Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33403 Publications

Hydrodynamic modeling of a pure-glue initial scenario in high-energy hadron and heavy-ion collisions

Vovchenko, V.; Pang, L.-G.; Niemi, H.; Karpenko, I. A.; Gorenstein, M. I.; Satarov, L. M.; Mishustin, I. N.; Kämpfer, B.; Stoecker, H.
Partonic matter produced in the early stage of ultrarelativistic nucleus-nucleus collisions is assumed to be composed mainly of gluons, and quarks and antiquarks are produced at later times. The comparable hydrodynamic simulations of heavy-ion collisions for (2+1)-flavor and Yang-Mills equations of state performed by using three different hydrodynamic codes are presented. Assuming slow chemical equilibration of quarks, the spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the LHC energy of √sNN=2.76 TeV. It is shown that a suppression of quarks at early times leads to a significant reduction of the yield of the thermal dileptons, but only to a rather modest suppression of the pT-distribution of direct photons. It is demonstrated that an enhancement of photon and dilepton elliptic flows might serve as a promising signature of the pure-glue initial state. Calculations based on Bjorken hydrodynamics suggest that collisions of small systems at intermediate energies available at RHIC or future FAIR facilities may show stronger effects associated with initial pure gluodynamic evolution.

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Permalink: https://www.hzdr.de/publications/Publ-24039
Publ.-Id: 24039


Vacuum particle-antiparticle creation in strong fields as a field induced phase transition

Smolyansky, S. A.; Panferov, A. D.; Blaschke, D. B.; Juchnowski, L.; Kämpfer, B.; Otto, A.
The features of vacuum particle creation in an external classical field are studied for simplest external field models in 3+1 dimensional QED. The investigation is based on a kinetic equation that is a nonperturbative consequence of the fundamental equations of motion of QED. The observed features of the evolution of the system apply on the qualitative level also for systems of other nature and therefore are rather general. Examples from cosmology and condensed matter physics illustrate this statement. The common basis for the description of these systems are kinetic equations for vacuum particle creation belonging to the class of integro-differential equations of non-Markovian type with fastly oscillating kernel. This allows to characterize processes of this type as belonging to the class of field induced phase transitions.

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Permalink: https://www.hzdr.de/publications/Publ-24038
Publ.-Id: 24038


Holographically emulating sequential versus instantaneous disappearance of vector mesons in a hot environment

Zöllner, R.; Kämpfer, B.
Descent extensions of the soft-wall model are used to accommodate two variants of Regge trajectories of vector meson excitations. At non-zero temperatures, various options for either sequential or instantaneous disappearance of vector mesons as normalisable modes are found, thus emulating deconfinement at a certain temperature in the order of the (pseudo-) critical temperature of QCD. The crucial role of the blackness function, which steers the thermodynamic properties of the considered system, is highlighted.

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Permalink: https://www.hzdr.de/publications/Publ-24037
Publ.-Id: 24037


The Link Between the Local Bubble and Radioisotopic Signatures on Earth

Feige, J.; Breitschwerdt, D.; Wallner, A.; Schulreich, M. M.; Kinoshita, N.; Paul, M.; Dettbarn, C.; Fifield, K. L.; Golser, R.; Honda, M.; Linnemann, U.; Matsuzaki, H.; Merchel, S.; Rugel, G.; Steier, P.; Tims, S. G.; Winkler, S. R.; Yamagata, T.
Traces of 2-3 Myr old 60Fe were recently discovered in a manganese crust and in lunar samples. We have found that this signal is extended in time and is present in globally distributed deep-sea archives. A second 6.5-8.7 Myr old signature was revealed in a manganese crust. The existence of the Local Bubble hints to a recent nearby supernova-activity starting 13 Myr ago. With analytical and numerical models generating the Local Bubble, we explain the younger 60Fe-signature and thus link the evolution of the solar neighborhood to terrestrial anomalies.
Keywords: supernova, AMS, radionuclide, local bubble, deep-sea samples, interstellar medium, accelerator mass spectrometry
  • Open Access Logo Contribution to proceedings
    14th International Symposium on Nuclei in the Cosmos XIV, 19.-24.06.2016, Toki Messe, Niigata, Japan
    Proceedings of the 14th International Symposium on Nuclei in the Cosmos XIV, JPS Conf. Proc. 14 (2017): JPS (Japan Physical Society) Conference Proceeding, 010304
    DOI: 10.7566/JPSCP.14.010304

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Permalink: https://www.hzdr.de/publications/Publ-24036
Publ.-Id: 24036


Moments-based ultrasound visual servoing: from mono to multi-plane approach

Nadeau, C.; Krupa, A.; Petr, J.; Barillot, C.
This paper presents a new image-based visual servoing approach to control a robotic system equipped with an ultrasound imaging device. The presented method allows an automatic positioning of the probe with respect to an object of interest. Moments-based image features are computed from three orthogonal ultrasound images to servo in-plane and out-of plane motions of the system. An efficient segmentation method, based on graph cut strategy, is proposed to extract the object contour in each image plane. Simulation results demonstrate that this approach improves upon techniques based on a single 2D US image in terms of probe positioning. Our method was also validated from robotic experiments performed on an ultrasound phantom with the use of a motorized 3D probe that provides the three US images.
Keywords: Visual servoing, ultrasound images, graph cut segmentation, moment features

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Permalink: https://www.hzdr.de/publications/Publ-24035
Publ.-Id: 24035


Magnetic properties and giant reversible magnetocaloric effect in the GdCoC2 compound

Meng, L.; Xu, C.; Yuan, Y.; Qi, Y.; Zhou, S.; Li, L.
The crystal structure, magnetic properties and magnetocaloric effect (MCE) of GdCoC2 have been studied. The compound crystallizes in an orthorhombic CeNiC2-type structure which belongs to Amm2 space group. A giant reversible MCE is observed in GdCoC2 accompanied by a second-order paramagnetic to ferromagnetic (PM-FM) phase transition around the Curie temperature ~15 K. For the magnetic field change of 0-5 T, the maximum values of the magnetic entropy change (-ΔSMmax), relative cooling power (RCP), and refrigerant capacity (RC) are 28.4J/kg K, 566 J/kg and 369 J/kg, respectively. The present results indicate that the GdCoC2 compound is a promising candidate for low temperature magnetic refrigeration.
Keywords: GdCoC2 compound; magnetocaloric effect; magnetic properties; magnetic refrigeration.

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Permalink: https://www.hzdr.de/publications/Publ-24034
Publ.-Id: 24034


Raman scattering at terahertz frequencies enabled by an infrared free electron laser

Pavlov, S.; Dessmann, N.; Zhukavin, R. K.; Shastin, V.; Hübers, H.-W.; Pohl, A.; Redlich, B.; van der Meer, A. F. G.; Winnerl, S.; Schneider, H.; Ortega, J.-M.; Prazeres, R.; Abrosimov, N. V.
In the last decade the use of infrared free electron laser facilities enabled observation of inelastic light (Raman) scattering in THz frequency range. Raman-active intracenter donor transitions in silicon fall into the THz range and serve as outgoing resonances in electronic Stokes scattering. At photon fluxes above 1E24 photon/cm2/s donor-related Raman stimulated emission occurs in the range 4.2-6.5 THz from natural and isotopically enriched silicon crystals with various dopants while the free electron laser wavelength was varied between 18 and 41 mkm (7.5-16.5 THz). Study of dynamics of the observed emission shows a transient picosecond-micropulse mode that indicates on significantly larger Raman gain realized in THz Raman silicon lasers. This research has been partly supported by the EC CALIPSO project for the Transnational access to the European FELs and Synchrotron facilities as well as joint German-Russian program "Research on technological advances of radiation sources of photons and neutrons based on accelerators and neutron sources in cooperation with research organizations and universities of the Federal Republic of Germany" (InTerFEL project, BMBF No. 05K2014 and the Russian Ministry of Science and Education (No. RFMEFl61614X0008).
Keywords: terahertz, infrared, free-electron laser, Raman scattering
  • Lecture (Conference)
    2016 International Conference "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2016), 04.-07.07.2016, Novosibirsk, Russia

Permalink: https://www.hzdr.de/publications/Publ-24033
Publ.-Id: 24033


Exciton dynamics in semiconductor quantum wells and single quantum dots studied with a THz free-electron laser

Schneider, H.; Stephan, D.; Zybell, S.; Winnerl, S.; Bhattacharyya, J.; Eßer, F.; Helm, M.
Excitons in III-V semiconductors are Coulomb-bound electron-hole pairs which are analogous to two-dimensional hydrogen atoms with terahertz (THz) binding energies. In semiconductor quantum wells (QW), confinement into the plane of the QW gives rise to essentially two-dimensional excitons, thus giving rise to a different symmetry and higher binding energy. In quantum dots (QD), three-dimensional confinement leads to discrete electronic and excitonic states, such that the system becomes similar to a trapped atom.
Using intense, spectrally narrow terahertz (THz) pulses from the free-electron laser (FEL) facility FELBE in Dresden, Germany, we have investigated the population dynamics between exciton states in III-V QWs and single QDs. To this end, carriers are optically injected by picosecond near-infrared optical pulses, which leads to a population of the lowest excitonic level. Using narrowband THz pulses provided by the free-electron laser at HZDR, excitons are resonantly excited into higher levels. Time-dependent photoluminescence (TDPL) measurements based on a streak camera system and on time-correlated photon counting, respectively, then allow us to study the transient population of dipole-allowed higher excitonic levels and to access the relaxation dynamics of these quasi-particles.
In QWs, the most prominent transition is from the 1s ground state into the 2p excited state (using hydrogen notation). While the 2p state is "optically dark", rapid scattering from the 2p into the 2s state occurs. TDPL originating from the 1s and 2s exciton states thus provides a unique signature which allows us to explore the relaxation dynamics involving 1s, 2s, and 2p excitons. Now turning to QDs, single QDs rather than QD ensembles should be investigated in order to prevent strong inhomogeneous broadening. We have therefore developed a micro-TDPL setup with a probe volume significantly below 1 µm^3 and high quantum efficiency to become sensitive to one single QD. In particular, we investigate the dynamics of the s-to-p inter-sublevel transition, which occurs in the range 13-20 meV for the QDs under study. Resonant excitation with a THz pulse, which is applied at about 0.7 ns time delay after interband excitation, causes an instantaneous reduction of the ground state TDPL. The signal recovers within about 100 ps towards a value which depends on the near-infrared excitation energy. In particular, qualitatively different behavior has been observed and analyzed using a phenomenological rate equation for interband excitation of the GaAs matrix, the InGaAs wetting layer, and quasi-resonant excitation of the QD.
Acknowledgements: We thank L. Schneebeli, C.N. Böttge, M. Kira, and S.W. Koch (Marburg, Germany) for fruitful discussions and collaboration.
Keywords: quantum well, exciton, terahertz, free-electron laser
  • Invited lecture (Conferences)
    International Workshop on "Terahertz Science, Nanotechnologies and Applications", 16.-22.07.2016, Erice, Italien

Permalink: https://www.hzdr.de/publications/Publ-24032
Publ.-Id: 24032


Semiconductor spectroscopy with infrared and THz free-electron lasers

Schneider, H.
This talk reviews some recent spectroscopic studies on semiconductor structures carried out using the mid-infrared and terahertz (THz) free-electron laser facility FELBE in Dresden, Germany. Its intense, nearly transform-limited picosecond pulses, which can also be combined with synchronous pico- or femtosecond pulses from near-infared tabletop lasers, provide unique research opportunities to advance our knowledge on the interaction of intense mid-infrared and THz fields with materials and devices.
Keywords: Semiconductor spectroscopy, infrared, terahertz, free-electron laser
  • Invited lecture (Conferences)
    2016 International Conference on "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2016), 04.-07.07.2016, Novosibirsk, Russia

Permalink: https://www.hzdr.de/publications/Publ-24031
Publ.-Id: 24031


Overcoming the diffraction limit with a GaAs-based plasmonic superlens

Fehrenbacher, M.; Winnerl, S.; Döring, J.; Kehr, S. C.; Eng, L. M.; Huo, Y. H.; Schmidt, O. G.; Yao, K.; Liu, Y.; Helm, M.; Schneider, H.
We report a semiconductor-based superlens for sub-diffraction-limited near-field imaging at mid-infrared wavelengths. The superlens is based on a sequence of intrinsic and doped GaAs layers. Resonant enhancement of evanescent waves is accomplished here by exploiting the Drude response of a highly doped n-GaAs layer. Operation as a near-field superlens is validated by utilizing an aperture-less scattering near-field optical microscope (s-SNOM), which allows us to probe the image plane of the superlens with sub-wavelength resolution.
In our experiments, gold stripes underneath the GaAs superlens are imaged by the s-SNOM. The s-SNOM comprises an atomic-force microscope (AFM), the tip of which is illuminated by mid-infrared radiation from a free-electron laser (FEL). Imaging results reveal sub-wavelength resolution better than λ/6 at the resonant wavelength of λ = 22.0 µm. In excellent accordance with the Drude-Lorentz model, the resonant wavelength for superlensing can easily be adjusted by changing the doping concentration. Our approach thus reveals a simple and versatile superlens implementation for infrared nanospectroscopy. Detector issues specific for s-SNOM will also be addressed.
[1] M. Fehrenbacher, S. Winnerl, H. Schneider, J. Döring, S. C. Kehr, L. M. Eng, Y. Huo, O. G. Schmidt, K. Yao, Y. Liu, M. Helm, Nano Lett. 15, 1057 (2015)
Keywords: Scattering near-field optical microscopy, s-snom, superlens, GaAs, sub-diffraction-limited
  • Lecture (Conference)
    Quantum Structured Infrared Photodetector International Conference (QSIP 2016), 12.-17.06.2016, Tel Aviv, Israel

Permalink: https://www.hzdr.de/publications/Publ-24030
Publ.-Id: 24030


The South Um Mongul Cu-Mo-Au prospect in the Eastern Desert of Egypt: From a mid-Cryogenian continental arc to Ediacaran post-collisional appinite-high Ba-Sr monzogranite

Abd El-Rahman, Y.; Gutzmer, J.; Said, A.; Hofmann, M.; Gärtner, M.; Linnemann, U.
The South Um Mongul prospect is a Cu-Mo-Au porphyry system. It is covered by porphyritic dacite and hornblende gabbro. Both units are intruded by monzogranite, which encloses xenoliths of both units. Using LA-ICP-MS U-Pb zircon method, the dacite is dated at ca. 773 ± 6.9 Ma, while the gabbro and the monzogranite are dated at 603 ± 3.5 and 558 ± 4.6 Ma, respectively. The dacite age is consistent with the mid-Cryogenian subduction-related magmatic stage and the gabbro-monzogranite age is comparable to the Ediacaran post-collisional magmatic stage during the evolution of the Arabian-Nubian Shield. The dacite is akin to high-K I-type granitoids and its primitive mantle-normalized trace element patterns show negative Nb anomalies and enrichment in LILE (large ion lithophile elements), Th and U over HFSE. These geochemical characteristics are similar to those of felsic magma formed in a subduction-related tectonic setting. The high La/Ybcn (7.2–30.9), Nb/Yb (2.63–4.41) and Th/Yb (2.07–3.04) ratios of the dacite are comparable to continental rather than oceanic arc systems. Its low Sm/Yb ratios (1.84–3.13) support the primitive nature of the crust beneath the continental arc and derivation from a garnet-free lower crustal source. The dacite has low Sr/Y ratios (5–9) and its Eu/Eu⁎ ratios range from 0.66 to 0.83. Similar to dacite, the primitive mantle-normalized trace element patterns of the post-collisional suite show a subduction-related geochemical signature. However, the gabbro is characterized by Th/Ta ratios (3.4–14.8), which are comparable with the within-plate tectonic setting. The subduction-related geochemical signature is inherited from long subduction history beneath the Arabian-Nubian Shield. Both the gabbro and monzogranite are characterized by high Ba (404–590 ppm and 936–1590 ppm, respectively) and Sr (611–708 ppm and 624–793 ppm, respectively) contents, which make them analogous to the Caledonian appinite-high Ba-Sr granite assemblage. The formation of these rocks is related to the Ediacaran lithospheric erosion accompanying slab break-off. This process induced asthenospheric upwelling, which led to partial melting of the lithosphere previously metasomatised by subducted sediments involving carbonates impregnated by hydrothermal barite. Melting of this lithosphere led to the formation of the hornblende gabbro. Underplating by the mafic magma led to melting of the lower crust and the formation of high Ba-Sr monzogranite in the area. The high Sm/Yb (2.94–4.19) and Sr/Y (52–74) ratios of the monzogranite may indicate the presence of garnet in the melted amphibolitic lower crust. The higher Sr/Y ratios, lower HFSE (high field strength elements) contents and the absence of pronounced Eu anomalies in monzogranite relative to dacite suggest the productive nature of the post-collisional magma relative to the continental arc magma in this prospect.
Keywords: Appinite; Arabian-Nubian Shield; Continental arc; High Ba-Sr granite; Neoproterozoic; Post-collisional porphyry copper

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Permalink: https://www.hzdr.de/publications/Publ-24029
Publ.-Id: 24029


Long-term diffusion of U(VI) in bentonite: Dependence on density

Joseph, C.; Mibus, J.; Trepte, P.; Müller, C.; Brendler, V.; Park, D. M.; Jiao, Y.; Kersting, A. B.; Zavarin, M.
As contribution to the safety assessment of nuclear waste repositories, U(VI) diffusion through the potential buffer material MX-80 bentonite was investigated at three clay dry densities over 6 years. Synthetic MX 80 model pore water was used as background electrolyte. Speciation calculations showed that Ca2UO2(CO3)3(aq) was the main U(VI) species. The in- and out-diffusion of U(VI) was investigated separately. U(VI) diffused about 3 mm, 1.5 mm, and 1 mm into the clay plug at ρ = 1.3, 1.6, and 1.9 g/cm3, respectively. No through-diffusion of the U(VI) tracer was observed. However, leaching of natural uranium contained in the clay occurred and uranium was detected in all receiving reservoirs. As expected, the effective and apparent diffusion coefficient, De and Da, decreased with increasing dry density. The Da values for the out-diffusion of natural U(VI) were in good agreement with previously determined values. Surprisingly, Da values for the in-diffusion of U(VI) were about two orders of magnitude lower than values obtained in short-term in-diffusion experiments reported in the literature. As potential reasons for this behavior, changes of the U(VI) speciation within the clay (precipitation, reduction) or changes of the clay porosity and pore connectivity with time were evaluated. By application of Archie’s law and extended Archie’s law, it was estimated that a significantly smaller effective porosity must be present for the long-term in-diffusion of U(VI). The results suggest that long-term studies of key transport phenomena may reveal additional processes that can directly impact long-term repository safety assessments.
Keywords: nuclear waste repository, MX-80, clay, uranium, speciation, extended Archie’s law

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Permalink: https://www.hzdr.de/publications/Publ-24028
Publ.-Id: 24028


The effect of microstructural heterogeneity on pore size distribution and permeability in Opalinus Clay (Mont Terri, CH): insights from an integrated study of laboratory fluid flow and pore morphology from BIB-SEM images

Philipp, T.; Amann-Hildenbrand, A.; Laurich, B.; Desbois, G.; Littke, R.; Urai, J. L.
Opalinus Clay (OPA) is considered as potential host rock for the deep-geological disposal of radioactive waste. One key-parameter in long-term storage prediction is permeability. In this study we investigated microstructural controls on permeability for the different facies of OPA. Permeability and porosity were determined under controlled pressure conditions. In addition, the pore space was investigated by SEM, using high quality surfaces prepared by Broad Ion Beam milling (BIB). Water permeability coefficients range from 1.6×10-21 to 5.6×10 20 m². Helium pycnometer porosities range between ~21% and ~12%. The sample with the highest helium porosity (shaly facies) is characterized by the lowest permeability, and vice versa (carbonate-rich sandy facies). This inverse behavior deviates from the generally reported trend of increasing permeability with increasing porosity, indicating that parameters other than porosity affect permeability. Visible porosities from SEM images revealed that 67-95% of the total porosity resides within pores smaller than the SEM detection limit. Pore sizes follow a power law distribution with characteristic power law exponents (D), strongly differing among the facies. The carbonate-rich sandy facies contains a network of much larger pores (D(shaly)~2.4, D(carbonate-rich)~2.0), because of the presence of load-supporting sand grains that locally prevent clay compaction, being responsible for a higher permeability.
Keywords: Opalinus Clay, permeability, porosity, BIB-SEM, microstructure, pore size distribution
  • Geological Society Special Publication 454(2017)1, 85
    DOI: 10.1144/SP454.3

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Permalink: https://www.hzdr.de/publications/Publ-24027
Publ.-Id: 24027


The asphericity of the metabolic tumour volume in NSCLC: correlation with histopathology and molecular markers

Apostolova, I.; Ego, K.; Steffen, I. G.; Buchert, R.; Wertzel, H.; Achenbach, J.; Riedel, S.; Schreiber, J.; Schultz, M.; Furth, C.; Derlin, T.; Amthauer, H.; Hofheinz, F.; Kalinski, T.
Purpose

Asphericity (ASP) is a tumour shape descriptor based on the PET image. It quantitates the deviation from spherical of the shape of the metabolic tumour volume (MTV). In order to identify its biological correlates, we investigated the relationship between ASP and clinically relevant histopathological and molecular signatures in non-small-cell lung cancer (NSCLC).

Methods

The study included 83 consecutive patients (18 women, aged 66.4 ± 8.9 years) with newly diagnosed NSCLC in whom PET/CT with 18F-FDG had been performed prior to therapy. Primary tumour resection specimens and core biopsies were used for basic histopathology and determination of the Ki-67 proliferation index. EGFR status, VEGF, p53 and ALK expression were obtained in a subgroup of 44 patients. The FDG PET images of the primary tumours were delineated using an automatic algorithm based on adaptive thresholding taking into account local background. In addition to ASP, SUVmax, MTV and some further descriptors of shape and intratumour heterogeneity were assessed as semiquantitative PET measures.

Results

SUVmax, MTV and ASP were associated with pathological T stage (Kruskal-Wallis, p = 0.001, p < 0.0005 and p < 0.0005, respectively) and N stage (p = 0.017, p = 0.003 and p = 0.002, respectively). Only ASP was associated with M stage (p = 0.026). SUVmax, MTV and ASP were correlated with Ki-67 index (Spearman’s rho = 0.326/p = 0.003, rho = 0.302/p = 0.006 and rho = 0.271/p = 0.015, respectively). The latter correlations were considerably stronger in adenocarcinomas than in squamous cell carcinomas. ASP, but not SUVmax or MTV, showed a tendency for a significant association with the extent of VEGF expression (p = 0.058). In multivariate Cox regression analysis, ASP (p < 0.0005) and the presence of distant metastases (p = 0.023) were significantly associated with progression-free survival. ASP (p = 0.006), the presence of distant metastases (p = 0.010), and Ki-67 index (p = 0.062) were significantly associated with overall survival.

Conclusion

The ASP of primary NSCLCs on FDG PET images is associated with tumour dimensions and molecular markers of proliferation and angiogenesis.
Keywords: Non-small cell lung cancer, FDG PET/CT, Asphericity, Intratumour heterogeneity, Histopathology, Molecular markers

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Permalink: https://www.hzdr.de/publications/Publ-24026
Publ.-Id: 24026


Dynamics of nonequilibrium electrons on neutral center states of interstitial magnesium donors in silicon

Pavlov, S. G.; Deßmann, N.; Pohl, A.; Shuman, V. B.; Portsel, L. М.; Lodygin, А. N.; Astrov, Y. A.; Winnerl, S.; Schneider, H.; Stavrias, N.; van der Meer, A. F. G.; Tsyplenkov, V. V.; Kovalesky, K. A.; Zhukavin, R. K.; Shastin, V. N.; Abrosimov, N. V.; Hübers, H.-W.
Subnanosecond dynamics of optically excited electrons bound to excited states of neutral magnesium donor centers in silicon has been investigated. Lifetimes of nonequilibrium electrons have been derived from the decay of the differential transmission at photon energies matching the intracenter and the impurity–to–conduction band transitions. In contrast to hydrogen-like shallow donors in silicon, significantly longer lifetimes have been observed. This indicates weaker two-phonon and off-resonant interactions dominate the relaxation processes in contrast to the single-intervalley-phonon assisted impurity-phonon interactions in the case of shallow donors in silicon.
Keywords: Extrinsic semiconductors, dynamics of electrons from impurities, magnesium doping of silicon

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Permalink: https://www.hzdr.de/publications/Publ-24025
Publ.-Id: 24025


An Evaluation of Hydroxamate Collectors for Malachite Flotation

Marion, C.; Jordens, A.; Li, R.; Rudolph, M.; Waters, K. E.
Copper oxide minerals, such as malachite, do not often respond well to traditional copper sulphide collectors, and require alternative flotation schemes. Hydroxamic acid collectors have been suggested as a means to directly float malachite, however, there is limited information on the effect of reagent structure on the performance of these collectors. This paper investigates the effect of five alkyl hydroxamates and two aromatic hydroxamates on the flotation of a synthetic ore composed of malachite and quartz. Zeta potential measurements were used to aid in understanding reagent adsorption onto the surface of the two minerals. The collectors were then evaluated using bench scale flotation results. While zeta potential measurements suggested that all the collectors investigated selectively adsorb onto the surface of malachite, only benzohydroxamic acid and C8 ¬alkyl hydroxamates were effective collectors in the flotation of malachite. Benzohydroxamic acid was the most selective, however, significantly lower dosages of C8¬ alkyl hydroxamates were required to obtain similar malachite recoveries, with minimal increases in quartz recovery. Benzo and octylhydroxamic acid were further examined for the flotation of fine (-38 µm) particles. For fine particle flotation experiments the effect of temperature was also investigated as a means to improve the flotation performance.
Keywords: Hydroxamates; Malachite; Flotation; Surface Chemistry

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Permalink: https://www.hzdr.de/publications/Publ-24024
Publ.-Id: 24024


Volumetrical Laser Ion Acceleration of Spherical Mass Limited Solid Density Targets

Huebl, A.; Hilz, P.; Schreiber, J.; Kluge, T.; Widera, R.; Bussmann, M.
Invited presentation at the LMU group of Jörg Schreiber about the results of the large scale 3D3V simulations for their experiments.
Keywords: Mass Limited Target, Paul Trap, PIConGPU, Simulation, 3D3V, GPGPU, OpenSource
  • Invited lecture (Conferences)
    LMU/MPI QO Munich: Prof. Schreiber Group Meeting (Laser-driven ion acceleration), 18.-20.07.2016, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24023
Publ.-Id: 24023


Scalable and Modular Online Data Processing for Ultrafast Computed Tomography Using CUDA Pipelines

Frust, T.; Juckeland, G.; Bieberle, A.
For investigations of rapidly moving structures in opaque technical devices ultrafast electron beam X-ray computed tomography (CT) scanners are available at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Currently, CT data must be downloaded initially after each CT scan from the scanner to a data processing machine. Afterwards, cross-sectional images are reconstructed.
This limits the application fields of the scanners. For on-line observations and even automated process control of scanned objects a new modular data processing tool is presented consisting of user-definable pipeline stages that work independently together in a so called data processing pipeline that can keep up with the frame rate of up to 8 kHz. The stages are arbitrarily programmable and combinable and are connected by a fast custom memory pool to optimize data transfer processes. As a result, this processing structure is not limited to CT application only. In order to achieve highest processing performances for the electron beam CT scanners all relevant data processing steps are individually implemented in separate stages using graphic processing units (GPUs) and NVIDIA's CUDA programming language. Data processing performance tests on two different high-end GPUs (Tesla K20c, GeForce GTX 1080) offer a slice image reconstruction performance that is well-suited for the required on-line application.
Keywords: Electron beam X-ray computed tomography, CUDA, data pipeline, real-time processing, in-situ visualization
  • Contribution to proceedings
    ISAV 2016: In Situ Infrastructures for Enabling Extreme-scale Analysis and Visualization, 13.11.2016, Salt Lake City, Utah, USA
    Proceedings of ISAV 2016
    DOI: 10.1109/ISAV.2016.007
  • Lecture (Conference)
    ISAV 2016: In Situ Infrastructures for Enabling Extreme-scale Analysis and Visualization, 13.11.2016, Salt Lake City, Utah, USA

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Permalink: https://www.hzdr.de/publications/Publ-24022
Publ.-Id: 24022


Trivalent f-elements in human saliva: A comprehensive speciation study by time-resolved laser-induced fluorescence spectroscopy and thermodynamic calculations

Barkleit, A.ORC; Wilke, C.; Heller, A.; Stumpf, T.; Ikeda-Ohno, A.
In the case of oral ingestion of radioactive contaminants, the first contact medium is saliva in the mouth. To gain a first insight into the interaction of radioactive contaminants in human saliva, the speciation of curium (Cm(III)) and europium (Eu(III)), i.e., trivalent f-elements, was investigated in different salivary media with time-resolved laser-induced fluorescence spectroscopy (TRLFS). The results indicate that these metal cations are primarily complexed with carbonates and phosphates, forming the ternary complexes with a possible stoichiometry of 1:1:2 (M(III) : carbonate : phosphate). For charge compensation, calcium is also involved in these ternary complexes. In addition to these inorganic components, organic substances, namely α-amylase, show a significant contribution to the speciation of the trivalent f-elements in saliva. This protein is the major enzyme in saliva and catalyzes the hydrolysis of polysaccharides. In this context, the effect of Eu(III) on the activity of α-amylase was investigated to reveal the potential implication of these metal cations for the in vivo functions of saliva. The results indicate that the enzyme activity is strongly inhibited by the presence of Eu(III), which is suppressed by an excess of calcium.
Keywords: Actinides, lanthanides, curium, europium, speciation, body fluids, fluorescence spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-24021
Publ.-Id: 24021


Test of Lorentz invariance in β decay of polarized 20Na

Sytema, A.; van den Berg, J. E.; Böll, O.; Chernowitz, D.; Dijck, E. A.; Grasdijk, J. O.; Hoekstra, S.; Jungmann, K.; Mathavan, S. C.; Meinema, C.; Mohanty, A.; Müller, S. E.; Noordmans, J. P.; Nunez Portela, M.; Onderwater, C. J. G.; Pijpker, C.; Timmermans, R. G. E.; Vos, K. K.; Willmann, L.; Wilschut, H. W.
Background: Lorentz invariance is key in our understanding of nature, yet relatively few experiments have tested Lorentz invariance in weak interactions.

Purpose: Our goal is to obtain limits on Lorentz-invariance violation in weak interactions, in particular rotational invariance in β decay.

Method: We search for a dependence of the lifetime of 20Na nuclei on the nuclear spin direction. Such directional dependence would be evidence for Lorentz-invariance violation in weak interactions. A difference in lifetime between nuclei that are polarized in the east and west direction is searched for. This difference is maximally sensitive to the rotation of the Earth, while the sidereal dependence is free from most systematic errors.

Results: The experiment sets a limit of 2×10-4 at 90% C.L. on the amplitude of the sidereal variation of the relative lifetime differences, an improvement by a factor 15 compared to an earlier result.

Conclusions: No significant violation of Lorentz invariance is found. The result sets limits on parameters of theories describing Lorentz-invariance violation.
Keywords: Lorentz violation, beta-decay

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Publ.-Id: 24020


Fractionated irradiation influences uptake of near-infrared-labeled Cetuximab: preliminaries on combination with radioimmunotherapy

Dietrich, A.; Koi, L.; Severin, J.; Baumann, M.; Krause, M.
External beam irradiation (EBRT) can precisely target the solid tumor mass but is limited by the surrounding normal tissue. Radioimmunotherapy mediates additional internal irradiation with the potential to strike also distant metastases. The combination of internal and external radiotherapy (CIERT) is a promising treatment strategy as it potentially combines the advantages of both modalities without increasing toxicity. In addition, patients could be stratified via a corresponding PET-tracer (1). We previously showed that CIERT using Y-90-Cetuximab (Y-90-Cet) massively increased tumor control probability compared to EBRT alone in a head and neck squamous cell carcinoma xenograft model (2). In the presented project, we investigated CIERT using clinical relevant fractionated EBRT with 30 fractions (fx) over 6 weeks. To study the best application timing, subcutaneous xenograft bearing mice were intravenously injected with near-infrared-labeled Cetuximab (NIR-Cet) at different time points during fxEBRT to model Y-90-Cet uptake. In addition, different dose groups were used for fxEBRT. NIR-Cet uptake was longitudinally followed by in-vivo optical imaging. Signal intensity was highest at day 3-4 post-injection in controls and was not altered by subsequent fxEBRT. In contrast, tumor uptake of NIR-Cet was increased if applied during fxEBRT. From these results, we concluded that low to moderate doses of fxEBRT can enhance Cet uptake but the effect is diminished if a certain threshold dose is exceeded. The interdependency of the total dose and the injection timing is not linearly and needs to be studied in more detail. However, based on the preliminary data, we injected Y-90-Cet after 10 fx of EBRT in ongoing CIERT tumor control probability experiments.

(1) Dietrich et al. Br J Radiol. 2015 Jul;88(1051):20150042
(2) Koi et al. Radiother Oncol. 2014 Feb;110(2):362-9.
  • Contribution to proceedings
    DKTK Retreat in Heidelberg, 11.-12.10.2016, Heidelberg, Deutschland
    Proceedings of DKTK Retreat

Permalink: https://www.hzdr.de/publications/Publ-24019
Publ.-Id: 24019


Laser proton acceleration from liquid crystal films of different thicknesses with ultra-high laser contrast

Obst, L.; Poole, P.; Metzkes, J.; Zeil, K.; Cochran, G.; Kluge, T.; Schlenvoigt, H.-P.; Kraft, S.; Prencipe, I.; Rehwald, M.; Schumacher, D.; Schramm, U.
We present results of our experimental campaign on laser proton acceleration, in which liquid crystal film targets of tunable thickness were irradiated with plasma mirror cleaned laser pulses. The data show a significant increase in proton cut-off energy up to 25 MeV for a target thickness of 10 nm as compared to the few- micron scale reference for this target configuration yielding roughly 12 MeV.

The performance of laser based ion acceleration strongly depends on the laser temporal contrast and its effect on the target plasma scale length. Plasma mirror setups have proven to be a valuable tool to improve the temporal contrast by several orders of magnitude, reducing the intensity of pre-pulses that emanate from the laser chain and steepening the rising edge of the main laser pulse. We present recent results obtained at the Titanium Sapphire laser system Draco, delivering 30 fs long laser pulses at an intensity exceeding 10^20 W/cm^2. Our recently commissioned single plasma mirror improves the contrast by four orders of magnitude while reflecting 80% of the initial pulse energy. Its influence on the laser proton acceleration process was studied in a campaign in collaboration with the High Energy Density Physics Group of Ohio State University using their tunable liquid crystal film target source. This device allows an on-demand variation of the target thickness from tens of micrometers down to 10 nm while keeping the target composition constant. The target was positioned under 45 degrees with respect to the incoming laser beam while accelerated protons and ions were monitored in both laser- and target normal direction by means of Thomson Parabolas and Radiochromic Film stacks. Hence, being sensitive to the identification of acceleration regimes beyond the well-known Target Normal Sheath Acceleration, preliminary results display a significant increase in proton cut-off energy when reaching thin targets. Up to 25 MeV could be observed for an optimum target thickness of 10 nm as compared to the few- micron scale reference for this target configuration yielding roughly 12 MeV.
Keywords: laser-driven proton acceleration, high-intensity lasers
  • Lecture (Conference)
    Advanced Accelerator Concepts Workshop 2016, 2.8.2016, National Harbor, Maryland, USA

Permalink: https://www.hzdr.de/publications/Publ-24018
Publ.-Id: 24018


Superconductivity in Weyl semimetal candidate MoTe2

Qi, Y.; Naumov, P. G.; Ali, M. N.; Rajamathi, C. R.; Schelle, W.; Barkalov, O.; Hanfland, M.; Wu, S.-C.; Shekhar, C.; Sun, Y.; Süß, V.; Schmidt, M.; Schwarz, U.; Pippel, E.; Werner, P.; Hillebrand, R.; Förster, T.; Kampert, E.; Parkin, S.; Cava, R. J.; Felser, C.; Yan, B.; Medvedev, S. A.
Transition metal dichalcogenides have attracted research interest over the last few decades due to their interesting structural chemistry, unusual electronic properties, rich intercalation chemistry and wide spectrum of potential applications. Despite the fact that the majority of related research focuses on semiconducting transition-metal dichalcogenides (for example, MoS2), recently discovered unexpected properties of WTe2 are provoking strong interest in semimetallic transition metal dichalcogenides featuring large magnetoresistance, pressure-driven superconductivity and Weyl semimetal states. We investigate the sister compound of WTe2, MoTe2, predicted to be a Weyl semimetal and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that bulk MoTe2 exhibits superconductivity with a transition temperature of 0.10 K. Application of external pressure dramatically enhances the transition temperature up to maximum value of 8.2 K at 11.7 GPa. The observed dome-shaped superconductivity phase diagram provides insights into the interplay between superconductivity and topological physics.

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Publ.-Id: 24017


Commensurate and incommensurate magnetic order in spin-1 chains stacked on the triangular lattice in Li2NiW2O8

Ranjith, K. M.; Nath, R.; Majumder, M.; Kasinathan, D.; Skoulatos, M.; Keller, L.; Skourski, Y.; Baenitz, M.; Tsirlin, A. A.
We report the thermodynamic properties, magnetic ground state, and microscopic magnetic model of the spin-1 frustrated antiferromagnet Li2NiW2O8, showing successive transitions at TN1 similar or equal to 18 K and TN2 similar or equal to 12.5 K in zero field. Nuclear magnetic resonance and neutron diffraction reveal collinear and commensurate magnetic order with the propagation vector k = (1/2,0,1/2) below TN2. The ordered moment of 1.8 µB at 1.5 K is directed along [0.89(9), - 0.10(5), - 0.49(6)] and matches the magnetic easy axis of spin-1 Ni2+ ions, which is determined by the scissor-like distortion of the NiO6 octahedra. Incommensurate magnetic order, presumably of spin-density-wave type, is observed in the region between TN2 and TN1. Density-functional band-structure calculations put forward a three-dimensional spin lattice with spin-1 chains running along the [01-1] direction and stacked on a spatially anisotropic triangular lattice in the ab plane. We show that the collinear magnetic order in Li2NiW2O8 is incompatible with the triangular lattice geometry and thus driven by a pronounced easy-axis single-ion anisotropy of Ni2+.

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Publ.-Id: 24016


Spin transport in tantalum studied using magnetic single and double layers

Montoya, E.; Omelchenko, P.; Coutts, C.; Lee-Hone, N. R.; Hübner, R.; Broun, D.; Heinrich, B.; Girt, E.
We report on spin transport in sputter-grown Ta films measured by ferromagnetic resonance. Spin diffusion length and spin mixing conductance are determined from magnetic damping measurements for a varying thickness of Ta layer 0 <= dTa <= 10 nm. The different boundary conditions of single- and double-magnetic-layer heterostructures Py|Ta and Py|Ta|[Py|Fe] allow us to significantly narrow down the parameter space and test various models.We showt hat a common approach of using bulk resistivity value in the analysis yields inconsistent spin diffusion length and spin mixing conductance values for magnetic single- and double-layer structures. X-ray diffraction shows that bulk Ta is a combination of β-Ta and bcc-Ta. However, in the region of significant spin transport, <~ 2 nm, there is an intermediate region of growth where the Ta lacks long-range structural order, as observed by transmission electron microscopy. Thickness-dependent resistivity measurements confirm that the bulk and intermediate regions have significantly different resistivity values. We find that the data can be well represented if the intermediate region resistivity value is used in the analysis. Additionally, the data can be fit if resistivity has the measured thickness dependence and spin diffusion length is restricted to be inversely proportional to resistivity. Finally, we rule out a model in which spin diffusion length is a constant, while the resistivity has the measured thickness dependence.
  • Physical Review B 94(2016), 054416

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TEM investigation of barrier-like anodic oxide films on aluminum

Schneider, M.; Lämmel, C.; Hübner, R.; Gierth, U.; Michaelis, A.
The present study focuses mainly on non-electrochemical investigation of thin barrier-like oxide films formed under different pulse frequencies. The TEM investigation principally shows amorphous oxide films, which are dense and free of pores. The various pulse experiments have no influence on these film properties. The oxide growth factor was calculated to 1.06 nmV-1 in all cases. The microstructure (crystallographic orientation, grain boundaries) of the underlying substrate does not affect the oxide films. Independent of the pulse frequency, electrolyte species are not incorporated into the oxide films. The evidenced differences in the filmthickness are caused by intrinsic peculiarities of the high-field mechanism of growing oxide.
Keywords: pulse anodizing; high field mechanism; anodic oxide; aluminum
  • Surface and Interface Analysis 48(2016), 906-912

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Publ.-Id: 24014


Who will benefit most from hydrogel rectum spacer implantation in prostate cancer radiotherapy? A model-based approach for patient selection

Vanneste, B. G. L.; Hoffmann, A. L.; van Lin, E. N.; van de Voorde, L.; Pinkawa, M.; Lambin, P.
Background and Purpose
Previous studies confirmed that implantable rectum spacers (IRS) decreased acute gastro-intestinal (GI) toxicity in a significant percentage of prostate cancer patients undergoing intensity modulated radiation therapy (IMRT). We developed decision rules based on clinical risk factors (CRFs) to select those patients who are expected to benefit most from IRS implantation.

Materials and Methods
For 26 patients dose distributions with (IMRT+IRS) and without (IMRT-IRS) IRS were calculated. Validated nomograms based on CRFs and dosimetric criteria (anorectal V40Gy and V75Gy) were used to predict probabilities for grade 2-3 (G2-3) acute GI toxicity, G2-3 late rectal bleeding (LRB), G3 LRB, and G2-3 fecal incontinence (FI) for IMRT+IRS and IMRT-IRS. All permutations of CRFs were generated to identify most benefit scenarios (MBS) in which a predicted toxicity reduction of ≥5% points in ≥25% of the cohort was present due to IRS implantation.

Results
IMRT+IRS revealed a significant reduction in V40Gy (p = 0.0357) and V75Gy (p < 0.0001) relative to IMRT-IRS. For G2-3 acute GI toxicity and G2-3 LRB, the predicted toxicity rates decreased in 17/26 (65%) and 20/26 (77%) patients, and decision rules were derived for 22/32 (69%) and 12/64 (19%) MBS, respectively. From the decision rules, it follows that diabetes status has no impact on G2-3 acute toxicity, and in absence of pre-RT abdominal surgery, the implantation of an IRS is predicted to show no clinically relevant benefit for G2-3 LRB.

Conclusions
Prostate cancer patients who are expected to benefit most from IRS implantation can be identified prior to IMRT based on their CRFs profile.
Keywords: Prostate cancer – Radiotherapy – Rectum spacer – Patient selection –Toxicity prediction

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Publ.-Id: 24013


Measuring error estimation of the ultrasound array flow mapping system by means of numerical simulations

Franke, S.; Eckert, S.
A new two-dimensional ultrasound Doppler flow mapping system based on the application of linear arrays has been developed recently. A main feature involves a multi-beam operation facilitating a high frame rate.
Previously, the effect of crosstalk between the beams was investigated in a rotational flow by comparing the results of multi- and single-beam operation with each other. However, due to slight variations in the flow conditions and the scattering particle distribution the determined systematic error of measurement was not very reliable. Likewise, flow phantoms suffer from a number of shortcomings as fluctuations of rotational speed of the phantom drive or inadequate parameters of scattering particles. For this reason, we developed a numerical model of our flow mapping system providing the echo signals of the particle motion in a model flow being similar to our typical small scale experiments. For each particle the scattering signal is calculated by solving the Rayleigh integral by means of systems theory and summed to the total echo signal. This task was performed by the FieldII toolbox for MATLAB. In our paper we will present a detailed analysis of the systematic error depending on the flow structure. The error of the multi-beam mode in comparison to the single beam operation will be estimated.
Keywords: Ultrasound array, flow mapping, numerical simulation of ultrasound systems, FIELD II
  • Lecture (Conference)
    10th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (ISUD 10), 28.-30.09.2016, Tokyo, Japan
  • Contribution to proceedings
    10th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (ISUD 10), 28.-30.09.2016, Tokyo, Japan

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Publ.-Id: 24011


Entwicklung, Synthese und biologische Evaluierung von 18F-markierten Imidazopyridotriazinderivaten zur molekularen Bildgebung der Phosphodiesterase 2A im Gehirn mittels Positronen-Emissions-Tomographie

Schröder, S.
Die Phosphodiesterase 2A (PDE2A) wird in bestimmten Hirnregionen exprimiert, die bei neuropsychiatrischen und neurodegenerativen Erkrankungen, wie Depressionen, Angstzuständen und der Alzheimerkrankheit, betroffen sind. Die Entwicklung eines spezifischen 18F-markierten PDE2A-Radioliganden würde die molekulare Bildgebung dieses Enzyms im Gehirn mittels Positronen-Emissions-Tomographie (PET) ermöglichen.
Basierend auf einer Imidazopyridotriazin-Leitstruktur wird in der vorliegenden Arbeit die mehrstufige Synthese von vier neuen, fluoralkylierten Derivaten beschrieben, deren inhibitorische Wirksamkeit für die PDE2A und die PDE10A in einem Enzym-Assay getestet wurde. Die potentesten und selektivsten PDE2A-Liganden wurden für eine 18F-Markierung ausgewählt und geeignete Vorläufermoleküle dargestellt. Basierend auf einer einstufigen, nukleophilen 18F-Radiomarkierung erfolgte die Synthese von drei neuen Radioliganden, deren Potential zur PET-Bildgebung der PDE2A im Gehirn untersucht wurde.
In-vitro-autoradiographische Untersuchungen an Rattenhirnschnitten zeigten für zwei 18F-markierte Derivate eine spezifische Aktivitätsverteilung, die mit dem immunhistochemisch nachgewiesenen Expressionsmuster der PDE2A übereinstimmt. In KleintierPET-Studien mit einem dieser Radioliganden wurde jedoch in vivo eine unspezifische Aktivitätsverteilung im Maushirn beobachtet, die auf eine Akkumulation von Radiometaboliten hindeutet. In-vivo-Stabilitätsuntersuchungen zeigten einen schnellen metabolischen Abbau der Radioliganden in Mäusen sowie die Bildung hirngängiger Radiometabolite. Demnach erfüllt keines der 18F-markierten Imidazopyridotriazinderivate die Voraussetzungen zur In-vivo-Bildgebung der PDE2A im Gehirn mittels PET.
In weiterführenden Arbeiten könnte die metabolische Stabilität der entwickelten PDE2A-Liganden durch strukturelle Modifikationen erhöht werden. Die inhibitorische Potenz und Selektivität für das PDE2A-Protein sowie die Hirngängigkeit der resultierenden Derivate wären zu prüfen.
Keywords: Phosphodiesterase (2A/10A), Imidazopyridotriazin, Selektivität, molekulare Bildgebung im Gehirn, Positronen-Emissions-Tomographie
  • Doctoral thesis
    Universität Leipzig, Fakultät für Chemie und Mineralogie, 2016
    Mentor: Prof. Dr. Christoph Schneider, Prof. Dr. Peter Brust
    210 Seiten

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Publ.-Id: 24010


Theoretical prediction of mass transfer coefficients in both gas-liquid and slurry bubble columns

Nedeltchev, S.
The gas-liquid contact time has been defined in a new way (bubble surface-to-rate of surface formation) and the range of applicability of the penetration theory in both gas-liquid and slurry bubble columns has been examined. In both reactors, the mass transfer coefficients were predicted successfully not only in the homogeneous regime but also in the heterogeneous regime (superficial gas velocities up to 0.08 ms-1).
The results in the article demonstrate the importance of the geometrical characteristics (length and height) of the oblate ellipsoidal bubbles for the accurate calculation of the contact time and thus the volumetric liquid-phase mass transfer coefficient kLa. The gas-liquid interfacial area has been calculated in both reactors in the classical way, i.e. as a function of the gas holdup and inversely proportional to the Sauter-mean bubble diameter. It was found that in the gas-liquid bubble column (0.095 m in ID) the modified penetration theory was applicable to tap water, 9 organic liquids (decalin, nitrobenzene, 2-propanol, 1,4-dioxane, ethanol (99 %), tetralin, xylene, 1,2-dichloroethane, ethylene glycol) and two liquid mixtures (water-glycol and tetralin-ethanol). Tetralin was aerated with both nitrogen and helium, whereas xylene was aerated with hydrogen and helium. The correction factor introduced by Calderbank (1967) was found useful for improving the kLa predictions in 1,2-dichloroethane, ethanol (99 %), xylene(-hydrogen) and toluene-ethanol 97.2 %. In the case of a slurry bubble column, the new approach was found applicable (at low solids concentrations) to four different gas-liquid-solid systems: air-tetralin-Al2O3, air-water-Al2O3, air-water-activated carbon and air-Na2SO4-kieselguhr. It is noteworthy that in some cases (air-water-Al2O3) the new definition of the contact time was found applicable up to solids concentrations of 6.29 %. In the case of a slurry bubble column, it was found that when the theoretical kLa value is multiplied by the inverse value of the correction factor the predictions improve with about 5 %.
Finally, in the slurry bubble column the contact time was defined on the basis of the length of the micro-eddies and the kLa values in both air-water-alumina and air-water-activated carbon systems were successfully predicted. This is also a potentially good approach.
Keywords: New definition of contact time; Penetration theory applicability; Prediction of mass transfer coefficients; Organic liquids; Gas-liquid bubble columns; Slurry bubble columns

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Publ.-Id: 24009


Ab initio description of the thermoelectric properties of heterostructures in the diffusive limit of transport

Hinsche, N. F.; Rittweger, F.; Hölzer, M.; Zahn, P.; Ernst, A.; Mertig, I.
The scope of this review is to present the recent progress in the understanding of the microscopic origin of thermoelectric transport in semiconducting heterostructures and to identify and elucidate mechanisms which could lead to enhanced thermoelectric conversion efficiency. Based on first-principles calculations a consistent and convenient method is presented to fully describe the thermoelectric properties in the diffusive limit of transport for bulk systems and their associated heterostructures. While fundamentals of the functionality of phonon-blocking and electron-transmitting superlattices could be unveiled, we provide also distinct analysis and ideas for thermoelectric enhancement for two archetypical thermoelectric heterostructures based on inline image and Si/Ge. A focus was on the influence of bulk and interfacial strain, varying charge carrier concentration, temperature, and superlattice periods on the thermoelectric transport properties.
Keywords: super lattices, electronic structure, first principles, transport theory, Boltzmann theory, electric transport, heat transport, thermoelectric transport, uniaxial strain, biaxial strain

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Publ.-Id: 24008


Tests of a Compton imaging prototype in a monoenergetic 4.44 MeV photon field—a benchmark setup for prompt gamma-ray imaging devices

Golnik, C.; Bemmerer, D.; Enghardt, W.; Fiedler, F.; Hueso-González, F.; Pausch, G.; Römer, K.; Rohling, H.; Schöne, S.; Wagner, L.; Kormoll, T.
The finite range of a proton beam in tissue opens new vistas for the delivery of a highly conformal dose distribution in radiotherapy. However, the actual particle range, and therefore the accurate dose deposition, is sensitive to the tissue composition in the proton path. Range uncertainties, resulting from limited knowledge of this tissue composition or positioning errors, are accounted for in the form of safety margins. Thus, the unverified particle range constrains the principle benefit of proton therapy. Detecting prompt gamma-rays, a side product of proton-tissue interaction, aims at an on-line and non-invasive monitoring of the particle range, and therefore towards exploiting the potential of proton therapy. Compton imaging of the spatial prompt gamma-ray emission is a promising measurement approach. Prompt gamma-rays exhibit emission energies of several MeV. Hence, common radioactive sources cannot provide the energy range a prompt gamma-ray imaging device must be designed for. In this work a benchmark measurement-setup for the production of a localized, monoenergetic 4.44MeV gamma-ray source is introduced. At the Tandetron accelerator at the HZDR, the proton-capture resonance reaction 15N(p , alpha gamma4.439)12C is utilized. This reaction provides the same nuclear de-excitation (and gamma-ray emission) occurrent as an intense prompt gamma-ray line in proton therapy. The emission yield is quantitatively described. A two-stage Compton imaging device, dedicated for prompt gamma-ray imaging, is tested at the setup exemplarily. Besides successful imaging tests, the detection efficiency of the prototype at 4.44MeV is derived from the measured data. Combining this efficiency with the emission yield for prompt gamma-rays, the number of valid Compton events, induced by gamma-rays in the energy region around 4.44MeV, is estimated for the prototype being implemented in a therapeutic treatment scenario. As a consequence, the detection efficiency turns out to be a key parameter for prompt gamma-ray Compton imaging limiting the applicability of the prototype in its current realization.
Keywords: Comptonimaging; Dosimetryconceptsandapparatus; Imagereconstructioninmedicalimaging; Instrumentation for hadron therapy

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Publ.-Id: 24007


Experimental investigations of rotary electromagnetic mould stirring in continuous casting using a cold liquid metal model

Willers, B.; Barna, M.; Reiter, J.; Eckert, S.
This paper presents the experimental study of an electromagnetically stirred mould flow using a 1:3 scale acrylic glass model of the round bloom caster from voestalpine Stahl Donawitz GmbH. An electromagnetic stirrer was installed at the strand producing a rotating magnetic field (RMF). Flow measurements were performed in the eutectic alloy GaInSn at room temperature by means of the ultrasound Doppler velocimetry (UDV). Up to 10 ultrasonic transducers were employed simultaneously in order to obtain a two-dimensional reconstruction of the flow structure. The experiments contribute to a better understanding of electromagnetically stirred mould flows and provide an extensive and valuable data base for the validation of numerical methods. The flow measurements reveal a distinct influence of the secondary flow on the distribution of the angular velocity in various regions of the mould. The submerged jet intensifies this secondary motion in the upper part of the mould and thus causes a strong deformation of the free surface of the melt. The jet is deflected, bent and rotates around the strand axis.
Keywords: continuous round bloom casting; eutectic alloy GaInSn; experiments; electromagnetic stirring; rotating magnetic field; ultrasound Doppler flow measurements

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Publ.-Id: 24006


Coulomb dissociation of N-20,N-21

Röder, M.; Adachi, T.; Aksyutina, Y.; Alcantara, J.; Altstadt, S.; Alvarez-Pol, H.; Ashwood, N.; Atar, L.; Aumann, T.; Avdeichikov, V.; Barr, M.; Beceiro, S.; Bemmerer, D.; Benlliure, J.; Bertulani, C.; Boretzky, K.; Borge, M.; Burgunder, G.; Caamano, M.; Caesar, C.; Casarejos, E.; Catford, W.; Cederkall, J.; Chakraborty, S.; Chartier, M.; Chulkov, L.; Cortina-Gil, D.; Crespo, R.; Pramanik, U.; Diaz-Fernandez, P.; Dillmann, I.; Elekes, Z.; Enders, J.; Ershova, O.; Estrade, A.; Farinon, F.; Fraile, L.; Freer, M.; Freudenberger, M.; Fynbo, H.; Galaviz, D.; Geissel, H.; Gernhauser, R.; Gobel, K.; Golubev, P.; Diaz, D.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heine, M.; Heinz, A.; Henriques, A.; Holl, M.; Ickert, G.; Ignatov, A.; Jakobsson, B.; Johansson, H.; Jonson, B.; Kalantar-Nayestanaki, N.; Kanungo, R.; Kelic-Heil, A.; Knobel, R.; Kroll, T.; Krucken, R.; Kurcewicz, J.; Kurz, N.; Labiche, M.; Langer, C.; Le Bleis, T.; Lemmon, R.; Lepyoshkina, O.; Lindberg, S.; Machado, J.; Marganiec, J.; Caro, M.; Movsesyan, A.; Najafi, M.; Nilsson, T.; Nociforo, C.; Panin, V.; Paschalis, S.; Perea, A.; Petri, M.; Pietri, S.; Plag, R.; Prochazka, A.; Rahaman, M.; Rastrepina, G.; Reifarth, R.; Ribeiro, G.; Ricciardi, M.; Rigollet, C.; Riisager, K.; Rossi, D.; Saez, J.; Savran, D.; Scheit, H.; Simon, H.; Sorlin, O.; Stoica, V.; Streicher, B.; Taylor, J.; Tengblad, O.; Terashima, S.; Thies, R.; Togano, Y.; Uberseder, E.; van de Walle, J.; Velho, P.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Weigand, M.; Wheldon, C.; Wilson, G.; Wimmer, C.; Winfield, J.; Woods, P.; Yakorev, D.; Zhukov, M.; Zilges, A.; Zuber, K.
Neutron-rich light nuclei and their reactions play an important role in the creation of chemical elements. Here, data from a Coulomb dissociation experiment on N-20,N-21 are reported. Relativistic
N-20,N-21 ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment.
Using the detailed balance theorem, the N-19(n,gamma)N-20 and
N-20(n,gamma)N-21 excitation functions and thermonuclear reaction rates have been determined. The N-19(n,gamma)N-20 rate is up to a factor of 5 higher at T < 1 GK with respect to previous theoretical calculations, leading to a 10% decrease in the predicted fluorine abundance.

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Publ.-Id: 24005


Transversal Kerr effect of In1− x Mn x As layers prepared by ion implantation followed by pulsed laser annealing

Gan'Shina, E.; Golik, L.; Kun'Kova, Z.; Bykov, I.; Novikov, A.; Rukovishnikov, A.; Yuan, Y.; Zykov, G.; Böttger, R.; Zhou, S.
In1− x Mn x As (x = 6.9%) layers prepared by ion implantation and subsequent pulsed laser annealing have been studied using the magnetooptical transversal Kerr effect (TKE) and spectral ellipsometry. Ellipsometry data reveal the good crystal quality of the layers. The samples show ferromagnetic behaviour below 77 K. Near the absorption edge of the parent InAs semiconductor, large TKE values are observed. In the energy regions of the transitions in the Γ and L critical points of the InAs Brillouin zone, there are several clearly defined structures in the low-temperature TKE spectra. We have calculated the spectral dependences of the diagonal and nondiagonal components of the permittivity tensor (PT), as well as the spectrum of magnetic circular dichroism (MCD) for our samples. A number of extrema in the obtained MCD and PT spectra are close to the energies of transitions in the critical points of the parent semiconductor band structure, which confirms the intrinsic ferromagnetism of the Mn-doped InAs layers.

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Permalink: https://www.hzdr.de/publications/Publ-24004
Publ.-Id: 24004


Magnetocaloric Effect with Very Small Magnetic Hysteresis Losses of CoMn1-xTixGe Alloys

Yildirim, O.; Tozkoparan, O.; Yuzuak, E.; Elerman, Y.; Dincer, I.
The effects of Ti substitution for Mn and heat treatment on structural, magnetic and magnetocaloric properties of CoMnGe alloy have been investigated by electron microscopy, X-ray diffraction, calorimetric and magnetic measurements. According to X-ray diffraction measurements, the CoMn1-xTixGe alloys are in a single phase, hexagonal structure at room temperature. It is found that the as-cast CoMn0:95Ti0:05Ge alloy shows a magnetostructural phase transition close to room temperature. The transition shows a large magnetic entropy change and a small hysteresis in the isothermal magnetic field dependent magnetization measurements. Upon annealing, the transition temperature decreases slightly. The decrease in temperature is accompanied by a significant increase in the magnetic entropy change, i.e., magnetic entropy change at 1T field change was increased from -3.3 J/Kg.K to -6.3 J/Kg.K. Moreover, after annealing, hysteresis losses reduced significantly for delH=7 T. Accordingly, we report that the heat treatment has a significant effect on magnetocaloric properties of the CoMn0:95Ti0:05Ge alloy.
Keywords: giant magnetocaloric effect, hysteresis losses

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Permalink: https://www.hzdr.de/publications/Publ-24003
Publ.-Id: 24003


Thermodynamics data of valuable elements relevant to e-waste processing through primary and secondary copper production: a review

Shuva, M. A. H.; Rhamdhani, M. A.; Brooks, G. A.; Masood, S.; Reuter, M. A.
Waste of electronics and electrical equipment (WEEE or e-waste) can be viewed as a resource for metals, as it does not only contain the common metals like iron (Fe), aluminium (Al), lead (Pb) and copper (Cu) but also traces of precious and rare elements such as gold (Au), silver (Ag), tin (Sn), selenium (Se), tellurium (Te), platinum (Pt), palladium (Pd), tantalum (Ta), cobalt (Co) and indium (In). The recovery of these trace elements is vital, not just because it has high commercial values, but also for resources efficiency. One of the existing industrial routes for processing of e-waste is through the primary and secondary Cu smelting processes. During these processes, the trace elements are distributed in different phases, i.e. in metal/matte, slag and gas.
Different elements have different thermodynamic properties that govern the partitioning behaviour during the process. There has been a number of studies on the distribution behaviour of the trace elements relevant to primary Cu smelting (extraction of metals from virgin ores). However, there are only limited thermodynamics data relevant to secondary Cu smelting (extraction of metals from secondary/recycled sources). This paper reviews the thermodynamics data relevant for recovering the trace valuable elements from the primary Cu as well as secondary Cu smelting.
These data and knowledge provide the basis for determining the optimum conditions favourable for recovering the trace valuable elements in e-waste through the industrial Cu pyrometallurgical processing.
Keywords: E-Waste, E-Waste processing, WEEE recycling, precious metals, secondary copper

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Permalink: https://www.hzdr.de/publications/Publ-24002
Publ.-Id: 24002


Gelatin-based hydrogel degradation and tissue interaction in vivo: insights from multimodal preclinical imaging in immunocompetent nude mice

Tondera, C.; Ullm, S.; Krüger-Genge, A.; Jung, F.; Neffe, A. T.; Lendlein, A.; Klopfleisch, R.; Steinbach, J.; Neuber, C.; Pietzsch, J.
Hydrogels based on gelatin have evolved as promising multifunctional biomaterials. Gelatin is crosslinked with lysine diisocyanate ethyl ester (LDI) and the molar ratio of gelatin and LDI in the starting material mixture determines elastic properties of the resulting hydrogel. In order to investigate the clinical potential of these biopolymers, hydrogels with different ratios of gelatin and diisocyanate (3-fold (G10_LNCO3) and 8-fold (G10_LNCO8)) molar excess of isocyanate groups) were subcutaneously implanted in mice (uni- or bilateral implantation). Degradation and biomaterial tissue interaction were investigated in vivo (MRI, optical imaging, PET) and ex vivo (autoradiography, histology, serum analysis). Multimodal imaging revealed that the number of covalent net points correlate well with degradation time, which allows for targeted modification of hydrogels based on properties of the tissue to be replaced. Importantly, the degradation time was also dependent on the number of implants per animal. Despite local mechanisms of tissue remodeling no adverse tissue responses could be observed neither locally nor systemically. Finally, this preclinical investigation in immunocompetent mice clearly demonstrated a complete restoration of the original healthy tissue.
Keywords: Autoradiography ex vivo, Biomaterials, Computed tomography, Magnetic resonance imaging, Optical imaging, Positron emission tomography

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Permalink: https://www.hzdr.de/publications/Publ-24001
Publ.-Id: 24001


Specific Surface Free Energy Component Distributions and Flotabilities of Mineral Microparticles in Flotation – An Inverse Gas Chromatography Study

Rudolph, M.; Hartmann, R.
In fundamental flotation studies often the contact angle with water is used to describe wettability of a mineral surface and it is correlated with flotability. A more fundamental parameter however is the specific surface free energy related to the contact angle via Young’s equation. Inverse gas chromatography (iGC) has recently been proven to be a suitable method to determine specific surface free energy components and their distributions of particulate surfaces. In this study the pure minerals quartz (SiO2), fluoro-apatite (Ca5[F,(PO4)3]), and magnetite (Fe3O4) are examined for flotabilities and surface energy component distributions considering different methods of sample treatment and the effect of the collectors sodium oleate and dodecyl ammonium acetate. The parameter of specific net free energy of interaction between bubbles and particles immersed in water ΔGpwb resulting from the complex surface energy analyses is introduced and used to evaluate the hydrophobicity of the mineral surface in correlation to microflotation recoveries. The results lead to the hypothesis that only small fractions of the surface and their change of wettability by flotation reagent adsorption will inherently define the flotability of minerals. Consequently, the main purpose of the amphiphilic collector molecules seems to be the reduction of high specific surface free energies of small fractions of the surface that lead to a strong attraction between particle surface sites and water molecules rather than the hydrophobization of the entire mineral surface, a new paradigm in flotation science.
Keywords: flotation; inverse gas chromatography; hyrophobicity; wettability; surface free energy; heterocoagulation

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Publ.-Id: 24000


Utility of established cell lines as in vivo models for (radio)-biological research on glioblastoma

Dietrich, A.; Jakob, A.; von Neubeck, C.; Fursov, A.; Tillner, F.; Baumann, M.; Krause, M.; Bütof, R.
On the translational axis from bench to bedside, it is important to have glioblastoma (GBM) models which closely reflect the clinical situation. Such models should be suitable for investigation of clinically relevant endpoints as well as reasonable regarding costs and feasible regarding statistically necessary animal numbers. Established cell lines are comprehensively characterized and can be efficiently engrafted in large cohorts of animals. In this project, a panel of five human GBM cell lines (U 87 MG, U 251 MG, A7, LN 229, HGL21) is characterized after subcutaneous and orthotopic xenograft transplantation (take rate, radiosensitivity, histology, putative stem cell markers (SM)) to investigate their potential as suitable GBM models.
Limiting dilution assays were performed using subcutaneous injection of decreasing cell numbers and take dose 50% (TD50) was low for the five GBM models. Intrinsic radiosensitivity and effectiveness of combined radiochemotherapy was studied by irradiation of subcutaneous tumors with different dose levels. Although high amounts of cancer initiating cells are indicated by the low TD50 values the surprisingly low tumor control dose 50% (TCD50) values are in contrast to the remarkable radioresistance of GBM in patients. Intracranial transplantation of mCherry- or luciferase-positive cell variants was performed with a stereotactic frame. Weekly optical imaging and contrast-enhanced magnetic resonance imaging revealed no tumor growth for one of four investigated models. After excision, tumors were analysed histologically (Haematoxylin/Eosin, SM). Three models grew within 30-60 days to end size but the histological phenotypes generally showed weak analogy to GBM patients. Although xenograft models from established cell lines of other entities very closely mirror the clinical situation, this remains questionable for GBM.
  • Lecture (Conference)
    Summer School in Translational Cancer Research, 24.-28.10.2016, Albufeira, Portugal

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Permalink: https://www.hzdr.de/publications/Publ-23999
Publ.-Id: 23999


Synchronized helicity oscillations: A link between planetary tides and the solar cycle?

Stefani, F.; Giesecke, A.; Weber, N.; Weier, T.
Recent years have seen an increased interest in the question of whether the gravitational action of planets could have an influence on the solar dynamo. Without discussing the observational validity of the claimed correlations, we ask for a possible physical mechanism that might link the weak planetary forces with solar dynamo action. We focus on the helicity oscillations that were recently found in simulations of the current-driven, kink-type Tayler instability, which is characterized by an m=1 azimuthal dependence. We show how these helicity oscillations can be resonantl excited by some m=2 perturbation that reflects a tidal oscillation. Specifically, we speculate that the 11.07 years tidal oscillation induced by the Venus-Earth-Jupiter system may lead to a 1:1 resonant excitation of the oscillation of the alpha-effect. Finally, in the framework of a reduced, zero-dimensional alpha-Omega dynamo model we recover a 22.14-year cycle of the solar dynamo.

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Permalink: https://www.hzdr.de/publications/Publ-23998
Publ.-Id: 23998


Pressure-tank technology for steam-water two-phase flow experiments at elevated pressure and temperature

Hampel, U.; Seidel, T.; Beyer, M.; Szalinski, L.; Lucas, D.
In this contribution we describe the TOPFLOW pressure tank as an experimental facility for thermal hydraulics experiments in pressure equilibrium. The facility has been designed for studying steam-water two-phase flows at pressures of up to 50 bar. It enables to run experiments in flow domains of complex shape without paying attention to high difference pressures across the wall. The concept therefore allows us to use thin metal walls or even glass windows to observe flows in complex geometry domains with the help of IR or video camera and to considerably reduce cost and complexity of experimental settings. Several experimental studies have been performed with this technology so far. This includes counter-current flow in a reactor hot-leg mock-up, an experimental study on the thermal hydraulics of emergency core-cooling injection as well as investigations of direct contact condensation phenomena. In the following we give an introduction to the technology, details of design and operation and demonstrate its applicability to fundamental experimental studies on the direct steam condensation at jets and free surfaces.
Keywords: pressure tank technology, high pressure steam-water experiments, pressurized two-phase flow, high-speed videometry, falling jet, contact condensation
  • Contribution to proceedings
    Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH), 15.-17.06.2016, Livorno, Italy
    Proceedings of SWINTH
  • Lecture (Conference)
    Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH), 15.-17.06.2016, Livorno, Italy

Permalink: https://www.hzdr.de/publications/Publ-23996
Publ.-Id: 23996


Ultrafast X-ray tomography for two-phase flow experiments

Hampel, U.; Banowski, M.; Krepper, E.; Szalinski, L.; Beyer, M.; Lucas, D.; Barthel, F.; Wagner, M.; Bieberle, M.
Non-invasive tomographic imaging techniques are appropriate tools for the study of two-phase flow in nuclear thermal hydraulic experiments. Ultrafast X-ray tomography developed at Helmholtz-Zentrum Dresden-Rossendorf can scan two-phase flows both fast and with good spatial resolution. In this paper we introduce the tomography scanner system ROFEX and discuss its application to the study of two-phase flow in pipes – a benchmark problem for two-fluid CFD code development.
Keywords: two-phase flow, ultrafast X-ray tomography, gas holdup measurement, image processing, bubble size measurement, CFD code validation
  • Contribution to proceedings
    Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH), 15.-17.06.2016, Livorno, Italy
    Proceedings of SWINTH
  • Lecture (Conference)
    Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH), 15.-17.06.2016, Livorno, Italy

Permalink: https://www.hzdr.de/publications/Publ-23995
Publ.-Id: 23995


Millisecond thermal processing using flash lamps for the advancement of thin layers and functional coatings

Skorupa, W.; Schumann, T.; Rebohle, L.
Thermal processing in the millisecond range provides advanced, non-equilibrium annealing techniques which allow dedicated material modifications at the surface without affecting the substrate volume below. The process called flash lamp annealing (FLA) is one of the most diverse methods of short time annealing with applications ranging from the classical field of semiconductor doping to the treatment of layers on glass, polymers and other flexible substrates. It still continues to extend to other material classes and applications, and becomes of interest for an increasing number of users. Other phrases for FLA used throughout the literature are intense pulsed light sintering (IPL) or photonic curing. This review presents a short and comprehensive view of the current state of the art of FLA with a focus on functional coatings. After an introduction including historical aspects a look is taken to equipment issues as well as to the pioneering role which semiconductor processing in the framework of advanced chip technology played for the development of short time annealing. Mostly, examples of processing for photovoltaics, including doping aspects, hydrogen engineering, copper indium gallium diselenide (CIGS), silicon crystallisation on glass, and transparent conductive oxides (TCO), including indium tin oxide (ITO), zinc oxide (also Al-doped AZO) as well as inkjet printing for flexible electronics will be presented.
Keywords: flash lamp annealing (FLA), intense pulsed light sintering (IPL), semiconductors, silicon, indium tin oxide (ITO), ink jet printing

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Publ.-Id: 23994


A combined EXAFS spectroscopic and quantum chemical study on the complex formation of Am(III) with formate

Froehlich, D. R.; Kremeleva, A.; Rossberg, A.; Skerencak-Frech, A.; Koke, C.; Krüger, S.; Roesch, N.; Panack, P. J.
The complexation of Am(III) with formate in aqueous solution is studied as a function of the pH value using a combination of extended X-ray absorption fine structure (EXAFS) spectroscopy, iterative transformation factor analysis (ITFA), and quantum chemical calculations. The Am LIII-edge EXAFS spectra are analyzed to determine the molecular structure (coordination numbers; Am −O and Am −C distances) of the formed Am(III) −formate species and to track the shift of the Am(III) speciation with increasing pH.
The experimental data are compared to predictions from density functional calculations. The results indicate that formate binds to Am(III) in a monodentate fashion, in agreement with crystal structures of lanthanide formates. Furthermore, the investigations are complemented by thermodynamic speciation calculations to verify further the results obtained.

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Publ.-Id: 23993


A small animal tumour model for in vivo studies with low energy laser accelerated particles

Beyreuther, E.; Brüchner, K.; Krause, M.; Leßmann, E.; Schmidt, M.; Pawelke, J.
Introduction: The long-term aim of developing laser based acceleration of protons and ions towards clinical application requires not only substantial technological progress, but also the radiobiological characterization of the resulting ultra-short and ultra-intensive particle beam pulses. Recent in vitro data showed similar effects of laser-accelerated versus “conventional” protons on clonogenic cell survival and DNA double-strand breaks. As the proton energies currently achieved for radiobiological experiments by laser driven acceleration are too low to penetrate standard tumour models on mouse legs, a small animal tumour model allowing for the penetration of low energy protons (~20 MeV) was developed to further verify the effects in vivo.

Methods: The originally for human HNSCC FaDu established mouse ear tumour model was adapted for LN229 human glioblastoma cells. For this, cells were injected subcutaneously in the right ear of NMRI nude mice and the growing tumours were characterized with respect to growth parameters and histology. After optimizing the number of injected cells and used medium (PBS, Matrigel) the radiation response was studied by 200 kV X-ray irradiation. Furthermore, a proof-of-principle full scale experiment with laser accelerated electrons was performed to validate the FaDu tumour model under realistic, i.e. harsh, conditions at experimental laser accelerators.

Results: Both human tumour models showed a high take rate and continuous tumour growth after reaching a volume of ~5 – 10 mm3. Moreover, immunofluorescence analysis revealed that already the small tumours interact with the surrounding tissue and activate endothelial cells to form vessels. By analysing the dose dependent tumour growth curves after 200 kV X-ray treatment a realistic dose range, i.e. for inducing tumour growth delay but not tumour control, was defined for both tumour entities under investigation.
Beside this basic characterization, the comparison of the influence of laser driven and conventional (clinical Linac) electrons on the growth of FaDu tumours reveal no significant difference in the radiation induced tumour growth delay.

Conclusion: The already established mouse ear tumour model was successfully upgraded now providing stable tumour growth with high take rate for two tumour entities (HNSCC, glioblastoma) that are of interest for future proton treatment. Experiments comparing laser driven and conventional proton beams in vivo as the next step towards clinical application of laser driven particle acceleration are under way.

Acknowledgement: The work was supported by the German Government, Federal Ministry of Education and Research, grant nos. 03ZIK445 and 03Z1N511.
  • Poster
    19. Jahrestagung der Gesellschaft für Biologische Strahlenforschung e.V., 26.-28.09.2016, Erlangen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23991
Publ.-Id: 23991


Radiobiology of pulsed particle beams

Beyreuther, E.
Current radiotherapy treatment modalities like Intensity Modulated Radiation Therapy (IMRT) and gated irradiation and new technological developments like laser-driven particle accelerators include the dose delivery by short radiation pulses of high dose rate that overlap in the tumor region. The doses are accumulated over sequent radiation pulses that vary in dose fraction and time structure, which might influence the radiation response of the irradiated tissue.
In order to understand the temporal and fractionation influence of sequent beam delivery basic radiobiological experiments and translational studies to the point of clinical implementation are necessary. Starting with fundamental radiobiological principles, like radiation action and the induction of DNA damage, the lecture will also introduce some standard methods in radiobiological research. On cellular level this includes the colony formation assay as so called “golden standard” to measure the cellular survival and the quantification of molecules involved in the recognition and repair of DNA damage. One step further in the translational research chain, the observation of the radiation induced tumor growth delay on small animals will be explained.
In the second part of the lecture preceding and recent radiobiological experiments with pulsed particle beams will be presented. Beginning in the 1950s, first experiments were carried out mainly to understand the mechanism of radiation action revealing that the radiobiological effect is influenced by dose rates below 1 Gy/min, but not by higher ones. In continuation of these experiments, several studies focusing on different aspects of pulsed radiation were performed during the last two decades.
Parallel to their clinical implementation the radiobiological consequences of the sequent pulse delivery of gating and IMRT techniques were investigated highlighting the overall fraction time as critical parameter. Contrary to the dose rates of < 104 Gy/min applied for these current clinical dose delivery techniques, the laser driven techniques are characterized by pulse dose rates higher than 109 Gy/min. Taking the ultra-high pulse dose rate and other specific properties of laser driven particle beams into account the replacement of conventional accelerators for particle radiotherapy was investigated by several groups worldwide. To sum up, the hitherto performed cell and animal studies disclose that the radiobiological response to laser driven particle beams is not influenced by their ultra-high pulse dose rate.
  • Invited lecture (Conferences)
    Lasers in Medicine and Life Sciences - Lamelis Summerschool, 07.07.2016, Szeged, Hungary
  • Invited lecture (Conferences)
    Lasers in Medicine and Life Sciences - Lamelis Summerschool, 18.-21.07.2017, Szeged, Hungary

Permalink: https://www.hzdr.de/publications/Publ-23990
Publ.-Id: 23990


Magnetic-field and composition-dependent Fermiology in correlated metals

Wosnitza, J.
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    Workshop on "Fermi-surface topology and emergence of novel electronic states in strongly correlated systems", 18.07.-01.08.2016, Natal, Brasilien

Permalink: https://www.hzdr.de/publications/Publ-23989
Publ.-Id: 23989


How To Analyze The Electronic Density - An Introduction To Some Useful Tools

Patzschke, M.
Understanding a molecular system is not possible by only doing an electronic structure calculation. The results have to be analysed. In this presentation we will show some useful tools to do that.
Keywords: computational chemistry, ELF/ELI, AIM, NCI
  • Invited lecture (Conferences)
    CSC Spring School 2016, 11.03.2016, Helsinki, Finnland
  • Invited lecture (Conferences)
    CSC Spring School in Theoretical Chemistry, 17.03.2017, Helsinki, Finnland

Permalink: https://www.hzdr.de/publications/Publ-23988
Publ.-Id: 23988


Understanding and advancing the coordination and redox chemistry of the actinides

Woodall, S.; Natrajan, L.; Kaden, P.; Kerridge, A.
Sean Woodall, Louise Natrajan, Peter Kaden and Andrew Kerridge highlight recent advances in the chemistry of actinide elements that have been made possible through the collaborative efforts of industry and academia
Keywords: uranyl, neptunyl, TPIP, NMR, emmission, spectroscopy, theory, Single-crystal, x-ray, Uranium, Neptunium
  • Contribution to external collection
    in: Nuclear Future, Volume 11 issue 6, London: The Nuclear Institute CK International House, 2015, 1745 2058, 21-26

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Permalink: https://www.hzdr.de/publications/Publ-23987
Publ.-Id: 23987


Monitoring Redox Behaviour of Actinide Ions by a Combination of Emission and NMR Spectroscopy

Natrajan, L. S.; Woodall, S. D.; Swinburne, A. N.; Randall, S.; Banik, N.; Adam, C.; Di Pietro, P.; Kaden, P.; Kerridge, A.
Europe currently holds a substantial nuclear legacy arising from fission activities, with a large proportion of high activity wastes that pose a radiological threat to natural and engineered environments. The decision to dispose of these high level wastes (following separation) in a suitable geological disposal facility (GDF) has provided some of the most demanding technical, and environmental challenges facing the EU in the coming century. In order to address these issues, we have begun a programme of work to establish a comprehensive understanding of the electronic properties and physical and chemical properties of the radioactive actinide metals using state of the art emission spectroscopic techniques in combination with NMR and computational methods.[1,2]
Our approach to this is to firstly use coordination chemistry to synthesise uranium compounds with ligands that model environmentally complexed species and use optical spectroscopy to understand and map both the chemical and physical behaviour of these species (Figure 1). We have recently established that U(IV) complexes are emissive and will demonstrate that uranium in the +IV and +VI oxidation states can be detected simultaneously at relatively low concentrations. Time gating techniques enable the long lived uranyl(VI) species to be separated from the shorter lived uranium(IV) species. Furthermore, the form of the emission spectra of uranyl(VI) compounds are extremely sensitive to the nature of the ligand bound in the equatorial plane and the complex nuclearity (extent of aggregation), potentially giving a sensitive method of assessing the solution forms of uranium in environmental conditions. We will next discuss how the optical properties of these model compounds can be extended to the trans-uranics and applied to disproportionation reactions and redox events in solution.
Financial support for this research was provided by the UK Engineering and Physical Sciences Research Council (EPSRC) and The Leverhulme Trust. The authors thank the European Commission Euratom FP7 funded project
(no. 269923) EURACT-NMR for support.
1. L.S. Natrajan, Coord. Chem. Rev., 2012, 256, 1583; Coord. Chem. Rev., 2014, 266–267, 171.
2. S.D. Woodall, A.N. Swinburne, N. lal Banik, A. Kerridge, P. Di Pietro, C. Adam, P. Kaden and L.S. Natrajan, Chem. Commun., 2015, 51, 5402.
Keywords: redox, actinide, emission, NMR, spectroscopy, uranium, U(IV), U(VI), uranyl
  • Lecture (Conference)
    Second Joint Student workshop on f-Element Chemistry, 09.-10.06.2015, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23986
Publ.-Id: 23986


Luminescence spectroscopy of uranium

Steudtner, R.; Drobot, B.; Haubitz, T.; Lehmann, S.; 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.
  • Lecture (others)
    Institutskolloquium, 27.07.2016, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23985
Publ.-Id: 23985


Comparison of Model-free Methods for Paramagnetic Chemical Shifts in Lanthanide and Americium(III) Complexes

Adam, C.; Kaden, P.; Beele, B. B.; Müllich, U.; Geist, A.; Panak, P. J.
NMR spectroscopy on paramagnetic compounds is a sensitive and versatile method for structural investigations of metal-organic complexes. Furthermore, separation of the overall observed paramagnetic chemical shift into parts due to covalently transferred electron spin density (Fermi contact shift, FCS) and distance- and angle-dependent dipolar electron-nucleus spin coupling (pseudo contact shift, PCS) yields insights into metal-ligand bonding. The evaluation of the pure FCS allows to determine the share of covalance in this bond. Covalence is thought to be the reason for some ligands’ selectivity for the selective complexation of actinide over lanthanide ions in potential partitioning processes.[1,2]
Since the advent of chemical shift reagents in NMR spectroscopy in 1969, several methods for the separation of FCS and PCS have been developed.[3-6] Modell-free methods rely on calculated values like spin expectation values, geometrical constants and crystal field parameters. All these values are still unknown for actinide compounds. On the other hand, the application of methods requiring a structural modell of the complex is only possible for metal ions with a large magnetic anisotropy, like the heavy lanthanides. As Am(III) has a low magnetic anisotropy, only modell-free methods can be applied to separate the observed paramagnetic shift and to elucidate the bonding in Am(III)-N-donor complexes.
Currently, we evaluate the applicability of several approaches for separation of FCS and PCS in lanthanide complexes and their transferability to actinide compounds. This includes methods based on calculated values as well
as temperature-dependent methods. We will report on our studies on a complete set of 15N-labeled lanthanide nPr-BTP and C5-BPP complexes and discuss the applicability of the methods on actinide complexes.
This work is supported by the German Federal Ministry of Education and Research (BMBF) under contract numbers 02NUK020A and 02NUK020D.
1. C. Adam, B. B. Beele, A. Geist, U. Mullich, P. Kaden and P. J. Panak, Chemical Science, 2015, 6, 1548-1561.
2. C. Adam, P. Kaden, B. B. Beele, U. Müllich, S. Trumm, A. Geist, P. J. Panak and M. A. Denecke, Dalton Trans.,
2013, 42, 14068-14074.
3. C. F. G. C. Geraldes, S. Zhang and A. D. Sherry, Inorg. Chim. Acta, 2004, 357, 381-395.
4. C. Piguet and C. F. G. C. Geraldes, in Handbook on the Physics and Chemistry of Rare Earths, eds. J. K.A. Gschneidner,
J. C. G. Bünzli and V. K. Pecharsky, Elsevier, 2003, vol. Volume 33, pp. 353-463.
5. S. Di Pietro, S. L. Piano and L. Di Bari, Coord. Chem. Rev., 2011, 255, 2810-2820.
6. A. G. Martynov, Y. G. Gorbunova and A. Y. Tsivadze, Dalton Trans., 2011, 40, 7165-7171.
Keywords: NMR, paramagnetic, lanthanide, Americium, chemical shift, BTP, BPP
  • Lecture (Conference)
    Second Joint Student Workshop on f-Element Chemistry, 09.06.-10.07.2015, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23984
Publ.-Id: 23984


Two-phase Flow Pattern Measurements with a Wire Mesh Sensor in a Direct Steam Generating Solar Thermal Collector

Berger, M.; Mokhtar, M.; Zahler, C.; Willert, D.; Neuhäuser, A.; Schleicher, E.
At Industrial Solar’s test facility in Freiburg (Germany), two phase flow patterns have been measured by using a wire mesh sensor from Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Main purpose of the measurements was to compare observed two-phase flow patterns with expected flow patterns from models. The two-phase flow pattern is important for the design of direct steam generating solar collectors. Vibrations should be avoided in the peripheral piping, and local dry-outs or large circumferential temperature gradients should be avoided in the absorber tubes. Therefore, the choice of design for operation conditions like mass flow and steam quality are an important step in the engineering process of such a project. Results of a measurement with the wire mesh sensor are the flow pattern and the plug or slug frequency at the given operating conditions. Under the assumption of the collector power, which can be assumed from previous measurements at the same collector and adaption with sun position and incidence angle modifier, also the slip can be evaluated for a wire mesh sensor measurement. Measurements have been performed at different mass flows and pressure levels. Transient behavior has been tested for flashing, change of mass flow, and sudden changes of irradiation (cloud simuation). This paper describes the measurements and the method of evaluation. Results are shown as extruded profiles in top view and in side view. Measurement and model are compared. The tests have been performed at low steam quality, because of the limits of the test facility. Conclusions and implications for possible future measurements at larger collectors are also presented in this paper.
  • Contribution to proceedings
    SolarPACES 2016, 11.-14.10.2016, Abu Dhabi, United Arab Emirates
    AIP Conference Proceedings 1850(2017) 070003
    DOI: 10.1063/1.4984417

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Permalink: https://www.hzdr.de/publications/Publ-23983
Publ.-Id: 23983


How Theory Can Probe The Chemical Bond: The Case Of Caged U2

Patzschke, M.
"Nothing is simple in actinide chemistry" B. Roos
We present results on the intricate changes in An-An bonding in differently sized cages.
Methods used model the compounds are introduced and analysis tools are presented.
Keywords: computational chemistry, ELI, AIM, actinides, endohedral complexes
  • Invited lecture (Conferences)
    15. Koordinierungsgespräch PSI/LES - HZDR/IRE, 28.08.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23982
Publ.-Id: 23982


Computational chemistry for actinide compounds: examine the U-U bond inside fullerenes

Patzschke, M.
Computational chemistry methods to further the understanding of chemical bonds in heavy-metal systems are presented. Results obtained in this manner are presented for U_2 inside various fullerenes and the usefulness of the presented methods demonstrated.
Keywords: computational chemistry, actinides, fullerenes
  • Lecture (others)
    Eingeladener Vortrag Universität Hannover, 13.04.2016, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23981
Publ.-Id: 23981


How can Theoretical Chemistry contribute to coordination chemistry?

Patzschke, M.
We present computational chemistry methods and tools useful in the understanding of coordination compounds, especially for complexes of actinides and technetium.
Keywords: computational chemistry, actinides, technetium
  • Invited lecture (Conferences)
    8th International Workshop on “Coordination Chemistry of Metals with Medical Relevance and Supramolecular Building Blocks“, 26.05.2016, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23980
Publ.-Id: 23980


Probing the chemical bond: The case of caged U_2

Patzschke, M.
We present computational results on the "unwilling" bonding of U2 in fullerenes. We explain the nature of the strong bond to cage and the weak U-U bond.
We show how this An-An bond changes whith cage size. We will show how understanding of this special bonding might help in development of An-An forcefields.
Keywords: computational chemistry, DFT, CASPT2, ELF, AIM, actinides, fullerenes
  • Invited lecture (Conferences)
    GöCH Vortrag Linz, 29.02.2016, Linz, Österreich

Permalink: https://www.hzdr.de/publications/Publ-23979
Publ.-Id: 23979


Uranyl Spectroscopy - Do We Know Everything?

Patzschke, M.
Highly accurate thermodynamic data is necessary to model the behaviour of toxic/radiotoxic species in the environment. We show for the uranyl system, that TRLFS/CW spectroscopy in combination with theory is a powerful tool for such predictions.
Keywords: computational chemistry, TRLFS, PARAFAC
  • Invited lecture (Conferences)
    IX MMQC Mariapfarr Workshop on Theoretical Chemistry, 26.02.2016, Mariapfarr, Österreich

Permalink: https://www.hzdr.de/publications/Publ-23978
Publ.-Id: 23978


Using ADF in computational actinide chemistry

Patzschke, M.
ADF (Amsterdam Density Functional code) is a quantum chemical code that allows computations for molecules containing all elements in the periodic table. We will present its capabilities, demonstrate its usage and instruct the participants to set up their own calculations.
Keywords: computational chemsitry, DFT, actinides
  • Invited lecture (Conferences)
    ThUL school 2105, 28.09.2015, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23977
Publ.-Id: 23977


Visualising Your Results - An Introduction to VMD

Patzschke, M.
Visualising the results of quantum chemical computations is an important part of research. Producing high quality graphics becomes more and more a required skill. We will present the use of the program VMD, show applications and teach students to use it on their own.
Keywords: computational chemistry, visualisation, VMD
  • Invited lecture (Conferences)
    CSC Spring School 2015, 12.03.2015, Helsinki, Finnland
  • Invited lecture (Conferences)
    CSC Spring School 2016, 10.03.2016, Helsinki, Finnland
  • Invited lecture (Conferences)
    CSC Spring School in Theoretical Chemistry, 17.03.2017, Helsinki, Finnland

Permalink: https://www.hzdr.de/publications/Publ-23976
Publ.-Id: 23976


Quantum Chemistry Workshop - using Orca & Gabedit

Patzschke, M.
The capabilities of the qc-code Orca and the versatile GUI gabedit are presented. Calculations with Orca are demonstrated and the students are taught to set up their own calculations.
Keywords: computational chemistry, Orca
  • Invited lecture (Conferences)
    CSC Spring School 2015, 11.03.2015, Helsinki, Finnland
  • Invited lecture (Conferences)
    CSC Spring School 2016, 09.03.2016, Helsinki, Finnland
  • Invited lecture (Conferences)
    CSC Spring School in Theoretical Chemistry, 13.-17.03.2017, Helsinki, Finland

Permalink: https://www.hzdr.de/publications/Publ-23975
Publ.-Id: 23975


Planned Projects of the New Theory- Group in Rossendorf

Patzschke, M.
We present research projects of the newly established computational chemistry group at the FWO.
Keywords: computational chemistry, actinides
  • Lecture (others)
    Helmholtz-Koordinierungstreffen 2015, 04.03.2015, Jülich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23974
Publ.-Id: 23974


Computational Methods for f-Elements

Patzschke, M.
Theoretical chemistry is a comparatively new research area in chemistry. In the last 100 years enormous progress has been made in understanding the electronic structures of molecules. Almost every publication nowadays has a theory section. This means, that all chemists have to understand the basics of quantum chemistry.

The f-elements, and especially the actinides are very challenging to work with in the laboratory, to make matters worse, they are even very challenging to treat computationally. The reason for this is threefold:

1) Each actinide atom adds a lot of electrons to the system and as computational methods get much more time consuming when the amount of electrons in the system is increased, special care has to be taken to make the computations as efficient as possible.
2) Actinides, especially the later ones in low oxidation states contain many unpaired electrons, making many of the actinide-containing species multi-reference cases, where simple computational methods do not work.
3) For heavy elements, the expectation value of the speed of the innermost electrons approaches the speed of light. This means, normal quantum-chemical methods as used for light elements will not work.

In the light of the above mentioned points we will have a look at the methods available in the quantum chemical treatment of f-elements. We will spend some time looking at density-functional theory, the work-horse of computational chemistry. Special care will be taken to explain were this theory excels and what its shortcomings are.

We will then move to so called multi-reference methods, useful for treating actinide systems. Here the difference between static and dynamic correlation will be explained and methods to treat both will be introduced. The concept of an active space will be presented in some detail and guidelines for a successful choice of this active space will be given.

Finally, we will spend some time looking at the fundamental ideas of relativistic quantum chemistry and the effect of relativity on chemical properties. In this part we will also discuss the special requirements relativistic calculations impose.
Keywords: computational chemistry, actinides
  • Invited lecture (Conferences)
    Second Joint Student Workshop on f-Element Chemistry, 09.06.2015, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23973
Publ.-Id: 23973


Investigating Catalytic Activity with DFT

Patzschke, M.
We present computational results for the regioselectivity of the Pauson-Khand reaction and the computationally validated catalytic cycle of the gold(III) catalyzed enynamine – cyclopentadiene cycloisomerisation.
Keywords: computational chemistry, DFT, CASPT2, catalysis
  • Invited lecture (Conferences)
    IXth Workshop on Modern Methods in Quantum Chemistry, 26.02.2015, Mariapfarr, Österreich

Permalink: https://www.hzdr.de/publications/Publ-23972
Publ.-Id: 23972


DFT in the f-block

Patzschke, M.
Computational chemistry has become an important tool. The most popular approaches are based on the electronic density, methods known as DFT calculations. We review the basic principles as well as the applicability to f-element systems.
Keywords: Computational chemistry, DFT, f-elements
  • Invited lecture (Conferences)
    EUFEN 4, 09.04.2015, Lissabon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-23971
Publ.-Id: 23971


Magnetically induced ring currents in actinide extraction ligand systems

Patzschke, M.
Aromaticity is an old concept in chemistry. With newly developed metods, like GIMIC, it is possible to quantify this concept. With this method the ring current induced by an external magnetic field is evaluated (in nA/T), paramagnetic and diamagnetic contributions can be seen and the stabilisation due to aromaticity predicted. We present latest results for some typical actinide extraction ligands like BTP and look on the influence of complexation on these currents.
Keywords: Computational chemistry, actinides, aromaticity
  • Lecture (others)
    Eingeladener Vortrag TU München, 05.02.2015, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23970
Publ.-Id: 23970


Nanoparticle dispersion in liquid metals by electromagnetically induced acoustic cavitation

Kaldre, I.; Bojarevics, A.; Grants, I.; Beinerts, T.; Kalvans, M.; Milgravis, M.
Ceramic nanoparticle dispersion in metallic matrix is a technical challenge to produce class of composite materials-Metal matrix nano-composites (MMNC). Current powder metallurgy has limitations producing these materials. Process is time consuming and dimensions of ingots are limited. Aim of this study is to investigate experimentally the effect of magnetically induced cavitation applied for the purpose of nanoparticle dispersion in liquid metals. We present a contactless electromagnetic method to induce ultrasound and disperse particles in liquid metals by simultaneously applied steady and alternating magnetic fields. The oscillating magnetic force due to the azimuthal induction currents and the axial magnetic field excites power ultrasound in the sample. If the fields are sufficiently high then it is possible to achieve the acoustic cavitation threshold in liquid metals. Cavitation bubble collapses create intense microscale jets, which can break nanoparticle agglomerates and disperse them. Cavitation bubble collapses are known to create microscale jets with a potential to break nanoparticle agglomerates and disperse them. The samples are solidified under the contactless ultrasonic treatment and later analyzed by electron microscopy and energy-dispersive X-ray spectroscopy (EDX). It is observed that SiC nanoparticles are dispersed in an aluminum magnesium alloy, whereas in tin the same particles remain agglomerated in micron-sizedclusters despite a more intense cavitation.
Keywords: Nanaoparticles, Metal matrix composites (MMCs), Cavitation, High magnetic field, Power ultrasound

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Permalink: https://www.hzdr.de/publications/Publ-23969
Publ.-Id: 23969


Scalable critical-path analysis and optimization guidance for hybrid MPI-CUDA applications

Schmitt, F.; Dietrich, R.; Juckeland, G.
The use of accelerators in heterogeneous systems is an established approach in designing petascale applications. Today, Compute Unified Device Architecture (CUDA) offers a rich programming interface for GPU accelerators but requires developers to incorporate several layers of parallelism on both the CPU and the GPU. From this increasing program complexity emerges the need for sophisticated performance tools. This work contributes by analyzing hybrid MPI-CUDA programs for properties based on wait states, such as the critical path, a metric proven to identify application bottlenecks effectively. We developed a tool to construct a dependency graph based on an execution trace and the inherent dependencies of the programming models CUDA and Message Passing Interface (MPI). Thereafter, it detects wait states and attributes blame to responsible activities. Together with the property of being on the critical path, we can identify activities that are most viable for optimization. To evaluate the global impact of optimizations to critical activities, we predict the program execution using a graph-based performance projection. The developed approach has been demonstrated with suitable examples to be both scalable and correct. Furthermore, we establish a new categorization of CUDA inefficiency patterns ensuing from the dependencies between CUDA activities.
Keywords: GPGPU, CUDA, MPI, wait states, critical-path analysis, performance analysis, performance optimization

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Permalink: https://www.hzdr.de/publications/Publ-23968
Publ.-Id: 23968


Advanced characterisation and optical simulation for the design of solar selective coatings based on carbon:transition metal carbide nanocomposites

Heras, I.; Krause, M.; Abrasonis, G.; Pardo, A.; Endrino, J. L.; Guillén, E.; Escobar-Galindo, R.
Solar selective coatings based on carbon transition metal carbide nanocomposite absorber layers were designed. Pulsed filtered cathodic arc was used for depositing amorphous carbon: metal carbide (a-C:MeC, Me = V, Mo) thin films. Composition and structure of the samples were characterized by ion beam analysis, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The optical properties were determined by ellipsometry and spectrophotometry. Three effective medium approximations (EMA), namely Maxwell-Garnett, Bruggeman, and Bergman, were applied to simulate the optical behaviour of the nanocomposite thin films. Excellent agreement was achieved between simulated and measured reflectance spectra in the entire wavelength range by using the Bergman approach, where in-depth knowledge of the nanocomposite thin film microstructure is included. The reflectance is shown to be a function of the metal carbide volume fraction and its degree of percolation, but not dependent on whether the nanocomposite microstructure is homogeneous or a self-organized multilayer. Solar selective coatings based on an optimized a-C:MeC absorber layer were designed exhibiting a maximum solar absorptance of 96% and a low thermal emittance of ~5 and 15% at 25 and 600ºC, respectively. The results of this study can be considered as predictive design tool for nanomaterial-based optical coatings in general.
Keywords: Solar selective coatings, Amorphous carbon:transition metal carbides, Effective Medium approximation, Pulsed filtered cathodic vacuum arc, Bergman representation

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Permalink: https://www.hzdr.de/publications/Publ-23967
Publ.-Id: 23967


Thermally induced formation of metastable nanocomposites in amorphous Cr-Zr-O thin films deposited using reactive ion beam sputtering

Rafaja, D.; Wüstefeld, C.; Abrasonis, G.; Braeunig, S.; Baehtz, C.; Hanzig, F.; Dopita, M.; Krause, M.; Gemming, S.
Successive crystallization ofamorphous Cr-Zr-O thin films, formation of the (Cr,Zr)2O3/(Zr,Cr)O2 nanocomposites and the thermally induced changes in the hexagonal crystal structure of metastable (Cr,Zr)2O3 were investigated by means of in situ high-temperature synchrotron diffraction experiments up to 1100 °C. The thin films were deposited at room temperature by using reactive ion beam sputtering, and contained 3–15 at.% Zr. At low Zr concentrations, chromium-rich (Cr,Zr)2O3 crystallized first, while the crystallization of zirconium-rich (Zr,Cr)O2 was retarded. Increasing amount of zirconium shifted the onset of crystallization in both phases to higher temperatures. For 3 at.% of zirconium in amorphous Cr-Zr-O, (Cr,Zr)2O3 crystallized at 600 °C. At 8 at.% Zr in the films, the crystallization of (Cr,Zr)2O3 started at 700 °C. At 15 at.% Zr, the Cr-Zr-O films remained amorphous up to the annealing temperature of 1000 °C.Metastable hexagonal (Cr,Zr)2O3 accommodated up to ~3 at.% Zr. Excess of zirconium formed tetragonal zirconia, which was stabilized by chromium.
Keywords: Metastable oxides In situ synchrotron diffraction Crystallization Reactive ion beam sputtering Rutherford backscattering spectrometry

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Permalink: https://www.hzdr.de/publications/Publ-23966
Publ.-Id: 23966


Evaluation of the enantiomer specific biokinetics and radiation doses of [18-F]-fluspidine – a new tracer in clinical translation for imaging of σ1 receptors

Kranz, M.; Sattler, B.; Wüst, N.; Deuther-Conrad, W.; Patt, M.; Meyer, P. M.; Fischer, S.; Donat, C. K.; Wünsch, B.; Hesse, S.; Steinbach, J.; Brust, P.; Sabri, O.
The enantiomers of [18F]-fluspidine, recently developed for imaging of σ1 receptors, exhibit promising and distinct pharmacokinetics which makes them attractive for different clinical questions. To support their clinical translation, human radiation dosimetry of (S)-(-)-[18F]-fluspidine and (R)-(+)-[18F]-fluspidine was estimated from ex vivo biodistribution and PET/MR imaging in mice after extrapolation to human scale. The results were validated by a first-in-human study where time-dependent activity data of (S)-(-)-[18F]-fluspidine was obtained by PET/CT. The time-activity curves were exponentially fitted and the integral used in OLINDA to calculate organ doses (ODs) and the effective dose (ED). According to different biokinetics of (S)-(-)-[18F]-fluspidine and (R)-(+)-[18F]-fluspidine, the EDs differ significantly with values of 12.9 µSv/MBq and 14.0 µSv/MBq (p<0.025, image-derived data of mice), respectively, as observed by ex vivo biodistribution too. In the human study, the ED was calculated to be 21.0 µSv/MBq. The preclinical dosimetry reveals the ED for [18F]-fluspidine comparable with other 18F-labeled PET imaging agents, despite differences of the EDs due to enantiomer specific kinetics. The first-in-human study confirmed that the radiation risk of (S)-(-)-[18F]-fluspidine imaging is within accepted limits. However, the ED in humans is underestimated when using preclinical imaging for dosimetry which needs to be considered when applying for first-in-human studies.

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Permalink: https://www.hzdr.de/publications/Publ-23965
Publ.-Id: 23965


[18F]FDG-PET/CT based response assessment of stage IV non-small cell lung cancer treated with paclitaxel-carboplatin-bevacizumab with or without nitroglycerin patches

de Jong, E.; van Elmpt, W.; Leijenaar, R.; Hoekstra, O.; Groen, H.; Smit, E.; Boellaard, R.; van der Noort, V.; Troost, E.; Lambin, P.; Dingemans, A.
Purpose
Nitroglycerin (NTG) is a vasodilatating drug, which increases tumor blood flow and consequently decreases hypoxia. Therefore, changes in [18F]fluorodeoxyglucose-positron emission tomography ([18F]FDG-PET) uptake pattern may occur. In this analysis, we investigated the feasibility of [18F]FDG-PET for response assessment to paclitaxel-carboplatin-bevacizumab (PCB) treatment with and without NTG patches. And we compared the [18F]FDG-PET response assessment to RECIST response assessment and survival.
Methods
A total of 223 stage IV non-small cell lung cancer (NSCLC) patients were included in a phase II study (NCT01171170) randomizing between PCB treatment with or without NTG patches. For 60 participating patients a baseline and a second [18F]FDG-PET/CT scan, performed between day 22-24 after the start of treatment, were available. Tumor response was defined as a 30% decrease in CT- and PET-parameters, and was compared to RECIST response at week 6. The predictive value of these assessments for progression free survival (PFS) and overall survival (OS) was assessed with and without NTG.
Results
A 30% decrease in SUVpeak assessment identified more patients as responders compared to a 30% decrease in CTdiameter assessment (73% vs. 18%), however, this was not correlated to OS (SUVpeak30 p=0.833; CTdiameter30 p=0.557). Changes in PET parameters between the baseline and the second scan were not significant different for the NTG group compared to the control group (p-value range 0.159 - 0.634). The CT (part of the [18F]FDG-PET/CT) based parameters showed a significant difference between the baseline and the second scan for the NTG group compared to the control group (CT diameter decrease of 7 ± 23% vs. 19 ± 14%, p=0.016, respectively).
Conclusions
The decrease in tumoral FDG uptake in advanced NSCLC patients treated with chemotherapy with and without NTG did not differ between both treatment arms. Early PET-based response assessment showed more tumor responders than CT-based response assessment (part of the [18F]FDG-PET/CT), this was not correlated to survival. This might be due to timing of the [18F]FDG-PET shortly after the bevacizumab infusion.
Keywords: NSCLC, FDG-PET, bevacizumab

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Permalink: https://www.hzdr.de/publications/Publ-23964
Publ.-Id: 23964


Precise tuning of the Curie temperature of (Ga,Mn)As-based magnetic semiconductors by hole compensation: Support for valence-band ferromagnetism

Zhou, S.; Li, L.; Yuan, Y.; Rushforth, A. W.; Chen, L.; Wang, Y.; Boettger, R.; Heller, R.; Zhao, J.; Edmonds, K. W.; Campion, R. P.; Gallagher, B. L.; Timm, C.; Helm, M.
For the prototype diluted ferromagnetic semiconductor (Ga,Mn)As, there is a fundamental concern about the electronic states near the Fermi level, i.e., whether the Fermi level resides in a well-separated impurity band derived from Mn doping (impurity-band model) or in the valence band that is already merged with the Mn-derived impurity band (valence-band model). We investigate this question by carefully shifting the Fermi level by means of carrier compensation. We use helium-ion implantation, a standard industry technology, to precisely compensate the hole doping of GaAs-based diluted ferromagnetic semiconductors while keeping the Mn concentration constant. We monitor the change of Curie temperature (TC) and conductivity. For a broad range of samples including (Ga,Mn)As and (Ga,Mn)(As,P) with various Mn and P concentrations, we observe a smooth decrease of TC with carrier compensation over a wide temperature range while the conduction is changed from metallic to insulating. The existence of TC below 10K is also confirmed in heavily compensated samples. Our experimental results are naturally explained within the valence-band picture.
Keywords: Magnetic semiconductors; Ion irradiation; Fermi level

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Permalink: https://www.hzdr.de/publications/Publ-23963
Publ.-Id: 23963


Magnetocapacitance in CdCr1.8In0.2S4 Single Crystal Annealed in Cadmium Vapor

Xie, Y.; Chen, X.; Zhang, Z.; Song, W.; Zhou, S.; Yang, Z.
CdCr2S4 single crystal was reported by Hemberger et al. to be multiferroic with the evidences of relaxor ferroelectricity and colossal magnetocapacitance (CMC), but whether these effects are intrinsic is under debate. Recently, we reported a one-to-one correlation between CMC and colossal magnetoresistance (CMR) in CdCr2S4 polycrystalline samples, and argued that CMC could be explained by the superposition of the CMR and the Maxwell-Wagner effects. In this paper, we further examined the magnetic, dielectric, and electric transport properties of CdCr2S4 and CdCr1.8In0.2S4 single crystals before and after annealing in cadmium vapor. The CdCr2S4 single crystal sample has no relaxor ferroelectricity and CMC, and in contrast to the CdCr2S4 single crystal reported by Hemberger et al., only the annealed CdCr1.8In0.2S4 displays CMC, but still does not exhibit the relaxor behavior. At the same time, it also shows CMR. All these results are in accordance with the results of our polycrystalline samples, and further confirm the resistive origin of the CMC in the CdCr2S4 system.
Keywords: Magnetocapacitance; Maxwell-Wagner effect; mangetoresistance; spinel

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Permalink: https://www.hzdr.de/publications/Publ-23962
Publ.-Id: 23962


Unraveling carrier’s kinetics in tuning the ferromagnetism of transparent Zn0.95Co0.05O epitaxial films

Satyarthi, P.; Ghosh, S.; Sekhar, B. R.; Wang, Y.; Zhou, S.; Skorupa, I.; Bürger, D.; Schmidt, H.; Srivastava, P.
The search of transparent conducting and ferromagnetic properties in Zn1−xCoxO based diluted magnetic semiconductor is explored either by chemically alloying the different concentration (x) of Co or by n-type co-doping. The present work aims to explore the electrical conduction process at variable temperatures, in order to probe the room and low temperature ferromagnetism triggered in transparent Zn0.95Co0.05O films using inert xenon ion irradiation. The origin of the paramagnetism and the tunable ferromagnetism in transparent Zn0.95Co0.05O films is explained from different degree of concentric bound magnetic polarons (BMPs) stabilization inside variable range hopping spheres through implication of strongly and weakly bound carriers to O/Zn related lattice defects and tetrahedrally substituted Co2+ ions. The paramagnetic behavior in as deposited Zn0.95Co0.05O film arises from the smallest density of isolated concentric BMPs resulted mainly from marginal concentration of strongly localized carrier due to its highly insulating nature. The progressive enhancement in strongly localized carriers in post irradiated Zn0.95Co0.05O films as a function of fluence results in overlapping of static concentric BMPs to trigger onset of ferromagnetism. The strength of ferromagnetism is found to be maximal at a particular density of concentric BMPs optimized from the highest concentration of strongly localized carriers in insulating regime and substantial substituted Co2+ ions. Further enhancement in carrier concentration and reduction in substituted Co2+ ions is detrimental to ferromagnetism owing to non-static concentric BMPs percolation from the presence of weakly localized nature of carriers in intermediate regime.
Keywords: Transparent conducting oxides; Dilute magnetic semiconductors; Opto-spintronics

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Permalink: https://www.hzdr.de/publications/Publ-23961
Publ.-Id: 23961


Leadership-Scale, Open-Source, Full-Scale In-Situ Simulations Beyond GPUs and PFlop/s with PIConGPU

Huebl, A.; Widera, R.; Zenker, E.; Worpitz, B.; Burau, H.; Pausch, R.; Grund, A.; Matthes, A.; Garten, M.; Eckert, C.; Debus, A.; Kluge, T.; Cowan, T.; Schramm, U.; Bussmann, M.
We present the scientific workflow and applications in plasma physics of the performance portable, open source, 3D3V electro-magnetic, many-core particle-in-cell (PIC) code PIConGPU. With an open and modern software environment, PIConGPU is already suited for the largest available supercomputers today and has now evolved to a single-source hardware independent PIC code running on conventional x86 architectures, upcoming OpenPOWER CPUs, many-core accelerators and as before, GPUs.
Keywords: PIC, GPGPU, PIConGPU, Simulation, LPA, OpenSource, Exascale
  • Poster
    17th Advanced Accelerator Concepts Workshop (AAC 2016), 31.07.-05.08.2016, National Harbor, Maryland, United States of America

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Permalink: https://www.hzdr.de/publications/Publ-23960
Publ.-Id: 23960


Quasi Mono-Energetic Ion Acceleration from Mass-Limited Targets with Realistic Laser Contrast

Huebl, A.; Kluge, T.; Widera, R.; Hilz, P.; Schreiber, J.; Cowan, T.; Schramm, U.; Bussmann, M.
We present first-principle, leadership-scale particle-in-cell simulations drawing a complete and consistent picture of the complex ion acceleration from truly isolated, spherical, mass-limited targets driven by a 500fs high-power laser with realistic contrast. Performing large-scale 3D3V simulations with PIConGPU on the Titan supercomputer allowed to correctly predict experimental observables such as charge, diction and divergence of generated mono-energetic, pencil-like proton beams that were otherwise unreproducible in simulations with reduced geometry or resolution.
Keywords: LPA, Ion Acceleration, Mass Limited, Paul Trap, PHELIX, PIC, Simulation, CUDA, PIConGPU, laser contrast
  • Invited lecture (Conferences)
    17th Advanced Accelerator Concepts Workshop (AAC 2016), 31.07.-05.08.2016, National Harbor, Maryland, United States of America

Permalink: https://www.hzdr.de/publications/Publ-23959
Publ.-Id: 23959


Beam transport and monitoring of laser-driven particle beams

Pawelke, J.
no abstract available
  • Invited lecture (Conferences)
    ELI-ALPS Seminar, 08.07.2016, Szeged, Hungary

Permalink: https://www.hzdr.de/publications/Publ-23958
Publ.-Id: 23958


Radiotherapy with laser-driven beams

Pawelke, J.
no abstract available
  • Invited lecture (Conferences)
    Lasers in Medicine and Life Sciences (LAMELIS), Advanced Summer School for Students in Medicine and Physics, 12.-21.07.2017, Szeged, Hungary
  • Invited lecture (Conferences)
    Lasers in Medicine and Life Sciences (LAMELIS), Advanced Summer School for Students in Medicine and Physics, 30.06.-09.07.2016, Szeged, Hungary

Permalink: https://www.hzdr.de/publications/Publ-23957
Publ.-Id: 23957


Second harmonic generation of diamond-blade diced KTiOPO4 ridge waveguides

Chen, C.; Rüter, C.; Volk, M.; Chen, C.; Shang, Z.; Lu, Q.; Akhmadaliev, S.; Zhou, S.; Chen, F.; Kip, D.
We report on the fabrication of ridge waveguides in KTiOPO4 nonlinear optical crystals through carbon ion irradiation followed by precise diamond blade dicing. The diced side-walls have low roughness, which allows for low propagation loss of ~1dB/cm in fabricated of ridges. The waveguide property investigation has been performed at 1064 nm as well as 532 nm, showing good guidance at both TE and TM polarizations. Based on type II phase matching configuration, efficient second harmonic generation of green light at room temperature has been realized. High conversion efficiencies of ~1.12%W^−1 and ~12.4% have been obtained for frequency doubling under the pump of continuous-wave (CW) and pulsed fundamental waves at 1064 nm, respectively.
Keywords: Waveguides; Nonlinear optical materials; Nonlinear optics; Integrated optics

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Permalink: https://www.hzdr.de/publications/Publ-23956
Publ.-Id: 23956


A highly-parallel Monte-Carlo-Simulation of X-Ray-Scattering using a Particle-Mesh-Code on GPUs (Zwischenpräsentation Diplomarbeit)

Grund, A.
Die Wechselwirkung extrem intensiver kurzer Laserpulse mit Festkörpern verspricht einige interessante Anwendungen und Einsichten in grundlegende Plasmaphysik. Eine Anwendung besteht darin, schnelle, durch die Laser-Plasmawechselwirkung erzeugte Ionen z.B. zur schonenderen und zielgerichteteren Behandlung von Krebspatienten zu nutzen als das mit klassischer Photonen-Strahlentherapie möglich wäre. Während die Ergebnisse der Wechselwirkung, nämlich die Ionenstrahlen, experimentell leicht untersuchbar sind, bleibt die Wechselwirkung selbst auf Grund der sehr kurzen Zeit- und Raumskalen und der Undurchdringlichkeit von Festkörpern für sichtbares Licht nur für Computersimulationen zugängig. Röntgenstreuexperimente werden als mögliche Lösung gesehen. Allerdings wird die Streuung der zur Beobachtung eingesetzten Röntgenstrahlen bislang hauptsächlich durch Fouriertransformationen angenähert, was insbesondere bei Mehrfachstreuung und zeitveränderlichen Dichten und Laserprofilen nicht mehr hinreichend ist. Im Rahmen dieser Arbeit wird eine Softwarelösung entwickelt, in der Propagation und Streuung der Röntgenstrahlung in einer Probe mit Monte-Carlo-Methoden simuliert werden und dadurch prinzipiell die vollen physikalischen Elementarprozesse berücksichtigt werden können. Durch die Nutzung von GPUs und einen skalierbaren Ansatz auf Basis der Bibliothek libPMacc können auch große Volumina verarbeitet werden. Da die numerische Genauigkeit eine große Rolle bei der Auswahl der Datentypen spielt, die wiederum die Geschwindigkeit beeinflusst, wird diese näher betrachtet. Anhand dieser Analyse werden die jeweils geeignetsten Lösungen vorgestellt und implementiert.
  • Other
    TU Dresden, 2016
    Mentor: Prof. Dr. W. Nagel, Dr. T. Kluge
    19 Seiten

Permalink: https://www.hzdr.de/publications/Publ-23955
Publ.-Id: 23955


Photo-neutron reaction cross-sections for natMo in the bremsstrahlung end-point energies of 12 - 16 and 45 - 70 MeV

Naik, H.; Kim, G. N.; Kapote Noy, R.; Schwengner, R.; Kim, K.; Zaman, M.; Shin, S. G.; Gey, Y.; Massarczyk, R.; John, R.; Junghans, A.; Wagner, A.; Cho, M.-H.
The nat Mo(γ, x n)90,91,99 Mo reaction cross-sections were experimentally determined for the bremsstrahlung end-point energies of 12, 14, 16, 45, 50, 55, 60 and 70 MeV by activation and off-line gamma-ray spectrometric technique and using the 20 MeV electron linac (ELBE) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany, and the 100 MeV electron linac at the Pohang Accelerator Laboratory (PAL), Pohang, Korea. The nat Mo(gamma, x n)88,89,90,91,99 Mo reaction cross-sections as a function of photon energy were also calculated using the computer code TALYS 1.6. The flux-weighted average cross-sections were obtained from the literature data and the calculated values of TALYS based on mono-energetic photons and are found to be in general agreement with the present results. The flux-weighted average experimental and theoretical cross-sections for the nat Mo(γ, x n)88,89,90,91,99 Mo reactions increase with the bremsstrahlung end-point energy, which indicates the role of excitation energy. After a certain energy, the individual nat Mo(gamma, x n) reaction cross-sections decrease with the increase of bremsstrahlung energy due to opening of other reactions, which indicates sharing of energy in different reaction channels. The 100 Mo(gamma, n) reaction cross-section is important for the production of 99 Mo, which is a probable alternative to the 98 Mo(n, gamma) and 235 U(n, f) reactions.
Keywords: Photonuclear reactions, photodissociation, cross sections.

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Permalink: https://www.hzdr.de/publications/Publ-23954
Publ.-Id: 23954


Covellite CuS as a matrix for “invisible” gold: X-ray spectroscopic study of the chemical state of Cu and Au in synthetic minerals

Tagirov, B. R.; Trigub, A. L.; Kvashnina, K. O.; Shiryaev, A. A.; Chareev, D. A.; Nickolsky, M. S.; Abramova, V. D.; Kovalchuk, E. V.
Geological processes leading to formation of sulfide ores often result in precipitation of gold-bearing sulfides which can contain high concentrations of this metal in “invisible” (or ”refractory”) state. Covellite (CuS) is ubiquitous mineral in many types of the ore deposits, and numerous studies of the natural ores show that covellite can contain high concentrations of Au. At the same time, Au-bearing covellite withstands cooling in contrast to other minerals of the Cu-Fe-S system (chalcocite, bornite, chalcopyrite), where Au exsolves at low temperatures. This makes covellite a convenient model system for investigation of the chemical state (local environment and valence) of the “invisible” Au in copper-sulfide ores (copper-porphyry, epithermal, volcanogenic massive sulfide, SEDEX deposits). Therefore, it is necessary to determine the location of Au in the covellite matrix as it will have important implications for the methods employed by mineral processing industry to extract Au from sulfide ores. Here we investigate the chemical state of Cu and Au in synthetic covellite containing up to 0.3 wt.% of Au in the “invisible” state. The covellite crystals were synthesized by hydrothermal and salt flux methods. Formation of the chemically bound Au is indicated by strong dependence of the concentration of Au in covellite on the sulfur fugacity in the experimental system (d(log C(Au))/d(log f(S2)) ∼ 0.65). The Au concentration of covellite grows with increasing temperature from 400 to 450 °C, whereas further temperature increase to 500 °C has only minor effect. The synthesized minerals were studied using X-ray absorption fine structure spectroscopy (XAFS) in high energy resolution fluorescence detection (HERFD) mode. Ab initio simulations of Cu K edge XANES spectra show that the Cu oxidation state in two structural positions in covellite (tetrahedral and triangular coordination with S atoms) is identical: the total loss of electronic charge for the 3d shell is ∼ 0.3 for both positions of Cu. This result is confirmed by theoretical analysis of electron density performed using quantum theory of atoms in molecules (QTAIM). Modeling of the Au L3 edge EXAFS/XANES spectra showed that Au in covellite exists in the form of the isomorphous solid solution formed by substitution for Cu atoms in triangular coordination with the Me-S distance in the first coordination shell increased by 0.18 Å relative to the pure CuS structure. The “formal” oxidation state of Au in covellite is +1. The Bader partial atomic charge for Au in covellite is lower than the charge of Cu (+0.2 e vs. +0.5 e) indicating that the degree of covalency for the Au-bearing covellite is higher than that of pure CuS. The analysis of electronic density of states shows that this structural position of Au results in strong interactions between hybridized Au s,p,d, S p, and Cu p,d orbitals. Such chemical bonding of Au to S and Cu can result in the formation of Au-bearing solid solution with other minerals in the Cu-Fe-S system.

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Permalink: https://www.hzdr.de/publications/Publ-23953
Publ.-Id: 23953


Curvilinear magnetism

Makarov, D.
Extending planar two-dimensional structures into the three-dimensional space has become a general trend in electronics, photonics, plasmonics and magnetics. In magnetism, a consequence of the curvilinear geometry is the appearance of novel curvature-driven effects including magnetochiral effects and topologically induced magnetization patterning, resulting in theoretically predicted unlimited domain wall velocities, chirality symmetry breaking and Cherenkov-like effects for magnons. These theoretical predictions and the application potential of 3D-shaped magnetic objects will be presented in this talk.
Keywords: curved magnetic thin films, magnetic caps
  • Invited lecture (Conferences)
    META2016: The 7th International Conference on Metamaterials, Photonic Crystals and Plasmonics, 25.-28.07.2016, Malaga, Spain

Permalink: https://www.hzdr.de/publications/Publ-23952
Publ.-Id: 23952


Eine Methode zur schnellen und genauen Berechnung und Kompensation der magnetischen Ablenkung des Protonenstrahls in der MRT-integrierten Protonentherapie

Schellhammer, S. M.; Hoffmann, A. L.
Deutsch:
Die Integration von Protonentherapie und Magnetresonanztomografie (MRT) mit dem Ziel der Echtzeit-Bildgebung während der Bestrahlung steht vor dem Problem, dass der Protonenstrahl vom Magnetfeld des MRT-Scanners abgelenkt wird. Wir stellen eine Methode zur schnellen und genauen Vorhersage und Kompensation dieses Effektes vor. Die so berechnete Ablenkung sowie die Kompensationsparameter werden in Abhängigkeit der Protonenenergie und der magnetischen Flussdichte für den einfachen Fall eines Wasserphantoms in einem homogenen transversalen Magnetfeld betrachtet.

English:
The integration of proton therapy and magnetic resonance (MR) imaging for real-time image-guidance faces the challenge that the proton beam is deflected by the magnetic field of the MR scanner. We propose a method for a fast and accurate quantification and correction of this effect. Deflection and correction parameters are studied as functions of the beam energy and magnetic flux density for the simple geometry of a water phantom in a uniform transverse magnetic field.
Keywords: proton therapy, image-guided radiotherapy, IGPT, magnetic resonance imaging, MR guidance, beam trajectory prediction
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP) e. V., 07.-10.09.2016, Würzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-23951
Publ.-Id: 23951


Introducing a novel method for fast and accurate estimation and compensation of beam deflection in MR-integrated proton therapy

Schellhammer, S. M.; Hoffmann, A. L.
Proton therapy is highly sensitive to anatomical variations due to steep dose gradients in proximity of the Bragg peak (BP). Magnetic resonance imaging (MRI) is a promising candidate to enable real-time tracking of such variations during treatment delivery with high spatial, temporal and contrast resolution and without ionizing radiation exposure. However, an MRI magnetic field applied during irradiation deflects the proton beam from its intended trajectory.
We present a numerical method for fast and accurate quantification and compensation of this effect. As compared to existing approaches, it features fewer approximations than analytical models and a strongly reduced computation time compared to Monte Carlo simulations. We use it to reconstruct the trajectory of a monoenergetic proton beam of energy E0 traversing a water phantom behind a 25 cm air gap inside a virtual MRI bore with a uniform transverse magnetic flux density B. We study the dislocation of the BP as function of E0 and B and introduce an optimization method to compensate for it.
The magnitude of BP dislocation ranges from 2 cm for E0=60 MeV and B=0.5 T up to 26 cm for E0=250 MeV and B=3.0 T. A unique solution exists for repositioning the BP by beam incidence angle and energy adjustment.
The predicted magnetic-field induced BP dislocation complies with results obtained by Monte Carlo methods and the model is more versatile than analytical methods. The proposed optimization of beam incidence angle and energy effectively repositions the BP to its intended location.
Keywords: proton therapy, image-guided radiotherapy, IGPT, magnetic resonance imaging, MR guidance, beam trajectory prediction
  • Poster
    55th Annual Conference of the Particle Therapy Co-operative Group (PTCOG 55), 22.-28.05.2016, Praha, Ceska republika
  • Poster
    10th HZDR PhD seminar, 02.-04.11.2015, Altenberg, Deutschland
  • Poster
    National Center for Radiation Oncology, 2nd Scientific Retreat, 14.-16.04.2016, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-23950
Publ.-Id: 23950


Characterisation of nano-particulate powder pellets

Garbe-Schönberg, D.; Renno, A. D.; Leißner, T.; Müller, S.; Nordstad, S.
Matrix-matched reference materials are urgently needed for calibration and validation of (micro-)analytical data. It is desirable that these materials can be analyzed by different analytical techniques like LA-ICP-MS, LIBS, μ-XRF, EPMA, PIXE, SIMS etc. accomplishing a better definition of elemental and isotopic composition of materials and also allowing for systematic studies on elemental fractionation. Nano-particulate powder pellets have now been produced from a large variety of materials and shown to be of excellent homogeneity and cohesiveness enabling accurate and high precision determination of elemental composition by LA-ICP-MS with RSD <1-5% even at high spatial resolution with <32μm spot size (Garbe-Schönberg and Müller 2014). Here we present new data on particle size and surface roughness being quality criteria for micro-analytical techniques using electron (EPMA) or ion beams (PIXE, SIMS). We demonstrate homogeneity within and between pellets, and significantly improved accuracy after matrix-matched calibration with nano-pellets is shown for granite AC-E as an example. Meanwhile, nano-pellets are succesfully used also for LA-based Rb-Sr age determination (Karlsson et al., EWLA 2016) and Li-B isotopic studies (LeRoex et al., 2015) and were analysed by EPMA and LIBS.
Keywords: Reference Material, Nano-particulate powder pellets, homogeneity
  • Poster
    European Workshop on Laser Ablation, 12.-15.07.2016, Ljubljana, Slovenien

Permalink: https://www.hzdr.de/publications/Publ-23949
Publ.-Id: 23949


Investigation of surfactant effect on the bubble shape and mass transfer in a milli-channel using high-resolution microfocus X-ray imaging

Haghnegahdar, M.; Boden, S.; Hampel, U.
In this paper we present an experimental study on the influence of surface active agents (surfactants) on Taylor bubble flow in a vertical millimeter-size channel. Moreover we give a short review on the subject and previous investigations. We investigated the shape and dissolution rate of individual elongated carbon dioxide Taylor bubbles, which were hydraulically fixed in a downward flow of water. Bubble shape and dissolution rate was determined from microfocus X-ray radiographs. From the shrinking rate we calculated the liquid side mass transfer coefficient.
The results show that the presence of surfactants causes a change of the bubble shape and leads to a slight increase of the liquid film thickness around the bubble and as a result the elongation of contaminated bubbles. In addition, the comparison of clean and contaminated bubbles indicate that presence of surfactant has a more significant impact on the dissolution rate of small bubbles. Furthermore, applying different concentrations of surfactant reveals that in our case, where surface coverage ratio of surfactant on the bubbles is high, increase of contamination does not have a noticeable influence on the mass transfer coefficient of bubbles.
Keywords: Surfactant; Film thickness; Mass transfer; Taylor bubble; Carbon dioxide; Milli-channels

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Permalink: https://www.hzdr.de/publications/Publ-23948
Publ.-Id: 23948


Investigation of influence of channel vibration on the dissolution rate of single bubbles in milli-channels

Haghnegahdar, M.; Boden, S.; Hampel, U.
In the past decades, milli- and microreaction technology had intensive development with the numerous advantages such as intensification of heat and mass transfer, easy scale-up, reducing energy and resource consumption. Optimization of the chemical processes is one of main requirements put forward by modern industry with the aim to achieve technological efficiency and environmental safety. A new design and method for measurement of mass transfer rate of single bubbles in vibrating milli-channels is being developed with the claimed goal of process intensification [1],[2].
In this work, the dissolution rate of a single Taylor bubble of carbon dioxide in water is investigated using high resolution X-ray radiography technique in a vibrating vertical channel. The liquid-side mass transfer coefficient is calculated by measuring the changes in the size of the bubble at constant pressure. The experiments cover a large range of initial Taylor bubble length varying from 8 to 24 mm. The channel is a glass pipe with 6 mm inside diameter and circular cross section. The bubble is unceasingly monitored by holding the bubble stationary using the technique of Schulze and Schluender [3]. The glass channel is vibrated using a calibrated vibrator in horizontal direction. The amplitude and frequency of vibration is controlled by a wave generator accurately. The method which is used to measure the variation of the bubble size is X-ray radiography. This technique was qualified to disclose the three-dimensional shape of Taylor bubbles in capillary and enabled the acquisition of a series of high-resolution radiographic images of nearly stationary Taylor bubbles. The processed images which give volume (and also the interfacial area) of the bubble with high accuracy as a function of time, are used to evaluate the liquid side mass transfer coefficient between bubble and liquid using the mass conservation equation. The liquid phase is filtered-deionized water and the gas phase is CO2.
The results for the short term dissolution of single CO2 bubbles show that the channel vibration with high frequency (50, 100, 1000 and 10000 Hz) does not have a detectable influence on the rate of mass transfer for stationary single bubbles however, for channel vibrations lower than 50 Hz, the liquid-side mass transfer coefficient increases by more than 32%. In addition, it is shown that the measured mass transfer coefficients do not have intensive dependency on the bubble length and also equivalent diameter (diameter of the sphere having the same volume).
Keywords: Taylor bubble, Mass transfer, CO2, Vibration, X-ray
  • Contribution to proceedings
    22nd International Congress of Chemical and Process Engineering, CHISA 2016, 28.-31.08.2016, Prague, Czech Republic
    Proceedings of CHISA 2016
  • Lecture (Conference)
    22nd International Congress of Chemical and Process Engineering, CHISA 2016, 28.-31.08.2016, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-23947
Publ.-Id: 23947


Experimental investigation of Taylor bubble dissolution in milli-channels

Haghnegahdar, M.; Boden, S.; Hampel, U.
In the work presented in this paper, the dissolution rate of a single Taylor bubble of carbon dioxide into water was compared within a square and circular channel of 6 mm hydraulic diameter. The bubbles were held stationary in the down-flowing liquid and observed with high resolution X-ray radiography and tomography. The acquired X-ray images of the bubbles were analyzed with respect to volume, surface area and length of the bubble and were utilized to obtain the liquid side mass transfer coefficient by measuring the changes in the size of the bubble at constant pressure. The X-ray method was chosen since it is not dependent on the refractive index; therefore it is the most accurate method in comparison with other conventional optical techniques. The results for the long term dissolution of single CO2 bubbles show that the dissolution curves for bubbles with different initial size follow the same trend and have relatively constant slope. In addition, the comparison of the results for the square and circular channels showed that, there are some distinguishable differences between the trend of the liquid side mass transfer coefficient, kL in two curves. For square channel, kL increases with decrease of bubble sizes, while no obvious trend could be detected for the circular channel.
Keywords: Taylor bubble, Mass transfer, milli-channel, CO2
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2016, 22.-27.05.2016, Firenze, Italy
    Proceedings of ICMF 2016
  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2016, 22.-27.05.2016, Firenze, Italy

Permalink: https://www.hzdr.de/publications/Publ-23946
Publ.-Id: 23946


Resonant Four-Wave Mixing in Landau-Quantized Graphene

König-Otto, J.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.
Graphene in magnetic fields is a unique material because of its anomalous Landau level spectrum. Due to the linear density of states in graphene the energy of the Landau-levels scales with the square root of the index number and a zeroth level exists [1] (cf. Fig. 2a). Consequently individual Landau-level transitions can be addressed by varying the photon energy, in contrast to a classical Landau-quantized two-dimensional electron gas where the transition energies are degenerate. Pump-probe spectroscopy on Landau-quantized graphene (LQG) reveals fascinating effects such as an Auger-driven depopulation of an optically pumped level, recently demonstrated by some of us [2]. Theoretical calculations predict a giant non-linear χ(3) response for LQG [3]. We present for the first time results of a degenerated time-integrated transient four-wave mixing (FWM) experiment on LQG (cf. Fig. 1), where the photon energy of the linear polarized free-electron laser FELBE is resonant to the transitions from LL-1 (LL0) → LL0 (LL1) in a magnetic field of around 4.55T (cf. Fig. 2a). Comparing FWM (cf. Fig. 2c) and pump-probe (cf. Fig. 2b) signals at the same experimental conditions we observe a rapid dephasing (faster than pulse duration of ~4ps). Furthermore, we have confirmed the expected linear and quadratic dependencies of the FWM signal on the excitation intensities in directions k1 and k2, respectively. By sweeping the magnetic field and consequently shifting the energy difference between the Landau levels, the resonance behaviour of pump-probe and FWM signals was measured. In summary, we have experimentally verified that Landau-quantized graphene exhibits a significant nonlinear optical response despite the fact that it features a short dephasing time. It is an attractive nonlinear material, which allows one to tune the spectral position of the resonance by the magnetic field.

References
[1]. A. H. Castro Neto et al., Rev. Mod. Phys. 81, 109 (2009).
[2]. M. Mittendorff et al., Nat. Phys. 11, 75 (2015).
[3]. X. Yao and A. Belyanin, J. Phys. Condens. Matter 25, 054203 (2013).
Keywords: Graphene, Landau-quantized graphene, THz, Spectroscopy, Dynamics, nonlinear Dynamics
  • Lecture (Conference)
    ICSNN 2016 - 19th International Conference on Superlattices, Nanostructures and Nanodevices, 25.-30.07.2016, Hong Kong, China

Permalink: https://www.hzdr.de/publications/Publ-23945
Publ.-Id: 23945


A Strong Diffusive Ion Mode in Dense Ionised Matter Predicted by Langevin Dynamics

Mabey, P.; Richardson, S.; White, T. G.; Appel, K.; Barbel, B.; Chapman, D. A.; Döppner, T.; Falcone, R. W.; Fletcher, L. B.; Fortmann, C.; Galtier, E.; Glenzer, S. H.; Hastings, J. B.; Heimann, P.; Lee, H. J.; Lepape, S.; Ma, T.; Monaco, G.; Nagler, B.; Pak, A.; Turnbull, D.; Vorberger, J.; Wei, M.; Welch, J.; Zastrau, U.; Gericke, D. O.; Gregori, G.
The state and the evolution of planetary cores, drown dwarfs and neutron star crusts is determined by microscopic properties, such as viscosity and thermal conductivity, of the dense and compressed matter of which such system are made of. Due to the inherent diffculties in modelling strongly coupled plasmas, where classical long-range Coulomb forces dominate interactions between ions while electrons are partially to fully degenerate, current predictions of transport coeffcients differ by many orders of magnitude. This not only affects our ability to understand the evolution of planets and evolved stars, but also impacts our ability to accurately predict the implosion material characteristics in inertial confinement fusion experiments. The response of the compressed matter to density perturbations gives rise to collective modes, either electrostatic or acoustic waves, that serve as an important tool to validate theoretical predictions. Until recently, only electron modes could be measured experimentally. With the recent advances in free electron laser technology, x-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter as well. Here, we present numerical predictions for these ion modes and demonstrate signifcant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. In particular, a strong diffusive mode around zero frequency arises which is not present, or much weaker, in standard simulations. Our results have profound consequences in the interpretation of transport coefficients in dense plasmas.
Keywords: warm dense matter, transport, ion acoustic modes, langevin dynamics

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Permalink: https://www.hzdr.de/publications/Publ-23944
Publ.-Id: 23944


Multistage bioassociation of uranium onto an extremely halophilic archaeon revealed by a unique combination of spectroscopic and microscopic techniques

Bader, M.; Müller, K.; Foerstendorf, H.; Drobot, B.; Schmidt, M.; Musat, N.; Swanson, J. S.; Reed, T. D.; Stumpf, T.; Cherkouk, A.
The interactions of two extremely halophilic archaea with uranium were investigated at high ionic strength as a function of time, pH and uranium concentration. Halobacterium noricense DSM-15987 and Halobacterium sp. putatively noricense isolated from the Waste Isolation Pilot Plant (WIPP) repository were used for these investigations. The kinetics of U(VI) bioassociation of both strains showed an atypical multistage behavior, meaning that after an initial phase of U(VI) sorption, an unexpected interim period of U(VI) release was observed, followed by a slow reassociation of uranium with the cells. By applying in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy, the involvement of phosphoryl and carboxylate groups in U(VI) complexation during the first biosorption phase was shown. Differences in cell morphology and uranium localization become visible at different stages of the bioassociation process, by using scanning electron microscopy (SEM) in combination with energy dispersive X-ray (EDX) spectroscopy. Our results demonstrate for the first time that association of uranium on the extremely halophilic archaeon is a multistage process, beginning with a sorption which is followed by another process, probably biomineralization.
Keywords: Uranium Biosorption Halophilic Archaea TRLFS in situ ATR FT-IR

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Permalink: https://www.hzdr.de/publications/Publ-23943
Publ.-Id: 23943


Pushing the Limits of Lattice Monte-Carlo Simulations using GPUs

Kelling, J.; Ódor, G.; Heinig, K. H.; Weigel, M.; Gemming, S.
Lattice Monte-Carlo methods are used to study out-of- and towards-equilibrium systems, like surface growth, spin systems and even phase separation in solid mixtures using kinetic Metropolis lattice Monte-Carlo (KLMC). Applications range from the study of universal scaling or aging behaviors to concrete systems, where coarsening of nanocomposites or self-organization of functional nanostructures is relevant, for example spinodal decomposition in solar cell absorber layers. In these systems, scaling needs to be followed for long times to allow structures to grow over orders of magnitude, which requires large-scale simulations. For the evolution of nanostructures, atomistic simulations at experimental spatiotemporal scales are often desired.

This talk will give an overview over a variety of lattice Monte-Carlo algorithms, which have been found or made suitable for implementation on GPUs: Stochastic cellular automata can be implemented very efficiently [1-3] and are suitable for many systems. The efficient implementation of random sequential dynamics is more challenging. Solutions will be presented for a dimer lattice gas mapped to surface growth [4,5] and KLMC [6]. The latter was also extended to implement dynamics driven by ion-beam mixing triggering long-range interactions. However, these implementations hinge on the fact, that only a very small number of states need to be encoded at each lattice site. A more flexible implementation, employing a variation of multisurface-coding to enable vectorization, will be presented for simulations of restricted solid-on-solid and Potts models with random sequential dynamics. [7]

[1] Block, B., Virnau, P., Preis, T.: Comp. Phys. Comm. 181(9), 1549 (2010)
[2] Lulli, M., Bernaschi, M., Parisi, G.: Comp. Phys. Comm. 196, 290 (2015)
[3] Kelling, J., Ódor, G., Gemming, S.: 2016 IEEE Int. Conf. Intell. Eng. Syst., arXiv:1606.00310 (2016)
[4] Kelling, J., Ódor, G.: Phys. Rev. E 84, 061150 (2011)
[5] Ódor, G., Kelling, J., Gemming, S.: Phys. Rev. E 89, 032146 (2014)
[6] Kelling, J., Ódor, G., Nagy, M. F., Schulz, H., Heinig, K.: EPJST 210, 175 (2012)
[7] Kelling, J., Ódor, G., Gemming, S.: arXiv:1605.02620 (2016)
  • Invited lecture (Conferences)
    Perspectives of GPU computing in Science, 26.-28.09.2016, Roma, Italia

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Publ.-Id: 23942


Experimental-Scale Kinetic Lattice Monte-Carlo Studies on GPU

Kelling, J.; Heinig, K.-H.; Gemming, S.
Resume : Micro- and nano-structured materials are crucial for future energy technologies. Key processes during production and life-time are governed by self-organization in phase separation processes at the micro and nano scale. Examples include nano-structured Silicon absorber layers in solar cells providing tailored band-gaps [Apl. Phys. Lett. 103, 133106 (2013)] as well as cheap production and micro-patterned electrolyte-matrices] enhancing life-time and efficiency in a range of fuel cell technologies. Simulations of these out-of-equilibrium, inhomogeneous real world systems provide important insights, finding potential for optimization of structures and process parameters. To this end, kinetic lattice Monte Carlo simulations can be used to model physical systems at experimental scales in an atomistic way, thereby side-stepping many caveats connected with the alternative phase-field simulations. In this contribution, we present two massively parallel implementations for large-scale simulations on GPUs: One is optimized to offer fast time-to-solution on experimental-scale simulations [Eur. J. Phys.: Spec. Top. 210, 175 (2012)], the other provides highly efficient parameter studies or large sample sizes for large-scale simulations [Phys. Rev. E (2016) submitted]. Harnessing the compute power of modern (multi-)GPU installations leads to increased energy efficiency as well as reduced time-to-solution.
  • Lecture (Conference)
    E-MRS Fall Meeting, 19.-22.09.2016, Warschau, Polen

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Permalink: https://www.hzdr.de/publications/Publ-23941
Publ.-Id: 23941


Aging In The (2+1)-Dimensional Kardar-Parisi-Zhang Model Under Various Dimer Lattice-Gas Dynamics

Kelling, J.; Ódor, G.; Gemming, S.
Extensive dynamical simulations of a 2 dimensional driven dimer lattice gas are presented, which can be mapped to (2+1) dimensional surface growth in the Kardar-Parisi-Zhang (KPZ) or Edwards-Wilkinson universality classes [1,2]. From this, autocorrelation and autoresponse functions have been determined for the KPZ universality class and the underlying lattice gas [3]. Studying the effects of different dimer lattice gas dynamics revealed strong differences in the aging behavior of the stochastic cellular automaton (SCA) and the random sequential update models. We show numerical evidence for nontrivial corrections and tests against log-local scale invariance [4] as well as different universal scaling behaviors. [1] G. Ódor, B. Liedke and K.-H. Heinig, Phys. Rev. E 79, 021125 (2009) [2] J. Kelling and G. Ódor, Phys. Rev. E 84, 061150 (2011) [3] J. Kelling, G. Ódor, S. Gemming, Phys. Rev. E 89, 032146 (2014) [4] M. Henkel, Nucl. Phy. B 869(2), 282 (2013)
  • Lecture (Conference)
    Stat'Phys 26 - Statistical Physics Conference Satellite Non-equilibrium dynamics in classical and quantum systems: From quenches to slow relaxations, 13.-22.07.2016, Pont-à-Mousson, France

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Publ.-Id: 23940


Experimental x-ray ghost imaging

Pelliccia, D.; Rack, A.; Scheel, M.; Cantelli, V.; Paganin, D. M.
We report an experimental proof of principle for ghost imaging in the hard x-ray energy range. We used a synchrotron x-ray beam that was split using a thin crystal in Laue diffraction geometry. With an ultra-fast imaging camera, we were able to image x-rays generated by isolated electron bunches. At this time scale, the shot noise of the synchrotron emission process is measurable as speckles, leading to speckle correlation between the two beams. The integrated transmitted intensity from a sample located in the first beam was correlated with the spatially resolved intensity measured on the second, empty, beam to retrieve the shadow of the sample. The demonstration of ghost imaging with hard x-rays may open the way to protocols to reduce radiation damage in medical imaging and in non-destructive structural characterization using Free Electron Lasers.
Keywords: Ghost imaging, optics, X-ray

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Permalink: https://www.hzdr.de/publications/Publ-23939
Publ.-Id: 23939


Low-energy M1 strength from shell-model calculations

Schwengner, R.
Large-scale shell-model calculations were performed for 56Fe, 60Fe, 64Fe, 68Fe. The collective properties of yrast states are reproduced in the used model space.
The low-energy enhancement of M1 strength decreases with increasing neutron number while a bump around E = 3 MeV develops, which can be related with the scissors mode. The strength around E = 3 MeV includes transitions from 1+ states to the ground state as well as to excited 0+ states and contributions from other spins. This may explain the higher strength found in ion-induced reactions compared with the one observed in photon scattering.
Keywords: Gamma-ray strength functions, low-energy M1 strength, scissors resonance, shell-model calculations.
  • Invited lecture (Conferences)
    ECT* Workshop on "Statistical properties of nuclei", 11.-15.07.2016, Trento, Italien

Permalink: https://www.hzdr.de/publications/Publ-23938
Publ.-Id: 23938


Gamma-ray strength functions at low energy

Schwengner, R.
Photon-scattering experiments were carried out with bremsstrahlung at gELBE and with quasi-monoenergetic gamma rays at HIGS. Strength in the quasicontinuum was included in the analysis. The observed strength was corrected for branching and feeding by means of statistical methods. Experimental information about E1 strength in the pygmy region and M1 strength in the spin-flip region is presented for nuclides around masses 80, 130 and 180.
Large-scale shell-model calculations of M1 and E2 strength were performed. The experimental low-energy upbend can be explained by enhanced M1 strength. Information about E2 strength at low energy is given. The described findings require modifications of phenomenological strength functions.
Keywords: Gamma-ray strength functions, photon scattering, bremsstrahlung, monoenergetic and polarized gamma rays, shell-model calculations.
  • Invited lecture (Conferences)
    1st Research Coordination Meeting of the IAEA Coordinated Research Project "Updating the Photonuclear Data Library and Generating a Reference Data Base for Photon Strength Functions"., 04.-08.04.2016, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-23937
Publ.-Id: 23937


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