Publication database - Helmholtz-Zentrum Dresden-Rossendorf

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26217 Publications
ZnO Luminescence and scintillation studied via photoexcitation, X-ray excitation, and gamma-induced positron spectroscopy
Ji, J.; Colosimo, A. M.; Anwand, W.; Boatner, L. A.; Wagner, A.; Stepanov, P. S.; Trinh, T. T.; Liedke, M. O.; Krause-Rehberg, R.; Cowan, T. E.; Selim, F. A.
Abstract: The luminescence and scintillation properties of ZnO single crystals were studied by photoluminescence and X-ray-induced luminescence (XRIL) techniques. XRIL allowed a direct comparison to be made between the near-band emission (NBE) and trap emissions providing insight into the carrier recombination efficiency in the ZnO crystals. It also provided bulk luminescence measurements that were not affected by surface states. The origin of a green emission, the dominant trap emission in ZnO, was then investigated by gamma-induced positron spectroscopy (GIPS) - a unique defect spectroscopy method that enables positron lifetime measurements to be made for a sample without contributions from positron annihilation in the source materials. The measurements showed a single positron decay curve with a 175 ps lifetime component that was attributed to Zn vacancies passivated by hydrogen. Both oxygen vacancies and hydrogen-decorated Zn vacancies were suggested to contribute to the green emission. By combining scintillation measurements with XRIL, the fast scintillation in ZnO crystals was found to be strongly correlated with the ratio between the defect luminescence and NBE. This study reports the first application of GIPS to semiconductors, and it reveals the great benefits of the XRIL technique for the study of emission and scintillation properties of materials.
Keywords: luminescence scintillation ZnO photoluminescence X-ray-induced luminescence XRIL gamma-induced positron spectroscopy GIPS defect spectroscopy

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Registration No. 24051 - Permalink

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.
Abstract: 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
Registration No. 24033 - Permalink

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.
Abstract: 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
Registration No. 24032 - Permalink

Semiconductor spectroscopy with infrared and THz free-electron lasers
Schneider, H.
Abstract: 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
Registration No. 24031 - Permalink

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.
Abstract: 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
Registration No. 24030 - Permalink

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.
Abstract: 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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Registration No. 24020 - Permalink

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.
Abstract: 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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Registration No. 24017 - Permalink

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.
Abstract: 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+. Registration No. 24016 - Permalink

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.
Abstract: 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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Registration No. 24015 - Permalink

TEM investigation of barrier-like anodic oxide films on aluminum
Schneider, M.; Lämmel, C.; Hübner, R.; Gierth, U.; Michaelis, A.
Abstract: 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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Registration No. 24014 - Permalink

Theoretical prediction of mass transfer coefficients in both gas-liquid and slurry bubble columns
Nedeltchev, S.
Abstract: 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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Registration No. 24009 - Permalink

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.
Abstract: 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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Registration No. 24008 - Permalink

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.
Abstract: 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.
Registration No. 24005 - Permalink

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.
Abstract: 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. Registration No. 24004 - Permalink

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.
Abstract: 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 Registration No. 24002 - Permalink

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.
Corresponding author: Pietzsch, J.
Abstract: 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 Registration No. 24001 - Permalink

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.
Abstract: 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
Registration No. 23996 - Permalink

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.
Abstract: 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
Registration No. 23995 - Permalink

Magnetic-field and composition-dependent Fermiology in correlated metals
Wosnitza, J.
Abstract: 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
Registration No. 23989 - Permalink

How To Analyze The Electronic Density - An Introduction To Some Useful Tools
Patzschke, M.
Abstract: 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
Registration No. 23988 - Permalink

Understanding and advancing the coordination and redox chemistry of the actinides
Woodall, S.; Natrajan, L.; Kaden, P.; Kerridge, A.
Abstract: 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
Registration No. 23987 - Permalink

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.
Abstract: 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
Registration No. 23986 - Permalink

Luminescence spectroscopy of uranium
Steudtner, R.; Drobot, B.; Haubitz, T.; Lehmann, S.; Vogel, M.
Abstract: 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
Registration No. 23985 - Permalink

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.
Abstract: 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
Registration No. 23984 - Permalink

How Theory Can Probe The Chemical Bond: The Case Of Caged U2
Patzschke, M.
Abstract: "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
Registration No. 23982 - Permalink

Computational chemistry for actinide compounds: examine the U-U bond inside fullerenes
Patzschke, M.
Abstract: 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
Registration No. 23981 - Permalink

How can Theoretical Chemistry contribute to coordination chemistry?
Patzschke, M.
Abstract: 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
Registration No. 23980 - Permalink

Probing the chemical bond: The case of caged U_2
Patzschke, M.
Abstract: 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
Registration No. 23979 - Permalink

Uranyl Spectroscopy - Do We Know Everything?
Patzschke, M.
Abstract: 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
Registration No. 23978 - Permalink

Using ADF in computational actinide chemistry
Patzschke, M.
Abstract: 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
Registration No. 23977 - Permalink

Visualising Your Results - An Introduction to VMD
Patzschke, M.
Abstract: 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
Registration No. 23976 - Permalink

Quantum Chemistry Workshop - using Orca & Gabedit
Patzschke, M.
Abstract: 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
Registration No. 23975 - Permalink

Planned Projects of the New Theory- Group in Rossendorf
Patzschke, M.
Abstract: 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
Registration No. 23974 - Permalink

Computational Methods for f-Elements
Patzschke, M.
Abstract: 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
Registration No. 23973 - Permalink

Investigating Catalytic Activity with DFT
Patzschke, M.
Abstract: 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
Registration No. 23972 - Permalink

DFT in the f-block
Patzschke, M.
Abstract: 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
Registration No. 23971 - Permalink

Magnetically induced ring currents in actinide extraction ligand systems
Patzschke, M.
Abstract: 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
Registration No. 23970 - Permalink

Nanoparticle dispersion in liquid metals by electromagnetically induced acoustic cavitation
Kaldre, I.; Bojarevics, A.; Grants, I.; Beinerts, T.; Kalvans, M.; Milgravis, M.
Abstract: 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 Registration No. 23969 - Permalink

Scalable critical-path analysis and optimization guidance for hybrid MPI-CUDA applications
Schmitt, F.; Dietrich, R.; Juckeland, G.
Abstract: 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 Registration No. 23968 - Permalink

Advanced characterization 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.
Abstract: 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 Registration No. 23967 - Permalink

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.
Abstract: 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 Registration No. 23966 - Permalink

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.
Abstract: 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 Registration No. 23963 - Permalink

Magnetocapacitance in CdCr1.8In0.2S4 Single Crystal Annealed in Cadmium Vapor
Xie, Y.; Chen, X.; Zhang, Z.; Song, W.; Zhou, S.; Yang, Z.
Abstract: 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 Registration No. 23962 - Permalink

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.
Abstract: 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

Downloads:

Registration No. 23956 - Permalink

A highly-parallel Monte-Carlo-Simulation of X-Ray-Scattering using a Particle-Mesh-Code on GPUs (Zwischenpräsentation Diplomarbeit)
Grund, A.
Abstract: 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
Registration No. 23955 - Permalink

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.
Abstract: 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. Registration No. 23954 - Permalink

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.
Abstract: 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. Registration No. 23953 - Permalink

Curvilinear magnetism
Makarov, D.
Abstract: 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
Registration No. 23952 - Permalink

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.
Abstract: 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
Registration No. 23950 - Permalink

Characterisation of nano-particulate powder pellets
Garbe-Schönberg, D.; Renno, A. D.; Leißner, T.; Müller, S.; Nordstad, S.
Abstract: 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
Registration No. 23949 - Permalink

Aging In The (2+1)-Dimensional Kardar-Parisi-Zhang Model Under Various Dimer Lattice-Gas Dynamics
Kelling, J.; Ódor, G.; Gemming, S.
Abstract: 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
Registration No. 23940 - Permalink

Experimental x-ray ghost imaging
Pelliccia, D.; Rack, A.; Scheel, M.; Cantelli, V.; Paganin, D. M.
Abstract: 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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Registration No. 23939 - Permalink

Euler-Euler Simulation und Modellvalidierung einer Blasensäule
Krauß, M.
Abstract: Die Anwendung von Methoden der CFD („Computational fluid dynamics“) für Scale-up und Intensivierung verfahrenstechnischer Prozesse bietet die Möglichkeit, energie- und ressourceneffiziente Lösungen zu identifizieren, deren Untersuchung mit konventionellen halb-empirischen Methoden kostspielig und langwierig wäre.
Eine solche Simulation im großtechnischen Maßstab ist im Rahmen der Euler-Euler Beschreibung möglich, in der Prozesse auf der Skala einzelner Blasen modelliert werden.
Ein solches Schließungsmodell für Hydrodynamik und Stofftransport in Blasenströmungen wird am HZDR entwickelt. Ziel dieser Entwicklung ist, ein vorhersagetaugliches Modell zu etablieren, das für einen breiten Bereich von Anwendungsbedingungen validiert ist.
Zu diesem Zweck werden Simulationsrechnungen mit experimentellen Daten verglichen, die zunehmend komplexere Geometrien und Effekte einbeziehen. Auf Basis der jeweils erzielten Übereinstimmung werden Modellerweiterungen und -verbesserungen vorgenommen. Im Rahmen der Belegarbeit soll eine mit Wasser befüllte, von Luft bzw. Kohlenstoffdioxid durchströmte, zylinderförmige Blasensäule mit einem Innendurchmesser von 142 mm untersucht werden.

Keywords: Blasensäule, Euler-Euler Modell, CFD-Simulation, Modellvalidierung
  • Study thesis
    TU Dresden, 2016
    Mentor: Dr. Roland Rzehak (HZDR), Prof. Rüdiger Lange (TU-Dresden)
    94 Seiten
Registration No. 23935 - Permalink

Effect of compression on the electronic, optical and transport properties of MoS2/graphene-based junctions
Ghorbani-Asl, M.; Bristowe, P. D.; Koziol, K.; Heine, T.; Kuc, A.
Abstract: Electronic, optical and transport properties of the MoS2/graphene heterostructure have been investigated as function of applied uniaxial compression normal to the interface plane using first principles calculations and a non-equilibrium Green’s function approach. The results show that a small compressive load (∼1 GPa) can open up the band gap (∼12 meV), reduce the optical absorption coefficient (∼7%), redshift the absorption spectrum, and create non-Ohmic I–V characteristics that depend on the magnitude of applied bias. This suggests that graphene/MoS2 heterostructure can be suitable for electromechanical and photomechanical devices where the electronic, optical and transport properties can be tuned by an appropriate application of bias and mechanical deformations.
Keywords: MoS2/graphene heterojunction, interlayer compression, transport properties, NEGF, DFT

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Registration No. 23934 - Permalink

Electron-beam induced transformations of layered tin dichalcogenides
Sutter, E.; Huang, Y.; Komsa, H.-P.; Ghorbani-Asl, M.; Krasheninnikov, A. V.; Sutter, P.
Abstract: By combining high-resolution transmission electron microscopy and associated analytical methods with first-principles calculations, we study the behavior of layered tin dichalcogenides under electron beam irradiation. We demonstrate that the controllable removal of chalcogen atoms due to electron irradiation, at both room and elevated temperatures, gives rise to transformations in the atomic structure of Sn−S and Sn−Se systems so that new phases with different properties can be induced. In particular, rhombohedral layered SnS2 and SnSe2 can be transformed via electron beam induced loss of chalcogen atoms into highly anisotropic orthorhombic layered SnS and SnSe. A striking dependence of the layer orientation of the resulting SnS parallel to the layers of ultrathin SnS2 starting material, but slanted for transformations of thicker few-layer SnS2is rationalized by a transformation pathway in which vacancies group into ordered S-vacancy lines, which convert via a Sn2S3 intermediate to SnS. Absence of a stable Sn2Se3 intermediate precludes this pathway for the selenides, hence SnSe2 always transforms into basal plane oriented SnSe. Our results provide microscopic insights into the transformation mechanism and show how irradiation can be used to tune the properties of layered tin chalcogenides for applications in electronics, catalysis, or energy storage.
Keywords: two-dimensional materials, defects, electron irradiation, structural transformation, sulfide, selenide

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Registration No. 23932 - Permalink

Surprising effects of electron-electron scattering in graphene revealed by THz pump-probe spectroscopy
Helm, M.; König-Otto, J. C.; Mittendorff, M.; Pashkin, A.; Schneider, H.; Winnerl, S.; Wendler, F.; Winzer, T.; Malic, E.; Knorr, A.
Abstract: Electron-electron scattering in graphene gives rise to some unexpected behavior in the electron dynamics, as observed by THz pump-probe measurements.
When excited with a near-infrared femtosecond laser pulse, the pump-probe signal depends on the angle between the linear polarization of the pump and the probe pulse, which is due to preferential excitation of electrons perpendicular to the laser electric field. This indicates an anisotropic distribution function in momentum space that is preserved by electron-electron scattering, since it mainly occurs collinearly along the Dirac cone. Only after 150 fs the distribution function is rendered isotropic through optical-phonon scattering. The effect is even more pronounced when exciting at small photon energies (88 meV), below the optical-phonon energy: In this case the anisotropic distribution function survives for as long as 5 ps, when it is finally thermalized by non-collinear Coulomb scattering. These results challenge the common view of ultrafast thermalization by electron-electron scattering.
When a magnetic field is applied to graphene, Landau levels are formed that can be selectively excited by circular-polarized radiation. In a pump-probe experiment, exciting and probing all possible transitions between the n=-1, n=0 and n=+1 Landau levels in slightly n-type graphene, we observe an unexpected sign reversal of the n=0 →1 probe signal when pumping the -1→0 transition. This directly reflects the fact that the n=0 Landau level is depleted by electron-electron Auger-type scattering, even though it is optically pumped at the same time.
Both effects can be quantitatively reproduced by a microscopic calculation based on the graphene Bloch equations, and shed new light on the possibility of infrared and THz devices based on hot carriers in graphene.

Keywords: THz, graphene, free electron laser, pump-probe spectroscopy
  • Invited lecture (Conferences)
    International Workshop on Terahertz Science, Nanotechnologies and Applications, 16.-22.07.2016, Erice, Italy
Registration No. 23927 - Permalink

Annual Report 2015 - Institute of Ion Beam Physics and Materials Research
Faßbender, J.; Heera, V.; Helm, M.; Zahn, P. (Editors)
Abstract: After the successful evaluation in 2015 we started research and further development of our largescale facilities, in particular the Ion Beam Center (IBC), in the framework of Helmholtz’s Programmeoriented Funding scheme (POF) which coordinates scientific cooperation on a national and international scale. Most of our activities are assigned to the Helmholtz program “From Matter to Materials and Life” within the research area “Matter”, in cooperation with several other German Helmholtz Centers. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a minor part of our activities in the program “Nuclear Waste Management and Safety” within the research area “Energy”.
A few highlights which have been published in 2015 are reprinted in this annual report in order to show the variety of the research being performed at the Institute, ranging from self-organized pattern formation during ion erosion or DNA origami patterning, over ferromagnetism in SiC and TiO2 to plasmonics and THz-spectroscopy of III-V semiconductors. A technological highlight published recently is the demonstration of nanometer scale elemental analysis in a Helium ion microscope, making use of a time-of-flight detector that has been developed at the IBC. In addition to these inhouse research highlights, also users of the IBC, in particular of the accelerator mass spectrometry (AMS), succeeded in publishing their research on geomorphology in Nepal in the high-impact journal Science (W. Schwanghart et al., Science 351, 147 (2015)), which demonstrates impressively the added value of transdisciplinary research at the IBC.
In order to further develop the IBC, we have started in 2015 the design and construction of our new low energy ion nanoengineering platform which was highly recommended by the POF evaluators. It will consist of two-dimensional materials synthesis and modification, high-resolution ion beam analysis and high-resolution electron beam analysis and will come into full operation in 2019.
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-069 2016

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Registration No. 23926 - Permalink

Synthesis and evaluation of a 18F-labeled 4-phenylpiperidine-4-carbonitrile radioligand for σ1 receptor imaging
Ye, J.; Wang, X.; Deuther-Conrad, W.; Zhang, J.; Li, J.; Zhang, X.; Wang, L.; Steinbach, J.; Brust, P.; Jia, H.
Abstract: We report the design and synthesis of several 4-phenylpiperidine-4-carbonitrile derivatives as σ1 receptor ligands. In vitro radioligand competition binding assays showed that all the ligands exhibited low nanomolar affinity for σ1 receptors (Ki(σ1) = 1.22–2.14 nM) and extremely high subtype selectivity (Ki(σ2) = 830–1710 nM; Ki(σ2)/Ki(σ1) = 680–887). [18F]9 was prepared in 42–46% isolated radiochemical yield, with a radiochemical purity of >99% by HPLC analysis after purification, via nucleophilic 18F- substitution of the corresponding tosylate precursor. Biodistribution studies in mice demonstrated high initial brain uptakes and high brain-to-blood ratios. Administration of SA4503 or haloperidol 5 min prior to injection of [18F]9 significantly reduced the accumulation of radiotracers in organs known to contain σ1 receptors. Two radioactive metabolites were observed in the brain at 30 min after radiotracer injection. [18F]9 may serve as a lead compound to develop suitable radiotracers for σ1 receptor imaging with positron emission tomography.
Keywords: fluorine-18; σ1 receptor; positron emission tomography; 4-phenylpiperidine-4-carbonitrile derivatives; molecular probe Registration No. 23925 - Permalink

Corrosion of hot-dip galvanized containment installations – A potential cause for thermal-hydraulic effects after LOCA in PWR?
Kryk, H.; Harm, U.; Hampel, U.
Abstract: During the sump recirculation phase after loss-of-coolant accidents (LOCA) in pressurized water reactors (PWR), coolant spilling out of the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by residual-heat removal pumps as part of the emergency core cooling system (ECCS). The contact of the coolant with several forms of debris may influence the sump strainer clogging behavior as well as the cooling water chemistry. Damage to fibrous insulation materials located near to the leak may compromise the operation of the ECCS, if insulation fibers are transported to the strainers. Furthermore, the long-term contact of the boric acid containing coolant with hot-dip galvanized containment internals (e.g. grating treads, supporting grids of sump strainers) may cause corrosion of the corresponding materials.
Generic investigations regarding the influence of such corrosion processes on strainer clogging as well as on the coolant chemistry and possible resulting in-core effects are subject of joint research projects of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), TU Dresden (TUD) and Zittau-Görlitz University of Applied Sciences (HSZG). Lab-scale experiments at HZDR and TUD are focused on elucidation of physico-chemical corrosion and precipitation processes as well as resulting clogging effects.
Results of generic experiments in a lab-scale corrosion test facility, representing the ECCS operation in a simplified manner, suggest that there is a multi-stage corrosion process. The first stage comprises dissolution of the zinc layer in the coolant forming zinc ions and in turn affecting the coolant chemistry. During the second stage, the base material (steel) corrodes forming insoluble corrosion particles, which can subsequently lead to accelerated clogging of fiber-laden strainers within a few hours. The main influences on corrosion were identified as impact of the coolant jet onto the corroding surface, water chemistry and zinc surface / coolant volume ratio.
Furthermore, retrograde solubility of zinc corrosion products in boric acid containing coolants with increasing temperature was observed. Thus, formation and deposition of solid corrosion products cannot be ruled out if zinc containing coolant is heated up during its recirculation into hot downstream components (e.g. hot-spots in core). Corrosion experiments, which included formation of corrosion products at a heated cladding tube, proved that zinc, dissolved in the coolant at low sump temperatures, turns into solid deposits of zinc borates when contacting heated zircaloy surfaces. Due to alternating heating and cooling of the coolant during sump recirculation operation, a cycle of zinc corrosion and zinc borate precipitation may be initiated, which may eventually influence the thermal hydraulics in downstream components during the post-LOCA stage. The results obtained at lab-scale were confirmed by corresponding experiments in semi-technical test facilities of the project partner HSZG.
Based on the experimental results, water chemical measures were tested to reduce corrosion and/or zinc borate precipitation effects. Additionally, joint research projects have been established by the TUD and the HSZG dealing with local effects of corrosion, corrosion product precipitation and the interplay thereof at LOCA-specific conditions.
The investigations have been supported by the German Federal Ministry for Economic Affairs and Energy under contract nos. 1501363, 1501430, 1501467 and 1501496.

Keywords: loss-of-coolant accident, LOCA, pressurized water reactor, PWR, sump strainer clogging, chemical effects, corrosion, zinc borate
  • Lecture (Conference)
    ICONE 24 – International Conference on Nuclear Engineering, 26.-30.06.2016, Charlotte, USA
Registration No. 23918 - Permalink

Optimisation of the bioleaching of REE from FP with chemoorgano-heterotrophic microorganisms.
Hopfe, S.; Kutschke, S.; Pollmann, K.
Abstract: Rare earth elements (REE) are used in mostly all new technologies and until now, there is nearly no recycling of REE containing end-of-life products [1]. Furthermore, only poor information is available regarding interactions of microorganisms with REE and there are almost no studies describing the bioleaching of REE. However, it can be assumed that microorganisms play an important role in the biogeochemistry of REE. This study investigates the potential of organic acid and metal binding molecules producing microbes to extract REE from technical waste.
During recycling of energy-saving bulbs fluorescent phosphor (FP) is collected as a distinct fraction. It contains about 10% REE-oxides bound in the hardly water-soluble triband dyes as oxides, phosphates, aluminates and silicates [2]. Previous experiments showed, that the chemoorgano-heterotrophic, organic acid producing micrrooganisms Yarrowia lipolytica, Komatogateiibacter xylinus and Lactobacillus casei as well as the mixed culture Kombucha are in principle suitable for the bioleaching of REE from FP. In this presentation the solubilisation process is investigated regarding the leaching metabolites and optimised with respect to maximal REE release. Thereto, the results are transferred from shake flasks to bioreactor and the media were adjusted. Furthermore, the influence of metal binding molecules like siderophores was tested.
It could be shown, that bioleaching is a potential alternative to technical leaching approaches, even though, the leaching efficiency is still low. This provides the basis for the development of an eco-friendly alternative to the currently applied methods.

[1] European Commission (2014) On the review of the list of critical raw materials for the EU and the implementation of the Raw Materials Initiative, Brüssel. [2] Haucke et al. (2011) Verfahren zur Rückgewinnung seltener Erden aus Leuchtstofflampen, Osram AG.
  • Poster
    Annual Conference 2016 of the Association for General and Applied Microbiology (VAAM), 13.-16.03.2016, Jena, Deutschland
Registration No. 23916 - Permalink

Magnetic Excitations in Spin-1/2 Triangular-lattice Antiferromagnets: High-field ESR studies
Zvyagin, S.
Abstract: es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    Lehrstuhl-Seminar (Seminar zur Statistischen Physik) an der Bergischen Universität Wuppertal, 23.06.2016, Wuppertal, Deutschland
Registration No. 23915 - Permalink

Operational Experience of SRF Gun II
Arnold, A.; Teichert, J.; Xiang, R.
Abstract: In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and a new cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time. With the improved parameters first user experiments of the superconducting CW accelerator ELBE are to be served, that benefit from an increased average beam current at a given repetition rate of some hundred kHz. Although the cavity performance stays behind its specifications (Ecath~12 MV/m), beam commissioning is underway. In this contribution we will report on our operational experiences of the first two years of SRF gun II.
Keywords: SRF gun, photo electron source, injector, ELBE, superconducting RF
  • Lecture (others)
    HOPE / SINEMP Projekttreffen im Rahmen BMBF Verbundforschungsinitiative, 21.-22.06.2016, Darmstadt, Deutschland
Registration No. 23914 - Permalink

Probing Ionization and Buried Layer Plasma Physics Driven by Optical High Power Lasers using XFELs
Huang, L. G.; Prencipe, I.; Kluge, T.; Cowan, T.
Abstract: In the presentation, the fundamental plasma physics driven by high power lasers on bulk electron heating,solid target and ion heating is discussed. Probing the relative dynamics using XFELs is also presented.
Keywords: Heating,Ionization,XFEL,high power lasers
  • Lecture (Conference)
    The 1st Asia-Pacific User Meeting for HIBEF at European XFEL, 23.-24.06.2016, Shanghai, China
Registration No. 23913 - Permalink

Numerical adiabatic potentials of orthorhombic Jahn-Teller effects retrieved from ultrasound attenuation experiments. Application to the SrF2:Cr crystal
Zhevstovskikh, I. V.; Bersuker, I. B.; Gudkov, V. V.; Averkiev, N. S.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Shakurov, G. S.; Ulanov, V. A.; Surikov, V. T.
Abstract: A methodology is worked out to retrieve the numerical values of all the main parameters of the sixdimensional adiabatic potential energy surface (APES) of a polyatomic system with a quadratic T-term Jahn-Teller effect (JTE) from the ultrasound experiments. The method is based on a verified assumption that ultrasound attenuation and speed encounter anomalies when the direction of propagation and polarization of its wave of strain coincides with the characteristic directions of symmetry breaking in the JTE. For the SrF2:Cr crystal, employed as a basic example, we observed anomaly peaks in the temperature dependence of attenuation of ultrasound at frequencies of 50-160 MHz in the temperature interval of 40-60 K for the wave propagating along the [110] direction, for both the longitudinal and the shear modes, the latter with two polarizations along the [001] and [11-0] axes, respectively. We show that these anomalies are due to the ultrasound Relaxation by the system of non-interacting Cr2+ JT centers with orthorhombic local distortions. The interpretation of the experimental findings is based on the T2g - (eg+t2g) JTE problem including the linear and the quadratic terms of vibronic interactions in the Hamiltonian and the same-symmetry modes reduced to one interaction mode. Combining the experimental results with a theoretical analysis, we show that on the complicated six-dimensional APES of this system with three tetragonal, four trigonal, and six orthorhombic extrema points, the latter are global minima, while the former are saddle points, and we estimate numerically all the main parameters of this surface, including the linear and quadratic vibronic coupling constants, the primary force constants, the coordinates of all the extrema points and their energies, the energy barrier between the orthorhombic minima, and the tunneling splitting of the ground vibrational states. To our knowledge, such a based-on-experimental-data numerical reconstruction of the APES of a JTE problem in the five-dimensional space of all active tetragonal and trigonal displacements has not been reported before. Registration No. 23911 - Permalink

Robust range prediction for arbitrary tissue mixtures based on dual-energy CT
Möhler, C.; Wohlfahrt, P.; Richter, C.; Greilich, S.
Abstract: The treatment planning of proton or ion radiation therapy is affected by uncertainties arising from the heuristic conversion of computed tomography (CT) images to stopping-power ratio (SPR) maps. In this work, we present how these uncertainties can potentially be reduced by the use of dual-energy CT (DECT), via a physics-based SPR prediction. According to the Bethe formula, the SPR is the product of the electron density and the stopping number relative to water. The latter ranges between 0.96 and 1.02 for human tissue at a therapeutic beam energy of 200 MeV/u and depends on the mean excitation energy (I-value).
As a first step, the relative electron density can be directly determined from DECT images in a universal and robust procedure, based on a simple assumption for the cross section parameterization. Secondly, we propose to infer the relative stopping number from the relative photon absorption cross section obtained from DECT scans - instead of using an effective atomic number as a proxy for the I-value, which has previously been suggested in literature. Our choice of variables makes a proper treatment of tissue mixtures possible, which inevitably occur in patient CT images, and allows for a convenient definition of the uncertainties.
A calculation-based analysis of tabulated body tissues and tissue base components - such as water, lipid, carbohydrates and protein - suggests a maximum uncertainty below one percent for arbitrary mixtures of human tissue. We performed first experiments, combining particle range measurements with DECT scans, to validate our method of stopping-number prediction.

Keywords: dual-energy CT, proton therapy, ion-beam therapy
  • Poster
    55th Annual Conference of the Particle Therapy Co-operative Group (PTCOG), 22.-28.05.2016, Prag, Czech Republic
Registration No. 23909 - Permalink

Numerical simulations for the precession dynamo experiment in the framework of the DRESDYN project
Giesecke, A.; Stefani, F.
Abstract: In a next generation dynamo experiment currently under development at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) a fluid flow of liquid sodium, solely driven by precession, will be considered as a possible source for magnetic field generation.

I will present results from hydrodynamic simulations of a precession driven flow in cylindrical geometry. In a second step, the velocity fields obtained from the hydrodynamic simulations have been applied to a kinematic solver for the magnetic induction equation in order to determine whether a precession driven flow will be capable to drive a dynamo at experimental conditions.

It turns out that excitation of dynamo action in a precessing cylinder at moderate precession rates is difficult, and future dynamo simulations are required in more extreme parameter regimes where a more complex fluid flow is observed in water experiments which is supposed to be beneficial for dynamo action.

Keywords: Dynamo Precession Magnetohydrodynamics Geodynamo DRESDYN
  • Lecture (Conference)
    European GDR Meeting 20016, 27.06.-01.07.2016, Barcelona, Spain
Registration No. 23908 - Permalink

Frustrated magnets in high magnetic fields—selected examples
Wosnitza, J.; Zvyagin, S. A.; Zherlitsyn, S.
Abstract: An indispensable parameter to study strongly correlated electron systems is the magnetic field. Application of high magnetic fields allows the investigation, modification and control of different states of matter. Specifically for magnetic materials experimental tools applied in such fields are essential for understanding their fundamental properties. Here, we focus on selected high-field studies of frustrated magnetic materials that have been shown to host a broad range of fascinating new and exotic phases. We will give brief insights into the influence of geometrical frustration on the critical behavior of triangular-lattice antiferromagnets, the accurate determination of exchange constants in the high-field saturated state by use of electron spin resonance measurements, and the coupling of magnetic degrees of freedom to the lattice evidenced by ultrasound experiments. The latter technique as well allowed new, partially metastable phases in strong magnetic fields to be revealed. Registration No. 23905 - Permalink

Magnetic properties of HoFe6Al6H hydride: A single-crystal study
Andreev, A. V.; Pelevin, I. A.; Sebek, J.; Tereshina, E. A.; Gorbunov, D. I.; Drulis, H.; Tereshina, I. S.
Abstract: Crystal structure and magnetic properties were studied on a single crystal of HoFe6Al6H and compared with those of the parent HoFe6Al compound with a tetragonal crystal structure of the ThMn126Al6 is a ferrimagnet with exact compensation of the Ho and Fe sublattices magnetizations at low temperatures. Both the hydride and the parent compound display a high magnetic anisotropy of the easy-plane type, a noticeable anisotropy exists also within the easy plane with the [110] axis as the easy magnetization direction. The hydrogenation increases slightly (from 10 to 10.45 µB) the magnetic moment of the Fe sublattice as a result of volume expansion. It leads to a decompensation of the Fe and Ho sublattices and HoFe6Al6H has a spontaneous moment 0.45 µB/f.u. The enhancement of the Fe-Fe intra-sublattice exchange interaction results in a higher Curie temperature (TC) value, 350 K in the hydride as compared to 315 K of HoFe6Al6. The Ho-Fe inter-sublattice interaction is also enhanced in the hydride. The molecular field Hmol created on Ho Ions by Fe sublattice is 38 T in HoFe6Al6 and 48 T in HoFe6Al6H. The inter-sublattice exchange constant nHoFe is 3.8 T/µB and 4.6 T/µB, respectively. High-field measurements confirm the enhancement of the Ho-Fe exchange interaction in the hydride found from the temperature dependence of magnetization.

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Registration No. 23904 - Permalink

A study of the reprocessing of fine and ultrafine cassiterite from gravity tailing residues by using various flotation techniques
Leistner, T.; Embrechts, M.; Leissner, T.; Chehreh Chelgani, S.; Osbahr, I.; Möckel, R.; Peuker, U. A.; Rudolph, M.
Abstract: This study investigates the reprocessing of once disposed tin tailings from a historic German tin operation through different surface properties based processing techniques. Froth flotation and agglomeration flotation, by using commercially available cassiterite collectors from Clariant, were chosen as processing techniques. Isooctane as a nonpolar oil was used to promote the collection of ultrafine (-10 µm) cassiterite by selective agglomeration, and thus, size enlargement. Results indicate that by using sulfosuccinamates as a collector, around 80% of the fine (-50 µm) to very fine (-20 µm) cassiterite can be recovered (representing ~50% of the total cassiterite in the tailings sample). Agglomeration flotation experiments showed inferior results for recovering the ultrafine cassiterite (for feed fractions in the -25 µm size range). Oil/froth interaction and increased pulp ion content are considered as the main contributing causes.
Keywords: Tailings, Reprocessing, Cassiterite, Flotation, Ultrafine, Oil-assisted flotation

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Registration No. 23900 - Permalink

Solid state spectroscopy with THz free electron lasers
Helm, M.
Abstract: Some applications of infrared and THz free electron lasers in solid state spectroscopy are discussed. In particular, nonlinear experiments on semiconductor quantum well excitons and pump-probe studies on carrier relaxation in graphene are presented.
Keywords: free electron laser, infrared, terahertz, quantum well, graphene
  • Invited lecture (Conferences)
    Laser Optics 2016, 27.06.-01.07.2016, St. Petersburg, Russland
Registration No. 23898 - Permalink

Interplay of the Open Circuit Potential-Relaxation and the Dissolution Behavior of a Single H2 Bubble generated at a Pt Microelectrode
Karnbach, F.; Yang, X.; Mutschke, G.; Fröhlich, J.; Eckert, J.; Gebert, A.; Tschulik, K.; Eckert, K.; Uhlemann, M.
Abstract: The dissolution behavior of a single H2 bubble electrochemically generated at a Pt microelectrode in 1 M H2SO4, was studied. The open circuit potential (OCP) relaxation after the polarization end was recorded and correlated with the dissolved H2 concentration at the interface electrode/electrolyte/gas. Simultaneously, the shrinking of the bubble was followed optically by means of a high speed camera. In addition, analytical modelling and numerical simulations for the bubble dissolution were performed. Three characteristic regions are identified in the OCP and the bubble radius transients: (i) slow relaxation and shrinking, (ii) transition region and (iii) a long-term slowed down dissolution process. The high supersaturation after polarisation remains longer than theoretically predicted and feeds the bubble in region (i). This reduces the dissolution rate of the bubble which differs significantly from that of non-electrochemically produced bubbles. Numerical multi-species simulations prove that oxygen and nitrogen dissolved in the electrolyte additionally influence the bubble dissolution and slow down its shrinkage compared to pure hydrogen diffusion. In region (iii), a complete exchange of hydrogen gas with nitrogen and oxygen has occurred in the gas bubble.
Keywords: electrochemistry, electrolysis, hydrogen evolution, gas dissolution, open circuit potential, numerical simulation Registration No. 23897 - Permalink

Transitions in a Magnetized Quasi-laminar Spherical Couette Flow
Kasprzyk, C.; Kaplan, E.; Seilmayer, M.; Stefani, F.
Abstract: First results from a new magnetized spherical Couette experiment are presented.
For a line in the Re-Ha instability diagram with constant Reynolds Number Re = 1000 and increasing Hartmann number Ha we study the liquid metal movement in a spherical gap under the influence of a vertical magnetic field.
The resulting flow structures are inspected with comprehensive ultrasound technique.
Increasing the magnetic field strength until Ha = 60, we observe the equatorially anti-symmetric jet instability with azimuthal wave number m = 3 at low Ha.
At intermediate Ha, no dominant m is identifiable.
At high Ha, an unstable, equatorially symmetric state with various transitions between different azimuthal modes becomes visible.
Our observations are in agreement with numerical linear instability analysis.

Keywords: Magnetized spherical Couette flow, Instabilities
  • Contribution to proceedings
    10th PAMIR International Conference Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italy
    Proceedings of the 10th PAMIR International Conference Fundamental and Applied MHD, 9788890551932, 547-551
  • Lecture (Conference)
    10th PAMIR International Conference Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italy
Registration No. 23894 - Permalink

Influence of magnetic fields on the behavior of single hydrogen bubbles generated via water electrolysis
Karnbach, F.; Uhlemann, M.; Yang, X.; Eckert, K.; Baczyzmalski, D.; Cierpka, C.; Mutschke, G.; Gebert, A.
Abstract: Hydrogen production via water electrolysis is an established method for energy storage the efficiency of which is limited by the gas bubbles blocking the electrode surface during the process. The application of a magnetic field can be a promising solution for an increased bubble detachment due to the Lorentz force induced electrolyte convection. Therefore single hydrogen bubbles offer a nice possibility for a detailed analysis of the underlying mechanisms. To analyze the impact of the magnetic field single hydrogen bubbles were produced potentiostatically at different potentials via electrolysis of sulfuric acid at a Pt microelectrode (Ø 100 μm) with a magnetic field superimposed in two different field configurations to the electrode surface for varying magnetic field strengths. The bubble behavior was visualized by a CCD camera and the electrolyte flow analyzed via Particle Image Velocimetry and Astigmatism Particle Tracking Velocimetry. Significant changes in the current signal were obtained (Fig. 1), depending on field orientation and strength, and are discussed due to the impact of the Lorentz force induced flow around the bubble, which possibly also influences the mass transfer in the vicinity of the bubble surface. If the magnetic field is applied parallel, a different bubble behavior is observed in comparison to a perpendicular applied magnetic field what may result in a higher efficiency.
Keywords: electrochemistry, electrolysis, renewable energy, hydrogen production, water splitting, magnetic field, Lorentz force, particle tracking velocimetry
  • Poster
    10th PAMIR International Conference on Fundamental and Applied MHD, 20.-24.06.2016, Cagliari (Sardinia), Italia
Registration No. 23892 - Permalink

Test Software
Henrion, K.
Abstract: Alles Test Registration No. 23889 - Permalink

Comparative evaluation of SUV, tumor-to-blood standard uptake ratio (SUR), and dual time point measurements for assessment of the metabolic uptake rate in FDG PET
Hofheinz, F.; van den Hoff, J.; Steffen, I. G.; Lougovski, A.; Ego, K.; Amthauer, H.; Apostolova, I.
Abstract: Background

We have demonstrated recently that the tumor-to-blood standard uptake ratio (SUR) is superior to tumor standardized uptake value (SUV) as a surrogate of the metabolic uptake rate K m of fluorodeoxyglucose (FDG), overcoming several of the known shortcomings of the SUV approach: excellent linear correlation of SUR and K m from Patlak analysis was found using dynamic imaging of liver metastases. However, due to the perfectly standardized uptake period used for SUR determination and the comparatively short uptake period, these results are not automatically valid and applicable for clinical whole-body examinations in which the uptake periods (T) are distinctly longer and can vary considerably. Therefore, the aim of this work was to investigate the correlation between SUR derived from clinical static whole-body scans and K m-surrogate derived from dual time point (DTP) measurements.

Methods

DTP 18F-FDG PET/CT was performed in 90 consecutive patients with histologically proven non-small cell lung cancer (NSCLC). In the PET images, the primary tumor was delineated with an adaptive threshold method. For determination of the blood SUV, an aorta region of interest (ROI) was delineated manually in the attenuation CT and transferred to the PET image. Blood SUV was computed as the mean value of the aorta ROI. SUR values were computed as ratio of tumor SUV and blood SUV. SUR values from the early time point of each DTP measurement were scan time corrected to 75 min postinjection (SURtc). As surrogate of K m, we used the SUR(T) slope, K slope, derived from DTP measurements since it is proportional to the latter under the given circumstances. The correlation of SUV and SURtc with K slope was investigated. The prognostic value of SUV, SURtc, and K slope for overall survival (OS) and progression-free survival (PFS) was investigated with univariate Cox regression in a homogeneous subgroup (N=31) treated with primary chemoradiation.


Results

Correlation analysis revealed for both, SUV and SURtc, a clear linear correlation with K slope (P<0.001). Correlation SUR vs. K slope was considerably stronger than correlation SUV vs. K slope (R 2=0.92 and R 2=0.69, respectively, P<0.001). Univariate Cox regression revealed SURtc and K slope as significant prognostic factors for PFS (hazard ratio (HR) =3.4/ P=0.017 and HR =4.3/ P=0.020, respectively). For SUV, no significant effect was found. None of the investigated parameters was prognostic for OS.

Conclusions

Scan-time-corrected SUR is a significantly better surrogate of tumor FDG metabolism in clinical whole-body PET compared to SUV. The very high linear correlation of SUR and DTP-derived K slope (which is proportional to actual K m) implies that for histologically proven malignant lesions, FDG-DTP does not provide added value in comparison to the SUR approach in NSCLC.

Keywords: PET FDG Tumor-to-blood ratio SUR Registration No. 23888 - Permalink

Subsecond thermal processing for the advancement of thin layers and functional coatings
Skorupa, W.
Abstract: This talk reviews the advances that subsecond thermal processing in the millisecond range using xenon-filled flash lamps (FLA) brings to the processing of the most advanced thin layer and coating materials, thus enabling the fabrication of novel electronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits. An important issue of our work was the formation and characterization of semiconductor materials and coatings for the green energy advancement. Regarding photovoltaic applications, we dealt with the ion beam doping and thermal processing of PV silicon demonstrating using FLA a distinct improvement of the minority carrier diffusion length compared to rapid thermal processing and furnace treatments. Moreover, we engineered the hydrogen content in photovoltaic silicon in correlation to the phosphorus doping using plasma immersion ion implantation and FLA. Recently, we demonstrated also FLA driven boron and phosphorus in-diffusion from surface coatings. Further, we prepared coarse grained dendritic crystal structures in thin silicon films on silicon dioxide to show that the addition of carbon prevents the agglomeration of the molten silicon films and largely influences the crystallisation process. Finally the strongly developing field of large area electronics is represented by reporting on our activities in regard to transparent conductive oxide (TCO) and copper paste coatings.
Keywords: subsecond thermal processing, flash lamp annealing, ion implantation, photovoltaics, transparent conductive oxide, copper paste,
  • Invited lecture (Conferences)
    SVC (Society of Vacuum Coaters) 59th Annual Technical Conference (TechCon), 09.-13.05.2016, Indianapolis, IN, USA
Registration No. 23885 - Permalink

Range prediction for tissue mixtures based on dual-energy CT
Möhler, C.; Wohlfahrt, P.; Richter, C.; Greilich, S.
Abstract: The use of dual-energy CT (DECT) potentially decreases range uncertainties in proton and ion therapy treatment planning via determination of the involved physical target quantities. For eventual clinical application, the correct treatment of tissue mixtures and heterogeneities is an essential feature, as they naturally occur within a patient’s CT. Here, we present how existing methods for DECT-based ion-range prediction can be modified in order to incorporate proper mixing behavior on several structural levels. Our approach is based on the factorization of the stopping-power ratio into the relative electron density and the relative stopping number. The latter is confined for tissue between about 0.95 and 1.02 at a therapeutic beam energy of 200 MeV/u and depends on the I-value. We show that convenient mixing and averaging properties arise by relating the relative stopping number to the relative cross section obtained by DECT. From this, a maximum uncertainty of the stopping-power ratio prediction below 1% is suggested for arbitrary mixtures of human body tissues.
Keywords: proton and ion radiation therapy, treatment planning, computed tomography, volume averaging Registration No. 23880 - Permalink

Clinical implementation of dual-energy CT for proton treatment planning to reduce CT-based range uncertainties
Wohlfahrt, P.; Möhler, C.; Baumann, M.; Enghardt, W.; Krause, M.; Greilich, S.; Richter, C.
Abstract: Purpose/Objective:
Particle treatment planning is particularly afflicted by CT-based range uncertainties. A clinical application of dual-energy CT (DECT) provides additional tissue information to potentially achieve more precise range predictions compared to single-energy CT (SECT). Therefore, the clinical implementation of DECT was aimed to be reached in this study.

Materials/Methods:
To define an optimal DECT protocol (Siemens Somatom Definition AS: 80/140kVp, kernel D34), CT scan settings were experimentally analyzed concerning beam hardening, image quality and influence on the heuristic conversion of CT numbers into stopping-power ratios (SPRs) per look-up table (HLUT) using phantoms consisting of tissues and tissue surrogates. Differences in range prediction and dose distribution between SECT and pseudo-monoenergetic CT datasets (MonoCT), derived by a weighted sum of both DECT scans, were quantified for phantoms and patients.

Results:
For treatment planning a DECT-based MonoCT of 79 keV is optimal, since CT-based HLUT uncertainties can be reduced (Figure 1). Dose distributions planned on SECT and MonoCT datasets reveal mean range deviations of 0.3mm, gamma passing rates (1%,1mm) greater than 99.9% and no clinically relevant changes in dose-volume histograms. Therefore, DECT was clinically implemented for patients treated with protons. 70 planning and 400 control DECT scans of overall 90 patients were acquired until January 2016.

Conclusions:
More precise range predictions and a wider diagnostic variety are feasible with DECT-based MonoCTs. Further improvements are expected from a direct, patient-specific, non-heuristic SPR determination. To quantify their possible benefits, first investigations of intra- and interpatient variations were performed on the still growing patient database.

Keywords: dual-energy CT, proton therapy
  • Poster
    PTCOG - annual conference, 23.-28.05.2016, Prag, Czech Republic
Registration No. 23879 - Permalink

Dual-energy CT for range prediction in proton and ion therapy
Möhler, C.; Wohlfahrt, P.; Richter, C.; Jäkel, O.; Greilich, S.
Abstract: Purpose/Objective:
Proton and ion therapy require accurate prediction of particle ranges in tissue. In current clinical practice, computed tomography (CT) images are voxel-wise converted to ion-stopping power ratio maps using direct heuristic relations. The general validity of these approaches is, however, limited due to the different physical regimes of photon and ion interaction. Using a more sophisticated method based on dual-energy CT (DECT), which provides access to the physical quantities influencing photon attenuation, Hünemohr et al. (2014) reported an improved ion-range prediction for homogeneous tissue surrogates. Here, we present a major modification of the latter method, enabling a proper treatment of heterogeneities and mixtures on several structural levels, which represent a crucial feature of the realistic clinical situation.

Material and Methods:
We treat the stopping-power ratio as the product of the electron density relative to water and a correction factor that implicitly involves the logarithmic dependence on the mean excitation energy (I-value). The relative electron density, being an important parameter in both photon and ion energy loss, can be derived directly from DECT scans using a universal and robust method. The correction factor, however, has to be determined with an empirical method. For this purpose, we propose to use the information from CT images that is complementary to the relative electron density, i.e. the electronic photon absorption cross section relative to water. Using the attenuation sum rule and Bragg’s additivity rule, the relative cross sections and correction factors were calculated for single elements, tissue base materials like water, lipid, etc. and tabulated real tissues.

Results:
For a therapeutic beam energy of 200 MeV/u, the correction factor varies between 1.15 and 0.70 for single elements with atomic numbers between 1 and 100. Building up compounds from a certain number of elements, a maximum spread of possible values for the correction factor can be quoted for a given relative cross section, due to the mathematical structure of the variable space. In practice, this could be used as an uncertainty estimate for a given calibration. The accessible variable space is drastically reduced by admitting only tissue base materials such as water, lipids and hydroxylapatite. The space is further reduced by admitting only mixtures of real tissue materials. For human tissue, the correction factor is thus limited overall to a small range around one (0.96 - 1.02).

Conclusions:
With the definition of the correction factor in the stopping-power ratio prediction and its relation to the relative cross section, a mathematically rigorous treatment of tissue mixtures was made possible. Such mixtures influence CT imaging of patients e.g. in the form of volume averaging in a CT voxel. This thorough treatment of mixtures, like the one presented here, is thus essential for the clinical applicability of DECT-based ion-range prediction.

Keywords: dual-energy CT, proton therapy
  • Poster
    ESTRO 35 - annual meeting, 29.04.-03.05.2016, Turin, Italy
Registration No. 23878 - Permalink

Trapping of hydrogen and helium at dislocations in tungsten: an ab initio study
Bakaev, A.; Grigorev, P.; Terentyev, D.; Bakaeva, A.; Zhurkin, E. E.; Posselt, M.
Abstract: Retention of plasma gas components such as hydrogen (H) isotopes and helium (He) is one of the limiting factors in selection of plasma facing materials for future thermonuclear fusion devices. Tungsten (W) is one of the promising candidates for such materials and was chosen for the divertor armor for International Thermonuclear Experimental Reactor (ITER) and the first wall material for the design of the demonstrational fusion power plant - DEMO. For the analytical estimation of accumulation of H/He components in tungsten, it is important to understand the relevant physical mechanisms of their trapping in the material and thoroughly parameterize them numerically.
Experiments involving high flux plasma exposures of tungsten at temperature below 500 K conclude on significant amount of retained hydrogen, which unlike helium, does not agglomerate in the form of clusters in the bulk defect-free material. The observed hydrogen isotope trapping and deep diffusion is conventionally attributed to the trapping at the natural lattice defects such as dislocations and grain boundaries.
Computational assessment of trapping strength and capacity of the dislocations is the subject of this work. Here the electronic structure calculations using density functional theory (DFT) are done to evaluate the affinity of hydrogen and helium to the screw and edge dislocations. For this, we calculate the interaction energy map around the dislocation core for hydrogen and helium atoms. The energetically favorable positions are rationalized on the basis of charge density distribution and local stress concentraion. The results obtained help to refine the input parameters of the macro-scale models of retention of plasma components, such as mean field rate theory methods.
The additional molecular statics simulations are also performed to analyze whether the contempory atomistic models using the recently developed interatomic potentials for W-H-He system can grasp adequately the interaction of H and He with dislocations.

Keywords: H and He in W, trapping at dislocation, DFT
  • Lecture (Conference)
    13th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2016), 19.-24.06.2016, Loughborough, UK
Registration No. 23877 - Permalink

Operation and sound field of an ultrasonic biplane-array
Hipp, R.; Gommlich, A.; Joneit, D.; Schubert, F.; Heuer, H.
Abstract: For ultrasonic non-destructive testing several types of transducers are available based on single-channel or multi-channel technology. Transducers with more than two individual elements are usually called arrays. These arrays can differ in geometry and arrangement of their individual elements, e.g. linear, matrix and annular geometry. The advantage of arrays in contrast to single element transducers is the ability to tilt and focus the sound beam to a desired region inside the specimen. The biplane phased array is a new possibility in NDE for combining the advantages of linear phased arrays, regarding low costs and high compatibility to existing phased array electronics with the goal of matrix arrays to get signal information from the evaluated specimen in all three dimensions. The biplane array consists of a piezoelectric sensor with a conventional line electrode structure on the top and a second perpendicular line electrode structure rotated by 90° on the bottom side of the piezo layer. By using appropriate excitation and control techniques the biplane array is able to perform a conventional sector scan in two spatial directions. Moreover it is also possible to excite or receive with one single element or a choice of adjacent elements which allows flexible 3-D reconstruction techniques. All these features go along with significantly less technological effort compared to 2-D matrix arrays where each single element needs to be electrically connected and a large number of individual channels needs to supported by the used ultrasonic hardware. The paper describes and visualizes the operation of a biplane array by calculating its spatio-temporal sound field. The numerical simulations are performed by the CEFIT-PSS technique, a powerful combination of the axisymmetric Elastodynamic Finite Integration Technique (EFIT) with transient Point Source Synthesis (PSS).
Keywords: sound field simulation, biplane-array, cefit, pss
  • Contribution to proceedings
    19th World Conference on Non-Destructive Testing 2016, 13.-17.06.2016, München, Deutschland

Downloads:

Registration No. 23876 - Permalink

Kinetic Monte Carlo simulation of irradiation-induced nanostructure evolution in Oxide Dispersion Strengthened Fe alloys
Liedke, B.; Posselt, M.; Murali, D.; Claisse, A.; Olsson, P.
Abstract: Rigid-lattice Kinetic Monte Carlo simulations are performed in order to investigate the modification of Y-Ti-O nanoclusters during irradiation, at selected temperatures, doses and dose rates. The simulations use input parameters for the atomic interactions and the migration barriers obtained by DFT calculations as well as data on representative examples of the cascade debris determined by Molecular Dynamics. Before irradiation the nanostructure is prepared by performing thermal relaxation of a system with randomly distributed Y, Ti, O atoms, and vacancies. The concentration of Y, Ti, and O is chosen according to the common 14 YWT ODS alloy and both low and high vacancy contents are considered. The nanostructures obtained in the preparation step were used subsequently in KMC simulations of irradiation. The results demonstrate the competition between ballistic effects leading to the dissolution and the growth of the clusters. While the former effect dominates at high doses and low temperatures the latter prevails at low doses and high temperatures. On the other hand, the nanoclusters formed in the preparation step show a very high stability under irradiation within the temperature and dose range relevant for the application of ODS alloys in advanced nuclear reactors. The findings of this work are consistent with the results of experimental studies of ion and neutron irradiation of ODS alloys.
Keywords: Oxide Dispersion Strengthened (ODS) Fe alloys, Kinetic Monte Carlo simulation, Irradiation
  • Lecture (Conference)
    13th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2016), 19.-24.06.2016, Loughborough, UK
Registration No. 23875 - Permalink

First-principles-based calculation of self- and solute diffusion in bcc-Fe
Posselt, M.; Abdou, J.; Murali, D.; Liedke, B.
Abstract: DFT calculations were performed in order to study self-diffusion as well as oxygen and titanium diffusion in bcc Fe. It is commonly accepted that self-diffusion proceeds via the exchange of a Fe atom with a vacancy. The octahedral interstitial site is the most stable position of oxygen in bcc Fe. Therefore, it is assumed that O diffuses via the interstitial mechanism, i.e. an O atom moves from one octahedral site to the other. As for other substitutional solutes in bcc Fe, in the case of Ti the vacancy mechanism is considered. The migration barriers occurring in all these processes were calculated using the Nudged Elastic Band method. The corresponding attempt frequencies were obtained from the difference between the vibrational contribution to the free energy of the related equilibrium and saddle point configurations. While in the case of self- and O-diffusion only one saddle point and one attempt frequency are relevant, several barriers and frequencies must be determined to consider Ti diffusion by the vacancy mechanism. Different models were used to obtain the diffusion coefficient of Ti: (i) the original nine-frequency model [1], (ii) a modified nine-frequency model [2], and (iii) the Self-Consistent Mean Field model [3]. The comparison between the calculated self-, O-, and Ti-diffusion coefficients with experimental data shows significant differences. This is mainly due to fact that electron and magnon excitations were neglected in the calculations, whereas the phonon excitations were taken into account via the vibrational free energy. Under the assumption that electron excitations are small different phenomenological models are applied to consider the magnon excitations, which decrease the spontaneous magnetization of bcc Fe with increasing temperature. Choosing suitable model parameters a good agreement with measurements is obtained for self- and Ti-diffusion. On the other hand, the agreement with the few existing experimental data on O diffusion is poor. Possible reasons for this are discussed.

[1] A. D. Le Claire, in Physical chemistry: an advanced treatise, edited by H. Eyring
(Academic Press, New York, 1970).
[2] L. Messina, M. Nastar, T. Garnier, C. Domain, P. Olsson, Phys. Rev. B 90, 104203 (2014)
[3] M. Nastar, Philos. Mag. 85, 3767 (2005).

Keywords: Self- and solute diffusion, bcc-Fe, DFT
  • Poster
    13th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2016), 19.-24.06.2016, Loughborough, UK
Registration No. 23873 - Permalink

On determination off focal laws for linear phased array probes as to the active and passive element size
Gommlich, A.; Schubert, F.
Abstract: Ultrasonic linear phased array probes consist of several single transducer elements. By exciting each single element at a particular time wave fronts can be tilted, focused or both combined. The required set of time delays is called ''focal law''. Hence, the shape of the resulting wave front depends significantly on focal law calculation. The typical single transducer element in linear phased array probes has a rectangle shape with a width-to-length-ratio of approximately 0.1 to 0.5. The width of the short side is called ''active aperture size'', the larger one is called ''passive aperture size''. In state of the art calculations of the focal laws only the pitch between the single elements is considered and the elements are approximated by a point source in the centre of their aperture. Therefore, the real dimensions of the elements - both the active and the passive dimension - have no further influence. Moreover the wave propagation process itself is modelled by geometrical acoustics.
The numerical CEFIT (Cylindrical Elastodynamic Finite Integration Technique) in combination with transient PSS (Point Source Synthesis) enables flexible and fast simulation of 4-D spatio-temporal sound fields in homogeneous and layered half spaces, espectively. Thereby all wave physical effects like diffraction, scattering and mode conversion will be considered. The calculations with different geometrical parameters for the probes show that both the active as well as the passive aperture size influence the time and frequency characteristic of the signal in the focal point. Based on the focal laws calculated with and without respect to the aperture size, sound fields were simulated for selected focal points. The results were qualitatively and quantitatively compared whereby the differences between both methods are distinguishable. It becomes evident that geometrical focus and acoustical focus are different. The feasibility of corrections for the focal laws with respect to time and frequency characteristics in the focal point as well as the improvement of resolution will be discussed. The results further allow an estimation of the optimal width-tolength-ratio for single transducer elements of linear phased arrays.

Keywords: focal law, phased array, sound field simulation, cefit, pss
  • Contribution to proceedings
    19th World Conference on Non-Destructive Testing 2016, 13.-17.06.2016, München, Deutschland

Downloads:

Registration No. 23872 - Permalink

Tuning pattern symmetry by choosing the substrate in reverse epitaxy
Engler, M.; Ou, X.; Facsko, S.
Abstract: Ion beam erosion of solid surfaces is long known to yield regular surface morphologies, like periodic ripples or hexagonal dot patterns. At room temperature, semiconductors are amorphized by the ion beam. Pattern formation under these conditions has been studied extensively in the last decades.

Ion beam erosion above a material dependent dynamic recrystallization temperature allows the formation of crystalline nano scale patterns on semiconductor surfaces. At these elevated temperature pattern formation is driven by diffusion of vacancies created by sputtering of atoms. Anisotropic diffusion on the surface and diffusion barriers across step edges lead to the formation of pattern reflecting the symmetry of the irradiated surface. We will discuss how the surface symmetry determines the pattern symmetry.

Keywords: reverse epitaxy ion beam pattern pattern formation semiconductor
  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Deutschland
Registration No. 23868 - Permalink

Time-Resolved Two Million Year Old Supernova Activity Discovered in the Earth’s Microfossil Record
Bishop, S.; Ludwig, P.; Egli, R.; Chernenko, V.; Deveva, B.; Faestermann, T.; Famulok, N.; Fimiani, L.; Gomez, J.; Hain, K.; Korschinek, G.; Hanzlik, M.; Merchel, S.; Rugel, G.
Abstract: Massive stars (M≥M⊙), which terminate their evolution as core collapse supernovae, are theoretically predicted to eject >10−5M⊙ of the radioisotope 60Fe (t1/2=2.6 Ma). If such an event occurs sufficiently close to our solar system, traces of the supernova debris could be deposited on Earth. Herein, we report a time-resolved 60Fe signal residing, at least partially, in a biogenic reservoir. Using accelerator mass spectrometry, this signal was found through the direct detection of live 60Fe atoms contained within secondary iron-oxides, among which are magnetofossils; the fossilized chains of magnetite crystals produced by magnetotactic bacteria. The magnetofossils were chemically extracted from two Pacific Ocean sediment drill cores. Our results show that the 60Fe signal onset occurs around 2.6−2.8 Ma, near the lower Pleistocene boundary, terminates around 1.7 Ma, and peaks at about 2.2 Ma.
Keywords: accelerator mass spectrometry, AMS
  • Invited lecture (Conferences)
    2016 Carpathian Summer School of Physics, Romania: http://cssp16.nipne.ro/, 26.06.-09.07.2016, Sinaia, Romania
Registration No. 23867 - Permalink

Validation of the surveillance concepts and trend curves by the investigation of decommissioned RPVs
Viehrig, H.-W.; Altstadt, E.; Houska, M.; Valo, M.
Abstract: The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald NPP representing the first generation of Russian type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The paper presents test results measured on trepans taken from the multilayer beltline welding seam SN0.1.4. and forged base metal ring 0.3.1. located in the reactor core region of the Unit 4 RPV. This unit was shut down after 11 years of operation and represents the irradiated condition. The characterisation of the irradiation response is based on the measurement of the hardness, the yield stress, the Master Curve reference temperature, T0, and the Charpy-V transition temperature through the thickness of multi-layer beltline welding seam SN0.1.4 and the forged base metal ring 0.3.1.
For the beltline welding seam we observed a large variation in the through thickness T0 values. The T0 values measured with the T-S-oriented Charpy size SE(B) specimens cut from different thickness locations of the multilayer beltline welding seam strongly depend on the intrinsic weld bead structure along the crack tip. In general, the fracture toughness values at cleavage failure, KJc-1T, measured on SE(B) specimens from beltline welding seam follow the Master Curve description, but more than the expected number lie outside the curves for 2 % and 98 % fracture probability. In this case the test standard ASTM E1921 indicates the investigated multi-layer weld metal as not uniform. The multi modal Master Curve based approach describes the temperature dependence of the specimen size adjusted KJc-1T values well.
The KJc values measured on L-S oriented Charpy size SE(B) specimens from defined thickness locations of the forged base metal ring 0.3.1. strongly scatter. The progression of the T0 values through the thickness lies in the range from 121 °C to 130 °C and indicate no irradiation induced embrittlement within the through the thickness fluence range from 5.38 to 1.20 ∙ 1019 n/cm2 (E > 0.5 MeV). The application of the multi modal extension [Wallin 2004, Viehrig 2006, Scibetta 2010] on the summarised dataset does essentially improve the situation. More than allowed 2% of the specimen size adjusted KJc-1T values lie below the fracture toughness curve for 2% fracture probability. The reason for the occurrence of very low KJc values is seen in intergranular planes detected on the fractured surfaces of the specimens. The application of modified MC based evaluation methods indicates the material as non-homogeneous.
The investigation show that Master Curve, T0, and Charpy-V, TT47J, based ductile-to-brittle transition temperature progressions through the thickness of the multi-layer welding seam and the forged base metal ring of the decommissioned Greifswald WWER-440 first generation RPV do not correspond to the forecast according to the current Russian code.

Keywords: reactor pressure vessel, multi-layer welding seam, forged base metal ring, neutron irradiation, hardness, tensile strength, fracture toughness, Master Curve approach, Charpy-V
  • Lecture (Conference)
    Workshop on Nuclear Reactor Pressure Vessel Surveillance Programs, 28.-29.06.2016, Chicago, USA
Registration No. 23866 - Permalink

Protective effects of 2,3-diaryl-substituted indole-based cyclooxygenase-2 inhibitors on oxidative modification of human low density lipoproteins in vitro
Pietzsch, J.; Laube, M.; Bechmann, N.; Pietzsch, F.-J.; Kniess, T.
Abstract: It has been suggested that 2,3-diaryl-substituted indole-based

cyclooxygenase-2 (COX-2) inhibitors (2,3-diaryl-indole coxibs) do not only appear as potent anti-inflammatory agents but also show the ability to scavenge reactive oxygen species (ROS). This led to the hypothesis that 2,3-diaryl-indole coxibs also may act as potent inhibitors of oxidative modification of low-density lipoprotein (LDL), which is considered a key factor in atherogenesis. The aim of this study was to explore i) the reactivity of a series of new synthesized 2,3-diaryl-indoles with several well characterized LDL oxidation systems and ii) subsequent effects on an inflammatory/atherogenic microenvironment. The results demonstrate that under the present experimental conditions 2,3-diaryl-indoles showed potent ROS scavenging activity and were able to markedly inhibit LDL oxidation. Subsequently, this led to a substantial decrease of modified LDL uptake by scavenger receptors in THP-1 macrophages in vitro and in rats in vivo. Moreover, modified LDL-mediated monocyte/neutrophil adhesion to endothelial cells, macrophage NF kappa B activation, as well as macrophage and endothelial cell cytokine release was diminished in vitro. The reduction of modified LDL-induced atherogenic effects by antioxidant 2,3-diaryl-indole coxibs may widen the therapeutic window of COX-2 targeted treatment.

Keywords: Antioxidants, atherogenesis, selective cyclooxygenase-2 (COX-2) inhibitors (coxibs), inflammation, lipid peroxidation, protein oxidation, radical scavenger, reactive oxygen species (ROS) Registration No. 23861 - Permalink

Visualization of trace-element zoning in apatite using BSE and CL imaging and EPMA and particle-induced X-ray/gamma-ray emission mapping
Gros, K.; Słaby, E.; Förster, H.-J.; Michalak, P. P.; Munnik, F.; Götze, J.; Rhede, D.
Abstract: In this paper, zonation patterns of trace elements in apatite were visualized using four analytical techniques, namely back-scattered electrons (BSE) and cathodoluminescence (CL) imaging and electron probe micro-analysis (EPMA) and micro-proton-induced X-ray/gamma-ray emission (μPIXE/μPIGE) mapping. Each method demonstrates the in-grain compositional variations in a slightly different way. Both BSE and CL provide qualitative data, and the internal textures are displayed in most detail. Additionally, CL points to specific elements enriched in certain growth zones. Qualitative EPMA maps show detailed zonation patterns for specific elements (with high spatial resolution), which are in general correspondence with the patterns observed in BSE and CL images. The µPIXE/µPIGE maps are fully quantitative and the detection limits are relatively low compared to EPMA mapping. In present spot measurements µPIXE demonstrates lower detection limits than EPMA, however, the latter could be considerably improved by extending the acquisition times. There is no significant overlap of REE (rare earth elements) peaks in the acquired µPIXE energy spectra, however, when multiple REEs are present with sufficiently high concentrations, peak deconvolution may pose some difficulties. Spatial resolution of µPIXE/µPIGE images is not sufficiently high to reflect minor textural features, which also result from the greater interaction depth of the proton beam. However, major growth zones are distinguishable. Even though each method has their advantages and limitations, when applied together, they provide an almost complete characterization of compositional variability in trace-element-bearing minerals.
Keywords: trace-element zoning, apatite, BSE, CL, EPMA, µPIXE/µPIGE

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Registration No. 23856 - Permalink

Qualification of CFD-models for multiphase flows in medium and large scale industrial applications
Lucas, D.
Abstract: Multiphase flows are frequently applied in industrial processes as e.g. in chemical engineering, oil industries or power plants. Reliable predictions of the flow characteristics such as local concentration of species, interfacial area density or heat transfer in gas-liquid flows can contribute to an optimization of the design of corresponding apparatuses and processes. Computational Fluid Dynamics (CFD) in principle allows the simulation of such flows and provides local flow characteristics. While it is frequently used for industrial problems in case of single phase flows it is not yet mature for two-phase flows. The reason is the complex gas-liquid interface. For medium and large scale flow domains it is not feasible to resolve all details of this interface. Averaging procedures have to be applied and in most cases the so-called two- or multi-fluid approach is used. It assumes interpenetrating phases and the information on the interface gets lost by these averaging procedures. This information has to be added to the basic balance equations by so-called closure models. The development and validation of such models is done at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) to obtain tools for reliable predictions of multiphase flow characteristics in medium and large industrial scales.
One difficulty for the model development and validation results from the fact that we still have a lack of knowledge on local phenomena which determine the two-phase flow characteristics and which should be considered in the closure models. Experimental data with high resolution in space and time are required. To get such information on the gas-liquid interface new innovative measuring techniques as wire-mesh sensors and ultrafast X-ray tomography were developed at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) and extensively used to establish comprehensive databases. The corresponding experiments were conducted at the TOPFLOW-facility of HZDR. It can be operated for air-water and steam-water flows with a pressure up to 7 MPa and the corresponding saturation temperature of 286 °C. An electrical steam generator with a power of 4 MW is able provide up to 1.5 kg steam per second.
In this lecture the strategy of the CFD-model development and validation for multiphase flows is presented. This includes the corresponding experimental work and development of innovative measuring techniques.

Keywords: CFD, two-phase flow, TOPFLOW
  • Invited lecture (Conferences)
    Lecture series of the Energy Department of Politecnico die Milano, 15.06.2016, Milano, Italy
Registration No. 23853 - Permalink

Radiation-Hard Ceramic Resistive Plate Chambers for Forward TOF and T0 Systems
Akindinov, A.; Dreyer, J.; Fan, X.; Kämpfer, B.; Kiselev, S.; Kotte, R.; Laso Garcia, A.; Malkevich, D.; Naumann, L.; Nedosekin, A.; Plotnikov, V.; Stach, D.; Sultanov, R.; Voloshin, K.
Abstract: Resistive Plate Chambers with ceramic electrodes are the main candidates to be used in precise multi-channel timing systems operating in high-radiation conditions. We report the latest R&D results on these detectors aimed to meet the requirements of the forward T0 counter at the CBM experiment. RPC design, gas mixture, limits on the bulk resistivity of ceramic electrodes, efficiency, time resolution, counting rate capabilities and ageing test results are presented. Registration No. 23851 - Permalink

Methoden zur Charakterisierung und Optimierung von Belebungsbecken
Reinecke, S. F.; Hampel, U.
Abstract: Für den Großteil der in Deutschland betriebenen Kläranlagen übersteigt die aufgewendete Energie zur Durchmischung und Belüftung des Abwassers oftmals den tatsächlich notwendigen Energiebedarf. Dies wird oft durch eine nicht-optimale Auslegung bzw. Anordnung der Begasungs- und Dispergierorgane im Belebtschlammbecken hervorgerufen. Im Vortrag werden die am HZDR durchgeführten Forschungsvorhaben zur Effizienzsteigerung von Abwasseraufbereitungsanlagen vorgestellt.
  • Lecture (Conference)
    25. Lehrer-Obmann-Tag der Kläranlagen- und Kanal-Nachbarschaften, 15.-16.03.2016, Dresden, Deutschland
Registration No. 23850 - Permalink

Tomographic Interrogation of Gas-Liquid Flows in Inclined Risers
Lokman, A. A.; Escrig, E.; Reinecke, S.; Hewakandamby, B. N.; Azzopardi, B. J.
Abstract: Measurements have been made with Electrical Capacitance Tomography (ECT) and a Wire Mesh Sensor (WMS) using air-silicone
oil (viscosity 5 mPa s) on a 67 mm diameter pipe. The experiments were carried out in a facility at Nottingham University different
inclinations. The cross-sectional distribution of gas fraction is obtained from the WMS and from the ECT the latter after post -
processing. The combined data is used to provide information on the size, frequency and velocity of large bubbles (Taylor bubbles
and spherical cap bubbles) and how they are influenced by the phase flow rates and the pipe inclinations. The boundary for spherical
cap bubbles is identified. In addition, WMS output presents the results for a radial void fraction, as well as bubble size distribution, in
particular that gives the percentage of void fraction in relation to bubble diameter. It is concluded that moving from horizontal to
inclined to vertical, there is an increase in the percentage of smaller bubbles. There are also large diameter bubbles forming for all the
inclinations. The cross-section averaged void fraction and its variation in time were measured. Taylor bubble frequency increases
with increasing of liquid flow rate and inclination angle of the pipe

Keywords: wire mesh sensor, electrical capacitance tomography, two phase flow, inclined riser
  • Contribution to proceedings
    ICMF-2016 - 9th International Conference on Multiphase Flow, 22.-27.05.2016, Florenz, Italien
    Proceedings of ICMF-2016
  • Lecture (Conference)
    ICMF-2016 - 9th International Conference on Multiphase Flow, 22.-27.05.2016, Florenz, Italien
Registration No. 23848 - Permalink

Untersuchung der Hydrodynamik von ovalen Biogasreaktoren mit instrumentierten Strömungsfolgern
Reinecke, S. F.; Hampel, U.
Abstract: Zur Untersuchung der ablaufenden Prozesse in großen Behältern, wie z. B. Biogasfermentern, Bioreaktoren und Belebtschlammbecken, wurde am HZDR das Konzept instrumentierter, strömungsfolgender Sensorpartikel entwickelt. Die Sensorpartikel werden als auftriebsneutrale Strömungsfolger eingesetzt und erfassen dabei kontinuierlich Prozessparameter. Diese Daten werden nach der Rückgewinnung der Sensorpartikel aus dem Prozess einem computergestützten Analysesystem zur Verfügung gestellt. Die erweiterten Sensorpartikel bestehen aus robusten Kapseln, welche mit einer integrierten Messelektronik und einer mechanischen Auftriebseinheit zur Tarierung und Rückgewinnung ausgestattet sind (Abb. 1). Das Systemkonzept berücksichtigt derzeit miniaturisierte Sensoren für die Umgebungstemperatur, die Eintauchtiefe als Funktion des hydrostatischen Drucks, die Beschleunigung und das Magnetfeld und offen für die Einbindung ergänzender miniaturisierter Messfühler, wie z.B. für pH-Wert und Gelöst-Sauerstoff.
Zur Erweiterung der Positionserfassung wurde die Detektion eines festen Positionsmarkers mit den Sensorpartikeln realisiert. Als Positionsmarker wird eine eigens entwickelte Tauschspule eingesetzt, deren kodiertes Anregungssignal über das entstehende Magnetfeld von den vorbeiströmenden Sensorpartikeln empfangen wird.
Die Sensorpartikel mit magnetischer Positionsdetektion wurden erstmals in einer hydrodynamischen Studie von drei Fermentern mit ovalen Behältergeometrien genutzt . Die Fermenter haben ein Füllvolumen von 1,5 m³, 2 m³ und 32 m³ und wurden mit je zwei horizontalen Rührwerken bei zwei Umfangsgeschwindigkeiten (5,5 m/s und 6,7m/s) in einer Xanthan-Lösung (5 g/L) betrieben (Abb. 2).
Mit der Positionsdetektion im Scheitelpunkt der Fermenter wurden die Zirkulationszeitverteilungen der Fluidelemente bestimmt (Abb. 3). Dies lässt Aussagen über das Mischverhalten in den Behältern zu. In Kombination mit den extrahierten vertikalen Aufenthaltsprofilen der Sensorpartikel erfolgt ein Vergleich der drei Fermenter.
  • Poster
    Jahrestreffen Reaktionstechnik 2016 zusammen mit der Fachgruppe Mischvorgänge, 02.-04.05.2016, Würzburg, Deutschland
Registration No. 23846 - Permalink

Instrumented flow-following sensor particles with magnetic position detection and buoyancy control
Reinecke, S. F.; Hampel, U.
Abstract: A concept for buoyancy control and magnetic position detection has been developed for the improvement of instrumented flow-following sensor particles. The sensor particles are used for investigation of hydrodynamic and biochemical processes in large-scale vessels such as biogas fermenters, bioreactors and aerated sludge basins. Neutral buoyancy of the sensor particles is required for tracing of the fluid flows. Buoyancy control is performed by adjustment of the sensor particles’ volume, which is altered by an integrated piston. A miniaturized linear actuator, namely a stepper motor with linear transmission, is operated by a microcontroller to drive the piston. The buoyancy control unit enables accurate automated taring of the sensor particles in the stagnant process fluid to achieve neutral buoyancy. Therefore, the measured vertical position of the sensor particle as a function of the hydrostatic pressure is used as feedback. It has an incremental density change of 0.0136 % as compared to water and a residual drift velocity of approximately 3.6 × 10−3 m s−1. Furthermore, a minimum density of 926 kg m−3 can be set by full extension of the piston, which allows floating of the sensor particles after a defined event, namely critical charge of battery, full data storage or the end of a fixed time cycle. Thus, recovery of the sensor particles can proceed easily from the fluid level. The sensor particles with a buoyancy control unit are tested for depths up to 15 m. Also, detection of a local magnetic position marker by the sensor particles has been implemented to enhance movement tracking. It was tested in a lab-scale biogas digester and was used for estimation of the liquid circulation time distribution and Peclét number to describe the macro-flow.
Keywords: Flow follower, sensor particle, autonomous sensor, position detection, buoyancy

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Registration No. 23845 - Permalink

In-situ study of high temperature stability and optical properties of aluminum-titanium oxynitride thin films
Heras, I.; Guillén, E.; Wenisch, R.; Krause, M.; Escobar-Galindo, R.
Abstract: Aluminum-titanium oxynitride AlTiO(x)N(y) thin films were investigated in order to understand the influence of the oxygen/nitrogen ratio on the optical properties and their failure mechanisms at high temperatures. The optical properties of oxynitride thin films as well as their high temperature stability showed a wide range of different responses according the oxygen/nitrogen ratio and the deposition pressure. AlTiO(x)N(y) thin films were deposited by cathodic vacuum arc and characterized at different temperatures to follow the temperature dependence of the composition and the optical constants. The samples were heated in vacuum from room temperature up to 800°C inside a multi-chamber cluster tool and the analysis of the thin films was carried out in-situ without intermittent sample exposure to air. Ellipsometry and Rutherford backscattering spectrometry (RBS) results showed the influence of the as-deposited oxygen content in the sample with the inward diffusion of oxygen into the coating and therefore oxidation resistance at high temperatures. Likewise, ex-situ annealing in air was performed to compare the results observed when exposed to ambient conditions. The low emittance properties of AlTiO(x)N(y) enabled in-situ RBS analysis at temperatures higher than 750°C. No significant changes of the optical properties and composition were found when heating in vacuum demonstrating excellent stability at high temperatures.
Keywords: solar-selective coatings, concentrated solar power, in situ RBS, cluster tool
  • Lecture (Conference)
    EMRS 2016 Spring Meeting, 02.-06.05.2016, Lille, Frankreich
Registration No. 23844 - Permalink

High-field paramagnetic Meissner effect up to 14 T in melt-textured YBa2Cu3O7–δ
Dias, F. T.; Vieira, V. N.; Wolff-Fabris, F.; Kampert, E.; Gouvea, C. P.; Campos, A. P. C.; Archanjo, B. S.; Schaf, J.; Obradors, X.; Puig, T.
Abstract: We have performed magnetization experiments in a melt-textured YBa2Cu3O7-δ (Y123) sample with Y2BaCuO5 (Y211) inclusions, under magnetic fields up to 14 T applied parallel or perpendicular to the ab plane. Magnetic anisotropy and paramagnetic moments were observed in both FC (field-cooling) and FCW (field-cooled warming) procedures and these features correspond to the so-called High-Field Paramagnetic Meissner Effect (HFPME). The HFPME effect increases monotonically as the magnetic field rises and a strong paramagnetic relaxation, toward increasing paramagnetic moment was additionally observed as a function of time. Microscopy analysis revealed a complex and correlated microstructure of the Y211 particles. These correlated defects are well known to cause strong flux pinning. Our results suggest a scenario of strong flux compression within weak or non-superconducting regions of the samples, developed as a consequence of the Meissner effect and assisted by strong flux pinning by the Y211 particles. This scenario is observed up to 14 T and clearly persists beyond. Registration No. 23843 - Permalink

Development of interatomic potential for bcc FeCrNi and its validation
Bonny, G.; Bakaev, A.; Olsson, P.; Domain, C.; Zhurkin, E. E.; Posselt, M.
Abstract: Potential:
Vac-Ni dragging possible
DFT logic substitutional configs reproduced
Most stable interstitial configs reproduced
Defect free Monte Carlo simulations:
Cr and Ni precipitate as separate fractions
Cr precipitation is independent of Ni content (<2%Ni)
Ni precipitation is enhanced by Cr

Keywords: FeCrNi alloy, interatomic potential
  • Lecture (Conference)
    8th N-FAME Workshop on modelling and modelling-oriented experiments in Fe alloys for nuclear applications, 13.-14.06.2016, Brussels, Belgium
Registration No. 23841 - Permalink

Radiation-induced segregation in FeNiCr model alloys
Bakaev, A.; Posselt, M.; Terentyev, D.; Bonny, G.; Zhurkin, E. E.
Abstract: Defect-free FeNiCr alloys:
No influence of Ni on Cr solubility, limited effect of Cr on Ni at 2%Ni : ↗100 K
Ni and Cr precipitate as separate fractions. Ni forms B2 FeNi clusters with {100} facets while the Cr atoms form pure Cr clusters with {110} facets
FeNiCr alloys with dislocation loops:
No mixing of Ni and Cr precipitates: Ni moves to compressive regions, Cr - tensile regions
Dislocation loops stabilize by 100-200 K Ni clusters only at Ni content in the alloy >=0.5%
Ni decreases significantly the segregation of Cr, cancelling the segregation or causing the depletion at Ni>=1%
Cr decreases the segregation of Ni at ½<111> loops for low Ni (0.25%) alloys, strongly enhances the Ni segregation at <100> loops for high Ni (2%) at T < 800 K due to Cr depletion
Enrichment values for Cr and Ni at ½<111 > loops at T = 600 K are consistent with experiments:
small ½<111> loops can serve as nucleus for NiCr(Si/P)-rich clusters

Keywords: FeCrNi alloys, radiation-induced segregation, Metropolis Monte Carlo simulation
  • Lecture (Conference)
    8th N-FAME Workshop on modelling and modelling-oriented experiments in Fe alloys for nuclear applications, 13.-14.06.2016, Brussels, Belgium
Registration No. 23840 - Permalink

Spatially-resolved sorption studies of Eu(III) on granite surface with time-resolved laser fluorescence microscopy (TRLFM)
Zesewitz, K.; Schmidt, M.
Abstract: The finding of an appropriate long-term repository for high-level nuclear waste is a highly relevant topic. To that end, it is required to research the interaction of occurring radionuclides with mineral phases contained in possible host rocks and construction materials. On a time scale of up to a million years, especially the scenario of a water intrusion into the repository and thus dissolution of radionuclides has to be considered. To investigate the sorption behavior of actinides and lanthanides, time-resolved laser fluorescence spectroscopy (TRLFS) is a widely used method, because of its trace concentration sensitivity and capability to distinguish multiple species in complex systems. On one hand this method gives the spectral information of the emitted fluorescence light, which allows determining the symmetry and the grade of complexation of the sorbed Ln/Ac. On the other hand the lifetimes of the excited electron states provide information about the surrounding quenchers, mainly water. Typically, TRLFS investigations will focus on the interaction of an actinide with one relevant mineral phase. For a real rock formation, e.g. granite, sorption will however be a competitive process involving multiple mineral phases at the same time.
In this study a new method called time-resolved laser fluorescence microscopy (TRLFM) is introduced, which will add a spatial dimension to TRLFS. By doing so, it is possible to separate the multi-phase system into discrete single-phase systems and therefore to make a step beyond model systems by researching, for example whole natural granite rock with TRLFS. Because of its advantageous fluorescence properties we use europium as an analogue for the trivalent actinides americium and curium. Sorption experiments with Eu(III) on granite under different solution conditions, regarding metal concentration and pH will be presented. These samples are excited by a focused pulsed laser beam at a wavelength of 394 nm, and scanned through the laser’s focal point by an XYZ-Stage with a resolution in the micrometer range. The sample is subsequently mapped by Raman-Microscopy to distinguish the different phases and the TRLFM data is then compared to the combination of Raman-data with TRLFS data of the single phases.
First results show that the different sorption behavior of the single phases can be resolved by this method. Lifetimes and emission spectra have been measured for quartz, feldspar and mica phases on granite plates, which evidence that the spatial resolution is sufficient to distinguish mineral grains in natural granite. XRD and XFA are done for the samples to determine all possible constituents. Partial maps of the europium distribution and speciation are presented together with phase identification by Raman microscopy and a comparison to optical microscopy images.

Keywords: TRLFS, granite, TRLFM, europium, speciation
  • Lecture (Conference)
    3rd International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 07.-10.11.2016, EMSL, Richland, Washington, USA
Registration No. 23839 - Permalink
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