Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The adsorption of small (bio-)organic molecules on clean, low-index TiO2 surfaces has been investigated by density-functional based tightbinding calculations with the goal to rationalise the propensity of such molecules to self-assemble into row-like structures or two-dimensionally ordered patches. The systems studied range from phosphonic acids to the nucleotide cytidin monophosphate adsorbed on TiO2 anatase(101) and rutile(110) surfaces. We studied the geometries and adsorption energies of several adsorption models and obtain several possible adsorption structures that can be present on the specific TiO2 surfaces with comparable probability. For the pure phosphonic acids the preferable coordination is exclusively bidentate with similar adsorption energies but several different geometries. Monodentate and tridentate arrangements have significantly smaller adsorption energies and tend to relax towards the bidentate coordination. Despite the different steric situation, cytidin monophosphate exhibits exactly the same trends as phosphonic acids with bidentate coordination via a combination of oxo, alkoxy and hydroxyl groups.

Transition metal chalcohalides MX2 can form a wealth of diverse nanostructures, which range from large octahedral and fullerene-like hollow clusters and cylindrical nanotubes close to the nominal composition M:X = 1:2 to smaller, two-dimensional platelet-shaped clusters under sulfur excess and to one-dimensionally elongated nanowires under sulfur-deficient conditions. All of those structures exhibit specific electronic properties that differ from the ones of the pure bulk and open up a large application spectrum, that includes the lubricant aspect, but extends to catalysis and electronic transport. One-dimensionally delocalized electronic states provide the basis for the higher activity, reactivity and conductivity in such nanostructures. One-dimensional MX wires are composed of a central metallic wire coated by a sulfur and/or halide shell. They exhibit a very high structural regularity, hence, ballistic conductivity may be obtained in such structures. DFT calculations showed that wires can act as electromechanical switches, because they undergo a symmetry-dependent metal-insulator transition upon twisting [Nano Lett.,10.1021/nl801456f; Nano Lett., 2008, 8, 3928-3931].

Ferromagnetic and ferroelectric oxides of composition REMn2O5 have become known for exhibiting a coupling between those properties. On substitution of Fe in YMn2−xFexO5, the crystal structure is conserved, but the magnetic structure changes and the ferroelectricity disappears. X-ray diffraction measurements on a series of powders with different Fe content were employed to inspect the crystal structure whereas extended X-ray absorption fine structure measurements were done to identify the iron substitution site. Density functional theory calculations of the electronic structure for YMnFeO5 were carried out using the experimentally determined crystal structure data and the FPLO-5 program. Different magnetic structures are studied to determine the type of interaction between the magnetic ions.

In many industrial processes the measurement and monitoring of process parameters is hampered by limited access to the process itself. This is especially true for large vessels, such as large size tanks, reactors, fermenters, etc. State of the art instrumentation is commonly applied locally and spatially resolved parameter measurement is either not feasible or too expensive. For the measurement of process parameters in a stirred fermentation biogas reactor we developed the concept of neutrally buoyant self-powered sensor particles. The prototype sensor performs logging of temperature, absolute pressure and 3D-acceleration data using appropriate commercial miniature sensors, a low power microcontroller and associated EEPROM modules integrated in a robust capsule which gives a balance between buoyancy and gravitation with respect to the liquid process substrate. In an initial test of the developed prototype its autonomous operation has been successfully proved showing feasibility for future application in a biogas reactor.

SrTiO3 is a commercially available wafer material e.g. for the integration of oxide superconductors or microwave filter applications. The electric properties of SrTiO3 are routinely modified by doping with additional elements such as Nb. A targeted defect engineering may, however, achieve similar or superior results, while remaining in the ternary system (Sr,Ti,O), i.e. without the need for extrinsic doping. Material characterization methods able to distinguish such defects in particular are needed. In the present study we combine all-electron first-principles calculations with electron energy loss and X-ray absorption spectroscopy to study the electronic properties of SrTiO3-related oxygen deficient compounds. In particular, such changes of the SrTiO3 core-level spectra are studied, which occur if O vacancies accumulate in SrTiO3, or if excess SrO(001) planes are inserted to form Ruddlesden-Popper-type compounds.

Nanoindentation and local ion irradiation (i.e., focused ion beam or broad beam irradiation through shadow masks, such as alumina templates or PMMA masks) are shown to be effective methods to generate periodic arrays of sub-micron ferromagnetic dots at the surface of paramagnetic Fe60Al40 alloys (both in the form of sheets and thin films). The fabricated entities exhibit a variety of magnetic properties depending on their size and shape. Remarkably, in some cases, the magnetic anisotropy of the dots is oriented perpendicular to the film plane. Furthermore, the ferromagnetic properties of the patterned structures can be removed by annealing at sufficiently high temperatures, thus evidencing the reversible character of this novel magnetic lithography procedure.

In nanostructured materials spatial confinement effects lead to structure-dependent modifications of the bulk transport properties. In part, such modifications can be accounted for by a classical master equation approach for the transport of the different charge carrier species. The rather large quantity of parameters, which enter such an approach, can more or less easily be adjusted to the dimensional characteristics and the electronic settings of the system as well as to temperature effects. On the other hand, a microscopically more detailed and mostly parameter-free picture is obtained from a quantum-mechanical treatment on the basis of the density-functional theory. An extension by a Green's function formalism allows the determination and analysis of electronic transport through contacted nanostructures. Examples will be given to demonstrate the applicability of the different approaches for dissipative and hopping transport through a regular array of nanostructures, for a mechanically triggered metal-insulator transition in nanowires, and for the enhanced conductivity at multiferroic domain walls.

In nanostructured materials spatial confinement effects lead to structure-dependent modifications of the bulk transport properties. In part, such modifications can be accounted for by a classical master equation approach for the transport of the different charge carrier species. The rather large quantity of parameters, which enter such an approach, can more or less easily be adjusted to the dimensional characteristics and the electronic settings of the system as well as to temperature effects. On the other hand, a microscopically more detailed and mostly parameter-free picture is obtained from a quantum-mechanical treatment on the basis of the density-functional theory. An extension by a Green's function formalism allows the determination and analysis of electronic transport through contacted nanostructures. Examples will be given to demonstrate the applicability of the different approaches for dissipative and hopping transport through a regular array of nanostructures, for a mechanically triggered metal-insulator transition in nanowires, and for the enhanced conductivity at multiferroic domain walls.

The last few decades have seen an amazing miniaturization of silicon microelectronics, to the extent that modern transistors are approaching quantum limits. Further miniaturization requires novel materials with a well-defined atomic structure that allows information to be processed and stored with a small and uniform number of charge carriers. Nanostructured materials have attracted the attention of researchers because they promise both improved processing and energy efficiency.

To check the general quality of our analytical results, we started an intercomparison between four more or less common non-destructive X-ray based methods:

• low energy particle induced X-ray emission with protons of 2 MeV (PIXE)
• high energy particle induced X-ray emission with protons of 68 MeV (HE-PIXE)
• X-ray fluorescence with a portable device (µ-XRF)
• synchrotron-induced X-ray fluorescence (SY-XRF)
As test objects we selected six Roman coins with corrosion layers of different occurrence. Each coin was analyzed at three locations: original surface, surface with fully removed and partially removed corrosion layer, respectively.
We used two different external beam set-ups for PIXE: A “classical” one at a 2 MV tandem accelerator (BAM) and a high-energy one at the Helmholtz-Zentrum Berlin. The low-energy proton beam was extracted into air through a thin polyimide window (8 µm thick) and focused by a magnetic quadrupole doublet followed by a carbon aperture (Ø=0.7 mm). X-rays were energy dispersively measured by a Si(Li) detector [1]. There are some advantages in using higher energy protons [2] over low-energy ones: The protons can penetrate more deeply the material and the excitation probability for K-lines of heavy elements is bigger, resulting in better detection limits for those elements. At our set-up the beam is extracted into air via a thin Kapton foil and the X-ray signals are collected by a HPGe (resolution: 180 eV at 5.9 keV). Measurement times were 200 s. The data evaluation was done using the Guelph PIXE software GUPIX.
SY-XRF was performed at the hard X-ray beamline BAMline at BESSY. We analysed the Roman coins by our typical set-up [3]: A Si(111) Double-Crystal-Monochromator (DCM), and a W/Si Double-Multilayer-Monochromator (DMM) were used to produce a monochromatic X-ray beam of 32 keV. Signals were collected by a Si(Li) detector.
Last but not least, a mobile XRF-device equipped with a Mo-X-ray tube (30 W) and a polycapillary (spot size: 70 µm) was used to check to which extent a method that could in principal analyse objects in the field or in the collections can keep up with the three stationary (and more expensive) methods.
The four different methods produced tolerable to horrendous differences of quantitative results. Some discrepancies can be e.g. explained by variations of the analysed volume. For instance, a possible inhomogeneity of the sample will differently influence analytical results, if one changes the spot-size and penetration depth. The influence of the corrosion layer on the obtained concentrations also depends on the analytical depth of each method. Quantification procedures for each method should be adapted to these effects.
References: [1] I. Reiche et al., X-Ray Spectrom. 34 (2005) 42. [2] A. Denker et al., X-Ray Spectrom. 34 (2005) 376. [3] H. Riesemeier et al., X-Ray Spectrom. 34 (2005) 160.

The aim of the modified magnetic spectrometer “Little John” [1] is to measure concentration profiles of light elements in thin layers with sub-nanometer depth resolution by Elastic Recoil Detection Analysis (ERDA). For these measurements heavy ions from the Rossendorf 5-MV-Tandem accelerator are directed to the sample. The ejected recoil atoms are detected and energy analysed under forward angles. The depth resolution depends directly on the energy resolution of the spectrometer. High energy resolutions can be obtained using magnetic particle spectrometers, where the energy measurement is transformed into a position measurement at the focal plane.
The depth scale is provided by the stopping power of energetic heavy ions moving in matter, the available data of which assume a dynamic charge state equilibrium due to electron loss and capture along the ion trajectory. In the case of ultrathin layers the path length of the particles are too short to achieve this equilibrium. Since magnetic spectrometers separate particles with identical energy but different charge states it is necessary to consider charge state dependent stopping cross sections for quantitative data analysis. Here only very few data are available in the literature.
In this work we introduce an experimental setup at “Little John” for charge state distribution measurements of light heavy ions and present first results.

References: [1] H.J. Gils, J. Buschmann, S. Zagromski, J. Krisch and H. Rebel, Nucl. Instr. and Meth. A276 (1989), p. 151.
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A new 5 MV tandem accelerator has been installed at the Centre Européen de Recherche et d’Enseignement des Géosciences de l’Environnement (CEREGE). The machine is fully dedicated to accelerator mass spectrometry (AMS) in applied research like environmental and Earth sciences. For ¹⁰Be and ³⁶Cl the troublesome isobar suppression is maintained by nuclear charge dependent energy loss in an absorber foil, subsequent energy selection by a 35° electrostatic deflector followed by a 30° vertical magnet, and final separation of the rare isotope in a high-resolution, 4-anode (ΔE1, ΔE2, ΔE3, E-final) gas ionisation chamber [1].

Since the acceptance test in March 2007, we have successfully established routine measurement conditions for the long-lived cosmogenic radionuclides ¹⁰Be and ²⁶Al. Using ⁹Be carrier derived in our laboratory from phenakite crystals originating from a deep mine, we determined a background-level as low as 1.5x10^-16 (10Be/9Be) [2]. Considerable time has been spent to investigate reasons for variability of ion currents and background. We have performed cross-calibrations for ²⁶Al and ⁴¹Ca and took part into international round-robin exercises of ¹⁰Be and ³⁶Cl to establish quality assurance at ASTER. For ⁴¹Ca (extracted as CaF₃ ^-) and ¹²⁹I, background levels are in the range of 2x10^-14. The original Cs-sputter ion source SO110 [3], that produced sample-to-sample cross-contamination at the ‰-level and unacceptable long-term memory effects for volatile elements as chlorine or iodine, had been continuously replaced by a number of newly developed versions enhancing the performance step by step. Under optimum conditions, i.e. using exclusively low-level standards (³⁶Cl/Cl=1.4x10^-13) for calibration and cathode material containing the lowest isobar (³⁶S) concentrations, the ³⁶Cl background can reach 3x10^-16 (³⁶Cl/³⁵Cl). The total transmission varies from 2% for ³⁶Cl with the post-stripping absorber foil to 38% for ²⁶Al.

The main focus of applications of ASTER is on geological and environmental topics with the broad goal of using isotopic techniques to help understand the timing and rates of processes in the earth system. Work so far has included reconstruction of past climate, determination of the rate and timing of seismic activity, volcanic eruptions and rock falls.

References: [1] M.G. Klein et al., Nucl. Instr. and Meth. B 266 (2008) 1828. [2] S. Merchel et al., Nucl. Instr. and Meth. B 266 (2008) 4921. [3] M.G. Klein et al., Nucl. Instr. and Meth. B 249 (2006) 764.

Acknowledgments: This work was partially funded by CRONUS-EU (Marie-Curie Action, 6th FP #511927).

Eine der großen Herausforderungen in den Nanowissenschaften ist die reproduzierbare und einfache Herstellung nanoskaliger Strukturen mit neuen Eigenschaften für technische Anwendungen. Hier kann die Biologie einen wichtigen Beitrag leisten. So besitzen 70% aller bekannten Bakterien und Archaeen parakristalline Zellwandschichten, so genannte S-Layer, als äußerste Zellwandkomponente. Diese nanoskaligen Proteingitter können sehr unterschiedliche Funktionen übernehmen wie zum Beispiel als Schutzschicht, sie können für die Formgebung notwendig sein, als Molekularsieb wirken oder aber als Ionen- und Molekülfalle dienen. Die intrinsische Eigenschaft der Proteinuntereinheiten als monomolekulare Schicht in Suspension, an Grenz- und zahlreichen Oberflächen zu assemblieren, machen diese Proteine äußerst interessant für die einfache Herstellung multifunktionaler Oberflächenbeschichtungen. Auf Grund der sehr guten Metall-bindenden Eigenschaften und der höhere Stabilität gegenüber chemischen Einflüssen sind die S-Layer verschiedener Uranabfallhaldenisolate besonders gut zur Herstellung stabiler metallischer und halbleitender Nanopartikel und Nanostrukturen geeignet. Der Vortrag gibt einen Überblick über die Möglichkeiten und Grenzen der technischen Anwendung bakterieller S-Layer-Proteine und stellt die aktuelle Arbeiten des Instituts für Radiochemie dazu vor.

Dipole-strength functions up to the neutron-separation energies Sn of the N=50 isotones 88Sr, 89Y, 90Zr, and the even-mass Mo isotopes from 92Mo to 100Mo have been studied in photon-scattering experiments using the bremsstrahlung facility at the superconducting electron accelerator ELBE of the Forschungszentrum Dresden-Rossendorf.
To estimate the distribution of inelastic transitions from high-lying levels at high level density to low-lying levels, simulations of gamma-ray cascades were performed. On the basis of these simulations intensities of inelastic transitions were subtracted from the experimental intensity distributions, including the resolved peaks as well as a continuous part formed by unresolved transitions, and the intensities of elastic transitions to the ground state were corrected for their branching ratios. The photoabsorption cross sections obtained in this novel way are combined with (gamma,n) and (gamma,p) data and give detailed information about the dipole-strength functions in the energy range from about 4 MeV up to the giant dipole resonance (GDR). In all nuclides extra strength in excess to simple Lorentzian-like approximations of the tail of the GDR is found in the energy range from about 5 MeV up to about the respective particle thresholds. Calculations in the framework of the quasiparticle-random-phase approximation (QRPA) underestimate the dipole strength at low energy because they do not take into account the coupling of two-quasiparticle to multi-quasiparticle excitations. A new approach is presented that calculates the dipole strength for nuclei with shape fluctuations by combining the interacting boson model (IBA) with QRPA. Based on the slow shape dynamics and the fast dipole vibrations an Instantaneous Shape Sampling (ISS) is performed that describes the photoabsorption at a fixed shape with QRPA with probabilities given by IBA. The ISS-QRPA improves the description of the experimental photoabsorption cross sections.

no abastract available

After a brief exposition of the Naimark dilated PT brachistochrone [PRL 101, 230404 (2008)] evidence is provided that the dilation (doubling of the Hilbert space dimension) preserves the brachistochrone features of the model. The dilated PT brachistochrone in 4D-Hilbert space behaves as an effective Hermitian brachistochrone in the 2D subspace spanned by the 4D initial and final states.

HADES is a secondary generation experiment operated at GSI Darmstadt with the main goal to study dielectron production in proton, pion and heavy ion induced reactions. The first part of the HADES mission is to reinvestigate the puzzling pair excess measured by the DLS collaboration in C+C and Ca+Ca collisions at 1A GeV. For this purpose dedicated measurements with the C+C system at 1 and 2 A GeV were performed. The pair excess above a cocktail of free hadronic decays has been extracted and compared to the one measured by DLS. Furthermore, the excess is confronted with predictions of various model calculations.

The plasma enhanced chemical vapour deposition of amorphous hydrogenated carbon films from pulsed discharges with frequencies in the range from 50 kHz to 250 kHz was investigated. A Pinnacle Plus+ generator (Advanced Energy Ind., Inc.) was used to power the discharges in the so called mid-frequency range. Five different hydrocarbons (acetylene C₂H₂, 2-methylpropene/isobutylene C₄H₈, cyclopentene C₅H₈, toluene C₇H₈ and cycolheptatriene C₇H₈) were probed as film growth precursors. The a-C:H films deposited in a parallel plate reactor were characterised for their thickness/deposition rate (profilometer), hardness (nanoindentation with Berkovich indentor) and hydrogen content (nuclear reaction analysis, NRA). The measurement of neutral reaction products in the gas phase was performed with quadrupole mass spectrometry. The formation of stable, higher molecular hydrocarbons, that means cyclic ring compounds and polyacetylenes, was detected in all precursor plasmas. The hydrogen concentration in the films varied between 20 atomic-% and 37 atomic-%. It is roughly in inverse proportion to the hardness. The film with the highest hardness of 25 GPa was formed at a deposition rate of 0.8 µm/h in the C₂H₂ discharge at the lowest investigated pressure of 2 Pa. With increasing molecular mass of the precursor mostly weaker films were deposited. Relatively high values of both deposition rate and hardness were achieved using the precursor isobutylene: a hardness of 21 GPa combined with a deposition rate of 4.1 µm/h. But, as an over-all trend the a-C:H hardness decreases with increasing deposition rate.

The NeuLAND detector is part of the R3B experiment at FAIR and will detect neutrons between 0.2 and 1 GeV. The high energy neutrons are converted to charged particles, mainly protons, which are detected by Multigap Resistive Plate Chambers (MRPC). For the detector, a time resolution of σt < 100 ps and a position resolution of σx,y,z ≈ 1 cm is required for given flight paths in the range from 10 to 35 m. An active area of 2 × 2 m2 of the neutron detector at a distance of 12.5 m to the target will match the angular acceptance of ±80 mrad for the neutrons defined by the gap of the superconducting dipole magnet. The salient features of the prototypes will be described, as well as electrical measurements and studies with cosmic rays.

The NeuLAND detector for fast neutrons (0.2-1\,GeV) at the R3B experiment at FAIR aims for high time and spatial resolutions ($\sigma_{\rm t}$$<$100\,ps, $\sigma_{\rm x,y,z}$$<$1\,cm). The detector will consist of about 60 sequences of a stacked structure from iron converter material and multigap resistive plate chambers (MRPC's). The secondary charged particles stemming from hadronic interactions of the high energetic neutrons in the converter will be detected in the MRPC's, with excellent timing properties. As part of the ongoing development of the NeuLAND detector, MRPC prototypes designed for this application have been studied at the superconducting electron linac ELBE in Dresden with its picosecond time structure. The ELBE experiments show that the prototypes studied so far have efficiency $\geq$90\% for minimum ionizing particles in a 2x2 gap structure and fulfill the called for time resolution. --- Supported by BMBF (06DR134I) and GSI (FuE DR-GROS).

I review the status of the prototyping effort for multigap resistive plate chamber (MRPC) based neutron detectors for the NeuLAND detector at FAIR. Several MRPC prototypes have been built at FZD Dresden and at GSI Darmstadt. They have been tested using the picosecond time structure of the ELBE electron beam facility at FZD Dresden, Germany. All detectors display the called for time resolution of sigma < 100 ps at > 90% efficiency for 30 MeV electrons. The cross-talk issue is still under investigation. Preliminary data obtained using the new single-electron mode of operation at ELBE are also shown here.

The present study concerns the directional solidification of grain-refined and non-refined AlSi7 alloys under the influence of a travelling magnetic field (TMF). Upwards and downwards travelling fields have been applied to provide a forced convection within the solidifying melt. The formation of a fine equiaxed structure is favoured by both the addition of grain refining AlTi5B1-particles and electromagnetic stirring as well, whereas the addition of grain refiners into the melt appears to be more efficient for achieving a reduction of the mean grain size. A minimum grain size has been observed of the electromagnetic agitation of a grain-refined alloy. A melt stirring by a sufficiently high magnetic field provides a homogeneous grain size distribution in the sample volume, but, gives rise to the formation of segregation zones.

In der Arbeitsgruppe Magnetohydrodynamik am Forschungszentrum Dresden-Rossendorf (FZD) werden die komplexen Wechselwirkungen zwischen elektrisch leitfähigen Flüssigkeiten und magnetischen Feldern untersucht, um Strömungsverhalten und Erstarrungsprozesse flüssiger Metalllegierungen kontrolliert zu steuern. Ziel sind optimierte Produktionsprozesse für die Gießereitechnik. Zur Analyse der metallischen Mikrogefüge setzen die Wissenschaftler ein automatisiertes System aus High-end-Mikroskop und PowerMosaic-Bildaufnahme ein, das große Probenoberflächen in hochaufgelösten Einzelbildern abrastert und ein präzises Gesamtbild für quantitative Auswertungen liefert.

Liquid metal cooling or liquid metal targets belong to innovative reactor concepts such as the sodium cooled fast breeder reactor or the lead-bismuth target in a transmutation system. The safe and reliable operation of liquid metal systems requires corresponding measuring systems and control units, both for the liquid metal single-phase flow as well as for gas bubble liquid metal two-phase flows. We report on some recent developments in this field.
Integral flow rate measurements are an important issue. We describe two new, fully contactless electromagnetic solutions and related test measurements at available sodium and lead loops. One of the sensors is of particular interest since its operation does not depend on the electrical conductivity of the liquid metal, hence it is independent on the melt temperature.
A development of the past decade is the local velocity measurement by application of the Ultrasound Doppler Velocimetry (UDV). It provides the velocity profile along the ultrasonic beam, and has the capability to work even through some channel wall. We report on measurements in liquid sodium at 150°C. For higher temperatures, an integrated ultrasonic sensor with an acoustic wave-guide has been developed to overcome the limitation of ultrasonic transducers to temperatures lower than 200°C. This sensor can presently be applied at maximum temperatures up to 700°C. Stable and robust measurements have been performed in various PbBi flows in our laboratory at FZD as well as at the THESYS loop of the KALLA laboratory of Forschungszentrum Karlsruhe, Germany (FZK). We will present experimental results obtained in a PbBi bubbly flow at 250...300°C. Argon bubbles were injected through a single orifice in a cylindrical container filled with stagnant PbBi. Velocity profiles were measured in the bubble plume. At the THESYS loop of FZK, stable velocity profiles were measured in a round tube of diameter 60 mm during a period of about 72 hours at temperatures between 180°C and 350°C.
Further, we report on the development of a contactless magnetic tomography of the mean flow in liquid metals. This method gives the full three-dimensional mean velocity distribution in a liquid metal volume. Results from a laboratory demonstration experiment will be presented.

Bremsstrahlung and related items

The toxicity of the uranium to the living organisms is because of its heavy metal characteristic. Proteins, the fundamental component of all living cells and the key to their metabolism, undergo conformational changes upon the heavy metal complexation, thus loss their proper cellular function. In this study, phosvitin, a highly water soluble 34 kDa protein containing roughly 35 phosphate groups and 29 carboxylic residues1, is chosen as an ideal model system for the spectroscopic investigation of the interaction of U(VI) with proteins allowing the differentiation between the U(VI)-phosphate and U(VI)-carboxylic complexation. For this purpose, two different U(VI) concentrations (10−4 M and 10−5 M) are set up at pH 4 with various amounts of phosvitin to acquire complexes with different U(VI)/phosphate group ratios. The aqueous solutions were investigated by ATR FT-IR spectroscopy. For the very first time, soluble protein U(VI) complexes are achieved in aqueous solution providing spectral evidence for U(VI) complexation by the unequivocal identification of the νas(UO22+) mode. The spectra of the soluble complex show that at a low U(VI)/phosphate ratio (1:10.2) U(VI) preferentially binds to the phosphate groups. Interestingly, the νas(UO22+) mode is found at 905 cm−1 which is bathochromic shifted about 60 cm−1 compared to the free uranyl ion2 reflecting a strong coordination to several phosphate groups. With increasing U(VI)/phosphate ratio, U(VI) complexation to carboxylic groups is observed by a hypsochromic shift of the νas(UO22+) mode and characteristic bands of the νs(COO−) and νas(COO−) modes. At a higher U(VI)/phosphate ratio (10:1), complexation between U(VI) and carboxylic groups becomes dominant. From the observed frequency of this mode (925 cm−1) a typical bidental complexation to U(VI) by carboxylic group can be assumed3. In order to reduce the impact of the carboxylic groups on the U(VI) binding, phosvitin is modified using EDC. After subsequent incubation with 10−3 M U(VI) in aqueous solution at pH 4, the obtained IR spectra of the precipitated U(VI)-protein complex confirm this assumption.

The dynamics of the magnetization reversal in single Pt/Co(0.5 nm)/Pt nano-discs with diameter 130 nm, fabricated by an He+ ion irradiation is investigated. They exhibit a very narrow distribution of small switching fields and a perpendicular magnetic anisotropy. In spite of the small involved magnetic volume, their dynamics cannot be interpreted within the usual Néel-Braun prediction developed and verified for uniform spin reversal in spherical nano-particles. Non-coherent magnetization reversal proceeds here by fast nucleation at nanodot borders and rather slow wall motion towards their center. Dynamics are perfectly accounted from a refined confined droplet model, involving the wall energy rather than the anisotropy energy. In counterpart, the blocking temperature for these nanodiscs is well described by the Néel-Braun model.

The skeleton of demosponges such as Ianthella basta is known to be a composite material formed from organic constituents, mostly collagenous proteins (spongin). Here, we show for the first time that a filigree, chitin-based scaffold is an integral constituent of the skeleton of I. basta. These chitin-based scaffolds can be isolated from the sponge skeletons using an extraction and purification technique based on the treatment with alkaline solutions. Solidstate 13C NMR, Raman, and FTIR spectroscopy as well as chitinase digestion reveal that the extracted material indeed consists of chitin. The morphology of the extracted material has been determined by light and electron microscopy. It consists of cross-linked chitin fibers of ca. 40 – 100 nm diameter forming a micro-structured network. The overall shape of this network closely resembles the shape of the integer sponge skeleton. For the first time, solidstate 13C NMR spectroscopy is used to characterize chitin from the skeleton of a marine sponge on a molecular level. The 13C NMR signals of the chitin-based scaffolds are relatively broad indicating a high amount of disordered chitin, possibly in the form of surface-exposed molecules. X-ray diffraction shows that the scaffolds extracted from I. basta are indeed lowly crystalline and consist of loosely packed chitin with large surfaces. The spectroscopic signature of these chitin-based scaffolds is closer to that of alpha-chitin than beta-chitin.

Long-term performance assessment of nuclear waste repositories is affected by the ability of the outer barrier systems to retain radionuclides after possible corrosive leakage of waste containers. The mobility of the radionuclides released from the spent fuel depends strongly on the processes that take place in the backfill material. The interaction of steel corrosion products and radionuclides is part of such a scenario. In this work, the sorption of Th(IV) onto 2-line-ferrihydrite (FeOOH center dot H2O) and magnetite (Fe3O4), used as models for steel corrosion products, has been studied using EXAFS spectroscopy. Sorption samples were prepared in 0.1 M NaClO4 solutions at acidic pH (initial pH values in the range 3.0-4.2) either from undersaturation and supersaturation conditions with respect to amorphous ThO2. Two oxygen subshells, one at 2.37 angstrom and another at 2.54 angstrom, were observed in the first hydration sphere of Th in the case of the ferrihydrite samples.
Th-Fe distances for the different ferrihydrite samples are similar to 3.60 angstrom. These results indicate a corner sharing surface complex of Th(IV) ion onto the ferrihydrite surface where the Th atom shares one 0 atom with each of two coordinated octahedra. The longer Th-O distance accounts for coordinated water molecules. No significant changes in the structural environment of Th in terms of coordination numbers and distances were detected as a function of Th(IV) concentration. Magnetite samples sorbing Th(IV) also showed also a strong distortion of the 0 shell, but in contrast to ferrihydrite, two types of nearest Fe atoms were detected at 3.50 angstrom and 3.70 angstrom. These results indicate that Th(IV) ion sorbs onto the magnetite surface as bidentate-corner sharing arrangements to [FeO6] octahedra and [FeO4] tetrahedra.

Die prinzipiellen Lagerungsmöglichkeiten für radioaktiven Abfall wurden mit den in Deutschland vorhandenen Lagern verglichen. Stand und Planung der möglichen Endlager wurde erläutert. Es wurden die technischen Anforderungen an ein sicheres Endlager beschrieben um Sicherheit für Mensch und Umwelt zu gewährleisten. Wichtige Prozesse der Schadstoffausbreitung wie Rückhaltung (Sorption, Ausfällung, Kristalleinbau), Mobilisierung (Anlagerung an Kolloide, Bildung stabiler in Wasser gelöster Verbindungen, Auflösung) und Diffusion durch Festgestein wurden beschrieben. Ausgewählte Arbeiten aus dem Institut für Endlager in Salz, Ton und Granit wurden vorgestellt, sowie die Möglichkeiten der Sorptionsdatenbank RES3T.

G-Protein coupled receptors (GPCRs) play a fundamental role in many physiological processes due to their ability to switch between different structures upon activation. The prototypical GPCR rhodopsin serves as a model to study molecular switching mechanisms. Upon photoisomerization of the chromophore retinal, protonation of a glutamic acid (Glu 134) in the highly conserved D(E)RY motif at the cytosolic end of transmembrane helix 3 (TM3) leads to breakage of an ionic lock which stabilizes the inactive state [1]. Due to the low dielectricity of the lipidic environment, side chain charges and their neutralization contribute to the energetics of conformational transitions much more than in a purely aqueous environment. Our aim is to elucidate the functional implication of lipid protein interactions and microstructure at the water lipid protein interface in controlling protein conformation. We have studied synthetic peptides derived from rhodopsin TM3 by fluorescence spectroscopy at different pH in a hydrophobic environment. In [2] pH dependency of FRET between Trp at the cytosolic side of a TM3-derived peptide and DANSYL-PE was used as a monitor for helix motion. The observed pH dependency argues for stabilization of the protonated state by lipid protein interactions. In addition, we studied a TM3-derived peptide with a Trp probe shifted into the hydrophobic region. This peptide showed a red-shifted emission maximum of Trp, indicative of water accessibility. Moreover, at low pH the red-shift was less pronounced supporting the hypothesis that the neutralized Glu134 repels water and in general provides a pH-regulated hydration site. We conclude that microstructure at the water lipid protein interface and lipid protein interaction play a key role in the switching mechanism of GPCRs. The predominance of these local interactions which are not strictly dependent on intramolecular contacts to specific amino acids reconciles the highly conserved proton uptake at the D(E)RY motif in GPCR activation on the one hand and the diverse ligand specificity of class-A GPCRs on the other hand.
References
[1] J. A. Ballesteros, A. D. Jensen, G. Liapakis, S. G.F. Rasmussen, L. Shi, U. Gether, J. A. Javitch, J. Biol. Chem. 276, 29171-29177 (2001)
[2] S. Madathil, G. Furlinski, K.Fahmy, Biopolymers 82, 329-333 (2006).

One of the most prominent features of Earth's magnetic field reversals is their asymmetric shape which includes a slow decay of the initial dipole and a fast recreation of the reversed dipole. This relaxation-oscillation-like behaviour can result from a simple mean-field dynamo model in its highly supercritical regime. The same model can also explain the deviation of paleomagnetic reversal sequences from Poisson statistics, as well as the stochastic resonance phenomenon with the Milankovitch cycle of the Earth's orbit eccentricity. Encouraged by this agreement, we utilize those three temporal reversal characteristics to constrain the most essential parameters of the geodynamo, among them the effective (turbulent) magnetic diffusivity, the degree of supercriticality, and the relative strength of the periodic forcing. Using a downhill simplex method we obtain an optimized dynamo model that yields reversal characteristics which are in surprising correspondence with paleomagnetic data.

The magnetorotational instability (MRI) is known to play a key role in the formation of stars and black holes by triggering turbulence in hydrodynamically stable Keplerian accretion discs. As discussed recently, it might also play a role in the angular momentum transport in the Earth's outer core. We report the experimental demonstration of this instability in a Taylor-Couette flow under the influence of a helical magnetic field. Special focus is laid on a new version of this experiment in which the Ekman pumping is strongly reduced by using split end-caps.

The magnetorotational instability (MRI) is believed to play a key role in the formation of stars and black holes by triggering turbulence in hydrodynamically stable Keplerian accretion discs. Although the MRI had been discovered by Velikhov as early as 1959, its key role for the understanding of accretion disks was revealed only in 1991 by Balbus and Hawley. While thousands of papers have been written on the astrophysical relevance of MRI since that time, experimental work on MRI is still rare.
In 2004, Sisan et al. had observed a new coupled mode of velocity and magnetic field perturbations in a spherical Couette flow, whose parameter dependencies resemble those of the MRI. However, the background flow in this experiment was already fully turbulent so that the original goal to investigate MRI as the first instability on an otherwise stable flow could not be met. Another MRI experiment, on the basis of a short Taylor-Couette flow, is presently pursued at Princeton University.
Both experiments are carried out with a purely axial magnetic field being applied. In this standard MRI (SMRI) configuration, the governing parameters for the onset of the instability are the magnetic Reynolds number and the Lundquist number. Surprisingly, by adding an azimuthal magnetic field to the axial magnetic field, the governing role is taken over by the hydrodynamic Reynolds number and the Hartmann number. Consequently, this helical MRI (HMRI) can be observed with much less experimental effort than the SMRI.
In previous experiments at the facility PROMISE (Potsdam ROssendorf Magnetic InStability Experiment), the HMRI was observed in a liquid metal Taylor-Couette flow at moderate Reynolds and Hartmann numbers. However, the observation of this HMRI was disrupted by a significant Ekman pumping driven by solid end-caps that confined the instability only to a part of the Taylor-Couette cell. We present the observation of the HMRI in an improved Taylor-Couette setup in which the Ekman pumping is strongly reduced by using split end-caps. The HMRI wave, which now spreads over the whole height of the cell, appears much sharper and in better agreement with numerical predictions. By analyzing various parameter dependencies we conclude that the observed HMRI represents a self-sustained global instability rather than a noise-sustained convective one.

In an attempt to understand why the dominating magnetic field observed in the von-K\'arm\'an-Sodium (VKS) dynamo experiment is axisymmetric, we investigate in the present paper the ability of mean field models to generate axisymmetric eigenmodes in cylindrical geometries. An $\alpha$-effect is added to the induction equation and we identify reasonable and necessary properties of the $\alpha$ distribution so that axisymmetric eigenmodes are generated. The parametric study is done with two different simulation codes. We find that simple distributions of $\alpha$-effect, either concentrated in the disk neighbourhood or occupying the bulk of the flow, require unrealistically large values of the parameter $\alpha$ to explain the VKS observations.

There is an increasing interest to apply beside system codes also Computational Fluid Dynamics (CFD) codes for special analyses related to Nuclear Reactor Safety (NRS). Presently CFD codes are frequently used in practical applications for single phase flows, e.g. in automobile or aviation industries. Also in nuclear reactor research CFD codes are successfully applied single phase flows, e.g. for problems related to boron mixing in the primary circuit of Pressure Water Reactors. On the other hand two-phase flow simulations using CFD codes are not yet mature due to the complex interactions between the phases. Examples are poly-dispersed bubbly flows which require a multi bubble size modelling or models for separated flows in horizontal or near horizontal channels which are characterized by large interfaces. For two-phase CFD codes additional closure models are needed to describe mass, momentum and energy transfer between the phases. Such models should consider only local flow parameters, i.e. correlations available for system codes cannot be transferred in general for the use in CFD codes. Instead closure models have to be developed and validated basing on new experimental data with high resolution in space and time. Due to the independency of CFD codes on the geometry and scale it is not necessary to do such experiments in real geometries, but the local flow conditions should be similar the ones expected in praxis. TOPFLOW is a unique thermal hydraulic test facility for such two-phase flow studies. Experiments can be carried out for air-water or steam-water two phase flows at pressures up to 7 MPa. For steam production up to 4 MW heating power are available. This allows to conduct experiments at condition which are close to the nuclear application. On the other hand local data characterizing the micro- or meso-scale structure of the flow are required. For this reason unique measurement devices, such as high-pressure wire-mesh sensors and fast X-ray tomography are applied in TOPFLOW experiments. They provide CFD like data, which means data in high resolution in space and time. The TOPFLOW facility was used for different types of flow experiments in vertical test sections and a large pressure chamber. New experimental setups are currently under preparation. The paper gives a general overview on the experiments done at the facility and their importance for CFD model development and validation for two-phase flows. This is illustrated in detail on the example of poly-dispersed bubbly flows. In addition examples for experimental data useful for the CFD code qualification in case of stratified flows are given. Finally the complex flow situation in case two-phase Pressurized Thermal Shock (PTS) is discussed.

For special analyses related to Nuclear Reactor Safety (NRS), there is an increasing interest to apply beside system codes also Computational Fluid Dynamics (CFD) codes. Presently CFD codes are frequently used in practical applications for single phase flows, e.g. in automobile or aviation industries. Also in the field of nuclear safety research CFD codes are successfully applied to single phase flows, e.g. for problems related to boron mixing in the primary circuit of Pressure Water Reactors. On the other hand two-phase flow simulations using CFD codes are not yet mature due to the complex interactions between the phases. Examples are poly-dispersed bubbly flows which require a multi bubble size modelling or models for separated flows in horizontal or near horizontal channels which are characterized by large interfaces. For two-phase CFD codes, additional closure models are needed to describe mass, momentum and energy transfer between the phases. Such models should consider only local flow parameters, i.e. correlations available for system codes cannot be transferred in general for the use in CFD codes. Instead, closure models have to be developed and validated basing on new experimental data with high resolution in space and time. Due to the independency of CFD codes on the geometry and scale, it is not necessary to do such experiments in real geometries, but the local flow conditions should be similar the ones expected in praxis. TOPFLOW is a unique thermal hydraulic test facility for such two-phase flow studies. Experiments can be carried out for air-water or steam-water two-phase flows at a pressure up to 7 MPa. For steam production, up to 4 MW heating power are available. This allows to conduct experiments at conditions close to the nuclear application. On the other hand, local data characterizing the micro- or meso-scale structure of the flow are required. For this reason unique measurement devices, such as high-pressure wire-mesh sensors and fast X-ray tomography are applied in TOPFLOW experiments. They provide CFD like data, which means data in high resolution in space and time. The TOPFLOW facility was used for different types of experiments in vertical test sections and in a large pressure chamber. New experimental setups are currently under preparation. The paper gives a general overview on the experiments done at the facility and their importance for CFD model development and validation for two-phase flows. This is illustrated in detail on the example of poly-dispersed bubbly flows. In addition, examples for experimental data useful for the CFD code qualification in case of stratified flows are given.

Die Fluoreszenzeigenschaften einer 0,1 M Lactatlösung wurden bei Raumtemperatur und im gefrorenen Zustand bei 200, 100, und 10 K bei einer Anregungswellenlänge von 266 nm durch Kopplung der zeitaufgelösten Laser-induzierten Fluoreszenzspektroskopie (TRLFS) mit einem Kryostatensystem untersucht. Bei Raumtemperatur konnte keine Fluoreszenz nachgewiesen werde. Allerdings war es mit abnehmender Temperatur möglich eine stark zunehmende Fluoreszenzintensität und -lebensdauer zu detektiert. Es konnte ein Intensitätsmaximum bei 472 ± 2 nm und bei 10 K eine Lebensdauer von 6737,5 ± 1,6 ns ermittelt werden.

Driven by the overall progress in the field of accelerator mass spectrometry (AMS) and its spreading application within the geosciences, measurements of increasing numbers of samples with low isotopic ratios of ¹⁰Be/⁹Be and ³⁶Cl/Cl will be required in the future. In order to check the quality of measurements at low ¹⁰Be concentrations, we have examined the linearity of ¹⁰Be/⁹Be as a function of isotope ratio. For this purpose we have prepared small quantities of three secondary standards and distributed these to nine AMS laboratories. Ratios can be calculated relative to the diluted NIST SRM 4325 after taking account of the ¹⁰Be contribution of the ⁹Be carrier (¹⁰Be/⁹Be=(1.24±0.23)x10^-14) @ ASTER, Gif, VERA). As the initial ¹⁰Be/⁹Be of the primary standard is under discussion, results of the secondary standards (~3x10^-12/-13/-14) will be discussed relatively to the primary standard ratio only.
The problem of low ratio samples is even more crucial for ³⁶Cl due to the high volatility of chlorine. Thus, we have prepared large quantities of three ³⁶Cl/Cl solutions from a certified ³⁶Cl activity (NIST SRM 4943) by step-wise dilution with NaCl (MERCK CertiPUR®, Cl traceable to NIST SRM 999a). AgCl precipitated from these solutions has been distributed to nine AMS laboratories. Calculated ³⁶Cl/Cl ratios are 1x10^-11/-12/-13.
Results for each nuclide show that these interlaboratory exercises are very valuable, as they show maximum differences between individual AMS labs up to 35% for ¹⁰Be, and 25% for ²⁵Cl, respectively. Possible reasons for these discrepancies are standard-like materials in use for calibration and cross-contamination in the ion sputter source. A full statistical data evaluation is in preparation and might help to identify more clearly error sources at individual AMS facilities. Thus, we are taking a step forward on the long way of improving quality assurance systems in the AMS community.
Acknowledgments: This round-robin could not have taken place without the interest and team effort of the participating AMS laboratories, as there are: Laboratory for Ion Beam Physics/ETH Zurich, PRIME Lab/Purdue University, The Australian National University/Canberra, CAMS/Lawrence Livermore National Laboratory, Scottish Universities Environmental Research Centre/East Kilbride, Centro Nacional de Aceleradores/University of Seville, University of Tsukuba/Ibaraki, Vienna Environmental Research Accelerator/Universität Wien. This work was partially funded by CRONUS-EU (Marie-Curie Action, 6^th FP #511927).

We have determined exposure ages of more than 50 quartz rich samples primarily from the Wohlthat Massiv / Queen Maud Land, Antarctica, via in situ produced ¹⁰Be (T_1/2 = 1.51 Ma) and ²⁶Al (T_1/2 = 0.7 Ma) using accelerator mass spectrometry (AMS). Measured radionuclide concentrations vary from extremely low values up to saturation. For a scenario with extremely low erosion and minimal tectonic uplift ¹⁰Be and ²⁶Al surface exposure ages are generally in good agreement. Long exposure ages up to >8 Ma were confirmed by measurement of stable ²¹Ne using noble gas mass spectrometry.
Our data call for a decisively higher ice stand in the Wohlthat Massiv / Queen Maud Land about 0.3 Ma ago, the ice level being 200 400 m higher than today. The following successive reduction of the glaciation down to the present level was essentially completed 0.1 Ma ago. Low level changes during the last glacial maximum occurred about 0.02 Ma ago and did affect only a region located close to the present shelf ice. As the extremely low erosion rates (<5 cm Ma^-1) inferred for several samples can only exist under extremely cold and hyperarid conditions, we exclude a scenario featuring a prolonged period with warm and humid climatic conditions within the last 8 Ma.

This study explores the basic thermal-hydraulic feasibility of a self-sustainable Th-U233 fuel cycle that can be adopted in the current generation of Pressurized Water Reactors. In previous studies we explored some fuel design strategies to achieve (or to approach as closely as possible) a sustainable fuel cycle, including the use of heterogeneous seed-blanket fuel assembly design. Preliminary neutronic analysis suggested that net breeding of U233 is feasible in principle within a typical PWR operating envelope. However considerable core design tradeoffs such as a reduction of core power density would be necessary to achieve such performance. The purpose of this work is to establish the maximum achievable power density for breeding core by evaluation of limiting thermal hydraulic parameters.

Synchrotrons and free-electron lasers (FELs) are the most powerful sources of Xray radiation. They constitute invaluable tools for a broad range of research in physics, biology, materials science, chemistry, and medicine. However, their dependence on large-scale radio-frequency electron accelerators restricted diversification of these X-ray sources to only several sites worldwide. Laser-driven plasma-wave accelerators provide dramatically increased accelerating fields and hence offer the potential to shrink the size and cost of these X-ray sources to the university-laboratory scale. Here we demonstrate the generation of soft-X-ray undulator radiation with laser-plasma-accelerated electron beams. The wellcollimated beams deliver soft-X-ray pulses with an expected pulse duration of ~10 fs, inferred from the physics of plasma-wave accelerators. Our source draws on a dedicated 30-cm-long undulator and a 1.5-cm-long accelerator delivering stable electron beams5 with energies of ~210 MeV. The spectrum of the generated undulator radiation typically consists of a main peak centered at a wavelength of ~18 nm (fundamental), a second peak near ~9nm (second harmonic) and a highenergy cutoff at ~7 nm. Magnetic quadrupole lenses ensure efficient electron beam transport and demonstrate an enabling technology for reproducible generation of tunable soft-X-ray undulator radiation. The source is scalable to shorter wavelengths by increasing the electron energy. Our results open the prospect of brilliant, ultrashort-pulsed X-ray sources becoming available in smallscale laboratories

Compact tuneable sources of ultrashort hard x-ray pulses can be realized by Thomson scattering, taking advantage of the comparatively short wavelength of a scattered laser pulse with respect to the period length of conventional undulators. Here, we present a detailed analysis and optimization of the efficiency of linear and non-linear Thomson scattering when the process is driven with relativistic laser pulses and when the conventional accelerator is replaced by a laser-plasma wakefield accelerator.

Despite intensive work in the past decades, hydrodynamics of the widely used trickle bed reactors are still on the focus of today’s research. There are a lot of questions and obstacles to be solved and simple but accurate and reliable measurement devices to be developed. In this study we present a new capacitance wire-mesh sensor system applied to a trickle bed reactor to investigate steady-state and dynamic hydrodynamic characteristics allowing to get new insights into the temporal and spatial behaviour of the trickle flow and pulse flow.

The incidence of inclination angle on the hydrodynamic behaviour of cocurrent gas-liquid flows through a packed bed is investigated experimentally in terms of liquid holdup, pressure gradient, and cross-wise and stream-wise gas-liquid segregation. Electrical capacitance tomography was applied for the analysis of the dynamic features of the two-phase flow as well as liquid saturation distribution. As a result of inclination angle, a segregated flow emerged in packed bed as a new flow regime intertwined between the trickle and the pulse flow regimes. Both segregated flow regime and pulse flow regimes were characterized and their relevant hydrodynamic features discussed.

Multiphase flows exist in many commercial areas such as the manufacture of petroleum-based products and fuels, the production of commodity and specialty chemicals, pharmaceuticals, production of polymers and pollution abatement. The trickle bed reactor (TBR) with a random packing operated in gas-liquid co-current downflow mode is the most widely used multiphase reactor in the chemical, biochemical and waste treatment industry.
There are several advantages of the downflow operation mode, including a wide operating range for gas/liquid flow rates, high capacities as well as high efficiencies. However, due to improper initial gas/liquid distributors, external bed porosity variations, wall effects, partial catalyst wetting and surface tension related effects, intricate problems arise which amongst others are non-uniformities in liquid distribution, liquid velocity and liquid holdup and their dynamics.
A new capacitance wire-mesh sensor for flow imaging is presented which succeeded in overcoming previous difficulties such as applicability for organic liquid flows in porous particle packings, velocity measurements, acquisition time etc. to explore dynamic hydrodynamic features in trickle bed reactors.

Hydrodynamische Studien in Rieselbettreaktoren unter erhöhten Drücken und Temperaturen beschäftigen sich hauptsächlich mit koaleszierenden, also nicht-schäumenden, Systemen. Obwohl in zahlreichen industriellen Prozessen schäumende Flüssigkeiten angewandt werden, ist keine aussagekräftige Datenbasis vorhanden. Für die verlässliche Auslegung und den sicheren Betrieb von Reaktoren wurden die Effekte von Temperatur und Druck auf die hydrodynamischen Kenngrößen für Newtonsche und nicht-Newtonsche schaumbildende Systeme untersucht. Außerdem wurde eine neue operative Methode entwickelt, bei der der Rieselbettreaktor alternierend zyklisch betrieben wird und die ohne die Dosierung von chemischen Zusätzen effektiv zur Begrenzung der Schaumbildung eingesetzt werden kann.

Schüttungen in Rieselbettreaktoren wirken gegenüber Feinpartikeln als Filter. Sowohl in Festbettbioreaktoren als auch bei petrochemischen Anwendungen wird durch die reduzierte Permeabilität und die damit verbundenen Druckverluste die Wirtschaftlichkeit der Prozesse stark beeinträchtigt. Obwohl den Anwendern das Problem bewusst ist, sind die Kenntnisse zur Filterwirkung von Rieselbettreaktoren bisher nicht intensiv erforscht.
Die Mechanismen der Ablagerung und die Auswirkungen auf die Hydrodynamik wurden am Beispiel von Kaolin-Feinpartikeln, die ein dominierender Bestandteil in den nachgelagerten Behandlungsstufen bei der Verarbeitung von Athabasca-Ölsanden sind, untersucht. Zusätzlich werden effektive technische Lösungen und operative Methoden zur Begrenzung der Ablagerungen vorgestellt.

Die Anwendung von Magnetfeldern hat sich als vielversprechender Ansatz zur Beeinflussung von Gas/Flüssig-Strömungen erwiesen. Obwohl organische Flüssigkeiten gewöhnlich kein magnetisches Verhalten zeigen, kann durch starke Gradienten-Magnetfelder mittels supraleitender Magneten auch in katalytischen Mehrphasenreaktoren, wie zum Beispiel Rieselbettreaktoren, der Schwerkraft entgegengewirkt und damit die Strömung einer erdgebundenen Mikrogravitation ausgesetzt werden. Unter diesen Bedingungen können der Flüssigkeitsanteil in der Katalysatorschüttung und der Benetzungsgrad an der Katalysatoroberfläche effektiv beeinflusst und damit Stofftransport und Umsatz einer katalytischen Reaktion deutlich gesteigert werden.

A number of papers reporting exotic native elements have been published within the last few decades. The "native" occurrences described are rather dubious in view of the lack of solid proof of their relationships with the host-rock minerals. Consequently, the genetic models proposed ranging from bio-reduction to the influence of deep-mantle, strongly-reduced fluids, are somewhat speculative. Here we present data for a unique Al⁰ flake protruding from the phlogopite matrix of a rock specimen collected from a desilicated pegmatite vein. The geologic setting suggests two processes that might have played a key role in the Al⁰ formation: (1) desilication of pegmatite, resulting in its Al residual enrichment; and (2) serpentinization of an ultramafic body, providing a strongly reduced front (H₂ and hydrocarbons) towards the serpentinite/pegmatite contact. These processes have presumably led to the reduction of Al to Al⁰ at discrete sites of alumina-rich minerals.

A new experimental measurement methodology was proposed to characterize the hydrodynamics in gas-liquid-solid semi-fluidized beds. Using pressure drop measurements in the lower fluidized bed section and a tracer response technique in the upper fixed bed portion, the six phase holdup components of the reactor were determined simultaneously. Available models for macroscopic predictions of holdups, initially proposed for three-phase fluidization, were extended and their applicability was discussed concerning semi-fluidized beds. Special attention was paid to the parameters of the generalized bubble wake model and their predictability with an artificial neural network. Phenomenological observations identified an additional interface region between both beds, which, viewed as an inchoate freeboard region determines the mechanisms of attachment and release of particles from the fluidized bed to the fixed bed portion.

In this work we investigate the miniband relaxation dynamics of electrons in doped GaAs/AlGaAs superlattices by two-color infrared pump-probe experiments using a free electron laser synchronized to a table top broadband IR source. In contrast to single color experiments, by this technique we are able to separate the different contributions from inter- and intraminiband relaxation to the transient behavior after an ultrafast excitation. In particular, the intraminiband relaxation is studied for different miniband widths, below and above the optical phonon energy of GaAs. For minibands wider than this critical value we find fast relaxation, nearly constant for different excitation intensities whereas for narrow minibands, a strong temperature and intensity dependence of the relaxation is found. The results are in good agreement with previously published Monte Carlo simulations.

The nuclear resonance fluorescence (NRF) setup at ELBE uses bremsstrahlung with endpoint energies up to 20 MeV. The setup consists of four 100% high-purity germanium detectors, each surrounded by a BGO escape-suppression shield and a lead collimator. The detection efficiency up to E = 12 MeV has been determined using the proton beam from the FZD Tandetron and well-known resonances in the 11B(p,gamma)12C, 14N(p,gamma)15O, and 27Al(p,gamma)28Si reactions. The deduced efficiency curve allows to check efficiency curves calculated with GEANT. Future photon-scattering work can be carried out with improved precision at high energy. — This work has been supported in part by the European Union (FP6 AIM RITA 025646).

The 15N(p,gamma)16O reaction lies at the intersection of the first and second CNO cycle of hydrogen burning. Recent R-matrix extrapolations suggest that its cross section may be lower by about a factor two with respect to previous work. Here we show new, direct experimental data on this reaction obtained at the LUNA 400 kV accelerator deep underground in the Gran Sasso laboratory in Italy.

Thermoelectromagnetic convection in electrically conducting cubic containers was studied experimentally. Two opposing side walls were cooled and heated, respectively, to produce a uniform temperature gradient. Inhomogeneous magnetic field distributions were achieved either with a small permanent magnet located above the melt layer, or with specifically shaped pole shoes of the magnetic system. Ultrasonic Doppler velocimetry measurements demonstrated that even a moderate temperature gradient may drive a distinct convection. Two different flow regimes were investigated with the permanent magnet. When it was positioned in the vicinity of an isothermal wall, with its direction of magnetization parallel to the temperature gradient, a single vortex spreading the whole container developed while the flow might be assessed as relatively stable. Moving the magnet to the center led to a modified distribution of the magnetic field, which altered the flow structure. The convective pattern changed to four vortices and the velocity fluctuations were intensified. A more generic case was realized with the pole shoes providing a gradient of the magnetic field only in one direction. Since the strength of the field could be raised significantly above that provided by the small permanent magnet and the area of impact onto the melt was larger, developed turbulent regimes were accomplished. Numerical results obtained for the Lorentz force and the rotor thereof support the experimental findings.

The advancement of high power (1e20 W/cm^2), short pulse (25 fs) laser systems has allowed for the production of high field gradients (~1e12 V/m) on the rear side of micron thick targets. This high field gradient is responsible for accelerating protons up to tens of MeV. This poster gives an overview of the work being performed at Forschungszentrum Dresden to study and develop the technique of proton laser acceleration into an Oncology based therapy unit, and it presents the first planned relative biological effectiveness experiments along with the associated dosimetry and beam transport.

The 14N(p,gamma)15O reaction controls the rate of the hydrogen burning CNO cycle. This reaction has recently been re-studied at E < 500keV at different facilities, including LUNA. However, also data at higher energy play a role in determining the extrapolated cross section in the R-matrix framework. Here we report on a new measurement of the absolute strength, decay branching ratio, and angular distribution of the E = 0.987 MeV (E_x = 8.284 MeV) resonance carried out at the high-current FZD Tandetron. --- This work has been supported in part by the European Union (FP6 AIM RITA 025646).

Thin films and superlattices of Py/Ta with an overall Py thickness of 20 nm and different number of Py/Ta stacks were irradiated with Ne ions in order to study the influence of interfacial mixing on their magnetic properties. With both, increasing ion fluence and increasing number of Py/Ta interfaces, a decrease of saturation magnetization and an increase of damping can be observed. However, the small uniaxial anisotropy of the samples remains unaffected. The critical ion fluence at which ferromagnetism, depending on the number of interfaces, vanishes has been determined.

High quality 3C-SiC nanocrystallites were epitaxially formed on 100 Si wafers covered by a 150 nm thick SiO2 capping layer after low dose carbon implantation and high temperature annealing in CO atmosphere. Carbon implantation is used to introduce nucleation sites by forming silicon-carbon clusters at the SiO2 / Si interface acting as nucleation sites for the growth of 3C-SiC nanocrystallites. The formation of the nucleation clusters as well as the morphology, the size, and the density of the nanocrystals were systematically studied by conventional and high resolution transmission electron microscopy. The nanocrystallites were developed following two different modes of growth: The first develops facets along the <100> crystallographic direction giving tetragonal grains and the second facets along the <110> direction resulting in elongated nanocrystallites. The formation mechanism of the nanocrystallites and the strain related with them are also discussed

Magnetic characteristics of both interacting and noninteracting Fe nanoparticle systems synthesized inside LaAlO3 matrices were investigated, utilizing SQUID magnetometry. The origin of the magnetic memory effect was explored. We found that not the interaction between magnetic nanoparticles but the size distribution is mainly responsible for that effect. Transmission electron micrographs support the finding by recording the FC/ZFC magnetization to evidence our illumination.

When amorphous silica is bombarded with energetic ions, various types of defects are created as a consequence of ion-solid interaction (peroxy radicals POR, oxygen deficient centres ODC, non-bridging oxygen hole centres NBOHC, E’-centres, etc.). The intensity of the electroluminescence from oxygen deficiency centres at 2.7 eV, non-bridging oxygen hole centres at 1.9 eV and defect centres with emission at 2.07 eV can be easily modified by the ion implantation of the different elements (H, N, O) into the full processed MOSLED structure. Nitrogen implanted into the SiO2:Gd layer reduces the concentration of the ODC and NBOHC while the doping of the oxygen increases the EL intensity observed from POR defect and NBOHC. Moreover, after oxygen or hydrogen implantation into the SiO2:Ge structure fourfold or fifth fold increase of the germanium related EL intensity was observed.

Epitaxial silicon nanowires (Si NWs) grown by molecular beam epitaxy on Si <111> substrates were separately doped p and n-type ex situ by implanting with B, P and As ions at room temperature with doses in the order of 1013 - 1014 cm-2. No implantation damage was observed in the B-implanted NWs after a rapid thermal annealing at 850°C for 30 s whereas the same could not heal out the P and As-implanted NWs completely. Electrical measurements showed that the desired doping concentrations were achieved for the B implanted NWs (p-type) while for the P and As implanted NWs (n-type) the measured carrier concentrations fell four orders of magnitude short of the intended. Incomplete electrical activation of the dopant atoms and out-diffusion/segregation at defects of dopants during annealing are probably responsible for such discrepancies in carrier concentrations in the n-type (P and As doped) NWs.

The strain Lysinibacillus sphaericus JG-A12, isolated from the uranium mining waste pile “Haberland” in Saxony (Germany), is capable of selective and reversible accumulation of radionuclides and toxic metals. It was demonstrated that metal binding is caused generally by the surface layer of the protein. This S-layer possesses a highly ordered lattice structure and can serve as a template spatially confined metal nanoparticle growth.
Our aim was to elucidate binding modes of Au to S-layer protein from L. sphaericus JG-A12.
In this study Au-complexes were produced by sorption of Au(III) on S-layer and reduction of these complexes to Au(0) nanoparticles. Au(III) complexes and Au(0) nanoparticles were studied by means of FTIR and EXAFS techniques.
EXAFS reveals the short range environment of the metal. No significant differences between the Au(III) and Au(0) were observed. Furthermore, EXAFS can only distinguish between elements in the short range order around the metal, the detected elements N, O and C cannot further be assigned to specific chemical groups.
FTIR measurements have shown that side chain carboxylates play a different role in Au(0) complex formation as compared to the complexation of Pd(II) or Pt(II).
For Au a weakening of asymmetric (1560 cm-1) and symmetric (1400 cm-1) carboxylate stretching mode indicates a different binding mode of Au to protein, probably involving stabilization of the protonated state of the carboxyls.
Hypothesize that Au causes hydrophobic burial, and thus protonation of carboxylic side chains rather than ionic interactions as found for Pd.
The results let us conclude that the binding mode of Au to S-layer from L. sphaericus JG-A12 is remarkably different from that of Pt or Pd.

Lightning research needs on-demand lightning strikes, because of the random character of natural lightning. Lasers have been proposed as alternatives to the current technique using rocket-pulled wires, because they would expectedly provide more flexibility. However, high-energy, nanosecond lasers cannot provide long connected plasma channels. In contrast, we recently reported the triggering of electric events in thunderclouds using ultrashort laser pulses. Further improvements of the laser pulse sequence and experimental geometry are discussed.

Introduction: The Monturaqui crater is the only meteorite impact related structure yet found in Chile. The simple crater of ~400 m diameter and ~34 m of depth [1] is localized at 3015 m altitude in the precordillera near the southern end of Salar de Atacama. The crater age was estimated as older than 0.1 Ma with an appreciable error by [2] by thermoluminescence analysis. We are reporting the first absolute ages of the Monturaqui impact following two approaches: a) the terrestrial age of the impactor by measuring the residual activities of ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca, ⁵⁹Ni, ⁶⁰Fe, and ⁵³Mn in iron shale samples, which corresponds to the altered fragments of the impactor (coarse octahedrite - group I - deduced from Fe-Ni-spherules found in impact melt ejecta [2,3]), and b) surface exposure ages by measuring in-situ produced ¹⁰Be in the granite outcrops exposed to cosmic radiation on Earth.
Experimental: Accelerator mass spectrometry of ¹⁰Be and ²⁶Al took place at ASTER, ³⁶Cl at CAMS, and ⁵³Mn at the Maier-Leibnitz-Laboratory. Other nuclides are foreseen soon.
Results: Measured concentrations are compared with depth-depending production rates (PRs) from theoretical Monte-Carlo calculations [priv.com., I. Leya]. As these PRs are based on the chemical composition (in space), remaining fragments are highly altered and precise chemical analyses could not yet be achieved, certain assumptions are influencing the discussion of our, thus preliminary, data.
The longest-lived radionuclide⁵³Mn (t_1/2=3.7 Ma), normalized to a fully corroded Fe₂O₃-sample, is the least sensitive nuclide to a varying terrestrial age, thus, providing us with the best value for a shielding depth: 62-71 cm. The best fit of the measured shortest-lived radionuclide ³⁶Cl (t_1/2=0.3 Ma) with theoretical PRs at that depth is for a terrestrial age of 500-600 ka. The ²⁶Al-activity (t_1/2=0.7 Ma) validates that age. The measured ¹⁰Be is far too high compared to theoretical PRs (based on a C-content of 0.1%, as Canyon Diablo). This goes along with earlier studies [4,5] demonstrating the big influence of inhomogeneously distributed traces as C, S, and P on the production of light nuclides.
Our second approach, using terrestrial ¹⁰Be, leads to a minimum in-situ exposure age of two quartz-rich samples from the crater wall of 200-250 ka. However, a larger age is very likely due to the subsequent erosion of the crater walls.
Preliminary paleomagnetic measurements of the granite within the crater revealed mixed normal and reverse magnetic field polarities suggesting a possible age for the impact remag-netization older than 780 ka.
Acknowledgements: CRONUS-EU, CNRS-CONICYT, M. Arnold, G. Aumaître, L. Benedetti, and I. Leya.
References: [1] Ugalde H. et al. 2007. Meteoritics & Planetary Science 42:2153. [2] Buchwald V. F. 1975. Handbook of iron meteorites 1:262. [3] Bunch P. E. and Cassidy W. 1972. Contrib. Mineral. Petrol. 36:95. [4] Leya I. and Michel R. 1998. Abstract #1172. 29th Lunar and Planetary Science Conference. [5] Leya I. et al. 1997. Meteoritics & Planetary Science 32:A78.

Rieselbettreaktoren sind von besonderer technischer Bedeutung für kontinuierliche Gas/Flüssig-Reaktionsprozesse. Voraussetzung für die strömungstechnische Analyse und Optimierung von Rieselbettprozessen ist die Kenntnis örtlich und zeitlich aufgelöster hydrodynamischer Parameter wie Phasen- und Geschwindigkeitsverteilung im Strömungsquerschnitt sowie Pulsfrequenz, -geschwindigkeit und Pulsform bei höheren Strömungsgeschwindigkeiten. Diese Aufgaben stellen hohe Anforderungen an neuartige Messsysteme.
Die Untersuchungen dieser charakteristischen Parameter wurden in einem Rieselbettreaktor im Pilotmaßstab (D = 100 mm, H = 1,4 m, Al2O3-Packung) durchgeführt. Als Messsysteme kamen 4 neuartige Gittersensoren zum Einsatz, die in verschiedenen Ebenen des Reaktors angeordnet sind. Die Sensoren bestehen aus zwei Ebenen, bei denen je 16 Edelstahldrähte rechtwinklig zueinander angeordnet sind, wodurch sich 208 Messpunkte je Sensor im Strömungsquerschnitt ergeben. Das kapazitive Messprinzip erlaubt die Anwendung industrierelevanter organischer Flüssigkeiten.
Durch eine hohe Abtastrate von bis zu 1000 Hz können auch transiente Strömungen im Reaktor, z. B. im Pulsregime oder bei instationärer Prozessführung, visualisiert werden. Die Verwendung eines Doppel-Gittersensors ermöglicht außerdem die Untersuchung von Strömungs- und Pulsgeschwindigkeiten mithilfe von Tracern. Die Untersuchungen dienen der Optimierung von Prozessführung und Apparatedesign sowie der Validierung von CFD-Simulationen.

The abundances of antiprotons and protons are considered within momentum-integrated Boltzmann equations describing Little Bangs, i.e., fireballs created in relativistic heavy-ion collisions. Despite of a large antiproton annihilation cross section we find a small drop of the ratio of antiprotons to protons from 170 MeV (chemical freeze-out temperature) until 100 MeV (kinetic freeze-out temperature) for CERN-SPS and BNL-RHIC energies thus corroborating the solution of the previously exposed ”antiproton puzzle”. In contrast, the Big Bang evolves so slowly that the antibaryons are kept for a long time in equilibrium resulting in an exceedingly small fraction. The adiabatic path of cosmic matter in the phase diagram of strongly interacting matter is mapped out.

Pseudo-scalar and scalar D mesons are considered within the QCD sum rule approach. We present an analysis of the mass splitting of the pseudo-scalar D - D mesons and the relation to QCD condensates. Weinberg type sum rules are derived for chiral partners which highlights the role of the chiral condensate.

The transition from the application of conservative models to the use of best-estimate models raises the question about the uncertainty of the obtained results. This question becomes especially important, if the best-estimate models should be used for safety analyses in the field of nuclear engineering. Different methodologies were developed to assess the uncertainty of the calculation results of computer simulation codes. One of them is the methodology developed by Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) which uses the statistical code package SUSA. In the past, this methodology was applied to the calculation results of the advanced thermal hydraulic system code ATHLET. In the frame of the recently finished EU FP5 funded research project VALCO, that methodology was extended and successfully applied to different coupled code systems, including the uncertainty analysis for neutronics. These code systems consist of a thermal hydraulic system code and a 3D neutron kinetic core model. Six different working groups applying different coupled code systems performed calculations. The involved system codes were ATHLET and SMABRE. They were used for the calculations together with the 3D neutron kinetic core models DYN3D, KIKO3D, BIPR8 and HEXTRAN.
Two real transients at NPPs with VVER-type reactors documented within the VALCO project were selected for analyses. One was the load drop of one of two turbines to house load level at the Loviisa-1 NPP (VVER-440), the second was a test with the switching-off of one of two main feed water pumps at the VVER-1000 Balakovo-4 NPP. Based on the relevant physical processes in both transients, lists of possible sources of uncertainties were compiled. They are specific for the two transients. Besides control parameters like control rod movement and thermal hydraulic parameters like secondary side pressure, mass flow rates, pressurizer sprayer and heater performance, different neutron kinetic parameters were included into the list of possible sources of uncertainties. These are the burn-up state of the core, the control rod efficiency for different control rod groups and the coefficients for Doppler and moderator density feed back. By use of the SUSA package, sets of input data with statistical variation of the relevant parameter values were generated for a large number of runs of the coupled codes for each transient.
Time-dependent rank correlation coefficients were calculated showing the influence of the varied parameters on the output parameter under investigation. The most interesting output parameters are the physical parameters for which experimental data are available. First of all, these are the core power, upper plenum pressure, core outlet and loop temperatures. The calculation results allowed also the determination of time-dependent tolerance intervals for given coverage and confidence. The comparison of the experimental data, the (best-estimate) reference solution and the tolerance intervals showed how the agreement between experiment and calculation could be quantified. In most of the cases the tolerance intervals include the experimental curves. A compiled list of the most important input parameters based on the rank correlation coefficients shows, which input parameters and models are responsible for the deviations. This list gives indications for further model improvements and code developments.

In the presentation, an overview on the validation activities for the coupled 3D neutron kinetic / thermal hydraulic system code DYN3D/ATHLET is given.

Ion sputtering of Si surfaces at normal incidence has been studied with and without metal codeposition. Metal impurities are necessary for dot pattern formation. Normal incidence ion sputtering of Si without metal codeposition has a smoothening instead of a roughening effect. The smoothening effect is effected by the presence of metal impurities and differs from „classical“ relaxation mechanisms where the decay coefficient has a power law dependence on the wavenumber.

The paper presents results of the circumferential core weld SN0.1.4 and the base metal ring 0.3.1 of the RPV from the unit 1 of the Greifswald WWER-440/230. The investigated trepans represent the irradiated-annealed-re-irradiated (IAI) condition. The working program is focussed on the characterisation of the RPV steels through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the ASTM Test Standard E1921 to determine the fracture toughness in different thickness locations.

Im Beitrag wird die Entwicklung der Laufwasserkraftnutzung an der Saale dargestellt. Einem starken Ausbau in der ersten Hälfte des 20. Jahrhunderts folgte ein Niedergang bis 1990. Heute arbeiten in Thüringen und Sachsen-Anhalt 32 Laufwasserwasserkraftanlagen mit einer Leistung von etwa 28 MW (Arbeit 120 GWh/a). Dazu kommen 110 GWh/a Strom aus regenerativer Wasserkraft von den PSW Bleiloch und Hohenwarthe I. Am bayrischen Oberlauf der Saale arbeiten 11 WKA mit einer Leistung von 0,7 MW (Arbeit 2 GWh/a). Unter den aktuellen Rahmenbedingungen kann noch mit einem Zubau von etwa 6 MW (24 GWh/a) gerechnet werden.
The development of the run-of-river hydropower on the river Saale is described. The extensive use in the first half of the last century was followed by a strong decrease between 1960 and 1990. Today 32 hydropower plants are again operating in Thuringia and Saxony-Anhalt with total power of 28 MW (120 GWh/a). The PSP Bleiloch and Hohenwarthe I additionally provide a renewable hydropwer generation of 110 GWh/a. Further 11 plants operate in Bavaria (power 0,7 MW, energy 2 GWh/a). A power increase of about 6 MW (corresponding to 24 GWh/a) can be expected taking into account the actual framework conditions.

High-spin level structures of 94,95Mo have been reinvestigated via the 16 O(82 Se, xn )94,95 Mo (x = 4, 3) reactions at E(82Se) = 460 MeV. The previously reported level schemes of these two nuclei have been largely modified up to 11 MeV in excitation energy due to identifications of some important linking transitions. Shellmodel calculations have been made in the model space of pi(p1/2 , g9/2 , d5/2 )4 and nu(d5/2 , s1/2 , d3/2 , g7/2 , h11/2 )2(3) and compared with the modified level schemes. The structures of the newly assigned high-spin states in 94,95Mo have been discussed.

The complexation of uranium(VI) with two nitrogen containing organic ligands, representing model substances for humic acid building blocks, has been investigated at pH values between 1.5 and 4.5 and an ionic strength of 0.1 M (NaClO4). Using two independent fluorescence spectroscopic methods, time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses (fs-TRLFS), the complex formation of uranium(VI) with anthranilic and nicotinic acid in aqueous solution was studied. In both systems a decrease in the luminescence intensity was observed with increasing ligand or metal ion concentration. Uranium(VI) complexes of the type MxLyHz were identified. Anthranilic acid forms a 1:1 complex under the given experimental conditions with a stability constant of log ß111 = 8.00 ± 0.10. For the uranium(VI) nicotinate system 1:1 and 1:2 complexes could be identified. The corresponding formation constants were calculated to be log ß111 = 8.60 ± 0.08 and log ß122 = 17.29 ± 0.10.

The coordination chemistry of uranium in differen toxidation states has recently gernerated much attention due to several reasons. The most important reason is the separation of U(VI) presentin radioactive waste, but also the effects of U(VI) on our environment. The extraction and separation of U(VI) and other actinides, especially the separation from lanthanides, is most difficult due to their similar chemical behaviour...

Die Grünalgen (Chlorophyta) gehören zur Gruppe der aquatischen „niederen“ Pflanzen, die in Süß-, Salzwasser und im Boden leben können. Aufgrund der weiten Verbreitung der Algen ist deren Einfluss auf die Migrationsprozesse von Uran und anderen Aktiniden in der Umwelt von grundlegendem Interesse. Außerdem spielen Algen eine wirtschaftlich relevante Rolle als Nahrungsmittel sowie Nahrungsergänzungsstoff, so dass von der Alge aufgenommene Schwermetalle und Aktiniden in die Nahrungskette gelangen und so auch eine Gesundheitsgefahr für den Menschen darstellen können.
Die einzellige Grünalge Chlorella vulgaris besitzt die Fähigkeit im pH-Wertbereich von 3 bis 7 größere Mengen an Uran (VI) zu binden.[1][2] Ziel dieser Studie war es die Wechselwirkung von Uran (VI) mit der Alge C. vulgaris quantitativ und strukturell insbesondere unter Einwirkung umweltrelevanten Urankonzentrationen bei metabolischer Aktivität der Zellen zu charakterisieren. Bei pH 4,4 wurde Uran (10-4 M, 5x10-6 M) sowohl von lebenden als auch toten Zellen unter den gegebenen experimentellen Bedingungen nahezu vollständig gebunden. Die Untersuchung der Wechselwirkung von Algen mit Uran bei Anfangs-pH-Werten von 4,4 bis 7 und niedriger Urankonzentration zeigte zunächst ebenfalls eine vollständige Sorption von Uran an die Zellen. Interessanterweise wird in Ansätzen mit metabolisch aktiven Algen ein Teil des gebundenen Urans im Verlauf der Inkubation wieder freigesetzt. Eine mögliche Erklärung dafür ist die Wechselwirkung des Urans mit Ausscheidungs¬produkten der Algen und eine dadurch bedingte Desorption. Für die Charakterisierung der in den Lösungen und an der Biomasse gebildeten Uranylspezies wurde die Laser-induzierte Fluoreszenzspektroskopie und die Röntgenabsorptionsspektroskopie genutzt. Die spektroskopischen Untersuchungen zeigen Unterschiede bei den gebildeten Komplexen zwischen Uran und der Algenbiomasse in Abhängigkeit von der metabolischen Aktivität der Algenzellen und der Uranspeziation in den Ausgangslösungen. Für die Bindung von Uran an die Algenzellen scheinen insbesondere Phosphatgruppen verantwortlich zu sein. Eine Beteiligung von Karboxylgruppen kann zum gegenwärtigen Zeitpunkt nicht eindeutig ausgeschlossen werden.

Literatur:

[1] A. Günther et al., Biometals 2008, 21, 333. [2] M. Vogel et al., Uranium, Mining and Hydrogeology 2008, 693.

The Monturaqui impact crater is the only meteorite impact related structure yet found in Chile. It is localized at 3,015 m altitude in the precordillera near the southern end of Salar de Atacama. It is a simple crater of ~400 m diameter and ~34 m of depth [1], first referred as an impact crater by [2]. The age of the crater was estimated as older than 0.1 Ma by [3] by thermoluminiscence analysis.
We are reporting the first absolute ages of the Monturaqui impact crater following two approaches: a) the terrestrial age of the impactor by measuring the residual activities of ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca, ⁵⁹Ni, ⁶⁰Fe, and ⁵³Mn in selected iron shale samples, which corresponds to the remaining altered fragments of the impactor, inferred to be an iron meteorite, and b) in-situ ages obtained through the use of long-lived terrestrial cosmogenic radionuclides ¹⁰Be and ²⁶Al in the granite outcrops exposed to cosmic radiation starting after the impact.
Chemical preparation of targets suitable for accelerator mass spectrometry (AMS) have been performed after [4] (for the iron meteorite sample) and a combination of slight modifications of [4] and [5] (for the granite samples).
AMS measurements of ¹⁰Be and ²⁶Al have been performed at the French 5 MV-AMS facility ASTER, ³⁶Cl at CAMS, LLNL, USA, and ⁵³Mn at the Maier-Leibnitz-Laboratory (MLL).
We can compare our measured radioactivities with depth-depending production rates from sophisticated theoretical Monte-Carlo calculations [priv.com. I. Leya]. As these production rates are a function of the chemical composition (of the impactor in space), remaining fragments are highly altered and precise chemical analyses could not yet be achieved, certain further assumptions are influencing the following discussion of our, thus preliminary, data.
The longest-lived radionuclide ⁵³Mn (t_1/2=3.7 Ma), normalized to a fully corroded Fe₂O₃-sample, is the least sensitive nuclide to a varying terrestrial age, thus, providing us with a shielding depth of 62-71 cm. The best fit of the measured shortest-lived radionuclide ³⁶Cl (t_1/2=0.3 Ma) with theoretical production rate at that depths is for a terrestrial age of 500-600 ka. The ²⁶Al-activity goes along with that age. Though, the measured ¹⁰Be-concentration is far too high in comparison to the theoretical production rate, which are based on an average carbon-content of 0.1% (as Canyon Diablo). As earlier studies [6,7] demonstrated the great influence of inhomogeneous distributed trace elements like C, S, and P on the production rates of lighter cosmogenic radionuclides in iron meteorite samples. Finally, under the contrary assumption of no corrosion of the impactor, the whole discussion changes only slightly: Deeper shielding position (66-80 cm), but as production rates of ⁵³Mn and ³⁶Cl are influenced the same way, the terrestrial age will not change.
Our second approach using terrestrial cosmogenic radionuclides leads to concordant results for ¹⁰Be only: The minimum in-situ exposure age of two samples from the crater wall could be calculated to 200-250 ka. A larger age of excavation is very likely due to the subsequent erosion of the crater walls.
We are looking forward to measurements of the most sensible ⁴¹Ca (t_1/2=0.1 ka) that might improve the accuracy of this age.

References: [1] H. Ugalde et al., MAPS 42 (2007) 2153. [2] J. Sanchez, W. Cassidy, J. Geophys. Res. 71 (1966) 4891. [3] V.F. Buchwald, Handbook of iron meteorites, Univ. of California Press, Berkeley. Vol. 1 (1975) 262. [4] S. Merchel, U. Herpers, RCA 84 (1999) 215. [5] E. T. Brown et al., GCA 55 (1991) 2269. [6] I. Leya, Michel R., Lunar Planet. Sci. 29 (1998) #1172. [7] I. Leya et al., MAPS 32 (1997) A78.

The basics of quantum mechanical brachistochrones are briefly sketched for Hermitian systems as well as for PT-symmetric systems --- as the latter have been recently proposed by Bender, Brody, Jones and Meister (BBJM) in [C. M. Bender et al, Phys. Rev. Lett. 98, 040403 (2007)]. Using a mainly geometric approach, the hidden new features of this PT-symmetric brachsistochrone with its close relation to non-diagonalizable operator realizations with non-trivial Jordan block structures and spectral singularities (spectral exceptional points) are discussed. Furthermore the Naimark dilation technique as basic tool for an extension toward possible experimental implementations is explained. The remarkable links to wormhole-type setups and entangled states (Einstein's 'spooky action') are highlighted and sketched geometrically. The talk is mainly based on [Phys. Rev. Lett. 101, 230404 (2008)].

Cosmic magnetic fields, including the fields of planets, stars, and galaxies, are produced by the hydromagnetic dynamo effect in moving electrically conducting fluids. They play also an active role in cosmic structure formation by enabling outward transport of angular momentum in accretion disks via the magnetorotational instability (MRI). The last ten years have seen tremendous efforts in studying both effects in liquid metal experiments. This paper is focused on the numerical attempts that were undertaken to understand, optimize, and analyze those experiments.

The magnetorotational instability (MRI) is thought to play a key role in the formation of stars and black holes by sustaining the turbulence in hydrodynamically stable Keplerian accretion discs. In previous experiments the MRI was observed in a liquid metal Taylor-Couette flow at moderate Reynolds numbers by applying a helical magnetic field. The observation of this helical MRI (HMRI) was interfered with a significant Ekman pumping driven by solid end-caps that confined the instability only to a part of the Taylor-Couette cell. This paper describes the observation of the HMRI in an improved Taylor-Couette setup with the Ekman pumping significantly reduced by using split end-caps. The HMRI, which now spreads over the whole height of the cell, appears much sharper and in better agreement with numerical predictions. By analyzing various parameter dependencies we conclude that the observed HMRI represents a self-sustained global instability rather than a noise-sustained convective one.

The asymmetric time dependence and various statistical properties of polarity reversals of the Earth's magnetic field are utilized to infer some of the most essential parameters of the geodynamo, among them the effective (turbulent) magnetic diffusivity, the degree of supercriticality, and the relative strength of the periodic forcing which is believed to result from the Milankovic cycle of the Earth's orbit eccentricity. A time-stepped spherically symmetric alpha² dynamo model is used as the kernel of an inverse problem solver in form of a downhill simplex method which converges to solutions that yield a stunning correspondence with paleomagnetic data.

The magnetorotational instability (MRI) plays a key role in the formation of stars and black holes. By destabilizing hydrodynamically stable Keplerian flows, the MRI triggers turbulence and enables outward transport of angular momentum in accretion discs. The Potsdam Rossendorf Magnetic InStability Experiment (PROMISE) is devoted to the experimental study of the so-called helical MRI. Preliminary experiments had confirmed the prediction that combined axial and azimuthal magnetic fields allow the investigation of the MRI in liquid metal Taylor-Couette flows at moderate Reynolds and Hartmann numbers. A drawback of these experiments was that the travelling MRI wave ceased at the radial jet that results from the Ekman pumping at the end-caps of the Taylor-Couette cell. However, by using split end-caps the Ekman pumping is strongly reduced so that the MRI wave can travel freely through the entire height. Consequently, the transition to MRI appears much sharper and in improved agreement with numerical predictions. By analyzing various parameter dependencies of the MRI wave we conclude that it represents a global instability and not a noise-triggered convective one.

The talk comprises a short summary of liquid metal experiments on dynamo action that have been carried out during the last decade. Its main focus, however, will be on recent experiments on the magnetorotational instability (MRI). The prospects for future experiments on dynamo action, MRI, and Tayler instability, as well as for possible combinations will also be discussed.

Oxide dispersion strengthening of high-Cr steels is a well-recognized way to extend the application window including nuclear applications for this class of materials. The experimental investigation of model alloys of less complexity is important in order to separate individual influence factors and to understand the irradiation behaviour. The present work is devoted to the mechanical properties of ODS Fe-9wt%Cr alloys produced by means of spark plasma sintering. The range of material conditions covers contents of nanodispersed yttria of 0 (reference), 0.3 wt% and 0.6 wt% as well as variations of the milling time. Results obtained for the density, elastic properties, hardness, tensile behaviour and brittle-ductile transition are reported and the effect of ODS content and PM process parameters is discussed.

In the talk we summarize the experimental activities to study dynamo action and the magnetorotational instability in the liquid metal laboratory. Both processes are thought to play a key role in the understanding of accretion disks and jets in which ultra-high energy cosmic particles are believed to be produced.

Encapsulated nanostructures formed by surface diffusion assisted phase separation during thin film growth are promising candidates for the multifunctional devices, high density magnetic storage media, multifunctional coatings, as large scale templates for nanowire fabrication. In this talk our activities concerning the investigation of the growth mechanisms of carbon: transition metal (TM=V,Co,Ni,Cu) thin films grown in the in the substrate temperature range of RT- RT-500 C will be summarized [1-5]. Vanadium (copper) is in the carbidic(metallic) state in the whole temperature range while Co and Ni undergo a transition from a carbidic towards a metallic state [3]. The vanadium carbide nanoparticles exhibit a globular shape independently on the growth temperature, while the other metals show a transition from a globular towards a columnar growth when the substrate temperature increases. At a fixed temperature, the morphology of Ni nanocolumns significantly depends on the substrate type which points out that the initial stages of the film growth determine the structure of the subsequently grown film [5]. The use of the hyperthermal species introduces an additional complexity in the phase separation process and allows obtaining a significantly larger variety of nanostructures due to the intperlay of vertical and lateral phase separation processes (disordered array of nanoparticles, self-organized multilayers, nanocolumns or liquid-like coalescence) [4].

[1] G. Abrasonis, M .Krause, A. Mucklich, K. Sedlackova, G. Radnoczi, U. Kreissig, A. Kolitsch, W. Moller, “Growth regimes and metal enhanced 6-fold ring clustering of carbon in carbon-nickel composite thin films”, Carbon 45, 2995 (2007).

[2] G. Abrasonis, A.C. Scheinost , S. Zhou, R. Torres, R. Gago, I. Jimenez, K. Kuepper, K. Potzger, M. Krause, A. Kolitsch, W. Moeller, S. Bartkowski, M. Neumann, R. R. Gareev, “X-ray spectroscopic and magnetic investigation of C : Ni nanocomposite films grown by ion beam cosputtering”, J. Phys. Chem. C 112, 12628 (2008).

[3] G. Abrasonis, M. Berndt, M. Krause, K. Kuepper, F. Munnik, A. Kolitsch, W. Moller, “Soft X-ray Absorption and Emission Spectroscopic Investigation of Carbon and Carbon: Transition Metal Composite Films”, J. Phys. Chem. C 112, 17161 (2008).

[4] G. Abrasonis, G. Kovacs, L. Ryves, M. Krause, A. Mucklich, F. Munnik, M. Bilek, W. Moller, “Phase separation in carbon-nickel films during hyperthermal ion deposition“, J. Appl. Phys. submitted.

[5] G. Abrasonis, A. Mucklich, G. Kovacs, D. Babonneau, A. Martinavicius, M. Berndt, F. Munnik, M. Vinnichenko, K. H. Heinig, J. Grenzer, A. Kolitsch, W. Moller, ”Substrate Effect on the Surface Diffusion Assisted Phase Separation during the Growth of C:Ni Nanocomposite Films”, J. Phys. Chem. C submitted.

Microstructure evolution as function of the substrate temperature and metal content of C:Ni nanocomposite films grown by hyperthermal ion deposition is investigated. The films were grown by pulsed filtered cathodic vacuum arc on thermally oxidized Si substrates held at temperatures in the range from room temperature (RT) to 500 °C and with the metal content ranging from 7 to 40 at. %. The elemental depth profiles and composition were determined by elastic recoil detection analysis. The film morphology and phase structure were studied by means of cross-sectional transmission electron microscopy and selected area electron diffraction. For RT deposition a transition from repeated nucleation dominated toward self-organized growth of alternating carbon and crystalline nickel carbide layers is observed at a Ni threshold content of ~40 at. %. The surface diffusion increases concomitantly with the growth temperature resulting in the formation of elongated/columnar structures and a complete separation of the film constituents into the coexisting carbon and fcc Ni phases. At the highest growth temperature (500 °C) Ni shows a tendency to segregate at the surface of the growing film and to form a continuous layer for integrated Ni contents of =>30 at. %. A corresponding structure zone model diagram is presented, and the results are discussed on the basis of the ion induced atomic displacement, temperature activated adatom diffusion, and the metallic island coalescence processes whose complex interplay results in the observed variety of the microstructures.

Encapsulated nanoparticles formed by surface diffusion assisted phase separation during thin film growth are promising candidates for the multifunctional devices or as large scale templates for nanowire fabrication. In this study, substrate type influence on the morphology of encapsulated metal nanoparticles in C:Ni films grown by ion beam cosputtering is investigated. C:Ni (∼15 atom %) nanocomposite thin films (∼50-70 nm thick) were grown at 400 °C on amorphous SiO2 and Nb2O5, polycrystalline TiN, and single crystalline MgO (001) substrates. Combined diagnostics using transmission electron microscopy, grazing incidence smallangle X-ray scattering, and superconducting quantum interference device magnetometry demonstrate that all the films exhibit metallic nanoparticles elongated along the film growth direction, while the substrate material strongly influences their morphology even far away from the film/substrate interface despite the fact that repeated nucleation occurs in all the films. The mean nanoparticle diameter is strongly substrate dependent and ranges from ∼2 to ∼18 nm in the sequence SiO2 < MgO < Nb2O5 < TiN. In addition, the substrate type influences strongly the vertical film constituent distribution, resulting in a homogeneous metal constituent distribution for the films grown on the SiO2 and MgO substrates while causing the metal segregation at the film surface for the films grown on the Nb2O5 and TiN substrates. The results strongly suggest that the metal diffusivity, not that of carbon, is the limiting factor determining the film structure. The results are consistent with the nucleation and growth mechanism, with the repeated nucleation events being correlated with the preceding film morphology, rather than that of spinodal decomposition. Furthermore, the findings suggest that a controlled growth of encapsulated nanoparticles may be achieved with an ordinary cosputtering technique by changing the substrate type or state or by applying a variety of prepatterning recipes.

no abstract necessary

Aufgabe der vorliegenden Erfindung ist es, einen Gittersensor vorzuschlagen, mit dem der Aufwand des Fertigungsprozesses sowie die Einbau- und Betriebskosten für den Gittersensor deutlich verringert und die Haltbarkeit sowie Druck- und Temperaturfestigkeit des Gittersensors gegenüber bisherigen Gittersensoren deutlich erhöht werden können.
Die technische Lösung beinhaltet im Wesentlichen, dass vom Rand des Messquerschnitts (2) aus Kanäle (3) mit einer Breite von mehr als dem Durchmesser der Drahtelektroden (6) und mit einer Tiefe von weniger als der halben Dicke der Sensorplatine (1) in dieser nach außen verlaufen, dass die Kanäle (3) mit einer Metallschicht (5) ausgekleidet sind, dass die Drahtelektroden (6) mit ihren beiden Enden jeweils in einem der gegenüberliegenden Kanäle (3) an der Peripherie des Messquerschnitts (2) eingelegt und in den Kanälen (3) mittels leitfähiger Verschlussmasse (8) fixiert sind, dass die leitfähige Verschlussmasse (8) in jedem Kanal (3) mit der Oberseite der Sensorplatine (1) plan abschließt und dass die Sensorplatine (1) zwischen zwei Spannplatten (10) eingespannt ist.
Fig. 2

We present the microstructural evolution in Ge-rich SiO2 doped with Er under different fabrication conditions. At sufficiently high Er contents and annealing temperatures, the Er2O3 and Er2Ge2O7 phases are eventually formed, leading to an electroluminescence quenching of Ge-related oxygen-deficiency centers. The correlation between the microstructure and electroluminescence is discussed based on: (i) an Er doping dependent fragmentation/amorphization of Ge nanocrystals, (ii) a temperature dependent Ge diffusion toward the Si/SiO2 interface, and (iii) the formation of different Er phases.

Optical response of a rare earth (RE)-doped SiO2 layer is known to deteriorate markedly at room temperature due to RE clustering. The key challenge is therefore to probe the ongoing processes at the microscopic level and the subsequent impact on the luminescence properties with increasing RE concentration. Here, we report how the Er electroluminescence in a metal-oxide-semiconductor structure has been affected by increasing Er content. Our results indicate that the Er oxide clustering is anticipated by the formation of Si-based oxygen-deficiency centers during postimplantation annealing and leads to a strong quenching of the short-wavelength (350–500 nm) Er electroluminescence.

Coolant mixing inside the nuclear reactor is the most important inherent safety mechanism against boron dilution or overcooling transients and in the case of pressurized thermal shock scenarios. In the frame of the TACIS Project R2.02/02 coolant mixing experiments have been performed at the 1:5 scaled Gidropress mixing test facility. This experimental facility consists of a model of the reactor pressure vessel (RPV) with four circulating loops. The RPV model is made of steel and reproduces in the given scale practically all the geometrical features of the RPV of the VVER-1000 at the NPP Novovoronezh-5 which are affecting the in-vessel mixing phenomena up to the core inlet, particularly the internal components such as the barrel, the lower ellipsoidal perforated shell, the core support columns and the lower core plate. In the carried-out experimental series the mixing processes during reactor coolant pump (RCP) start-up, during natural circulation conditions with the variation of density ratio differences and during stationary flow conditions with different number of RCP in operation were investigated.
At Forschungszentrum Dresden-Rossendorf, the 1:5 scaled mixing test facility ROCOM (Rossendorf Coolant Mixing Model) has been in operation since ten years. This facility models the primary circuit of the German PWR KONVOI with all four loops. The vessel of the facility is made from Perspex. The geometrical similarity between the model and the original reactor is fully respected within the region in-between the bends in the cold legs, which are closest to the reactor inlet and the core entrance. The geometry of the inlet nozzles with their diffuser segments and the curvature radius of the inner wall at the junction with the pressure vessel were modeled in detail. Similarity is also taken into account for the core support plate with the orifices for the coolant and the perforated sieve drum (flow skirt below the core barrel) in the lower plenum. Beside others, experiments have been performed at the ROCOM test facility for the first and the third classes mentioned above for the Gidropress test facility. That allows comparing the experimental results obtained at both test facilities.
The analysis of the slug mixing experiments showed comparable flow behavior. The first part of the tracer is found on the opposite side in regard to the position of the starting-up loop. In this region, the maximum tracer is measured in both facilities. These maximum values differ by about the same value as the initial slug sizes in the experiments.
In stationary experiments at both test facilities a clear sector formation at the core inlet could be observed. Coolant from the loop with the perturbation arrives nearly unmixed in both cases at single measurement positions at the core inlet. In one of the Gidropress experiments an additional counterclockwise swirl was found which is responsible for moving the sector. In the corresponding ROCOM experiment such an additional swirl is fully absent. Contrary to that, a shift of the sector is found in a four-loop experiment at reduced flow rate.

The formation of regular nanopatterns during low energy ion sputtering of solid surfaces has become a topic of intense research. This research is mainly motivated by promising applications of nanopatterned surfaces e.g. in thin film growth. On the other hand, these surfaces represent an interesting example of spontaneous pattern formation in non-equilibrium systems exhibiting different features like wavelength coarsening or a transition to spatiotemporal chaos. Different pattern types are observed for different experimental conditions, i.e. wavelike ripple patterns and hexagonally ordered dot arrays under oblique and normal ion incidence, respectively [1].
According to the model of Bradley and Harper (BH) [2], the regular patterns result from the competition between curvature dependent roughening and diffusional smoothing of the surface. Since the local erosion rate is higher in troughs than on crests, the eroded surface is unstable against any periodic perturbances. In the presence of a smoothing mechanism, however, wave vector selection occurs and a periodic pattern with a characteristic spatial frequency is observed. During recent years, several nonlinear extensions of the linear BH model have been proposed with the stochastic Kuramoto-Sivashinsky (KS) equation having played a prominent role [3]. However, although most experimental investigations on ion-induced pattern formation were performed under oblique ion incidence, only few theoretical studies focused on the corresponding anisotropic KS (aKS) equation.
In this work, we have investigated the influence of anisotropy on the morphology evolution in numerical integrations of the aKS equation. For a strong nonlinear anisotropy, a rotation by 90° of the initially formed ripple pattern was observed for intermediate and long integration times. Comparison with analytical predictions indicates that the observed rotated ripple pattern arises from anisotropic renormalization properties of the aKS equation. This result may also offer an explanation for the recent observation of transient structures in high-temperature experiments on Si(111) [4].

[1] W. L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007)
[2] R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)
[3] R. Cuerno and A.-L. Barabási, Phys. Rev. Lett. 74 4746 (1995)
[4] A.-D. Brown, J. Erlebacher, W.-L. Chan, and E. Chason, Phys. Rev. Lett. 95 056101 (2005)

Magnetism is a collective phenomena. Hence, a local variation on the nanoscale of material properties which act on the magnetic properties affect the overall magnetism in an intriguing way. In particular important are the length scales on which a material property changes. These might be related to the exchange length, the domain wall width, a typical roughness correlation length or a length scale introduced by patterning of the material. Here we report on the influence of two artificially created length scales: i) Ion erosion templates which serve as a source of a predefined surface morphology and hence allow for the investigation of roughness phenomena, ii) Ion implantation through a lithographically defined mask which is used for a magnetic property patterning on various length scales. The resulting magnetic properties are neither present in non-implanted nor in homogeneously implanted films. In both cases the magnetic properties, the magnetization reversal process as well as the magnetic domain configurations depend sensitively on the artificially introduced length scale.

A consequence of a loss of coolant accident is the damage of adjacent insulation materials (IM). IM may then be transported to the containment sump strainers where water is drawn into the ECCS (emergency core cooling system). Blockage of the strainers by IM lead to an increased pressure drop acting on the operating ECCS pumps. IM can also penetrate the strainers, enter the reactor coolant system and then accumulate in the reactor pressure vessel.
An experimental and theoretical study that concentrates on mineral wool fiber transport in the containment sump and the ECCS is being performed. The study entails fiber generation and the assessment of fiber transport in single and multi-effect experiments. The experiments include measurement of the terminal settling velocity, the strainer pressure drop, fiber sedimentation and resuspension in a channel flow and jet flow in a rectangular tank. An integrated test facility is also operated to assess the compounded effects. Each experimental facility is used to provide data for the validation of equivalent computational fluid dynamic models.
The channel flow facility allows the determination of the steady state distribution of the fibers at different flow velocities. The fibers are modeled in the Eulerian-Eulerian reference frame as spherical wetted agglomerates. The fiber agglomerate size, density, the relative viscosity of the fluid-fiber mixture and the turbulent dispersion of the fibers all affect the steady state accumulation of fibers at the channel base. In the current simulations, two fiber phases are separately considered. The particle size is kept constant while the density is modified, which affects both the terminal velocity and volume fraction. The relative viscosity is only significant at higher concentrations. The numerical model finds that the fibers accumulate at the channel base even at high velocities; therefore, modifications to the drag and turbulent dispersion forces can be made to reduce fiber accumulation.

Details on the generation of multiple quasimonoenergetic electron bunches in the self-modulated laser wakefield acceleration SMLWFA regime are presented. This type of laser-plasma interaction can result in pronounced longitudinal laser pulse fragmentation, dependent on plasma density and laser intensity. It is shown by experiments and particle-in-cell simulations that these laser pulse fragments can be powerful enough to trigger nonlinear plasma wave breaking, injection, and acceleration of electrons to quasimonoenergetic energies. With high plasma densities, selfmodulation is promoted, and the advantages of SMLWFA such as especially high accelerating fields and short electron bunches (<5 fs) can be harvested. In addition, more than one quasimonoenergetic electron bunch can be created, with a temporal spacing between each bunch of only few tens of femtoseconds, again governed by plasma density.

A consequence of a loss of coolant accident is that the local insulation material is damaged and maybe transported to the containment sump where it can penetrate and/or block the sump strainers. An experimental and theoretical study, which examines the transport of mineral wool fibers via single and multi-effect experiments is being performed. This paper focuses on the experiments and simulations performed for validation of numerical models of sedimentation and resuspension of mineral wool fiber agglomerates in a racetrack type channel. Three velocity conditions are used to test the response of two dispersed phase fiber agglomerates to two drag correlations and to two turbulent dispersion coefficients. The Eulerian multiphase flow model is applied with either one or two dispersed phases.