. The in vitro data are consistent with in vivo PET data showing a pronounced temporary association of 18F-S100 proteins with tissues expressing RAGE, e.g., lung and vessels. Moreover, a significant accumulation of 18F-S100 proteins in tissues that are rich in cells expressing scavenger receptors (tissue macrophages) such as liver and spleen was observed. In conclusion, 18F-labeling of S100 proteins and the use of small animal PET provide a valuable tool to discriminate the kinetics and the metabolic fate of S100 proteins in vivo. Furthermore, the approach provides novel probes for imaging of RAGE-ligand interaction in inflammatory processes, e.g., in rodent models of disease.
  • Poster
    5th International EDHF Symposium - Endothelium, Vasoactive Factors and Inflammation, 24.-27.06.2008, Tampere, Finland
  • Abstract in refereed journal
    Basic & Clinical Pharmacology & Toxicology 102(2008)S1, 49

Publ.-Id: 11354 - Permalink


Labelling methods in (PET-)Radiopharmacy: Do we need alternatives?
Steinbach, J.;
Labelling of molecules was introduced by Georg von Hevesy already decades ago utilizing radiophosphorus. With the availability of C-14 and H-3 a long period of isotopic labelling started in the fifties of the last century following Rudolf Schönheimer´s idea to label biomolecules with deuterium. This was the scientific base of the modern biochemistry enabling detailed study of metabolism and of modern pharmacokinetics. With the use of radioiodine fur human investigations and therapy the era of Nuclear Medicine began during that time.
All these applications require different labelling techniques for the radiotracer synthesis. Most of them have been derived from organic microchemistry and have been further developed for the special radiochemical conditions such as radiation protection and the limited amount of substance matter.
The introduction of radiometals to Nuclear Medicine, first of all Tc-99m, opened a new challenge. This was the need to mimic organic molecules by coordination compounds – utilizing knowledge from inorganic, organic and radiochemistry.
At the end of the seventies the Positron Emission Tomography came into the focus of science and later on of medicine. Completely new methods had to be developed due to the application of the no carrier added positron emitting radionuclides in connection with their short half lifes first of all for F-18 and C-11.

Nowadays thousands of compounds have been labelled – organic and inorganic. Hundreds of methods have been developed to introduce e.g. carbon isotopes, radiohalogens and radiometals into the desired positions of molecules comprising a wide variety of substance classes.
Have we reached a saturation of demand for labelling methods?
Of course – for small molecules the requirements for real new developments may be limited. But new demands are at the horizon: This are biomacromolecules such as proteins, peptides, oligonucleotides which are sensitive to the “classic” conditions of chemical reactions. Other problems are connected with the need for regioselective, site specific labelling.
There is and will be done a lot of work – also in the future for applied purposes.
  • Invited lecture (Conferences)
    15th Workshop "The Synthesis and Applications of Isotopes and Isotopically Labelled Compounds", 12.-13.06.2008, Bad Soden, Deutschland
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 52(2009)7, 257

Publ.-Id: 11352 - Permalink


Retrospective dosimetry study at the RPV of NPP Greifswald unit 1
Konheiser, J.; Mittag, S.; Noack, K.; Rindelhardt, U.; Borodkin, G.; Borodkin, P.; Gleisberg, B.;
For the first time, trepans from a decommissioned VVER-440 (Greifswald-1) reactor pressure vessel (RPV) have been examined. Activities of a trepan, taken at the RPV weld with the highest fast-neutron load, were measured and estimated on the basis of fluence calculations by the codes TRAMO and DORT. A maximum fluence of 4.05*1019 n/cm2 (E>0.5 MeV) was calculated. The average deviation between the two codes is 2.6 %. Activities resulting from the reaction 93Nb(n,n’)93mNb were measured, niobium being a trace element in the RPV steel. Unfortunately, 93mNb is also produced by neutron capture in the alloy component 92Mo, the built-up 93Mo decaying by electron capture. The ratios of calculated to measured (C/E) 93mNb gamma activities for several trepan samples are between 0.42 and 0.97. The fact that all C/E ratios are below unity suggests that the measured values may have been additionally heightened by activities from other nuclides.
Keywords: reactor, retrospective dosimetry, neutron, fluence, VVER-440, TRAMO, Greifswald
  • Lecture (Conference)
    13th International Symposium on reactor Dosimetry, 25.-31.05.2008, Alkmaar, Netherlands
  • Contribution to proceedings
    13th International Symposium on Reactor Dosimetry, 25.-31.05.2008, JRC Petten, Netherlands
    Reactor Dosimetry State of the Art 2008, New Jersey London Singapore: World Scientific Publishing Co. Pte. Ltd., 13 978-981-4271-10-3, 23-33

Publ.-Id: 11351 - Permalink


Mass occurrence of penetrative trace fossils in triassic lake deposits (Madygen mossil site, Kyrgyzstan, Central Asia)
Voigt, S.; Hoppe, D.;
Bioturbation and the breakdown of organic detritus by burrowing macro-invertebrates are key factors for the energy flow in recent freshwater ecosystems due to the acceleration of nutrient cycling. According to the current state of knowledge, food webs similar to those ones of modern lakes were not operating until the Late Mesozoic, when a well-established freshwater infauna evolved. Here we describe laterally extended networks of irregularly branched burrows that constitute the most common ichnofossils in lacustrine deposits of the Middle to Late Triassic Madygen Formation, SW Kyrgyzstan. The shallow penetrative trace fossils assigned to Thalassinoides paradoxicus (Woodward, 1830) give evidence that underground exploitation of lake-bottom sediments by benthic invertebrates set up in the Early Mesozoic at the latest. Architecture and size of the fossil burrows indicate deposit-feeding, worm-like trace makers of similar morphology and behaviour to extant oligochaetes or aquatic insect larvae. Maximum intensity of bioturbation is recorded in mudstones of the transitional sublittoral to profundal lake zone which usually represents the thermocline/chemocline level in modern stratified lakes. Taking into account the low-oxygen tolerance of many recent oligochaetes and insect larvae we propose, that ecospace utilisation of deep-water lacustrine settings was originally impelled by two things: exploitation of additional food resources and avoidance of predation by carnivorous animals from well-aerated lake zones. Spatial restriction of the described fossil traces could offer a basic approach to subdivide the Mermia ichnofacies.
Keywords: Thalassinoides, bioturbation, Mermia ichnofacies, oligochaeta, insect larvae

Publ.-Id: 11350 - Permalink


Quality check of wire-mesh sensor measurements in a vertical air/water flow
Beyer, M.; Lucas, D.; Kussin, J.;
Extensive measurements were executed for a vertical upward air/water flow to gen-erate a high-quality database for the development and validation of CFD-Codes for two-phase flows (e.g. for models on bubble forces or on coalescence and break-up). Thereto, in a pipe with a nominal diameter of 200 mm, the wire-mesh sensor technology was used. The present paper aims on the assessment of errors caused by the experimental procedure and especially global errors arising from the use of the wire-mesh sensor technology. Special attention was paid to the plausibility and accuracy of the data regarding the evolution of the vertical multiphase flow. In the result, a clear and consistent trend regarding their evolution with increasing distance from the position of the gas injection was found. Comparisons of the trend of time and cross-section averaged gas volume fraction along the pipe height with the theoretically expected values were carried out. From the measured radial profiles of the void fraction and the velocity of the gas phase, the superficial gas velocity at the wire-mesh sensor integrated over the cross-section is calculated and compared with the set value. Thus, a general error assessment of the sensor data is possible.
Keywords: multiphase flow, bubbly flow, bubble size distribution, wire-mesh sensor, accuracy check, drift velocity

Publ.-Id: 11349 - Permalink


Defect formation in Mn-implanted silicon probed by frequency and temperature dependent capacitance measurements on MOS capacitors
Zhou, S.; Bürger, D.; Beyer, V.; Schmidt, B.; Helm, M.; Schmidt, H.;
In order to obtain magnetic Si the doping of it by Mn is one of the topics in this field. This opens the possibility to fabricate Si-based spintronic devices. Most of the research activities focused on material science, e.g. reporting higher Curie temperatures, and on characterizing their structural properties. However exploring the electrical properties after Mn doping is also important, so that the knowledge can be directly transferred to spintronic device fabrication. In these devices, an MIS (metal-insulator-semiconductor) structure is usually used and a high-quality oxide-semiconductor interface is therefore highly demanded. In this contribution, we investigate the defects in Si and in the interface between SiO2 and Si after the doping by Mn implantation into both p-type and n-type Si wafers. The implantation energy was 60 keV with a fluence of 2×10^15 cm^-2, resulting in a peak concentration of 5×10^20 cm^-3. A 15 nm thick SiO2 layer was grown during subsequent thermal oxidation at 900 °C. After this thermal treatment, the Mn atoms are solved in the Si wafer and partially in the SiO2 layer. Additionally, Mn in the region of the implanted profile with a nominal concentration above the solubility limit causes the formation of Mn-silicide nanoparticles [1]. The quality of SiO2/Si interface was checked by frequency dependent CV measurements. A large amount of defects was found at the SiO2/implanted-Si interface. Temperature dependent capacitance transient measurements reveal the formation of deep traps in the implanted Si, with energies of EV+0.54 eV, EV+0.41 eV in p-Si, and EC-0.57 eV, EC-0.23 eV, EC-0.11 eV in n-Si, respectively. All these electrical defects have to be considered when fabricating transition metal/SiO2/Mn-implanted Si structures for spin-dependent tunnelling devices.

[1] Shengqiang Zhou et al., Phys. Rev. B 75, 085203 (2007)
Keywords: Si, Mn, Ion implantation, DLTS
  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.08, Dresden, Germany

Publ.-Id: 11348 - Permalink


Ferromagnetic transition metal implanted ZnO: a diluted magnetic semiconductor?
Zhou, S.; Potzger, K.; Xu, Q.; Lorenz, M.; Skorupa, W.; Helm, M.; Fassbender, J.ORC; Grundmann, M.; Schmidt, H.
Traditional electronics can be greatly stimulated by a combination of magnetic and semiconducting properties where spins provide an additional degree of freedom. Recently theoretical works predict that some semiconductors (e.g. ZnO) doped with transition metal are diluted magnetic semiconductors (DMS) [1]. In binary DMS materials, transition metal ions substitute cation sites of the host semiconductor and are coupled by free carriers resulting in ferromagnetism. One of the main obstacles in creating DMS materials is the formation of secondary phases because of the solid-solubility limit. Ion implantation is a non-equilibrium method, and has been successfully used to create GaAs-based DMS [2]. In our study transition metal ions were implanted into ZnO single crystals with the peak concentrations of 0.5-10 at.%. We established a correlation between structural and magnetic properties. By synchrotron radiation X-ray diffraction secondary phases (Fe, Ni, Co and ferrite nanocrystals) were observed and have been identified as the source for ferromagnetism [3-6]. Due to their different crystallographic orientation with respect to the host crystal these nanocrystals in some cases are very difficult to be detected by a simple Bragg-Brentano scan. This results in the pitfall of using XRD to exclude secondary phase formation in DMS materials. For comparison, the solubility of Co diluted in ZnO films amounts to 10 at.% using pulsed laser deposition (PLD) [7]. Such diluted, Co-doped ZnO films show paramagnetic behaviour. However, only the magnetoresistance of Co-doped ZnO films reveals possible s-d exchange interaction as compared to Co-implanted ZnO single crystals.
References
[1] T. Dietl, et al., Science 2000; 287:1019.
[2] M. A. Scarpulla, et al, Appl. Phys. Lett. 2003; 82:1251.
[3] K. Potzger, et al., Appl. Phys. Lett. 2006; 88 :052508.
[4] Shengqiang Zhou, et al., J. Appl. Phys. 2008; 103:023902.
[5] Shengqiang Zhou, et al., Phys. Rev. B 2008 ; 77:035209.
[6] Qingyu Xu, et al., Phys. Rev. B 2006; 73:205342.
Keywords: ZnO, diluted magnetic semiconductor, Magnetic nanoparticles, Magnetoresistance
  • Invited lecture (Conferences)
    VII-th International Conference on Ion Implantation and other Applications of Ions and Electrons, 16.-19.06.08, Kazimierz Dolny, Poland
  • Vacuum 83(2009), S13

Publ.-Id: 11347 - Permalink


High-Transmission Planar X-ray Waveguides
Salditt, T.; Krüger, S. P.; Fuhse, C.; Bähtz, C.;
We have studied the propagation of hard x rays in a planar x-ray waveguide with a sub-20 nm guiding layer. To optimize the transmission and to minimize absorption losses, a novel waveguide design based on a two-component cladding was implemented. Optimized transmission is achieved by placing an appropriate interlayer between the cladding and the guiding core. The experimental results along with simulations of field propagation show that high transmission values can be obtained in waveguide optics at parameters relevant for x-ray imaging. These are small beam diameters below 20 nm and the relatively long guiding length necessary for efficient blocking of multi-keV photon energy beams.
Keywords: X-ray optics, X-ray imaging, X-ray scattering

Publ.-Id: 11346 - Permalink


Model experiments on macroscopic thermoelectromagnetic convection
Zhang, X.; Cramer, A.; Lange, A.; Gerbeth, G.;
The interaction between a thermoelectric current and an imposed magnetic field may produce thermoelectromagnetic convection (TEMC). In the present paper, an experimental study on TEMC in a generic configuration is reported. While the necessary temperature gradient grad T in a square box was accomplished by heating and cooling of two opposing side walls, respectively, utilising a massive nickel plate for the bottom of the electrically conducting container established a material discontinuity with respect to the liquid metal layer. In first place, such a jump in the related Seebeck coefficient non-parallel to grad T is a pre-requisite for the existence of a thermoelectric current. The second condition for TEMC, which is a non-vanishing curl of the Lorentz force, was fulfilled with a permanent magnet producing an inhomogeneous magnetic field. Ultrasonic Doppler velocimetry was used to quantify the TEMC flow field. The measurements demonstrate that even a moderate temperature difference can produce distinct convection. Locating the magnet, the direction of magnetization of which was parallel to grad T, close to either side wall produced a single vortex spreading throughout the entire box. Moving the magnet to the center led to a modified distribution of the magnetic field, which, in turn, altered the flow structure. A convective pattern consisting of four vortices developed and the velocity fluctuations were intensified. The numerical results for the distribution of the magnetic field in presence of the ferromagnetic bottom support the experimental findings.
  • Magnetohydrodynamics 45(2009), 25-42

Publ.-Id: 11345 - Permalink


Electromagnetic stirring with superimposed travelling and rotating magnetic fields.
Cramer, A.; Pal, J.; Gerbeth, G.;
Velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating (RMF) and a travelling magnetic field (TMF). The combination of both fields gives rise to an inherent three-dimensional constituent of the electromagnetic force distribution, which implies an intense mixing of the melt.
  • Lecture (Conference)
    XVI International Congress on Electricity applications in modern world - UIE'08, 19.-21.05.2008, Krakow, Poland
  • Contribution to proceedings
    XVI International Congress on Electricity applications in modern world - UIE'08, 19.-21.05.2008, Krakow, Poland, 83-88415-80-8, 41-42

Publ.-Id: 11344 - Permalink


DNA double-strand break signalling: X-ray energy dependence of residual co- localised foci of -H2AX and 53BP1
Beyreuther, E.; Lessmann, E.; Pawelke, J.; Pieck, S.;
The foci of gamma-H2AX alone or colocated with 53BP1 are currently used in a lot of different studies to detect DNA double-strand breaks (DSB) after ionizing radiation. The primary objective of our study was to compare the radiation energy, dose dependent induction and kinetics of DNA DSB, in particular with regard to differences between soft and higher energy X-rays with the colocated gamma-H2AX and 53BP1 foci. We chose the human mammary epithelial cell line 184A1 for these experiments due to the medical application of 25 kV X-rays, e.g. in mammography. X-ray energies applied were 25 kV and 10 kV, the latter one by reason of the proposed maximum biological effectiveness at this energy, and 200 kV X-rays as reference radiation source.
The time courses of foci appearance and loss showed a similarity in the kinetics for all energies applied with maxima at 2 h (2 Gy) and 0.5 h for (0.25 Gy) after irradiation. Despite these uniform kinetics, we investigated the dose dependence of the colocated foci, allowing to calculate the RBE of soft X-rays in the range of 1.3 to 2.2 (25 kV) and 2.9 to 6.4 (10 kV).
  • International Journal of Radiation Biology 85(2009)11, 1042-1050
    DOI: 10.3109/09553000903232884
  • Poster
    2nd Workshop on "Radiation and Multidrug Resistance Mediated via the Tumor Microenvironment", 09.-10.02.2009, Dresden, Germany

Publ.-Id: 11343 - Permalink


Characterisation of dissolved thioarsenite complexes and precipitated arsenic species in a low-pH sulphate-reducing bioreactor
Crouzet, C.; Delorme, F.; Battaglia-Brunet, F.; Burnol, A.; Scheinost, A.; Morin, D.; Touzelet, S.;
Some mining effluents and mine drainage waters are acidic and highly polluted with arsenic. A bio-process performing the precipitation of arsenic sulphide would be very attractive, because the final solid waste would contain up to 60% arsenic in weight. In the framework of Biomine European Integrated project (contract NMP2-CT-2005-500329), a bacterial population able to reduce sulphate at pH 4.5 was selected and used to inoculate column bioreactors that were continuously fed with arsenic in acidic conditions. Arsenic precipitates with sulphide in acidic and low-sulphide solutions. With excess sulphide, soluble thioarsenite species are expected to form.The present work showed that sulphate-reducing bacteria can mediate the precipitation of arsenic sulphide in acidic conditions. The main part of the precipitate is composed of amorphous orpiment, however crisrtallised phases could be detected. The new method developed here to analyse of thioarsenite species in solution will facilitate the monitoring of anaerobic bioreactors treating arseniccontaining effluents and will allow the biogeochemical modelling of such systems.
Keywords: Arsenic, EXAFS, acid mine drainage
  • Poster
    2nd International Congress: As in the environment, 21.-23.05.2008, Valencia, Spain

Publ.-Id: 11342 - Permalink


Megawatt PV plants in Germany: A south-north performance comparison
Rindelhardt, U.; Dietrich, A.; Kedziora, K.; Hahn, A.;
Purpose
Stimulated by the German Feed-in-Law, a large number of grid-connected Megawatt PV plants have been put into operation during the last 5 years. Because of the higher irradiance these plants were originally concentrated in the southern part of Germany (Bavaria and Baden-Wuerttemberg). Starting in 2004 some plants have been also installed in other regions of Germany. The paper describes design and operation results of nine plants operating in different regions.

Locations and design
The plant locations are distributed between 47 and 52 degrees northern latitude (Fig.1), covering Germany from South to North. Some technical features of the investigated plants are given in the table below.

The most plants were built on heavily used or loaded areas (former industrial sites or waste sites). Different types of fundaments and rack support constructions (desks) were used for the module mounting (Fig.2.). The connection with the grid was done in the 10 to 20 kV voltage level, the distance between the plants and the grid was several thousands meters in some cases. The most plants started their operation before 2006. The operation of the plants is monitored by the owners or by professional service providers.

Results and conclusions
The operation results of the year 2007 are exemplarily presented. The solar irradiance in 2007 was higher than the long year average, similar to the years before. The final yield of the plants ranges between 940 and 1180 kWh/kW (Fig. 3). The final yield of the tracked plant in Borna surpasses the yield of the other plants by 25%.
The performance ratios were determined to be between 0.75 and 0.92 (Fig. 4). In the most cases the PR values surprisingly ranges between 0,82 and 0.86. The sources of energy losses are analysed and discussed. Finally a long term estimation of the yield for the different plants will be given.
Keywords: PV plants, performance, MW plants
  • Lecture (Conference)
    23rd European Photovoltaic Solar Energy Conference and Exhibition, 01.-05.09.2008, Valencia, Spain
  • Contribution to proceedings
    23rd European Photovoltaic Solar Energy Conference and Exhibition, 01.-05.09.2008, Valencia, Spain
    Proc. of the International Conference held in Valencia, Spain, 1-5 September 2008, München, 3-936338-24-8, 3236-3239

Publ.-Id: 11341 - Permalink


Kernenergie im 21. Jahrhundert
Rindelhardt, U.;
Im Vortrag wird einleitend die Entwicklung der Kernenergie im 20. Jahrhundert dargestellt. Ausgehend vom bisher erreichten Stand werden die Perspektiven im 21. Jahrhundert entwickelt. Schwerpunkte dabei sind der Einsatz von Kraftwerken der 3. Generation, der Abfallbehandlung durch Transmutation und die Entwicklung von schnellen Brutreaktoren.
Keywords: Nuclear energy, neclear reactors, electricity
  • Lecture (others)
    Seniorenkolleg TU Chemnitz, 27.05.2008, Chemnitz, Deutschland

Publ.-Id: 11340 - Permalink


Electrochemical and Complexation Behavior of Neptunium in Aqueous Perchlorate and Nitrate Solutions
Ikeda, A.; Hennig, C.; Rossberg, A.; Funke, H.; Scheinost, A. C.; Bernhard, G.; Yaita, T.;
Electrochemical and complexation properties of neptunium (Np) are investigated in aqueous perchlorate and nitrate solutions by means of cyclic voltammetry, bulk electrolysis, UV-visible absorption and Np LIII-edge X-ray absorption spectroscopies. The redox reactions of Np(III)/Np(IV) and Np(V)/Np(VI) couples are reversible or quasi-reversible, while the electrochemical reaction between Np(III/IV) and Np(V/VI) is irreversible because they undergo the structural rearrangement from spherical coordinating ions (Np3+ and Np4+) to transdioxo neptunyl ions (NpO2n+, n = 1 for Np(V) and 2 for Np(VI)). The redox reaction of the Np(V)/Np(VI) couple involves no structural rearrangement on their equatorial planes in acidic perchlorate and nitrate solutions. A detailed analysis on extended X-ray absorption fine structure (EXAFS) spectra suggests that Np(IV) forms a decaaquo complex of [Np(H2O)10]4+ in 1.0 M HClO4, while Np(V) and -(VI) exist dominantly as pentaaquo neptunyl complexes, [NpO2(H2O)5]n+ (n = 1 for Np(V) and 2 for Np(VI)). A systematic change is observed on the Fourier transforms (FTs) of the EXAF spectra for all the Np oxidation states as increasing the nitrate concentration in the sample, revealing that the hydrate water molecules are replaced by bidentate-coordinating nitrate ions on the primary coordination sphere of Np.
Keywords: Neptunium, Electrochemistry, Complexation, Cyclic Voltammetry, Electrolysis, UV-visible Absorption, X-ray Absorption Spectroscopy, Hydrate, Perchlorate, Nitrate, Aqueous Solution
  • Inorganic Chemistry 47(2008)18, 8294-8305

Publ.-Id: 11339 - Permalink


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