Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

In this contribution we present an electro-optic arrival time monitor for coherent THz pulses. The monitor operates robustly at high repetitionrates and extremely low THz pulse energies. It thereby has the potential to provide few femtosecond-level synchronization on next generation large scale X-ray photon sources based on high repetition rate electron accelerators such as X-ray FEL´s or energy recovery linacs.

Since the mid-1950s, pulsed (iron-free) high-field magnets have become a common, versatile research tool. Applications in solid state physics have promoted the development of sophisticated magnets that nowadays can achieve fields above 90 T repeatedly.

We report here another area of application for pulsed power magnet technology; namely the use of pulsed magnets as effective devices for particle beam optics with application in the fields of radiation and accelerator physics as well as medical physics: Pulsed power solenoids for focusing of laser-accelerated particle beams might allow for the use of these new radiation qualities in medical radiation therapy or could function as a crucial part of a compact, laser-based ion source. The development of pulsed high field multipoles could permit highly compact beam guidance systems.

The presentation gives a survey of pulsed power developments, including various pulsed high field magnets as well as pulsed power sources. The scalability to cancer therapy relevant application will be critically discussed.

Bacterial isolates from a uranium mining waste pile are adapted in a very special kind of way to their heavy metal contaminated environment. Genome analyses identified many genes that might support the incidence of these strains in their special habitat. Using the Next Generation Sequencing Technology multiple surface (S-) layer genes and different kinds of metal transporter genes were identified. These data give the genetic affirmation that these strains are adapted substantial to their environment.

Spin polarized currents can exert a so-called spin-transfer torque to the magnetic moment of a ferromagnetic layer. One application of this phenomenon is the spin torque nano-oscillator (typically an MgO-based magnetic tunnel junction (MTJ)) which can act as a tunable microwave emission source. However, a more detailed understanding of the spin-torque physics is needed. For example, the spin torque bias dependence of the two spin torque components (in-plane and fieldlike) is still widely discussed in the community [1]. We present results for MgO-MTJs obtained by thermally excited ferromagnetic resonance (TE-FMR). With the help of TE-FMR, the bias dependence of the two spin-transfer torques can be determined from the peak position and linewidth [2]. Microwave measurements were carried out in the frequency range of 1-9 GHz at positive and negative magnetic fields and for different dc current values. Analyzing this data, we could separate the in-plane and field-like spin torque components and determine their bias dependence.

The interactions of trivalent lanthanides and actinides with secondary mineral phases such as calcite is of high importance for the safety assessment of deep geological repositories for high level nuclear waste (HLW). Due to similar ionic radii, calcium-bearing mineral phases are suitable host minerals for Ln(III) and An(III) ions. Especially calcite has been proven to retain these metal ions effectively by both surface complexation and bulk incorporation. Since anionic ligands (e.g., nitrate) are omnipresent in the geological environment and due to their coordinating properties, their influence on retentive processes should not be underestimated. Nitrate is a common contaminant in most HLW forms as a result of using nitric acid in fuel reprocessing. It is also formed by microbial activity under aerobic conditions. In this study, atomic force microscopy investigations revealed a major influence of nitrate upon the surface of calcite crystals. NaNO₃ causes serious modifications even in trace amounts (<10^-7 M) and forms a soft surface layer of low crystallinity on top of the calcite crystal. Time-resolved laser fluorescence spectroscopy of Eu(III) showed that, within this layer, Eu(III) ions are incorporated, while losing most of their hydration shell. The results show that solid solution modelling for actinides in calcite must take into account the presence of nitrate in pore and ground waters.

Recent observations of 6Li in metal poor stars suggest a large production of this isotope during Big Bang Nucleosynthesis (BBN). In standard BBN calculations, the 2H(α,γ)6Li reaction dominates 6Li production. Unfortunately, this reaction has never been directly measured inside the BBN energy region because its cross section drops exponentially at low energy. Indirect measurements using the Coulomb dissociation of 6Li only give upper limits owing to the dominance of nuclear breakup processes. Here, we report on the results of the first measurement of the 2H(α,γ)6Li cross section directly at Big Bang energies. The experiment was performed deep underground at the LUNA 400kV accelerator in Gran Sasso, Italy. The 6Li/7Li isotopic abundance ratio from standard BBN has been determined to be (1.5±0.3)×10−5, entirely from experimental data. The much higher 6Li/7Li values reported for halo stars will likely require a non-standard physics explanation.

After the resolution of the solar neutrino problem in 2002, the study of the Sun has now entered a precision era, and an entirely new dilemma has come up: New elemental abundance data from Fraunhofer line analyses are in contradiction with helioseismological observables. Observations of 13N and 15O neutrinos from the Sun may address this so-called solar abundance problem, but their interpretation will require precise nuclear reaction data. Due to the low cross sections involved, such data can only be provided by experiments in an underground low-background setting. Work at the world's only underground accelerator, the 0.4 MV LUNA machine in Gran Sasso (Italy), on solar fusion reactions and on the Big Bang production of lithium-6 and -7 will be reviewed. Higher-energy underground accelerators are planned in Italy and also at the Dresden Felsenkeller in Germany.

I give a brief review of the progress of underground nuclear astrophysics work within EuroGENESIS.

I review the status of underground nuclear astrophysics work in Germany.

The status of nuclear astrophysics related work at the Dresden Felsenkeller is reviewed.

Polycrystalline Bi1−xYxFeO3 films with varying x from 0 to 0.30 were prepared by pulsed laser deposition (PLD) on surface oxidized Si (100) substrates with LaNiO3 as buffer layer. The influence of Y doping on the structure, ferroelectric properties and exchange bias have been systematically investigated. X-ray diffraction and Raman spectroscopy studies revealed the structural transition from rhombohedral R3c to orthorhombic Pn21a with increasing x above 0.10. The leakage current density of BiFeO3 has been effectively suppressed by Y doping, and well saturated P-E loops have been observed in Bi1-xYxFeO3 (0.01≤x≤0.07). Exchange bias field with a 3.6 nm thick NiFe layer increases with increasing x to 0.01, then decreases with further increasing x.

The automotive industry is an essential branch for the industrial site Saxony. Within the past 20 years high-tech production centers have been built by the leading German car producers Volkswagen, BMW, and Porsche in Zwickau, Dresden, Chemnitz and Leipzig. According to estimations about 10 % of the jobs in Saxony subjected to social insurance are settled in the car related industry. This industrial sector on the one hand faces strong competitors from Asia and the USA, and on the other hand is challenged by the CO2 emission goals of the European Union for the next decade. These complex circumstances have to be dealt with innovative concepts in general and new approaches in research and development (R & D) in particular. The subproject ECEMP D1 is developing new, nanostructured, wear-resistant tribological coatings for the automotive engineering. These coatings provide a significant reduction of the friction in wear loaded car components and enable the more efficient use of fuel and materials.

Interfacial wave characteristics have been studied experimentally in stratified-wavy configuration for oil-air two-phase flow at Tulsa University Fluid Flow Projects (TUFFP) 6-inch low pressure flow loop. Flow rates of each test fluid are adjusted such that the superficial liquid and gas velocities vary between 0.01m/s ≤ υSL ≤ 0.02m/s and 10m/s ≤ υSG ≤ 16m/s, respectively, in horizontal pipe configuration.
During the course of the investigation, the cross-sectional distributions of void fraction are synchronously obtained at two different streamwise locations of the pipe by using two wire mesh sensors, each with a 32 x 32 grid resolution. The spatial distribution of the phases, obtained by analyzing the measured void fractions, reveal several instantaneous quantities of the flow configuration at each cross-section such as interface geometry, liquid holdup, wetted pipe area and liquid height. The sequential acquisition of the void fractions reveal the temporal evolution of these quantities within the planes of measurement. In addition, the cross-correlation of the data from both of the wire mesh sensors enable the characterization of important surface wave parameters such as wave celerity, and structural frequency.
The instantaneous information on the liquid holdup, wetted pipe area and liquid height are the advantages of the current experimental technique over conventional methods employing quick closing valves, and high-speed flow visualization. In order to understand the effect of sensor grid resolution on these quantities, the results have also been re-arranged using coarser mesh configurations by analyzing the same data also on 24 x 24, and 16 x 16 grid sizes. Furthermore, the analysis on the grid size is enriched by the comparison with the results obtained by using other methods for similar flow conditions in other experiments.
The wave celerity is observed to increase with superficial liquid and gas velocities, which is in good agreement with the previous studies. Spectral analyses performed on each element of the data matrix reveal the distribution of the dominant wave numbers within the pipe cross-section. In addition, a unique void fraction reconstruction technique is employed to quantitatively visualize the phase distributions passing through the wire mesh sensor in a three-dimensional fashion. This type of visualization is shown to be effective on the identification of the important wave structures and their spatial distributions within the pipe cross-section. This is a strong advantage over the window crossing method, due to the accuracy in spectral analysis, and over the capacitance sensors due to the global cross-sectional information.

Purpose: To evaluate the impact of fractionation schedule on the size of the gross tumour volume (GTV) effect on tumour control after radiotherapy of NSCLC.
Material and methods: A subgroup analysis on 163 patients treated in a randomized phase III trial of CHARTWEL (continuous hyperfractionated accelerated radiotherapy-weekend less) vs conventional radiotherapy was performed. The influence of GTV and other baseline factors on local failure (LF), disease-free survival (DFS), distant metastases (DM), and overall survival (OS) was estimated using the Cox Proportional Hazards model.
Results: Superior local control was achieved by CHARTWEL compared to conventional radiotherapy (HR 0.54, p = 0.015). The hazard of LF increased with increasing GTV for both conventional fractionation and CHARTWEL, however the increase for the latter was less pronounced and not significant.
Conclusion: Highly accelerated CHARTWEL treatment was significantly more effective than conventional radiotherapy for locoregional control of NSCLC. GTV had a significant effect on locoregional control after conventional fractionation, an effect that was not significant with CHARTWEL. This is the first study to demonstrate that the magnitude of the time factor of fractionated radiotherapy increases with tumour volume. (C) 2012 Elsevier Ireland Ltd. All rights reserved.

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A two-phase flow often exhibits a complicated three-dimensional structure by nature even in a simple vertical pipe. In order to model such a complicated flow structure and to validate multiphase flow CFD, experimental database for three dimensional velocity and void fraction distributions are crucial. The paper addresses an algorithm to measure three-dimensional velocity of individual bubble with a bubble paring scheme. The bubble paring scheme finds a pair of bubble in two sets of wire-mesh sensor data to determine the direction and magnitude of velocity vector for each bubble. The devised scheme was applied to the vertical upward air-water flow (jG=0.64m/s, jL=0.64m/s) in a large diameter pipe (i.d. 224mm). The bubble pairing scheme visualized the developing process of two-phase flow: large bubbles coalesced with each other to move toward the center, while the rest of bubbles broke up into smaller bubbles and decelerated.

Modelle einer Kernkollaps-Supernova sagen vorher, dass ⁴⁴Ti (Halbwertszeit = 58,9 a) produziert wird. Dementsprechend werden mehrere ⁴⁴Ti-Gammastrahlungsquellen in unserer Galaxie erwartet. Jedoch konnte ⁴⁴Ti bisher nur in den Supernovaüberresten Cassiopeia A und SN 1987A nachgewiesen werden. ⁴⁰Ca(α,γ)⁴⁴Ti ist die wichtigste Reaktion, die ⁴⁴Ti erzeugt. Ihre Reaktionsrate wird durch mehrere Resonanzen dominiert. Es ist geplant, die astrophysikalisch wichtige Resonanz bei 2758 keV am 3,7 MV Van-de-Graaff-Beschleuniger der Physikalisch-Technischen Bundesanstalt zu aktivieren und anschließend die Resonanzstärke durch eine Aktivierungsmessung im Niederniveaumesslabor Felsenkeller zu bestimmen.

The strength of the E_p = 1.842 MeV resonance in the ⁴⁰Ca(p,γ)⁴¹Sc reaction is determined with two different methods: First, by an absolute strength measurement using calcium hydroxide targets, and second, relative to the well-determined strength of the resonance triplet at E_α = 4.5 MeV in the ⁴⁰Ca(α,γ)⁴⁴Ti reaction. The present new value of ωγ = (0.192 ± 0.017) eV is 37% (equivalent to 3.5 σ) higher than the evaluated literature value. In addition, the ratio of the strengths of the 1.842 MeV ⁴⁰Ca(p,γ)⁴¹Sc and 4.5 MeV ⁴⁰Ca(α,γ)⁴⁴Ti resonances has been determined to be 0.0229 ± 0.0018. The newly corrected strength of the 1.842-MeV resonance can be used in the future as a normalization point for experiments with calcium targets.

Background: The O17(p,γ)F18 reaction affects the production of key isotopes (e.g., F18 and O18) in the explosive hydrogen burning that powers classical novae. Under these explosive conditions, the reaction rate is dominated by contributions from a narrow resonance at Ec.m.=183keV and by the combined contributions of direct capture and low-energy tails of broad resonances. At present, the astrophysical reaction rate is not well constrained because of the lack of data in the energy region appropriate to classical novae.
Purpose: This study aims at the measurement of the O17(p,γ)F18 reaction cross section in order to determine its reaction rate in the temperature region appropriate to explosive hydrogen burning in novae.
Method: The O17(p,γ)F18 reaction cross section was measured using both the prompt detection of the emitted γ rays and an activation technique. Measurements were carried out at the Laboratory for Underground Nuclear Astrophysics (Gran Sasso, Italy) where the strongly reduced cosmic-ray-induced background allows for improved sensitivity compared to previous studies.
Results: The O17(p,γ)F18 reaction cross section was measured in the range Ec.m.=160 to 370keV. The strength of the Ec.m.=183keV resonance, ωγ=1.67±0.12μeV, was determined with unprecedented precision. The total S factor was obtained through a combined fit of prompt γ-ray and activation results. An overall global fit including other existing data sets was also carried out and a recommended astrophysical reaction rate is presented.
Conclusions: The reaction rate uncertainty attained in this work is now below the required precision for nova models. We verified, following a full set of hydrodynamic nova models, that the abundances of oxygen and fluorine isotopes obtained with the present reaction rate are determined with 10% precision and put firmer constraints on observational signatures of novae events.

Sharpless asymmetric dihydroxylation of styrene derivative 6 afforded chiral triols (R)-7 and (S)-7, which were cyclized with tosyl chloride in the presence of Bu₂SnO to provide 2-benzopyrans (R)-4 and (S)-4 with high regioselectivity. The additional hydroxy moiety in the 4-position was exploited for the introduction of various substituents.
Williamson ether synthesis and replacement of the Boc protective group with a benzyl moiety led to potent σ₁ ligands with high σ₁/σ₂-selectivity. With exception of the ethoxy derivative 16, the (R)-configured enantiomers represent eutomers with eudismic ratios of up to 29 for the ester (R)-18. The methyl ether (R)-15 represents the most potent σ₁ ligand of this series of compounds, with a K_i value of 1.2 nM and an eudismic ratio of 7. Tosylate (R)-21 was used as precursor for the radiosynthesis of [18F]-(R)-20, which was available by nucleophilic substitution with K[¹⁸F]F K222 carbonate complex. The radiochemical yield of [¹⁸F]-(R)-20 was 18%–20%, the radiochemical purity greater than 97% and the specific radioactivity 175–300 GBq/μmol. Although radiometabolites were detected in plasma, urine and liver samples, radiometabolites were not found in brain samples. After 30 min, the uptake of the radiotracer in the brain was 3.4% of injected dose per gram of tissue and could be reduced by coadministration of the σ₁ antagonist haloperidol. [¹⁸F]-(R)-20 was able to label those regions of the brain, which were reported to have high density of σ₁ receptors.

The long-term safety of nuclear waste in a deep geological repository is an important issue in our society. For the safety assessment of such a repository it is necessary to know what microorganisms are present in the potential host rocks (e.g. clay, salt) and how these microorganisms can influence the performance of a repository to potentially reduce their activity.
In this study, the analysis of bacterial diversity in a sample from the Mont Terri Opalinus clay demonstrated the predominance of representatives of Firmicutes, Betaproteobacteria, and Bacteriodetes. Alpha-, Beta- and Gammaproteobacteria were detected in the porewater samples from the Mont Terri rock laboratory, whereas Gammaproteobacteria especially Pseudomonas sp. dominated the bacterial community.
Among other isolates, a Paenibacillus sp., as a representative of Firmicutes, was isolated from the clay under anaerobic conditions. Accumulation experiments and potentiometric titrations showed a strong interaction of Paenibacillus sp. cells with U(VI) within a broad pH range (3-7) [1].
Additionally, we will present a study on the interactions of the halophilic archaea Halobacterium noricense DSM 15987, an salt rock representative reference strain, with U(VI) at high ionic strength. These results contribute to the safety assessment of a prospective nuclear waste repository.

The work described in this thesis is concerned with the experimental investigation of the acceleration of high energy proton pulses generated by relativistic laser-plasma interaction and their application. Using the high intensity 150TW Ti:sapphire based ultra-short pulse laser Draco, a laser-driven proton source was set up and characterized. Conducting experiments on the basis of the established target-normal sheath acceleration (TNSA) process, proton energies of up to 20MeV were obtained. The reliable performance of the proton source was demonstrated in the first direct and dose controlled comparison of the radiobiological effectiveness of intense proton pulses with that of conventionally generated continuous proton beams for the irradiation of in vitro tumour cells. As potential application radiation therapy calls for proton energies exceeding 200MeV. Therefore the scaling of the maximum proton energy with laser power was investigated and observed to be near-linear for the case of ultra-short laser pulses. This result is attributed to the efficient predominantly quasi-static acceleration in the short acceleration period close to the target rear surface. This assumption is furthermore confirmed by the observation of prominent non-target-normal emission of energetic protons reflecting an asymmetry in the field distribution of promptly accelerated electrons generated by using oblique laser incidence or angularly chirped laser pulses. Supported by numerical simulations, this novel diagnostic reveals the relevance of the initial prethermal phase of the acceleration process preceding the thermal plasma heath expansion of TNSA. During the plasma expansion phase, the efficiency of the proton acceleration can be improved using so called reduced mass targets (RMT). By confining the lateral target size which avoids the dilution of the expanding sheath and thus increases the strength of the accelerating sheath fields a significant increase of the proton energy and the proton yield was observed.

Nuclear waste is supposed to be stored in deep geological formations. An example is the Opalinus clay formation located in the North-Western part of Switzerland (Mont Terri URL) which is currently studied in terms of its suitability as host rock for future nuclear waste storage. In this talk, results will be presented and discussed describing the interactions of a specific novel Sporomusa sp. isolate with plutonium. Results from accumulation experiments as well as detailed plutonium oxidation state changes in the presence and absence of an electron donor will be discussed.

We present a detailed investigation of the magnetic properties in SiC single crystals bombarded with neon ions. Through careful measuring of the magnetization of virgin and irradiated SiC, we decompose the magnetization of SiC into paramagnetic, superparamagnetic, and ferromagnetic contributions. The ferromagnetic contribution persists well above room temperature and exhibits a pronounced magnetic anisotropy. We qualitatively explain the magnetic properties as a result of the intrinsic clustering tendency of defects.

Approximately 1.8 to 2.8 Myr before the present our planet was subjected to the debris of a supernova explosion. The terrestrial proxy for this event was the discovery of live atoms of ⁶⁰Fe in a deep-sea ferromanganese crust [Knie et al., Phys. Rev. Lett. (2004)]. The signature for this supernova event should also reside in magnetite (Fe₃O₄) magnetofossils produced by magnetotactic bacteria extant at the time of the Earth-supernova interaction; these bacteria were and are ubiquitous in all ocean sediments. We have conducted accelerator mass spectrometry (AMS) measurements, searching for live ⁶⁰Fe in the magnetofossil component of a Pacific Ocean sediment core (ODP Core 848); additional AMS measurements are now ongoing with a second Sediment core (ODP Core 851) in which we expect to find a higher ⁶⁰Fe signal. This talk will present the current preliminary status of our ⁶⁰Fe search results for both sediment cores.

The quantification of surface process rates is crucial for understanding the topographic evolution of high mountains. Spatial and temporal variations in fluvial incision and basin-wide erosion enable to decipher the role of tectonic and climatic drivers. The Pamir is peculiar in both aspects because of its location at the western end of the India-Asia collision zone, and its position at the edge of two atmospheric circulation systems, the Westerlies and the Indian Summer Monsoon. The architecture of the Panj river network indicates prominent variations across the main tectonic structures of the Pamir. The trunk stream, deflects from the predominantly westward river orientation and cuts across the southern and central Pamir domes before doubling back to the west and leaving the orogen.
Optically stimulated luminescence (OSL) dating of fluvial terraces reveals short-term sedimentation along the trunk stream during the last ~25 kyr. The agreement of OSL results to new exposure ages based on the cosmogenic nuclide (CN) ¹⁰Be confirms accurate terrace age modelling and treatment of incomplete bleaching. The consistent terrace sedimentation and exposure ages suggest also fast terrace abandonment and rapid onset of incision. Considerable differences in terrace heights reflect high spatial variations of fluvial incision, independent of time interval, change in rock type or catchment increase. Highest rates of (5.9 + 1.1) mm/yr to (10.0 + 2.0) mm/yr describe the fluvial dynamic across the Shakhdara Dome and that related to the Darvaz Fault Zone. Lower rates of (3.9 + 0.6) mm/yr to (4.5 + 0.7) mm/yr indicate a transient stage north of the Yazgulom Dome. Fluvial incision decreases to rates ranging from (1.7 + 0.3) mm/yr to (3.9 + 0.7) mm/yr in graded river reaches associated to southern dome boundaries. The pattern agrees to the interpretation of successive upstream river captures across the southern and central Pamir domes inferred from morphometric analyses of river and valley profiles.
Basin-wide erosion rates based on ¹⁰Be concentrations in modern fluvial sediments yield relatively consistent rates between (0.61 + 0.1) mm/yr and (0.75 + 0.14) mm/yr along the Panj. The increasing Panj catchment averages variations of tributary basins, but minor variations in erosion rates of along-stream sub-basins resemble the pattern of OSL-based incision rates. In contrast, basin-wide erosion rates of tributary basins clearly differentiate between plateau-related sub-basins of (0.05 + 0.01) mm/yr to (0.17 + 0.03) mm/yr, and plateau margin-related sub-basins of (0.38 + 0.06) mm/yr to (1.43 + 0.26) mm/yr. The differentiation in plateau-related and marginal sub-basins and the northward increase in erosion rates correlate with the 75-percentile of the slope distribution within respective basins and to a minor degree to cumulative annual precipitation.

Due to their low solubility, tetravalent actinides, An(IV), are usually assumed to be immobile in natural waters. However, insoluble precipitation products can also be mobile if they occur as colloids. For An(IV) oxyhydroxides this phenomenon has thoroughly been studied. The formation of a further type of An(IV) colloids is described (cf. [1]): Silica-containing U(IV), Th(IV) and Np(IV) colloids formed in near-neutral to slightly alkaline solutions of background chemicals of geogenic nature (carbonate, silicic acid, Na+). Whereas the silica-containig colloids addressed in the BELBaR project are formed by the adsorption of radionuclides onto pre-existing silica particles, the colloids here under discussion result from a reaction of dissolved An(IV) with dissolved silicic acid (co-precipitation). An-O-Si bonds, which increasingly replace the An-O-An bonds of the amorphous actinide(IV) oxyhydroxide with increasing silica concentration, make up the internal structure of these colloids as was elucidated by EXAFS spectroscopy and further spectroscopic methods. A strong shift of the particles’ isoelectric point by silica incorporation is observed. The particles remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne An(IV) was observed. The prevailing size of the particles is below 20 nm (about 10 to 100 kDa). The question if such An(IV) colloids may contribute to the mobility of the actinides in the near-field or the far-field of a nuclear waste repository is discussed.

The Pamir is located at the western edge of the Indian indenter and results from the India-Asia collision. The Pamir also lies at the transition between zones dominated either by the Westerlies or the Indian Summer Monsoon. The ongoing tectonic deformation together with the climatic gradients from the two prevailing atmospheric circulation systems provide a natural laboratory to study surface processes and their rates. To determine and quantify the interaction between tectonics and the drainage system in the Tajik Pamir we use cosmogenic nuclide based techniques.
We measured ¹⁰Be and ²⁶Al concentrations of modern fluvial sediments sampled from drainage system of Pamirs. Depth profiles enable to determine exposure ages of fluvial terraces, while the modern river sediments reveal basin-wide erosion rates.
However, accurate measurement results depend on the quality of the sample preparation. The samples from Pamir contain a high amount of various feldspars that are very difficult to separate from quartz using standard procedures such as magnetic or density separation. Unclean samples cause uncertainties in chemical procedures, especially in the case of combined ¹⁰Be and ²⁶Al analysis. We developed a feldspar flotation in addition to our sample preparation procedure that allowed an almost complete separation of the quartz, up to 95%. Several depth profiles were analyzed to determine the exposure age of fluvial terraces. The first results of one terrace along the southern Panj River east of Langar, and one along the Shakhdara River are promising. The AMS results demonstrated that the depth profiles are consistent, with ¹⁰Be and ²⁶Al concentrations decreasing with depth. The results of both fluvial terraces show similar denudation rates 0.5 mm/yr., while exposure age analysis yields 3.5 ka for the Langar and 19 ka Shakhdara terrace. Further analyses are ongoing. These ages are validated by OSL dates at or nearby the same sites. ¹⁰Be denudation rates on modern river samples refine the picture produced by one of us (see Fuchs et al., same session).

In the previously published part 1 of the paper the uncertainty analysis of the large break loss-of-coolant accident (LBLOCA) for German PWR Konvoi was performed using a statistical method, which is based on the Wilks’ theory. The evaluated output parameter is the peak cladding temperature (PCT). The primary goal of this (second) part of the paper is a ranking of the input uncertainties, according to their contributions to the PCT uncertainty in the ATHLET simulation of PWR LBLOCA, by performing a sensitivity analysis. It was shown, that the first extended set of varied parameters used in part 1 can be considerably reduced without any statistically significant influence on the uncertainty analysis results. Thus, it can be shown that the input uncertainty vector based on the LBLOCA PIRT of AREVA GmbH was complete.
To minimize the number of varied parameters the statistical t-test was used and, thus, a set of uncertainty parameters with significant impact on the uncertainty of the PCT was identified. The main contribution to the uncertainty of the first cladding temperature maximum during the blowdown phase of the accident is produced by the core parameters that affect the fuel’s stored energy at the beginning of the accident. However, the major contributors to the uncertainty of the second PCT maximum are the uncertainties in the code models, and first of all the uncertainties in the heat transfer coefficients for dispersed and pure steam flows.

Fluid flowing through pipelines often encounters fittings such as elbows. Although it is true that two-phase flow patterns observed in elbows are qualitatively the same as those seen in straight pipes, the presence of a pipe elbow can modify relative positions and local velocities of the two phases as they are subjected to forces in addition to those encountered in a straight pipe. That redistribution can affect pressure drop values, chemical inhibitor concentration and distribution to the top of the pipe, as well as the erosion pattern occurring from solid particles such as sand that is entrained in oil and gas transportation pipelines. In this work, a Wire-Mesh Sensor technique based on conductance measurements of void fraction was applied to investigate two-phase pipe flow through a standard elbow. The horizontal flow test section, consisting of a 76 mm ID, 18 m long pipe, was employed to generate stratified-wavy and annular flow conditions. Two 16×16 Wire-Mesh configuration sensors were positioned either 0.9 m upstream or 0.6 m downstream of the bend. The experiments were conducted at different liquid and gas superficial velocities that ranged from 0.03 m/s to 0.2 m/s and from 9 m/s to 34 m/s, respectively. The effects of liquid viscosity on the measured parameters are also investigated using two different viscosities of 1 and 10 cP. Stratified-slug transition, stratified wavy and annular flow patterns were observed visually in the clear section placed upstream of the Wire-Mesh sensors. Analysis of time series void fraction data from the dual Wire-Mesh sensors allows the determination of mean void fraction, local time average void fraction distribution, liquid phase distribution around the tube periphery, interfacial structure velocities, as well as Probability Density Function characteristic signatures within the cross-section of pipe before and after the elbow. The results indicate that the distribution of gas and liquid phases and interfacial velocities are significantly altered even 20 diameters downstream of the elbow.

Slug flow is a very common flow pattern encountered during the production of petroleum fluids. Likewise, pipe bends are often used to change the direction of the fluids during transportation. This work focuses on comparing various slug characteristics before and after a pipe bend. For this investigation, a dual Wire Mesh Sensor (WMS) is utilized. Measurements are made by placing the sensor before and after the bend. In order to obtain higher spatial and temporal resolution of the signals, a sampling frequency of 10,000 Hz is used. Experiments were conducted in a 76.2 mm (3-inch) diameter pipe utilizing air and water as fluids. Effect of fluid viscosity is also studied by conducting the experiments using three different liquid viscosities: 1, 10 and 40 cP. The experiments were conducted with superficial gas velocity ranging from 9.1 m/s to 35 m/s, and superficial liquid velocity ranged from 0.45 to 0.76 m/s. The three-dimensional time series void data from the Wire-Mesh sensor before and after the bend are analyzed to obtain averaged void fractions, structure of the slugs, void in liquid slugs, bubble size distributions, and radial profiles of gas velocity. Also, this study presents the differences in the void fraction distributions in slugs and pseudo slugs. Since pseudo slugs occur between slug and annular regimes, this information can further the understanding of the effect of flow characteristics on erosion occurring from solid particles for this flow pattern. Finally, from this comprehensive analysis the influence of the bend on the gas and liquid distributions over the cross-section has been discussed.

Purpose To study the effects of BAY-84-7296, a novel orally bioavailable inhibitor of mitochondrial complex I and hypoxia-inducible factor 1 (HIF-1) activity, on hypoxia, microenvironment, and radiation response of tumors. Methods and Materials UT-SCC-5 and UT-SCC-14 human squamous cell carcinomas were transplanted subcutaneously in nude mice. When tumors reached 4 mm in diameter BAY-84-7296 (Bayer Pharma AG) or carrier was daily administered to the animals. At 7 mm tumors were either excised for Western blot and immunohistologic investigations or were irradiated with single doses. After irradiation animals were randomized to receive BAY-84-7296 maintenance or carrier. Local tumor control was evaluated 150 days after irradiation, and the dose to control 50% of tumors (TCD50) was calculated. Results BAY-84-7296 decreased nuclear HIF-1α expression. Daily administration of inhibitor for approximately 2 weeks resulted in a marked decrease of pimonidazole hypoxic fraction in UT-SCC-5 (0.5% vs 21%, P<.0001) and in UT-SCC-14 (0.3% vs 19%, P<.0001). This decrease was accompanied by a significant increase in fraction of perfused vessels in UT-SCC-14 but not in UT-SCC-5. Bromodeoxyuridine and Ki67 labeling indices were significantly reduced only in UT-SCC-5. No significant changes were observed in vascular area or necrosis. BAY-84-7296 before single-dose irradiation significantly decreased TCD50, with an enhancement ratio of 1.37 (95% confidence interval [CI] 1.13-1.72) in UT-SCC-5 and of 1.55 (95% CI 1.26-1.94) in UT-SCC-14. BAY-84-7296 maintenance after irradiation did not further decrease TCD50. Conclusions BAY-84-7296 resulted in a marked decrease in tumor hypoxia and substantially reduced radioresistance of tumor cells with the capacity to cause a local recurrence after irradiation. The data suggest that reduction of cellular hypoxia tolerance by BAY-84-7296 may represent the primary biological mechanism underlying the observed enhancement of radiation response. Whether this mechanism contributes to the improved outcome of fractionated chemoradiation therapy warrants further investigation.

Plasmonic off-axis unidirectional beaming of luminescence is demonstrated using nitride semiconductor quantum wells. The underlying mechanism involves the near-field excitation of surface plasmon polaritons on an ultrathin metal film, which are then diffractively scattered by an adjacent periodic array of asymmetric metallic nanoparticles. By tailoring the nanoparticles shape, we show that forward scattering can be suppressed in favor of backward diffraction (or vice versa), thereby enabling unidirectional beaming at geometrically tunable oblique angles. These nanostructures can be used to control the output light directionality of arbitrary planar luminescent devices, with a spatial resolution that would be unattainable with bulk optics.

An attempt is made to quantify the contributions of different types of defect-solute clusters to the total irradiation-induced yield stress increase in neutron-irradiated (300 °C, 0.6 dpa), commercial-purity Fe-Cr alloys (target Cr contents of 2.5, 5, 9 and 12 at% Cr). Former work based on the application of transmission electron microscopy, atom probe tomography, and small-angle neutron scattering revealed the formation of dislocation loops, NiSiPCr-enriched clusters and alpha’-phase particles, which act as obstacles to dislocation glide. The values of the dimensionless obstacle strength are estimated in the framework of a three-feature dispersed-barrier hardening model. Special attention is paid to the effect of measuring errors, experimental details and model details on the estimates. The three families of obstacles and the hardening model are well capable of reproducing the observed yield stress increase as a function of Cr content, suggesting that the nanostructural features identified experimentally are the main, if not the only, causes of irradiation hardening in these alloys.

Polyanuclear An(IV) carboxylate complex were identified in aqueous solution. The related complex species were preserved in crystals and their structures were determined. The structural identity of the species in solution and in solid state was tested by EXAFS spectroscopy.

We present a systematic study of the ultrashort pulse laser driven acceleration of protons from thin targets of finite lateral size, so-called reduced mass targets (RMTs). Reproducible series of targets, manufactured with lithographic techniques, and varying in size, thickness, and mounting geometry were irradiated at the 150 TW Draco Laser facility of the Helmhotz-Zentrum Dresden-Rossendorf with ultrashort (30 fs) laser pulses of intensities of about 8 • 10^20 W/cm^2. A robust maximum energy enhancement of almost a factor of two was found when compared to reference irradiations of plain foils of the same thickness and material. Furthermore, these targets exhibit a reduced performance dependence on target thickness compared to standard foils, which, based on detailed PIC simulations can be explained by the influence of the RMT geometry on the electron sheath. The performance gain was, however, restricted to lateral target sizes of about 50 μm which was attributed to edge and mounting structure influences. The contribution of the large electric fields at the target edges to the proton acceleration performance was investigated with measurements of the proton beam profile as well as optical pump and probe experiments.

Gas-liquid two-phase flows have become increasingly important in engineering equipment and technology (e.g. in chemical or process industries). Depending on mass flow rates, geometry and the fluid properties, different flow regimes can occur (e.g. bubble flow, stratified flow, droplet flow etc.). The current project focuses on stratified two-phase flows with heat and mass transfer across a moving interface due to direct contact condensation (DCC) in horizontal pipes or channels. In case of direct contact condensation, the resistance to condensation heat transfer considerably lower compared to film-wise condensation. Hence, DCC allows a considerably better heat exchange between the phases. Direct contact condensation is used in a variety of heat transfer devices (such as direct contact condensers), which offer the possibility of increased per-formance. DCC has also been of major importance in connection with the analysis of nuclear reactor safety systems, in particular during two-phase pressurized thermal shock (PTS) scenari-os. PTS occurs when there are large thermal loads on the Reactor Pressure Vessel wall during an accident. Therefore, the modeling of direct contact condensation is a task of considerable im-portance. Condensation phenomena depend on the turbulence in the liquid phase. To consider pronounced 3D effects and local phenomena CFD methods need to be used. Generally, two-phase CFD models are not yet mature and have to be qualified for two-phase flows. The work aims at the development and validation of CFD models for two-phase stratified flows including heat and mass exchange between the phases. A promising model development strategy implies experimental data with high resolution both in space and time for the entire domain of interest. To investigate two-phase PTS scenarios with DCC, the TOPFLOW-PTS experiments were carried out at the TOPFLOW test facility of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) [1]. The goal of the paper is to present the CFD simulations of a TOPFLOW-PTS steam-water experiment and to discuss the limits of the models used.

Infrared spectra of La₂@C₈₀ and a series of Ce-based endohedral metallofullerenes (EMFs), including Ce@C₈₂, Ce₂@C₇₂, Ce₂@C₇₈, and Ce₂@C₈₀ are reported. DFT calculations are used for their thorough analysis and assignment. The vibrations of the fullerene cages in all studied EMFs differ from those of their empty, charged cage analogues. Furthermore, EMFs with the same carbon cage but different type of encapsulated species also show significant differences in their cage vibrational patterns. These phenomena are explained by a different coupling of the vibrational modes as well as by the different charge distributions in EMFs and empty, isostructural fullerene anions.

DYN3D is a well-known and widely used computer code for reactor physics simulation of nuclear power plants, in particular for reactors with hexagonal fuel assembly structures. It has been developed in Helmholtz-Zentrum Dresden-Rossendorf, Germany. The standard version of the DYN3D code can be used for investigations of transients in light water reactors cores with hexagonal or quadratic fuel assemblies. In order to determine the pin with the maximum power in selected assemblies, a two-dimensional pin power reconstruction can be performed based on the node homogenized neutron flux. A superposition of global diffusion solution of the full core calculation with the assembly pin powers obtained in the cell calculations is used therefore. This method is implemented in DYN3D for reconstruction of power inside selected assemblies. An improved onset would be a hybrid solution, the coupling of the full core diffusion solver with an advanced transport solver on fuel assembly base. This method can be used to directly determine the power distribution for each rod inside fuel assemblies by applying a transport solver using unstructured mesh and boundary conditions extracted from the full core diffusion solution. Nowadays, this mentioned methodology is under development. In the present work an advanced multigroup transport method of current coupling collision probability (CCCP) with orthonormal flux expansion inside the calculation regions is being developed and tested for cylindrical, hexagonal geometries and for assemblies of hexagonal cells. The results of test calculations demonstrate very good agreement with the results obtained from Monte Carlo calculations. Multigroup calculations for hexagonal assemblies with cross-sections prepared using the HELIOS code show good agreement with HELIOS reference solution, too. These convincing results encourage the implementation of this advanced pin power calculation method into DYN3D as future pin-power determination method using currents from nodal solution as boundary conditions.

Crystallization and sintering, which occur during firing, during the production of strontium-anortite glass ceramics by means of powder metallurgy are studied. It is shown that the dispersity of the initial glass powder and the temperature–time firing regimes affect the crystallization temperature and heat, the nature of the precipitating phases and the sintering temperature interval and kinetics of the particles. It is determined that for ceramizing glass compositions there exists a narrow powder dispersity interval in which densely sintered materials with the required composition and high mechanical properties can be obtained using multistep heat-treatment.

Cross sections for neutron capture in heavy nuclei in the energy range of unresolved resonances are predicted simultaneously to data on level densities at the neutron threshold and average photon widths from 132 spin-0 target nuclei with 70

In a fast neutron spectrum essentially all long-lived actinides (e.g. Plutonium) undergo fission and thus can be transmuted into generally short lived fission products. Innovative nuclear reactor concepts e.g. accelerator driven systems (ADS) are currently in development that foresee a closed fuel cycle. The majority of the fissile nuclides (uranium, plutonium) shall be used for power generation and only fission products will be put into final disposal that needs to last for a historical time scale of only 1000 years. For the transmutation of high-level radioactive waste a lot of research and development is still required. One aspect is the precise knowledge of nuclear data for reactions with fast neutrons. Nuclear reactions relevant for transmutation are being investigated in the framework of the european project ERINDA. First results from the new neutron time-of-flight facility nELBE at Helmholtz-Zentrum Dresden-Rossendorf will be presented.

In this work the kinetics of the reaction of glutathione (GSH) with different organoarsenic(V) compounds is investigated. This includes phenylarsonic acid (PAA), 4-hydroxy-3-nitrophenylarsonic acid (HNPAA), p-aminophenylarsonic acid (p-APAA) and o-aminophenylarsonic acid (o-APAA) as well as monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA). The reaction progress was monitored in real time by ¹H-NMR, which allowed the determination of rate coefficients and half-lives as well as activation energies, enthalpies and entropies of activation and, eventually, Gibbs free energies of activation. The reaction consists of two steps: redox reaction and conjugation. In all investigated systems, the conjugation is fast compared to the redox reaction, which therefore is rate determining. All investigated phenylarsonic acids are subject to the same rate law, showing overall reaction orders of 3 and half-life values between 47.7 ± 0.2 and 71.0 ± 3.6 min, corresponding to reaction rates between 1330 ± 10 L² mol^-2 min^-1 and 850 ± 5 L² mol^-2 min^-1, respectively. The methylated compounds react slower, showing half-lives of 76.6 ± 0.4 and 444 ± 10 min for DMAA and MMAA, respectively. The obtained enthalpies of activation range from 20 to 36 (± 2) kJ mol^-1 and the entropies of activation are within −154 and −97 (± 7) J mol^-1 K^-1. The results reveal a correlation of the toxicity of the arsenic compound and the reaction rate with GSH. This may pave the way for the estimation of the toxicity of such compounds by simple kinetic studies.

We demonstrate all-optical magnetic switching (AOS) in an amorphous Tb30Fe70 thin film, triggered by a 5.1 MHz laser oscillator. The magnetic layer is grown on a SiO2/Si substrate. An identical magnetic film deposited on a microscope glass slide shows no AOS and only exhibits thermally induced demagnetization. This effect is due to heat accumulation by multiple laser pulses because of the low thermal conductivity of the glass substrate. In contrast, the use of a proper heat sink (e.g. SiO2/Si) abolishes need for low repetitive laser amplifier systems to induce AOS and paves the way for a cheap and easy to use technological implementation with conventional laser oscillators.

We present a combined numerical and experimental investigation of an electromagnetic system dedicated for an operative detection of non-metallic enclosures (gas bubbles) into the liquid metal flows. The method is based on the generation of eddy currents in the electrically conducting medium by applying AC magnetic field and the detection of the electromagnetic distortions caused by heterogeneity of electrical conductivity of the medium. We defined an optimal position and configuration of detector and excitation coil in order to get maximal sensitivity of the system to the spatial distribution of admixture.

To measure the fluid motion in liquid metal experiments Ultrasound Doppler Velocimetry (UDV) is used very often. The very small UDV signals can be disturbed by high direct current sources due to electromagnetic noise coming from these devices. The presentation will give some ideas and work around to common problems arising with magnetic field generation. All this will be explained on an ongoing experiment to the magneto rotatorical instability (MRI) in our laboratory. Finally some concepts and results will be given to rise measurement quality.

We present a combined numerical and experimental investigation of an electromagnetic system dedicated for an operative detection of non-metallic enclosures (gas bubbles) into the liquid metal flows. The method is based on generation of eddy currents in the electrically conducting medium by applying of ac magnetic field and detection of the electromagnetic distortions caused by inhomogeneity of electrical conductivity of the medium. We defined an optimal position and configuration of detector in order to get maximal sensitivity of the system to the spatial distribution of admixture.

Bubble columns are widely used in the chemical industry for gas-liquid operations. In-spite of the wide spread use of bubble column reactors, fundamental understanding of interactions between hydrodynamics, mass transfer and chemical reaction in dense systems is still lacking. Several experimental techniques are available to study gas-liquid flows: photographic imaging, particle image velocimetry, X-ray tomography, wire mesh sensors, etc. We developed a digital image analysis technique (DIA) to study the gas-liquid flows in bubble column reactor.

Texture is preferred orientation of crystallites in some polycrystalline materials. Different methods are applied to characterize the orientation patterns and determine the orientation distribution. Most of these methods rely on diffraction. This paper introduces the principle of a method used for characterization of ceramics texture based on anisotropy of electrical properties of crystallites in ceramics. The mathematical framework of this method is presented in theoretical part of our work. In experimental section we demonstrate how the theoretical result could be used to evaluate technology texture of ceramic material intended for the production of electronic insulators.

We report the structural properties of thin magnetic Permalloy films treated by two different methods: broad-beam Ga+ ion implantation at an energy of 30keV as well as annealing at different temperatures under ultra-high vacuum. Transmission electron microscope imaging and X-ray diffraction measurements have demonstrated that both ion implantation and annealing (above 300°C) lead to further material crystallization and crystallite growth. Whereas, annealing (above 400°C) leads to a strain-free state with an almost constant lattice parameter and to a further enhancement of the initial (111) texture, ion beam implantation boosts the growth of small arbitrary oriented crystallites and leads to an linear increase of the lattice parameter introducing mirco-strain to the sample. The observed decrease of the saturation magnetization for the implanted samples is mainly attributed to the presence of the non-magnetic Ga atoms incorporated in the Permalloy film itself. The rise of the saturation magnetization for the samples annealed at temperatures above 500°C is explained by an arising de-wetting effect since no ordered FeNi3 phase was detected with anomalous X-ray diffraction.

Model experiments with low melting point liquid metals are used to evaluate the flow structure and its related transport processes in metallurgical applications in melt flows. Water model experiments are less important, in particular, in case of strong temperature gradients, two-phase flows or flows exposed to electromagnetic fields. Here we present the Mini-LIMMCAST experimental facility to illustrate the continuous steel casting process using a GalnSn room-temperature liquid metal alloy. The parameters of the facility and the dimensions of the test sections will be given and possibilities to evaluate the flow in the mold will be discussed.
The effect which the magnetic field has on the flow structure turned out to be complex. The flow measurements do not show a general braking effect which would be expected as an overall damping of the flow velocity and its resulting fluctuations in the mold. Not only different magnetic field intensities had a big influence on the flow field, but also the variation of the electromagnetic field position had a striking impact on the resulting flow structures. The flow intensity in the upper part of the mold is also significantly influenced by the movement on the free surface of the metal. During continuous casting, this movement of the free surface is an important parameter to indicate the quality of steel. The experiments provide a substantial database for the validation of respective numerical simulations.

Positron production based on the generation of channeling radiation by relativistic electrons channeled along the (110) crystallographic plane of a W crystal and the subsequent conversion of radiation into e+e−-pairs in an amorphous tungsten target is described. Electron dechanneling is considered by solving of the Fokker-Planck equation. The continuous potential of the channeling plane is calculated using the Doyle–Turner approximation to the atomic scattering factor taking into account thermal vibrations of the crystal atoms. The trajectories, velocities and accelerations of planar channeled electrons are obtained by solving the classical equation of motion. In the framework of classical electrodynamics, the spectral-energy distribution of radiation is obtained from the Fourier transforms of realistic electron trajectories, velocities and accelerations within the W crystal. The calculations of channeling radiation and dechanneling are carried out by means of our Mathematica codes. The conversion of radiation into e+e− -pairs and the energy distributions of produced positrons are simulated using the GEANT4 package.

We report on the development of a contactless measurement technique for torsional shear stress τ in ferromagnetic axles or hollow shafts, based on the magneto-elastic effect. In general two different measuring principles for ferromagnetic materials can be realised, based on: the evaluation of the change of magnetic polarisation influenced by mechanical stress ΔJ(τ ) or, the change of the magnetic susceptibility ΔχA(τ). The comprehension of the magnetic polarisation or the magnetic susceptibility in a sensor concept requires an external magnetic field. Preferably alternating magnetic fields were used as mechanical stress can disturb the amplitude but also the phase distribution of the applied magnetic field. As a result of a torsional moment acting on an axle or hollow shaft an angle of twist η appears, which is constant over the length of the twisted object. This angle of twist can be understood as a shift of infinitesimal thin cross-sections in which the whole length of the axle is separated. Beside the macroscopic deformation effect, shear forces taking also effect on the Weiss domains in the microscale of the ferromagnetic material. The effects in the microscale are the base of the magneto-eleastic effect. The combination of the deformation effect in the macro-scale with the deformation of the Weiss domains in the microscale leading to a sophisticated measurement principle for torsional stress in axles or hollow shafts. Magneto-sensitive detectors along or around the measurement object open the possibility for a contactless detection of torsional stress in ferromagnetic materials. Beside a strong measuring signal, free from electromagnetic interference, the introduced contactless measurement principle offers different advantages, like an independence from compression strength, nominal tensile stress, impact load, ferromagnetic hysteresis effects and an independence from the temperature dependent electrical conductivity of the axle or hollow shaft. The characteristics of such a type of sensor are analysed by an electrotechnical model based on Maxwells equations. Beside the chosen design of a contactless torsion sensor and an experimental set-up, the obtained test results are illustrated and reported in the present paper.

The survival of cancer patients suffering from glioblastoma multiforme is limited to just a few months even after treatment with the most advanced techniques. The indefinable borders of glioblastoma cell infiltration into the surrounding healthy tissue prevent complete surgical removal. In addition, genetic mutations, epigenetic modifications and microenvironmental heterogeneity cause resistance to radio- and chemotherapy altogether resulting in a hardly to overcome therapeutic scenario. Therefore, the development of efficient therapeutic strategies to combat these tumors requires a better knowledge of genetic and proteomic alterations as well as the infiltrative behavior of glioblastoma cells and how this can be targeted. Among many cell surface receptors, members of the integrin family are known to regulate glioblastoma cell invasion in concert with extracellular matrix degrading proteases. While preclinical and early clinical trials suggested specific integrin targeting as a promising therapeutic approach, clinical trials failed to deliver improved cure rates up to now. Little is known about glioblastoma cell motility, but switches in invasion modes and adaption to specific microenvironmental cues as a consequence of treatment may maintain tumor cell resistance to therapy. Thus, understanding the molecular basis of integrin and protease function for glioblastoma cell invasion in the context of radiochemotherapy is a pressing issue and may be beneficial for the design of efficient therapeutic approaches. This review article summarizes the latest findings on integrins and extracellular matrix in glioblastoma and adds some perspective thoughts on how this knowledge might be exploited for optimized multimodal therapy approaches.

Control of the flow rate of liquid metals is required in a number of technological processes such as the cooling of nuclear reactors, transmutation systems and the dosing and casting of liquid metals. Electromagnetic flow meters play an important role in the diagnostics and automatic control of such processes. For example, the electromagnetic control of casting processes can be used to improve the quality of products by reducing their brittleness and increasing durability at high production efficiency, especially for complex shape components. A number of different electromagnetic flow meter designs have been developed starting from the end of the forties of the last century. One such flowmeter - themagnetic flywheel,which is described in the textbook of Shercliff uses the electromagnetic force exerted by the flow on a close magnet. Commercial electromagnetic flow meters are typically based on the flow-induced electrical voltage measurements by electrodes in direct contact to the melt in a steady magnetic field. In view of the typical problems coming along with applications at liquid metal flows such as high temperatures, interfacial effects and corrosion, the main disadvantage of this type of flow meter is the electrical contact to the liquidmetal, which is necessary to measure the electric potential difference. Therefore, contactless operating measurement techniques are very attractive for liquid metal applications.

When a liquid metal flows around a truncated cylinder in the presence of a magnetic field which is parallel to the axis of the cylinder, a stagnant region develops above the cylinder. This region is called Ludford column. The Ludford column represents the magnetohydrodynamic (MHD) analogue to the well-known Taylor columns in rotating flows. Whereas Taylor columns can be easily visualised using dye, the visualisation of Ludford columns remained elusive up to now because liquid metals are opaque. We demonstrate that this fundamental limitation of experimental MHD can be overcome by using a superconducting 5-Tesla magnet. This facility permits us to perform MHD experiments in which the opaque liquid metals are replaced with a transparent electrolyte while maintaining the key MHD-effects. We report results of a series of flow experiments in which an aqueous solution of sulphuric acid flows around a bar with square cross section. We vary the Reynolds number in the range 5 < Re < 100 and the Hartmann number in the range 0 < Ha < 14. The experimental procedure involves flow visualisations using tracer particles as well as velocity measurements using particle image velocimetry (PIV). Our experiments provide direct access to the Ludford columns for the first time and reveal the spatial structure of this basic feature of MHD flows.

The intention of this work was to get a distinct conformation of the s-layer Lysinibacillus sphaericus JG-A12. S-layers are interesting for e.g. functional surfaces and filtration media. A distinct conformation of the proteins is important to optimize processes and the range of applications.
The conformation is influenced by different solution compositions for e.g. the pH-value, the buffer concentration and different concentrations of salt. This work summarizes some strategies to achieve a solution of s-layer monomers.

The Opalinus clay layer of the Mont Terri Underground Rock Laboratory (Switzerland) is one potential host rock tested for nuclear waste disposal [1]. It is well known that bacteria indigenous to such subterranean environments can affect the speciation and hence the mobility of actinides [2]. The unknown interactions between U(VI), Cm(III)/Eu(III) and Pu with Sporomusa sp. MT-2.99 cells was explored. This bacterium was recently isolated from Mont Terri Opalinus clay core samples by our group. Strong An/Ln interactions of this clay isolate within a broad pH range (2-8) were detected. Thermodynamic stability constants of bacterial U(VI)/Cm(III)/Eu(III) surface species were determined and will be discussed. The biosorption process of U(VI)/Cm(III)/Eu(III) can be described as a pH-dependent binding on phosphoryl and carboxyl sites of the cell membrane. For Pu a complex interaction mechanism was identified. Besides biosorption strong abiotic and biotic plutonium reduction processes were observed. The information obtained in our study is of great importance for predicting the safety of a planned nuclear waste repository.

Acknowledgements. The authors thank the BMWi for financial support (contract no.: 02E10618 and 02E10971) and the BGR for providing the clay samples.

References
[1] M. Thury, P. Bossart (1999). The Mont Terri Rock Laboratory, a new international research project in a Mesozoic shale formation, in Switzerland. Eng. Geol. 52,347-359.
[2] J.R. Lloyd, G.M. Gadd (2011). The Geomicrobiology of Radionuclides. Geomicrobiol. J. 28, 383-386.

In the contribution, the recent activites on mass transfer and hydrodynamics in structured packings are presented

Low energy ion beam pattern formation on Si with simultaneous co- deposition of Ag, Pd, Pb, Ir, Fe or C impurities was investigated by in-situ scanning tunneling microscopy as well as ex-situ atomic force microscopy, scanning electron microscopy, transmission electron microscopy and Rutherford backscattering spectrometry. The impurities were supplied by sputter deposition. Additional insight into the mechanism of pattern formation was obtained by more controlled supply through e-beam evaporation. For the situations investigated, the ability of the impurity to react with Si, i.e. to form a silicide, appears to be a necessary, but not a sufficient condition for pattern formation. Comparing the effects of impurities with similar mass and nuclear charge the collision kinetics is shown to be not of primary importance for pattern formation. To understand the observed phenomena, it is necessary to assume a bi-directional coupling of composition and height fluctuations. This coupling gives rise to a sensitive dependence of the final morphology on the conditions of impurity supply. Because of this history dependence the final morphology cannot be uniquely characterized by a steady state impurity concentration.

Mehrphasenreaktoren wie Blasensäulen, Festbetten und Wirbelschichten sind das Herzstück der chemischen und biochemischen Industrie. Trotz der weitgefächerten Anwendungsgebiete, stellen Auslegung und Skalierung von Mehrphasenreaktoren immer noch große Herausforderungen dar, insbesondere aufgrund fehlender Messdaten unter industriell relevanten Betriebsbedingungen. Darüber hinaus liegen in industriellen Prozessen meist lichtundurchlässige Strömungen vor – beispielsweise bei hohen Gas- und Flüssigkeitsleerrohrgeschwindigkeiten – die mit bloßem Auge aber auch mit herkömmlicher optischer Messtechnik nicht erfasst werden können. Der Beitrag fast Ergebnisse hydrodynamischer Studien in Blasensäulen mittels gering-invasiver Gittersensorik zusammen. Insbesondere werden Übergänge von Strömungsregimen, Blasengrößenverteilungen und Gasgehalte in Abhängigkeit vom Blasensäulendurchmesser als wesentliche Auslegungsparameter analysiert.

In the recent years, the performance of gas-liquid-solid fixed bed reactors with structured catalysts instead of catalyst particles has been intensively discussed. Structured catalysts based on solid foams with an open cell structure are in particular very promising. Such porous structures combine high specific surface area up to 2000 m²/m³, low single-phase and two-phase pressure drop due to bed porosities between 75 and 95 %, and interconnected pores for enhanced heat and mass transfer (Stemmet et al., 2005; Grosse and Kind, 2011). The performance of fixed bed reactors with structured catalysts depends heavily on the gas-liquid-solid contacting pattern. For a broad range of flow conditions, the liquid phase does not cover the solid surface homogeneously, which is known as partial wetting. The externally wetted fraction, which is defined as fraction of the external solid foam area covered by the liquid phase to the total external solid foam area, is directly linked to the liquid-solid and gas-solid mass transfer and thus, to the overall rate of reaction. The wetting fraction is a function of the superficial gas and liquid velocity and depends also on the physical properties of the liquid phase as well as catalyst shape, surface, porosity, etc. (Nigam and Larachi, 2005). However, studies on the wetting efficiency in trickle bed reactors also indicated the impact of the pre-wetting mode (Joubert and Nicol, 2012).
The aim of this work was to adopt an electrochemical method for: (a) measuring the wetting fraction in tubular reactors with solid foam packings and (b) to study the effect of pre-wetting.

Solid foam catalysts are a potential replacement for conventional catalyst particles such as extrudates, tablets, hollow cylinders and spheres. They improve the fixed-bed reactor performance in gas-liquid-solid reactions due to their high specific surface area and low pressure drop. Furthermore foam has very narrow residence time distribution which enhances the selectivity. However, there is still a lack of knowledge on the evolving flow patterns in solid foams and the proper design of liquid-phase distributors for industrial applications and conditions. In our contribution, gas-liquid distribution of downward two-phase flow with solid foam packings was studied experimentally. The packings varied in solid foam pore density.
The measurements in a column with 0.1 m inner diameter are based on a combination of a segmented collector (25 compartments of same size) and imaging wire-mesh sensors with 16×16 wires and a pixel resolution of 6.25 mm. Both techniques provided the same results regarding the quality assessment of the flow distribution. The setup was applied to investigate the effect of: different liquid distributors, gas and liquid flow rates, and pre-wetting conditions. The experiments revealed information on liquid spreading along the reactor axis. The flow patterns inside the column are quantified by a maldistribution factor. The results indicate that foam packings cannot effectively counterbalance initial liquid maldistribution. Based on this study results, the design of packed-bed reactors can be improved towards much higher productivity and energy efficiency.

Kolonnen mit Siebböden als trennwirksame Einbauten werden vielfältig zur intensiven Phasenkontaktierung und Stofftrennung eingesetzt. Eine verlässliche Beschreibung der Fluiddynamik auf Kolonnenböden ist die Grundlage für eine effiziente Gestaltung der Trennprozesse, erfolgt jedoch gegenwärtig hauptsächlich erfahrungsbasiert. Voraussetzung zur modellunterstützten Auslegung von Siebböden, vor allem im Hinblick auf die Optimierung von Strömungsmustern, sind Bodenprüfstände mit hochauflösender Spezialmesstechnik. Zur Charakterisierung der Strömungsverhältnisse (z. B. Totzonen, Wirbeln, Kurzschluss- und Rückströmungen) und zur Extraktion fluiddynamischer Kenngrößen (z. B. Verweilzeit) in einem 800 mm Kolonnenprüfstand mit Siebböden (4 % Öffnungsverhältnis, 5 mm Lochdurchmesser) wurde u. a. ein leitfähigkeitsbasierter Gittersensor implementiert. Der Gittersensor besteht aus zwei um 90° versetzt angeordneten Drahtebenen aus 64×51 Drähten mit einem Ebenenabstand von 10 mm. In den Kreuzungspunkten wird in Abhängigkeit der lokalen Leifähigkeit ein Strom mit hoher Abtastfrequenz gemessen, der Aussagen über die transienten Strömungszustände (z. B. Tracermenge, Gas-/Flüssigkeitsanteil) erlaubt. Im Beitrag werden Tracerstudien zur Bestimmung der Flüssigphasenverweilzeit und der Strömungsmuster in Abhängigkeit der hydraulischen Belastungen und der Wehrhöhen vorgestellt.

In the present work, we have studied the photoluminescence (PL) and decay lifetime of Tb and Eu nanoparticles (NPs) at low temperatures. The NPs were obtained by ion implantation into a SiO2 matrix. Concerning the PL yield of Tb, it has a maximum at 12 K and decreases with increasing temperatures reaching a minimum at 300 K. On the other hand, the PL lifetime of the PL band centered at 542 nm remains almost constant at a value of 1.6 ms. Concerning Eu, two bands are observed, one narrow centered around 618 nm and the other in the blue-green region (from 400 up to 550 nm). Both PL bands show a minimum yield at 12 K, and then they start to increase with increasing temperatures, reaching their maximum at around 100 K. Then, they start to decrease their yield reaching a minimum at 300 K, being this yield similar to the one obtained at 12 K. For the Eu PL lifetime, two different results were obtained. The narrow PL band centered at 618 nm shows a lifetime of the order of 1.6 ms independent of the temperature. Conversely, the blue-green PL band is strongly temperature dependent, being of the order of several ms for temperatures lower than 100 K down to 500 µs at 300 K.

Higher conversion efficiencies while reducing costs at the same time is the ultimate goal driving the advancement of solar cell development. In this work, solar cell emitters are formed in Si substrates by plasma immersion ion implantation (PIII) of phosphine and posterior millisecond-range flash lamp annealing (FLA). In Si-based solar cells, hydrogen plays a fundamental role due to its excellent passivation properties and the optical and electrical properties of the fabricated emitters will be studied, with particular interest in their dependence on the hydrogen content present in the samples. The influence of different FLA annealing parameters and a comparison with traditional thermal treatments such as rapid thermal annealing (RTA) and furnace annealing (FA) will be presented. The samples treated by FLA at 1200 °C for 20 ms in forming gas shows sheet resistance values of the order of 60 Ω/□, and minority carrier diffusion lengths in the range of ~ 200 µm without the use of a capping layer for surface passivation. Those results are significantly better than the ones observed from RTA or FA annealed samples. The simultaneous implantation of hydrogen during the doping process combined with optimal FLA annealing parameters gave promising results for the application of this technology in replacing the conventional POCl3 deposition and diffusion.

Solid foams were found to be promising replacements of conventional fixed bed reactor catalysts due to their high specific surface area, high porosity and low pressure drop. Especially, high gas-liquid mass transfer rates were observed in solid foams (Stemmet et al., 2008). However, for liquid limited reactions, high liquid-solid mass transfer rates are required. The liquid-solid mass transfer is strongly affected by the wetting of the packing surface and thus, depends also on the pre-wetting mode. For example Joubert and Nicol (2012) found that solid-liquid mass transfer coefficients in trickle bed reactors exhibit significant multiplicity behavior due to different flow textures. However, to the best of our knowledge, studies on the liquid-solid mass transfer in down flow solid foam tubular reactors are not yet available. To determine liquid-solid mass transfer coefficient we applied the electrochemical diffusion current method (ferricyanide system with excess of NaOH) The method is based on the measurement of current (i.e. electron transfer from cathode to anode) at mass transfer diffusion limited condition, pure nickel foam (Alantum Europe) of same foam density was applied as cathode.
The aim of this study is to determine the effective liquid-solid mass transfer coefficient in tubular solid foam reactors at different axial positions in down-flow trickle mode taking “LEVEC” and “KAN-LIQUID” pre-wetting mode into account.

Bubble column reactors are widely preferred in the petro/chemical industries due to flexible residence time, excellent heat and mass transfer characteristics and the absence of moving parts. Here, proper sparger design is essential to tune bubble size and bubble rise velocity and to provide optimal holdup and mixing behavior (Kulkarni and Joshi, 2011). Information pertaining to bubble size distribution, pressure distribution in various distributor is scantily available. Therefore, we provide a comparative study on different gas distributors in terms of gas hold-up and bubble size distribution using gamma-ray computed tomography and wire-mesh sensor techniques. Four different types of gas distributor were used, e.g. sieve plate, ring sparger, spider and radial sparger. In addition, the influence of the gas distributor on the above mentioned parameters is also predicted using Euler-Euler approached and validated with the experimental results.

We report on the experimental observation of transverse modulations in proton beams accelerated from micrometer thick targets which were irradiated with ultra-short (30 fs) laser pulses of a peak intensity of 5·10^20 W/cm^2. The net-like proton beam modulations were recorded using radiochromic film and the data suggest a dependence on laser energy and target thickness for their onset and strength. Numerical simulations suggest that intensity-dependent instabilities in the laser-produced plasma at the target front side lead to electron beam break-up or filamentation, then serving as the source of the observed proton beam modulations.

The aim of this study is the evaluation of on-the-fly volume of intersection computation for system’s geometry modelling in 3D PET image reconstruction. For this purpose we propose a simple geometrical model in which the cubic image voxels on the given Cartesian grid are approximated with spheres and the rectangular tubes of response (ToRs) are approximated with cylinders. The model was integrated into a fully 3D list-mode PET reconstruction for performance evaluation. In our model the volume of intersection between a voxel and the ToR is only a function of the impact parameter (the distance between voxel centre to ToR axis) but is independent of the relative orientation of voxel and ToR. This substantially reduces the computational complexity of the system matrix calculation. Based on phantom measurements it was determined that adjusting the diameters of the spherical voxel size and the ToR in such a way that the actual voxel and ToR volumes are conserved leads to the best compromise between high spatial resolution, low noise, and suppression of Gibbs artefacts in the reconstructed images. Phantom as well as clinical datasets from two different PET systems (Siemens ECAT HR+ and Philips Ingenuity-TF PET/MR) were processed using the developed and the respective vendor-provided (line of intersection related) reconstruction algorithms. A comparison of the reconstructed images demonstrated very good performance of the new approach. The evaluation showed the respective vendor-provided reconstruction algorithms to possess 34–41% lower resolution compared to the developed one while exhibiting comparable noise levels.
Contrary to explicit point spread function modelling our model has a simple straight-forward implementation and it should be easy to integrate into existing reconstruction software, making it competitive to other existing resolution recovery techniques.

Die Bestimmung von Stofftransportraten mittels der Grenzstrommethode hat in der Vergangenheit bereits häufig Anwendung in der Untersuchung von Mehrphasenströmungen durch strukturierte Packungen und regellose Schüttungen gefunden. Bis auf eine Ausnahme beschränkten sich bisherige Untersuchungen aber auf wässrige Stoffsysteme, die hinsichtlich ihrer physikalischen Eigenschaften (Dichte, Oberflächenspannung und Viskosität) eher einen Spezialfall in der Durchströmung von Packungen darstellen und sich kaum auf industriell relevante, organische Systeme übertragen lassen. Zur Adaption der Grenzstrommethode auf organische Systeme befasst sich die vorliegende Belegarbeit mit der Suche, Synthese und Langzeitbeständigkeit verschiedener organischer Redoxsysteme und Lösungsmittel sowie potenziell geeigneter Leitelektrolyte für die organische Grenzstrommethode. Untersucht werden hierbei die organometallischen Metallkomplex-Systeme des Eisens mit Bipyridin sowie des Ferrocens in verschiedenen Oxidationsstufen. Weiterhin kommt ein Tetraalkylammoniumsalz als Leitfähigkeitverbesserer in verschiedenen organischen Lösungsmitteln zum Einsatz. In Langzeittests zeigten UV-VIS-Messungen, dass lediglich das Ferrocen-System unter Argonatmosphäre über längere Zeit hinweg seine Zusammensetzung nicht ändert. Lichteinfluss zeigte dabei eine stabilisierende Wirkung. In ersten Vortests wird die Einsetzbarkeit des Systems für die organische Grenzstrommethode unter bestimmten Bedingungen bewiesen.
Betreuer: Johannes Zalucky

Simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) is a new whole-body hybrid PET/MR imaging technique that combines metabolic and cross-sectional diagnostic imaging. Since the use of MRI in imaging of soft-tissue sarcoma is extremely beneficial, investigation of the combined PET/MRI is of great interest. In this paper, we present three cases and first data. Combined PET/MRI technique can support the process of clinical decision-making and give answers to some meaningful questions when treating patients with STS. Therefore, the combined modality of simultaneous PET/MRI offers new pieces to the puzzle of sarcoma treatment.

On the occasion of annual project status report, work package progress is presented. The first part includes demarcation of work topics of hydrodynamic groups, status of setup construction and preliminary experimental matrix for CT measurements. The second part is related to actions in mass transfer investigations and reports progress and upcoming investigations with the electrochemical method as well as first successes in zeolite coating of SiSiC foams.

Within HZDR annual PhD seminar, the PhD motivation, conception, approaches and first results are presented.

On the occasion of half-annual PhD meeting of projekt group at TU Hamburg-Harburg, the status of hydrodynamic setup and current research subproject SiSiC zeolite coating which were investigated under SEM are orally presented.

The well-controlled formation of large silicon grains on predetermined positions is a key issue in order to produce single-grain thin film transistors on insulating substrates and thus to enable monolithic 3D integration. One way to achieve this is to artificially control the solidification of molten silicon during the flash crystallization of amorphous silicon. In this work, we present such an approach in which we used patterned metal layers below the amorphous silicon. The metal spots act as embedded micro mirrors and consequently introduce a lateral temperature gradient into the silicon film during flash crystallization. As a result, the grain growth from molten silicon is seeded from the predefined regions with the lowest temperature and thus the formation of large crystal silicon islands proceeds in a controlled manner. In the scope of this study, we evaluated a variety of different mirror patterns with respect to their suitability for this approach and observed that patterns of both circular and line-shaped mirrors are the most promising variants. The resulting silicon islands have pillow-like shapes and are located exclusively in regions between neighboring mirrors. They exhibit dimensions of a few tens of micrometers and consist of grains with sizes up to 28 µm. The formation of single-grain silicon pillow-like structures was observed for particular mirror patterns having circular mirrors. On the other hand, the application of mirror patterns with line-shaped mirrors resulted in the formation of elongated silicon grains which we explained in terms of lateral solidification starting from one edge. Furthermore, this approach exhibits grain filter characteristics leading to the controlled growth of large single grains at predetermined positions.

After an introduction of the research activities at the Institue of Fluid Dynamics, especially of the Experimental Thermal Fluid Dynamics Department, process intensification is illustrated by working examles from science and industry.
The new reactor concept "inclined rotating fixed bed reactor" is introduced with detailed explanations of the idea, the benefits as well as aspects of the design.
Selected results from hydrodynamic experiments coupled with tomographic imaging are presented.

We present a combined experimental and theoretical study of the spin-½ compound CuP₂O₆ that features a network of two-dimensional (2D) antiferromagnetic (AFM) square planes, interconnected via one-dimensional (1D) AFM spin chains. Magnetic susceptibility, high-field magnetization, and electron spin resonance (ESR) data, as well as microscopic density-functional band-structure calculations and subsequent quantum Monte Carlo simulations, show that the coupling J _2D ≃ 40 K in the layers is an order of magnitude larger than J _1D ≃ 3 K in the chains. Below T_N ≃ 8 K, CuP₂O₆ develops long-range order, as evidenced by a weak net moment on the 2D planes induced by anisotropic magnetic interactions of Dzyaloshinsky-Moriya type. A striking feature of this 3D ordering transition is that the 1D moments grow significantly slower than the ones on the 2D units, which is evidenced by the persistent paramagnetic ESR signal below T_N . Compared to typical quasi-2D magnets, the ordering temperature of CuP₂O₆ T_N /J _2D ≃ 0.2 is unusually low, showing that weakly coupled spins sandwiched between 2D magnetic units effectively decouple these units and impede the long-range ordering.

Nanoscale Mo_mS_n compounds exist in a large variety of compositions with many different characteristic structural elements and related electronic properties. The structural wealth of Mo_mS_n compounds comprises finite structures such as small clusters and hollow inorganic fullerenes, one-dimensionally extended wires and stripes, or two-dimensional platelets. The structural elements are based either on a three-dimensional Mo_m framework or on platelet-shaped elements derived from the layered MoS_2 bulk structure. The electronic features range from large energy gaps in closed-shell systems over the semiconducting two-dimensional MoS_2 sheet to the metallic conductivity of the brim state in platelets or along the Mo core of wires.
With the help of density-functional calculations the preferred structural elements and the relative stabilities could be correlated with the chemical potentials of sulfur and molybdenum in the system. As structural elements and electronic features are related, this result is the basis for a further tailoring of electronic properties via the preparation conditions. For very small systems Mo_mS_n, with m <= 4, n <= 14 the cluster-platelet transition depends on a sulfur excess of the system of at least one additional S atom per MoS_2 formula unit, i.e. to MoS_3. In the small size regime the most important species are the extremely stable large-gap Mo_4S_6 cluster, Mo_3S_6 as smallest member of (MoS_2)_n platelet family and Mo_3S_3 and Mo_3S_5 as stable building blocks of wires. For one-dimensionally extended conducting structures the termination exhibits a length-dependent crossover of the termination group from (Mo_3S_3)_nS_2 to (Mo_3S_3)_n-1(MoS_4)_2 provided that the chemical potential of sulfur is low and constant. Sulfur-terminated two-dimensional (MoS_2)_nS_m platelets are stable only at the enhanced sulfur chemical potential required to saturate the platelet edges with sulfur up to a stoichiometry of Mo:S = 1:3 in the smallest clusters. In even more sulfur-rich conditions all systems tend to form chemically active, but electronically inert S_2^2- ions.

DGK Symposium MS17 - Materials for Electronics:

Energy and Data Storage through the Eyes of Crystallographers

At the Center for High-Power Radiation Sources at Helmholtz-Zentrum Dresden-Rossendorf fast neutron-induced fission cross section experiments on U(235) and Pu(242) will be investigated by a parallel plate fission ionization chamber. An optimization of chamber parameters was performed using extensive Geant4 simulations with GEF code generated fission observable inputs. Pile-up effects due to the high alpha activity of the plutonium targets have been considered in a realistic geometry. Beyond that, a setup for the determination of the areal density and homogeneity of targets will be presented with a focus on current simulation work.

kein Abstract verfügbar

Both enantiomers of the epibatidine analogue flubatine display high affinity towards the α4β2 nicotinic acetylcholine receptor (nAChR) in vitro, accompanied by negligible interactions with diverse off-target proteins. Extended single dose toxicity studies in rodent indicated a NOEL (No Observed Effect Level) of 6.2μg/kg for (-)-flubatine and 1.55μg/kg for (+)-flubatine. We developed syntheses for both flubatine enantiomers and their corresponding precursors for radiolabeling. The newly synthesized trimethylammonium precursors allowed for highly efficient (18)F-radiolabelling in radiochemical yields >60% and specific activities >750GBq/μmol, thus making the radioligands practical for clinical investigation.

Positron emission tomography (PET) is an in vivo molecular imaging tool which is widely used in nuclear medicine for early diagnosis and treatment follow-up of many brain diseases. PET uses biomolecules as probes which are labeled with radionuclides of short half-lives, synthesized prior to the imaging studies. These probes are called radiotracers. Fluorine-18 is a radionuclide routinely used in the radiolabeling of neuroreceptor ligands for PET because of its favorable half-life of 109.8 min. The delivery of such radiotracers into the brain provides images of transport, metabolic, and neutotransmission processes on the molecular level.
After a short introduction into the principles of PET, the review mainly focuses on the strategy of radiotracer development bridging from basic science to biomedical application. Successful radiotracer design as described here provides molecular probes which not only are useful for imaging of huma brain diseases, but also allow molecular neuroreceptor imaging studies in various small-animal models of diseases, including genetically-engineered animals. Furthermore, they provide a powerful tool for in vivo pharmacology during the process of pre-clinical drug development to identify new drug targets, to investigate phathophysiology, to discover potential drug candidates, and to evaluate the pharmacokinetics and pharmacodynamics of drugs in vivo.

In Computersimulationen wurden Schwankungen der Kühlmitteltemperatur (KMT) am Kerneintritt und des Kühlmittelmassenstromes als mögliche Ursache für erhöhtes Neutronenflussrauschen in Druckwasserreaktoren untersucht. Das Ziel ist die Vermeidung von Neutronenflußschwankungen in einer Größenordnung, die zu einer unbeabsichtigten Auslösung von Signalen zur Reaktorschnellabschaltungführen können.
Als Simulationstool wurde dafür der Rossendorfer Reaktordynamikcode DYN3D eingesetzt. Es wurden transiente Rechnungen mit verschiedenen aufgeprägten Randbedingungen für die Kühlmitteleintrittstemperatur oder den Kühlmittelmassenstrom durchgeführt, in denen dreidimensional die zeitlich variierenden lokalen linearen Stableistungen berechnet wurden. Diese lokalen linearen Stableistungen werden als In-Core-Detektorsignale interpretiert. Dabei wurden zunächst harmonische Oszillationen, dann auch stochastische Fluktuationen der lokalen Kühlmitteleintrittstemperatur oder des Massenstroms betrachtet, die zwischen den einzelnen Brennelementen oder Bereichen des Reaktorkerns auf unterschiedliche Weise korreliert sein können. Mittels Fast Fourier Transformation (FFT) wurden Übertragungsfunktionen zwischen Temperaturstörung und Responsesignal (lokale lineare Stableistung) ermittelt und ausgewertet.
Um den Einfluss von unterkühltem Sieden des Kühlmittels und der Wärmeleitung im Brennstab zu klären, wurden Variantenrechnungen mit verstärktem unterkühltem Sieden sowie mit verändertem Wärmedurchgangskoeffizienten im Gasspalt zwischen Brennstoff und Hülle durchgeführt. Unterkühltes Sieden wurde durch eine Reduzierung des Massenstroms bzw. Erhöhung der Eintrittstemperatur generiert. Weiterhin wurden für einen Referenzfall Untersuchungen zum Einfluss der numerischen Diffusion durchgeführt.
Der größte Teil der Rechnungen wurde für eine generische Kernbeladung eines DWR vom Typ Konvoi durchgeführt. Teilweise wurden auch konkrete, reaktor- und zyklusspezifische thermohydraulische Randbedingungen sowie neutronenphysikalische Wirkungsquerschnitte (WQS) benutzt, um quantitativ belastbare Aussagen zu erhalten.
Die Ergebnisse der DYN3D-Simulationen zum können wie folgt zusammengefasst werden:

• Stochastische, unkorrelierte Schwankungen der KMT am Eintritt in die einzelnen Brennelemente (BE) führen bei realistischer Amplitude nur zu sehr kleinen Schwankungen in der Leistungsdichte, die für eie eventuelle unbeabsichtigte Auslösung eines Signals zur Reaktorschnellabschaltung nicht relevant sind.
• Stochastische Temperaturschwankungen mit Korrelationen zwischen den BE (z. B. bedingt durch Schwankungen der Kaltstrangtemperaturen) können Leistungsdichteschwankungen mit relevanten Amplituden generieren (je nach Grad der Korrelation).
• Schwankungen der Leistungsdichte, die durch Schwankungen der Eintrittstemperatur oder durch Massenstromschwankungen hervorgerufen werden, zeigen ein deutlich unterschiedliches Signalverhalten.
• Unterkühltes Sieden und Variation des WÜ im Gasspalt Brennstoff-Hülle haben nur geringen Einfluss auf das Neutronenflussrauschen.

Exchange coupled ferromagnetic-antiferromagnetic Ni81Fe19/Ir23Mn77 films with a zigzag alignment of magnetization are prepared by local ion irradiation in order to shape the anisotropic magneto-resistive behavior of the magnetic thin film structures. A unique uniaxial field sensitivity along the net magnetization alignment is obtained through the orthogonally modulated and magnetic domain wall stabilized magnetic ground state. Controlling local thin film magnetization distributions and thus the overall magnetization response opens unique ways to tailor the magneto-resistive sensitivity of functional magnetic thin film devices.

Es ist kein Abstract vorhanden.