Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35858 Publications

Efficient melt stirring using pulse sequences of a rotating magnetic field: I - Flow field in a liquid metal column

Eckert, S.; Nikrityuk, P. A.; Räbiger, D.; Eckert, K.; Gerbeth, G.

The utilization of a pulsed rotating magnetic field (RMF) is presented as an auspicious method to obtain an intensive stirring and mixing in a pool of liquid metal. The RMF pulses within a sequence have been applied with constant or alternating direction, respectively. The resulting flow structure in a cylindrical liquid metal column has been explored by numerical simulations and by model experiments using the ternary alloy GaInSn. The ultrasonic Doppler velocimetry (UDV) has been used to determine profiles of the vertical velocity. The numerical results as well as the velocity measurements demonstrate the capability of the proposed stirring regimes to overcome the limited mixing character of conventional rotary stirring. The application of a time-modulated RMF offers a considerable potential to provide optimal flow pattern in a solidifying melt for reasons of a well-aimed modification of casting properties.

Keywords: electromagnetic stirring; rotating magnetic field; Ultrasonic Doppler Velocimetry; solidification

Publ.-Id: 9740

Synthesis of an 11C-labelled cyclooxygenase-2 (COX-2) inhibitor and PET imaging in HT-29 and FaDu tumor bearing mice

Knieß, T.; Bergmann, R.; Wüst, F.

Cyclooxygenase-2 (COX-2) is an enzyme induced during inflammation by various stimuli, but overexpression of COX-2 has been observed also in oncogenesis in a variety of tumors. Although several COX-2 inhibitors have recently been radiolabeled with isotopes for positron emission tomography (PET), their potential for tumor imaging has not been explored extensively. Herein we report the synthesis and radiopharmacological evaluation of 1-(4-[11C]methoxyphenyl)-2-(4-methylsulfonylphenyl)-1-cyclopentene as novel 11C-labelled radiotracer for PET imaging of COX-2.

The radiolabeling was performed via a 11C-methylation reaction of the corresponding desmethyl precursor using [11C]MeI in a TRACERLab FXC module.
Biodistribution studies were performed in normal Wistar rats. Small animal PET studies were performed using xenografted HT-29 and FaDu tumors in mice using a micro-PET® P4 scanner.

The radiolabeling was achieved by the reaction of 1-(4-hydroxyphenyl)-2-(4-methylsulfonylphenyl)-1-cyclopentene at 60°C in DMF/aqueous NaOH with [11C]CH3I. After semi-preparative HPLC purification and solid phase extraction the 11C-labelled COX-2 inhibitor was obtained in 12-14 % decay-corrected radiochemical yield at a specific activity of 30 GBq/µmol at the end-of-synthesis. The radiochemical purity exceeded 97%. Biodistribution in normal rats showed high radioactivity accumulation in the liver, adrenals and brown adipose tissue, reaching 0.6±0.1, 0.7±0.2 and 0.8±0.1 %ID/g after 1 h post injection, respectively. Tumor-to-muscle ratios of 1.7±0.2 and 2.1±0.3, respectively, were determined with small animal PET-studies of xenografted HT-29 and FaDu tumors in mice after 1 h post injection.

  • Poster
    2nd International Conference of the European Society for Molecular Imaging, 14.-15.06.2007, Naples, Italy

Publ.-Id: 9739

Modified “4+1” Mixed Ligand Technetium Labeled Fatty Acids for Myocardial Imaging: Evaluation of Myocardial Uptake and Biodistribution

Mirtschink, P.; Stehr, S. N.; Pietzsch, H.-J.; Bergmann, R.; Pietzsch, J.; Wunderlich, G.; Heintz, A. C.; Kropp, J.; Spies, H.; Kraus, W.; Deussen, A.; Walther, M.

Our group previously synthesized 99mTc-labeled fatty acids suitable for myocardial metabolism and flow imaging. In this set of experiments 28 new analogues were synthesized according to the “4+1” mixed ligand approach with some specific differences. Conventional “4+1” 99mTc-fatty acids are built in the sequence Tc-chelate, alkyl chain and carboxylic group. We developed compounds with a new design with the sequence carboxylic group, alkyl chain, Tc-chelate, and lipophilic tail. Therefore the 99mTc-chelate was transferred to a more central position of the compound, aiming towards an improved myocardial profile and an accelerated liver clearance. In this context several functional groups incorporated in the lipophilic tail section were tested to evaluate their influence on the compound’s character. In addition to biodistribution studies in vivo the myocardial first-pass extraction of the compounds was tested in an isolated Langendorff rat heart model. A satisfactory myocardial uptake up to 20% of the injected dose (% ID) in the perfused heart and a fast liver clearance in vivo with only 0.29% ID/g at 60 min post injection demonstrates that the induced molecular modifications affect the kinetics of 99mTc-radiolabeled fatty acid compounds favorably. From the data set rules for estimating the biodistribution of fatty acids tracers are deduced.

Publ.-Id: 9738

First results in 64Cu-production and copper complexation by new ligands derived from bispidine and 1,4,7-triazacyclononane

Walther, M.; Preusche, S.; Gasser, G.; Tjioe, L.; Graham, B.; Spiccia, L.; Juran, S.; Künstler, J.-U.; Stephan, H.; Steinbach, J.

64Cu (t1/2 = 12.7 h; ß+ 0.653 MeV, 17.4%; ß-: 0.578 MeV, 39%) [1,2] is the most used copper isotope in nuclear medicine due to its favorable decay characteristics and its ability to be produced with high specific activity. Bispidines and azamacrocycles containing pyridine pendant arms form thermodynamically stable complexes with copper(II) [1,2]. These chelating agents – possessing an additional linker group – provide an attractive lead for labelling biomolecules with copper radionuclides.

First experiments to adapt the described 64Cu-production process [3,4] at a biomedical cyclotron CYCLONE 18/9 were performed. A bombarding energy of 10 MeV and a proton beam current of 10 µA for 15 to 60 min were used. The yields of the 64Ni(p,n)64Cu reaction were comparable to reference values [179-331 MBq/µA/h versus 185-248 MBq/µA/h [3,4]].
Two novel ligands with carboxylic groups – a hexadentate bispidine 1 and a derivative of 1,4,7-triazacyclononane (TACN) 2 [5] were prepared. Labelling experiments of these ligands indicated the rapid formation of stable 64Cu-complexes under mild conditions. The bioconjugates 3 and 4 were obtained by coupling the bombesin (BBN) derivate βAla-βAla-[Cha13, Nle14]BBN(7-14) [6] to the ligands 1 and 2 (HBTU, DIPEA, DMF, r.t.).

Results and Discussion:
The bioconjugation of 1 and 2 to a bombesin derivative was successfully achieved via amide coupling to give 3 and 4. The free ligands and the bioconjugates were labelled with 64Cu and the resulting complexes were found to be stable in the presence of a large excess of competing ligands such as cyclam and even in rat plasma.

The bispidine ligand 1, the TACN derivative 2 and their bombesin bioconjugates 3 and 4 are able to form complexes with high stability. These bifunctional chelating agents may be attractive candidates for the development of new copper radiopharmaceuticals for diagnosis (64Cu) and therapy (67Cu). Preliminary studies on the bio-distribution of 64Cu-complexes of 3 and 4 are currently underway [5].

[1] C. Bleiholder et al., Inorg. Chem. 2005, 44, 8145-8155.
[2] G. A. McLachlan et al., Inorg. Chem. 1994, 33, 4663-4668.
[3] F. Szelecsényi et al., Appl. Radiat. Isotopes 1993, 44, 575-580.
[4] D. W. McCarthy et al., Nucl. Med. Biol. 1997, 24, 35–43.
[5] G. Gasser et al., Bioconjugate Chemistry, 2007, in prep.
[6] E. Garcia Garayoa et al., Nucl. Med. Biol. 2007, 34, 17-28.

  • Lecture (Conference)
    2nd International Conference on Radiopharmaceutical Therapy, 03.-07.09.2007, Ulaanbaatar, Mongolia

Publ.-Id: 9737

Diagnostics Beamline for the SRF Gun Project

Kamps, T.; Dürr, V.; Goldammer, K.; Krämer, D.; Kuske, P.; Kuszynski, J.; Lipka, D.; Marhauser, F.; Quast, T.; Richter, D.; Lehnert, U.; Michel, P.; Teichert, J.; Evtushenko, P.

A superconducting radio-frequency photo electron injector (SRF gun) is currently under construction by a collaboration of BESSY, DESY, FZR and MBI. The project aims at the design and setup of a CW SRF gun including a diagnostics beamline for the ELBE FEL and to address R&D issues on low emittance injectors for future light sources such as the BESSY FEL. Of critical importance for the injector performance is the control of the electron beam parameters. For this reason a compact diagnostics beamline is under development serving a multitude of operation settings ranging from low-charge (77pC), low-emittance (1 mm mrad) mode to high-charge (2.5nC) operation of the gun. For these operation modes beam dynamics simulations are resulting in boundary conditions for the beam instrumentation. Proven and mature technology is projected wherever possible, for example for current and beam position monitoring. The layout of the beam profile and emittance measurement systems is described. For the bunch length, which varies between 5 ps and 50 ps, two schemes using electro-optical sampling and Cherenkov radiation are detailed. The beam energy and energy spread is measured with a 180o spectrometer.

  • Contribution to proceedings
    27th International Free Elektron Laser Conference FEL 2005, 21.-26.08.2005, Stanford, CA, USA
    Proceedings of the 27th International Free Electron Laser Conference 2005, 530-533


Publ.-Id: 9736

Status of the 7Be(p,g)8B S-factor

Junghans, A.

We present new measurements of the 7Besp,gd8B cross section from Ec.m.=116 to 2460 keV (where c.m. means center-of-mass), which incorporate several improvements over our previously published experiment, also discussed here. Our new measurements lead to S17s0d=22.1±0.6sexptd±0.6stheord eV b based on data from Ec.m.=116 to 362 keV, where the central value is based on the theory of Descouvemont and Baye. The theoretical error estimate is based on the fit of 12 different theories to our low-energy data. We compare our results to other S17s0d values extracted from both direct f7Besp,gd8Bg and indirect (Coulomb-dissociation and heavy-ion reaction) measurements, and show that the results of these three types of experiments are not mutually compatible. We recommend a “best” value, S17s0d=21.4±0.5sexptd±0.6stheord eV b, based on the mean of all modern direct measurements below the 1+ resonance. We also present S factors at 20 keV which is near the center of the Gamow window: the result of our measurements is S17s20d =21.4±0.6sexptd±0.6stheord eV b, and the recommended value is S17s20d=20.6±0.5sexptd±0.6stheord eV b.

  • Invited lecture (Conferences)
    Advances and Challenges in Nuclear Astrophysics, 24.05.2004, Trento, Italy

Publ.-Id: 9735

Precise measurement of the 7Be(p,g)8B S-factor

Junghans, A.

We present new measurements of the 7Besp,gd8B cross section from Ec.m.=116 to 2460 keV (where c.m. means center-of-mass), which incorporate several improvements over our previously published experiment, also discussed here. Our new measurements lead to S17s0d=22.1±0.6sexptd±0.6stheord eV b based on data from Ec.m.=116 to 362 keV, where the central value is based on the theory of Descouvemont and Baye. The theoretical error estimate is based on the fit of 12 different theories to our low-energy data. We compare our results to other S17s0d values extracted from both direct f7Besp,gd8Bg and indirect (Coulomb-dissociation and heavy-ion reaction) measurements, and show that the results of these three types of experiments are not mutually compatible. We recommend a “best” value, S17s0d=21.4±0.5sexptd±0.6stheord eV b, based on the mean of all modern direct measurements below the 1+ resonance. We also present S factors at 20 keV which is near the center of the Gamow window: the result of our measurements is S17s20d =21.4±0.6sexptd±0.6stheord eV b, and the recommended value is S17s20d=20.6±0.5sexptd±0.6stheord eV b.

  • Invited lecture (Conferences)
    Bothe Kolloquium, 19.5.2004, Heidelberg, Deutschland

Publ.-Id: 9734

Combined TEM, PAS and SANS investigation of neutron-irradiated pure iron

Bergner, F.; Al Mazouzi, A.; Hernandez-Mayoral, M.; Ulbricht, A.

Fission spectrum neutron irradiation of pure Fe at irradiation temperatures of about 300 °C gives rise to the formation of two populations of defects: planar dislocation loops and spherical vacancy-type clusters. Knowledge of the type and size distributions of these populations is important for the purpose of multi-scale modelling of the mechanical behaviour of Fe-based alloys. Among the experimental techniques with nanometer size resolution, transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) allow to gain information on both nature and size distribution of particular types of defects. Furthermore, positron annihilation spectroscopy (PAS) is sensitive to sub-nanometer size open-volume defects. However, there is no single experimental technique capable of providing the full set of information required for calibration and validation of advanced models. The complementarity between the three techniques to identify and quantify the defects created by irradiation in pure Fe is emphasised in the paper. It is shown that while TEM allows direct size-resolved evidence of dislocation loops, PAS a qualitative appreciation of the existing sub-nanometer size vacancy-type clusters, SANS yields indirect size-resolved evidence of vacancy-type clusters, which form a sound basis for the quantification of the size distributions.

  • Lecture (Conference)
    Workshop on Structural Materials for Innovative Nuclear Systems (SMINS), 04.-06.06.2007, Karlsruhe, Germany
  • Contribution to proceedings
    Structural Materials for Innovative Nuclear Systems (SMINS), 04.-06.06.2007, Karlsruhe, Germany
    Workshop Proceedings: OECD 2008, 283-290

Publ.-Id: 9733

Spallation residues in the reaction 56Fe+ p at 0.3A, 0.5A, 0.75A, 1.0A, and 1.5A GeV

Villagrasa-Canton, C.; Boudard, A.; Ducret, J.-E.; Fernandez, B.; Leray, S.; Volant, C.; Armbruster, P.; Enqvist, T.; Hammache, F.; Helariutta, K.; Jurado, B.; Ricciardi, M. V.; Schmidt, K.-H.; Sümmerer, K.; Vives, F.; Yordanov, O.; Audouin, L.; Bacri, C.-O.; Ferrant, L.; Napolitani, P.; Rejmund, F.; Stephan, C.; Tassan-Got, L.; Benlliure, J.; Casarejos, E.; Fernandez-Ordonez, M.; Pereira, J.; Czajkowski, S.; Karamanis, D.; Pravikoff, M.; George, J. S.; Mewaldt, R. A.; Yanasak, N.; Wiedenbeck, M.; Connell, J. J.; Faestermann, T.; Heinz, A.; Junghans, A.

The spallation residues produced in the bombardment of 56Fe at 1.5A, 1.0A, 0.75A, 0.5A, and 0.3A GeV on a liquid-hydrogen target have been measured using the reverse kinematics technique and the fragment separator at GSI (Darmstadt). This technique has permitted the full identification in charge and mass of all isotopes produced with cross sections larger than 10−2 mb down to Z = 8. Their individual production cross sections and recoil velocities at the five energies are presented. Production cross sections are compared with previously existing data and with empirical parametric formulas, often used in cosmic-ray astrophysics. The experimental data are also extensively compared with the results of different combinations of intranuclear cascade and deexcitation models. It is shown that the yields of the lightest isotopes cannot be accounted for by standard evaporation models. The GEMINI model, which includes an asymmetric fission decay mode, gives an overall good agreement with the data. These experimental data can be directly used for the estimation of composition modifications and damages in materials containing iron in spallation sources. They are also useful for improving high-precision cosmic-ray measurements.

Publ.-Id: 9732

X-ray diffraction study of low-energy carbon-ion implanted Si(001)

Markwitz, A.; Barry, B.; Eichhorn, F.

In the search for Si- and C-based crystalline phases in low-energy ion implanted and electron-beam annealed Si surface layers, X-ray diffraction (XRD) measurements were performed at grazing incidence on samples of large SiC nanocrystals grown on a 90 nm thick Si layer containing C atoms. Diffraction patterns and reciprocal space maps did not reveal XRD patterns originating from the nanocrystals or the implanted layer, but did show that distortions of the Si crystal structure were introduced into the implanted layer. After annealing, the strain in the implanted layer is reduced, possibly by carbon atoms that have moved to locations close to dislocations and dislocation loops. This investigation underpins the growth theory of the SiC nanocrystals on Si, with carbon atoms migrating to form the nanostructures.

  • Surface and Interface Analysis 39(2007)5, 415-418

Publ.-Id: 9731

Characterization of Ni-Ti (Shape Memory Alloy) thin film by in-situ XRD and complementary ex-situ techniques

Martins, R. M. S.; Schell, N.; Reuther, H.; Pereira, L.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.

Ni-Ti SMA are smart materials undergoing first order martensitic transformations driven by temperature and/or stress. In the form of film they are very attractive candidates for microelectro-mechanical system (MEMS) applications. Future directions include the production of functionally graded films by changing deliberately the ratio Ti/Ni across their thickness. However, for the successful development of this type of films, it is important to characterize, model and control the variations in composition, crystalline structure and transformation temperatures. Our approach is in-situ XRD study of the actual growth of the films of varying composition along the thickness carried out using a deposition chamber installed at a synchrotron radiation beamline. These studies were complemented with ex-situ analysis techniques. The results achieved on a Ni-Ti film co-sputtered from Ni-Ti and Ti targets on a TiN buffer layer are presented in this paper. The deposition started by using optimised parameters for a near equiatomic composition. After 1 h (≈330 nm thick film), the Ti power was increased from 20 to 25 W, leading to the precipitation of Ti2Ni. The evolution of the lattice parameter values of the B2 phase, calculated from the corresponding XRD data, is clearly linked with the increase of the Ti power. The depth profile of the atomic concentrations determined by Auger Electron Spectroscopy (AES) is in agreement with the in situ XRD results. The temperature dependence of the electrical resistivity was used to monitor phase transformations, Scanning Electron Microscopy (SEM) has shown the presence of twinned martensite on the film’s surface at room temperature.

  • Lecture (Conference)
    Materials 2007 (IV International Materials Symposium), 01.-04.04.2007, Porto, Portugal
  • Materials Science Forum 587-588(2008), 672-676

Publ.-Id: 9730

The interfacial diffusion zone in magnetron sputtered Ni-Ti thin films deposited on different Si substrates studied by HR-TEM

Martins, R. M. S.; Beckers, M.; Mücklich, A.; Schell, N.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.

Ni-Ti Shape Memory Alloy thin films are suitable materials for microelectromechanical devices. During the deposition of Ni-Ti thin films on Si substrates, there exist interfacial diffusion and chemical interactions at the interface due to the high temperature processing necessary to crystallize the film. For the present study, Ni-Ti thin films were prepared by magnetron cosputtering from Ni-Ti and Ti targets in a specially designed chamber mounted on the 6-circle goniometer of the ROssendorf BeamLine (ROBL-CRG) at ESRF, Grenoble (France). The objective of this study has been to investigate the interfacial structure resulting from depositions (at a temperature of ≈ 470°C) on different substrates: naturally oxidized Si(100), Si(111) and poly-Si substrates. A detailed High-Resolution TEM analysis of the interfacial structure has been performed. When Ni-Ti is deposited on Si(100) substrate, a considerable diffusion of Ni into the substrate takes place, resulting in the growth of semi-octaeder A-NiSi2 silicide. In the case of Ni-Ti deposited on Si(111), there appears an uniform thickness plate, due to the alignment between substrate orientation and the [111]-growth front. For Ni-Ti deposited on poly-Si, the diffusion is inhomogeneous. Preferential diffusion is found along the columnar grains of poly-Si, which are favourably aligned for Ni diffusion. These results show that for the Ni-Ti/Si system, the morphology of the diffusion interface is strongly dependent on the type of substrates.

  • Poster
    Materiais 2007 (IV International Materials Symposium), 01.-04.04.2007, Porto, Portugal
  • Materials Science Forum 587-588(2008), 820-823

Publ.-Id: 9729

Sputter deposition of high-temperature NiTiHf shape memory thin films

Martins, R. M. S.; Schell, N.; Zhou, S.; Beckers, M.; Silva, R. J. C.; Mahesh, K. K.; Braz Fernandes, F. M.

  • Poster
    Materiais 2007 (IV International Materials Symposium), 01.-04.04.2007, Porto, Portugal

Publ.-Id: 9728

In-situ study of the ion bombardment of Ni-Ti thin films

Martins, R. M. S.; Schell, N.; von Borany, J.; Braz Fernandes, F. M.

  • Poster
    ESRF Users' Meeting 2007, 07.02.2007, Grenoble, France

Publ.-Id: 9727

Experiments with real photons for nuclear astrophysics

Wagner, A.

Research on experiments using real photons from bremsstrahlung production at ELBE is presented in an invited talk at the annual spring meeting of the german physical society.

Keywords: bremsstrahlung ELBE photons nuclear astrophysics

  • Invited lecture (Conferences)
    DPG Frühjahrstagung, 12.-16.03.2007, Giessen, Germany

Publ.-Id: 9726

Fast optical tomography for transient process diagnostics

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

Optical tomography is a potential technique for the visualisation of fast transient phenomena in multiphase flows. It can be applied for liquid-liquid, gas-liquid and gas-solid flows as long as the flow consists of a major transparent component/phase, such as a liquid or gas, and a minor component/phase that alters the intensity or light ray propagation path, such as solid particles or gas bubbles. The technique is also applicable in single phase flows with dye tracer marked fluid volumes. Recently we have built a fast optical tomography system that achieves frame rates up to 5 kfps and can be applied to study bubbly two-phase flows in pipes with an inner diameter of two inches. High frame rate at high spatial resolution in the range of 3 mm is obtained by application of a specially developed fully parallel 64 channel data logger with 1MSample simultaneous sampling frequency. The tomography system works similar to an X-ray computed tomography system. As radiation emitters we use 256 LEDs and as detector elements 32 avalanche photo diodes which are optically connected to the tomographic cross section be means of plastic optical fibres. For image reconstruction we use conventional CT algorithms. These algorithms, however, suffer to some degree from the non-linear attenuation of the light at phase boundaries due to total reflection or refraction. Therefore, we currently develop improved image reconstruction algorithms which use a binary reconstruction scheme together with a-priori information on the gas phase. With the new fast optical tomograph we have investigated different two and single phase flow phenomena and compared different image reconstruction algorithms concerning their quantitative accuracy. Especially for lower void fractions in bubble flow or lower particle numbers in liquids we get reliable high resolution images of the cross section at very high temporal resolution.

Keywords: Optical tomography; multiphase flow sensors

  • Contribution to proceedings
    5th World Congress on Industrial Process Tomography, 03.-06.09.2007, Bergen, Norway
  • Invited lecture (Conferences)
    5th World Congress on Industrial Process Tomography, 03.-06.09.2007, Bergen, Norway

Publ.-Id: 9725

A comparative experimental analysis of the a-C:H deposition processes using CH4 and C2H2 as precursors

Peter, S.; Graupner, K.; Grambole, D.; Richter, F.

The plasma enhanced chemical vapor deposition of a-C:H films using methane and acetylene as precursors was studied. Non-invasive in-situ techniques were used to analyze the plasma processes with respect to the self-bias voltage, the displacement currents to the grounded electrode, the neutral gas composition, the optical sheath thickness as well as current and energy of the ions hitting the powered electrode. The a-C:H films were characterized for their deposition rate, surface roughness, hardness, mass density and hydrogen content. Ion mean free paths, suitable for low pressure RF sheaths, have been quantified for both precursors. The film with the highest hardness of 25 GPa was formed in the C2H2 discharge when the mean energy per deposited carbon atom was about 50 eV. The hardness obtained with the CH4 discharge was lower at 17 GPa and less sensitive to changes in the process parameters. It was found that the creation of hard (hardness > 15 GPa) a-C:H films from both precursors is possible if the mean energy per deposited carbon atom exceeds only ~ 15 eV. Further film characteristics like surface roughness and hydrogen content show the interplay of ion flux and deposition from radicals to form the a-C:H structure and properties.

  • Journal of Applied Physics 102(2007)5, 53304

Publ.-Id: 9724

Spectroscopic identifications of U(VI) species sorbed by the green algae Chlorella vulgaris

Günther, A.; Raff, J.; Geipel, G.; Bernhard, G.

The green algae Chlorella vulgaris has the ability to bind high amounts of uranium(VI) in the pH range from 3 to 6. At pH 3 up to 40 % of the uranium was bound by the algal cells. The uranium removal is almost complete at pH 5 and 6 under the given experimental conditions. Scanning electron microscopy and laser-induced fluorescence spectroscopy were used to characterize formed uranyl species in the selected pH range. Thus demonstrating the regular distribution of U(VI) on the cell surface. Fluorescence spectroscopic investigations of formed complexes outside/inside the cells indicate, the binding of U(VI) to carboxyl groups plays a dominating role at pH 3. Whereas a minor impact of organic phosphate compounds on the U(VI) sorption can not be excluded. In contrast the phosphate groups are mainly responsible for the removal and immobilization of U (VI) at pH 5 and 6 by formation of organic or/and inorganic uranyl phosphates.

Keywords: uranium(VI); green algae; sorption; complexation; TRLFS; REM-EDX

Publ.-Id: 9723

Entrapped Bonded Hydrogen in a Fullerene - the five atomic Cluster Sc3CH in C80

Krause, M.; Ziegs, F.; Popov, A. A.; Dunsch, L.

The synthesis and characterisation of the new endohedral clusterfullerene Sc3CH@C80 is reported. The encapsulation of the first hydrocarbon cluster inside a fullerene was achieved by the arc burning method in a reactive CH4 atmosphere. The extensive characterisation by MS, HPLC, Sc-NMR, ESR, UV-Vis-NIR and Raman spectroscopy provided the experimental evidence for the caging of the five-atomic Sc3CH cluster inside the C80 cage isomer with icosahedral symmetry. The proposed new structure was confirmed by DFT calculations, which gave a closed shell and large energy gap structure. Thus a pyramidal Sc3CH cluster and the Ih-C80 cage were shown to be the most stable configuration for Sc3CH@C80 whereas alternative structures give a smaller bonding energy as well as a smaller energy gap.

Keywords: Endohedral Fullerenes; Hydrogen Encapsulation in Carbon Nanostructures; Molecular Clusters; Mass Spectrometry; NMR Spectroscopy

Publ.-Id: 9721

Application of the small-punch-test to irradiated reactor vessel steels in the brittle-ductile transition region

Linse, T.; Kuna, M.; Schuhknecht, J.; Viehrig, H.-W.

The warranty of the high safety standards of existing nuclear power plants requires the assessment and characterization of the actual material state changing during service, e.g. embrittlement due to irradiation. In the brittle and brittle-ductile transition region, ferritic steels fail due to transcrystalline or intercrystalline cleavage fracture starting at flaws resulting from microplastic deformations. The large scatter of fracture mechanical properties in the transition region originating from statistically distributed flaws can be described by Weibull theory. Using the Beremin local approach model, the probability of cleavage fracture at a certain load state can be quantified.
In the small-punch-testing, a quadratical specimen lying on a die is loaded centrically and deformed vertically by a spherical punch, hence starting at plate-like bending and ending in a deep drawing process. Large parts of the specimen are exposed to a biaxial stress state, making the test rather suitable to represent the actual stress state observed in pressure vessel steels in service than other miniaturized methods such as tension or bending tests. Due to the tiny specimen size, material remnants of ongoing surveillance programs (slices of Charpy-specimen) can be used. A special small-punch device was manufactured to be installed into a testing machine in hot cells. To enable testing at temperatures down to -185°C, a cooling system based on liquid nitrogen is used. Neural networks are used to solve the inverse problem of finding material parameters from measured load-displacement-curves. Having identified the parameters describing hardening, Weibull-parameters are determined from both experimental data, e.g. displacement of the punch at fracture, and calculated stress distribution inside the specimen, obtained from FE calculations using the identified plastic properties. The reactor vessel steel A508 (IAEA JFL) is characterized at different levels of irradiation and different temperatures, covering brittle and brittle-ductile transition region of the steel.

Keywords: small specimen testing; small punch test; parameter identification; transition region; inverse method

  • Lecture (Conference)
    ASTM E10 Fifth Symposium on Small Specimen Test Techniques, 31.01.-01.02.2007, Anaheim, USA
  • Journal of ASTM International 5(2008)4
    DOI: 10.1520/JAI101008

Publ.-Id: 9720

Usage of small-punch-test for the characterisation of reactor vessel steels in the brittle-ductile transition region

Linse, T.; Kuna, M.; Schuhknecht, J.; Viehrig, H.-W.

This paper presents a method for the identification of hardening parameters in the brittle-ductile transition region and the determination of WEIBULL parameters in the brittle region. A small-punch-test device is developed for hot cells, where a miniaturised disk-like specimen is manufactured and deformed by a spherical punch. Its load-displacement-curve is analysed regarding its information about the material behaviour. Using Neural Networks, an identification routine is presented, which avoids time-consuming calculations with FEM during an optimisation algorithm. Identified material properties are compared with data from tensile tests. WEIBULL parameters are calculated for temperatures at which cleavage fracture occurs using the identified hardening parameters.

Keywords: small specimen testing; small punch test; parameter identification; transition region; inverse method

Publ.-Id: 9719

Photoluminescence from cadmium sulfide nanoclusters formed in the matrix of a Langmuir-Blodgett film

Bagaev, E. A.; Zhuravlev, K. S.; Sveshnikova, L. L.; Badmaeva, I. A.; Repinskii, S. M.; Voelskow, M.

Photoluminescence (PL) from CdS nanoclusters formed in the matrix of a Langmuir-Blodgett film and from the same clusters with the matrix removed has been studied. The PL spectrum of clusters in the matrix has the form of a broad band (full width at half-maximum (FWHM) ∼ 0.6 eV) peaked at 2.4 eV. After removing the matrix with hexane, the PL spectrum consists of a high-energy band at 2.9 eV (FWHM ∼ 0.2 eV) and two low-energy bands at 2.4 and 2.0 eV (FWHM ∼ 0.5 eV). The high-energy band is attributed to exciton recombination in the nanoclusters, and the bands at 2.4 and 2.0 eV, to recombination via levels related to defects in the bulk of the matrix and at the nanocluster-matrix interface, respectively.

Keywords: Photoluminescence; CdS; nanocluster

  • Semiconductors 37(2003)11, 1321-1325
  • Fizika i Tekhnika Poluprovodnikov 37(2003)11, 1358-1362

Publ.-Id: 9718

Annealing studies of Al-implanted 6H-SiC in an induction furnace

Ottaviani, L.; Lazar, M.; Locatelli, M. L.; Chante, J. P.; Heera, V.; Skorupa, W.; Voelskow, M.; Torchio, P.

6H-SiC samples were amorphised by multiple Al implantations at room temperature, in order to study the annealing process. The paper deals with the influence of specific annealing conditions, such as furnace atmosphere and heating rate, on SiC reordering and Al profile. Below a certain deposited nuclear energy, solid phase epitaxy is possible and leads to recrystallisation under precise conditions (high heating rate, silicon partial pressure prescribed). Above it, material etching and dopant losses are observed, even though annealing has proven to be efficient for avoiding surface impairment (due to a specific cleaning process).

Keywords: Silicon carbide; Annealing; Surface roughness; SIMS

  • Materials Science and Engineering B 91-92(2002), 325-328

Publ.-Id: 9717

Post mortem investigations of the NPP Greifswald WWER-440 reactor pressure vessels

Viehrig, H.-W.; Rindelhardt, U.; Schuhknecht, J.

The investigation of reactor pressure vessel (RPV) materials from decommissioned NPPs offers the unique opportunity to scrutinize the irradiation behaviour under real conditions. Trepans taken from the whole RPV wall enable a comprehensive material characterisation. The paper describes the trepanning technology applied to the decommissioned WWER-440/230 RPVs of the Greifswald NPP. The Greifswald RPVs represent different material conditions such as irradiated, irradiated and recovery annealed and irradiated, recovery annealed and re-irradiated. 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 material of the core welding seam was investigated. It could be shown that the Master Curve approach as adopted in E1921 is applicable to the investigated original RPV weld metal. The weld metal located in a distance of about 22 mm from the inner surface of the RPV wall yielded a T0 of 50°C which is about 40K higher than T0 close to the inner surface. This outcome is important for the assessment of results retrieved from so called boat samples taken directly from the RPV surface after the recovery annealing. It shows that boat samples do not represent the material with the lowest toughness.

Keywords: nuclear power plant; WWER type; reactor pressure vessel; weld metal; integrity assessment; neutron embrittlement; mechanical testing; fracture toughness; Master Curve concept

  • Contribution to proceedings
    19th International Conference on Structural Mechanics in Reactor Technology (SMiRT-19), 12.-17.08.2007, Toronto, Canada
    Proceedings of the 19th International Conference on Structural Mechanics in Reactor Technology
  • Lecture (Conference)
    19th International Conference on Structural Mechanics in Reactor Technology (SMiRT-19), 12.-17.08.2007, Toronto, Canada

Publ.-Id: 9716

Properties of Ge nanocrystals formed by implantation of Ge+ ions into SiO2 films with subsequent annealing under hydrostatic pressure

Tyschenko, I. E.; Talochkin, A. B.; Cherkov, A. G.; Zhuravlev, K. S.; Misiuk, A.; Voelskow, M.; Skorupa, W.

The influence of hydrostatic compression on the implantation-induced synthesis of Ge nanocrystals in SiO2 host was studied. It is found that high-temperature annealing under pressure leads to retardation of Ge diffusion in SiO2. It is shown that unstressed Ge nanocrystals are formed as a result of conventional annealing (under atmospheric pressure). Annealing under pressure is accompanied by formation of hydrostatically stressed Ge nanocrystals. The stress in Ge nanocrystals was determined from optical-phonon frequencies in the Raman spectra. The shift of Raman resonance energy (E 1, E 1 + Δ1) corresponds to the quantization of the ground-state energy for a two-dimensional exciton at the critical point M 1 of germanium. It is ascertained that a photoluminescence band peaked at 520 nm is observed only in the spectra of the films which contain stressed Ge nanocrystals.

Keywords: Ge; Ion implantation; SiO2; diffusion; nanocrystals

  • Semiconductors 37(2003)4, 462-467
  • Fizika i Tekhnika Poluprovodnikov 37(2003)4, 479-484

Publ.-Id: 9715

Curium(III) complexation with pyoverdins secreted by a groundwater strain of Pseudomonas fluorescens

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

Pyoverdins, bacterial siderophores produced by ubiquitous fluorescent Pseudomonas species, have great potential to bind and thus transport actinides in the environment. Therefore, the influence of pyoverdins secreted by microbes on the migration processes of actinides must be taken into account in strategies for the risk assessment of potential nuclear waste disposal sites. The unknown interaction between curium(III) and the pyoverdins released by Pseudomonas fluorescens (CCUG 32456) isolated from the granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden, is the subject of this paper.
The interaction between soluble species of curium(III) and pyoverdins was studied at trace curium(III) concentrations (3  10 -7 M) using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Three Cm3+  P. fluorescens (CCUG 32456) pyoverdin species, MpHqLr, could be identified from the fluorescence emission spectra, CmH2L+, CmHL, and CmL-, having peak maxima at 601, 607, and 611 nm, respectively. The large formation constants, log β121 = 32.50 ± 0.06, log β111 = 27.40 ± 0.11, and log β101 = 19.30 ± 0.17, compared to those of other chelating agents illustrate the unique complexation properties of pyoverdin-type siderophores. An indirect excitation mechanism for the curium(III) fluorescence was observed in the presence of the pyoverdin molecules.

Keywords: Curium; Pyoverdin; Fluorescence spectroscopy; TRLFS; Complexation

Publ.-Id: 9714

Real-time spectroscopic ellipsometry of silver nanoparticle formation in poly(vinyl alcohol) thin films

Oates, T. W. H.; Christalle, E.

Silver nanoparticle formation in poly(vinyl alcohol) thin films is analyzed in real time by spectroscopic ellipsometry. Modeling the data using the Maxwell-Garnett theory shows that the silver content predicted by the model depends of the film thickness. This is conjectured to be due to the absence of plasmon resonances in very small particles affecting the model. The size dependence of the free electron relaxation frequency is used to analyze the particle size during nucleation and growth. Evaporation of the polymer matrix is also monitored by real time ellipsometry and the plasmon resonance is observed to shift from 3.0 to 2.2 eV as the particles are liberated from the polymer. The particle density on the surface can be controlled by the silver concentration and the initial polymer thickness. The exposed particles are easily imaged with scanning electron microscopy, and the particle sizes are compared to the parameters predicted from the Maxwell-Garnett theory.

  • Journal of Physical Chemistry C 111(2007), 182-187

Publ.-Id: 9713

Heating of the edge of a metal sheet in the container-less melt extraction of fibres

Cramer, A.; Priede, J.; Galindo, V.; Gerbeth, G.; Andersen, O.; Kostmann, C.

The present work is concerned with the metallurgical process of melt extraction. Certain industrial requirements, e.g. high purity and small cross-sectional area of the extracted fibres, require a geometrically strictly confined melt volume that is not in contact with any other material being a potential source of pollution. Hitherto, the pending drop method is embodied on small scale facilities. It suffers from low productivity because only one edge can be used to tear a filament out off the molten droplet forming at the tip of a heated rod. Here, a modification is proposed that uses extraction from a pending molten edge at the lower end of a metal sheet. Being a trivial task by all appearances, closer examination shows that it is not. Almost any embodiment of the pending drop technique makes use of locally confined sources of heat, i.e. an acetylene-oxygen torch, or, in the case of high valued materials, laser or electron beams. As attempts to employ induction heating to a single drop did not work even there, it is all the more difficult to melt a sheet along its entire edge rather than between the two opposing branches of an inductor. Tailoring of the induction heating magnetic field, the basic feature of which is the same direction of the electric current in both branches of the inductor, solved the problem. A proper choice of geometry, electrical conductivities of both extraction and substrate material, and the frequency of the alternating magnetic field have proven to be essential for the extraction process. Melting a platinum sheet at the edge and extraction of fibres only 25 micron in effective cross-section from a tin sheet was successfully demonstrated in model experiments.

  • Contribution to proceedings
    HES-07 International Symposium on Heating by Electromagnetic Sources, 20.-22.06.2007, Padua, Italy, 88-89884-07-X, 445-452
  • Lecture (Conference)
    HES-07 International Symposium on Heating by Electromagnetic Sources, 20.-22.06.2007, Padua, Italy

Publ.-Id: 9712

Magnetization of RuSr2GdCu2O8 in pulsed magnetic fields up to 47 T

Papageorgiou, T. P.; Casini, E.; Skourski, Y.; Herrmannsdörfer, T.; Freudenberger, J.; Braun, H. F.; Wosnitza, J.

Magnetization measurements in pulsed magnetic fields up to 47 T were utilized to estimate the average Ru moment in polycrystalline RuSr2GdCu2O8. A NbSr2GdCu2O8 sample was used as reference. The extracted Ru moment of about 1.8µB at 4.2 K and 47 T is indicative of a mixed-valence state of Ru involving Ru5+ and Ru4+ ions with magnetic moments of 2µB/Ru5+ and 0.9µB/Ru4+. The estimated ratio of Ru5+:Ru4+≈ 87%:13% corresponds to a hole concentration p≈0.065 in the CuO2 planes suggesting an underdoped nature of the superconducting state. We propose that the magnetic structure of the Ru moments corresponds to an antiferromagnetic phase, involving only Ru5+ ions, interrupted by ferromagnetic stripes, where charge transfer between Ru4+and Ru5+ ions takes place.

  • Physical Review B 75(2007), 104513

Publ.-Id: 9711

Topotaxial growth of Ti2AlN by solid state reaction in AlN/Ti(0001)multilayer thin films

Höglund, C.; Beckers, M.; Schell, N.; von Borany, J.; Birch, J.; Hultman, L.

The formation of Ti2AlN by solid state reaction between layers of wurtzite-AlN and alpha-Ti was characterized by in situ x-ray scattering. The sequential deposition of these layers by dual magnetron sputtering onto Al2O3 (0001) at 200°C yielded smooth, heteroepitaxial (0001) oriented films, with abrupt AlN/Ti interfaces as shown by x-ray reflectivity and Rutherford backscattering spectroscopy. Annealing at 400°C led to AlN decomposition and diffusion of released Al and N into the Ti layers, with formation of Ti3AlN. Further annealing at 500°C resulted in a phase transformation into Ti2AlN(0001) after only 5 min.

Publ.-Id: 9709

Ultra-shallow junctions produced by plasma doping and flash lamp annealing

Skorupa, W.; Yankov, R. A.; Anwand, W.; Voelskow, M.; Gebel, T.; Downeyc, D. F.; Arevaloc, E. A.

The capabilities of plasma doping (PLAD) and flash lamp annealing (FLA) for use in ultra-shallow junction (USJ) fabrication have been evaluated. Silicon wafers have been doped in a BF3 plasma using wafer biases ranging from 0.6 to 1 kV and a dose of 4 × 1015 cm−2. The wafers so implanted have been heat-treated by FLA using pre-heating temperatures in the range of 500–700 °C, peak temperatures of 1100–1350 °C, and effective anneal times of 20 and 3 ms. Secondary ion mass spectrometry (SIMS) and sheet resistance measurements have been undertaken to determine the junction depth and the sheet resistance, respectively. Optimum processing conditions have been identified under which both high electrical activation and insignificant dopant diffusion occur compared to the as-implanted state. In this way, one can obtain combinations of junction depth and sheet resistance that meet the 45 nm technology node requirements.

Keywords: Flash lamp annealing; Plasma doping; Ultra-shallow junctions

  • Materials Science and Engineering B 114-115(2004), 358-361

Publ.-Id: 9707

Comparative Study of Scintillators for PET/CT Detectors

Nassalski, A.; Kapusta, M.; Batsch, T.; Wolski, D.; Möckel, D.; Enghardt, W.; Moszynski, M.

A growing interest in the development of dual modality PET/CT scanners prompts the comparative study of numerous scintillators to select the best one, which could be used simultaneously in PET detectors working in the pulsing mode and in the CT detectors working in the current mode. In the comparative measurements, done in the same experimental conditions, various samples of BGO, GSO, GSO:Ce,Zr, LGSO, LSO, LYSO, MLS, LaCl3, LaBr3 and CWO scintillators were tested. The measurements covered a determination of the light output, energy resolution, non-proportionality of the light yield, decay times of the light pulses and for the selected crystals their time resolution for 511 keV annihilation quanta. Moreover, a comparative study of afterglow, induced by 60 keV gamma-rays from a strong 241-Am source (13.9 GBq), was done in the second range of time. The LSO-like crystals are best in the PET scanners application. However, they do not fit to the CT requirements, due to a high afterglow. The studies conclude that besides of the well known BGO, only GSO:Ce and most likely LaBr3 might be considered for the simultaneous PET/CT detectors.

Keywords: Image analysis and processing; NMIS; PET instrumentation; reconstruction algorithms

Publ.-Id: 9706

Behavior of germanium ion-implanted into SiO2 near the bonding interface of a silicon-on-insulator structure

Tyschenko, I. E.; Voelskow, M.; Cherkov, A. G.; Popov, V. P.

The properties of germanium implanted into the SiO2 layers in the vicinity of the bonding interface of silicon-on-insulator structures are studied. It is shown that, under conditions of high-temperature (1100 degrees C) annealing, germanium nanocrystals are not formed, while the implanted Ge atoms segregate at the Si/SiO2 bonding interface. It is established that, in this case, Ge atoms are found at sites that are coherent with the lattice of the top silicon layer. In this situation, the main type of traps is the positive-charge traps; their effect is interpreted in the context of an increase in the surface-state density due to the formation of weaker Ge-O bonds. It is found that the slope of the drain-gate characteristics of the back MIS transistors increases; this increase is attributed to an increased mobility of holes due to the contribution of an intermediate germanium layer formed at the Si/SiO2 interface.

Keywords: SOI; SiO2

  • Semiconductors 41(2007)3, 291-296

Publ.-Id: 9705

Scanning spreading resistance microscopy of defect engineered low dose SIMOX samples

Vines, L.; Kögler, R.; Kuznetsov, A. Y.

SIMOX (separation by implanted oxygen) process was studied using cross section scanning spreading resistance microscopy (SSRM). Firstly, open volume defects, nanocavities, have been introduced by He+ ion implantation in the region, where SiO2 precipitates were subsequently formed. Secondly, dual (simultaneous) oxygen (O+) and silicon (Si+) implantation was used to modify SiO2 reaction kinetics too. The results show that the He-induced nanocavities enhance the SiO2 formation presumably releasing excess strain associated with Si oxidation, while the use of a dual O+/Si+ beam do not influence significantly the oxidation kinetics in the initial state of the SIMOX process in our samples. Overall, SSRM was shown to be a suitable method for observation of the early stage of buried oxide formation in Si, since it measures the local resistivity, the main functional parameter of a SIMOX structure.

Keywords: Silicon on insulator; ion beam synthesis; SIMOX; simultaneous dual implantation

  • Microelectronic Engineering 84(2007), 547-550

Publ.-Id: 9704

Magnetic order in the S=1/2 two-dimensional molecular antiferromagnet copper pyrazine perchlorate Cu(Pz)2(ClO4)2

Lancaster, T.; Blundell, S. J.; Brooks, M. L.; Baker, P. J.; Pratt, F. L.; Manson, J. L.; Conner, M. M.; Xiao, F.; Landee, C. P.; Chaves, F. A.; Soriano, S.; Novak, M. A.; Papageorgiou, T. P.; Bianchi, A. D.; Herrmannsdörfer, T.; Wosnitza, J.; Schlueter, J. A.

We present an investigation of magnetic ordering in the two-dimensional S=1/2 quantum magnet Cu(Pz)2(ClO)4)2 using specific heat and zero-field muon-spin relaxation (µ+SR). The magnetic contribution to the specific heat is consistent with an exchange strength of 17.7(3) K. We find unambiguous evidence for a transition to a state of three-dimensional long-range order below a critical temperature TN=4.21(1) K using µ+SR even though there is no feature in the specific heat at that temperature. The absence of a specific heat anomaly at TN is consistent with recent theoretical predictions. The ratio of TN/J=0.24 corresponds to a ratio of intralayer to interlayer exchange constants of |J´ /J| =6.8x10−4, indicative of excellent two-dimensional isolation. The scaled magnetic specific heat of [Cu(Pz)2(HF2)]BF4, a compound with an analogous structure, is very similar to that of Cu(Pz)2(ClO)4)2 although both differ slightly from the predicted value for an ideal 2D S=1/2 Heisenberg antiferromagnet.

  • Physical Review B 75(2007), 094421

Publ.-Id: 9703

Electron spin resonance in S = 1/2 Heisenberg chains with alternating g-tensor and the Dzyaloshinskii–Moriya interaction

Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Krzystek, J.; Feyerherm, R.

Low-temperature ESR studies of copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and the Dzyaloshinskii–Moriya interaction, are presented. The ESR linewidth and g-factor shift are investigated as function of temperature. The data are interpreted in frame of a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82 (1999) 5136] and applied for precise calculations of the ESR parameters in S ¼ 1/2 antiferromagnetic chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained.

  • Journal of Magnetism and Magnetic Materials 310(2007), 1209-1211

Publ.-Id: 9702

Spin-triplet excitons and anisotropy effects in the S = 1/2 gapped antiferromagnet BaCuSi2O6

Zvyagin, S. A.; Wosnitza, J.; Krzystek, J.; Stern, R.; Jaime, M.; Sasago, Y.; Uchinokura, K.

BaCuSi2O6 can be regarded as an almost ideal realization of an S = 1/2 system of weakly interacting spin dimers with spin-singlet ground state and gapped excitation spectrum. We argue that the fine structure observed in low-temperature EPR spectra of BaCuSi2O6 is a fingerprint of triplet excitations (excitons). Analyzing the angular dependence of the exciton modes allows us to precisely calculate the zero-field splitting within the triplet states and, correspondingly, the anisotropy parameter, D = 0.07cm-1. The proposed procedure can be applied for studying anisotropy effects in a large number of S = 1/2 gapped quantum antiferromagnets with dimerized or alternating spin structure.

  • Journal of Magnetism and Magnetic Materials 310(2007), 1206-1208

Publ.-Id: 9701

An intense channeling radiation source

Wagner, W.; Pawelke, J.; Azadegan, B.; Sobiella, M.; Steiner, J.; Zeil, K.

A nonconventional x-ray source based on the production of electron channeling radiation in a diamond crystal has been installed at the Radiation source ELBE. The brilliant electron beam with an average current up to 100 microA available in the radiation physics cave allows to reach photon rates of quasi-monochromatic channeling radiation of the order of 10^(11) s^(-1) per 10% bandwidth. On-line x-ray monitoring was realised using a Compton spectrometer. The photon energy can be tuned by variation of the beam energy. Monochromisation of channeling radiation and bremsstrahlung background reduction have been investigated applying x-ray diffraction on a HOPG crystal.

Keywords: channeling radiation; x-ray source; Compton spectrometer; HOPG crystal

  • Nuclear Instruments and Methods in Physics Research B 266(2008)2, 327-334

Publ.-Id: 9700

Fermi surfaces of the half-Heusler compounds Ce1-xLaxBiPt

Bianchi, A. D.; Wosnitza, J.; Kozlova, N.; Freudenberger, J.; Schultz, L.; Opahle, I.; Elgazzar, S.; Richter, M.; Goll, G.; von Löhneysen, H.; Yoshino, T.; Takabatake, T.

We report on the Fermi surface in the correlated half-Heusler compounds Ce1xLaxBiPt. In CeBiPt, as well as in Ce0:95La0:05BiPt, we find a temperature-dependent Fermi-surface topology. In addition, we observe a field-induced change of the electronic band structure as discovered by electrical-transport measurements in pulsed magnetic fields. For magnetic fields above 25 T, in a simple one band picture, the charge-carrier concentration determined from Hall-effect measurements increases nearly 30%, whereas the Shubnikov-de Haas (SdH) signal disappears at the same field. In the non-4f compound LaBiPt the Fermi surface remains unaffected, suggesting that these features are intimately related to the Ce 4f electrons. Electronic band–structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology.

  • Journal of Magnetism and Magnetic Materials 310(2007), e261-e263

Publ.-Id: 9699

From Thermodynamically Driven Phase Transitions to Quantum Critical Phenomena

Wosnitza, J.

In this short review some basic concepts of phase transitions at non-zero and zero temperature are highlighted. For that the critical behavior of classical, thermodynamically driven magnetic phase transitions is exemplified for conventional universality classes as well as for systems reflecting chiral order. Finally the quantum critical phenomena for two magnetic-field-driven phase transitions are presented.

  • Journal of Low Temperature Physics 147(2007), 249-278

Publ.-Id: 9698

Intrinsic vs. extrinsic inelastic scattering contributions in κ-(BEDT-TTF)2Cu[N(CN)2]Br - Transport measurements under hydrostatic pressure

Strack, C.; Akinci, C.; Paschenko, V.; Wolf, B.; Uhrig, E.; Assmus, W.; Schreuer, J.; Wiehl, L.; Schlueter, J.; Wosnitza, J.; Schweitzer, D.; Lang, M.

Interlayer-resistivity measurements have been performed on a variety of single crystals of the quasi-two-dimensional organic superconductor k-(BEDT-TTF)2Cu[N(CN)2]Br. These crystals, which have been synthesized along two somewhat different routes, reveal strongly sample-dependent resistivity profiles: while the majority of samples shows a more or less pronounced r(T) maximum around 90 K with a semiconducting behaviour above, some crystals remain metallic at all temperatures T 300 K. In the absence of significant differences in the crystals’ structural parameters and chemical compositions, as proved by high-resolution X-ray and electron-probe-microanalysis [C. Strack et al., Phys. Rev. B 72 (2005) 054511], these results indicate that real structure phenomena, i.e. disorder and/or defects, may strongly affect the inelastic scattering. Comparative resistivity measurements under He-gas pressure on two crystals with strongly differing r(T) profiles indicate that these additional, sample-dependent scattering contributions are characterized by an extraordinarily strong pressure response which is highly non-monotonous as a function of temperature. No correlations have been found between the strength of these scattering contributions and other characteristic properties such as the glass transition at Tg ¼ 77 K, the temperature T*z40 K, where the temperature dependence of the resistivity changes rather abruptly, or the superconducting transition temperature Tc.

  • Comptes Rendus Chimie 10(2007), 96-100

Publ.-Id: 9697

Flavonoids affect actin functions in cytoplasm and nucleus

Boehl, M.; Tietze, S.; Sokoll, A.; Madathil, S.; Pfennig, F.; Apostolakis, J.; Fahmy, K.; Gutzeit, H. O.

Based on the identification of actin as a target protein for the flavonol quercetin, the binding affinities of quercetin and structurally related flavonoids were determined by flavonoid-dependent quenching of tryptophan fluorescence from actin. Irrespective of differences in the hydroxyl pattern, similar Kd values in the 20 µM range were observed for six flavonoids encompassing members of the flavonol, isoflavone, flavanone, and flavane group. The potential biological relevance of the flavonoid/actin interaction in the cytoplasm and the nucleus was addressed using an actin polymerization and a transcription assay, respectively. In contrast to the similar binding affinities, the flavonoids exert distinct and partially opposing biological effects: while flavonols inhibit actin functions, the structurally related flavane epigallocatechin promotes actin activity in both test systems. Infrared spectroscopic evidence reveals flavonoid-specific conformational changes in actin which may mediate the different biological effects. Docking studies provide models of flavonoid binding to the known small molecule-binding sites in actin. Among these, the mostly hydrophobic tetramethylrhodamine-binding site is a prime candidate for flavonoid binding and rationalizes the high efficiency of quenching of the two closely located fluorescent tryptophans. The experimental and theoretical data consistently indicate the importance of hydrophobic, rather than H-bond-mediated actin-flavonoid interactions. Depending on the rigidity of the flavonoid structures, different functionally relevant conformational changes are evoked through an induced fit.

Keywords: binding studies; fluorescence spectroscopy; infrared spectroscopy; molecular modelling

Publ.-Id: 9696

Tollmien-Schlichting wave cancellation using an oscillating Lorentz force

Albrecht, T.; Metzkes, H.; Mutschke, G.; Grundmann, R.; Gerbeth, G.

Oscillating Lorentz forces are used to control transition in a flat-plate boundary layer.

Keywords: boundary layer; transition; control; Lorentz force

  • Lecture (Conference)
    5th International Symposium on Turbulence and Shear Flow Phenomena, 27.-29.08.2007, München, Germany
  • Contribution to proceedings
    5th International Symposium on Turbulence and Shear Flow Phenomena, 27.-29.08.2007, München, Germany
    Proceedings of the 5th International Symposium on Turbulence and Shear Flow Phenomena, vol. 2, 419-423

Publ.-Id: 9695

Tollmien-Schlichting wave cancellation using an oscillating Lorentz force

Albrecht, T.; Metzkes, H.; Mutschke, G.; Grundmann, R.; Gerbeth, G.

Oscillating Lorentz forces are used to control the development of Tollmien-Schlichting waves in a flat-plate boundary layer

Keywords: boundary layer; transition control; Lorentz force

  • Lecture (Conference)
    ETC11 - EUROMECH European Turbulence Conference, 25.-28.06.2007, Porto, Portugal
  • Contribution to proceedings
    ETC11 - EUROMECH European Turbulence Conference, 25.-28.06.2007, Porto, Portugal
    ADVANCES IN TURBULENCE XI. Springer Proceedings in Physics vol. 117. Proceedings of the 11th EUROMECH European Turbulence Conference, Heidelberg: Springer, 978-3-540-72603-6, 218-220

Publ.-Id: 9694

Electromagnetic control of separation at hydrofoils

Mutschke, G.; Weier, T.; Albrecht, T.; Gerbeth, G.; Grundmann, R.

Lorentz forces originating from surface-mounted actuators of permanent magnets and electrodes in weakly conducting fluids like seawater provide a convenient tool for separation control at hydrofoils. A well-known actuator design of alternating stripes of permanent magnets and externally fed electrodes is considered which creates a mainly streamwise Lorentz force that is exponentially decaying in wall-normal direction. Separation control by steady forcing at the suction side and by oscillatory forcing near the leading edge of a symmetric foil is investigated numerically, mostly in the post-stall regime. The results are based on direct numerical simulations in the laminar flow regime in order to reveal basic control phenomena as well as on simulations using turbulence modelling at higher Reynolds numbers which are closer to possible naval application.
By applying a strong enough steady control, separation can always be completely suppressed. The scaling behaviour of the maximum lift gain Delta C_L^{max} in the turbulent regime nicely agrees with experimental results. - Oscillatory forcing always has to compete with the natural shedding process, lock-in behavior may occur. Lift-optimum control for strong amplitudes is found in a frequency band around the natural shedding frequency. In terms of the momentum coefficient describing the control effort, appropriate excitation frequencies in relation to the natural vortex shedding frequency allow for a more effective lift control than steady forcing for small lift gains; for large lift enhancement the energetic effort seems to approach the level of steady control.

Keywords: electromagnetic flow control; separation control; wings; numerical simulation; incompressible flow

  • Lecture (Conference)
    IUTAM Symposium on Unsteady Separated Flows and their Control, 18.-22.06.2007, Kerkyra (Corfu), Greece

Publ.-Id: 9693

Inhomogeneous MUSIG model – a population balance approach for polydispersed bubbly flows

Krepper, E.; Frank, T.; Lucas, D.; Prasser, H.-M.; Zwart, P. J.

A generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into CFX-10. Simulating a poly-dispersed gaseous liquid two phase flow along with the mass exchanged between bubble size classes by bubble coalescence and bubble fragmentation and the momentum exchange of bubble size dependent bubble forces have to be considered. Particularly the lift force has been proved to play an important role establishing a certain flow regime.
The derived model has been validated against experimental data from the TOPFLOW test facility at the Forschungszentrum Dresden (FZD). The wire mesh measuring technology measuring local gas volume fractions, bubble size distributions and velocities of gas and liquid was applied. Numerous tests investigating air water flow and steam water flow at saturation conditions in vertical pipes having a length up to 8 m and a diameter up to 200 mm were performed and used for model validation. To check the model framework for a more complex flow situation in further experiments on the flow field around a half moon shaped asymmetric obstacle were performed and simulated by applying the inhomogeneous MUSIG model.
The paper describes the main concepts of the model approach and presents model validation and application cases. The inhomogeneous MUSIG model approach was shown to be able to describe of bubbly flow with higher gas content. Particularly the separation phenomenon of small and large bubbles which was proven to be a key phenomenon for the establishment of the corresponding flow regime is well described. Weaknesses in this approach can be attributed to the characterization of bubble coalescence and bubble fragmentation, which must be further investigated.

Keywords: Bubbly flow; CFD; Non-drag forces; bubble break up; bubble coalescence; population balance; validation

  • Contribution to proceedings
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, USA
  • Lecture (Conference)
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, USA

Publ.-Id: 9692

CFD-modelling of insulation debris transport phenomena in water flow

Krepper, E.; Cartland-Glover, G.; Grahn, A.; Weiss, F.-P.; Alt, S.; Hampel, R.; Kästner, W.; Seeliger, A.

The investigation of insulation debris generation, transport and sedimentation becomes more important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core coolant systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems.
Open questions of generic interest are for example the particle load on strainers and corresponding pressure drop, the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow. A joint research project on such questions is being performed in cooperation with Institute of Process Technology, Process Automation and Measuring Technology (IPM) Zittau. The project deals with the experimental investigation and the development of CFD models for the description of particle transport phenomena in coolant flow. While the experiments are performed at the IPM-Zittau, the theoretical work is concentrated at Forschungszentrum Dresden-Rossendorf.
Whereas the paper Alt et al. is focused on the experiments in the current paper the basic concepts for CFD modeling are described and feasibility studies including the conceptual design of the experiments are presented.

Keywords: CFD; two-fluid approach; fiber flows

  • Contribution to proceedings
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, USA
  • Lecture (Conference)
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.12.2007, Pittsburgh, USA

Publ.-Id: 9691

Review of available data for validation of nuresim two-phase CFD software applied to CHF investigations

Bestion, D.; Anglart, H.; Peturaud, P.; Smith, B.; Krepper, E.; Moretti, F.; Macek, J.

The NURESIM Integrated Project of the 6th European Framework Program is envisaged to initiate the development of the next-generation common European Standard Software Platform for simulating nuclear reactors. The overall objective of NURESIM Thermalhydraulic sub-project is to improve the understanding and the predictive capabilities of the simulation tools for key two-phase flow thermal-hydraulic processes such as the Critical Heat Flux (CHF). A multi-scale analysis of reactor thermalhydraulics is envisaged and two-phase CFD is developed to allow some zoom on local processes when the resolution of system codes is not sufficient.
Current industrial methods for CHF mainly use the sub-channel analysis and empirical CHF correlations based on large scale experiments having the real geometry of the reactor assembly. The NURESIM-TH activities regarding CHF aim at using two-phase CFD as a tool for understanding boiling flow processes, in order to subsequently help new fuel assembly design and to develop better CHF predictions in both PWR and BWR. A “Local Predictive Approach” may be envisaged for the long term where CHF empirical correlations would be based on local T/H parameters provided by CFD.
This paper presents a review of existing experimental data bases which can be used for validation of the two-phase CFD application to Critical Heat Flux (CHF) investigations with respect to nuclear reactors. The phenomenology of DNB and Dry-Out are detailed identifying all basic flow processes which require a specific modeling in CFD tool. The resulting program of work is given and the current state of the art of the modeling is presented.
The resulting program of work is presented and the present state of the art in the modeling is detailed.

Keywords: Critical heat flux; experimenbtal data; CFD simulation

  • Contribution to proceedings
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, USA
  • Lecture (Conference)
    NURETH-12 - International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.09.-04.10.2007, Pittsburgh, USA

Publ.-Id: 9690

Application of the moment-density method in CFD code to model bubble size distribution

Ruyer, P.; Seiler, N.; Beyer, M.; Weiß, F.-P.

This study, carried out at Institut de Radioprotection et de Sûreté Nucléaire, concerns the model of a polydispersed bubble population in the frame of an ensemble averaged two-phase flow formulation. We consider the ability of the moment density approach, e.g. Kamp et al. (2001), to represent bubble population size distribution within a multi-dimensional CFD code based on the two-fluid model. Special attention is given to the closure issue of the method. We consider in particular the influence of the polydispersion on (i) coalescence and break-up phenomena and on (ii) momentum inter-phase transfers related to drag and lift forces. A first approach formulation is developed allowing to represent a full spectrum of bubble size with a very reduced number of parameters. The latter property constitutes one of the main advantages of the moment density method with regard to alternative methods for polydispersion representation like population balance. The system of transport equations and corresponding main closure terms are derived in the case of adiabatic flows with spherical bubbles of an incompressible fluid that is immiscible in the continuous phase. Air-water polydispersed bubbly flows in a vertical pipe with obstacle of the TOPFLOW experiments series performed at FZD, e.g. Prasser et al. (2006), are then used as simulations test cases. The numerical results, obtained with NEPTUNE_CFD, e.g. Guelfi et al. (2005), allow to attest the validity of the approach. Perspectives concerning the improvement of the model, its validation, as well as the extension of its applicability range are discussed.

Keywords: two-phase flow; NEPTUNE_CFD; bubble size distribution; moment density

  • Lecture (Conference)
    European Two-Phase Flow Group Meeting 2007, 29.-31.05.2007, Toulouse, France

Publ.-Id: 9689

Numerical investigations of the transport of submerged insulation particle

Cartland-Glover, G.; Alt, S.; Kästner, W.; Krepper, E.

A numerical investigation of insulation debris transport and sedimentation is being performed as part of a joint research project with the Institute of Process Technology, Process Automation and Measuring Technology (IPM) Zittau. The study considers the impact of the transport of insulation wool debris on the long-term behaviour of emergency core coolant systems during all types of LOCA that occur in PWR and BWR. In order to implement models into computational fluid dynamic codes (CFD), the models that characterize insulation debris (particle buoyancy, drag, turbulent dispersion and the fluid-particle mixture viscosity) must be tested. Experimental investigations are being performed at the IPM-Zittau to provide detailed information with which the numerical models can be validated.

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany

Publ.-Id: 9688

Application of multiphase flow modeling techniques to the transport of submerged mineral wool fibers

Cartland-Glover, G.; Alt, S.; Kästner, W.; Krepper, E.

The transport of mineral wool insulation debris, which is generated during all types of loss of coolant accidents (LOCA) could impede the long-term operation of emergency core coolant systems (ECCS) in nuclear power plants. Therefore, a combined experimental and numerical investigation of mineral wool fibers is being pursued to improve the understanding of how ECCS can be undermined by the transport, sedimentation and resuspension of mineral wool fibers.
The application of the Eulerian-Eulerian multiphase flow model to the transport of the fibers is discussed here with regard to the transport of fibers in a racetrack type channel. The study examines the application of closure models such as the Favre-Averaged turbulence dispersion force and the mixture viscosity and the impact that they have on fiber transport. The intention of the study is to aid the experimental part of the study by determining which parameters influence the particle forces and which conditions can be used in analyzing the parameters for further model development and evaluation. The phenomena observed in the calculations correspond qualitatively to preliminary experimental observations.

Keywords: CFD; Eulerian-Eulerian Multiphase; Nuclear Reactor Containment Sump; Mineral Wool Fibers; Sedimentation and Resuspension

  • Contribution to proceedings
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Lecture (Conference)
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9687

Application of a population balance approach for polydispersed bubbly flows

Krepper, E.; Beyer, M.; Frank, T.; Lucas, D.; Prasser, H.-M.

A population balance model was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into CFX-10 (Frank et al. 2005, Krepper et al. 2007). The current paper presents the application of the model to upward flow in vertical pipes for air/water and for steam/water bubbly flow. Finally the application to a bubbly flow around a half moon shaped obstacle arranged in a 200 mm pipe is shown (see Frank et al. 2007).
Applying the inhomogeneous MUSIG approach a more deep understanding of the flow structure is possible. For upward two phase flow in vertical pipes the core peak in the cross sectional gas fraction distribution could be reproduced very well. For complex flows the general structure of the flow could be well reproduced in the simulations. This test case of the obstacle demonstrates the complicated relationship between size dependent bubble migration and bubble coalescence and break-up effects for real flows. While the closure models for bubble forces, which are responsible for the simulation of bubble migration are in agreement with the experimental observations, clear deviations occur for bubble coalescence and fragmentation. The presently applied models describing bubble fragmentation and coalescence could be proved as weak points in numerous CFD analyses of vertical upward two phase pipe flow. Further work on this topic is considered for future investigations.

Keywords: Bubbly flow; CFD; Non drag forces; bubble break up; bubble coalescence; population balance; validation

  • Contribution to proceedings
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    Poster No PS6_6
  • Poster
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9686

Inhomogeneous MUSIG model – a population balance approach for polydispersed bubbly flows

Krepper, E.; Frank, T.; Lucas, D.; Prasser, H.-M.; Zwart, P. J.

A generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into CFX-10. Simulating a poly-dispersed gaseous liquid two phase flow along with the mass exchanged between bubble size classes by bubble coalescence and bubble break-up and the momentum exchange of bubble size dependent bubble forces have to be considered. Particularly the lift force has been proved to play an important role establishing a certain flow regime. The paper describes the main concepts of the model approach and presents a model validation case. Further application test cases are presented by Krepper et al. 2007.
The inhomogeneous MUSIG model approach was shown to be able to describe of bubbly flow with higher gas content. Particularly the separation phenomenon of small and large bubbles which was proven to be a key phenomenon for the establishment of the corresponding flow regime is well described. Weaknesses in this approach can be attributed to the characterization of bubble coalescence and bubble break-up, which must be further investigated.

Keywords: Bubbly flow; CFD; Non drag forces; bubble break up; bubble coalescence; population balance; validation

  • Contribution to proceedings
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    Paper No S_6_Thu_B_51
  • Lecture (Conference)
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9685

Compositional and structural changes in ZrOxNy films depending on growth condition

Carvalho, P.; Fernandes, A. C.; Rebouta, L.; Vaz, F.; Cunha, L.; Kreissig, U.; Barradas, N. P.; Ramos, A. R.; Alves, E.

The present work focuses on the analysis of ZrOxNy thin films, the composition evolution with changing growth conditions and its relation with the structural and morphological properties of the films. The films were prepared by rf reactive magnetron sputtering, using different reactive gas flows. Composition and structure were measured combining ion beam analysis (IBA) and X-ray diffraction (XRD) techniques. The depth profiles of nitrogen and oxygen have been obtained by elastic recoil detection analysis (ERDA). Results showed that the oxygen fraction in the films increases with gas flow, reaching a value of x ~ 0.33 for a reactive gas flow mixture of 6.25 sccm. During growth mixed zirconium nitride and oxide phases form. Furthermore, the deposition rate correlates with the oxygen content variations, showing a continuous decrease with reactive gas flow.

Keywords: Decorative films; XRD; Nitrides; Oxides; Ion beams

  • Nuclear Instruments and Methods in Physics Research B 249(2006), 458-461

Publ.-Id: 9684

Study of anomalous behaviour of LiTaO3 during the annealed proton exchange process of optical waveguide´s formation - comparison with LiNbO3

Salavcova, L.; Spirkova, J.; Ondracek, F.; Mackova, A.; Vacik, J.; Kreissig, U.; Eichhorn, F.; Groetzschel, R.

This paper deals with detailed study of changes that lithium tantalate (LT) and lithium niobate (LN) single crystals undergo during the APE (Annealed Proton Exchange) process of optical waveguides´ formation. It is a well-known fact that several cases of anomalous behaviour are connected to the APE:LT samples, bringing thus serious limitations for the practical utilization of the APE:LT waveguides. As the LT crystal posseses even better optical properties than the LN (e.g., it is less susceptible to optical damage), it is highly desirable to provide research focused on its behaviour during the APE in order to get a control over fabrication of the APE:LT devices.
Neutron Depth Profiling (NDP), Elastic Recoil Detection Analysis (ERDA) and High Ion Energy ERDA (HIERDA) were performed to study changes in the surface of the LT and LN Z-cut wafers caused by the APE treatment and to determine the concentration depth profiles of the exchanged ions (lithium and hydrogen). Information on modifications of the crystals during the APE were obtained using X-Ray Diffraction (XRD) analysis. Optical/waveguiding properties of the samples were obtained by means of the standard mode spectroscopy at 633 nm.
The experiments proved that the LT is significantly less affected by the APE process compared to the LN and that most characteristics of the APE:LT layers are relatively easily restored back towards that of the virgin crystal by the annealing process.

Keywords: APE; Ion exchange; Lithium niobate; Lithium tantalate

  • Optical Materials 29(2007), 913-918

Publ.-Id: 9683

Das Komplexbildungsverhalten von Uran(IV) mit Phosphat – Untersuchungen mittels Zeitaufgelöster Fluoreszenzspektroskopie

Lehmann, S.; Geipel, G.

Die Zeitaufgelöste Fluoreszenzspektroskopie erlaubt die unmittelbare Untersuchung fester und flüssiger Systeme in mikro- und submikromolaren Stoffmengenkonzentrationen. Dies prädestiniert die Etablierung und den Einsatz der Fluoreszenzspektroskopie als analytische Methode für Untersuchungen von Festphasen- und aquatischen Umweltsystemen in ihren entsprechenden relevanten Konzentrationsbereichen. Die hier gezeigten Forschungsergebnisse repräsentieren die ersten Resultate zur Komplexbildung von Uran(IV) im Phosphatsystem, welche mit Hilfe der Zeitaufgelösten Fluoreszenzspektroskopie ermittelt wurden.
Zur Untersuchung der Komplexbildung zwischen Uran(IV) und Phosphat wurde die Konzentration des Uran(IV) im perchlorsauren Medium konstant gehalten und die Konzentration des zugegebenen Phosphat in einem Bereich zwischen einem 5fachen Unterschuss und einem 5fachen Überschuss variiert. Fluoreszenzspektroskopische Aufnahmen des Uran(IV) ohne Zusatz von Phosphat zeigen die Übereinstimmung der Peakpositionen mit [1] und [2]. Die Positionen der 5 Hauptpeaks wurden wie folgt ermittelt: 291, 320, 335, 394 and 409 nm. Die Auswertung der aufgenommenen zeitaufgelösten Spektren von Uran(IV) mit Phosphatzusatz zeigt insbesondere an den intensivsten Peaks bei 320 und 409nm, dass mit zunehmender Phosphatkonzentration die Fluoreszenzintensität abnimmt, freies Uran(IV) folglich im Komplex gebunden wird, bis freies Uran(IV) bei äquimolaren Stoffmengenkonzentrationen von Uran(IV) und Phosphat nicht mehr nachweisbar ist und somit vollständig mit Phosphat reagiert hat.
Die über die äquimolare Konzentration hinaus bis hin zum 5fachen Überschuss an Phosphat aufgenommenen Spektren sind gegenüber den zuvor beschriebenen gänzlich verändert und zeigen nur eine einzige breite Bande zwischen 290 und 400nm mit einem Peak schwacher Intensität bei 374nm. Die undefinierte Bande lässt sich möglicherweise auf die gelartigen Ausfällungen zurückführen, welche bei stöchiometrischen Konzentrationen und bei Phosphatüberschuss unter den hier gewählten Versuchsbe-dingungen zu beobachten sind.

Weitergehende Untersuchungen haben als Ziel, die Natur des Peaks bei 374nm zu klären und die gebildeten Uran(IV)-Phosphatspezies sowie die entsprechenden Komplexbildungskonstanten zu bestimmen.

Keywords: uranium(IV) phosphate; TRLFS; complex formation constant

  • Poster
    GDCh - Wissenschaftsforum Chemie 2007, 16.-19.09.2007, Ulm, Germany

Publ.-Id: 9682

Gas-liquid flow around an obstacle in a vertical pipe – CFD simulation & comparison to experimental data

Frank, T.; Prasser, H.-M.; Beyer, M.; Al Issa, S.

A novel technique to study the two-phase flow field around an asymmetric diaphragm in a vertical pipe is presented, that allows to obtain detailed 3-dimensional data for CFD code validation in complex geometries. The investigated validation test case consists of an air-water two-phase bubbly flow around a half-moon shaped obstacle in a DN200 vertical pipe (TOPFLOW test facility), where the 3-dimensional flow field shows flow phenomena like curved stream lines, flow separation at sharp edges and
recirculation zones in the obstacle wake, like they are common to complex flow situations in bends, T-junctions, valves, safety valves and other components of power plant and other industrial equipment. Pre-test calculations with the commercial flow solver ANSYS CFX have been performed using an Eulerian two-phase flow model with a monodisperse bubble diameter assumption and by taking into account all significant drag and non-drag forces contributing to the interphase momentum transfer. Results of the CFD simulation have been compared to the 3-dimensional air volume fraction and water velocity fields, which were obtained from the wire-mesh sensor data, where the comparison showed a general very good agreement. Therefore CFD code validation on this type of complex 3-dimensional flow geometries permits the assessment of flow solver accuracy for other industrial type applications and contributes to further multiphase flow model development for ANSYS CFX.

Keywords: bubbly flows; CFD; wire-mesh sensor; 3-dimensional validation

  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9681

[18F]FBAM and [18F]FBOM: Novel Thiol-reactive prosthetic groups derived from 4-[18F]fluorobenzaldehyde

Vogler, L.; Berndt, M.; Pietzsch, J.; Wüst, F.

The incorporation of 18F into peptides and proteins usually takes advantage of prosthetic groups, also referred to as bifunctional labeling agents. This approach comprises 18F incorporation into a small organic molecule capable of being linked to peptides and proteins under mild conditions.
Two new prosthetic groups derived from 4-[18F]fluorobenzaldehyde for the mild and selective conjugation to thiol-group containing biomacromolecules are described: N-[6-(4-[18F]fluorobenzylidene)aminooxyhexyl]-maleimide ([18F]FBAM) and 4-[18F]fluorobenzaldehyde-O-(2-{2-[2-(pyrol-2,5-dion-1-yl)ethoxy]ethoxy}ethyl)oxim ([18F]FBOM.
The aminooxy-functionalized labeling precursor for radiosynthesis of [18F]FBAM was prepared in a convenient three-step synthesis sequence in a total yield of 59%. The corresponding labeling precursor for the radiosynthesis of [18F]FBOM succeeded in a four-step reaction sequence in 14% total yield. Formation of the prosthetic groups [18F]FBAM and [18F]FBOM was achieved through condensation reaction with [18F]fluorobenzaldehyde to form the desired oximes in radiochemical yields of 20-30% ([18F]FBAM) and of 14-19% ([18F]FBOM), respectively. The syntheses were carried out in a remotely-controlled radiofluorination module allowing the convenient and reliable performance of the radiolabeling reactions. The radiochemical purity exceeded 95% and the specific activity ranged from 50 to 80 GBq/μmol. The total synthesis time was 70 to 80 min. The lipophilicity was determined to be logP=2.71 for [18F]FBAM and logP=0.84 for [18F]FBOM. Both prosthetic groups could successfully be used in the radiolabeling of thiol-group containing compounds such as glutathion, low density lipoproteins (LDL) and modified neurotensin derivatives.

  • Lecture (Conference)
    14th Workshop der International Isotope Society, 21.-22.06.2007, Bad Soden, Germany
  • Journal of Labelled Compounds and Radiopharmaceuticals 50(2007), 1276-1286

Publ.-Id: 9680

Mobilisation and speciation of depleted uranium in water and soils

Geipel, G.; Baumann, N.; Arnold, T.; Bernhard, G.; Gerstmann, U.; Schimmack, K.; Read, D.

Depleted uranium (DU) from penetrating ammunition was exposed to several environmental conditions in order to determine the binding forms of uranium as well as in its dissolved and solid forms.
In a first series fresh disks of DU were treated with a calcium phosphate solution. The results from time-resolved laser-induced fluorescence spectroscopy clearly show that metaautunite Ca(UO2)2(PO4)2 x 2-6(H2O) has formed during alteration [1].
In a second experiment the corrosion and leaching of used up DU was investigated for three years in a column with a soil core. The columns were irrigated with synthetic rainwater.
The luminescence spectrum of a yellow material, which was crystallized at the soil surface was assigned clearly to be the mineral sabugalite AlH(UO2)(PO4)4 x 16(H2O).
In contrast to the luminescence spectra of the solid material the spectra of the uranium species in the dissolved samples could only obtained at temperatures below 220 K. From the shape of the spectrum and the emission maxima of the luminescence of seepage water samples it could be clearly concluded that the solution species are mostly uranyl carbonate species UO2(CO3)34- [2].

Keywords: Depleted uranium; TRLFS; Binding form

  • Contribution to proceedings
    Goldschmidt 2007, 19.-24.08.2007, Köln, Germany

Publ.-Id: 9679

Model studies with DU to assess the mobilisation and speciation of U in soils

Geipel, G.; Baumann, N.; Arnold, T.; Bernhard, G.; Gerstmann, U.; Schimmack, K.; Read, D.

Since the 1990th, depleted uranium (DU) was used in several conflict regions as 'penetrator' in munition rounds designed to pierce battle tanks. Lots of this amunition undergo wheatering processes under environmental conditions. One goal of our studies was the determination of the binding forms of uranium, if the DU is exposed to several environmental conditions.
The formed uranium species were detected by time-resolved laser-induced fluorescence spectroscopy (Geipel 2005). By use of spectroscopic databases including U(VI)-oxides, U(VI)-hydroxides, U(VI)-sulphates and U(VI)-phosphates the different formed uranium species in solution as well as solid species can be clearly assigned.
In a first series disks of DU were treated with a calcium phosphate solution at ambient temperature for 182 days. The weathering solution contained 2.49 mM calcium and 1.05 mM phosphate, representing enhanced pore water concentrations of agricultural soils. The TRLFS results clearly show that metaautunite, a U(VI) phosphate, has formed during low temperature alteration of the DU disc. The TRLFS spectrum is characterized by six fluorescence emission bands at 486, 501, 522, 546, 573, and 601 nm, and two fluorescence life times of 50±5 ns and 700±25 ns (Baumann, 2006).
In a second experiment the corrosion and leaching of depleted uranium (DU) was investigated for three years in a column with a soil core. The columns were installed in a laboratory with controlled temperature of (21 ± 1) °C and a relative humidity of (55 ± 10) %. The columns were irrigated weekly with 16 mm synthetic rainwater of pH 6 consisting mainly of 0.09 mM NH4NO3, 0.08 mM (NH4)2SO4 and 0.05 mM CaSO4.
The luminescence spectrum of a yellow material, which was crystallized at the soil surface was measured and the comparison with the TRLFS database assigned this luminescence spectrum clearly to be the mineral sabugalite AlH(UO2)(PO4)4 x 16(H2O).
In contrast to the luminescence spectra of the solid material the spectra of the uranium species in the dissolved samples could only obtained at temperatures below 220 K. From the shape of the spectrum and the emission maxima of the luminescence of seepage water samples it could be clearly concluded that the solution species are mostly uranyl carbonate species UO2(CO3)34- (Schimmack, Schimmack 2007).

Keywords: Depleted uranium; binding form

  • Invited lecture (Conferences)
    International Symposium Protecting Water Bodies from Negative Impacts of Agriculture, 04.-06.06.2007, Braunschweig, Germany

Publ.-Id: 9678

FT-IR investigation of the uranium S-layer interaction in aqueous solutions

Li, B.; Foerstendorf, H.; Raff, J.; Bernhard, G.

Many bacteria possess so-called surface layer (S-layer) proteins, forming paracrystalline lattice structures on the cell wall (1). Beside its ecological relevance for the retention of toxic metals, they are a good model system for investigations of the interaction of bio-ligands, e.g. proteins, with uranium in aqueous solutions. Several S-layers from different Bacillus strains were proved to have high binding capacity to uranium. But there is still little knowledge of the interactions between the functional groups of the protein with the actinyl ions at a molecular level (2).
In this work we present results of batch experiments where the uranium binding capacities of different S-layer protein from different Bacilllus strains were determined. The experiments were carried out at different pH values (pH 4, 6, and 8) for each isolated S-layer protein. It was found that the uranium binding capacities of each gram S-layer range from 5.0 mg and 63.9 mg, from 11.1 mg and 561.1 mg, and from 14.2 mg and 33.5 mg at pH 4, 6, and 8, respectively, depending on the respective S-layer.
For a deeper understanding of the molecular binding of the uranyl ion to the protein we used Attenuated Total Reflectance Fourier-transform Infrared spectroscopy (ATR-FTIR) which allows vibrational spectroscopic investigations of aqueous solutions containing actinide ions and disolved proteins as well (3, 4). The spectra clearly demonstrate carboxyl groups are the major functional groups which interact with the uranyl ions at pH 4. Additionally, the infrared spectra suggest the formation of different uranium-protein complexes depending on the incubation period (1 h vs. 48 h) which can be observed by a peak shift of the absorption band representing the antisymetric uranyl stretch to lower wavenumbers.
This spectroscopic approach constitutes the foundation of more detailed investigations on the impact of the pH value and of other functional groups (e.g. phosphate or amino groups) on the uranium complexation by bio-systems.

(1) Sleytr, U.B., Beveridge T.J., Trends Microbiol. 1999 7(6), 253-260
(2) Merroun, M.L., et al. Appl. Environ. Microbiol. 2005, 71(9), 5532–5543
(3) Quilès, F.; Burneau, A. Vib. Spec. 2000, 23, 231-241.
(4) Fahmy, K. et al. Biophys. J. 2006, 91(3), 996-1007

  • Contribution to proceedings
    17th Annual Goldschmidt Conference, Cologne, Germany, 19.-24.08.2007, Köln, Germany
    FT-IR investigation of the uranium S-layer interaction in aqueous solutions

Publ.-Id: 9677

Complexation of Uranium(VI) with Nitrate in Nonaqueous and Aqueous solutions: Speciation and Structural Studies

Ikeda, A.; Hennig, C.; Rossberg, A.; Tsushima, S.; Scheinost, A. C.; Bernhard, G.

Understanding the complexation behavior of uranium(VI) with nitrate ions in solution is important for the assessment of environmental impact on the geological disposal of radioactive wastes or for the development of nuclear fuel reprocessing since the present reprocessing plants employ PUREX process, that separates uranium and plutonium from other actinides and fission products in nitric acid solution and, as a result, produces radioactive liquid wastes in nitrate solution. In this study, the chemical speciation and the structure of uranium(VI) nitrate complexes have been investigated in nonaqueous (acetonitrile) and aqueous (nitric acid) solutions by UV-visible absorption spectroscopy, U LIII-edge x-ray absorption spectroscopy, and quantum chemical calculations.

In acetonitrile, the complexation between uranium(VI) and nitrate ions is very strong and the trinitrato complex, [UO2(NO3)3]-, becomes the dominant species when [NO3]/[U] is above 3. The extended x-ray absorption fine structure (EXAFS) spectrum of this trinitrato species indicates that the nitrate ions coordinate to the uranyl ion in a bidentate mode and the average U-Oax, U-Oeq, and U-N distances are 1.77, 2.50, and 2.95 Å, respectively. These values are in good agreement with the results of DFT calculations in acetonitrile (i.e. 1.76, 2.50, and 2.96 Å for U-Oax, U-Oeq, and U-N distances, respectively). By varying the [NO3]/[U] ratio from 0 to 3, we observe a complex speciation diagram composed of four species (UO22+, [UO2NO3(H2O)n]+, [UO2(NO3)2(H2O)m]0, and [UO2(NO3)3]-). However, it is impossible to determine the complex structures of these species directly by EXAFS. In order to estimate their structure, we have isolated their individual EXAFS spectra from the spectra of the mixtures by performing factor analysis [1] on the basis of the speciation diagram obtained from the UV-visible spectral titration. The data analysis of the isolated EXAFS spectra demonstrates that the dinitrato complex has a coordination number of 6 in the equatorial plane of the uranyl ion and forms the complex [UO2(NO3)2(H2O)2]0. On the other hand, the estimated EXAFS spectrum for the mononitrato complex indicates that it has a coordination number of 5 and forms the complex [UO2NO3(H2O)3]+. These results are supported by DFT calculations. The same data treatment (i.e. factor analysis combined with the speciation diagram from spectral titration) has also applied to the EXAFS spectra in aqueous solutions of nitric acid. The results suggest that the nitrate complexation of uranium(VI) is far weaker in aqueous solution than that in acetonitrile and almost no trinitrato complex is formed even when the [NO3]/[U] ratio exceeds 360.

Keywords: uranium(VI); nitrate; solution; acetonitrile; nitric acid; XAFS; UV-visible absorption; DFT; factor alanysis; speciation

  • Poster
    Migration 2007, 26.-31.08.2007, Arabella Sheraton Grand Hotel, Munich, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 178

Publ.-Id: 9676

Infrared spectroscopic identification of aqueous uranium(VI) species

Müller, K.; Foerstendorf, H.; Bernhard, G.

Migration of uranium(VI), the most stable form of uranium in environmental waters, is largely controlled by its geochemical reactions, both in solution and at the mineral-water interface. Current knowledge about U(VI) speciation is mainly based on thermodynamic calculations using data obtained by non-structural experiments, i.e. potentiometric titration [1]. A spectroscopic verification of the speciation of aqueous U(VI) is still insufficient. For the identification of different molecular species previous studies applied primarily EXAFS and Raman spectroscopy at very high uranyl concentrations (>100 mM) unreasonably in an environmental context [2-4].
In this study we used Attenuated Total Reflectance Fourier-transform Infrared (ATR-FTIR) spectroscopy, that allows the direct measurement of liquid samples. Our aim was to obtain additional vibrational spectroscopic information on the U(VI) species and especially to verify the U(VI) speciation throughout a wide pH range (pH 2-10) at a micromolar concentration level. The obtained spectral information was compared to previously reported thermodynamic data [1].
ATR-FTIR spectra were recorded at UO22+ concentrations ranging from 5 to 0.005 mM at pH 4. The spectroscopic results indicate distinctly that dimer and trimer hydroxo complexes become dominant upon lowering the uranyl concentration at pH 4. The thermodynamic data predict an absolute predominance of the free uranyl species UO22+ until pH 5 at these conditions.
At the micromolar concentration level the calculations predict the dominance of the uncomplexed uranyl ion until pH 5 and the formation of uranyl hydroxo complexes at neutral pH. Uranyl complexes with atmospheric carbonate in alkaline solutions are proposed above pH 6.5. However, the obtained ATR-FTIR spectra of low concentrated 0.02 mM uranyl solutions already show the coexistence of free and hydroxo complexed uranyl at pH 2.5. The appearance of carbonate complexes in solution becomes noticeable at the spectra of solutions at pH 7. Since the results are partially contradictionary to previous predictions of U(VI) speciation a critical review of the present knowledge of uranium migration in the environment is required.

[1] Guillaumont, R. et al. (2003) Update on the Chemical Thermodynamics of U, Np, Pu, Am and Tc. (Elsevier, Amsterdam)
[2] Moll, H. et al. (2000) Radiochim. Acta 88, 411-415.
[3] Nguyen-Trung, C. et al. (1992) Inorg. Chem. 31, 5280-5287.
[4] Quiles, F. et al. (2000) Vib. Spec. 23, 231-241.

  • Lecture (Conference)
    Goldschmidt 2007, 19.-24.08.2007, Köln, Germany
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 71(2007)15S, A694

Publ.-Id: 9675

Additional FDG PET-CT in week 5-6 of radiotherapy for patients with NSCLC as a means of dose escalation planning

Gillham, C.; Zips, D.; Pönisch, F.; Evers, C.; Enghardt, W.; Abolmaali, N.; Zöphel, K.; Appold, S.; Hölscher, T.; Steinbach, J.; Kotzerke, J.; Herrmann, T.; Baumann, M.

To detect a reduction in disease volume during radical radiotherapy for non-small cell lung cancer (NSCLC) using PET-CT and to determine whether this would facilitate dose escalation.

Ten patients with localised inoperable NSCLC were prospectively enrolled. Each received conformally planned radiotherapy to a dose of 66Gy/33# over 6.5 weeks using 6-15MV photons and prescribed to the 100% isodose. PET-CT imaging was performed just prior to and following 50 or 60Gy. Target volume definition was performed by one senior radiation oncologist with the help of a senior radiologist and nuclear medicine physician. For all patients and at both time points CT and PET-delineated gross tumour volumes were generated (GTVCT, GTVPET). A composite GTV was then created (GTVCT+PET) and 15mm added in all planes to form the planning target volume (PTV). No correction for organ movement was incorporated and no elective nodal irradiation performed. Each of the different volumes were compared before and after 50-60 Gray. Two plans were then created and compared: 78Gy delivered to the initial PTV and 66Gy to the initial PTV with a 12Gy boost to the post 50/60Gy PTV.

All patients (mean age 64 years) had stage III disease (4 IIIA and 6 IIIB). There were 4 squamous cell and 6 adeno-carcinomas. After 50/60 Gray the GTVCT, GTVPET, GTVCT+PET and PTV reduced by a mean of 22%, 43%, 30% and 22% respectively. The delivery of 78 Gray to the initial PTV could have been safely achieved in 4/10 patients. Of these delivering treatment in two phases would have substantially spared normal tissue in 2 patients. In the remaining 6 patients, delivering 78 Gray to the initial PTV would have exceeded normal tissue constraints
and no benefit was seen when planned in 2 phases.

The PTV, consequent on changes seen on PET-CT, reduces during a course of radical radiotherapy for NSCLC. Such a reduction permits dose escalation in a subset of patients and may lead to improved therapeutic outcomes.

  • Lecture (Conference)
    14th European Cancer Conference, 23.-27.09.2007, Barcelona, Spanien

Publ.-Id: 9674

Rising gas bubbles in a liquid metal under the influence of external magnetic fields

Zhang, C.; Eckert, S.; Gerbeth, G.

In the present paper we consider the impact of various external DC magnetic fields on the motion of a single bubble rising in a cylindrical column of stagnant liquid metal and the flow structure of a bubble plume, respectively. The ultrasound Doppler method (UDV) has been used to measure the velocity non-intrusively. The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC vertical magnetic field was examined. The bubble terminal velocity showed oscillations indicating a zizag movement of ellipsoidal bubbles. The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. A global damping of the flow field was also observed if a vertical magnetic field has been imposed on a bubble plume. By contrast, a restructuring of the flow pattern being typical for a bubble plume was observed in the case of a horizontal magnetic field. The DC field gave rise to non-steady, non-isotropic and large-scale flow structures which was rather unknown until now and therefore not sufficiently considered for electromagnetic processing of materials.

Keywords: single bubble; bubble plume; liquid metal; magnetic field; ultrasound Doppler velocity measurements

  • Lecture (Conference)
    International Conference on Multiphase Flow - ICMF2007, 09.-13.07.2007, Leipzig, Germany
  • Contribution to proceedings
    International Conference on Multiphase Flow - ICMF2007, 09.-13.07.2007, Leipzig, Germany, No. 279

Publ.-Id: 9673

Diagnostic impact of PET with 18F-FDG, 18F-DOPA and 3-O-methyl-6-[18F]fluoro-DOPA in recurrent or metastatic medullary thyroid carcinoma

Beuthien-Baumann, B.; Strumpf, A.; Zessin, J.; Bredow, J.; Kotzerke, J.

In patients with medullary thyroid carcinoma (MTC), rising levels of the tumour markers calcitonin and CEA after primary surgery indicate tumour recurrence or metastases. The only chance of cure is the resection of localised tumour tissue. For positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG) and 18F-dihydroxyphenylalanine (18F-DOPA), sensitivities of 78% and 63% have been reported, but in a considerable percentage of MTC patients the source of tumour marker elevation is not detected. The aim of this retrospective data evaluation was to compare the value of PET with 18F-FDG, 18F-DOPA and the amino acid tracer 3-O-methyl-6-[18F] fluoro-DOPA (18F-OMFD) in the detection of MTC recurrence.

Fifteen patients with elevated calcitonin were investigated with PET as part of their individual clinical work-up. All patients underwent 18F-FDG PET and 18FDOPA PET, and ten patients underwent 18F-OMFD PET.

With 18F-FDG, seven patients showed foci in the neck, mediastinum, upper abdomen or bone. In seven patients, 18F-DOPA revealed suspicious foci; five of these seven patients showed partially corresponding uptake of 18F-FDG in the neck and mediastinum. Two of these patients underwent surgery and metastases were verified. With 18F-OMFD, a small focus in the liver was suspected in one patient without a correlate on 18F-FDG PET, 18FDOPA PET or conventional imaging.

18F-FDG and 18F-DOPA showed foci that were highly suspicious for local recurrence or metastasis of MTC, although histological verification in these patients with numerous previous surgical interventions was performed in only two patients. The amino acid tracer 18FOMFD had no diagnostic impact in these patients.

Keywords: Medullary thyroid carcinoma; Positron emission tomography; 18F-fluorodeoxyglucose; 18F-DOPA; 3-O-methyl-6-[18F]fluoro-DOPA

Publ.-Id: 9672

Data acquisition system for angle synchronized gamma-ray tomography of rapidly rotating objects

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

We developed a fast read-out electronics which is used in conjunction with a radiation detector for gamma ray computed tomography. The detector comprises 320 single scintillation detector elements and is operated in pulse counting mode. Digital pulses corresponding to gamma or x-ray absorption events in the scintillation crystals are counted by a counter bank implemented fully parallel in FPGA electronics. The counter data may be read-out at a maximum rate of 5 MHz via micro controller and USB 2.0 interface. This enables to take full projection data within intervals of down to 23 µs which in turn gives the opportunity to produce sharp tomographic slice images of objects rotating with more than 1000 rotations per minute. As an example we demonstrate the reconstruction of the gas distribution in the turbine region of a stirred tank reactor.

Keywords: high-resolution gamma ray tomography; multi-phase flow

  • Measurement Science and Technology 18(2007), MST/248418/PAP/167103

Publ.-Id: 9671

Uranium(VI) complexation studies with selected aromatic acids - a comparison of different spectroscopic techniques

Glorius, M.; Moll, H.; Geipel, G.; Bernhard, G.

To understand the actinide interaction processes in biological systems on a molecular level it is necessary to explore the complexation behaviour of actinides with selected bioligands of relevant functionalities as model compounds. We used salicylhydroxamic acid (SHA), benzohydroxamic acid (BHA) and benzoic acid (BA) as model compounds for pyoverdins, which are natural bioligands secreted from Pseudomonas ssp. possessing a high potential to bind actinides [1]. The different U(VI) species, MpLqHr, were characterized by UV-vis spectroscopy and laser-induced spectroscopic techniques (TRLFS, fs-TRLFS).
From the UV-vis measurements different coordination modes of uranyl can be postulated [2]. If uranyl is coordinated to hydroxamic acids this results in a blue shift of the absorption maxima in comparison to the bands of the free uranyl ion of app. 25 nm. Whereas in the case of coordination to the carboxylic acid group of benzoic acid, a red shift of the absorption maxima of app. 2.5 nm was observed.
The U(VI)-TRLFS measurements show, that all uranyl ligand species emit no fluorescence light. In all three systems a static quench process of the uranyl fluorescence due to the complex formation was observed.
In the U(VI)-SHA system the stability constant for the 1:1 complex, UO2[HOC6H4CONHO]+, is log β 0111 = 16.33 0.16 and for the 1:2 complex, UO2[HOC6H4CONHO]2, log β 0122 = 33.43 0.11. In the U(VI)-BHA system the stability constants results to log β 0110 = 7.49 0.03 for UO2C6H4CONHO+ and log β 0120 = 15.40 1.15 for UO2[C6H4CONHO]2. In the U(VI)-BA system the stability constant for the 1:1 complex, UO2C6H4COO+, was determined to log β 0110 = 3.02 0.13. All stability constants were averaged from the measurements by UV-vis and TRLFS.
The higher formation constants of uranyl with the aromatic hydroxamate compounds compared to benzoic acid points to the high potential of the pyoverdins to bind and mobilize uranium(VI) in the environment.

[1] M. Bouby, I. Billard, H. J. Maccordick, Czechoslovak. J. Phys. 49, 769-772 (1999).
[2] M. Glorius, H. Moll, G. Bernhard, Complexation of uranium(VI) with aromatic acids in aqueous solution – A comparison of hydroxamic acids and benzoic acid, Radiochimica Acta, in press (2007).

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

Keywords: Uranium; aromatic acids; spectroscopy; TRLFS; complexation

  • Poster
    Migration 2007, 26.-31.08.2007, München, Germany
  • Contribution to proceedings
    Migration 2007, 26.-31.08.2007, München, Germany
    11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 175-176

Publ.-Id: 9670

3He(alpha,gamma)7Be cross section at low energies

Gyürky, G.; Confortola, F.; Costantini, H.; Formicola, A.; Bemmerer, D.; Bonetti, R.; Broggini, C.; Corvisiero, P.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Imbriani, G.; Junker, M.; Laubenstein, M.; Lemut, A.; Limata, B.; Lozza, V.; Marta, M.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.

The flux of 7Be and 8B neutrinos from the Sun and the production of 7Li via primordial nucleosynthesis depend on the rate of the 3He(alpha,gamma)7Be reaction. In extension of a previous study showing cross section data at 127 - 167 keV center of mass energy, the present work reports on a measurement of the 3He(alpha,gamma)7Be cross section at 106 keV performed at Italy's Gran Sasso underground laboratory by the activation method. This energy is closer to the solar Gamow energy than ever reached before. The result is sigma = 0.567 +- 0.029(stat) +- 0.016(syst) nbarn. The data are compared with previous activation studies at high energy, and a recommended S(0) value for all 3He(alpha,gamma)7Be activation studies, including the present work, is given.

Publ.-Id: 9669

g-factor measurements on relativistic isomeric beams produced by fragmentation and U-fission: the g-Rising project at GSI

Neyens, G.; Atanasova, L.; Balabanski, D. L.; Becker, F.; Bednarczyk, P.; Caceres, L.; Doornenbal, P.; Gerl, J.; Gorska, M.; Grebosz, J.; Hass, M.; Ilie, G.; Kurz, N.; Kojouharov, I.; Lozeva, R.; Maj, A.; Pfutzner, M.; Pietri, S.; Podolyak, Z.; Prokopowicz, W.; Saitoh, T. R.; Schaffner, H.; Simpson, G.; Vermeulen, N.; Werner-Malento, E.; Walker, J.; Wollersheim, H. J.; Bazzacco, D.; Benzoni, G.; Blazhev, A.; Blasi, N.; Bracco, A.; Brandau, C.; Camera, F.; Chamoli, S. K.; Chmel, S.; Crespi, F. C. L.; Daugas, J. M.; de Rydt, M.; Detistov, P.; Fahlander, C.; Farnea, E.; Georgiev, G.; Gladnishki, K.; Hoischen, R.; Ionescu-Bujor, M.; Iordachescu, A.; Jolie, J.; Jungclaus, A.; Kmiecik, M.; Krasznahorkay, A.; Kulessa, R.; Lakshmi, S.; Lo Bianco, G.; Mallion, S.; Mazurek, K.; Meczynski, W.; Montanari, D.; Myalsky, S.; Perru, O.; Rudolph, D.; Rusev, G.; Saltarelli, A.; Schwengner, R.; Styczen, J.; Turzo, K.; Valiente-Dobon, J. J.; Wieland, O.; Zieblinski, M.

Within the RISING (Rare ISotope INvestigations @ GSI) Collabora-tion at GSI, g factor measurements have been performed on isomeric states in neutron-rich isotopes approaching 132 Sn and in the neutron deficient Pb-region (the g-RISING campaign). We present the experimental technique and some typical aspects related to such studies on relativistic beams selected with the FRS fragment separator. First results are presented for the (19/2+ ) 4.5 µs isomeric state in 127 Sn, which has been produced by means of fission of a relativistic 238 U beam on the one hand, and by the fragmentation of a relativistic 136 Xe beam on the other hand. Spin-alignment has been observed in both reactions. It was the first time that spin-alignment has been established in a relativistic fission reaction.

Keywords: Nuclear structure; radioactive beams; g-factor measurements

  • Contribution to proceedings
    Zakopane Conference on Nuclear Physics, 04.-10.10.2006, Zakopane, Poland
    Acta Physica Polonica B 38, 1237-1245

Publ.-Id: 9668

U(VI) sorption on sandstone: Experiments and modeling

Richter, A.; Nebelung, C.; Brendler, V.

The sorption of U(VI) on natural and synthetic sandstone was investigated in batch sorption experiments (air atmosphere, 0.1M NaClO4, pH 3-11, [U(VI)] 10-9-10-4M. The synthetic sandstone was a mixture of quartz with muscovite and hematite. The surface area (N2-BET) of quartz was 0.047 m2/g, of muscovite 0.88 m2/g, of hematite 0.89 m2/g and of natural sandstone (mainly quartz) 0.69 m2/g.
The pH dependence shows a maximal sorption between pH 5.5-7.5. The U(VI) sorption varied between 95% (10-9M) and 7% (10-4) on natural sandstone, and between 80% (10-9M) and 2% (10-4M) on synthetic sandstone. Fig. 1 shows the comparison of sandstone with pure components (at similar conditions) quartz, muscovite, and hematite. More U(VI) was adsorbed on natural and on synthetic sandstone, than on quartz. The higher sorption are caused by the other components muscovite and hematite, and by the higher surface area.
The linear Freundlich sorption isotherms indicate one binding type. Sorption predicted by the Diffuse Double Layer Model (using the code FITEQL) agreed with the experimental sorption values within their uncertainty.

Keywords: sorption; uranium; sandstone; surface complexation; diffuse double layer model

  • Lecture (Conference)
    Goldschmidt 2007, 19.-24.08.2007, Köln, Germany
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 71(2007), A838

Publ.-Id: 9667

Ultra fast electron beam X-ray CT for two-phase flow measurements

Bieberle, M.; Schleicher, E.; Fischer, F.; Hampel, U.; Do Couto Aktay, K. S.; Koch, D.; Menz, H.-J.; Mayer, H.-G.

Nuclear reactor safety concerns for todays operated light water reactors are closely linked to thermal hydraulic phenomena in the primary and secondary coolant circuits of nuclear systems. To gain an improved understanding of phenomena associated with certain types of accidents as well as for the optimisation of fuel elements regarding the heat transfer in the reactor core simulation tools, such as system codes and more recently CFD codes are frequently applied. However, both types of tools today still exhibit some problems when treating two-phase flow scenarios. Therefore, in recent years much effort has been spent on further code development as well as on validation. This, however, was and is always accompanied by the requirement for reliable measurement data from two-phase flows under typical nuclear thermal hydraulic conditions. Experimental thermal hydraulic facilities, such as the TOPFLOW facility at FZD [1], may provide such data if they are equipped with sophisticated two-phase flow measurement sensors. One example is the wire-mesh sensor [2] that can provide phase and velocity data from steam-water two-phase flows at frame rates of up to 10 kHz and spatial resolution down to 2 mm. Since the wire mesh sensor is intrusive it has some influence on the flow. More appropriate would be tomographic imaging techniques based on either X-ray or gamma rays. However, classical CT systems, though being non-intrusive and sufficiently penetrative even for thicker metallic vessel walls, suffer from low temporal resolution, which is due to the requirement for taking different angular views of an object prior to reconstruction. So far this problem has been considered as intractable and unavoidable and tomographic techniques have almost exclusively been used to measure time averaged quantities, such as the gas hold-up.
We recently suggested [1] a computed tomography (CT) system which uses a fast moving electron beam X-ray source for the application in two-phase flow measurements. We have experimentally shown that frame rates of 10000 images per second can be reached. The static installation of the detector, however, limits the angular range of the source path which leads to so called limited-angle artefacts in the reconstructed images. Although these artefacts cannot be completely eliminated, because they are due to missing data, they can be reduced by maximizing the angular viewing range and by adequate image reconstruction algorithms [4].

Keywords: electron beam x-ray CT; two-phase flow

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Germany
    Proc. Jahrestagung Kerntechnik 2007, CD-ROM plus, 27-30

Publ.-Id: 9666

Gründungsidee und Geschäftskonzept - BIOREM

Raff, J.

Im Rahmen der zweiten Phase des Businessplan-Wettbewerbs FutureSAX hat es die Geschäftsidee "BIOREM" erneut unter die besten Teams geschafft.
Vor der eigentlichen Prämierung muss die Geschäftsidee und die Marketingstrategie vor der Expertenjury der Branche Bio-/ Nanotechnologie verteidigt werden. Erst nach Prüfung aller Anträge werden die eigentlichen Gewinner gekürt.

  • Lecture (others)
    2. Phase FutureSAX-Businessplan-Wettbewerb, 19.04.2007, Leipzig, Deutschland

Publ.-Id: 9665

Direct Time-of-Flight for Quantitative, Real-Time In-Beam PET: Concept and Feasibility Study

Crespo, P.; Shakirin, G.; Fiedler, F.; Enghardt, W.; Wagner, A.

We extrapolate the impact of recent detector and scintillator developments, enabling sub-nanosecond coincidence timing resolution t, onto in-beam positron emission tomography (in-beam PET) for monitoring charged-hadron radiation therapy. For t <= 200 ps full width at half maximum, the information given by the time-of-flight (TOF) difference between the two opposing gamma-rays enables shift-variant (fixed dual-head), artifact-free tomograms to be utilized for in-beam PET. We present the corresponding fast, TOF-based and backprojection-free, 3D reconstruction algorithm that, coupled with a real-time data acquisition and a fast detector encoding scheme, allows the sampled beta-plus-activity to be visualized in the object during the course of the irradiation. Despite the very low statistics scenario typical of in-beam PET, real-treatment simulations show that in-beam TOF-PET enables high-precision, quantified images to be obtained in real-time, either with closed-ring or with fixed, dual-head in-beam TOF-PET systems. The latter alleviates greatly the installation of in-beam PET at radiotherapeutic sites.

Keywords: TOF-PET; radiotherapy; proton therapy; ion therapy

Publ.-Id: 9664

On projective Hilbert space structures at exceptional points

Günther, U.; Rotter, I.; Samsonov, B.

We consider a non-Hermitian complex symmetric 2×2 matrix toy model to study projective Hilbert space structures in the vicinity of exceptional points (EPs). After Puiseux-expanding the bi-orthogonal eigenvectors of a diagonalizable matrix in terms of the root vectors at the EP we resolve the apparent contradiction between the two incompatible normalization conditions with finite and singular behavior in the EP-limit by projectively extending the original Hilbert space. The complementary normalization conditions correspond then to two different affine charts of this enlarged projective Hilbert space. Geometric phase and phase jump behavior are analyzed and the usefulness of the phase rigidity as measure for the distance to EP configurations is demonstrated. Finally, EP-related aspects of PT-symmetrically extended Quantum Mechanics are discussed and the zero limit of the optimal passage time in non-Hermitian quantum brachistochrone problems is identified as an EP-related artifact.

Keywords: exceptional points; branch points; projective Hilbert space; geometric phase; singularities; PT-symmetric Quantum Mechanics; quantum brachistochrone problem

  • Invited lecture (Conferences)
    Many-body open quantum systems: From atomic nuclei to quantum dots, 14.-18.05.2007, Trento, Italy

Publ.-Id: 9663

Projective Hilbert space structures at exceptional points

Günther, U.; Rotter, I.; Samsonov, B.

A non-Hermitian complex symmetric 2×2 matrix toy model is used to study projective Hilbert space structures in the vicinity of exceptional points (EPs). The bi-orthogonal eigenvectors of a diagonalizable matrix are Puiseux-expanded in terms of the root vectors at the EP. It is shown that the apparent contradiction between the two incompatible normalization conditions with finite and singular behavior in the EP-limit can be resolved by projectively extending the original Hilbert space. The complementary normalization conditions correspond then to two different affine charts of this enlarged projective Hilbert space. Geometric phase and phase jump behavior are analyzed and the usefulness of the phase rigidity as measure for the distance to EP configurations is demonstrated. Finally, EP-related aspects of PT-symmetrically extended Quantum Mechanics are discussed.

Keywords: exceptional points; branch points; projective Hilbert space; geometric phase; singularities; PT-symmetric Quantum Mechanics; quantum brachistochrone problem

Publ.-Id: 9662

L-Type Amino Acid Transporters LAT1 and LAT4 in Cancer: Uptake of 3-O- Methyl-6-18F-Fluoro-L-Dopa (18F-OMFD) in Human Adenocarcinoma and Squamous Cell Carcinoma in vitro and in vivo

Haase, C.; Bergmann, R.; Füchtner, F.; Hoepping, A.; Pietzsch, J.

Expression of system L amino acid transporters (LAT) is strongly increased in many types of tumor cells. The purpose of this study was to demonstrate that 18F-labeled amino acids, e.g., 3-O-Methyl-6-18F-Fluoro-L-Dopa (18F-OMFD), that were accumulated in tumors via LAT, represent an important class of imaging agents for visualization of tumors in vivo by positron emission tomography (PET).
In the present study 18F-OMFD uptake kinetics, transport inhibition, and the system L mRNA expression were studied in vitro in human adenocarcinoma (HT-29), squamous cell carcinoma (FaDu) cells, macrophages (THP-1) and primary aortic endothelial cells (HAEC), and in vivo in the corresponding mouse tumor xenograft models. Results: It was demonstrated that uptake of 18F-OMFD in all cell lines tested was mediated mainly by the sodium-independent high-capacity LAT. We found an increased uptake in FaDu cells (Vmax 10.6±1.1 nmol/min ´ mg cell protein) and in the corresponding FaDu tumor xenografts in comparison to the other cells and corresponding xenograft models studied. Quantitative mRNA analysis revealed that tumor cells and xenografts have a higher expression of LAT1 compared to HAEC and THP-1 macrophages. However, only in the FaDu tumor model an increased OMFD uptake seems to be explained by increased LAT expression. Furthermore, we demonstrated a high expression for LAT4, a recently new identified system L amino acid transporter.
Our findings support the hypothesis that 18F-OMFD is a tracer for visualization of tumor cells, and, in particular, seems to be a suitable tracer for diagnostic imaging of amino acid transport in poorly differentiated squamous cell head and neck carcinoma with increased LAT1 and LAT4 expression.

Publ.-Id: 9661

Aspects of 6-[18F]fluoro-L-DOPA preparation: Deuterochloroform as a substitute solvent for Freon 11

Füchtner, F.; Zessin, J.; Mäding, P.; Wüst, F.

Replacement of the ecologically harmful solvent Freon 11 (CFCl3) by chloroform for the module-assisted preparation of 6-[18F]fluoro-L-DOPA based on the electrophilic radiofluorodestannylation of the precursor N-formyl-3,4-di-tert-butoxycarbonyloxy-6-(trimethylstannyl)-L-phenylalanine ethyl ester.

Materials and methods:
The TRACERlab Fx FDOPA module (GE Medical Systems) was used for the preparation of 6-[18F]fluoro-L-DOPA. Cyclotron-produced [18F]F2 gas (5 GBq) was passed through a cooled solution (5°C) of the stannyl precursor (45 mg) in CDCl3 (10 ml). After the [18F]fluorination step, HCl (2 ml, 6 M) was added to the solution. Then the reaction mixture was heated at 80°C for 5 min under vacuum to evaporate the chloroform. The hydrolysis to remove the protecting groups was completed by heating the closed reactor at 130°C for 8 min. After cooling to 20°C the reaction mixture was purified by HPLC with two polymer-based RP columns (PRP 1, 7 μm, 10×250 mm, Hamilton) using a solution of AcOH/AcONa (pH 4.7) as eluent. The [18F]fluoro-L-DOPA fraction was collected and sterile filtrated.

Three types of stabilised chloroform were tested for the radiofluorination of the precursor. Only by use of deuterochloroform stabilised with silver no significant losses of radioactivity were observed. Thus, 6 [18F]fluoro-L-DOPA purified by HPLC was obtained in decay-corrected radiochemical yields of 25±3%, ready for human use.

CDCl3 has proved to be a convenient solvent for the module-assisted preparation of 6-[18F]fluoro-L-DOPA. In this way the use of the polluting Freon 11 can be avoided.

Keywords: 6-[18F]fluoro-L-DOPA; electrophilic radiofluorodestannylation; Freon 11 substitution; deuterochloroform

Publ.-Id: 9660

Multimodal electronic–vibronic spectra of luminescence in ion-implanted silica layers

Fitting, H.-J.; Salh, R.; Schmidt, B.

Thermally oxidized SiO2 layers of 100 and 500 nm thickness have been implanted by oxygen and sulfur ions with a dose of 3x1016 and 5x1016 ions/cm2, respectively, leading to an atomic dopant fraction of about 4 at.% at the half depth of the SiO2 layers. The cathodoluminescence spectra of oxygen and sulfur implanted SiO2 layers show besides characteristic bands a sharp and intensive multimodal structure beginning in the green region at 500nm over the yellow-red region extending to the near IR measured up to 820 nm. The energy step differences of the sublevels amount on average 120meV and indicate vibration associated electronic states, probably of O2- interstitial molecules, as we could demonstrate by a respective configuration coordinate model.

Keywords: Cathodoluminescence; defect luminescence; vibronic spectra; photonic crystals

Publ.-Id: 9659

Multimodal Luminescence Spectra of Ion-Implanted Silica

Fitting, H.-J.; Salh, R.; Schmidt, B.

The main luminescence bands in silica SiO2 are the red luminescence R (650 nm, 1.9 eV) of the non-bridging oxygen hole center, and the blue band B (460 nm, 2.7 eV) and ultraviolet luminescence UV (290 nm, 4.3 eV), both commonly related to oxygen-deficient centers. In the present work, we will enhance or replace either the first or second constituent of SiO2, i.e., silicon or oxygen, isoelectronically by additional implantation of the respective ions. Thus, thermally oxidized SiO2 layers have been implanted by different ions of the IV group (C, Si, Ge, Sn, Pb) and of the VI group (O, S, Se) with doses up to 5x1016 cm-2, leading to an atomic dopant fraction of about 4 at % at the half depth of the SiO2 layers. Very surprisingly, the cathodoluminescence spectra of oxygen- and sulfur-implanted SiO 2 layers show, besides the characteristic bands, a sharp and intensive multimodal structure beginning at the green region at 500 nm up to the near infrared. The energy step differences of the sublevels equal on average 120 meV, and indicate vibration associated electronic states, probably of O2- interstitial molecules.

Keywords: Cathodoluminesence; silicon dioxide; ion implantation

Publ.-Id: 9658

Nanosized allotropes of molybdenum disulfide

Enyashin, A. N.; Gemming, S.; Seifert, G.

The present review provides an overview of the rich polymorphism encountered on different length scales within the very versatile material class of transition metal chalcogenides. On the mesoscopic to nanoscopic scale such compounds exhibit a wide variety of nanostructured allotropes with varying dimensionality and competing internal structure, such as nanorods, nanostripes, nanotubes, fullerene-like particles and fullerenes. On the atomistic scale, competing local atomic arrangements within one type of allotrope determine crucially the stability, the chemical potential, and the electronic properties. Thus, any modeling of such structures can not be restricted to purely classical or quantum-mechanical approaches, but rather the development of classical models on the basis of electronic-structure calculations is required to fully account for all relevant nano- and meso-scale effects. The main part of this review is dedicated to the stability of such nanosystems in relation with the stable size regimes, with their electronic structure, and the derived analysis of the reactivity and application potential.
The calculations explain, why the nano-scale properties of the MoS allotropes can be quite different from the bulk ones, and predict novel effects both within and in addition to the established applications of MoS2 compounds in catalysis, tribology, electronics and electrochemistry.

Keywords: MoS2; nanostructures

Publ.-Id: 9657

Finding polymorphic structures during vicinal surface growth

Radke De Cuba, M.; Emmerich, H.; Gemming, S.

A hybrid scheme is developed to describe vicinal surface growth during epitaxy on two different time and length scales. For this purpose this algorithm combines two modules based on a continuum and an atomistic approach. The continuum module is realized by a phase-field-model which traces back to the Burton-Cabrera-Frank theory, the atomistic module is based on the anisotropic Ising model which is mapped onto a lattice-gas model. The latter provides thermal density fluctuations resulting in adatom clustering. With increasing temperature the probability for island nucleation on the terraces decreases according to1-p where p is an Arrhenius-type activation probability which prevents clusters from becoming islands. Within this framework it is possible to find the transition from a rough surface at low temperatures to an evenly stepped surface at high temperatures where slight step meandering is observed. Furthermore two competing mechanisms of step bunching are investigated within this algorithm: alternating anisotropic diffusion and different Ehrlich-Schwoebel barriers at the step edges. Step bunching is found on two different time and length scales.

Keywords: self-assembly; patterning; phase-field; Ising; roughening; multi-scale modelling

Publ.-Id: 9656

Modelling Ferroic Functional Elements

Gemming, S.; Luschtinetz, R.; Alsheimer, W.; Seifert, G.; Loppacher, C.; Eng, L. M.

The present study aims at the modelling of an organic field-effect transistor generated by the self-assembly of field-sensitive molecules on the surfaces of ferroic oxides. Electronic-structure-based methods for the microscopic properties of the surface, the molecules, and the respective interactions are combined with classical modelling on the self-assembly of larger adsorbate arrays on a scale-hopping basis. The structural and electronic characteristics of a realistic, stepped titanate surface as well as the electric field strength above such a surface are modelled quantum-mechanically by a combination of density-functional theory (DFT) and density-functional-based tight-binding (DF-TB). The effect of such fields on the electronic and optical properties of polarizable organic molecules is investigated by the time-dependent analogues of the DFT and DF-TB methods. For the integration of organic components via self-assembly a classical Ising Hamiltonian is developped for the coverage of stepped surfaces with molecules and parametrized on the basis of ab-initio and first-principles data.

Keywords: functional materials; ferroelectric; multi-scale modelling

Publ.-Id: 9655

Simulation and AFM-Measurement Of PTCDA On Ag-supported KBr Films

Loppacher, C.; Zerweck, U.; Eng, L. M.; Gemming, S.; Seifert, G.; Olbrich, C.; Morawetz, K.; Schreiber, M.

Ordered growth of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on Ag(111) partially covered by one or two monolayers of KBr was investigated by non-contact AFM and Monte-Carlo simulation. PTCDA grows partially ordered on pure Ag(111), smaller PTCDA aggregates occur on the first ML KBr, and large clusters and ordered planar growth are observed on the typical quadratic islands of the second KBr ML. In analogy to KBr covered Cu(111) we conclude that weak silver-bromine bonds are formed. In contrast, for a more weakly interacting substrate such as KBr|Au(111) PTCDA forms single crystals along step edges [1]. The delicate balance of vertical, adsorbate-substrate interactions and lateral, intermolecular ones was investigated by Metropolis-Monte-Carlo (MC) simulations with an extended Ising Hamiltonian on a periodically repeated 2D square lattice [2]. At fixed lateral interactions J12 = J13 the simulation reproduces the experimentally observed cluster formation by varying the adsorbate-substrate interaction H as the substrate changes from Ag(111) to 2 ML KBr|Ag(111): (i) on Ag(111) H dominantes (H >> J) (ii) on 2 ML KBr|Ag(111) J12 and J13 are dominant (J >> H) (iii) on 1 ML KBr|Ag(111) J12, J13, and H are competing (H ~ J) In the simulation the cases (i) and (ii) lead to the observed large and regular clusters, for case (iii) the competition of the different cluster stabilization mechanisms leads to the pinning of many smaller clusters. [1] Kunstmann T., Schlarb A., Fendrich M. et al., Phys. Rev. B, 71 (2005) 121403(R). [2] Loppacher C., Zerweck U., Eng L. M., Gemming S., et al., Nanotechnol., 17 (2006) 1-6.

Keywords: self-assembly; patterning; PTCDA; OLED

  • Poster
    E-MRS 2007 Spring Meeting, 27.05.-01.06.2007, Strasbourg, Frankreich

Publ.-Id: 9654

Theory of DNA-wrapped Carbon Nanotubes

Enyashin, A. N.; Gemming, S.; Seifert, G.

Carbon nanotubes embedded in single-stranded DNA (CNT@DNA) were investigated by self-consistent density-functional-based tight-binding calculations (DFTB). A phenomenological model for the stability was derived, which gives the CNT-DNA interaction energy as a function of the nanotube radii and the number of DNA chains. Single CNTs are readily complexed by the DNA, but for CNT bundles an essential energy gain is only obtained, if multiple chains wrap around the tubes. Hence, the destruction of the CNT bundles, e.g. by sonication, can promote the CNT@DNA complex formation. Pyrimidine-based homopolymeric DNA more effectively wraps the DNA, whereas purine-based DNA exhibits the larger radius selectivity. The CNT-DNA interaction is not a genuine Van-der-Waals’ interaction. In general, the electronic structure is close to the superposition of the DOS curves of the “free” DNA and CNT fragments, but the most strongly bonding systems are characterized by a number of the mixed electronic states below Fermi level. Hence, magic matching occurs in conjunction with remarkable charge transfer.

Keywords: DNA; carbon nanotubes; nanoelectronics; functional materials

  • Lecture (Conference)
    E-MRS 2007 Spring Meeting, 27.05.-01.06.2007, Strasbourg, France

Publ.-Id: 9653

Molecular scale characterization of speciation of uranium(VI) associated with bacterial strains isolated form extreme habitats

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

This paper deals with the speciation of U(VI) associated with the cells of bacterial strains isolated from extreme habitats. For this propose, a combination of synchrotron-based X-ray absorption spectroscopy (XAS), time-resolved laser-induced fluorescence spectroscopy (TRLFS), transmission electron microscope (TEM) coupled with energy dispersive-X ray (EDX) analysis and electron diffraction were used. XAS analysis indicated that the effect of pH on the local coordination of U in the U-complexes formed by the different bacterial strains is species specific. No structural differences were found between the U complexes formed by three different eco-types of Acidothiobacillus ferrooxidans at pH 2, 3 and 4.5. In contrast, the cells of Bacillus sphaericus JG-B7, Microbacterium oxydans M2, and Sphingomonas sp. S15-S1 precipitate U(VI) as a meta-autunite-like phase at pH 4.5, probably due to the release of the inorganic phosphate from the cells. At pH 2, the U is coordinated to the organic phosphate groups of the cells of the listed bacteria. Both organic and inorganic uranyl/bacterial complexes were formed at pH 3. TEM/EDX analysis confirms these results and showed strain-specific extracellular and/or intracellular uranium accumulation to varying degrees. We applied Iterative Target Test Factor Analysis to determine the uranium speciation at different pH values quantitatively from the EXAFS spectra. Different hypothesis explaining the different coordination chemistry of uranium to bacteria as a function of pH of uranium solution in terms of solubility of m-autunite and/or microbial activity will be discussed.

  • Lecture (Conference)
    9th Symposium on Bacterial Genetics and Ecology (Bageco 9), 23.-27.06.2007, Wernigerode, Germany

Publ.-Id: 9652

Characterization of a novel Idiomarina loihiensis strain isolated from the westernmost Mediterranean: heavy-metal resistance and biomineralization capability

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

This communication presents the identification of a bacterial strain, MAH1, isolated from a seawater sample collected from the westernmost Mediterranean surface waters. This strain was characterized using polyphasic taxonomy. It is Gram-negative, growing between 2--43 ºC (optimum 28-37 ºC), heterotrophic, aerobic and required NaCl for growth (0.7-20.0%, optimum being 2%). This strain is rod-shaped slightly curved with a single polar flagellum. Results of phylogenetic analyses evidenced that the strain belongs to Idiomarina loihiensis species (Donachie et al., 2003). The strain MAH1 displays a DNA base composition in G+C of the 48.2 mol%. The similarity of the 16S rDNA sequence and of the DNA-DNA hybridization to I. loihiensis (AF288370) is 100% and 96.1% respectively. Polar lipids were predominantly odd-numbered and iso-branched (15 and 17). According to these data we propose that the isolated MAH1 is a strain of the I. loihiensis species.
A preliminary study of the MAH1 strain mineralization capability and heavy metal resistance has also been performed. When the MAH1 strain is cultivated in a sea water solid medium (yeast extract 0.5%, triptone 1%, purified agar-agar 2% in seawater, pH 7.6) produces carbonates and phosphates. On the other hand, the minimal inhibitory concentrations of Ag, Cd, Pb, U, Ni, Cu, Cr, Mn and Zn for the growth of this bacterial strain are (concentration expressed as mM) 0.125, 0.125, 8.00, 8.00, 4.00, 4.00, 1.00, 8.00 and 2.00, respectively.
The obtained results are especially interesting in relation to the Idiomarina genus (Ivanova et al 2000), a member of the family Alteromonadaceae (Ivanova and Mikhailov, 2001) belonging to the subclases of the Proteobacteria.

Donachie, S. P., S. Hou, T. S. Gregory, A. Malahoff, and M. Alam. 2003. Int. J. Syst. Evol. Microbiol. 53:1873-1879
Ivanova, E. P., and V. V. Mikhailov. 2001. Mikrobiologia 70:15-23
Ivanova, E. P., L. A. Romanenko, J. Chun, M. H. Matte, G. R. Matte, V. V. Mikhailov, V. I. Svetashev, A. Huq, T. Maugel, and R. R. Colwell. 2000. Int. J. Syst. Evol. Microbiol. 50:901–907

  • Poster
    9th Symposium on Bacterial Genetics and Ecology (Bageco 9), 23.-27.06.2007, Wernigerode, Germany

Publ.-Id: 9651

Development of a high-speed capacitive surface sensor for fluid distribution imaging

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

Experimental investigation of multiphase flows plays an important role in many research and industrial application areas. We introduce a novel surface sensor based on electrical capacitance (permittivity) measurements to imaging near-wall fluid distributions of multiphase flows. The sensor is formed by 32 x 32 interdigitated sensing structures and can be mounted on the edges of a pipe or vessel and thus has a minimal influence on the flow. An associated electronics measures the capacitance of the fluid overlaying each sensing structure in a multiplexed manner. This way, images of the fluid distribution can be achieved directly without the need for any reconstruction procedure. Images at up to 10,000 frames per second can be obtained. The system was evaluated showing good reproducibility and adequate accuracy. The system is able to well distinguish permittivity differences of up to one, which corresponds, for instance, to a two-phase flow of air and oil (rel. permittivity about 2).

Keywords: capacitance measurements; relative permittivity; multiphase flow

  • Contribution to proceedings
    IEEE SENSORS 2007 Conference, 28.-31.10.2007, Atlanta, USA
    Proceedings of the 6th Annual IEEE Conference on Sensors 2007 Atlanta, Stoughton, Wisconsin, USA: The Printing House, Inc., 1-4244-1262-5, 236-239
  • Poster
    IEEE SENSORS 2007 Conference, 28.-31.10.2007, Atlanta, USA

Publ.-Id: 9650

A new wire-mesh tomograph for multiphase flow measurement

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

We have developed and tested a new wire-mesh tomograph based on capacitance measurements, which may now be used for the investigation of non-conducting fluids. It can at the moment acquire up to 625 frames per second. For the experimental measurements we have employed a 16 x 16 laboratory wire-mesh sensor. The evaluation of the wire-mesh tomograph prototype has shown good reproducibility and accuracy in capacitance measurements, thus allowing the system to be employed in the investigation of a wide range of substances even with close relative permittivity values, such as for air and oil. Furthermore, time resolved measurements of different flow patterns for oil-air mixtures have been performed.

Keywords: capacitance measurement; multiphase flow; relative permittivity

  • Contribution to proceedings
    Multi-Phase Flow: Simulation, Experiment and Application, 25.-27.04.2007, Dresden, Germany
    Proceedings of FZR & ANSYS Multiphase Flow Workshop
  • Lecture (Conference)
    Multi-Phase Flow: Simulation, Experiment and Application, 25.-27.04.2007, Dresden, Germany

Publ.-Id: 9649

TRLFS: Analysing Spectra with an Expectation-Maximization (EM) Algorithm

Steinborn, A.; Taut, S.; Brendler, V.; Geipel, G.; Flach, B.

A new approach for fitting statistical models to time-resolved laser-induced fluorescence spectroscopy (TRLFS) spectra is presented. Such spectra result from counting emitted photons in defined intervals. Any photon can be described by emission time and wavelength as observable attributes and by component and peak affiliation as hidden ones. Understanding the attribute values of the emitted photons as drawn from a probability density distribution, the model estimation problem can be described as a statistical problem with incomplete data. To solve the maximum likelihood task, an expectation maximization (EM) algorithm is derived and tested. In contrast to the well known least squares method, the advantage of the new approach is the ability to decompose the spectrum into its components and peaks using the revealed hidden attributes of the photons. The simultaneous detection of temporal and spectral model parameters provides a mutually consistent description of TRLFS spectra. Theoretical aspects were investigated using simulated spectra and the applicability in practice is illustrated by spectra originating from uranyl species.

Keywords: Time-resolved laser-induced fluorescence spectroscopy; expectation maximization

  • Spectrochimica Acta Part A 71(2008)4, 1425-1432

Publ.-Id: 9648

95 MeV neutron scattering on hydrogen, deuterium, carbon, and oxygen

Mermod, P.; Blomgren, J.; Johansson, C.; Ohrn, A.; Osterlund, M.; Pomp, S.; Bergenwall, B.; Klug, J.; Nilsson, L.; Olsson, N.; Tippawan, U.; Nadel-Turonski, P.; Jonsson, O.; Prokofiev, A.; Renberg, P.; Maeda, Y.; Sakai, H.; Tamii, A.; Amos, K.; Crespo, R.; Moro, A.

Three neutron-deuteron scattering experiments at 95 MeV have been performed recently at The Svedberg Laboratory in Uppsala. Subsets of the results of these experiments have been reported in two short articles, showing clear evidence for three-nucleon force effects. In this paper, we present a more detailed description of the experimental methods as well as further discussion of the results. In addition to neutron-deuteron scattering data, neutron-proton and C-12(n,n) elastic scattering data have been measured for normalization purposes, and O-16(n,n) data have been obtained for the first time at this energy.
It was possible to extract C-12(n,n(')) and O-16(n,n(')) inelastic scattering cross sections to excited states below 12 MeV excitation energy. The inelastic scattering data (for both carbon and oxygen) are shown to have a significant impact on the determination of nuclear recoil kerma coefficients.

Publ.-Id: 9647

Dynamics of Molten Salt Reactors

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

Dynamics of the Molten Salt Reactor, one of the 'Generation IV International Forum' concepts, was studied in this paper. The graphite-moderated channel type MSR was selected for the numerical simulation. The MSR represents a liquid fueled reactor with very specific dynamics because of two physical peculiarities: the delayed neutrons precursors are drifted by the fuel flow and the fission energy is immediately released directly into the coolant. Presently, there are not many accessible numerical codes appropriate for the MSR simulation, therefore the DYN1D-MSR and DYN3D-MSR codes were developed based on the Light Water Reactor dynamics code DYN3D. It allows calculating of full 3D transient neutronics in combination with parallel channel type thermal-hydraulics. The codes were validated on experimental results of Molten Salt Reactor Experiment from Oak Ridge National Laboratory and applied to several transients typical for the liquid fuel system. Those transients were initiated by reactivity insertion, by overcooled or overfueled fuel slug, by the fuel pump start-up or coast-down, or by the blockage of single fuel channels. In these considered transients, the response of the MSR is characterized by the immediate change of the fuel temperature according to the power level. This causes fast feedback reactivity insertion, which is negative in the case of power increase. On the other hand, the graphite response is slower and its feedback coefficient is in some cases positive. The addition of erbium to the graphite can ensure the negative feedback and inherent safety features. The DYN1D-MSR and DYN3D-MSR codes have been shown as an effective tools for MSR dynamics studies.

Keywords: Molten Salt; Reactor; Dynamics; MSR; MSRE; MSBR

  • Nuclear Technology 164(2008), 34-44

Publ.-Id: 9645

Switchable two-color electroluminescence based on a Si metal-oxide-semiconductor structure doped with Eu

Prucnal, S.; Sun, J. M.; Skorupa, W.; Helm, M.

A Si metal-oxide-semiconductor (MOS) electroluminescent device structure is reported which emits two colors, while being doped with a single rare-earth element. Thermally grown SiO2 oxide layers were implanted with Eu and subseqently annealed. Depending on the electrical excitation current, the luminescence is red or blue, which can be ascribed to electronic transitions in tri- and di-valent europium (Eu3+ and Eu2+), respectively.

Keywords: electroluminescence; rare earth; Si MOS; light emitter

Publ.-Id: 9644

Coherent structure eduction from PIV data of an electromagnetically forced separated flow

Weier, T.; Cierpka, C.; Gerbeth, G.

Periodic addition of momentum by wall–parallel electromagnetic forces has a strong influence on the separated region of a stalled airfoil. As in the case of periodic blowing and suction, actuation frequency and momentum input are the main factors of influence. However, the control authority depends as well on the actuation wave form. This latter aspect is investigated in the present paper by means of time resolved particle image velocimetry data from the suction side of an inclined flat plate. The control effect is rated by the size of the remaining recirculation region in the time averaged flow fields. The controlled flow possesses typically a small number of relatively large vortices, which are believed to be related to the control mechanism. Consequently, the time resolved flow fields have been analyzed by proper orthogonal decomposition and continuous wavelet transform to extract dominant features of the flow.

Keywords: active flow control; proper orthogonal decomposition; continuous wavelet transform; waveform; coherent structures

  • Lecture (Conference)
    IUTAM Symposium on Unsteady Separated Flows and Their Control, 18.-22.06.2007, Korfu, Greece
  • Contribution to proceedings
    IUTAM Symposium on Unsteady Separated Flows and Their Control, 18.-22.06.2007, Korfu, Greece
    IUTAM Symposium on Unsteady Separated Flows and their Control
  • Journal of Fluids and Structure 24(2008), 1339-1348
    DOI: 10.1016/j.jfluidstructs.2008.06.005

Publ.-Id: 9643

Complex formation between UO2+2 and CO2-3: Studied by laser-inducted photoacoustic spectroscopy (LIPAS)

Geipel, G.; Bernhard, G.; Brendler, V.; Nitsche, H.

wird nachgereicht

  • Radiochimica Acta 82(1998), 59-62

Publ.-Id: 9642

PT-symmetric Quantum Mechanics, the hydrodynamic Squire equation and UV-IR-duality

Günther, U.; Stefani, F.; Znojil, M.

Some facts about the spectrum of a PT-symmetric quantum mechanical (PTSQM) toy model with potential V(x)=Gx2(ix)ν in a box x∈[-L,L] are presented for the parameter region ν∈[-2,0]. The corresponding Hamiltonian is selfadjoint in an appropriately chosen Krein space and for ν=-1 the spectral problem maps into that of the hydrodynamic Squire equation. It is shown that in the limit L→∞ a spectral singularity occurs and that the PTSQM ⇄ Squire mapping can be interpreted as a special type of strong-coupling ⇄ weak-coupling (UV-IR) duality. Finally, the system behavior in the vicinity of a spectral triple point is sketched.
partially based on:
J. Math. Phys. 46, (2005), 063504, math-ph/0501069.
Czech. J. Phys. 55, (2005), 1099-1106, math-ph/0506021.

Keywords: PT-symmetric Quantum Mechanics; Krein space; spectral analysis; spectral triple point; UV-IR duality

  • Lecture (Conference)
    International conference "Modern Analysis and Applications (MAA 2007)" dedicated to the centenary of Mark Krein, 09.-14.04.2007, Odessa, Ukraine

Publ.-Id: 9641

On the observation of vacuum birefringence

Heinzl, T.; Liesfeld, B.; Amthor, K.; Schwoerer, H.; Sauerbrey, R.; Wipf, A.

We suggest an experiment to observe vacuum birefringence induced by intense laser fields. A high-intensity laser pulse is focused to ultra-relativistic intensity and polarizes the vacuum which then acts like a birefringent medium. The latter is probed by a linearly polarized X-ray pulse. We calculate the resulting ellipticity signal within strong-field QED assuming Gaussian beams. The laser technology required for detecting the signal will be available within the next three years.

  • Optics Communications 267(2006)2, 318-321

Publ.-Id: 9640

Self-induced transparency assisted by electromagnetically induced transparency

Nazarkin, A.; Netz, R.; Sauerbrey, R.

We show the possibility of transparency and soliton effects for an intense pulse propagating in a V-type medium in which two upper resonant sublevels experience fast field-induced decay due to incoherent coupling to an upper lying state or continuum. The transparency arises as a result of the combined action of population trapping on the sublevels leading to interference suppression of the relaxation channel, and coherent Rabi cycling induced by the laser field.

  • Physical Review A 7404(2006)4, 1806

Publ.-Id: 9639

Fingerprinting of a thin secondary mineral film on DU

Baumann, N.; Arnold, T.; Foerstendorf, H.; Read, D.; Black, S.; Massanek, A.

Discs of depleted uranium (DU), obtained from a British pristine military tank shell were used in our experiments. One sample was placed in a solution containing 2.5 • 10−3 M Ca(NO3)2 and 1.05 • 10−3 M (NH4)3PO4. After a contact time of 360 days the sample was taken out of the solution. IR- and TRLFS measurements were made on the surface of the sample. The spectra obtained were compared with those of natural uranium minerals, formed under oxidising weathering conditions. Comparison of the IR-spectra from the DU surface with those of the reference minerals revealed that the newly formed secondary mineral on DU is a uranium (VI) phosphate. Further identification of the respective uranium phosphate mineral was not possible with IR. However, a comparison between the TRLFS spectra of the newly formed unknown uranium phase on the DU disc with well-known TRLFS spectra of uranium reference compounds clearly showed the presence of meta-autunite.

Keywords: depleted uranium; IR; TRLFS; uranium minerals

  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 71(2007)15S, A66-A66
  • Poster
    Goldschmidt 2007, 20.-24.08.2007, Köln, Germany

Publ.-Id: 9638

Influence of humic colloids on the migration of U(VI) in compacted clay

Mibus, J.; Sachs, S.

Clay minerals and organic substances are widespread components of many soils, sediments, and rocks. As humic acids (HA) possess a strong ability for metal complexation, they can influence the migration of radioactive and toxic metal ions in clayey environments. However, the migration behavior of humic colloids and its impact on the actinide migration in clay formations is poorly understood.
Former studies discuss the influence of HA on the radionuclide migration in clays controversially. Wold and Eriksen [1] reported the diffusion of humic colloids through compacted bentonite without strong physical hindrance mobilizing metal ions. In contrast, Wang et al. [2] found a significant immobilization of Eu(III) by humic substances. Maes et al. [3] stressed the reversibility of the interaction between radionuclide, organic matter, and clay. The competition of the adsorbents for radionuclides is kinetic and determines their distribution between mobile and immobile phase.
In the present study we investigated the diffusion behavior of humic colloids in compacted clay as a function of compaction and pH. The impact on the uranium transport was studied by comparing the uranium diffusion in absence and presence of HA.
The migration of HA in clay is governed by diffusion. It is influenced by the colloidal behavior of HA. At higher clay bulk densities, size fractionation affects the diffusion parameters. In presence of HA colloids U(VI) is immobilized in association with HA near the high concentration boundary.
The German Federal Ministry of Economics and Technology funded this study under contract 02E9673. The technical assistance of Ch. Müller is gratefully acknowledged.
[1] Wold, S., Eriksen, T.E. (2005) Proceedings of the 2nd International Symposium Clays in natural and engineered barriers for radioactive waste confinement. Tours, France, 14-18 March 2005, 547.
[2] Wang, X. et al. (2005) Adsorption Science and Technology, 23, 801-811.
[3] Maes, N. et al. (2004) Report SCK•CEN-BLG-988. SCK•CEN, Mol, Belgium.
[4] Sachs, S. et al. (2004) Report FZR-399, FZ Rossendorf, Dresden, Germany.
[5] Lead, et al. (2000) Environ. Sci. Technol. 34, 1365-1369.

  • Contribution to proceedings
    3rd International Meeting "Clays in natural and engineered barriers for radioactive waste confinement", 17.-20.09.2007, Lille, France
    Clays in Natural & Engineered Barriers for Radioactive Waste Confinement, 467-468
  • Poster
    3rd International Meeting "Clays in natural and engineered barriers for radioactive waste confinement", 17.-20.09.2007, Lille, France

Publ.-Id: 9637

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