Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33828 Publications

Niedermolekulares Heparin senkt Thromboserisiko bei chemotherapeutisch behandelten Tumorpatienten

Heller, S.; Krause, M.

there ist no abstract

Permalink: https://www.hzdr.de/publications/Publ-19996
Publ.-Id: 19996


Molecular radiation biology/oncology at its best: cutting edge research presented at the 13th International Wolfsberg Meeting on Molecular Radiation Biology/Oncology.

Baumann, M.; Bodis, S.; Dikomey, E.; van der Kogel, A.; Overgaard, J.; Rodemann, H.; Wouters, B.

there ist no abstract

Permalink: https://www.hzdr.de/publications/Publ-19995
Publ.-Id: 19995


Modification of staging and treatment of head and neck cancer by FDG-PET/CT prior to radiotherapy.

Abramyuk, A.; Appold, S.; Zöphel, K.; Baumann, M.; Abolmaali, N.

BACKGROUND AND PURPOSE:
Reliable tumor staging is a fundamental pre-requisite for efficient tumor therapy and further prognosis. The aim of this study was to compare head and neck cancer (HNC) staging before and after FDG-PET/CT, evaluating the stage modifications for radiotherapy (RT) planning.
PATIENTS AND METHODS:
A total of 102 patients with untreated primary HNC, who underwent conventional staging and staging including FDG-PET/CT before RT, were enrolled in this retrospective study. Blinded pre-FDG-PET/CT and post-FDG-PET/CT staging data were compared. The impact on patient management was tested by comparing the intention before and after FDG-PET/CT.
RESULTS:
Significant modifications of T, N, and M stage as well as clinical stage were detected after inclusion of FDG-PET/CT data (p = 0.002, 0.0006, 0.001, 0.03, respectively). Overall, the implementation of FDG-PET/CT led to modification of RT intention decision in 14 patients.
CONCLUSIONS:
FDG-PET/CT demonstrates essential influence on tumor staging in HNC patients scheduled for irradiation. Implementation of FDG-PET/CT in imaging protocol improves selection of candidates for curative and palliative RT and allows further optimization of treatment management and therapy intention.

Permalink: https://www.hzdr.de/publications/Publ-19994
Publ.-Id: 19994


Arbeiten zur MHD am HZDR mit Bezug zur Kristallzüchtung

Gerbeth, G.

Es wird eine Übersicht zur magnetischen Strömungsbeeinflussung in Kristallzüchtungsprozessen gegeben.

  • Invited lecture (Conferences)
    Fraunhofer Forschungszentrum für Silizium.Photovoltaik (FhG-CSP), 13.12.2013, Halle, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19993
Publ.-Id: 19993


Magnetic stirring of melts

Gerbeth, G.

Basics and applications on magnetic stirring of melts are given

  • Invited lecture (Conferences)
    Sommerschule des DFG-Graduiertenkollegs der TU Ilmenau, 01.10.2013, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19992
Publ.-Id: 19992


Arbeiten zur Flüssigmetall-Magnetohydrodynamik (MHD) am Institut für Fluiddynamik des HZDR - Grundlagen und Anwendungen

Gerbeth, G.

Es wird eine Übersicht zu MHD-Arbeiten am HZDR gegeben

  • Invited lecture (Conferences)
    Klausur des SFB 799 der TU Bergakademie Freiberg, 04.09.2013, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19991
Publ.-Id: 19991


Concluding Remarks and Outlook on the Helmholtz-Alliance Liquid Metal Technologies (LIMTECH)

Gerbeth, G.

A summary of the SFB works is giben with an outlook on future cooperative activities.

  • Lecture (Conference)
    International Symposium on Electromagnetic Flow Control in Metallurgy, Crystal Growth and Electrochemistry, 25.-27.03.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19990
Publ.-Id: 19990


Hydrogen Plasma Induced Modification of Photoluminescence from a-SiN(x):H Thin Films

Bommali, R.; Ghosh, S.; Prakash, G. V.; Gao, K.; Zhou, S.; Khan, S. A.; Srivastava, P.

Low temperature (250-350oC) hydrogen plasma annealing (HPA) treatments have been performed on amorphous hydrogenated silicon nitride (a-SiNx:H) thin films having a range of compositions and subsequent modification of photoluminescence (PL) is investigated. The PL spectral shape and peak positions for the as deposited films could be tuned with composition and excitation energies. HPA induced modification of PL of these films is found to depend on the N/Si ratio (x). Upon HPA the PL spectra show an emergence of a red emission band for x≤1, whereas an overall increase of intensity without change in the spectral shape is observed for x>1. The emission observed in the Si rich films is attributed to nanoscale a-Si:H inclusions. The enhancement is maximum for off-stoichiometric films (x~1) and decreases as the compositions of a-Si (x=0) and a-Si3N4 (x=1.33) are approached, implying high density of non-radiative defects around x=1. The diffusion of hydrogen in these films is also analyzed by Elastic Recoil Detection Analysis (ERDA) technique.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-19989
Publ.-Id: 19989


Design and construction for a moving temperature sensor inside a jet condensation experiment

Lahmer, O.

Keywords: temperature sensor; jet condensation; design

  • Study thesis
    ENSAME Valencienne Fr, 2013
    54 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19988
Publ.-Id: 19988


Survival of the best heads: The physical merits of lipid headgroup adaptation in anhydrobiosis

Abu Sharkh, S.; Erkut, C.; Kurzchalia, T.; Fahmy, K.

Anhydrobiotic organisms down-regulate their metabolism and preserve their cellular architecture at strongly reduced water potential to resume life after periods of desiccation. We have studied the dauer larva of the nematode Caenorhabditis elegans which represents an anhydrobiotic state of this genetically fully described organism. After preconditioning, an adaptational 4 days period of reduced humidity, survival of harsh desiccation occurs and depends on the synthesis of the disaccharide trehalose [1]. Using the temperature-sensitive strain daf-2(e1370), which arrests in the dauer state when grown at 25 °C, we show by thin layer chromatography that the phospholipid composition is altered from high to low PC/PE content during preconditioning. Time-resolved FTIR spectroscopy of lyotropic phase transitions induced within seconds in extracted C.elegans phospholipids by short hydration pulses, reveals that the decreased PC content allows a larger coupling of headgroup hydration to acyl chain packing as compared to the PE-rich state. The compressibility modulus was derived from CH-stretching frequency changes and the effect of trehalose studied. The data suggest a dynamic interaction of trehalose with the lipids during fast hydration at low humidity (75-85 % relative humidity) such that hydration water is transiently directed to the sub-headgroup carbonyl region, rather than being stably entrapped by trehalose. In combination with film balance experiments we show that the headgroup remodelling during preconditioning specifically increases the interaction of trehalose with the phospholipids, leading to a "softer" PC-depleted membrane which responds with larger lateral expansion during fast hydration transients. We explain the advantage of a reduced PC/PE ratio for anydrobiosis by the different intrinsic hydration properties of the two headgroups [2-3] which allows a more flexible water-mediated H-bond-network to form in the presence of trehalose. As a consequence, phase transitions on the seconds time-scale can proceed under close to equilibrium conditions in membranes of preconditioned worms. These molecular processes result in the relief of osmotic strain during membrane rehydration, thereby preventing membrane rupture during the critical phase of typically instantaneous rehydration of the desiccated anhydrobiotic organism before resuming its normal metabolism.

Keywords: Fourier transform infrared; time-resolved; membrane; hydration

  • Contribution to proceedings
    International Workshop "Molecular Membrane Biophysics", 03.-05.03.2014, Hünfeld, Germany

Permalink: https://www.hzdr.de/publications/Publ-19987
Publ.-Id: 19987


Hydrodynamische Untersuchung zum Einfluss von Flüssigviskosität und Feststoffanteil in Blasensäulen

Kahsnitz, D.

Keywords: bubble column; solid fraction; liquid viscosity

  • Study thesis
    TU Dresden, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19986
Publ.-Id: 19986


Analysis and Applications of a Generalized Multi-Field Two-Fluid Approach for Treatment of Multi-Scale Interfacial Structures in High Void-Fraction Regimes

Montoya, G.; Lucas, D.; Krepper, E.; Hänsch, S.; Baglietto, E.

High void fraction multiphase-flow regimes are commonly encountered in the nuclear industry where safety analysis of nuclear power plants requires reliable predictions on steam-water flows in case of different accident scenarios. Within the boiling phenomena in pipes, a transition throughout different flow patterns from bubbly to churn to annular flow is expected to occur. Those flow regimes, characterized by very high void fractions, are represented by different scales in terms of their gas structures.

It is known that computational fluid dynamics (CFD) has been widely developed for single phase flows, but strongly limited in the case of multiphase flows. This is due to the high complexity on representing its gas-liquid interface. Furthermore, most of the recent advances in code development and validation for multiphase flow have been addressed specifically to bubbly flows. In the case of such low void fraction regimes, the widely known averaging Eulerian multi-fluid approach is commonly used to describe its scales characterized by interfacial structures smaller than the grid size. For flow situations with large-scale interfaces, like annular or horizontal stratified flows, interface tracking methods are commonly used. Since in the case of high void fraction regimes, such as churn-turbulent flow, dispersed flows and large interfaces occur simultaneously, a combination of these modeling approaches could be needed.

This paper presents the application of a recently developed concept for the treatment of multiphase flows where different scales in terms of interfacial structures can be found. This approach, known as Generalized TwO Phase flow or GENTOP, considers the definition of fully-resolved continuous gas phase where the continuous gas summarizes all gas structures which are large enough to be resolved within the computed mesh. The concept works as part of an extension of the bubble population balance approach known as the inhomogeneous MUltiple SIze Group (MUSIG), which allows the consideration of different bubble size groups, each with its own velocity field inside the dispersed phase. Within the polydispersed gas, bubble coalescence and breakup allow the transfer between different size structures, while the modeling of mass transfer between the polydispersed and continuous gas, allows considering transitions between different gas morphologies depending of the flow situations. Within the concept, different parametric studies have been made for co-current vertical gas-water pipe flow, and comparisons against experimental data for all the current calculations are shown. The experiments have been conducted in the TOPFLOW and the MT Loop facilities at the Helmholtz-Zentrum Dresden-Rossendorf.

Keywords: CFD; GENTOP; MUSIG; multi-scale; multiphase-flow

  • Contribution to proceedings
    2014 International Congress on Advances in Nuclear Power Plants (ICAPP 2014), 06.-09.04.2014, Charlotte, North Carolina-Westin, United States of America
    Proceedings of ICAPP 2014, Volume 3, 1639-1654
  • Lecture (Conference)
    2014 International Congress on Advances in Nuclear Power Plants (ICAPP 2014), 06.-09.04.2014, Charlotte, North Carolina-Westin, United States of America
  • Poster
    2014 International Congress on Advances in Nuclear Power Plants (ICAPP 2014), 06.-09.04.2014, Charlotte, North Carolina-Westin, United States of America

Permalink: https://www.hzdr.de/publications/Publ-19985
Publ.-Id: 19985


A Generalized Multi-Field Two-Fluid Approach for Treatment of Multi-Scale Interfacial Structures in High Void-Fraction Regimes

Montoya, G.; Baglietto, E.; Lucas, D.; Krepper, E.

High void fraction multiphase-flow regimes are commonly encountered in the nuclear industry where safety analysis of nuclear power plants requires reliable predictions on steam-water flows in case of different accident scenarios. Within the boiling phenomena in pipes, a transition throughout different flow patterns from bubbly to churn to annular flow is expected to occur. Those flow regimes, characterized by very high void fractions, are represented by different scales in terms of their gas structures.

A concept has been recently developed for the treatment of multiphase flows where different scales in terms of interfacial structures can be found. This approach, known as Generalized TwO Phase flow or GENTOP, considers the definition of a fully-resolved continuous gas phase where the continuous gas summarizes all gas structures which are large enough to be resolved within the computed mesh. The concept works as part of an extension of the bubble population balance approach known as the inhomogeneous MUSIG, which allows the consideration of different bubble size groups, each with its own velocity field. Within the polydispersed gas, bubble coalescence and breakup allow the transfer between different size structures, while the modeling of mass transfer between the polydispersed and continuous gas, allows considering transitions between different gas morphologies depending of the flow situations.

Keywords: CFD; GENTOP; MUSIG; multi-scale; multiphase-flow

  • Poster
    MIT Energy Night, 18.10.2013, Cambridge, United States of America

Permalink: https://www.hzdr.de/publications/Publ-19984
Publ.-Id: 19984


Comparative Analysis of High Void Fraction Regimes using an Averaging Euler-Euler Multi-Fluid Apporach and a Generalized Two-Phase Flow (GENTOP) Concept

Montoya, G.; Baglietto, E.; Lucas, D.; Krepper, E.; Hoehne, T.

Complex multiphase gas-liquid flows, including boiling, are usually encountered in safety related nuclear applications. For CFD purposes, modeling the transition from low to high void fraction regimes represents a non-trivial challenge due to the increasing complexity of its interface. For example, churn-turbulent and annular flows, which are typically encounter for these gas volume fraction ranges, are dominated by highly deformable bubbles. Multiphase CFD has been so far relying on an averaged Euler-Euler simulation approach to model a wide regime of two-phase applications. While this methodology has shown to date demonstrated reasonable results (Montoya et al., 2013), it is evidently highly dependable on the accuracy and validity of the mechanistic models for interfacial forces, which are necessary to recover information lost during the averaging process. Unfortunately existing closures, which have been derived from experimental as well as DNS data, are hardly applicable to high void fraction highly-deformable gas structures. An alternative approach for representing the physics behind the high void fraction phenomena, is to consider a multi-scale method. Based on the structure of the gas-liquid interfaces, different gaseous morphologies should be described by different CFD approaches, such as interface tracking methods for larger than the grid size interfacial-scales, or the averaged Euler-Euler approach for smaller than grid size scales, such as bubbly or droplet flow. A novel concept for considering flow regimes where both, dispersed and continuous interfacial structures could occur, has been developed in the past (Hänsch et al., 2012), and has been further advanced and validated for pipe flows under high void fraction regimes (Montoya et al., 2014) and other relevant cases, such as the dam-break with an obstacle (Hänsch et al., 2013). Still, various short-comings have been shown in this approach associated mostly to the descriptive models utilized to obtain the continuous gas morphology from within the averaged Eulerian simulations. This paper presents improvements on both concepts as well as direct comparison between the two approaches, based on newly obtained experimental data. Both models are based on the bubble populations balance approach known as the inhomogeneous MUltiple SIze Group or MUSIG (Krepper et al., 2008) in order to define an adequate number of bubble size groups with its own velocity fields. The numerical calculations have been performed with the commercially available ANSYS CFX 14.5 software, and the results have been validated using experimental data from the MT-Loop and TOPFLOW facilities from the Helmholtz-Zentrum Dresden-Rossendorf in Germany (Prasser et al., 2007).

Keywords: CFD modeling; high void fraction; multiphase flow; two-fluid model; GENTOP; CFD validation

  • Contribution to proceedings
    2014 22st International Conference on Nuclear Engineering (ICONE22), 07.-11.07.2014, Prague, Czech Republic
    Proceedings of ICONE22
  • Lecture (Conference)
    2014 22st International Conference on Nuclear Engineering (ICONE22), 07.-11.07.2014, Prague, Czech Republic
  • Poster
    2014 22st International Conference on Nuclear Engineering (ICONE22), 07.-11.07.2014, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-19983
Publ.-Id: 19983


Verbesserte Behandlungschancen durch molekulares Targeting in der Radioonkologie

Cordes, N.; Gurtner, K.; Belka, C.

Hintergrund
Intensitätsmodulierte und biologisch geführte Hochpräzisionsbestrahlung bestimmt heute die moderne Radioonkologie. Wenig ausgeschöpft hingegen ist die Gabe zielgerichteter molekularer Medikamente zur Strahlensensibilisierung maligner solider Tumoren.
Ziel
Der aktuelle Stand neuer molekularer Behandlungsstrategien simultan zur Strahlentherapie soll aufgrund von präklinischen und klinischen Daten in diesem Beitrag diskutiert werden.
Material und Methoden
Recherche und Auswertung von Literatur und klinischen Studien.
Ergebnisse
Durch besseres Verständnis der Tumorbiologie konnten potenzielle Zielmoleküle für pharmakologischen Inhibitoren und Antikörpern identifiziert werden, von denen einige bereits präklinisch und klinisch evaluiert werden. Lokoregionäre Tumorkontrolle und Gesamtüberleben wurden z. B. durch die antikörpervermittelte Hemmung des epidermalen Wachstumsfaktorrezeptors (EGFR) in Kombination mit Strahlentherapie bei Kopf-Hals-Tumoren verbessert. Aktuell zeichnet sich ab, dass Antikörper gegen den vaskulären endothelialen Wachstumsfaktor (VEGF) die Wirkung der Strahlentherapie bei Glioblastomen verbessern könnten.

Permalink: https://www.hzdr.de/publications/Publ-19981
Publ.-Id: 19981


EGFR/JIP-4/JNK2 signaling attenuates cetuximab-mediated radiosensitization of squamous cell carcinoma cells.

Eke, I.; Schneider, L.; Förster, C.; Zips, D.; Kunz-Schughart, L.; Cordes, N.

EGF receptor (EGFR) promotes tumor growth as well as radio- and chemoresistance in various human malignancies including squamous cell carcinomas (SCC). In addition to deactivation of prosurvival signaling, cetuximab-mediated EGFR targeting might concomitantly induce self-attenuating signaling bypasses. Identification of such bypass mechanisms is key to improve the efficacy of targeted approaches. Here, we show great similarity of EGFR signaling and radiation survival in cetuximab-treated SCC cells grown in a more physiologic three-dimensional extracellular matrix and as tumor xenografts in contrast to conventional monolayer cell cultures. Using phosphoproteome arrays, we observed strong induction of JNK2 phosphorylation potentially resulting from cetuximab-inhibited EGFR through c-jun-NH(2)-kinase (JNK)-interacting protein-4 (JIP-4), which was identified using an immunoprecipitation-mass spectrometric approach. Inhibition of this signaling bypass by JIP-4 or JNK2 knockdown or pharmacologic JNK2 inhibition enhanced cetuximab efficacy and tumor cell radiosensitivity. Our findings add new facets to EGFR signaling and indicate signaling bypass possibilities of cancer cells to improve their survival on cetuximab treatment. By deactivation of cetuximab-self-attenuating JNK2-dependent signaling, the cytotoxicity, and radiosensitizing potential of cetuximab can be augmented.

Permalink: https://www.hzdr.de/publications/Publ-19980
Publ.-Id: 19980


Flüssig-fest Stoffübertragung in Festbettreaktoren

Hermann-Heber, R.

Keywords: solid bed reactors; mass transfer

  • Study thesis
    TU Dresden, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19979
Publ.-Id: 19979


Fabrication and Characterization of Patterned Exchange-Coupled Trilayers

Langer, M.

In 1998 Demokritov et al. succeeded in altering the coupling of exchange coupled Fe/Cr/Fe-trilayers from ferro- to antiferromagntic for the first time by using ion irradiation. Since then, ion irradiation has been used as an advanced technique for magnetic patterning of antiferromagnetically coupled trilayers. In this work patterning by means of ion implantation was applied on exchangecoupled Co90Fe10-trilayers by using (Eirr = 80 keV) Co+-Ions. For that purpose a transition towards appropriate ferromagnetic properties was achieved with an ion-fluence of F = 5 · 1015 Co+=cm2. Stripe patterns fabricated by this techinique were investigated and compared to conventionally patterned (by means of reactive plasma etching) stripes. By using Kerr-microscopy domain structure and the shape of the magnetization reversal was studied. At the boundary of implanted elements edge curling walls were observed (field orientation perpendicular to the stripes) which did not occur in etched samples. Observed differences in the switching behavior could primarily be explained with changes of the magnetic material properties (e.g. anisotropy and saturation magnetization) due to the ion irradiation. Implanted 2 μm wide stripes showed a collective switching with quasi-domains during the magnetic reversal. In this process interactions of the transversal magnetization component with the adjacent non-irradiated antiferromagnetically coupled trilayers were observed. It was found that this transversal component governs the intensity of the collective switching behavior, via extensions of an intermediate domain wall which was simulated micromagnetically in this work. The results for the domain wall widths which were calculated for different anisotropy directions provide a comprehensive picture together with the Kerr-microscopy analysis.

  • Diploma thesis
    HZDR, TU Dresden, 2012
    90 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19978
Publ.-Id: 19978


Fabrication and characterization of patterned exchange-coupled trilayers

Langer, M.; Osten, J.; Neudert, A.; Körner, M.; Banholzer, A.; Mönch, I.; Mattheis, R.; Fassbender, J.; McCord, J.

Magnetic patterning by means of ion-implantation is an advanced technique to fabricate ferromagnetic micro-/nanostructures. In this case antiferromagnetically exchange coupled trilayers, consisting of two Co90Fe10 layers with a Ru interlayer, were used. The ion induced intermixing of the interlayer with its surrounding magnetic layers alters the coupling to a ferromagnetic one. Therefore Co ions with energies of 40-80 keV and a fluence of 5·1015 cm−2 were used. Hence, applying masks, ferromagnetically coupled micro-/nanometer sized elements (stripes, squares, circles etc.), embedded in a so-called artificial antiferromagnetic environment, have been fabricated. These structures were characterized by the use of Kerr-microscopy and MOKE-magnetometry to determine the mutual influence of the ferromagnetic elements with the antiferromagnetically coupled environment. Also their magnetic switching behavior was compared to etched single ferromagnetic structures. Domain pinning at the element boundaries was observed.

  • Lecture (Conference)
    DPG Frühjahrstagung 2012, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19977
Publ.-Id: 19977


Two-magnon scattering and mode-splitting in 1-dimensional quasi-magnonic crystals

Langer, M.; Gallardo, R.; Lenz, K.; Banholzer, A.; Grebing, J.; Körner, M.; Landeros, P.; Lindner, J.; Fassbender, J.

The magnetic relaxation in quasi 1-dimensional periodic nanostructures (magnonic crystals) is investigated by ferromagnetic resonance (FMR). In thin ferromagnetic films, the magnetization dynamics are governed by intrinsic effects like Gilbert damping and spin-pumping but also by extrinsic effects like two-magnon scattering due to inevitable defect structures. By using nanoscale periodically modulated magnetic films we are able to artificially create and thus control those defect structures necessary to induce two-magnon scattering. The results are compared to available analytical theory [1].
The magnetic modulation was created by lithographically defined stripes and subsequent ion beam irradiation. The ion beam energy was chosen such that the ions create a magnetic perturbation at the surface. This slightly reduces the saturation magnetization in the irradiated stripes and hence the effective magnetic thickness. These stripe defects resemble a periodic dipolar scattering potential, which couples the uniform with the final-state magnons in the two-magnon scattering process.
Broadband ferromagnetic resonance is used to measure the resonance field Hres and linewidth ΔH for different field directions and frequencies. The frequency-dependent measurements with the external magnetic field aligned parallel to the stripes show only a single resonance mode and linear increase of ΔH. Therefore the magnetic relaxation is purely Gilbert-like. With the magnetic field aligned perpendicular to the periodic structure the frequency dependence exhibits a rich mode-splitting, which can be calculated analytically.

  • Poster
    IEEE Magnetics Society Summer School 2013, 10.06.2013, Assisi, Italy

Permalink: https://www.hzdr.de/publications/Publ-19976
Publ.-Id: 19976


Entwicklung einer logarithmischen Vorverstärkerschaltung für ein Röntgendetektorsystem

Thomas, P.

Keywords: logarithmic preamplifier; x-ray detector system

  • Diploma thesis
    HTW Dresden, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19975
Publ.-Id: 19975


Effect of Ga+ irradiation in molecular-beam epitaxy grown Pt/Co/Pt thin films studied by magneto-optic spectroscopy

Jakubisova-Liskova, E.; Visnovsky, S.; Wawro, A.; Baczewski, L. T.; Mazalski, P.; Maziewski, A.; Liedke, M. O.; McCord, J.; Fassbender, J.

In-depth profile changes induced by Ga+ ion irradiation in Pt(5 nm)/Co(3.3 nm)/Pt(20 nm)/Mo(20 nm) sandwiches MBE grown on Al2O3 substrates are deduced from complex magneto optic polar Kerr effect (PMOKE) measurements at photon energies between 1 and 5 eV. The Ga+ irradiation stimulate a redistribution of Pt and Co and leads to broadening of alloyed regions at Pt Co and Co Pt interfaces, which is evaluated using PMOKE spectra. The effect of four Ga+ fluences D between zero and 6×1015 Ga+/cm2 was studied. The observed PMOKE azimuth rotation peak centered at 4.5 eV reaches the maximum of 0.42 degree at D=1×1015 Ga+/cm2 and becomes thus enhanced by a factor of 3.2 with respect to that in the non-irradiated sample. At D=6×1015 Ga+/cm2 the peak amplitude falls to 0.05 degree. To find the in-depth profile of Co concentration s in the sandwiches as a function of D, the PMOKE azimuth rotation and ellipticity spectra are compared with a multilayer model, where ideal flat interfaces are replaced by sequences of CosPt1-s layers. The dependence on D is compared with that evaluated by simulation of the structural effects of ion irradiation. At the highest D, the irradiation produces an almost complete erosion of the top Pt and Co accompanied by mixing at the Pt-Mo interface.

Keywords: MBE; ion irradiation; PMOKE; CoPt

Permalink: https://www.hzdr.de/publications/Publ-19973
Publ.-Id: 19973


Image segmentation using level set method in presence of time varying noise

Datta, A.

Keywords: image segmentation; level set method

  • Diploma thesis
    IIT Kanpur, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19972
Publ.-Id: 19972


Costimulation improves the killing capability of T cells redirected to tumor cells expressing low levels of CD33: Description of a novel modular targeting system

Arndt, C.; Feldmann, A.; von Bonin, M.; Cartellieri, M.; Ewen, E.-M.; Koristka, S.; Michalk, I.; Stamova, S.; Berndt, N.; Gocht, A.; Bornhäuser, M.; Ehninger, G.; Schmitz, M.; Bachmann, M.

Owing to their clinical success, there is growing interest in novel bispecific antibodies (bsAbs) for retargeting of T cells to tumor cells including for the treatment of acute myeloid leukemia (AML). One potential target for retargeting of T cells to AML blasts is the surface molecule CD33. Here we describe a novel modular targeting platform that consists of a universal effector module (EM) and individual target modules (TMs). Both modules can form an immune complex via a peptide epitope. The resulting targeting complex can functionally replace a conventional bsAb. By fusion of a costimulatory domain (for example, the extracellular CD137 ligand domain) to the TM, the targeting complex can even provide a costimulatory signal to the redirected T cells at their side of interaction with the tumor cell. Furthermore, we observed that an efficient killing of tumor cells expressing low levels of the tumor target CD33 becomes critical at low effector-to-target cell ratios but can be improved by costimulation via CD137 using our novel targeting system.

Keywords: acute myeloid leukemia; CD33; costimulatory immunoligands; immunotherapy; single-chain bispecific antibodies; T-cell retargeting

Permalink: https://www.hzdr.de/publications/Publ-19971
Publ.-Id: 19971


Untersuchung der Stoffübertragung flüssig-fest in einem geneigt rotierenden Festtbettreaktor

Wendel, H.

Keywords: solid bed reaktor; material transmission; rotating ractor

  • Diploma thesis
    TU Dresden, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19970
Publ.-Id: 19970


Entwicklung einer zweidimensionalen Verfahreinheit für die hoch auflösende Gamma-Computertomographie am HZDR

Strohbach, A.

Keywords: gamma tomography; high resolution; drive unit

  • Diploma thesis
    TU Dresden, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19969
Publ.-Id: 19969


Ion irradiation induced enhancement of out-of-plane magnetic anisotropy in ultrathin Co films

Mazalski, P.; Kurant, Z.; Maziewski, A.; Liedke, M. O.; Fassbender, J.; Baczewski, L. T.; Wawro, A.

Ga+ or He+ irradiated MBE grown ultrathin films of sapphire/Pt/Co(d Co)/Pt(d Pt) were studied using polar Kerr effect in wide ranges of both cobalt d Co and platinum d Pt thicknesses as well as ion fluences F. Two branches of increased magnetic anisotropy and enhanced Kerr rotation angle induced by Ga+ or He+ irradiation are clearly visible in two-dimensional (d Co, LogF) diagrams. Only Ga+ irradiation induces two branches of out-of-plane magnetization state.

Keywords: MBE; ultrathin films; Co; CoPt; Pt; ion irradiation; magnetic anisotropy; MOKE; phase transition

Permalink: https://www.hzdr.de/publications/Publ-19968
Publ.-Id: 19968


Modellierung der Mischvorgänge in Rührreaktoren

Kipping, R.

Die Bearbeitung des vorliegenden Beleges umfasste eine umfassende Literaturrecherche zur Untersuchung und Charakterisierung von Mischvorgängen in Rührkesselreaktoren. Zudem wurden experimentelle Arbeiten mit Nadelsonden in einem bestehenden Versuchsbeh¨alter und im Zusammenhang damit Drehzahl- und Leistungsmessungen am Rührwerk durchgeführt. Weiterhin wurden CFD Simulationen für den Rührbehälter betrieben. Diese umfasste neben dem Aufbau der Geometrie und Diskretisierung des Gitters, die Durchführung eines Particle-Tracks. Abschließend wurde ein Vergleich der ermittelten Daten zwischen Simulation, Experiment und vorhandenen Daten der autonomen Sensorpartikel angestellt.

Keywords: Rührprozess; Mischvorgang; Zirkulationszeit; CFD; Particle-Track; mixing process; stirring process; circulation time; particle track

  • Study thesis
    TU Dresden, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19967
Publ.-Id: 19967


X-ray radioscopy studies of solidification processes

Shevchenko, N.; Eckert, S.

Real-time and in-situ observations of the density distribution within thin solidifying samples reach a spatial resolution of a few microns and contribute essentially to an improved understanding of dendritic growth processes. The dimension of the solute boundary layers ahead of the solidification front as well as the onset of solutal-driven melt convection in the mushy zone and the bulk liquid can also be derived from image processing. Exemplarily, we present a bottom-up solidification of a Ga-25wt%In alloy under the influence of buoyancy-driven and electromagnetically driven convection.

Keywords: solidification; in situ X-ray imaging; Ga-In alloy; flow pattern; freckle formation

  • Lecture (Conference)
    The International Symposium on Electromagnetic Flow Control in Metallurgy, Crystal Growth and Electrochemistry, 25.-27.03.2013, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-19966
Publ.-Id: 19966


Entwicklung und Test einer Auftriebssteuerung für strömungsfolgende Sensorpartikel

Schneider, C.

In der vorliegenden Arbeit ist ein Prototyp zur Auftriebssteuerung entstanden. Die Auftriebssteuerung beruht auf dem Prinzip der Verringerung der spezifischen Dichte des Sensorkörpers. Mit dem neuen Sensorgehäuse wurde durch das Ausfahren eines Kolbens eine Volumenerhöhung von 8,8 % erreicht. Die Masse des Sensorgehäuses wurde dabei nicht verändert. Verglichen mit den in der Vorstudie durchgeführten Versuchsdurchgängen, kann für dieses Gehäuse eine sehr gute Aufenthaltshäufigkeit nah an der Oberfläche des Mediums vorhergesagt werden. Für die Betätigung des Kolbens wurden zwei Aktor-Konzepte vorgestellt. Eines basiert auf der in einem Federschnappverschluss gespeicherten potentiellen Energie, das Andere auf das Ausfahren eines Linear-Aktors. Der entwickelte Schnappverschluss konnte dabei erfolgreich in das Gehäuse integriert und evaluiert werden. Die Verwendung des Linear-Aktors besteht bis jetzt lediglich als Konzept. Vorteil dieses Systems könnte eine mögliche Regelbarkeit der Auftriebsneutralität sein. Soll der Linear-Aktor eingesetzt werden, so ist wegen seiner Masse eine Anpassung des Gehäuses notwendig. Die Änderung beschränkt sich dabei lediglich auf eine Verlängerung des Gehäuserohres.

Keywords: Sensorpartikel; Auftrieb; Rückgewinnung; Aktor; sensor particle; buoyancy; recovery; actuator

  • Diploma thesis
    TU Dresden, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19965
Publ.-Id: 19965


Leitfähigkeits- und Gasgehaltsmessung für instrumentierte Strömungsfolger

Reichel, S.

Im Rahmen dieser Diplomarbeit ist erfolgreich ein Messsystem zur Leitfähigkeits- und Gasphasenbestimmung entstanden. Durch die zweiteilige Konzipierung des Messmoduls in Hauptplatine und Sensoreinheit konnte das Messsystem charakterisiert werden, wobei eine Kompatibilität zum autonomen Sensorpartikel gewährleistet werden konnte. Die entstandene Soft- und die modular strukturierte Firmware ermöglichte die Steuerung der Messung sowie die Verarbeitung und Visualisierung von Messergebnissen. Eine elektrische Charakterisierung ermöglichte es, entworfene Elektrodenstrukturen auszuwählen. Mit den Ausgewählte Elektrodenstrukturen wurden Leitfähigkeiten in einem Bereich von 200 µS/cm bis 1300µS/cm in Wässrigen-Salzlösungen bestimmt und verschiedene Gasphasen ermittelt. Desweitern wurden die Eindringtiefe der Elektrodenanordnungen in das Medium untersucht.

Keywords: Sensorpartikel; Leitfähigkeit; Gasgehalt; Elektroden; Eindringtiefe; sensor particle; conductivity; gas content; electrodes; penetration depth

  • Diploma thesis
    TU Dresden, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19964
Publ.-Id: 19964


Numerische Untersuchung von Gasverteilern in Blasensäulen

Ramasetti, E. K.

Keywords: bubble columns; numerical analysis; gas distribution

  • Master thesis
    Manchester Metropolitan University, Manchester, UK, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19963
Publ.-Id: 19963


Tomographische Untersuchung zur Phasenverteilung in statischen Mischern

Grugel, F.

Keywords: tomography; phase distribution; static mixer

  • Diploma thesis
    TU Dresden, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19962
Publ.-Id: 19962


Gittersensorstudien zur gasgetriebenen Fluiddynamik auf Kolonnenböden

Chi, B.

Keywords: wire-mesh sensor; fluid dynamics; bubble columns; gas driven fluid dynamics

  • Study thesis
    TU Dresden, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19960
Publ.-Id: 19960


Instrumentierte Strömungsfolger zur Prozessdiagnose in gerührten Fermentern

Reinecke, S.

In der Arbeit wurde ein Konzept instrumentierter, strömungsfolgender Sensoren zur Erfassung räumlich verteilter Parameter in Mischbehältern entwickelt. Die Sensorpartikel ermöglichen die Analyse hydrodynamischer und thermodynamischer Prozessbedingungen in Mischbehältern. Das Strömungsverhalten der Sensorpartikel wurde in einem Rührbehälter untersucht. Der Vergleich zu Referenzmessungen zeigt ein hinreichendes Strömungsfolgeverhalten und einen vernachlässigbaren Schlupf bei dem Einsatz in realen Biosubstraten von Biogas-fermentern. Aus den Messdaten der Sensorpartikel können räumliche Parameterprofile der Aufenthaltswahrscheinlichkeit und der Zirkulationszeit sowie Phasen-portraits extrahiert werden, welche schlüssige Interpretationen hin-sichtlich der Strömungsform und des Zustandes des Mischprozesses zulassen. Weiterhin konnten relevante Modellparameter, wie Zirkulationsbeiwert, Förderhöhe und PECLÉT-Zahl, bestimmt werden. Die Bestimmung der Suspensionsgüte aus den Daten der Sensorpartikel ermöglicht den objektiven Vergleich des Suspensionsverhaltens in unterschiedlichen Behältergeometrien und Rührwerkskonfigurationen.

Keywords: Strömungsfolger; Sensorpartikel; Autonomer Sensor; Makrovermischung; Modellparameter; sensor particles; autonomous sensor; macro mixing; model parameters; flow follower

  • Doctoral thesis
    TU Dresden, 2014
    Mentor: Prof. G. Gerlach, Prof. U. Hampel
    158 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19959
Publ.-Id: 19959


Transmission Electron Microscopy at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR)

Hübner, R.

  • Invited lecture (Conferences)
    Kolloquium des Instituts für Strukturphysik der TU Dresden, 28.01.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19958
Publ.-Id: 19958


Memristive effects in thermal oxidized Ti and magnetron sputtered TiOx films

Blaschke, D.; Zahn, P.; Gemming, S.; Cornelius, S.; Scholz, A.; Skorupa, I.; Scheumann, B.; Potzger, K.

ReRAM devices based on TiO2 seems to be a promising candidate for the next generation memory storage systems.
We will compare thermal oxidation of Ti films and DC magnetron sputtering for the preparation of TiO2 thin films in terms of crystallinity and resistive switching.
The oxidation process of 100nm Ti on Pt/Ti/SiO2/Si substrates leads to polycrystalline rutile TiO2 layers. In contrast to this with dc magnetron sputtering on Nb:STO substrates, it was possible to grow epitaxial anatase TiO2 layers.
Subsequent I-V characterization revealed interesting differences between both structures. In case of the rutile films unipolar switching, which is supposed to correlate with a filamentary mechanism and the phase change between TiO2 and so called Magnéli phases TinO2n-1, mostly n = 4 or 5 [1]. The epitaxial anatase films showed the bipolar switching mode, which is in literature correlated with the modification of the metal/oxide interface due to the drift of oxygen vacancies in an applied electric field [2].
Furthermore retention measurements were performed, which showed opposite behavior for the unipolar and bipolar switching mode. This result could be attributed to the different mechanisms behind.

The project is funded by the Initiative and Networking Fund of the Helmholtz Association (VH-VI-422).

[1] Deok-Hwang Kwon et al., “Atomic structure of conducting nanofilaments in TiO2 resistive switching memory”, Nature Nanotechnology, vol.5, pp.148 – 153 (2010)

[2] J. Joshua Yang et al., “Memristive switching mechanism for metal/oxide/metal nanodevices”, Nature Nanotechnology, vol.3, pp.429 – 433 (2008)

Keywords: resistive switching; thermal oxidation; magnetron sputtering; TiO2

  • Lecture (others)
    DETI.2 Midterm meeting, 09.-14.10.2013, Moskau, Russland

Permalink: https://www.hzdr.de/publications/Publ-19957
Publ.-Id: 19957


Memristive effects in Titanium Dioxide

Blaschke, D.; Zahn, P.; Gemming, S.; Cornelius, S.; Scholz, A.; Skorupa, I.; Scheumann, B.; Potzger, K.

In recent years, the resistive switching of binary transition metal oxides has attracted considerable attention for application in nonvolatile memories.

For our investigations, polycrystalline rutile TiO2 thin films were prepared on Pt/Ti/SiO2/Si substrates by thermal oxidation of 100nm thick e-beam evaporated Ti films. The oxidation temperature was varied between 500°C and 800°C at an oxygen partial pressure of 1 atmosphere.
Electrical contacts are provided by the Pt bottom electrode and sputtered 100nm thick Au top electrodes of 240um diameter.
We observed stable nonvolatile unipolar switching in the films oxidized at 600-800°C with an interesting long-term evolution of the resistance after the abrupt RESET process.
Furthermore, we present structural investigations of the TiO2 films.

The project is funded by the Initiative and Networking Fund of the Helmholtz Association (Virtual Institute MEMRIOX VH-VI-422).

Keywords: resistive switching; TiO2; thermal oxidation

  • Poster
    Functional oxides for emerging technologies, 14.-18.10.2013, Bremen, Germany

Permalink: https://www.hzdr.de/publications/Publ-19956
Publ.-Id: 19956


Characterization of gas-liquid flow mixing with static mixers

Schubert, M.; Rabha, S.; Grugel, F.; Banowski, M.; Hampel, U.

Static mixers are attractive alternatives to conventional gas-liquid contactors, widely used for mixing and heat transfer between two fluids in various process applications. Knowledge on the limits of number and gemoetry of the static mixer elements is important for optimization for the desired mixing purpose. The present work is designed to investigate the performance of static mixers in upward gas-liquid (air - water) flows. The experiments are carried out in a tube (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, etc. and pressure drop across the static mixer will be presented and conclusions will be drawn for a proper mixer selection.

Keywords: static mixer; ultrafast electron beam X-ray tomography; pressure drop

  • Invited lecture (Conferences)
    Jahrestreffen der Fachgruppen Mehrphasenströmungen und Wärme-und Stoffübertragung, 24.-25.03.2014, Fulda, Germany

Permalink: https://www.hzdr.de/publications/Publ-19955
Publ.-Id: 19955


Resistive Switching in thermally oxidized Titanium

Blaschke, D.; Skorupa, I.; Scheumann, B.; Scholz, A.; Zahn, P.; Gemming, S.; Potzger, K.

In recent years the resistive switching of binary transition metal oxides like NiO, Nb2O5 and TiO2 has attracted considerable attention for application in nonvolatile memory storage systems.

For our investigations we used a thin rutile TiO2 film, which was prepared by the thermal oxidation of a 100nm thick e-beam evaporated Ti film. The oxidation temperatures were varied from 500°C to 800°C at an oxygen partial pressure of 1 atmosphere. We will present the dependence of the crystal structure and the switching behavior on the oxidation temperature as well as an interesting feature on the time-dependent evolution of the resistance during the Reset process.

The project is funded by the Initiative and Networking Fund of the Helmholtz Association (VH-VI-422).

Keywords: resistive switching; TiO2; thermal oxidation

  • Lecture (Conference)
    DPG-Frühjahrstagung, 10.-15.03.2013, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19954
Publ.-Id: 19954


Millisecond-range liquid phase recrystallization for III-V/Si heteronanojunction fabrication

Prucnal, S.; Zhou, S. Q.; Bregolin, F. L.; Ou, X.; Liedke, M. O.; Huebner, R.; Helm, M.; Zuk, J.; Turek, M.; Pyszniak, K.; Drozdziel, A.; Skorupa, W.

The downscaling and stressor technology of Si based devices are extending the performance of the silicon channel to its limits. One promising solution for the performance progress which can overcome those limits is the integration of different functional optoelectronic elements within one chip.
We have developed a compact, CMOS compatible and fully integrated solution for the integration of III-V compound semiconductors with silicon technology for optoelectronic applications. The III-V nanostructured semiconductors are synthesized in silicon based matrixes using the combination of ion beam implantation and millisecond flash lamp annealing (FLA) techniques via millisecond range liquid phase epitaxy [1, 2]. In this paper we will present investigations of the microstructural, optical and electrical properties of InAs and InP nanostructures formed in silicon and on SOI wafers. The growth evolution of the III-V nanostructures during FLA and the influence of the annealing parameters on their crystallographic orientation, shape and size will be explored. Conventional selective etching was used to form the n-III-V/p-Si heterojunction. The current-voltage measurement confirms the heterojunction diode formation between n-type III-V quantum dots and p-type Si. The main advantage of our method is its integration with large-scale silicon technology, which also allows its application for the fabrication of Si-based optoelectronic devices.

Keywords: silicon; III-V; flash lamp annealing; ion implantation

  • Poster
    16th International Conference on Modulated Semiconductor Structures, MSS-16, 01.-05.07.2013, Wroclaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-19953
Publ.-Id: 19953


Experimente zur blasengetriebenen Strömung bei der Wasserelektrolyse

Simon, R.

Der steigende Bedarf an Stromspeicherkapazitäten durch den Ausbau von Windkraft– und Photovoltaikanlagen erfordert neue oder die Optimierung bereits bestehender Konzepte.
Durch die Elektrolyse von Wasser kann elektrischer Strom flexibel in Form von Wasserstoff gespeichert werden. Aktuelle alkalische Wasserelektrolyseure wandeln nur 60–70 % des eingesetzten Stroms in Wasserstoff um. Besonders die Überspannungen an den Elektroden, unter anderem hervorgerufen durch die Ansammlung von Gasblasen, haben großen Anteil an den Verlusten.
Durch den Aufbau einer Versuchselektrolysezelle konnte das Geschwindigkeitsfeld der Elektrolytflüssigkeit umfangreich untersucht werden. Die Auswertung erfolgte über Particle Image Velocimetry und Particle Tracking Velocimetry aufeinanderfolgender Bilder einer Highspeed-Kamera. Es zeigte sich, wie in anderen Arbeiten bereits untersucht, dass die Veränderungen von Elektrodenabstand und angelegter Stromdichte entscheidende Einflussfaktoren auf die Effektivität der Stoffumwandlung sind. Am Blasenvorhang wurde die Fluktuation von auftretenden Wellenbergen und –tälern untersucht. Die regelmäßige Frequenz könnte in einen Zusammenhang mit der Geschwindigkeit der Einzelblasenentstehung stehen.
Das gezielte Einbringen eines Magnetfelds in den Elektrodenzwischenraum induziert eine zusätzliche Kraft, die Lorentzkraft. Diese verursacht, nach oben orientiert, starke Beschleunigungen des Gasblasenauftriebs und der Flüssigkeitsströmung. Darstellungen von Geschwindigkeitsprofilen und –verteilungen verdeutlichen die Auswirkungen unterschiedlicher Magnetfeldkonfigurationen.
Mit Hilfe des Durchlichtverfahrens konnten die Wasserstoffeinzelblasen abgebildet werden. Die Auswertung über Bildverarbeitungsverfahren zeigte die Veränderung der Gasblasengrößen und die optimierende Wirkung der induzierten Lorentzkräfte auf die Strömung an der Phasengrenzfläche.
Im Ergebnis wurden die Geschwindigkeitsverteilungen im Zwischenraum der Elektrode umfassend charakterisiert. Es zeigte sich, dass das Anlegen eines Magnetfelds durch die Verringerung der Überspannungen an den Elektroden einen signifikanten Beitrag zur Wirkungsgradsteigerung der alkalischen Elektrolyse leisten kann. Die konstruktive Umsetzung dieses Konzepts für den industriellen Einsatz sollte zukünftig weiter untersucht werden.

Keywords: water electrolysis; bubble driven flow; Lorentz force

  • Diploma thesis
    TU Dresden, 2013
    93 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19952
Publ.-Id: 19952


Hydrodynamische Untersuchung von Gasverteilern in Blasensäulen mit bildgebenden Messverfahren

Donath, T.

Keywords: Blasensäulen; bubble columns; Gasverteiler; bildgebende Messverfahren; imaging

  • Study thesis
    TU Dresden, 2013
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19951
Publ.-Id: 19951


Kompensation von thermischen Einflüssen bei der Durchflussmessung in Flüssigmetall mit einem Versuchssensor EMD.ps

Meyer, F.

Faraday legte mit seinem „Waterloo Bridge experiment“ den Grundstein für die induktive Durchflussmessung. In den folgenden 180 Jahren hat sich die induktive Strömungsmessung zu einem wichtigen Bestandteil in der industriellen Messtechnik entwickelt. Die kontaktbehaftete Durchflussmesstechnik ist jedoch nicht für das Einsatzbereich der flüssigen Metalle geeignet, da flüssige Metalle eine hohe chemische Aggressivität besitzen. Flüssiges Metall verfügt außerdem über ein äußerst komplexes und nicht kontrollierbares Benetzungsverhalten wodurch messtechnisch das kontaktbehaftete System keine verlässlichen Ergebnisse liefern kann. Die Forderung der Industrie nach einer in diesem Gebiet einsetzbaren Messtechnik ist groß, da viele innovative Anwendungsfelder bedient werden müssten. Um der Forderung nachzukommen ist das EMD Messsystem entwickelt worden. Das EMD Sensorkonzept beruht auf der Messung eines elektrischen Feldes, das von einem alternierenden magnetischen Feld induziert wird und mittels einer geschickten Anordnung der Empfänger entkoppelt wird. Die Auswertung in drei Bestimmungsgrößen (Amplitude, Phase und Frequenz) ist durch den Einsatz von periodisch erregten Magnetfeldern möglich. Die für dieses System typische dimensionslos Kenngröße, die magnetische Reynoldszahl (Rm=μ0συ0L0), lässt eine erste Näherung des theoretisch postulierten Messeffekts zu. Im isothermen Betrieb liefert das Messsystem verlässliche Angaben. Problematisch ist bei anderen Bedingungen der temperaturbedingte Drift, der die gemessenen Werte von den Ist- Werten abweichen lässt. Zentrales Thema dieser Arbeit ist die Notwendigkeit der Temperatur und Driftkompensation am EMD Messsystem um die vorhandene Messtechnik einsatzbereit für die Anforderungen in der Anwendung zu machen. Mit theoretischen und praktischen Untersuchungen wird das Verhalten des Sensors unter thermischer Belastung und bezüglich des Messeffekts auf das System untersucht. Als Belastung wird einmal die Eigenerwärmung und die Fremderwärmung untersucht. Die folgende Arbeit ist folgendermaßen strukturiert. In der Einleitung wird auf die Grundlagen der induktiven Strömungsmessung laut Faraday eingegangen. Folgend werden die Einsatzbereiche, Anwendungsmöglichkeiten und Limitationen des EMD Messsystems näher betrachtet. Der Stand von Wissenschaft und Technik ist der nachfolgende Punkt, hier wird auf die aktuelle Lage der Forschung und die Aussicht auf weitere Entwicklung auf dem Gebiet eingegangen. Das grundlegende Funktionsprinzip des Sensorsystems bildet den Abschluss der Einleitung und den geeigneten Übergang zum Hauptteil der Arbeit. Im Hauptteil der Arbeit wird kurz auf die theoretischen Grundlagen zur Messung der Fluidgeschwindigkeit eingegangen. Nachfolgend werden die Messergebnisse der praktischen Versuche zur Eigenerwärmung und Fremderwärmung diskutiert und ein Algorithmus zur Kompensierung des Temperaturdrifts vorgestellt. Der abschließende Ausblick soll auf folgende Problemstellungen des Messsystems vor dem endgültigen Einsatz in der Industrie aufmerksam machen.

Keywords: Phasensensor; EMD.ps; Flüssigmetall; Eigenerwärmung; Fremderwärmung; Drift

  • Diploma thesis
    Hochschule für Technik und Wirtschaft Dresden, 2013
    80 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19950
Publ.-Id: 19950


A thesis on the accuracy of wire-mesh sensor in dependence of bubble size and liquid flow rates

Nuryadin, S.

An experimental study to assess the accuracy of wire-mesh sensor in dependence of bubble sizes and flow rates has been performed in a 50 mm x 50 mm transparent rectangular channel. The liquid superficial velocities were ranging from 0 m/s up to 0.62 m/s with the obtained bubble size ranging from 3 mm – 7 mm. A single wire-mesh sensor with 16x16 electrode wires was used with a temporal and spatial resolution of 10 kHz and 3.125 cm, respectively. A single bubble with known bubble size or termed as the reference bubble size was injected through the test section via bubble injector approx. 25 cm upstream of the wire-mesh sensor. The bubble size measurement by using wire-mesh sensor cannot be obtained directly since it requires the information of bubble velocity which is not available only by installing a single sensor. Therefore, a stereoscopic observation was conducted to obtain the bubble velocity by tracking the successive frames as well as to study the intrusiveness of the sensor. This configuration gave an advantage that the registered bubble will be assigned with its own velocity and a better agreement is expected. As the result, a direct comparison of all individual bubble with the reference bubble size showed an agreement within ±10%. However, the deceleration effect was found for low liquid superficial and observed to disappear as the liquid superficial velocity increased then vanish at observed J L =0.62 m/s.

Keywords: Wire-mesh sensor; bubble velocity; bubble size; bubble flow

  • Master thesis
    GADJAH MADA UNIVERSITY, 2014
    84 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19949
Publ.-Id: 19949


Simulation of planar channeling-radiation spectra of relativistic electrons and positrons channeled in a diamond-structure or tungsten single crystal (classical approach)

Azadegan, B.; Wagner, W.

We present a Mathematica package for simulation of spectral-angular distributions and energy spectra of planar channeling radiation of relativistic electrons and positrons channeled along major crystallographic planes of a diamond-structure or tungsten single crystal. The program is based on the classical theory of channeling radiation which has been successfully applied to study planar channeling of light charged particles at energies higher than 100 MeV. Continuous potentials for different planes of diamond, Si, Ge and W single crystals are calculated using the Doyle-Turner approximation to the atomic scattering factor and taking thermal vibrations of the crystal atoms into account. Numerical methods are applied to solve the classical one-dimensional equation of motion. The code is designed to calculate the trajectories, velocities and accelerations of electrons (positrons) channeled by the planar continuous potential. In the framework of classical electrodynamics, these data allow realistic simulations of spectral-angular distributions and energy spectra of planar channeling radiation. Since the generated output is quantitative, the results of calculation may be useful, e.g., for setup configuration and crystal alignment in channeling experiments, for the study of the dependence of channeling radiation on the input parameters of particle beams with respect to the crystal orientation, but also for the simulation of positron production by means of pair creation what is mandatory for the design of efficient positron sources necessary in high-energy and collider physics. Although the classical theory of channeling is well established for long time, there is no adequate library program for simulation of channeling radiation up to now, which is commonly available, sufficiently simple and effective to employ and, therefore, of benefit as for special investigations as for a quick overview of basic features of this type of radiation.

Keywords: channeling radiation; electrons; positrons; single crystals

Permalink: https://www.hzdr.de/publications/Publ-19948
Publ.-Id: 19948


Beiträge zur Erweiterung der Einsetzbarkeit der kontaktlosen induktiven Strömungstomographie für das kontinuierliche Stranggießen

Klotsche, K.

Die vorliegende Arbeit ist der Weiterentwicklung der kontaktlosen induktiven Strömungstomographie (CIFT) gewidmet, welche die Rekonstruktion der Strömung eines Flüssigmetalls aus der Messung der strömungsinduzierten Änderungen eines angelegten Anregungsmagnetfeldes ermöglicht. Im Vordergrund steht die Erweiterung der Einsetzbarkeit der CIFT-Messtechnik für die experimentelle Modellierung des kontinuierlichen Stranggiessens an der Modellanlage “Mini-LIMMCAST“ am Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Insbesondere wird die Funktionsweise des Verfahrens unter Nutzung von Induktionsspulen und eines alternierenden Anregungsmagnetfeldes unter dem Einfluss der ferromagnetischen Teile einer elektromagnetischen Bremse untersucht.
Zunächst wird die Kalibrierung der Induktionsspulen zur Ermittlung der Übertragungsfaktoren dokumentiert. Die dabei festgestellten Messunsicherheiten werden zusammen mit einer theoretischen Abschätzung des Signal-Rausch-Verhältnisses der Messkette hinsichtlich der Anforderungen an das Auflösungsvermögen der Messtechnik eingeschätzt. Anhand zweier numerischer Simulationen des Versuchsstandes werden die Auswirkungen der ferromagnetischen Komponenten auf die zeitliche und örtliche Ausprägung des Anregungsmagnetfeldes sowie des strömungsinduzierten Magnetfeldes erläutert. Daran schließt sich die Beschreibung der Messungen des strömungsinduzierten Magnetfeldes mit einfachen und gradiometrischen Induktionsspulen an der Modellanlage ohne und mit überlagertem statischen Magnetfeld an. Die Ergebnisse dieser Experimente zeigen eine gute Übereinstimmung mit den Simulationsergebnissen und belegen die prinzipielle Einsatzfähigkeit der verwendeten Messtechnik für das CIFT-Verfahren in den untersuchten Konfigurationen.
Anschließend wird der Entwurf eines neuen Sensorsystems dargelegt, das aus 14 Induktionsspulen besteht und für das sowohl neuartige Gradienten- als auch Einfachspulen konstruiert wurden. Es folgt die Beschreibung einer Messkampagne an der Mini-LIMMCAST-Anlage, bei der die neuen Induktionsspulen zum Einsatz kamen. Hierbei wird an ausgewählten Messungen die korrekte Ermittlung des strömungsinduzierten Magnetfeldes für verschiedene Konfigurationen gezeigt. Abschließend werden daraus berechnete Strömungsrekonstruktionen für einen Vergleich mit dem jeweils zu erwartenden Strömungsbild herangezogen. Die Ergebnisse der Messkampagne verdeutlichen die mit dem neuen Induktionsspulensystem erzielten Verbesserungen.

Keywords: liquid metal; continuous casting; contactless inductive flow tomography

  • Diploma thesis
    TU Dresden, 2013
    115 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19947
Publ.-Id: 19947


Investigation of Gas Bubble Velocities from Experimental Data of Ultrafast two-layer electron beam X-ray Tomography

Patmonoaji, A.

While for measurements in diluted two-phase flows optical methods are frequently applied there is a clear demand for measurement systems for dense two-phase flows. Measurement systems which have the capability to measure flow condition in high accuracy and high detail is needed for understanding the physical mechanism of flow phenomena and also especially for improvement and validation of new two phase flow simulation code model.
At the Fluid Dynamics Institute at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) a unique ultrafast X-ray tomography named ROFEX (Rossendorf fast electron beam X-ray tomography) is being developed. This non-intrusive measurement technique with high spatial and temporal resolution; enables to measure gas liquid phase distribution with detail and high accuracy. A frame rate up to 8000 Hz for simultaneous dual plane measurement and a spatial resolution of 2 mm can be reached. Large range of combination of gas-liquid velocities can be measured without any disturbance.
ROFEX works according to scanned electron beam principle. An electron beam is aimed to a circular metallic target using focusing and deflecting system. Hence rotating X-ray fan that radiates the flow in circular pattern is generated. A detector ring is employed to capture the attenuation value of the X-ray intensity. Further processing with filtered back-projection, reconstructed data result in the form of 3D gray value array. This array is processed with special bubble segmentation algorithm which results in bubble parameters such as bubble volume, detected position, and detected time are able to be obtained at the end of this process.
Presently gas bubble velocities are determined by a cross-correlation from dual measurement planes data which results in gas velocity profiles. In this work a new improved method which has capability to derive velocities of single gas bubble inside the flow has been developed. The new method works by pairing the correct bubbles that are detected at both measurement planes. In order to acquire correct bubble pair, comparison of bubble parameters for instance volume, detected position, and detected time are used. Therefore probability functions are defined for each parameter. If the correct bubbles pair is found, the difference of bubble time shift between both measurement planes can be determined. Therefore, gas bubble velocity is obtained by dividing the measurement plane distance with difference of bubble time detection.
In this report, detailed explanation of the algorithm working principle is given. The algorithm was tested for wide range of flow characteristic and validated by comparison with established theoretical prediction and also cross-correlation method. Velocity field result for wide range of flow structure was also created for further understanding of gas bubbles movement physical mechanism.

Keywords: two-phase flow; bubble velocity; bubble pair detection

  • Master thesis
    Gadjah Mada University, 2013
    140 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19946
Publ.-Id: 19946


Ferromagnetic resonance of perpendicular magnetic anisotropy MgO/CoFeB based tri-layers

Aleksandrov, Y.; Fowley, C.; Bernert, K.; Sluka, V.; Kowalska, E.; Farle, M.; Lindner, J.; Ocker, B.; Fassbender, J.; Deac, A. M.

Magnetic tunnel junctions with perpendicular magnetic anisotropy (PMA) are good candidates for next generation spin-transfer-torque magnetic random access memory (STT-MRAM) [1]. Besides a comparatively higher thermal stability than in-plane MA, the recently reported appearance of PMA in MgO/Co40Fe40B20/Ta structures allows for lower switching currents while maintaining high quality MgO barrier growth.
In this report we use the ferromagnetic resonance technique to investigate the magnetic properties of a CoFeB layer sandwiched by Ta and MgO layers. Samples were grown by RF or DC sputtering using a TIMARIS cluster deposition tool (Singulus Technologies AG) [2] and annealed in N2 environment for 30 minutes at temperatures between 150 and 250°C in steps of 50°C. FMR measurements are performed at room temperature using a microwave cavity [3]. Thin films are also investigated by standard magnetometry measurements in a SQUID/VSM and also by the extraordinary Hall effect to extract the saturation magnetization and effective anisotropy.
Through FMR we are able to simultaneously extract the out-of-plane anisotropy, the effective magnetization and the damping co-efficient, as a function of annealing temperature. Our results show that post-annealing systematically shifts the magnetic easy axis from in-plane to out-of-plane direction. As the annealing temperature is increased the effective magnetization also increases.
[1] S. Ikeda et al., Nature Materials 9,721–724 (2010).
[2] B. Ocker, Singulus Technologies AG, Hanauer Landstrasse 103, 63796 Kahl am Main, Germany.
[3] J. Lindner and M. Farle: Magnetic Anisotropy of Heterostructures, STMP 227, 45–96 (2007).

Keywords: CoFeB; FMR; MTJ; magnetic anisotropy; PMA; spintronics

  • Poster
    The 58th Annual Magnetism and Magnetic Materials (MMM) Conference, 04.-08.11.2013, Denver, Colorado, USA

Permalink: https://www.hzdr.de/publications/Publ-19945
Publ.-Id: 19945


Kerr Microscopy Analysis of Stripe Elements Embedded in a Synthetic Antiferromagnet

Langer, M.; Neudert, A.; Osten, J.; Mönch, J. I.; Mattheis, R.; Lenz, K.; Fassbender, J.; McCord, J.

  • Lecture (others)
    TU Kaiserslautern, Institutsseminar, 21.01.2013, Kaiserslautern, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19943
Publ.-Id: 19943


Editorial for Electromagnetic flow control in metallurgy, crystal growth and electrochemistry

Gerbeth, G.; Eckert, K.; Odenbach, S.

The results of the collaboration Research Centre SFB 609 during 2002 to 2012 are summarized.

Keywords: Electromagnetic flow control in metallurgy; crystal growth and electrochemistry

Permalink: https://www.hzdr.de/publications/Publ-19942
Publ.-Id: 19942


Blasengrößen- und Liquidgeschwindigkeitsbestimmung in Blasensäulen

Chen, K.

Die Bestimmung der Geschwindigkeitskomponenten zur Validierung von CFD-Simulation zählt zu den elementarsten Messaufgaben in einer Blasensäule. Während besonders in einphasigen Strömungen Particle Imaging Velocimetry (PIV) und Constant Temperature Anemometry (CTA) etabliert sind, ist deren Einsatz in Zweiphasenströmung deutlich durch die auftretenden Phasenwechsel gestört.
Während der Einsatz eines PIV-Systems bereits bei geringen Gasanteilen durch fehlende optische Zugänglichkeit nicht mehr möglich ist, besteht bei CTA-Systemen, bedingt durch ihr Messprinzip, theoretisch die Möglichkeit auch bei höheren Gasdurchsätzen zu messen, sofern eine Maskierung der durch Gas verfälschten Daten erfolgt. Zur Klärung dieser Hypothese werden im Rahmen der Bachelorarbeit zwei Aspekte in Vorstudien untersucht. Zunächst widmet sich die Arbeit der einphasigen Kalibrierung des CTA-Systems auf die erwarteten Flüssigkeitsgeschwindigkeiten und deren Reproduzierbarkeit. Die Untersuchungen umfassen desweiteren Studien zur erforderlichen CTA-Messfrequenz. Anschließend werden erste Messungen in einer 2D-Blasensäule qualitativ ausgewertet, die mittels gekoppelter Messung einer Highspeed-Kamera, eine phasensensitiven Nadelsonde sowie eines pseudo-kalibrierten, zweidimensionalen CTA-Systems gemacht wurden. Die Arbeit verzichtet mangels einer ausreichend genauer Kalibrierungen des CTA-Systems und mangels Sensitivität der Phasensonde auf quantitative Bewertungen der Messungen.
Betreuer: Johannes Zalucky

Keywords: constant temperature anemometry; phase sensitive needle probe; conductivity probe; flow velocimetry; bubble column; qualitative data analysis

  • Bachelor thesis
    Hochschule Zittau-Görlitz, 2013
    78 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19941
Publ.-Id: 19941


Numerical study of a continuous casting process with electromagnetic brake

Miao, X.

This dissertation investigates the effect of electromagnetic braking and gas injection on the fluid flow in a continuous casting slab mold numerically and makes verifications on basis of a small Liquid Metal Model for Continuous Casting of steel (mini-LIMMCAST). Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The nonisotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model. The numerical results were validated by flow measurements at the mini-LIMMCAST facility. Numerical simulations disclose the damping effect on the flow closely depending on the wall conductance ratio. In addition, specific modifications of the turbulence model play a crucial role in reconstructing the peculiar phenomenon of an excitation of nonsteady, nonisotropic, largescale flow perturbations caused by the application of the DC magnetic field.

  • Doctoral thesis
    TU Bergakademie Freiberg, 2014
    128 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19940
Publ.-Id: 19940


A droplet entrainment model for horizontal segregated flows

Höhne, T.; Hänsch, S.

One limitation today in simulating horizontal segregated flows is that there is no treatment of droplet formation mechanisms at wavy surfaces. For self-generating waves and slugs, the interfacial momentum exchange and the turbulence parameters have to be modelled correctly. Furthermore, understanding the mechanism of droplet entrainment for heat and mass transfer processes is of great importance in the chemical and nuclear industry.
The development of general computational fluid dynamics (CFD) models, which are closer to physics and include less empiricism, is a long-term objective of the activities of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) research programs. Such models are an essential precondition for the application of CFD codes to the modelling of flow related phenomena in the chemical and nuclear industries. The new formulation for the interfacial drag at the free surface and turbulence parameters within the algebraic interfacial area density model (AIAD) is one result of these HZDR activities. The AIAD approach allows the use of different physical models depending on the local morphology inside a macro-scale multi-fluid framework.
A further step of improvement of modelling interfaces is the consideration of droplet entrainment mechanisms. The proposed entrainment model assumes that due to liquid turbulence the interface gets rough and wavy leading to the formation of droplets. The new approach is validated against existing horizontal two-phase flow data from the HAWAC channel.

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

  • Contribution to proceedings
    ANSYS Conference & 32. CADFEM Users´ Meeting 2014 (ACUM), 04.-06.06.2014, Nürnberg, Deutschland
    CD-ROM
  • Invited lecture (Conferences)
    ANSYS Conference & 32. CADFEM Users´ Meeting 2014 (ACUM), 04.-06.06.2014, Nürnberg, Deutschland
  • Nuclear Engineering and Design 286(2015), 18-26
    DOI: 10.1016/j.nucengdes.2015.01.013

Permalink: https://www.hzdr.de/publications/Publ-19939
Publ.-Id: 19939


Numerical modelling of sub-grid wave turbulence at the interface of horizontal multiphase flows

Höhne, T.

In the last decade, applications of Computational Fluid Dynamic (CFD) methods for nuclear applications received more and more attention, as they proved to be a valuable complementary tool for design and safety. The main interest towards CFD consists in fact in the possibility of obtaining detailed 3D complete flow-field information on relevant physical phenomena at lower cost than experiments.

Typically free surfaces manifest as stratified and wavy flows in horizontal flow domain where gas and liquid are separated by gravity.

Stratified two-phase flows are relevant in many nuclear applications, e.g. pipelines, main coolant lines, horizontal heat exchangers and storage tanks. Special flow characteristics as flow rate, pressure drop and flow regimes have always been of engineering interest. Wallis (1973) analyzed the onset of slugging in horizontal and near horizontal gas-liquid flows. Flow maps which predict transitions between horizontal flow regimes in pipes were introduced e.g. by Taitel and Dukler (1976) and Mandhane et al. (1974). The most important flow regimes are smooth stratified flow, wavy flow, slug flow and elongated bubble flow. Taitel and Dukler (1976) explained the formation of slug flow by the Kelvin-Helmholtz instability. They also proposed a model for the frequency of slug initiation (Taitel and Dukler, 1977).

CFD simulations for free surface flows require the modeling of the non-resolved scales. For modeling of interfacial transfers it is necessary to select the adequate interfacial transfer models and to determine the interfacial area. The numerical solution can resolve the statistically averaged motion of the free surface (including waves) which may not be too small relatively to the channel height and to the characteristic length of the spatial discretization. However, the detailed structure of interacting boundary layers of the separated continuous phases and surface ripples cannot be resolved. Instead, its influence on the average flow must be modeled.

Non-resolved small scale structures of the interface have influence on mass, momentum and heat transfer between the phases. The type of required models depends on the general modeling approach used. To model the momentum transfer e.g. in the frame of the two-fluid model the correlations for the interfacial drag are used. In the past due to the lack of appropriate models often drag correlations valid for bubbly flows or correlations developed for 1D codes were used to simulate the interfacial momentum transfer at the free surface. Such approaches use simplifications and therefore are not able to represent completely the phenomena.

Keywords: AIAD; CFD; multi-phase flow; sub-grid wave turbulence

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2014, 06.-08.05.2014, Frankfurt, Deutschland
    CD-ROM
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2014, 06.-08.05.2014, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19938
Publ.-Id: 19938


Validierung der Widerstands- und Turbulenzmodellierung an der freien Oberfläche

Porombka, P.

Am HZDR werden in enger Zusammenarbeit mit ANSYS neue Ansätze wie das Algebraic Interfacial Area Density (AIAD)-Modell zur numerischen Beschreibung horizontaler, stratifizierter Strömungen entwickelt. Der Inhalt dieser Diplomarbeit ist die Weiterentwicklung des AIAD-Modells hinsichtlich des Impulsaustausches und der Turbulenzbehandlung an der freien Oberfläche.
Die Diplomarbeit ist sehr anspruchsvoll. Das Dokument gliedert sich in Einleitung und Stand der Technik, Grundlagen der Berechnung von Mehrphasenströmungen, Modellierung des Widerstandsbeiwertes, Turbulenzmodellierung und Validierung der Modelle an einem Experiment. Eigene Lösungsansätze wurden selbständig entwickelt und in den Rechencode eingearbeitet. Andere Lösungsansätze werden diskutiert, konnten aber in der Laufzeit der Arbeit nicht umgesetzt werden. Die Arbeiten wurden sehr sorgfältig durchgeführt und die Interpretation der Ergebnisse ist fundiert. Insgesamt ist es eine sehr gute wissenschaftliche Arbeit.

Keywords: AIAD; CFD; multi-phase flow

  • Diploma thesis
    TU Dresden, 2013
    66 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19937
Publ.-Id: 19937


THz based electron bunch length monitoring at the quasi-cw SRF accelerator ELBE

Green, B.; Kovalev, S.; Fisher, A. S.; Bauer, C.; Kuntzsch, M.; Lehnert, U.; Schurig, R.; Golz, T.; Michel, P.; Stojanovic, N.; Gensch, M.

In the past few years the quasi-cw SRF electron accelerator ELBE has been upgraded so that it now allows to compress electron bunches to the sub-picosecond regime. The actual optimization and control of the electron bunch form represents one of the largest challenges of the coming years. In particular with respect to the midterm goal to utilize the ultra-short electron bunches for Laser-Thomson scattering experiments or high field THz experiments. Current developments of THz based electron bunch diagnostic are discussed and an outlook into future developments is given.

  • Poster
    DPG Spring Meeting, Dresden 2014, 30.03.-04.04.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19936
Publ.-Id: 19936


CFD simulation of multiphase flows in porous solid foam structures

Subramanian, K.; Schubert, M.; Lucas, D.; Hampel, U.

Ceramic foam packings, due to their high porosity, high specific surface area and low pressure drop are promising alternatives for reactor internals used in chemical engineering processes. The applications of solid foam packings as burners and heat exchangers have been widely studied, but as catalyst carriers particularly for gas-liquid reaction systems solid foam behaviour is not yet well understood. Due to its highly porous nature, it is very tough to understand the influence of hydrodynamics on the process performance. [1] The goal of this work is to perform three-dimensional Computational Fluid Dynamics (3D CFD) simulations of the evolving gas-liquid flow patterns considering ceramic foams as column internals and to validate them with experimental X-ray tomographic data. It is noteworthy to mention that up to now no 3D CFD simulation has been performed considering ceramic foams as column internals in pilot-scale. On the other hand, a few simulation studies are available considering spherical particles as packings in trickle bed reactors. The trickle bed closures will be modified according to the ceramic foam specifications.

A two-phase Eulerian model is used considering the flow domain as porous body. The influence of the liquid and gas drag is added as external source terms to liquid and gas momentum equations separately. The drag force between the phases has been taken into account using the relative permeability approach, which was developed by Saez and Carbonell [2] for packed beds using capillary pressure and relative permeabilities of two-phase flows. First results from the single-phase pressure drop and the two-phase gas-liquid distribution will be presented.

[1] Calvo. S., Beugre. D., Crine. M., Leonard. A., Marchot. P., Toye. D., Phase distribution measurements in metallic foam packing using X-ray radiography and micro-tomography, Chemical Engineering and Processing, Vol. 48, pp. no. 1030–1039, (2009).
[2] Saez, A.E., Carbonell, R.G., Hydrodynamic Parameters for Gas-Liquid Cocurrent Flow in Packed Beds, AIChE Journal, Vol. 31, No.1, pp no. 52- 62, 1985.

Acknowledgement

This work was funded by the Helmholtz Association within the frame of the Helmholtz Energy Alliance "Energy Efficient Chemical Multiphase Processes".

Keywords: CFD; Ceramic foams; Relative permeability; Multiphase flow

  • Lecture (Conference)
    Chemcon 2013, 26.-31.12.2013, Mumbai, India

Permalink: https://www.hzdr.de/publications/Publ-19935
Publ.-Id: 19935


Photoemission spectroscopy study of the lanthanum lutetium oxide/silicon interface

Nichau, A.; Schnee, M.; Schubert, J.; Besmehn, A.; Rubio-Zuazo, J.; Breuer, U.; Bernardy, P.; Holländer, B.; Mücklich, A.; Castro, G. R.; von Borany, J.; Buca, D.; Mantl, S.

Rare earth oxides are promising candidates for future integration into nano-electronics. A key property of these oxides is their ability to form silicates in order to replace the interfacial layer in Si-based complementary metal-oxide field effect transistors. In this work a detailed study of lanthanum lutetium oxide based gate stacks is presented. Special attention is given to the silicate formation at temperatures typical for CMOS processing. The experimental analysis is based on hard x-ray photoemission spectroscopy complemented by standard laboratory experiments as Rutherford backscattering spectrometry and high-resolution transmission electron microscopy. Homogenously distributed La silicate and Lu silicate at the Si interface are proven to form already during gate oxide deposition. During the thermal treatment Si atoms diffuse through the oxide layer towards the TiN metal gate. This mechanism is identified to be promoted via Lu–O bonds, whereby the diffusion of La was found to be less important.

Permalink: https://www.hzdr.de/publications/Publ-19934
Publ.-Id: 19934


Terahertz electro-optical detection: optical phase or energy measurements

Kovalev, S.; Kitaeva, G.

Models of different available single-photodetector electro-optic sampling schemes are considered from the unified theoretical position. It is taken into account that under electro-optic terahertz wave detection, not only do the polarization states of the femtosecond optical pulse components change but the modules of their amplitudes are also varied. As a result, information concerning the terahertz wave can be obtained not only using the conventional ellipsometry readout scheme (probe-phase sampling) but also by simple measuring of the induced power of the optical pulses (probe-energy sampling). Spectral sensitivities of both of these electro-optic sampling methods are calculated for the cases of nonlinear-optical crystals with zinc-blende symmetry (like ZnTe) and the crystals with one active component of the second-order optical susceptibility tensor (like PPLN). It is found that the ratio between spectral sensitivities of the pure probe-phase and pure probe-energy schemes is proportional to the ratio between the optical and terahertz wave frequencies in all types of the crystals. It is shown that the signal in the near-zero optical transmission point scheme, which is the best for terahertz imaging, has a mixed character. While the contribution of the probe-phase sensitivity appears to be due to spatially nonuniform residual birefringence of the nonlinear zinc-blende crystal, the probe-energy part of the sensitivity has a uniform distribution and can be increased by the angle misalignment of the optical polarization element.

Keywords: Nonlinear wave mixing; Ultrafast nonlinear optics

Permalink: https://www.hzdr.de/publications/Publ-19933
Publ.-Id: 19933


Preclinical [18F]FDG PET/MR: The influence of thyroid dysfunction on the activity of brown adipose tissue (BAT) in mice

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

Thyroid hormones (TH) are crucial regulators of energy metabolism. This is in particular exemplified in patients with thyroid dysfunction disorders leading to hyperthyroidism or hypothyroidism (Brent et al. 2012). Hyperthyroidism, which is associated with excessive levels of TH, leads to an increased metabolic rate and weight loss despite increased food intake. In contrast, hypothyroid patients exhibit a decreased metabolic rate and gain weight despite reduced food intake (Lopez et al. 2010). These effects have been attributed on direct actions of TH on metabolically active tissues, such as brown adipose tissue (BAT) (Bianco et al. 2005). In this study we aimed to evaluate the impact of hyper- and hypothyroidism on BAT activity of C57BL/6 mice using [18F]FDG PET/MRI. To generate hyperthyroidism, mice received L-thyroxine daily (2 µg/ml diluted in drinking water). Hypothyroidism was generated by application of an iodine deficient diet containing 0.15% propylthiouracil (TD.95125, Harlan Laboratories). After 4 weeks of treatment n=4 mice per group (23.7 g±1.2 g body weight) were injected i.p. with [18F]FDG (14.5±1.3 MBq). Thirty minutes post injection the mice were imaged in a small animal PET/MR device (nanoscan®, Mediso, Hungary) up to 30 min. Followed by a whole-body MR scan (gradient echo sequence, TR=20 ms, TE= 3.2 ms) for anatomical orientation and attenuation correction. Metabolic activity of BAT was determined by quantification of the glucose uptake (SUVmean) in typical regions of BAT (supraclavicular neck) using MR-based VOI analysis (PMOD v. 3.3).
The comparison of SUVmean (Figure 1) of the hyperthyroid mice showed a significantly increased [18F]FDG uptake compared to the control group (SUVmean 8.78 ± 2.08 and 6.16 ± 0.57, respectively; p = 0.05). However, in hypothyroid mice, a reduced FDG uptake was observed (SUVmean = 3.53 ± 0.65; p<0.01 vs. hyperthyroid and vs. control, respectively).
In conclusion, these findings substantiate the use of [18F]FDG PET/MRI as a valuable tool to map the effects of thyroid hormones on BAT activity. Furthermore, this is the first study confirming decreased supraclavicular BAT activation in hypothyroid mice.

Brent GA. JCI 2012(122):3035-3043
Lopez et. al. Nat. Med. 2010 (16) 2010:1001-1008
Bianco AC et. al Biosci.Rep. 2005; 191-208

  • Lecture (Conference)
    XIII Turku PET Symposium, 24.-27.05.2014, Turku, Finnland

Permalink: https://www.hzdr.de/publications/Publ-19931
Publ.-Id: 19931


Analysis of SANS measurements on highly irradiated15H2MFA steel

Ulbricht, A.; Török, G.; Gillemot, F.; Bergner, F.; Wagner, A.

A 15H2MFA type VVER440 RPV forging material in the unirradiated reference condition and three different irradiation conditions (samples : A; B and C) up to neutron fluences of 2.94x1e20, 9.52x1e20 and 14.5x1e20 cm-2 (E> 0.5 MeV), respectively, were investigated by SANS at the Budapest Research Reactor. The size distributions of the clusters were calculated using the indirect Fourier transform method. The absolute value of volume fraction of clusters is estimated under the assumption that the clusters are non-magnetic scatterers. The nuclear scattering contrast can vary for different irradiation levels. Differences in scaling of both magnetic and nuclear size distributions give a hint of different cluster composition. Information about the cluster composition is included in the A-ratio. Primary, the A-ratio was defined by the ratio of the SANS intensities perpendicular and parallel to the magnetic field direction. In practice, we observe a Q-dependence of the A-ratio.
We observed a difference are in the scaling of the magnetic and nuclear size distributions. The reason of this difference is discussed.

Keywords: reactor pressure vessel; neutron irradiation; SANS

  • Poster
    International Conference on Neutron Scattering, 08.-12.07.2013, Edinburgh, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-19930
Publ.-Id: 19930


Oxiddispersionsverfestigte (ODS) Stähle für nukleare Anwendungen

Hilger, I.

Die Eigenschaften von ODS stählen werden mit Hinblick auf die Anwendung in der Kernfusion gezeigt. Neben Mechanismen bei Ionen- und Neutronenbestrahlung werden Ergebnisse der Gefügeuntersuchung und der Nanohärtemessung nach Ionenbestrahlung gezeigt.

Keywords: ODS steels

  • Lecture (others)
    IFAM Seminar, 22.11.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19929
Publ.-Id: 19929


Characterization of spark plasma sintered ODS alloys

Hilger, I.; Bergner, F.; Palasse, L.; Shariq, A.; Kölling, S.; Garcia-Junced, A.

Besides the fabrication route via mechanical alloying and spark plasma sintering, the microstructure characterization by means of electron diffraction techniques (EBSD, TKD), atom probe tomography (APT) and small-angle neutron scattering is shown.

Keywords: EBSD; APT; SANS; ODS alloys

  • Lecture (Conference)
    ODISSEUS workshop on ODS steels, 09.12.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19928
Publ.-Id: 19928


Ferritische ODS Stähle für die Kernfusion

Hilger, I.; Heintze, C.; Bergner, F.; Ulbricht, A.; Weißgärber, T.; Garcia-Junced, A.; Palasse, L.; (Editors)

Die Eigenschaften von ODS Stählen werden mit Hinblick auf die Anwendung in der Kernfusion gezeigt. Neben Mechanismen bei Ionen- und Neutronenbestrahlung werden Ergebnisse der Gefügeuntersuchung und der Nanohärtemessung nach Ionenbestrahlung gezeigt.

Keywords: ion irradiation; EBSD; Nanoindentation; SANS; APT

  • Poster
    4. Dresdner Werkstoffsymposium, 18.11.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19927
Publ.-Id: 19927


The structure evolution of yttria in ferritic ODS alloys during mechanical alloying

Hilger, I.; Tegel, M.; Bergner, F.

Oxide dispersion strengthened (ODS) ferritic steels are usually fabricated via mechanical alloying and subsequent consolidation via hot extrusion or hot isostatic pressing. During the individual process steps, a complex evolution of the nanoparticle structure is taking place. Powders with different Y2O3 contents were milled and examined by means of X-ray diffraction (XRD) and atom probe tomography (APT). It has been observed that the Y2O3 is fragmented and becomes partially X-ray amorphous upon milling. This effect is due to the grain refinement of Y2O3 during the milling process and not because of its dissociation in the steel matrix.

Keywords: mechanical alloying; dissolution; ODS alloys

  • Lecture (others)
    HZDR PhD Seminar 2013, 07.10.2013, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19926
Publ.-Id: 19926


Microstructural properties of Spark Plasma Sintered ODS Fe-14Cr alloys

Hilger, I.; Bergner, F.; Weißgärber, T.; Garcia-Junceda, A.; Palasse, L.

Besides the fabrication route via mechanical alloying and spark plasma sintering, the microstructure characterization by means of electron diffraction techniques (EBSD, TKD), atom probe tomography (APT) and small-angle neutron scattering is shown.

Keywords: EBSD; TKD; SPS; SANS; APT; ODS

  • Poster
    GETMAT final workshop, 17.09.2013, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19925
Publ.-Id: 19925


Dual-Beam irradiation of spark plasma sintered ODS Fe-14Cr alloys

Hilger, I.; Bergner, F.; Palasse, L.; Shariq, A.; Kölling, S.; Garcia-Junced, A.

ODS Fe14Cr alloys are considered as candidates for the replacement of austenitic steels in nuclear applications such as cladding tubes for future sodium fast rectors. This requires a background on the fabrication route, properties and irradiation behavior. Samples with yttria contents of 0.6wt% were produced by mechanical alloying and subsequent consolidation via spark plasma sintering (SPS). The grain size and particle type and size were characterized by means of electron backscatter diffraction (EBSD) and atom probe tomography (APT), respectively. The microstructural homogeneity was evaluated by a combination of EBSD and scanning nanoindentation (SNI). SNI mappings are displayed in Fig. 1. A pronounced inhomogeneity of the hardness value at the µm size scale is observed. The homogeneity is clearly influenced by the milling parameters. The relationship between hardness, grain size and spatial distribution of nanoparticles is considered.
The compacted samples were irradiated with iron ions and with iron and helium ions (dual-beam irradiation) in order to investigate the influence of yttria particles on the helium bubble formation. The irradiated and unirradiated materials are characterized with respect to indentation hardness and microstructure.

Keywords: ODS; EBSD; TKD; ion irradiation; Spark plasma sintering

  • Lecture (Conference)
    EUROMAT 2013, 10.09.2013, Sevilla, España

Permalink: https://www.hzdr.de/publications/Publ-19924
Publ.-Id: 19924


Microstructure of spark plasma sintered ODS Fe-14Cr

Hilger, I.; Bergner, F.; Tegel, M.; Palasse, L.; Shariq, A.; Kölling, S.; García-Junceda, A.; Gorley, M.

The fabrication route of an ODS Fe-14Cr alloy via mechanical alloying and spark plasma sintering is shown. The results of electron diffraction techniques (EBSD; TKD), atom probe tomography and X-ray diffraction are shown with respect to the goal to achieve a higher radiation resistance of the material.

Keywords: ion irradiation; spark plasma sintering; ODS; EBSD; TKD

  • Lecture (Conference)
    International ODS meeting, 08.07.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19923
Publ.-Id: 19923


Fabrication of oxide-dispersion strengthened (ODS) steels for nuclear applications

Hilger, I.

An overview about the fabrication, microstructure characterization and irradiation behaviour of oxide-dispersion strengthened steels ist given. The shown techniques include mechanical alloying and spark plasma sintering as well as the characterization by means of electron backscatter diffraction and atom probe tomography.

Keywords: EBSD; atom probe tomography; Spark plasma Sintering; ODS steels

  • Lecture (others)
    FWI PhD Seminar, 17.06.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19922
Publ.-Id: 19922


Germanium nanocrystals in SiO2: Relevance of the defect state distribution at the Si-SiO2 interface

Beyer, R.; Burghardt, H.; von Borany, J.

Nanocrystals (NC's) in metal-oxide-semiconductor structures are considered as storage nodes for non-volatile memory devices. The application of germanium NC's is essentially driven by the prospect of improved charge retention, however, the trade-off between short write/erase operation and long data retention is still an unsolved issue as long as the electronic states contributing to the memory effect and the charge transfer paths for capture and emission are not clearly identified. Recently we have shown, that a thermally stimulated process is involved in the hole emission from
embedded nanocrystals and that interface states might play a key role as transfer nodes. In order to inspect this supposition we examine in this study the charge response from interface states and near-interfacial border traps by means of temperature dependent capacitance-voltage measurements and deep level transient spectroscopy. NC's were introduced into 20 nm SiO2 layers on p-type silicon by Ge implantation and subsequent annealing.
The temperature dependence of the programming window was established for different samples, and the interface state density distribution was reconstructed from the DLTS spectrum. A particular feature was found in the spectrum which is not associated with the emission of the dispersed interface states, but likely related to the charge emission of the NC's based on a second order process. A scheme of the write/erase mechanisms is discussed, pointing out the crucial role of the interface states with respect to the device operation.

Keywords: germanium nanocrystals; non-volatile memory; charge trapping; interface states

Permalink: https://www.hzdr.de/publications/Publ-19921
Publ.-Id: 19921


Resonance fine-splitting in a spin-torque nano-oscillator containing two stacked vortices

Sluka, V.; Kákay, A.; Deac, A. M.; Bürgler, D. E.; Schneider, C. M.; Hertel, R.

Magnetic vortices have become subject of increasingly intense study in spintronics during the past years. These structures develop as flux-closure patterns in cylindrical ferromagnetic disks of dimensions between the single- and multi-domain regimes. The magnetization is basically in-plane and circulates the disk center while the sense of the circulation can be either clockwise or counter-clockwise, defining the chirality of the vortex. As a result of the curling magnetization, the exchange energy density increases when approaching the center region, leading to the formation of a tiny out-of-plane magnetized volume referred to as the vortex core [1]. This core has lateral dimensions in the order of the exchange length and can point either “up” or “down” with respect to the disk plane. Once dislocated from its equilibrium position, the vortex core performs a circular motion around the disk center which is referred to the gyrotropic mode [2,3]. Its frequency depends on the material parameters and the disk aspect ratio and is typically of the order of a few 100 MHz. The sense of gyration is thereby determined by the polarity of the vortex core.
It has been shown that the gyrotropic mode can be excited by spin-transfer torque [4], opening up the possibility of vortex-based spin-torque oscillators, which offer extremely narrow linewidths and operate at zero applied field. Most of the studies concerning spin-transfer torque-induced vortex motion involved systems consisting of a homogeneously magnetized polarizing layer and a vortex free layer.
Here, we study a nanopillar that comprises two magnetic vortices stacked on top of each other. The pillar consists of two Fe disks of 30 and 15 nm thickness, respectively, separated by a 6 nm Ag spacer (Fig. 1). The pillar diameter is about 150 nm. We investigate the magnetization dynamics in the double vortex system both experimentally, where the oscillator is excited by spin-transfer torque, and by means of micromagnetic simulations using the TetraMag [5] code. Specifically, we focus on configurations where the two vortices have opposed chiralities. We find that depending on the chirality combination and the relative core polarities, the resonances split into a fine-structure of four modes (Fig. 2). The four mode frequencies differ by hundreds of MHz, so that our spin-torque oscillator resembles a flute: Each combination of chiralities and relative core polarities results in a different “tone”, and all tones can be excited at zero field and equal currents. The frequencies obtained from micromagnetic simulations are in good agreement with the measured values, showing that the mode fine-splitting results from the magnetostatic interaction between the two ferromagnetic disks.
These results are not only interesting for designing new vortex-based spin-torque oscillators. They also show how to detect changes in vortex core polarity without resorting to high resolution imaging techniques and may thus open new perspectives on how to make use of vortex cores in, for example, core-based non-volatile memory applications.

[1] E. Feldtkeller and H. Thomas. Phys. Kondens. Mater. 4, 8 (1965).
[2] D. L. Hubert. Phys. Rev. B 26, 3758 (1982).
[3] B. van Wayenberge et al. Nature 444, 461 (2006).
[4] V.S. Pribiag et al. Nature Phys. 3, 498 (2007).
[5] A. Kákay, E. Westphal and R. Hertel. IEEE Trans. Magn. 46, 2303 (2010).

Keywords: magnetic vortex; spintronics; spin-torque oscillator; spin-valve; vortex-oscillator; magnetization dynamics; spin-transfer torque; vortex-core

  • Lecture (Conference)
    8th International Symposium on Metallic Multilayers (MML2013), 19.-24.05.2013, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-19920
Publ.-Id: 19920


Terahertz spectroscopy on single buried InAs quantum dots by scanning near-field nano-microscopy

Jacob, R.; Winnerl, S.; Fehrenbacher, M.; Bhattacharyya, J.; Schneider, H.; Wenzel, M. T.; von Ribbeck, H.-G.; Eng, L. M.; Atkinson, P.; Schmidt, O. G.; Helm, M.

Quantum dots have shown to be a highly interesting material system for many application purposes such as single photon emitters in the near-infrared involving interband transitions, but also for mid- and far-infrared applications using intersublevel transitions. Studying the linewidth of these transitions offers valuable clues to the dephasing mechanisms of the trapped electrons. However, due to size fluctuations of the quantum dots, inhomogeneous broadening of the signals usually hides this information when investigating ensembles of dots. Therefore, single-dot spectroscopy has to be performed for this purpose. In contrast to studies of interband transitions (e.g. via micro-photoluminescence) this is not well established at all for intersublevel transitions. In this work, scattering type scanning near-field optical microscopy (s-SNOM) in combination with a free-electron laser is used to investigate intersublevel transitions in single self-assembled buried InAs quantum dots. Thereby, spectrally resonant optical contrast to the surrounding GaAs substrate is observed at photon energies of 83 meV and 123 meV with a linewidth of 5-8 meV. Supported by photoluminescence data these signals can clearly be assigned to the s-d and p-d transitions of single conduction band electrons.

  • Lecture (Conference)
    International Workshop on Optical Terahertz Science and Technology (OTST), 01.-05.04.2013, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-19919
Publ.-Id: 19919


Spectroscopy on single buried InAs quantum dots by scattering scanning near-field infrared microscopy

Fehrenbacher, M.; Jacob, R.; Winnerl, S.; Bhattacharyya, J.; Schneider, H.; Wenzel, M. T.; von Ribbeck, H.-G.; Eng, L. M.; Akinson, P.; Schmidt, O. G.; Helm, M.

Quantum dots are a highly interesting material system for many application purposes such as single photon emitters in the near-infrared, but also for mid- and far-infrared applications. Studying the linewidth of involved optical transitions off ers valuable clues to the dephasing mechanisms of the trapped electrons. However, due to size fluctuations of the quantum dots, inhomogeneous broadening of the signals usually hides this information when investigating ensembles of dots. Therefore, single-dot spectroscopy has to be performed for this purpose. In contrast to studies of interband transitions this is not well established at all for intersublevel transitions. In this work, scattering type scanning near-fi eld optical microscopy (s-SNOM) in combination with a free-electron laser is used to investigate intersublevel transitions in single self-assembled buried InAs quantum dots. Thereby, spectrally resonant optical contrast to the surrounding GaAs substrate is observed at photon energies of 83 meV and 123 meV, which can clearly be assigned to the s-d and p-d transitions of single conduction band electrons.

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19918
Publ.-Id: 19918


New THz and Far-infrared Lightsources

Gensch, M.

There is a grow­ing in­ter­est in THz and far in­frared light sources for use in ma­te­r­ial stud­ies. Both co­her­ent ra­dia­tive sources (CSR, COTR, etc.) and FEL sources have been de­vel­oped in the last few years to ad­dress this need. This talk will de­scribe re­cent de­vel­op­ments in this grow­ing field.

  • Invited lecture (Conferences)
    FEL13 - 35th International Free Electron Laser Conference, 25.-30.08.2013, New York, USA

Permalink: https://www.hzdr.de/publications/Publ-19917
Publ.-Id: 19917


THz based electron bunch length monitoring at the quasi-cw SRF accelerator ELBE

Green, B.; Kovalev, S.; Fisher, A.; Bauer, C.; Kuntzsch, M.; Lehnert, U.; Schurig, R.; Goltz, T.; Michel, P.; Stojanovic, N.; Gensch, M.

In the past few years the quasi-cw SRF electron accelerator ELBE has been upgraded so that it now allows to compress electron bunches to the sub-picosecond regime. The actual optimization and control of the electron bunch form represents one of the largest challenges of the coming years. In particular with respect to the midterm goal to utilize the ultra-short electron bunches for Laser-Thomson scattering experiments or high field THz experiments. Current developments of THz based electron bunch diagnostic are discussed and an outlook into future developments is given.

  • Poster
    APS Spring Meeting, 05.-08.04.2014, Savannah, USA

Permalink: https://www.hzdr.de/publications/Publ-19916
Publ.-Id: 19916


New Methodology for Realistic Integration of Sorption Processes Safety Assessments

Noseck, U.; Britz, S.; Flügge, J.; Mönig, J.; Brendler, V.; Stockmann, M.

Sorption on mineral surfaces of sediments is one important retardation process for radionuclides to be considered in long-term safety assessments for radioactive waste repositories. In the past the Kd-concept with temporally constant values was applied to describe radionuclide retardation in the far field of a repository. This modeling approach has the advantage of being simple and computationally fast but it does not take into account the spatial and temporal changes of geochemical conditions that will occur during the evolution of the repository system, e.g. due to long-term climatic changes. One option to describe the impact of such geochemical changes on radionuclide transport and retardation is the so-called smart Kd-concept. In the present study this new modeling approach is developed allowing the consideration of geochemical changes over time without strongly affecting the computational times of transport calculations. The state-of-the-art transport program r3t, used for large model areas and very long time scales, was modified to incorporate the smart Kd-concept. The methodology is based on a description of the radionuclide sorption as a function of selected, important environmental parameters (e.g. pH, pCO2, ionic strength and Ca2+, DIC and the respective radionuclide concentration) using mechanistic sorption models.

First, this approach is developed for a typical sedimentary system covering rock salt and clay formations in Northern Germany. This system mainly consists of tertiary and quaternary sands and clays. However, the approach is applicable to any site of interest. Thermodynamic data were missing for some major minerals present in the model area, such as feldspars and mica, and for relevant elements. To fill these data gaps, an experimental program including batch and column experiments has been conducted. By prior calculations of distribution coefficients for each radionuclide and sediment as functions of the environmental parameters, multidimensional Kd-matrixes are established combining surface complexation and ion exchange. The calculations are performed coupling the geochemical speciation code PHREEQC with the parameter estimation tool UCODE. After implementation of the methodology in r3t, transport calculations considering long-term changes of geochemical conditions have been performed for selected test cases. The results of the concept applied here are very promising. The concept allows the description of radionuclide sorption and transport through large model areas over very long time frames in dependence of variable geochemical conditions.

Keywords: Sorption; Nuclear Waste; Model; Reactive Transport; Hydrology; Risk Assessment; Geochemistry; Climate Change; Radionuclides; Actinides; Thermodynamic; Retardation

  • Lecture (Conference)
    WM2014 Conference, 02.-06.03.2014, Phoenix, Arizona, USA

Permalink: https://www.hzdr.de/publications/Publ-19915
Publ.-Id: 19915


A wrap up of modeling sorption processes of Eu3+ under varying geochemical conditions

Britz, S.; Noseck, U.; Brendler, V.; Durner, W.; Zachmann, D.

In safety assessments for radioactive waste repositories detailed knowledge about surface processes regarding long-term safety relevant elements (e.g. Am3+) is of fundamental importance. Surface reactions such as sorption as well as other processes lead to retardation and influence radionuclide migration. These processes occur in nature and therefore, they must be considered for realistic transport calculations. These processes function as a natural barrier and might reduce contaminant dissemination of potentially hazardous pollutants in natural environments.

So far, the Kd-concept has been applied using distribution coefficients constant in time and space to describe radionuclide transport in the far field of a repository. This approach does not take temporally and spatially changing geochemical conditions into account. In order to include varying geochemical conditions the smart Kd-concept based on thermodynamic sorption models was developed. Combining the state-of-the-art codes r3t (radionuclide, reaction, retardation, and transport) with d3f (distributed, density-driven flow) it is possible to model transport processes as a function of important environmental parameters e.g. pH, pCO2, ionic strength, Ca concentration, DIC, and radionuclide concentration. By including the smart Kd-concept into r3t, multidimensional Kd-matrices are calculated for each radionuclide and sediment a-priori, which are subsequently applied for reactive transport calculations.

To model sorption processes that are controlled by geochemical conditions robust data sets of so called surface complexation parameters (SCP) are required. These parameters, such as protolyses constants (pK-values), specific surface area (SSA) and surface site density (SSD) as well as stability constants of surface complexes (logK-values) are derived from measurements. Generally speaking, here SCP are obtained by fitting experimental data sets applying the geochemical speciation code PhreeqC in combination with the parameter estimation code UCODE. The SCP are iteratively optimized by UCODE to obtain the best fitted data set. Thereby derived SCP are subsequently applied as fixed parameters in reactive transport models.

Literature studies revealed that for important mineral phases such as muscovite and orthoclase nearly no SCP data sets are available at present. Hence, we performed extensive laboratory studies to derive experimental data. This study describes the approach to assess surface complexation parameters of Eu3+ (as a homologue for trivalent actinides). Experimental data of titration, batch and column experiments are discussed and evaluated. Exemplarily, we demonstrate the approach for muscovite. However, this method may be applied to any mineral or sediment of interest.

Keywords: Sorption; Surface; Complexation; Europium; Muscovite; Modelling

  • Lecture (Conference)
    TRePro III – Workshop on Modelling of Coupled Reactive and Transport Processes, 05.-07.03.2014, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19914
Publ.-Id: 19914


Uranium sorption onto single mineral phases – approaching consistency and robustness

Brendler, V.; Bok, F.; Müller, K.

One of the contaminants gaining special public attention is uranium. Though in almost all cases natural uranium (or depleted uranium) is of concern – and thus its chemotoxicity – radioactivity dominates most debates. But in any case the environmental fate of uranium and factors retarding or enhancing its transport are of high relevance. There are many studies addressing the sorption properties of uranium(VI) – and to a much lesser amount also of uranium(IV) – that produce a very patchy figure when it comes to a generalized view based on quasi-thermodynamic surface complexation models (SCM). This talk summarizes the current state-of-the-art with respect to and tries to homogenize the facts, also pointing out some steps to be done next.

Keywords: Sorption; Thermodynamic; Surface; Complexation; Uranium; Database; Uncertainty; Geochemistry; Consistency

  • Invited lecture (Conferences)
    ACTINIDES 2013, 21.-26.07.2013, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19913
Publ.-Id: 19913


THEREDA revisited – project status in 2013

Brendler, V.; Bok, F.; Marquardt, C.; Altmaier, M.

Safety analysis for a geological repository for radioactive waste as well as remediation measures for uranium mining and processing legacies share an essential: the need for a reliable, traceable and accurate assessment of potential migration of toxic constituents into the biosphere. The respective computational codes require site-independent thermodynamic data concerning aqueous speciation, solubility limiting solid phases and ion-interaction parameters. Such databases, however, show several constraints:
- Incompleteness in terms of major and trace elements
- Inconsistencies between species considered and corresponding formation constants
- Restricted variation ranges of intensive parameters (temperature, density, pressure)
- Limitations with respect to solution compositions (ionic strength)
To overcome these limitations to a significant degree, an ambitious database project – THEREDA – has been launched in 2006 by institutions leading in the field of safety research for nuclear waste disposal in Germany

Keywords: Thermodynamic; Database; Nuclear Waste; Disposal; Solution; Solid; Complexation; Reaction; Ion-Ion-Interaction; Geochemistry

  • Poster
    MIGRATION conference 2013, 08.-13.09.2013, Brighton, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-19912
Publ.-Id: 19912


Resistive switching in thin multiferroic films

Bogusz, A.; You, T.; Blaschke, D.; Scholz, A.; Shuai, Y.; Luo, W.; Du, N.; Bürger, D.; Skorupa, I.; Schmidt, O. G.; Schmidt, H.

Resistive switching properties of multiferroic BiFeO3 and YMnO3 thin films grown by pulsed laser deposition technique have been investigated. Both material systems sandwiched between Au top and Pt/Ti bottom electrodes reveal nonvolatile resistive switching upon application of an electric field. BiFeO3 is switching in bipolar mode when a positive and negative bias is applied. The resistance ratio between high resistance and low resistance state is larger than two orders of magnitude. In contrary to BiFeO3, YMnO3 shows a unipolar resistive switching of abrupt nature with the difference up to five orders of magnitude between both resistance states. This work presents the results on resistive switching in BiFeO3 and YMnO3 and discusses the mechanisms of observed phenomena. Possible applications of our findings are shown on the example of nonvolatile data storage devices.

  • Contribution to proceedings
    2013 International Semiconductor Conference Dresden-Grenoble (ISCDG), 26.-27.09.2013, Dresden, Germany
    Semiconductor Conference Dresden-Grenoble (ISCDG), 2013 International, 978-1-4799-1250-6
    DOI: 10.1109/ISCDG.2013.6656319
  • Lecture (Conference)
    International Semiconductor Conference Dresden-Grenoble, 26.-27.09.2013, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-19911
Publ.-Id: 19911


Resistive switching properties of multiferroic YMnO3

Bogusz, A.; Blaschke, D.; Skorupa, I.; Scholz, A.; Schmidt, O. G.; Schmidt, H.

Multiferroics, materials with simultaneous presence of any two or more of primary ferroic orderings in the same phase have gained a great attention both from scientists and industry [1]. Multiferroism gives an opportunity for a development of new materials and concepts for multifunctional devices. Presented work investigates the resistive switching properties of YMnO3, known as an improper multiferroic [2]. Thin YMnO3 films were grown by pulsed laser deposition on Si substrates with Ti/Pt bottom electrode at 800°C and varying oxygen partial pressure. Characterization of as-grown samples by X-ray diffraction and scanning electron microscopy was followed by determination of electrical properties of films in metal-insulator-metal (MIM) configuration. Results indicate a non-volatile unipolar resistive switching with high resistance ratio of high over low resistance state (>10^4). Switching mechanism is ascribed to the formation and rupture of conductive paths in the YMnO3 films upon applied current. In addition, the role of film microstructure and defect formation/distribution resulting from different growth conditions and its effect on the resistive switching behavior are discussed.

[1] N.A. Spaldin et al., Physics Today 63 (2010) 38.
[2] B.B. Van Aken et al., Nature Mater. 3 (2004) 164.

  • Poster
    6th European School on Multiferroics (ESMF6), 21.-26.07.2013, Wittenberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-19910
Publ.-Id: 19910


Spatial and temporal resolution of a Local Lorentz Force Flowmeter

Heinicke, C.; Wondrak, T.

Electromagnetic measurement techniques are very promising for accessing the flow properties of liquid melts. We extend one of the recently developed techniques, Lorentz Force Velocimetry, to the measurement of spatial flow structures close to the wall of the confining container. The sensor we use is called Local Lorentz Force Flowmeter (L2F2). It comprises a small permanent magnet which is attached to a force measurement system. We demonstrate that it is possible to reconstruct the complex flow in the vicinity of the wall of a confined vessel using the L2F2. Additionally, we show with the help of a solid body experiment that the L2F2 responds to temporal changes in the flow on the order of 1 Hz.

Keywords: local flow measurement; liquid metal; lorentz force velocimetry

Permalink: https://www.hzdr.de/publications/Publ-19909
Publ.-Id: 19909


Renaissance enamels - colouring and state of preservation Non-destructive studies by external PIXE–PIGE–RBS

Neelmeijer, C.; Hasselmeyer, L.; Eulitz, J.

The work mechanism of the orbit clock, a masterpiece of Eberhard Baldewein in the 1560s [1] and permanent exhibit in the Math.-Phys. Salon of Dresden, houses in a fire-gilded brass body carrying rich silver-made ornamental strips plus decorative ornaments of coloured enamel. Recently, this unique object of art was under general restoration. PIXE analysis of dismount metal pieces searched for differences in composition possibly revealing former coaction of several workshops. Substantial studies of enamels used PIXE, PIGE and RBS simultaneously at the external 3.85 MeV proton beam in He-atmosphere, allowing both the detection of elements Z ≥ 5 and, in particular by RBS, the identification of surface deterioration [2].
The detailed enamel artworks show opaque but also translucent layers lying upon another for achieving visual depth effects or being singly arranged on/between gold (sometimes silver) ornamentation. Chromaticity of the vitreous materials was induced due to embedding of specific metallic ions. In accordance with ref. [3] the enamels under analysis – red, green, brown, blue, black, white – show the corresponding accompanying elements – Cu, Cu plus Fe, mainly Fe, Co plus Cu, Mn plus Fe, Pb plus Sn – respectively. Enamel composition analysis (wt% of elemental oxides) took place in consideration of small adjacent gold or silver filigrees casually hidden by the proton beam. Maximum MnO concentration of 9% was obtained for black enamel improved by 1% CoO. The translucent red material (~2% CuO) includes ~1% MnO for plastic shading effects. Tints of green enamel were tuned by the addition of both ~10% Cu- and ~6% Fe-oxide. A brown-orange detail shows 22% Fe2O3 plus 0.4% CuO. Just about 1% CoO proves quite enough for blue enamel colouration, shaded by adding ~6% CuO.
For blue, black and green enamels the concentrations of the glass network former SiO2 are in the order of 60% or above, just sufficient for resistance to humidity (hydrolysis, leaching) [2]. High concentration of 10-20% Na2O (fluxing agent) along with only 2-8% K2O (network modifier) contribute to the enamel long-term stability. These criteria, ensuring durability, are diminished in case of the red material characterized by CSiO2 < 60% and CK2O > 16%. Therefore, conservation activities should mainly concentrate on decorations made from red enamel. Altogether, not one of the RBS spectra identifies oxygen enrichment in the vicinity of the enamel surface as a characteristic signal of progressing leaching effects [2].
Two positions were found pointing to potential earlier restoration work. The small blackish detail of a complex ornamentation shows 1% MnO only but nearly twice of the current concentrations for both Fe2O3 and CoO. In addition, the RBS spectrum shows a striking carbon surface-signal reflecting probably carbon containing material for blackening. On a peculiar opaque detail of CuO-based light blue enamel Co is missing and Pb originates from potential lead white pigment.


[1] http://www.tschirnhaus-gesellschaft.de/e_g_mps.html
[2] M. Mäder, C. Neelmeijer, Nucl. Instrum. Methods Phys. Res., Sect. B 226 (2004) 110-118.
[3] K. H. Wedepohl, Die Herstellung mittelalterlicher und antiker Gläser, F. Steiner, Akademie der Wissenschaften und der Literatur, Mainz, Stuttgart, 1993

Keywords: Eberhard Baldewein; orbit clock; enamel; nondestructive analysis; external proton beam; PIXE-PIGE-RBS

  • Lecture (Conference)
    PIXE2013 - 13th International Conference on Particle induced X-Ray Emission, 03.-08.03.2013, Gramado, Brazil

Permalink: https://www.hzdr.de/publications/Publ-19908
Publ.-Id: 19908


Impact of carbon ion irradiation on epidermal growth factor receptor signaling and glioma cell migration in comparison to conventional photon irradiation.

Stahler, C.; Roth, J.; Cordes, N.; Taucher-Scholz, G.; Mueller-Klieser, W.

PURPOSE:
Radiotherapy of malignant gliomas may be limited by an interference of radiation with the migratory potential of tumor cells. Therefore, the influence of conventional photon and modern carbon ion ((12)C) irradiation on glioblastoma cell migration and on epidermal growth factor receptor-related (EGFR) signaling was investigated in vitro. MATERIALS AND METHods: EGFR overexpressing glioblastoma cell lines U87 EGFR++ and LN229 EGFR++ were irradiated with 0, 2 or 6 Gy photons or (12)C heavy ions. Migration was analyzed 24 h after treatment in a standardized Boyden Chamber assay. At different time points EGFR, protein kinase B (PKB/AKT) and extracellular signal-related kinases (ERK1/2) were analyzed by Western blotting.

RESULTS:
2 Gy photon irradiation increased U87 EGFR++ migration and decreased motility of LN229 EGFR++ cells. Heavy ions decreased migration of both cell lines as a function of dose. There was a time-dependent increase of phosphorylation of EGFR, AKT and ERK1/2 in U87 EGFR++ after 2 Gy photon irradiation. After heavy ion irradiation EGFR, AKT or ERK1/2 remained unchanged.

CONCLUSIONS:
Results suggest that the impact of irradiation on tumor cell migration depends on radiation type and cell line. Photons, but not heavy ions, potentially contribute to treatment failure by increasing EGFR-related tumor cell migration.

Permalink: https://www.hzdr.de/publications/Publ-19907
Publ.-Id: 19907


CDK2 knockdown enhances head and neck cancer cell radiosensitivity.

Soffar, A.; Storch, K.; Aleem, E.; Cordes, N.

PURPOSE:

Cyclin-dependent kinase 2 (CDK2) is critically involved in cell cycling and has been proposed as a potential cancer target. It remains largely elusive whether CDK2 targeting alters the tumor cell radiosensitivity.

MATERIALS AND METHODS:
CDK2(-/-) and wild type (WT) mouse embryonic fibroblasts (MEF) as well as six human head and neck squamous cell carcinoma (HNSCC) cell lines (SAS, FaDu, Cal-33, HSC-4, UTSCC-5, UTSCC-8) were used. Upon CDK2 knockdown using small interfering technology, colony formation, DNA double-strand breaks (DSB), cell cycle distribution and expression and phosphorylation of major proteins regulating cell cycle and DNA damage repair were examined.

RESULTS:
CDK2(-/-) MEF and CDK2 HNSCC knockdown cell cultures were more radiosensitive than the corresponding controls. Repair of DSB was attenuated under CDK2 knockout or knockdown. In contrast to data in MEF, combined CDK2 knockdown with irradiation showed no cell cycling alterations in SAS and FaDu cultures. Importantly, CDK2 knockdown failed to radiosensitize SAS and FaDu when cultured in a more physiological three-dimensional (3D) extracellular matrix environment.

CONCLUSIONS:
Our findings suggest that targeting of CDK2 radiosensitizes HNSCC cells growing as monolayer. Additional studies performed under more physiological conditions are warranted to clarify the potential of CDK2 as target in radiotherapy.

Permalink: https://www.hzdr.de/publications/Publ-19905
Publ.-Id: 19905


Double targeting of Survivin and XIAP radiosensitizes 3D grown human colorectal tumor cells and decreases migration.

Hehlgans, S.; Petraki, C.; Reichert, S.; Cordes, N.; Rödel, C.; Rödel, F.

BACKGROUND AND PURPOSE:

In the present study, we aimed to investigate the effect of single and double knockdown of the inhibitor of apoptosis proteins (IAP) Survivin and X-linked IAP (XIAP) on three-dimensional (3D) clonogenic survival, migration capacity and underlying signaling pathways.

MATERIALS AND METHODS:
Colorectal cancer cell lines (HCT-15, SW48, SW480, SW620) were subjected to siRNA-mediated single or Survivin/XIAP double knockdown followed by 3D colony forming assays, cell cycle analysis, Caspase activity assays, migration assays, matrigel transmigration assays and Western blotting (Survivin, XIAP, Focal adhesion kinase (FAK), p-FAK Y397, Akt1, p-Akt1 S473, Extracellular signal-regulated kinase (ERK1/2), p-ERK1/2 T202/Y204, Glycogen synthase kinase (GSK)3β, p-GSK3β S9, nuclear factor (NF)-κB p65).

RESULTS:
While basal cell survival was altered cell line-dependently, Survivin or XIAP single and Survivin/XIAP double knockdown enhanced cellular radiosensitivity of all tested cancer cell lines grown in 3D. Particularly double knockdown conditions revealed accumulation of cells in G2/M, increased subG1 fraction, elevated Caspase 3/7 activity, and reduced migration. Intracellular signaling showed dephosphorylation of FAK and Akt1 upon Survivin and/or Survivin/XIAP silencing.

CONCLUSIONS:
Our results strengthen the notion of Survivin and XIAP to act as radiation resistance factors and further indicate that these apoptosis-regulating proteins are also functioning in cell cycling and cell migration.

Keywords: Colorectal cancer; Invasion; Ionizing radiation; Migration; Survivin; Three-dimensional cell culture; XIAP

Permalink: https://www.hzdr.de/publications/Publ-19904
Publ.-Id: 19904


Ion beam induced structural modifications in nano-crystalline permalloy thin films

Roshchupkina, O.

In the last years, there is a rise of interest in investigation and fabrication of nanometer sized magnetic structures due to their various applications (e.g. for data storage or micro sensors). Over the last several decades ion beam implantation became an important tool for the modification of materials and in particular for the manipulation of magnetic properties. Nanopatterning and implantation can be done simultaneously using focused-ion beam (FIB) techniques. FIB implantation and standard ion implantation differ in their beam current densities by 7 orders of magnitude. This difference can strongly influence the structural and magnetic properties, e.g. due to a rise of the local temperature in the sample during ion implantation.

In previous investigations both types of implantation techniques were studied separately. The aim of the current research was to compare both implantation techniques in terms of structural changes and changes in magnetic properties using the same material system. Moreover, to separate any possible annealing effects from implantation ones, the influence of temperature on the structural and magnetic properties were additionally investigated.

For the current study a model material system which is widely used for industrial applications was chosen: a 50 nm thick non-ordered nano-crystalline permalloy (Ni81Fe19) film grown on a SiO2 buffer layer based onto a (100)-oriented Si substrate. The permalloy films were implanted with a 30 keV Ga+ ion beam; and also a series of as-deposited permalloy films were annealed in an ultra-high vacuum (UHV) chamber.

Several investigation techniques were applied to study the film structure and composition, and were mostly based on non-destructive X-ray investigation techniques, which are the primary focus of this work. Besides X-ray diffraction (XRD), providing the long-range order crystal structural information, extended X-ray absorption fine structure (EXAFS) measurements to probe the local structure were performed. Moreover, the film thickness, surface roughness, and interface roughness were obtained from the X-ray reflectivity (XRR) measurements. Additionally cross-sectional transmission electron microscope (XTEM) imaging was used for local structural characterizations. The Ga depth distribution of the samples implanted with a standard ion implanter was measured by the use of Auger electron spectroscopy (AES) and Rutherford backscattering (RBS), and was compared with theoretical TRIDYN calculation. The magnetic properties were characterized via polar magneto-optic Kerr effect (MOKE) measurements at room temperature.

It was shown that both implantation techniques lead to a further material crystallization of the partially amorphous permalloy material (i.e. to an increase of the amount of the crystalline material), to a crystallite growth and to a material texturing towards the (111) direction. For low ion fluences a strong increase of the amount of the crystalline material was observed, while for high ion fluences this rise is much weaker. At low ion fluences XTEM images show small isolated crystallites, while for high ones the crystallites start to grow through the entire film. The EXAFS analysis shows that both Ni and Ga atom surroundings have a perfect near-order coordination corresponding to an fcc symmetry. The lattice parameter for both implantation techniques increases with increasing ion fluence according to the same linear law. The lattice parameters obtained from the EXAFS measurements for both implantation types are in a good agreement with the results obtained from the XRD measurements. Grazing incidence XRD (GIXRD) measurements of the samples implanted with a standard ion implanter show an increasing value of microstrain with increasing ion fluence (i.e. the lattice parameter variation is increasing with fluence). Both types of implantation result in an increase of the surface and the interface roughness and demonstrate a decrease of the saturation polarization with increasing ion fluence.

From the obtained results it follows that FIB and standard ion implantation influence structure and magnetic properties in a similar way: both lead to a material crystallization, crystallite growth, texturing and decrease of the saturation polarization with increasing ion fluence. A further crystallization of the highly defective nano-crystalline material can be simply understood as a result of exchange processes induced by the energy transferred to the system during the ion implantation. The decrease of the saturation polarization of the implanted samples is mainly attributed to the simple presence of the Ga atoms on the lattice sites of the permalloy film itself.

For the annealed samples more complex results were found. The corresponding results can be separated into two temperature regimes: into low (<400 C) and high (>400 C) temperatures. Similar to the implanted samples, annealing results in a material crystallization with large crystallites growing through the entire film and in a material texturing towards the (111) direction. The EXAFS analysis shows a perfect near-order coordination corresponding to an fcc symmetry. The lattice parameter of the annealed samples slightly decreases at low annealing temperatures, reaches its minimum at about ~400 C and slightly rises at higher ones. From the GIXRD measurements it can be observed that the permalloy material at temperatures above >400 C reaches it's strain-free state. On the other hand, the film roughness increases with increasing annealing temperature and a de-wetting of the film is observed at high annealing temperatures. Regardless of the material crystallization and texturing, the samples annealed at low temperatures demonstrate no change in saturation polarization, while at high temperatures a rise by approximately ~15% at 800 C was observed. The rise of the saturation polarization at high annealing temperatures is attributed to the de-wetting effect.

Keywords: permalloy; focused ion beam; broad beam ion implantation; annealing; magneto-optic Kerr effect; extended X-ray absorption fine structure; X-ray diffraction

  • Doctoral thesis
    TU Dresden, 2013
    130 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19903
Publ.-Id: 19903


The novel HDAC inhibitor NDACI054 sensitizes human cancer cells to radiotherapy.

Hehlgans, S.; Storch, K.; Lange, I.; Cordes, N.

BACKGROUND AND PURPOSE:

Inhibition of histone deacetylases (HDACs) has preclinically and clinically shown promise to overcome radio- and chemoresistance of tumor cells. NDACI054 is a novel HDAC inhibitor, which has been evaluated here for its effects on cell survival and radiosensitization of human tumor cell lines from different origins cultured under more physiological three-dimensional (3D), extracellular matrix (ECM)-based conditions.

MATERIAL AND METHODS:
A549 lung, DLD-1 colorectal, MiaPaCa2 pancreatic and UT-SCC15 head and neck squamous cell carcinoma cells were treated with increasing NDACI054 concentrations (0-50 nM, 24 h) either alone or in combination with X-rays (single dose, 0-6 Gy). Subsequently, 3D clonogenic cell survival, HDAC activity, histone H3 acetylation, apoptosis, residual DNA damage (γH2AX/p53BP1 foci assay 24h post irradiation) and phosphorylation kinetics of Ataxia telangiectasia mutated (ATM), DNA-dependent protein kinase (DNA-PK), Caspase-3 and Poly(ADP-ribose)-Polymerase 1 (PARP 1) cleavage were analyzed.

RESULTS:
NDACI054 potently decreased HDAC activity with concomitant increase in acetyl-histone H3 levels, mediated significant cytotoxicity and radiosensitization. These effects were accompanied by a significant increase of residual γH2AX/p53BP1-positive foci, slightly elevated levels of Caspase-3 and PARP 1 cleavage but no induction of apoptosis.

CONCLUSIONS:
Our data show potent antisurvival and radiosensitizing effects of the novel HDAC inhibitor NDACI054 encouraging further preclinical examinations on this compound for future clinical use.

Keywords: 3D cell culture; Cancer cell lines; DNA repair; HDAC inhibitor; Ionizing radiation

Permalink: https://www.hzdr.de/publications/Publ-19902
Publ.-Id: 19902


Contactelss Inductive Flow Tomography

Wondrak, T.; Timmel, K.; Klotsche, K.; Gerbeth, G.; Stefani, F.

The Contactless Inductive Flow Tomography (CIFT) allows for determining flow structures in conducting liquids which are exposed to one or more external magnetic fields. Measuring the induced fields around the fluid volume for each of the applied fields, it is possible to infer the velocity field by solving an inverse problem with appropriate regularization techniques. We will give an overview of the CIFT method and present the measurement system for the model of a continuous caster at the HZDR. We will conclude with new developments towards a robust measurement of the very small induced magnetic fields.

  • Lecture (Conference)
    The International Symposium on Electromagnetic Flow Control in Metallurgy, Crystal Growth and Electrochemistry, 25.-27.03.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19901
Publ.-Id: 19901


Nonvolatile resistive switching in multiferroic YMnO3 thin films

Bogusz, A.; Skorupa, I.; Blaschke, D.; Schmidt, O. G.; Schmidt, H.

Intensive research on multiferroic materials [1] is driven by the possibility of creating novel, miniaturized tunable multifunctional devices [2]. This work investigates resistive switching behavior of YMnO3 thin films, which can be utilized in new generation memory devices. Series of YMnO3 films were grown by pulsed laser deposition on Si substrates with Pt bottom electrode at temperatures varying between 500∘C and 850∘C. Characterization of as-grown samples by X-ray diffraction and scanning electron microscopy was followed by determination of electrical properties of films in metal-insulator-metal (MIM) configuration. Results showed that the YMnO3 films grown at 800∘C exhibit the best resistive switching properties with high resistance ratio (>10000) of high over low resistance state. Switching mechanism is ascribed to the structural transitions within the film upon applied current.
[1] A. Bogusz et al., Defect Diffus. Forum 323-325, 115 (2012)
[2] Y. Shuai, H. Schmidt et al., J. Appl. Phys. 109, 124117 (2011); J. Appl. Phys. 111, 07D906 (2012)

  • Lecture (Conference)
    DPG Spring Meeting, 10.-15.03.2013, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-19900
Publ.-Id: 19900


Current-induced magnetization dynamics in a spin-valve comprising two spin-transfer torque-coupled ferromagnetic layers

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

Typical all-metallic spin-torque oscillators are nanopillars comprising two easy-plane ferromagnetic elements separated by a nonmagnetic metal spacer. One of the layer magnetizations is fixed and serves as the polarizer for the current while the second layer is susceptible to spin-transfer torque. Subjected to d.c. currents and external magnetic fields, these devices exhibit wellknown types of magnetization dynamics such as small-/ large-angle or clamshell precession, generating microwave signals at several Gigahertz [1]. Here, we investigate a system that differs from the above in two ways. First, our nanopillar combines an uniaxial in-plane anisotropy-ferromagnet (FM1) with a second layer (FM2) exhibiting a perpendicular anisotropy (PMA). Thus our system resembles the one studied in [2], however, in our case none of the layers is fixed, meaning that both layer magnetizations are coupled by the current and can move freely under the action of the spin-torque. Using the generalization of Slonczewski’s model [3] to asymmetric spin-valves [4,5], the d.c. current-induced magnetization dynamics in perpendicular applied field is studied numerically within the framework of the macrospin model. The resulting current-field phase diagram displays regimes of single and combined layer motion. Within fields below the effective PMA and currents smaller than -2 mA or larger than 4 mA (for the parameters chosen), the magnetization of FM1 basically precesses in-plane for the external field exceeding a threshold value. The latter increases with the current magnitude for both current polarities, climbing up to ±176 mT at +25 mA. The simultaneous excitation of FM1 and FM2 however exhibits a more asymmetric current dependence (Fig. 1). Within the simultaneously excited regime, the complexity of the trajectories is found to vary strongly with applied currents and fields. Fig. 2 shows example spectra taken at the locations indicated in Fig. 1. Viewed from a commoving frame, some trajectories correspond to largeangle precession, while others behave entirely differently from what is found in common fixed-free layer spin-valves. This is reflected in the obtained power spectra which range from near-harmonic to broad noise-like.

[1] S. I. Kiselev et al., Nature 425, 380 (2003).
[2] W. H. Rippard et al., Phys. Rev. B 81, 014426 (2010).
[3] J. C. Slonczewski, J. Magn. Magn. Mater. 247, 324 (2002).
[4] J. Xiao et al., Phys. Rev. B 70, 172405 (2004).
[5] J. Xiao et al., Phys. Rev. B 72, 014446 (2005).

Keywords: spin-transfer torque; magnetization dynamics; spin-valve; spin-torque oscillator

  • Poster
    12th Joint MMM/Intermag Conference, 14.-18.01.2013, Chicago, Illinois, USA

Permalink: https://www.hzdr.de/publications/Publ-19899
Publ.-Id: 19899


Measurement techniques for liquid metal flows

Wondrak, T.

The measurement of flow properties in liquid metals is usually hampered by the high temperature and the opaqueness of liquid melts.
In this lecture we will give an overview of the available measurement techniques including potential probes, ultrasound Doppler velocimetry, x-ray radioscopy, phase shift flow meters, Lorentz force velocimetry and contactless inductive flow tomography.

Keywords: liquid metal; flow measurement

  • Invited lecture (Conferences)
    549. WE-Heraeus-Seminar on Liquid Metal MHD, 15.-18.10.2013, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19898
Publ.-Id: 19898


Contactless inductive flow tomography and mutual inductance tomography for a model of continuous casting

Wondrak, T.; Timmel, K.; Gundrum, T.; Stefani, F.; Eckert, S.; Gerbeth, G.; Peyton, A. J.; Yin, W.; Terzija, N.

We present the results of simultaneous measurements of the flow field in a slab casting mould by the Contactless Inductive Flow Tomography (CIFT) and of the gas/liquid distribution in one cross section of the submerged entry nozzle (SEN) by the Mutual Inductance Tomography (MIT) for a physical model consisting of a mould with the cross section of 140 x 35 mm^2. Additionally, we present a new measuring system for CIFT using pickup coils and the first measurement of the flow field in a mould with the cross section of 400 x 100 mm^2.

Keywords: continuous casting; flow measurement; contactless inductive flow tomography; liquid metal; mutual inductance tomography

  • Open Access Logo Contribution to proceedings
    7th World Congress on Industrial Process Tomography - WCIPT7, 02.-05.09.2013, Krakow, Poland
    Procedia Engineering, 650-659
  • Lecture (Conference)
    7th World Congress on Industrial Process Tomography - WCIPT7, 02.-05.09.2013, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-19897
Publ.-Id: 19897


Interaction of electronic excitations of Tm3+ ions with acoustic vibrations in KTm(MoO4)2

Kamenskyi, D.; Poperezhai, S.; Gogoi, P.; Engelkamp, H.; Maan, J. C.; Wosnitza, J.; Kut’Ko, V.

Electron paramagnetic resonance spectra of KTm(MoO4)2 were measured as a function of magnetic field between 3 and 11.5 cm−1 at T = 2 K. We found that in addition to the absorption line caused by the electronic excitation of Tm3+ ions, the spectra contain sidebands. Far-infrared transmission measured with polarized light from 10 to 75 cm−1 revealed vibration modes at 16.7 and 25.7 cm−1 for polarizations Eω ∥ a and Eω ∥ c, respectively. We show that sidebands in the spectra of paramagnetic resonance result from a parametric resonance between the electronic excitations of the Tm3+ ions and the acoustic vibrations of the crystal lattice.

Permalink: https://www.hzdr.de/publications/Publ-19896
Publ.-Id: 19896


Visualization of the flow in the mold by contactless inductive flow tomography in the presence of a magnetic brake

Wondrak, T.; Klotsche, K.; Timmel, K.; Gundrum, T.; Stefani, F.; Eckert, S.; Gerbeth, G.

In order to enhance the productivity and to achieve higher steel cleanliness in continuous casting the application of various magnetic fields is considered an efficient tool for controlling the flow in the mold. For instance, DC magnetic fields perpendicular to the wide faces of the mold are used to dampen the jets emerging from the submerged entry nozzle (SEN). Especially in this case, even a rough knowledge of the flow structure in the mold would be highly desirable.
The Contactless Inductive Flow Tomography (CIFT) allows reconstructing the dominating two-dimensional flow structure in a slab casting mold by applying one external magnetic field and by measuring the flow induced magnetic fields along the narrow faces of the mold.
For a physical model of a continuous caster, consisting of a mold with a cross section of 140 mm x 35 mm, we will present first measurements of the flow induced magnetic field in the presence of a magnetic brake of the ruler type. The first results demonstrate the viability of the CIFT measurement technique in such a configuration.

Keywords: continuous casting; flow measurement; contactless inductive flow tomography; liquid metal

  • Contribution to proceedings
    5th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking - STEELSIM 2013, 10.-12.09.2013, Ostrava, Czech Republic
    Proceedings of STEELSIM 2013, 978-80-260-3912-9
  • Lecture (Conference)
    5th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking - STEELSIM 2013, 10.-12.09.2013, Ostrava, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-19895
Publ.-Id: 19895


Experimental studies of dark current in a superconducting RF photo-injector

Xiang, R.; Arnold, A.; Kamps, T.; Lu, P.; Michel, P.; Murcek, P.; Vennekate, H.; Staats, G.; Teichert, J.

A superconducting RF photo injector (SRF gun) has been put in operation successfully at the radiation source ELBE. It produces a 13 MHz, low emittance, CW beam with beam current up to 400 μA and energy of 3 MeV. During the gun operation, the field emission from the niobium cavity and the Cs2Te cathodes produces dark current. In this work, we studied the dark current of the SRF gun by using the existing diagnostics beam line. The dependency of the intensity and the energy spectrum on the cavity gradient and the cathode voltage were examined, and the emission sources were analyzed. Furthermore, the new project of installing a strip line kicker to reduce the dark current effect is presented.

Keywords: SRF gun; field emission; dark current; niobium cavity; Cs2Te cathode; energy spectrum

Permalink: https://www.hzdr.de/publications/Publ-19894
Publ.-Id: 19894


The status of new transport chamber and the problem of cathode-puck

Xiang, R.; Murcek, P.

We present here the status of the new cathode transport system at HZDR and also discuss the problem of the cathode-puck design

Keywords: photocathode; transport; high vacuum

  • Invited lecture (Conferences)
    Photocathode Research For High Brightness Electron Beams (PCHB)-Meeting, 05.08.2013, Mainz, Germany

Permalink: https://www.hzdr.de/publications/Publ-19893
Publ.-Id: 19893


Konstruktion der Transportkammer und der Kathodenhalterung und Manipulatoren

Xiang, R.; Murcek, P.

In this talk we present the design of a new cathode transport system.

Keywords: cathode transport; high vacuum

  • Invited lecture (Conferences)
    PCHB kickoff meeting: Photokathoden-Treffen in Dresden-Rossendorf, 06.03.2013, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-19892
Publ.-Id: 19892


Photocathode for Rossendorf SRF gun

Xiang, R.

Rossendorf SRF gun is an electron source for high current electron beams based on superconducting RF technology and laser driven photocathode. Semiconductor Cs2Te photocathodes are the standard electron sources. Up to now eight Cs2Te photocathodes have been operated in the SRF gun. Quantum efficiency (Q.E.) of 1% and life time of months satisfy the gun operation. Besides the present Cs2Te photocathode, GaAs(Cs, O) attracts a lot of attention because of its high QE in the visible light range and the probability to produce high polarization beams. A new preparation system for GaAs is developing, and we will later examine the activation and performance of GaAs photocathodes in SRF gun.

Keywords: electron source; SRF gun; photocathode; QE; Cs2Te; GaAs

  • Lecture (Conference)
    1st Topical Workshop on Laser Based Particle Sources, 20.-22.02.2013, CERN, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-19891
Publ.-Id: 19891


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