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Publication database - Helmholtz-Zentrum Dresden-Rossendorf

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< Seite 1 von 183 >   Gesamtzahl lt. Auswahl: 18237 Title records (100 Title records je Seite)
22481 Publications
Sponge-like Si-SiO2 nanocomposite for PV applications
Liedke, B.; Heinig, K.-H.; Friedrich, D.; Schmidt, B.; Mücklich, A.; Keles, U.; Bulutay, C.
Abstract: The aim of this talk is to explain method of fabrication, modification and optimization of Sponge-like Si-SiO2 nanocomposite.
It consists of Si embedded in SiO2 fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide SiOx≈1. Thermal treatment using rapid thermal processing and oven annealing requires annealing times of few tens of sec. up to few tens of min. However, in a thin film technology the phase separation of SiOx at high temperatures requires a very rapid thermal processing of few tens of ms in order to avoid substrate damage.
Here, the structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography and atom probe tomography, which revealed a percolated Si morphology. This is in excellent agreement with atomistic simulations using kinetic Monte-Carlo method. Depending on the annealing time and temperature a feature size in the range of 2...5 nm was found, which is small enough for band gap widening due to quantum confinement.
We show that the favorable properties of Si-SiO2 nanocomposite, e.g. quantum size effect and percolated morphology, make it a suitable material for PV absorber.

Keywords: sponge-like nanocomposite, SiOx, photovoltaic, absorber, phase separation, band-gap engineering
  • Lecture (others):
    Seminar in Bergakademie Freiberg, 15.07.2014, Technische Universität Bergakademie Freiberg, Germany
Registration No. 20668

Variability and lower bound of fracture toughness of welds in the ductile-to-brittle transition regime
Hans-Jakob, S.; Dietmar, K.; Hans-Werner, V.
Abstract: The reference temperature T0 was measured for both T-S and T-L- specimen orientation in 24 layers across the thickness of the beltline weld of a reactor pressure vessel. It turned out to vary in a bandwidth of more than 40K. Because of a high scatter, no clear pattern of T0 as a function of the thickness position could be recognized. A more detailed analysis revealed that the median of KJc was considerably steeper than predicted by the Master-Curve, which leads to a bias of T0 with respect to the testtemperature relative to T0. By a modified evaluation procedure, the scatter of the reference temperature could be significantly reduced, which enabled the global pattern of T0 to be recognized. By comparing the theoretical lower bound to KJc-data of the used specimens with the individual measured KJc a representative T0 that characterizes the overall toughness behaviour of the weld was determined. It turned out to be about 10 K lower than the maximum local T0.
Keywords: welding seam, fracture toughness, ductile-tobrittle, Master Curve, Registration No. 20655

Uniaxial anisotropy and its manipulation in amorphous Co68Fe24Zr8 thin films
Fu, Y.; Barsukov, I.; Meckenstock, R.; Lindner, J.; Zhai, Y.; Hjörvarsson, B.; Farle, M.
Abstract: We have proven that the growth of Co68Fe24Zr 8 layers under external field yields a uniaxial anisotropy, defined by the direction of the field. No magnetic coupling is present between Co 68Fe24Zr8 layers when separated by a 3nm of Al70Zr30. The anisotropy axis can therefore be manipulated at will and the direction can be tailored, layer by layer in multilayers, by the choice of the direction of the applied field during growth. The g-factor (2.13) and the anisotropy constant, obtained from ferromagnetic resonance, support the existence of short-range order. The relation between the temperature dependences of magnetic anisotropy and magnetization are partially captured by Callen-Callen power law. Registration No. 20653

Kurzzeitspektroskopie: Kürzeste Laserpulse für Materialuntersuchungen
Mittendorff, M.
Abstract: Mit Hilfe der Kurzzeitspektroskopie ist es möglich die Ladungsträgerdynamik in unterschiedlichen Materialsystemen direkt zu untersuchen. Bei sog. „Pump-Probe-Messungen“ werden z.B. Ladungsträger oder Moleküle mit einem sehr intensiven, aber auch sehr kurzen Laserpuls angeregt. Ein zweiter, wesentlich schwächerer Puls wird verwendet um die verursachte Änderung zu messen. Durch eine zeitliche Verschiebung des zweiten Pulses kann gemessen werden, wie lange das System braucht um die Energie wieder abzugeben. Eine einfache Skizze eines Aufbaus für Pump-Probe-Messungen, sowie ein Beispiel für das Ergebnis einer Messung sind in Abb. 1 gezeigt. Diese Untersuchungen sind beispielsweise besonders wichtig zur Entwicklung und Optimierung elektro-optischer Bauelemente wie z. B. Detektoren oder optische Modulatoren.
Die erreichbare zeitliche Auflösung bei diesen Messungen hängt im Wesentlichen von der Pulsdauer des Lasersystems ab. In diesem Vortrag werden verschieden Lasersysteme zur Erzeugung ultra-kurzer Laserpulse in einem breiten Spektralbereich vom nahen bis zum fernen Infrarot vorgestellt (800 nm – 250 µm). Zu jedem vorgestellten System wird als Beispiel eine Messung der Ladungsträgerdynamik in Graphen gezeigt, das aus einem zweidimensionalen Gitter aus Kohlenstoffatomen besteht. Dieses relativ neue Material, für dessen Untersuchung der Nobelpreis für Physik 2010 verliehen wurde, ist neben der Verwendung in der Elektronik speziell für Anwendungen in der Optoelektronik interessant. Durch die Verwendung verschiedener Wellenlängen können in diesem Material unterschiedliche physikalische Effekte untersucht werden.
  • Lecture (others):
    2. Fortbildungsveranstaltung zu Optotechnik und Bildverarbeitung, 27.06.2014, Darmstadt, Deutschland
Registration No. 20651

Microscopic Description of Intraband Absorption in Graphene: The Occurrence of Transient Negative Differential Transmission
Kadi, F.; Winzer, T.; Malic, E.; Knorr, A.; Göttfert, F.; Mittendorff, M.; Winnerl, S.; Helm, M.
Abstract: We present a microscopic explanation of the controversially discussed transient negative differential transmission observed in degenerate optical pump-probe measurements in graphene. Our approach is based on the density matrix formalism allowing a time- and momentum-resolved study of carrier-light, carrier-carrier, and carrier-phonon interaction on microscopic footing. We show that phonon-assisted optical intraband transitions give rise to transient absorption in the optically excited hot carrier system counteracting pure absorption bleaching of interband transitions. While interband transition bleaching is relevant in the first hundreds of fs after the excitation, intraband absorption sets in at later times. In particular, in the low excitation regime, these intraband absorption processes prevail over the absorption bleaching resulting in a zero crossing of the differential transmission. Our findings are in good qualitative agreement with recent experimental pump-probe studies.
Keywords: graphene, carrier-dynamics, ultrafast spectroscopy Registration No. 20649

A Survivin-XIAP regulates Complexity of the Signaling Molecules FAK and Aktl Radiation Sensitivity as well as Motility of Colorectal Tumor Cells
Hehlgans, S.; Petraki, C.; Cordes, N.; Oppermann, J.; Rodel, C.; Rodel, F.
Abstract: kein Abstract vorhanden
  • Abstract in refereed journal:
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 35-35
Registration No. 20647

Effect of EGF Receptor and beta 1-Integrin Inhibition on the Radiosensitivity three dimensions growing colorectal Cancer cells / Einfluss von EGF Rezeptor und β1-Integrin Hemmung auf die Strahlenempfindlichkeit dreidimensional wachsender kolorektaler Karzinomzellen
Poschau, M.; Zscheppang, K.; Cordes, N.
Abstract: kein Abstract vorhanden
  • Abstract in refereed journal:
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 44-44
Registration No. 20646

Pharmacological Inhibition of Focal Adhesion Kinase affects Cell Survival and Cell death but not Radiosensitivity of human Glioblastoma Cells / Pharmakologische Hemmung der Fokalen Adhäsionskinase beeinflusst Zellüberleben und Zelltod aber nicht Strahlenempfindlichkeit von humanen Glioblastomzellen
Sagerer, A.; Storch, K.; Cordes, N.
Abstract: kein Abstract vorhanden
  • Abstract in refereed journal:
    Strahlentherapie und Onkologie 190(2014)Suppl. 1, 35-35
Registration No. 20645

Fractionated radiotherapy and cetuximab: EGFR amplification and histological markers as potential biomarkers / Fraktionierte Bestrahlung und Cetuximab: EGFR-Amplifikation und histologische Marker als potenzielle Biomarker
Gurtner, K.; Thurow, C.; Koi, L.; Yaromina, A.; Eicheler, W.; Baumann, M.; Krause, M.
Abstract: kein Abstract vorhanden
  • Abstract in refereed journal:
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 27-27
Registration No. 20644

Effects of a Combined Radio (chemo) therapy and HMG-CoA Reductase-Inhibition in Patients with Head-and-neck-Cancer / Effekte einer kombinierten Radio(chemo)therapie und HMG-CoAReduktase-Inhibition bei Patienten mit Kopf-Hals-Tumoren
Ebert, N.; Thiele, C.; Gurtner, K.; Dorr, W.; Lock, S.; Baumann, M.; Krause, M.
Abstract: kein Abstract vorhanden
  • Abstract in refereed journal:
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 144-144
Registration No. 20643

Influence of Chromatin Condensation on cellular Radiosensitivity in three dimensions growing human Tumor Cells / Einfluss der Chromatinkondensierung auf die zelluläre Strahlenempfindlichkeit dreidimensional wachsender humaner Tumorzellen
Storch, K.; Borgmann, K.; Eke, I.; Krause, M.; Becker, K.; Schrock, E.; Cordes, N.
Abstract: kein Abstract vorhanden
  • Abstract in refereed journal:
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 45-45
Registration No. 20642

Radiation sensitization of human squamous by alpha3 integrin Inhibition / Strahlensensibilisierung humaner Plattenepithelkarzinomzellen durch alpha3 Integrin Hemmung
Steglich, A.; Eke, I.; Vehlow, A.; Cordes, N.
Abstract: kein Abstract vorhanden
  • Abstract in refereed journal:
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 22-22
Registration No. 20641

The LIM only Protein FHL2 modulates the MAPK Signal Pathways and influences the Radiation Sensitivity of growing 3D Pancreatic Carcinoma Cells / Das LIM only Protein FHL2 moduliert MAPK Signalwege und beeinflusst die Strahlenempfindlichkeit von 3D wachsenden Pankreaskarzinomzellen
Zienert, E.; Eke, I.; Cordes, N.
Abstract: kein Abstract vorhanden
  • Abstract in refereed journal:
    Strahlentherapie und Onkologie 190(2014)Suppl 1, 14-15
Registration No. 20640

From a non-magnet to a ferromagnet: Mn implantation into different TiO2 structures
Yildirim, O.; Cornelius, S.; Butterling, M.; Anwand, W.; Wagner, A.; Smekhova, A.; Baehtz, C.; Potzger, K.
Abstract: As one of the most promising candidates for a diluted magnetic oxide material for spintronic and magneto optic applications, transition metal (TM) doped titanium dioxide (TiO2) has been extensively studied for last two decades. Up to date room temperature ferromagnetism (RTFM) has been reported for different types of TM dopants and also different types of preparation methods, such as ion implantation [1] or magnetron sputtering [2]. There is an ongoing debate on the origin of the ferromagnetic properties of TiO2, whether RTFM arises from unwanted clustering of the TM atoms, magnetic contamination from sample handling or the desired substitution of Ti by the TM dopants.
We have investigated Mn implanted TiO2 films with respect to the effect of the crystalline structure of the pristine film on the magnetic properties of the doped films. The films were prepared by DC magnetron sputtering using a high purity oxygen deficient ceramic TiO2-x target in Ar/O2 atmosphere. SrTiO3 (100) single crystals were used as substrates. In order to achieve different structures of TiO2, namely amorphous, polycrystalline anatase and epitaxial anatase, different substrate temperatures and post-growth annealing were applied. The as-prepared TiO2 samples have been implanted with Mn ions of 30 keV to 190 keV kinetic energy and variable fluence resulting in a homogenous Mn concentration of 5 at.% within a 150 nm thin layer below the film surface.
The structural changes upon implantation were followed by means of X-ray diffraction (XRD) measurements. Comparison of the diffraction patterns indicates ion-induced damage in the epitaxial film and the formation of Mn containing secondary phases in the polycrystalline material. Depth resolved defect concentration profiles of as-grown and Mn implanted films were determined by means positron annihilation spectroscopy (PAS) measurements based on Doppler broadening spectroscopy. Magnetometry measurements of Mn implanted films reveal ferromagnetism for amorphous and polycrystalline films whereas paramagnetism is observed for epitaxial films. The local environments of implanted Mn ions in different TiO2 structures were probed by X-ray absorption spectroscopy (XAS) in fluorescence mode.
In summary, we have found a significant influence of the as-grown film structure on the magnetic properties of Mn:TiO2. During the presentation the PAS and XAS data will be discussed with respect to the presence of defects and secondary phases in the Mn doped TiO2 films.
  • Lecture (Conference):
    Moscow International Symposium on Magnetism MISM-2014, 29.06.-03.07.2014, Moscow, Russia
Registration No. 20639

Angular dependent ferromagnetic resonance analysis in a single micron sized cobalt stripe
Schoeppner, C.; Wagner, K.; Stienen, S.; Meckenstock, R.; Farle, M.; Narkowicz, R.; Suter, D.; Lindner, J.
Abstract: We demonstrate how planar microresonators (PMRs) can be utilized to investigate the angular dependent magnetic resonance response of single magnetic nanostructures. In contrast to alternative detection schemes like electrical or optical detection, the PMR approach provides a classical means of investigating the high frequency dynamics of single magnetic entities, enabling the use of well-established analysis methods of ferromagnetic resonance (FMR) spectroscopy. To demonstrate the performance of the PMR-based FMR setup for angular dependent measurements, we investigate the microwave excited magnons in a single Co stripe of 5x1x0.02 µm^3 and compare the results to micromagnetic simulations. The evolution of excited magnons under rotation of one individual stripe with respect to a static magnetic field is investigated. Besides quasi uniform excitations, we observe magneto-static as well as localized excitations. We find a strong influence of inhomogeneous dynamic and static demagnetizing fields for all modes. Registration No. 20638

CFD simulations on TOPFLOW-PTS tests
Apanasevich, P.; Coste, P.; Merigoux, N.
Abstract: Pressurized Thermal Shock (PTS) has been identified as one of the most important industrial needs related to nuclear reactor safety. The PTS analysis is required to assure the integrity of the Reactor Pressure Vessel (RPV) throughout the reactor life. One important part of the PTS analysis is the thermal hydraulic analysis which must predict the local temperature fields experienced by the structural parts of the cold leg and especially of the RPV wall close to the cold leg nozzle. Such results are applied as the input data for further structural analyses. Several scenarios that describe what could occur in Small Break Loss Of Coolant Accidents (SB-LOCA) result in an Emergency Core Cooling (ECC) water injection into the cold leg of a Pressurized Water Reactor (PWR). The cold water mixes there with the hot coolant, which is present in the primary circuit. The mixture flows to the downcomer where further mixing of the fluids takes place. Single-phase as well as two-phase PTS situations have to be considered. In case of two-phase PTS situations the water level in the RPV has dropped down to or below the height of the cold leg nozzle, which leads to a partially filled or totally uncovered cold leg. Pressurized Thermal Shock implies the occurrence of thermal loads on the Reactor Pressure Vessel wall. In order to predict thermal gradients in the structural components of the Reactor Pressure Vessel (RPV) wall, knowledge of transient temperature distribution in the downcomer is needed. The prediction of the temperature distribution requires reliable Computational Fluid Dynamic simulations. The CFD models should be able to model the complex mixing processes taking place in the cold leg and the downcomer of the reactor pressure vessel (IAEA, 2001; Lucas et al., 2008, 2009).

In the framework of the NURESAFE project attempts have been made to continue improvement and validation of CFD modeling for two-phase PTS situations. The NEPTUNE_CFD, ANSYS CFX and TransAT codes are used in the project for PTS investigations. A CFD benchmark test on a reference TOPFLOW-PTS steam-water experiment is a part of these activities within the project.

Keywords: TOPFLOW-PTS experiments, direct contact condensation, CFD
  • Lecture (Conference):
    NURESAFE 1st Open Seminar, 16.-17.06.2014, Budapest, Hungary
Registration No. 20630

Ge(1-x)Sn(x) alloys synthesized by ion implantation and pulsed laser melting
Gao, K.; Prucnal, S.; Huebner, R.; Baehtz, C.; Skorupa, I.; Wang, Y.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: The tunable bandgap and the high carrier mobility of Ge(1-x)Sn(x) alloys stimulate a large effort for bandgap and strain engineering for Ge based materials using silicon compatible technology. In this letter we present the fabrication of highly mismatched Ge(1-x)Sn(x) alloys by ion implantation and pulsed laser melting with Sn concentration ranging from 0.5 at. % up to 1.5 at. %. According to the structural investigations, the formed Ge(1-x)Sn(x) alloys are monocrystalline with high Sn-incorporation rate. The shrinkage of the bandgap of Ge(1-x)Sn(x) alloys with increasing Sn content is proven by the red-shift of the E1 and E1+Δ1 critical points in spectroscopic ellipsometry. Our investigation provides a chip technology compatible route to prepare high quality monocrystalline Ge(1-x)Sn(x) alloys.
Keywords: Ge(1-x)Sn(x) alloys, ion implantation, pulsed laser melting Registration No. 20629

Charakterisierung von anisotropen Magnetowiderstandseffekten in Nanostrukturen aus Permalloy und Eisenaluminium
Warnatz, T.
Abstract: Magnetic field induced resistance effects are used in digital storage media - like hard- disk read heads [1]. To produce commercial devices it is of utmost importance to understand and tune the effect. The ion beam induced change of ferromagnetic or paramagnetic effects is known since 1986 [2,3]. However, most of the research was done on bulk material. Due to the increasing miniaturization of digital storage devices it is essential to investigate also the behavior in thin films. Taking into account that a commercial use of the devices is favored, it was focused on easy and reproducible sample geometries. The aim of this thesis was to produce, tune and character- ize magnetic field induced resistance changes in thin films of permalloy and iron-aluminum. Af- terwards, the results have been used to create well-defined nanostructures with potential giant magnetoresistance effects. It is shown, that magnetoresistance effects can be created (iron- aluminum) or reduced (permalloy) by ion beam irradiation. The measurements were performed by a self-programmed LabVIEW program with a precise four-terminal sensing setup at low tempera- tures and with a variable magnetic field up to 2.5 T. The variation of the angle between current flow and the magnetic field as well as measurements at different temperatures led to a very good understanding of the occurring phenomena.
Keywords: FeAl, anisotropic magnetoresistance
  • Thesis / Students' report:
    Westsächsische Hochschule Zwickau, 2013
Registration No. 20622

Herstellung und Charakterisierung eines Spinventils zur Untersuchung der Spindiffusionslänge von FeAl
Liersch, V.
Abstract: Spintronic devices hold great potential for future applilcations in information technology. In this work, the design and fabrication of a lateral spin valve for investigating the spin diffusion length of paramagnetic Fe60Al40 will be discussed. Samples were prepared by defining polycrystalline circuits using electron beam lithography, thin film deposition, and lift-off processing. The developed sample layout allows for both local and non-local measurement routines. Cobalt was employed as ferromagnetic polarizing material, while aluminium holds for reference measurements of the spin diffusion length. The determination of the so far unknown spin diffusion length of paramagnetic Fe60Al40 shall then be performed by detecting resistance changes at different temperatures and for different polarizer distances. Highly sensitive electric transport measurements were carried out in a so-called probe station, which allows for achieving very low temperatures via liquid He cooling. Additionally, paramagnetic ferromagnetic heterostructures were investigated with respect to possible giant magneto resistance effects.
Keywords: FeAl, spin valve, spin diffusion length
  • Thesis / Students' report:
    Westsächsische Hochschule Zwickau, 2014
Registration No. 20621

Experimental evidence for nonaxisymmetric magnetorotational instability in a rotating liquid metal exposed to an azimuthal magnetic field
Seilmayer, M.; Galindo, V.; Gerbeth, G.; Gundrum, T.; Stefani, F.; Gellert, M.; Rüdiger, G.; Schultz, M.; Hollerbach, R.
Abstract: The azimuthal version of the magnetorotational instability (MRI) is a nonaxisymmetric instability of a hydrodynamically stable differentially rotating flow under the influence of a purely or predominantly azimuthal magnetic field. It may be of considerable importance for destabilizing accretion disks, and plays a central role in the concept of the MRI dynamo. We report the results of a liquid metal Taylor-Couette experiment that shows the occurrence of an azimuthal MRI in the expected range of Hartmann numbers. Registration No. 20618

Magnetic fields in space: phenomena and related lab experiments
Stefani, F.
Abstract: The magnetic fields of cosmic bodies are generated by the homogeneous dynamo effect in moving electrically conducting fluids. Cosmic magnetic fields also play an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. In 1999 the threshold of magnetic-field self-excitation was exceeded in the two liquid sodium experiments in Riga and Karlsruhe. Since 2006, the Cadarache dynamo experiment has successfully reproduced many features of geophysical interest such as reversals and excursions. In the same year, the helical version of the magnetorotational instability was observed in the PROMISE facility in Dresden-Rossendorf.
The lecture gives an overview about liquid metal experiments on dynamo action and magnetically triggered instabilities, and it concludes with an overview about future experiments, including a precession driven dynamo and a large-scale Tayler-Couette experiment to be set-up in the framework of the DRESDYN project.
  • Invited lecture (Conferences):
    Space trips summer school on thermo-acoustic and space technologies, 17.-20.06.2014, Riga, Latvia
Registration No. 20617

The azimuthal MRI in experiment: confirmations and surprises
Stefani, F.
Abstract: The azimuthal magnetorotational instability (AMRI) may be of considerable importance for destabilizing accretion disks and plays also a central role in the concept of the MRI dynamo. We report the results of a liquid metal Taylor-Couette experiment that shows the occurrence of an azimuthal MRI in the expected range of Hartmann numbers. We also discuss some peculiarities of the experimental results which are connected with the slight symmetry breaking of the applied magnetic field.
  • Invited lecture (Conferences):
    General Meeting of the Max Planck/Princeton Center for Plasma Physics, 28.06.-01.07.2014, Berlin, Germany
Registration No. 20616

Dynamo action and related magnetic instabilities in the liquid metal lab
Stefani, F.
Abstract: Magnetic fields of cosmic bodies are generated by the hydromagnetic dynamo effect in moving electrically conducting fluids, such as liquid metals or plasmas. Once produced, cosmic magnetic fields are able to act back on moving fluids. This back-reaction may have dramatic consequences for cosmic structure formation, with the magnetorotational instability (MRI) in accretions disks as the most prominent example. Considerable theoretical and computational progress has been made in understanding both the dynamo effect as well as magnetically triggered flow instabilities. Complementary to this, the last fifteen years have seen much effort in studying both effects in liquid metal experiments.
In the talk, we summarize the history of these experiments, discuss their main results and their limitations, and give an outlook on future activities. As for dynamo action, we focus on the Riga, Karlsruhe and Cadarache experiments, and discuss the present status of a large-scale precession-driven dynamo experiment to be set-up in the framework of the DRESDYN project. As for magnetically triggered instabilities, we review the recent experiments on the helical and azimuthal versions of the MRI, as well as on the current-driven Tayler instability (TI). After discussing the astrophysical relevance of those basically induction-less instabilities, we motivate the set-up of a large-scale liquid sodium experiment for studying the continuous transition to the standard version of MRI.
  • Invited lecture (Conferences):
    EUROMECH Colloquium 561: Dimensionality of Turbulence, 19.-21.05.2014, Coventry, United Kingdom
Registration No. 20614

Liquid metal experiments on dynamo action and related magnetic instabilities
Stefani, F.
Abstract: The magnetic fields of planets, stars and galaxies are generated by self-excitation in moving electrically conducting fluids. Once produced, cosmic magnetic fields can play an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. For a long time, both effects, i.e. hydromagnetic dynamo action and the magnetorotational instability, have been the subject of purely theoretical investigations. This situation changed in 1999 when the threshold of magnetic-field self-excitation was exceeded in the two liquid sodium experiments in Riga and Karlsruhe. Since 2006, the Cadarache dynamo experiment has successfully reproduced many features of geophysical interest such as reversals and excursions. In the same year, the helical version of the magnetorotational instability was observed in the PROMISE facility in Dresden-Rossendorf. The lecture gives an overview about liquid metal experiments on dynamo action and magnetically triggered instabilities, it asks for the lessons they have taught us about real cosmic dynamos and accretion disks, and it concludes with an overview about future experiments, including a precession driven dynamo and a large-scale Tayler-Couette experiment to be set-up in the framework of the DRESDYN project.
  • Invited lecture (Conferences):
    LSTM Fluid Mechanics Seminar, 07.02.2014, Erlangen, Germany
Registration No. 20613

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

Keywords: ODS ferritic alloys, DFT, Monte Carlo simulation
  • Lecture (Conference):
    2nd International Workshop on ODS Materials, 26.-27.06.2014, Dresden, Germany
Registration No. 20612

Liquid phase epitaxy of Ge(1-x)Sn(x) alloy using ion-implantation and pulsed laser melting
Gao, K.; Prucnal, S.; Huebner, R.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: Group IV semiconductor alloys have drawn substantial attention for their potential applications in optoelectronic devices capable of integration with the existing Si IC circuitry. Single crystalline Ge1-xSnx alloys are promising for electronic and optical applications in virtue of their high carrier mobility. In this contribution we present the fabrication of Ge1-xSnx by ion-implantation and pulsed laser melting (PLM). Sn was implanted into commercial Ge wafers to form 0.2 µm thick layers with different atomic concentrations from 0.5 % 3.0 %. The as-implanted Ge layer becomes amorphous due to the bombardment of Sn ions with high kinetic energy. The regrowth of the Ge1-xSnx layer after PLM and the lattice expansion were confirmed by X-ray diffraction and micro-Raman spectroscopy. Field emission scanning electron microscopy was applied to determine the surface morphology. High resolution transmission electron microscopy and Rutherford backscattering and channeling analysis confirmed the monocrystalline structure of the Ge1-xSnx layer. Our investigation provides an efficient technique to prepare high quality monocrystalline Ge1-xSnx alloys.
Keywords: GeSn, ion implantation, pulsed laser melting
  • Lecture (Conference):
    E-MRS 2014 SPRING MEETING, 26.05.-01.08.2014, Lille, France
Registration No. 20610

Photoluminescence from GaAs(1-x)N(x) dilute nitride achieved by nitrogen-implantation and flash lamp annealing
Gao, K.; Prucnal, S.; Huebner, R.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: Nitrogen atoms are isoelectronic substituents for arsenic in GaAs. A small amount of nitrogen doping can lead to a pronounced bandgap reduction. Therefore nitrogen-doping can be applied as a powerful technique to modify GaAs based materials for long wavelength optoelectronic devices. In this contribution we present the fabrication of dilute nitride material GaAs1-xNx by nitrogen-implantation and flash lamp annealing (FLA). N was implanted in to the commercial GaAs wafer to form a 0.2 ?m thick layer with atomic concentration of about 0.76 % and 0.38 %. The as-implanted GaAs layer becomes amorphous due to the bombardment of nitrogen ions with high kinetic energy. The GaAs1-xNx layer with compressive strain is epitaxially regrown on GaAs during FLA treatment as confirmed by X-ray diffraction and micro-Raman spectroscopy. In the meantime the bandgap shrinkage is proven by photoluminescence spectroscopy. Based on the redshift of the GaAs1-xNx near band-edge emission, up to 60 % of the implanted N atoms are successfully incorporated into the lattice after FLA. According to our investigation, ion-implantation followed by ultrashort flash lamp treatment, which is quite efficient and low-cost, exhibits a promising prospect on bandgap engineering of GaAs based semiconductors.
Keywords: GaAsN, ion implantation, flash lamp annealing
  • Poster:
    E-MRS 2014 SPRING MEETING, 26.05.-01.08.2014, Lille, France
Registration No. 20609

Formation and photoluminescence of GaAs(1-x)N(x) dilute nitride achieved by N-implantation and flash lamp annealing
Gao, K.; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: In this paper we present the fabrication of dilute nitride semiconductor GaAs(1-x)N(x) by nitrogen-ion-implantation and flash lamp annealing (FLA). N was implanted into the GaAs wafers with atomic concentration of about ximp1=0.38% and ximp2=0.76%. The GaAs1-xNx layer is regrown on GaAs during FLA treatment in a solid phase epitaxy process. Room temperature near band-edge photoluminescence (PL) has been observed from the FLA treated GaAs(1-x)N(x) samples. According to the redshift of the near band-edge PL peak, up to 80% and 44% of the implanted N atoms have been incorporated into the lattice by FLA for ximp1=0.38% and ximp2=0.76%, respectively. Our investigation shows that ion implantation followed by ultrashort flash lamp treatment, which allows for large scale production, exhibits a promising prospect on bandgap engineering of GaAs based semiconductors.
Keywords: GaAs(1-x)N(x), ion implantation, flash lamp annealing, photoluminescence Registration No. 20607

Nanoscale Transport Phenomena
Erbe, A.; Gemming, S.
Abstract: The miniaturization and concurrent diversification of functional devices is one of the key technology drivers in science and technology. Following the ITRS roadmap the length scales of functional elements have shrunk to the nanoscale, permitting comparison between controlled experiments and a realistic, scale-adapted modeling of their physical properties.
In this presentation we show studies of transport properties in nanoscale systems, such as electrical current transport through single molecules, magnetic nanoparticles, and nanowires in experiment and simulation. Our results open possible routes towards new functional devices on the molecular and nanometer scale using effects like light-induced switching of single molecules or charging of single electrons to magnetic single electron transistors. Future integration of these nanostructures into micronsize electrical circuits requires structuring techniques, which form contacts by using combinations of self-assembly and top-down approaches. We demonstrate charge transport through self-organized structures and their placement on large electrodes.

Keywords: nanoscale transport, molecular electronics, charge transport, density-functional theory, functional oxides, nanocomposite materials
  • Lecture (others):
    Abengoa Research Seminar, 20.05.2014, Sevilla, Spanien
Registration No. 20604

Kleinste Strukturen ganz groß – Forschung mit Großgeräten
Gemming, S.
Abstract: allg. Vorstellung der Forschungsanagen am HZDR
Keywords: -
  • Lecture (others):
    Seniorenkolleg der TU Chemnitz, 27.05.2014, Chemnitz, Deutschland
Registration No. 20603

Selbstorganisation – Wie kommt das Muster auf die Oberfläche?
Gemming, S.
Abstract: Muster auf Oberflächen können sich durch eine Vielzahl verschiedener Mechanismen ausbilden. Regelmäßige mikro- und nanoskalige Muster für mobile elektronische Geräte lassen sich zum Beispiel nach vorgegebenen Vorlagen durch aktive top-down Strukturierungsverfahren wie Lithographie oder Drucken erzeugen.

Aus der Natur ist demgegenüber spontane Musterbildung unter Gleichgewichtsbedingungen bekannt, wenn ordnende Wechselwirkungen mit entropischen Faktoren erfolgreich konkurrieren. Induzierte Musterbildung durch Einwirkung externer Faktoren wie den Ionenstrahl ergänzt die Palette möglicher Wege zur Bildung geordneter Oberflächenstrukturen.

Strukturelle Muster finden sich auf verschiedensten Längen- und Zeitskalen von der dreidimensionalen Anordnung von Materie in Galaxien bis hin zur Dekoration von Sensor- oder Katalysatoroberflächen mit Atomen und Molekülen. Gerade die Mustererkennung auf molekularer Ebene bildet die Basis vieler biologischer Prozesse. Darauf basierende Ansätze wie die DNA-Origami-Technik versprechen eine gezielte Strukturierung größerer, technologisch relevanter Oberflächen aus kleinen molekularen Bausteinen. Selbstorganisation auf atomarer Ebene treibt dagegen die Ausbildung von meso- und nanoskopischen Strukturen wie Quantenpunkten, Rippeln oder Nanokompositen durch Ionenstrahlerosion oder ionenstrahlgestützte Abscheidung. Hierbei ist die Strukturierung gekoppelt an das Entstehen funktionaler Muster, wie man sie auch bei Materialien beobachtet, in denen sich am Ordnungs-Unordnungs-Übergang Domänen spontaner Magnetisierung oder spontaner elektrischer Polarisation ausbilden. Einige Beispiele aus der aktuellen Materialforschung sollen verdeutlichen, dass die Musterbildung jenseits des rein Dekorativen eine Vielzahl fundamentaler Aspekte der Physik berührt.

Keywords: Musterbildung, crystal structure, space groups, frieze groupd, rod groups
  • Invited lecture (Conferences):
    Workshop Nanostrukturbildung, 15.04.2013, Dresden, Deutschland
  • Lecture (others):
    Physikalisches Kolloquium, 17.04.2013, Chemnitz, Deutschland
Registration No. 20602

Strontium titanate: An all-in-one rechargeable energy storage material
Hanzig, J.; Zschornak, M.; Nentwich, M.; Hanzig, F.; Gemming, S.; Leisegang, T.; Meyer, D. C.
Abstract: Redistribution of oxygen vacancies in a strontium titanate single crystal is caused by an external electric field. We present electrical measurements during and directly after electroformation, showing that intrinsic defect separation establishes a non-equilibrium state in the transition metal oxide accompanied by an electromotive force. A comprehensive thermodynamic deduction in terms of theoretical energy and entropy calculations indicate an exergonic electrochemical reaction after the electric field is switched off. Based on that driving force the experimental and theoretical proof of concept of an all-in-one rechargeable SrTiO3 single crystal energy storage is reported here.
Keywords: Solid state energy storage; Transition metal oxides; Defects; Density functional theory Registration No. 20601

Investigation of contaminated soil
Richter, C.; Fahmy, K.
Abstract: Investigation of microbial growth in natural minerals using the TAM Air 3 channel calorimeter.
  • Lecture (Conference):
    ISBC Meeting, Lund 2014, 03.06.2014, Lund, Schweden
Registration No. 20599

Single-crystalline Ga- and In- based compound semiconductor nanocrystals in Si by ion implantation and short time flash lamp annealing
Wutzler, R.; Rebohle, L.; Prucnal, S.; Bregolin, F.; Hübner, R.; Helm, M.; Skorupa, W.
Abstract: The integration of III-V compound semiconductors into silicon is a substantial research field for the progress of micro- and optoelectronic device technology. We fabricated various III-V compound semiconductor nanocrystals (NCs) in Si and SOI substrates by sequential high fluence ion beam implantation and ultra-short flash lamp annealing (FLA). Single-crystalline GaAs, GaP, GaSb, InAs, InP and InSb NCs were grown by liquid phase epitaxy during FLA. Additionally, precise positioning of NCs was achieved by using a lithographically patterned aluminum mask layer for ion implantation.

The characterization of the NCs was performed by using Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and Rutherford Backscattering (RBS). Raman measurements confirmed the formation of III-V NCs. AFM and SEM were used to control surface morphology and to investigate the lateral NC distribution. RBS monitored the distribution of the implanted ions. TEM images show distinct, single-crystalline NCs of various shapes. The shape and size of the NCs varies from large domes over small spherical precipitates to conical and pyramidal nanostructures depending on the processing conditions.

Keywords: Ion Implantation, Flash Lamp Annealing, III-V Integration, SOI
  • Lecture (Conference):
    X-th International Conference Ion Implantation and other Applications of Ions and Electrons, 23.-26.06.2014, Kazimierz Dolny, Poland
Registration No. 20598

PET Imaging of the α4β2* Nicotinic Acetylcholine Receptors in Alzheimer's Disease
Sabri, O.; Meyer, P. M.; Gertz, H.-J.; Brust, P.; Barthel, H.; Hesse, S.
Abstract: Alzheimer's disease (AD) is a progressive neurodegenerative disease and the most common form of dementia in the elderly. The subunits α4 and β2 of the nicotinic acetylcholine receptors (α4β2*-nAChRs) are widely abundant throughout the human Brain and play an important role as neuromodulators in different neuronal systems. They are particularly important for cognitive functions and the loss of α4β2*-nAChRs, especially in cholinergic neurons may underlie memory loss in AD. Postmortem autoradiographic and immunohistochemical studies identified cortical and subcortical reductions in α4β2*-nAChR binding in patients with AD. Recently, the α4β2*-nAChR-specific PET and SPECT tracers 2-[18F]FA-85380 (2-FA) and 5-[123I]IA-85380 (5-IA) were developed enabling to study the α4β2*nAChR availability in the living human brain. With such specific radioligands, α4β2*-nAChR binding and its association to cognitive symptoms can be quantitatively determined in patients with AD and mild cognitive impairment (MCI). Initial results show that α4β2*-nAChR availability is reduced in AD but also in amnestic MCI patients who progressed into AD. Hence, the prediction of conversion from MCI to AD seems to be feasible, and therefore, quantitative assessment of α4β2*-nAChR binding using 2-FA-PET or 5-IA-SPECT might become an early biomarker of mental dysfunction in AD. However, the devvelopment of new α4β2*-nAChR PET radioligands characterized by faster kinetics, higher receptor affinity and selectivity is needed and currently underway. Registration No. 20592

Surface nanostructuring by ion-induced localized plasma expansion in zinc oxide
El-Said, A. S.; Moslem, W. M.; Djebli, M.
Abstract: Creation of hillock-like nanostructures on the surface of zinc oxide single crystals by irradiation with slow highly charged ions is reported. At constant kinetic energy, the nanostructures were only observed after irradiation with ions of potential energies above a threshold between 19.1 keV and 23.3 keV. The size of the nanostructures increases as a function of potential energy. A plasma expansion approach is used to explain the nanostructures creation. The calculations showed that the surface nanostructures became taller with the increase of ionic temperature. The influence of charged cluster formation and the relevance of their polarity are discussed.
Keywords: Surface Nanostructuring; highly charged ions; Zinc oxide; plasma expansion Registration No. 20590

Defects and localized states in silica layers implanted with lead ions
Zatsepin, A. F.; Fitting, H.-J.; Buntov, E. A.; Pustovarov, V. A.; Schmidt, B.
Abstract: The luminescence of silica films and glasses implanted with Pb+ ions was studied by means of time-resolved photoluminescence spectroscopy under synchrotron excitation. The ion-modified silica layers are "metal- dielectrics" composites the oxide part of which is represented by amorphous micro-heterogeneous phase with variable Pb2+ions. Two groups of emission centers are identified: such as: (1) radiation-induced oxygen-deficient centers (ODCs) and non-bridging oxygen atoms (NBOs) in the SiO2 matrix and (2) localized electronic states (LS) of the amorphous lead-silicate phase
Keywords: Lead ion implantation; Metal-dielectric composites; Photoluminescence excitation; Silica; UV-vis-photoluminescence Registration No. 20584

APPL proteins modulate DNA repair and radiation survival of pancreatic carcinoma cells by regulating ATM
Hennig, J.; Mcshane, M.; Cordes, N.; Eke, I.
Abstract: Despite intensive multimodal therapies, the overall survival rate of patients with ductal adenocarcinoma of the pancreas is still poor. The chemo- and radioresistance mechanisms of this tumor entity remain to be determined in order to develop novel treatment strategies. In cancer, endocytosis and membrane trafficking proteins are known to be utilized and they also critically regulate essential cell functions like survival and proliferation. On the basis of these data, we evaluated the role of the endosomal proteins adaptor proteins containing pleckstrin homology domain, phosphotyrosine binding domain and a leucine zipper motif (APPL) 1 and 2 for the radioresistance of pancreatic carcinoma cells. Here, we show that APPL2 expression in pancreatic cancer cells is upregulated after irradiation and that depletion of APPL proteins by small interfering RNA (siRNA) significantly reduced radiation survival in parallel to impairing DNA double strand break (DSB) repair. In addition, APPL knockdown diminished radiogenic hyperphosphorylation of ataxia telangiectasia mutated (ATM). Activated ATM and APPL1 were also shown to interact after irradiation, suggesting that APPL has a more direct role in the phosphorylation of ATM. Double targeting of APPL proteins and ATM caused similar radiosensitization and concomitant DSB repair perturbation to that observed after depletion of single proteins, indicating that ATM is the central modulator of APPL-mediated effects on radiosensitivity and DNA repair. These data strongly suggest that endosomal APPL proteins contribute to the DNA damage response. Whether targeting of APPL proteins is beneficial for the survival of patients with pancreatic adenocarcinoma remains to be elucidated. Registration No. 20581

EGFR-Mediated Chromatin Condensation Protects KRAS-Mutant Cancer Cells against Ionizing Radiation
Wang, M.; Kern, A.; Hulskotter, M.; Greninger, P.; Singh, A.; Pan, Y.; Chowdhury, D.; Krause, M.; Baumann, M.; Benes, C.; Efstathiou, J.; Settleman, J.; Willers, H.
Abstract: Therapeutics that target the epidermal growth factor receptor (EGFR) can enhance the cytotoxic effects of ionizing radiation (IR). However, predictive genomic biomarkers of this radiosensitization have remained elusive. By screening 40 non-small cell lung cancer cell (NSCLC) lines, we established a surprising positive correlation between the presence of a KRAS mutation and radiosensitization by the EGFR inhibitors erlotinib and cetuximab. EGFR signaling in KRAS-mutant NSCLC cells promotes chromatin condensation in vitro and in vivo, thereby restricting the number of DNA double-strand breaks (DSB) produced by a given dose of IR.
Chromatin condensation in interphase cells is characterized by an unexpected mitosis-like colocalization of serine 10 phosphorylation and lysine 9 trimethylation on histone H3. Aurora B promotes this process in a manner that is codependent upon EGFR and protein kinase C alpha (PKC alpha). PKC alpha, in addition to MEK/ERK signaling, is required for the suppression of DSB-inducible premature senescence by EGFR. Blockade of autophagy results in a mutant KRAS-dependent senescence-to-apoptosis switch in cancer cells treated with IR and erlotinib. In conclusion, we identify EGFR as a molecular target to overcome a novel mechanism of radioresistance in KRAS-mutant tumor cells, which stands in contrast to the unresponsiveness of KRAS-mutant cancers to EGFR-directed agents in monotherapy. Our findings may reposition EGFR-targeted agents for combination with DSB-inducing therapies in KRAS-mutant NSCLC. Cancer Res; 74(10); 2825-34. (C) 2014 AACR.
Registration No. 20580

Bispidine dioxotetraaza macrocycles: a new class of bispidines for 64Cu PET imaging
Comba, P.; Kubeil, M.; Pietzsch, J.; Rudolf, H.; Stephan, H.; Zarschler, K.
Abstract: The three new dioxo-tetraazamacrocyclic ligands with a fused, very rigid bispidine (3,7-diazabicyclo[3.3.1]nonane) group connecting the two tertiary amine donors, and ethyl, propyl, or benzene groups connecting the two amide donors are highly preorganized and lead to very stable, uncharged CuII complexes. Solution spectroscopy and solid state structures indicate that these are square pyramidal with a solvent molecule occupying the apical position. Cyclic voltammetry defines a reversible CuIII/II couple and a strongly negative irreversible CuII/I couple (ca. −2 V vs Fc/Fc+), indicating that the CuII complexes are very stable in solution. This is supported by superoxide dismutase (SOD) and human serum challenge experiments as well as the biodistribution, which all show that the benzene-based ligand has the highest in vitro and in vivo stability and that this was expected on the basis of the macrocycle ring size and shape and the highest degree of preorganization. This ligand is easy to functionalize for a possible coupling to biological vector molecules and/or fluorescence markers for PET (positron emission tomography) and multimodal imaging (i.e., PET and optical imaging). Registration No. 20579

Development of New PET Tracers for Clinical Use: Challenges and Problems
Brust, P.
Abstract: Es ist kein Abstract vorhanden.
  • Lecture (Conference):
    4. Dresdner Workshop „Molekulare Bildgebung in den Lebenswissenschaften“, 26.06.2014, Rossendorf, Deutschland
Registration No. 20575

Proinflammatory human 6-sulfo LacNAc-positive dendritic cells accumulate in intestinal acute graft-versus-host disease
Sommer, U.; Larsson, B.; Tuve, S.; Wehner, R.; Zimmermann, N.; Kramer, M.; Kloß, A.; Günther, C.; Babatz, J.; Schmelz, R.; Brückner, S.; Schetelig, J.; Bornhäuser, M.; Schäkel, K.; Bachmann, Michael P.; Aust, D.; Baretton, G.; Schmitz, M.
Abstract: kein Abstract verfügbar
Keywords: Acute graft versus host disease; b-sulfo LacNAc positive; Dendritic cells; Proinflammatory Registration No. 20573

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

Keywords: Positron emission tomography; Prognosis; Uterine cervical carcinoma Registration No. 20572

64Cu-labeling of dendritic polyglycerol derivatives for biodistribution studies
Pant, K.; Steinbach, J.; Stephan, H.; Gröger, D.; Nowag, S.; Haag, R.
Abstract: Dendritic polyglycerols (dPG) and polyglycerol sulfates (dPGS) are promising compounds for biomedical applications due to their easy synthesis and high biocompatibility. Dendritic polyglycerol sulfate shows strong anti-inflammatory
properties [1, 2] which makes it a promising agent for diagnostic and therapeutic applications [3].

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

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

References:
[1] H. Türk et al., Bioconjugate Chem. 2004, 15, 162.
[2] J. Dernedde et al., PNAS 2010, 117, 19679.
[3] K. Licha et al., Bioconjugate Chem. 2011, 22, 2453.
[4] G. Gasser et al., Bioconjugate Chem.2008, 19, 719.
  • Poster:
    GDCh-Wissenschaftsforum Chemie 2013, 01.-04.09.2013, Darmstadt, Deutschland
Registration No. 20571

64Cu-labelling and biodistribution of dendritic polyglycerol derivatives
Pant, K.; Stephan, H.; Bergmann, R.; Steinbach, J.; Gröger, D.; Haag, R.
Abstract: Dendritic polyglycerols are highly biocompatible polymers which can be synthesized on a multi gram scale in a one-pot synthesis. The properties of these derivatives can be influenced by using various surface groups, such as sulfates, carbonates, phosphates etc. Some derivatives have been already known for inflammation and bone targeting [1]. Dendritic polyglycerol sulfates (dPGS) are promising candidates to be applied as anti-inflammation and anti-coagulation agents [2]. The presence of amine surface groups in dPGS derivatives allows the attachment of various fluorescence tags and/or radiolabels. Fluorescence imaging using near IR probes visualizes a specific accumulation of dendritic polyglycerol sulfates (dPGS) in inflamed lesions [3]. With respect to radioactive labelling, 35S-labelled dPGS amines have been prepared. This allows ex vivo experiments using autoradiography[4]. However, there is a need of detailed information about bio-distribution and pharmacokinetic properties for dendritic polyglycerol derivatives.

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

Herein, we report the synthesis, radiolabelling and biodistribution studies of the dPGS scaffolds using BFCAs on the basis of 1,4,7-triazacyclononane with various functional end groups (carboxylic, maleimide, isothiocyanate groups) for easy bioconjugation onto the dPGS scaffolds (amine/mercapto surface groups). 64Cu-labeling experiments confirmed rapid CuII complex formation under mild conditions. The stability of the 64Cu radiolabelled conjugates has been studied in the presence of competing ligands, human serum and super oxide dismutase (SOD)[5] For stability studies in the presence of human serum and SOD, two complementary in vitro assays have been applied. Small animal PET studies with 64Cu-labelled dPGS derivatives in male Wistar rats have been performed and discussed.
  • Poster:
    Biodendrimer 2014, 4th International Symposium on Biomedical Applications of Dendrimers, 18.-20.06.2014, Lugano, Schweiz
Registration No. 20569

Effect of [18F]FMISO stratified dose-escalation on local control in FaDu hSCC in nude mice
Schütze, C.; Bergmann, R.; Brüchner, K.; Mosch, B.; Yaromira, A.; Zips, D.; Hessel, F.; Krause, M.; Thames, H.; Kotzerke, J.; Steinbach, J.; Baumann, M.; Beuthien-Baumann, B.
Abstract: Objective To investigate the effect of radiation dose-escalation on local control in hypoxic versus non-hypoxic hypoxic tumours defined using [18F]fluoromisonidazole ([18F]FMISO) PET. Materials and methods FaDu human squamous cell carcinomas (hSCCs) growing subcutaneously in nude mice were subjected to [18F]FMISO PET before irradiation with single doses of 25 or 35 Gy under normal blood flow conditions. [18F]FMISO hypoxic volume (HV) and maximum standardised uptake value (SUVmax) were used to quantify tracer uptake. The animals were followed up for at least 120 days after irradiation. The endpoints were permanent local tumour control and time to local recurrence. Results HV varied between 38 and 291 mm3 (median 105 mm3). Non-hypoxic tumours (HV below median) showed significantly better local control after single dose irradiation than hypoxic tumours (HV above median) (p = 0.046). The effect of dose was significant and not different in non-hypoxic and in hypoxic tumours (HR = 0.82 [95% CI 0.71; 0.93], p = 0.002 and HR = 0.86 [0.78; 0.95], p = 0.001, respectively). Dose escalation resulted in an incremental increase of local tumour control from low-dose hypoxic, over low-dose non-hypoxic and high-dose hypoxic to high-dose non-hypoxic tumours. SUVmax did not reveal significant association with local control at any dose level. Conclusions The negative effect of [18F]FMISO HV on permanent local tumour control supports the prognostic value of the pre-treatment [18F]FMISO HV. Making the assumption that variable [18F]FMISO uptake in different FaDu tumours which all have the same genetic background may serve as an experimental model of intratumoural heterogeneity, the data support the concept of dose-escalation with inhomogeneous dose distribution based on pre-treatment [18F]FMISO uptake. This result needs to be confirmed in other tumour models and using fractionated radiotherapy schedules.
Keywords: Dose escalation; Human tumour xenografts; Hypoxic volume; Local control; Single dose irradiation; Squamous cell carcinoma Registration No. 20565

Cytotoxic response of human regulatory T cells upon T-cell receptor-mediated activation: a matter of purity
Koristka, S.; Cartellieri, M.; Arndt, C.; Feldmann, A.; Töpfer, K.; Michalk, I.; Temme, A.; Ehninger, G.; Bachmann, M.
Abstract: kein Abstract verfügbar Registration No. 20564

Multiscale and multiphysics simulation of pessurized thermal shock (PTS)
Lucas, D.
Abstract: An overview on the activities related to the work package 32 on pressurized thermal shock in frame of the European project NURESAFE is given in this presentation
Keywords: CFD, PTS
  • Lecture (Conference):
    First NURESAFE open seminar, 16.-17.06.2014, Budqapest, Hungary
Registration No. 20562

CFD-Modelle für Zweiphasenströmungen im Rahmen des Mehr-Fluid-Konzepts
Lucas, D.; Rzehak, R.; Krepper, E.; Höhne, Th.; Liao, Y.; Montoya, G.; Hänsch, G.
Abstract: Mehrphasenströmungen kommen u.a. in verschiedenen industriellen Prozessen der chemischen Verfahrenstechnik, der Energietechnik und der Ölindustrie vor. Zuverlässige Vorhersagen der zu erwartenden Strömungs- und Energietransfereigenschaften sind für die Auslegung, Optimierung und auch Sicherheitsbetrachtung dieser Prozesse wichtig. Für CFD-Simulationen von Strömungen in mittleren und großen Volumina wird meist das Zwei- bzw. Mehr-Fluid-Konzept (Euler-Euler-Modell) genutzt. Eine wesentliche Unsicherheit der Simulationsergebnisse resultiert dabei aus den Schließungsmodellen. Oft werden diese Modelle sowie damit verbundene freie Parameter so ausgewählt, dass eine gute Überstimmung mit vorhanden experimentellen Daten erzielt wird. Da die Vorhersagefähigkeit für unbekannte Strömungen dadurch nicht verbessert wird, wurden am HZDR so genannte Standardmodelle für polydisperse Blasenströmungen und separierte Strömungen definiert. Die allgemeine Strategie der Modellentwicklung sowie die Standardmodelle selbst werden in dem Vortrag vorgestellt. Weiterhin wird ein neuer Modellansatz diskutiert, der eine kombinierte Simulation der beiden Strömungsmorphologien einschließlich der Berücksichtigung von Übergängen zwischen diesen ermöglicht.
Keywords: CFD, Mehrphasenströmungen
  • Invited lecture (Conferences):
    Institutsseminar des Instituts für Kern- und Energietechnik (IKET) am Karlsruher Institut für Technologie (KIT), 08.07.2014, Karlsruhe, Deutschland
Registration No. 20561

GENTOP – a multi-field 2-fluid model
Lucas, D.; Hänsch, S.; Krepper, E.; Höhne, Th.; Montoya, G.
Abstract: In this presentation the main ideas of the GENTOP-concept are presented. The concept allows the modelling of different morphologies of two-phase flows including transitions between them. Simulation results are shown for four different demonstration cases.
Keywords: CFD, two-phase, multi-scale
  • Invited lecture (Conferences):
    Joint Hungarian-Korean Laboratory (JHKL) Workshop, 19.-20.06.2014, Budapest, Hungary
Registration No. 20560

Potential of a Cetuximab-based radioimmunotherapy combined with external irradiation manifests in a 3-D cell assay
Ingargiola, M.; Runge, R.; Heldt, J.-M.; Freudenberg, R.; Steinbach, J.; Cordes, N.; Baumann, M.; Kotzerke, J.; Brockhoff, G.; Kunz-Schughart, Leoni A.
Abstract: Targeting epidermal growth factor receptor (EGFR)-overexpressing tumors with radiolabeled anti-EGFR antibodies is a promising strategy for combination with external radiotherapy. In this study, we evaluated the potential of external plus internal irradiation by [90Y]Y-CHX-A''-DTPA-C225 (Y-90-C225) in a 3-D environment using FaDu and SAS head and neck squamous cell carcinoma (HNSCC) spheroid models and clinically relevant endpoints such as spheroid control probability (SCP) and spheroid control dose 50% (SCD 50, external irradiation dose inducing 50% loss of spheroid regrowth). Spheroids were cultured using a standardized platform. Therapy response after treatment with C225, CHX-A''-DTPA-C225 (DTPA-C225), [ 90Y]Y-CHX-A''-DTPA (Y-90-DTPA) and Y-90-C225 alone or in combination with X-ray was evaluated by long-term monitoring (60 days) of spheroid integrity and volume growth. Penetration kinetics into spheroids and EGFR binding capacities on spheroid cells were identical for unconjugated C225 and Y-90-C225. Spheroid-associated radioactivity upon exposure to the antibody-free control conjugate Y-90-DTPA was negligible. Determination of the SCD50 demonstrated higher intrinsic radiosensitivity of FaDu as compared with SAS spheroids. Treatment with unconjugated C225 alone did not affect spheroid growth and cell viability. Also, C225 treatment after external irradiation showed no additive effect. However, the combination of external irradiation with Y-90-C225 (1 μg/ml, 24 hr) resulted in a considerable benefit as reflected by a pronounced reduction of the SCD50 from 16 Gy to 9 Gy for SAS spheroids and a complete loss of regrowth for FaDu spheroids due to the pronounced accumulation of internal dose caused by the continuous exposure to cell-bound radionuclide upon Y-90-C225-EGFR interaction.
Keywords: Cetuximab; EGFR; tumor spheroids; Y-90 Registration No. 20559

Climatic vs tectonic forcing: the case of Pamir
Gloaguen, R.; Fuchs, M.; Pohl, E.; Sulaymonova, V.; Andreani, L.
Abstract: Surface processes in Pamir are temporally and spatially extremely variables. Our collaborative research demonstrated that, (1) the controlling forces such as climate and tectonic deformation have evolved during the Quaternary, (2) Westerlies and Monsoon have varying domains of influence and (3) the rates of deformation, erosion and incision are locally extremely high. The determination of the localization and intensity of active tectonic structures was allowed by the production of remote sensing based geomorphometric maps combined with published GPS and seismological data. Incision rates were measured by OSL and cosmogenic dating of river terraces. Modern erosion rates were calculated using AMS 10Be concentrations in river sediments. Tectonic deformation principally occurs along the borders of the Pamir domes, probably along propagating strike-slip faults reactivating older structures such as sutures and dome bounding faults. Most rivers are in imbalance and witness a strong reorganization of the drainage system during the Late Quaternary. The Panj itself is built by the concatenation of rivers by successive captures, the last one probably younger than MIS2. The average incision rate of the Panj, the main river draining Pamir and its main tributaries is about 4 mm/yr. Peak incisions reach 10 mm/yr where river captures induced high offsets with respect to base levels. Erosion rates are high at the Pamir periphery (ca 0.7 mm/yr) and very low on the plateau (ca 0.005 mm/yr). The Pamir can be subdivided in zones in which specific controlling forces are dominating. The Pamir plateau is dominated by diffusive hillslope processes contributing to further flattening. The main rivers are located in or nearby active faults. High erosion rates are probably sustained by steep hillslopes generated by high incision rates. Highest erosion rates are found were both Monsoon and Westerlies occur.
  • Lecture (Conference):
    EGU General Assembly 2014, 27.04.-02.06.2014, Vienna, Austria
Registration No. 20557

A new set of MATLAB functions (TecDEM toolbox) to analyze erosional stages in landscapes and base-level changes in river profiles
Andreani, L.; Gloaguen, R.; Shahzad, F.
Abstract: We implemented three new functions in the MATLAB-based TecDEM toolbox [1,2]: surface index, topographic position index, and the analysis of base-levels in river longitudinal profiles. These tools provide useful ways to understand the effects of base-level changes on topography such as stream captures, erosion or rejuvenation of pre-existing topographic features and anomalies in river longitudinal profiles. We developed a new index (referred as “surface index”) which provides a quick way to map simultaneously preserved and eroded portions of an elevated landscape. This index classifies landscapes according to their erosional stages using the combination of the hypsometric integral, which efficiently highlights flat surfaces, and the surface roughness, which substantially increases with incision. We also implemented the commonly used “topographic position index”. This index provides a simple way to classify the landscapes as valleys, ridges and flat areas. However, its application in tectonic geomorphology can go far beyond as it discriminates valleys shapes and reveals other important features such as wind gaps and knickpoints when associated to the extracted river system. Finally, we implemented a tool allowing the estimation of base-level changes using the reconstruction of river longitudinal profiles. River profiles can be decomposed in concave or convex segments. Relict base-levels are typically associated to gently concave segments in river profiles. By restoring the initial shape of these segments we are able to estimate the amount of incision between the present day base-level and the relict base-level. All these tools were successfully tested in different settings such as Central America, Central Europe and Pamir. In addition to the description of these tools we provide examples from these different areas.
[1] Shahzad, F., & Gloaguen, R. (2011). TecDEM: A MATLAB based toolbox for tectonic geomorphology, Part 1: Drainage network preprocessing and stream profile analysis. Computers & Geosciences, 37, 250–260.
[2] Shahzad, F., & Gloaguen, R. (2011). TecDEM: A MATLAB based toolbox for tectonic geomorphology, Part 2: Surface dynamics and basin analysis. Computers & Geosciences, 37, 261–271.
  • Poster:
    EGU General Assembly 2014, 27.04.-02.05.2014, Vienna, Austria
Registration No. 20556

Model experiments for investigations of heat transfer phenomena in the Czochralski crystal growth
Pal, J.; Cramer, A.; Eckert, S.; Gerbeth, G.; Grants, I.
Abstract: A low temperature liquid metal model of the Czochralski crystal growth process is considered experimentally under conditions of high aspect ratio. We focus on the influence of a rotating magnetic field (RMF) and/or crystal rotation on temperature fluctuation near the crystal edge. The radial flow structure is observed by ultrasound Doppler velocimetry (UDV). It is concluded that the effect of RMF on the temperature fluctuation is less expressed than in a Rayleigh-Bénard cell.
Keywords: Czochralski crystal growth, electromagnetic processing, buoyant flow, heat transfer
  • Lecture (Conference):
    The 9th. International PAMIR conference on Fundamental and Applied MHD, Thermo Acoustic and Space Technologies, 16.-20.06.2014, Riga, Latvia
  • Contribution to proceedings:
    The 9th. International PAMIR Conference on Fundamental and Applied MHD, Thermo Acoustic and Space Technologies, 16.-20.06.2014, Riga, Latvia
    Proceedings, 110-114
Registration No. 20553

Experimental Investigation of Rayleigh-Benard convection in a liquid metal layer exposed to a horizontal magnetic field
Igaki, K.; Tasaka, Y.; Yanagisawa, T.; Vogt, T.; Eckert, S.
Abstract: Rayleigh-Benard convection has been investigated inside a liquid metal layer under the influence of a DC magnetic field. Similar configurations can be found in geophysical or steel production. Our group reported recently that spontaneous flow reversals of quasi two-dimensional rolls randomly occur in Rayleigh-Benard convection of liquid metal exposed to a horizontal magnetic field (Yanagisawa, et al., PRE, 2011). In fluid layers with relatively large aspect ratios the flow pattern consisting of several convection rolls appears to be almost isotropic. However, the rolls are aligned with the magnetic field direction if the Lorentz force becomes either comparable to the buoyancy or larger. In our experiment, where the fluid layer has a dimension of 200x200x40 mm (corresponding to an aspect ratio of 5), the convection pattern can show 3, 4 or 5 rolls regimes depending on the Rayleigh number Ra and the Chandrasekhar number Q. Flow reversals occur spontaneously between these steady states in the Ra-Q parameter space.
Keywords: Rayleigh-Benard
  • Contribution to proceedings:
    9th International Pamir Conference, 16.-20.06.2014, Riga, Latvia
  • Poster:
    9th International Pamir Conference, 16.-20.06.2014, Riga, Latvia
Registration No. 20552

Experimental investigation of inertial waves inside a cylindrical liquid metal column
Vogt, T.; Räbiger, D.; Eckert, S.
Abstract: The dynamics of free inertial waves inside a cylindrical volume was investigated experimentally in this study. The liquid metal GaInSn was chosen as fluid in order to enable a contactless stimulation of the flow inside the cylinder by means of a rotating magnetic field which generates a supercritical rotating motion of the liquid. The experiment demonstrates that inertial waves may be excited spontaneously by turbulent structures in the rotating flow. The ultrasound Doppler velocimetry was used to record the flow structure and to identify the inertial waves occurring in the setup.
Keywords: inertial waves, rotating flow
  • Lecture (Conference):
    9th International PAMIR Conference, 16.-20.06.2014, Riga, Latvia
  • Contribution to proceedings:
    9th International PAMIR Conference, 16.-20.06.2014, Riga, Latvia
    Proceedings of the 9th International PAMIR Conference
Registration No. 20550

Regime transition in viscous and pseudo viscous systems: A comparative study
Rabha, S.; Schubert, M.; Hampel, U.
Abstract: A comprehensive quantitative study on the effect of liquid viscosity (1 ≤ µL ≤ 1149 mPa-s) on the local flow phenomena of the gas phase in a small diameter bubble column is performed using ultrafast electron beam X-ray tomography. The internal dynamic flow structure and the bubble size distribution have proven a dual role of the liquid viscosity on the hydrodynamics. Further, effect of solid concentration (Cs = 0.05, 0.20) on the local flow behavior of the gas phase is studied for the pseudo (slurry) viscosities similar to the liquid viscosities of the gas-liquid systems. The effects of liquid and pseudo (slurry) viscosity on flow structure, bubble size distribution and gas phase distribution are compared. The bubble coalescence is significantly enhanced with the addition of particles as compared to the system without particles for apparently same viscosity. The superficial gas velocity at which transition occurs from homogeneous bubbly to slug flow regime is initiated by the addition of particles as compared to the particle free system for apparently same viscosity.
Keywords: Liquid viscosity, Pseudo (slurry) viscosity, Gas holdup, Bubble size distribution, Ultrafast electron beam X-ray tomography Registration No. 20548

Surface-near modifications of SrTiO3 local symmetry due to nitrogen implantation investigated by grazing incidence XANES
Stöcker, H.; Zschornak, M.; Richter, C.; Hanzig, J.; Hanzig, F.; Hinze, V.; Potzger, K.; Gemming, S.; Meyer, Dirk C.
Abstract: Nitrogen ion implantation into strontium titanate single crystals causes a slight shift of the Ti-K edge position compared to pristine SrTiO3 and a strong increase of the second pre-edge peak in X-ray absorption near-edge spectroscopy (XANES) using graz- ing incidence geometry. Calculations by a finite difference method demonstrate that the strong increase of the second pre-edge fea- ture in the defect distorted phase can be attributed to a static displacement of the Ti atom relative to the surrounding oxygen octahedron.
Keywords: ferroic functional oxides, density functional theory, doping, strontium titanate Registration No. 20540

Evaluation and automatic correction of metal-implant-induced artifacts in MR-based attenuation correction in whole-body PET/MR imaging
Schramm, G.; Maus, J.; Hofheinz, F.; Petr, J.; Lougovski, A.; Beuthien-Baumann, B.; Platzek, I.; van den Hoff, J.
Abstract: The aim of this paper is to describe a new automatic method for compensation of metal-implant-induced segmentation errors in MR-based attenuation maps (MRMaps) and to evaluate the quantitative influence of those artifacts on the reconstructed PET activity concentration. The developed method uses a PET-based delineation of the patient contour to compensate metal-implant-caused signal voids in the MR scan that is segmented for PET attenuation correction. PET emission data of 13 patients with metal implants examined in a Philips Ingenuity PET/MR were reconstructed with the vendor-provided method for attenuation correction (MRMap(orig), PETorig) and additionally with a method for attenuation correction (MRMap(cor), PETcor) developed by our group. MRMaps produced by both methods were visually inspected for segmentation errors. The segmentation errors in MRMap(orig) were classified into four classes (L1 and L2 artifacts inside the lung and B1 and B2 artifacts inside the remaining body depending on the assigned attenuation coefficients). The average relative SUV differences (epsilon(av)(rel)) between PETorig and PETcor of all regions showing wrong attenuation coefficients in MRMap(orig) were calculated. Additionally, relative SUVmean differences (epsilon(rel)) of tracer accumulations in hot focal structures inside or in the vicinity of these regions were evaluated. MRMap(orig) showed erroneous attenuation coefficients inside the regions affected by metal artifacts and inside the patients' lung in all 13 cases. In MRMap(cor), all regions with metal artifacts, except for the sternum, were filled with the soft-tissue attenuation coefficient and the lung was correctly segmented in all patients. MRMap(cor) only showed small residual segmentation errors in eight patients. (epsilon(av)(rel)) (mean +/- standard deviation) were: (-56 +/- 3)% for B1, (-43 +/- 4)% for B2, (21+/- 18)% for L1, (120 +/- 47)% for L2 regions. epsilon(rel) (mean +/-standard deviation) of hot focal structures were: (-52 +/- 12)% in B1, (-45 +/- 13)% in B2, (19 +/- 19)% in L1, (51 +/- 31)% in L2 regions.
Consequently, metal-implant-induced artifacts severely disturb MR-based attenuation correction and SUV quantification in PET/MR. The developed algorithm is able to compensate for these artifacts and improves SUV quantification accuracy distinctly.
Registration No. 20534

Superconducting RF Guns: Emerging Technology for Future Accelerators
Teichert, J.
Abstract: This talk should give an overview of Superconducting photo injectors (SRF guns) and focus on the present status of SRF gun development, the technical requirements and the critical issues like cavity design, photocathode integration, and emittance compensation methods.
Keywords: photo injector, superconducting RF, electron source, SRF gun
  • Invited lecture (Conferences):
    IPAC'14 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Germany
Registration No. 20531

TecLines: A MATLAB-Based Toolbox for Tectonic Lineament Analysis from Satellite Images and DEMs, Part 1: Line Segment Detection and Extraction
Rahnama, M.; Gloaguen, R.
Abstract: Geological structures, such as faults and fractures, appear as image discontinuities or lineaments in remote sensing data. Geologic lineament mapping is a very important issue in geo-engineering, especially for construction site selection, seismic, and risk assessment, mineral exploration and hydrogeological research. Classical methods of lineaments extraction are based on semi-automated (or visual) interpretation of optical data and digital elevation models. We developed a freely available Matlab based toolbox TecLines (Tectonic Lineament Analysis) for locating and quantifying lineament patterns using satellite data and digital elevation models. TecLines consists of a set of functions including frequency filtering, spatial filtering, tensor voting, Hough transformation, and polynomial fitting. Due to differences in the mathematical background of the edge detection and edge linking procedure as well as the breadth of the methods, we introduce the approach in two-parts. In this first study, we present the steps that lead to edge detection. We introduce the data pre-processing using selected filters in spatial and frequency domains. We then describe the application of the tensor-voting framework to improve position and length accuracies of the detected lineaments. We demonstrate the robustness of the approach in a complex area in the northeast of Afghanistan using a panchromatic QUICKBIRD-2 image with 1-meter resolution. Finally, we compare the results of TecLines with manual lineament extraction, and other lineament extraction algorithms, as well as a published fault map of the study area.
Keywords: TecLines; Matlab; tectonic; lineament; edge detection; tensor voting Registration No. 20530

Surface modifications of BaF2 and CaF2 single crystals by slow highly charged ions
El-Said, A. S.; Heller, R.; Wilhelm, R.; Facsko, S.; Aumayr, F.
Abstract: Ion-irradiation of solid surfaces is considered as one of the promising and powerful techniques for material nanostructuring. Recently, slow highly charged ions (HCI) have shown their potential in creating surface nanostructures in various solids. Here, we focus on the surface modifications of BaF2 and CaF2 single crystals by HCI. Despite the fact that both materials belong to alkaline-earth fluorides with the same crystalline structure, they exhibit different sensitivity for HCI-induced nanostructure. We discuss similarities and differences for the creation of HCI-induced nanohillocks and etch pits in both materials and their dependence on potential and kinetic energy deposition. Furthermore, we compare the results with modifications induced by swift heavy ions (SHI), in order to reach a better understanding of the mechanisms responsible for the creation of nanostructures in ionic fluoride single crystals.
Keywords: Highly charged ions; Nanostructures; Ion–surface interaction; BaF2; CaF2 Registration No. 20527

Investigation of H+ implanted Fe-Al alloys
Lukac, F.; Cizek, J.; Prochazka, I.; Jiraskova, Y.; Janickovic, D.; Simeg Veternikova, J.; Anwand, W.; Butterling, M.
Abstract: In the present work hydrogen interaction with vacancies was investigated in Fe-Al alloys with various concentration of vacancies. The Fe-Al samples were implanted with low energy H+ ions (100 keV). This procedure introduced high hydrogen concentration into relatively narrow sub-surface region in the depth of ~500 nm. Variable energy positron annihilation spectroscopy (VEPAS) was employed for investigation of hydrogen interaction with vacancies in the sub-surface region. This study revealed formation of vacancy hydrogen complexes in the sub-surface region. Thermal stability of vacancy-hydrogen complexes was investigated as well.
Keywords: FeAl alloys, hydrogen implantation, vacancies, positron annhilation Registration No. 20526

Bayes Hilbert Spaces
van den Boogaart, K. G.; Egozcue, J. J.; Pawlowsky-Glahn, V.
Abstract: A Bayes linear space is a linear space of equivalence classes of proportional -finite measures, including probability measures. Measures are identified with their density functions. Addition is given by Bayes’ rule and substraction by Radon–Nikodym derivatives. The present contribution shows the subspace of square-log-integrable densities to be a Hilbert space, which can include probability and infinite measures, measures on the whole real line or discrete measures. It extends the ideas from the Hilbert space of densities on a finite support towards Hilbert spaces on general measure spaces. It is also a generalisation of the Euclidean structure of the simplex, the sample space of random compositions. In this framework, basic notions of mathematical statistics get a simple algebraic interpretation. A key tool is the centred-log-ratio transformation, a generalization of that used in compositional data analysis, which maps the Hilbert space of measures into a subspace of square-integrable functions. As a consequence of this structure, distances between densities, orthonormal bases, and Fourier series representing measures become available. As an application, Fourier series of normal distributions and distances between them are derived, and an example related to grain size distributions is presented. The geometry of the sample space of random compositions, known as Aitchison geometry of the simplex, is obtained as a particular case of the Hilbert space when the measures have discrete and finite support.
Keywords: Aitchison geometry of the simplex; distance between measures; Fourier coefficients; infinite measures; normal distribution; perturbation; probability measures Registration No. 20525

A quasi-likelihood approach to parameter estimation for simulatable statistical models
Baaske, M.; Ballani, F.; van den Boogaart, K. G.
Abstract: This paper introduces a parameter estimation method for a general class of statistical models. The method exclusively relies on the possibility to conduct simulations for the construction of interpolation-based metamodels of informative empirical characteristics and some subjectively chosen correlation structure of the underlying spatial random process. In the absence of likelihood functions for such statistical models, which is often the case in stochastic geometric modelling, the idea is to follow a quasi-likelihood (QL) approach to construct an optimal estimating function surrogate based on a set of interpolated summary statistics. Solving these estimating equations one can account for both the random errors due to simulations and the uncertainty about the meta-models. Thus, putting the QL approach to parameter estimation into a stochastic simulation setting the proposed method essentially consists of finding roots to a sequence of approximating quasiscore functions. As a simple demonstrating example, the proposed method is applied to a special parameter estimation problem of a planar Boolean model with discs. Here, the quasi-score function has a half-analytical, numerically tractable representation and allows for the comparison of the model parameter estimates found by the simulation-based method and obtained from solving the exact quasi-score equations.
Keywords: Keywords: kriging meta-modelling, parameter estimation, quasi-likelihood, simulation-based optimization. Registration No. 20524

Structural studies of thin Mg films
Hruska, P.; Cizek, J.; Anwand, W.; Bulir, J.; Lancok, J.; Straska, J.; Melikhova, O.; Prochazka, I.
Abstract: In the present work variable energy positron annihilation spectroscopy (VEPAS) was employed for investigation of defects in Mg films. VEPAS characterization was combined with scanning electron microscopy and X-ray diffraction in order to determine grain size and texture, respectively. The aim of this study was to examine the effect of deposition temperature and various substrates on structure and defects in Mg films prepared by RF magnetron sputtering. SEM observations revealed that films deposited on sapphire (0001) substrate exhibit always smaller grains than films deposited on amorphous fused silica and silicon (100) substrates, which have comparable grain size. Defect studies by VEPAS showed that positrons in Mg films studied are trapped at misfit dislocations and at vacancy-like defects in grain boundaries. Moreover, the films deposited on a substrate heated at 300°C exhibited lower concentration of defects and larger grain size compared to the films deposited at room temperature. Subsequent annealing at 300°C for 1 h of the films deposited at room temperature causes a slight decrease of defect density due to coarsening of grains.
Keywords: Mg films, RF magnetron sputtering, defects, positron annihilation Registration No. 20523

A study of the structural and magnetic properties of ZnO implanted by Gd ions
Macková, A.; Malinsky, P.; Sofer, Z.; Šimek, P.; Sedmidubsky, D.; Mikulics, M.; Wilhelm, R. A.
Abstract: The structural and magnetic properties of ZnO (0 0 0 1) single crystals implanted with 200 keV Gd ions up to a fluence of 5 × 1015 cm−2 and subsequently annealed at 800 °C in various atmospheres were studied. The chemical composition and concentration depth profiles of ion-implanted layers were characterised by Rutherford Back-Scattering spectrometry (RBS) and compared to SRIM simulations. The as-implanted Gd depth profiles were found to be broader than those simulated by SRIM, but the projected range coincided well with that simulated. After annealing at 800 °C, the depth profiles became narrower. The structural changes in the layers modified by ion implantation and subsequent annealing were characterised by RBS channelling. The annealing led to partial recrystallisation and a decrease in the number of Gd atoms situated in substitutional positions. Raman spectroscopy showed that the point defects in Zn and O vacancies had been created by implantation and that these defects are most effectively cured after annealing in oxygen atmosphere. AFM analysis was used to determine the surface-morphology changes after the implantation and annealing procedures. The as-implanted samples exhibited ferromagnetism persisting up to room temperature. The annealing procedure led to paramagnetic behaviour, probably caused by the formation of gadolinium clusters.
Keywords: ZnO; Gd implantation; Depth profiles; RBS channelling; Raman spectroscopy; AFM Registration No. 20522

A combinatorial study of the mechanical and magnetic properties of a gradually nitrided austenitic stainless steel single crystal
Menéndez, E.; Templier, C.; Abrasonis, G.; Lopez-Barbera, J. F.; Nogués, J.; Temst, K.; Sortef, J.
Abstract: The mechanical and magnetic properties of a nitrided austenitic stainless steel are studied using a combinatorial approach. Plasma nitriding of a [100]-oriented 316L single crystal is carried out using a loose shadow mask to produce an in-plane lateral gradient of nitrogen concentration that extends up to 100 μm. The local mechanical and magnetic properties across the gradually nitrided area are resolved by nanoindentation and the polar magneto-optic Kerr effect, respectively. The hardness, reduced Young's modulus and remanence qualitatively depict the nitrogen profile, suggesting that the nitrogen concentration is a central effect for these observed dependencies. Conversely, the coercivity exhibits a non-monotonic behaviour due to the interplay between magnetic anisotropy and the strength of the induced ferromagnetism. Fingerprints of the expected transition from a nitrogen supersaturated solid solution to a multiphase nature of expanded austenite are evidenced along the gradually nitrided area.
Keywords: Austenitic stainless steel, plasma nitriding, magnetic and mechanical properties Registration No. 20521

The structural changes and optical properties of LiNbO3 after Er implantation using high ion fluencies
Macková, A.; Malinsky, P.; Pupíková, H.; Nekvindová, P.; Cajzl, J.; Sofer, Z.; Wilhelm, R. A.; Kolitsch, A.; Oswald, J.
Abstract: The structural and compositional changes of LiNbO3 implanted with 190 keV Er+ ions into various crystallographic cuts with fluencies of 1 × 1016 and 5 × 1016 cm−2 were studied. The effect of post-implantation annealing at 1000 °C in oxygen atmosphere was also examined. Concentration depth profiles of implanted erbium, determined by Rutherford Backscattering Spectrometry (RBS), are broader than those from the SRIM simulation. The maximum erbium concentration (of up to 8 at.%) is observed at the depth of about 50 nm, for all crystal cuts. The structure of the implanted layers were characterised by RBS-channelling method. The lower relative number of disordered atoms in the crystalline matrix was observed in the lithium niobate (LN) implanted at a fluence of 1 × 1016 cm−2, where also the preferential position of the erbium in substitutional sites was observed when compared to the randomly distributed erbium in interstitial positions at a fluence of 5 × 1016 cm−2 after the annealing. Surface-morphology changes at the highest implantation fluencies were studied using Atomic Force Microscopy (AFM). Since we were interested in the relation between the structural changes and optical properties, erbium luminescence properties were measured in the region of 1440–1650 nm. The positive effect of post-implantation annealing on the luminescence properties caused by structural recovery was proved.
Keywords: Implanted lithium niobate; Erbium implantation; RBS channeling structural study; Luminesent properties Registration No. 20520

Introduction to the Minimum Rainbow Subgraph problem
Matos Camacho, S.
Abstract: Consider an p edge coloured graph G, then a Minimum Rainbow Subgraph is a subgraph H of G of minimum order, such that every colour occurs in H. This phd thesis provides a comprehensive introduction to this problem.
Keywords: graph theory, chromatic index, colouring
  • Thesis / Students' report:
    TU Bergakademie Freiberg, 2012
    Mentor: Prof. Dr. Ingo Schiermeyer
    59 Seiten
Registration No. 20518

The rainbow connection number of 2-connected graphs
Ekstein, J.; Holub, P.; Kaiser, T.; Koch, M.; Matos Camacho, S.; Ryjáček, Z.; Schiermeyer, I.
Abstract: The rainbow connection number of a graph G is the least number of colours in a (not necessarily proper) edge-colouring of G such that every two vertices are joined by a path which contains no colour twice. Improving a result of Caro et al., we prove that the rainbow connection number of every 2-connected graph with n vertices is at most ⌈n/2⌉. The bound is optimal.
Keywords: Rainbow connection number; Graph; Connectivity Registration No. 20517

Algorithmic approaches for the minimum rainbow subgraph problem
Koch, M.; Matos Camacho, S.; Schiermeyer, I.
Abstract: We consider the Minimum Rainbow Subgraph problem (MRS): Given a graph G, whose edges are coloured with p colours. Find a subgraph F⊆G of minimum order and with p edges such that each colour occurs exactly once. This problem is APX-hard. In this paper we will show that the Greedy algorithm for the MRS problem has an approximation ratio of Δ/2 + (lnΔ+1)/2 for graphs with maximum degree Δ. If the average degree d of a minimum rainbow subgraph is known, then the approximation ratio is d/2 + (ln[d]+1)/2.
Keywords: 10.1016/j.endm.2011.10.028 Registration No. 20516

Approximation algorithms for the minimum rainbow subgraph problem
Matos Camacho, S.; Schiermeyer, I.; Tusa, Z.
Abstract: We consider the minimum rainbow subgraph problem (MRS): given a graph G, whose edges are coloured with p colours. Find a subgraph F⊆G of G of minimum order and with p edges such that each colour occurs exactly once. For graphs with maximum degree Δ(G) there is a greedy polynomial-time approximation algorithm for the MRS problem with an approximation ratio of Δ(G). In this paper we present a polynomial-time approximation algorithm with an approximation ratio of View the MathML source for Δ≥2.
Keywords: Edge colouring; Minimum rainbow subgraph; Approximation algorithm Registration No. 20515

Colourings of graphs with prescribed odd cycle lengths
Matos Camacho, S.; Schiermeyer, I.
Abstract: In 1992 Gyárfás showed that a graph G having only k odd cycle lengths is (2k+1)-colourable, if it does not contain a K2k+2. In this paper, we will present the results for graphs containing only odd cycles of length 2m−1 and 2m+1 as done in [S. Matos Camacho, Colourings of graph with prescribed cycle lengths, diploma thesis, TU Bergakademie Freiberg, 2006. [3]]. We will show that these graphs are 4-colourable.
Keywords: Colouring; Cycles; Chromatic number Registration No. 20514

Temperature dependence of ion-beam mixing in crystalline and amorphous germanium isotope multilayer structures
Radek, M.; Bracht, H.; Posselt, M.; Liedke, B.; Schmidt, B.; Bougeard, D.
Abstract: The renewed interest in Germanium as base material for electronic applications has stimulated extensive experimental and theoretical studies. Successful integration of Ge in nanoelectronic devices requires fundamental understanding of ion-implantation-induced target modification and damage. In this contribution the temperature dependence of ion-beam mixing induced by 310 keV gallium (Ga) ion implantation in crystalline and preamorphized germanium (Ge) is reported. Isotopically enriched multilayer structures of alternating 70Ge and natGe layers are used to visualize the self-atom mixing. The distribution of the implanted Ga atoms and the ion-beam induced self-atom mixing was determined by means of secondary ion mass spectrometry. Different temperature regimes of self-atom mixing are observed. At temperatures up to 423 K the mixing is independent of the initial structure whereas at 523 K the intermixing of the preamorphized Ge structure is about twice as high as that of the crystalline material. At 623 K the intermixing of the initially amorphous Ge structure is strongly reduced and approaches the mixing of the crystalline material. The temperature dependence of ion-beam mixing is consistently described by competitive amorphization and recrystallization processes.
Keywords: ion beam mixing, isotopically enriched multilayer structures, amorphous germanium, self mixing, thermal spike
  • Lecture (Conference):
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France
Registration No. 20512

Formation, coarsening and band gap engineering of sponge-like Si-SiO2 nanocomposites – materials design by theoretical predictions
Liedke, B.; Heinig, K. H.; Friedrich, D.; Schmidt, B.; Mücklich, A.; Hübner, R.; Keles, U.; Bulutay, C.
Abstract: It has been found by energy filtered transmission electron microscopy (EFTEM) that metastable SiOx≈1 films decay during thermal treatment by spinodal decomposition into a Si nanowire network embedded in SiO2 forming a nanocomposite [1,2]. This nanoscale material is promising candidate as absorber layer for next generation solar cells as it exhibits a widened band gap due to quantum confinement and electrical interconnectivity due to percolation of the nanostructured Si. The formation of Si-SiO2 nanocomposites was predicted by a kinetic Monte Carlo simulations [1,3]. Additionally, the band gap and the band offset of the nanocomposite were predicted by large scale atomistic pseudopotential computations [4]. Experimentally, the sponge-like morphology was verified by EFTEM and atom probe tomography [2], whereas its band gap measured via light absorption is still under discussion. The predicted morphology of the sponge-like Si-SiO2 nanocomposite appears to be almost identical to the measured ones. Also the predicted scaling behavior of the coarsening of the nanostructure during thermal treatment was verified experimentally. Combining theory with experiments delivers the understanding for tailoring the properties like quantum confinement of the sponge-like Si. [1] Müller, et al. Appl. Phys. Lett. 85, 2373 (2004) [2] Friedrich, et al. Appl. Phys. Lett. 103, 133106 (2013) [3] Liedke, et al. Appl. Phys. Lett. 103, 131911 (2013) [4] Keles, et al. Appl. Phys. Lett. 103, 203103 (2013)
Keywords: sponge, Si-SiO2 nanocomposite, kinetic Monte-Carlo, modeling, EFTEM, PV, nanostructure
  • Lecture (Conference):
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France
Registration No. 20511

Sponge-like Si-SiO2 nanocomposite absorber for next generation PV cells
Liedke, B.; Friedrich, D.; Schmidt, B.; Heinig, K. H.; Mücklich, A.; Hübner, R.; Wolf, D.; Kölling, S.
Abstract: To increase the market share of Si-based thin film PV cells their efficiency has to be improved without increasing of the module costs. Sponge-like Si-SiO2 nanocomposite has a potential to be a low cost and efficient absorber for next generation PV. It consists of Si embedded in SiO2 fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide SiOx≈1. Thermal treatment using rapid thermal processing and furnace annealing requires annealing times of few tens of sec. up to few tens of min. However, in a thin film technology the phase separation of SiOx at high temperatures requires a very rapid thermal processing of few tens of ms in order to avoid substrate damage. Here, the structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography and atom probe tomography which revealed a percolated Si morphology [1]. This is in excellent agreement with atomistic simulations using kinetic Monte-Carlo method [2]. Depending on the annealing time and temperature a feature size in the range of 2..5 nm was found, which is small enough for band gap widening due to quantum confinement [3]. We show that the favorable properties of Si-SiO2 nanocomposite, e.g. quantum size effect and percolated morphology, make it a suitable material for PV absorber. [1] Friedrich, et al. Appl. Phys. Lett. 103,133106(2013) [2] Liedke, et al. Appl. Phys. Lett. 103,131911(2013) [3] Keles, et al. Appl. Phys. Lett. 103,203103(2013)
Keywords: sponge, Si-SiO2 nanocomposite, PV, quantum confinement, absorber, thin-film solar cells
  • Poster:
    EMRS 2014 Spring Meeting, 26.-30.05.2014, Lille, France
Registration No. 20510

Structural studies of thin Pd films loaded with hydrogen
Melikhova, O.; Cizek, J.; Vlcek, M.; Lukac, F.; Prochazka, I.; Anwand, W.; Brauer, G.
Abstract: In this work variable energy positron annihilation spectroscopy was employed for investigation of defects created in Pd films electrochemically charged with hydrogen. The development of hydrogen-induced defects in nanocrystalline, polycrystalline and epitaxial Pd films were compared. It was found that absorbed hydrogen causes plastic deformation and increases defect density in all Pd films studied. Moreover, buckling was observed in nanocrystalline and polycrystalline films loaded above certain critical hydrogen concentration.
Keywords: Pd films, hydrogen loading, defects, positron annihilation Registration No. 20509

Sintering of zirconia-based nanomaterials studied by variable-energy slow-positron beam
Prochazka, I.; Cizek, J.; Melikhova, O.; Anwand, W.; Brauer, G.; Konstantinova, T. E.; Danilenko, I. A.
Abstract: A variable-energy slow-positron beam was applied to the investigations of the tetragonal yttria-stabilised zirconia (YSZ), the YSZ co-doped with small amount of Cr2O3. The initial nanopowders exhibiting the mean particle size of ≈ 20 nm were prepared by co-precipitation technique. Prior the sintering, the nanopowders were calcined and compacted using a pressure of 500 MPa. The ordinary shape parameters of the Doppler-broadened annihilation peak and the relative positronium 3γ-fractions were determined as functions of positron energy. The results are consistent with a remarkable sintering-induced grain growth and disappearance of porosity which is driven out from the sample interior toward a thin sub-surface layer.
Keywords: yttria-stabilised zirconia, sintering, positronium, positron annihilation Registration No. 20508

Defect studies of thin ZnO films prepared by pulsed laser deposition
Vlcek, M.; Cizek, J.; Prochazka, I.; Novotny, M.; Bulir, J.; Lancok, J.; Anwand, W.; Brauer, G.; Mosnier, J. P.
Abstract: Thin ZnO films were grown by pulsed laser deposition on four different substrates: sapphire (0 0 0 1), MgO (1 0 0), fused silica and nanocrystalline synthetic diamond. Defect studies by slow positron implantation spectroscopy (SPIS) revealed significantly higher concentration of defects in the studied films when compared to a bulk ZnO single crystal. The concentration of defects in the films deposited on single crystal sapphire and MgO substrates is higher than in the films deposited on amorphous fused silica substrate and nanocrystalline synthetic diamond. Furthermore, the effect of deposition temperature on film quality was investigated in ZnO films deposited on synthetic diamond substrates. Defect studies performed by SPIS revealed that the concentration of defects firstly decreases with increasing deposition temperature, but at too high deposition temperatures it increases again. The lowest concentration of defects was found in the film deposited at 450°C.
Keywords: ZnO films, pulsed laser deposition, defects, positron annihilation Registration No. 20507

Untersuchung von Gammakaskaden und Stärkefunktionen in der Neutroneneinfangsreaktion 77Se(n,γ)
Robert, J.
Abstract: Eine der wichtigsten nuklearen Prozesse stellt der Neutroneneinfang dar. In der kosmischen Nukleosynthese (s-Prozess) schwerer Elemente werden Kerne mit Massenzahlen größer als die von Eisen (A = 56) produziert, welche durch Kernfusion nicht produziert werden können. Dabei fängt ein Kern ein Neutron ein, wird durch die frei werdende Bindungsenergie angeregt und kann sich anschließend unter Aussenden von Photonen (Gamma-Quanten) wieder abregen. Aus der Abregung über Gammastrahlung können Rückschlüsse auf die Struktur des aktivierten Nuklids gezogen werden. Im Rahmen dieser Arbeit werden die ausgesendeten Photonen des angeregten Elements 78Se, welches durch Neutroneneinfang an 77Se am Reaktor des Instituts Laue-Langevin in Grenoble, Frankreich produziert wurde, näher untersucht. Dazu mussten zunächst Effizienzkalibrierung und Addback-Korrekturen vorgenommen werden. Im Anschluss konnten mit Hilfe des EXILL-Multidetektoraufbaus Koinzidenzbeziehungen mehrerer aufeinander folgender Photonen untersucht und in einem Niveauschema zusammengefasst werden. Mit Hilfe der Winkelverteilung konnten diversen Zuständen Spins zugeordnet werden. Des Weiteren wurden die Ergebnisse einer Simulation von Gammakaskaden (DEX) und eines Photonenstreuungsexperiments am Elektronenbeschleuniger ELBE des HZDR mit den in Grenoble aufgenommenen experimentellen Daten verglichen.
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-046 2014
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Registration No. 20505

Analysis and simulation of photon scattering and neutron capture gamma spectra
Schramm, G. A.
Abstract: Within this thesis two twin experiments consisting of neutron capture and photon scattering on the neighbour isotopes 77Se / 78Se and 195Pt / 196Pt have been analysed to gain qualitative and quantitative information about the photon strength function and level density in the respective compound nuclei. For the analysis and simulation of both experimental types a new Monte Carlo simulation using a fast and efficient, extreme statistical treatment of radiative nuclear deexcitations, was developed. Furthermore the influence of fluctuations of transition widths on photon scattering were investigated and quantified. It could be shown that those lead to an enhancement of elastic scattering processes. The data analysis of both twin experiments reveals non-Lorentzian extra E1 photon strength below the neutron separation energy.
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-045 2014
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Registration No. 20504

Positron Emission Tomography for the dose monitoring of intra-fractionally moving Targets in ion beam therapy
Stützer, K.
Abstract: Ion beam therapy (IBT) is a promising treatment option in radiotherapy. The characteristic physical and biological properties of light ion beams allow for the delivery of highly tumour conformal dose distributions. Related to the sparing of surrounding healthy tissue and nearby organs at risk, it is feasible to escalate the dose in the tumour volume to reach higher tumour control and survival rates. Remarkable clinical outcome was achieved with IBT for radio-resistant, deep-seated, static and well fixated tumour entities. Presumably, more patients could benefit from the advantages of IBT if it would be available for more frequent tumour sites. Those located in the thorax and upper abdominal region are commonly subjected to intra-fractional, respiration related motion. Different motion compensated dose delivery techniques have been developed for active field shaping with scanned pencil beams and are at least available under experimental conditions at the GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt, Germany.
High standards for quality assurance are required in IBT to ensure a safe and precise dose application. Both underdosage in the tumour and overdosage in the normal tissue might endanger the treatment success. Since minor unexpected anatomical changes e.g. related to patient mispositioning, tumour shrinkage or tissue swelling could already lead to remarkable deviations between planned and delivered dose distribution, a valuable dose monitoring system is desired for IBT. So far, positron emission tomography (PET) is the only in vivo, in situ and non-invasive qualitative dose monitoring method applied under clinical conditions. It makes use of the tissue autoactivation by nuclear fragmentation reactions occurring along the beam path. Among others, +-emitting nuclides are generated and decay according to their half-life under the emission of a positron. The subsequent positron-electron annihilation creates two 511 keV photons which are emitted in opposite direction and can be detected as coincidence event by a dedicated PET scanner. The induced three-dimensional (3D) +- activity distribution in the patient can be reconstructed from the measured coincidences. Conclusions about the delivered dose distribution can be drawn indirectly from a comparison between two +-activity distributions: the measured one and an expected one generated by a Monte-Carlo simulation. This workflow has been proven to be valuable for the dose monitoring in IBT when it was applied for about 440 patients, mainly suffering from deep-seated head and neck tumours that have been treated with 12C ions at GSI.
In the presence of intra-fractional target motion, the conventional 3D PET data processing will result in an inaccurate representation of the +-activity distribution in the patient. Fourdimensional, time-resolved (4D) reconstruction algorithms adapted to the special geometry of in-beam PET scanners allow to compensate for the motion related blurring artefacts. Within this thesis, a 4D maximum likelihood expectation maximization (MLEM) reconstruction algorithm has been implemented for the double-head scanner Bastei installed at GSI. The proper functionality of the algorithm and its superior performance in terms of suppressing motion related blurring artefacts compared to an already applied co-registration approach has been demonstrated by a comparative simulation study and by dedicated measurements with moving radioactive sources and irradiated targets. Dedicated phantoms mainly made up of polymethyl methacrylate (PMMA) and a motion table for regular one-dimensional (1D) motion patterns have been designed and manufactured for the experiments. Furthermore, the general applicability of the 4D MLEM algorithm for more complex motion patterns has been demonstrated by the successful reduction of motion artefacts from a measurement with rotating (two-dimensional moving) radioactive sources. For 1D cos2 and cos4 motion, it has been clearly illustrated by systematic point source measurements that the motion influence can be better compensated with the same number of motion phases if amplitudesorted instead of time-sorted phases are utilized. In any case, with an appropriate parameter selection to obtain a mean residual motion per phase of about half of the size of a PET crystal size, acceptable results have been achieved. Additionally, it has been validated that the 4D MLEM algorithm allows to reliably access the relevant parameters (particle range and lateral field position and gradients) for a dose verification in intra-fractionally moving targets even from the intrinsically low counting statistics of IBT-PET data.
To evaluate the measured +-activity distribution, it should be compared to a simulated one that is expected from the moving target irradiation. Thus, a 4D version of the simulation software is required. It has to emulate the generation of +-emitters under consideration of the intra-fractional motion, their decay at motion state dependent coordinates and to create listmode data streams from the simulated coincidences. Such a revised and extended version that has been compiled for the special geometry of the Bastei PET scanner is presented within this thesis. The therapy control system provides information about the exact progress of the motion compensated dose delivery. This information and the intra-fractional target motion needs to be taken into account for simulating realistic +-activity distributions. A dedicated preclinical phantom simulation study has been performed to demonstrate the correct functionality of the 4D simulation program and the necessity of the additional, motionrelated input parameters.
Different to the data evaluation for static targets, additional effort is required to avoid a potential misleading interpretation of the 4D measured and simulated +-activity distributions in the presence of deficient motion mitigation or data processing. It is presented that in the presence of treatment errors the results from the simulation might be in accordance to the measurement although the planned and delivered dose distribution are different. In contrast to that, deviations may occur between both distributions which are not related to anatomical changes but to deficient 4D data processing. Recommendations are given in this thesis to optimize the 4D IBT-PET workflow and to prevent the observer from a mis-interpretation of the dose monitoring data. In summary, the thesis contributes on a large scale to a potential future application of the IBT-PET monitoring for intra-fractionally moving target volumes by providing the required reconstruction and simulation algorithms. Systematic examinations with more realistic, multi-directional and irregular motion patterns are required for further improvements. For a final rating of the expectable benefit from a 4D IBT-PET dose monitoring, future investigations should include real treatment plans, breathing curves and 4D patient CT images.
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-044 2014
Downloads:
54 MB PDF
Registration No. 20503

Mini-Proceedings of the 15th meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies
van der Bij, J. J.; Czyż, H.; Eidelman, S.; Fedotovich, G.; Ferber, T.; Ivanov, V.; Korobov, A.; Liu, Z.; Lukin, P. A.; Müller, S. E.; Venanzoni, G.; Zaremba, J. (Editors)
Abstract: The mini-proceedings of the 15th Meeting of the "Working Group on Rad. Corrections and MC Generators for Low Energies" held in Mainz on April 11, 2014, are presented. These meetings, started in 2006, have as aim to bring together experimentalists and theorists working in the fields of meson transition form factors, hadronic contributions to (g−2)μ and the effective fine structure constant, and development of Monte Carlo generators and Radiative Corrections for precision e+e- and tau physics.
  • Contribution to proceedings:
    15th meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies, 11.04.2014, Mainz, Germany
    Mini-Proceedings of the 15th meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies
Downloads:
Arxiv Server PDF
Registration No. 20502

Wechselwirkung von Uran und Plutonium mit Ton, Tonorganika und bakteriellen Tonisolaten
Schmeide, K.; Jordan, N.; Moll, H.; Cherkouk, A.; Lippold, H.; Poetsch, M.; Kulenkampff, J.; Fritsch, K.
Abstract: In the talk, the most important results obtained in the project for the system radionuclide/clay organics/clay rock are presented. The influence of salinity and temperature on complexation, sorption as well as diffusion/transport of radionuclides is discussed.
Keywords: Uranium, plutonium, terbium, fulvic acid, propionic acid, microorganisms, montmorillonite, Opalinus Clay, PET
  • Lecture (others):
    6. Workshop des Verbundprojekts "Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen", 08.-09.04.2014, Mainz, Deutschland
Registration No. 20500

Ferromagnetism and structural defects in V-doped titanium dioxide
Yildirim, O.; Butterling, M.; Cornelius, S.; Mikhailovskiy, Yu.; Novikov, A.; Semisalova, A.; Orlov, A.; Gan’Shina, E.; Perov, N.; Anwand, W.; Wagner, A.; Potzger, K.; Granovsky, A. B.; Smekhova, A.
Abstract: We report recent experimental results about influence of negatively charged structural defects on room-temperature ferromagnetism in V-doped TiO2-δ thin films with different electric conductivities. Films were prepared on LaAlO3 (001) substrates by RF magnetron sputtering in reduced argon-oxygen atmosphere, while the V to Ti metal ratio was fixed at 1 at.%. The ferromagnetic order at room temperature (RT) was confirmed by SQUID magnetometry. Positron annihilation spectroscopy (PAS) was applied to check the presence of open-volume defects in the TiO2-δ matrix. The relation between ferromagnetic properties and amount of negatively charged defects in the studied films was established. The collection of structural, magnetometry, magnetotransport, magneto-optic and PAS data hints towards the defect-induced model of ferromagnetism in1 at.% V-doped TiO2-δ thin films.
Keywords: diluted magnetic semiconductors, defect-induced ferromagnetism, doped TiO2, PAS Registration No. 20499

Ferromagnetic Resonance Analysis on Periodic Surface Defects: The Transition from Perturbed Thin Films to Magnonic Crystals
Langer, M.; Gallardo, R.; Banholzer, A.; Jansen, A.; Schneider, T.; Wagner, K.; Demidov, V.; Demokirtov, Sergej O.; Landeros, P.; Lenz, K.; Lindner, J.; Fassbender, J.
Abstract: The magnetic relaxation in 1-dimensional periodic nanostructures (quasi magnonic crystals) is investigated by ferromagnetic resonance (FMR). In thin ferromagnetic films, the magnetization dynamics are governed by intrinsic effects like Gilbert damping and spin-pumping but also by extrinsic effects like two-magnon scattering (TMS). The latter is in demand for latest research and can be induced within magnetic thin films by defects and inhomogeneities. Thereby, acting as scattering centers, defects cause a dipolar field at the film surface crucial for the magnon-magnon interaction. By ion Irradiation of the material, a local variation of the magnetic properties can be achieved [1], where the TMS strength is set by the properties of the modification such as the reduction of the effective magnetic moment and the geometry (depth d , periodicity a 0 ). The investigated films consist of 30 nm thick permalloy (Ni80Fe20) deposited by molecular beam epitaxy at room temperature on Si/SiO2 substrate. All films are protected by a Cr Cap layer of 3 – 5 nm. On top of the structure, PMMA resist of 140 nm thickness was added and patterned by EBL, to create a symmetric array of stripe defects with a periodicity ranging from 100 – 400 nm optimal for the investigation of TMS. Subsequently, the mask was employed for ion beam patterning. Parameters for the Cr ion irradiation were selected according to Monte-Carlo simulations calculating the effects of the ion irradiation on the depth-dependent composition using SRIM [2] and TRIDYN [3]. The irradiation energies were defined in the range of 5 – 10 keV in which the fluence varies from 5·1015 1/cm2 to 8·1015 1/cm2. Due to the lowering of the Curie temperature underneath room temperature when Cr content in permalloy is extending 8 at.% [4], after irradiation, magnetically dead layers are generated. For lower Cr concentrations, the saturation magnetization of permalloy is reduced and hence, the dead layers are accompanied by a concentration gradient where MS increases gradually to the value of the saturation magnetization of permalloy. By varying the ion energy and fluence, this gradient and hence, the effective defect depth can be set. This allows the investigation of the transition from a surface perturbed thin film to a full magnonic crystal. The energies and fluences used to prepare the samples presented in this work are summarized in Table I. The spin wave dynamics and TMS are studied using FMR and Brillouin light scattering (BLS). The dispersion relation of backward volume modes in an unperturbed thin film is known to be quadratically dependent on the wave vector k due to exchange interaction. If an array of surface perturbations is assumed to exist on the surface of such a thin film, an additional dipolar field contribution to the magnons dispersion must be taken into account. This term is proportional to –k (for ultrathin films: k ·d << 1) and hence, causes a degeneration. Investigating such system by FMR, spin wave excitation is carried out uniformly. Thus, to scatter into the degenerate spin wave mode, the k -vector must match a multiple reciprocal lattice vector g 0 = 2/a 0 . If this is valid, TMS can be observed and mode repulsion takes place. We measured the FMR spectra f (H ) of different defect samples showing repulsion at each crossing point of higher spin wave modes with the uniform mode. Theoretical calculations based on a model using perturbation theory [5] are accompanied and reveal a good agreement of experiment and theory. Applying the external field parallel to the axis of the stripe’s edge, the f (H ) measurement of the FMR signal reveals one single FMR mode, referred to as the Kittel mode, equal to the one of unperturbed films. Since in this orientation magnetization aligns parallel to the stripe axis, there are no dipolar fields present to generate a coupling between several magnons. By a field rotation towards the axis perpendicular to the stripes, the TMS is switched on and multiple resonance modes can be observed with a culminating mode splitting at a field direction perpendicular to the stripe axis. The f (H ) mode spectra of Sample 1 (for details see Table I) for several in-plane field angles were measured to show the gradual development of TMS-induced mode splitting and are accompanied by theoretical calculations. The angular dependent measurement of the same sample for a fixed frequency of 15 GHz can be found in Fig. 1. To study the impact of the defect depth on the resonance mode positions, the resonance spectra f (H ) perpendicular to the stripe axis were analyzed for all samples shown in Table I. Again, the available theoretical model was used to explain the observed mode structures. For a precise determination of the dispersion relation of the magnons in such systems, BLS measurements have been performed showing a good Agreement to the theoretically predicted band structure.
  • Poster:
    IEEE International Magnetics Conference - Intermag 2014, 08.05.2014, Dresden, Deutschland
Registration No. 20497

Vacancy type defect formation in irradiated α-iron investigated by positron beam Doppler broadening technique
He, C. W.; Dawi, K.; Platteau, C.; Barthe, M. F.; Desgardin, P.; Akhmadaliev, S.
Abstract: Vacancy type defects formations have been investigated in virgin and irradiated a-iron samples using slow positron beam Doppler broadening technique.
Mono-vacancies and vacancy clusters are observed in 1.5 MeV 4He ions irradiated Fe samples at varying fluences from 1×1013 to 1×1017 cm-2.
In the 1.2 MeV Yttrium ions implantation at low fluence 1×1014 cm-2 vacancy clusters with higher concentration and larger size are formed.
In this sample, vacancy defects are detected deeper than predicted by SRIM calculation due to channelling.
Registration No. 20496

Ion Beam Induced Periodic Surface Defects: The Transi- tion from a Thin Film to a Magnonic Crystal
Langer, M.; Gallardo, R.; Banholzer, A.; Jansen, A.; Schneider, T.; Wagner, K.; Demidov, V.; Demokirtov, Sergej O.; Landeros, P.; Lenz, K.; Lindner, J.; Fassbender, J.
Abstract: Periodic arrays of magnetic stripe defects are fabricated by Cr+ ion implantation on a 30 nm permalloy lm. Modifying the mean ion penetration depth, the defect height can be controlled, which allows an investigation of the gradual transition from a magnetic thin lm towards a magnonic crystal.
Spin wave dispersion and two-magnon scattering are studied using brillouin light scattering (BLS) as well as broadband ferromagnetic resonance (FMR). The obtained results are corroborated by theoretical calculations based on a perturbation theory.

Keywords: Magnonics, Magnonic Crystals, Magnetization Dynamics, Spin Waves, Magnons, Ferromagnetic Resonance
  • Poster:
    DPG Spring Meeting 2014, 04.04.2014, Dresden, Deutschland
Registration No. 20495

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

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

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

Keywords: microorganisms, radionuclide speciation, nuclear waste disposal
  • Invited lecture (Conferences):
    8th European Summer School on supramolecular, intermolecular, interaggregate interactions and separation chemistry, 07.-09.07.2014, Bonn - Bad Godesberg, Deutschland
Registration No. 20493

High conversion Th-U233 fuel cycle for current generation of PWRs
Baldova, D.; Fridman, E.
Abstract: The main goal of this study is to evaluate the operational feasibility of the high conversion (HC) Th-U233 PWR core through performing the 3D fully coupled neutronic and thermal-hydraulic (T-H) analysis. The proposed HC core model consists of 193 typical 17×17 PWR fuel assemblies. Each fuel assembly is subdivided into two regions designated as seed and blanket. The central seed re-gion, which has high U233 content, serves as a neutron supplier for the peripheral blanket region. The blanket region consists mostly of Th232 and acts as a U233 breeder.
  • Poster:
    Thorium Energy Conference THEC13, 27.-31.10.2013, CERN, Geneva, Switzerland
Registration No. 20492

64Cu-labelled dendritic polyglycerol derivatives for biodistribution studies
Pant, K.; Steinbach, J.; Stephan, H.; Bergmann, R.; Haag, R.; Gröger, D.; Nowag, S.; Graham, B.; Spiccia, L.
Abstract: Objectives
Dendritic polyglycerols (dPG) and dendritic polyglycerol sulfates (dPGS) are easily synthesized macromolecules. These polymers are highly water-soluble, biocompatible, practically non-toxic and non-immunogenic. Hence, these properties make them highly interesting for application in biomedicine and offers excellent prospects for the development of new non-invasive strategies for the diagnosis and treatment of diseases. dPGS have already been developed as fully synthetic heparin analogues that show anti-inflammatory properties and accumulation in tumor tissue, which makes them promising agents for therapeutic applications. Since information about the biodistribution and the metabolism of dPGS in living systems is quite scarce, one approach is to radiolabel them so as to be able to track them with, for example, positron emission tomography (PET). 64Cu has suitable decay characteristics that allow for PET imaging and a variety of chelator systems are available for attachment to these macromolecules using appropriate anchor groups. Herein, we report the conjugation of bifunctional chelating agents based on bis(2-pyridylmethyl)triaza-cyclononane [DMPTACN] onto the dPG/dPGS scaffolds. The structure of DMPTACN allows for the introduction of various functional groups, such as carboxylic, maleimide or isothiocyanate groups, for coupling to various functional groups
(amino and mercapto surface groups) on the dPG derivatives. 64Cu-labeling experiments and stability studies of the resulting radiocopper complexes are presented and discussed.
Methods & materials
DMPTACN was synthesized by a 10-step process starting from diethylenetriamine to form a TACN ring containing tosyl protecting groups. After deprotection and subsequent introduction of two pendant 2-picolyl arms, coupling
groups, such as a carboxylic acid, maleimide or isothiocyanate, have been attached. The dPG and dPGS samples can be synthesized on a kilogram scale by utilizing ring-opening and copolymerization reactions. Surface modification with
amino and mercapto groups provides the target molecules needed for attachment of copper-binding agents. After conjugation of BFCAs to the dPG/dPGS, the compounds were purified by size exclusion chromatography. 64Cu-labeling of DMPTACN-dPG(dPGS) conjugates were performed using [64Cu]CuCl2 in 0.1 M MES/NaOH buffer at a pH of 5.5 at room temperature, resulting in a radiochemical purity of higher than 95% within a few minutes. Animal experiments were carried out in male Wistar rats.
Results & conclusion
dPG and dPGS have been synthesized with various percentages of amine and mercapto functionalities capable of coupling to BFCAs based on a DMPTACN backbone with maleimide, carboxylic and isothiocyanate groups. The
conjugates can be purified by size exclusion chromatography, and have been obtained in good yields. 64Cu-labeling experiments confirmed rapid copper(II) complex formation under mild conditions. The 64Cu-labelled conjugates exhibit high in vitro stability in human serum. These probes can thus be utilized to derive quantitative distribution data in vivo. Biodistribution and pharmacokinetic properties of 64Cu-labelled dendritic polyglycerol derivatives can be conveniently studied by PET.
Financial disclosure
This work is part of a research initiative within the Helmholtz-Portfoliothema “Technologie und Medizin - Multimodale Bildgebung zur Aufklaerung des In vivo-Verhaltens von polymeren Biomaterialien”.
  • Poster:
    World Conference on Regenerative Medicine, 21.-23.10.2013, Leipzig, Deutschland
  • Abstract in refereed journal:
    Regenerative Medicine 8(2013)6s, 297
Registration No. 20491

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

Keywords: PIGE, light elements
  • Poster:
    14th International Conference on Nuclear Microprobe Technology and Applications, 07.-11.07.2014, Padua, Italy
Registration No. 20487

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

Keywords: Monte Carlo simulations, Oxide Dispersion Strengthened Fe-Cr alloys, nanoclusters, Density Functional Theory calculations
  • Poster:
    Computer Simulation of Radiation Effects in Solids 2014 (COSIRES 2014), 08.-13.06.2014, Alicante, Spain
Registration No. 20485

Geometric degree of non-conservativity
Lerbet, J.; Aldowaji, M.; Challamel, N.; Kirillov, O. N.; Nicot, F.; Darve, F.
Abstract: This paper deals with nonconservative mechanical systems subjected to nonconservative positional forces leading to nonsymmetric tangential stiffness matrices. The geometric degree of nonconservativity of such systems is then defined as the minimal number of kinematic constraints necessary to convert the initial system into a conservative one. Finding this number and describing the set of corresponding kinematic constraints is reduced to a linear algebra problem. This index of nonconservativity is the half of the rank of the skew-symmetric part S of the stiffness matrix K that is always an even number. The set of constraints is extracted from the eigenspaces of the symmetric matrix S^2. Several examples including the well-known Ziegler column illustrate the results.
Keywords: Stability, nonconservative systems, constraints Registration No. 20483

A systematic study to unravel the role of preparation and implantation-related defects for the magnetic properties of Zn0.9Co0.1O epitaxial films
Ney, V.; Lenz, K.; Ollefs, K.; Wilhelm, F.; Rogalev, A.; Ney, A.
Abstract: A systematic variation of preparation conditions for epitaxial Zn0.9Co0.1O films grown by reactive magnetron sputtering on c-plane sapphire has been carried out to study the correlation of crystalline perfection with the corresponding magnetic properties. The crystalline perfection of the resulting films was found to vary over a wide range, nonetheless all samples were found to be paramagnetic. The further extent the study, three samples, which were paramagnetic in the as-grown state, were subsequently implanted using Cu, Li and Zn ions. Only Zn ion-implantation was found to slightly alter the magnetic properties at low temperatures, however, synchrotron-based techniques could not evidence the formation of a secondary, metallic Co phase. The origin of this weak, low-temperature magnetism is more likely to be carrier-mediated rather than defect-induced.
Keywords: ZnO, diluted magnetic semiconductors, ion implantation, induced magnetism Registration No. 20482

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

Keywords: ferromagnetism, ripples, electron holography, nanostructures
  • Lecture (Conference):
    IEEE International Magnetics Conference 2014, 08.05.2014, Dresden, Deutschland
Registration No. 20481

Electroluminescent properties of Tb-doped carbon-enriched silicon oxide
Tiagulskyi, S. I.; Nazarov, A. N.; Gordienko, S. O.; Vasin, A. V.; Rusavsky, A. V.; Rebohle, L.; Voelskow, M.; Skorupa, W.
Abstract: An electroluminescent device utilizing a heterostructure of amorphous Terbium doped carbon-rich SiOx (a - SiOx : C : Tb) on silicon has been developed. The a - SiOx : C : Tb active layer was formed by RF magnetron sputtering of a - SiO1–x : Cx : H(:Tb) film followed by high-temperature oxidation. It was shown that, depending on the polarity of the applied voltage, the electroluminescence is either green or white, which can be attributed to different mechanisms of current transport through the oxide film – space charge limited bipolar double injection current for green electroluminescence and trap assisted tunneling or Fowler-Nordheim tunneling for White electroluminescence.
Keywords: electroluminescence, a-SiO:C/Si heterostructure, Tb, RF magnetron sputtering, charge transport mechanisms
  • Semiconductor Physics, Quantum Electronics & Optoelectronics 17(2014)1, 34-40
Registration No. 20480

Recent advances in the study of the UO2–PuO2 phase diagram at high temperatures
Böhler, R.; Welland, M. J.; Prieur, D.; Cakir, P.; Vitova, T.; Pruessmann, T.; Pidchenko, I.; Hennig, C.; Guéneau, C.; Konings, R. J. M.; Manara, D.
Abstract: Recently, novel container-less laser heating experimental data have been published on the melting behaviour of pure PuO2 and PuO2-rich compositions in the uranium dioxide–plutonium dioxide system. Such data showed that previous data obtained by more traditional furnace heating techniques were affected by extensive interaction between the sample and its containment. It is therefore paramount to check whether data so far used by nuclear engineers for the uranium-rich side of the pseudo-binary dioxide system can be confirmed or not. In the present work, new data are presented both in the UO2-rich part of the phase diagram, most interesting for the uranium–plutonium dioxide based nuclear fuel safety, and in the PuO2 side. The new results confirm earlier furnace heating data in the uranium-dioxide rich part of the phase diagram, and more recent laser-heating data in the plutonium-dioxide side of the system. As a consequence, it is also confirmed that a minimum melting point must exist in the UO2–PuO2 system, at a composition between x(PuO2) = 0.4 and x(PuO2) = 0.7 and 2900 K 6 T 6 3000 K. Taking into account that, especially at high temperature, oxygen chemistry has an effect on the reported Phase boundary uncertainties, the current results should be projected in the ternary U–Pu–O system. This aspect has been extensively studied here by X-ray diffraction and X-ray absorption spectroscopy. The current results suggest that uncertainty bands related to oxygen behaviour in the equilibria between condensed phases and gas should not significantly affect the qualitative trend of the current solid–liquid phase boundaries
Keywords: EXAFS PuO2 Registration No. 20479

Innovative Methoden in der Bionanotechnologie – Die Quarzkristallmikrowaage (QCM-D)
Suhr, M.
Abstract: Funktionsprinzip und Modellierungsansätze der QCM-D.
Anwendungsmöglichkeiten und Grenzen der QCM-D.
Nutzung der QCM-D in der ressourcenökologischen Forschung.

Keywords: QCM-D, AFM, Biosorption, Metalle
  • Lecture (others):
    Umweltkolloquium der Fakultät Maschinenbau/ Verfahrenstechnik, Studiengang Chemieingenieurwesen, 20.05.2014, Dresden, Deutschland
Registration No. 20475
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