Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Identification of the Main Flow Regime Boundaries in Two Bubble Columns Based On a New Parameter Extracted from Gas Holdup Fluctuations

Nedeltchev, S. N.; Schubert, M.; Donath, T.; Rabha, S.; Hampel, U.

The time series (60,000 points) of the cross-sectional averaged gas holdup in two bubble columns (0.15 and 0.4 m in ID) were measured by conductivity wire-mesh sensors. Both columns were equipped with perforated plate distributors (having an open area of 1 %). The sampling frequency was set at 2000 Hz. These data were used successfully for the flow regime identification. For this purpose a new parameter called maximum number of visits in a region Nvmax was introduced. Both bubble columns were operated with an air−tap water system at ambient conditions. The clear liquid height in both columns was adjusted at 2.0 meters. The wire-mesh sensors were installed at a height of 1.3 m above the sparger plates. The new dimensionless parameter Nvmax is based on a division of the signal’s range into different regions and the maximum number of signal visits in one of the regions. In both small and large bubble columns the Nvmax profiles exhibited two well-defined local minima, which identified two transition velocities Utrans. In the small column (0.15 m in ID), the two Utrans values were identified at 0.034 and 0.089 m/s, respectively. In the large column (0.4 m in ID) the first Utrans value remained the same, whereas the second Utrans value decreased slightly to 0.078 m/s. A comparison with the Kolmogorov entropy results and another dimensionless statistical parameter was also performed.

  • Contribution to proceedings
    Second International Symposium On Multiscale Multiphase Process Engineering (MMPE-2), 24.-27.09.2014, Hamburg, Deutschland: Dechema, 42-47

Permalink: https://www.hzdr.de/publications/Publ-21146
Publ.-Id: 21146


Statistical Validation of the Mixing Length Concept in Bubble Columns Operated in the Transition Flow Regime

Nedeltchev, S. N.; Schubert, M.

A new statistical parameter was defined in order to determine the range of applicability of the mixing length concept (Kawase and Tokunaga, 1991) in two bubble columns. Gas holdup time series (60 000 points) were measured in two bubble columns (0.15 and 0.4 m in ID) by a conductivity wire-mesh sensor. The new statistical parameter Φ was defined as a ratio of the mean value of the signal to three times the average absolute deviation (3AAD) and it was correlated to the mixing length equation derived by Kawase and Tokunaga (1991). It was found that this new correlation was not valid in all flow regimes. It is applicable only in the transition flow regime. Such a clarification has not been provided in the literature hitherto. In the narrow bubble column the results were also confirmed on the basis of the Kolmogorov entropy and another statistical parameter.
The new parameter Φ was also used for flow regime identification. In the narrow bubble column the first transition velocity Utrans was identified at 0.034 m/s, whereas the second Utrans occurred at 0.112 m/s. In the large bubble column the two Utrans values were identified at 0.045 and 0.101 m/s, respectively.

Permalink: https://www.hzdr.de/publications/Publ-21145
Publ.-Id: 21145


Investigations on centrifugal pumps under air entrainment conditions

Schäfer, T.; Bieberle, A.; Hampel, U.

Centrifugal pumps are widely used in process industry and power engineering, e.g. in refineries as feeding pumps or in power plants in cooling circuits. In nuclear power plants they are operated in various places and particularly in safety-related functions, like emergency core cooling. Though simple in design centrifugal pumps offer advantages, like high efficiency and low energy consumption, smooth and steady operation and high reliability. Gas entrainment as well as internal steam generation by cavitation is known as being detrimental and critical to the operation of centrifugal pumps, since they were primarily designed for single phase operation. Gas entrainment may for instance occur in situations, where water is conveyed from a reservoir with a shallow liquid height. There hollow vortices may form as a consequence of low liquid level and pre-existing fluid swirling. Particularly, such a situation may be prevailing in nuclear power plants, e.g. when emergency cooling water is taken from a liquid reservoir, like the condensation chamber.
Presence of gas in pumps may lead to abrasion at impeller blades, strong vibrations with damaging of bearings and loss of cooling for shaft and bearings and early fatigue as a consequence. At least the presence of gas will lead to decreasing pump performance even to the point of abrupt collapse of flow rate. Up to now, the effects of air entrainment have been investigated exemplarily under various operating conditions [Caruso et al., 2013], [Kimura et al., 2008], but the characteristics of gas phase fraction accumulation inside centrifugal pumps, particularly in the impeller and nearby the shaft seal region, are insufficiently understood. The presented work contributes quantitative measurements, visualizations and analyses of gasliquid phase distributions to the fundamental understanding of the effects of gas entrainment in centrifugal pumps. Advanced tomographic measuring methods with high spatial and temporal resolution were applied to investigate the two-phase distribution in the impeller region of an industrial centrifugal pump and a miniature centrifugal pump.
The presented investigations are founded by the German Federal Ministry of Education and Research (BMBF) under the funding code 02NUK023.

Keywords: centrifugal pump; advanced tomography; phase fraction visualization

  • Lecture (Conference)
    16th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA
  • Contribution to proceedings
    16th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA

Permalink: https://www.hzdr.de/publications/Publ-21144
Publ.-Id: 21144


THz driven Dynamics in Mattter: Sources and Applications

Gensch, M.

  • Invited lecture (Conferences)
    Kolloquium des Instituts für Analytische Wisschenschaften (ISAS), 17.11.2014, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21143
Publ.-Id: 21143


Optical Synchronization and Electron Bunch Diagnostic at ELBE

Kuntzsch, M.

The recent upgrade of the ELBE accelerator included the installation of a new beamline section which will be used to compress the electron bunches to a duration of 100 fs at a charge of 1 nC. Two THz sources based on coherent transition or diffraction radiation und and an undulator source making use of the compressed bunches. In addition an Xray source based on Thomson backscattering, combining high power lasers with the relativistic electrons, is currently in commissioning phase and will deliver narrow bandwidth and tunable pulses.
To enable time resolved experiments on a 100 fs scale an optical synchronization system has been installed. It is based on a low noise fiber laser oscillator as optical reference. The signal is distributed to the remote stations via singlemode fibers. Drifts introduced by temperature variations and mechanical stress are measured by a balanced optical cross-correlator detection scheme and compensated with fast actuators. A stability of better than 30 fs over several hours has been demonstrated.
Based on the optical synchronization system a bunch arrival time monitor (BAM) has been set up. It is modulating the laser pulse train with a pickup signal from the electric field surrounding the electron bunch. The arrival time information is mapped into an amplitude modulation which can be detected by fast readout electronics. This technique enables arrival time measurements with a few femtosecond resolution.
The talk will give an overview on the ELBE upgrade and in particular on the installation of the synchronization system. First results of the arrival time measurements for both injectors (DC gun, SRF gun) are discussed.

Keywords: Synchronization Timing Diagnostic BAM

  • Invited lecture (Conferences)
    Beschleunigerseminar Helmholtz-Zentrum Berlin, 18.11.2014, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21142
Publ.-Id: 21142


Progress on Bunch Arrival Time Measurements at ELBE

Kuntzsch, M.; Gensch, M.; Lehnert, U.; Schurig, R.; Bousonville, M.; Czwalinna, M. K.; Sydlo, C.; Vilcins, S.; Schlarb, H.; Angelovski, A.; Penirschke, A.

The superconducting continuous wave (CW) accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is currently upgraded to generate electron bunches with sub picosecond duration, charges of up to 1 nC at repetition rates of up to 500 kHz (CW). The electron pulses are compressed to their desired length using two magnetic chicanes. To measure the timing of the electron bunches with respect to ELBEs RF reference at the target position a Bunch Arrival-time Monitor (BAM) has been setup and commissioned. Improvements concerning the beamline pickup and readout electronics are discussed which leads to a higher temporal resolution. First measurement results carried out are presented.

Keywords: ELBE Synchronization Bunch Diagnostic Timing

  • Poster
    IPAC14 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21141
Publ.-Id: 21141


CW Beam Stability Analysis in Time and Frequency Domain

Kuntzsch, M.; Lehnert, U.; Schurig, R.; Teichert, J.; Gensch, M.; Kovalev, S.; Green, B.; Michel, P.

The superconducting quasi CW Linac ELBE has been characterized in terms of energy and timing stability. The measurement results presented show a combination of a laser-based bunch arrival-time measurements (BAM), a fast beam position monitor (BPM) readout with single bunch resolution and a compression monitor (BCM) based on a fast pyro-electric detector. By changing the bunch compression factor a separation and identification of jitter sources has been achieved. The quasi CW mode of operation enables frequency domain data analysis with high dynamic range, which gives a better understanding of the main sources of jitter. Experimental results for both injectors (thermionic DC, superconducting RF) are presented.

Keywords: ELBE Synchronization Timing Stability BAM

  • Open Access Logo Contribution to proceedings
    IBIC 2014 - 3rd International Beam Instrumentation Conference, 14.-18.09.2014, Monterey, USA
    Proceedings of IBIC 2014
  • Poster
    IBIC 2014 - 3rd International Beam Instrumentation Conference, 14.-18.09.2014, Monterey, USA

Permalink: https://www.hzdr.de/publications/Publ-21140
Publ.-Id: 21140


Sponge-like Si-SiO2 nanocomposite as photovoltaic absorber - influence of composition of the SiOx precursor

Schumann, E.; Heinig, K.-H.; Hübner, R.; Endrino, J. L.; Abrasonis, G.

Absorber layers consisting of nanostructured Si are candidates to improve the effciency of thin film Si solar cells. Si-SiO2 nanocomposites with sponge-like Si embedded in SiO2 are promising materials as they exhibit a widened band gap and maintain the electrical interconnectivity. These structures can be formed upon annealing of SiOx films (x<1), which leads to spinodal phase separation into a percolacated network of Si nanowires embedded in SiO2. This can be accompanied by crystallization of the silicon. The influence of the composition of the precursor SiO2 on the evolving sponge-like nanostructure is investigated. SiOx layers have been grown by reactive sputter deposition. SiOx layers with compositions between x=0 and x=1.2 have been studied. The transformation of SiOx into Si-SiO2 nanocomposites has been performed by scanning a diode laser line source. Dwell times in the ms range and power densities of the red laser light of about 103 W/cm2 have been investigated. while thin a-Si films show crystallization under our annealing conditions, oxygen-rich films with Si structures smaller than 2 nm do not crystallize. Our results demonstrate that the composition of the precursor material is of crucial importance to obtain a Si-SiO2 nano sponge-like material suitable as photovoltaic absorber.

Keywords: Silicon; Silicon oxide; Nanocomposites; Energy Filtered TEM

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 30.03.-04.04.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21139
Publ.-Id: 21139


Sponge-like Si-SiO2 Nanocomposite as Photovoltaic Absorber – Influence of Composition of the SiOx Precursor

Schumann, E.; Heinig, K.-H.; Hübner, R.; Carcelén Valero, V.; Endrino, J. L.

Nano structured Si absorber layers are candidates to improve efficiencies of thin film Si solar cells without increasing costs. Si-SiO2 nano sponge-like nanocomposites are promising materials as they exhibit a widened band gap due to quantum confinement and electrical interconnectivity due to percolation of the nanostructured Si. The sponge-like structures can be formed upon annealing of substoichiometric SiOx films (x<1), which leads to spinodal phase separation into a perlocated network of Si nanowires embedded in SiO2, tentatively accompanied by crystallization of the Si.
Here the influence of the precursor composition on the evolving sponge-like nanostructure and on the optical properties is investigated. SiOx layers have been grown by reactive sputter deposition where the composition of SiOx films was controlled by varying the oxygen flow during the deposition and subsequently measured by Rutherford Backscattering Spectroscopy (RBS). SiOx layers with compositions between x=0 and x=1.2 have been addressed. The Si-SiO2 nanocomposites are fabricated using a very rapid thermal processing by scanning a diode laser line source. Dwell times in the ms range and power densities of the red laser light of about 103 W/cm2 have been investigated.
Laser treatment of the precursor SiOx layers leads to decomposition into Si and SiO2 thereby forming Si-SiO2 sponge-like structures as observed by energy filtered transmission electron microscopy (EFTEM). While thin a-Si films show crystallization, oxygen rich films with Si structures smaller than 2nm do not show crystallization. The widening of the band gap due to quantum confinement has been confirmed by optical measurements.
Our results demonstrate that the composition of the precursor material is of crucial importance to obtain a Si-SiO2 nano sponge-like material suitable as PV absorber.

Keywords: Silicon; Silicon oxide; Nanocomposite; Energy Filtered TEM

  • Lecture (Conference)
    2014 MRS Spring Meeting & Exhibit, 21.-25.04.2014, San Francisco, United States of America

Permalink: https://www.hzdr.de/publications/Publ-21137
Publ.-Id: 21137


Partikelentstehung und –transport im Kern von Druckwasserreaktoren; Physikochemische Mechanismen (Abschlussbericht zum BMWi-Vorhaben 150 1430)

Kryk, H.; Hoffmann, W.

Im Rahmen der deutschen Reaktorsicherheitsforschung wurden generische experimentelle Untersuchungen zur systematischen Aufklärung physikochemischer Mechanismen der Korrosionsproduktbildung und –ablagerung unter den wasserchemischen Bedingungen des Sumpfumwälzbetriebes in der Spätphase von Kühlmittelverluststörfällen in Druckwasserreaktoren durchgeführt. Das Vorhaben wurde in enger Kooperation mit der Hochschule Zittau/Görlitz (Vorhaben 150 1431) realisiert. Der Kontakt des borsäurehaltigen Kühlmittels mit feuerverzinkten Containment-Einbauten bewirkt eine Korrosion der Verzinkung, wodurch Zink im Kühlmittel gelöst wird. Als entscheidendes Ergebnis von Batch-Experimenten wurde eine abnehmende Löslichkeit von Zink-Korrosionsprodukten mit zunehmender Kühlmitteltemperatur gefunden. Somit ist die Bildung und Ablagerung fester Korrosionsprodukte nicht auszuschließen, wenn zinkhaltiges Kühlmittel in heiße Regionen innerhalb des Kühlkreislaufes gelangt (z.B. Hot-Spots im Kern). Experimente in einer Labor-Korrosionsversuchsanlage, die Untersuchungen zum Ablagerungsverhalten von Korrosionsprodukten an heißen Hüllrohroberflächen im Einzelkanal einschlossen, zeigten, dass auch unter diesen Bedingungen die Entstehung und Ablagerung von festen Korrosionsprodukten erfolgen kann. Die Korrosionsprodukte wurden als Zink-Borate identifiziert, wobei die chemische Zusammensetzung sowie das Ablagerungs- und Mobilisierungsverhalten entscheidend von der Bildungstemperatur beeinflusst werden. Untersuchungen zur Kinetik der Bildung von gelöstem Zink durch Korrosion von verzinkten Einbauten im Sicherheitsbehälter waren nicht Projektgegenstand, weshalb eine direkte quantitative Übertragbarkeit der Ergebnisse auf postulierte KMV in DWR derzeit nicht gegeben ist.

Keywords: Druckwasserreaktor; Kühlmittelverluststörfall; Korrosion; Zink; Zinkborat; Experiment

  • Other report
    Dresden: HZDR\FWD\2014\01, 2014

Permalink: https://www.hzdr.de/publications/Publ-21136
Publ.-Id: 21136


Mechanism of spin crossover in LaCoO3 resolved by shape magnetostriction in pulsed magnetic fields

Rotter, M.; Wang, Z.-S.; Boothroyd, A. T.; Prabhakaran, D.; Tanaka, A.; Doerr, M.

In the scientific description of unconventional transport properties of oxides (spin-dependent transport, superconductivity etc.), the spin-state degree of freedom plays a fundamental role. Because of this, temperature- or magnetic field-induced spin-state transitions are in the focus of solid-state physics. Cobaltites, e.g. LaCoO3, are prominent examples showing these spin transitions. However, the microscopic nature of the spontaneous spin crossover in LaCoO3 is still controversial. Here we report magnetostriction measurements on LaCoO3 in magnetic fields up to 70 T to study the sharp, field-induced transition at Hc ≈ 60 T. Measurements of both longitudinal and transversal magnetostriction allow us to separate magnetovolume and magnetodistortive changes. We find a large increase in volume, but only a very small increase in tetragonal istortion at Hc. The results, supported by electronic energy calculations by the configuration interaction cluster method, provide compelling evidence that above Hc LaCoO adopts a correlated low spin/high spin state.

Permalink: https://www.hzdr.de/publications/Publ-21135
Publ.-Id: 21135


Computational Fluid Dynamics for energy efficient multiphase flow processes

Lucas, D.

Multiphase flows are frequently applied in industrial processes as e.g. in chemical engineering. Reliable predictions of the flow characteristics such as local concentration of species and interfacial area density in gas-liquid flows can contribute to an optimization of the design of corresponding apparatuses and processes. Due to the high energy consumption of such process there is a considerable potential to save energy and materials. Computational Fluid Dynamics (CFD) in principle allows the simulation of such flows and provides local flow characteristics. While it is frequently used for industrial problems in case of single phase flows it is not yet mature for two-phase flows. The reason is the complex gas-liquid interface. For medium and large scale flow domains it is not feasible to resolve all details of this interface. Averaging procedures have to be applied and in most cases the so-called two- or multi-fluid approach is used. It assumes interpenetrating phases and the information on the interface gets lost by these averaging procedures. This information has to be added to the basic balance equations by so-called closure models. The development and validation of such models is done at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) to obtain tools for reliable predictions of multiphase flow characteristics in medium and large industrial scales.

Keywords: multiphase; simulation; optimisation; CFD

  • Contribution to proceedings
    EST - Energy Science Technology, 20.-22.05.2015, Karlsruhe, Deutschland
  • Lecture (Conference)
    EST - Energy Science Technology, 20.-22.05.2015, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21134
Publ.-Id: 21134


Ultrasound study of FeCr2S4 in high magnetic fields

Felea, V.; Yasin, S.; Günther, A.; Deisenhofer, J.; Krug Von Nidda, H.-A.; Scheidt, E.-W.; Quach, D. V.; Groza, J. R.; Zherlitsyn, S.; Tsurkan, V.; Lemmens, P.; Wosnitza, J.; Loidl, A.

We report on ultrasound studies of FeCr2S4 in static and pulsed magnetic fields exhibiting an orbital-order transition at 9K. A longitudinal acoustic mode exhibits distinct features in the phase space of temperature and magnetic field due to magnetic and structural transformations. Pulsed-field measurements show significant differences in the sound velocity below and above the orbital-ordering transition as well as the spin-reorientation transition at 60 K. Our results indicate a reduction of the magnetocrystalline anisotropy on entering the orbitally ordered phase.

Permalink: https://www.hzdr.de/publications/Publ-21133
Publ.-Id: 21133


Coexistence of localized and collective magnetism in the coupled-spin-tetrahedra system Cu4Te5O12Cl4

Choi, K.-Y.; Do, S.; Lemmens, P.; van Tol, J.; Shin, J.; Jeon, G. S.; Skourski, Y.; Rhyee, J.-S.; Berger, H.

We report high-field magnetization, electron spin resonance (ESR), and Raman scattering measurements of the coupled spin-tetrahedra system Cu4Te5O12Cl4 with magnetic ordering at TN = 13.6 K. We find thermodynamic and spectroscopic signatures for the concomitant occurrence of localized and collective magnetism. Magnetization measurements up to 60 T exhibit a spin-flop transition at μ0HSF = 16 T only for H∥c as well as periodic magnetization steps at μ0H = 16.5, 24.8, 33.8, 42.3, and 49.7 T, which are independent of the crystallographic orientations. For T > TN, the temperature dependence of ESR linewidth is described by a critical power law, ΔBpp(T) ∝ (T−TN)−0.56±0.02. For T < TN, an antiferromagnetic resonance mode is observed for H ∥ c, and its linewidth is given by ΔBpp(T) ∝ T3.13±0.04, being close to T4 expected for a classical magnet. Raman spectra show three one-magnon-like excitations superimposed on a broad two-magnon continuum. While the two higher frequency modes show an intensity variation in accordance to a three-dimensional Heisenberg antiferromagnet, the lower frequency mode clearly deviates. These results suggest that Cu4Te5O12Cl4 is a unique material which shows a dual character of zero-dimensional, localized and three-dimensional, collective magnetic behaviors.

Permalink: https://www.hzdr.de/publications/Publ-21132
Publ.-Id: 21132


Anwendung des Systemcodes ATHLET zur Modellierung der Fluiddynamik in solarthermischen Kraftwerken mit Direktverdampfung

Hoffmann, A.; Hirsch, T.

Anwendung des Systemcodes ATHLET zur Modellierung der Fluiddynamik in solarthermischen Kraftwerken mit Direktverdampfung

Keywords: Parabolrinnenkraftwerk; Siphoninstabilität; Zweiphasenströmung; ATHLET; Thermische Oszillationen

  • Poster
    46. Kraftwerkstechnisches Kolloquium 2014, 14.-15.10.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21131
Publ.-Id: 21131


Full access to nanoscale Bismuth-Palladium intermetallics by low-temperature syntheses

Heise, M.; Chang, J.-H.; Schönemann, R.; Herrmannsdörfer, T.; Wosnitza, J.; Ruck, M.

The microwave-assisted polyol process was applied and modified to synthesize phase-pure micro- or nanocrystalline samples of all intermetallic phases in the bismuth−palladium system. Reaction temperatures range between 170 and 240 °C, whereas conventional syntheses from melt necessitate 500 to 1000 °C. Reaction times of few minutes up to 1 h are sufficient. Although not stable at the temperature of synthesis, high-temperature phases are accessible as well. Differences in the redox potentials of the two metals have effectively been compensated by adding auxiliaries such as oleylamine, oleic acid, and potassium hydroxide. The samples were characterized by X-ray powder diffraction, scanning electron microscopy, and energy-dispersive electron spectroscopy. Magnetic properties and electrical conductivity of the nanocrystalline samples were measured. The high temperature compound γ-BiPd showed superconductivity with Tc = 3.2 K. Nanocrystalline nc-Bi2Pd5 revealed an unusual temperature dependence of the electrical conductivity indicating an electronic phase transition at about 230 K. The electronic band structures of γ-BiPd, Bi2Pd5, Bi12Pd31, and BiPd3 were calculated including spin−orbit coupling.

Permalink: https://www.hzdr.de/publications/Publ-21130
Publ.-Id: 21130


Modellierung und Simulation hydrodynamischer Vorgänge in Bioreaktoren

Liao, J.

Am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) wurde für zweiphasige disperse Systeme von Gasblasen in einer Flüssigkeit eine Modellsammlung („HZDR-Baseline-Modell“) zusammengefasst. Das Ziel der vorliegenden Arbeit war die Validierung des Modells für andere Reaktortypen wie beispielsweise den in der Bioverfahrenstechnik weit verbreiteten Airlift-Reaktor und die Entwicklung einer Modellierung für das dreiphasige System mit den Mikroorganismen als zusätzliche Feststoffphase zwecks der weiteren Anwendungen in der Biotechnologie.

Das Modell wurde aufgrund der physikalischen Grundlage und empirischer Modelle aus der Literatur und den Experimenten entwickelt. Danach wurde das Modell in der Software CFX implementiert und durch den Vergleich der Simulationsergebnisse mit den Daten aus der Literatur validiert. Nach der Literaturstudie wurde Luos Arbeit wegen ihrer ausführlichen Beschreibung der experimentellen Einrichtungen, Mess- und Auswertungsmethode, Daten sowie CFD Berechnung ausgewählt. Eine 2D-Simulation wurde wegen des günstigen Rechnungsaufwands und der Genauigkeit durchgeführt. Das Simulationsergebnis wurde mit einer Gitterstudie und einem Konvergenzkriterium von dem Gitter und der Zeit unabhängig gemacht und mit derselben Auswertungsmethode im Experiment behandelt. Nach einem graphischen Vergleich wurde festgelegt, dass die Simulationsergebnisse mit den experimentellen Messwerten hinreichend genau übereinstimmen und das HZDR-Baseline-Modell gültig für die Geometrie Airlift-Reaktor ist. Das Modell kann für die Schätzung des Systemzustands eingesetzt werden.

Wegen einer fehlenden Blasengröße aus der Messung ist die weitere Verbesserung der Simulation allerdings nicht möglich. Um das Verständnis der Fluiddynamik im Airlift-Reaktor zu vertiefen, wurde ein neues Experiment im HZDR durchgeführt. Zunächst wurden Trends und Wertebereiche wesentlicher Einflussgrößen für die Fluiddynamik mit Hilfe der Simulation vorab untersucht, um die Auslegung des Experiments zu optimieren. Danach wurden die Simulationsergebnisse mit den experimentellen Daten verglichen.

Drei Blasengrößengruppen wurden nach dem Ziel der Untersuchung von der Blasenschicht im Außenraum ausgewählt und in der Simulation implementiert. Nach den vorhandenen Ergebnissen kann das HZDR-Baseline-Modell das Phänomen der Blasenschicht beschreiben und relativ gute Ergebnisse zu den Messdaten liefern.

Des Weiteren, wurden die Partikel als eine weitere disperse Phase in der Euler-Beschreibung modelliert. Eine Übersicht solcher dreiphasiger Euler- Simulationen aus der Literatur und die dabei in den jeweiligen Schließungsmodellen berücksichtigten Effekte wurden ausführlich angefertigt. Mit Hilfe dieser Literaturstudie und einer Analoge zum HZDR-Baseline-Modell im zwei-phasigen System wurde das Modell für ein drei-phasiges System erweitert und erste Berechnungen durchgeführt. Es ergab sich eine Notwendigkeit für die weitere Untersuchung der Mechanik zwischen den Phasen. Eine Parameterstudie mittels Simulation und Literaturstudie für die Messmethoden im drei-phasigen System wurden deswegen für die zukünftige Arbeit durchgeführt.

  • Diploma thesis
    TU Dresden, 2014

Permalink: https://www.hzdr.de/publications/Publ-21129
Publ.-Id: 21129


On the low-field Hall coefficient of graphite

Esquinazi, P.; Krüger, J.; Barzola-Quiquia, J.; Schönemann, R.; Herrmannsdörfer, T.; Garcia, N.

We have measured the temperature and magnetic field dependence of the Hall coefficient (RH) in three, several micrometer long multigraphene samples of thickness between ∼ 9 to ∼ 30 nm in the temperature range 0.1 to 200 K and up to 0.2 T field. The temperature dependence of the longitudinal resistance of two of the samples indicates the contribution from embedded interfaces running parallel to the graphene layers. At low enough temperatures and fields RH is positive in all samples, showing a crossover to negative values at high enough fields and/or temperatures in samples with interfaces contribution. The overall results are compatible with the reported superconducting behavior of embedded interfaces in the graphite structure and indicate that the negative low magnetic field Hall coefficient is not intrinsic of the ideal graphite structure.

Permalink: https://www.hzdr.de/publications/Publ-21128
Publ.-Id: 21128


Complex formation of tetravalent metal ions with small carboxylic ligands

Hennig, C.

The complex formation mechanisms of M(IV) ions with carboxylates in aqueous solution is still widely unknown. This presentation gives an overwiew about the actual knowledge, presents new insights and gives an perspective for large molecules.

Keywords: EXAFS; XRD; actinides(IV); Ce(IV); Zr(IV)

  • Invited lecture (Conferences)
    Institut de Chimie de Nice Université de Nice Sophia Antipolis, 31.10.2014, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-21127
Publ.-Id: 21127


Carrier dynamics in Landau-quantized graphene featuring strong Auger scattering

Mittendorff, M.; Wendler, F.; Malic, E.; Knorr, A.; Orlita, M.; Potemski, M.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.; Winnerl, S.

The energy spectrum of common two-dimensional electron gases consists of a harmonic (that is, equidistant) ladder of Landau levels, thus preventing the possibility of optically addressing individual transitions. In graphene, however, owing to its non-harmonic spectrum, individual levels can be addressed selectively. Here, we report a time-resolved experiment directly pumping discrete Landau levels in graphene. Energetically degenerate Landau-level transitions from n = -1 to n = 0 and from n = 0 to n = 1 are distinguished by applying circularly polarized THz light. An analysis based on a microscopic theory shows that the zeroth Landau level is actually depleted by strong Auger scattering, even though it is optically pumped at the same time. The surprisingly strong electron–electron interaction responsible for this eect is directly evidenced through a sign reversal of the pump–probe signal.

Permalink: https://www.hzdr.de/publications/Publ-21126
Publ.-Id: 21126


Intraband carrier dynamics in Landau-quantized multilayer epitaxial graphene

Mittendorff, M.; Orlita, M.; Potemski, M.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.; Winnerl, S.

We investigate the low-energy carrier dynamics in Landau quantized multilayer epitaxial graphene on (0001 ̅) SiC, using 14 meV photons. The THz absorption is dominated by Landau-level transitions within the conduction bands of several graphene layers with different doping. Varying the magnetic field allows us to tune the THz-induced response from induced transmission around B = 0 to induced absorption at intermediate fields (1.5 T – 3.3 T) and back to induced transmission at higher fields (3.3 T - 7 T). The main features of this complex response are explained by a strong dependence of the absorption on the electron temperature. Furthermore a prolonged relaxation at high fields, which is attributed to reduced scattering via optical phonons, is observed.

Permalink: https://www.hzdr.de/publications/Publ-21125
Publ.-Id: 21125


Development of a Novel Compact Particle Therapy Facility With Laser Driven Ion Beams via Gantry Systems Based on Pulsed Magnets

Masood, U.; Baumann, M.; Bussmann, M.; Cowan, T.; Enghardt, W.; Herrmannsdoerfer, T.; Hofmann, K.; Kaluza, M.; Karsch, L.; Kroll, F.; Schramm, U.; Schuerer, M.; Wilkens, J.; Pawelke, J.

Purpose/Objective(s)
The advancement in laser particle acceleration has made Laser-based Ion Beam Therapy (LIBT) an attractive alternative to existing Ion Beam Therapy (IBT) facilities as it has a great potential to reduce size and cost. Ultra-intense laser pulses interact with thin targets and accelerates intense ion bunches on μm scale. Unlike conventional beams, laser-driven ion beams are characterized by short pulses of intense particle flux with peak dose rates exceeding conventional values by 8-9 orders of magnitude, low repetition rate, broad energy spectrum and large divergence. The presented work is an ongoing joint multidisciplinary translational research project of several institutions aiming to establish LIBT.

Materials/Methods
In addition to laser particle accelerator development, LIBT poses new challenges. Conventional solutions cannot be applied directly as LIBT demands full characterization of radiobiological effects, development of new beam monitoring and dosimetry, a treatment planning system (TPS) for broad energy beams and an optimized gantry with energy selection system. Laser-based technology has been established for cell and small animal irradiation using a fixed beamline and is being utilized for systematic radiobiological studies. For translation to patient irradiation highly compact 360° isocentric proton and carbon gantry systems are designed based on light-weight iron-less pulsed magnets. A dedicated 3D TPS is being developed. Moreover, increasing the laser power to petawatt level is needed to achieve therapeutic ion energies.

Results
Radiobiologically no overall difference is observed for laser-driven ultra-high dose rates compared to conventional IBT beams. Our double achromatic pulsed gantry systems are ∼2.5 times smaller than conventional IBT gantries. For the gantry realization, key components have been designed and developed. A pulsed solenoid as particle capturing and focusing device was successfully tested. A novel 12 Tesla compact iron-less pulsed 50° sector magnet was developed. In addition, a pulsed high acceptance quadrupole with 230 T/m gradient has been designed and is being realized for tests. Our 3D TPS can be used to explore dose delivery and treatment planning strategies for LIBT.

Conclusions
The 3D TPS combined with our compact gantry provide a solution for LIBT. The realization and tests of pulsed gantry magnets are being continued. A new conventional proton therapy facility is under commissioning and is additionally equipped with a petawatt laser laboratory and an experimental bunker for further LIBT development toward clinical applicability with the conventional proton beam as reference.

Acknowledgment
This project was supported by German BMBF grant 03Z1N511 and DFG cluster of excellence MAP.

Permalink: https://www.hzdr.de/publications/Publ-21124
Publ.-Id: 21124


Numerical modeling of a horizontal annular flow experiment using a droplet entrainment model

Höhne, T.; Geissler, T.; Bieberle, A.; Hampel, U.

One limitation in current simulating horizontal annular flows is the lack of treatment of droplet formation mechanisms. For self-generating annular flows in horizontal pipes, the interfacial momentum exchange and the turbulence parameters have to be modelled correctly. Furthermore the understanding of the mechanism of droplet entrainment in annular flow regimes for heat and mass transfer processes is of great importance in the chemical and nuclear industry.
A new entrainment model is proposed. It assumes that due to liquid turbulence the interface gets rough and wavy and forms droplets. The new approach is validated with HZDR annular flow experiments. Important phenomena like the pressure drop, the wave pumping effect, the droplet entrainment, the liquid film formation and the transient flow behavior could be calculated, analyzed and some of the phenomena compared with the measurement.

Keywords: CFD; horizontal annular flow; AIAD; droplet entrainment; two-phase flow

Permalink: https://www.hzdr.de/publications/Publ-21123
Publ.-Id: 21123


Optics, Mechanics, and Energetics of Two-Dimensional MoS2 Nanostructures from a Theoretical Perspective

Joswig, J.-O.; Lorenz, T.; Wendumu, T.; Gemming, S.; Seifert, G.

Nanostructures based on molybdenum disulfide (MoS2) are by far the most common and well-studied systems among two-dimensional (2D) semiconducting materials. Although still being characterized as a “promising material”, the catalytic activity of MoS2 nanostructures has been found and applications in lubrication processes are pursued. As exfoliation techniques have improved over the past years, monolayer MoS2 is easily at hand;thus, experimental studies on the electronic properties and the applicability of monolayer MoS2 are in scientific focus now, and some electronic devices based on MoS2 have been reported already. The improvement of atomic force microscopy additionally led to nanoindentation experiments, in which the exceptional mechanical properties of MoS2 could be confirmed. In this Account, we present results from density-functional based calculations on several MoS2-based nanostructures; we have chosen to follow several experimental routes focusing on several nanostructures and their specific properties.

Keywords: 2D materials; molybdenum disulfide; platelets; nanoindentation; thermodynamic stability

Permalink: https://www.hzdr.de/publications/Publ-21122
Publ.-Id: 21122


Diaryl-substituted (dihydro)pyrrolo[3,2,1-hi]indoles, a class of potent COX-2 inhibitors with tricyclic core structure

Laube, M.; Gassner, C.; Sharma, S. K.; Günther, R.; Pigorsch, A.; König, J.; Köckerling, M.; Wuest, F.; Pietzsch, J.; Kniess, T.

A new compound class of diaryl-substituted heterocycles with tricyclic dihydropyrrolo[3,2,1-hi]indole and pyrrolo[3,2,1-hi]indole core structures has been designed and was synthesized by a modular sequence of Friedel-Crafts acylation, amide formation, and McMurry cyclization. This synthesis route represents a novel and versatile access towards dihydropyrrolo[3,2,1-hi]indoles and is characterized by good chemical yields and high modularity. From a set of nineteen derivatives, eleven candidates were selected for determination of their COX inhibition potency and were found to be highly affine and selective inhibitors with IC50 to COX-2 ranging from 20 – 2500 nM and negligible inhibition of COX-1. The binding mode of the novel inhibitors in the active side of COX-2 was calculated in silico using the protein-ligand docking program GOLD by application of the molecular structures of two compounds derived from X-ray crystallography. Two novel compounds with high affinity to COX-2 (6k = 70 nM, 8e = 60 nM) have got a fluoro-substituent making them to promising candidates for the development of 18F-radiolabeled COX-2 inhibitors for imaging purposes with positron emission tomography (PET).

Keywords: pyrrolo[3; 2; 1-hi]indoles; selective COX-2 inhibitors; McMurry cyclization; GOLD; docking studies; radiotracer

Permalink: https://www.hzdr.de/publications/Publ-21121
Publ.-Id: 21121


Baseline model for simulation of bubbly flows

Rzehak, R.; Ziegenhein, T.; Liao, Y.; Kriebitzsch, S.; Krepper, E.; Lucas, D.

A key parameter appearing in closure relations for the Euler-Euler two-fluid model is the bubble size. A distribution of bubble sizes is established as a result of bubble-coalescence and -breakup processes. These processes are very complex and models are considerably less developed than e.g. for bubble forces and even bubble-induced turbulence. Therefore, a two-step procedure is adopted for model validation where in a first step measured values are substituted for the bubble size distribution. In this way the uncertainties of the less developed modeling for bubble-coalescence and -breakup are bypassed and a validation of the other parts of the overall model becomes possible. In a second step the previously qualified models for bubble forces and bubble-induced turbulence are used without any change and the validity of models for bubble-coalescence and -breakup can be assessed. This procedure is illustrated by application to a set of data obtained for vertical upward flow in a pipe. In the first step satisfactory agreement is achieved like in previous investigations. A first attempt at the second step shows promising results as well. From the observed level of agreement between simulation and experiment, issues requiring further investigation are identified.

Keywords: Dispersed gas-liquid multiphase flow; Euler-Euler two-fluid model; closure relations; bubble-coalescence and -breakup

  • Contribution to proceedings
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Germany
    Proceedings of the 2nd International Symposium on Multiscale Multiphase Process Engineering
  • Lecture (Conference)
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Germany
  • Chemical Engineering & Technology 38(2015), 1972
    DOI: 10.1002/ceat.201500118

Permalink: https://www.hzdr.de/publications/Publ-21120
Publ.-Id: 21120


Laboratory formation of a scaled protostellar jet by coaligned poloidal magnetic field

Albertazzi, B.; Ciardi, A.; Nakatsutsumi, M.; Vinci, T.; Béard, J.; Bonito, R.; Billette, J.; Borghesi, M.; Burkley, Z.; Chen, S. N.; Cowan, T. E.; Herrmannsdörfer, T.; Higginson, D. P.; Kroll, F.; Pikuz, S. A.; Naughton, K.; Romagnani, L.; Riconda, C.; Revet, G.; Riquier, R.; Schlenvoigt, H.-P.; Skobelev, I. Y.; Faenov, A. Y.; Soloviev, A.; Huarte-Espinosa, M.; Frank, A.; Portugall, O.; Pépin, H.; Fuchs, J.

Although bipolar jets are seen emerging from a wide variety of astrophysical systems, the issue of their formation and morphology beyond their launching is still under study. Our scaled laboratory experiments, representative of young stellar object outflows, reveal that stable and narrow collimation of the entire flow can result from the presence of a poloidal magnetic field whose strength is consistent with observations. The laboratory plasma becomes focused with an interior cavity. This gives rise to a standing conical shock from which the jet emerges. Following simulations of the process at the full astrophysical scale, we conclude that it can also explain recently discovered x-ray emission features observed in low-density regions at the base of protostellar jets, such as the well-studied jet HH 154.

Permalink: https://www.hzdr.de/publications/Publ-21119
Publ.-Id: 21119


Dynamics of gas-liquid flow in helical static mixer: An experimental and numerical study

Krepper, E.; Rabha, S.; Hampel, U.; Rzehak, R.; Schubert, M.

Static mixer is an attractive alternative to conventional gas-liquid contactor, widely used for mixing and heat transfer between two fluids in various process applications. Knowledge on the limits of number and dimension of the static mixer element are important for packing optimization for desired mixing. The present work are designed to investigate the flow mixing pattern in a upward gas-liquid (air - water) flows in a column packed with helical static mixer both experimentally and numerically.
Experiments are carried out in a column of diameter (DT = 0.08 m) packed with helical static mixer (length 80 mm/ diameter 80 mm) using ultrafast electron beam X- ray tomography. The effect of number of static mixer element (3 – 9), liquid velocity (UL = 0.02 & 0.6 m/s), gas velocity (0.15 ≤ UG ≤ 0.6 m/s) on hydrodynamic parameters like gas holdup, bubble size distribution and pressure drop across the static mixer are studied.
Corresponding CFD simulations using the Euler-Euler model implemented in CFX 14 for some selective cases are done. The predicted axial and radial gas phase distribution considering different mono-dispersed bubbles classes (3, 5.8 and 8 mm) and poly-dispersed bubble classes are studied and validated against experimental results. The dependency of non-drag forces on the bubble size was considered. Consequently, the bubble size dependent effect of the non-drag forces on the flow and on the cross sectional gas volume fraction distribution are shown (see Fig. 1). The predicted axial gas volume fraction and velocity contour plots for different mono-dispersed bubbles classes within the helical static mixer are shown in Fig 2. The detailed effect of helical static mixer configuration and operating conditions on the predicted gas phase distribution & pressure drop and their validation with the measured results will be presented in our contribution.

Keywords: Static Mixer; Bubbly polydispersed flow; CFD modeling; momentum exchange

  • Poster
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Germany
  • Contribution to proceedings
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-21118
Publ.-Id: 21118


Extended validation of a baseline closure model

Krepper, E.; Rzehak, R.; Lucas, D.

For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. In dispersed gas-liquid multiphase flow, closure is needed for bubble forces, bubble-induced turbulence, as well as bubble-coalescence and -breakup. The quest for models with a broad range of applicability allowing predictive simulations is an ongoing venture (Lucas, 2014).
A large part of the necessary validation work was directed towards vertical upward bubbly turbulent flow since here quite well defined boundary conditions can be realized. Examples are the HZDR-facilities MT_Loop and TOPFLOW, which are equipped with wiremesh sensor techniques (e.g. Rzehak et al. 2012, 2013a, Rzehak & Krepper 2013b).
In the present paper the range of considered flow phenomena is extended. From the vertical tube experiments the change of void fraction distribution particularly in the near injection region is used to validate the closure models for drag and non-drag forces and for bubble-induced turbulence. Furthermore the influence of a slight inclination of the vertical tube on the void fraction distribution is investigated. In a preliminary first step bubble coalescence and breakup were excluded, i.e. the investigations were focussed on tests, which can be simulated assuming a monodispersed bubble size distribution.

Keywords: CFD; multiphase flow; momentum exchange; model validation

  • Contribution to proceedings
    Application of CFD/CMFD Codes to Nuclear Reactor Safety and Design and their Experimental Validation, CFD4NRS, 09.-11.09.2014, Zurich, Switzerland
  • Lecture (Conference)
    Application of CFD/CMFD Codes to Nuclear Reactor Safety and Design and their Experimental Validation, CFD4NRS, 09.-11.09.2014, Zurich, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-21117
Publ.-Id: 21117


Experimental evidence for the formation of titanium vacancies in TiO2 based transparent conductive oxides

Neubert, M.; Lungwitz, F.; Butterling, M.; Gebel, T.; Vinnichenko, M.; Cornelius, S.; Potzger, K.; Anwand, W.; Wagner, A.; Gemming, S.

The work is focused on understanding the physical mechanism leading to limited free electron density and mobility by variation of the oxygen content in polycrystalline tantalum doped TiO2 films. The films were prepared on glass substrates using a two-step approach involving direct-current magnetron sputtering of non-conducting amorphous films followed by annealing in vacuum. It is demonstrated that that fine tuning of the oxygen content during growth is crucial to ensure the formation of anatase films with low resistivity in the range of 10-3 Ωcm and high optical transmittance after the annealing process. An increase of the oxygen content in the anatase film leads to a decrease of the free electron density and the mobility. This dependence of the film electrical properties is discussed in terms of the effective electrical activation of the Ta dopant taking into account the formation of negatively charged acceptor like defects.
Doppler broadening positron annihilation spectroscopy was used to determine the density of negatively charged open-volume defects as a function of oxygen deficiency of the Ta-doped anatase TiO2 films. It is observed that the density of these negatively charged defects increases with increasing oxygen content in the films, which is attributed to the formation of Ti-related vacancies. These acceptor like defects are considered to counteract n-type doping by Ta resulting in a decreasing electron density with increasing oxygen content. Furthermore, due to their maximum charge state of q = -4, Ti vacancies are effective scattering centers for free electrons [1]. Thus, their presence is believed to contribute to the observed decrease of the free electron mobility with increasing oxygen content in the films. These experimental results are consistent with previously reported first-principles calculations [1] of the point defect formation enthalpies for Ti substitution by Ta and for intrinsic Ti-vacancies in anatase TiO2 in dependence of the oxygen chemical potential.

1. J. Osorio-Guillen, S. Lany, and A. Zunger, Phys. Rev. Lett. 100, 036601 (2008).

Keywords: TCO; Transparent Conductive Oxide; Titanium; Tantalum; TiO2; Positron Annihilation; negative defects

  • Poster
    5th International Symposium on Transparent Conductive Materials, 12.-17.10.2014, Platanias - Chania, Greece

Permalink: https://www.hzdr.de/publications/Publ-21116
Publ.-Id: 21116


Broken axial symmetry as essential feature to predict radiative capture in heavy nuclei

Grosse, E.; Junghans, A. R.; Massarczyk, R.

Cross sections for neutron capture in the range of unresolved resonances are predicted for more than 140 spin-0 target nuclei with A >50. Allowing the breaking of spherical and axial symmetry in nearly all these nuclei a combined parameterization for bothlevel density and photon strength is obtained which employs with surprisingly few fit parameters only. The strength functions used are based on a global fit to IVGDR shapes by the sum of three Lorentzians. They are based on theoretical predictions for the A-dependence of pole energies and spreading widths and add up to the TRK sum rule. For the small spins reached by capture resonance spacings are well described by a level density parameter close to the nuclear matter value; a significant collective enhancement is apparent due to the deviation from axial symmetry. Reliable predictions for compound nuclear reactions also outside the valley of stability – important for nuclear astrophysics and for the transmutation of nuclear waste – are expected to result from the global parameterization presented.

Keywords: Radiative neutron capture; Level density; Isovector giant dipole resonance; Lorentzian; Photon strength function; Triaxiality

Permalink: https://www.hzdr.de/publications/Publ-21115
Publ.-Id: 21115


The application of radiolabelled nanoparticles in transport studies

Schymura, S.; Hildebrand, H.; Kuhlenkampff, J.; Franke, K.; Lippmann-Pipke, J.

The radiolabelling of nanoparticles allows the tracking of these particles at low concentrations. Results for the radiolabelling of TiO2, Ag and MWCNTs and their consequent use for environmental transport studies including PET-studies are shown.

  • Lecture (Conference)
    CYCLEUR Meeting 2014, 13.-14.11.2014, Ispra, Italy

Permalink: https://www.hzdr.de/publications/Publ-21114
Publ.-Id: 21114


Numerical and experimental investigation of the contactless inductive flow tomography in the presence of strong static magnetic fields

Ratajczak, M.; Wondrak, T.; Stefani, F.; Eckert, S.

In the continuous casting industry, electromagnetic brakes (EMBr) are used to influence the mould flow, although their effect on the flow cannot be directly examined due to a lack of market-ready measurement techniques for liquid metal flows. The contactless inductive flow tomography (CIFT) is a technique that is able to reconstruct the mean flow structure of an electrically conducting melt by measuring the flow-induced perturbations of an applied magnetic field outside the melt and solving the linear inverse problem. Since CIFT relies on the measurement of magnetic fields, the question arises: Does CIFT work in the presence of a strong static magnetic field, like that of an EMBr, that superimposes and distorts the applied excitation magnetic field? In this paper we will examine the effects of an EMBr on CIFT with simulations and accompanying measurements.

  • Magnetohydrodynamics 51(2015)3, 461-471

Permalink: https://www.hzdr.de/publications/Publ-21113
Publ.-Id: 21113


Large size crystalline vs. co-sintered ceramic Yb3+:YAG disk performance in diode pumped amplifiers

Albach, D.; Chanteloup, J.-C.

A comprehensive experimental benchmarking of Yb3+:YAG crystalline and ceramic disks of similar thickness and doping level is presented in the context of high average power laser amplifier operation. Comparison is performed considering gain, depolarization and wave front deformation quantitative measurements and analysis.

Keywords: Lasers; Lasers, solid-state; Laser, ytterbium; Thermal effects

Permalink: https://www.hzdr.de/publications/Publ-21112
Publ.-Id: 21112


High-Speed PIXE: Large area irradiation effects

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

The so-called “High-Speed PIXE” is a novel combination of the SLcam® [1,2] and PIXE. The pixel-detector comprising 264 x 264 pixels in combination with a polycapillary 1:1 X-ray optics allows a fast detection of elements over a field of 12 x 12 mm² simultaneously with a lateral resolution below 100 μm.
In order to approach the final goal of quantitative analysis of geological samples, a homogeneous proton irradiation is essential. This can be realised by scanning a finefocused beam electrostatically across the area of interest which also minimises the required over-scan area.
However, the corresponding high proton density favours pile-up effects. In contrast to a classical micro-beam PIXE set-up, charge is collected in all pixels simultaneously for 1 ms. To enable trace element analysis, pile-up effects have to be suppressed calling for lower current densities.
[1] O. Scharf et al., Anal. Chem., Vol. 83, pp. 2532-2538 (2011).
[2] I. Ordavo et al., NIM A, Vol. 654, pp. 250-257 (2011).

  • Lecture (Conference)
    14th International Conference on Particle Induced X-ray Emission (PIXE 2015), 26.02.-03.03.2015, Somerset West, South Africa

Permalink: https://www.hzdr.de/publications/Publ-21111
Publ.-Id: 21111


High-Speed PIXE - First results: Laterally resolved trace element maps of geological samples

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

The so-called “High-Speed PIXE” is a novel combination of the SLcam® [1,2] and proton-induced X-ray emission (PIXE). The fluorescence radiation is excited by 3-4 MeV protons provided by the 6 MV tandem accelerator at HZDR. The pixel-detector comprising 264 x 264 pixels in combination with a polycapillary X-ray optics allows a fast detection of laterally resolved elemental maps over a detection area of 12 x 12 mm² simultaneously for all pixels.
Based on the pixel size of 48 x 48 μm² and considering the Nyquist-Shannon sampling theorem a lateral resolution better than 100 μm should be achievable. By measuring well-known structures of copper and chromium with appropriate dimensions, this assumption could be verified.
The system is intended for the detection of trace elements in geological samples by using a pnCCD-chip with an energy resolution better than 160 eV (@Mn Kα) for each pixel. The distribution of known trace element concentrations (<0.1%) in minerals could be proven in a short measurement time with this new PIXE set-up.
[1] O. Scharf et al., Anal. Chem., Vol. 83, pp. 2532-2538 (2011).
[2] I. Ordavo et al., NIM A, Vol. 654, pp. 250-257 (2011).

  • Poster
    8th International Symposium on BioPIXE, 14.-19.09.2014, Bled, Slovenia

Permalink: https://www.hzdr.de/publications/Publ-21110
Publ.-Id: 21110


Bright X-ray Pulse Generation by Laser Thomson-Backscattering and Traveling Wave Optical Undulators

Schramm, U.; Bussmann, M.; Couperus, J. P.; Cowan, T.; Debus, A.; Irman, A.; Jochmann, A.; Pausch, R.; Sauerbrey, R.; Steiniger, K.

Measured Thomson-backscattering X-ray spectra recorded as a function of the observation angle and quantitatively reproduced in simulations are presented. A traveling wave scheme is proposed to increase the yield and may allow for all-optical free-electron laser operation.

Keywords: Thomson scattering; laser plasma acceleration; optical undulators

  • Invited lecture (Conferences)
    Frontiers in Optics, 19.-23.10.2014, Tucson, AZ, USA
  • Contribution to proceedings
    Frontiers in Optics, 19.-23.10.2014, Tucson, AZ, USA
    Relativistic Light Sources (FTu4G) Optics InfoBase Conference Papers FiO: Optics InfoBase, OSA, 1-55752-286-3, FTu4G.2

Permalink: https://www.hzdr.de/publications/Publ-21109
Publ.-Id: 21109


Impact of thyroid hormones on the regulation of brown adipose tissue (BAT) activity in mice detected by combined [18F]FDGPET/ MR imaging

Steinhoff, K.; Kranz, M.; Zeisig, V.; Deuther-Conrad, W.; Faßhauer, M.; Stumvoll, M.; Tönjes, A.; Brust, P.; Sabri, O.; Hesse, S.; Krause, K.

Aim: Brown adipose tissue (BAT) is essential in regulation of energy balance, body temperature and body weight in rodents as in humans. A main BAT activation path leads via β3 adrenoceptors to an increased thyroid hormone (TH) conversion from T4 in T3 followed by mitochondrial heat production. As a direct BAT regulation via TH was not shown before our aim was to prove a direct influence of peripheral TH on BAT by combined [18F]FDG‐PET/MR measurements and gene expression studies.

Materials and methods: We induced hyperthyroidism in C57BL/6 mice by oral application of L‐thyroxine as well as hypothyroidism by an iodine deficient diet containing propylthiouracil. In these mice as well as in an euthyroid control cohort (each n=3) [18F]FDG‐PET/MR (nanoScan®, Mediso) was performed after i.p. injection of 15 MBq [18F]FDG. Glucose uptake (SUVmean) in interscapular BAT (iBAT) was measured by using MR‐based VOI analysis (PMOD v. 3.3). In order to evaluate the effects of TH on gene expression patterns in adipose tissue, microarray analyses were performed on visceral, subcutaneous and BAT. Results: Hyperthyroid mice showed a non‐significant increased [18F]FDG uptake in iBAT compared to the control group (SUVmean 8.78 ± 2.08 and 6.16 ± 0.57, p=0.16 ). In contrast, hypothyroid mice were found with significant reduced FDG uptake in iBAT (SUVmean 3.53 ± 0.65; p<0.01 vs. hyperthyroid and vs. control, respectively). In addition, differential gene expression analysis between the three mice cohorts are pointing to a discrepancy in the expression of brown and beige adipocyte differentiation markers in visceral and subcutaneous adipose tissue in hyper‐ and hypothyroid mice.
Conclusion: These findings confirm the impact of TH on iBAT activity in mice and substantiate the use of [18F]FDG PET/MR as a valuable tool to map the effects of TH on BAT activity. In addition, this is the first study confirming decreased iBAT activity in hypothyroid mice.
Furthermore, a current clinical study is investigating the translation of these results into humans with thyroid disorders in order to further explore the complex regulation of BAT as a potential treatment target, particularly in obesity. Acknowledgement: The first two authors contributed equally.

  • Lecture (Conference)
    EANM 2014, 18.-22.10.2014, Gothenburg, Sweden
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 41(2014)2, S264

Permalink: https://www.hzdr.de/publications/Publ-21108
Publ.-Id: 21108


Simultaneous measurements of the liquid phase velocity and gas bubble trajectories in a two-phase flow at gas-evolving electrodes

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

In water electrolysis the efficiency is related to the free area of the electrodes. Therefore a fast transport of the hydrogen bubbles away from the electrodes into the bulk is beneficial. To characterize the flow close to the cathodes surface simultaneous measurements of the fluid velocity and the size and trajectories of hydrogen bubbles were performed. The liquid phase velocity was measured by particle image velocimetry (PIV) as well as particle tracking velocimetry (PTV) using fluorescent tracer particles and laser light illumination. Gas bubble trajectories were determined using particle tracking on bubble shadow images obtained by a second camera. The images were separated by the different wavelength of the illumination/fluorescence. The void fraction in the vicinity of the electrode can become so high that determining both gas bubble and tracer particle velocities becomes quite challenging or even impossible. A comparison between results obtained by PIV and PTV clearly shows that in these regions PTV is better suited for the determination of the liquid phase velocities rather than PIV. A combination of both methods allow for the precise characterization of the evolving wall jet. The use of Lorentz forces, generated by magnets, result in significantly increased wall parallel liquid velocities close to the electrodes [1]. This enhances the transport of the bubbles away from the electrode surface and decreases the fractional bubble coverage. Consequently, the amount of active area for the reduction process is increased and the efficiency of the water electrolysis process can be improved.

Keywords: water electrolysis; particle image velocimetry; particle tracking velocimetry

  • Lecture (Conference)
    Sensor + Test 2015, 19.-21.05.2015, Nürnberg, Deutschland
  • Contribution to proceedings
    Sensor + Test 2015, 19.-21.05.2015, Nürnberg, Deutschland
    Proceedings SENSOR 2015, 978-3-9813484-8-4, 329-333
    DOI: 10.5162/sensor2015/B8.2

Permalink: https://www.hzdr.de/publications/Publ-21107
Publ.-Id: 21107


Azimuthal MRI as a dissipation-induced instability

Kirillov, O.

With the use of the formal short-wavelength asymptotic expansions of geometric optics we derive the local transport equations for the amplitude of the localized non-axisymmetric perturbation of a rotating flow under the influence of an azimuthal magnetic field with arbitrary radial dependence. Looking for the solution of the local transport equations in the modal form we derive a dispersion relation of the azimuthal magnetorotational instability that is suitable for testing stability in the case of both ideal and dissipative MHD. It is found that the marginally stable Chandrasekhar’s equipartition solution is generically destabilized by weak but finite electrical resistivity and in particular cases already by infinitesimally weak electrical resistivity resulting in AMRI, which is therefore a dissipation-induced instability.

Keywords: Azimuthal magnetorotational instability; inductionless limit; ideal MHD; dissipation-induced instabilities

  • Lecture (Conference)
    European GdR Dynamo Meeting, 01.-04.09.2014, Cambridge, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-21106
Publ.-Id: 21106


Inductionless AMRI as a dissipation-induced instability of the Chandrasekhar’s equipartition solution and its connection to Tayler instability

Kirillov, O.; Stefani, F.; Fukumoto, Y.

We present a study of destabilization of a rotating flow of an electrically conducting and viscous fluid in an external azimuthal magnetic field of arbitrary radial dependence.
With the use of the WKB approximation we obtain a dispersion relation which gives us the growth rates of the non-axisymmetric perturbation and conditions for the onset of the azimuthal magnetorotational instability in an explicit form.
We demonstrate that in the absence of the dissipation the flow is marginally stable if the ratio of the magnetic Rossby number and the hydrodynamic Rossby number is equal to the squared ration of the angular velocity of the fluid to the Alfven angular velocity.
In particular, this constraint contains the Chandrasekhar's equipartition solution - a special solution of ideal MHD equations for which the fluid velocity is parallel to the direction of the magnetic field and magnetic and kinetic energies are finite and equal.
With the use of the explicit expression for the onset of AMRI we demonstrate that AMRI is a destabilized by the electrical resistivity Chandrasekhar's equipartition solution that is marginally stable in the ideal MHD. Finally, we establish an expression that allows for a qualitative and quantitative analysis of the transition between the AMRI and Tayler instability.

Keywords: magnetorotational instability; azimuthal magnetic field; diffusive MHD instability; Tayler instability

  • Lecture (Conference)
    Max Planck/Princeton Center for Plasma Physics General Meeting, 28.06.-01.07.2014, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-21105
Publ.-Id: 21105


Inductionless instabilities in rotational MHD flows: A comprehensive short-wavelength analysis

Kirillov, O.; Stefani, F.

We perform a local stability analysis of rotational ows in the presence of a constant vertical magnetic eld and an azimuthal magnetic eld with a general radial dependence characterized by an appropriate magnetic Rossby number. Employing the short-wavelength approximation we develop a unied framework for the investigation of the standard, the helical, and the azimuthal version of the magnetorotational instability, as well as of current-driven kink-type instabilities. Considering the viscous and resistive setup, our main focus is on the case of small magnetic Prandtl numbers which applies, e.g., to liquid metal experiments but also to the colder parts of accretion disks. We show in particular that the inductionless versions of MRI that were previously thought to be restricted to comparably steep rotation proles extend well to the Keplerian case if only the azimuthal eld slightly deviates from its current-free prole.

Keywords: Magnetorotational instability; asymptotic analysis; WKB; MHD

  • Invited lecture (Conferences)
    The Seventh International Conference on Differential and Functional Differential Equations, 22.-29.08.2014, Moscow, Russia
  • Invited lecture (Conferences)
    Workshop ISTROF-2014: Instabilities and Turbulence in Stratified Rotational Flows, 23.-25.06.2014, Le Havre, France

Permalink: https://www.hzdr.de/publications/Publ-21104
Publ.-Id: 21104


Chandrasekhar's equipartition solution, dissipation-induced instabilities and azimuthal magnetorotational instability (MRI)

Kirillov, O. N.

I present a WKB study of the azimuthal magnetorotational instability (MRI) of a viscous electrically conducting rotating fluid with arbitrary radial profiles of the angular velocity and azimuthal component of the magnetic field. In the ideal setting II recover the results of Ogilvie and Pringle of 1996, whereas in the non- ideal case the azimuthal MRI is treated as a dissipation- induced instability of a Chandrasekhar equipartition solution for which the fluid velocity is parallel to the direction of the magnetic fiield and magnetic and kinetic energies are finite and equal.

Keywords: magnetorotational instability; rotating flow; dissipation-induced instabilities; Chandrasekhar's equipartition solution; azimuthal field

  • Invited lecture (Conferences)
    XXXIV Dynamics Days Europe, Minisymposium on Nonlinear Phenomena in Plasma Astrophysics, 08.-12.09.2014, Bayreuth, Germany

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-21103
Publ.-Id: 21103


Particle deposition and resuspension in gas-cooled reactors – Activity overview of the two European research projects THINS and ARCHER

Barth, T.; Lecrivain, G.; Jayaraju, S. T.; Hampel, U.

The deposition and resuspension behaviour of radio-contaminated aerosol particles is a key issue for the safety assessment of depressurization accidents of gas-cooled high temperature reactors. Within the framework of two European research projects, namely Thermal Hydraulics of Innovative Nuclear Systems (THINS) and Advanced High-Temperature Reactors for Cogeneration of Heat and Electricity R&D (ARCHER), a series of investigations was performed to investigate the transport, the deposition and the resuspension of aerosol particles in turbulent flows. The experimental and numerical tests can be subdivided into four different parts: 1. Monolayer particle deposition, 2. Monolayer particle resuspension, 3. Multilayer particle deposition and 4. Multilayer particle resuspension. The experimental results provide a new insight into the formation and removal of aerosol particle deposits in turbulent flows and are used for the development and validation of numerical procedures in gas-cooled reactors. Good agreement was found between the numerical and the experimental results.

Keywords: aerosol particle; turbulent flow; deposition; resuspension; high temperature reactor

Permalink: https://www.hzdr.de/publications/Publ-21102
Publ.-Id: 21102


Uran im Wasser – ein alltägliches Thema ?

Geipel, G.; Osman, A. A. A.

In allen Wässern kann das Ca2UO2(CO3)3 nachgewiesen werden, allerdings unterscheiden sich die Gehalte. Diese steigen von 69% des Gesamturans für Adelholzener auf über 99% für die Extalerquelle. Das restliche Uran liegt in Form von UO2(CO3)22- und UO2(CO3)34- vor. Generell kann auch geschlussfolgert werden, dass in Mineralwässer vom Typ „Classic“ höhere Anteile an Uranylkarbonaten enthalten, während die Wässer vom Typ „Still“ höhere Anteile an Ca2UO2(CO3)3 aufweisen. Letztere weisen damit eine geringere Urantoxizität auf, obwohl alle genannten Mineralwässer Urangehalte aufweisen, die deutlich unter dem Grenzwert für Trinkwasser liegen.

Keywords: Uran; Trinkwasser; Spektroskopie

  • Communication & Media Relations
    Wochenschau Wasserchemische Gesellschaft 10.11.2014
    2 Seiten

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-21100
Publ.-Id: 21100


The angular distribution of neutrons scattered from deuterium below 2 MeV

Nankov, N.; Plompen, A. J. M.; Kopecky, S.; Kozier, K. S.; Roubtsov, D.; Rao, R.; Beyer, R.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Massarczyk, R.; Schwengner, R.; Yakorev, D.; Wagner, A.; Stanoiu, M.; Canton, L.; Nolte, R.; Röttger, S.; Beyer, J.; Svenne, J.

Neutron elastic scattering measurements were carried out at the nELBE neutron time-of-flight facility at a 6 m fight path.
Energies below 2 MeV were studied using a setup consisting of eight 6Li-glass detectors placed at nominal angles of 15° and 165° with respect to the incident neutron beam. A deuterated polyethylene sample with 99.999% enrichment in deuterium was used. These angles were chosen since an earlier study showed that the ratio of the differential cross section at these angles is the most sensitive to differences in evaluated modes and model calculations. Accurate 165°/15° angle ratios were obtained. Above 1 MeV these are are somewhat larger than given by ENDF/B-VII. Simultaneously the early day experiments using a proportional counter to infer angular distributions from deuterium recoil pulse height distributions are being studied through a new experiment with such a device at the Physikalisch-Technische Bundesanstalt (PTB). At 500 keV this experiment favors ENDF/B-VII over JENDL-4.0, while at lower energies agreement with the data is similar.

Keywords: Neutron elastic scattering time-of-flight 6Li-glass deuterium cross section

Permalink: https://www.hzdr.de/publications/Publ-21099
Publ.-Id: 21099


Dosimetrie und First-in-man Studie (+)[18F]Flubatine

Kranz, M.; Sattler, B.; Patt, M.; Schildan, A.; Patt, J.; Tiepolt, S.; Wilke, S.; Deuther-Conrad, W.; Smits, R.; Hoepping, A.; Steinbach, J.; Brust, P.; Sabri, O.

Ziel
(+)[18F]Flubatine ist ein neuer vielversprechender Radiotracer zur Bildgebung nikotinischer Acetylcholin-Rezeptoren (α4β2) mit PET. Zur Abschätzung des Strahlenrisikos am Menschen wurde die Biodistribution erhoben und inkorporationsdosimetrische Messungen an 3 gesunden Probanden vorgenommen. Die Organdosis (OD), sowie die Effektive Dosis (ED) wurden berechnet und mit dem (-)-Enantiomer des Liganden verglichen.

Methodik
3 gesunde Probanden (Alter 58,3 ± 5,8 a, Gewicht: 80,7 ± 5,5 kg) wurden nach i.v. Injektion von 28 6 ± 13MBq (+)[18F]Flubatine sequentiell bis zu 7 h an einem PET/CT (SIEMENS Biograph16) gemessen. Das Untersuchungsprotokoll umfasste 9 Bettpositionen (BP), 1,5 – 6 min/BP, CT-Schwächungskorrektur, und iterative Rekonstruktion (OSEM, 4 Iterationen, 8 Subsets). In den Scanpausen wurde der Urin gesammelt, in einem Gammacounter gemessen und in der Dosisberechnung berücksichtigt. Mit Hilfe von ROVER (ABX, Radeberg, Germany) wurden 13 den Tracer anreichernde Organe identifiziert und per VOI-Analyse die entsprechenden Aktivitäten/Organ ermittelt. Die Zeit-Aktivitäts Daten wurden durch exponentielle Kurven approximiert, die Anzahl der Zerfälle/Organ berechnet und die OD mit OLINDA (V.1.0) abgeschätzt. Die ED wurde unter Hinzuziehung der Gewebewichtungsfaktoren aus ICRP 103 ermittelt.

Ergebnisse
Die Harnblase erhält die höchste OD (µSv/MBq) mit 102,4, gefolgt von der Leber (53,1), Nieren (38,1), Colon transversum (32,4), Dünndarm (29,4) und Gehirn (28,6). Den größten Beitrag zur ED (µSv/MBq) leistet die Harnblase (4,1), gefolgt von den Lungen (3,24), Magen (2,4), Leber (2,1), Colon transversum (1,9) und rotem Knochenmark (1,8). Resultierend ergibt sich die ED am Menschen nach i.v. Injektion von (+)[18F]Flubatine zu 23,0 µSv/MBq.

Schlussfolgerung
Die ED, als Maß für das Gesamtstrahlenrisiko, nach Injektion von 300 MBq (+)[18F]Flubatine ergibt sich zu 6,9 mSv. Sie liegt in der Größenordnung von anderen 18F-markierten Tracern (z.B. FDG = 5,7 mSv) und ist mit der ED des (-) Enantiomers (6,7 mSv) nahezu identisch.

  • Lecture (Conference)
    Nuklearmedizin2015, 53. Jahrestagung der DGN, 22.-25.04.2015, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A47

Permalink: https://www.hzdr.de/publications/Publ-21098
Publ.-Id: 21098


Heavy-quark expansion for D and B mesons in nuclear matter

Buchheim, T.; Hilger, T.; Kämpfer, B.

The planned experiments at FAIR enable the study of medium modifications of D and B mesons in (dense) nuclear matter. Evaluating QCD sum rules as a theoretical prerequisite for such investigations encounters heavy-light four-quark condensates. We utilize an extended heavy-quark expansion to cope with the condensation of heavy quarks.

Permalink: https://www.hzdr.de/publications/Publ-21097
Publ.-Id: 21097


Polyoxometalates - potent and selective ecto-nucleotidase inhibitors

Lee, S.-Y.; Fiene, A.; Li, W.; Hank, T.; Brylev, K.; Fedovrov, V.; Lecka, J.; Haider, A.; Pietzsch, H.-J.; Zimmermann, H.; Sévigny, J.; Kortz, U.; Stephan, H.; Müller, C. E.

Polyoxometalates (POMs) are inorganic cluster metal complexes that possess versatile biological activities, including antibacterial, anticancer, antidiabetic, and antiviral effects. Their mechanisms of action at the molecular level are largely unknown. However, it has been suggested that the inhibition of several enzyme families (e.g., phosphatases, protein kinases or ecto-nucleotidases) by POMs may contribute to their pharmacological properties. Ecto-nucleotidases are cell membrane-bound or secreted glycoproteins involved in the hydrolysis of extracellular nucleotides thereby regulating purinergic (and pyrimidinergic) signaling. They comprise four distinct families: ecto-nucleoside triphosphate diphosphohydrolases (NTPDases), ecto-nucleotide pyrophosphatases / phosphodiesterases (NPPs), alkaline phosphatases (APs) and ecto-5’-nucleotidase (eN). In the present study, we evaluated the inhibitory potency of a series of polyoxometalates as well as rhenium sulfur/selenium cluster complexes at a broad range of ecto-nucleotidases. [Co4(H2O)2(PW9O34)2]10- (5, PSB-POM142) was discovered to be the most potent inhibitor for human NTPDase1 described so far (Ki: 3.88 nM). Other investigated POMs selectively inhibited human NPP1, [TiW11CoO40]8-(4, PSB-POM141, Ki: 1.46 nM) and [NaSb9W21O86]18-(6, PSB-POM143, Ki: 4.98 nM) representing the most potent and selective human NPP1 inhibitors described to date. [P5W30O110]15- (8, PSB-POM144) strongly inhibited NTPDase 1-3 and NPP1 and may therefore be used as a pan-inhibitor to block ATP hydrolysis. The polyoxoanionic compounds displayed a non-competitive mechanism of inhibition at NPPs and eN, but appeared to be competitive inhibitors of TNAP. Future in vivo studies with selected inhibitors identified in the current study are warranted.

Permalink: https://www.hzdr.de/publications/Publ-21095
Publ.-Id: 21095


Entwicklung eines nicht-peptidischen F-18-markierten Liganden mit dem Ziel der molekularen Bildgebung des Oxytocinrezeptors im Gehirn

Wenzel, B.; Mollitor, J.; Deuther-Conrad, W.; Kranz, M.; Günther, R.; Teodoro, R.; Fischer, S.; Ludwig, F.-A.; Smits, R.; Steinbach, J.; Hoepping, A.; Brust, P.

1. Ziel
Oxytocin ist ein zyklisches Nonapeptid, welches im Hypothalamus synthetisiert und in der Hypophyse gespeichert wird. Sein Rezeptor (OTR) ist in spezifischen Hirnarealen exprimiert und wird mit psychiatrischen Erkrankungen, wie Schizophrenie, Autismus und Depression in Zusammenhang gebracht.
Ziel unserer Arbeiten ist die Entwicklung eines nicht-peptidischen, F-18-markierten Radiotracers zur Untersuchung der Expressionsdichte des OTR im gesunden bzw. erkrankten Gehirn.

2. Methodik
Die Bindungsaffinitäten neuer Derivate zum humanen OTR wurden mittels Radioligand-Verdrängungsstudien bestimmt. Die Radiomarkierung von [18F]ABX163 erfolgte sowohl thermisch als auch mikrowellenunterstützt in einer Zwei-Schritt-Synthese ausgehend von einem MOM-geschützen Tosylatpräkursor. Metabolismus und Organverteilung wurden in Mäusen untersucht. Dynamische PET-Scans erfolgten in Mäusen und in einem Ferkel.

3. Ergebnisse
Gegenüber der thermischen Reaktionsführung führte die mikrowellenunterstützte F-18-Markierung und Entschützung von [18F]ABX163 (Ki=13,3 nM ) zu höheren radiochemischen Ausbeuten in kürzerer Zeit (RCA: 25,4 ± 3,1% (n = 5); SA: 35-160 GBq/µmol). Sowohl die Organverteilung als auch PET-Scans von [18F]ABX163 in der Maus zeigten eine Anreicherung in der Hypophyse (SUV60=0,85), jedoch wurde eine geringe Hirnaufnahme (SUV60=0,04) beobachtet. Im Ferkel lagen die SUV-Werte für das Gesamthirn bei 0,43 (120 Min.), mit einer höheren Aufnahme im Bulbus olfactorius (SUV120=0,73; OTR-reiche Hirnregion). In-vitro-Autoradiographien am Rattenhirn zeigten eine Anreicherung von [18F]ABX163 in OTR-typischen Regionen, die jedoch nur partiell durch Oxytocin blockiert werden konnte. Selektivitätsstudien deuten auf eine Bindung von ABX163 an den ebenfalls im Gehirn exprimierten Vasopressin-Rezeptor V2 hin.

4. Schlussfolgerung
Auf Grund der geringen Hirnaufnahme und der vermuteten unzureichenden Selektivität ist eine Weiterentwicklung dieses Radioliganden nicht vorgesehen.

  • Lecture (Conference)
    Nuklearmedizin2015, 53. Jahrestagung der DGN, 22.-25.04.2015, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A66

Permalink: https://www.hzdr.de/publications/Publ-21094
Publ.-Id: 21094


Silicon Nanoparticles for Bioapplications

Hsu, C.-W.; Licciardello, N.; Septiadi, D.; Hunoldt, S.; Viehweger, K.; Stephan, H.; de Cola, L.

Silicon based nanomaterials have been well studied and applied in bio-applications such as cell imaging, targeting, and drug delivery. The major interests for these nanoparticles (NPs), rely in their biocompatibility, intrinsic luminescence as well as photo- and electro- stability. Many in vitro and in vivo studies have indeed shown that Si NPs do not display any cytotoxicity and are good candidate for cancer labeling.
Here we report on the synthesis of Si NPs via wet chemistry methods either by reducing Si(OMe)4[2] in reverse micelle or oxidizing Mg2Si.[6] The Si NPs were fully characterized by HR-TEM, EDX, XPS, FT-IR, and their photophysical properties are discussed. Furthermore, we show that it is possible to control the surface functionalization of the NPs by covalently binding different functional groups for multimodal bio-imaging. The in vitro study, cellular localization, and cell viability test of Hela cells also give us a tool to understand these materials for further nanomedicine research.

  • Poster
    5th EuCheMS Chemistry Congress, 31.08.-04.09.2014, Istanbul, Turkey

Permalink: https://www.hzdr.de/publications/Publ-21093
Publ.-Id: 21093


Synthese und Anwendung eines F-18-markierten PDE10A Inhibitors zur Untersuchung adipöser Mäuse

Wagner, S.; Kranz, M.; Hankir, M.; Scheunemann, M.; Fischer, S.; Deuther-Conrad, W.; Teodoro, R.; Wenzel, B.; Egerland, U.; Fenske, W. K.; Hesse, S.; Höfgen, N.; Steinbach, J.; Brust, P.

Ziel: Phosphodiesterasen (PDEs) katalysieren die Spaltung zyklischer Mononukleotide und sind daher Schlüsselenzyme der intrazellulären Signalübertragung. Die PDE10A ist maßgeblich an der Kontrolle der dopaminergen Transmission beteiligt. Es wird vermutet, dass zur Adipositas führende Hyperphagie mit einer Dysregulation dieses Systems im Gehirn einhergeht. Aus einer Serie von PDE10-Inhibitoren wurde daher eine Verbindung (AQ-28a) mit hoher Affinität (IC50 = 2,95 nM) und Selektivität zur F-18-Markierung ausgewählt, charakterisiert und in einem Tiermodell adipöser Mäuse mittels TierPET/MR untersucht.

Methode: Auf Basis eines Brom- bzw. Nitropräkursors wurde das 2-fluorpyridylsubstituierte AQ-28a durch nukleophile aromatische Substitution in einer Einstufenreaktion radiomarkiert. Untersuchungen zur metabolischen Stabilität wurden in Mäuseplasma und -hirnhomogenat 30 min p.i. durchgeführt. 8 Wochen alte weibliche CD1-Mäuse wurden einer 2-monatigen fettreichen Diät unterzogen und die Aufnahme von [18F]AQ-28a im Striatum und braunen Fettgewebe (BAT) durch dynamische PET/MR-Studien vor und nach der Diät untersucht.

Results: [18F]AQ-28a wurde ausgehend vom Brompräkursor mit einer radiochemischen Ausbeute von 11,0±0,1% (n=2), einer spezifischen Aktivität von 40,2±3,5 GBq/μmol (n=2) sowie einer radiochemischen Reinheit von ≥ 98% synthetisiert. Die Markierungsausbeute betrug 35±9% (n=7). Der Nitropräkursor konnte in ersten Experimenten in besseren Ausbeuten 69±5% (n=2) markiert werden. [18F]AQ-28a ist in vitro stabil und wird in vivo nicht defluoriert. PET/MR-Studien an Mäusen zeigen eine hohe Hirnaufnahme insbesondere im Striatum (SUVmax=2,3±0,9), die durch MP-10 gehemmt wird. Bei einer noch geringen Fallzahl (n=3) wurde nach fettreicher Diät eine signifikant um ca 60% erhöhte Aufnahme im Striatum und eine um ca. 130% erhöhte Aufnahme im BAT festgestellt.

Schlussfolgerungen: Mit [18F]AQ-28a wurde ein neuer hochaffiner PET-Radioligand für die Bildgebung der PDE10A im Gehirn entwickelt. Die bisherigen Ergebnisse weisen darauf hin, dass [18F]AQ-28a geeignet ist, Veränderungen der dopaminergen Transmission bei Adipositas anzuzeigen.

  • Lecture (Conference)
    Nuklearmedizin2015, 53. Jahrestagung der DGN, 22.-25.04.2015, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 54(2015), A68

Permalink: https://www.hzdr.de/publications/Publ-21092
Publ.-Id: 21092


A multi-scale modelling approach for industrial multiphase flows

Lucas, D.

A new modelling approach for gas-liquid flows which involve a wide spectrum of typical length scales for the interfaces between the phases is presented. It aims on medium and large scale industrial applications and bases for that reason on the multi-fluid approach. In many flow situations dispersed and segregated morphologies of the phases occur not only simultaneously, but the flow is characterized by transitions between these morphologies. The recently developed GENTOP concept provided a modelling frame for such flow situations. Examples for application are bubble entrainment by jets impinging on a liquid pool, flashing flows, e.g. in the feed line of distillation columns, flows in column tray and many others. The inhomogeneous MUSIG approach is extended to include beside a number of bubble size classes also a continuous gas phase. Interfaces which are at least 4 times larger than the cell size of the numerical grid are resolved, while smaller structures are handled as dispersed phase as usual in Euler-Euler methods. The resolved interfaces are treated in a similar way as in the Algebraic Interfacial Area Density model (AIAD). Transitions between these different morphologies are considered as coalescence and breakup processes. In several demonstration cases the capabilities of the concept are shown.

Keywords: CFD; multiphase; multi-fluid

  • Contribution to proceedings
    13th International Conference Multiphase Flow in Industrial Plants, 17.-19.09.2014, Sestri Levante, Italy
  • Lecture (Conference)
    13th International Conference Multiphase Flow in Industrial Plants, 17.-19.09.2014, Sestri Levante, Italy

Permalink: https://www.hzdr.de/publications/Publ-21091
Publ.-Id: 21091


Numerical simulations for effects of pipe size on countercurrent flow limitation in slightly inclined pipes

Murase, M.; Utanohara, Y.; Kusunoki, T.; Lucas, D.; Tomiyama, A.

Under postulated accident conditions in a pressurized water reactor (PWR) such as loss-of-RHR (residual heat removal systems) during mid-loop operation, steam and condensate water form countercurrent flows in a hot leg and a pressurizer surge line, so that countercurrent flow limitation (CCFL) may occur. For CCFL in the hot leg, we measured CCFL characteristics in a 1/15-scale model using air and water [1], carried out numerical simulations for a full-scale hot leg using a volume of fluid method (VOF), and derived a CCFL correlation [2] using Wallis parameters [3]. For CCFL in the surge line (consisting of a vertical pipe, a vertical elbow, and a slightly inclined pipe with elbows), we measured CCFL characteristics in a 1/10-scale model using air and water [4]. However, the layout of the surge line is different in each PWR plant and a generalized method to predict CCFL characteristics in the inclined pipe with elbows is necessary. Therefore, we did one-dimensional (1D) computations [5] and three-dimensional (3D) numerical simulations [6] for the 1/10-scale air-water experiments [4] to validate the 1D computation and 3D simulation.
In this study, we did 1D computations and 3D simulations for the 1/10-scale and full scale models to confirm effects of the pipe size on CCFL characteristics. Working fluids in the computation were air and water at room pressure and temperature and these conditions allowed us to evaluate pure effects of the pipe size.

Keywords: counter-current flow limitation; inclined pipe

  • Contribution to proceedings
    ANS Annual Meeting, 07.-11.06.2015, San Antonio, TX, USA
    Transactions of the American Nuclear Society, Volume 112, 2015, 955-957

Permalink: https://www.hzdr.de/publications/Publ-21090
Publ.-Id: 21090


Effects of inclination angles on countercurrent flow limitation in slightly inclined pipes

Murase, M.; Utanohara, Y.; Kusunoki, T.; Lucas, D.; Tomiyama, A.

Under postulated accident conditions in a pressurized water reactor (PWR), steam and condensate water form countercurrent flows in a hot leg and a pressurizer surge line, so that countercurrent flow limitation (CCFL) may occur. There are many studies for CCFL in hot leg models, but there are only a few studies for CCFL in a pressurizer surge line (consisting of a vertical pipe, a vertical elbow, and a slightly inclined pipe with elbows). In our previous studies, we measured CCFL characteristics in a 1/10-scale model of a pressurizer surge line using air and water, developed a one-dimensional (1D) computation model, and also did three-dimensional (3D) simulations for the inclination angle of 0.6 deg (slope of 1/100) to validate simulation capability. 1D computations and 3D simulations gave good agreement with the 1/10-scale air-water data for the inclination angle of 0.6 deg. In the present study, we did 1D computations and 3D simulations for air-water countercurrent flows in the 1/10-scale model of the pressurizer surge line to validate them for effects of inclination angles on CCFL. Although 1D computations and 3D simulations gave good agreement with measured data for the inclination angle of 0.6 deg, they slightly underestimated effects of inclination angles on CCFL for the inclination angles of 0 deg and 1.0 deg.

Keywords: counter-current flow limitation; pressure surge line

  • Contribution to proceedings
    23rd International Conference on Nuclear Engineering - ICONE-23, 17.-20.05.2015, Chiba, Japan

Permalink: https://www.hzdr.de/publications/Publ-21089
Publ.-Id: 21089


Sensitivity analyses for countercurrent flow limitation in a pressurizer surge line

Murase, M.; Utanohara, Y.; Kusunoki, T.; Lucas, D.; Tomiyama, A.

Sensitivity analyses for countercurrent flow limitation (CCFL) in a pressurizer surge line were done to predict CCFL in an
actual surge line. The results showed that CCFL on the Wallis diagram was mitigated in a large diameter line.

Keywords: pressurizer surge line; countercurrent flow limitation; numerical simulation

  • Contribution to proceedings
    2015 Annual Meeeting of the Atomic Energy Society of Japan, 20.-22.03.2015, Hitachi, Japan

Permalink: https://www.hzdr.de/publications/Publ-21088
Publ.-Id: 21088


Partial Wave Analysis of the Reaction p(3.5GeV)+p→pK+Λ to Search for the "ppK−" Bound State

Agakishiev, G.; Arnold, O.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Chernenko, S.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Göbel, K.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kornakov, G.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kunz, T.; Kurepin, A.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Sarantsev, A. V.

mploying the Bonn-Gatchina partial wave analysis framework (PWA), we have analyzed HADES data of the reaction p(3.5GeV)+p→pK+Λ. This reaction might contain information about the kaonic cluster "ppK−" via its decay into pΛ. Due to interference effects in our coherent description of the data, a hypothetical KbarNN (or, specifically "ppK−") cluster signal must not necessarily show up as a pronounced feature (e.g. a peak) in an invariant mass spectra like pΛ. Our PWA analysis includes a variety of resonant and non-resonant intermediate states and delivers a good description of our data (various angular distributions and two-hadron invariant mass spectra) without a contribution of a KbarNN cluster. At a confidence level of CLs=95\% such a cluster can not contribute more than 2-12\% to the total cross section with a pK+Λ final state, which translates into a production cross-section between 0.7 μb and 4.2 μb, respectively. The range of the upper limit depends on the assumed cluster mass, width and production process.

Permalink: https://www.hzdr.de/publications/Publ-21087
Publ.-Id: 21087


FDG PET/MR for the Assessment of Lymph Node Involvement in Lymphoma: Initial Results and Role of Diffusion-Weighted MR

Platzek, I.; Beuthien-Baumann, B.; Ordemann, R.; Maus, J.; Schramm, G.; Kitzler, H. H.; Laniado, M.; Kotzerke, J.; van den Hoff, J.

Rationale and Objectives: The purpose of this study was to evaluate the sensitivity and specificity of positron emission tomography/magnetic resonance imaging (PET/MR) with 18F-fluorodeoxyglucose (FDG) for nodal involvement in malignant lymphoma.
Materials and Methods: Twenty-seven patients with malignant lymphoma (16 men and 11 women; mean age, 45 years) were included in this retrospective study. The patients underwent FDG PET/MR after intravenous injection of FDG (176-357 MBq FDG, 282 MBq on average). Follow-up imaging and histology served as the standard of reference.
Results: One-hundred and twenty-seven (18.1%) of 702 lymph node stations were rated as having lymphoma-involvement based on the standard of reference. One-hundred and twenty-four (17.7%) of 702 lymph node stations were rated as positive by FDG PET/MR. The sensitivity and specificity of FDG PET/MR for lymph node station involvement were 93.8% and 99.4%.
Conclusions: FDG PET/MR is feasible for lymphoma staging and has a high-sensitivity and specificity for nodal involvement in lymphoma. Comparison with PET/CT is necessary to determine whether FDG PET/MR can replace PET/CT for lymphoma staging.

Permalink: https://www.hzdr.de/publications/Publ-21084
Publ.-Id: 21084


Investigation of Feedback on Neutron Kinetics and Thermal Hydraulics from Detailed Online Fuel Behavior Modelling during a Boron Dilution Transient in a PWR with the Two-way Coupled Code System DYN3D-TRANSURANUS

Holt, L.; Rohde, U.; Kliem, S.; Baier, S.; Seidl, M.; Macían-Juan, R.

Recently the reactor dynamics code DYN3D (including an internal fuel behavior model) was coupled to the fuel performance code TRANSURANUS at assembly level. The coupled code system applies the new general TRANSURANUS coupling interface, hence it can be used for one-way or two-way coupling. In the coupling, DYN3D provides process time, time-dependent rod power and thermal hydraulics conditions to TRANSURANUS, which in case of the two-way coupling approach replaces completely the internal DYN3D fuel behavior model and transfers parameters like radial fuel temperature distribution and cladding temperature back to DYN3D. For the first time results of the coupled code system are presented for a post-critical-heat-flux heat transfer. The corresponding heat transfer regime is mostly film boiling, where the cladding temperature can rise several hundreds of degrees. The simulated boron dilution transient assumed an injection of a 36 m3 slug of under-borated coolant into a German PWR core initiated from a sub-critical reactor state (extreme RIA conditions). The feedback from detailed fuel behavior modelling was found negligible on the neutron kinetics and thermal hydraulics during the first power rise. In a later phase of the transient, the node injected energy can differ 25 J/g, even still around 20 J/g for nodes without film boiling. Furthermore the thermal hydraulics can be affected strongly even in fresh fuel assemblies, where film boiling appeared in one node in the two-way approach in spite of no onset of film boiling in the one-way approach. For nodes with film boiling in both coupling approaches the two-way approach determined always higher maximum node average fuel enthalpies by about 100 J/g and higher maximum node clad surface temperatures by about 230 °C for the corresponding fresh fuel assemblies. Since the numerical performance of DYN3D-TRANSURANUS was fast and stable for these extreme transient conditions, it is therefore concluded that the coupled code system can improve the assessment of safety criteria, at a reasonable computational cost.

Permalink: https://www.hzdr.de/publications/Publ-21083
Publ.-Id: 21083


Zero-field spin-transfer oscillators combining in-plane and out-of-plane magnetized layers

Fowley, C.; Sluka, V.; Bernert, K.; Lindner, J.; Fassbender, J.; Rippard, W. H.; Pufall, M. R.; Russek, S. E.; Deac, A. M.

Excited magnetization dynamics in a spin-valve device consisting of an in-plane polarizer and an out-of-plane free layer were studied numerically. Such devices hold promise for nanoscale wireless transmitters operating at gigahertz frequencies, compatible with current technologies [1]. We solve the Landau Lifschitz-Gilbert-Slonczewski equation taking into account the spin-transfer-torque asymmetry.
This asymmetry is directly responsible for the appearance of excited dynamics in this specific geometry as it leads to a net spin transfer torque over one precession cycle. Unfortunately, when the free layer lacks any in-plane anisotropy components, i.e. is circular in shape and posesses purely uni-axial perpendicular magnetic anisotropy, a finite external field is required to generate steady-state dynamics, in agreement with previous reports[2][3].
We demonstrate that this constraint can be removed and precession can be stabilized in zero applied field by introducing an additional in-plane anisotropy axis, in this case an elongation of the free layer in the direction of the injected spin polarized current. Moreover, the in-plane anisotropy offers an additional degree of freedom for tuning the frequency response of the device[4].
The shape anisotropy introduces a variable in-plane magnetic field whose direction is dependent on the exact location of the magnetisation of the free layer around the precession trajectory. The field induced by the shape anisotropy is sufficient to balance the action of the spin transfer torque and leads to steady state precession in suitably shaped devices. The frequency dependence, frequency spectra as well as a selected precession orbit for a 90nmx80nm free layer at zero applied field are shown in the figure to the right.
Our results show that the use of an intrinsic shape anisotropy is beneficial for spin transfer oscillators in order to achieve consistent high-power, zero-field, out-of plane precessional states without any initial magnetization direction dependence.
[1] S. I. Kiselev et al., Nature 425, 380 (2003).
[2] W. H. Rippard et al., Phys. Rev. B 81, 014426 (2010).
[3] S. M. Mohseni et al., Phys. Status Solidi: Rapid Res. Lett. 5, 432 (2011).
[4] C. Fowley et al., Applied Physics Express 7, 043001 (2014)

Keywords: Spin-transfer-torque; spin-transfer-oscillators; spin-valves; magnetoresistance; spin dynamics; microwave oscillators; zero-field spin-transfer-oscillators

  • Lecture (Conference)
    Moscow International Symposium on Magnetism MISM-2014, 29.06.-03.07.2014, Moscow, Russia
  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS), 12.-17.07.2015, Krakow, Poland
  • Poster
    International Magnetics Conference, 11.-15.05.2015, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-21082
Publ.-Id: 21082


Guided-wave phase-matched second-harmonic generation in KTiOPO4 waveguide produced by swift heavy-ion irradiation

Cheng, Y.; Jia, Y.; Akhmadaliev, S.; Zhou, S.; Chen, F.

We report on the guided-wave second-harmonic generation in a KTiOPO4 nonlinear optical waveguide fabricated by a 17  MeV O5+ ion irradiation at a fluence of 1.5×1015  ions/cm2. The waveguide guides light along both TE and TM polarizations, which is suitable for phase-matching frequency doubling. Second harmonics of green light at a wavelength of 532 nm have been generated through the KTiOPO4 waveguide platform under an optical pump of fundamental wave at 1064 nm in both continuous-wave and pulsed regimes, reaching optical conversion efficiencies of 5.36%/W and 11.5%, respectively. The propagation losses have been determined to be ∼3.1 and ∼5.7  dB/cm for the TE and TM polarizations at a wavelength of 632.8 nm, respectively.

Keywords: Second-harmonic generation; Waveguides; Ions; Planar waveguides; Crystals

Permalink: https://www.hzdr.de/publications/Publ-21081
Publ.-Id: 21081


Preparation of 4-Halobenzoate Containing Phosphane Based Building Blocks for Labeling Reactions Using the Traceless Staudinger Ligation

Mamat, C.; Köckerling, M.

Functionalized phosphane-containing key building blocks were synthesized that are suitable for the labeling of biologically active molecules by the traceless Staudinger ligation. Thus, a 2-(diphenylphosphanyl)phenyl 4-stannylbenzoate building block was converted into the 4-iodobenzoate by the introduction of iodine. The traceless Staudinger ligation was used to introduce the resulting 4-iodobenzoate moiety into selected molecules of pharmacological interest. Furthermore, the labeling procedure was used to transferred the 4-iodobenzoate moiety to a peptide on solid support. Finally, a convenient recovery procedure of the key phosphane building block 2-(diphenylphosphanyl)phenol from 2-(diphenylphosphoryl)phenol was evaluated

Permalink: https://www.hzdr.de/publications/Publ-21080
Publ.-Id: 21080


Geomorpho-tectonic evolution of the Jamaican restraining bend

Domínguez-González, L.; Andreani, L.; Stanek, K. P.; Gloaguen, R.

This work applies recent advances in tectonic geomorphology in order to understand the geomorphic evolution of the Jamaican restraining bend located along the Caribbean–Gonâve–North American plate boundary. We propose a classification of landscapes according to their erosional stages. The approach is mainly based on the combination of two DEM-based geomorphic indices: the hypsometric integral which highlights elevated surfaces, and the surface roughness which increases when the relief is incised by the drainage network. River longitudinal profiles were also analyzed as the drainage network responds quickly to base-level change triggered by external forcing such as tectonics. Anomalies in river profiles (knickpoints and convex segments) were mapped using stream length-gradient (SL) and normalized steepness (ksn) indices. The results provide new insights for understanding the complex evolution of the Jamaican restraining bend. Three main morphotectonic regions were identified in Jamaica: (1) the Blue Mountain–Wagwater unit located at the eastern tip of the island, (2) the Jamaican highlands plateau which covers most of the northern and central areas and (3) the tilted block province located along the southern part of Jamaica. Each region has a specific morphological signature which marks a different stage in the Late Miocene to present evolution of the Jamaican restraining bend. The evolution of the bend is mainly associated with the western propagation of major E-trending strike-slip faults and NW-trending thrusts. In the western and central parts of Jamaica the present-day motion between the Caribbean plate and the Gonâve microplate is broadly distributed along several structures, while in the easternmost part of the island this motion seems to be almost completely accommodated along the Blue Mountain range and the Plantain-Garden Fault.

Keywords: Jamaican restraining bend; Tectonic geomorphology; Geomorphic indices; Caribbean plate; North American plate; Gonâve microplate

Permalink: https://www.hzdr.de/publications/Publ-21079
Publ.-Id: 21079


Scale-Resolving Simulations for bubble columns

Ma, T.; Lucas, D.; Fröhlich, J.

This seminar presents detailed Euler-Euler Large Eddy Simulation and Scale-Adaptive Simulation of dispersed bubbly flow in different kinds of bubble columns. The main objective is to investigate the potential of these approaches for the prediction of bubbly flows with anisotropic liquid velocity fluctuations. The set of physical models describing the momentum exchange between the phases was chosen according to previous experiences of the authors. Experimental data are used for comparison. It was found that the presented modelling provides very good agreement with experimental data for the mean flow and the liquid velocity fluctuations. The energy spectra obtained from the simulations are presented and compared to the experimental spectra.

  • Lecture (Conference)
    East German Centre of Competence in Nuclear Technology, 04.12.2014, Zittau, Deuschland

Permalink: https://www.hzdr.de/publications/Publ-21078
Publ.-Id: 21078


Large Eddy Simulations for dispersed bubbly flows

Ma, T.; Lucas, D.

Die Untersuchungen zur Einbeziehung eines geeigneteren Turbulenzmodells für das GENTOP-Konzept wurden fortgesetzt. Der erste Schritt zur Untersuchung des Turbulenzanteils der nicht aufgelösten Blasen wurde durchgeführt. Es wurden Scale-Resolving Simulationen (hier, LES und SAS) auf unterschiedliche Blasensäulen gerechnet.

  • Lecture (Conference)
    HZDR PhD-Seminar, 07.-09.10.2014, Altenberg, Deuschland

Permalink: https://www.hzdr.de/publications/Publ-21077
Publ.-Id: 21077


Large Eddy Simulation of a bubble plume

Ma, T.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.

The paper presents Euler-Euler Large Eddy Simulations (LES) of dispersed bubbly flow in a rectangular bubble column. The flow is characterized by a low Reynolds number. The set of physical models describing the momentum exchange between the phases was chosen according to previous experiences of the authors. The emphasis of the study is the analysis of bubbly flows concerning the investigation of the influence of the subgrid-scale model and the bubble induced turbulence model. It was found that the presented modelling combination provides good agreement with experimental data for the mean flow and liquid velocity fluctuations. The energy spectrum obtained from the resolved velocity is presented and discussed.

  • Book chapter
    Jochen Fröhlich, Stefan Odenbach, Konrad Vogeler: Strömungstechnische Tagung 2014 - Tagung anlässlich des 100. Geburtstags von Werner Albring, Dresden: TUDpress, 2014, 978-3-944331-78-2
  • Poster
    Strömungstechnische Tagung 2014, 10.10.2014, Dresden, Deuschland

Permalink: https://www.hzdr.de/publications/Publ-21076
Publ.-Id: 21076


X-ray structure of 2-(diphenylphosphano)phenyl-4-(hydroxymethyl)benzoate

Mamat, C.; Flemming, A.; Köckerling, M.

The title compound, C26H21O3P, was obtained as by-product due to the hydrolysis of the desired tosylated compound. The dihedral angles between the three aromatic rings attached to the P atom lie in the range 78.1 (1)–87.6 (1) . The hydroxymethyl group is disordered between two conformations in a 0.719 (9):0.281 (9) ratio. The hydroxy H atom is not involved in intermolecular interactions, while the hydroxy O atom serves as a donor for weak C-H...O hydrogen bonds, which link the molecules into chains propagating in [011].

Keywords: crystal structure; benzoate functionalized 2-(di­phenyl­phosphano)phenol derivative; hydrogen bonding

Permalink: https://www.hzdr.de/publications/Publ-21075
Publ.-Id: 21075


Experimental investigation of the influence of column scale, gas density and liquid properties on gas holdup in bubble columns

Rollbusch, P.; Becker, M.; Ludwig, M.; Bieberle, A.; Grünewald, M.; Hampel, U.; Franke, R.

Measurements of gas holdups in bubble columns of 0.16, 0.30 and 0.33 m diameter were carried out. These columns were operated in concurrent flow of gas and liquid phases and in semibatch mode. The column of 0.33 m diameter was operated at elevated pressures of up to 3.6 MPa. Nitrogen was employed as the gas phase and deionized water, aqueous solutions of ethanol and acetone and pure acetone and cumene as the liquid phase. The effects of differing liquid properties, gas density (due to elevated pressure), temperature, column diameter and superficial liquid velocity on gas holdup were studied. The gas holdup measurements were utilized by differential pressure measurements at different positions along the height of the bubble columns which allowed for the identification of axial gas holdup profiles. A decrease of gas holdup with increasing column diameter and an increase of gas holdup with increasing pressure was observed. The effect of a slightly decreasing gas holdup with increasing liquid velocity was found to be existent at smaller column diameters. The use of organic solvents as the liquid phase resulted in a significant increase in gas holdup compared to deionized water. It is found that published gas holdup models are mostly unable to predict the results obtained in this study.

Keywords: multiphase flow; bubble column; scale-up; gas density; organic solvents; coalescence

Permalink: https://www.hzdr.de/publications/Publ-21074
Publ.-Id: 21074


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

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

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

Keywords: Magnetic body force; Vortical flow; Metal matrix composite

  • Magnetohydrodynamics 51(2015)3, 419-424

Permalink: https://www.hzdr.de/publications/Publ-21073
Publ.-Id: 21073


Exploiting the material-specific current-voltage-pressure relationship of the reactive magnetron discharge for the growth of transparent conductive (Al,Ga):ZnO and Nb:TiO2

Cornelius, S.; Vinnichenko, M.; Möller, W.

Reactive magnetron sputtering is an attractive technique for the fabrication of transparent conductive oxide thin films, due to several advantages compared to other PVD methods. These include the scalability to large substrate areas and the use of cost efficient metallic alloy targets as well as
(pulsed) DC technology for plasma excitation. Besides these technological benefits reactive magnetron sputtering (MS) inherently offers great flexibility for the control of the film stoichiometry. In particular for transparent conductive oxide (TCO) materials, the precise control of the oxygen deficiency of the layers is of utmost importance to achieve the desired electrical and optical properties.
The present work demonstrates that the material-specific shape of the current-voltage-pressure relationship of the reactive magnetron discharge may be used to tailor the electrical and optical properties of transpar-ent conductors by controlling the metal to oxygen flux ratio towards the growing film. It is shown that two groups of metals with distinctly different reactive behavior in Ar/O2 magnetron plasmas exist. Consequently, the reactive process control must be adapted in a material-specific way in order to stabilize the reactive discharge in the transition mode. This enables both control of oxygen deficiency as well as high film growth rates. In contrast to conventional reactive MS operation schemes like optical plasma emission to oxygen flow feedback, in this work an alternative technique is explained which allows controlling the oxygen partial pressure without changing the oxygen gas flow. The effect is based on the interplay of changes in secondary electron emission and sputter yield at the (partially) oxidized sputter target surface in conjunction with the internal reactive gas gettering effect of the MS setup itself.
Model experiments for the reactive magnetron sputter deposition of transparent conductive (Al,Ga) doped ZnO and Nb doped TiO2 layers are presented in detail. The effect of oxygen deficiency induced by exploiting the current-voltage-pressure relationship on the electrical and optical film properties will be discussed. The results demonstrate that the proposed method of reactive MS control is suitable to prepare high quality transparent conductive oxide thin films. Crucial parameters for TCO performance like free electron mobility and dopant activation are found to be highly dependent on oxygen to metal flux ratio during growth.

Keywords: physical vapor deposition; reactive magnetron sputtering; transparent conductive oxide; ZnO; TiO2

  • Poster
    5th International Symposium on Transparent Conductive Materials, 12.-17.10.2014, Chania, Crete, Greece
  • Poster
    14th International Conference on Plasma Surface Engineering, 15.-19.09.2014, Garmisch-Partenkirchen, Germany

Permalink: https://www.hzdr.de/publications/Publ-21072
Publ.-Id: 21072


Interplay of phase formation, oxygen deficiency, dopant activation and charge transport in Nb doped TiO2 prepared by reactive pulsed magnetron sputtering

Cornelius, S.; Vinnichenko, M.; Möller, W.; Potzger, K.

Intense research on TiO2 as a transparent conductor material was triggered less than ten years ago by a series of breakthrough publications demonstrating a combination of resistivity below
5x10-4 Ωcm and average visible transmittance above 80% for Nb doped anatase phase TiO2 thin films [1]. Scientific as well as commercial interest in transparent conducting TiO2 is further driven by the prospective additional functionality and low production costs due to the exceptionally high refractive index, the chemical inertness and the very high abundance of TiO2 compared to the conventional transparent conductive oxides (TCOs). Early experiments were focused on pulsed laser deposition (PLD) on single crystalline substrates resulting in record free electron mobilities of up to ~25 cm²/Vs in epitaxial anatase layers [1,2]. However, neither the PLD technique nor epitaxial substrates are suitable for typical large area TCO applications. Consequently, the investigations were extended to magnetron sputter (MS) deposition and low-cost glass substrates. Here, the main focus was put on radio-frequency MS [3] and more recently on direct current MS [4] using (electrically conductive) oxygen deficient ceramic sputter targets. After initial reports on poor electron mobilities of ~1cm²/Vs in sputtered TiO2 films directly grown onto heated amorphous (glass) sub-strates, it was soon realized that controlling the crystallization from the amorphous state, the suppression of the rutile phase formation and the extrinsic doping level in conjunction with the oxygen deficiency are crucial to obtain high quality TiO2 based TCO layers. However, there are several drawbacks associated with sputtering from ceramic targets such as limited variability of the oxygen deficiency, low growth rates and higher material costs compared to metallic targets.
Therefore, this contribution is aimed at understanding the influence of the oxygen deficiency and the phase composition on the electrical and optical film properties of Nb:TiO2 prepared by pulsed direct current MS of TiNb alloy targets in Ar/O2 atmosphere. For this purpose, three routes for film preparation, including direct growth at elevated substrate temperatures, post deposition annealing of amorphous layers and epitaxial growth on SrTiO3(100), are investigated. A non-conventional process stabilization method based on the material specific current-voltage-pressure characteristics of the reactive MS discharge is employed to obtain high growth rates as well as precisely tunable oxygen partial pressures in the so-called transition mode. This approach enables the investigation of the effect of the oxygen deficiency on the crystallization of amorphous films during annealing, the Nb dopant activation (Rutherford Backscattering), the phase composition (X-ray diffraction), the charge transport (Hall Effect) and the optical properties of the Nb:TiO2 films. Using spectroscopic ellipsometry together with spectral photometry, an optical model of the dielectric function of Nb:TiO2 with different crystalline structure and conductivity is established. Moreover, charge transport in degenerately doped anatase TiO2 films will be discussed in the framework of a unified charge transport model including optical phonon scattering, ionized impurity scattering and grain boundary effects. Implications for the maximum achievable electron mobility in polycrystalline anatase TiO2 films are derived from a comparison of transport data of epitaxial and polycrystalline thin films, revealing the crucial role of the highly anisotropic effective electron mass.

Keywords: physical vapor deposition; reactive magnetron sputtering; transparent conductive oxide; TiO2; charge transport; charge carrier mobility

  • Lecture (Conference)
    5th International Symposium on Transparent Conductive Materials, 12.-17.10.2014, Chania, Crete, Greece
  • Poster
    TCO 2014 - Transparent Conductive Oxides - Fundamentals and Applications, 29.09.-02.10.2014, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-21071
Publ.-Id: 21071


Limits to charge transport and electrical dopant activation in transparent conductive (Al,Ga):ZnO prepared by reactive pulsed magnetron sputtering

Cornelius, S.; Vinnichenko, M.; Möller, W.; Munnik, F.

Degenerately doped ZnO is a highly promising material for applications as transparent electrode (TE) in a variety of modern opto-electronic applications. All of them have in common that the TE material should be highly conductive and transparent at the same time. However, both properties cannot be improved simultaneously due to the optical absorption caused by the free charge carriers. Therefore, a well accepted strategy of materials design is the improvement of the free electron mobility resulting in both decreased resisitivity and enhanced near-infrared transmittance. The present work discusses the limitations to the charge carrier mobility in Al and Ga doped ZnO thin films prepared by reactive magnetron sputtering.
The dominant scattering mechanisms are identified by comparison of experimental data to different charge transport models. A systematic study covering a wide range of dopant concentrations and deposition conditions allows to estimate a material limit for the minimum resisitivity of transparent conductive zinc oxide. It is shown that this limit may be reached by a proper choice of depositions conditions during reactive magnetron sputtering – demonstrating the potential of the method for practical applications. Further, it is shown that electron scattering caused by the incorporation of the Al and Ga dopant into the ZnO host lattice is one of the main limitations for the electron mobility.
Therefore, the effective dopant activation in ZnO is quantified by a combination of electrical, optical and ion-beam analysis characterization methods. Possible mechanisms leading to the deactivation of the dopant at high growth temperatures are discussed. It is demonstrated that Ga is a more efficient electron donor than Al, confirming theoretical predictions on the point defect formation energetics in ZnO.

Keywords: physical vapor deposition; reactive magnetron sputtering; transparent conductive oxide; ZnO; charge transport; charge carrier mobility

  • Lecture (Conference)
    14th International Conference on Plasma Surface Engineering, 15.-19.09.2014, Garmisch-Partenkirchen, Germany

Permalink: https://www.hzdr.de/publications/Publ-21069
Publ.-Id: 21069


Speciation studies of uranyl(VI) using combined theoretical and luminescence spectroscopic methods

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

Continuous wave luminescence spectra of uranyl(VI) hydrolysis were analyzed using parallel factor analysis (PARAFAC). Distribution patterns of five major species were thereby derived under a fixed uranyl concentration (10-5 M) over a wide pH range from 2 to 11. UV (180 nm to 370 nm) excitation spectra were extracted for individual species. Time-dependent density functional theory (TD-DFT) calculations revealed ligand excitation (water, hydroxo, oxo) in this region and ligand-to-metal charge transfer responsible for luminescence. Thus excitation in the UV is extreme ligand sensitive and highly specific.

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

Permalink: https://www.hzdr.de/publications/Publ-21067
Publ.-Id: 21067


Risk management in companies - a questionnaire as an instrument for analysing the the present situation

Stiller, D.; Joehnk, P.

The topic risk management receives new impulses in the context of the financial and economic crisis in the years 2007 until 2011 as well as the question whether companies took consequences. The article briefly describes the importance of risk management and then explained the theoretical principles of empirical methods. Excerpts from developed questionnaire will be presented.

Keywords: Industrial management; risk management; ermirical research; qualitative and quantitative survey

  • Open Access Logo Contribution to proceedings
    International Doctoral Seminar 2014, 19.-21.05.2014, Zielona Gora, Poland
    Research Papers Faculty of Materials Science and Technology in Trnava, Vol. 22, 83-88
  • Lecture (Conference)
    International Doctoral Seminar 2014, 19.-21.05.2014, Zielona Gora, Poland

Permalink: https://www.hzdr.de/publications/Publ-21065
Publ.-Id: 21065


Abundance of live 244Pu in deep-sea reservoirs on Earth points to rarity of actinide nucleosynthesis

Wallner, A.; Faestermann, T.; Feige, J.; Feldstein, C.; Knie, K.; Korschinek, G.; Kutschera, W.; Ofan, A.; Paul, M.; Quinto, F.; Rugel, G.; Steier, P.

Half of the heavy elements including all actinides are produced in r-process nucleosynthesis, whose sites and history remain a mystery. If continuously produced, the Interstellar Medium is expected to build up a quasi-steady state of abundances of short-lived nuclides (with half-lives ≤100My), including actinides produced in r-process nucleosynthesis. Their existence in today’s Interstellar Medium would serve as a radioactive clock and would establish that their production was recent. In particular 244Pu, a radioactive actinide nuclide (81My half-life), can place strong constraints on recent r-process frequency and production yield. Here we report the detection of live interstellar 244Pu, archived in Earth’s deep-sea floor during the last 25My, at abundances lower than expected from continuous production in the Galaxy by about two orders of magnitude. This large discrepancy may signal a rarity of actinide r-process nucleosynthesis sites, compatible with neutron-star mergers or with a small subset of actinide-producing supernovae.

Permalink: https://www.hzdr.de/publications/Publ-21064
Publ.-Id: 21064


Coherent and nonlinear terahertz spectroscopy of low-dimensional semiconductors with a free-electron laser

Schneider, H.

This talk reviews recent experimental studies carried out using the mid-infrared and terahertz (THz) free-electron laser (FEL) facility FELBE in Dresden, Germany. Its intense, nearly transform-limited picosecond pulses, which can also be combined with synchronous pico- or femtosecond pulses from near-infared tabletop lasers, provide unique research opportunities to advance our knowledge on the interaction of mid-infrared and THz fields with materials and devices.

Keywords: terahertz spectroscopy; free-electron laser

  • Invited lecture (Conferences)
    7th International Symposium on Ultrafast Phenomena and Terahertz Waves (ISUPTW 2014), 13.-14.10.2014, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-21063
Publ.-Id: 21063


Dark current mechanism of terahertz quantum-well photodetectors

Jia, J. Y.; Gao, J. H.; Hao, M. R.; Wang, T. M.; Shen, W. Z.; Zhang, Y. H.; Cao, J. C.; Guo, X. G.; Schneider, H.

Dark current mechanisms of terahertz quantum-well photodetectors (THz QWPs) are systematically investigated experimentally and theoretically by measuring two newly designed structures combined with samples reported previously. In contrast to previous investigations, scattering-assisted tunneling dark current is found to cause significant contributions to total dark current. A criterion is also proposed to determine the major dark current mechanism at different peak response frequencies. We further determine background limited performance (BLIP) temperatures, which decrease both experimentally and theoretically as the electric field increases. This work gives good description of dark current mechanism for QWPs in the THz region and is extended to determine the transition fields and BLIP temperatures with response peaks from 3 to 12 THz.

Keywords: terahertz quantum-well photodetector; dark current; GaAs/AlGaAs

Permalink: https://www.hzdr.de/publications/Publ-21062
Publ.-Id: 21062


A route toward the development of 3D magnetic scaffolds with tailored mechanical and morphological properties for hard tissue regeneration: preliminary study

de Santis, R.; Gloria, A.; Russo, T.; D'Amora, U.; Zeppetelli, S.; Tampieri, A.; Herrmannsdörfer, T.; Ambrosio, L.

A basic approach toward the design of three-dimensional (3D) rapid prototyped magnetic scaffolds for hard-tissue regeneration has been proposed. In particular, 3D scaffolds consisting of a poly(ε-caprolactone) (PCL) matrix and iron oxide (Fe3O4) or iron-doped hydroxyapatite (FeHA) nanoparticles were fabricated through a 3D fibre deposition technique. As a first approach, a polymer to nanoparticle weight ratio of 90/10 (wt/wt) was used. The effect of the inclusion of both kinds of nanoparticles on the mechanical, magnetic, and biological performances of the scaffolds was studied. The inclusion of Fe3O4 and FeHA nanoparticles generally improves the modulus and the yield stress of the fibres if compared to those of neat PCL, as well as the modulus of the scaffolds. Micro-computed tomography has confirmed the possibility to design morphologically-controlled structures with a fully interconnected pore network. Magnetisation analyses performed at 37°C have highlighted M-H curves that are not hysteretic; values of saturation magnetisation (Ms) of about 3.9 emu/g and 0.2 emu/g have been evaluated for PCL/Fe3O4 and PCL/FeHA scaffolds, respectively. Furthermore, results from confocal laser scanning microscopy (CLSM) carried out on cell-scaffold constructs have evidenced that human mesenchymal stem cells (hMSCs) better adhered and were well spread on the PCL/Fe3O4 and PCL/FeHA nanocomposite scaffolds in comparison with the PCL structures.

Permalink: https://www.hzdr.de/publications/Publ-21061
Publ.-Id: 21061


Sample preparation of cosmogenic nuclides apart from C-14

Merchel, S.

invited talk - no abstract

Keywords: AMS; sample preparation

  • Invited lecture (Conferences)
    Cosmogenic nuclide dating workshop at the 14C Dating Centre, 06.11.2014, Aarhus, Danmark

Permalink: https://www.hzdr.de/publications/Publ-21060
Publ.-Id: 21060


A basic approach toward the development of nanocomposite magnetic scaffolds for advanced bone tissue engineering

de Santis, R.; Gloria, A.; Russo, T.; D'Amora, U.; Zeppetelli, S.; Dionigi, C.; Sytcheva, A.; Herrmannsdörfer, T.; Dediu, V.; Ambrosio, L.

Magnetic scaffolds for bone tissue engineering based on a poly(e-caprolactone) (PCL) matrix and iron oxide (Fe3O4) magnetic nanoparticles were designed and developed through a three-dimensional (3D) fiber-deposition technique. PCL/Fe3O4 scaffolds were characterized by a 90/10 w/w composition. Tensile and magnetic measurements were carried out, and nondestructive 3D Imaging was performed through microcomputed tomography (Micro-CT). Furthermore, confocal analysis was undertaken to investigate human mesenchymal stem cell adhesion and spreading on the PCL/Fe3O4 nanocomposite fibers. The results suggest that nanoparticles mechanically reinforced the PCL matrix; the elastic modulus and the maximum stress increased about 10 and 30%, respectively. However, the maximum strain decreased about 50%; this suggested an enhanced brittleness. Magnetic results evidenced a superparamagnetic behavior for these nanocomposite scaffolds. Micro-CT suggested an almost uniform distribution of nanoparticles. Confocal Analysis highlighted interesting results in terms of cell adhesion and spreading. All of these results show that a magnetic feature could be incorporated into a polymeric Matrix that could be processed to manufacture scaffolds for advanced bone tissue engineering and, thus, provide new opportunity in terms of scaffold fixation and functionalization.

Permalink: https://www.hzdr.de/publications/Publ-21059
Publ.-Id: 21059


Nuklearchemie Forschung & Perspektiven

Fachgruppe Nuklearchemie in der Gesellschaft Deutscher Chemiker; Merchel, S.; Steinbach, J.

Die Fachgruppe Nuklearchemie in der Gesellschaft Deutscher Chemiker repräsentiert die Wissenschaftler* und Ingenieure, die bei ihren Arbeiten mit radioaktiven Stoffen und ionisierender Strahlung umgehen und diese für Zwecke der Forschung, Industrie, Medizin und Lehre nutzen.
Die Tätigkeiten ihrer Mitglieder reichen von den rein grundlagenwissenschaftlichen Gebieten der Chemie radioaktiver Stoffe, wie den schwersten synthetischen Elementen über nuklearchemische Aspekte der Kernenergienutzung bis hin zur Verwendung von Radionukliden in den Lebens und Umweltwissenschaften. Die Nuklearchemie umfasst die Bereiche der Kern-, Radio- und Strahlenchemie.
In ihrer mehr als 100-jährigen Geschichte, die mit der Entdeckung der Radioaktivität und der Radioelemente, hat die Nuklearchemie mit bahnbrechenden Entdeckungen, mit der Einführung bedeutender neuer Arbeitsmethoden und mit einer Vielzahl von innovativen wissenschaftlichen und technischen Anwendungen die Entwicklung der modernen Industriegesellschaft beeinflusst. In der öffentlichen Wahrnehmung werden jedoch nuklearchemische Arbeiten überwiegend der nuklearen Energiegewinnung und dem nuklearen Brennstoffkreislauf zugeordnet – Themen, die in der Öffentlichkeit sehr kontrovers diskutiert werden. Diese Bereiche stellen nach wie vor bedeutende Themen für die Nuklearchemie dar.
Entsprechend der vielfältigen Möglichkeiten und der Fortentwicklung von Wissenschaft und Technik haben sich aber seit langem weitere Schwerpunkte herausgebildet, die ebenfalls von großer grundlegender, gesellschaftlicher, ökologischer und ökonomischer Relevanz sind. Nuklearchemische Therapie- und Diagnoseverfahren sind beispielsweise aus den Lebenswissenschaften und der Medizin nicht mehr wegzudenken. Nuklearchemiker untersuchen die Elementsynthese in Sternen, sie erforschen die Struktur von Atomkernen, erzeugen die schwersten Elemente jenseits des Urans, die alle radioaktiv sind, und untersuchen deren chemische und physikalische Eigenschaften.
Sie treibt unter anderem die Suche nach dem Verständnis an, was die Materie im Innersten zusammenhält.
Das breite Spektrum nuklearchemischer Methoden macht deren Einsatz auch für ganz andere Sparten interessant: Auch in der Geologie, der Hydrologie, der Umweltforschung,
dem Strahlenschutz oder der nuklearen Forensik kommt man nicht ohne das Handwerkszeug der Nuklearchemie aus.
Die vorliegende Broschüre soll einen Einblick in die vielfältigen Themen und Arbeitsfelder nuklearchemischer Forschung und Anwendung geben, die in den folgenden
Schwerpunkten zusammengefasst werden können:
-Grundlagenforschung
-Chemie der schwersten Elemente
-Actinidenchemie
-Kosmochemie
-Radioanalytik
-Gesundheit und Umwelt
-Nuklearchemie in den Lebenswissenschaften (Radiopharmazie)
-Isotopengeochemie
-Strahlenschutz und Radioökologie
-Nukleare Forensik
-Energie
-Partitioning & Transmutation
-Endlagerforschung
-Reaktorchemie
-Tritiumchemie
-Lehre, Ausbildung und Kompetenzerhalt

Keywords: fundamental research; heavy elements; actinides; cosmochemistry; radioanalytics; health; environment; nuclear chemistry; life sciences; radiopharmacy; geochemistry; isotopes; radioecology; radiation safety; nuclear forensics; energy; partitioning; transmutation; nuclear waste disposal; nuclear reactor; tritium

  • Other report
    Frankfurt am Main: Herausgeber: Gesellschaft Deutscher Chemiker e.V. (GDCh), 2015
    25 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21058
Publ.-Id: 21058


The effect of natural and forced melt convection on dendritic solidification in Ga-In alloys

Shevchenko, N.; Roshchupkina, O.; Sokolova, O.; Eckert, S.

The directional solidification of Ga–25wt%In alloys within a Hele-Shaw cell was visualized by means of X-ray radioscopy. The experimental investigations are especially focused on the impact of melt convection on the dendritic growth. Natural convection occurs during a bottom up solidification because lighter solute is rejected at the solid-liquid interface leading to an unstable density stratification. Forced convection was produced by a rotating wheel with two parallel disks containing at their inner sides a set of permanent NdFeB magnets with alternating polarization. The direction of forced melt flow is almost horizontal at the solidification front whereas local flow velocities in the range between 0.1 and 1.0 mm/s were achieved by controlling the rotation speed of the magnetic wheel. Melt flow induces various effects on the grain morphology primarily caused by the convective transport of solute. Our observations show a facilitation of the growth of primary trunks or lateral branches, suppression of side branching, dendrite remelting and fragmentation. The manifestation of all phenomena depends on the dendrite orientation, local direction and intensity of the flow. The forced flow eliminates the solutal plumes and damps the local fluctuations of solute concentration. It provokes a preferential growth of the secondary arms at the upstream side of the primary dendrite arms, whereas the high solute concentration at the downstream side of the dendrites can inhibit the formation of secondary branches completely. Moreover, the flow changes the inclination angle of the dendrites and the angle between primary trunks and secondary arms.

Keywords: X-ray radioscopy; in situ studies; melt convection; directional solidification; forced convection; dendritic growth

Permalink: https://www.hzdr.de/publications/Publ-21057
Publ.-Id: 21057


Partialoxidation von Isobutan

Willms, T.

Im Rahmen des Helmholtz-Energy-Allianz-Projektes „Energieeffiziente chemische Mehrphasenprozesse“ wird das Potential der Energieeffizienzverbesserung der partiellen Oxidation von Isobutan mit Sauerstoff bzw. Luft zu tert.-Butylhydroperoxid (TBHP) angesichts der Technologie mikrostrukturierter Reaktoren evaluiert. Zur Untersuchung der Zusammensetzung des Reaktionsgemisches wird eine gaschromatographische Methode entwickelt, die es ermöglicht, die laut Literatur im Reaktionsgemisch oder aus der Zersetzung von TBHP zu erwartenden flüssigen Substanzen (TBHP, di-t-Butylperoxid (DTBP), t-Butanol, Methanol, Azeton, Ameisensäure, Isobutylenoxid, Methylethylketon, Isobutanol) sowie zahlreiche andere Komponenten wie Lösungsmittel (Acetonitril, Hexan, Ethanol, Dioxan, Dekan), potentielle interne Standards (Methyl-t-Butylether) sowie weitere Substanzen (Hexanol, Essigsäure) zu trennen. Des Weiteren können auch die zu erwartenden gasförmigen Substanzen (Sauerstoff, Stickstoff, Isobutan, Kohlenmonoxid, Kohlendioxid, Methan, Isobuten) getrennt werden. Dazu wird eine STABILWAX-Säule verwendet, die mittels eines Switch sowohl mit einer Molsiebsäule als auch mit dem Massenspektrometer (MS) verbunden ist. Im Falle der Trennung von flüssigen Produkten wird das Gas durch einen geeigneten Befehl an den Switch nur ins MS geleitet. Zur Trennung der Gase wird der Gasstrom die ersten paar Minuten über die Molsiebsäule geleitet und die getrennten Permanentgase Stickstoff, Sauerstoff, Kohlenmonoxid und Kohlendioxid) über einen Wärmeleitfähigkeitsdetektor detektiert. Die restlichen Gase werden über die STABILWAX -Säule getrennt und dann mittels des MS detektiert.

In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“ the potential to improve the energy efficiency of the partial oxidation of isobutane by oxygene and air to t-Butyl hydroperoxide in view of the technology of microstructured reactors is evaluated.
To investigate the composition of the reaction mixture a gaschromatographic method has been developed, which is able to separate the substances expected according to literature in the reaction mixture or due to the decomposition of TBHP (TBHP, di-t-Butyl peroxide (DTBP), t-butanol, methanol, acetone, formic acid, Isobutylen oxide, Methylethyl ketone, Isobutanol) as well as numerous other compounds like solvents (acetonitrile, ethanol, dioxane, decane), potential internal standards (Methyl-t-butyl ether) as well as further substances (hexanol, acetic acid). Furthermore, also the expected gaseous substances (oxygen, nitrogen, isobutane, carbon monoxide, methane, carbon dioxide, isobutene) can be separated. To achieve this a STABILWAX column is used, which can be connected either to a mol sieve column or the mass spectrometer. In case of the separation of liquid products, the gas flow will only be separated by the STABILWAX column and conducted to the mass spectrometer by an adequate command to the switch. To separate gases, the gas flow is conducted within the first minutes to the molsieve column and the separated permanent gases (oxygen, nitrogen, isobutane, carbon monoxide, methane) are detected by a thermal conductivity detector. The other gases are detected by the mass spectrometer.

Keywords: gas chromatography; GC-MS; isobutane oxidation; reaction products; t-butyl hydroperoxide

  • Open Access Logo SHIMADZU NEWS 03(2014), 8-9

Permalink: https://www.hzdr.de/publications/Publ-21056
Publ.-Id: 21056


Organotypical vascular model for characterization of radioprotective compounds: Studies on antioxidant 2,3-diaryl-substituted indole-based cyclooxygenase-2 inhibitors

Ullm, S.; Laube, M.; Bechmann, N.; Knieß, T.; Pietzsch, J.

Radiotherapy of various cancers is closely associated with increased cardiovascular morbidity and mortality. Arachidonic acid metabolites are supposed to play a key role in radiation-induced vascular dysfunction. This study was designed to evaluate the effects of novel, antioxidative 2,3-diaryl-substituted indole-based selective cyclooxygenase-2 (COX-2) inhibitors (2,3-diaryl-indole coxibs) on radiation-induced formation of arachidonic acid metabolites via COX-2 and oxidant stress pathways in an organotypical vascular model of rat aortic rings. Acute and subacute effects of X-ray radiation (4 and 10 Gy; 1 and 3 days post irradiation) with or without the presence of 1 µM of the 2,3-diaryl-indole coxib 2-[4-(aminosulfonyl)phenyl]-3-(4-methoxyphenyl)-1H-indole (C1) or celecoxib as reference compared to sham-irradiated controls were assessed. The following parameters were measured: metabolic activity of the aortic rings; induction and regulation of COX-2 expression; release of prostaglandin E2 and F2alpha-isoprostane. Irradiation without presence of coxibs resulted in a dose-dependent augmentation of all parameters studied. When aortic rings were exposed to the 2,3-diaryl-indole coxib 1 h before irradiation, metabolic activity was restored and the release of both prostaglandin and isoprostane was inhibited. The latter indicates a direct interaction with oxidant stress pathways. By contrast, celecoxib exhibited only slight effects on the formation of isoprostane. The reduction of radiation-induced vascular dysfunction by antioxidative coxibs may widen the therapeutic window of COX-2 targeted treatment.

Keywords: Aortic ring model; coxibs; prostanoids; normal tissue damage; radiation therapy; adjuvant radioprotective therapy; cardiovascular disease

  • Clinical Hemorheology and Microcirculation 58(2014), 281-295
    DOI: 10.3233/CH-141902

Permalink: https://www.hzdr.de/publications/Publ-21055
Publ.-Id: 21055


Role of Mn in a Magnetic Semiconductor: InMnP

Khalid, M.; Weschke, E.; Hübner, R.; Baehtz, C.; Skorupa, W.; Helm, M.; Zhou, S.

The manganese induced magnetic, electrical and structural modification in InMnP epilayers, prepared by Mn ion implantation and pulsed laser annealing, are investigated in the following work. All samples exhibit clear hysteresis loops and strong spin polarization at the Fermi level. The degree of magnetization, the Curie temperature and the spin polarization depend on the Mn concentration. The bright-field transmission electron micrographs show that InP samples become almost amorphous after Mn implantation but recrystallize after pulsed laser annealing. We did not observe an insulator-metal transition in InMnP up to a Mn concentration of 5 at.%. Instead all InMnP samples show insulating characteristics up to the lowest measured temperature. Magneotresistance results obtained at low temperatures support the hopping conduction mechanism in InMnP. We find that the Mn impurity band remains detached from the valence band in InMnP up to 5 at.% Mn doping. Our findings indicate that the local environment of Mn ions in InP is similar to GaMnAs, GaMnP and InMnAs, however, the electrical properties of these Mn implanted III-V compounds are different. This is one of the consequences of the different Mn binding energy in these compounds.

Keywords: III-V magnetic semiconductors

  • Poster
    Moscow International Symposium on Magnetism MISM-2014, 29.06.-03.07.2014, Moscow, Russia

Permalink: https://www.hzdr.de/publications/Publ-21054
Publ.-Id: 21054


Extremely High Energy Density Deposition by Heavy Polyatomic Ion Impacts – Surface Nanopatterning and Frozen Phase Diagram Pathways

Böttger, R.; Heinig, K.-H.; Bischoff, L.; Anders, C.; Urbassek, H. M.; Hübner, R.; Liedke, B.

Bi and Au ions of a few tens of keV deposit a high energy density into the collision cascade volume of due to (i) their high mass and (ii) their low projected range. At higher energies, this density becomes diluted as the cascade volume increases super-linearly with ion energy.
Compared to monatomic ions, polyatomic ions deposit a much higher energy density. This is sufficient to form a pool of a localized, almost classical melt in a semiconductor surface lasting up to half of a nanosecond. Local melting and resolidification by single polyatomic ion impacts is proven by molecular dynamics calculations.
Well-ordered, self-organized dot patterns on Si and Ge surfaces have been found after heavy polyatomic ion irradiation, which can be attributed to the impact-induced local transient melting. The kinetics of localized melt pools leads to a generic, Bradley-Harper-type partial differential equation for the surface evolution. Whereas so far the mechanisms of ion-induced surface pattern evolution are assumed to be surface curvature dependent ion erosion or ion-momentum-induced mass drift of surface atoms, for heavy polyatomic ions we have identified a completely different mechanism.
The local melting and quenching process is so far from equilibrium that particularities of phase diagrams like the Bi state in Si or Ge are frozen into the nanostructure of the resolidified volume. This opens the possibility to study extremely fast solid-liquid phase transitions.

Keywords: self-organization; nanopatterning; polyatomic ions; energy deposition

  • Lecture (Conference)
    Workshop Ionenstrahlen & Nanostrukturen, 20.-22.07.2014, Paderborn, Deutschland
  • Lecture (Conference)
    19th International Conference on Ion Beam Modification of Materials, 14.-19.09.2014, Leuven, Belgium

Permalink: https://www.hzdr.de/publications/Publ-21053
Publ.-Id: 21053


Experimente mit schnellen Neutronen an der Flugzeit-Anlage nELBE

Beyer, R.

Beschreibung der verschiedenen bisher an der Neutronen-Flugzeit-Anlage nELBE durchgeführten Experimente.

Keywords: nELBE; neutron time-of-flight; transmission; inelastic scattering; fission

  • Invited lecture (Conferences)
    Fachbereichsseminar, 19.09.2014, Braunschweig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21052
Publ.-Id: 21052


Frequency-Domain Magnetic Resonance—Alternative Detection Schemes for Samples at the Nanoscale

Möller, M.; Lenz, K.; Lindner, J.

Magnetic Resonance in the frequency domain provides a tool to investigate and quantitatively measure many important magnetic key parameters, such like the effective magnetization, magnetic anisotropies, magnetic damping parameters or coupling field strengths. Although it has been widely employed for studying magnetic bulk and thin film samples, the sensitivity of this classical method often suffers from being too low when single nanostructures are of interest. This review discusses Magnetic Resonance as technique, providing an introduction also to non-experts in the field. The theoretical background is discussed on an ‘easy to read’ basis, followed by a brief summary of methods that are capable of investigation spin dynamics within single nanostructures (nearfield microscopy, Brillouin Light Scattering, time-resolved Magneto-optical Kerr-effect). Focusing on frequency-domain approaches we then give a detailed explanation of what we call conventional way of experimentally detecting Magnetic Resonance which is based on the use of microwave cavities. This serves a basis to discuss different approaches to enhance sensitivity within a frequency-domain Magnetic Resonance experiment. As shown this includes either improving the conventional setup itself (microresonators) or using alternative detection routes, such as optical or electrical detection.

Keywords: FMR; ferromagnetic resonance; Kerr effect; MOKE; Microresonators; Magnetism; Magnetic nanostructures

Permalink: https://www.hzdr.de/publications/Publ-21051
Publ.-Id: 21051


Magnetic Bioinspired Hybrid Nanostructured Collagen - Hydroxyapatite Scaffolds Supporting Cell Proliferation and Tuning Regenerative Process

Tampieri, A.; Iafisco, M.; Sandri, M.; Panseri, S.; Cunha, C.; Sprio, S.; Savini, E.; Uhlarz, M.; Herrmannsdörfer, T.

A bioinspired mineralization process was applied to develop biomirnetic hybrid scaffolds made of (Fe2+/Fe3+)-doped hydroxyapatite nanocrystals nucleated on self-assembling collagen fibers and endowed with super-paramagnetic properties, minimizing the formation of potentially cytotoidc magnetic phases such as magnetite or other iron oxide phases. Magnetic composites were prepared at different temperatures, and the effect of this parameter on the reaction yield in terms of mineralization degree, morphology, degradation, and magnetization was investigated. The influence of scaffold properties on cells was evaluated by seeding human osteoblast-like cells on magnetic and nonmagnetic materials, and differences in terms of viability, adhesion, and proliferation were studied. The synthesis temperature affects mainly the chemical-physical features of the mineral phase of the composites influencing the degradation, the microstructure, and the magnetization values of the entire scaffold and its biological performance. In vitro investigations indicated the biocompatibility of the materials and that the magnetization of the super-paramagnetic scaffolds, induced applying an external static magnetic field, improved cell proliferation in comparison to the nonmagnetic scaffold.

Permalink: https://www.hzdr.de/publications/Publ-21050
Publ.-Id: 21050


Quantitative molecular plating of large-area 242Pu Targets with improved layer properties

Vascon, A.; Runke, J.; Trautmann, N.; Cremer, B.; Eberhardt, K.; Düllmann, C. E.

For measurements of the neutron-induced fission cross section of 242Pu, large-area (42 cm2) 242Pu targets were prepared on Ti-coated Si wafers by means of constant current density molecular plating. Radiochemical separations were performed prior to the platings. Quantitative deposition yields (495%) were determined for all targets by means of alpha-particle spectroscopy. Layer densities in the range of 100–150 μg/cm2 were obtained. The homogeneity of the targets was studied by radiographic imaging.
A comparative study between the quality of the layers produced on the Ti-coated Si wafers and the quality of layers grown on normal Ti foils was carried out by applying scanning electron microscopy and energy dispersive X-ray spectroscopy. Ti-coated Si wafers resulted clearly superior to Ti foils in the production of homogeneous 242Pu layers with minimum defectivity.

Keywords: 242Pu Large-area targets; Molecular plating; Quantitative deposition yield

Permalink: https://www.hzdr.de/publications/Publ-21049
Publ.-Id: 21049


Thermal properties of point defects and their clusters in bcc Fe

Devaraj, M.; Posselt, M.; Schiwarth, M.

Ferritic Fe and Fe-Cr alloys are basic structural materials of present and future nuclear fission and fusion reactors. The formation of the micro- and nanostructure of these alloys and the structural evolution under irradiation is essentially influenced by the interaction between solutes, vacancies and self-interstitials. These processes take place in different alloys such as reactor-pressure-vessel and oxide-dispersion-strengthened steels. The understanding of the nanostructure of those materials and of its radiation-induced evolution is indispensable for nuclear reactor safety. First-principle calculations based on the Density Functional Theory (DFT) are a very useful method to get atomistic insights into the interactions between solutes, vacancies and self-interstitials in bcc Fe. Traditionally, formation and binding energies of these species are investigated at T=0 and these data are further used in calculations on larger length and time scales such as in kinetic Monte Carlo simulations and Rate Theory.
The main objective of present work is the determination of the temperature-dependent free formation and binding energy of selected point defects and their clusters in bcc Fe. For this purpose DFT is used to obtain the corresponding vibrational free energies within the framework of the harmonic approximation. The substitutional solutes Cu, Y and Ti, the interstitial solute atom O, the vacancy as well as small clusters consisting of solute atoms and vacancies are considered. The results are compared with theoretical data obtained by other authors and discussed in relation to experimental solubility data. It is found that the free energies show a significant dependence on temperature. This must be taken into account in multiscale simulations that use DFT input data.

Keywords: point defects; nanoclusters; bcc-Fe; free energy; temperature dependence; Density Functional Theory

  • Lecture (Conference)
    7th International Conference on Multiscale Materials Modeling (MMM 2014), 06.-10.10.2014, Berkeley, USA

Permalink: https://www.hzdr.de/publications/Publ-21048
Publ.-Id: 21048


Establishing the Fundamental Magnetic Interactions in the Chiral Skyrmionic Mott Insulator Cu2OSeO3 by Terahertz Electron Spin Resonance

Ozerov, M.; Romhanyi, J.; Belesi, M.; Berger, H.; Ansermet, J. P.; van den Brink, J.; Wosnitza, J.; Zvyagin, S. A.; Rousochatzakis, I.

The recent discovery of Skyrmionics in Cu2OSeO3 has established a new platform to create and manipulate Skyrmionic spin textures. We use high-field electron spin resonance with a terahertz free-electron laser and pulsed magnetic fields up to 64 T to probe and quantify its microscopic spin-spin interactions. In addition to the previously observed long-wavelength Goldstone mode, this technique probes also the high-energy part of the excitation spectrum which is inaccessible by standard low-frequency electron spin resonance. Fitting the behavior of the observed modes in magnetic field to a theoretical framework establishes experimentally that the fundamental magnetic building blocks of this Skyrmionic magnet are rigid, highly entangled and weakly coupled tetrahedra.

Permalink: https://www.hzdr.de/publications/Publ-21047
Publ.-Id: 21047


Solid phase recrystallization of Si nanowires

Posselt, M.; Liedke, B.; Baldauf, S.

Advanced Si and Ge nanowire transistors can be produced by top-down or bottom-up approaches. In order to obtain the desired electrical properties doping of the nanowires is required. Ion implantation is one of the favored methods to introduce dopant atoms in a controlled manner. If relatively high ion fluences are needed the originally single-crystalline nanowire is amorphized. Subsequently, thermal processing must be used to restore the Si or Ge crystal and to activate the dopants electrically. In planar structures a complete restoration can be achieved by solid-phase epitaxial recrystallization, whereas more complex processes take place in nanowires, due to the significant influence of surfaces and interfaces. In order to understand the solid-phase recrystallization in such confined systems molecular dynamics simulations are performed. Partially amorphized nanowires embedded in a matrix as well as free nanowires and nanopillars are considered. In dependence on whether embedded or free nanowires are investigated several phenomena are observed, such as stacking fault and twin formation, random nucleation of separate crystalline grains, as well as edge rounding and necking. The simulation results are in qualitative agreement with experimental findings.

Keywords: Solid phase recrystallization; Si nanowires; Molecular dynamics simulation

  • Poster
    7th International Conference on Multiscale Materials Modeling (MMM 2014), 06.-10.10.2014, Berkeley, USA

Permalink: https://www.hzdr.de/publications/Publ-21046
Publ.-Id: 21046


Properties of oxide nanoclusters in ODS ferritic steels: A combined DFT and Monte Carlo simulation study

Devaraj, M.

Not available, please contact the author.

Keywords: oxide nanoclusters; ferritic steels; Density Functional Theory; Monte Carlo simulations

  • Lecture (others)
    Seminarvortrag im Department of Mathematical Sciences, Loughborough University, UK, 02.10.2014, Loughborough, UK

Permalink: https://www.hzdr.de/publications/Publ-21045
Publ.-Id: 21045


Electronic properties of a distorted kagome lattice antiferromagnet Dy3Ru4Al12

Gorbunov, D. I.; Henriques, M. S.; Andreev, A. V.; Gukasov, A.; Petricek, V.; Baranov, N. V.; Skourski, Y.; Eigner, V.; Paukov, M.; Prokleska, J.; Goncalves, A. P.

Electronic properties of Dy3Ru4Al12 (hexagonal crystal structure, Dy atoms form distorted kagome nets) are studied on a single crystal by means of magnetization, neutron diffraction, specific heat, and resistivity measurements. The onset of a long-range magnetic order of Dy moments occurs at 7 K through a first-order phase transition. The compound has a noncollinear antiferromagnetic structure with a propagation vector (1/2 0 1/2). The configuration of the Dy moments is consistent with the monoclinic Shubnikov group Cc2/c. The gamma coefficient in the temperature linear term of the specific heat is strongly enhanced to 500 mJ mol-1 K-2 taking into account the localized nature of Dy magnetism. An additional contribution originates from spin fluctuations induced in the 4d subsystem of Ru by the exchange field acting from the Dy 4f moments. In an applied magnetic field Dy3Ru4Al12 displays magnetization jumps along all crystallographic directions. All the metamagnetic transitions are accompanied by large positive magnetoresistance. The maximum effect (125%-140%) is attained for current along the [100] axis and field along the [120] or [001] axes. The large positive effect is explained by changes in the conduction electron spectra through the jumps as the conduction electrons interact with localized magnetic moments.

Permalink: https://www.hzdr.de/publications/Publ-21044
Publ.-Id: 21044


Temperature and flux dependence of ion-beam mixing in crystalline and amorphous germanium isotope multilayers

Radek, M.; Posselt, M.; Liedke, B.; Schmidt, B.; Bischoff, L.; Prucnal, S.; Bougeard, D.; Bracht, H.

The availability of highly enriched stable isotopes enables the preparation of isotopically controlled semiconductors. By means of crystalline (c-Ge) and preamorphized (a-Ge) germanium isotope multilayer structures we investigated the temperature and flux dependence of ion-beam induced self-atom mixing. Low,intermediate,and high temperature regions with different mixing behavior are identified after Ga implantation at 310 keV and various temperatures. In the first region (0K - 470K) the amount of mixing in c-Ge and a-Ge is very similar, an increasing mixing with increasing temperature is observed. Region 2 (470K - 540K) reveals a strong drop of mixing in c-Ge whereas the mixing in a-Ge still increases with temperature. In region 3 (570K and above) the mixing in a-Ge drops to the level of c-Ge. Within region 2 no significant structural change occurs during implantation suggesting an efficient annealing of the radiation damage. In addition we performed Focused-Ion-Beam (FIB) implantations with 60 keV Si ions into Ge using two different fluxes at two different temperatures. The experimental results indicate that the annealing of radiation damage is not only temperature but also flux dependent.
Molecular dynamics simulations with a Stillinger-Weber type potential are used to study the self-atom mixing observed in the experiment. It is found that the dominant mechanisms of mixing are thermal spikes formed by transferring kinetic energy of the incident ion to the lattice. If the transferred energy is high enough,locally molten regions are created in which the atoms can move more freely compared to the lattice atoms. With increasing temperature the thermal spikes last longer and the mixing increases. This is in accord with the experimentally observed mixing behavior in region 1. Differences between the mixing in a-Ge and c-Ge in region 2 are related to the initial crystal structure. Qualitative agreement is achieved with molecular dynamics simulations.

Keywords: ion-beam mixing; Ge isotope multilayers; temperature and flux dependence

  • Lecture (Conference)
    19th International Conference on Ion Beam Modification of Materials (IBMM 2014), 14.-19.09.2014, Leuven, Belgium

Permalink: https://www.hzdr.de/publications/Publ-21043
Publ.-Id: 21043


Magnetization Reversal of Disorder Induced Ferromagnetic Regions in Fe60Al40 Thin Films

Tahir, N.; Gieniusz, R.; Maziewski, A.; Bali, R.; Kostylev, M. P.; Wintz, S.; Schultheiss, H.; Facsko, S.; Potzger, K.; Lindner, J.; Fassbender, J.

Magnetization reversal processes were investigated in iron-aluminum (Fe60Al40) alloy films of 40 nm thickness by employing magnetometry and magnetic domain imaging using magneto-optical longitudinal and polar effects. The films were initially chemically ordered and weakly ferromagnetic, and a large increase in the saturation magnetization was induced due to disorder magnetization induced by Ne+-ion irradiation. Three different sample geometries were investigated; a) continuous film; b) homogenously irradiated wire; and c) magnetic stripe-patterned wire. Specific magnetization reversal mechanism were identified for the different sample geometries.

Keywords: magnetic patterning; magnetic nanostructures; magneto-optical magnetometry; ions irradiation effects; magnetic domains

Permalink: https://www.hzdr.de/publications/Publ-21042
Publ.-Id: 21042


Quo vadis?: Ion Beam Engineeering and beyond…

Skorupa, W.

There is no doubt that ion beam based research and applications- like all semiconductor-based revolutionary developments of our society- have reached a kind of saturation overlooking the last 60 years when ion implantation started as a child of the early nuclear weapon development. It was the mass separator as a key part of the ion implanter allowing the formation of atomically pure beams. Doping of semiconductor materials with a clear dominance of silicon was the technology driver for the development of ion beam technology. Moreover, the physical and chemical modification of surfaces as well as regions in shallow and deeper regions below the surface of solid materials was the matter of interest for using this efficient tool. At all times, annealing/thermal treatment of ion beam treated materials within different time ranges –from hours down to picoseconds- was a close relative of ion beam engineering. Even flash lamp annealing as one of the annealing methods based on early experiments performed for the simulation of strong optical radiation impact on materials during nuclear weapon attacks. In this talk I will shortly discuss historical and future aspects of ion beam engineering to initiate a discussion on: From nuclear weapons to superchips…, what remains to be done? or, ...what more do people really need? I will extend this lecture to issues that should be of broader interest, but also, to our community!

Keywords: ion beam engineering; flash lamp annealing; ion beam technology

  • Invited lecture (Conferences)
    X-th International Conference Ion Implantation and other Applications of Ions and Electrons, 23.-26.06.2014, , Poland, 23.-26.06.2014, Kazimierz Dolny, Poland

Permalink: https://www.hzdr.de/publications/Publ-21041
Publ.-Id: 21041


Development and Characterization of a tunable ultrafast X-ray source via Inverse Compton Scattering

Jochmann, A.

Ultrashort, nearly monochromatic hard X-ray pulses enrich the understanding of the dynamics and function of matter, e.g., the motion of atomic structures associated with ultrafast phase transitions, structural dynamics and (bio)chemical reactions. Inverse Compton backscattering of intense laser pulses from relativistic electrons not only allows for the generation of bright X-ray pulses which can be used in a pumpprobe experiment, but also for the investigation of the electron beam dynamics at the interaction point.
The focus of this PhD work lies on the detailed understanding of the kinematics during the interaction of the relativistic electron bunch and the laser pulse in order to quantify the influence of various experiment parameters on the emitted X-ray radiation.
The experiment was conducted at the ELBE center for high power radiation sources using the ELBE superconducting linear accelerator and the DRACO Ti:sapphire laser system. The combination of both these state-of-the-art apparatuses guaranteed the control and stability of the interacting beam parameters throughout the measurement.
The emitted X-ray spectra were detected with a pixelated detector of 1024 by 256 elements (each 26μm by 26μm) to achieve an unprecedented spatial and energy resolution for a full characterization of the emitted spectrum to reveal parameter influences and correlations of both interacting beams. In this work the influence of the electron beam energy, electron beam emittance, the laser bandwidth and the energy-anglecorrelation on the spectra of the backscattered X-rays is quantified.
A rigorous statistical analysis comparing experimental data to ab-initio 3D simulations enabled, e.g., the extraction of the angular distribution of electrons with 1.5% accuracy and, in total, provides predictive capability for the future high brightness hard X-ray source PHOENIX (Photon electron collider for Narrow bandwidth Intense X-rays) and potential all optical gamma-ray sources.
The results will serve as a milestone and starting point for the scaling of the Xray flux based on available interaction parameters of an ultrashort bright X-ray source at the ELBE center for high power radiation sources. The knowledge of the spatial and spectral distribution of photons from an inverse Compton scattering source is essential in designing future experiments as well as for tailoring the X-ray spectral properties to an experimental need.

  • Doctoral thesis
    TU Dresden, 2014
    Mentor: Prof. Dr. Roland Sauerbrey
    103 Seiten
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-055 2014
    ISSN: 2191-8708, eISSN: 2191-8716

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Permalink: https://www.hzdr.de/publications/Publ-21040
Publ.-Id: 21040


The development of a compact EBIS with integrated ion optics for FIB applications

Schmidt, M.; Zschornack, G.; Gierak, J.

  • Lecture (Conference)
    Condensed Matter in Paris 2014, CMD 25 – JMC 14, 25.08.2014, Paris, France

Permalink: https://www.hzdr.de/publications/Publ-21039
Publ.-Id: 21039


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