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31860 Publications
Batch sorption and spectroscopic speciation studies of neptunium uptake by montmorillonite and corundum
Elo, O.; Müller, K.; Ikeda-Ohno, A.; Bok, F.; Scheinost, A.; Hölttä, P.; Huittinen, N.;
Detailed information on neptunium(V) speciation on montmorillonite and corundum surfaces was obtained by batch sorption and desorption studies combined with surface complexation modelling using the Diffuse Double-Layer (DDL) model and in situ time-resolved Attenuated Total Reflection Fourier-Transform Infrared (ATR FT-IR) and X-ray Absorption (XAS) spectroscopies. The pH-dependent batch sorption studies and the spectroscopic investigations were conducted under carbonate-free conditions in 10 mM NaClO4 or 10 mM NaCl. Solid concentrations of 0.5 g/l and 5 g/l were used depending on the experiment. The reversibility of the neptunium(V) uptake reaction by the two minerals was investigated in desorption experiments using the replenishment technique. Neptunium(V) sorption was found to be highly reversible, however, the degree of reversibility was dependent on the solution pH. The reversibility of the sorption reaction was confirmed in the ATR FT-IR spectroscopic studies at pH 10, where all of the identified inner-sphere complexed neptunium(V), characterized by a vibrational band at 790 cm-1, was desorbed from both mineral surfaces upon flushing the mineral films with a blank electrolyte solution. In XAS investigations of neptunium(V) uptake by corundum, the obtained structural parameters confirm the formation of an inner-sphere sorbed complex adsorbed on the surface in a bidentate fashion. As the inner-sphere complexes found in the IR-studies are characterized by identical sorption bands on both corundum and montmorillonite, we tentatively assign the neptunium(V) inner-sphere complex on montmorillonite to the same bidentate complex found on corundum in the XAS investigations. Finally, surface complexation modelling using obtained batch sorption and spectroscopic results were performed to explain the neptunium(V) speciation on montmorillonite over the entire investigated pH range. The modelling results show that cation exchange in the interlayer space as well as both outer-sphere and inner-sphere complexation are required to fully explain the neptunium(V) speciation on the montmorillonite surface

Publ.-Id: 22804 - Permalink


Interaction of highly charged ions with carbon nano membranes
Gruber, E.; Wilhelm, R. A.; Smejkal, V.; Heller, R.; Facsko, S.; Aumayr, F.;
Charge state and energy loss measurements of slow highly charged ions (HCIs) after transmission through nanometer and sub-nanometer thin membranes are presented. Direct transmission measurements through carbon nano membranes (CNMs) show an unexpected bimodal exit charge state distribution, accompanied by charge exchange dependent energy loss. The energy loss of ions in CNMs with large charge loss shows a quadratic dependency on the incident charge state, indicating charge state dependent stopping force values. Another access to the exit charge state distribution is given by irradiating stacks of CNMs and investigating each layer of the stack with high resolution imaging techniques like transmission electron microscopy (TEM) and helium ion microscopy (HIM) independently. The observation of pores created in all of the layers confirms the assumption derived from the transmission measurements that the two separated charge state distributions reflect two different impact parameter regimes, i.e. close collision with large charge exchange and distant collisions with weak ion-target interaction.

Publ.-Id: 22803 - Permalink


Incorporation of Cm3+ and Eu3+ in LnPO4 ceramics – a site-selective TRLFS study
Huittinen, N.; Arinicheva, Y.; Holthausen, J.; Neumeier, S.; Stumpf, T.;
The chemical durability and structural flexibility of lanthanide phosphates make these ceramics attractive as host phases for the conditioning of long-lived radionuclides produced during the nuclear fuel cycle. In the present work we have studied the structural incorporation of Cm3+ and Eu3+ in various LnPO4 monazite and xenotime phases with site-selective time-resolved laser fluorescence spectroscopy (TRLFS). The europium results indicate a full structural incorporation in the LnPO4 ceramics crystallizing in the nine-fold coordinated monazite structure (LaPO4-GdPO4) independent of the host cation radius. A local disordering can, however, be seen in mixed monazite solid solutions when going from the pure endmembers (LaPO4 and GdPO4) toward the La0.5Gd0.5PO4 composition. The smaller lanthanides crystallizing in the eight-fold coordinated xenotime structure (TbPO4-LuPO4) show only a partial uptake of Eu3+ within the host cation sites. The remainder of the dopant appears to be present as an ill-defined, partially hydrated europium species on or within the xenotime solid. Actinide (Cm3+)-doped LnPO4 samples have been synthesized similarly to the Eu3+ solids. The results of the Cm-TRLFS measurements will be compared to the Eu3+-data and presented at the symposium.
  • Lecture (Conference)
    Scientific Basis for Nuclear Waste Management XXXIX, 02.-06.11.2015, Montpellier, France

Publ.-Id: 22802 - Permalink


Curium(III) and europium(III) incorporation in lanthanide phosphate ceramics for conditioning of radioactive wastes
Huittinen, N.; Arinicheva, Y.; Holthausen, J.; Schmidt, M.; Neumeier, S.; Stumpf, T.;
The high-level radioactive waste (HLW) from spent nuclear fuel reprocessing facilities is currently immobilized in borosilicate glass. The vitrification process is well established and the flexible glass matrix is able to incorporate a very large range of elements present in the waste solution [1]. With the development of partitioning strategies, enabling the extraction of long-lived fission products and minor actinides (MA) from the PUREX raffinate, specific waste streams will be created that may require durable host matrices for their safe disposal. Especially for MA immobilization, some ceramic materials have been envisioned as host materials due to their thermal stability, high radiation tolerance, and chemical durability [2].
Lanthanide phosphate ceramics (LnPO4) are able to incorporate radionuclides in well-defined atomic positions within the crystal lattice [3] up to high (27 %) loadings [2]. The existence of very old natural analogues containing high concentrations of uranium and thorium shows that the crystalline phosphate structure is very tolerant towards self-irradiation damages as well as chemical weathering [4]. The dehydrated, high-temperature LnPO4 phases are known to crystallize in two distinct structures, depending on the ionic radius of the lanthanide cation: the larger lanthanides from La3+ to Gd3+ crystallize in the nine-fold coordinated monazite structure with a low symmetry, while the smaller lanthanides Tb3+ to Lu3+ form tetragonal, eight-fold coordinated xenotime structures.
In the present study we have used site-selective time-resolved laser fluorescence spectroscopy (TRLFS) to investigate the influence of the host cation radius as well as the crystal structure of the ceramic (monazite vs. xenotime) on the incorporation of the trivalent metal ions Eu3+ and Cm3+. We have synthesized pure monazites and xenotimes doped with 500 ppm Eu3+ or 50 ppm Cm3+ by precipitation of LnPO4 from a 0.3-0.5 M lanthanide nitrate solution with phosphoric acid followed by sintering of the precipitate at 1450°C to obtain the crystalline ceramic. The laser spectroscopy was performed either with a pulsed Nd:YAG-pumped tunable optical parametric oscillator or dye laser setup at cryogenic temperatures (~ 10 K). Excitation and emission spectra as well as luminescence lifetimes were collected for all measured samples.
Results on Eu3+-doped monazites show very narrow excitation spectra (Figure 1, left) for all investigated phases (LaPO4, SmPO4, GdPO4), indicating a complete incorporation of the dopant within the monazite crystal structure independent of the host cation radius. The emission spectra show a maximum splitting of the 7F1 and 7F2 bands (Figure 1, right), confirming the incorporation of Eu3+ on the low symmetry cation sites in the monazites.
The xenotime structure is not able to fully incorporate the europium ion within the crystal lattice. The excitation spectrum of Eu3+-doped LuPO4 in Figure 2 shows two regions of europium intensity that, upon excitation, decay with very different lifetimes. The broad signal in the wavelength region 575-580 nm corresponds to an ill-defined, partially hydrated europium species with a lifetime of approximately 580 µs (1.2 H2O). The species at 583.00 nm has a lifetime of 2700 µs indicating a full loss of the europium hydration sphere upon incorporation. The emission spectrum at this excitation wavelength shows a 2 and 4-fold splitting of the 7F1 and 7F2 bands, respectively, which is expected for an ion within the tetragonal cation site in the xenotime structure.
Our Eu3+ results demonstrate the importance of spectroscopic methods to probe the local environment of a guest cation within a solid matrix. According to our results, monazites can be considered as suitable host matrices for the immobilization of trivalent dopants. The xenotime structure on the other hand is not an ideal host for the larger lanthanide or actinide dopants due to the structure mismatch that does not allow for a complete guest ion substitution within the ceramic structure. Actinide (Cm3+)-doped LnPO4 samples have been synthesized similarly to the Eu3+ solids. The samples will be measured with TRLFS in the near future and results will be analyzed and compared to the existing Eu3+-data in order to confirm the incorporation behavior of trivalent dopants in the investigated solids. The results obtained for both dopants will be presented at the conference.
  • Lecture (Conference)
    15th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 13.-18.09.2015, Santa Fe, USA

Publ.-Id: 22801 - Permalink


Mass transfer measurement in a square milli-channel and comparison with results from a circular channel
Haghnegahdar, M.; Boden, S.; Hampel, U.;
In this work, we report on an experimental investigation of mass transfer from stagnant Taylor bubbles in a small square channel via measurement of the dissolution rate of an individual elongated bubble of carbon dioxide into water. As a measurement technique we used high resolution X-ray radiography and tomography. The changes in the size of the bubble at constant pressure obtained from the high-resolution X-ray images were used to calculate the liquid side mass transfer coefficient. The bubbles were continuously monitored by hydrodynamic fixation of the bubble in a down flow of the liquid. The results are compared with the available recently published data for circular channels.
The results show that the bubble dissolution curves in square channels are relatively even while the dissolution curves for bubbles in circular channels show some noticeable change in the slope. Furthermore, it is shown that the calculated liquid side mass transfer coefficient based on the measured data show good agreement with the data predicted by the penetration theory when the contact time between two phases is defined as the ratio of bubble length to the relative velocity. In addition, the comparison of the results with the data for circular channels showed that despite the fact that the rise velocity of bubbles in square channel is about three times faster than in circular channel, the liquid side mass transfer coefficients are approximately the same.
Keywords: mass transfer, Taylor bubble, carbon dioxide, square channels, X-ray imaging

Publ.-Id: 22800 - Permalink


High-energy resolution XAS/XES reveals insight into unique selectivity of La-based nanoparticles for CO2
Hirsch, O.; Kvashnina, K. O.; Luo, L.; Suess, M.; Glatzel, P.; Koziej, D.;
The lanthanum-based materials, due to their layered structure and f-electron configuration, are relevant for electrochemical application. Particularly, La2O2CO3 shows a prominent chemoresistive response to CO2. However, surprisingly less is known about its atomic and electronic structure and electrochemically significant sites and therefore, its structure–functions relationships have yet to be established. Here we determine the position of the different constituents within the unit cell of monoclinic La2O2CO3 and use this information to interpret in situ high-energy resolution fluores cence-detected (HERFD) X-ray adsorption near-edge structure (XAS) and valence-to-core X-ray emission spectroscopy (vtc XES). Compared with La(OH)3 or previously known hexagonal La2O2CO3 structures, La in the monoclinic unit cell has a much lower number of neighboring oxygen atoms, which is manifested in the whiteline broadening in XAS spectra. Such a superior sensitivity to subtle changes is given by HERFD method, which is essential for in situ studying of the interaction with CO2. Here, we study La2O2CO3-based sensors in real operando conditions at 250 °C in the presence of oxygen and water vapors. We identify that the distribution of unoccupied La d states and occupied O p- and La d states changes during CO2 chemoresistive sensing of La2O2CO3. The correlation between these spectroscopic findings with electrical resistance measurements leads to a more comprehensive understanding of the selective adsorption at La site and may enable the design of new materials for CO2 electrochemical applications.
Keywords: lanthanum oxycarbonate, HERFD XAS, valence-to-core XES, structure, CO2 sensing
  • Proceedings of the National Academy of Sciences of the United States of America 112(2015)52, 15803-15808
    DOI: 10.1073/pnas.1516192113

Publ.-Id: 22799 - Permalink


Neptunium characterization in uranium dioxide fuel: Combining a XAFS and a thermodynamic approach
Chollet, M.; Martin, P.; Degueldre, C.; Poonoosamy, J.; Belin, R. C.; Hennig, C.;
The effect of Np incorporation in a UO2 matrix on redox state of U and Np cations has been investigated by X-ray absorption spectroscopy (XAS) on three samples: (U0.9Np0.1)O2, (U0.9Np0.1)O2+x and pure NpO2 as a reference for Np(IV) oxidation state. XANES and EXAFS analysis show that only Uranium is oxidized in higher (V) and (VI) oxidation states in the hyperstoichiometric (U0.9Np0.1)O2+x sample in comparison to the stoichiometric (U0.9Np0.1)O2 where U appears at the (IV) oxidation state. Neptunium cation always remains at the (IV) oxidation state whatever the oxygen stoichiometry. Thermodynamic calculations performed to complete the experimental study, lead to the same conclusion. Separate UO2-NpO2 phases and homogeneous solid solution were considered. The latter case shows that the energy of mixing is insignificant in this system. These combined experimental and theoretical approaches demonstrate that any excess of oxygen in the system is carried by Uranium.
Keywords: neptunium oxide, uranium oxide, solid solution, stoichiometry, oxidation state

Publ.-Id: 22798 - Permalink


Magnetic structure of the antiferromagnetic half-Heusler compound NdBiPt
Müller, R. A.; Desilets-Benoit, A.; Gauthier, N.; Lapointe, L.; Bianchi, A. D.; Maris, T.; Zahn, R.; Beyer, R.; Green, E.; Wosnitza, J.; Yamani, Z.; Kenzelmann, M.;
We present results of single-crystal neutron-diffraction experiments on the rare-earth, half-Heusler antiferromagnet (AFM) NdBiPt. This compound exhibits an AFM phase transition at TN = 2.18 K with an ordered moment of 1.78(9) μB per Nd atom. The magnetic moments are aligned along the [001] direction, arranged in a type-I AFM structure with ferromagnetic planes, alternating antiferromagnetically along a propagation vector τ of (100). The RBiPt (R = Ce–Lu) family of materials has been proposed as candidates for a new family of antiferromagnetic topological insulators (AFTIs) with a magnetic space group that corresponds to a type-II AFM structure where ferromagnetic sheets are stacked along the space diagonal. The resolved structure makes it unlikely that NdBiPt qualifies as an AFTI.

Publ.-Id: 22797 - Permalink


Quantum Oscillation Signatures of Pressure-induced Topological Phase Transition in BiTeI
Park, J.; Jin, K. H.; Jo, Y. J.; Choi, E. S.; Kang, W.; Kampert, E.; Rhyee, J.-S.; Jhi, S.-H.; Kim, J. S.;
We report the pressure-induced topological quantum phase transition of BiTeI single crystals using Shubnikov-de Haas oscillations of bulk Fermi surfaces. The sizes of the inner and the outer FSs of the Rashba-split bands exhibit opposite pressure dependence up to P = 3.35 GPa, indicating pressure-tunable Rashba effect. Above a critical pressure P ~ 2 GPa, the Shubnikov-de Haas frequency for the inner Fermi surface increases unusually with pressure, and the Shubnikov-de Haas oscillations for the outer Fermi surface shows an abrupt phase shift. In comparison with band structure calculations, we find that these unusual behaviors originate from the Fermi surface shape change due to pressure-induced band inversion. These results clearly demonstrate that the topological quantum Phase transition is intimately tied to the shape of bulk Fermi surfaces enclosing the time-reversal invariant momenta with band inversion.

Publ.-Id: 22796 - Permalink


Interface control by homoepitaxial growth in pulsed laser deposited iron chalcogenide thin films
Molatta, S.; Haindl, S.; Trommler, S.; Schulze, M.; Wurmehl, S.; Hühne, S.;
Thin film growth of iron chalcogenides by pulsed laser deposition (PLD) is still a delicate issue in terms of simultaneous control of stoichiometry, texture, substrate/film interface properties, and superconducting properties. The high volatility of the constituents sharply limits optimal deposition temperatures to a narrow window and mainly challenges reproducibility for vacuum based methods. In this work we demonstrate the beneficial introduction of a semiconducting FeSe1−xTex seed layer for subsequent homoepitaxial growth of superconducting FeSe1−xTex thin film on MgO substrates. MgO is one of the most favorable substrates used in superconducting thin film applications, but the controlled growth of iron chalcogenide thin films on MgO has not yet been optimized and is the least understood. The large mismatch between the lattice constants of MgO and FeSe1−xTex of about 11% results in thin films with a mixed texture, that prevents further accurate investigations of a correlation between structural and electrical properties of FeSe1−xTex. Here we present an effective way to significantly improve epitaxial growth of superconducting FeSe1−xTex thin films with reproducible high critical temperatures (≥17 K) at reduced deposition temperatures (200 °C–320 °C) on MgO using PLD. This offers a broad scope of various applications.

Publ.-Id: 22795 - Permalink


Severe accident management research at HZDR
Tusheva, P.; Schäfer, F.; Altstadt, E.; Kliem, S.;
Presentation at the 1st Sino-German Symposium on Fundamentals of Advanced Nuclear Safety Technology.
Keywords: severe accidents, accident management measures
  • Invited lecture (Conferences)
    1st Sino-German Symposium on Fundamentals of Advanced Nuclear Safety Technology, 09.-12.03.2015, Shanghai, China

Publ.-Id: 22794 - Permalink


EDUKEM project - first spectroscopic insights into the U(IV)/U(VI) speciation in concentrated NaCl solution
Lehmann, S.; Steudtner, R.; Brendler, V.;
This work is embedded into the EDUKEM project, a collaboration with GRS Braunschweig and KIT-INE. Its major purpose is the provision of quality assured thermodynamic data for both tetra- and hexavalent uranium. This shall enable a better assessment of speciation and solubility limits in diluted to highly saline solutions as expected near nuclear waste repositories.
Respective experiments are based on parallel developments in electrochemical and spectroscopic tools being complementary to each other. In such a way difficult to access, systems and conditions should be explored to obtain an integral overview about aqueous uranium chemistry. This especially holds for reducing conditions. This will not only promote the characterization of complex system, e.g., encountered in nuclear waste management, but also allow a fingerprinting of unknown substances and mixtures.
We started to investigate the spectroscopic characteristics of 0.01M U(IV) and U(VI) in different background media (ClO4-, Cl-, SO42-, PO43-, CO32-) using UV/vis and fluorometry. The U(VI) was reduced by potentiostatic electrolysis using Ag/AgCl reference electrode. The reduction was monitored by UV/vis spectroscopy. The residual content of U(VI) was less than 1 %. We observed no formation of precipitations under the experimental conditions with exception of the PO43- system. There, we changed the uranium/ligand ratio from 1:100 to 1:5000 to suppress uranium phosphate precipitation. In general, the UV/vis spectra show variations in intensities and peak shifts to higher wavelengths in dependence of complexation strength in following order ClO4– < Cl– < SO42– < PO43– < CO32–.
In contrast to U(VI), which is often quenched by ions in the solution such as chloride, we obtained a luminescence spectrum of U4+ in 0.1 M HCl excited by λexc = 245 nm at a temperature of 1°C. The obtained luminescence spectrum is similar to the luminescence spectra of the free U4+ ion in acidic published by Kirishima et al. [1]. Under the experimental conditions, hydrolysis species as well as a complex formation between U(IV) and chloride should occur. The UV/vis spectra show spectral modifications which could be induced by the hydrolysis species. However, the luminescence spectra do not show spectral modifications.
In case of U(VI), first TRLFS results show the capabilities of fluorescence spectroscopy even in high chloride concentrated solutions to study U(VI) speciation. Despite the high concentration of 3 M chloride, a luminescence spectrum could be recorded in presence of carbonate in the alkaline pH region. Comparing the position of these bands with literature, we suggest a U(VI) complexation by carbonate [2].
The preliminary results of this study and of Bader et al. [3] shown that chloride quench mechanism for U(IV) and U(VI) luminescence is not fully understood yet in literature. Therefore, further studies will be performed on the spectroscopic behavior and chemistry of U(IV) as well as for U(VI) in highly concentrated chloride solutions.

Literature:
1. A. Kirishima et al., “Luminescence properties of tetravalent uranium in aqueous solution” Radiochim. Acta, 92, 705-710 (2004).
2. Z. Wang et al., “Cryogenic laser induced fluorescence characterization of U(VI) in Hanford vadose zone pore waters“, Environ. Sci. Technol., 38, 5591-5597 (2004).
3. M. Bader et al., “Biosorption of uranium on the cells of the halophilic archaea Halobacterium noricense DSM 15987 under highly saline conditions”, Abstract – ABC-Salt IV Workshop 2015 – Heidelberg, Germany.
Keywords: Uranium, high salinity, fluorescence, UV/vis, speciation
  • Poster
    ABC-Salt IV Workshop 2015, 14.-15.04.2015, Heidelberg, Deutschland
  • Poster
    The ThUL School in Actinide Chemistry, 28.09.-02.10.2015, Karlsruhe, Deutschland

Publ.-Id: 22793 - Permalink


Effect of anisotropic microstructure of a 12Cr ODS steel on the fracture behaviour in the small punch test
Altstadt, E.; Serrano, M.; Houska, M.; Garcia-Junceda, A.;
Oxide dispersed strengthened steels can exhibit a strongly anisotropic microstructure with elongated pancake-like grains in the rolling plane. This gives rise to intergranular fracture and subsequent delamination along large-area grain boundaries. We investigated an oxide dispersed strengthened alloy with 12 mass percent Cr, manufactured by mechanical alloying, hot extrusion and cold rolling by means small punch tests and subsequent fractographic analysis. The fracture behaviour was analysed in dependence of the specimen orientation. The results from small punch tests were contrasted with those from impact tests with sub-sized samples. In both tests, the ductile to brittle transition temperatures as well as the upper shelf energies depend significantly on the orientation of the specimens. However, the delamination affects the fracture of impact and small punch test samples in different ways. Thus, it depends on the load situation whether delamination has a beneficial or a detrimental effect on the fracture behaviour.
Keywords: ODS-steel, small punch test, anisotropy, delamination

Publ.-Id: 22792 - Permalink


Disclosing the hydrodynamics of 3D foam networks for application in advanced catalytic multiphase reactors
Zalucky, J.;
In the course of the 10th PhD seminar, the so-far achieved results of the PhD are presented in a short presentation. Starting with the economical and scientific background, the topic of multiphase hydrodynamics in solid foam trickle bed reactors is presented. The results cover the highlights of the regime transition measurements as well as studies carried out using ultrafast X-ray computed tomography.
Keywords: SiSiC solid foam packed trickle-bed reactors; co-current downflow hydrodynamics; ultrafast X-ray computed tomography
  • Lecture (Conference)
    10th HZDR PhD seminar, 02.-04.11.2015, Altenberg, Deutschland

Publ.-Id: 22791 - Permalink


Disclosing the hydrodynamics of 3D cellular networks for application in multiphase reactors
Zalucky, J.; Wagner, M.; Bieberle, M.; Schubert, M.; Hampel, U.;
On behalf of the closing symposium of the Helmholtz Energy Alliance 'Energy Efficient Chemical Multiphase Processes' the scientific highlights of working packages 3.1 and 5.3 are presented. In the first part, the results concering the regime transition measurements for SiSiC solid foam packed trickle-bed reactors are presented. In the second part, the investigations concering the liquid and gas distribution studied by using ultrafast X-ray computed tomography are discussed. In the third part, the hydrodynamics in bubble columns packed with periodic open-cellular structures (POCS) are presented.
Keywords: SiSiC solid foam packed trickle-bed reactor; regime transition; phase distribution; bubble column; periodic open-cellular structures; ultrafast X-ray computed tomography
  • Lecture (Conference)
    Abschlusssymposium der Helmholtz-Energie-Allianz Energieeffiziente Chemische Mehrphasenprozesse, 30.11.-01.12.2015, Dresden, Deutschland

Publ.-Id: 22790 - Permalink


Qualitative and quantitative analysis of liquid flow distribution in SiSiC foams using X-ray tomography
Zalucky, J.; Claußnitzer, T.; Schubert, M.; Hampel, U.;
In the recent years, solid foams have attracted engineer’s interest as novel functional internals for different chemical process applications. Beside their potential usage as static mixers, distillation packings and heat transfer equipment, solid foams have been envisaged as single and multiphase catalytic support as well. The present contribution focusses on the investigation of the liquid flow distribution inside SiSiC solid foams operated in co-current downward flow. Time-averaged and dynamic flow behaviour has been studied over wide ranges of gas and liquid su-perficial velocities using the non-invasive ultrafast X-ray tomography system.
Keywords: SiSiC solid foam hydrodynamics; co-current downflow; ultrafast X-ray computed tomography; liquid saturation; pulse flow parameters
  • Poster
    European Symposium on Chemical Reaction Engineering, 27.-30.10.2015, Fürstenfeldbruck, Deutschland

Publ.-Id: 22789 - Permalink


Hydrodynamics and transport processes in structured reactor devices: Project status report april 2015
Zalucky, J.; Schubert, M.; Hampel, U.;
On the occasion of half-annual project status report, work package progress is presented. The first part covers the regime transition measurement and modelling for the co-current downflow in SiSiC solid foam packed trickle-bed reactor. The second part summarizes the results found by investigating the time-dependent liquid gas distribution using ultrafast X-ray computed tomography in the same reactor system.
Keywords: regime transition measurement; regime transition modelling; SiSiC solid foam hydrodynamcs; ultrafast X-ray computed tomography
  • Lecture (others)
    Helmholtz-Energie-Allianz EECMP: Half-annular project meeting, 13.-14.04.2015, Fürth, Deutschland

Publ.-Id: 22788 - Permalink


Co-current downward flow regime transition in solid SiSiC foams: Flow regime prediction and measurement
Zalucky, J.; Möller, F.; Schubert, M.; Hampel, U.;
In recent years, solid foams have gained rising interest as multiphase reactor internals for highly exo- or endothermic processes due to relatively low pressure drop, high specific surface areas and elevated radial transport properties. Beside the geometric bed properties, the over-all reactor performance is significantly affected by the prevailing flow regime. In the present contribution, the flow regime transition of co-current downward flows in open-cell SiSiC solid foams has been investigated by optical and acoustical observations as well as fast pressure transducer. Measurements were performed with a water-air system in different bed geometries of varied pore densities and packing diameters of 20, 30, and 45 ppi and DN50 and DN100, respectively. Additionally, aqueous systems with reduced surface tension and increased viscosity have been tested. In order to predict the regime transition from trickle to pulse flow in multiphase systems, the two predictive models of Grosser et al. (1988) and Attou & Ferschneider (2000) have been adapted from trickle bed reactors to structured solid foam fixed bed reactors and validated by the experimental transition data. Determining the onset of flow instabilities at different liquid and gas velocities based on different force balances, both models allow the prediction of regime transition by means of known single phase pressure drop, static liquid holdup and characteristic geometric parameters of the solid foam.
Keywords: Stability based regime transition predictive modelling, SiSiC solid foam
  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Mehrphasenströmung, 19.-20.03.2015, Lüneburg, Deutschland

Publ.-Id: 22787 - Permalink


INTRA r³+ Vernetzung der r³ Projekte und Transfer der Ergebnisse
Dürkoop, A.;
In diesem Vortrag werden die Ergebnisse der Begleitforschung zu r³ vorgestellt. Dabei werden Methoden zur Bewertung von innovativen Technologien und Verfahren präsentiert, erfolgte Vernetzung der r³ Projekte erläutert und der Transfer der r³ Ergebnisse in die Anwendung gezeigt.
Keywords: Ressourceneffizienz, Strategische Metalle und Mineralien
  • Invited lecture (Conferences)
    Berliner Recycling- und Rohstoffkonferenz 2016, 07.-08.03.2016, Berlin, Deutschland

Publ.-Id: 22786 - Permalink


INTRA r³+ Integration und Transfer der r³ Fördermaßnahme - Ergebnisse der Begleitforschung
Dürkoop, A.; Brandstetter, P.; Erdmann, M.; Gräbe, G.; Höck, M.; Kleeberg, K.; Moller, B.; Ostertag, K.; Schneider, K.; Tercero, L.; Wilken, H.; Pfaff, M.; Büttner, P.;
Die r³ Fördermaßnahme wurde in einem Zeitraum von gut vier Jahren zwischen Ende 2011 bis Anfang 2016 durch das Bundesministerium für Bildung und Forschung mit 30 Mio. € gefördert. In 28 r³ Verbundprojekten forschten bundesweit mehr als 100 Unternehmen, Forschungseinrichtungen und Behörden daran, wie nicht-energetische mineralische Rohstoffe zukünftig effizienter genutzt werden können (Abb. 1). Der Fokus lag auf den wirtschaftsstrategisch wichtigen Metallen wie Indium, Germanium, Gallium und seltene Erden, aber auch Industrieminerale wie beispielsweise Flussspat, die zukünftig effizienter gewonnen, recycelt und in Produkten verwendet werden sollen (BMBF 2010). Strategische Metalle und Mineralien werden vor allem für die Herstellung von Hightech-Produkten (Abb. 2) und Energiesparlampen, aber auch für Dauermagnete benötigt. Zwar werden diese Ressourcen nicht in großen Mengen verwendet, sind aber wirtschaftsstrategisch von großer Bedeutung. Da die Rohstoffe zunehmend schlechter verfügbar sind, steigen die Produktionskosten für solche Hightech-Produkte. Die Versorgungslage für diese strategischen Rohstoffe ist in Deutschland unsicher, was zu Versorgungsengpässen im Rohstoffimportland Deutschland führen könnte. Die Ergebnisse der r³ Verbundprojekte zeigen, dass die Versorgungslage für einige dieser Rohstoffe für Deutschland verbessert werden könnte.
Die Bewertung der Ergebnisse aus r³ erfolgte im Rahmen des Projekts INTRA r³+ (Abb. 3) unter der Leitung des Helmholtz-Instituts Freiberg für Ressourcentechnologie (HIF). Zur Bewertung der Nachhaltigkeit der r³ Ergebnisse wurden zum einen ökonomisch-ökologisch-soziale Aspekte analysiert und zum anderen gesamtwirtschaftliche Betrachtungen durchgeführt. Zudem wurde die Vernetzung der r³ Verbundprojekte untereinander aber auch mit externen Initiativen und Projekten mit diversen Maßnahmen angeregt. Darüber hinaus wurde mit Öffentlichkeitsarbeit-Maßnahmen durchgeführt und der Technologietransfer in die Wirtschaft vorbereitet. Partner von INTRA r3+ sind neben dem HIF die Technische Universität Bergakademie Freiberg (TUBAF), der Lehrstuhl für Ganzheitlich Bilanzierung an der Universität Stuttgart (LBP), das Fraunhofer Institut für System- und Innovationsforschung (ISI), das Fraunhofer-Institut für Chemische Technologie (ICT) und die Deutsche Rohstoffagentur (BGR/DERA).
Keywords: Ressourceneffizienz, strategische Metalle, Versorgungssicherheit, Nachhaltigkeitsbewertung
  • Open Access LogoContribution to proceedings
    Berliner Recycling- und Rohstoffkonferenz, 07.-08.03.2016, Berlin, Deutschland
    Recycling und Rohstoffe Band 9, Neuruppin: TK Verlag, 978-3-944310-27-5, 253-272
  • Book chapter
    Karl J. Thomé-Kozmiensky; Daniel Goldmann: Recycling und Rohstoffe Band 9, Neuruppin: TK Verlag, 2016, 978-3-944310-27-5

Publ.-Id: 22785 - Permalink


Experimental investigation of cocurrent water/air down flow in SiSiC solid foam packed reactors
Claußnitzer, T.;
Trickle bed reactors (TBR) are widely used in the chemical industry, especially for oxidation, hydrogenation and hydrodesulfurization processes. Since overall performance of TBR is essentially affected by the hydrodynamic properties of the package, lot of work has been done to improve characteristics of the reactor interior. Decreasing the particle size of conventional packings like spheres and cylinders increases the specific surface area but also the pressure drop.
Compared to commonly used packings, solid foams are promised to provide less pressure drop but higher surface area at once. To investigate to hydrodynamics in these packings, solid foams of three different pore densities (20 ppi, 30 ppi, 45 ppi) have been studied in an air/water cocurrently downflow system using ultrafast X-ray tomography to determine their hydrodynamic properties as well as their suitability as reactor packing.
Experiments were carried out at a broad range of gas and liquid superficial velocities of 0.2 ms-1 to 1.0 ms-1 and 0.01 ms-1 to 0.04 ms-1, respectively, covering different flow regimes, namely trickle flow, pulsing flow as well as the transition region.
With spatially-resolved measurements the liquid distribution behavior of solid foams has been investigated. It was shown, that the initial liquid distribution primarily depends on liquid distributor and the pore density of the applied foam, but is not as good as expected.
Following, temporally-resolved measurements at fixed measurement height were carried out. There, for each measurement setup the liquid saturation has been determined and a correlation has been proposed to describe the liquid saturation as a function of pore size as well as gas and liquid flow rate.
In the pulsing regime, investigations were accomplished regarding pulse properties like frequency and velocity. A strong influence of the pore density of the applied foams was found.
Keywords: trickle bed reactor; SiSiC solid foams; ultrafast X-ray tomography; hydrodynamics; co-current downflow
  • Diploma thesis
    TU Dresden, 2015
    Mentor: Zalucky, J., Hampel, U.
    160 Seiten

Publ.-Id: 22784 - Permalink


Zum Verständnis der Flotierbarkeit - Untersuchungen zu spezifischen Oberflächenenergieverteilungen und hydrophoben Wechselwirkungen
Rudolph, M.;
Spätestens seit dem Patent der Gebrüder Bessel aus Dresden von 1877 nutzt man die Anhaftung hydrophober Partikel an Gasblasen in der Flotation, einer Heterokoagulationstrennung, technologisch aus, um Partikelgemische auf Basis ihrer chemisch veränderlichen Benetzungseigenschaften voneinander zu trennen. Ein wesentlicher Mikroprozess ist hierbei der Anlagerungsvorgang, bestimmt durch das Wechselwirkungspotential zwischen einem Partikel und einer Gasblase. Die klassische DLVO Wechselwirkungstheorie beinhaltet für diese Partner nur repulsive Terme, d.h. abstoßende Doppelschichtwechselwirkung und abstoßende van der Waals Wechselwirkung durch eine negative Hamaker-Konstante. Über die Physik der zwingend notwendigen, weil prozessbestimmenden, weit reichenden, anziehenden Wechselwirkungskomponente ist man sich in der Literatur noch nicht einig. Viele Wissenschaftler sehen feinste Gasdomänen auf hydrophoben Oberflächen, oft als Nanobubbles oder Micropancakes bezeichnet, als Vermittler von weit reichenden kapillaren Anziehungskräften. Andere sehen eine weit reichende Wasserstrukturstörung an hydrophoben Oberflächen als Ursache für eine somit entropisch begründete Anziehung.
Am Helmholtz-Institut Freiberg für Ressourcentechnologie werden in Grundlagenuntersuchungen zur Flotation atomare Gesamtwechselwirkungen zwischen unterschiedlich benetzenden Oberflächen (z.B. Mineralen) und hydrophoben Modellpartikeln in Lösung mit Hilfe der Partikelsonden Rasterkraftmikroskopie analysiert. Zudem wird mit der Methode der inversen Gas Chromatographie die Änderung der spezifischen Oberflächenenergieverteilung als fundamentaler Benetzungsparameter untersucht und mit der Flotierbarkeit in der Mikroflotation in Verbindung gebracht. Der Vortrag fasst den aktuellen Stand der grundlegenden Untersuchungen zusammen. Im Zusammenhang mit den rasterkraftmikroskopischen Untersuchungen werden hydrophobe Wechselwirkungen diskutiert. Auf Basis der Analyse von Oberflächenenergieverteilungen im Zusammenhang mit der Mikroflotation wird ein neues Flotierbarkeitskriterium, die freie Wechselwirkungsenthalpie zwischen einem Partikel und einer Gasblase im Wasser eingeführt und kritisch diskutiert.
Keywords: Flotation, iGC, AFM, Hydrophobicity, Minerals, Collectors
  • Lecture (Conference)
    Aufbereitung und Recycling Jahrestagung 2015, 11.-12.11.2015, Freiberg, Deutschland

Publ.-Id: 22783 - Permalink


The energy of interactions between bubbles and particles – specific surface free energy distributions and microflotation
Rudolph, M.; Chelgani, S.; Meier, K.; Hartmann, R.;
In fundamental flotation studies typically the contact angle is used to describe wettability and correlated with floatability. However, a more fundamental parameter is the specific surface free energy, related to the contact angle via Young’s equation. Inverse gas chromatography (iGC) is a suitable method to determine specific surface free energy components and their distributions on particulate surfaces. In this study the pure minerals quartzite (SiO2), fluoro-apatite (Ca5[F,(PO4)3]) and magnetite (Fe3O4) are examined for microflotation floatability and surface energy considering different methods of sample treatment and the effect of the collectors sodium oleate and dodecyl ammonium acetate. The parameter of specific net free energy of interaction between bubbles and particles immersed in water ΔGpwb derived from the complex surface energy analysis is introduced and used to evaluate the hydrophobicity of the mineral surface correlated with microflotation floatability. Results lead to the provocative hypothesis that only small fractions of the surface and their change by flotation reagent adsorption will inherently define floatability of minerals.
Keywords: Flotation, iGC, Apatite, Quartz, Surface Free Energy, Heterogeneity, Interfaces, Collectors
  • Lecture (Conference)
    Flotation '15, 16.-19.11.2015, Cape Town, South Africa

Publ.-Id: 22782 - Permalink


Laser Ion Acceleration of Spherical Mass Limited Solid Density Targets
Huebl, A.; Kluge, T.; Widera, R.; Hilz, P.; Schreiber, J.; Schramm, U.; Bussmann, M.;
We present simulation results regarding the acceleration of ions from mass limited solid density targets with short-pulse high power lasers. Taking advantage of large scale 3D3V PIC simulations (8000 GPUs each, INCITE award 2015) allows to give a detailed insight into the dynamics and unique features of truly isolated targets that were used in recent experiments.
We discuss the pre-plasma evolution, its dependence on laser contrast and its crucial influence on the dominant acceleration mechnanism and on the directionality of the laser-accelerated ion beams. Extensive 2D3V parameter scans are presented for comparison with commonly used flat, wire or mounted target designs.
Keywords: Laser Ion Acceleration, Mass Limited Target, Simulation, PIC, HPC, GPU, PIConGPU
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Atome, Moleküle, Quantenoptik und Plasmen (SAMOP), 29.02.-04.03.2016, Hannover, Deutschland

Publ.-Id: 22781 - Permalink


Charge Exchange and Energy Loss of Slow Highly Charged Ions in Graphene
Wilhelm, R. A.; Gruber, E.; Kozubek, R.; Smejkal, V.; Schleberger, M.; Facsko, S.; Aumayr, F.;
Slow highly charged ion (HCI) interaction with surfaces 100 was studied extensively in recent years and revealed many 7+ interesting aspects of the underlying processes [1]. Nanostructure formation by single HCI impact was successfully 10 linked to defect mediated desorption or even surface melting due to HCI induced local electronic excitations. The neutralization dynamics of a slow (v ≪ v0 = αc, α: fine structure constant, c: speed of light) HCI in front of a solid surface is well described by the classical-over-barrier model. However, not much is known about the neutralization below the surface, i.e. in the material. Below surface neutralization becomes important for normal incidence, because here the interaction time above the surface is not sufficient for neutralization and relaxation of the HCI. We present results on charge exchange and energy loss measurements of slow highly charged Xe ions with charge states of 10 < Q < 35 transmitted through freestanding single Xe16+ layer graphene as the thinnest and lightest solid target material there is. We find that the charge exchange is not bimodal as in case of transmission through 1 nm thick carbon 1 nanomembranes [2], but only very large charge exchange is observed. We attribute this to (1) the availability of solely smallimpactparameters (p<1.5Å ̊) in graphene as well as (2) very high mobilities of charge carriers and subsequently transfer of (at least) 20-30 electrons within less than 10 fs. Especially the second fact is surprising, because here the charge transfer is hardly conceivable as a sequential, but rather as a collective electron transfer process. For incident charge states Q > 25 we observe a saturation of charge exchange, i.e. the exit charge state distribution has a mean value Qmean ≈ Qin − 20 (see fig. 1). The contributions of above surface charge transfer and charge transfer during collision as well as energy loss and its dependence on the charge state and charge exchange will be discussed.
  • Invited lecture (Conferences)
    International Workshop on Inelastic Ion-Surface Collisions (IISC), 18.-23.10.2015, San Sebastian, Spanien

Publ.-Id: 22780 - Permalink


Co2Mn0.6Fe0.4Si: A Heusler compound opening new perspectives in magnon spintronics
Sebastian, T.; Hillebrands, B.;
This chapter addresses magnon propagation in the Heusler compound Co2Mn0.6Fe0.4Si and the corresponding perspectives for the emerging field of magnon spintronics. The concept of magnon spintronics requires the utilization of advanced materials providing, in particular, a low magnetic Gilbert damping and compatibility with industrial standards concerning the fabrication ofmicro-and nanostructures. We present how this challenge can be addressed by the use of low-damping Co2Mn0.6Fe0.4Si films on the basis of recent studies using micro-focus Brillouin light scattering spectroscopy. The low damping in this Heusler compound not only allows for the realization of increased propagation distances. The pronounced occurrence of nonlinear phenomena might even lead the way towards novel concepts and functionalities in magnonic devices.
  • Book chapter
    Claudia Felser, Atsufumi Hirohata: Häusler Alloys - Properties, Growth, Applications, Switzerland: Springer, 2015
    DOI: 10.1007/978-3-319-21449-8_13

Publ.-Id: 22779 - Permalink


Slow highly charged ion transmission through carbon nanomembranes and graphene
Wilhelm, R. A.; Gruber, E.; Heller, R.; Facsko, S.; Aumayr, F.;
Slow highly charged ions (HCI) showed in many studies their efficiency in formation of surface nanostructures especially on insulating surfaces [1]. Here we report on transmission of HCI through carbon foils with a thickness of only 1nm and below (graphene). At these thicknesses the neutralization of the slow HCI is not completed in the solid and thus effects of pre-charge-equilibrium stopping of slow ions can be addressed experimentally.
We find that transmitted highly charged Xe ions with charge states between Q=10 and Q=30 show a bimodal charge state distribution, i.e. one part of the ions is transmitted in low exit charge states combined with a large charge exchange enhanced kinetic stopping. The other part of the ions, however, shows only a very small charge exchange with almost no kinetic energy loss [2]. Both charge exchange regimes are attributed to different impact parameter regimes, i.e. close collision lead to extremely large charge exchanges and distant collisions are connected with weak ion-target interactions. Thus, our measurements reveal that sub-surface neutralization of HCI proceeds in a step-like fashion, i.e. either the ion approaches a target atom closely and correspondingly neutralizes almost completely (∆Q > 20 for Q = 30) or it passes through the material almost unchanged (∆Q < 5) until it hits a target atom at some larger depth. A bimodal charge state distribution could therefore not be observed for larger target thicknesses [3], except for the inverse case of a swift heavy ion charging up during transmission through a silicon single crystal under random vs. channeling direction [4]. Gas phase experiments on the other hand cannot lead to slow HCI neutralization in one single scattering event using light target atoms (e.g. carbon), because here only atomically bound electrons can contribute to the neutralization process (6 electrons in case of carbon) rather than de-localized electrons in a solid target.
  • Poster
    International Summer School on Vacuum, Electron and Ion Technologies, 21.-25.09.2015, Sozopol, Bulgarien

Publ.-Id: 22778 - Permalink


Electron emission from solid surfaces due to slow highly charged ion impact
Wilhelm, R. A.; Heller, R.; Meissl, W.; Aumayr, F.; Facsko, S.;
Slow highly charged ions (HCI) and their interaction with surfaces reveal many interesting phenomena, e.g. nanostructure formation, non-equilibrium ion stopping and charge exchange as well as extremely large electron emission yields [1,2].
The emission of electrons is tightly connected to the neu- tralization process of the HCI above and below the sur- face. When the ion approaches the surface it starts to capture electrons near the Fermi edge into high Rydberg states in the ion and subsequently emits Auger electrons upon de-excitation. The process is well described by the classical-over-barrier model [3]. However, for normal incidence the time for neutralization of the ion above the surface is not sufficient. Hence, the neutralization pro- ceeds below the surface with accompanied sub-surface electron emission.
We present here recent experimental data on the second- ary electron emission yield from highly charged Xe im- pinging on Au, KBr, LiF and CaF2 surfaces (see fig. 1). The data shows that so called potential emission, i.e. secondary electron emission by neutralization (potential energy conversion) becomes significant for low ion ve- locities (v < 105 m/s) [4].
The large amount of HCI induced electrons emitted from the surface opens the possibility of correlative studies of nanostructuring by HCI and subsequent electron spec- tromicroscopy.
Our planned Low Energy Ion Nano-Engineering Facility (LEINEF) at the Ion Beam Center of the Helmholtz- Zentrum Dresden-Rossendorf will comprise several HCI sources, a medium and low energy ion scattering set-up, a focused ion beam set-up, Auger and x-ray photoelec- tron spectroscopy as well as a low energy electron mi- croscope (LEEM). The latter one may be equipped with an ion gun or a HCI source to perform correlative nanostructuring and electron spectromicroscopy with electrons from the LEEM source as well as ion induced secondary electrons.
  • Poster
    Low Energy Electrons: Dynamics and Correlation near Surfaces and Nanostructures (LEE2015), 07.-11.09.2015, Hernstein, Österreich

Publ.-Id: 22777 - Permalink


Interaction of Slow Highly Charged Ions with Ultrathin Membranes - Potential Sputtering, Energy Loss and Charge Exchange
Wilhelm, R. A.; Gruber, E.; Ritter, R.; Heller, R.; Facsko, S.; Aumayr, F.;
Slow highly charged ions (HCI) are known as an efficient tool for sur- face nano structuring of various insulating and semi-conducting sur- faces. We show here that slow HCI can also be used to perforate a free-standing carbon nano membrane (CNM) with a thickness of only 1 nm. Round pores with sizes of up to 15 nm in diameter and corre- sponding sputter yields of up to a few thousand atoms are observed. Recent energy loss and charge exchange measurements on ions trans- mitted through a 1 nm thick CNM and free-standing Graphene reveal a strong dependence of the ion energy loss on charge exchange. Sur- prisingly, two distinct exit charge state distributions are observed, i.e. one part of the ions is almost neutralized and the other part remains in very high charge states after transmission. The ions potential and kinetic energy dependence on pore formation is discussed in terms of charge exchange and energy loss.
  • Lecture (Conference)
    Frühjahrestagung der Deutschen Physikalischen Gesellschaft, Sektion Kondensierte Materie, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 22776 - Permalink


Highly charged ion induced nanostructures by strong electronic excitations
Wilhelm, R. A.; El-Said, A. S.; Krok, F.; Heller, R.; Gruber, E.; Aumayr, F.; Facsko, S.;
The formation of nanostructures on surfaces without bulk damage by slow highly charged ion (HCI) irradiation was studied intensively in recent years. Especially single HCI impact on ionic crystals revealed interesting new phenomena. On alkali halides, e.g. KBr or KCl, defect mediated desorption with corresponding yields of a few thousand desorbed atoms per ion was observed [1]. Associated structures are pits with a diameter of up to 20nm and a depth of only 1 or 2 monolayers. The HCI’s potential energy was identified as the driving force for the desorption process. On alkaline earth halides (CaF2), however, hillocks were observed and this process was linked to a solid-liquid phase transition after surpassing a certain potential energy threshold. Even before nanomelting occurs damage could be revealed by wet-chemical etching of the surface [2]. Since HCI interaction with surfaces involves electron capture from and electron emission to the surface, we compare here HCI induced structures to structures observed after low energy electron bombardment [3]. Electrons and HCIs produce strong electronic excitations at the surface and subsequent de-excitation by electron-phonon interaction leads to the structure formation. Thus, potential sputtering and HCI induced phase transitions result from electronic excitations (and subsequent de-excitation) in contrast to single charged ions in the nuclear sputtering regime. To study the neutralization process of HCI in more detail we present recent data on the transmission of HCI through ultra-thin materials.
  • Lecture (Conference)
    International Workshop on Nanoscale Pattern Formation at Surfaces, 12.-16.07.2015, Kraków, Polen

Publ.-Id: 22775 - Permalink


Threshold and Efficiency for Perforation of 1nm Thick Carbon Nanomembranes with Slow Highly Charged Ions
Wilhelm, R. A.; Gruber, E.; Ritter, R.; Heller, R.; Facsko, S.; Aumayr, F.;
Ion collision with surfaces leads to nano-structure formation usually by cumulative ef-fects. Large ion fluencies are needed to lead to observable topographic surface features. For special classes of ions, i.e. swift heavy ions or slow highly charged ions (HCI) already single ion impacts may give rise to structural changes with a lateral extent of a few nm. Desired sur-face-only modification, however, can solely be achieved by HCI due to the very localized re-lease of their potential energy.
Different kinds of surface structures have been observed on insulating [1] and semi-conducting surfaces [2]. All these studies have in common that a certain ion charge state or potential ener-gy threshold has to be exceeded in order to form nano-hillocks, nano-pits, nano-craters, or even sub-surface damage only visible after chemical etching [3]. For high ion charge states the effi-ciency for nano-structure formation is consid-ered to be 100%, i.e. every ion produces a struc-ture upon impact. However, an accurate fluence measurement necessary to determine the struc-turing yield for HCI irradiation is challenging, because of very low ion currents (fA-range). Also it is an open question how well defined the potential energy threshold is.
Here we show that transmission of HCI through 1nm thick carbon nanomembranes (CNM) and subsequent determination of their charge state distribution and energy loss [4] allows us to measure the ion-induced nano-structure for-mation yield much more accurately. Since these insulating membranes are a surface-only mate-rial and HCI energy deposition is limited typi-cally to the surface of a solid we consider this as a model system for insulating surfaces.
Figure 1 shows the efficiency for pore for-mation by single HCI impact as function of the incident charge state. It is obvious that a thresh-old exists at about Q = 28, where the yield in-creases from 0 to about 70%. For even higher charge states the efficiency increases to about 100% for Q = 40. Thus, only for sufficiently highly charged ions the structure formation yield may be considered to be 100%.
  • Poster
    International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC), 22.-28.07.2015, Toledo, Spanien
  • Open Access LogoJournal of Physics: Conference Series 635(2015)3, 032011
    DOI: 10.1088/1742-6596/635/3/032011

Publ.-Id: 22774 - Permalink


Influence of irradiation on release of endothelial microparticles (EMP) in vitro
Neuber, C.; Pufe, J.; Pietzsch, J.;
Survivors of Hodgkin's disease as well as of breast and lung cancer are at risk of radiation-associated cardiovascular disease. Recent studies demonstrated a correlation between cardiovascular risk factors and circulating endothelial microparticles (EMP) and thereby suggest increased EMP levels in circulation to be an early biomarker of endothelial dysfunction and cardiovascular risk. This prompted us to analyze the amount of EMP released by human aortic endothelial cells (HAEC) after exposure to different doses of X-ray (0.4, 2, 4, 6, and 20 Gy) using antibodies against the endothelial cell markers CD31, CD144, and CD146 by flow cytometry. In this pilot experiment only CD146 proved appropriate for quantification of HAEC-derived EMP. Exposure of HAEC to different doses of X-ray did not significantly influence formation of CD146-positive EMP. However, low doses (0.4 Gy) tended to decrease EMP formation, whereas higher doses (2 or 4 Gy) slightly increased release of CD146-positive EMP. By contrast, inflammatory activation of HAEC by TPA significantly increased EMP release about 15-fold (P <  0.01). In conclusion, under the present experimental conditions EMP did not prove a suitable biomarker for radiation-induced endothelial dysfunction in vitro.
  • Clinical Hemorheology and Microcirculation 61(2015)2, 291-299
    DOI: 10.3233/CH-151987

Publ.-Id: 22773 - Permalink


Higher Cd adsorption on biogenic elemental selenium nanoparticles
Jain, R.; Dominic, D.; Jordan, N.; Rene, E. R.; Weiss, S.; van Hullebusch, E. D.; Hübner, R.; Lens, P. N. L.;
Cadmium (Cd) is a carcinogenic metal contaminating the environment and ending up in wastewaters. There is therefore a need for improved methods to remove Cd by adsorption. Biogenic elemental selenium nanoparticles have been shown to adsorb Zn, Cu and Hg, but these nanoparticles have not been tested for Cd removal. Here we studied the time-dependency and adsorption isotherm of Cd onto biogenic elemental selenium nanoparticles using batch adsorption experiments. We measured ζ-potential values to assess the stability of nanoparticles loaded with Cd. Results show that the maximum Cd adsorption capacity amounts to 176.8 mg of Cd adsorbed per g of biogenic elemental selenium nanoparticles. The ζ-potential of Cd-loaded nanoparticles became less negative from −32.7 to −11.7 mV when exposing nanoparticles to an initial Cd concentration of 92.7 mg L−1. This is the first study that demonstrates the high Cd uptake capacity of biogenic elemental selenium nanoparticles, of 176.8 mg g−1, when compared to that of traditional adsorbents such as carboxyl-functionalized activated carbon, of 13.5 mg g−1. An additional benefit is the easy solid–liquid separation by gravity settling due to coagulation of Cd-loaded biogenic elemental selenium nanoparticles.
Keywords: Cd, BioSeNPs, adsorption kinetics, adsorption isotherms, ζ-potential

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Publ.-Id: 22772 - Permalink


Kaon pair production in proton-nucleus collisions at 2.83 GeV kinetic energy
Kiselev, Y. T.; Hartmann, M.; Polyanskiy, A.; Paryev, E. Y.; Barsov, S.; Büscher, M.; Dymov, S.; Gebel, R.; Hejny, V.; Kacharava, A.; Keshelashvili, I.; Lorentz, B.; Maeda, Y.; Merzliakov, S.; Mikirtytchiants, S.; Ohm, H.; Serdyuk, V.; Sibirtsev, A.; Sinitsyna, V. Y.; Stein, H. J.; Ströher, H.; Trusov, S.; Valdau, Y.; Wilkin, C.; Wüstner, P.; Ye, Q. J.;
The production of non-φ K+K pairs by protons of 2.83 GeV kinetic energy on C, Cu, Ag, and Au targets has been investigated using the COSY-ANKE magnetic spectrometer. The K momentum dependence of the differential cross section has been measured for laboratory polar angles θK± < 12° over the 0.2–0.9 GeV/c range. The comparison of the data with detailed model calculations indicates an attractive K-nucleus potential of about −60 MeV at normal nuclear matter density at a mean momentum of 0.5 GeV/c. However, this approach has difficulty in reproducing the smallness of the observed cross sections at low K momenta.

Publ.-Id: 22771 - Permalink


Temperature relaxation in laser excited aluminium
Vorberger, J.;
Energy- and temperature relaxation processes after laser excitation of the electrons in solids and warm dense matter take place in virtually every high-energy density experiment and play an important role in a great number of industrial processes. In inertial fusion, they are essential for a successfull burn phase of the hydrogen pellet. Here, we report on new theoretical and experimental results concerning the energy transfer between electrons and phonons in solid aluminium on a femto to pico-second timescale. The results suggest that the two-temperature model is insufficient to describe the relaxation. We instead introduce a non-thermal lattice model. Within this model, electron-phonon couplings as derived from density functional theory and Bragg-peak decay rates as measured via electron diffraction are consistent with each other.
Keywords: warm dense matter, inertial fusion, energy relaxation, temperature relaxation, energy transfer rate, electron-phonon coupling, two-temperature model
  • Invited lecture (Conferences)
    Seminar der Arbeitsgruppen Quantentheorie und Vielteilchensysteme, Statistische Physik, Molekulare Quantendynamik, Theoretische Clusterphysik und Nanophotonik, 01.12.2015, Rostock, Deutschland

Publ.-Id: 22770 - Permalink


Determination of long-lived cosmogenic radionuclides by accelerator mass spectrometry
Merchel, S.; Khojasteh Mohammadi, N. B.; Pavetich, S.; Rugel, G.; Scharf, A.; DREAMS-Users; DREAMS-Friends;
Applications: Long-lived radionuclides with half-lives of 0.1-16 Ma have nowadays thousands of exciting applications, especially within environmental and geosciences. In nature, the so-called cosmogenic nuclides (CNs) are products of nuclear reactions induced by primary and secondary cosmic rays. Hence, they can be found in extraterrestrial material such as meteorites - originating from the asteroid belt, the Moon or Mars - and lunar samples in higher concentrations (e.g. ~1010 10 Be atoms/g or < 0.5 mBq/g). A combination of several CNs is used to reconstruct the exposure history of this unique material while in space (irradiation age) and on Earth (terrestrial age).
Though, in terrestrial material the concentrations are typically only on the order of 104 - 109 atoms/g (i.e. μBq/g - nBq/g) for 10Be produced in the Earth’s atmosphere, then transported to the surface and further absorbed and incorporated at and in, e.g. sediments or ice. Some of the lowest 10Be concentrations (~103 atoms/g), produced in-situ by neutron- and muon-induced nuclear reactions from e.g. O and Si in quartz, can be found in samples taken from the Earth’s surface. The concentrations of atmospheric or in-situ produced CNs record information to reconstruct sudden geomorphological events such as volcanic eruptions, rock avalanches, tsunamis, meteor impacts, earthquakes and glacier movements. Additionally, glacier movements and data from ice cores give hints for the reconstruction of historic climate changes and providing information for the validation of climate model predicting future changes. Slower processes such as sedimentation, river incision and erosion rates can also be investigated and last but not least, indirect dating of bones as old as several Ma’s is possible.
Anthropogenic production by release from nuclear reprocessing, accidents and weapon tests led to increased levels of CNs in surface water and soil (129I,…), ice (36Cl,…) and material from nuclear installations themselves (41Ca,…). Some of the CNs can, thus, be used as tracers to follow pathways in oceanography, to date and identify sources of groundwater, to perform retrospective dosimetry and to study aspects in radioecology and pharmacology.
Method: The analytical method of choice for CN determination is accelerator mass spectrometry (AMS). After simple radiochemical separation, AMS reduces enormously background and interfering signals resulting from molecular ions and isobars. Thus, AMS provides much lower detection limits compared to conventional MS or decay counting. The DREAMS (DREsden AMS) system at HZDR offers excellent measurement capabilities (Akhmadaliev et al., NIMB 294 (2013) 5) also for external users (see www.hzdr.de/ibc).
Keywords: Accelerator mass spectrometry, cosmogenic nuclides, AMS
  • Invited lecture (Conferences)
    International Conference on Radioanalytical and Nuclear Chemistry (RANC-2016), 10.-15.04.2016, Budapest, Hungary

Publ.-Id: 22768 - Permalink


Understanding Cu mobilisation from copper shale leaching: [64Cu]CuS: Ligand identification, kinetic rates and modelling
Barthen, R.; Gründig, M.; Karimzadeh, L.; Schössler, C.; Mansel, A.; Grenzer, J.; Schymura, S.; Kulenkampff, J.; Franke, K.; Lippold, H.; Lippmann-Pipke, J.;
Es ist kein Abstract vorhanden.
  • Poster
    General Meeting 4, Ecometals, 01.-02.12.2015, Pau, Frankreich

Publ.-Id: 22767 - Permalink


Sorption of environmentally relevant radionuclides (U(VI), Np(V)) and lanthanides (Nd(III)) on feldspar and mica
Richter, C.;
Presentation of the sorption of environmentally relevant radionuclides (UO22+, NpO2+) and lanthanides (Nd3+) on feldspar and mica
  • Lecture (Conference)
    Kompetenzzentrum Ost für Kerntechnik (KOMPOST) 10.Doktorandenseminar, 08.12.2015, Dresden, Deutschland

Publ.-Id: 22766 - Permalink


Sorption of environmentally relevant radionuclides (UO22+, NpO2+) and lanthanides (Nd3+) on feldspar and mica
Richter, C.;
Presentation of the results of the study about Sorption of environmentally relevant radionuclides (UO22+, NpO2+) and lanthanides (Nd3+) on feldspar and mica.
  • Lecture (others)
    Abteilungsseminar der Abteilung Hydrogeochemie und Hydrogeologie, Institut für Geowissenschaften, Universität Heidelberg, 03.12.2015, Heidelberg, Deutschland

Publ.-Id: 22765 - Permalink


Positron spectroscopy of point defects in the skyrmion-lattice compound MnSi
Reiner, M.; Bauer, A.; Leitner, M.; Gigl, T.; Anwand, W.; Butterling, M.; Wagner, A.; Kudejova, P.; Pfleiderer, C.; Hugenschmidt, C.;
Outstanding crystalline perfection is a key requirement for the formation of new forms of electronic order in a vast number of widely different materials. Whereas excellent sample quality represents a standard claim in the literature, there are, quite generally, no reliable microscopic probes to establish the nature and concentration of lattice defects such as voids, dislocations and different species of point defects on the level relevant to the length and energy scales inherent to these new forms of order. Here we report an experimental study of the archetypical skyrmion-lattice compound MnSi, where we relate the characteristic types of point defects and their concentration to the magnetic properties by combining different types of positron spectroscopy with ab-initio calculations and bulk measurements. We find that Mn antisite disorder broadens the magnetic phase transitions and lowers their critical temperatures, whereas the skyrmion lattice phase forms for all samples studied underlining the robustness of this topologically non-trivial state. Taken together, this demonstrates the unprecedented sensitivity of positron spectroscopy in studies of new forms of electronic order.
Keywords: positron annihilation spectroscopy point defects MnSi magnetism skyrmion lattice

Publ.-Id: 22764 - Permalink


Shaping and compositional modification of zinc oxide nanowires under energetic manganese ion irradiation
Möller, W.; Johannes, A.; Ronning, C.;
The development of the surface contour and the local elemental composition of ZnO nanowires of 150 to 200 nm diameter under 170 keV Mn irradiation is addressed both experimentally and by means of three-dimensional dynamic Monte Carlo computer simulation using the binary collision approximation. A random rotation of the incident beam around the nanowire axis mimics the experimental irradiation under sample rotation. The simulation results demonstrate a complex interplay of sputter erosion, implant incorporation and resputtering, as well as atomic mixing, which is discussed in detail. The sputter-induced thinning of the wire is in good quantitative agreement with experimental results obtained from pre- and post-irradiation scanning electron microscopy. The experiments also confirm the predicted sharpening of the top and neck formation at the bottom interface. Due to the latter, the wire detaches from the substrate at high ion fluence. Good agreement with experimental results from nano-X-ray fluorescence is also obtained for the continuously increasing Mn/Zn ratio as function of ion fluence. The simulation yields manifold additional information which has not been accessible to the experiments, such as fractional sputtering data and three-dimensional elemental composition profiles at increasing ion fluence. From these, preferential sputtering of O vs. Zn is deduced. A significant contamination of the wires with substrate material arises from ion mixing at the wire/substrate interface rather than from redeposition of sputtered substrate atoms. Surprising hollow profiles are observed. Their formation is attributed to a special mechanism of collisional transport which is characteristic for the irradiation of nanowires at a suitable combination of wire diameter and ion energy.
Keywords: nanowire, ion irradiation, high-fluence doping, sputtering, zinc oxide, computer simulation

Publ.-Id: 22763 - Permalink


Interaction of technetium with neptunium in acidic media
Chotkowski, M.; Weiss, S.; Scheinost, A. C.;
Spent nuclear fuel
Chemical properties of Tc and Np
Spectroelectrochemistry of Tc
Electrochemistry of Tc and Np in acidic media
Liquid-liquid extraction of Tc in the presence of Np
EXAFS analyses
Keywords: Spent nuclear fuel Chemical properties of Tc and Np Spectroelectrochemistry of Tc Electrochemistry of Tc and Np in acidic media Liquid-liquid extraction of Tc in the presence of Np EXAFS analyses
  • Lecture (Conference)
    3rd Academic Symposium on Nuclear Fuel Cycle, 02.-05.12.2015, Tokyo, Japan

Publ.-Id: 22762 - Permalink


Inductive detection of gas bubbles in a liquid metal flow
Gundrum, T.; Büttner, P.; Dekdouk, B.; Peyton, A.; Wondrak, T.; Galindo, V.; Eckert, S.;
The detection of bubbles in liquid metals flow is important for many technical applications. The opaqueness and the high temperature of liquid metals set high demands on the measurement system. The electrical conductivity of the liquid metal is relatively high, which can be exploited with contactless methods based on electromagnetic induction. We will present a measurement system which consists of one transmitting coil and a planar gradiometric coil on opposite sides of the pipe. With this sensor we were able to detect bubbles in a Sodium flow inside a stainless steel pipe.
Keywords: inductive contactless measurement; two phase flow; liquid metal; bubble detection; void fraction
  • Poster
    IEEE Sensors 2015, 01.-04.11.2015, Busan, Süd Korea
  • Contribution to proceedings
    IEEE Sensors 2015, 01.-04.11.2015, Busan, Süd Korea
    2015 IEEE SENSORS Proceedings: IEEE, 10.978-1-4799-8202-8, 1001-1002

Publ.-Id: 22761 - Permalink


The reactor Dynamics code DYN3D – models, Validation and applications
Rohde, U.; Kliem, S.; Grundmann, U.; Baier, S.; Bilodid, Y.; Duerigen, S.; Fridman, E.; Gommlich, A.; Holt, L.; Grahn, A.; Kozmenkov, Y.; Mittag, S.;
The article provides an overview on the reactor dynamics code DYN3D. The code comprises various 3D neutron kinetics solvers, a thermal-hydraulics reactor core model and a thermo-mechanical fuel rod model. The implemented models and methods and the capabilities and features of the code are described. Latest developments of models and methods are delineated. An overview on the status of verification and validation is given. Code applications for selected safety analyses are described. Furthermore, multi-physics code couplings to thermal-hydraulic system codes, CFD and sub-channel codes as well as to the fuel performance code TRANSURANUS are outlined. Developments for innovative reactor concepts, in particular Molten Salt Reactor, High Temperature Gas-cooled Reactor and Sodium Fast Reactor are delineated. The management of code maintenance is briefly described.
Keywords: Reactor dynamics, neutron kinetics, thermal-hydraulics model, fuel rod model, code coupling, verification and validation, transient analysis, innovative reactors, code maintenance

Publ.-Id: 22760 - Permalink


68Ga-DATATOC: synthesis, radiolabeling, and first in vivo studies
Waldron, B.; Seemann, J.; Bergmann, R.; Nagel, J.; Rösch, F.; Sinnes, J. P.;
Objectives: 68Ga-DOTATOC is currently used as the industry standard for diagnostic imaging of NETs and its metastases. Radiolabeling can be performed manually and automated at 95°C. In order to approach the application of 68Ga following a kit-type procedure, a DATA-based chelator (6-amino-1,4-diazepine-triacetate) was used in the study as it has shown to radiolabel under very mild conditions. Conjugation with TOC to afford a DOTATOC analog may enable radiolabeling of the peptide at room temperature.
Methods: DATATOC was synthesized in a seven-step synthesis. Radiolabeling with 68Ga was performed manually at room temperature, and stability was assessed in human serum. An automated setup was also examined, using the Modular-Lab eazy (Eckert & Ziegler, Berlin, Germany). First in vivo studies using MPC-mCherry tumor–bearing mice were performed and compared with DOTATATE.
Research: Radiolabeling was performed at room temperature using N2 solution, NaOAc buffer, and 14 nmol DATATOC. An RCY of 96.3% ± 1.2% was obtained within 3 min. Stability was tested in human serum over a period of 2 h (Δ, 1.3%). Automated labeling with a 23 nmol precursor achieved quantitative complexation of 68Ga. In vivo PET/CT studies with 68Ga-DATATOC indicate a high specific uptake in the tumor region after 10 min (SUV of 3.73 ± 1.49). In a blocking study with OC, the SUV in the tumor was reduced to 0.45 ± 0.15. In addition, 68Ga-DATATOC showed high stability in mouse plasma with 93.7% of the tracer remaining intact after 120 min. Compared with 68Ga-DOTATATE a faster renal excretion of the tracer was observed.
Conclusion: DATATOC can be labeled with 68Ga in a manual or automated setup rapidly at room temperature, offering significant advantages over similar DOTA-based derivatives. Furthermore, first in vivo studies confirm excellent targeting and excretion characteristics for the novel tracer. With the perspective toward a kit-type formulation, the superior characteristics of this new compound pave the way for a new generation of 68Ga radiopharmaceuticals.
  • Abstract in refereed journal
    Journal of Nuclear Medicine 56(2015)2, 27
    DOI: 10.2967/jnm565abs
  • Lecture (Conference)
    3rd Theranostics World Congress (3TWC) on Gallium-68 and PRRT, 12.-14.03.2015, Baltimore, USA

Publ.-Id: 22759 - Permalink


[Ga-68]Ga-DATATOC imaging, biodistribution and kinetics in a pheochromocytoma model
Bergmann, R.; Ullrich, M.; Ziegler, C.; Waldron, B.; Seemann, J.; Nagel, J.; Roesch, F.; Eisenhofer, G.; Steinbach, J.; Pietzsch, J.;
Objectives The novel DATA (6-Amino-1,4-diazepine-triacetate) based octreotide derivative TOC allows radiolabeling at room temperature in contrast to DOTATOC that needs 95°C for effective labeling. The main goal of this study was to evaluate the potential of [68Ga]Ga-DATATOC for SSTR2 imaging in a syngeneic mouse pheochromocytoma (Pheo) model.

Methods Radiolabeling of the DATATOC with 68Ga was performed manually at room temperature. The in vivo studies (PET, metabolic stability, biodistribution and elimination) were carried out in Pheo (MPC-mCherry) bearing mice and Wistar rats. For comparison the pheo were also imaged with [68Ga]Ga-DOTATOC and [68Ga]Ga-DOTATATE. Blocking studies in vivo were performed with octreotide (OC).

Results The radiotracer showed high in vivo stability. A faster renal elimination of the radiotracer was observed in comparison to DOTATOC and DOTATATE. [68Ga]Ga-DATATOC showed fast, highly specific uptake in the pheo and the pancreas (SUV at 1 h p.i., tumor 3.7 ± 1.5, pancreas 0.57 ± 0.17), whereas blocking with OC (3.3 mg/kg body weight) reduced the uptake in the tumor to 0.45 ± 0.15 and Patlak analysis showed that both parameters - the influx rate and the distribution volume - were significantly decreased by OC.

Conclusions [68Ga]Ga-DATATOC can be radiolabeled with 68Ga rapidly at room temperature with high radiochemical yields. The preclinical in vivo studies confirm the high stability, excellent specific targeting and fast elimination. This pharmacological profile and the perspective towards a kit-type formulation provide a great potential for diagnostic somatostatin receptor imaging.

Research Support This work was supported by The Deutsche Forschungsgemeinschaft (Grants ZI-1362/2-1 [to C.G.Z. and G.E.] and BE-2607/1-1 [to R.B. and J.P.]).
  • Abstract in refereed journal
    Journal of Nuclear Medicine 56(2015), 1129
  • Poster
    SNMMI 2015 Annual Meeting, 06.-10.06.2015, Baltimore, USA

Publ.-Id: 22758 - Permalink


Data processing performance analysis for ultrafast electron beam X-ray CT using parallel processing hardware architectures
Bieberle, A.; Frust, T.; Wagner, M.; Bieberle, M.; Hampel, U.;
The ultrafast electron beam X-ray computed tomography measuring system (Fischer et al., 2008) of the Helmholtz-Zentrum Dresden - Rossendorf (HZDR) is primarily operated for fundamental multiphase flow investigations, e.g. in various technical devices, and for validation of enhanced flow simulation models, e.g. developed for computational fluid dynamic codes (CFD). The ultrafast computed tomography (CT) scanner delivers cross-sectional material distributions by contactless measurement with a spatial resolution of approximately 1 mm and a temporal resolution of maximal 8 kHz. Currently, two central time-consuming processes have been identified limiting the efficient usage of that worldwide unique CT technique: a) the data transfer from the detector system to central data storages (e.g. computer or data base) and b) the data processing. Thus, data processing and data reconstruction has been adapted for the use at multi-core central processing units (CPUs) and many-core graphics processing units (GPUs). For optimal performance an advanced performance PC (AP-PC) with two parallel operated high performance graphics processing units (Tesla K20c, NVIDIA®), a six-core Intel® processor (Xeon E5-1650 v3,), a high internal data bus speed and a large memory block (DDR4, 2133 MHz, 128 GByte) was assembled. Finally, the modified combined multi-core CPU and many-core GPU optimized algorithms generate a performance improvement of app. 137 for the entire data processing sequence compared to the established single core CPU based data processing tool.
Keywords: computed tomography, many-core graphics processing units, multi-core central processing units, massive parallel data processing

Publ.-Id: 22757 - Permalink


Off-target FDG-PET parameters have prognostic value in head and neck squamous cell carcinomas undergoing primary radiochemotherapy and can be used to generate radiobiological hypotheses
Zschaeck, S.; Loeck, S.; Leger, S.; Richter, C.; Zoephel, K.; Kotzerke, J.; Steinbach, J.; Zips, D.; Krause, M.; Baumann, M.;
kein Abstract verfügbar
  • Abstract in refereed journal
    European Journal of Cancer 51(2015), S570
    DOI: 10.1016/S0959-8049(15)30053-8
  • Poster
    European Cancer Congress 2015, 25.-29.09.2015, Wien, Österreich

Publ.-Id: 22756 - Permalink


Stand der Technik experimenteller Untersuchungen dichter Blasenströmungen
Kipping, R.; Kryk, H.; Hampel, U.;
In der chemischen und biochemischen Industrie werden oftmals Blasensäulenreaktoren für Mehrphasenprozesse eingesetzt. Sie zeichnen sich durch ihren einfachen Aufbau, sowie gute Stoff-und Wärmeübertragungseigenschaften aus. In der Literatur sind umfangreiche Studien zur Auslegung und Dimensionierung solcher Reaktoren zu finden. Zur weiteren Prozessoptimierung ist zunehmend die Aufklärung der lokalen Mechanismen innerhalb des Reaktors, insbesondere die Interaktion von Hydrodynamik, Stofftransport und chemischer Reaktion, erforderlich. Die ortsaufgelöste Untersuchung von Hydrodynamik und Stofftransport in Blasenströmungen erfolgt bisher vornehmlich mit Hilfe optischer Verfahren, wie z.B. der Particle Image Velocimetry (PIV), Laser Doppler Anemometrie (LDA) und laserinduzierter Fluoreszenz (LIF). Während diese Messtechniken für die Untersuchung von Blasenströmungen geringen Gasgehaltes gut geeignet sind, stoßen sie bei hohen Gasgehalten an ihre Grenzen. Ziel dieses Beitrages ist es, eine Übersicht über den aktuellen Stand der Technik in Hinblick auf experimentelle Studien zur Hydrodynamik und gekoppelter Vorgänge, wie Stofftransport und Reaktion in Blasensäulenreaktoren zu geben. Dabei sollen die Notwendigkeit künftiger Studien in diesem Bereich und damit einhergehend die Anforderungen an die Messtechnik aufgezeigt werden.
Keywords: Blasensäulen, Hydrodynamik, Stofftransport, Mehrphasenströmung
  • Lecture (Conference)
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Mehrphasenströmungen, 19.-20.03.2015, Lüneburg, Deutschland

Publ.-Id: 22755 - Permalink


Bestimmung der zerebrovaskulären Reserve mit BOLD-MRT unter Atemanhalten bei Patienten mit Stenosen der hirnversorgenden Gefäße
Krukowski, P.; Petr, J.; Puetz, V.; Abramyuk, A.; Linn, J.; Gerber, J.;
Die Autoregulation der zerebralen Perfusion ist wichtiger Mechanismus der Homöostase. Hyperkapnie führt im gesunden Gefäßbett zur Dilatation präkapillärer Gefäße und zur Aktivierung der zerebralen Perfusionsreserve (CVR). BOLD (Blood Oxygen Level Dependent)-MRT unter Atemanhalten stellt die Veränderungen dar. Bei Patienten mit Stenosen hirnversorgender Arterien akquirierten wir prospektiv ein BOLD-MRT unter Atemanhalten, evaluierten die Machbarkeit und korrelierten die Zielstenose mit den BOLD-Veränderungen.
  • Poster
    50. Jahrestagung der Deutschen Gesellschaft für Neuroradiologie e.V., 15.-17.10.2015, Gürzenich, Köln, D

Publ.-Id: 22754 - Permalink


Algorithms for flow pattern identification based on Wire-Mesh Sensor data
Kipping, R.; Brito, R.; Schleicher, E.; Hampel, U.;
Within the development of an industrial type of Wire-Mesh Sensor (WMS) algorithms for flow pattern identification were developed. Based on the statistical evaluation of gas holdup distribution, the distinction of the main flow patterns in gas-liquid flow is carried out. Experimental validation of the algorithm was carried using experimental flow loop from The University of Tulsa Horizontal Well and Artificial Lift Project (TUHWALP).
Keywords: Wire-Mesh Sensor, two-phase flow, flow pattern recognition, vertical pipe flow, horizontal pipe flow
  • Lecture (Conference)
    7th International Symposium on Process Tomography (ISPT7), 01.-03.09.2015, Dresden, Deutschland

Publ.-Id: 22753 - Permalink


Simulation of turbulent bubbly flow in pipes of different diameter
Kriebitzsch, S.; Rzehak, R.;
Many technical processes in industries such as chemical or electricity but also numerous natural phenomena involve multiphase flow. Due to the complex physics and the broad range of relevant length scales involved, it is a formidable task to achieve a better understanding of such flows. A detailed insight into the local flow field can be obtained from multiphase computational fluid dynamics, which therefore is a potentially valuable tool for the optimisation of existing and the design of new technical equipment. Such simulations are feasible within the Eulerian two-fluid framework of interpenetrating continua. Within this framework the interfacial transfer processes need to be modelled by suitable closure relations, many of which have been proposed in the literature. Predictions with multiphase CFD are only possible if a fixed set of closures is available that has been validated for a wide range of flow conditions and can therefore reliably be used also for unknown flow problems. As a safe starting point a baseline model applicable for adiabatic bubbly flows has recently been defined by Rzehak and Krepper (2013).
In this work we compare simulation results obtained using the baseline model with three different sets of experimental data for dispersed gas-liquid pipe flow given by Liu (1998), Shawkat et al. (2008), and Hosokawa and Tomiyama (2009). Air and water under similar flow conditions have been used in the different experiments, so that the main difference between the experiments is the variation of the pipe diameter from 25 mm to 200 mm. Overall all three experimental data sets are reasonably well reproduced by the simulation results, in particular in the bulk of the flow. The need for improved modelling of multiphase turbulence as well as wall effects manifests itself through larger differences with the experimental data in the near-wall region of the pipes.
Keywords: Euler-Euler, bubbly flow, CFD, two-fluid model
  • Lecture (Conference)
    Jahrestreffen der ProcessNet Fachgruppen Computational Fluid Dynamics und Mehrphasenströmungen, 19.-20.03.2015, Lüneburg, Deutschland

Publ.-Id: 22752 - Permalink


Synthesis and evaluation of 18F-labeled indole-based analogs as highly selective sigma-2 receptor probes
Wang, L.; Ye, J.; Deuther-Conrad, W.; He, Y.; Zhang, J.; Steinbach, J.; Brust, P.; Jia, H.;
Objectives: The sigma-2 (σ2) receptors are overexpressed in a wide variety of human and rodent tumor cells and play a pivotal role in cancer biology. Moreover, they showed an approximately 10-fold higher expression in proliferating tumor cells compared to that in quiescent tumor cells. And thus, they proved to be a unique receptor-based biomarker of cell proliferation in solid tumors. Herein we report the synthesis and evaluate of a series of indole-based analogs with 5,6-dimethoxyisoindoline or 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline moiety as highly selective σ2 receptor ligands.

Results and discussion: The newly synthesized indole-based analogs showed low nanomolar affinity for σ2 receptors (Ki2) = 1.79-5.23 nM ) and excellent subtype selectivity (Ki1)/Ki2) = 56-708 folds). The carbon chain length of the linker between the indole group and 5,6-dimethoxyisoindoline or 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline moiety displayed significant influence on the subtype selectivity. The compounds with a butyl linker exhibited highest subtype selectivity. We synthesized 2-(4-(4-(2-[18F]fluoroethoxy)-1H-indol-1-yl)butyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline and 1-(4-(5,6-dimethoxyisoindolin-2-yl)butyl)-4-(2-[18F]fluoroethoxy)-1H-indole. The log D values of the above radioligands are 2.17 ± 0.13 and 2.14 ± 0.02, respectively. The in vivo biological evaluations are in progress.

Conclusions: These findings suggest that 18F-labeled indole-based ligands warrant further evaluation as potential PET radiotracers for σ2 receptor imaging.

Acknowledgements: Supported by NSFC (21471019).

References:
[1] van Waarde A, et al. Curr Pharm Des, 2010, 16, 3519-3537.
[2] Megalizzi V, et al. Med Res Rev, 2012, 32, 410-427.
[3] Mach RH, et al. J Med Chem, 2013, 56, 7137-7160.
Keywords: F-18, sigma-2 receptors, indole-based analogs
  • Invited lecture (Conferences)
    RANC-2016 - International Conference on Radioanalytical and Nuclear Chemistry, 10.-15.04.2016, Budapest, Ungarn
  • Contribution to proceedings
    RANC-2016 - International Conference on Radioanalytical and Nuclear Chemistry, 10.-15.04.2016, Budapest, Ungarn
    Book of Abstracts, Budabest: Akadémiai Kiadó, 35

Publ.-Id: 22751 - Permalink


Exploring ice core drilling chips from a cold Alpine glacier for cosmogenic radionuclide (10Be) analysis
Zipf, L.; Merchel, S.; Bohleber, P.; Rugel, G.; Scharf, A.;
Ice cores offer unique multi-proxy paleoclimate records, but provide only very limited sample material, which has to be carefully distributed for various proxy analyses. Beryllium-10, for example, is analysed in polar ice cores to investigate past changes of the geomagnetic field, solar activity, and the aerosol cycle, as well as to more accurately date the material. This paper explores the suitability of a drilling by-product, the so-called drilling chips, for 10Be-analysis. An ice core recently drilled at a cold Alpine glacier is used to directly compare 10Be-data from ice core samples with corresponding drilling chips. Both sample types have been spiked with 9Be-carrier and identically treated to chemically isolate beryllium. The resulting BeO has been investigated by accelerator mass spectrometry (AMS) for 10Be/9Be-ratios to calculate 10Be-concentrations in the ice. As a promising first result, four out of five sample-combinations (ice core and drilling chips) agree within 2-sigma uncertainty range. However, further studies are needed in order to fully demonstrate the potential of drilling chips for 10Be-analysis in alpine and shallow polar ice cores.
Keywords: 10Be, cosmogenic nuclide, accelerator mass spectrometry, ice core analysis

Publ.-Id: 22750 - Permalink


Felsenkeller shallow-underground accelerator laboratory for nuclear astrophysics (CGS conf.proc.)
Bemmerer, D.; Cowan, T. E.; Gohl, S.; Ilgner, C.; Junghans, A. R.; Reinhardt, T. P.; Rimarzig, B.; Reinicke, S.; Röder, M.; Schmidt, K.; Schwengner, R.; Stöckel, K.; Szücs, T.; Takács, M.; Wagner, A.; Wagner, L.; Zuber, K.;
Favored by the low background in underground laboratories, low-background accelerator-based experiments are an important tool to study nuclear reactions involving stable charged particles. This technique has been used for many years with great success at the 0.4 MV LUNA accelerator in the Gran Sasso laboratory in Italy, proteced from cosmic rays by 1400 m of rock. However, the nuclear reactions of helium and carbon burning and the neutron source reactions for the astrophysical s-process require higher beam energies than those available at LUNA. Also the study of solar fusion reactions necessitates new data at higher energies. As a result, in the present NuPECC long range plan for nuclear physics in Europe, the installation of one or more higher-energy underground accelerators is strongly recommended.
An intercomparison exercise has been carried out using the same HPGe detector in a typical nuclear astrophysics setup at several sites, including the Dresden Felsenkeller underground laboratory. It was found that its rock overburden of 45m rock, together with an active veto against the remaining muon flux, reduces the background to a level that is similar to the deep underground scenario.
Based on this finding, a used 5 MV pelletron tandem with 250 μA upcharge current and external sputter ion source has been obtained and transported to Dresden. Work on an additional radio-frequency ion source on the high voltage terminal is underway. The project is now fully funded. The installation of the accelerator in the Felsenkeller is expected for the near future. The status of the project and the planned access possibilities for external users will be reported.
Keywords: Nuclear Astrophysics Underground laboratory Hydrogen burning Solar fusion Helium burning Carbon burning
  • Open Access LogoContribution to proceedings
    Fifteenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, 25.-29.08.2014, Dresden, Germany
    EPJ Web of Conferences: EDP Sciences, 03010
    DOI: 10.1051/epjconf/20159303010

Publ.-Id: 22749 - Permalink


Origin and geochemistry of agates in Permian volcanic rocks of the Sub-Erzgebirge basin, Saxony (Germany)
Götze, J.; Möckel, R.; Vennemann, T.; Müller, A.;
Mineralogical and geochemical investigations of agates from Permian volcanic rocks of the Sub-Erzgebirge basin (Saxony, Germany) were made to constrain the genesis and characteristics of these spectacular forms of silica. Samples from the main agate occurrences of Chemnitz, Hohenstein-Ernstthal, St. Egidien and Zwickau were selected for detailed analyses.
The results of the study show that agate formation can be related to volcanic activity (Rochlitz ignimbrite) and the subsequent alteration of the volcanic rocks. Most agates originate from the infill of silica into cavities of lithophysae (high-temperature crystallization domains), which formed during cooling of welded ignimbrite. Agate formation temperatures of probably >150°C were calculated from fluid inclusion and oxygen isotope studies, which indicate that the mobilization and accumulation of silica started already during a late phase of or soon after the volcanic activity.
The trace-element composition of chalcedony and macro-crystalline quartz in agates is dif-ferent from that of quartz from magmatic or metamorphic rocks and pegmatites. Elements of the volcanic rock matrix (Al, Ca, Fe, Na, K) were released during the alteration processes and accumulated in the SiO2 matrix of the agates. Extraordinary high contents of Ge (>90 ppm), B (46 ppm) and U (>18 ppm) were also detected, which can exceed the Clark concentration and sometimes the element concentration in the surrounding host rocks. In addition, chondrite-normalized REE distribution patterns of the agates show strong negative Eu-anomalies, enriched HREE as well as tetrad effects. These patterns are different from the REE patterns of the volcanic host rocks and point to fractionation processes during agate formation. The specific geochemical features indicate interactions of the host rocks with heated meteoric water and volatile fluids, and transport of SiO2 and other elements both in aqueous solution and via stable fluorine (and chlorine) compounds such as SiF4, BF3, GeF4, and UO2F2.
The results of cathodoluminescence (CL) microscopy and spectroscopy revealed a microstructure of the agates that is similar for all occurrences. Characteristic features are irregular internal textures and sector zoning in quartz as well as luminescence colours and spectra, respectively, which are caused by a typical high defect density (oxygen vacancies, silanol groups). According to these results, the formation of agates can be explained by crystallization via an amorphous silica precursor under non-equilibrium conditions.
Keywords: Agate, Quartz, Permian volcanics, Saxony, Trace elements, Oxygen isotopes, Cathodoluminescence

Publ.-Id: 22748 - Permalink


Emergence of comparable covalency in isostructural cerium(IV)- and uranium(IV)-carbon multiple bonds
Gregson, M.; Lu, E.; Tuna, F.; Mcinnes, E. J. L.; Hennig, C.; Scheinost, A. C.; Mcmaster, J.; Lewis, W.; Blake, A. J.; Kerridge, A.; Liddle, S. T.;
The chemical bonding of actinide and transition metal cations is known to exhibit variable levels of covalency, whereas that of the lanthanides is characterised as overwhelmingly ionic like alkali and alkaline earth metals. Here, we report a structural, spectroscopic, magnetic, and computational study of the iso-structural carbene complexes [M(BIPMTMS)(ODipp)2] [M = Ce (1), U (2), Th (3); BIPMTMS = C(PPh2NSiMe3)2; Dipp = C6H3-2,6-Pri 2]. In order to avoid the deficiencies of orbitalbased theoretical treatments we probed the bonding of 1-3 with a RASSCF density-based approach that explicitly treats the orbital energy near-degeneracy and overlap contributions to covalency. For these complexes unexpected similar levels of covalency are found for cerium(IV) and uranium(IV), whereas thorium(IV) is found to be more ionic. This trend is found in all computational methods employed and is reproduced in experimental covalency-driven exchange reactions of 1-3 with MCl4 salts (M = Ce, U, Th).
Keywords: cerium bonding covalency XANES

Publ.-Id: 22747 - Permalink


Spatial distribution of FMISO in head and neck squamous cell carcinomas during radio-chemotherapy and its correlation to pattern of failure
Zschaeck, S.; Haase, R.; Abolmaali, N.; Perrin, R.; Stützer, K.; Appold, S.; Steinbach, J.; Kotzerke, J.; Zips, D.; Richter, C.; Gudziol, V.; Krause, M.; Zöphel, K.; Baumann, M.;
Background. Tumour hypoxia can be measured by FMISO-PET and negatively impacts local tumour control in patients with head and neck squamous cell carcinoma (HNSCC) undergoing radiotherapy. The aim of this post hoc analysis of a prospective clinical trial was to investigate the spatial variability of FMISO hypoxic subvolumes during radio-chemotherapy and the co-localisation of these volumes with later recurrences as a basis for individualised dose prescription trials with dose escalation defined by FMISO-PET. Methods. Sequential FMISO scans of 12 (of 25) patients presenting residual hypoxia taken before (FMISOpre) and during (FMISOw1–FMISOw5) radio-chemotherapy were analysed regarding the stability of the FMISO subvolumes and, in case of local failure, their correlation to local relapse. Results. Consecutive FMISO-PET positive volumes could be classified as moderately stable with Dice conformity indices of 62% and 58% up to the second week of treatment. Substantial volumetric variation during treatment was observed, with more than 20% geographic miss in all patients and more than 40% in half of the patients. The localisation of the maximum standardised uptake value (SUVmax) differed with a mean distance of 7.0 mm and 13.5 mm between the pre-therapeutic and first or second FMISO-PET during treatment. A stable hypoxic consensual volume (i.e. overlap of pre-therapeutic FMISO and intra-treatment FMISO subvolumes up to week two, generated by different contouring methods) was determined for six patients with imaging information of local recurrence. Three of these six local recurrences were located within this consensual volume. Conclusions. Our data suggest that selective dose painting to hypoxic tumour subvolumes requires adaptation during treatment and sufficient margins. An alternative strategy is to escalate the dose to the gross tumour volume, accepting lesser escalation of dose outside hypoxic areas if indicated by constraints for organs at risk.

Publ.-Id: 22746 - Permalink


Multilayered Magnetic Gelatin Membrane Scaffolds
Samal, S. K.; Goranov, V.; Dash, M.; Russo, A.; Shelyakova, T.; Graziosi, P.; Lungaro, L.; Riminucci, A.; Uhlarz, M.; Banobre-Lopez, M.; Rivas, J.; Herrmannsdörfer, T.; Rajadas, J.; de Smedt, S.; Braeckmans, K.; Kaplan, D. L.; Dediu, V. A.;
A versatile approach for the design and fabrication of multilayer magnetic scaffolds with tunable magnetic gradients is described. Multilayer magnetic gelatin membrane scaffolds with intrinsic magnetic gradients were designed to encapsulate magnetized bioagents under an externally applied magnetic field for use in magnetic-field-assisted tissue engineering. The temperature of the individual membranes increased up to 43.7 °C under an applied oscillating magnetic field for 70 s by magnetic hyperthermia, enabling the possibility of inducing a thermal gradient inside the final 3D multilayer magnetic scaffolds. On the basis of finite element method simulations, magnetic gelatin membranes with different concentrations of magnetic nanoparticles were assembled into 3D multilayered scaffolds. A magnetic-gradient-controlled distribution of magnetically labeled stem cells was demonstrated in vitro. This magnetic biomaterial-magnetic cell strategy can be expanded to a number of different magnetic biomaterials for various tissue engineering applications.

Publ.-Id: 22745 - Permalink


Nanopatterned Polymer Brushes by Reactive Writing
Nawroth, J. F.; Neisser, C.; Erbe, A.; Jordan, R.;
Nanopatterned polymer brushes were prepared selectively by self-initiated photografting and photopolymerization (SIPGP) on carbonaceous deposits created by electron beam induced damage of self-assembled monolayers (SAMs) of 1H,1H,2H,2H-perfluorooctyltriethoxysilane SAM (PF-SAM) on silicon oxide. This patterning approach is referred to as reactive writing (RW). With the monomer, N,N-dimethylaminoethyl methacrylate (DMAEMA), we demonstrate the straightforward formation of polymer brush gradients and single polymer lines of sub-100 nm lateral dimensions because of the high reactivity contrast to the nonirradiated PF-SAM background. The lithography parameters acceleration voltage, irradiation dose, beam current and dwell time were systematically varied to optimize conditions for the conversion of the SAM into carbonaceous deposit and overall resolution of the e-beam based patterning. The results of RW were compared to patterns prepared by carbon templating (CT) under analogue conditions revealing a dwell time dependency, which differs from previous reports. This new RW technique adds new aspects to e-beam lithography techniques as not only the chemistry of the created polymer patterns can be varied but also the surrounding surface chemistry.

Publ.-Id: 22744 - Permalink


Bistable self-assembly in homogeneous colloidal systems for flexible modular architectures
Steinbach, G.; Nissen, D.; Albrecht, M.; Novak, E.; Sanchez, P. A.; Kantorovich, S. S.; Gemming, S.; Erbe, A.;
This paper presents a homogeneous system of magnetic colloidal particles that self-assembles via two structural patterns of different symmetry. Based on observations of a real magnetic particles system, analytical calculations and molecular dynamics simulations, it is shown that the bistability is a result of an anisotropic magnetization distribution with rotational symmetry inside the particles. The presented bistability opens new possibilities to form two-dimensionally extended and flexible structures, where the connectivity between the particles can be changed in-vivo.
Keywords: colloids, magnetic anisotropy, modular architectures, molecular dynamics simulations, self-assembly

Publ.-Id: 22743 - Permalink


Auf der Suche nach Kleinigkeiten - Veränderungen von Arbeitsbedingungen durch den Betrieb von wissenschaftlichen Großgeräten
Joehnk, P.;
Die Technik- und Geräteentwicklung in den letzten 100 Jahren wirkt sich auch massiv auf die Arbeitsbedingungen in der Wissenschaft aus. Während früher der "geniale" Einzelwissenschaftler Ideengeber für Weiterentwicklungen war, erfordert der experimentelle Nachweis an wissenschaftlichen Großgeräten disziplinübergreifende Teamarbeit auf internationaler Ebene. Daraus ergeben sich Konsequenzen für die Arbeitswelt in Großforschungseinrichtungen, die einige der sozialen Errungenschaften in der Arbeitswelt der vergangenen 60 Jahre konterkarieren. Die Gründe und die Rahmenbedingungen dafür warden nachfolgend dargelegt und beschrieben.
Keywords: Wissenschaftliches Arbeiten, Arbeitsbedingungen, Großforschungsgeräte
  • Lecture (Conference)
    Gesellschaft für Arbeitswissenschaft - Herbstkonferenz 2015, 21.-22.09.2015, Dresden, Deutschland

Publ.-Id: 22742 - Permalink


Experimental study on the mass transfer of a CO2 Taylor bubble using X-ray microfocus tomography
Haghnegahdar, M.; Boden, S.; Hampel, U.;
Several experimental and mathematical modeling studies have been done to quantify the effect of different parameters such as liquid properties, bubble velocity, bubble size and contamination level of fluid on the mass transfer from gas bubbles to liquids and various correlations have been proposed. However, little attention has been paid to the influence of pipe wall on mass transfer coefficient particularly for millimeter sized channels and the available correlations do not provide Sherwood numbers with acceptable accuracy.
In this work, the absorption rate of a single Taylor bubble of carbon dioxide in water is investigated using a new technique in vertical capillaries. The liquid side mass transfer coefficient is calculated by measuring the changes in the size of the bubble at constant pressure. The experiments cover a large range of initial Taylor bubble length varying from 5 to 25 mm. The pipe is a glass pipe with 6 mm inside diameter and circular cross section. The bubble is unceasingly monitored by holding the bubble stationary using downward flow of liquid. The method which is used to measure the variation of the bubble size is X-ray tomography. This technique was qualified to disclose the three-dimensional shape of Taylor bubbles in capillary and enabled the acquisition of a series of high-resolution radiographic images of nearly stationary Taylor bubbles. The processed images which give volume (and also the interfacial area) of the bubble with high accuracy as a function of time, are used to evaluate the liquid side mass transfer coefficient between bubble and liquid using the mass conservation equation. The liquid phase is filtered-deionized water and the gas phase is 99,999% purity CO2.
The results show that the measured mass transfer coefficients and also Sherwood numbers have intensive dependency on the bubble length and also equivalent diameter (diameter of the sphere having the same volume) which have the same trend with previous results for larger pipe sizes. However the values of measured Sherwood numbers could not be predicted by available correlations which are valid only for larger pipes. As a result a new mass transfer coefficient in the form of Sherwood number and as a function of Peclet number and ratio of bubble equivalent diameter to capillary diameter (deq/D) is presented. The proposed correlation is applicable for a large range of deq/D ratio that varies from 0.8 to 1.7 with high accuracy. The maximum relative error between measured Sherwood number and the calculated with new correlation is less than 12%.
Keywords: Mass transfer, X-ray, Taylor bubble
  • Poster
    10th European Congress of Chemical Engineering, 27.09.-01.10.2015, Nice, France

Publ.-Id: 22741 - Permalink


Observation of long-range magnetic ordering in pyrohafnate Nd2Hf2O7: A neutron diffraction studyObservation of long-range magnetic ordering in pyrohafnate Nd2Hf2O7: A neutron diffraction study
Anand, V. K.; Bera, A. K.; Xu, J.; Herrmannsdörfer, T.; Ritter, C.; Lake, B.;
We have investigated the physical properties of a pyrochlore hafnate Nd2Hf2O7 using acmagnetic susceptibility χac(T ), dc magnetic susceptibility χ(T ), isothermal magnetization M(H), and heat capacity Cp(T) measurements, and determined the magnetic ground state by neutron powder diffraction. An upturn is observed below 6 K in Cp(T )/T , however both Cp(T ) and χ(T ) do not show any clear anomaly down to 2 K. The χac(T) shows a well-pronounced anomaly indicating an antiferromagnetic transition at TN = 0.55 K. The long-range antiferromagnetic ordering is confirmed by neutron diffraction. The refinement of the neutron diffraction pattern reveals an all-in/all-out antiferromagnetic structure, where for successive tetrahedra the four Nd3+ magnetic moments point alternatively all-into or all-out-of the tetrahedron, with an ordering wave vector k = (0, 0, 0) and an ordered state magnetic moment of m = 0.62(1)μB/Nd at 0.1 K. The ordered moment is strongly reduced, reflecting strong quantum fluctuations in ordered state.

Publ.-Id: 22740 - Permalink


Electron doping dependence of the anisotropic superconductivity in BaFe2−xNixAs2
Wang, Z.; Xie, T.; Kampert, E.; Förster, T.; Lu, X.; Zhang, R.; Gong, D.; Li, S.; Herrmannsdörfer, T.; Wosnitza, J.; Luo, H.;
The upper critical field Hc2 in superconducting BaFe2−xNixAs2 single crystals has been determined by magnetotransport measurements down to 0.6 K over the whole superconducting dome with 0.065 ≤ x ≤ 0.22 for both the interplane (H ‖ c, Hcc2) and in-plane (H ‖ ab, Habc2 ) field directions in static magnetic fields up to 16 T and pulsed magnetic fields up to 60 T. The temperature dependence of Habc2 follows the Werthamer-Helfand-Hohenberg model incorporating orbital and spin paramagnetic effects, while Hcc2(T ) can only be described by the effective two-band model with unbalanced diffusivity. The anisotropy of the upper critical fields, γ (T ) = Habc2/Hcc2, monotonically increases with increasing temperature for all dopings, and its zero-temperature limit γ (0) has an asymmetric doping dependence with a significant enhancement in the overdoped regime, where the optimally doped compound has the most isotropic superconductivity. Our results suggest that the anisotropy in the superconductivity of iron pnictides is determined by the topology of the Fermi surfaces together with the doping-induced impurity scattering.

Publ.-Id: 22739 - Permalink


Relaxation attenuation of ultrasound by the jahn-teller centers in ZnSe:Cr in high magnetic fields
Averkiev, N. S.; Bersuker, I. B.; Gudkov, V. V.; Zherlitsyn, S.; Yasin, S.; Zhevstovskikh, I. V.; Baryshnikov, K. A.; Monakhov, A. M.; Sarychev, M. N.; Korostelin, Y.; Landman, A.;
The magnetic field dependence of ultrasonic attenuation α(B) of slow shear waves in the ZnSe:Cr2+ crystal at a number of fixed temperatures from T = 1.4 K to 20 K in magnetic fields of up to B = 14 T was investigated. For magnetic fields B above 5 T we found that the attenuation increases with B monotonically, and at a given temperature it is proportional to the magnitude of relaxation attenuation at B = 0. We show that the magnetic field dependent attenuation is due to the change in populations of the lowest energy levels of the impurity centers CrZn4Se, produced by the Jahn-Teller effect and split by the spin-orbital interaction and the magnetic field. The calculations carried out without fitting parameters are in good agreement with the experimental data.

Publ.-Id: 22738 - Permalink


Destabilization of rotating flows with positive shear by azimuthal magnetic fields
Stefani, F.; Kirillov, O.;
According to Rayleigh’s criterion, rotating flows are linearly stable when their specific angular momentum increases radially outward. The celebrated magnetorotational instability opens a way to destabilize those flows, as long as the angular velocity is decreasing outward. Using a local approximation we demonstrate that even flows with very steep positive shear can be destabilized by azimuthal magnetic fields which are current free within the fluid. We illustrate the transition of this instability to a rotationally enhanced kink-type instability in the case of a homogeneous current in the fluid, and discuss the prospects for observing it in a magnetized Taylor-Couette flow.

Publ.-Id: 22737 - Permalink


Mass transfer measurement in a square milli-channel using high-resolution microfocus X-ray imaging
Haghnegahdar, M.; Boden, S.; Hampel, U.;
For milli- and micro-reactors the bubble shape and relative velocity between two phases are mainly governed by the cross-sectional shape of the channel. For channels with circular cross section (pipes) enormous attention has been paid in the last decades and many studies on hydrodynamics and mass transfer to be found in literature. However other channel cross sections such as square channels were a subject of only a few studies [1]. Concerning the role and importance of square channels in various existing and potential industrial applications such as micro-electromechanical systems, monolith froth reactors, there exist still some gaps particularly in related aspects of transport phenomena in these channels and there needs to be further experimental work to provide detailed heat and mass transfer data for model validation.

In the work presented in this paper, the dissolution rate of a single Taylor bubble of carbon dioxide in water was investigated using high resolution X-ray radiography and tomography technique in vertical channels. The liquid side mass transfer coefficient was calculated by measuring the changes in the size of the bubble at constant pressure. The experiments cover a large range of initial Taylor bubble length varying from 4 to 26 mm. The pipe is a glass pipe with 6 mm inside diameter and square cross section. The bubbles were held stationary using the technique of Schulze and Schluender [2]. The method which is used to measure the variation of the bubble size is X-ray tomography. The X-ray method was chosen since it is not dependent on the refractive index; therefore it is the most accurate method in comparison with other conventional optical techniques. Furthermore this technique allows tomography for square channels, while full 3D shape determination by optical techniques is difficult in square channels. The processed images which give volume (and also the interfacial area) of the bubble as a function of time, are used to evaluate the liquid side mass transfer coefficient between bubble and liquid using the mass conservation equation.

The results for the long term dissolution of single CO2 bubbles show that the dissolution curves for bubbles with different initial size follow the same trend and have relatively constant slope. In addition, it is shown that the measured mass transfer coefficient increases as the equivalent diameter of the bubble (diameter of the sphere having the same volume) decreases. The trend for the change of liquid-side mass transfer coefficient as a function of bubble size is in accordance with the data predictivd by the penetration theory. However there is large deviation which is attributed to the bubble shape [3] and particular hydrodynamics governing in the square channels.

REFERENCES
[1] T. Taha and Z. F. Cui, “CFD modelling of slug flow inside square capillaries,” Chem. Eng. Sci., vol. 61, pp. 665–675, 2006.
[2] G. Schulze and E. U. Schlünder, “Physical absorption of single gas bubbles in degassed and preloaded water,” Chem. Eng. Process., vol. 19, pp. 27–37, 1985.
[3] P. Painmanakul, K. Loubière, G. Hébrard, M. Mietton-Peuchot, and M. Roustan, “Effect of surfactants on liquid-side mass transfer coefficients,” Chem. Eng. Sci., vol. 60, pp. 6480–6491, 2005.
Keywords: Mass transfer coefficient, Taylor bubble, Carbon dioxide
  • Lecture (Conference)
    International Conference on Transport Processes at Fluidic Interfaces, 05.-07.10.2015, Darmstadt, Germany

Publ.-Id: 22736 - Permalink


Sorption of Trivalent Rare Earth Elements on Calcite
Hellebrandt, S. E.; Hofman, S.; Stubbs, J. E.; Eng, P. J.; Stumpf, T.; Schmidt, M.;
A unique surface-destabilizing effect of NaNO3 on calcite, one of the most abundant minerals on earth, has been studied on the molecular scale by X-ray reflectivity. Upon exposure to NO3- the crystal structure at the surface of the mineral is heavily destabilized, resulting in partial dissolution and the formation of an amorphous substrate layer at the interface. The effect extends more than 15 Å deep into the crystal, and changes the mineral water interface considerably. The influence upon the adsorption of the rare earth ion Y(III) reveals the change in interfacial reactivity that accompanies the reaction. Both inner-sphere and outer sphere sorption species can be identified by resonant anomalous X-ray reflectivity (RAXR) in the absence of NO3-, but both species were found to be desorbed quantitatively from the surface in its presence.
Keywords: Calcite, Interfaces, Rare earth, X-ray surface diffraction
  • Lecture (Conference)
    Goldschmidt Conference, 16.-21.08.2015, Praha, Česká republika
  • Lecture (Conference)
    GDCh-Wissenschaftsforum Chemie 2015, 30.08.-02.09.2015, Dresden, Deutschland
  • Lecture (Conference)
    Migration, 13.-18.09.2015, Santa Fe, USA

Publ.-Id: 22735 - Permalink


Prognostic Value of Pretherapeutic Tumor-to-Blood Standardized Uptake Ratio in Patients with Esophageal Carcinoma
Bütof, R.; Hofheinz, F.; Zöphel, K.; Stadelmann, T.; Schmollack, J.; Jentsch, C.; Loeck, S.; Kotzerke, J.; Baumann, M.; van den Hoff, J.;
Despite ongoing efforts to develop new treatment options, the prognosis for patients with inoperable esophageal carcinoma is still poor and the reliability of individual therapy outcome prediction based on clinical parameters is not convincing. The aim of this work was to investigate whether PET can provide independent prognostic information in such a patient group and whether the tumor-toblood standardized uptake ratio (SUR) can improve the prognostic
value of tracer uptake values. Methods: 18F-FDG PET/CT was performed in 130 consecutive patients (mean age ± SD, 63 ± 11 y; 113 men, 17 women) with newly diagnosed esophageal cancer before definitive radiochemotherapy. In the PET images, the metabolically active tumor volume (MTV) of the primary tumor was delineated with an adaptive threshold method. The blood standardized uptake value (SUV) was determined by manually delineating the aorta in the low-dose CT. SUR values were computed as the ratio of tumor SUV and blood SUV. Uptake values were scan-time-corrected to 60 min after injection. Univariate Cox regression and Kaplan–Meier analysis with respect to overall survival (OS), distant metastases-free survival (DM), and locoregional tumor control (LRC) was performed. Additionally, a multivariate Cox regression including clinically relevant
parameters was performed.
Results: In multivariate Cox regression with respect to OS, including T stage, N stage, and smoking state, MTV- and SUR-based parameters were significant prognostic factors for OS with similar effect size.Multivariate analysis with respect to DM revealed smoking state, MTV, and all SUR-based parameters as significant prognostic factors. The highest hazard ratios (HRs) were found for scan-time-corrected maximum SUR (HR 5 3.9) and mean SUR (HR 5 4.4). None of the PET parameters was associated with LRC. Univariate Cox regression with respect to LRC revealed a significant effect only for N stage greater than 0 (P 5 0.048).
Conclusion: PET provides independent prognostic information for OS and DM but not for LRC in patients with locally advanced esophageal carcinoma treated with definitive radiochemotherapy in addition to clinical parameters.
Among the investigated uptake-based parameters, only SUR was an independent prognostic factor for OS and DM. These results suggest that the prognostic value of tracer uptake can be improved when characterized by SUR instead of SUV. Further investigations are required to confirm these preliminary results.
Keywords: PET; esophageal cancer; definitive radiochemotherapy; SUV; SUR

Publ.-Id: 22734 - Permalink


Threshold concentration for ion implantation-induced Co nanocluster formation in TiO2:Co thin films
Yildirim, O.; Cornelius, S.; Smekhova, A.; Butterling, M.; Anwand, W.; Wagner, A.; Baehtz, C.; Böttger, R.; Potzger, K.;
Structural, defect and magnetic properties of the TiO2:Co films are investigated. We varied the maximum Co+-implantation concentration from 0.5 at.% up to 5 at.%. A concentration window, which is considered as a threshold for the formation of metallic secondary phases is found. At this concentration it is also observed that the majority of the dopant atoms are incorporated into the host lattice.
Keywords: dilute magnetic oxide, nanoclusters, ion implantation

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Publ.-Id: 22733 - Permalink


177Lu-labelled macrocyclic bisphosphonates for targeting bone metastasis in cancer treatment
Bergmann, R.; Meckel, M.; Kubicek, V.; Pietzsch, J.; Steinbach, J.; Hermann, P.; Rösch, F.;
Background: Metastatic bone lesion is a common syndrome of many cancer diseases in an advanced state. The major symptom is severe pain, spinal cord compression, and pathological fracture, associated with an obvious morbidity. Common treatments including systemic application of bisphosphonate drugs aim on pain reduction and on improving the quality of life of the patient. Particularly, patients with multiple metastatic lesions benefit from bone-targeting therapeutic radiopharmaceuticals. Agents utilizing beta-emitting radionuclides in routine clinical praxis are, for example, [89Sr]SrCl2 and [153Sm]Sm-EDTMP. No-carrier-added (n.c.a.) 177Lu is remarkably suitable for an application in this scope.
Methods: Five 1,4,7,10-tetraazacyclododecane N,N',N'',N''-tetra-acetic acid (DOTA)- and DO2A-based bisphosphonates, including monomeric and dimeric structures and one 1,4,7-triazacyclononane-1,4-diacetic acid (NO2A) derivative, were synthesized and labelled with n.c.a. 177Lu. Radio-TLC and high-performance liquid chromatography (HPLC) methods were successfully established for determining radiochemical yields and for quality control. Their binding to hydroxyapatite was measured in vitro. Ex vivo biodistribution experiments and dynamic in vivo single photon computed tomography (SPECT)/CT measurements were performed in healthy rats for 5 min and 1 h periods. Data on %ID/g or standard uptake value (SUV) for femur, blood, and soft-tissue organs were analyzed and compared with [177Lu]citrate.
Results: Radiolabelling yields for [177Lu]Lu-DOTA and [177Lu]Lu-NO2A monomeric bisphosphonate complexes were >98 % within 15 min. The dimeric macrocyclic bisphosphonates showed a decelerated labelling kinetics, reaching a plateau after 30 min of 60 to 90 % radiolabelling yields. All 177Lu-bisphosphonate complexes showed exclusive accumulation in the skeleton. Blood clearance and renal elimination were fast. SUV data (all for 1 h p.i.) in the femur ranged from 3.34 to 5.67. The bone/blood ratios were between 3.6 and 135.6, correspondingly. 177Lu-bisphosphonate dimers showed a slightly higher bone accumulation (SUVfemur = 4.48 ± 0.38 for [177Lu] Lu-DO2A(PBP)2; SUVfemur = 5.41 ± 0.46 for [177Lu]Lu-DOTA(MBP)2) but a slower blood clearance (SUVblood = 1.25 ± 0.09 for [177Lu]Lu-DO2A(PBP)2; SUVblood = 1.43 ± 0.32 for [177Lu]Lu-DOTA(MBP)2).
Conclusions: Lu-complexes of macrocyclic bisphosphonates might become options for the therapy of skeletal metastases in the near future, since they show high uptake in bone together with a very low soft-tissue accumulation.
Keywords: Bisphosphonate, Bone metastases, 177Lu, DO2A, DOTA, Biodistribution, Theranostics

Publ.-Id: 22732 - Permalink


Algebraic vacuum limits of QCD condensates from in-medium projections of Lorentz tensors
Buchheim, T.; Kämpfer, B.; Hilger, T.;
Utilizing the in-medium Lorentz decomposition of operators generating QCD condensates we derive general constraints among the latter ones by the requirement of a smooth transition from medium to vacuum. In this way we relate the vacuum limits of heretofore unrelated condensates and provide consistency checks for the vacuum saturation hypothesis and the heavy quark mass expansion. The results are general and depend only on the rank and symmetry of the Lorentz tensors to be decomposed. The derived prescription enables to uniquely and directly identify operator product expansion contributions which are algebraically specific for in-medium situations and in particular useful for operators with a higher rank, i.e. larger than three. Four-quark condensates in mass dimension six are exemplified.

Publ.-Id: 22731 - Permalink


Imprints of a critical point on photon emission
Wunderlich, F.; Kämpfer, B.;
The linear sigma model with linearized fluctuations of all involved fields facilitates the onset of a sequence of first-order phase transitions at a critical point. This phase structure has distinctive imprints on the photon emission rates. We argue that analogously a critical point in the QCD phase diagram manifests itself by peculiarities of the photon spectra, in particular when the dynamical expansion path of matter crosses the phase transition curve in the vicinity of the critical point.

Publ.-Id: 22730 - Permalink


Fission product yield distribution in the 12, 14, and 16 MeV bremsstrahlung-induced fission of 232Th
Naik, H.; Kim, G. N.; Schwengner, R.; Kim, K.; John, R.; Massarczyk, R.; Junghans, A.; Wagner, A.; Goswami, A.;
The absolute cumulative yields of various fission products in the 12, 14, and 16 MeV bremsstrahlung-induced fission of 232 Th were determined using a recoil catcher and an off-line γ-ray spectrometric technique using the ELBE electron linac of Helmholtz-Zentrum Dresden-Rossendorf in Dresden, Germany. The mass chain yields were obtained from the absolute cumulative yields by correcting the charge distribution. The peak-to-valley ratio, average light mass ( AL ) and heavy mass ( AH ) values, and average number of neutrons ( exp ) in the bremsstrahlung-induced fission of 232 Th at different excitation energies were obtained from the mass chain yield data. The present study and existing literature data for the 232 Th(γ, f) reaction are compared with similar data for the 238 U(γ, f) reaction at various excitation energies, and surprisingly different behavior was found in the two fissioning systems.
Keywords: Photofission, bremsstrahlung, fission product yield.

Publ.-Id: 22729 - Permalink


Ecological and industrial aspects of the interaction of radionuclides with bacterial S-layer proteins
Raff, J.; Vogel, M.; Schmoock, C.; Lehmann, F.; Drobot, B.; Moll, H.; Matys, S.; Börnick, H.; Worch, E.; Pollmann, K.;
Radionuclides interact with biomass in various ways. In general, the different interaction mechanisms can be assigned to two physiological aspects, first a radiological toxicity and second a chemical toxicity. Bacteria and archaea developed very early in evolution a multifunctional cell envelope called surface-layer (S-layer) which protects bacteria in extreme environments. This layer is a para-crystalline protein lattice formed by the self-assembly of secreted proteins on the cell wall of bacteria and archaea. S-layers are often glycosylated and phosphorylated and their lattice formation depends often on bivalent cations such as calcium. In case of bacteria living in radionuclide and heavy metal contaminated environments, S-layers are able to act first of all as scavenger for reactive oxygen species (ROS) formed by either radiolysis of water or Fenton reaction. The inactivation of the radicals is achieved by intermolecular crosslinking of tyrosine residues of the protein monomers. Secondly, S-layer proteins are able to selectively bind several radionuclides such as uranium and curium but also other toxic elements such as arsenic. By restraining these metals on the surface of the cell a toxication of the organism is prevented. Interestingly, the mechanism and binding behavior is different for different elements and is highly dependent on pH. Whereas the hexavalent uranium is bound by several surface exposed functional groups and is easily released at acidic pH, the trivalent curium substitutes calcium and is only released at pH 2.5 or below. The stable and selective curium complexation is especially interesting as lanthanides are considered as chemical analogous for trivalent actinides. Thusly, S-layers bind also rare earth elements very effectively, being highly interesting for the development of metal selective filter materials for their enrichment and recovery.
Keywords: radionuclides, lanthanides, S-layers, reactive oxygen species
  • Poster
    Annual Conference 2016 of the Association for General and Applied Microbiology (VAAM), 13.-16.03.2016, Jena, Deutschland

Publ.-Id: 22728 - Permalink


Effect of external stress on dislocation bias factor in Fe-based alloy
Bakaev, A.; Terentyev, D.; Chang, Z.; Posselt, M.;
not available, please contact the authors
Keywords: ferritic steels, dislocation bias factor, external stress, molecular statics.
  • Lecture (Conference)
    Workshop on nuclear Fe alloys: Modelling and Experiments, 21.-22.09.2015, Getafe/Madrid, Spain

Publ.-Id: 22727 - Permalink


Numerical Simulations for the planned precession dynamo experiment at HZDR
Giesecke, A.; Stefani, F.;
In a next generation dynamo experiment currently under development at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) a fluid flow of liquid sodium, solely driven by precession, will be considered as a possible source for magnetic field generation. The experiment is mainly motivated by alternative concepts for astrophysical dynamos that are based on mechanical flow driving like the geodynamo model by Malkus (Science 1968, 160, 3825, 259-264) or the model for the ancient lunar dynamo from Dwyer (Nature 2011, 479, 7372, 212-214).

I will present results from non-linear hydrodynamic simulations with moderate precessional forcing dedicated to the planned experiment.
The simulations reveal a non-axisymmetric forced mode with an amplitude of up to one fourth of the rotation velocity of the cylindrical container confirming that precession provides a rather efficient flow driving mechanism even at moderate precession rates.

Promising candidates for exciting a dynamo may be triadic resonances in terms of three distinct inertial modes (so called Kelvin modes, the natural flow eigenmodes in a rotating cylinder) which may emerge from first order non-linear interactions when the height of the container matches their axial wave lengths.
The involved free Kelvin modes are characterized by a high azimuthal wave number and an axial structure comparable to the structure of the columnar convection cells that are responsible for dynamo action in geodynamo simulations.
We find triadic resonances at aspect ratios close to those predicted by the quasi-linear theory except around the primary resonance of the forced mode. In that regime the fundamental forced mode becomes unstable at low Ekman number thus inhibiting the triadic resonance.

Our results will enter into the development of flow models that will be used in kinematic simulations of the electromagnetic induction equation in order to determine whether a precession driven flow will be capable to drive a dynamo at all and to limit the parameter space within which the occurrence of dynamo action is most promising.
Keywords: Dynamo Precession DRESDYN
  • Lecture (Conference)
    MHD-Days 2015, 07.-09.12.2015, Ilmenau, Deutschland

Publ.-Id: 22726 - Permalink


Self-assembly of Ge quantum dots on periodically corrugated Si surfaces
Buljan, M.; Facsko, S.; Delač Marion, I.; Mikšić Trontl, V.; Kralj, M.; Jerčinović, M.; Baehtz, C.; Muecklich, A.; Holý, V.; Grenzer, J.; Radić, N.;
The fabrication of regularly ordered Gequantum dot arrays on Si surfaces usually requires extensive preparation processing, ensuring clean and atomically ordered substrates, while the ordering parameters are quite limited by the surface properties of the substrate. Here, we demonstrate a simple method for fabrication of ordered Gequantum dots with highly tunable ordering parameters on rippled Si surfaces. The ordering is achieved by magnetron sputter deposition, followed by an annealing in high vacuum. We show that the type of ordering and lattice vector parameters of the formed Gequantum dot lattice are determined by the crystallographic properties of the ripples, i.e., by their shape and orientation. Moreover, the ordering is achieved regardless the initial amorphisation of the ripples surface and the presence of a thin oxide layer.

Publ.-Id: 22725 - Permalink


P1409 - Thermisches Anemometer
Barthel, F.; Schleicher, E.;
Die Erfindung betrifft ein thermisches Anemometer zum Erfassen der Strömungscharakteristik einer mehrphasigen Fluidströmung mit einer flüssigen Phase und einer gasförmigen Phase, wobei das Anemometer ein elektrisch beheizbares Strömungssensorelement zum Einbringen in die Fluidströmung und eine Impedanzmessvorrichtung zum Erfassen der Impedanz eines an das Strömungssensorelement angrenzenden Volumens der Fluidströmung aufweist, und wobei von dem Anemometer die Heizleistung des Sensorelements in Abhängigkeit von der erfassten Impedanz eingestellt wird.
  • Patent
    DE102014113031 - Erteilung 19.11.2015

Publ.-Id: 22724 - Permalink


Three new low-energy resonances in the 22Ne(p,γ)23Na reaction
Cavanna, F.; Depalo, R.; Aliotta, M.; Anders, M.; Bemmerer, D.; Best, A.; Böltzig, A.; 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.; Mossa, V.; Pantaleo, F. R.; Prati, P.; Scott, D. A.; Somorjai, E.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.;
The 22Ne(p,γ)23Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle affects the synthesis of the elements between 20Ne and 27Al in asymptotic giant branch stars and novae. The 22Ne(p,γ)23Na reaction rate is very uncertain because of a large number of unobserved resonances lying in the Gamow window. At proton energies below 400\,keV, only upper limits exist in the literature for the resonance strengths. Previous reaction rate evaluations differ by large factors. In the present work, the first direct observations of the 22Ne(p,γ)23Na resonances at 156.2, 189.5, and 259.7\,keV are reported. Their resonance strengths have been derived with 2-7\% uncertainty. In addition, upper limits for three other resonances have been greatly reduced. Data were taken using a windowless 22Ne gas target and high-purity germanium detectors at the Laboratory for Underground Nuclear Astrophysics in the Gran Sasso laboratory of the National Institute for Nuclear Physics, Italy, taking advantage of the ultra-low background observed deep underground. The new reaction rate is a factor of 5 higher than the recent evaluation at temperatures relevant to novae and asymptotic giant branch stars nucleosynthesis.
Keywords: Nuclear Astrophysics Asymptotic giant branch stars Hot bottom burning LUNA Underground nuclear astrophysics Hydrogen burning Nova nucleosynthesis Supernova nucleosynthesis

Publ.-Id: 22723 - Permalink


A systemic approach to the problems of the rare earth market
Klossek, P.; Kullik, J.; van den Boogaart, K. G.;
China’s dominance of the rare earth market created issues of major concern since 2010: Limited export quotas and consecutive price peaks led to fears concerning supply security. Forward integration is shifting the rare earth-dependent high-technology value chain to China. China’s export embargo to Japan showed the world the strategic relevance of its economic dependence on China’s rare earth products. Despite multiple political and industrial efforts outside China, it was not possible to build up an independent rare earth supply chain. We think that this is prevented by systemic problems of the market. This paper examines these distortions of the rare earth market with a systemic approach. Problems are identified and structured qualitatively in order to expose their economic and political connections. They are (1) competing political-economic models, (2) resource nationalism, (3) market opacity, (4) a lack of trust, (5) weak cooperation and (6) short- versus long-term approaches and profit orientation. These problems are interconnected and create vicious circles. In this context, the paper discusses literature solutions and a new proposal, which provides incentives for a higher diversification of the REE market.
Keywords: Systemic approach, rare earth elements, supply security, state involvement, resource markets

Publ.-Id: 22722 - Permalink


Gemeinsames Recycling von Flachbildschirmen und Bleigläsern
Wolf, R.; Stelter, M.;
Derzeit werden weder Bleigläser noch Flachbildschirme wirtschaftlich recycelt. Kathodenstrahlröhren von Monitoren und alten Fernsehgeräten enthalten Blei, ein Massenmetall mit moderatem Preis. Flachbildschirme enthalten Indium und Zinn in so geringen Konzentrationen, dass ein Recycling unwirtschaftlich ist. Ein neues Verfahren wird präsentiert, das beide Abfälle in einem Prozess recycelt, um alle enthaltenen Metalle sowie Glas zurück zu gewinnen. Ein zusätzlicher Vorteil ist das Zero-Waste-Konzept des Verfahrens, da die Endprodukte verwertbares Glas sowie eine Metallphase, die alle Wertmetalle enthält, sind.

Neither lead glass nor flat screens are recycled in an economic way today. Glass from the cathode-ray tubes (CRTs) contains lead, a base metal with a moderate price. Flat screens (LCDs) contain indium and tin in low concentrations. These metals are highly valued, but low concentrations in the panels prohibited recycling. Therefore, a new recycling process is presented to recycle both wastes (CRTs and flat screens) in one process to recover all metals and glass. An additional benefit is the zero waste concept of this process because the products are usable glass and a metal phase containing all valuable metals.
Keywords: Blei; Flachbildschirme; Glas; Indium; Recycling Flat screens; Glass; Indium; Lead; Recycling

Publ.-Id: 22721 - Permalink


Focused ion beam optical patterning of ta-C films
Tsvetkova, T.; Berova, M.; Sandulov, M.; Kitova, S.; Avramov, L.; Boettger, R.; Bischoff, L.;
Optical contrast formation by Ga+ ion implantation has been made use of for focused ion beam (FIB) writing of nano-scale optical patterns in tetrahedral amorphous carbon (ta-C). Initial UV-VIS optical spectroscopy results with Ga+ broad-beam ion implantation have shown well expressed ion beam induced photo-darkening effect in thin ta-C films. It is manifested by a significant shift of the optical absorption edge to lower photon energies as obtained from optical transmission measurements of ta-C samples, implanted with Ga+ at ion energy E = 20 keV and ion fluences D = 3e14 and 3e15 cm-2. This shift is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). The obtained optical contrast (between implanted and unimplanted film material) could be made use of in the area of high-density optical data storage using focused Ga+ ion beams. The underlying structural modifications, induced by the Ga+ ion bombardment, have been investigated by x-ray photo-electron spectroscopy (XPS), transmission (TEM) and scanning (SEM) electron microscopy measurements. Focused ion beam (FIB) implanted patterns in ta-C samples, obtained with a fluence of 5e15 cm-2, are also presented.
Keywords: Tetrahedral amorphous carbon; Focused ion beams; Optical data storage.
  • Lecture (Conference)
    19th International Conference on Surface Modification of Materials by Ion Beams (SMMIB - 2015), 22.-27.11.2015, Chiang Mai, Thailand
  • Open Access LogoSurface & Coatings Technology 306(2016), 341-345
    DOI: 10.1016/j.surfcoat.2016.07.088

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Publ.-Id: 22720 - Permalink


Magnetic dipole excitations of 50Cr
Pai, H.; Beck, T.; Beller, J.; Beyer, R.; Bhike, M.; Derya, V.; Gayer, U.; Isaak, J.; Krishichayan, J. K.; Löher, B.; Nesterenko, V. O.; Pietralla, N.; Martinez-Pinedo, G.; Ponomarev, V. Y.; Reinhard, P.-G.; Repko, A.; Ries, P. C.; Romig, C.; Savran, D.; Schwengner, R.; Tornow, W.; Werner, V.; Wilhelmy, J.; Zilges, A.; Zweidinger, M.;
The low-lying M 1-strength of the open-shell nucleus 50 Cr has been studied with the method of nuclear resonance fluorescence up to 9.7 MeV, using bremsstrahlung at the superconducting Darmstadt linear electron accelerator S-DALINAC and Compton backscattered photons at the High Intensity γ-ray Source (HIγS) facility between 6 and 9.7 MeV of the initial photon energy. Fifteen 1+ states have been observed between 3.6 and 9.7 MeV. Following our analysis, the lowest 1+ state at 3.6 MeV can be considered as an isovector orbital mode with some spin admixture. The obtained results generally match the estimations and trends typical for the scissors mode. Detailed calculations within the Skyrme Quasiparticle Random-Phase-Approximation method and the Large-Scale Shell Model justify our conclusions. The calculated distributions of the orbital current for the lowest 1+ -state suggest the schematic view of Lipparini and Stringari (isovector rotation-like oscillations inside the rigid surface) rather than the scissors-like picture of Lo Iudice and Palumbo. The spin M1 resonance is shown to be mainly generated by spin-flip transitions between the orbitals of the f p-shell.
Keywords: Photon scattering, nuclear resonance fluorescence, bremsstrahlung, monoenergetic and polarized gamma radiation, magnetic dipole excitations, QRPA, shell model.

Publ.-Id: 22719 - Permalink


Study of the Interaction of Eu3+ with Microbiologically Induced Calcium Carbonate Precipitates using TRLFS
Johnstone, E. V.; Hofmann, S.; Cherkouk, A.; Schmidt, M.;
The microbial induced biomineralization of calcium carbonate using the ureolytic bacterium Sporosarcina pasteurii in the presence of trivalent europium, a substitute for trivalent actinides, was investigated by time resolved laser-induced fluorescence spectroscopy (TRLFS) and a variety of physicochemical techniques. Results showed that the bacterial-driven hydrolysis of urea provides favorable conditions for CaCO3 precipitation and Eu3+ uptake due to subsequent increases in NH4+ and pH in the local environment. Precipitate morphologies were characteristic of biogenically formed CaCO3 and consistent with the respective mineral phase compositions. The formation of vaterite with some calcite was observed after one day, calcite with some vaterite after one week, and pure calcite after two weeks. The presence of organic material associated with the mineral was also identified and quantified. TRLFS was used to track the interaction and speciation of Eu3+ as a molecular probe with the mineral as a function of time. Initially, Eu3+ is incorporated into the vaterite phase, while during CaCO3 phase transformation Eu3+ speciation changes resulting in several species incorporated in the calcite phase either substituting at the Ca2+ site or in a previously unidentified, low-symmetry site. Comparison of the biogenic precipitates to an abiotic sample shows mineral origin can affect Eu3+ speciation within the mineral.
Keywords: Biomineralization, TRLFS, fluorescence, europium, calcite, CaCO3

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Publ.-Id: 22718 - Permalink


Characterization of Smithsonian microbeam standards by micro-PIXE and -PIGE methods.
Le Bras, L.;
High quality and certified standards are necessary to perform accurate and reliable measurements. However, it is complicated to find certified mineral reference materials to calibrate analytical devices like electron microprobe. The aim of the study is to characterize with a high accuracy and precision existing mineral standards in order to perform these calibrations. Standards are coming from the Smithsonian Institute collections at Washington D.C. (U.S.A). Last results of analyzes performed of these standards have been published in 1980 and have been achieved by chemical wet analyzes. It is necessary to perform further investigations to characterize these standards from the chemical and mineralogical point of view in order to use them. 10 mineral standards have been selected in the Smithsonian Microbeam Standard collection according to chemical, crystallographic and geologic criteria. The 3 target are, first to find new trace elements which have not been detected yet, then to quantify all the elements in the standards and at last to check the homogeneity of the samples, an important parameter for performing high quality measurements. Therefore, 2 methods have been selected. They are based on an X- and Gamma-ray emission of samples atoms after collision with an incident proton beam. They are called PIXE and PIGE. They are used respectively for heavy (Z>18) and light (Z<18) element analyzes. An ion microprobe has been used with a particle accelerator in order to provide a 3.54 MeV proton beam to perform analyzes. Results are raw PIXE and PIGE spectra. They are processed with different methods to reach the targets of the study. New trace elements have been found and quantified thanks to data processing. Quantification is irrelevant for minerals with high light elements concentrations because they cannot be quantified. Statistics have been performed on elements distribution through the analyzed particles. Further analyses, and in particular X-ray fluorescence, have to be achieved in order to bring more precisions about the obtained data.
Keywords: Standards, Trace element, Quantification, PIXE, PIGE
  • Master thesis
    Institut Polytechnique LaSalle Beauvais, 2015
    Mentor: Dr. Axel Renno; Dr. Mohamed Nasraoui
    174 Seiten

Publ.-Id: 22717 - Permalink


Electron-Phonon Coupling in Aluminium
Vorberger, J.;
An experimental-theoretical investigation of the electron-phonon-coupling in aluminium.
Keywords: electron-phonon coupling, aluminium, two-temperature model, non-equilibrium, phonons, DFT, DFT-MD, electron diffraction
  • Invited lecture (Conferences)
    Laser- und Quantenoptikseminar, 13.11.2015, Kaiserslautern, Deutschland

Publ.-Id: 22716 - Permalink


Alignment of Gold Nanoparticle-Decorated DNA Origami Nanotubes: Substrate Prepatterning versus Molecular Combing
Teschome, B.; Facsko, S.; Gothelf, K. V.; Keller, A.;
DNA origami has become an established technique for designing well-defined nanostructures with any desired shape and for the controlled arrangement of functional nanostructures with few nanometer resolution. These unique features make DNA origami nanostructures promising candidates for use as scaffolds in nanoelectronics and nanophotonics device fabrication. Consequently, a number of studies have shown the precise organization of metallic nanoparticles on various DNA origami shapes. In this work, we fabricated large arrays of aligned DNA origami decorated with a high density of gold nanoparticles (AuNPs). To this end, we first demonstrate the high-yield assembly of high-density AuNP arrangements on DNA origami adsorbed to Si surfaces with few unbound background nanoparticles by carefully controlling the concentrations of MgCl2 and AuNPs in the hybridization buffer and the hybridization time. Then, we evaluate two methods, i.e., hybridization to prealigned DNA origami and molecular combing in a receding meniscus, with respect to their potential to yield large arrays of aligned AuNP-decorated DNA origami nanotubes. Because of the comparatively low MgCl2 concentration required for the efficient immobilization of the AuNPs, the prealigned DNA origami become mobile and displaced from their original positions, thereby decreasing the alignment yield. This increased mobility, on the other hand, makes the adsorbed origami susceptible to molecular combing, and a total alignment yield of 86% is obtained in this way.
Keywords: DNA origami, gold nanoparticles, alignment, molecular combing, nanopatterning.

Publ.-Id: 22715 - Permalink


Covellite (Bio)-Leaching with Amino Acids
Barthen, R.; Karimzadeh, L.; Gründig, M.; Lippold, H.; Franke, K.; Lippmann-Pipke, J.;
Covellite is one of the main copper sulfides found in Kupferschiefer [1]. Besides that there are also indications of secondary covellite formation during leaching processes of related sulfides [2]. Therefore, understanding of covellite dissolution in the context of Kupferschiefer bioleaching is of great importance. However, conventional bioleaching employing acidophilic microorganisms is impeded due to its high acid neutralizing capacity. The Use of neutrophilic bacteria secreting metabolites capable of metal interactions may circumvent this problem. Thus, we synthesized an artificial covellite [3] and subjected it to both chemical and biological leaching. Parameters considered important for covellite dissolution involve e.g. type and concentration of leaching agent, pH, and temperature, presence of other metals or solid phases with adsorptive capacities. First results from batch assays revealed that amino acids might be suitable leaching agents. Physicochemical parameters, which determine leaching success, differ between different amino acids. We found that covellite dissolution is strongly pH dependent for glutamic acid, aspartic acid and arginine, whereas for glutamine and asparagine this could not be shown. The different behavior is currently attributed to the differences in stability of the formed copper-amino acid complexes. In addition pH determines chemical speciation of leaching agent which in turn is a key factor in complex formation. Growth of bacteria sometimes is heavily influencing pH and thus leaching success. Knowledge of these crucial parameters and how they interact, allows for optimization of the leaching process. Furthermore, it is planned to produce amino acids in-situ, by e.g. Corynebacterium glutamicum, to ensure an economical feasible process.

1. Kutschke, S., et al., Bioleaching of Kupferschiefer blackshale – A review including perspectives of the Ecometals project. Minerals Engineering, 2015. 75: p. 116-125.
2. Kostudis, S., et al., Leaching of copper from Kupferschiefer by glutamic acid and heterotrophic bacteria. Minerals Engineering, 2015. 75: p. 38-44.
3. Xin, M., K. Li, and H. Wang, Synthesis of CuS thin films by microwave assisted chemical bath deposition. Applied Surface Science, 2009. 256(5): p. 1436-1442.
  • Poster
    Annual Conference 2016 of the Association for General and Applied Microbiology(VAAM) / Jahrestagung 2016 der Vereinigung für Allgemeine und Angewandte Mikrobiologie (VAAM), 13.-16.03.2016, Jena, Deutschland

Publ.-Id: 22714 - Permalink


Glioblastoma multiforme: emerging treatments and stratification markers beyond new drugs.
von Neubeck, C.; Seidlitz, A.; Kitzler, H. H.; Beuthien-Baumann, B.; Krause, M.;
Glioblastoma multiforme (GBM) is the most common primary brain tumour in adults. The standard therapy for GBM is maximal surgical resection followed by radiotherapy with concurrent and adjuvant temozolomide (TMZ). In spite of the extensive treatment, the disease is associated with poor clinical outcome. Further intensification of the standard treatment is limited by the infiltrating growth of the GBM in normal brain areas, the expected neurological toxicities with radiation doses >60 Gy and the dose-limiting toxicities induced by systemic therapy. To improve the outcome of patients with GBM, alternative treatment modalities which add low or no additional toxicities to the standard treatment are needed. Many Phase II trials on new chemotherapeutics or targeted drugs have indicated potential efficacy but failed to improve the overall or progression-free survival in Phase III clinical trials. In this review, we will discuss contemporary issues related to recent technical developments and new metabolic strategies for patients with GBM including MR (spectroscopy) imaging, (amino acid) positron emission tomography (PET), amino acid PET, surgery, radiogenomics, particle therapy, radioimmunotherapy and diets.

Publ.-Id: 22713 - Permalink


Radiation therapy and the global health agenda
Jaffray, D. A.; Atun, R.; Barton, M.; Baumann, M.; Gospodarowicz, M.; Hoskin, P.; Knaul, F. M.; Lievens, Y.; Rosenblatt, E.; Torode, J.; van Dyk, J.; Vikram, B.; Union for International Cancer Control'S Global Task Force On Radiotherapy For Cancer Control;
There ist no abstract

Publ.-Id: 22711 - Permalink


γH2AX assay in ex vivo irradiated tumour specimens: A novel method to determine tumour radiation sensitivity in patient-derived material.
Menegakis, A.; von Neubeck, C.; Yaromina, A.; Thames, H.; Hering, S.; Hennenlotter, J.; Scharpf, M.; Noell, S.; Krause, M.; Zips, D.; Baumann, M.;
PURPOSE:

To establish a clinically applicable protocol for quantification of residual γH2AX foci in ex vivo irradiated tumour samples and to apply this method in a proof-of-concept feasibility study to patient-derived tumour specimens.
MATERIAL AND METHODS:

Evaluation of γH2AX foci formation and disappearance in excised FaDu tumour specimens after (a) different incubation times in culture medium, 4Gy irradiation and fixation after 24h (cell recovery), (b) 10h medium incubation, 4Gy irradiation and fixation after various time points (double strand break repair kinetics), and (c) 10h medium incubation, irradiation with graded single radiation doses and fixation after 24h (dose-response). The optimised protocol was applied to patient-derived samples of seminoma, prostate cancer and glioblastoma multiforme.
RESULTS:

Post excision or biopsy, tumour tissues showed stable radiation-induced γH2AX foci values in oxic cells after >6h of recovery in medium. Kinetics of foci disappearance indicated a plateau of residual foci after >12h following ex vivo irradiation. Fitting the dose-response of residual γH2AX foci yielded slopes comparable with in situ irradiation of FaDu tumours. Significant differences in the slopes of ex vivo irradiated patient-derived tumour samples were found.
CONCLUSION:

A novel clinically applicable method to quantify residual γH2AX foci in ex vivo irradiated tumour samples was established. The first clinical results suggest that this method allows to distinguish between radiosensitive and radioresistant tumour types. These findings support further translational evaluation of this assay to individualise radiation therapy.
Keywords: Biomarker; DNA repair; Radiotherapy; Tumour biopsy; γH2AX foci

Publ.-Id: 22709 - Permalink


In vivo studies of the PARP inhibitor, AZD-2281, in combination with fractionated radiotherapy: An exploration of the therapeutic ratio
Gani, C.; Coackley, C.; Kumareswaran, R.; Schütze, C.; Krause, M.; Zafarana, G.; Bristow, R. G.;
BACKGROUND AND PURPOSE:

Pre-clinical data have shown that PARP inhibitors (PARPi) may increase the efficacy of radiotherapy in prostate cancer. However, it is uncertain as to whether PARPi lead to clonogenic kill when combined with radiotherapy (RT).
MATERIAL AND METHODS:

We tested the PARP inhibitor AZD-2281 as a radiosensitizing agent under oxic and hypoxic conditions for clonogenic survival in vitro and in vivo using the human prostate cancer cell line, 22Rv1. In addition, the effects of PARPi+RT on normal tissue were investigated using a crypt clonogenic assay.
RESULTS:

AZD-2281 inhibited cellular PARP activity under both oxic and hypoxic conditions. The addition of AZD-2281 radiosensitized 22Rv1 cells under oxia, acute hypoxia and chronic hypoxia in vitro. The combination of AZD-2281 with fractionated radiotherapy resulted in a significant growth delay and clonogenic kill in vivo. No increased gut toxicity was observed using this combined PARPi+radiotherapy regimen.
CONCLUSIONS:

This is the first preclinical study to demonstrate direct clonogenic kill in vivo by the addition of AZD-2281 to radiotherapy. As we did not observe gut toxicity, the use of PARPi in the context of prostate cancer radiotherapy warrants further investigation in clinical trials.
Keywords: AZD-2281; Clonogenic assay; EF5; Gamma H2AX; Growth delay; Gut toxicity; PARP inhibitors; Prostate cancer

Publ.-Id: 22708 - Permalink


Residual γH2AX foci after ex vivo irradiation of patient samples with known tumour-type specific differences in radio-responsiveness
Menegakis, A.; de Colle, C.; Yaromina, A.; Hennenlotter, J.; Stenzl, A.; Scharpf, M.; Fend, F.; Noell, S.; Tatagiba, M.; Brucker, S.; Wallwiener, D.; Boeke, S.; Ricardi, U.; Baumann, M.; Zips, D.;
PURPOSE:

To apply our previously published residual ex vivo γH2AX foci method to patient-derived tumour specimens covering a spectrum of tumour-types with known differences in radiation response. In addition, the data were used to simulate different experimental scenarios to simplify the method.
MATERIALS AND METHODS:

Evaluation of residual γH2AX foci in well-oxygenated tumour areas of ex vivo irradiated patient-derived tumour specimens with graded single doses was performed. Immediately after surgical resection, the samples were cultivated for 24h in culture medium prior to irradiation and fixed 24h post-irradiation for γH2AX foci evaluation. Specimens from a total of 25 patients (including 7 previously published) with 10 different tumour types were included.
RESULTS:

Linear dose response of residual γH2AX foci was observed in all specimens with highly variable slopes among different tumour types ranging from 0.69 (95% CI: 1.14-0.24) to 3.26 (95% CI: 4.13-2.62) for chondrosarcomas (radioresistant) and classical seminomas (radiosensitive) respectively. Simulations suggest that omitting dose levels might simplify the assay without compromising robustness.
CONCLUSION:

Here we confirm clinical feasibility of the assay. The slopes of the residual foci number are well in line with the expected differences in radio-responsiveness of different tumour types implying that intrinsic radiation sensitivity contributes to tumour radiation response. Thus, this assay has a promising potential for individualized radiation therapy and prospective validation is warranted.
Keywords: DNA repair; Intrinsic radiation sensitivity; Personalized radiation oncology; Radiotherapy; Tumour specimens; γH2AX foci

Publ.-Id: 22707 - Permalink


EGFR and β1-integrin targeting differentially affect colorectal carcinoma cell radiosensitivity and invasion.
Poschau, M.; Dickreuter, E.; Singh-Müller, J.; Zscheppang, K.; Eke, I.; Liersch, T.; Cordes, N.;
BACKGROUND AND PURPOSE:

Simultaneous targeting of β1 integrin receptor and epidermal growth factor receptor (EGFR) showed higher level of radiosensitization in head and neck cancers than monotherapies. As EGFR inhibition is similarly performed in colorectal cancer (CRC), we investigated the radiosensitizing and anti-invasive potential of β1-integrin/EGFR inhibition in CRC cell lines grown in more physiological three-dimensional (3D) matrix-based cell cultures.
MATERIALS AND METHODS:

DLD-1 and HT-29 cells were used for 3D-colony formation, invasion and proliferation assays and Western blotting. β1 integrin, focal adhesion kinase and EGFR were inhibited by AIIB2, TAE226 and Cetuximab, respectively. KRAS and BRAF knockdown were accomplished using small-interfering RNA technology. Single doses of X-rays ranged from 2Gy to 6Gy and 5-fluorouracil (5-FU) concentration was 10μM.
RESULTS:

Neither β1-integrin/EGFR inhibition nor KRAS or BRAF depletion nor 5-FU significantly modified CRC cell radiosensitivity. Cetuximab, AIIB2 and Cetuximab/AIIB2 differentially modulated MAPK, JNK and AKT phosphorylation. AIIB2 and TAE226 significantly decreased cell invasion.
CONCLUSIONS:

Our data show inefficiency of Cetuximab and AIIB2 on top of radiochemotherapy. The functions of KRAS and BRAF in therapy resistance remain unanswered and warrant further preclinical molecular-driven investigations. One promising approach might be β1 integrin targeting for reducing metastatic CRC cell spread.
Keywords: Colorectal carcinoma; EGFR; Invasion; Ionizing radiation; β1 integrin

Publ.-Id: 22706 - Permalink


Summary of Working Group 2: Ion beams from plasmas
Schramm, U.; Borghesi, M.;
Extenive summary of the working group of the 2nd European Advanced Accelerator Workshop held on ELBA 2015 on ion acceleration with lasers including a summary of published maximum proton energies.
Keywords: Plasma ion acceleration

Publ.-Id: 22705 - Permalink


Voronoï analysis of bubbly flows via ultra fast X-ray tomographic imaging
Lau, Y. M.; Müller, K.; Azizi, S.; Schubert, M.;
Although clustering of bubbles plays a signifant role in bubble column reactors regarding the heat and mass transfer due to bubble-bubble and flow field interactions, it has yet to be fully understood. Contrary to flows in bubble columns, most literature studies on clustering report numerical and experimental results on dilute or micro-bubbly flows. In this paper, clustering of bubbles in a cylindrical bubble column of 100 mm diameter is experimentally investigated. Ultra fast X-ray tomographic imaging is used to obtain the bubble positions within a hybrid Eulerian framework. By means of Voronoï analysis, the clustering behaviour of bubbles is investigated. Experiments are performed with different superficial gas velocities, where Voronoï diagrams are constructed at several column heights. From the PDFs of the Voronoï diagrams, it is shown that the bubble structuring in terms of hybrid volume dimensions develops slower than the bubble size distribution. The measured PDFs are compared with the PDF of randomly distributed points, which showed that the amount of bubbles as part of clusters (Voronoï cells < V/V_cluster ) as well as bubbles as part of voids (Voronoï cells > V/V_void) increases with the superficial gas velocity. It is found that all experiments have an approximate cluster limit V/V cluster of 0.63, while the void limit V/V void varies between 1.5 and 3.0.
Keywords: Bubble clustering, ultra fast X-ray tomography, bubble column, bubble size distribution, Voronoï diagrams.

Publ.-Id: 22703 - Permalink


Modeling 3-D bubble heat transfer in gas-solid fluidized beds using DEM
Patil, A. V.; Peters, E. A. J. F.; Lau, Y. M.; Kuipers, J. A. M.;
Computational fluid dynamics discrete element method simulations of a 3D fluidized bed at nonisothermal conditions are presented. Hot gas injection into a colder bed that is slightly above minimum fluidization conditions is modeled in a 3D square bed containing up to 8 million particles. In this study, bubbles formed in monodisperse beds of different glass particle sizes (0.25, 0.5, 0.75, and 1 mm) and using hot-gas-injection temperatures ranging from 700 to 1100 K are analyzed. Bubble heat-transfer coefficients in 3D fluidized beds are reported and compared with theoretical predictions on the basis of the Davidson and Harrison model.

Publ.-Id: 22702 - Permalink


Formation of solution species and nanoparticles of tetravalent metal ions in aqueous solution
Hennig, C.;
The presentation summarizes (i) technical configuration and equipment of the Rossendorf Beamline at the European Synchrotron Radiation Facility / Grenoble, (ii) structure - mobility relationship of An(IV) oxyhydroxy nanoparticles in the environment, and (iii) coordination of An(IV) and Zr(IV) with small carboxylate ligands.
Keywords: ROBL, EXAFS, An(IV), Zr(IV)
  • Invited lecture (Conferences)
    Vortrag im Rahmen des Schwerpunktprogramms „Understanding of Metal Oxide/Water Systems at the Molecular Scale: Structural Evolution, Interfaces, and Dissolution“, 15.10.2015, Berlin, Deutschland

Publ.-Id: 22700 - Permalink


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