Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Functionalization of Printed Metal-Particle Suspensions by Millisecond Thermal Processing.
Wiesenhütter, K.; Schumann, T.; Zichner, R.; Gebel, T.; Wiesenhütter, U.; Skorupa, W.;
The global quest towards novel, flexible and low-cost electronic products with functionality far beyond that offered by conventional size-restricted and rigid semiconductor devices, demands a rapid development of advanced material and deposition technology concepts. One of the most promising pathways to realize this ambitious goal is printed flexible electronics (PFE). Over the past years, printing has successfully demonstrated its potential for manufacture of manifold electronic products such as flexible displays, thin-film solar cells, large-area sensors etc. Importantly, by employing bendable, inexpensive media (e.g.: polymer foils, paper-like substrates) and high-throughput roll-to-roll (R2R) processing, a significant reduction of the overall costs associated with electronic device fabrication has been achieved.
Herein, we report on a successful application of ultra-fast millisecond flash lamp annealing (FLA) as a highly-attractive technique for the functionalization of Ag- and Cu-layers screen printed on low-thermal budget PET and paper-like media for e.g. antenna applications. The effect of the FLA parameters (i.e. pulse duration and energy density), on the substrate behavior as well as on the microstructure and electrical response of the as-flashed films was studied. A significant drop of the sheet resistance of the FL-treated layers as compared to the as-printed films was observed for the selected samples. As ms-FLA permits selective, near-surface heating, a damage of the sensitive substrates was avoided. Being highly-efficient (ultra-short), “non-destructive” (suitable for low-thermal tolerance flexible media) and compatible with R2R processing, FLA offers the realization of advanced PFE products.
Keywords: printed electronics, flash lamp annealing, roll-to-roll, flexible inexpensive substrates, Ag- and Cu-based inks
  • Poster
    E-MRS Spring Meeting 2014, 26.-30.05.2014, Lille, France

Publ.-Id: 21213 - Permalink

Advanced AZO processing via flash lamp annealing.
Bregolin, F. L.; Lindberg, P.; Wiesenhütter, K.; Vines, L.; Prucnal, S.; Svensson, B.; Skorupa, W.;
Currently, indium tin oxide (ITO) is the most widely used transparent conductive oxide due to its outstanding properties. However, because of its high cost, several alternatives are being sought to replace it. Among them, the aluminum-doped zinc oxide (AZO) films are one of the most promising candidates for PV applications due their low resistivity, high transparency and most of all, their relative low cost of fabrication.
In this work, AZO films were deposited over Si wafers via r.f. magnetron sputtering and subsequently treated by millisecond-range flash lamp annealing (FLA). The fabricated layers were then characterized by sheet resistance, photoluminescence spectroscopy, X-ray diffraction and Hall effect measurements. The influence of the deposition temperature and FLA parameters on the microstructure and optoelectronic response of the AZO layers was studied in detail. It was demonstrated that the FLA technique significantly improves the electrical conductivity of the as-deposited AZO layers due to the Al activation, the increase in crystallinity as well as the passivation of defects and grain boundaries. In particular, the room temperature sputtered AZO films subsequently treated by FLA have shown performance characteristics similar to those sputtered at 400 ºC, opening the possibility for further cost reductions in the fabrication process. The FLA technique is a cost-effective and high-throughput alternative for the processing of Si-based heterojunction solar cells.
Keywords: Transparent Conductive Oxides, Al-doped ZnO, Flash Lamp Annealig, Photovoltaics
  • Poster
    E-MRS Spring Meeting 2014, 26.-30.05.2014, Lille, France

Publ.-Id: 21212 - Permalink

PolCarr - Smarte Trägermaterialien für die Biotechnologie
Schmidt, H.; Wiesenhütter, K.; Teichmann, D.;
Das smarte Trägermaterial PolCarr® besteht aus dotiertem Silizium und umfasst eine isolierende Deckschicht sowie eine strukturierte Rückseitenelektrode. Die Dotierung des Siliziums verursacht die Ausbildung oberflächennaher, elektrostatischer Kräfte, deren Stärke und Richtung durch die Konzentration und Spezies der implantierten Ionen auf der Nanometer- bis Millimeterlängenskale kontrolliert eingestellt wird. Elektrisch polarisierbare Zellen oder Moleküle können an PolCarr® angezogen, ausgerichtet und immobilisiert werden.
Keywords: Trägermaterialien, Biosensoren, Zellwachstumsplatten
  • Lecture (others)
    Cross Cluster Cooperation-Projekt „C3-Saxony“, IDEA CALL zum 9. Silicon Saxony Day, 03.07.2014, Dresden, Deutschland
  • Lecture (others)
    Cross Cluster Cooperation-Projekt „C3-Saxony“ IDEA CALL zum 9. Silicon Saxony Day, 03.07.2014, Dresden, Deutschland

Publ.-Id: 21211 - Permalink

Smart carriers for advanced nano-sensors and tissue engineering applications.
Wiesenhütter, K.; Skorupa, I.; Rüb, M.; Müller, M.; Skorupa, W.; Schmidt, O. G.; Schmidt, H.;
A paramount drive of the rapidly growing biotechnology sector is the further development of intelligent, highly-efficient and inexpensive concepts for biosensors. As the key component of a biochip platform, biosensors hold a responsibility for immobilization, modification, transport and detection of a variety of biological analytes broadly utilized in health care, food industry and environmental monitoring. To augment the overall biosensor performance, much effort has been dedicated to designate the new, superior carrier materials, which permit easy-to-control immobilization of the target analytes. Consequently, herein we do propose a novel, promising concept for the smart carriers’ fabrication which is named PolCarr. PolCarr consists of doped silicon wafers and ultra-thin insulating top layers and exploits surface-near electrostatic forces (SNEF) [1-2] for the selective adsorption of electrically polarizable bioanalytes and functionalized polymers [3]. The binding and release of molecules onto the PolCarr substrate is purely driven by SNEF. By attaching a structured bottom electrode to locally doped silicon wafers and by a careful voltage altering, the SNEF can precisely be controlled on the nm-length scale, enabling realization of new, advanced products for manifold medical applications (for instance: nano-sensors). Further on, the excellent control degree at both the nm- and µm-range and the superb inertness of SNEF to environmental influences make PolCarr carriers very attractive candidates for tissue engineering and regenerative medicine, as they allow the growth of the target cells in a highly-desirable ordered manner. As PolCarr permits exceptionally facile manufacture by ion implantation and thermal dopant activation [4] and as PolCarr is compatible with well-developed standard semiconductor processing, the significant throughput and overall cost-reduction associated with the entire carrier’s production and its subsequent use as an integral part of a medical device (e.g.: biochip), can be achieved. Considering the whole benefits offered by our smart carriers, we strongly believe that the PolCarr concept can thoroughly transform traditional biosensor- and tissue engineering-oriented technologies [5]. Finally, the unique selling points of the innovative and proprietary technology offer from our point of view a high value proposition compared to state of the art technology. In order to protect the valuable intellectual property, patent applications were filed in 2011 and 2012. For the future commercialization of the technology a spin-off company is planned. The start-up team is formed by an experienced business developer and key scientists. Cooperations for the biochip development are already established. In addition, the team is supported by technology transfer partners of the Helmholtz Zentrum Dresden Rossendorf. [1] Quantitative dopant profiling in semiconductors: A Kelvin probe force microscopy model, C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80 (2009) 085305. [2] Kelvin probe force microscopy in the presence of intrinsic local electric fields, C. Baumgart, A.-D. Müller, F. Müller, H. Schmidt, Phys. Stat. Sol. (A) 208 (2011) 777–789. [3] Kelvin probe force microscopy for characterizing doped semiconductors for future sensor applications in nano- and biotechnology, H. Schmidt, S. Habicht, S. Feste, A.D. Müller, O.G. Schmidt, Appl. Surf. Sci. 281 (2013) 24-29 (invited). [4] Subsecond Annealing of Advanced Materials Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Eds.: Wolfgang Skorupa, Heidemarie Schmidt), Springer-Verlag, ISBN: 978-3-319-03130-9 (2014). [5] Selective polyelectrolyte adsorption at novel charge patterned carrier materials for future biosensor applications, M. Müller, B. Urban, A.-D. Müller, M. Rüb, K. Wiesenhütter, I. Skorupa, O.G. Schmidt, H. Schmidt, Materials (2014), in preparation (invited).
Keywords: Biotechnology, biosensors, tissue engineering, carriers, doped Si-wafers, Surface-Near Electrostatic Forces
  • Poster
    Saxon Biotechnology Symposium 2014, Dresden, 19.03.2014, Dresden, Deutschland

Publ.-Id: 21210 - Permalink

Pressure-induced shift of energy levels and structural phase transition in CdSe/ZnS quantum dots
Tauch, J.; Braun, J. M.; Keller, J.; Hinz, C.; Haase, J.; Seletskiy, D. V.; Leitenstorfer, A.; Pashkin, A.;
Electronic band structure of CdSe/ZnS quantum dots under high pressures is studied using fluorescence spectroscopy. We observe a strong blue shift of about 50 meV/GPa for the emission line at 655 nm. At moderate pressures (below 3 GPa) this shift is linear and it is dominated by increase of the fundamental band gap of CdSe under pressure [1]. In contrast to bulk CdSe where the fluorescence is quenched above 3 GPa as a results of the phase transition into the rock-salt structure, the CdSe/ZnS quantum dots remain structurally stable up to 6.5 GPa. The shift of the fluorescence line below this pressure is strongly nonlinear with tendency to saturation. This behavior can be well described using the Murnaghan equation of state giving the deformation potential value of -3.5 eV.
The remarkably high pressure of the structural phase transition in the studied CdSe/ZnS quantum dots exceeds previously reported values for CdSe nanocrystals [2] and bulk CdSe [1]. Presumably, the wurtzite structure of the quantum dots is stabilized by the ZnS shell. This structural robustness together with the high fluorescence yield and the large pressure coefficient of the wavelength shift make CdSe quantum dots a promising alternative to bulk ruby crystals for precise pressure calibration at moderate pressures.

[1] W. Shan et al., Appl. Phys. Lett. 84, 67 (2004).
[2] S. H. Tolbert and A. P. Alivisatos, J. Chem. Phys. 102, 4642 (1995).
Keywords: quantum dots, high pressure, structural phase transition
  • Poster
    Pressure and Strain Effects in Correlated Electron Materials, 06.-10.10.2014, Dresden, Germany

Publ.-Id: 21209 - Permalink

Above Room Temperature Ferromagnetism in Co- and V-Doped TiO2 — Revealing the Different Contributions of Defects and Impurities
Semisalova, A. S.; Mikhailovsky, Yu. O.; Smekhova, A.; Orlov, A. F.; Perov, N. S.; Gan’shina, E. A.; Lashkul, A.; Lahderanta, E.; Potzger, K.; Yildirim, O.; Aronzon, B.; Granovsky, A. B.;
We report recent experimental results on themagnetic, magnetotransport, and magneto-optical properties of Co- and V-doped TiO2−δ magnetic oxides at the doping level around 1 at. %. The samples were prepared using rf magnetron sputtering in identical conditions that allows to compare the mechanisms of above-room-temperature ferromagnetism observed in both cases of doping. In spite of the comparable values of magnetic moment around 1 ÷ 2.5 μB per 3d impurity derived from macroscopic magnetic measurements for both systems, the magneto-optical response of TiO2−δ :V was at least 2 orders of magnitude weaker. The anomalous Hall effect was absent in V-doped TiO2−δ, and no appreciable magnetic moment on V impurities was found by X-ray magnetic circular dichroism (XMCD) technique in contrast to Co-doped TiO2−δ. The obtained experimental data indicate dissimilar origin of intrinsic ferromagnetismin TiO2−δ:Co and TiO2−δ:V.
Keywords: Doped TiO2 · Magnetic semiconductors ·Oxygen vacancy · Defect-induced ferromagnetism

Publ.-Id: 21207 - Permalink

Ultrafast dynamics in CeTe3 across the pressure-induced charge-density-wave transition
Tauch, J.; Schäfer, H.; Obergfell, M.; Demsar, J.; Giraldo, P.; Fisher, I. R.; Pashkin, A.;
Time-resolved optical spectroscopy is a powerful tool for studying ultrafast dynamics of quasiparticles and phonons in strongly correlated electronic systems. In particular, this technique has been efficiently utilized for investigation of charge-density-wave (CDW) compounds [1-3]. In all these studies the system has been tuned across the boundary of the CDW phase by temperature variation. However, application of external (or chemical) pressure can also lead to a suppression of a CDW state caused by an impairment of the Fermi surface nesting [4].
Here, we combine femtosecond time-resolved optical spectroscopy and a diamond anvil cell technology to study the electron and lattice dynamics in tri-telluride compound CeTe3. The optical pump-probe measurements (400 nm pump and 800 nm probe wavelength, respectively) are performed on single crystals mounted inside the pressure cell. CsI has been used as a pressure transmitting medium. Around pressures of 4 GPa we observe a gradual vanishing of the relaxation process related to the recombination of the photoexcited quasiparticles. The coherent oscillations of the phonon modes coupled to the CDW order parameter demonstrate even more dramatic suppression with increasing pressure . These observations clearly indicate a transition into the metallic state of CeTe3 induced by the external pressure.

[1] J. Demsar et al., Phys. Rev. Lett. 83, 800 (1999).
[2] J. Demsar et al., Phys. Rev. B 66, 041101 (2002).
[3] R.V. Yusupov et al., Phys. Rev. Lett. 101, 246402 (2008).
[4] A. Sacchetti et al., Phys. Rev. Lett. 98, 026401 (2007).
Keywords: Time-resolved optical spectroscopy, high pressure, charge-density-waves
  • Poster
    Pressure and Strain Effects in Correlated Electron Materials, 06.-10.10.2014, Dresden, Germany

Publ.-Id: 21206 - Permalink

Simulation and Experimental Verification of Prompt Gamma-ray Emissions during Proton Irradiation
Schumann, A.; Petzoldt, J.; Dendooven, P.; Enghardt, W.; Golnik, C.; Hueso-González, F.; Kormoll, T.; Pausch, G.; Roemer, K.; Fiedler, F.;
Irradiation with protons and light ions offers new possibilities for tumor therapy but has a strong need for novel imaging modalities for treatment verification. The development of new detector systems, which can provide an in vivo range assessment or dosimetry, requires an accurate knowledge of the secondary radiation field and reliable Monte Carlo simulations. This paper presents multiple measurements to characterize the prompt γ-ray emissions during proton irradiation and benchmarks the latest Geant4 code against the experimental findings. Within the scope of this work, the total photon yield for different target materials, the energy spectra as well as the γ-ray depth profile were assessed. Experiments were performed at the superconducting AGOR cyclotron at KVI-CART, University of Groningen. Properties of the γ-ray emissions were experimentally determined. The prompt γ-ray emissions were measured utilizing a conventional HPGe detector system (Clover) and quantitatively compared to simulations. With the selected physics list QGSP BIC HP, Geant4 strongly verestimates the photon yield in most cases, sometimes up to 50 %. The shape of the spectrum and qualitative occurrence of discrete γ lines is reproduced accurately. A sliced phantom was designed to determine the depth profile of the photons. The position of the distal fall-off in the simulations agrees with the measurements, albeit the peak height is also overestimated. Hence, Geant4 simulations of prompt γ-ray emissions from irradiation with protons are currently not as reliable as simulating electromagnetic processes. Deviations from experimental findings were observed and quantified. Although there has been a constant improvement of Geant4 in the hadronic sector, there still remains a gap to close.
Keywords: proton therapy, prompt gamma imaging, Geant4

Publ.-Id: 21205 - Permalink

HADES results in elementary reactions
Ramstein, B.; Adamczewski-Musch, J.; Arnold, O.; Atomssa, E. T.; Behnke, C.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Deveaux, C.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gill, K.; Golubeva, M.; Guber, F.; Gumberidze, M.; Harabasz, S.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Kardan, K.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Krása, A.; Krebs, E.; Kuc, H.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petousis, V.; Pietraszko, J.; Przygoda, W.; Rehnisch, L.; Reshetin, A.; Rost, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmidt-Sommerfeld, K.; Schuldes, H.; Sellheim, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Wendisch, C.; Wirth, J.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.;
Recent results obtained with the HADES experimental set-up at GSI are presented with a focus on dielectron production and strangeness in pp and quasi-free np reactions. Perspectives related to the very recent experiment using the pion beam at GSI are also discussed.

Publ.-Id: 21204 - Permalink

Transmutation von Transuranen unter den Randbedingungen des Kernenergieausstiegs – Ist das technisch machbar?
Merk, B.; Rohde, U.;
Die deutsche Regierung hat den Ausstieg aus der Kernenergie beschlossen, aber der Umgang mit den hochradioaktiven Abfällen ist noch nicht geklärt. Partitionierung und Transmutation (P&T) kann als technologische Option im Prozess des Umgangs mit hochradioaktiven Abfällen betrachtet werden, dazu wurde eine umfangreiche Studie durchgeführt. In diesem Rahmen wurden auch Ziele für P&T unter der Maßgabe des Kernenergieausstiegs diskutiert. In den vorliegenden Simulationsrechnungen wird analysiert inwieweit diese Ziele unter dem Einsatz von Salzschmelzenreaktoren mit schnellem Neutronenspektrum erreicht werden können. Er wird gezeigt, dass eine effiziente Transmutation aller in Deutschland zum Abschaltzeitpunkt existierenden Transurane mit 3 bis 4 Anlagen in 45 bis 60 Jahren machbar wäre. Ferner wird eine detaillierte Bilanzierung verschiedener Inventare zum tieferen Verständnis der Vorgänge in der Transmutation präsentiert.
The German government has decided for the nuclear phase out, but a decision on a strategy for the management of the highly radioactive waste is not defined yet. Partitioning and Transmutation (P&T) could be considered as a technological option in the process of management of highly radioactive waste management, therefore a wide study has been conducted. In this group objectives for P&T und the boundary conditions of the phase out have been discussed. The fulfillment of the given objectives is analyzed using simulations of molten salt reactors with fast neutron spectrum. It is shown that the efficient transmutation of all existing transuranium isotopes would be possible in 3 to 4 reactors in a time frame of 45 to 60 years. Further on a detailed balance of different isotopic inventories is given to allow a deeper understanding of the processes during transmutation.
Keywords: nuclear, nuclear reactor, molten salt, molten salt reactor, transmutation, nuclear waste management, nuclear phase out
  • Contribution to proceedings
    Jahrestagung Kerntechnik, 05.05.2015, Berlin, Deutschland

Publ.-Id: 21203 - Permalink

Two-dimensional and tubular structures of misfit compounds: Structural and electronic properties
Lorenz, T.; Joswig, J.-O.; Seifert, G.;
Misfit layer compounds are structures that consist of two sublattices differing in at least one of their lattice constants. The two different layers are stacked either an alternating or in a more complex series resulting in mono- or multi-layer misfit compounds. To date, planar and bent misfit structures, such as tubes, scrolls or nanoparticles, have been synthesized and interesting magnetic and physical properties have been observed as a result of their special structures. Based on these observations, we present an overview of such misfit systems and summarize and discuss their electronic structure as well as the interlayer bonding behaviour, which is not completely understood yet. Furthermore, a more detailed insight into the SnS–SnS2 system is given, which was the first tubular misfit compound that has been synthesized and extensively investigated.
Keywords: 2D layered materials; misfit layer compounds

Publ.-Id: 21202 - Permalink

Optical properties of triangular molybdenum disulfide nanoflakes
Wendumu, T. B.; Seifert, G.; Lorenz, T.; Joswig, J.-O.; Enyashin, A.;
The results from calculations of optical and electronic properties of triangular MoS2 nanoflakes with edge lengths ranging from 1.6 to 10.4 nm are presented. The optical spectra were calculated using the time-dependent extension of the density-functional tight-binding method (TD-DFTB). The size effect in the optical absorption spectra is clearly visible. With decreasing length of the nanoflakes edges, the long-wavelength absorption in the range of visible light is shifted toward short-wavelength absorption, confirming a quantum-confinement-like behavior of these flakes. In contrast, the edges of the nanoflakes exhibit a distinct metallic-like behavior. The relation of the absorption properties to the observed photoluminescence of MoS2 nanoflakes is discussed in a qualitative manner.
Keywords: Molybdenum disulfide; Nano-flakes
  • The Journal of Physical Chemistry Letters 5(2014)21, 3636-3640
    DOI: 10.1021/jz501604j

Publ.-Id: 21201 - Permalink

Linear thermal expansion, thermal diffusivity and melting temperature of Am-MOX and Np-MOX
Prieur, D.; Belin, R. C.; Manara, D.; Staicu, D.; Richaud, J.-C.; Vigier, J.-F.; Scheinost, A. C.; Somers, J.; Martin, P.;
The thermal properties of Np- and Am-MOX solid solutions were investigated. The linear thermal expansion was investigated with high temperature X-ray diffraction from room temperature to 1973 K. No significant difference was observed between the Np and the Am doped MOX. The thermal conductivity of Am-MOX is about 10% higher than that of Np-MOX. The melting temperatures of Np-MOX and Am-MOX were measured using a laser heating setup and are equal to 3020 ± 30 K and 3005 ± 30 K, respectively.
Keywords: Transmutation minor actinides MOX XANES XRD thermal conductivity laser melting

Publ.-Id: 21200 - Permalink

Drag and turbulence modelling for free surface flows within the two-fluid Euler-Euler framework
Porombka, P.; Höhne, T.;
Two-phase flows are regularly involved in the heat and mass transfer in industrial processes. To ensure the safety and efficiency of such processes, an accurate prediction of the flow field and phase distribution by means of Computational Fluid Dynamics (CFD) is required. Nowadays, Direct numerical simulations (DNS) of large-scale two-phase flow problems are not feasible due to the computational costs involved. Therefore the Euler-Euler framework is often employed for large-scale simulations which involves macro-scale modelling of turbulence, mass and momentum transfer. The research activities at Helmholtz-Zentrum Dresden - Rossendorf (HZDR) focus on general closure models for multiphase flows that are closer to physics and include less empiricism. As part of this effort an Algebraic Interfacial Area Density model (AIAD) is developed for the morphology detection in the two-fluid Euler-Euler approach. Drag models for free surface flows are often based on experimental correlations, their applicability thus being limited to certain flow regimes. In this paper a modified free-surface drag model based on local shear stress is investigated that avoids this limitation. For this purpose the algebraic morphology detection mechanism of the AIAD model is revised. In DNS of free surface flow a dampening of the gas side turbulent fluctuations in the near surface region was found by previous investigators. This effect has also been accounted for in Euler-Euler simulations by means of dampening functions. In this work the significance of turbulence dampening in case of free surface flows is examined quantitatively for the k-omega turbulence model. For this purpose steady-state simulations of countercurrent stratified air-water flow have been performed using the commercial CFD code ANSYS CFX. The results are here presented and compared to experimental data. The revised morphology detection mechanism is seen as an improvement with respect to the detection of sharp interfaces. Satisfactory quantitative agreement is achieved for the modified free surface drag model based on experimental pressure difference, liquid levels and interfacial shear stress. Furthermore, it is demonstrated that turbulence dampening has to be accounted for in the k-omega model to qualitatively reproduce the mean flow and turbulence quantities from the experiment. More CFD grade experimental data is required for further model validation.
Keywords: CFD, two-phase flow, drag modelling, free surface, turbulence dampening, AIAD

Publ.-Id: 21199 - Permalink

Closures for simulation of gas-liquid flows in solid foam structures
Subramanian, K.; Baldota, R.; Schubert, M.; Lucas, D.; Hampel, U.;
Ceramic foam packings are promising alternatives for packing internals used in chemical engineering processes due to their high porosity and high specific surface area, which results in low pressure drop and high catalytically utilization of the packing. The aim of this work is to perform three-dimensional Computational Fluid Dynamics (CFD) simulations of the evolving gas-liquid flow patterns considering ceramic foams as column internals and to validate them with experimental X-ray tomographic studies. The closures from trickle bed studies are modified according to the ceramic foam specifications considering the flow domain as porous.
Keywords: Multiphase flow, CFD, Ceramic foams, X-ray tomography
  • Lecture (Conference)
    ISCRE 23 & APCRE 7, 07.-10.09.2014, Bangkok, Thailand

Publ.-Id: 21198 - Permalink

Speciation of uranium in compartments of living cells
Geipel, G.; Viehweger, K.;
Depleted uranium used a ammunition corrodes in the environment forming mineral phases and then dissolved uranium species like uranium carbonates (Schimmack et al. 2007) and hydroxides. These hydroxide species were contacted with plant cells (canola). After 24 h contact time the cells were fractionated and the uranium speciation in the fraction was determined by TRLFS (time resolved laser-induced fluorescence spectroscopy) at room temperature as well at 150K. It could be shown that the uranium speciation in the fractions is different to that in the nutrient solution. Comparison of the emission bands with literature data allows assignment of the uranium binding forms.
Keywords: Uranium, plant cells, Spectroscopy


Publ.-Id: 21197 - Permalink

Evolution of Spin Wave Modes in Periodically Perturbed Thin Films
Langer, M.; Gallardo, R.; Banholzer, A.; Jansen, A.; Schneider, T.; Wagner, K.; Demidov, V.; Demokritov, S. O.; Landeros, P.; Lenz, K.; Lindner, J.; Fassbender, J.ORC
Periodic perturbations of a magnetic thin film lead to a dipolar contribution proportional to –k (for ultrathin films: k•d << 1) in the dispersion relation of backward volume spin waves additional to the exchange term, which goes quadratically with k. If the scattering condition is fulfilled, meaning the k-vector matches a multiple of the reciprocal lattice vector g0 = 2π/a0, spin waves can scatter into excited magnonic states. This process is referred to as two-magnon scattering (TMS).
In this work, TMS is investigated by introducing periodic defects by Cr+ ion beam irradiation on the surface of a d = 30 nm thick permalloy (Ni80Fe20) film. Patterning was achieved using a PMMA mask, which was pre-structured by electron beam lithography (EBL) and subsequently exposed to a low energy Cr ion beam. Selecting ion energy and fluence, the effective depth of such perturbations can be controlled to investigate the transition from a surface perturbed thin film towards a full magnonic crystal.
The FMR spectra f(H) (see Fig.1) of different samples with varying perturbation depth h and a periodicity a0 ranging from 200 nm to 400 nm have been measured showing mode splitting at each crossing point of higher spin wave modes with the uniform mode due to TMS. Moreover, brillouin light scattering (BLS) measurements have been performed to directly measure the dispersion relation of such periodically perturbed film.
In a further experiment, the evolution of FMR mode splitting dependent on the perturbation depth h was investigated performing multi-step reactive Ar+ ion beam etching (RIBE) of surface steps on a 30 nm permalloy film.
Theoretical calculations based on a perturbation theory[1,2] are accompanied and reveal a good agreement of experiment and theory (see Fig.1). Amongst that, numerical simulations of the FMR spectra were carried out using the MuMax3 code allowing for deeper understanding of the micromagnetic structure of the observed magnonic modes, such as the visualization of the dynamic magnetization.
This work has been supported by DFG grant no. LE2443/5-1.
[1] P. Landeros and D. L. Mills, Phys. Rev. B 85, 054424 (2012).
[2] R. A. Gallardo, A. Banholzer, K. Wagner, M. Körner, K. Lenz, M. Farle, J. Lindner, J. Fassbender and P. Landeros, New J. Phys 16, 023015 (2013).
[3] M. Körner, K. Lenz, R. A. Gallardo, M. Fritzsche, A. Mücklich, S. Facsko, J. Lindner and J. Fassbender, Phys. Rev. B 88, 054405 (2103).
Keywords: Spin Waves, Magnons, Manonics, Magnetization Dynamics, Ferromagnetic Resonance, FMR, Ion Irradiation, Micromagnetic Simulation
  • Lecture (Conference)
    59th Annual Magnetism and Magnetic Materials Conference (MMM) 2014, 03.-07.11.2014, Honolulu, Hawaii, USA

Publ.-Id: 21196 - Permalink

Underground nuclear astrophysics for the Sun, and for the Big Bang (updated)
Bemmerer, D.;
After the resolution of the solar neutrino problem in 2002, the study of the Sun has now entered a precision era, and an entirely new dilemma has come up: New elemental abundance data from Fraunhofer line analyses are in contradiction with helioseismological observables. Observations of 13N and 15O neutrinos from the Sun may address this so-called solar abundance problem, but their interpretation will require precise nuclear reaction data. Due to the low cross sections involved, such data can only be provided by experiments in an underground low-background setting. Work at the world's only underground accelerator, the 0.4 MV LUNA machine in Gran Sasso (Italy), on solar fusion reactions and on the Big Bang production of lithium-6 and -7 will be reviewed. In addition, some surface-based data on radiative capture reactions on 12C, 14N, and 40Ca will be shown. The status and working program of the planned higher-energy underground accelerator at the Dresden Felsenkeller in Germany will be discussed.
Keywords: Felsenkeller Underground nuclear astrophysics Big Bang nucleosynthesis
  • Invited lecture (Conferences)
    Joint Institute for Nuclear Astrophysics Seminar, 10.11.2014, South Bend, Indiana, USA
  • Lecture (others)
    Seminar, 14.11.2014, Seattle, Washington, USA

Publ.-Id: 21195 - Permalink

A new study of the 22Ne(p,γ)23Na reaction deep underground: Feasibility, setup, and first observation of the 186 keV resonance
Cavanna, F.; Depalo, R.; Menzel, M.-L.; Aliotta, M.; Anders, M.; Bemmerer, D.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Corvisiero, P.; Davinson, T.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Prati, P.; Rossi Alvarez, C.; Scott, D. A.; Somorjai, E.; Straniero, O.; Strieder, F.; Szücs, T.; Trezzi, D.;
The 22Ne(p,γ)23Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle is active in asymptotic giant branch stars as well as in novae and contributes to the nucleosythesis of neon and sodium isotopes. In order to reduce the uncertainties in the predicted nucleosynthesis yields, new experimental efforts to measure the 22Ne(p,γ)23Na cross section directly at the astrophysically relevant energies are needed. In the present work, a feasibility study for a 22Ne(p,γ)23Na experiment at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400\,kV accelerator deep underground in the Gran Sasso laboratory, Italy, is reported. The ion beam induced γ-ray background has been studied. The feasibility study led to the first observation of the Ep = 186\,keV resonance in a direct experiment. An experimental lower limit of 0.12\,×\,10−6\,eV has been obtained for the resonance strength. Informed by the feasibility study, a dedicated experimental setup for the 22Ne(p,γ)23Na experiment has been developed. The new setup has been characterized by a study of the temperature and pressure profiles. The beam heating effect that reduces the effective neon gas density due to the heating by the incident proton beam has been studied using the resonance scan technique, and the size of this effect has been determined for a neon gas target.
Keywords: LUNA underground nuclear astrophysics asymptotic giant branch stars novae

Publ.-Id: 21194 - Permalink

Process-based forward numerical ecological modelling for carbonate sedimentary basins
Clavera-Gispert, R.; Carmona, A.; Gratacós, O.; Tolosana-Delgado, R.;
Nowadays, numerical modelling is a significant tool used both by researchers and the industry in the study of sedimentary basins, since it allows to quantify the simulated processes and to determine interactions among them. One of such programs is SIMSAFADIM-CLASTIC, a 3D forward-model process-based code to simulate the sedimentation in a marine basin at geological scale. It models the fluid flow, siliciclastic transport and sedimentation, and carbonate production. In this article, we present the last improvements in carbonate production, in particular the usage of Generalized Lotka-Volterra equations, that include logistic growth and interaction among species. Logistic growth is linked to environment parameters such as water depth, energy of the medium, and slope to the model the growing of species. The environmental parameters are factorized and combined to obtain an environment parameter that is applied to compute the modelled species development. The interaction among species is quantified using the community matrix that captures the beneficial or detrimental effects of the presence of each species on the other. A theoretical example of a carbonate ramp is computed to model the interaction among carbonate and siliciclastic sediment, the affection of environmental parameters to the modelled species, and the interaction among species. The distribution of the modelled species associations in the theoretical example is compared with Asmari Formation in Iran and Ragusa Platform in Italy.
Keywords: Forward-Model, process-based, sedimentary basin, ecological model, carbonate production, SIMSAFADIM-CLASTIC


  • Secondary publication expected

Publ.-Id: 21193 - Permalink

Measurement of the analysing power in proton-proton elastic scattering at small angles
Bagdasarian, Z.; Chiladze, D.; Dymov, S.; Kacharava, A.; Macharashvili, G.; Barsov, S.; Gebel, R.; Gou, B.; Hartmann, M.; Keshelashvili, I.; Khoukaz, A.; Kulessa, P.; Kulikov, A.; Lehrach, A.; Lomidze, N.; Lorentz, B.; Maier, R.; Mchedlishvili, D.; Merzliakov, S.; Mikirtychyants, S.; Nioradze, M.; Ohm, H.; Papenbrock, M.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Shmakova, V.; Stassen, R.; Stockhorst, H.; Strakovsky, I. I.; Ströher, H.; Tabidze, M.; Täschner, A.; Trusov, S.; Tsirkov, D.; Uzikov, Y.; Valdau, Y.; Wilkin, C.; Workman, R. L.;
The proton analysing power in p→p elastic scattering has been measured at small angles at COSY-ANKE at 796 MeV and five other beam energies between 1.6 and 2.4 GeV using a polarised proton beam. The asymmetries obtained by detecting the fast proton in the ANKE forward detector or the slow recoil proton in a silicon tracking telescope are completely consistent. Although the analysing power results agree well with the many published data at 796 MeV, and also with the most recent partial wave solution at this energy, the ANKE data at the higher energies lie well above the predictions of this solution at small angles. An updated phase shift analysis that uses the ANKE results together with the World data leads to a much better description of these new measurements.

Publ.-Id: 21192 - Permalink

High-performance QWIPs and time-resolved terahertz spectroscopy with a free-electron laser
Schneider, H.;
There is no abstract.
  • Lecture (others)
    Seminar, Kunming Institute of Physics, 17.10.2014, Kunming, China

Publ.-Id: 21190 - Permalink

Microstructural changes in highly irradiated 15Kh2MFA steel
Gillemot, F.; Horváth, A.; Horváth, M.; Kovács, A.; Radiguet, B.; Cammelli, S.; Pareige, P.; Hernandez-Mayoral, M.; Ulbricht, A.; Kresz, N.; Oszwald, F.; Török, G.;
15Kh2MFA-type steel forgings were irradiated in an accelerated surveillance position of a power reactor, up to about 1 × 1021 n/cm2, E> 1 MeV with medium flux. This steel is a Cr-Mo-V-type low-copper reactor pressure vessel material. 15Kh2MFA was microstructurally tested as received and in three different irradiation states within the frame of the LONGLIFE project. The following microstructural tests were performed: metallography, fractography, transmission electron microscopy, small angle neutron scattering, and atom-probe tomography. The aim of the current paper is to summarize the results that were evaluated by the six European institutes performing the study. The SANS tests show that the cluster volume fraction growth is nearly linear as a function of the fluence, and atom-probe tomography concludes that vanadium carbide precipitations were already originally present in the as-received steel. During irradiation these precipitates are enriched with Mo, Cu, and Cr. At the highest dose Mn, Si, and Ni are also attached to these clusters.
Keywords: Clusters; Dislocations; Irradiation; Microstructural testing; Precipitations
  • Contribution to proceedings
    26th International Symposium - Effects of Radiation on Nuclear Materials, 12.-13.06.2013, Indianapolis, US
    Effects of Radiation on Nuclear Materials: 26th Volume, ASTM STP 1572, West Conshohocken, PA, USA: ASTM International, 978-0-8031-7589-1, 45-56
    DOI: 10.1520/STP157220130098

Publ.-Id: 21189 - Permalink

Quantitative differentiation of sulfur in different oxidation states (-II and +VI) by WD-XRF
Uhlig, S.; Möckel, R.; Pleßow, A.;
Sulfur is one of the most abundant non-metals in the Earth’s crust and a key component of sulfidic ores. A number of methods for the determination of the total sulfur content in geochemical samples are available in the literature. However, sulfur appears in numerous oxidation states. Sulfide (-II) and sulfate (+VI) are the most common ones, but options for a analytical chemical differentiation between them are quite limited. This distinction could be achieved by combustion with stepwise adjustable decomposition temperatures (Brumsack 1981) or by classical wet-chemical methods (e.g., Kokkonen et al. 1987), but these methods require special efforts and can not be implemented during high throughput routine analyses.
Selective separation of different oxidation states by WD-XRF has been reported for sulfur (Perino et al. 2002), aluminium and silicon (Perino et al. 2002), iron (Finkelshtein and Chubarov 2010), and chromium (Malherbe and Claverie 2013). Referring to these known methods, two techniques for the quantitative differentiation between the most common sulfur species were developed, respectively improved that are based on a routine WD-XRF measurement. The first method is predicated on the exact position of the Kα1,2 peak in the XRF spectra, depending on the sulfide and sulfate content. The second option is based on the Kβ’/Kβ-ratio. As opposed to sulfides, sulfates show a Kβ’ satellite peak and its area and height depend on the sulfate concentration.
Both methods provide simple and time-saving options to differentiate between sulfide and sulfate, because the separation of the different oxidation states can be done during a routine WD-XRF measurement without any special efforts. Furthermore, samples with high amounts of fluorine, which could cause damages of technical devices, can be measured without any problems in the vacuum of the spectrometer. We aware that our research results may have two limitations. The first relates to the sulfur content. The method can not be used for samples with concentrations of the sulfatic and/or sulfatic component smaller than 10 g kg-1. The second one is the overlap of the lead (Pb) Mβ peak and the sulfur Kβ’ satellite peak. Samples with detectable lead amounts can only be investigated by the so-called Kα method.
We are currently in the process of a validation of our results by a second, independent method to further advance our investigations. Samples from Saxon mining dump drill holes appear suitable. Their total sulfur content and sulfide and sulfate concentration vary with depth. Suitable applications of these techniques are the high throughput routine analyses of samples that contain or consist of sulfidic ores.
Brumsack, H.-J., 1981. A Simple Method for the Determination of Sulfide- and Sulfate-Sulfur in Geological Materials by Using Different Temperatures of Decomposition. Fresenius' Journal of Analytical Chemistry, 307, 206.
Finkelshtein, A.L. and Chubarov, V.M., 2010. X-ray fluorescence determination of the FeO/Fe2O3tot ratio in igneous rocks. X-Ray Spectrometry, 39 (1), 17–21.
Kokkonen, P., Palko, M., and Lajunen, Lauri H. J., 1987. Indirect determination of sulfate and sulfide by flame atomic absorption spectrometry. Atomic Spectroscopy, 8 (3), 98–100.
Malherbe, J. and Claverie, F., 2013. Toward chromium speciation in solids using wavelength dispersive X-ray fluorescence spectrometry Cr Kbeta lines. Analytica Chimica Acta (773), 37–44.
Perino, E., et al., 2002. Determination of oxidation states of aluminium, silicon and sulfur. X-Ray Spectrometry, 31 (2), 115–119.
Keywords: sulfur oxidation state, WD-XRF
  • Lecture (Conference)
    CANAS - Colloquium Analytische Atomspektroskopie, 08.-10.03.2015, Leipzig, Deutschland

Publ.-Id: 21188 - Permalink

P1315 - Energiespeicheranordnung, deren Verwendung und Energiespeicherzellenanordnung
Galindo, V.; Gerbeth, G.; Stefani, F.; Weber, N.; Weier, T.;
Gemäß verschiedenen Ausführungsformen wird eine Energiespeicheranordnung bereitgestellt, wobei diese Folgendes aufweisen kann: mindestens eine elektrochemische Zelle, wobei die mindestens eine elektrochemische Zelle eine im Betrieb flüssige Anode, einen im Betrieb flüssigen Elektrolyten und eine im Betrieb flüssige Kathode aufweist; eine außerhalb der mindestens einen elektrochemischen Zelle angeordnete Magnetfelderzeugungsstruktur zum Erzeugen eines Magnetfeldes, wobei die Magnetfelderzeugungsstruktur derart eingerichtet ist, dass das erzeugte Magnetfeld die mindestens eine elektrochemische Zelle durchdringt.
  • Patent
    DE102013112555 - Erteilung 06.11.2014, Nachanmeldung: WO, CN, EP, US

Publ.-Id: 21187 - Permalink

Level-set reconstruction algorithm for ultrafast limited angle X-ray computed tomography of two-phase flows
Bieberle, M.; Hampel, U.;
Tomographic image reconstruction is based on recovering an object distribution from its projections, which have been acquired from all angular views around the object. If the angular range is limited to less than 180° of parallel projections, typical reconstruction artefacts arise when using standard algorithms. To compensate for this, specialized algorithms using a priori information about the object need to be applied.
The application behind this work is ultrafast limited angle X-ray computed tomography of two-phase flows. Here, only a binary distribution of the two phases needs to be reconstructed, which reduces the complexity of the inverse problem. To solve it, a new reconstruction algorithm (LSR) based on the level set method is proposed. It includes one force function term accounting for matching the projection data and one incorporating a curvature dependent smoothing of the phase boundary. The algorithm has been validated using simulated as well as measured projections of known structures and its performance has been compared to the algebraic reconstruction technique (ART) and a binary derivative of it. The validation as well as the application of the level set reconstruction on a dynamic two-phase flow demonstrated its applicability and its advantages over other reconstruction algorithms.
Keywords: Level set method, X-ray CT, image reconstruction, two-phase flow, ultrafast

Publ.-Id: 21186 - Permalink

X-ray Absorption Spectroscopy of Nuclear Materials at the Rossendorf Beamline, ESRF
Scheinost, A. C.; Prieur, D.; Smith, A.; Martin, P. M.; Lebreton, F.; Belin, R. C.;
The Rossendorf Beamline is a dedicated X-ray absorption spectroscopy beamline for research on actinides. Embedded in the Helmholtz research program Safety of Nuclear Waste Disposal, inhouse research deals with the chemical behavior of actinides and fission products in the context of nuclear waste disposal, encompassing both near-field and far-field retention mechanisms. In the framework of European research programs, e.g. ACTINET, TALISMAN, ESRF, there is also a vivid body of research conducted on nuclear materials in the context of GenIV fuels, minor actinide transmutation, and the behavior of fuels under operational and accident conditions. In this talk I will focus on the latter aspect, presenting results from collaborations with CEA and ITU on a variety of topics including the oxidation state and local structure of Am in uranium dioxide and MOX fuels, self-irradiation effects of minor actinides in fuel matrices, and structure and oxidation state of U in sodium uranates.
Keywords: ROBL XANES Actinet Talisman Nuclear fuel
  • Invited lecture (Conferences)
    NES Colloquium, 19.11.2014, Villigen, Schweiz

Publ.-Id: 21185 - Permalink

Characterizing intra-exciton Coulomb scattering in terahertz excitations
Zybell, S.; Bhattacharyya, J.; Winnerl, S.; Eßer, F.; Helm, M.; Schneider, H.; Schneebeli, L.; Böttge, C. N.; Kira, M.; Koch, S. W.; Andrews, A. M.; Strasser, G.;
An intense terahertz field is applied to excite semiconductor quantum wells yielding strong non-equilibrium exciton distributions. Even though the relaxation channels involve a complicated quantum kinetics of Coulomb and phonon effects, distinct relaxation signatures of Coulomb scattering are identified within time-resolved photoluminescence by comparing the experiment with a reduced model that contains all relevant microscopic processes. The analysis uncovers a unique time scale for the Coulomb scattering directly from experiments and reveals the influence of phonon relaxation as well as radiative decay.
Keywords: Exciton dynamics, GaAs quantum well, terahertz, intra-exciton transition, Coulomb scattering

Publ.-Id: 21184 - Permalink

Uranyl(VI) binding by bis(2-hydroxyaryl)diimine and bis(2-hydroxyaryl)diamine ligand derivatives. Synthetic, X-ray, DFT and solvent extraction studies
Jeazet, H. B. T.; Gloe, K.; Doert, T.; Mizera, J.; Kataeva, O. N.; Tsushima, S.; Bernhard, G.; Weigand, J. J.; Lindoy, L. F.; Gloe, K.;
The interaction of uranyl(VI) nitrate with a series of bis(2-hydroxyaryl)imine and bis(2-hydroxyaryl)amine derivatives (H2L1- H2L7) incorporating 1,3-dimethylenebenzene or 1,3-dimethylenecyclohexane bridges between nitrogen sites is reported. Crystalline complexes of type [UO2(H2L)(NO3)2] (where H2L is H2L1 -H2L4) were isolated from methanol. X-ray structures of the complexes of H2L1, H2L2 and H2L4 show that each of these neutral ligands bind to their respective UO22+ centres in a bidentate fashion in which coordination only occurs via each ligand's hydroxy functions. Two bidentate nitrate anions complete the metal's coordination sphere in each complex to yield hexagonal bipyramidal coordination geometries. A DFT investigation of [UO2(H2L1)(NO3)2] in a simulated methanol environment is in accord with this complex maintaining its solid state conformation in solution. Solvent extraction experiments (water/chloroform) employing H2L1 - H2L7 in the organic phase and uranyl(VI) nitrate in the aqueous phase showed that both amine derivatives, H2L8 and H2L9, yielded enhanced extraction of UO22+ over the corresponding imine derivatives, H2L1 and H2L2. These results were further compared with those obtained for the corresponding Schiff bases incorporating 1,2-phenylene and 1,2-cyclohexane bridged ligands, H2L6 and H2L7; these more rigid systems also yielded enhanced extraction of UO22+ relative to the more flexible Schiff bases H2L1 - H2L5. A very significant synergistic enhancement of the extraction of UO22+ by H2L1‐H2L4 and H2L7 was observed in the presence of a 10-fold excess of octanoic acid; the influence of pH on extraction efficiency was also investigated. A parallel set of experiments employing H2L1 - H2L9 as extractants for europium(III) nitrate indicated a clear uptake preference for UO22+ over Eu3+ in all cases; separation of the uranyl ion from the rare earths is important in mineral processing;
Keywords: Uranyl(VI), Schiff base, Europium(III), X-ray, Solvent extraction, Density functional theory

Publ.-Id: 21183 - Permalink

Dual-modality Impedance Wire-Mesh Sensor for Investigation of Multiphase Flows
Dos Santos, E. N.; Da Silva, M. J.; Morales, R. E.; Reinecke, S.; Schleicher, E.; Hampel, U.;
For the investigation of multiphase flows, i.e. in oil production, there are only few suitable measuring techniques. For this reason, in this paper a new multichannel complex impedance measuring system using wire-mesh sensors is presented. The novel system measures amplitude and phase components of impedance (at single frequency) and is thus able to evaluate simultaneously the conductive and the capacitive parts of a fluid (complex permittivity). In the future this system can be employed for the investigation of dynamic processes in multiphase flow. The performance in measuring amplitude and phase of a signal is evaluated. First promising results for the three-phase flow are presented.
Keywords: Complex impedance measurement, multiphase flow, wire-mesh sensor
  • Lecture (Conference)
    International Conference on Imaging Systems and Techniques (IST), 14-17.10.2014, Santorini, Greece, 14.-17.10.2014, Santorini, Griechenland
  • Contribution to proceedings
    International Conference on Imaging Systems and Techniques (IST), 14-17.10.2014, Santorini, Greece, 14.-17.10.2014, Santorini, Griechenland
    Proceedings of International Conference on Imaging Systems and Techniques (IST), 14-17.10.2014, Santorini, Greece, 9781479952199, 316-319

Publ.-Id: 21181 - Permalink

Configurational anisotropy effects in 90 degree domain wall imprinted thin films - statics and dynamics
Trützschler, J.; Sentosun, K.; Langer, M.; Mattheis, R.; Fassbender, J.ORC; McCord, J.
The dynamic magnetic behavior of magnetic films has gained increased attention due to the use of magnetic films for high frequency inductors and their application as microwave filters. Moreover, the excitation and modification of spin waves has led to considerable interest in the field of magnonic crystals[1]. In general, the high frequency behavior of magnetic film stacks is determined by the material’s magnetic properties and by structural patterning. Yet, dynamic magnetization modes are not only inherent to the physical structure of magnetic films, but are also strongly influenced by e.g. ripplelike magnetic domain states[2] and as well as the pure existence of domain walls (DW)[3] in magnetic films. One way to introduce DWs in a controlled way in thin films is by local ion-irradiation[4,5,6].
In order to introduce a periodic DW pattern, extended Ni19Fe81(50nm)/Ir23Mn77(7nm) films with an initial unidirectional anisotropy are patterned by local He-ion irradiation into stripe-like twodimensional structures with periodically alternating directions of exchange bias. Magnetization patterns with zigzag oriented exchange bias directions are obtained. The influence of the DW density on static and dynamic magnetization properties is investigated for a stripe period (stripe width) from 12 μm (6 μm) down to 1 μm (500 nm). By this, exactly oriented and magnetically charged 90 N´eel-type domain walls with a DW density up to 2x103/mm are imprinted in the film.
Static and dynamic magnetization properties of the thin films are analyzed by complementary methods.
In Figure 1 (a) and (c) exemplary magnetization loops are presented for a stripe period of 2 μm. Perpendicular to the stripe axis an effective exchange bias field, which is caused by the magnetic interaction of the individual exchanged biased stripes, results in a net exchange bias direction. Due to DW interactions with increasing stripe period the samples correspondingly exhibit a decrease of remanent magnetization. Applying the external magnetic field parallel to the stripe axis, a two staged reversal loop is obtained. Even down to low stripe periods and despite of the straightening of magnetization the two step magnetization process remains for low stripe widths.
The corresponding change of high frequency permeability maps (up to 5 GHz) with bias fields in accordance with the shown magnetization reversal loops are displayed in Fig. 1 (b) and (d). Increasing the external magnetic field perpendicular to the stripes two distinct precessional frequencies, corresponding to an acoustic and an optical dynamic mode, are exhibited over the whole field range (Fig. 1(b)). Applying the field parallel to the stripe axis, in the central plateaued region (Fig. 1(d)) a bi-modal dynamic behavior is observed, that transforms into a single mode with higher permeability outside the plateau region. With increasing stripe period, the precessional frequencies at zero magnetic field decrease.
The occurring magnetic configurations are verified by high resolution Kerr microscopy in the longitudinal mode, examples of which are given in Fig. 2. The displayed images for different applied field values match the situation in Fig. 1 (c) and (d). The domain imaging data proves the existence of a pronounced magnetic modulation with high stability to magnetic fields even for a highly remanent state. The domain states, shown in Fig. 2 (b, c, d), exist in a magnetic field range, which is in accordance with the plateau in the magnetization loop and the change in the permeability spectrum around zero field.
Quasi-static and dynamic behavior are explained in terms of an increased domain wall mediated configurational magnetic anisotropy that results from variable magnetic charges at the imprinted domain walls due to the zigzagged alignment of magnetization. The magnetic charges increase with the rotational magnetization process. The DW stabilization induced effect has also significant influence on the dynamic magnetic characteristics. The effect of DW orientation relative to the alignment of exchange bias will be discussed. The controlled introduction of high density and locked micromagnetic objects opens new ways to control the static and dynamic magnetic properties of continuous magnetic thin films.
Funding from the German Science Foundation DFG through the grants MC9/7-2, FA314/3-2, and the Heisenberg programme of the DFG (MC9/9-1) is highly acknowledged.
[1] A. V. Chumak, A. A. Serga, B. Hillebrands, M. P. Kostylev, Appl. Phys. Lett. 93, 022508 (2008)
[2] C. Patschureck, K. Lenz, M. O. Liedke, M. U. Lutz, T. Strache, I. M¨onch, R. Sch¨afer, L. Schultz, and J. McCord, Phys. Rev. B 86, 054426 (2012)
[3] U. Queitsch, J. McCord, A. Neudert, R. Sch¨afer, L. Schultz, K. Rott, H. Br¨uckl, J. Appl. Phys. 100, 093911 (2006)
[4] J. Fassbender, J. McCord, J. Magn. Magn. Mater. 320, 579 (2008)
[5]C. Hamann, R. Mattheis, I. M¨onch, J. Fassbender, L. Schultz, J. McCord, Magnetization dynamics of magnetic domain wall imprinted magnetic films, submitted
[6] J. Tr¨utzschler, K. Sentosun, M. Langer, I. M¨onch, R. Mattheis, J. Fassbender, J. McCord, Magnetoresistive and domain investigations of zigzag folded magnetization structures, submitted
Keywords: Magnetic Domains, Anisotropic Magneto-Resistance, Kerr-Microscopy, Ferromagnetic Resonance
  • Lecture (Conference)
    IEEE Internation Magnetics Conference - Intermag Dresden 2014, 04.-08.05.2014, Dresden, Deutschland

Publ.-Id: 21180 - Permalink

P1211 - Verfahren und System zur Abtrennung von Schwermetallen
Lütke, L.; Moll, H.;
Die Erfindung betrifft das Gebiet der Aufreinigung schwermetallbelasteter Gewässer, sowie den Nachweis von Schwermetallen in Lösungen. Der Erfindung liegt die Aufgabe zugrunde, eine effektive Abtrennung von Uran (Schwermetallen allgemein) durch mikrobielle Zellen ohne einen zusätzlichen Immobilisierungsschritt zu erzielen. Die Lösung der Aufgabe erfolgt durch ein erfindungsgemäßes Verfahren zur Abtrennung von Schwermetallen, enthaltend die folgenden Schritte: a. Bereitstellen einer Lösung enthaltend ein Minimalmedium und metabolisch aktive Biomasse aus gramnegativen Bakterien, b. Inkontaktbringen dieser Lösung mit einer Lösung enthaltend Schwermetalle, c. Einstellen der Phosphatkonzentration auf, 0,05 mmol/l bis 0,1 mol/l, bevorzugt 0,2 mmol/l bis 0,5 mmol/l, wobei die Schritte b und c in beliebiger Reihenfolge erfolgen können. Ebenfalls erfindungsgemäß ist ein System zur Abtrennung von Schwermetallen, enthaltend ein Minimalmedium, metabolisch aktive Biomasse aus gramnegativen Bakterien und Phosphat in einer Konzentration von 0,05 mM bis 0,1 M, bevorzugt 0,2 mM bis 0,5 mM. Ebenfalls erfindungsgemäß ist die Verwendung des erfindungsgemäßen Verfahrens oder des erfindungsgemäßen Systems zur Aufreinigung schwermetallbelasteter Gewässer oder zum Nachweis von Schwermetallen in Gewässern.
  • Patent
    DE102013207197 - Offenlegung 23.10.2014

Publ.-Id: 21179 - Permalink

Tomographie an technischen Anlagen – für effizientere Prozesse in der Chemie- und Verfahrenstechnik
Bieberle, M.; Bieberle, A.; Hampel, U.;
Tomographie an technischen Anlagen – für effizientere Prozesse in der Chemie- und Verfahrenstechnik
Keywords: tomography
  • Lecture (others)
    Vortrags-/Besichtigungsprogramm für Besuchergruppen, 02.07.2014, Dresden, Deutschland

Publ.-Id: 21178 - Permalink

Ultrafast X-ray computed tomography for the analysis of multiphase flows
Bieberle, M.; Hampel, U.;
This presentation addresses the question, why tomographic imaging of multiphase flows is needed and explains the principle of computed tomography as well as the ultrafast X-ray computed tomography system. Examples of application are presented as well as present developments.
Keywords: X-ray computed tomography, ultrafast
  • Lecture (others)
    summer school MIMENIMA, 18.09.2014, Dresden, Deutschland

Publ.-Id: 21177 - Permalink

Np-237 sorption onto montmorillonite and corundum
Elo, O.; Huittinen, N.; Müller, K.; Heim, K.; Hölttä, P.; Lehto, J.;
The bentonite buffer in Engineered Barrier Systems (EBS), planned for spent nuclear fuel (SNF) repositories, consists mainly of the clay mineral montmorillonite. Montmorillonite and other aluminosilicates are known to retain radionuclides found in the SNF, thus, contributing to the retention or immobilization of these metal ions in the environment. The neptunyl cation, NpO2+, is rather soluble, poorly sorbed, and readily mobile under environmental conditions making it highly relevant for research concerning SNF repository safety. In the present study we have investigated the sorption of neptunium on the clay mineral montmorillonite under carbonate free, but environmentally relevant conditions. The interaction of neptunium with α-Al2O3 (corundum) has also been investigated in order to study the aluminol surface sites present on clay minerals, which are regarded as the main adsorption sites for radionuclide attachment. We have performed batch sorption studies both as a function of pH and as a function of neptunium concentration 5×10-10 M-5×10-6 M. The NpO2+ uptake on the two different minerals is rather weak. Sorption on the mineral surfaces begins at pH 7, and at pH 8 which is the pH-value expected to prevail in the deep underground in Olkiluoto, Finland, the final disposal site for the Finnish SNF, only ~ 10% of the actinyl ion is retained. To gain insight into the surface speciation of neptunium on the two minerals, we performed in situ ATR-FT-IR spectroscopic investigations at pH 9 and 10. Upon NpO2+ sorption onto corundum and montmorillonite we observe a shift of the antisymmetric stretch vibration of the neptunyl ion from 818 cm-1 obtained for the free aquo ion to 790 cm-1. The large shift of the asymmetric stretch vibration indicates the formation of an inner-sphere bound neptunium com-plex on the mineral surface. A similar shift has previously been observed by Gückel et al. (2013) for NpO2+ sorption onto gibbsite (α-Al(OH)3). In contrast to the results obtained in Gückel et al., where neptunium desorption could not be observed after flushing the mineral film on the ATR crystal, we see a high reversibility of the sorption on both corundum and montmorillonite. This high reversibility of the sorption process speaks for a weaker bonding to the surface. In upcoming EXAFS (Extended X-ray Absorption Fine Structure) measurements, we hope to be able to find an explanation for the deviating desporption behaviour of NpO2+ on montmorillonite and corundum in comparison to gibbsite. In addition, information on structural parameters and the complexation mechanism of neptunium sorption onto montmorillonite and corundum will be obtained.
Keywords: neptunium, sorption, in situ ATR-FT-IR, montmorillonite, corundum
  • Poster
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, Dresden, Germany

Publ.-Id: 21176 - Permalink

Site-selective TRLFS of Eu(III) doped rare earth phosphates for conditioning of radioactive wastes
Huittinen, N.; Arinicheva, Y.; Holthausen, J.; Neumeier, S.; Stumpf, T.;
Crystalline ceramic materials show promise as potential waste forms for immobilization of high-level radioactive wastes. Rare earth (RE) phosphate ceramics have been found to be extremely stable over geological time scales and they show good tolerance to high radiation doses. These ceramics are able to incorporate radionuclides in well-defined atomic positions within the crystal lattice up to high (~25%) loadings, which will reduce the volume of waste in the radionuclide conditioning process. The dehydrated RE phosphates are known to crystallize in two distinct structures, depending on the ionic radius of the cation: the larger lanthanides from La3+ to Gd3+ crystallize in the nine-fold coordinated monazite structure, while the smaller lanthanides such as Lu3+ form eight-fold coordinated xenotime structures.
In the present work we have used site-selective time-resolved laser fluorescence spectroscopy (TRLFS) to investigate the structural incorporation of Eu3+, an analogue for the actinides Pu3+, Am3+ and Cm3+, in rare earth phosphate ceramics. The very narrow excitation spectra of LaPO4 and GdPO4 monazites doped with 500 ppm Eu3+ indicate that Eu3+ is fully incorporated on the host cation sites in the highly ordered ceramic materials independent of the ionic radii of the host cations. The LuPO4 xenotime phase, however, shows a very low incorporation of the Eu3+ ion within the crystal lattice. The majority of the signal in the Eu3+-LuPO4 excitation spectrum could be assigned to partly hydrated europium in the LuPO4 ceramic. In experiments where we increased the dopant concentration up to 50 % in the xenotime host matrix, a larger amount of Eu3+ incorporation within the crystal structure in relation to the hydrated species could be seen. A similar increase of the dopant concentration in the monazite phases caused a broadening of the excitation spectra as a result of local disordering of the crystal structures. This disordering, however, had no influence on the Ln3+ site symmetry in the monazites.
Our site-selective TRLFS investigations have shown that the host cation size in the monazites has very little influence on the Eu3+ incorporation into these materials. The structure of the ceramic, however, seems to play a decisive role in how well the dopant is substituted within the crystal lattice.
Keywords: rare earth phosphate ceramics, incorporation, Eu(III), site-selective TRLFS
  • Lecture (Conference)
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, Dresden, Germany

Publ.-Id: 21175 - Permalink

A few remarks on the structure of PT quantum mechanics
Günther, U.;
In the first part of the talk, starting from a historical discussion of the 2-dimensional Ising model, the Yang-Lee analysis of the zeros of the corresponding partition function and the occurrence of the Yang-Lee edge singularities the structural origin of the quantum mechanical toy model Hamiltonian with ix^3 potential is elucidated. The close relationship of this Hamiltonian to the Landau theory of phase transitions and conformal field theories (CFTs) is sketched what provides an intuitive explanation for the operator-theoretic difficulties in treating a conjectured Hermitian structure of the ix^3 model in full depth.
In the second part of the talk, the Krein space and Hilbert space metric structures of quasi-Hermitian PT-symmetric matrix models are discussed with emphasis on the underlying general Lie group structures of these metric operators. The Cartan decomposition into compact and noncompact metric components is used to show the existence of an underlying Lie triple system and its relation to the curvature of homogeneous coset spaces.
Finally, several extension schemes from finite-dimensional Lie groups toward ∞−dimensional Lie groups and Hilbert-Schmidt Lie groups are sketched.
Keywords: Yang-Lee model, Yang-Lee edge singularity, Ising model, Landau theory of phase transitions, conformal field theory, PT quantum mechanics, metric operator, Krein space, Lie groups, Cartan decomposition, Lie triple systems, homogeneous coset spaces, Hilbert-Schmidt Lie groups
  • Invited lecture (Conferences)
    14th International Workshop on Pseudo-Hermitian Hamiltonians in Quantum Physics, 05.-10.09.2014, Setif, Algeria

Publ.-Id: 21174 - Permalink

Validierung der Nutzbarkeit eines zweikanaligen Heißfilmanemometers in Mehrphasenströmungen durch Vergleichsmessungen mittels Particle Imaging Velocimetry
Chi, B.;
Die Bestimmung der Geschwindigkeitskomponenten zur Validierung von CFD-Simulation zählt zu den elementarsten Messaufgaben in einer Blasensäule. Während besonders in einphasigen Strömungen Particle Imaging Velocimetry (PIV) und Constant Temperature Anemometry (CTA) etabliert sind, ist deren Einsatz in Zweiphasenströmung deutlich durch die auftretenden Phasenwechsel gestört.
Während der Einsatz eines PIV-Systems bereits bei geringen Gasanteilen durch fehlende optische Zugänglichkeit nicht mehr möglich ist, besteht bei CTA-Systemen, bedingt durch ihr Messprinzip, die Möglichkeit auch bei höheren Gasdurchsätzen zu messen.
Im Rahmen der Diplomarbeit sind systematische Studien zur Validierung der Nutzbarkeit eines Flüssigkeits-CTA-Systems in Mehrphasenströmung mit verschiedenen Gasgehalten durchzuführen. Die Validierung erfolgt hierbei durch parallele, zeitgemittelte Vermessung lokaler Strömungsgeschwindigkeiten mittels PIV. Um der Verfälschung von Flüssigkeits-Messdaten des CTA-Systems durch Phasenwechsel vorzubeugen, ist das Messsystem mit einer HZDR-eigenen Nadelsonde zu koppeln und entsprechend verfälschte Daten zu maskieren. Zudem ist eine vorherige Kalibrierung des CTA-Systems vorzunehmen.
Keywords: hot film anemometry, multiphase velocimetry, particle imaging velocimetry
  • Diploma thesis
    TU Dresden, 2014
    Mentor: Zalucky, J., Hampel, U.

Publ.-Id: 21173 - Permalink

Hydrodynamics and transport processes in structured reactor devices: Project status report
Zalucky, J.; Wagner, M.; Rabha, S. S.; Schubert, M.; Bieberle, M.; Hampel, U.;
On the occasion of half-annual project status report, work package progress is presented. The first part covers the presentation of pre-liminary experiments in the x-ray investigation of multiphase hydrodynamics in solid foam packed fixed bed and packed bubble column reactors. The second part reports on pre-liminary actions in mass transfer investigations. The presentation concludes with the planed project schedule and upcoming milestones.
Keywords: ultrafast x-ray CT, solid foam reactors, multiphase hydrodynamics, mass transfer investigations
  • Lecture (others)
    Helmholtz-Energie-Allianz EECMP: Half-annular project meeting, 03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 21172 - Permalink

Advances in multiphase hydrodynamic characterization of solid foams and cubic cell structures - Project status report
Zalucky, J.; Wagner, M.;
On the occasion of annual project status report, work package progress is presented. The first part includes conventionally measured hydrodynamic characteristics such as static liquid holdup, flow maps and pressure drop measurements. Second part includes deeper data mining on ultrafast x-ray computed tomography measurements. The second part is related to actions in mass transfer investigations and reports progress and upcoming investigations with the electrochemical method.
Keywords: project status report, ultrafast x-ray computed tomography, liquid-solid mass transfer, multiphase hydrodynamics
  • Lecture (others)
    Jahrestreffen Helmholtz-Energie-Allianz "Energieeffiziente chemische Mehrphasenprozesse", 08.-09.10.2014, Hamburg, Deutschland

Publ.-Id: 21171 - Permalink

Pulse dynamic visualization in foam packed reactors - flow path evolution
Zalucky, J.; Rabha, S. S.; Schubert, M.; Hampel, U.;
In co-currently downward operated packed bed reactors, pulse flow is well known for its performance enhancing effects. Though suffering from a lot higher pressure drop than trickle flow, it offers the high advantage of continuous re-wetting, liquid flow re-routing and enhanced mass transfer due to higher, liquid induced shear stress. In our contribution, the evolution of liquid flow is addressed and visualized by the used of our ultrafast X-ray computed tomography system. As novel catalyst internal, foam blocks made of silicon infiltrated silicon carbide (SiSiC) were investigated.
Keywords: Pulse flow visualization, co-current downward flow, ceramic foams, ultrafast x-ray computed tomography
  • Poster
    ProcessNET Jahrestagung, 29.09.-02.10.2014, Aachen, Deutschland

Publ.-Id: 21170 - Permalink

Advances in application of the limiting current technique for solid-liquid mass transfer investigations
Zalucky, J.; Rabha, S. S.; Schubert, M.; Hampel, U.;
The limiting current technique has widely been used to study liquid-solid mass transfer in various reactor configurations. In the present contribution several underlying physical aspects have been investigated in order to improve the design of mass transfer experiments. Experimentally, the significant influence of electrolyte composition and hydrodynamic conditions have been studied and quantified to ensure conditions of high reproducibility. In the course of single phase COMSOL simulations, different electrode configurations have been examined with emphasis on concentration fields and electric current distribution showing a large sensitivity of the experimental configuration on the absolute current values.
Keywords: Liquid-solid mass transfer, limiting current technique, electric field simulation, ceramic solid foams
  • Poster
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland
  • Contribution to proceedings
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland
    Book of full-length manuscript, Fr: DECHEMA/VDI, 313-318

Publ.-Id: 21169 - Permalink

The Bubbles Breakup and Coalescence Rates in Bubble Columns
Azizi, S.; Schubert, M.;
Bubble size distribution has important role in bubble columns in point view of available interfacial area for interphase exchange phenomena. The difficulty in determining of bubble size is due to uncertain breakup and coalescence models for using in population balance equations. Variety of mechanism and coefficients for the each of the models prevents to generalize them. Furthermore, measurement of each rate individually is not possible except for single bubble trajectory in transparent systems (mostly air-water dispersions) that some of the existing models based on it. Here, a novel algorithm demonstrated to calculate breakup and coalescence rates using the bubble size distribution, bubble rise velocity, and hold-up profiles along the bubble column.
Keywords: Bubble Column, Bubbles Breakup and Coalescence, Mechanisms, Experimental Study, Population Balance
  • Poster
    HZDR Annual PhD Seminar, 06.-08.10.2014, Altenberg, Germany

Publ.-Id: 21168 - Permalink

Morphological Characterization of Open-Cell Solid Foams
Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.;
Reactors with a fixed-bed of catalyst particles are widely applied for continuous multi-phase processes in the petrochemical, chemical, and biochemical industry. However, the performance of these reactors often suffers from some drawbacks, such as energy consuming high-pressure drop and mass and heat transfer limitations. One solution is to replace randomly packed catalysts with structured packings, e.g open-cell solid foam catalysts as they provide high specific surface area of up to 2000 m2/m3 at high open porosities between 75 - 97%. As result, the pressure drop of the gas-liquid two-phase flow is comparatively low (Mohammed et al. 2013). Studies argued that both the bulk material and the foam morphological properties like the number and shape of the pores and struts have a strong impact on heat transfer rates and on the hydrodynamic behavior (Tekog˜lu et al., 2011). Thus, a key factor in the foam characterization is to properly define foam structural parameters and to choose an appropriate predictive morphological model. Due to the highly random, irregular and non-ideal solid foam structure it is difficult to specify one geometrical property. At same time, although several models and correlations have been proposed to calculate morphological properties, each of these correlations was proposed for specific materials and pore shape. Therefore, the goal of this study is to characterize the solid foam, and find the most suitable morphological model for the characterization of the packing, which is applicable for different solid foam shape, material, and structure. In order to distinguish the influence of the foam materials, foam samples of different materials (polyurethane, carbon, and nickel) but same foam density are investigated. Different measurements techniques (light microscopy, electron scanning microscopy, and X-ray micro tomography) were used to reveal the impact of the material. The morphological analysis indicated that polyurethane foam mimics both the carbon and the nickel foam. Furthermore, all solid foams show similar strut properties (see Fig 1) which is confirmed by tomographic measurements of window (pore) diameter and specific surface area. In the contribution, the methodology of the foam characterization and the comparison between the foam morphologies will be shown.
  • Poster
    6th International FEZA Conference, 08.-11.09.2014, Leipzig, Deutschland

Publ.-Id: 21167 - Permalink

Bubble Size and Velocity Measurements in Bubble Columns using Ultrafast X-ray Tomography
Lau, Y. M.; Schubert, M.;
We present measurements of bubble size distribution in bubble columns using X-ray tomography. The experimental setup is an ultrafast electron beam X-ray tomographic system applied to a cylindrical bubble column with a diameter of 0.07 m. Measurements are taken placed on two planes, which are separated with an axial distance of 10 mm. The obtained reconstructed images are filtered, segmented and stacked in the time-domain to form a three-dimensional matrix of bubble objects. By cross-examining the matrices of both planes, we can identify the corresponding bubble objects and determine bubble velocities and volumes as well.
  • Lecture (Conference)
    2014 AIChE Annual Meeting, 16.-21.11.2014, Atlanta, USA

Publ.-Id: 21166 - Permalink

Analysis of Breakup & Coalescence Rates inside the Bubble Columns
Azizi, S.; Lau, Y. M.; Schubert, M.;
The prediction of bubble size distributions (BSD) in bubble column reactors is a great challenge for the column design and for the optimization of the operating conditions to enhance the gas-liquid mass transfer rates. The implementation of population balance equations (PBE) for bubbly flows into computational fluid dynamics (CFD) codes allowed better understanding of the hydrodynamic behavior of bubble columns and better quantification of the interfacial area for the estimation of interphase transport phenomena. On the other hand, the complexity of numerical models increased with the introduction of new sub-models for the determination of the BSDs. The formulation of sink and source terms of such PBEs is a very controversial issue. These terms depend on assumption on the dominating mechanisms due to turbulence, buoyancy, wake, shear, etc. However, the unknown physical effects, the variety of constants of breakup and coalescence (B&C) kernels as well as their complex coupling with the hydrodynamics of the flow prevent to generalize existing models.
In this work, a new approach was used to determine ‘experimental’ B&C rates along the axial height of bubble columns using measured BSD data at different axial positions. The required bubble size distributions were determined by dual plane ultrafast X-ray tomography applied at several heights of the bubble column. Tomographic images are obtained at high frequencies (>1000Hz) for two measurement planes. By cross examining the images of the two planes, bubbles can be identified and the velocities, hence the sizes can be determined.
Subsequently, the liquid velocity distributions were determined by an Eulerian-Eulerian CFD model based on the multi-size group (MUSIG) poly-disperse model approach using the ‘experimental’ B&C rates. Excellent agreement was found between the measured and the predicted BSDs, gas holdups and bubble velocities. The liquid flow patterns are very important since the existing theoretical correlations for the B&C models are based on the liquid hydrodynamic properties. Accordingly, the validated hydrodynamic data from CFD simulations can be utilized to determine the dominating mechanisms for the B&C models at different axial regions of the bubble columns, and to investigate the role of B&C rates for each mechanisms.
Keywords: Breakup and Coalescence, Bubbly Flow, Bubble Column, CFD, Eulerian-Eulerian
  • Lecture (Conference)
    21st International Congress of Chemical and Process Engineering, CHISA 2014, 23.-27.08.2014, Prague, Czech Republic

Publ.-Id: 21165 - Permalink

Investigation of hydrodynamics and mass transfer of solid foam packings for gas-liquid applications
Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.;
Chemical reactors with a fixed bed of catalyst particles are widely applied in the chemical industry. However, the performance of these reactors often suffers from some drawbacks, such as high energy consumption caused by pressure loss and low productivity due to mass and heat transfer limitations. One solution is to replace catalyst particles with catalysts packings based on solid foams with an open cell structure. Such porous structures combine large specific surface areas, high bed porosities, and interconnected pores for enhanced heat and mass transfer (Zhang et al. 2012). The performance of reactors with solid foam catalysts depends on the interaction of the fluids with the foam structure and, hence, the mass transfer to the foam surface. These two aspects are directly linked to the overall reactor performance and need to be understood in detail for reactor design. This work focuses on an experimental investigation of hydrodynamics and mass transfer. The hydrodynamics investigation was based on applying novel wire-mesh sensors to study gas and liquid distribution at high spatial resolution. The particular liquid-solid mass transfer was studied by a modified electrochemical method. The experiments are based on the measurement of electrical current under mass transfer diffusion limited condition. The experimental results of this work demonstrate clearly the potential of solid foam as suitable packing for gas-liquid applications.
  • Lecture (Conference)
    248th ACS National Meeting, 10.-14.08.2014, San Francisco, USA

Publ.-Id: 21164 - Permalink

Hydrodynamics, mass and heat transfer in bubble columns with vertical internals: an experimental study
Simic, N.; Breiler, K.; Schubert, M.;
The objective of this study is to examine the influence of different vertical tube bundle designs on the bubble dynamics and on the mass and heat transfer rates in a bubble column. The studies in the open literature examining the performance of bubble columns with vertically inserted tube bundles have focused primarily on the coverage of the cross-sectional area of the bubble column by the tube bundle (CSA). The most frequently used coverages are the 5% and the 25% (± 3%) which mimic the heat exchangers utilized in the processes of methanol and Fischer-Tropsch syntheses. Other than that, the designs of tube bundles seem to be arbitrarily chosen and feature a number of different configurations of layouts, tube diameters and tube lengths. From the current state of research, it is thus rather difficult to draw conclusions on the optimal design of a heat exchanger suitable for use in bubble columns. Intuitively, it can be concluded that the most important design features of tube bundles affecting the flow are the distance between the tubes and the unit cell area enclosed by the tubes in their respective arrangements. Accordingly, the study aims on a systematic analysis on the effect of these geometric parameters.
The experiments are conducted in a 10-cm bubble column equipped with a perforated plate gas distributor in the air-water system. Four tube bundle designs have been chosen and arranged in the triangular and square pattern layouts, which represent the two most widely used heat exchanger designs according to TEMA (Tubular Exchange Manufacturer´s Association) and are known to affect the fluid turbulence to different extents. The volumetric mass transfer coefficient, kLa, is measured by the oxygen absorption method using a commercially available oxygen probe and the heat transfer is measured using the extended heat exchanger probe. The gas phase dynamics are obtained with the use of the in-house developed dual-plane ultrafast electron beam X-ray tomography.
Keywords: bubble column, internals, heat exchanger, tube bundle, hydrodynamics, gas holdup, bubble size distribution, mass transfer, X-ray tomography
  • Poster
    HZDR PhD Seminar 2014, 06.-08.10.2014, Altenberg, Deutschland

Publ.-Id: 21163 - Permalink

Langzeitspezifische Alterungseffekte in RDB-Stahl
Bergner, F.; Ulbricht, A.; Wagner, A.;
Ziel des BMWi-Fördervorhabens 1501393 ist es, durch den Einsatz von Untersuchungsmethoden auf der nm-Skala einen Beitrag zur Aufklärung von Flusseffekten und von Late-Blooming-Effekten in bestrahlten RDB-Stählen zu leisten. Zur Untersuchung dieser Effekte wurde auf RDB-Stähle deutscher Reaktoren aus zwei bei der AREVA GmbH abgeschlossenen Vorhaben zurückgegriffen. Die Auswahl der Grundwerkstoffe und Schweißgüter erfolgte so, dass sich optimale Voraussetzungen für das Erreichen des Gesamtziels des Vorhabens ergeben. Die ausgewählten Untersuchungsmethoden umfassen mit der Neutronenkleinwinkelstreuung, der Atomsondentomographie und der Positronen-annihilationsspektroskopie solche Techniken, die die nm-skaligen bestrahlungsinduzierten Defekt-Fremdatom-Cluster bestmöglich und in komplementärer Weise zu detektieren und zu charakterisieren gestatten. Es wurde ein Flusseffekt auf die Größe der bestrahlungsinduzierten Fremdatomcluster, jedoch nicht auf den Volumenanteil und die mechanischen Eigenschaften gefunden. In einem Cu-armen RDB-Schweißgut wurde ein Late-Blooming-Effekt nachgewiesen, der sich in einem steilen Anstieg des Clustervolumenanteils und der Übergangstemperaturverschiebung nach einer Phase schwacher oder fehlender Zunahme niederschlägt.

The BMWi project 1501393 aimed at contributing to the clarification of flux effects and late blooming effects in irradiated RPV steels by means of experimental techniques of sensitivity at the nm scale. The investigation of these effects was focussed on RPV steels, both base metal and weld of German reactors selected according to the objectives of the present project from two previous projects performed at AREVA GmbH. The complementary techniques of small-angle neutron scattering, atom probe tomography and positron annihilation spectroscopy were applied to detect and characterize the irradiation-induced nm-scale defect-solute clusters. A flux effect on the size of the irradiation-induced clusters but no flux effect on both cluster volume fraction and mechanical properties was found. For a low-Cu RPV weld, a late blooming effect was observed, which results in a steep slope of both cluster volume fraction and transition temperature shift after an initial stage of small or no change.
Keywords: pressure vessel steel, base metal, weld metal, microstructure, irradiation effects, rate theory
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-056 2014
    ISSN: 2191-8708


Publ.-Id: 21162 - Permalink

Mixing efficiency of cross-bar and helical static mixer in upward gas-liquid flows
Rabha, S.; Schubert, M.; Banowski, M.; Hampel, U.;
The process of dispersing gaseous phases into liquid bulks is one of the most widely used mixing processes in the chemical and process industry. The choice of an appropriate agitation system for the desired processes depends essentially on the efficiency to ensure high interfacial area at economically justifiable energy input. In this context, the static mixer technology emerges in many areas as an attractive alternative to conventional agitators such as continuous stirred tank reactors 1-3. Numerous static mixer designs, for example Helical (Kenics), SMV (Sulzer), SMX (Koch-Sulzer), LPD and ISG (Charles Ross & Son) have been proposed but only few designs are used in the industry. However, comparative performance studies of these mixers are scarce. In this contribution, the mixing capabilities of cross-bar and helical static mixers for upward gas-liquid flows will be presented at turbulent gas-liquid flow regime.
Keywords: static mixer
  • Poster
    International Symposium on Catalysis Multiphase Reactors, 07.-10.12.2014, Lyon, France

Publ.-Id: 21161 - Permalink

Dual Role of B7 Costimulation in Obesity-Related Nonalcoholic Steatohepatitis and Metabolic Dysregulation
Chatzigeorgiou, A.; Chung, K.-J.; Garcia-Martin, R.; Alexaki, V.-I.; Klotzsche-Von Ameln, A.; Phieler, J.; Sprott, D.; Kanczkowski, W.; Tzanavari, T.; Bdeir, M.; Bergmann, S.; Cartellieri, M.; Bachmann, M.; Nikolakopoulou, P.; Androutsellis-Theotokis, A.; Siegert, G.; Bornstein, S. R.; Muders, M. H.; Boon, L.; Karalis, K. P.; Lutgens, E.; Chavakis, T.;
The low-grade inflammatory state present in obesity contributes to obesity-related metabolic dysregulation, including nonalcoholic steatohepatitis (NASH) and insulin resistance. Intercellular interactions between immune cells or between immune cells and hepatic parenchymal cells contribute to the exacerbation of liver inflammation and steatosis in obesity. The costimulatory molecules, B7.1 and B7.2, are important regulators of cell-cell interactions in several immune processes; however, the role of B7 costimulation in obesity-related liver inflammation is unknown. Here, diet-induced obesity (DIO) studies in mice with genetic inactivation of both B7.1 and B7.2 (double knockout; DKO) revealed aggravated obesity-related metabolic dysregulation, reduced insulin signalling in the liver and adipose tissue (AT), glucose intolerance, and enhanced progression to steatohepatitis resulting from B7.1/B7.2 double deficiency. The metabolic phenotype of B7.1/B7.2 double deficiency upon DIO was accompanied by increased hepatic and AT inflammation, associated with largely reduced numbers of regulatory T cells (Tregs) in these organs. In order to assess the role of B7 costimulation in DIO in a non-Treg-lacking environment, we performed antibody (Ab)-mediated inhibition of B7 molecules in wild-type mice in DIO. Antibody-blockade of both B7.1 and B7.2 improved the metabolic phenotype of DIO mice, which was linked to amelioration of hepatic steatosis and reduced inflammation in liver and AT. Conclusion: Our study demonstrates a dual role of B7 costimulation in the course of obesity-related sequelae, particularly NASH. The genetic inactivation of B7.1/B7.2 deteriorates obesity-related liver steatosis and metabolic dysregulation, likely a result of the intrinsic absence of Tregs in these mice, rendering DKO mice a novel murine model of NASH. In contrast, inhibition of B7 costimulation under conditions where Tregs are present may provide a novel therapeutic approach for obesity-related metabolic dysregulation and, especially, NASH.

Publ.-Id: 21160 - Permalink

Bifunctional Cyclam-Based Ligands with Phosphorus Acid Pendant Moieties for Radiocopper Separation – Thermodynamic and Kinetic Studies
Paúrová, M.; Havlíčková, J.; Pospíšilová, A.; Vetrík, M.; Císařová, I.; Stephan, H.; Pietzsch, H.-J.; Hrubý, M.; Hermann, P.; Kotek, J.;
Two novel macrocyclic ligands based on trans-substituted cyclam with N-methyl and N-(4-aminobenzyl) groups as well as with two methylphosphinic (H2L1) or methylphosphonic (H4L2) acid pendant arms were synthesised and investigated in solutions. The ligands form stable complexes with transition metal ions. Both ligands show a high thermodynamic selectivity for divalent copper over nickel(II) and zinc(II) (K(CuL) is higher than K(Ni/ZnL) by about 7 orders of magnitude). Complexation is significantly faster for the phosphonate ligand H4L2 probably due to stronger coordination ability of more basic phosphonate groups, which efficiently bind the metal ion in the out-of-cage complex and helps its in-cage binding. The rate of complexation of Cu(II) by the phosphinate ligand H2L1 is comparable to that of cyclam itself and it derivatives with non-coordinating substituents. Acid-assisted decomplexation of the copper(II) complexes is relatively fast (½ 44 and 42 s in 1 M aq. HCl at 25 °C for H2L1 and H4L2, respectively). Combination of the properties is convenient for selective copper removal/purification. Thus, the title ligands were employed in preparation of ion-selective resins for radiocopper(II) separation. Glycidyl-methacrylate copolymer beads were modified with the ligands through diazotation reaction. The separation ability of the modified polymers was tested with cold copper(II) or non-carrier-added (NCA) 64Cu in the presence of a high excess of both nickel(II) and zinc(II). The experiments exhibited high overall separation efficiency leading to 60–70 % recovery of radiocopper with high selectivity over the other metal ions originally present in 900-times molar excess. The results showed the concept of chelating resins with properly tuned selectivity of complexing moieties can be employed for radiocopper separation.

Publ.-Id: 21159 - Permalink

Multiphase flow imaging – between physics and contemporary art
Hampel, U.; (Editor)
The presentation gives an overview over various multiphase flow imaging techniques, their functional principles, hardware and image processing aspects. Furthermore different applications on industrial and scientific flow analysis problems are being discussed.
Keywords: multiphase flow imaging, process tomography, image processing
  • Invited lecture (Conferences)
    Netherlands Process Technology Symposium NPS14, 03.-05.11.2014, Utrecht, The Netherlands

Publ.-Id: 21158 - Permalink

Two-phase flow measurements with ultrafast X-ray tomography
Hampel, U.; Banowski, M.; Barthel, F.; Hoppe, D.; Lucas, D.; Rabha, S.; Wagner, M.;
Ultrafast X-ray tomography provides a means for the contactless high-resolution scanning of multiphase flows. In the current version the technique is able to scan flows in vessels of up to 160 mm diameter with scan rates of several thousand frames per second, a nominal spatial resolution of around one millimeter and in two consecutive planes. One of the main advantages is that two-phase flows in opaque and complex structures can be disclosed.
A challenging subject in the frame of ultrafast X-ray tomography is data processing and analysis. The high scanning rates yield large data sets and automated image processing must be applied to extract typical hydrodynamic parameters of interest, such as gas hold-up profiles, bubble and particle size distributions and velocities and interfacial area. On the other hand it is difficult to obtain some parameters from the continuous phase, such as continuous phase velocities or turbulence parameters. Here combination of different measurement techniques has further potential.
The presentation will provide an overview over the capacities and limits of ultrafast X-ray tomography by discussing different two-phase flow problems with increasing complexity: two-phase flow in vertical pipes, slurry bubble columns and static mixers. Moreover different image processing and data analysis techniques will be introduced and discussed in detail.
Keywords: ultrafast X-ray tomography, two-phase flow
  • Invited lecture (Conferences)
    The 52nd European Two-Phase Flow Group Meeting (ETPFGM2014), 07.-09.05.2014, Dresden, Germany

Publ.-Id: 21157 - Permalink

Ultrafast X-ray tomography for multiphase flow analysis
Hampel, U.; Banowski, M.; Barthel, F.; Hoppe, D.; Rabha, S. S.; Schubert, M.;
Ultrafast X-ray tomography provides a means for the contactless high-resolution scanning of multiphase flows. In the current version the technique is able to scan flows in vessels of up to 195 mm diameter with scan rates of several thousand frames per second, a nominal spatial resolution of around one millimetre and in two consecutive planes. One of the main advantages is that two-phase flows in opaque and complex structures can be disclosed. A challenging subject in the frame of ultrafast X-ray tomography is data processing and analysis. The high scanning rates yield large data sets and automated image processing must be applied to extract typical hydrodynamic parameters of interest, such as gas hold-up profiles, bubble and particle size distributions, disperse phase velocities and interfacial area. On the other hand it is difficult to obtain certain parameters from the continuous phase, such as continuous phase velocities or turbulence. Here combination of different measurement techniques has further potential.
Keywords: ultrafast X-ray tomography, multiphase flow, tomographic image processing
  • Contribution to proceedings
    5th International Workshop on Process Tomography (IWPT-5), 16.-18.09.2014, Jeju, Korea
  • Invited lecture (Conferences)
    5th International Workshop on Process Tomography (IWPT-5), 16.-18.09.2014, Jeju, Korea

Publ.-Id: 21156 - Permalink

Reactor pressure vessel surveillance
Ballesteros, A.; Hein, H.; May, J.; Planman, T.; Todeschini, P.; Brumovsky, M.; Gillemot, F.; Chaouadi, R.; Rouden, J.; Efsing, P.; Altstadt, E.;
The Euratom LONGLIFE project has proposed multiple ways of monitoring radiation embrittlement of RPVs during long-term operation. An overview is presented.
Keywords: Embrittlement, Surveillance, Reactor pressure vessel
  • Nuclear Engineering International 59(2014)724, 19-20

Publ.-Id: 21155 - Permalink

Surface-mediated formation of Pu(IV) nanoparticles on muscovite
Schmidt, M.; Knope, K. E.; Lee, S. S.; Stubbs, J. E.; Eng, P. J.; Bellucci, F.; Fenter, P.; Soderholm, L.;
Nanoparticles have long been recognized as an important factor in actinide chemistry,[1] as well as reactive transport.[2, 3] The formation of Pu(IV) nanoparticles can be enhanced by the presence of a mineral surface[4], even if Pu is not initially present as Pu(IV).[5] Redox activity of the mineral surface is not a prerequisite for this oxidation/ polymerization reaction.[6]
Upon reaction of a solution of Pu(III) with muscovite mica the formation of Pu(IV)-oxo-nanoparticles was observed by surface x-ray scattering [crystal truncation rods (CTR) and resonant anomalous x-ray reflectivity (RAXR)] and atomic force microscopy (AFM).[6] The surface-mediated polymerization has been related to the enhanced concentration of mobile plutonium near the interface, as well as the redox equilibrium of Pu(III) and Pu(IV) under atmospheric conditions.
Here we present our recent findings demonstrating that the same mechanism is also found when Pu is initially present in its hexavalent state PuO22+, thus requiring reduction instead of oxidation to reach the tetravalent state. Surface x-ray scattering in combination with x-ray absorption near-edge spectroscopy (XANES) reveal the presence of Pu(IV) nanoparticles after 12 hours reaction time. Grazing incidence XANES shows only Pu(IV) at the interface, within the detection limits. The interfacial structure revealed by CTR and RAXR will be discussed and compared to the structures formed upon sorption of preformed Pu(IV) nanoparticles[7], as well as after surface-mediated formation of nanoparticles from trivalent plutonium.[6]
[1] Knope, K.E., et al., Chem. Rev., 2012. 113(2): 944; [2] Kersting, A.B., et al., Nature, 1999. 397: 56; [3] Novikov, A.P., et al., Science, 2006. 314: 638; [4] Powell, B.A., et al., ES&T, 2011. 45(7): 2698; [5] Kirsch, R., et al., ES&T, 2011. 45(17): 7267; [6] Schmidt, M., et al., ES&T, 2013. 47(24): 14178; [7] Schmidt, M., et al., Langmuir, 2012. 28: 2620.
Keywords: Plutonium, Redox chemistry, CTR, RAXR, AFM, XANES
  • Lecture (Conference)
    Goldschmidt 2014, 08.-13.06.2014, Sacramento, CA, USA

Publ.-Id: 21154 - Permalink

Interfacial Reactivity of Pu and Th at the Muscovite (001) Basal Plane
Schmidt, M.; Fenter, P.; Lee, S. S.; Bellucci, F.; Wilson, R. E.; Knope, K. E.; Soderholm, L.;
The geochemistry of the actinides is of utmost importance in understanding and predicting their behavior in contaminated legacy sites as well as nuclear waste storage facilities. The unique chemistry of this group of elements including strong hydrolysis, complex redox chemistry, and the potential for polymerization reactions in combination with the actinides’ inherent radioactivity and toxicity makes studies challenging. However, especially for artificial elements like Pu and other transuranics, no natural analogues are available and homologues frequently fall short in accurately reproducing the actinides’ behavior.
We will present and discuss recent results from in situ resonant anomalous x-ray reflectivity (RAXR) and crystal truncation rod (CTR) experiments, shedding light on the inter-action of Th(IV) as well as Pu(III) and Pu(IV) with the negatively charged muscovite (001) basal plane. The example of Th(IV) demonstrates how the strong hydration of the highly charged cations prevents a close approach to the surface, instead favoring adsorption as a highly hydrated extended outer sphere complex. Subsequently, it will be shown how similar adsorption behavior in combination with the complex redox chemistry of plutonium, leads to a surface-enhanced formation of nanoparticles.
Results from surface x-ray scattering will be supplemented by ex situ alpha-spectrometry quantification and atomic force microscopy (AFM), to yield a more complete understanding of the interfacial structure.
Keywords: Plutonium, Thorium, RAXR, CTR, AFM
  • Invited lecture (Conferences)
    ActinideXAS 2014: 7th Workshop on Speciation, Techniques, and Facilities for Radioactive Materials at Synchrotron Light Sources, 20.-22.05.2014, Böttstein, Schweiz

Publ.-Id: 21153 - Permalink

High-temperature ferromagnetism of Si1−xMnx (x≈0.52−0.55) alloys
Rylkov, V. V.; Bugaev, A. S.; Novodvorskii, O. A.; Tugushev, V. V.; Kulatov, E. T.; Zenkevich, A. V.; Semisalova, A. S.; Nikolaev, S. N.; Vedeneev, A. S.; Shorokhova, A. V.; Aver′Yanov, D. V.; Chernoglazov, K. Y.; Gan′Shina, E. A.; Granovsky, A. B.; Wang, Y.; Panchenko, V. Y.; Zhou, S.;
The paper reports on the comprehensive study of properties of nonstoichiometric Si1−xMnx alloys slightly enriched in Mn (x≈0.51–0.55) as compared to the stoichiometric monosilicide MnSi. Mosaic type Si1−xMnx films 55–70 nm in thickness were produced by the pulsed laser deposition (PLD) method onto the single crystalline Al2O3 substrates at 340 °C. The Curie temperature TC in nonstoichiometric Si1−xMnx (x≈0.52–0.55) films exceeds room temperature, while in their stoichiometric counterpart, MnSi, the TC value does not exceed ≈30 К. The consistent data on anomalous Hall effect and transverse Kerr effect prove the global character of ferromagnetic (FM) order caused by magnetic defect formation rather than the presence of FM clusters. Аt Mn content x≤0.55, the magnetization data testify to a good homogeneity in the distribution of magnetic defects without their segregation: variations of the saturation magnetization Ms do not exceed 6% in the temperature range T=10–100 К and are well described by the Bloch law. It is also revealed that textured high-quality Si1−xMnx films with x≈0.52 and ТС~300 К could be formed by PLD method in the “shadow” geometry (at lower energy of deposited atoms).
Keywords: Si–Mn alloy; High-temperature ferromagnetism; Anomalous Hall effect; Magnetic and magneto-optical properties

Publ.-Id: 21152 - Permalink

Analytical computation of prompt gamma ray emission and detection for proton range verification
Sterpin, E.; Janssens, G.; Smeets, J.; Vander Stappen, F.; Prieels, D.; Priegnitz, M.; Perali, I.; Vynckier, S.;
A prompt gamma (PG) slit camera prototype recently demonstrated that Bragg Peak position in a clinical proton scanned beam could be measured with 1–2 mm accuracy by comparing an expected PG detection profile to a measured one. The computation of the expected PG detection profile in the context of a clinical framework is challenging but must be solved before clinical implementation. Obviously, Monte Carlo methods (MC) can simulate the expected PG profile but at prohibitively long calculation times. We implemented a much faster method that is based on analytical processing of precomputed MC data that would allow practical evaluation of this range monitoring approach in clinical conditions. Reference PG emission profiles were generated with MC simulations (PENH) in targets consisting of either 12 C, 14 N, 16 O, 31 P or 40 Ca, with 10% of 1 H. In a given geometry, the local PG emission can then be derived by adding the contribution of each element, according to the local energy of the proton obtained by continuous slowing down approximation and the local composition. The actual incident spot size is taken into account using an optical model fitted to measurements and by super sampling the spot with several rays (up to 113). PG transport in the patient/camera geometries and the detector response are modelled by convolving the PG production profile with a transfer function. The latter is interpolated from a database of transfer functions fitted to MC data (PENELOPE) generated for a photon source in a cylindrical phantom with various radiuses and a camera placed at various positions. As a benchmark, the analytical model was compared to MC and experiments in homogeneous and heterogeneous phantoms. Comparisons with MC were also performed in a thoracic CT. For all cases, the analytical model reproduced the prediction of the position of the Bragg peak computed with MC within 1 mm for the camera in nominal configuration. When compared to measurements, the shape of the profiles was well reproduced and agreement for the estimation of the position of the Bragg peak was within 2.7 mm on average (1.4 mm standard deviation). On a non-optimized MATLAB code, computation time with the analytical model is between 0.3 to 10 s depending on the number of rays simulated per spot. The analytical model can be further used to determine which spots are the best candidates to evaluate the range in clinical conditions and eventually correct for over- and under-shoots depending on the acquired PG profiles.
Keywords: prompt gamma, range monitoring, Monte Carlo

Publ.-Id: 21151 - Permalink

How polytypism in InAs nanowires is affected by the presence of liquid indium during the growth on silicon
Dimakis, E.; Biermanns, A.; Davydok, A.; Sasaki, T.; Geelhaar, L.; Takahasi, M.; Pietsch, U.;
The self-assisted growth of vertical InAs nanowires on Si(111) substrates offers the possibil-ity to integrate monolithically the two materials, e.g. for novel transistor architectures, without the risk of contamination by foreign catalysts. However, arsenide nanowires that grow along the [111] crystallographic orientation are prone to wurtzite-zincblende polytypism, making the control of the crystal phase very challenging. In this work, we attempt to describe the dynamic relation between the growth conditions and the structural composition of the nanowires, and to identify potential ways to achieve phase-pure, particularly wurtzite, InAs nanowires.
Using in-situ X-ray scattering and diffraction measurements during the growth by molecular beam epitaxy, we were able to monitor the liquid phase of indium and the crystal structure of the growing nanowires throughout the growth process (Fig. 1). Although we used a much higher flux for arsenic than for indium as it is typically done for InAs nanowires, we directly observed the spontaneous build-up of liquid indium in the beginning of the growth process. Most im-portantly, the presence of liquid indium was associated with the simultaneous nucleation of InAs nanowires predominantly in the wurtzite phase. Since the build-up of liquid indium is driven by the surface diffusion of indium adatoms on the Si substrate under extremely arsenic-rich conditions, only a limited number of liquid indium sites were possible to form on the substrate, while their existence lasted for a limited period of time. In fact, the number and the lifetime of the liquid indium sites were the two parameters that defined the nucleation phase for the nan-owires.
After their nucleation, the nanowires continue to grow in the absence of liquid indium, and with a highly defective wurtzite structure. Numerical simulations based on a Monte Carlo ap-proach were employed to fit the ex-situ diffuse X-ray scattering measurements, showing that the structural degradation of the nanowires is due to the formation of planar stacking faults with their planes perpendicular to the growth direction. The onset of the formation of stacking faults is correlated with the transition from indium- to arsenic-rich conditions on each nanowire shortly after their nucleation.
After all, our study reveals the role of liquid indium in the nucleation and the structural com-position of InAs nanowires that grow on Si(111), implying that pure wurtzite nanowires may be obtained if the growth is performed in the continuous presence of liquid indium, i.e. the vapour-liquid-solid mode.
  • Lecture (Conference)
    Nanowire Growth Workshop, 25.08.2014, Eindhoven, The Netherlands

Publ.-Id: 21150 - Permalink

2nd International Workshop on Advanced Techniques for Actinide Spectroscopy (ATAS 2014) Abstract Book
Foerstendorf, H.; Müller, K.; Steudtner, R.; (Editors)
In 2012, The Institute of Resource Ecology at the Helmholtz-Zentrum Dresden Rossendorf organized the first international workshop of Advanced Techniques in Actinide Spectroscopy (ATAS). A very positive feedback and the wish for a continuation of the workshop were communicated from several participants to the scientific committee during the workshop and beyond.
Today, the ATAS workshop has been obviously established as an international forum for the exchange of progress and new experiences on advanced spectroscopic techniques for international actinide and lanthanide research. In comparison to already established workshops and conferences on the field of radioecology, one main focus of ATAS is to generate synergistic effects and to improve the scientific discussion between spectroscopic experimentalists and theoreticians.
The exchange of ideas in particular between experimental and theoretical applications in spectroscopy and the presentation of new analytical techniques are of special interest for many research institutions working on the improvement of transport models of toxic elements in the environment and the food chain as well as on reprocessing technologies of nuclear and non-nuclear waste.
Spectroscopic studies in combination with theoretical modelling comprise the exploration of molecular mechanisms of complexation processes in aqueous or organic phases and of sorption reactions of the contaminants on mineral surfaces to obtain better process understanding on a molecular level. As a consequence, predictions of contaminant’s migration behaviour will become more reliable and precise. This can improve the monitoring and removal of hazardous elements from the environment and hence, will assist strategies for remediation technologies and risk assessment.
Particular emphasis is placed on the results of the first inter-laboratory Round-Robin test on actinide spectroscopy (RRT). The main goal of RRT is the comprehensive molecular analysis of the actinide complex system U(VI)/acetate in aqueous solution independently investigated by different spectroscopic and quantum chemical methods applied by leading laboratories in geochemical research. Conformities as well as sources of discrepancies between the results of the different methods are to be evaluated, illuminating the potentials and limitations of cou-pling different spectroscopic and theoretical ap-proaches as tools for the comprehensive study of actinide molecule complexes. The test is understood to stimulate scientific discussions, but not as a competitive exercise between the labs of the community.
Hopefully, the second ATAS workshop will continue to bundle and strengthen respective research activities and ideally act as a nucleus for an international network, closely collaborating with international partners. I am confident that the workshop will deliver many exciting ideas, promote scientific discussions, stimulate new developments and collaborations and in such a way be prosperous.
This workshop would not take place without the kind support of the HZDR administration which is gratefully acknowledged. Finally, the or-ganizers cordially thank all public and private sponsors for generous funding which makes this meeting come true for scientists working on the heavy metal research field.

Thorsten Stumpf
Director of the Institute of Resource Ecology
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-054 2014
    ISSN: 2191-8708


Publ.-Id: 21149 - Permalink

3 × 3 rod bundle investigations, CFD single-phase numerical simulations
Lifante, C.; Krull, B.; Frank, T.; Franz, R.; Hampel, U.;
The work here presented has been performed in the framework of a research project aimed to investigate two-phase (boiling) flows in pressurized water reactors (PWR). CFD investigations of a rod bundle have been conducted while a new experimental facility (ROFEX) was constructed in Helmholtz Zentrum Dresden-Rossendorf (HZDR) for the generation of quality validation data. The apparatus consists of a 3 × 3 rod bundle inside a Plexiglas vertical pipe. The results summarized in this paper are considered as a pre-investigation, being the final goal to be able to predict accurately boiling water flows under high pressure around rods. For this purpose, three steps were defined: analysis of single-phase flows in such geometry, analysis of the multiphase flow when using a refrigerant as a working fluid and, finally, the analysis of a multiphase flow using water. The single-phase approach allows gaining experience regarding the turbulence behaviour of the flow, while the multiphase investigation of the refrigerant simplifies the experimental conditions since it is possible to get boiling situations at lower pressure level. At the moment of writing this paper, the authors were focused on the first step (single-phase flows at low pressure), since this not only made possible to better understand the turbulence in that geometry, but it also resulted in valuable feedback to the experimentalists on improving the construction of the facility. In parallel, HZDR researchers have been developing a new tomography measurement technique to measure gas content in multiphase flows.
Keywords: Rod bundles

Publ.-Id: 21148 - Permalink

A new statistical parameter for identifying of the main transition velocities in bubble columns
Nedeltchev, S. N.; Rabha, S.; Hampel, U.; Schubert, M.;
The identification of the main flow regime boundaries in bubble columns is essential since the degrees of mixing, mass and heat transfer vary with the flow regime. Most of the available methods in the literature for flow regime identification provide controversial results about the transition velocities and they are applicable mainly to pressure fluctuations. That is why, in this work a new statistical parameter was extracted from gas holdup time series (60,000 points) of the cross-sectional averaged gas holdup. The measurements were performed in a narrow (0.15 m in ID) and a large (0.4 m in ID) bubble column by means of conductivity wire-mesh sensors at very high sampling frequency (2000 Hz). The wire-mesh sensors in both columns were always installed at a height of 1.3 m above the gas distributor. Both columns were equipped with a perforated plate distributor, each with an open area of 1 %. The columns operated with an air-deionized water system at ambient conditions.
As a regime indicator, a new dimensionless statistical parameter called ‘relative maximum number of visits in a region’ Nrmax was introduced. This new parameter is a function of the difference between the maximum number of visits in a region arising from two different division schemes of the signal’s range. The identified two transition velocities were found to be independent of the different division schemes studied in this work. In both small and large bubble columns, the Nrmax profiles exhibited two well-defined local minima, which identified two transition velocities Utrans, indicating the end of the gas maldistribution regime and the onset of the churn-turbulent regime. It was found that the column diameter affects only the second transition velocity.
Keywords: flow regime identification, bubble column, maximum number of visits in a region, gas maldistribution, gas holdup fluctuations, conductivity wire-mesh sensor

Publ.-Id: 21147 - Permalink

Identification of the Main Flow Regime Boundaries in Two Bubble Columns Based On a New Parameter Extracted from Gas Holdup Fluctuations
Nedeltchev, S. N.; Schubert, M.; Donath, T.; Rabha, S.; Hampel, U.;
The time series (60,000 points) of the cross-sectional averaged gas holdup in two bubble columns (0.15 and 0.4 m in ID) were measured by conductivity wire-mesh sensors. Both columns were equipped with perforated plate distributors (having an open area of 1 %). The sampling frequency was set at 2000 Hz. These data were used successfully for the flow regime identification. For this purpose a new parameter called maximum number of visits in a region Nvmax was introduced. Both bubble columns were operated with an air−tap water system at ambient conditions. The clear liquid height in both columns was adjusted at 2.0 meters. The wire-mesh sensors were installed at a height of 1.3 m above the sparger plates. The new dimensionless parameter Nvmax is based on a division of the signal’s range into different regions and the maximum number of signal visits in one of the regions. In both small and large bubble columns the Nvmax profiles exhibited two well-defined local minima, which identified two transition velocities Utrans. In the small column (0.15 m in ID), the two Utrans values were identified at 0.034 and 0.089 m/s, respectively. In the large column (0.4 m in ID) the first Utrans value remained the same, whereas the second Utrans value decreased slightly to 0.078 m/s. A comparison with the Kolmogorov entropy results and another dimensionless statistical parameter was also performed.
  • Contribution to proceedings
    Second International Symposium On Multiscale Multiphase Process Engineering (MMPE-2), 24.-27.09.2014, Hamburg, Deutschland: Dechema, 42-47

Publ.-Id: 21146 - Permalink

Statistical Validation of the Mixing Length Concept in Bubble Columns Operated in the Transition Flow Regime
Nedeltchev, S. N.; Schubert, M.;
A new statistical parameter was defined in order to determine the range of applicability of the mixing length concept (Kawase and Tokunaga, 1991) in two bubble columns. Gas holdup time series (60 000 points) were measured in two bubble columns (0.15 and 0.4 m in ID) by a conductivity wire-mesh sensor. The new statistical parameter Φ was defined as a ratio of the mean value of the signal to three times the average absolute deviation (3AAD) and it was correlated to the mixing length equation derived by Kawase and Tokunaga (1991). It was found that this new correlation was not valid in all flow regimes. It is applicable only in the transition flow regime. Such a clarification has not been provided in the literature hitherto. In the narrow bubble column the results were also confirmed on the basis of the Kolmogorov entropy and another statistical parameter.
The new parameter Φ was also used for flow regime identification. In the narrow bubble column the first transition velocity Utrans was identified at 0.034 m/s, whereas the second Utrans occurred at 0.112 m/s. In the large bubble column the two Utrans values were identified at 0.045 and 0.101 m/s, respectively.

Publ.-Id: 21145 - Permalink

Investigations on centrifugal pumps under air entrainment conditions
Schäfer, T.; Bieberle, A.; Hampel, U.;
Centrifugal pumps are widely used in process industry and power engineering, e.g. in refineries as feeding pumps or in power plants in cooling circuits. In nuclear power plants they are operated in various places and particularly in safety-related functions, like emergency core cooling. Though simple in design centrifugal pumps offer advantages, like high efficiency and low energy consumption, smooth and steady operation and high reliability. Gas entrainment as well as internal steam generation by cavitation is known as being detrimental and critical to the operation of centrifugal pumps, since they were primarily designed for single phase operation. Gas entrainment may for instance occur in situations, where water is conveyed from a reservoir with a shallow liquid height. There hollow vortices may form as a consequence of low liquid level and pre-existing fluid swirling. Particularly, such a situation may be prevailing in nuclear power plants, e.g. when emergency cooling water is taken from a liquid reservoir, like the condensation chamber.
Presence of gas in pumps may lead to abrasion at impeller blades, strong vibrations with damaging of bearings and loss of cooling for shaft and bearings and early fatigue as a consequence. At least the presence of gas will lead to decreasing pump performance even to the point of abrupt collapse of flow rate. Up to now, the effects of air entrainment have been investigated exemplarily under various operating conditions [Caruso et al., 2013], [Kimura et al., 2008], but the characteristics of gas phase fraction accumulation inside centrifugal pumps, particularly in the impeller and nearby the shaft seal region, are insufficiently understood. The presented work contributes quantitative measurements, visualizations and analyses of gasliquid phase distributions to the fundamental understanding of the effects of gas entrainment in centrifugal pumps. Advanced tomographic measuring methods with high spatial and temporal resolution were applied to investigate the two-phase distribution in the impeller region of an industrial centrifugal pump and a miniature centrifugal pump.
The presented investigations are founded by the German Federal Ministry of Education and Research (BMBF) under the funding code 02NUK023.
Keywords: centrifugal pump, advanced tomography, phase fraction visualization
  • Lecture (Conference)
    16th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA
  • Contribution to proceedings
    16th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA

Publ.-Id: 21144 - Permalink

THz driven Dynamics in Mattter: Sources and Applications
Gensch, M.;
  • Invited lecture (Conferences)
    Kolloquium des Instituts für Analytische Wisschenschaften (ISAS), 17.11.2014, Berlin, Deutschland

Publ.-Id: 21143 - Permalink

Optical Synchronization and Electron Bunch Diagnostic at ELBE
Kuntzsch, M.;
The recent upgrade of the ELBE accelerator included the installation of a new beamline section which will be used to compress the electron bunches to a duration of 100 fs at a charge of 1 nC. Two THz sources based on coherent transition or diffraction radiation und and an undulator source making use of the compressed bunches. In addition an Xray source based on Thomson backscattering, combining high power lasers with the relativistic electrons, is currently in commissioning phase and will deliver narrow bandwidth and tunable pulses.
To enable time resolved experiments on a 100 fs scale an optical synchronization system has been installed. It is based on a low noise fiber laser oscillator as optical reference. The signal is distributed to the remote stations via singlemode fibers. Drifts introduced by temperature variations and mechanical stress are measured by a balanced optical cross-correlator detection scheme and compensated with fast actuators. A stability of better than 30 fs over several hours has been demonstrated.
Based on the optical synchronization system a bunch arrival time monitor (BAM) has been set up. It is modulating the laser pulse train with a pickup signal from the electric field surrounding the electron bunch. The arrival time information is mapped into an amplitude modulation which can be detected by fast readout electronics. This technique enables arrival time measurements with a few femtosecond resolution.
The talk will give an overview on the ELBE upgrade and in particular on the installation of the synchronization system. First results of the arrival time measurements for both injectors (DC gun, SRF gun) are discussed.
Keywords: Synchronization Timing Diagnostic BAM
  • Invited lecture (Conferences)
    Beschleunigerseminar Helmholtz-Zentrum Berlin, 18.11.2014, Berlin, Deutschland

Publ.-Id: 21142 - Permalink

Progress on Bunch Arrival Time Measurements at ELBE
Kuntzsch, M.; Gensch, M.; Lehnert, U.; Schurig, R.; Bousonville, M.; Czwalinna, M. K.; Sydlo, C.; Vilcins, S.; Schlarb, H.; Angelovski, A.; Penirschke, A.;
The superconducting continuous wave (CW) accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is currently upgraded to generate electron bunches with sub picosecond duration, charges of up to 1 nC at repetition rates of up to 500 kHz (CW). The electron pulses are compressed to their desired length using two magnetic chicanes. To measure the timing of the electron bunches with respect to ELBEs RF reference at the target position a Bunch Arrival-time Monitor (BAM) has been setup and commissioned. Improvements concerning the beamline pickup and readout electronics are discussed which leads to a higher temporal resolution. First measurement results carried out are presented.
Keywords: ELBE Synchronization Bunch Diagnostic Timing
  • Poster
    IPAC14 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Deutschland

Publ.-Id: 21141 - Permalink

CW Beam Stability Analysis in Time and Frequency Domain
Kuntzsch, M.; Lehnert, U.; Schurig, R.; Teichert, J.; Gensch, M.; Kovalev, S.; Green, B.; Michel, P.;
The superconducting quasi CW Linac ELBE has been characterized in terms of energy and timing stability. The measurement results presented show a combination of a laser-based bunch arrival-time measurements (BAM), a fast beam position monitor (BPM) readout with single bunch resolution and a compression monitor (BCM) based on a fast pyro-electric detector. By changing the bunch compression factor a separation and identification of jitter sources has been achieved. The quasi CW mode of operation enables frequency domain data analysis with high dynamic range, which gives a better understanding of the main sources of jitter. Experimental results for both injectors (thermionic DC, superconducting RF) are presented.
Keywords: ELBE Synchronization Timing Stability BAM
  • Open Access LogoContribution to proceedings
    IBIC 2014 - 3rd International Beam Instrumentation Conference, 14.-18.09.2014, Monterey, USA
    Proceedings of IBIC 2014
  • Poster
    IBIC 2014 - 3rd International Beam Instrumentation Conference, 14.-18.09.2014, Monterey, USA

Publ.-Id: 21140 - Permalink

Sponge-like Si-SiO2 nanocomposite as photovoltaic absorber - influence of composition of the SiOx precursor
Schumann, E.; Heinig, K.-H.; Hübner, R.; Endrino, J. L.; Abrasonis, G.;
Absorber layers consisting of nanostructured Si are candidates to improve the effciency of thin film Si solar cells. Si-SiO2 nanocomposites with sponge-like Si embedded in SiO2 are promising materials as they exhibit a widened band gap and maintain the electrical interconnectivity. These structures can be formed upon annealing of SiOx films (x<1), which leads to spinodal phase separation into a percolacated network of Si nanowires embedded in SiO2. This can be accompanied by crystallization of the silicon. The influence of the composition of the precursor SiO2 on the evolving sponge-like nanostructure is investigated. SiOx layers have been grown by reactive sputter deposition. SiOx layers with compositions between x=0 and x=1.2 have been studied. The transformation of SiOx into Si-SiO2 nanocomposites has been performed by scanning a diode laser line source. Dwell times in the ms range and power densities of the red laser light of about 103 W/cm2 have been investigated. while thin a-Si films show crystallization under our annealing conditions, oxygen-rich films with Si structures smaller than 2 nm do not crystallize. Our results demonstrate that the composition of the precursor material is of crucial importance to obtain a Si-SiO2 nano sponge-like material suitable as photovoltaic absorber.
Keywords: Silicon, Silicon oxide, Nanocomposites, Energy Filtered TEM
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 30.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 21139 - Permalink

Sponge-like Si-SiO2 Nanocomposite as Photovoltaic Absorber – Influence of Composition of the SiOx Precursor
Schumann, E.; Heinig, K.-H.; Hübner, R.; Carcelén Valero, V.; Endrino, J. L.;
Nano structured Si absorber layers are candidates to improve efficiencies of thin film Si solar cells without increasing costs. Si-SiO2 nano sponge-like nanocomposites are promising materials as they exhibit a widened band gap due to quantum confinement and electrical interconnectivity due to percolation of the nanostructured Si. The sponge-like structures can be formed upon annealing of substoichiometric SiOx films (x<1), which leads to spinodal phase separation into a perlocated network of Si nanowires embedded in SiO2, tentatively accompanied by crystallization of the Si.
Here the influence of the precursor composition on the evolving sponge-like nanostructure and on the optical properties is investigated. SiOx layers have been grown by reactive sputter deposition where the composition of SiOx films was controlled by varying the oxygen flow during the deposition and subsequently measured by Rutherford Backscattering Spectroscopy (RBS). SiOx layers with compositions between x=0 and x=1.2 have been addressed. The Si-SiO2 nanocomposites are fabricated using a very rapid thermal processing by scanning a diode laser line source. Dwell times in the ms range and power densities of the red laser light of about 103 W/cm2 have been investigated.
Laser treatment of the precursor SiOx layers leads to decomposition into Si and SiO2 thereby forming Si-SiO2 sponge-like structures as observed by energy filtered transmission electron microscopy (EFTEM). While thin a-Si films show crystallization, oxygen rich films with Si structures smaller than 2nm do not show crystallization. The widening of the band gap due to quantum confinement has been confirmed by optical measurements.
Our results demonstrate that the composition of the precursor material is of crucial importance to obtain a Si-SiO2 nano sponge-like material suitable as PV absorber.
Keywords: Silicon, Silicon oxide, Nanocomposite, Energy Filtered TEM
  • Lecture (Conference)
    2014 MRS Spring Meeting & Exhibit, 21.-25.04.2014, San Francisco, United States of America

Publ.-Id: 21137 - Permalink

Partikelentstehung und –transport im Kern von Druckwasserreaktoren; Physikochemische Mechanismen (Abschlussbericht zum BMWi-Vorhaben 150 1430)
Kryk, H.; Hoffmann, W.;
Im Rahmen der deutschen Reaktorsicherheitsforschung wurden generische experimentelle Untersuchungen zur systematischen Aufklärung physikochemischer Mechanismen der Korrosionsproduktbildung und –ablagerung unter den wasserchemischen Bedingungen des Sumpfumwälzbetriebes in der Spätphase von Kühlmittelverluststörfällen in Druckwasserreaktoren durchgeführt. Das Vorhaben wurde in enger Kooperation mit der Hochschule Zittau/Görlitz (Vorhaben 150 1431) realisiert. Der Kontakt des borsäurehaltigen Kühlmittels mit feuerverzinkten Containment-Einbauten bewirkt eine Korrosion der Verzinkung, wodurch Zink im Kühlmittel gelöst wird. Als entscheidendes Ergebnis von Batch-Experimenten wurde eine abnehmende Löslichkeit von Zink-Korrosionsprodukten mit zunehmender Kühlmitteltemperatur gefunden. Somit ist die Bildung und Ablagerung fester Korrosionsprodukte nicht auszuschließen, wenn zinkhaltiges Kühlmittel in heiße Regionen innerhalb des Kühlkreislaufes gelangt (z.B. Hot-Spots im Kern). Experimente in einer Labor-Korrosionsversuchsanlage, die Untersuchungen zum Ablagerungsverhalten von Korrosionsprodukten an heißen Hüllrohroberflächen im Einzelkanal einschlossen, zeigten, dass auch unter diesen Bedingungen die Entstehung und Ablagerung von festen Korrosionsprodukten erfolgen kann. Die Korrosionsprodukte wurden als Zink-Borate identifiziert, wobei die chemische Zusammensetzung sowie das Ablagerungs- und Mobilisierungsverhalten entscheidend von der Bildungstemperatur beeinflusst werden. Untersuchungen zur Kinetik der Bildung von gelöstem Zink durch Korrosion von verzinkten Einbauten im Sicherheitsbehälter waren nicht Projektgegenstand, weshalb eine direkte quantitative Übertragbarkeit der Ergebnisse auf postulierte KMV in DWR derzeit nicht gegeben ist.
Keywords: Druckwasserreaktor, Kühlmittelverluststörfall, Korrosion, Zink, Zinkborat, Experiment
  • Other report
    Dresden: HZDR\FWD\2014\01, 2014

Publ.-Id: 21136 - Permalink

Mechanism of spin crossover in LaCoO3 resolved by shape magnetostriction in pulsed magnetic fields
Rotter, M.; Wang, Z.-S.; Boothroyd, A. T.; Prabhakaran, D.; Tanaka, A.; Doerr, M.;
In the scientific description of unconventional transport properties of oxides (spin-dependent transport, superconductivity etc.), the spin-state degree of freedom plays a fundamental role. Because of this, temperature- or magnetic field-induced spin-state transitions are in the focus of solid-state physics. Cobaltites, e.g. LaCoO3, are prominent examples showing these spin transitions. However, the microscopic nature of the spontaneous spin crossover in LaCoO3 is still controversial. Here we report magnetostriction measurements on LaCoO3 in magnetic fields up to 70 T to study the sharp, field-induced transition at Hc ≈ 60 T. Measurements of both longitudinal and transversal magnetostriction allow us to separate magnetovolume and magnetodistortive changes. We find a large increase in volume, but only a very small increase in tetragonal istortion at Hc. The results, supported by electronic energy calculations by the configuration interaction cluster method, provide compelling evidence that above Hc LaCoO adopts a correlated low spin/high spin state.

Publ.-Id: 21135 - Permalink

Computational Fluid Dynamics for energy efficient multiphase flow processes
Lucas, D.;
Multiphase flows are frequently applied in industrial processes as e.g. in chemical engineering. Reliable predictions of the flow characteristics such as local concentration of species and interfacial area density in gas-liquid flows can contribute to an optimization of the design of corresponding apparatuses and processes. Due to the high energy consumption of such process there is a considerable potential to save energy and materials. 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.
Keywords: multiphase, simulation, optimisation, CFD
  • Contribution to proceedings
    EST - Energy Science Technology, 20.-22.05.2015, Karlsruhe, Deutschland
  • Lecture (Conference)
    EST - Energy Science Technology, 20.-22.05.2015, Karlsruhe, Deutschland

Publ.-Id: 21134 - Permalink

Ultrasound study of FeCr2S4 in high magnetic fields
Felea, V.; Yasin, S.; Günther, A.; Deisenhofer, J.; Krug Von Nidda, H.-A.; Scheidt, E.-W.; Quach, D. V.; Groza, J. R.; Zherlitsyn, S.; Tsurkan, V.; Lemmens, P.; Wosnitza, J.; Loidl, A.;
We report on ultrasound studies of FeCr2S4 in static and pulsed magnetic fields exhibiting an orbital-order transition at 9K. A longitudinal acoustic mode exhibits distinct features in the phase space of temperature and magnetic field due to magnetic and structural transformations. Pulsed-field measurements show significant differences in the sound velocity below and above the orbital-ordering transition as well as the spin-reorientation transition at 60 K. Our results indicate a reduction of the magnetocrystalline anisotropy on entering the orbitally ordered phase.

Publ.-Id: 21133 - Permalink

Coexistence of localized and collective magnetism in the coupled-spin-tetrahedra system Cu4Te5O12Cl4
Choi, K.-Y.; Do, S.; Lemmens, P.; van Tol, J.; Shin, J.; Jeon, G. S.; Skourski, Y.; Rhyee, J.-S.; Berger, H.;
We report high-field magnetization, electron spin resonance (ESR), and Raman scattering measurements of the coupled spin-tetrahedra system Cu4Te5O12Cl4 with magnetic ordering at TN = 13.6 K. We find thermodynamic and spectroscopic signatures for the concomitant occurrence of localized and collective magnetism. Magnetization measurements up to 60 T exhibit a spin-flop transition at μ0HSF = 16 T only for H∥c as well as periodic magnetization steps at μ0H = 16.5, 24.8, 33.8, 42.3, and 49.7 T, which are independent of the crystallographic orientations. For T > TN, the temperature dependence of ESR linewidth is described by a critical power law, ΔBpp(T) ∝ (T−TN)−0.56±0.02. For T < TN, an antiferromagnetic resonance mode is observed for H ∥ c, and its linewidth is given by ΔBpp(T) ∝ T3.13±0.04, being close to T4 expected for a classical magnet. Raman spectra show three one-magnon-like excitations superimposed on a broad two-magnon continuum. While the two higher frequency modes show an intensity variation in accordance to a three-dimensional Heisenberg antiferromagnet, the lower frequency mode clearly deviates. These results suggest that Cu4Te5O12Cl4 is a unique material which shows a dual character of zero-dimensional, localized and three-dimensional, collective magnetic behaviors.

Publ.-Id: 21132 - Permalink

Anwendung des Systemcodes ATHLET zur Modellierung der Fluiddynamik in solarthermischen Kraftwerken mit Direktverdampfung
Hoffmann, A.; Hirsch, T.;
Anwendung des Systemcodes ATHLET zur Modellierung der Fluiddynamik in solarthermischen Kraftwerken mit Direktverdampfung
Keywords: Parabolrinnenkraftwerk, Siphoninstabilität, Zweiphasenströmung, ATHLET, Thermische Oszillationen
  • Poster
    46. Kraftwerkstechnisches Kolloquium 2014, 14.-15.10.2014, Dresden, Deutschland

Publ.-Id: 21131 - Permalink

Full access to nanoscale Bismuth-Palladium intermetallics by low-temperature syntheses
Heise, M.; Chang, J.-H.; Schönemann, R.; Herrmannsdörfer, T.; Wosnitza, J.; Ruck, M.;
The microwave-assisted polyol process was applied and modified to synthesize phase-pure micro- or nanocrystalline samples of all intermetallic phases in the bismuth−palladium system. Reaction temperatures range between 170 and 240 °C, whereas conventional syntheses from melt necessitate 500 to 1000 °C. Reaction times of few minutes up to 1 h are sufficient. Although not stable at the temperature of synthesis, high-temperature phases are accessible as well. Differences in the redox potentials of the two metals have effectively been compensated by adding auxiliaries such as oleylamine, oleic acid, and potassium hydroxide. The samples were characterized by X-ray powder diffraction, scanning electron microscopy, and energy-dispersive electron spectroscopy. Magnetic properties and electrical conductivity of the nanocrystalline samples were measured. The high temperature compound γ-BiPd showed superconductivity with Tc = 3.2 K. Nanocrystalline nc-Bi2Pd5 revealed an unusual temperature dependence of the electrical conductivity indicating an electronic phase transition at about 230 K. The electronic band structures of γ-BiPd, Bi2Pd5, Bi12Pd31, and BiPd3 were calculated including spin−orbit coupling.

Publ.-Id: 21130 - Permalink

Modellierung und Simulation hydrodynamischer Vorgänge in Bioreaktoren
Liao, J.;
Am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) wurde für zweiphasige disperse Systeme von Gasblasen in einer Flüssigkeit eine Modellsammlung („HZDR-Baseline-Modell“) zusammengefasst. Das Ziel der vorliegenden Arbeit war die Validierung des Modells für andere Reaktortypen wie beispielsweise den in der Bioverfahrenstechnik weit verbreiteten Airlift-Reaktor und die Entwicklung einer Modellierung für das dreiphasige System mit den Mikroorganismen als zusätzliche Feststoffphase zwecks der weiteren Anwendungen in der Biotechnologie.

Das Modell wurde aufgrund der physikalischen Grundlage und empirischer Modelle aus der Literatur und den Experimenten entwickelt. Danach wurde das Modell in der Software CFX implementiert und durch den Vergleich der Simulationsergebnisse mit den Daten aus der Literatur validiert. Nach der Literaturstudie wurde Luos Arbeit wegen ihrer ausführlichen Beschreibung der experimentellen Einrichtungen, Mess- und Auswertungsmethode, Daten sowie CFD Berechnung ausgewählt. Eine 2D-Simulation wurde wegen des günstigen Rechnungsaufwands und der Genauigkeit durchgeführt. Das Simulationsergebnis wurde mit einer Gitterstudie und einem Konvergenzkriterium von dem Gitter und der Zeit unabhängig gemacht und mit derselben Auswertungsmethode im Experiment behandelt. Nach einem graphischen Vergleich wurde festgelegt, dass die Simulationsergebnisse mit den experimentellen Messwerten hinreichend genau übereinstimmen und das HZDR-Baseline-Modell gültig für die Geometrie Airlift-Reaktor ist. Das Modell kann für die Schätzung des Systemzustands eingesetzt werden.

Wegen einer fehlenden Blasengröße aus der Messung ist die weitere Verbesserung der Simulation allerdings nicht möglich. Um das Verständnis der Fluiddynamik im Airlift-Reaktor zu vertiefen, wurde ein neues Experiment im HZDR durchgeführt. Zunächst wurden Trends und Wertebereiche wesentlicher Einflussgrößen für die Fluiddynamik mit Hilfe der Simulation vorab untersucht, um die Auslegung des Experiments zu optimieren. Danach wurden die Simulationsergebnisse mit den experimentellen Daten verglichen.

Drei Blasengrößengruppen wurden nach dem Ziel der Untersuchung von der Blasenschicht im Außenraum ausgewählt und in der Simulation implementiert. Nach den vorhandenen Ergebnissen kann das HZDR-Baseline-Modell das Phänomen der Blasenschicht beschreiben und relativ gute Ergebnisse zu den Messdaten liefern.

Des Weiteren, wurden die Partikel als eine weitere disperse Phase in der Euler-Beschreibung modelliert. Eine Übersicht solcher dreiphasiger Euler- Simulationen aus der Literatur und die dabei in den jeweiligen Schließungsmodellen berücksichtigten Effekte wurden ausführlich angefertigt. Mit Hilfe dieser Literaturstudie und einer Analoge zum HZDR-Baseline-Modell im zwei-phasigen System wurde das Modell für ein drei-phasiges System erweitert und erste Berechnungen durchgeführt. Es ergab sich eine Notwendigkeit für die weitere Untersuchung der Mechanik zwischen den Phasen. Eine Parameterstudie mittels Simulation und Literaturstudie für die Messmethoden im drei-phasigen System wurden deswegen für die zukünftige Arbeit durchgeführt.
  • Diploma thesis
    TU Dresden, 2014

Publ.-Id: 21129 - Permalink

On the low-field Hall coefficient of graphite
Esquinazi, P.; Krüger, J.; Barzola-Quiquia, J.; Schönemann, R.; Herrmannsdörfer, T.; Garcia, N.;
We have measured the temperature and magnetic field dependence of the Hall coefficient (RH) in three, several micrometer long multigraphene samples of thickness between ∼ 9 to ∼ 30 nm in the temperature range 0.1 to 200 K and up to 0.2 T field. The temperature dependence of the longitudinal resistance of two of the samples indicates the contribution from embedded interfaces running parallel to the graphene layers. At low enough temperatures and fields RH is positive in all samples, showing a crossover to negative values at high enough fields and/or temperatures in samples with interfaces contribution. The overall results are compatible with the reported superconducting behavior of embedded interfaces in the graphite structure and indicate that the negative low magnetic field Hall coefficient is not intrinsic of the ideal graphite structure.

Publ.-Id: 21128 - Permalink

Complex formation of tetravalent metal ions with small carboxylic ligands
Hennig, C.;
The complex formation mechanisms of M(IV) ions with carboxylates in aqueous solution is still widely unknown. This presentation gives an overwiew about the actual knowledge, presents new insights and gives an perspective for large molecules.
Keywords: EXAFS, XRD, actinides(IV), Ce(IV), Zr(IV)
  • Invited lecture (Conferences)
    Institut de Chimie de Nice Université de Nice Sophia Antipolis, 31.10.2014, Nice, France

Publ.-Id: 21127 - Permalink

Carrier dynamics in Landau-quantized graphene featuring strong Auger scattering
Mittendorff, M.; Wendler, F.; Malic, E.; Knorr, A.; Orlita, M.; Potemski, M.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.; Winnerl, S.;
The energy spectrum of common two-dimensional electron gases consists of a harmonic (that is, equidistant) ladder of Landau levels, thus preventing the possibility of optically addressing individual transitions. In graphene, however, owing to its non-harmonic spectrum, individual levels can be addressed selectively. Here, we report a time-resolved experiment directly pumping discrete Landau levels in graphene. Energetically degenerate Landau-level transitions from n = -1 to n = 0 and from n = 0 to n = 1 are distinguished by applying circularly polarized THz light. An analysis based on a microscopic theory shows that the zeroth Landau level is actually depleted by strong Auger scattering, even though it is optically pumped at the same time. The surprisingly strong electron–electron interaction responsible for this eect is directly evidenced through a sign reversal of the pump–probe signal.

Publ.-Id: 21126 - Permalink

Intraband carrier dynamics in Landau-quantized multilayer epitaxial graphene
Mittendorff, M.; Orlita, M.; Potemski, M.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.; Winnerl, S.;
We investigate the low-energy carrier dynamics in Landau quantized multilayer epitaxial graphene on (0001 ̅) SiC, using 14 meV photons. The THz absorption is dominated by Landau-level transitions within the conduction bands of several graphene layers with different doping. Varying the magnetic field allows us to tune the THz-induced response from induced transmission around B = 0 to induced absorption at intermediate fields (1.5 T – 3.3 T) and back to induced transmission at higher fields (3.3 T - 7 T). The main features of this complex response are explained by a strong dependence of the absorption on the electron temperature. Furthermore a prolonged relaxation at high fields, which is attributed to reduced scattering via optical phonons, is observed.

Publ.-Id: 21125 - Permalink

Development of a Novel Compact Particle Therapy Facility With Laser Driven Ion Beams via Gantry Systems Based on Pulsed Magnets
Masood, U.; Baumann, M.; Bussmann, M.; Cowan, T.; Enghardt, W.; Herrmannsdoerfer, T.; Hofmann, K.; Kaluza, M.; Karsch, L.; Kroll, F.; Schramm, U.; Schuerer, M.; Wilkens, J.; Pawelke, J.;
The advancement in laser particle acceleration has made Laser-based Ion Beam Therapy (LIBT) an attractive alternative to existing Ion Beam Therapy (IBT) facilities as it has a great potential to reduce size and cost. Ultra-intense laser pulses interact with thin targets and accelerates intense ion bunches on μm scale. Unlike conventional beams, laser-driven ion beams are characterized by short pulses of intense particle flux with peak dose rates exceeding conventional values by 8-9 orders of magnitude, low repetition rate, broad energy spectrum and large divergence. The presented work is an ongoing joint multidisciplinary translational research project of several institutions aiming to establish LIBT.

In addition to laser particle accelerator development, LIBT poses new challenges. Conventional solutions cannot be applied directly as LIBT demands full characterization of radiobiological effects, development of new beam monitoring and dosimetry, a treatment planning system (TPS) for broad energy beams and an optimized gantry with energy selection system. Laser-based technology has been established for cell and small animal irradiation using a fixed beamline and is being utilized for systematic radiobiological studies. For translation to patient irradiation highly compact 360° isocentric proton and carbon gantry systems are designed based on light-weight iron-less pulsed magnets. A dedicated 3D TPS is being developed. Moreover, increasing the laser power to petawatt level is needed to achieve therapeutic ion energies.

Radiobiologically no overall difference is observed for laser-driven ultra-high dose rates compared to conventional IBT beams. Our double achromatic pulsed gantry systems are ∼2.5 times smaller than conventional IBT gantries. For the gantry realization, key components have been designed and developed. A pulsed solenoid as particle capturing and focusing device was successfully tested. A novel 12 Tesla compact iron-less pulsed 50° sector magnet was developed. In addition, a pulsed high acceptance quadrupole with 230 T/m gradient has been designed and is being realized for tests. Our 3D TPS can be used to explore dose delivery and treatment planning strategies for LIBT.

The 3D TPS combined with our compact gantry provide a solution for LIBT. The realization and tests of pulsed gantry magnets are being continued. A new conventional proton therapy facility is under commissioning and is additionally equipped with a petawatt laser laboratory and an experimental bunker for further LIBT development toward clinical applicability with the conventional proton beam as reference.

This project was supported by German BMBF grant 03Z1N511 and DFG cluster of excellence MAP.

Publ.-Id: 21124 - Permalink

Numerical modeling of a horizontal annular flow experiment using a droplet entrainment model
Höhne, T.; Geissler, T.; Bieberle, A.; Hampel, U.;
One limitation in current simulating horizontal annular flows is the lack of treatment of droplet formation mechanisms. For self-generating annular flows in horizontal pipes, the interfacial momentum exchange and the turbulence parameters have to be modelled correctly. Furthermore the understanding of the mechanism of droplet entrainment in annular flow regimes for heat and mass transfer processes is of great importance in the chemical and nuclear industry.
A new entrainment model is proposed. It assumes that due to liquid turbulence the interface gets rough and wavy and forms droplets. The new approach is validated with HZDR annular flow experiments. Important phenomena like the pressure drop, the wave pumping effect, the droplet entrainment, the liquid film formation and the transient flow behavior could be calculated, analyzed and some of the phenomena compared with the measurement.
Keywords: CFD, horizontal annular flow, AIAD, droplet entrainment, two-phase flow

Publ.-Id: 21123 - Permalink

Optics, Mechanics, and Energetics of Two-Dimensional MoS2 Nanostructures from a Theoretical Perspective
Joswig, J.-O.; Lorenz, T.; Wendumu, T.; Gemming, S.; Seifert, G.;
Nanostructures based on molybdenum disulfide (MoS2) are by far the most common and well-studied systems among two-dimensional (2D) semiconducting materials. Although still being characterized as a “promising material”, the catalytic activity of MoS2 nanostructures has been found and applications in lubrication processes are pursued. As exfoliation techniques have improved over the past years, monolayer MoS2 is easily at hand;thus, experimental studies on the electronic properties and the applicability of monolayer MoS2 are in scientific focus now, and some electronic devices based on MoS2 have been reported already. The improvement of atomic force microscopy additionally led to nanoindentation experiments, in which the exceptional mechanical properties of MoS2 could be confirmed. In this Account, we present results from density-functional based calculations on several MoS2-based nanostructures; we have chosen to follow several experimental routes focusing on several nanostructures and their specific properties.
Keywords: 2D materials, molybdenum disulfide, platelets, nanoindentation, thermodynamic stability

Publ.-Id: 21122 - Permalink

Diaryl-substituted (dihydro)pyrrolo[3,2,1-hi]indoles, a class of potent COX-2 inhibitors with tricyclic core structure
Laube, M.; Gassner, C.; Sharma, S. K.; Günther, R.; Pigorsch, A.; König, J.; Köckerling, M.; Wuest, F.; Pietzsch, J.; Kniess, T.;
A new compound class of diaryl-substituted heterocycles with tricyclic dihydropyrrolo[3,2,1-hi]indole and pyrrolo[3,2,1-hi]indole core structures has been designed and was synthesized by a modular sequence of Friedel-Crafts acylation, amide formation, and McMurry cyclization. This synthesis route represents a novel and versatile access towards dihydropyrrolo[3,2,1-hi]indoles and is characterized by good chemical yields and high modularity. From a set of nineteen derivatives, eleven candidates were selected for determination of their COX inhibition potency and were found to be highly affine and selective inhibitors with IC50 to COX-2 ranging from 20 – 2500 nM and negligible inhibition of COX-1. The binding mode of the novel inhibitors in the active side of COX-2 was calculated in silico using the protein-ligand docking program GOLD by application of the molecular structures of two compounds derived from X-ray crystallography. Two novel compounds with high affinity to COX-2 (6k = 70 nM, 8e = 60 nM) have got a fluoro-substituent making them to promising candidates for the development of 18F-radiolabeled COX-2 inhibitors for imaging purposes with positron emission tomography (PET).
Keywords: pyrrolo[3,2,1-hi]indoles, selective COX-2 inhibitors, McMurry cyclization, GOLD, docking studies, radiotracer

Publ.-Id: 21121 - Permalink

Baseline model for simulation of bubbly flows
Rzehak, R.; Ziegenhein, T.; Liao, Y.; Kriebitzsch, S.; Krepper, E.; Lucas, D.;
A key parameter appearing in closure relations for the Euler-Euler two-fluid model is the bubble size. A distribution of bubble sizes is established as a result of bubble-coalescence and -breakup processes. These processes are very complex and models are considerably less developed than e.g. for bubble forces and even bubble-induced turbulence. Therefore, a two-step procedure is adopted for model validation where in a first step measured values are substituted for the bubble size distribution. In this way the uncertainties of the less developed modeling for bubble-coalescence and -breakup are bypassed and a validation of the other parts of the overall model becomes possible. In a second step the previously qualified models for bubble forces and bubble-induced turbulence are used without any change and the validity of models for bubble-coalescence and -breakup can be assessed. This procedure is illustrated by application to a set of data obtained for vertical upward flow in a pipe. In the first step satisfactory agreement is achieved like in previous investigations. A first attempt at the second step shows promising results as well. From the observed level of agreement between simulation and experiment, issues requiring further investigation are identified.
Keywords: Dispersed gas-liquid multiphase flow, Euler-Euler two-fluid model, closure relations, bubble-coalescence and -breakup
  • Contribution to proceedings
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Germany
    Proceedings of the 2nd International Symposium on Multiscale Multiphase Process Engineering
  • Lecture (Conference)
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Germany
  • Chemical Engineering & Technology 38(2015), 1972
    DOI: 10.1002/ceat.201500118

Publ.-Id: 21120 - Permalink

Laboratory formation of a scaled protostellar jet by coaligned poloidal magnetic field
Albertazzi, B.; Ciardi, A.; Nakatsutsumi, M.; Vinci, T.; Béard, J.; Bonito, R.; Billette, J.; Borghesi, M.; Burkley, Z.; Chen, S. N.; Cowan, T. E.; Herrmannsdörfer, T.; Higginson, D. P.; Kroll, F.; Pikuz, S. A.; Naughton, K.; Romagnani, L.; Riconda, C.; Revet, G.; Riquier, R.; Schlenvoigt, H.-P.; Skobelev, I. Y.; Faenov, A. Y.; Soloviev, A.; Huarte-Espinosa, M.; Frank, A.; Portugall, O.; Pépin, H.; Fuchs, J.;
Although bipolar jets are seen emerging from a wide variety of astrophysical systems, the issue of their formation and morphology beyond their launching is still under study. Our scaled laboratory experiments, representative of young stellar object outflows, reveal that stable and narrow collimation of the entire flow can result from the presence of a poloidal magnetic field whose strength is consistent with observations. The laboratory plasma becomes focused with an interior cavity. This gives rise to a standing conical shock from which the jet emerges. Following simulations of the process at the full astrophysical scale, we conclude that it can also explain recently discovered x-ray emission features observed in low-density regions at the base of protostellar jets, such as the well-studied jet HH 154.

Publ.-Id: 21119 - Permalink

Dynamics of gas-liquid flow in helical static mixer: An experimental and numerical study
Krepper, E.; Rabha, S.; Hampel, U.; Rzehak, R.; Schubert, M.;
Static mixer is an attractive alternative to conventional gas-liquid contactor, widely used for mixing and heat transfer between two fluids in various process applications. Knowledge on the limits of number and dimension of the static mixer element are important for packing optimization for desired mixing. The present work are designed to investigate the flow mixing pattern in a upward gas-liquid (air - water) flows in a column packed with helical static mixer both experimentally and numerically.
Experiments are carried out in a column of diameter (DT = 0.08 m) packed with helical static mixer (length 80 mm/ diameter 80 mm) using ultrafast electron beam X- ray tomography. The effect of number of static mixer element (3 – 9), liquid velocity (UL = 0.02 & 0.6 m/s), gas velocity (0.15 ≤ UG ≤ 0.6 m/s) on hydrodynamic parameters like gas holdup, bubble size distribution and pressure drop across the static mixer are studied.
Corresponding CFD simulations using the Euler-Euler model implemented in CFX 14 for some selective cases are done. The predicted axial and radial gas phase distribution considering different mono-dispersed bubbles classes (3, 5.8 and 8 mm) and poly-dispersed bubble classes are studied and validated against experimental results. The dependency of non-drag forces on the bubble size was considered. Consequently, the bubble size dependent effect of the non-drag forces on the flow and on the cross sectional gas volume fraction distribution are shown (see Fig. 1). The predicted axial gas volume fraction and velocity contour plots for different mono-dispersed bubbles classes within the helical static mixer are shown in Fig 2. The detailed effect of helical static mixer configuration and operating conditions on the predicted gas phase distribution & pressure drop and their validation with the measured results will be presented in our contribution.
Keywords: Static Mixer, Bubbly polydispersed flow, CFD modeling, momentum exchange
  • Poster
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Germany
  • Contribution to proceedings
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Germany

Publ.-Id: 21118 - Permalink

Extended validation of a baseline closure model
Krepper, E.; Rzehak, R.; Lucas, D.;
For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. In dispersed gas-liquid multiphase flow, closure is needed for bubble forces, bubble-induced turbulence, as well as bubble-coalescence and -breakup. The quest for models with a broad range of applicability allowing predictive simulations is an ongoing venture (Lucas, 2014).
A large part of the necessary validation work was directed towards vertical upward bubbly turbulent flow since here quite well defined boundary conditions can be realized. Examples are the HZDR-facilities MT_Loop and TOPFLOW, which are equipped with wiremesh sensor techniques (e.g. Rzehak et al. 2012, 2013a, Rzehak & Krepper 2013b).
In the present paper the range of considered flow phenomena is extended. From the vertical tube experiments the change of void fraction distribution particularly in the near injection region is used to validate the closure models for drag and non-drag forces and for bubble-induced turbulence. Furthermore the influence of a slight inclination of the vertical tube on the void fraction distribution is investigated. In a preliminary first step bubble coalescence and breakup were excluded, i.e. the investigations were focussed on tests, which can be simulated assuming a monodispersed bubble size distribution.
Keywords: CFD, multiphase flow, momentum exchange, model validation
  • Contribution to proceedings
    Application of CFD/CMFD Codes to Nuclear Reactor Safety and Design and their Experimental Validation, CFD4NRS, 09.-11.09.2014, Zurich, Switzerland
  • Lecture (Conference)
    Application of CFD/CMFD Codes to Nuclear Reactor Safety and Design and their Experimental Validation, CFD4NRS, 09.-11.09.2014, Zurich, Switzerland

Publ.-Id: 21117 - Permalink

Experimental evidence for the formation of titanium vacancies in TiO2 based transparent conductive oxides
Neubert, M.; Lungwitz, F.; Butterling, M.; Gebel, T.; Vinnichenko, M.; Cornelius, S.; Potzger, K.; Anwand, W.; Wagner, A.; Gemming, S.;
The work is focused on understanding the physical mechanism leading to limited free electron density and mobility by variation of the oxygen content in polycrystalline tantalum doped TiO2 films. The films were prepared on glass substrates using a two-step approach involving direct-current magnetron sputtering of non-conducting amorphous films followed by annealing in vacuum. It is demonstrated that that fine tuning of the oxygen content during growth is crucial to ensure the formation of anatase films with low resistivity in the range of 10-3 Ωcm and high optical transmittance after the annealing process. An increase of the oxygen content in the anatase film leads to a decrease of the free electron density and the mobility. This dependence of the film electrical properties is discussed in terms of the effective electrical activation of the Ta dopant taking into account the formation of negatively charged acceptor like defects.
Doppler broadening positron annihilation spectroscopy was used to determine the density of negatively charged open-volume defects as a function of oxygen deficiency of the Ta-doped anatase TiO2 films. It is observed that the density of these negatively charged defects increases with increasing oxygen content in the films, which is attributed to the formation of Ti-related vacancies. These acceptor like defects are considered to counteract n-type doping by Ta resulting in a decreasing electron density with increasing oxygen content. Furthermore, due to their maximum charge state of q = -4, Ti vacancies are effective scattering centers for free electrons [1]. Thus, their presence is believed to contribute to the observed decrease of the free electron mobility with increasing oxygen content in the films. These experimental results are consistent with previously reported first-principles calculations [1] of the point defect formation enthalpies for Ti substitution by Ta and for intrinsic Ti-vacancies in anatase TiO2 in dependence of the oxygen chemical potential.

1. J. Osorio-Guillen, S. Lany, and A. Zunger, Phys. Rev. Lett. 100, 036601 (2008).
Keywords: TCO, Transparent Conductive Oxide, Titanium, Tantalum, TiO2, Positron Annihilation, negative defects
  • Poster
    5th International Symposium on Transparent Conductive Materials, 12.-17.10.2014, Platanias - Chania, Greece

Publ.-Id: 21116 - Permalink

Broken axial symmetry as essential feature to predict radiative capture in heavy nuclei
Grosse, E.; Junghans, A. R.; Massarczyk, R.;
Cross sections for neutron capture in the range of unresolved resonances are predicted for more than 140 spin-0 target nuclei with A >50. Allowing the breaking of spherical and axial symmetry in nearly all these nuclei a combined parameterization for bothlevel density and photon strength is obtained which employs with surprisingly few fit parameters only. The strength functions used are based on a global fit to IVGDR shapes by the sum of three Lorentzians. They are based on theoretical predictions for the A-dependence of pole energies and spreading widths and add up to the TRK sum rule. For the small spins reached by capture resonance spacings are well described by a level density parameter close to the nuclear matter value; a significant collective enhancement is apparent due to the deviation from axial symmetry. Reliable predictions for compound nuclear reactions also outside the valley of stability – important for nuclear astrophysics and for the transmutation of nuclear waste – are expected to result from the global parameterization presented.
Keywords: Radiative neutron capture Level density Isovector giant dipole resonance Lorentzian Photon strength function Triaxiality

Publ.-Id: 21115 - Permalink

The application of radiolabelled nanoparticles in transport studies
Schymura, S.; Hildebrand, H.; Kuhlenkampff, J.; Franke, K.; Lippmann-Pipke, J.;
The radiolabelling of nanoparticles allows the tracking of these particles at low concentrations. Results for the radiolabelling of TiO2, Ag and MWCNTs and their consequent use for environmental transport studies including PET-studies are shown.
  • Lecture (Conference)
    CYCLEUR Meeting 2014, 13.-14.11.2014, Ispra, Italy

Publ.-Id: 21114 - Permalink

Numerical and experimental investigation of the contactless inductive flow tomography in the presence of strong static magnetic fields
Ratajczak, M.; Wondrak, T.; Stefani, F.; Eckert, S.;
In the continuous casting industry, electromagnetic brakes (EMBr) are used to influence the mould flow, although their effect on the flow cannot be directly examined due to a lack of market-ready measurement techniques for liquid metal flows. The contactless inductive flow tomography (CIFT) is a technique that is able to reconstruct the mean flow structure of an electrically conducting melt by measuring the flow-induced perturbations of an applied magnetic field outside the melt and solving the linear inverse problem. Since CIFT relies on the measurement of magnetic fields, the question arises: Does CIFT work in the presence of a strong static magnetic field, like that of an EMBr, that superimposes and distorts the applied excitation magnetic field? In this paper we will examine the effects of an EMBr on CIFT with simulations and accompanying measurements.
  • Magnetohydrodynamics 51(2015)3, 461-471

Publ.-Id: 21113 - Permalink

Large size crystalline vs. co-sintered ceramic Yb3+:YAG disk performance in diode pumped amplifiers
Albach, D.; Chanteloup, J.-C.;
A comprehensive experimental benchmarking of Yb3+:YAG crystalline and ceramic disks of similar thickness and doping level is presented in the context of high average power laser amplifier operation. Comparison is performed considering gain, depolarization and wave front deformation quantitative measurements and analysis.
Keywords: Lasers; Lasers, solid-state; Laser, ytterbium; Thermal effects

Publ.-Id: 21112 - Permalink

High-Speed PIXE: Large area irradiation effects
Buchriegler, J.; Hanf, D.; Merchel, S.; Munnik, F.; Nowak, S. H.; Renno, A. D.; Scharf, O.; von Borany, J.; Ziegenrücker, R.;
The so-called “High-Speed PIXE” is a novel combination of the SLcam® [1,2] and PIXE. The pixel-detector comprising 264 x 264 pixels in combination with a polycapillary 1:1 X-ray optics allows a fast detection of elements over a field of 12 x 12 mm² simultaneously with a lateral resolution below 100 μm.
In order to approach the final goal of quantitative analysis of geological samples, a homogeneous proton irradiation is essential. This can be realised by scanning a finefocused beam electrostatically across the area of interest which also minimises the required over-scan area.
However, the corresponding high proton density favours pile-up effects. In contrast to a classical micro-beam PIXE set-up, charge is collected in all pixels simultaneously for 1 ms. To enable trace element analysis, pile-up effects have to be suppressed calling for lower current densities.
[1] O. Scharf et al., Anal. Chem., Vol. 83, pp. 2532-2538 (2011).
[2] I. Ordavo et al., NIM A, Vol. 654, pp. 250-257 (2011).
  • Lecture (Conference)
    14th International Conference on Particle Induced X-ray Emission (PIXE 2015), 26.02.-03.03.2015, Somerset West, South Africa

Publ.-Id: 21111 - Permalink

High-Speed PIXE - First results: Laterally resolved trace element maps of geological samples
Buchriegler, J.; Hanf, D.; Merchel, S.; Munnik, F.; Nowak, S. H.; Renno, A. D.; Scharf, O.; von Borany, J.; Ziegenrücker, R.;
The so-called “High-Speed PIXE” is a novel combination of the SLcam® [1,2] and proton-induced X-ray emission (PIXE). The fluorescence radiation is excited by 3-4 MeV protons provided by the 6 MV tandem accelerator at HZDR. The pixel-detector comprising 264 x 264 pixels in combination with a polycapillary X-ray optics allows a fast detection of laterally resolved elemental maps over a detection area of 12 x 12 mm² simultaneously for all pixels.
Based on the pixel size of 48 x 48 μm² and considering the Nyquist-Shannon sampling theorem a lateral resolution better than 100 μm should be achievable. By measuring well-known structures of copper and chromium with appropriate dimensions, this assumption could be verified.
The system is intended for the detection of trace elements in geological samples by using a pnCCD-chip with an energy resolution better than 160 eV (@Mn Kα) for each pixel. The distribution of known trace element concentrations (<0.1%) in minerals could be proven in a short measurement time with this new PIXE set-up.
[1] O. Scharf et al., Anal. Chem., Vol. 83, pp. 2532-2538 (2011).
[2] I. Ordavo et al., NIM A, Vol. 654, pp. 250-257 (2011).
  • Poster
    8th International Symposium on BioPIXE, 14.-19.09.2014, Bled, Slovenia

Publ.-Id: 21110 - Permalink

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