Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Radiofluorination and first radiopharmacological characterization of a SWLAY peptide-based ligand targeting EphA2

Pretze, M.; Mosch, B.; Bergmann, R.; Steinbach, J.; Pietzsch, J.; Mamat, C.

Peptides labeled with short-lived positron-emitting radionuclides are of considerable interest as probes for molecular imaging by positron emission tomography (PET). Herein, the regioselective and convenient radiofluorination of a biologically relevant alkyne-modified SWLAY peptide bound on solid support with the radiolabeling building block 1-(3-azidopropyl)-4-(3-fluoropropyl)piperazine ([18F]AFP) is described.
The desired 18F-peptide could be prepared in a total synthesis time of 140 min including the removal of the catalytic copper species and was obtained with a RCY of 7–13% and a RCP > 98%. The method’s feasibility for a robust and bioorthogonal radiolabeling via the 1,3-dipolar Huisgen cycloaddition was demonstrated. Preliminary radiopharmacological studies regarding the metabolic stability of the peptides in cell culture supernatants and rat plasma were accomplished as well as the cellular association of the 18F-peptide in EphA2-overexpressing human melanoma cells in vitro. Furthermore, an initial in vivo PET experiment was performed which showed a fast metabolism of the novel 18F-peptide followed by an accumulation in the kidneys, followed by elimination into the bladder.

  • Journal of Labelled Compounds and Radiopharmaceuticals 57(2014), 660-665
    DOI: 10.1002/jlcr.3237

Publ.-Id: 20576

Development of New PET Tracers for Clinical Use: Challenges and Problems

Brust, P.

Es ist kein Abstract vorhanden.

  • Invited lecture (Conferences)
    4. Dresdner Workshop "Molekulare Bildgebung in den Lebenswissenschaften", 26.06.2014, Rossendorf, Deutschland

Publ.-Id: 20575

Aufbereitung von [18O]Wasser für die Produktion und Verwendung von [18F]Fluorid

Rötering, S.; Franke, K.; Zessin, J.; Brust, P.; Füchtner, F.; Fischer, S.; Steinbach, J.

Bestrahltes [18O]H2O kann nach Aufbereitung erneut für Bestrahlungen eingesetzt werden1. Wir berichten über einen einfachen Aufbereitungsprozess und eine genaue Charakterisierung des [18O]H2O.

1 l bestrahltes [18O]Wasser mit 396 mg l–1 Ethanol und 44 mg l–1 Aceton sowie Ionen im g-l–1-Bereich wurde in unterschiedlichen Ansätzen zur Oxidation der organischen Lösungsmittel mit KMnO4/NaOH bei 50°C bzw. mit UV-Strahlung1 (254 nm, 1 W) behandelt. Anschließend erfolgte eine Vakuumdestillation. Nach genauer Charakterisierung mit Gas- und Ionenchromatographie Pyknometrie wurde das gewonnene Wasser in einem Nirta®Fluor - Target an einem Cylcone®18/9 (IBA, Belgien) bestrahlt und die Produktionsaktivitäten mit denen von (verdünntem) [18O]Originalwasser verglichen. Das produzierte [18F]Fluorid wurde für die Entwicklung von Radiosynthesen und für standardisierte Herstellungsverfahren eingesetzt.
Für einen Vergleich der beiden Oxidationsmethoden wurde [16O]H2O mit Methanol, Ethanol, Aceton und Acetonitril kontaminiert und entsprechend aufbereitet.

Mit beiden Oxidationsmethoden wurden die organischen Lösungsmittel innerhalb von max. 2 Tagen unter einen Grenzwert von 50 mg l–1 abgebaut. Nach der Vakuumdestillation zeichneten sich die einzelnen Chargen durch übereinstimmende 18O-Anreicherungen sowie geringe Ionengehalte aus. Der Vergleich der Produktionsaktivitäten zeigt eine Übereinstimmung zu verdünntem Originalwasser. Die Verwendung des [18F]F– in radiochemischen Umsetzungen war erfolgreich.

Abbildung 1: Produktionsaktivitäten mit aufbereitetem Wasser und verdünntem Originalwasser
Die Aufbereitung von Modelllösungen mit [16O]H2O ergab, dass Acetonitril durch KMnO4/NaOH defakto nicht abgebaut wird. Es wurden für beide Methoden ≥97% des eingesetzten Wassers gewonnen.

Die Ergebnisse zeigen einen zuverlässigen, nahezu verlustfreien Aufbereitungsprozess von bestrahltem [18O]H2O. Dies ermöglicht einen ökonomisch sinnvollen Gebrauch von [18O]H2O.

[1] Gebrauchsmuster DE 29504388 U1 (15.03.95), Forschungszentrum Jülich GmbH

  • Lecture (Conference)
    22. Jahrestagung der AGRR 2014, 11.-13.09.2014, Mainz, Deutschland

Publ.-Id: 20574

Proinflammatory human 6-sulfo LacNAc-positive dendritic cells accumulate in intestinal acute graft-versus-host disease

Sommer, U.; Larsson, B.; Tuve, S.; Wehner, R.; Zimmermann, N.; Kramer, M.; Kloß, A.; Günther, C.; Babatz, J.; Schmelz, R.; Brückner, S.; Schetelig, J.; Bornhäuser, M.; Schäkel, K.; Bachmann, M. P.; Aust, D.; Baretton, G.; Schmitz, M.

kein Abstract verfügbar

Keywords: Acute graft versus host disease; b-sulfo LacNAc positive; Dendritic cells; Proinflammatory

Publ.-Id: 20573

Combined measurement of tumor perfusion and glucose metabolism for improved tumor characterization in advanced cervical carcinoma: A PET/CT pilot study using [15O]water and [18F]fluorodeoxyglucose

Apostolova, I.; Hofheinz, F.; Buchert, R.; Steffen, I. G.; Michel, R.; Rosner, C.; Prasad, V.; Köhler, C.; Derlin, T.; Brenner, W.; Marnitz, S.

Background and purpose:
The aim of this pilot study was (1) to evaluate the combination of [18F]fluorodeoxyglucose (FDG) and [ 15O]water for detection of flow-metabolism mismatch in advanced cervical carcinomas, i.e., increased glycolysis at low blood flow, as a possible parameter for prediction of response to treatment, and (2) to propose a method for automated quantification of its spatial extent.
Patients and methods:
The study retrospectively included 10 women with advanced cervical carcinoma in whom PET with both FDG and [15O]water had been performed prior to therapy. The metabolically active tumor volume was delineated automatically in the FDG images. For computation of the regional blood flow in the tumor, a recovery corrected image-derived arterial input function was used. A tumor voxel was classified as mismatched when the voxel SUV of FDG was larger than the median tumor SUV and the voxel perfusion (K1) was smaller than the median perfusion. The absolute mismatch volume (aMMV) was defined as the volume of all mismatched voxels in ml, and the relative mismatch volume (rMMV) as the ratio of the aMMV to the metabolic tumor volume in percent.
The tumors were quite heterogeneous with respect to both FDG uptake and perfusion. The aMMV clustered into 2 groups: "large aMMV" ∈10 ml in 40∈% of patients and "small aMMV" 5 ml in 60∈% of patients. The rMMV ranged from 12.7-24.9∈%. There was no correlation between rMMV and metabolic tumor volume. There was a tendency (p∈=∈0.126) for an association between rMMV and histological grading, rMMV being about 20∈% higher in G3 than in G2 tumors. rMMV did not correlate with SUV or perfusion.
These results suggest that combined PET with FDG and [15O]water allows detection and quantitative characterization of flow-metabolism mismatch in advanced cervical carcinomas.

Keywords: Positron emission tomography; Prognosis; Uterine cervical carcinoma

Publ.-Id: 20572

64Cu-labeling of dendritic polyglycerol derivatives for biodistribution studies

Pant, K.; Steinbach, J.; Stephan, H.; Gröger, D.; Nowag, S.; Haag, R.

Dendritic polyglycerols (dPG) and polyglycerol sulfates (dPGS) are promising compounds for biomedical applications due to their easy synthesis and high biocompatibility. Dendritic polyglycerol sulfate shows strong anti-inflammatory
properties [1, 2] which makes it a promising agent for diagnostic and therapeutic applications [3].

Information about the biodistribution and the metabolism of dendritic polyglycerol derivatives in living systems are quite scarce. In order to obtain quantitative information about the biodistribution of dPGS in vivo, methods like positron emission tomography (PET) will be applied. Among the metal-based positron emitting radionuclides, 64Cu is one of the most intensively evaluated isotopes. Incorporation of 64Cu into dPG/dPGS derivatives requires the use of chelate ligands capable of tightly binding the radionuclide.

Herein, we report the conjugation of bifunctional chelating agents (BFCA), based on bis(2-pyridylmethyl)triazacyclononane (DMPTACN) [4], on the dPG/dPGS scaffold. The structure of DMPTACN allows for the introduction of linker groups, such as carboxylic acids, maleimides or isothiocyanates, thereby facilitating coupling to the dendritic polyglycerol derivatives that contain amino and mercapto surface groups. 64Cu-labeling experiments and studies of the stability of the resulting radiocopper complexes in the presence of human serum or the competing ligand EDTA will be discussed.

[1] H. Türk et al., Bioconjugate Chem. 2004, 15, 162.
[2] J. Dernedde et al., PNAS 2010, 117, 19679.
[3] K. Licha et al., Bioconjugate Chem. 2011, 22, 2453.
[4] G. Gasser et al., Bioconjugate Chem.2008, 19, 719.

  • Poster
    GDCh-Wissenschaftsforum Chemie 2013, 01.-04.09.2013, Darmstadt, Deutschland

Publ.-Id: 20571

Magnetic dipole strength in 128Xe and 134Xe in the spin-flip resonance region

Massarczyk, R.; Rusev, G.; Schwengner, R.; Dönau, F.; Bhatia, C.; Gooden, M. E.; Kelley, J. H.; Tonchev, A. P.; Tornow, W.

The magnetic dipole strength in the energy region of the spin-flip resonance has been investigated in {128}Xe and {134}Xe using quasi-monoenergetic and linearly polarized gamma-ray beams at the HI gamma S facility in Durham, USA. Absorption cross sections were deduced for the electric and magnetic Dipole distributions separately for various intervals of excitation energy, including the strength of states in the unresolved quasi-continuum. Spin-flip like resonance structures were found in the magnetic dipole strength distribution around an excitation energy of 8 MeV. The E1 strength distributions deduced from the present experiments are compatible with the data of an experiment using bremsstrahlung that are based on simulations of statistical gamma-ray cascades. The experimental E1 and M1 strengths are compared with phenomenological approximations and with deformed-basis quasiparticle-random-phase-approximation predictions.

Keywords: Photon scattering; nuclear resonance fluorescence; polarized $\gamma$-ray beams; electric and magnetic dipole strength functions; nuclear deformation; quasiparticle-random-phase-approximation

Publ.-Id: 20570

64Cu-labelling and biodistribution of dendritic polyglycerol derivatives

Pant, K.; Stephan, H.; Bergmann, R.; Steinbach, J.; Gröger, D.; Haag, R.

Dendritic polyglycerols are highly biocompatible polymers which can be synthesized on a multi gram scale in a one-pot synthesis. The properties of these derivatives can be influenced by using various surface groups, such as sulfates, carbonates, phosphates etc. Some derivatives have been already known for inflammation and bone targeting [1]. Dendritic polyglycerol sulfates (dPGS) are promising candidates to be applied as anti-inflammation and anti-coagulation agents [2]. The presence of amine surface groups in dPGS derivatives allows the attachment of various fluorescence tags and/or radiolabels. Fluorescence imaging using near IR probes visualizes a specific accumulation of dendritic polyglycerol sulfates (dPGS) in inflamed lesions [3]. With respect to radioactive labelling, 35S-labelled dPGS amines have been prepared. This allows ex vivo experiments using autoradiography[4]. However, there is a need of detailed information about bio-distribution and pharmacokinetic properties for dendritic polyglycerol derivatives.

For this reason, appropriate imaging techniques should be applied to achieve reliable information about the bio-distribution and the metabolic fate of these macromolecules in vivo. Nuclear imaging, especially positron emission tomography (PET) is known to be one of the most reliable techniques to follow the fate of substances in vivo and to examine the biological and pathological processes considering the small dose requirement of the radiolabelled substances to diminish the pharmacological effects. 64Cu has suitable decay characteristics that allow for PET imaging and a variety of bifunctional chelator agents (BFCAs) are available for attachment to dendritic polyglycerol derivatives using appropriate anchor groups.

Herein, we report the synthesis, radiolabelling and biodistribution studies of the dPGS scaffolds using BFCAs on the basis of 1,4,7-triazacyclononane with various functional end groups (carboxylic, maleimide, isothiocyanate groups) for easy bioconjugation onto the dPGS scaffolds (amine/mercapto surface groups). 64Cu-labeling experiments confirmed rapid CuII complex formation under mild conditions. The stability of the 64Cu radiolabelled conjugates has been studied in the presence of competing ligands, human serum and super oxide dismutase (SOD)[5] For stability studies in the presence of human serum and SOD, two complementary in vitro assays have been applied. Small animal PET studies with 64Cu-labelled dPGS derivatives in male Wistar rats have been performed and discussed.

  • Poster
    Biodendrimer 2014, 4th International Symposium on Biomedical Applications of Dendrimers, 18.-20.06.2014, Lugano, Schweiz

Publ.-Id: 20569

Carbon redistribution and precipitation in high temperature ion-implanted strained Si/SiGe/Si multi-layered structures

Gaiduk, P. I.; Lundsgaard Hansen, J.; Larsen, A. N.; Korolik, O. V.; Bregolin, F. L.; Skorupa, W.

We report on the segregation of carbon atoms and structural transformations in strained multilayered Si/SiGe/Si structures after molecular-beam epitaxial (MBE) growth, carbon ion implantation and thermal treatment at different conditions. The idea behind this study was that due to their specific strain distribution, pseudomorphic layers of Si/SiGe promote spatial separation of vacancies and interstitials followed by segregation of foreign dopant atoms. High temperature ion implantation was used for injection of carbon atoms as well as point defects in the strained layers. The defects were investigated by transmission electron microscopy (TEM), dopant depth profiles by secondary-ion-mass spectrometry (SIMS), and optical properties by Raman scattering measurements. Based on SIMS data we demonstrate anomalous redistribution of the implanted carbon atoms around the strained SiGe/Si layers which results in their accumulation on the Si side and depletion on the SiGe side of the structure. The TEM study demonstrates formation of plate-like defects, stacking faults and thin carbon-precipitated flakes distributed along the Si/SiGe interfaces. Raman spectra reveal peaks at 1600 and 2700 cm -1 which might be associated with carbon-related phases. The concept of strain-enhanced separation of point defects and dopant precipitation is discussed.

Keywords: Carbon redistribution; Defects; Precipitates; Si-SiGe heterostructures; Voids

Publ.-Id: 20568

Gangue mineralogy and deportment of titanium (Ti) and vanadium (V) in the Kiirunavaara iron ore deposit, Northern Sweden

Aupers, K.; Niiranen, K.; Birtel, S.; Höfig, T. W.; Krause, J.; Gutzmer, J.

The Paleoproterozoic Kiirunavaara Fe oxide-apatite intrusive body has long been known as the most productive iron ore deposit of Europe. Because of the production in the mine is advancing deeper levels and demand for iron ore is increasing, the importance of understanding the deposit from both mineralogical and geochemical point of view is obvious. Among other it is thus important to characterise the abundance and chemical composition of ore and gangue minerals in terms of their variable impact as potential Ti-V hosts, which might be critical elements for production in the future. For this purpose, 55 samples from deeper parts of the orebody were studied combining optical microscopy, SEM-based MLA, and EPMA. Three minerals with stoichiometric Ti-contents have been identified: titanite, ilmenite, and rutile. Moreover, phlogopite hosts Ti in significant amounts (Ø 4300 ppm). For the P-poor parts of the orebody (B-type ore), ilmenite and rutile form the major Ti-hosts in Fe-rich intervals (Fe > 66 wt. %), whereas titanite is predominant in P-poor intervals with slightly lower Fe contents. In contrast, Ti-minerals are fairly rare in P-rich zones of the orebody (P > 0.1 wt. %, D-type ore) and, if present, represented by titanite. Magnetite, being the major commodity at Kiirunavaara, has not revealed any significant Ti contents in its crystal structure. However, Ti is associated with magnetite in the form of Ti-rich exsolution lamellae, being restricted to magnetite crystals in B-type ore (Fig. 1). Incorporation of V has been exclusively detected in magnetite and titanite, revealing average concentrations of c. 600 ppm and 650 ppm respectively. Due to the exploration and grade control drilling the Ti-grade increases with depth. Consequently also the abundance of Ti-bearing silicate (titanite, phlogopite) and oxide (ilmenite, rutile) rises. In the future, additional flotation steps besides the reverse apatite flotation may be required to ensure their efficient elimination during the beneficiation process. It also appears unreasonable to mechanically separate the Ti-rich exsolution lamellae and lattice-bound V from the magnetite sinter feed product of the Kiruna Mine.

Keywords: deleterious elements; element deportment; geometallurgy

  • Lecture (Conference)
    92nd Annual Meeting Deutsche Mineralogische Gesellschaft, 21.-24.09.2014, Jena, Germany
  • Contribution to proceedings
    92nd Annual Meeting Deutsche Mineralogische Gesellschaft, 21.-24.09.2014, Jena, Germany
    Minerals at Focal Point, 115

Publ.-Id: 20567

Solution of the OECD/NEA neutronic SFR benchmark with Serpent-DYN3D and Serpent-PARCS code systems

Nikitin, E.; Fridman, E.; Mikityuk, K.

In this study, the Serpent Monte Carlo code was used as a tool for preparation of homogenized group constants for the nodal diffusion analysis of a large U-Pu MOX fueled Sodium-cooled Fast Reactor (SFR) core specified in the OECD/WPRS neutronic SFR benchmark. The group constants generated by Serpent were employed by DYN3D and PARCS nodal diffusion codes in 3D full core calculations. The DYN3D and PARCS results were verified against the references full core Serpent Monte Carlo solution. A good agreement between the reference Monte Carlo and nodal diffusion results was observed demonstrating the feasibility of using Serpent as a group constant generator for the deterministic SFR analysis.

Keywords: Group constant generation; Monte-Carlo; SFR; Serpent; DYN3D; PARCS

Publ.-Id: 20566

Effect of [18F]FMISO stratified dose-escalation on local control in FaDu hSCC in nude mice

Schütze, C.; Bergmann, R.; Brüchner, K.; Mosch, B.; Yaromira, A.; Zips, D.; Hessel, F.; Krause, M.; Thames, H.; Kotzerke, J.; Steinbach, J.; Baumann, M.; Beuthien-Baumann, B.

Objective To investigate the effect of radiation dose-escalation on local control in hypoxic versus non-hypoxic hypoxic tumours defined using [18F]fluoromisonidazole ([18F]FMISO) PET. Materials and methods FaDu human squamous cell carcinomas (hSCCs) growing subcutaneously in nude mice were subjected to [18F]FMISO PET before irradiation with single doses of 25 or 35 Gy under normal blood flow conditions. [18F]FMISO hypoxic volume (HV) and maximum standardised uptake value (SUVmax) were used to quantify tracer uptake. The animals were followed up for at least 120 days after irradiation. The endpoints were permanent local tumour control and time to local recurrence. Results HV varied between 38 and 291 mm3 (median 105 mm3). Non-hypoxic tumours (HV below median) showed significantly better local control after single dose irradiation than hypoxic tumours (HV above median) (p = 0.046). The effect of dose was significant and not different in non-hypoxic and in hypoxic tumours (HR = 0.82 [95% CI 0.71; 0.93], p = 0.002 and HR = 0.86 [0.78; 0.95], p = 0.001, respectively). Dose escalation resulted in an incremental increase of local tumour control from low-dose hypoxic, over low-dose non-hypoxic and high-dose hypoxic to high-dose non-hypoxic tumours. SUVmax did not reveal significant association with local control at any dose level. Conclusions The negative effect of [18F]FMISO HV on permanent local tumour control supports the prognostic value of the pre-treatment [18F]FMISO HV. Making the assumption that variable [18F]FMISO uptake in different FaDu tumours which all have the same genetic background may serve as an experimental model of intratumoural heterogeneity, the data support the concept of dose-escalation with inhomogeneous dose distribution based on pre-treatment [18F]FMISO uptake. This result needs to be confirmed in other tumour models and using fractionated radiotherapy schedules.

Keywords: Dose escalation; Human tumour xenografts; Hypoxic volume; Local control; Single dose irradiation; Squamous cell carcinoma

Publ.-Id: 20565

Investigations of the liquid steel flow in slab casters with electromagnetic brakes and round bloom casters with electromagnetic stirring

Barna, M.; Willers, B.; Javurek, M.; Reiter, J.; Eckert, S.

In the continuous casting of steel the application of electromagnetic fields to modify the flow is steadily increasing. Electromagnetic stirring fields are used to excite a rotary motion in the strand thereby – among other benefits – promoting the columnar to equiaxed transition. In slab casters stationary fields shall break the submerged jets, dampen the turbulent movement and calm the liquid steel flow.
The influence of an electromagnetic brake onto the liquid steel flow is investigated through numerical simulations and experimental work. A 1:10 scale model of a continuous slab caster is built and flow measurements are conducted with Ga68In20Sn12 (Galinstan), a low melting point alloy. The results are then used for the validation of fully coupled numeric simulations, where the flow influences the magnetic field and vice versa.
For round bloom casting with electromagnetic stirring the impact of stirring frequency and stirring field current will be shown. From the results a simple analytical model can be deduced, which describes the average azimuthal velocity close to the wall. When combined with an estimation of the power losses, optimal stirring parameters can be chosen.

Keywords: Continuous casting of steel; electromagnetic braking; electromagnetic stirring; multiphysics; fully coupled numeric simulation; computational fluid dynamics (CFD); experiments; low melting point alloy Galinstan; Ultra Sound Doppler Velocimetry

  • Open Access Logo Contribution to proceedings
    8th European Continuous Casting Conference, 23.-26.06.2014, Graz, Austria
    Proceedings of ECCC

Publ.-Id: 20563

Multiscale and multiphysics simulation of pessurized thermal shock (PTS)

Lucas, D.

An overview on the activities related to the work package 32 on pressurized thermal shock in frame of the European project NURESAFE is given in this presentation

Keywords: CFD; PTS

  • Lecture (Conference)
    First NURESAFE open seminar, 16.-17.06.2014, Budqapest, Hungary

Publ.-Id: 20562

CFD-Modelle für Zweiphasenströmungen im Rahmen des Mehr-Fluid-Konzepts

Lucas, D.; Rzehak, R.; Krepper, E.; Höhne, T.; Liao, Y.; Montoya, G.; Hänsch, G.

Mehrphasenströmungen kommen u. a. in verschiedenen industriellen Prozessen der chemischen Verfahrenstechnik, der Energietechnik und der Ölindustrie vor. Zuverlässige Vorhersagen der zu erwartenden Strömungs- und Energietransfereigenschaften sind für die Auslegung, Optimierung und auch Sicherheitsbetrachtung dieser Prozesse wichtig. Für CFD-Simulationen von Strömungen in mittleren und großen Volumina wird meist das Zwei- bzw. Mehr-Fluid-Konzept (Euler-Euler-Modell) genutzt. Eine wesentliche Unsicherheit der Simulationsergebnisse resultiert dabei aus den Schließungsmodellen. Oft werden diese Modelle sowie damit verbundene freie Parameter so ausgewählt, dass eine gute Überstimmung mit vorhanden experimentellen Daten erzielt wird. Da die Vorhersagefähigkeit für unbekannte Strömungen dadurch nicht verbessert wird, wurden am HZDR so genannte Standardmodelle für polydisperse Blasenströmungen und separierte Strömungen definiert. Die allgemeine Strategie der Modellentwicklung sowie die Standardmodelle selbst werden in dem Vortrag vorgestellt. Weiterhin wird ein neuer Modellansatz diskutiert, der eine kombinierte Simulation der beiden Strömungsmorphologien einschließlich der Berücksichtigung von Übergängen zwischen diesen ermöglicht.

Keywords: CFD; Mehrphasenströmungen

  • Invited lecture (Conferences)
    Institutsseminar des Instituts für Kern- und Energietechnik (IKET) am Karlsruher Institut für Technologie (KIT), 08.07.2014, Karlsruhe, Deutschland

Publ.-Id: 20561

GENTOP – a multi-field 2-fluid model

Lucas, D.; Hänsch, S.; Krepper, E.; Höhne, T.; Montoya, G.

In this presentation the main ideas of the GENTOP-concept are presented. The concept allows the modelling of different morphologies of two-phase flows including transitions between them. Simulation results are shown for four different demonstration cases.

Keywords: CFD; two-phase; multi-scale

  • Invited lecture (Conferences)
    Joint Hungarian-Korean Laboratory (JHKL) Workshop, 19.-20.06.2014, Budapest, Hungary

Publ.-Id: 20560

Potential of a Cetuximab-based radioimmunotherapy combined with external irradiation manifests in a 3-D cell assay

Ingargiola, M.; Runge, R.; Heldt, J.-M.; Freudenberg, R.; Steinbach, J.; Cordes, N.; Baumann, M.; Kotzerke, J.; Brockhoff, G.; Kunz-Schughart, L. A.

Targeting epidermal growth factor receptor (EGFR)-overexpressing tumors with radiolabeled anti-EGFR antibodies is a promising strategy for combination with external radiotherapy. In this study, we evaluated the potential of external plus internal irradiation by [90Y]Y-CHX-A''-DTPA-C225 (Y-90-C225) in a 3-D environment using FaDu and SAS head and neck squamous cell carcinoma (HNSCC) spheroid models and clinically relevant endpoints such as spheroid control probability (SCP) and spheroid control dose 50% (SCD 50, external irradiation dose inducing 50% loss of spheroid regrowth). Spheroids were cultured using a standardized platform. Therapy response after treatment with C225, CHX-A''-DTPA-C225 (DTPA-C225), [ 90Y]Y-CHX-A''-DTPA (Y-90-DTPA) and Y-90-C225 alone or in combination with X-ray was evaluated by long-term monitoring (60 days) of spheroid integrity and volume growth. Penetration kinetics into spheroids and EGFR binding capacities on spheroid cells were identical for unconjugated C225 and Y-90-C225. Spheroid-associated radioactivity upon exposure to the antibody-free control conjugate Y-90-DTPA was negligible. Determination of the SCD50 demonstrated higher intrinsic radiosensitivity of FaDu as compared with SAS spheroids. Treatment with unconjugated C225 alone did not affect spheroid growth and cell viability. Also, C225 treatment after external irradiation showed no additive effect. However, the combination of external irradiation with Y-90-C225 (1 μg/ml, 24 hr) resulted in a considerable benefit as reflected by a pronounced reduction of the SCD50 from 16 Gy to 9 Gy for SAS spheroids and a complete loss of regrowth for FaDu spheroids due to the pronounced accumulation of internal dose caused by the continuous exposure to cell-bound radionuclide upon Y-90-C225-EGFR interaction.

Keywords: Cetuximab; EGFR; tumor spheroids; Y-90

  • International Journal of Cancer 135(2014), 968-980
    Online First (2014) DOI: 10.1002/ijc.28735

Publ.-Id: 20559

Multiscale thermalhydraulic analyses performed in NURESAFE project

Bestion, D.; Lakehal, D.; Tregoures, N.; Lucas, D.; Anglart, H.; Niceno, B.; Hazi, G.; Vyskocil, L.

An overview on the activities on thermal hydraulics with in the NURESAFE project is given in this presentation.

Keywords: CFD; PTS; BWR; multi-scale modelling

  • Lecture (Conference)
    22th International Conference on Nuclear Engineering (ICONE22), 06.-10.07.2014, Prague, Czech Republic

Publ.-Id: 20558

Climatic vs tectonic forcing: the case of Pamir

Gloaguen, R.; Fuchs, M.; Pohl, E.; Sulaymonova, V.; Andreani, L.

Surface processes in Pamir are temporally and spatially extremely variables. Our collaborative research demonstrated that, (1) the controlling forces such as climate and tectonic deformation have evolved during the Quaternary, (2) Westerlies and Monsoon have varying domains of influence and (3) the rates of deformation, erosion and incision are locally extremely high. The determination of the localization and intensity of active tectonic structures was allowed by the production of remote sensing based geomorphometric maps combined with published GPS and seismological data. Incision rates were measured by OSL and cosmogenic dating of river terraces. Modern erosion rates were calculated using AMS 10Be concentrations in river sediments. Tectonic deformation principally occurs along the borders of the Pamir domes, probably along propagating strike-slip faults reactivating older structures such as sutures and dome bounding faults. Most rivers are in imbalance and witness a strong reorganization of the drainage system during the Late Quaternary. The Panj itself is built by the concatenation of rivers by successive captures, the last one probably younger than MIS2. The average incision rate of the Panj, the main river draining Pamir and its main tributaries is about 4 mm/yr. Peak incisions reach 10 mm/yr where river captures induced high offsets with respect to base levels. Erosion rates are high at the Pamir periphery (ca 0.7 mm/yr) and very low on the plateau (ca 0.005 mm/yr). The Pamir can be subdivided in zones in which specific controlling forces are dominating. The Pamir plateau is dominated by diffusive hillslope processes contributing to further flattening. The main rivers are located in or nearby active faults. High erosion rates are probably sustained by steep hillslopes generated by high incision rates. Highest erosion rates are found were both Monsoon and Westerlies occur.

  • Lecture (Conference)
    EGU General Assembly 2014, 27.04.-02.06.2014, Vienna, Austria

Publ.-Id: 20557

A new set of MATLAB functions (TecDEM toolbox) to analyze erosional stages in landscapes and base-level changes in river profiles

Andreani, L.; Gloaguen, R.; Shahzad, F.

We implemented three new functions in the MATLAB-based TecDEM toolbox [1,2]: surface index, topographic position index, and the analysis of base-levels in river longitudinal profiles. These tools provide useful ways to understand the effects of base-level changes on topography such as stream captures, erosion or rejuvenation of pre-existing topographic features and anomalies in river longitudinal profiles. We developed a new index (referred as “surface index”) which provides a quick way to map simultaneously preserved and eroded portions of an elevated landscape. This index classifies landscapes according to their erosional stages using the combination of the hypsometric integral, which efficiently highlights flat surfaces, and the surface roughness, which substantially increases with incision. We also implemented the commonly used “topographic position index”. This index provides a simple way to classify the landscapes as valleys, ridges and flat areas. However, its application in tectonic geomorphology can go far beyond as it discriminates valleys shapes and reveals other important features such as wind gaps and knickpoints when associated to the extracted river system. Finally, we implemented a tool allowing the estimation of base-level changes using the reconstruction of river longitudinal profiles. River profiles can be decomposed in concave or convex segments. Relict base-levels are typically associated to gently concave segments in river profiles. By restoring the initial shape of these segments we are able to estimate the amount of incision between the present day base-level and the relict base-level. All these tools were successfully tested in different settings such as Central America, Central Europe and Pamir. In addition to the description of these tools we provide examples from these different areas.
[1] Shahzad, F., & Gloaguen, R. (2011). TecDEM: A MATLAB based toolbox for tectonic geomorphology, Part 1: Drainage network preprocessing and stream profile analysis. Computers & Geosciences, 37, 250–260.
[2] Shahzad, F., & Gloaguen, R. (2011). TecDEM: A MATLAB based toolbox for tectonic geomorphology, Part 2: Surface dynamics and basin analysis. Computers & Geosciences, 37, 261–271.

  • Poster
    EGU General Assembly 2014, 27.04.-02.05.2014, Vienna, Austria

Publ.-Id: 20556

Planned high-brightness channeling radiation experiment at FERMILAB’s Advanced Superconducting Test Accelerator

Blomberg, B.; Brau, C. A.; Choi, B. K.; Gabella, W. E.; Ivanov, B.; Mendenhall, M.; Lynn, C.; Mihalcea, D.; Panuganti, H.; Piot, P.; Sen, T.; Wagner, W.

In this contribution we describe the technical details and experimental setup toward the production of high-brightness channeling radiation (CR) at the Fermilab’s Advanced Superconducting Test Accelerator (ASTA). In the ASTA photoinjector area electrons are accelerated up to 40-MeV and focused to a sub-micron spot on a 40 micron thick diamond, the electrons channel through the crystal and emit CR up to 80-KeV. Our study utilizes ASTA’s long pulse train capabilities and ability to preserve ultra-low emittance, to produce the desired brightness.

Keywords: electron channeling; channeling radiation; ASTA

  • Open Access Logo Contribution to proceedings
    IPAC 2014 - 5th International Particle Accelerator Conference, 16.-20.06.2014, Dresden, Germany
    Proceedings of IPAC 2014, 1457

Publ.-Id: 20555

A new multi-region solver for liquid metal batteries

Weber, N.; Galindo, V.; Stefani, F.; Weier, T.

Liquid metal batteries (LMBs) are a very innovative approach intending to fill the gap of grid-scale electricity storage, as induced by the expand of highly fluctuating renewable energies. Earth-abundant raw materials, simple construction and easy scalability allow for very cheap batteries – the biggest advantage of LMBs.
A LMB is made up of two liquid metals, separated by a liquid salt electrolyte. Properly chosen densities ensure a stable stratification. Taking a Na/Bi LMB, on dis-charge, the Na will lose one electron. The ion Na+ will pass the electrolyte layer and alloy with the Bi to NaBi.
The high resistivity of the salt requires a very thin electrolyte layer, but thick enough to avoid a short-circuit. Fluid flows in LMBs may involve the risk of displacing the electrolyte, resulting in a short-circuit. One of the most important sources of motion are electro vortex flows: the different cross-sections of feeding lines, current collectors and the battery itself induces Lorentz forces in the liquid metal, which are driving a fluid flow.
The fluid flow is governed by the incompressible Navier-Stokes equation (NSE) with the Lorentz force as source term. In order to obtain the latter, we solve a Laplace equation for the electric potential in the liquid metal as well as the current collectors and compute it's gradient giving the current density. With the help of the Biot-Savart law we can compute the magnetic field. The cross product of both is the desired Lorentz force.
Our solver is modeled analogous to chtMultiRegionFoam. We solve the NSE by the PISO algorithm as electro vortex flows are instationary. Solving the Laplace equation for the electric potential we alternate between the liquid and solid regions. The interface condition is given by the demand that there is no jump of the electric potential, and that the normal electric current must be continuous. We combine these two conditions to a single Dirichlet boundary condition for fastest Dirichlet-Neumann partitioning. We stop the iteration between the regions, when both boundary conditions are fulfilled at all interfaces.
The last step, the computation of the magnetic induction using the Biot-Savart law, is a N x N problem. In order to speed up the computation we propose a fast MPI implementation.
Finally, we present some exemplary results and show how electro vortex flows scale in LMBs with the applied current, the current collectors aspect ratio and it's conductivity.

Keywords: liquid metal battery; electro vortex flow; instability; OpenFOAM

  • Lecture (Conference)
    OpenFOAM User Conference, 07.-09.10.2014, Berlin, Deutschland

Publ.-Id: 20554

Model experiments for investigations of heat transfer phenomena in the Czochralski crystal growth

Pal, J.; Cramer, A.; Eckert, S.; Gerbeth, G.; Grants, I.

A low temperature liquid metal model of the Czochralski crystal growth process is considered experimentally under conditions of high aspect ratio. We focus on the influence of a rotating magnetic field (RMF) and/or crystal rotation on temperature fluctuation near the crystal edge. The radial flow structure is observed by ultrasound Doppler velocimetry (UDV). It is concluded that the effect of RMF on the temperature fluctuation is less expressed than in a Rayleigh-Bénard cell.

Keywords: Czochralski crystal growth; electromagnetic processing; buoyant flow; heat transfer

  • Lecture (Conference)
    The 9th. International PAMIR conference on Fundamental and Applied MHD, Thermo Acoustic and Space Technologies, 16.-20.06.2014, Riga, Latvia
  • Contribution to proceedings
    The 9th. International PAMIR Conference on Fundamental and Applied MHD, Thermo Acoustic and Space Technologies, 16.-20.06.2014, Riga, Latvia
    Proceedings, 110-114

Publ.-Id: 20553

Experimental Investigation of Rayleigh-Benard convection in a liquid metal layer exposed to a horizontal magnetic field

Igaki, K.; Tasaka, Y.; Yanagisawa, T.; Vogt, T.; Eckert, S.

Rayleigh-Benard convection has been investigated inside a liquid metal layer under the influence of a DC magnetic field. Similar configurations can be found in geophysical or steel production. Our group reported recently that spontaneous flow reversals of quasi two-dimensional rolls randomly occur in Rayleigh-Benard convection of liquid metal exposed to a horizontal magnetic field (Yanagisawa, et al., PRE, 2011). In fluid layers with relatively large aspect ratios the flow pattern consisting of several convection rolls appears to be almost isotropic. However, the rolls are aligned with the magnetic field direction if the Lorentz force becomes either comparable to the buoyancy or larger. In our experiment, where the fluid layer has a dimension of 200x200x40 mm (corresponding to an aspect ratio of 5), the convection pattern can show 3, 4 or 5 rolls regimes depending on the Rayleigh number Ra and the Chandrasekhar number Q. Flow reversals occur spontaneously between these steady states in the Ra-Q parameter space.

Keywords: Rayleigh-Benard

  • Contribution to proceedings
    9th International Pamir Conference, 16.-20.06.2014, Riga, Latvia
  • Poster
    9th International Pamir Conference, 16.-20.06.2014, Riga, Latvia

Publ.-Id: 20552

Application of magnetically driven tornado-like vortex for stirring floating particles into liquid metal

Grants, I.; Räbiger, D.; Vogt, T.; Eckert, S.; Gerbeth, G.

A tornado-like vortex is driven by magnetic body forces. A continuously applied rotating magnetic field provides source of the angular momentum. A pulse of a much stronger travelling magnetic field drives a converging flow that temporarily focuses this angular momentum towards the axis of the container. A highly concentrated vortex forms that produces a funnel-shaped surface depression. The ability of this vortex to entrain floating unwetted particles in liquid metal is investigated experimentally.

Keywords: Electromagnetic processing of materials; magnetohydrodynamics

  • Lecture (Conference)
    9th PAMIR conference on Fundamental and Applied MHD, 16.-20.06.2014, Riga, Latvia
  • Contribution to proceedings
    9th PAMIR conference on Fundamental and Applied MHD, 16.-20.06.2014, Riga, Latvia

Publ.-Id: 20551

Experimental investigation of inertial waves inside a cylindrical liquid metal column

Vogt, T.; Räbiger, D.; Eckert, S.

The dynamics of free inertial waves inside a cylindrical volume was investigated experimentally in this study. The liquid metal GaInSn was chosen as fluid in order to enable a contactless stimulation of the flow inside the cylinder by means of a rotating magnetic field which generates a supercritical rotating motion of the liquid. The experiment demonstrates that inertial waves may be excited spontaneously by turbulent structures in the rotating flow. The ultrasound Doppler velocimetry was used to record the flow structure and to identify the inertial waves occurring in the setup.

Keywords: inertial waves; rotating flow

  • Lecture (Conference)
    9th International PAMIR Conference, 16.-20.06.2014, Riga, Latvia
  • Contribution to proceedings
    9th International PAMIR Conference, 16.-20.06.2014, Riga, Latvia
    Proceedings of the 9th International PAMIR Conference

Publ.-Id: 20550

Regime transition in viscous and pseudo viscous systems: A comparative study

Rabha, S.; Schubert, M.; Hampel, U.

A comprehensive quantitative study on the effect of liquid viscosity (1 ≤ µL ≤ 1149 mPa-s) on the local flow phenomena of the gas phase in a small diameter bubble column is performed using ultrafast electron beam X-ray tomography. The internal dynamic flow structure and the bubble size distribution have proven a dual role of the liquid viscosity on the hydrodynamics. Further, effect of solid concentration (Cs = 0.05, 0.20) on the local flow behavior of the gas phase is studied for the pseudo (slurry) viscosities similar to the liquid viscosities of the gas-liquid systems. The effects of liquid and pseudo (slurry) viscosity on flow structure, bubble size distribution and gas phase distribution are compared. The bubble coalescence is significantly enhanced with the addition of particles as compared to the system without particles for apparently same viscosity. The superficial gas velocity at which transition occurs from homogeneous bubbly to slug flow regime is initiated by the addition of particles as compared to the particle free system for apparently same viscosity.

Keywords: Liquid viscosity; Pseudo (slurry) viscosity; Gas holdup; Bubble size distribution; Ultrafast electron beam X-ray tomography

Publ.-Id: 20548

Methods for extraction of velocity information from ultrafast X-ray tomography

Barthel, F.; Bieberle, M.; Hoppe, D.; Hampel, U.

The ultrafast electron beam X-ray tomography scanner “ROFEX” is widely used for investigations on multiphase flows, such as two-phase pipe flow, bubble columns, flows in structured packings, in monolith ceramics, in foams, in rod bundle geometries and others. The use of X-rays allows to discriminate phases, i.e. to distinguish between gas and liquid, gas and solid, liquid and solid and so on. It is, however, more difficult, to obtain velocity information from two-phase flows. Measuring velocities in the continuouse phase is only possible, if there is density contrast in it. In case of disperse flows the disperse phase self may act as a tracer. This gives rise to application of velocity measurement methods, which are based on correlation techniques. Adding liquid contrast agents to the continuous liquid phase is another choice. The paper introduces three methods of velocity measurements along with the associated data processing and gives some demonstration examples to discuss capabilities and limits of the methods.

Keywords: Ultrafast X-ray Tomography; velocity measurement; cross correlation; ROFEX

  • Lecture (Conference)
    5th International Workshop on Process Tomography (IWPT5), 16.-18.09.2014, Jeju, Korea
  • Contribution to proceedings
    5th International Workshop on Process Tomography (IWPT5), 16.-18.09.2014, Jeju, Korea
    Proceedings of IWPT5

Publ.-Id: 20547

Effective spin meron pairs in ferromagnetic multilayer elements

Wintz, S.; Raabe, J.; Fassbender, J.

Topological spin textures, such as vortices or skyrmions, are attracting significant attention because of both their intriguing fundamental properties and their promising applicability in memory devices or spin torque oscillators. A particular topological texture that was theoretically predicted is the two-dimensional hedgehog state, also known as a ’spin meron’. It had been unclear, however, whether this kind of highly divergent magnetization structure may exist in real systems. Only recently, evidence for the occurrence of meron-like pair states was reported for the case of trilayer elements consisting of two ferromagnetic layers and a non-ferromagnetic interlayer.On this background we present a direct proof for the existence of meron-like states in trilayer elements via direct magnetic imaging. We also show that in the presence of biquadratic interlayer exchange coupling, such meron-like pair states may even represent the magnetic ground state of the system. Interestingly, the highly divergent magnetization distribution induces an additional, three-dimensional torus vortex that in-turn causes a symmetry break for the allowed topological pair configurations.In the second part of our presentation we will address the dynamic properties of vertically coupled topological spin textures, where the focus will be on spin wave emission processes in such systems.

Keywords: vortex multilayer meron

  • Invited lecture (Conferences)
    59th Annual Magnetism & Magnetic Materials Conference, 03.-07.11.2014, Honolulu, USA

Publ.-Id: 20545

Cluster models for random particle aggregates-Morphological statistics and collision distance

Teichmann, J.; van den Boogaart, K. G.

In this paper, new models for particle-cluster and cluster-cluster-like aggregates are investigated trough detailed Monte Carlo simulation to model aggregation of micro-sized particles in turbulent flows.
These structures are built up by mechanisms which occur for instance in homogeneous isotropic turbulence flows with absence of Brownian motion and can be studied without a predefined motion field. The models are compared among each other in two and three dimensions with respect to several morphological properties, such as Feret diameter, radius of gyration, convexity, aspect ratio, fractal dimension and coordination number averaged over hundreds of thousands of aggregates of each size. An important part is devoted to approximation of these aggregates by spherical particles. For this, a particular radius, based on the collision distance to other particles is used, measured and approximated for both aggregate models. It can be useful for calculations related to agglomeration kernels in the framework of Smoluchowski’s coagulation equation.

Keywords: agglomeration; cluster-cluster aggregation; morphology; coagulation; micro-sized

Publ.-Id: 20544

Simultane Messung des Geschwindigkeitsfeldes und der Blasentrajektorien in einer ungeteilten Elektrolysezelle

Baczyzmalski, D.; Weier, T.; Kähler, C. J.; Cierpka, C.

Die Effizienz bei der Wasserstoffelektrolyse wird durch die Bedeckung der aktiven Elektrodenoberfläche durch die entstehenden Wasserstoff- und Sauerstoffblasen beeinträchtigt. Zur Effizienzsteigerung werden derzeit Strömungsbeeinflussungsmethoden untersucht, die zum beschleunigten Ablösen der Gasblasen von den Elektrodenoberflächen führen und so die Oberfläche schneller zur erneuten Reaktion freigeben. Zur Entwicklung solcher Strömungsbeeinflussungsmethoden müssen die hierdurch hervorgerufenen Strömungseffekte verstanden werden. Dies setzt die Kenntnis des Strömungsfeldes an der Elektrode und um die Gasblasen voraus. Im Sinne einer Machbarkeitsstudie zur gemeinsamen Messung von Gasblasenbewegung und umgebenden Strömungsfeld wurden hierzu im Rahmen der dargelegten Experimente in einer Wasserstoffelektrolysezelle simultane Messungen des Geschwindigkeitsfeldes und der Gasblasenbeladung durchgeführt. Zur Geschwindigkeitsmessung wurden fluoreszente Partikel mit einer sCMOS-Kamera beobachtet und deren Bewegung mittels PIV (Particle Image Velocimetry) ausgewertet. Die Gasblasen wurden hingegen durch Hintergrundbeleuchtung im Durchlichtverfahren mit einer weiteren sCMOS-Kamera aufgenommen und deren Bewegung mittels PTV (Particle Tracking Velocimetry) bestimmt. Zur Strömungsbeeinflussung wurden mit Hilfe eines Permanentmagneten Lorentzkräfte erzeugt. Abhängig von der vorherrschenden Stromstärke kann eine deutliche Beschleunigung der Strömung und Gasblasen durch die Lorentzkräfte festgestellt werden. Sowohl die Messung der Strömungsgeschwindigkeiten als auch der Blasenbewegung in unmittelbarer Wandnähe war aufgrund der dort vorherrschenden hohen Gasbeladung mit großen Unsicherheiten behaftet. Außerhalb dieses Bereiches konnten die Blasenbewegungen bestimmt und deren Einfluss auf das umgebende Strömungsfeld visualisiert werden. In Abhängigkeit des Blasendurchmessers führen die Blasen eine wellenförmige Aufwärtsbewegung parallel zur Elektrode aus, die mit dem elektrodennahen wellenförmigen Blasenteppich zusammenhängen oder auf Nachlaufinstabilitäten zurückzuführen sein könnte.

Keywords: two-phase flow; gas bubbles; water electrolysis

  • Open Access Logo Contribution to proceedings
    22. Fachtagung "Lasermethoden in der Strömungsmesstechnik", 09.-11.09.2014, Karlsruhe, Deutschland, 9783981676402, 51-1-51-8
  • Lecture (Conference)
    Fachtagung "Lasermethoden in der Strömungsmesstechnik", 09.-11.09.2014, Karlsruhe, Deutschland

Publ.-Id: 20543

URANS simulation of continuous casting mold flow: Assessment of revised turbulence models

Kratzsch, C.; Timmel, K.; Eckert, S.; Schwarze, R.

A time-resolved numerical model of the mini-LIMMCAST facility is investigated in the frame of RANS simulations. Three revised eddy viscosity turbulence models besides the often used Standard k-epsilon model for steady and unsteady RANS simulations are evaluated with the CFD software tool OpenFOAM. The data is compared with experimental results focusing the jet flow[1]. Different turbulence models lead to slight deviations from the experimental data in the case of steady state calculation with first order accuracy. For the time-averaged URANS results a crucial in uence by the discretization order is observed. In case of unsteady results a mix between first and higher order accuracy schemes is necessary for representative results. The use of the Standard k-epsilon model and the Realizable k-epsilon model can lead to unstable behavior in the case of URANS simulations. Conclusively, the study shows, that in case of qualitative temporal resolved informations and temporal averaged results an unsteady RANS simulation can keep up with a LES.

Keywords: unsteady mold flow; RANS; URANS; OpenFOAM; mini-LIMMCAST

Publ.-Id: 20542

Impedance analysis of secondary phases in a Co-implanted ZnO single crystal

Younas, M.; Zou, L. L.; Nadeem, M.; Ur-Rehman, N.; Su, S. C.; Wang, Z. L.; Anwand, W.; Wagner, A.; Hao, J. H.; Leung, C. W.; Lortz, R.; Ling, F. C. C.

Co ions with 100 keV energy with a fluence of 1 x 10^15 cm-2 are implanted into ZnO(0001) single crystals at 300 °C under vacuum. The resulting Co-implanted ZnO single crystals and the subsequent 750 °C and 900 °C annealed samples are analysed with respect to their structural, optical, electronic, magnetic and ac electrical properties. Photoluminescence and X-ray photoelectron spectroscopy results indicate the signatures of the Co^2+ state and its substitution at the tetrahedrally coordinated Zn-sites. X-ray diffraction and X-ray photoelectron spectroscopy identify the presence of the ZnCo2O4 and Co3O4 phases in the 900 °C annealed sample. By comparing the resistance response of the identified phases towards different magnetic environments, the impedance spectroscopy results successfully identify two magnetic phases (ZnCo2O4 and Co3O4) and a paramagnetic (CoZn) phase for the 750 °C and 900 °C annealed samples, implying the extrinsic nature of room temperature erromagnetism. The observed ferromagnetism in each sample is not of single origin, instead the mutual effects of the secondary phases embedded in the paramagnetic host matrix are in competition with each other.

Keywords: ZnO; Co implantation; secondary phases; impedance analysis

Publ.-Id: 20541

Surface-near modifications of SrTiO3 local symmetry due to nitrogen implantation investigated by grazing incidence XANES

Stöcker, H.; Zschornak, M.; Richter, C.; Hanzig, J.; Hanzig, F.; Hinze, V.; Potzger, K.; Gemming, S.; Meyer, D. C.

Nitrogen ion implantation into strontium titanate single crystals causes a slight shift of the Ti-K edge position compared to pristine SrTiO3 and a strong increase of the second pre-edge peak in X-ray absorption near-edge spectroscopy (XANES) using graz- ing incidence geometry. Calculations by a finite difference method demonstrate that the strong increase of the second pre-edge fea- ture in the defect distorted phase can be attributed to a static displacement of the Ti atom relative to the surrounding oxygen octahedron.

Keywords: ferroic functional oxides; density functional theory; doping; strontium titanate

Publ.-Id: 20540

Multiple point statistics understood in Matheronian principles

van den Boogaart, K. G.

In the last years the conditional simulation of geological structures with the multiple point statistics (MPS) approach has created new opportunities for a better description of the uncertainty in inference from spatial observations to knowledge and uncertainty about the geological reality. A new paradigm of geostatistics has been created based on simulation algorithms rather than on stochastic theory. The talk thus aims at discussing MPS in the light of the ideas behind Matheron’s geostatistic. Matheron simplified the problem to linear functions due to the lack of computer power. MPS now allows incorporating nonlinearities. The normal distribution assumption was a tool to teach uncertainty to the computer. MPS now allows new tools like the training image to take that role. In this perspective MPS can be seen as the extension of Matheron’s ideas to new computational possibilities. On the other hand some of the stochastic background of Matheron’s geostatistic has been lost in the fast course of development of MPS. The talk aims at rebuilding these basics. This stochastic view to MPS allows to discuss strengths and weaknesses of various MPS applications and to ask new questions potentially improving their future performance: Which of two simulation algorithms is better? Is the training image large enough to capture the uncertainty? Does the training image adequately describe the reality? Which criteria can be used to describe the performance of a conditional simulation algorithm for a specific purpose? How large should search neighborhoods be? Adding these stochastic viewpoints is a step towards not only having good algorithms, but also good tools to judge the appropriateness of an algorithm, to anticipate possible artefacts and to see MPS as the natural evolution of Materon’s geostatistic, rather than as an alternate approach.

Keywords: Multiple Point Statistics; Uncertainty Modelling

  • Invited lecture (Conferences)
    IAMG 2014, 16th conference of the international association for mathematical geosciences, 17.-20.10.2014, New Dehli, India

Publ.-Id: 20539

1-Arylimidazo[1,5a]chinoxalines as lead compounds for a PDE10A PET tracer

Wagner, S.; Scheunemann, M.; Fischer, S.; Egerland, U.; Ludwig, F.-A.; Hoefgen, N.; Steinbach, J.; Brust, P.

Aim: Phosphodiesterase 10A (PDE10A) plays a key role in cellular signaling by inactivation of the second messengers cAMP and cGMP. The abundant expression of PDE10A in the striatum makes this enzyme a prime target in the therapy of diseases related to this brain area, e.g. schizophrenia and movement disorders. Imaging by PET would allow to investigate the pathomechanism of such diseases and the relation to PDE10A and its expression. Therefore our aim is to develop a PET tracer for PDE10A. Recently 1-arylimidazo[1,5a]quinoxalines have been reported as very potent and selective PDE10A inhibitors.[1] This structural motif was selected as lead structure for the development of a new PET tracer.
Methods: To enable an easy incorporation of F-18 fluoride the 2-fluoropyridine moiety was chosen as fluorine containing building block. For synthesis of the reference compounds different 2-fluoropyridine boronic acids were linked to the tricyclic key intermediate by a palladium catalyzed Suzuki coupling. Characterization of these compounds was done by NMR, HRMS and HPLC. The inhibitory potency of these new fluorinated derivatives was tested in an enzyme assay towards PDE10A and further PDEs. For one candidate which was selected to be labeled with F-18 a precursor was synthesized likewise by a Suzuki coupling with 2-bromopyridine boronic acid. Different reaction conditions were tested for the one step F-18 fluoro-for-bromo substitution.
Results: A small library of reference compounds was synthesized. All compounds possess a high affinity for PDE10A (IC50 < 10 nM) with good to moderate selectivity versus other PDEs. The most selective inhibitor (IC50 = 2.91 nM) was chosen to be further developed as PET tracer. The logD7.4 value of the inhibitor (2.41 ± 0.33) was estimated by HPLC. When the precursor was reacted with F-18 fluoride in DMSO at 140°C under standard conditions (K2CO3, K222) radiolabeling efficiency of 30-50% was obtained within 10 min. At longer reaction times the labeling efficiencies decreased. A purification process including semi-preparative HPLC was established to isolate the radiotracer.
Conclusion: A new fluorinated, potent and selective PDE10A inhibitor was identified. The bromo precursor proved to be a suitable precursor for the F-18 labeling. Good conditions for the nucleophilic aromatic bromo-to-fluoro exchange were found. Further investigations of the tracer including small animal PET studies are currently underway.
Reference: [1] Malamas et. al. J. Med. Chem. 2011,54, 7621-7638.

  • Lecture (Conference)
    EANM'14 - Annual Congress of the European Association of Nuclear Medicine, 17.-22.10.2014, Göteborg, Sweden
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 41(2014)2, 197

Publ.-Id: 20538

Development, synthesis and F-18 labelling of a fluoroalkylated triazine derivative for PET imaging of phosphodiesterase 2A

Schröder, S.; Wenzel, B.; Kranz, M.; Egerland, U.; Teodoro, R.; Deuther-Conrad, W.; Fischer, S.; Höfgen, N.; Steinbach, J.; Brust, P.

Phosphodiesterases (PDEs) are a class of enzymes expressed in mammalian cells using the cyclic nucleotides cAMP and/or cGMP as secondary messengers. Inhibitors of PDEs prevent the breakdown of these molecules and thus affect various physiological processes. The PDE2A is highly and specifically expressed in the brain and in certain tumours and is involved in the pathophysiology of related diseases (e.g. neurodegenerative and highly proliferative processes). With this project we aim to develop a radiolabelled inhibitor of PDE2A for PET imaging of this new target.
Materials and Methods:
Starting from a triazine key compound [1] a new fluoropropyl derivative (9-(2-fluoro-5-(3-fluoropropoxy)phenyl)-2-methoxy-7-methylimidazo[5,1-c]pyrido[2,3-e][1,2,4]triazine) as reference structure for in vitro studies and the corresponding tosylate precursor for a one-step radiosynthesis strategy were designed and synthesised. The nucleophilic F-18 labelling was performed in acetonitrile at 80°C for 15 minutes. After isolation by semi-preparative HPLC the radioligand was purified using a Sep-Pak® C18 Plus light cartridge and formulated in 0.9% NaCl. The final product was analysed by radio-TLC and radio-HPLC. In vitro autoradiography was accomplished by incubating sagittal sections of rat brain with 1 MBq of the radioligand for
60 minutes at ambient temperature. Blocking studies were performed by addition of the triazine compound [1] in different concentrations.
The triazine key compound [1] (IC50 hPDE2A: 4.1 nM), the new fluoropropyl derivative
(IC50 hPDE2A: 11.4 nM) and the tosylate precursor were obtained with overall yields of 70 - 80%. The radioligand was synthesised with a labelling yield of 75.4 ± 4.9% (n = 5), a radiochemical yield of 57.2 ± 0.4% (end of synthesis; n = 3), a specific activity of 60.4 ± 11.6 GBq/µmol (n = 3) and a radiochemical purity of ≥ 99.5%. In first autoradiographic experiments a high and specific accumulation of the radioligand in cortex and striatum and a low uptake in cerebellum was observed, which is consistent with the distribution pattern of PDE2A protein in the brain.
A new F-18 labelled and highly affine PDE2A inhibitor was successfully developed and synthesised. Further characterisation of this new radioligand is currently performed by small animal PET/MR, metabolism studies and autoradiography.
[1] Patent WO2010/054253 A1

  • Lecture (Conference)
    EANM'14 - Annual Congress of the European Association of Nuclear Medicine, 18.-22.10.2014, Göteborg, Sweden
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 41(2014)2, 197

Publ.-Id: 20537

Development of a suitable PET ligand for the vesicular acetylcholine transporter (vAChT) - an extensive qualitative structure affinity relationship study

Barthel, C.; Wenzel, B.; Sorger, D.; Schweiger, S.; Deuther-Conrad, W.; Jäckel, P.; Roghani, A.; Schüürmann, G.; Steinbach, J.; Sabri, O.; Brust, P.

Aim: The vesicular acetylcholine transporter (vAChT) is an interesting target for in vivo imaging of cholinergic deficits. Vesamicol (2-(4-phenylpiperidin-1-yl)cyclohexanol) acts as a highly potent inhibitor for this transporter and thus represents the chemical lead for the development of vAChT radioligands. Due to its comparably high affinity towards σ1/σ2 receptors and hence its lack of selectivity it is not suitable for in vivo imaging of cholinergic neurons. The aim of our studies was to develop a selective ligand by varying the vesamicol skeleton in a systematic manner and determining the binding profile of the resulting derivatives. These in vitro data were correlated with the various chemical structures leading to an extensive qualitative structure affinity relationship study.
Materials and methods: Based on suitable epoxide precursors, the derivatives were synthesised by nucleophilic ring opening using structurally varied amines. The regioisomers resulting from asymmetrical epoxides were separated by semi-preparative HPLC and all analogues were characterised using MS, NMR, and HPLC. To obtain the binding profile of all compounds, competitive binding assays were performed in vitro with rvAChT-cDNA stably transfected PC12 cells, rat cortex (σ1), and rat liver (σ2) using (-)-[H-3]vesamicol, (+)-[H-3]pentazocine and [H-3]DTG as radioligands for vAChT, σ1, and σ2 receptor, respectively.
Results: 57 new analogues and seven reference compounds from literature were synthesised and characterised regarding to their in vitro binding profile. Based on different epoxide precursors, the lead structure of vesamicol was modified at the cyclohexyl ring A. Variations on the piperidinyl ring B and phenyl ring C, respectively, were achieved using several amines. In vitro binding studies showed vAChT affinities in the range of low nanomolar to micromolar Ki values. As expected, we found a strong variability regarding affinity and selectivity within each class of derivatives (modified in ring B and C). But surprisingly, also similar analogues from different classes (modified in ring A) varied substantially in their affinities. The resulting selectivity factors (Ki(σ1)/Ki(vAChT) and Ki(σ2)/Ki(vAChT)) ranged from 0.003 to 72.7 indicating none to moderate selectivities towards vAChT.
Conclusion: The results show a great variability of the in vitro binding profile of ligands based on the vesamicol lead structure. Even small structural changes led to unexpected changes in affinities and selectivities towards vAChT and we obtained evidence that an increased vAChT affinity correlated with an increase of σ1/σ2 receptor affinity. Based on our results we conclude that future development of a selective vAChT radioligand might be based on another lead compound.

  • Poster
    EANM'14 - Annual Congress of the European Association of Nuclear Medicine, 18.-22.10.2014, Göteborg, Sweden
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 41(2014)2, 452

Publ.-Id: 20536

The surface speciation of the ternary sorption system U(VI)/phosphate/silica

Foerstendorf, H.; Steudtner, R.; Comarmond, M. J.; Heim, K.; Müller, K.

The impact of inorganic ligands on the sorption behavior of actinide ions is commonly known. However, detailed knowledge of the molecular events occurring during the sorption processes is often lacking. In particular, the presence of inorganic anions forming actinide complexes of low solubility hampers the application of many spectroscopic approaches due to the formation of binary complexes precipitating from the aqueous solutions.
This study sustains our preliminary results on the ternary sorption system U(VI)/phosphate/silica introduced at ATAS 2012 [1]. The advanced results obtained from a combined approach of in situ vibrational and luminescence spectroscopy provide a more detailed insight into the surface speciation of this ternary sorption system.
From in situ vibrational spectroscopic sorption experiments of the binary system U(VI)/silica, infrared data exhibit the formation of a uranyl inner sphere complex at the silica surface, whereas from the ternary sorption system, spectra showing great homologies to spectra of solid U(VI)phosphate phases are obtained. The results obtained from the in situ IR experiments strongly suggest the formation of a solid U(VI)phosphate as a surface precipitate on the silica phase.
Laser fluorescence spectroscopy reveals the presence of U(VI) phosphate species in aqueous solution most probably solid or colloidal (UO2)(PO4)2∙4H2O. For the U(VI) sorption samples, two different surface species were derived from luminescence spectra irrespective of the absence or presence of phosphate [2]. However, the spectral differences became more apparent after prolonged equilibration of the solid phase with a stable U(VI) phosphate solution suggesting chemical rearrangements of the sorbed U(VI) ion towards a ternary surface species.
In summary, IR and luminescence data suggest the formation of a ternary surface species where the U(VI) acts as a bridging ion to the SiO2 surface with subsequent formation of the ternary surface species SiO2–U(VI)-phosphate. This ternary species most likely constitutes a precursor of the formation of a surface precipitate showing spectral properties similar to U(VI) phosphate minerals.

  • Poster
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, Dresden, Deutschland

Publ.-Id: 20535

Evaluation and automatic correction of metal-implant-induced artifacts in MR-based attenuation correction in whole-body PET/MR imaging

Schramm, G.; Maus, J.; Hofheinz, F.; Petr, J.; Lougovski, A.; Beuthien-Baumann, B.; Platzek, I.; van den Hoff, J.

The aim of this paper is to describe a new automatic method for compensation of metal-implant-induced segmentation errors in MR-based attenuation maps (MRMaps) and to evaluate the quantitative influence of those artifacts on the reconstructed PET activity concentration. The developed method uses a PET-based delineation of the patient contour to compensate metal-implant-caused signal voids in the MR scan that is segmented for PET attenuation correction. PET emission data of 13 patients with metal implants examined in a Philips Ingenuity PET/MR were reconstructed with the vendor-provided method for attenuation correction (MRMap(orig), PETorig) and additionally with a method for attenuation correction (MRMap(cor), PETcor) developed by our group. MRMaps produced by both methods were visually inspected for segmentation errors. The segmentation errors in MRMap(orig) were classified into four classes (L1 and L2 artifacts inside the lung and B1 and B2 artifacts inside the remaining body depending on the assigned attenuation coefficients). The average relative SUV differences (epsilon(av)(rel)) between PETorig and PETcor of all regions showing wrong attenuation coefficients in MRMap(orig) were calculated. Additionally, relative SUVmean differences (epsilon(rel)) of tracer accumulations in hot focal structures inside or in the vicinity of these regions were evaluated. MRMap(orig) showed erroneous attenuation coefficients inside the regions affected by metal artifacts and inside the patients' lung in all 13 cases. In MRMap(cor), all regions with metal artifacts, except for the sternum, were filled with the soft-tissue attenuation coefficient and the lung was correctly segmented in all patients. MRMap(cor) only showed small residual segmentation errors in eight patients. (epsilon(av)(rel)) (mean +/- standard deviation) were: (-56 +/- 3)% for B1, (-43 +/- 4)% for B2, (21+/- 18)% for L1, (120 +/- 47)% for L2 regions. epsilon(rel) (mean +/-standard deviation) of hot focal structures were: (-52 +/- 12)% in B1, (-45 +/- 13)% in B2, (19 +/- 19)% in L1, (51 +/- 31)% in L2 regions.
Consequently, metal-implant-induced artifacts severely disturb MR-based attenuation correction and SUV quantification in PET/MR. The developed algorithm is able to compensate for these artifacts and improves SUV quantification accuracy distinctly.

Publ.-Id: 20534

Modellierung und numerische Berechnung monodisperser Blasenströmungen: Ein Vergleich zweier CFD Programme

Kriebitzsch, S.; Rzehak, R.; Lucas, D.

Die numerische Simulation von der Mehrphasenströmungen in technischen Apparaten kann einen wertvollen Beitrag zum Design und zur Optimierung der Prozesse liefern, da man detaillierte Informationen über lokale Strömungsgrößen erhält. Üblicherweise sind die Apparateabmessungen deutlich größer als die charakteristische Größe der dispersen Phase, weshalb das sogenannte Zwei-Fluid-Modell verwendet wird. In diesem werden die verschiedenen Phasen als sich gegenseitig durchdringende Kontinua modelliert. Hierbei muss Wechselwirkung der Phasen durch geeignete Schließungsansätze beschrieben werden und üblicherweise stehen viele unterschiedliche Ansätze in kommerziellen CFD Programmen zu Auswahl. Ein für die Berechnung adiabater, monodisperser Blasenströmungen geeigneter Satz von Schließungsmodellen wurde in einer früheren Studie (Rzehak & Krepper, 2013) identifiziert und in der kommerziellen Software Ansys CFX verwendet.
Diese physikalischen Modelle wurden nun in das frei verfügbare Programmpaket OpenFOAM übertragen und verschiedene aufwärtsgerichtete Rohrströmungen von Luft-Wasser Gemischen berechnet und mit Experimenten verglichen. Insgesamt zeigen die Ergebnisse der Berechnungen beider Programmpakete eine vergleichbare, zufriedenstellende Übereinstimmung mit den Experimenten. Abweichungen findet man insbesondere in Wandnähe und in den turbulenten Größen.

Keywords: multiphase flow; CFD; bubbly flow

  • Poster
    ProcessNet-Jahrestagung und 31. DECHEMA-Jahrestagung der Biotechnologen 2014 - GENERALTHEMA: ProcessNet 21plus - Zukunft gestalten, 30.09.-02.10.2014, Aachen, Deutschland

Publ.-Id: 20533

Combining Luminescence Spectroscopy, Parallel Factor Analysis and Quantum Chemistry to Reveal Metal Speciation - a Case Study of Uranyl (VI) Hydrolysis

Drobot, B.; Steudtner, R.; Raff, J.; Geipel, G.; Brendler, V.; Tsushima, S.

This study of aqueous metal speciation is an advanced combination of theoretical and experimental methods. Continuous wave (CW) and time-resolved laser-induced fluorescence spectroscopy (TRLFS) data of uranyl(VI) hydrolysis were analyzed using parallel factor analysis (PARAFAC). Distribution patterns of five major species were thereby derived under a fixed uranyl concentration (10-5 M) over a wide pH range from 2 to 11. UV (180 nm to 370 nm) excitation spectra were extracted for individual species. Time-dependent density functional theory (TD-DFT) calculations revealed ligand excitation (water, hydroxo, oxo) in this region and ligand to metal charge transfer (LMCT) responsible for luminescence. Thus excitation in the UV region is extreme ligand sensitive and not unspecific. Combining findings from PARAFAC and DFT the UO22+ cation (aquo complex 1:0) and four hydroxo complexes (1:1, 3:5, 3:7 and 1:3) were identified.

Keywords: U(VI); uranyl hydrolysis; TRLFS; continuous wave spectroscopy; site selective excitation; TD-DFT; PARAFAC

Publ.-Id: 20532

Superconducting RF Guns: Emerging Technology for Future Accelerators

Teichert, J.

This talk should give an overview of Superconducting photo injectors (SRF guns) and focus on the present status of SRF gun development, the technical requirements and the critical issues like cavity design, photocathode integration, and emittance compensation methods.

Keywords: photo injector; superconducting RF; electron source; SRF gun

  • Invited lecture (Conferences)
    IPAC'14 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Germany
  • Open Access Logo Contribution to proceedings
    IPAC'14 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Germany
    Proceedings of IPAC'14: Jacow

Publ.-Id: 20531

TecLines: A MATLAB-Based Toolbox for Tectonic Lineament Analysis from Satellite Images and DEMs, Part 1: Line Segment Detection and Extraction

Rahnama, M.; Gloaguen, R.

Geological structures, such as faults and fractures, appear as image discontinuities or lineaments in remote sensing data. Geologic lineament mapping is a very important issue in geo-engineering, especially for construction site selection, seismic, and risk assessment, mineral exploration and hydrogeological research. Classical methods of lineaments extraction are based on semi-automated (or visual) interpretation of optical data and digital elevation models. We developed a freely available Matlab based toolbox TecLines (Tectonic Lineament Analysis) for locating and quantifying lineament patterns using satellite data and digital elevation models. TecLines consists of a set of functions including frequency filtering, spatial filtering, tensor voting, Hough transformation, and polynomial fitting. Due to differences in the mathematical background of the edge detection and edge linking procedure as well as the breadth of the methods, we introduce the approach in two-parts. In this first study, we present the steps that lead to edge detection. We introduce the data pre-processing using selected filters in spatial and frequency domains. We then describe the application of the tensor-voting framework to improve position and length accuracies of the detected lineaments. We demonstrate the robustness of the approach in a complex area in the northeast of Afghanistan using a panchromatic QUICKBIRD-2 image with 1-meter resolution. Finally, we compare the results of TecLines with manual lineament extraction, and other lineament extraction algorithms, as well as a published fault map of the study area.

Keywords: TecLines; Matlab; tectonic; lineament; edge detection; tensor voting

Publ.-Id: 20530

How Forward Integration Along the Rare Earth Value Chain Threatens the Global Economy

van den Boogaart, K. G.; Klossek, P.; Klossek, A.

At the moment the first steps of the REE value chain are already dominated by a monopolistic power. Current developments, however, show a tendency of a monopolistic takeover of the subsequent steps of the value chain with finally having control over the whole chain. Such tendency, in our view, represents a serious threat to the key industries in the ROW and, therefore, to the global economy.

The takeover of subsequent steps is induced by the price differences between domestic prices and the world market price, which is dominated by the monopolist’s FOB (free on board) price, and executed by so created market forces. The rebuilding of the first steps in ROW (rest of world) like REE mining, processing and soon separation is demotivated by the de facto monopoly on the subsequent steps controlling the products markets and, possibly, by a well chosen price policy. The strategic dominance of the monopolist creates enormous price risks scaring off independent investment into the ROW value chain. Likewise, it generates a default risk scaring off strategic investors. Investment in ROW enterprises and JVs (joint ventures) are other important tools of the monopolist to gain control over the value chain with respect to technological know-how, business relations, and production capacity. This takeover seems to be a part of a well-planned long-term strategy of a major state actor and requires cooperative actions of industry and state in ROW in order to stop this dangerous trend.

  • Invited lecture (Conferences)
    Critical Minerals 2014, Rare earths and beyond, mines, markets, and manufacturing, 03.-05.08.2014, Denver, USA

Publ.-Id: 20528

Surface modifications of BaF2 and CaF2 single crystals by slow highly charged ions

El-Said, A. S.; Heller, R.; Wilhelm, R.; Facsko, S.; Aumayr, F.

Ion-irradiation of solid surfaces is considered as one of the promising and powerful techniques for material nanostructuring. Recently, slow highly charged ions (HCI) have shown their potential in creating surface nanostructures in various solids. Here, we focus on the surface modifications of BaF2 and CaF2 single crystals by HCI. Despite the fact that both materials belong to alkaline-earth fluorides with the same crystalline structure, they exhibit different sensitivity for HCI-induced nanostructure. We discuss similarities and differences for the creation of HCI-induced nanohillocks and etch pits in both materials and their dependence on potential and kinetic energy deposition. Furthermore, we compare the results with modifications induced by swift heavy ions (SHI), in order to reach a better understanding of the mechanisms responsible for the creation of nanostructures in ionic fluoride single crystals.

Keywords: Highly charged ions; Nanostructures; Ion–surface interaction; BaF2; CaF2

Publ.-Id: 20527

Investigation of H+ implanted Fe-Al alloys

Lukac, F.; Cizek, J.; Prochazka, I.; Jiraskova, Y.; Janickovic, D.; Simeg Veternikova, J.; Anwand, W.; Butterling, M.

In the present work hydrogen interaction with vacancies was investigated in Fe-Al alloys with various concentration of vacancies. The Fe-Al samples were implanted with low energy H+ ions (100 keV). This procedure introduced high hydrogen concentration into relatively narrow sub-surface region in the depth of ~500 nm. Variable energy positron annihilation spectroscopy (VEPAS) was employed for investigation of hydrogen interaction with vacancies in the sub-surface region. This study revealed formation of vacancy hydrogen complexes in the sub-surface region. Thermal stability of vacancy-hydrogen complexes was investigated as well.

Keywords: FeAl alloys; hydrogen implantation; vacancies; positron annhilation

Publ.-Id: 20526

Bayes Hilbert Spaces

van den Boogaart, K. G.; Egozcue, J. J.; Pawlowsky-Glahn, V.

A Bayes linear space is a linear space of equivalence classes of proportional -finite measures, including probability measures. Measures are identified with their density functions. Addition is given by Bayes’ rule and substraction by Radon–Nikodym derivatives. The present contribution shows the subspace of square-log-integrable densities to be a Hilbert space, which can include probability and infinite measures, measures on the whole real line or discrete measures. It extends the ideas from the Hilbert space of densities on a finite support towards Hilbert spaces on general measure spaces. It is also a generalisation of the Euclidean structure of the simplex, the sample space of random compositions. In this framework, basic notions of mathematical statistics get a simple algebraic interpretation. A key tool is the centred-log-ratio transformation, a generalization of that used in compositional data analysis, which maps the Hilbert space of measures into a subspace of square-integrable functions. As a consequence of this structure, distances between densities, orthonormal bases, and Fourier series representing measures become available. As an application, Fourier series of normal distributions and distances between them are derived, and an example related to grain size distributions is presented. The geometry of the sample space of random compositions, known as Aitchison geometry of the simplex, is obtained as a particular case of the Hilbert space when the measures have discrete and finite support.

Keywords: Aitchison geometry of the simplex; distance between measures; Fourier coefficients; infinite measures; normal distribution; perturbation; probability measures

  • Australian & New Zealand Journal of Statistics 56(2014)2, 171-194
    DOI: 10.1111/anzs.12074

Publ.-Id: 20525

A quasi-likelihood approach to parameter estimation for simulatable statistical models

Baaske, M.; Ballani, F.; van den Boogaart, K. G.

This paper introduces a parameter estimation method for a general class of statistical models. The method exclusively relies on the possibility to conduct simulations for the construction of interpolation-based metamodels of informative empirical characteristics and some subjectively chosen correlation structure of the underlying spatial random process. In the absence of likelihood functions for such statistical models, which is often the case in stochastic geometric modelling, the idea is to follow a quasi-likelihood (QL) approach to construct an optimal estimating function surrogate based on a set of interpolated summary statistics. Solving these estimating equations one can account for both the random errors due to simulations and the uncertainty about the meta-models. Thus, putting the QL approach to parameter estimation into a stochastic simulation setting the proposed method essentially consists of finding roots to a sequence of approximating quasiscore functions. As a simple demonstrating example, the proposed method is applied to a special parameter estimation problem of a planar Boolean model with discs. Here, the quasi-score function has a half-analytical, numerically tractable representation and allows for the comparison of the model parameter estimates found by the simulation-based method and obtained from solving the exact quasi-score equations.

Keywords: Keywords: kriging meta-modelling; parameter estimation; quasi-likelihood; simulation-based optimization

Publ.-Id: 20524

Structural studies of thin Mg films

Hruska, P.; Cizek, J.; Anwand, W.; Bulir, J.; Lancok, J.; Straska, J.; Melikhova, O.; Prochazka, I.

In the present work variable energy positron annihilation spectroscopy (VEPAS) was employed for investigation of defects in Mg films. VEPAS characterization was combined with scanning electron microscopy and X-ray diffraction in order to determine grain size and texture, respectively. The aim of this study was to examine the effect of deposition temperature and various substrates on structure and defects in Mg films prepared by RF magnetron sputtering. SEM observations revealed that films deposited on sapphire (0001) substrate exhibit always smaller grains than films deposited on amorphous fused silica and silicon (100) substrates, which have comparable grain size. Defect studies by VEPAS showed that positrons in Mg films studied are trapped at misfit dislocations and at vacancy-like defects in grain boundaries. Moreover, the films deposited on a substrate heated at 300°C exhibited lower concentration of defects and larger grain size compared to the films deposited at room temperature. Subsequent annealing at 300°C for 1 h of the films deposited at room temperature causes a slight decrease of defect density due to coarsening of grains.

Keywords: Mg films; RF magnetron sputtering; defects; positron annihilation

Publ.-Id: 20523

A study of the structural and magnetic properties of ZnO implanted by Gd ions

Macková, A.; Malinsky, P.; Sofer, Z.; Šimek, P.; Sedmidubsky, D.; Mikulics, M.; Wilhelm, R. A.

The structural and magnetic properties of ZnO (0 0 0 1) single crystals implanted with 200 keV Gd ions up to a fluence of 5 × 1015 cm−2 and subsequently annealed at 800 °C in various atmospheres were studied. The chemical composition and concentration depth profiles of ion-implanted layers were characterised by Rutherford Back-Scattering spectrometry (RBS) and compared to SRIM simulations. The as-implanted Gd depth profiles were found to be broader than those simulated by SRIM, but the projected range coincided well with that simulated. After annealing at 800 °C, the depth profiles became narrower. The structural changes in the layers modified by ion implantation and subsequent annealing were characterised by RBS channelling. The annealing led to partial recrystallisation and a decrease in the number of Gd atoms situated in substitutional positions. Raman spectroscopy showed that the point defects in Zn and O vacancies had been created by implantation and that these defects are most effectively cured after annealing in oxygen atmosphere. AFM analysis was used to determine the surface-morphology changes after the implantation and annealing procedures. The as-implanted samples exhibited ferromagnetism persisting up to room temperature. The annealing procedure led to paramagnetic behaviour, probably caused by the formation of gadolinium clusters.

Keywords: ZnO; Gd implantation; Depth profiles; RBS channelling; Raman spectroscopy; AFM

Publ.-Id: 20522

A combinatorial study of the mechanical and magnetic properties of a gradually nitrided austenitic stainless steel single crystal

Menéndez, E.; Templier, C.; Abrasonis, G.; Lopez-Barbera, J. F.; Nogués, J.; Temst, K.; Sortef, J.

The mechanical and magnetic properties of a nitrided austenitic stainless steel are studied using a combinatorial approach. Plasma nitriding of a [100]-oriented 316L single crystal is carried out using a loose shadow mask to produce an in-plane lateral gradient of nitrogen concentration that extends up to 100 μm. The local mechanical and magnetic properties across the gradually nitrided area are resolved by nanoindentation and the polar magneto-optic Kerr effect, respectively. The hardness, reduced Young's modulus and remanence qualitatively depict the nitrogen profile, suggesting that the nitrogen concentration is a central effect for these observed dependencies. Conversely, the coercivity exhibits a non-monotonic behaviour due to the interplay between magnetic anisotropy and the strength of the induced ferromagnetism. Fingerprints of the expected transition from a nitrogen supersaturated solid solution to a multiphase nature of expanded austenite are evidenced along the gradually nitrided area.

Keywords: Austenitic stainless steel; plasma nitriding; magnetic and mechanical properties

Publ.-Id: 20521

The structural changes and optical properties of LiNbO3 after Er implantation using high ion fluencies

Macková, A.; Malinsky, P.; Pupíková, H.; Nekvindová, P.; Cajzl, J.; Sofer, Z.; Wilhelm, R. A.; Kolitsch, A.; Oswald, J.

The structural and compositional changes of LiNbO3 implanted with 190 keV Er+ ions into various crystallographic cuts with fluencies of 1 × 1016 and 5 × 1016 cm−2 were studied. The effect of post-implantation annealing at 1000 °C in oxygen atmosphere was also examined. Concentration depth profiles of implanted erbium, determined by Rutherford Backscattering Spectrometry (RBS), are broader than those from the SRIM simulation. The maximum erbium concentration (of up to 8 at.%) is observed at the depth of about 50 nm, for all crystal cuts. The structure of the implanted layers were characterised by RBS-channelling method. The lower relative number of disordered atoms in the crystalline matrix was observed in the lithium niobate (LN) implanted at a fluence of 1 × 1016 cm−2, where also the preferential position of the erbium in substitutional sites was observed when compared to the randomly distributed erbium in interstitial positions at a fluence of 5 × 1016 cm−2 after the annealing. Surface-morphology changes at the highest implantation fluencies were studied using Atomic Force Microscopy (AFM). Since we were interested in the relation between the structural changes and optical properties, erbium luminescence properties were measured in the region of 1440–1650 nm. The positive effect of post-implantation annealing on the luminescence properties caused by structural recovery was proved.

Keywords: Implanted lithium niobate; Erbium implantation; RBS channeling structural study; Luminesent properties

Publ.-Id: 20520

Europium(III) lactate structure determination using spectroscopic (ATR FT-IR, NMR) and theoretical (DFT) methods

Barkleit, A.; Kretzschmar, J.; Tsushima, S.; Acker, M.

Small organic molecules like lactic acid (HO-CH(CH3)-COOH), which can bind heavy metal ions, are ubiquitous in nature. They can be found in nearly all biological systems as a product of various biochemical processes and in the geosphere as well, i.e. as part of organic matter of argillaceous rocks. This renders lactate a suitable model molecule for a multi-technique structure determination. Eu(III) was chosen as non-radioactive model for trivalent actinides.
Current structural suggestions for the Eu(III) lactate are only assumptions from indirect methods [1,2]. We want to provide direct structural information. ATR FT-IR spectroscopy combined with calculations of structure and spectroscopic data using DFT reveals structural features. Lanthanide induced shifts (LIS) in NMR spectroscopy as caused by the interaction of nuclear spins with electronic unpaired spins can be used as a helpful tool for signal separation, probing the potential binding sites and structure including geometries and distances [3].
The combination of all these methods offers new insights concerning the structure of the Eu(III) lactate 1:1 complex thereby resolving contradictions in the previous works whether the hydroxyl group is protonated or not.
From ATR FT-IR measurements, bidentate coordination of exclusively the carboxylate group could be ruled out because of the characteristic degree of spectral splitting of the asymmetric and symmetric stretching vibrations νas and νs of the carboxylate group. The best accordance of the DFT calculated vibrational spectra to the measured spectrum is given for monodentate coordinating carboxylate group and additional coordination of the deprotonated hydroxyl group (Fig. 1). NMR findings strongly support the results obtained from ATR FT-IR measurements in combination with DFT calculations. The correlation between the chemical shift changes of the 13C NMR signals and the Eu-C distances calculated by DFT suites perfectly this structure model [4].
The finding that the hydroxyl group seems to be deprotonated under complex formation [4] contradicts former structure suggestions, which suppose a coordination of the trivalent metal ion with the protonated hydroxyl group [1,2]. Both experimental methods, ATR FT-IR and NMR, as well as the DFT calculations yielded an impressively homogeneous structural explanation of the investigated Eu(III) lactate 1:1 species.

[1] Tian, G.X. et al. (2010) Inorg. Chem. 49, 10598-10605.
[2] Dickins, R.S. et al. (2002) J. Am. Chem. Soc. 124, 12697-12705.
[3] Mayo, B.C. (1973) Chem. Soc. Rev. 2, 49-74.
[4] Barkleit, A. et al. (2014) Dalton Trans. DOI: 10.1039/c4dt00440j

  • Poster
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, Dresden, Deutschland
  • Open Access Logo Contribution to proceedings
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, Dresden, Deutschland
    Wissenschaftlich-Technische Berichte HZDR-054: Helmholtz-Zentrum Dresden-Rossendorf

Publ.-Id: 20519

Introduction to the Minimum Rainbow Subgraph problem

Matos Camacho, S.

Consider an p edge coloured graph G, then a Minimum Rainbow Subgraph is a subgraph H of G of minimum order, such that every colour occurs in H. This phd thesis provides a comprehensive introduction to this problem.

Keywords: graph theory; chromatic index; colouring

  • Doctoral thesis
    TU Bergakademie Freiberg, 2012
    Mentor: Prof. Dr. Ingo Schiermeyer
    59 Seiten

Publ.-Id: 20518

The rainbow connection number of 2-connected graphs

Ekstein, J.; Holub, P.; Kaiser, T.; Koch, M.; Matos Camacho, S.; Ryjáček, Z.; Schiermeyer, I.

The rainbow connection number of a graph G is the least number of colours in a (not necessarily proper) edge-colouring of G such that every two vertices are joined by a path which contains no colour twice. Improving a result of Caro et al., we prove that the rainbow connection number of every 2-connected graph with n vertices is at most ⌈n/2⌉. The bound is optimal.

Keywords: Rainbow connection number; Graph; Connectivity

Publ.-Id: 20517

Algorithmic approaches for the minimum rainbow subgraph problem

Koch, M.; Matos Camacho, S.; Schiermeyer, I.

We consider the Minimum Rainbow Subgraph problem (MRS): Given a graph G, whose edges are coloured with p colours. Find a subgraph F⊆G of minimum order and with p edges such that each colour occurs exactly once. This problem is APX-hard. In this paper we will show that the Greedy algorithm for the MRS problem has an approximation ratio of Δ/2 + (lnΔ+1)/2 for graphs with maximum degree Δ. If the average degree d of a minimum rainbow subgraph is known, then the approximation ratio is d/2 + (ln[d]+1)/2.

Keywords: 10.1016/j.endm.2011.10.028

Publ.-Id: 20516

Approximation algorithms for the minimum rainbow subgraph problem

Matos Camacho, S.; Schiermeyer, I.; Tusa, Z.

We consider the minimum rainbow subgraph problem (MRS): given a graph G, whose edges are coloured with p colours. Find a subgraph F⊆G of G of minimum order and with p edges such that each colour occurs exactly once. For graphs with maximum degree Δ(G) there is a greedy polynomial-time approximation algorithm for the MRS problem with an approximation ratio of Δ(G). In this paper we present a polynomial-time approximation algorithm with an approximation ratio of View the MathML source for Δ≥2.

Keywords: Edge colouring; Minimum rainbow subgraph; Approximation algorithm

Publ.-Id: 20515

Colourings of graphs with prescribed odd cycle lengths

Matos Camacho, S.; Schiermeyer, I.

In 1992 Gyárfás showed that a graph G having only k odd cycle lengths is (2k+1)-colourable, if it does not contain a K2k+2. In this paper, we will present the results for graphs containing only odd cycles of length 2m−1 and 2m+1 as done in [S. Matos Camacho, Colourings of graph with prescribed cycle lengths, diploma thesis, TU Bergakademie Freiberg, 2006. [3]]. We will show that these graphs are 4-colourable.

Keywords: Colouring; Cycles; Chromatic number

Publ.-Id: 20514

Studying the constancy of the galactic cosmic rays using cosmogenic noble gases and radionuclides on iron meteorites

Smith, T.; Leya, I.; Merchel, S.; Rugel, G.; Pavetich, S.; Wallner, A.; Fifield, K.; Tims, S.; Korschinek, G.

Introduction: The constancy of the galactic cosmic rays (GCR) is a long-standing question in meteorite research. The temporal variability of GCR intensities over the last billion years can be investigated studying meteorites [1]. Indeed, during their travel in space, meteoroids are exposed to GCRs; the interactions producing (among others) stable and radioactive cosmogenic nuclides. Being interested in the long-term GCR variability, we study iron meteorites because they typically have cosmic ray exposure (CRE) ages in range of a few hundred millions years (Myr) and – for some – even up to two billion years [2]. It has been demonstrated that periodic GCR flux variations can induce peaks in CRE age histograms. Therefore, setting up a consistent exposure age histogram and searching for periodic peaks permits us to study hypothetical GCR flux variations.
Experimental methods: Noble gas isotopes (He, Ne, and Ar) are analyzed by noble gas mass spectrometry at the University of Bern, using two self-made mass spectrometers [3,4]. Analyses of the cosmogenic radionuclides (10Be, 26Al, 36Cl, and 41Ca) are performed at the DREsden Accelerator Mass Spectrometry facility (DREAMS, [5]) adapted from the procedure described in [6].
Results: So far, 28 iron meteorite samples, mainly of class IIIAB, have been investigated for their noble gas and cosmogenic radionuclide contents. The first terrestrial ages have been deter-mined using the 36Cl/10Be-10Be method [1]. They range between 10 kyr and 500 kyr. Because doubts exist on the use of 26Al, 21Ne and probably 10Be as proxies for CRE age determination, due to inhomogeneous sulfur and phosphorus distribution [3,7], the CRE ages were calculated using the radioactive-stable nuclide pair 36Cl-36Ar, as described in [1]. The calculated ages range between ~5 and ~700 Myr, which is in the expected range for iron meteorites [2,8]. Additionally, the first 53Mn and 60Fe measurements have been performed at the Australian National University (ANU) and at the TUM in Munich. On the CRE ages histogram, two peaks, centered at ~50 and ~350 Myr are visible, but statistics are still poor. Additional measurements of iron meteorites are thus needed and ongoing, that will help to study possible variation in the GCR intensities over the last billion years.
References: [1] Lavielle B. et al. 1999. Earth Planetary and Science Letters 170:93–104. [2] Wieler R. et al. 2013. Space Science Reviews 176:351-363. [3] Ammon K. et al. 2008. Meteoritics and Planetary Science 43:685-699. [4] Ammon K. et al. 2011. Meteoritics and Planetary Science 46:785-792. [5] Akhmadaliev S. et al. 2013. Nuclear Instruments and Methods in Physic B 294:5-10. [6] Merchel S. and Herpers U. 1999. Radiochimica Acta 84:215-219. [7] Ott U. et al., Meteoritics and Planetary Science, in press. [8] Eugster O. et al. 2006. Meteorites and the Early Solar System II, Part IX: 829-851.

Keywords: GCR; AMS; accelerator mass spectrometry; cosmogenic nuclide; cosmic radiation

  • Lecture (Conference)
    77th Annual Meeting of the Meteoritical Society, 07.-12.09.2014, Casablanca, Marocco
  • Abstract in refereed journal
    Meteoritics & Planetary Science 49(2014), A371


Publ.-Id: 20513

Temperature dependence of ion-beam mixing in crystalline and amorphous germanium isotope multilayer structures

Radek, M.; Bracht, H.; Posselt, M.; Liedke, B.; Schmidt, B.; Bougeard, D.

The renewed interest in Germanium as base material for electronic applications has stimulated extensive experimental and theoretical studies. Successful integration of Ge in nanoelectronic devices requires fundamental understanding of ion-implantation-induced target modification and damage. In this contribution the temperature dependence of ion-beam mixing induced by 310 keV gallium (Ga) ion implantation in crystalline and preamorphized germanium (Ge) is reported. Isotopically enriched multilayer structures of alternating 70Ge and natGe layers are used to visualize the self-atom mixing. The distribution of the implanted Ga atoms and the ion-beam induced self-atom mixing was determined by means of secondary ion mass spectrometry. Different temperature regimes of self-atom mixing are observed. At temperatures up to 423 K the mixing is independent of the initial structure whereas at 523 K the intermixing of the preamorphized Ge structure is about twice as high as that of the crystalline material. At 623 K the intermixing of the initially amorphous Ge structure is strongly reduced and approaches the mixing of the crystalline material. The temperature dependence of ion-beam mixing is consistently described by competitive amorphization and recrystallization processes.

Keywords: ion beam mixing; isotopically enriched multilayer structures; amorphous germanium; self mixing; thermal spike

  • Lecture (Conference)
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France

Publ.-Id: 20512

Formation, coarsening and band gap engineering of sponge-like Si-SiO2 nanocomposites – materials design by theoretical predictions

Liedke, B.; Heinig, K. H.; Friedrich, D.; Schmidt, B.; Mücklich, A.; Hübner, R.; Keles, U.; Bulutay, C.

It has been found by energy filtered transmission electron microscopy (EFTEM) that metastable SiOx≈1 films decay during thermal treatment by spinodal decomposition into a Si nanowire network embedded in SiO2 forming a nanocomposite [1,2]. This nanoscale material is promising candidate as absorber layer for next generation solar cells as it exhibits a widened band gap due to quantum confinement and electrical interconnectivity due to percolation of the nanostructured Si. The formation of Si-SiO2 nanocomposites was predicted by a kinetic Monte Carlo simulations [1,3]. Additionally, the band gap and the band offset of the nanocomposite were predicted by large scale atomistic pseudopotential computations [4]. Experimentally, the sponge-like morphology was verified by EFTEM and atom probe tomography [2], whereas its band gap measured via light absorption is still under discussion. The predicted morphology of the sponge-like Si-SiO2 nanocomposite appears to be almost identical to the measured ones. Also the predicted scaling behavior of the coarsening of the nanostructure during thermal treatment was verified experimentally. Combining theory with experiments delivers the understanding for tailoring the properties like quantum confinement of the sponge-like Si. [1] Müller, et al. Appl. Phys. Lett. 85, 2373 (2004) [2] Friedrich, et al. Appl. Phys. Lett. 103, 133106 (2013) [3] Liedke, et al. Appl. Phys. Lett. 103, 131911 (2013) [4] Keles, et al. Appl. Phys. Lett. 103, 203103 (2013)

Keywords: sponge; Si-SiO2 nanocomposite; kinetic Monte-Carlo; modeling; EFTEM; PV; nanostructure

  • Lecture (Conference)
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France

Publ.-Id: 20511

Sponge-like Si-SiO2 nanocomposite absorber for next generation PV cells

Liedke, B.; Friedrich, D.; Schmidt, B.; Heinig, K. H.; Mücklich, A.; Hübner, R.; Wolf, D.; Kölling, S.

To increase the market share of Si-based thin film PV cells their efficiency has to be improved without increasing of the module costs. Sponge-like Si-SiO2 nanocomposite has a potential to be a low cost and efficient absorber for next generation PV. It consists of Si embedded in SiO2 fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide SiOx≈1. Thermal treatment using rapid thermal processing and furnace annealing requires annealing times of few tens of sec. up to few tens of min. However, in a thin film technology the phase separation of SiOx at high temperatures requires a very rapid thermal processing of few tens of ms in order to avoid substrate damage. Here, the structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography and atom probe tomography which revealed a percolated Si morphology [1]. This is in excellent agreement with atomistic simulations using kinetic Monte-Carlo method [2]. Depending on the annealing time and temperature a feature size in the range of 2..5 nm was found, which is small enough for band gap widening due to quantum confinement [3]. We show that the favorable properties of Si-SiO2 nanocomposite, e.g. quantum size effect and percolated morphology, make it a suitable material for PV absorber. [1] Friedrich, et al. Appl. Phys. Lett. 103,133106(2013) [2] Liedke, et al. Appl. Phys. Lett. 103,131911(2013) [3] Keles, et al. Appl. Phys. Lett. 103,203103(2013)

Keywords: sponge; Si-SiO2 nanocomposite; PV; quantum confinement; absorber; thin-film solar cells

  • Poster
    EMRS 2014 Spring Meeting, 26.-30.05.2014, Lille, France

Publ.-Id: 20510

Structural studies of thin Pd films loaded with hydrogen

Melikhova, O.; Cizek, J.; Vlcek, M.; Lukac, F.; Prochazka, I.; Anwand, W.; Brauer, G.

In this work variable energy positron annihilation spectroscopy was employed for investigation of defects created in Pd films electrochemically charged with hydrogen. The development of hydrogen-induced defects in nanocrystalline, polycrystalline and epitaxial Pd films were compared. It was found that absorbed hydrogen causes plastic deformation and increases defect density in all Pd films studied. Moreover, buckling was observed in nanocrystalline and polycrystalline films loaded above certain critical hydrogen concentration.

Keywords: Pd films; hydrogen loading; defects; positron annihilation

Publ.-Id: 20509

Sintering of zirconia-based nanomaterials studied by variable-energy slow-positron beam

Prochazka, I.; Cizek, J.; Melikhova, O.; Anwand, W.; Brauer, G.; Konstantinova, T. E.; Danilenko, I. A.

A variable-energy slow-positron beam was applied to the investigations of the tetragonal yttria-stabilised zirconia (YSZ), the YSZ co-doped with small amount of Cr2O3. The initial nanopowders exhibiting the mean particle size of ≈ 20 nm were prepared by co-precipitation technique. Prior the sintering, the nanopowders were calcined and compacted using a pressure of 500 MPa. The ordinary shape parameters of the Doppler-broadened annihilation peak and the relative positronium 3γ-fractions were determined as functions of positron energy. The results are consistent with a remarkable sintering-induced grain growth and disappearance of porosity which is driven out from the sample interior toward a thin sub-surface layer.

Keywords: yttria-stabilised zirconia; sintering; positronium; positron annihilation

Publ.-Id: 20508

Defect studies of thin ZnO films prepared by pulsed laser deposition

Vlcek, M.; Cizek, J.; Prochazka, I.; Novotny, M.; Bulir, J.; Lancok, J.; Anwand, W.; Brauer, G.; Mosnier, J. P.

Thin ZnO films were grown by pulsed laser deposition on four different substrates: sapphire (0 0 0 1), MgO (1 0 0), fused silica and nanocrystalline synthetic diamond. Defect studies by slow positron implantation spectroscopy (SPIS) revealed significantly higher concentration of defects in the studied films when compared to a bulk ZnO single crystal. The concentration of defects in the films deposited on single crystal sapphire and MgO substrates is higher than in the films deposited on amorphous fused silica substrate and nanocrystalline synthetic diamond. Furthermore, the effect of deposition temperature on film quality was investigated in ZnO films deposited on synthetic diamond substrates. Defect studies performed by SPIS revealed that the concentration of defects firstly decreases with increasing deposition temperature, but at too high deposition temperatures it increases again. The lowest concentration of defects was found in the film deposited at 450°C.

Keywords: ZnO films; pulsed laser deposition; defects; positron annihilation

Publ.-Id: 20507

Paleoarchean sulfur cycling: multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa

Montinaro, A.; Strauss, H.; Mason, P. R. D.; Roerdink, D.; Münker, C.; Schwarz-Schampera, U.; Arndt, N.; Farquhar, J.; Beukes, N.; Gutzmer, J.; Peters, M.

Mass-dependent and mass-independent sulfur isotope fractionation archived in volcanic and sedimentary rocks from the Barberton Greenstone Belt (3550–3215 Ma), South Africa, provide constraints for sulfur cycling on the early Earth. Four different samples suites were studied: komatiites and tholeiites, barite, massive and disseminated sulfide ores, and non-mineralized black shales. Previous multiple sulfur isotope centered either on specific areas and/or lithologies from the Barberton Greenstone Belt, while this study provides results for a much wider sample selection across the stratigraphic succession.
Variable but generally slightly positive δ34S values between -0.7 and +5.0‰, negative Δ33S values between -0.51 and -0.09‰, and a negative correlation between δ34S and Δ33S as well as between Δ33S and Δ36S for komatiites and tholeiites from the Komati Formation and from the Weltevreden Formation are outside the expected range of unfractionated juvenile sulfur. Instead, results indicate variable degrees of alteration through ambient seawater during serpentinisation of these rocks.
Barite from the Mapepe Formation displays positive δ34S values between 3.1 and 8.1‰ and negative Δ33S values between -0.77 and -0.34‰. Moreover, samples reveal a linear negative correlation between Δ33S and Δ36S with a slope of -0.7. The mass-independent sulfur isotope fractionation indicates an atmospheric sulfur source, whereas the positive δ34S values suggest bacterial sulfate reduction of the marine sulfate reservoir. The latter process is further discernible through a weak positive correlation between δ34S and δ18O of the barite.
Non-mineralized black shales from the presumed stratigraphic equivalent of the Mapepe Formation show positive δ34S values between 0.0 and 1.2‰ and positive Δ33S values between 0.59 and 2.48‰. These results are interpreted to result from the mixing between the two principal atmospheric sources, i.e. elemental sulfur, carrying a positive Δ33S signature and sulfate, carrying a negative Δ33S value, with its δ34S signature subsequently modified through bacterial sulfate reduction.
Positive δ34S values ranging from +0.5 to +3.4‰ and slightly negative Δ33S values between -0.17 and -0.13‰ characterize massive and disseminated sulfides from the Bien Venue Prospect. Results suggest a mixture between the unfractionated juvenile magmatic sulfur source and a contribution from recycled seawater sulfate indicative of submarine hydrothermal activity. Considering the isotope values, these three sets of samples show a common source of sulfur, characterized by negative Δ33S and positive Δ36S, represented by seawater sulfate.
Massive and disseminated sulfides from the M’hlati prospect are characterized by different values compared to massive and disseminated sulfide from the Bien Venue Prospect. They show negative δ34S values between -1.4 and -0.1‰ and positive Δ33S values between +2.66 and +3.17‰, thus, displaying a sizeable mass-independent sulfur isotopic fractionation. Again, these samples clearly exhibit the incorporation of an atmospheric MIF-S signal. The source of sulfur for these samples has positive Δ33S values, thus this is related to elemental sulfur.
In conclusion, the sulfur isotope inventories in the Paleoarchean rocks and hydrothermal precipitates from the Barberton Greenstone Belt are quite diverse and indicate the incorporation of at least two sources of sulfur. Komatiites and tholeiites, barite and massive and disseminated sulfides from Bien Venue show a common sulfur source, related to seawater sulfate, while massive and disseminated sulfides from M’hlati are related to elemental sulfur and not mineralized black shales with a mixing between these two sulfur sources.

Keywords: Archean; multiple sulfur isotopes; Barberton Greenstone Belt

Publ.-Id: 20506

Untersuchung von Gammakaskaden und Stärkefunktionen in der Neutroneneinfangsreaktion 77Se(n,γ)

Robert, J.

Eine der wichtigsten nuklearen Prozesse stellt der Neutroneneinfang dar. In der kosmischen Nukleosynthese (s-Prozess) schwerer Elemente werden Kerne mit Massenzahlen größer als die von Eisen (A = 56) produziert, welche durch Kernfusion nicht produziert werden können. Dabei fängt ein Kern ein Neutron ein, wird durch die frei werdende Bindungsenergie angeregt und kann sich anschließend unter Aussenden von Photonen (Gamma-Quanten) wieder abregen. Aus der Abregung über Gammastrahlung können Rückschlüsse auf die Struktur des aktivierten Nuklids gezogen werden. Im Rahmen dieser Arbeit werden die ausgesendeten Photonen des angeregten Elements 78Se, welches durch Neutroneneinfang an 77Se am Reaktor des Instituts Laue-Langevin in Grenoble, Frankreich produziert wurde, näher untersucht. Dazu mussten zunächst Effizienzkalibrierung und Addback-Korrekturen vorgenommen werden. Im Anschluss konnten mit Hilfe des EXILL-Multidetektoraufbaus Koinzidenzbeziehungen mehrerer aufeinander folgender Photonen untersucht und in einem Niveauschema zusammengefasst werden. Mit Hilfe der Winkelverteilung konnten diversen Zuständen Spins zugeordnet werden. Des Weiteren wurden die Ergebnisse einer Simulation von Gammakaskaden (DEX) und eines Photonenstreuungsexperiments am Elektronenbeschleuniger ELBE des HZDR mit den in Grenoble aufgenommenen experimentellen Daten verglichen.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-046 2014
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 20505

Analysis and simulation of photon scattering and neutron capture gamma spectra

Schramm, G. A.

Within this thesis two twin experiments consisting of neutron capture and photon scattering on the neighbour isotopes 77Se / 78Se and 195Pt / 196Pt have been analysed to gain qualitative and quantitative information about the photon strength function and level density in the respective compound nuclei. For the analysis and simulation of both experimental types a new Monte Carlo simulation using a fast and efficient, extreme statistical treatment of radiative nuclear deexcitations, was developed. Furthermore the influence of fluctuations of transition widths on photon scattering were investigated and quantified. It could be shown that those lead to an enhancement of elastic scattering processes. The data analysis of both twin experiments reveals non-Lorentzian extra E1 photon strength below the neutron separation energy.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-045 2014
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 20504

Positron Emission Tomography for the dose monitoring of intra-fractionally moving Targets in ion beam therapy

Stützer, K.

Ion beam therapy (IBT) is a promising treatment option in radiotherapy. The characteristic physical and biological properties of light ion beams allow for the delivery of highly tumour conformal dose distributions. Related to the sparing of surrounding healthy tissue and nearby organs at risk, it is feasible to escalate the dose in the tumour volume to reach higher tumour control and survival rates. Remarkable clinical outcome was achieved with IBT for radio-resistant, deep-seated, static and well fixated tumour entities. Presumably, more patients could benefit from the advantages of IBT if it would be available for more frequent tumour sites. Those located in the thorax and upper abdominal region are commonly subjected to intra-fractional, respiration related motion. Different motion compensated dose delivery techniques have been developed for active field shaping with scanned pencil beams and are at least available under experimental conditions at the GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt, Germany.
High standards for quality assurance are required in IBT to ensure a safe and precise dose application. Both underdosage in the tumour and overdosage in the normal tissue might endanger the treatment success. Since minor unexpected anatomical changes e.g. related to patient mispositioning, tumour shrinkage or tissue swelling could already lead to remarkable deviations between planned and delivered dose distribution, a valuable dose monitoring system is desired for IBT. So far, positron emission tomography (PET) is the only in vivo, in situ and non-invasive qualitative dose monitoring method applied under clinical conditions. It makes use of the tissue autoactivation by nuclear fragmentation reactions occurring along the beam path. Among others, +-emitting nuclides are generated and decay according to their half-life under the emission of a positron. The subsequent positron-electron annihilation creates two 511 keV photons which are emitted in opposite direction and can be detected as coincidence event by a dedicated PET scanner. The induced three-dimensional (3D) +- activity distribution in the patient can be reconstructed from the measured coincidences. Conclusions about the delivered dose distribution can be drawn indirectly from a comparison between two +-activity distributions: the measured one and an expected one generated by a Monte-Carlo simulation. This workflow has been proven to be valuable for the dose monitoring in IBT when it was applied for about 440 patients, mainly suffering from deep-seated head and neck tumours that have been treated with 12C ions at GSI.
In the presence of intra-fractional target motion, the conventional 3D PET data processing will result in an inaccurate representation of the +-activity distribution in the patient. Fourdimensional, time-resolved (4D) reconstruction algorithms adapted to the special geometry of in-beam PET scanners allow to compensate for the motion related blurring artefacts. Within this thesis, a 4D maximum likelihood expectation maximization (MLEM) reconstruction algorithm has been implemented for the double-head scanner Bastei installed at GSI. The proper functionality of the algorithm and its superior performance in terms of suppressing motion related blurring artefacts compared to an already applied co-registration approach has been demonstrated by a comparative simulation study and by dedicated measurements with moving radioactive sources and irradiated targets. Dedicated phantoms mainly made up of polymethyl methacrylate (PMMA) and a motion table for regular one-dimensional (1D) motion patterns have been designed and manufactured for the experiments. Furthermore, the general applicability of the 4D MLEM algorithm for more complex motion patterns has been demonstrated by the successful reduction of motion artefacts from a measurement with rotating (two-dimensional moving) radioactive sources. For 1D cos2 and cos4 motion, it has been clearly illustrated by systematic point source measurements that the motion influence can be better compensated with the same number of motion phases if amplitudesorted instead of time-sorted phases are utilized. In any case, with an appropriate parameter selection to obtain a mean residual motion per phase of about half of the size of a PET crystal size, acceptable results have been achieved. Additionally, it has been validated that the 4D MLEM algorithm allows to reliably access the relevant parameters (particle range and lateral field position and gradients) for a dose verification in intra-fractionally moving targets even from the intrinsically low counting statistics of IBT-PET data.
To evaluate the measured +-activity distribution, it should be compared to a simulated one that is expected from the moving target irradiation. Thus, a 4D version of the simulation software is required. It has to emulate the generation of +-emitters under consideration of the intra-fractional motion, their decay at motion state dependent coordinates and to create listmode data streams from the simulated coincidences. Such a revised and extended version that has been compiled for the special geometry of the Bastei PET scanner is presented within this thesis. The therapy control system provides information about the exact progress of the motion compensated dose delivery. This information and the intra-fractional target motion needs to be taken into account for simulating realistic +-activity distributions. A dedicated preclinical phantom simulation study has been performed to demonstrate the correct functionality of the 4D simulation program and the necessity of the additional, motionrelated input parameters.
Different to the data evaluation for static targets, additional effort is required to avoid a potential misleading interpretation of the 4D measured and simulated +-activity distributions in the presence of deficient motion mitigation or data processing. It is presented that in the presence of treatment errors the results from the simulation might be in accordance to the measurement although the planned and delivered dose distribution are different. In contrast to that, deviations may occur between both distributions which are not related to anatomical changes but to deficient 4D data processing. Recommendations are given in this thesis to optimize the 4D IBT-PET workflow and to prevent the observer from a mis-interpretation of the dose monitoring data. In summary, the thesis contributes on a large scale to a potential future application of the IBT-PET monitoring for intra-fractionally moving target volumes by providing the required reconstruction and simulation algorithms. Systematic examinations with more realistic, multi-directional and irregular motion patterns are required for further improvements. For a final rating of the expectable benefit from a 4D IBT-PET dose monitoring, future investigations should include real treatment plans, breathing curves and 4D patient CT images.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-044 2014
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 20503

Mini-Proceedings of the 15th meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies

van der Bij, J. J.; Czyż, H.; Eidelman, S.; Fedotovich, G.; Ferber, T.; Ivanov, V.; Korobov, A.; Liu, Z.; Lukin, P. A.; Müller, S. E.; Venanzoni, G.; Zaremba, J.; (Editors)

The mini-proceedings of the 15th Meeting of the "Working Group on Rad. Corrections and MC Generators for Low Energies" held in Mainz on April 11, 2014, are presented. These meetings, started in 2006, have as aim to bring together experimentalists and theorists working in the fields of meson transition form factors, hadronic contributions to (g−2)μ and the effective fine structure constant, and development of Monte Carlo generators and Radiative Corrections for precision e+e- and tau physics.

  • Open Access Logo Contribution to proceedings
    15th meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies, 11.04.2014, Mainz, Germany
    Mini-Proceedings of the 15th meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies


Publ.-Id: 20502

International round robin test on Master Curve reference temperature evaluation utilizing Miniature C(T) specimen

Yamamoto, M.; Onizawa, K.; Yoshimoto, K.; Ogawa, T.; Mabuchi, Y.; Valo, M.; Lambrecht, M.; Viehrig, H.-W.; Miura, N.; Soneda, N.

The Master Curve (MC) method is a promising technique for evaluating the fracture toughness of ferritic steels. It enables the determination of the reference temperature, To, of a probabilistic fracture toughness curve using small specimens. The Central Research Institute of Electric Power Industry (CRIEPI) investigated this capability of the MC method using different size of C(T) specimens, and it was found that 0.16T-C(T) specimen with the dimensions of 10mm by 10mm by 4mm, hereafter called “Mini-CT specimen”, can be used to obtain valid To values. The advantage of this Mini-CT specimen technique is that multiple specimens can be machined from one of broken halves of Charpy size specimens, which are used in a standard surveillance capsule of a reactor pressure vessel (RPV).
In order to ensure the robustness of this technique, a round-robin test was planned. The idea is to perform MC tests using Mini-CT specimens by different investigators to see if consistent To values can be obtained. All the specimens used were machined and pre-cracked by one fabricator from unique RPV material to avoid any possible effect of specimen preparation on To values. Seven institutes participated in this exercise, and obtained valid To values. No specific difficulty was found in the MC tests performed in accordance to the ASTM E1921 protocol. The scatter of the obtained To values was well within the uncertainty range defined in Appendix X4.2 of ASTM E1921, indicating the robustness of the Mini-CT specimen technique in terms of the testing procedure.
Throughout this activity, we could obtain 182 KJc (1Teq) for a single material. We investigated the statistics of this large database, and found that there is no remarkable difference not only in the To values but also in the fracture toughness distribution between the Mini-CT specimen and the standard 1T-C(T) specimen results.

Keywords: reactor pressure vessel steel; fracture toughnes; miniature specimen; Master Curve approach

  • Contribution to proceedings
    6th International Symposium on Small Specimen Test Techniques, 29.-31.01.2014, Houston, United States
    ASTM Special Technical Publication, Vol. STP 1576: ASTM, 978-080317597-6, 53-69
    DOI: 10.1520/STP157620140020

Publ.-Id: 20501

Wechselwirkung von Uran und Plutonium mit Ton, Tonorganika und bakteriellen Tonisolaten

Schmeide, K.; Jordan, N.; Moll, H.; Cherkouk, A.; Lippold, H.; Poetsch, M.; Kulenkampff, J.; Fritsch, K.

In the talk, the most important results obtained in the project for the system radionuclide/clay organics/clay rock are presented. The influence of salinity and temperature on complexation, sorption as well as diffusion/transport of radionuclides is discussed.

Keywords: Uranium; plutonium; terbium; fulvic acid; propionic acid; microorganisms; montmorillonite; Opalinus Clay; PET

  • Lecture (others)
    6. Workshop des Verbundprojekts "Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen", 08.-09.04.2014, Mainz, Deutschland

Publ.-Id: 20500

Ferromagnetism and structural defects in V-doped titanium dioxide

Yildirim, O.; Butterling, M.; Cornelius, S.; Mikhailovskiy, Y.; Novikov, A.; Semisalova, A.; Orlov, A.; Gan’Shina, E.; Perov, N.; Anwand, W.; Wagner, A.; Potzger, K.; Granovsky, A. B.; Smekhova, A.

We report recent experimental results about influence of negatively charged structural defects on room-temperature ferromagnetism in V-doped TiO2-δ thin films with different electric conductivities. Films were prepared on LaAlO3 (001) substrates by RF magnetron sputtering in reduced argon-oxygen atmosphere, while the V to Ti metal ratio was fixed at 1 at.%. The ferromagnetic order at room temperature (RT) was confirmed by SQUID magnetometry. Positron annihilation spectroscopy (PAS) was applied to check the presence of open-volume defects in the TiO2-δ matrix. The relation between ferromagnetic properties and amount of negatively charged defects in the studied films was established. The collection of structural, magnetometry, magnetotransport, magneto-optic and PAS data hints towards the defect-induced model of ferromagnetism in1 at.% V-doped TiO2-δ thin films.

Keywords: diluted magnetic semiconductors; defect-induced ferromagnetism; doped TiO2; PAS

Publ.-Id: 20499

Uranium(VI) retention in clay and crystalline rock: How and why does it differ

Schmeide, K.; Joseph, C.; Brendler, V.

The long-term disposal of high-level nuclear waste in deep geological formations is discussed worldwide as main strategy for nuclear waste management. This approach requires the use of a multiple barrier system consisting of engineered, geo-engineered, and geological barriers to prevent any release of radionuclides into the geo- and biosphere. Sorption of radionuclides on the host rock of a repository is one important process for retarding their migration. Potential host rocks for nuclear waste repositories that are investigated internationally are salt domes, clay rock, and crystalline rock.
In the present work, the retention behavior of clay and crystalline rock towards U(VI) is compared. For this, sorption of U(VI) onto Opalinus Clay from the Mont Terri rock laboratory (Switzerland) was studied in the presence of Opalinus Clay pore water (pH = 7.6; I = 0.36 M) [1]. This is compared to U(VI) sorption onto anoxic diorite from Äspö Hard Rock Laboratory (Sweden) that was studied in the presence of Äspö groundwater (pH = 7.8; I = 0.18 M) [2]. The impact of various parameters, such as solid-to-liquid ratio, initial U(VI) concentration, temperature and atmosphere, on U(VI) sorption was studied.
Distribution coefficients, Kd values, determined for the U(VI) sorption onto Opalinus Clay and diorite at 25 °C, amount to 22.2 ± 0.4 L/kg [1] and 3.8 ± 0.6 L/kg [2], respectively. Thus, U(VI) sorption onto Opalinus Clay is stronger than onto diorite, which can be attributed to its larger surface area. TRLFS and ATR FT-IR spectroscopic measurements showed that the U(VI) speciation in Opalinus Clay pore water as well as in diorite groundwater is predominated by the weakly sorbing Ca2UO2(CO3)3(aq) complex. Reduction processes of U play only a subordinate role. The U(VI) sorption increases with increasing temperature.
U(VI) diffusion experiments with intact Opalinus Clay bore cores [3] also showed that Opalinus Clay has a good retardation potential for U(VI) since the molecular diffusion process through Opalinus Clay retards the migration of Ca2UO2(CO3)3(aq).
Generally, it can be concluded that U(VI) retention by clay rock is stronger than that by crystalline rock. This supports decisions to use clay rock not only as host rock but also as backfill material. In case of crystalline rock the natural retention capacity for U is insufficient and has to be strengthened by additional geo-technical and technical barriers that preserve their enclosing capabilities over very long time scales.

[1] Joseph, C. et al. (2011) Chem. Geology 284, 240-250.
[2] Schmeide, K. et al. (2014) Appl. Geochem. 49, 116-125.
[3] Joseph, C. et al. (2013) Geochim. Cosmochim. Acta 109, 74-89.

Keywords: Uranium; sorption; retention; clay rock; crystalline rock

  • Invited lecture (Conferences)
    8th European Summer School on Separation Chemistry and Conditioning as well as Supramolecular, Intermolecular, Interaggregate Interactions, 07.-09.07.2014, Bonn/Bad Godesberg, Deutschland
  • Contribution to proceedings
    8th European Summer School on Separation Chemistry and Conditioning as well as Supramolecular, Intermolecular, Interaggregate Interactions, 07.-09.07.2014, Bonn/Bad Godesberg, Deutschland
    Berichte des Forschungszentrums Jülich, Jül-4376, Institut für Energie- und Klimaforschung, Nukleare Entsorgung und Reaktorsicherheit (S. Neumeier, P. Kegler, D. Bosbach, eds.), Jülich, 46 (2014).

Publ.-Id: 20498

Ferromagnetic Resonance Analysis on Periodic Surface Defects: The Transition from Perturbed Thin Films to Magnonic Crystals

Langer, M.; Gallardo, R.; Banholzer, A.; Jansen, A.; Schneider, T.; Wagner, K.; Demidov, V.; Demokirtov, S. O.; Landeros, P.; Lenz, K.; Lindner, J.; Fassbender, J.

The magnetic relaxation in 1-dimensional periodic nanostructures (quasi magnonic crystals) is investigated by ferromagnetic resonance (FMR). In thin ferromagnetic films, the magnetization dynamics are governed by intrinsic effects like Gilbert damping and spin-pumping but also by extrinsic effects like two-magnon scattering (TMS). The latter is in demand for latest research and can be induced within magnetic thin films by defects and inhomogeneities. Thereby, acting as scattering centers, defects cause a dipolar field at the film surface crucial for the magnon-magnon interaction. By ion Irradiation of the material, a local variation of the magnetic properties can be achieved [1], where the TMS strength is set by the properties of the modification such as the reduction of the effective magnetic moment and the geometry (depth d , periodicity a 0 ). The investigated films consist of 30 nm thick permalloy (Ni80Fe20) deposited by molecular beam epitaxy at room temperature on Si/SiO2 substrate. All films are protected by a Cr Cap layer of 3 – 5 nm. On top of the structure, PMMA resist of 140 nm thickness was added and patterned by EBL, to create a symmetric array of stripe defects with a periodicity ranging from 100 – 400 nm optimal for the investigation of TMS. Subsequently, the mask was employed for ion beam patterning. Parameters for the Cr ion irradiation were selected according to Monte-Carlo simulations calculating the effects of the ion irradiation on the depth-dependent composition using SRIM [2] and TRIDYN [3]. The irradiation energies were defined in the range of 5 – 10 keV in which the fluence varies from 5·1015 1/cm2 to 8·1015 1/cm2. Due to the lowering of the Curie temperature underneath room temperature when Cr content in permalloy is extending 8 at.% [4], after irradiation, magnetically dead layers are generated. For lower Cr concentrations, the saturation magnetization of permalloy is reduced and hence, the dead layers are accompanied by a concentration gradient where MS increases gradually to the value of the saturation magnetization of permalloy. By varying the ion energy and fluence, this gradient and hence, the effective defect depth can be set. This allows the investigation of the transition from a surface perturbed thin film to a full magnonic crystal. The energies and fluences used to prepare the samples presented in this work are summarized in Table I. The spin wave dynamics and TMS are studied using FMR and Brillouin light scattering (BLS). The dispersion relation of backward volume modes in an unperturbed thin film is known to be quadratically dependent on the wave vector k due to exchange interaction. If an array of surface perturbations is assumed to exist on the surface of such a thin film, an additional dipolar field contribution to the magnons dispersion must be taken into account. This term is proportional to –k (for ultrathin films: k ·d << 1) and hence, causes a degeneration. Investigating such system by FMR, spin wave excitation is carried out uniformly. Thus, to scatter into the degenerate spin wave mode, the k -vector must match a multiple reciprocal lattice vector g 0 = 2/a 0 . If this is valid, TMS can be observed and mode repulsion takes place. We measured the FMR spectra f (H ) of different defect samples showing repulsion at each crossing point of higher spin wave modes with the uniform mode. Theoretical calculations based on a model using perturbation theory [5] are accompanied and reveal a good agreement of experiment and theory. Applying the external field parallel to the axis of the stripe’s edge, the f (H ) measurement of the FMR signal reveals one single FMR mode, referred to as the Kittel mode, equal to the one of unperturbed films. Since in this orientation magnetization aligns parallel to the stripe axis, there are no dipolar fields present to generate a coupling between several magnons. By a field rotation towards the axis perpendicular to the stripes, the TMS is switched on and multiple resonance modes can be observed with a culminating mode splitting at a field direction perpendicular to the stripe axis. The f (H ) mode spectra of Sample 1 (for details see Table I) for several in-plane field angles were measured to show the gradual development of TMS-induced mode splitting and are accompanied by theoretical calculations. The angular dependent measurement of the same sample for a fixed frequency of 15 GHz can be found in Fig. 1. To study the impact of the defect depth on the resonance mode positions, the resonance spectra f (H ) perpendicular to the stripe axis were analyzed for all samples shown in Table I. Again, the available theoretical model was used to explain the observed mode structures. For a precise determination of the dispersion relation of the magnons in such systems, BLS measurements have been performed showing a good Agreement to the theoretically predicted band structure.

  • Poster
    IEEE International Magnetics Conference - Intermag 2014, 08.05.2014, Dresden, Deutschland

Publ.-Id: 20497

Vacancy type defect formation in irradiated α-iron investigated by positron beam Doppler broadening technique

He, C. W.; Dawi, K.; Platteau, C.; Barthe, M. F.; Desgardin, P.; Akhmadaliev, S.

Vacancy type defects formations have been investigated in virgin and irradiated a-iron samples using slow positron beam Doppler broadening technique.
Mono-vacancies and vacancy clusters are observed in 1.5 MeV 4He ions irradiated Fe samples at varying fluences from 1×1013 to 1×1017 cm-2.
In the 1.2 MeV Yttrium ions implantation at low fluence 1×1014 cm-2 vacancy clusters with higher concentration and larger size are formed.
In this sample, vacancy defects are detected deeper than predicted by SRIM calculation due to channelling.

Publ.-Id: 20496

Ion Beam Induced Periodic Surface Defects: The Transi- tion from a Thin Film to a Magnonic Crystal

Langer, M.; Gallardo, R.; Banholzer, A.; Jansen, A.; Schneider, T.; Wagner, K.; Demidov, V.; Demokirtov, S. O.; Landeros, P.; Lenz, K.; Lindner, J.; Fassbender, J.

Periodic arrays of magnetic stripe defects are fabricated by Cr+ ion implantation on a 30 nm permalloy lm. Modifying the mean ion penetration depth, the defect height can be controlled, which allows an investigation of the gradual transition from a magnetic thin lm towards a magnonic crystal.
Spin wave dispersion and two-magnon scattering are studied using brillouin light scattering (BLS) as well as broadband ferromagnetic resonance (FMR). The obtained results are corroborated by theoretical calculations based on a perturbation theory.

Keywords: Magnonics; Magnonic Crystals; Magnetization Dynamics; Spin Waves; Magnons; Ferromagnetic Resonance

  • Poster
    DPG Spring Meeting 2014, 04.04.2014, Dresden, Deutschland

Publ.-Id: 20495

Uranium Contents in Plants and Mushrooms Grown on a Uranium Mining Waste Tip Site in Former Eastern Germany

Baumann, N.; Arnold, T.; Haferburg, G.

There were extensive uranium mining-activities in former Eastern Germany in 1945 to 1990, with ecological consequences, like districts with U contaminated grounds. U concentrations in plants, and mushrooms, grown on a test site within a U-contaminated area in Eastern Thuringia, were analyzed. This test site is situated on the ground of a former U mine waste leaching heap. For determination of the U concentrations, the saps of the samples were squeezed out by an ultracentrifuge; after that, the U concentrations in the saps and in the remaining residues were measured by ICP-MS. The study showed that U concentrations observed in plant compartment and mushroom sap samples were always higher than in their associated solid residues. Also, it was found that the detected U concentrations in the root samples were always higher than those in their associated above ground biomass. But, the U concentrations in plants and mushrooms were always lower than in the associated surface and soil waters. This study confirmed that the amount of extracted U from plants and mushrooms is insufficient comparing to the U contaminated in soil and water. Thus these results indicated that none of the plant and mushroom species turned out to be a hyper-accumulator for U. In addition, it was found that the detected U concentrations in the sap samples, proved to be too low - in combination with the presence of fluorescence quenching substances, e.g., Fe and Mn, and/or organic quenchers - to extract a useful fluorescence signal, which could have helped to identify the uranium speciation in plants.

Keywords: uranium; TRLFS; heavy metal-contaminated soil; phytoremediation

  • Lecture (Conference)
    International Nuclear Science and Technology Conference 2014 (INST 2014), 28.-30.08.2014, Bangkok, Thailand
  • Contribution to proceedings
    International Nuclear Science and Technology Conference 2014 (INST 2014), 28.-30.08.2014, Bangkok, Thailand

Publ.-Id: 20494

Microorganisms and their impact on radionuclide speciation

Moll, H.; Cherkouk, A.

Microorganisms are ubiquitous in the environment. Hence, for the long-term safety assessment of a nuclear waste repository it is necessary to know which microorganisms are present in the potential host rocks (e.g., clay) and how these microorganisms can influence the performance of a repository. The Opalinus clay layer of the Mont Terri Underground Rock Laboratory (Switzerland) is one potential host rock for nuclear waste disposal [1]. It is well known that indigenous bacteria in such underground environments can affect the speciation and the mobility of actinides [2-5].
From our point of view, the understanding of the speciation and the structure of the actinide (An)/lanthanide (Ln) complexes formed in presence of indigenous bacteria over a wide range of geochemical parameters (e.g., pH, metal concentration) becomes indispensable for predicting the safety of a planned nuclear waste repository.
Our research is focused on broaden the knowledge concerning the bacterial diversity in potential host rocks for nuclear waste storage (e.g., Mont Terri Opalinus Clay) by applying direct molecular culture-independent retrievals and cultivation experiments. After cultivation and characterization of dominant bacterial populations we investigate their influence on the geo-chemical behaviour of selected An/Ln (uranium, plutonium, and curium/europium). The indirect (e.g., actinide mobilization by microbially produced bioligands) and direct (e.g., biosorption, bioaccumulation, biotransformation) influence of microorganisms on the speciation/migration processes of An/Ln will be highlighted during the lecture by using selected examples. This helps to understand the manifold interaction processes in such biological systems on a molecular level.

Acknowledgements. The authors thank the BMWi for financial support (contract no.: 02E9985, 02E10618 and 02E10971) and the BGR for providing the clay samples.

[1] M. Thury, P. Bossart, Eng. Geol., 52 (1999) 347-359
[2] J.R. Lloyd, G.M. Gadd, Geomicrobiol. J., 28 (2011) 383-386
[3] H. Moll, et al. Geomicrobiol. J., 30 (2013) 337-346
[4] L. Lütke, et al. Dalton Trans., 42 (2013) 6979-6988
[5] M.P. Neu, et al. Radiochim. Acta, 93 (2005) 705-714

Keywords: microorganisms; radionuclide speciation; nuclear waste disposal

  • Invited lecture (Conferences)
    8th European Summer School on supramolecular, intermolecular, interaggregate interactions and separation chemistry, 07.-09.07.2014, Bonn - Bad Godesberg, Deutschland

Publ.-Id: 20493

High conversion Th-U233 fuel cycle for current generation of PWRs

Baldova, D.; Fridman, E.

The main goal of this study is to evaluate the operational feasibility of the high conversion (HC) Th-U233 PWR core through performing the 3D fully coupled neutronic and thermal-hydraulic (T-H) analysis. The proposed HC core model consists of 193 typical 17×17 PWR fuel assemblies. Each fuel assembly is subdivided into two regions designated as seed and blanket. The central seed re-gion, which has high U233 content, serves as a neutron supplier for the peripheral blanket region. The blanket region consists mostly of Th232 and acts as a U233 breeder.

  • Contribution to proceedings
    Thorium Energy Conference THEC13, 27.-31.10.2013, CERN, Geneva, Switzerland
    Proceedings of the Thorium Energy Conference THEC13
  • Poster
    Thorium Energy Conference THEC13, 27.-31.10.2013, CERN, Geneva, Switzerland

Publ.-Id: 20492

64Cu-labelled dendritic polyglycerol derivatives for biodistribution studies

Pant, K.; Steinbach, J.; Stephan, H.; Bergmann, R.; Haag, R.; Gröger, D.; Nowag, S.; Graham, B.; Spiccia, L.

Dendritic polyglycerols (dPG) and dendritic polyglycerol sulfates (dPGS) are easily synthesized macromolecules. These polymers are highly water-soluble, biocompatible, practically non-toxic and non-immunogenic. Hence, these properties make them highly interesting for application in biomedicine and offers excellent prospects for the development of new non-invasive strategies for the diagnosis and treatment of diseases. dPGS have already been developed as fully synthetic heparin analogues that show anti-inflammatory properties and accumulation in tumor tissue, which makes them promising agents for therapeutic applications. Since information about the biodistribution and the metabolism of dPGS in living systems is quite scarce, one approach is to radiolabel them so as to be able to track them with, for example, positron emission tomography (PET). 64Cu has suitable decay characteristics that allow for PET imaging and a variety of chelator systems are available for attachment to these macromolecules using appropriate anchor groups. Herein, we report the conjugation of bifunctional chelating agents based on bis(2-pyridylmethyl)triaza-cyclononane [DMPTACN] onto the dPG/dPGS scaffolds. The structure of DMPTACN allows for the introduction of various functional groups, such as carboxylic, maleimide or isothiocyanate groups, for coupling to various functional groups
(amino and mercapto surface groups) on the dPG derivatives. 64Cu-labeling experiments and stability studies of the resulting radiocopper complexes are presented and discussed.
Methods & materials
DMPTACN was synthesized by a 10-step process starting from diethylenetriamine to form a TACN ring containing tosyl protecting groups. After deprotection and subsequent introduction of two pendant 2-picolyl arms, coupling
groups, such as a carboxylic acid, maleimide or isothiocyanate, have been attached. The dPG and dPGS samples can be synthesized on a kilogram scale by utilizing ring-opening and copolymerization reactions. Surface modification with
amino and mercapto groups provides the target molecules needed for attachment of copper-binding agents. After conjugation of BFCAs to the dPG/dPGS, the compounds were purified by size exclusion chromatography. 64Cu-labeling of DMPTACN-dPG(dPGS) conjugates were performed using [64Cu]CuCl2 in 0.1 M MES/NaOH buffer at a pH of 5.5 at room temperature, resulting in a radiochemical purity of higher than 95% within a few minutes. Animal experiments were carried out in male Wistar rats.
Results & conclusion
dPG and dPGS have been synthesized with various percentages of amine and mercapto functionalities capable of coupling to BFCAs based on a DMPTACN backbone with maleimide, carboxylic and isothiocyanate groups. The
conjugates can be purified by size exclusion chromatography, and have been obtained in good yields. 64Cu-labeling experiments confirmed rapid copper(II) complex formation under mild conditions. The 64Cu-labelled conjugates exhibit high in vitro stability in human serum. These probes can thus be utilized to derive quantitative distribution data in vivo. Biodistribution and pharmacokinetic properties of 64Cu-labelled dendritic polyglycerol derivatives can be conveniently studied by PET.
Financial disclosure
This work is part of a research initiative within the Helmholtz-Portfoliothema “Technologie und Medizin - Multimodale Bildgebung zur Aufklaerung des In vivo-Verhaltens von polymeren Biomaterialien”.

  • Poster
    World Conference on Regenerative Medicine, 21.-23.10.2013, Leipzig, Deutschland
  • Abstract in refereed journal
    Regenerative Medicine 8(2013)6s, 297

Publ.-Id: 20491

Microstructure and mechanical properties of sub-rapidly solidified Fe-18wt%Mn-C alloy strip

Song, C.; Lu, W.; Xie, K.; Zhang, Y.; Xia, W.; Han, K.; Zhai, Q.

High-Mn steels exhibit both high tensile strength and good ductility and have attracted much attention as a promising candidate for next-generation automotive steel. However, there are still problems in conventional production, such as severe slab crack and pronounced element segregation, which restrict their widespread applications. An alternative way to produce this alloy is the near net shape method under a sub-rapid solidification process. We studied the microstructure and mechanical properties of Fe-18Mn-(0.14, 0.50)C alloy thin strip produced by injecting casting at a sub-rapid solidification rate, in which the cooling rate was about 5×103K/s. The results demonstrated that the formation of cementite particles was suppressed, but apart from the γ-phase, the ε-martensite and α'-martensite also formed in the Fe-18Mn-C thin strips. The lath width of ε-martensite is lower than that of sample produced by conventional method. The mechanical properties of Fe-18Mn-0.50C surpass the Fe-18Mn-0.60C alloy steel processed by hot rolled and heat treated. This paper discusses the relationship between the microstructure and the mechanical properties of the strips.

Keywords: Mechanical property; Microstructure; Sub-rapid solidification; TWIP steel

Publ.-Id: 20490

Examination of the interaction of a halophilic Archaea with uranium regarding the long term storage of radioactive waste in rock salt

Liebe, M.; Cherkouk, A.; Stumpf, T.

For the long term storage of radioactive waste in a deep geological repository rock salt is one of the possible host rocks, next to clay and crystalline formations. To date only little is known about the microbial diversity in German rock salt and the interactions of halophilic microorganisms with radionuclides. Microorganisms indigenous to potential host rocks are able to influence the oxidation state and speciation and hence the mobility of radionuclides. Therefore, for the safety assessment of a radioactive waste disposal it is important to know what microorganisms are present in the potential host rocks (e.g. salt) and how these microorganisms can affect the performance of a repository.
The reference organism Halobacterium noricense DSM 15987 was used to investigate the interactions with uranium at high ionic strength. For instance this halophilic Archaea was found in an Austrian salt mine1 and in the halite of the Waste Isolation Pilot Plant (WIPP, Carlsbad, USA)2. The cells were incubated for 48 h with uranium concentrations between 5 - 60 μM in 3.0 M NaCl (pH 6.0, room temperature, shaking) for sorption studies. After 48 h the cells were still living when incubated with uranium concentrations up to 60 μM, which demonstrates that Halobacterium noricense can tolerate uranium concentrations up to this level. The formed uranium sorption species were examined with IR-spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). Furthermore the time-depending and pH-depending biosorption of Halobacterium noricense with uranium will be presented.
1. Gruber, C.; Legat, A.; Pfaffenhuemer, M.; Radax, C.; Weidler, G.; Busse, H. J.; Stan-Lotter, H., Halobacterium noricense sp. nov., an archaeal isolate from a bore core of an alpine Permian salt deposit, classification of Halobacterium sp. NRC-1 as a strain of H. salinarum and emended description of H. salinarum. Extremophiles 2004, 8 (6), 431-439.
2. Swanson, J. S.; Reed, D. T.; Ams, D. A.; Norden, D.; Simmons, K. A., Status report on the microbial characterization of halite and groundwater samples from the WIPP. Los Alamos National Laboratory 2012.

  • Poster
    Microbiology and Infection 2014, 4. Gemeinsamer Kongress von DGHM und VAAM, 05.-08.10.2014, Dresden, Deutschland

Publ.-Id: 20489

High-Speed PIXE: Fast multi-elemental analysis with lateral resolution using a Colour X-Ray Camera

Buchriegler, J.; Munnik, F.; Hanf, D.; von Borany, J.; Nowak, S. H.; Scharf, O.; Ziegenrücker, R.; Merchel, S.; Renno, A. D.

A new PIXE-beamline equipped for fast, laterally resolved elemental analysis has recently been put into operation at HZDR. The system uses a full-field energy dispersive X-ray camera, the SLcam® [1,2]. It consists of a poly-capillary lens guiding the proton-induced Xray fluorescence radiation towards a pnCCD-chip with 264×264 pixels, each with an energy resolution of 156 eV (@Mn Kα). The CCD pixel size is 48×48 µm². In combination with a 1:1 X-ray lens, this results in a lateral resolution better than 100 µm with a field of view of 12×12 mm². A 6:1 X-ray lens with a field of view of 2×2 mm² and envisaged lateral resolution < 10 µm is also available.
The camera is mounted on a vacuum chamber containing a precision sample manipulator. The chamber is optimised for high throughput of large samples. A beam broadening system is needed to ensure a homogeneous illumination of the entire detection area. The installed optical microscope together with the image processing software allows correlative superimposition of the PIXE-maps with optical images or electron microprobe element distribution maps. The simultaneous measurement of a large pixel array enables a fast overview over a large region of the sample with first tentative results becoming visible almost immediately.
The new setup is mainly developed for the investigation of geological samples for resource technology research, which comprises the analysis of grain composition and intergrowths as well as the determination of trace element distributions, e.g. rare earth elements. However, the setup can be used for the analysis of every kind ofsample respecting dimensions, roughness and vacuum stability.
First results concerning lateral resolution and detection limits are encouraging. Due to the low background in the PIXE-spectra investigation of trace elements with concentrations below hundreds of µg/g is achievable. The main limitation s for the detection limits are pile-up and the small solid angle of the capillaries. Total count-rate is not a limitation due to the different readout compared to conventional detectors; therefore high beam currents of a few µA can be used.
[1] O. Scharf et al., Anal. Chem., Vol. 83, pp. 2532-2538 (2011).
[2] I. Ordavo et al., NIM A, Vol. 654, pp. 250-257 (2011).

Keywords: PIXE; lateral resolution; colour camera

  • Invited lecture (Conferences)
    8th International Symposium on BioPIXE, 15.-19.09.2014, Bled, Slovenia

Publ.-Id: 20488

Light element analysis and imaging using Particle Induced Gamma-ray Emission

Munnik, F.; Freiherr, C.; Renno, A.

Spatially resolved analytical methods are important in many fields of application. One area of research is the interdisciplinary field of geometallurgy, which combines geology with extractive metallurgy to explore and exploit ore bodies and extract valuable minerals. The characterisation of the chemical composition and structure of ores and intermediate products is important for the material- and energy-efficient utilization of primary and secondary resources of minerals and metals.
Information on “mineralogical light” elements, i.e. hydrogen to fluorine, is needed over a broad concentration range from traces to major elements. These elements can be a useful resource in itself, like lithium. Besides, they provide information about the genesis of e.g. ore deposits and rocks or have a strong influence on the mechanical behaviour of rocks.
The analysis of such elements, especially at the trace level, is a challenge for many standard microanalytical methods. Particle Induced Gamma-ray Emission has the advantage of 1) obtaining quantitative results without matrix-matched standards, 2) being non-destructive and 3) wide applicability. In addition, it can be combined with other ion beam analysis methods like Rutherford Backscattering Spectrometry and Particle Induced X-ray Emission, for which a new set-up has been developed (see the presentation of Josef Buchriegler).
The nuclear microprobe of the Helmholtz-Zentrum Dresden-Rossendorf has been upgraded with a Gamma-ray detector (HPGe) to facilitate the spatially-resolved analysis of light elements (lithium to phosphorus). This upgrade is presented in this work. Extensive calibrations have been performed. Next, the implementation of the analysis and imaging procedures are discussed. Finally, the first results of the application on mineralogical samples are shown.

Keywords: PIGE; light elements

  • Poster
    14th International Conference on Nuclear Microprobe Technology and Applications, 07.-11.07.2014, Padua, Italy

Publ.-Id: 20487

Energetics, structure, and composition of nanoclusters in oxide dispersion strengthened Fe-Cr alloys

Posselt, M.; Murali, D.

The main structural characteristic of Oxide Dispersion Strengthened (ODS) Fe-Cr alloys is the finely dispersed distribution of nm-size clusters that may contain O, Y, and Ti. Many details of the structure and composition of these nanoclusters are not yet fully understood. Numerous experiments demonstrated that number and size of the nanoclusters do not change significantly when ODS alloys are exposed to high dose irradiation and/or high temperatures. Furthermore, it was shown that the fine dispersion of the nanoclusters prevents recrystallization, i.e. the increase of grain size, which usually occurs at elevated temperatures. The extraordinary properties of the nanoclusters are deemed to be the cause of the superior high-temperature creep strength and the high radiation resistance of the ODS Fe-Cr alloys. Therefore, these materials are promising candidates for applications as structural materials in extreme environments, i.e. at high temperature and intense particle irradiation, such as in advanced nuclear fission and fusion reactors.
In this work a multiscale modeling approach is developed and successfully applied to interpret a large number of experimental data on the properties of nanoclusters in the ODS Fe-Cr alloys. Extensive first-principle calculations on embedded clusters containing few O, Y, Ti, and Cr atoms as well as vacancies are performed to obtain interaction parameters to be applied in Metropolis Monte Carlo simulations, within the framework of a rigid lattice model. A novel description using both pair and triple parameters is shown to be more precise than the commonly used pair parameterization. Simulated annealing provides comprehensive data on the energetics, structure and stoichiometry of nm-size clusters at T=0. The results are fully consistent with the experimental finding of negligible coarsening and a high dispersion of the clusters, with the observation that the presence of Ti reduces the cluster size, and with the reported radiation tolerance of the clusters. In alloys without vacancies clusters show a planar structure, whereas the presence of vacancies leads to three-dimensional configurations. Additionally, Metropolis Monte Carlo simulations are carried out at high temperature in order to investigate the dependence of nanocluster composition on temperature. A good agreement between the existing experimental data on the ratios (Y+Ti):O, Y:Ti, (Y+Cr):O, and Y:Cr, and the simulation results is found. In some cases it is even possible to draw the conclusion that the respective alloys contained a certain amount of vacancies, or that the clusters analyzed were frozen-in high-temperature configurations. The comparison of experimental data with those obtained by simulations demonstrates that the assumption of nanoclusters which are coherent with the bcc lattice of the Fe-Cr matrix leads to reasonable results.

Keywords: Monte Carlo simulations; Oxide Dispersion Strengthened Fe-Cr alloys; nanoclusters; Density Functional Theory calculations

  • Poster
    Computer Simulation of Radiation Effects in Solids 2014 (COSIRES 2014), 08.-13.06.2014, Alicante, Spain

Publ.-Id: 20485

Phase diagrams of MgO magnetic tunnel junctions including the perpendicular spin-transfer torque in different geometries

Bernert, K.; Sluka, V.; Fowley, C.; Lindner, J.; Fassbender, J.; Deac, A. M.

We calculate the switching voltages for MgO-based magnetic tunnel junctions taking into account both the inplane and the fieldlike spin-torque terms. To this end, we analytically solve the Landau-Lifshitz-Gilbert equation for a generalized geometry. We assume that the in-plane spin-torque varies linearly with the applied voltage, while the fieldlike torque exhibits a quadratic voltage dependence. Specifically, we consider that the free layer has two generic, orthogonal anisotropy components, one of which is along the direction defined by the magnetization of the reference layer, which also serves as a polarizer. The resulting formalism is applied to three different, experimentally relevant geometries: tunnel junctions with both the free and the reference layers magnetized in the plane of the layers, junctions with fully perpendicular anisotropy, and perpendicular junctions with an additional in-plane easy axis, respectively. We find that for in-plane devices, the quadratic dependence of the fieldlike torque on the applied voltage can lead to back hopping, which remains possible if we insert an additional linear term for the bias dependence of the fieldlike spin-torque comparable to current experimental results. For perpendicular anisotropy junctions neither back hopping nor spin-transfer-driven steady-state precession are expected. An additional in-plane shape anisotropy component stabilizes canted states in tunnel junctions with perpendicular anisotropy for specific values of voltage and field. The results are consistent with numerical integration of the Landau-Lifshitz-Gilbert equation and in good agreement with recent experiments involving perpendicular magnetic anisotropy magnetic tunnel junctions.

Keywords: Spin-transfer torque; Spin transport effects; magnetic tunnel junctions; switching phase diagrams; voltage-induced magnetisation switching; back hopping

Publ.-Id: 20484

Geometric degree of non-conservativity

Lerbet, J.; Aldowaji, M.; Challamel, N.; Kirillov, O. N.; Nicot, F.; Darve, F.

This paper deals with nonconservative mechanical systems subjected to nonconservative positional forces leading to nonsymmetric tangential stiffness matrices. The geometric degree of nonconservativity of such systems is then defined as the minimal number of kinematic constraints necessary to convert the initial system into a conservative one. Finding this number and describing the set of corresponding kinematic constraints is reduced to a linear algebra problem. This index of nonconservativity is the half of the rank of the skew-symmetric part S of the stiffness matrix K that is always an even number. The set of constraints is extracted from the eigenspaces of the symmetric matrix S^2. Several examples including the well-known Ziegler column illustrate the results.

Keywords: Stability; nonconservative systems; constraints

Publ.-Id: 20483

Role of preparation and implantation-related defects for the magnetic properties of Zn0.9Co0.1O epitaxial films

Ney, V.; Lenz, K.; Ollefs, K.; Wilhelm, F.; Rogalev, A.; Ney, A.

A systematic variation of preparation conditions for epitaxial Zn0.9Co0.1O films grown by reactive magnetron sputtering on c-plane sapphire has been carried out to study the correlation of crystalline perfection with the corresponding magnetic properties. The crystalline perfection of the resulting films was found to vary over a wide range, nonetheless all samples were found to be paramagnetic. The further extent the study, three samples, which were paramagnetic in the as-grown state, were subsequently implanted using Cu, Li and Zn ions. Only Zn ion-implantation was found to slightly alter the magnetic properties at low temperatures, however, synchrotron-based techniques could not evidence the formation of a secondary, metallic Co phase. The origin of this weak, low-temperature magnetism is more likely to be carrier-mediated rather than defect-induced.

Keywords: ZnO; diluted magnetic semiconductors; ion implantation; induced magnetism

Publ.-Id: 20482

Quantitative imaging of the magnetic fields of a nano-modulated permalloy thin film by electron holography

Lenz, K.; Körner, M.; Röder, F.; Fritzsche, M.; Lindner, J.; Lichte, H.; Fassbender, J.

Dipolar magnetic stray fields are the origin of most coupling and interaction effects among patterned ferromagnetic micro- and nanostructures. For example, they are the source of Neel coupling in trilayer films with orange-peel-type or modulated interfaces [1], they are responsible for two-magnon scattering in ultrathin films [2] or uniaxial magnetic anisotropy, and many other effects. Although intuitively clear and easy to grasp the detailed magnetic configuration of nanostructured films is not easy to detect. Micromagnetic simulations are a possible method to calculate the stray fields and magnetic configuration. However, they results relies on the exact modeling of the magnetic structure and knowledge of sample parameters.
Off-axis electron holography (EH) using a transmission electron microscope (TEM) is the method of choice to image the magnetization and stray field of a ferromagnetic sample directly. Moreover it allows a quantitative analysis compared to conventional imaging of magnetic domains. Modern aberration corrected TEMs provide enough resolution to image the stray fields even of nanostructures.
In our work we have investigated those stray fields as well as the magnetic state of a thin permalloy film deposited on a rippled Si template quantitatively.
The rippled Si template was prepared by Xe+ ion beam erosion of a Si substrate under an oblique angle of 65°. The ion beam energy determines the period of the ripples, which was selected such to yield ripples with a periodicity of about 220 nm. A 30 nm thick Permalloy (Ni81Fe19) film with a 3 nm Cr cap layer was subsequently evaporated onto this template [4]. The film follows the morphology of the template as cross-checked by atomic force microscopy before and after deposition. From this sample a cross-section lamella was cut out and subsequently thinned to below 100 nm using a focused ion beam system for the transmission electron holography imaging. The geometry for the micromagnetic simulations was taken from the conventional TEM images.
The cross-sectional electron holographic measurements yield the electric and magnetic phase images [3]. The magnetic phase image allows to determine the local orientation of the magnetization inside the permalloy film (see Fig. 1). The magnetization follows nearly perfectly the surface modulation of the film with a saturation magnetization of roughly 1000 mT. Regarding the magnetic stray field outside the film the micromagnetic simulation shows the periodic change due to rising and falling ripple slopes in good agreement with the holographic images.
The resulting dipolar stray fields are around 10-20 mT [5].

Keywords: ferromagnetism; ripples; electron holography; nanostructures

  • Lecture (Conference)
    IEEE International Magnetics Conference 2014, 08.05.2014, Dresden, Deutschland

Publ.-Id: 20481

Electroluminescent properties of Tb-doped carbon-enriched silicon oxide

Tiagulskyi, S. I.; Nazarov, A. N.; Gordienko, S. O.; Vasin, A. V.; Rusavsky, A. V.; Rebohle, L.; Voelskow, M.; Skorupa, W.

An electroluminescent device utilizing a heterostructure of amorphous Terbium doped carbon-rich SiOx (a - SiOx : C : Tb) on silicon has been developed. The a - SiOx : C : Tb active layer was formed by RF magnetron sputtering of a - SiO1–x : Cx : H(:Tb) film followed by high-temperature oxidation. It was shown that, depending on the polarity of the applied voltage, the electroluminescence is either green or white, which can be attributed to different mechanisms of current transport through the oxide film – space charge limited bipolar double injection current for green electroluminescence and trap assisted tunneling or Fowler-Nordheim tunneling for White electroluminescence.

Keywords: electroluminescence; a-SiO:C/Si heterostructure; Tb; RF magnetron sputtering; charge transport mechanisms

  • Open Access Logo Semiconductor Physics, Quantum Electronics & Optoelectronics 17(2014)1, 34-40

Publ.-Id: 20480

Recent advances in the study of the UO2–PuO2 phase diagram at high temperatures

Böhler, R.; Welland, M. J.; Prieur, D.; Cakir, P.; Vitova, T.; Pruessmann, T.; Pidchenko, I.; Hennig, C.; Guéneau, C.; Konings, R. J. M.; Manara, D.

Recently, novel container-less laser heating experimental data have been published on the melting behaviour of pure PuO2 and PuO2-rich compositions in the uranium dioxide–plutonium dioxide system. Such data showed that previous data obtained by more traditional furnace heating techniques were affected by extensive interaction between the sample and its containment. It is therefore paramount to check whether data so far used by nuclear engineers for the uranium-rich side of the pseudo-binary dioxide system can be confirmed or not. In the present work, new data are presented both in the UO2-rich part of the phase diagram, most interesting for the uranium–plutonium dioxide based nuclear fuel safety, and in the PuO2 side. The new results confirm earlier furnace heating data in the uranium-dioxide rich part of the phase diagram, and more recent laser-heating data in the plutonium-dioxide side of the system. As a consequence, it is also confirmed that a minimum melting point must exist in the UO2–PuO2 system, at a composition between x(PuO2) = 0.4 and x(PuO2) = 0.7 and 2900 K 6 T 6 3000 K. Taking into account that, especially at high temperature, oxygen chemistry has an effect on the reported Phase boundary uncertainties, the current results should be projected in the ternary U–Pu–O system. This aspect has been extensively studied here by X-ray diffraction and X-ray absorption spectroscopy. The current results suggest that uncertainty bands related to oxygen behaviour in the equilibria between condensed phases and gas should not significantly affect the qualitative trend of the current solid–liquid phase boundaries

Keywords: EXAFS; PuO2

Publ.-Id: 20479

Natural Distribution of Heavy Metals in Wetlands - Evaluation of Sources and Processes

Franzen, C.

kein Abstract vorhanden

  • Lecture (others)
    Lecture at North-West University, 28.08.2014, Vanderbijlpark, South Africa

Publ.-Id: 20478

Berufsfelder in den Geowissenschaften - Als Mineralogin in der Endlagerforschung

Franzen, C.

kein Abstract vorhanden

  • Lecture (others)
    Berufsfelder in den Geowissenschaften, 23.06.2014, Heidelberg, Deutschland

Publ.-Id: 20477

Electrophysical and Structure-Sensitive Properties of liquid Ga-In Alloys

Plevachuk, Y.; Sklyarchuk, V.; Shevchenko, N.; Eckert, S.

The broad interest in the thermophysical properties of gallium-based melts is stimulated by their extensive use in various applications, such as sliding contacts, heat-sensitive elements of liquid-metal thermometers and thermocouples, carrier liquid for electrically conducting magnetic fluids and the working medium for physical modeling in solidification and magnetohydrodynamic studies. The electrical conductivity, thermal conductivity, viscosity, density and thermoelectric power were determined for different alloy compositions in a wide temperature range below and above the liquidus temperature. Respective scaling relations are proposed. A comparison with data available in the literature is given.

Keywords: Liquid metal; Gallium--indium; Thermophysical properties

Publ.-Id: 20476

Innovative Methoden in der Bionanotechnologie – Die Quarzkristallmikrowaage (QCM-D)

Suhr, M.

Funktionsprinzip und Modellierungsansätze der QCM-D.
Anwendungsmöglichkeiten und Grenzen der QCM-D.
Nutzung der QCM-D in der ressourcenökologischen Forschung.

Keywords: QCM-D; AFM; Biosorption; Metalle

  • Lecture (others)
    Umweltkolloquium der Fakultät Maschinenbau/ Verfahrenstechnik, Studiengang Chemieingenieurwesen, 20.05.2014, Dresden, Deutschland

Publ.-Id: 20475

A comparison of the structural changes and optical properties of LiNbO3, Al2O3 and ZnO after Er+ ion implantation

Mackova, A.; Malinsky, P.; Pupikova, H.; Nekvindova, P.; Cajzl, J.; Svecova, B.; Oswald, J.; Wilhelm, R. A.; Kolitsch, A.

This paper reports on the structural as well as compositional changes of LiNbO3, Al2O3 and ZnO crystals, implanted with Er+ ions at 190 keV a with fluence of 1.0 × 1016 cm−2 into the <0001> crystallographic cuts. Post-implantation annealing at 1000 °C in oxygen atmosphere was also done. The chemical compositions and erbium concentration-depth profiles of implanted layers were studied by Rutherford Backscattering Spectrometry (RBS) and compared to SRIM simulations. The same value of the maximum erbium concentration (up to 2 at.%) was observed at a depth of about 40 nm for all crystals. The structural properties of the prepared layers were characterised by RBS/channelling. The relative numbers of disordered atoms in the prepared implanted layers were compared with each other and discussed for various crystals. It has been found that erbium is located in LiNbO3 and in Al2O3 preferably in interstitial positions, unlike ZnO, where the largest amount of erbium (about 83%) is placed in substitutional positions after the implantation. The erbium position in the host matrix was substantially influenced by the annealing procedure. In ZnO, after the annealing, the erbium amount in substitutional positions significantly decreased; in LiNbO3 and Al2O3 the increase of erbium in substitutional positions was observed simultaneously with the improvement of the quality of the reconstructed host matrix. Since we are interested in the relationship between structural changes and optical properties, the erbium luminescence properties were measured in the region of wavelength 1440–1650 nm for all crystals. After ion implantation LiNbO3 samples had zero luminescence intensity, while ZnO and Al2O3 samples had one significant luminescence band at 1537 and 1530 nm, respectively. The annealing improved the luminescent properties significantly in all investigated crystalline materials.

Keywords: Er ion implantation; Crystals; Depth profiles; RBS; RBS/channelling; Photoluminescence

Publ.-Id: 20474

Verification of the spectral history correction method with fully coupled Monte Carlo code BGCORE

Bilodid, Y.; Fridman, E.; Kotlyar, D.; Margulis, M.; Shwageraus, E.

Recently, a new method for accounting for burnup history effects on few-group cross sections was developed and implemented in the reactor dynamic code DYN3D. The method relies on the tracking of the local Pu-239 density which serves as an indicator of burnup spectral history. The validity of the method was demonstrated in PWR and VVER applications. However, the spectrum variation in BWR core is more pronounced due to the stronger coolant density change. Therefore, the purpose of the current work is to further investigate the applicability of the method to BWR analysis. The proposed methodology was verified against recently developed BGCore system, which couples Monte Carlo neutron transport with depletion and thermal hydraulic solvers and thus capable of providing a reference solution for 3D simulations. The results clearly show that neglecting the spectral history effects leads to a very large deviation (e.g. 2000 pcm in reactivity) from the reference solution. However, a very good agreement between DYN3D and BGCore is observed (on the order of 200 pcm in reactivity), when the Pu-correction method is applied.

Keywords: history effects; spectral history; DYN3D; BGCore; Monte-Carlo

  • Contribution to proceedings
    PHYSOR 2014, 28.09.-03.10.2014, Kyoto, Japan
    Proceedings of the PHYSOR 2014
  • Lecture (Conference)
    PHYSOR 2014, 02.10.2014, Kyoto, Japan

Publ.-Id: 20473

Investigation of spark plasma sintered oxide-dispersion strengthened steels by means of small-angle neutron scattering

Hilger, I.; Bergner, F.; Ulbricht, A.; Wagner, A.; Weißgärber, T.; Kieback, B.; Heintze, C.; Dewhurst, C. D.

Spark plasma sintering (SPS) is an advanced consolidation technique, which particularly allows coarsening of the microstructure to be limited. The basis for the characteristics of the strengthening nanofeatures is already set in the milling process preceding SPS. The present study is focused on the dependence of the size distribution and nature of the nanofeatures in an ODS Fe-14Cr-1W-0.4Ti alloy as a function of the applied milling parameters and amount of added yttria while keeping the SPS parameters constant. Statistically reliable averages of the particle characteristics representative of a macroscopic sample volume have been obtained by means of small-angle neutron scattering (SANS). The measured magnetic-to-nuclear scattering ratios have been critically compared to values calculated on the basis of structures and compositions reported in the literature. Milling parameters suitable to completely transform the added yttria into Ti-containg nm-sized oxide particles have been identified. Two size ranges of particles have been analyzed separately: 0.5 to 3 nm and 3 to 15 nm (radius). The former size range is dominant in all ODS samples, the magnetic-to-nuclear scattering ratio indicates these particles to be predominantly Y2Ti2O7.

Keywords: ODS; oxide dispersion strengthened steel; nuclear materials; Fe-14Cr; small-angle neutron scattering; SANS; spark plasma sintering; SPS; nano particles

Publ.-Id: 20472

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