Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
A treatment planning study to assess the feasibility of laser-driven proton therapy using a compact gantry design
Hofmann, K. M.; Masood, U.; Pawelke, J.; Wilkens, J. J.;
Purpose: Laser-driven proton acceleration is suggested as a cost- and space-efficient alternative for future radiation therapy centers, although the properties of these beams are fairly different compared to conventionally accelerated proton beams. The laser-driven proton beam is extremely pulsed containing a very high proton number within ultrashort bunches at low bunch repetition rates of few Hz and the energy spectrum of the protons per bunch is very broad. Moreover, these laser accelerated bunches are subject to shot-to-shot fluctuations. Therefore, the aim of this study was to investigate the feasibility of a compact gantry design for laser-driven proton therapy and to determine limitations to comply with. Methods: Based on a published gantry beam line design which can filter parabolic spectra from an exponentially decaying broad initial spectrum, a treatment planning study was performed on real patient data sets. All potential parabolic spectra were fed into a treatment planning system and numerous spot scanning proton plans were calculated. To investigate limitations in the fluence per bunch, the proton number of the initial spectrum and the beam width at patient entrance were varied. A scenario where only integer shots are delivered as well as an intensity modulation from shot to shot was studied. The resulting plans were evaluated depending on their dosimetric quality and in terms of required treatment time. In addition, the influence of random shot-to-shot fluctuations on the plan quality was analyzed. Results: The study showed that clinically relevant dose distributions can be produced with the system under investigation even with integer shots. For small target volumes receiving high doses per fraction, the initial proton number per bunch must remain between 1.4×108 and 8.3×109 to achieve acceptable delivery times as well as plan qualities. For larger target volumes and standard doses per fraction, the initial proton number is even more restricted to stay between 1.4×109 and 2.9×109. The lowest delivery time that could be reached for such a case was 16 min for a 10 Hz system. When modulating the intensity from shot to shot, the delivery time can be reduced to 6 min for this scenario. Since the shot-to-shot fluctuations are of random nature, a compensation effect can be observed, especially for higher laser shot numbers. Therefore, a fluctuation of ±30% within the proton number does not translate into a dosimetric deviation of the same size. However, for plans with short delivery times these fluctuations cannot cancel out sufficiently, even for ±10% fluctuations. Conclusions: Under the analyzed terms, it is feasible to achieve clinically relevant dose distributions with laser-driven proton beams. However, to keep the delivery times of the proton plans comparable to conventional proton plans for typical target volumes, a device is required which can modulate the bunch intensity from shot to shot. From the laser acceleration point of view, the proton number per bunch must be kept under control as well as the reproducibility of the bunches.
Keywords: laser accelerated protons; novel accelerators; proton beam therapy; treatment planning

Publ.-Id: 22386 - Permalink


The influence of the beam charge state on the analytical calculation of RBS and ERDA spectra
Baradas, N. P.; Kosmata, M.; Hanf, D.; Munnik, F.;
Analytical codes dedicated to the analysis of Ion Beam Analysis data rely on the accuracy of both the calculations and of basic data such as scattering cross sections and stopping powers. So far, the effect of the beam charge state of the incoming beam has been disregard by general purpose analytical codes such as NDF. In fact, the codes implicitly assume that the beam is always in the equilibrium charge state, by using tabulated stopping power values e.g. from SRIM, which are in principle valid for the equilibrium charge state. The dependence of the stopping power with the charge state is ignored. This assumption is reasonable in most cases, but for high resolution studies the actual change of the charge state from the beam charge state towards equilibrium as it enters and traverses the sample must be taken into account, as it influences the shape of the observed data. In this work, we present an analytical calculation, implemented in NDF, that takes this effect into account. For elastic recoil detection analysis (ERDA), the changing charge state of the recoils can also be taken into account. We apply the calculation to the analysis of experimental high depth resolution ERDA data for various oxide layers collected using a magnetic spectrometer.
Keywords: NDF; RBS; ERDA; beam charge state

Publ.-Id: 22385 - Permalink


High-temperature scintillation of alumina under 32 MeV 63Cu5+ heavy-ion irradiation
Lederer, S.; Akhmadaliev, S.; von Borany, J.; Gütlich, E.; Lieberwirth, A.; Zimmermann, J.; Ensinger, W.;
Polycrystalline alumina samples (α-Al2O3, purity: 99.8%) were irradiated with 63Cu5+63Cu5+ ions of 32 MeV kinetic energy (≈0.5 MeV/u) up to fluences of 1E14 ions/cm2 at various temperatures ranging from 295 to 973 K. Ion beam induced luminescence and emission spectra were monitored at wavelengths from 320 to 800 nm. Optical absorption measurements were performed to deduce color center formation. Results were evaluated by the Birks model to determine the material’s radiation hardness. The applicability of alumina as scintillation screens for ion beam diagnostics could be extended by enhanced temperature operation. Analysis of the emission spectra shows a complex color center formation behavior as a function of fluence and temperature.
Keywords: Alumina; Heavy-ion irradiation; Scintillation yield decrease; High-temperature scintillation; Thermal annealing

Publ.-Id: 22384 - Permalink


MHz Repetion Rate Yb:YAG and Yb:CaF2 Regenerative Picosecond Laser Amplifiers with a BBO Pockels Cell
Bergmann, F.; Siebold, M.; Loeser, M.; Röser, F.; Albach, D.; Schramm, U.;
We present picosecond Yb:YAG and Yb:CaF2 regenerative laser amplifiers with ultra-high repetition rates in the MHz range. A maximum pulse energy of 40 uJ was obtained at 20 kHz while we achieved around 1 uJ at 1 MHz. We demonstrated a pulse duration of 2.1 ps for Yb:YAG and 4.8 ps for Yb:CaF2 when seeded by a mode-locked Yb:KGW fs-oscillator without pulse stretching or phase compensation.
Keywords: high repetition rate; regenerative amplifiers; picosecond lasers; ytterbium-doped laser materials

Publ.-Id: 22383 - Permalink


Structural Characterization of Aluminum (Oxy)hydroxide Films at the Muscovite (001)−Water Interface
Lee, S. S.; Schmidt, M.; Fister, T. T.; Nagy, K. L.; Sturchio, N. C.; Fenter, P.;
The formation of Al (oxy)hydroxide on the basal surface of muscovite mica was investigated to understand how the structure of the substrate controls the nucleation and growth of secondary phases. Atomic force microscopy images showed that solid phases nucleated on the surface initially as two-dimensional islands that were ≤10 Å in height and 100–200 Å in diameter after 16–50 h of reaction in a 100 μM AlCl3 solution at pH 4.2 at room temperature. High-resolution X-ray reflectivity data indicated that these islands had an internal atomic structure that resembles a single gibbsite layer, i.e., a plane of Al ions octahedrally coordinated to oxygen or hydroxyl groups. The formation of a gibbsite layer is likely favored because of the structural similarity between its basal plane and the underlying mica surface. After 700–2000 h of reaction, thicker and continuous films formed on top of the gibbsite-layer coated mica surface. X-ray diffraction data showed that these films were composed of diaspore whose formation was predicted by thermodynamic calculations. This diaspore film grew predominantly with its (040) and (140) crystallographic directions oriented along the muscovite (001) direction, indicating that the preformed metastable gibbsite layer acted as a structural anchor for the subsequent growth of thermodynamically stable diaspore.

Publ.-Id: 22382 - Permalink


Solidification characteristics of Fe-Ni peritectic alloy thin strips under a near-rapid solidification condition
Song, C.-J.; Yang, Y.; Guo, Y.-Y.; Zhang, Y.-H.; Lu, W.; Zhai, Q.-J.;
This paper is an experimental investigation of the structure evolution and the solute distribution of 2 mm thick strips of Fe-(2.6, 4.2, 4.7, 7.9wt.%)Ni peritectic alloy under a near-rapid solidification condition, which were in the regions of d-ferrite single-phase, hypo-peritectic, hyper-peritectic and γ-austenite single-phase, respectively. The highest area ratio of equiaxed grain zone in the hyper-peritectic of Fe-4.7wt.%Ni alloy strip was observed, while other strips were mainly columnar grains. The lowest micro-segregation was obtained in the Fe7.9wt.%Ni alloy strip, while micro-segregation in the Fe-4.7wt.%Ni alloy was the highest. As opposed to the microsegregation, the macro-segregation of all the Fe-Ni strips was suppressed due to the rapid solidification rate. Finally, the structure formation mechanism of Fe-Ni alloy strips was analyzed.
Keywords: Fe-Ni peritectic alloy; Near-rapid solidification; Solidification characteristics
  • Open Access LogoChina Foundry 12(2015)3, 189-195

Publ.-Id: 22381 - Permalink


Resistance fluctuations in insulating silicon films with superconducting nanopreciptitates – superconductor-to-metal or vortex matter phase transition?
Heera, V.; Fiedler, J.; Skorupa, J.; Skorupa, W.;
Silicon films with Ga-rich nanoprecipitates are superconductors or insulators in dependence on their normal state resistance. Even in the insulating state of the film superconducting nanoprecipitates exist below the critical temperature of 7 K and determine its complex transport behavior. In this range sometimes large, random resistance jumps appear that are accompanied by little temperature changes. The resistance fluctuates between a well-defined low-resistance value and a broader band of higher resistances. Jumps to higher resistance are associated with a temperature decrease and vice versa. We present experimental results on these fluctuations and suppose a first order phase transition in the film as probable origin.
Keywords: resistance fluctuations, silicon film, superconducting nanoprecipitates, first order phase transition, vortex matter

Publ.-Id: 22380 - Permalink


Ion implantation of the 4H SiC epitaxial layers and substrates with 2MeV Se+ and 1MeV Al+ ions
Wierzchowski, W.; Turos, A.; Wieteska, K.; Stonert, A.; Ratajczak, R.; Jóźwik, P.; Wilhelm, R.; Akhamadaliev, S.; Mazur, K.; Paulmann, C.;
The implantations were performed in 4H silicon carbide homoepitaxial layers deposited on (00.1) substrates with 8° offcut, and reference 4H-SiC substrates. The 2MeV Se+ ions and 1MeV Al+ ions were implanted with four fluences subsequently increased by the factor of 4-5×. The samples were studied by means of X-ray diffraction topography, high-resolution diffractometry, specular X-ray reflectometry, and Rutherford backscattering spectrometry\channeling method. The dislocation density in the samples evaluated from the diffraction topographs did not exceed 5×103cm-2. The representative roughness values evaluated from the reflectometric measurements was 2.3±0.1nm for the substrates and less than 1.4±0.1nm for the epitaxial layers. A significantly higher damage level in the case of 2MeV Se+ ions in comparison with 1MeV Al+ ion and a linear increase of the strain with the fluence was indicated, but the highest doses of selenium ions caused the amorphization of the implanted layer. It was also possible to obtain a good fitting of the theoretical and experimental diffraction curves approximating the strain profiles by the distribution of the point defects calculated with the SRIM 2008 code. It was confirmed that the maximum coming from surface damages observed in channeling spectra of the virgin substrate wafers was significantly higher than in the case of epitaxial layers.

Publ.-Id: 22379 - Permalink


Effect of pressure and high magnetic field on phase transitions and magnetic properties of Ni1.92Mn1.56Sn0.52 and Ni2MnSn Heusler compounds
Kastil, J.; Kamarad, J.; Isnard, O.; Skourski, Y.; Misek, M.; Arnold, Z.;
Complex study of magnetic, magnetocaloric and structural properties of the Ni2MnSn and Ni1.92Mn1.56Sn0.52 compounds was performed. The stoichiometric single-crystal of Ni2MnSn was prepared by Czochralski method. The remarkable pressure effect on the martensitic magnetization and the martensite-austenite transition temperature TM–A was observed in the Ni1.92Mn1.56Sn0.52 compound. The coefficient dTM–A/dp reached value of 18 K/GPa. The already low value of martensite magnetization of Ni1.92Mn1.56Sn0.52 was further substantially decreased by external pressure, in contrast with pressure almost insensitive magnetization of the stoichiometric Ni2MnSn single-crystal. The pulse magnetic field of 58 T invoked the structural transition at temperature 180 K that is of about 100 K below TM–A of Ni1.92Mn1.56Sn0.52 at zero field. An anomalous increase of resistivity of the compound has been observed at temperature range below TM–A, however, it does not copy the sharp change of magnetization at TM–A. The obtained results indicate the important role of interatomic distances on the magnetic ordering and electronic structure of the studied Heusler alloys and are in agreement with the Jahn-Teller mechanism of the martensitic transition in these compounds.

Publ.-Id: 22378 - Permalink


ISPT 7 - Book of Proceedings
Bieberle, A.; Schlessiger, H.; Hampel, U.; (Editors)
Process tomography aims at non-invasive dynamic imaging and measurement of industrial processes and multiphase flows. In recent years different modalities, based on e.g. electrical measurements, X-ray, gamma ray or neutron transmission, positron emission, ultrasound and visible light, have been developed into technical solutions and stimulated the work of scientists and engineers in many application fields, such as chemical and process engineering, oil and gas production, power engineering, fundamental research on flow mechanics as well as CFD code development.

The symposium provides a platform for scientists and engineers to introduce and discuss recent advances in process tomography and its application in industrial process analysis and control, multiphase flow measurement and dynamic non-destructive testing. It continues a series of preceding events in Jurata 2000, Wroclaw 2002, Lodz 2004, Warzaw 2006, Zakopane 2008, and Cape Town 2011.
Keywords: Process tomography systems and Hardware | Inverse problems and reconstruction methods | Image processing and data visualization | Multi-modality and multi-sensor approaches | Mathematical modeling | Multiphase flow studies | Data generation for computational fluid Dynamics | Industrial application | Dynamic non-destructive testing
  • Book (Editorship)
    Dresden: HZDR, 2015

Publ.-Id: 22377 - Permalink


ISPT7 - Book of Abstracts
Bieberle, A.; Schlessiger, H.; Hampel, U.; (Editors)
Process tomography aims at non-invasive dynamic imaging and measurement of industrial processes and multiphase flows. In recent years different modalities, based on e.g. electrical measurements, X-ray, gamma ray or neutron transmission, positron emission, ultrasound and visible light, have been developed into technical solutions and stimulated the work of scientists and engineers in many application fields, such as chemical and process engineering, oil and gas production, power engineering, fundamental research on flow mechanics as well as CFD code development.

The symposium provides a platform for scientists and engineers to introduce and discuss recent advances in process tomography and its application in industrial process analysis and control, multiphase flow measurement and dynamic non-destructive testing. It continues a series of preceding events in Jurata 2000, Wroclaw 2002, Lodz 2004, Warzaw 2006, Zakopane 2008, and Cape Town 2011.
Keywords: Process tomography systems and Hardware | Inverse problems and reconstruction methods | Image processing and data visualization | Multi-modality and multi-sensor approaches | Mathematical modeling | Multiphase flow studies | Data generation for computational fluid Dynamics | Industrial application | Dynamic non-destructive testing
  • Book (Editorship)
    Dresden: HZDR, 2015

Publ.-Id: 22376 - Permalink


Investigation into the Formation of Nanoparticles of Tetravalent Neptunium in Slightly Alkaline Aqueous Solution
Husar, R.;
Considering the worldwide growing discharge of minor actinides and the current need for geological disposal facilities for radioactive waste, this work provides a contribution to the safety case concerning Np transport if it would be released from deep repository sites and moving from alkaline cement conditions (near-field) to more neutral environmental conditions (far-field). The reducing conditions in a nuclear waste repository render neptunium tetravalent, which is assumed to be immobile in aqueous environment due to the low solubility solution of Np(IV). For tetravalent actinide nuclides, the most significant transport should occur via colloidal particles. This work demonstrates the formation of intrinsic neptunium dioxide nanocrystals and amorphous Np(IV) silica colloids under environmentally relevant conditions.

The dissociation of the initial soluble Np(IV) complex (i.e. [Np(IV)(CO3)5]6-) induces the intrinsic formation of nanocrystalline NpO2 in the solution phase. The resulting irregularly shaped nanocrystals with an average size of 4 nm exhibit a face-centered cubic (fcc), fluorite-type structure (space group ). The NCs tend to agglomerate under ambient conditions due to the weakly charged hydrodynamic surface at neutral pH (zetapotential ~0 mV). The formation of micron-sized agglomerates, composed of nanocrystals of 2-5 nm in size, and the subsequent precipitation cause immobilization of the major amount of Np(IV) in the Np carbonate system. Agglomeration of NpO2 nanocrystals in dependence on time was indicated by PCS and UV-vis absorption spectroscopy with the changes of baseline characteristics and absorption maximum at 742 nm.

Hitherto, unknown polynuclear species as intermediate species of NpO2 nanocrystal formation were isolated from solution and observed by HR-TEM. These polynuclear Np species appear as dimers, trimers and hexanuclear compounds in analogy with those reported for other actinides.

Intrinsic formation of NpO2 (fcc) nanocrystals under ambient environmental conditions is prevented by admixing silicic acid: amorphous Np(IV) silica colloids are formed when silicate is present in carbonate solution.

Herein, the initial molar ratio of Si to Np in solution lead to the formation of Np(IV) silica particles of different composition and size where Si content determines the structure and stability of resulting colloids. Implications for different electronic structures of Np(IV) in dependence on Si content in the solid phase are given by the shift of the absorption maximum at 742 nm characteristic for Np(IV) colloids, silica excess of 5 times the magnitude of Si to Np reveal a redshift up to 6 nm in the colloidal UV-vis spectrum. Precipitation of Np(IV) particles in the ternary system results in a different coordination sphere of Np(IV) compared to the binary system, and the incorporation of Si into internal structure of Np(IV) silica colloids in coffinite-like structure is confirmed by EXAFS. TEM confirms different kinds of particle morphologies in dependence on the silica content. Silica-poor systems reveal porous particles in the micron-range which consist of irregular cross-linked hydrolyzed Np(IV) silica compartments with pores <15 nm.

In contrast, long-term stabilized and silica-enriched systems are characterized by isolated particles with an average particle size of 45 nm. Agglomerates of such isolated Np(IV) silica particles appear as consolidated amorphous solids with a densely closed surface and exhibit no internal fractures. The latter mentioned morphology of Np(IV) silica particles might facilitate the migration behavior of Np(IV) in a stabilized colloidal form under environmental conditions. The silica-enriched particles with densely closed surface are long-term stabilized as colloidal dispersion (>1 year) due to repulsion effects caused by significant surface charge. Particles synthesized from Si/Np = 9/1 carry exclusively negative surface charge in nearly the whole pH range from pH 3 to pH 10 with zetapotential = (-) 5 to (-) 30 mV. The zeta potentials of all particle systems containing silica are significantly shifted to more negative values below pH 7 where the isoelectrical point shifts from pH = 8.0 to 2.6 effecting negative charge under ambient conditions which supports electrostatic stabilization of Np(IV) particles. Particle surface charge at the slipping plane, particle size and shape necessarily depend on the initial magnitude of Si content in solution during particle formation. Particular changes of the morphology and internal structure of different Np(IV) silica colloids by aging are indicated by TEM and XPS. The composition and the crystallinity state of the initially formed amorphous phases partially changed into well-ordered nanocrystalline units characterized with fcc structure.

The presence of silicate under conditions expected in a nuclear waste repository significantly influences the solubility of Np(IV) and provoke the stabilization of waterborne Np(IV) up to concentrations of 10-3 M, exceeding Np´s solubility limit by a factor of up 10.000.

Neptunium and silicate significantly interact with each other, and thereby changing their individual hydrolysis and polymerization behavior. Silicate prevents the intrinsic formation of NpO2 NCs in fcc-structure, and at the same time, Np(IV) prevents the polymerization of silicate. Both processes result in the formation of Np(IV) silica colloids which possibly influence the migration behavior and fate of Np in the waste repositories and surrounding environments. For tetravalent actinides in general, the most significant transport in the environment would occur by colloidal particles. Therefore, Np(IV) silica colloids could have a significant implication in the migration of Np, the important minor actinide in the waste repositories, via colloidal transport.
Keywords: Actinides, neptunium, nanoparticles, nanocrystals, environmental chemistry
  • Doctoral thesis
    TU Dresden, 2015
    Mentor: Prof. Dr. Thorsten Stumpf
    113 Seiten

Publ.-Id: 22375 - Permalink


Remote sensing based improvement of the geological map of the Neoproterozoic Ras Gharib segment in the Eastern Desert (NE-Egypt) using texture features
Jakob, S.; Bühler, B.; Gloaguen, R.; Breitkreuz, C.; Eliwa, H. A.; El Gameel, K.;
Geological mapping in the Eastern Desert is impeded by difficult accessibility. We improve the existing geological maps by including texture features in a classification scheme of ASTER and Landsat 8 data. We tested the improvement of support vector machine classification using band ratios, principal component analysis (PCA) and texture analysis in the Ras Gharib segment (NE Egypt). A very high classification overall accuracy of 99.85% was achieved. We demonstrate that the input of textures provide valuable additional data for lithological mapping. With the gained information, the existing geological map of the study area was improved distinctly in precision and resolution, but also in terms of correction of yet wrong or inaccurate locations and of lithological unit extents.
Keywords: Remote sensing; North Eastern Desert of Egypt; Texture analysis; Lithological mapping; ASTER and Landsat 8 image analysis; Support vector machine classification

Publ.-Id: 22374 - Permalink


Actinide oxidation state and O/M ratio in hypostoichiometric uranium-plutonium-americium U0.750Pu0.246Am0.004O2-x mixed oxides
Vauchy, R.; Belin, R. C.; Robisson, A.-C.; Lebreton, F.; Scheinost, A. C.; Aufore, L.; Martin, P. M.;
Innovative americium-bearing uranium-plutonium mixed oxides U1-yPuyO2-x are envisioned as nuclear fuel for next generation Sodium-cooled Fast neutron Reactors (SFRs). The Oxygen-to-Metal (O/M) ratio, directly related to the oxidation state of cations, affects many of the fuel properties. Thus, a thorough knowledge of its variation with the sintering conditions is essential. The aim of this work is to follow the oxidation state of uranium, plutonium and americium, and so the O/M ratio, in U0.750Pu0.246Am0.004O2-x samples sintered for 4 h at 2023 K in various Ar + 5% H2 + z vpm H2O (z = ~15, ~90 and ~200) gas mixtures. The O/M ratios were determined by gravimetry, XAS and XRD and evidenced a partial oxidation of the samples at room temperature. Finally, by comparing XANES and EXAFS results to that of a previous study, we demonstrate that the presence of uranium does not influence the interactions between americium and plutonium and that the differences in the O/M ratio between the investigated conditions is controlled by the reduction of plutonium. We also discuss the role of the homogeneity of cation distribution on the mechanisms involved into the reduction process.
Keywords: Nuclear fuel Sodium-cooled fast-neutron reactors actinide oxide Americium Plutonium Uranium EXAFS XANES

Publ.-Id: 22373 - Permalink


Interstellar 60Fe on the surface of the Moon
Fimiani, L.; Cook, D. L.; Faestermann, T.; Gómez-Guzmán, J. M.; Hain, K.; Herzog, G.; Knie, K.; Korschinek, G.; Ludwig, P.; Park, J.; Reedy, R. C.; Rugel, G.;
A dying massive star ends in a supernova explosion ejecting a large fraction of its mass into the interstellar medium. If this happens nearby, part of the ejecta might end on Solar System bodies and, in fact, radioactive 60Fe has been detected on the Pacific ocean floor in about 2 Ma old layers. Here, we report on the detection of this isotope also in lunar samples, originating presumably from the same event. The concentration of the cosmic ray produced isotope 53Mn, measured in the same samples, proves the supernova origin of the 60Fe. From the 60Fe concentrations found we deduce a reliable value for the local interstellar fluence in the range of 1 × 108 at/cm2. Thus, we obtain constraints on the recent and nearby supernova(e).
Keywords: AMS, Fe-60, Moon, Supernova

Publ.-Id: 22371 - Permalink


Simulation of the Secondary Radiation Field at Proton Therapy Facilities Modelling of the IBA Universal Nozzle at the University Hospital Carl Gustav Carus with the TOPAS Software
Lutz, B.; Enghardt, W.; Swanson, R.; Fiedler, F.;
no abstract available
  • Lecture (Conference)
    PPRIG Proton Therapy Physics Workshop, 01.-02.10.2015, London, United Kingdom

Publ.-Id: 22370 - Permalink


Modelling of turbulence modulation in bubbly flows with the aid of direct numerical simulation
Ma, T.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.;
a new BIT model dependent on bubble Reynolds number is proposed and validated in a more complex bi-dispersed bubbly channel flow.
Keywords: Direct Numerical Simulations, RANS
  • Lecture (Conference)
    9th International Conference on Multiphase Flow - ICMF 2016, 22.-27.05.2016, Firenze, Italy

Publ.-Id: 22369 - Permalink


Large eddy simulations of the gas–liquid flow in a rectangular bubble column
Ma, T.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.;
The paper presents Euler-Euler Large Eddy Simulations of dispersed bubbly flow in a rectangular bubble column at a low Reynolds number. The physical models describing the momentum exchange between the phases including drag, lift and wall force were chosen according to previous experiences of the authors. The emphasis of the study is the analysis of bubbly flows concerning the investigation of the influence of the bubble-induced turbulence model. It is found that the presented modeling combination provides fairly good agreement with experimental data for the mean flow. The impact of the modeling on the liquid velocity fluctuations is investigated and the energy spectrum obtained from the resolved velocity is discussed.
Keywords: LES, bubble column, energy spectrum

Publ.-Id: 22368 - Permalink


Large Eddy Simulation of a rectangular bubble column
Ma, T.; Lucas, D.;
Prediction of mean flow and turbulent parameter with Euler-Euler-LES
Keywords: Two-fluid model; LES
  • Poster
    Dynamics of bubbly flow, 08.-12.06.2015, Udine, Italy

Publ.-Id: 22367 - Permalink


lll-V integration in Si and Ge by ion beam synthesis and flash lamp annealing
Wutzler, R.; Rebohle, L.; Prucnal, S.; Hübner, R.; Skorupa, M.; Helm, W.;
In order to follow Moore’s law on the path to smaller and smaller devices, more and more materials have to be integrated into Si technology. Current research activities focus on the integration of Ge and binary III-V compounds into Si, as these materials promise a further transistor performance increase due to their high hole and electron mobility, respectively. In addition, the direct band gap of most of the compound semiconductors is of great interest for optoelectronic applications. However, the integration into Si generates a lot of challenges regarding both the quality of the III-V material itself and the quality of its interfaces. At present, most integration technologies rely on molecular beam epitaxy or similar growth mechanisms. Recently, we showed that III-V nanocrystals (NC) in Si can also be fabricated by sequential ion implantation followed by flash lamp annealing (FLA) [1]. Moreover, the use of a patterned implantation mask allows the fabrication of III-V NCs in a Si nanowire at defined positions [2].

In this presentation we extend our previous investigations to the case of Ge. In order to get a better understanding of the NC formation process, InAs and GaAs NCs were fabricated in Si and Ge by ion implantation and FLA, and their structural and electric properties were compared to each other. It will be shown that the recrystallization of the near-surface layer of amorphous substrate material (Si or Ge), together with the NC formation, is rather governed by liquid phase than by solid phase epitaxy. This scenario is supported by the evaluation of the corresponding segregation and diffusion coefficients, the temperature profile during FLA and the final size distribution of the NCs.

[1] S. Prucnal, S. Facsko, C. Baumgart, H. Schmidt, M.O. Liedke, L. Rebohle, A. Shalimov, H. Reuther, A. Kanjilal, A. Mucklich, M. Helm, J. Zuk, and W. Skorupa, Nano Lett. 11, Issue 7, 2814-2818 (2011)
[2] S. Prucnal, M. Glaser, A. Lugstein, E. Bertagnolli, M. Stöger-Pollach, S. Zhou, M. Helm, D. Reichel, L. Rebohle, M. Turek, J. Zuk, and W. Skorupa, Nano Res. 7, 1769 (2014)
Keywords: III-V integration, ion implantation, flash lamp annealing, silicon, germanium
  • Lecture (Conference)
    Gettering and Defect Engineering in Semiconductor Technology (GADEST) 2015, 20.-25.09.2015, Bad Staffelstein, Deutschland

Publ.-Id: 22366 - Permalink


High-temperature photon-noise-limited performance terahertz quantum-well photodetectors
Jia, J. Y.; Wang, T. M.; Zhang, Y. H.; Shen, W. Z.; Schneider, H.;
In this paper, we propose using a terahertz quantumwell photodetector (THz QWP) in combination with a terahertz source to realize a detection system with photon-noise limited performance (PLIP) at high temperatures. Systematical investigations on the high-temperature performances of THz QWPs, including required signal power density for PLIP, detectivity, and the signal-to-noise ratio, have been carried out by elaborating their dark current mechanism and photocurrent response both experimentally and theoretically. We also present the optimal doping concentration of THz QWPs designed for different peak wavelengths and the resulting optimum performance regarding the above three key parameters. Numerical results show that optimal designed QWP with peak response frequency of 5.5 THz is expected to achieve PLIP at 77 K at signal power density at 819 W/cm and above. This work gives a precise description of PLIP performance of THz QWPs and will open ways for new applications for high-temperature detection in the THz regime.
Keywords: High temperature, detectivity, photon-noise limited, quantum-well photodetector (QWP), Terahertz (THz)

Publ.-Id: 22365 - Permalink


Nanoscale femtosecond imaging of transient hot solid density plasmas with elemental and charge state sensitivity using resonant coherent diffraction
Kluge, T.; Bussmann, M.; Chung, H.-K.; Gutt, C.; Huang, L. G.; Zacharias, M.; Schramm, U.; Cowan, T. E.;
Here we propose to exploit the low energy bandwidth, small wavelength and penetration power of ultrashort pulses from XFELs for resonant Small Angle Scattering (SAXS) on plasma structures in laser excited plasmas. Small angle scattering allows to detect nanoscale density fluctuations in forward scattering direction. Typically, the SAXS signal from laser excited plasmas is expected to be dominated by the free electron distribution. We propose that the ionic scattering signal becomes visible when the X-ray energy is in resonance with an electron transition between two bound states (Resonant coherent X-ray diffraction, RCXD). In this case the scattering cross-section dramatically increases so that the signal of X-ray scattering from ions silhouettes against the free electron scattering background which allows to measure the opacity and derived quantities with high spatial and temporal resolution, being fundamentally limited only by the X-ray wavelength and timing. Deriving quantities such as ion spatial distribution, charge state distribution and plasma temperature with such high spatial and temporal resolution will make a vast number of processes in shortpulse laser-solid interaction accessible for direct experimental observation e.g. hole-boring and shock propagation, filamentation and instability dynamics, electron transport, heating and ultrafast ionization dynamics.

Publ.-Id: 22364 - Permalink


Tunneling breakdown of a strongly correlated insulating state in VO2 induced by intense multiterahertz excitation
Mayer, B.; Schmidt, C.; Grupp, A.; Bühler, J.; Oelmann, J.; Marvel, R. E.; Haglund, R. F.; Oka, T.; Brida, D.; Leitenstorfer, A.; Pashkin, A.;
We directly trace the near- and midinfrared transmission change of a VO2 thin film during an ultrafast insulator-to-metal transition triggered by high-field multiterahertz transients. Nonthermal switching into a metastable metallic state is governed solely by the amplitude of the applied terahertz field. In contrast to resonant excitation below the threshold fluence, no signatures of excitonic self-trapping are observed. Our findings are consistent with the generation of spatially separated charge pairs and a cooperative transition into a delocalized metallic state by THz field-induced tunneling. The tunneling process is a condensed-matter analog of the Schwinger effect in nonlinear quantum electrodynamics. We find good agreement with the pair production formula by replacing the Compton wavelength with an electronic correlation length of 2.1 A° .

Publ.-Id: 22363 - Permalink


Probing ultrafast, transient plasma dynamics at solid density with X-ray lasers
Bussmann, M.; Kluge, T.; Huang, L.; Cowan, T. E.; Chung, H.-K.;
Combining high power lasers with x-ray lasers provides unique opportunities to study ultrafast, transient processes in solid-density plasmas. We present simulation studies of probing ionization dynamics, electron transport and heating of solid-density targets driven by high power lasers with state-of-the-art X-ray lasers. We show that a precise understanding of the underlying atomic physics processes is necessary and needs to be implemented in kinetic simulations of the laser plasma interaction. Our results show that albeit the complexity of atomic processes happening during the laser plasma interaction, the very same processes can be exploited to understand the temporal evolution of the plasma.
  • Lecture (Conference)
    Radiative Properties of Hot Dense Matter, 29.09.-03.10.2014, Wien, Österreich

Publ.-Id: 22362 - Permalink


Bispecific antibody releasing-mesenchymal stromal cell machinery for retargeting T cells towards acute myeloid leukemia blasts
Aliperta, R.; Cartellieri, M.; Feldmann, A.; Arndt, C.; Koristka, S.; Michalk, I.; von Bonin, M.; Ehninger, A.; Bachmann, J.; Ehninger, G.; Bornhäuser, M.; Bachmann, M. P.;
Bispecific antibodies (bsAbs) engaging T cells are emerging as a promising immunotherapeutic tool for the treatment of hematologic malignancies. Because their low molecular mass, bsAbs have short half-lives. To achieve clinical responses, they have to be infused into patients continously, for a long period of time. As a valid alternative we examined the use of mesenchymal stromal cells (MSCs) as autonomous cellular machines for the constant production of a recently described, fully humanized anti-CD33-anti-CD3 bsAb, which is capable of redirecting human T cells against CD33-expressing leukemic cells. The immortalized human MSC line SCP-1 was genetically modified into expressing bsAb at sufficient amounts to redirect T cells efficiently against CD33 presenting target cells, both in vitro and in an immunodeficient mouse model. Moreover, T cells of patients suffering from acute myeloid leukemia (AML) in blast crisis eliminated autologous leukemic cells in the presence of the bsAb secreting MSCs over time. The immune response against AML cells could be enhanced further by providing T cells an additional co-stimulus via the
CD137-CD137 ligand axis through CD137L expression on MSCs. This study demonstrates that MSCs have the potential to be used as cellular production machines for bsAb-based tumor immunotherapy in the future.

Publ.-Id: 22361 - Permalink


Surface Modificationwith heavy Mon- and Polyatomic Ions
Bischoff, L.; Böttger, R.; Heinig, K.-H.;
Self-organization of nanopatterns on solid surfaces by ion irradiation is a well-established technique to create regular and ordered structures like ripples or dots. Characteristics of patterns can be controlled selecting different ion species as well as by varying their energy, fluence, incidence angle or the sample temperature during irradiation. To date, mostly monatomic ions with masses between 40 (Ar) and 131 amu (Xe) were used for self-organized nanopatterning or contrary for surface smoothing. A comprehensive review is given.Here, self-organization of periodic patterns by bombardment with polyatomic/cluster ion species with masses of up to ~835 amu is studied – a regime not explored so far. Each impact of a very heavy polyatomic projectile deposits within femtoseconds an extremely high energy density into a local, near-surface volume. The achieved energy density exceeds that of irradiation with monatomic ions of medium mass considerably, it is of the order of femtosecond laser irradiation or swift heavy ion bombardment. Therefore, compared to former ion-induced pattern formation, different pattern based on different mechanisms can be expected.A new quality of pattern on Ge surfaces are obtained by Bi2, Bi3, Bi4 and Au2, Au3 ion irradiation. Polyatomic ions are provided by liquid metal (alloy) ion sources (LM(A)IS) in a mass-separating 30 kV focused ion beam (FIB) system. Results are compared to monatomic Bi and Au ion irradiation using otherwise equivalent irradiation parameters. For this, SEM and AFM were applied to investigate the pattern formation in dependence on ion species, energy per projectile atom, fluence, incidence angle and target temperature. Finally, a consistent, qualitative model for the surface evolution relating on energy density deposition sufficient for localized, transient nano melt pool formation is discussed.
Keywords: Self-organization, ripples, dots, mon- and polyatomic ions, FIB
  • Invited lecture (Conferences)
    The 22nd International Conference on Ion-Surface Interactions, ISI - 2015, 20.-24.08.2015, Moscow, Russia

Publ.-Id: 22360 - Permalink


Denudation rates across the Pamir based on 10Be concentrations in fluvial sediments: dominance of topographic over climatic factors
Fuchs, M. C.; Gloaguen, R.; Merchel, S.; Pohl, E.; Sulaymonova, V. A.; Andermann, C.; Rugel, G.;
A clear understanding of erosion processes is fundamental in order to comprehend the evolution of actively deforming mountain ranges. However, the relative contributions of tectonic and climatic factors and their feedbacks remain highly debated. In order to contribute to the debate, we quantify basin-wide denudation rates from cosmogenic 10Be concentrations in modern river sediments in the Pamir. This mountain range is a unique natural laboratory because the ongoing India–Eurasia collision sustains high deformation rates and, on account of its position at the transition between Westerlies and monsoon, a strong regional climatic variability arises. Sample acquisition and preparation for accelerator mass spectrometry measurements were challenging due to difficult field accessibility, low quartz and high feldspar concentrations and crystal coating. Six samples along the main draining river, the Panj, and five samples within the major, east–west elongated tributary basins allow us to quantify basin-wide denudation rates for the first time in this orogen. An average denudation rate of 0.64 mm yr-1 reveals a rapid evolution of the entire Pamir. Denudation rates of tributary sub-basins highlight the strong contrast between the Pamir Plateau (0.05 to 0.16 mm yr-1) and its margins (0.54 to 1.45 mm -1). The intensity of denudation is primarily correlated with geometric properties of the surface, such as slope steepness (0.75 quartiles; R2 of 0.81), and to a lesser extent to climatic factors such as precipitation. We thus argue that either tectonic uplift or base-level lowering are the main contributors to denudation processes. Multiple linear regression analysis (best R2of 0.93) suggests that precipitation may act as a limiting factor to denudation.
The highest denudation rates coincide with areas of the northwestern Pamir margin that receive precipitation predominantly from the Westerlies during winter. There, the concentrated discharge during spring and early summer may sustain the pronounced denudation and allow the rapid sediment transport out of the basins. Low slope angles and dry conditions hamper the sediment flux on the plateau and, consequently, denudation. The magnitude of denudation in the Pamir is similar to rates determined in the southern Himalaya despite very different climatic and tectonic conditions. The discrepancy between rates of basin-wide denudation and the fluvial incision that is up to 10 times higher evidences a transient landscape in the Pamir. This underpins the hypothesis that river captures may have caused the strong base-level lowering that drives the enhanced incision of the Panj and its main tributaries.
Keywords: erosion, geomorphology, accelerator mass spectrometry, AMS, cosmogenic nuclide

Publ.-Id: 22359 - Permalink


Quantitative analysis of sulphides and sulphates by WD-XRF: Capability and constraints
Uhlig, S.; Möckel, R.; Pleßow, A.;
Geochemical characterisations are implemented to get information about the composition of unknown samples but some elements occur in different oxidation states that can not be determined by established techniques without special efforts like sample dissolution or extra equipment. One example is sulphur with its most common species, sulphide and sulphate. Different approaches, based on WD-XRF routine measurements, provide simple alternatives for a quantitative speciation. A set of 100 synthetic samples has been prepared in different concentrations and were measured by a Panalytical Axios minerals spectrometer. The first approach is based on the shift of the Kα1,2 doublet. Sulphide peaks are located at 2309 eV, sulphates at 2310 eV and mixtures can be found on a linear regression of energy and sulphide amount. As opposed to sulphides, sulphates show sulphur Kβ’ satellite peaks. Another procedure is based on this difference because the intensity of S Kβ’ increases with increasing sulphate content. The amount of sulphide can be calculated by a linear regression based the quotient Kβ’/Kβ of the sulphur peak height or area. However, this method has two limitations: low sulphide concentrations (<10 g/kg sulphide in the sample) and interferences with lead (Pb Mβ peak). The WD-XRF based strategies provide simple and reliable methodologies for a quantitative speciation of sulphides and sulphates whereupon the matrix influence can be neglected. These approaches have been implemented in investigations of ore-containing samples from mining dumps in Saxony/Germany. These procedures can be applied to give previously not measurable data on solid samples containing different sulphur species.
Keywords: Sulphur speciation, Satellite lines, Fluorescence peak shift

Publ.-Id: 22358 - Permalink


Particle acceleration with the Dresden PW lasers
Schramm, U.;
Invited review talk on particle acceleration and PW laser development in Dresden
  • Invited lecture (Conferences)
    SPIE optics and optoelectronics, 13.-16.04.2015, Prague, Czech Republic

Publ.-Id: 22357 - Permalink


Single-pulse picking at kHz repetition rates using a Ge plasma switch at the free-electron laser FELBE
Schmidt, J.; Winnerl, S.; Seidel, W.; Bauer, C.; Gensch, M.; Schneider, H.; Helm, M.;
We demonstrate a system for picking of mid-infrared and terahertz (THz) radiation pulses from the free-electron laser (FEL) FELBE operating at a repetition rate of 13 MHz. Single pulses are reflected by a dense electron-hole plasma in a Ge slab that is photoexcited by amplified near-infrared (NIR) laser systems operating at repetition rates of 1 kHz and 100 kHz, respectively. The peak intensity of picked pulses is up to 400 times larger than the peak intensity of residual pulses. The required NIR fluence for picking pulses at wavelengths in the range from 5 μm to 30μm is discussed. In addition, we show that the reflectivity of the plasma decays on a time scale from 100 ps to 1 ns dependent on the wavelengths of the FEL and the NIR laser. The plasma switch enables experiments with the FEL that require high peak power but lower average power. Furthermore, the system is well suited to investigate processes with decay times in the μs to ms regime, i.e., much longer than the 77 ns long pulse repetition period of FELBE.
Keywords: Pulse picking, plasma switch

Publ.-Id: 22356 - Permalink


Erbium-ion implantation into various crystallographic cuts of Al2O3
Nekvindova, P.; Mackova, A.; Malinsky, P.; Cajzl, J.; Svecova, B.; Oswald, J.; Wilhelm, R. A.;
This paper reports on the importance of crystallographic cuts with a different orientation on the luminescent properties and structural changes of Al2O3 implanted with Er+ ions at 190 keV and with a fluence of 1.0 × 1016 cm−2. Post-implantation annealing at 1000 °C in oxygen atmosphere was also done. The chemical compositions and erbium concentration-depth profiles of implanted layers were studied by Rutherford Backscattering Spectrometry (RBS) and compared to SRIM simulations. The same value of the maximum erbium concentration (up to 2 at.%) was observed at a depth of about 40 nm for all crystallographic cuts. The structural properties of the prepared layers were characterised by RBS/channelling. The relative amount of disordered atoms of 70–80% was observed in the prepared implanted layers and discussed for various cuts. It has been found that erbium is positioned randomly in the Al2O3 crystalline matrix, and no preferential positions appeared even after the annealing procedure. Erbium luminescence properties were measured in the wavelength range of 1440–1650 nm for all samples. As-implanted Al2O3 samples had a significant luminescence band at 1530 nm. The best luminescence was repeatedly observed in the 〈0 0 0 1〉 cut of Al2O3. The annealing procedure significantly improved the luminescent properties.
Keywords: Sapphire; Erbium; Ion implantation; Luminescence

Publ.-Id: 22355 - Permalink


Magnetoelectricity of the spin-ice compound Ho2Ti2O7
Herrmannsdörfer, T.; Schönemann, R.; Green, E.; Opherden, L.; Skrotzki, R.; Wang, Z.; Kaneko, H.; Suzuki, H.; Wosnitza, J.;
  • Lecture (Conference)
    ICM2015 - 20th International Conference on Magnetism, 05.-10.07.2015, Barcelona, Espana

Publ.-Id: 22354 - Permalink


Recent near-Earth supernovae probed by global deposition of interstellar radioactive 60Fe
Wallner, A.; Feige, J.; Kinoshita, N.; Paul, M.; Fifield, L. K.; Golser, R.; Honda, M.; Linnemann, U.; Matsuzaki, H.; Merchel, S.; Rugel, G.; Tims, S.; Steier, P.; Yamagata, T.; Winkler, S. R.;
The rate of supernovae (SNe) in our local galactic neighborhood within a distance of ~100 parsec from Earth (1 parsec (pc)=3.26 light years) is estimated at 1 SN every 2-4 million years (Myr), based on the total SN-rate in the Milky Way (2.0±0.7 per century). Recent massive-star and SN activity in Earth’s vicinity may be evidenced by traces of radionuclides with half-lives t1/2 ≤ 100 Myr, if trapped in interstellar dust grains that penetrate the Solar System (SS). One such radionuclide is 60Fe (t1/2=2.6 Myr) which is ejected in supernova explosions and winds from massive stars. Here we report that the 60Fe signal observed previously in deep-sea crusts, is global, extended in time and of interstellar origin from multiple events. Deep-sea archives from all major oceans were analyzed for 60Fe deposition via accretion of interstellar dust particles. Our results, based on 60Fe atom-counting at state-of-the-art sensitivity, reveal 60Fe interstellar influxes onto Earth 1.7–3.2 Myr and 6.5–8.7 Myr ago. The measured signal implies that a few percent of fresh 60Fe was captured in dust and deposited on Earth. Our findings indicate multiple supernova and massive-star events during the last ~10 Myr at nearby distances ≤100 pc.
Keywords: accelerator mass spectrometry, AMS, supernova, cosmogenic radionuclide

Publ.-Id: 22353 - Permalink


Separation of Diastereomeric Flubatine Metabolites using Sciex’ SelexION™ Technology
Fabritz, S.; Smits, R.; Ludwig, F.-A.;
Es ist kein Abstract vorhanden.

Publ.-Id: 22352 - Permalink


Synthese, 18F-Markierung und radiopharmakologische Charakterisierung eines 30mer-Peptids als potentieller Radiotracer für die molekulare Bildgebung von Claudin-4 mittels PET
Bader, M.; Kuchar, M.; Wodtke, R.; Lenk, J.; Bergmann, R.; Pufe, J.; Haase-Kohn, C.; Steinbach, J.; Pietzsch, J.; Löser, R.;
Der Zelloberflächenrezeptor Claudin-4 (Cld-4) wird in verschiedenen Tumoren überexprimiert und stellt daher ein potentielles Target sowohl für die Diagnose als auch die Therapie von Tumoren epithelialen Ursprungs dar. Dies lässt die Entwicklung von Sonden, die das in vivo-Imaging dieses Proteins ermöglichen, attraktiv erscheinen. Im Rahmen dieser Arbeit sollte untersucht werden, inwiefern sich das C-terminale Fragment der C-terminalen Domäne des Clostridium perfringens-Enterotoxins cCPE(290-319) für die PET-Bildgebung von Cld-4 eignet. Dieses Fragment besteht aus 30 Aminsäuren und weist die Sequenz SLDAGQYVLVMKANSSYSGNYPYSILFQKF auf, was den Positionen 290-319 im cCPE entspricht.
Die Synthese des cCPE(290-319) und davon abgeleiteter Analoga, insbesondere N-terminal fluorbenzoylierter und FITC-konjugierter Derivate sowie Varianten, in denen kritische Aminosäuren (Tyr 306 und Leu 315) ausgetauscht wurden, sollte durch Festphasenpeptidsynthese erfolgen. Unter verschiedenen erprobten Strategien erwies sich die sequentielle Festphasenpeptidsynthese unter Einsatz von drei Pseudoprolin-Dipeptiden am effizientesten, um cCPE(290-319) und dessen Derivate zugänglich zu machen. Die Affinität der erhaltenen Peptide zu einem artifiziellen Proteinkonstrukt bestehend aus beiden extrazellulären Domänen des Cld-4 wurde mit Hilfe der Oberflächen-Plasmonenresonanz (SPR) untersucht, wodurch ein Kd-Wert von 1.4 µM für das N-terminal 4-fluorbenzoylierte cCPE(290-319) ermittelt wurde. Die Markierung von CPE(290-319) mit Fluor-18 erfolgte an fester Phase mit Hilfe von N-Succinimidyl-4-[18F]fluorbenzoat ([18F]SFB) und 4-[18F]Fluorobenzoylchlorid. Dabei wurden die besten Resultate erzielt, wenn harzgebundenes cCPE(290-319) mit N-terminalem 6-Aminohexansäure-Spacer mit [18F]SFB zur Reaktion gebracht wurde. Die Inkubation des auf diese Weise erhaltenen Radiotracers mit Zellüberstand und Blutplasma ließ keine Anzeichen von Instabilität in diesen physiologischen Medien erkennen. Die Zellbindung von 18F-markiertem cCPE(290-319) wurde mit den Tumorzelllinien HT29, A375 und A431 untersucht. Dabei konnte die zeitabhängige Bindung des radiomarkierten Peptids an Cld-4-positive A375- und A431-Zellen beobachtet werden, die stärker war als im Fall der Cld-4-negativen HT29-Zellen. Dieses Ergebnis wird gestützt durch konfokale Fluoreszenzmikroskopie mit FITC-konjugiertem cCPE(290-319) an A431-Zellen. Das in vivo-Verhalten von 18F-markiertem cCPE(290-319) wurde durch dynamisches PET-Imaging und Radiometabolit-Analysen in NMRI nu/nu-Mäusen bzw. Wistar-Ratten evaluiert. Dabei hat sich gezeigt, dass 18F-markiertes cCPE(290-319) schnell metabolisiert wird und einer deutlichen Aufnahme in die Leber unterliegt.
  • Poster
    GDCh-Wissenschaftsforum 2015, 30.08.-02.09.2015, Dresden, Deutschland

Publ.-Id: 22351 - Permalink


Targeting of tissue transglutaminase for functional tumour imaging: Studies on novel assay methods and inhibitors for this enzyme
Wodtke, R.; Hauser, C.; Jäckel, E.; Ruiz-Gómez, G.; Wong, A.; Steinbach, J.; Pietzsch, J.; Pietsch, M.; Löser, R.;
An increased activity of tissue transglutaminase (TGase 2) in tumours correlates with enhanced invasive potential as well as resistance to chemo- and radiotherapy. Therefore, this enzyme represents an interesting target for the development of PET tracers for functional in vivo imaging of tumours.
One important prerequisite for the identification and characterisation of TGase 2-binding compounds are reliable assay methods to measure the enzymatic activity. For this, a continuous fluorimetric activity assay was established, which allows the detection of the TGase 2-activity through the measurement of an increase in fluorescence. In this context, six novel water-soluble fluorogenic acyl donors containing either 7-hydroxycoumarin or 7-hydroxy-4-methylcoumarin (HMC) as fluorogenic leaving groups were developed and extensively characterised concerning their enzymatic hydrolysis and aminolysis. Within these substrates, the dipeptide Z-Glu(HMC)-Gly-OH exhibits not only the most favourable substrate properties of all compounds in this study but also within the peptidic acyl donors described for TGase 2 so far. In addition to that, a fluorescence anisotropy-based assay method was established where the TGase 2-mediated incorporation of either fluorescein- or rhodamine-conjugated cadaverine into N,N-dimethylcasein is quantified.
For the development of PET tracers for molecular imaging of TGase 2, different approaches are pursued. One of those exploits the use of irreversible inhibitors for this enzyme. Among the TGase 2 inhibitors described in the literature, the recently reported Nα-acyl-Nε-acryloyl-lysine-4-pyridylpiperazides seem to be most suitable for radiotracer development as these compounds exhibit strong inhibitory potential and selectivity towards TGase 2 as well as favourable pharmacokinetic properties. Hence, derivatives based on this class of compounds that allow the labelling with radionuclides such as fluorine-18 and iodine-124 were prepared and their inhibitory potential towards TGase 2 was evaluated by the two independent assay methods outlined above. The kinetic characterisation of the compounds revealed interesting structure-activity relationships. Particularly, the introduction of iodine into the C-terminal pyridyl moiety resulted in a significantly increased inhibitory potential towards TGase 2 compared to the lead structure. This was further illustrated by investigations on covalent docking of the lysine-derived inhibitors within the catalytic centre of TGase 2 which simultaneously will open strategies for the design of even more potent inhibitors.
  • Lecture (Conference)
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich

Publ.-Id: 22350 - Permalink


III-V nanocrystals in Silicon via Liquid Phase Epitaxy: Microstructure and related properties
Wutzler, R.; Rebohle, L.; Prucnal, S.; Böttger, R.; Hübner, R.; Grenzer, J.; Helm, M.; Skorupa, W.;
The integration of III-V compound semiconductors into existing semiconductor technology is a milestone in future development of micro- and opto-electronics. However, one of the main problems is the presence of defects both inside the III-V semiconductor and at its interfaces. In the present case, III-V compound semiconductor nanocrystals (NCs) were fabricated in Si based systems. For NC formation ion implantation and short-time flash lamp annealing (FLA) were used. After the implanted Si is molten by FLA, the NCs grow via liquid phase epitaxy (LPE) in a millisecond regime. Several binary and ternary III-V compounds have been produced using this approach. While binary compounds are fabricated stoichiometrically, ternary compounds can be achieved with varying compositions. Raman spectroscopy measurements confirmed the formation of III-V NCs within the particular, recrystallized matrices and Si doping. Microstructural properties were investigated by scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (TEM) and X-ray diffraction analysis. SEM and TEM images show crystalline, strained III-V nanocrystals in recrystallized Si layers.
Keywords: ion implantation, flash lamp annealing, III-V integration, silicon, liquid phase epitaxy
  • Poster
    28th International Conference on Defects in Semiconductors (ICDS), 27.-31.07.2015, Espoo, Finland

Publ.-Id: 22349 - Permalink


Experimental investigations on the influence of adhesive oxides on the metal-ceramic bond
Enghardt, S.; Richter, G.; Richter, E.; Reitemeier, B.; Walter, M. H.;
The objective of this study was to test the influence of selected base metals, which act as oxide formers, on the metal-ceramic bond of dental veneer systems. Using ion implantation techniques, ions of Al, In and Cu were introduced into near-surface layers of a noble metal alloy containing no base metals. A noble metal alloy with base metals added for oxide formation was used as a reference. Both alloys were coated with a low-temperature fusing dental ceramic. Specimens without ion implantation or with Al2O3air abrasion were used as controls. The test procedures comprised the Schwickerath shear bond strength test (ISO 9693-1), profile height (surface roughness) measurements (ISO 4287; ISO 4288; ISO 25178), scanning electron microscopy (SEM) imaging, auger electron spectroscopy (AES) and energy dispersive X-ray analysis (EDX). Ion implantation resulted in no increase in bond strength. The highest shear bond strengths were achieved after oxidation in air and air abrasion with Al2O3 (41.5 MPa and 47.8 MPa respectively). There was a positive correlation between shear bond strength and profile height. After air abrasion, a pronounced structuring of the surface occurred compared to ion implantation. The established concentration shifts in alloy and ceramic could be reproduced. However, their positive effects on shear bond strength were not confirmed. The mechanical bond appears to be of greater importance for metal-ceramic bonding.
Keywords: Alloy; Chemical bond; Ion implantation; Mechanical bond; Metal-ceramic bond; Shear bond strength

Publ.-Id: 22348 - Permalink


III-V nanocrystal formation in ion-implanted Ge and Si via liquid phase epitaxy during short-time flash lamp annealing
Wutzler, R.; Rebohle, L.; Prucnal, S.; Hübner, R.; Facsko, S.; Böttger, R.; Helm, M.; Skorupa, W.;
A combination of n-type III-V compound semiconductors and p-type Ge for future CMOS device technology is a possible way to satisfy the demand for higher device performance. In this work, an alternative method to integrate III-V’s into Ge is achieved by using a combination of ion implantation and short-time flash lamp annealing. With this process InAs nanocrystals are formed within a Ge substrate for the first time. Raman spectroscopy, scanning electron microscopy, Auger electron spectroscopy element mapping as well as transmission electron microscopy are performed to investigate these nanocrystal regarding size, shape and crystalline quality. Experiments show epitaxial growth of the III-V compound within the Ge matrix and a liquid phase epitaxy mechanism is used to describe the nanocrystal formation. Finally, the microstructural properties are compared for InAs nanocrystals in a Ge and a Si matrix.
Keywords: ion implantation, flash lamp annealing, III-V integration, germanium, liquid phase epitaxy

Publ.-Id: 22347 - Permalink


Linear magnetoresistance in mosaic-like bilayer graphene
Kisslinger, F.; Ott, C.; Heide, C.; Kampert, E.; Butz, B.; Spiecker, E.; Shallcross, S.; Weber, H. B.;
The magnetoresistance of conductors usually has a quadratic dependence on magnetic field, however, examples exist of non-saturating linear behaviour in diverse materials. Assigning a specific microscopic mechanism to this unusual phenomenon is obscured by the co-occurrence and interplay of doping, mobility fluctuations and a polycrystalline structure. Bilayer graphene has virtually no doping fluctuations, yet provides a built-in mosaic tiling due to the dense network of partial dislocations. We present magnetotransport measurements of epitaxial bilayer graphene that exhibits a strong and reproducible linear magnetoresistance that persists to B = 62 T at and above room temperature, decorated by quantum interference effects at low temperatures. Partial dislocations thus have a profound impact on the transport properties in bilayer graphene, a system that is frequently assumed to be dislocation-free. It further provides a clear and tractable model system for studying the unusual properties of mosaic conductors.

Publ.-Id: 22346 - Permalink


Solid-phase synthesis of selectively monofluorobenzoylated polyamines for targeting of transglutaminases and polyamine transporters in tumours
Wodtke, R.; Steinbach, J.; Pietzsch, J.; Pietsch, M.; Löser, R.;
Transglutaminases and polyamine transporters are promising targets for functional imaging of tumours. Therefore, our aim is to synthesise polyamine-based radiotracers that allow the in vivo imaging of the aforementioned targets by positron emission tomography (PET). Labelling with the radionuclide fluorine-18 can be accomplished via attaching a [18F]fluorobenzoyl group with the prosthetic labelling reagent N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). To access the required non- radioactive analogues, a solid-phase synthesis was developed that enables selective fluorobenzoylation at distinct amino groups of various polyamines (e.g. cadaverine, spermidine, spermine) on the basis of a recently described synthetic concept for the selective functionalisation of polyamines. The established route can be directly applied to synthesise the 18F-labelled analogues.
The mono-fluorobenzoylated polyamines were obtained by solidphase synthesis of the corresponding oxopolyamines and subsequent reduction of the amide bond with BH3-THF. By applying Dde and Boc as orthogonal protecting groups and taking advantage of the selective reaction of 2-acetyldimedone with primary amino groups in the presence of secondary amines, the selective fluorobenzoylation (FBz) of different amino groups becomes possible.
Additionally, the selective mono-fluorobenzylation (FBn) of selected diamines by reaction with 4-fluorobenzaldehyde and subsequent reduction of the resulting imine using sodium triacetoxyborohydride was performed. Based on the established methodology, the following compounds among others were obtained in good yields: N-FBzcadaverine, N-FBn-cadaverine, N1-FBz- spermidine, N4-FBz-spermidine, N8-FBz-spermidine and N1-FBz-spermine. Furthermore, the naturally occurring diamine cadaverine was conjugated to different reporter groups such as biotin. The identity of the compounds was confirmed by NMR spectroscopy and mass spectrometry. The kinetic parameters towards transglutaminase 2-catalysed acyl transfer were determined for selected compounds with an in-house fluorimetric assay using the fluorogenic acyl donor Cbz–Glu(HMC)–Gly–OH.
  • Abstract in refereed journal
    Amino Acids 47(2015)8, 1630
  • Poster
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich

Publ.-Id: 22345 - Permalink


Synthesis, 18F-labeling and radiopharmacological characterization of a 30mer peptide as potential radiotracer for PET imaging of claudin-4
Kuchar, M.; Bader, M.; Wodtke, R.; Lenk, J.; Pufe, J.; Bergmann, R.; Haase-Kohn, C.; Steinbach, J.; Pietzsch, J.; Löser, R.;
The cell surface receptor claudin-4 (Cld-4) represents a single-chain protein containing four transmembrane domains and constitutes cell–cell contacts of the tight-junction type by engaging in homophilic interactions. Cld-4 is upregulated in various tumors and represents a promising target for both diagnosis and treatment of solid tumors of epithelial origin. Therefore, the development of agents that allow imaging of Cld-4 in vivo such as 18F-labeled compounds for positron emission tomography (PET) appears to be attractive. A suitable ligand to target Cld-4 in vivo seems to be the C-terminal peptidic fragment of the C-terminal domain of the Clostridium perfringens enterotoxin cCPE(290-319). This fragment is of 30 amino acids in length and has the sequence SLDAGQYVLVMKANSSYSGNYPYSILFQKF corresponding to positions 290-319 of cCPE.
The synthesis of cCPE(290–319) and analogues derived thereof, such as N-terminally modified derivatives (fluorobenzoylated and FITC-conjugated) and variants in which critical amino acids (Tyr 306 and Leu 315) have been replaced, was envisaged to be accomplished by solid-phase peptide synthesis (SPPS). Among several approaches, sequential SPPS using three pseudoproline-dipeptide building blocks revealed to be the most efficient one to afford cCPE(290–319) and its derivatives. The affinity of the furnished peptides to a soluble protein construct that contains both extracellular loops of Cld-4 was studied by surface plasmon resonance (SPR), which allowed determining a Kd value of 1.4 lM for the N-terminally fluorobenzoylated cCPE(290-319). Labeling of cCPE(290–319) with fluorine-18 was achieved on solid phase using N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) and 4-[18F]fluorobenzoyl chloride as 18F-acylating agents. Most advantageous results were obtained when [18F]SFB was reacted with resin-bound cCPE(290–319) containing an N-terminal 6-aminohexanoic spacer. Stability assays in cell supernatants and plasma indicated no degradation of the resulting radiotracer in these physiological media. Cell binding of 18F-labeled cCPE(290–319) was investigated using the HT29, A375 and A431 tumor cell lines. Timedependent binding of the radiolabeled peptide to the Cld-4-positive A375 and A431 cells was observed, which was stronger than for the Cld-4-negative HT29 cell line. These findings are in accordance with results of confocal microscopy studies using FITC-conjugated cCPE(290–319) and A431 cells. The in vivo behavior of 18F-labeled cCPE(290–319) was studied in NMRI nu/nu mice and Wistar rats by dynamic PET imaging and radiometabolite analyses, respectively. These investigations have shown that 18F-labeled cCPE(290–319) is subject to substantial liver uptake and rapid metabolic degradation in vivo.
In conclusion, the synthesis and 18F-labeling of cCPE(290-319) were successfully established. Its binding to Cld-4 in vitro and in cellulo has been demonstrated. Initial radiopharmacological studies suggest the limited suitability of this peptide in its current non-stabilized form to target Cld-4 in vivo.
  • Abstract in refereed journal
    Amino Acids 47(2015)8, 1629-1630
  • Poster
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich

Publ.-Id: 22344 - Permalink


A new fluorescence anisotropy-based assay for activity determination of tissue transglutaminase
Hauser, C.; Wodtke, R.; Löser, R.; Pietsch, M.;
Considerable evidence for the implication of tissue transglutaminase (TGase 2) in a variety of pathological processes, such as neurodegenerative diseases, disorders related to autoimmunity and inflammation as well as tumor progression, has been revealed over the recent years. This renders TGase 2 attractive for developing agents which allow the enzyme’s targeting for both therapeutic and imaging purposes. The development of such molecules requires the establishment of reliable methods to assess the interaction with TGase 2, which can be done most conveniently in continuous kinetic assays.
Several assays have been published over the last decades to determine TGase 2 activity, with only very few using the method of fluorescence anisotropy. Measurement of fluorescence anisotropy offers a better signal to noise ratio than other techniques, such as those based solely on fluorescence emission and does not need washing or separation of unbound fluorescent substance.
Here, we report a fluorescence anisotropy-based approach for the determination of TGase 2’s transamidase activity, established and validated by using fluorescein- and rhodamine B-labeled cadaverines as acyl acceptor substrates. The synthesis of the cadaverine derivatives has been accomplished in a solid-phase approach. To allow efficient conjugation of the rhodamine B moiety, different linkers providing secondary amine functions have been introduced between the cadaverine and xanthenyl entities.
The increase in fluorescence anisotropy resulting from covalent binding of the relatively small cadaverine derivatives to the much larger acyl donor substrate N,N-dimethylated casein was followed over time and enzyme activities were derived thereof. The assay was found to be highly reproducible and shows no background signal in the absence of the enzyme for all synthesized cadaverine derivatives. After characterization of the enzyme–substrate interaction by determination of the Michaelis constants, Km, and the maximum velocities of substrate conversion, Vmax, the assay was validated for screening of non-covalent and covalent inhibitors by using the literature-known substances GTP and iodoacetamide, respectively, as well as a recently reported L-lysine acrylamide derivative.
  • Abstract in refereed journal
    Amino Acids 47(2015)8, 1629
  • Poster
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich

Publ.-Id: 22343 - Permalink


18F-Labeled 1,4-Dioxa-8-azaspiro[4.5]decane Derivative: Synthesis and Biological Evaluation of a σ1 Receptor Radioligand with Low Lipophilicity as Potent Tumor Imaging Agent
Xie, F.; Bergmann, R.; Kniess, T.; Deuther-Conrad, W.; Mamat, C.; Neuber, C.; Liu, B.; Steinbach, J.; Brust, P.; Pietzsch, J.; Jia, H.;
We report the syntheses and evaluation of series of novel piperidine compounds with low lipophilicity as σ1 receptor ligands. 8-(4-(2-Fluoroethoxy)benzyl)-1,4-dioxa-8-azaspiro[4.5]decane (5a) possessed high affinity (Ki = 5.4 ± 0.4 nM) for σ1 receptors and selectivity for σ2 receptors (30-fold) and the vesicular acetylcholine transporter (1404-fold). [18F]5a was prepared using a one-pot, two-step labeling procedure in an automated synthesis module, with a radiochemical purity of >95%, and a specific activity of 25−45 GBq/μmol. Cellular association, biodistribution, and autoradiography with blocking experiments indicated specific binding of [18F]5a to σ1 receptors in vitro and in vivo. Small animal positron emission tomography (PET) imaging using mouse tumor xenograft models demonstrated a high accumulation in human carcinoma and melanoma. Treatment with haloperidol significantly reduced the accumulation of the radiotracer in tumors. These findings suggest that radiotracer with suitable lipophilicity and appropriate affinity for σ1 receptors could be used for tumor imaging.
Keywords: 8 [4 (2 fluoroethoxy)benzyl) 1,4 dioxa 8 azaspiro[4.5]decane f 18; fluorine 18; haloperidol; piperidine derivative; radioligand; radiopharmaceutical agent; sigma 1 opiate receptor; sigma 2 opiate receptor; unclassified drug; vesicular acetylcholine transporter

Publ.-Id: 22342 - Permalink


Complex antiferromagnetic structure in the intermediate-valence intermetallic Ce2RuZn4
Hartwig, S.; Prokes, K.; Hansen, T.; Ritter, C.; Gerke, B.; Pöttgen, R.; Mydosh, J. A.; Förster, T.;
Neutron powder diffraction experiments were performed on the intermediate-valence Ce2RuZn4 intermetallic compound and combined with magnetic bulk measurements including high magnetic field experiments up to 58 T. Previous theoretical studies suggest that only one (here Ce1) out of two inequivalent Ce sites ismagnetically active. Ce2RuZn4 orders antiferromagnetically at TN = 2.3 K. The magnetic structure is characterized by an incommensurate propagation vector qm = (0.384, 0.384, 1/2). Assuming that the Ce2 site does not carry any substantial moment, Ce1 magnetic moments are confined to the (110)-type planes and transversely modulated with an amplitude of 1.77(3) μB.

Publ.-Id: 22341 - Permalink


Atomic scale interface design and characterisation
Bittencourt, C.; Ewels, C.; Krasheninnikov, A. V.;
There is no abstract
Keywords: nanotechnology

Publ.-Id: 22339 - Permalink


Development and Validation of Advanced Theoretical Modeling for Churn-Turbulent Flows and Subsequent Transitions
Montoya Zabala, G. A.;
The applicability of CFD codes for two-phase flows has always been limited to special cases due to the very complex nature of its interface. Due to its tremendous computational cost, methods based on direct resolution of the interface are not applicable to most problems of practical relevance. Instead, averaging procedures are commonly used for these applications, such as the Eulerian-Eulerian approach, which necessarily means losing detailed information on the interfacial structure. In order to allow widespread application of the two-fluid approach, closure models are required to reintroduce in the simulations the correct interfacial mass, momentum, and heat transfer.
It is evident that such closure models will strongly depend on the specific flow pattern. When considering vertical pipe flow with low gas volume flow rates, bubbly flow occurs. With increasing gas volume flow rates larger bubbles are generated by bubble coalescence, which further leads to transition to slug, churn-turbulent, and annular flow. Considering, as an example, a heated tube producing steam by evaporation, as in the case of a vertical steam generator, all these flow patterns including transitions are expected to occur in the system. Despite extensive attempts, robust and accurate simulations approaches for such conditions are still lacking.
The purpose of this dissertation is the development, testing, and validation of a multifield model for adiabatic gas-liquid flows at high gas volume fractions, for which a multiple-size bubble approach has been implemented by separating the gas structures into a specified number of groups, each of which represents a prescribed range of sizes. A fully-resolved continuous gas phase is also computed, and represents all the gas structures which are large enough to be resolved within the computational mesh. The concept, known as GENeralized TwO Phase flow or GENTOP, is formulated as an extension to the bubble population balance approach known as the inhomogeneous MUltiple SIze Group (iMUSIG). Within the polydispersed gas, bubble coalescence and breakup allow the transfer between different size structures, while the modeling of mass transfer between the polydispersed and continuous gas allows including transitions between different gas morphologies depending on the flow situations. The calculations were performed using the computational fluid dynamic code from ANSYS, CFX 14.5, with the support of STAR-CCM+ v8.06 and v9.02. A complete three-field and four-field model, including a continuous liquid field and two to three gas fields representing bubbles of different sizes, were first tested for numerical convergence and then validated against experimental data from the TOPFLOW and MT-Loop facilities.
Keywords: CFD, GENTOP, Surface Tension, MT-Loop, TOPFLOW
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-063 2015

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Publ.-Id: 22338 - Permalink


Solubility of boron, carbon, and nitrogen in transition metals: getting insight into trends from first-principles calculations
Hu, X.; Björkman, T.; Lipsanen, H.; Sun, L.; Krasheninnikov, A. V.;
Efficient chemical vapor deposition synthesis of two-dimensional (2D) materials such as graphene, boron nitride, and mixed BCN systems with tunable band gaps requires precise knowledge of the solubility and mobility of B/C/N atoms in the transition metals (TMs) used as substrates for the growth. Yet, surprisingly little is known about these quantities either from experiments or simulations. Using first-principles calculations, we systematically study the behavior of B/C/N impurity atoms in a wide range of TMs. We compute formation energies of B/C/N interstitials and demonstrate that they exhibit a peculiar but common behavior for TMs in different rows of the periodic table, as experimentally observed for C. Our simulations indicate that this behavior originates from an interplay between the unit cell volume and filling of the d- shell electronic states of the metals. We further assess the vibrational and electronic entropic contributions to the solubility, as well as the role of anharmonic effects. Finally, we calculate the migration barriers, an important parameter in the growth kinetics. Our results not only unravel the fundamental behavior of interstitials in TMs but also provide a large body of reference data, which can be used for optimizing the growth of 2D BCN materials.
Keywords: graphene, solubility, interstitials

Publ.-Id: 22337 - Permalink


Implementation and Validation of a Surface Tension Model for the Multi-scale approach GENTOP
Montoya Zabala, G. A.; Baglietto, E.; Lucas, D.;
Multiphase flows encountered in the nuclear industry are largely of a complex nature, and knowledge of the accurate distribution of the void fraction is of utmost importance for operation of the reactor under steady, transient, and accident conditions. At high void fractions, strong coalescence leads to the formation of large deformable bubbles. An appropriate multiphase CFD modeling of these flow regimes should be able to account for both, large and small interfacial structures, also including the effect on closure modeling of the large structures. A concept known as GEneralized TwO Phase flow or GENTOP, has been developed at the Helmholtz-Zentrum Dresden-Rossendorf in order to address such flow configurations, by dealing with a resolved potentially-continuous gas field, one or more polydispersed gas fields, and a continuous liquid phase. Application of the model to churn-turbulent and slug flow in vertical pipes [1], have evidenced an important limitation related to the lack of a surface tension modeling within the free surface, which leads to an unphysical accumulation of void near the pipe wall. This work discusses the implementation of surface tension and contact angle within the GENTOP approach, as well as the validation of these models against analytical and experimental results. The validation of the surface tension has been performed against analytically calculated oscillating periods of different shapes of ethanol droplets suspended in air. Furthermore, different contact angles are analyzed for a drop of water residing on a smooth surface. Rising velocities and deformation of a single large bubble rising in a vertical pipe were finally validated against analytical solutions. The implementation of the surface tension model in the GENTOP approach demonstrated improvements on the resolution of the bubble and stability of the interface, with considerable reduction of the numerical diffusion.
Keywords: CFD, GENTOP, Surface Tension, Contact Angle, MT-Loop
  • Contribution to proceedings
    16th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 30.08.-04.09.2015, Chicago, USA
    Proceedings of the 16th International Topical Meeting on Nuclear Reactor Thermalhydraulics, Chicago, USA
  • Lecture (Conference)
    16th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 30.08.-04.09.2015, Chicago, USA

Publ.-Id: 22336 - Permalink


A review on mechanisms and models for the churn-turbulent flow regime
Montoya Zabala, G. A.; Lucas, D.; Baglietto, E.; Liao, Y.;
The modeling of two-phase flows has always been limited to special cases due to the very complex nature of its interface. When considering vertical pipe flows with low gas volume flow rates, bubbly flow occurs. With increasing gas volume flow rates larger bubbles are generated by bubble coalescence, which further leads to transition to slug, churn-turbulent, and annular flow. Considering, as an example, a heated tube producing steam by evaporation, as in the case of a vertical steam generator, all these flow patterns including transitions are expected to occur in the system. Despite extensive attempts, robust and accurate simulations approaches for such conditions are still lacking. This paper summarizes the state-of-the-art on the understanding of the physics behind churnturbulent flow, and transitions to and from this flow pattern. Both, benefits and limitations of the existent experimental approaches and their usefulness for model development and validation at these high void fraction conditions are discussed. Limitation of both, low-dimensional approaches (0D, 1D, and 2D), and high resolution approaches such as Direct Numerical Simulations (DNS) are analyzed. Averaging procedures, such as the Eulerian-Eulerian approach including the interfacial momentum closures which has been used in the past for simulating churn flow, are review thoroughly. Finally, possible improvements are proposed.
Keywords: churn-turbulent; CFD; multiphase; review

Publ.-Id: 22335 - Permalink


Broadband THz detection from 0.1 to 22 THz with large area field-effect transistors
Regensburger, S.; Mittendorff, M.; Winnerl, S.; Lu, H.; Gossard, A. C.; Preu, S.;
We report on ultrafast detection of radiation between 100 GHz and 22 THz by field-effect transistors in a large area configuration. With the exception of the Reststrahlenband of GaAs, the spectral coverage of the GaAs-based detectors is more than two orders of magnitude, covering the entire THz range (100 GHz - 10 THz). The temporal resolution of the robust devices is yet limited by the 30GHz oscilloscope used for read out. The responsivity roll-off towards higher frequencies is weaker than expected from an RC-roll-off model. Terahertz pulses with peak powers of up to 65 kW have been recorded without damaging the devices.
Keywords: terahertz detetector, field-effect transistor, braodband and fast THz detection

Publ.-Id: 22334 - Permalink


From a non-magnet to a ferromagnet: Mn implantation into different TiO2 structures
Yildirim, O.; Cornelius, S.; Butterling, M.; Anwand, W.; Wagner, A.; Smekhova, A.; Fiedler, J.; Böttger, R.; Bähtz, C.; Potzger, K.;
We study effect of the initial structural order on the resulting magnetic properties of the manganese implanted TiO2 films. Different microstructures of as-grown TiO2 films, namely amorphous, polycrystalline anatase and epitaxial anatase, have been implant-doped with Mn+ up to a concentration of 5 at.%. We found that the different initial structures lead to different defect and charge carrier concentrations, and as a result, strongly influence the magnetic properties upon implantation. Depending on the initial microstructure, paramagnetism, secondary phases related magnetic properties as well as ferromagnetism could be observed in the films.

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Publ.-Id: 22333 - Permalink


X-ray Absorption Spectroscopy for Actinide Chemistry - Basics, Experiments and Applications
Ikeda-Ohno, A.;
Synchrotron-based X-ray spectroscopy is an emerging and powerful tool for actinide chemistry. This lecture focuses particularly on X-ray absorption spectroscopy, and will provide a comprehensive overview of the basics and experiments of this technique, as well as their applications to actinide chemistry.
Keywords: X-ray absorption spectroscopy; XAS; XANES; EXAFS; synchrotron; actinide; chemistry; overview; introduction
  • Invited lecture (Conferences)
    The ThUL School in Actinide Chemistry, 28.09.-02.10.2015, Karlsruhe, Germany

Publ.-Id: 22332 - Permalink


Targeting lysyl oxidase for molecular imaging in breast cancer
Wuest, M.; Kuchar, M.; Sharma, S. K.; Richter, S.; Hamann, I.; Wang, M.; Vos, L.; Mackey, J. R.; Wuest, F.; Löser, R.;
Introduction: Lysyl oxidase (LOX; ExPASy ENZYME entry: EC 1.4.3.13) and members of the LOX-like family, LOXL1–LOXL4, are copper-dependent enzymes that can modify proteins of the extracellular matrix. Expression of LOX is elevated in many human cancers, including breast cancer. LOX expression correlates with the level of tissue hypoxia, and it is known to play a critical role in breast cancer metastasis. The goal of the present study was to target LOX with (1) molecular probe fluorescent labeling to visualize LOX in vitro and (2) a radiolabeled peptide to target LOX in vivo in three different preclinical models of breast cancer.
Methods: Gene expression of all five members of the LOX family was analyzed at the transcript level via microarray analysis using tissue biopsy samples from 176 patients with breast cancer. An oligopeptide sequence (GGGDPKGGGGG) was selected as a substrate-based, LOX-targeting structure. The peptide was labeled with fluorescein isothiocyanate (FITC) for confocal microscopy experiments with the murine breast cancer cell line EMT-6. In vivo molecular imaging experiments were performed using a C-terminal amidated peptide, GGGDPKGGGGG, labeled with a short-lived positron emitter, fluorine-18 (18F), for positron emission tomography (PET) in three different breast cancer models: EMT6, MCF-7 and MDA-MB-231. The PET experiments were carried out in the presence or absence of β-aminopropionitrile (BAPN), an irreversible inhibitor of LOX.
Results: Immunostaining experiments using a LOX-specific antibody on EMT-6 cells cultured under hypoxic conditions confirmed the elevation of LOX expression in these cells. An FITC-labeled oligopeptide, FITC-Ava- GGGDPKGGGGG-NH2, was found to be localized in different cellular compartments under these conditions. After injection of [18F]fluorobenzoate-GGGDPKGGGGG-NH2, radioactivity uptake was visible in all three breast cancer models in vivo. Tumor uptake was reduced by predosing the animals with 2 mg of BAPN 4 h or 24 h before injection of the radiotracer.
Conclusions: The present data support further investigation into the development of LOX-binding radiolabeled peptides as molecular probes for molecular imaging of LOX expression in cancer.

Publ.-Id: 22331 - Permalink


Ultrasound Doppler flow measurements in a liquid metal column under the influence of a strong axial electric current
Starace, M.; Weber, N.; Seilmayer, M.; Kasprzyk, C.; Weier, T.; Stefani, F.; Eckert, S.;
Magnetohydrodynamic instabilities can constitute a serious hazard to the functionality of liquid metal batteries. Here we consider the Tayler instability, which appears when the electric current, passing through a conducting fluid, reaches a critical value. The experiment discussed in this article involves a column of a eutectic GaInSn alloy, along whose axis an electric current passes. Ultrasound transducers encased in a copper electrode bounding the top of the column were used to obtain the vertical component of fluid flow, once a noise suppression system had been devised. The data thus retrieved will be discussed here.
  • Magnetohydrodynamics 51(2015)2, 249-256

Publ.-Id: 22330 - Permalink


Ion acceleration enhanced by target ablation
Zhao, S.; Lin, C.; Wang, H. Y.; Lu, H.; Tu He, X.; Chen, J.; Cowan, T. E.; Q. Yan, X.;
Laser proton acceleration can be enhanced by using target ablation, due to the energetic electrons generated in the ablation preplasma. When the ablation pulse matches main pulse, the enhancement gets optimized because the electrons' energy density is highest. A scaling law between the ablation pulse and main pulse is confirmed by the simulation, showing that for given CPA pulse and target, proton energy improvement can be achieved several times by adjusting the target ablation.

Publ.-Id: 22329 - Permalink


Caustic structures in the spectrum of x-ray Compton scattering off electrons driven by a short intense laser pulse
Seipt, D.; Surzhykov, A.; Fritzsche, S.; Kämpfer, B.;
We study the Compton scattering of x-rays off electrons that are driven by a relativistically intense short optical laser pulse. The frequency spectrum of the laser-assisted Compton radiation shows a broad plateau in the vicinity of the laser-free Compton line due to a nonlinear mixing between x-ray and laser photons. Special emphasis is placed on how the shape of the short assisting laser pulse affects the spectrum of the scattered x-rays. In particular, we observe sharp peak structures in the plateau region, whose number and locations are highly sensitive to the laser pulse shape. These structures are interpreted as spectral caustics by using a semiclassical analysis of the laser-assisted QED matrix element.

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Publ.-Id: 22328 - Permalink


Directional Spin Wave Emission From Topological Spin Textures
Sluka, V.; Weigand, M.; Kakay, A.; Schultheiss, K.; Erbe, A.; Tyberkevych, V.; Slavin, A.; Deac, A.; Lindner, J.; Fassbender, J.ORC; Raabe, J.; Wintz, S.
In the present contribution we will show that in a stacked vortex pair system with uniaxial magnetic anisotropy, directional spin waves of different symmetries and dimensionalities can be excited.
Keywords: spin waves, multilayers, dipole-exchange, non-reciprocity
  • Lecture (Conference)
    13th Joint MMM/Intermag Conference, 11.-15.01.2016, San Diego, USA

Publ.-Id: 22327 - Permalink


Parameter-free determination of the exchange constant in thin films using magnonic patterning
Langer, M.; Wagner, K.; Sebastian, T.; Hübner, R.; Grenzer, J.; Wang, Y.; Kubota, T.; Schneider, T.; Stienen, S.; Linder, J.; Lenz, K.; Linder, J.; Takanashi, K.; Arias, R.; Fassbender, J.ORC
An all-electrical method is presented to determine the exchange constant of magnetic thin films using ferromagnetic resonance. For films of 20 nm thickness and below, the determination of the exchange constant A, a fundamental magnetic quantity, is anything but straightforward. Among others, the most common methods are based on the characterization of perpendicular standing spin-waves. These approaches are however challenging, due to (i) very high energies and (ii) rather small intensities in this thickness regime. In the presented approach, surface patterning is applied to a permalloy (Ni80Fe20) film and a CFMS (Co2Fe0.4Mn0.6Si) Heusler compound. Acting as a magnonic crystal, such structures enable the coupling of backward volume spin-waves to the uniform mode. Subsequent ferromagnetic resonance measurements give access to the spin-wave spectra free of unquantifiable parameters, and thus, to the exchange constant A with high accuracy.

Publ.-Id: 22326 - Permalink


Breaking of axial symmetry in excited heavy nuclei as identified in GDR data
Grosse, E.; Junghans, A. R.; Massarczyk, R.;
A recent theoretical prediction of a breaking of axial symmetry in quasi all heavy nuclei is confronted to a new critical analysis of photon strength functions of nuclei in the valley of stability. For the photon strength in the isovector giant dipole resonance (IVGDR) regime a parameterization of GDR shapes by the sum of three Lorentzians (TLO) is extrapolated to energies below and above the IVGDR. The impact of non-GDR modes adding to the low energy slope of photon strength is discussed including recent data on photon scattering and other radiative processes. These are shown to be concentrated in energy regions where various model calculations predict intermediate collective strength; thus they are obviously separate from the IVGDR tail. The triple Lorentzian (TLO) ansatz for giant dipole resonances is normalized in accordance to the dipole sum rule. The nuclear droplet model with surface dissipation accounts well for positions and widths without local, nuclide specific, parameters. Very few and only global parameters are needed when a breaking of axial symmetry already in the valley of stability is admitted; a reliable prediction for electric dipole strength functions also outside of it is expected.

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Publ.-Id: 22325 - Permalink


Post-test calculations of UPTF experiments with ANSYS CFX
Höhne, T.;
The last decade has seen an increasing use of three-dimensional CFD codes to predict steady state and transient flows in nuclear reactors because a number of important phenomena such as pressurized thermal shocks, coolant mixing, and thermal striping cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.
The nuclear industry now also recognizes that CFD codes have reached the desired level of maturity (at least for single-phase applications) for them to be used as part of the Nuclear Power Plant (NPP) design process, and it is the objective the research and development teams to assess the current capabilities of such codes in this regard, and contribute to the technology advance in respect to their verification and validation. CFD is already well-established in addressing certain safety issues in NPPs, as reported and discussed at various international workshops. The development, verification and validation of CFD codes in respect to NPP design necessitates further work on the complex physical modelling processes involved, and on the development of efficient numerical schemes needed to solve the basic equations. In parallel, it remains an overriding necessity to benchmark the performance of the CFD codes, and for this experimental databases need to be established, first for separate-effect tests but especially for full-size integral tests.
In order to validate the CFD Code ANSYS CFX for reactor safety relevant flow phenomena it is essential to use the UPTF experiments, since they are full scale tests. All other separate effect test rigs and test facilities like ROCOM (Höhne, 2000) are scaled. Scaling parameters of flow conditions are one of the still open topics for the use of CFD codes in nuclear reactor safety. Three UPTF tests were selected and post-test calculation were performed. The major focus was analyzing the qualitative flow behavior.
Keywords: UPTF, CFX, LOCA, PTS
  • Other report
    Dresden: HZDR, 2015
    25 Seiten

Publ.-Id: 22324 - Permalink


H trapping and mobility in nanostructured tungsten grain boundaries: A combined experimental and theoretical approach
González, C.; Panizo-Laiz, M.; Gordillo, N.; Tejado, E.; Munnik, F.; Guerrero, C.; Piaggi, P.; Iglesias, R.; Perlado, J. M.; González-Arrabal, R.;
The H trapping and mobility in nanostructured W grain boundaries has been studied by combining experimental and density functional theory (DFT) data. Experimental results show that nanostructured W coatings with a columnar structure and a large number of (110)/(211) interfaces retain more H than the coarsed grained W tungsten samples do. To investigate the possible influence of grain boundaries on the H retention, a complete energetic analysis has been done in a semi-coherent W(110)/W(112) interface built by DFT. Our results show that this kind of non-coherent interface largely attract points defects (both H atom and metallic monovacancy separately) and that the presence of these interfaces contribute to decrease the migration energy of the H atoms with respect to the bulk. When both W monovacancy and H atom are introduced together into the system, the HV complex results the most stable configuration suggesting an explanation to the H retention in the GB observed experimentally.
Keywords: Fusion, H trapping

Publ.-Id: 22323 - Permalink


The first four years of the AMS-facility DREAMS: Status and developments for more accurate radionuclide data
Rugel, G.; Pavetich, S.; Akhmadaliev, S.; Enamorado Baez, S. M.; Scharf, A.; Ziegenrücker, R.; Merchel, S.;
DREAMS, the DREsden AMS-facility, is performing routine accelerator mass spectrometry of 10Be, 26Al, 36Cl, 41Ca, and 129I for diverse kinds of applications. All DREAMS data is normalised directly to primary standards or traceable via cross-calibration of secondary standards to those.
Recent technical developments such as a low-memory ion source for 36Cl and 129I and sophisticated tuning strategies for 129I led to improved accuracy data.Tests of ion source output have been performed with different metal binders, sample-to-binder mixing ratios, and compaction pressures in order to find optimal parameters. The highest and most stable outputs have been obtained for 10Be, 26Al, and 41Ca for the following binders and mixing ratios (by weight): BeO:Nb, 1:4; Al2O3:Ag, 1:1; CaF2:Ag, 1:4. Higher beam currents generally result in reduced statistical uncertainty. Cross-contamination and long-term memory seem to be underestimated problems asking for further tests and improvements such as the development of low-level in-house-standards.
Keywords: accelerator mass spectrometry, cosmogenic nuclides

Publ.-Id: 22322 - Permalink


Terahertz spectroscopy of 0D and 2D semiconductors with a free-electron laser
Schneider, H.;
This talk reviews recent experimental studies carried out using the free-electron laser (FEL) facility FELBE in Dresden, Germany. Intense, nearly transform-limited ps pulses in the mid-infrared and terahertz (THz) regimes provide unique research opportunities to study novel materials and devices.
Keywords: free-electron laser, terahertz spectroscopy
  • Lecture (others)
    Seminar, Xi'an University of Technology, 04.05.2015, Xi'an, China
  • Lecture (others)
    Seminar, CAEP, 07.05.2015, Mianyang, China

Publ.-Id: 22321 - Permalink


Spin-based nanoelectronic devices for mobile Information-Communication Technology
Deac, A. M.;
Abstract
Perhaps the best known (or most successfully implemented) spin-based device is the hard-disk read-head. Indeed, the discovery of giant magnetoresistance enabled a paradigm shift in the miniaturization of magnetic storage technology, which was disruptive enough to earn its discoverers a Nobel price [1]. More recently, it has been demonstrated that non-volatile, ultra-fast spin-based memory bit devices can be designed so that they can scale down to more than one fifth of all other available technologies, including SRAM [2]. Other spin-based nanoelectronics devices currently under consideration - which will be discussed here - range from tuneable radio-frequency oscillators to magnetic field sensors, negative resistors, amplifiers, write heads and random number generators. [1] http://www.nobelprize.org/nobel_prizes/physics/laureates/2007/index.html [2] http://www.avalanche-technology.com/technology/ram

Biography
Alina Deac is currently the leader of the Spintronics Group at the Helmholtz-Zentrum Dresden - Rossendorf in Dresden, Germany. During the last 15 years, her research has been focused on spin-torque induced phenomena and their potential applications for mobile ICT devices. After obtaining her PhD in Physics at the Universite Joseph Fourier Grenoble, France in 2005, she pursued her career by working with top-notch institutions in Japan, US and Switzerland. She is a Senior Member of the IEEE Magnetics Society and an expert in the field of spintronics for the EU.
Keywords: spintronics, magnetic storage, information-communication technology
  • Invited lecture (Conferences)
    SEMICON Europa 2015, 06.-08.10.2015, Dresden, Germany

Publ.-Id: 22317 - Permalink


In Situ Tuning the Conductance of Single Molecular Diarylethene Switches
Sendler, T.; Luka-Guth, K.; Wieser, M.; Lokamani, M.; Wolf, J.; Huhn, T.; Scheer, E.; Kerbusch, J.; Gemming, S.; Erbe, A.;
A major goal of molecular electronics is the development and implementation of molecular electronic devices such as single molecular switches. In this work we present a detailed study of single diarylethene molecules that were in situ switched from their non-conductive to conductive state in the presence of gold nanoelectrodes via controlled light irradiation. The molecules were dissolved in two different solvents and measured with two different side-groups. Histograms of conductance traces were taken and complemented by extracting the relative position of the current carrying molecular level and its level broadening from current-voltage characteristics by means of the single level transport model. The obtained results show a clear light-induced ring forming isomerization, which is almost independent of the side-groups, while electron withdrawing side groups lead to a reduction of conductance, a decrease of the level broadening and an increased difference between the molecular level and the Fermi energy of the metals. Quantum chemical calculations of the light-induced switching processes correlate these observations with the fundamentally different low-lying electronic states of the opened and closed forms and their comparably small modification by the electron-withdrawing substituents.
  • Poster
    Annual Workshop IHRS NanoNet 2014, 29.-30.09.2014, Lohmen/Bastei, Deutschland
  • Poster
    DCCMS Annual Workshop and General Assembly 2014, 20.10.2014, Dresden, Deutschland

Publ.-Id: 22316 - Permalink


Spin-based nanoelectronic devices for mobile Information-Communication Technology
Deac, A. M.;
Perhaps the best known (or most successfully implemented) spin-based device is the hard-disk read-head. Indeed, the discovery of giant magnetoresistance enabled a paradigm shift in the miniaturization of magnetic storage technology, which was disruptive enough to earn a Nobel for the two researchers who carried out the initial studies [1]. In a nutshell, giant magnetoresistance refers to the fact that the electrical properties of a multilayer containing at least two magnetic layers depend on the orientation of their magnetic moment. For instance, if the magnetic layers are cobalt, iron or nickel (or their alloys), the resistance of the structure is maximum when the magnetic moments are antiparallel to each other, and minimum when they are parallel.

More recently, it has been demonstrated the inverse phenomenon can also be observed: the relative orientation of the magnetic moments of two ferromagnetic layers can be manipulated by applying an electrical bias (i.e. a current or a voltage) across the structure. This is a consequence of spin-momentum transfer between the conduction electrons and the magnetization of the layer they are travelling across, which effectively induces a torque on the magnetization, the so-called ‘spin-transfer torque’ or ‘spin-torque’ [2-6]. Two main effects can be induced exploiting this torque: the magnetic moment of a given layer can be switched to a chosen direction – for instance, from parallel to antiparallel to the magnetization of the second layer – or it can be induced to gyrate around a given direction for as long as the electrical bias is applied.

Spin-transfer switching as the first spin-transfer induced phenomenon to be demonstrated experimentally, with the first report published at the end of 2000 [5]. Today, spin-transfer switching is the write scheme for non-volatile, ultra-fast Spin-Transfer Torque Random Access Memory (STT-RAM) bit devices. STT-RAM can be designed so that they can scale down to more than one fifth of all other available technologies, including SRAM [7,8]. Spin-transfer driven precession, first demonstrated in 2003 [6], has been suggested as working principle for other spin-based nanoelectronics devices currently under consideration, which range from tuneable, low input power radio-frequency oscillators wireless communication, to magnetic field sensors, negative resistors, amplifiers, write heads and random number generators. Indeed, the frequency of such devices can be adjusted simply by changing the applied bias, and they provide sufficient power [9] while at the same time being about 50 times smaller than present devices used in mobile telecommunication [10]. Moreover, novel materials hold the promise of pushing the frequency limit beyond what present-day technology can achieve [11]. Possible applications include anti-collision systems for cars, remote hospitals and immersive audio-video entertainment systems.

[1] http://www.nobelprize.org/nobel_prizes/physics/laureates/2007/index.html
[2] J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996).
[3] L. Berger, Phys. Rev. B 54, 9353 (1996).
[4] M. D. Stiles, A. Zangwill, Phys. Rev. B 66, 014407 (2002).
[5] J. A. Katine, F. J. Albert, R. A. Buhrman et al., Phys. Rev. Lett. 84, 3149 (2000).
[6] S. I. Kiselev, J. C. Sankey, I. N. Krivorotov et al., Nature (London) 425, 380 (2003).
[7] http://www.avalanche-technology.com/technology/ram
[8] http://www.everspin.com/
[9] A. Deac, A. Fukushima, H. Kubota, et al., Nature Phys. 4, 803 (2008).
[10] P. Villard, U. Ebels, D. Houssameddine, et al., IEEE J. Solid-State Circuits 45, 214
(2010).
[11] S. Mizukami, F. Wu, A. Sakuma, et al., Phys. Rev. Lett. 106, 117201 (2011).
Keywords: spintronics, wireless communication, magnetic data storage
  • Invited lecture (Conferences)
    The 12th Japanese-German Frontiers of Science (JGFoS) Symposium, 01.-04.10.2015, Kyoto, Japan

Publ.-Id: 22315 - Permalink


Spin-Torque Devices Based on MgO-Based Magnetic Tunnel Junctions
Deac, A. M.;
Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless communication applications [1-3]. In particular, it has recently been demonstrated that STNOs utilizing an in-plane magnetized polarizer (also acting as read-out layer) and out-of-plane magnetized free layer allow for the full parallel-to-antiparallel resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power [1]. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices [1]. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based magnetic tunnel junctions (MTJs) under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence [4,5]. These results have so far been interpreted based on the formalism for metallic devices.

Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based STNOs with this specific geometry. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation under a constant perpendicular applied current and field. We take into account both the angular and the bias dependence of the resistance of the nanopillar in order to convert the current into voltage, which is the relevant parameter in an MgO-MTJ. The field-like torque is neglected. We demonstrate that the angular dependence of the resistance introduces sufficient asymmetry of the in-plane spin-torque term to sustain precession in this system, but the bias dependence of the resistance gradually quenches this asymmetry as the current is increased and consequently suppresses precession above a given threshold. We furthermore prove that in an STNO with circular cross-section an external field is required to observe steady-state dynamics, but this constraint is lifted when introducing an in-plane easy axis, which opens new avenues to be explored for designing devices for mobile communication.

[1] W. H. Rippard, A. M. Deac, M. R. Pufall, et al., Physical Review B 81, 014426 (2010).
[2] A. M. Deac, A. Fukushima, H. Kubota, et al., Nature Physics 4, 308 (2008).
[3] S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, et al., Nature 425, 380 (2003).
[4] H. Kubota, K. Yakushiji, A. Fukushima, et al., Applied Physics Express 6, 103003 (2013).
[5] T. Taniguchi, H. Arai, S. Tsunegi, et al., Applied Physics Express 6, 123003 (2013).
Keywords: magnetism, magnetic tunnel junctions, spin-transfer torque
  • Invited lecture (Conferences)
    Spin Dynamics in Nanostructures Gordon Research Conference Nanoscale Spintronics with Magnons, Phonons, and Photons, 26.-31.07.2015, The Hong Kong University of Science and Technology, China

Publ.-Id: 22314 - Permalink


International research environment and career development
Deac, A. M.;
This talk provides mentoring for students seeking an international career.
Keywords: carrer development
  • Invited lecture (Conferences)
    Spin Dynamics in Nanostructures (GRS) Gordon Research Seminar Interplay of Spin, Charge and Lattice Dynamics, 25.-26.07.2015, The Hong Kong University of Science and Technology, China

Publ.-Id: 22313 - Permalink


Zero-field precession and suppression of the output power due to the biasdependence of the TMR in MgO-based spin-torque oscillators Alina Maria Deac
Kowalska, E.; Sluka, V.; Fowley, C.; Kakay, A.; Aleksandrov, Y.; Lindner, J.; Deac, A. M.; Fassbender, J.ORC
Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless
communication applications [1-3]. In particular, it has recently been demonstrated that STNOs utilizing an in-plane magnetized polarizer (also acting as read-out layer) and out-of-plane magnetized free layer allow for the full parallel-to-antiparallel resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power [1]. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices [1]. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based magnetic tunnel junctions (MTJs) under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence [4,5]. These results have so far been interpreted based on the formalism for metallic devices.

Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based STNOs with this specific geometry. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation under a constant perpendicular applied current and field. We take into account both the angular and the bias dependence of the resistance of the nanopillar in order to convert the current into voltage, which is the relevant parameter in an MgO-MTJ. The field-like torque is neglected. We demonstrate that the angular dependence of the resistance introduces sufficient asymmetry of the in-plane spin-torque term to sustain precession in this system, but the bias dependence of the resistance gradually quenches this asymmetry as the current is increased and consequently suppresses precession above a given threshold. We furthermore prove that in an STNO with circular cross-section an external field is required to observe steady-state dynamics, but this constraint is lifted when introducing an in-plane easy axis, which opens new avenues to be explored for designing devices for mobile communication.

[1] W. H. Rippard, A. M. Deac, M. R. Pufall, et al., Physical Review B 81, 014426 (2010).
[2] A. M. Deac, A. Fukushima, H. Kubota, et al., Nature Physics 4, 308 (2008).
[3] S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, et al., Nature 425, 380 (2003).
[4] H. Kubota, K. Yakushiji, A. Fukushima, et al., Applied Physics Express 6, 103003 (2013).
[5] T. Taniguchi, H. Arai, S. Tsunegi, et al., Applied Physics Express 6, 123003 (2013).
Keywords: magnetism, spin-transfer torque, magnetic tunnel junction
  • Invited lecture (Conferences)
    20th International Conference on Magnetism, 06.-10.07.2015, Barcelona, Spain
  • Poster
    12th Japanese-German Frontiers of Science Symposium 2015, 01.-04.10.2015, Kyoto, Japan

Publ.-Id: 22312 - Permalink


Atomic transport during solid-phase epitaxial recrystallization of amorphous germanium
Radek, M.; Bracht, H.; Mccallum, J. C.; Johnson, B. C.; Posselt, M.; Liedke, B.;
The atomic mixing of matrix atoms during solid-phase-epitaxy (SPE) is studied by means of isotopically enriched germanium (Ge) multilayer structures grown by molecular beam epitaxy on natural Ge wafers. The entire isotope structure and parts of the natural Ge wafer were preamorphized by Ge implantation. Recrystallization of the amorphous Ge layer is performed at temperatures between 350 ˚C and 450 ˚C. The position of the amorphous/crystalline (a/c) interface was monitored during SPE regrowth using a time-resolved-reflectivity (TRR) system. The SPE process was stopped before the a/c interface reached the surface, i.e, before the recrystallization of the amorphous layer was completed. Secondary-ion-mass-spectrometry (SIMS) was applied to determine the self-atom distribution within the amorphous and recrystallized part of each sample. An upper limit of 0.5 nm is determined for the displacement length of the matrix atoms. This small displacement length is consistent with theoretical models and atomistic simulations of SPE predicting that bond-switching with nearest-neighbours across the a/c interface controls the SPE regrowth.
Keywords: Germanium, Solid-phase epitaxial recrystallization, atomic transport, isotope multilayers
  • Poster
    28th International Conference on Defects in Semiconductors (ICDS 2015), 27.-31.07.2015, Espoo, Finland

Publ.-Id: 22311 - Permalink


Characterisation and properties of f-element complexes with amide and amidine ligands
März, J.; Schmid, M.; Ikeda-Ohno, A.;
The lanthanide (Ln) complexes with N-chelating ligands have attracted considerable attentions because of their unique tuneable steric and electronic properties.[1] Amongst such Ln complexes with N-chelating ligands, amide-based complexes are known to offer a wide range of applications, e.g., as efficient luminescent agents employed in bio-analytical fields.[2] Furthermore, amidine-based complexes enable the Ln metals to stabilise in exotic oxidation states (i.e., di- and tetravalent) with remarkable catalytic activity.[3]
These unique properties of amide- and amidine-based complexes of f-elements motivate us to perform the present study focusing on the synthesis and characterisation of the f-element complexes with newly synthesised amide- and amidine ligands shown in Figure 1. The aim of this study is to investigate the physical/chemical properties (e.g., optical properties) of f-elements (i.e., Ln and actinides (An)) complexed with the amide- and amidine ligands and compare their properties between Ln and An, and between solid and solution states, by means of single-crystal X-ray diffraction, X-ray absorption spectroscopy, etc. A comprehensive overview of the amide- and amidine complexes of f-elements will be presented particularly in terms of structural point of view.

References
1 A. A. Trifonov, Coord. Chem. Rev. 2010, 254, 1327 –1347.
2 e.g., Y. Tang et al., Inorg. Chem. Commun. 2005, 8, 1018-1021; J. Xu et al., J. Am. Chem. Soc. 2011, 133, 19900–19910.
3 F. T. Edelmann, Chem. Soc. Rev. 2009, 38, 2253-2268.
Keywords: lanthanide actinide complex amide amidine single-crystal XRD
  • Poster
    International conference on f-elements, 06.-09.09.2015, Oxford, United Kingdom

Publ.-Id: 22310 - Permalink


Dilute ferromagnetic InMnP
Khalid, M.; Weschke, E.; Skorupa, W.; Helm, M.; Zhou, S.;
We have synthesized a new magnetic semiconductor,InMnP, by Mn ion implantation and pulsed laser annealing [1, 2]. Clear ferromagnetic hysteresis loops and a perpendicular magnetic anisotropy are observed up to a Curie temperature of 42 K. Large values of negative magnetoresistance and magnetic circular dichroism as well as anomalous Hall effect are further evidences of a ferromagnetic order in InMnP. An effort is made to understand the transport mechanism in InMnP using the theoretical models. We find that the valence band of InP does not merge with the impurity band of the heavily doped InMnP (8 %). Our results suggest that impurity band conduction is a characteristic of Mn‐doped InP and GaP which have deep Mn‐ cceptor levels. [1] M. Khalid, et al., Phys. Rev. B 89, 121301(R) (2014) [2] M. Khalid, et al., J. Appl. Phys. 117, 043906 (2015).
  • Poster
    20th International Conference on Mangetism, 05.-10.07.2015, Barcelona, Spain

Publ.-Id: 22309 - Permalink


Mid-infrared ridge waveguide in MgO:LiNbO3 crystal produced by combination of swift O5+ ion irradiation and precise diamond blade dicing
Cheng, Y.; Lv, J.; Akhmadaliev, S.; Zhou, S.; Kong, Y.; Chen, F.;
We report on the fabrication of ridge waveguide operating at mid-infrared wavelength in MgO:LiNbO3 crystal by using O5+ ion irradiation and precise diamond blade dicing. The waveguide shows good guiding properties at the wavelength of 4 μm along the TM polarization. Thermal annealing has been implemented to improve the waveguiding performances. The propagation loss of the ridge waveguide has been reduced to be 1.0 dB/cm at 4 μm after annealing at 310 °C. The micro-Raman spectra indicate that the microstructure of the MgO:LiNbO3 crystal has no significant change along the ion track after swift O5+ ion irradiation.
Keywords: Optical waveguide; MgO:LiNbO3 crystal; Ion irradiation; Diamond blade dicing; Mid-infrared waveguides

Publ.-Id: 22308 - Permalink


Enhancing Robustness and Applicability of Contactless Inductive Flow Tomography
Ratajczak, M.; Wondrak, T.; Zürner, T.; Stefani, F.;
Measuring the flow velocity in hot, chemically aggressive and opaque melts is a challenging task even for today’s measurement techniques. The contactless inductive flow tomography (CIFT) could provide a solution by applying magnetic fields to an electrically conducting melt and measuring the small flow-induced magnetic perturbances outside of the container. In this paper we will demonstrate how the robustness of CIFT can be enhanced by means of excitation with time-harmonic magnetic fields, making it more insensitive to the ubiquitous changes of the environmental magnetic field. Further we will show how the problem of an electrically conducting container can be treated, which is necessary, e.g., for industrial application in continuous casting.
  • Contribution to proceedings
    IEEE Sensors 2015, 01.-04.11.2015, Busan, Südkorea
    Proceedings of IEEE Sensors 2015, 662-665
  • Lecture (Conference)
    IEEE Sensors 2015, 01.-04.11.2015, Busan, Südkorea

Publ.-Id: 22307 - Permalink


Ferromagnetism induced by vacancy clusters in Silicon
Liu, Y.; Zhang, X. H.; Yuan, Q.; Han, J. C.; Zhou, S. Q.; Song, B.;
Defect-induced ferromagnetism provides an alternative for organic and semiconductor spintronics. Though it is weak, it can be stable above room temperature. Till now it has been confirmed at least in oxides [1, 2] and carbon based materials [3, 4]. Interestingly, the relation between magnetism and defects in Silicon was demonstrated decades ago [5]. Since then, some progresses were made [6-9] and push forward the research of magnetic Mn doped Si a lot but it is drawn little attention itself. Here, with the latest growth purifying technique and sensitive measurements, we investigated the magnetism in Silicon after neutron irradiation and try to correlate the observed magnetism to particular defects in Si.
Keywords: defect-induced ferromagnetism, silicon, neutron irradiation, semiconductors
  • Poster
    28th International Conference on Defects in Semiconductors, 27.-31.07.2015, Espoo, Finland

Publ.-Id: 22306 - Permalink


Strong Auger scattering in Landau-quantized graphene evidenced by circularly polarized pump-probe spectroscopy
Winnerl, S.; Mittendorff, M.; Wendler, F.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.;
While the carrier dynamics in graphene in absence of magnetic fields is well researched in a large spectral range ranging from UV to THz, the dynamics in Landau quantized graphene is almost unexplored. We investigate the carrier dynamics within the system of Landau levels (LLs) of index n = -1, n = 0 and n = 1 by pump-probe experiments complemented by microscopic modelling. Using circularly polarized terahertz radiation (at 18 THz) allows one to selectively excite the two energetically degenerate transitions LL-1 → LL0 and LL0 → LL1, respectively (at B  4 T). While three of the four possible configurations give intuitive results (bleaching, when pumping and probing with the same polarization, induced absorption with opposite polarizations), surprisingly, one configuration counterintuitively leads to bleaching while pumping and probing with opposite polarizations (Fig. 1 lower panel). This implies that even though LL0 is being optically pumped, its population decreases [1] ! Calculations show that LL0 is actually depleted by strong Auger scattering. Note that the two configurations shown in the Figure are distinguishable only because of the slight (n-type) doping of the graphene sample.
We discuss the role of carrier-carrier and carrier-phonon scattering in Landau quantized graphene and provide an outlook on the application potential of this system for tunable THz lasers.
Keywords: Graphene, Landau levels, carrier relaxation, pump-probe, free electron laser
  • Lecture (Conference)
    Electronic Properties Of Two-Dimensional Electron Systems (EP2DS-21), 26.-31.07.2015, Sendai, Japan

Publ.-Id: 22305 - Permalink


Effect of an upward magnetic field on nanosized sulfide precipitation in ultra-low carbon steel
Duan, K. J.; Zhang, L.; Yuan, X. Z.; Han, S. S.; Liu, Y.; Huang, Q. S.;
An induction levitation melting (ILM) refining process is performed to remove most microsized inclusions in ultra-low carbon steel (UCS). Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nm remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthening phase.
Keywords: ultra-low carbon steel; magnetic field; sulfide precipitation; induction levitation; titanium

Publ.-Id: 22304 - Permalink


Comparative study of ultrafast X-ray tomography and wire-mesh sensors for vertical gas-liquid pipe flows
Banowski, M.; Beyer, M.; Szalinski, L.; Lucas, D.; Hampel, U.;
At the Institute of Fluid Dynamics of the Helmholtz-Zentrum Dresden-Rossendorf the wire-mesh sensor and the ultrafast X-ray tomography were developed to investigate two-phase flows with high spatial and temporal resolution. In the TOPFLOW facility, a test section was constructed for a comparative study of wire-mesh sensors and ultrafast X-ray tomography. Due to a minimum vertical distance between X-ray and wire-mesh positions, the results can be compared directly neglecting flow developing effects. Varying water and air superficial velocities in a wide range, flow regimes from bubble flow via slug flow to annular flow were investigated. Four typical experimental results are presented and discussed in this paper. Finally, the application ranges for both measurement techniques are briefly discussed.
Keywords: X-ray tomography, Wire-mesh sensor, vertical pipe, two-phase flow
  • Contribution to proceedings
    7th International Symposium on Process Tomography, 01.-03.09.2015, Dresden, Deutschland
  • Lecture (Conference)
    7th International Symposium on Process Tomography, 01.-03.09.2015, Dresden, Deutschland
  • Flow Measurement and Instrumentation 53(2017), 95-106
    DOI: 10.1016/j.flowmeasinst.2016.02.001

Publ.-Id: 22303 - Permalink


In-situ observation of 3D particle assembly
Josten, E.; Wetterskog, E.; Glavic, A.; Boesecke, P.; Rücker, U.; Bergström, L.; Brückel, T.;
The self-assembly of magnetic nanoparticles has a high potential for future applications [1], as it allows mass production processes of very small structures without the use of expensive equipment. The process itself is complex, including several interactions between nanoparticles, solvent, and substrate. A deeper understanding is the key for a better control of the self-organization process.

The present work adds a novel quantitative contribution to the study of the kinetics in 3D long range ordered nanoparticle superstructures. These superstructures have been investigated in-situ during the self-assembly using an optimized GISAXS setup to explore the dynamic growthmodes during deposition. The nanoparticles investigated are well-characterized γ-Fe2O3 nanospheres [2,3], which have been deposited on a substrate to form an ensemble of highly ordered superstructures (mesocrystals) [4].

The time-dependent GISAXS study of the self-assembly process, carried out at the ID01 beamline at ESRF, resulted in an understanding of how the structures evolve with time and how the evaporation can be controlled by external parameters. The in-situ cell (fig.1), which was developed to monitor the structure as well as the height and shape of the droplet, was employed for additional control of the process parameters and the possibility of an accurate identification of key physical parameters governing the process. The time evolution of the ordering process was analyzed by fitting position and width of multiple peaks for all recorded GISAXS patterns (for example fig.2). New insights into the drying and self-assembly process of an ensemble of 3D highly ordered superstructures were obtained and evaporation time-dependent stages of the mesocrystal growth and their spatial positions were identified [5].
Keywords: magnetic nanoparticles, in-situ GISAXS, self-assembly, X-ray scattering, mesocrystals
  • Lecture (Conference)
    GISAS2015, 08.-11.09.2015, Nice, Frankreich
  • Poster
    GISAXS2016 workshop, 16.-18.11.2016, Hamburg, Deutschland

Publ.-Id: 22302 - Permalink


Reduction of phase noise in nanowire spin orbit torque oscillators
Yang, L.; Verba, R.; Tiberkevich, V.; Schneider, T.; Smith, A.; Duan, Z.; Youngblood, B.; Lenz, K.; Lindner, J.; Slavin, A. N.; Krivorotov, I. N.;
Spin torque oscillators (STOs) are compact, tunable sources of microwave radiation that serve as a test bed for studies of nonlinear magnetization dynamics at the nanometer length scale. In particular, the spin torque in an STO can be created by spin-orbit interaction, but low spectral purity of the microwave signals generated in spin orbit torque oscillators hinders practical applications of these magnetic nanodevices. Here we demonstrate a method for decreasing the phase noise of spin orbit torque oscillators based on Pt/Ni80Fe20 nanowires. We experimentally demonstrate that tapering of the nanowire, which serves as the STO active region, significantly decreases the spectral linewidth of the generated signal. We explain the observed linewidth narrowing in the framework of Ginzburg-Landau auto-oscillator model. The model reveals that spatial non-uniformity of the spin current density in the tapered nanowire geometry hinders the excitation of higher order spin-wave modes, thus stabilizing the single-mode generation regime. This non-uniformity also generates a restoring force acting on the excited self-oscillatory mode, which reduces thermal fluctuations of the mode spatial position along the wire. Both these effects improve the STO spectral purity.
Keywords: n.n

Publ.-Id: 22301 - Permalink


Stability of MR brain-perfusion measurement using arterial spin labeling
Petr, J.; Hofheinz, F.; Platzek, I.; Schramm, G.; van den Hoff, J.;
Arterial spin labeling (ASL) is an MR technique for assessment of cerebral blood flow (CBF) that does not require use of contrast agents which makes it a less invasive alternative to the 15O-H2O-PET measurement. The repeatability of ASL has been studied extensively but mainly in young healthy volunteers. We have tested repeatability of ASL under realistic clinical conditions in elderly brain tumor patients acquired with a Philips Ingenuity TF PET/MR in the context of an ongoing 11C-Methionine PET/MR study. Twenty three patients (age 54.8±13.0 y) were scanned on two or more session. The patients underwent 6 weeks of concurrent radiochemotherapy with Temozolomide between the first session and second measurement. The mean relative difference of gray matter CBF was 18.6% between the first two session and 13.0% for the second session and further on. The mean gray matter CBF was 46.6±7.2 mL/min/100 g on the first sessions and there was a significant decrease of 9.8% between first and second session (p=0.027). In summary, the ASL presents measurement of CBF with reasonable repeatability also in elderly patients under clinical conditions when it is not possible to control for all sources of variation. Significant decrease of CBF in healthy tissue was observed after the radiochemotherapy. Prospectively, the ASL data together with the also acquired 11C-Methionine PET will be evaluated regarding their separate and combined ability to predict patient outcome and effectiveness of the performed radiochemotherapy.
  • Lecture (Conference)
    PSMR 2015: 4th Conference on PET/MR and SPECT/MR, 17.-21.05.2015, La Biodola, Isola d’Elba, Italy
  • Open Access LogoAbstract in refereed journal
    EJNMMI Physics 2(2015)Suppl. 1, A67
    DOI: 10.1186/2197-7364-2-S1-A67

Publ.-Id: 22300 - Permalink


Measuring the Influence of Vessel Geomery on PCASL Labeling Efficiency
Petr, J.; Schramm, G.; van den Hoff, J.;
TARGET AUDIENCE: Clinicians and researcher interested in efficient planning of the pseudo-continuous arterial spin labeling (ASL).
PURPOSE: The labeling efficiency of pseudo-continuous ASL1 (pCASL) and its inter- and intra-subject reproducibility is a crucial point for reliable cerebral-blood-flow (CBF) measurements with ASL. Potential causes of varying labelling efficiency are, for example, B0 field inhomogeneity2, blood velocity3, or labeling-plane positioning3. The common recommendation is to position the labeling plane on a straight part of the vessel and perpendicular to them6. However, it is not always possible to avoid tortuous parts of the vessels if angiography is not available. Here, we study the effect of vessel geometry on the labeling efficiency both trough simulations and experiments.
METHODS: Simulations: Labeling efficiency was calculated for three cases of vessels geometry using numerical simulations as described by Wu4. Blood velocities between 1 and 40 cm/s were investigated and laminar flow was assumed. First, efficiency was calculated for a plane perpendicular to a straight vessel and angulated at 12.5°, 22.5°, or 45°. Second, a simple bend of the vessel was assumed with a length of the horizontal section of 0, 5, or 10 mm and the labeling plane positioned on the center of it and 2, 6, or 12 mm below (see Fig. 1a). Third, the bend was rotated 0°, 12.5°, 22.5°, or 45° so that the labeling plane intersected the vessel three times (Fig. 1b). Acquisitions: Five healthy young volunteers (age 31.8±3.9 y) were scanned at 3T using an eight-channel head-coil. A 3D TFE T1-weighted sequence and five pCASL sequences (pCASL1-pCASL5) with different position of the labeling plane were acquired. The T1-weighted sequence had voxel size 1×1×1 mm3. The common parameters of the pCASL sequence were: TR/TE = 3765/11 ms, FOV = 220×220 mm2,
pixel size = 2.75×2.75×6 mm3, 17 slices (0.6 mm gap), flip angle = 90°, 20 averages, background suppression with 2 pulses, 2D multi-slice EPI readout, labeling with a Hanning RF-pulse with duration 0.5 ms, tip angle 18°, and inter-pulse pause 0.5 ms, labeling time/post-labeling delay 1525/1650 ms. A reference image was acquired 5000 ms after saturation. For pCASL1, the labeling plane was set parallel with the imaged slices and the gap
was set in a way that the labeling plane intersected vertebral arteries (VA) at the level of siphon. The labeling plane was placed as parallel to the horizontal section of the VAs as possible (Fig. 1c). For pCASL2,3, the labeling plane was positioned 6 and 12 mm lower, respectively, than in pCASL1 (Fig. 1c). In pCASL4, 5 the labeling plane was positioned as in pCASL3 and rotated in the sagittal plane -30° and 30° with the center of rotation in the internal
carotid arteries (ICA), see Fig. 1c.
Preprocessing: The dynamics of all sequences were aligned with the first dynamics of pCASL1, thus coregistering the sequences and compensating for motion within each sequence. The T1-weighted image was aligned to the mean control image and segmented to obtain partial volume fractions for gray matter (GM). CBF was quantified according to the ASL white-paper6. Mean CBF (GM > 70%) in the vascular territories corresponding to the anterior cerebral artery (ACA), posterior cerebral artery (PCA), middle cerebral artery (MCA), and vertebral artery (VA) were computed for each sequence and subject. For pCASL1,2,4,5, the relative difference of the
mean CBF for each region was calculated relative to pCASL3 which was considered optimal as it contained no twists or angulations.
RESULTS: According to the numerical simulations, the decrease in labeling efficiency due to plane angulation is under 5% for most blood velocities and angle up to 30°, but it can go up to 10% for 45° angulation (Fig. 2c). For a bend in the vessel (Fig. 1a) of length 10 mm, the labeling efficiency can be decreased 20-25% (Fig. 2b). With increasing distance of the labeling plane, the decrease is only about 10% at 2mm (Fig. 2a), under 3% at 6mm and under 1% at 12 mm distance. For multiple intersections (Fig. 1b), the labeling efficiency decreased 25-30% regardless of the examined angle. The mean relative difference from sequence pCASL3 for different vascular territories is displayed in Tab. 2.
DISCUSSION: The experiments confirmed that labeling plane shift (pCASL1,2 in Tab. 1) or angulation up to 30° on ICA (pCASL4,5) produced less than 4% change of CBF in the ACA and MCA regions. Positioning the labeling plane on a section of VA parallel with it (pCASL1) caused 5.0% and 14.7% CBF decrease in PCA and VA regions respectively, although only in VA the change was significant. By increasing the distance from the bend (pCASL2), the CBF decrease became lower and not significant. Significant decrease of CBF of 8.4% and 16.9% in both PCA and VA regions, respectively, was achieved by positioning the labeling plane in a way to intersect VA at siphon multiple times. More significant decrease was expected from the simulations. The reason can be, that the actual vessel geometry was different from the worst modeled case. More measurements need to be done to find out why the decrease was lower in PCA than in VA. There are several limitations in this study. The magnetization transfer effects on the label were not taken into account5. Laminar flow profile was assumed, however the vessel thickness with regards to gradient fields was neglected for simplicity. By angulating the labeling plane, it is possible that it can intersect the imaged volume and thus directly or by magnetization transfer effects lower the measured perfusion signal. To minimize influence of this, the pixels where minimal-maximal intensity difference for all sequences was more than 10% were excluded from the analysis.
CONCLUSION: Reasonable angulation of the labeling plane causes only insignificant changes in labeling efficiency and measured CBF. On the other hand, twist and loops of the vessels as well as multiple crossing of the vessels by a labeling plane can cause significant changes of up to 25% and possibly even more, although this has been experimentally demonstrated only in VA region and not in PCA region.
REFERENCES:
1. W Dai, et al. Magn Reson Med, 2008;60(6):1488–97.
2. H Jahanian, et al. NMR in Biomedicine, 2011;24(10):1202–9.
3. S Aslan, et al. Magn Reson Med, 2010;63(3):765–71.
4. WC Wu, et al. Magn Reson Med, 2007;58(5):1020–7.
5. L Hernandez-Garcia, et al. NMR in Biomedicine, 2007;20(8):733–42.
6. Alsop, et al. Magn Reson Med, 2014; DOI: 10.1002/mrm.25197.
  • Poster
    23rd Annual Meeting of the International Society for Magnetic Resoonance in Medicine (ISMRM), 30.05.-05.06.2015, Toronto, Canada
  • Contribution to proceedings
    23rd Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM), 30.05.-05.06.2015, Toronto, Canada
    ISMRM '15: Proceedings of the 23rd Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 2952

Publ.-Id: 22299 - Permalink


An implementation of dead-time corrections in microbeam measurements on a pixel by pixel basis
Munnik, F.;
In microbeam measurements on inhomogeneous samples large variations in count-rate can occur. These variations result in variations in dead-time that have to be used to correct elemental distribution maps. However, the dead-time is usually not available on a pixel by pixel basis. In this work, a simple model is proposed to calculate the dead-time for each pixel. Measurements to determine the dead-time per event, needed in the model, are presented and the dead-time corrections are presented for real samples.
  • Poster
    Workshops für Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Deutschland

Publ.-Id: 22298 - Permalink


Ionenstrahlanalyseverfahren in der Materialforschung
Schmidt, B.; Wetzig, K.;
Der Schwerpunkt der Materialanalyse mittels Ionenstrahlen ist die Bestimmung der Zusammensetzung und Struktur von oberflächennahen Festkörperschichten im Tiefenbereich von wenigen nm bis zu einigen µm. Charakteristisch für die verschiedenen Ionenstrahlanalysetechniken sind die Verwendung geeigneter Ionenstrahlen (z.B. Ionenart, Ionenenergie und -strom, Strahlfokus usw.), die Art der Ionen-Festkörper-Wechselwirkung (und deren Wirkungsquerschnitt), die entstehende Strahlungsart (z.B. gesputterte Sekundärionen, gestreute Ionen sowie Ionen-induzierte Photonen- und Elektronenemission). Die Vielzahl der Ionenstrahl-analyseverfahren kann bezüglich der verwendeten Ionenenergien in drei Gruppen eingeteilt werden [1]: 1) niedrige Ionenenergien von einigen keV, 2) mittlere Ionenenergien im Bereich 30-300 keV, und 3) hohe Ionenenergien im Bereich ~0,5-100 MeV. Schwere Ionen (Mi > Moxygen) für eine hinreichende Sputterausbeute an Targetatomen sind notwendig im weit verbreiteten Verfahren der Sekundärionen-Massen-Spektrometrie (SIMS). Leichte Ionen (M < 10, meistens H+, He+) werden in einem breiten Energiebereich für verschiedene Ionenstreuverfahren (LEIS, MEIS, RBS) sowie verschiedene Verfahren der Ionen-induzierten Photonenemission (PIXE, PIGE) eingesetzt. Dagegen werden schwerere, hochenergetische Ionen (z.B. N, O, Cl usw.) hauptsächlich für NRA und ERDA verwendet.
Im Vortrag werden die verschiedenen Ionenstrahlanalyseverfahren mit ihren charakteristischen Analyseparametern und Einsatzgebieten kurz vorgestellt und miteinander verglichen. Dabei wird besonders auf die hochauflösende Tiefen-profilierung für Dotierungsprofile in Halbleitern und die Elementanalyse von Dünnschichtsystemen eingegangen. Hierfür sind besonders die modernen Mikroelektronik- und Dünnschichttechnologien mit Forderungen nach immer dünneren Schichtsystemen und somit nach steigender Tiefenauflösung sowie kleineren Nachweisgrenzen die treibende Kraft. Weiterhin werden ausgewählte Beispiele für den Einsatz von Ionenstrahlanalyseverfahren in anderen Gebieten der Materialwissenschaften, z.B. in der Kunst und Archäometrie sowie in der Medizin diskutiert.
  • Invited lecture (Conferences)
    18. Tagung Festkörperanalytik, 06.07.2015, Wien, Österreich

Publ.-Id: 22297 - Permalink


Probing defect driven tunable spontaneous magnetization in paramagnetic Zn0.95Co0.05O epitaxial films by X-ray absorption investigations
Satyarthi, P.; Ghosh, S.; Wang, Y.; Zhou, S.; Kumar, P.; Kanjilal, D.; Olivi, L.; Bürger, D.; Skorupa, I.; Schmidt, H.; Srivastava, P.;
In order to address existing unresolved issues related to intrinsic and extrinsic origins of ferromagnetism in Zn1−xCoxO based diluted magnetic semiconductors for varying x, the present work aims to investigate the tunable ferromagnetism triggered in paramagnetic Zn0.95Co0.05O films using 500 KeV inert xenon ion irradiation of different fluences. The origin of ferromagnetism in post irradiated Zn0.95Co0.05O films is understood from different densities of bound magnetic polarons (BMPs) formation through correlated spins of tetrahedrally substituted Co2+ ions and anionic vacancies. The alteration in crystallographic positions of Zn, Co cations, and O anions in the tetrahedral environment as analyzed from Zn and Co K-edgeX-ray absorption and O 1s photoemission is a crucial factor for the stabilization of different density of BMPs. Magnetic field and temperature dependence of X-ray magnetic circular dichroism at the Co L2,3 edge provide experimental evidence of purely paramagnetic contribution from well localized Co2+ ions of Co sublattice for paramagnetic Zn0.95Co0.05O film. The paramagnetic Co2+ ions of Co sublattice persist in irradiated films, which reveal BMPs formation as the origin of ferromagnetism.
Keywords: Diluted magnetic semiconductors; X-ray absorption; Spintronics

Publ.-Id: 22296 - Permalink


Identification and quantification of PGMs by combining MLA and EPMA with a new approach to the offline overlap correction of major and trace PGE concentrations
Osbahr, I.; Krause, J.; Bachmann, K.; Gutzmer, J.;
The identification and accurate characterisation of platinum-group minerals (PGMs) is usually a very cumbersome procedure due to their small grain size (typically below 10 µm) and inconspicuous appearance under reflected light. A novel strategy for finding and quantifying PGMs by combining mineral liberation analysis (MLA), a point logging system and electron probe microanalysis (EPMA) was thus developed.
As a first step, the PGMs are identified using the MLA. Grains identified as PGMs are then marked and coordinates recorded with the point logger are then transferred to the EPMA. Case studies e.g. from the platiniferous reefs (Merensky Reef and UG2) of the Bushveld Complex (South Africa) illustrate that the combination of MLA, point logger and EPMA results in the identification of a significantly (up to 20 times) higher number of PGM grains than by careful reflected light microscopy.
The analysis of PGEs as major elements in PGMs or as trace elements in e.g. base metal sulfides by EPMA requires considerable effort. Due to the often significant overlaps between the X-ray spectra of almost all platinum-group and associated elements, X-ray lines suitable for quantitative analysis need to be carefully selected. As peak overlaps cannot be avoided completely, an offline overlap correction based on weight proportions has been developed. A reliable overlap correction is of particular importance e.g. in Ru-sulfides as laurite if the overlapped element is a trace element (Rh) and the overlapping element is a major constituent (Ru). Results obtained with the procedure attain acceptable totals and atomic proportions, indicating that the applied corrections are appropriate.
Keywords: Mineral Liberation Analyser, Electron Probe Microanalyser, Offline Overlap Correction, Platinum-Group Minerals
  • Poster
    Goldschmidt2015, 16.-21.08.2015, Prag, Tschechien

Publ.-Id: 22295 - Permalink


A novel approach for efficient identification and accurate chemical characterisation of platinum-group minerals by combining Electron Probe Microanalysis and Mineral Liberation Analysis
Osbahr, I.; Krause, J.; Bachmann, K.; Gutzmer, J.;
The identification and accurate characterisation of platinum-group minerals (PGMs) is usually a very cumbersome procedure due to their small grain size (typically below 10 µm) and inconspicuous appearance under reflected light. A novel strategy for finding PGMs and quantifying their composition was developed. It combines SEM-based automated mineralogy, in this study mineral liberation analyser (MLA) Quanta 650F by FEI, a point logging system (JEOL) and a FE-EPMA (JEOL JXA-8530F). Thin sections from a layered intrusion (UG2) in the Bushveld Complex and from two Uralian-Alaskan-type complexes in the Ural Mountains, Russia, were investigated as case studies.
As a first step, the PGMs are identified using the MLA. Grains identified as PGMs are then marked and coordinates recorded and transferred to the EPMA. Case studies illustrate that by introducing MLA for the efficient and largely automated identification of PGM grains in polished thin sections, up to 20 times more PGM grains were identified, whilst shortening time needed and avoiding the effects of human error invariably associated with reflected light microscopy. This is mainly due to the facts that (a) PGM with grain sizes < 5µm are reliably identified and (b) PGM and closely associated base metal sulfides and sulfosalts are well differentiated with the MLA. The analysis of PGMs by EPMA requires considerable effort due to the often significant overlaps between the X-ray spectra of almost all platinum-group and associated elements (e.g. OsMβ on IrMα and AuMβ on HgMα). X-ray lines suitable for quantitative analysis need to be carefully selected. As peak overlaps cannot be avoided completely, an offline overlap correction based on weight proportions has been developed. Considerable variations in the repeatedly determined overlap factors illustrate the need for a re-determination of the overlap factors with each calibration. Results obtained with the procedure proposed in this study attain acceptable totals and atomic proportions, indicating that the applied corrections are appropriate.
Keywords: Mineral Liberation Analyser, Electron Probe Microanalyser, Platinum-Group Minerals, Platinum-group Elements, offline overlap correction
  • Poster
    Geoanalysis 2015 - The 9th International Conference on the Analysis of Geological and Environmental Materials, 09.-14.08.2015, Leoben, Österreich

Publ.-Id: 22294 - Permalink


Working with uncertainty in adaptive process optimisation
van den Boogaart, K. G.; Tolosana Delgado, R.; Matos Camacho, S.;
This contribution is concerned with adaptive processing decisions, where the process parameters are optimally adapted to the varying properties of the material input stream. Our starting point is the geometallurgical paradigm that the varying properties of the input stream are considered known e.g. from a geometallurgical model of the mined ore body, and optimal processing parameters are computed from them, by finding the parameter seaming optimal in a computer simulation.
This approach however has to work with a lot of uncertainties: The prediction of the geometallurgical ore parameters can only be done with some geostatistical uncertainty. The parameters themselves are only proxies for true ore properties. Model prediction can differ relevantly from actual process results, due to model simplifications. Due to these uncertainties the computed processing choices can turn out to be inferior to simple non-adaptive processing.
We systematically analysed this effect, by modelling this uncertainty effect mathematically and in computer simulations.
The most important findings are:
(a) Processing choices not taking into account the uncertainty sometimes even perform worse than simple non-adaptive processing, for the sole reason of ignoring the uncertainty effect.
(b) Ore properties, not adequately reflected in the ore description, might require different approaches, in which the observed processing behaviour feeds back into process control.
(c) Bayesian decision theory allows computing optimal processing choices combining the information from the mine (geostatistical predictions) and from the process feedback. These choices give much more robust choices and do not suffer from the drawbacks described for the simple approach we started from.
This new approaches can substantially improve the performance of adaptive processing in existing plants.
Keywords: Geometallurgy, Adpative Processing, Bayesian Optimisation
  • Lecture (Conference)
    IMPC 2016, XXVIII International Mineral Processing Congress, 11.-15.09.2016, Québec, Canada
  • Contribution to proceedings
    IMPC 2016, XXVIII International Mineral Processing Congress, 11.-15.09.2016, Quebec, Canada
    IMPC 2016: XXVIII International Mineral Processing Congress Proceedings: Canadian Institute of Mining, Metallurgy and Petro, 978-1-926872-29-2

Publ.-Id: 22293 - Permalink


Programme IAMG 2015 Freiberg, Germany, September 5-13, 2015, The 17th Annual Conference of the International Association for Mathematical Geosciences
Schaeben, H.; Tolosana Delgado, R.; van den Boogaart, K. G.; van den Boogaart, R.; (Editors)
Das ist das Programmheft der IAMG2015 Konferenz
  • Book (Editorship)
    Freiberg: IAMG Office, 2015
    40 Seiten

Publ.-Id: 22292 - Permalink


Proceedings IAMG 2015 Freiberg, Germany, September 5-13, 2015, The 17th Annual Conference of the International Association for Mathematical Geosciences
Schaeben, H.; Tolosana Delgado, R.; van den Boogaart, K. G.; van den Boogaart, R.; (Editors)
These are the proceedings with the long Abstracts of the IAMG 2015 conference
Keywords: Mathematical Geosciences, Mathematical Geology, Geoinformatics
  • Book (Editorship)
    Freiberg: IAMG Office, 2015
    1372 Seiten
    ISBN: 978-3-00-050337-5

Publ.-Id: 22291 - Permalink


Short Abstracts IAMG 2015 Freiberg, Germany, September 5-13, 2015, The 17th Annual Conference of the International Association for Mathematical Geosciences
Schaeben, H.; Tolosana Delgado, R.; van den Boogaart, K. G.; van den Boogaart, R.; (Editors)
This is the shorts abstracts volume of the IAMG2015 Conference
Keywords: Mathematical Geosciences, Mathematical Geology, Geoinformatics
  • Book (Editorship)
    Freiberg: IAMG Office, 2015
    249 Seiten

Publ.-Id: 22290 - Permalink


Two-photon quantum well infrared photodetectors below 6 THz
Franke, C.; Walther, M.; Helm, M.; Schneider, H.;
Two-photon quantum well infrared photodetectors (QWIPs) are nonlinear detectors for the mid-infrared and terahertz regimes optimized for resonant two-photon absorption. Here we present first results on two-photon QWIP samples based on the GaAs/AlGaAs material system with intersubband energies between 25 and 12 meV (6 to 3 THz) confirmed by photocurrent spectra. The dark current showed large discontinuities, presumably caused by impact ionization. We performed interferometric autocorrelation experiments at the free-electron laser FELBE and observed nonlinear interferograms for all samples.
Keywords: quantum well infrared photodetector; QWIP; interferometric autocorrelation; nonlinear optics; two-photon absorption

Publ.-Id: 22289 - Permalink


Innovative once-through thorium fuel cycle for the PTVM LWR concept
Rachamin, R.; Fridman, E.; Galperin, A.;
An advanced once-through thorium fuel cycle for the novel reactor concept, termed the pressure tube light water reactor with variable moderator control (PTVM LWR), is proposed. The main innovation of the concept is described. The PTVM LWR makes use of a seed-blanket geometry, whereby the core is divided into separated regions of thorium fuel channel assemblies (blanket) and low-enriched uranium fuel channel assemblies (seed). A scheme based on two separate fuel flow routes (i.e., seed route and blanket route) is proposed. Neutronic analysis indicates that the novel scheme has the potential to utilize both seed and blanket in an efficient manner.
Keywords: pressure tube reactor, “breed & burn”, moderator variation, seed-blanket geometry, once-through thorium fuel cycle
  • Open Access LogoContribution to proceedings
    Thorium Energy Conference 2015 (ThEC15), 12.-15.10.2015, Mumbai, India
  • Poster
    Thorium Energy Conference 2015 (ThEC15), 12.-15.10.2015, Mumbai, India

Publ.-Id: 22288 - Permalink


Liquid metal modelling of continuous steel casting
Gerbeth, G.; Wondrak, T.; Stefani, F.; Shevchenko, N.; Eckert, S.; Timmel, K.;
Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. We present recent results from the three LIMMCAST facilities working either with room-temperature alloy GaInSn or with the alloy SnBi at temperatures of 200-350°C. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution, which is essential for code validation. Experimental results are presented covering the following phenomena: contactless electromagnetic tomography of the flow in the mold, flow monitoring by ultrasonic sensors, mold flow under the influence of an electromagnetic brake, injection of argon bubbles through the stopper rod, X-ray visualization of gas bubble two-phase flow in the nozzle and in the mold.
Keywords: Continuous casting, physical modeling, flow measurements, magnetic field, flow control, electromagnetic brake
  • Invited lecture (Conferences)
    6th Baosteel Biannual Academic Conference and the 10th CSM Steel Congress, 21.-23.10.2015, Shanghai, China
  • Contribution to proceedings
    The 10th CSM Steel Congress and the 6th Baosteel Biennial Academic Conference, 21.-23.10.2015, Shanghai, China
    Proceedings of the 10th CMS Steel Congress & the 6th Baosteel Biennial Academic Conference: Metallurgical Industry Press, Book of Abstracts: 978-7-5024-7006-7, 8-13

Publ.-Id: 22287 - Permalink


Experimentelle Modellierung von Stranggussprozessen mit niedrig schmelzenden Legierungen
Timmel, K.; Wondrak, T.; Röder, M.; Shevchenko, N.; Miao, X.; Stefani, F.; Eckert, S.;
Die Strömung der Metallschmalze beim kontinuierlichen Stranggießen hat wesentlichen Einfluss auf das erreichte Gussergebnis. Probleme entstehen beispielsweise durch Einschlüsse von Oxiden, intermetallischen Verbindungen oder Gasblasen, die durch eine unkontrollierte Strömung in die Erstarrungszone gelangen. Die Untersuchung und Optimierung der Strömungsvorgänge erfolgte bisher vorwiegend anhand von numerischen Simulationen sowie Wassermodellen und lieferte bereits viele Erkenntnisse. Aufgrund der Materialeigenschaften sind jedoch Wassermodelle in ihrer Anwendung begrenzt und können nicht alle im Prozess auftretende physikalische Phänomene abdecken, wie z.B. Temperaturgradienten in der Schmelze, Interaktion mit elektromagnetischen Feldern oder Mehrphasenströmungen. In diesen Fällen unterscheiden sich die Kennzahlen z.T. um mehrere Größenordnungen.
Am Helmholtz-Zentrum Dresden-Rossendorf stehen drei Anlagen zur Verfügung, welche sich mit der Modellierung des Stranggussprozesses unter der Verwendung niedrigschmelzender Legierungen befassen. Die Anlagen unterscheiden sich z.T. in der Ausrichtung ihrer Untersuchungsschwerpunkte und ergänzen sich so gegenseitig ideal. Das Mini-LIMMCAST Experiment arbeitet mit einer bei Raumtemperatur flüssigen Legierung und ist sehr flexibel aufgebaut. Viele unterschiedliche Untersuchungen können und sind hier bereits durchgeführt worden. Die große LIMMCAST-Anlage ist insbesondere für einen längeren kontinuierlichen Betrieb ausgelegt und operiert im Temperaturbereich von 200 – 350 °C. Die dritte Anlage X-LIMMCAST ist speziell für die Röntgenbildgebung und die Visualisierung der Zweiphasenströmung mit Gasblasen konzipiert. Die Flexibilität der Anlagen erlaubt eine Anpassung an konkrete Gegebenheiten.
Neben den experimentellen Anlagen müssen für einen sinnvollen Betrieb auch entsprechende Messtechniken zu Erfassung der Strömungsvorgänge in flüssigen Metallen zur Verfügung stehen. Für die Geschwindigkeitsmessung sind dazu in den Versuchen die Ultraschall-Doppler-Velocimetry, die kontaktlose, induktive Strömungstomographie und die Potentialsondenmethode zum Einsatz gekommen. Für die Auflösung der Zweiphasenströmung sind wiederum eine tomographische Methode als auch die Röntgenbildgebung verwendet worden. Ziel ist neben einem tieferen Verständnis des Prozesses, die Bereitstellung eine breiteren Datenbasis für die Validierung numerischer Modelle.
Es sollen in diesem Beitrag die drei Versuchsanlagen und ausgewählte Messtechniken beispielhaft anhand von Messergebnissen vorgestellt werden.
Keywords: Stranggießen, Flüssigmetallmodell, Strömungsmessung, elektromagnetische Strömungsbeeinflussung, Zweiphasenströmung
  • Lecture (Conference)
    WERKSTOFFWOCHE, 14.-17.09.2015, Dresden, Deutschland

Publ.-Id: 22286 - Permalink


Dipole strength distribution of 74Ge
Massarczyk, R.; Schwengner, R.; Bernstein, L. A.; Anders, M.; Bemmerer, D.; Beyer, R.; Elekes, Z.; Hannaske, R.; Junghans, A. R.; Kögler, T.; Röder, M.; Schmidt, K.; Wagner, A.; Wagner, L.;
The dipole strength distribution of 74Ge was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.0 and 12.1 MeV at the linear accelerator ELBE. We identified 94 levels with spin J = 1 up to an excitation energy of 8.9 MeV and analyzed the strength in the quasi-continuum of states. Simulations of statistical gamma-ray cascades were performed to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section below the neutron-separation energy derived in this way is combined with the photoabsorption cross section obtained from an earlier (gamma, n) experiment and compared with phenomenological approximations.
Keywords: Nuclear resonance fluorescence, photon scattering, bremsstrahlung, photoabsorption cross section.

Publ.-Id: 22285 - Permalink


Nanofabrication of self-organized periodic ripples by ion beam sputtering
Iacob, E.; Dell’Anna, R.; Giubertoni, D.; Demenev, E.; Secchi, M.; Böttger, R.; Pepponi, G.;
Ion beam sputtering of solid surfaces with ions of low keV energies can produce self-organized periodic ripple patterns of nanometer size on the surface of semiconductors, metals and insulators, therefore looking to be a single-step, cost-effective method to fabricate surface topographies over large areas for various electronic and bio-devices.
To date, a comprehensive theoretical understanding of the ripple development is still missing, and the achievement of the application-specific surface topography still relay on properly tuning different ion-beam parameters, since the experiments have highlighted the dependence of ripple characteristics on them.
The success of technological applications often requires an a-priori defined ratio of ripple height to wavelength. Here we discuss how to obtain regular ripples of height h~10 nm and wavelength λ<=50 nm on silicon surfaces. Xe+ and O+ ions were used to also investigate the role of the surface chemical reactivity.
The results show the development of regular ripples with wavelengths of ~40 nm and heights of ~2 nm superimposed on a less regular periodic topography for O+ bombardment on Si; the Xe+ on Si bombardment produced structures of regularity below the expected values. We discuss the gained insights and the best recipe for the required nano-patterns.
Keywords: ion bombardment, self-organization, silicon, ripples
  • Lecture (Conference)
    41st Micro and Nano Engineering, 21.-24.09.2015, The Hague, The Netherlands
  • Microelectronic Engineering 155(2016), 50-54
    DOI: 10.1016/j.mee.2016.02.025

Publ.-Id: 22284 - Permalink


Nanoporous Ge surface decomposition under ion bombardment: towards settling the dispute about driving forces
Böttger, R.; Liedke, B.; Liedke, M. O.; Heinig, K.-H.; Bischoff, L.;
First detailed studies of the nanoporous decomposition of Ge under ion irradiation date back more than 30 years. Irradiated Ge alters its (near-)surface morphology into a nanostructure, which remains stable after irradiation even under thermal treatment up to several hundred degrees Celsius. In recent years, this peculiar transformation of Ge has been studied extensively. However, a conclusive assessment of the driving force for the nanoporous Ge decomposition has not been reached yet.

We show that hole patterns and sponge-like layers of irradiated Ge surfaces originate from the same driving force, namely the kinetics of irradiation-induced defects in amorphous Ge layers. Ge hole patterns reported earlier for irradiation with low ion energies around 5 keV were reproduced for low energy Bi+ but also for Ge+ self-irradiation, which proves that the dominating driving force for morphology evolution cannot originate from the implanted impurities. At higher ion energies up to 100 keV the well-known formation of sponge-like Ge surface layers after heavy ion irradiation was found for Bi+ irradiation and Ge+ self-irradiation, too. The transition from smooth surfaces via hole patterns to sponge-like morphologies with increasing ion energy has been studied in detail. A model based on the kinetics of ion beam-induced defects was developed and implemented in 3D kinetic Monte Carlo simulations, which reproduce the transition from hole patterns to sponge-like layers with increasing ion energy. Finally, the proposed defect kinetics driven mechanism is undergird by a systematic positron annihilation spectroscopy investigation.
The authors acknowledge financial funding by the German Research Foundation via the Research Unit 845 “Selforganized nanostructures induced by low-energy ion beam erosion.”
Keywords: porous germanium, ion irradiation, defect kinetic, kinetic Monte-Carlo
  • Lecture (Conference)
    Workshop Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Deutschland
  • Lecture (Conference)
    8th International Workshop on Nanoscale Pattern Formation at Surfaces, 12.-16.07.2015, Krakow, Poland
  • Lecture (Conference)
    The 19th International Conference on Surface Modification of Materials by Ion Beams, 22.-27.11.2015, Chiang Mai, Thailand

Publ.-Id: 22283 - Permalink


Interactions of natural occurring eukaryotic microorganisms isolated from the uranium mine Königstein (Saxony, Germany) with U(VI)
Gerber, U.; Krawczyk-Bärsch, E.; Arnold, T.; Merroun, M. L.;
Despite high uranium concentrations (up to 14 mg L-1) and low pH (2.5 - 3.0) a high microbial diversity was detected by culture independent methods in the flooding water of the former uranium mine Königstein (Saxony, Germany). In this study we used culture dependent techniques for the isolation of eukaryotic microorganisms from the flooding water. It was possible to isolate different eukaryotic fungi with a glucose riche medium. The microbial isolates identified by 16S rDNA and 18S rDNA analysis were tested for their uranium tolerance abilities by the determination of the minimal inhibitory concentration (MIC) on solid media. The results showed high tolerances of uranium (up to 6 mM) on solid agar plates. Based on these results isolate KS5 (Rhodosporidium toruloides) and one reference organism DSM 10134 (Rhodosporidium toruloides) were selected for further uranium interaction experiments. Uranium biosorption tests indicated that the cells of the strain KS5 remove high amounts of uranium (120 mg uranium/ 1 g dry biomass). Temperature dependent biosorption tests with a U(VI) concentration of 100 µM showed significant differences: KS5 revealed twice as much uranium removal at 30°C compared to at 4°C (s. Fig. 1). Since active processes, e.g., bioaccumulation do not occur at low temperature, only minor amounts of U(VI) are taking up in the cytoplasm of the cells. Hence, U(VI) is preferentially sorbed on the cell membrane by the passive process of biosorption.
In order to test the uranium tolerance quantitatively in liquid media flow cytometry experiments with the strains KS5 and DSM 10134 were performed. For this purpose live-dead staining were done to test the cell viability. The cells were stained with Propidium Iodid (PI - non viable cells) and Fluorescein Diacetate (FDA - viable cells). Furthermore the oxidative stress response was measured with the fluorescent dye 3,3'-Dihexyloxacarbocyanine Iodide (DiOC6 - cell membrane of living cells). The results showed that the isolate KS5 are able to tolerate higher U(VI) concentrations compared to the reference culture DSM 10134. More than 50 % of the KS5 cells are viable at an initial U(VI) concentration of 100 µM. In contrast less than 10 % of the reference cells are viable at the same uranium concentration. The results of the oxidative stress response showed a slight difference to the cell viability test. The isolate KS5 showed that nearly 50 % of the cells are active, like the cell viability test. Whereas the results for the reference DSM 10134 revealed that more than 30 % of the cells are active and exhibit an active membrane potential, in contrast to the results of the cell viability test. This can be explained by the stress response in the presence of heavy metals. Some cells produce mechanic-sensitive receptors which are permeable for Propidium Iodide, resulting in a wrong fluorescent staining signal. Thus, it would be an asset to combine both methods, like cell viability test and oxidative stress response tests.
Summarizing the results of this study, we were able to prove that eukaryotic microorganisms within a uranium-contaminated environment exhibit adaption mechanisms against high U(VI) concentrations. The expensive chemical treatment of the flooding water in Königstein could take a long time probably for the next 100 years. For that reason, these isolated eukaryotic microorganisms might play an important role in the bioremediation of radionuclides within the waste water treatment in Königstein.
Keywords: Uranium, Bioremediation, Biosorption, Tolerance
  • Lecture (others)
    Remediation Symposium 2015, 30.09.-01.10.2015, Jena, Deutschland

Publ.-Id: 22282 - Permalink


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