Publication database - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Without submitted and only approved publications
Only approved publications

25778 Publications
The inhibitory potency of polyoxometalates at P2X receptors
Spanier, C.; Abdelrahman, A.; Tang, J.; Hausmann, R.; Kortz, U.; Schmalzin, G.; Stephan, H.; Wang, W.; Müller, C. E.
Abstract: P2X receptors are trimeric ligand-gated ion channels activated by ATP and permeable for cations such as Na+, K+ and Ca2+. Seven different subunits exist, assembled as homo- or heterotrimers of various stoichiometry.1 Polyoxometalates (POMs) are polynuclear metal-oxo anions of early transition metals in high oxidation states (e. g. W6+, Mo6+, V5+). This class of inorganic metal cluster compounds exhibits great variability with respect to shape, size, charge and composition.2 POMs bear several negative charges and in this respect resemble ATP, which binds to P2X receptors in its negatively charged state. We previously found that certain POMs can inhibit ATP-hydrolyzing ectonucleotidases.2-4 In the present study we investigated whether tungsten-containing POMs can interact with P2X receptors. A series of POMs was investigated for their ability to inhibit ATP-induced calcium influx in recombinant 1321N1 astrocytoma cells stably transfected with P2X receptor subtypes. Several POMs were found to be highly potent inhibitors of P2X receptors exhibiting low nanomolar potency. PEGylation of POMs to increase their metabolic stability was tolerated by the receptors. Structure-activity relationships at P2X receptor subtypes differed from those observed for ecto¬nucleotidases. The majority of POMs were found to be non-cytotoxic at pharmacologically active concentrations.
  • Poster
    Frontiers in Medicinal Chemistry (FiMC) Meeting 2016, 13.-16.03.2016, Bonn, Deutschland
Registration No. 23622 - Permalink

In vivo demonstration of an active tumor pretargeting approach with peptide nucleic acid bioconjugates as complementary system
Leonidova, A.; Foerster, C.; Zarschler, K.; Schubert, M.; Pietzsch, H.-J.; Steinbach, J.; Bergmann, R.; Metzler-Nolte, N.; Stephan, H.; Gasser, G.
Abstract: Aim
The ability of early-stage diagnosis of tumor malignancies and personalized treatment ultimately relies on the availability of highly tumor-affine compounds with purposeful pharmacological profile. Although monoclonal antibodies (mAbs) specifically bind to tumor-associated epitopes, the conventional concept of directly radiolabeled tumor-specific mAb has several drawbacks most prominently the prolonged radiation exposure of non-cancerous tissue. However, the concept of tumor pretargeting allows for the rational use of long-circulating high-affinity mAbs for non-invasive cancer radioimmunodetection and therapy. Our work describes a successful tumor pretargeting utilizing an EGFR-specific mAb and peptide nucleic acid (PNA) derivatives as the complementary system for specific radionuclide delivery to pretargeted tumor tissue.

After chemical synthesis, purification and detailed characterization of the individual components including antibody-PNA conjugates and different PNA oligomers, biodistribution studies were carried out using healthy Wistar rats. Finally, the pretargeting approach was evaluated in murine A431 tumor xenografts by single photon emission computed tomography.

After optimizing the pharmacokinetic properties of PNA oligomers and investigating their hybridization properties, we elaborated a versatile conjugation protocol based on coupling a cysteine-functionalized PNA oligomer to a maleimido-functionalized mAb. The in vivo studies demonstrated a rapid and efficient accumulation of activity at the tumor site with a tumor-to-muscle ratio of > 8 and clearly distinguishable tumor visualization.

This successful tumor pretargeting study has demonstrated the high potential of this concept by applying radiolabeled complementary PNA strands as an alternative in vivo recognition and radionuclide transporting system. The next step involves the translation of these results to the application of therapeutic relevant radionuclides.
  • Lecture (Conference)
    NuklearMedizin 2016 - 54. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin e.V., 20.-23.04.2016, Dresden, Deutschland
Registration No. 23616 - Permalink

Field-Induced Magnonic Liquid in the 3D Spin-Dimerized Antiferromagnet Sr3Cr2O8
Wang, Z.; Quintero-Castro, D. L.; Zherlitsyn, S.; Yasin, S.; Skourski, Y.; Islam, A. T. M. N.; Lake, B.; Deisenhofer, J.; Loidl, A.
Abstract: We report on ultrasound and magnetization studies in three-dimensional, spin-dimerized Sr3Cr2O8 as a function of temperature and external magnetic field up to 61 T. It is well established [A. A. Aczel et al., Phys. Rev. Lett. 103, 207203 (2009)] that this system exhibits a magnonic-superfluid phase between 30 and 60 T and below 8 K. By mapping ultrasound and magnetization anomalies as a function of magnetic field and temperature we establish that this superfluid phase is embedded in a domelike phase regime of a hightemperature magnonic liquid extending up to 18 K. Compared to thermodynamic results, our study indicates that the magnonic liquid could be characterized by an Ising-like order but has lost the coherence of the transverse components. Registration No. 23607 - Permalink

Measurement of the 92,93,94,100Mo(γ,n) reactions by Coulomb Dissociation
Göbel, K.; Adrich, P.; Altstadt, S.; Alvarez-Pol, H.; Aksouh, F.; Aumann, T.; Babilon, M.; Behr, K.-H.; Benlliure, J.; Berg, T.; Böhmer, M.; Boretzky, K.; Brünle, A.; Beyer, R.; Casarejos, E.; Chartier, M.; Cortina-Gil, D.; Chatillon, A.; Pramanik, U. D.; Deveaux, L.; Elvers, M.; Elze, T. W.; Emling, H.; Erhard, M.; Ershova, O.; Fernandez-Dominguez, B.; Geissel, H.; Górska, M.; Heftrich, T.; Heil, M.; Hellstroem, M.; Ickert, G.; Johansson, H.; Junghans, A. R.; Käppeler, F.; Kiselev, O.; Klimkiewicz, A.; Kratz, J. V.; Kulessa, R.; Kurz, N.; Labiche, M.; Langer, C.; Bleis, T. L.; Lemmon, R.; Lindenberg, K.; Litvinov, Y. A.; Maierbeck, P.; Movsesyan, A.; Müller, S.; Nilsson, T.; Nociforo, C.; Paar, N.; Palit, R.; Paschalis, S.; Plag, R.; Prokopowicz, W.; Reifarth, R.; Rossi, D. M.; Schnorrenberger, L.; Simon, H.; Sonnabend, K.; Sümmerer, K.; Surówka, G.; Vretenar, D.; Wagner, A.; Walter, S.; Waluś, W.; Wamers, F.; Weick, H.; Weig, M.; Winckler, N.; Winkler, M.; Zilges, A.
Abstract: The Coulomb Dissociation (CD) cross sections of the stable isotopes 92,94,100 Mo , of the unstable isotope 93 Mo were measured at the L, /R 3 B setup at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Experimental data on these isotopes may help to explain the problem of the underproduction of 92,94 Mo , 96,98 Ru in the models of p-process nucleosynthesis. The CD cross sections obtained for the stable Mo isotopes are in good agreement with experiments performed with real photons, thus validating the method of Coulomb Dissociation. The result for the reaction 93 Mo(γ,n) is especially important since the corresponding cross section has not been measured before. A preliminary integral Coulomb Dissociation cross section of the 94 Mo(γ,n) reaction is presented. Further analysis will complete the experimental database for the (γ,n) production chain of the p-isotopes of molybdenum.


Registration No. 23603 - Permalink

U(VI) reduction by anaerobic microorganisms isolated from the flooding water of the former uranium mine Königstein (Saxony)
Gerber, U.; Röder, G.; Krawczyk-Bärsch, E.; Arnold, T.; Scheinost, A. C.
Abstract: The former uranium mine Königstein (Saxony, Germany) is currently in the process of remediation. The underground is flooded in a controlled way, and the flooding water is cleaned up in a dedicated waste water treatment plant. Despite high U concentrations up to 13 mg/L and a low pH of 2.9, these waters contain a high microbial diversity as detected by culture-independent methods. Microorganisms are known to interact with metals and radionuclides in different ways [1]. Anaerobic bacteria which are able to gain energy from the reduction of several metals, are known to change the redox state of metals and radionuclides. For instance, anaerobic sulfate-reducing bacteria (SRB) reduce U(VI) to U(IV) and thus change the migration behavior from the more soluble U(VI) into the less soluble U(IV) [2]. Genomic sequence analysis of the flooding water revealed the presence of such anaerobic SRB. By culture-dependent methods it was possible to isolate anaerobic microorganisms from the flooding water. They were incubated with 10 mM glycerol using the flooding water as background medium. During an incubation time of six weeks the redox potential decreased from 660 mV to 300 mV. After four and six weeks of incubation, the cells were separated from the incubation medium by centrifugation and than analyzed by U-LIII edge EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) measurements. By Iterative Target-Factor Analysis (ITFA) we determined that 100 % of U(VI) was reduced to U(IV). Simultaneously, investigations of the supernatant with UV-vis resulted in the same findings. The results show that naturally occurring anaerobic microorganisms within the flooding water of the former uranium mine Königstein are able to reduce U(VI) to U(IV).

1. Lloyd, J.R.M., L. E. , Interactions of microorganisms with radionuclides. Elsevier Science. 2002.
2. Lovley, D.R., et al., Enzymatic Iron and Uranium Reduction by Sulfate-Reducing Bacteria. Marine Geology, 1993. 113(1-2): p. 41-53.

Keywords: Uranium, Reduction, Sulfate-reducing bacteria, Bioremediation
  • Lecture (others)
    5. Workshop - TransAqua, 06.-07.04.2016, Dresden, Deutschland
Registration No. 23587 - Permalink

Polyglycerol-Based Copper Chelators for Transport and Release of Copper Ions in Biological Environments
Albrecht, R.; Fehse, S.; Pant, K.; Nowag, S.; Stephan, H.; Haag, R.; Tzschucke, C. C.
Abstract: Here, the synthesis and characterization of three improved nanosystems is presented based on amino functionalized hyperbranched polyglycerol (hPG; M w = 16.8 kDa) as potential copper( II ) chelators. The ligands, N -methyl- N -picolylglycine amide, 2,6-pyridine dicarboxylic acid monoamide, and cyclam tetraacetic acid (TETA) monoamide, are covalently attached to the polymer with amide bonds. In this paper, the Cu( II ) loading capacity, the stability of the Cu( II )- loaded carriers at different pHs, with competing ligands and in human serum, as well as the transport of Cu( II ) in biological systems are investigated. For the fi rst time, a different cytotoxicity of functionalized polymer nanoparticles with and without Cu( II ) is observed. The cyclam-based carrier combines the highest loading capacity (29 Cu ions/nanoparticle), best stability with respect to pH and EDTA (45% remaining Cu after 24 h), lowest cytotoxicity (IC 50 > 100 × 10 −6 M (unloaded), 1500 × 10 −6 M Cu( II ); Cu:carrier 29:1), and the highest stability in human serum. Registration No. 23584 - Permalink

ESR modes in a Strong-Leg Ladder in the Tomonaga-Luttinger Liquid Phase
Zvyagin, S.; Ozerov, M.; Maksymenko, M.; Wosnitza, J.; Honecker, A.; Landee, C. P.; Turnbull, M.; Furuya, S.; Giamarchi, T.
Abstract: es hat kein Abstract vorgelegen
  • Lecture (Conference)
    APS March Meeting 2016, 14.-18.03.2016, Baltimore, USA
Registration No. 23580 - Permalink

Numerical simulation of liquid metal batteries
Weber, N.; Beckstein, P.; Galindo, V.; Herreman, W.; Landgraf, S.; Nore, C.; Stefani, F.; Weier, T.
Abstract: Considering the increasing deployment of renewable energies, large-scale stationary energy storage will be a key-technology for the future. One potentially ideal grid-scale energy storage system is the liquid metal battery (LMB), consisting of a totally liquid interior. The long life time and abundant raw materials of LMBs offer a very cheap way of building batteries.

Building LMBs cheap means to make them large. Strong currents in the order of kA will drive a fluid flow, which may increase the battery's performance, or lead to a short circuit in the worst case.

A numerial model for describing the MHD fluid flow is presented and used to describe the Tayler instability, electro-vortex flow and interface instabilities in LMBs.
  • Lecture (others)
    Vortrag am Departament de Física Aplicada an der Universitat Politècnica de Catalunya, 26.04.2016, Barcelona, Spanien
Registration No. 23578 - Permalink

Open Access-Transformationsinitiative "OA2020"
Reschke, E.
Abstract: Vorstellung der Open Access Transformationsinitiative OA2020
Keywords: Open Access, OA2020, publication fees, author publication charge, White Paper, DEAL
  • Lecture (others)
    Arbeitskreis Spezialbibliotheken Dresden - Frühjahrstreffen,, 20.04.2016, Dresden, Deutschland
Registration No. 23577 - Permalink

Kerndatensatz Forschung
Reschke, E.
Abstract: Vorstellung der Kategorien, die sich auf das Publizieren beziehen.
Keywords: Kerndatensatz, Research, Publications
  • Lecture (others)
    Arbeitskreis Spezialbibliotheken Dresden - Frühjahrstreffen, 20.04.2016, Dresden, Deutschland
Registration No. 23576 - Permalink

Dynamical properties of the sine-Gordon quantum spin magnet Cu-PM at zero and finite temperature
Tiegel, A. C.; Honecker, A.; Pruschke, T.; Ponomaryov, A.; Zvyagin, S. A.; Feyerherm, R.; Manmana, S. R.
Abstract: The material copper pyrimidine dinitrate (Cu-PM) is a quasi-one-dimensional spin system described by the spin-1/2 XXZ Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interactions. Based on numerical results obtained by the density-matrix renormalization group, exact diagonalization, and accompanying electron spin resonance (ESR) experiments we revisit the spin dynamics of this compound in an applied magnetic field. Our calculations for momentum and frequency-resolved dynamical quantities give direct access to the intensity of the elementary excitations at both zero and finite temperature. This allows us to study the system beyond the low-energy description by the quantum sine-Gordon model. We find a deviation from the Lorentz invariant dispersion for the single-soliton resonance. Furthermore, our calculations only confirm the presence of the strongest boundary bound state previously derived from a boundary sine-Gordon field theory, while composite boundary-bulk excitations have too low intensities to be observable. Upon increasing the temperature, we find a temperature-induced crossover of the soliton and the emergence of new features, such as interbreather transitions. The latter observation is confirmed by our ESR experiments on Cu-PM over a wide range of the applied field. Registration No. 23562 - Permalink

Comparison Between the Magnetic Irreversibility and Zero Resistance of High-Quality Melt-Processed YBaCuO Superconductors
Dias, F. T.; Vieira, V. D. N.; Wolff-Fabris, F.; Kampert, E.; Hneda, M.; Schaf, J.; Farinela, G. F.; Gouvea, C. D.; Rovira, J. J. R.
Abstract: This paper portrays a detailed study of the magnetic irreversibility limit Tirr (H) and of the zero resistance point Tc0 (H) of three different top-seeding melt-textured YBa2Cu3O7−δ superconducting samples, with well-aligned c-axis and doped with a high density of nonsuperconducting Y2Ba1Cu1O5 (Y211) pinning centers. We have performed measurements for applied magnetic fields up to 140 kOe and for the whole set of the different field–current configurations. The magnetization measurements were performed using an MPMS-XL SQUID magnetometer and a vibrating sample magnetometer, both from Quantum Design. The electric transport measurements were made using a physical properties measurement system from Quantum Design. The goal of this exhaustive study is obtaining precise data about magnetic flux mobility along the various directions in the sample for the different field–current configurations, thereby defining the nature and effects, due to the strength and anisotropy of the pinning mechanisms and disclosing the various physical mechanisms dissipating electric transport in these systems below the superconducting transition temperature. We discuss our results in terms of the anisotropic flux pinning by the Y211 grains dispersed into the superconducting matrix. Registration No. 23561 - Permalink

Electron spin resonance in a strong-rung spin-1/2 Heisenberg ladder
Ponomaryov, A. N.; Ozerov, M.; Zviagina, L.; Wosnitza, J.; Povarov, K. Y.; Xiao, F.; Zheludev, A.; Landee, C.; Cizmar, E.; Zvyagin, A. A.; Zvyagin, S. A.
Abstract: Cu(C8H6N2)Cl2, a strong-rung spin-1/2 Heisenberg ladder compound, is probed by means of electron spin resonance (ESR) spectroscopy in the field-induced gapless phase above Hc1. The temperature dependence of the ESR linewidth is analyzed in the quantum field theory framework, suggesting that the anisotropy of magnetic interactions plays a crucial role, determining the peculiar low-temperature ESR linewidth behavior. In particular, it is argued that the uniform Dzyaloshinskii-Moriya interaction (which is allowed on the bonds along the ladder legs) can be the source of this behavior in Cu(C8H6N2)Cl2. Registration No. 23560 - Permalink

The TurbEFA Field Experiment - Measuring the Influence of a Forest Clearing on the Turbulent Wind Field
Queck, R.; Bernhofer, C.; Bienert, A.; Schlegel, F.
Abstract: Abstract Forest ecosystems play an important role in the interaction between the land surface and the atmosphere. Measurements and modelling efforts have revealed significant uncertainties in state-of-the-art flux assessments due to spatial inhomogeneities in the air-flow and land surface. Here, a field experiment is used to describe the turbulent flow across a typical Central European forest clearing. A three-dimensional model of the inhomogeneous forest stand was developed using an innovative approach based on terrestrial laser-scanner technology. The comparison of the wind statistics of two measurement campaigns (5 and 12 months long) showed the spatial and temporal representativeness of the ultrasonic anemometer measurements within the canopy. An improved method for the correction of the vertical velocity enables the distinction between the instrumental offsets and the vertical winds due to the inclination of the instrument. Despite a 13 % fraction of deciduous plants within the otherwise evergreen canopy, the effects of phenological seasons on the velocity profiles were small. The data classified according to the wind speed revealed the intermittent nature of recirculating air in the clearing. Furthermore, the development of sub-canopy wind-speed maxima is explained by considering the velocity moments and the momentum equation (including measurements of the local pressure gradient). Clearings deflect the flow downward and feed the sub-canopy flow, i.e., advective fluxes, according to wind speed and, likely, clearing size, whereas local pressure gradients play an important role in the development of sub-canopy flow. The presented dataset is freely available at the project homepage.
Keywords: Forest inhomogeneity, Metström, Momentum balance, Turbulence measurements, Vegetation model Registration No. 23548 - Permalink

Multimodal Somatostatin Receptor Theranostics Using [64Cu]Cu-/[177Lu]Lu-DOTA-(Tyr3)octreotate and AN-238 in a Mouse Pheochromocytoma Model.
Ullrich, M.; Bergmann, R.; Peitzsch, M.; Zenker, E.; Cartellieri, M.; Bachmann, M.; Ehrhart-Bornstein, M.; Block, N.; Schally, A.; Eisenhofer, G.; Bornstein, S.; Pietzsch, J.; Ziegler, C.
Abstract: Pheochromocytomas and extra-adrenal paragangliomas (PHEO/PGLs) are rare catecholamine-producing chromaffin cell tumors. For metastatic disease, no effective therapy is available. Overexpression of somatostatin type 2 receptors (SSTR2) in PHEO/PGLs promotes interest in applying therapies using somatostatin analogs linked to radionuclides and/or cytotoxic compounds, such as [(177)Lu]Lu-DOTA-(Tyr(3))octreotate (DOTATATE) and AN-238. Systematic evaluation of such therapies for the treatment of PHEO/PGLs requires sophisticated animal models. In this study, the mouse pheochromocytoma (MPC)-mCherry allograft model showed high tumor densities of murine SSTR2 (mSSTR2) and high tumor uptake of [(64)Cu]Cu-DOTATATE. Using tumor sections, we assessed mSSTR2-specific binding of DOTATATE, AN-238, and somatostatin-14. Therapeutic studies showed substantial reduction of tumor growth and tumor-related renal monoamine excretion in tumor-bearing mice after treatment with [(177)Lu]Lu-DOTATATE compared to AN-238 and doxorubicin. Analyses did not show agonist-dependent receptor downregulation after single mSSTR2-targeting therapies. This study demonstrates that the MPC-mCherry model is a uniquely powerful tool for the preclinical evaluation of SSTR2-targeting theranostic applications in vivo. Our findings highlight the therapeutic potential of somatostatin analogs, especially of [(177)Lu]Lu-DOTATATE, for the treatment of metastatic PHEO/PGLs. Repeated treatment cycles, fractionated combinations of SSTR2-targeting radionuclide and cytotoxic therapies, and other adjuvant compounds addressing additional mechanisms may further enhance therapeutic outcome.
Keywords: neuroendocrine tumors, catecholamines, DOTATATE, PET, SPECT, optical in vivo imaging, doxorubicin


Registration No. 23539 - Permalink

The strange implications of electron-electron scattering in graphene
Helm, M.; König-Otto, J. C.; Mittendorff, M.; Pashkin, A.; Schneider, H.; Winnerl, S.; Wendler, F.; Winzer, T.; Malic, E.; Knorr, A.
Abstract: Electron-electron scattering in graphene gives rise to some unexpected behavior in the electron dynamics, as observed by pump-probe measurements.
When excited with a near-infrared femtosecond laser pulse, the pump-probe signal depends on the angle between the linear polarization of the pump and the probe pulse, which is due to preferential excitation of electrons perpendicular to the laser electric field. This indicates an anisotropic distribution function in momentum space that is preserved by electron-electron scattering, since it mainly occurs collinearly along the Dirac cone. Only after 150 fs the distribution function is rendered isotropic through optical-phonon scattering. The effect is even more pronounced when exciting at small photon energies (88 meV), below the optical-phonon energy: In this case the anisotropic distribution function survives for as long as 5 ps, when it is finally thermalized by non-collinear Coulomb scattering. These results challenge the common view of ultrafast thermalization by electron-electron scattering.
When a magnetic field is applied to graphene, Landau levels are formed that can be selectively excited by circular-polarized radiation. In a pump-probe experiment, exciting and probing all possible transitions between the n=-1, n=0 and n=+1 Landau levels in slightly n-type graphene, we observe an unexpected sign reversal of the n=0 →1 probe signal when pumping the -1→0 transition. This directly reflects the fact that the n=0 Landau level is depleted by electron-electron Auger-type scattering, even though it is optically pumped at the same time.
Both effects can be quantitatively reproduced by a microscopic calculation based on the graphene Bloch equations, and shed new light on the possibility of infrared and THz devices based on hot carriers in graphene.

Keywords: graphene, pump-probe, free-electron laser, Landau levels
  • Invited lecture (Conferences)
    International Conference on Terahertz Emission, Metamaterials and Nanophotonics (TERAMETANANO 2016), 03.-10.04.2016, Cartagena, Colombia
Registration No. 23533 - Permalink

Prompt γ-ray based proton range verification: From experiments to clinical application
Priegnitz, M.; Nenoff, L.; Barczyk, S.; Golnik, C.; Hotoiu, L.; Keitz, I.; Smeets, J.; Trezza, A.; Vander Stappen, F.; Werner, T.; Fiedler, F.; Prieels, D.; Baumann, M.; Enghardt, W.; Pausch, G.; Richter, C.
Abstract: no abstract available
  • Poster
    National Center for Radiation Oncology 2nd Scientific Retreat, 14.-16.04.2016, Dresden, Deutschland
Registration No. 23531 - Permalink

Modellierung und Validierung von Feldionisation in parallelen Particle-in-Cell-Codes
Garten, M.
Abstract: Die Modellierung von Feldionisation in Particle-in-Cell(PIC)-Codes ist eine wichtige Voraussetzung zur Untersuchung der Wechselwirkung hochintensiver, ultrakurzer Laserpulse mit Materie. Es existieren bereits zahlreiche Modelle, die akkurate Vorhersagen im Bereich nicht-relativistischer Intensitäten und oberhalb atomarer Zeitskalen treffen können. Weiterhin existieren auch zahlreiche PIC-Codes, die für den Einsatz auf CPUs konzipiert wurden und Feldionisation berücksichtigen. Das Ziel dieser Arbeit ist die Modellierung von Feldionisation auf neuen, hochparallelen GPU-Architekturen. Diese werden in den letzten Jahren verstärkt für wissenschaftliche Simulationen eingesetzt und bieten einen deutlichen Geschwindigkeitsvorteil gegenüber CPUs. Die Modellierung von Feldionisation auf GPGPUs birgt einige Herausforderungen und es ist das erweiterte Ziel dieser Arbeit, die Implementierung auch zu verifizieren. Dabei wird ein Einblick in die Schwierigkeiten gegeben, die bei der Anwendung existierender Ionisationsmodelle durch Einschränkungen der Modelle selbst, des PIC-Schemas sowie der Plasmadynamik zu beachten sind. In Folge dieser Arbeit wurde PIConGPU, der derzeit schnellste, vollständig relativistische Particle-in-Cell-Code der Welt, um ein allgemeines Werkzeug zur Modellierung von Ionisation erweitert. Dieses ermöglicht die Simulation neuer und spannender physikalischer Anwendungsfälle im Bereich der Laser-Plasmaphysik.
Keywords: Particle-In-Cell, field ionization, GPGPU, PIConGPU, ADK, BSI
  • Master thesis
    HZDR, TU Dresden, 2015
    Mentor: Prof. Dr. Thomas Cowan, Prof. Dr. Ulrich Schramm, Dr. Michael Bussmann
    0097 Seiten
Registration No. 23518 - Permalink

Application of X-ray absorption spectroscopy to actinide research
Scheinost, A. C.
Abstract: An overview will be given on the applications of x-ray absorption spectroscopy to actinide research, including topics in nuclear waste management and development of fourth generation nuclear fuel
Keywords: XAFS Nuclear fuel nuclear waste disposal
  • Invited lecture (Conferences)
    11th School on the Physics and Chemistry of the Actinides, 13.-16.03.2016, Grenoble, France
Registration No. 23514 - Permalink

Distillation Tray Efficiency Modeling: A Forgotten Chapter
Vishwakarma, V.; Schubert, M.; Hampel, U.
Abstract: Cross-flow trays are highly reputed among vapour-liquid contacting devices due to their versatility. They have been into existence for two centuries; still the estimation of their mass transfer efficiency relies mostly on experience. There have been numerous attempts in the past to understand the nature of liquid mixing and flow patterns on trays. However, very few have managed to relate their findings with tray efficiency.
The present work aims at reviewing mathematical models developed for predicting distillation tray efficiency. These models were developed by considering simplified assumptions namely plug flow, uniform vapour composition, constant froth height etc. It is needless to mention the requirement of an improved mathematical model accounting real flow scenarios. This work also attempts to encourage the fraternity of fluid separation technology to revive the efficacy of tray modeling.

Keywords: Distillation Trays, Murphree Tray Efficiency, Eddy Diffusion Model, Residence Time Distribution
  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Fluidverfahrenstechnik, 16.-17.03.2016, Garmisch-Partenkirchen, Germany
Registration No. 23512 - Permalink

A gas cell for stopping, storing and polarizing radioactive particles
Sytema, A.; van den Berg, J. E.; Böll, O.; Chernowitz, D.; Dijck, E. A.; Grasdijk, J. O.; Hoekstra, S.; Jungmann, K.; Mathavan, S. C.; Meinema, C.; Mohanty, A.; Müller, S. E.; Nuñez Portela, M.; Onderwater, C. J. G.; Pijpker, C.; Willmann, L.; Wilschut, H. W.
Abstract: A radioactive beam of 20Na is stopped in a gas cell filled with Ne gas. The stopped particles are polarized by optical pumping. The degree of polarization that can be achieved is studied. A maximum polarization of 50% was found. The dynamic processes in the cell are described with a phenomenological model.
Keywords: β decay; Gas catcher; Polarization in buffer gas; Plasma Registration No. 23511 - Permalink

Controlled polar asymmetry of few-cycle and intense mid-infrared pulses
Schmidt, C.; Bühler, J.; Mayer, B.; Pashkin, A.; Leitenstorfer, A.; Seletskiy, D.
Abstract: We demonstrate synthesis of ultrabroadband and phase-locked two-color transients in the multi-terahertz frequency range with amplitudes exceeding 13 MV cm−1. Subcycle polar asymmetry of the electric field is adjusted by changing the relative phase between superposed fundamental and second harmonic components. The resultant broken symmetry of the field profile is directly resolved via electro-optic sampling. Access to such waveforms provides a direct route for control of low-energy degrees of freedom in condensed matter as well as non-perturbative light–matter interactions under highest non-resonant electric bias.
Keywords: polar asymmetry, THz, harmonic synthesis, quantum control, mid-infrared, high field, non-perturbative light–matter interaction Registration No. 23510 - Permalink

Polycrystalline ZnTe thin film on silicon synthesized by pulsed laser deposition and subsequent pulsed laser melting
Xu, M.; Gao, K.; Wu, J.; Cai, H.; Yuan, Y.; Prucnal, S.; Hübner, R.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: ZnTe thin films on Si substrates have been prepared by pulsed laser deposition and subsequent pulsed laser melting (PLM) treatment. The crystallization during PLM is confirmed by Raman scattering, x-ray diffraction and room temperature photoluminescence (PL) measurements. The PL results show a broad peak at 574 nm (2.16 eV), which can be assigned to the transitions from the conduction band to the acceptor level located at 0.145 eV above the valence band induced by zinc-vacancy ionization. Our work provides an applicable approach to low temperature preparation of crystalline ZnTe thin films.
Keywords: ZnTe, Pulsed laser melting


Registration No. 23505 - Permalink

Crystalline Electric Field and Kondo Effect in SmOs4Sb12
Mombetsu, S.; Yanagisawa, T.; Hidaka, H.; Amitsuka, H.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Ho, P.-C.; Maple, M. B.
Abstract: Our ultrasound results obtained in pulsed magnetic fields show that the filled-skutterudite compound SmOs4Sb12 has the Γ67 quartet crystalline-electric-field ground state. This fact suggests that the multipolar degrees of freedom of the Γ quartet play an important role in the unusual physical properties of this material. On the other hand, the elastic Response below ≈20 T cannot be explained using the localized 4f-electron model, which does not take into account the Kondo effect or ferromagnetic ordering. The analysis result suggests the presence of a Kondo-like screened state at low magnetic fields and its suppression at high magnetic fields above 20 T even at low temperatures. Registration No. 23504 - Permalink

Measurement of the photodissociation of the deuteron at energies relevant to Big Bang nucleosynthesis
Hannaske, R.
Abstract: Zwischen 10 und 1000 s nach dem Urknall bildeten sich während der Big Bang Nukleosynthese (BBN) die ersten leichten Elemente aus Protonen und Neutronen. Die primordialen Häufigkeiten dieser Elemente hingen von denWirkungsquerschnitten der beteiligten Kernreaktionen ab. Vergleiche zwischen den Ergebnissen nuklearer Netzwerkrechnungen mit astronomischen Beobachtungen bieten eine einzigartige Möglichkeit, etwas über das Universum zu dieser Zeit zu erfahren.
Da es für die p(n,g)d-Reaktion, die eine Schlüsselreaktion der BBN ist, kaum Messungen im relevanten Energiebereich gibt, beruht deren Reaktionsrate in Netzwerkrechnungen auf theoretischen Berechnungen. Darin fließen auch experimentelle Daten der Nukleon-Nukleon-Streuung, des Einfangquerschnitts für thermische Neutronen sowie (nach Anwendung des Prinzips des detaillierten Gleichgewichts) der d(g,n)p-Reaktion mit ein. Diese Reaktion, die Photodissoziation des Deuterons, ist bei BBN-Energien (Tcm = 20–200 keV) ebenfalls kaum vermessen. Die großen experimentelle Unsicherheiten machen Vergleiche mit den präzisen theoretischen Berechnungen schwierig. In den letzten Jahren wurde die d(g,n)p-Reaktion und insbesondere der M1-Anteil des Wirkungsquerschnitts mit quasi-monoenergetischen g-Strahlen aus Laser-Compton-Streuung oder durch Elektrodesintegration untersucht. Üblicherweise verwendete man für Messungen des d(g,n)p-Wirkungsquerschnitts entweder die auf wenige diskrete Energien beschränkte Strahlung des g-Zerfalls oder Bremsstrahlung, für die aber eine genaue Photonenflussbestimmung sowie der Nachweis von einem der Reaktionsprodukte und dessen Energie nötig ist. Da diese Energie im Bereich der BBN relativ gering ist, gab es bisher noch keine absoluten Messung des d(g,n)p-Wirkungsquerschnitts bei Tcm < 5 MeV mit Bremsstrahlung.
Das Ziel dieser Dissertation ist eine solche Messung mit einer Unsicherheit von 5 % im für die BBN relevanten Energiebereich und darüber hinaus bis Tcm ~ 2,5 MeV unter Verwendung gepulster Bremsstrahlung an der Strahlungsquelle ELBE. Dieser supraleitende Elektronenbeschleuniger befindet sich am Helmholtz-Zentrum Dresden-Rossendorf und stellte einen Elektronenstrahl hoher Intensität bereit. Die kinetische Elektronenenergie von 5 MeV wurde mit einem Browne-Buechner-Spektrometer präzise gemessen. Die Energieverteilung der in einer Niob-Folie erzeugten Bremsstrahlungsphotonen wurde berechnet. Die Photonenflussbestimmung nutzte die Kernresonanzstreuung an 27Al, das sich mit deuteriertem Polyethylen in einem mehrschichtigen Target befand. Die 27Al-Abregungen wurden mit abgeschirmten, hochreinen Germanium-Detektoren nachgewiesen, deren Effektivität mit GEANT4 simuliert und durch Quellmessungen normiert wurde. Die Messung der Energie der Neutronen aus der d(g,n)p-Reaktion erfolgte mittels deren Flugzeit in Plastikszintillatoren, die an zwei Seiten von Photoelektronenvervielfachern mit hoher Verstärkung ausgelesen wurden. Die Nachweiseffektivität dieser Detektoren wurde in einem eigenen Experiment in den Referenz-Neutronenfeldern der PTB Braunschweig kalibriert. Die Nachweisschwelle lag bei etwa 10 keV kinetischer Neutronenenergie.Wegen der guten Zeitauflösung der Neutronendetektoren und des ELBE-Beschleunigers genügte eine Flugstrecke von nur 1 m. Die Energieauflösung betrug im d(g,n)p-Experiment 1–2 %. Leider gingen viele Neutronen bereits durch Streuung in dem großen Target verloren oder sie wurden erst durch Teile des kompakten Experimentaufbaus in die Detektoren gestreut. Beide Effekte wurden mit Hilfe von FLUKA simuliert um einen Korrekturfaktor zu bestimmen, der aber bei niedrigen Energien relativ groß war.
Der d(g,n)p-Wirkungsquerschnitts wurde daher nur im Bereich 0.7 MeV < Tcm < 2.5 MeV bestimmt. Die Ergebnisse stimmen mit anderen Messungen, Daten-Evaluierungen sowie theoretischen Rechnungen überein. Die Gesamtunsicherheit beträgt circa 6.5 % und kommt zu fast gleichen Teilen von den statistischen und systematischen Unsicherheiten. Die statistische Unsicherheit könnte durch eine längere FLUKA Simulation noch von 3–5 % auf 1 % verringert werden. Die systematische Unsicherheit von 4.5 % ist vorrangig auf die Photonenflussbestimmung, die Neutronen-Nachweiseffektivität und die Target-Zusammensetzung zurückzuführen.

Keywords: Big Bang nucleosynthesis, bremsstrahlung, gamma-ray spectroscopy, neutron time-of-flight, nuclear astrophysics, photon scattering, neutron detector, efficiency, FLUKA
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-071 2016


Registration No. 23501 - Permalink

Single-shot betatron source size measurement from a laser-wakefield accelerator
Köhler, A.; Couperus, J. P.; Zarini, O.; Jochmann, A.; Irman, A.; Schramm, U.
Abstract: Betatron radiation emitted by accelerated electrons in laser-wakefield accelerators can be used as a diagnostic tool to investigate electron dynamics during the acceleration process. We analyse the spectral characteristics of the emitted betatron pattern utilizing a 2D x-ray imaging spectroscopy technique. Together with simultaneously recorded electron spectra and x-ray images, the betatron source size, thus the electron beam radius, can be deduced at every shot.
Keywords: Betatron radiation, Laser wakefield acceleration, x-rays
  • Lecture (Conference)
    DPG-Frühjahrstagung Darmstadt, 14.-18.03.2016, Darmstadt, Deutschland
Registration No. 23499 - Permalink

Quantum oscillations and the Fermi surface topology of the Weyl semimetal NbP
Klotz, J.; Wu, S.-C.; Shekhar, C.; Sun, Y.; Schmidt, M.; Nicklas, M.; Baenitz, M.; Uhlarz, M.; Wosnitza, J.; Felser, C.; Yan, B.
Abstract: The Weyl semimetal NbP was found to exhibit topological Fermi arcs and exotic magnetotransport properties. Here, we report on magnetic quantum-oscillation measurements on NbP and construct the three-dimensional Fermi surface with the help of band-structure calculations. We reveal a pair of spin-orbit-split electron pockets at the Fermi energy and a similar pair of hole pockets, all of which are strongly anisotropic. The Weyl points that are located in the kz ≈ π/c plane are found to exist 5 meV above the Fermi energy. Therefore, we predict that the chiral anomaly effect can be realized in NbP by electron doping to drive the Fermi energy to the Weyl points. Registration No. 23498 - Permalink

Exotic Ground State and Elastic Softening under Pulsed Magnetic Fields in PrTr2Zn20 (Tr = Rh, Ir)
Ishii, I.; Goto, H.; Kamikawa, S.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Onimaru, T.; Matsumoto, K. T.; Takabatake, T.; Suzuki, T.
Abstract: To investigate a field-induced level crossing of the ground-state doublet in PrTr2Zn20 (Tr = Rh, Ir), we performed ultrasonic measurements in pulsed magnetic fields applied along the [110] and [001] directions and analyzed the results in the framework of the strain-susceptibility approach. Above 40 T for H ∣∣ [110], we observed an elastic softening of the transverse modulus (C11 − C12)/2 corresponding to the ground-state doublet. In both compounds the softening is followed by a minimum at about 47 T at low temperatures. We predict the presence of a new field-induced phase boundary in PrTr2Zn20 at this field with two possible cases. The magnetic field of the minimum cannot be explained by only the quadrupole interaction. Registration No. 23497 - Permalink

Magnetic phase diagram of the helimagnetic spinel compound ZnCr2Se4 revisited by small-angle neutron scattering
Cameron, A. S.; Tymoshenko, Y. V.; Portnichenko, P. Y.; Gavilano, J.; Tsurkan, V.; Felea, V.; Loidl, A.; Zherlitsyn, S.; Wosnitza, J.; Inosov, D. S.
Abstract: We performed small-angle neutron scattering (SANS) measurements on the helimagnetic spinel compound ZnCr2Se4. The ground state of this material is a multi-domain spin-spiral phase, which undergoes domain selection in a magnetic field and reportedly exhibits a transition to a proposed spin-nematic phase at higher fields. We observed a continuous change in the magnetic structure as a function of field and temperature, as well as a weak discontinuous jump in the spiral pitch across the domain-selection transition upon increasing field. From our SANS results we have established the absence of any long-range magnetic order in the high-field (spin-nematic) phase. We also found that all the observed phase transitions are surprisingly isotropic with respect to the field direction. Registration No. 23496 - Permalink

Performance and Application Status of the Superconducting Photoinjector at ELBE
Teichert, J.; Arnold, A.; Lu, P.; Murcek, P.; Vennekate, H.; Xiang, R.
Abstract: A new SRF gun has been commissioned at the ELBE linac. The gun has an improved 3.5-cell cavity and a superconducting solenoid is integrated. Beam parameter measurements have been carried out with a Cu photocathode.
Keywords: photoinjector, superconducting cavity, electron source, photocathode
  • Invited lecture (Conferences)
    OSA High-Brightness Sources and Light-Driven Interaction Congress, 20.-22.03.2016, Long Beach, USA
Registration No. 23486 - Permalink

Synthesis and characterization of modified ultrasmall nanoparticles as multimodal imaging agents
Singh, G.; Hunoldt, S.; Licciardello, N.; Stephan, H.; Faramus, A.; De Cola, L.
Abstract: The synthesis of multimodal imaging agents is indeed a growing field and a lot of research is currently being done in this area because of its wide biomedical applications.[1] The idea behind this research is to prepare a single molecule/nanoparticle which is suitable for two or more imaging techniques and thus can act as a multimodal imaging agent, for example, the combination of optical and nuclear imaging modalities may provide complementary information for improving diagnosis as well as the treatment of diseases. These imaging agents combat the limitations of sensitivity, spatial and temporal resolution and also tissue penetrability. The high hydrophilicity of the nanoparticles and fast renal clearance of the complex from the body are the major highlights.
Amine terminated ultrasmall Silicon nanoparticles[2] (Si NPs) of size <5 nm were synthesized by hydrothermal method and purified by dialysis. Sulfo-Cyanine 5[3] dye was attached selectively to the amine terminated Si NPs. The single domain antibody is also conjugated with the particles for specific targeting of the cancerous tumors via a molecular handle such as PEG-Maleimide, which facilitates the targeting as well as maintains the hydrophilicity of the particles at the same time. Bispidines[4] are to be used as a copper chelator for radiolabeling the particles by 64Cu and could be used for the in vitro and in vivo studies by Positron emission tomography.
The substituents after coupling with the USNPs are assumed to act as excellent multimodal imaging agent which can be used for the cancer diagnosis and therapy.

[1] G. J. Cheon, Y. Chang, J. Yoo, J. Cheon, Angew. Chem. 2008, 120, 6355 –6358.
[2] Y. Zhong, F. Peng, F. Bao, S. Wang, X. Ji, L. Yang, Y. Su, S. Lee, Y. He, J. Am. Chem. Soc. 2013, 135, 8350−8356.
[3] K. Viehweger, L. Barbaro, K. P. García, T. Joshi, G. Geipel, J. Steinbach, H. Stephan, L. Spiccia, B. Graham, Bioconjugate Chem. 2014, 25, 1011−1022.
[4] H. Stephan, M. Walther, S. Fähnemann, P. Ceroni, J. Molloy, G. Bergamini, F. Heisig, C. E. Müller, W. Kraus, P. Comba, Chem. Eur. J. 2014, 20, 17011-17018.
  • Poster
    Ananlytica Conference 2016, 10.-12.05.2016, Münich, Germany
Registration No. 23480 - Permalink

Intrinsic diamagnetism in the Weyl semimetal TaAs
Liu, Y.; Li, Z.; Guo, L.; Chen, X.; Yuan, Y.; Liu, F.; Prucnal, S.; Helm, M.; Zhou, S.
Abstract: We investigate the magnetic properties of TaAs, a prototype Weyl semimetal. TaAs crystals show diamagnetism with magnetic susceptibility of about −7×10−7 emu/(g Oe) at 5 K. A general feature is the appearance of a minimum at around 185 K in magnetization measurements as a function of temperature, which resembles that of graphite. No phase transition is observed in the temperature range between 5 K and 400 K.
Keywords: Diamagnetism; Weyl semimetal; TaAs; Magnetic susceptibility Registration No. 23479 - Permalink

Untersuchung zum Einfluss lokaler Strömungszustände auf das Auftreten der Siedekrise
Geißler, T.; Franz, R.; Hampel, U.
Abstract: Die Effizienz von Verdampfungssystemen hängt maßgeblich von der übertragbaren Wärmestromdichte ab. Eine Leistungssteigerung ist durch das Auftreten der Siedekrise limitiert. Dabei kommt es durch ein abruptes Abfallen des Wärmeübergangskoeffizienten in leistungsbestimmten Systemen zu einem starken Temperaturanstieg der Heizfläche, welcher zu einem Versagen der Strukturelemente führen kann. Sicherheitsmargen sorgen in industriellen Anwendungen für einen ausreichenden Schutz vor diesem kritischen Zustand. Mit einer verlässlichen Vorhersage der Siedekrise können diese Margen allerdings reduziert werden. Durch Experimente mit hochaufgelöster Messung der Wandtemperatur und Bestimmung der Phasenverteilung während des Siedens werden Verdampfungsprozesse besser verstanden und CFD-Modell-Entwicklung unterstützt.
  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Wärme- und Stoffübertragung, 01.-02.03.2016, Kassel, Deutschland
Registration No. 23475 - Permalink

Electron Dynamics in Silicon−Germanium Terahertz Quantum Fountain Structures
Sabbagh, D.; Schmidt, J.; Winnerl, S.; Helm, M.; Di Gaspare, L.; de Seta, M.; Virgilio, M.; Ortolani, M.
Abstract: Asymmetric quantum well systems are excellent candidates to realize semiconductor light emitters at far-infrared wavelengths not covered by other gain media. Group-IV semiconductor heterostructures can be grown on silicon substrates, and their dipole-active intersubband transitions could be used to generate light from devices integrated with silicon electronic circuits. Here, we have realized an optically pumped emitter structure based on a three-level Ge/Si0.18Ge0.82 asymmetric coupled quantum well design. Optical pumping was performed with a tunable free-electron laser emitting at photon energies of 25 and 41 meV, corresponding to the energies of the first two intersubband transitions 0 → 1 and 0 → 2 as measured by Fourier-transform spectroscopy. We have studied with a synchronized terahertz timedomain spectroscopy probe the relaxation dynamics after pumping, and we have interpreted the resulting relaxation times (in the range 60 to 110 ps) in the framework of an out-of-equilibrium model of the intersubband electron−phonon dynamics. The spectral changes in the probe pulse transmitted at pump−probe coincidence were monitored in the range 0.7−2.9 THz for different samples and pump intensity and showed indication of both free carrier absorption increase and bleaching of the 1 → 2 transition. The quantification from data and models of the free carrier losses and of the bleaching efficiency allowed us to predict the conditions for population inversion and to determine a threshold pump power density for lasing around 500 kW/cm2 in our device. The ensemble of our results shows that optical pumping of germanium quantum wells is a promising route toward siliconintegrated far-infrared emitters.
Keywords: silicon photonics, quantum wells, chemical vapor deposition, terahertz spectroscopy, pump−probe spectroscopy, germanium Registration No. 23472 - Permalink

Terahertz Near-Field Investigation of a Plasmonic GaAs Superlens
Fehrenbacher, M.
Abstract: This work presents the first demonstration of a semiconductor based plasmonic near-field superlens, utilizing highly doped GaAs to generate infrared optical images with a spatial resolution beyond the difraction limit. Being easily transferable to other semiconductor materials, the concept described in this thesis can be exploited to realize spectrally adjustable superlenses in a wide spectral range. The idea of superlensing has been introduced theoretically in 2000, followed by numerous publications including experimental studies. The effect initiated great interest in optics, since in contrast to difraction limited conventional optical microscopy it enables subwavelength resolved imaging by reconstructing the evanescent waves emerging from an object. With techniques like scanning near-field optical microscopy (SNOM) and stimulated emission depletion (STED) being already successfully established to overcome the conventional restrictions, the concept of superlensing provides a novel, different route towards high resolution. Superlensing is a resonant phenomenon, relying either on the excitation of surface plasmons in metallic systems or on phonon resonances in dielectric structures. In this respect a superlens based on doped semiconductor benefits from the potential to be controlled in its operational wavelength by shifting the plasma frequency through adjustment of the free carrier concentration.
For a proof of principle demonstration, we investigate a superlens consisting of a highly n-doped GaAs layer (n = 4 x 10^18 cm-3) sandwiched between two intrinsic layers. Recording near-field images of subwavelength sized gold stripes through the trilayer structure by means of SNOM in combination with a free-electron laser, we observe both enhanced signal and improved spatial resolution at radiation wavelengths close to l = 22 µm, which is in excellent agreement with simulations based on the Drude-Lorentz model of free electrons. Here, comparative investigations of a purely intrinsic reference sample confirm that the effect is mediated by the charge carriers within the doped layer. Furthermore, slightly differently doped samples provide indications for the expected spectral shift of the resonance. According to our calculations, the wavelength range to be exploited by n-GaAs based superlenses reaches far into the terahertz region, whereas other semiconductor materials are required to explore the near infrared.
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-070 2016


Registration No. 23470 - Permalink

Design Study of a Traveling-Wave Thomson-Scattering Experiment for the Realization of Optical Free Electron Lasers
Steiniger, K.; Albach, D.; Debus, A.; Loeser, M.; Pausch, R.; Roeser, F.; Schramm, U.; Siebold, M.; Bussmann, M.
Abstract: We present an experimental setup strategy for the realization of an optical free-electron laser (OFEL) in the Traveling-Wave Thomson-Scattering geometry (TWTS). In TWTS, the electric fi eld of petawatt class, pulse-front tilted laser pulses is used to provide an optical undulator fi eld. This is passed by a relativistic electron bunch so that electron direction of motion and laser propagation direction enclose an interaction angle. The combination of side scattering and pulse-front tilt provides continuous overlap of electrons and laser pulse over meter scale distances which are achieved with centimeter wide laser pulses.
An experimental challenge lies in shaping of these wide laser pulses in terms of laser dispersion compensation along the electron trajectory and focusing. In the talk we show how diff raction gratings in combination with mirrors are used to introduce and control dispersion of the laser in order to provide a plane wave laser fi eld along the electron trajectory. Furthermore we give tolerance limits on alignment errors to operate the OFEL. Example setups illustrate functioning and demonstrate feasibility of the scheme.

Keywords: traveling-wave, thomson-scattering, FEL, x-ray, pulse-front tilt, out-of-focus
  • Lecture (Conference)
    DPG-Frühjahrstagung Darmstadt, 14.-18.03.2016, Darmstadt, Deutschland
Registration No. 23469 - Permalink

Design Study for an Optical Free-Electron Laser Realized by Traveling-Wave Thomson-Scattering
Steiniger, K.; Albach, D.; Bussmann, M.; Irman, A.; Jochmann, A.; Loeser, M.; Pausch, R.; Röser, F.; Schramm, U.; Debus, A.
Abstract: We present an experimental setup strategy for the realization of an optical free-electron laser (OFEL) in the Traveling-Wave Thomson-Scattering geometry (TWTS). In TWTS, the electric field of petawatt class, pulse-front tilted laser pulses is used to provide an optical undulator field. This is passed by a relativistic electron bunch so that electron direction of motion and laser propagation direction enclose an interaction angle. The combination of side scattering and pulse-front tilt provides continuous overlap of electrons and laser pulse over meter scale distances which are achieved with centimeter wide laser pulses. An experimental challenge lies in shaping of these wide laser pulses in terms of laser dispersion compensation along the electron trajectory and focusing. The poster shows how diffraction gratings in combination with mirrors are used to introduce and control dispersion of the laser in order to provide a plane wave laser field along the electron trajectory. Furthermore we give limits on alignment tolerances to operate the OFEL. Example setups illustrate functioning and demonstrate feasibility of the design.
Keywords: traveling-wave, Thomson scattering, FEL, x-ray, tilted laser pulse, out-of-focus
  • Lecture (Conference)
    Student Retreat@2. Annual MT Meeting, 07.-08.03.2016, Karlsruhe, Deutschland
  • Poster
    2. Annual MT Meeting, 08.-11.03.2016, Karlsruhe, Deutschland
Registration No. 23468 - Permalink

Free - Surface Modelling in the Ribbon Growth on Substrate (RGS)process
Beckstein, P.; Galindo, V.; Gerbeth, G.
Abstract: The cost efficient, high throughput production of metal- and semiconductor alloys is the foundation of many advanced technologies. With the development of the Ribbon Growth on Substrate (RGS) technology, a new crystallization technique is available that allows the controlled, high crystallization rate production of silicon wafers and advanced metal-silicide alloys. In contrast to other crystallization methods, like e.g. melt spinning or even directional solidification, the RGS process allows high volume manufacturing, better crystallization control and a high material yield due to a substrate driven process. To optimize the application of RGS further, insights from modelling the liquid metal flow are very desirable. We have already conducted extensive numerical investigations in order to study the involved AC magnetic fields. For the RGS technology, these magnetic fields play an essential role in realizing inductive heating and an additional magnetic retention effect.
New simulation results demonstrate the effect of the applied AC magnetic fields on the melt flow of liquid silicon. The focus is thereby devoted to the simulation of the melt surface deformation based on a multi-physical modelling approach in OpenFOAM (foam-extend). Our developed numerical tool allows us to model hydrodynamic and magnetodynamic effects and their interaction. Studies of the time-dependent free-surface flow under the influence of magnetic forces are the key for improving the RGS process as main flow structures and possible instabilities strongly depend on the melt shape.

Keywords: RGS process, OpenFOAM extend, Free-Surface Modelling
  • Poster
    1st German Czechoslovak Conference on Crystal Growth, GCCCG-1 / DKT2016, 16.-18.03.2016, Dresden, Germany
Registration No. 23466 - Permalink

First clinical application of a prompt gamma based in vivo proton range verification using a knife-edge slit camera
Richter, C.; Pausch, G.; Barczyk, S.; Priegnitz, M.; Keitz, I.; Thiele, J.; Smeets, J.; Vander Stappen, F.; Bombelli, L.; Fiorini, C.; Hotoiu, L.; Perali, I.; Prieels, D.; Enghardt, W.; Baumann, M.
Abstract: To improve precision of particle therapy, in vivo range verification is highly desirable. Methods based on prompt gamma rays emitted during treatment seem promising but have not yet been applied clinically. Here we report on the worldwide first clinical application of prompt gamma imaging (PGI) based range verification.
  • Lecture (Conference)
    ICTR-PHE 2016, International Conference on Translational Research in Radio-Oncology | Physics for Health in Europe, 15.-19.02.2016, Geneva, Switzerland
  • Abstract in refereed journal
    Radiotherapy and Oncology 118(2016)Suppl. 1, S89-S90
    Button zum Volltext
Registration No. 23457 - Permalink

Comparison of SIMS and RBS for depth profiling of silica glasses implanted with metal ions
Lorinčík, J.; Veselá, D.; Vytykáčová, S.; Švecová, B.; Nekvindová, P.; Macková, A.; Mikšová, R.; Malinský, P.; Böttger, R.
Abstract: Ion implantation of metal ions, followed by annealing, can be used for the formation of buried layers of metal nanoparticles in glasses. Thus, photonic structures with nonlinear optical properties can be formed. In this study, three samples of silicaglasses were implanted with Cu+, Ag+, or Au+ ions under the same conditions (energy 330 keV and fluence 1 × 1016 ions/cm2), and compared to three identical silicaglass samples that were subsequently coimplanted with oxygen at the same depth. All the implantedglasses were annealed at 600 °C for 1 h, which leads to the formation of metal nanoparticles. The depth profiles of Cu,Ag, and Au were measured by Rutherford backscattering and by secondary ion mass spectrometry and the results are compared and discussed.
Keywords: Rutherford backscattering, Secondary ion mass spectroscopy, Gold, Silver, Amorphous metals Registration No. 23456 - Permalink

A strategy for the qualification of multi-fluid approaches for nuclear reactor safety
Lucas, D.; Rzehak, R.; Krepper, E.; Ziegenhein, Th.; Liao, Y.; Kriebitzsch, S.; Apanasevich, P.
Abstract: CFD-simulations for two-phase flows applying the multi-fluid approach are not yet qualified to provide reliable predictions for unknown flows. Among others, one important reason is the missing agreement within the community on closure models to be used. Considering specific phenomena or not, using different models and adjustable constants, most papers presenting a model validation end up with a good agreement with experimental data. However a case by case selection of models and constants does not help to improve the predictive capabilities of such models. For this reason the definition of baseline models considering all known phenomena that could be important is proposed. In such baseline models all parameter have to be defined, i.e., there are no tuning parameters by definition. Therefore these baseline models have to be applied to many experiments with different complexity. Shortcomings of the models and our physical understanding of the complex flow phenomena have to be identified by detailed analyses on the deviations between experimental data and simulation results. A modification of the baseline model will only be done if it bases on physical considerations and improves the overall performance of the model. This requires a huge effort, but seems to be the only way to improve the situation. In particular more complete experimental data are required. Joint activities on the development of such baseline models are desirable. The paper illustrates this strategy by a baseline model for polydisperse bubbly flows which is presently developed at HZDR.
Keywords: CFD, two-phase flow, multi-fluid, bubbly flow, validation Registration No. 23455 - Permalink

Terahertz spectroscopy of individual donors in silicon by low-temperature s-SNOM
Lang, D.; Winnerl, S.; Schneider, H.; Li, J.; Clowes, S.; Murdin, B.; Döring, J.; Kehr, S. C.; Eng, L. M.; Helm, M.
Abstract: Isolated atoms or ions, typically confined in traps, are ideal systems for studying fascinating coherent quantum effects such as photon echoes. Likewise, isolated donor impurity atoms in semiconductors like silicon show a hydrogen-like spectrum, shifted to the far infrared due to the small effective mass and high dielectric constant [1]. Excited Rydberg states are of particular interest for quantum information, because they allow one to prepare long-living microscopic polarization states.

In contrast to previous far-field spectroscopic studies which probed ensembles of many impurities, we aim here at studying individual impurity centers. To this end, low-temperature scattering-type scanning near-field optical microscopy (s-SNOM) is employed and a free-electron laser is used as a precisely tunable terahertz source [2]. Our silicon samples contain different donors (P, Bi) with different defect densities, respectively, and are pre-characterized by conventional Fourier transform infrared spectroscopy.

[1] Greenland et al., Nature 465, 1057 (2010).
[2] Döring et al., Appl. Phys. Lett. 105, 053109 (2014).

Keywords: terahertz, silicon, nanoscopy, s-SNOM, spectroscopy, low-temperature, impurities, free-electron laser
  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Deutschland
Registration No. 23454 - Permalink

Bipolar resistive switching of p-YMnO3/n-SrTiO3:Nb junctions
Bogusz, A.; Blaschke, D.; Abendroth, B.; Skorupa, I.; Bürger, D.; Schmidt, O. G.; Schmidt, H.
Abstract: Resistive switching (RS) phenomena of oxides in metal-insulatormetal structures have been widely investigated due to promising applications as a non-volatile memory and in neuromorphic circuits. In our previous works, we have demonstrated unipolar RS of YMnO3-based structures [1]. This work investigates the non-volatile RS switching in Au/YMnO3-/Nb:SrTiO3-/Al structures with (p-YMnO3-)-(n-Nb:SrTiO3-) junctions. The YMnO3- films are deposited by pulsed laser deposition on the (100)-SrTiO3- doped with 0.5 wt.% of Nb substrates and exhibit bipolar RS. Observed RS behavior is assigned to the coupled electronic and ionic processes which depend on the depletion layer extension in the p-n junction. Exploitation of RS in p-n junctions offers additional functionalities of memristive devices, e.g. related to their optical properties.
[1] A. Bogusz et al., AIP Advances 4 (2014), A. Bogusz et al., Adv. Mater. Res. 1101 (2015).
  • Lecture (Conference)
    DPG Spring Meeting, 06.-11.03.2016, Regensburg, Germany
Registration No. 23452 - Permalink

Nonlinear Terahertz Absorption of Graphene Plasmons
Jadidi, M. M.; König-Otto, J. C.; Winnerl, S.; Sushkov, A. B.; Drew, H. D.; Murphy, T. E.; Mittendorff, M.
Abstract: Subwavelength graphene structures support localized plasmonic resonances in the terahertz and mid-infrared spectral regimes. The strong field confinement at the resonant frequency is predicted to significantly enhance the light-graphene interaction, which could enable nonlinear optics at low intensity in atomically thin, subwavelength devices. To date, the nonlinear response of graphene plasmons and their energy loss dynamics have not been experimentally studied. We measure and theoretically model the terahertz nonlinear response and energy relaxation dynamics of plasmons in graphene nanoribbons. We employ a terahertz pump − terahertz probe technique at the plasmon frequency and observe a strong saturation of plasmon absorption followed by a 10 ps relaxation time. The observed nonlinearity is enhanced by 2 orders of magnitude compared to unpatterned graphene with no plasmon resonance. We further present a thermal model for the nonlinear plasmonic absorption that supports the experimental results. The model shows that the observed strong linearity is caused by an unexpected red shift of plasmon resonance together with a broadening and weakening of the resonance caused by the transient increase in electron temperature. The model further predicts that even greater resonant enhancement of the nonlinear response can be expected in high-mobility graphene, suggesting that nonlinear graphene plasmonic devices could be promising candidates for nonlinear optical processing.
Keywords: Graphene, plasmons, nonlinear, pump−probe, terahertz Registration No. 23451 - Permalink

Fast graphene-based hot-electron bolometer covering the spectral range from terahertz to visible
Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. J.; Murphy, T. E.; Chatterjee, S.; Kolata, K.; Ohser, J.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.
Abstract: By using broadband absorber materials, bolometric detectors can typically cover an extremely large spectral range. However, since their response relies on the lattice temperature of the employed material, they exhibit slow response times. Hot electron bolometers (HEBs), on the other hand, can be extremely fast, because they exploit a change in device resistance caused by a varying electron temperature. A major drawback of HEBs based on superconductors is the required cooling to very low temperatures. We have developed a detector for room temperature operation, where the broadband absorption of the gapless material graphene is utilized. To this end, a graphene flake grown by chemical vapor deposition (CVD) is transferred to a SiC substrate and coupled to a logarithmic periodic antenna. Fast detection with a rise time of 40 ps is demonstrated for frequencies ranging from 0.6 THz to 390 THz [1]. Interestingly, the detector properties do not deteriorate for wavelength within the Reststrahlen band of SiC (25 – 50 THz). With a noise-equivalent power of 20 µW/Hz½ (800 µW/Hz½) in the near infrared (mid- and far infrared) the detector is capable of recording pulses with energies of the order of 10 pJ (1 nJ). We show that the detector is a versatile device for timing measurements in multi-color ultrafast spectroscopy studies.
Keywords: Detector, graphene, fast detctor, broadband detector
  • Lecture (Conference)
    7th international workshop on terahertz technology and applications, 15.-16.03.2016, Kaiserslautern, Deutschland
Registration No. 23447 - Permalink

Graphene-based fast hot-electron bolometer with bandwidth from THz to VIS
Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. S.; Murphy, T. E.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.
Abstract: We present a fast detector (rise time 40 ps) operating at room temperature that is capable to detect radiation from the THz to visible spectral range (demonstrated wavelengths 500 µm – 780 nm) [1]. The detector consists of a CVD-grown graphene flake contacted by a broadband logarithmic periodic antenna. SiC acts as a substrate material that does not interfere with the detection mechanism in the desired frequency range, even within the Reststrahlen band of SiC (6 – 12 µm). The detector is ideal for timing purposes. Near infrared (mid- and far infrared) pulse energies of the order of 10 pJ (1 nJ) are sufficient to obtain good signal-to-noise ratios. We suggest that the bandwidth is limited by the antenna dimensions (typically several mm) on the long wavelength side and by the bandgap of SiC (380 nm) on the short wavelength side.
[1] M. Mittendorff et al., Opt. Express 23, 28728 (2015).

Keywords: detector, graphene, fast detector, broadband detector
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 06.-11.03.2016, Regensburg, Deutschland
Registration No. 23446 - Permalink

Noncollinear Coulomb scattering in graphene
König-Otto, J.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.
Abstract: Utilizing the anisotropy of the optical excitation in graphene, we reveal the twofold nature of Coulomb scattering in graphene. The initial nonequilibrium charge carrier distribution in graphene created by linearly polarized light possesses a pronounced anisotropy, which has been observed in our recent experiment [1]. In the present study we perform polarization-dependent pump-probe measurements using a photon energy of 88 meV to suppress efficiently the optical phonon scattering. In this case the relaxation dynamics leading to an isotropic distribution is dominated by noncollinear Coulomb scattering. By varying the pump fluence over a range of several orders of magnitudes we are able to successfully control the efficiency of this process. This reveals a surprising twofold nature of Coulomb scattering in graphene: Whereas collinear Coulomb scattering is known to be a very fast process on the fs timescale, noncollinear scattering is remarkably slow, resulting in a thermalization time of several ps in our experiment. Our experimental findings are complemented by the results of microscopic modelling.
[1] M. Mittendorff et al., Nano Lett. 14, 1504 (2014).

Keywords: graphene, ultrafast dynamics, anisotropy
  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Deutschland
Registration No. 23445 - Permalink

Unusual Coulomb Effects in Graphene
Winnerl, S.
Abstract: After a brief overview on the ultrafast carrier dynamics in graphene we focus on two Coulomb-mediated effects. The first one is related to the very different scattering times for collinear versus non-collinear scattering. Collinear Coulomb scattering, due to many possibilities to fulfill energy and momentum conservation requirements, is extremely fast (sub-100 fs timescale). Non-collinear scattering, on the other hand, can be surprisingly slow, namely on the scale of a few ps. This observation is in contrast to the common belief that a non-equilibrium carrier distribution in graphene fully thermalizes on a sub-100 fs timescale. We show that polarization resolved pump-probe experiments at low photon energies, i.e. below the optical phonon energy of ~200 meV, allow one to trace the non-collinear Coulomb scattering and to control its efficiency by varying the pump fluence. The second surprising Coulomb effect is the direct observation of strong Auger scattering in Landau quantized graphene. The Auger scattering in this case can efficiently deplete an energy level while that level is optically pumped at the same time. Finally the potential of graphene for photonic and fast optoelectronic devices such as THz sources and detectors will be discussed.
Keywords: graphene, ultrafast dynamics
  • Lecture (others)
    Seminarvortrag im Rahmen des Graduiertenkollegs Electronic Properties of Carbon Based Nanostructures, 22.01.2016, Regensburg, Deutschland
Registration No. 23444 - Permalink

Arguing on entropic and enthalpic first-order phase transitions in strongly interacting matter
Wunderlich, F.; Yaresko, R.; Kämpfer, B.
Corresponding author: Kämpfer, B.
Abstract: The pattern of isentropes in the vicinity of a first-order phase transition is proposed as a key for a sub-classification. While the confinement–deconfinement transition, conjectured to set in beyond a critical end point in the QCD phase diagram, is often related to an entropic transition and the apparently settled gas-liquid transition in nuclear matter is an enthalphic transition, the conceivable local isentropes w.r.t. ”incoming” or ”outgoing” serve as another useful guide for discussing possible implications, both in the presumed hydrodynamical expansion stage of heavy-ion collisions and the core-collapse of supernova explosions. Examples, such as the quark-meson model and two-phase models, are shown to distinguish concisely the different transitions. Registration No. 23439 - Permalink

Laser assisted Breit-Wheeler and Schwinger processes
Nousch, T.; Otto, A.; Seipt, D.; Kämpfer, B.; Titov, A. I.; Blaschke, D.; Panferov, A. D.; Smolyansky, S. A.
Abstract: The assistance of an intense optical laser on electron-positron pair production by the Breit-Wheeler and Schwinger processes in XFEL fields is analyzed. The impact of a laser beam on high-energy photon collisions with XFEL photons consists in a phase space redistribution of the pairs emerging in the Breit-Wheeler sub-process. We provide numerical examples of the differential cross section for parameters related to the European XFEL. Analogously, the Schwinger type pair production in pulsed fields with oscillating components referring to a superposition of optical laser and XFEL frequencies is evaluated. The residual phase space distribution of created pairs is sensitive to the pulse shape and may differ signifcantly from transiently achieved mode occupations. Registration No. 23438 - Permalink

Electromagnetic probes of pure glue initial state in nucleus-nucleus collisions at LHC
Vovchenko, V.; Karpenko, I. A.; Gorenstein, M. I.; Satarov, L. M.; Mishustin, I. N.; Kämpfer, B.; Stöcker, H.
Abstract: Partonic matter produced at the early stage of ultrarelativistic nucleus-nucleus collisions is assumed
to be composed mainly of gluons, but quarks and antiquarks are produced at later times.
The dynamical evolution of this chemically nonequilibrium system is described by the ideal (2+1)–dimensional hydrodynamics with a time dependent (anti)quark fugacity. The equation of state is taken as a linear interpolation of the lattice data for the pure gluonic matter and the chemically equilibrated quark-gluon plasma. The spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the LHC energy. The results are obtained assuming different equilibration times, including the case when the complete chemical equilibrium of partons is reached already at the initial stage. It is shown that a suppression of quarks at early times leads to a significant reduction of the invariant mass spectra of dileptons, but a rather modest suppression of the pT -distributions of direct photons. It is demonstrated that a noticeable enhancements of photon and dilepton elliptic flows might be a good signature of the pure glue initial state.
Registration No. 23437 - Permalink

Bonding structure and morphology of chromium oxide films grown by pulsed-DC reactive magnetron sputter deposition
Gago, R.; Vinnichenko, M.; Hübner, R.; Redondo-Cubero, A.
Abstract: Chromium oxide (CrOx) thin films were grown by pulsed-DC reactive magnetron sputter deposition in an Ar/O2 discharge as a function of the O2 fraction in the gas mixture (f) and for substrate temperatures, Ts, up to 450 ºC. The samples were analysed by Rutherford backscattering spectrometry (RBS), spectroscopic ellipsometry (SE), atomic force microscopy (AFM), scanning (SEM) and transmission (TEM) electron microscopy, X-ray diffraction (XRD), and X-ray absorption near-edge structure (XANES). On unheated substrates, by increasing f the growth rate is higher and the O/Cr ratio (x) rises from ~2 up to ~2.5. Inversely, by increasing Ts the atomic incorporation rate drops and x falls to ~1.8 . XRD shows that samples grown on unheated substrates are amorphous and that nanocrystalline Cr2O3 (x = 1.5) is formed by increasing Ts. In amorphous CrOx , XANES reveals the presence of multiple Cr environments that indicate the growth of mixed-valence oxides, with progressive promotion of hexavalent states with f. XANES data also confirms the formation of single-phase nanocrystalline Cr2O3 at elevated Ts. These structural changes also reflect on the optical and morphological properties of the films.
Keywords: oxide materials; vapour deposition; atomic scale structure; NEXAFS/XANES Registration No. 23435 - Permalink

Attachment of hydrophobic particles to the surface of an immersed gas bubble
Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.
Abstract: The transport of colloidal particles at the fluidic interface of a binary fluid is of significant importance to the flotation process. Flotation is a separation process in which hydrophobic particles attach to the surface of rising air bubbles while the undesired hydrophilic particles settle down the bottom of the cell to eventually be discharged. Current numerical models developed for the simulation of the particle attachment process are still at an early stage of development. The fine attaching particles have so far been modelled as point particles, thereby neglecting the deformation of the fluidic interface. Here the combination of the smooth profile method with an in-house binary fluid model is suggested to directly simulate the attachment of a single particle to an immersed bubble under various capillary numbers.
Keywords: Froth flotation, Three-phase system, Particle attachment
  • Contribution to proceedings
    81st Annual meeting of the Society of Chemical Engineers Japan, 13.-15.03.2016, Kansai University, Senriyama Campus, Japan
    Proceedings of the 81st Annual meeting of the Society of Chemical Engineers Japan
Registration No. 23434 - Permalink

Proton Beams for Physics Experiments at OncoRay
Helmbrecht, S.; Fiedler, F.; Meyer, M.; Kaever, P.; Kormoll, T.
Abstract: Purpose: At the OncoRay center in Dresden at proton therapy facility is in operation. The first patient was treated in December 2014. The system is driven by an IBA (IBA Proton Therapy, Louvain-la-Neuve, Belgium) Cyclone 230 isochronous cyclotron with a maximum proton energy of 230 MeV. Patients are treated in one room equipped with a 360° rotating gantry. Besides patient treatment a strong focus is on research. A dedicated experimental room is part of the facility. In the current state of expansion this room is equipped with a fixed beam line. Beam energies between 70 and 230 MeV and currents up to about 120 nA at 230 MeV can be provided.
Materials and Methods: An in house developed control system (figure 1) allows for a parallel operation of the treatment and the experimental beamline. Absolute priority for the treatment room is ensured by the control software.
The beam current is controlled by a dedicated hardware directly. Continuous wave beams as well as pulsed beams with repetition rates up to 333 Hz with variable duty cycles are available. The beam is monitored by means of a segmented ionization chamber. The beam can be activated manually, for a defined time or until a certain charge has been reached at the beam exit. A direct continuance after a beam switch to the treatment room is possible.
Results: The proton therapy system itself is operated by an IBA team, that ensures excellent beam stability and availability. Since only one treatment room is present, experiments can be performed conveniently during the day shifts. Requests from the treatment room cause interruptions of 1-2 min duration in intervals of about 20 min.
Conclusions: In summary, the OncoRay center is equipped with an experimental beamline that combines the reliability and beam quality of a commercial clinical proton therapy system with the flexibility of an in house developed control system whose design parameters are governed by the needs of physical and translational research.
  • Poster
    ICTR-PHE 2016 - International Conference on Translational Research in Radio-Oncology - Physics for Health in Europe, 15.05.2016, Genf, Schweiz
  • Radiotherapy and Oncology 118(2016), 60-61
    Button zum Volltext


Registration No. 23433 - Permalink

Development of antioxidant COX-2 inhibitors as radioprotective agents for radiation therapy – a hypothesis-driven review
Laube, M.; Kniess, T.; Pietzsch, J.
Corresponding author: Laube, M.
Corresponding author: Pietzsch, J.
Abstract: Radiation therapy (RT) evolved to be a primary treatment modality for cancer patients. Unfortunately, the cure or relief of symptoms is still accompanied by radiation-induced side effects with severe acute and late pathophysiological consequences. Inhibitors of cyclooxygenase-2 (COX-2) are potentially useful in this regard because radioprotection of normal tissue and/or radiosensitizing effects on tumor tissue have been described for several compounds of this structurally diverse class. This review aims to substantiate the hypothesis that antioxidant COX-2 inhibitors are promising radioprotectants because of intercepting radiation-induced oxidative stress and inflammation in normal tissue, especially the vascular system. For this, literature reporting on COX inhibitors exerting radioprotective and/or radiosensitizing action as well as on antioxidant COX inhibitors will be reviewed comprehensively with the aim to find cross-points of both and, by that, stimulate further research in the field of radioprotective agents.
Keywords: Coxibs, Cyclooxygenases, Normal tissue, NSAIDS, Oxidative stress, Radiation-induced vascular dysfunction, Radioprotection, Radiosensitization, Reactive oxygen/nitrogen species, Tumor models Registration No. 23428 - Permalink

Modellierung von Tayler-Instabilität und Elektrowirbelströmungen in Flüssigmetallbatterien
Weber, N.
Abstract: Diese Arbeit behandelt numerisch die Fluiddynamik in Flüssigmetallbatterien. Insbesonders die Tayler-Instabilität und Elektrowirbelströmungen werden ausführlich betrachtet. Die Motivation der Untersuchungen besteht zum einen in einer Steigerung von Leistung und Sicherheit und zum anderen in der Senkung von Produktions- und Betriebskosten von Flüssigmetallbatterien.
Es wird ein Lösungsverfahren für zeitabhängige magnetohydrodynamische Strömungen entwickelt und in OpenFOAM implementiert. Die Basisversion des Lösers erlaubt die Analyse einer flüssige Elektrode. Eine Erweiterung dient der Untersuchung des Einflusses von Stromsammler und Zuleitung der Batterie. Simulationen werden vorwiegend für zylindrische, aber auch für quaderförmige Elektrodengeometrien durchgeführt.
Der Hauptteil der Arbeit widmet sich der stromgetriebenen Tayler-Instabilität, die in großen Batterien bei Strömen von einigen Kiloampere auftritt und dort zu einer Strömung in Form von Konvektionszellen führt. Das Auftreten, Wachstum und die Geschwindigkeiten dieser Instabilität werden analysiert und deren Bedeutung für die Batterie diskutiert. Zur Dämpfung bzw. Unterdrückung der Strömung werden eine Reihe von Gegenmaßnahmen vorgestellt und deren praktischer Nutzen bewertet. Der zweite, kürzere Teil der Arbeit befasst sich mit Elektrowirbelströmungen, deren Charakterisierung und ihren Wechselwirkungen mit der Tayler-Instabilität. Die besondere Bedeutung von Elektrowirbelströmungen für die Integrität der Elektrolytschicht sowie ihre Anwendbarkeit für die Verbesserung des Stofftransports in Flüssigmetallbatterien werden hervorgehoben.

Keywords: Tayler Instabilität, Elektrowirbelströmung; Flüssigmetallbatterie
  • Doctoral thesis
    TU Dresden, 2016
Registration No. 23425 - Permalink

Vibrational spectroscopy of Ga+ ion implanted ta-C films
Berova, M.; Sandulov, M.; Tsvetkova, T.; Bischoff, L.; Boettger, R.; Abrashev, M.
Abstract: In the present work, low energy Ga+ ion beam implantation was used for the structural and optical properties modification of tetrahedral amorphous carbon (ta-C) thin films, using gallium (Ga+) as the ion species. Thin film samples (d~40nm) of ta-C, deposited by filtered cathodic vacuum arc (FCVA), have been implanted with Ga+ at ion energy E = 20 keV and ion doses D=3.1014÷3.1015 cm-2. The Ga+ ion beam induced structural modification of the implanted material results in a considerable change of its optical properties, displayed in a significant shift of the optical absorption edge to lower photon energies as obtained from optical transmission measurements. This shift is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). These effects could be attributed both to additional defect introduction and increased graphitisation, as well as to accompanying formation of bonds between the implanted ions and the host atoms of the target, as confirmed by infra-red (IR) and Raman measurements. The optical contrast thus obtained (between implanted and unimplanted film material) could be made use of for information archiving, in the area of high-density optical data storage, while using focused Ga+ ion beams.
Keywords: ta-C, ion implantation, Raman, FTIR, spectroscopy Registration No. 23423 - Permalink

Fe doped InAs: what is the exchange interaction?
Yuan, Y.; Hübner, R.; Potzger, K.; Liu, F.; Sawicki, M.; Dietl, T.; Helm, M.; Zhou, S.
Abstract: Fe doped InAs layers have been prepared by ion implantation and pulsed laser annealing. Fe ions exist in the +3 valence state when located in Indium sites, which indicates that Fe atoms do not introduce free carriers in the InAs layer and only act as the local spins. However, (In, Fe)As or (In, Fe)As codoped with Se (provide free electrons) exhibits typically superparamagnetic behavior, which is proven by both static and dynamic magnetic measurements. This is most probably due to the formation of Fe-rich nanoregions in the InAs matrix, similarly to the case of Cr-doped ZnTe [1]. However, the co-doping by Zn (which introduces free holes) increases both the saturation magnetization and the Curie temperature. A systematic comparison between (In, Fe)As, (In, Fe)As:Zn and (In, Fe)As:Se leads to the re-affirmation of the pd-exchange as the key gradient in dilute ferromagnetic semiconductors [2].

[1]. K. Kanazawa et al., Nanoscale, 6, 14667-14673 (2014)
[2]. T. Dietl et al., Science, 287, 1019-1022 (2000)
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie 2016, 06.-11.03.2016, Regensburg, Germany
Registration No. 23419 - Permalink

Thallium dispersal and contamination in surface sediments from South China and its source identification
Liu, J.; Wang, J.; Chen, Y.; Shen, C.-C.; Jiang, X.; Xi, X.; Chen, D.; Lippold, H.; Wang, C.
Abstract: Thallium (Tl) is a non-essential element in humans, and it is considered to be highly toxic. In this study, the contents, sources, and dispersal of Tl were investigated in surface sediments from a riverine system (the western Pearl River Basin, China), whose catchment has been contaminated by mining and roasting of Tl-bearing pyrite ores. The isotopic composition of Pb and total contents of Tl and other relevant metals (Pb, Zn, Cd, Co, and Ni) were measured in the pyrite ores, mining and roasting wastes, and the river sediments. Widespread contamination of Tl was observed in the sediments across the river, with the highest concentration of Tl (17.3 mg/kg) measured 4 km downstream from the pyrite industrial site. Application of a modified Institute for Reference Materials and Measurement (IRMM) sequential extraction scheme in representative sediments unveiled that 60 - 90% of Tl and Pb were present in the residual fraction of the sediments. The sediments contained generally lower 206Pb/207Pb and higher 208Pb/206Pb ratios compared with the natural Pb isotope signature (1.2008 and 2.0766 for 206Pb/207Pb and 208Pb/206Pb, respectively). These results suggested that a significant fraction of non-indigenous Pb could be attributed to the mining and roasting activities of pyrite ores, with low 206Pb/207Pb (1.1539) and high 208Pb/206Pb (2.1263). Results also showed that approximately 6 - 88% of Tl contamination in the sediments originated from the pyrite mining and roasting activities. This study highlights that Pb isotopic compositions could be used for quantitatively fingerprinting the sources of Tl contamination in sediments.
Keywords: Tl contamination; Pb isotope; pyrite; binary model Registration No. 23418 - Permalink

Micrometer-sized highly ordered 3D nanoparticle superlattices investigated by microresonator ferromagnetic resonance
Josten, E.; Narkowicz, R.; Kakay, A.; Meertens, D.; Banholzer, A.; Bergström, L.; Suter, D.; Brückel, T.; Lenz, K.; Fassbender, J.; Lindner, J.
Abstract: Magnetic nanoparticles and their assembly into highly correlated structures are of great interest for future applications as e.g. spin-based data storage. These systems are not only distinguished by the obvious miniaturization but by the novel physical properties emerging due to their limited size and ordered arrangement. These superstructures are formed from nanometer-sized building blocks - ordered like atoms in a crystal - which renders them a new class of materials.

Fundamental investigation of magnetic nanostructures represents an important step towards the control and understanding of these systems. Recently, single micrometer-sized 3-dimensional nanoparticle assemblies (so called mesocrystal) became available, exhibiting a high degree of structural order close to that of an atomic crystal. This system provides a good basis for the magnetic investigation of static and dynamic processes inside and of the nanoparticle superstructure.

Microresonators, provide a straightforward method for the investigation of static and dynamic magnetic properties of nm and micrometer sized objects using ferromagnetic resonance (FMR) [1,2]. Due to the much higher filling factor as compared to conventional microwave cavities, they offer several orders of magnitude increased sensitivity. A focused ion beam (FIB) approach is used to isolate an individual 3D mesocrystal from an ensemble [3] and to transfer it into a microresonator loop. The FMR study reveals the dynamic magnetic properties and magnetic anisotropy of the single mesocrystal - an object composed of highly ordered nanoparticles.

Keywords: magnetic nanoparticles, self-assembly, mesocrystals, microresonator, FMR
  • Poster
    603. Wilhelm und Else Heraeus-Seminar, Magnonics, Spin Waves Connecting Charges, Spins and Photons, 06.-08.01.2016, Physikzentrum Bad Honnef, Deutschland
Registration No. 23413 - Permalink

Measurement of isomeric ratios for 89g,mZr, 91g,mMo, and 97g,mNb in the bremsstrahlung end-point energies of 16 and 45-70 MeV
Naik, H.; Kim, G. N.; Schwengner, R.; Kim, K.; Zaman, M.; Yang, S. C.; Shin, S. G.; Kye, Y.-U.; Massarczyk, R.; John, R.; Junghans, A.; Wagner, A.; Goswami, A.; Cho, M.-H.
Abstract: The independent isomeric yield ratios of 89g,mZr from the nat Zr(gamma,xn) reactions and those of 91g,mMo and 97g,m Nb from the nat Mo(g,x) reactions with the bremsstrahlung end-point energy of 45 - 70 MeV were determined by an off-line gamma-ray spectrometric technique using the 100 MeV electron linac at the Pohang Accelerator Laboratory, Korea. The isomeric yield ratios of 89g,mZr and 97g,mNb from the nat Zr(g,xn) and nat Mo(gamm,x) reactions at the bremsstrahlung end-point energy of 16 MeV were also determined by the same technique using the 20 MeV electron linac at Helmholtz-Zentrum Dresden-Rossendorf, Germany. The measured isomeric yield ratios of 89g,mZr, 91g,mMo, and 97g,mNb were compared with literature data to examine the role of the Giant Dipole Resonance (GDR). The isomeric yield ratios of the 89g,mZr, 91g,mMo, and 97g,mNb from the above reactions were also calculated by using the computer code TALYS 1.6 and compared with the experimental data to examine the validity of the theoretical model for independent isomeric yield ratio calculations.
Keywords: Photodissociation, Photoactivation, isomeric yield ratios. Registration No. 23409 - Permalink

Further insights into the chemistry of the Bi-U-O system
Popa, K.; Prieur, D.; Manara, D.; Naji, M.; Vigier, J.-F.; Martin, P.; Blanco, O. D.; Scheinost, A. C.; Prüssmann, T.; Vitova, T.; Raison, P. E.; Somers, J.; Konings, R. J. M.
Abstract: Cubic fluorite-type phases have been reported in the UIVO2-Bi2O3 system for the entire compositional range, but an unusual non-linear variation of the lattice parameter with uranium substitution has been observed. In the current extensive investigation of the uranium(IV) oxide - bismuth (III) oxide system, this behaviour of the lattice parameter evolution with composition has been confirmed and its origin identified. Even under inert atmosphere at 800 oC, UIV oxidises to UV/UVI as a function of the substitution degree. Thus, using a combination of three methods (XRD, XANES and Raman) we have identified the formation of the BiUVO4 and Bi2UVIO6 compounds, within this series. Moreover, we present here the Rietveld refinement of BiUVO4 at room temperature and we report the thermal expansion of both BiUVO4 and Bi2UVIO6 compounds.
Keywords: XRD XANES XAFS Raman lead bismuth eutectic fast reactor Registration No. 23406 - Permalink

Synthesis and characterization of ultrasmall nanoparticles for biomedical applications
Singh, G.; Hunoldt, S.; Faramus, A.; Licciardello, N.; Stephan, H.; De Cola, L.
Abstract: The synthesis of multimodal imaging agents is indeed a growing field and a lot of research is currently being done in this area because of its wide biomedical applications. The idea behind this research is to prepare a single molecule/nanoparticle which is suitable for two or more imaging techniques and thus can act as a multimodal imaging agent, for example, the combination of optical and nuclear imaging modalities may provide complementary information for improving diagnosis as well as the treatment of diseases. These imaging agents combat the limitations of sensitivity, spatial and temporal resolution and also tissue penetrability. The high hydrophilicity of the nanoparticles and fast renal clearance of the complex from the body are the major highlights.
Amine terminated ultrasmall Silicon nanoparticles of size <4 nm were synthesized by hydrothermal method and purified by dialysis. Sulfo-Cy5 and NOTA-Bn-SCN was attached selectively to the amine terminated Si USNPs. Next step would be the radiolabeling of the particles by 64Cu and could be used for the in vitro and in vivo studies. Bispidines can also be tried as a copper chelator in the complex. Further, we could also attach single domain antibodies via PEG linkers bearing maleimide group.
The substituents after coupling with the USNPs are assumed to act as excellent multimodal imaging agent which can be used for the cancer diagnosis and therapy.

Keywords: multimodal imaging agent, ultrasmall silicon nanoparticles, bispidines
  • Poster
    2nd International Symposium on Nanoparticles/Nanomaterials and Applications, 18.-21.01.2016, Caparica, Portugal
Registration No. 23400 - Permalink

Magnetic storage technology and spintronic applications
Fassbender, J.
Abstract: Review of magnetic storage technology and spintronic applications
Keywords: magnetic storage, spintronics
  • Lecture (others)
    Invited talk at ICT / Applied Materials, 09.03.2016, München, Deutschland
Registration No. 23397 - Permalink

Ion beam modification of magnetic materials - revisited
Fassbender, J.
Abstract: In 2009 the Gaede prize was awarded for the ion induced modification and patterning of thin magnetic films. At that time most of the investigations were dealing with the local modification of magnetic anisotropies and exchange bias phenomena. In recent years we could show that also other magnetic properties, e.g. magnetic relaxation processes [1], can be tailored, but also the ferromagnetic state itself can be created [2] or destroyed depending on the material system under investigation. In particular the latter modifications open a route to the creation of nanomagnets [3] and magnonic crystals [4] by local ion irradiation. A current review will be given.
[1] M. Körner et al., Phys. Rev. B 88, 054405 (2013).
[2] R. Bali et al., Nano Lett. 14, 435 (2014).
[3] F. Röder et al., Sci. Rep. 5, 16786 (2015).
[4] B. Obry et al., Appl. Phys. Lett. 102, 202403 (2013).

Keywords: ion beam modification, magnetism
  • Invited lecture (Conferences)
    DPG Spring Meeting, 06.-11.03.2016, Regensburg, Deutschland
Registration No. 23396 - Permalink

Petawatt Lasers for Particle Acceleration at the HZDR Dresden
Schramm, U.
Abstract: Vortrag zum Status der Petawattlaserentwicklung beim Symposium Advanced Concepts for High Peak Power Ultrafast Lasers 2016
der DPG Frühjahrstagung

Keywords: Petawatt Laser
  • Invited lecture (Conferences)
    DPG Frühjahrstagung, 29.02.-04.03.2016, Hannover, Deutschland
Registration No. 23395 - Permalink

Engineering for NEMS with ion beams & flash annealing
Skorupa, W.
Abstract: Engineering for NEMS with ion beams & flash annealing will be presented based on recent results of the Rossendorf group working for Semiconductor Materials Modification by Ion Beams.
Keywords: NEMS, ion implantation, flash annealing
  • Invited lecture (Conferences)
    Workshop on Ion Implantation - improving the MEMS processes?, 03.03.2016, Erfurt, Germany
Registration No. 23390 - Permalink

Magnetic hydroxyapatite coatings as a new tool in medicine: A scanning probe investigation
Gambardella, A.; Bianchi, M.; Kaciulis, S.; Mezzi, A.; Brucale, M.; Cavallini, M.; Herrmannsdörfer, T.; Chanda, G.; Uhlarz, M.; Cellini, A.
Abstract: Hydroxyapatite films enriched with magnetite have been fabricated via a Pulsed Plasma Deposition (PPD) system with the final aim of representing a new platform able to disincentivate bacterial adhesion and biofilm formation. The chemical composition and magnetic properties of films were respectively examined by X-ray photoelectron spectroscopy (XPS) and Superconducting Quantum Interference Device (SQUID) measurements. The morphology and conductive properties of the magnetic films were investigated via a combination of scanning probe technologies including atomic force microscopy (AFM), electrostatic force microscopy (EFM), and scanning tunneling microscopy (STM). Interestingly, the range of adopted techniques allowed determining the preservation of the chemical composition and magnetic properties of the deposition target material while STM analysis provided new insights on the presence of surface inhomogeneities, revealing the presence of magnetite-rich islands over length scales compatible with the applications. Finally, preliminary results of bacterial adhesion tests, indicated a higher ability of magnetic hydroxyapatite films to reduce Escherichia coli adhesion at 4 h from seeding compared to control hydroxyapatite films. Registration No. 23389 - Permalink

Magnetic irreversibility: An important amendment in the zero-field-cooling and field-cooling method
Dias, F. T.; Vieira, V. D.; Nunes, S. E.; Pureur, P.; Schaf, J.; Da Silva, G. F. F.; Gouvea, C. D.; Wolff-Fabris, F.; Kampert, E.; Obrados, X.; Puig, T.; Rovira, J. J. R.
Abstract: The present work reports about experimental procedures to correct significant deviations of magnetization data, caused by magnetic relaxation, due to small field cycling by sample transport in the inhomogeneous applied magnetic field of commercial magnetometers. The extensively used method for measuring the magnetic irreversibility by first cooling the sample in zero field, switching on a constant applied magnetic field and measuring the magnetization M(T) while slowly warming the sample, and subsequently measuring M(T) while slowly cooling it back in the same field, is very sensitive even to small displacement of the magnetization curve. In our melt-processed YBaCuO superconducting sample we observed displacements of the irreversibility limit up to 7K in high fields. Such displacements are detected only on confronting the magnetic irreversibility limit with other measurements, like for instance zero resistance, in which the sample remains fixed and so is not affected by such relaxation. We measured the magnetic irreversibility, Tirr(H), using a vibrating sample magnetometer (VSM) from Quantum Design. The zero resistance data, Tc0(H), were obtained using a PPMS from Quantum Design. On confronting our irreversibility lines with those of zero resistance, we observed that the Tc0(H) data fell several degrees K above the Tirr(H) data, which obviously contradicts the well known properties of superconductivity. In order to get consistent Tirr(H) data in the H–T plane, it was necessary to do a lot of additional measurements as a function of the amplitude of the sample transport and extrapolate the Tirr(H) data for each applied field to zero amplitude. Registration No. 23388 - Permalink

Anomalous Magnetothermopower in a Metallic Frustrated Antiferromagnet
Arsenijevic, S.; Ok, J. M.; Robinson, P.; Ghannadzadeh, S.; Katsnelson, M. I.; Kim, J. S.; Hussey, N. E.
Abstract: We report the temperature T and magnetic field H dependence of the thermopower S of an itinerant triangular antiferromagnet PdCrO2 in high magnetic fields up to 32 T. In the paramagnetic phase, the zerofield thermopower is positive with a value typical of good metals with a high carrier density. In marked contrast to typical metals, however, S decreases rapidly with increasing magnetic field, approaching zero at the maximum field scale for T > 70 K. We argue here that this profound change in the thermoelectric response derives from the strong interaction of the 4d correlated electrons of the Pd ions with the shortrange spin correlations of the Cr3+ spins that persist beyond the Néel ordering temperature due to the combined effects of geometrical frustration and low dimensionality. Registration No. 23385 - Permalink

Dynamical Effects of the Martensitic Transition in Magnetocaloric Heusler Alloys from Direct ΔTad Measurements under Different Magnetic-Field-Sweep Rates
Gottschall, T.; Skokov, K. P.; Scheibel, F.; Acet, M.; Ghorbani Zavareh, M.; Skourski, Y.; Wosnitza, J.; Farle, M.; Gutfleisch, O.
Abstract: Large magnetocaloric effects can be obtained in Ni-Mn-based Heusler alloys due to the magnetostructural transition between martensite and austenite. This phase transformation proceeds via nucleation and growth. By direct measurements of the adiabatic temperature change ΔTad using different magneticfield-sweeping rates from 0.01 up to 1500 Ts−1, we study the dynamic behavior of the two Heusler compounds Ni50Mn35In15 and Ni45Mn37In13Co5 transforming near room temperature. From these experiments, we conclude that the nucleation process is rather slow in contrast to the relatively fast movement of the phase boundary between martensite and austenite. This is a limiting factor for cooling concepts operating at frequencies beyond 100 Hz. However, the dynamic effects of the transition are negligible in field rates typically used in magnetic refrigeration. These findings are essential considering the suitability of Heusler compounds for energy-efficient solid-state cooling. Registration No. 23384 - Permalink

High Magnetic Field Study of Elastic Constants of the Cage-structure Compound SmBe13
Mombetsu, S.; Murazumi, T.; Hiura, K.; Yamazaki, S.; Shimizu, Y.; Hidaka, H.; Yanagisawa, T.; Amitsuka, H.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.
Abstract: Ultrasonic measurements were performed on the cage-structure compound SmBe13. We have investigated the magnetic field-temperature phase diagram of this material by using pulsed magnetic fields. We found that the low-temperature magnetic order is suppressed by a magnetic field of 43 T for H ‖, which is smaller than the estimated value from mean-field approximation assuming the Г8 quartet crystal-electric-field ground state and simple antiferromagnetic order. We found that the elastic constant C44 shows softening below the ordering temperature and has a local minimum below 7 T. These facts suggest that the lowtemperature state is not a simple antiferromagnetically ordered state. In addition, no elastic anomaly due to rattling modes was found in the present measurements. Registration No. 23383 - Permalink

Narrow-band near-field nanoscopy in the spectral range from 1.3 to 8.5 THz
Kuschewski, F.; von Ribbeck, H.-G.; Döring, J.; Winnerl, S.; Eng, L. M.; Kehr, S. C.
Abstract: Nano-spectroscopy in the terahertz frequency range remains challenging despite recent technological progress in developing both THz emitter sources and near-field optical microscopy (SNOM). Here we combine scattering-type SNOM with a free-electron laser (FEL) light source, to tune into the 1.3 - 8.5 THz range. A significant portion of this range, namely the frequencies above ~3 THz, is not covered by previously reported near-field microscopy systems. However, it constitutes an indispensable regime where many elementary processes in solids including collective lattice excitations, charge and spin transport occur. Our approach of nano-spectroscopy and nano-imaging provides a versatile analysis of nanostructures as small as 50 nm, hence beating the optical diffraction limit by λ/4600.
Keywords: near-field microscopy, nanoscopy, terahertz Registration No. 23382 - Permalink

Origin of the Zero-Field Splitting in Mononuclear Octahedral MnIV Complexes: A Combined Experimental and Theoretical Investigation
Zlatar, M.; Gruden, M.; Vassilyeva, O. Y.; Buvaylo, E. A.; Ponomarev, A. N.; Zvyagin, S.; Wosnitza, J.; Krzystek, J.; Garcia-Fernandez, P.; Duboc, C.
Abstract: The aim of this work was to determine and understand the origin of the electronic properties of MnIV complexes, especially the zero-field splitting (ZFS), through a combined experimental and theoretical investigation on five well-characterized mononuclear octahedral MnIV compounds, with various coordination spheres (N6, N3O3, N2O4 in both trans (trans-NO) and cis configurations (cis-N2O4) and O4S2). High-frequency and -field EPR (HFEPR) spectroscopy has been applied to determine the ZFS parameters of two of these compounds, MnLtrans‑N2O4 and MnLO4S2. While at X-band EPR, the axial-component of the ZFS tensor, D, was estimated to be +0.47 cm−1 for MnLO4S2, and a D-value of +2.289(5)cm−1 was determined by HFEPR, which is the largest D-magnitude ever measured for a Mn complex. A moderate D value of −0.997(6) cm−1 has been found for MnLtrans‑N2O4. Quantum chemical calculations based on two theoretical frameworks (the Density Functional Theory based on a coupled perturbed approach (CP-DFT) and the hybrid Ligand-Field DFT (LF-DFT)) have been performed to define appropriate methodologies to calculate the ZFS tensor for MnIV centers, to predict the orientation of the magnetic axes with respect to the molecular ones, and to define and quantify the physical origin of the different contributions to the ZFS. Except in the case of MnLtrans‑N2O4, the experimental and calculated D values are in good agreement, and the sign of D is well predicted, LF-DFT being more satisfactory than CP-DFT. The calculations performed on MnLcis‑N2O4 are consistent with the orientation of the principal anisotropic axis determined by single-crystal EPR, validating the calculated ZFS tensor orientation. The different contributions to D were analyzed demonstrating that the d-d transitions mainly govern D in Mn ion. However, a deep analysis evidences that many factors enter into the game, explaining why no obvious magnetostructural correlations can be drawn in this series of MnIV complexes. Registration No. 23380 - Permalink

Large pinning forces and matching effects in YBa2Cu3O7-δ thin films with Ba2Y(Nb/Ta)O6 nanoprecipitates
Opherden, L.; Sieger, M.; Pahlke, P.; Hühne, R.; Schultz, L.; Meledin, A.; van Tendeloo, G.; Nast, R.; Holzapfel, B.; Bianchetti, M.; Macmanus-Driscoll, J. L.; Hänisch, J.
Abstract: The addition of mixed double perovskite Ba2Y(Nb/Ta)O6 (BYNTO) to YBa2Cu3O7−δ (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m3 at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it. Registration No. 23379 - Permalink

Direct numerical simulations and experiments of a pseudo-2D gas-fluidized bed
Tang, Y.; Lau, Y. M.; Deen, N. G.; Peters, E. A. J. F.; Kuipers, J. A. M.
Abstract: This paper reports our study on fluidization of 5000 spherical particles in a pseudo-2D gas-fluidized bed by direct numerical simulations (DNS) and experiments as well. Simulations are performed using an immersed boundary method, together with the methodology developed in our earlier work for accurate prediction of gas–solid interactions at relatively low grid resolutions. This modelling approach provides detailed information on the gas flow and the motion of individual particles, which allows for a priori calculation of the bed hydrodynamics. Experimental measurements of solids mean motion are conducted using a combined technique of Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA). Fur- ther, the PIV technique is extended and applied for instantaneous measurements of the particle granular temperature, which is the key characteristics of particle velocity fluctuations. For the first time, this paper reports a direct comparison in great detail between DNS results and experimental data for realistic gas fluidization. The detailed comparison reveals a reasonably good agreement with respect to the time-averaged solids motion and the pressure fluctuations. In addition, the granular temperatures calculated from the simulations agree well with the experimental data, but provide more details with respect to the variations corresponding to bubble formation and eruption. From our investigation, it also becomes clear that attention should be paid on the measurement and interpretation of the granular temperature.
Keywords: DIA; DNS; Gas-fluidized bed; Granular temperature; PIV Registration No. 23374 - Permalink

Activities of the Institute of Resource Ecology in the field of radioecology
Arnold, T.; Sachs, S.
Abstract: Our presentation will give a short overview of the Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology (HZDR/IRE), its main objectives, its structure, and its analytical and spectroscopic capabilities.
The main part of the talk will focus on our current activities in the field of radioecology on the European level. Here, our engagement in the European Radioecological Alliance (ALLIANCE), including our role as leader of the roadmap working group NORM (Naturally Occurring Radioactive Materials) is described. In addition, our EU project activities will be discussed.
Some examples of current research activities of the IRE in the field of radioecology, including water analyses of uranium contaminated surface and underground environments, as well as uranium plant, fungi and uranium cell interactions related to former uranium mining activities in Eastern Germany are presented.

Keywords: Radioecology, European Radioecology ALLIANCE, Working group NORM, Research activities
  • Lecture (others)
    SUBATECH Seminar, 10.03.2016, Nantes, France
Registration No. 23371 - Permalink

Geometallurgy of iron ores - a mineralogists' perspective
Gutzmer, J.
Abstract: To the superficial observer iron ore deposits appear as huge and uniform bodies comprising of iron oxide - or carbonate - and little else. They should, therefore, be simple to exploit and beneficiate. This may have indeed applied to the giant high-grade BIF-hosted deposits that have dominated global iron supply for the last half a century. However, it does certainly not apply to iron ore deposits that will govern future supply. The latter deposits will still be very large, but of lower grade and marked by increasing concentrations of deleterious elements such as phosphorous, titanium or alkali elements. Careful ore characterization and geometallurgical modelling will be key drivers to convert iron ore resources into reserves – and deposits into new mines.
Keywords: iron ore, geometallurgy
  • Invited lecture (Conferences)
    Mineralteknik 2016, 02.-03.02.2016, Lulea, Sweden
  • Contribution to proceedings
    Mineralteknik 2016, 02.-03.02.2016, Lulea, Sweden
    Mineralteknik 2016 - Proceedings, Lulea: Lulea Technical University, 18-19
Registration No. 23366 - Permalink

The Paleoproterozoic Manganese Bonanza in Africa
Gutzmer, J.; Beukes, N. J.
Abstract: Africa hosts just over 80 percent of the currently known land-based resources of manganese (Mn). The bulk of the African Mn resource is of sedimentary origin and hosted by strata of Paleoproterozoic age, although epigenetic processes, including hydrothermal enrichment and/or deep chemical weathering, have significantly enriched some of the deposits. Host strata and geological context have been used to categorize the deposits into four types, namely BIF-associated, black shale-associated, sandstone-associated (oolitic) and karst-associated. Mn deposits occur geographically clustered and related to a number of prominent sedimentary successions of Late Archean to Late Paleoprozerozoic age. The greatest concentration and genetic diversity occurs undoubtedly on the Kaapvaal Craton of Southern Africa. The Transvaal Supergroup (TVL SG) hosts the ~ 2,2 Ga BIF-associated deposits of the Kalahari Manganese Field – with an estimated 4,2 Gt of contained Mn by far the largest of all land-based Mn deposits globally. However, the TVL SG also hosts the ~ 2,4 Ga BIF-associated Rooinekke deposit and the 2,0-2.2 Ga Postmasburg Manganese Field, the latter comprising the worlds oldest karst-associated Mn deposits. The record of sedimentary Mn deposits of Paleoproterozoic age on the Kaapvaal Craton is complemented by the Tolwe deposit of the ~1,9 Ga Soutpansberg Group, the oldest known example of sandstone-associated oolitic Mn ores.
Other important Paleoproterozoic manganese deposits in Africa are all limited to sedimentary strata of ~ 2,1-2,2 Ga age. These successions may comprise cratonic cover sequences, such as the Francevillian Supergroup on the northwestern part of the Congo Craton, or are associated with the formation of Paleoproterozoic juvenile crust, such as the Birimian Supergroup of West Africa or the Lukoshi Complex in the DRC. Manganiferous carbonate beds closely associated with greywackes and pyritic black shales are geographically and stratigraphically widespread in these successions. In most cases, Late Mesozoic and Cenozoic lateritic weathering markedly enrich the manganiferous strata to form high-grade manganese oxide ores.
All major African Mn deposits occur in strata that immediately postdate the great oxidation event (GOE). Furthermore, they are associated with – or immediately postdate the deposition of banded iron formations. Together with an abundance of geochemical evidence this close temporal affiliation may be used to invoke that the unique concentration of Mn in the sedimentary environment is a consequence of the establishment of oxic conditions in the shallow marine as well as the terrestrial environment.

Keywords: Manganese, Africa, ore deposits
  • Invited lecture (Conferences)
    5th International Geologica Bellica Meeting, 26.-29.01.2016, Mons, Belgium
  • Contribution to proceedings
    5th International Geologica Belgica 2016 Congress, 26.-29.01.2016, Mons, Belgium
    5th International Geologica Belgica 2016 Congress Abstract Book, Mons: Geological Society of Belgium, 197-197
Registration No. 23365 - Permalink

In-situ X-ray observations showing the impact of natural and forced convection on dendritic solidification
Eckert, S.; Shevchenko, N.; Roshchupkina, O.; Sokolova, O.
Abstract: The directional solidification of Ga–25wt%In alloys was investigated using X-ray radioscopy, which offers a visual access to opaque melts and enables a basic, intuitional understanding of the complex interplay between melt flow and dendritic growth. Natural convection occurs owing to an unstable density stratification at the solid-liquid interface. Forced convection was produced by a rotating wheel. Our observations show a facilitation of the growth of primary trunks or lateral branches, suppression of side branching, dendrite remelting and fragmentation. The manifestation of all phenomena depends on the dendrite orientation, local direction and intensity of the flow. The forced flow eliminates the solutal plumes and damps the local fluctuations of solute concentration. It provokes a preferential growth of the secondary arms at the upstream side of the primary dendrite arms, whereas the high solute concentration at the downstream side of the dendrites can inhibit the formation of secondary arms.
Keywords: solidification, dendritic growth, macrosegregation, fragmentation, X-ray radioscopy
  • Invited lecture (Conferences)
    Michel Rappaz Honory Symposium: Frontiers in Solidification; TMS2016, 145th Annual Meeting and Exhibition, 14.-18.02.2016, Nashville, USA
Registration No. 23359 - Permalink

Mechanistic sorption models: Species, Thermodynamic, Application
Bok, F.; Richter, C.; Stockmann, M.; Brendler, V.
Abstract: During the last two decades mechanistic sorption models not only continued their development and parameterization, but also gained ground for application in real-world scenarios such as in the long-term safety analysis of potential nuclear waste repositories. This was only possible because fundamentals such as a proper identification of surface species (their numbers, stoichiometries, structures & denticity) could be based on combinations of spectroscopic experiments, thermodynamic modelling and quantum chemical calculations. Similar progress can be reported for the mineral characterization (specific surface area, binding sites, protolysis reactions). Based on realistic species set and mineral properties, respective formation constants can be derived from batch sorption experiments, also providing information about temperature dependence and kinetics (namely reversibility). Nowadays, mechanistic sorption models are not only a synonym for surface complexation models (SCM), but ideally also account for additional phenomena such as ion exchange or surface precipitation, as well as the formation of secondary phases (smart Kd-values).
The above sketched developments are illustrated for a recent case study about Np(V) and U(VI) sorption onto components of Gorleben overburden sediments. The talk presents the analysis of the on-site data situation. Then own measurements to complete the thermodynamic data base including species identification by means of time-resolved laser-induced fluorescence and attenuated total reflection Fourier-transform infrared spectroscopies are addressed, together with the fit procedure to obtain SCM parameter sets. Next, the scheme utilized for smart Kd computation (including its implementation into reactive transport codes) is explained, and results from an uncertainty and sensitivity analysis are discussed.
Conclusions will incorporate a strategy to join international expertise (and man power) aiming at a comprehensive sorption raw data re-evaluation. This would allow to derive an internally consistent (with respect to EDL definition, mineral characteristics and species set) data set for the computation of smart Kd-values. This strategy covers data assembly, evaluation, processing and storage into an appropriate data structure.

Keywords: smart Kd, Sorption, Surface species, reactive transport modelling
  • Invited lecture (Conferences)
    American Chemical Society Spring meeting, 13.-17.03.2016, San Diego, USA
Registration No. 23357 - Permalink

Changes in Binding of [123I]CLINDE, a High-Affinity Translocator Protein 18 kDa (TSPO) Selective Radioligand in a Rat Model of Traumatic Brain Injury
Donat, C. K.; Gaber, K.; Meixensberger, J.; Brust, P.; Pinborg, L. H.; Hansen, H. H.; Mikkelsen, J. D.
Abstract: The neuropathology following traumatic brain injury (TBI) is poorly understood. From the primary biomechanical injury, secondary injuries develop, including neuro-inflammatory processes. These secondary injuries are regarded as a potential targets for treatment and diagnostics. The translocator protein 18 kDa (TSPO) is robustly upregulated in response to brain injury, making it a suitable biomarker for glia activation and the neuro-inflammatory response. Second-generation radioligands of TSPO, such as [123I]CLINDE, offer higher affinity and signal-to-noise ratio compared to PK11195, the prototypical ligand. Applicability of [123I]CLINDE was demonstrated in both neurodegenerative disease models and patient studies and therefore demonstrate the translational value of this tracer. We therefore investigated TSPO expression in a rat model of TBI with [123I]CLINDE , a selective and clinically relevant TSPO-radioligand.
Adult Sprague-Dawley rats were subjected to moderate Controlled-Cortical-Impact injury (CCI, n=5 per group). Sham (n=5), craniotomy (n=3), and naïve animals (n=3) served as different control groups. Animals were sacrificed at 6h, 24h, 72h, and 28 days post-surgery, and TSPO expression was assessed in brain section employing [123I]CLINDE in vitro autoradiography.
From 24 h to 28 d post-surgery, injured animals exhibited a marked and time-dependent increase of binding in the ipsilateral motor, somatosensory and parietal cortex, as well as in the hippocampus and thalamus. Furthermore, binding was significantly elevated in the contralateral motor cortex following TBI. Craniotomy also caused a significant increase in [123I]CLINDE binding per se. Radioligand binding was consistent with an increase in TSPO mRNA expression and OX-42 immunoreactivity at the contusion site.
In conclusion, this study demonstrates the applicability of [123I]CLINDE for brain regional and quantitative assessment of neuro-inflammatory activity in experimental models of TBI.
Registration No. 23355 - Permalink

A Local Superlens
Kehr, S. C.; Mcquaid, R. G. P.; Ortmann, L.; Kämpfe, T.; Kuschewski, F.; Lang, D.; Döring, J.; Gregg, J. M.; Eng, L. M.
Abstract: Superlenses enable near-field imaging beyond the optical diffraction limit. However, their widespread implementation in optical imaging technology so far has been limited by large-scale fabrication, fixed lens position, and specific object materials. Here we demonstrate that a dielectric lamella of subwavelength size in all three spatial dimensions behaves as a compact superlens that operates at infrared wavelengths and can be positioned to image any local microscopic area of interest on the sample. In particular, the lamella superlens may be placed in contact with any type of object and therefore enables examination of hard-to-scan samples, for example, with high topography or in liquids, without altering the specimen design. This lamella-based local superlens design is directly applicable to subwavelength light-based technology, such as integrated optics.
Keywords: superlens; subwavelength imaging; near-field microscopy; barium titanate; mid-infrared; free-electron laser Registration No. 23354 - Permalink

Electron-phonon coupling and energy flow in a simple metal beyond the two-temperature approximation
Waldecker, L.; Bertoni, R.; Ernstorfer, R.; Vorberger, J.
Abstract: The electron-phonon coupling and the corresponding energy exchange was investigated experimentally and by ab initio theory in non-equilibrium states of the free-electron metal aluminium. The temporal evolution of the atomic mean squared displacement in laser-excited thin free-standing films was monitored by femtosecond electron diffraction. The electron-phonon coupling strength was obtained for a range of electronic and lattice temperatures from density functional theory molecular dynamics (DFT-MD) simulations. The electron-phonon coupling parameter extracted from the experimental data in the framework of a two-temperature model (TTM) deviates significantly from the ab initio values. We introduce a non-thermal lattice model (NLM) for describing non-thermal phonon distributions as a sum of thermal distributions of the three phonon branches. The contributions of individual phonon branches to the electron-phonon coupling are considered independently and found to be dominated by longitudinal acoustic phonons. Using all material parameters from first-principle calculations besides the phonon-phonon coupling strength, the prediction of the energy transfer from electrons to phonons by the NLM is in excellent agreement with time-resolved diffraction data. Our results suggest that the TTM is insufficient for describing the microscopic energy flow even for simple metals like aluminium and that the determination of the electron-phonon coupling constant from time-resolved experiments by means of the TTM leads to incorrect values. In contrast, the NLM describing transient phonon populations by three parameters appears to be a sufficient model for quantitatively describing electron-lattice equilibration in aluminium. We discuss the general applicability of the NLM and provide a criterion for the suitability of the two-temperature approximation for other metals.
Keywords: two temperature model, electron-phonon coupling, laser interaction with solids, warm dense matter, non-equilibrium


Registration No. 23350 - Permalink

Tailoring nonlinear optical properties of Bi2Se3 through ion irradiation
Tan, Y.; Guo, Z.; Shang, Z.; Liu, F.; Böttger, R.; Zhou, S.; Shao, J.; Yu, X.; Zhang, H.; Chen, F.
Abstract: The nonlinear optical property of topological insulator bismuth selenide (Bi2Se3) is found to be welltailored through ion irradiation by intentionally introducing defects. The increase of the optical modulation depth sensitively depends on the careful selection of the Irradiation condition. By implementing the ion irradiated Bi2Se3 film as an optical saturable absorber device for the Q-switched wave-guide laser, an enhanced laser performance has been obtained including narrower pulse duration and higher peak power. Our work provides a new approach of tailoring the nonlinear optical properties of materials through ion irradiation, a well-developed chip-technology, which could find wider applicability to other layered two-dimensional materials beyond topological insulators, such as graphene, MoS2, black phosphours etc.
Keywords: ion Irradiation, Bi2Se3 film, chip-technology Registration No. 23343 - Permalink

Ultrasmall inorganic nanoparticles: state-of-the-art and perspectives for biomedical applications
Zarschler, K.; Rocks, L.; Licciardello, N.; Boselli, L.; Polo, E.; Pombo Garcia, K.; de Cola, L.; Stephan, H.; Dawson, K. A.
Abstract: Ultrasmall nanoparticulate materials with core sizes in the 1-3 nm range bridge the gap between single molecules and classical, larger-sized nanomaterials, not only in terms of spatial dimension, but also as regards physicochemical and pharmacokinetic properties. Due to these unique properties, ultrasmall nanoparticles appear to be promising materials for nanomedicinal applications.
This review overviews the different synthetic methods of inorganic ultrasmall nanoparticles as well as their properties, characterization, surface modification and toxicity. We moreover summarize the current state of knowledge regarding pharmacokinetics, biodistribution and targeting of nanoscale materials. Aside from addressing the issue of biomolecular corona formation and elaborating on the interactions of ultrasmall nanoparticles with individual cells, we discuss the potential diagnostic, therapeutic and theranostic applications of ultrasmall nanoparticles in the emerging field of nanomedicine in the final part of this review.

Keywords: ultrasmall nanoparticles; nanomedicine; pharmacokinetics; protein corona; active targeting; cancer; renal excretion Registration No. 23338 - Permalink

Atomistic study on mixed-mode fracture mechanisms of ferrite iron interacting with coherent copper and nickel nanoclusters
Al-Motasem, A. T.; Mai, N. T.; Choi, S. T.; Posselt, M.
Abstract: The effect of copper and/or nickel nanoclusters, generally formed by neutron irradiation, on fracture mechanisms of ferrite iron was investigated by using molecular statics simulation. The equilibrium configuration of nanoclusters was obtained by using a combination of an on-lattice annealing based on Metropolis Monte Carlo method and an off-lattice relaxation by molecular dynamics simulation. Residual stress distributions near the nanoclusters were also calculated, since compressive or tensile residual stresses may retard or accelerate, respectively, the propagation of a crack running into a nanocluster. One of the nanoclusters was located in front of a straight crack in ferrite iron with a body-centered cubic crystal structure. Two crystallographic directions, of which the crack plane and crack front direction are (010)[001] and (111)[-110], were considered, representing cleavage and non-cleavage orientations in ferrite iron, respectively. Displacements corresponding to pure opening-mode and mixed-mode loadings were imposed on the boundary region and the energy minimizationwas performed. It was observed that the fracture mechanisms of ferrite iron under the pure opening-mode loading are strongly influenced by the presence of nanoclusters, while under the mixed-mode loading the nanoclusters have no significant effect on the crack propagation behavior of ferrite iron.
Keywords: fracture, Molecular Dynamics, Monte Carlo, nanoclusters, deformation twinning, dislocation. Registration No. 23336 - Permalink

High-Rate Timing Resistive Plate Chambers with Ceramic Electrodes
Laso Garcia, A.; Kotte, R.; Naumann, L.; Stach, D.; Wendisch, C.; Wüstenfeld, J.; Kämpfer, B.
Abstract: We describe recent advances in developing radiation-hard ceramic resistive plate chambers (CRPCs) with Si3N4/SiC composites. Bulk resistivity measurements for this material for different manufacturing processes are reported. The results show that the bulk resistivity can vary between 10^7 - 10^13 Ohm cm. The varistor type behaviour of the material is analyzed. A comparison with other materials used in timing RPCs is given.
We describe the assembly and tests of CRPC prototypes in electron and proton beams. For a prototype with bulk resistivity 5 x 10^9 Ohm cm, the effciency of the detectors is 95% at a fux of 2 x 10^5 cm^-2 s^-1. The time resolution at the same fux is about 120 ps. A prototype with bulk resistivity 2 x 10^10 Ohm cm shows an effciency of about 85% up to fuxes of 5 x 10^4 cm^-2 s^-1 with a time resolution better than 80 ps. The results are compared with RPC models.

Keywords: RPC; Timing; Ceramic; High-rate capabilities; High flux


Registration No. 23335 - Permalink

Inter-sublevel dynamics in single InAs/GaAs quantum dots induced by strong terahertz excitation
Stephan, D.; Bhattacharyya, J.; Huo, Y. H.; Schmidt, O. G.; Rastelli, A.; Helm, M.; Schneider, H.
Abstract: We combine micro-photoluminescence with terahertz excitation to investigate the response of single self-assembled InAs/GaAs quantum dots to intense terahertz pulses tuned to the s-to-p transition. Spectra and transients of single photoluminescence lines reveal the dynamics of electrons upon excitation and subsequent relaxation back into the initial state. Under certain circumstances, the terahertz pulse can release trapped charge carriers which relax into the quantum dot. Furthermore, we demonstrate near-total depletion of the positive trion PL by an intense terahertz pulse.
Keywords: Quantum dots, Photoluminescence, Terahertz, Carrier relaxation Registration No. 23333 - Permalink

Direct evidence of defect coordination and magnetic interaction in local structure of wurtzite type Zn1-xCoxO thin films
Satyarthi, P.; Ghosh, S.; Wang, Y.; Zhou, S.; Bürger, D.; Skorupa, I.; Schmidt, H.; Olivi, L.; Srivastava, P.
Abstract: The local structure of as deposited and post treated Zn0.95Co0.05O films is investigated to understand the origin of their paramagnetic and tunable ferromagnetic properties for scientific advancements in spintronics. The crystallographic perfect short range ordering in the vicinity of tetrahedrally substituted Zn and Co atoms is responsible for mediating purely paramagnetic behavior in Zn0.95Co0.05O film grown by pulsed laser deposition. Irradiating the as deposited Zn0.95Co0.05O films with 500 keV inert xenon ions of different fluences, leads to creation of O, Zn and Co related defects in coordination shells of tetrahedrally substituted Zn and Co atoms. Apart from defect creation, spinel type ZnCo2O4 phase is evident for the film irradiated at highest fluence, in which Zn and Co atoms exist in tetrahedral and octahedral symmetry around the oxygen atoms. The tunable ferromagnetism in post irradiated Zn0.95Co0.05O films is understood from a model that includes strong ferromagnetic and weak antiferromagnetic interactions operating within their local structure. The ferromagnetic interaction is explained from (i) dopant defect hybridization of O vacancies and high spin (S = 3/2) Co atoms and (ii) spin interaction at O 2p orbital's in Zn vacancy rich regions in tetrahedral symmetry. The weak antiferromagnetic interaction is discussed from the presence of octahedral coordinated low spin (S = 0) Co atoms in ZnCo2O4 structure.
Keywords: Diluted Magnetic Semiconductors; Spintronics; EXAFS Registration No. 23328 - Permalink

Assessment of a hybrid CFD model for simulation of complex vertical upward gas-liquid churn flow
Parsi, M.; Agrawal, M.; Srinivasan, V.; Vieira, R. E.; Torres, C. F.; Mclaury, B. S.; Shirazi, S. A.; Schleicher, E.; Hampel, U.
Abstract: Gas-liquid multiphase flow can be observed within different industrial processes, and Computational Fluid Dynamics (CFD) can be utilized as a tool for scrutiny of this kind of flows. Although the CFD simulations of multiphase are computationally-demanding, they can deliver a great deal of information. But, the larger point is whether the available CFD multiphase flow models are able to deliver a realistic solution for a complex flow pattern like churn flow? And if yes, to what extent are the results accurate?To shed light on these issues, the Eulerian-Eulerian MultiFluid VOF model offered by ANSYS FLUENT 15 (2015 15.0 User's Guide, ANSYS Inc.) was used to simulate high flow rate air-water multiphase flow in a 76.2 mm-diameter pipe upstream of an elbow in the vertical-horizontal configuration. In the simulations, superficial gas velocity ranged from 10.3 m/s to 33.9 m/s, and two superficial liquid velocities of 0.3, and 0.79 m/s were employed. From the CFD simulations, data such as phase distributions, mean void fractions, and average void fraction time series were extracted. They were then compared to experimental Wire Mesh Sensor (WMS) data formerly obtained. Interestingly, evaluation of the model revealed that it was successful in terms of capturing different liquid structures present within the flow and delivering void fraction data which were in agreement with those of experiments.
Keywords: CFD; Churn flow; Huge wave; MultiFluid VOF; Multiphase flow; Wire mesh sensor Registration No. 23324 - Permalink

Ferromagnetic Mn-Implanted GaP: Microstructures vs Magnetic Properties
Yuan, Y.; Hübner, R.; Liu, F.; Sawicki, M.; Gordan, O.; Salvan, G.; Zahn, D. R. T.; Banerjee, D.; Baehtz, C.; Helm, M.; Zhou, S.
Abstract: Ferromagnetic GaMnP layers were prepared by ion implantation and pulsed laser annealing (PLA). We present a systematic investigation on the evolution of microstructure and magnetic properties depending on the pulsed laser annealing energy. The sample microstructure was analyzed by high-resolution X-ray diffraction (HR-XRD), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), ultraviolet Raman spectroscopy (UV-RS), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The presence of X-ray Pendellösung fringes around GaP (004) and RBS channeling prove the epitaxial structure of the GaMnP layer annealed at the optimized laser energy density (0.40 J/cm2). However, a forbidden TO vibrational mode of GaP appears and increases with annealing energy, suggesting the formation of defective domains inside the layer. These domains mainly appear in the sample surface region and extend to almost the whole layer with increasing annealing energy. The reduction of the Curie temperature (TC) and of the uniaxial magnetic anisotropy gradually happens when more defects and the domains appear as increasing the annealing energy density. This fact univocally points to the decisive role of the PLA parameters on the resulting magnetic characteristics in the processed layers, which eventually determine the magnetic (or spintronics) figure of merit.
Keywords: GaMnP, ion implantation, pulsed laser annealing, dilute ferromagnetic semiconductors, microstructures, magnetic properties Registration No. 23323 - Permalink

First-order magnetization process as a tool of magnetic-anisotropy determination: Application to the uranium-based intermetallic U3Cu4Ge4
Gorbunov, D. I.; Henriques, M. S.; Andreev, A. V.; Skourski, Y.; Richter, M.; Havela, L.; Wosnitza, J.
Abstract: Uranium-based intermetallic compounds often display very strong magnetic anisotropies, the energy of which is usually not directly accessible by common experimental methods. Here, we report on static- and pulsed-field studies of U3Cu4Ge4. This material orders ferromagnetically at TC = 73 K with the easy magnetization direction along the a axis and a strong bc-plane anisotropy. The magnetization measured for fields along the hard b direction displays a first-order magnetization process that can be described well by use of a phenomenological theory yielding anisotropy constants up to the sixth order. This phenomenological description,working excellently for U3Cu4Ge4, may also be applied for other uranium-based compounds. Registration No. 23320 - Permalink

The abanico plot: Visualising chronometric data with individual standard errors
Dietze, M.; Kreutzer, S.; Burow, C.; Fuchs, M.; Fischer, M.; Schmidt, C.
Abstract: Numerical dating methods in Quaternary science are faced with the need to adequately visualise data consisting of estimates that have differing standard errors. Recent approaches either focus on the display of age frequency distributions that ignore the standard errors or on radial plots, that support comparisons between estimates allowing for their differing precisions, but without giving an explicit picture of the age frequency distribution. Hence, visualising both aspects requires at least two plots. Here, an alternative is introduced: The abanico plot. It combines both aspects and therefore allows comprehensive presentation of chronometric data with individual standard errors. It extends the radial plot by a kernel density estimate plot, histogram or dot plot and contains elements that link both plot types. As part of the R package 'Luminescence' (version >0.4.5), the abanico plot is designed as the final part of a comprehensive analysis chain of luminescence data but is open to a wide range of other Quaternary dating communities, as illustrated by several examples.
Keywords: Luminescence dating, Fission track, Cosmogenic nuclides, Radial plot, KDE, R


Registration No. 23317 - Permalink

Relaxation dynamics in photoexcited semiconductor quantum wells studied by time-resolved photoluminiscence
Zybell, S.
Abstract: Gegenstand der vorliegenden Arbeit ist die Untersuchung der Photolumineszenzdynamik von Halbleiter-Quantentöpfen (Quantum Wells), die durch Anregung von Intraband-Übergängen mittels resonanter Laserpulse im mittleren Infrarot- und Terahertz-Spektralbereich verändert wird. Diese Zweifarbenexperimente wurden mit Hilfe eines optischen Aufbaus für zeitaufgelöste Photolumineszenzspektroskopie am Großgerät Freie-Elektronen Laser FELBE am Helmholtz-Zentrum Dresden-Rossendorf realisiert. Zeitlich verzögert zur gepulsten optischen Anregung über die Bandlücke wurden Intersubband- oder Intraexziton-Übergange in den Quantum Wells resonant angeregt. Die dadurch erreichte Ladungsträgerumverteilung zeigt sich in einer deutlichen Verringerung der Photolumineszenzintensität zum Zeitpunkt des zweiten Anregepulses, die im Folgenden als Photolumineszenz-Quenching bezeichnet wird.
Zunächst wird die Stärke des Photolumineszenz-Quenchings in Abhängigkeit der Polarisationsrichtung des midinfraroten Laserstrahls ausgewertet. Während die Absorption durch freie Ladungsträger für beide Polarisationsrichtungen nachweisbar ist, wird experimentell gezeigt, dass Intersubbandabsorption nur möglich ist, wenn ein Anteil der anregenden Strahlung senkrecht zur Quantum-Well-Ebene polarisiert ist.
Das Photolumineszenzsignal ist überwiegend an der energetischen Position der 1s-Exzitonresonanz unterhalb der Bandkante messbar. Die intraexzitonischen Übergangsenergien in Quantum Wells liegen typischerweise im Terahertzbereich. Unter intraexzitonischer 1s-2p Anregung erscheint auch auf dieser Energieskala ein abrupter Intensitätsverlust in der langsam abklingenden Photolumineszenztransiente. Erstmalig wurde im Photolumineszenzspektrum bei höheren Energien im Abstand der Terahertz-Photonenenergie ein zusätzliches 2s-Photolumineszenzsignal detektiert. Eine detaillierte theoretische Beschreibung dieses Problems durch unsere Kooperationspartner Koch et al. von der Phillips-Universität Marburg zeigt, dass unter intraexzitonischer 1s-2p Anregung eine effiziente Coulombstreuung zwischen den nahezu entarteten exzitonischen 2p- und 2s-Zustanden stattfindet. Während der 2p-Zustand optisch dunkel ist, kann die 2s-Population strahlend rekombinieren, was zu dem besagten 2s-Photolumineszenzsignal führt. Die Zeitkonstanten der untersuchten Ladungsträgerdynamik werden durch ein phänomenologisches Modell bestimmt, das die experimentellen Kurven sehr gut abbildet. Es wird ein Ratengleichungsmodell eingeführt, bei dem die involvierten Zustände auf optisch helle und optisch dunkle Besetzungsdichten reduziert werden.
Darüber hinaus werden mit einem modifizierten Versuchsaufbau die Terahertz-induzierten Photolumineszenzsignaturen von Magnetoexzitonen untersucht. Die Stärke des 1s-Photolumineszenz-Quenchings ändert sich dabei entsprechend der magnetoexzitonischen Übergänge, die im betrachteten Feldstärkebereich zwischen 0T und 7T liegen. Für Magnetfelder größer als 3T sind keine 2s-Photolumineszenzsignale mehr messbar, da durch das externe magnetische Feld die Entartung der 2p- und 2s-Zustände aufgehoben wird.
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-064 2015
    ISSN: 2191-8716


Registration No. 23316 - Permalink

Enhancement of single bullet mode stability in nanowire spin-Hall oscillator with spatially nonuniform current bias
Verba, R. V.; Yang, L.; Tyberkevych, V.; Schneider, T.; Smith, A.; Duan, Z.; Lindner, J.; Slavin, A. N.; Krivorotov, I. N.
Abstract: Spin torque oscillators (STO) are compact tunable sources of microwave radiation that serve as a test bed for the studies of nonlinear magnetization dynamics at the nanoscale. It has been shown that spin-Hall torque in ferromagnetic - heavy metal bilayers can provide spin torque necessary for the STO operation. However, multimode generation and low spectral purity of the microwave signals generated in spin-Hall oscillators (SHOs) hinders practical applications of these nanoscale devices.
Here we experimentally demonstrate that tapering of a Pt/Ni80Fe20 nanowire that serves as the SHO active region, results in a sizable extension of the bias current range of single-mode generation (Fig.1) and in the significant decrease of the spectral linewidth of the generated signal.
The observed features are explained in the framework of Ginzburg-Landau auto-oscillator model. The model reveals that in both straight and tapered nanowires the spin torque excites a self-localized spin wave bullet mode, which, owing to the increased role of magnetodipolar interaction, has a micrometer size. The key factor leading to the improvement of the generation characteristics in a tapered nanowire SHO is shown to be a nonuniformity of the bias current density. In particular, this nonuniformity leads to a current-induced displacement of the bullet mode from the nanowire center, which results in the extension of the region of stability of the single-mode generation regime. Also, the nonuniform current density provides a restoring force that reduces the amplitude of thermal fluctuations in the position of the bullet mode along the nanowire, and, thereby, decreases the SHO phase noise. Finally, the current-induced spatial separation of two bullets in 2-mode generation regime results in different nonlinear shifts of the bullets frequency, which leads to a larger intermode frequency separation, in accordance with experiment (Fig.1).
  • Lecture (Conference)
    MMM | Intermag 2016, 11.-15.01.2016, San Diego, USA
Registration No. 23311 - Permalink

Nanowire spin Hall oscillators: nanowire width dependence
Smith, A.; Schneider, T.; Yang, L.; Krivorotov, I. N.
Abstract: We present experimental studies of auto-oscillatory magnetization dynamics in nanowire spin Hall oscillators (SHOs) as a function of the nanowire width. The oscillators schematically shown in Fig. 1 consist of a long Pt(7 nm)/Py(5 nm)/AlOx (2 nm) nanowire on a sapphire substrate with two Cr/Au leads attached to the wire [1]. The 2 μm gap between the leads defines the active region of the oscillator. A 750 Oe saturating magnetic field is applied in the plane of the sample at 85 deg with respect to the nanowire axis, and direct current generating anti-damping spin torque is applied between the leads. Figure 2 shows microwave emission spectra for four oscillator devices with the active region width ranging from 0.17 μm to 1.07 μm. All devices show onset of auto-oscillations at similar critical current densities. For the 0.17 μm wide nanowire SHO, auto-oscillatory modes arising from the bulk and edge eigenmodes of the nanowire are clearly seen in the emission spectra. For SHO devices based on wider wires, the bulk auto-oscillatory modes dominate the emission spectrum due to the larger wire volume occupied by the bulk modes. The maximum integrated power generated is similar for all four SHO devices (~ 10^-10 W). Our work demonstrates robust operation of nanowire-based SHOs over a wide range of nanowire widths and presents an example of a spin torque oscillator with the active area extended into the um^2 domain.
  • Lecture (Conference)
    MMM | Intermag 2016, 11.-15.01.2016, San Diego, USA
Registration No. 23310 - Permalink

Spin Current Control of Damping in YIG/Pt Nanowires
Safranski, C. J.; Barsukov, I.; Lee, H.; Schneider, T.; Jara, A. A.; Smith, A.; Chang, H.; Wu, M.; Krivorotov, I. N.
Abstract: Insulating ferromagnet(IF)/normal metal(NM) interfaces are important for understanding of pure spin current injection and have great potential for spintronic applications. Here we report studies of the effect of pure spin currents on damping of spin wave eigenmodes in YIG(30 nm)/Pt(6 nm) bilayer nanowires that are 60–250 nm wide and 1–13 um long. The samples show magneto-resistance (MR) arising from two distinct mechanisms: (i) spin Hall magnetoresistance (SMR) and (ii) inverse spin Hall effect (iSHE) in conjunction with spin Seebeck current (SSC) induced by Ohmic heating of the Pt layer. Utilizing the SMR and iSHE effects, we measure the properties of spin wave eigenmodes of the nanowires by spin-torque ferromagnetic resonance (ST-FMR) with magnetic field modulation.
Application of direct current to the Pt layer results in injection of spin Hall current into YIG that acts as either damping or anti-damping spin torque depending on the current polarity. In addition, Ohmic heating in Pt gives rise to a SSC injected into YIG, which acts as anti-damping torque independent of the current polarity. ST-FMR measurements reveal current-induced variation of the linewidth of spin wave modes that is asymmetric in the bias current as shown in Fig. 1. The linewidth decreases to zero for the current polarity that gives rise to anti-damping spin Hall torque. Near this current value, we observe complex interaction among the spin wave eigenmodes of the nanowire that we asses using micromagnetic simulations. Our results advance understanding of magnetization dynamics driven by pure spin currents in nanoscale IF/NM systems.
  • Lecture (Conference)
    MMM | Intermag 2016, 11.-15.01.2016, San Diego, USA
Registration No. 23309 - Permalink

Controlled electron bunch generation in the few-cycle ultra-intense laser-solid interaction scenario
Kluge, T.; Bussmann, M.; Cowan, Thomas E.; Schramm, U.
Abstract: The generation of Maxwellian or exponentially decaying spectra in the interaction of ultra-intense ultra-short laser pulses with solid foils is very general observation both in experiments and simulations. Yet, the physical origin of this observation is not well understood. For a very idealized situation of plane wave, plane and cold target interaction, we show that both randomization between individual electron bunches accelerated by the laser through the plasma as well as randomization during a single bunch are not observable in particle-in-cell simulations. Hence they are not accountable for the apparent thermalization (exponential spectrum).
  • Contribution to proceedings
    European Advanced Accelerator Concepts Workshop, 13.09.2015, La Biodola, Isola d'Elba, Italien
    Proceedings of the European Advanced Accelerator Concepts Workshop
Registration No. 23308 - Permalink

Magnetic stirring and sonication of liquid metals
Gerbeth, G.
  • Invited lecture (Conferences)
    International Workshop MHD-Days 2015, 07.-09.12.2015, Ilmenau, Germany
Registration No. 23303 - Permalink
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