Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Bioaccumulation of Uranium by Euglena mutabilis Cells

Arnold, T.; Lünsdorf, H.; Brockmann, S.

Bioaccumulation experiments, together with transmission electron microscopy together with electron energy loss spectroscopy (TEM/EELS) and confocal laser scanning microscopy (CLSM) were used to study the uranium uptake by metabolically active Euglena mutabilis cells and by dead biomass of Euglena mutabilis cells. For the experiments the Euglena cells were separated from the culture medium and placed in 1×10-5 M and 5×10-4 M uranyl solution (in Na2SO4 medium) at pH 3, respectively to relate to uranium contaminated acid mine drainage conditions and the uranium uptake was monitored over time. It was found that the immobilization by living Euglena cells is a slow but metabolically driven active process which takes up to 10 days, before it reaches equilibrium with the surrounding bulk solution. However, this active process leads to higher amounts of immobilized uranium in comparison to the fast immobilization of uranium by comparable amounts of dead biomass, which is completed within 20 to 25 minutes.
The immobilization of uranium by dead biomass is a different process. Here, uranium could only be observed in some instances on the Euglena pellicle by EF-TEM/EELS in concentrations close to the detection limit. This process was interpreted as a passive but very fast biosorption process in which uranium was eventually heterogeneously distributed as adsorbed species on accessible Euglena surfaces coordinated to carboxyl and also possibly to phosphate groups.
CLSM studies showed that uranium was transported into living Euglena cells. The respective fluorescence spectra obtained from the interior of the cell indicated a uranium phosphate or uranium carboxyl speciation. No such signals could be obtained for dead Euglena biomass, neither on E. mutabilis surfaces nor in the cells.
The above shown results showed that Euglena mutabilis cells do have the capacity to remove very mobile uranium(VI) species under AMD relevant conditions and could be a promising microorganisms for low-maintenance remediation strategies.

Keywords: Euglena mutabilis; uranium; bioaccumulation

  • Poster
    Goldschmidt2014, 08.-13.06.2014, Sacramento, USA

Publ.-Id: 20049

Guided continuous-wave and graphene-based Q-switched lasers in carbon ion irradiated Nd:YAG ceramic channel waveguide

Tan, Y.; Akhmadaliev, C.; Zhou, S.; Sun, S.; Chen, F.

We demonstrate the lasing performance in the Nd:YAG ceramic channel waveguide produced by the carbon ion irradiation, including the continuous-wave (cw) and graphene Q-switched configurations. The highest slope efficiency of 56% and the lowest threshold of 40 mW have been obtained for the cw waveguide laser. With graphene as a saturable absorber, the Q-switched laser produces stable pulses with 57 ns pulse duration and 77 nJ pulse energy, respectively. Under the variation of the pumping power, the repetition of the pulse laser could be modified from 1.5 MHz to 4.1 MHz.

Keywords: Q-switched; Rare-earth-doped materials; Waveguides; Ion irradiation

Publ.-Id: 20048

Electromagnetic flow control in metallurgy, crystal growth and electrochemistry
The European Physical Journal Special Topics Vol. 220 (2013)

Gerbeth, G.; Eckert, K.; Odenbach, S.; (Editors)

  • Book (Editorship)
    Berlin Heidelberg: Springer, 2013
    322 Seiten

Publ.-Id: 20047

DRESDYN - A new platform for liquid metal thermohydraulic studies and measurement technique

Gerbeth, G.; Eckert, S.; Stefani, F.; Gundrum, T.

  • Contribution to proceedings
    International Conference on Fast Reactors and Related Fuel Cycles: Safe Technologies and Sustainable Scenarios (FR13), 04.-07.03.2013, Paris, France

Publ.-Id: 20046

Investigation of Irregular Motion Influence for Future 4D In-Beam PET Imaging

Tian, Y.; Stützer, K.; Enghardt, W.; Priegnitz, M.; Helmbrecht, S.; Fiedler, F.

Particle therapy PET (PT-PET) has been established for dose monitoring and particle range assessment in hadron therapy. Imaging is up to now restricted to static organs. However, by means of phantom irradiation it has been shown that a 4D maximum likelihood expectation maximization (4D MLEM) reconstruction method is able to compensate for blurring artefacts of regular motion in in-beam PET images. Nevertheless, respiratory curves often show inconsistent amplitude variation, frequency modulation and baseline drift during radiotherapy. Since the anatomical information is not updated by a CT scanner during treatment, transformation of data from each phase could only rely on the 4D CT obtained prior to irradiation, which might be incorrectly transformed. Based on that clinical situation, this study aims to investigate the effect of irregularity in motion on 4D PET image reconstruction.

  • Lecture (Conference)
    ICTR-PHE 2014, 10.-14.02.2014, Geneva, Switzerland
  • Abstract in refereed journal
    Radiotherapy and Oncology 110 Supl 1(2014), 194

Publ.-Id: 20045

The (non-) detectability of failures in motion mitigated ion beam delivery by means of in-beam PET

Stützer, K.; Enghardt, W.; Bert, C.; Saito, N.; Priegnitz, M.; Parodi, K.; Fiedler, F.

The qualitative positron emission tomography for the dose monitoring in ion beam therapy (PT-PET) has been approved for static tumors under clinical conditions. The detection of dose deviations is based on a comparison between the measured and an anticipated β+-activity distribution. Also for intra-fractionally moving targets, the 4D simulation as well as the 4D reconstruction of in-beam PET data has been established. Within dedicated experiments the results of the comparison between measured and anticipated activities were investigated with regard to the detection of failures in the motion mitigated ion beam delivery.

  • Lecture (Conference)
    ICTR-PHE 2014, 10.-14.02.2014, Geneva, Switzerland
  • Abstract in refereed journal
    Radiotherapy and Oncology 110 Supl 1(2014), 190

Publ.-Id: 20044

Prediction of β+-activity distributions from PT-PET by means of a yield approach

Helmbrecht, S.; Enghardt, W.; Priegnitz, M.; Fiedler, F.

Particle therapy PET (PT-PET) is a clinically approved method for the verification of ion beam therapy. The evaluation of the obtained images is based upon the comparison of the measurement and a prediction. A new approach for the simulation of the activity distribution using measured yields in reference materials has recently been published. This approach provides the possibility to take the elemental composition of the different tissues into account. In this work first results of simulation in real patient cases are presented.

  • Lecture (Conference)
    ICTR-PHE 2014, 10.-14.02.2014, Geneva, Switzerland
  • Abstract in refereed journal
    Radiotherapy and Oncology 110 Supl 1(2014), 85

Publ.-Id: 20043

Analysis of metabolic washout of positron emitters produced during carbon ion head and neck radiotherapy

Helmbrecht, S.; Enghardt, W.; Parodi, K.; Didinger, B.; Debus, J.; Kunath, D.; Priegnitz, M.; Fiedler, F.

Purpose: Particle Therapy Positron Emission Tomography (PT-PET) is a suitable method for verification of therapeutic dose delivery by measurements of irradiation-induced β+-activity. Due to metabolic processes in living tissue β+-emitters can be removed from the place of generation. This washout is a limiting factor for image quality. The purpose of this study is to investigate whether a washout model obtained by animal experiments is applicable to patient data.
Methods: A model for the washout has been developed by Mizuno et al. [Phys. Med. Biol. 48(15), 2269–2281 (2003)] and Tomitani et al. [Phys. Med. Biol. 48(7), 875–889 (2003)]. It is based upon measurements in a rabbit in living and dead conditions. This model was modified and applied to PET data acquired during the experimental therapy project at GSI Helmholtzzentrum für Schwerionenforschung Darmstadt, Germany. Three components are expected: A fast one with a half life of 2 s, a medium one in the range of 2–3 min, and a slow component of the order of 2–3 h. Ten patients were selected randomly for investigation of the fast component. To analyze the other two components, 12 one-of-a-kind measurements from a single volunteer patient are available.
Results: A fast washout on the time scale of a few seconds was not observed in the patient data. The medium processes showed a mean half life of 155.7 ± 4.6 s. This is in the expected range. Fractions of the activity not influenced by the washout were found.
Conclusions: On the time scale of an in-beam or in-room measurement only the medium-time washout processes play a remarkable role. A slow component may be neglected if the measurements do not exceed 20 min after the end of the irradiation. The fast component is not observed due to the low relative blood filled volume in the brain.

Keywords: in-beam PET; PT PET; ion therapy; in-vivo dosimetry

Publ.-Id: 20042

Self-organized Nanopatterns on Silicon Surfaces by Ion-Beam-Sputtering with Metal Co-deposition

Gago-Fernandez, R.; Redondo-Cubero, A.; Palomares, J.; Hübner, R.; Vazquez, L.

The capability of ion beam sputtering (IBS) to induce surface nanopatterns on different materials (metals, semiconductors or insulators) is well-known since the early 60’s [1]. The first description of such phenomenology was proposed by Bradley and Harper (BH) [2] invoking the interplay between surface relaxation mechanisms and the sputtering yield dependence on the local surface curvature. BH model and posterior generalizations [1] predict pattern formation for any ion incidence angle and successfully account for the observation of nanoripple or nanodot structures depending on the irradiation geometry (anisotropic or isotropic, respectively). However, the universality of the BH approach has been recently questioned by the disparity of (sometimes conflicting) results. This ambiguous scenario has been partially clarified after the awareness of the role played by compositional modifications during IBS for both monoelemental [3] and binary [4] semiconductors and, specially, for nanodot pattern formation. In these studies, silicon has become a sort of model system due to its technological relevance but also from the mono-elemental nature as well as extreme flatness. Thus, IBS of silicon surfaces yields (ripple) pattern formation only above an incidence angle threshold (~45° for low-energy Ar+ [5]) unless (metal) impurities prone to react with the target (forming silicides) are inadvertently or intentionally added during the irradiation [6,7]. Despite the a-priori undesirable presence of impurities, IBS with simultaneous co-deposition has emerged as a novel method to tune and modify the pattern morphology and characteristics [6-10]. In addition, the morphological pattern is correlated with a compositional one, offering new potential applications. However, assessing such compositional variations at the nanoscale is not straightforward and demands of advanced characterization tools. In this talk, the present status of metal co-deposition during low- (< 10 keV) and medium-energy (10-200 keV) IBS of silicon surfaces will be presented, making special emphasis on the efforts to elucidate correlated morphological and compositional issues.

[1] J. Muñoz-García, L. Vázquez, R. Cuerno, M. Castro, R. Gago, “Toward Functional Nanomaterials: Self-organized surface nanopatterning by IBS” pp.323-398 (Springer, 2009); [2] R.M. Bradley, J.M.E. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988); [3] G. Ozaydin et al. Appl. Phys. Lett. 87,163104 (2005); [4] S. Le Roy et al. J. Appl. Phys. 106, 094308 (2009); [5] M. Castro, R. Gago et al. Phys. Rev. B 86, 214107 (2012) ; [6] J.A. Sánchez-García, R. Gago et al. J. Phys.: Condens. Matter 21, 224009 (2009); [7] H. Hofsäss et al. Appl. Phys. A 111, 653 (2013); [8] J.A. Sánchez-García, L. Vázquez, R. Gago et al. Nanotechnology 19, 355306 (2008); [9] K. Zhang et al. New J. Phys. 13, 013033 (2011); S. Macko et al. New J. Phys. 13, 073017 (2011); [10] A. Redondo-Cubero, R. Gago et al. Phys. Rev. B 86, 085436 (2012).

Keywords: Synthesis & Processing/Transformation/ion-beam processing; Composition & Microstructure/Chemical Element/Si; Composition & Microstructure/Features/morphology

  • Invited lecture (Conferences)
    2014 MRS Spring Meeting, 21.-25.04.2014, San Francisco, USA

Publ.-Id: 20041

Time-resolved electronic capture in n-type germanium doped with antimony

Deßmann, N.; Pavlov, S. G.; Shastin, V. N.; Zhukavin, R. K.; Tsyplenkov, V. V.; Winnerl, S.; Mittendorff, M.; Abrosimov, N. V.; Riemann, H.; Hübers, H.-W.

The low temperature (T = 5–40 K) capture of free electrons into hydrogenlike antimony centers in germanium has been studied by a time-resolving experiment using the free electron laser FELBE. The analysis of the pump-probe signal reveals a typical capture time of about 1.7 ns that decreases with pump energy to less than 1 ns while the number of ionized donors increases. The dependence on the pump-pulse energy is well described by an acoustic phonon-assisted capture process. In the cases when (i) a significant number of the electrons is in the conduction band (flux densities larger than 5 × 10^25 photons/(cm^2 s), (ii) the lattice temperature is above ∼20 K, or (iii) a static electric field above ∼2 V/cm is applied to the crystal, the pump-probe technique reveals an additional intraband relaxation process with a characteristic time of ∼100 ps, which is much shorter than that of the capture of free electrons into the antimony ground state.

Publ.-Id: 20040

Effect of ionic strength on the mobility of radionuclides in the presence of natural organic matter: Testing the Linear Additive Model

Poetsch, M.; Claus, M.; Lippold, H.

Interaction with natural organic complexants such as humic substances can be decisive for the mobility of radiotoxic metals in case of release from an underground repository. Depending on the geochemical surroundings, their migration can be both enhanced and retarded. Models must be able to describe such complex systems by few parameters. According to the Linear Additive Model [1], total metal adsorption in the presence of humic matter is calculated by linking parameters for adsorption of both components and for their interaction with each other. The applicability of this approach is, however, not unanimously accepted.
Clay rock is discussed as a potential host formation for a final repository, mainly because of its high adsorption capacity. This barrier function may, however, be subverted by screening or competition effects due to high salt contents of pore waters. Complexation of radionuclides with humic-like clay organics may cause an additional mobilisation.
In this study, the influence of electrolyte concentration (up to 4 M) on interactions within the system Tb(III) / fulvic acid (FA) / Opalinus clay was investigated for the major electrolyte constituents of pore waters: Na+, Mg2+ and Ca2+. 160Tb was employed as a tracer analogue of trivalent actinides. FA (humic matter) was radiolabelled with 14C by an azo-coupling reaction. The sensitivity of radiotracer analysis allows experiments at low concentrations, in accordance with relevant scenarios. Complexation of Tb(III) with FA was investigated by means of ultrafiltration. For adsorption studies, clay suspensions were conditioned to a constant pH value of 5.0.
Effects of Na+, Mg2+ and Ca2+ proved to be very different. On the whole, interaction of Tb(III) with FA and clay is suppressed at increasing electrolyte contents, whereas interaction of FA with clay is promoted because electrostatic repulsion is screened. For this reason, mobilising effects of humic-like complexants are generally counteracted in saline systems; metals are solely mobilised due to common salt effects. For the bivalent electrolytes, these relationships can be quantitatively described by the Linear Additive Model.

[1] Zachara et al. (1994) Geochim. Cosmochim. Acta 58, 553-566.

  • Lecture (Conference)
    Goldschmidt Conference 2014, 08.-13.06.2014, Sacramento (CA), United States of America

Publ.-Id: 20039

Precision in prompt gamma-based range monitoring of proton pencil beams in heterogeneous media

Janssens, G.; Celani, A.; Clementel, E.; Fiorini, C.; Frizzi, T.; Enghardt, W.; Helmbrecht, S.; Perali, I.; Prieels, D.; Priegnitz, M.; Roellinghoff, F.; Smeets, J.; Stichelbaut, F.

No abstract available

  • Poster
    ICTR-PHE 2014, 10.-14.02.2014, Geneva, Switzerland
  • Abstract in refereed journal
    Radiotherapy and Oncology 110 Supl 1(2014), 94

Publ.-Id: 20038

Extraction properties of 25,27-bis(carbonylmethoxy)calix[4]arenes towards Sr2+: competitive extraction and extraction in a synthetic groundwater.

Haupt, S.; Schnorr, R.; Poetsch, M.; Mansel, A.; Handke, M.; Kersting, B.

The Sr2+ extraction properties of some 25,27-bis(carbonylmethoxy)calix[4]arenes, in which ester (-CH2CO2Et), keto (-CH2COCH3) and acid functionalities (-CH2CO2H) have been attached to the lower rim, are reported. Strontium ion extraction experiments were performed in a chloroform/water system, and the extraction performance analyzed by radiotracing using the short-lived radio nuclide 85Sr. Effects of pH value, ligand to metal ratio, temperature, extraction time and strontium species on the extraction behavior were examined. It was observed that the 25,27-bis(carboxymethoxy)calix[4]arene derivatives are potent extracting agents towards the strontium ion, showing remarkable extraction performance in competition with a series of organic and inorganic impurities and in a synthetic groundwater. The crystal structure of 25,27-bis(acetonyloxy)calix[4]arene is also reported.

Keywords: calix[4]arene; strontium; liquid-liquid extraction; groundwater

Publ.-Id: 20037

Magnetization and magnetoacoustics of single-crystalline ErFe5Al7 in high magnetic fields

Gorbunov, D. I.; Yasin, S.; Andreev, A. V.; Skourski, Y.; Zherlitsyn, S.; Wosnitza, J.

The magnetization and sound propagation in single-crystalline ErFe5Al7 (tetragonal crystal structure) have been studied in steady (up to 18 T) and pulsed magnetic fields (up to 60 T). The compound orders ferrimagnetically at a Curie temperature T C=201 K and has a compensation point at T comp=34 K. ErFe5Al7 displays a strong magnetic easy-plane anisotropy. A strong magnetic anisotropy is present as well within the basal plane; the [100] axis is the easy magnetization direction with a spontaneous magnetic moment M s=1.3 µB/f.u. at 2 K. Field-induced magnetic transitions, two along the [100] axis and two along the [110] axis, have been found in the vicinity of T=T comp. Changes in the magnetic state at the transitions result in significant alterations of the spin–phonon coupling, which is manifested by sharp anomalies in the sound velocity and sound attenuation. Along the easy [100] axis the forced ferromagnetic state is reached in a field of about 50 T at 2 K, whereas along the [110] direction saturation is expected only above 60 T. A magnetic field-temperature phase diagram has been extracted up to 60 T. From the experimental data a value of n ErFe=3.3 T/µB for the inter-sublattice Er–Fe exchange interaction has been obtained.

Keywords: Rare-earth intermetallics; Ferrimagnetism; Magnetic anisotropy; High magnetic field; Field-induced transition

Publ.-Id: 20036

Americium(III) and Europium(III) Complex Formation with Lactate at Elevated Temperatures Studied by Spectroscopy and Quantum Chemical Calculations

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

Thermodynamic parameters for the complex formation of Am(III) and Eu(III) with lactate were determined with UV-vis and time-resolved laser-induced fluorescence spectroscopy (TRLFS) in a temperature range between 25 and 70 °C. The reaction enthalpy decreased with increasing ionic strength. FT-IR and NMR spectroscopy in combination with density functional theory (DFT) calculations revealed structural details of the Eu(III) lactate complex: a chelating coordination mode of the lactate with a monodentate binding carboxylate group and the hydroxyl group being deprotonated.

Publ.-Id: 20034

Uptake of selenium oxyanions by hematite

Jordan, N.; Domaschke, S.; Foerstendorf, H.; Scheinost, A. C.; Franzen, C.; Zimmermann, V.; Weiss, S.; Heim, K.

Performance assessments of nuclear waste disposals evidenced 79Se (t1/2 ~ 3.27 × 105 years) to be one of the most important contributors to the overall dose in long-time safety assessments. The concentration, the bioavailability, the mobility, the distribution and the oxidation state of selenium in the environment are greatly influenced by the pH, nature of mineral sorbent and temperature. Hematite was studied because it is a ubiquitous iron oxide mineral present in the environment, thus often found in rocks and soils in the vicinity of underground repositories. This work combined batch and spectroscopic studies to characterize the interaction of Se(VI) and Se(IV) with hematite, which was so far not well understood.
At the macroscopic level, sorption of both oxyanions was found to decrease with increasing pH. An increase of the ionic strength (from 0.01 M to 0.1 M) decreased the sorption of Se(VI), while the Se(IV) uptake remained unchanged. Electrophoretic mobility measurements revealed that Se(IV) sorption shifted the isoelectric point (pHIEP) of hematite to lower pH values, while the pHIEP was not significantly modified upon Se(VI) uptake. At the molecular level, in situ ATR FT-IR and EXAFS measurements revealed the formation of inner-sphere complexes (IS) during Se(IV) sorption onto hematite. Concerning Se(VI), sorption proceeded predominantly via the formation of outer-sphere complexes, together with a small fraction of IS complexes.
High level and long-lived radioactive wastes are well-known to increase the temperature at the vicinity of the waste disposal site. Such a thermal effect raises the question how the retention of selenium is influenced at elevated temperatures. Therefore, information and insights about mechanisms working at higher temperatures (from 25 °C to 60 °C) are also provided.

Keywords: selenium; hematite; uptake; ATR FT-IR; EXAFS

  • Lecture (Conference)
    Goldschmidt 2014, 08.-13.06.2014, Sacramento, USA

Publ.-Id: 20032

Effect of high ionic strengths on U(VI) retention in montmorillonite

Fritsch, K.; Schmeide, K.

Argillaceous rock and clay minerals have properties that make them very valuable for nuclear waste storage. They are practically insoluble and have high sorption capacities. North German clay deposits feature pore waters of particularly high ionic strengths. In the depths that are relevant for nuclear waste repositories, the ionic strength of the pore water ranges from 1.8 mol/l to 3.3 mol/l. To be able to make an informed decision about the long term safety of nuclear waste disposal, the effect of high ionic strengths on radionuclide retention needs to be taken into account.
This work focuses on the uranium retention on montmorillonite in sodium and calcium chloride solutions of high ionic strengths. Montmorillonite serves as a model clay. It is the main component of some North German clay formations that conform to the criteria for deep-level nuclear waste disposals. Furthermore, it is a component of the backfill material that will be used in nuclear waste repositories. Sodium and calcium chloride are the main constituents of the pore waters found in North German argillaceous rock. The sorption experiments presented here were conducted in presence and absence of carbon dioxide.

Keywords: uranium sorption; argillaceous rock; clay; uranium; montmorillonite; high ionic strength

  • Contribution to proceedings
    17th Radiochemical Conference, 11.-16.05.2014, Marianske Lazne, Česká republika
  • Poster
    17th Radiochemical Conference, 11.-16.05.2014, Mariánské Lázně, Česká republika

Publ.-Id: 20031

Performance of global and regional nested meteorological models

Bertotti, L.; Cavaleri, L.; Soret, A.; Tolosana-Delgado, R.

We discuss the performance of two global meteorological models in a difficult enclosed sea area and the possible improvements using two respectively nested high resolution local models. Each of the four sets of wind fields has been used to drive the same wave model. The performances are judged on the base of measured, buoys and satellites, wind and wave data. The analysis shows clearly the general benefits of a higher resolution. However, it also highlights the sensitivity of the nested models to apparently minor changes in the input information from the global models and their consequent possibility of larger errors, particularly in complex meteorological situations.

Keywords: Meteorological modelling; Wave modelling; Nested models; Model accuracy; Model sensitivity

Publ.-Id: 20030

Spin-lattice effects in selected antiferromagnetic materials

Zherlitsyn, S.; Yasin, S.; Wosnitza, J.; Zvyagin, A. A.; Andreev, A. V.; Tsurkan, V.

Spin-lattice effects play an important role in many magnetic materials. In this short review, we give some ex-amples of such effects studied in low-dimensional, frustrated as well as uranium-based antiferromagnets. Utiliz-ing ultrasound measurements at low temperatures and high magnetic fields provides valuable information on the spin-strain interactions. Specifically phase transformations and critical phenomena in magnetic systems with strong spin-lattice interactions are fruitful grounds for sound-velocity and sound-attenuation measurements.

Keywords: low-dimensional spin systems; frustrated chromium spinels; spin-strain interaction; uranium-based compounds

Publ.-Id: 20029

Combined effect of electron and lattice temperatures on the long intersubband relaxation times of Ge/Si_x Ge_1−x quantum wells

Virgilio, M.; Ortolani, M.; Teich, M.; Winnerl, S.; Helm, M.; Sabbagh, D.; Capellini, G.; de Seta, M.

In this paper, we have experimentally and numerically studied the nonradiative intersubband (ISB) relaxation in n-type Ge/SiGe quantum well (QW) systems. Relaxation times have been probed by means of pump-probe experiments. An energy balance model has been used to interpret the experimental differential transmission spectra and to assess the relevance in the nonradiative relaxation dynamics of both electron and lattice temperature as well as of the carrier density. The comparison between experimental data and theoretical simulation allowed us to calibrate the interaction parameters which describe the electron-optical phonon scattering in two-dimensional (2D) Ge systems. Characteristic relaxation times has been calculated and compared with those of GaAs QWs as a function of the 2D electron density, of the subband energy separation, and of the lattice and electronic temperature. We found that ISB relaxation times for the Ge/SiGe systems are generally shorter than that previously calculated when the electron distribution was neglected. Nonetheless, our main result is that the relaxation time in Ge/SiGe QW systems is longer than 10 ps, also for transition energies above the Ge optical phonon energy, up to 300 K. Furthermore, we obtained that the relaxation times are at least one order of magnitude longer than in GaAs-based systems.

Keywords: Ge/SiGe quantum well; intersubband relaxation times; FEL

Publ.-Id: 20028

BN project – contribution from HZDR/IRE

Cherkouk, A.; Radeva, G.; Selenska-Pobell, S.

First it will give a short overview about my expertise and background as well as the research topic I am working on at HZDR/IRE at the moment. Then I will present the results from our past contribution to the BN project. And finally I will give a short overview about what is planned for the next phase of the project from the HZDR/IRE.

  • Lecture (others)
    BN/Mont Terri meeting, 10.-12.02.2014, St. Ursanne, Schweiz

Publ.-Id: 20027

Knowledge Management as a tool to reduce Personal Market Risks

Stiller, D.; Joehnk, P.

Knowledge management is an instrument to ensure knowledge in organisations. The article defines the terms information and knowledge and the different kinds of knowledge. After a description why knowledge is important for organisations the term knowledge management and its objectives and tasks will be investigated. After that one of the first and famous models – the building block model from Probst et al. - will be explained.

Keywords: knowledge; knowledge management; implicit and explicit knowledge; strategic and operational knowledge management level; risk management

  • Invited lecture (Conferences)
    International Scientific Events – Economy & Business, 01.-05.09.2013, Burgas, Bulgaria

Publ.-Id: 20026

Untersuchung des Lebenszyklus von TiO2- und Ag0-Nanopartikeln NanoTRACK

Franke, K.; Hildebrand, H.; Schymura, S.

  • Lecture (Conference)
    3. Clustertreffen der BMBF-Fördermaßnahmen NanoCare und NanoNature, 14.-15.01.2013, Frankfurt, Deutschland

Publ.-Id: 20025

Risk Management: Management of Commodity Price Risks

Stiller, D.; Joehnk, P.

The article discribes the current situation of commodity markets and the influence of the profit situation of industry companies and which contribution risk management can achieve to improve the economical situation of a company. One effective methode is to ensure commodity risks through financial instruments as a part of treasury management. The article describes the reasons and products of these method.

Keywords: commodity market; commodity risks; risk management; treasury management; financial instruments; forward transactions

  • Invited lecture (Conferences)
    International Doctoral Seminar, 20.-22.05.2012, Smolenice, Slovakei

Publ.-Id: 20024

Changing General Conditions in Energy Industry as a Challenge for the Management of Energy Supply Companies

Stiller, D.

The article deals with the general conditions in energy industrie as a basis for new management tasks of energy supply companies. First, the changing market situation as a reason for the regulation will be explained, followed by the development of directives and regulations in european law and their impact on the german energy law. Finally, the influence of regulation on the legal structure and the organization as well as the accounting of energy supply companies will be shown.

Keywords: energy supply company; energy law; competition on energy markets; natural monopoly; regulation; unbundling

  • Invited lecture (Conferences)
    International Doctoral Seminar, 15.-17.05.2011, Smolenice, Slovakei

Publ.-Id: 20023

Using XFELs for Probing of Complext Interaction Dynamics of Ultra-Intense Laers with Solid Matter

Cowan, T. E.; Kluge, T.; Gutt, C.; Huang, L.; Metzkes, J.; Schramm, U.; Bussmann, M.

  • Invited lecture (Conferences)
    55th Annual Meeting of the APS Division of Plasma Physics, 11.-15.11.2013, Denver, USA

Publ.-Id: 20022

Using XFELs to probe the interaction dynamics of ultra-intense laers with solid-density matter

Cowan, T. E.; Kluge, T.; Huang, L.; Gutt, C.; Pelka, A.; Bussmann, M.

  • Invited lecture (Conferences)
    55th Annual Meeting of the APS Division of Plasma Physics, 11.-15.11.2013, Denver, USA

Publ.-Id: 20021

Helmholtz International Beamline for Extreme Fields at European XFEL

Cowan, T.

  • Invited lecture (Conferences)
    HIBEF Kickoff Workshop, 03.-05.06.2013, Hamburg, Deutschland
  • Invited lecture (Conferences)
    UK FEL Forum, 14.06.2013, London, Großbritannien

Publ.-Id: 20020

DESY & HZDR: Common Activities, HGF Beamline at European XFEL

Cowan, T.

  • Invited lecture (Conferences)
    18th Photon Science Committee Meeting, 29.-30.04.2013, Hamburg, Deutschland

Publ.-Id: 20019

Exploring Solid-Density HED Plasmas and Ultra-Intense Laser-Matter Interactions at the European XFEL

Cowan, T. E.; Kluge, T.; Gutt, C.; Bussmann, M.; Huang, L.; Schlenvoigt, H. P.; Schramm, U.

  • Invited lecture (Conferences)
    Conference on High Energy Density Sciences 2013 - HEDS2013, 24.-25.04.2013, Yokohama, Japan

Publ.-Id: 20018

Helmholtz International Beamline at XFEL

Cowan, T.

  • Lecture (others)
    ART Meeting XFEL-HED Instrument, 11.03.2013, Hamburg, Deutschland

Publ.-Id: 20017

Status of the Helmholtz Beamline Proposal

Cowan, T.

  • Lecture (Conference)
    2013 European XFEL Users' Meeting and Satellite Meeting, 24.01.2013, Hamburg, Deutschland

Publ.-Id: 20016

Assessments of the oxidation resistance of technical TiAl-alloys under the influence of fluorine and depending on the high temperature exposure technique

Pflumm, R.; Schütze, M.; Donchev, A.; Yankov, R.; Kolitsch, A.

TiAl-intermetallics show great potential for applications in high temperature-components due to their low density and excellent high-temperature strength. Their major drawback is the oxidation resistance at temperatures above 750°C. It has been shown that one way to improve this resistance by several orders of magnitude is the fluorination of the surface zone of the material. This fluorine treatment occurs at low temperatures and influences only the surface region of the components, so that the bulk properties are not affected. The fluorination changes the oxidation mechanism during subsequent oxidation exposure at temperatures higher than 750°C in such a way that the formation of a thick mixed oxide scale is replaced by the growth of a thin protective alumina scale. No additional coatings are necessary for the full protection of the substrate against further oxidation. One efficient and simple technique for bring the fluorine onto the TiAl surface is by using different liquid phases. This work focuses on the influence of liquid phase composition on the lifetime of the protective alumina layer. Possible beneficial synergistic effects between F and Si on the oxide nucleation behaviour are discussed in comparison to alternative fluorination methods such as plasma immersion ion implantation. Furthermore, the influence of the high temperature exposure needed for the initiation of the change in the oxidation mechanism of TiAl-alloys (i.e. conventional furnace exposure versus short-time laser treatment) on the stability of the protective character of alumina is examined.

Keywords: Oxidation resistance of TiAl alloys; high temperature oxidation

  • Lecture (Conference)
    International Conference Intermetallics 2013, 30.09.-04.10.2013, Bad Staffelstein, Germany

Publ.-Id: 20015

Ion Implantation Based Surface Modification of TiAl Materials

Kolitsch, A.; Yankov, R.

Titanium aluminide (TiAl) alloys are attractive lightweight materials for medium-temperature (500°-750°C) structural applications including components such as jet engine and industrial gas turbine blades, turbocharger rotors and automotive engine valves. However, envisaged service temperatures for future advanced applications will have to be in the range of 750° to 1000°C, over which these alloys suffer from both oxidation and oxygen embrittlement. Therefore, development of surface-engineering techniques for preventing high-temperature environmental damage is critical in exploiting the advantages of TiAl alloys to their fullest extent. Two efficient approaches to protecting candidate TiAl alloys from high-temperature (>750°C) environmental degradation have been developed at HZDR. The first technique involves a single step, namely treating TiAl alloy components directly by plasma immersion ion implantation (PIII) of fluorine using a mixture of difluoromethane and argon (CH2F2 + 25% Ar) as the precursor gas. The oxidation performance of the fluorine-implanted alloys has been evaluated by thermal gravimetric analysis (TGA) over the temperature range of 750° to 1050°C under conditions of both isothermal and thermal cyclic oxidation in air, and for times as long as 6000 h. This type of surface modification has been shown to produce a stable, adherent and highly protective alumina scale. The second technique involves the fabrication of a durable protective coating in a two-step process, namely formation of a thin aluminum-rich TiAl layer (Ti-60Al) by chemical vapor deposition (CVD) employing a mixture of inorganic precursors, followed by PIII of fluorine. Subsequent long-term oxidation exposures to air at 900°C of a GE 4822 alloy (Ti-48Al-2Cr-2Nb; alloy composition qualified for aerospace applications) have shown that the coating so developed is able to successfully prevent oxidation damage to the base material while maintaining up to 90% of its initial mechanical properties (strength and ductility).

Keywords: Ion Implantation; TiAl alloys; protective coatings; aerospace applications

  • Lecture (Conference)
    19th International Vacuum Congress (IVC’19), 09.-13.09.2013, Paris, France

Publ.-Id: 20014

Oxidation protection coatings for titanium, titanium-base alloys and titanium aluminides in high-temperature oxidizing environments

Yankov, R.; Kolitsch, A.; Johannes, V. B.; Donchev, A.; Bortolotto, L.; Masset, P.; Schütze, M.

Titanium and its alloys with aluminum have been widely used as engineering materials for a number of advanced technical applications, and particularly in aeronautics, because of their high strength-to-weight ratio and good oxidation resistance in the medium temperature range (up to 500°C for Ti and ~ 750°C for TiAl). However, environmental durability at higher temperatures is presently still a concern due to insufficient oxidation and embrittlement resistance. Therefore, oxidation protection coatings are needed to fulfill the high temperature structural potential of these materials.
This work consists of two parts. The first part deals with the development of an oxygen barrier coating to prevent oxidation of Ti and low-Al-content Ti-base alloys (< 10 at.% Al) at temperatures not exceeding 600°C. The surface modification process has involved magnetron co-sputtering of Ti and Al onto the base alloy material followed by vacuum annealing and plasma immersion ion implantation (PIII) of fluorine to activate the so-called halogen effect. Oxidation exposure in air at 600°C for 100 h has shown that the coating is able to form a protective Al2O3-containing scale and, moreover, exhibits good substrate compatibility.
The second part of the work has focused on the development of an oxidation resistant coating for γ-TiAl alloys (Ti-48Al-2Cr-2Nb). The fabrication process has involved formation of an Al-rich (50-60 at.%) TiAl overlayer by chemical vapor deposition followed by PIII of fluorine. Subsequent oxidation exposures of the coated γ-TiAl alloy to air at 900°C for 350 h have shown that the coating prevents effectively both oxidation and embrittlement to the baseline material while preserving 90% of its initial mechanical properties.

Keywords: Oxidation protection; coatings for titanium; titanium-base alloys; titanium aluminides; high-temperature oxidation

  • Poster
    EUROMAT2013 - European Congress and Exhibition on Advanced Materials and Processes, 08.-13.09.2013, Sevilla, Spain

Publ.-Id: 20013

Surface treatment for improved high temperature environmental stability of Ti-alloys

Donchev, A.; Galetz, M.; Schütze, M.; Yankov, R.; Kolitsch, A.

Titanium alloys are widely used as light weight structural materials at low temperatures. Due to their high affinity towards oxygen a protective TiO2-passive layer is formed. This layer is only protective at temperatures below about 500°C. With increasing temperature this layer gets deteriorated and hence oxygen inward diffusion is accelerated. This inward diffusion leads to an oxygen enriched subsurface zone which is brittle because Ti has quite high oxygen solubility. The enriched zone can cause failure of Ti-components under thermocyclic and/or mechanical load. To prevent this failure mode a two step process was developed. The first step was enrichment of Al in a narrow surface zone to form the intermetallic TiAl-phase with low oxygen solubility and a high Al-content. The second step consisted of fluorination. Unfluorinated -TiAl-alloys usually form a mixed non protective oxide scale but a protective alumina layer develops after addition of small amounts of fluorine into the surface zone. This so called fluorine effect works for TiAl-alloys with an Al-content above 40at.%. The alumina layer suppresses the oxygen inward diffusion and slows down the oxidation kinetics. The intermetallic TiAl subsurface prevents oxygen uptake into the metal and, thus, embrittlement. In this work results of high temperature exposure tests of untreated and treated technical Ti-alloys will be presented and compared. The results will be discussed considering a use of protected Ti-components in high temperature environments.

Keywords: Magnesium; aluminium; titanium; science and technology

  • Lecture (Conference)
    Euro LightMAT 2013 - International Congress and Exhibition on Light Materials – Aluminium, Magnesium, Titanium and their Alloys, 03.-05.09.2013, Bremen, Deutschland

Publ.-Id: 20012

Surface modification of protective coatings on titanium aluminides by plasma immersion ion implantation of fluorine to suppress environmental embrittlement at high temperatures

Yankov, R.; Bleicher, F.; Bortolotto, L.; Geiger, G.; Kolitsch, A.; Langlade, C.; Masset, P.; Paul, J.; Pelic, B.; Pyczak, F.; Rafaja, D.; Schumacher, P.; Schütze, M.; Wolf, G.

Due to their excellent density-specific properties, titanium aluminide (TiAl) alloys have been identified as high-payoff materials for advanced aerospace and power generation applications in the medium-temperature (600°-750°C) range. They have recently been applied as structural materials for turbine blades in the low-pressure section of the GEnx jet engine. These alloys, however, are prone to both oxidation and embrittlement when exposed to oxidizing environments at temperatures above ~ 750°C. Under such conditions, TiAl alloys form a mixed (TiO2+Al2O3) non-protective oxide scale resulting from the difference in both the growth kinetics of the two oxides, and the chemical activity of the constituent elements, Ti and Al. Thus, for high-temperature (> 750°C) applications, an oxidation protection coating is needed to prevent environmental damage of the base alloy without degrading its initial mechanical properties.
The present work has focused on the development of coatings for the efficient oxidation protection of TiAl alloys at high temperatures. Aluminum-rich TiAl coatings (50 to 60 at.%Al) have been produced by either chemical vapor deposition (MO-CVD), physical vapor deposition (PVD) or thermal spraying (HVOF, APS) techniques onto a GE alloy (Ti-48Al-2Cr-2Nb) qualified for aerospace applications. The coating surface has then been modified by plasma immersion ion implantation (PIII) of fluorine to promote the formation of a protective alumina-containing scale relying on the so-called halogen effect. For the PIII processing, either difluoromethane and argon (CH2F2/Ar) or silicon tetrafluoride and argon (SiF4/Ar) has been used as the F-containing precursor gas. The resulting F-implanted coatings have been exposed to oxidative/corrosive environments at 850°C for 350 h, and have shown a high degree of oxidation resistance. The mechanical properties of the coated samples have been examined by 4-point bend, tensile and fatigue testing after oxidation in laboratory air at 900°C for 100 h. Combining a CVD process with PIII of F (the CH2F2/Ar process) has been found to give the best results in terms of efficient environmental protection against oxidation and embrittlement. It has also been established that more than 90% of the initial mechanical properties of the substrate TiAl alloy can be retained after the application of such a protective coating.

Keywords: titanium aluminides; oxidation protection; coating; fluorine; plasma immersion ion implantation

  • Lecture (Conference)
    12th International Workshop on Plasma Based Ion Implantation and Deposition (PBII&D 2013), 01.-05.07.2013, Poitiers, France

Publ.-Id: 20011

Surface engineering of gamma-titanium aluminide alloys for combined improvements in environmental durability at elevated temperatures

Yankov, R.; Kolitsch, A.; Johannes, V. B.; Masset, P.; Bortolotto, L.; Donchev, A.; Schütze, M.

γ-TiAl alloys are attractive materials for medium-temperature (500-750°C) aeronautical applications. Current technology progress, however, is driven by the trend towards new concepts requiring temperatures > 750°C at which γ-TiAl components fail to perform because of poor oxidation and embrittlement resistance. We have developed two approaches to protecting γ-TiAl alloys from high-T oxidation. The first one involves treating γ-TiAl alloys by plasma-based ion implantation (PBII) of fluorine. This type of modification produces a highly protective Al2O3 scale upon oxidation in air at temperatures up to 1050°C. The second method is based on the fabrication of a protective coating in a two-step process, namely formation of an Al-rich TiAl overlay by chemical vapor deposition followed by PBII of F. Subsequent oxidation exposures to air at 900°C have shown that the coating prevents both oxidation and embrittlement to the base alloy while maintaining 90% of its initial mechanical properties.

Keywords: gamma-TiAl; oxidation protection; plasma based ion implantation; protective coating

  • Poster
    International Workshop on Gamma TiAl Alloy Technology (GAT 2013), 11.-14.06.2013, Toluese, France

Publ.-Id: 20010

Protonen mit Licht beschleunigen – Dosimetrische Charakterisierung laserbeschleunigter Protonen mittels Festkörperspurdetektoren im Rahmen von Zellexperimenten

Knaute, J.

Für eine neuartige Krebstherapie mit Protonen ist es wichtig zu wissen, welche Energie die Protonen haben. Für einen speziellen Detektor wurde eine automatische Auswertung entwickelt.

Keywords: laserbeschleunigter Protonen

  • Junge Wissenschaft 97(2013), 48-59

Publ.-Id: 20009

Theoretical investigation of the saturation correction for ionization chambers irradiated with pulsed beams of arbitrary pulse length
Theoretische Untersuchung der Sättigungskorrektion von Ionisationskammern in gepulsten Strahlungsfeldern bei beliebiger Pulsdauer

Karsch, L.; Pawelke, J.

In ionization chambers, not all released charge is collected due to the recombination of charge carriers. This effect is taken into account by the saturation correction factor kS. A physical description of the correction factor has been established for pulsed radiation. However, it is only accurate when the pulse length is short compared with the collection time of the ionization chamber. In this paper we develop a description of the saturation correction for radiation pulses of arbitrary length. For this, a system of partial differential equations is solved iteratively. The numerical solutions are verified experimentally for a Roos ionization chamber (PTW TM34001) exposed to a pulsed electron beam. The results of this iterative procedure describe the experimental data well. The calculations are also possible for beam structures which are experimentally hard to get and thereby contribute to a better understanding and correct description of the saturation correction at arbitrary pulse length. Among other things the pulse length dependent distributions of the charge carriers in the ionization chamber is calculated, inclusive of the transition to the conditions prevailing in the case of continuous irradiation. Furthermore is shown that the formula for kS established by Hochhäuser and Balk [1] is applicable even at arbitrary pulse length, if pulse duration dependent effective values are used for the parameters a and p. These effective values have been determined for the Roos chamber at pulse lengths up to 300μs

Keywords: ionization chamber

Publ.-Id: 20008

Realizing a laser-driven electron source applicable for radiobiological tumor irradiation

Nicolai, M.; Sävert, A.; Reuter, M.; Schnell, M.; Polz, J.; Jäckel, O.; Karsch, L.; Schürer, M.; Oppelt, M.; Pawelke, J.; Kaluza, M.

Laser-accelerated electron pulses have been used to irradiate human tumors grown on mice’s ears during radiobiological experiments. These experiments have been carried out with the JETI laser system at the Institute of Optics and Quantum Electronics in Jena, Germany. To treat a total of more than 50 mice, a stable and reliable operation of the laser-electron accelerator with a dose rate exceeding 1 Gy/min was necessary. To achieve this, a sufficient number of electrons at energies in excess of 5 MeV had to be generated. The irradiation time for a single mouse was a few minutes. Furthermore, the particle pulses’ parameters needed to remain achievable for a time period of several weeks. Due to the online detection of the radiation dose, the unavoidable shot-to-shot fluctuations, currently still typical for laser-based particle accelerators, could be compensated. The results demonstrate that particle pulses generated with laser-based accelerators have the potential to be a future alternative for conventional particle accelerators used for the irradiation of tumors.

Keywords: laser-driven electron source; radiobiology

Publ.-Id: 20007

Influence of pulse length on collection efficiency of ionization chambers irradiated with pulsed beams.

Karsch, L.; Gotz, M.; Pawelke, J.

In ionization chambers not all released charge is collected due to recombination of charge carriers. A physical description of the correction factor has been established for pulsed beams for many decades. However, it is only accurate if the pulse length is short compared to the collection time of the ionization chamber. In this contribution a new, more generalized description of the Saturation correction (i.e. for arbitrary pulse lengths) is presented.
Experiments have been performed using a Roos ionization chamber (TM34001, PTW Freiburg, Germany) because this model is a planparallel chamber often used in clinics. The pulse length dependence was investigated at the superconducting electron linear accelerator ELBE. For the new theoretical description a system of partial differential equations is solved iteratively. The free parameters were adjusted for best agreement with the experiment.
The experiment shows, that the established description of saturation correction is only valid for pulses shorter than 10 μs. Furthermore, our new theoretical description allows the determination of Saturation correction in a wide range, e.g., for beam time structures which are experimentally difficult to realize and for longer pulse durations. Hereby the calculation results in a better understanding of the recombination process by giving insight into the dynamics of charge carrier distributions. In this way we can show that the established theoretical formalism is also valid at longer pulses, if the previoulsy used fixed parameters are reintroduced as pulse length dependent. For the Roos chamber the dependence of these parameters is demonstrated.

Keywords: ionization chamber; pulsed beam

  • Open Access Logo Abstract in refereed journal
    Medical Physics International 1(2013)2, 401

Publ.-Id: 20006

Concept of a compact rotating gantry for laser acceleration based proton therapy

Karsch, L.; Bussmann, M.; Enghardt, W.; Kroll, F.; Masood, U.; Pawelke, J.

n ionization chambers not all released charge is collected due to recombination of charge carriers. A physical description of the correction factor has been established for pulsed beams for many decades. However, it is only accurate if the pulse length is short compared to the collection time of the ionization chamber. In this contribution a new, more generalized description of the Saturation correction (i.e. for arbitrary pulse lengths) is presented.
Experiments have been performed using a Roos ionization chamber (TM34001, PTW Freiburg, Germany) because this model is a planparallel chamber often used in clinics. The pulse length dependence was investigated at the superconducting electron linear accelerator ELBE. For the new theoretical description a system of partial differential equations is solved iteratively. The free parameters were adjusted for best agreement with the experiment.
The experiment shows, that the established description of saturation correction is only valid for pulses shorter than 10 μs. Furthermore, our new theoretical description allows the determination of Saturation correction in a wide range, e.g., for beam time structures which are experimentally difficult to realize and for longer pulse durations. Hereby the calculation results in a better understanding of the recombination process by giving insight into the dynamics of charge carrier distributions. In this way we can show that the established theoretical formalism is also valid at longer pulses, if the previoulsy used fixed parameters are reintroduced as pulse length dependent. For the Roos chamber the dependence of these parameters is demonstrated.

Keywords: proton therapy; gantry; laser acceleration

  • Open Access Logo Abstract in refereed journal
    Medical Physics International 1(2013)2, 566

Publ.-Id: 20005

Platinum-group minerals (PGM) nuggets from alluvial-eluvial placer deposits in the concentrically zoned mafic-ultramafic Uktus complex (Central Urals, Russia)

Zaccarini, F.; Pushkarev, E.; Garuti, G.; Krause, J.; Dvornik, G.; Stanley, C.; Bindi, L.

We report the results of a detailed mineralogical investigation of platinum-group minerals (PGM) and copper-gold nuggets from the Uktus Ural-Alaskan type complex in the Central Urals (Russia). The studied nuggets were sampled in alluvial-eluvial deposits from three small valleys, with temporary water flows, cutting across the Uktus massif. The volume of the washed samples varies from 0.03 to 0.08 m3 and a few tens of PGM nuggets, ranging in size from about 100 m m to about 2 mm, were collected. According to their chemical composition, the most abundant PGM are native Ir-Os and alloys in the Pt-Fe-Cu-Ni system. The following less abundant PGM were also recognised: sulfarsenides of the irarsite-hollingworthite-platariste series, sulfides such as laurite, cuproiridsite, kashinite and the sulfantimonide tolovkite. One alloy corresponding to the formula Cu3Au2 was found, and proved to be Cu-rich tetraauricupride. The nuggets of Uktus have, in some cases, a polygonal shape. However, most of them have an irregular morphology and are characterised by a porous rim and zoning. The investigated nuggets occur as single-phase crystals or as polyphase grains, composed of different PGM. One nugget displays a very complex texture, being composed of a Pt-Fe alloy associated with osmium and Cu-rich tetraauricupride. These minerals are in contact with quartz that contains minute inclusions of hollingworthite and platarsite. The mineralogical similarity with the PGM inclusions in the Uktus chromitites indicates these rocks as a possible source for the PGM nuggets. The presence of faceted morphology in some nuggets suggests that they were mechanically liberated and transported for a relatively short distance from their lode deposits. The nuggets characterized by a rounded shape and occurring in association with quartz and Cu-rich tetraauricupride have probably been reworked in the placer environment. Therefore, in the Uktus placers deposits, two types of PGM nuggets can coexist: (i) primary with a magmatic origin, i.e., only mechanically liberated from their source rock, and (ii) secondary, i.e., reworked and grown in the placers. The mineralogical assemblage of the Uktus PGM nuggets, the fact that the Uktus PGM placers have never been mined and the recent exponential increase in demand for noble metals make the placer deposits associated with the Uktus complex potentially important for the economic recovery of these rare metals, at least on a small scale.

Keywords: PGM nuggets; Cu-Au alloy; Uktus massif; Urals

Publ.-Id: 20003

Optimization of depolarization losses and scaling of a high average power diode pumped laser amplifier using Yb3+ doped CaF2

Albach, D.; Loeser, M.; Röser, F.; Siebold, M.; Schramm, U.

We compare different optimization techniques for high average-power diode-pumped solid-state laser amplifiers currently developed at the PENELOPE project. Amplified spontaneous emission and thermally induced depolarization losses are the main limiting factors besides laser induced damage. Optimizing the laser gain medium geometry and the choice of the gain medium are the key factors for highly efficient laser amplifiers.

Keywords: amplifier; depolarization; depolarization compensation; CaF2; diode pumping

  • Poster
    The 2nd Advanced Lasers and Photon Sources (ALPS’13), 23.-25.04.2013, Yokohama, Japan

Publ.-Id: 20002

X-ray diffraction investigations under non ambient conditions at the Rossendorf Beamline ROBL

Baehtz, C.; Grenzer, J.; Roshchupkina, O.; Kidambi, P. R.; Bayer, B.; Wheaterup, R.; Hofmann, S.

The Rossendorf Beamline ROBL at the ESRF is operated since 1998 by the Institute of Resource Ecology and Ion Beam Physics and Materials Research of the HZDR. In 2011-2012 the optics of the beamline such as mirrors double crystal monochromator and diagnostic was modernized to meet future experimental demands. The Materials Research Station is focusing on in-situ investigations. These are in thin film synthesis by magnetron sputtering, in-operando measurements on lithium ion batteries, surface modification by ion implantation and high temperature investigations using reactive atmosphere like in chemical vapor deposition (CVD) processes.
Iron nano-crystals are a common catalyst in the CVD growth reaction of carbon nano tubes. These crystals were formed by dewetting of the corresponding iron thin film at raised temperatures. Under reaction condition different iron phases such as Fe3C, alpha-Fe and gamma-Fe were detected. Their concentrations are strongly varying before, after and during the CVD process. This leads to the conclusion that besides Fe3C also metallic iron is catalytically active [1].
In graphene CVD nickel and copper are commonly used as catalyst. High resolution diffraction data were collected at reaction temperature. The lattice parameter was calculated using Lebail fit, corrected due to small shifts in sample surface temperature by the thermal expansion determined before. The results show a lattice expansion of nickel under different CVD atmospheres, indicating an uptake of hydrogen and carbon on interstitials in the metallic Ni. The carbon uptake is only partially reversible, but additional hydrogen can be assimilated .

Keywords: Diffraction; synchrotron; graphene; CNT; CVD

  • Lecture (Conference)
    Annual Conference of the German Crystallographic Society (DGK) 2013, 19.-22.3.2013, Freiberg, Germany

Publ.-Id: 20001

Recent experimental results on Thomson Scattering

Jochmann, A.; Debus, A.; Irman, A.; Couperus, J. P.; Zarini, O.; Steiniger, K.; Pausch, R.; Bussmann, M.; Schlenvoigt, H. P.; Helbig, U.; Kraft, S. D.; Cowan, T. E.; Sauerbrey, R.; Schramm, U.; Lehnert, U.; Kuntzsch, M.; Wagner, A.; Teichert, J.; Arnold, A.; Michel, P.; Mccanny, T.; Ledingham, K. D.; Troitsenko, S.; Stöhlker, T.

Thomson backscattering of intense laser pulses from relativistic electrons not only allows for the generation of bright X-ray pulses but also for the investigation of the complex particle dynamics at the interaction point. For this purpose a complete spectral characterization of a Thomson source powered by a compact linear electron accelerator was performed with unprecedented angular and energy resolution. A rigorous statistical analysis comparing experimental data to 3D simulations enabled, e.g., the extraction of the angular distribution of electrons with 1.5% accuracy and, in total, provides predictive capability for future high brightness hard X-ray and potential gamma-ray sources. We further present a novel Thomson scattering geometry in order to avoid the restrictions on the X-ray photon yield imposed by the Rayleigh limit. The suggested traveling-wave setup (TWTS) allows an overlap of electron and laser beams, even after propagating over distances in the centimeter to meter range. Experimental designs are discussed and optimized for different scattering angles.

Keywords: Thomson scattering; x-ray; Traveling-wave Thomson scattering; TWTS

  • Lecture (Conference)
    3rd International Conference Frontiers in Diagnostic Technologies, 25.-27.11.2013, Frascati, Italien

Publ.-Id: 19999

Reproducibility of target coverage in stereotactic spot scanning proton lung irradiation under high frequency jet ventilation.

Santiago, A.; Jelen, U.; Ammazzalorso, F.; Engenhart-Cabillic, R.; Fritz, P.; Mühlnickel, W.; Enghardt, W.; Baumann, M.; Wittig, A.

To investigate scanned-beam proton dose distribution reproducibility in the lung under high frequency jet ventilation (HFJV).
For 11 patients (12 lesions), treated with single-fraction photon stereotactic radiosurgery under HFJV, scanned-beam proton plans were prepared with the TRiP98 treatment planning system using 2, 3-4 and 5-7 beams. The planning objective was to deliver at least 95% of the prescription of 33 Gy (RBE) to 98% of the PTV. Plans were subsequently recomputed on localization CT scans. Additionally, for selected cases, the effects of range uncertainties were investigated.
Median GTV V(98%) was 98.7% in the original 2-field plans and 93.7% in their recomputation (p=0.039). The respective values were 99.0% and 98.0% (p=0.039) for the 3-4-field plans and 100.0% and 99.6% (p=0.125) for the 5-7-field plans. CT calibration uncertainties of ±3.5% led to a GTV V(98%) reduction below 1.5 percentual points in most cases and reaching 3 percentual points for 2-field plans with beam undershoot.
Through jet ventilation, reproducible tumor fixation for proton radiotherapy of lung lesions is achievable, ensuring excellent target coverage in most cases. In few cases, non-optimal patient setup reproducibility induced density changes across beam entrance channels, leading to dosimetric deterioration between planning and delivery.

Publ.-Id: 19998

Niedermolekulares Heparin senkt Thromboserisiko bei chemotherapeutisch behandelten Tumorpatienten

Heller, S.; Krause, M.

there ist no abstract

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

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.

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.
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.
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.
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.

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

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

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

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

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.

  • Journal of Applied Physics 115(2014), 053525-1-053525-6
    Online First (2014) DOI: 10.1063/1.4864255


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

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

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

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

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

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

Publ.-Id: 19983

Verbesserte Behandlungschancen durch molekulares Targeting in der Radioonkologie

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

Intensitätsmodulierte und biologisch geführte Hochpräzisionsbestrahlung bestimmt heute die moderne Radioonkologie. Wenig ausgeschöpft hingegen ist die Gabe zielgerichteter molekularer Medikamente zur Strahlensensibilisierung maligner solider Tumoren.
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.
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.

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.

Publ.-Id: 19980

Flüssig-fest Stoffübertragung in Festbettreaktoren

Hermann-Heber, R.

Keywords: solid bed reactors; mass transfer

  • Study thesis
    TU Dresden, 2013
    70 Seiten

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Publ.-Id: 19951

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

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;; Flüssigmetall; Eigenerwärmung; Fremderwärmung; Drift

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

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
    84 Seiten

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

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

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

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

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

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

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

Publ.-Id: 19941

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