Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Long-lived Anisotropy of Photoexcited Graphene Electrons

Winnerl, S.; König-Otto, J. C.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Pashkin, A.; Schneider, H.; Helm, M.

In polarization resolved pump-probe experiments complemented by microscopic modeling we show that an anisotropic carrier distribution persists on ps timescales. In particular, we evaluate the role of non-collinear Coulomb scattering.

Keywords: Carrier dynamics; graphene; ultrafast spectroscopy; Coulomb scattering

  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO) 2016, 05.-11.06.2016, San Jose, USA

Permalink: https://www.hzdr.de/publications/Publ-24873
Publ.-Id: 24873


All-electric measurement of the field-invariant magnetization of antiferromagnets

Kosub, T.; Kopte, M.; Schmidt, O. G.; Makarov, D.

Antiferromagnetic materials combine magnetic properties in peculiar combination that is not found in their ferromagnetic counterparts. They are more robust against magnetic disturbances and show great promises in e.g. magnetoelectric applications [1,2]. Despite these fascinating fundamental properties, both the understanding of antiferromagnets and their commercial establishment have progressed slower than for ferromagnets. The tiny uncompensated magnetic moment of the locally uncompensated antiferromagnetic lattice is often the linking element to intrinsic processes that experimenters can exploit or devices can rely on.
One of the most sensitive techniques for thin film magnetometry, the anomalous Hall effect (AHE) [3], is routinely employed to study magnetization eversal in ferromagnets [4] by monitoring the magnetization-proportional anomalous Hall resistance.
However, this typically suffers from a sizable parasitic signal offset due to imperfect device geometry. But, the offset also contains real AHE signals generated by field-invariant magnetization components which are inaccessible in conventional Hall measurements.
We demonstrate, that AHE magnetometry using the spinning-current technique can measure such field-invariant magnetization on an absolute scale by dynamically compensating the parasitic resistance contribution (Fig.) [5]. Thus, we acquire previously unattainable figures about antiferromagnetic materials and refine existing measurements due to the great precision and time-efficiency of AHE magnetometry.
We establish that this technique is suitable to probe a wide range of materials by applying it to polycrystalline IrMn thin films as well insulating Cr 2 O 3 films. Moreover, our all-electric measurements also prove that it is feasible to entirely omit ferromagnets in antiferromagnet-based applications. Doing so paves the way to all-antiferromagnet spintronics with improved performance or improved reliability [6].

[1] X. He, Y. Wang, N. Wu, A. N. Caruso, E. Vescovo, K. D. Belashchenko, P. A. Dowben, and C. Binek, Nature Materials 9, 579 (2010).
[2] J. Heron, J. Bosse, Q. He, Y. Gao, M. Trassin, L. Ye, J. Clarkson, C. Wang, J. Liu, S. Salahuddin, and others, Nature 516, 370 (2014).
[3] N. Nagaosa, J. Sinova, S. Onoda, A. MacDonald, and N. Ong, Rev. Mod. Phys. 82, 1539 (2010).
[4] D. Bhowmik, L. You, and S. Salahuddin, Nature Nanotechnology 9, 59 (2014).
[5] T. Kosub, M. Kopte, F. Radu, O. G. Schmidt, and D. Makarov, Phys. Rev. Lett. 1, 1 (2015).
[6] T. Kosub, O. G. Schmidt, and M. Denys, Patent Applied For (n.d.).

Keywords: Zero-Offset-Hall; antiferromagnetic spintronics

  • Lecture (Conference)
    Joint MMM/Intermag San Diego, 11.-15.01.2016, San Diego, USA
  • Lecture (Conference)
    DPG Regensburg, 14.-18.03.2016, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24872
Publ.-Id: 24872


Analytical Electron Microscopy Study to Resolve the Phase Morphology of Organic Solar Cell Blends

Sedighi, M.; Löffler, M.; Röder, F.; Zschech, E.

To increase the efficiency of bulk heterojunctions for organic photovoltaic devices, the complicated photon-to-electron conversion process has to be understood in detail. To this aim, one challenge is to resolve the correlation between processing parameters of organic solar cells (OSC), the resulting nanoscale morphology of the absorber layer, and efficiency of the completed device. Here, we present the effect of substrate heating on the morphology of the OSC where the active layer is a blend of two small molecules; ZnPc (ZnC32H18N8) as donor and C60 as acceptor.

Obtaining insights into the morphology of the active layer requires the spatial resolution and a contrast mechanism to discriminate two phases with similar average atomic number. To tackle this challenge, we combine electron microscopy imaging with different analytical techniques; energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) in TEM, as well as Energy selective Backscattered (EsB) imaging in SEM.

We imaged different phases of the donor and acceptor, forming ordered and non-ordered regions, depending on the way the heterojunction is fabricated. To this aim, we fabricated samples at substrate temperatures of 110°C and 150°C, each in two different configurations:

1) Focused ion beam prepared ultrathin lamella of a complete solar cell stack with glass substrate, Indium tine oxide (ITO) electrode, ZnPc:C60 blend of the active layer between electron and hole transport layers and aluminum top electrode.
2) Plane view sample as ZnPc:C60 blend deposited on a TEM grid coated with ITO layer.

It was shown that at a substrate temperature of 110°C, the solar cell device has high efficiency [1]., so we consider this as the optimum substrate temperature.

Since identification of the composition of each phase in the plane view sample is more straight forward, we use the plane view sample to attribute each structure to one component of the blend. SEM images recorded by using secondary electron detector show that, the high temperature sample consists of rod-like features and cube-shaped material in between the rods. By combination of analytical microscopy techniques, we can attribute the rod-like structures to ZnPc.

An energy-selective backscatter (EsB) electron detector in a SEM is used to obtain backscattered contrast of the plane view sample. Due to the atomic number difference between the donor phase and the acceptor phase, (the average atomic number of 8.6 for ZnPc and 6 for the C60) sufficient contrast can be achieved [2].

A clear confirmation for the attribution of the ZnPc phase to the rod-like features and the attribution of C60 to the granular structure in between can be drawn from the investigation of the sample in SEM using EDX and with even higher precision in TEM using an improved EDX system. The chemical mapping of zinc and carbon, proves the correct phase assignment, in both plane view and ultrathin samples, prepared at high temperature. For the sample produced at optimum temperature, a much smaller roughness was observed because of the absence of large ordered regions. Even in the plane view sample, the imaging contrast is low due to less separated phases and smaller domains.

To conclude, we clearly resolved the phase morphology of the interpenetrating network of ZnPc:C60 blends for high and optimum temperature samples in plane view and furthermore we were even able to reveal the morphology from TEM images of cross-section lamellas of the real solar cell stacks.

Since the ideal active layer should have domain sizes at the range of the exciton diffusion length (10-20nm), the sample produced at high temperature does not show the desired microstructure. Due to the domain sizes of ~100 nm there is no closed path for exciton dissociation. In addition to that, the sample shows a quite high roughness.

Acknowledgement:
Authors thank A. G. Cid for SEM images. This work was supported by the German Science Council Center of Advancing Electronics Dresden (cfaed). TEM-EDX results were achieved by funding (support code 03SF0451) through the Helmholtz Energy Materials Characterization Platform (HEMCP) initiated by the Helmholtz Association and the German Federal Ministry of Education and Research (BMBF).

References:
[1] S. Pfuetzner, C. Mickel, J. Jankowski, M. Hein, J. Meiss, C. Schuenemann, C. Elschner, A.A. Levin, B. Rellinghaus, K. Leo and M. Riede, “The influence of substrate heating on morphology and layer growth in C60:ZnPc bulk heterojunction solar cells” Org. Electron., 12 (2010), pp. 435–441
[2] A. G. Cid, M. Sedighi, M. Löffler, W. F. van Dorp and E. Zschech, “Energy-Filtered Backscattered Imaging Using Low-Voltage Scanning Electron Microscopy: Characterizing Blends of C60:ZnPc for Organic Solar Cells”. (DOI: 10.1002/adem.201600063)

  • Poster
    EMRS Fall Meeting 2016, 19.-22.09.2016, Warschau, Polen

Permalink: https://www.hzdr.de/publications/Publ-24871
Publ.-Id: 24871


Surprising Coulomb-scattering effects in graphene revealed by polarization-resolved THz spectroscopy

Winnerl, S.; König-Otto, J. C.; Mittendorff, M.; Pashkin, A.; Schneider, H.; Helm, M.; Winzer, T.; Wendler, F.; Malic, E.; Knorr, A.

We present experiments complemented by microscopic theory that highlight surprising Coulomb scattering effects. In particular, we find that non-collinear Coulomb scattering is compa-rably slow, namely on a scale of few ps. For the case of Landau-quantized graphene we find evidence for strong Auger scattering that can deplete a Landau level that is optically pumped at the same time. Both Coulomb effects are relevant for graphene based THz devices.

Keywords: graphene; carrier dynamcis; Coulomb scattering; Auger scattering; Landau quantization

  • Invited lecture (Conferences)
    5th EOS Topical Meeting on Terahertz Science & Technology, 08.-11.05.2016, Pecs, Hungary

Permalink: https://www.hzdr.de/publications/Publ-24870
Publ.-Id: 24870


Fast graphene-based hot-electron bolometer covering the spectral range from terahertz to visible

Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. J.; Murphy, T. E.; Chatterjee, S.; Kolata, K.; Ohser, J.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.

By using broadband absorber materials, bolometric detectors can typically cover an extremely large spectral range. However, since their response relies on the lattice temperature of the employed material, they exhibit slow response times. Hot electron bolometers (HEBs), on the other hand, can be extremely fast, because they exploit a change in device resistance caused by a varying electron temperature. A major drawback of HEBs based on superconductors is the required cooling to very low temperatures. We have developed a detector for room temperature operation, where the broadband absorption of the gapless material graphene is utilized. To this end, a graphene flake grown by chemical vapor deposition (CVD) is transferred to a SiC substrate and coupled to a logarithmic periodic antenna. Fast detection with a rise time of 40 ps is demonstrated for frequencies ranging from 0.6 THz to 390 THz [1]. Interestingly, the detector properties do not deteriorate for wavelength within the Reststrahlen band of SiC (25 – 50 THz). With a noise-equivalent power of 20 µW/Hz½ (800 µW/Hz½) in the near infrared (mid- and far infrared) the detector is capable of recording pulses with energies of the order of 10 pJ (1 nJ). We show that the detector is a versatile device for timing measurements in multi-color ultrafast spectroscopy studies.
[1] M. Mittendorff et al., Opt. Express 23, 28728 (2015).

Keywords: high-speed detector; broadband detector; graphene

  • Lecture (Conference)
    7th internationale Workshop Terahertz Technology and Applications, 15.-16.03.2016, Kaiserslautern, Germany

Permalink: https://www.hzdr.de/publications/Publ-24869
Publ.-Id: 24869


Radio-U(H)PLC - the search on the optimal flow cell for the gamma-detector

Kniess, T.; Meister, S.; Fischer, S.; Steinbach, J.

kein Abstract verfügbar

  • Poster
    18th European Symposium on Radiopharmacy and Radiopharmaceuticals, 07.-10.04.2016, Salzburg, Österreich

Permalink: https://www.hzdr.de/publications/Publ-24868
Publ.-Id: 24868


HgCdTe-based heterostructures for Terahertz photonics

Ruffenach, S.; Kadykov, A.; Rumyantsev, V. V.; Torres, J.; Coquillat, D.; But, D.; Krishtopenko, S. S.; Consejo, C.; Knap, W.; Winnerl, S.; Helm, M.; Fadeev, M. A.; Mikhailov, N. N.; Dvoretskii, S. A.; Gavrilenko, V. I.; Morozov, S. V.; Teppe, F.

Due to their specific physical properties, HgCdTe-based heterostructures are expected to play an important role in terahertz photonic systems. Here, focusing on gated devices presenting inverted band ordering, we evidence an enhancement of the terahertz photoconductive response close to the charge neutrality point and at the magnetic field driven topological phase transition. We also show the ability of these heterostructures to be used as terahertz imagers. Regarding terahertz emitters, we present results on stimulated emission of HgCdTe heterostructures in their conventional semiconductor state above 30THz, discussing the physical mechanisms involved and promising routes towards the 5–15 THz frequency domain.

Keywords: narrow-gap semiconductors; HgCdTe (MCT); THz detectors; THz sources

Permalink: https://www.hzdr.de/publications/Publ-24867
Publ.-Id: 24867


A fluorine-18 radiolabelled celecoxib-based PET probe for Cyclooxygenase-2 monitoring - COX-2 affinity, radiosynthesis and in vitro studies

Kniess, T.; Bechmann, N.; Steinbach, J.; Pietzsch, J.

kein Abstract verfügbar

  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 43(2016)S1, EP844
  • Poster
    Annual Congress of the European Association of Nuclear Medicine, EANM, 15.-19.10.2016, Barcelona, Spanien

Permalink: https://www.hzdr.de/publications/Publ-24866
Publ.-Id: 24866


Dynamics of non-equilibrium charge carriers in p-germanium doped by gallium

Deßmann, N.; Pavlov, S. G.; Tsyplenkov, V. V.; Orlova, E. E.; Pohl, A.; Shastin, V. N.; Zhukavin, R. K.; Winnerl, S.; Mittendorff, M.; Klopf, J. M.; Abrosimov, N. V.; Schneider, H.; Hübers, H.-W.

The low-temperature relaxation processes of non-equilibrium holes into gallium centers in moderately doped p-germanium (NA ≈ 2×10^15 cm-3) has been investigated by a degenerate pump-probe experiment using the free electron laser FELBE. The capture time decreases with increasing average photon flux density of the excitation pulse from about 10.9 ns (at ~1.2×10^24 cm-2 s-1) to ~1.2 ns (~2×10^26 cm-2 s-1). Relaxation inside the valence band is almost independent on pump light intensity and its characteristic time is about 200 ps. In Addition, the intracenter relaxation times of the lowest excited Ga states were measured. The lifetimes scale with the phonon density of states controlling a bound hole – acoustic phonon interaction. The lifetime of the lowest excited state, 1Γ_8^-, was measured to be ~275 ps; while the lifetimes of the higher excited states, 2Γ_8^-and 3Γ_8^-, were found to be ~157 ps and 162 ps, respectively.

Keywords: extrinsic semiconducturs; impurity transitions; carrier dynamics

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-24865
Publ.-Id: 24865


Improving the quantification accuracy of a PET/CT-scanner with pixelated large area detector

Nemer, U.; Maus, J.; Schramm, G.; Meyer, P. T.; Hennig, J.; Mix, M.

One of the main benefits of PET/CT imaging is its ability for absolute quantification. Calibration according to the manufacturer‘s procedure specifies an accuracy of about 10%, whereas especially in dynamic clinical studies a higher quantification accuracy is desired. Therefore a more accurate calibration is needed. At the Gemini TF, a scanner with pixelated large-area LYSO detectors, there are differences in the measurement set-up between calibration and clinical acquisition. This study intends to evaluate the influence of those differences on the calibration with the aim to increase the accuracy of quantification. The major difference herein is the acquisition format, as calibration is performed in histogram-mode (HM-Cal) and clinical acquisition in list-mode format. Using the list-mode format for the calibration (LM-Cal), increases the activity recovery coefficient for the histogram-based acquisition from 0.93±0.08 up to 1.00±0.03. This is however only valid for the calibration set-up but not for clinical situations. Considering more realistic situations like lesions outside the centre of the field of view (FOV) or additional random events coming from highly accumulating regions outside the FOV (like bladder or brain), a different calibration can be found (ALL-Cal). In the evaluation of clinical oncological datasets with low count rates, a significant improvement of the reconstructed mean activity concentration in the bladder (compared to measured urine samples) up to 4% (LM-Cal) was achieved. For very high count rates the normalization of the scanner has to be adapted to improve the quantification accuracy as well.

Keywords: Calibration; Image reconstruction; Phantoms; Table lookup; Positron emission tomography; Bladder; Detectors

  • Contribution to proceedings
    2015 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 31.10.-07.11.2015, San Diego, USA
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2015 IEEE, USA: IEEE, 978-1-4673-9862-6
    DOI: 10.1109/NSSMIC.2015.7582097

Permalink: https://www.hzdr.de/publications/Publ-24864
Publ.-Id: 24864


Unconventional double-bended saturation of optical transmission in graphene due to many-particle interactions

Winzer, T.; Mittendorff, M.; Winnerl, S.; Mittenzwey, H.; Jago, R.; Helm, M.; Malic, E.; Knorr, A.

We present a joint theory-experiment study on the transmission/absorption saturation after ultrafast pulse excitation in graphene. We reveal an unconventional double-bended saturation behavior: Both bendings separately follow the standard saturation model exhibiting two saturation fluences, however, the corresponding fluences differ by three orders of magnitude and have different physical origin. Our results reveal that this new and unexpected behavior can be ascribed to an interplay between fluence- and time-dependent many-particle scattering processes and phase-space filling effects.

Keywords: graphene; nonlinear optics; saturation; carrier dynamics

Permalink: https://www.hzdr.de/publications/Publ-24863
Publ.-Id: 24863


Radiosynthesis of O-3-(2-[18F]fluoroethyl)-L-DOPA ([18F]OFED) – a new fluorine-18 labeled phenylalanine derivative.

Kniess, T.; Schröder, S.; Hoepping, A.; Zessin, J.; Fuechtner, F.; Bergmann, R.; Steinbach, J.

kein Abstract verfügbar

  • Abstract in refereed journal
    Journal of Nuclear Medicine 57(2016)S2, 1039
  • Poster
    Annual Meeting of the Society of Nuclear Medicine and Molecular Imaging, SNMMI, 11.-15.06.2016, San Diego, USA

Downloads:

  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-24862
Publ.-Id: 24862


Symmetry-Breaking Supercollisions in Landau-Quantized Graphene

Wendler, F.; Mittendorff, M.; König-Otto, J. C.; Brem, S.; Berger, C.; de Heer, W. A.; Böttger, R.; Schneider, H.; Helm, M.; Winnerl, S.; Malic, E.

Recent pump-probe experiments performed on graphene in a perpendicular magnetic field have revealed carrier relaxation times ranging from picoseconds to nanoseconds depending on the quality of the sample. To explain this surprising behavior, we propose a novel symmetry-breaking defect-assisted relaxation channel. This enables scattering of electrons with single out-of-plane phonons, which drastically accelerate the carrier scattering time in low-quality samples. The gained insights provide a strategy for tuning the carrier relaxation time in graphene and related materials by orders of magnitude.

Keywords: Carrier dynamics; graphene; Landau quantization; supercollisions

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-24861
Publ.-Id: 24861


Automatisierte Radiosynthese von O-2[18F]Fluorethyl-L-DOPA ([18F]OFED) – eine neue 18F-markierte Aminosäure für die Tumor-Diagnostik

Kniess, T.; Schröder, S.; Hoepping, A.; Füchtner, F.; Zessin, J.; Bergmann, R.; Steinbach, J.

kein Abstract vorhanden

  • Poster
    Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin 2016, 20.-23.04.2016, Dresden, Deutschland
  • Open Access Logo Abstract in refereed journal
    Nuklearmedizin 55(2016)2, P51

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-24860
Publ.-Id: 24860


Ultrafast processes in graphene: from fundamental manybody interactions to device applications

Winnerl, S.; Mittendorff, M.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winzer, T.; Knorr, A.; Malic, E.

A joint experiment-theory investigation of the carrier dynamics in graphene, in particular in the energetic vicinity of the Dirac point, is reviewed. Radiation of low photon energy is employed in order to match the intrinsic energy scales of the material, i.e. the optical phonon frequency (~200 meV) and the Fermi energy (10-20 meV), respectively. Significant slower carrier cooling is predicted and observed for photon energies below the optical phonon frequency. Furthermore, a strongly anisotropic distribution of electrons in k-space upon excitation with linearly polarized radiation is discussed. Depending on photon energy, the anisotropic distribution decays either rapidly via optical phonon emission, or slowly via non-collinear Coulomb scattering. Finally, a room temperature operated ultra-broadband hot-electron bolometer is demonstrated. It covers the spectral range from the THz to visible region with a single detector element featuring a response time of 40 ps.

Keywords: graphene; carrier dynamics; detectors

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-24859
Publ.-Id: 24859


Eddy current flowrate and local ultrasonic velocity measurements in liquid sodium

Krauter, N.; Franke, S.; Gerbeth, G.; Eckert, S.; Stefani, F.; Gastaldi, O.; Girard, M.

For the safe operation of sodium cooling systems a monitoring of the flow field is often desirable. We report first on the development of a new eddy current flowmeter (ECFM) and related tests in sodium. The objective of this sensor is its positioning above the fuel subassemblies and the detection of possible blockages of the sodium flow through the multitude of subassemblies. The sensor consists of a number of coils a part of which is fed by an excitation AC current. The assembly of coils is placed in a thimble and the measured flowrate is proportional to the integral flow around this thimble. In the second part we report on local ultrasonic velocity measurements. Here, the objective is to study the flow field resulting from a large electromagnetic pump installed at the PEMDYN facility of CEA. Both measuring techniques were tested at the sodium facility NATAN of HZDR.

Keywords: Eddy Current Flow Meter; Ultrasound Doppler Method; Liquid metal flow

  • Contribution to proceedings
    International Conference on Fast Reactors and Related Fuel Cycles: Next Generation Nuclear Systems for Sustainable Development (FR17), 26.-29.06.2017, Yekaterinburg, Russland
  • Lecture (Conference)
    International Conference on Fast Reactors and Related Fuel Cycles: Next Generation Nuclear Systems for Sustainable Development (FR17), 28.06.2017, Yekaterinburg, Russland

Permalink: https://www.hzdr.de/publications/Publ-24858
Publ.-Id: 24858


Design, synthesis, radiosynthesis, and biological evaluation of radiofluorinated quinoline derivatives for PET imaging of PDE5A in brain

Liu, J.; Wenzel, B.; Dukic-Stefanovic, S.; Teodoro, R.; Ludwig, F.-A.; Deuther-Conrad, W.; Schröder, S.; Chezal, J.-M.; Moreau, E.; Brust, P.; Maisonial-Besset, A.

kein Abstract vorhanden

  • Poster
    EFMC – International Symposium on Medicinal Chemistry 2016, 28.08.2016, Manchester, UK

Permalink: https://www.hzdr.de/publications/Publ-24857
Publ.-Id: 24857


The IAEA Coordinated Research Project on Sodium Properties and Safe Operation of Experimental Facilities in Support of the Development and Deployment of Sodium-cooled Fast Reactors (NAPRO)

Azpitarte, O.; Japas, M.; Chocrón, M.; Vázquez, E.; Villanueva, A.; Long, B.; Xu, C.; Xie, C.; Latgé, C.; Gerschenfeld, A.; Anderhuber, M.; Chacon, L.; Matteo, L.; Cavaro, M.; Féron, D.; Trabuc, P.; Bubelis, E.; Perez-Martin, S.; Stieglitz, R.; Eckert, S.; Krauter, N.; Selvaraj, P.; Raghvachary, S.; Athmalingam, S.; Chellapandi, P.; Ohira, H.; Lee, J.; Park, S.; Lee, Y.; Hong, J.; Jayaraju, S.; Roelofs, F.; Marinenko, E.; Zagorulko, Y.; Passerini, S.; Gerardi, C.; Grandy, C.; Monti, S.; Kriventsev, V.

The International Atomic Energy Agency (IAEA) recently established a Coordinated Research Project (CRP) on “Sodium Properties and Safe Operation of Experimental Facilities in Support of the Development and Deployment of Sodium-cooled Fast Reactors - NAPRO”, to be carried out in the period 2013 – 2017. Eleven institutions from ten Member States participate in this CRP. The complete scope of this CRP is covered by three work packages. A specific work package (WP1), under the coordination of ANL (USA), is focused on the compilation and expert assessment of data sets of Na physical and chemical properties, as well as correlations for pressure drops and heat transfer in Na facilities. A second work package (WP2), under the coordination of IPPE (Russian Federation), addresses the compilation, evaluation and development of best practices and guidelines for the design, operation and maintenance of Na facilities. Finally, Work Package 3 (WP3), coordinated by CEA (France), concentrates on the compilation and development of guidelines and rules for the safe operation of Na facilities, including the prevention, detection and mitigation of Na leaks and fires. Finally, this work presents some examples of the principal results obtained so far by WP 1.

Keywords: sodium properties; sodium facilities design; sodium safety

  • Contribution to proceedings
    International Conference on Fast Reactors and Related Fuel Cycles: Next Generation Nuclear Systems for Sustainable Development (FR17), 26.-29.06.2017, Yekaterinburg, Russland

Permalink: https://www.hzdr.de/publications/Publ-24856
Publ.-Id: 24856


Local etching of a SiOx layer on Si(111) by Ga droplets and its influence on GaAs nanowire growth

Tauchnitz, T.; Schneider, H.; Helm, M.; Dimakis, E.

GaAs nanowires (NWs) can be grown epitaxially on Si(111) substrates in the vapour-liquid-solid mode. Typically, Au is used as catalyst, but affects the NW and substrate properties due to contamination. Thus, the self-catalyzed mode appears to be advantageous. The NW growth is initialized by the formation of Ga droplets on the substrate surface, which is normally covered by a thin SiOx layer. The yield of vertical NWs depends on the thickness and the nature of the SiOx, pointing out the complex interaction of the liquid Ga with the SiOx. This work investigates the local etching of a native SiOx on Si(111) by liquid Ga droplets, a mechanism, which is thought to precede the NW nucleation. The droplet formation, the etching process, and their effect on the NW growth were studied as a function of the substrate temperature and the etching time using molecular beam epitaxy. In contrast to previous studies, the oxide etching is distinguished from the subsequent NW nucleation by inserting a thermal annealing step, during which the Ga droplets are evaporated completely from the surface. Finally, the yield of vertical NWs and the NW number density can be controlled just by choosing the appropriate conditions for the oxide etching, independent of those used for the subsequent NW growth.

  • Poster
    DPG Spring Meeting, 06.03.2016, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-24855
Publ.-Id: 24855


Erstellung einer Benutzeroberfläche in LabVIEW zur Steuerung der Mikroreaktoranlage zur Partialoxidation von Isobutan in flüssiger Phase.

Lu, X.

Im Rahmen des Belegs wurde eine graphische Oberfläche unter Labview entwickelt, die zur Durchführung von Steuerungs-, Regelungs- und Messaufgaben für einen im Rahmen des Projektes Helmholtz-Energieallianz entworfenen und aufgebauten Reaktor benötigt wurde.

Keywords: Labview; GUI; MSR software; Mikroreaktor

  • Study thesis
    TU-Dresden, 2014
    Mentor: Thomas Willms
    31 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24854
Publ.-Id: 24854


The effect of deposition processing on structural and luminescent properties of a-SiOC: H thin films fabricated by RF-magnetron sputtering

Vasin, A. V.; Rusavsky, A. V.; Kysil, D. V.; Prucnal, S.; Piryatinsky, Y.; Starik, S. P.; Nasieka, I.; Strelchuk, V. V.; Lysenko, V. S.; Nazarov, A. N.

Amorphous silicon oxicarbide thin films (a-SiOC(:H)) were deposited by RF-magnetron sputtering using Si or SiC target in Ar/CH4/O2 flow. Interatomic bonding and light emission properties were analyzed by FTIR in transmission and attenuation total reflection (ATR) mode, Raman scattering and photoluminescence spectroscopy. Comparison of the results obtained by FTIR and ATR allows us to suggest that structural properties of the near-surface region and the bulk of the films are significantly different. The surface layer contains a significant fraction of polymer-like SiOC structural components in the form of Si-O-Si/Si-O-C chains and cages, while bulk of the film is represented by inorganic amorphous SiOx network with amorphous carbon precipitates. Samples with the high fraction of carbon precipitates exhibit white luminescence at room temperature. The origin of strong photoluminescence is discussed.

Keywords: Amorphous silicon oxicarbide thin films; ATR; FTIR; Photoluminescence

Permalink: https://www.hzdr.de/publications/Publ-24853
Publ.-Id: 24853


Untersuchungen zur Partialoxidation von Isobutan in einem Mikroreaktor unter überkritischen Bedingungen.

Huiras, J.

Die partielle Oxidation von Isobutan durch Sauerstoff in einem Mikroreaktor wurde im überkritischem Zustand zwischen 135 °C und 145 °C unter Verwendung von di-t-butyl peroxide (DTBP) als Initiator untersucht. Dabei wurden das Verhältnis zwischen Isobutan und Sauerstoff, die Verweilzeit, der Druck, die Initiatorkonzentration und die Temperatur variiert. Ziel war es, die Effizienz des Prozesses durch eine Erhöhung der Selektivität des Produkts t-Butyl hydroperoxide (TBHP) und des Umsatzes zu verbessern. Es war insbesondere zu überprüfen, ob sich der Prozess unter diesen Bedingungen durch die Aufhebung von Stofftransportwiderständen gegenüber dem Zweiphasenprozess bei niedrigeren Temperaturen optimieren lässt. Die Reaktionsprodukte TBHP, Azeton, t-butanol und DTBP wurden mittels GC\MS analysiert. Im Rahmen der Arbeit gelang es die höchsten bisher mit einem Mikroreaktor erzielten Umsätze für die Isobutanoxidation zu erzielen. Jedoch gingen die Umsätze nicht wesentlich über die Umsätze hinaus, die aufgrund des zu erwartenden Temperatureffekts bei der Nutzung von überkritischen Bedingungen zu erwarten waren. Auch war die Umsatzerhöhung nur auf Kosten der Selektivität des TBHP zu erzielen. Die Arbeit bietet jedoch aufgrund Ihrer Ergebnisse eine wichtige Grundlage für weitere Untersuchungen.

Keywords: Isobutanoxidation; überkritischer Prozess; Effizienzoptimierung; t-Butylhydroperoxid; Mikroreaktor

  • Study thesis
    TU-Dresden, 2016
    Mentor: Thomas WIllms
    63 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24852
Publ.-Id: 24852


Time-Resolved Studies of the Light-Induced Insulator-Metal Transition in NbO2 and VO2 Thin Films

Beebe, M.; Klopf, J. M.; Wang, Y.; Kittiwatanakul, S.; Lu, J.; Wolf, S. A.; Lukaszew, R. A.

While vanadium dioxide (VO2) is one of the most extensively studied highly correlated materials, there are intriguing similarities and differences worth exploring in another highly correlated oxide, niobium dioxide (NbO2). Both materials exhibit a thermally-induced first-order insulator-metal transition at a material-dependent critical temperature, which is considerably higher in NbO2 than in VO2 – approximately 1080 K and 340 K in bulk, respectively. This transition, evidenced by up to 6 orders of magnitude change in DC and optical conductivities, can also be induced in VO2 via photo-doping on a sub-picosecond timescale. Here, we present the first ultrafast pump-probe studies on the optically-induced transition of NbO2 thin films and the comparison with similar VO2 films. It is observed that NbO2 films transition faster and exhibit significantly faster recovery time than VO2 films of similar thickness and microstructure, showcasing that NbO2 is a promising material for next generation high-speed optoelectronic devices.

Keywords: (240.0310) Thin films; (310.6860) Thin films, optical properties; (310.6845) Thin film devices and applications; (320.7100) Ultrafast measurements; (320.7130) Ultrafast processes in condensed matter, including semiconductors

Permalink: https://www.hzdr.de/publications/Publ-24851
Publ.-Id: 24851


The double role of Ga droplets in the self-catalyzed growth of GaAs nanowires on SiOx/Si(111) substrates

Tauchnitz, T.; Schneider, H.; Helm, M.; Dimakis, E.

We have investigated the in-situ surface modification of a SiOx/Si(111) substrate by Ga droplets and its effect on the subsequent self-catalyzed growth of GaAs nanowires. Using a procedure of Ga droplet formation and subsequent re-evaporation prior to the nanowire growth, we found that the number density of nanowires at a given growth temperature can be varied deliberately within four orders of magnitude without affecting the nanowire diameter. A detailed study of the Ga droplet formation in a wide range of substrate temperatures revealed the physical processes that control the number density and size of the droplets.

Keywords: Nanowire; Ga droplets; oxide etching; nanoholes; GaAs; Si substrate

  • Lecture (Conference)
    International Conference on Molecular Beam Epitaxy, 04.09.2016, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-24850
Publ.-Id: 24850


Optimierung und Validierung der GC/MS-Methode zur Bestimmung der Reaktionsprodukte der Partialoxidation von Isobutan mit Sauerstoff im Mikroreaktor.

Liu, W.

Die partielle Oxidation von Isobutan, t-Butyl Hydroperoxid (TBHP) wurde zum ersten Mal als ein Zwei-Phasen-Prozess in einer Kapillare als Mikro Reaktor durchgeführt und analytisch untersucht. Um detaillierte Informationen über Produkte, Ausbeute, Selektivität und Reaktion Wege zu erhalten, mussten die Produkte mittels GC-MS analysiert werden. Zur Trennung der flüssigen Produkte wurde eine GC-MS Methode erstellt, optimiert und validiert, die eine Rxi-5ms-Säule und einen PTV-Injek-tors verwendet. Im Rahmen der Validierung wurden der Konzentrationsfehler wie auch der Mess¬fehler des MS-Signals aus sämtlichen Kalibrierschritten ermittelt sowie die entsprechenden analytischen Normen (z.B. DIN 38402) für die Kalibrierung berücksichtigt. Außerdem wurden statistische Tests auf Trends (nach Neumann), Ausreißer (nach Dixon), Normalverteilung (nach David) etc. durchgeführt. Die flüssigen Produkte wurden mittels MS identifiziert: Als Hauptprodukte traten TBHP, di-t-Butyl-Peroxid (DTBP), t-Butanol (TBA) und Propanone auf. Für die Zielprodukte TBHP und DTBP wurden Korrelationkoeffiuienten von r2 > 0,999, für TBA und Azeton r2 > 0,995 erzielt. Daneben traten Nebenprodukte wie z.B. Methanal, Methanol, Isopropanol, Isobutanol und Isobutanal auf, von denn alle bis auf Methanol und Methanal ebenfalls kalibriert wurden.

Keywords: TBHP; DTBP; Vslidierung; isobutanoxidation

  • Study thesis
    TU-Dresden, 2016
    Mentor: Thomas Willms
    68 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24849
Publ.-Id: 24849


“Reverse Epitaxy” on semiconductor surfaces by low energy ion irradiation

Engler, M.; Ou, X.; Facsko, S.

Ion beam irradiation can produce different patterns on semiconductor surface. While the surface is amorphized at low temperatures, the surface remains crystalline above the dynamic recrystallization temperature. Reverse Epitaxy leads to pattern formation, which is driven by diffusion of vacancies and adatoms on the surface, above this temperature. The mechanisms of Reverse Epitaxy epitaxy are quite similar to mound formation in homoepitaxial growth. The surface is destabilized in both cases by an effective uphill diffusion current driven by Ehrlich-Schwoebel barriers. The patterns formed depend of step formation energies, diffusion on terraces, and Ehrlich-Schwoebel barriers, which all are anisotropic. Their anisotropy is determined by the surface symmetry. By changing the surface symmetry the resulting patterns are be changed.

  • Invited lecture (Conferences)
    XI-th International Conference on Ion Implantation and other Applications of Ions and Electrons - ION 2016, 13.06.2016, Kazimierz Dolny, Polska

Permalink: https://www.hzdr.de/publications/Publ-24848
Publ.-Id: 24848


Compositional Non-parametric Tests

van den Boogaart, K. G.; Tolosana-Delgado, R.

Current compositional methods typically rely on some sort of normality hypothesis for testing. Typical well-known non-parametric tests rely on ranks transforms, which are undefined for multivariate problems. The aim of this contribution is thus to investigate the possibilities for truly multivariate non-parametric tests of location and distribution for compositonal data. The challenge is the to ensure subcompositional coherence, which would bring the possibility to attribute deviations to certain subcompositions.

For the case of tests for a known compositional mean, we propose a bootstrap method, measuring how extreme this mean is with respect to a bootstrap sample of the empirical compositional mean. The extremity is checked in each of the pairwise log-ratios. This ensures a subcompositional coherence in the sense that a rejected hypothesis will always be rejected in at least one subcomposition.

For the case of a two sample test comparing two populations, the same principle can be extended. The mean difference is compared with bootstrap samples of mean differences. The same subcompositional coherence applies.

For multiple samples we can extend the idea of ANOVA of measuring the variability of the group means. The variability is measured in terms of the variation matrix. For each entry of the variatin matrix we quantify its quantile in the bootstrap population. We take then the maximum of the quantiles and bootstrap this maximum. In this way we again get a subcompositionally test for equal mean in all samples. Weighted modifications might improve power of the test in case of unequal sample sizes.

  • Lecture (Conference)
    CoDaWork 2017, 06.-9.6.2017, Abbadia San Salvatore, Italia

Permalink: https://www.hzdr.de/publications/Publ-24847
Publ.-Id: 24847


Compositional Non-parametric Regression

Tolosana-Delgado, R.; van den Boogaart, K. G.

Compositional regression is concerned with modelling the dependence of a composition on one or more covariables, or vice versa. State of the art methods typically rely on the assumptions of linearity of the dependence and for tests on the additive logistic normal distribution of the errors. Several different solutions for non-linear regression and tests without normality assumption are available for non-compositional data. Based on them, this contribution derives non-parametric regression models and methods valid for compositional data.

With respect to the non-linear dependence, some sort of regularisation assumption is always required. Different classical approaches can be adapted for compositonal data. LOESS smoothing on pairwise log-ratios or logratio transforms would correspond to some sort of smooth (compositional) derivatives. Regression splines and smoothing splines are already defined in a multivariate way and allow to control the degree of continuity and smoothness by explicit parameters. Piecewise regression needs to be applied to log-ratio transforms and allows to model non-continuous dependence. Geostatistical interpolation or, equivalently, reproducing kernel splines, allow a precise control over the level of continuity and complexity through the variogram.

All methods mentioned admit a multivariate extension which, by virtue of the principle of working in coordinates, automatically give rise to compositional versions of those methods. Moreover, all are either affine equivariant, or else very slight restrictions of them are. Thus, the associated compositional versions deliver results which are: invariant with respect to the choice of basis, scaling invariant, and subcompositionally coherent (in the case of regression with compositional response).


With regard to testing, there are some philosophical difficulties in a classical ``zero slope hypothesis''. A strict test for dependence could be very misleading when used for model selection in a non-parametric setting. As an alternative we propose to check, whether the prediction by the non-parametric model outperforms the prediction by parametric (constant) one. We propose to compare the jacknifed residuals of the two models. This construction allows to construct all meaningful tests of compositional dependence, namely: global lack of dependence, lack of dependence within a subcomposition, as well as restricted dependence within a subcomposition.

  • Lecture (Conference)
    CoDaWork 2017, 06.-09.06.2017, Abbadia San Salvatore, Italia

Permalink: https://www.hzdr.de/publications/Publ-24846
Publ.-Id: 24846


Fluid dynamics in novel sandwich packings for absorption and distillation

Sohr, J.; Schubert, M.; Hampel, U.

Poster zum EMR-Meeting am 21.09.2016 am HZDR

  • Poster
    EMR-Meeting, 21.09.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24845
Publ.-Id: 24845


X-Ray Photoelectron Study of Ion Implanted Tetrahedral Carbon

Berova, M.; Sandulov, M.; Tsvetkova, T.; Avramova, I.; Boettger, I.; Bischoff, L.

Samples of thin film (d~40nm) tetrahedral amorphous carbon (ta-C), deposited by filtered cathodic vacuum arc (FCVA), have been implanted with N+ and Ga+ at ion energy E = 20 keV and ion fluences D = 3.1014÷3.1015 cm-2. This results in optical properties modification, best manifested by a significant shift of the optical absorption edge to lower photon energies, which is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). These effects could be attributed both to additional defect introduction and increased graphitization, as confirmed by X-ray photo-electron spectroscopy (XPS) measurements. The nonimplanted films show the expected variety of carbon-carbon chemical bonds: three- and fourfold coordinated carbon, while the X-ray results show that ion implantation leads to the introduction of additional disorder in the films. The X-ray photoelectron spectra of the implanted films show that, in addition to the already mentioned changes, the ion bombardment results in an increase of the threefold coordinated as compared to the fourfold coordinated carbon bonds, i.e. increased graphitization of the carbon content in the films. These structural modifications, due to the ion implantation, are the reasons for the observed changes in the optical properties of the films, which could be made use of in the area of high-density optical data storage using focused Ga+ ion beams.

Keywords: tetrahedral amorphous carbon; focused ion beams; optical data storage

Permalink: https://www.hzdr.de/publications/Publ-24844
Publ.-Id: 24844


Metalle schürfen aus Elektronikschrott

Ell, R.; Scharf, C.; (Editors)

Metallurgen entwickeln neue Strategien, um Rohstoffe aus alten Handys zurückzugewinnen.

  • VDI-Nachrichten 44(2016), 23-23

Permalink: https://www.hzdr.de/publications/Publ-24843
Publ.-Id: 24843


Kritische Rohstoffe aus zweiter Hand

Scharf, C.

Seit drei Jahren lehre und forsche ich als Professorin für Metallurgie und Recycling der Hochtechnologiemetalle in Freiberg. Mein Team und ich setzen uns für einen nachhaltigen Umgang mit kritischen Metallen und anderen Industriemineralen ein. Wir erforschen neue Verfahren, um beispielsweise Produktionsabfälle zu reduzieren und die Wiederverwertung von Rohstoffen aus Altgeräten zu verbessern. Schlacken, Schlämme, Stäube, Späne oder Abwässer — in der Mineralrohstoff und Metallindustrie gibt es, technisch bedingt, viele Rückstände und damit auch eine große Menge bisher nicht genutzter Wertstoffe. Gemeinsam mit den wiederverwertbaren Stoffen, die in alten Elektrogeräten und sonstigen ausgedienten Produkten stecken, gelten sie inzwischen
als wichtiger Hebel für das Erreichen einer maximalen Ressourceneffizienz in der Kreislaufwirtschaft. Um solche „Rohstoffe aus zweiter Hand“, auch sekundäre Ressourcen genannt, dreht sich die Arbeit meines Forscherteams.

  • Contribution to external collection
    Prof. Roewer: ACAMONTA - Zeitschrift für Freunde und Förderer der Technischen Universität Bergakademie Freiberg, Marienberg: Erzdruck GmbH, 2016, ISSN 2193-309X, 27-28

Permalink: https://www.hzdr.de/publications/Publ-24842
Publ.-Id: 24842


Synthese neuer Imidazol-Derivate für die Entwicklung eines 18F-PET-Radioliganden zur Bildgebung des Cannabinoid Rezeptors 2 im Gehirn

Hausmann, K.

Es ist kein Abstract vorhanden.

  • Master thesis
    Universität Leipzig, 2016
    Mentor: Dr. R.-P. Moldovan
    71 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24841
Publ.-Id: 24841


Entwicklung eines 18F-markierten Radioliganden zur Bildgebung der Phosphodiesterase 10A im Gehirn durch Positronen-Emissions-Tomographie

Wagner, S.

Es ist kein Abstract vorhanden.

  • Doctoral thesis
    Universität Leipzig, 2016
    Mentor: Dr. Matthias Scheunemann
    166 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24840
Publ.-Id: 24840


Preliminary Studies on the Partial Oxidation of Isobutane with Oxygen in Multiphase Flows.

Lu, X.

Oxidation of hydrocarbon is an industrially important reaction. Many valuable chemicals are synthesized by the oxidation of relatively cheap raw materials derived from petroleum. The oxidation of isobutane is one of the most important oxidation oxidation processes. For example, isobutane oxidation can be conducted as the preoxidation in oxirane process to produce propylene oxide and tert.-butanol, in which propylene oxide and TBA are important industrial raw materials and widely used in the syntheses of pharmaceuticals, agrochemicals and other fine chemicals (Qi et al., 2014).
In more recent times, there is more and more interest of researchers in the application of microreactors in chemical engineering because of the opportunities of microreactors in chemical process development and intensification, such as excellent heat and mass transfer (Kashid et al., 2014). In this thesis, the oxidation of isobutane in two-phase flow is investigated in a microreactor (100 m long, 1mm ID). The experiments were carried out under different conditions. The start-up behavior of the oxidation of isobutane has been investigated and discussed. In addition, the effect of temperature, pressure, residence time, oxygen-isobutene ratio, the nitrogen dilution and initiator concentration on the performance of isobutane has also been preliminary investigated and discussed. Furthermore, the rate constant of isobutene oxidation has been calculated for 130 °C.

Keywords: microreactor; isobutane oxidation; two phase flow

  • Diploma thesis
    TU-Dresden, 2016
    Mentor: Thomas WIllms
    89 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24839
Publ.-Id: 24839


Partikelentstehung und -transport im Reaktorwasser von DWR nach Kühlmittelverluststörfällen (KMV) - Untersuchungen im Labormaßstab

Harm, U.; Kryk, H.; Hampel, U.; Seliger, A.; Renger, S.; Kästner, W.

Im Rahmen der nuklearen Sicherheitsforschung des Bundesministeriums für Wirtschaft und Energie (BMWi) erfolgten an der Hochschule Zittau/Görlitz (HSZG) in Kooperation mit der Technischen Universität Dresden (TUD) und dem Helmholtz-Zentrum Dresden-Rossendorf (HZDR) experimentelle und methodische Untersuchungen für die systematische Klärung physiko-chemischer Mechanismen im Kühlmittel und deren Auswirkungen auf thermo-fluiddynamische Prozesse im Reaktorkern, welche während des Sumpfumwälzbetriebes als Langzeitnachkühlung nach Kühlmittelverluststörfällen (KMV) in Druckwasserreaktoren (DWR) auftreten können. Durch Korrosionsprozesse an feuerverzinkten Installationen im Sicherheitsbehälter (SHB) von DWR wird Zink in ionischer Form im borierten Kühlwasser gelöst. Die freigesetzten Zink-Ionen werden aus dem Reservoir des Nachkühlmittels im SHB über die Not- und Nachkühlsysteme bis in den Reaktorkern gefördert. Im Reaktor wird das eingespeiste Kühlmittel (KM) aufgeheizt.
Im Fokus generischer Experimente standen Untersuchungen zum Verhalten derart zusam-mengesetzter Fluide unter Berücksichtigung von Temperaturunterschieden zwischen dem Kühlmittelreservoir im SHB und dem Reaktorwasser an den Brennstäben im Reaktorkern. Diese generischen Untersuchungen erfolgten an elektrisch beheizten Stabkonfigurationen, welche die durch Nachzerfallsleistung beheizten Brennstäbe im Kern von DWR nachbildeten. Bei der Aufheizung des zinkhaltigen KM innerhalb solcher Konfigurationen wurden Trübungen durch Kolloidbildung beobachtet, gefolgt von Ausscheidungen partikelförmiger, fester Korrosionsprodukte in Form von Zinkboraten. Diese erschienen in Abhängigkeit von der umgebenden KM- bzw. Staboberflächentemperatur als leicht mobilisierbare, flockenartige Dispersphase oder wiesen schichtenbildenden Charakter auf.
Die temperaturabhängigen Umwandlungen von gelösten Zink-Ionen in feststoffartige Zinkborate bewirkten sowohl Ablagerungen an den Heizstäben als auch an den Abstandshaltern (AH) und führten zu erhöhtem Differenzdruckaufbau über die AH sowie Strömungsumverteilungen in der Stabkonfiguration. In Folge dieser Ablagerungen wurden Änderungen des Wärmetransports vom beheizten Stab ans Fluid nachgewiesen, die eine Aufheizung der Heizstäbe bewirkten und damit sicherheitsrelevanten Charakter hinsichtlich der Nachwärmeabfuhr tragen. Aktuell wird dieses generisch ermittelte Verhalten des Reaktorwassers hinsichtlich der Übertragbarkeit auf sicherheitsrelevante Fragestellungen realer DWR mit Bezug auf anzunehmende Leckgrößen und Nachkühlbedingungen und den daraus resultierenden thermohydraulischen Randbedingungen im Sicherheitsbehälter und im Reaktorkern untersucht. Hierfür werden durch Störfallanalysen die Zustände und Bedingungen abgrenzend ermittelt, bei denen eine Gefährdung der Kernkühlung aus Sicht vorhandener Erkenntnisse zu den physiko-chemischen Effekten eintreten könnte. Wesentliche Untersuchungsschwerpunkte bilden die im SHB von DWR auftretenden chemischen und thermodynamischen Einflüsse auf die Zinkfreisetzung und das Ausfällungs- und Ablagerungsverhalten der Korrosionsprodukte an Heißstellen im Reaktorkern.
Die Untersuchungsergebnisse finden u.a. für die Parametrierung von Simulationscodes sowie in alternativen Modellansätzen Verwendung und dienen der sicherheitstechnischen Einschätzung des DWR-Reaktorverhaltens für verschiedene KMV-Störfallszenarien. Die quantitative Analyse der experimentellen Daten zum zeitlichen Ablauf des Quelle-Senke-Mechanismus der Zinkkorrosion und der Umwandlung des gelösten Zinks in feste Produkte unter realen Störfallbedingungen stellt auf Grund der Komplexität und der gegebenen Rückwirkungen eine Herausforderung dar.
Die Vorhaben werden mit Mitteln des Bundesministeriums für Wirtschaft und Energie (BMWi) unter den Förderkennzeichen 150 1491 und 150 1496 gefördert und fachlich von einer Monitoring Group begleitet, welche sich aus Repräsentanten der Forschungsbetreuung des Projektträgers, Gutachtern, Herstellern und Anlagenbetreibern zusammensetzt.

Keywords: Nuclear energy; Loss of coolant accident; corrosion; zinc release; experiments

  • Contribution to proceedings
    Wasser im Kraftwerk und in der Energietechnik, Zittauer Kraftwerkschemisches Kolloquium, 22.-23.09.2016, Zittau, Deutschland
    Proceedings des Zittauer Kraftwerkschemischen Kolloquiums
  • Lecture (Conference)
    Wasser im Kraftwerk und in der Energietechnik, Zittauer Kraftwerkschemisches Kolloquium, 23.09.2016, Zittau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24838
Publ.-Id: 24838


Helmholtz-Zentrum Dresden-Rossendorf Helmholtz Institute Freiberg for Resource Technology Introduction CHROMIC

Scharf, C.; Kelly, N.; Helbig, T.

Helmholtz-Zentrum Dresden-Rossendorf
Helmholtz Institute Freiberg for Resource Technology
Introduction
CHROMIC
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730471
This presentation reflects only the author’s views and neither Agency nor the Commission are responsible for any use that may be made of the information contained therein.

  • Invited lecture (Conferences)
    CHROMIC, Kick-Off-Meeting, 07.-08.12.2016, Mol, Belgien

Permalink: https://www.hzdr.de/publications/Publ-24837
Publ.-Id: 24837


CHROMIC WP4 Presentation

Scharf, C.; Kelly, N.; Helbig, T.

CHROMIC
WP4 Presentation
Prof. Dr.-Ing. Christiane Scharf (HZDR, HIF)
This project has received funding from the European Union’s Horizon 2020 research and
innovation programme under grant agreement No 730471
This presentation reflects only the author’s views and neither Agency nor the Commission are responsible for any use that may be made of the information contained therein.

  • Invited lecture (Conferences)
    CHROMIC, Kick-Off-Meeting, 07.-08.12.2016, Mol, Belgien

Permalink: https://www.hzdr.de/publications/Publ-24836
Publ.-Id: 24836


Koordinierungsgespräch HIF – Technikum

Scharf, C.

Koordinierungsgespräch
HIF – Technikum
Christiane Scharf
29.4.2016, Helmholtz-Zentrum Dresden-Rossendorf

  • Lecture (others)
    Koordinierungsgespräch, SMWK, SAB, SIB, HZDR, 29.04.2016, Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24835
Publ.-Id: 24835


„Der Weg ist für jeden hürdenreich“ Neue Veranstaltungsreihe beleuchtet Karrierewege für Frauen in der Wissenschaft

Scharf, C.

Obwohl sich die Anzahl weiblicher und männlicher Hochschulabsolventen in etwa die Waage hält, sind auf den akademischen Führungspositionen nur selten Frauen zu finden. Über die Gründe wird viel diskutiert. Unter anderem würden den jungen Forscherinnen geeignete Vorbilder fehlen. Die HZDR-Zentralabteilung Verwaltung hat eine Veranstaltungsreihe aufgesetzt, in der Professorinnen des Zentrums ihren Weg in der Wissenschaft vorstellen. Den Anfang machte im März Prof. Christiane Scharf. Sie hält seit Oktober 2013 die Professur für Metallurgie und Recycling von Hochtechnologiemetallen an der TU Bergakademie Freiberg. Außerdem leitet sie die Abteilung Metallurgie und Recycling am Helmholtz-Institut Freiberg für Ressourcentechnologie. insider hat sich mit ihr über die Situation für Frauen in der Wissenschaft unterhalten.

insider: Frau Scharf, Sie sind ein seltener Fall. Nur ein Fünftel aller deutschen Professuren ist weiblich besetzt. Wie kommt das?
Christiane Scharf: Ich persönlich denke, dass das deutsche Familien- und vor allem Frauenbild hier immer noch eine sehr starke Rolle spielt. Der Einfluss des direkten familiären Umfeldes hat enorme Auswirkungen auf die Karriere. Kommt aus dieser Richtung zusätzlicher Widerstand, was wohl leider nicht selten der Fall ist, wird es sehr schwierig, die ohnehin hohen Hürden zu meistern. Wenn man allerdings den Rückhalt spürt, wird Vieles wesentlich leichter. Häufig genügen dafür schon ein oder zwei Personen, auf die man sich verlassen kann.

Gerade bei Frauen kommt es relativ häufig vor, dass sie einen Ruf nicht annehmen. Könnte das in diesen Fällen auch eine Rolle spielen?
Absolut. Industrie und Wissenschaft haben mittlerweile zum großen Teil begriffen, dass viele Frauen alle Qualifikationen mitbringen und neue Ideen beisteuern können. Eine Führungsposition bringt jedoch automatisch neue Pflichten und einen höheren Grad an Verantwortung mit sich. Ob man sich selbst zutraut, dies zu erfüllen, hängt wiederum stark vom persönlichen Umfeld ab. Dabei sollten auch gesellschaftliche Vorstellungen – ich nenne hier zum Beispiel den Begriff der Rabenmutter, selbst wenn das altertümlich klingen mag – nicht unterschätzt werden.

An welcher Stelle könnte man ansetzen, um das zu ändern?
Zu meiner Schulzeit wurde noch stark das Bild vermittelt, dass Frauen in technischen und naturwissenschaftlichen Berufen nichts verloren hätten. Glücklicherweise ändert sich das seit etwa fünfzehn Jahren. Gesellschaftlich hat sich schon viel getan. Am Ende ist es natürlich trotzdem eine Persönlichkeitsfrage: Wie gehe ich zum Beispiel mit Niederlagen um? Nach meinem Chemieingenieursstudium habe ich mehr als 100 Absagen erhalten.

Und wie gingen Sie damit um?
Ich habe als chemische Fachkraft bei einem Privatunternehmen angefangen. Diese Erfahrungen aus der Industrie haben mir später sehr weitergeholfen. In den meisten Fällen ist die größte Hürde, erst einmal in das gewünschte Feld hineinzukommen. Sobald man auf einer sachlichen Ebene diskutiert, sind die Vorurteile sehr schnell entkräftet.

Könnte das auch eine Lösung für ein zurückhaltendes Umfeld sein?
Aus meiner persönlichen Erfahrung würde ich sagen ja. Mit zunehmendem Erfolg wird auch das kritische Umfeld immer ruhiger. Jungen Forscherinnen, und natürlich auch jungen Forschern, kann ich deswegen nur den Mut zusprechen, in sich selbst zu vertrauen, auch wenn die Herausforderungen hoch erscheinen. Man sollte sich immer selbst klar machen, welche Chancen dieser Weg mit sich bringt.

Was war dabei Ihr Erfolgsrezept?
Ich würde sagen, eine Strategie der kleinen Schritte. Wenn ich mir schon beim Abitur denke, in 20 Jahren musst du auf dieser Position sitzen, dann ist das eine riesige Hürde. Es kann dann schnell passieren, dass man bei den ersten Niederlagen, die mit großer Wahrscheinlichkeit kommen werden, zu verzweifeln beginnt. Es geht eher darum, immer am Ball zu bleiben. Der rote Faden muss erkennbar bleiben, ohne krampfhaft auf ein einziges Ziel hinzuarbeiten. Jeder erfolgreiche Schritt, auch wenn er klein sein mag, bringt dann neue positive Energie.
Das Interview führte Simon Schmitt.

  • Communication & Media Relations
    Interview 11.03.2016
    1 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24834
Publ.-Id: 24834


Frauen in der Wissenschaft - Karrierewege

Scharf, C.

Frauen in der Wissenschaft - Karrierewege
Christiane Scharf
Helmholtz-Zentrum Dresden-Rossendorf, 4.3.2016

  • Lecture (others)
    Einladung HZDR-Veranstaltung, Gleichstellungsbüro, 10.03.2016, Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24833
Publ.-Id: 24833


KIC – Network of Infrastructure for Metal-based Lightweight Materials Metallurgy and Recycling Department

Scharf, C.; Balinski, A.

KIC – Network of Infrastructure for Metal-based Lightweight Materials
Metallurgy and Recycling Department
Christiane Scharf
Freiberg, 29th November 2016

  • Invited lecture (Conferences)
    KIC – Network of Infrastructure for Metal-based Lightweight Materials Kick-Off-Meeting, 29.11.2016, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24832
Publ.-Id: 24832


High Magnetic Moment in Ferrimagnetic NiCo2O4 films via He Ion Irradiation

Pandey, P.; Bitla, Y.; Zschornak, M.; Wang, M.; Xu, C.; Grenzer, J.; Gemming, S.; Helm, M.; Chu, Y.-H.; Zhou, S.

The spinel NiCo2O4 (NCO) exhibits unique combination of electrical conductivity, infrared transparency, electro catalytic activity, and ferrimagnetic order, which makes it an attractive material for spintronic applications.1 The NCO thin-films electrical and magnetic properties can be manipulated from high temperature ferrimagnetic and metallic to low temperature ferromagnetic and insulating by changing the growth temperature.2 The high quality epitaxial NCO films were grown on MgAl2O4 (100) substrate at ~ 400°C exhibits metallic behavior accompanied by ferrimagnetic order with moment ~ 2 μB/fu.1,2 Here, we report the impact of He-ion irradiation with fluence ranging from 5×1015/cm2 – 3×1016/cm2 on these metallic NCO films. The use of He-ion irradiation results in the coherent control of out-of-plane lattice parameter of these films without changing its in-plane lattice parameter (Figure 1). The comprehensive study of magnetization data reveals the magnetic moment increases drastically to ~ 4 μB/fu (Figure 1). The X-ray absorption spectroscopic study also suggests the possible charge redistribution within the octahedral sites of the NCO films which corroborates well with the increase in the magnetic moment.

  • Poster
    MEMRIOX International Workshop 2016, 25.-27.09.2016, Berghotel Bastei, Germany

Permalink: https://www.hzdr.de/publications/Publ-24831
Publ.-Id: 24831


SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch Calixarene

Scharf, C.; Balinski, A.

Ausgangssituation und Zielsetzung
Die Gewinnung von Seltenen Erden (SE) ist aufgrund ihrer Eigenschaften sehr komplex, aufwendig und dadurch kostspielig. Die größten Herausforderungen liegen in der Separation der einzelnen SE-Elemente sowie in der notwendigen Abtrennung von Uran und Thorium. Ziel des Projektes SE-FLECX ist die Entwicklung neuer Extraktionsmittel zur effizienten Trennung der Actinoide (Typ A) und der SE-Elemente (Typ B) und die Auslegung ihres Herstellungsprozesses im industriellen Maßstab.

  • Poster
    r4-Konferenz, Statusveranstaltung, 20.-21.10.2016, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24830
Publ.-Id: 24830


SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch präorganisierte Calixarene

Scharf, C.; BASF; CMI UVK; TU BAF; Universität Leipzig; Balinski, A.

SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch präorganisierte Calixarene
Koordinator: Prof. Dr. Christiane Scharf
Förderkennzeichen: 033R132A
r4-Konferenz 2016 | Hannover | 20. und 21. Oktober 2016
Verbundpartner
BASF SE, Ludwigshafen
Helmholtz-Zentrum Dresden-Rossendorf,
Helmholz-Institut Freiberg für Ressourcentechnologie, Freiberg
Und Institut für Ressourcenökologie, Leipzig
CMI UVK GmbH, Montabaur
Technische Universität Bergakademie Freiberg, Freiberg
Universität Leipzig, Leipzig

  • Invited lecture (Conferences)
    r4-Konferenz, Innovative Technologien für Ressourceneffizienz, Statusveranstaltung, 20.-21.10.2016, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24829
Publ.-Id: 24829


Turn on/off the high-temperature ferromagnetism in Si1-xMnx thin films through Mn-ion implantation

Pandey, P.; Rylkov, V. V.; Yuan, Y.; Semisalova, A. S.; Mikhalevskiy, V. A.; Novodvorskii, O. A.; Tugushev, V. V.; Helm, M.; Zhou, S.

Silicon based alloys with Mn-ions are a potential candidate for the spintronics applications, as they exhibit complex electric and magnetic phenomena which can be effectively utilized as the integrated-circuit elements in the contemporary microelectronic technology. Though, The Si1-xMnx alloys shows high-temperature ferromagnetism at low Mn concentration x ~ 0.05 – 0.1, but the small solubility of Mn-ions in Si leads to the formation of MnSi1.7 nanoparticles,1 which drives the system in an inhomogeneous phase and makes it irrelevant for the technological applications. However, a high Mn concentration in the Si1-xMnx alloys screens the precipitation of different inhomogeneous magnetic phases with high Curie temperature (TC).2 In this context, a set of thin films of Si1-xMnx (x = 0.44 – 0.57) alloy were prepared by the pulsed laser deposition technique on Al2O3 (0001) substrate. We have found room temperature ferromagnetism and a large magnetic moment for the Si0.43Mn0.57 film as compared to the rest of samples. But, surprisingly, the TC (as well as the moment) of Si0.43Mn0.57 film drastically decreases from 300 K to ~ 40 K as the Mn-ion concentration was increased in the film through the ion implantation process. In contrast, the stoichiometric film Si0.5Mn0.5 exhibits a huge increase in the magnetic moment by one-order in magnitude after ~ 2% Mn-ion implantation. The TC of the stoichiometric film also increases from 50 K to 300 K with the increase in the Mn-ion concentration.

  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft e.V, 06.-11.03.2016, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-24828
Publ.-Id: 24828


Hydrodynamic characterization of a novel external loop airlift inverse semi-fluidized bed reactor packed with loofa particles

Hegeholz, G.; Mohammed, I. H. M.; Schubert, M.

In biochemical processes, column reactors replaced the stirred tank reactors for their advantages, like mild agitation. Among different configurations of column reactors airlift reactors constitute attractive systems for bio-catalyzed reactions due to the simple de-sign, low investment and operation costs. The advantages of combined external loop airlift and fluidized bed reactor in the downcomer over three-phase fluidized bed reactor and other configuration of airlift reactors are the unique hydrodynamic properties as it requires lower liquid flow rate for complete suspension of solid and good contact among the phases, easy removal of particles, rapid mixing, and easier scale up. This enables inverse fluidizing of low-density particles in the downcomer zone, characterized by low shear rates.

Keywords: fluidized airlift reactor; riser; downcomer; low-density particles; wire mesh sensor

  • Diploma thesis
    TU Dresden, 2016
    Mentor: Hampel Uwe

Permalink: https://www.hzdr.de/publications/Publ-24827
Publ.-Id: 24827


Metallurgy and Recycling Division

Scharf, C.

Metallurgy and Recycling Division
Christiane Scharf
Freiberg, 10th March 2016

  • Lecture (others)
    Metallurgy and Recycling Division, Visit of the company Outotec, 10.03.2016, HIF, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24826
Publ.-Id: 24826


Recycling of metals by vacuum distillation and solvent extraction

Scharf, C.

  • Invited lecture (Conferences)
    METYK Metallialan ympäristö- ja kiertotalous, METYK Seminar, 14.06.2016, Pori, Finnland

Permalink: https://www.hzdr.de/publications/Publ-24825
Publ.-Id: 24825


Metallurgy and Recycling Department

Scharf, C.

Metallurgy and Recycling Department
Visit of Prof. Mari Lundström
Christiane Scharf
Freiberg, 15th Dezember 2016

  • Lecture (others)
    Metallurgy and Recycling Department Visit of Prof. Mari Lundström (Aalto University), 15.12.2016, HIF, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24824
Publ.-Id: 24824


Direct numerical simulations of particle attachment to solids and deformable surfaces

Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.

The present talk deals with the transport and the deposition of micron particles to solid wall surfaces and fluid-fluid interfaces. Various particle-interface models are presented and tested with direct numerical flow simulations. The various micro processes observed during the particle attachment and particle detachment are well captured. The results compare well with those experimentally obtained on-site.

  • Lecture (others)
    Institute seminar, 14.12.2016, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-24823
Publ.-Id: 24823


Metallurgy and Recycling Department

Scharf, C.

Metallurgy and Recycling Department
Visit of Prof. Peter Tasker
Christiane Scharf
Freiberg, 13th Dezember 2016

  • Lecture (others)
    Metallurgy and Recycling Department Visit of Prof. Peter Tasker (University Edinburgh), 13.12.2016, HIF, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24822
Publ.-Id: 24822


Optical components in harsh space environment

Pelizzo, M. G.; Corso, A. J.; Tessarolo, E.; Zuppella, P.; Böttger, R.; Hübner, R.; Della Corte, V.; Palumbo, P.; Taglioni, G.; Preti, G.; Foggetta, L.; Valente, P.; Rancoita, P.; Martucci, A.; Napolitani, E.

Space exploration is linked to the development of increasingly innovative instrumentation, able to withstand the operation environment, rich in ion particles and characterized by high temperatures. Future space missions such as JUICE and SOLAR ORBITER will operate in a very harsh and extreme environment-. Electrons and ions are considered among the causes of potential damage of the optical instrumentation and components. Development of hard coatings capable to preserve their optical properties is pivotal. Different coating materials have been exposed to ion irradiation in particle accelerators. Change in optical performances has been observed in the extreme ultraviolet and visible spectral region and structural properties have been analyzed by different techniques. The knowledge of the damage mechanisms and thresholds allows the selection of more promising candidate materials to realize the optical components for the new frontiers space missions. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Keywords: Optical components; Optical properties; Particle accelerators; Particles; Coating; Electrons; Extreme ultraviolet; Hard coatings; Ions

Permalink: https://www.hzdr.de/publications/Publ-24821
Publ.-Id: 24821


Metallurgy and Recycling Division

Scharf, C.

Metallurgy and Recycling Division
Christiane Scharf
Freiberg, 8th September 2016

  • Lecture (others)
    Metallurgy and Recycling Division, Einladung Herr Wilson (Aalto University), 08.09.2016, HIF, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24820
Publ.-Id: 24820


Recycling of Strategic Elements by Extractive Metallurgy

Scharf, C.

Summer School 2016
Recycling of Strategic Elements by Extractive Metallurgy
Christiane Scharf
5th October 2016, TU Dresden

  • Invited lecture (Conferences)
    Summer School 2016, 05.10.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24819
Publ.-Id: 24819


Sub-Channel Flow Behavior in Vertical Tube Bundles in Bubble Columns

Möller, F.; Hampel, U.; Schubert, M.

Bubble columns are simple multiphase reactor and contactor devices, which are widely applied due to their superior heat and mass transfer characteristics. Furthermore, they are relatively simple in construction due to the absence of moving parts. Bubble columns are used for various chemical processes such as methanol and Fischer-Tropsch synthesis. Since most of the processes running in bubble columns are of exothermic nature, a variety of heat exchangers, e.g. internal heat exchanging tube bundles, are installed in order to ensure proper reaction conditions. Such tube bundles cover a significant ratio (up to 60 %) of the entire column cross-section. Accordingly, the column performance is dominated by the hydrodynamics proceeding at smaller characteristic length scale in the sub-channels. However, the evolving sub-channel flow has not been studied yet.
Therefore, this study focusses on the analysis of the multiphase flow in the sub-channels of an internal heat exchanging tube bundle with longitudinal flow of various configurations (square and triangular pattern) and tube diameter sizes (8 mm and 13 mm). The investigations were carried out in a 100 mm (inner diameter) bubble column for an air / deionized water system using a perforated plate type sparger. To ensure comparability, the covered rector’s cross-sectional area was kept similar for all configurations.
The hydrodynamic parameters were studied separately for sub-channels at various radial positions in the bundles as well as for the entire column. Approaches to link experimental data from both scales for a multiscale evaluation are suggested. Furthermore, the results are compared with an advanced horizontal stage-model considering breakup and coalescence mechanisms to calculate the bubble size distribution, breakup and coalescence rates and the overall gas holdup.

  • Lecture (Conference)
    Jahrestreffen Dresden - Jahrestreffen der ProcessNet-Fachgruppen Mehrphasenströmungen, Partikelmesstechnik, Zerkleinern und Klassieren, Computational Fluid Dynamics, Mischvorgänge und dem TAK Aerosoltechnologie, 14.-17.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24817
Publ.-Id: 24817


Mechanical properties and current-carrying capacity of Al reinforced with graphene/BN nanoribbons: a computational study

Kvashnin, D. G.; Ghorbani-Asl, M.; Shtansky, D. V.; Golberg, D.; Krasheninnikov, A. V.; Sorokin, P. B.

Record high values of Young’s modulus and tensile strength of graphene and BN nanoribbons as well as their chemically active edges make them promising candidates for serving as fillers in metal-based com- posite materials. Herein, using ab initio and analytical potential calculations we carry out a systematic study of the mechanical properties of nanocomposites constructed by reinforcing an Al matrix with BN and graphene nanoribbons. We consider a simple case of uniform distribution of nanoribbons in an Al matrix under the assumption that such configuration will lead to the maximum enhancement of mechanical characteristics. We estimate the bonding energy and the interfacial critical shear stress at the ribbon/metal interface as functions of ribbon width and show that the introduction of nanoribbons into the metal leads to a substantial increase in the mechanical characteristics of the composite material, as strong covalent bonding between the ribbon edges and Al matrix provides efficient load transfer from the metal to the ribbons. Using the obtained data, we apply the rule of mixtures in order to analytically assess the relationship between the composite strength and concentration of nanoribbons. Finally, we study carbon chains, which can be referred to as the ultimately narrow ribbons, and find that they are not the best fillers due to their weak interaction with the Al matrix. Simulations of the electronic transport properties of the composites with graphene nanoribbons and carbyne chains embedded into Al show that the inclusion of the C phase gives rise to deterioration in the current carrying capacity of the material, but the drop is relatively small, so that the composite material can still transmit current well, if required.

Keywords: nanocomposites; atomistic simulation; mechanical properties

Permalink: https://www.hzdr.de/publications/Publ-24816
Publ.-Id: 24816


Creating nanoporous graphene with swift heavy ions

Vazquez, H.; Ahlgren, E. H.; Ochedowski, O.; Leino, A. A.; Mirzayev, R.; Kozubek, R.; Lebius, H.; Karlusic, M.; Jaksic, M.; Krasheninnikov, A. V.; Kotakoski, J.; Schleberger, M.; Nordlund, K.; Djurabekova, F.

We examine swift heavy ion-induced defect production in suspended single layer graphene using Raman spectroscopy and a two temperature molecular dynamics model that couples the ionic and electronic subsystems.We show that an increase in the electronic stopping power of the ion results in an increase in the size of the pore-type defects, with a defect formation threshold at 1.22e1.48 keV/layer. We also report calculations of the specific electronic heat capacity of graphene with different chemical potentials and discuss the electronic thermal conductivity of graphene at high electronic temperatures, suggesting a value in the range of 1Wm?1 K?1. These results indicate that swift heavy ions can create nanopores in graphene, and that their size can be tuned between 1 and 4 nmdiameter by choosing a suitable stopping power.

Keywords: Graphene; ion irradiation; two-temperature model; atomistic simulations

Downloads:

  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-24815
Publ.-Id: 24815


Vibrational properties of a two-dimensional silica Kagome lattice

Björkman, T.; Skakalova, V.; Kurasch, S.; Kaiser, U.; Meyer, J. C.; Smet, J. H.; Krasheninnikov, A. V.

Kagome lattices are structures possessing fascinating magnetic and vibrational properties, but in spite of a large body of theoretical work, experimental realizations and investigations of their dynamics are scarce. Using a combination of Raman spectroscopy and density functional theory calculations, we study the vibrational properties of two- dimensional silica (2D-SiO2), which has a kagome lattice structure. We identify the signatures of crystalline and amorphous 2D-SiO2 structures in Raman spectra and show that, at finite temperatures, the stability of 2D-SiO2 lattice is strongly influenced by phonon−phonon interaction. Our results not only provide insights into the vibrational properties of 2D-SiO2 and kagome lattices in general but also suggest a quick nondestructive method to detect 2D-SiO2.

Keywords: Raman spectroscopy; first-principles calculations; 2D materials

Permalink: https://www.hzdr.de/publications/Publ-24814
Publ.-Id: 24814


Effect of Fluid Dynamics on Separation Efficiency of Sieve Tray

Vishwakarma, V.; Schubert, M.; Hampel, U.

Sieve trays are popular among vapour-liquid contacting devices in distillation columns due to their versatility and simple construction. Flow and mixing patterns on the trays have strong influence on their mass-transfer efficiency. Plug flow is considered ‘ideal’ whereas flow non-idealities such as liquid channelling, bypassing, re-circulation and stagnant zones are disadvantageous for the tray efficiency. Flow patterns quantified by Schubert et. al. (2016) using wire-mesh sensor are analysed using existing mathematical models for efficiency predictions. A serious loss in efficiency is predicted for the tray with large stagnant zones.

(1) M. Schubert, M. Piechotta, M. Beyer, E. Schleicher, U. Hampel and J. Paschold, ‘An imaging technique for characterization of fluid flow pattern on industrial-scale column sieve trays’, Chemical Engineering Research and Design, vol. 111, pp.138–146, 2016.

Keywords: Distillation Column; Sieve Tray; Tray Efficiency; Flow Non-idealities

  • Poster
    Treffen des Wissenschaftlichen Programmausschusses EMR, 21.-22.09.2016, HZDR, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-24813
Publ.-Id: 24813


CFD codes benchmark on TOPFLOW-PTS experiment

Mérigoux, N.; Apanasevich, P.; Mehlhoop, J.-P.; Lucas, D.; Raynaud, C.; Badillo, A.

In the frame of the European Union NURESAFE project a benchmark test between NEPTUNE_CFD, CFX and TransAT CFD codes on a reference TOPFLOW-PTS experiment was conducted. The work is a part of the work package on multi-scale and multi-physics simulation of Pressurized Thermal Shock (PTS). The article includes a short description of the TOPFLOW-PTS facility and the reference steam-water experiment. Furthermore the boundary and initial conditions for the CFD simulations are presented. The computational grids that are used for the benchmark simulations and the models used are introduced. Finally, the results of CFD calculations are compared with the experimental data and differences between simulations and experiment are discussed.

Keywords: Benchmark tests; Boundary and initial conditions; CFD simulations; Computational grids; European union; Multiphysics simulations; Pressurized thermal shock; Work packages

Permalink: https://www.hzdr.de/publications/Publ-24812
Publ.-Id: 24812


Quantum regime of a free-electron laser: relativistic approach

Kling, P.; Sauerbrey, R.; Preiss, P.; Giese, E.; Endrich, R.; Schleich, W. P.

In the quantum regime of the free-electron laser, the dynamics of the electrons is not governed by continuous trajectories but by discrete jumps in momentum. In this article, we rederive the two crucial conditions to enter this quantum regime: (1) a large quantum mechanical recoil of the electron caused by the scattering with the laser and the wiggler field and (2) a small energy spread of the electron beam. In contrast to our recent approach based on nonrelativistic quantum mechanics in a co-moving frame of reference, we now pursue a model in the laboratory frame employing relativistic quantum electrodynamics.

Keywords: Electrodynamics; Free electron lasers; Quantum electronics; Quantum theory

Permalink: https://www.hzdr.de/publications/Publ-24811
Publ.-Id: 24811


Discovering complex groundwater dynamics of a multiple aquifer system on the base of stable and radio-isotope patterns

Wilske, C.; Roediger, T.; Suckow, A.; Geyer, S.; Weise, S.; Merchel, S.; Rugel, G.; Pavetich, S.; Merkel, B.; Siebert, C.

The water supply in semi-arid Israel and Palestine, predominantly relies on groundwater as freshwater resource, stressed by increasing demand and low recharge rates. Sustainable management of such resources requires a sound understanding of its groundwater migration through space and time, particularly in structurally complex multi-aquifer systems as the Eastern Mountain Aquifer, affected by salting. To differentiate between the flow paths of the different water bodies and their respective residence times, a multi-tracer approach, combining age dating isotopes (36Cl/Cl; 3H) with rock specific isotopes like 87Sr/86Sr and δ34S-SO4 was applied. As a result, the investigated groundwaters from the two Cretaceous aquifers and their respective flow paths are differentiable by e.g. their 87Sr/86Sr signatures, resembling the intensity of the rock-water interaction and hence indirectly residence times. In the discharge areas within the Jordan Valley and along the Dead Sea shore, δ34S-SO4 ratios reveal the different sources of salinity (ascending brines, interstitial brines and dissolved salts). Based on 36Cl and 3H and the atmospheric input functions, very heterogeneous infiltration times and effective flow velocities, respectively, indicate an at least dual porosity system, resulting in distinctly different regimes of matrix and pipe flow.

Keywords: 36Cl/Cl; 3H; groundwater age dating; 87Sr/86Sr; δ34S; aquifer characterization; western Dead Sea Basin

  • Poster
    European Geosciences Union (EGU) General Assembly, 23.-28.04.2017, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-24810
Publ.-Id: 24810


Self-assembly of single Si quantum dots in SiO2

Heinig, K.-H.; Stegemann, K.-H.; von Borany, J.; Facsko, S.; Hlawacek, G.; Hübner, R.; Bischoff, L.; Möller, W.; Prüfer, T.; Xu, X.

However, such structures are not small enough to operate at room temperature (RT) quantum devices with switching mechanisms different from CMOS. E.g., the extremely low-power device Single Electron Transistor (SET) works at RT only if the size of the quantum dot is below 5 nm, and if the tunnel distances through SiO2 are a few nm only.
Here we present a directed self-assembly process of a 2-3 nm small single Si dot located in the middle of a SiO2 layer with distances of ~2 nm to the upper and lower Si. The self-assembly occurs by phase separation of metastable SiOx during a heat treatment. The self-assembly becomes directed by constraining and shaping the SiOx volume in such a manner that a single Si quantum dot in the requested position forms. The SiOx is fabricated by collisional mixing of Si atoms from above and below in the SiO2 layer. Two methods to form a local, constrained volume of SiOx are presented: (i) A large-area Si/SiO2/Si layer stack is irradiated with a 2 nm narrow energetic Ne+ beam in a Helium Ion Microscope (HIM), which results in a ~10 nm disk of SiOx in the buried SiO2 layer. (ii) Si pillars (<20 nm) with an embedded SiO2 layer are irradiated with a broad beam of energetic Si+ ions. Method (ii) will be used to fabricate SETs in a CMOS technology.
This work has been funded by the European Union's Horizon 2020 research and under grant agreement No 688072 innovation program.

Keywords: quantum dots; nano-electronics; ion irradiation; ion beam mixing; phase separation

  • Lecture (Conference)
    E-MRS 2016 Fall Meeting, 19.-22.09.2016, Warszawa, Poland

Permalink: https://www.hzdr.de/publications/Publ-24808
Publ.-Id: 24808


A multivariate discrimination scheme of detrital garnet chemistry for use in sedimentary provenance analysis

Tolosana-Delgado, R.; von Eynatten, H.; Krippner, A.; Meinhold, G.

Garnet chemistry provides a well-established tool in the discrimination and interpretation of sediment provenance. Current discrimination approaches, however, (i) suffer from using less variables than available, (ii) subjective determination of discrimination fields with strict boundaries suggesting clear separations where in fact probabilities are converging, and (iii) significant overlap of compositional fields of garnet from different host-rock groups. The new multivariate discrimination scheme is based on a large database, a hierarchical discrimination approach involving three steps, linear discriminant analysis at each step, and the five major host-rock groups to be discriminated: eclogite- (A), amphibolite- (B) and granulite- (C) facies metamorphic rocks as well as ultramafic (D) and igneous rocks (E). The successful application of statistical discrimination approaches requires consideration of the a priori knowledge of the respective geologic setting. This is accounted for by the use of prior probabilities. Three sets of prior probabilities (priors) are introduced and their advantages and disadvantages are discussed. The user is free to choose among these priors, which can be further modified according to the specific geologic problem and the level of a priori knowledge. The discrimination results are provided as integrated probabilities of belonging to the five major host-rock groups. For performing calculations and results a supplementary Excel® spreadsheet is provided. The discrimination scheme has been tested for a large variety of examples of hard rocks covering all of the five major groups and several subgroups from various settings. In most cases, garnets are assigned correctly to the respective group. Exceptions typically reflect the peculiarities of the regional geologic situation. Evaluation of detrital garnets from modern and ancient sedimentary settings of the Western Gneiss Region (Norway), Eastern Alps (Austria) and Albertine Rift (Uganda) demonstrates the power to reflect the respective geologic situations and corroborate previous results. As most garnet is derived from metamorphic rocks and many provenance studies aim at reconstructing the tectonic and geodynamic evolution in the source area, the approach and the examples emphasize discrimination of metamorphic facies (i.e., temperature-pressure conditions) rather than protolith composition.

Keywords: garnet; mineral chemistry; linear discriminant analysis; compositional data; prior probabilities; provenance

  • Contribution to proceedings
    European Geosciences Union General Assembly 2017, 23.-28.04.2017, Wien, Österreich
    Proceedings of the European Geoscience Union General Assembly 2017
  • Open Access Logo Sedimentary Geology 375(2018), 14-26
    DOI: 10.1016/j.sedgeo.2017.11.003

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-24807
Publ.-Id: 24807


Hybride 3D Modellierungen im Gifhorner Trog für die Kombination von Übertage und Untertage-Gravimetrie

Götze, H.-J.; Schmidt, S.; Menzel, P.

Für die hier dargestellte Studie im Bereich des Gifhorner Trogs wurden neben ca. 500 Messpunkten mit vollständig korrigierten Bougueranomalien ca. 4400 digitalisierte ältere Drehwaagemessungen aus dem beginnenden 20. Jahrhundert verwendet. Mit Hilfe der „alten“ Drehwaagemessungen konnten im Detail dann die Schwerehorizontalgradienten Wxz und Wyz sowie die Krümmungsgrößen der Schwere (WΔ = Wyy – Wxx und 2Wxy) in die 3D-Modellierung integriert werden. Neben den an der Oberfläche gemessenen Anomalien standen auch Untertagemessungen des Schwerefeldes zur Verfügung.
Modelliert wurde mit der hauseigenen Modelliersoftware IGMAS+, die nicht nur die simultane 3D Modellierung von Potentialfeldern (GravMag) ermöglicht, sondern auch deren Gradienten. Ein Vergleich von häufig verwendeten 2D-Modellierungen natürlicher 3D-Strukturen im Untergrund mit 3D-Berechnungen zeigt deutlich, wie groß die Gefahr von Fehlinterpretation eines solchen methodisch fragwürdigen Vorgehens ist. Die Modelldichten können variabel – in Abhängigkeit von den „wahren Geschwindigkeitsverhältnissen“ im Modelliergebiet angegeben werden. Als Beispiel zeigen wir das 3D Dichtemodell der Tiefbohrung KTB zusammen mit der Bohrlochgravimetrie – in Ermangelung anderer, frei zugänglicher Datensätze.
Die vorliegende Modellierung von Detailstrukturen im Gifhorner Trog belegt eindeutig, dass eine hybride 3D Modellierung von Potentialfeldern zusammen mit ihren Gradienten wertvolle Informationen über den Untergrund bis in Tiefen von 5 – 10 km liefert, die gemeinsam mit seismischen Informationen einen erheblichen Mehrwert für die Interpretation darstellen.

Keywords: 3D Potentialfeldmodellierung; Geophysik; Untergrundmodellierung

  • Lecture (Conference)
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Deutschland
  • Contribution to proceedings
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Deutschland
    DGMK-Tagungsbericht 2016-1, Hamburgf: DGMK, 978-3-941721-64-7, 91-96

Permalink: https://www.hzdr.de/publications/Publ-24806
Publ.-Id: 24806


Magnetic Nanostructures Designed For Hard Disk Drive Applications

Hellwig, O.

Continued progress in hard disk drive areal density for conventional perpendicular magnetic recording (PMR) based on granular media has become increasingly difficult. Although adoption of energy assisted magnetic recording (EAMR), specifically Heat Assisted Magnetic Recording (HAMR) is widely viewed as a promising solution for thermal stability issues, challenges in grain size scaling and managing media noise may limit the rate of progress for EAMR based on granular media. Bit patterned recording (BPR) stands as an attractive alternative to granular media, offering a path to thermally stable recording at high density and significantly reduced media noise by replacing the segregated random grains of PMR media with lithographically defined single domain islands. Figure 1 compares and summarizes basic characteristics of currently used conventional PMR based on granular media and BPR based on pre-defined bits. In my talk I will discuss various choices for BPR magnetic materials, such as Co/Pd and Co/Pt multilayers as well as CoCrPt and FePt L10 alloys. I will highlight advantages and disadvantages of the different magnetic material systems with respect to potential applications in BPR and outline the specific challenges when comparing conventional PMR, BPR and currently emerging HAMR systems.

Keywords: magnetic recording; hard disk drive; perpendicular magnetic recording; bit patterned recording; heat assisted magnetic recording

  • Invited lecture (Conferences)
    International Conference on Solid Films and Surfaces, 28.08.-02.09.2016, Chemnitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-24805
Publ.-Id: 24805


Karrat Zinc 2016 - Personal field report

Zimmermann, R.

Results of the 2016 Karrat fieldwork, 11.08.2016 – 24.08.2016

  • Other report
    Kopenhagen: Geological Survey of Denmark and Greenland, 2016
    224 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24804
Publ.-Id: 24804


Experimental Investigation of Bubble Column Reactors with Longitudinal Flow Heat Exchanging Internals Using Ultrafast X-Ray Tomography

Seiler, T.

Bubble column reactors are multiphase devices which are commonly applied in the chemical process industry due to their advantageous heat and mass transfer properties as well as the abstinence of moving parts. Since most of the reactions operated in these devices are of exothermic nature, the developed heat has to be sufficiently removed off the system in order the guarantee optimal reaction conditions. One, among others, of those heat exchanging devices can be internally inserted tube bundles, which have the advantage to remove the heat directly at its source. On the downside, a large portion of the reactor's cross-sectional area has to be covered by the tube bundle, whereas typical values range between 20 and 30%. Hence, the influence of the internals is not negligible and has a strong effect on the global and local hydrodynamics. Therefore, the influence of various tube bundle layouts (square and triangular pitch) with two tube sizes (8 and 13 mm) having the same coverage of the reactor's cross-sectional area (~25%) have been investigated using the ultrafast X-ray CT to get insight into the local and global hydrodynamics. A cylindrical column with 10 cm ID and a height of 2m was used. Furthermore, to cover all hydrodynamic flow regimes, the superficial gas velocity was varied between 2 – 20 cm/s. It has been found out that the tube configuration has strong impact on the radial holdup profile, which governs the liquid mixing and gas velocity profile. Furthermore, square configurations showed better hydrodynamic performance regarding holdup, holdup profiles and bubble size distribution.

  • Study thesis
    TU Dresden, 2016
    Mentor: Felix Möller, Uwe Hampel

Permalink: https://www.hzdr.de/publications/Publ-24803
Publ.-Id: 24803


Dynamical universality classes of simple growth and lattice gas models

Kelling, J.; Odor, G.; Gemming, S.

Large scale, dynamical simulations have been performed for the two dimensional octahedron model, describing Kardar-Parisi-Zhang (KPZ) for nonlinear, or Edwards-Wilkinson (EW) for linear surface growth. The autocorrelation functions of the heights and the dimer lattice gas variables are determined with high precision. Parallel random-sequential (RS) and two-sub-lattice stochastic dynamics (SCA) have been compared. The latter causes a constant correlation in the long time limit, but after subtracting it one can find the same height functions as in case of RS. On the other hand the ordered update alters the dynamics of the lattice gas variables, by increasing (decreasing) the memory effects for nonlinear (linear) models with respect to RS. Additionally, we support the KPZ ansatz in 2+1 dimensions and provide a precise growth exponent value β = 0.2414(2).. We show the emergence of finite size corrections, which occur much earlier than the height saturation.

Keywords: Non-Equilibrium Thermodynamics; Surface Growth; GPU; Kardar-Parisi-Zhang

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Permalink: https://www.hzdr.de/publications/Publ-24802
Publ.-Id: 24802


The spatial coefficient of variation in arterial spin labeling cerebral blood flow images

Mutsaerts, H. J.; Petr, J.; Václavů, L.; van Dalen, J. W.; Robertson, A. D.; Caan, M. W.; Masellis, M.; Nederveen, A. J.; Richard, E.; Macintosh, B. J.

Macro-vascular artifacts are a common arterial spin labeling (ASL) finding in populations with prolonged arterial transit time (ATT) and result in vascular regions with spuriously increased cerebral blood flow (CBF) and tissue regions with spuriously decreased CBF. This study investigates whether there is an association between the spatial signal distribution of a single post-label delay ASL CBF image and ATT. In 186 elderly with hypertension (46% male, 77.4+-2.5 years), we evaluated associations between the spatial coefficient of variation (CoV) of a CBF image and ATT. The spatial CoV and ATT metrics were subsequently evaluated with respect to their associations with age and sex – two demographics known to influence perfusion. Bland–Altman plots showed that spatial CoV predicted ATT with a maximum relative error of 7.6%. Spatial CoV was associated with age (b=0.163, p=0.028) and sex (b=-0.204, p=0.004). The spatial distribution of the ASL signal on a standard CBF image can be used to infer between-participant ATT differences. In the absence of ATT mapping, the spatial CoV may be useful for the clinical interpretation of ASL in patients with cerebrovascular pathology that leads to prolonged transit of the ASL signal to tissue.

Keywords: Arterial spin labeling; ASL; cerebral blood flow; cerebral hemodynamics; perfusion weighted MRI

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-24801
Publ.-Id: 24801


Kooperative Entwicklung ressourceneffizienter Verfahren in der Produktion

Rädecker, P.; Scharf, C.; Zeidler, O.

Kooperative Entwicklung ressourceneffizienter Verfahren in der Produktion
Philipp Rädecker, Oliver Zeidler & Prof. Christiane Scharf
Freiberg, 24. November 2016

  • Invited lecture (Conferences)
    Ressourceneffizienz vor Ort Wettbewerbsplus Ressourceneffizienz Angebote für KMU in Sachsen, 24.11.2016, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24800
Publ.-Id: 24800


Influence of realignment-induced interpolation errors on the estimation of cerebral blood flow using arterial spin labeling fMRI

Petr, J.; Mutsaerts, H.; de Vita, E.; Shirzadi, Z.; Cohen, S.; Blokhuis, C.; Pajkrt, D.; Hofheinz, F.; van den Hoff, J.; Asllani, I.

Purpose/Introduction: The realignment transformation needed for motion correction in fMRI has been shown to have the adverse effect of smoothing the realigned images1. This effect is independent of the accuracy of the estimated motion parameters (it can occur even for accurately estimated motion parameters) and can, in ASL, cause gray-matter (GM) cerebral-blood-flow (CBF) underestimation compared to an acquisition without motion. Here, we investigated the smoothing of the realignment transformation in ASL by creating simulated CBF maps based on T1-weighted (T1w) images and motion parameters obtained from ASL images acquired on patients2.
Methods: ASL data from 66 children (age: 8-18y, median: 12.8y, 34 males) were obtained from the NOVICE study2. This dataset is characterized by a relatively high head motion often associated with scanning children. Images were acquired on Philips 3T Ingenia (pCASL: voxel-size 3x3x6.6mm3, 30 controls/label pairs; T1w: voxel-size 1x1x1mm3).
To simulate ASL time-series that reflect motion from real acquisition, the following processing steps were implemented: (1) T1w-image was co-registered to the first ASL volume and segmented into gray and white-matter posterior probability maps (pGM/pWM) using SPM12. (2) ASL images were realigned with respect to the first volume3 (average motion >1mm or >1° was considered 'high'). (3) The motion-parameters from step 2 were applied to pGM/pWM maps, and the maps were down-sampled to the ASL resolution. This resulted in 60 pGM/pWM volumes mimicking a real ASL acquisition (Fig. 1b). (4) The pGM/pWM maps were realigned to their first respective volume (Fig. 1d) and averaged (Fig. 2d).
Two sets of simulated CBF maps were created: (1) from the pGM/pWM corresponding to the first ASL volume (CBF-static), (2) from the realigned pGMs/pWMs described above (CBF-motion), assuming GM-CBF of 80 mL/min/100g and GM/WM CBF ratio of 3. Local and global GM-CBF values of CBF-motion were compared against the idealized CBF-static case.
Results: Figures 1d and 2d show ‘blurring’ of the realigned pGM in high movement cases. The local GM-CBF in CBF-motion was up to 10% lower than in CBF-static (Fig. 2e); negligible differences (<1%) were seen in relatively low movement cases (Fig. 2f). In all 'high-motion' participants, 4-7% lower global GM-CBF was observed (Fig. 3).
Discussion/Conclusion: Relatively high motion during ASL acquisitions appears to result in a GM-CBF underestimation of 4-7% globally and up to 10% locally. This finding can have important implications in studying patients who tend to move more than their healthy counterparts, which may lead to a GM-CBF underestimation in patients relative to controls.

Keywords: cerebral blood flow; perfusion; arterial spin labeling; motion correction

  • Contribution to proceedings
    ESMRMB 2016, 33rd Annual Scientific Meeting, 29.09.2016, Vienna, Austria
    Magnetic Resonance Materials in Physics, Biology and Medicine: Springer, 0968-5243
    DOI: 10.1007/s10334-016-0568-x
  • Lecture (Conference)
    ESMRMB 2016, 33rd Annual Scientific Meeting, 29.09.2016, Vienna, Austria

Permalink: https://www.hzdr.de/publications/Publ-24799
Publ.-Id: 24799


Retargeting of T lymphocytes to PSCA- or PSMA positive prostate cancer cells using the novel modular chimeric antigen receptor platform technology “UniCAR”

Feldmann, A.; Arndt, C.; Bergmann, R.; Loff, S.; Cartellieri, M.; Bachmann, D.; Aliperta, R.; Hetzenecker, M.; Ludwig, F.; Albert, S.; Ziller-Walter, P.; Kegler, A.; Koristka, S.; Gärtner, S.; Schmitz, M.; Ehninger, A.; Ehninger, G.; Pietzsch, J.; Steinbach, J.; Bachmann, M.

New treatment options especially of solid tumors including for metastasized prostate cancer (PCa) are urgently needed. Recent treatments of leukemias with chimeric antigen receptors (CARs) underline their impressive therapeutic potential. However CARs currently applied in the clinics cannot be repeatedly turned on and off potentially leading to severe life threatening side effects. To overcome these problems, we recently described a modular CAR technology termed UniCAR: UniCAR T cells are inert but can be turned on by application of one or multiple target modules (TMs). Here we present preclinical data summarizing the retargeting of UniCAR T cells to PCa cells using TMs directed to prostate stem cell-(PSCA) or/and prostate membrane antigen (PSMA). In the presence of the respective TM(s), we see a highly efficient target-specific and target-dependent activation of UniCAR T cells, secretion of proinflammatory cytokines, and PCa cell lysis both in vitro and experimental mice.

Permalink: https://www.hzdr.de/publications/Publ-24798
Publ.-Id: 24798


Crystal structure and magnetism of UOsAl

Andreev, A. V.; Danis, S.; Sebek, J.; Henriques, M. S.; Vejpravova, J.; Gorbunov, D. I.; Havela, L.

Crystal structure, magnetization, and specific heat were studied on single crystal of uranium intermetallic compound UOsAl. It is a hexagonal Laves phase of MgZn2 type, space group P63/mmc, with lattice parameters a = 536.4 pm, c = 845.3 pm. Shortest inter-uranium distance 313 pm (along the c-axis) is considerably smaller than the Hill limit (340 pm). The compound is a weakly temperature-dependent paramagnet with magnetic susceptibility of ≈1.5*10−8 m3 mol (at T=2 K), which is slightly higher with magnetic field along the a-axis compared to the c-axis. The Sommerfeld coefficient of electronic specific heat has moderate value of γ = 36 mJ mol−1 K−2.

Permalink: https://www.hzdr.de/publications/Publ-24797
Publ.-Id: 24797


Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-Point fluctuations, and possible two-dimensional universal behavior

Brambleby, J.; Goddard, P. A.; Singleton, J.; Jaime, M.; Lancaster, T.; Huang, L.; Wosnitza, J.; Topping, C. V.; Carreiro, K. E.; Tran, H. E.; Manson, Z. E.; Manson, J. L.

We present the magnetic and thermal properties of the bosonic-superfluid phase in a spin-dimer network using both quasistatic and rapidly changing pulsed magnetic fields. The entropy derived from a heat-capacity study reveals that the pulsed-field measurements are strongly adiabatic in nature and are responsible for the onset of a significant magnetocaloric effect (MCE). In contrast to previous predictions we show that the MCE is not just confined to the critical regions, but occurs for all fields greater than zero at sufficiently low temperatures. We explain the MCE using a model of the thermal occupation of exchange-coupled dimer spin states and highlight that failure to take this effect into account inevitably leads to incorrect interpretations of experimental results. In addition, the heat capacity in our material is suggestive of an extraordinary contribution from zero-point fluctuations and appears to indicate universal behavior with different critical exponents at the two field-induced critical points. The data at the upper critical point, combined with the layered structure of the system, are consistent with a two-dimensional nature of spin excitations in the system.

Permalink: https://www.hzdr.de/publications/Publ-24796
Publ.-Id: 24796


The cancer cell adhesion resistome: mechanisms, targeting and translational approaches

Dickreuter, E.; Cordes, N.

Cell adhesion-mediated resistance limits the success of cancer therapies and is a great obstacle to overcome in the clinic. Since the 1990s, where it became clear that adhesion of tumor cells to the extracellular matrix is an important mediator of therapy resistance, a lot of work has been conducted to understand the fundamental underlying mechanisms and two paradigms were deduced: cell adhesion-mediated radioresistance (CAM-RR) and cell adhesion-mediated drug resistance (CAM-DR). Preclinical work has evidently demonstrated that targeting of integrins, adapter proteins and associated kinases comprising the cell adhesion resistome is a promising strategy to sensitize cancer cells to both radiotherapy and chemotherapy. Moreover, the cell adhesion resistome fundamentally contributes to adaptation mechanisms induced by radiochemotherapy as well as molecular drugs to secure a balanced homeostasis of cancer cells for survival and growth. Intriguingly, this phenomenon provides a basis for synthetic lethal targeted therapies simultaneously administered to standard radiochemotherapy. In this review, we summarize current knowledge about the cell adhesion resistome and highlight targeting strategies to override CAM-RR and CAM-DR.

Keywords: adhesion; CAM-DR; CAM-RR; EGFR; integrin; resistome

Permalink: https://www.hzdr.de/publications/Publ-24795
Publ.-Id: 24795


Insights into the sonochemical synthesis and properties of salt-free intrinsic plutonium colloids

Dalodière, E.; Virot, M.; Morosini, V.; Chave, T.; Dumas, T.; Hennig, C.; Wiss, T.; Blanco, O. D.; Shuh, D. K.; Tyliszcak, T.; Venault, L.; Moisy, P.; Nikitenko, S. I.

For the first time, stable intrinsic plutonium colloid was prepared by ultrasonic treatment of PuO2 suspensions in pure water at room temperature. The yield of Pu colloid was found to increase with PuO2 specific surface area and by using reducing carrier gas mixture. Kinetic data evidenced that both chemical and mechanical effects of ultrasound strongly contribute to the mechanism of Pu colloid formation. At first, the fragmentation of initial PuO2 particles accelerates the overall process providing larger surface of contact between cavitation bubbles and solids. Furthermore, hydrogen formed during sonochemical water splitting enables reduction of Pu(IV) to more soluble Pu(III), which then reoxidizes yielding Pu(IV) colloid. Sonochemical colloid was compared with hydrolytic one using HRTEM, Pu LIII XAS, and STXM/NEXAFS (O K-edge) techniques. Both colloids are composed of quasi-spherical nanocrystalline particles of PuO2 (fcc, Fm¯3 m space group) measuring about 7 nm and 3 nm, respectively. Moreover, HRTEM revealed nanostructured morphology for initial PuO2. The EXAFS spectra of colloidal PuO2 nanoparticles were fitted using triple oxygen shell model for the first coordination sphere of Pu(IV). HRTEM and EXAFS studies revealed the correlation between the number of Pu-O and Pu-Pu contacts and atomic surface-to-volume ratio of studied PuO2 nanoparticles. The STXM/NEXAFS study indicated that the oxygen state of hydrolytic Pu colloid is influenced by hydrolyzed Pu(IV) species in much more extent than PuO2 nanoparticles of sonochemical colloid. In general, hydrolytic and sonochemical colloids can be described as core-shell nanoparticles composed of quasi stoichiometric PuO2 core and hydrolyzed Pu(IV) moieties at the surface shell.

Keywords: sonochemistry; Pu(IV) colloids

Permalink: https://www.hzdr.de/publications/Publ-24794
Publ.-Id: 24794


Luminescence spectroscopy of An/Ln in environmental systems

Steudtner, R.; Drobot, B.; Haubitz, T.; Schernikau, M.; Lehmann, S.; Bader, M.; Vogel, M.

Luminescence spectroscopy is a powerful tool to study the chemistry of f-elements (actinides – An, lanthanides – Ln) in trace concentration. Manifold operating mode, e.g. steady-state, time-resolved, laser-induced, site-selective, cryogenic, etc. were used to investigate the environmental behavior of An/Ln in various geological and biological systems.

  • Invited lecture (Conferences)
    ATAS 2016 - International Workshop on Advanced Techniques in Actinide Spectroscopy, 07.-10.11.2016, Richland, USA

Permalink: https://www.hzdr.de/publications/Publ-24793
Publ.-Id: 24793


Structural and electrical characterization of ALD grown HfO2 thin films

Blaschke, D.; Munnik, F.; Zviagin, V.; Schmidt-Grund, R.; Grundmann, M.; Bogusz, A.; Hübner, R.; Scholz, A.; Schmidt, H.; Zahn, P.; Gemming, S.

HfO2 films were grown on 4-inch native SiO2/Si wafers by Atomic Layer Deposition (ALD) from tetrakis(dimethylamido)hafnium and deionized water in a Savannah S100 system. The temperature was varied from 100°C to 350°C in steps of 50 K. All other ALD process parameters were fixed. The resulting HfO2 layers were characterized in terms of thickness homogeneity, growth rate per cycle, surface roughness, crystal structure, stoichiometry, mass density, optical bandgap and index of refraction. Based on the obtained growth rate of HfO2 on SiO2/Si, 25 nm thick HfO2 layers were grown on Pt/Ti/SiO2/Si substrates for electrical characterization. Furthermore, the most important structural properties were compared for the growth of HfO2 on Pt/Ti/SiO2/Si and SiO2/Si substrates.
HfO2 breakdown voltages show a clear decrease with increasing growth temperature, which was correlated to the crystallinity of the films due to the preferred breakdown along grain boundaries. For resistive switching, an amorphous HfO2 layer grown at 150°C was compared to a crystalline one grown at 300°C. Furthermore, resistive switching characteristics were tuned by the use of two different top electrode materials, namely an inert Pt or a reactive Ti/Pt electrode. The contact diameter was 50 μm. In the majority of cases, the resistive switching mode was found to be unipolar. Only the combination of a crystalline HfO2 layer with an inert Pt bottom and a reactive Ti/Pt top electrode led to a “pseudo-bipolar” switching mode with a convertible SET and RESET polarity.

Keywords: HfO2; thin film deposition; ALD; resistive switching

  • Poster
    MEMRIOX International Workshop 2016, 25.-27.09.2016, Berghotel Bastei, Lohmen, Germany

Permalink: https://www.hzdr.de/publications/Publ-24792
Publ.-Id: 24792


Doping by flash lamp annealing

Prucnal, S.; Rebohle, L.; Skorupa, W.

After a short introduction we will highlight processing issues (setup, comparison of annealing methods, relevant requirements for annealing due to doping, diffusion, activation, recrystallization, defect engineering), as well as doping issues for group IV-semiconductors (shallow junctions, hyperdoping, solar cells, superconductivity) and other semiconductors (manganese doping of GaAs for diluted magnetic semiconductors, doping for transparent conductive oxides). Mostly ion implantation serves as a source of dopants, but also diffusion from deposited layers is of growing importance.

Keywords: flash lamp annealing; pulsed light sintering; group IV-semiconductors; doping; diffusion; activation; recrystallization; defect engineering; diluted magnetic semiconductors; transparent conductive oxides

Permalink: https://www.hzdr.de/publications/Publ-24791
Publ.-Id: 24791


Bergbau und Konfliktminerale in Afrika

Sterbik, N.

Einerseits sind die Rohstofflieferungen Afrikas für die Versorgung der Weltwirtschaft von Bedeutung, andererseits spielen die Exporte aber auch eine wesentliche Rolle für die Wirtschaft dieser Länder. Die steigende Nachfrage (auch in Schwellenmärkten) und der Preisanstieg für einzelne Rohstoffe könnten eine günstige Gelegenheit für die afrikanischen Bergbauländer darstellen.

In großen Teilen des subsaharischen Afrikas wird der Bergbau jedoch noch in sehr kleinem Maßstab und – aufgrund keiner oder nur geringer Mechanisierung – mit hohem Arbeitsaufwand betrieben. Diese Arbeiten werden allgemein als Einzel- und Kleinbergbau (Artisanal and Small-Scale Mining, ASM) kategorisiert. In Zentralafrika steht der ASM zusätzlich auch mit sogenannten „Konfliktmineralien“ in Verbindung (kurz gesagt, „Konfliktressourcen sind natürliche Ressourcen, deren systematische Ausbeutung und Handel im Kontext eines Konfliktes zu schwersten Menschenrechtsverletzungen, Verletzungen des humanitären Völkerrechts oder Verwirklichung völkerstrafrechtlicher Tatbestände führen kann“ (BICC, 1994)).

Diese Präsentation vermittelt einen Überblick über den Bergbau in Afrika, sowohl über industriellen Bergbau als auch Kleinbergbau, und behandelt das Thema der Konfliktmineralien. Es wird ebenfalls die Verbindung zwischen den beteiligten Akteuren und den Initiativen rund um ASM und Konfliktmineralien aufgezeigt.

Keywords: Bergbau; Kleinbergbau; Afrika; Konflikt-Minerale

  • Invited lecture (Conferences)
    145. Freiberger Kolloquium, 14.04.2016, Freiberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-24790
Publ.-Id: 24790


A lab scale froth flotation study of tungsten bearing tailings of the Barruecopardo mine (Spain) within the EU Horizon 2020 OptimOre Project

Compañero, R. J.

This study was done under the framework of the “OptimOre” project which is part of EU Horizon 2020. Froth flotation is applied for obtaining a pre-concentrate from tailings material sourced from an old mine in the Barruecopardo district, located in the province of Salamanca in Spain. Representative samples from the as-received material were submitted to several characterization analyses: MLA, particle size measurements, contact angle measurements, and ICP-AES. Information from the preceding tests were used to design flotation experiments where five factors: collector type, frother type, depressant addition, pH level, and collector dosage were investigated.

Milling was performed on the feed material before flotation because the starting size was too coarse. The flotation behavior of the material was examined and different factor level combinations resulted in varying degrees of recovery and concentrate grades --- the highest attained averaging 35% and 0.36% W (Enrichment ratio = 14) respectively. Further improvements on these results were targeted and thus the grinding time was increased. The merits of this step in terms of mass collection, grade, and recovery are discussed. Exploratory ideas on the effect of the factor levels investigated were also presented.

Keywords: froth flotation; scheelite; depressant; Barruecopardo

  • Master thesis
    HIF/HZDR, 2016
    Mentor: Sterbik, N.

Permalink: https://www.hzdr.de/publications/Publ-24789
Publ.-Id: 24789


Back-calculating froth flotation rates of scheelite by size fractions and liberation classes : first results

Sterbik, N.; Rudolph, M.

This paper is part of an EU funded collaboration under the Horizon 2020 program on the optimization of mineral processing operations of European tungsten and tantalum complex low-grade ores, called OptimOre. There froth flotation is an important process especially for scheelite. It is a versatile mineral processing method, which still lacks of physical and chemical comprehensive, accurate and internationally recognized models. The work package on froth flotation within OptimOre is thus dedicated to developing improved fundamental flotation models with the help of advanced automated mineralogical analyses of the input and output streams of flotation cells.

Reliable flotation models can be potentially used to simplify and shorten lab testing procedures, better understand and predict ore behavior but also establish the potential recovery and grade of the targeted mineral(s).

A first step in fundamental flotation modelling is to obtain the flotation rates of minerals with respect to their size and liberation. This is achieved by back calculation of recovery rates typically under the assumption of a first-order rate process.

In this paper, froth flotation rates of scheelite are back-calculated by size fractions and liberation classes. Flotation parameters such as reagent regime, cell hydrodynamics and pulp and froth properties are systematically varied in properly designed experiments with measured effects on the bubble surface area flux. Finally these flotation rates are then used to critically assess several existing first principle flotation models (Yoon, Pyke and others), which are compared with each other in terms of applicability and limitations.

The scheelite bearing ore used for the experiments is from the Mittersill deposit (Austria). The particle properties (e.g. liberation, mineral composition) are studied with automated mineralogy (Mineral Liberation Analysis) as well as elemental assays by ICP-MS analyses. Froth flotation tests are conducted with a bottom-driven Magotteaux cell equipped with a bubble cam sizer and froth cam.

Keywords: flotation rates; automated mineralogy; scheelite; size-by-liberation; MLA

  • Poster
    XXVIII International Mineral Processing Congress, 11.-15.09.2016, Québec city, Canada

Permalink: https://www.hzdr.de/publications/Publ-24788
Publ.-Id: 24788


Technical and Modelling Aspects of Subsecond Thermal Processing with Flash Lamps

Schumann, T.; Rebohle, L.; Skorupa, W.

This poster gives an overview of the complex technical aspects of Flash-lamp-annealing-tools for thermal processing in the millisecond range used at the Helmholtz Research Center Dresden-Rossendorf (HZDR). It outlines that Flash Lamp Annealing (FLA) is established as a high-performance alternative to Rapid Thermal Annealing and Furnace Annealing when it comes to treatment of the most advanced thin layer and coating materials, thus enabling the fabrication of novel electronic structures and materials. It shows the unique variety of parameters the HZDR is able to provide for applications ranging from annealing of implanted Si and Ge, transparent conductive oxides, photovoltaic materials, silver and copper inks on various non-metal substrates to exceptional applications (roof tiles, watchcases). It explains, how crucial parameters, such as emission spectrum, energy density, and preheat temperature are monitored to provide a reliable reproducibility. Modelling aspects regarding temperature distribution and heat transport within the millisecond range will also be addressed. Furthermore, a summary will be given of characteristic features of our tools to convey the diversity of the fields of application and the enormous range of possible research.

Keywords: Flash-lamp-annealing; millisecond range thermal processing; modelling aspects; thin layers; novel electronic structures

  • Poster
    SVC (Society of Vacuum Coaters) 59th Annual Technical Conference (TechCon), 09.-13.05.2016, Indianapolis, IN, USA

Permalink: https://www.hzdr.de/publications/Publ-24787
Publ.-Id: 24787


A lab scale froth flotation study of tungsten-bearing tailings of the Barruecopardo mine (Spain)

Sterbik, N.; Compañero, R. J.; Rudolph, M.

The “OptimOre” project, as part of the EU Horizon 2020, proposes the research and development of improved modelling and control technologies of tantalum and tungsten ore processing using advanced sensing and artificial intelligence techniques. The Helmholtz Institute Freiberg for Resource Technology is responsible for the Work Package „Froth flotation”.
Within the frame of the OptimOre project, a lab scale froth flotation study was conducted on the tailings of the Barruecopardo mine (Spain) with scheelite as the main tungsten-bearing mineral and a feed grade of 0,025% tungsten. Barruecopardo is part of the world-class tungsten deposits and is being redeveloped for mining.
The reagent system is the main focus of this study, with an emphasis on the influence of depressant combinations aimed at depressing silicates in the gangue. Two collectors at four dosages, two frothers and four depressant combinations were tested at two different pH.
The results show that a higher pH usually stabilizes the froth regardless of the frother and increases the mass pull but does not impact the tungsten recovery. The depressant combination is highly relevant in grade, as expected, but also in recovery. It can hinder it badly or increase it tremendously. Furthermore, the performance of the first collector without depressant is significantly higher than after adding depressant. On the contrary, the second collector that performed poorly in a depressant-less environment yields the best results in presence of depressants. The presence of sodium carbonate (Na2CO3) enhances that effect. Possible interpretations for these observations are given.

Keywords: flotation; scheelite; depressants

  • Poster
    Tagung Aufbereitung und Recycling, 09.-10.11.2016, Freiberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-24785
Publ.-Id: 24785


Vertebral fractures – An underestimated side-effect in patients treated with radio(chemo)therapy

Pilz, K.; Hoffmann, A. L.; Baumann, M.; Troost, E. G. C.

There is no abstract available, since this is an Editorial.

Permalink: https://www.hzdr.de/publications/Publ-24784
Publ.-Id: 24784


Technical feasibility of integrating 7 T anatomical MRI in image‑guided radiotherapy of glioblastoma: a preparatory study

Compter, I.; Peerlings, J.; Eekers, D. B. P.; Postma, A. A.; Ivanov, D.; Wiggins, C. J.; Kubben, P.; Küsters, B.; Wesseling, P.; Ackermans, L.; Schijns, O. E. M. G.; Lambin, P.; Hoffmann, A. L.

Objectives: The use of 7 Tesla (T) magnetic resonance imaging (MRI) has recently shown great potential for high-resolution soft-tissue neuroimaging and visualization of microvascularization in glioblastoma (GBM). We have designed a clinical trial to explore the value of 7 T MRI in radiation treatment of GBM. For this aim we performed a preparatory study to investigate the technical feasibility of incorporating 7 T MR images into the neurosurgical navigation and radiotherapy treatment planning (RTP) systems via qualitative and quantitative assessment of the image quality.
Materials and methods: The MR images were acquired with a Siemens Magnetom 7 T whole-body scanner and a Nova Medical 32-channel head coil. The 7 T MRI pulse sequences included magnetization-prepared two rapid acquisition gradient echoes (MP2RAGE), T2-SPACE, SPACE-FLAIR and gradient echo sequences (GRE). A pilot study with three healthy volunteers and an anthropomorphic 3D phantom was used to assess image quality and geometrical image accuracy.
Results: The MRI scans were well tolerated by the volunteers. Susceptibility artefacts were observed in both the cortex and subcortical white matter at close proximity to air-tissue interfaces. Regional loss of signal and contrast could be minimized by the use of dielectric pads. Image transfer and processing did not degrade image quality. The system-related spatial uncertainty of geometrical distortion-corrected MP2RAGE pulse sequences was ≤2 mm.
Conclusion: Integration of high-quality and geometrically-reliable 7 T MR images into neurosurgical navigation and RTP software is technically feasible and safe.

Keywords: Ultra-high field MRI; Radiotherapy; Treatment planning; Glioblastoma; Geometrical distortion

Permalink: https://www.hzdr.de/publications/Publ-24783
Publ.-Id: 24783


Mineral exploration using hyperspectral remote sensing

Laakso, K.

There is no abstract associated with the talk.

Keywords: Hyperspectral; remote sensing; mineral exploration

  • Invited lecture (Conferences)
    An informal lecture to the students of Mathias Burisch (Tu Bergakademie Freiberg), associate professor., 06.02.2017, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24782
Publ.-Id: 24782


Hyperspectral applications of mineral exploration

Laakso, K.

The talk does not have an abstract.

Keywords: Hyperspectral; mineral exploration; remote sensing; drill core imaging

  • Invited lecture (Conferences)
    University of Lorraine - an informal meeting where scientific collaboration will be discussed, 24.01.2017, Nancy, France

Permalink: https://www.hzdr.de/publications/Publ-24781
Publ.-Id: 24781


Extended soft wall model with background related to features of QCD thermodynamics

Zöllner, R.; Kämpfer, B.

The soft wall model is extended to accommodate at the same time (i) approximately linear ρ meson Regge trajectories at zero temperature T, (ii) various options for the thermodynamics with reference to QCD (cross over or second-order transition or first-order transition at Tc), and (iii) the appearance of vector meson states at T≤Tc. While the vector meson masses display some modest model dependence very near to Tc, they stay below Tc to good accuracy independent of the temperature, that is nearly as at T=0, thus being very consistent with the thermo-statistical models widely employed in analyses of the hadron yields in relativistic heavy-ion collisions in a region where baryon densitiy effects can be neglected and the vacuum hadron masses are used.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-24780
Publ.-Id: 24780


Fragment Molecular Orbital Calculations for Studying Lanthanide-Protein Interaction

Tsushima, S.

no abstract for this talk

  • Invited lecture (Conferences)
    Institute Colloquium at Institute of Innovative Research, Tokyo Institute of Technology, 27.01.2017, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-24779
Publ.-Id: 24779


Optik einmal anders

Schultheiss, H.

Erstmals konnten Forscher experimentell das Brechungsgesetz für Spinwellen direkt nachweisen.

Keywords: Magnonik; Spinwellen; Magnetisierungsdynamik

  • Physik Journal 15(2016)10, 16-17

Permalink: https://www.hzdr.de/publications/Publ-24778
Publ.-Id: 24778


CdZnTe als Strahlungsdetektor in der therapeutischen Medizin

Weinberger, D.; Römer, K.; Lutz, B.; Fiedler, F.; Kormoll, T.

Alternativ zu Operation und Chemotherapie bei der Behandlung von Tumoren hat die Strahlentherapie einen festen Platz in der medizinischen Behandlung eingenommen. Neben der Therapie mit Röntgenstrahlung werden auch geladene Atome als Teilchenstrahl verwendet. Diese haben eine endliche Reichweite in Materie und deponieren keine schädliche Dosis dahinter. Um diesen Vorteil nutzen zu können muss die Eindringtiefe des Strahls erfasst werden. CdZnTe als Strahlungsdetektor besitzt dieses Potential.

Keywords: Strahlungsdetektor; CdZnTe-Streifendetektor; Driftstrom; Pulsformenanalyse; Tiefenkorrektur

  • Contribution to proceedings
    18. Nachwuchswissenschaftlerkonferenz ost- und mitteldeutscher Fachhochschulen, 31.05.2017, Mittweida, Deutschland
    Proceedings der 18. Nachwuchswissenschaftlerkonferenz ost- und mitteldeutscher Fachhochschulen

Permalink: https://www.hzdr.de/publications/Publ-24777
Publ.-Id: 24777


Level-Of-Detail Strategie zur Vereinfachung komplexer Untergrundmodelle - Gifhorner Trog

Menzel, P.; Götze, H.-J.; Schmidt, S.

In dieser Präsentation werden Verfahren gezeigt, um triangulierte 3D-Untergrundmodelle für die Berechnung ihres „full tensor gravity“-Effektes zu optimieren. Es handelt sich dabei um zwei etablierte Algorithmen aus der Computergrafik zur Vereinfachung von triangulierten Flächen, sowie um ein drittes, an die Erfordernisse der Potentialverfahren angepasstes, Verfahren. Alle drei Algorithmen erzeugen eine Vereinfachungshierarchie für die initiale 3D-Geometrie. Diese „Level-of-Detail“-Hierarchien erlauben es, verschiedene Modell-auflösungen sukzessive ineinander zu überführen. Ein explizites Vorhalten der vereinfachten Geometrieversionen ist aus diesem Grund nicht notwendig.
Die drei verwendeten „Mesh-Simplification“-Ansätze werden auf ein synthetisches 3D-Modell und auf das triangulierte Untergrundmodell zweier realer Salzstöcke angewendet. Die erzeugten vereinfachten Geometrieversionen werden für ihre Verwendbarkeit zur Berechnung des Effektes in den Komponenten der Schwere und des Schweregradienten-tensors evaluiert. Es wird gezeigt, dass die Ergebnisse aller drei Methoden grundsätzliche für eine Berechnung des „full tensor gravity“-Effektes verwendet werden können. Die Ergebnisse der beiden etablierten Verfahren sind allerdings nur bis zu einem relativ geringen Vereinfachungsgrad verwendbar, wenn eine gegebene Fehlertoleranz nicht überschritten werden soll. Das dritte, angepasste Verfahren erzeugt Geometriemodelle, deren Effekt auch für Modellversionen mit sehr wenigen Dreiecken mit dem Effekt des initialen Modells annähernd übereinstimmt.
Die präsentierten Ergebnisse basieren auf den Arbeiten im DGMK-Projekt 771 und das gezeigte 3D-Modell zweier Salzstöcke im Gifhorner Trog wurde von unseren Projektpartnern zur Verfügung gestellt.

Keywords: Mesh-Simplification; Potentialfeldmodellierung; geometrische 3D Modellierung

  • Lecture (Conference)
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Deutschland
  • Contribution to proceedings
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Germany
    DGMK-Tagungsbericht 2016-1, Hamburg: DGMK, 978-3-941721-64-7, 97-104

Permalink: https://www.hzdr.de/publications/Publ-24776
Publ.-Id: 24776


Nickel-Enhanced Graphitic Ordering of Carbon Ad-Atoms during Physical Vapor Deposition

Wenisch, R.; Hübner, R.; Munnik, F.; Gemming, S.; Abrasonis, G.; Krause, M.

Compatibility with commonly used substrate materials is of crucial importance for graphene device production. Low-temperature synthesis approaches are needed to cope with this challenge. Therefore it has to be clarified, to which extend physical vapor deposition can be used to produce ordered graphene structures.

In this contribution, the mechanism of graphitic ordering of atomic C on Ni was investigated at temperatures ranging from room temperature to 550 °C. The C/Ni films were prepared by ion beam sputtering. A temperature-induced and a Ni-induced enhancement of graphitic ordering is demonstrated. The Ni-effect is responsible for the formation of a bi-layer structure of the C films at higher deposition temperatures. In the bi-layers, C forms graphenic planes parallel to the Ni surface within a thickness range of 1-2 nm. Further deposited C grows preferentially perpendicular to the surface. The results are discussed on the basis of hyperthermal atom deposition, surface diffusion, metal-induced crystallization and dissolution-precipitation. Our findings point to a dominating role of surface diffusion-assisted crystallization in the carbon ordering process.

Keywords: graphitic carbon; graphene; physical vapour deposition; Raman; TEM

  • Poster
    International Winterschool on Electronic Properties of Novel Materials 2016, 13.-20.02.2016, Kirchberg, Österreich

Permalink: https://www.hzdr.de/publications/Publ-24775
Publ.-Id: 24775


Helmholtz Institute Freiberg for Resource Technology - Helmholtz-Zentrum Dresden-Rossendorf - Introduction

Kelly, N.

Helmholtz Institute Freiberg for Resource Technology
Helmholtz-Zentrum Dresden-Rossendorf
Introduction

  • Lecture (others)
    Meeting FWGM und UIT, 06.01.2017, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24774
Publ.-Id: 24774


Radiation oncology in the era of precision medicine

Baumann, M.; Krause, M.; Overgaard, J.; Debus, J.; Bentzen, S. M.; Daartz, J.; Richter, C.; Zips, D.; Bortfeld, T.

Technological advances and clinical research over the past few decades have given radiation oncologists the capability to personalize treatments for accurate delivery of radiation dose based on clinical parameters and anatomical information. Eradication of gross and microscopic tumours with preservation of health-related quality of life can be achieved in many patients. Two major strategies, acting synergistically, will enable further widening of the therapeutic window of radiation oncology in the era of precision medicine: technology-driven improvement of treatment conformity, including advanced image guidance and particle therapy, and novel biological concepts for personalized treatment, including biomarker-guided prescription, combined treatment modalities and adaptation of treatment during its course.

Permalink: https://www.hzdr.de/publications/Publ-24773
Publ.-Id: 24773


Magnetic anisotropy of III-Mn-V dilute ferromagnetic semiconductors

Xu, C.; Yuan, Y.; Sawicki, M.; Böttger, R.; Helm, M.; Zhou, S.

As one of the most important physical properties of III-Mn-V dilute ferromagnetic semiconductors (DFS), the magnetic anisotropy could be tailored by Mn/hole concentrations and by the lattice strain [1, 2]. Particularly, the crystal symmetry lowering in-plane uniaxial anisotropy still remains one of the most puzzling properties of the DFS family. Using a perturbation method and ab initio computations, Birowska et al. showed that the preferential distribution of Mn along (Ga,Mn)As [11(_)0] can produce bulk uniaxial in-plane and out-of-plane anisotropies [3]. This preferential Mn distribution is due to the fact that the nearest-neighbor Mn pair on the GaAs (001) surface has a lower energy for the [11(_)0] axis than the [110] case. However, such a preferential Mn distribution probably will not occur when the material is not grown in a layer-by-layer mode but by a liquid-phase-epitaxy-like process with the growth speed of meters per second, as for the case of ion implantation and pulsed laser melting (II-PLM) [4]. In this work, three typical III-Mn-V DFSs [(In,Mn)As, (Ga,Mn)As, and (Ga,Mn)P] are obtained through II-PLM. We find that both (Ga,Mn)P and (Ga,Mn)As samples exhibit the easy behavior in plane (as shown in Fig. 1) while the (In,Mn)As one reveals perpendicular magnetic anisotropy (not shown). The latter is attributed to the lattice strain due to lattice mismatch between the film and the substrate. The in-plane uniaxial anisotropy is much weakened for (Ga,Mn)P and (Ga,Mn)As from the magnetic hysteresis at 5 K. However, as shown in the inset to Fig. 1, the anisotropy changes with temperature increasing. More experimental results including magnetic hysteresis at different temperatures will be discussed during the conference.

Figure 1: Magnetic hysteresis along different crystalline axis for (Ga,Mn)P and (Ga,Mn)As with different Mn concentration measured at 5 K. The inset shows the magnetic remanence along different crystalline axis for the corresponding sample.
[1] M. Sawicki et al., Phys. Rev. B 70, 245325 (2004).
[2] C. Bihler et al., Phys. Rev. B 78, 045203 (2008).
[3] M. Birowska, et al., Phys. Rev. Lett. 108, 237203 (2012).
[4] M. A. Scarpulla et al., Appl. Phys. Lett. 82, 1251-1253 (2003).

Keywords: Magnetic anisotropy; dilute ferromagnetic semiconductors (DFSs); ion implantation; pulsed laser annealing

  • Lecture (Conference)
    61st Annual Conference on Magnetism and Magnetic Materials (2016 MMM), 31.10.-04.11.2016, New Orleans, United States of America

Permalink: https://www.hzdr.de/publications/Publ-24772
Publ.-Id: 24772


The magnetic anisotropy of III-Mn-V ferromagnetic semiconductors prepared by ion implantation and pulsed laser melting

Xu, C.; Yuan, Y.; Sawicki, M.; Helm, M.; Zhou, S.

As one of the most important physical properties of dilute ferromagnetic semiconductors (DFS), the magnetic anisotropy exhibits a complicated character and its origin is under continuous discussion [1, 2]. From the point of view of application, different magnetic anisotropies could meet various needs of spintronic devices. Due to different physical parameters (e.g. band gap, lattice constant) in various Mn doped III-V DMSs, various magnetic anisotropies are expected and could be tailored by Mn or hole concentrations [3-5]. To investigate this in greater detail, we prepare three typical III-Mn-V DFSs, InMnAs, GaMnAs, and GaMnP by ion implantation and pulsed laser annealing, which is a complementary approach to low-temperature molecular beam epitaxy. We report a systematic investigation on the magnetic anisotropy with the aim to understand its physical origin.

[1]. T. Dietl et al., Rev. Mod. Phys. 86, 187-251 (2014)
[2]. M. Birowska et al., Phys. Rev. Lett. 108, 237203 (2012)
[3]. U. Welp et al., Phys. Rev. Lett. 90, 167206 (2003)
[4]. M. Sawicki et al., Phys. Rev. B 70, 245325 (2004)
[5]. C. Bihler et al., Phys. Rev. B 78, 045203 (2008)

Keywords: Magnetic anisotropy; dilute ferromagnetic semiconductors (DFSs); ion implantation; pulsed laser annealing

  • Lecture (Conference)
    European Materials Research Society (E-MRS) 2016 Spring Meeting, 02.-06.05.2016, Lille, France

Permalink: https://www.hzdr.de/publications/Publ-24771
Publ.-Id: 24771


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